Polímeros: Ciência e Tecnologia (Polimeros) 1st. issue, vol. 35, 2025

Volume XXXV - Issue I - March., 2025

Prof. Ailton de Souza Gomez Emeritus Professor, IMA/UFRJ

021 Pol, 2 B C 16 Preto Ouro th

Oil absorption of natural rubber latex (A) and polyurethane (B) foams.

18º CONGRESSO BRASILEIRO DE POLÍMEROS

18°

DATA: 19 A 23 DE OUTUBRO DE 2025 LOCAL: CAMPOS DO JORDÃO CONVENTION CENTER/SP

SUBMISSÕES DE TRABALHOS ABERTAS! Compartilhe suas pesquisas no maior evento técnico-científico de polímeros do Brasil.

Envie seu trabalho até 02 de Junho de 2025.

Inscreva-se e submeta seu trabalho em : www.cbpol.com.br

INOVAÇÃO EM POLÍMEROS, NATUREZA E GASTRONOMIA EM UM SÓ LUGAR!

COMISSÃO JOVEM Essa edição do CBPol traz uma novidade: a Comissão Jovem. Os integrantes dessa Comissão atuarão como co-chairs nas sessões orais e de pôsteres, colaborando com a organização e a condução das apresentações científicas.

Quem pode participar?

Estudantes de graduação, mestrado, doutorado e pós-doutorado que sejam Sócios da Associação Brasileira de Polímeros (ABPol) e que estejam vinculados a uma instituição no período do congresso.

Patrocinadores Ouro:

Patrocinadores Prata:

Organização e Realização:

Associação Brasileira de Polímeros

Fundada em 1988

Acesse o site do evento:

Acesse o site do ABPol:

www.cbpol.com.br

www.abpol.org.br

Patrocinadores Bronze:

Apoio:

Patrocinador Master:

ISSN 0104-1428 (printed) ISSN 1678-5169 (online)

P o l í m e r o s - I ss u e I - V o l u m e X X X V - 2 0 2 5 I n d e x e d i n : “ C h e m ic a l A b s t r a c t s ” — “ RA P RA A b s t r a c t s ” — “A l l - R u s s i a n I n s t i t u t e o f S ci e n c e a n d ­T e c h n ic a l I n f o r m a t i o n ” — “ L a t i n d e x ” — “ W e b o f S ci e n c e ”

Polímeros E d i t o r i a l C o u nci l

Editorial Committee

Antonio Aprigio S. Curvelo (USP/IQSC) - President

Sebastião V. Canevarolo Jr. – Editor-in-Chief

Members Ailton S. Gomes (UFRJ/IMA), Rio de Janeiro, RJ (in memoriam) Alain Dufresne (Grenoble INP/Pagora) Artur José Monteiro Valente (UC/DQ) Bluma G. Soares (UFRJ/IMA) César Liberato Petzhold (UFRGS/IQ) Cristina T. Andrade (UFRJ/IQ) Edson R. Simielli (Simielli - Soluções em Polímeros) Edvani Curti Muniz (UEM/DQI) Elias Hage Jr. (UFSCar/DEMa) José Alexandrino de Sousa (UFSCar/DEMa) José António C. Gomes Covas (UMinho/IPC) José Carlos C. S. Pinto (UFRJ/COPPE) Júlio Harada (Harada Hajime Machado Consutoria Ltda) Luiz Antonio Pessan (UFSCar/DEMa) Luiz Henrique C. Mattoso (EMBRAPA) Marcelo Silveira Rabello (UFCGU/AEMa) Marco Aurelio De Paoli (UNICAMP/IQ) Nikos Hadjikristidis (KAUST/ PSE) Osvaldo N. Oliveira Jr. (USP/IFSC) Paula Moldenaers (KU Leuven/CIT) Raquel S. Mauler (UFRGS/IQ) Regina Célia R. Nunes (UFRJ/IMA) Richard G. Weiss Washington (GU/DeptChemistry) (in memoriam) Roberto Pantani, (UNISA/DIIn) Rodrigo Lambert Oréfice (UFMG/DEMET) Sebastião V. Canevarolo Jr. (UFSCar/DEMa) Silvio Manrich (UFSCar/DEMa)

A ss o ci at e E d i t o r s Alain Dufresne Artur José Monteiro Valente Bluma G. Soares César Liberato Petzhold José António C. Gomes Covas José Carlos C. S. Pinto Marcelo Silveira Rabello Paula Moldenaers Richard G. Weiss (in memoriam) Roberto Pantani Rodrigo Lambert Oréfice

D e s k t o p P u b l is h in g

www.editoracubo.com.br

“Polímeros” is a publication of the Associação Brasileira de Polímeros São Paulo 994 St. São Carlos, SP, Brazil, 13560-340 Phone: +55 16 3374-3949 emails: abpol@abpol.org.br / revista@abpol.org.br http://www.abpol.org.br Date of publication: March 2025

Financial support:

Available online at: www.scielo.br

Polímeros / Associação Brasileira de Polímeros. vol. 1, nº 1 (1991) -.- São Carlos: ABPol, 1991Quarterly v. 35, nº 1 (March 2025) ISSN 0104-1428 ISSN 1678-5169 (electronic version)

Website of the “Polímeros”: www.revistapolimeros.org.br

1. Polímeros. l. Associação Brasileira de Polímeros.

Polímeros, 35(1), 2025

E1

E E E E E E E E E E E E E E E E E E E E E E E E E E E E

I I I I I I I I I I I I I I I I I

Editorial Section News....................................................................................................................................................................................................E3 Agenda.................................................................................................................................................................................................E4 Funding Institutions.............................................................................................................................................................................E5

O r i g in a l A r t ic l e Magnesium layered double hydroxide nanofiller in PMMA exposed to gamma irradiation Dandara Luz Souza de Oliveira, Amanda Damasceno Leão, Fábio de Oliveira da Silva Ribeiro, Alyne Rodrigues de Araújo, Pietro Paolo Jorge Correia de Oliveira e Silva, José Lamartine Soares-Sobrinho, Elmo Silvano de Araújo, Renata Francisca da Silva Santos and Kátia Aparecida da Silva Aquino .............................................................................................................................................. e20250001

Valorization of passion fruit: development, characterization and optimization of biodegradable edible films Maria Clara Coutinho Macedo, Viviane Dias Medeiros Silva, Camila Gonçalves Rodrigues, Débora Tamires Vitor Pereira, Maria Aparecida Vieira Teixeira Garcia, Christiano Vieira Pires and Camila Argenta Fante ....................................................... e20250002

Micro and nanoparticulate PP/CaCO3 composites mechanical, thermal and transport properties - DOE

Juliano Martins Barbosa, Caroline Valadão Pacheco, Gisele Szilágyi, Patrícia Candioto de Oliveira, Renato Meneghetti Peres and Hélio Ribeiro ............................................................................................................................................................................. e20250003

Coating based on Montmorillonite, essential oils, and amaranth to preserve mango Evelyn Erika Pillco Ramos, Maria Cecilia Pacco-Huamani, Sandriane Pizato, Rosalinda Arévalo Pinedo, William Renzo Cortez-Vega and Grethel Teresa Choque Delgado ............................................................................................................................................... e20250004

Application of natural rubber latex foam as an effective oil absorbent

Abdulhakim Masa, Nureeyah Jehsoh and Nabil Hayeemasae ......................................................................................................... e20250005

Influence of alkali treatment on physical-mechanical properties of mallow fiber/BOPP composites

Hannah Alagoas Litaiff, Gabrielle Machado dos Santos, Gabriel de Melo, Claudia da Cunha and Virginia Mansanares Giacon ......... e20250006

Anchoring of ex-situ MOF-199 and MOF-UiO-66-NH2 onto TEMPO-oxidized cotton: potential antibacterials

Sergio Alejandro Torres-Cortés, Mauricio Velasquez and César Sierra.......................................................................................... e20250007

Fungal biocomposites production from packaging industry residue: PET-coated SBS paperboard

Nicole Fernanda Souza, Mariane Bonatti-Chaves, Denise Abatti Kasper Silva, Josiane Costa Riani and Elisabeth Wisbeck ...... e20250008

Direct-joining of a polylactide acid-hydroxyapatite biocomposite with a titanium alloy

Renan Adauto, Gean Henrique Marcatto de Oliveira, Mário Augusto Morozo, Márcio Antônio Fiori and Leonardo Bresciani Canto ..e20250009

Physical and mechanical evaluation of polymeric blends with residues of polypropylene masks

Anderson Ravik Santos, Tiago Vieira da Silva, Ítalo Rocha Coura, Patrícia Santiago de Oliveira Patrício and Wanna Carvalho Fontes .e20250010

Thermal behavior of NBR vulcanizates activated with plant-extract-derived magnesium oxidea

Arianne Aparecida da Silva, Ana Maria Furtado de Sousa, Cristina Russi Guimarães Furtado and Nakédia M. F. Carvalho..... e20250011

Polypropylene reinforced with hollow glass microspheres: effect of thermal aging and reprocessing

Hiroshi Cavalcante Medeiros Koseki, Marlove Bergozza, Cristiano José de Farias Braz, Tatianny Soares Alves and Renata Barbosa ........ e20250012

E2

Polímeros, 35(1), 2025

Pioneering the next generation of bio-based polymers in partnership with London-listed Synthomer Chemists at the Green Chemistry Centre of Excellence, in partnership with Synthomer, are developing new bio-derived monomers to help drive the defossilisation of the chemical industry.

The research team aims to co-deliver bio-derived, lower carbon footprint monomers in a move towards more sustainable production processes. Synthomer is a British manufacturer of high-performance speciality polymers and ingredients that play vital roles in key sectors such as coatings, construction, adhesives, and health and protection. The three-year ‘Prosperity Partnership’ project is supported by funding from Engineering and Physical Sciences Research Council (EPSRC), Synthomer and the University of York, with a combined value of £2 million. EPSRC Prosperity Partnerships are business-academia collaborations with a focus on relevant industrial outcomes. This collaboration will help Synthomer meet their 2050 net zero target, and help train the next generation of synthetic and polymer chemists in aspects of Green Chemistry needed by future industry.

Professor Helen Sneddon, Director of the Green Chemistry Centre of Excellence at the University of York, said: “We›re delighted to be building on our existing collaborations with Synthomer on the challenge of Bio-based Monomers for a Defossilised Speciality Polymer Industry. “This research is a key topic of interest as the plastics industry increasingly looks to move away from petrochemicals. Whilst bulk plastics, such as plastic bottles and bags, have garnered much media focus in recent times, there is a critical need for a versatile platform of high quality, reproducible, bio-derived monomers, with differentiated properties, formed from reliable sources of biomass (and/or CO2), on a scale of 100’s-1000’s of tonnes per annum that does not compete with food.”

Robin Harrison, Vice President of Technology Platforms and External Innovation at Synthomer, comments: “This project embodies our strategic focus on innovation and sustainability, and our investment in long term R&D as a key driver of our sustainability commitment. “Bringing together our expertise and leadership in speciality sustainable polymers with the University of York’s world-leading authority in sustainable polymer research, this partnership aims to bring sustainable bio-based alternatives to our markets.”

Visible light control over ring-shaped polymer structures

N

A new photochemical process allows the targeted production of cyclic polymer structures – without unwanted cross-linking. Researchers present an organocatalyzed, light-driven radical process that could provide new impetus for the development of functional coating systems.

A research team led by Gaoyuan Yu and Dian-Feng Chen, from Hefei National Research Center, China, has developed a new process for controlled radical cyclopolymerisation. The focus is on novel methacrylate and acrylamide crotonate hybrid monomers that are polymerised under visible light. The process uses an organocatalysed photoredox-active ATRP strategy (atom transfer radical polymerisation) for initiation.

The polymerisation occurs via a sequential cascade of intramolecular ring formation and intermolecular chain extension. The result is structure-defined homopolymers and block copolymers with recurring cyclic units – without any unwanted network formation. The cyclic structure gives the polymers special properties, for example in terms of flexibility or stability, which makes them interesting for functional coatings and special applications.

Another key finding of the study is the high degree of control over the polymer architecture. The researchers were able to show that parameters such as light intensity and the targeted use of additives have a significant influence on chain length and cycle formation. This enables fine-tuning of the macromolecular structure during synthesis – a decisive advantage for the development of customised coating systems with defined properties.

The results demonstrate the potential of photocontrolled organocatalytic polymerisations for demanding coating applications – especially where conventional radical processes reach their limits. The research paves the way for new material solutions in the field of functional polymers.

Source: European Coatings– european-coatings.com Polymer Chemistry, 16(13), 2025, DOI: 10.1039/d4py01369g

Source: University of York – york.ac.uk

Polímeros, 35(1), 2025

E3

E

W

S

A

G

E

2025

July

May

14th International Symposium on Polyelectrolytes - ISP2025 Date: July 13-18, 2025 Location: Campinas, São Paulo, Brazil Website: isp25.com

8th International Conference on Composite Material, Polymer Science and Engineering - CMPSE 2025 Date: May 16-17, 2025 Location: Bangkok, Thailand Website: cmpse.org Polymer Sourcing and Distribution Date: May 19-21, 2025 Location: Malaga, Spain Website: ami-events.com/event/f82e6fcc-bfc5-4deb-b4814f20b4c03717/summary?RefId=Website_AMI Plastic Closure Innovations Date: May 19-21, 2025 Location: Malaga, Spain Website: ami-events.com/event/2738902d-d7c8-4610-8199ec58a3f6f9d8/summary?RefId=Website_AMI Polymers in Energy Date: May 21-22, 2025 Location: Tampa, Florida, United States of America Website: ami-events.com/event/ee6dd45c-66e3-4791-a77a9678202743cf/home?RefId=Website_Home

June

N

D

A

5th Edition of Chemistry World Conference Date: June 2-4, 2025 Location: Rome, Italy Website: chemistryworldconference.com Plastics Recycling Technology Date: June 10-11, 2025 Location: Long Beach, California, United States of America Website: ami-events.com/event/8663c550-b6d5-496e-9ca315f9fd54094e/summary?RefId=Website_AMI 4th Bioplastics Brazil – International Seminar on Compostable and Renewable Plastic Materials Date: June 11-12, 2025 Location: São Paulo, São Paulo, Brazil Website: bioplasticsbrazil.com/?lang=en 11th International Meeting of the Hellenic Society of Rheology - HSR 2025 Date: June 11-14, 2025 Location: Syros, Greece Website: mathweb.aegean.gr/hsr2025 International Conference on Macromolecular and Supramolecular Chemistry - ICMSC 2025 Date: June 21-22, 2025 Location: Vienna, Austria Website: waset.org/macromolecular-and-supramolecularchemistry-conference-in-june-2025-in-vienna EPF 2025 — European Polymer Congress 2025 Date: June 22-25, 2025 Location: Groningen, Netherlands Website: www.epf2025.org Fluoropolymers 2025 Date: June 22-25, 2025 Location: Savannah, Georgia, United States of America Website: polyacs.org/25fluoropolymers International Conference on Materials for Advanced Technologies – ICMAT 2025 Date: June 30 – July 4, 2025 Location: Singapore, Singapore Website: icmat2025.mrs.org.sg

E4

August 14th World Congress on Biopolymers and Biomaterials Date: August 18-19, 2025 Location: Valencia, Spain Website: biopolymerscongress.conferenceseries.com Bioplastics Date: August 26-27, 2025 Location: Cleveland, Ohio, United States of America Website: ami-events.com/event/5e7218cb-45fb-4e84-bb428c3ca9fbcf6c/summary?RefId=Website_AMI

September Polymers in Hydrogen and CCUS Infrastructure Date: September 10-11, 2025 Location: Düsseldorf, Germany Website: ami-events.com/event/024afd7e-7a6a-40b7-b4a893a6eb9b92f2/summary?RefId=Website_AMI 39th International Conference on Solution Chemistry - ICSC 2025 Date: September 14-17, 2025 Location: Monastir, Tunisia Website: sctunisie.org/icsc2025 International Conference on Materials Science & Engineering Date: September 25-26, 2025 Location: Dubai, United Arab Emirates Website: materials-science.nexovoconferences.com XXIII B-MRS Meeting Date: September 28 – October 2, 2025 Location: Salvador, Bahia, Brazil Website: sbpmat.org.br/23encontro/

October 18th Brazilian Polymer Conference (CBPol) Date: October 19-23, 2025 Location: Campos do Jordão, São Paulo, Brazil Website: cbpol.com.br/?lang=en_US XVII Argentine Symposium on Polymers - SAP 2025 Date: October 22-24, 2025 Location: Salta Capital, Argentina Website: sap2025.ing.unsa.edu.ar/en/ 96th Annual Meeting of the Society of Rheology Date: October 19-23, 2025 Location: Santa Fe, New Mexico, United States of America Website: rheology.org/sor/Annual_Meeting/Default.aspx

November Polymers for Fuel Cells, Energy Storage, and Conversion Date: November 2-5, 2025 Location: Safety Harbor, Florida, United States of America Website: aiche.org/conferences/aiche-annual-meeting/2025 2025 AIChE Annual Meeting Date: November 2-6, 2025 Location: Boston, Massachusetts, United States of America Website: polyacs.org/2025fuelcells/ 6th World Expo on Biopolymers and Bioplastics Date: November 6-7, 2025 Location: Dubai, United Arab Emirates Website: biopolymers.materialsconferences.com

Polímeros, 35(1), 2025

ABPol Associates Sponsoring Partners

Polímeros, 35(1), 2025

E5

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20240077

Magnesium layered double hydroxide nanofiller in PMMA exposed to gamma irradiation Dandara Luz Souza de Oliveira1 , Amanda Damasceno Leão2 , Fábio de Oliveira da Silva Ribeiro3 , Alyne Rodrigues de Araújo3 , Pietro Paolo Jorge Correia de Oliveira e Silva4 , José Lamartine Soares-Sobrinho2 , Elmo Silvano de Araújo1 , Renata Francisca da Silva Santos1  and Kátia Aparecida da Silva Aquino1*  Departamento de Energia Nuclear, Universidade Federal de Pernambuco – UFPE, Recife, PE, Brasil Departamento de Ciências Farmacêuticas, Universidade Federal de Pernambuco – UFPE, Recife, PE, Brasil 3 Centro de Pesquisa em Biodiversidade e Biotecnologia – BIOTEC, Universidade Federal do Delta do Parnaíba – UFDPar, Parnaíba, PI, Brasil 4 Instituto Federal de Pernambuco – IFPE, Recife, PE, Brasil 1

2

*aquino@ufpe.br

Abstract Poly(methyl methacrylate) (PMMA) is a polymer that can be used in applications requiring its exposition to gamma radiation, nevertheless, the radiation induces main chain scission backbone, leading to modification in some properties.

Therefore, using materials such as layered double hydroxide (LDH), was evaluated as a new radiation shielding agent.

This work synthesized LDH and added to PMMA by an in-situ polymerization method. Viscosimetric analysis showed that LDH at 0.25 wt% concentration promotes polymer radiolytic protection of 90% against damage caused by gamma radiation. The topographic images obtained by AFM revealed increasing PMMA/LDH film roughness, which impacted the lower film transmittance. The combined effect of LDH and gamma radiation interferes with the degradation process of PMMA, promoting reduced rigidity, greater mobility of polymer chains, and lower optical gap energy. Thus, these results open a promising path for using LDH as additives in polymers exposed to gamma radiation.

Keywords: gamma irradiation, layered double hydroxide, poly(methyl methacrylate), radiolytic protection.

Howe to cite: Oliveira, D. L. S., Leão, A. D., Ribeiro, F. O. S., Araújo, A. R., Silva, P. P. J. C. O., Soares-Sobrinho, J. L., Araújo, E. S., Santos, R. F. S., & Aquino, K. A. S. (2025). Magnesium layered double hydroxide nanofiller in PMMA exposed to gamma irradiation. Polímeros: Ciência e Tecnologia, 35(1), e20250001. https://doi.org/10.1590/01041428.20240077

1. Introduction Layered Double Hydroxides (LDHs) are inorganic materials that have attracted attention due to their properties, such as large surface area, adsorption capacity, ion intercalation, and synthesis through various synthetic routes[1,2]. LDHs are considered an emerging class of nanofillers for preparing nanocomposites[3]. These compounds, also known as hydrotalcite, consist of lamellar inorganic sheets positively charged by cations such as Zn2+ and Mg2+, balanced by hydroxide ions and anions such as fluorides, chlorides, and carbonates. LDHs have received significant attention due to their various applications, considering their properties, composition, thermal stability, and other physicochemical parameters[4,5].

On the other hand, poly(methyl methacrylate) (PMMA) is a rigid thermoplastic polymer with excellent optical properties, easy processability, and good thermal and mechanical properties. Its use dates back to the 1930s in manufacturing removable prosthetics, orthodontic appliances, and splints that can be sterilized through exposure to gamma

Polímeros, 35(1), e20250001, 2025

radiation. However, gamma radiation induces the scission of the polymer main chain[6]. In light of this, PMMA has been studied with commercial additives[7] and nanoparticles[8,9] to make the polymer resistant to gamma radiation.

Studies indicate that the PMMA/LDH nanocomposite can be obtained through various methods, such as sonication, LDH gel formation, reflux synthesis, and intercalation with dodecyl sulfate[3,10]. The recorded results demonstrate an enhancement of PMMA properties by incorporating zinc and magnesium LDH in small proportions[11]. One key feature that makes the PMMA/LDH system promising is the ease with which LDH can disperse in the polar polymeric matrix since PMMA[5,12].

However, in the sources analyzed thus far, no records have been found regarding the effects of gamma radiation exposure in systems composed of PMMA/LDH. PMMA produces displays, dental materials, and artifacts subjected to radiation sterilization[13-16]. Therefore, there is relevance in carrying out studies that investigate the influence of LDH on the radiolytic effects in the PMMA matrix. Consequently,

1/11

O O O O O O O O O O O O O O O O O

Oliveira, D. L. S., Leão, A. D., Ribeiro, F. O. S., Araújo, A. R., Silva, P. P. J. C. O., Soares-Sobrinho, J. L., Araújo, E. S., Santos, R. F. S., & Aquino, K. A. S. there is a need to prospect new formulations in which LDH provides radiolytic protection to PMMA. Additionally, in this context, this study will analyze the changes that the PMMA/LDH nanocomposite may undergo when exposed to gamma radiation. Thus, this research may contribute to the field of materials science by providing insights into the interaction between radiation and the PMMA/LDH nanocomposite to enhance its utility in situations that require radiation resistance.

at 25 °C using a Stabinger Anton Paar SVM 3000/G2s viscometer. The relative (ƞr), specific (ƞsp), reduced (ƞred), and intrinsic ([ƞ]) viscosities were obtained using the kinematic viscosity through the equations described in Table S1 (Supplementary Material)[5,6,19-27]. The value of [ƞ] was used to obtain the viscosity molar mass (Mv) using the Mark-Houwink-Sakurada relationship (Equation 1)[28]. η 

KM va

(1)

2. Materials and Methods

K and a are 0.72 and 6.8 x 10−5 (dL/g), respectively, for the PMMA/MEK system, at 25 °C[29]. From the viscosity

2.1 LDH and PMMA/LDH nanocomposites preparation

molar mass values before (Mvo) and after (Mv) irradiation,

This study synthesized magnesium LDH using the constant pH co-precipitation method in an unheated methanolic solution as previously reported by our group[1,17,18].

The PMMA/LDH nanocomposites were produced through an in-situ polymerization reaction. Initially, the methyl methacrylate (MMA) monomer required a purification process as it typically contains inhibitors and water that can influence polymerization yield. MMA was washed with 5% (w/v) sodium hydroxide and distilled water. Subsequently, it was collected in a flask containing calcium chloride to remove inhibitors, filtered, and stored in a freezer for 12 hours at -15 °C to crystallize residual water.

The crystallized water was removed, and pure MMA was used in the polymerization reaction. The benzoyl peroxide (BPO) initiator was purified by solubilizing it in chloroform (30 μg/mL), precipitating it in methanol, and storing it at -15 °C. The crystals were filtered and dried in an oven at 40 °C until reaching a constant weight[2].

In a typical in situ polymerization procedure for PMMA, 9.36 g of MMA monomer was mixed with 0.096 g of BPO initiator, and the resulting system was shaken in an orbital shaker for 2 hours at 80 °C. The nanocomposite systems were removed from the shaker and kept at room temperature for 24 hours to complete the polymerization reaction. For nanocomposite preparation, the appropriate amount of LDH was dispersed in the monomer, stirring for 20 minutes at room temperature (≈ 25 °C) before adding BPO. PMMA/ LDH systems were obtained at 0.25, 0.5, 1.0, and 2.0 wt% concentrations.

The PMMA/LDH nanocomposites and the synthesized PMMA were dissolved in 20 mL of methyl ethyl ketone (MEK) under magnetic stirring for 24 hours at room temperature.

Then, the films were obtained by casting method in an oven at 45 °C for 4 hours[2,17].

the degradation index ( ID  =

2.2 Films irradiation PMMA and PMMA/LDH films were irradiated with gamma rays from a [60]Co source (dose rate of 4.606 kGy/h) at 25 kGy (sterilization dose). The sample irradiations were carried out in ambient air at room temperature.

2.3 Viscosimetric analysis Solutions of 10 mL were produced in triplicate at 0.6 g/dL of concentration with PMMA and PMMA/LDH films (irradiated and non-irradiated). The kinematic viscosity of the solutions (ν) and the solvent (ν0) were determined 2/11

degree

 M vo   − 1 ) and the protection  Mv   ID − ID  ( P =   x100 ) where calculated.  ID 

2.4 Spectroscopic tests Infrared spectra were acquired using the FT-IR Jasco Spectrophotometer, model 4600, with 32 scans, a resolution of 4 cm−1, in transmission mode within the range of 4000400 cm−1, employing the Attenuated Total Reflectance (ATR) technique.

UV-vis spectra were obtained using the UV-vis Spectrophotometer Jasco, model V-730, covering the absorption range from 200 to 800 nm. From the absorption edge (A), determined by the position of the maximum absorption band in the spectrum, it was possible to ascertain the optical parameters of the films since their absorption coefficient (α) depends on the frequency of the absorbed photon (ν) and can be defined by the Beer-Lambert law5 as shown in Equations S1-S9 (Supplementary Material).

2.5 Mechanical properties Mechanical tensile testing was carried out on three samples from each system on an Instron IMIC machine, 500 N, with a 2 mm/s crosshead speed. The ASTM-D822 standard was used with films measuring 7.5 × 2.5 cm. The results were expressed as average ± standard deviation, and a p-value < 0.05 was considered statistically significant after the Tukey test. The mechanical properties analyzed were tensile stress (MPa), Young modulus (MPa), and elongation at break (mm).

2.6 Scanning electron microscopy Scanning Electron Microscopies (SEM) were obtained using HITACHI equipment, model TM3000, with an acceleration voltage of 15 kV. Using plasma in an argon atmosphere, the samples were metalized with gold in a Quorum QI50R metallizer for 30 s at 20 mA.

2.7 Atomic force microscopy The morphological analysis of the films was carried out by Atomic Force Microscopy (AFM) in TT-AFM equipment (AFM Workshop, USA), in intermittent contact mode (vibrating), with a resolution of 512 × 512 pixels, using TAP300-G silicon probes (Ted Pella, USA), with a resonance frequency of approximately 247 kHz. The images Polímeros, 35(1), e20250001, 2025

Magnesium layered double hydroxide nanofiller in PMMA exposed to gamma irradiation were examined using the Gwyddion 2.59 program, from which the average roughness values were extracted. Statistical analyses were performed using the GraphPad Prism® 8.0.1 program, using one-way ANOVA with Tukey’s post-test.

The results were expressed as average ± standard error of the mean, and a p-value <0.05 was considered statistically significant.

3. Results and Discussions 3.1 Viscosimetric tests Figure S1 (Supplementary Material) shows a micrograph (x50,000) of the magnesium LDH synthesized for this study.

LDH presented a flat surface morphology with platelets with irregular edges and an average size of 100 to 200 nm in the horizontal axis. The results of the complete characterization of the magnesium LDH and the synthesized PMMA were recorded in our previous work[11].

The PMMA and PMMA/LDH films, obtained by the casting method, exhibited a homogeneous appearance, with an average thickness of 0.112 ± 0.002 mm. No change in film thickness was recorded with the addition of LDH to the system.

For the viscosimetric tests, initially, the Huggins constant (Kh) was calculated to find out which equation would be most suitable for obtaining the intrinsic viscosity ([ƞ]) by a single-point method. Figure S2 (Supplementary Material) shows the relationship between the concentrations of nonirradiated PMMA solutions and their respective reduced viscosities by the Huggins model[20].

The Kh = 0.49 was calculated using the obtained straightline equation of Figure S2, indicating the Solomon-Ciuta equation (see Table S1 in Supplementary Material) to get the intrinsic viscosity by a single-point method. Table 1 shows the viscosimetric results obtained for the systems under study.

When comparing the Mv values of non-irradiated systems, the values of systems with LDH are slightly lower than those of pure PMMA. These results highlight the influence of LDH on the PMMA matrix. Typically, the PMMA molecule exhibits dipole-dipole attraction due to electrostatic interactions between the oxygen atom of the ester group in a polymer chain (negative pole) and the hydrogen atom of another polymer molecule (positive pole).

For example, LDH molecules may induce contraction of PMMA molecules due to a lack of chemical affinity. Thus, the contracted coil of PMMA/LDH systems results in a smaller hydrodynamic volume, facilitating the passage of the polymeric solution through the capillary tube of the viscometer and reducing its intrinsic viscosity, as shown in Table 1[30].

On the other hand, when analyzing the irradiated systems, Mv values are lower than those of non-irradiated systems.

The decrease in Mv is attributed to the scission of the main chain of PMMA, a well-established mechanism[6,31]. Pure PMMA exhibited a reduction in Mv of approximately 31.5%.

Unlike those with lower concentrations, the PMMA/LDH systems at concentrations of 1 and 2 wt% showed a decrease in Mv very close to PMMA, with a modest percentage of radiolytic protection.

The PMMA/LDH system at a concentration of 0.25 wt% exhibited an ID of 0.05, and the system with a concentration of 0.5% (w/w) showed an ID of 0.09. In other words, these systems reduced radiolytic degradation effects. Compared to the ID of pure PMMA (ID=0.46), protection of over 80% from LDH against the chain scission effects caused by gamma radiation exposure was calculated. PMMA undergoes radiolytic degradation by a radical mechanism 6. Therefore, it was inferred that LDH acts as a scavenger agent, preventing the action of radicals formed in the radiolysis process.

Based on the results presented thus far, the sample that demonstrated the best performance in radioprotective action for PMMA was the one with LDH at a concentration of 0.25 wt%. The reduction in the protection factor in systems with higher concentrations of LDH indicates that, as the amount of LDH in the system increases, an impurity-like behavior establishes itself, competing with its radioprotective action. Similar outcomes were found in other studies employing PMMA and additives with radioprotective properties[8,9,32,33]. Consequently, the following sections will show characterization results for the PMMA/LDH system at a concentration of 0.25 wt%.

3.2 AFM and SEM Figure 1 shows topographic images of irradiated and non-irradiated PMMA and PMMA/LDH (0.25 wt%) films.

The 2D-amplitude image of the non-irradiated PMMA film exhibits a flatter and more homogeneous surface when compared to the PMMA/LDH samples, which show a globular

Table 1. Viscosimetric results of PMMA and PMMA/LDH films.

Dose (kGy) 0 25 0 25 0 25 0 25 0 25

LDH Concentration (% wt)) 0 0.25 0.5 1 2

Polímeros, 35(1), e20250001, 2025

[η] dL/g 0.54 ± 0.01 0.42 ± 0.02 0.46 ± 0.01 0.45 ± 0.02 0.53 ± 0.01 0.49 ± 0.02 0.51 ± 0.02 0.38 ± 0.01 0.52 ± 0.04 0.40 ± 0.03

Mv ± SD (x 104) (g/mol) 26.41 ± 0.56 18.09 ± 0.12 19.97 ± 0.10 19.06 ± 0.31 25.55 ± 0.57 23.53 ± 0.18 24.14 ± 0.16 17.04 ± 0.22 24.37 ± 0.46 17.33 ± 0.82

ID

Protection (%) -

0.46 0.05

89.61

0.09

81.36

0.42

9.10

0.41

11.48

3/11

Oliveira, D. L. S., Leão, A. D., Ribeiro, F. O. S., Araújo, A. R., Silva, P. P. J. C. O., Soares-Sobrinho, J. L., Araújo, E. S., Santos, R. F. S., & Aquino, K. A. S.

Figure 1. Topographic images of PMMA and PMMA/LDH (0.25 wt%), irradiated and non-irradiated samples, with a resolution of 512×512 pixels.

surface due to the lateral spreading of the LDH lamellae.

On the other hand, for irradiated PMMA and PMMA/ LDH films, the formation of fragments corresponds to the degradation process induced by gamma radiation. This action is better observed in the 2D-phase image when comparing irradiated and non-irradiated films. For the PMMA samples, the 2D-phase images show some polymer aggregates, while the irradiated sample displays fragmentation of the aggregates with a higher number of pores, likely obtained due to chain scission in the polymer caused by radiation 6.

For the PMMA/LDH films, delaminated LDH lamellae are observed against a continuous background of PMMA, with no significant difference between the samples except for a reduced aggregate size.

In the 3D-phase images, the behavior of the film surfaces can be better observed. When irradiated, PMMA exhibits the formation of pores and increased roughness. The average roughness value for PMMA is 2.51 ± 0.29 nm, which rises to 13.36 ± 0.89 nm in irradiated films, representing a difference of 10.85 nm according to the Tukey test (p=0.0018). This result highlights the extent of radiation-induced damage to the PMMA matrix.

The 3D images also reveal that PMMA/LDH films are rougher than irradiated PMMA films. However, radiation has the opposite effect on PMMA/LDH systems. The roughness of the irradiated PMMA/LDH becomes lower than the nonirradiated film. The average roughness value for the nonirradiated PMMA/LDH is 57 ± 4 nm, while 11 ± 1 nm was found for the irradiated film. According to the Tukey test, this result signifies a decrease of 46 nm (p=0.001). Although the roughness of LDH-containing samples decreased with irradiation, no pores were observed in the irradiated film, 4/11

which may be associated with the protective effect of LDH in the PMMA matrix, consistent with the results obtained in viscosimetric tests.

SEM micrographs were obtained for a more precise structural characterization of the LDH dispersion in the polymeric film. Figure 2 depicts the micrographs obtained for PMMA and PMMA/LDH (0.25 wt%), non-irradiated and irradiated samples.

It is possible to observe that the micrograph of the nonirradiated PMMA film (Figure 2a) exhibits some agglomeration points referred to as clusters, which are common in films produced by the casting method[11]. The irradiated films did not find clusters (Figure 2b). However, many fissures indicate the effect of radiolysis and, consequently, the degradation of PMMA. Such fissures may explain the higher number of pores and increased roughness in the films, as shown in the topographic images obtained by AFM (Figure 1).

The micrographs of non-irradiated and irradiated PMMA/ LDH films exhibit a clear difference from pure PMMA samples.

It is observed that LDH is homogeneously distributed in the polymeric matrix. The structure found in the PMMA/LDH samples (Figures 2c and 2d) showed a completely different cluster form, highlighting the lamellar agglomerates. These agglomerates may contribute to the increased roughness of the films with LDH, shown in Figure 1. The reduction in the roughness of the irradiated PMMA/LDH film may be associated with the production of pores with irregular structures formed by the radiolytic degradation of polymer chains (Figure 2d). However, the structural preservation of the irradiated PMMA/LDH film is evident when compared to the film without LDH (Figure 2b). This result reinforces the radioprotective action of LDH at 0.25 wt%.

Polímeros, 35(1), e20250001, 2025

Magnesium layered double hydroxide nanofiller in PMMA exposed to gamma irradiation

Figure 2. SEM images (x 10,000) for (a) PMMA 0 kGy; (b) PMMA 25 kGy; (c) PMMA/LDH 0 kGy; and (d) PMMA/LDH 25 kGy (LDH at 0.25wt%).

3.3 Mechanical properties Table 2 shows the results of the mechanical properties obtained for irradiated and non-irradiated films of PMMA and PMMA/LDH (0.25 wt%). It was observed that PMMA non-irradiated has a higher value of elastic modulus and higher tensile strength values when compared to the values obtained for PMMA/LDH. These results indicate higher stiffness of PMMA, although the polymer exhibits a higher elongation at break.

Changes in the elongation at break, tensile strength, and elastic modulus in non-irradiated PMMA/LDH films indicate the adhesion between the polymer and LDH phases, as these properties are sensitive to the transfer of load between the components. The elastic modulus depends on the nature of the material chemical bonding and electronic structures, while the morphology, size of domains, and film homogeneity are related to the tensile strength. The decrease in the tensile strength of PMMA/LDH films may be associated with their increased roughness (see Figure 1) and the distribution of clusters with larger sizes (see Figure 2c), causing reduced load transfer between the PMMA and LDH phases[34]. The same discussion extends to irradiated PMMA films when compared to non-irradiated samples. Figure 2b shows several Polímeros, 35(1), e20250001, 2025

Table 2. Mechanical properties obtained for irradiated and nonirradiated PMMA and PMMA/LDH (0.25 wt%) films.

Sample

Elastic Tensile Elongation modulus Strength at break (Mpa) (MPa) PMMA (0 kGy) 2395 ± 763a 36 ± 5a 3.0 ± 1.0a PMMA (25 kGy) 1551 ± 733b 13 ± 6b 0.9 ± 0.1b PMMA/LDH (0 kGy) 1485 ± 685b 27 ± 6c 0.6 ± 0.2c PMMA/LDH (25 kGy) 1871 ± 574b 16 ± 8b 0.7 ± 0.1c Different letters in the columns indicate a statistically significant difference at p < 0.05.

fissures in the film due to main chain scissions caused by gamma radiation. Reduced load transfer is caused by radiolytic damage, creating points of force yield, causing lower tensile strength and a lower elastic modulus.

Comparing irradiated and non-irradiated PMMA/LDH films, there were no significant changes (p < 0.05) in the tensile strength or elongation at break. This result may be associated with the lesser damage caused by radiation to PMMA (see Figure 2d) due to the radioprotective effect of LDH. On the other hand, the decrease in tensile strength in irradiated PMMA/LDH films can be explained by the few 5/11

Oliveira, D. L. S., Leão, A. D., Ribeiro, F. O. S., Araújo, A. R., Silva, P. P. J. C. O., Soares-Sobrinho, J. L., Araújo, E. S., Santos, R. F. S., & Aquino, K. A. S. pores and a different distribution of clusters (see Figure 2d), which reduce the interfacial interaction between PMMA and LDH, leading to a lower stress transfer at that location[34].

These results indicate that PMMA/LDH films, subjected to gamma radiation sterilization, nearly maintain their mechanical properties, strengthening the radioprotective action of LDH in the system.

3.4 Spectroscopic analyzes Figure 3 shows the FT-IR spectra of PMMA and PMMA/ LDH (0.25 wt%). Generally, it is possible to observe that the bands that characterize PMMA appear at a frequency similar to that of PMMA with LDH. Figure 3a shows that the characteristic bands of PMMA appear for all studied systems (see Table S2 in Supplementary Material). Thus, the similarity between the bands or the absence of new bands, when comparing the spectra obtained for PMMA and PMMA/LDH, irradiated and non-irradiated, indicates that the nanofiller at a concentration of 0.25 wt% does not establish strong chemical bonds with the polymer.

Regarding the stereoregularity of the PMMA used in this work, the absorption band in the region around 840 cm-1 is characteristic of syndiotactic PMMA. A doublet is found in the region between 1240 and 1270 cm-1, which is attributed

to the stretching of the C-O bond in the ester group with cis conformation, which is energetically favored for syndiotactic PMMA[27].

Figure 3b shows the UV-vis spectrum for the studied films. The absorbance between 290 and 300 nm is related to the π-π* electronic transition. The PMMA film exhibited absorption around 285 nm, corresponding to the C=O group[35,36]. The addition of LDH did not influence the behavior of the film, but a slight shift in the absorption band was observed in the irradiated systems, with a particular emphasis on the PMMA/LDH. The increased load from the LDH and the radiolysis products may contribute to a different arrangement of molecules in the system. The optical absorption coefficient (α) reflects the ability of material to absorb light. Figure 4a shows the intersection of the extrapolation of the linear part of the α versus hν graph with the horizontal axis, providing an estimate of the photon energy absorbed by each film. Films irradiated with LDH exhibited lower energy than non-irradiated PMMA. The decrease from 4.21 eV for non-irradiated PMMA to 3.93 eV for the irradiated PMMA/LDH system provides evidence of changes in the valence and conduction band structures of the film due to the combined action of LDH and irradiation[37].

Figure 3. (a) FT-IR spectra for non-irradiated and irradiated PMMA and PMMA/LDH (0.25 wt%) films; and (b) UV-vis spectra for PMMA and PMMA/LDH (0.25 wt%), irradiated and non-irradiated films.

Figure 4. (a) Absorption coefficient (α) for PMMA and PMMA/LDH (0.25 wt%), irradiated and non-irradiated films; and (b) Transmittance behavior of irradiated and non-irradiated PMMA and PMMA/LDH (0.25 wt%) films.

6/11

Polímeros, 35(1), e20250001, 2025

Magnesium layered double hydroxide nanofiller in PMMA exposed to gamma irradiation Based on the absorbance values obtained in the UV/ vis spectrum (Figure 3b), the transmittance (T) calculation was performed, and the results are shown in Figure 4b. The irradiated and non-irradiated PMMA film exhibited a T value of around 90%, indicating that the irradiation process did not induce changes in this property. However, whether irradiated or non-irradiated, PMMA/LDH films showed a decrease in T of approximately 8%. This result may be associated with the increased roughness of the irradiated and non-irradiated PMMA/LDH systems (see Figure 1).

Nevertheless, no significant differences were found in the refractive index (n) of the films. The n value was 1.36 for PMMA (irradiated and non-irradiated) and 1.37 for PMMA/ LDH (irradiated and non-irradiated) at 500 nm.

The dielectric constant of the studied films, both in the real part (Figure 5a) and the imaginary part (Figure 5b), increases

with the photon energy. The real part (𝜀𝑟) is related to the speed of light and the electronic polarization of a material, while the imaginary part (𝜀𝑖) indicates dipolar movement due to energy absorption generated by an electric field[38]. In Figure 5a the extrapolation of the linear portion of the curves with the x-axis showed the lowest photon energy is absorbed in the irradiated PMMA/LDH system. This behavior can be explained by the presence of charges from LDH and defects caused by irradiation in the PMMA matrix, albeit smaller than in the LDH-free film (see Figure 2), forming dipoles that govern the dielectric properties of the irradiated films[39].

The combined effect of LDH and irradiation also impacted the optical gap (Eg) of the films. Figure 6 shows a reduction in Eg for LDH-containing systems, particularly in the irradiated film. Eg, values were obtained using the Tauc’ s model[40] and compared with the energy obtained from the 𝜀𝑖 parameter

Figure 5. The behavior of the dielectric constant (a) imaginary part and (b) real part for PMMA and PMMA/LDH (0.25 wt%), irradiated and non-irradiated films.

Figure 6. Optical gap energy obtained by the Tauc’s model for (a) allowed direct transition; (b) allowed indirect transition; (c) forbidden direct transition; and (d) forbidden indirect transition.

Polímeros, 35(1), e20250001, 2025

7/11

Oliveira, D. L. S., Leão, A. D., Ribeiro, F. O. S., Araújo, A. R., Silva, P. P. J. C. O., Soares-Sobrinho, J. L., Araújo, E. S., Santos, R. F. S., & Aquino, K. A. S. (Figure 5a) to identify the predominant electronic transition in the systems. Table S3 (Supplementary Material) shows the Eg values obtained through both methods. The results suggest that the predominant electronic transition in all systems is the allowed direct transition, given the similarity of values for this transition obtained by the Tauc method and 𝜀𝑖.

The result suggests that the electronic structure of the PMMA film undergoes changes when LDH is introduced, when it is irradiated, and especially when there is a combined effect of LDH and irradiation. These electronic changes may promote a different band arrangement capable of reducing the energy required for an electron to move from the valence band to the conduction band[41]. This finding is consistent with the discussion regarding the optical absorption coefficient (α), where lower energies for LDH-containing and irradiated systems were identified through the graph in Figure 4a.

On the other hand, optical conductivity (σopt) informs about the movement of charge carriers when excited by incident electromagnetic radiation. The influence of LDH and irradiation on the σopt of the films is shown in Figure 7. The values of σopt decrease with the increase in wavelength, but no significant changes are observed in the maximum value of σopt for the films. However, the curve of the irradiated PMMA/LDH system is shifted towards a longer wavelength, which may be due to new levels within the band gap. New levels facilitate the movement of electrons from the valence band to the conduction band due to increased photon-atom interaction[42]. This result corroborates with the lower Eg found for irradiated PMMA/LDH (see Table S3 in Supplementary Material) and highlights the influence of the combined effect of LDH and gamma irradiation on the polymeric system.

4. Conclusion In this study, nanoscale magnesium LDH was synthesized and incorporated into the PMMA matrix through in situ polymerization. Viscosimetric assays revealed that Mg-LDH 0.25 wt% acts as a radioprotector in the PMMA matrix exposed to gamma radiation at a dose of 25 kGy. In this way, LDH provided approximately 90% protection against the chain scission effect caused by radiolysis in the main PMMA chain, probably as a scavenger agent.

Characterization of irradiated and non-irradiated PMMA/ LDH (0.25 wt%) films reveals that the combined effect of

LDH and gamma radiation induces changes in the polymeric system structure. SEM images confirmed the damaging effect of radiation on PMMA while also revealing the homogeneous distribution of nanofillers in the system and the more preserved appearance of the irradiated LDH-containing film.

Moreover, the higher roughness of the PMMA/LDH system decreased the film transmittance by 8% for both irradiated and non-irradiated conditions. The FT-IR spectra did not show new bands or shifts when comparing systems with and without LDH. These results indicate that there are no strong chemical bonds between PMMA and LDH and that PMMA/ LDH films exposed to gamma radiation practically maintain their mechanical properties, reinforcing the radioprotective action of LDH in the system. The UV-vis analysis revealed that PMMA and PMMA/LDH films (irradiated and nonirradiated) absorb energy around 290 nm, attributed to the π-electron transition of the carbonyl group.

Thus, the optical parameters were also influenced by the combined effect of LDH and gamma irradiation. The optical conductivity and dielectric constant values remained the same, with peak values associated with lower energies in the irradiated and LDH-containing systems. The impact of this behavior was to decrease the optical gap value of irradiated PMMA/LDH films. These results indicate that the optical properties of PMMA/LDH films can be modulated under gamma irradiation.

5. Author’s Contribution • Conceptualization – Kátia Aparecida da Silva Aquino.

• Data curation – Dandara Luz Souza de Oliveira, Amanda Damasceno Leão.

• Formal analysis – Dandara Luz Souza de Oliveira, Amanda Damasceno Leão.

• Funding acquisition – Kátia Aparecida da Silva Aquino.

• Investigation – Kátia Aparecida da Silva Aquino.

• Methodology – Dandara Luz Souza de Oliveira; Amanda Damasceno Leão; Pietro Paolo Jorge Correia de Oliveira e Silva; Fábio de Oliveira da Silva Ribeiro, Alyne Rodrigues de Araújo Silva.

• Project administration – Kátia Aparecida da Silva Aquino.

• Resources – Elmo Silvano de Araújo; Renata Francisca da Silva Santos, Kátia Aparecida da Silva Aquino.

• Software – Fábio de Oliveira da Silva Ribeiro; Alyne Rodrigues de Araújo.

• Supervision – Elmo Silvano de Araújo; Kátia Aparecida da Silva Aquino.

• Validation – Kátia Aparecida da Silva Aquino; José Lamartine Soares-Sobrinho.

• Visualization – Kátia Aparecida da Silva Aquino; José Lamartine Soares-Sobrinho.

• Writing – original draft – Dandara Luz Souza de Oliveira; Amanda Damasceno Leão.

Figure 7. The behavior of optical conductivity (σopt) for PMMA and PMMA/LDH (0.25 wt%), irradiated and non-irradiated films.

8/11

• Writing – review & editing – Kátia Aparecida da Silva Aquino.

Polímeros, 35(1), e20250001, 2025

Magnesium layered double hydroxide nanofiller in PMMA exposed to gamma irradiation

6. Acknowledgements This project was supported by the Brazilian Federal Agency for Support and Evaluation of Graduate Education (CAPES). The authors also thank the Laboratory of Phytochemistry and Process Integration-LAFIP (CETENEBrazil) for its support in experimental activities.

7. References 1. Leão, A. D., França, L. M., Cunha, C. N. L. C., Marinho, F. A., Soares, M. F. L., & Soares-Sobrinho, J. L. (2019). In-line monitoring of layered double hydroxide synthesis and insights on formation mechanism and kinetics. Applied Clay Science, 179, 105130. http://doi.org/10.1016/j.clay.2019.105130.

2. Leão, A. D., Alvarez-Lorenzo, C., & Soares-Sobrinho, J. L. (2020). One-pot synthesis of the organomodified layered double hydroxides - glibenclamide biocompatible nanoparticles.

Colloids and Surfaces. B, Biointerfaces, 193, 111055. http:// doi.org/10.1016/j.colsurfb.2020.111055. PMid:32403034.

3. Nagendra, B., Mohan, K., & Gowd, E. B. (2015). Polypropylene/ layered double hydroxide (LDH) nanocomposites: influence of LDH particle size on the crystallization behavior of polypropylene.

ACS Applied Materials & Interfaces, 7(23), 12399-12410. http://doi.org/10.1021/am5075826. PMid:25741910.

4. Hoxha, A., Gillam, D. G., Agha, A., Karpukhina, N., Bushby, A. J., & Patel, M. P. (2020). Novel fluoride rechargeable dental composites containing MgAl and CaAl layered double hydroxide (LDH). Dental Materials, 36(8), 973-986. http:// doi.org/10.1016/j.dental.2020.04.011. PMid:32536588.

5. Manzi-Nshuti, C., Wang, D., Hossenlopp, J. M., & Wilkie, C. A. (2008). Aluminum-containing layered double hydroxides: the thermal, mechanical, and fire properties of (nano)composites of poly(methyl methacrylate). Journal of Materials Chemistry, 18(26), 3091-3102. http://doi.org/10.1039/b802553c.

6. Charlesby, A. (1960). Atomic radiation and polymers. Oxford: Pergamon Press. http://doi.org/10.1016/C2013-0-07861-9.

7. Aquino, K. A. S., Araújo, E. S., & Guedes, S. M. L. (2010).

Influence of a hindered amine stabilizer on optical and mechanical properties of poly(methyl methacrylate) exposed to gamma irradiation. Journal of Applied Polymer Science, 116(2), 748-753. http://doi.org/10.1002/app.31544.

8. Garcia, O. P., Albuquerque, M. C. C., Aquino, K. A. S., Araujo, P. L. B., & Araujo, E. S. (2015). Use of lead (II) sulfide nanoparticles as stabilizer for PMMA exposed to gamma irradiation. Materials Research, 18(2), 365-372. http://doi. org/10.1590/1516-1439.330214.

9. Albuquerque, M. C. C., Garcia, O. P., Aquino, K. A. D. S., Araujo, P. L. B., & Araujo, E. S. (2015). Stibnite nanoparticles as a new stabilizer for poly(methyl methacrylate) exposed to gamma irradiation. Materials Research, 18(5), 978-983. http:// doi.org/10.1590/1516-1439.000814.

10. Chen, H., Mousty, C., Cosnier, S., Silveira, C., Moura, J. J. G., & Almeida, M. G. (2007). Highly sensitive nitrite biosensor based on the electrical wiring of nitrite reductase by [ZnCrAQS] LDH. Electrochemistry Communications, 9(9), 22402245. http://doi.org/10.1016/j.elecom.2007.05.030.

11. Leão, A. D., Silva, L. A., Ribeiro, F. O. S., Silva, D. A., França, E. J., Aquino, K. A. S., & Soares-Sobrinho, J. L. (2021).

Influence of nonmodified layered double hydroxide (LDH) metal constituents in PMMA/LDH nanocomposites. Journal of Inorganic and Organometallic Polymers and Materials, 31(2), 836-850. http://doi.org/10.1007/s10904-020-01742-z.

12. Lu, X., Wang, C., & Wei, Y. (2009). One‐dimensional composite nanomaterials: synthesis by electrospinning and their Polímeros, 35(1), e20250001, 2025

applications. Small, 5(21), 2349-2370. http://doi.org/10.1002/ smll.200900445. PMid:19771565.

13. Ding, Y., Gui, Z., Zhu, J., Hu, Y., & Wang, Z. (2008). Exfoliated poly(methyl methacrylate)/MgFe-layered double hydroxide nanocomposites with small inorganic loading and enhanced properties. Materials Research Bulletin, 43(12), 3212-3220. http://doi.org/10.1016/j.materresbull.2008.03.002.

14. Wang, Q., Undrell, J. P., Gao, Y., Cai, G., Buffet, J.-C., Wilkie, C. A., & O’Hare, D. (2013). Synthesis of flame-retardant polypropylene/LDH borate nanocomposites. Macromolecules, 46(15), 6145-6150. http://doi.org/10.1021/ma401133s.

15. Demir, M. M., Memesa, M., Castignolles, P., & Wegner, G. (2006). PMMA/Zinc oxide nanocomposites prepared by in-situ bulk polymerization. Macromolecular Rapid Communications, 27(10), 763-770. http://doi.org/10.1002/marc.200500870.

16. Li, B., Hu, Y., Liu, J., Chen, Z., & Fan, W. (2003). Preparation of poly(methyl methacrylate)/LDH nanocomposite by exfoliation-adsorption process. Colloid & Polymer Science, 281(10), 998-1001. http://doi.org/10.1007/s00396-003-0874-5.

17. Miyata, S., & Okada, A. (1977). Synthesis of hydrotalcite-like compounds and their physico-chemical properties– the systems Mg2+-Al3+-SO2− and Mg2+-Al3+-CrO2−. Clays and Clay Minerals, 25(1), 14-18. http://doi.org/10.1346/CCMN.1977.0250103.

18. Mayo-Pedrosa, M., Alvarez-Lorenzo, C., Lacík, I., MartinezPacheco, R., & Concheiro, A. (2007). Sustained release pellets based on poly(N-isopropyl acrylamide): matrix and in situ photopolymerization-coated systems. Journal of Pharmaceutical Sciences, 96(1), 93-105. http://doi.org/10.1002/jps.20708.

PMid:16967440.

19. Schoff, C. K. (1999). Concentration dependence of the viscosity of dilute polymer solutions: Huggins and Schulz-Blaschke constants. In J. Brandrup, E. H. Immergut & E. A. Grulke (Eds.), Polymer handbook (pp. 265-289). New York: WileyInterscience. http://doi.org/10.1002/0471532053.bra053.

20. Huggins, M. L. (1942). The viscosity of dilute solutions of long-chain molecules. IV. Dependence on concentration.

Journal of the American Chemical Society, 64(11), 2716-2718. http://doi.org/10.1021/ja01263a056.

21. Solomon, O. F., & Ciutǎ, I. Z. (1962). Détermination de la viscosité intrinsèque de solutions de polymères par une simple détermination de la viscosité. Journal of Applied Polymer Science, 6(24), 683-686. http://doi.org/10.1002/app.1962.070062414.

22. Qian, J. W., Qi, G. R., & Cheng, R. S. (1997). Association of ethylene-vinylacetate copolymer in dilute solutions-I. Solvent, concentration and annealing temperature effect. European Polymer Journal, 33(8), 1263-1265. http://doi.org/10.1016/ S0014-3057(96)00264-9.

23. Ubale, A. U., Sangawar, V. S., & Kulkarni, D. K. (2007). Size dependent optical characteristics of chemically deposited nanostructured ZnS thin films. Bulletin of Materials Science, 30(2), 147-151. http://doi.org/10.1007/s12034-007-0026-5.

24. Davis, E. A., & Mott, N. F. (1970). Conduction in non-crystalline systems V. Conductivity, optical absorption and photoconductivity in amorphous semiconductors. Philosophical Magazine, 22(179), 903-922. http://doi.org/10.1080/14786437008221061.

25. Guo, M., & Du, J. (2012). First-principles study of electronic structures and optical properties of Cu, Ag, and Au-doped anatase TiO2. Physica B, Condensed Matter, 407(6), 10031007. http://doi.org/10.1016/j.physb.2011.12.128.

26. Pankove, J. I., & Kiewit, D. A. (1972). Optical processes in semiconductors. Journal of the Electrochemical Society, 119(5), 156C. http://doi.org/10.1149/1.2404256.

27. Booth, H. (1992). Review of Spectrometric identification of organic compounds, by R. M. Silverstein, G. C. Bassler, & T. C. Morrill. Magnetic Resonance in Chemistry, 30(4), 364. http://doi.org/10.1002/mrc.1260300417.

9/11

Oliveira, D. L. S., Leão, A. D., Ribeiro, F. O. S., Araújo, A. R., Silva, P. P. J. C. O., Soares-Sobrinho, J. L., Araújo, E. S., Santos, R. F. S., & Aquino, K. A. S. 28. Guillet, J. E. (Ed.). (1985). Polymer photophysics and photochemistry: an introduction to the study of photoprocesses in macromolecules. Cambridge: Cambridge University Press. http://doi.org/10.1002/zfch.19860261131.

29. Brandrup, J., & Immergut, E. H. (Eds.). (1989). Polymer handbook. New York: Wiley-Interscience. http://doi.org/10.1002/ actp.1990.010410614.

30. Lovell, P. A. (1989). Dilute solution viscometry. In G. Allen & J. C. Bevington (Eds.), Comprehensive polymer science and supplements (pp. 173-197). New York: Elsevier. http://doi. org/10.1016/B978-0-08-096701-1.00009-4.

31. Bel, T., Arslan, C., & Baydogan, N. (2019). Radiation shielding properties of poly (methyl methacrylate) / colemanite composite for the use in mixed irradiation fields of neutrons and gamma rays. Materials Chemistry and Physics, 221, 58-67. http://doi. org/10.1016/j.matchemphys.2018.09.014.

32. Aquino, K. A. S., & Araújo, E. S. (2008). Effects of a hindered amine stabilizer (HAS) on radiolytic and thermal stability of poly (methyl methacrylate). Journal of Applied Polymer Science, 110(1), 401-407. http://doi.org/10.1002/app.28465.

33. Aquino, K. A. S., Oliveira, D. L. S., Santos, R. F. S., & Araújo, E. S. (2023). Study of commercial additive effects on poly(methyl methacrylate) exposed to gamma irradiation by viscosimetric analysis. Materials Research, 26, e20230382. http://doi.org/10.1590/1980-5373-mr-2023-0382.

34. Koning, C., Duin, M. V., Pagnoulle, C., & Jerome, R. (1998).

Strategies for compatibilization of polymer blends. Progress in Polymer Science, 23(4), 707-757. http://doi.org/10.1016/ S0079-6700(97)00054-3.

35. Wang, X., Huang, J., Fan, W., & Lu, H. (2015). Identification of green tea varieties and fast quantification of total polyphenols by near-infrared spectroscopy and ultraviolet-visible spectroscopy with chemometric algorithms. Analytical Methods, 7(7), 787792. http://doi.org/10.1039/C4AY02106A.

10/11

36. Al-Kadhemy, M. F. H., Saeed, A. A., Khaleel, R. I., & AlNuaimi, F. J. K. (2017). Effect of gamma ray on optical characteristics of (PMMA/PS) polymer blends. Journal of Theoretical and Applied Physics, 11(3), 201-207. http://doi. org/10.1007/s40094-017-0259-7.

37. Aziz, S. B., Rasheed, M. A., Hussein, A. M., & Ahmed, H. M. (2017). Fabrication of polymer blend composites based on PVA-PVP:(Ag2S)x (0.01 ≤ x ≤ 0.03) with small optical band gaps: structural and optical properties. Materials Science in Semiconductor Processing, 71, 197-203. http://doi.org/10.1016/j. mssp.2017.05.035.

38. Omar, M. A. (1987). Elementary solid state physics: principles and applications. Reading: Addison-Wesley Publishing Company.

39. Tahir, K. J. (2017). Effect of gamma irradiation on optical properties of CdS thin films. Journal of Kerbala University, 15(1), 49-55. Retrieved in 2024, August 13, from https://www. iasj.net/iasj/article/122592 40. Tauc, J. (Ed.). (1974). Amorphous and liquid semiconductors.

London: Plenum Publishing Company Ltd. http://doi. org/10.1007/978-1-4615-8705-7.

41. Ersen, Y. (2022). Compatibilizer effect on optical properties of immiscible PMMA/PS blends. International Journal of Pure and Applied Sciences, 8(1), 149-156. http://doi.org/10.29132/ ijpas.1054866.

42. Mansour, A. F., Mansour, S. F., & Abdo, M. A. (2015).

Improvement of structural and optical properties of ZnO/ PVA nanocomposites. IOSR Journal of Applied Physics, 7(2), 60-69. http://doi.org/10.9790/4861-07226069.

Received: Aug. 13, 2024 Revised: Oct. 21, 2024 Accepted: Oct. 29, 2024

Polímeros, 35(1), e20250001, 2025

Magnesium layered double hydroxide nanofiller in PMMA exposed to gamma irradiation

Supplementary Material Supplementary material accompanies this paper.

Table S1. Viscosimetric parameters and their mathematical relationships.

Table S2. Band assignment in the FT-IR spectrum of PMMA. Adapted from Booth et al.[11].

Table S3. Eg values obtained through the Tauc’s model and from the parameter 𝜀𝑖.

Figure S1. SEM micrograph (x50,000) of the magnesium LDH synthesized for this study.

Figure S2. Reduced viscosity vs concentration for non-irradiated PMMA solutions.

This material is available as part of the online article from https://doi.org/10.1590/0104-1428.20240077

Polímeros, 35(1), e20250001, 2025

11/11

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20240043

Valorization of passion fruit: development, characterization and optimization of biodegradable edible films Maria Clara Coutinho Macedo1 , Viviane Dias Medeiros Silva1 , Camila Gonçalves Rodrigues2 , Débora Tamires Vitor Pereira3* , Maria Aparecida Vieira Teixeira Garcia1 , Christiano Vieira Pires2  and Camila Argenta Fante1  1

Departamento de Alimentos, Faculdade de Farmácia, Universidade Federal de Minas Gerais – UFMG, Belo Horizonte, MG, Brasil 2 Departamento de Engenharia de Alimentos, Universidade Federal de São João del-Rei – UFSJ, São João del-Rei, MG, Brasil 3 Departamento de Engenharia e Tecnologia de Alimentos, Universidade Estadual de Campinas – Unicamp, Campinas, SP, Brasil *deboratvpereira@gmail.com

Abstract This work aimed to develop biodegradable films from yellow passion fruit (Passiflora edulis f. flavicarpa) peel flour.

The Central Composite Rotational Design was used in a total of 11 tests, in which the independent variables were the concentrations of starch and glycerol, characterized with regard to physical, mechanical and barrier properties. The films were classified as soluble and showed low permeability to water vapor. The tensile strength, elastic modulus and deformation rate were directly related to the concentration of starch and glycerol. The film of test 7 had the best characterization results; therefore, it was analyzed for biodegradability. As for biodegradability, the film obtained an average mass loss of 92.77 ± 4.28%, being a great alternative to the use of non-biodegradable polymers. The films showed acceptable degree of plasticization, which was favored by intermolecular interactions between the components of the flour, starch and glycerol.

Keywords: by-products, coating, fruits, packaging.

How to cite: Macedo, M. C. C., Silva, V. D. M., Rodrigues, C. G., Pereira, D. T. V., Garcia, M. A. V. T., Pires, C. V., & Fante, C. A. (2025). Valorization of passion fruit: development, characterization and optimization of biodegradable edible films. Polímeros: Ciência e Tecnologia, 35(1), e20250002. https://doi.org/10.1590/0104-1428.20240043

1. Introduction Wastes generated by the disposal of packaging produced from non-renewable sources is increasing in quantity every year and constitute a major environmental problem.

Approximately 30 to 40% of the total solid wastes produced in Brazil are the plastic materials used for packaging, such as that for food, for example[1]. Thus, there are numerous problems generated by the complexity of recycling most synthetic packaging available, associated with the generation of waste. With that, research is being carried out in order to develop biodegradable materials such as biodegradable films obtained from biopolymers, with features that allow their use in the industry[2,3].

Edible or biodegradable coatings work as a barrier to external elements deposited on the surface of the food.

They are characterized by their small thickness, so they can protect the product and increase its lifetime[4,5]. The peel of the passion fruit Passiflora edulis, known as yellow passion fruit, is a residue of the food industry, rich in phenolic compounds with antioxidant activity, pectin, fibers and carbohydrates[6,7]. Several studies on passion fruit peel and

Polímeros, 35(1), e20250002, 2025

peel flour demonstrate their technological potential for use in the food industry[8-10] among others.

As for the coatings, these constitute one of the methods with significant impact on the processes of preservation, distribution and marketing of food[11,12]. Therefore, the use of coatings produced from biodegradable compounds such as passion fruit peel, in addition to contributing to the environment, minimizing the environmental impact for not generating waste, can also increase the shelf-life of foods, allowing their marketing for a longer period and contributing to scientific development in the Food Science field. In this context, the present study aimed to develop and characterize biodegradable films prepared with passion fruit (P. edulis) residue flour.

2. Materials and Methods 2.1 Material The raw material was obtained from passion fruit peels (Passiflora edulis f. flavicarpa), acquired in the retail trade of the city of Belo Horizonte, MG, Brazil. Cornstarch (Maizena®, Unilever Brasil Industrial Ltda., Garanhuns,

1/8

O O O O O O O O O O O O O O O O O

Macedo, M. C. C., Silva, V. D. M., Rodrigues, C. G., Pereira, D. T. V., Garcia, M. A. V. T., Pires, C. V., & Fante, C. A. PE, Brazil) was purchased in a market in Belo Horizonte.

Glycerol (Dinâmica Química Contemporânea Ltda., Indaiatuba, SP, Brazil) and all chemicals employed in this work were reagent grade.

2.2 Methods Rigid and yellowish peels of passion fruit, were sanitized in running water and subjected to drying in an oven with forced air circulation (FANEM, 320, Brazil) at 60 ± 5 °C for 24 hours. After drying, the peels were crushed in a blender (Philips Walita, Walita Brasilia LB model, Brazil), and sieved through a sieve (Bertel Indústria Metalúrgica Ltda., 32 mesh, 500 mm, Brazil).

2.3 Statiscal design In this work, for the preparation and characterization of the biodegradable films, we decided to conduct a secondorder experimental design: the Central Composite Rotational Design (CCRD), which contains a central point carried out with replicates, which provides an estimate of pure error, and axial points, which in turn, determine the quadratic terms.

As parameters for this design, as the chosen independent variables the concentration of starch (w/w), in relation to the Passion Fruit Peel Flour (PFPF), and the content of plasticizer (w/w), in relation to PFPF. The dependent variables were the physical properties (thickness and water solubility), barrier properties (water vapor permeability), and mechanical properties (tensile strength, percentage of elongation,elastic modulus, puncture strength and deformation). Thus, this CCRD covered a total of 11 tests, comprising 3 central points, 4 factorial points and 4 axial points, as described in Table 1.

2.4 Development of biodegradable films For the development of biodegradable films, the casting technique was used according to Pelissari et al.[13], varying the amount of starch and plasticizer. In this way, the films were produced from aqueous filmogenic solutions, with the mixture of PFPF (10 g) and distilled water (375 mL), addition of cornstarch (at concentrations of the experimental design); heated under constant stirring (magnetic stirrer VELP Scientifica, Italy; water bath GMA Médica, Brazil) at 90 °C for 15 minutes; homogenization (Ultra-turrax Ultra Table 1. Statistical design for preparation and characterization of biodegradable films from passion fruit peel flour.

Run 1 2 3 4 5 6 7 8 9 10 11

2/8

Starch (g/100 g of flour) 40.00 (-1) 60.00 (+1) 40.00 (-1) 60.00 (+1) 35.85 (-1.41) 64.14 (+1.41) 50.00 (0) 50.00 (0) 50.00 (0) 50.00 (0) 50.00 (0)

Plasticizer (%) (g/100 g of flour) 20.00 (-1) 20.00 (-1) 40.00 (+1) 40.00 (+1) 30.00 (0) 30.00 (0) 15.85 (-1.41) 44.14 (+1.41) 30.00 (0) 30.00 (0) 30.00 (0)

Stirrer, Ultra80-II model) at 18000 rpm for 5 min; addition of glycerol (at concentrations of the experimental design); heated under stirring (magnetic stirrer VELP Scientifica, Italy; bath GMA Médica, Brazil) at 90 °C for 15 minutes; filtering; distribution (50 g) on polystyrene plates with 15 cm diameter and drying in forced air ventilation oven (FANEM, 320, Brazil) at 40 °C for 24 hours. The films obtained were then stored (58 ± 2% relative humidity RH, 25 °C) in desiccators containing saturated solution of sodium bromide for 48 hours before the analysis.

2.5 Film characterization All films were characterized with regard to physical properties, barrier properties and mechanical properties, according to the standards of the ASTM[14-17]. The film that showed the best parameters of continuity, homogeneity, handling and characterization was selected for determination of the biodegradability.

2.5.1 Hydrogen potential of filmogenic solutions Hydrogen potential (pH) was measured in the filmogenic solutions of each test of the experimental planning. The pH reading was conducted using a benchtop pHmeter (Bante, 920 model), according to the procedures described in the analytical standards of the Adolfo Lutz Institute[18]. All tests were carried out in triplicate.

2.5.2 F ilm thickness Film thickness was determined using a digital micrometer (Digimess Model, Electronic Outside Micrometer, São Paulo) with 0-25 mm scale and precision of 0.001 mm.

The values represented an average of 10 measurements randomly taken along each sample evaluated, following the ASTM F2251-13[15].

2.5.3 Solubility in water Water solubility was determined according to the method proposed by Gontard et al.[19].

2.5.4 Water vapor permeability (WVP) WVP was determined gravimetrically, following the standard method E96/E96M[17].

2.5.5 Mechanical properties The determination of the mechanical properties of the films, tensile strength (TS) (MPa), percent elongation at break (ε) (%), elastic modulus (EM) (MPa), puncture test (PT) (MPa) and puncture deformation (PD) (%), followed ASTM D638-14[16] and ASTM D882-12[14], using a texturometer (Stable Micro Systems, TA.XT2i, England).

2.5.6 Biodegradability The degree of biodegradation of the film was determined as the weight loss (WL;%), conducted according to the methodology proposed by Martucci and Ruseckaite[20].

2.6 Data analysis After performing all experiments, a quadratic model was fitted to the response data using Statistica software (Statsoft, Tulsa, OK, USA) version 10. The significant Polímeros, 35(1), e20250002, 2025

Valorization of passion fruit: development, characterization and optimization of biodegradable edible films terms (p < 0.05) in the model were found by analysis of variance (ANOVA) and the interactive effects between the factors were observed using response surface and contour plot, derived from the fitted quadratic model.

3. Results and Discussions

where y corresponds to the concentration of glycerol.

The model of thickness was satisfactory and valid, with determination coefficient of 83.44%. Thickness values are higher at maximum contents of glycerol (44.14% glycerol w/w) and lower at minimum contents (15.85% glycerol w/w) (Figure 1).

3.1 Hydrogen potential (pH) of the filmogenic solutions

3.3 Mechanical properties

The pH values of the filmogenic solutions corresponding to the experimental planning tests are shown in Table 2. In this study, the different filmogenic solutions did not differ statistically, showing average pH of 4.48 ± 0.06, which classifies a medium with acidic pH. According to Guilbert and Gontard[21] the use of edible coatings or films that promote pH reduction on food surface can reduce microbial growth. Thus, the use of a coating with low pH value may be desirable and beneficial to food preservation.

The values of mechanical properties concerning tensile strength, elongation at break, elastic modulus, puncture resistance and puncture deformation are shown in Table 3.

3.2 Thickness As shown in Table 2, the film with the highest amount of plasticizer (film 8, with 44.14% w/w of glycerin) was thicker, while the one with lowest amount of plasticizer (film 7, with 15.85% w/w of glycerin) showed lower value of this parameter when compared to the others. The concentration of the raw materials used may interfere with the thickness of the films formed, because viscous solutions tend to form thicker films[22].

Nascimento et al.[8] developed and characterized flexible films from starch and passion fruit mesocarp flour with nanoparticles and the values found for their thickness ranged from 0.133 to 0.185 mm. These values are higher than those measured in the present study for the films prepared with the PFPF. Therefore, depending on the form of processing, raw material used, homogeneity, among other factors, the films can have different values of thickness.

When evaluating the regression coefficients and the p-value, it was observed that the linear effect of glycerol content was significant at a 95% confidence interval. Thus, a mathematical model for thickness can be defined, Equation 1: Thickness = 0.068267 + 0.006347 y

3.3.1 Tensile strength The film with the lowest levels of glycerol (film 7, 15.85% glycerol w/w) had greater tensile strength, 1.60 ± 0.24 MPa, while film 8, with the highest concentration of glycerol (44.14%), showed lower resistance (0.52 ± 0.14 MPa). This result is due to the presence of glycerol in the filmogenic solutions, which increases the molecular mobility, thus reducing the strength of the hydrogen bonds between the starch molecules, making the films less resistant[23].

According to the analysis of the regression coefficients, the levels of starch and glycerol influenced the response, generating the following mathematical model, Equation 2: Tensile Strength (TS ) = 0.830273 + 0.231648 X − 0.406920 y (2)

where x corresponds to the concentration of starch and y to the concentration of glycerol.

Based on the ANOVA, the fitted model for the response was satisfactory, with R2 = 0.86071, and it was possible to observe (Figure 2) that higher levels of glycerol led to lower TS, while higher values of starch led to higher values of TS. 3.3.2 Elongation In this study, the elongation of the films ranged from 49.56 to 21.25%, and the films with the highest values (1, 2, 4, 6, 7, 8, 9, 10, and 11) differed significantly (p < 0.05) only from film 5, which was developed with lowest starch content. Starch also has hydrophilic character, which

(1)

Table 2. Average values of pH of the filmogenic solutions and thickness of the films obtained by tests of the experimental planning.

Film pH Thickness (mm) 1 4.47 ± 0.01a 0.066 ± 0.010bc a 2 4.60 ± 0.01 0.071 ± 0.018bcd 3 4.46 ± 0.01a 0.070 ± 0.011 bc 4 4.40 ± 0.03a 0.081 ± 0.013ab a 5 4.44 ± 0.02 0.072 ± 0.005bcd 6 4.40 ± 0.03a 0.076 ± 0.010abc 7 4.52 ± 0.01a 0.061 ± 0.011d a 8 4.46 ± 0.04 0.087 ± 0.025a a 9 4.42 ± 0.04 0.068 ± 0.008cd 10 4.42 ± 0.02a 0.068 ± 0.010cd 11 4.41 ± 0.03a 0.069 ± 0.007cd Average values ± standard deviation, n = 10. Equal letters in the same column do not differ by Tukey test at 5% significance level.

Polímeros, 35(1), e20250002, 2025

Figure 1. Response surface and contour curve of the thickness of films.

3/8

Macedo, M. C. C., Silva, V. D. M., Rodrigues, C. G., Pereira, D. T. V., Garcia, M. A. V. T., Pires, C. V., & Fante, C. A. Table 3. Average values of mechanical properties of films prepared with passion fruit peel flour.

Film

Tensile Strength Elongation Elastic Modulus (MPa) (%) (MPa) 1 1.55 ± 0.67ab 48.70 ± 9.21a 2.85 ± 0.66bc 2 1.47 ± 0.24abc 49.56 ± 5.46a 3.14 ± 0.44ab de ab 3 0.47 ± 0.08 34.40 ± 8.75 1.35 ± 0.14d 4 0.90 ± 0.33 bcd 44.02 ± 10.86a 2.23 ± 0.26c 5 0.13 ± 0.00e 21.25 ± 6.80b 0.74 ± 0.15d 6 1.28 ± 0.06abc 44.68 ± 2.66a 3.27 ± 0.26ab a a 7 1.60 ± 0.27 39.76 ± 4.15 3.86 ± 0.22a 8 0.52 ± 0.14de 43.68 ± 10.50a 1.18 ± 0.19d 9 0.82 ± 0.20cd 41.34 ± 10.58a 2.53 ± 0.20bc cd a 10 0.83 ± 0.09 41.38 ± 2.61 2.55 ± 0.11bc 11 0.83 ± 0.22cd 41.32 ± 8.98a 2.55 ± 0.15bc Equal letters in the same column do not differ significantly at 5% level.

Figure 2. Response surface and contour curve of the tensile strength of films.

is responsible for increasing the mobility of the chains, increasing elasticity.

The presence of PFPF in films produced from starch may favor an increase in the percentage of elongation, as shown in Table 3, where, with the exception of film 5, all others showed greater elongation, even with high levels of plasticizer. This is interesting because higher values of elongation indicate high flexibility[24] and make it easier for films to adhere, when applied to the surface of the food[25].

In general, films with greater thickness (> 0.100 mm) have values of elongation greater than 100%[26]. The developed films show small thickness, between 0.061 ± 0.011 mm and 0.087 ± 0.025 mm, i.e., they are thinner, consequently having elongation percentage lower than 100%.

3.3.3 Elastic modulus The films with lowest rigidity were those from the test 3 (40.00% starch and 40.00% glycerol), test 5 (35.85% starch and 30.00% glycerol) and test 8 (50.00% starch and 44.14% glycerol). The films 3 and 8 were developed with higher levels of glycerol, while film 5 was prepared with an intermediate content of glycerol, but with the lowest content of starch among the other films.

4/8

Puncture resistance (MPa) 10.63 ± 2.64a 10.27 ± 0.25ab 3.43 ± 1.88 de 5.71 ± 0.38cd 2.42 ± 0.41e 8.12 ± 1.68abc 9.51 ± 1.66ab 3.37 ± 1.21de 7.57 ± 0.89abc 7.73 ± 1.67abc 7.48 ± 0.87bc

Puncture Deformation (%) 25.55 ± 2.40abc 19.03 ± 0.82de 25.94 ± 1.83ab 23.92 ± 0.97abcd 29.10 ± 0.38a 20.00 ± 2.30cde 18.49 ± 0.43e 24.00 ± 3.53bcde 25.72 ± 2.97ab 25.71 ± 2.92ab 25.71 ± 2.92ab

Larger quantities of plasticizers in the preparation of films can reduce the intermolecular forces between the polymer chains[23]. Consequently, films with high glycerol concentrations and low starch concentrations are less rigid. Values close to that of this study were found by Arquelau et al.[27], in films developed with flour from ripe “Prata” banana peels, with lower concentrations of starch.

In the present study, the average pH value of the filmogenic solutions was 4.47, that is, acidic pH, which was one of the factors that influenced the lower values of the elastic modulus. Maniglia et al.[28] stated that, in alkaline medium, the turmeric proteins may have reached maximum dissolution, undergoing some conformation changes, which affected the mechanical properties of the films. Other studies also report how high pH values are able to produce a stronger and denser polymer matrix, with higher values of elastic modulus[29]. The elastic modulus was influenced by the contents of starch and glycerol, according to the analysis of the regression coefficients, generating the following mathematical model, Equation 3: EM = 2.54497 + 0.607340 x − 0.781538 y

(3)

where x corresponds to the concentration of starch and y to the concentration of glycerol.

Based on the ANOVA, the fitted model for the response was satisfactory, with R2= 0.89407, with a tendency of increase in EM at higher concentrations of starch and lower concentrations of glycerol (Figure 3).

3.3.4 Puncture resistance It is possible to see that the films prepared with the lowest values of plasticizers, for example, film 1 (20.00% glycerol and 40.00% starch), film 2 (20.00% glycerol and 60% starch, w/w) and film 7 (15.85% glycerol and 50% starch), have better mechanical resistance in the puncture test. By contrast, the films 6, 9 and 10, which did not differ from those with lower levels of plasticizers, were developed with intermediate concentrations of glycerol (30% w/w) and starch (films 9 and 10), while the film 6 was developed with the highest starch concentration among all tests. I Another parameter that has direct influence on resistance to puncture is thickness, because the higher the thickness, the greater the resistance of the film[30]. When compared Polímeros, 35(1), e20250002, 2025

Valorization of passion fruit: development, characterization and optimization of biodegradable edible films

Figure 3. Contour curve for elastic modulus.

Figure 4. Contour curve for puncture.

with other studies, the films of the present study have intermediate thickness, which makes them more flexible.

In relation to the puncture test, the analysis of the regression coefficients revealed along with p-value that the analyzed parameters (concentrations of starch and glycerol) are not statistically significant. Therefore, it was not possible to generate the mathematical model, variance analysis and the response surface and contour graphs.

Table 4. Average solubility (%) and average water vapor permeability (g mm h-1 m-2 kPa-1) of the films obtained by tests of the experimental planning.

3.3.5 Puncture deformation The deformation rate or puncture deformation is related to how far the film extends without breaking, so it is also a parameter involved with the flexibility of the material.

For the puncture deformation, there was a variation from 18.49 ± 0.43% (film 7) to 29.10 ± 0.38% (film 5). In regard to the puncture deformation, the analysis of the regression coefficients and the p-value revealed that the concentrations of glycerol and starch were statistically significant. Hence, it was possible to generate the mathematical model predicted for PD, with a significance level of 5%, Equation 4: Puncture Deformation = 2.571589 − 2.67690 x + 1.63418 y − 2.01545 y 2

(4)

where x is the concentration of starch and y corresponds to the concentration of glycerol.

The fitted model for PD is satisfactory (Table 2), with R2 = 0.96313. There is a higher rate of deformation for films with higher levels of glycerol and lower concentrations of starch, Figure 4.

3.4 Barrier properties The values of the barrier properties for permeability to water vapor and solubility are presented in Table 4.

3.4.1 Water vapor permeability The average values of water vapor permeability of the films processed with PFPF are presented in Table 4.

The values of WVP for the films were on average 0.32 ± 0.05 g mm h-1 m-2 kPa-1, with the exception of the film 7, with WVP of 0.029 ± 0.00 g mm h-1 m-2 kPa-1, statistically Polímeros, 35(1), e20250002, 2025

Film

Solubility Water vapor permeability (%) (mm h–1 m–2 kPa–1) 1 67.22 ± 8.64a 0.39 ± 0.12a ab 2 64.07 ± 1.30 0.30 ± 0.05a 3 34.32 ± 4.49d 0.29 ± 0.04a 4 54.75 ± 4.44bc 0.32 ± 0.01a c 5 51.91 ± 9.77 0.24 ± 0.02a abc 6 58.84 ± 1.63 0.33 ± 0.01a 7 61.07 ± 5.55 abc 0.029 ± 0.00b 8 58.43 ± 2.21 abc 0.36 ± 0.02a abc 9 57.46 ± 2.70 0.33 ± 0.05a 10 57.82 ± 1.63 abc 0.33 ± 0.04a 11 57.83 ± 1.91 abc 0.34 ± 0.02a Equal letters in the same column do not differ significantly at 5% level.

differing from the others. The developed films had low WVP, an extremely important factor in the development of materials used in food coating.

Han and Aristippos[31] classified films and common plastics with respect to barrier properties and, for water vapor permeability values lower than 0.1 (g.mm h-1 m-2 kPa-1), the films are characterized as of top quality, between -1 and 1 (0.1g mm h-1 m-2 kPa-1) as good, between 1 and 10 (g mm h-1 m-2 kPa-1) as intermediate, and greater than 10 g (mm h-1 m-2 kPa-1) as of lower quality. As for the classification of Han and Aristippos[31], it can be inferred that the developed films, except for film 7, are good in relation to WVP and can be compared to cellophane, for example, which is a natural polymer derived from cellulose and has the appearance of a thin, transparent, flexible and stressresistant film. For film 7, a mean WVP of 0.029 ± 0.00 g mm h-1 m-2 kPa-1 was obtained. This assay was performed with the lowest plasticizer content and intermediate amount of starch (50.00% starch and 15.85% glycerol, w/w), and the film was classified as a good with respect to the barrier properties. Considering this parameter, the film is comparable to materials such as polyethylene terephthalate (PET) and polyvinyl chloride (PVC)[31].

5/8

Macedo, M. C. C., Silva, V. D. M., Rodrigues, C. G., Pereira, D. T. V., Garcia, M. A. V. T., Pires, C. V., & Fante, C. A. The presence of higher plasticizer contents increased the WVP of the films, regardless of the amount of starch.

Glycerol has the ability to increase water absorption of the material[32]. However, films with higher WVP values are still good barrier materials.

Values very close to that of this study were found by Rocha et al.[33] when developing biodegradable films based on cassava starch and soy protein, where the maximum WVP was 0.393 g mm h-1 m-2 kPa-1 for films made with the maximum content of soy protein extract (47%) and glycerol (47%), at pH 4.0. WVP is influenced by pH. It is known that, when the filmogenic solution is in an acidic medium, the glycosidic/peptide bonds undergo hydrolysis, resulting in fragments of smaller size, with the possibility of forming empty spaces in the film, leading to increase in WVP[33].

As for the WVP of the films developed with PFPF, the pH did not show influence on this parameter, since all the tests presented good characteristics for WVP. 3.4.2 Solubility in water The solubility of the films with PFPF (Table 4) ranged from 34.32 ± 4.49% (film 3) to 67.22 ± 8.64% (film 1), classifying them as soluble. Films that have high solubility are not inferior to films with low solubility because each film, with its characteristic solubility, will be used according to the application.

High solubility in films is required for foods that, throughout the processing, are in direct contact with water and when the coating can be consumed. Water-soluble films can be used in products that, prior to consumption, need a certain amount of hydration, in encapsulated food additives and even in the agro sector, for example in agricultural seeds that require accelerated germination in the field[34].

Eça et al.[35], when developing films made of pectin, glycerol and calcium chloride containing fruit extract (acerola, cashew and strawberry), also found high solubility in water: 65.3 ± 1.5% using acerola extract, 73.1 ± 4.3% using cashew extract, and 70.5 ± 3.7% using strawberry extract, which are close to the maximum solubility values of the films developed.

The analysis of the regression coefficients for elongation, puncture test, WVP (water vapor permeability) and solubility revealed, together with the p-value, that the analyzed parameters (starch and glycerol concentrations) were not statistically significant, making it not possible to generate the mathematical model, analysis of variance and o response surface and contour plots.

3.5 Biodegradability The quantitative index of degradability of the films was calculated based on the mass loss. At the end of 10 days, the test film 7 (50% starch w/w; 15 min of heating, 15.86% plasticizer w/w), which had the best barrier properties, used for evaluation of biodegradability, obtained an average mass loss of 92.77 ± 4.28%, being a great alternative to the use of non-biodegradable polymers.

It is known that products derived from natural fibers in general are characterized by high biodegradability[36]. In other words, in this experiment, during the 10 days, microorganisms and their enzymes used the organic compounds present in 6/8

the films as food source, converting and redistributing them in cycles, such as the carbon and nitrogen cycles, promoting their biodegradation[36].

For a plastic to be considered biodegradable in the soil under real field conditions, it must not only disintegrate, but also undergo biodegradation, which should be greater than 90% without detrimental effects on the soil[37]. Therefore, with the loss of mass of 92.77 ± 4.28, the films developed with PFPF can be considered as biodegradable materials, and the short degradation period can reduce expenses in the processing of materials, besides not affecting the environment because they are developed with polymers from natural sources.

4. Conclusion Passion fruit peel flour has technological potential for the development of biodegradable films, due to the results obtained for mechanical, physical and barrier properties in the films developed. For the experiment, the concentration of cornstarch in the films influenced resistance to stress, elastic modulus and deformation rate, while the glycerol interfered in thickness, resistance to stress, elastic modulus, resistance to puncture and deformation rate in the films. The developed films have low WVP, an extremely important factor in materials used in food coating, especially the film 7 (50 g starch /100 g of flour and 15.85 g glycerol/ 100 g of flour), which is comparable to materials such as PET and PVC. With regard to biodegradability, the films showed significant loss of mass and were characterized as biodegradable. The production of films from passion fruit peel can contribute to the development of an environmentally correct technology that can allow food preservation time to be increased at low cost.

5. Author’s Contribution • Conceptualization – Maria Clara Coutinho Macedo; Viviane Dias Medeiros Silva; Camila Gonçalves Rodrigues; Débora Tamires Vitor Pereira; Camila Argenta Fante.

• Data curation – Maria Clara Coutinho Macedo; Viviane Dias Medeiros Silva.

• Formal analysis – Maria Clara Coutinho Macedo; Viviane Dias Medeiros Silva; Camila Gonçalves Rodrigues; Débora Tamires Vitor Pereira.

• Funding acquisition - Camila Argenta Fante; Maria Aparecida Vieira Teixeira Garcia; Christiano Vieira Pires.

• Investigation – Maria Clara Coutinho Macedo; Viviane Dias Medeiros Silva; Camila Gonçalves Rodrigues.

• Methodology – Maria Clara Coutinho Macedo; Viviane Dias Medeiros Silva; Camila Gonçalves Rodrigues; Débora Tamires Vitor Pereira.

• Project administration – Maria Clara Coutinho Macedo; Camila Argenta Fante; Maria Aparecida Vieira Teixeira Garcia; Christiano Vieira Pires.

• Resources – Camila Argenta Fante; Maria Aparecida Vieira Teixeira Garcia; Christiano Vieira Pires.

Polímeros, 35(1), e20250002, 2025

Valorization of passion fruit: development, characterization and optimization of biodegradable edible films • Software – Maria Clara Coutinho Macedo; Viviane Dias Medeiros Silva.

• Supervision – Camila Argenta Fante; Maria Aparecida Vieira Teixeira Garcia; Christiano Vieira Pires.

• Validation – Maria Clara Coutinho Macedo; Viviane Dias Medeiros Silva; Camila Gonçalves Rodrigues; Débora Tamires Vitor Pereira.

• Visualization – Maria Clara Coutinho Macedo; Viviane Dias Medeiros Silva.

• Writing – original draft – Maria Clara Coutinho Macedo; Viviane Dias Medeiros Silva.

• Writing – review & editing – Maria Clara Coutinho Macedo; Viviane Dias Medeiros Silva; Débora Tamires Vitor Pereira; Camila Argenta Fante.

6. Acknowledgements The authors are grateful for the financial support from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – CAPES and Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG).

7. References 1. Das, P., & Tiwari, P. (2018). Valorization of packaging plastic waste by slow pyrolysis. Resources, Conservation and Recycling, 128, 69-77. http://doi.org/10.1016/j.resconrec.2017.09.025.

2. Razavi, S. M. A., Mohammad Amini, A., & Zahedi, Y. (2015).

Characterisation of a new biodegradable edible film based on sage seed gum: influence of plasticiser type and concentration.

Food Hydrocolloids, 43, 290-298. http://doi.org/10.1016/j. foodhyd.2014.05.028.

3. Sun, X.-Z., Minowa, T., Yamaguchi, K., & Genchi, Y. (2015). Evaluation of energy consumption and greenhouse gas emissions from poly(phenyllactic acid) production using sweet sorghum. Journal of Cleaner Production, 87, 208-215. http://doi.org/10.1016/j.jclepro.2014.09.041.

4. Assis, O. B. G., & Britto, D. (2014). Revisão: coberturas comestíveis protetoras em frutas: fundamentos e aplicações.

Brazilian Journal of Food Technology, 17(2), 87-97. http:// doi.org/10.1590/bjft.2014.019.

5. Luvielmo, M., & Lamas, S. (2012). Edible coating in fruits.

Estudos Tecnológicos em Engenharia, 8(1), 8-15. http://doi. org/10.4013/ete.2012.81.02.

6. Alcântara, S. R., Sousa, C. A. B., Almeida, F. A. C., & Gomes, J. P. (2013). Caracterização físico-química das farinhas do pendúnculo do caju e da casca do maracujá. Revista Brasileira de Produtos Agroindustriais, 15(4), 349-355. http://doi. org/10.15871/1517-8595/rbpa.v15n4p349-355.

7. Zeraik, M. L., Yariwake, J. H., Wauters, J.-N., Tits, M., & Angenot, L. (2012). Analysis of 570 passion fruit rinds (Passiflora edulis): isoorientin quantification by HPTLC and 571 evaluation of antioxidant (radical scavenging) capacity.

Quimica Nova, 35(3), 541-545. http://doi.org/10.1590/S010040422012000300019.

8. Nascimento, T. A., Calado, V., & Carvalho, C. W. P. (2012).

Development and characterization of flexible film based on starch and passion fruit mesocarp flour with nanoparticles.

Food Research International, 49(1), 588-595. http://doi. org/10.1016/j.foodres.2012.07.051.

9. Pineli, L. L. O., Rodrigues, J. S. Q., Costa, A. M., Lima, H. C., Chiarello, M. D., & Melo, L. (2015). Antioxidants and sensory properties of the infusions of wild passiflora from Brazilian Polímeros, 35(1), e20250002, 2025

savannah: potential as functional beverages. Journal of the Science of Food and Agriculture, 95(7), 1500-1506. http:// doi.org/10.1002/jsfa.6852. PMid:25087571.

10. Seixas, F. L., Fukuda, D. L., Turbiani, F. R. B., Garcia, P. S., Petkowicz, C. L. O., Jagadevan, S., & Gimenes, M. L. (2014).

Extraction of pectin from passion fruit peel (Passiflora edulis f.flavicarpa) by microwave-induced heating. Food Hydrocolloids, 38, 186-192. http://doi.org/10.1016/j.foodhyd.2013.12.001.

11. Silva, J. B. A., Nascimento, T., Costa, L. A. S., Pereira, F. V., Machado, B. A., Gomes, G. V. P., Assis, D. J., & Druzian, J. I. (2015). Effect of source and interaction with nanocellulose cassava starch, glycerol and the properties of films bionanocomposites. Materials Today: Proceedings, 2(1), 200-207. http://doi.org/10.1016/j.matpr.2015.04.022.

12. Silva-Weiss, A., Ihl, M., Sobral, P. J. A., Gómez-Guillén, M. C., & Bifani, V. (2013). Natural additives in bioactive edible films and coatings: functionality and applications in foods. Food Engineering Reviews, 5(4), 200-216. http://doi.org/10.1007/ s12393-013-9072-5.

13. Pelissari, F. M., Andrade-Mahecha, M. M., Sobral, P. J. A., & Menegalli, F. C. (2013). Comparative study on the properties of flour and starch films of plantain bananas (Musa paradisiaca).

Food Hydrocolloids, 30(2), 681-690. http://doi.org/10.1016/j. foodhyd.2012.08.007.

14. American Society for Testing and Materials – ASTM. (2001).

ASTM D882-12: Standard test method for tensile properties of thin plastic sheeting. West Conshohocken: ASTM International.

15. American Society for Testing and Materials – ASTM. (2013).

ASTM F2251-13: standard test method for thickness measurement of flexible packaging material. West Conshohocken: ASTM International.

16. American Society for Testing and Materials – ASTM. (2015).

ASTM D638-14: standard test method for tensile properties of plastics. West Conshohocken: ASTM International.

17. American Society for Testing and Materials – ASTM. (2016).

ASTM E96/E96M-16: standard test methods for water vapor transmission of materials. West Conshohocken: ASTM International.

18. Instituto Adolfo Lutz – IAL. (1985). Analytical norms of the Adolfo Lutz Institute: physical-chemical methods for food analysis (2nd ed.). São Paulo: IAL. 19. Gontard, N., Duchez, C., Cuq, J.-L., & Guilbert, S. (1994).

Edible composite films of wheat gluten and lipids: water vapour permeability and other physical properties. International Journal of Food Science & Technology, 29(1), 39-50. http:// doi.org/10.1111/j.1365-2621.1994.tb02045.x.

20. Martucci, J. F., & Ruseckaite, R. A. (2009). Biodegradation of three-layer laminate films based on gelatin under indoor soil conditions. Polymer Degradation & Stability, 94(8), 13071313. http://doi.org/10.1016/j.polymdegradstab.2009.03.018.

21. Guilbert, S., & Gontard, N. (2005). Agro-polymers for edible and biodegradable films: review of agricultural polymeric materials, physical and mechanical characteristics. In J. H. Han (Ed.), Innovations in food packaging (pp. 263-276). London: Academic Press. http://doi.org/10.1016/B978-0123116321/50048-6.

22. Cuq, B., Aymard, C., Cuq, J.-L., & Guilbert, S. (1995). Edible packaging films based on fish myofibrillar proteins: formulation and functional properties. Journal of Food Science, 60(6), 1369-1374. http://doi.org/10.1111/j.1365-2621.1995.tb04593.x.

23. Orue, A., Corcuera, M. A., Peña, C., Eceiza, A., & Arbelaiz, A. (2016). Bionanocomposites based on thermoplastic starch and cellulose nanofibers. Journal of Thermoplastic Composite Materials, 29(6), 817-832. http://doi.org/10.1177/0892705714536424.

24. Silva, V. D. M., Macedo, M. C. C., Rodrigues, C. G., Santos, A. N., Loyola, A. C. F., & Fante, C. A. (2020). Biodegradable 7/8

Macedo, M. C. C., Silva, V. D. M., Rodrigues, C. G., Pereira, D. T. V., Garcia, M. A. V. T., Pires, C. V., & Fante, C. A. edible films of ripe banana peel and starch enriched with extract of Eriobotrya japonica leaves. Food Bioscience, 38, 100750. http://doi.org/10.1016/j.fbio.2020.100750.

25. Cardoso, T., Demiate, I. M., & Danesi, E. D. G. (2017).

Biodegradable films with Spirulina platensis as coating for cambuci peppers (Capsicum sp.). American Journal of Food Technology, 12(4), 236-244. http://doi.org/10.3923/ ajft.2017.236.244.

26. Fakhouri, F. M., Martelli, S. M., Caon, T., Velasco, J. I., & Mei, L. H. I. (2015). Edible films and coatings based on starch/gelatin: film properties and effect of coatings on quality of refrigerated Red Crimson grapes. Postharvest Biology and Technology, 109, 57-64. http://doi.org/10.1016/j.postharvbio.2015.05.015.

27. Arquelau, P. B. F., Silva, V. D. M., Garcia, M. A. V. T., Araújo, R. L. B., & Fante, C. A. (2019). Characterization of edible coatings based on ripe “Prata” banana peel flour. Food Hydrocolloids, 89, 570-578. http://doi.org/10.1016/j.foodhyd.2018.11.029.

28. Maniglia, B. C., Domingos, J. R., Paula, R. L., & TapiaBlácido, D. R. (2014). Development of bioactive edible film from turmeric dye solvent extraction residue. LebensmittelWissenschaft + Technologie, 56(2), 269-277. http://doi. org/10.1016/j.lwt.2013.12.011.

29. Andrade-Mahecha, M. M., Tapia-Blácido, D. R., & Menegalli, F. C. (2012). Development and optimization of biodegradable films based on achira flour. Carbohydrate Polymers, 88(2), 449-458. http://doi.org/10.1016/j.carbpol.2011.12.024.

30. Mali, S., Sakanaka, L. S., Yamashita, F., & Grossmann, M. V. E. (2005). Water sorption and mechanical properties of cassava starch films and their relation to plasticizing effect.

Carbohydrate Polymers, 60(3), 283-289. http://doi.org/10.1016/j. carbpol.2005.01.003.

31. Han, J. H., & Aristippos, G. (2005). Edible films and coatings: a review. In J. H. Han (Ed.), Innovations in food packaging (pp.

8/8

239-262). London: Academic Press. http://doi.org/10.1016/ B978-012311632-1/50047-4.

32. Silva, E. C. O., Silva, W. P., Silva, E. T., Lopes, J. D., & Gusmão, R. P. (2016). Obtenção e caracterização da farinha do albedo de maracujá (Passiflora edulis f. Flavicarpa) para uso alimentício.

Revista Verde de Agroecologia e Desenvolvimento Sustentável, 11(3), 69-74. http://doi.org/10.18378/rvads.v11i3.4062.

33. Rocha, G. O., Farias, M. G., Carvalho, C. W. P., Ascheri, J. L. R., & Galdeano, M. C. (2014). Biodegradable composite films based on cassava starch and soy protein. Polímeros: Ciência e Tecnologia, 24(5), 587-595. http://doi.org/10.1590/01041428.1355.

34. Bertuzzi, M. A., Armada, M., & Gottifredi, J. C. (2007).

Physicochemical characterization of starch based films. Journal of Food Engineering, 82(1), 17-25. http://doi.org/10.1016/j. jfoodeng.2006.12.016.

35. Eça, K. S., Machado, M. T. C., Hubinger, M. D., & Menegalli, F. C. (2015). Development of active films from pectin and fruit extracts: light protection, antioxidant capacity, and compounds stability. Journal of Food Science, 80(11), C2389-C2396. http:// doi.org/10.1111/1750-3841.13074. PMid:26444565.

36. Azwa, Z. N., Yousif, B. F., Manalo, A. C., & Karunasena, W. (2013). A review on the degradability of polymeric composites based on natural fibres. Materials & Design, 47, 424-442. http://doi.org/10.1016/j.matdes.2012.11.025.

37. Briassoulis, D., & Dejean, C. (2010). Critical review of norms and standards for biodegradable agricultural plastics part I. biodegradation in soil. Journal of Polymers and the Environment, 18(3), 384-400. http://doi.org/10.1007/s10924-010-0168-1.

Received: Apr. 29, 2024 Revised: Oct. 29, 2024 Accepted: Oct. 31, 2024

Polímeros, 35(1), e20250002, 2025

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20240071

Micro and nanoparticulate PP/CaCO3 composites mechanical, thermal and transport properties - DOE* Juliano Martins Barbosa1,2* , Caroline Valadão Pacheco1 , Gisele Szilágyi1 , Patrícia Candioto de Oliveira1 , Renato Meneghetti Peres1  and Hélio Ribeiro1  Departamento de Engenharia de Materiais, Escola de Engenharia, Universidade Presbiteriana Mackenzie, São Paulo, SP, Brasil 2 Programa de Pós-graduação em Ciência e Engenharia de Materiais - PPGCEM, Departamento de Engenharia de Materiais – DEMa, Universidade Federal de São Carlos - UFSCar, São Carlos, SP, Brasil 1

*barbosa_jm@yahoo.com.br *This paper has been partially presented at the 17th Brazilian Polymer Congress, held in Joinville, SC, 29/Oct - 02/Nov/2023.

Abstract Composite based on PP/CaCO3 contained micro and nanoparticles were investigated in relation its activation volume, mechanical, thermal and transport properties. The additives were initially dispersed in homopolymer polypropylene (hPP) blended with compatibilizer maleic anhydride grafted polypropylene (PP-g-MA) in twin-screw extruder, producing CaCO3 masterbatches, that were subsequently diluted in hPP. To optimize fillers dispersion in the polymer matrix, a Design of Experiment (DOE) was used, that combined Extruder screw rotation (N: 250 and 500 rpm); Extruder feed flow (Q:10 and 15 kg/h) and Average particle size (ϕ: 40 nm and 1.7 μm) at four different filler concentrations. Based on mechanical characterization results, the best process found was 500 rpm@10 kg/h, which provided suitable Specific Mechanical Energy (SME), increasing the nanocomposites strength. Finally, improvements of Impact Resistance up to 7.8% and Young’s Modulus up to 9.3% related to microcomposite and Tensile Strength (Fmax), up to 7.9%, related to hPP, with higher strain.

Keywords: activation volume, calcium carbonate, design of experiment, mineral fillers, nanocomposites.

How to cite: Barbosa, J. M., Pacheco, C. V., Szilágyi, G., Oliveira, P. C., Peres, R. M., & Ribeiro, H. (2024). Micro and nanoparticulate PP/CaCO3 composites mechanical, thermal and transport properties - DOE. Polímeros: Ciência e Tecnologia, 35(1), e20250003. https://doi.org/10.1590/0104-1428.20240071

1. Introduction Polymers have been filled with various materials to enhance different properties such as thermal, mechanical, electrical, or transport properties[1-3]. In this context, inorganic mineral fillers like talc, mica, silica, and calcium carbonate are commonly, also have been used in different proportions added to the polymeric matrix[4], owing to their varied aspect ratio and interfacial interactions[5]. These fillers interactions have been studied to seek improvements since macroscopic reinforcing elements typically have imperfections. Therefore, smaller reinforcing elements, even reaching the nanometric scale, are sought to reduce these imperfections in desired materials[6].One of the most commonly used mineral fillers is CaCO3, available in natural or synthetic forms[7]. Micrometric particles are typically selected using sieves, while the nanometric are prepared using various techniques, such as physical vapor deposition, chemical vapor deposition, reactive precipitation, sol-gel, and microemulsion methods[8], among these, industrial reactive precipitation is of particular interest[8]. Additionally,

Polímeros, 35(1), e20250003, 2025

the shape of the particles also influences its properties when used in composites. For instance, using spherical or elongated nanoparticles can influence their physical and chemical properties differently, due to its distinct aspect ratios[4]. Typically, the electrical, mechanical and thermal properties obtained from nanocomposites usually are superior to the microcomposites, without affect the polymer processability[8,9]. Additionally, dispersing nanoparticles in a polymeric matrix can create new levels of interaction, not present in microparticle systems, leading to changes their features and improvements in its physical properties.

Nanocomposite processing can be achieved using various techniques including in-situ polymerization, melt mixing, and the sol-gel process, among others, each with its own advantages and disadvantages[8]. To enhance dispersion during the melt mixing process, one option is to modify the surface of the nanoparticles[10] This strategy can prevent agglomeration, improves dispersion quality, and enhances adhesion with the polymeric matrix. Usually, nanoparticles are treated with surfactants or organic agents, like those used in conventional composites. Although these agents

1/10

O O O O O O O O O O O O O O O O O

Barbosa, J. M., Pacheco, C. V., Szilágyi, G., Oliveira, P. C., Peres, R. M., & Ribeiro, H. can improve filler dispersion, they may not always facilitate strong adhesion between components, leading to limited interaction and short-distance bonding in nanocomposites, mainly in thermoplastic polymers[9]. Alternatively, adjusting the process itself can be considered. It’s worth noting that smaller particles have a larger surface area, increasing the system’s surface energy and promoting enhanced interaction between components[11]. Dispersing particles without modification is difficult as they tend to aggregate. Hence, efficient shear processes with Specific Mechanical Energy (SME) are crucial for nanoparticle dispersion[12,13]. The SME can be modulated during extrusion by adjusting the extruder screw rotation (N) and extruder feed flow (Q), aiding in better filler dispersion, and breaking up the aggregates[14]. Rocha et al.

[15] investigated this phenomenon, by the influence of twinscrew extruder rotation on incorporating various CaCO3 nanoparticles into hPP, resulting in a significant increase in flexural strength without compromising impact resistance.

Similarly, Thio et al.[16] examined the impact of CaCO3 particle size on PP mechanical properties. They analyzed three CaCO3 types sized at 0.07, 0.7, and 3.5 µm, dispersed in PP at concentrations from 0.05 to 0.30 wt%. With low filler levels, Young’s Modulus increased, and tensile strength decreased regardless of filler size. Impact resistance improved with filler content until a critical concentration. Notably, the 0.7 µm filler increased composite impact resistance by fourfold compared to unfilled PP at a 5wt%[16]. Chan et al.[17] investigated the addition of CaCO3 nanoparticles (44,0 nm) into hPP via a twin-screw extruder at various concentrations, observing an increase in the composite’s impact resistance.

Zhang et al.[18] fabricated PP/CaCO3 nanocomposites using a twin-screw extruder, integrating a small amount of nonionic modifier (poly-oxyethylene noni-phenol) during extrusion to enhance compatibility between filler and the polymer matrix. Considering the properties of CaCO3 nanoparticles, there is potential for its utilization in several materials, such as: plastics, rubbers, paints and other natural or synthetic materials, as reinforcement or additives[3,19]. For example, its addition in PP can raise both impact resistance and Young’s modulus at the same time[19]. Thus, this study focused on crafting PP/CaCO3 composites using a PP-g-MA compatibilizer agent and employing a Design of Experiment (DOE)[20,21]. In this case, the processing was used in two stages: initially preparing the masterbatches followed by different dilutions steps. Essential tests were conducted at each stage to evaluate the properties of interest[22,23].

2. Materials and Methods The study unfolded in two phases: First involved designing experiments (DOE) to prepare and dilute the concentrates,

while second, it was focused on characterizing micro and nanocomposites. Initially, a concentrate was created using a co-rotational twin-screw extruder, employing DOE and adjusting shear levels via SME, varying extrusion parameters such as extruder screw rotation (N) and feed flow (Q) to modulate it. Subsequently, dilutions of each concentrate were conducted to produce micro and nanocomposites, which were characterized to evaluate mechanical, thermal, and transportation properties. The used nanoparticulate precipitated of CaCO3 NPCC-201 (D50: 40 nm, surface area: 40 m2/g, purity > 94.5% treated with fatty acid), was manufactured

by NanoMaterial Technology Pte Ltd – Singapore[24] and Microparticulate CaCO3 Omyacarb 1T-AV (D50: 1.6 to 1.7μm, purity > 97.3%, also treated with fatty acid), was manufactured

by Omya International AG - Italy[25]. Compatibilizer maleic anhydride grafted polypropylene (PP-g-MA) - Fusabond P MD353D (MFI: 450 g/10min - 2.16 kg@190 ºC, MP: 136 °C and maleic anhydride concentration > 1,0%), were supplied by DOW Inc[26]. Polypropylene (PP) homopolymer, H301 (MFI: 10 g/10min - 2.16 kg@230 ºC), was supplied by Braskem S/A[27]. The Desig of Experiment (DOE) combined three variables at two levels: Extruder screw rotation (N: 250 and 500 rpm), Extruder feed flow (Q: 10 and 15 kg/h) and D50 (ϕ: 40nm and 1.7μm). The samples were identified according to the methodology shown in Figure 1 below[22].

Combining the variables, it was obtained eight processing conditions, as shown in Table 1.

To prepare the concentrates (masterbatchs), it was used 20% of CaCO3 (micro or nanoparticulate), 70% hPP, and 10% PP-g-MA, processed in a co-rotational twin-screw extruder (ZSK18 Coperion GmbH, D: 18 mm, L/D: 48, power of 4 kW /5.43 hp, max amperage of 15.2 A, max screw rotation of 600 rpm, and a max feed rate of 140 kg/h) using the main feeder (without side feeder). The thermal profile ranged from 140 to 180 °C, and the extruder screw profile was based on the scheme shown in Figure 2[28], with adaptations due to differences in the L/D of the extruders.

The concentrates previously prepared were diluted in hPP using the same twin-screw extruder (Temp.: 140–180°C, N: 500 rpm, Q: 10 kg/h). Dilutions were carried out at four dosages for each concentrate: 2.5%, 7.5%, 25.0%, and 50.0%. Consequently, the CaCO3 content in each composite depended on the proportion added to hPP, calculated as the dosage multiplied by the CaCO3 content in the concentrate, resulting in 0.5%, 1.5%, 5.0%, and 10.0%. These values were used to identify each composite. In relation to the MFI (Melt Flow Index) of hPP, it was obtained a value of 10.8 g/10 min (2.16 kg@230 ºC). Due to the very low viscosity of PP-g-MA, its exact value could not be accurately determined, but it was detected to be >200 g/10 min under

Figure 1. Methodology for identifying samples.

2/10

Polímeros, 35(1), e20250003, 2025

Micro and nanoparticulate PP/CaCO3 composites mechanical, thermal and transport properties - DOE Table 1. Process conditions for the concentrates.

Run Concentrate 1 Concentrate 2 Concentrate 3 Concentrate 4 Concentrate 5 Concentrate 6 Concentrate 7 Concentrate 8

Sample N_250_10 M_250_10 N_250_15 M_250_15 N_500_10 M_500_10 N_500_15 M_500_15

Screw rotation N (rpm) 250 250 250 250 500 500 500 500

Feed flow Q (kg/h) 10 10 15 15 10 10 15 15

Particle size ϕ (μm) 0.04 1.70 0.04 1.70 0.04 1.70 0.04 1.70

Figure 2. Diagram of the screw profile used in processing.

the same conditions. The ash content (inorganic part) of masterbatches samples were conducted in triplicate, and the values are shown in Table 2. To determine the crystallinity degree of the concentrates, each peak area, along with the amorphous halo (Ac + Aa), was calculated, generating a sum of the areas. This determination was performed using the Origin Pro8 program with the Fit Multi-peaks tool, applying the Lorentzian peak function. After establishing a baseline to eliminate the amorphous halo, the same peaks areas were measured again (Ac).

5KN; deformation speeds: 50 mm/min)[31]. The Activation Volume was determined by the Eyring equation, that is associated with mobility at the organic-inorganic interface, specifically the polymer-filler interface. Therefore, the smaller the activation volume of the composite, the greater the restriction on the mobility of chain segments at the polymer-filler interface, indicating stronger interaction.

This model is represented in Equation 1[32]. σ≅

V  A RT + × ln   V V  V0 

(1)

α=

RT V

(2)

2.1. Characterization For the CaCO3 particles morphological characterization was used Scanning Electron Microscopy (SEM) on the Zeiss-Supra 35 equipment. The average particle sizes of CaCO3 micro and nanoparticles were characterized with size measurements conducted via Image J software.

X-ray Diffraction (WADX) on the Rigaku DMax 2500 PC equipment (radiation source: CuKα, λ: 1.54056 Å, scan at 2θ: 5 to 75°). The surface area (BET) was determined by the Micromeritics Instrument Corporation model ASAP 2000 V3.03 A, with a N2 atmosphere. For the polymers, hPP and PP-g-MA. The MFI[29] was determined using the Aflow Extrusion Plastometer (ZwickRoell GmbH & Co) at 2.16 kg@230 ºC. For concentrate characterization, the Ash Content[30] was determined by heating until constant mass in an oven (600 °C). Additionally, X-ray Diffraction (with a CuKα radiation source, λ: 1.54056 Å, scan at 2θ: 1 to 30°) was used to determine the crystallinity degree. The composite specimens were molded by injection molding in the Romi Primax 65R equipment (Injection temperature: 200 ºC@70 bar, mold: 23±2 ºC@35 s). Tensile tests were executed on the Universal Testing Machine (Z100-100 kN equipment) from ZwickRoell GmbH & Co. To determine the Young’s modulus, tensile strength and elongation of the composites, it was used the following parameters (load cell: Polímeros, 35(1), e20250003, 2025

Where σ is the tensile strength (εmax), A is the activation energy, V is the activation volume, T is the temperature, R is the universal gas constant (8.31 J.mol-1.K-1). The correlation between σ and the logarithm of the Deformation Speed ​​is linear, whose slope of the generated line, can be represented

by Equation 2[32]. The tensile strength (σ) was determined at three different deformation speeds (20, 50 and 100 mm/ min) at temperature of 25 ºC. The Izod Impact Resistance tests were performed on Pendulum Impact Testers, (HIT50P model) from ZwickRoell GmbH & Co, specimen 3.17 x 12.7 mm, notched, pendulum: 2.75 J and velocity 3.46 m/s[33,34].

3. Results and Discussion As shown in Figure 3a, the CaCO3 microparticulates presented itself in the form of flakes with medium size of ~1.5 µm. Figure 3c, presents the CaCO3 nanoparticulates micrograph with spherical shapes with size of ~70 nm. The histograms in Figures 3b, d show the size distributions of the respective CaCO3 particles. Comparing the smallest microparticles to the largest nanoparticles reveals a relative 3/10

Barbosa, J. M., Pacheco, C. V., Szilágyi, G., Oliveira, P. C., Peres, R. M., & Ribeiro, H. Table 2. Results of the characterization of concentrates and SME used.

Sample hPP M_250_10 M_250_15 M_500_10 M_500_15 N_250_10 N_250_15 N_500_10 N_500_15

N (rpm) 250 250 500 500 250 250 500 500

Q (kg/h) 10 15 10 15 10 15 10 15

ϕ (μm) 1.7 1.7 1.7 1.7 0.04 0.04 0.04 0.04

Ash Content (%) 0.15 ± 0.01 21.19 ± 0.41 18.88 ± 0.26 20.17 ± 0.10 20.27 ± 0.06 20.14 ± 0.02 19.68 ± 0.10 17.16 ± 0.14 18.66 ± 0.06

Xc (%) 65.9 63.6 54.5 59.7 63.2 61.5 59.7 57.3 63.6

Torque (%) 69.8 78.4 58.6 65.8 73.3 80.7 62.4 66.4

SME (kWh/kg) 0.12 0.09 0.20 0.15 0.12 0.09 0.21 0.15

Figure 3. Microscopy: (a) microparticulates CaCO3 – 30,000x and (c) nanoparticulates CaCO3 – 75,790x in different magnification.

Particle size distribution: (b) microparticulates and (d) nanoparticulates.

size distribution difference of about 4x. Considering the D50 value, this relative distribution difference increases to about 20x. A similar distribution between the CaCO3 micro and nanoparticles also was observed by Thio et al.[16].

Regarding the diffraction patterns of the micro and nanoparticle CaCO3 samples shown in Figure 4, the main diffraction peaks in 2θ can be observed at 23.2º, 29.6º, 36.3º, 39.6º, 43.3º, 47.7º, 48.6º, 56.6º and 57.6º characteristics of the crystallographic planes (102), (104), (110), (113), (202), (108), (116), (211) and (212) respectively in different phases of CaCO3[35].

The specific surface area (BET) of CaCO3 particles, the nanoparticles presented value of 24.19 ± 0.18 m2/g, while the microparticles had a value of 6.89 ± 0.16 m2/g. These values differ from those reported by the manufacturers, likely due 4/10

Figure 4. X-ray diffractogram of micro and nanoparticle CaCO3.

Polímeros, 35(1), e20250003, 2025

Micro and nanoparticulate PP/CaCO3 composites mechanical, thermal and transport properties - DOE to the interference of the surface treatment on the particles.

Despite the nominal value being 20.0%, the obtained results closely matched as expected, except for sample N_500_10, which was 2.8 points below the nominal value, likely due to processing losses. However, this discrepancy didn’t affect the results, as the studies were based on the actual sample values rather than the nominal ones. Important information from the X-ray diffraction test (range: 1 to 30º) enabled the identification of fillers and determination of the degree of crystallinity in the concentrate samples. Figures 5a-b display the diffractogram for the nano and microparticulate CaCO3 concentrates, with characteristic peaks at 23.2º and 29.6º, confirming its presence[35], which are characteristic of planes (102) and (104) respectively, as also observed in the diffractogram in Figure 04.

However, it is important to mention the presence of an important signal of 2θ = 16.0° related to the (300) plane, characteristic of the formation of the β phase of PP as also observed by Sakahara et al.[36].According to these authors, the increase in the intensity of the β phase in PP positively interferes in different mechanical properties, such as tensile strength, flexural modulus and impact resistance. This feature is explained by the tenacity of the beta crystalline phase and its metastability, which allows its conversion to the most common α crystalline phase observed under mechanical

load and thermal stress[36]. In this study, it was found that the intensities of this 2θ = 16.0° peak are more intense for the PP/CaCO3 nanocomposites, which had a positive impact on its mechanical properties, as will be discussed later. The ratio between these two areas results in the crystallinity degree (Xc), as shown in Equation 3[36,37]. Figure 6 shows a treatment example applied to the hPP diffractogram, both with and without the amorphous halo, and the concentrate results are presented in Table 2.

Xc =

Ac Ac + Aa

(3)

The Xc results, is consistent with literature values, which range between 60 and 70%[38]. For the concentrates, lower values are observed, possibly due to the high CaCO3 content interfering with crystallite formation and growth. Using the extrusion parameters shown in Table 1, it was possible to determine and modulate the SME of the process according to extruder screw rotation (N) and extruder feed flow (Q)[14].

The parameters associated are presented in Equation 4[12,13] T   N0 ×Wmax ×   100 N max  SME =    Q    

(4)

Figure 5. X-ray diffractogram of micro (a) and nanoparticle (b) CaCO3 concentrate.

Figure 6. X-ray diffractogram of hPP with amorphous halo (a) and without amorphous halo (b).

Polímeros, 35(1), e20250003, 2025

5/10

Barbosa, J. M., Pacheco, C. V., Szilágyi, G., Oliveira, P. C., Peres, R. M., & Ribeiro, H. Here, N0 is the extruder screw rotation (rpm), Nmax is the maximum extruder screw rotation (rpm), Wmax is the maximum power of the extruder engine (kW), T is the extruder torque (%), and Q is the feed flow (kg/h). The SME values are shown in Table 2.

The compounds prepared with different SME levels did not show significant differences in Xc, likely due to the high mineral filler concentration. Specific conditions can favor or hinder the degree of crystallinity. Higher screw rotations combined with lower feed flows can provide more energy to the system, enhancing particle dispersion in the polymer matrix, particularly for smaller particles that are more difficult to disperse due to their high surface area[12,15].

The composites inorganic material content was determined, considering the raw material purity. The actual CaCO3 content in each sample was used, as shown in Tables 3, to minimize concentration effects. It was observed that the CaCO3 content in the composites was very close to the nominal values, indicating minimal losses during processing.

Samples prepared with a feed flow of 10 kg/h showed equivalent values for both nano and microparticles. At 15 kg/h, microparticles performed better at a screw rotation of 250 rpm, while nanoparticles performed better at 500 rpm. Regarding Table 3. CaCO3 content for micro and nanocomposite

CaCO3 content, microparticles showed stable properties with increasing filler content. However, nanocomposites exhibited an increasing tendency in impact resistance with increasing filler content, as depicted in Figure 7. As studied

by Yang et al.[4], Huang et al.[9] and Eiras[19], the addition of nanoparticulate CaCO3 increases the composite impact resistance, in relation to original polymer.

Regarding mechanical properties under tension, the Young’s Modulus, Tensile Strength (Fmax), and Strain (Fmax), were studied. For Young’s Modulus, the microparticulate showed superior results at 250 rpm, while the nanoparticulate performed better at 500 rpm. The best results for both were achieved with a feed rate (Q) of 10 kg/h, as seen in Figure 8. However, these results are below those reported in the literature[4,9,39].

In terms of Tensile Strength (Fmax), all configurations exhibited better results for nanoparticles, particularly the sample processed at 500 rpm and 10 kg/h, showed superior properties compared to others, as depicted in Figure 9 and consistent with Yang et al.[4] For the strain (Fmax) property, with 500 rpm exhibited higher deformation values, particularly when fed at 10 kg/h,

Sample

Ash content (%)

CaCO3 content (%)

Sample

Ash content (%)

CaCO3 content (%)

M_250_10_0.50

0.56 ± 0.01

0.55

N_250_10_0.50

0.60 ± 0.02

0.57

M_250_10_1.50

1.07 ± 0.04

1.04

N_250_10_1.50

1.54 ± 0.05

1.45

M_250_10_5.00

5.27 ± 0.07

5.14

N_250_10_5.00

4.96 ± 0.07

4.69

M_250_10_10.0

10.68 ± 0.19

10.41

N_250_10_10.0

10.16 ± 0.11

9.60

M_250_15_0.50

0.57 ± 0.01

0.56

N_250_15_0.50

0.57 ± 0.06

0.54

M_250_15_1.50

1.55 ± 0.08

1.51

N_250_15_1.50

1.56 ± 0.01

1.47

M_250_15_5.00

5.08 ± 0.11

4.95

N_250_15_5.00

5.05 ± 0.16

4.77

M_250_15_10.0

9.87 ± 0.17

9.62

N_250_15_10.0

9.97 ± 0.10

9.25

M_500_10_0.50

0.64 ± 0.06

0.62

N_500_10_0.50

0.51 ± 0.04

0.48

M_500_10_1.50

1.55 ± 0.10

1.51

N_500_10_1.50

1.31 ± 0.02

1.24

M_500_10_5.00

5.17 ± 0.07

5.04

N_500_10_5.00

4.36 ± 0.04

4.12

M_500_10_10.0

10.33 ± 0.03

10.07

N_500_10_10.0

8.33 ± 0.09

7.87

M_500_15_0.50

0.67 ± 0.04

0.65

N_500_15_0.50

0.54 ± 0.01

0.51

M_500_15_1.50

1.68 ± 0.09

1.64

N_500_15_1.50

1.50 ± 0.02

1.42

M_500_15_5.00

5.32 ± 0.03

5.19

N_500_15_5.00

5.06 ± 0.07

4.78

M_500_15_10.0

10.19 ± 0.18

9.94

N_500_15_10.0

9.63 ± 0.06

9.11

Figure 7. Impact resistance for microparticulated (a) and nanoparticulated composite (b).

6/10

Polímeros, 35(1), e20250003, 2025

Micro and nanoparticulate PP/CaCO3 composites mechanical, thermal and transport properties - DOE where the highest SME (0.21 kWh/kg) was observed. In other conditions, the values between micro and nanoparticulated composites were similar. Analyzing the influence of particle size (ϕ), in microparticles, there is a strong tendency to reduce the strain increasing CaCO3 content, but less pronounced for nano, as Figure 10.

The Activation Volume (V), determined by the Eyring equation, reflects the polymer-filler interface mobility. A smaller activation volume indicates greater restriction on the

mobility of the chain segments, suggesting better dispersion and interaction between the filler and the matrix. Using Equation 2 and the values of σ at different speeds[22] for each composition, the V of the composites, was determined[23,40] based on filler content, as shown in Figure 11.

The Activation Volume was indirectly measured by the Tensile Resistance (Fmax), where it can observe that the results obtained are consistent with those reported by Rocha et al.[15].

Higher rotations, coupled with lower feed flow, increase the

Figure 8. Young´s Modulus under tensile for microparticulated (a) and nanoparticulated composite (b).

Figure 9. Tensile Strength (Fmax) for microparticulated (a) and nanoparticulated composite (b).

Figure 10. Strain (Fmax) for microparticulate (a) and nanoparticulated composite (b).

Polímeros, 35(1), e20250003, 2025

7/10

Barbosa, J. M., Pacheco, C. V., Szilágyi, G., Oliveira, P. C., Peres, R. M., & Ribeiro, H. SME used in the extrusion process, leading to better particle dispersion. This, in turn, enhances the mechanical properties of the composite due to increased surface interaction, as evidenced by the activation volume[12]. The best composite formulations M_500_10 and N_500_10, with different wt% of micro and nanoparticulate CaCO3 were investigated by SEM, after cryogenic fracture. Micrographs are shown in

Figures 12, revealing the CaCO3 different morphology in the polymeric matrix. At 0.15wt% content of both micro (a1) and nanocomposite (a2) displayed effective dispersion, showed no agglomerates of additives, although with larger micrometric particles. At 1.50wt%, better dispersion of nanometric particles (b2) was observed compared to the microcomposite (b1). The same was observed at 5.00 wt%

Figure 11. Activation volume for microparticulated (a) and nanoparticulated composite (b).

Figure 12. Micrographs of micro (a) and nanoparticulated composite (b) with 0.15% (1), 1.50% (2), 5.0% (3) and 10.0% (4) of CaCO3 in different magnification.

8/10

Polímeros, 35(1), e20250003, 2025

Micro and nanoparticulate PP/CaCO3 composites mechanical, thermal and transport properties - DOE (c), with good dispersion and distribution of particles in the nanocomposite (c2), with few agglomerates. Finally, at 10.00% (d), good particles distribution was observed in the nanocomposite (d2) with few agglomerates, which is indicative of efficiency in the dispersion process and potentially better particle-matrix adhesion compared to the microcomposite (d1). As is known, the higher level of agglomerates indicates poor dispersion and a lower level of reinforcement. Our mechanical results correlated with the microscopy images are quite consistent with the mechanical properties, as also observed previously by Yang et al.[4] and Thio et al.[16].

Based on the results from Impact, Tensile Strength, and Activation Volume, along with the micrographs, the condition: extruder screw rotation of 500 rpm and feed of 10 kg/h, exhibited the most favorable properties balance, credited to the higher SME utilized in the dispersion process (0.21 kWh/kg). Subsequent tests will be performed using these parameters (M_500_10 and N_500_10), with the outcomes detailed in Second Part of this study.

4. Conclusion The study identified the processing condition with superior filler dispersion with Q:10 kg/h and N: 500 rpm.

Under these conditions, the nanocomposite presented Young’s Modulus with 4.12wt% increased by 9.2% compared to the hPP. The tensile strength (Fmax) increased by 7.9% with just 0.48wt% of nanoparticulate CaCO3, compared to hPP. Deformation (Fmax) values remained similar for nano and microcomposites, with a notable increase of 5.1% for the 0.48wt% nanoparticle content compared to hPP. The nanocomposites with 0.48wt% and 1.24wt% stood out due to their smaller Activation Volume, compared to microparticles at the same content. The impact resistance of nanocomposite, increased by 22.4% compared to hPP, with 7.9wt%. Based on these results, it was determined the most favorable process parameters for achieving superior mechanical properties for the studied PP/CaCO3 composites. The increase in the intensity of the beta phase diffraction peak for the CaCO3 nanocomposites positively influenced the improvement of its mechanical properties in relation to the pure polymer and the microcomposites. However, it is advisable to explore other additional properties, such as thermal and barrier, using these parameters already determined for these systems.

Furthermore, it is also necessary to investigate the influence of the D50 filler content on the mechanical and thermal behavior at different wt% in PP. This type of investigation will be better explored in future work.

5. Author’s Contribution • Conceptualization – Juliano Martins Barbosa; Caroline Valadão Pacheco; Gisele Szilágyi; Patrícia Candioto de Oliveira; Renato Meneghetti Peres; Hélio Ribeiro.

• Data curation – Juliano Martins Barbosa; Hélio Ribeiro.

• Formal analysis – Juliano Martins Barbosa; Caroline Valadão Pacheco; Gisele Szilágyi; Patrícia Candioto de Oliveira; Renato Meneghetti Peres; Hélio Ribeiro.

• Funding acquisition –​ NA. Polímeros, 35(1), e20250003, 2025

• Investigation –​Juliano Martins Barbosa; Hélio Ribeiro.

• Methodology – Juliano Martins Barbosa; Hélio Ribeiro.

• Project administration – Juliano Martins Barbosa; Hélio Ribeiro.

• Resources – Juliano Martins Barbosa; Caroline Valadão Pacheco; Gisele Szilágyi; Patrícia Candioto de Oliveira; Renato Meneghetti Peres; Hélio Ribeiro.

• Software – NA. • Supervision – Juliano Martins Barbosa; Hélio Ribeiro.

• Validation – Juliano Martins Barbosa; Caroline Valadão Pacheco; Gisele Szilágyi; Patrícia Candioto de Oliveira; Renato Meneghetti Peres; Hélio Ribeiro.

• Visualization – Juliano Martins Barbosa; Hélio Ribeiro.

• Writing – original draft – Juliano Martins Barbosa; Gisele Szilágyi; Hélio Ribeiro.

• Writing – review & editing – Juliano Martins Barbosa; Hélio Ribeiro.

6. Acknowledgements This study received partial funding from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. The authors acknowledge the Materials Engineering Department of Mackenzie Presbyterian University (MACKENZIE), the Materials Engineering Department (DEMa) and the Graduate Program in Materials Science and Engineering (PPGCEM) of the Federal University of São Carlos (UFSCar), ZwickRoell do Brasil and Cromex S/A for their technical support and donation of raw materials.

7. References 1. Padilha, A. F. (2000). Materiais de engenharia – microestrutura e propriedades. São Paulo: Editora Hemus.

2. Callister, W. D. (2002). Ciência e engenharia dos materiais: uma introdução. Barueri: Editora LTC. 3. Wypych, G. (1999). Handbook of fillers. New York: Plastics Design Library.

4. Yang, K., Yang, Q., Li, G., Sun, Y., & Feng, D. (2006).

Morphology and mechanical properties of polypropylene/ calcium carbonate nanocomposites. Materials Letters, 60(6), 805-809. http://doi.org/10.1016/j.matlet.2005.10.020.

5. Rabelo, M. (2000). Aditivação de polímeros. São Paulo: Artliber Editora.

6. Fischer, H. (2003). Polymer nanocomposite: from fundamental research to specific application. Materials Science and Engineering C, 23(6-8), 763-772. http://doi.org/10.1016/j. msec.2003.09.148.

7. Rodolfo, A., Nunes, L. R., & Ormanji, W. (2006). Tecnologia do PVC. São Paulo: ProEditores/Braskem. Retrieved in 2024, May 19, from https://www.braskem.com/Portal/Principal/ Arquivos/Download/Upload/Tecnologia%20do%20PVC%20 2a%20edi%C3%A7%C3%A3o_22.pdf 8. Mai, Y.-W., & Yu, Z.-Z. (Eds.) (2006). Polymer nanocomposites.

Cambridge, England: Woodhead Publishing Limited. http:// doi.org/10.1533/9781845691127.

9. Huang, Z., Lin, Z., Cai, Z., & Mai, K. (2004). Physical and mechanical properties of nano-CaCO3/PP composites modified with acrylic acid. Plastics, Rubber and Composites, 33(8), 343-351. http://doi.org/10.1179/174328904X22314.

9/10

Barbosa, J. M., Pacheco, C. V., Szilágyi, G., Oliveira, P. C., Peres, R. M., & Ribeiro, H. 10. Ribeiro, H., Silva, W. M., Neves, J. C., Calado, H. D. R., Paniago, R., Seara, L. M., Camarano, D. M., & Silva, G. G. (2015).

Multifunctional nanocomposites based on tetraethylenepentaminemodified graphene oxide/epoxy. Polymer Testing, 43, 182-192. http://doi.org/10.1016/j.polymertesting.2015.03.010.

11. Barbosa, J. M. (2021). Influência da incorporação de negro de fumo e carbonato de cálcio micro e nanoparticulado nas propriedades reológicas, colorimétricas e mecânicas de filmes de polietileno de baixa densidade (Doctoral dissertation).

Universidade Federal de São Carlos, São Carlos.

12. Domenech, T., Peuvrel-Disdier, E., & Vergnes, B. (2013). The importance of specific mechanical energy during twin screw extrusion of organoclay based polypropylene nanocomposites.

Composites Science and Technology, 75, 7-14. http://doi. org/10.1016/j.compscitech.2012.11.016.

13. Century Extrusion Group. (2018). Torque vs Specific Energy.

Process Technology [Webinar]. Century Extrusion Group. Retrieved in 2024, January 13, from https://ekc.cpmextrusiongroup.com/ project/torque-vs-specific-energy/ 14. Barbosa, J. M., Beatrice, C. A. G., & Pessan, L. A. (2022).

Influence of carbon black trimodal mixture on LDPE films properties: Part2 – SME. Polímeros: Ciência e Tecnlogia, 32(3), e2022030. http://doi.org/10.1590/0104-1428.20220053.

15. Rocha, M. C. G., Silva, A. H. F. T., Coutinho, F. M. B., & Silva, A. L. N. (2005). Study of composites based on polypropylene and calcium carbonate by experimental design.

Polymer Testing, 24(8), 1049-1053. http://doi.org/10.1016/j. polymertesting.2005.05.008.

16. Thio, Y. S., Argon, A. S., Cohen, R. E., & Weinberg, M. (2002).

Toughening of Isotactic polypropylene with CaCO3 particles.

Polymers, 43(13), 3661-3674. http://doi.org/10.1016/S00323861(02)00193-3.

17. Chan, C.-M., Wu, J., Li, J.-X., & Cheung, Y.-K. (2002). Polypropylene/ Calcium carbonate nanocomposite. Polymer, 43(10), 2981-2992. http://doi.org/10.1016/S0032-3861(02)00120-9.

18. Zhang, Q.-X., Yu, Z.-Z., Xie, X.-L., & Mai, Y.-W. (2004).

Crystallization and Impact energy of Polypropyle/CaCO3 nanocomposite with nonionic modifier. Polymer, 45(17), 5985-5994. http://doi.org/10.1016/j.polymer.2004.06.044.

19. Eiras, D. (2009). Tenacificação de polipropileno com nanopartículas de carbonato de cálcio (Master’s thesis).

Universidade Federal de São Carlos, São Carlos.

20. Silva, A. L. N., Bertolino, L. C., Nasser, R. O., Costa, L. S., Melo, A. A., Marquezine, L. P. S., Silva, A. H. M. F. T., Alves, V. O., & Nascimento, C. R. V. (2013). Application of a factorial planning for the evaluation of mechanical, thermal, morphologic and flow properties of PEAD and CaCO3 composites. Matéria (Rio de Janeiro), 18(3), 1382-1394. http://doi.org/10.1590/ S1517-70762013000300006.

21. Barbosa, J. M., Beatrice, C. A. G., & Pessan, L. A. (2022).

Influence of carbon black trimodal mixture on LDPE films properties: Part1 – DOE. Polímeros: Ciência e Tecnologia, 32(3), e2022029. http://doi.org/10.1590/0104-1428.20220039.

22. Barbosa, J. M. (2011). Estudo das propriedades mecânicas, térmicas e de transporte do compósito com carbonato de cálcio nano e microparticulado em polipropileno (Master’s thesis).

Universidade Federal de São Carlos, São Carlos.

23. Barbosa, J. M., Pacheco, C. P., Szilágyi, G., Oliveira, P. C. M., Peres, R. M., & Ribeiro, H. (2022). Mechanical properties of polypropylene/calcium carbonate micro and nanocomposites.

In Anais do 17° Congresso Brasileiro de Polimeros – CBPol (p.760). São Paulo: ABPol.

10/10

24. NanoMaterials Technology Pte Ltd. (2024). Retrieved in 2024, January 13, from https://nanomt.com/products/npcc/ 25. Omya International AG. (2023). Retrieved in 2023, December 20, from https://www.omya.com/en/products/polymers 26. Dow Inc. (2024) Retrieved in 2024, May 11, from https://www. dow.com/pt-br/pdp.fusabond-p353-functional-polymer.1891762z. html#overview 27. Braskem S/A. (2024). Retrieved in 2024, May 19, from https:// www.braskem.com/busca-de-produtos?p=309 28. Lotti, C., Isaac, C. S., Branciforti, M. C., Alves, R. M. V., Liberman, S., & Bretas, R. E. S. (2008). Rheological, mechanical and transport property of blow films of high density polyethylene nanocompósitos. European Polymer Journal, 44(5), 1346-1357. http://doi.org/10.1016/j.eurpolymj.2008.02.014.

29. American Society for Testing and Materials – ASTM. (2023).

ASTM D1238-23a: Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer. West Conshohocken: ASTM International. http://doi.org/10.1520/D1238-23A. 30. American Society for Testing and Materials – ASTM. (2022).

ASTM D5630-22: Standard Test Method for Ash Content in Plastics. West Conshohocken: ASTM International. http://doi. org/10.1520/D5630-22.

31. American Society for Testing and Materials – ASTM. (2022).

ASTM D638-22: Standard Test Method for Tensile Properties of Plastics. West Conshohocken: ASTM International. http:// doi.org/10.1520/D0638-22.

32. Ward, I. M., & Pinnock, P. R. (1983). Mechanical properties of solid polymers. West Sussex: John Wiley and Sons.

33. Brown, R. (2002). Handbook of polymer testing – short-term mechanical tests. Shawburry: Rapra Technology.

34. American Society for Testing and Materials – ASTM. (2023).

ASTM D256-23e1: Standard Test Method for Determining the Izod Pendulum Impact Resistance of Plastics. West Conshohocken: ASTM International. http://doi.org/10.1520/D0256-23E01.

35. Saraya, M. E.-S. I., & Rokbaa, H. H. A. L. (2016). Preparation of vaterite calcium carbonate in the form of spherical nanosize particles with the aid of polycarboxylate superplasticizer as a capping agent. American Journal of Nanomaterials, 4(2), 44-51. http://doi.org/10.12691/ajn-4-2-3.

36. Sakahara, R., Lima, A., & Wang, S. H. (2014). Influence of the beta crystalline phase fraction on the mechanical behavior of polypropylene/calcium carbonate/polypropylene - graft maleic anhydride composites. Polímeros: Ciência e Tecnologia, 24(5), 554-560. http://doi.org/10.1590/0104-1428.1692.

37. Uzun, İ. (2023). Methods of determining the degree of crystallinity of polymers with X-ray diffraction. Journal of Polymer Research, 30(10), 394. http://doi.org/10.1007/s10965023-03744-0.

38. Canevarolo, S. V. (2004). Técnicas de caracterização de polímeros. São Paulo: Artliber Editora.

39. Mareri, P., Bastide, S., Binda, N., & Crespy, A. (1998).

Mechanical behaviour of PP Composites containing fine mineral filler: effect of filler surface tratament. Composites Science and Technology, 58(5), 747-752. http://doi.org/10.1016/ S0266-3538(97)00156-5.

40. Barbosa, J. M., & Ruvolo, A., Fo. (2009). Estudo das propriedades mecânicas do nanocompósito e microcompósito de carbonato de cálcio em polipropileno. In Anais do 10° Congresso Brasileiro de Polimeros – CBPol (p. 690). São Paulo: ABPol. Received: July 03, 2024 Revised: Sept. 24, 2024 Accepted: Nov. 03, 2024

Polímeros, 35(1), e20250003, 2025

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20240099

Coating based on Montmorillonite, essential oils, and amaranth to preserve mango Evelyn Erika Pillco Ramos1* , Maria Cecilia Pacco-Huamani1 , Sandriane Pizato2 , Rosalinda Arévalo Pinedo3 , William Renzo Cortez-Vega2  and Grethel Teresa Choque Delgado1  Departamento Académico de Ingeniería de Industrias Alimentarias, Universidad Nacional de San Agustín de Arequipa, Arequipa, Perú 2 Departamento de Engenharia Agrícola e de Solos, Faculdade de Ciências Agrárias, Universidade Federal do Amazonas, Manaus, AM, Brasil 3 Departamento de Engenharia de Alimentos, Faculdade de Engenharia de Alimentos, Universidade Federal da Grande Dourados, Dourados, MS, Brasil 1

*epillcor@unsa.edu.pe

Abstract This study aimed to evaluate the coating based on Amaranthus flour (AF), montmorillonite, and three essential oils (clove, muña, and matico) to extend the shelf life of minimally processed mango. The mango cubes were divided into four different treatments. T1- control (uncoated mango), T2 (0.3% w/v of clove), T3 (0.3% w/v of muña), and T4 (0.3% w/v of matico). All treatments had 0.6% w/v Amaranth flour and 0.02% w/v montmorillonite (MMT) and were subjected to 5°C for 12 days. Water activity (Aw), pH, Total soluble solids, acidity, weight loss, color, texture, and antimicrobial activity were evaluated for each treatment. Matico treatment maintained pH and had the lowest count of yeast and mold forming units on mango (3.47 log UFC g-1). On the last day of storage, all coating treatments showed less weight loss and favorable results than the control. The matico treatment showed higher efficiency for mango preservation.

Keywords: amaranthus caudatus, buddleja globose, minthostachys mollis, montmorillonite, syzygium aromaticum.

How to cite: Pillco Ramos, E. E., Pacco-Huamani, M. C., Pizato, S., Arévalo Pinedo, R., Cortez-Vega, W. R., & Choque Delgado, G. T. (2025). Coating based on Montmorillonite, essential oils, and amaranth to preserve mango. Polímeros: Ciência e Tecnologia, 35(1), e20250004.https://doi.org/10.1590/0104-1428.20240099

1. Introduction Mango (Mangifera indica L) belongs to the Anacardiaceae family and it is one of the most popular tropical fruits with high nutritional value and good organoleptic characteristics[1].

This fruit is climacteric and has a short shelf life of 4-8 days, however, this could last longer if post-harvest handling and storage conditions are adequate[2]. Mango export requires refrigeration or freezing due to its metabolic changes and fast maturation process[3]. Consequently, alterations in fruit occur in the sensory attributes such as color and texture[4].

Additionally, the hydrolysis of starch into sugars causes softening in mango[3].

Currently, there are new technologies to preserve fruits and increase their shelf life[5]. Edible films and coatings have been shown to have a good gas barrier effect. However, these preservation methods lack antimicrobial agents against molds and yeasts that could improve their preservation properties[6,7]. Coatings act as a protective layer that delays the ripening and respiration of fruits[8].

Coatings could maintain the fruit’s quality and extend its shelf life due to the addition of biodegradable polymers and essential oils. Montmorillonite is an easily adsorbed nanoclay, with a porous structure, and a uniform surface that could improve the permeability capacity coating[9]. Kiwicha

Polímeros, 35(1), e20250004, 2025

(Amaranthus caudatus L.) is an Andean grain and has high nutritional value due to its essential amino acids, vitamins, and dietary fiber[10]. In addition, its starch has water-soluble, gelling, and thickening characteristics[11]. On the other hand, essential oils have antioxidant and antimicrobial properties.

Clove essential oil (Syzygium aromaticum) presents bioactive antioxidants such as eugenol and its derivatives. Eugenol is a phenolic compound with antifungal and antioxidant properties[12]. Muña (Minthostachys mollis) is a shrub native to the high Andean area of South America[13]. It also presents monoterpenes of the menthone and pulegone type[14]. Matico (Buddleja globosa) is a shrub native to Chile, Peru, and Argentina. Its main component is flavonoids[15].

Coating studies based on native essential oils applied to fruits are scarce. This manuscript aimed to evaluate three different Andean essential oils in coating based on Amaranth and nanoclay to extend the shelf life of minimally processed mango.

2. Materials and Methods 2.1 Materials Mangoes from the Tommy Atkins variety were purchased from a local market in Dourados-MS, Brazil. The fruits were

1/7

O O O O O O O O O O O O O O O O O

Pillco Ramos, E. E., Pacco-Huamani, M. C., Pizato, S., Arévalo Pinedo, R., Cotez-Vega, W. R., & Choque Delgado, G. T. selected according to their color and size. The matico oil was acquired from the ORUM Company in Tacna, Peru. The muña oil was bought from the Nua Company in Tarapoto, Peru. Finally, clove oil was obtained from the local market of Dourados-MS, Brazil. Amaranth flour was obtained from a milling process and previously selected raw grains from Arequipa, Peru.

2.2 Mango processing Mango stems were removed with a stainless steel knife.

Then, the mango was sanitized in a sodium hypochlorite solution at 2gL-1 for 3 minutes and the water was drained into sieves for 3 minutes. The mango peel was removed and the pulp was cut into pieces of 2 x 2 x 2.5cm.

2.3 Development of coatings To 500 mL of heated water, 500 mL of a mixture of distilled water and amaranth flour (0.6%) was added with slow homogenization. The mixture was heated at 80 °C for 20 minutes with constant magnetic stirring. Subsequently, 0.02% of montmorillonite (MMT) was added with constant magnetic stirring for 20 minutes until reaching 60 °C. At that temperature, 0.1% of glycerol was added, and stirring continued for another 20 minutes. Finally, 0.3% of essential oils were added at different solubilization temperatures (Clove at 40°C, Muña and matico at 35°C). The mango pieces were divided into four treatments: T1 - Control (uncoated); T2 - clove oil (0.3%); T3 - muña oil (0.3%); and T4 - matico oil (0.3%). All treatments contained 0.6% of Amaranth flour, 0.1% of glycerol, and 0.02% of MMT. The mango pieces were immersed in the different coatings for 5 minutes and they drained in sieves for another 5 minutes.

Then, they were packaged in polyethylene terephthalate (PET) with a lid (Sandpack). Finally, they were refrigerated at 5 °C for 12 days.

2.4 Characterization of coatings Physical, chemical, and microbiological analyses were performed in triplicate for days 0, 1, 3, 5, 7, 9, and 12 of storage.

2.4.1 pH, Total Soluble Solids (TSS), and Titratable acidity To determine the pH, 5 g of sample was mixed in 50 ml of distilled water and it was measured in a Quimis benchtop pH meter. The analysis was carried out according to the official method[16] with some modifications. The total soluble solids content was examined using an Abbé bench refractometer and the results were expressed in °Brix. The titratable acidity was determined by titrating 5 ml of the sample, previously homogenized with 50 mL of distilled water, and 4 drops of phenolphthalein using 0.1 mol/L NaOH. 2.4.2 Weight loss To determine weight loss, mango pieces refrigerated at 5±1°C were weighed on an analytical balance on days 0, 1, 3, 5, 7, 9, and 12 of storage. The weight loss was obtained from the difference in the initial and final weight of the mango multiplied by 100 in each analysis. Results were expressed as a percentage of weight loss.

2/7

2.4.3 Color Color measurements were performed with a Konica Minolta colorimeter (Model CR-400/CR-410, Osaka, Japan) previously calibrated, using the CIE L*a*b system (Commission Internationale de LÉclairage).

2.4.4 Texture The mango pieces were cut and sheared uniaxially. Its texture was determined with a texturometer (TA-XT Plus, Godalming, UK). The cutting of the samples was at 2 mm/s uniaxially. Shearing of the sample was carried out with a blade at a distance traveled of 35 mm. The cutting force was expressed in Newton (N)[17].

2.4.5 Antimicrobial activity Microbiological analyses were performed for molds and yeasts, Salmonella spp., and Escherichia coli (ATCC 25922), following the methods described in APHA - American Public Health Association[18].

2.5 Statistical analysis The results were statistically evaluated using the Analysis of Variance (ANOVA) and the Tukey test at 5% significance.

It used the STATISTIX ® 10.0 program.

3. Results and Discussions 3.1 pH, Total Soluble Solids (TSS), and Titratable acidity Table 1 shows the pH values for the mango pieces coated for 12 days at 5 ± 1°C. Treatments T1 and T2 decreased their pH significantly during storage time compared to treatments T3 and T4, which maintained their values. At the end of the storage period, T3 (0.3% Muña) showed a significant difference in pH (3.5) compared to the other treatments.

Other studies showed similar pH values. Sánchez Aldana et al.[19] made edible coatings based on a pectic extract of Mexican lemon and essential oil applied to Haden mango. They obtained pH values of 3.2 on the 15th day of storage. Moreover, Ploy and Rungsinee[20] showed pH values between 3-4 in mango coated with nanocomposites based on hydroxypropylmethylcellulose and Thai essential oils during 15 days of storage. The decrease in pH in the coated mango during storage would be caused by carbonic acid due to the fermentation of sugar in the fruit during its ripening[21].

Regarding TSS values in mango pieces coated with Amaranth flour and different essential oils, all treatments significantly increased TSS during the 12 days of storage except treatment 2 (0.3% clove). The control treatment showed a significant increase in TSS compared to the coating treatments at the end of storage. Studies carried out

by Passafiume et al.[22] showed a similar behavior in mango pieces coated with neem oil during the storage period. They reported 13.9 °Brix on the last day of storage. Moreover, Gupta et al.[23] showed an increase in TSS of 18-21°Brix in mango coated with polysaccharides during storage. The increase in TSS in mango pieces during storage is due to the transformation of organic matter into sugars, acids, and minerals[24].

Polímeros, 35(1), e20250004, 2025

Coating based on Montmorillonite, essential oils, and amaranth to preserve mango Table 1. pH, Total soluble solids, and Titratable acidity values of mango coated with essential oil of clove, muña, and matico at 5 ± 1°C during 12 days of storage.

Treatments T1 T2 T3 T4 pH 0 3.53 ± 0.14aB 3.75 ± 0.00aA 3.58 ± 0.04aAB 3.59 ± 0.06aAB 1 3.47 ± 0.08abB 3.73 ± 0.03aA 3.56 ± 0.01aB 3.55 ± 0.09aB abcB aA abAB 3 3.38 ± 0.04 3.73 ± 0.04 3.54 ± 0.10 3.52 ± 0.13aAB 5 3.13 ± 0.01dB 3.35 ± 0.02bcAB 3.43 ± 0.02bcAB 3.51 ± 0.27aA 7 3.29 ± 0.01bcdA 3.30 ± 0.03bcA 3.41 ± 0.01cA 3.37 ± 0.18aA bcA bA bcA 9 3.33 ± 0.05 3.43 ± 0.04 3.43 ± 0.03 3.42 ± 0.04aA 12 3.23 ± 0.02cdB 3.27 ± 0.12cB 3.53 ± 0.01abcA 3.30 ± 0.02aB Total soluble solids 0 10.25 ± 0.35cA 10.17 ± 0.29aA 9.75 ± 0.35bA 9.83 ± 0.29bA (°Brix) 1 10.67 ± 0.76bcA 10.25 ± 0.29aA 9.83 ± 0.29abA 9.88 ± 0.25bA bcA aA abA 3 11.00 ± 0.58 10.33 ± 0.29 10.00 ± 0.41 10.13 ± 0.63bA 5 11.75 ± 0.35bA 10.50 ± 0.41aB 10.25 ± 0.35abB 10.17 ± 0.29bB 7 13.17 ± 0.29aA 10.67 ± 0.29aB 10.50 ± 0.50abB 10.33 ± 0.29abB 9 13.67 ± 0.29aA 10.75 ± 0.65aB 10.63 ± 0.48abB 10.67 ± 0.29abB 12 14.00 ± 0.50aA 10.83 ± 0.29aB 10.88 ± 0.25aB 11.38 ± 0.48aB Titratable Acidity 0 0.41 ± 0.05aA 0.36 ± 0.02aA 0.41 ± 0.04aA 0.40 ± 0.09aA (g/100ml citric acid) 1 0.37 ± 0.02abA 0.34 ± 0.03aA 0.39 ± 0.05abA 0.36 ± 0.09abA 3 0.35 ± 0.07abA 0.34 ± 0.05aA 0.32 ± 0.04abcA 0.33 ± 0.01abA 5 0.33 ± 0.05abA 0.34 ± 0.01aA 0.30 ± 0.00bcA 0.30 ± 0.01abA 7 0.31 ± 0.01abA 0.32 ± 0.03aA 0.29 ± 0.00cA 0.29 ± 0.01abA abA aA cA 9 0.26 ± 0.08 0.29 ± 0.03 0.28 ± 0.05 0.24 ± 0.07bA 12 0.19 ± 0.03bB 0.28 ± 0.02aA 0.28 ± 0.01cA 0.23 ± 0.02bAB Averages of three repetitions ± standard deviation, followed by the lowercase letter in the column (difference between storage days) and the row (differences between treatments) by Tukey test (p > 0.05). T1: control (uncoated); T2: 0.3% clove essential oil; T3: 0.3% muña essential oil; T4: 0.3% matico essential oil.

Days

During the 12 days of storage, all treatments showed a decrease in titratable acidity (Table 1). For T1, T3 and T4, its decrease was significant. At the end of storage, the coating treatments showed acidity values of 0.23 - 0.28 and they were significantly different from the control treatment.

The decrease in titratable acidity was also reported by Ali et al.[25], they applied a coating based on tragacanth gum to the mango and showed values between 0.1 – 0.6% on the last day of storage. In addition, Coelho et al.[26] applied biodegradable coating with 10% gelatin and rice flour on mango and obtained 0.75 g.100-1 of citric acid during 10 days of storage. This result would be associated with the degree of ripeness of the mango.

3.2 Weight loss Figure 1 shows the weight loss values of the minimally processed mango for a storage period of 12 days at 5 ± 1°C. All treatments showed a significant increase in weight loss during storage days. The control treatment obtained greater weight loss compared to the coating treatments that presented values of 8.21-8.58%. Other studies have presented weight loss results, such as those by Yu et al.[24] evaluated the coating of chitosan with cinnamon essential oil on mangoes.

Weight loss ranged from 13.76 - 18.24% during 12 days of storage. Moreover, Santacruz and Hurel[27] reported an 8.4% weight loss in mangoes coated with cassava starch, cinnamaldehyde, and thymol after 14 days of storage. Fruit weight loss is caused by damage to the plasma membrane under cold conditions. This is due to the production of malondialdehyde, a byproduct of lipid peroxidation and Polímeros, 35(1), e20250004, 2025

Figure 1. Weight loss of mango coating based on amaranth flour, montmorillonite, clove, muña, and matico essential oil in different concentrations at 5±1 ºC, for 12 days.

oxidative stress that damages the cell membrane and causes electrolyte leakage[28]. Our study shows lower values of weight loss compared to the studies mentioned above. This coating could reduce cell membrane damage and protect the fruit from chilling injury.

3.3 Color Our results showed a decrease in L*, C, and h color levels. This could be due to the presence of the polyphenol oxidase enzyme that causes the oxidation of phenol and produces the browning of the fruit during cold storage[28].

3/7

Pillco Ramos, E. E., Pacco-Huamani, M. C., Pizato, S., Arévalo Pinedo, R., Cotez-Vega, W. R., & Choque Delgado, G. T. Table 2 shows the color values L*, C*, and h. Regarding L*, all treatments decreased significantly during the 12 days of storage. However, T1 and T2 show a greater decrease compared to T3 and T4 at the end of storage.

Similar studies reported a progressive and significant decrease in L* values during storage days. Passafiume et al.

[22] applied edible coating based on neem oil on cut mango.

After 9 days of storage, L* values of 65 – 70 were reported.

On the other hand, Lieu and Dang[29] used a 2.5% pectin/nanochitosan coating applied to mango and showed a decrease in L* during the 15 days of storage. Moreover, Marín et al.

[30] evaluated edible coatings with carboxymethylcellulose, aloe vera powder, whey protein isolate, potassium ascorbate, and antioxidants (citric acid and acetyl-N-cysteine). After 14 days of storage, L* values decreased from 72 to 66 on the last day of storage for the Tommy Atkins-type mango.

Regarding C values, all treatments showed a significant decrease during the 12 days of storage. The treatment values on the last day were 24 – 41. However, studies carried out by Mshora et al.[31] presented C* values of 65 – 75 on the last day of storage for mango coated with chitosan. In addition, Sarria et al.[32] carried out studies on mango with edible avocado oil coating where the C* value presented values of 45 – 67.

Finally, Treatments 3 and 4 showed a significant decrease in h values during storage time (81-86). Studies carried out by Mshora et al.[31] obtained lower h values (65 - 78) in mango coated with chitosan during 28 days of storage. On the other hand, Hernández-Guerrero et al.[33] coated mango with banana, soursop, and mango starch for 15 days of storage. They presented h values of 90 -100 the first 10 days, however, this value decreased to 70 on day 15 in all their treatments.

3.4 Texture Figure 2 shows the texture values, T1 had a significant increase during the 12 days of storage. A study carried out

by Almeida et al.[34] also demonstrated an increase in the texture of the control sample over the days of storage on minimally processed pineapple. The authors related this increase to the loss of mass (moisture) of the control sample during the 12 days of storage, whereas treatments with gum tragacanth and tea tree essential oil managed to maintain the texture of the pineapples for longer. On the other hand, our coating treatments showed a significant decrease during storage days. On the last day, their values were 16, 19, and 23 for muña, matico and clove, respectively. Studies carried out by Wang et al.[35] on dip coating with chitosan, sodium alginate, and cinnamon essential oil on mango also showed decreasing texture values during 10 days of storage. Their values were 25.47 and 17.62 (N). Moreover, Chuacharoen and Sabliov[36] presented decreasing texture values during the storage of mango coated with zein nanoparticles loaded with curcumin. On the ninth day, 6.91 (N/cm2) was reported.

3.5 Antimicrobial activity Figure 3 shows the growth of molds and yeasts in fresh-cut mangoes. The presence of Escherichia coli (<102 CFU.g-1) and Salmonella sp. (absence in 25 g) was not detected in fresh-cut mango pieces. It confirms the efficiency of good manufacturing practices and the effectiveness of the organic chlorine used to disinfect the fruits. Similar results were found in other studies with minimally processed fruits coated with gums. They presented low E. coli counts and the absence of Salmonella[37,38].

Table 2. Color obtained from mango coated with essential oil of clove, muña, and matico at 5±1°C for 12 days of storage.

Treatments T1 T2 T3 T4 L* 0 64.13 ± 0.46aB 56.97± 0.93aC 67.98 ± 0.01aA 70.97± 1.40aA 1 56.60± 0.53bB 55.02± 0.82bB 67.05± 0.94abA 67.85 ± 0.45aA cB bcB bcA 3 54.99± 0.37 53.65± 0.57 65.91 ± 0.58 66.50 ± 1.00aA 5 53.38 ± 0.21dB 52.28± 0.32cB 64.77± 0.25cA 65.14± 1.55aA 7 51.78 ± 0.64eB 47.86± 0.47dC 62.11± 0.91dA 62.03± 0.58bA 9 50.06 ± 0.62fC 46.04± 0.05dD 58.26 ± 0.27eB 59.79± 0.57bcA 12 48.25 ± 0.10gB 43.51 ± 1.07eC 58.14± 0.45eA 57.86 ± 0.75cA C 1 49.58 ± 0.39bA 43.33 ± 0.65bB 48.43 ± 1.09aA 50.97 ± 1.66aA 3 43.28 ± 0.58cA 35.91 ± 0.46cB 45.72 ± 1.43abA 44.59 ± 1.29bA 5 36.98 ± 0.77dB 28.47 ± 0.27dC 43.01 ± 1.32bcA 38.21 ± 0.93dB 7 32.49 ± 0.13eC 34.22 ± 0.06cC 41.40 ± 0.61cdA 38.07 ± 1.46dB 9 31.53 ± 0.56efB 24.88 ± 1.92eC 39.42 ± 0.45deA 39.11 ± 0.42cdA 12 30.37 ± 0.53fC 24.18 ± 0.02eD 37.98 ± 0.20eB 41.83 ± 0.20bcA h 1 84.06 ± 0.01cB 84.04 ± 1.08cB 89.16 ± 0.53aA 88.16 ± 0.91aA 3 84.64 ± 0.52bcB 84.87 ± 0.86cB 88.37 ± 0.71abA 87.82 ± 0.55aA 5 85.20 ± 0.74abcB 85.70 ± 0.65bcB 87.72 ± 0.40abA 87.48 ± 0.21aA 7 87.07 ± 0.30aA 87.47 ± 0.65abA 87.26 ± 0.97abA 88.49 ± 0.86aA 9 86.22 ± 0.89abB 88.09 ± 0.28abA 86.50 ± 0.98bAB 86.90 ± 0.18aAB 12 85.11 ± 0.80abcB 89.15 ± 0.91aA 86.39 ± 0.45bB 81.49 ± 1.07bC Averages of three repetitions ± standard deviation, followed by the lowercase letter in the column (difference between storage days) and the row (differences between treatments) by Tukey test (p > 0.05). T1: control (uncoated); T2: 0.3% clove essential oil; T3: 0.3% muña essential oil; T4: 0.3% matico essential oil.

Days

4/7

Polímeros, 35(1), e20250004, 2025

Coating based on Montmorillonite, essential oils, and amaranth to preserve mango hydrophobic components of essential oils penetrate the plasma membrane and it produces inhibition of the cell’s functional activity. Moreover, it produces the separation of lipids from the cell and mitochondrial membrane and causes cell death[40].

Figure 2. Texture (N) from coated mango with amaranth flour, montmorillonite, and essential oil of clove, muña, and matico at 5±1°C for 12 days of storage.

Barbosa et al.[41] obtained a similar microbial inhibition.

They used polymeric capsules of rosewood and cinnamon essential oil. Nandhavathy et al.[42] determined the efficiency of biocomposite films made from pomegranate peel fibers incorporated with thyme and clove essential oil. Thyme oil was more effective than clove oil, with an inhibition percentage of up to 66%. Cai et al.[43] also had promising results, they used starch films containing thyme essential oil microcapsules. These films slowed down the mango ripening and reduced the loss of vitamin C. The starch film with the addition of thyme essential oil inhibited the appearance of spoilage microorganisms. These results are similar to the present study and essential oils delayed the growth of molds and yeasts in fresh-cut mangoes.

4. Conclusions

Figure 3. Count of molds and yeasts in minimally processed mangoes coated with Amaranth flour, montmorillonite, and different essential oils. T1 – control treatment; T2 – clove essential oil; T3 – muña essential oil; T4 – matico essential oil.

Rojas-Graü et al.[39] affirm that the excessive growth of molds and yeasts can compromise the sensorial acceptance of fruits. The acceptable microbial load was established at 106 CFU.g-1 as numbers exceeding this limit can lead to the appearance of toxic substances. Our results show that there was a growth of molds and yeasts over the days of storage for all treatments evaluated. The control treatment (T1) showed the greatest increase. From day 5 onwards, the difference between the other treatments was significant and on the 12th day, the minimally processed uncoated mangoes showed a growth of 5.26 log CFU.g-1. Treatments T2 and T3 (4.21 and 3.97 log CFU.g-1 respectively) showed similar behavior during the days of analysis. At the end of 12 days of cold storage, they did not notice any significant difference.

Treatment T4, which contained matico essential oil, was the one with the lowest mold and yeast counts during refrigerated storage. This differs statistically from the other treatments evaluated (3.47 log UFC g-1).

The lowest mold and yeast counts were for treatments T2, T3, and T4. It is due to essential oils that have antimicrobial properties, especially matico essential oil.

The mechanism of antimicrobial action of essential oils could be related to the ability of phenolic compounds to disrupt the cytoplasmic membrane of microorganisms. The Polímeros, 35(1), e20250004, 2025

This study showed the effectiveness of coatings based on biopolymers and native essential oils to extend the shelf life of minimally processed mangoes. Coated treatments using essential oils presented prominent results in physicochemical and less growth for mold and yeast. Matico treatment stands out for having the lowest antimicrobial activity in freshly cut mangoes. In addition to essential oils, elicitors such as γ-aminobutyric acid are suggested to improve tolerance against abiotic stress and regulate the physiological processes of the fruit. Coatings or films with those components would have a synergistic effect and would prolong the shelf life and preserve the quality of the fruit.

5. Author’s Contribution • Conceptualization – Evelyn Erika Pillco Ramos; Grethel Teresa Choque Delgado; William Renzo Cortez Vega • Data curation – Evelyn Erika Pillco Ramos; Maria Cecilia Pacco Huamani • Formal analysis – Evelyn Erika Pillco Ramos; Maria Cecilia Pacco Huamani • Funding acquisition ​– Evelyn Erika Pillco Ramos • Investigation – ​Evelyn Erika Pillco Ramos • Methodology – William Renzo Cortez Veja; Maria Cecilia Pacco Huamani • Project administration – Grethel Teresa Choque Delgado • Resources – William Renzo Cortez Veja; Sandriane Pizato; Rosalinda Arévalo Pinedo; Evelyn Erika Pillco Ramos • Software – NA • Supervision – Grethel Teresa Choque Delgado • Validation – Evelyn Erika Pillco Ramos • Visualization – Evelyn Erika Pillco Ramos; Grethel Teresa Choque Delgado 5/7

Pillco Ramos, E. E., Pacco-Huamani, M. C., Pizato, S., Arévalo Pinedo, R., Cotez-Vega, W. R., & Choque Delgado, G. T. • Writing – original draft – ​Evelyn Erika Pillco Ramos; Grethel Teresa Choque Delgado • Writing – review & editing – Grethel Teresa Choque Delgado

6. Acknowledgements The authors would like to thank the Bioengineering Laboratory of the Federal University of Grande Dourados, Brazil.

7. References 1. Gentile, C., Di Gregorio, E., Di Stefano, V., Mannino, G., Perrone, A., Avellone, G., Sortino, G., Inglese, P., & Farina, V. (2019). Food quality and nutraceutical value of nine cultivars of mango (Mangifera indica L.) fruits grown in Mediterranean subtropical environment. Food Chemistry, 277, 471-479. http:// doi.org/10.1016/j.foodchem.2018.10.109. PMid:30502173.

2. Lin Aung, Y., Lorjaroenphon, Y., Rumpagaporn, P., Saetan, S., & Na Jom, K. (2021). Comparative investigation of combined metabolomics-flavoromics during the ripening of mango (Mangifera indica L.) cv. ‘Nam Dok Mai Si Thong’ and ‘Nam Dok Mai No. 4’. Plants, 10(10), 2198. http://doi. org/10.3390/plants10102198. PMid:34686007.

3. Kumar, N., Pratibha, Upadhyay, A., Trajkovska Petkoska, A., Gniewosz, M., & Kieliszek, M. (2023). Extending the shelf life of mango (Mangifera indica L.) fruits by using edible coating based on xanthan gum and pomegranate peel extract.

Journal of Food Measurement and Characterization, 17(2), 1300-1308. http://doi.org/10.1007/s11694-022-01706-6.

4. Liu, X., Xiao, Y., Zi, J., Yan, J., Li, C., Du, C., Wan, J., Wu, H., Zheng, B., Wang, S., & Liang, Q. (2023). Differential effects of low and high-temperature stress on pollen germination and tube length of mango (Mangifera indica L.) genotypes.

Scientific Reports, 13(1), 611. http://doi.org/10.1038/s41598023-27917-5. PMid:36635467.

5. Tiamiyu, Q. O., Adebayo, S. E., & Yusuf, A. A. (2023). Gum Arabic edible coating and its application in preservation of fresh fruits and vegetables: a review. Food Chemistry Advances, 2, 100251. http://doi.org/10.1016/j.focha.2023.100251.

6. Carrasco, P. B., Oliveira, V. S., Paz Gonçalvez, G. C., Gandra, E. A., Mendonça, C. R. B., & Borges, C. D. (2022).

Conservation of minimally processed pinhão using chitosan and gelatin coatings. Brazilian Journal of Food Technology, 25, e2021095. http://doi.org/10.1590/1981-6723.09521.

7. Wang, W., Zhang, W., Li, L., Deng, W., Liu, M., & Hu, J. (2023). Biodegradable starch-based packaging films incorporated with polyurethane-encapsulated essential oil microcapsules for sustained food preservation. International Journal of Biological Macromolecules, 235, 123889. http:// doi.org/10.1016/j.ijbiomac.2023.123889. PMid:36870661.

8. Salehi, F. (2020). Edible coating of fruits and vegetables using natural gums: a review. International Journal of Fruit Science, 20(2), 570-589. http://doi.org/10.1080/15538362.2020.1746730.

9. Wu, L., Liu, Q., Wang, X., Cao, S., Tang, N., Wang, Q., Lv, G., & Liao, L. (2020). Preparation of two-dimensional nano montmorillonite/stearic acid energy storage composites with excellent stability and heat storage properties. Applied Clay Science, 191, 105614. http://doi.org/10.1016/j.clay.2020.105614.

10. Choque Delgado, G. T., Carlos Tapia, K. V., Pacco Huamani, M. C., & Hamaker, B. R. (2023). Peruvian Andean grains: nutritional, functional properties and industrial uses. Critical Reviews in Food Science and Nutrition, 63(29), 9634-9647. http://doi.org/10.1080/10408398.2022.2073960. PMid:35544604.

6/7

11. Fonseca-Florido, H. A., Méndez-Montealvo, G., Velazquez, G., & Gómez-Aldapa, C. A. (2016). Thermal study in the interactions of starches blends: amaranth and achira. Food Hydrocolloids, 61, 640-648. http://doi.org/10.1016/j.foodhyd.2016.06.027.

12. Wang, H., Ma, Y., Liu, L., Liu, Y., & Niu, X. (2022). Incorporation of clove essential oil nanoemulsion in chitosan coating to control Burkholderia gladioli and improve postharvest quality of fresh Tremella fuciformis. Lebensmittel-Wissenschaft + Technologie, 170, 114059. http://doi.org/10.1016/j.lwt.2022.114059.

13. Villar Calero, K. A., Ruiz Pacco, G. A., & Fuertes Ruitón, C. M. (2021). Biopelículas a base de quitosano y aceite esencial de Minthostachys Mollis (muña) con propiedades antioxidante y antimicrobiana. Revista de la Sociedad Química del Perú, 87(4), 309-320. http://doi.org/10.37761/rsqp.v87i4.357.

14. Otoya, V. L. (2020). Considerations for the use and study of the Peruvian “muña” Minthostachys mollis (Benth.) Griseb and Minthostachys setosa (Briq.) Epling. Ethnobotany Research and Applications, 19, 1-9.

15. Vogel, H., Razmilic, I., & González, B. (2004). Matico (Buddleja globosa Hope): evaluación de diferentes accesiones, número de cosechas, humedad del suelo y extracción de nutrientes.

Agricultura Técnica (Chillán), 64(4), 413-420. http://doi. org/10.4067/S0365-28072004000400010.

16. AOAC. (2000). AOAC: Official methods of analysis (Vol. 1).

Arlington, VA: AOAC International.

17. American Meat Science Association – AMSA. (2015). Research guidelines for cookery, sensory evaluation, and instrumental tenderness measurements of meat (2nd ed., Vol. 1). Champaign, IL: AMSA. Retrieved in 2024, September 28, from https:// tinyurl.com/y5nrxrbc 18. American Public Health Association – APHA. (2001).

Compendium of methods for the microbiological examination of foods. Washington, DC: American Public Health Association.

19. Sánchez Aldana, D., Aguilar, C. N., Contreras-Esquivel, J. C., Souza, M. P., Carneiro-da-Cunha, M. G., & Nevárez-Moorillón, G. V. (2021). Use of a Mexican lime (Citrus aurantifolia Swingle) edible coating to preserve minimally processed mango (Mangifera indica L). Horticulture, Environment and Biotechnology, 62(5), 765-775. http://doi.org/10.1007/s13580021-00347-w.

20. Ploy, K., & Rungsinee, S. (2022). Effect of Thai herb essential oils incorporated in hydroxypropyl methylcellulose-based nanocomposite coatings on quality of fresh mango stored at ambient temperature. Agriculture and Natural Resources (Bangkok), 56(2), 331-342. http://doi.org/10.34044/j.anres.2022.56.2.11.

21. Handojo, L. A., Shofinita, D., Evelina, G., & Nasution, A. N. (2022). Edible coating development to extend shelf life of mangoes (Mangivera indica L.). IOP Conference Series.

Earth and Environmental Science, 980(1), 012046. http://doi. org/10.1088/1755-1315/980/1/012046.

22. Passafiume, R., Tinebra, I., Gaglio, R., Settanni, L., Sortino, G., Allegra, A., & Farina, V. (2022). Fresh-cut mangoes: how to increase shelf life by using neem oil edible coating. Coatings, 12(5), 664. http://doi.org/10.3390/coatings12050664.

23. Gupta, V., Meena, N. K., Sharma, Y. K., & Choudhary, K. (2023). Comparative study of different polysaccharide-based edible coatings on physicochemical attributes and bioactive compounds of mango cv dashehari fruits. Food, 4(1), e55. http://doi.org/10.1002/efd2.55.

24. Yu, K., Xu, J., Zhou, L., Zou, L., & Liu, W. (2021). Effect of chitosan coatings with cinnamon essential oil on postharvest quality of mangoes. Foods, 10(12), 3003. http://doi.org/10.3390/ foods10123003. PMid:34945553.

25. Ali, S., Zahid, N., Nawaz, A., Naz, S., Ejaz, S., Ullah, S., & Siddiq, B. (2022). Tragacanth gum coating suppresses the disassembly of cell wall polysaccharides and delays softening Polímeros, 35(1), e20250004, 2025

Coating based on Montmorillonite, essential oils, and amaranth to preserve mango of harvested mango (Mangifera indica L.) fruit. International Journal of Biological Macromolecules, 222, 521-532. http:// doi.org/10.1016/j.ijbiomac.2022.09.159.

26. Coelho, P. B., Figueiredo Neto, A., Costa, M. S., Pereira Filho, A., Silva, T. D., & Sánchez-Sáenz, C. M. (2021). Application of biodegradable coatings on ‘Tommy Atkins’ mango for export. Dyna, 88(219), 197-202. http://doi.org/10.15446/dyna. v88n219.95148.

27. Santacruz, S., & Hurel, J. C. (2022). Salicylic acid, cinnamaldehyde, and thymol incorporated into cassava starch coatings for mango preservation. Revista Facultad Nacional de Agronomía, 75(3), 10119-10124. http://doi.org/10.15446/rfnam.v75n3.100538.

28. Khaliq, G., Ali, S., Ejaz, S., Abdi, G., Faqir, Y., Ma, J., Siddiqui, M. W., & Ali, A. (2023). γ-Aminobutyric acid is involved in overlapping pathways against chilling injury by modulating glutamate decarboxylase and defense responses in papaya fruit.

Frontiers in Plant Science, 14, 1233477. http://doi.org/10.3389/ fpls.2023.1233477. PMid:38034576.

29. Lieu, M. D., & Dang, T. K. T. (2021). Improvement of shelf-life of mangoes by chitosan coating enriched with cinnamon oil dissolved in Tween 80 combined with ethanol. Food Bioscience, 44, 101341. http://doi.org/10.1016/j.fbio.2021.101341.

30. Marín, A., Baldwin, E. A., Bai, J., Wood, D., Ference, C., Sun, X., Brecht, J. K., & Plotto, A. (2021). Edible coatings as carriers of antibrowning compounds to maintain appealing appearance of fresh-cut mango. HortTechnology, 31(1), 27-35. http://doi.org/10.21273/HORTTECH04687-20.

31. Mshora, A., Gill, P. P. S., Jawandha, S. K., Sinha, A., & Singh, M. (2022). Effect of chitosan coatings on physico-chemical and enzymatic activities in mango cv Dashehari stored at low temperature. Journal of Horticultural Sciences, 17(2), 381-387. http://doi.org/10.24154/jhs.v17i2.1015.

32. Sarria, S. D., Zapata, J. I. H., & Bermúdez, A. A. (2023). Edible coatings with avocado oil on the quality of ‘Tommy Atkins’ mangoes. Ciência e Agrotecnologia, 47, e001423. http://doi. org/10.1590/1413-7054202347001423.

33. Hernández-Guerrero, S. E., Balois-Morales, R., PalominoHermosillo, Y. A., López-Guzmán, G. G., Berumen-Varela, G., Bautista-Rosales, P. U., & Alejo-Santiago, G. (2020). Novel edible coating of starch-based stenospermocarpic mango prolongs the shelf life of mango “ataulfo” fruit. Journal of Food Quality, 2020, e1320357. http://doi.org/10.1155/2020/1320357.

34. Almeida, M. M. M., Pizato, S., Basaglia, R. R., Pacco-Huamani, M. C., Pinedo, R. A., & Cortez-Vega, W. R. (2024). Effect of tragacanth gum (Astragalus gummifer) and melaleuca essential oil to extend the shelf life of minimally processed pineapples. Acta Scientiarum. Technology, 46(1), e65407. http://doi.org/10.4025/actascitechnol.v46i1.65407.

35. Wang, T., Zhai, X., Huang, X., Li, Z., Zhang, X., Zou, X., & Shi, J. (2023). Effect of different coating methods on coating

Polímeros, 35(1), e20250004, 2025

quality and mango preservation. Food Packaging and Shelf Life, 39, 101133. http://doi.org/10.1016/j.fpsl.2023.101133.

36. Chuacharoen, T., & Sabliov, C. M. (2022). Development of coating material by incorporating curcumin-loaded zein nanoparticles to maintain the quality of mango (Mangifera indica L. cv. Nam Dokmai). Journal of Agriculture and Food Research, 10, 100444. http://doi.org/10.1016/j.jafr.2022.100444.

37. Pizato, S., Chevalier, R. C., Santos, M. F., Costa, T. S., Arévalo Pinedo, R., & Cortez Vega, W. R. (2019). Evaluation of the shelf-life extension of fresh-cut pineapple (Smooth cayenne) by application of different edible coatings. British Food Journal, 121(7), 1592-1604. http://doi.org/10.1108/BFJ-11-2018-0780.

38. Pizato, S., Vega-Herrera, S. S., Chevalier, R. C., Pinedo, R. A., & Cortez-Vega, W. R. (2022). Impact of chitosan coatings enriched with clove essential oil on quality of minimally processed strawberries. Brazilian Archives of Biology and Technology, 65, e22210278. http://doi.org/10.1590/16784324-2022210278.

39. Rojas-Graü, M. A., Tapia, M. S., Rodríguez, F. J., Carmona, A. J., & Martin-Belloso, O. (2007). Alginate and gellan-based edible coatings as carriers of antibrowning agents applied on fresh-cut Fuji apples. Food Hydrocolloids, 21(1), 118-127. http://doi.org/10.1016/j.foodhyd.2006.03.001.

40. Li, Y., Kong, D., & Wu, H. (2013). Analysis and evaluation of essential oil components of cinnamon barks using GC–MS and FTIR spectroscopy. Industrial Crops and Products, 41, 269-278. http://doi.org/10.1016/j.indcrop.2012.04.056.

41. Barbosa, R. F. S., Yudice, E. D. C., Mitra, S. K., & Rosa, D. S. (2021). Characterization of Rosewood and Cinnamon Cassia essential oil polymeric capsules: stability, loading efficiency, release rate, and antimicrobial properties. Food Control, 121, 107605. http://doi.org/10.1016/j.foodcont.2020.107605.

42. Nandhavathy, G., Dharini, V., Anand Babu, P., Nambiar, R. B., Periyar Selvam, S., Sadiku, E. R., & Mahesh Kumar, M. (2021). Determination of antifungal activities of essential oils incorporated-pomegranate peel fibers reinforced-polyvinyl alcohol biocomposite film against mango postharvest pathogens.

Materials Today: Proceedings, 38(Part 2), 923-927. http://doi. org/10.1016/j.matpr.2020.05.384.

43. Cai, C., Ma, R., Duan, M., Deng, Y., Liu, T., & Lu, D. (2020). Effect of starch film containing thyme essential oil microcapsules on physicochemical activity of mango.

Lebensmittel-Wissenschaft + Technologie, 131, 109700. http:// doi.org/10.1016/j.lwt.2020.109700.

Received: Sept. 28, 2024 Revised: Oct. 30, 2024 Accepted: Nov. 05, 2024

7/7

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20240027

Application of natural rubber latex foam as an effective oil absorbent Abdulhakim Masa1 , Nureeyah Jehsoh2  and Nabil Hayeemasae2*  Rubber Engineering Program, Department of Interdisciplinary Engineering, Faculty of Engineering, Prince of Songkla University, Hat Yai, Songkhla, Thailand 2 Department of Rubber Technology and Polymer Science, Faculty of Science and Technology, Prince of Songkla University, Pattani Campus, Pattani, Thailand 1

*nabil.h@psu.ac.th

Abstract Oil spills have had catastrophic effects on marine ecosystems. The removal of oil spills from the water surface has then attracted worldwide attention. Natural rubber (NR) is a well-known example of a hydrophobic material, due to its hydrocarbon structure. For this purpose, the potential of NR as an oil absorbent is demonstrated. NR was formed into a cellular structure where oil absorbency can be controlled by their densities. It can be done by varying the foaming volume from 2-8 fold (2×, 4×, 6×, and 8×) the original volume of the beater. Increasing the foaming volume has reduced the densities. Over the variations of densities, the oil absorbencies were 10.58 to 16.76 g/g for crude oil, and 6.56 to 13.18 g/g for diesel oil. This indicated that the absorbent based on NR latex foam provided excellent performance and could be practically used as an oil-absorbent material.

Keywords: natural rubber latex foam, oil absorbency, foam, environment.

How to cite: Masa, A., Jehsoh, N., & Hayeemasae, N. (2025). Application of natural rubber latex foam as an effective oil absorbent. Polímeros: Ciência e Tecnologia, 35(1), e20250005. https://doi.org/10.1590/0104-1428.20240027

1. Introduction Oil spills in the sea have become a major issue in marine areas. The need for marine oil transportation and the growth of the offshore oil industry are making this problem more serious[1-3]. This also extends to oil spills in workshops or in the industry, particularly when machinery and piping systems are involved. Oil spills have historically been cleaned up using a variety of methods, such as in situ burning, mechanical dispersion collection, bioremediation, or by application of absorbent materials[4-6]. A combined approach is the best option because oil collection and remediation are cost-effective and efficient. Thus, finding workable ways to create absorbent materials for oil cleanup is crucial.

Natural rubber latex (NRL) is a fascinating water-based bio-polymer derived from the milky white sap of Hevea brasiliensis trees[7]. Natural rubber (NR) consists of long polymer chains that make it durable, flexible, and resistant to abrasion[8,9]. However, NR has many disadvantages, such as poor resistance to oxidation, chemicals, and in particular oils. This is mainly due to the hydrocarbon structure of NR. This has made this raw material interesting to convert to an oil-absorbent material. Scientific and applied research groups are becoming more interested in the nonpolar side chains in NR. The physical characteristics of rubber can be altered by converting the common solid form of rubber into a cellular structure, in order to increase its oil absorbency. Cellular rubber, or rubber foam, has such a structure with air-filled cells. NR foam is a popular option for many applications

Polímeros, 35(1), e20250005, 2025

since it is lightweight, good thermal insulator, and absorbs sounds[10,11]. Additionally, the porosity can improve the rate at which oil penetrates into rubber. NR foam can be made in a number of ways, using either dry or latex form as the main ingredient. In addition, there are tons of other benefits that NR latex foam offers over the synthetic sponge materials.

This is a preliminary study on the potential of NR latex foam to serve as an absorbent for oil in surface water. Here, a series of experiments was designed and the absorption capacities for crude oil and diesel oil were determined.

The results are compared with the commercially available oil-absorbent materials polyurethane foam (PUF) and nonwoven polypropylene (PP). These two polymers are representative of cost-effective oil-absorbent materials.

Hoang et al.[12] prepared the PU filled with rice straw and found that this material could absorb the oil equal to 12.012 g/g. The capacity was around 3 to 4 times higher than that of material fabricated by pristine PU. Zaro et al.[13] reported on the absorption capacity of the commercial nonwoven PP blanket relative to diesel, petroleum, and lubricant oil in long-term tests, it was found to have a capacity of 5.3, 12.3, and 18.7 g/g respectively. The results of the short and long-term tests did not show a statistical difference in the absorption capacity of the blanket. PU foams can be more flexible than nonwoven PP, semi-rigid, rigid, and have different densities. The use of PU in upholstery composed of reinforced materials with absorption capacity can be more advantageous[14]. Oil absorption and desorption are made possible by the viscoelastic characteristics of foams

1/8

O O O O O O O O O O O O O O O O O

Masa, A., Jehsoh, N., & Hayeemasae, N. produced with high open-cell concentrations. However, a lot of absorbents have low oil retention, restricted buoyancy, and inadequate absorption capability[15,16]. If they are administered loosely, they are difficult to regulate and recover. Even if their recovery is facilitated by enclosing them in an outer net or cloth, they frequently become soaked too quickly and may sink. Therefore, the use of PUF and nonwoven PP is very limited by their poor environmental compatibility[17].

This study focused on the use of NR latex foam as oil absorbent material. To optimize oil absorbency, NR latex foams with various foam densities were prepared. This is because the foam density of the foam reflects the proportions of rubber and gas phases in the cellular structure. It is believed that the optimum oil absorbency can be obtained by tuning the proportions of these two phases. The ability of oil to penetrate throughout the cellular structure can be optimized by preparing various foam densities. The results obtained from this study will be used to support further experiments for improving oil absorbency by applying other key factors. This is considered a proof of concept study for preparing oil-absorbent materials based on scraps from raw rubber production.

2. Experimental Details 2.1 Materials The high ammonia centrifuged latex with 60% dry rubber content (or 60% HA) was acquired from Yala Latex Industry, Co., Ltd., Thailand. The quality of the latex was tested, and it had total solids content (TSC) of 61.4%, dry rubber content (DRC) of 60%, alkalinity of 0.53%, volatile fatty acids (VFA) content of 0.06%, and mechanical stability time (MST) of 875 sec. The other additives namely 20% potassium oleate, 50% zinc diethyl dithiocarbamate (ZDEC), 50% zinc 2-mercaptobenzothiazole (ZMBT), 50% zinc oxide (ZnO), 50% Wingstay L, 50% sulfur, 15% diphenylguanidine (DPG), and 50% sodium silicofluoride (SSF), were supplied

by Siamnavakam Co. Ltd., Thailand. Polyurethane foam (PUF) was supplied by 3M Thailand Co. Ltd., Thailand. The density of PUF is 0.0170 ± 0.0008 g/cm3 with an average cell size of 304.62 ± 79.24 µm. Nonwoven Polypropylene (PP) was purchased from Benetech Products Co. Ltd., Thailand. The average fibrous diameters of Nonwoven PP is 19.42 ± 4.48 µm.

2.2 Preparation of NR latex foam The formulation for lab-scale production of NR latex foam is displayed in Table 1. The components in dispersion or emulsion forms were incorporated alongside the HA latex.

The Dunlop process was used to prepare NR latex foam.

First, a cake beater was filled with a specific amount of NR latex (HA-type), and ammonia was gradually evaporated for 3 min. Subsequently, 20% potassium oleate, 50% ZDEC, 50% ZMBT, 50% Wingstay™ L, and 50% sulfur were added.

The beating speed was increased and then maintained such that the desired foam volume was achieved at 5 mins. From this step onwards, the foaming volumes varied depending on the experimental design. Figure 1 illustrates the foamforming behaviour of NR latex foam during beating. The 2/8

Table 1. Compounding ingredients for preparing the NR latex foam.

Ingredient 60% HA 20% Potassium oleate 50% ZDEC 50% ZMBT 50% Sulfur 50% Wingstay L 15% DPG 50% ZnO 20% SSF

Amount (phr) 100 2.0 1.0 1.0 2.5 1.5 1.2 2.0 1.2

Figure 1. Illustration of preparing NR latex foams to various desired foaming volumes.

foaming volumes varied from 2× to 8× the original volume of total batch.

Next, 50% DPG and 50% ZnO were added, followed by quick addition of the gelling agent (20% SSF) and the mixture was beaten for another 1 min. Finally, the un-gelled foam was immediately poured into an aluminium mould and allowed to be set for 2 mins at ambient temperature.

The gelled foam was cured for 45 mins at 100°C in a hot air oven. To remove soap and unreacted substances, the dried foam was thoroughly cleaned with water after removal from the mould. The cured NR latex foam was washed and dried for 4 hrs in a hot air oven at 80°C.

2.3 Oil absorbency The test samples were cut to 1.5 cm × 1.5 cm × 1.0 cm dimensions. This equals a volume of 2.25 cm3. Each sample was then weighed before immersion in crude oil for 15 min. After that, the equilibrium swelling was determined by measuring the development of swelling uptake or oil absorbency. The sample was weighed on a scale after gentle removal of extra oil from surfaces by tapping with a filter paper, in order to estimate the amount of swelling. The oil absorbency was calculated by the Equation 1.

Oil absorbency =

Wa Wb

(1)

where Wa is the weight of absorbed oil, and Wb is the weight of the sample. The unit of oil absorbency is g/g, representing the mass of oil absorbed per 1 g of sample. In this study, PUF and nonwoven PP were also tested for oil absorbency.

This was done to enable a comparison with commercially available products.

Polímeros, 35(1), e20250005, 2025

Application of natural rubber latex foam as an effective oil absorbent The reusability test of the material was also conducted by repeating the test at each absorption cycle. Before repeating the steps, ensure that the sample is clean for each reuse cycle. After each cycle, record the weight of oil absorbed to calculate the oil absorption capacity of the absorbent material across multiple cycles.

2.4 Measurement of physical properties The foam density of the foam was calculated as mass per volume. Initially, 1.0 × 1.0 × 1.0 cm3 cubes of NR foam were made. Each sample was weighed and its mass per volume was determined. Compression–deflection test was done according to ASTM D575. A sample of dimensions 10.0 × 10.0 × 2.5 cm3 was prepared for this testing. A universal testing machine (Tinius Olsen, H10KS, Tinius Olsen Ltd., Surrey, UK) was used to compress the specimen between its parallel metal plates until the thickness had decreased by 25% with the cross-head speed of 50 mm/min. The load was promptly read and recorded. The same specimen was cycled through the test multiple times until the load measurements did not vary by more than 5%. The force per area was recorded. Compression set was measured according to ASTM D395. A representative sample of dimensions 5.0 × 5.0 × 2.5 cm3 was used for testing. The test specimen was compressed to 50% of its original thickness. The load was released after 70 h and the thickness was measured after 30 min at room temperature. The compression set calculation based on the Equation 2.  t −t  Compression = set  0 1  ×100  t0 − ts 

(2)

where t0 is the original thickness, t1 is the thickness of the specimen after the specified recovery period, and tS is the thickness of the spacer bar used. An average of five replicates is reported for each type of sample.

2.5 The optical images of the samples The cellular structure of the samples was screened using a light microscope at 40× magnifications. The image was then captured and imported to the Image J software to measure the cell size and fibrous diameters.

3. Results and Discussion 3.1 Physical properties of NR latex foam The oil absorbency of a NR latex foam depends on two main factors: the physical and chemical characteristics of the foam. Here, the focus was more on the physical characteristics. The density of the foam was manipulated, since increasing the air phase will both increase the number of cells and porosity of the NR latex foam. Controlling the density of foam was simply done by fixing the foaming volume achieved by beating. The relationship of foaming volume with density of NR latex foam is shown in Table 2, where increasing foaming volume reduces density of the foam. This is because the proportion of air phase increased with the foaming volume. The porosity of the foam increased accordingly. Various densities of the foam can be achieved by varying the foaming volume during whipping in the cake beater. This method can be done easily without adding Polímeros, 35(1), e20250005, 2025

Table 2. Foam density, compression set and compressive strength of NR latex foams prepared to various foaming volumes.

Foaming volume (ɸ) 2× 4× 6× 8×

Foam Density Compression (g/cm3) set (%) 0.1888 ± 0.0099 62.68 ± 1.93 0.1752 ± 0.0098 62.15 ± 1.24 0.1567 ± 0.0083 59.37 ± 1.62 0.1296 ± 0.0099 58.12 ± 1.11

Compressive strength (MPa) 0.38 ± 0.02 0.31 ± 0.02 0.23 ± 0.01 0.18 ± 0.01

more foam promoter or blowing agent from fatty acid soap.

This is not similar to other works that control the density by varying the foam promoter or blowing agent from fatty acid soap. For instance, Suethao et al.[18] reported that the chemical blowing agent also affected the morphology of the foam where reducing the blowing agent showed more interconnected foam structures with smaller cell sizes than those of the control sample.

Figures 2 and 3 show the characteristics and sizes of the sponge cells obtained for each foaming volume tested, before and after thermal aging. In the samples before thermal aging, roughly uniform distributions of cell sizes were found at low foaming volumes. However, the cell size of the foam tends to increase with foaming volume. On increasing the fraction of air phase by beating, the wall separating adjacent bubbles could collapse, so that they combined to a larger sized foam cell. This resulting increased cell size is associated with increased porosity of the foam. The porosity is expected to be coupled with the interfacial area of the solid and gas phases, and also porosity contributes to the permeability of the foam to oil. This is an important factor contributing to the efficiency of oil absorption.

The compression set and compression–deflection stress are also listed in Table 2 for NR latex foams prepared to various foaming volumes. The compression set indicates the ability of the sample to elastically recover its original shape after prolonged compressive deformation. Low values mean that the material has rebounded nearly to its original thickness, and there is very little residual deformation. Here, the foaming volume affected the compression set, which decreased with the foaming volume. Larger foaming volume increased the cell size and air diffusion through the sample.

This also helps recovery of the shape after compression.

As for the compressive strength, it also decreased with the foaming volume, so a lesser force was required to deform a bulkier more porous sample. Generally, the compressive strength of a foam depends on its cell size distribution, along with the number of cells that is associated with porosity.

In this experiment, the foam density was varied affecting compressive strength.

3.2 Oil absorbency of NR latex foam Figure 3 depicts oil absorbency versus foaming volume for the samples. It was observed that the oil absorbency increased up to 6× foaming volume, and then decreased: the maximum value was 16.76 g/g. This suggests that initially increasing the cell size facilitated penetration of oil and consequent swelling of the rubber. However, when the cell size is excessive, there are less rubber-air interfaces and the too large pores cannot hold the liquid in place, so less penetration and retention of oil is observed at an excessive 3/8

Masa, A., Jehsoh, N., & Hayeemasae, N.

Figure 2. Optical images at 40× magnification of natural NR foams prepared to various foaming volumes, taken before aging.

Figure 3. Crude oil absorbency and their optical images after absorption (40× magnification) of NRlatex foams prepared to various foaming volumes.

foaming volume. Previous work by Ratcha et al.[19], who prepared oil-absorbent materials based on NR and NR-gPMMA, indicates that cellular structure of foam affects its oil absorbency. This is further explained in a study by Lee et al.[20], which stated that the swelling of NR foam is influenced by the cell structure and bulk density, and a lower bulk density was associated with a larger swelling uptake. Figure 4 also shows the expansion of cell size after absorption of crude oil. Clearly, it can be seen that the oil was dispersed throughout the sample (see the dark areas) especially when the foaming volume was high.

Figure 4 shows the absorbency of diesel oil by the various NR latex foams. This is similar to what was found for crude oil. The foaming volume affected the absorbency, and 6× foaming gave the highest oil absorbency of 13.18 g/g, 4/8

Figure 4. Diesel oil absorbency and their optical images after absorption (40× magnification) of NR latex foams prepared to various foaming volumes.

while for 8× case the absorbent decreased. The diesel oil is a specific type of oil derived from crude oil, although it contains hydrocarbons as do other types of petroleum oils[21,22]. Diesel primarily contains straight-chain and branched-chain alkanes, which is not similar to crude oil. Crude oil contains many types of hydrocarbons including alkanes that are saturated hydrocarbons without double bonds, alkenes that have one or more double bonds, and aromatic hydrocarbons with a ring-like structure, such as benzene[23,24]. In general, NR is very compatible with aromatic hydrocarbons, and this may be responsible for the higher oil absorbency observed for crude oil than for diesel.

In addition to this, it can be observed from optical images after immersion in diesel oil, that the cell size was greatly expanded and some were completely swollen (see Polímeros, 35(1), e20250005, 2025

Application of natural rubber latex foam as an effective oil absorbent the embedded images in Figure 4). Figure 5 also shows the physical appearances of NR latex foam cubes before and after immersion in crude oil and diesel oil. Clearly the samples have been expanded by the absorption of oil.

3.3 Material comparison, reusability and simulation Based on the previous results, it can be concluded that the NR latex foams prepared to various foaming volumes provided remarkable oil absorbencies. The NR latex foam prepared to 6× foaming was selected for further experiments, comparing it with two commercially available products namely PUF and nonwoven PP. Figure 6 shows the oil absorbencies of NR latex foam, PUF, and non-woven PP. It was observed that NR latex foam presents significantly higher absorbency than PUF or non-woven PP, in this rank order. The compatibility with oil of the solid material is the main factor affecting the oil absorbency. NR latex foam may be more compatible with the oil than PUF or PP. Another possible reason is the physical form of each material. For example, the non-woven PP is fibrous and may be less permeable to oil, while the cellular materials NR latex foam and PUF had cell size and cell characteristics favorable to oil absorption. Furthermore, PUF and nonwoven PP might be efficient in oil spill remediation, but they are based on

Figure 5. Physical appearances of sample cubes before and after absorbing oil.

synthetic materials. Consequently there are concerns about residues and contamination from the use of such materials.

Figure 7 shows optical images of PUF and nonwoven PP. The average cell size of PUF measured from Image J software is 304.62 ± 79.24 µm while the average fibrous diameters of Nonwoven PP is 19.42 ± 4.48 µm. It was also observed that there was less change in the size and diameters of both PUF and nonwoven PP after oil absorption. These indicate that after oil absorption, no expansion has occurred, suggesting less strong interactions with the oil than in NR latex foam.

The nonwoven PP showed only slight amounts of oil that were absorbed, apparently due to its comparatively low porosity (pore volume in proportion to bulk volume).

Reusability was also tested in this study, and the results are shown in Figure 8. The values of absorbency from the first to fifth absorption cycles of NR latex foam were found to be 16.76, 6.38, 5.49, 5.1, and 4.75 g/g for crude oil, while

Figure 6. Comparison of oil absorbencies of NR latex foam, polyurethane foam (PUF), and nonwoven polypropylene (PP), with both crude and diesel oils.

Figure 7. Optical images at 40× magnification of PUF before (A) and after absorption of crude oil (B) and of diesel oil (C); and of PP before (D) and after absorption of crude oil (E) and diesel oil (F).

Polímeros, 35(1), e20250005, 2025

5/8

Masa, A., Jehsoh, N., & Hayeemasae, N. for diesel oil they were similarly 13.18, 5.02, 4.32, 3.95, and 3.74 g/g. Meanwhile, the values of absorbency from the first to fifth absorption cycles of PUF were found to be 10.51, 8.31, 7.62, 7.25, and 6.90 g/g for crude oil, while for diesel oil they were similarly 16.04, 12.40, 11.32, 11.05, and 10.49 g/g. However, the reusability test for nonwoven PP was unable to be tested due to its limited absorption. Nonwoven PP absorbed only one cycle and cannot be further reused.

It is interesting to note that the oil absorbency of NR latex foam decreased dramatically in the second absorption cycle. As expected, part of the rubber was swollen and destroyed during the first absorption cycle. This decreased the efficiency in the next absorption cycle. However, the rate

Figure 8. Reusability tested with crude and diesel oils, of NR latex foam when prepared to 6× foaming volume and PUF as absorbents.

of decrease in oil absorbency was much less from the second cycle onwards, which is acceptable when considering the level of absorption. While the absorbency initially dropped drastically, the material remains practically functional for several cycles of reuse. The constant level of absorption is believed to be due to the physical absorption of NR foam.

Nevertheless, there was a gradual reduction in the oil absorbency of PUF over the absorption cycle. As can be seen from Figure 7, there is less destruction of the cellular structure of PUF after being absorbed by crude and diesel oils. Therefore, the oil efficiency was still presented over the absorption cycles.

To highlight the selectivity for oil over water, Figure 9 shows the oil removal efficiency of NR latex foam in oil-water dispersion. Obviously the hydrophobicity of NR latex foam greatly influenced oil-water separation. The high selectivity for oil is an advantage that also enables the recovery of oil by simply squeezing. This can be done rapidly, and in this laboratory study, the oil was completely removed from seawater within 15 mins. In contrast, PUF had non-selective absorption of both oil and water, as polyurethane is polar by its character, matching water in this aspect.

To check whether NR latex foam really performs better than PUF, a simulation test was done, and an image captured during the test is shown in Figure 10. The NR latex foam has the special characteristic of selectively absorbing oil on the water surface, while PUF has no selectivity by type of liquid.

Therefore, the latter collected more water, which reduced the amount of oil absorbed. As a result, the NR latex foam is effective as an absorbent in the removal and collection of oil residues off of the water surface, in case of an oil spill. In summary, NR latex foam is a better-performing oil absorbent than the commercially available products tested.

Figure 9. Physical appearances of samples after absorbing oil for 15 min: NR latex foam (A), and PUF (B).

6/8

Polímeros, 35(1), e20250005, 2025

Application of natural rubber latex foam as an effective oil absorbent

Figure 10. Physical appearances of sample after absorbing crude oil floating on sea water: NR latex foam on left, and PUF on right.

4. Conclusions Oil-absorbent materials based on NR were successfully prepared in this study, namely NR latex foams made with the Dunlop process. To control the foam density (associated with cell structure) and assess its effects on oil absorbency, the foaming volume was manipulated by adjusting the rotation speed of the beater. It is clear that foaming volume greatly influenced oil absorbency, whether tested with crude or diesel oil. Increasing the speed of the beater initially tended to open the cell structure and provide remarkable improvements in the oil absorbency of the NR latex foam.

Oil absorbency of NR latex foam prepared at 6× foaming volume was near optimal. Due to the hydrophobicity of NR, as oil absorbent the NR latex foam was more selective, favoring oil over water, than the other tested absorbents.

NR latex foam can be applied to remove spilled oil either from the water surfaces or from a dispersion with water.

Cell size and cell structure can be further manipulated via the compounding formulation by the use of foaming agents and other additives. Using a stable and precise beating speed range will give consistent cell characteristics.

5. Author’s Contribution • Conceptualization – Nabil Hayeemasae • Data curation – Abdulhakim Masa; Nabil Hayeemasae • Formal analysis – Abdulhakim Masa; Nureeyah Jehsoh • Funding acquisition ​– Nabil Hayeemasae • Investigation – Abdulhakim Masa; Nureeyah Jehsoh • Methodology – Nabil Hayeemasae • Project administration – Nabil Hayeemasae • Resources – Abdulhakim Masa; Nabil Hayeemasae • Software – NA • Supervision – Nabil Hayeemasae • Validation – Abdulhakim Masa; Nabil Hayeemasae • Visualization – Abdulhakim Masa; Nabil Hayeemasae Polímeros, 35(1), e20250005, 2025

• Writing – original draft – Abdulhakim Masa; Nabil Hayeemasae • Writing – review & editing – Nabil Hayeemasae

6. Acknowledgements This research was supported by the National Science, Research and Innovation Fund (NSRF) and Prince of Songkla University for the Fundamental Funds through grant No. SAT. SAT6601107S.

7. References 1. Liu, Y., Ma, J., Wu, T., Wang, X., Huang, G., Liu, Y., Qiu, H., Li, Y., Wang, W., & Gao, J. (2013). Cost-effective reduced graphene oxide-coated polyurethane sponge as a highly efficient and reusable oil-absorbent. ACS Applied Materials & Interfaces, 5(20), 10018-10026. http://doi.org/10.1021/ am4024252. PMid:24050505.

2. Wang, J., Zheng, Y., & Wang, A. (2012). Superhydrophobic kapok fiber oil-absorbent: preparation and high oil absorbency.

Chemical Engineering Journal, 213, 1-7. http://doi.org/10.1016/j. cej.2012.09.116.

3. Prendergast, D. P., & Gschwend, P. M. (2014). Assessing the performance and cost of oil spill remediation technologies.

Journal of Cleaner Production, 78(1), 233-242. http://doi. org/10.1016/j.jclepro.2014.04.054.

4. Pham, V. H., & Dickerson, J. H. (2014). Superhydrophobic silanized melamine sponges as high efficiency oil absorbent materials. ACS Applied Materials & Interfaces, 6(16), 1418114188. http://doi.org/10.1021/am503503m. PMid:25039789.

5. Zhang, T., Li, Z., Lü, Y., Liu, Y., Yang, D., Li, Q., & Qiu, F. (2019). Recent progress and future prospects of oil-absorbing materials. Chinese Journal of Chemical Engineering, 27(6), 1282-1295. http://doi.org/10.1016/j.cjche.2018.09.001.

6. Chin, C. C., Musbah, N. D. L., Abdullah, I., & Lazim, A. M. (2018). Characterization and evaluation of prudent liquid natural rubber-based foam for oil spill control application.

Arabian Journal for Science and Engineering, 43(11), 60976108. http://doi.org/10.1007/s13369-018-3256-5.

7. Jadhav, A. C., & Jadhav, N. C. (2021). Graft copolymerization of methyl methacrylate on Meizotropis Pellita fibres and their 7/8

Masa, A., Jehsoh, N., & Hayeemasae, N. applications in oil absorbency. Iranian Polymer Journal, 30(1), 9-24. http://doi.org/10.1007/s13726-020-00869-7.

8. Ramasamy, S., Ismail, H., & Munusamy, Y. (2013). Soil burial, tensile properties, morphology, and biodegradability of (rice husk powder)-filled natural rubber latex foam. Journal of Vinyl and Additive Technology, 21(2), 128-133. http://doi. org/10.1002/vnl.21389.

9. Panploo, K., Chalermsinsuwan, B., & Poompradub, S. (2019). Natural rubber latex foam with particulate fillers for carbon dioxide adsorption and regeneration. RSC Advances, 9(50), 28916-28923. http://doi.org/10.1039/C9RA06000F. PMid:35528441.

10. Baru, F., Saiwari, S., & Hayeemasae, N. (2022). Classification of natural rubber foam grades by optimising the azodicarbonamide content. Polímeros, 32(2), e2022014. http://doi.org/10.1590/01041428.20210111.

11. Harpell, G. A., Gallagher, R. B., & Novits, M. F. (1977). Use of azo foaming agents to produce reinforced elastomeric foams.

Rubber Chemistry and Technology, 50(4), 678-687. http://doi. org/10.5254/1.3535165.

12. Hoang, A. T., Le, V. V., Al-Tawaha, A. R. M. S., Nguyen, D. N., Al-Tawaha, A. R. M. S., Noor, M. M., & Pham, V. V. (2018).

An absorption capacity investigation of new absorbent based on polyurethane foams and rice straw for oil spill cleanup.

Petroleum Science and Technology, 36(5), 361-370. http://doi. org/10.1080/10916466.2018.1425722.

13. Zaro, M., Silvestre, W. P., Fedrigo, J. G., Zeni, M., & Baldasso, C. (2021). Sorption of oils by a commercial non-woven polypropylene sorbent. Research Social Development, 10(14), e554101422671. http://doi.org/10.33448/rsd-v10i14.22671.

14. Zimmermann, M. V. G., Junca, E., Almeida, M. K., Ponsoni, L. V., Zattera, A. J., Mari, T., & Santana, R. M. C. (2023).

Hydrophobic polyurethane foams reinforced with microcrystalline cellulose for oil spill clean up. Polímeros, 33(4), e20230040. http://doi.org/10.1590/0104-1428.20230054.

15. Cheng, H., Gu, B., Pennefather, M. P., Nguyen, T. X., PhanThien, N., & Duong, H. M. (2017). Cotton aerogels and cotton-cellulose aerogels from environmental waste for oil spillage cleanup. Materials & Design, 130, 452-458. http:// doi.org/10.1016/j.matdes.2017.05.082.

16. Shiu, R.-F., Lee, C.-L., Hsieh, P.-Y., Chen, C.-S., Kang, Y.-Y., Chin, W.-C., & Tai, N.-H. (2018). Superhydrophobic graphene-based sponge as a novel sorbent for crude oil removal under various environmental conditions. Chemosphere, 207,

8/8

110-117. http://doi.org/10.1016/j.chemosphere.2018.05.071.

PMid:29793022.

17. Hoang, A. T., Nižetić, S., Duong, X. Q., Rowinski, L., & Nguyen, X. P. (2021). Advanced super-hydrophobic polymerbased porous absorbents for the treatment of oil-polluted water. Chemosphere, 277, 130274. http://doi.org/10.1016/j. chemosphere.2021.130274. PMid:33770690.

18. Suethao, S., Phongphanphanee, S., Wong-ekkabut, J., & Smitthipong, W. (2021). The relationship between the morphology and elasticity of natural rubber foam based on the concentration of the chemical blowing agent. Polymers, 13(7), 1091. http:// doi.org/10.3390/polym13071091. PMid:33808133.

19. Ratcha, A., Yoosuk, B., & Kongparakul, S. (2013). Grafted methyl methacrylate and butyl methacrylate onto natural rubber foam for oil sorbent. Advanced Materials Research, 844, 385390. http://doi.org/10.4028/www.scientific.net/AMR.844.385.

20. Lee, H.-K., Chung, T.-K., Kim, S.-C., Kim, H.-G., Choi, K.M., Kim, Y.-M., & Han, D.-H. (2008). Influence of the type of curing agent on swelling behaviour of natural rubber foam.

Journal of the Korea Academia-Industrial Cooperation Society, 9(6), 1775-1781. http://doi.org/10.5762/KAIS.2008.9.6.1775.

21. Mullins, O. C., Betancourt, S. S., Cribbs, M. E., Dubost, F. X., Creek, J. L., Andrews, A. B., & Venkataramanan, L. (2007). The colloidal structure of crude oil and the structure of oil reservoirs. Energy & Fuels, 21(5), 2785-2794. http:// doi.org/10.1021/ef0700883.

22. Edward, O. B., Wade, T. L., Radović, J. R., Meyer, B. M., Miles, M. S., & Larter, S. R. (2016). Chemical composition of macondo and other crude oils and compositional alterations during oil spills. Oceanography (Washington, D.C.), 29(3), 50-63. http://doi.org/10.5670/oceanog.2016.62.

23. Guo, Y., Ristovski, Z., Graham, E., Stevanovic, S., Verma, P., Jafari, M., Miljevic, B., & Brown, R. (2020). The correlation between diesel soot chemical structure and reactivity. Carbon, 161, 736-749. http://doi.org/10.1016/j.carbon.2020.01.061.

24. Wang, X., Wang, Y., Bai, Y., Wang, P., & Zhao, Y. (2019). An overview of physical and chemical features of diesel exhaust particles. Journal of the Energy Institute, 92(6), 1864-1888. http://doi.org/10.1016/j.joei.2018.11.006.

Received: Mar. 19, 2024 Revised: Sept. 03, 2024 Accepted: Sept. 12, 2024

Polímeros, 35(1), e20250005, 2025

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20240040

Influence of alkali treatment on physical-mechanical properties of mallow fiber/BOPP composites Hannah Alagoas Litaiff1* , Gabrielle Machado dos Santos2 , Gabriel de Melo3 , Claudia da Cunha3  and Virginia Mansanares Giacon1  Programa de Pós-graduação em Ciência e Engenharia de Materiais – PPGCEM, Faculdade de Tecnologia – FT, Universidade Federal do Amazonas – UFAM, Manaus, AM, Brasil 2 Programa de Pós-graduação em Engenharia e Ciência de Materiais – PPG EnCiMat, Faculdade de Zootecnia e Engenharia de Alimentos – FZEA, Universidade de São Paulo – USP, Pirassununga, SP, Brasil 3 Laboratório de Materiais da Amazônia e Compósitos – LaMAC, Faculdade de Tecnologia, Universidade Federal do Amazonas – UFAM, Manaus, AM, Brasil

1

*hannah.litaiff@ufam.edu.br

Abstract This study investigated the impact of alkaline treatment on mallow fibers used as reinforcement in bi-axially oriented polypropylene (BOPP) waste composites. Fibers were treated with a 5% NaOH solution and characterized by XRD, FTIR, TGA, and tensile testing. Composites were fabricated with both untreated and treated fibers, and their physical, thermal, morphological, and mechanical properties were evaluated. XRD analysis revealed an increase in crystallinity index after treatment, correlating with enhanced breaking stress in treated fibers. Composites with treated fibers exhibited significantly reduced thickness swelling and water absorption, indicating improved fiber-matrix compatibility.

SEM micrographs confirmed enhanced fiber-matrix adhesion in composites using treated fibers. Overall, the results demonstrate that alkali treatment significantly improves the properties of mallow fiber/BOPP composites, promoting their use as sustainable and eco-friendly materials. This research highlights the potential of valorizing agricultural waste and recycled plastics for the development of high-performance composites.

Keywords: lignocellulosic fiber, mercerization, polymer composite.

How to cite: Litaiff, H. A., Santos, G. M., Melo, G., Cunha, C., & Giacon, V. M. (2025). Influence of alkali treatment on physical-mechanical properties of mallow fiber/BOPP composites. Polímeros: Ciência e Tecnologia, 35(1), e20250006. https://doi.org/10.1590/0104-1428.20240040

1. Introduction Industry sectors, especially civil construction, are increasingly looking for sustainable technological solutions that meet their demands. For that, research has been carried out to develop new materials derived from natural resources, which can be used to add value to these raw materials, as well as guarantee their preservation[1].

In this context, vegetable fibers are biodegradable materials of renewable origin, found in great abundance and constitute an alternative to synthetic materials, such as fiberglass, widely used since the 1950s[2]. The advantages of natural fibers are several, including low density, low production cost, high specific strength and modulus of elasticity, in addition to being non-abrasive and non-toxic[3,4].

Mallow fiber (Urena Lobata L.) stands out among these diversities because it has great potential and economic viability to be used as a reinforcement material in polymeric composites[5]. It is cultivated in regions with hot and humid climates, being produced on a large scale in the Amazon region[6]. It is used as the basis for a variety of manufactured products, the main one being the manufacture of bags for storing food products[7]. It is widely available, lightweight,

Polímeros, 35(1), e20250006, 2025

inexpensive, and has superior mechanical properties to other plant fibers such as kenaf fiber[8].

From another perspective, polypropylene is one of the most versatile thermoplastic polymers and most used in industrial applications[9]. Bi-axially oriented polypropylene (BOPP) are materials widely used in the flexible packaging sector, mainly for food products, due to their efficiency in physically and chemically preserving packaged products, in line with their low cost and lower environmental impact[10].

They are recyclable, however, they are not recycled on a large scale, which generates a large amount of waste from this material that has no destination[11]. One of the ways to reuse this material is to use it in the production of sustainable materials, such as in composite matrix reinforced with vegetable fibers[12].

However, lignocellulosic fibers are highly hydrophilic due to their chemical components, especially cellulose, which cause poor compatibility with the thermoplastic matrix, which has a polar character, resulting in composites with low resistance to moisture absorption[13]. On the other hand, there are surface modification methods that minimize these problems and provide better adhesion between fiber and matrix[14].

1/10

O O O O O O O O O O O O O O O O O

Litaiff, H. A., Santos, G. M., Melo, G., Cunha, C., & Giacon, V. M. To address the challenge of poor adhesion between I (002) − I ( am) CI % × 100 (1) mallow fibers and PP, a hydrophobic thermoplastic matrix, = I (002) mercerization can be a suitable option, as it is a well-established treatment for lignocellulosic fibers[15]. This method reduces I(002) is related to the crystalline region, corresponding to the hydrophilicity of the fiber, improving compatibility with the maximum diffraction intensity and I(am) is related to the the polymer, which increases surface roughness and provides amorphous part, corresponding to the minimum diffraction more mechanical anchoring points for stronger fiber-resin intensity. bonding[16]. Through this, it is possible to obtain an improved 2.2.3. Fourier Transform Infrared Spectroscopy (FTIR) material with sustainable characteristics and competitive with industrial raw materials, which come from non-renewable sources and cause damage to the environment[15].

The main objective of this study is to produce polymeric composites with a waste from the manufacturing process of bi-axially oriented polypropylene (BOPP) as matrix and to evaluate the effect of mercerization on the surface of mallow fibers, used as reinforcement material, on their physical, thermal, mechanical and morphological properties.

2. Materials and Methods 2.1. Materials The mallow fiber used in this study was donated by Companhia Têxtil de Castanhal, located in the municipality of Manacapuru, metropolitan region of Manaus-AM. Waste from the manufacturing process of bi-axially oriented polypropylene (BOPP) films, in the form of flackes and powder, came from the Videolar-Innova S/A factory, located in Manaus-AM. The NaOH used was Anidrol brand.

2.2. Methods 2.2.1. Alkali treatment Initially, the fibers were cut to a nominal length of 1 cm. The alkaline treatment was carried out according to the methodology adopted by Giacon et al.[17], which consisted of immersing the mallow fibers in a 5% by weight NaOH solution for 60 min. Subsequently, the fibers were washed with running water until reaching pH 7 and dried at room temperature for 96hrs. The untreated and treated fibers were characterized to investigate the effects of mercerization using the following techniques: XRD, FTIR, TGA and Tensile test.

2.2.2. X-ray diffraction (XRD) The fibers were analyzed by X-ray diffraction using a Shimadzu diffractometer, model Máxima XDR-7000, operating with copper radiation (CuKα), in which a continuous sweep was performed in the range of 10° < 2θ < 80°, at a rate of 2°/ min and a step size of 0.02°. The crystallinity index (CI %) was determined according to Segal et al.[18] using Equation 1:

FTIR spectroscopy was performed on the treated and untreated fibers using a Shimadzu spectrometer (IRAffinity1s) by horizontal Attenuated Total Reflection (ATR) with diamond prism. Scanning was performed in the infrared region from 4000 to 500 cm-1, with an average of 32 scans for each spectrum.

2.2.4. Thermogravimetric analysis (TGA)

Thermal analysis (TGA/DTG) of samples of about 10 mg of treated and untreated fibers were performed using the SDT Q600 equipment from TA Instrument with a heating rate of 10 °C/min until the final temperature of 700 °C, with 5.0 nitrogen gas flow of 30 ml/min in a 90 microliter alumina crucible without lid.

2.2.5. Tensile test The single fiber tensile test was performed on treated and untreated fibers with a length of 30 mm according to the ASTM 3379-75[19] standard in an Oswaldo Filizola universal testing machine, model AME-5KN, with a capacity of 500 Kgf. The specimen model for this test according to ASTM 3379-75[19] is shown in Figure 1: To determine the rupture stress, the modulus of elasticity and the deformation, Equations 2, 3 and 4 were used: σ=

F A

(2)

E=

σ ε

(3)

∆ ε= l

(4)

l0

2.2.6. Composite production Two types of composites were produced, using untreated mallow fibers (UMC) and mallow fibers treated with 5% NaOH (TMC), according to the methodology adopted by Chatterjee et al.[20], through thermoforming. The proportion

Figure 1. Specimen of single fiber tensile test with ASTM 3379-75 standard.

2/10

Polímeros, 35(1), e20250006, 2025

Influence of alkali treatment on physical-mechanical properties of mallow fiber/BOPP composites adopted in the production of composites was 70% by weight of fibers and 30% of BOPP (50% in flakes and 50% in powder). The components were weighed and manually mixed until the fibers were completely enveloped by the BOPP, for approximately 30 min. Afterwards, the mixture was uniformly distributed in a metallic mold with dimensions of 28 × 28 × 1 cm coated with Teflon film and kept in a thermo-hydraulic press at 15 MPa, 170 °C, for 20 min. After pressing, the composites were cooled for 20 min with the aid of a fan and then removed from the mold. Finally, the panels were cut to produce the specimens used in the characterizations. The UMC and TMC composites (Figure 2) were characterized using the following techniques: density, thickness swelling, thermal conductivity, SEM and izod impact test.

2.2.7. Physical properties The composites were physically characterized according to the Brazilian standard ABNT NBR 15316-2:2019[21] for the determination of density and thickness swelling for 24 hours and according to the ASTM D570-22[22] standard to perform the water absorption test. For the density and thickness swelling tests, 10 specimens with dimensions of 50 × 50 mm were used for each type of composite. For the water absorption test, 5 specimens were used for each type of composite, with dimensions of 76.2 × 25.4 mm.

2.2.8. Thermal conductivity The thermal conductivity test was carried out following the specifications of the ASTM D7984-21[23] standard using a TCi Thermal Conductivity analyzer from the C-Therm brand with thermal capacity from 0 to 50 W m-1 K-1 and temperature range from -50 to 200 °C. The thermal conductivity was calculated through the average of 10 cycles obtained from 10 samples of 50 × 50 mm of each type of composite.

2.2.9. Scanning electron microscopy (SEM) The composites were morphologically characterized through Scanning Electron Microscopy (SEM), using a TESCAN VEGA3 scanning electron microscope. Samples from the internal region and from the surface of the MUC and

MTC composites were fixed with double-sided adhesive tape in aluminum sample holders and metallized with platinum, for 5 min, using the Bal-Tec equipment, model SCD 050.

The images were obtained with the microscope operated at a voltage of 15.0 kV. 2.2.10. Izod impact test The Izod impact test was carried out on the composites according to ASTM D256-10[24] standard using a Tinius Olsen impact pendulum together with the model 104 controller. 10 specimens of each type of composite were analyzed, with dimensions of 62.5 × 12.7 mm.

2.2.11. Statistical analysis The data obtained were treated statistically with analysis of variance (ANOVA), at 5% significance. The null hypothesis (H0) is the equivalence of the response variables and the alternative hypothesis (H1) is the non-equivalence; p-value>0.05 of the test implies accepting H0, otherwise it is rejected.

3. Results and Discussions 3.1. X-ray diffraction (XRD) From the XDR diffractogram (Figure 3) it is possible to notice that the untreated and treated mallow fiber samples present three well-defined main reflection peaks: at 2θ = 18.7º, 2θ = 22.3º and 2θ = 35º, corresponding to the crystallographic planes (101), (002) and (040), respectively, characteristic planes of type 1 cellulose[25]. The most intense reflection occurs in the (002) plane for both samples, which corresponds to the lattice planes of the densest glycosidic rings in the structure of cellulose I, being the only naturally occurring polymorphic form of cellulose[26]. It is also possible to observe that the samples present the same diffraction behavior, with variations only in the intensity of the peaks, thus, it is clear that there was influence of the alkali treatment on the crystallinity of the mallow fiber. The values found for the crystallinity index were 64.64% and 71.28% for untreated and treated mallow

Figure 2. Composite (a) UMC and (b) TMC. Polímeros, 35(1), e20250006, 2025

3/10

Litaiff, H. A., Santos, G. M., Melo, G., Cunha, C., & Giacon, V. M.

Figure 3. Diffractogram of treated and untreated mallow fibers.

fiber, respectively. This increase indicates that the treatment promoted the reduction of materials such as lignin, hemicellulose and other components that do not confer crystallinity to the fiber. Crystallinity, which is related to the amount of cellulose present in the fiber, increases compared to the untreated fiber due to the formation of hydrogen bonds between the cellulose chains, which results in better packing in the fiber[27].

3.2. Fourier Transform Infrared Spectroscopy (FTIR) The FTIR spectra of untreated and treated fibers (Figure 4) show bands characteristic of lignocellulosic fibers. The spectra presents a band at 3400 cm-1, which corresponds to the stretching of hydroxyl groups O-H of cellulose, hemicellulose and lignin[28]. The transmittance in this peak for the treated fiber spectrum was modified compared with the spectrum of untreated fiber, which is related to the presence of free hydroxyl groups with the breaking of cellulose, hemicellulose and lignin bonds resulting from the mercerization process[28]. The band at 2897 cm-1 is related to the stretching of aliphatic C-H from the methyl -CH3 and methylene -CH2 groups, a characteristic functional group of lignocellulosic components present in vegetable fibers[29]. The band at 1740 cm-1 is associated with the C=O stretching of the carbonyl group, present in the acetyl ester or carboxylic groups of hemicellulose, which disappears in the spectrum of the mercerized fiber, indicating high removal of this component and also a change in the chemical composition of the surface fiber after chemical treatment. The band at 1600 cm−1 corresponds to the C=C stretching of the aromatic rings, typical of the lignin structure[30]. There was also a decrease in the band observed at 1242 cm-1, which corresponds to the C-O-C group, present in hemicellulose and lignin, indicating the reduction of these components after chemical treatment[31].

This same characteristic is found in the bands at 1427 cm-1 and 1370 cm-1, associated with vibrations of the C-C bond of aromatic rings and the asymmetric deformation of the methyl group[7]. The band at 1172 cm-1 is associated with stretching of the C-O group of esters and lignin[7]. The most intense band occurs at 1033 cm-1, which can be associated with the C-H 4/10

group and C-O deformations, which are naturally occurring in lignocellulosic fibers[29]. These results show that the alkali treatment is efficient in removing hemicellulose and lignin fractions from mallow fiber.

3.3. Thermogravimetric analysis (TGA) From the TGA and DTG curves of untreated and treated fibers (Figure 5) it is possible to observe the existence of four well-defined degradation events. In the first event, there are mass losses of 10.37% and 10.16% in the temperature range of 25-118°C and 25-150°C for untreated and treated fiber, respectively, related to moisture loss due to to the evaporation of water[1]. The second event is related to the process of degradation mainly of hemicellulose, also occurring the beginning of the decomposition of lignin[32]. For the untreated fiber, the process occurred in the temperature range of 220-310 °C with a mass loss of 14.62%. It is noticed the absence of the characteristic peak of hemicellulose for the treated fiber, indicating that chemical treatment was efficient in its removal[15]. The third event is due to the decomposition of cellulose, for the untreated fiber there is a mass loss of 51.20% between 309-384 °C and for the treated fiber there is a mass loss of 52.93% between 200-400 °C[33].

Decomposition of lignin starts at approximately 272 °C for the untreated mallow fiber and at 240 °C for the treated fiber, along with the degradation of the hemicellulose[32]. Lignin is the most complex lignocellulosic component to degrade, with thermal decomposition over a wide temperature range due to its complex structure, which is overlapped by other peaks[34]. The fourth event refers to the decomposition of lignin and residual inorganic material[6]. For the untreated fiber, the degradation occurs in the range of 394-563 °C, with a mass loss of 20.96%, while the treated fiber has a curve longer in this region, starting at approximately 384 °C and extending to a temperature of 674 °C, with a mass loss of 32.30%. At the end of the curves, the ash content, remaining at high temperatures, presented by the untreated and treated fibers of 0.29% and 0.11%, respectively, is observed. In general, the treated fiber is decomposed at Polímeros, 35(1), e20250006, 2025

Influence of alkali treatment on physical-mechanical properties of mallow fiber/BOPP composites

Figure 4. FTIR spectra of treated and untreated mallow fibers.

Figure 5. TGA/DTG curves of treated and untreated mallow fiber.

lower temperatures and has greater mass loss compared to the untreated fiber, indicating that the chemical treatment removed the fiber constituents that are thermally unstable, such as hemicelluloses, holocellulose and ash[35].

3.4. Tensile test The results of the single-fiber tensile test for tensile strength, modulus of elasticity, elongation at break and the average diameter of treated and untreated mallow fibers are shown in Table 1, which showed a significant difference between them (p<0.05). Also, the table reports the mean values for most common lignocellulosic fibers in raw form, as mentioned in scientific literature[36].

Compared to the most common lignocellulosic fibers studied in the scientific literature, the already-high mechanical performance of treated mallow fibers stands out, suggesting the potential of mercerization to enhance the mechanical properties of lignocellulosic fibers.

The significant increase in the values obtained for the tensile strength rupture, modulus of elasticity and elongation Polímeros, 35(1), e20250006, 2025

at break of the treated fiber in relation to the untreated fiber can be related to the diameter of the fibers[37]. The average diameters of the fibers decreased with the treatment, from 0.050 mm to 0.042 mm, due to the action of the chemical treatment that acts to remove amorphous materials and cause fibrillation of the fiber bundle, reducing its diameter and increasing its roughness, making them more resistant and rigid[38]. According to Margem[7], fibers with smaller diameters have better mechanical tensile properties because they have a greater capacity to absorb energy before fracturing.

In addition, the crystallinity index is directly related to the tensile strength and modulus of elasticity of the fiber, that is, the higher the cellulose content present in the fiber, the better its mechanical performance[39]. Furthermore, the crystallinity index is directly related to the tensile strength and elastic modulus of the fiber[39]. However, Fonseca[40] reported that increasing the tensile strength of individual fibers will not necessarily indicate composites with greater mechanical strength. Other characteristics also influence these properties, such as those related to fiber anatomy.

5/10

Litaiff, H. A., Santos, G. M., Melo, G., Cunha, C., & Giacon, V. M. Table 1. Mean values of tensile strength (σ), modulus of elasticity (E), elongation at break (ε) and diameter of treated and untreated mallow fibers, as well as other lignocellulosic fibers.

Material Untreated mallow fiber Treated mallow fiber Coconut Fiber Flax Fiber Hemp Fiber Jute Fiber Sisal Fiber

σ (MPa) 447.76 ± 103.03a 1039.45 ± 128.15b 100 - 230 345 - 1035 270 - 900 393 - 800 458 - 720

E (GPa) 59.62 ± 10.28a 88.23 ± 14.49b 2.8 - 6 27.6 - 70 23.5 - 90 8 - 55 9 - 24

ε (%) 0.76 ± 0.17a 1.20 ± 0.21b 15 - 38 1.2 - 3.2 1.0 - 3.5 1.0 - 1.8 2 - 4.3

Diameter (mm) 0.050 ± 0.008a 0.042 ± 0.006b -

Thickness Swelling (%) 10.59 ± 4.52a 4.97 ± 1.71b

Water Absorption (%) 31.14 ± 0.45a 27.41 ± 0.24b

Table 2. Physical properties of UMC and TMC composites Composite Density (Kg/m3) D% UMC 797.80 ± 39.42a 7.47 TMC 798.43 ± 16.82a 3.96 Mean values with same letter do not present significant statistical variation (p<0.05).

Table 3. Thermal conductivity of UMC and TMC composites.

Composite Thermal Conductivity (Wm-1K-1) Effusiveness (Ws½m-2K-1) UMC 0.140 ± 0.048a 313.154 ± 62.703a a TMC 0.117 ± 0.042 278.144 ± 70.757a Mean values with same letter do not present significant statistical variation (p<0.05).

3.5. Physical properties Table 2 presents the mean values obtained for the density, density variation (D%), thickness swelling and water absorption of the UMC and TMC composites. With regard to density, the composites do not present a significant difference between them (p>0.05). Both composites showed characteristics of Medium Density Fibreboard (MDF), in accordance with the Brazilian standard ABNT NBR 153162:2019[21], which establishes average density values between 651-800 Kg/m3. The UMC composite showed the highest maximum density variation modulus (D%), corresponding to 7.47%, indicating that the TMC composite has greater stability in relation to this property. For the properties of thickness swelling and water absorption, both composites show a significant difference between them (p<0.05). As for the thickness swelling, both composites showed average values within the limit established by the Brazilian standard ABNT NBR 15316-2:2019[21] for medium density fiberboard used in dry and wet conditions, which determine maximum values of 17% and 12%, respectively. With regard to water absorption, the minimum requirements are not included in the standard used to carry out the test, however, both composites meet the European Standard EN 317:1993[41], which establishes a maximum of 35% for this property in fiberboard. For the UMC fiber composite, the higher thickness swelling and water absorption content is associated with the presence of hydroxyl and non-polar groups in various components of the fiber, which are susceptible to water[42].

Thickness swelling and water absorption in polymeric composites have an intrinsic relationship. In general, the absorption of water causes gradual swelling in the cell walls of the fibers, which expand until saturation. Thus, the micro voids, pores and cracks at the fiber/matrix interface are now occupied by water, increasing the thickness and weight of the composites[43]. According to Marinho[44], the higher the residual lignin content in the fiber after chemical treatment, 6/10

Diffusivity (m2s-110-7) 1.923 ± 0.576a 1.703 ± 0.373a

the lower its vulnerability to water absorption. From this, it is understood that mercerization removed a small part of lignin from the fiber, resulting in a significant improvement in the physical properties of the composites.

3.6. Thermal conductivity In Table 3, it is possible to compare the results obtained for conductivity, effusivity and diffusivity for the UMC and TMC composites, which did not present a significant difference between them (p>0.05). Fiorelli et al.[45] characterized particleboard panels of bagasse and sugarcane, curaua and jute fibers and reported results similar to those found in the present study, with an average value of 0.14 W/mK. The alkali treatment tends to increase the thermal conductivity of polymeric composites due to the reduction of voids present at the fiber/matrix interface, increasing the contact area between these components, which facilitates heat transport[46]. Furthermore, the alkali treatment removes the amorphous components present in the fiber, leading to an increase in crystallinity which in turn improves packing and heat flux in the structure[47]. Therefore, it was expected that there would be an increase in thermal conductivity for the TMC composite, according to the literature[46,48], which did not occur in this study. However, both composites showed good thermal conductivity properties and are classified as insulating materials, as they have average values below 0.25 W/mK[49]. Thus, these materials can be used in applications that require thermal insulation.

3.7. Scanning Electron Microscopy (SEM) Figure 6 shows the SEM images of the cross section of the UMC and TMC composites, at a scale of 100 μm. As shown in Figure 6a, it was verified that the UMC composite presented a low adhesion between fiber and matrix, being little homogeneous and having empty spaces due to the lack of wettability with the matrix. The TMC composite Polímeros, 35(1), e20250006, 2025

Influence of alkali treatment on physical-mechanical properties of mallow fiber/BOPP composites

Figure 6. SEM analysis of cross section of (a) UMC and (b) TMC composites

Figure 7. SEM analysis of surface of (a) UMC and (b) TMC composites.

(Figure 6b) presented different characteristics, being homogeneous and uniform, showing that there was good adhesion between fiber/matrix due to the surface treatment.

The treatment promoted an increase in the fibrillar surface area, facilitating the anchoring of the fiber to the polymeric matrix and favoring the interfacial adhesion mechanism[15].

Figure 7 shows SEM images of the surface of UMC and TMC composites. It is possible to observe that the UMC composite (Figure 7a) has pores and cracks throughout its surface, unlike the TMC composite (Figure 7b), which has a smooth surface and no surface defects. These pores and fissures influence the physical properties of the material as they leave the fiber exposed, accumulate water, making the composite heavier and thicker[43]. These evidenced aspects corroborate the results obtained in the thickness swelling and water absorption tests.

Polímeros, 35(1), e20250006, 2025

3.8. Izod impact test Table 4 presents the results obtained in the Izod impact test for the UMC and TMC composites, which did not present a significant difference between them (p>0.05). However, it was expected that the TMC composite would present a higher average value of impact strength when compared to the UMC composite, so that the alkali treatment would make the mallow fiber more resistant to load transfer between fiber/ matrix on impact[50]. As seen in the SEM images, the alkali treatment promoted a better interfacial bond between the fiber and the matrix caused by the removal of amorphous components such as waxes and oils from the fiber surface.

According to Senthilkumar et al.[51], this can lead to a strong mechanical lock between the fiber and the matrix, reducing fiber pullout, which promotes a negative effect on the impact 7/10

Litaiff, H. A., Santos, G. M., Melo, G., Cunha, C., & Giacon, V. M. Table 4. Izod impact strength of UMC and TMC composites.

Composite UMC TMC

Impact strength (J/m) 293.9 ± 0.3a 288.2 ± 16.5a

Mean values with same letter do not present significant statistical variation (p<0.05).

strength of the composite. Similar results are found in the literature reported by Senthilkumar et al.[51] and Goud and Rao[52], in which an improvement in adhesion between fiber/ matrix and a decrease in impact strength was observed with the alkali treatment. Despite this, both composites showed results superior to the impact resistance of other polymeric composites reinforced with other natural fibers, such as PHBV and curaua fiber with impact strength of 169.4 J/m[53] and recycled PP and royal palm fiber with 35 J/m[54].

4. Conclusions The alkali treatment reduced the average diameter of mallow fibers due to the removal of amorphous components from its surface, such as lignin, hemicellulose and organic materials. This led to an increase in the crystallinity index, thermal stability and tensile strength of a single fiber.

Thickness swelling and water absorption of the TMC composite were significantly lower compared to the UMC composite. The alkaline treatment did not influence the thermal conductivity of the composites, however, both can be classified as insulating materials. The impact resistance of the composites was not influenced by the chemical treatment.

The improvement in the interfacial adhesion mechanism between fiber/matrix with treatment, observed from the SEM images, may have had an impact on this property. Based on this, mallow fibers showed results that demonstrate their potential for use as a source of raw material in polymeric composites, considering that in addition to their satisfactory properties, they promote the reduction of the consumption of non-renewable raw materials, as well as the use of BOPP as a matrix, which adds value to industry waste that has a negative impact on the environment.

5. Author’s Contribution • Conceptualization – Virginia Mansanares Giacon; Gabrielle Machado dos Santos.

• Data curation – Hannah Alagoas Litaiff.

• Formal analysis – Hannah Alagoas Litaiff; Gabriel de Melo.

• Funding acquisition ​– Virginia Mansanares Giacon.

• Investigation – ​Hannah Alagoas Litaiff; Gabrielle Machado dos Santos.

• Methodology – Hannah Alagoas Litaiff; Gabrielle Machado dos Santos.

• Project administration – Virginia Mansanares Giacon.

• Resources – Virginia Mansanares Giacon.

• Software – N.A. • Supervision – Virginia Mansanares Giacon.

• Validation – Virginia Mansanares Giacon.

8/10

• Visualization – Hannah Alagoas Litaiff; Gabriel de Melo; Claudia da Cunha.

• Writing – original draft – ​Hannah Alagoas Litaiff.

• Writing – review & editing – Gabrielle Machado dos Santos; Gabriel de Melo; Claudia da Cunha; Virginia Mansanares Giacon.

6. Acknowledgements The authors gratefully acknowledge Companhia Têxtil de Castanhal, Videolar-Innova, Universidade Federal do Amazonas (UFAM) and Laboratório de Materiais da Amazônia e Compósitos (LaMAC). Also, the authors are grateful to the Fundação de Amparo à Pesquisa do Estado do Amazonas (FAPEAM) for financial support. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001.

7. References 1. Nurazzi, N. M., Asyraf, M. R. M., Rayung, M., Norrrahim, M. N. F., Shazleen, S. S., Rani, M. S. A., Shafi, A. R., Aisyah, H. A., Radzi, M. H. M., Sabaruddin, F. A., Ilyas, R. A., Zainudin, E. S., & Abdan, K. (2021). Thermogravimetric analysis properties of cellulosic natural fiber polymer composites: a review on influence of chemical treatments. Polymers, 13(16), 2710. http://doi.org/10.3390/polym13162710. PMid:34451248.

2. Shaker, K., Nawab, Y., & Jabbar, M. (2020). Bio-composites: eco-friendly substitute of glass fiber composites. In O. Kharissova, L. Martínez, & B. Kharisov (Eds.), Handbook of nanomaterials and nanocomposites for energy and environmental applications (pp. 1-25). Cham: Springer. http://doi.org/10.1007/978-3-03011155-7_108-1.

3. Labib, W. A. (2022). Plant-based fibres in cement composites: a conceptual framework. Journal of Engineered Fibers and Fabrics, 17, 15589250221078922. http://doi. org/10.1177/15589250221078922.

4. Mousavi, S. R., Zamani, M. H., Estaji, S., Tayouri, M. I., Arjmand, M., Jafari, S. H., Nouranian, S., & Khonakdar, H. A. (2022). Mechanical properties of bamboo fiber-reinforced polymer composites: a review of recent case studies. Journal of Materials Science, 57(5), 3143-3167. http://doi.org/10.1007/ s10853-021-06854-6.

5. Costa, U. O., Nascimento, L. F. C., Garcia, J. M., Bezerra, W. B. A., & Monteiro, S. N. (2020). Evaluation of Izod impact and bend properties of epoxy composites reinforced with mallow fibers. Journal of Materials Research and Technology, 9(1), 373-382. http://doi.org/10.1016/j.jmrt.2019.10.066.

6. Cunha, J. S. C., Oliveira, H. E., No., Giacon, V. M., Manzato, L., & Silva, C. G. (2021). Study on mechanical and thermal properties of amazon fibers on the polymeric biocomposites: malva and Tucum. Fibers and Polymers, 22(11), 3203-3211. http://doi.org/10.1007/s12221-021-0843-y.

7. Araújo, K. S., & Pereira, H. S. (2017). Public policies and natural fibers: the recent experience of the Amazonian malva and jute production chain. Amazonian Journal of Agricultural and Environmental Sciences, 60(1), 60-69. http://doi.org/10.4322/ rca.60102.

8. Oliveira, P. F., & Marques, M. F. V. (2015). Chemical treatment of natural malva fibers and preparation of green composites with poly (3-hydroxybutyrate). Chemistry & Chemical Technology, 9(2), 211-222. http://doi.org/10.23939/chcht09.02.211.

Polímeros, 35(1), e20250006, 2025

Influence of alkali treatment on physical-mechanical properties of mallow fiber/BOPP composites 9. Liu, W., Cheng, L., & Li, S. (2018). Review of electrical properties for polypropylene based nanocomposite. Composites Communications, 10, 221-225. http://doi.org/10.1016/j. coco.2018.10.007.

10. Ščetar, M., Kurek, M., Režek Jambrak, A., Debeaufort, F., & Galić, K. (2017). Influence of high power ultrasound on physical–chemical properties of polypropylene films aimed for food packaging: barrier and contact angle features. Polymer International, 66(11), 1572-1578. http://doi.org/10.1002/ pi.5415.

11. Yugue, E. T., Mancini, S. D., & Roveda, J. A. F. (2022). Desafios e potenciais soluções para reciclagem de embalagens plásticas flexíveis pós-consumo no Brasil. Revista DAE, 70(237), 100120. http://doi.org/10.36659/dae.2022.055.

12. Rohit, K., & Dixit, S. (2016). Mechanical properties of waste biaxially oriented polypropylene metallized films (BOPP), LLDPE: LDPE films with sisal fibres. American Journal of Engineering and Applied Sciences, 9(4), 913-920. http://doi. org/10.3844/ajeassp.2016.913.920.

13. Lee, C. H., Khalina, A., & Lee, S. H. (2021). Importance of interfacial adhesion condition on characterization of plant-fiberreinforced polymer composites: a review. Polymers, 13(3), 438. http://doi.org/10.3390/polym13030438. PMid:33573036.

14. Nunes, J. V. S., Silva, E. X. B., Miranda, M. H. P., Rios, A. S., & Deus, E. P. (2022). Caracterização mecânica e morfológica de fibras de coco tratadas superficialmente para utilização como reforço em polímeros. Matéria, 27(2), e20220046. http://doi. org/10.1590/1517-7076-rmat-2022-0046.

15. Rebelo, V., da Silva, Y., Ferreira, S., Filho, R. T., & Giacon, V. (2019). Effects of mercerization in the chemical and morphological properties of Amazon Piassava. Polímeros: Ciência e Tecnologia, 29(1), e2019013. http://doi.org/10.1590/0104-1428.01717.

16. Tavares, F. F. C., Almeida, M. D. C., Silva, J. A. P., Araújo, L. L., Cardozo, N. S. M., & Santana, R. M. C. (2020). Thermal treatment of açaí (Euterpe oleracea) fiber for composite reinforcement. Polímeros: Ciência e Tecnologia, 30(1), e2020003. http://doi.org/10.1590/0104-1428.09819.

17. Giacon, V. M., Rebelo, V. S. M., Santos, G. M., Sanches, E. A., Fiorelli, J., Costella, Â. M. S., Melo, G. M. M., & Brito, L. M. A. F. (2021). Influence of mercerization on the physical and mechanical properties of polymeric composites reinforced with Amazonian Fiber. Fibers and Polymers, 22(7), 1950-1956. http://doi.org/10.1007/s12221-021-0460-9.

18. Segal, L., Creely, J. J., Martin, A. E., Jr., & Conrad, C. M. (1959). An Empirical method for estimating the degree of crystallinity of native cellulose using the X-Ray diffractometer.

Textile Research Journal, 29(10), 786-794. http://doi. org/10.1177/004051755902901003.

19. American Society for Testing and Materials – ASTM. (1975).

ASTM D3379-75: standard test method for tensile strength and young’s modulus for high-modulus. West Conshohocken, PA: ASTM International.

20. Chatterjee, A., Kumar, S., & Singh, H. (2020). Tensile strength and thermal behavior of jute fibre reinforced polypropylene laminate composite. Composites Communications, 22, 100483. http://doi.org/10.1016/j.coco.2020.100483.

21. Associação Brasileira de Normas Técnicas – ABNT. (2019).

ABNT NBR 15316-2:2019: painéis de fibras de média densidade - parte 2: requisitos e métodos de ensaio. Rio de Janeiro: ABNT. 22. American Society for Testing and Materials – ASTM. (2022).

ASTM D570-22: standard test method for water absorption of plastics. West Conshohocken, PA: ASTM International.

23. American Society for Testing and Materials – ASTM. (2021).

ASTM D7984-21: standard test method for measurement of thermal effusivity of fabrics using a Modified Transient Plane Polímeros, 35(1), e20250006, 2025

Source (MTPS) instrument. West Conshohocken, PA: ASTM International.

24. American Society for Testing and Materials – ASTM. (2010).

ASTM D256-10: standard test methods for determining the izod pendulum impact resistance of plastics. West Conshohocken, PA: ASTM International.

25. Tkachenko, T. V., Kamenskyh, D. S., Sheludko, Y. V., & Yevdokymenko, V. O. (2022). Structural and morphological features of microcrystalline cellulose from soybean straw by organosolvent treatment. Chemistry. Physics and Technology of Surface, 13(4), 455-466. http://doi.org/10.15407/hftp13.04.455.

26. Gabriel, T., Belete, A., Hause, G., Neubert, R. H. H., & GebreMariam, T. (2022). Is mercerization the only factor for (Partial) polymorphic transition of cellulose I to cellulose II in cellulose nanocrystals? Cellulose Chemistry and Technology, 56(5-6), 495507. http://doi.org/10.35812/CelluloseChemTechnol.2022.56.42.

27. Shahril, S. M., Ridzuan, M. J. M., Majid, M. A., Bariah, A. M. N., Rahman, M. T. A., & Narayanasamy, P. (2022). Alkali treatment influence on cellulosic fiber from Furcraea foetida leaves as potential reinforcement of polymeric composites.

Journal of Materials Research and Technology, 19, 2567-2583. http://doi.org/10.1016/j.jmrt.2022.06.002.

28. Suryanto, H., Sukarni, S., Pradana, Y. R. A., Yanuhar, U., & Witono, K. (2019). Effect of mercerization on properties of mendong (Fimbristylis globulosa) fiber. Songklanakarin Journal of Science and Technology, 41(3), 624-630. http:// doi.org/10.14456/sjst-psu.2019.73.

29. Monteiro, S. N., Margem, F. M., Margem, J. I., Martins, L. B. S., Oliveira, C. G., & Oliveira, M. P. (2014). Infra-red spectroscopy analysis of malva fibers. Materials Science Forum, 775-776, 255-260. http://doi.org/10.4028/www.scientific.net/ MSF.775-776.255.

30. Furtado, J. B. M., Furtado, P. A., Fo, Oliveira, T. P., Caetano, M. R. S., Araújo, I. M. S., Figueiredo, F. C., & Santos, J. R., Jr. (2020). Caracterização química da fibra do caule da palmeira de babaçu natural e após tratamento. Revista de Engenharia e Pesquisa Aplicada, 5(3), 56-64. http://doi.org/10.25286/repa. v5i3.1254.

31. Fatkhurrohman, Rochardjo, H. S. B., Kusumaatmaja, A., & Yudhanto, F. (2019). Extraction and effect of vibration duration in ultrasonic process of cellulose nanocrystal (CNC) from ramie fiber. In Proceedings of the 1st International Seminar on Advances in Metallurgy and Materials (i-SENAMM 2019) (pp. 030004).

Jakarta: AIP Publishing. http://doi.org/10.1063/5.0015794.

32. Asim, M., Paridah, M. T., Chandrasekar, M., Shahroze, R. M., Jawaid, M., Nasir, M., & Siakeng, R. (2020). Thermal stability of natural fibers and their polymer composites. Iranian Polymer Journal, 29(7), 625-648. http://doi.org/10.1007/s13726-02000824-6.

33. Xia, L., Zhang, C., Wang, A., Wang, Y., & Xu, W. (2020).

Morphologies and properties of Juncus effusus fiber after alkali treatment. Cellulose, 27(4), 1909-1920. http://doi.org/10.1007/ s10570-019-02933-9.

34. Ornaghi, H. L., Jr., Ornaghi, F. G., Neves, R. M., Monticeli, F., & Bianchi, O. (2020). Mechanisms involved in thermal degradation of lignocellulosic fibers: a survey based on chemical composition. Cellulose (London, England), 27(9), 4949-4961. http://doi.org/10.1007/s10570-020-03132-7.

35. Singh, J. K., & Rout, A. K. (2022). Characterization of raw and alkali-treated cellulosic fibers extracted from Borassus flabellifer L. Biomass Conversion and Biorefinery, 14(10), 11633-11646. http://doi.org/10.1007/s13399-022-03238-x.

36. Laverde, V., Marin, A., Benjumea, J. M., & Ortiz, M. R. (2022).

Use of vegetable fibers as reinforcements in cement-matrix composite materials: a review. Construction & Building Materials, 340, 127729. http://doi.org/10.1016/j.conbuildmat.2022.127729.

9/10

Litaiff, H. A., Santos, G. M., Melo, G., Cunha, C., & Giacon, V. M. 37. Silva, F. M. (2018). Caracterização mecânica de um compósito de matriz poliéster insaturado reforçado com fibras de sisal em diferentes orientações utilizando correlação digital de imagens (Master’s thesis). Universidade Federal Rural do Semiárido, Mossoró.

38. Baskaran, P. G., Kathiresan, M., & Pandiarajan, P. (2022). Effect of alkali-treatment on structural, thermal, tensile properties of dichrostachys cinerea bark fiber and its composites. Journal of Natural Fibers, 19(2), 433-449. http://doi.org/10.1080/15 440478.2020.1745123.

39. Arul Marcel Moshi, A., Ravindran, D., Sundara Bharathi, S. R., Padma, S. R., Indran, S., & Divya, D. (2020). Characterization of natural cellulosic fiber extracted from Grewia damine flowering plant’s stem. International Journal of Biological Macromolecules, 164, 1246-1255. http://doi.org/10.1016/j. ijbiomac.2020.07.225. PMid:32738327.

40. Fonseca, R. P. (2021). Influência de diferentes tipos de fibras vegetais amazônicas no desempenho de uma argamassa a base de cimento Portland e Metacaulim (Doctoral dissertation).

Universidade Federal de Santa Catarina, Florianópolis.

41. British Standards Institution – BSI. (1993). EN 317:1993: particleboards and fiberboards: determination of swelling in thickness after immersion in water. London: BSI. 42. Kamaruddin, Z. H., Jumaidin, R., Ilyas, R. A., Selamat, M. Z., Alamjuri, R. H., & Md Yusof, F. A. (2022). Influence of Alkali treatment on the mechanical, thermal, water absorption, and biodegradation properties of cymbopogan citratus fiberreinforced, thermoplastic cassava starch–palm wax composites.

Polymers, 14(14), 2769. http://doi.org/10.3390/polym14142769.

PMid:35890548.

43. Aparicio, R. R. (2019). Influência das razões de pré-polímero na matriz poliuretânica de óleo de mamona em compósito com alto teor fibras de fibras de piaçava da Amazônia (Master’s thesis). Universidade Federal do Amazonas, Manaus.

44. Marinho, N. P. (2012). Características das fibras do bambu (Dendrocalamus giganteus) e potencial de aplicação em painéis de fibra de média densidade (MDF) (Master’s thesis).

Universidade Tecnológica Federal do Paraná, Curitiba.

45. Fiorelli, J., Galo, R. G., Castro, S. L., Jr., Belini, U. L., Lasso, P. R. O., & Savastano, H., Jr. (2018). Multilayer particleboard produced with agroindustrial waste and Amazonia vegetable fibres. Waste and Biomass Valorization, 9(7), 1151-1161. http:// doi.org/10.1007/s12649-017-9889-x.

46. Sudha, S., & Thilagavathi, G. (2018). Analysis of electrical, thermal and compressive properties of alkali-treated jute fabric

10/10

reinforced composites. Journal of Industrial Textiles, 47(6), 1407-1423. http://doi.org/10.1177/1528083717695840.

47. Jena, H., Kumar Pradhan, A., & Kumar Pandit, M. (2017).

Effect of cenosphere on thermal conductivity of bamboo fibre reinforced composites. Advanced Materials & Processes, 2(2), 97-102. http://doi.org/10.5185/amp.2017/207.

48. Scalioni, L. V., Gutiérrez, M. C., & Felisberti, M. I. (2017).

Green composites of poly(3-hydroxybutyrate) and curaua fibers: morphology and physical, thermal, and mechanical properties. Journal of Applied Polymer Science, 134(14), 44676. http://doi.org/10.1002/app.44676.

49.

Karwa, R., & Karwa, R. (2020). Onedimensional steady-state heat conduction. In: R. Karwa (Ed.), Heat and mass transfer (pp. 7-112). Singapore: Springer. http:// doi.org/10.1007/978-981-15-3988-6_2.

50. Marichelvam, M. K., Manimaran, P., Verma, A., Sanjay, M. R., Siengchin, S., Kandakodeeswaran, K., & Geetha, M. (2021). A novel palm sheath and sugarcane bagasse fiber based hybrid composites for automotive applications: an experimental approach. Polymer Composites, 42(1), 512-521. http://doi. org/10.1002/pc.25843.

51. Senthilkumar, K., Rajini, N., Saba, N., Chandrasekar, M., Jawaid, M., & Siengchin, S. (2019). Effect of alkali treatment on mechanical and morphological properties of pineapple leaf fibre/polyester composites. Journal of Polymers and the Environment, 27(6), 1191-1201. http://doi.org/10.1007/ s10924-019-01418-x.

52. Goud, G., & Rao, R. N. (2011). Effect of fibre content and alkali treatment on mechanical properties of Roystonea regiareinforced epoxy partially biodegradable composites. Bulletin of Materials Science, 34(7), 1575-1581. http://doi.org/10.1007/ s12034-011-0361-4.

53. Beltrami, L. V. R., Scienza, L. C., & Zattera, A. J. (2014).

Efeito do tratamento alcalino de fibras de Curauá sobre as propriedades de compósitos de matriz biodegradável. Polímeros: Ciência e Tecnologia, 24(3), 388-394. http://doi.org/10.4322/ polimeros.2014.024.

54. Sá, B. S. R. (2019). Obtenção e caracterização do compósito de polipropileno reciclado com fibra de palmeira-real (Archontophoenix cunninghamiana) (Master’s thesis).

Universidade Tecnológica Federal do Paraná, Londrina.

Received: June 27, 2024 Revised: Sept. 25, 2024 Accepted: Oct. 30, 2024

Polímeros, 35(1), e20250006, 2025

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20240068

Anchoring of ex-situ MOF-199 and MOF-UiO-66-NH2 onto TEMPO-oxidized cotton: potential antibacterials Sergio Alejandro Torres-Cortés1*, Mauricio Velasquez2  and César Sierra1  Grupo de Investigación en Macromoléculas, Departamento de Química, Facultad de Ciencias, Universidad Nacional de Colombia, Bogotá, Colombia 2 Estado Sólido y Catálisis Ambiental – ESCA, Departamento de Química, Facultad de Ciencias, Universidad Nacional de Colombia, Bogotá, Colombia

1

*satorresc@unal.edu.co

Abstract This study reports the ex-situ anchoring of two metal organic frameworks (MOF-199 and MOF UiO-66-NH2) onto TEMPO-oxidized cotton fibers. While in-situ anchoring methodologies are reported, ex-situ protocols are underreported despite their advantages in industrial scaling-up and control. The functionalized composites were characterized after 48 h of Soxhlet treatment. X-ray diffraction and infrared spectra confirmed MOFs anchorage through super positioning signals corresponding to cotton and MOFs. Likewise, X-ray photoelectron spectra (XPS) show the presence of Cu2+ (4.73% molar ratio) and Zr4+ (12.06%) coordinated to the -COO groups of the organic linkers, indicating a stable chemical interaction. Finally, SEM confirmed the expected MOF morphology. The potential antibacterial activity of these materials was evaluated. The assays revealed a bacteriostatic effect for MOF UiO-66-NH2@cotton, even after 48 h of contact. Meanwhile, the MOF-199@cotton showed a bactericide effect under the same conditions.

Keywords: antibacterial material, ex-situ chemical anchorage, MOF, TEMPO-oxidation.

How to cite: Torres-Cortés, S. A., Velasquez, M., & Sierra, C. (2025). Anchoring of ex-situ MOF-199 and MOF-UiO66-NH2 onto TEMPO-oxidized cotton: potential antibacterials. Polímeros: Ciência e Tecnologia, 35(1), e20250007. https://doi.org/10.1590/0104-1428.20240068

1. Introduction The chemical modification of textile fibers is a broad field that continues to be explored due to the importance of its applications. It is highly spread for industrial use in food, textiles, pharmaceuticals, and environmental remediation[1]. Cotton, the principal product obtained from natural cellulose, is a desired material principally for its abundance of -OH groups, which make it an ideal material for surface modifications that include oxidation, carboxylation, and carboxymethylation, among others[2,3].

Various inorganic and metalorganic-like materials have been evaluated to carry out modifications on the surface of cotton[4-6]. However, the use of metal-organic frameworks (MOFs) to functionalize fibers is a promising and innovative strategy that could offer significant advantages over traditional methods. The unique physicochemical properties of MOFs, such as their porosity, surface area, and structural flexibility, make them exceptional materials for a wide range of applications[7-9]. In fact, antibacterial properties of nanomaterials like MOFs depend on the chemical properties given to these materials and the synergy between metal centers and ligands. MOFs can act as metal reservoirs, allowing their gradual release, a mechanism to which their antibacterial activity is attributed. Once released, the metallic species undergo biocidal activity by

Polímeros, 35(1), e20250007, 2025

internalization and damage in DNA and protein synthesis or by inhibiting membrane synthesis[10,11].

Nevertheless, direct applications of MOFs at the industrial level have some issues associated with the thermal and mechanical fragility and powder-like aggregation state, which can lead to the leaching of the metal cluster or the destruction of the initial structure. One way to solve this problem is by anchoring MOFs to textile fibers through chemical bonds between the metallic coordination nodes of MOFs and functional groups present on the fiber surface.

Then, in most cases, textile fibers need to be functionalized before the anchorage to produce the coordination sites required to attach MOFs[12] is a methodology in which a sodium bromo- or chloroacetate solution, in the presence of a base, is used to convert primary and secondary -OH cellulose groups into carboxymethyl-ether groups. On the other hand, TEMPO (2,2,6,6-tetramethylpiperidinyloxy) carboxylation is a regioselective, catalytic, and easy-todo reaction in which this stable free radical is used in the presence of NaClO as primary oxidant, NaClO2 as co-oxidant and NaBr as reducing agent to oxidate primary -OH groups into carboxylate groups. This methodology, first reported by de Nooy et al.[13], has been widely spread to oxidate fique, starch, and pullulan, among other cellulosic materials[14,15].

Biermann published the first attempt to introduce an MOF

1/11

O O O O O O O O O O O O O O O O O

Torres-Cortés, S. A., Velasquez, M., & Sierra, C. into a cellulosic material[16]. Like this, other works have been reported with the goal to anchorage the MOF structures on fibers[17-19]. Some of them are related to the antibacterial applications. However, all these works are focused on the in-situ anchored procedures where most of the synthesized MOF is not attached efficiently to the modified fiber, showing low MOF charges. Additionally, functionalized materials commonly present a substantial leaching of the MOF. Because of these problems, few authors have reported ex-situ approaches to anchor previously synthesized MOFs on modified textile fibers. These methodologies can offer several advantages, such as higher amounts of anchored material, stronger interactions between MOF and fiber, and the possibility of higher recovery of non-anchored the MOF material[20-22]. Therefore, in the present work, the chemical anchoring of ex-situ obtained MOF-199 and MOF UiO-66-NH2 onto TEMPO/NaClO/NaClO2 oxidized cotton fibers is reported, and finally, their antibacterial potential was tested against E. coli and S. aureus.

2. Materials and Methods

using an Al-Κα monochromatic (1486.7 eV, 13 kV, 100 W) source with a passing energy of 90 eV. High-resolution spectra were recorded using an analysis area of 300 μm x 700 μm and a 20eV pass. Data were acquired with 0.5 eV steps. All the binding energies were calibrated with the C1s binding energy fixed at 284.6 eV as an internal reference. SEM micrographs were recorded using a Jeol-JSM-6490 probe for EDX analysis, operated at an acceleration 20 kV beam voltage, and using a Jeol-JSM-6490 probe with a 20 kV beam and a magnification power of 3000x. The quantification of the carboxylate groups after the fiber oxidation were determined by a coulometric titration. The carboxylated fiber was introduced in a glass reactor and pretreated with HCl 0.1 M solution to protonate the carboxylate groups. Then, the fiber was washed to obtain the conductivity of the water. The titration was carried out using 20 mL of 0.1 M KCl as the electrolyte, a Pt electrode (cathode), an Ag electrode (anode), and the pH sensor as the indicator electrode in the acid-base titration. The electrodes were connected in series through a multimeter, and a constant current of 9.97 mA was applied. Finally, UV-visible analyses of bacterial cultures were performed using a Thermo Evolution-3000 with a double beam and xenon lamp.

2.1 Materials Free radical 2,2,6,6-tetramethyl-1-piperidinil-oxyl (TEMPO) was obtained from Sigma-Aldrich Chemie® GmbH. 15% sodium hypochlorite was purchased from Químicos J.J. Ltda. Reference textile cotton 100% (TIC 400, 98 g m-2, 1 m2) was obtained from Testfabrics Inc. Zirconium chloride, sodium chloride, acetone, ethanol (EtOH), and copper (II) nitrate trihydrate (Cu(NO3)2 · 3H2O) were obtained from Merck KgaA. 2-Amino terephthalic acid (H2BDCNH2), methanol, and deionized water were purchased from Merck Millipore®. 1,3,5-Benzene tricarboxylic acid (H3BTC), zinc nitrate hexahydrate, N,N,N-triethylamine, TEA, and dimethylformamide (DMF) were obtained from PanReac AppliChem®. The reactants were used as purchased without purification.

2.2 MOFs synthesis With these materials the procedures of MOF synthesis (Scheme S1a and S1b), cotton functionalization (Scheme S2), and ex-situ chemical MOF anchoring (Scheme S3) were carried out similar to our previous report[23].

2.3 Materials characterization The MOFs and the fibers were characterized separately.

Then, the fibers functionalized with the MOFs were characterized after 48 h of Soxhlet treatment using a methanol-water solution. Thus, the structure and chemical composition of all materials were analyzed by Attenuated Total ReflectanceFourier Transformed Infrared spectroscopy (FTIR-ATR).

The spectra were recorded with a Shimadzu® FTIR solutions spectrophotometer with an ATR module (attenuated total reflectance) with germanium crystal (4000-600 cm-1).

The X-ray diffraction (XRD) patterns were recorded using a Philips Analytical® PW3050/60 diffractometer with Cu anode (Kα: 1.54056 Å), operated at 45 kV voltage and 40 mA acceleration current. The X-ray photoelectron (XPS) spectra were measured with an X-ray photoelectronic spectrometer X (NAP-XPS) Specs® with a PHOIBOS 150 1D-DLD analyzer, 2/11

3. Results and Discussions 3.1 Characterization of MOF-199 and UiO-66-NH2 For the synthesized MOF-199, the FTIR-ATR signals and their corresponding vibration modes were found at 1644 cm-1 (-C=O, stretching); 1450 cm-1 (O-C=O, bending); 1372 cm-1 (νas =C-O, stretching); 1112 cm-1 (O-C=O, stretching) and 725 cm-1 (Cu-O, stretching) (Figure S1a). These signals agree with the previously reported analysis[24]. The band over 3300 cm-1 corresponds to the presence of remanent water. Likewise, The XRD pattern (Figure S1b) shows the characteristic peaks at (° 2θ) = 5.75 (200); 9.57 (220); 11.68 (222); 13.56 (400); 15.12 (420); 17.56 (422) which confirm the formation of the material.

On the other hand, for the MOF UiO-66-NH2, the FTIR-ATR signals (Figure S2a) and its corresponding vibration modes were found at 3868 cm-1 (N-H, stretching); 1652 cm-1 (-C=O, stretching), 1567 cm-1 (O-C=O, bending); 1388 cm-1 (N-H, bending) and 764 cm-1 (p C-C, stretching) which are the typical bands of this MOF as were previously reported[25]. Over 3800 cm-1 are appreciated the bands of symmetric and asymmetric stretching of N-H bonds in 2-amino terephthalic acid.

The XRD patterns in Figure S2b show the 2θ peaks at 7.60° (111); 8.92° (002); 12.34° (004); 22.44° (115), and 25.95° (006), which match well with the reported standard pattern[26].

3.2 characterization of cotton fibers The pure and carboxylated cotton fibers were also characterized by FTIR-ATR and XRD spectroscopies.

The infrared spectrum of the pure cotton (Figure 1a) shows typical signals at 3346 cm-1 (stretching, O-H), 1315 (flexion, C-H in cellulose skeleton), 1160-1107 cm-1 (stretching, C-O alcohol), and 1050 cm-1 (stretching, C-O primary alcohol), which indicate the presence of the hydroxyl groups.

Consequently, the XRD pattern (Figure 1b) shows the typical Polímeros, 35(1), e20250007, 2025

Anchoring of ex-situ MOF-199 and MOF-UiO-66-NH2 onto TEMPO-oxidized cotton: potential antibacterials peaks of the cotton structure (° 2θ) = 14.88, 16.51, 22.87 and 34.26. According to previews reports, the crystalline domains in cotton textiles are less reactive and more inert than the amorphous ones. Nevertheless, the surface modifications onto cotton fibers can diminish the crystalline domains and increase the presence of amorphous domains in cotton fibers[15].

The carboxylated cotton, depicted in Figure 1a, shows an evident transformation with the peak at 1610 cm-1 corresponding to the presence of -C=O bonds of carboxylate groups, which do not appear in the spectrum of pure cotton. Although the complementary band at 3346 cm-1 does not show a relevant change, the loss of symmetry in this for the carboxylated fiber can be interpreted as the loss of -OH groups from primary alcohols that became carboxylate groups after the treatment. Likewise, The XRD spectra in Figure 1b show no appreciable modification of the crystalline properties of the textile, and the diffraction peaks are in good agreement with a previous report[27].

From the FTIR-ATR results, the carbonyl index (IC) was calculated, which provides an estimation of the functionalization of the cellulose. According to eq. 1, ACO is the absorbance of the carbonyl stretching band (1610 cm-1), and ARB is the absorbance of the reference band, which should be a peak with constant intensity in both pure and carboxylated cotton spectra. In this work, the band at 1315 cm-1 was chosen, as suggested in a former report[28]. On the other hand, the crystallinity index (CI, eq. 2). This was estimated using the empirical method of Segal et al.[29] through the relation of intensities of the diffraction peaks at 22.5° 2θ, corresponding to (200) peak (I22.5), and the intensity of the amorphous fraction (IAM), corresponding to 18° 2θ. The carbonyl and crystallinity indexes were measured for the cotton textile before and after modification, and the results are summarized in Table 1.

IC= (% )

ACO × 100 ARB

I 22.5 − I am = CI (%) × 100 I 22.5

(1)

domains suffer a loss of crystallinity with the chemical treatment.

According to earlier reports regarding the characterization of cellulose, the crystallinity index decreases significantly with extensive large reaction times. In this study, the reaction time did not exceed 2 hours, and according to the XRD spectra in Figure 1b, the crystal domain was not changed.

On the other hand, the result of the carbonyl index for the TEMPO-oxidized cotton fibers shows a higher percentage of carbonyl groups on their surface, giving evidence of the effectiveness of the functionalization.

As previously described, the concentration of carboxylic groups (-COOH) was tested by coulometric titration, confirming FTIR-ATR observations. The titration curves were analyzed by using the OriginPro® software, and the number of carboxylic groups was calculated using eq. 3, where tEND corresponds to the time (expressed in seconds) in which POINT the titration reaches the endpoint, i is the constant current (in Amperes) provided by the potentiostat. The results are depicted in Table 2 (titration experiments were carried out several times, the values herein reported are representative amounts, selected as the best and most reliable data). mmol COOH = tend point ( s ) ⋅ i ( A ) ⋅ g textile 1 mol e− 1 mol H + ⋅ ⋅ 96485,33 C 1 mol e− 1 mol COOH 1 mol H +

⋅

(3)

1000 mmol 1 ⋅ g textile 1 mol

These results from two different experiments show good repeatability of the functionalization method, where an amount of around 0.066 mmol/g was obtained. These results are in good agreement, or even better, with the previous Table 1. Obtained results of CI and IC for cotton composites.

(2)

The CI results show a lower value for the carboxylated fiber, which may be explained by the fact that some crystalline

Fiber Cotton Cotton-COOH

Carbonyl index (CI) (%) 71.43

Crystallinity index (IC) (%) 68.76 49.83

Figure 1. (a) FTIR-ATR spectrum of pure cotton (black) and cotton-COOH (red) and (b) DRX pattern of pure cotton (black) and cottonCOOH (red).

Polímeros, 35(1), e20250007, 2025

3/11

Torres-Cortés, S. A., Velasquez, M., & Sierra, C. reports of COOH concentrations onto cellulosic fibers also used for anchoring in-situ obtained metal nanoparticles[30].

In previous work, similar functionalization was made for polyester/cotton (PETco) fibers for the same applications.

As expected, the presence of the synthetic material mixed with cotton halves the performance of fiber functionalization.

Therefore, the performance of these pure cotton fibers in biological applications is expected to be higher[31,32].

3.3 Chemical immobilization of ex-situ MOF-199@cotton Figure 2a shows the FTIR-ATR spectra of MOF-199, carboxylated cotton (Cotton-COOH), and the MOF anchored onto carboxylated cotton (MOF-199@cotton). In general, for the MOF-199@cotton spectrum, the same signals of MOF199 (specifically at 725, 1372, 1546, and 1644 cm-1 can be observed). Likewise, in this case, the signals of carboxylated cotton, specifically at 1056 and 1610 cm-1, which overlap with the signal at 1644 cm-1. However, the disappearance of the signal at 3328 cm-1 characteristics of carboxylic groups indicates a change in this vibration mode due to the formation of new chemical bonds between MOF-199 and carboxylic groups in the cotton. Additionally, after the anchorage process, the remanent signal around 1056 cm-1 reveals the presence of non-functionalized hydroxyl groups, which implies that this process can be improved.

On the other hand, the XRD pattern of the hybrid MOF/textile material (Figure 2b) can be analyzed as a superposition of the diffraction pattern of MOF-199 and the textile at low diffraction angles, where the MOF peaks are not overlapped by the broad and high peak at 22.5° 2θ, corresponding to the crystalline phase of cotton, which is in good agreement with previous

Table 2. Concentration of surface COOH groups in cotton-COOH fiber.

Experiment 1 2

Mass of carboxylated cotton fiber (g) 285.23 295.84

[COOH] (mmol/g) 0.064 0.068

reports. These results complement and support the analyses made by infrared confirming the anchorage of the MOF-199 onto the carboxylated fiber.

The obtained materials also underwent SEM analysis to verify the morphology of the crystals of MOF after the chemical immobilization. The SEM micrographs in Figure 3a and 3b show irregular particles covering the fibers. However, some crystals of MOF-199 maintained the octahedral morphology after the anchorage. The crystals have a broad size distribution, from 1 to 40 μm. This can be attributed to the prolonged times of stirring in suspension, which could affect the form and size of the crystals. The complementary EDX results also confirms the presence of copper (Figure S3).

The MOF-199@cotton composites were also analyzed

by XPS. The general XPS spectrum of this material is shown in Figure S5a. This spectrum shows the characteristic signals for Cu2p, Zn2p, O1s, and C1s, confirming the presence of Cu and Zn species in chemical interactions with cottonCOOH textile fibers near the surface. The binding energy corresponding to Zn2p is observed at 1044.4 and 1021.3 eV (Figure S5c), indicating that the cation exchange with the copper was incomplete. The deconvoluted signals in the highresolution spectrum of C1s in Figure S5b show the different chemical interactions of the carbon in the organic linkers at 284.6 and 287.9 eV and the carbon related to the bond with the oxygen and metal core at 286.1 eV. Likewise, the signals observed in the O1s (536-526 eV) and Cu2p (940-930 eV) high-resolution spectra are shown in Figure 4a and 4b, respectively. The analysis of these spectra was reported in the previous work for ex-situ anchored MOFs in PET-cotton fabrics[23]. The most characteristic interactions found from the XPS spectrum of MOF-199@cotton are summarized in Table 3. Therefore, these chemical interactions confirm the presence of the MOF-199 on the surface of the textile fibers.

XPS analyses of MOF-199@cotton fibers also helped to estimate the concentration of Cu2+ and Zn2+ on the surface.

As shown in Table 3, the surface concentration of Cu2+ was quantified as 4.47% atomic, whereas, for Zn2+, the concentration was 2.52%. This critical amount of remanent Zn2+ suggests that the yield of the cation exchange process was lower. Therefore, optimizing the synthesis parameters may improve the amount of copper in the MOF.

Figure 2. a) FTIR-ATR spectra of cotton-COOH (red), MOF-199 (black), and MOF-199@cotton (blue). b) XRD spectra of cotton-COOH (red), MOF-199 (black), and MOF-199@cotton (blue).

4/11

Polímeros, 35(1), e20250007, 2025

Anchoring of ex-situ MOF-199 and MOF-UiO-66-NH2 onto TEMPO-oxidized cotton: potential antibacterials

Figure 3. SEM images at (a) 5 μm - 3000x and (b) 10 μm - 1500x for MOF-199@cotton material.

Figure 4. Deconvoluted XPS signals for a) O1S and b) Cu2p for MOF-199@cotton materials.

Table 3. Significant XPS atomic interactions in MOF-199@cotton materials.

Species C(1s) O(1s) Cu(2p) Zn(2p)

Atomic % 41.29 51.45 4.73 2.52

3.4 Chemical immobilization of ex-situ MOF-UiO-66NH2@cotton Regarding MOF UiO-66-NH2@cotton, the chemical immobilization of MOF UiO-66-NH2 was made according to the same procedure depicted in Scheme S3. In the case of this MOF, there was no previous treatment of the carboxylated fibers with Zn2+ solution to make a cationic exchange with metal ions in the MOF structure, as previously explained for MOF-199. The main reason is the strong chemical interaction between the Zr4+ and carboxylate ligands in textile fibers due to Pearson´s hard acid character of Zr4+ and the Polímeros, 35(1), e20250007, 2025

Interaction C-Ar; Ar-C-O-Cu Ar-(C=O)-OH; C-O-Cu Cu2p(3/2)-O-C; Cu2p(1/2)-O-C Zn2p(3/2)-O-C; Zn2p(1/2)-O-C

B.E. (eV) 284.6; 287.9 531.8; 533.3 953.6; 933.6 1044.4; 1021.3

nucleophilic nature of the carboxylates. Specifically, Zr4+ is a little charge-concentrated cation with low polarizability and a highly energetic LUMO orbital without readily excitable electrons[32]. The FTIR-ATR spectrum of MOF UiO-66NH2@cotton in Figure 5a shows the expected signals as an overlapping of MOF UiO-66-NH2 and carboxylated textile fiber bands. The most relevant signals observed are the band’s disappearance at 3868 cm-1 in the composite spectrum, corresponding to the disappearance of -OH from carboxy groups by coordination with the Zr4+ cation. Additionally, the intensity of the signal at 1652 cm-1 increased by the overlapping of the O-C=O of the carboxylate groups in 5/11

Torres-Cortés, S. A., Velasquez, M., & Sierra, C. cotton and in BDC ligands. Finally, at 764 cm-1, the band appears to be related to Zr-O stretching mode in MOF UiO-66-NH2[33].

The XRD spectra of the composites, shown in Figure 5b, describe a good overlapping of the signals of the diffraction peaks of MOFs over the textile fibers. As mentioned before, the oxidation treatments with TEMPO, in the case of these experiments, exert no influence on the diffraction pattern of the fibers. As seen in the XRD diffraction pattern for pure cotton in Figure 1b (black) and for cotton-COOH in Figure 1b (red), the peaks corresponding to (1 1 0), (110), (200), and (004) diffraction planes for cotton remain with no modifications, maintaining the pristine topology of the hybrid textile/MOF material[20].

The obtained SEM/EDX of MOF UiO-66-NH2@cotton composites are shown in Figure 6a and 6b. The micrographs show a semispherical particles of approximately 500 nm to 1 μm which is characteristic of this MOF according with a previous report[34,35]. The covering seems to be homogeneous as the size distribution of the MOF particles. Additionally, the EDX spectrum confirms the presence of Zr4+ cation (Figure S7).

A complementary superficial analysis of the composite was made by XPS. The general spectrum can be seen in Figure S6a, where the binding energy signals corresponding to Zr3d, C1s, O1s, N1s were observed. In the high-resolution spectra of Zr3d (Figure 7b), the presence of Zr4+ bonded to oxygen is indicated by two signals at 182.8 eV (Zr3d(5/2)) and 185.2 eV (Zr3d(3/2)), suggesting that the Zr4+ ion is coordinated to the -COO groups of the organic linkers, but also to the -COO groups of the cotton-COOH. This finding aligns with previous reports by the mentioned authors and by Wagner et al.[36].

On the other hand, the deconvoluted O1s spectrum (Figure 7a) in the fiber revealed signals assigned as C-O-Zr (533.2 eV), -C-(C=O)-OH (531.6 eV), and Zr-O (529 eV) based on the research conducted by Ardila-Suárez et al.[37], who investigated the XPS study of three Zr MOFs using H2BDC-NH2 as a linker. The signals containing Zr are particularly significant as a comparison between the general XPS spectrum of carboxylated cotton fibers as a reference (Figure S4) and those of MOF UiO-66-NH2@cotton (Figure S6) confirms the occurrence of Zr4+ ion anchoring. The binding energy of the C-O-Zr and Zr-O bonds remains consistent in the MOF UiO66-NH2@cotton fiber, indicating similar energy as observed

Figure 5. (a) FTIR-ATR spectra of cotton-COOH (red), MOF UiO-66-NH2 (yellow), and cotton@MOF UiO-66-NH2 (blue). (b) XRD spectra of cotton-COOH (red), MOF UiO-66-NH2 (yellow), and MOF UiO-66-NH2@cotton (blue).

Figure 6. SEM images at (a) 15000x and (b) 10000x of MOF UiO-66-NH2@cotton.

6/11

Polímeros, 35(1), e20250007, 2025

Anchoring of ex-situ MOF-199 and MOF-UiO-66-NH2 onto TEMPO-oxidized cotton: potential antibacterials

Figure 7. High-resolution XPS spectra for (a) O1s and (b) Zr3d in MOF UiO-66-NH2@cotton.

Table 4. Significant XPS atomic interactions in MOF UiO-66-NH2@cotton materials.

Species C(1s) O(1s) Zr(3d) N(1s)

Atomic % 44.28 41.99 12.06 1.67

in the pure state of the MOFs.[37] The deconvoluted signals of the other analyzed elements (C1s and N1s) are also present and displayed in Figure S6b and S6c. Finally, Table 4 shows the semiquantitative analysis of these elements. The atomic percentage of Zr4+ was 12.06, higher than values reported in other studies involving MOFs from the UiO family on this type of fiber[38].

4. Inhibition assays 4.1 Inhibition assays in solid cultures The bactericidal experiments conducted with MOFs/ cotton systems revealed the formation of inhibitory zones around the fibers in the nutrient agar culture. Compared with preliminary trials using in-situ attached MOFs/cotton systems, these results do not show any leaching of MOF, indicating a stronger chemical interaction between the metal-organic framework and the textile fiber. Among the tested systems, MOF-199@cotton and MOF UiO-66-NH2@ cotton exhibited noticeable inhibitory zones in the E. coli assay (Figure S8a). In this case, the MOFs inhibited growth in the contact area with the nutrient gel. However, partial inhibition zones farther from the textile fiber were also observed, in which bacterial growth was present but at a lower rate. The size of halos for the MOF UiO-66-NH2@ cotton was a little larger than halos formed around MOF199@cotton (ø of 11.3 mm for MOF UiO-66-NH2@cotton and 10.7 mm for MOF-199@cotton), the higher metal content in the MOF UiO-66-NH2@cotton could explain this. However, under the same observation, it is possible to suggest that MOF-199@cotton has a higher bactericidal potential due to the low metal content.

In the S. aureus test (Figure S8b), the MOF-199@cotton also showed a total inhibition in the surroundings of the Polímeros, 35(1), e20250007, 2025

Interaction C-Ar; Ar-C-O-Zr Ar-(C=O)-OH; C-O-Zr Zr3d(3/2)-O-C; Zr3d(5/2)-O-C C-N1s-H

B.E. (eV) 284.6; 286.0 531.6; 532.8 185.2; 182.8 399.3

textile fibers, and the inhibition halos were larger than those for the MOF UiO-66-NH2@cotton in which was observed principally a bacteriostatic effect (ø of 7.0 mm for MOF UiO-66-NH2@cotton and 16.4 mm for MOF-199@cotton).

Surprisingly, the positive control (pure cotton soaked in DMSO) did not inhibit the growth of E. coli and S. aureus, contradicting previous reports[39]. Therefore, assuming that the growth rate of bacteria is directly correlated to the intensity of the color of the coating formed by the culture around the fabric (considering cotton blanks and positive controls), it is possible to conclude that MOF UiO-66-NH2@cotton exhibited a mayor bacteriostatic effect. At the same time, MOF-199@cotton displayed a major antibacterial effect.

4.2 Inhibition assays in liquid cultures Considering the outcomes observed in the Petri dish experiments, conducting an analysis using liquid cultures would help validate the previous findings and enable more precise quantification of the antibacterial or bacteriostatic effects of the textiles. The inhibition curves for E. coli (Figure S9a) demonstrate a significant inhibitory effect exerted by the textile/MOF systems. Starting with an initial bacterial inoculum of approximately 2.02 × 108 (with an OD625 of 0.161), the cotton blank exhibited no inhibition over the 48h duration of the experiment but rather a rapid increase in bacterial growth after 10 h. Conversely, the MOF-199@ cotton and MOF UiO-66-NH2@cotton systems significantly reduce bacterial populations throughout the experiment.

Although the textile/MOF systems resulted in a substantial decrease in the growth rate of E. coli compared to the cotton blank (reducing the number of bacteria by at least threefold), complete inhibition or eradication of the bacteria did not occur. Therefore, for these bacteria, it is possible to suggest that these MOFs have mainly a bacteriostatic effect, and 7/11

Torres-Cortés, S. A., Velasquez, M., & Sierra, C. the MOF-199@cotton also has a bactericide effect. Still, the kinetic of the process is slow. This finding suggests that the copper content in the textile may not directly correlate with antibacterial activity. Similarly, MOFs containing Zr4+, such as those in the UiO MOF family, have been reported to possess inferior antibacterial properties when obtained in-situ compared to MOF-199. The Zr-MOF-based materials are commonly post-functionalized with other biocidal agents like Ag nanoparticles (AgNP) or subjected to ultraviolet light irradiation[40-42]. Nevertheless, other factors, such as the strength of the bond between textile fibers and MOF and the size of the MOF crystals, cannot be discounted as potential influences on the intensity of antibacterial activity, as these factors are currently under investigation. For the inhibition against S. aureus (Figure S9b), the textile/MOF systems exhibited a significantly more potent inhibition with the MOF-199@cotton material, reducing the bacterial population by nearly half within 48 hours and confirming the powerful inhibitory effect of copper. In contrast, the inhibitory power of the MOF UiO-66-NH2@cotton with these bacteria was notably weaker within the timeframe of the experiment. Furthermore, comparing the bacterial count at 0 hours with that at 48 hours, it did not reach or fall below the initial count, leading to the conclusion that MOF UiO-66-NH2@cotton textile does not completely inhibit bacterial growth but instead slows it down while maintaining effective population control. It is important to note that during the first 3 hours, population growth is observed for both materials. After this time, the bactericide effect of copper is remarkable, indicating that the growth kinetics of these bacteria is greater than the death kinetics during the first hours.

Finally, Figure S10a and S10b demonstrate that the inhibition was more pronounced and significant for S. aureus than E. Coli. Figure S6 indicates that the percentage of inhibition was notably higher with the MOF-199@cotton material (29.91% for E. coli and 54.92% for S. aureus) compared to the MOF UiO-66-NH2@PETco material after 48 h. It is also worth noting that the contrast of the color (white) in the Petri dish cultures corresponds to the bacterial concentration, and the liquid culture assays support these analyses, as can be observed in Figure S7.

5. Conclusions This article reports a successfully modification of cotton textile fibers were via the TEMPO selective oxidation method, resulting in surface functionalization with carboxylate groups capable of anchoring MOFs. This modification enabled the ex situ synthesis of MOF-199@cotton and MOF UiO-66-NH2@ cotton composites. These composites demonstrated excellent resistance to Soxhlet washing, indicating that strong chemical interactions formed between the MOFs and the carboxylated cotton fibers. XPS, XRD, and FTIR-ATR analyses confirmed the integration of functional, atomic, and crystalline properties of both cotton and MOF, as well as the coordination between MOF metal centers and the textile fibers. The MOF-199@cotton composite exhibited a 4.73% Cu2+ composition in surface, and a notable antibacterial activity against E. coli and S. aureus, while MOF UiO-66-NH2@cotton showed a composition of 12.06% of Zr4+ in surface, alonside a bacteriostatic effect with 8/11

a trend of increasing efficacy over time. These results highlight the potential of the ex situ methodology for developing durable functional textiles with promising antimicrobial properties.

The approach allowed for precise MOF anchoring, leading to stable and well-integrated composite materials suitable for various applications, particularly in textiles with enhanced performance.

6. Author’s Contribution • Conceptualization – Sergio Torres-Cortés; César Sierra • Data curation – Sergio Torres-Cortés; Mauricio Velasquez • Formal analysis – Sergio Torres-Cortés; Mauricio Velasquez • Funding acquisition –​ Sergio Torres-Cortés; César Sierra • Investigation – ​Sergio Torres-Cortés; Mauricio Velasquez • Methodology – Sergio Torres-Cortés; Mauricio Velasquez • Project administration – César Sierra • Resources – Mauricio Velasquez; César Sierra • Software – NA • Supervision – César Sierra • Validation – Sergio Torres-Cortés; Mauricio Velasquez • Visualization – Sergio Torres-Cortés; Mauricio Velasquez; César Sierra • Writing – original draft – ​Sergio Torres-Cortés; Mauricio Velasquez • Writing – review & editing – Sergio Torres-Cortés; Mauricio Velasquez

7. Acknowledgements The authors thank to Ministry of Science, Technology, and Innovation and to Universidad Nacional de Colombia – Sede Bogotá.

8. References 1. Kim, J., Yun, S., & Ounaies, Z. (2006). Discovery of cellulose as a smart material. Macromolecules, 39(12), 4202-4206. http:// doi.org/10.1021/ma060261e.

2. Habibi, Y., Lucia, L. A., & Rojas, O. J. (2010). Cellulose nanocrystals: chemistry, self-assembly, and applications.

Chemical Reviews, 110(6), 3479-3500. http://doi.org/10.1021/ cr900339w. PMid:20201500.

3. Hyde, K., Dong, H., & Hinestroza, J. P. (2007). Effect of surface cationization on the conformal deposition of polyelectrolytes over cotton fibers. Cellulose (London, England), 14(6), 615623. http://doi.org/10.1007/s10570-007-9126-z.

4. Mowafi, S., Rehan, M., Mashaly, H. M., Abou El-Kheir, A., & Emam, H. E. (2017). Influence of silver nanoparticles on the fabrics functions prepared by in-situ technique. Journal of the Textile Institute, 108(10), 1828-1839. http://doi.org/10 .1080/00405000.2017.1292649.

5. Abbas, M., Iftikhar, H., Malik, M. H., & Nazir, A. (2018).

Surface coatings of TiO2 nanoparticles onto the designed fabrics for enhanced self-cleaning properties. Coatings, 8(1), 35. http://doi.org/10.3390/coatings8010035.

6. Marković, D., Korica, M., Kostić, M., Radovanović, Ž., Šaponjić, Z., Mitrić, M., & Radetić, M. (2018). In situ synthesis of Cu/Cu2O nanoparticles on the TEMPO oxidized cotton Polímeros, 35(1), e20250007, 2025

Anchoring of ex-situ MOF-199 and MOF-UiO-66-NH2 onto TEMPO-oxidized cotton: potential antibacterials fabrics. Cellulose (London, England), 25(1), 829-841. http:// doi.org/10.1007/s10570-017-1566-5.

7. Assen, A. H., Yassine, O., Shekhah, O., Eddaoudi, M., & Salama, K. N. (2017). MOFs for the sensitive detection of ammonia: deployment of fcu-MOF thin-films as effective chemical capacitive sensors. ACS Sensors, 2(9), 1294-1301. http://doi.org/10.1021/acssensors.7b00304. PMid:28809112.

8. Ozer, R. R., & Hinestroza, J. P. (2015). One-step growth of isoreticular luminescent metal–organic frameworks on cotton fibers. RSC Advances, 5(20), 15198-15204. http://doi. org/10.1039/C4RA15161E. 9. Smith, M. K., & Mirica, K. A. (2017). Self-Organized Frameworks on Textiles (SOFT): conductive fabrics for simultaneous sensing, capture, and filtration of gases. Journal of the American Chemical Society, 139(46), 16759-16767. http://doi.org/10.1021/jacs.7b08840. PMid:29087700.

10. Wyszogrodzka, G., Marszałek, B., Gil, B., & Dorożyński, P. (2016). Metal-organic frameworks: mechanisms of antibacterial action and potential applications. Drug Discovery Today, 21(6), 1009-1018. http://doi.org/10.1016/j.drudis.2016.04.009.

PMid:27091434.

11. Horcajada, P., Gref, R., Baati, T., Allan, P. K., Maurin, G., Couvreur, P., Férey, G., Morris, R. E., & Serre, C. (2012). Metalorganic frameworks in biomedicine. Chemical Reviews, 112(2), 1232-1268. http://doi.org/10.1021/cr200256v. PMid:22168547.

12. Heinze, T., & Koschella, A. (2005). Carboxymethyl ethers of cellulose and starch - A review. Macromolecular Symposia, 223(1), 13-40. http://doi.org/10.1002/masy.200550502.

13. Nooy, A. E. J., Besemer, A. C., & van Bekkum, H. (1995).

Highly selective nitroxyl radical-mediated oxidation of primary alcohol groups in water-soluble glucans. Carbohydrate Research, 269(1), 89-98. http://doi.org/10.1016/0008-6215(94)00343-E. 14. Ovalle-Serrano, S. A., Díaz-Serrano, L. A., Hong, C., Hinestroza, J. P., Blanco-Tirado, C., & Combariza, M. Y. (2020). Synthesis of cellulose nanofiber hydrogels from fique tow and Ag nanoparticles. Cellulose (London, England), 27(17), 99479961. http://doi.org/10.1007/s10570-020-03527-6.

15. Saito, T., & Isogai, A. (2004). TEMPO-mediated oxidation of native cellulose. The effect of oxidation conditions on chemical and crystal structures of the water-insoluble fractions.

Biomacromolecules, 5(5), 1983-1989. http://doi.org/10.1021/ bm0497769. PMid:15360314.

16. Biermann, C. J. (1996). Handbook of Pulping and Papermaking.

London: Academic Press Limited.

17. Pinto, M. S., Sierra-Avila, C. A., & Hinestroza, J. P. (2012). In situ synthesis of a Cu-BTC metal-organic framework (MOF 199) onto cellulosic fibrous substrates: cotton. Cellulose (London, England), 19(5), 1771-1779. http://doi.org/10.1007/ s10570-012-9752-y.

18. Rodríguez, H. S., Hinestroza, J. P., Ochoa-Puentes, C., Sierra, C. A., & Soto, C. Y. (2014). Antibacterial activity against escherichia coli of Cu-BTC (MOF-199) metal-organic framework immobilized onto cellulosic fibers. Journal of Applied Polymer Science, 131(19), 40815. http://doi.org/10.1002/app.40815.

19. Emam, H. E., Darwesh, O. M., & Abdelhameed, R. M. (2020).

Protective cotton textiles via amalgamation of cross-linked zeolitic imidazole framework. Industrial & Engineering Chemistry Research, 59(23), 10931-10944. http://doi.org/10.1021/acs. iecr.0c01384.

20. Zhang, X.-F., Feng, Y., Wang, Z., Jia, M., & Yao, J. (2018).

Fabrication of cellulose nanofibrils/UiO-66-NH2 composite membrane for CO2/N2 separation. Journal of Membrane Science, 568, 10-16. http://doi.org/10.1016/j.memsci.2018.09.055.

21. Fu, H., Ou, P., Zhu, J., Song, P., Yang, J., & Wu, Y. (2019).

Enhanced protein adsorption in fibrous substrates treated with zeolitic imidazolate framework-8 (ZIF-8) nanoparticles.

Polímeros, 35(1), e20250007, 2025

ACS Applied Nano Materials, 2(12), 7626-7636. http://doi. org/10.1021/acsanm.9b01717.

22. Chen, Z., Ma, K., Mahle, J. J., Wang, H., Syed, Z. H., Atilgan, A., Chen, Y., Xin, J. H., Islamoglu, T., Peterson, G. W., & Farha, O. K. (2019). Integration of metal-organic frameworks on protective layers for destruction of nerve agents under relevant conditions. Journal of the American Chemical Society, 141(51), 20016-20021. http://doi.org/10.1021/jacs.9b11172.

PMid:31833359.

23. Torres-Cortés, S. A., Velasquez, M., Pérez, L. D., & Sierra, C. A. (2022). Ex situ synthesis of MOF@PET/cotton textile fibers as potential antibacterial materials. Journal of Polymer Research, 29(10), 427. http://doi.org/10.1007/s10965-02203216-x.

24. Tranchemontagne, D. J., Hunt, J. R., & Yaghi, O. M. (2008).

Room temperature synthesis of metal-organic frameworks: MOF-5, MOF-74, MOF-199, and IRMOF-0. Tetrahedron, 64(36), 8553-8557. http://doi.org/10.1016/j.tet.2008.06.036.

25. Kandiah, M., Nilsen, M. H., Usseglio, S., Jakobsen, S., Olsbye, U., Tilset, M., Larabi, C., Quadrelli, E. A., Bonino, F., & Lillerud, K. P. (2010). Synthesis and Stability of Tagged UiO-66 Zr-MOFs. Chemistry of Materials, 22(24), 6632-6640. http://doi.org/10.1021/cm102601v.

26. Zhao, H., Kwak, J. H., Conrad Zhang, Z., Brown, H. M., Arey, B. W., & Holladay, J. E. (2007). Studying cellulose fiber structure by SEM, XRD, NMR and acid hydrolysis.

Carbohydrate Polymers, 68(2), 235-241. http://doi.org/10.1016/j. carbpol.2006.12.013.

27. French, A. D. (2014). Idealized powder diffraction patterns for cellulose polymorphs. Cellulose (London, England), 21(2), 885-896. http://doi.org/10.1007/s10570-013-0030-4.

28. Porras, J. D., Arteta, S. M., & Pérez, L. D. (2020). Development of an adsorbent for Bisphenol A based on a polymer grafted from microcrystalline cellulose. Water, Air, and Soil Pollution, 231(10), 499. http://doi.org/10.1007/s11270-020-04861-y.

29. Segal, L., Creely, J. J., Martin, A. E. Jr, & Conrad, C. M. (1959). An empirical method for estimating the degree of crystallinity of native cellulose using the x-ray diffractometer.

Textile Research Journal, 29(10), 786-794. http://doi. org/10.1177/004051755902901003.

30. Prestipino, C., Regli, L., Vitillo, J. G., Bonino, F., Damin, A., Lamberti, C., Zecchina, A., Solari, P. L., Kongshaug, K. O., & Bordiga, S. (2006). Local structure of framework Cu(II) in HKUST-1 metallorganic framework: spectroscopic characterization upon activation and interaction with adsorbates.

Chemistry of Materials, 18(5), 1337-1346. http://doi.org/10.1021/ cm052191g.

31. Neufeld, M. J., Harding, J. L., & Reynolds, M. M. (2015).

Immobilization of Metal-Organic Framework Copper(II) Benzene-1,3,5-tricarboxylate (CuBTC) onto cotton fabric as a nitric oxide release catalyst. ACS Applied Materials & Interfaces, 7(48), 26742-26750. http://doi.org/10.1021/acsami.5b08773.

PMid:26595600.

32. Hamisu, A. M., Ariffin, A., & Wibowo, A. C. (2020). Cation exchange in metal-organic frameworks (MOFs): the hard-soft acid-base (HSAB) principle appraisal. Inorganica Chimica Acta, 511, 119801. http://doi.org/10.1016/j.ica.2020.119801.

33. DeCoste, J. B., Peterson, G. W., Jasuja, H., Glover, T. G., Huang, Y.-G., & Walton, K. S. (2013). Stability and degradation mechanisms of metal-organic frameworks containing the Zr6O4(OH)4 secondary building unit. Journal of Materials Chemistry. A, Materials for Energy and Sustainability, 1(18), 5642-5650. http://doi.org/10.1039/c3ta10662d.

34. Abdelhameed, R. M., Rehan, M., & Emam, H. E. (2018).

Figuration of Zr-based MOF@cotton fabric composite for potential kidney application. Carbohydrate Polymers, 195, 9/11

Torres-Cortés, S. A., Velasquez, M., & Sierra, C. 460-467. http://doi.org/10.1016/j.carbpol.2018.04.122.

PMid:29805000.

35. Schelling, M., Kim, M., Otal, E., & Hinestroza, J. (2018).

Decoration of cotton fibers with a water-stable metal–organic framework (UiO-66) for the decomposition and enhanced adsorption of micropollutants in water. Bioengineering (Basel, Switzerland), 5(1), 14. http://doi.org/10.3390/ bioengineering5010014. PMid:29439527.

36. Wagner, C. D., Riggs, W. M., Davis, L. E., Moulder, J. F., & Muilenberg, G. E. (1979). Handbook of X-ray Photoelectron Spectroscopy. USA: Perkin-Elmer Corporation.

37. Ardila-Suárez, C., Rodríguez-Pereira, J., Baldovino-Medrano, V. G., & Ramírez-Caballero, G. E. (2019). An analysis of the effect of zirconium precursors of MOF-808 on its thermal stability, and structural and surface properties. CrystEngComm, 21(9), 1407-1415. http://doi.org/10.1039/C8CE01722K. 38. Tian, S., Yi, Z., Chen, J., & Fu, S. (2023). In situ growth of UiO-66-NH2 in wood-derived cellulose for iodine adsorption.

Journal of Hazardous Materials, 443, 130236. http://doi. org/10.1016/j.jhazmat.2022.130236.

39. Ansel, H. C., Norred, W. P., & Roth, I. L. (1969). Antimicrobial activity of dimethyl sulfoxide against Escherichia coli,

10/11

Pseudomonas aeruginosa, and Bacillus megaterium. Journal of Pharmaceutical Sciences, 58(7), 836-839. http://doi. org/10.1002/jps.2600580708. PMid:4980332.

40. Mao, K., Zhu, Y., Rong, J., Qiu, F., Chen, H., Xu, J., Yang, D., Zhang, T., & Zhong, L. (2021). Rugby-ball like Ag modified zirconium porphyrin metal–organic frameworks nanohybrid for antimicrobial activity: synergistic effect for significantly enhancing photoactivation capacity. Colloids and Surfaces.

A, Physicochemical and Engineering Aspects, 611, 125888. http://doi.org/10.1016/j.colsurfa.2020.125888.

41. Zhao, W., Deng, J., Ren, Y., Xie, L., Li, W., Wang, Q., Li, S., & Liu, S. (2021). Antibacterial application and toxicity of metal– organic frameworks. Nanotoxicology, 15(3), 311-330. http:// doi.org/10.1080/17435390.2020.1851420. PMid:33259255.

42. Mortada, B., Matar, T. A., Sakaya, A., Atallah, H., Kara Ali, Z., Karam, P., & Hmadeh, M. (2017). Postmetalated zirconium metal organic frameworks as a highly potent bactericide.

Inorganic Chemistry, 56(8), 4740-4744. http://doi.org/10.1021/ acs.inorgchem.7b00429. PMid:28338319.

Received: June 27, 2024 Revised: Oct. 05, 2024 Accepted: Nov. 19, 2024

Polímeros, 35(1), e20250007, 2025

Anchoring of ex-situ MOF-199 and MOF-UiO-66-NH2 onto TEMPO-oxidized cotton: potential antibacterials

Supplementary Material Supplementary material accompanies this paper.

Scheme S1. Synthetic conditions and polyhedral representations utilized in the obtention of (a) MOF-99 and (b) MOF UiO-66-NH2.

Scheme S2. Synthetic pathway for the TEMPO/NaCl/NaClO2 carboxylation reaction in primary hydroxyl groups on cotton.

Scheme S3. Synthetic pathway for the TEMPO/NaCl/NaClO2 carboxylation reaction in primary hydroxyl groups on cotton.

Figure S1. (a) FTIR-ATR spectrum and (b) XRD spectrum of pristine MOF-199 (HKUST-1).

Figure S2. (a) FTIR-ATR spectrum and (b) XRD spectrum of pristine MOF UiO-66-NH2.

Figure S3. EDX spectrum for MOF-199@cotton material.

Figure S4. XPS reference spectrum of carboxylated cotton linter. Retrieved with permission of Bastidas Gómez.

Figure S5. a) General XPS spectrum of MOF-199@cotton and deconvoluted HR-XPS signals of b) C1S and c) Zn2p(1/2) and Zn2p(3/2) of MOF-199@cotton.

Figure S6. a) General XPS spectrum of MOF UiO-66-NH2@cotton and deconvoluted HR-XPS signals of b) C1S and c) N1s of MOF UiO-66-NH2@cotton.

Figure S7. EDX spectrum for MOF UiO-66-NH2@cotton material.

Figure S8. Petri dishes with solid agar cultures and for a) E. coli and b) S. aureus after 48 h. For both of them, numbers corresponds to: 1: Cu-alg (Cotton composite anchored to MOF 2: Cu-PET (PET-cotton composite anchored to MOF-199), 3: Zr-alg (Cotton composite anchored to MOF UiO-66-NH2), 4: Zr-PET (PET-cotton composite anchored to MOF UiO-66NH2), 5: Blanco PET (PET-cotton composite blank), 6: Algodon ⊕ (Positive control for cotton consisting of cotton fiber rinsed in DMSO), 7: PET ⊕ (Positive control for PET-cotton rinsed in DMSO), 8: Blanco alg. (cotton composite blank).

Figure S9. Inhibition curves in liquid cultures of cotton blank (red), MOF-199@cotton (purple), and MOF UiO-66NH2@cotton (orange) for (a) E. coli and (b) S. Aureus.

Figure S10. Inhibition activity expressed as the number of bacteria after 48 h of experiment (green columns) and inhibition percentage (blue columns) for cotton blank, MOF-199@cotton and MOF UiO-66-NH2@cotton for a) E. coli and b) S. aureus.

This material is available as part of the online article from https://doi.org/10.1590/0104-1428.20240068

Polímeros, 35(1), e20250007, 2025

11/11

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20240038

Fungal biocomposites production from packaging industry residue: PET-coated SBS paperboard Nicole Fernanda Souza1 , Mariane Bonatti-Chaves2 , Denise Abatti Kasper Silva1 , Josiane Costa Riani3  and Elisabeth Wisbeck1,2*  Programa de Pós-graduação em Engenharia de Processos – PPGEP, Universidade da Região de Joinville – UNIVILLE, Joinville, SC, Brasil 2 Programa de Pós-graduação em Sistemas Produtivos – PPGSP, Universidade da Região de Joinville – UNIVILLE, Joinville, SC, Brasil 3 Departamento de Engenharia Mecânica, Universidade da Região de Joinville – UNIVILLE, Joinville, SC, Brasil

1

*elisabeth.wisbeck@univille.br

Abstract Packaging generates approximately 40 tons/month of waste from Solid Bleached Sulfate (SBS) paperboard coated with Poly (Ethylene Terephthalate) PET. Concerns about environmental sustainability are pushing innovative materials with diverse applications to replace conventional synthetic materials. Biocomposites, which use fungal mycelium as a binder for the particles, are an emerging option in biodegradable and naturally sourced materials. This study aimed to make Pleurotus sajor-caju biocomposites, employing SBS paperboard packages coated with PET as the substrate. The study investigated two inoculum fractions (30% and 50%) and two drying methods (conventional and vacuum) at 60 °C. The biocomposites produced with a 50% inoculum and conventional drying displayed favorable characteristics, including a shorter processing time (16 days), a higher drying rate (5.58 g/day), low porosity (21,7%), compressive strength of 0.16 MPa, apparent density of 315 kg/m3 and satisfactory thermal stability.

Keywords: biocomposites, fungal mycelium, packaging waste, Pleurotus sajor-caju, sustainable production.

How to cite: Souza, N. F., Bonatti-Chaves, M., Silva, D. A. K., Riani, J. C., & Wisbeck, E. (2025). Fungal biocomposites production from packaging industry residue: PET-coated SBS paperboard. Polímeros: Ciência e Tecnologia, 35(1), e20250008. https://doi.org/10.1590/0104-1428.20240038

1. Introduction The modernization of society, which increasingly depends on packaged products, has increased solid waste generation[1].

The combination of Solid Bleached Sulfate (SBS) paperboard coated with Poly (Ethylene Terephthalate) (PET) is widely utilized in the production of thermoformed trays for storing partially prepared foods, permitting temperature variation between -40 ºC and 220 ºC[2]. It has been estimated that graphic industries alone generate approximately 40 tons of this waste each month[3]. Treating these residues is challenging due to the polymer coating[4].

Plastics made from petroleum take decades to decompose, making their replacement essential for environmental conservation. Today, industrial sectors have numerous opportunities to move toward a cleaner, more sustainable, and greener environment. These long-term goals can be achieved using various biopolymers, which offer advantages such as abundant availability, suitable mechanical properties, and easy biodegradability[5,6]. Then, an alternative use for packaging waste could be as a substrate for producing fungal biocomposites. This involves inoculating a filamentous fungus in a substrate composed of a nutrient material and discontinuous particles. The fungus metabolizes the nutrient material over a sufficient period for the growth of its hyphae,

Polímeros, 35(1), e20250008, 2025

forming an interconnected mycelial network in and around the residue. This process binds the material particles and assumes the shape of the container in which it will be cultivated[7], potentially replacing wooden, plastic, foam, and styrofoam packaging[8]. In the process, the material must be dehydrated to stop fungal growth, unmolded and there must be no active fungal spores that could contaminate the environment. The most commonly used methods for material dehydration are convection drying (conventional drying)[9] and freeze drying (lyophilization). Nevertheless, in freeze drying, the product must be subjected to freezing and vacuum, which makes the process slower and more expensive[10]. However, vacuum drying is recommended for temperature-sensitive materials[11,12] and can be tested.

There is currently research in the literature involving mycelial biocomposites, and each work uses a different production condition for these biocomposites, but all to demonstrate the potential of this material[13-19].

Amidst the challenges of waste accumulation, sustainable consumption has gained prominence[20]. Fungi of the genus Pleurotus offer a promising solution with their ability to produce white mycelium and degrade both lignin and cellulose. They possess an enzymatic complex with a wide

1/10

O O O O O O O O O O O O O O O O O

Souza, N. F., Bonatti-Chaves, M., Silva, D. A. K., Riani, J. C., & Wisbeck, E. range of enzymes, such as cellulase, ligninase, cellobiase, laccase, and hemicellulase, enabling them to degrade a diverse array of lignocellulosic residues[21]. This versatility makes them ideal candidates for the proposed research on waste management.

In an evaluation of the biodegradation of recycled poly (ethylene terephthalate) (PET) by Pleurotus ostreatus[22], a mass loss of 3.3% was observed after 45 days of biodegradation.

The production of P. sajor-caju mushrooms using PET-coated SBS cardboard packaging waste yielded 47.3%[23]. Therefore, the potential of SBS paperboard waste coated with PET for Pleurotus cultivation and the ability of fungal mycelium to act as a binder for waste particles have been demonstrated.

Based on the above, this work aimed to evaluate the production of fungal biocomposites with P. sajor-caju mycelium using waste from the packaging industry, PETcoated SBS paperboard. To seek solutions to environmental problems linked to the accumulation of waste, this work aims to use and add value to waste from the packaging industry, using the abilities presented by fungi, contributing to the reduction of raw material waste and environmental impacts.

2. Materials and Methods 2.1 Microorganisms and maintenance The fungal species utilized was Pleurotus sajor-caju, obtained from the Collection of Cultures of Basidiomycetes at the Instituto de Botânica (São Paulo/SP) under the code CCB 019. The strain was maintained in a WDA medium (Wheat Dextrose Agar)[24]. The plates were stored in a refrigerator at 4 ºC, and replications were conducted every 3 months.

The inoculum consisted of wheat grains colonized with P. sajor-caju mycelium and refrigerated at 4 °C until use[25].

2.2 Preparation of biocomposites The residue from the thermoforming process of food packaging, composed of SBS (Solid Bleached Sulfate) paperboard with PET coating, was obtained from Baumgarten Gráfica Ltda company, located in the municipality of Blumenau - SC, and used in this work.

The residue with a thickness of 0.4 mm, defined as substrate, was fragmented (2 x 10 mm) and immersed in water for 24 hours (Fig 1a, 1b and 1c). After this period, the excess water was drained, and the moist substrate was packed in polypropylene packages (28 x 40 cm) in the proportion of 150 g (dry mass), and 5% rice bran was added. The packages were sterilized at 121°C for one hour.

Inoculation was performed in a laminar flow chamber using 30 or 50% of the inoculum relative to the mass of the dry substrate[18,23]. Incubation occurred in the absence of light, at 30ºC, until the fungal mycelium’s complete colonization of the substrate (Fig 1d). The time from inoculation to complete colonization of the substrate by the fungal mycelium was recorded for each inoculum fraction used and defined as mycelial growth time (tg - days). The substrates colonized with 30% or 50% inoculum were ground in a mini food processor until a homogeneous mixture was obtained[18]. This mixture was then aseptically introduced and compacted into 2/10

cylindrical plastic trays (6 cm Ø) up to a height of 2.5 cm in order to obtain test specimens by NBR 8082[26]. The trays were sealed and placed in a bacteriological oven without light at 30 ± 2 °C until the fungal mycelium hyphae were recolonized and reestablished (Fig 1e). The duration of this process was recorded for each inoculum fraction used and defined hyphae recolonization time (tr – days).

2.3 Drying of biocomposites The test specimens were dried at 60 ºC using the conventional and vacuum methods. Eq. (1) obtained the average drying speed (v - g/day), Eq. (2) obtained the initial moisture content (iMo - %), and Eq. (3) obtained the final moisture content (fMo - %).  g  Mi − M f v = ts  day  iMo ( % ) =

fMo ( % ) =

(1)

M i − M105℃ *100 M105℃

(2)

M f − M105℃

(3)

M105℃

*100

Where Mi is the initial mass (g – wet mass), Mf is the final mass (g – dry mass at 60 ºC), ts is the final drying time (days - where the test specimens reached a constant mass at 60 ºC), and M105 °C is the mass without moisture (g – dry mass at 105 ºC).

2.4 Parameters evaluated Adding tg, tr and ts accounts for the total process time (tt - days) for obtaining the biocomposites test specimens. Measurements were performed to calculate the apparent density (⍴ - kg ) (Eq. 4), porosity determination m3

(P - %)[27] (Eq. 5a and 5b), water sorption (W - %)[28] (Eq. 6), air humidity sorption (AirHS - %)[18] (Eq. 7), and the compression stress (𝜎𝑐 - MPa) was calculated at 10% deformation, as gded by NBR 8082[26] (Eq. 8).  kg  M f ρ = 3 m  V

(4)

ρc − ρ ρc

(5a)

P (%) =

Mf ρc ( % ) = x100 Vs = W (%)

Mt − M f Mf

= AirHS ( % )

σ c ( MPa ) =

(5b)

M air − M f Mf F A0

(6)

× 100

× 100

(7) (8)

Polímeros, 35(1), e20250008, 2025

Fungal biocomposites production from packaging industry residue: PET-coated SBS paperboard

Figure 1. SBS paperboard package coated with PET. (a) before fragmentation; (b) after fragmentation; (c) immersed in water; (d) colonized by fungal mycelium; (e) molds with processed substrate after recolonization and reestablishment of hyphae; (f) biocomposites dried.

Where MF is the mass of the test specimen immediately after drying, MT is the mass (g) of the specimen after immersion in distilled water (2, 24, and 48 h), MAIR is the mass (g) measured at each sampling period (58 days), V is the geometric volume of the test specimens after drying, Vs is the skeletal volume of the porous test speciments was measured by volume displacement in water by soaking the samples in water for 5 hours in a graduate cylinder, F is the compression force (N), and A0 is the cross-sectional area of the test specimen (mm2).

Thermogravimetric analysis (TGA) was performed using TGA-Q50 equipment (TA Instruments). The heating Polímeros, 35(1), e20250008, 2025

rate was 10 °C/min, starting from 25 to 600 °C in a nitrogen atmosphere (60 mL/min flow rate).

Biocomposite samples were analyzed using scanning electron microscopy (SEM) to examine their surface morphology. Samples measuring approximately 3 to 5 mm were taken, covered with a conductive layer of gold, applying an electron acceleration voltage of 5 kV and magnifying the images from 25 to 2000 times. The biocomposites produced under the optimal conditions were also analyzed using FTIR (Fourier transform infrared spectroscopy). FTIR spectra were obtained using a Perkin-Elmer Spectrum One B spectrophotometer in 12 scans in the spectral region from 3/10

Souza, N. F., Bonatti-Chaves, M., Silva, D. A. K., Riani, J. C., & Wisbeck, E. 4000 to 650 cm-1, with a resolution of 4 cm-1, using the attenuated total reflectance (ATR) accessory.

2.5 Statistical analysis The obtained values were submitted to the outlier rejection test (Dixon Q test)[29] and later to the variance analysis of the mean values of the samples using the Tukey test with a significance level of 5% (ANOVA).

3. Results and Discussions 3.1 Mycelial growth time The mycelial growth time (tg – days) for the substrate with 30% inoculum was 14 days, and 7 days for the substrate with 50% inoculum. The time for recolonization and reestablishment of fungal mycelium hyphae (tr – days) in the trays was 5 and 7 days, respectively, for substrates with 30% and 50% inoculum.

3.2 Drying of biocomposites The test specimens were subjected to two dehydration conditions to stop fungal growth: conventional oven drying and vacuum drying, both at 60 °C. Figure 2 shows the drying curve behavior of the biocomposites produced with 30% and 50% inoculum and the performance of the two tested methodologies.

The final drying time (ts – dias) occurred in 48 h (2 days) for all biocomposites (Figure 2), and no statistical difference was observed in the final moisture content (Table 1). The inoculum fraction influenced the initial moisture value and the drying speed, being higher with the inoculum fraction of 50%. The more significant amount of mycelium in biocomposites with 50% inoculum may have influenced these parameters[14].

Deschamps[30] produced biocomposites from the brewery residue with banana leaves and 30% Pleurotus sajor-caju inoculum; the initial moisture obtained was 78,6%. In the present work, the initial moisture content was 75.82% for biocomposites with 30% inoculum and 92,84% with 50% inoculum (Table 1). The inoculum fraction influenced the initial moisture content, probably due to the greater quantity of wheat grains present.

Rocha et al.[18] interrupted the fungal growth after 2 days of specimens with an inoculum fraction of 20% and 30% of Pleurotus sajor-caju at drying temperatures of 40 and 60 ºC,

observing that the inoculum fraction did not influence the drying speed and the final moisture content. The authors obtained a higher drying speed at 60 ºC. In line with Deacon[31], the moisture at which no fungus can grow is below 14%. However, a slight increase in moisture to from 15 to 16% allows the growth of Aspergillus spp., a stress-tolerant fungus. The moisture content in our final product is below 14% (5.51 to 6.23%), effectively inhibiting the growth of fungi. This practical implication makes these biocomposites viable and functional, opening up new possibilities in materials science.

The analysis of the mycelial growth time (tg – item 3.1), the time for reestablishment of fungal mycelium hyphae (tr – item 3.1), and the final drying times (Figure 2) reveals an expressive efficiency in the 50% inoculum condition with conventional drying. This condition presented the shortest overall production process time (Table 1), a mere 16 days. Notably, the drying condition in a conventional oven demonstrated the highest average drying speed, 5.58 g/day, further highlighting the efficiency of these production processes.

3.3 Biocomposites analysis Figure 3 shows the results obtained from the water sorption of the biocomposite specimens.

It is clear from Figure 3 that after 2 hours of immersion, all biocomposites absorbed at least 200% of water regardless of the inoculum fraction and the type of drying.

Furthermore, it is observed that the biocomposites dried

Figure 2. Drying curves, mass (g) x time (h), of the biocomposites produced with 30% and 50% inoculum under conventional and vacuum drying.

Table 1. Average values of initial moisture content (iMo) ± standard deviation (sd) and final moisture content (fMo) ± sd, average drying speed (v) ± sd, final drying time (ts) and total process time (tt) of the test specimens produced with 30 and 50% inoculum and dried at 60 °C. Inoculum fraction (%)

iMo

30

75.82 ± 8.38 a*

Conventional Vacuum

92.84 ± 3.97 b

Conventional Vacuum

(%)

30 50 50

Drying

v

ts

tt

(%)

(g/day)

(days)

(days)

5.51 ± 0.84 c

4.53 ± 0.99 d

2

21

6.23 ± 1.49 c

4.46 ± 1.23 d

2

21

5.79 ± 0.68 c

5.58 ± 0.49 e

2

16

5.94 ± 1.23 c

5.18 ± 0.47 f

2

16

fMo

*Equal letters in the columns indicate means without significant differences according to Tukey’s test with a confidence level of 95%.

4/10

Polímeros, 35(1), e20250008, 2025

Fungal biocomposites production from packaging industry residue: PET-coated SBS paperboard in a vacuum oven did not show a significant difference in water sorption between 2 and 24 hours, showing that they reached saturation in 2 hours. In conventional drying, there is a significant difference between 2 and 24 hours of immersion, indicating that in 2 hours, the biocomposites did not absorb the maximum amount of water, reaching saturation between 2 and 24 hours.

On the other hand, the water sorption behavior was different under conventional and vacuum drying conditions.

Reis et al.[32], when drying eggplant slices in a conventional and vacuum oven at a temperature of 65 oC, they observed different evaporation rates, being 577 g water per day for the convective (conventional) drying process and 513 g water per day in the vacuum drying process. When the eggplant slices were rehydrated, those dried under vacuum demonstrated a greater rehydration capacity (101.68%), while those dried by convection had a lower rehydration content (37.41%).

Similar behavior was observed for biocomposites with 50% inoculum. When dried under vacuum, they had a lower drying speed (5.18 g/day - Table 1) and greater rehydration capacity, presenting water saturation in just 2 hours (Figure 3).

Water sensitivity is essential for many practical applications of biocomposites and thus determines their performance in adverse conditions[33]. For a material to absorb less water,

its density must be increased, or its external surface must be coated with a hydrophobic material[34].

The greater the material’s porosity, the greater its water absorption capacity through water entry into the empty spaces (pores), indicating a lower density[35]. It is known that the initial amount of inoculum could interfere with the mycelial density and, consequently, the density of the material[21].

Figure 4 presents the porosity values. Biocomposites with 50% inoculum and conventional drying showed lower porosity, with a statistically significant difference from the other biocomposites. Biocomposites with 50% inoculum and conventional drying reached saturation after two hours of immersion in water (Figure 4), probably due to lower porosity.

The same did not happen when 30% of inoculum was used, proving the influence of mycelial density on the density of the material. Furthermore, this behavior only occurred when drying the biocomposites conventionally, as in vacuum drying, the porosity was the same for biocomposites with 30 and 50% inoculum. Vacuum conditions promote higher pore formation than atmospheric pressure drying[11]. The water vapor liberated from the material expands. This expansion mitigates structural collapse and fosters the formation of pores[12].

Using scanning electron microscopy (SEM) images of biocomposite specimens, Figure 5a shows the most prominent

Figure 3. Water sorption (W%) ± standard deviation at 2 and 24 hours of biocomposites immersion with 30% and 50% of inoculum dried in a conventional and vacuum oven. Equal letters between drying conditions (vacuum or conventional) indicate values without significant differences according to Tukey’s test with a confidence level of 95%.

Figure 4. Porosity (%) ± standard deviation values for the biocomposites specimens produced with 30% and 50% inoculum and dried in a vacuum and conventional oven. Equal letters indicate values without significant differences according to Tukey’s test with a confidence level of 95%.

Polímeros, 35(1), e20250008, 2025

Figure 5. Scanning electron microscopy images of biocomposite specimens at 100x (a) and 500x (b) magnification produced with 50% inoculum and dried in a conventional oven, with arrows highlighting the pores.

5/10

Souza, N. F., Bonatti-Chaves, M., Silva, D. A. K., Riani, J. C., & Wisbeck, E. structures corresponding to cellulose fibers and the smaller structures corresponding to the mixed and overlapping mycelial and polymeric structures (PET). The polymeric structures are detached from the fibers, probably due to grinding, drying and degradation during the biocomposite production. Figure 5b is an enlarged inset of Figure 5a, showing the pores in the biocomposite with 50% inoculum and conventional drying.

The graph represented by Figure 6 shows the air humidity sorption in biocomposite test specimens, during the 58 days of exposure. The air humidity sorption is an important property that determines the quality and durability of the final product[36]. This analysis aimed to simulate the product’s exposure to ambient conditions.

Analyzing the results in Figure 6, it is observed that all biocomposites, regardless of their inoculum fraction and drying condition, were influenced by the relative air humidity (RairH %) following its daily variation. It is also noteworthy that there was no variation in the behavior of AirHS (%) among biocomposites with the same inoculum fraction, showing coincident curves. An increase in moisture in a product is known to promote the ease of microbial contamination[31,37], as the humidity at which no fungus can grow is below 14%[31]. Among the most common contaminants in fungal cultures are the genera Aspergillus, Trichoderma and Penicillium[31,37]. These fungi exhibit dark sporulation, which is easily detectable by the naked eye[38]. Despite the sorption of moisture from the air by the biocomposites (Figure 6), no contamination was observed during the 58 days of exposure to ambient air. The moisture content in the final product (Table 1) is below 14% (5.51% to 6.23%).

During the 58-day exposure period, the RairH ranged from 40 to 100%, while the moisture sorption from the air by the biocomposites ranged from 0.5 to 6.5%; that is, even the biocomposite with the highest final moisture (6,23%) content did not reach the 14% critical moisture content.

The biocomposites with 50% inoculum fractions exhibited an average AirHS of 4.6 ± 1.1%, while biocomposites with 30% inoculum showed significantly lower air humidity sorption (3.3 ± 1.1%) according to the Tukey test with 95% confidence.

Rocha et al.[18] also monitored the air humidity sorption in biocomposites made from mate/guarana waste with 30% P. sajor-caju inoculum and obtained a maximum air humidity sorption of 13.1% with a relative air humidity of around 80%. Appels et al.[14] analyzed the behavior of biocomposites made from beech sawdust, rapeseed straw, and cotton fibers with P. ostreatus when exposed to an environment with a relative air humidity of 80% at 40 °C, and the biocomposites exhibited an AirHS of 11.6%. It is evident that humidity sorption depends primarily on the substrate used, but it can be influenced by the fungal species, as some fungi exhibit a hydrophobic nature due to certain proteins found in the mycelium, such as hydrophobins[39].

Compression stress is an essential property for analyzing the biocomposite’s applicability, as higher resistance suggests greater durability[13]. In Figure 7, the compression strength was not influenced by the inoculum fraction or the drying method, remaining around 0.16 MPa. 6/10

In the biocomposites of yerba mate and guaraná, using P. sajor-caju, Rocha et al.[18] obtained a compression strength of 0.094 MPa. Ghazvinian et al.[16], cultivating P. ostreatus with straw substrate achieved 0.02 MPa. Meanwhile, Bruscato et al.[15] obtained a higher compression strength value (0.4 MPa) in biocomposites with sawdust and wheat bran using P. albidus.

The compression strength found in the present study falls within the range of values reported in the literature, which does not rule out the possibility of improving the production conditions of this biocomposite for packaging applications. The mechanical properties of the biocomposites can be enhanced by incorporating cold or hot pressing into the process. With applied pressure, material porosity is reduced, material density increases, and fibers are reoriented within the material plane[17,40].

One of the leading products used for packaging is expanded polystyrene (EPS), commonly known as StyrofoamⓇ, a trademark of the Knauf company. The compressive strength of EPS type 1 to 6, resulting from the polymerization of styrene in water, must be between 0.035 and 0.173 MPa, with a density of 10 to 30 kg/m3[41]. Therefore, the compression strength obtained for this studied biocomposite is similar to this type of EPS.

Figure 6. Air humidity sortion (AirHS %) per exposure time (days) in biocomposites produced with 30% and 50% inoculum and dried at 60 °C in a conventional and vacuum oven. The gray and green lines refer to the measurement of relative air humidity (RairH%) and ambient temperature (°C), respectively, at the time of weighing.

Figure 7. Compression strength (MPa) ± standard deviation for the test specimens of biocomposites produced with 30% and 50% inoculum and dried in vacuum and conventional ovens. Equal letters indicate values without significant differences according to the Tukey test with a confidence level of 95%.

Polímeros, 35(1), e20250008, 2025

Fungal biocomposites production from packaging industry residue: PET-coated SBS paperboard Figure 8 presents the apparent densities of the biocomposites.

It is observed that inoculum fractions of 30% and 50% dried in a vacuum oven showed no statistically significant difference, remaining around 300 kg/m3. However, the densities of the biocomposites dried in a conventional oven are statistically different, with 315 kg/m3 for the 50% fraction and 274 kg/m3 for the 30% fraction, being in agreement with the lower porosity (Figure 4) of biocomposites with 50% inoculum and higher for those with 30%, as according to Thibault et al.[42], materials with more pores have lower density.

The density of biocomposite materials varies depending on the applied substrate. Girometta et al.[36] discuss in their work that the density of mycelium alone ranges from 30 to 50 kg/m3. Biocomposites produced from agricultural residues have lower density (60 – 130 kg/m3) compared to those produced with forest residues, such as sawdust (87 – 300 kg/m3), for different fungal species[17], poplar sawdust (220 kg/m3 for Pleurotus ostreatus)[19], hemp (170 - 260 kg/m3 for Coriolus versicolor)[43]. The biocomposites in the present study, which used cardboard with PET, resemble the biocomposite of the literature in terms of density (274 to 325 kg/m3 - Figure 8).

Despite having a high density compared to EPS (which typically ranges from 10 to 30 kg/m3), biocomposites are still lighter than other types of biocomposites. According to

Figure 8. Apparent density (kg/m3) ± standard deviation for the specimens of biocomposites produced with 30% and 50% inoculum and dried in a vacuum and conventional oven. Equal letters indicate values without significant differences according to Tukey’s test with a confidence level of 95%.

López-Nava et al.[44], these biocomposites are lightweight enough to be utilized in a variety of applications, including food and appliance packaging.

Regarding the thermal performance of the biocomposites, 3 stages of mass loss were observed for the biocomposites produced on SBS paperboard coated with PET (Figure 9 and Table 2). According to Mano et al.[45], this analysis aids in determining the maximum processing temperature limit that can be used without material decomposition.

The first stage can be related to water loss, which occurs from 25 to 150/200 ºC (Figure 9). For the biocomposite with a 30% inoculum fraction dried in a vacuum oven, this first thermal event had a lower percentage of mass loss (2.730% - Table 2) than in the subsequent events, indicating a lower initial moisture percentage in the cultivated biocomposite. This corresponds to the loss due to the evaporation of surface water.

The second stage characterizes cellulose and hemicellulose degradation[46]. The condition of vacuum drying and 50% inoculum stood out with temperatures 331.94 and 357.52 ºC followed by 331.04 and 356.46 ºC for conventional oven drying, showing more excellent thermal stability than the control (without fungal mycelium), indicating that the fungal mycelium influences this stability[47]. The third event is associated with a residue of approximately 13% for the biocomposite with 50% inoculum and around 11% for biocomposites with 30% inoculum. Bruscato et al.[15] with pure EPS, analyzed only one stage of thermal manipulation, with Tonset at 318 ºC, Tmax of 440 ºC and a residue percentage of nearly null, showing that this polymeric material is more stable than the biocomposites here studied. However, Jones et al.[17], in a Trametes versicolor biocomposite, obtained 25% residue formed at 500 °C and demonstrated that at temperatures higher than this, there are insignificant drops in mass loss for mycelium-based materials.

The biocomposites with 50% inoculum and conventional drying were produced in 16 days. They presented an average drying speed of 5.58 g/day, a compressive stress of 0.16 MPa, an apparent density of 315 kg/m3, low porosity (21,7%) and satisfactory thermal performance.

Figure 9. Thermogravimetry (TG)(A) and derivative thermogravimetry (DTG)(B) curves for the biocomposites produced with 30% and 50% inoculum of and dried in conventional and vacuum ovens. The control is only cardboard substrate coated (SBS) with PET (SBS + PET).

Polímeros, 35(1), e20250008, 2025

7/10

Souza, N. F., Bonatti-Chaves, M., Silva, D. A. K., Riani, J. C., & Wisbeck, E. Table 2. Thermogravimetric analysis data of biocomposites cultivated on the cardboard substrate coated (SBS) with PET (SBS + PET) with 30% and 50% inoculum and dried in conventional and vacuum ovens.

Biocomposites

Weight loss 1

Weight loss 2

T2onset T2max

T3max

Weight loss 3

T3endset

Residue

(%)

(%)

(ºC)

(%)

(ºC)

(%)

Control (SBS + PET)

5.44

69.47

323.21

12.84

410.41

12.23

30% - conventional

4.35

63.82

30% - vacuum

2.73

67.65

348.71 328.95

446.22 21.21

423.43

355.66 328.56

442.18 16.91

426.56

358.37 50% - conventional

3.75

71.56

331.04

3.02

65.81

331.94

12.68

449.83 11.34

416.65

356.46 50% - vacuum

10.63

13.33

448.30 17.85

422.13

357.52

13.32

447.47

Figure 10 confirms what had already been observed in Figure 5, PET is still present in biocomposites. However, the degree of PET degradation by P. sajor-caju must be verified[4].

4. Conclusions

Figure 10. Infrared spectroscopy of opaque and transparent phase of biocomposites produced with 50% inoculum and dried in conventional oven.

Thus, the condition with 50% inoculum and conventional drying was the best for producing biocomposites from cardboard substrate coated (SBS) with PET (SBS + PET).

FTIR analyses were performed to better understand this biocomposite’s chemistry (Figure 10).

The opaque phase of the material shows a spectrum characteristic of cellulose, indicating the presence of O-H at 3300 cm-1 and the set of bands between 1200 and 1000 cm-1.

The band near 1030 cm-1, related to C-O stretching in carbohydrates, stands out.

The infrared spectrum of the transparent phase of the composite corroborates the presence of bands characteristic of polyethylene terephthalate (PET), namely, those that identify the presence of the ester group and, in this case, the aromatic ester. Consequently, the PET spectrum exhibits an intense band at approximately 1720 cm-1, which is attributed to the stretching of the carbonyl group (C=O). In addition, two other bands are observed at 1245 cm-1 and 1100 cm-1, which relate to C-C-O and aromatic O-C-C stretching, respectively[48].

The prominent band at 720 cm-1, attributed to out-of-plane C-H deformation of the aromatic ring, is also included.

Thus, it appears that although fungi of the genus Pleurotus have an enzymatic complex capable of degrading PET[22], 8/10

Biocomposites with 50% inoculum demonstrated superiority over those with 30% inoculum because they were produced in a shorter time (16 days) and exhibited a higher average drying speed (5.58 g/day conventional drying) and had low porosity (21.7%). With the density (315 kg/m3), these biocomposites are light enough to be used in various applications, including food packaging and household appliances, as they have satisfactory thermal performance. Despite absorbing more humidity from the air than the biocomposites with 30% inoculum, no contaminations were observed during the 58 days of exposure to ambient air. About the drying method, no advantage was observed when using vacuum drying, as conventional drying was sufficient to achieve satisfactory results.

Although fungi of the genus Pleurotus have an enzyme complex capable of degrading PET, this material remained present in the biocomposites, verified by FTIR analyses.

However, verifying the extent of PET degradation by P. sajor-caju is necessary.

It is interesting to see how waste generated by the packaging industry can be transformed into something useful.

Combining these residues with the fungal specie P. sajor-caju is an excellent step towards solving environmental issues related to improper waste disposal. This approach can get a biomaterial (fungal biocomposite) that can substitute materials like expanded polystyrene (EPS) due to its superior compressive strength and similar thermal performance.

5. Author’s Contribution • Conceptualization – Elisabeth Wisbeck; Nicole Fernanda Souza • Data curation – NA Polímeros, 35(1), e20250008, 2025

Fungal biocomposites production from packaging industry residue: PET-coated SBS paperboard • Formal analysis – Denise Abatti Kasper Silva; Elisabeth Wisbeck; Josiane Costa Riani • Funding acquisition – Elisabeth Wisbeck • Investigation – Elisabeth Wisbeck; Mariane BonattiChaves; Nicole Fernanda Souza • Methodology – Elisabeth Wisbeck; Mariane BonattiChaves • Project administration – Elisabeth Wisbeck • Resources – Denise Abatti Kasper Silva; Josiane Costa Riani • Software – NA • Supervision – Elisabeth Wisbeck; Mariane BonattiChaves • Validation – Elisabeth Wisbeck; Nicole Fernanda Souza • Visualization – Elisabeth Wisbeck; Nicole Fernanda Souza • Writing – original draft – Elisabeth Wisbeck; Nicole Fernanda Souza • Writing – review & editing – Elisabeth Wisbeck; Mariane Bonatti-Chaves

6. Acknowledgements The authors thank the Foundation for Research Support of Santa Catarina – FAPESC, for the assistance with the scholarship. This study was supported by the Research Support Fund (FAP) from University of Region of Joinville - UNIVILLE.

7. References 1. Landim, A. P. M., Bernardo, C. O., Martins, I. B. A., Francisco, M. R., Santos, M. B., & Melo, N. R. (2016). Sustainability concerning food packaging in Brazil. Polímeros: Ciência e Tecnologia, 26, 82-92. http://doi.org/10.1590/0104-1428.1897.

2. Ito, D. (2009). Desenvolvimento de materiais de embalagens para forno de micro-ondas. Boletim de Tecnologia e Desenvolvimento de Embalagens, 21(2), 1-3. Retrieved in 2024, March 28, from https://ital.agricultura.sp.gov.br/arquivos/cetea/informativo/ v21n2/v21n2_artigo1.pdf 3. Ferri, G. N. (2015). Utilização do resíduo de papel cartão revestido com PET na remoção biológica de corante rodamina B (Master’s thesis). Universidade Regional de Blumenau, Blumenau.

4. Berdugo-Clavijo, C., Scheffer, G., Sen, A., & Gieg, L. M. (2022). Biodegradation of polymers used in oil and gas operations: towards enzyme biotechnology development and field application. Polymers, 14(9), 1871. http://doi.org/10.3390/ polym14091871. PMid:35567040.

5. Khalid, M. Y., & Arif, Z. U. (2022). Novel biopolymer-based sustainable composites for food packaging applications: A narrative review. Food Packaging and Shelf Life, 33, 100892. http://doi.org/10.1016/j.fpsl.2022.100892.

6. Xie, Y., Gao, S., Zhang, D., Wang, C., & Chu, F. (2023).

Bio-based polymeric materials synthesized from renewable resources: A mini-review. Resources Chemicals and Materials, 2(3), 223-230. http://doi.org/10.1016/j.recm.2023.05.001.

7. Bayer, E., McIntyre, G., & Swersey, B. L. (2008). US 2008 0145577 A1. USA: United States Patent Application. Retrieved in 2024, March 28, from https://patentimages.storage.googleapis. com/74/46/74/6deee8ee51a2f1/US20080145577A1.pdf Polímeros, 35(1), e20250008, 2025

8. Ecovative. (2023, March 17). Retrieved in 2024, March 28, from https://ecovative.com 9. Maisnam, D., Rasane, P., Dey, A., Kaur, S., & Sarma, C. (2017). Recent advances in conventional drying of foods.

Journal of Food Technology and Preservation, 1, 25-34.

Retrieved in 2024, March 28, from https://www.researchgate. net/publication/316507291 10. Shukla, S. (2011). Freeze drying process: A review. International Journal of Pharmaceutical Sciences and Research, 2(12), 30613068. http://doi.org/10.13040/IJPSR.0975-8232.2(12).3061-68.

11. Giri, S. K., & Prasad, S. (2006). Modeling shrinkage and density changes during microwave-vacuum drying of button mushroom. International Journal of Food Properties, 9(3), 409-419. http://doi.org/10.1080/10942910600596472.

12. Rahman, M. S., Al-Amri, O. S., & Al-Bulushi, I. M. (2002).

Pores and physico-chemical characteristics of dried tuna produced by different methods of drying. Journal of Food Engineering, 53(4), 301-313. http://doi.org/10.1016/S02608774(01)00169-8.

13. Yang, Z., Zhang, F., Still, B., White, M., & Amstislavski, P. (2017). Physical and mechanical properties of fungal myceliumbased biofoam. Journal of Materials in Civil Engineering, 29(7), 04017030. http://doi.org/10.1061/(ASCE)MT.19435533.0001866.

14. Appels, F. V. W., Camere, S., Montalti, M., Karana, E., Jansen, K. M. B., Dijksterhuis, J., Krijgsheld, P., & Wösten, H. A. B. (2019). Fabrication factors influencing mechanical, moistureand water-related properties of mycelium-based composites.

Materials & Design, 161, 64-71. http://doi.org/10.1016/j. matdes.2018.11.027.

15. Bruscato, C., Malvessi, E., Brandalise, R. N., & Camassola, M. (2019). High performance of macrofungi in the production of mycelium-based biofoams using sawdust: sustainable technology for waste reduction. Journal of Cleaner Production, 234, 225-232. http://doi.org/10.1016/j.jclepro.2019.06.150.

16. Ghazvinian, A., Farrokhsiar, P., Vieira, F., Pecchia, J., & Gursoy, B. (2019). Mycelium-based bio-composites for architecture: assessing the effects of cultivation factors on compressive strength. In J. P. Sousa, G. C. Henriques, & J. P. Xavier (Eds.), Proceedings of the 37th eCAADe and XXIII SIGraDi Joint Conference, “Architecture in the Age of the 4th Industrial Revolution (pp. 505-514). Porto: Blucher. http://doi. org/10.5151/proceedings-ecaadesigradi2019_465.

17. Jones, M., Mautner, A., Luenco, S., Bismarck, A., & John, S. (2020). Engineered mycelium composite construction materials from fungal biorefineries: A critical review. Materials & Design, 187, 108397. http://doi.org/10.1016/j.matdes.2019.108397.

18. Rocha, M. I., Benkendorf, S., Gern, R. M. M., Riani, J. C., & Wisbeck, E. (2020). Desenvolvimento de biocompósitos fúngicos utilizando resíduos industriais. Matéria (Rio de Janeiro), 25(4), e-12840. http://doi.org/10.1590/s1517-707620200004.1140.

19. Aquino, M., Rugolo, M., Robledo, G., & Kuhar, F. (2022).

Evaluation of mycelium composite materials produced by five Patagonian fungal species. Maderas. Ciencia y Tecnología, 24(35), 1-14. http://doi.org/10.4067/S0718-221X2022000100435.

20. Kenig-Witkowska, M. (2017). The concept of sustainable development in the European Union policy and law. Journal of Comparative Urban Law and Policy, 1(1), 6. Retrieved in 2024, March 28, from https://readingroom.law.gsu.edu/jculp/ vol1/iss1/6 21. Miles, P. G., & Chang, S. T. (2004). Mushrooms: Cultivation, nutritional value, medicinal effect and environmental impact.

Boca Raton: CRC Press. http://doi.org/10.1201/9780203492086 22. Faria, P. C., Wisbeck, E., & Dias, L. C. (2015). Biodegradação de polipropileno reciclado (PPR) e de poli(tereftalato de etileno) reciclado (PETR) por Pleurotus ostreatus. Matéria 9/10

Souza, N. F., Bonatti-Chaves, M., Silva, D. A. K., Riani, J. C., & Wisbeck, E. (Rio de Janeiro), 20(2), 452-459. http://doi.org/10.1590/ S1517-707620150002.0045.

23. Santos, B. C., Silva, K. C., Bonatti-Chaves, M., & Wisbeck, E. (2021). Produção de cogumelos de Pleurotus sajor-caju em resíduos de embalagens de papel cartão revestido com PET. In Anais do II Congresso Brasileiro Interdisciplinar em Ciência e Tecnologia. Retrieved in 2024, March 28, from https://even3. blob.core.windows.net/anais/389548.pdf 24. Furlan, S. A., Virmond, L. J., Miers, D. A., Bonatti, M., Gern, R. M. M., & Jonas, R. (1997). Mushroom strains able to grow at high temperatures and low pH values. World Journal of Microbiology & Biotechnology, 13(6), 689-692. http://doi. org/10.1023/A:1018579123385.

25. Bonatti, M., Karnopp, P., Soares, H. M., & Furlan, S. A. (2004). Evaluation of Pleurotus ostreatus and Pleurotus sajorcaju nutritional characteristics when cultivated in different lignocellulosic wastes. Food Chemistry, 88(3), 425-428. http:// doi.org/10.1016/j.foodchem.2004.01.050.

26. Associação Brasileira de Normas Técnicas (2016). NBR 8082-16: Espuma rígida de poliuretano para fins de isolação térmica — determinação da resistência à compressão. Rio de Janeiro: ABNT. Retrieved in 2024, March 28, from https:// normas.com.br/visualizar/abnt-nbr-nm/2855/abnt-nbr8082espuma-rigida-de-poliuretano-para-fins-de-isolacao-termicadeterminacao-da-resistencia-a-compressao 27. Hossen, M. R., Talbot, M. W., Kennard, R., Bousfield, D. W., & Mason, M. D. (2020). A comparative study of methods for porosity determination of cellulose-based porous materials.

Cellulose (London, England), 27(12), 6849-6860. http://doi. org/10.1007/s10570-020-03257-9.

28. American Society for Testing and Materials (1999). D570-95: Standard test method for water absorption of plastics. USA: ASTM. 29. Rorabacher, D. B. (1991). Statistical treatment for rejection of deviant values: critical values of Dixon’s “Q” parameter and related subrange ratios at the 95% confidence level. Analytical Chemistry, 63(2), 139-146. http://doi.org/10.1021/ac00002a010.

30. Deschamps, J. L. N. (2020). Produção e caracterização de biocompósitos obtidos do cultivo de Pleurotus sajor-caju em substrato composto por bagaço de malte e folhas de bananeira (Master’s thesis). Universidade da Região de Joinville, Joinville.

31. Deacon, J. W. (2006). Fungal biology. UK: Blackwell Publishing Ltd. 32. Reis, F. R., Masson, M. L., & Waszczynskyj, N. (2006).

Efeitos da secagem convectiva e a vácuo sobre parâmetros de qualidade de fatias de berinjela. Revista Brasileira de Produtos Agroindustriais, 8(2), 167-173. http://doi.org/10.15871/15178595/rbpa.v8n2p163-169.

33. Ma, X., Chang, P. R., Yu, J., & Stumborg, M. (2009). Properties of biodegradable citric acid-modified granular starch/thermoplastic pea starch composites. Carbohydrate Polymers, 75(1), 1-8. http://doi.org/10.1016/j.carbpol.2008.05.020.

34. Klyosov, A. A. (2007). Wood-plastic composites. USA: John Wiley & Sons, Inc.. http://doi.org/10.1002/9780470165935.

35. Sjöqvist, M., Boldizar, A., & Rigdahl, M. (2010). Processing and water absorption behaviour of foamed potato starch.

Journal of Cellular Plastics, 46(6), 497-517. http://doi. org/10.1177/0021955X10377802.

36. Girometta, C., Picco, A. M., Baiguera, R. M., Dondi, D., Babbini, S., Cartabia, M., Pellegrini, M., & Savino, E. (2019). Physicomechanical and thermodynamic properties of mycelium-based biocomposites: A review. Sustainability (Basel), 11(1), 281. http://doi.org/10.3390/su11010281.

10/10

37. Sánchez-Vázquez, J. E., & Royse, D. J. (2001). La biología y el cultivo de Pleurotus spp. Mexico: El Colegio de la Frontera Sur. 38. Cha, J. S. (2004). Pest and disease management. In R. Gush & J. Poppe (Eds.), Mushroom grower’s handbook – Oyster mushroom cultivation (pp. 172-186). Seoul: Mushword-Heineart Inc. 39. Ziegler, A. R., Bajwa, S. G., Holt, G. A., McIntyre, G., & Bajwa, D. S. (2016). Evaluation of physico-mechanical properties of mycelium reinforced green biocomposites made from cellulosic fibers. Applied Engineering in Agriculture, 32(6), 931-938. http://doi.org/10.13031/aea.32.11830.

40. Dai, C., Yu, C., & Zhou, X. (2007). Heat and mass transfer in wood composite panels during hot pressing. Part II. Modeling void formation and mat permeability. Wood and Fiber Science, 37(2), 242-257. Retrieved in 2024, March 28, from https://wfs. swst.org/index.php/wfs/article/view/412 41. Associação Brasileira de Normas Técnicas (2016). NBR 11752-16: Materiais celulares de poliestireno para isolamento térmico na construção civil e refrigeração industrial – Especificação. Rio de Janeiro: ABNT. Retrieved in 2024, March 28, from https://www.normas.com.br/ visualizar/abnt-nbr-nm/787/nbr11752-materiais-celularesde-poliestireno-para-isolamento-termico-na-construcaocivil-e-refrigeracao-industrial-especificacao 42. Thibault, B., Aghajanzadeh, S., Sultana, A., Ratti, C., & Khalloufi, S. (2024). Characteristics of open and closed pores, their measurement techniques and exploitation in dehydrated food products. Food Engineering Reviews, 16(3), 323-355. http://doi.org/10.1007/s12393-024-09376-4.

43. Lelivelt, R. J. J. (2015). The mechanical possibilities of mycelium materials (Master’s thesis). Eindhoven University of Technology, Eindhoven, Netherlands. Retrieved in 2024, March 28, from https://research.tue.nl/en/studentTheses/themechanical-possibilities-of-mycelium-materials 44. López-Nava, J. A., González, J. M., Chacón, X. R., & Luna, J. A. N. (2016). Assessment of edible fungi and films bio-based material simulating expanded polystyrene. Materials and Manufacturing Processes, 31(8), 1085-1090. http://doi.org/1 0.1080/10426914.2015.1070420.

45. Mano, J. F., Koniarova, D., & Reis, R. L. (2003). Thermal properties of thermoplastic starch/synthetic polymer blends with potential biomedical applicability. Journal of Materials Science. Materials in Medicine, 14(2), 127-135. http://doi. org/10.1023/A:1022015712170. PMid:15348484.

46. Sánchez, R., Espinosa, E., Domínguez-Robles, J., Loaiza, J. M., & Rodríguez, A. (2016). Isolation and characterization of lignocellulose nanofibers from different wheat straw pulps.

International Journal of Biological Macromolecules, 92, 1025-1033. http://doi.org/10.1016/j.ijbiomac.2016.08.019.

PMid:27514440.

47. Alemdar, A., & Sain, M. (2008). Biocomposites from wheat straw nanofibers: Morphology, thermal and mechanical properties.

Composites Science and Technology, 68(2), 557-565. http:// doi.org/10.1016/j.compscitech.2007.05.044.

48. Smith, B. C. (2022). Infrared spectroscopy of polymers, VIII: polyesters and the rule of three. Spectroscopy (Springfield, Or.), 37(10), 25-28. http://doi.org/10.56530/spectroscopy.ta9383e3.

Received: Mar. 28, 2024 Revised: Oct. 27, 2024 Accepted: Nov. 19, 2024

Polímeros, 35(1), e20250008, 2025

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20240095

Direct-joining of a polylactide acid-hydroxyapatite biocomposite with a titanium alloy Renan Adauto1 , Gean Henrique Marcatto de Oliveira1 , Mário Augusto Morozo1 , Márcio Antônio Fiori2  and Leonardo Bresciani Canto1,3*  1

Programa de Pós-Graduação em Ciência e Engenharia de Materiais – PPGCEM, Universidade Federal de São Carlos – UFSCar, São Carlos, SP, Brasil 2 Departamento de Física, Universidade Tecnológica Federal do Paraná, Pato Branco, PR, Brasil 3 Departamento de Engenharia de Materiais – DEMa, Universidade Federal de São Carlos – UFSCar, São Carlos, SP, Brasil *leonardo@ufscar.br

Abstract A promising yet underexplored alternative for biomedical applications involves incorporating polymer, metal, and ceramic materials into hybrid structures. In this study, a biocomposite consisting of polylactic acid (PLA) with 20 wt% of nearly spherical sub-micron hydroxyapatite (HA) particles was successfully synthesized. The HA particles were uniformly dispersed and distributed within the PLA matrix, leading to a biocomposite with a well-balanced combination of thermal and mechanical properties. This PLA−HA biocomposite was then directly joined through injection overmolding onto a laser-surface-structured titanium alloy Ti6Al4V substrate. The PLA−HA/Ti6Al4V hybrid joints demonstrated robust mechanical anchorage, achieved through the thorough filling of the polymer biocomposite into the micro-scale structures engineered onto the metal surface. This mechanism ensured good lap-shear strength, making these hybrid joints promising candidates for orthopedic applications.

Keywords: polymer-metal hybrids, polylactide acid, hydroxyapatite, injection overmolding.

How to cite: Adauto, R., Oliveira, G. H. M., Morozo, M. A., Fiori, M. A., & Canto, L. B. (2025). Direct-joining of a polylactide acid–hydroxyapatite biocomposite with a titanium alloy. Polímeros: Ciência e Tecnologia, 35(1), e20250009. https://doi.org/10.1590/0104-1428.20240095

1. Introduction The development of new materials for biomedical applications has advanced significantly. Single-class material structures often fail to meet all the requirements for specific applications. Consequently, combining different material classes has become a common approach to achieve the desired properties.

Biocomposites of polylactic acid (PLA) and hydroxyapatite (HA) have been the focus of intense research aimed at advancing biomaterials and tissue regeneration[1-8]. Polylactic acid (PLA), an aliphatic thermoplastic polyester from renewable resources, stands as one of the most extensively researched and widely utilized polymers in biomedical applications. Granted approval by the United States Food and Drug Administration (FDA) for medical use, PLA boasts biodegradability, bioresorsability, biocompatibility and ease of processing[1]. Hydroxyapatite (HA) is a calcium phosphate (Ca10(PO4)6(OH)2) with composition similar to that of biological apatite found in human hard tissues, making it ideal for orthopedic and dental applications[9,10].

The incorporation of HA into PLA enhances the resemblance of the biocomposite to natural bone tissue, conferring osteobiological properties suitable for targeted biomedical applications[1-4]. Increasing HA content in the PLA matrix

Polímeros, 35(1), e20250009, 2025

improves its degree of crystallinity[5-7], reduces thermal stability[6,7], and slows down hydrolytic degradation[8].

Furthermore, the addition of HA increases the elastic modulus but compromises tensile strength and elongation at break[6,7].

Meanwhile, titanium alloy Ti6Al4V is distinguished as a widely used metal alloy for bone-anchoring implants, prized for its unique combination of beneficial attributes.

These include a comparable elastic modulus to bone, outstanding fatigue resistance, favorable hardness, lightweight construction, remarkable corrosion and wear resistance, minimal ion release rates, biocompatibility, and hypoallergenic nature[11,12]. Moreover, Ti6Al4V has been modified with HA through composites[13] and coatings[14] to satisfy the specific demands of biomedical applications.

The integration of a PLA−HA biocomposite with a Ti6Al4V titanium alloy into a single structure remains an unexplored approach, but one with significant potential to meet a wide range of mechanical, physicochemical and biological requirements for biomedical applications.

The use of injection overmolding with direct-adhesion is particularly advantageous for this purpose, as it is a wellestablished and highly efficient processing method for assembling polymer-metal hybrids of various sizes and

1/9

O O O O O O O O O O O O O O O O O

Adauto R., Oliveira G. H. M., Morozo M. A., Fiori M. A., & Canto L. B. shapes, combining automation, high-speed production, costeffectiveness, precise dimensional control, and exceptional bond strength[15,16]. Optimal adhesion between polymer and metal parts in injection overmolding can be further enhanced by preparing the metal surface with laser structuring[17-19].

This study investigates the direct-joining of a biocomposite consisting of polylactic acid (PLA) and hydroxyapatite (HA) with a Ti6Al4V titanium alloy for biomedical applications, using metal laser structuring and injection overmolding techniques.

The research focuses on the preparation of the biocomposite via melt-state processing, as weel as its morphological, thermal, and mechanical characterization, alongside the manufacturing process, interfacial characterization, and evaluation of the joining strength of the PLA−HA/Ti6Al4V hybrid.

2. Materials and Methods 2.1 Materials Polylactide acid (PLA) is a commercial grade (IngeoTM 4043D) supplied by NatureWorks company with density of 1.24 g/cm3. It has a number-average molecular weight of 41 kg/ mol and weight-average molecular weight of 76 kg/mol[8].

Hydroxyapatite (HA) with a Ca/P molar ratio of 1.71 was synthesized in an aqueous medium through the precipitation method. The precursors used were calcium oxide (CaO, 95%) and phosphoric acid (H3PO4, 85%), with ammonium hydroxide (NH3OH, 30%) acting as the pH regulator. A total of 159.1 g of calcium oxide was added to 1000 mL of distilled water in a 1500 mL beaker. The mixture was stirred for 24 hours at 25°C using a mechanical stirrer set at 1000 rpm, forming a Ca(OH)2 suspension with excess distilled water. Next, a solution of 194.6 g of 85% phosphoric acid was added to the suspension at a rate of 1.8 mL/min. During the addition, the pH was monitored using universal pH indicator strips.

The suspension was then stirred for 4 hours at 80°C. At the end of this period, the pH was adjusted to 7 by adding 37.6 g of ammonium hydroxide. The final suspension was left to rest for 24 hours to stabilize the pH and allow the formation of a liquid phase and precipitate. The precipitate was separated

from the suspension by filtration using Whatman filter paper (No. 1) and a vacuum pump. The filtered material was then dried in an oven at 100°C for 24 hours. After drying, the sample was cooled in a desiccator to room temperature.

It was then ground into a fine powder using a mortar and agate pestle. The dried powder was subsequently calcined in a muffle furnace with a heating rate of 8°C/min until it reached 800°C, where it remained for 2 hours. The characterization of hydroxyapatite is shown elsewhere[20].

Ti6Al4V ELI is a 3.5 mm thick rolled sheet supplied by Shaanxi Aone Titanium Metal Materials Company (China).

2.2 Experimental procedure The experimental workflow of this study is depicted in Figure 1. It involved two main stages: the preparation and characterization of the PLA–HA biocomposite, and the joining of the PLA–HA biocomposite onto a Ti6Al4V substrate, followed by its mechanical and interfacial characterization.

2.3 Preparation and characterization of the PLA−HA biocomposite A PLA−HA biocomposite with 20 wt% filler was prepared using the melt-compounding procedure described below.

The filler content was selected based on the study conducted

by Ferri et al.[6], which demonstrated that this composition provides a good balance of mechanical properties.

The PLA−HA biocomposite was produced using an APV Baker Perkins Equipment and Systems intermeshing co-rotating twin-screw extruder (model MP-19TC) with a 19 mm screw diameter (D) and a length to diameter ratio (L/D) of 25:1.

The barrel temperature was maintained at 200°C, and the screw speed was set to 100 rpm. Before processing, PLA pellets were cryogenically ground into a fine powder using a CF Bantam Micron Powder Systems mill. The dried powders of PLA and HA were mixed thoroughly in the desired ratio and fed into the extruder at a rate of 2.4 kg/h using a Brabender feeder.

The extruded strands were cooled in a water bath immediately after exiting the die and then pelletized.

Figure 1. Experimental workflow.

2/9

Polímeros, 35(1), e20250009, 2025

Direct-joining of a polylactide acid-hydroxyapatite biocomposite with a titanium alloy Specimens (Type I tensile bars – ASTM D638) were injection molded using an Arburg Allrounder 270V 300120 machine with the following parameters: a barrel temperature of 200°C, an injection speed of 50 cm3/s, a holding pressure of 250 bar for 7 seconds, a mold temperature of 25°C, and a cooling time of 55 seconds.

The phase morphology of the PLA−HA biocomposite was examined using scanning electron microscopy (SEM) with an FEI Inspect S50 instrument, operating at an acceleration voltage of 10 kV and a magnification of 20,000. A sample taken from the injection-molded specimen was fractured after being immersed in liquid nitrogen and subsequently sputter-coated with gold before undergoing SEM examination. The morphology of the hydroxyapatite (HA) was evaluated using SEM with an FEI Magellan 400 L instrument, operating at an acceleration voltage of 7 kV and a magnification of 170,000. The HA sample was dispersed in ethyl alcohol using ultrasound, dripped onto a thin aluminum sheet, and then sputter-coated with gold before SEM analysis.

The thermal decomposition of PLA in both neat PLA and PLA−HA samples was assessed using thermogravimetric analysis (TGA) with a TA Instruments Q500. Samples (15 ± 0.5 mg) were taken from the inner section of the injectionmolded specimens and heated from 25 to 800°C at a rate of 20°C/min under a nitrogen atmosphere (50 mL/min).

The crystallinity of PLA in both neat PLA and PLA−HA samples was analyzed using modulated differential scanning calorimetry (MDSC) with a TA Instruments DSC Q2000.

Samples (11 ± 0.5 mg) were taken from the inner section of the injection-molded specimens and scanned from 25°C to 200°C at a heating rate of 2°C/min, with a modulation period of 60 s and an amplitude of 0.318°C, under a nitrogen atmosphere (50 mL/min), following the procedure outlined in[21].

Tensile testing was performed according to ASTM D638 on injection-molded Type I specimens using an Instron 5569 system, with a crosshead speed of 5 mm/min.

Flexural testing was conducted following ASTM D790 on standard bars machined from injection-molded specimens, using the Instron 5569 system, with a crosshead speed of 1.27 mm/min. Five replicate specimens were tested, which were conditioned at 23°C and 50% relative humidity for 48 hours before testing.

2.4 Joining of PLA−HA biocomposite onto a Ti6Al4V substrate Hybrid joints with a half-lap splice configuration (Figure 2) were fabricated. The joint dimensions were adapted from the ASTM D1002 standard, which serves as a guideline for testing the strength of adhesives in metal bonding. This standard is commonly employed for assessing the joining strength of polymer-metal hybrids.

Ti6Al4V substrates were cut and machined from rolled sheets into the symmetrical side of a half-lap splice joint (Figure 2). The recessed surface was structured using a pulsed laser to enhance adhesion with the polymer. A Trotec Speed Marker 50 instrument was used, featuring an average power of 20 watts, a wavelength of 1064 nm, a spot diameter of 40 μm, and a pulse duration of 110 ns. The frequency was set at 20 kHz and the scan speed at 500 mm/s. The laser beam Polímeros, 35(1), e20250009, 2025

Figure 2. Schematic illustration of half-lap splice PLA−HA/ Ti6Al4V hybrid joint specimens manufactured by injection overmolding. The dimensions are given in mm.

was scanned line by line in both directions with a line spacing of 100 µm. The laser was first scanned in one direction back and forth until the entire area of the metal insert recess was covered. The scanning was then repeated in the orthogonal direction. The procedure was carried out a total of four times.

Before each step of surface structuring and injection molding, the metal parts were rinsed with compressed air followed by immersion in isopropyl alcohol in an ultrasonic bath for 3 min. The surface of the laser-structured Ti6Al4V part was analyzed using scanning electron microscopy (SEM) with an FEI Inspect S50 instrument at an acceleration voltage of 25 kV. Additionally, laser confocal microscopy was performed using an Olympus LEXT OLS4100 instrument with a wavelength of 405 nm.

The hybrid joints were fabricated using an Arburg Allrounder 270V 300-120 injection molding machine.

The machine was operated in semi-automatic mode, where the metal substrate was manually placed in the mold cavity before initiating the injection molding cycle. The optimized operating conditions included a barrel temperature of 200°C, an injection speed of 30 cm3/s, a holding pressure of 500 bar, a holding time of 7 seconds, a mold temperature of 25°C, and a cooling time of 30 seconds.

Lap-shear testing was conducted according to a modified version of the ASTM D1002 standard, using an Instron 5569 system. The distance between grips was set to 60 mm, and the test was conducted at a crosshead speed of 1.27 mm/min. Five replicate specimens were tested, which were conditioned at 23°C and 50% relative humidity for 48 hours before testing.

The cross-section of the hybrid joint was analyzed using optical microscopy with a LEXT OLS 4100 (Olympus, Japan) instrument. The specimen was sectioned, embedded in epoxy resin, and polished prior to examination.

3. Results and Discussion 3.1 PLA−HA biocomposite The morphology of hydroxyapatite (HA) and its dispersion within the PLA−HA biocomposite were evaluated using SEM, with representative images displayed in Figure 3a-b. HA appears as compact agglomerates of globular particles with size in 3/9

Adauto R., Oliveira G. H. M., Morozo M. A., Fiori M. A., & Canto L. B. the range of 150 to 250 nm (Figure 3a), which are typical of the synthesis route adopted[20]. In the biocomposite, HA is in the form of small clusters of approximately 2-5 particles (< 1 µm) well distributed in the PLA matrix (Figure 3b).

This indicates that the melt-processing route adopted was efficient in dispersing and distributing the HA in the polymer matrix. The dispersion of sub-micrometer-sized particles, especially those capable of forming hydrogen bonds like the HA used in this study, is hindered by their high surface energy, which can lead to agglomeration[9,10]. On the other hand, PLA is polar and has the ability to form hydrogen bonds with HA. These interactions create a robust polymer/particle interface, which facilitates the dispersion and distribution of particles within the polymer matrix during the melting process[7]. Moreover, the mixing energy generated by the applied shear stress during the melt-compounding of the PLA−HA biocomposite can surpass the cohesive energy between the HA particles[22]. The literature indicates that the dispersion of HA particles on a submicron scale offers

a high surface area to volume ratio, which increases the mechanical properties and bioactivity of the material[4].

The thermal decomposition behavior of the PLA matrix in the PLA−HA biocomposite was evaluated by thermogravimetric analysis (TGA). The TG and derivative (DTG) curves for neat PLA (control), PLA−HA biocomposite and neat hydroxyapatite HA (control) are shown in Figure 4.

Thermal decomposition data are shown in Table 1. HA exhibits thermal stability, showing no measurable weight loss up to 800°C. Both PLA and PLA−HA biocomposite exhibited a single-step thermal decomposition event. This behavior has been attributed to the depolymerization of PLA, resulting in the formation of oligomers and lactides[23,24]. The residual mass of PLA consists of char, whereas for the PLA−HA biocomposite, it additionally consists of undecomposed hydroxyapatite (HA). The PLA−HA biocomposite exhibited slightly lower decomposition temperatures compared to neat PLA, which may be attributed to the prior degradation that PLA experienced during the melt processing of the PLA−HA

Figure 3. Scanning electron microscopy (SEM) images of the hydroxyapatite (HA) (a) and PLA−HA biocomposite (b).

Figure 4. Thermogravimetric (TG) and derivative thermogravimetric (dTG) curves for neat PLA, PLA−HA biocomposite and neat HA under N2 atmosphere.

4/9

Polímeros, 35(1), e20250009, 2025

Direct-joining of a polylactide acid-hydroxyapatite biocomposite with a titanium alloy biocomposite. Dedicated studies reported in the literature have shown that melt processing can induce thermomechanical degradation of PLA through chain scission, leading to a decrease in molecular weight[25,26].

The crystallinity behavior of the PLA matrix in both neat PLA (control) and PLA−HA biocomposite injection-molded parts was evaluated using MDSC analysis. The MDSC curves are shown in Figure 5, and the data are summarized in Table 2. MDSC is a more reliable technique than standard DSC for measuring the crystallinity behavior of polymers with low crystallization kinetics, such as PLA. The cold crystallization of PLA appears as an exothermic peak in the non-reversing curve. The maximum cold crystallization temperature of PLA in the PLA−HA biocomposite shifts to a lower temperature by approximately 5 °C, indicating that hydroxyapatite acts as a heterogeneous nucleating agent for the PLA matrix. Addtionally, the degradation of PLA during compounding with HA, as indicated by the TGA analysis (Figure 4; Table 1), may also have contributed to the reduction in the cold crystallization temperature. The cold crystallization enthalpy of PLA, measured from the non-reversing signal and normalized to the PLA content in the sample, is nearly equivalent between the PLA−HA biocomposite and neat

PLA. Melting occurs over a wide range of temperatures, beginning shortly after cold crystallization, as indicated by the endothermic peak observed in the non-reversing signal.

This melting is accompanied by recrystallization, observed as an exothermic event in the reversing signal. This process is associated with crystal perfection, where smaller and less perfect crystals melt and recrystallize successively, using the remaining crystals as templates to form more perfect structures. The enthalpies related to crystal perfection, normalized to the PLA content in the sample, are higher in the neat PLA sample compared to the PLA−HA biocomposite.

This indicates that the previous thermal history (injection molding) of the PLA in the PLA−HA biocomposite resulted in more perfect crystals, making them less susceptible to the crystal perfection phenomenon.

The degrees of crystallinity of PLA in both the neat PLA and PLA−HA biocomposite samples, related to their previous crystallization history (injection molding) and independent of the thermal history acquired during DSC heating, were calculated using Equation 1. The terms in Equation 1 are defined as follows: ∆H mnon − reversing is the melting enthalpy non − reversing measured in the non-reversing curve; ∆H cc is the cold crystallization enthalpy measured in the non-reversing

Table 1. Thermogravimetric data for neat PLA (control) and PLA−HA biocomposite under N2 atmosphere.

Sample

Tstart (oC)

Tpeak (oC)

Tend (oC)

Mass residue (%)

PLA

303

388

413

1.9

PLA−HA

275

375

394

20.1

Table 2. MDSC data for neat PLA (control) and PLA−HA biocomposite. The data are normalized to the PLA content in each sample.

Sample PLA PLA−HA

∆H ccnon − reversing

∆H mnon − reversing

reversing ∆H rec

(J g-1) 25.2 22.8

(J g-1) 49.3 36.8

(J g-1) 20.2 4.4

X

c (%) 4 10

Figure 5. MDSC curves for neat PLA (control) (a) and PLA−HA biocomposite (b).

Polímeros, 35(1), e20250009, 2025

5/9

Adauto R., Oliveira G. H. M., Morozo M. A., Fiori M. A., & Canto L. B. reversing curve; ∆H rec is the recrystallization enthalpy related to crystal perfection phenomena measured in the reversing 100% curve; and ∆H m is the melting enthalpy for 100% crystalline PLA (93 J/g[6]). All enthalpies are normalized to the PLA content in each sample.

Xc =

reversing ∆H mnon − reversing − ∆H ccnon − reversing − ∆H rec 100% ∆H m

(1)

Therefore, the MDSC analysis demonstrated that PLA crystallization is enhanced in the presence of HA, leading to greater crystal perfection and a higher degree of crystallinity in injection-molded samples. This finding corroborates the results of other studies on PLA−HA composites[5-7].

The mechanical behavior of the PLA−HA biocomposite was evaluated through tensile and flexural tests. PLA specimens were tested for comparison. Mechanical properties are shown in Table 3.

In tensile tests, PLA exhibited ductile behavior, though fracture occurred shortly after yielding. In contrast, the PLA−HA biocomposite displayed brittle behavior, with fracture occurring at a slightly lower stress level than that for the yielding of the neat PLA. The increase in modulus with HA incorporation into PLA is achieved at the expense of tensile strength and strain at break. A similar trend was observed in the flexural test, where the incorporation of HA into PLA resulted in an increased modulus but a decrease in flexural strength. In general, the mechanical behavior observed in this study for the PLA−HA biocomposite is similar to that reported in the literature for other biocomposites processed in the molten state with similar filler contents[6,7].

The increased stiffness of PLA upon incorporating HA particles are attributed in the literature to the mechanical

anchoring of PLA chains around the HA particles, which restricts the movement of PLA chains and hinders the deformation of the PLA matrix[6,7]. The modest increase in modulus, along with the lower mechanical strength and elongation at break, can be attributed to the low aspect ratio of the nearly spherical HA particles (Figure 3a), despite their fine dispersion and good distribution within the PLA matrix (Figure 3b). The increased degree of crystallinity in the PLA matrix (Table 2) may have also contributed to the enhanced modulus, while decreasing the strength and elongation at break of the biocomposite. On the other hand, the degradation of PLA during compounding with HA, as indicated by the TGA analysis (Figure 4; Table 1), may have negatively affected the modulus, strength, and elongation at break.

3.2 PLA−HA/Ti6Al4V hybrid joint The topography of the laser-surface-structured Ti6Al4V substrate was analyzed using scanning electron microscopy (SEM) and confocal laser microscopy, and the images are shown in Figure 6a-b. Laser structuring produced structures in the form of valleys and hills arranged in a square grid of 100 × 100 μm. The valleys are formed by the material removed by laser ablation, while the hills are formed by the re-solidified metal, often referred to as remelted metal, which is expelled and deposited in the space between the valleys. The average width and depth of the valleys were 57 ± 5 μm and 55 ± 9 μm, respectively, and the average width and height of the hills were 50 ± 7 μm and 27 ± 7 μm, respectively.

Figure 7 shows the lap-shear force-displacement curves for the PLA−HA/Ti6Al4V hybrid joint specimens. Similar patterns were observed among the examined specimens, indicating the robust repeatability of the adopted laser structuring and injection overmolding methodology.

Table 3. Mechanical properties of PLA (control) and PLA−HA biocomposite in tensile and flexural tests.

Material PLA (control) PLA−HA biocomposite

Tensile Modulus (GPa) 4.8 ± 0.6 5.4 ± 0.3

Tensile Strength (GPa) 63.9 ± 1.1* 59.9 ± 0.7**

Strain at Break (%) 3.1 ± 0.2 1.9 ± 0.1

Flexural Modulus (GPa) 3.6 ± 0.3 4.7 ± 0.1

Flexural Strength (GPa) 104.4 ± 1.8 93.3 ± 3.7

*Tensile stress at yield. **Tensile stress at break.

Figure 6. Scanning electron microscopy (SEM) (a) and confocal laser microscopy (b) images of the surface of laser-structured Ti6Al4V substrate.

6/9

Polímeros, 35(1), e20250009, 2025

Direct-joining of a polylactide acid-hydroxyapatite biocomposite with a titanium alloy All specimens exhibited macroscopic failure due to brittle fracture of the PLA−HA part outside the bonding zone, near the end of the metal part, as shown in Figure 8. The PLA− HA/Ti6Al4V joint exhibited an ultimate lap-shear force (ULSF) of 1190 ± 21 N and displacement at break of 0.33 ± 0.03 mm. The mechanical performance of the PLA−HA/ Ti6Al4V joints was slightly lower than that of the joints fabricated with neat PLA, which exhibited an ULSF of 1592 ± 28 N and a displacement at break of 0.84 ± 0.23 mm.

This trend is consistent with the behavior observed in the tensile tests (Table 3). The ULSF of the PLA−HA/Ti6Al4V joint is approximately 50% of the nominal force required for the PLA−HA part to break, based on its tensile strength of 59.9 ± 0.7 MPa (Table 3). This behavior is to be expected in an overlap hybrid joint specimen with a polymeric component exhibiting brittle mechanical behavior, such as PLA−HA. In the lap-shear test of half-lap splice joints, such as that employed in this study, the polymeric component is subjected to complex strain fields involving tension, shear, and bending, resulting in fracture occurring at lower stress levels than those observed in a tensile test[27]. In contrast, overlap hybrid joints with polymer components exhibiting ductile behavior can withstand stresses in the lap-shear test

Figure 7. Lap-shear curves for PLA−HA/Ti6Al4V hybrid joint specimens. Each of the five replicate specimens is given a corresponding number in the figure legend.

that are very close to those obtained in the tensile test for the polymer component[17,18].

The good mechanical anchorage at the interface between the PLA−HA biocomposite and the structured surface of the Ti6Al4V substrate was due to the complete filling of the metal cavities with the biocomposite, as shown in the cross-section view of the PLA−HA/Ti6Al4V hybrid joint (Figure 9). In injection overmolding, the degree to which a polymer fills micro-patterns on a metal surface is contingent upon the process parameters. In general, any parameter that reduces the thickness of the frozen polymer layer and compensates for shrinkage during solidification has a positive effect[15,19]. Therefore, in the injection overmolding process of the PLA−HA/Ti6Al4V joint specimens, the barrel and mold temperatures, along with the injection speed, holding pressure, and holding time, were optimized within the PLA processing window to ensure full penetration of the polymer biocomposite into the micro-scale features on the metal surface. It is suggested that mechanical interlocking is the main adhesion mechanism for the PLA−HA/Ti6Al4V joint. Nevertheless, there is speculation that adsorption and chemical bonding may serve as possible secondary mechanisms. Interfacial adhesion is primarily influenced by the interaction between the PLA surface layer of the biocomposite part and the oxide layer of the metal surface.

Hydroxyapatite (HA) particles in the PLA−HA composite are not expected to directly affect the adhesion with the Ti6Al4V substrate. This is because, in the injection molding of polymer composites, a thin, filler-free polymer skin is formed on the surface of the composite part. This prevents contact between the HA particles of the biocomposite and the metal surface during injection overmolding of PLA−HA/Ti6Al4V hybrid joint. Chemical interactions at the joint interface may occur between the ester groups of the PLA chains and the oxide layer on the metal surface.

This hypothesis is based on a study that, through X-ray photoelectron spectroscopy (XPS) measurements and a critical review of the literature, suggested the formation of covalent bonds between polymers containing carbonyl groups and the oxide layer of metal substrates[28].

The good mechanical performance of the injection overmolded PLA–HA/Ti6Al4V joints indicates they are promising for the development of hybrid structures for biomedical applications, especially in the field of orthopedics.

Figure 8. Image of an PLA–HA/Ti6Al4V hybrid joint specimen subjected to lap-shear testing, showing the transverse brittle fracture of PLA–HA biocomposite outside the bonding zone, near the end of the metal part.

Polímeros, 35(1), e20250009, 2025

7/9

Adauto R., Oliveira G. H. M., Morozo M. A., Fiori M. A., & Canto L. B.

Figure 9. Cross-section optical microscopy image of the PLA–HA/ Ti6Al4V hybrid joint. Polymer is on the top, and metal is on the bottom.

However, in practical applications, the mechanical performance of this joint warrants further assessment with regard to additional criteria, including temperature and media exposure simulating biological systems.

4. Conclusions A methodology has been devised for fabricating a robust hybrid overlap structure consisting of a polylactide acid– hydroxyapatite (PLA−HA) biocomposite with titanium alloy Ti6Al4V. The procedure consisted of developing the PLA biocomposite with 20 wt% of nearly spherical sub-micron HA particles by melt processing, laser surface structuring of the Ti6Al4V, followed by injection overmolding of the PLA−HA biocomposite onto the surface-structured Ti6Al4V. This ensured effective anchoring of the polymer biocomposite to the metal part, leading to high shear strength in the joints, with the fracture of the polymer component occurring outside the bonding zone. The promising mechanical performance exhibited by the injection overmolded PLA−HA/Ti6Al4V joint suggests their potential for advancing hybrid structures in biomedical applications, particularly within the orthopedic field.

5. Author’s Contribution • Conceptualization – Márcio Antônio Fiori; Leonardo Bresciani Canto.

• Data curation – Renan Adauto; Gean Henrique Marcatto de Oliveira; Mário Augusto Morozo.

• Formal analysis – Renan Adauto; Gean Henrique Marcatto de Oliveira; Mário Augusto Morozo.

• Funding acquisition ​- Márcio Antônio Fiori; Leonardo Bresciani Canto.

• Investigation – ​Renan Adauto; Gean Henrique Marcatto de Oliveira; Mário Augusto Morozo.

• Methodology – Márcio Antônio Fiori; Leonardo Bresciani Canto.

• Project administration – Márcio Antônio Fiori; Leonardo Bresciani Canto.

8/9

• Resources – Márcio Antônio Fiori; Leonardo Bresciani Canto.

• Software – NA. • Supervision – Márcio Antônio Fiori; Leonardo Bresciani Canto.

• Validation – Márcio Antônio Fiori; Leonardo Bresciani Canto.

• Visualization – Renan Adauto; Gean Henrique Marcatto de Oliveira; Leonardo Bresciani Canto.

• Writing – original draft – R ​ enan Adauto; Gean Henrique Marcatto de Oliveira; Leonardo Bresciani Canto.

• Writing – review & editing – Renan Adauto; Gean Henrique Marcatto de Oliveira; Leonardo Bresciani Canto.

6. Acknowledgements This study was supported by FAPESP – São Paulo Research Foundation, Brazil (grant number 2018/24296-0), CNPq – National Council for Scientific and Technological Development, Brazil (grant numbers 309258/2020-0, 132355/2020-5 and 164791/2018-3) and CAPES – Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brazil (grant number 23038.021524.2016.88).

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) – Finance Code 001. The authors are grateful to the Laboratory of Structural Characterization (LCE/DEMa/ UFSCar) for use of the general facilities.

7. References 1. Liu, S., Qin, S., He, M., Zhou, D., Qin, Q., & Wang, H. (2020).

Current applications of poly(lactic acid) composites in tissue engineering and drug delivery. Composites. Part B, Engineering, 199, 108238. http://doi.org/10.1016/j.compositesb.2020.108238.

2. Pérez-Davila, S., Garrido-Gulías, N., González-Rodríguez, L., López-Álvarez, M., Serra, J., López-Periago, J. E., & González, P. (2023). Physicochemical properties of 3D-printed polylactic acid/hydroxyapatite scaffolds. Polymers, 15(13), 2849. http:// doi.org/10.3390/polym15132849. PMid:37447495.

3. Wang, W., Zhang, B., Li, M., Li, J., Zhang, C., Han, Y., Wang, L., Wang, K., Zhou, C., Liu, L., Fan, Y., & Zhang, X. (2021).

3D printing of PLA/n-HA composite scaffolds with customized mechanical properties and biological functions for bone tissue engineering. Composites. Part B, Engineering, 224, 109192. http://doi.org/10.1016/j.compositesb.2021.109192.

4. Zhou, H., Lawrence, J. G., & Bhaduri, S. B. (2012). Fabrication aspects of PLA-CaP/PLGA-CaP composites for orthopedic applications: A review. Acta Biomaterialia, 8(6), 1999-2016. http://doi.org/10.1016/j.actbio.2012.01.031. PMid:22342596.

5. Senatov, F. S., Niaza, K. V., Zadorozhnyy, M. Y., Maksimkin, A. V., Kaloshkin, S. D., & Estrin, Y. Z. (2016). Mechanical properties and shape memory effect of 3D-printed PLA-based porous scaffolds. Journal of the Mechanical Behavior of Biomedical Materials, 57, 139-148. http://doi.org/10.1016/j. jmbbm.2015.11.036. PMid:26710259.

6. Ferri, J. M., Jordá, J., Montanes, N., Fenollar, O., & Balart, R. (2018). Manufacturing and characterization of poly(lactic acid) composites with hydroxyapatite. Journal of Thermoplastic Composite Materials, 31(7), 865-881. http:// doi.org/10.1177/0892705717729014.

Polímeros, 35(1), e20250009, 2025

Direct-joining of a polylactide acid-hydroxyapatite biocomposite with a titanium alloy 7. Kryszak, B., Biernat, M., Tymowicz-Grzyb, P., Junka, A., Brozyna, M., Worek, M., Dzienny, P., Antonczak, A., & Szustakiewicz, K. (2023). The effect of extrusion and injection molding on physical, chemical, and biological properties of PLLA/HAp whiskers composites. Polymer, 287, 126428. http://doi.org/10.1016/j.polymer.2023.126428.

8. Watai, J. S., Calvão, P. S., Rigolin, T. R., Bettini, S. H. P., & Souza, A. M. C. (2020). Retardation effect of nanohydroxyapatite on the hydrolytic degradation of poly (lactic acid). Polymer Engineering and Science, 60(9), 2152-2162. http://doi. org/10.1002/pen.25459.

9. Abere, D. V., Ojo, S. A., Oyatogun, G. M., Paredes-Epinosa, M. B., Niluxsshun, M. C. D., & Hakami, A. (2022). Mechanical and morphological characterization of nano-hydroxyapatite (nHA) for bone regeneration: a mini review. Biomedical Engeneering Advances, 4, 100056. http://doi.org/10.1016/j. bea.2022.100056.

10. Lim, Q. R. T., Cheng, X. Y., & Wee, C. Y. (2023). An insight to the various applications of hydroxyapatite. Advanced Materials Science and Technology, 5(2), 0520879. http://doi. org/10.37155/2717-526X-0502-1.

11. Koju, N., Niraula, S., & Fotovvati, B. (2022). Additively manufactured porous Ti6Al4V for bone implants: a review.

Metals, 12(4), 687. http://doi.org/10.3390/met12040687.

12. Sidambe, A. T. (2014). Biocompatibility of advanced manufactured titanium implants-a review. Materials (Basel), 7(12), 81688188. http://doi.org/10.3390/ma7128168. PMid:28788296.

13. Fereiduni, E., Mahmoud, D., Balbaa, M., & Elbestawi, M. (2022). Laser powder bed fusion of hydroxyapatite functionalized Ti-6Al-4V biomaterial with potential biomedical applications.

Materials Letters, 326, 132973. http://doi.org/10.1016/j. matlet.2022.132973.

14. Sukhodub, L. F., Sukhodub, L. B., Simka, W., & Kumeda, M. (2019). Hydroxyapatite and brushite coatings on plasma electrolytic oxidized Ti6Al4V alloys obtained by the thermal substrate deposition method. Materials Letters, 250, 163-166. http://doi.org/10.1016/j.matlet.2019.05.018.

15. Vasconcelos, R. L., Oliveira, G. H. M., Amancio-Filho, S. T., & Canto, L. B. (2023). Injection overmolding of polymer-metal hybrid structures: a review. Polymer Engineering and Science, 63(3), 691-722. http://doi.org/10.1002/pen.26244.

16. Grujicic, M., Sellappan, V., Omar, M. A., Seyr, N., Obieglo, A., Erdmann, M., & Holzleitner, J. (2008). An overview of the polymer-to-metal direct-adhesion hybrid technologies for loadbearing automotive components. Journal of Materials Processing Technology, 197(1-3), 363-373. http://doi. org/10.1016/j.jmatprotec.2007.06.058.

17. Luiz, G. M., Oliveira, G. H. M., & Canto, L. B. (2024).

Development of polyamide 6-graphene oxide nanocomposite and direct-joining with aluminum alloy for lightweight engineering applications. Polymer Engineering and Science, 64(2), 663-674. http://doi.org/10.1002/pen.26575.

18. Oliveira, G. H. M., Morozo, M. A., Fiori, M. A., & Canto, L. B. (2024). A method for manufacturing a mechanically strong and durable hybrid structure of polyethylene–hydroxyapatite

Polímeros, 35(1), e20250009, 2025

composite and titanium alloy. Polymer Engineering and Science, 64(4), 1548-1554. http://doi.org/10.1002/pen.26644.

19. Oliveira, G. H. M., Amancio-Filho, S. T., & Canto, L. B. (2024). Processing understanding, mechanical durability and hygrothermal stability of PC/AA6061hybrid joints produced via injection overmolding. International Journal of Adhesion and Adhesives, 130, 103617. http://doi.org/10.1016/j. ijadhadh.2023.103617.

20. Morozo, M. A., Duarte, G. W., Silva, L. L., Mello, J. M. M., Zanetti, M., Colpani, G. L., Fiori, M. A., & Canto, L. B. (2023).

A Design of Experiments Approach to analyze the effects of hydroxyapatite and maleic anhydride grafted polyethylene contents on mechanical, thermal and biocompatibility properties of green high-density polyethylene-based composites. Materials Research, 26(suppl. 1), e20220548. http://doi.org/10.1590/19805373-mr-2022-0548.

21. Tanaka, F. H., Cruz, S. A., & Canto, L. B. (2018).

Morphological, thermal and mechanical behavior of sepiolitebased poly(ethylene terephthalate)/polyamide 66 blend nanocomposites. Polymer Testing, 72, 298-307. http://doi. org/10.1016/j.polymertesting.2018.10.027.

22. Sharifzadeh, E., & Maleki, M. (2022). An energy-based approach to study the aggregation/agglomeration phenomenon in polymer nanocomposites: dispersion force against interparticle cohesion. Polymer Composites, 43(8), 5145-5158. http://doi.org/10.1002/pc.26804.

23. Benhami, V. M. L., Longatti, S. M. O., Moreira, F. M. S., & Sena Neto, A. R. (2024). Biodegradation of poly(lactic acid) waste from 3D printing. Polímeros: Ciência e Tecnologia, 34(2), e20240013. doi:10.1590/0104-1428.20230058 24. Fan, Y., Nishida, H., Shirai, Y., Tokiwa, Y., & Endo, T. (2004). Thermal degradation behaviour of poly(lactic acid) stereocomplex. Polymer Degradation & Stability, 86(2), 197208. http://doi.org/10.1016/j.polymdegradstab.2004.03.001.

25. Gonçalves, L. M. G., Rigolin, T. R., Frenhe, B. M., & Bettini, S. H. P. (2020). On the recycling of a biodegradable polymer: multiple extrusion of poly (lactic acid). Materials Research, 23(5), e20200274. http://doi.org/10.1590/1980-5373-mr-2020-0274.

26. Backes, E. H., Pires, L. N., Costa, L. C., Passador, F. R., & Pessan, L. A. (2019). Analysis of the degradation during melt processing of PLA/Biosilicate® composites. Journal of Composites Science, 3(2), 52. http://doi.org/10.3390/jcs3020052.

27. Oliveira, G. H. M, Sciuti, V. F., Canto, R. B., Arneitz, S., Minkowitz, L., Amancio-Filho, S. T., & Canto, L. B. (2024).

Additive manufacturing of surface structured metal parts for high strength lightweight injection overmolded polymer-metal hybrid joints. International Journal of Adhesion and Adhesives.

28. Liu, F. C., Dong, P., Lu, W., & Sun, K. (2019). On formation of Al–O–C bonds at aluminum/polyamide joint interface.

Applied Surface Science, 466, 202-209. http://doi.org/10.1016/j. apsusc.2018.10.024.

Received: Sept. 25, 2024 Revised: Dec. 05, 2024 Accepted: Dec. 11, 2024

9/9

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20240056

Physical and mechanical evaluation of polymeric blends with residues of polypropylene masks* Anderson Ravik Santos1 , Tiago Vieira da Silva2 , Ítalo Rocha Coura3 , Patrícia Santiago de Oliveira Patrício3*  and Wanna Carvalho Fontes2*  Departamento de Engenharia Civil, Universidade Federal de Ouro Preto – UFOP, Ouro Preto, MG, Brasil 2 Departamento de Engenharia Urbana, Universidade Federal de Ouro Preto – UFOP, Ouro Preto, MG, Brasil 3 Laboratório IntechLab, Departamento de Química, Centro Federal de Educação Tecnológica de Minas Gerais – CEFET-MG, Belo Horizonte, MG, Brasil

1

*patricia@cefetmg.br; wanna.fontes@ufop.edu.br *This paper has been partially presented at the 17th Brazilian Polymer Congress, held in Joinville, SC, 29/Oct - 02/Nov/2023.

Abstract The SARS-CoV-2 Coronavirus pandemic and the rise in climate disasters have fueled a surge in disposable mask production, exacerbating waste challenges. The study proposes a sustainable pathway for recycling Non-Woven Fabric (NWF) originating from masks made of Polypropylene (PP) used as Personal Protective Equipment (PPE). Eco-friendly blends of virgin polypropylene (vPP) and recycled non-woven fabric (NWF) were produced through extrusion, and the physicochemical and mechanical properties of the blends were evaluated. The addition of NWF resulted in lower tensile and flexural strengths than vPP. However, from 50%wt of recycled NWF, the blends proved to be as stiff as, or even stiffer than, the virgin polymer. While slightly lower, the 50%wt NWF blend achieved properties close to those of vPP, making it the ideal composition for replacing PP in conventional applications. This approach offers a sustainable solution for mask recycling, reducing disposal impacts and supporting a circular economy.

Keywords: Non-Woven Fabric, pandemic waste, polymeric blend, polypropylene.

How to cite: Santos, A. R., Silva, T. V., Coura, I. R., Patrício, P. S. O., & Fontes, W. C. (2025). Physical and mechanical evaluation of polymeric blends with residues of polypropylene masks. Polímeros: Ciência e Tecnologia, 35(1), e20250010. https://doi.org/10.1590/0104-1428.20240056

1. Introduction Human activities have substantially affected natural cycles, consequently impacting the production chain and global economy. During the SARS-CoV-2 Coronavirus pandemic, the spread of the virus increased the demand for Personal Protective Equipment (PPE), such as procedure gowns and surgical masks[1,2]. According to the WHO, the global consumption of surgical masks reached 89 million per month for the health sector alone[3]. These PPEs are extensively used in surgical centers, wards, and clinics and are primarily made of Non-Woven Fabric (NWF), a polymeric material based on Polypropylene (PP). Due to the disposable nature of these products, their consumption by society has skyrocketed, particularly for masks, which are recommended for single use for up to 8 hours[4]. This has led to significant waste generation, worsening environmental issues associated with their disposal, as their decomposition can take centuries[5].

However, the demand for masks is not only due to the SARS-CoV-2 Coronavirus pandemic. Climate disasters worldwide, such as intense heat waves, wildfires, and increasingly frequent and devastating storms, have increased

Polímeros, 35(1), e20250010, 2025

the need for respiratory protection[6]. This increase in the demand for masks, along with the disposable nature of these products, has further aggravated the problem of waste generation and its environmental impact.

In this context, polymeric blends emerge as a strategic alternative for the reuse of NWF. These eco-friendly blends allow for combining individual properties of polymers, creating materials with new characteristics[7], and offer an economical option for developing new materials compared to synthesizing new polymers[8]. Incorporating recycled materials, especially residual plastics, into polymeric blends can reduce the demand for incinerations, landfills, and virgin raw materials, while conserving natural resources and promoting a circular economy[9,10]. This practice helps mitigate waste accumulation by transforming it into valueadded materials[11]. Polymer blends have wide applications in sectors such as adhesive films, electronics, biomedicine, and the automotive industry[12,13], in addition to being used in civil construction for masonry components[14] and flame retardants[15].

1/9

O O O O O O O O O O O O O O O O O

Santos, A. R., Silva, T. V., Coura, I. R., Patrício, P. S. O., & Fontes, W. C. Numerous studies confirm the feasibility of using recycled polymers in blend production, with their properties evaluated and associated with their main applications[16-19].

Generally, recycled polymer costs about 40% less than virgin polymer; thus, replacing the virgin part with recycled material reduces cost and increases competitiveness while reducing dependence on non-renewable resources and environmental preservation[20]. However, as Ohta et al.[21] demonstrated, recycled polymers exhibit inferior mechanical properties compared to other materials and virgin polymers[22]. Adding fillers or producing blends is a viable path to minimize the impact of recycling on polymer properties[23,24]. PP is one of the most commercially sold thermoplastics. It is advantageous due to its low cost, recyclability, and high thermal stability, facilitating the production of various blends[25]. However, like other polymeric materials, the recycling of PP degrades its mechanical and thermal properties due to the high temperatures and shear involved in the process[26].

Recent studies on the properties of polymer blends based on virgin (vPP) and recycled PP (rPP) demonstrate variations in mechanical properties depending on the proportions used.

Gabriel and Tiana[27] identified that the 30/70% rPP/vPP composition resulted in optimal improvement across four mechanical properties analyzed. Hyie et al.[28] found that the blend consisting of 75% vPP and 25% rPP was ideal, with a positive influence on tensile strength, elongation at break, and Young’s modulus. Stoian et al.[29] observed a 20% increase in tensile strength and elastic modulus in a blend with 50% vPP, along with improved thermal stability in all combinations compared to virgin PP. These studies highlight the potential to optimize mechanical and thermal properties in blends of vPP and rPP. Despite the widespread use of PP in polymeric blends, few studies have been conducted on incorporating rPP from NWF waste. Therefore, this work has investigated how adding rPP from NWF masks affects the physical and mechanical properties of polymeric blends.

2. Materials and Methods 2.1 Materials, engineered recycled polymer, and design for blends The commercial vPP used to prepare the polymeric blends has a flow index of 3.5 g/10 minutes and a density of 0.905 g/cm3[30]. The NWF waste (wNWF) was obtained from the controlled disposal of surgical masks. The masks, with a base weight of 0.0025 g/cm2, were purchased new and used for 24 hours. After disposal, they were washed in a Colormaq LCB semi-automatic washing machine using the Delicate wash program. They were soaked in 0.1% chlorine water for one minute for decontamination, then rinsed and air-dried[31]. After sanitization, non-PP components (elastics, metallic wires, etc.) were removed from the masks.

The obtained rPP was fragmented in a Marconi brand knife mill, model MA 580, equipped with a 1.75 mm sieve.

Mixtures of wNWF and vPP, with a total mass of 100 g, were processed according to the content indicated in Table 1. For this purpose, a Thermo Scientific laboratory single-screw extruder, model HAAKE Polylab, was used with a temperature of 175 ºC in all three heating zones and a screw speed of 45 rpm. The extruded material, with an 2/9

Table 1. Composition and Codes of Polypropylene Blends.

Samples 100vPP 75vPP25wNWF 50vPP50wNWF 25vPP75wNWF 100wNWF

vPP (wt %) 100 75 50 25 0

wNWF (wt %) 0 25 50 75 100

average diameter of 3.40 mm, was pelletized in an AXPlástico Granulator, Model AX Gran, into pellets approximately 3.70 mm in length.

Samples were molded from the pelletized grains by hot compression in a Solab brand hydraulic press, model SL11, at 180 ºC and 5 tons of closure (approximately 25 MPa) for 5 minutes. Two compression plates and a metal mold for dumbbell-shaped samples were used with the following dimensions: narrow section length of 57.0 mm, narrow section width of 13.0 mm, and thickness of 3.2 mm. After pressing, the samples were left to rest for 30 minutes under the same pressure as molding before being demolded. Figure 1 presents a flowchart of the raw materials and processes producing the blends and control samples.

2.2 Characterization of polymeric blends Tensile tests were conducted on an Instron Universal Testing Machine, model EMIC 23-20, following the standard D638[32], using a 20 kN load cell with a 50 mm/min crosshead separation speed at room temperature. The results were obtained from the arithmetic mean of 6 tested specimens, with an accuracy of 0.1%. Tensile deformation parameters, modulus of elasticity, and maximum tensile stress were evaluated. After the tests, the fracture surface morphology of the specimens was analyzed by Scanning Electron Microscopy (SEM) through the TESCAN microscope, Model VEGA 3, using secondary electrons. Before tests, the fractured specimens were gold sputtered in a QUORUM Metalizer, Model Q150R. The flexural tests followed the standard D790[33], using the same Instron Universal Testing Machine, model EMIC 23-20, with a 20 kN load cell and a test speed of 30 mm/min. The distance between supports for the flexural test was 60 mm. Flexural strength and deformation properties were determined. The results were obtained from the arithmetic mean of 6 tested specimens, with an accuracy of 0.1%.

Six specimens were also used to evaluate the water absorption percentage of the blends. Their masses were determined using a Mettler Toledo precision scale, model PG203-S. The specimens were placed in distilled water at (25 ± 2) °C for 24 hours, then removed and surface dried.

After drying, a new weighing was performed to determine the mass of the saturated samples, as indicated by the ASTM D570 standard[34].

For the thermogravimetric analysis (TGA), Shimadzu equipment, model DTG-60H, was used with a heating rate of 10 °C/min and a nitrogen atmosphere (50 ml/min).

Samples with an average mass of 9 mg were used. The pure polymers and the produced blends were evaluated, heating the equipment from room temperature to 600 °C. Differential scanning calorimetry (DSC) analyses were conducted on Polímeros, 35(1), e20250010, 2025

Physical and mechanical evaluation of polymeric blends with residues of polypropylene masks

Figure 1. Schematic representation of the blends and control samples preparation.

a DSC-60 device from Shimadzu. The samples, with an average mass of 7 mg, were analyzed in aluminum cells under a nitrogen atmosphere at a 20 mL/min flow rate.

Two heating runs were performed: (i) from room temperature up to 190 °C, holding the final temperature for 3 minutes, followed by cooling to -30 °C; (ii) from -30 °C up to 250 °C. In all stages, the heating rate was 10 °C/min. The degree of crystallinity ( X c ) was calculated using Equation 1, where it is defined as the ratio of the melting enthalpy variation of the sample ( ∆H m) to the melting enthalpy of a sample with 100% crystallinity ( ∆H 100 m ). = Xc

∆H m

∆H 100 m

× 100

(1)

−1[35] In this case, ∆H 100 . m has a constant value of 169 Jg

3. Result and Discussion The results from the uniaxial tensile test, illustrated in Figure 2a, indicate that all the blends exhibit tensile strength values that are intermediate between those of the pure polymers, as observed in other studies[29,36,37]. Specifically, the Polímeros, 35(1), e20250010, 2025

tensile strength of the blends is higher than that of recycled polypropylene (wNWF) (22.8 ± 0.9 MPa) but lower than that of virgin polypropylene (vPP) (30.5 ± 1.2 MPa). As the proportion of rPP increases in the blends, there is a decrease in tensile strength. For instance, the 25vPP75wNWF (23.2 ± 1.7 MPa) blend shows lower strength than 75vPP25wNWF (28.6 ± 1.3 MPa) and 50vPP50wNWF (26.9 ± 1.7 MPa), reducing 18.8 and 13.8%, respectively. These values suggest that the higher the recycled material content in the blend, the weaker the resulting material tends to be, likely due to polymer chain degradation from prior processing cycles.

The reduced tensile strength in polymer blends with a higher recycled content can also be attributed to the presence of macroscopic particles remaining in the rPP and to contaminants and processing aids typically present in recycled polymers.

Such materials are likely subjected to multiple thermal and mechanical stresses, which deteriorate the polymer chains, contributing to a lower performance compared to virgin plastic[38,39]. The vPP typically has higher mechanical properties due to its unaltered molecular structure, which provides greater strength. On the other hand, the recycled wNWF often exhibits slightly degraded properties due to prior processing and potential contamination, which can reduce molecular weight and some degree of polymer 3/9

Santos, A. R., Silva, T. V., Coura, I. R., Patrício, P. S. O., & Fontes, W. C. chain scission as also reported in the literature[40-42]. This intermediate strength demonstrates the influence of blending different proportions of virgin and recycled polymers, which balances the mechanical properties through the synergistic effects of the mixed polymers.

The modulus of elasticity appears relatively consistent across all samples (Figure 2b), suggesting that the vPP and wNWF blend ratios do not drastically alter the material’s stiffness. Finally, the elongation at break for vPP is higher than wNWF and blends vPP/wNWF (Figure 2a). The decrease in elongation is more pronounced when the blend has a higher content of wNWF, 25vPP75wNWF. This trend underscores the importance of considering the proportions of virgin and recycled materials in applications where elasticity and the ability to withstand deformation without fracturing are critical.

The SEM images shown in Figure 3 reveal that the inclusion of rPP affects the microstructure of the blend. The vPP exhibits

significant plastic deformation, characterized by the presence of elongated fibrils, indicative of its ductile nature. The vPP generally exhibits a ductile failure and good distribution of the matrix filaments in the deformation[43,44]. In contrast, the SEM image of the 50vPP50wNWF blend exhibits a markedly different morphology and shows a noticeably rougher surface compared to the control sample of 100% vPP. The incorporation of recycled material results in a morphology with reduced plastic deformation, displaying a more brittle behavior, as evidenced by the absence of fibrils and the presence of flat regions[44]. This suggests that the recycled content compromises the material’s ability to deform plastically. Compared to pure virgin PP, this morphological disparity typically results in reduced mechanical properties, such as lower tensile strength and reduced elasticity (Figure 2b).

Comparing these results with similar studies in the literature, all blends produced by extrusion followed by hot

Figure 2. Bar graph showing (a) tensile strength, deformation, and (b) modulus of elasticity of pure polymers vPP and wNWF and blends vPP/wNWF.

Figure 3. SEM images of the fracture surface after tensile test of the samples (a) 100vPP and (b) 50vPP50wNWF. 4/9

Polímeros, 35(1), e20250010, 2025

Physical and mechanical evaluation of polymeric blends with residues of polypropylene masks compression showed superior tensile strength compared to those made by Barbosa et al.[45], who used injection to mix vPP with wNWF provided by a plastic waste recycling company. On the other hand, these blends showed lower strength than the samples produced by Raj et al.[46] via extrusion followed by injection, using mixtures of vPP with wNWF from a municipal collection center. Therefore, the type of processing appears to be a decisive factor for the performance of the polymeric blends with vPP, being more promising when the extrusion process is combined with compression or injection. The injection products with superior mechanical properties are attributed to better compaction of the samples and the induction of molecular orientation[47,48].

The results of stress and elongation at break to blend are presented in Figure 4. It is noted that pure rPP showed a significant reduction of 37.3% in the blend strength, decreasing from 57.4 MPa to 36.0 MPa compared to vPP. Furthermore, as in the tensile test, the deformation of the blends is intermediate for wNWF compared to vPP. This decrease was expected, as wNWF has a more brittle characteristic and lower deformation capacity than virgin resin[49]. However, the properties are superior to those of wNWF. The values of the blend strength and maximum flexural deformation with higher vPP contents, 75% and 50%wt, are similar to those obtained for pure vPP, considering the standard deviation. For the blend with 75% wNWF, the obtained values were intermediate between those of the pure materials.

Table 2 presents the average values of absorption of the vPP, wNWF, and blends after 24 hours of immersion in distilled water. All blends, as well as the pure polymer, showed an absorption close to 0.01%. The control sample of wNWF showed absorption of 0.04% by mass, higher than the blends containing virgin resin. This may be due to the additives in the masks, even in small quantities. Overall, the absorption values of all samples indicate an effective interaction between the vPP and wNWF, as well as adequate coating of the blends, without the presence of pores on the surface of the specimens.

The thermogravimetric (TG) and derivative (DTG) curves of the polymeric blends and pure polymers are shown in Figure 5, and the respective temperature data are described in Table 3. The initial degradation temperatures of the samples ranged from 375.7 °C for the blend to 419.4 °C. Although thermal stability in industrial applications is influenced by

Figure 4. Bar graph of flexural Strength and deformation of blends and pure polymers.

Polímeros, 35(1), e20250010, 2025

operational temperature and exposure time, the high onset temperature of degradation further suggests that the materials have adequate thermal stability to withstand a wide range of operational temperatures[50].

The comparison between the thermal degradation curves of vPP and the blend with 25% wNWF shows similar behavior, suggesting good integration of wNWF into the vPP matrix.

In contrast, the blend with 75% wNWF exhibits a thermal profile closer to that of wNWF pure, which may indicate a predominance of the wNWF matrix over vPP. Notably, the samples with a lower proportion of wNWF demonstrate thermal degradation at temperatures lower than those of the blends with higher wNWF content and of wNWF pure, reinforcing the idea that rPP can positively contribute to the thermal stability of the blends. At the same time, vPP has a less significant effect in this regard[51].

The blend 50%wt showed a reduction of about 25 °C in thermal stability compared to pure vPP. In contrast, Stoian et al.[29] reported increased thermal stability of blends 50%wt based on vPP and industrial rPP (recycled PP). This difference in results can be attributed to the nature of the recycled PP used in the two studies. In the present work, the recycled PP came from post-consumer waste, which may have resulted in a less efficient dispersion between the polymers, forming heterogeneous regions and compromising thermal stability. This observation is supported by the Differential Scanning Calorimetry (DSC) curves (Figure 6), where during cooling (Figure 6a), two overlapping peaks can be identified, indicating that the materials are not completely mixed and that there is a phase separation, where each PP (virgin and recycled) maintains its distinct crystals, resulting in two thermal events instead of one, as observed in other

Table 2. Average absorption values (%) and respective standard deviations pure polymers vPP and wNWF and blends vPP/ wNWF. Sample 100vPP 75vPP25wNWF 50vPP50wNWF 25vPP75wNWF 100wNWF

absorption (%) 0.013±0.009 0.012±0.020 0.014±0.012 0.014±0.017 0.037±0.026

Figure 5. TG and DTG curves.

5/9

Santos, A. R., Silva, T. V., Coura, I. R., Patrício, P. S. O., & Fontes, W. C. samples. Similarly, in the second heating curve, there is a broadening in the melting for the mentioned sample, where the initial temperature is 141.80 °C, lower than the initial melting temperature of the control vPP sample, which is 145.23 °C (Figure 6b).

Meanwhile, the study by Stoian et al.[29] used recycled PP from an industrial source, which likely contained inorganic additives and fillers that act by delaying the transfer of decomposition products through mass transport. This mechanism was evidenced by the continuous increase in residual mass with the increment of the rPP proportion, which reached twice that of vPP[29]. This difference between the types of recycled PP used in the two studies highlights the importance of the specific characteristics and composition of recycled materials in determining the thermal properties and stability of the resulting polymer blends.

The Table 4 presents data on melting temperature (Tm), crystallization temperature (Tc), and crystallinity index for different blends vPP/wNWF. The analysis of the data reveals how the presence of wNWF affects the thermal and

crystallization properties of the samples. The wNWF showed higher crystalline organization, likely due to its initial fiber morphology, which may have provided additional alignment of the polymer chains. Consequently, the presence of wNWF in the blends increased both the melting and crystallization temperatures. Additionally, wNWF increases the crystallinity of the blend, but in a nonlinear behavior. This variation in crystallinity indices suggests that crystallization efficiency depends not only on the presence of wNWF but also on how it interacts with the PP matrix. In the 50vPP50wNWF blend, the drop in melting temperature can be attributed to the reduced efficiency of interaction between wNWF and the virgin PP matrix, promoting greater difficulty in structural ordering. These disruptions can weaken the chemical bonds, especially at the interfaces between the wNWF and the vPP. The chemical structure of the polymer chains, such as the presence of crystalline regions as opposed to amorphous regions, also plays a fundamental role. Higher crystallinity indicates more ordered regions with stronger intermolecular forces, which increases stiffness.

Table 3. Thermal degradation temperatures and weight loss of blends and control samples.

Sample 100vPP 75vPP25wNWF 50vPP50wNWF 25vPP75wNWF 100wNWF

T OnSet (°C) 400.99 401.38 375.71 419.40 415.38

T Mid Point (°C) 417.70 423,84 392.75 431.56 433.31

T EndSet (°C) 442.49 447.52 424.02 452.97 455.26

weight loss (%) 99.645 99.818 99.860 99.139 99.767

Table 4. Thermal properties and crystallinity index for different blends vPP/ wNWF. Sample 100vPP 75vPP25wNWF 50vPP50wNWF 25vPP75wNWF 100wNWF

Tm (°C) 154.6 156.1 157.1 150.1 162.1

Tc (°C) 119.8 119.8 120.2 120.9 122.6

Crystallinity index (%) 57.7 58.4 55.9 58.5 68.1

Figure 6. DSC curves of (a) Cooling and (b) second heating of the samples.

6/9

Polímeros, 35(1), e20250010, 2025

Physical and mechanical evaluation of polymeric blends with residues of polypropylene masks The stiffness results (Young’s modulus) obtained in the tensile and flexural tests are aligned with the crystallinity indices observed in the different samples. The samples with higher rPP (100% wNWF and 75% wNWF) showed greater stiffness, which can be explained by the higher crystallinity of these blends. However, the tensile strength, which is associated with the material’s ability to withstand stress before breaking, was negatively influenced by the lower efficiency of the blend between the wNWF and the PP matrix.

The wNWF may act as a defect point in the matrix, weakening the structure and resulting in lower tensile strength. This decrease in strength occurs because wNWF compromises the integrity of the matrix by introducing discontinuities that reduce material cohesion. On the other hand, tensile strength involves plastic deformation of the matrix, unlike stiffness, which is evaluated in the elastic regime and is, therefore, less impacted by defects caused by the presence of wNWF. The same applies to elongation at break, which reflects the material’s ability to deform before failure. Thus, while wNWF increases stiffness due to higher crystallinity, it negatively impacts tensile strength, especially at higher concentrations, due to its less efficient interaction with the PP matrix. Nonetheless, the use of wNWF remains a valuable strategy for reducing environmental impact, as it promotes sustainable solutions by incorporating waste materials into polymer blends, aligning with broader industry efforts to minimize natural resource exploitation and manage industrial waste responsibly[10,23].

4. Conclusion This study investigated the effects of combining rPP from non-woven fabric (NWF) masks (wNWF) and vPP to produce polymeric blends. The mixing was easily accomplished since they are composed of the same polymer (PP), although one is post-consumer. While preparing rPP, fragmentation in a knife mill was chosen to facilitate extrusion, as the equipment used requires manual feeding in the case of low-density materials like NWF. Although the 75vPP25wNWF sample showed behavior closer to the control vPP sample, its mechanical properties were superior to those of other studies with commercial and recycled PP blends. The addition of wNWF resulted in lower tensile and flexural strengths compared to vPP, but from 50 wt% wNWF, the blends proved to be as rigid as or more rigid than vPP, indicating less tendency to deform.

Considering also that the onset temperatures of degradation of the blends are considerably higher than those used during their production, the findings of thermal stability reinforce the viability of the blends as a sustainable alternative for managing plastic waste.

It is concluded that the production of blends contributes to a more appropriate disposal of waste, such as wNWF, than landfilling or incineration processes, which can release harmful emissions into the atmosphere and worsen the effects of climate change. Furthermore, the evaluated methodology can be extended to other hospital waste made with NWF, such as aprons and caps, offering a sustainable solution that reduces environmental impact and promotes recycling valuable resources.

Polímeros, 35(1), e20250010, 2025

5. Author’s Contribution • Conceptualization – Anderson Ravik Santos; Patrícia Santiago de Oliveira Patricio; Wanna Carvalho Fontes.

• Data curation – Anderson Ravik Santos; Ítalo Rocha Coura.

• Formal analysis – Anderson Ravik Santos; Ítalo Rocha Coura.

• Funding acquisition – Patrícia Santiago de Oliveira Patricio; Wanna Carvalho Fontes.

• I⁠ nvestigation – Anderson Ravik Santos; Ítalo Rocha Coura; Tiago Vieira da Silva.

• M ⁠ ethodology – Anderson Ravik Santos; Ítalo Rocha Coura; Tiago Vieira da Silva.

• Project administration – Patrícia Santiago de Oliveira Patricio; Wanna Carvalho Fontes.

• Resources – Patrícia Santiago de Oliveira Patricio; Wanna Carvalho Fontes • S ⁠ oftware – NA. • S ⁠ upervision – Patrícia Santiago de Oliveira Patricio; Wanna Carvalho Fontes.

• Validation –Patrícia Santiago de Oliveira Patricio; Wanna Carvalho Fontes.

• Visualization – NA. • Writing – original draft – Anderson Ravik Santos; Patrícia Santiago de Oliveira Patricio; Wanna Carvalho Fontes.

• Writing – review & editing – Patrícia Santiago de Oliveira Patricio; Wanna Carvalho Fontes.

6. Acknowledgements The authors would like to express their gratitude to PROPPI/UFOP (Pro-Rectory of Research and Innovation at the Federal University of Ouro Preto), PROPEC (Civil Engineering Post-Graduation Program), Nanolab/ UFOP, and the Intechlab/CEFET-MG (Federal Center for Technological Education) for their invaluable support in conducting the tests. Additionally, we are grateful for the collaboration of the EcoUrb Research and Extension Group – CNPq and INCT-MIDAS. Financial support was provided

by CAPES (Coordination for the Improvement of Higher Education Personnel - master’s scholarship for Anderson Ravik dos Santos, grant number 88887.581924/2020-00), CNPq (National Council for Scientific and Technological Development - scientific initiation grant awarded to Tiago Vieira da Silva), and FINEP (Financier of Studies and Projects - Reference 1636/22, Contract 01.22.0546.00).

7. References 1. Rajak, K. (2020). COVID-19 crisis prompting innovation in addressing personal protective equipment shortage. Journal of Patan Academy of Health Sciences, 7(1), 69-72. http://doi. org/10.3126/jpahs.v7i1.28867.

2. Cohen, J., & Rodgers, Y. V. D. M. (2020). Contributing factors to personal protective equipment shortages during the COVID-19 pandemic. Preventive Medicine, 141, 106263. http://doi.org/10.1016/j.ypmed.2020.106263. PMid:33017601.

7/9

Santos, A. R., Silva, T. V., Coura, I. R., Patrício, P. S. O., & Fontes, W. C. 3. Fischer, E. P., Fischer, M. C., Grass, D., Henrion, I., Warren, W. S., & Westman, E. (2020). Low-cost measurement of face mask efficacy for filtering expelled droplets during speech.

Science Advances, 6(36), eabd3083. http://doi.org/10.1126/ sciadv.abd3083. PMid:32917603.

4. Raurell-Torredà, M., Martínez-Estalella, G., Frade-Mera, M. J., Rodríguez-Rey, L. F. C., & San Pío, E. R. (2020). Reflections arising from the COVID-19 pandemic. Enfermeria Intensiva, 31(2), 90-93. http://doi.org/10.1016/j.enfie.2020.03.001.

PMid:32284182.

5. Pathak, V. M., & Navneet, (2017). Review on the current status of polymer degradation: a microbial approach. Bioresources and Bioprocessing, 4(1), 15. http://doi.org/10.1186/s40643017-0145-9.

6. D’Amato, G., Cecchi, L., D’Amato, M., & Annesi-Maesano, I. (2014). Climate change and respiratory diseases.

European Respiratory Review, 23(132), 161-169. http://doi. org/10.1183/09059180.00001714. PMid:24881071.

7. Tekade, R. R., & Vidhale, S. G. (2023). Advancement in polymer blends and composites: a comprehensive review of structural, optical, thermal and electrical attributes for multifaceted Applications. Journal of Propulsion Technology, 44(4), 7190-7201. http://doi.org/10.52783/tjjpt.v44.i4.2554.

8. Dorigato, A. (2021). Recycling of polymer blends. Advanced Industrial and Engineering Polymer Research, 4(2), 53-69. http://doi.org/10.1016/j.aiepr.2021.02.005.

9. Yousaf, A., Al Rashid, A., Polat, R., & Koç, M. (2024). Potential and challenges of recycled polymer plastics and natural waste materials for additive manufacturing. Sustainable Materials and Technologies, 41, e01103. http://doi.org/10.1016/j.susmat.2024. e01103.

10. Silva, R. N., Santos, A. R., Patrício, P. S. O., & Fontes, W. C. (2024). Development and analysis of artificial ornamental stone with industrial wastes and epoxy resin. Sustainability, 16(17), 7715. http://doi.org/10.3390/su16177715.

11. Pan, D., Su, F., Liu, C., & Guo, Z. (2020). Research progress for plastic waste management and manufacture of value-added products. Advanced Composites and Hybrid Materials, 3(4), 443-461. http://doi.org/10.1007/s42114-020-00190-0.

12. Begum, S. A., Rane, A. V., & Kanny, K. (2020). Applications of compatibilized polymer blends in automobile industry. In A. A. Ajitha & S. Thomas (Eds.), Compatibilization of polymer blends: micro and nano scale phase morphologies, interphase characterization and properties (Chap. 20, pp. 563-593).

Netherlands: Elsevier. http://doi.org/10.1016/B978-0-12816006-0.00020-7.

13. Hou, X., Chen, S., Koh, J. J., Kong, J., Zhang, Y.-W., Yeo, J. C. C., Chen, H., & He, C. (2021). Entropy-driven ultratough blends from brittle polymers. ACS Macro Letters, 10(4), 406-411. http://doi.org/10.1021/acsmacrolett.0c00844. PMid:35549235.

14. Ferreira, T., Mendes, G. A., de Oliveira, A. M., & Dias, C. G. B. T. (2022). Manufacture and characterization of Polypropylene (PP) and High-Density Polyethylene (HDPE) blocks for potential use as masonry component in civil construction.

Polymers, 14(12), 2463. http://doi.org/10.3390/polym14122463.

PMid:35746039.

15. Huang, W., Wang, K., Tu, C., Xu, X., Tian, Q., Ma, C., Fu, Q., & Yan, W. (2022). Synergistic effects of DOPO-based derivative and organo-montmorillonite on flame retardancy, thermal stability and mechanical properties of polypropylene.

Polymers, 14(12), 2372. http://doi.org/10.3390/polym14122372.

PMid:35745948.

16. Matias, Á. A., Lima, M. S., Pereira, J., Pereira, P., Barros, R., Coelho, J. F. J., & Serra, A. C. (2020). Use of recycled polypropylene/poly (ethylene terephthalate) blends to manufacture water pipes: an industrial scale study. Waste Management, 8/9

101, 250-258. http://doi.org/10.1016/j.wasman.2019.10.001.

PMid:31634811.

17. Velásquez, E. J., Garrido, L., Guarda, A., Galotto, M. J., & López de Dicastillo, C. (2019). Increasing the incorporation of recycled PET on polymeric blends through the reinforcement with commercial nanoclays. Applied Clay Science, 180, 105185. http://doi.org/10.1016/j.clay.2019.105185.

18. Koh, J. J., Zhang, X., & He, C. (2018). Fully biodegradable Poly(lactic acid)/Starch blends: a review of toughening strategies. International Journal of Biological Macromolecules, 109, 99-113. http://doi.org/10.1016/j.ijbiomac.2017.12.048.

PMid:29248552.

19. Chen, R. S., Ab Ghani, M. H., Salleh, M. N., Ahmad, S., & Gan, S. (2014). Influence of blend composition and compatibilizer on mechanical and morphological properties of recycled HDPE/ PET blends. Materials Sciences and Applications, 5(13), 943952. http://doi.org/10.4236/msa.2014.513096.

20. Fernandes, B. L., & Domingues, A. J. (2007). Caracterização mecânica de polipropileno reciclado para a indústria automotiva.

Polímeros. Ciência e Tecnologia, 17(2), 85-87. http://doi. org/10.1590/S0104-14282007000200005.

21. Ohta, H., Tohno, H., & Uruji, T. (2002). Use of recycled plastic as truck and bus component material (Technical Review, No. 14). Tokyo: Mitsubishi Motors Corporation. Retrieved in 2024, June 12, from http://mmc-manuals.ru/manuals/misc/ technical_review/technical_review_2002.pdf 22. Ladhari, A., Kucukpinar, E., Stoll, H., & Sängerlaub, S. (2021).

Comparison of properties with relevance for the automotive sector in mechanically recycled and virgin polypropylene.

Recycling, 6(4), 76. http://doi.org/10.3390/recycling6040076.

23. Santos, A. R., Silva, R. N., Santos, N. M., Vieira, M. F. C., Patrício, P. S. O., & Fontes, W. C. (2024). Production of a wood-plastic composite with wastes from disposable masks and corrugated cardboard: a sustainable post-pandemic approach.

Sustainability, 16(22), 9726. http://doi.org/10.3390/su16229726.

24. Coura, I. R., Carmignano, O. R. D. R., Heitmann, A. P., Lameiras, F. S., Lago, R. M., & Patrício, P. S. O. (2021). Use of iron mine tailing as fillers to polyethylene. Scientific Reports, 11(1), 7091. http://doi.org/10.1038/s41598-021-86456-z.

PMid:33782479.

25. Qiu, W., Zhang, F., Endo, T., & Hirotsu, T. (2003). Preparation and characteristics of composites of high-crystalline cellulose with polypropylene: effects of maleated polypropylene and cellulose content. Journal of Applied Polymer Science, 87(2), 337-345. http://doi.org/10.1002/app.11446.

26. Kim, H.-S., Lee, B.-H., Choi, S.-W., Kim, S., & Kim, H.J. (2007). The effect of types of maleic anhydride-grafted polypropylene (MAPP) on the interfacial adhesion properties of bio-flour-filled polypropylene composites. Composites.

Part A, Applied Science and Manufacturing, 38(6), 1473-1482. http://doi.org/10.1016/j.compositesa.2007.01.004.

27. Gabriel, D. S., & Tiana, A. N. (2020). Mechanical properties improvement of recycled polypropylene with material value conservation schemes using virgin plastic blends. Materials Science Forum, 1015, 76-81. http://doi.org/10.4028/www. scientific.net/MSF.1015.76.

28. Hyie, K. M., Budin, S., Martinus, N., Salleh, Z., & Masdek, N. R. N. (2019). Tensile and flexural investigation on polypropylene recycling. Journal of Physics: Conference Series, 1174, 012005. http://doi.org/10.1088/1742-6596/1174/1/012005.

29. Stoian, S. A., Gabor, A. R., Albu, A.-M., Nicolae, C. A., Raditoiu, V., & Panaitescu, D. M. (2019). Recycled polypropylene with improved thermal stability and melt processability. Journal of Thermal Analysis and Calorimetry, 138(4), 2469-2480. http:// doi.org/10.1007/s10973-019-08824-2.

Polímeros, 35(1), e20250010, 2025

Physical and mechanical evaluation of polymeric blends with residues of polypropylene masks 30. Braskem. (2017). Data sheet: polypropylene H 503. Retrieved in 2024, June 12, from https://www.braskem.com.br/buscade-produtos?p=314 31. World Health Organization – WHO. (2020). Advice on the use of masks in the context of COVID-19: interim guidance.

Geneva: WHO. Retrieved in 2024, June 12, from https://iris. who.int/handle/10665/332293 32. American Society for Testing and Materials – ASTM. (2014).

ASTM D638-14: standard test method for tensile properties of plastics. West Conshohocken: ASTM. 33. American Society for Testing and Materials – ASTM. (2007).

ASTM D790-07: standard test methods for flexural properties of unreinforced and reinforced plastics and electrical insulating materials. West Conshohocken: ASTM. 34. American Society for Testing and Materials – ASTM. (1998).

ASTM D570-98: standard test method for water absorption of plastics. West Conshohocken: ASTM. 35. Lanyi, F. J., Wenzke, N., Kaschta, J., & Schubert, D. W. (2020).

On the determination of the enthalpy of fusion of α-crystalline isotactic polypropylene using differential scanning calorimetry, X-ray diffraction, and fourier-transform infrared spectroscopy: an old story revisited. Advanced Engineering Materials, 22(9), 1900796. http://doi.org/10.1002/adem.201900796.

36. Traxler, I., Kaineder, H., & Fischer, J. (2023). Simultaneous modification of properties relevant to the processing and application of virgin and post-consumer polypropylene. Polymers, 15(7), 1717. http://doi.org/10.3390/polym15071717. PMid:37050331.

37. Tratzi, P., Giuliani, C., Torre, M., Tomassetti, L., Petrucci, R., Iannoni, A., Torre, L., Genova, S., Paolini, V., Petracchini, F., & Di Carlo, G. (2021). Effect of hard plastic waste on the quality of recycled polypropylene blends. Recycling, 6(3), 58. http://doi.org/10.3390/recycling6030058.

38. Zander, N. E., Gillan, M., Burckhard, Z., & Gardea, F. (2019).

Recycled polypropylene blends as novel 3D printing materials.

Additive Manufacturing, 25, 122-130. http://doi.org/10.1016/j. addma.2018.11.009.

39. Handayani, S. U., Fahrudin, M., Mangestiyono, W., & Muhamad, A. F. H. (2021). Mechanical properties of commercial recycled polypropylene from plastic waste. Journal of Vocational Studies on Applied Research, 3(1), 1-4. http://doi.org/10.14710/jvsar. v3i1.10868.

40. Bahlouli, N., Pessey, D., Raveyre, C., Guillet, J., Ahzi, S., Dahoun, A., & Hiver, J. M. (2012). Recycling effects on the rheological and thermomechanical properties of polypropylenebased composites. Materials & Design, 33, 451-458. http:// doi.org/10.1016/j.matdes.2011.04.049.

41. Jones, H., McClements, J., Ray, D., Hindle, C. S., Kalloudis, M., & Koutsos, V. (2023). Thermomechanical properties of virgin and recycled polypropylene: high-density polyethylene blends. Polymers, 15(21), 4200. http://doi.org/10.3390/ polym15214200. PMid:37959880.

42. Bernagozzi, G., Arrigo, R., Ponzielli, G., & Frache, A. (2024).

Towards effective recycling routes for polypropylene: influence of a repair additive on flow characteristics and processability.

Polímeros, 35(1), e20250010, 2025

Polymer Degradation & Stability, 223, 110714. http://doi. org/10.1016/j.polymdegradstab.2024.110714.

43. Mohamad, N., Abd Latiff, A., Abd Razak, J., Ab Maulod, H. E., Liew, P. J., Kasim, M. S., & Ahsan, Q. (2021). Morphological characteristics and wear mechanism of recycled carbon fibre prepreg reinforced polypropylene composites. Malaysian Journal on Composites Science and Manufacturing, 5(1), 1-10. http://doi.org/10.37934/mjcsm.5.1.110.

44. Caicedo, C., Vázquez-Arce, A. R., Ossa, O. H., De La Cruz, H., & Maciel-Cerda, A. (2018). Physicomechanical behavior of composites of polypropylene, and mineral fillers with different process cycles. Dyna, 85(207), 260-268. http://doi. org/10.15446/dyna.v85n207.71894.

45. Barbosa, L. G., Piaia, M., & Ceni, G. H. (2017). Analysis of impact and tensile properties of recycled polypropylene.

International Journal of Materials Engineering, 7(6), 117-120. http://doi.org/10.5923/j.ijme.20170706.03.

46. Raj, M. M., Patel, H. V., Raj, L. M., & Patel, N. K. (2013).

Studies on mechanical properties of recycled polypropylene blended with virgin polypropylene. International Journal of Science Innovations Today, 2(3), 194-203. Retrieved in 2024, June 12, from http://www.ijsit.com/admin/ijsit_files/STUDIES%20 ON%20MECHANICAL%20PROPERTIES%20OF%20 RECYCLED%20POLYPROPYLENE%20BLENDED%20 WITH%20VIRGIN%20POLYPROPYLENE_IJSIT_2.3.3.pdf 47. Pantani, R., Sorrentino, A., Speranza, V., & Titomanlio, G. (2004). Molecular orientation in injection molding: experiments and analysis. Rheologica Acta, 43(2), 109-118. http://doi. org/10.1007/s00397-003-0325-8.

48. Sha, B., Dimov, S., Griffiths, C., & Packianather, M. S. (2007).

Investigation of micro-injection moulding: factors affecting the replication quality. Journal of Materials Processing Technology, 183(2-3), 284-296. http://doi.org/10.1016/j. jmatprotec.2006.10.019.

49. Wang, K., Addiego, F., Bahlouli, N., Ahzi, S., Rémond, Y., & Toniazzo, V. (2014). Impact response of recycled polypropylene-based composites under a wide range of temperature: effect of filler content and recycling. Composites Science and Technology, 95, 89-99. http://doi.org/10.1016/j. compscitech.2014.02.014.

50. Mourad, A.-H. I. (2010). Thermo-mechanical characteristics of thermally aged polyethylene/polypropylene blends.

Materials & Design, 31(2), 918-929. http://doi.org/10.1016/j. matdes.2009.07.031.

51. Luna, C. B. B., Silva, W. A., Araújo, E. M., Silva, L. J. M. D., Melo, J. B. D. C. A., & Wellen, R. M. R. (2022). From waste to potential reuse: mixtures of polypropylene/recycled copolymer polypropylene from industrial containers: seeking sustainable materials. Sustainability, 14(11), 6509. http://doi. org/10.3390/su14116509.

Received: June 12, 2024 Revised: Dec. 06, 2024 Accepted: Dec. 14, 2024

9/9

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20240072

Thermal behavior of NBR vulcanizates activated with plant-extract-derived magnesium oxidea Arianne Aparecida da Silva1* , Ana Maria Furtado de Sousa1 , Cristina Russi Guimarães Furtado1  and Nakédia M. F. Carvalho1  Instituto de Química, Universidade do Estado do Rio de Janeiro – UERJ, Rio de Janeiro, RJ, Brasil

1

*ariannesilvado20201@ppgq.uerj.br This paper has been partially presented at the 17th Brazilian Polymer Congress, held in Joinville, SC, 29/Oct - 02/Nov/2023

a

Abstract This study compares the thermal degradation and aging resistance of NBR compounds activated with ZnO or MgO-green synthesized with the assistance of Camellia sinensis extract. Thermal degradation was studied using the Flynn-WallOzawa method. Aging resistance was investigated by the changes in crosslink density and mechanical properties before and after the samples are exposed in a forced-air oven at 100 °C/72 h. The activation energies for NBR compounds with MgO-green and ZnO are, respectively, 220 kJ mol-1 and 700–200 kJ mol-1. After oxidative-thermal aging, the crosslink density of NBR compounds goes up by 24% with MgO-green and 120% with ZnO. Consequently, the changes in hardness and tensile properties of the NBR with MgO-green are more subtle than those observed with ZnO. Based on Fisher’s minimum significant difference procedure, the data analysis shows that MgO-green can be used instead of ZnO as an activator in the vulcanization of NBR. Keywords: activator, green magnesium oxide, NBR, thermal behavior, zinc oxide.

How to cite: Silva, A. A., Sousa, A. M. F., Furtado, C. R. G., & Carvalho, N. M. F. (2025). Thermal behavior of NBR vulcanizates activated with plant-extract-derived magnesium oxide. Polímeros: Ciência e Tecnologia, 35(1), e20250011. https://doi.org/10.1590/0104-1428.20240072

1. Introduction Nitrile rubber (NBR) is a synthetic elastomer with excellent resistance to oil and nonpolar solvents. NBR is used extensively in the automotive, aerospace, chemical, and petrochemical industries, for instance for sealing purposes[1-4].

To produce technical goods, rubber must undergo vulcanization to form a three-dimensional network. The vulcanization system in rubber formulations is complex and consists of a combination of cure agents, accelerators, and activators, with ZnO being the most employed activator[5]. Nevertheless, the use of ZnO in rubber has faced opposition due to its potential toxicity, particularly in aquatic environments[6].

Therefore, research efforts aimed that replacing ZnO with alternative oxides can contribute to solving this problem[7-9].

Many potential alternative materials were investigated for reducing or replacing the ZnO content in rubber formulations, including zinc(II) complexes[10], zinc-based activators incorporated into porous materials like Zn-clay or supported on a substrate[11,12], and environmentally friendly activators[7,13,14]. Additionally, studies are conducted to evaluate the substitution of ZnO with MgO in natural rubber and nitrile rubber to mitigate the associated toxicity of the rubber compositions[9,15,16].

MgO is a metallic oxide with a well-known crystalline phases, regular structure, ionic nature and basic properties.

Polímeros, 35(1), e20250011, 2025

It has interesting characteristics and a wide range of uses[17,18]. In our previous paper[9], we showed that the use of MgO produced by a green synthesis with the assistance of Camellia sinensis extract (also referred to as MgO-green) has the potential to replace ZnO in equivalent amounts in phr, mainly demonstrating convincing mechanical properties and higher cross-linking density. In the formulations with MgO-green compared to the formulations with ZnO, shorter initial vulcanization time, higher cross-link density, and excellent stress relaxation values were observed in the rheometric properties. However, further research must be conducted to establish the viability of replacing ZnO with MgO-green in NBR compounds.

Thermal properties are usually assessed using thermogravimetric analysis, which can provide valuable information about the decomposition kinetics of materials using an appropriate test method[19]. Isothermal (constant temperature) and/or non-isothermal (constant heating rate) methods have been reported for calculating kinetic parameters such as apparent activation energy (Ea), pre-exponential factor (A), reaction order (n), and rate constant (k)[20].

A widely used method is the Flynn–Wall–Ozawa integral isoconversional known as a model-free approach method, which allows the calculation of the activation energy using the Doyle approximation of the exponential integral[21].

1/8

O O O O O O O O O O O O O O O O O

Silva, A. A., Sousa, A. M. F., Furtado, C. R. G., & Carvalho, N. M. F. Thermal aging plays a crucial role in materials research.

Shuhaimi et al.[22] studied how the efficient (EV), semiefficient (SEV), and conventional (CV) vulcanization systems, in the presence of natural antioxidants, play a key role in the thermal degradation of natural rubber (NR) compounds. Mechanical tests including tensile and tear essays, as well as cross-link density measurements, were conducted both before and after aging. Thermal aging analysis results are influenced by variations in the vulcanization system. Sun et al.[23] studied the activation energy for thermal air degradation of hydrogenated nitrile butadiene rubber (HNBR) filled with carbon black. The authors stated that the energy barrier for the degradation of the molecular chains of HNBR under air atmosphere increases because of the high energy of carbon-carbon single bonds. Zhang et al.[24] investigated the thermal degradation of HNBR stated that the filling with sodium methacrylate decreases the diffusion rate of the decomposition products, resulting in enhancement of the thermal stability of the composites. Furthermore, elevating the sodium methacrylate content could improve the activation energy of the composites.

Motivated by developing a sustainable rubber formulation and showing the viability of replacing ZnO with MgOgreen in NBR compounds, this study aims to compare the thermal behavior of NBR/carbon black composites, activated with equal amounts in phr of ZnO or MgO-green.

To address this point, we used the Flynn-Wall-Ozawa integral isoconversional method and the thermal-oxidative aging method to investigate the NBR compounds activated with ZnO or MgO-green, and compare their activation energy for degradation, and changes in crosslink density, Shore A hardness, and tensile properties.

2. Materials and Methods 2.1 Materials – Green Synthesis Magnesium acetate tetrahydrate (Mg(CH3COO)2.4H2O) were purchased from Neon Comercial Ltda. Dehydrated leaves of Camellia Sinensis (green tea) were obtained from Midori Indústria de Chá Ltda. Acetone and isopropyl alcohol was acquired from Sigma-Aldrich and Tedia Company, respectively. The synthesis protocol and characterization of MgO-green are described in Silva et al.[9].

2.2 Materials - Rubber composite NBR N-615 (33% acrylonitrile), carbon black N330, sulfur (S), ZnO, stearic acid, N-tert-butyl-2-benzothiazolesulfenamide (TBBS) were donated by Nitriflex S.A. Indústria e Comércio.

2.3 Preparation of NBR/Carbon black composites Table 1 shows the NBR formulations (based on ASTM D3187). The compounds were prepared in a two-roll mixing mill (Luxor, model BML 150) based on the ASTM D3187 standard. Rubber Process Analyzer 2000 (Alpha Technologies) was used to determine the t90 values of all rubber composites at 160 °C in accordance with ASTM D5289. Rubber sheets (150 × 150 × 2mm) were vulcanized in a hydraulic press at 18 MPa of pressure, 160 °C of 2/8

Table 1. NBR formulation (amount in phr) (Based on ASTM D3187).

Component NBR Carbon black N330 Sulfur ZnO MgO-green (82.4% of purity) Stearic acid TBBS*

NBR-ZnO 100 40 1.5 3 1 0.7

NBR-MgO-green 100 40 1.5 3.6 1 0.7

*N-tert-butyl-2-benzothiazole-sulfenamide.

temperature, and t90 time. The experimental code used was NBR-X, where X is ZnO or MgO-green.

2.4 Flynn-Wall-Ozawa integral isoconversional method The pyrolysis of NBR/carbon black composites was carried out in a thermogravimetric analyzer (Q50, TA Instruments) with a scanning temperature from 25 to 600 °C and a heating rate of 5, 10, or 30 °C/min under nitrogen atmosphere. The activation energy of vulcanizate decomposition was computed using Equation 1 based on the Flynn-Wall-Ozawa method[21] outlined in ASTM E1641.  − R  dln β Ea =    b d 1    T 

(1)

wherein Ea is the estimated activation energy, R is the universal gas constant, b is the constant assuming n = 1, β is the heating rate (°C/min), and T is the temperature of weight loss (°C). The Ea can be determined using the slope between lnß and 1/T at a constant weight loss. Given that the goal of our study is to investigate the impact of cross-linking on pyrolysis, this analysis focused only on the beginning of the rubber degradation. The specified weight loss values used were 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 5.0, and 20 wt%.

2.5 Thermal-oxidative aging The relative properties of the NBR/Carbon black composites were investigated by comparing the changes in crosslink density[25], Shore A hardness (ASTM D2240), and tensile properties (ASTM D412), before and after thermal aging in the presence of air. The test specimens were exposed in a forced-air oven at 100 °C for 72 h, according to ASTM D573.

2.6 Cross-link density The cross-link density was determined based on solvent swelling measurements using the Flory-Rehner equation[25] (Equation 2).

 X  = −

ln (1 − v ) + v + χ v 2  r r r    1  v   V0  vr3 − r  2    

(2)

Polímeros, 35(1), e20250011, 2025

Thermal behavior of NBR vulcanizates activated with plant-extract-derived magnesium oxide wherein [X] is the cross-link density; vR is the volume fraction of rubber in a swollen vulcanized sample in equilibrium; V0 is the molar volume of the solvent (acetone: 73.4 cm3 g mol-1); χ is the interaction parameter between the solvent and the elastomer[26]. In this determination, the volume of carbon black, zinc and magnesium oxides was discounted in the value of vR.

2.7 Mechanical property Shore A hardness was measured using a Parabor hardness meter in accordance with ASTM D2240. Tensile tests were conducted on EMIC DL2000 according to ASTM D412.

Five Type C dumbbell specimens were used, and the rate of grip separation was set at 500 mm min-1.

3. Results and Discussion 3.1 Thermal degradation Figure 1 shows the thermogravimetric curves for NBR-ZnO and NBR-MgO-green at a heating rate of 10 °C min-1. These curves show the weight loss and first derivative of weight loss as a function of temperature, or DTG. Figure 2 shows the only the superposition of weight loss versus temperature curves for NBR-ZnO and NBR-MgO-green at heating rates of 5, 10, and 30 °C min-1. As expected, the TGA curves shift to higher temperatures as heating rates increase.

According to Figures 1 and 2, although the curves have similar profiles, it is clear that the NBR-ZnO starts to lose mass before the NBR-MgO-green. The temperature at which a mass loss of 5% (T5%) occurs for the NBR-MgO-green is 12 °C higher than the T5% for the NBR-ZnO (Figure 1). Roy et al.

[7] observed the same behavior for natural rubber vulcanized with MgO in comparison to ZnO. Furthermore, at a heating rate of 10 °C min-1, the NBR-ZnO and NBR-MgO-green exhibit weight losses of 3.0 and 1.5%, respectively, between 150 and 300 °C (Figure 1). The temperature corresponding to the maximum degradation rate (maximum peak in DTG curves, Tmax, Figure 1) is similar to the two NBR compounds since the difference between the two NBR compounds is 4 °C. The Tmax values shown in Figure 1 are in line with the findings

of Lee et al.[27], who reported a temperature of 456 °C for NBR (34% of acrylonitrile) compounds that were filled with 55 phr carbon black and activated with 5 phr of zinc oxide.

The finding about the difference in initial thermal degradation behavior of NBR-MgO-green and NBR-ZnO is particularly interesting, given that the only difference between these two samples is the type of oxide used as activator. A possible reason for this behavior is that ZnO and MgO drive the vulcanization processes differently, resulting in the formation of different types of chemical links and/ or by-products, and consequently, the activation energies required to start the degradation of NBR composite would be different. So, to investigate the hypothesis further, a pyrolysis kinetic study is conducted utilizing the Flynn-Wall-Ozawa model (Equation 1), which employs a model-free kinetic isoconversional approach[28,29].

The investigation of the pyrolysis kinetics for NBR-ZnO and NBR-MgO-green involves plotting the ln (β) against 1/T graphs for weight losses in the early stages of degradation (0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 5.0, and 20 wt%), as shown in Figure 3. The apparent activation energy (Ea) at a specific conversion can be derived from the slop ln (β) against 1/T. The results shown in Table 2 demonstrate the very strong correlation coefficient, showing that the model describes the experimental data properly. Figure 4 shows the comparison of Ea values for the two composites.

The Ea values for NBR-MgO-green range around 220 kJ/ mol during the early stages of degradation, whereas Ea values for NBR-ZnO tend to decrease as the conversion proceeds from 0.5 to 5%wt. Furthermore, NBR-ZnO has greater Ea values than NBR-MgO-green, with the exception of 5 and 20%wt, when they have comparable Ea values. Liu et al.

[30] said that the rubber pyrolysis initiates by the breakdown of side or end chains and defect structures, which required intense energy to be activated. Given that the rubber is the same in both composites, the differences in Ea in the early stages of pyrolysis (0.5 – 1.0%wt.) can be attributed to the types of crosslinks or defects presents in the network; thus, there is evidence that ZnO and MgO affect the products of the vulcanization reaction in different ways, confirming the

Figure 1. TGA curves of (a) NBR-ZnO and (b) NBR-MgO-green at a heating rate of 10 °C min-1.

Polímeros, 35(1), e20250011, 2025

3/8

Silva, A. A., Sousa, A. M. F., Furtado, C. R. G., & Carvalho, N. M. F.

Figure 2. TGA at different heating rates of (a) NBR-ZnO; (b) NBR-MgO-green.

Figure 3. Ln (β) variation as a function of 1/T for composite with: (a) NBR-ZnO and (b) NBR- MgO-green.

previous hypothesis. Ren et al.[31] investigated the effect of conventional (CV), semi-efficient (SEV), and efficient (EV) 4/8

system curing on the thermal degradation of sulfur-cured natural rubber using the Flynn-Wall-Ozawa method for Polímeros, 35(1), e20250011, 2025

Thermal behavior of NBR vulcanizates activated with plant-extract-derived magnesium oxide Table 2. Activation energy (Ea) by Flynn–Wall–Ozawa method.

Weight loss (wt%)

NBR-ZnO

NBR-MgO-green

Ea (kJ/mol)

R2

Ea (kJ/mol)

R2

700 614 427 411 352 309 194 211

0.8314 0.8786 0.8975 0.9430 0.9493 0.9623 0.9991 0.9954

272 242 237 215 196 194 205 215

0.8910 0.9404 0.9463 0.9647 0.9660 0.9551 0.9997 0.9969

0.5 0.6 0.7 0.8 0.9 1 5 20

Table 3. Cross-link Density of NBR composites before (B) and after (A) aging.

Composite NBR-ZnO (B) NBR-ZnO (A) NBR-MgO-green (B) NBR-MgO-green (A)

Figure 4. Activation energy (Ea) behavior for NBR-ZnO and NBR-MgO-green.

conversion rates ranging from 5 to 40%. According to the authors, the Ea increases in the following order CV > SEV > EV. Given that the CV system is used in this study, and based on Ren et al.’s results[31], the higher activation energy of NBR-ZnO compared to NBR-MgO-green by only 0.5 to 1%wt (Figure 4) can be attributed to the presence of defects in the network, and the amount of polysulfide linkages in NBR-MgO-green may be slightly higher than in NBR-ZnO.

3.2 Thermal-oxidative aging Thermal-oxidative aging study is an essential test for assessing and comparing materials designed for industrial applications. Exposure of rubber material to oxidative thermal aging often results in changes in cross-links densities and mechanical properties. An increase in cross-link density leads to higher hardness and a decrease in final elongation[32-35].

The cross-links densities of NBR-ZnO and NBR-MgOgreen before (B) and after (A) thermal-oxidative aging in a forced-air oven at 100 °C for 72 h are shown in Table 3.

Prior to thermal aging, NBR-MgO-green has a slightly higher cross-link density than NBR-ZnO. After oxidative-thermal aging, the crosslink density of NBR-ZnO increased and surpassed that of NBR-MgO-green. This result suggests Polímeros, 35(1), e20250011, 2025

Crosslink Density (mol cm-3) 3.8E-04 8.4E-04 5.9E-04 7.3E-04

the occurrence of extra cross-linking in both samples, but with greater intensity in NBR-ZnO. Figure 5 shows the mean plot of hardness Shore A, stress at 100% of strain, tensile strength, and ultimate elongation of NBR-ZnO and NBR-MgO-green before and after thermal-oxidative aging. The intervals of mean of mechanical properties were calculated based on Fisher’s least significant difference (LSD) procedure[36]. In this method, if two means are the same, their intervals will overlap 95.0% of the time.

For example, Han et al.[33] studied thermo-oxidative aging in NBR composites through cross-link density and mechanical properties. Thermal oxidative aging was carried out with aging at 125, 135, and 150 °C and aging time of 10, 22, 34, 46, 58, and 70 h. The crosslink density increased as the temperature and heating time increased, associated with oxidative cross-linking reactions of unsaturated bonds in the NBR molecular chains. Tensile strength gradually decreased[33].

Hardness increased after thermal aging in line with the cross-link density, observed in Figure 5a, with a more significant increase in the NBR-ZnO composite. The stress at 100% strain before aging the compositions had similar values and after aging it increased for both compositions in agreement with the increase in cross-links also after aging.

And this increase in tension at 100% strain is greater for NBR-ZnO, observed in Figure 5b, as it presented higher values in the crosslinking network with aging, as shown in Table 3. The Tensile strength before heating presented similar values for the compositions, after aging the influence of cross-link density also influenced the increase in the value for the NBR-ZnO composite. The increase in crosslink density also had an effect on the ultimate elongation, decreasing the values in both compositions after aging (Figure 5d). Overall NBR composition with ZnO and MgOgreen exhibited good aging resistance. The NBR-MgO were 5/8

Silva, A. A., Sousa, A. M. F., Furtado, C. R. G., & Carvalho, N. M. F.

Figure 5. Mechanical properties before (B) and after (A) Thermal Aging: (a) Shore A Hardness, (b) Stress at 100% of Strain, (c) Tensile Strength, and (d) Ultimate Elongation.

less sensitive to changes when compared to the difference in property values after thermal aging. This sensitivity of the NBR-ZnO composites is related to the fact that the difference in cross-link density after and before ageing is much greater than for the NBR-MgO-green compositions.

4. Conclusions The possibility of replacing the current ZnO activator in the vulcanization system with green-MgO synthesized by a more ecologically viable route was investigated in this study, focusing on thermal behavior. The conclusion was that MgO-green is a promising and valuable activator to replace ZnO. A lower sensitivity with thermal aging when compared to ZnO showed a potential improvement in the thermal stability of the MgO-green, especially in general in the mechanical properties based on Fisher’s least significant difference (LSD) procedure.

5. Author’s Contribution • Conceptualization – Ana Maria Furtado de Sousa; Nakédia Maysa Freitas Carvalho.

• Data curation – Arianne Aparecida da Silva.

• Formal analysis – Arianne Aparecida da Silva.

• Funding acquisition ​- Ana Maria Furtado de Sousa; Nakédia Maysa Freitas Carvalho.

• Investigation – ​Arianne Aparecida da Silva.

6/8

• Methodology – NA. • Project administration – Cristina Russi Guimarães Furtado.

• Resources – Ana Maria Furtado de Sousa; Nakédia Maysa Freitas Carvalho.

• Software – NA. • Supervision – Cristina Russi Guimarães Furtado.

• Validation – NA. • Visualization – NA. • Writing – original draft – Arianne Aparecida da Silva.

• Writing – review & editing – Ana Maria Furtado de Sousa; Nakédia Maysa Freitas Carvalho; Cristina Russi Guimarães Furtado.

6. Acknowledgements The authors thank Nitriflex for donating the raw materials and for the use of its facilities. This study was supported by the CAPES) [Financing code 001,: PhD Scholarship received by Arianne A. da Silva]; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPQ) [P2-309461/2021-9 received by Ana Maria Furtado de Sousa and PQ-2/2021: 316550/2021–3 received by Nakédia M. F. Carvalho] and Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro – FAPERJ [CNE 2021: E-26/200.416/2023 and Grupos Emergentes 2019: E-26/010.002171/2019 received by Nakédia M. F. Carvalho; APQ1 2019: Polímeros, 35(1), e20250011, 2025

Thermal behavior of NBR vulcanizates activated with plant-extract-derived magnesium oxide E-26/010.001927/2019 received by Ana Maria Furtado de Sousa.

7. References 1. Lou, W., Zhang, W., Wang, H., Jin, T., & Liu, X. (2018). Influence of hydraulic oil on degradation behavior of nitrile rubber O-rings at elevated temperature. Engineering Failure Analysis, 92, 1-11. http://doi.org/10.1016/j.engfailanal.2018.05.006.

2. Wei, X., Wu, H., Zhang, L., Zhang, S.-y., Xiao, Y., & Luo, T.-y. (2018). Failure analysis of nitrile rubber o-rings static sealing for packaging barrel. Journal of Failure Analysis and Prevention, 18(3), 628-634. http://doi.org/10.1007/s11668018-0451-3.

3. Chopra, A., & Singh, S. (2022). Major application and impact after modified bituminous with nitrile rubber and thermoset: an analysis. Materials Today: Proceedings, 51(Pt 1), 977-987. http://doi.org/10.1016/j.matpr.2021.07.021.

4. Ghamarpoor, R., & Jamshidi, M. (2022). Preparation of superhydrophobic/superoleophilic nitrile rubber (NBR) nanocomposites contained silanized nano silica for efficient oil/water separation. Separation and Purification Technology, 291, 120854. http://doi.org/10.1016/j.seppur.2022.120854.

5. Zou, Y., Sun, Y., He, J., Tang, Z., Zhu, L., Luo, Y., & Liu, F. (2016). Enhancing mechanical properties of styrene–butadiene rubber/silica nanocomposites by in situ interfacial modification with a novel rare-earth complex. Composites. Part A, Applied Science and Manufacturing, 87, 297-309. http://doi.org/10.1016/j. compositesa.2016.05.006.

6. Mostoni, S., Milana, P., Di Credico, B., D’Arienzo, M., & Scotti, R. (2019). Zinc-based curing activators: new trends for reducing zinc content in rubber vulcanization process.

Catalysts, 9(8), 664. http://doi.org/10.3390/catal9080664.

7. Roy, K., Alam, M. N., Mandal, S. K., & Debnath, S. C. (2015).

Preparation of zinc‐oxide‐free natural rubber nanocomposites using nanostructured magnesium oxide as cure activator.

Journal of Applied Polymer Science, 132(43), app.42705. http://doi.org/10.1002/app.42705.

8. Zanchet, A., Sousa, F. D. B., Crespo, J. S., & Scuracchio, C. H. (2018). Activator from sugar cane as a green alternative to conventional vulcanization additives. Journal of Cleaner Production, 174, 437-446. http://doi.org/10.1016/j.jclepro.2017.10.329.

9. Silva, A. A., Rocha, E. B. D., Furtado, C. R. G., Sousa, A. M. F., & Carvalho, N. M. F. (2021). Magnesium oxide biosynthesized with Camellia sinensis extract as activator in nitrile rubber vulcanization. Polymer Bulletin, 78(11), 6205-6219. http:// doi.org/10.1007/s00289-020-03430-x.

10. Przybyszewska, M., Zaborski, M., Jakubowski, B., & Zawadiak, J. (2009). Zinc chelates as new activators for sulphur vulcanization of acrylonitrile-butadiene elastomer. Express Polymer Letters, 3(4), 256-266. http://doi.org/10.3144/expresspolymlett.2009.32.

11. Heideman, G., Noordermeer, J. W. M., Datta, R. N., & Van Baarle, B. (2003). Modified clays as activator in sulphur vulcanisation: A novel approach to reduce zinc oxide levels in rubber compounds. Kautschuk und Gummi, Kunststoffe, 56(12), 650.

12. Heideman, G., Noordermeer, J. W. M., Datta, R. N., & Van Baarle, B. (2004). Zinc loaded clay as activator in sulfur vulcanization: a new route for zinc oxide reduction in rubber compounds. Rubber Chemistry and Technology, 77(2), 336355. http://doi.org/10.5254/1.3547827.

13. Moresco, S., Giovanela, M., Carli, L. N., & Crespo, J. S. (2016). Development of passenger tire treads: reduction in zinc content and utilization of a bio-based lubricant. Journal of Cleaner Production, 117, 199-206. http://doi.org/10.1016/j. jclepro.2016.01.013.

Polímeros, 35(1), e20250011, 2025

14. Zanchet, A., Demori, R., Sousa, F. D. B., Ornaghi, H. L., Jr., Schiavo, L. S. A., & Scuracchio, C. H. (2019). Sugar cane as an alternative green activator to conventional vulcanization additives in natural rubber compounds: thermal degradation study. Journal of Cleaner Production, 207, 248-260. http:// doi.org/10.1016/j.jclepro.2018.09.203.

15. Alam, M. N., Kumar, V., & Park, S.-S. (2022). Advances in rubber compounds using ZnO and MgO as co-cure activators.

Polymers, 14(23), 5289. http://doi.org/10.3390/polym14235289.

PMid:36501682.

16. Silva, A. A., Rocha, E. B. D., Linhares, F. N., Sousa, A. M. F., Carvalho, N. M., & Furtado, C. R. G. (2022). Replacement of ZnO by ecofriendly synthesized MgO in the NBR vulcanization.

Polymer Bulletin, 79(10), 8535-8549. http://doi.org/10.1007/ s00289-021-03921-5.

17. Pilarska, A. A., Klapiszewski, Ł., & Jesionowski, T. (2017).

Recent development in the synthesis, modification and application of Mg(OH)2 and MgO: A review. Powder Technology, 319, 373-407. http://doi.org/10.1016/j.powtec.2017.07.009.

18. Hornak, J., Trnka, P., Kadlec, P., Michal, O., Mentlík, V., Šutta, P., Csányi, G. M., & Tamus, Z. Á. (2018). Magnesium oxide nanoparticles: dielectric properties, surface functionalization and improvement of epoxy-based composites insulating properties. Nanomaterials (Basel, Switzerland), 8(6), 381. http://doi.org/10.3390/nano8060381. PMid:29848967.

19. Flynn, J. H., & Wall, L. A. (1966). A quick, direct method for the determination of activation energy from thermogravimetric data. Journal of Polymer Science. Part B: Polymer Letters, 4(5), 323-326. http://doi.org/10.1002/pol.1966.110040504.

20. Rajeshwari, P. (2016). Kinetic analysis of the non-isothermal degradation of high-density polyethylene filled with multi-wall carbon nanotubes. Journal of Thermal Analysis and Calorimetry, 123(2), 1523-1544. http://doi.org/10.1007/s10973-015-5021-2.

21. Erbetta, C. D. C., Azevedo, R. C. S., Andrade, K. S., Silva, M. E. S. R., Freitas, R. F. S., & Sousa, R. G. (2017). Characterization and lifetime estimation of high density polyethylene containing a prodegradant agent. Materials Sciences and Applications, 8(13), 979-991. http://doi.org/10.4236/msa.2017.813072.

22. Shuhaimi, N. H. H., Ishak, N. S., Othman, N., Ismail, H., & Sasidharan, S. (2014). Effect of different types of vulcanization systems on the mechanical properties of natural rubber vulcanizates in the presence of oil palm leaves-based antioxidant.

Journal of Elastomers and Plastics, 46(8), 747-764. http://doi. org/10.1177/0095244313489910.

23. Sun, J., Wang, X., & Zong, C. (2020). Evaluation of hot air degradation activation energy of carbon black filled hydrogenated nitrile butadiene rubber using Flynn-Wall-Ozawa approach.

IOP Conference Series: Earth and Environmental Science, 514, 052002. http://doi.org/10.1088/1755-1315/514/5/052002.

24. Zhang, J., Li, J., Liu, M., Zhao, Y., & Wang, S. (2016). Thermal decomposition kinetics and mechanism of low-temperature hydrogenated acrylonitrile butadiene rubber composites with sodium methacrylate. Chemical Research in Chinese Universities, 32(6), 1045-1051. http://doi.org/10.1007/s40242-016-6148-9.

25. Hwang, W.-G., Wei, K.-H., & Wu, C.-M. (2004). Mechanical, thermal, and barrier properties of NBR/organosilicate nanocomposites. Polymer Engineering and Science, 44(11), 2117-2124. http://doi.org/10.1002/pen.20217.

26. Oliveira, I. T., Pacheco, É. B. A. V., Visconte, L. L. Y., Oliveira, M. R., & Rubinger, M. M. M. (2010). Effect of a new accelerator of vulcanization in the rheometric properties of nitrile rubber compositions with different AN amounts. Polímeros: Ciência e Tecnologia, 20(5), 366-370. http://doi.org/10.1590/S010414282010005000059.

27. Lee, Y. S., & Ha, K. (2021). Effects of acrylonitrile content on thermal characteristics and thermal aging properties of carbon 7/8

Silva, A. A., Sousa, A. M. F., Furtado, C. R. G., & Carvalho, N. M. F. black-filled NBR composite. Journal of Elastomers and Plastics, 53(5), 402-416. http://doi.org/10.1177/0095244320941243.

28. Hong, I. K., & Lee, S. (2013). Cure kinetics and modeling the reaction of silicone rubber. Journal of Industrial and Engineering Chemistry, 19(1), 42-47. http://doi.org/10.1016/j. jiec.2012.05.006.

29. Plota, A., & Masek, A. (2020). Lifetime prediction methods for degradable polymeric materials—A short review. Materials, 13(20), 4507. http://doi.org/10.3390/ma13204507 30. Liu, S., Yu, J., Bikane, K., Chen, T., Ma, C., Wang, B., & Sun, L. (2018). Rubber pyrolysis: kinetic modeling and vulcanization effects. Energy, 155, 215-225. http://doi.org/10.1016/j. energy.2018.04.146.

31. Ren, T., Wan, C., Song, P., Rodrigue, D., Zhang, Y., & Wang, S. (2024). Thermo-oxidative degradation behavior of natural rubber vulcanized by different curing systems. Chemical Engineering Science, 295, 120147. http://doi.org/10.1016/j. ces.2024.120147.

32. Krishnamurthy, S., & Balakrishnan, P. (2019). Dynamic mechanical behavior, solvent resistance and thermal degradation of nitrile rubber composites with carbon black‐halloysite nanotube hybrid fillers. Polymer Composites, 40(S2), E1612-E1621. http://doi.org/10.1002/pc.25101.

8/8

33. Han, R., Wu, Y., Quan, X., & Niu, K. (2020). Effects of crosslinking densities on mechanical properties of nitrile rubber composites in thermal oxidative aging environment.

Journal of Applied Polymer Science, 137(36), 49076. http:// doi.org/10.1002/app.49076.

34. Mengistu, T., & Pazur, R. J. (2021). The thermal oxidation of hydrogenated acrylonitrile-co-butadiene rubber from ambient to 150°C. Polymer Degradation & Stability, 188, 109574. http://doi.org/10.1016/j.polymdegradstab.2021.109574.

35. Senthilvel, K., Pasupathy, J., Kumar, A. A. J., Rathinam, N., & Prabu, B. (2022). Investigation on the ageing properties of nitrile rubber reinforced halloysite nanotubes/carbon black hybrid composites. Materials Today: Proceedings, 68(Pt 6), 2665-2675. http://doi.org/10.1016/j.matpr.2022.09.559.

36. Meier, U. (2006). A note on the power of Fisher’s least significant difference procedure. Pharmaceutical Statistics: The Journal of Applied Statistics in the Pharmaceutical Industry, 5(4), 253-263. http://doi.org/10.1002/pst.210.

PMid:17128424.

Received: Aug. 19, 2024 Revised: Dec. 03, 2024 Accepted: Dec. 17, 2024

Polímeros, 35(1), e20250011, 2025

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20240047

Polypropylene reinforced with hollow glass microspheres: effect of thermal aging and reprocessing Hiroshi Cavalcante Medeiros Koseki1 , Marlove Bergozza1 , Cristiano José de Farias Braz1 , Tatianny Soares Alves1  and Renata Barbosa1*  1 Laboratório de Polímeros e Materiais Conjugados – LAPCON, Programa de Pós-graduação em Ciência e Engenharia de Materiais, Centro de Tecnologia, Universidade Federal do Piauí – UFPI, Teresina, PI, Brasil

*rrenatabarbosa@yahoo.com

Abstract The hollow glass microspheres (HGM), exhibit low density, reduced dielectric constant, and good thermal conductivity.

This study assessed the mechanical performance of polypropylene (PP) reinforced with HGM under artificial thermal aging conditions. The compositions underwent two rounds of reprocessing in a single-screw extruder, and samples were prepared for both tensile and impact testing. Tensile specimens were subjected to thermal aging at 100 ºC for seven and 21 days. Mechanical tests were carried out on samples before and after aging, while exposed samples underwent visual inspection, optical microscopy, and Fourier transform infrared spectroscopy analysis. Visual inspection and microscopy revealed improved PP-HGM interaction due to the additives, with no deformation or damage from reprocessing. Infrared spectroscopy showed minor degradation in the PP structure post-exposure. In summary, the presence and content of HGM, reprocessing, and aging time significantly affect the mechanical properties (elastic modulus, breaking stress, elongation at break, and impact resistance).

Keywords: impac test, HGM, mechanical behavior.

How to cite: Koseki, H. C. M., Bergozza, M., Braz, C. J. F., Alves, T. S., & Barbosa, R. (2025). Polypropylene reinforced with hollow glass microspheres: effect of thermal aging and reprocessing. Polímeros: Ciência e Tecnologia, 35(1), e20250012, https://doi.org/10.1590/0104-1428.20240047

1. Introduction Polypropylene (PP), a semi-crystalline thermoplastic polymer similar to polyethylene (PE), is widely used in the plastics industry due to its versatility and processing capacity at temperatures close to 165 ºC. Its advantages include low cost, ease of molding, chemical resistance to solvents, good mechanical and thermal properties, and an excellent electrical insulators[1,2].

PP is essential in the production of plastics and is mainly used in extrusion and injection processes. However, extrusion can cause material degradation after reprocessing cycles[3]. To prevent this degeneration, multiple additives are added to the polymer matrix, improving processing and inhibiting degradation[4].

On the other hand, composites are considered an alternative to the high costs of processes for obtaining polymeric mixtures[5]. It is worth mentioning that the type of filler will directly depend on the desired properties[6].

Therefore, the application of hollow glass microspheres (HGM), which are particles 15 to 65 μm in diameter with thin walls of 0.5 to 1.5 μm containing an inert gas[7], results in unique properties such as low density (0.12 to 0.60 g/ cm3), low thermal conductivity, and a reduced dielectric constant. Its presence has minimal impact on composite processing due to the low content applied[8]. HGM have wide applications, from the manufacture of explosives to

Polímeros, 35(1), e20250012, 2025

increase their performance to cement mortars to improve thermal insulation[7].

Bharath et al.[9] evaluated the effect of HGM in HDPEbased composites and verified that the mechanical properties were considerably impacted by HGM, becoming less ductile and more rigid. In a similar vein, Niazi et al.[10] discovered that the mechanical characteristics of HGM/PP composites were influenced by the content as well as the density of HGM fillers. However, Ferreira et al.[7] discovered that the incorporation and content of HGM in hybrid composites with glass fiber based on polyamide 6 (PA6), with mass fraction maintained at 70%, significantly affected the behavior of mechanical properties and impact resistance from 5 wt% HGM. Understanding the interaction between the polymer matrix and the filler, the degradation mechanisms in the face of environmental and accelerated aging processes are essential for the development of durable materials of satisfactory quality[11]. Accelerated aging tests, which simulate weathering, processing, or service use, are an alternative to avoid high costs. These results allow a better understanding of the material’s stability[12].

Polymeric materials containing HGM could experience a reduction in mechanical properties and lose recyclability due to accelerated aging or repeated

1/9

O O O O O O O O O O O O O O O O O

Koseki, H. C. M., Bergozza, M., Braz, C. J. F., Alves, T. S., & Barbosa, R. reprocessing. Therefore, this study aims to evaluate the mechanical behavior of PP composites reinforced with HGM. The composites were reprocessed in a single-screw extrusion and artificial thermal aging for up to 21 days.

The presence and content of HGM, the reprocessing, and exposure time were evaluated using mechanical tensile and impact tests, visual inspection, optical microscopy, and Fourier transform infrared spectroscopy.

2.4. Accelerated aging The accelerated aging test followed the guidelines of ASTM D3045[14]. Test specimens were hung from the top of a Solab SL-100 (Piracicaba, SP, Brazil) oven and spaced 10 mm apart. The aging duration was divided into two withdrawal cycles of seven and 21 days, respectively, and the exposure temperature was maintained at 100 ºC (± 1 ºC). After each removal from the oven, the samples were placed in desiccators.

2. Materials and Methods

2.5 Characterizations of the systems

2.1 Materials

2.5.1 Fourier transform infrared spectroscopy (FTIR)

Polypropylene (PP) homopolymer H301, produced by Braskem (Camacari, BA, Brazil), was used as a polymer matrix. It has a melt flow index of 10 g/10 min (230°C/2.16kg - ASTM D 1238) and a density of 0.905g/ cm3.

Hollow glass microspheres (HGM) iM16K, produced by 3M Company (Maplewood, MI, USA), were used as aninorganic filler. These have a density of 0.46 g/cm3, an average diameter of 20 µm, and a crush strength of 110 MPa. Orevac CA 100, manufactured by SK Geo Centric (Seoul, South Korea), is a PP copolymer grafted with maleic anhydride (5-10 wt%) (PP-g-MA), was used as a compatibilizing agent. It has a melting point close to 167 °C, a density is 0.905 g/cm3, melt index is 10 g/10 min (190°C, 0.325 kg, ISO 1133), and a breaking strength (BS) of 22 MPa. Irganox 1010, produced by Basf (Ludwigshafen am Rhein, Germany), is a phenolic antioxidant, and was used to protect the polymer against thermo-oxidative degradation.

This antioxidant has good compatibility, high extraction resistance, and low volatility. Its density is 1.116 g/cm3, and its melting point varies between 113 and 126 °C.

FTIR was used to evaluate the chemical reactions occurring in the systems studied before and after accelerated aging, seeking to identify the functional groups present in the systems. The analyses were carried out on a Perkin-Elmer Spectrum 400 IR (Waltham, MA, USA) spectrophotometer, between 4000 and 400 cm-1 and a resolution of 4 cm-1.

2.5.2 Mechanical behavior The tensile test was carried out on an Instron Emic DL 30000 (Caxias do Sul, RS, Brazil) universal testing machine in accordance with ASTM D638[13] with a load cell of 5KN at room temperature and a crosshead speed of 50 mm/min.

At least six specimens were evaluated for each system.

Izod impact tests were performed in accordance with ASTM D256[15] using Instron Ceast Resil 5.5 (Norwood, MA, USA) equipment, operating with a 2.75J hammer at room temperature. The specimens were notched (notch depth = 2.5 mm) before impact. All results reported are a mean of six specimens.

All measurements of mechanical properties were reported as mean ± standard deviation. Analysis of Variance (Anova) was applied considering a significance level of 5% and the means were compared using the Tukey test (p < 0.05) using OriginPro 2024 software (OriginLab, Northampton, MA, USA).

2.2 Preparation of composites The systems were processed in a single-screw extruder AX Plásticos AX-16 (L/D = 26) with a temperature profile of the three zones (180, 190, and 200ºC) and a screw rotation speed of 50 rpm. The PP matrix and HGM-containing systems were mixed in two cycles in parts per hundred resin (phr) of the systems as listed in Table 1.

2.5.3 Visual aspect and optical microscopy Visual inspection was conducted before and after aging to identify surface defects on specimens, including cracks, lack of additive homogeneity, roughness, opacity, and color changes. Images were captured using a digital camera with a maximum resolution of 13 megapixels. In addition, the morphology of the specimens was evaluated using a Leica Microsystems MD500 (Wetzlar, Germany) optical microscope in reflection mode with an ICC50E capture camera and 40x magnification (200µm scale). The fracture region after tensile testing was also assessed.

2.3 Preparation of the specimen The systems specimens were injection molded with recommended dimensions for testing (type I ASTM D638[13]) using a Eurostec BL52 (Caxias do Sul, RS, Brazil) injection molding machine. The temperature profile used was 185, 190, 200, and 205 ºC. The mold temperature was set at 25°C and the cooling time was 35 seconds.

Table 1. Formulations of PP systems containing HGM, compatibilizing, and stabilizing agents.

Systems

PP

HGM (M)

Compatibilizing

Stabilizing

PP

100

-

-

-

PP/1M

100

1

5

0.05

PP/3M

100

3

5

0.05

The formulations were prepared in parts per hundred of resin (phr).

2/9

Polímeros, 35(1), e20250012, 2025

Polypropylene reinforced with hollow glass microspheres: effect of thermal aging and reprocessing

3. Results and Discussions 3.1 Spectroscopy FTIR The spectrograms of the PP filled with HGM and reprocessed before and after 21 days of aging are shown in Figure 1. The region between 4000 and 1300 cm-1 corresponds to the functional groups[16]. Generally, few absorption bands appear in this region, which refers to the bond stretching of the main functional groups, such as –OH and C=O[17].

In the region between 1400 and 1600 cm-1, there are the C=O bonds[18]. A slight attenuation of the band is observed, which suggests a slight increase in this binding through aging cycles[19].

Syakti et al.[20] noted that PP can be distinguished by peaks at 2951, 2911, and 2844 cm-1. Nevertheless, the FTIR analysis of the surface area of PP did not reveal spectra near 1740 cm-1, typically associated with carbonyl groups. The peak at 1167 cm-1 is identified as the phenolic C=O stretch, while the peak at 1376 cm-1 was assigned to the C–H bending vibration in methylene group’s (CH3)[21].

The interface between the polymeric matrix and the HGM is made through the hydroxyl group (–OH), which is on the surface of the microsphere. The bands between 2957 and 2871 cm-1 correspond to the asymmetric and symmetric axial

deformation of the hydrogen of the methyl group. The bands at 1800 and 1650 cm-1 refer to the carbonyl group, which could indicate the degradation of PP. A slight inflections could suggest the degradation of the PP[22].

The bands observed between 2970 and 2840 cm-1 correspond to the symmetric and asymmetric stretching vibrations of the aliphatic –CH2 and –CH3 groups, indicative of the organic component of PP. Conversely, the bands identified between 1300 and 880 cm-1 pertain to the inorganic phase of HGM[23,24].

Similarly, the reprocessed samples showed no significant variations, consistent with findings by Hahladakis et al.,[23] who examined the effect of additives on PP processability.

FTIR spectrograms confirmed that the chemical structure of PP was preserved, showing no indications of deterioration.

No bands were detected at 1637 and 1720 cm-1, which are attributed to the carbonyl group, in addition to the absence of peaks in the ranges of 1850–1630 (carbonyl), 1680–1620 (alkene) and 908 cm−1 (C=CH, vinyl), indicating the non-occurrence of degradation processes in polypropylene under the conditions analyzed[21].

The PP/HGM systems, aged up to 21 days, present FTIR spectra very similar to the other samples, with no notification of the presence of new peaks. Senatova et al.[25]

Figure 1. FTIR spectrograms of of PP systems filled with HGM and reprocessed: (a) and (b) before, (c) and (d) after 21 days of aging.

Legend: “1x” and “2x” correspond to the number of processing.

Polímeros, 35(1), e20250012, 2025

3/9

Koseki, H. C. M., Bergozza, M., Braz, C. J. F., Alves, T. S., & Barbosa, R. observed that PP exposed to ultraviolet radiation exhibited signs of degradation only after 1,200 hours (50 days), with the formation of a surface oxide layer that directly impacted its properties.

3.2 Morphological analysis The optical micrographs of the composites recorded at the end of each reprocessing cycle are shown in Figure 2 damage

caused to the filler for future correlations with the properties of the systems.

In all systems, the filler was distributed homogeneously in the matrix. No damage or crushing was observed in the HGM due to reprocessing in an extruder, resulting in a satisfactory index of HGM integrity. Cunha et al.[26] attributed the filler’s lack of severe damage to its uniform distribution within the polymer matrix, which reflects the material’s resilience to shear.

Figure 2. Microscopy of PP systems filled with HGM and reprocessed before and after aging for 21 days. Magnification of 40x (200µm scale). Legend: “1x” and “2x” correspond to the number of processing.

4/9

Polímeros, 35(1), e20250012, 2025

Polypropylene reinforced with hollow glass microspheres: effect of thermal aging and reprocessing While Zhang et al.[27] suggested that the substantial polarity difference between polyester resin and HGM may reduce adhesion, adversely affecting the composite’s mechanical properties. Adding silane agents can strengthen the composite’s mechanical performance and improve HGM dispersion.

After 21 days of exposure, a homogeneous distribution of the components suggested that the integrity of the microspheres was maintained, thus artificial aging was not sufficient to cause significant damage or any type of unwanted reaction in the HGM. These results align with He et al.[28] who studied accelerated aging in PP and observed increasing surface roughness over time. Notable surface degradation, with significant roughness and corrosion occurring after nine days of artificial aging and ninety days of natural aging.

On the other hand, Weingart et al.[29] reported that PP exposed to accelerated aging for 96 days at 90 ºC showed no cracks, suggesting that this aging period was insufficient to induce degradation or damage. Thus, longer thermal degradation intervals would likely be necessary to observe significant reactions. The study also confirmed PP’s high morphological stability, with crystallinity levels fluctuating—decreasing at lower temperatures and increasing with prolonged exposure to higher temperatures.

He et al.[30] evaluated the compressive strength of hollow glass microspheres as a function of hydrostatic pressure applied to epoxy-based composites. They reported that composites with a higher HGM content (50 vol%) showed mechanical stability up to a hydrostatic pressure of 40 MPa. Above this value, the microspheres fractured, drastically increasing water absorption and thermal conductivity.

These results indicate that HGM could be used in mechanical recycling conditions and that, with adequate treatment, its addition to polymer composites can greatly

improve its thermal and mechanical properties. Also, these results show that HGM has good resistance even after the reprocessing and aging conditions.

3.3 Mechanical behavior under tensile test Mechanical properties behavior of the different PP systems filled with HGM and reprocessed before and after thermal aging is listed in Table 2.

The composition-reprocessing-time interaction did not significantly (p > 0.05) affect any of the mechanical properties evaluated (elastic modulus, breaking stress, and elongation at break). The composition-aging and number of process interactions significantly affected (p < 0.05) only the breaking stress (BS). The composition-reprocessing interaction significantly affected (p < 0.05) only the elastic modulus (EM). Finally, significant effects (p < 0.05) individually were observed: (i) compositional variations affect all mechanical properties, (ii) reprocessing only changed the EM, and (iii) aging time affected BS and EB. Cunha et al.[26] reported that increasing the HGM content in composites increased the storage modulus and viscosity, in addition to significantly reducing the density of the material, a desirable characteristic for industrial applications. However, Afolabi et al.[31] pointed out that the interfacial adhesion between HGM and the matrix can be enhanced by using modifiers in the polymer matrix or on the reinforcing surface, leading to better tensile properties.

At first glance, the PP matrix’s reprocessing and aging did not yield statistically significant effects (p > 0.05) on the assessed mechanical properties. However, the presence and HGM content did demonstrate a significant impact (p < 0.05). It was conversely, reprocessing led to notable variations (p > 0.05) in systems filled with HGM.

Table 2. Mechanical properties of PP systems filled with HGM and reprocessed before and after thermal aging.

Systems

Number of processing

PP

1

2

PP/1M

1

2

PP/3M

1

2

Time

Elastic modulus

Breaking strength

(days)

(MPa)

(MPa)

Elongation at break (%)

0 7 21 0 7 21 0 7 21 0 7 21 0 7 21 0 7 21

604.10 ± 9.05a 555.78 ± 13.13cdefg 551.52 ± 15.74efgh 594.02 ± 8.68ab 557.08 ± 14.09cdef 536.60 ± 3.65fghi 577.74 ± 13.37bcd 514.70 ± 9.16ij 529.40 ± 10.35hi 563.70 ± 9.42cde 516.10 ± 5.19ij 529.60 ± 8.98hi 589.10 ± 11.7ab 504.10 ± 8.33j 557.10 ± 7.87cdef 579.30 ± 8.98abc 531.90 ± 5.36ghi 553.60 ± 7.78defgh

18.84 ± 1.67b 18.88 ± 0.80b 19.48 ± 0.98b 19.02 ± 1.03b 18.10 ± 1.72b 18.70 ± 2.43b 17.56 ± 1.57b 17.40 ± 1.62b 18.10 ± 1.01b 17.46 ± 1.19b 17.04 ± 0.67b 18.34 ± 2.23b 27.82 ± 0.66a 27.87 ± 3.62a 30.69 ± 0.94a 16.87 ± 2.42b 15.09 ± 8.18b 19.22 ± 0.40b

19.66 ± 0.45d 25.63 ± 6.24a 22.36 ± 0.92abcd 20.09 ± 1.36cd 22.92 ± 0.44abcd 22.06 ± 0.75abcd 21.47 ± 0.26abcd 24.44 ± 0.42ab 23.00 ± 0.35abcd 22.86 ± 1.64abcd 24.03 ± 0.29abc 23.90 ± 0.75abc 19.66 ± 0.73d 22.20 ± 1.55abcd 21.23 ± 0.40bcd 21.07 ± 0.46bcd 23.35 ± 0.31abcd 22.13 ± 0.29abcd

Measurements of mechanical properties were reported as mean ± standard deviation. Analysis of Variance (Anova) was applied considering a significance level of 5%. Different superscript letters indicate significant difference (p < 0.05) between the means by Tukey’s post-hoc test with a 95% significance level.

Polímeros, 35(1), e20250012, 2025

5/9

Koseki, H. C. M., Bergozza, M., Braz, C. J. F., Alves, T. S., & Barbosa, R. The most substantial decrease (16.6%) in ME values relative to PP (zero days) was observed in the PP/3M system (no reprocessing and aging for up to seven days).

Notably, in the BS assessments, significant variations were only evident in the non-reprocessed PP/3M formulation.

A notable increase (p < 0.05) of up to 62.9% in average BS value was noted for the PP/3M system aged for up to 21 days, in comparison to non-reprocessed PP (zero days).

The reduction in the EM due to the increase in HGM content was intensified. Carvalho, Canevaloro, and Sousa[32] reported similar mechanical behavior in PP hybrid composites reinforced with glass fibers and HGM, attributed to the reduction in the aspect ratio of HGM relative to glass fibers.

On the other hand, Abbas et al.[33] explored the potential of HGM and glass fibers in hybrid composites with a polyester resin matrix. They found that the addition of HGM to the resin plays a crucial role in improving the interfacial bonding between the fiber and matrix. This enhancement leads to a progressive increase in tensile strength and modulus as the HGM percentage in the resin rises. Niazi et al.[10] reported different outcomes in polyester composites reinforced with fumed silica and HGM. When specimens were reinforced with up to 20 wt% of HGM and 10 wt% of fumed silica, the authors noticed an increase in modulus, which was followed by a decrease. The potential for filler agglomeration at higher loadings, which weakened interfacial bonding and decreased reinforcement wettability, was blamed for the modulus decrease.

Sai and Tambe[34] observed that adding HGM to an acrylonitrile butadiene styrene (ABS) matrix resulted in a slight decrease in tensile strength compared to the matrix.

Highlighting more pronounced decreases for higher HGM contents. This behavior suggested the formation of clusters of microspheres due to the absence of a compatibilizing agent, which reduced the reinforcement effectiveness.

The low ability of microspheres to increase matrix stiffness is related to the microstructure of PP/HGM composites, as in hollow particles, the effective EM depends on the wall thickness of the particles and, more specifically, on the ratio of wall thickness to the size of the reinforcing particle. Similar results were found by Afolabi et al.[31] when analyzing the composites reinforced with hollow particles.

Regarding EB behavior, both the presence and variations in HGM content, as well as aging time, had a significant effect (p < 0.05) on this property. The most notable variations of 30.4% and 24.3% were recorded for the PP and PP/1M systems, not reprocessed and aged for up to seven days, respectively, concerning non-reprocessed PP (zero days).

No significant variations (p > 0.05) were observed between the other systems.

According to Jang[35], HGM behave akin to flaws within the matrix, altering the material’s behavior from ductile to brittle. This decrease in tensile strength aligns with the notion that solely the matrix opposes mechanical tensile stress, indirectly suggesting limited phase interaction and weak load transmission between the matrix and filler.

In addition, the residual thermal stresses at the interface between the matrix and reinforcement resulting from the aging test are sufficient to guarantee stress transfer[7,32].

Therefore, replacing a certain volumetric fraction of the 6/9

polymer matrix with the component with the highest EM influences the final EM of the composite.

Wang and Petru[36] observed, when evaluating the accelerated aging of PP and fiberglass samples, no significant change in mechanical properties up to 60 days of aging.

On the other hand, La Mantia et al.[37] found, when analyzing the mechanical properties of samples of virgin, recycled PP and their blends exposed to accelerated aging, that the ultimate properties decrease significantly with extended photo-oxidation time while the elastic modulus increases.

Interestingly, the PP turns ductile after 144 hours, and the sample’s higher crystallinity – brought on by macromolecular cleavage accelerating the crystallization rate – was attributed to its higher elastic modulus.

3.4 Visual aspect The macroscopic appearance of samples of PP systems filled with HGM and reprocessed before and after thermal aging after tensile testing are in Figure 3.

The largest deformations recorded occurred in the PP/1M systems in both reprocessing cycles (1x and 2x). As signaled

by Pei et al.[38] the low deformation in the PP/3HGM-1x system is due to the higher HGM content in the polymer matrices, which prevents the chains from sliding. Even with a suitable matrix/filler interaction, the rigid structure of the microspheres did not allow them to undergo pronounced elongations, such as those presented by the matrix, further restricting their deformation.

The EB is more pronounced in the PP/3M-2x system, as observed by Ferreira et al.[7] the addition of HGM to polyamide-6 (PA6) reduced the modulus of elasticity, tensile strength, and elongation at break. Similarly, Bharath et al.

[9] found behavior in extruded HDPE/HGM composites in the presence of compatibilizer and with a good interaction interface; however the increase in the amount of microspheres did not significantly change the tensile strength values of the composite.

The EB behavior was similar to that occurring in unexposed samples. The PP/2M-1x system again showed a lower EB value. The short exposure time to thermal degradation was the preponderant factor for this behavior.

3.5 Impact behavior The behavior of the impact resistance (IR) of PP systems filled with HGM and reprocessed are shown in Figure 4.

The analysis of variance (Anova) indicated that the interaction composition x reprocessing has a significant effect (p < 0.05) on the impact resistance values. Furthermore, it is also observed that variations in compositions and the amount of reprocessing act significantly (p < 0.05) on the IR. Thus, it was observed that all systems presented significantly (p < 0.05) different values compared to unprocessed PP, providing significant (p < 0.05) effects due to each processing and each applied HGM content.

No significant difference (p > 0.05) was found in the PP/1M system due to reprocessing. It was noted that reprocessing significantly (p < 0.05) increased the PP system by 36.1% and reduced the PP/3M systems by 38.5%.

Polímeros, 35(1), e20250012, 2025

Polypropylene reinforced with hollow glass microspheres: effect of thermal aging and reprocessing

Figure 3. Macrophotographs of PP systems specimens filled with HGM and reprocessed: (a) before and (b) after 21 days of aging. From left to right: (A.1) PP-1x, (A.2) PP-2x, (B.1) PP/1M-1x, (B.2) PP/1M-2x, (C.1) PP/3M-1x, and (C.2) PP/3M-1x.

Poulakis and Papaspyrides[39] reported that the degree of crystallinity of polypropylene increased after double recycling. Therefore, recycling itself may act as a form of annealing process. Nonetheless, the prior processing of the assessed samples had no appreciable impact on the mechanical properties of the assessed recycled PP. Ha and Kim[40] on the other hand, discovered that a material with a lower yield stress can more readily start the fibrillated damage zone at the notch front. The reprocessed PP (PP2x) may have a higher impact resistance (p < 0.05) due to this behavior, as the linking molecules act as local stress transmitters between the lamellae and only break when more energy is needed for the deformation or fracture.

Cosse et al.[41] reported similar results when evaluating the effects of microspheres in HDPE foams on impact resistance when differentiating processing routes: singlescrew and twin-screw extruders. These authors observed that the presence of HGM significantly increases the RI values, but the subsequent increase in the content reduces this property. However, higher values were observed than in the pure HDPE matrix. On the other hand, Ozkutlu et al.

[42] obtained opposite results in poly(methyl methacrylate) (PMMA) composites filled with HGM of different densities and sizes. They reported that in all systems, the presence of HGM reduced the IR values, and increasing the HGM content further reduced this property.

Polímeros, 35(1), e20250012, 2025

Figure 4. Impact resistence of PP systems filled with HGM and processed (once and twice). Means labeled with the same letter do not exhibit statistically significant differences, according to the Tukey test (p < 0.05).

4. Conclusions The primary question of this study aimed to answer was whether polymeric materials containing hollow glass 7/9

Koseki, H. C. M., Bergozza, M., Braz, C. J. F., Alves, T. S., & Barbosa, R. microspheres (HGM) might experience a decline in mechanical properties and a reduction in recyclability due to accelerated aging or repeated reprocessing. To address this, the present study focused on the production of polypropylene (PP) composites incorporating HGM followed by reprocessing in a single-screw extruder and artificial aging in an oven at 100°C for up to 21 days. Mechanical tests, structural analyses, and morphological analyses were carried out before and after aging. Mechanical properties were significantly influenced (p < 0.05) by the presence of HGM, reprocessing, and exposure time. Uniform distribution of HGM was observed within the PP matrix, with no signs of damage or deformation in the microspheres, indicating excellent shear resistance during extrusion. Composites containing HGM showed a slight decline in their mechanical properties. However, they shown recyclable even after accelerated aging, and surface treatment on the HGM could further improve the affinity between this filler and the PP matrix. In summary, achieving the desired mechanical properties, crucial for various applications, depends on optimizing the compatibility system and processing parameters. These composites have potential for applications where weight reduction is essential, such as replacing synthetic foams in construction.

5. Author’s Contribution ● Conceptualization – Hiroshi Cavalcante Medeiros Koseki; Renata Barbosa. ● Data curation – Hiroshi Cavalcante Medeiros Koseki; Marlove Bergozza. ● Formal analysis – Hiroshi Cavalcante Medeiros Koseki; Cristiano José de Farias Braz. ● Funding acquisition – NA. ● Investigation – Hiroshi Cavalcante Medeiros Koseki. ● Methodology – Hiroshi Cavalcante Medeiros Koseki; Marlove Bergozza. ● Project administration – Renata Barbosa. ● Resources – Renata Barbosa; Tatianny Soares Alves. ● Software – NA. ● Supervision –Renata Barbosa. ● Validation – NA. ● Visualization – NA. ● Writing – original draft – Hiroshi Cavalcante Medeiros Koseki; Cristiano José de Farias Braz. ● Writing – review & editing – Tatianny Soares Alves; Renata Barbosa.

6. Acknowledgements The authors want to acknowledge the Universidade Federal do Piauí (UFPI), National Council for Scientific and Technological Development (CNPq), and Piauí State Research Support Foundation (FAPEPI).

7. References 1. Gahleitner, M., & Paulik, C. (2017). Polypropylene and other polyolefins. In M. Gilbert (Ed.), Brydson’s plastics materials 8/9

(pp. 279-309). Oxford: Elsevier. http://doi.org/10.1016/B9780-323-35824-8.00011-6.

2. Vasile, C., & Pascu, M. (2005). Practical guide to polyethylene.

Shrewsbury: Rapra Technology.

3. Alsabri, A., Tahir, F., & Al-Ghamdi, S. G. (2022). Environmental impacts of polypropylene (PP) production and prospects of its recycling in the GCC region. Materials Today: Proceedings, 56(Pt 4), 2245-2251. http://doi.org/10.1016/j.matpr.2021.11.574.

4. Wypych, G. (2020). UV stabilizers and other components of formulations. In G. Wypych (Ed.), Handbook of UV degradation and stabilization (pp. 433-438). Toronto: ChemTec Publishing. http://doi.org/10.1016/B978-1-927885-57-4.50013-9.

5. Biswal, T., BadJena, S. K., & Pradhan, D. (2020). Synthesis of polymer composite materials and their biomedical applications.

Materials Today: Proceedings, 30(Pt 2), 305-315. http://doi. org/10.1016/j.matpr.2020.01.567.

6. DeArmitt, C., & Rothon, R. (2016). Particulate fillers, selection, and use in polymer composites. In S. Palsule (Ed.), Polymers and polymeric composites: a reference series (pp. 1-26). Berlin: Springer. http://doi.org/10.1007/978-3-642-37179-0_1-2.

7. Ferreira, T. R. M., Lechtman, M. A., Dias, F. L., & Silva, A. B. (2022). Effect of hollow glass microspheres addition on density reduction and mechanical properties of PA6/glass fibers composites. Polímeros: Ciência e Tecnologia, 32(1), e2022001. http://doi.org/10.1590/0104-1428.210060.

8. Imran, M., Rahaman, A., & Pal, S. (2019). Effect of low concentration hollow glass microspheres on mechanical and thermomechanical properties of epoxy composites. Polymer Composites, 40(9), 3493-3499. http://doi.org/10.1002/pc.25211.

9. Bharath, H. S., Bonthu, D., Prabhakar, P., & Doddamani, M. (2020). Three-dimensional printed lightweight composite foams. ACS Omega, 5(35), 22536-22550. http://doi.org/10.1021/ acsomega.0c03174. PMid:32923813.

10. Niazi, P., Karevan, M., & Javanbakht, M. (2023). Mechanical and thermal insulation performance of hollow glass microsphere (HGMS)/fumed silica/polyester microcomposite coating. Progress in Organic Coatings, 176, 107387. http://doi.org/10.1016/j. porgcoat.2022.107387.

11. Maraveas, C., Kyrtopoulos, I. V., Arvanitis, K. G., & Bartzanas, T. (2024). The aging of polymers under electromagnetic radiation.

Polymers, 16(5), 689. http://doi.org/10.3390/polym16050689.

PMid:38475374.

12. Qin, J., Jiang, J., Tao, Y., Zhao, S., Zeng, W., Shi, Y., Lu, T., Guo, L., Wang, S., Zhang, X., Jie, G., Wang, J., & Xiao, M. (2021).

Sunlight tracking and concentrating accelerated weathering test applied in weatherability evaluation and service life prediction of polymeric materials: a review. Polymer Testing, 93, 106940. http://doi.org/10.1016/j.polymertesting.2020.106940.

13. American Society for Testing and Materials – ASTM. (2022).

ASTM D638-22: standard test method for tensile properties of plastics. West Conshohocken: ASTM. 14. American Society for Testing and Materials – ASTM. (2018).

ASTM D3045-18: standard practice for heat aging of plastics without load. West Conshohocken: ASTM. 15. American Society for Testing and Materials – ASTM. (2023).

ASTM D256-23e1: standard test methods for determining the Izod pendulum impact resistance of plastics. West Conshohocken: ASTM. 16. Hay, M. B., & Myneni, S. C. B. (2007). Structural environments of carboxyl groups in natural organic molecules from terrestrial systems. Part 1: infrared spectroscopy. Geochimica et Cosmochimica Acta, 71(14), 3518-3532. http://doi.org/10.1016/j. gca.2007.03.038.

17. Larkin, P. J. (2017). Infrared and Raman spectroscopy: principles and spectral interpretation. Amsterdam: Elsevier. http://doi. org/10.1016/C2015-0-00806-1.

Polímeros, 35(1), e20250012, 2025

Polypropylene reinforced with hollow glass microspheres: effect of thermal aging and reprocessing 18. Fuente, E., Menéndez, J. A., Díez, M. A., Suárez, D., & Montes-Morán, M. A. (2003). Infrared spectroscopy of carbon materials: A quantum chemical study of model compounds.

The Journal of Physical Chemistry B, 107(26), 6350-6359. http://doi.org/10.1021/jp027482g.

19. Li, J., Wang, L., Xu, Z., Zhang, J., Li, J., Lu, X., Yan, R., & Tang, Y. (2023). A new point to correlate the multi-dimensional assessment for the aging process of microfibers. Water Research, 235, 119933. http://doi.org/10.1016/j.watres.2023.119933. PMid:37023644.

20. Syakti, A. D., Hidayati, N. V., Jaya, Y. V., Siregar, S. H., Yude, R., Suhendy, L., Asia, L., Wong-Wah-Chung, P., & Doumenq, P. (2018). Simultaneous grading of microplastic size sampling in the Small Islands of Bintan water, Indonesia. Marine Pollution Bulletin, 137, 593-600. http://doi.org/10.1016/j. marpolbul.2018.11.005. PMid:30503472.

21. Khoironi, A., Hadiyanto, H., Anggoro, S., & Sudarno, S. (2020).

Evaluation of polypropylene plastic degradation and microplastic identification in sediments at Tambak Lorok coastal area, Semarang, Indonesia. Marine Pollution Bulletin, 151, 110868. http://doi. org/10.1016/j.marpolbul.2019.110868. PMid:32056648.

22. Baptista, C. A., & Canevarolo, S. V. (2019). Grafting polypropylene over hollow glass microspheres by reactive extrusion. Polímeros: Ciência e Tecnologia, 29(3), e2019037. http://doi.org/10.1590/0104-1428.06118.

23. Hahladakis, J. N., Velis, C. A., Weber, R., Iacovidou, E., & Purnell, P. (2018). An overview of chemical additives present in plastics: migration, release, fate and environmental impact during their use, disposal and recycling. Journal of Hazardous Materials, 344, 179-199. http://doi.org/10.1016/j. jhazmat.2017.10.014. PMid:29035713.

24. Varghese, A. M., Rangaraj, V. M., Luckachan, G., & Mittal, V. (2020). UV aging behavior of functionalized mullite nanofiberreinforced polypropylene. ACS Omega, 5(42), 27083-27093. http://doi.org/10.1021/acsomega.0c02437. PMid:33134668.

25. Senatova, S. I., Senatov, F. S., Kuznetsov, D. V., Stepashkin, A. A., & Issi, J. P. (2017). Effect of UV-radiation on structure and properties of PP nanocomposites. Journal of Alloys and Compounds, 707, 304-309. http://doi.org/10.1016/j. jallcom.2016.11.170.

26. Cunha, M. P., Grisa, A. M. C., Klein, J., Poletto, M., & Brandalise, R. N. (2018). Preparation and characterization of hollow glass microspheres- reinforced poly (acrylonitrile-cobutadiene-co-styrene) composites. Materials Research, 21(6), e20180201. http://doi.org/10.1590/1980-5373-mr-2018-0201.

27. Zhang, X., Liu, M., Chen, Y., He, J., Wang, X., Xie, J., Li, Z., Chen, Z., Fu, Y., Xiong, C., & Wang, S. (2022). Epoxy resin/ hollow glass microspheres composite materials with low dielectric constant and excellent mechanical performance.

Journal of Applied Polymer Science, 139(33), e52787. http:// doi.org/10.1002/app.52787.

28. He, M., Sawut, A., Guan, L., Li, Y., & Yimit, M. (2021).

Study on the weathering performance of polypropylene by artificial accelerated aging and natural aging. Journal of Polymer Materials, 38(3-4), 191-203. http://doi.org/10.32381/ JPM.2021.38.3-4.2.

29. Weingart, N., Raps, D., Lamka, M., Demleitner, M., Altstädt, V., & Ruckdäschel, H. (2023). Influence of thermo-oxidative aging on the mechanical properties of the bead foams made of polycarbonate and polypropylene. Journal of Polymer Science, 61(21), 2742-2757. http://doi.org/10.1002/pol.20230267.

30. He, Z.-Q., Yang, Y., Yu, B., Yang, J.-P., Jiang, X.-B., Tian, B., Wang, M., Li, X.-Y., Sun, S.-Q., & Sun, H. (2022). Research on properties of hollow glass microspheres/epoxy resin composites applied in deep rock in-situ temperature-preserved coring.

Polímeros, 35(1), e20250012, 2025

Petroleum Science, 19(2), 720-730. http://doi.org/10.1016/j. petsci.2021.10.028.

31. Afolabi, O. A., Kanny, K., & Mohan, T. P. (2022). Analysis of particle variation effect on flexural properties of hollow glass microsphere filled epoxy matrix syntactic foam composites.

Polymers, 14(22), 4848. http://doi.org/10.3390/polym14224848.

PMid:36432973.

32. Carvalho, G. B., Canevarolo, S. V., Jr., & Sousa, J. A. (2020).

Influence of interfacial interactions on the mechanical behavior of hybrid composites of polypropylene / short glass fibers / hollow glass beads. Polymer Testing, 85, 106418. http://doi. org/10.1016/j.polymertesting.2020.106418.

33. Abbas, Z., Shahid, S., Nawab, Y., Shaker, K., & Umair, M. (2020). Effect of glass microspheres and fabric weave structure on mechanical performance of hemp/green epoxy composites.

Polymer Composites, 41(11), 4771-4787. http://doi.org/10.1002/ pc.25751.

34. Sai, B. L. N. K., & Tambe, P. (2022). Surface modified hollow glass microsphere reinforced 70/30 (wt/wt) PC/ABS blends: influence on rheological, mechanical, and thermo-mechanical properties. Composite Interfaces, 29(6), 617-641. http://doi.or g/10.1080/09276440.2021.1986974.

35. Jang, K.-S. (2020). Low-density polycarbonate composites with robust hollow glass microspheres by tailorable processing variables. Polymer Testing, 84, 106408. http://doi.org/10.1016/j. polymertesting.2020.106408.

36. Wang, X., & Petru, M. (2020). Degradation of bending properties of flax fiber reinforced polymer after natural aging and accelerated aging. Construction & Building Materials, 240, 117909. http://doi.org/10.1016/j.conbuildmat.2019.117909.

37. La Mantia, F. P., Mistretta, M. C., & Titone, V. (2021).

Rheological, mechanical and morphological characterization of monopolymer blends made by virgin and photo-oxidized polypropylene. Recycling, 6(3), 51. http://doi.org/10.3390/ recycling6030051.

38. Pei, L., Ya, B., Ding, Z., Fan, Z., & Zhang, X. (2023). Effect of curing agents and hollow glass microspheres on the compression properties of syntactic foams. Journal of Materials Research and Technology, 27, 5321-5331. http://doi.org/10.1016/j. jmrt.2023.11.002.

39. Poulakis, J. G., & Papaspyrides, C. D. (1997). Recycling of polypropylene by the dissolution/reprecipitation technique: I. A model study. Resources, Conservation and Recycling, 20(1), 31-41. http://doi.org/10.1016/S0921-3449(97)01196-8.

40. Ha, K. H., & Kim, M. S. (2012). Application to refrigerator plastics by mechanical recycling from polypropylene in waste-appliances. Materials & Design, 34, 252-257. http:// doi.org/10.1016/j.matdes.2011.08.014.

41. Cosse, R. L., Morais, A. C. L., Silva, L. R. C., Carvalho, L. H., Reis Sobrinho, J. F., Barbosa, R., & Alves, T. S. (2019).

Preparation of syntactic foams made from green polyethylene and glass microspheres: morphological and mechanical characterization. Materials Research, 22(Suppl 1), e20190035. http://doi.org/10.1590/1980-5373-mr-2019-0035.

42. Ozkutlu, M., Dilek, C., & Bayram, G. (2018). Effects of hollow glass microsphere density and surface modification on the mechanical and thermal properties of poly(methyl methacrylate) syntactic foams. Composite Structures, 202, 545-550. http://doi.org/10.1016/j.compstruct.2018.02.088.

Received: Apr. 25, 2024 Revised: Nov. 18, 2024 Accepted: Dec. 18, 2024

9/9

São Paulo 994 St. São Carlos, SP, Brazil, 13560-340 Phone: +55 16 3374-3949 Email: abpol@abpol.org.br 2021

2025