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Polímeros VOLUME XXX - Issue II - Apr./June, 2020

São Paulo 994 St. São Carlos, SP, Brazil, 13560-340 Phone: +55 16 3374-3949 Email: abpol@abpol.org.br 2020


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

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

and

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 Adhemar C. Ruvolo Filho (UFSCar/DQ) Ailton S. Gomes (UFRJ/IMA) Alain Dufresne (Grenoble INP/Pagora) Bluma G. Soares (UFRJ/IMA) César Liberato Petzhold (UFRGS/IQ) Cristina T. Andrade (UFRJ/IMA) 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 (UFCG/UAEMa) Marco Aurelio De Paoli (UNICAMP/IQ) 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 (GU/DeptChemistry) 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 Adhemar C. Ruvolo Filho Alain Dufresne Bluma G. Soares César Liberato Petzhold José António C. Gomes Covas José Carlos C. S. Pinto Paula Moldenaers Richard G. Weiss 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: June 2020

Financial support:

Available online at: www.scielo.br

Polímeros / Associação Brasileira de Polímeros. vol. 1, nº 1 (1991) -.- São Carlos: ABPol, 1991Quarterly v. 30, nº 2 (Apr./June 2020) ISSN 0104-1428 ISSN 1678-5169 (electronic version)

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

1. Polímeros. l. Associação Brasileira de Polímeros. Polímeros, 30(2), 2020

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

O r i g in a l A r t ic l e Thermal performance of nanoencapsulated phase change material in high molecular weight polystyrene Tamara Agner, Amadeo Zimermann, Fabricio Machado, Brenno Amaro da Silveira Neto, Pedro Henrique Hermes de Araújo and Claudia Sayer .................................................................................................................................................................................................. 1-7

Antioxidant stone water (human/friendly environment) thermal (thermogravimetric-TGA) combustion properties in biohazard (insect/fungus) wood Hüseyin Tan, Hatice Ulusoy and Hüseyin Peker............................................................................................................................................... 1-7

Preparation and characterization of Chitosan/Collagen blends containing silver nanoparticles Jonacir Novaes, Eloi Alves da Silva Filho, Paulo Matheus Ferro Bernardo and Enrique Ronald Yapuchura................................................. 1-5

Relationship between stress relaxation behavior and thermal stability of natural rubber vulcanizates Nabil Hayeemasae and Abdulhakim Masa ...................................................................................................................................................... 1-7

Synthesis and properties of fluorinated copolymerized polyimide films Chuanhao Cao, Lizhu Liu, Xinyu Ma, Xiaorui Zhang and Tong Lv................................................................................................................. 1-7

Synthesis of novel organocatalyzed phenoxazine for free metal atom transfer radical polymerization Thu Hoang Vo, Huong Thi Le, Tien Anh Nguyen, Nhu Quang Ho, Thang Van Le, Dat Hung Tran, Thuy Thu Truong and Ha Tran Nguyen ............................................................................................................................................................................................... 1-5

Synthesis, characterization and thermokinetic analysis of the novel sugar based styrene co-polymer Fatma Cetin Telli .............................................................................................................................................................................................. 1-8

Synergistic improvement of mechanical and magnetic properties of a new magnetorheological elastomer composites based on natural rubber and powdered waste natural rubber glove Nabil Hayeemasae and Hanafi Ismail............................................................................................................................................................. 1-7

Development of active PHB/PEG antimicrobial films incorporating clove essential oil Ivo Diego de Lima Silva, Michelle Félix de Andrade, Viviane Fonseca Caetano, Fernando Hallwass, Andréa Monteiro Santana Silva Brito and Glória Maria Vinhas.................................................................................................................................................................................. 1-8

Rosin maleic anhydride adduct antibacterial activity against methicillin-resistant Staphylococcus aureus Zahid Majeed, Muhammad Mushtaq, Zainab Ajab, Qingjie Guan, Mater Hussen Mahnashi, Yahya Saeed Alqahtani and Basharat Ahmad ............................................................................................................................................................................................... 1-7

Polymeric nanoemulsions enriched with Eucalyptus citriodora essential oil Flávia Oliveira Monteiro da Silva Abreu, Emanuela Feitoza Costa, Mayrla Rocha Lima Cardial and Weibson Pinheiro Paz André............ 1-9

Advances and perspectives in the use of polymers in the environmental area: a specific case of PBS in bioremediation Priscilla Braga Antunes Bedor, Rosana Maria Juazeiro Caetano, Fernando Gomes de Souza Júnior and Selma Gomes Ferreira Leite.......... 1-10

Cover: TEM of silver nanoparticles adhered to collagen-chitosan blends blend and histogram simulation of the silver average nanoparticles size. Arts by Editora Cubo.

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Polímeros, 30(2), 2020


SABIC develops innovative TF-BOPE film for frozen food packaging SABIC, a global leader in diversified chemicals, has launched a sustainable packaging solution for frozen food which combines a new polyethylene (PE) grade with innovative film production technology. Compared to conventional blow PE film solutions, it offers significantly higher throughput and also has potential for down-gauging, making it attractive from both a commercial and sustainability standpoint. The solution is based on a mono web TF-BOPE film structure which has a thickness of only 20 micrometers – an unprecedented benefit in this market. This thin gauge provides a potential packaging material reduction of approximately 35-50% compared to incumbent blown PE film. The reduced thickness of the packaging solution minimizes environmental impact and supports brand owners and retailers who are aiming to reduce their packaging material consumption. The new packaging solution is also 100% recyclable and fits mono-PE recycling streams. The TF-BOPE stands for Tenter Frame Biaxially Oriented Polyethylene. This is a PE grade that can run in tenter frame machines traditionally used to make Biaxially Oriented Polypropylene (BOPP) film. It has the potential to be used in new applications and markets which support the circular economy, where mono material solutions are required to enhance recyclability. It also can replace multi material laminates into a mono-PE structure. TF-BOPE film offers tear direction and low tear strength, providing an easy unidirectional opening. Compared to conventional solutions, it offers much better visibility of packaged products due to higher light transmission and lower haze. Meanwhile the high gloss delivers first-class design and aesthetics. This innovative packaging solution for frozen food is the result of SABIC’s close collaboration with film suppliers/ extruders Ticinoplast and Plastchim-T, as well as packaging machine manufacturer Syntegon Technology. The 20 micrometer thin film was successfully tested on Syntegon’s vertical form, fill and seal machines, which feature the newly-developed PHS 2.0 sealing technology. This technology reduces the amount of clamped film by 25 percent and increases packaging speed by up to 25 percent. The thin TF-BOPE film also requires less cooling time which increases packaging speed even more. During the evaluations, a constant speed of 130 bags per minute was achieved. For packers, TF-BOPE film delivers a robust sealing performance and increased productivity resulting from improved packaging speed. The thin gauge results in increased film roll efficiency which reduces logistic handling, storage space and transport costs. For converters and brand owners, SABIC’s TFBOPE film material offers a wide range of benefits that include good printability, cost-saving opportunities, higher yield, less consumption of plastic materials and lower packaging taxes due to reduced material consumption. It further reduces the package weight to product weight ratio, resulting in a more optimized packaging design. SABIC® TF-BOPE polymer is part of the “Design for Recyclability” under TRUCIRCLE™ solutions supports easy and full recyclability through enabling mono-PE material structure in multilayer tenter frame of flexible packaging, aiming to minimize waste. This new product can be also available as certified circular polymer from the company’s TRUCIRCLE™ portfolio. At SABIC, the TRUCIRCLE™ initiative encompasses the company’s circular materials and technologies, which include certified circular polymers from the chemical recycling of mixed plastic waste and certified renewable polymers based on bio-based renewable feedstock. Source: SABIC - www.sabic.com

Braskem advances in research into chemical recycling of plastics Committed to developing innovative solutions that promote the circular economy and sustainable development, Braskem

takes another important step in enhancing the technology for the chemical recycling of post-consumer plastics. The company, which already had been working in partnership with the Polymers Engineering Laboratory (EngePol) of the Alberto Luiz Coimbra Institute for Postgraduate Studies and Engineering Research of the Federal University of Rio de Janeiro (COPPE/UFRJ) and with the training institute SENAI CETIQT, through the SENAI Innovation in Biosynthetics and Fibers Institute, now has signed a cooperation agreement for the next research phases with the same academic institutions, as well as with the company Fábrica Carioca de Catalisadores (FCC S.A.). The contract was obtained after Braskem participated in a selection process conducted by National Industrial Learning Service (Senai) through a public competitive bid process. The investments in this research phase are estimated at R$2.7 million (U$0.5 million), which includes the financial and human resources of the institutions and companies involved. Since 2018, Braskem has been working on capturing efficiency gains in the technology for pyrolysis, a process that breaks down plastic resin molecules with heat to transform them once again into raw material that can be reintroduced into the plastics production chain. The project aims to develop catalysts to improve the quality of the products created in the chemical plastics recycling process. “We identified, last year, after our initial first studies into chemical recycling, the need to develop new catalysts. After evaluating some options, we reached out to FCC S.A., the catalysts supply leader of FCC in the South American market, to get involved in the studies already in progress with SENAI CETIQT and COPPE/UFRJ. Now that we have an even more complete body of research and access to adequate technologies, we will be able to accelerate progress in the development of a chemical recycling solution that is technically and economically viable,” said Gus Hutras, head of the Process Technology team at Braskem. “The project, which for now is experimental, already shows great potential for causing a positive impact on society, the circular economy and sustainability,” he added. “The strategic planning of FCC S.A. covers explicitly the development of new products and markets. We have identified priority applications in the circular economy and in the bioeconomy, which are areas with enormous growth potential. We are very confident in the results of this project in conjunction with Braskem, SENAI CETIQT and COPPE/UFRJ for the chemical recycling of plastics that are not urban solid waste,” said Sidney Martins, New Business coordinator at FCC S.A. Fabiana Quiroga, head of the Circular Economy at Braskem in South America, highlights the main advantage of investing in chemical recycling. “With the process, discarded plastic waste is processed and transformed into raw material once again, which is used to make new plastic resins. We are moving forward on this path of connecting research and innovation to create sustainable solutions. We want to constantly be developing new businesses and initiatives that increase the value of plastic waste in order to close the cycle as a whole,” she concluded. Braskem’s partner research and academic institutions in the effort also are aligned with the goal of contributing to the circular economy. “We have the mission of promoting the sustainability and competitiveness of Brazil’s chemical industry through the development of new products and processes. In the circular economy, we are positioned as a strategic link for the development of solutions that have positive impacts on the businesses of our partner companies and on society as a whole,” said Paulo Coutinho, manager of the SENAI Innovation in Biosynthetics and Fibers Institute of SENAI CETIQT. José Carlos Pinto, a full professor in the Chemical Engineering Program at COPPE/UFRJ and coordinator of the Polymerization Engineering Laboratory (EngePol), also believes in this joining of forces. “Seeking to establish and consolidate circular economy concepts in the plastics industry, we have been working in recent years on chemical recycling processes, with thermal and catalytic pyrolysis the most promising technique. The partnership with Braskem, FCC S.A. and SENAI CETIQT is an excellent opportunity to take this research to a whole new scale,” he said. Source: Braskem - www.braskem.com

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March Oil & Gas Polymer Engineering Texas 2021 Date: March 2-3, 2021 Location: Houston, United States Website: www.ami.international/events/event?Code=C1126 12th SPE European Thermoforming Conference Date: March 3-5, 2021 Location: Geneva, Switzerland Website: thermoforming-europe.org Polymers in Footwear Date: March 23-24, 2021 Location: Portland, United States Website: www.ami.international/events/event?Code= C1120 2nd PHA platform World Congress Date: March 30-31, 2021 Location: Cologne, Germany Website: www.bioplasticsmagazine.com/en/event-calendar/ termine/2nd-pha-world-congress-2020

April PVC Formulation Date: April 19-21, 2021 Location: Cologne, Germany Website: www.ami.international/events/event?Code=C1104 Plastic Pouches Date: April 26-28, 2021 Location: Barcelona, Spain Website: www.ami.international/events/event?Code=C1097

May World Polymer Congress (IUPAC-MACRO2020+) Date: May 16-20, 2021 Location: Jeju Island, South Korea Website: www.macro2020.org Polymers 2021: New Trends in Polymer Science: Health of the Planet, Health of the People Date: May 17-19, 2021 Location: Turin, Italy Website: polymers2021.sciforum.net

June Gordon Research Conference — Polymers Date: June 5-6, 2021 Location: South Hadley, United States Website: www.grc.org/polymers-conference/2021 Biopolymer – Processing & Moulding Date: June 15-16, 2021 Location: Halle (Saale), Germany Website: https://polykum.de/en/biopolymer-mkt-2021 RosUpack - 25th International Exhibition for the Packaging Industry Date: June 15-18, 2021 Location: Moscow, Russia Website: www.rosupack.com Gordon Research Conference — Polyamines Date: June 27 - July 2, 2021 Location: Waterville Valley, United States Website: www.grc.org/polyamines-conference/2021

July 25th IUPAC International Conference on Physical Organic Chemistry Date: July 10–15, 2021 Location: Hiroshima, Japan Website: icpoc25.jp

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84th Prague Meeting on Macromolecules - Frontiers of Polymer Colloids Date: July 18–22, 2021 Location: Prague, Czech Republic Website: mns-20.com 2nd International Conference on Materials and Nanomaterials (MNs-20) Date: July 26–28, 2021 Location: Rome, Italy Website: www.imc.cas.cz/sympo/84pmm

August International Conference on Electronic Materials (2021 IUMRS-ICEM) XIX Brazilian Materials Research Society Meeting (XIX B-MRS) Date: August 29 – September 2, 2021 Location: Foz do Iguaçu, Brazil Website: www.sbpmat.org.br/19encontro

September Global Summit and Expo on Materials Science and Nanoscience Date: September 6-8, 2021 Location: Lisbon, Portugal Website: www.thescientistt.com/materials-science-nanoscience CIRM – Workshop — Directed Polymers and Folding Date: September 6-10, 2021 Location: Marseille, France Website: https://conferences.cirm-math.fr/2021-calendar.html 100 Years Macromolecular Chemistry Date: September 12-14,, 2021 Location: Freiburg, Germany Website: veranstaltungen.gdch.de/tms/frontend/index. cfm?l=9162&sp_id=2 9th International Conference on Fracture of Polymers, Composites and Adhesives Date: September 26-30, 2021 Location: Les Diablerets, Switzerland Website: www.elsevier.com/events/conferences/esistc4conference 36th International Conference of the Polymer Processing Society Date: September 26-30, 2021 Location: Montreal, Canada Website: www.polymtl.ca/pps-36/en 13th PVC Formulation Date: September 27-29, 2021 Location: Cologne, Germany Website: www.ami.international/events/event?Code=C1104

October International Conference on Materials Science and Engineering Date: October 11-14, 2021 Location: Brisbane, Australia Website: www.materialsconferenceaustralia.com Sustainable Polymers Date: October 17-20, 2021 Location: Safety Harbor, United States Website: www.polyacs.net/21sustainablepolymers 16th Brazilian Polymer Conference – (16thCBPol) Date: October 24-28, 2021 Location: Ouro Preto, Brazil Website: www.cbpol.com.br

Polímeros, 30(2), 2020


ABPol Associates Sponsoring Partners

PolĂ­meros, 30(2), 2020

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.01320

Thermal performance of nanoencapsulated phase change material in high molecular weight polystyrene †

Tamara Agner1 , Amadeo Zimermann1 , Fabricio Machado2 , Brenno Amaro da Silveira Neto3 , Pedro Henrique Hermes de Araújo1  and Claudia Sayer1*  1 Laboratório de Controle e Processos de Polimerização – LCP, Departamento de Engenharia Química e Engenharia de Alimentos – EQA, Universidade Federal de Santa Catarina – UFSC, Florianópolis, SC, Brasil 2 Laboratório de Desenvolvimento de Processos Químicos – LDPQ, Instituto de Química – IQ, Universidade de Brasília – UnB, Brasília, DF, Brasil 3 Laboratório de Química Medicinal e Tecnológica – LaQuiMeT, Instituto de Química – IQ, Universidade de Brasília – UnB, Brasília, DF, Brasil † Selected paper presented at the 15th Brazilian Polymer Conference – (15thCBPol) held in Bento Gonçalves, Brazil, on 27–31 October, 2019.

*claudia.sayer@ufsc.br

Abstract A novel nanoencapsulation of n-hexadecane in high molecular weight polystyrene nanoparticles for thermal energy storage was carried out by miniemulsion polymerization using an iron-containing imidazolium-based ionic liquid (IL) as catalyst. The particle size, morphology, molecular weight, and thermal performance of nanoparticles containing the phase change material (PCM) were measured by dynamic light scattering, transmission electron microscopy, gel permeation chromatography, and differential scanning calorimetry, respectively. The nanoparticles were regular spherical, with narrow size distribution and particle size ranged from 138 nm to 158 nm. The enthalpy of melting for the nanoencapsulated PCM increased from 19 J/g to 72 J/g, as the content of n-hexadecane used increased from 20 wt% to 50 wt%. In addition, the nanoparticles showed thermal reversibility after 100 thermal cycles. The high molecular weights of the polymer, up to 1800 kDa, that could be reached with this IL may have contributed positively to this thermal behavior. Keywords: cationic miniemulsion polymerization, ionic liquid, nanoencapsulation, phase change material. How to cite: Agner, T., Zimermann, A., Machado, F., Neto, B. A. D., Araújo, P. H. H., & Sayer, C. (2020). Thermal performance of nanoencapsulated phase change material in high molecular weight polystyrene. Polímeros: Ciência e Tecnologia, 30(2), e2020013. https://doi.org/10.1590/0104-1428.01320

1. Introduction The tireless search for new technologies to capture and store energy in more efficient, ecologically friendly, and low-cost ways has been boosting the development of phase change materials. Latent heat storage materials or simply phase change materials (PCMs) are capable of storing and releasing large amounts of energy during melting and solidification at specific temperatures[1]. Due to its useful properties, such a higher energy storage densities, and phase change behaviors at almost constant temperatures[2] they are widely developed for several applications especially for thermal comfort building, solar heating system, thermal protection, air-conditioning, thermal regulated textiles, electronic devices, among others.[3] Phase change materials are classified into two main categories, organic and inorganic. Most of the organic PCMs have low thermal conductivity and poor thermal response as well as being flammable, however, these limitations may be overcome by employing encapsulation technologies[1]. The encapsulation provides protection of PCM from external

Polímeros, 30(2), e2020013, 2020

environmental influences, increases the surface of heat transfer, and the capsule shell helps to retain the changes in the volume that result from the phase change[4]. Several techniques have been used to encapsulate PCMs such as in-situ polymerization which includes miniemulsion polymerization, complex coacervation, sol-gel methods, and solvent extraction/evaporation method, among others.[1] Miniemulsion polymerization is a versatile technique for the in-situ encapsulation of different compounds into polymeric nanoparticles. In general, miniemulsions consist of small (50 – 500 nm)[5], stable, and narrowly distributed monomer droplets in a continuous phase[6]. The miniemulsion design involves the manipulation of the monomer-water interface stability and the dispersion mechanism (e.g., ultrasonic homogenizers[7-9], rotor-stator systems[7,9], high-pressure homogenizers[8,10], static mixers[7,11], or membranes[9]). The high stability of the droplets is ensured by the combination of the surfactant, and the costabilizer, which retards the droplet diffusional degradation (Ostwald ripening). Typically,

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Agner, T., Zimermann, A., Machado, F., Neto, B. A. D., Araújo, P. H. H., & Sayer, C. highly hydrophobic and low molecular weight compounds, such as hexadecane, are used as costabilizer. The monomer nanodroplets become the polymerization locus, and in an idealized concept each of these nanodroplets can be regarded as a nanoreactor, without major secondary nucleation or monomer mass transport through the aqueous phase[5]. Then, different compounds such as PCMs can be added into the monomer droplets before the miniemulsification step in the water phase, and followed by the polymerization leading to high encapsulation efficiencies. Luo and Zhou[12] employed the miniemulsion polymerization process to nanoencapsulate a paraffin (Tm = 52 °C) using a styrene-methacrylic acid copolymer. They noticed that the amount and type of surfactant, the concentration of comonomer (methacrylic acid), and the monomer/paraffin ratio, as well as the amount of the chain-transfer agent, and the nucleation mechanism did have a significant influence on the process. de Cortazar and Rodríguez[13] obtained stable nanocapsules containing up to 60 wt% of paraffin (Tm = 60 °C) by miniemulsion polymerization. The droplet nucleation was the main nucleation mechanism for the systems containing under 20 wt% of paraffin, for higher paraffin contents (40 – 60 wt%) secondary unwanted nucleation mechanism took place. Whereas systems with even higher paraffin concentration (80 wt%) showed phase separation. Fang et al. published a series of works in which the encapsulation of n-octadecane[14,15] (ΔHm = 232.3 J/g), n-tetradecane[2] (ΔHm = 220.6 J/g) or n-dotriacontane[16] (ΔHm = 286 J/g) in polystyrene nanoparticles (100 – 170 nm) via miniemulsion polymerization was evaluated. They used a monomer mixture of styrene and up to 2 wt% of acrylate (butyl, acrylic, or ethyl) to prepare the polystyrene shells. The latent heat of melting of nanoencapsulated PCM was 124.4 J/g for n-octadecane, 98.71 J/g for n-tetradecane, and 174.8 J/g for n-dotriacontane. Fuensanta et al.[17] encapsulated a paraffin type phase change material (5 – 20 wt%), RT80 (Tm = 85 °C, ΔHm = 161.1 J/g) in a styrene-butyl acrylate copolymer shell. The particle sizes ranged from 52 nm to 112 nm with encapsulation efficiencies close to 80%, and good thermal reversibility after 200 thermal cycles. The thermal energy storage capacity of the nanoparticles was measured by DSC, obtaining melting and crystallization enthalpies in the range of 10 – 20 J/g. Chen et al. produced nanocapsules (90 – 200 nm) containing n-dodecanol (Tm = 27 °C, ΔHm = 222 – 248 J/g) with poly(methyl methacrylate) (PMMA)[18] or styrene-butyl acrylate copolymer[19] as the shell materials by miniemulsion polymerization. The latent heat of nanocapsules was 98.8 J/g at 18.2 °C for the n-dodecanol/PMMA system and 109.2 J/g at 18.4 °C for the n-dodecanol /styrene-butyl acrylate system. Many types of polymerization reaction mechanisms can be carried out in miniemulsion. Radical polymerization is the most common mechanism, but non-radical polymerization such as ionic polymerization, anionic[20-22] and cationic[23-26], can also be adapted to be carried out in miniemulsion. Recently, Alves et al.[26] showed that the ironcontaining imidazolium-based ionic liquid 1-n-butyl-32/7

methylimidazolium heptachlorodiferrate (BMI.Fe2Cl7), proposed by Rodrigues et al.[27] as a new class of cationic catalysts for the styrene polymerization, is water tolerant for the miniemulsion polymerization. BMI.Fe2Cl7 not only proved to be an efficient initiator in aqueous medium as well as provided the synthesis of polystyrene nanoparticles (150 – 175 nm) of high molecular weights (Mv up to 2220 kDa), higher than those obtained with the commonly used initiators. Combining the high molecular weights obtained in the cationic miniemulsion polymerization of styrene catalyzed by the ionic liquid BMI.Fe2Cl7 and the encapsulation feature that miniemulsion polymerization technique offers, this work aims to study the encapsulation of n-hexadecane as phase change material in high molecular weight polystyrene nanoparticles. It is expected that the n-hexadecane combines its properties as hydrophobic agent, retarding the droplet diffusional degradation (Ostwald ripening), and acts simultaneously as a phase change material storing and releasing energy during the melting and solidification process.

2. Materials and Methods 2.1 Materials Technical grade monomer styrene (Sty, Innova) used to prepare the polymeric matrix was distilled under reduced pressure before use and stored at -4 °C. n-Hexadecane (HD, Sigma Aldrich) was used as costabilizer and as phase change material. Hexadecyltrimethylammonium bromide (CTAB, Sigma Aldrich) was used as surfactant. HD and CTAB were used as received. The ionic liquid 1-n-butyl-3methylimidazolium heptachlorodiferrate (BMI.Fe2Cl7) used as catalyst was synthesized as reported by Rodrigues et al.[27]. Deionized water was used in all reactions.

2.2 Synthesis of nPCM by miniemulsion polymerization The nanoparticles containing the phase change material (nPCM) were synthesized by cationic miniemulsion polymerization using the ionic liquid BMI.Fe2Cl7 as catalyst according to the following procedures. The surfactant CTAB (60 mg) was dissolved in deionized water (11 mL). Different HD contents were evaluated, and the organic phase compositions (HD/Sty wt%/wt%) were 5/95, 20/80, 30/70, 35/65, 40/60, and 50/50. Regardless of composition, 3.3 g of organic phase was used in all reactions. The aqueous phase and the organic phase were magnetically stirred for 20 min (150 rpm) before being mixed and pre-emulsified under magnetic stirring (1500 rpm) for further 20 min. The coarse emulsion formed was sonicated for 1 min (10 s on/5 s off) at 70 % amplitude (Sonic Dismembrator Model 500 – Fisher Scientific, tip probe size of ½ in) using an ice-bath to avoid thermal polymerization. Then, an aliquot (1 mL) of a BMI.Fe2Cl7 aqueous solution, used at 1:1000 molar ratio of IL:Sty, was added to the miniemulsion. All the polymerizations were carried out for 8 h under nitrogen atmosphere at 85 °C. After polymerization, the latex was cooled down to room temperature. Right after the latex was demulsified with ethanol, and filtered to obtain the nanoparticles containing the PCM. The nanoparticles were washed three times with ethanol to remove the unencapsulated n-hexadecane and then were dried at room temperature. Polímeros, 30(2), e2020013, 2020


Thermal performance of nanoencapsulated phase change material in high molecular weight polystyrene Reactions were performed in duplicate. The monomer conversion was determined by gravimetry.

2.3 Characterization and performance of nPCM 2.3.1 Dynamic Light Scattering (DLS) Intensity average sizes of monomer droplets and polymer nanoparticles were determined by Dynamic Light Scattering – DLS (Zetasizer Nano S, Malvern). Miniemulsion samples were diluted before measurement with a water solution saturated with styrene containing an amount of CTAB below the critical micelle concentration. Latex samples were diluted with deionized water. 2.3.2 Transmission Electron Microscopy (TEM) Nanoparticles morphology was observed by Transmission Electron Microscopy with a JEM-1011 TEM (Jeol) electron microscope operating at an accelerating voltage of 100 kV. The diluted latex (0.01 wt%) was mounted on a carbon-coated copper grid and was left to dry at room temperature before analysis. Different regions were analyzed to assure representative images. 2.3.3 Differential Scanning Calorimetry (DSC) Nanoparticles energy storage capacity was measured by Differential Scanning Calorimetry (Jade DSC, Perkin Elmer) under nitrogen atmosphere at a heating and cooling rate of 10 °C/min. The heating scans were from -10 °C to 30 °C, and the cooling scans were performed in the same range. The phase change latent heat (ΔHm) and the melting temperature (Tm) were recorded from the second heating ramp. 2.3.4 PCM content in the nanoparticles The PCM (n-hexadecane) content in the nanoparticles was calculated based on the enthalpy value of pure n-hexadecane by using the following Equation 1[4,13,18]: PCM content in nanoparticles ( wt % ) =

∆H nPCM . 100 (1) ∆H PCM

where ΔHnPCM is the enthalpy of melting for the nanoencapsulated PCM (J/g) and ΔHPCM is the enthalpy of melting for the pure n-hexadecane (J/g). 2.3.5 Gel permeation chromatography (GPC) Molecular weight distributions were determined by gel permeation chromatography. The analyses were conducted in a high-performance liquid chromatography instrument (HPLC, model LC 20-A, Shimadzu) equipped with a PLgel MiniMIX-C (PL1510-1500) guard column, and two in series PLgel MiniMIX-C (PL1510-5500) HPLC columns, from

Agilent. Tetrahydrofuran (THF) was used as eluent (flow rate of 0.3 mL/min) at 40 °C. The calibration was performed using polystyrene standards with molecular weights ranging from 580 g/mol to 9.225x106 g/mol.

3. Results and Discussions Polystyrene nanoparticles with different n-hexadecane contents were prepared by miniemulsion polymerization using the ionic liquid BMI.Fe2Cl7 as catalyst. In all cases, highly stable latexes containing PCM nanoparticles have been obtained, and no phase separation was observed. Monomer conversion was higher than 80 % in all cases studied. Dynamic light scattering (DLS) was used to analyze droplet (dd) and particle (dp) sizes of the miniemulsion and the latex, respectively. Table 1 summarizes the droplet (dd) and particle (dp) sizes before and after polymerization, respectively, and their dispersities (PdI). PCM nanoparticles synthesized with different amounts of n-hexadecane ranged from 138 nm to 158 nm. According to the sizes obtained from droplets (miniemulsion, before polymerization) and polymeric particles (latex, after polymerization), droplet nucleation was the main nucleation mechanism and droplets/particles remained stable during polymerization. The miniemulsions produced with a higher amount of n-hexadecane had a slightly bigger droplet size. Increasing the amount of HD from 5 wt% to 50 wt%, droplet size increased from 131 nm (nPCM-5) to 168 nm (nPCM-50). This behavior was also observed by Shirin-Abadi et al.[28] in the synthesis of poly(methyl methacrylate) nanocapsules containing n-hexadecane as PCM. They suggested that this behavior may be due to the decreasing of the contribution of the surfactant molecules per particle when the HD amount is increased using the same amount of surfactant. However, added to the contribution of the surfactant molecules per particle there is the viscosity effect. An increase in the amount of HD increases the viscosity of the organic phase, and since the ultrasonication conditions were kept constant for all HD contents used, i.e. the same amount of energy was supplied to the system to break the organic phase into smaller droplets, the higher viscosity may have led to the increase in the droplet sizes. In the systems containing amounts of HD greater than 5 wt% it was observed a decrease in the difference between droplet and particle size compared to the system containing 5 wt% (nPCM-5). The narrow particle size distributions, Figure 1, also suggest that the main nucleation mechanism was the droplet nucleation and that secondary nucleation (homogeneous or micellar nucleation) did not take place.

Table 1. Effect of the n-hexadecane (HD) content on the droplet size (dd) and particle size (dp) and their dispersities (PdI). (Average values refer to duplicate reactions). Entry nPCM-5 nPCM-20 nPCM-30 nPCM-35 nPCM-40 nPCM-50

HD/Sty 5/95 20/80 30/70 35/65 40/60 50/50

Polímeros, 30(2), e2020013, 2020

dd (nm) 131.2 ± 8.8 138.4 ± 4.8 141.4 ± 4.8 148.9 ± 1.3 154.4 ± 1.1 168.0 ± 9.2

PdI (-) 0.10 ± 0.01 0.10 ± 0.01 0.10 ± 0.01 0.11 ± 0.01 0.09 ± 0.01 0.16 ± 0.06

dp (nm) 158.4 ± 2.4 137.5 ± 2.4 142.3 ± 3.9 140.6 ± 2.1 139.7 ± 4.4 150.6 ± 1.5

PdI (-) 0.02 ± 0.01 0.04 ± 0.02 0.06 ± 0.02 0.06 ± 0.02 0.07 ± 0.01 0.08 ± 0.02

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Agner, T., Zimermann, A., Machado, F., Neto, B. A. D., Araújo, P. H. H., & Sayer, C. The morphology of nanoparticles containing the phase change material (nPCM) was observed by Transmission Electron Microscopy (TEM). The micrographs of the nPCM with 50 wt% of HD in relation to the organic phase (sample nPCM-50), Figure 2, show that the nanoparticles obtained have a spherical shape with a fairly uniform size distribution. From the TEM images it is not possible to identify a capsule morphology (lighter core of HD surrounded by a darker PS shell), but according to Tiarks et al.[29] for the same system HD/Sty due to the similarity of the particle sizes obtained by DLS (150.6 nm) and TEM, it is deduced that the HD is located within the particles, presumably in a spongelike morphology. Molecular weight distributions were obtained using gel permeation chromatography. The weight-average molecular weight (Mw) and the molecular-weight dispersity (Ð) of the polystyrene nanoparticles are summarized in Table 2. GPC data shows that the cationic miniemulsion polymerization of styrene catalyzed by the ionic liquid BMI.Fe2Cl7 provided the synthesis of high molecular weight polystyrene nanoparticles. Under similar experimental conditions of the nPCM-5 system, 5 wt% of HD in relation to the organic phase, 1:1000 molar ratio of IL:Sty and at 85 °C, Alves et al.[26] obtained average viscosity molar mass (Mv) up to 2150 kDa, at conversions slightly higher than 80 %. It is worth mentioning that the high amount of HD in the system (nPCM-20 to nPCM-50) did not affect the high molecular weights obtained which were similar to those achieved when the HD was used only as costabilizer (nPCM-5). The molecular-weight dispersities (Ð) denote broad molecular weight distributions. Rodrigues et al.[27] by on-line direct infusion electrospray mass spectrometry (ESI-MS(/MS)) detected three active catalytic species in the cationic polymerization of styrene catalyzed by the ionic liquid BMI.Fe2Cl7. These three active catalytic species: (i) the chloronium cation (derived from styrene), (ii) the chloronium cation associated with [FeCl4]- and (iii) the chloronium cation associated with Cl− have different reactivities. The presence of active catalytic species with different reactivities elucidates the broad molecular weight distributions obtained. Thermal properties of the nPCM were measured by DSC. The DSC curves of the n-hexadecane nanoencapsulated in high molecular weight polystyrene polymeric matrix synthesized using different HD weight ratios in relation to the organic phase are presented in Figure  3 and summarized in Table 3. Also measured by DSC, the heat storage capacity of pure n-hexadecane, defined as the heat storage of melting (ΔHm), and its melting temperature (Tm) were 290.35 J/g and 16.4 °C, respectively. The enthalpy of melting for the nanoencapsulated PCM ranged from 19 J/g to 72 J/g, increasing as the amount of HD in the system also increased. By increasing the HD content in the organic phase, the values of melting enthalpy also increased due to the higher contribution of HD during the encapsulation process. Similar behavior was described by Shirin-Abadi et al.[28] in the in situ encapsulation of n-hexadecane with poly(methyl methacrylate) shell by 4/7

Figure 1. Particle size distribution of polymeric latexes synthesized with different HD/Sty weight ratios.

Figure 2. TEM micrographs of the polystyrene nanoparticles obtained in miniemulsion polymerization at 85 °C using an IL:Sty molar ratio of 1:1000 and 50 wt% of HD in relation to the organic phase, sample nPCM-50 (Table 1). Table 2. Molecular weight of nPCM synthesized with different HD weight ratios in relation to the organic phase. (Average values refer to duplicate reactions). Entry HD/Sty Mw (kDa) Ð (-) nPCM-5 nPCM-20 nPCM-30 nPCM-35 nPCM-40 nPCM-50

5/95 20/80 30/70 35/65 40/60 50/50

1771 ± 24 1572 ± 43 1370 ± 19 1238 ± 20 1456 ± 26 1693 ± 228

2.1 ± 0.1 2.7 ± 0.1 2.9 ± 0.1 3.0 ± 0.1 2.7 ± 0.1 2.2 ± 0.1

Polímeros, 30(2), e2020013, 2020


Thermal performance of nanoencapsulated phase change material in high molecular weight polystyrene

Figure 3. DSC curves of nPCM synthesized with different HD/Sty weight ratios. Table 3. Thermal properties of nPCM synthesized with different HD/Sty weight ratios. (Average values refer to duplicate reactions). Sample HD/Sty ΔHm (J/g) PCM content (wt%) Tm (°C) nPCM-5 nPCM-20 nPCM-30 nPCM-35 nPCM-40 nPCM-50

5/95 20/80 30/70 35/65 40/60 50/50

18.77 ± 0.78 27.30 ± 7.44 43.58 ± 0.07 50.85 ± 1.30 71.77 ± 5.01

miniemulsion polymerization. They obtained enthalpy of melting for the nanoencapsulated PCM ranging from 67 J/g to 86 J/g for HD:MMA weight ratios ranging from 1:3 to 3:1. Final PCM content in the nanoparticles ranged from 6.46 wt% to 24.72 wt% for an increase in HD content from 20 wt% (nPCM-20) to 50 wt% (nPCM-50) in relation to the organic phase. The nPCM-5 that was synthesized with 5 wt% of HD did not exhibit enthalpy of melting. This absence of enthalpy denotes an unwanted plasticizing effect of the n-hexadecane on nanoparticles. By acting as plasticizer part of the HD is incorporated into the polymer matrix, reducing the amount of free HD that can act as PCM. The plasticizing effect significantly decreases the glass transition temperature of the polymer. To evaluate the plasticizing effect, the glass transition temperature of samples nPCM-5 and nPCM-50 was determined by DSC under nitrogen atmosphere at a heat rate of 10 °C/min in a temperature range from -10 °C to 140 °C. The glass transition temperature (Tg) was recorded from the second heating ramp. The Tg of sample nPCM-5 was 77.3 °C, while the Tg of sample nPCM-50 dropped to 54.5 °C. The phase change temperature of the n-hexadecane contained in the nanoparticles was below the melting temperature of pure n-hexadecane (16.4 °C) and ranged from 5.67 °C to 7.92 °C when the HD content was increased from 20 wt% (nPCM-5) to 50 wt% (nPCM-50). Chen et al.[18,19]. also observed a reduction in the phase change temperature of the n-dodecanol contained in the nanocapsules in relation to the pure n-dodecanol (Tm = 27 °C) used as PCM. The nanocapsules containing n-dodecanol as the core and poly(methyl methacrylate) (PMMA)[18] or styrene-butyl acrylate copolymer[19] as the shell showed a Polímeros, 30(2), e2020013, 2020

5.67 ± 0.28 6.01 ± 0.01 6.60 ± 0.67 6.83 ± 0.12 7.92 ± 0.33

6.46 9.40 15.01 17.51 24.72

Table 4. Thermal properties of the nPCM synthesized with 40 wt% of HD in relation to the organic phase (nPCM-40) after different numbers of thermal cycles. Thermal cycles ΔHm (J/g) Tm (°C) 0 20 40 60 80 100

49.66 49.84 50.34 50.11 50.15 50.16

6.91 6.92 6.92 6.92 6.92 6.91

phase change temperature of 18.2 °C and 18.4 °C, respectively. Fang et al.[2] reported a slight difference in the melting points between the core material and the nanocapsules. The melting temperature for pure n-tetradecane (Tet) used as PCM was 6.94 °C, whereas the change phase temperature for the Tet/PS nanocapsules was 4.04 °C. They suggested that this difference may be related to the slower heat conduction rate of the polymer shell that delays the phase change process of the nanocapsules. The thermal reversibility of the nPCM was investigated until 100 thermal cycles (heat/cooling) carried out by using DSC. The thermal properties of nPCM-40 after different numbers of thermal cycles are summarized in Table 4. The phase change latent heat of sample nPCM-40 remained virtually constant after 100 cycles, ranging from 49 to 50 J/g. Thus, the nanoencapsulated n-hexadecane nanoparticles show thermal reversibility after 100 thermal cycles. The melting temperature also remained constant at 6.9 °C. 5/7


Agner, T., Zimermann, A., Machado, F., Neto, B. A. D., Araújo, P. H. H., & Sayer, C.

4. Conclusions The cationic miniemulsion polymerization of styrene catalyzed by the ionic liquid BMI.Fe2Cl7 has proved to be a convenient one-step encapsulation technique to encapsulate a phase change material into high molecular weight polymeric nanoparticles. Particle size analyses (DLS) and TEM micrographs indicated that polymeric particles are spherical, with narrow size distribution and particle size ranging from 138 nm to 158 nm. In addition, these analyses also denoted that the HD is located within the particles, presumably in a spongelike morphology. The presence of HD in the nanoparticles was confirmed by the DSC analyses that have shown the enthalpy of melting for the nanoencapsulated n-hexadecane. The enthalpy of melting increased from 19 J/g to 72 J/g, as the content of n-hexadecane used increased from 20 wt% to 50 wt% in relation to the organic phase. DSC analyses also supported the thermal reversibility of nanoparticles after 100 thermal cycles. DLS, TEM, and DSC results also indicated that the HD acted simultaneously as hydrophobic agent and as phase change material. As expected, the low ionic liquid concentration (1:1000 molar ratio of IL:Sty) used as catalyst leaded to high molecular weights, up to 1800 kDa, even in the presence of high amounts of HD. These high molecular weights may have contributed positively to the thermal behavior of the nanoparticles.

5. Acknowledgements The authors thank the financial support from CAPES − Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Finance Code 001 and CNPq − Conselho Nacional de Desenvolvimento Científico e Tecnológico. The authors also thank the Central Laboratory of Electron Microscopy − LCME and the Analysis Center of Chemical Engineering and Food Engineering Department from the Federal University of Santa Catarina for the TEM and DSC analyses, respectively.

6. References 1. Su, W., Darkwa, J., & Kokogiannakis, G. (2015). Review of solid-liquid phase change materials and their encapsulation technologies. Renewable & Sustainable Energy Reviews, 48, 373-391. http://dx.doi.org/10.1016/j.rser.2015.04.044. 2. Fang, Y., Yu, H., Wan, W., Gao, X., & Zhang, Z. (2013). Preparation and thermal performance of polystyrene/n-tetradecane composite nanoencapsulated cold energy storage phase change materials. Energy Conversion and Management, 76, 430-436. http://dx.doi.org/10.1016/j.enconman.2013.07.060. 3. Khadiran, T., Hussein, M. Z., Zainal, Z., & Rusli, R. (2015). Encapsulation techniques for organic phase change materials as thermal energy storage medium: A review. Solar Energy Materials and Solar Cells, 143, 78-98. http://dx.doi.org/10.1016/j. solmat.2015.06.039. 4. Rezvanpour, M., Hasanzadeh, M., Azizi, D., Rezvanpour, A., & Alizadeh, M. (2018). Synthesis and characterization of micro-nanoencapsulated n-eicosane with PMMA shell as novel phase change materials for thermal energy storage. Materials Chemistry and Physics, 215, 299-304. http://dx.doi. org/10.1016/j.matchemphys.2018.05.044. 6/7

5. Landfester, K. (2003). Miniemulsions for nanoparticle synthesis. Topics in Current Chemistry, 227, 75-123. http:// dx.doi.org/10.1007/3-540-36412-9_4. 6. Landfester, K. (2009). Miniemulsion polymerization and the structure of polymer and hybrid nanoparticles. Angewandte Chemie International Edition, 48(25), 4488-4507. http://dx.doi. org/10.1002/anie.200900723. PMid:19455531. 7. Ouzineb, K., Lord, C., Lesauze, N., Graillat, C., Tanguy, P. A., & McKenna, T. (2006). Homogenisation devices for the production of miniemulsions. Chemical Engineering Science, 61(9), 2994-3000. http://dx.doi.org/10.1016/j.ces.2005.10.065. 8. Tang, P. L., Sudol, E. D., Silebi, C. A., & El-Aasser, M. S. (1991). Miniemulsion polymerization - A comparative study of preparative variables. Journal of Applied Polymer Science, 43(6), 1059-1066. http://dx.doi.org/10.1002/app.1991.070430604. 9. Agner, T., Zimmermann, A., Di Luccio, M., Araújo, P. H. H., & Sayer, C. (2017). Monomer-in-water miniemulsions by membrane emulsification. Chemical Engineering and Processing - Process Intensification, 120, 251-257. http:// dx.doi.org/10.1016/j.cep.2017.07.016. 10. do Amaral, M., & Asua, J. M. (2004). Synthesis of large, high-solid-content latexes by miniemulsion polymerization. Journal of Polymer Science. Part A, Polymer Chemistry, 42(17), 4222-4227. http://dx.doi.org/10.1002/pola.20287. 11. Farzi, G., Bourgeat-Lami, E., & McKenna, T. F. L. (2009). Miniemulsions using static mixers: A feasibility study using simple in-line static mixers. Journal of Applied Polymer Science, 114(6), 3875-3881. http://dx.doi.org/10.1002/app.30343. 12. Luo, Y., & Zhou, X. (2004). Nanoencapsulation of a hydrophobic compound by a miniemulsion polymerization process. Journal of Polymer Science. Part A, Polymer Chemistry, 42(9), 21452154. http://dx.doi.org/10.1002/pola.20065. 13. de Cortazar, M. G., & Rodríguez, R. (2013). Thermal storage nanocapsules by miniemulsion polymerization. Journal of Applied Polymer Science, 127(6), 5059-5064. http://dx.doi. org/10.1002/app.38124. 14. Fang, Y., Kuang, S., Gao, X., & Zhang, Z. (2008). Preparation and characterization of novel nanoencapsulated phase change materials. Energy Conversion and Management, 49(12), 37043707. http://dx.doi.org/10.1016/j.enconman.2008.06.027. 15. Fang, Y., Kuang, S., Gao, X., & Zhang, Z. (2009). Preparation of nanoencapsulated phase change material as latent functionally thermal fluid. Journal of Physics D: Applied Physics, 42(3), 035407. http://dx.doi.org/10.1088/0022-3727/42/3/035407. 16. Fang, Y., Liu, X., Liang, X., Liu, H., Gao, X., & Zhang, Z. (2014). Ultrasonic synthesis and characterization of polystyrene/ndotriacontane composite nanoencapsulated phase change material for thermal energy storage. Applied Energy, 132, 551-556. http://dx.doi.org/10.1016/j.apenergy.2014.06.056. 17. Fuensanta, M., Paiphansiri, U., Romero-Sánchez, M. D., Guillem, C., López-Buendía, Á. M., & Landfester, K. (2013). Thermal properties of a novel nanoencapsulated phase change material for thermal energy storage. Thermochimica Acta, 565, 95-101. http://dx.doi.org/10.1016/j.tca.2013.04.028. 18. Chen, Z.-H., Yu, F., Zeng, X.-R., & Zhang, Z.-G. (2012). Preparation, characterization and thermal properties of nanocapsules containing phase change material n-dodecanol by miniemulsion polymerization with polymerizable emulsifier. Applied Energy, 91(1), 7-12. http://dx.doi.org/10.1016/j. apenergy.2011.08.041. 19. Chen, C., Chen, Z., Zeng, X., Fang, X., & Zhang, Z. (2012). Fabrication and characterization of nanocapsules containing n-dodecanol by miniemulsion polymerization using interfacial redox initiation. Colloid & Polymer Science, 290(4), 307-314. http://dx.doi.org/10.1007/s00396-011-2545-2. Polímeros, 30(2), e2020013, 2020


Thermal performance of nanoencapsulated phase change material in high molecular weight polystyrene 20. Barrère, M., Ganachaud, F., Bendejacq, D., Dourges, M.-A., Maitre, C., & Hémery, P. (2001). Anionic polymerization of octamethylcyclotetrasiloxane in miniemulsion II. Molar mass analyses and mechanism scheme. Polymer, 42(17), 7239-7246. http://dx.doi.org/10.1016/S00323861(01)00207-5. 21. Barrère, M., Maitre, C., Dourges, M. A., & Hémery, P. (2001). Anionic polymerization of 1,3,5-tris(trifluoropropylmethyl) cyclotrisiloxane (F3) in miniemulsion. Macromolecules, 34(21), 7276-7280. http://dx.doi.org/10.1021/ma010559z. 22. Crespy, D., & Landfester, K. (2005). Anionic polymerization of ε-caprolactam in miniemulsion: Synthesis and characterization of polyamide-6 nanoparticles. Macromolecules, 38(16), 68826887. http://dx.doi.org/10.1021/ma050616e. 23. Cauvin, S., Sadoun, A., Santos, R., Belleney, J., Ganachaud, F., & Hemery, P. (2002). Cationic polymerization of p-methoxystyrene in miniemulsion. Macromolecules, 35(21), 7919-7927. http:// dx.doi.org/10.1021/ma0202890. 24. Touchard, V., Graillat, C., Boisson, C., D’Agosto, F., & Spitz, R. (2004). Use of a Lewis acid surfactant combined catalyst in cationic polymerization in miniemulsion: Apparent and hidden initiators. Macromolecules, 37(9), 3136-3142. http:// dx.doi.org/10.1021/ma0355352. 25. Cauvin, S., Ganachaud, F., Moreau, M., & Hémery, P. (2005). High molar mass polymers by cationic polymerisation in emulsion

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and miniemulsion. Chemical Communications, 1(21), 27132715. http://dx.doi.org/10.1039/b501489a. PMid:15917929. 26. Alves, R. C., Agner, T., Rodrigues, T. S., Machado, F., Neto, B. A. D., Costa, C., Araújo, P. H. H., & Sayer, C. (2018). Cationic miniemulsion polymerization of styrene mediated by imidazolium based ionic liquid. European Polymer Journal, 104, 51-56. http://dx.doi.org/10.1016/j.eurpolymj.2018.04.035. 27. Rodrigues, T. S., Machado, F., Lalli, P. M., Eberlin, M. N., & Neto, B. A. D. (2015). Styrene polymerization efficiently catalyzed by iron-containing imidazolium-based ionic liquids: Reaction mechanism and enhanced ionic liquid effect. Catalysis Communications, 63, 66-73. http://dx.doi.org/10.1016/j. catcom.2014.11.002. 28. Shirin-Abadi, A. R., Mahdavian, A. R., & Khoee, S. (2011). New approach for the elucidation of PCM nanocapsules through miniemulsion polymerization with an acrylic shell. Macromolecules, 44(18), 7405-7414. http://dx.doi.org/10.1021/ ma201509d. 29. Tiarks, F., Landfester, K., & Antonietti, M. (2001). Preparation of polymeric nanocapsules by miniemulsion polymerization. Langmuir, 17(3), 908-918. http://dx.doi.org/10.1021/la001276n. Received: Feb. 10, 2020 Revised: May 23, 2020 Accepted: June 15, 2020

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.00720

Antioxidant stone water (human/friendly environment) thermal (thermogravimetric-TGA) combustion properties in biohazard (insect/fungus) wood Hüseyin Tan1* , Hatice Ulusoy2 and Hüseyin Peker3 Department of Furniture and Decoration Technology, Recep Tayyip Erdoğan University, Rize, Turkey 2 Department of Forest, Muğla Sıtkı Koçman University, Muğla, Turkey 3 Department of Forestry, Artvin Çoruh University, Artvin, Turkey

1

*gakkomtan@hotmail.com

Abstract In this study, four different wood species walnut (Juglans regia L.), chestnut (Castanea sativa Mill.), Poplar (Populus nigra), scotch pine (Pinus sylvestris L.) were chosen and test samples were prepared according to TS 2470 principles. Especially the pine wood by taking the structure (with fungus, fungus/insect, insect), flawless wood structure is compared with the flawed wood structure. The impregnation process was carried out according to ASTM D 1413 -76 principles. Effects of the chemical characteristics of the determined Stone Water (Firetex) on the thermal decomposition properties of wood (burning degrees, degradation temperature points and residue amount) were determined with TGA (thermogravimetric analysis). According to the results of the experiment; the highest retention value was found in poplar (23.56%) and the lowest retention (12.79%) in chestnut was determined. Amount of residue; 60.84% of the highest on scotch pine wood with fungus and 56.70% of the lowest value was determined on poplar wood. Thermal deterioration was determined between 226.41-405.04 oC on wood . Keywords: stone water, walnut, chestnut, poplar, scots pine, thermal properties. How to cite: Tan, H., Ulusoy, H., & Peker, H. (2020). Antioxidant stone water (human/friendly environment) thermal (thermogravimetric-tga) combustion properties in biohazard (insect/fungus) wood. Polímeros: Ciência e Tecnologia, 30(2), e2020014. https://doi.org/10.1590/0104-1428.00720

1. Introduction Nowadays, due to the rapidly increasing world population and the increasing needs of humankind due to developing technology and living standards, natural resources are decreasing as a result of unconscious consumption. This forces producers to engage in studies on how they can use natural resources more efficiently and in a variety of ways. Wood material, which has a wide range of usage, is a natural and renewable raw material that can be applied to all areas. Due to its light weight compared to concrete, iron, aluminum, PVC and various other construction materials, being easy to be processed, having continuous production, having superior physical and mechanical properties in various places for use; the wood has a wide range of unique uses in construction techniques, many industries such as paper and cellulose, sheet, furniture. At the same time, due to the sensitivity towards fire safety, it is emphasized that fire resistance of wood material is provided in the most effective way. In addition to the known combustion properties of wood material, it is of great importance to determine the effect of impregnation process on combustion resistance. Wood is a flammable material since it is an organic based material containing carbon and hydrogen. The temperature must be

Polímeros, 30(2), e2020014, 2020

increased to 275 ° C to able to burn for wood. However, it can ignite in any kind of flame source even at much lower temperatures. In order to burning of wood, there must be one of the three; oxygen, a source of burning heat and a flammable substance. If this trio is not available, there will be no ignition[1]. One of the negative properties of wood material is that it is an organic material. Therefore, burning is one of the important negative properties in case of proper conditions. Apart from the flammability of wood material, other negative properties cause only material losses, while life-threatening of wood material also occurs. The flames and gases created by the burning of wood material threaten human life and may cause death[2]. One of the most negative properties of wood material is that it is flammable. In order to eliminate this negative feature of wood material, many chemicals are applied to prevent or delay fire. Combustion properties of scotch pine wood treated with a mixture of boric acid and borax, various natural sepi materials as an anti-combustion or retarding agent in wood material were investigated. It was found that natural sepi substances had a negative effect on the examined combustion parameters, the combustion

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


Tan, H., Ulusoy, H., & Peker, H. properties of scotch pine treated with natural sepi substances were similar to control or worse than the control and it has been determined that some of the burning characteristics of the scotch pine wood treated with natural sepi substances have improved significantly statistically[3]. The wood begins to break its chemical bond at temperatures above 100 °C. Regular weight loss in wood occurs between 100 and 200 °C and CO2, acetic acid, water vapor and small amounts of formic acid are released in this temperature range. Lignin decomposes at 160 °C, cellulose disintegrates above 200 °C, tar and flammable volatiles can spread into the environment. Exothermic reactions start at 200-260 °C, combustion also occurs in parts where hydrocarbons with a low boiling point are exposed. Heat release occurs at 275-280 °C, while ethanoic acid, methanol and homologs of these substances increase in gas and liquid products. The wood can also continue to burn after the heat source has been removed. Depending on the characteristics, burning in wood that ignites in the range of 300-400 °C continues to approximately 450 °C. When the temperature rises above 450 °C, while coal remains, decomposition, carbon dioxide, carbon monoxide and oxidation water accelerate and goes to even further stages[4,5]. In a study; In order to protect wood against biotic and abiotic pests, the effect of various impregnating agents on the firing properties of firewood was investigated. As a result, it was found that aqueous solutions of boron compounds showed significant anti-fire effect[6]. In the study, the effects of various impregnation agents on the burning properties of alder wood were investigated and as a result of the study, it was investigated that boron compounds significantly reduced combustion of alder wood[7]. In addition to the effect of boron compounds against fungi and insects, it has many activities such as preventing the transfer of heat and preventing the material from meeting with oxygen as a fire inhibitor[8,9].The rate of combustion and the degree of combustion are important for the effect of fire on wood material. Since no combustion occurs in the absence of oxygen, carbonization begins after a slow combustion occurs in the wide cross-section material[7]. This carbonization acts as an insulating material on thick wood surfaces and reduces the degree of fire damage on the inner parts of wood material[10,11]. Stone water (firetex) is a water based fireproof containing limestone mineral formula; It has been reported that it has no adverse effects on humans and animals and that stone water can be applied to increase the burning resistance of wood materials[12-14]. The wood material consists of a mixture of complex organic polymers. Changes in wood material components occur due to temperature. Thermogravimetric Analysis (TGA) method is implemeted to determine the thermal stability of wood material. By determining the mass losses that occur while heating the material whose thermal properties will be determined, the temperature value at which the fracture occurs from the graph of temperature-mass loss is provided as the decomposition temperature. The 1st degree derivative of weight loss (DTGA/Differential Thermal Analysis) is utilized to determine decomposition temperatures. The wood material consists of a mixture of complex organic polymers. Changes in wood material components occur with temperature[15]. 2/7

2. Materials and Methods 2.1 Material (Wood and Chemical) In this study, scotch wood (with fungus, insect, insect +fungus), poplar, chestnut and walnut material was preferred, stone water (firetex) was used at a concentration of 100% in the impregnation process.

2.2 Preparation of test samples Boric Wood sample of scotch pine (coniferous wood species) species with fungus, insect-fungus, and (leafed wood species) walnut, chestnut and poplar were taken as wood chips to represent the whole mass of the sample, milled in laboratory Willey mill and sieved in 40 and 60 mesh sieves. The obtained samples were subjected to impregnation process.

2.3 Impregnation method For the impregnation procedure, distilled water was used to prepare aqueous solutions of the wood preservatives which have concentration of 3%. Approximately 100 g of the wood flour was immersed in the solutions for 2 h at 60 ºC. Until obtaining the unchangeable weight, The treated wood specimens were exposed to drying at 60 ºC. They were followed for the impregnation procedure of wood flour and wood specimens[16,17]. Then, for two weeks, wood specimens were moistured at 65% relative humidity and at 20 °C.

2.4 Thermal analysis In conditions with heating rate of 10 °C/min and a purge rate of 50 mL / min (Argon) by using a LABSYS TG-DTA analyzer between room temperature to 600 °C, thermogravimetric analysis (TGA) and Differential thermal analysis (DTA) were implemented under nitrogen atmosphere. 10 mg of the sample was analyzed and weight loss of the sample was noted continuously for each individual experiment. By using TG curve as a function of time, derivative TG (DTG) curves were applied.

3. Results and Discussions 3.1 Experimental results The solution properties are given in (Table 1). The solution concentration was used as 100% and the pH/density values were determined before and after impregnation. It has been reported in the literature that acidic structure may cause adversities in anatomical/technological structure of wood.

3.2 % Retention % Retention values are given in (Table 2) and related graph in (Figure 1) According to BVA and Duncan test results; When % retention was evaluated, wood structure with low specific gravity had a positive effect on % retention, whereas wood structure with high specific gravity gave low results. It is evaluated that the highest retention value was 23.56% in poplar and the lowest retention was 12.79% in chestnut. Differences in retention rates may arise from the type of wood, the anatomical structures of the trees, and therefore their physical properties, the impregnation Polímeros, 30(2), e2020014, 2020


Antioxidant stone water (human/friendly environment) thermal (thermogravimetric-tga) combustion properties in biohazard (insect/fungus) wood process and the solution. It is investigated that many factors related to anatomical structure such as heartwood, sapwood, spring wood, summer wood, density, heart beam, tracheid, resin in wood affect permeability[18].

3.3 Thermogravimetric (TGA) Analysis Samples impregnated using four different tree species were compared with control (non-impregnated) samples. TGA analysis was applied for thermal strength of the

samples and DTG curves were generated. The results of thermogravimetric (TGA) analysis of scotch pine wood are given below. Figure 2 shows the TGA (2-a) and DTG (2-b) curves of firetex-treated scotch pine with insect-fungus and control sample. While the turning point temperature of the control sample was 381.14 °C, the decomposition temperature of the firetex applied samples decreased to 361.24 °C. The acceleration of degradation is due to the fact that bonds such as P-O-C (Phosphorus-Carbon) in fire retardants are much less stable than C-C bonds in the control

Table 1. The solution properties. Solution (%)

Impregnation material

Solvent material

Temperature (0C)

100%

Stone Water

Destile water

220C

pH BI 1.65

Density AI 1.65

BI 1.215

AI 1.215

BI: Before impregnation, AI: After impregnation.

Table 2. % Retention values and duncan test results. S.No 1 2 3 4 5 6

Wood Type

Treatment

(Control) Yellow pine (With fungi+insect) Yellow pine (With insect) Yellow pine (With fungus) Walnut Chestnut Poplar

Wood Yellow Pine (Firetex) Walnut (Firetex) Chestnut (Firetex) Poplar (Firetex)

% Retention

HG

18,17

B

14,35 12,79 23,56

C D A

Figure 1. % Retention change.

Figure 2. TGA (a), and DTG (b) curves in Scotch pine (with fungus+insect). Polímeros, 30(2), e2020014, 2020

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Tan, H., Ulusoy, H., & Peker, H. sample and are usually caused by degradation of 180 °C [16] . This early decomposition prevents the formation of flammable gases and also supports formation of carbonized coal[19]. While the amount of residues from combustion result of the control sample was 19.10%, the amount of residues from carbonization result in the sample containing firetex increased to 56.73%. Figure 2 shows the TGA (Figure 3a) and DTG (Figure 3b) curves of scotch pine wood with insects. While the turning point temperature of the control sample was 370.62 °C, the decomposition temperature of the firetex applied samples decreased to 262.26 °C. The acceleration of degradation is due to the fact that bonds such as P-O-C (Phosphorus-Carbon) in fire retardants are much less stable than C-C bonds in the control sample and are usually caused by degradation of 180 °C[16]. This early decomposition prevents the formation

of flammable gases and also supports the formation of carbonized coal[19]. While the amount of residues from combustion result of the control sample was 20.39%, the amount of residue from carbonization result in the sample containing firetex increased to 53.19%. Figure 4 shows the TGA (Figure 4a) and DTG (Figure 4b) curves of scotch pine wood with fungus. While the turning point temperature of the control sample was 373.71 °C, the decomposition temperature of the firetex treated samples decreased to 281.20 °C. The reason for the accelerated degradation may result from the chemical structure of the wood. While the amount of residues from combustion result of the control sample was 18.59%, the amount of residue of from firetex containing sample from carbonization increased to 60.84%. The degradation of the wood components was very rapid, weight loss after the decomposition temperature

Figure 3. TGA (a), and DTGA (b) curves in Scotch pine with insect.

Figure 4. TGA (a), and DTG (b) curves in scotch pine wood with fungi. 4/7

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Antioxidant stone water (human/friendly environment) thermal (thermogravimetric-tga) combustion properties in biohazard (insect/fungus) wood was less. The degradation of wood components in defective scotch pine with fungus was very rapid and the weight loss was lower after the decomposition temperature. The rapid degradation may arise from the destruction of the fungus inside the wood. Figure 5 shows the TG (Figure 5a) and DTG (Figure 5b) curves of walnut wood. While the turning point temperature of the control sample was 370.14 °C, the decomposition temperature of the firetex treated samples decreased to 226.41 °C. The reason for the accelerated degradation may result from the chemical structure of the wood. While the amount of residues from combustion result of the control sample was 21.00%, the amount of residue from carbonization result was 59.00% in the sample containing firetex. The degradation of the wood components was very rapid, weight loss was less after the decomposition temperature. In these two stages, the stone water in the lumens forming the cavities of the wood cells was removed

from the environment depending on the temperature. It is found that thermal decomposition of wood flour and wood components was between 300-500 °C [15]. Figure 6 shows the TG (Figure 6-a) and DTG (Figure 6-b) curves of chestnut wood. Chestnut wood is in the category of leafed trees such as walnut wood. Therefore, TG and DTG analysis showed similar results like walnut samples. While the turning point temperature of the control sample was 405.04 °C, the decomposition temperature of the firetex treated samples decreased to 265.96 °C. The reason for the accelerated degradation result from the chemical structure of the wood. While the amount of residues from combustion result of the control sample was 26.37%, the amount of residue increased to 58.03% from carbonization result in the sample containing firetex. The degradation of the wood components was very rapid, weight loss after the decomposition temperature was less. In these two stages, the stone water in the lumens forming the cavities of the

Figure 5. TGA (a), and DTG (b) curves in Walnut wood.

Figure 6. TGA (a), and DTG (b) curves in Chestnut wood. Polímeros, 30(2), e2020014, 2020

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Tan, H., Ulusoy, H., & Peker, H. wood cells was removed from the environment depending on the temperature. This may arise from anatomical structure. Cellulose depolymerization is very quick and anhydro-sugars at above 300 °C, haphazardly connected oligosaccharides and levoglucosan are shaped[20]. Collard and Blin clairified that char has an aromatic polycyclic structure. Higher crosslinking and thermal stability of the residue arise from intra- and intermolecular rearrangements lead to[21]. Figure 7 shows the TG (Figure 7-a) and DTG (Figure 7-b) curves of poplar wood. Poplar wood is in the category of leafy trees such as walnut and chestnut wood. Therefore, TG and DTG analyses showed similar behaviors to walnut and chestnut samples. While the turning point temperature of the control sample was 382.580 °C, the decomposition temperature of the firetex treated samples decreased to 247.04 °C. The reason of accelerated degradation may arise from the chemical structure of the wood. While the amount of residues from combustion result of the control sample was 17.03%, the amount of residue from carbonization result in the sample containing firetex increased to 56.70%. The degradation of the wood components was very rapid, weight loss after the decomposition temperature was less. In these two stages, the stone water in the lumens forming the cavities of the wood cells was removed from the environment depending on the temperature. This may arise from anatomical structure. Normally, wood has a bigger shoulder area because of debasement of cellulose[22,23]. Then, because of cellulose macromolecules, the sharp decline in weight can be seen at 351 °C. Degradation of lignin begins and the residue includes primarily of charcoal from lignin decomposition at temperatures above 351 °C[24]. In this study, in which TG / DTG analyzes of pine, walnut, chestnut and poplar wood impregnated with stone water (Firetex) were carried out, it was determined that the effects of stone water against combustion were thermally demonstrated. When the variations were compared with the control samples, increases in the remaining mass ratios ranging from 53.19% (scotch pine with insect) to 60.84%

(scotch pine with fungus) were observed. In the retention rate changes, different rates were determined depending on the physical and anatomical structure of the wood. In a study, according to the results of the combustion test carried out on scotch pine wood treated impregnation with stone water using immersion process, significant differences were found in the remaining mass and released CO gas ratios[13].

4. Conclusions Due to their anatomical structure and texture differences, the resistance of wood material against burning is also different. In this study, the thermal properties of wood impregnated with stone water were investigated. In this study, TG/DTG analyzes of defective woods of scotch pine with insect and fungus (impregnated with stone water (Firetex)), and walnut, chestnut and poplar woods; It has been determined that the effects of stone water against combustion are also thermally demonstrated. Wood structure with low specific gravity positively affected % retention, wood structure with high specific gravity gave low results. When the variations were compared with the control samples in itself, increases in mass losses were observed depending on species. On the other hand, it showed different rates depending on the physical and anatomical structure of the wood. It was observed that stone water affects thermal properties. To clarify this situation, comparisons can be made with the results of thermal analysis by calculating the impregnated stone water at different times (2, 4, 6, 12 hours). TGA results can be applied in the production of wood material such as medium-density fiberboard (MDF), particle board, plywood and wood/plastic composites, to explain some of the behavior of wood material against combustion, to evaluate the performance of fire retardants and to obtain fuel from biomass. All chemical compounds are effective on the combustion, physical and mechanical properties of wood. The fireproofing

Figure 7. TGA (a), and DTG (b) curves in poplar wood. 6/7

Polímeros, 30(2), e2020014, 2020


Antioxidant stone water (human/friendly environment) thermal (thermogravimetric-tga) combustion properties in biohazard (insect/fungus) wood ability, color, density, odor, taste and resistance to pressure of wood vary depending on the amount of extractive material. As the amount of extractive material decreases in wood, its ability to burn decreases. The increase in lignin and inorganic material (ash) ratio decreases combustion resistance. For further, studies can be conducted on how these substances affect TGA results. In Balıkesir / Edremit, stone water, whose effects are tested in different areas, is used as a preventive agent against fires and it has been determined that the stone water registered as a strong oks antioxidant ’by Balıkesir Univer Eskişehir Osman Gazi University Faculty of Arts and Sciences Department of Biology. Dr. Adnan Ayhanci, stone water and lung and prostate cancer has reported that the effect of preventing the cells reported.sity has the power to kill germs in 6 tons when it is mixed with 1.5 tons of sewage water[25].

5. References 1. Kolman, F., & Cote, J. R. (1968). Principles of wood science and technology: I Solid Wood. Berlin: Springer-Verlag Berlin Heidelberg. http://dx.doi.org/10.1007/978-3-642-87928-9. 2. Terzi, E. (2008). Combustion properties of wood material impregnated with Ammonium Compounds (Master’s dissertation). İstanbul University Institute of Science, Turkey. 3. Baysal, E., Peker, H., Çolak, M., & Tarımer, İ. (2003). Combustion properties of varnished wood material and the effect of preimpregnation with boron compounds on fire retardant effect. Fırat Unıversity Journal of Science and Engineering Sciences, 15(4), 645-653. 4. Evan, S. L. (1989). Thermal degredation. In: A. P. Schniewind, Concise encylopedia of wood&wood based materials (pp. 271-273). New York: Pergamon Press. 5. Russel, L. J., Marney, D. C. O., Humphrey, D. G., Hunt, A. C., Dowling, V. P., & Cookson, L. J. (2007). Combining fire retardantand preservative systems fortimber products in exposedapplications-state of the art review (Project no: PN04, 10-12). Australia: Forest and Wood Products Research and Development Corporation. 6. Yalınkılıç, M. K., Demirci, Z., & Baysal, E. (1998). Effects of various impregnating agents on the burning properties of duglas [Pseudotsuga menziesii (Mirb.) Frankco] wood. Pamukkale Ünversity Engineering Science Journal, 4(2), 613-624. 7. Uysal, B. (1998). Burning properties of alder wood of various water-repellent and fire-retardant chemicals. Zonguldak Karaelmas Unıversity Technology Journal, 2, 81-89. 8. Çavdar, A. D., Mengeloğlu, F., & Karakuş, K. (2015). Effect of boric acid and borax on mechanical, fire and thermal properties of wood flour filled high density polyethylene composites. Measurement, 60, 6-12. http://dx.doi.org/10.1016/j. measurement.2014.09.078. 9. Price, D., Anthony, G., & Carty, P. (2001). Polymer combustion, condensed phase pyrolysis and smoke formation. In A. R. Horrocks, & D. Price (Eds.), Fire Retardant Materials (pp. 1-30). Cambridge, UK: Woodhead Publishing. 10. Uysal, B. (1997). Effects of various chemicals on the fire resistance of wood materials (Master’s dissertation). Turkey: Gazi Ünıversity Institute of Science. 11. White, R. H., & Dietenberger, M. A. (1999). Fire safety. In Forest Products Laboratory. Wood handbook: wood as an

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engineering material (pp. 17.1-17.16). Madison, WI: USDA Forest Service. 12. Tomak, E. D., & Çavdar, A. D. (2013). Limited oxygen index levels of impregnated Scots pine wood. Thermochimica Acta, 573, 181-185. http://dx.doi.org/10.1016/j.tca.2013.09.022. 13. Kesik, H. İ., Aydoğan, H., Çağatay, K., Özkan, O. E., & Maraz, E. (2015). Fire Properties of Scots Pine Impregnated with Firetex. In International Conference on Environmental Science and Technology (pp. 122-127). Sarajevo: ICOEST. 14. Özcan, C., Kurt, Ş., Esen, R., & Korkmaz, M. (2016). The determinate combustion properties of fir wood impregnated with fire-retardants. The Online Journal of Science and Technology, 6(3), 77-82. 15. Tutuş, A., Kurt, R., Alma, M. H., & Meriç, H. (2010). Chemıcal analysis of scotch pine wood and its thermal properties. In III Ulusal Karadeniz Ormancılık Kongresi (pp. 1845-1851). Artvin: Artvin Çoruh Üniversitesi Orman Fakültesi. Retrieved in 2020, June 17. from http://karok3.artvin.edu.tr/V.Cilt/(1845-1851). pdf 16. Jiang, J., Li, J., Hu, J., & Fan, D. (2010). Effect of nitrogen phosphorus flame retardants on thermal degradation of wood. Construction & Building Materials, 24(12), 2633-2637. http:// dx.doi.org/10.1016/j.conbuildmat.2010.04.064. 17. Yunchu, H., Peijang, Z., & Songsheng, Q. (2000). TG-DTA studies on wood treated with flame retardants. Holz als Roh- und Werkstoff, 58(1), 35-38. http://dx.doi.org/10.1007/ s001070050382. 18. Flynn, K. A. (1995). Review of the permeability, fluid flow, and anatomy of spruce (Picea spp.). Wood Fiber Scieence. 27(3), 278-284. 19. Basak, S., Samanta, K. K., Chattopadhyay, S. K., & Narkar, R. (2015). Thermally stable cellulosic paper made using banana pseudostem sap, a wasted by-product. Cellulose, 22(4), 27672776. http://dx.doi.org/10.1007/s10570-015-0662-7. 20. Shafizadeh, F. (1982). Introduction to pyrolysis of Biomass. Journal of Analytical and Applied Pyrolysis, 3(4), 283-305. http://dx.doi.org/10.1016/0165-2370(82)80017-X. 21. Collard, F.-X., & Blin, J. (2014). Review on pyrolysis of biomass constituents: mechanisms and composition of the products obtained from the conversion of cellulose, hemicelluloses and lignin. Renewable & Sustainable Energy Reviews, 38, 594-608. http://dx.doi.org/10.1016/j.rser.2014.06.013. 22. Beall, F. C., & Eickner, H. W. (1970). Thermal degradation of wood components: a review of the literature. Madison, WI: U.S. Forest Products Laboratory. US Department of Agriculture United States Forest Service. 23. Jeske, H., Schirp, A., & Cornelius, F. (2012). Development of a Thermogravimetric Analysis (TGA) method for quantitative analysis of wood flour and polypropylene in Wood Plastic Composites (WPC). Thermochimica Acta, 543, 165-171. http:// dx.doi.org/10.1016/j.tca.2012.05.016. 24. Slopiecka, K., Bartocci, P., & Fantozzi, F. (2012). Thermogravimetric analysis and kinetic study of poplar wood pyrolysis. Applied Energy, 97, 491-497. http://dx.doi. org/10.1016/j.apenergy.2011.12.056. 25. Haberler.com. Balıkesir ‘stone water’ study against cancer. (2019). Retrieved in 2020, June 17, Retrieved from https:// www.haberler.com/balikesir-kansere-karsi-tas-suyu-calismasi12430326-ha/ Received: Apr. 23, 2020 Accepted: June 17, 2020

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.00919

Preparation and characterization of Chitosan/Collagen blends containing silver nanoparticles Jonacir Novaes1, Eloi Alves da Silva Filho1* , Paulo Matheus Ferro Bernardo1 and Enrique Ronald Yapuchura2 Laboratório de Físico-Química, Departamento de Química, Universidade Federal do Espírito Santo, Vitória, ES, Brasil 2 Laboratório de Materiais Carbonosos e Cerâmicos – LMC, Departamento de Física, Universidade Federal do Espírito Santo – UFES, Vitória, ES, Brasil

1

*eloisilv@gmail.com

Abstract This work consists of preparation of the Chitosan(CHI)/Collagen(COL) blends loaded with silver nanoparticles by method of evaporation of the solvent. This blends were characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results obtained demonstrated that the mass ratio of CHI/COL was important for the maintenance of the collagen structure since in the ratio 3:1 (m/m of CHI/COL) decrease in the ratio between the peaks of 1235 cm-1 and 1450 cm-1, respectively. Moreover the silver nanoparticles added to the polymer matrix of the obtained chitosan had an average size of 25 nm confirmed by TEM for silver nanoparticle. Keywords: chitosan, collagen, blend, silver nanoparticles. How to cite: Novaes, J., Silva Filho, E. A., Bernardo, P. M. F., & Yapuchura, E. R. (2020). Preparation and characterization of Chitosan/Collagen blends containing silver nanoparticles. Polímeros: Ciência e Tecnologia, 30(2), e2020015. https:// doi.org/10.1590/0104-1428.00919.

1. Introduction The new nanoparticles (NPs) incorporated in natural polymer as Chitosan (CHI) and Collagen (COL) have emerged as blends with potential application due to their unique physical and chemical properties. The Chitosan is a copolymer obtained through the deacetylation of acetamide groups of chitin, which originates from the exoskeleton of crustaceans[1-3], where the D-glucosamine (GlcN) and N-acetyl-D-Glycosamine (GlcNAC) groups of chitin result in the formation of this copolymer of β-(1,4)-D-glucosamine and β- (1,4)-N-acetyl-D-glucosamine units[4,5]. This copolymer is notable for its high bactericidal, fungicidal and bioactivity potential, which, together with its specific interactions with the extracellular matrix components and cell growth factors[6], give it high employability in a wide range of scientific areas. Another biopolymer, the Collagen, has been very promising in this field of research, this protein has been applied in the manufacture of bioactive membranes, as they serve as a support for cell growth, in addition to transporting drugs or releasing other substances with anti-inflammatory, antibacterial and antioxidant properties at the lesion site[3-5]. The Collagen is a fibrous protein, being the largest component of the extracellular matrix in mammals, it presents ease of combination with other materials, easy processing, hydrophilicity, low antigenicity, body absorption capacity, etc[7-9]. Based on the individual characteristics of each polymer, the associated CHI/COL can offer a non-cytotoxic, non-allergenic, biodegradable and porous biomaterial. According with Antunes et al.[10] in your work with Chitosan/Arginine have demonstrated that many combinations this materials shown to be promising where obtained membranes with non-cytotoxic highly porous

Polímeros, 30(2), e2020015, 2020

nanostructure and with bactericidal activity in vivo with tissue regeneration[10]. Therefore the many blends formed by a combination of two polymers are of great interest in the area of biomaterials, as in the case of this study, which is of potential application. The preparation and characterization of this blends with silver nanoparticles it is a new study and and few are described in the literature, among which we highlight the most similar to what we have done but that there are differences regarding its physicochemical analysis, as the focus in on its biological and biomedical application. The studies carried out by Cardoso et al.[11] in 2014 show three formulations of silver nanoparticles with collagen (AgNPCol) and your characterization by ultraviolet-visible spectroscopy, dynamic light scattering, X-ray diffraction and antibacterial activity in vitro and cell viability assays. Where the results showed that the its nanoparticles AgNPcol at molar ratio of 1:6 have antimicrobial activity against both Staphylococcus aureus and Escherichia coli and no toxicity to the cells. In 2016 a study by Sionkowska et al.[12] using chitosan and collagen blends with the addition of hyaluronic acid, a glycosaminoglycan polysaccharide present in the extracellular matrix of the skin, connective tissue obtained promising results since the addition of hyaluronic acid to the biomaterial formed by chitosan and collagen increased thermal stability, elasticity, facilitated proliferation and served as the basis for tissue regeneration, mainly cartilage tissues[12]. In the work of Archana et al.[13] that using chitosan, polyvinylpyrrolidone (PVP) and silver oxide nanoparticles prepared and evaluated for cytotoxicity and antibacterial

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


Novaes, J., Silva Filho, E. A., Bernardo, P. M. F., & Yapuchura, E. R. activity against Staphylococcus aureus and Escherichia coli where they obtained satisfactory results with different concentrations of silver nanoparticles. The aim of this work is obtained Chitosan/Collagen blends with silver nanoparticles and characterize by infrared spectroscopy (FTIR), SEM and TEM microscopy.

2. Materials and Methods 2.1 Materials The chitosan employed, with presents a 63% deacetylation degree and a medium molar mass of 1.61×106 g/mol[14], was obtained in previous studies[15]. The bovine collagen, purity of 98% was provided of NovaProm Food Ingredients. Glacial acetic acid and glutaraldehyde 25% (v/v) both from Dinamica Chemicals.

2.2 Experimental Procedure to preparation of Chitosan/Collage blends For the preparation of CHI/COL was initially a volume of 100 mL of 1.5% (w/v) solution of the polymers were prepared at 25°C, dissolving both chitosan and collagen in 5% (v/v) solutions of acetic acid. Then, a 10 mL aliquot of the chitosan solution was transferred and conditioned in erlenmeyer flask (100 mL), to which 1 mL of glutaraldehyde solution 5% (v/v) was added. The mixture was stirred with magnetic stirrer for 30 min, and then different aliquots of the 1.5% (w/v) collagen solution were added. The CHI/COL ratios were 1:1, 1:2, 2:1, 3:1 and 1:3 respectively. Stirring was continued for 2 h and then the polymer blend was transferred to polypropylene forms for drying at room temperature, 25 °C. After drying, the characterizations of the blends were made by infrared spectroscopy (FTIR) in the spectrophotometers FTIR 400 from Perkin-Elmer and Cary 630 from Agilent. The scanning electron microscopy (SEM) images were made using the SSX-550 SEM-EDX from Shimadzu and transmission electron microscopy (TEM) using the JEM 2100 from JEOL.

superimposed with the stretching band N-H. Also, the angular deformation of N-H (around 1550 cm-1) was observed, probably overlapping the axial deformation of C=O of the amide and axial deformation of C-N of amino groups (1400 cm-1). The bands of polysaccharide structures in the region of 890-1156 cm-1 in agreement with literature[16] were observed as well. The collagen spectrum showed the characteristic bands of amide I, II and III at 1650, 1560 and 1235 cm-1, respectively. It is also composed of vibration absorptions of -CH2 groups of the glycine skeleton and proline side chains[13]. In addition, bands of 3270, 2920 and 1430 cm-1, which represent the elongation of rings -OH, -CH3 and pyrrolidine, respectively, were observed[13]. The interactions between collagen and chitosan may occur through the formation of hydrogen bonds. The -OH, -NH2 and -C=O groups in the collagen are capable of forming hydrogen bonds with -OH and -NH2 present on chitosan[14]. As reported in a previous study[13], in a slightly acid medium occurs protonation of the amino groups of chitosan, which favors the electrostatic attraction with –COO- groups of aspartic and glutamic acid residues of collagen. The FTIR spectra of the blends in different proportions of chitosan and collagen are observed in Figure 2, where no additional bands were identified. As previously identified in other works[13], there is an increase of the band corresponding to amide I and decrease of amide II as the proportion of collagen increases.

2.3 Synthesis of Silver nanoparticles and insertion in CHI/COL blends The synthesis of silver nanoparticles (AgClNP) from silver nitrate (AgNO3) was based on the work of Loza et al.[16] with modifications. Using the chitosan purification filtrate, obtained according to the methodology described previously[11], where a aliquots of 50 mL this filtrate was removed and packed in erlenmeyer flask (100 mL), then added 2 mL of the 25 mmol/L solution of AgNO3, and stirred for 2 h with heating at 80 °C. Then the suspension obtained was centrifuged for 30 min at 5000 rpm, the supernatant was discarded and the AgClNP precipitate was added to chitosan solution after washed and dried at 45 °C in stove with air circulation. Finally was added 12 mg of the AgClNP in CHI/COL blends obtained in 2.2 subsection. This polymer blend loaded with silver nanoparticles was transferred to polypropylene forms for drying at room temperature (25 °C) for 7 days.

Figure 1. FTIR spectra of chitosan, chitosan/collagen (1:1), and collagen.

3. Results and Discussions 3.1 Spectra of infrared spectroscopy to CHI/COL blend In the infrared spectroscopy analysis (Figure 1) the chitosan spectrum presented the axial stretching bands of O-H (between 3300 and 3400 cm-1), which appeared 2/5

Figure 2. FTIR spectra of chitosan/collagen blends: (a)1:1; (b) 1:2; (c) 1:3 and (d) 3:1. Polímeros, 30(2), e2020015, 2020


Preparation and characterization of Chitosan/Collagen blends containing silver nanoparticles The integrity of the triple helix of the collagen can be evaluated by the ratio between the absorbance at 1235 and 1450 cm-1 [16]. That is an very important, since this three-dimensional collagen characteristic gives it important biological and mechanical properties[13]. The values of this ratio for the denatured collagen are about 0.5 and those of intact structures are about 1. For the samples in the proportion of 1:1, 1:2 and 1:3 chitosan/collagen, the ratios obtained were above of 1, but for the 3:1 proportion the value obtained was 0.46, which is indicative that the increase in the amount of chitosan in relation to the collagen destabilizes the triple helix of the protein structure of the collagen[17].

scanning electron microscopy (SEM), the chitosan/collagen blends showed a porous structure, with open pores and a high degree of interconnectivity between the blends phases like show in Figure 4d.

3.2 Morphological analysis to CHI/COL blend

The TEM images revealed that the synthesized silver nanoparticles formed were predominantly spherical, polydisperse and with diameters in the range of 15-35 nm, may also observed that the silver nanoparticles are surrounded

The Figure 3, shows the macroscopic appearance of the blends, where it can be observed that the malleability of the blends decreases with increasing chitosan. In analysis of the

3.3 Microscopy analysis to CHI/COL blend with Silver nanoparticles Transmission electron microscopy (TEM) was used to provide more information about the size, shape and morphology of the synthesized silver nanoparticles added to the chitosan polymer matrix, these micrographs (Figure 5) were treated with the imageJ software to obtain the size of the particles.

Figure 3. Macroscopic appearance of (a) collagen; and blends CHI/COL (b) (1:1); (c) (1:2); (d) (3:1); (e) (1:3) and (f) lateral view (1:1).

Figure 4. SEM micrographs of chitosan-collagen magnification of (a) 50x; (b) 400x; (c) cross section of 120x and (d) 270x. Polímeros, 30(2), e2020015, 2020

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Novaes, J., Silva Filho, E. A., Bernardo, P. M. F., & Yapuchura, E. R.

Figure 5. TEM of Silver nanoparticles adhered to CHI/COL blend: (A) and (B) in 20 nm scale, (B), (C) 50 nm scale (D) histogram to average size of the silver nanoparticles estimated by imageJ software.

by a thin layer of other material, which is believed be of organic material of the polymer. These limiting organic materials prevent the aggregation of silver nanoparticles and thus provide additional stability for them, the same observation has been reported in the work of Parveen et al.[18]. Similar micrographs to Figure  5 were obtained by Kim et al.[19] who synthesized silver and gold nanoparticles from ginseng extract and by Shen et al.[20] who obtained AgClNP by microemulsion. The average size of the nanoparticles obtained together with the chitosan matrix was 25 nm, the size of the nanoparticles is an important factor since the silver ions cross the membrane of the microorganism have the capacity to inhibit bacterial multiplication by the binding and denaturation of the DNA, affecting ribosomal subunit and some enzymes important for the growth of bacterial cells, hence the efficiency of this process is dependent on the size of these nanoparticles as reported in the literature[21]. 4/5

4. Conclusions Using the method of phase inversion by solvent evaporation of the polymer solutions, chitosan-collagen blends were successfully produced with porous and interconnected structures confirmed in SEM, compatible with other methods used in the literature. The chitosan-collagen ratio is important for the maintenance of the collagen structure, since the ratio 3:1 showed a possible protein denaturation of the collagen, causing a possible loss of its properties as biomaterial. The FTIR confirmed regions in both chitosan and collagen responsible for the intermolecular interaction between the polymers that make them compatible for future use in regenerative medicine.

5. Acknowledgments The authors gratefully thanks Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for MS scholarship, the analysis by Nucleus of Competences Polímeros, 30(2), e2020015, 2020


Preparation and characterization of Chitosan/Collagen blends containing silver nanoparticles in Petrochemical Chemistry (NCQP-UFES) for FTIR and the LUCCAR laboratory by SEM and TEM images of CHI/COL blends.

6. References 1. Badawy, M. E. I., & Rabea, E. I. (2011). A biopolymer chitosan and Its derivatives as promising antimicrobial agents against plant pathogens and their applications in crop protection. International Journal of Carbohydrate Chemistry, 460381, 1-29. http://dx.doi.org/10.1155/2011/460381. 2. Mi, F. L., Shyu, S. S., Wu, Y. B., Lee, S. T., Shyong, J. Y., & Huang, R. N. (2001). Fabrication and characterization of a sponge-like asymmetric chitosan membrane as a wound dressing. Biomaterial, 22(2), 165-173. http://dx.doi.org/10.1016/ S0142-9612(00)00167-8. PMid:11101160. 3. Costa, S. (2006). Quitosana: derivados hidrossolúveis, aplicações farmacêuticas e avanços. Quimica Nova, 29(4), 776-785. http:// dx.doi.org/10.1590/S0100-40422006000400026. 4. Anitha, A., Sowmya, S., Kumar, P. T. S., Deepthi, S., Chennazhi, K. P., Ehrlich, H., Tsurkan, M., & Jayakumar, R. (2014). Chitin and chitosan in selected biomedical applications. Progress in Polymer Science, 39(9), 1644-1667. http://dx.doi.org/10.1016/j. progpolymsci.2014.02.008. 5. Lee, D. W., Lim, C., Israelachvili, J. N., & Hwang, D. S. (2013). Strong adhesion and cohesion of chitosan in aqueous solutions. Langmuir, 29(46), 14222-14229. http://dx.doi. org/10.1021/la403124u. PMid:24138057. 6. Sharma, C., Amit, K. D., Pravin, D. P., & Narayan, C. M. (2015). Fabrication of quaternary composite scaffold from silk fibroin, chitosan, gelatin, and alginate for skin regeneration. Journal of Applied Polymer Science, 132(44), 42743. http:// dx.doi.org/10.1002/app.42743. 7. Shoulders, M. D., & Raines, R. T. (2009). Collagen structure and stability. Annual Review of Biochemistry, 78(1), 929-958. http://dx.doi.org/10.1146/annurev.biochem.77.032207.120833. PMid:19344236. 8. Moraes, M. A., Silva, M. F., Weska, R. F., & Beppu, M. M. (2014). Silk fibroin and sodium alginate blend: miscibility and physical characteristics. Materials Science and Engineering C, 40, 85-91. http://dx.doi.org/10.1016/j.msec.2014.03.047. PMid:24857469. 9. Li, J., Barrow, D., Howell, H., & Kalachandra, S. (2010). In vitro drug release study of methacrylate polymer blend system: effect of polymer blend composition, drug loading and solubilizing surfactants on drug release. Journal of Materials Science. Materials in Medicine, 21(2), 583-588. http://dx.doi. org/10.1007/s10856-009-3899-6. PMid:19856082. 10. Antunes, B. P., Moreira, A. F., Gaspar, V. M., & Correia, I. J. (2015). Chitosan/arginine–chitosan polymer blends for assembly of nanofibrous membranes for wound regeneration. Carbohydrate Polymers, 130, 104-112. http://dx.doi.org/10.1016/j. carbpol.2015.04.072. PMid:26076606. 11. Cardoso, V. S., Quelemes, P. V., Amorim, A., Primo, F. L., Gobo, G. G., Tedesco, A. C., Mafud, A. C., Mascarenhas, Y. P., Corrêa, J. R., Kuckelhaus, S. A. S., Eiras, C., Leite, J.

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R. S. A., Silva, D., & Júnior, J. R. S. (2014). Collagen-based silver nanoparticles for biological applications: synthesis and characterization. Journal of Nanobiotechnology, 12(36), 2-9. http://dx.doi.org/10.1186/s12951-014-0036-6. PMid:25223611. 12. Sionkowska, A., Kaczmarek, B., Lewandowska, K., Grabska, S., Pokrywczynska, M., Kloskowski, T., & Drewa, T. (2016). 3D composites based on the blends of chitosan and collagen with theaddition of hyaluronic acid. International Journal of Biological Macromolecules, 89, 442-448. http://dx.doi. org/10.1016/j.ijbiomac.2016.04.085. PMid:27151670. 13. Archana, D., Singh, B. K., Dutta, J., & Dutta, P. K. (2015). Chitosan-PVP-nano silver oxide wound dressing: in vitro and in vivo evaluation. International Journal of Biological Macromolecules, 73, 49-57. http://dx.doi.org/10.1016/j. ijbiomac.2014.10.055. PMid:25450048. 14. Alessandro, C. S., Silva, E. A., Fo., Coelho, E. R. C., & Kock, F. V. C. (2015). Preparação e caracterização de blendas híbridas de Poliacrilonitrila e Quitosana. Orbital: The Electronic Journal of Chemistry, 7, 391-394. http://dx.doi.org/10.17807/orbital. v7i4.778. 15. Silva, E. A., Fo., Kock, F. V. C., & Castro, E. V. R. (2011). BR PI 11064145. INPI. 16. Loza, K., Sengstock, S., Chernousova, S., K’oller, M., & Epple, M. (2014). The predominant species of ionic silver in biological media is colloidally dispersed nanoparticulate silver chloride. RSC Advances, 4(67), 35290-35297. http://dx.doi. org/10.1039/C4RA04764H. 17. Horn, M. M., Martins, V. C. A., & Plepis, A. M. G. (2009). Interaction of anionic collagen with chitosan: effect on thermal and morphological characteristics. Carbohydrate Polymers, 77(2), 239-243. http://dx.doi.org/10.1016/j.carbpol.2008.12.039. 18. Parveen, M., Ahmad, F., Malla, A. M., & Azaz, S. (2016). Microwave-assisted green synthesis of silver nanoparticles from Fraxinus excelsior leaf extract and its antioxidant assay. Applied Nanoscience, 6(2), 267-276. http://dx.doi.org/10.1007/ s13204-015-0433-7. 19. Kim, Y., Farh, M., & Yang, D. (2016). Biogenic silver and gold nanoparticles synthesi using red ginseng root extract, and their applications. Artificial Cells, Nanomedicine, and Biotechnology, 44(3), 811-816. http://dx.doi.org/10.3109/21 691401.2015.1008514. PMid:25706249. 20. Shen, J., Zheng, X., Ruan, H., Wu, L., Qiu, J., & Gao, G. (2007). Synthesis of AgCl/PMMA hybrid membranes and their sorption performance of cyclohexane/cyclohexene. Journal of Membrane Science, 304(1-2), 118-124. http://dx.doi. org/10.1016/j.memsci.2007.07.022. 21. Durán, N., Marcato, P. D., Conti, R., Alves, O. L., Costa, F. T. M., & Brocchi, M. (2010). Potential Use of Silver Nanoparticles on Pathogenic bacteria, their toxicity and possible mechanisms of action. Journal of the Brazilian Chemical Society, 21(6), 949-959. http://dx.doi.org/10.1590/S0103-50532010000600002. Received: Mar. 04, 2019 Revised: Apr. 11, 2020 Accepted: June 17, 2020

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.03120

Relationship between stress relaxation behavior and thermal stability of natural rubber vulcanizates Nabil Hayeemasae1 and Abdulhakim Masa2*  Department of Rubber Technology and Polymer Science, Faculty of Science and Technology, Prince of Songkla University, Pattani Campus, Pattani, Thailand 2 Sino-Thai International Rubber College, Prince of Songkla University, Hat Yai, Songkhla, Thailand 1

*abdulhakim.m@psu.ac.th

Abstract It is well-recognized that different sulphur curing systems have greatly influenced to the final properties of the rubber vulcanizates. In this study, the properties of vulcanizates with conventional vulcanization (CV) and efficiency vulcanization (EV) systems were correlated in the aspect of stress relaxation and thermal stability. The stress relaxation behaviour and thermal stability were studied with the temperature scanning stress relaxation (TSSR) and with thermogravimatric analysis (TGA) techniques, respectively. Thermo-oxidative degradation of rubber chains in the CV system was greater than the EV system, leading to easier stress relaxation and poorer aging resistance of the CV system. Also, thermal stability of the rubber crosslinked with CV system was poorer than that with the EV system as corroborated by the activation energy of degradation. TSSR result correlated well with TGA result, and both revealed type of crosslinkages governed the thermo-oxidative degradation and thermal stability of vulcanizates. Keywords: natural rubber, stress relaxation, thermal stability, crosslink system. How to cite: Hayeemasae, N., & Masa, A. (2020). Relationship between stress relaxation behavior and thermal stability of natural rubber vulcanizates. Polímeros: Ciência e Tecnologia, 30(2), e2020016. https://doi.org/10.1590/0104-1428.03120.

1. Introduction It is well known that unvulcanised NR has low strength, is unstable over a wide range of temperatures, and cannot recover its original shape after a large deformation[1,2]. Therefore, all typical NR products require vulcanizing. This is a chemical process, converting viscous rubber materials into three-dimensional elastic crosslinked networks by using chemicals and heat[3]. As a result, the vulcanizates are less sensitive to heat or cold and have elasticity, strength and stability in the ranges needed in applications[4]. By far, sulfur is the most extensively used crosslinking agent in the rubber industries as it is cost-effective, broadly compatible with compounding ingredients, and allows to predict the eventual vulcanizate properties[5]. In general, sulfur vulcanization systems are either conventional (CV), semi-efficient (Semi-EV), or efficient (EV) types, and the linkages generated by vulcanization reactions can be either mono- (C-S-C), di- (C-S2-C), or polysulfidic (C-Sx-C; x>2) crosslinks, depending on accelerator/sulfur ratio. The CV systems have accelerator/sulfur ratio below 0.7; EV has this ratio above 2.5; and semi-EV is used to label the remaining cases[6,7]. It has been proven that the CV systems give a large proportion of polysulfidic linkages with bond strengths less than 262 kJ/mol, while EV systems tend to create more monosulfidic linkages with bond strengths of about 280 kJ/mol[8,9]. Due to the lower bond strength, poorer thermal ageing is typical with the CV system. Several prior studies have assessed the properties of NR with different types of crosslinks. Pimolsiriphol et al.[8] investigated thermal

Polímeros, 30(2), e2020016, 2020

aging degradation of CV and EV crosslinked NR, and found that the thermal ageing properties of NR vulcanizates depend strongly on crosslink density. On the other hand, Larpkasemsuk et al.[10] reported that for epoxidized natural rubber the highest tensile strength and oil resistance were obtained with a CV system, but the highest thermal stability was achieved with a semi-EV system due to high crosslink density with thermally comparatively stable mono- and disulfidic linkages. Boonkerd et al.[11] found that adding polysulfidic linkages gave the vulcanizate a higher tensile strength but a lower reversion resistance. Rattanasom et al.[12] also found that NR/tire tread reclaimed rubber blend vulcanizates had better heat aging resistance with an EV system than with CV, due to the better thermal stability of mono- and di-sulfidic crosslinks compared to polysulfidic linkages. Although various studies have reported on mechanical and thermal properties achieved with CV and EV systems but the discussions remained in contradiction. Temperature scanning stress relaxation (TSSR) measurement is a well-known technique used for determining stress relaxation behaviors of thermoplastic elastomers[13]. However, it was also useful for analysing relaxation behaviour or thermo-mechanical behaviour of unfilled rubbers vulcanizates[14-16]. Vennemann et al.[14] determined the relaxation behavior of NR crosslinked with different vulcanization systems by using TSSR. They found that the ratio of sulfur to accelerator has a large influence on the

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Hayeemasae, N., & Masa, A. relaxation behavior of vulcanizates. Furthermore, they also found that the change of stress relaxation behavior was caused by the cleavage of crosslinks or scission of main chains. Similar observation was also noticed by Oncel et al.[15] when they studied the oxidative thermal aging behaviour of the NR containing new type of antioxidants. Karaagac et al.[16] used TSSR to investigate the stress relaxation of NR and ethylene propylene diene rubber and revealed the effect of molecular weight on the pattern of stress relaxation. For the same polymer, the higher molecular weight shifted the pattern of stress relaxation to higher temperature. Though there have been reports on the relaxation behaviour of the NR but an attempt to correlate low temperature relaxation behaviour (lower than 300 °C) with thermal properties tested are still largely unexplored. To address this aspect, alternative sulfur vulcanizing systems were used to experimentally assess the effect of vulcanization system on stress relaxation and thermal properties of NR, along with other properties. The aim is to reveal the consistency between relaxation behavior and thermal properties of two different crosslink systems. Unfilled NR is crosslinked with two alternative sulfur vulcanization systems, namely of CV and EV types, with fixed total contents of the crosslinking agent and accelerator, the relation of stress relaxation behavior with thermal degradation resistance is discussed.

2. Materials and Methods 2.1 Materials

2.3 Characterization 2.3.1 Curing characteristics The curing characteristics of different NR compounds were measured at 160 °C for 20 minutes, using a Moving die rheometer, MDR 3000 Basic (Montech, Germany). The rheometric parameters scorch time (Ts1), cure time (Tc90), maximum torque (MH), torque difference (MH-ML) and cure rate index (CRI) were determined. Tc90 is the time at which 90% of cure has taken place and can be estimated as: Tc90 = M L + 0.9 ( M H − M L ) (1)

The cure rate indexes (CRIs) for the compounds were calculated from: CRI =

100 (2) Tc90 − Ts1

where, Tc90 is the time at 90% vulcanization (min) and Ts1 is the scorch time (min). 2.3.2 Aging resistance The aging resistance of NR vulcanizates at high temperatures was quantified in terms of the percentage of reversion in rubber vulcanizates after 300s from maximum torque value (R300). The percentage of reversion was comparatively calculated according to the equations given by Khang and Ariff and Kok[17,18] which was expressed as follows:

M H − M 300s The NR (STR 5L) was purchased from Chalong = × 100 (3) R300 MH Concentrated Natural Rubber Latex Industry Co., Ltd., Thailand. Stearic acid and zinc oxide (ZnO) used as where MH is the maximum torque in rheometric test and M300s activators for the sulfur curing system were manufactured is the torque 300 seconds after the maximum torque peak[17]. by Imperial Chemical Co. Ltd., Pathumthani, Thailand and Global Chemical Co. Ltd., Samutprakarn, Thailand, (Tmax − Tt ) × 100 (4) R300 respectively. N-cyclohexyl-benzothiazyl-sulphenami = (Tmax − Tmin ) de (CBS) purchased from Flexsys America L.P., West Here, Tmax is maximum torque, Tt is torque at t seconds after Virginia, USA, was used as accelerator, and the sulfur maximum and Tmin is minimum torque[18]. was manufactured by Siam Chemical Co., Ltd., Samut Prakan, Thailand. 2.3.3 Temperature Scanning Stress Relaxation (TSSR) Measurement

2.2 Sample preparation NR was compounded with other ingredients, namely stearic acid, ZnO, CBS and sulfur, using an internal mixer (Brabender GmbH & Co. KG, Duisburg, Germany) at a fixed fill factor of 0.8, initial temperature of 40 °C and a rotor speed of 60 rpm. The chemical formulations, mixing steps and mixing times are displayed in Table 1. Total ingredient contents were kept constant at 107 part(s) per hundred parts of rubber (phr) while mixing time of all samples was fixed at 5 min. The mixing torque was recorded and the compounds were finally compression molded at 160 °C using a laboratory hot press according to their respective curing times. In this study, the compound formulation was designed to incorporate only necessary additives in order to minimize undesired properties. Thus, the effect of crosslink types on thermal property can be truly estimated. 2/7

The TSSR measurement (Brabender, Duisburg, Germany) was performed in order to investigate thermo-mechanical behavior of the NR vulcanizates[19]. The NR specimens were placed in the electrical heating chamber at temperature of about 23 °C and at the strain of 50% for 2 h. Non-isothermal Table 1. Compound formulations of NR with two alternative sulfur crosslinking systems. Chemical NR (STR 5L) Stearic acid ZnO CBS Sulfur Total

Quantity (phr) CV

EV

100 1 3 0.5 2.5 107

100 1 3 2.5 0.5 107

Time at which chemical was added (min) 0 2 3 4 Dump at 5 min

Polímeros, 30(2), e2020016, 2020


Relationship between stress relaxation behavior and thermal stability of natural rubber vulcanizates test was then performed with heating rate of 2 K/min until the specimens were ruptured. The crosslink density (υ) was estimated from the initial part of the normalized force curve according to the following correlations[13]: σ = υ ⋅ R ⋅ T (λ − λ −2 ) (5) = υ

κ = ; κ σ / T (6) R(λ − λ −2 )

where, R is the universal gas constant, λ is the strain ratio, σ is mechanical stress and T is absolute temperature. 2.3.4 Thermal properties Thermal properties of the crosslinked NR were investigated from thermogravimetric analysis with TGA4000 (PerkinElmer, USA). The samples were tested from 30 to 500 °C with a heating rate of 10 °C/min and N2 flushing at 30 ml/min. The degradation kinetics of crosslinked NR was also determined from thermogravimetric analysis with TGA4000 (PerkinElmer, USA) done at the heating rates of 5 °C/ min, 10 °C/ min and 20 °C/ min. The formula of Flynn-Wall Ozawa (FWO) was applied to estimate the activation energy (Ea) of degradation as follows[20,21]:

τ = K γ n (10)

where K is the consistency index, τ refers to the shear stress and γ is the rate of strain. Since the final mixing torques were almost identical across the cases, it is reasonable to assume that the differences in weight-average molecular weights were negligible.

3.2 Curing characteristics Rheometer curves for NR crosslinked with CV and EV systems are shown in Figure 2. It can be seen that the curves show differently. As for the EV system, the torque increased steeply with vulcanization time until reaching its maximum, after which it remained constant (plateau). This is not similar to CV system where the torque decreased (reversion) after its maximum. This pattern of behaviour is frequently found when NR is crosslinked with CV and EV systems[24]. It has been reported that the majority crosslink formation in the CV systems was poly and disulfidics (> 90%), while the monosulfidic was dominant in the EV system (> 80%)[25]. The plateau behaviour with EV system is thus due to thermally stable crosslinks of monosulfidic types, while decreasing

0.4567 Ea E  (7) Ln( β= ) [ Ln  a  − Ln( g (α )) − 2.315] − RT  R 

Here, β is the heating rate, Ea is the activation energy, R is the universal gas constant (8.314 j.mol-1.K-1), g(α) is a degree of conversion and T is the absolute temperature. By plotting the Ln (β) against 1/T, the value of E can be evaluated from the slope -0.4567 Ea /R.

3. Results and Discussions 3.1 Torque-time curves of mixing Mixing torque profiles of the NR compounds were recorded in order to investigate changes in their molecular weights. Figure 1 shows time profiles of torque during mixing. In all cases the first peak comes from introduction of NR into the mixer. The sudden drops of torque after 2 to 3 min was due to ram opening to add activator and curing agents. The torque at the end of mixing was almost constant, and it is widely accepted that for polymer mixes the final torque in an internal mixer relates to the weight-average molecular weight as follows[22,23].

Figure 1. Torque-time curves during mixing the NR compounds.

Torque = C.N n .η0 (8)

and η0 = B(T ).M w3.4 (9)

Here C and N are a factor related to the geometry and the rotor speed, respectively. Mw is the weight-averaged molecular weight, η0 is the zero-shear viscosity, B (T) is a temperature dependent factor, and n is determined from: Polímeros, 30(2), e2020016, 2020

Figure 2. Rheometeric curves for NR crosslinked with CV and EV systems. 3/7


Hayeemasae, N., & Masa, A. torque after the maximum with the CV system is attributed to breakdown of some thermally unstable polysulfidic crosslinks with lesser bond strength (˂ 262 kJ/mol) than the monosulfidic linkages (~ 280 kJ/mol)[8,9]. The curing parameters in term of maximum torque (MH) and torque difference (MH-ML) obtained with the CV and EV systems are shown in Table 2. The Ts1 and Tc90 were shorter with EV than with CV systems, indicating that the EV system had shorter scorch safety and vulcanization times. As a result of fast curing, the CRI value of EV system is higher than that of the CV system. This was probably resulted from high dosages of accelerator to sulfur. Furthermore, the MH and MH-ML values were much higher with CV than with EV systems. The higher value of the MH indicates the higher stiffness of the CV sample after fully vulcanization, while the greater MH-ML is the higher the crosslink density[26]. The higher stiffness and crosslink density with CV system is due to the higher concentration of sulfur for initiating crosslink reactions than in the EV system. As a result, more extensive vulcanization takes place with the CV system.

Table 2. Curing properties in terms of Ts1, Tc90, CRI, MH and MH-ML for NR crosslinked with CV and EV systems. Cure characteristic Ts1 (min) Tc90 (min)

Curing system CV EV 1.17 ± 0.05 0.89 ± 0.00 4.38 ± 0.22

1.95 ± 0.09

CRI (min-1)

31.20 ±1.65

95.15 ±8.29

MH (dN.m)

18.88 ± 0.48

16.10 ± 0.15

MH-ML (dN.m)

15.81 ± 0.44

12.93 ± 0.16

3.3 Reversion resistance Reversion resistance of NR crosslinked with CV and EV systems was investigated by exposure to shear and elevated temperature for a certain period of time. Figure 3 displays the percentage of reversion according to the equations given by Khang and Ariff [17] and Kok[18]. As the percentage of reversion was estimated after a certain time past the maximum torque, a greater value means higher reversion. A larger value R300 was detected for the CV system, meaning that the NR crosslinked with CV system had poorer reversion resistance as compared with the EV system. As previously mentioned, polysulfidic linkages are dominant with the CV system but monosulfidic linkages are dominant with the EV system. The polysulfidic linkages have poorer bond strength (<265 kJ mol−1)[8,9], and were easier to break by shear and heat.

Figure 3. Reversion resistances (R300) of NR crosslinked with CV and EV systems calculated according to (A) Ref 17, and (B) Ref 18.

3.4 Temperature scanning stress relaxation (TSSR) Figure 4 shows normalized force curves of the samples crosslinked with CV and EV systems as a function of temperature. The embedded figure was a magnifying of the initial curves in the temperature range of 30 to 40 °C. It is generally seen from Figure 4 that the initial normalized force of both samples increased slightly at temperatures of 30- 40 °C due to the entropy effect[27] and the increase of force was sharper in the CV system (see embedded figure), implying the higher crosslink density of the CV sample. The crosslink density of the CV and EV systems was about 111.25 and 87.32 mol/m3. At elevated temperature, the force decrease toward zero due to chain scission caused by thermo-oxidative reaction occurs[19]. It is also seen that the force at any given temperature of the EV system was shifted to higher temperature, compared to the CV system. In some cases, the shift of these parameters was attributed to the molecular weight differences[16] and crosslink densities[8,10], but these two reasons were not applicable for this study due to the negligible change in molecular weight(see Figure 1) and a higher crosslink was gained from the CV system. Thus, influence of crosslink degree and molecular weight can be eliminated. As previously 4/7

Figure 4. Normalized force curves of NR crosslinked with CV and EV systems.

mentioned, the EV system contains majority high thermal stability monosulfidic linkages while the less thermal stability polysulfidic linkages are dominant in the CV system. Thus, it is reasonable to conclude that the lower thermo-oxidative degradation level in the EV system was attributed to the higher thermal stability of monosulfidic linkages. The result clearly confirmed that the type of crosslinks is the main parameter controlling thermal behaviour of the rubber vulcanizates. The TSSR relaxation spectra of various samples are shown in Figure 5. In the unfilled vulcanizates, the relaxation peak was usually caused by cleavage of sulfur bridges and/or scission of the polymer main chain[14]. It is seen that Polímeros, 30(2), e2020016, 2020


Relationship between stress relaxation behavior and thermal stability of natural rubber vulcanizates aging resistance of the CV was poorer than that of the EV system can be confirmed. It is widely accepted that within temperature range of TSSR measurement, the changes in mechanical properties due to crosslink scission of the rubber structures can be detected. But at higher temperature, crosslink scission and main chain degradation occur simultaneously. To further understand the degradation of CV and EV systems at high temperature and to correlate high temperature properties with low temperature behaviors, TGA was performed.

3.5 Thermal properties

Figure 5. Relaxation spectrum of NR crosslinked with CV and EV systems.

Figure 6. Thermogravimetric curves: (A) weight loss (%), and (B) derivative weight loss versus temperature of NR samples at 10 °C/min heating rate.

the peak of relaxation spectrum of EV system was shifted toward higher temperature, revealing that the breakage of sulfur bridges and/or chain scission of the main chains occur at higher temperature as compared to the CV system. This was attributed to the fact that the higher thermal stability of monosulfidic linkages formed with the EV system[8,9]. As a result of stronger bonding energy of monosulfidic linkage, the stress relaxation behaviour of the EV system was found at higher temperature than the CV system. Therefore, the Polímeros, 30(2), e2020016, 2020

TGA analysis was performed in order to observe thermal degradation behavior and thermal stability for NR crosslinked with CV and EV systems. In this study, the thermal stability of the NR vulcanizates was evaluated from that temperature at which the sample had lost 5% of its initial weight (Td5). The relationship of weight loss (%) with temperature and the derivative weight loss curves at heating rate of 10 °C/min are shown in Figure 6B. It is seen from Figure 6Athat the crosslinked NR samples showed two regions of degradation: a minor weight loss at 180 – 300 °C, and a major loss at 300 – 470 °C. The former weight loss was attributed to volatile substances including stearic acid and moisture, and the latter was due to the degradation of rubber molecules[28]. The Td5 with the CV system appeared at 328 °C, which is lower than the corresponding temperature with the EV system (331 °C), meaning that the CV system gave poorer thermal stability than the EV system. Considering the derivative weight loss curves (Figure  6B), the maximum degradation rate with the EV system (-14.19 wt %/min) was slower than with the CV system (-15.47 wt %/min). The degradation of NR chains crosslinked with the EV system was slightly harder than with the CV system. Again, this was attributed to the higher thermal stability of linkages formed with the EV system. As the CV system provided higher crosslinking degree but the thermal properties with CV were poorer than with the EV system. Therefore, the degree of crosslinking does not determine the thermal stability (or resistance to degradation). Only type of crosslinkage is responsible for this change. Higher thermal stability of monosulfidic linkage formed with the EV system may retard both the scission of crosslink and degradation of main chain. The TGA results are in accordance well with the TSSR result as previously shown. To gain further confirm the degradation process of NR crosslinked with CV and EV systems, activation energies associated with degradation was estimated. The activation energy is the minimum energy required of molecules for them to undergo a phase transition during heating[29]. Plots of Ln (β) versus 1/T for NR crosslinked with the two alternative systems are shown in Figure 7, and the estimates of activation energies are shown in Figure 8. The degradation after curing with the CV system required a lesser activation energy than with the EV system, so the former case was easier to degrade. The higher activation energy with the EV system clearly confirms that the NR crosslinked with EV system had harder degradation and better thermal stability than with the CV system. This is here tentatively attributed to the crosslink system. 5/7


Hayeemasae, N., & Masa, A.

4. Conclusions In this study, influences of two alternative sulfur vulcanization systems, of CV and EV types, on curing reaction, stress relaxation behavior and thermal properties of NR vulcanizates were investigated. The CV system provided higher maximum toque and torque different. From TSSR measurements, the degree of crosslinking was greater with the CV system. However, higher crosslink and chain scissions caused by thermo-oxidative occurs in the CV system due to the polysulfidic crosslinks having comparatively poorer thermal stability. The monosulfidic linkage in the EV system tentatively provided better resistance to the scission of both crosslink and rubber chains as revealed by TGA analysis. The degradation of the rubber main chain was found to hinder by the EV system as was later confirmed by higher activation energy. Both TSSR measurement and TGA analysis showed well agreement that the better aging property, thermo-oxidative resistance and thermal stability were greater with the EV system.

5. Acknowledgements The authors gratefully acknowledged Prince of Songkla University for financial support (Grant no. RDO6202102S). Research and Development Office (RDO) of Prince of Songkla University and Assoc. Prof. Dr. Seppo Karrila are also acknowledged for assistance in editing the English language in this manuscript.

6. References Figure 7. Plot of Ln (β) versus 1/T for NR crosslinked with (A) CV, and (B) EV systems.

Figure 8. Activation energy of thermal degradation for NR crosslinked with CV, and EV systems.

Since the high temperature results obtained from TGA measurement agreed well with the low temperature behavior tested by TSSR technique, it is reasonable to assume that the thermal behavior at higher temperature can be partially estimated by using temperature stress relaxation technique which was tested at lower temperature. 6/7

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Relationship between stress relaxation behavior and thermal stability of natural rubber vulcanizates Benarey (Eds.), Rubber products manufacturing technology (pp. 315-396). New York: Marcel Dekker Inc. 10. Larpkasemsuk, A., Raksaksri, L., Chuayjuljit, S., Chaiwuthinan, P., & Boonmahidthisud, A. (2019). Effects of sulfur vulcanization system on cure characteristics, physical properties and thermal aging of epoxidized natural rubber. Journal of Metals Materials and Minerals, 29(1), 49-57. 11. Boonkerd, K., Deeprasertkul, C., & Boonsomwong, K. (2016). Effect of sulfur to accelerator ratio on crosslink structure reversion, and strength in natural rubber. Rubber Chemistry and Technology, 89(3), 450-464. http://dx.doi.org/10.5254/ rct.16.85963. 12. Rattanasom, N., Poonsuk, A., & Makmoon, T. (2005). Effect of curing system on the mechanical properties and heat aging resistance of natural rubber/tire tread reclaimed rubber blends. Polymer Testing, 24(6), 728-732. http://dx.doi.org/10.1016/j. polymertesting.2005.04.008. 13. Vennemann, N., Bokamp, K., & Broker, D. (2006). Crosslink density of peroxide cured TPV. Macromolecular Symposia, 245246(1), 641-650. http://dx.doi.org/10.1002/masy.200651391. 14. Vennemann, N., Schwarze, C., & Kummerlowe, C. (2014). Determination of crosslink density and network structure of NR Vulcanizates by means of TSSR. Advanced Materials Research, 844, 482-485. http://dx.doi.org/10.4028/www. scientific.net/AMR.844.482. 15. Oncel, S., Kurtoglu, B., & Karaagac, B. (2019). An alternative antioxidant for sulfur-vulcanized natural rubber: henna. Journal of Elastomers and Plastics, 51(5), 440-456. http://dx.doi. org/10.1177/0095244318796594. 16. Karaagac, B., Cengiz, S. C., Bayram, T., & Sen, M. (2018). Identification of temperature scanning stress relaxation behaviors of new grade ethylene propylene diene elastomers. Advances in Polymer Technology, 37(8), 3027-3037. http:// dx.doi.org/10.1002/adv.21973. 17. Khang, T. H., & Ariff, Z. M. (2012). Vulcanization kinetics study of natural rubber compounds having different formulation variables. Journal of Thermal Analysis and Calorimetry, 109(3), 1545-1553. http://dx.doi.org/10.1007/s10973-011-1937-3. 18. Kok, C. M. (1987). The effects of compounding variables on the reversion process in the sulphur vulcanization of natural rubber. European Polymer Journal, 23(8), 611-615. http:// dx.doi.org/10.1016/0014-3057(87)90006-1. 19. Srinivasan, N., Bokamp, K., & Vennemann, N. (2005). New test method for the characterisation of filled elastomers. KGK. Kautschuk, Gummi, Kunststoffe, 2005(58), 650. 20. Alwaan, I. M., & Hassan, A. (2014). Pyrolysis, kinetic and kinetic model study of epoxidized natural rubber. Progress in

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Rubber, Plastics and Recycling Technology, 30(3), 153-168. http://dx.doi.org/10.1177/147776061403000303. 21. Chrissafis, K. (2009). Kinetics of thermal degradation of polymer, complementary use of isoconversional and modelfitting methods. Journal of Thermal Analysis and Calorimetry, 95(1), 273-283. http://dx.doi.org/10.1007/s10973-008-9041-z. 22. Jung, C., Jana, S. C., & Gunes, I. S. (2007). Analysis of polymerization in chaotic mixers using time scales of mixing and chemical reactions. Industrial & Engineering Chemistry, 46(8), 2413-2422. http://dx.doi.org/10.1021/ie0613319. 23. Verhoeven, V. W. A., van Vondel, M. P. Y., Ganzeveld, K. J., & Janssen, L. P. B. M. (2004). Rheoâ&#x20AC;?kinetic measurement of thermoplastic polyurethane polymerization in a measurement kneader. Polymer Engineering and Science, 44(9), 1648-1655. http://dx.doi.org/10.1002/pen.20163. 24. Rabiei, S., & Shojaei, A. (2016). Vulcanization kinetics and reversion behavior of natural rubber/styrene-butadiene rubber blend filled with nanodiamond - The role of sulfur curing system. European Polymer Journal, 81, 98-113. http://dx.doi. org/10.1016/j.eurpolymj.2016.05.021. 25. Akiba, M., & Hashim, A. S. (1997). Vulcanization and crosslinking in elastomer. Progress in Polymer Science, 22(3), 475-521. http://dx.doi.org/10.1016/S0079-6700(96)00015-9. 26. Surya, I., & Ismail, H. (2016). Alkanolamide as a novel accelerator and vulcanising agent in carbon black-filled polychloroprene rubber compounds. Plastics, Rubber and Composites, 45(7), 287-293. http://dx.doi.org/10.1080/14658011.2016.1187477. 27. Barbe, A., Bokamp, K., Kummerlowe, C., Sollmann, H., Vennemann, N., & Vinzelberg, S. (2005). Investigation of modified SEBS-based thermoplastic elastomers by temperature scanning stress relaxation measurements. Polymer Engineering and Science, 45(11), 1498-1507. http://dx.doi.org/10.1002/ pen.20427. 28. Hayeemasae, N., Ismail, H., Matchawet, S., & Masa, A. (2019). Kinetic of thermal degradation and thermal stability of natural rubber filled with titanium dioxide nanoparticles. Polymer Composites, 40(8), 3149-3155. http://dx.doi.org/10.1002/ pc.25163. 29. Tripathy, S. P., Mishra, R., Fink, D., & Dwivedi, K. K. (2004). Irradiation effect on the activation energy of thermal decomposition of polymers. Radiation Effects and Defects in Solids, 159(11-12), 607-612. http://dx.doi.org/10.1080/1042 0150412331330502. Received: Mar. 16, 2020 Revised: June 17, 2020 Accepted: June 18, 2020

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.10019

Synthesis and properties of fluorinated copolymerized polyimide films Chuanhao Cao1 , Lizhu Liu1,2*, Xinyu Ma1, Xiaorui Zhang1,2 and Tong Lv1 School of Materials Science and Engineering, Harbin University of Science and Technology, Harbin, China 2 Key Laboratory of Engineering Dielectric and Its Application, Harbin University of Science and Technology, Ministry of Education, Harbin, China

1

*mrliu_hust@163.com

Abstract Two series of fluorinated copolymerized polyimide films with different dianhydride ratios were prepared via the conventional two-step method by using 4,4-oxydianiline(ODA) as the diamine monomer, 4,4’-(hexafluoroisopropylidene) diphthalic anhydride(6FDA), 4,4’-oxydiphthalic anhydride(ODPA) and 3,3’,4,4’- biphenyl tetracarboxylic dianhydride(BPDA) as the dianhydride monomer in N, N-dimethylacetamide. With the increase of 6FDA in the proportion of dianhydride, the tensile strength of the polyimide film showed a decreasing trend. This work provided a high performance film. The mass retention rate at 800°C was above 50%. The glass transition temperatures of the two films were 260 °C and 275 °C. The storage modulus of the two were 1500 MPa and 1250 MPa. The loss modulus were 218.70 MPa and 120.74 MPa. The transmittance of the film was 71.43%. The transmittance of fluorinated copolymerized polyimide films were significantly improved in the visible region of ultraviolet light, indicating that the polyimide film with high transmittance, high tensile strength, high heat resistance and high storage modulus was successfully prepared. It had an excellent application prospect in the field of flexible display. Keywords: fluoropolymers, polyimides, copolymerization, solubility, transparency. How to cite: Cao, C., Liu, L., Ma, X., Zhang, X., & Lv, T. (2020). Synthesis and properties of fluorinated copolymerized polyimide films. Polímeros: Ciência e Tecnologia, 30(2), e2020017. https://doi.org/10.1590/0104-1428.10019

1. Introduction Polyimides were widely used in aerospace [1], microelectronics[2], national defense technology[3] and other fields[4], due to its excellent thermal stability, mechanical properties, chemical stability and good dielectric properties[5-7]. Polyimide is one of the high performance polymers. However, the Kapton polyimide materials developed by DuPont Company have different defects, such as large structural rigidity, poor transmittance and high glass transition temperature, which leads to complicated subsequent processing[8-10]. Because of the close packing of polyimide chains and the strong transfer(CT) effect between molecules, the molecular chain has strong absorption and low transparency in the UV visible band, which restricts its application in the field of optical and photoelectron[11,12]. The introduction of functional groups in diamine monomers or dianhydride monomers was currently the main method for preparing different kinds of polyimide materials[13-15]. Fluorinated polyimides were widely used in improving the transmittance of polyimide films. The introduction of fluorine group increases the free volume of the polyimide molecular chain, thereby improving the solubility, dielectric properties, etc[16,17]. In addition, the introduction of such groups could reduce the moisture absorption rate and increase the flame retardancy. The most important was that the

Polímeros, 30(2), e2020017, 2020

fluorine-containing groups could weaken the intermolecular forces and increase the transparency. But beyond that, another approached to achieving the desired material properties utilizes copolymerization. The third monomer was introduced into the molecular chain by a method of copolymerization, which changes the symmetry and regularity of the molecular chain, at the same time, the thermal stability of the polyimide film has not changed. This regularity could lead to a reduction in intermolecular interactions, which in turn results in new features, such as modified thermomechanical and gas permeation properties, and altered solubility. Furthermore, the properties of copolymer polyimides could be easily adjusted and controlled by varying the ratio of the dianhydride and diamine monomers. The traditional aromatic benzene type PI was usually brownish yellow and the light transmittance was low, which was mainly due to the strong charge transfer complex (CTC) formed between aromatic dianhydride and aromatic diamine. Therefore, the surface of PI film has a certain orientation structure by introducing F group, lipid ring structure and so on into the Polyimide system.For example Xiao et al.[18] researched the effects of the effect of the fluorine-containing group on the transmittance of the whole frequency band.

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


Cao, C., Liu, L., Ma, X., Zhang, X., & Lv, T. Moon et al.[19] had a transmittance of 60%at 400 nm. Shen et al.[20] added nano-silica particles in the F-containing system. Wu et al. added fillers to the polyimide film, which greatly improved the performance of the film[21,22]. This article used 4,4-oxydianiline(ODA) as the diamine monomer, 4,4’-(hexafluoroisopropylidene) diphthalic anhydride(6FDA), 4,4’-oxydiphthalic anhydride(ODPA) and 3,3’,4,4’- biphenyl tetracarboxylic dianhydride(BPDA) as the dianhydride monomer to synthesize two series of fluorinated copolymerized polyimide films with different proportions. The thermal properties, mechanical properties, solubility and optical properties of copolymer polyimide with different copolymerization ratios were investigated, and the polyimide with good thermal stability and light transmittance was developed, and its application field was expanded.

2. Experiment 2.1 Experiment Materials For fabrication of fluorinated copolymerized polyimide films, the materials were listed in Table 1.

3. Measurement Fourier transform infrared (FTIR) spectra for fluorinated copolymerized polyimide films were measured in the range of 500-4000 cm-1 using the Bruker infrared spectrum analyzer EQUINOX55. In order to analyze the structural changes during the imidization process; The thermal stability of copolymerized polyimide films were recorded by using thermogravimetric analyzer(TGA), the residual mass was measured at a boost rate of 20 °C/min under the nitrogen environment medium from 20°C to 800°C; The storage modulus(E’), loss modulus(E”) and glass transition(Tg) of fluorinated copolymerized polyimide films with different dianhydride ratios were measured by dynamic thermal analyzer(DMA) Q800; The tensile strength of the copolymerized polyimide was measured by Shimadzu AGS-J electronic almighty material experiment machine, the standard of the sample was 100×15 mm and the clamping distance was 100 mm; Ultraviolet-visible (UV-vis) spectra of the polymer films were recorded on a Shimadzu UV-2450 instrument. It was intended to analyze the relationship between the transmittance of the films and the presence of different ratios of 6FDA and ODPA/BPDA.

2.2 Experimental Procedure

4. Results and Discussion

The polyamic acid (PAA) was prepared by solution polycondensation among ODA, 6FDA and ODPA/BPDA. The solid content in the PAA solution was 10 wt%. The specific experimental steps were as follow: the solvent DMAc and the corresponding mass of ODA were added to the three-necked flask and stirred under nitrogen gas. After the ODA was completely dissolved, 6FDA and ODPA(n ODA:n 6FDA &ODPA=1:1) or 6FDA and BPDA(nODA:n6FDA &BPDA=1:1) were added in batches to three bottles until the “climbing-bar” phenomenon occurs and mechanically stirred at room temperature for 3h. After cleaning the glass plate, the standing polyamic acid(PAA) was poured onto the glass plate and spread with scraper of a certain thickness. The film was put into oven, and the thermal imidization was carried out by gradient heating. Imidization process was 80 °C/60 min, 120 °C/30 min, 160 °C/30 min, 200 °C/30 min, 250 °C/30 min, 300 °C/30 min, 350 °C/60 min. When the temperature of the oven was cooled to room temperature, the polyimide films were obtained. The composition and name of the polyimide were shown in Table 2. The reaction equation of ODA as diamine monomer, 6FDA and ODPA as dianhydride monomer was taken as an example. The reaction equation of the polymerization was shown in Figure 1.

4.1 Structure characterization of fluorinated polyimide films The properties of polyimide were closely related to the degree of imidization during the preparation process. The current means of characterizing the degree of imidization include the deuteration method, the cyclization thermal effect method, and the nuclear magnetic resonance method, and the degree of imidization was calculated by measuring the moisture released during the cyclization. In this paper, the degree of imidization of polyimide films was qualitatively analyzed by infrared absorption spectroscopy. The infrared spectra of fluorinated copolymerized polyimide films were shown in Figure 2. As could be seen from Figure 2, the absorption peaks of the above three locations disappeared, and it could be concluded that the amide structure have been reacted, and the structure of the prepared films were analyzed. It was found that the films had -cm-1 corresponded to the asymmetric expansion vibration of C=O, and the 1729 cm-1 corresponded to the C=O symmetric expansion vibration. Compared with ordinary polyimide, we found that the carbonyl stretching vibrations on the fluorinated polyimide-imide rings moved toward higher wave numbers. It may be due to the inducing effect of trifluoromethyl group that made the carbonyl double bond enhance and the frequency of stretching vibration increase. 1500 cm-1 and 1050cm-1 corresponded to the vibration of the benzene ring skeleton. The absorption

Table 1. Experiment Materials.

4,4-oxydianiline(ODA)

Molecular Formula C12H8N2O

4,4’-(hexafluoroisopropylidene) diphthalic anhydride(6FDA)

C19H6F6O6

Shanghai Macklin Biochemical Co.,Ltd.

4,4’-oxydiphthalic anhydride(ODPA)

C16H6O7

Shanghai Macklin Biochemical Co.,Ltd.

3,3’,4,4’- biphenyl tetracarboxylic dianhydride(BPDA)

C16H6O6

Shanghai Macklin Biochemical Co.,Ltd.

Name

2/7

Source Sinopharm Group Chemical Reagent Co., Ltd.

Polímeros, 30(2), e2020017, 2020


Synthesis and properties of fluorinated copolymerized polyimide films peak at 1380 cm-1 represented the symmetric contraction vibration of the C-N, and the 725 cm-1 corresponded to the bending vibration of the C=O. These characteristic peaks were consistent with the standard peak positions of the polyimide in Table 2, indicating the presence of polyimide structure and characterizing the polyimide structure.

4.2 Thermal stability of fluorinated polyimide films Figure 3 displayed the thermogravimetric curves of fluorinated copolymerized polyimide films with different proportions of dianhydride. From Figure 3a, it could be seen that the copolymerized polyimide began to decompose at 500 °C, and the weight loss at 5% was 533.7, 550.31, 546.4, 557.8, and 560.7 °C, respectively. With the increase of 6FDA content in dianhydride, the initial decomposition temperature of the polyimide film also increased slightly. This was mainly due to the presence of C-F bond in the fluorinated polyimide polymer. The C-F bond energy was as high as 486 kJ/mol, which required a large amount of heat for thermal decomposition to break it, so it had a high initial thermal decomposition temperature. Figure 3b had the same principle. The temperature of polyimide film weightlessness 5% was increased from 490.6 to 580.6 C. In contrast to Figure 3a and Figure 3b, we could get that the thermal stability of PI(BPDA) was better than that of PI(ODPA). This was mainly due to the fact that BPDA, a raw material for the synthesis of polyimide films, had a highly symmetrical structure and a high degree of molecular rigidity[23,24], resulting in the improvement of molecular heat resistance. As the temperature continued to increase, the pendant groups on the main chain of the polyimide decomposed, the imine bond broke with the formation of short-chain molecules, and the benzene ring side chain dehydrogenatee to produce H2, CO2, CO[25]. With the increase of pyrolysis temperature, the quality of the film decreased obviously. Finally, the polyimide decomposed completely and the curve became stable. The quality retention rate at 800°C was 54.5%, 55.3%, 57.2%, 59.5%, 63.3%, and 50.1%, 51.1%, 51.5%, 52.2%, 60.1%, respectively. In general, fluorinated polyimide films with different proportions of dianhydride have good thermal stability.

4.3 Dynamic thermo-mechanical analysis of fluorinated polyimide films

and the interaction forces between molecules. The change of loss modulus (E”) represented the intensity of the movement of molecular chains. The change of storage modulus(E′) represented the strength of intermolecular forces[26]. The dynamic thermo-mechanical analysis of fluorinated polyimide films were appeared in Figure 4 (take PI(ODPA-3) and PI(BPDA-3)as examples). From the curves of loss modulus (E′′) versus temperature in Figure 4a and Figure 4b, it could be seen that the peak temperature of the respective loss modulus represented the

Figure 1. Polymerization reaction equation.

Figure 2. The infrared spectra of fluorinated copolymerized polyimide films.

Dynamic thermo-mechanical analysis (DMA) characterizes the glass transition temperature of a material by measuring the change in the modulus of the material with temperature, that is, the manifestation of the movement of molecular chains Table 2. The composition and name of the polyimide. 6FDA:ODPA

6FDA:BPDA

Dianhydride ratios 1:9 3:7 5:5 7:3 9:1 1:9 3:7 5:5 7:3 9:1

Polímeros, 30(2), e2020017, 2020

PI PI(ODPA-1) PI(ODPA-2) PI(ODPA-3) PI(ODPA-4) PI(ODPA-5) PI(BPDA-1) PI(BPDA-2) PI(BPDA-3) PI(BPDA-4) PI(BPDA-5)

Figure 3. The thermogravimetric curves of fluorinated copolymerized polyimide films. (a) Different monomer ratio PI( 6FDA/BPDA) films; (b) Different monomer ratio PI(6FDA/OPDA)films. 3/7


Cao, C., Liu, L., Ma, X., Zhang, X., & Lv, T.

Figure 4. DMA diagram of fluorinated polyimide film. (a) Thermal performance of different monomer ratio PI(6FDA/BPDA)films; (b) Thermal performance of different monomer ratio PI(6FDA/OPDA)films.

glass transition temperature, the Tg of PI(ODPA-3) and PI(BPDA-3) was 260 °C and 275 °C, respectively. This was due to the existence of oxygen ether bridging bonds in ODPA, which improved the flexibility of molecular chains, resulting in a decrease in the glass transition temperature compared with BPDA. Both have glass transition temperature between 250 °C and 280 °C, and the loss modulus reached a peak, which indicated that the material had a sharp loss of modulus in this temperature range, that is, the polymer macromolecular chain forging moved violently. At the same time, there was a close relationship between the E′′ of the polyimide film and the molecular weight of the polymer. The larger the molecular weight of the material, the more tangles between the molecules, the displacement of molecules under external forces, and the resistance between the molecular chains, the more heat generated by friction, the greater the corresponding E′′. From Figure 4, we could conclude that the loss modulus(E”) of PI(ODPA-3) was 218.70 MPa, and the loss modulus(E”) of PI(BPDA-3) was 120.74 MPa, indicating that the existence of ODPA made the molecular chain more flexible, the molecular weight greater, and the resistance to be overcome larger. From the curve of the storage temperature(E’) change with temperature in Figure 4a and Figure 4b, the modulus at the cut-point of the storage modulus change curve was 1500 MPa and 1250 MPa, respectively. The existence of 6FDA would make the film have more free space and the ether bond in ODA could effectively stabilize the structure and improve the tangles between the molecules. The heat generated by the film friction of ODA is higher than the film friction of BPDA.

4.4 The mechanical properties of fluorinated polyimide films Figure 5 illustrated the effect of different dianhydride ratios on the mechanical properties of polyimide films. It could be seen from Figure 5 that the tensile strength of the same series of polyimide films decreased with the increase of 6FDA ratio. The reason was that the fluorine side group existed in the 6FDA. The introduction of the side group in the polyimide chain destroyed the charge transfer complex (CTC) interaction between the polyimide chains and weakened the interaction between the molecules. Thus, the tensile strength of the polyimide film decreased 4/7

Figure 5. The mechanical properties of fluorinated polyimide films.

significantly. The tensile strength of PI(ODPA) decreased from 198.832 MPa to 120.625 MPa. The tensile strength of PI(BPDA) decreased from 229.195 MPa to 146.75 MPa. When the proportions of two dianhydrides were the same, the flexibility of polyimide molecular chain was better, the free volume increased and the rigidity of the molecular chain was reduced because of the presence of oxygen ether bridging bonds in ODPA, thus the tensile strength of the film was reduced.

4.5 Optical properties of fluorinated polyimide films Traditional polyimide films were generally brown or yellow with low transparency. This was mainly due to the formation of intramolecular and intermolecular charge transfer complexes (CTCs).During the preparation of polyimide, polyamic acid were obtained by ring-opening polycondensation of the dianhydride monomer and an equal amount of the diamine monomer in the aprotic organic solvents such as DMAc and DMF. This process was accomplished through charge transfer complex (CTC) intermediates. In order to weaken the formation of CTC and obtain a highly transparent polyimide film, we use a fluorine-containing dianhydride monomer as a raw material to prepare polyimide film. Figure 6 was UV spectrogram of fluorinated polyimides. It could be seen from Figure 6a and 6b that the transmittance of polyimide film increased with the increase of 6FDA ratio in the dianhydride. Polímeros, 30(2), e2020017, 2020


Synthesis and properties of fluorinated copolymerized polyimide films

Figure 6. UV spectrogram of fluorinated polyimide films. (a) Transmittance of different monomer ratio PI(6FDA/BPDA)films; (b) Transmittance of different monomer ratio PI(6FDA/OPDA)films; (c) Formulation comparison of polyimide with optimal transparency.

When 6FDA:ODPA=1:9, the transmittance of polyimide film at a wavelength of 400 nm was 24.43%. With the increase of 6FDA content, the transmittance of the film gradually increased. When 6FDA:ODPA=9:1, the transmittance of the film reached its maximum, its transmittance was 71.43%, which was increased by 3 times. With the increase of the ratio of 6FDA to BPDA, the transmittance of the films increased from 14.44% to 69.28%, and had a significant increase, which was five times higher than that of the original one. The reason for this phenomenon was that the steric hindrance effect of the bis-trifluoromethyl group in the dianhydride causes the conformation of the molecular chain to be distorted and the stacking of the molecular chains to be loose, which could effectively weaken the intermolecular forces caused by the accumulation of molecular chains[27,28]. Therefore, the transmittance of the polyimide film has been significantly improved. From Figure 6c, it could be observed that the transmittance of the polyimide films at the wavelength of 400 nm were more than 69% and the transmittance was more than 90% at 470nm. Both of these films had good transparency in the UV-visible region. In contrast, PI(ODPA) had a lower cut-off wavelength and a higher transmittance at 400 nm, indicating that the PI(ODPA) film was lighter and more transparent. From Figure 6a, Figure 6b and Table 3, It describes that the light transmittance of the film increases with the increase of 6FDA content. The transparent of PI films which were Synthesised by 6FDA:OPDA increased from 24.43% to 71.43%. The transparent of PI films which were Synthesised by 6FDA:BPDA increased from 14.45% to 69.28%.The reason was that the introduction of the side group in the PI chain Polímeros, 30(2), e2020017, 2020

Table 3. The transparent of the polyimide.

6FDA:ODPA

6FDA: BPDA

Dianhydride ratios 1:9 3:7 5:5 7:3 9:1 1:9 3:7 5:5 7:3 9:1

PI PI(ODPA-1) PI(ODPA-2) PI(ODPA-3) PI(ODPA-4) PI(ODPA-5) PI(BPDA-1) PI(BPDA-2) PI(BPDA-3) PI(BPDA-4) PI(BPDA-5)

Transparent of 400 nm 71.43% 69.02% 61.27% 60.58% 24.43% 69.28% 68.95% 53.28% 37.53% 14.45%

destroyed the charge transfer complex(CTC). It was an effective way to reduce the CTC effect by weakening the intermolecular and intramolecular interactions, reducing the number of free monomers and introducing large resistance side groups. At the same time, the fluorine atoms with larger electronegativity had effectively prevented the formation of charge transfer complexes within the PI chain due to the electron-withdrawing and electron-inducing effects, further improving the optical properties of the polymer and making it exhibit good transparency[29,30].

5. Conclusion Two series of polyimides were synthesized by the two-step method from ODA and several commercial dianhydrides. The initial decomposition temperature of the films was greater than 500 °C, and the mass retention rate at 800 °C was 5/7


Cao, C., Liu, L., Ma, X., Zhang, X., & Lv, T. above 50%, which had good thermal stability. The fluorinated Copolymer films obviously have better optical transmittance and storage modulus. Taking the 6FDA and ODPA as well as 6FDA and BPDA molar ratios of 5:5 as examples, the glass transition temperatures of the two films were 260 °C and 275 °C, respectively. The storage modulus of the two were 1500 MPa and 1250 MPa, respectively, and the loss modulus were 218.70 MPa and 120.74 MPa, respectively. In the same series of fluorinated polyimide films, the tensile strength of the films decreased with the increase of 6FDA ratio. When the wavelength of ultraviolet light was 400 nm, the transmittance of PI (ODPA) film increased from 24.43% to 71.43% with the increase of 6FDA content; At the same time, the transmittance of the PI(BPDA) film increased from 14.44% to 69.28%. When the wavelength was 400 nm, the transmittance of the film was 71.43%, indicating that fluorination polymerization could effectively increase the flexibility of the film, eliminate the effect of CTC, and improve the transmittance of the film. Due to the good solubility of the polyimide in the low-boiling solvent, it was possible to achieve a low-temperature curing film formation process, which lays the foundation for further widening the application of the PI film in the field of microelectronics. Therefore, this article provide a polyimide film with high transmittance(reached 71.43% at 400 nm), high tensile strength(218.70 MPa), high heat resistance(Half loss temperature more than 800 °C) and high storage modulus (1500 GPa).

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content. Polymer, 163(1), 106-114. http://dx.doi.org/10.1016/j. polymer.2018.12.045. 26. Li, Z., Kou, K., Zhang, J., Zhang, Y., Wang, Y., & Pan, C. (2017). Solubility, electrochemical behavior and thermal stability of polyimides synthesized from 1,3,5-triazine-based diamine. Journal of Materials Science Materials in Electronics, 28(8), 6079-6087. http://dx.doi.org/10.1007/s10854-016-6284-5. 27. Wang, C., Cao, S., Chen, W., Xu, C., Zhao, X., Li, J., & Ren, Q. (2017). Synthesis and properties of fluorinated polyimides with multi-bulky pendant groups. RSC Advances, 7(42), 2642026427. http://dx.doi.org/10.1039/C7RA01568B. 28. Kim, M. K., Hwang, S. H., Jung, H. S., Oh, T. S., Kim, J. H., & Yoo, J. B. (2018). Inkjet Printing of SiO2 Hollow Spheres/Polyimide Hybrid Films for Foldable Low-k ILD. Macromolecular Research, 26(12), 1123-1128. http://dx.doi. org/10.1007/s13233-019-7001-z. 29. Yang, C. Y., Hsu, L. C., & Chen, J. S. (2005). Synthesis and properties of 6fda-bisaaf-ppd copolyimides for microelectronic applications. Journal of Applied Polymer Science, 98(5), 20642069. http://dx.doi.org/10.1002/app.22410. 30. Chang, H. C., Byung, H. S., & Chang, J. (2013). Colorless and transparent polyimide nanocomposites: comparison of the properties of homo- and copolymers. Journal of Industrial and Engineering Chemistry, 19(5), 1593-1599. http://dx.doi. org/10.1016/j.jiec.2013.01.028. Received: Feb. 11, 2020 Revised: Apr. 21, 2020 Accepted: June 20, 2020

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.10119

Synthesis of novel organocatalyzed phenoxazine for free metal atom transfer radical polymerization Thu Hoang Vo1,2, Huong Thi Le1,3, Tien Anh Nguyen3, Nhu Quang Ho1, Thang Van Le2,4, Dat Hung Tran1, Thuy Thu Truong2 and Ha Tran Nguyen1,2*  National Key Laboratory of Polymer and Composite Materials, Ho Chi Minh city University of Technology, Vietnam National University - VNU–HCM, Ho Chi Minh City, Vietnam 2 Faculty of Materials Technology, Ho Chi Minh City University of Technology, Vietnam National University, Ho Chi Minh City, Vietnam 3 Faculty of Chemistry, Ho Chi Minh City University of Education, Ho Chi Minh City, Vietnam 4 Materials Technology Key Laboratory, Vietnam National University Ho Chi Minh City, Ho Chi Minh City, Vietnam

1

*nguyentranha@hcmut.edu.vn

Abstract In this research, a novel organic photocatalyst of 10-(Perylene-3-yl-10H-Phenoxazine (PHP) has been synthesized successfully from perylene and phenoxazine via Buchwald-Hartwig C-N coupling. The chemical structure of catalyst was determined via proton nuclear magnetic resonance (1H-NMR) spectrum and optical properties were investigated through UV-Vis spectroscopy. The PHP has been used as the reducing photoredox catalyst for organocatalyzed atom transfer radical polymerization (ATRP) under UV irradiation. The well controlled molecular weight of polymers based on methyl methacrylate monomers have been obtained with monomer conversion up to 77.61% and low polydispersity index under 1.5. Keywords: methacrylate monomer, phenoxazine, organic photocatalyst, atom transfer radical polymerization. How to cite: Vo, T. H., Le, H. T., Nguyen, T. A., Ho, N. Q., Le, T. V., Tran, D. H., Truong, T. T., & Nguyen, H. T. (2020). Synthesis of novel organocatalyzed phenoxazine for free metal atom transfer radical polymerization. Polímeros: Ciência e Tecnologia, 30(2), e2020018. https://doi.org/10.1590/0104-1428.10119.

1. Introduction The polymerization for synthetic polymers according to metal catalysts by the ATRP mechanism is considered as the advanced process in the polymer industry[1-3]. The use of transition metal during synthetic procedure gives many advantages including controlled the molecular weight and polydispesity index of obtained polymer as well as controlled the end-groups of obtained polymers but the obtained polymeric products always remain the trace of transition metals[4,5]. This elimination of metals catalyst caused tremendous damage in the subsequent use of polymer products in bio-medicine, opto-electronic application. To overcome this issue, the organic photocatalyst (O-ATRP/metal-free ATRP) has been developed for synthesis of the metal-free polymer via controlled radical polymerization[6] which gradually replace the traditional ATRP-based transition metal catalysts[6-8]. There have been many studies on the field of O-ATRP polymerization using organic photocatalyst[7,8] and light for the catalyst activation process[9]. Matyjaszewski and colleagues have used phenoloxazine and phenolthiazine as organic photocatalysts for the controlled polymerization of acrylonitrile[10]. Miyake and colleagues used organic catalysts (perylene, diaryl dihydrophenazines) for ATRP of

Polímeros, 30(2), e2020018, 2020

MMA monomer under visible light[11]. Further, Cheng and colleagues used fluorescein as an organic catalyst to control polymerization of MMA[12]. In addition, the metal-free ATRP has been applied for modification/functionalization of polymer surfaces which enhanced the reactivity of polymers[13]. It is clearly that a number of phenoxazine derivatives have been developed as visible light absorbing as organic photoredox catalysts (PCs) with excited state reduction potentials. The phenoxazine derivatives have been modified through extending the conjugation on the phenoxazine core via installation of biphenyl core substituents[14,15]. In addition, the perylene was the first organic photoredox catalysts for O-ATRP using visible light-absorbing, but it is less efficient compared to these other PC families[7]. However, the combination of phenoxazine with perylene as a photocatalyst 10-(Perylene-3-yl-10H-Phenoxazine) have not been reported which can be proposed to enhance the excited state reduction potentials of PC that would be efficient for O-ATRP process. In this research, the novel organic photocatalyst 10-(Perylene3-yl-10H-Phenoxazine) (PHP) have been synthesized and applied for the polymerization of MMA monomer as the

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


Vo, T. H., Le, H. T., Nguyen, T. A., Ho, N. Q., Le, T. V., Tran, D. H., Truong, T. T., & Nguyen, H. T. first time. The structure of PHP has been characterized via FTIR and 1H NMR spectroscopy. In addition, the optical properties of PHP catalyst have been evaluated via UV-Vis spectroscopy. We also investigated the efficiency of PHP organic photocatalyst for O-ATRP process of MMA monomer.

using column chromatography (3.3% EtOAc/hexane). The product was dried under reduced pressure to yield 78% of a red orange solid.

2. Materials and Methods

2.5 Synthesis of initiator of phenyl 2-bromo-2methylpropanoate (PhBMP-initiator).

2.1 Materials Perylene (99%), Phenoxazine (99%), Pd(OAc)2 (99%) were purchased by Sigma Aldrich. NBS (99%), P(t-Bu)3 (98%), NaOt-Bu (97%), MMA (99%) were purchased by Merck. Phenyl 2-bromo-2-methylpropanoate (C10H11BrO2) was synthesized at our lab. All the solvents were purchased from Fisher Chemicals.

2.2 Characterization H-NMR spectra were recorded in deuterated chloroform (CDCl3) with tetramethylsilane as an internal reference, on a Bruker Avance 500 MHz. UV-vis spectrum of polymer samples was recorded at the key laboratory, Department of Materials Technology - Ho Chi Minh City University of Technology, on Shimadzu UV-Vis 2450 of Shimadzu Sciencetific at room temperature (25 °C) with a range of 300 nm to 800 nm, scanning speed of 200 nm/min. The spectra of GPC were recorded at the key laboratory, Department of Materials Technology - Ho Chi Minh City University of Technology, on Polymer PL-GPC 50. 1

2.3 Synthesis of 1-Bromoperylene Perylene (600 mg, 2.378 mmol) and 10 ml anhydrous DMF were added into 50 ml two – necked flask at 0 °C. Aluminum foil was thoroughly wrapped around to cover the reaction vial, blocking out light. In the dark, N-bromosuccinimide (NBS) (423.25 mg, 2.378 mmol) in 5 ml anhydrous DMF was slowly added to this solution using dropping funnel, and stirred for 4 h at 0°C and 20 h at room temperature. Following, the reaction was terminated with a 2M HCl solution, extracted with 100 ml CHCl3 and dried with anhydrous K2SO4. The product was precipitated in cold n-hexane and dried under vacuum to give a yellow powder (590.71 mg; 75%). 1 H NMR (500 MHz, CDCl3), δ (ppm): 8.23 (d, 1H), 8.20 (d, 1H), 8.15 (d, 1H), 8.07 (d, 1H), 7.99 (d, 1H), 7.76 (d, 1H), 7.71 (d, 2H), 7.58 (t, 1H), 7.49 (t, 2H).

2.4 Synthesis of 10- (Perylene-3-yl-10H-Phenoxazine (PHP) A literature procedure was adapted for this synthesis. A 50 ml storage flask was charged with magnetic stir bar, flamed under vacuum and back-filled with nitrogen three times. The flask was then charged with phenoxazine (183.21 mg), NaOtBu (144.15 mg), Pd(OAc)2 catalyst (4.49 mg), P(tBu)3 (8.09 mg) and dry toluene (45 ml). The flask was evacuated and back-filled three times with nitrogen before 3-bromoperylene (331.21 mg) was added. The flask was then placed in an oil bath at 110 oC under while stirring for 24 hours. The flask was then cooled to room temperature and solution was diluted with CHCl3, washed with water, brine, dried with K2CO3 and purified 2/5

1 H NMR (500 MHz, CDCl3), δ (ppm): 8.34 – 7.48 (m, 11H), 6.73 (d, 2H), 6.64 (t, 2H), 6.53 (t, 2H), 5.89 (d, 2H).

A 50 ml storage flask was charged with magnetic stir bar, flamed under vacuum and back-filled with nitrogen three times. 10 mg (0.106 mmol) of phenol was added to anhydrous THF (10 ml) at 0 oC under nitrogen. Then, 21.45 mg (0.116 mmol) of 2-bromo-2-methylpropanoyl chloride in 10 ml of THF was dropwise added to the mixture reaction at 0 oC. The mixture was continuously stirred at room temperature for 4 h. After completion of the reaction, 10 mL of distilled water was added to the reaction mixture, which was extracted with dichloromethane. The organic layer was washed with 10% solution of Na2S2O3 and 10% solution of KOH, dried over anhydrous K2CO3. The product was purified via column chromatography using eluent of EtOAc/hexane (50/50) to obtained the pure product of phenyl 2-bromo-2-methylpropanoate as colorless liquid (Yield: 97%, Rf = 0.7). H NMR (500 MHz, CDCl3), δ (ppm): 7.31 (t, 3H), 7.520 (d, 2H), 1.98 (d, 6H). 1

2.6 Measure UV-vis of PHP and Perylene at different concentrations 10-(Perylene-3-yl-10H-Phenoxazine (PHP) and perylene were analyzed by UV-vis to compare the spectral absorption in soluble form in THF solvent. Perylene and PHP were dissolved in THF at different concentrations of 50, 40, 30, 20, 10 (μM) as measured by Shimadzu UV-Vis 2450 at room temperature range of 200 nm to 800 nm, 50 nm/min.

2.7 General Synthesis of Polymers PMMA was synthesized via UV light-induced metal-free ATRP using the PhBMP-initiator and PHP as organic photocatalyst. In a typical experiment, 11.43 mg (47 μmol) of PhBMP initiator was placed in a 25 mL flask, to the solution 1 mL of degassed THF was added by a syringe. The solution was stirred until it became homogeneous solution. Then, MMA monomer (0.5 mL, 4.7 mmol) and PHP (2.1 mg, 4.7 μmol) was added separately. The mixture was degassed by three freeze-pump-thaw cycles. The solution was continuously stirred until it became homogeneous and placed in a UV-box (wavelength of 365 nm) for 24 h at room temperature. Finally, the resulted polymer solution was precipitated in cold methanol, followed drying under vacuum to give the desired product.

3. Results and Discussion The synthesis of organic photocatalyst 10- (Perylene3-yl-10H-Phenoxazine (PHP) was illustrated in Scheme 1. 1-bromo perylene was synthesized through bromination of electrophilic substitution using NBS in DMF, and the yield of reaction was obtained as 95%. Then 1-bromo pyrelene was reacted with phenothiazine via Buchwald-Hartwig Polímeros, 30(2), e2020018, 2020


Synthesis of novel organocatalyzed phenoxazine for free metal atom transfer radical polymerization C-N coupling in the presence of Pd(OAc)2 and P(t-Bu)3 as catalyst and ligand, respectively (Yield: 78%). The chemical structure of PHP was analyzed via 1H NMR spectrum in Figure 1. The data showed that 1H NMR spectrum of PHP exhibited fully characteristic peaks of PHP including peaks of phenoloxazine and perylene. The peaks from 7.48 ppm to 8.34 ppm are corresponding to the protons of perylene. The peaks from 5.89 ppm to 6.73 ppm which assigned to the protons of phenoloxazine ring. Based on the characteristics peaks are reasonable their integration, the obtained product has been concluded that PHP catalyst was synthesized successfully. Based on the UV-vis spectrum of PHP catalyst (Figure 2), we recognized that that the PHP absorbs the wavelength from 200 – 500 nm while the pyrene absorbs the wavelength from 200 – 450 nm. The UV-vis spectrum of 10-(Perylene-3-yl-10H-Phenoxazine (PHP) curves exhibited two distinct absorption peaks at 250 and 450 nm

which corresponding to the absorption of phenoxazine and pyrene moieties, respectively. Moreover, the spectra showed a linear correlation between concentration and absorbance, and the molar extinction coefficient was determined through the Lambert – Beer law. In addition, the PHP exhibited the high intensity light absorption at wavelength λmax1 = 441 nm, λmax2 = 417 nm with coefficient is ε1 = 40870 (M-1.cm-1), ε2 = 36980 (M-1.cm-1). This results confirmed that 10-(Perylene-3-yl-10H-Phenoxazine (PHP) catalyst can be activated in visible light (violet/blue light). To see more clearly, we consider the same concentration of perylene precursor and PHP at 50 µM (Figure 3) The spectrum showed that PHP has higher absorbance than perylene in the same range of wavelength. For example, at a wavelength of λ = 440 nm, the absorbance of perylene was 0.536 while PHP was 2.093. This result suggested that the high absorption intensity of PHP is higher than those of

Scheme 1. Synthesis of PHP organic photocatalyst and general O-ATPP of methyl mathacrylate monomer.

Figure 1. 1H NMR of 10-(Perylene-3-yl-10H-Phenoxazine (PHP) catalyst. Polímeros, 30(2), e2020018, 2020

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Vo, T. H., Le, H. T., Nguyen, T. A., Ho, N. Q., Le, T. V., Tran, D. H., Truong, T. T., & Nguyen, H. T.

Figure 2. UV-Vis spectrum of 10-(Perylene-3-yl-10H-Phenoxazine (PHP).

Figure 3. UV-Vis spectrum of PHP and Perylene at 50 µM

perylene that lead to the activation efficiency for organic photocatalyst polymerization. According to the pioneer work of Hawker[16], Matyjaszewski[5,13], and Miyake[8,17], we carried out the following process for metal-free ATRP where PHP is used as the organic photocatalyst. Under UV irradiation, PHP is excited to form a reductant PHP*, which activates phenyl 2-bromo-2-methylpropanoate (PBMP) initiator and generates radicals. The generated radical can be added to methyl methacrylate monomers (MMA) to form alkyl radicals which are deactivated by the oxidized radical cation PHP* to regenerate the ground state of PHP. In this typical O-ATRP, we also investigated the solvents, the molar ratio of PHP catalyst with initiator, monomers which impact to the efficiency of polymerization. The polymerization process is performed in the presence of the PHP catalyst following the O-ATRP procedure. The content of catalyst at 0.5; 0.1; 0.05; 0.02 equivalent has been investigated for polymerization of methyl methacrylate. The reactions were carried out in THF solvent under UV irradiation of 365 nm, 24 hours. The results of O-ATRP for MMA polymerization using PHP catalyst are presented in the following Table 1. The result showed that the amount of PHP about 5% molar ratio comparing with initiator give the high monomer conversion of 77.61% for 24 h. On the other hand, the conversion of monomer in the polymerization was decreased if the amount of PHP catalyst decreased. It should be noted that the resulted PMMA exhibited the Mn of 30.450 g/mol which is with the polydispersity index (Đ) of obtained PMMA exhibited the value of 1.28 which is reasonable for controlled polymerization (normally Đ is required below 1.5) (Figure 4).

4. Conclusion 10-(perylen-yl)-10H-phenoxazine (PHP) has been synthesized based on phenoxazine and pyrene has been proved to be an efficient metal-free catalyst for O-ATRP which produced polymethacrylates with controlled molecular weight of 30.457 g/mol as well as narrow polydispersity of 1.28 by UV irradiation. This research enables the synthesis procedure for potential bio/electronic polymeric materials which will eliminate the trace metal element in final polymeric compound. Figure 4. GPC of obtained PMMA.

5. Acknowledgement

[MMA]:[I]:[PHP]

Conv(%)

Mn (g/mol)

Mw (g/mol)

Dispersity (Đ)

Table 1. Macromolecular Characteristic Features of PMMA Synthesized by O-ATRP Using PHP Catalyst.

[100]:[1]:[0.5] [100]:[1]:[0.1] [100]:[1]:[0.05] [100]:[1]:[0.02]

62.69 60 77.61 56.42

21670 17970 30450 24910

31160 25742 38880 33677

1.44 1.43 1.28 1.35

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This research is funded by Vietnam National University Ho Chi Minh City (VNU-HCM) under grant number NV2019-20-03.

6. References 1. Zetterlund, P. B., Kagawa, Y., & Okubo, M. (2008). Controlled/ Living radical polymerization in dispersed systems. Chemical Reviews, 108(9), 3747-3794. http://dx.doi.org/10.1021/ cr800242x. PMid:18729519. 2. Moad, G., Rizzardo, E., & Thang, S. H. (2008). Radical additionfragmentation chemistry in polymer synthesis. Polymer, 49(5), 1079-1131. http://dx.doi.org/10.1016/j.polymer.2007.11.020. Polímeros, 30(2), e2020018, 2020


Synthesis of novel organocatalyzed phenoxazine for free metal atom transfer radical polymerization 3. Keddie, D. J., Carlos, G. S., Moad, G., Rizzardo, E., & Thang, S. H. (2011). Switchable Reversible Addition–Fragmentation Chain Transfer (RAFT) polymerization in aqueous solution, N, N-Dimethylacrylamide. Macromolecules, 44(17), 6738-6745. http://dx.doi.org/10.1021/ma200760q. 4. Matyjaszewski, K., & Xia, J. (2001). Atom transfer radical Polymerization. Chemical Reviews, 101(9), 2921-2990. http:// dx.doi.org/10.1021/cr940534g. PMid:11749397. 5. Matyjaszewski, K. (2012). Atom Transfer Radical Polymerization (ATRP): Current status and future perspectives. Macromolecules, 45(10), 4015-4039. http://dx.doi.org/10.1021/ma3001719. 6. Shanmugam, S., Xu, J., & Boyer, C. (2017). Photocontrolled living polymerization systems with reversible deactivations through electron and energy transfer. Macromolecular Rapid Communications, 38(13), 1700143. http://dx.doi.org/10.1002/ marc.201700143. PMid:28556363. 7. Miyake, G. M., & Theriot, J. C. (2014). Perylene as an organic photocatalyst for the radical polymerization of functionalized vinyl monomers through oxidative quenching with alkyl bromides and visible light. Macromolecules, 47(23), 82558261. http://dx.doi.org/10.1021/ma502044f. 8. Theriot, J. C., Lim, C. H., Yang, H., Ryan, M. D., Musgrave, C. B., & Miyake, G. M. (2016). Organocatalyzed atom transfer radical polymerization driven by visible light. Science, 352(6289), 1082-1086. http://dx.doi.org/10.1126/science. aaf3935. PMid:27033549. 9. Corrigan, N., Yeow, J., Judzewitsch, P., Xu, J., & Boyer, C. (2019). Seeing the light: advancing materials chemistry through Photopolymerization. Angewandte Chemie International Edition, 58(16), 5170-5189. http://dx.doi.org/10.1002/anie.201805473. PMid:30066456. 10. Pintauer, T., Zhou, P., & Matyjaszewski, K. (2002). General method for determination of the activation, deactivation, and initiation rate constants in transition metal-catalyzed atom transfer radical processes. Journal of the American Chemical Society, 124(28), 8196-8197. http://dx.doi.org/10.1021/ ja0265097. PMid:12105893. 11. Dadashi‐Silab, S., Pan, X., & Matyjaszewski, K. (2017). Phenyl Benzo [b] Phenothiazine as a visible light Photoredox Catalyst

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for metal‐free atom transfer radical Polymerization. Chemistry (Weinheim an der Bergstrasse, Germany), 23(25), 5972-5977. http://dx.doi.org/10.1002/chem.201605574. PMid:28009492. 12. Corrigan, N., Shanmugam, S., Xu, J., & Boyer, C. (2016). Photocatalysis in organic and polymer synthesis. Chemical Society Reviews, 45(22), 6165-6212. http://dx.doi.org/10.1039/ C6CS00185H. PMid:27819094. 13. Matyjaszewski, K., & Tsarevsky, N. V. (2014). Macromolecular engineering by atom transfer radical polymerization. Journal of the American Chemical Society, 136(18), 6513-6533. http:// dx.doi.org/10.1021/ja408069v. PMid:24758377. 14. McCarthy, B., & Miyake, G. M. (2018). Organocatalyzed atom transfer radical polymerization catalyzed by core modified N-Aryl Phenoxazines Performed under Air. ACS Macro Letters, 7(8), 1016-1021. http://dx.doi.org/10.1021/ acsmacrolett.8b00497. PMid:31827976. 15. McCarthy, B. G., Pearson, R. M., Lim, C. H., Sartor, S. M., Damrauer, N. H., & Miyake, G. M. (2017). StructureProperty relationships for Tailoring Phenoxazines as reducing Photoredox Catalysts. Journal of the American Chemical Society, 140(15), 5088-5101. http://dx.doi.org/10.1021/jacs.7b12074. PMid:29513533. 16. Treat, N. J., Sprafke, H., Kramer, J. W., Clark, P. G., Barton, B. E., Read de Alaniz, J., Fors, B. P., & Hawker, C. J. (2014). Metal-free atom transfer radical Polymerization. Journal of the American Chemical Society, 136(45), 16096-16101. http:// dx.doi.org/10.1021/ja510389m. PMid:25360628. 17. Pearson, R. M., Lim, C. H., McCarthy, B. G., Musgrave, C. B., & Miyake, G. M. (2016). Organocatalyzed atom transfer radical polymerization using N-Aryl Phenoxazines as Photoredox Catalysts. Journal of the American Chemical Society, 138(35), 11399-11407. http://dx.doi.org/10.1021/ jacs.6b08068. PMid:27554292. Received: Feb. 09, 2020 Revised: June 21, 2020 Accepted: June 22, 2020

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.02620

Synthesis, characterization and thermokinetic analysis of the novel sugar based styrene co-polymer Fatma Cetin Telli1*  Department of Chemistry, Faculty of Science, Ege University, Bornova, İzmir, Turkey

1

*fatma.cetin@ege.edu.tr

Abstract A new α-chloralose (1,2-O-(R)-trichloroethylidene-α-D-glucofuranose)-based copolymer of styrene (PSVTEG) (2) was synthesized from vinyl (hydroxyl) furan monomer (1) and styrene by a conventional free radical polymerization reaction. The thermal decomposition kinetics of polymer were investigated by means of thermogravimetric analysis in dynamic nitrogen atmosphere at different heating rates. The apparent activation energy for the main stage thermal decomposition of the copolymer PSVTEG (2) was calculated using the Flynn-Wall-Ozawa and found to be 159.0±3 kj/mol. In addition, the activation energy value was calculated according to Coats-Redfern method and found to be compatible with the obtained result. The thermogram of the glycopolymer (PSVTEG) (2) has two decomposition stages and the calculated activation energy indicated that the main degradation stage is a nonspontaneous process (integral form 1/(1−α)2 for F3). Keywords: glycopolymers, carbohydrate based vinyl copolymer, α-chloralose, thermal analysis, decomposition kinetic. How to cite: Telli, F. C. (2020). Synthesis, characterization and thermokinetic analysis of the novel sugar based styrene co-polymer. Polímeros: Ciência e Tecnologia, 30(2), e2020019. https://doi.org/10.1590/0104-1428.02620

1. Introduction Glycopolymer is synthetic polymer with pendant carbohydrates[1]. Carbohydrates are important natural sources of building blocks for the synthesis of biodegradable polymers. They are also easily accessible and some are even coming from agricultural wastes[2]. Furthermore, they are found in different kinds of chemical structures with great stereochemical diversity and constituted as renewable sources as being more sustainable than fossil fuels[3,4]. Recently, the basic raw materials used for polymers have expanded by sugars including glucose, galactose, fructose and sucrose. Therefore, carbohydrates are excellent substitutes for products of fossil origin for industrial developments[5]. Chemically containing sugar moieties onto synthetic polymers are induvidual methods for the functionalization of synthetic polymers. With these use of these methods, the polymer is not only functionalized, but also other desirable properties such as biodegradability, biocompatibility and biorenewability can be achieved[6]. Thus, these could be avaiable alternatives for developing environmental friendly products. Synthetic carbohydrate polymers were investigated as biodegradable, biocompatible, biorenewable materials as water absorbents, chromatographic supports, drug delivery systems and medical devices[7,8], in dental medicine, bioimplants, contect lenses, tissue engineering and electrochemical applications[9-12]. Moreover, polymers with pendant carbohydrate moieties have been useful in clinical diagnostic trials and targeted gene therapies. The use of these polymers are essential in surgery, prosthetic systems and pharmacology[6,13-16]. In addition, using sugar functionalized petrochemical polymers of polystyrene for use as biodegradable polymers is a newly discovered application of a sugar linked synthetic polymer[17,18].

Polímeros, 30(2), e2020019, 2020

During the last three decades, the synthesis of glycopolymers became popular with an effort towards biomimics and most of the attempts were based on the polymerization of monomers containing carbohydrate moieties[15-25]. These glycomonomers (sugar carrying monomers) were reported to be polymerized by controlled/living radical polymerisation, radical, anionic, cationic ring-opening polymerization, ring-opening metathesis polymerization and post-functionalization techniques[19,24,25]. Until the last decade, there had been limited attempts to react a functional polymeric backbone with a carbohydrate to obtain a glycopolymer. A significant reason for this was the difficulty of introducing sufficiently reactive pendant groups onto the polymer backbone to react with carbohydrates. With respect to a sustainable chemistry, unsaturated sugar monomers are useful building blocks for copolymers with special properties like biocompatibility, biodegradability, hydrophilicity/hydrophobicity balance and skin compatibility. These properties are of major importance in many fields such as pharmaceuticals, drugs and cosmetics. Up to now; several saccharide monomers have been investigated in free radical polymerization with a wide range of commercially available co-monomers. Vinylsaccharides give rise to polymers bearing sugar appendages in the side chains[26]. For example, sugar-containing vinyl monomers were synthesized from isopropylidene[27], chloralosed[28] and other protected sugars[6,29]. Additionally, poly(vinyl saccharide)s attracted much attention since vinyl sugars can easily be copolymerized with various comonomers. Thus,the resulting copolymers have a chemically stable C-C backbone and hydrophilic side chains. Klein and coworkers have studied the synthesis and solubility of poly(vinyl saccharide)[30,31].

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


Telli, F. C. Nakamae et. al have copolymerized 2-(glycosyloxy)ethyl methacrylate with methyl methacrylate or styrene and investigated the surface properties of cast films[32,33]. Wulff and coworkers have investigated the synthesis of C-glycosyl compounds containing polymerizable double bonds without protecting groups. They have used poly(vinyl saccharide)s with N,N-dimethylbarbituric acid as linkers between sugar and styrene[34,35]. Other types of vinyl sugar monomers and polymers have been reviewed elsewhere[36,37]. Since poly(vinyl sugar)s constitute polymers of a new structural type, they may have high potentials in modifying the surface of conventional polymer materials and improve the antistatic property, dyeability, adhesion, printability, and biocompatibility of bulk polymers[38]. Monosaccharides mostly react in their furanose forms with chloral to give trichloroethylidene acetals. Chloraloses (β-chloralose or α-chloralose) have been prepared by the simple reaction of chloral and glucose[39]. 1,2-O-(R)trichloroethylidene-D-glucofuranose is a commercially available compound, also known as α-chloralose, which is used as an anesthetic for animals[40,41]. Unlike most acetals, 1,2-O-trichloroethylidene acetals are very stable as protecting groups under acidic conditions due to the inductive effect of the trichloromethyl group. In addition, this protecting group is stable under mildly basic conditions. However, they are converted to the more reactive ketene acetals in the presence of strong bases such as potassium tert-butoxide. The only reported method for the removal of this protecting group is a Raney Nickel procedure[42]. Additionally,

trichloroethylidene acetals are suitable protecting groups for the synthesis of some biologically important compounds such as amines[43], orthoesters[44], spiroendoperoxides[45], spirodifuranoseç[46], oxetanes[47], NHC ligands[48], Schiff base[49], glyconanoconjugates[50], etc. In this work, new vinyl (hydroxyl) furan monomer (1) of α-chloralose has been synthesized (Scheme 1) and characterized by Fourier transform infrared spectroscopy (FTIR), elemental analysis and optical rotation. In addition, it is used for the preparation of copolymer styrene (2) (Scheme 2). The thermal degradation kinetics of the copolymer was studied to compare its thermal properties. The apparent activation energies for thermal degradation of the copolymer were obtained by using Flynn-Wall-Ozawa and Coats-Redfern methods. Accordingly, in the further studies, the new carbohydrate-based copolymer of styrene will be a good candidate to prepare the metacomposites with negative electromagnetic parameters by a biomass conversion method[51-53].

1.1 Kinetic Analysis[54-56] Thermogravimetric analysis can be used for the determination of the degradation kinetics of many polymers. In general, the thermal degradation reaction of a solid polymer is shown as: Asolid → Bsolid + C gas

Scheme 1. Synthesis of new vinyl (hydroxyl) furan monomer (1) from α-chloralose.

Scheme 2. Synthesis of the new copolymer styrene (2) from vinyl (hydroxyl) furan monomer (1). 2/8

Polímeros, 30(2), e2020019, 2020


Synthesis, characterization and thermokinetic analysis of the novel sugar based styrene co-polymer where A is the starting material, Bsolid and Cgas are the solid residue and the gas product, respectively. The following typical kinetic equation is generally expressed by the thermal degradation kinetics of the polymers. = r dα= / dt k . (T ) × f (α )

(1)

where T is the absolute temperature (K); r is the conversion per f(α) unit time (t) is the conversion function which represents the reaction model. The degree of conversion (α) is calculated by Equation 2 where mo, mt and mf are the weights of sample before degradation, after complete degradation and at time t, respectively. α =− mo mt / mo − m f (2)

The Arrhenius equation is the reaction constant which can be expressed by calculating k k (T ) = Ao e−( E

/ RT )

(3)

where A is called pre-exponential factor, R is the gas constant and E is the activation energy By combining Equation 1 and Equation 3 the following equation is obtained dα / dt = Ao e−( E

/ RT )

xf (α ) (4)

According to the kinetic theory for the non-isothermal decomposition reactions, the fractional conversion α is expressed as a function of temperature which depends on the time of heating. Therefore, the heating rate (β) can be described as: β = dT / dt (5)

that Equation 6 is modified as follows: dα / dT = (1 / β ) Ao e−( E

/ RT )

x f (α ) (6)

Equation 5 and Equation 6 are the basis for the many equations derived to evaluate thermal analysis data. 1.1.1. Coats-Redfern Method[57] This method is based on the following equation 2 ln ( g (α ) / T= ) ln ( AR / E β (1 − 2RT / E )) − ( E / RT ) (7)

as E is calculated from the slope –E/R of the plot ln (g(α)/T2) versus 1000/T which is a straight line. The most commonly used reaction models can be estimated for the solid-state processes by calculating the possible thermal degradation mechanism. The activation energy calculated by using this method was found to be as 159.2±3 kj/mol. 1.1.2. Flynn-Wall-Ozawa (FWO) Method[58,59] In this method, there is no need of any knowledge for the reaction mechanism for the calculation of the activation energy. The activation energy (E) and pre-exponential factor (A) are not dependent on the fraction of degradation while they depend on temperature. This method uses Equation 8. logg= (α ) log ( AE / R) − log β + log p( E / RT ) (8) Polímeros, 30(2), e2020019, 2020

Equation 9 is obtained by means of the Doyle approximation. log = β log ( AE / R) − logg (α ) − 2.315 − 0.4567 ( E / RT ) (9)

Thus, from the slope -E/R of the linear plot of log β versus 1000/T, E is readily obtained. The activation energies calculated by using this method was found to be 159.0±3 kj/mol.

2. Experimental 2.1 Materials 1,2-O-(R)-trichloroethylidene-α-D-glucofuranose (α- chloralose) (stated purity ≥ 98%), triphenylphosphine (TPP) (stated purity ≥ 99%), imidazole (stated purity, 99%), iodine (I2) (stated purity 99%), toluene (stated purity 99%),sodium thiosulphate (Na2S2O3) toluene (stated purity 99%), diethyl ether (stated purity ≥ 99%), ethyl acetate (EtOAc) (stated purity 99%), n-hexane (stated purity 99%), sodium hydrogen carbonate (NaHCO3) (stated purity 98%), Na2SO4 (stated purity 98%), styrene, ABIN, toluene were purchased from Merck A.G and Sigma-Aldrich. The materials and chemicals were used without any further purification.

2.2 Instrumentation All 1H NMR and 13C NMR spectra were recorded using a Varian AS 400+ Mercury FT NMR spectrometer at ambient temperature. FTIR spectra were recorded on a Perkin Elmer 100 FTIR spectrometer. The test wavenumber range of FTIR spectra were 400-4000 cm-1. Optical rotations were determined using a Rudolph Research Analytical Autopol I automatic polarimeter with a wavelength of 589 nm. The concentration ‘c’ has units of g/100 mL. Elemental analyses were performed on a Perkin-Elmer PE 2400 elemental analyzer. TLC and column chromatography were performed on precoated aluminum plates (Merck 5554) and silica gel G-60 (Merck 7734), respectively. The TG (Thermogravimetric Analysis) curves were recorded using a Perkin Elmer, Diamond TG/DTA. The samples were heated under a N2 atmosphere over a temperature range of 30 to 600 °C with a heating rate of 10 °C min-1. The weight loss (TG curve) and its first derivative according to the temperature (DTG curve) were recorded simultaneously. Molecular weights were determined by a gel permeation chromatography (GPC), viscotek GPC(UK)-max an instrument Autosampler system, consisting of a pump, three visco GEL GPC columns (G2000HHR, G3000HHR and G4000HHR) a viscotek UVdetector and a viscotek differential refractive index (RI) detector with a THF flow rate of 1.0 mL/min at 30 °C were employed.

2.3 Synthesis of the 5,6-dideoxy-1,2-O-(R)trichloroethylidene-α-D-xylo-hekso-5-enofuranose (1) A solution of α- chloralose (3.1 g, 10 mmol), triphenylphosphine (TPP) (10.8 g, 40 mmol) and imidazole (3.1 g, 10 mmol) in dry toluene (100 mL) was stirred and warmed to 50 °C. Iodine (10.2 g, 40 mmol) was added to above reaction mixture in small lots during 30 min with the temperature of the reactants being maintained aproximetly 60 °C. The reaction mixture was heated 3/8


Telli, F. C. to reflux for 4 h, cooled room temperature and solvent removed on a rotary evaporator to produce a dark brown syrupy. The purification of the residue is well documented in the literature[60]. After this process, the white crystal of the title product was synthesized %86 yield (2.4 g). m.p. 102-103 oC, [α]23D -14.3 (c 0.7, MeOH). 1H NMR (DMSO, 400 MHz): δ 6.05 (d, 1H, J1,2=4.0 Hz, H-1), 5.85 (m, 1H, H-5), 5.41 (s, 1H, HCCl3), 5.34 (dd, 1H, J6a,6b=0.8, J5,6a=16.8 Hz, H-6a), 5.23 (dd, J6a,6b=0.8, J5,6b=14.8 Hz, H-6b), 4.79 (dd, 1H, J4,5 =2.8 Hz, J3,4=3.2 Hz, H-4), 4.51 (d, 1H, J1,2=4.0 Hz, H-2), 4.07 (t, 1H, J3,4=3.2 Hz, H-3), 2.50 (br s, 1H, OH). 13C NMR: 133.3 (C-5), 119.2 (C-6), 106.2, 105.7 (HC-CCl3, C-1), 97.6 (HC-CCl3), 87.8, 83.7, 75.2(C-2, C-3, C-4). Anal. Calc. for C8H9Cl3O4: C, 34.88; H, 3.29. Found: C, 34.55; H, 3.34.

2.4 Synthesis of the new glyco-polymer (PSVTEG) (2) from vinyl (hydroxyl) furan monomer (1) The new copolymer (PSVTEG) (2) from vinyl (hydroxyl) furan monomer (1) (2.4 g, 8,7 mmol) and styrene (1 mL, 8,7 mmol) (1:1 mol monomer rate) were obtained through a conventional free radical polymerization using 2,2-azobisisobutyronitrile (AIBN) (2%, based on the total weight of the monomer) as initiator in 10 mL of toluene at 70 °C in an all glass Schlenk flask under inert atmosphere. After 24 hours, copolymer 2 was obtained with approximetly 90% conversion. The resulting polymer was precipitated in methanol and dried under vacuum at 40 °C for overnight. The polymer was then characterized using FTIR and NMR spectroscopy. The synthetic route is presented in Scheme 2. The apparent activation energies for the main degradation stage of the copolymer were calculated from the TG data by using Flynn-Wall-Ozawa (FWO) and Coats-Redfern methods. The activation energies calculated by these methods were found to be 159.0±3 kj/mol and 159.2±3 kj/mol, respectively. 1H NMR (DMSO, 400 MHz): δ 7.05-6.55 (d, 5H, aromatic H), 6.05 (d, 1H, J1,2=4.0 Hz, H-1), 5.40 (s, 1H, HCCl3), 4.78 (dd, 1H, H-4), 4.52 (d, 1H, H-2), 4.10 (t, 1H, H-3), 2.62 (m, 1H, CH-), 2.50 (br s, 1H, OH), 1.62-1.25 (m, 5H, CH2-, CH-). 13C NMR: 142.0-128.2 (aromatic carbons), 106.2, 105.7 (HC-CCl3, C-1), 97.6 (HC-CCl3), 87.8, 83.7, 75.2(C-2, C-3, C-4), 40.4-21.6 (alifatic carbons).

C-O-C peak in the sugar ring at 1107 cm-1; C-Cl peaks of trichloroethylidine protective group at 832 and 812 cm-1. Finally, the absorption band at 3440 cm-1 corresponds to the presence of the C-3 OH group. Instead of the vinyl C=CH2 at 1505 cm-1peak observed in the FTIR spectrum of new vinyl (hydroxyl) furan monomer (1), the mono substitute benzene ring peak at 698 cm-1 was observed in the FTIR spectrum of the copolymer PSVTEG (2). 3.1.2 The 1H and 13C NMR spectra of the monomer 1 and copolymer PSVTEG (2) In the 1H-NMR spectrum of the monomer 1 the anomeric H-1 proton usually appears at a low field and is a very characteristic and distinct signal. Two doublets are observed in this 1H-NMR spectrum. One is the H-1 doublet at δ 6.05 and another is the H-2 doublet at δ 4.51. The coupling constant between H-1 and H-2 is 4.0 Hz which is typical for an α-D-furanose derivative. Due to the twisted conformation of the furanose rings, the dihedral angle between the H-2 and H-3 protons are usually 90°. Hence, in the 1H NMR spectrum of compound 1, the coupling constant between H-2 and H-3 is 0 Hz. The H-5 protons give a complex multiplet at δ 5.85. One of the H-6 signals obtained is H-6a which is resolved into add at δ 4.34 with one of the coupling constant between H-6a and H-5 of 16.8 Hz. The another of the coupling constant between H-6a and H-6b of is 0.8 Hz and H-6b signal is observed at δ 5.23 with one of the coupling constant between H-5 and H-6b of 14.8 H. The H-4 signals are resolved giving a triplet signal at δ 4.79 with a coupling constant between H-4 and H-5 of 3.2 The H-3 signals are resolved giving a triplet signal at δ 4.07 with a coupling constant between H-3 and H-4 of 3.2 Hz. The hydroxyl proton is resolved giving a br singlet at δ 2.50. Finally, the trichloroethylidene acetal proton (HCCl3) gives a signal at δ 5.41. Also, the13C NMR peak performance of the monomer 1 was described and similarly, the expected indications were observed. In the 13C NMR spectrum of monomer 1, the peaks at 133.3 and 119.2 ppm (C-5 and C-6) assigned thevinyl carbon. In addition, trichloroethylidene acetal carbon (HC-CCl3) was observed at 106.2 ppm. 13C NMR peak of the sugar moiety for the monomer 1 was observed as predicted from C-1 at 105.7 ppm. In the 1H NMR spectrum of the copolymer PSVTEG (2), disappearance of characteristic vinyl peaks for the the monomer is observed. And also, the acetal proton, the

3. Results and Discussion 3.1 Characterization Studies 3.1.1 The FTIR spectra of the monomer 1 and copolymer PSVTEG (2) The FTIR spectra of compound 1 and copolymer PSVTEG (2) are shown in Figure 1. The peak assignments in the FTIR spectrum of compound 1 are as follows: C-H in CH3 and C-H in CH2 at 2925 cm-1; vinyl C=CH2 at 1505 cm-1; C-O-C peak in the sugar ring at 1162 cm-1; C-Cl peaks of trichloroethylidine protective group at 854 and 823 cm-1. Finally, the absorption band at 3294 cm-1 corresponds to the presence of the C-3 OH group. The FTIR spectrum of copolymer 2 (Figure 1) is as follows: C-H in CH3 and C-H in CH2 at 2800-3000 cm-1; C=C double bond peaks in the benzene ring at 1493 and 1452 cm-1; 4/8

Figure 1. The FTIR spectra of new vinyl (hydroxyl) furan monomer (1) and the copolymer PSVTEG (2). Polímeros, 30(2), e2020019, 2020


Synthesis, characterization and thermokinetic analysis of the novel sugar based styrene co-polymer trichloroethylidene acetal proton (HCCl3) and other sugar protons give a signal at δ 6.05, 5.40, 4.78-4.10, respectively. Besides, the appearance of the aromatic proton peaks for the styrene are observed as multiplet at δ 7.05 and 6.55 in the 1H NMR spectrum of the copolymer PSVTEG (2). In the case of the polymer, it is observed that alkyl group carbon peaks of the copolymer PSVTEG (2) appeared in the range from 40.4 to 21.6 ppm in the 13C NMR spectrum. Therefore, vinyl carbons of glycopolymer shifted to a higher field as a result of increased electron intensity. 13C NMR peaks of the sugar moiety of the copolymer 2 are observed from C-1 to C-4, as predicted. Furhermore, the appearance of the aromatic carbon peaks for the styrene appeared in the range from 142.0 to128.2 ppm in 13C NMR spectrum of the glycopolymer 2.

Figure 2. DTG curves of glycopolymer PSVTEG (2).

3.2 Thermogravimetric analysis of the copolymer PSVTEG (2) Thermal properties of glycopolymer (PSVTEG) (2) were investigated by TG and DTG under argon atmosphere over a temperature range 30 to 600 °C with a heating rate of 10oC/min. The thermogram of the glycopolymer (PSVTEG) (2) shows two decomposition stages (Figure 2). The thermal decomposition in the first stage is in a weight loss of nearly 10%. The main degrading process involving random scission starts around 350 °C. According to the literature data, using the TG/DTG-DTA-FTIR analysis, the following releasing gases after pyrolysis could be seen u.a: H2O, C=O, CH4, C2H2, and C2H4O2[61]. The degradation reactions began at the temperature of circa 200 °C, when the thermal condensation between hydroxyl groups of copolymer chains started the formation of ether fragments, and the release of water molecules was obtained. When dehydratation was located in the neighborhood of itself, hydroxyl groups in the glycosidic ring cause the formation of the C=C bond or degradation of the glycosidic ring. All of aldehyde groups were formed at the same time as terminal groups, while the monosaccharide ring was damaged. The main degradation reactions began at the temperature of circa 350 °C, aromatic rings such as substituted benzene and furan structures with groups such as –CH2– or –CH2–O–CH2– as main binders between the aromatic rings could be seen[62].

3.3 Thermal degradation kinetics of the copolymer (PSVTEG) (2) The glycopolymer (PSVTEG) (2) was heated thermogravimetrically under various heating rates such as 5, 10, 15, and 20 °C/min in a temperature range of 30 to 600 oC to determine their thermal degradation mechanisms and the activation energies. The TG curves obtained for the copolymer is shown in Figure 3 and 4, respectively. The individual degradation behavior of the glycopolymer (PSVTEG) (2) was analogous at all heating rates as seen from these figures. The apparent activation energies and thermal degradation models for the copolymer was estimated by FWO and Coats-Redfern. The thermal degradation mechanism of the copolymer (PSVTEG) (2) for the main degradation stage is confirmed by comparing the mean activation energy value (EFWO) Polímeros, 30(2), e2020019, 2020

Figure 3. TG curves of glycopolymer PSVTEG (2).

Figure 4. FWO plots for the thermal decomposition of glycopolymer PSVTEG (2) at varying conversion in N2.

with those calculated by the Coats-Redfern method for different models. The activation energies and correlations obtained from Coats-Redfern method at different heating rates are represented in Table 1. The E calculated from the F3 model is nearly the same with EFWO for PSVTEG (2) and found as 159.0±3 kJ/mol leading to a conclusion that the most probable mechanism for the thermal degradation of PSVTEG (2) is the third-order. Therefore, the calculated activation energy indicates that the main degradation stage is a nonspontaneous process (integral form 1/(1−α)2 for F3). In literature, the activation energry value of polystrene homopolymer and vinyl sugar- carrying copolymer viz., 5/8


Telli, F. C. Table 1. Algebraic expressions of f(α) and g(α) for the reaction models considered in the present work. Symbol

Reaction model

f(α)

g(α)

Sigmoidal curves A2

Avrami–Erofěev (n = 2)

2(1−α)[−ln(1−α)]1/2

[−ln(1−α)]1/2

A3

(Nucleation and growth) Avrami–Erofěev (n = 3)

3(1−α)[−ln(1−α)]2/3

[−ln(1−α)]1/3

A4

(Nucleation and growth) Avrami–Erofěev (n = 4)

4(1−α)[−ln(1−α)]3/4

[−ln(1−α)]1/4

An

(Nucleation and growth) Avrami–Erofěev (n = n)

n(1−α)[−ln(1−α)](n-1)/n

[−ln(1−α)]1/n

1

α

2(1−α)1/2 3(1−α)2/3 (1−α)

[1−(1−α)1/2] [1−(1−α)1/3] −ln(1−α)

(Nucleation and growth) Deceleration curves R1

Zero-order (Polany–Winger equation) Phase-boundary controlled reaction

R2 R3 F1

(one dimensional movement) Phase-boundary controlled reaction (contracting area, i.e., bidimensional shape) Phase-boundary controlled reaction (contracting area, i.e., bidimensional shape) First-order (Mampel)

F2

(Random nucleation with two nucleus on the individual particle) Second-order

(1−α)2

1/(1−α)

F3

(Random nucleation with two nucleus on the individual particle) Third-order

(1−α)3

1/(1−α)2

D1 D2 D3 D4

(Random nucleation with two nucleus on the individual particle) One-dimensional diffusion 1/2α Two-dimensional diffusion (bidimensional particle shape) Valensi equation 1/[−ln(1−α)] Three-dimensional diffusion (tridimensional particle shape) Jander equation 3(1−α)1/3/2[(1−α)−1/3 −1] Three-dimensional diffusion (tridimensional particle shape) Ginstling–Brounshtein 3/2[(1−α)−1/3 −1]

poly(galactomethacrylate-co-styrene) (P(gm-co-st)) were stated as circa 50±5 kJ/mol and 185±28 kJ/mol, respectively[63,64]. In addition, Pană et  al. have indicated the avarage activation energy value of a glycopolymer derived from a D-mannose oligomer with maleic backbone and 2-hydroxypropyl acrylate inside as 105.98 kJ/mol by using Flynn–Wall–Ozawa method[65]. When these values in the literature was compared with the activation energy value of the copolymer PSVTEG (2), it was concluded that the copolymer was a sugar-based styrene copolymer.

3.4 Molecular weight study of the copolymer (PSVTEG) (2) The number average molecular weight (Mn), weight average molecular weight (Mw) and polydispersity index (PDI) for glyco-polymer (PSVTEG) (2) was analysed by GPC. The number average molecular weight (Mn), mass average molecular weight (Mw) and polydispersity index (PDI) of glyco-polymer (PSVTEG) (2) were found to be 14000 g/mol, 18900 g/mol and 1.35, respectively.

4. Conclusions A new carbohydrate-based the copolymer of styrene (2) from vinyl (hydroxyl) furan monomer (1) were synthesized by a conventional free radical polymerization reaction using AIBN as an initiator in toluene. The thermal degradation of the copolymer of styrene (2) from vinyl (hydroxyl) furan monomer (1) under nitrogen atmosphere is a one-stage reaction. The thermal degradation kinetics of the compounds 6/8

α2 (1−α)ln(1−α) + α [1−(1−α)1/3]2 (1−2α/3)−(1−α)2/3

was evaluated using the Flynn-Wall-Ozawa (FWO) and CoatsRedfern methods. The activation energies calculated by these methods were found to be 159.0±3 kj/mol and 159.2±3 kj/mol, respectively. Consequently, the calculated activation energy shows that the main degradation stage is a nonspontaneous process (integral form 1/(1−α)2 for F3).

5. Acknowledgements I would like to Ege University for financial support of this work (2017 FEN 077).

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Polímeros, 30(2), e2020019, 2020


ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.10719

Synergistic improvement of mechanical and magnetic properties of a new magnetorheological elastomer composites based on natural rubber and powdered waste natural rubber glove Nabil Hayeemasae1*  and Hanafi Ismail2 1

Department of Rubber Technology and Polymer Science, Faculty of Science and Technology, Prince of Songkla University, Pattani Campus, Pattani, Thailand 2 School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, Nibong Tebal, Penang, Malaysia *nabil.h@psu.ac.th

Abstract Recycling of rubber waste and finding the effective methods to extend its use are one of major challenges nowadays. In the present study, waste natural rubber glove (wNRg) was used in an attempt to extend its use and create a value-added composite based on natural rubber (NR) and wNRg. Another interesting focus was to develop such material into a new Magnetorheological Elastomer (MRE). This MRE can be prepared by incorporating Ferromagnetic particles namely carbonyl iron (CI) to the rubber composite. Carbon black (CB) was also added to obtain MRE with remarkably mechanical properties. CI was fixed at 60 phr where the CB was varied from 10 – 30 phr. Higher thermal conductivity and magneticity in nature of CI had made the composites faster cure and higher magnetic strength. On the contrary, superior tensile strength, modulus and elongation at break were found in the presence of CB. From the experimental results, hybridization of 60/10 phr/phr of CI and CB is highly suggested to gain the synergistic strength and magneticity. This is expected to solve a big problem in the application of MRE. Keywords: natural rubber, carbonyl iron, carbon black, magnetic properties. How to cite: Hayeemasae, N., & Ismail, H. (2020). Synergistic improvement of mechanical and magnetic properties of a new magnetorheological elastomer composites based on natural rubber and powdered waste natural rubber glove. Polímeros: Ciência e Tecnologia, 30(2), e2020020. https://doi.org/10.1590/0104-1428.10719

1. Introduction Smart materials is an intelligent or responsive materials that have one or more properties simultaneously by changing external stimuli, such as stress, moisture, electric or magnetic fields, light, temperature, pH, or chemical compound. There are many types of smart materials available in our daily life. Magnetorheological elastomer (MRE) is also one of them[1,2]. MRE can be fluid, gel or even a solid material such as elastomer. This kind of elastomer material offers multiple advantages as compared to conventional rubber materials. MRE is prepared by incorporating magnetically permeable particles (ferromagnetic filler)[3] into a non-magnetic matrix which is the rubber matrix. The bahaviors of magnetic particles depends on the methods of fabrication. Isotropic MRE refers to the MRE containing a uniform suspension of magnetic particles whereas Anisotropic MRE is found when a magnetic field is applied during curing where chain-like structures of magnetic particles are formed in this stage[4,5]. Recently, there are several types of ferromagnetic fillers that are used to prepare MRE. Each of them possesses its own advatanges depending on the density, size and shape. The examples of magnetic particles are carbonyl iron,

Polímeros, 30(2), e2020020, 2020

magnetite, iron oxides, barium ferrite and so forth[6-8]. Among them, carbonyl iron (CI) seems to provide excellent properties to MRE[9]. CI is spherical in shape and has some advantages when using as ferromagnetic particles. These include high magnetic susceptibility, high magnetic saturation, high inter-particle interaction forces and low remnant magnetization required for quick and reversible control in MRE applications[10-12]. At the present time, the effects of individual fillers on the properties of composites are relatively well-known[13]. As for example, the use of carbonyl iron for producing magnetoelastomer generally provides excellent magnetic properties. However, the mechanical properties cannot usually be improved by such filler. The idea of using a hybrid filler comprised of two or more traditional filler materials has already been explored in the literature. This approach has been demonstrated to provide great performance to the rubber vulcanizate. Therefore, synergistic advantages can be achieved by combining such fillers. Carbon black (CB) is again the filler of chioce to be used as hybrid filler especially in the composite where non-reinforcing filler

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


Hayeemasae, N., & Ismail, H. has been originally incorporated. The carbon black consists wide variety of grades depending on their size, surface area and structures. The commercial carbon blacks are spherical particles with diameters of the order 15 – 50 nm and tend to exist in fused chainlike agglomerates which are referred to as the structure[14]. The presence of carbon black in vulcanized rubber enormously enhances the tensile strength, elastic modulus, and abrasion resistance. So far, MRE has been prepared from many types of rubber matrices both general propose and specialty rubbers. For examples, natural rubber, silicone rubber, polybutadiene, polyisobutylene, polyisoprene and polyurethene rubber[15-18]. However, none of them has been designed to develop new MRE from waste natural rubber. In this study, natural rubber (NR) and waste natural rubber glove (wNRg) were used as matrices in association with a combination of high magnetic filler (CI) and high reinforcing filler (CB). By varying the volume fraction of hybrid fillers, a new kind of value-added rubber composites with simultaneous improvement of magnetic and mechanical properties are developed. CI possesses a very high magnetic strength but not compatible to the natural rubber. This is not happened when incorporating CB to the natural rubber. CI may affect the magnetic properties to the rubber matrices. Thus, MRE can be prepared successfully. In the meantime, the mechanical properties can be modified through hybridization with CB. The work described here was part of a broader study aimed at developing a class of inexpensive MRE with good mechanical properties. It is a preliminary investigation to determine whether or not significant mechanical improvements could be achieved using readily accessible, relatively cheap commercial filler. It is expected that the results obtained in this study will be of importance for new MRE of further increasing of working frequency and miniaturization of materials that required these two properties.

the sequence followed the order arranged in the formula. Later, the compounds were kept in the freezer for conditioning and the compounds were finally compression molded into specific shapes by a hydraulic hot press, using the curing times determined by a Moving Die Rheometer (MDR).

2.3 Measurement of curing characteristics The curing characteristics of the composites were obtained by using MDR 2000 (Alpha Technologies, USA), which was used to determine torques, scorch time (ts2) and curing time (tc90) according to ASTM D5289. Samples of the respective compounds were tested at 150oC.

2.4 Measurement of mechanical properties Dumbbell-shaped samples were cut from the molded sheets according to ASTM D412, and tensile tests were performed at a cross-head speed of 500 mm/min. The tensile tests were carried out with Instron Universal Testing Machine, model 3366, to determine 100% modulus, 300% modulus, tensile strength and elongation at break. As for tear strength, the crescent shape test pieces or type C test pieces were cut out according to ASTM D624. The tear test was carried out using the same machine and setting up.

2.5 Scanning electron microscopy The fractured surfaces obtained from tensile and tear test were used to capture the morphological characteristics of CI/CB hybrid filled NR/wNRg composites. The fractured

2. Materials and Methods 2.1 Materials The natural rubber (NR) used was SMR L grade, which was obtained from Mardec Sdn. Bhd., Malaysia. Waste natural rubber glove (wNRg) was supplied by Juara One Resources Sdn. Bhd., Malaysia. The wNRg was crushed into a size range from 100 – 500 µm using Table Type Pulverizing Machine from Chyun Tseh Industrial Co. LTD, Taiwan. Carbon Iron (CI) powder was purchased from Sigma Aldrich (M) Sdn. Bhd., Malaysia. The carbon iron was in spherical shapes as seen in Figure 1 and the particle size is ranging from 0.7 – 1.0 µm. Other compounding ingredients such as N330 grade carbon black (CB), Zinc oxide, Stearic acid, Vulkanox BKF, N-cyclohexyl-2-benzothiazole sulfonamide (CBS) and Sulfur were purchased from Bayer (M) Sdn. Bhd., Malaysia.

2.2 Preparation of CI/CB hybrid filled NR/wNRg composites Table 1 shows the ingredients used in the CI/CB hybrid filled NR/wNRg composites. Before the compounding process, the CI powder was dried using oven at 80°C for 3 hours to expel the moisture. Then, the entire amount of ingredients was compounded on a laboratory size two roll mill model XK-160. The mixing procedure followed ASTM D3182 and 2/7

Figure 1. SEM Micrograph of carbonyl iron used in this study[19]. Table 1. Compounding formulation of the CI/CB hybrid filled NR/wNRg composites[19]. Ingredient SMR L Waste NR Glove ZnO Stearic Acid BKF CI Carbon Black (N330) CBS Sulfur

Amount (phr) 50 50 5 3 1 60 0, 10, 20 & 30 1 2.5

Polímeros, 30(2), e2020020, 2020


Synergistic improvement of mechanical and magnetic properties of a new magnetorheological elastomer composites based on natural rubber and powdered waste natural rubber glove pieces were coated with a layer of gold palladium to eliminate electrostatic charge buildup during examination. The observations were performed using a Supra-35VP Field Emission and Quanta 400 Scanning Electron Microscope (FESEM). The geometry of the CI was determined using Tabletop Microscope TM3030 (see Figure 1). A double sided tape was applied on the mold plate. Then, the mold plate with tape was dipped into the powder of CI. After that, the mold plate was inserted into the tabletop SEM to carry out morphological analysis.

2.6 Swelling behaviour and crosslink density Swelling uptake was done according to ASTM D471. The vulcanized samples with dimension of 30 mm × 5 mm × 2 mm were weighed before being swollen in toluene until equilibrium, which took approximately 72 hours at room temperature. The samples were taken out from the toluene, wiped off and finally weighted before calculation based on the Equation 1. Swelling =

(W2 − W1 ) × 100 (1) W1

where W1 and W2 is the mass (g) of samples before and being swollen respectively. The swelling outputs were further applied to calculate the molecular weight between crosslinking points (MC) and crosslink density (VC) through the Flory-Rehner Equation (see Equations 2 and 3)[20]. Mc =

Vr =

− ρ pVsVr1/ 3

ln ( 1 − Vr ) + Vr + χVr2

(2)

1 (3) 1 + Qm

where ρ is the density of rubber (NR and wNRg) which is equal to 0.92 and 0.94 g/cm3 respectively, VS is the molecular volume of toluene which is 106.4 cm3/mol, VR is the volume fraction of rubbers in the swollen sample, QM is the mass increase of the samples after swelling and χ is the interaction parameter of the rubber network and toluene (χ of NR or wNRg is 0.393). The degree of crosslink density (VC) is given below; Vc =

1 2M c

(4)

2.7 Magnetic property The magnetic flux density or magnetic induction of the MRE samples were measured using a hand type gaussmeter with the probe connected to the Tesla Meter, model TM-801AXL (Axial Probe). This axial probe was brought into direct contact with the vulcanized rubber sheet to measure the magnetic flux density in the axial direction. The rubber sheets were magnetized using a magnet with approximate 200 millitesla (mT) prior to be tested. The probe was placedseveral points and recorded. Polímeros, 30(2), e2020020, 2020

3. Results and Discussions 3.1 Curing characteristics Table 2 shows the curing characteristics of CI/CB hybrid filled NR/wNRg composites. The scorch time (ts2) decreased gradually with increasing CB loading. The result of scorch time obtained from graph was 2.21 min, 1.85 min, 1.6 min and 1.53 min for 0 phr, 10 phr, 20 phr and 30 phr respectively. This is indicated that CB facilitates the formation of crosslinks in the vulcanization process. Such finding is responsible to the heat history of the rubber compounds. Medalia et al.[21] reported that CB can cause to delay the total mixing time of rubber compounding, consequently more heat was generated due to the additional friction. This has brought to take shorter time to reach the onset of vulcanization. On the other hand, the curing time (tc90) is inversely found for the CI/CB filled NR/wNRg composites. It gives a longer trend upon the addition of CB. This is a clear indication that the time taken to complete the vulcanization depends strongly on the presence of CI. More heat transfer occurs in the presence of CI. CI possesses the thermal conductivity value of 0.1922 cal/cm.sec.oC[22]. This value is way bigger than the thermal conductivity of CB which is about 0.00067 cal/cm.sec.oC[23,24]. Even though the CB also provide the thermal conductive characteristics but higher amount of CB can restrict the thermal conductive pathway of CI unlike the composites with solely CI. This makes the heat transfer less efficient to the rubber chain and takes longer time to complete the vulcanization process. The torque difference (MH – ML) is a measure of the difference between stiffness or shear modulus of the fully vulcanized and unvulcanized test specimens taken at the lower point of the vulcanizing curve. The MH – ML was found to increase with increasing CB loading. The increment of the MH – ML was due to the presence of CB, which has a higher restriction to molecular motion of the macromolecule or tends to increase resistance to flow[25]. Regarding to such positive finding, it can be verified that these properties are dependent on the CB content. CB has a smaller particle size and higher surface activity, as well as higher structure, in comparison to CI powder. This may have improved the rubber-filler interactions. Wolff and Wang[26] reported that MH – ML depends on the crosslink density and chain entanglement and may also be dependent on the CB, which has a higher structure than other fillers, thus resulting in the NR molecular chains being more easily trapped and occluded in the voids of the CB aggregates. Increasing the amount of occluded rubber increased the effective concentration of the CB aggregates in the rubber and decreased the fluidity of the gross rubber during the mixing process as well. Hence, higher values of torque difference occurred when increasing CB content in the composites. Table 2. Curing characteristics of CI/CB hybrid filled NR/wNRg composites[19]. CI/CB Content (phr/phr) 60/0 60/10 60/20 60/30

MH – ML (d.Nm) 9.04 11.01 13.1 15.35

ts2 (min)

t90 (min)

2.21 1.85 1.6 1.53

5.42 5.43 5.68 6.43

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Hayeemasae, N., & Ismail, H. 3.2 Mechanical properties Figure 2 presents the tensile strength and elongation at break of CI/CB hybrid filled NR/wNRg composites. The tensile strength improved up to 10 phr of CB, but above this level the strength was reduced. CB has a very unique structure and high aspect ratio, so it is frequently combined with various rubbers to increase the mechanical strength of composites. The particle size of CB is very small compared to CI, hence resulting in strong interfacial interaction in the rubber matrix. Another probable reason might be due to the surface chemistry of CB which is more compatible to the rubber matrix. This could make the CB disperse well in rubber matrix and lead to improved stress transfer in the rubber matrix. Similar trend was also found for the elongation at break of the composites, indicating that better interfacial interaction of CB and rubbers can prolong the breaking strain which then improved the elasticity of the rubber composites. The reduction in tensile strength and elongation at break with loadings beyond 10 phr of CB is simply due to the dilution effect. When more CB is integrated into the rubber matrix, the CB particles tend to interact with each other, known as filler-filler interactions or aggregation of CB, which is seen in the SEM micrographs later. It can be seen that the stresses at 100% and 300% elongations (M100, M300) increased significantly with CB loading (see Table 3). As more CB gets into the rubber; the total amount of fillers is high, the elasticity of the rubber is then reduced, resulting in more rigid, stiffer and harder composites. This is in good agreement with the crosslink density reported in the next section. The tear strength of CI/CB hybrid filled NR/wNRg composites is shown in Figure 3. Tear strengths of the composites are shown different trend as compared to tensile strength and elongation at break. It can be seen that the addition of CB to the hybrid system had increased the tear strength upwards. This is simply due to the nature of CB itself which has already mentioned in the previous results. Since the tensile and tear tests are not similar, the optimum loading of CB to give optimum properties of each tensile and tear strengths are not the same. Therefore, higher energy was required to cause the tearing failure upon the use of CB in the hybrid system.

chains[27]. Low swelling uptake indicates higher crosslink density. The swelling percentages decreased with increasing CB loading. The highest swelling percentage is at 0 phr CB where the value is about 187.51%. Then it was decreased with increasing CB loading at 162.98%, 134.78% and 122.03%. for 10 – 30 phr of CB respectively. The presence of CB has brought to a strong interfacial interaction. As a consequence, less penetration of toluene is observed upon inclusion of CB. Despite being due to the reduction of the free volume in the vulcanizate, CB also affects the crosslinking efficiency of the rubber. As reported by Baccaro et al.[28], they have explained that CB enables to involve both physical and chemical crosslinks. A physical entrapment is due to the interactions between rubber chains and microstructure defects and surface porosity of CB. While, the chemical crosslinks are associated to the electron acceptors on the surfaces of rubber macroradicals and CB during mixing. This has brought to an increase in crosslink density in the presence of CB.

Figure 2. Tensile strength and elongation at break of CI/CB hybrid filled NR/wNRg composites.

3.3 Swelling uptake The swelling uptake and corresponding crosslink density of CI/CB hybrid filled NR/wNRg composites are also listed in Table 3. The swelling percentage was investigated by toluene uptake until equilibrium swelling was reached at room temperature. It is well-established that swelling resistance correlates to the crosslink density in a network

Figure 3. Tear strength of CI/CB hybrid filled NR/wNRg composites.

Table 3. Tensile modulus, swelling uptake and crosslink density of CI/CB hybrid filled NR/wNRg composites. CI/CB hybrid content (phr/phr) 60/0 60/10 60/20 60/30

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M100 (MPa) 1.14 ± 0.034 1.71 ± 0.012 2.52 ± 0.025 3.30 ± 0.031

M300 (MPa) 2.66 ± 0.011 4.63 ± 0.033 7.14 ± 0.015 9.51 ± 0.018

Swelling (%) 187.51 ± 2.22 162.98 ± 3.29 134.78 ± 4.55 122.03 ± 5.78

Crosslink density (× 10-5 mol/cm3) 1.51 ± 0.55 2.18 ± 0.35 2.48 ± 0.42 2.97 ± 0.19

Polímeros, 30(2), e2020020, 2020


Synergistic improvement of mechanical and magnetic properties of a new magnetorheological elastomer composites based on natural rubber and powdered waste natural rubber glove 3.4 Morphology of fracture surface analysis Figure 4 illustrates the tensile fractured surfaces of CI/CB hybrid filled NR/wNRg composites at 500× magnifications. As for the control sample (0 phr of CB), some detachment of CI is visible, showing many voids, loose, and agglomeration of CI particles on the fractured surface. This indicates a weak rubber-filler interaction. The presence of voids on the samples leads to localize the stress concentration during deformation. Thus, premature failure of CI/CB hybrid filled NR/wNRG composites occurred. However, surface roughness of the fractured surfaces was more visible when the CB was used as hybrid filler due to better rubber-filler interaction take place. Comparing the composites at 20 and 30 phr of CB, they reveal how roughness and the tortuous path of the fractured surface increased when CB was further used. The occurrence of these two failure samples are more towards difficult manner compared to the composites with the CI alone, resulted in a higher tensile strength. This observation can be visibly seen after adjusting the contrast between the voids (black)

and tearing pathways (white) of the composites. The voids formation is towards smaller size when increasing the CB loadings, indicating that CB can enhance the distribution of CI throughout the rubber matrices. As a result, higher strength is found upon inclusion of CB Figure 5 displays the tear fractured surfaces of CI/CB hybrid filled NR/wNRg composites at 500× magnification. Based on the SEM images, there are some explanation can be made. Typical image was found for CI filled NR/wNRg composite (0 phr of CB). With the addition of 10 phr of CB, the failure surfaces show feature of well-developed interfacial interaction. An augmentation in surface roughness and a homogeneous pattern are more pronounced when more CB was incorporated as hybrid filler, indicating a coherence of the CB particles and the rubber phases. It is interesting to highlight that, for the addition of 30 phr of CB, there were a few voids on the fractured surface (see the black areas in the monochrome images provided). This showed that it was a strong interfacial adhesion between phase occurred.

Figure 4. SEM micrographs obtained from tensile fractured surfaces of CI/CB hybrid filled NR/wNRg composites at 500× magnifications (CB loadings at 0-30 phr from left to right).

Figure 5. SEM micrographs obtained from tear fractured surfaces of CI/CB hybrid filled NR/wNRg composites at 500× magnifications (CB loadings at 0-30 phr from left to right). Polímeros, 30(2), e2020020, 2020

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Hayeemasae, N., & Ismail, H. As a result, higher energy is needed to cause a failure to the sample. Here, both SEM images obtained from tensile and tear fractured surfaces showed very similar existence of CI throughout the matrix. As widely known, two types of MRE can be prepared i.e., Isotropic and Anisotropic MREs[4,5]. In this preliminary experiment, Isotropic MRE was prepared, a random suspension of CI particles was then seen without showing specific orientation of CI. As a result, no chain-like columnar structures of magnetic particles are formed within the rubber. Similar observations were reported elsewhere, concerning the existence of magnetic particles in MREs[11,29].

3.5 Magnetic property The magnetic strength of the samples was measured by placing the probe directly to the rubber sample. The sample was then magnetized with approximate 200 mT prior to measure the magnetic strength. Here, the magnetic property is defined to a measure of the magnetic flux density or magnetic induction of the samples. From the results obtained (see Figure 6), the magnetic strength of the composites decreased with increasing of CB loading. The magnetic strengths were varied from 0.49, 0.34, 0.28 and 0.26 mT respectively. The decrement of magnetic strength is simply due to the nature of CB which is considered non-magnetic filler[30]. Even though the magnetic strength reduced upon inclusion of CB but the value is still acceptable for MRE. This is clear that simultaneous improvement of mechanical and magnetic properties can be completely achieved by the hybridization with CB. The blockage of CB to the magnetic

Figure 6. Magnetic strength (mT) of CI/CB hybrid filled NR/wNRg composites.

pathway of CI is less enough to provide an acceptable value of the magnetic strength to the composites. Based on the mechanical strength, swelling, crosslink density and magnetic behaviors of the composites, a schematic illustration representing the reinforcement is proposed in Figure 7. In this model, CI is dispersed in the NR/wNRg composites where it can generate high magnetic strength due to its magnetic behavior in nature of CI. Thus, CI plays an important role in inducing the magnetic pathway to the composite. Upon adding the CB, part of the rubber is trapped inside the aggregate and is shielded from macroscopic deformation due to rubber-filler interaction. These aggregates are dispersed well within a labile rubber matrix and a percolating network. As a result, the penetration of solvent steeply reduces together with higher requirement of energy to break the sample, leading to a significant increase in the tensile strength and tear strength of the composites.

4. Conclusions In this study, NR and wNRg were used as matrices in association with a combination of high magnetic filler (CI) and high reinforcing filler (CB). By varying the volume fraction of hybrid fillers, a new kind of value-added rubber composites with simultaneous improvement of magnetic and mechanical properties were developed. It is interesting to highlight that the tensile strength increased up to 10 phr of CB whereas the tear strength continuously increased upon the addition of CB. Such observation can be clearly confirmed by SEM images. Shorter scorch times, longer cure time and higher torque difference were found for CI/CB hybrid filled NR/wNRg composites at higher loading of CB. As for the magnetic strength of the composites, it was found to decrease with increasing the CB. Lower magnetic strength upon the addition of CB was due to the less magnetic property of CB and the blockage of CB in creating the magnetic pathway of CI. Even though the magnetic strength reduced upon inclusion of CB but the value is still acceptable for magnetorheological elastomer or MRE. Hybridization of 60/10 phr/phr of CI and CB is highly suggested to gain the synergistic strength and magneticity. The output obtained in this study will give scientific understanding on how these two fillers could influence the properties of MRE, and will provide useful information for preparing MRE in the further stages of this experiment.

Figure 7. Schematic representation the CI and CB behaviors in CI/CB hybrid filled NR/wNRg composites[19]. 6/7

PolĂ­meros, 30(2), e2020020, 2020


Synergistic improvement of mechanical and magnetic properties of a new magnetorheological elastomer composites based on natural rubber and powdered waste natural rubber glove

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16. Guyomar, D., Matei, D. F., Guiffard, B., Le, Q., & Belouadah, R. (2009). Magnetoelectricity in polyurethane films loaded with different magnetic particles. Materials Letters, 63(6-7), 611-613. http://dx.doi.org/10.1016/j.matlet.2008.11.058. 17. Sun, T. L., Gong, X. L., Jiang, W. Q., Li, J. F., Xu, Z. B., & Li, W. H. (2008). Study on the damping properties of magnetorheological elastomers based on cis-polybutadiene rubber. Polymer Testing, 27(4), 520-526. http://dx.doi.org/10.1016/j.polymertesting.2008.02.008. 18. Wang, Y., Hu, Y., Deng, H., Gong, P. G., Jiang, W., & Chen, Z. (2006). Magnetorheological elastomers based on isobutylene– isoprene rubber. Polymer Engineering and Science, 46(3), 264-268. http://dx.doi.org/10.1002/pen.20462. 19. Hayeemasae, N., & Ismail, H. (2019). Curing and swelling kinetics of new magnetorheological elastomer based on natural rubber/waste natural rubber gloves composites. Journal of Elastomers and Plastics, 51(7-8), 583-602. http://dx.doi.org/10.1177/0095244318803987. 20. Flory, P. J., & Rehner, J. Jr (1943). Statistical mechanics of cross‐linked polymer networks I. Rubberlike elasticity. The Journal of Chemical Physics, 11(11), 512-520. http://dx.doi. org/10.1063/1.1723791. 21. Medalia, A. I. (1978). Effect of carbon black on dynamic properties of rubber vulcanizates. Rubber Chemistry and Technology, 51(3), 437-523. http://dx.doi.org/10.5254/1.3535748. 22. Qing, Y., Min, D., Zhou, Y., Luo, F., & Zhou, W. (2015). Graphene nanosheet-and flake carbonyl iron particle-filled epoxy-silicone composites as thin–thickness and wide-bandwidth microwave absorber. Carbon, 86(1), 98-107. http://dx.doi.org/10.1016/j. carbon.2015.01.002. 23. Hamilton, R., & Crosser, O. (1962). Thermal conductivity of heterogeneous two-component systems. Industrial & Engineering Chemistry Fundamentals, 1(3), 187-191. https://doi.org/10.1021/ i160003a005 24. Gehman, S. (1967). Heat transfer in processing and use of rubber. Rubber Chemistry and Technology, 40(1), 36-99. http://dx.doi. org/10.5254/1.3539047. 25. Ismail, H., Rosnah, N., & Rozman, H. (1997). Curing characteristics and mechanical properties of short oil palm fibre reinforced rubber composites. Polymer, 38(16), 4059-4064. http://dx.doi.org/10.1016/ S0032-3861(96)00993-7. 26. Wolff, S., & Wang, M. J. (1992). Filler-elastomer interactions. Part IV. The effect of the surface energies of fillers on elastomer reinforcement. Rubber Chemistry and Technology, 65(2), 329-342. http://dx.doi.org/10.5254/1.3538615. 27. Bigg, D. M. (1987). Mechanical properties of particulate filled polymers. Polymer Composites, 8(2), 115-122. http://dx.doi. org/10.1002/pc.750080208. 28. Baccaro, S., Cataldo, F., Cecilia, A., Cemmi, A., Padella, F., & Santini, A. (2003). Interaction between reinforce carbon black and polymeric matrix for industrial applications. Nuclear Instruments & Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms, 208, 191-194. http://dx.doi.org/10.1016/ S0168-583X(03)00638-4. 29. Khimi, S. R., & Pickering, K. L. (2015). Comparison of dynamic properties of magnetorheological elastomers with existing antivibration rubbers. Composites. Part B, Engineering, 83(1), 175-183. http://dx.doi.org/10.1016/j.compositesb.2015.08.033. 30. Jovanović, V., Samaržija-Jovanović, S., Budinski-Simendić, J., Marković, G., & Marinović-Cincović, M. (2013). Composites based on carbon black reinforced NBR/EPDM rubber blends. Composites. Part B, Engineering, 45(1), 333-340. http://dx.doi. org/10.1016/j.compositesb.2012.05.020. Received: Feb. 03, 2020 Revised: June 08, 2020 Accepted: June 29, 2020 7/7


ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.09319

Development of active PHB/PEG antimicrobial films incorporating clove essential oil Ivo Diego de Lima Silva1* , Michelle Félix de Andrade2, Viviane Fonseca Caetano3, Fernando Hallwass4, Andréa Monteiro Santana Silva Brito5 and Glória Maria Vinhas3 Programa de Pós-graduação em Ciência de Materiais – PGMTR, Universidade Federal de Pernambuco – UFPE, Recife, PE, Brasil 2 Unidade Acadêmica de Engenharia de Materiais – UAEMa, Universidade Federal de Campina Grande – UFCG, Campina Grande, PB, Brasil 3 Departamento de Engenharia Química – DEQ, Universidade Federal de Pernambuco – UFPE, Recife, PE, Brasil 4 Departamento de Química Fundamental – DQF, Universidade Federal de Pernambuco – UFPE, Recife, PE, Brasil 5 Unidade Acadêmica de Serra Talhada – UAST, Universidade Federal Rural de Pernambuco – UFRPE, Serra Talhada, PE, Brasil 1

*ivo.diego@ufpe.br

Abstract In this work were developed and evaluated new antimicrobial films of polyhydroxybutyrate (PHB) additivated with polyethyleneglycol (PEG) and clove essential oil (CEO). The PHB/PEG/CEO films were prepared using the solution casting technique. The CEO concentrations varied between 0.0 and 15% (w/w), related to the total mass (1.4 g), without considering the solvent used. The CG-MS analysis showed that the major component of the CEO was eugenol (72.96%). The antimicrobial activity from the CEO was evaluated against three bacteria (E. coli, E. aerogenes and S. aureus). The migration of CEO in the films occurred with all tested simulants. Thermal analysis has shown that the addition of 15% w/w of the CEO causes the biggest changes in the chemical structure of the material, resulting in less energy during film processing. The mechanical data demonstrated that the addition of 15% w/w of the CEO results in more flexible films. Keywords: active packaging antimicrobial films, clove essential oil, Polyhydroxybutyrate, Polyethyleneglycol. How to cite: Silva, I. D. L., Andrade, M. F., Caetano, V. F., Hallwass, F., Brito, A. M. S. S., & Vinhas, G. M. (2020). Development of active PHB/PEG antimicrobial films incorporating clove essential oil. Polímeros: Ciência e Tecnologia, 30(2), e2020021. https://doi.org/10.1590/0104-1428.09319

1. Introduction In the food industry, packaging are responsible for preserving food quality and safety[1-3]. They can be classified into passive, intelligent and active[4,5]. Recently, the attention to active packaging has been increased, due to its performance in changing the environmental conditions to maintain the sensory properties of the food, thus providing quality assurance, increasing its shelf life, in addition to hygiene and food safety[6,7, 8]. Antimicrobial packaging is a kind of active packaging that is beneficial to the consumers and the food[9,10], which interfere in the lag period (growth period of the microorganisms) and inhibits microbial growth by the migration of the functional agents towards the food[11]. An ecologically friendly alternative for the production of antimicrobial packaging is the use of biodegradable polymers with natural antimicrobial agents. This combination can be an option to reduce the demand for degradable packaging

Polímeros, 30(2), e2020021, 2020

Polyhydroxybutyrate (PHB) is a well know biodegradable polymer used worldwide due to its crystalline structure, superior characteristics of aroma barrier, and water vapor permeability[9]. PHB is a thermoplastic polymer obtained from renewable natural sources that shown characteristics of biodegradability, biocompatibility, UV resistance and properties similar to the synthetic polypropylene[12-14]. However, the high crystallinity of PHB makes it very rigid and brittle, limiting its applications[15,16]. To overcome this limitation, plasticizers are added to the PHB. Poly (ethylene glycol) (PEG) is a polymer that can have a plasticizing effect when mixed with other polymers, in addition it is biodegradable and non-toxic[17]. According to the literature, PEG acts by decreasing intermolecular forces between PHB structures[18]. Regarding natural agents, there are essential oils (EO) that have been widely used in the food industry as natural antimicrobial agents in packaging material[19]. EOs are aromatic products of secondary plant metabolism, extracted

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


Silva, I. D. L., Andrade, M. F., Caetano, V. F., Hallwass, F., Brito, A. M. S. S., & Vinhas, G. M. from leaves, flowers, stems, roots, seeds or fruit peels[20-22]. The antimicrobial activity of the EO is mainly related to its main components, and it can also have a synergistic effect with some trace compounds[23]. Among the essential oils with proven antimicrobial activity is the clove essential oil (CEO) of the Eugenia caryophyllata plant. This oil has eugenol as its main component[24]. It has antibacterial, antifungal, antioxidant, insecticidal and antiviral properties[25]. It has been cited in the literature some works that incorporated and evaluated the effect of CEO in different polymer matrices for antimicrobial packaging applications. Among them, Wang et al.[26], Mulla et al.[27], De Lima et al.[28] and Mupalla et al.[29], studied chitosan, low density linear polyethylene, polyvinyl chloride, and blends of carboxymethylcellulose/ polyvinyl alcohol, respectively. In all these works CEO showed great potential for applications in antimicrobial packaging. The aim of this work was to develop a new antimicrobial films PHB/PEG-based incorporating CEO, and to determine its antimicrobial potential, as well as its migration towards food, in order to fulfill the requirements of an antimicrobial active packaging able to combat pathogenic microorganisms.

2.3 Antimicrobial activity of the clove essential oil In order to evaluate the antimicrobial activity of CEO, three kinds of bacteria were used Escherichia coli, Enterobacter aerogenes and Staphylococcus aureus (Culture collection of the Department of Antibiotics, Federal University of Pernambuco-Brazil). Filter paper discs were used for the diffusion experiment in a solid environment for every specie. The discs had 52 mm diameter and were sterilized by autoclaving (121 °C for 15 minutes). The culture medium (agar-agar) was prepared in a Petri dish. Later, the discs were soaked with pure CEO and placed in a Petri dish. Finally, each Petri dish was inoculated with 0.1 mL of bacterial suspension (10-4 on MacFarland scale). The Petri dishes were incubated for 24 hours at 30 °C and then the inhibition halos were measured.

2.4 Film preparation The polymeric films were produced using the solution casting technique[30]. The total weight of all formulated films was 1.4 g (polymer and CEO, without considering the weight of the solvent). Table 1 shows the weight of each component in the preparation of each film formulation. For the film preparation, PHB was weighed and mixture with 50 mL of chloroform. The bottle containing the polymeric solution was closed, in order to avoid solvent evaporation. The mixture was homogenized under stirring for 5 hours at 60 °C.

2. Materials and Methods 2.1 Materials PHB was provided by PHB Industrial S/A (São Paulo - Brazil). Before the preparation of the polymeric films, the PHB powder was strained through a 150-mesh strainer. PEG with molecular mass of 6000g/mol was purchased from Sigma‑Aldrich (San Luis - USA). CEO was provided by Solua Comercial Ltda (São Paulo - Brazil). Chloroform and ethanol were purchase from VETEC (Rio de Janeiro - Brazil), and acetic acid from Dinâmica (Indaiatuba - Brazil), all reagents were PA grade without further purification. The culture medium used Agar-agar was brand Kasvi (Paraná – Brazil).

2.2 Gas Chromatography Mass Spectrometry (CG-MS) The identification and quantification of the constituents of CEO was performed using TRACE 1300 Series gas Thermo Xcalibur Instrument (Massachusetts, USA) equipped with a TGMS-5 (5% phenyl/ polydimethylsiloxane) capillary column. The temperature parameters were: oven ramp of CG: 60 °C for 3min and then a heating rate of 10 °C/min was used until the temperature of the oven reached 300 °C, and this temperature remained constant for 15min. Injector temperature: 270 °C. Temperature of the transfer line to the MS: 280 °C, and temperature of ions source of MS: 250 °C.

The solution was left standing for 12 hours at room temperature. Afterwards, the mixture was again stirred for 4 hours at room temperature for complete solubilization. The film-forming solution was filtered and the PEG was added into the solution which was again stirred at room temperature for 1 hour. The mass of the CEO was weighed to prepared the following solutions: 5, 10 and 15% w/w, dissolved in 5 mL of chloroform, and added into the film‑forming solution, mixing for 15 minutes at room temperature. PHB/PEG control films were prepared without CEO addition. Finally, the solution was poured on a Petri dish with a 13 cm diameter until the solvent was completely evaporated.

2.5 Fourier-transform infrared spectroscopy (FTIR) The study of the incorporation of CEO, and the evaluation of the migration on antimicrobial films were carried out through Fourier-transform infrared spectrometer (FTIR) of the company Perkin Elmer (Massachusetts, USA), using the Universal Attenuated Total Reflectance (UATR) accessory. All the spectra were acquired at spectral infrared region of 4000-650 cm-1, at 4 cm-1 resolution and 16 scans[31].

Table 1. Weight of PHB, PEG and CEO for the preparation of each formulation of polymeric films. Samples PHB/PEG PHB/PEG + CEO (5%) PHB/PEG + CEO (10%) PHB/PEG + CEO (10%)

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CEO (g) % compared to 1.4g 0.070 0.140 0.210

PHB (g)

PEG (g) 9:1 aspect ratio

1.260 1.197 1.134 1.071

0.140 0.133 0.126 0.119

Total weight (g) 1.4 1.4 1.4 1.4

Polímeros, 30(2), e2020021, 2020


Development of active PHB/PEG antimicrobial films incorporating clove essential oil 2.6 Migration test In order to investigate the migration of the essential oil (5, 10 and 15% (w/w) concentrations) in the antimicrobial films of the simulated food, the active films were cut into rectangles with sections of 1 cm x 3 cm width. For the migration test, the following simulant were prepared: a) acid: 3% (v/v) acetic acid solution, b) alcoholic: 10% (v/v) of ethanol, and c) neutral: distilled water. The assays were carried out in duplicate for each concentration of the CEO and kind of simulant, at a room temperature (25 °C) and cooled (5 °C). The antimicrobial films remained immersed in the 7 mL simulant solution for 90 hours. It is important to mention that every 18 hours the films were removed from the solution, washed with distilled water, dried in the oven, and two distinct points on the film were analyzed at the FTIR spectrometer. After the assay period of migration, the average of the spectra for each assay was analyzed. The baseline correction was applied. A fixed point was chosen in the region with the highest absorbance relative to the essential oil (1515 cm-1) and its behavior was observed by applying the Equation 1 to convert the absorbance into concentration (%). Concentration = (%)

AX hours × 100 A0hours

(1)

Where A0hours corresponds to the absorbance at the initial time of the experiment and AXhours the absorbance at the end of the assay. Finally, the graphics for concentration x time for each assay were drawn.

2.7 Exploratory differential calorimetry (DSC) The thermal parameters of PHB/PEG and samples containing 5, 10 and 15% (w/w) of essential oil were evaluated using differential scanning calorimetry (DSC) of the company Mettler Toledo (Ohio, USA) – Star System 1. The samples of 3 and 5 mg were introduced into an aluminum crucible under a nitrogen atmosphere at a flow rate of 50 mL/min. Thermal analysis was performed using a temperature range of 0 °C to 200 °C, which involved three stages regarding heating and cooling the samples, which were as follows: first stage: Heating from 0 – 200 °C with a heating rate of 30 °C/min; second stage: Cooling of 200 – 0 °C with a cooling rate of 10 °C/min; and third stage: heating from 0 – 200 °C with a heating rate of 10 °C/min.

2.8 Thermogravimetric analysis (TGA) All the films were subjected to thermogravimetric tests in equipment of the company Shimadzu DTG 60H (Kyoto, Japan) in order to evaluate the rates of weight loss. Therefore, approximately 20 mg of the samples were introduced into a thermobalance. The thermogravimetric analyzes were performed in a temperature range of 35-600 °C, using a heating rate of 10 °C/min under a nitrogen atmosphere.

2.8 Tensile Test Mechanical tensile tests were carried out according to the ASTM 882-12 standard[32]. For the analysis, EMIC 500 equipment was used (Paraná, Brazil). It was Polímeros, 30(2), e2020021, 2020

performed at room temperature without humidity control, and followed the procedure: claw speed of 5 mm/min; initial distance between 40 mm claws; size of the test piece of 2.5 x 7.5 cm. For each film manufactured, three samples were obtained. Since the tensile test was carried out in triplicate, it was obtained 9 samples for each concentration. Duncan’s statistical test was used to evaluate statistically significant changes.

2.9 Statistical Analysis Mechanical properties data were carried out by analysis of variance (ANOVA) using the Statistica software, version 10.0.228.8. Duncan’s test was used to determine differences at a level of significance of 5% (p ≤ 0,05).

3. Results and Discussion 3.1 Gas chromatography–mass spectrometry (GC-MS) GC-MS was used in order to investigate the chemical composition of the CEO. Table 2 shows the percentage of the principal compounds present in the mixture of CEO. The major compound found in the oil was eugenol. This compound is well known for its great antimicrobial potential against various pathogenic microorganisms[33].

3.2 Evaluation of antimicrobial activity of the CEO After the incubation period, the CEO exhibited inhibition of the microbial growth for the three studied bacteria, as shown in Figure 1. The bacterial colony Escherichia coli (Figure 1a) an average halo inhibition of approximately 9.0 mm, was observed; for the Enterobacter aerogenes (Figure 1b) the halo was 6.6 mm; and for the Staphylococcus aureus (Figure 1c) the halo inhibition was 8.1 mm. Using the classification of Ostrosky et al.[34], we observed that this indicates that the CEO is an excellent antimicrobial agent, because of its halo above 3.0 mm, emphasizing its potential as an active agent for food packaging. The CEO has been evaluated as antimicrobial additives in other polymers and the results show that this oil has a strong inhibitory potential in the metabolism of Gram negative as well as Gram positive bacterias[35-37].

3.3 Fourier-transform infrared spectroscopy (FTIR) The antimicrobial films with 5, 10 and 15% (w/w) of CEO showed a characteristic peak between 1500-1535 cm-1 (Figure 2). This peak is associated with the C=C stretching due to the eugenol aromatic group[33]. It can be inferred through this analysis that the CEO was incorporated into the polymeric matrix PHB/PEG after total chloroform evaporation. Table 2. Composition of the CEO obtained by CG-MS. Compound Eugenol Caryophyllene Humulene Other compounds

(%) 73.0 17.9 4.9 4.2

3/8


Silva, I. D. L., Andrade, M. F., Caetano, V. F., Hallwass, F., Brito, A. M. S. S., & Vinhas, G. M.

Figure 1. Microbial Inhibition test in solid state of clove essential oil: (a) Escherichia coli (b) Enterobacter aerogenes (c) Staphylococcus aureus.

Figure 2. FT-IR spectra from PHB/PEG films: pure (bottom) and with 5, 10 e 15% (w/w) of CEO.

3.4 CEO migration kinetics Figure 3 shows the graphs of the CEO migration kinetics in the PHB/PEG films. The films were subjected to two different temperature and three different simulants: neutral simulant at 25 °C (neutral simulant); acid simulant at 25°C (neutral simulant); alcoholic simulant at 25 °C (alcoholic simulant); neutral simulant at 5 °C (neutral simulant-cold); acid simulant at 5 °C (neutral simulant-cold) and alcoholic simulant at 5 °C (alcoholic simulant-cold). Considering the effect of the simulant and the concentration of CEO in the films it was observed that the migration of the CEO occurs more quickly in the first 18 hours of exposure to the simulants, and more slowly after that period. Analyzing the effect of the temperature is verified that the films submitted to 25 °C resulted in a faster migration rate at the same period of time (18 hours) when compared to those submitted to 5 °C. Therefore, temperature is a variable that also contributes significantly to migration. According to Bart[38], several factors contribute to migration, among which we can highlight: starting concentration of migrant in the polymer; affinity and solubility of the migrant for the polymer or for the contact medium; molecular structure and molecular weight the migrant; and mobility of the migrant in the polymer. 4/8

At 5 °C, PHB/PEG films with 10% (w/w) CEO concentration showed the highest percentage of CEO migration in the 18 h period. In this composition, 46%, 44% and 39% of CEO occurred for the neutral, acid and alcoholic simulants, respectively, in the 18 h period. This behavior was similar for the other concentrations (5 and 15% w/w) in the PHB/PEG films at the same temperature. At 25 °C, PHB/PEG films with a concentration of 15% w/w of CEO showed the highest percentage migration of CEO in the period of 18 hours for the acid and alcoholic simulants. In this composition, 81% and 72% of CEO migration occurred for the acid and alcoholic simulants, respectively. At 25°C, PHB/PEG films with 10% w/w CEO concentration showed the highest CEO migration (73%) in the 18 h period in the neutral simulant. At the end of the 90 hs period, it can be observed that the PHB/PEG films with 15% w/w CEO concentration showed the highest percentage of CEO migration to the acid and alcoholic simulants at 25 oC. There was a percentage migration of CEOs of 80 and 90% for the alcoholic and acidic simulants, respectively. Also, for this composition, there was a 66% CEO match in the neutral simulant. According to Tawakkal et al.[39] the tendency towards migration is greater when submitted to the simulant with polarities closer to the antimicrobial agent. This explain the accentuated migration in acid and alcoholic simulants, when compared to the neutral simulator, which is polar in nature. These results show either the CEO behavior in simulants to various types of food. The results shown that the CEO has the potential to migrate and therefore plays the role as an antimicrobial agent, an essential requirement to provide a protective action to the food and prevent its deterioration.

3.5 Exploratory differential calorimetry (DSC) The crystallization temperature (Tc), cold crystallization temperature (Tcc), melting temperature (Tm), melting enthalpy change (ΔHm) and degree of crystallinity (Xc) were obtained by the DSC technique, and the results are shown in Table 3. According to the results shown in Table 3, can be observed that the melting temperature (Tm) of PHB/PEG polymer matrix decreases with increasing of the essential oil concentration. Silva et al.[40] used CEO as a plasticizer in bocaiuva (Acromonia aculeata) flour films. They observed Polímeros, 30(2), e2020021, 2020


Development of active PHB/PEG antimicrobial films incorporating clove essential oil

Figure 3. Migration test of active PHB / PEG films supplemented with (a) 5% w/w, (b) 10% w/w and (c) 15% w/w of the CEO. Table 3. Thermal parameters of pure PHB / PEG samples and added with 5, 10 and 15% (w/w) of CEO. Samples

Tc (°C)

Tcc (°C)

Tm (°C)

ΔHm (J/g)

Xc (%)

56.64 46.77 -

21.59 39.52 31.41

171.38 172.47 168.64 160.80

70.21 72.26 72.18 31. 41

48.09 49.49 49.44 21.51

PHB/PEG PHB/PEG + CEO (5%) PHB/PEG + CEO (10%) PHB/PEG + CEO (15%)

that the decrease of the melting temperature is related to the reduction of the secondary forces between the polymer structures caused by the incorporation of the additive. Therefore, the reduction of the melting temperature that occurred in the PHB/PEG blend with the addition of the CEO is likely related to a decrease in the secondary forces of the PHB polymer structures. The degree of crystallinity (Xc) of the samples presented similar values, except for the polymer films with 15% (w/w) of CEO. For this sample the Xc value is smaller, showing that the polymer became less crystalline, an important feature for PHB processing. The decrease in degree of crystallinity is related to the mechanical properties of the polymers (the lower the degree of crystallinity, the greater the elasticity of the material) and the melting temperature (the higher the crystallinity, the higher the thermal energy required to melt the material). It is possible to observe, from Table 3, a marked reduction in the melting enthalpy (ΔHm) with the addition of 15% (w/w) of oil, and values close to the pure PHB / PEG in Polímeros, 30(2), e2020021, 2020

the other compositions. This behavior indicates that the addition of 15% (w/w) of CEO causes greater changes in the chemical structure of the material. In addition, with this change, less energy will be needed for this material to melt during processing[41]. As shown in Table 3, only films incorporated with essential oil presented the temperature of cold crystallization (Tcc). This effect indicates that the polymeric matrix has sufficient mobility to reorganize the amorphous phase, forming new crystallites. For crystallization temperature (Tc) it was only possible to observe this effect in samples of pure PHB/PEG and with 5% (w/w) of the CEO.

3.6 Thermogravimetric analysis (TGA) In the graph of TGA (Figure 4a) and DTG (Figure 4b) was observed that the PHB/PEG blend showed two stages of degradation. The first stage occurs between the temperatures of 258-325 °C, and is related to the thermal degradation of PHB. The second stage is observed between 334-437 °C, caused by thermal decomposition of PEG. 5/8


Silva, I. D. L., Andrade, M. F., Caetano, V. F., Hallwass, F., Brito, A. M. S. S., & Vinhas, G. M.

Figure 4. Thermogram of PHB / PEG samples and active films with 5, 10 and 15% (w/w) of CEO. (a) TGA curves in relation to mass percentage (b) Curves derived from TGA (DTG). Table 4. Tensile stress, specific deformation and Young module values of PHB/PEG films at different CEO concentration. Samples PHB/PEG PHB/PEG + 5% CEO PHB/PEG + 10% CEO PHB/PEG + 15% CEO

Tensile stress (MPa) 12.57a± 1.09 13.76a± 0.35 12.22a± 0.32 8.10b± 1.84

Specific deformation (%) 3.34a± 0.93 3.70a± 0.49 3.08a± 0.08 9.77b± 1.01

Young module (MPa) 430.97a± 31.09 405.27a± 25.46 388.67a± 50.24 301.90b± 20.29

Means followed by vertical letters do not differ significantly (p> 0.05) by the Duncan test.

In terms of the antimicrobial films, the presence of three degradation phases can be seen in the TGA and DTG, shown in Figure 4, and the first weight loss occurs in the temperature range of 140-225°C. According to Choi et al.[42], this stage refers to the thermo-oxidation and boiling temperature of eugenol present in CEO. The other stages of degradation are related to PHB / PEG blends. Furthermore, by analyzing the results shown in Figure 4, may conclude that the CEO interferes with the degradation of the polymer because the increasing oil concentration decreases the initial PHB/PEG degradation temperature. The degradation of the PEG (third event) in the blend did not change regardless of the concentration of the CEO.

3.7 Tensile Test Mechanical assays of active polymer films were performed to observe the influence of CEO on the mechanical properties of the PHB/PEG blend. Observing the results of the tensile test (Table 4) it can be seen that there was no significant change in tensile strength, specific deformation and modulus of elasticity of pure PHB / PEG samples and added with 5 and 10% (w/w) of the CEO. However, the film with 15% (w/w) of the CEO showed a significant change in all the studied mechanical parameters, resulting in a more flexible film when compared with the lower percentage of essential oil in the film. The plasticizer effect of the essential oil was also observed in the other polymer films. According to Giménez et al.[43], CEO in the egg white gelatin film decreased the modulus of elasticity and 6/8

increased its elongation to traction also contributing to the reduction of secondary forces between the polymer chains.

4. Conclusions In this study, active packaging were prepared by incorporating CEO, in different concentrations, into polyhydroxybutyrate and polyethyleneglycol films, using the solution casting technique. Antimicrobial analysis by disc diffusion of CEO revealed the potential of CEO to inhibit pathogenic microorganisms, such as: Escherichia coli, Enterobacter aerogenes and Staphylococcus aureus. The migration test demonstrated the efficiency of the CEO as an active agent for active packaging, since these packaging must have a substance that migrates to the food, providing a protective barrier against the microorganisms. Therefore, as seen in the tests the migration occurred in all simulants, with a higher rate for the acid simulant. It has also been seen that the cooling of the system contributes to the reduction of the migration rate in all food simulants tested. From the mechanical and thermal analysis, it was observed that the increase in the CEO concentration (15% w/w) influences the decrease of the intermolecular interactions between the polymeric matrix structures, obtaining a less crystalline and consequently more elastic films. It can be concluded that PHB/PEG films, to which has been added with CEO, have potential for applications in antimicrobial protection packaging, contributing to the increase in the shelf life of perishable foods. Polímeros, 30(2), e2020021, 2020


Development of active PHB/PEG antimicrobial films incorporating clove essential oil

5. Acknowledgments The authors would like to thank the Laboratório de Materiais Poliméricos e Caracterização (LMPC/UFPE), the Grupo de Instrumentação e Análises Químicas (GIAQ/Unidade Acadêmica de Serra Talhada/UFRPE) and the Núcleo de Química Analítica Avançada de Pernambuco (NUQAAPE/FACEPE/PRONEX/APQ-0346-1.06/14). This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco (FACEPE). IDLS thanks to FACEPE for the master fellowship.

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Silva, I. D. L., Andrade, M. F., Caetano, V. F., Hallwass, F., Brito, A. M. S. S., & Vinhas, G. M. 25. Chaieb, K., Hajlaoui, H., Zmantar, T., Kahla-Nakbi, A. B., Rouabhia, M., Mahdouani, K., & Bakhrouf, A. (2007). The chemical composition and biological activity of clove essential oil, Eugenia caryophyllata (Syzigium aromaticum L. Myrtaceae): a short review. Phytotherapy Research, 21(6), 501-506. http:// dx.doi.org/10.1002/ptr.2124. PMid:17380552. 26. Wang, L., Liu, F., Jiang, Y., Chai, Z., Li, P., Cheng, Y., Jing, H., & Leng, X. (2011). Synergistic antimicrobial activities of natural essential oils with chitosan films. Journal of Agricultural and Food Chemistry, 59(23), 12411-12419. http://dx.doi. org/10.1021/jf203165k. PMid:22034912. 27. Mulla, M., Ahmed, J., Al-Attar, H., Castro-Aguirre, E., Arfat,Y. A., & Auras, R. (2017). Antimicrobial efficacy of clove essential oil infused into chemically modified LLDPE film for chicken meat packaging. Food Control, 73(Part B), 663-671. http:// dx.doi.org/10.1016/j.foodcont.2016.09.018 28. Lima, M. S., Carvalho, D. S., Silva, S. H., Caetano, V. F., & Vinhas, G. M. (2017). Avaliação do efeito antimicrobiano do óleo essencial de cravo em filmes de poli (cloreto de vinila). Revista Brasileira de Agrotecnologia, 7(2), 294-298. 29. Mupalla, S. R., Kanatt, S. R., Chawla, S. P., & Sharma, A. (2014). Carboxymethyl cellulose–polyvinyl alcohol films with clove oil for active packaging of ground chicken meat. Food Packaging and Shelf Life, 2(2), 51-58. http://dx.doi. org/10.1016/j.fpsl.2014.07.002. 30. Martelli, S. M., Sabirova, J., Fakhouri, F. M., Dyzma, A., de Meyer, B., & Soetaert, W. (2012). Obtention and characterization of poly(3-hydroxybutyricacid-co-hydroxyvaleric acid)/mclPHA based blends. Lebensmittel-Wissenschaft + Technologie, 47(2), 386-392. http://dx.doi.org/10.1016/j.lwt.2012.01.036. 31. Giaquinto, C. D. M., Souza, G. K. M., Caetano, V. F., & Vinhas, G. M. (2017). Evaluation of the mechanical and thermal properties of PHB/canola oil films. Polímeros: Ciência Tecnologia, 27(3), 201-207. http://dx.doi.org/10.1590/01041428.10716. 32. American Society for Testing and Materials – ASTM. (2012). D882-12: Standard Test Method for Tensile Properties of Thin Plastic Sheeting. Philadelphia: ASTM. 33. Narayanan, A., Neera, Mallesha, & Ramana, K. V. (2013). Synergized antimicrobial activity of eugenol incorporated polyhydroxybutyrate films against food spoilage microorganisms in conjunction with pediocin. Applied Biochemistry and Biotechnology, 170(6), 1379-1388. http://dx.doi.org/10.1007/ s12010-013-0267-2. PMid:23666640. 34. Ostrosky, E. A., Mizumoto, M. K., Lima, M. E. L., Kaneko, T. M., Nishikawa, S. O., & Freitas, B. R. (2008). Métodos para avaliação da atividade antimicrobiana e determinação da Concentração Mínima Inibitória (CMI) de plantas medicinais.

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Revista Brasileira de Farmacognosia, 18(2), 301-307. http:// dx.doi.org/10.1590/S0102-695X2008000200026. 35. Ahmed, J., Mulla, M., Jacob, H., Luciano, G., Bini, T. B., & Almusallam, A. (2019). Polylactide/poly(ε-caprolactone)/zinc oxide/clove essential oil composite antimicrobial films for scrambled egg packagings. Food Packaging and Shelf Life, 21, 100355. http://dx.doi.org/10.1016/j.fpsl.2019.100355. 36. Song, N., Lee, J., Mijan, M., & Song, K. B. (2014). Development of a chicken feather protein film containing clove oil and its application in smoked salmon packaging. LebensmittelWissenschaft + Technologie, 57(2), 453-460. http://dx.doi. org/10.1016/j.lwt.2014.02.009. 37. Cui, H., Zhao, C., & Lin, L. (2015). The specific antibacterial activity of liposome-encapsulated Clove oil and its application in tofu. Food Control, 56(2), 128-134. http://dx.doi.org/10.1016/j. foodcont.2015.03.026. 38. Bart, J. C. J. (2006). Polymer Additive Analytics: Industrial Practice and Case Studies. Italy: Firenze University Press. http://dx.doi.org/10.36253/8884533783 39.Tawakkal, I. S. M. A., Cran, M. J., & Bigger, S. W. (2016). Release of thymol from poly(lactic acid)-based antimicrobial films containing kenaffibres as natural filler. LebensmittelWissenschaft + Technologie, 66, 629-637. http://dx.doi. org/10.1016/j.lwt.2015.11.011. 40. Silva, A. O., Cortez-Veja, W. R., Prentice, C., & Fonseca, G. G. (2019). Development and characterization of biopolymer films based on bocaiuva (Acromonia aculeata) flour. International Journal of Biological Macromolecules, 155, 1157-1168. http:// dx.doi.org/10.1016/j.ijbiomac.2019.11.083. PMid:31726125. 41. Andrade, M. F., Silva, I. D. L., Silva, G. A., Cavalcante, P. V. D., Silva, F. T., Almeida, Y. M. B., Vinhas, G. M., & Carvalho, L. H. (2020). A study of poly (butylene adipate-co-terephthalate)/ orange essential oil films for application in active antimicrobial packaging. Lebensmittel-Wissenschaft + Technologie, 125, 1-22. http://dx.doi.org/10.1016/j.lwt.2020.109148. 42. Choi, M., Soottitantawat, A., Nuchuchua, O., Min, S., & Ruktanonchai, U. (2009). Physical and light oxidative properties of eugenol encapsulated by molecular inclusion and emulsiondiffusion method. Food Research International, 42(1), 148-156. http://dx.doi.org/10.1016/j.foodres.2008.09.011. 43. Giménez, B., Gomez-Guillén, M. C., López-Caballero, M. E., Gomezestaca, J., & Montero, P. (2012). Role of sepiolite in the release of active compounds from gelatin-egg white films. Food Hydrocolloids, 27(2), 475-486. http://dx.doi. org/10.1016/j.foodhyd.2011.09.003. Received: Feb. 02, 2020 Revised: July 17, 2020 Accepted: July 19, 2020

Polímeros, 30(2), e2020021, 2020


ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.03820

Rosin maleic anhydride adduct antibacterial activity against methicillin-resistant Staphylococcus aureus Zahid Majeed1*# , Muhammad Mushtaq1# , Zainab Ajab2 , Qingjie Guan2 , Mater Hussen Mahnashi3 , Yahya Saeed Alqahtani3  and Basharat Ahmad4  Environmental Biotechnology Laboratory, Department of Biotechnology, University of Azad Jammu and Kashmir, Chehla Campus, Muzaffarabad, Azad Kashmir, Pakistan 2 Key Laboratory of Saline-alkali Vegetation Ecology Restoration, Ministry of Education, College of Life Sciences, Northeast Forestry University, Harbin, Heilongjiang, China 3 Department of Pharmaceutical Chemistry, College of Pharmacy, Najran University, Najran, Kingdom of Saudi Arabia 4 Department of Zoology, University of Azad Jammu and Kashmir, Chehla Campus, Muzaffarabad, Azad Kashmir, Pakistan

1

#

*zahidfdb@gmail.com; zahid.majeed@ajku.edu.pk Zahid Majeed and Muhammad Mushtaq contributed equally as first author.

Abstract The emergence of antibiotic resistance in microorganisms is a serious challenge globally. Natural hydrophobic diterpene carboxylic acids present in rosin have unsatisfactory inhibitory properties against pathogens due to their poor water solubility. Therefore, the objective of research work was to modify the natural rosin into rosin maleic anhydride adduct with improved bioinhibitory properties for methicillin-resistant Staphylococcus aureus (MRSA). Prescreened MRSA isolates were found 78.05% and 29.27% resistant to oxacillin and vancomycin antibiotics respectively. The dosage effect of 0, 25, 50, and 100 mg L-1 rosin maleic anhydride adduct revealed the best inhibition response at 25 mg L-1. Moreover, bacteriostatic as well as the inhibitory effect of rosin maleic anhydride adduct was noticed against MRSA isolates. Gompertz model predicted better uptake of maleic anhydride adduct as compared to rosin. The higher specific growth rate of MRSA at reduced lag time correlated with increased toxicity of maleic anhydride adduct. This research concludes rosin maleic anhydride adduct has superior inhibitory properties against MRSA strains. Keywords: drug resistance, growth kinetics, growth inhibition, MRSA, rosin maleic anhydride adduct. How to cite: Majeed, Z., Mushtaq, M., Ajab, Z., Guan, Q., Mahnashi, M. H., Alqahtani, Y. S., & Ahmad, B. (2020). Rosin maleic anhydride adduct antibacterial activity against methicillin-resistant Staphylococcus aureus. Polímeros: Ciência e Tecnologia, 30(2), e2020022. https://doi.org/10.1590/0104-1428.03820

1. Introduction MRSA is a multidrug-resistant gram-positive resistant bacterium and it is a worldwide challenge for all clinicians to treat this Methicillin Resistant S. aureus (MRSA) infection. The resistant strain of MRSA, which acquired resistance against oxacillin/methicillin and other antibiotics that contain β-lactam rings in their structure. Currently, vancomycin inhibits MRSA strains in the range of 1.0-2.0 µg mL-1. Until today, vancomycin has shown excellent activity against clinical isolates of MRSA[1]. However, vancomycin resistance is relatively a new pattern in emerging MRSA strains. MRSA causes intractable human infections[2]. β-lactamase mediated resistance in S. aureus has been developed within the last decade due to the overuse of penicillin[3,4]. Besides, the production of Penicillin-binding proteins 2a (PBP2a) in MRSA is responsible for the development of S. aureus resistance to methicillin antibiotics. This protein was encoded by the mecA, a gene that is placed on chromosome mec cassette – a mobile genetic element (MGE) of S. aureus.

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It shows a very low affinity against antibiotics that contain β-lactam ring[5,6]. Due to this fact, the resistance of S. aureus against antibiotics of many classes is a current challenge for all physicians that work in a hospital environment to cure infections caused by MRSA[7]. Rosin consists of abietic acid, pimaric acid, and labdane acids. Abietic acid and dehydroabietic acid are potent compounds against bacteria[8]. Augmenting the rosin concentration is known for an increase in the microbicidal effect of the rosin against S. aureus, MRSA, Escherichia coli (E. coli), Pseudomonas aeruginosa, Bacillus subtilis, and Candida albicans. The minimum concentration of rosin 10% (w/w) has prevented the growth of the microbes in the rosin‐salve media[9]. Antibacterial activity of reduced gum rosin-acrylamide copolymer-based novel nanogel have shown 19.3-19.8 mm and 11.2-12.5 mm of the zone of inhibition against S. aureus and E. coli respectively[10]. Rosin acids-loaded polyethylene glycol-poly(lactic-co-glycolic acid)

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Majeed, Z., Mushtaq, M., Ajab, Z., Guan, Q., Mahnashi, M. H., Alqahtani, Y. S., & Ahmad, B. nanoparticles are known with enhanced antimicrobial properties against foodborne bacterial pathogens[11]. Rosin acid and their derived nanoparticles were strongly active against antibiotic-resistant S. aureus. Earlier mechanisms of rosin activity revealed that the coniferous rosin destroys the bacterial cell wall and cell membrane. In electrophysiologic experiments, the rosin exposure decreased the cell membrane proton gradient in bacterial cells. This phenomenon is associated with the disruption of proton transport in the membrane‐bound ATPase, and resulting in uncoupling of the oxidative phosphorylation. It results in cell metabolism would cease and the supply of energy is lost. By electron microscopy, an increase in the thickness of the cell wall promotes cell to cell aggregation which facilitated by rosin and lysis of bacterial cells finally occur. Based on literature studies, it is evident that rosin has poor antibacterial properties. The improvement of its inhibitory properties with maleic anhydride for its use as a drug against MRSA is not studied yet. To overcome MRSA drug resistance, this research proposed the use of rosin modified with maleic anhydride adduct[12] as an antibacterial drug. There are limited studies that have used the rosin as an antimicrobial drug against MRSA[2]. Rosin’s reaction with maleic anhydride has been reported for rosin maleic anhydride adduct. Maleic anhydride has increased the water solubility in water in a pH-dependent manner[13]. Pine trees are abundantly present in Azad Jammu and Kashmir, Pakistan which are biofactories for natural rosin which are composed of acids known for their promising antimicrobial activity. These acids are abietic acid, dehydroabietic acid, and the less stable acids of the abietadiene-type (levopimaric acid, palustric acid, and neoabietic acid)[14]. Under this work, we prepared different concentrations of rosin maleic anhydride adduct with improved solubility than rosin and evaluated inhibitory properties against MRSA screened from different infected patients visited Combined Military Hospital Muzaffarabad, Azad Jammu, and Kashmir, Pakistan.

2. Materials and Methods 2.1 Media and reagents Mannitol Salt Agar (99%), Muller-Hunton Agar, Nutrient Broth were purchased from Sigma Aldrich (USA). Antibiotics (Oxacillin, Vancomycin, Cefoxitin, Piperacillin, Tazobactam, Fosfomycin, Cephradine, Amoxicillin) a product of Oxoid, (UK) were used. Rosin (Mw 303 g/mol)[15,16] of P. roxburghii was provided by the Environmental Biotechnology Laboratory of the Department of Biotechnology, University of Azad Jammu and Kashmir, Muzaffarabad. Any plant residues present in rosin were removed manually, and purified it after passing melted rosin through 0.1 mm mesh strainer.

2.2 MRSA screening 2.2.1 Infectious samples collection Total 60 clinical isolates were screened from different infectious samples of pus, urine, blood, ear swab, vaginal fluid submitted to Microbiology Laboratory of Combined 2/7

Military Hospital, Muzaffarabad, Azad Jammu and Kashmir during Year - 2019. 2.2.2 Culturing, isolation, and identification of S. aureus The collected samples were enriched in nutrient broth and incubated for 24 h at 37°C. After this, the broth was immediately streaked on Nutrient Agar plate under sterile conditions and incubated further at 37°C for 24 h. Microbial colonies were further isolated for the identification of S. aureus. For S. aureus identification, isolates were cultured on Mannitol Salt Agar as a specific media for S. aureus at 37°C for 24 h for colony appearance and identification. S. aureus was identified by observing a yellow colony and yellowish background on Mannitol Salt Agar[17]. Catalase and coagulase tests[18] tests were conducted for confirmation of S. aureus. In a catalase-positive test, bacterial colonies produced bubbles after adding and homogenizing with 1-2 drops of 3% H2O2. For a positive coagulase test, one drop of plasma citrate added to 1-2 bacterial colonies which developed plasma flocculation. Out of non-duplicate 60 samples, 41 (68.3%) samples were detected positive for S. aureus. Isolates of S. aureus (N= 41) recovered was as follows; 17 (41.46%) from pus, urine 10 (24.39%), vaginal fluid 6 (14.63%), blood 3 (7.32%), ear swab 3 (7.32%), and other body fluid 2 (4.88%). Maximum number/percentage of S. aureus in pus followed by urine. The lowest number or percentage of S. aureus recovered in other body fluids. 2.2.3 Antibiotics sensitivity screening of S. aureus and detection of MRSA Antibiotics susceptibility testing was performed using the disc diffusion method as per the criteria are given by the British Society for Antimicrobial Chemotherapy[19]. Antimicrobial drug susceptibility testing was performed against all isolates of S. aureus by using a modified disk diffusion method. About 3-5 selected colonies of bacteria were taken from the pure culture and transferred to a tube containing 5 mL of distilled water and mixed gently until a homogenous suspension was formed. The suspension mixture distributed the bacteria over the entire surface of Mueller-Hinton agar. The following concentrations of antibiotics were tested against S. aureus: oxacillin, 1 µg; amoxicillin, 25 µg; cefoxitin, 30 µg; vancomycin, 30 µg, piperacillin/tazobactam, 110 µg; fosfomycin, 50 µg. All the S. aureus strains were tested against oxacillin disk by using the disk diffusion method which is a benchmark for MRSA. The oxacillin disk was applied on the Mueller-Hinton agar plate against S. aureus and incubated at 37 °C for 24 h. After this incubation period, oxacillin resistant strains were confirmed for MRSA according to the zone of inhibition (ZOI) measured against S. aureus. Oxacillin ZOI ≤ 10 mm - MRSA ZOI 11-12 mm - intermediate sensitivity ZOI was ≥ 13 mm then it is methicillin-sensitive S. aureus (MSSA) All these resistant strains were further re-confirmed by testing against cefoxitin disk and incubated at 37 °C for 24 h. After this incubation the ZOI was measured by using the following scale Polímeros, 30(2), e2020022, 2020


Rosin maleic anhydride adduct antibacterial activity against methicillin-resistant Staphylococcus aureus Cefoxitin ZOI ≤ 21 mm - MRSA ZOI ≥ 22mm – MSSA This technique was adopted as an agreement standard by the Clinical and Laboratory Standards Institute (CLSI)[20,21]. The distribution of S. aureus in different clinical samples was determined. Table 1 details the antibiotics sensitivity and resistivity trends found in S. aureus. Antibiotic susceptibility test was performed against (N = 41) S. aureus through the disk diffusion method. The S. aureus confirmed isolates were 32 (78.05%) resistant, 9 (21.95%) sensitive to oxacillin (Table 1). The antibiotics piperacillin/tazobactam (85.37%) and vancomycin (70.73%) showed maximum sensitivity against S. aureus and higher resistance to amoxicillin, (82.93%) fosfomycin, (80.49%) and oxacillin (78.05%). These isolates show maximum sensitivity for piperacillin/ tazobactam and higher resistance against amoxicillin.

2.3 Rosin maleic anhydride adduct antimicrobial sensitivity 2.3.1 Synthesis of Rosin maleic anhydride For conversion of rosin into rosin maleic anhydride adduct, conditions for synthesis, a scheme for chemical reactions, confirmation of chemical structure by infrared spectroscopy are reported in detail in our previous published research work[15]. 2.3.2 Antimicrobial sensitivity 2.3.2.1 Disk diffusion assay To estimate the antibacterial effects of rosin and rosin maleic anhydride, the well diffusion method was used. During this method, the rosin and rosin maleic anhydride adduct were melted separately and placed thereafter on an aluminum file until they solidify. After that it was ground into smaller pieces, added acetone for dissolution and after that 10 times diluted with distal water to obtain concentration 25, 50, 100, and 150 mg L-1[12]. The Muller Hinton Agar was prepared by using distal water and autoclave at 121°C for 1 h. After this, 1 mL of bacterial broth mixed with 20 mL of Muller-Hinton Agar and poured into Petri plates and left for solidification. Wells were formed by using the yellow tip and pouring rosin suspension into the well in different concentrations after that plate was incubated at 37°C for 24 h. The zone of inhibition was measured by using Vernier caliper (Mitutoyo, Japan). Table 1. Sensitivity and resistivity pattern of S. aureus against antibiotics. Antibiotic Oxacillin Vancomycin Cefoxitin Piperacillin/Tazobactum Fosfomycin Cephradine Amoxicillin

S. aureus (N= 41) Sensitive % Resistant % (No. of isolates) 21.95 (9) 70.73 (29) 26.83 (11) 85.37 (35) 19.51 (8) 41.46 (17) 17.07 (7)

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(No. of isolates) 78.05 (32) 29.27 (12) 73.17 (30) 14.63 (6) 80.49 (33) 58.54 (24) 82.93 (34)

The shake tube method was used to quantitatively evaluate the antibacterial activity[22]. The ultraviolet light under laminar flow was used for the sterilization of rosin and rosin maleic anhydride adduct before use. The S. aureus culture of 10 mL (diluted to 103 fold of the original level) added separately with 0.1 mL of rosin and rosin maleic anhydride adduct. Then, the two test tubes were shaken in the shaking incubator (IRMECO, GmbH Germany) with 120 rpm for 24 h at 37°C. 10 mL of the stimulated bacterial solution was diluted and spread on the agar plate, individually. The quality of bacterial colonies on the agar plate after incubating for 24 h at 37°C was counted on the colony counter (Galaxy 230 - Rocker Scientific Co., Ltd, Taiwan). Bacterial reduction percentage was calculated by the following Equation 1:  B−A = R   ×100 (1)  B 

Where percentage bacterial reduction is represented by “R”. The quality of live bacterial cells in the flask after shaking is represented by “B”. The quality of live bacterial cells in the flask before shaking is represented by “A”. 2.3.2.2 Growth kinetics The antimicrobial testing of S. aureus was performed qualitatively by using turbidity analysis on the spectrophotometer. The pure 3-5 selected colonies of S. aureus were cultured into the nutrient broth in 20 mL glass test tube and incubate at 37oC for 24 h. After 24 h incubation, the fresh culture of these bacteria was re-cultured in nutrient broth 10:1 (10:1 mL bacterial culture) into three test tubes. The rosin and rosin maleic anhydride concentration 25, 50, and 100 mg L-1 were used for screening of inhibitory and bactericidal activity against MRSA. All tubes were incubated in a shaking incubator at 37oC for 24 h. Colonies were counted on the colony counter prior to the start of the experiment and then after 24 h incubation at 37oC. The culture was further 10 times diluted and spread on agar and incubated at 37°C for 24 h. After this incubation, the S. aureus colonies were counted on agar plate by using the colony counter. The colony-forming units of S. aureus were counted as a number of colonies multiplied 1010 µL-1. The antimicrobial testing was performed qualitatively for turbidity analysis by using T60 spectrophotometer (PG Instruments Ltd, UK). Pure 3 to 5 selected colonies of S. aureus were cultured in a test tube containing nutrient broth and incubate at 37°C for 24 h. After 24 h incubation, the fresh culture of this bacteria was re-cultured in a nutrient broth 10:1 (10 mL broth and 1 mL bacterial culture) into three test tubes. Tube one containing 10 mL nutrient broth along with rosin maleic anhydride and 1 mL bacterial culture, tube two containing 10 mL nutrient broth along with pure rosin and 1 mL bacterial culture and tube three containing only 10 mL nutrient broth and 1 mL bacterial culture as a control for turbidity analysis. By using a spectrophotometer, the turbidity of culture was measured at 650 nm wavelength and taken absorbance from zero time to 24 h at different intervals of times up to 24 h for each treatment. By using Origin Pro software, version 9.0.0 (Origin Lab Corporation, Northampton, MA, USA), predicted the response of S. aureus under treatment according to Equation 2 adopted from literature[23]. 3/7


Majeed, Z., Mushtaq, M., Ajab, Z., Guan, Q., Mahnashi, M. H., Alqahtani, Y. S., & Ahmad, B.

Figure 1. Different concentrations of rosin and rosin maleic anhydride adduct inhibition of MRSA and S. aureus.  e µ  = X A exp −exp  MAX ( λ − t ) + 1  (2)  A  

X is logarithm of the relative population size of S. aureus against time; A is asymptote which represents the maximal soil microbial biomass; t is time (h), λ is a lag phase (h); µMAX is maximum specific growth rate (day-1) and e is constant.

3. Results and Discussions 3.1 Inhibitory activity of rosin maleic anhydride adduct In Figure 1, the inhibitory activity of rosin and rosin maleic anhydride against MRSA and S. aureus are shown. At all concentrations, rosin activity was not observed against MRSA and S. aureus. However, the rosin maleic anhydride showed better activity against both MRSA and S. aureus. This difference shows successful chemically transformation of rosin into a form that has activity against MRSA and S. aureus. Average data for zone of inhibition recorded for rosin maleic anhydride treated MRSA and S. aureus further revealed in Figure 2, 25 mg L-1 of rosin maleic anhydride effective to inhibit the maximum growth of MRSA. The rosin maleic anhydride at 25 mg L-1 developed 7 mm of the zone of inhibition. While at the same concentration, a lower value of 4.25 mm of the zone of inhibition noticed for S. aureus treated with rosin maleic anhydride. The further analysis explained that the increase of concentration of rosin maleic anhydride did not increase the zone of inhibition. While an increase of rosin maleic anhydride concentration up to 100 mg L-1 increased the zone of inhibition against S. aureus. Therefore, better solubility in water and effectiveness against MRSA made the rosin maleic anhydride a better formulation. Rosin’s activity against MRSA is given in Figure 3. At different concentration rosin, the bacterial culture of MRSA grows up to 24 h. An increase in the concentration 4/7

Figure 2. Rosin maleic anhydride inhibitory activity against MRSA and S. aureus.

Figure 3. Rosin inhibition of S. aureus growth. Polímeros, 30(2), e2020022, 2020


Rosin maleic anhydride adduct antibacterial activity against methicillin-resistant Staphylococcus aureus of rosin from 25 to 100 mg L-1 showed significant inhibition of MRSA growth. On day 6 maximum growth for each composition was noticed. Based on optical density at 6 h, the value of optical density was 1.47 for 25 mg L-1 of rosin. The addition of 50 mg L-1 of rosin reduced the optical density of MRSA from 1.47 to 1.23 with a difference of 16.32% of inhibition. Further increase of rosin up to 100 mg L-1 reduced optical density from 1.47 to 0.79 with a change of 42.25%. In Figure 4 is given, rosin maleic anhydride activity against MRSA. At different concentration rosin, the bacterial culture of MRSA grows up to 24 h. An increase in the concentration of rosin from 25 to 100 mg L-1 showed significant inhibition of MRSA growth. On day 4 maximum growth for each composition was noticed. Based on optical density at 4 h, the value of optical density was 0.77 for 25 mg L-1 of rosin. The addition of 50 mg of rosin reduced the optical density of MRSA from 0.77 to 0.65 with a difference of 15.58% of

inhibition. Further increase of rosin up to 100 mg L-1 reduced optical density from 0.77 to 0.37 with a change of 51.48%. Our findings are in agreement with results[10], rosin has shown inhibitory activity against different fungus and bacterial strains. The possible effect induced by rosin on the strain was due to cell to rosin adhesion. Figure 5 explains Gompertz kinetics of S. aureus and MRSA to find out the growth parameters according to kinetic model Equation 2. The pattern of growth of S. aureus in response to rosin and rosin maleic anhydride fits well to Gompertz parameterization and a reliable prediction through characterization of the curve could be obtained. The parameters obtained after Gompertz kinetic parameters predicted as are given in Table 2. The asymptote (A) of growth for S. aureus showed no significant change in values over an increase in the dosage of rosin. The growth increase was observed at 10.90% after the rise in the concentration of rosin. In case, the increase of concentration of rosin maleic anhydride causes significant decrease (69.36%) in S. aureus growth parameters. The µMAX of S. aureus shows a different trend for rosin and rosin maleic anhydride. As noticed µMAX declined 85.03% for an increase in dosages of rosin. This trend deviates when S. aureus was treated with rosin Table 2. Rosin and rosin maleic anhydride adduct effect on growth kinetics of MRSA. Composition

Figure 4. Rosin maleic anhydride adduct inhibition of MRSA growth.

Conc.

(mg L-1) Rosin 25 50 100 Rosin maleic 25 50 Anhydride 100 adduct

A 0.486 0.537 0.539 1.221 0.771 0.374

μMAX

λ

ti

(h-1) 0.401 0.386 0.060 0.716 2.409 2.403

(h) 0.179 0.197 0.204 0.449 0.284 0.138

(day) 2.089 1.885 0.000 1.347 2.874 2.360

Figure 5. Gompertz kinetic model fitting to growth data of MRSA at different inhibitory concentrations of rosin (A) and rosin maleic anhydride adduct (B) over different incubation hours. Polímeros, 30(2), e2020022, 2020

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Majeed, Z., Mushtaq, M., Ajab, Z., Guan, Q., Mahnashi, M. H., Alqahtani, Y. S., & Ahmad, B. maleic anhydride. The µmax response was 72.20% higher when S. aureus was treated with rosin maleic anhydride. Rosin’s treatment prolonged the lag period (λ) for the growth of S. aureus. The change in the lag period was 13.96%. In contrast, the use of rosin maleic anhydride preferably impacts more on minimizing the lag phase which determines the early growth response of S. aureus. The reduction in lag phase was 69.26% after an increase of rosin maleic anhydride. The inflection point which determines the shape of the growth curve. This change was higher in the case of rosin maleic anhydride compared to rosin with an opposite trend over the time of growth.

4. Conclusion This work concludes that the adduct form of rosin with maleic anhydride is an effective means of improving the rosin bacteriostatic and inhibitory action against S. aureus in general and MRSA in particular. In Pakistani Hospitals, MRSA is prevalent and is found resistant against oxacillin and vancomycin. This work provides a solution to this problem successfully by increasing the efficacy of the rosin after its modification. MRSA could be treated with a dose of 25 mg L-1 rosin maleic anhydride adduct. Rosin maleic anhydride adduct was better metabolized compared to rosin in MRSA supported with a rise in specific growth rate (μMAX) reciprocate with short lag phase (λ) data.

5. Acknowledgements Authors are highly grateful to the Department of Biotechnology, University of Azad Jammu & Kashmir, Muzaffarabad for financial and technical support and the Deanship of Scientific Research at Najran University, Najran, Saudi Arabia for a financial assistant to publish this research work successfully.

6. References 1. Seyfried, P. L., Tobin, R. S., Brown, N. E., & Ness, P. F. (1985). A prospective study of swimming-related illness. II. Morbidity and the microbiological quality of water. American Journal of Public Health, 75(9), 1071-1075. http://dx.doi.org/10.2105/ AJPH.75.9.1071. PMid:4025657. 2. McDougal, L. K., Steward, C. D., Killgore, G. E., Chaitram, J. M., McAllister, S. K., & Tenover, F. C. (2003). Pulsed-field gel electrophoresis typing of oxacillin-resistant Staphylococcus aureus isolates from the United States: establishing a national database. Journal of Clinical Microbiology, 41(11), 51135120. http://dx.doi.org/10.1128/JCM.41.11.5113-5120.2003. PMid:14605147. 3. Witte, W., Strommenger, B., Klare, I., & Werner, G. (2004). Antibiotic-resistant nosocomial pathogens. Part I: diagnostic and typing methods. Bundesgesundheitsblatt, Gesundheitsforschung, Gesundheitsschutz, 47(4), 352-362. http://dx.doi.org/10.1007/ s00103-004-0810-y. PMid:15205778. 4. Yau, V., Wade, T. J., de Wilde, C. K., & Colford, J. M., Jr. (2009). Skin-related symptoms following exposure to recreational water: a systematic review and meta-analysis. Water Quality, Exposure, and Health, 1(2), 79-103. http://dx.doi.org/10.1007/ s12403-009-0012-9. 5. McCarthy, A. J., Witney, A. A., & Lindsay, J. A. (2012). Staphylococcus aureus temperate bacteriophage: carriage 6/7

and horizontal gene transfer is lineage associated. Frontiers in Cellular and Infection Microbiology, 2, 6. http://dx.doi. org/10.3389/fcimb.2012.00006. PMid:22919598. 6. Hartman, B. J., & Tomasz, A. (1984). Low-affinity penicillinbinding protein associated with beta-lactam resistance in Staphylococcus aureus. Journal of Bacteriology, 158(2), 513-516. http://dx.doi.org/10.1128/JB.158.2.513-516.1984. PMid:6563036. 7. Tavares, A. L. (2014). Community-associated methicillinresistant Staphylococcus aureus (CA-MRSA) in Portugal (Doctoral dissertation). Universidade NOVA de Lisboa, Portugal. Retrieved in 2020, April 18, from https://run.unl. pt/handle/10362/14236 8. Söderberg, T. A., Gref, R., Holm, S., Elmros, T., & Hallmans, G. (1990). Antibacterial activity of rosin and resin acids in vitro. Scandinavian Journal of Plastic and Reconstructive Surgery and Hand Surgery, 24(3), 199-205. http://dx.doi. org/10.3109/02844319009041279. PMid:2281306. 9. Sipponen, A., & Laitinen, K. (2011). Antimicrobial properties of natural coniferous rosin in the European Pharmacopoeia challenge test. APMIS, 119(10), 720-724. http://dx.doi. org/10.1111/j.1600-0463.2011.02791.x. PMid:21917009. 10. Jindal, R., Sharma, R., Maiti, M., Kaur, A., Sharma, P., Mishra, V., & Jana, A. (2017). Synthesis and characterization of novel reduced gum rosin-acrylamide copolymer-based nanogel and their investigation for antibacterial activity. Polymer Bulletin, 74(8), 2995-3014. http://dx.doi.org/10.1007/s00289-016-1877-y. 11. Santovito, E., Neves, J., Greco, D., D’Ascanio, V., Sarmento, B., Logrieco, A. F., & Avantaggiato, G. (2018). Antimicrobial properties of rosin acids-loaded nanoparticles against antibioticsensitive and antibiotic-resistant foodborne pathogens. Artificial Cells, Nanomedicine, and Biotechnology, 46(Suppl 3), S414-S422. https://doi.org/10.1080/21691401.2018.1496 924. 12. Sipponen, A., Peltola, R., Jokinen, J. J., Laitinen, K., Lohi, J., Rautio, M., Männistö, M., Sipponen, P., & Lounatmaa, K. (2009). Effects of Norway spruce (Picea abies) resin on cell wall and cell membrane of Staphylococcus aureus. Ultrastructural Pathology, 33(3), 128-135. http://dx.doi. org/10.1080/01913120902889138. PMid:19479653. 13. Atta, A. M., & Elsaeed, A. M. (2011). Use of rosin‐based nonionic surfactants as petroleum crude oil sludge dispersants. Journal of Applied Polymer Science, 122(1), 183-192. http:// dx.doi.org/10.1002/app.34052. 14. Karlberg, A. T., & Hagvall, L. (2018). Colophony: Rosin in unmodified and modified form. In T. Rustemeyer, P. Elsner, S. M. John & H. I. Maibach (Eds.), Kanerva’s occupational dermatology (pp. 607-624). Berlin Heidelberg: Springer. http://dx.doi.org/10.1007/978-3-31940221-5_41-2. 15. Mumtaz, I., Majeed, Z., Ajab, Z., Ahmad, B., Khurshid, K., & Mubashir, M. (2019). Optimized tuning of rosin adduct with maleic anhydride for smart applications in controlled and targeted delivery of urea for higher plant’s uptake and growth efficiency. Industrial Crops and Products, 133, 395-408. http:// dx.doi.org/10.1016/j.indcrop.2019.02.036. 16. National Center for Biotechnology Information PubChem Database. Retrieved in 2020, April 18, from https://pubchem. ncbi.nlm.nih.gov/compound/Rosin 17. Johnson, T. R., Case, C. L., Cappuccino, J. G., & Sherman, N. (2013). Great adventures in the microbiology laboratory: microbiology 22. UK: Pearson Learning Solutions. 18. Ekawati, E. R., Darmanto, W., & Wahyuningsih, S. P. A. (2020). Detection of Staphylococcus aureus in wound infection on the skin surface. IOP Conference Series: Earth and Environmental Polímeros, 30(2), e2020022, 2020


Rosin maleic anhydride adduct antibacterial activity against methicillin-resistant Staphylococcus aureus Science, 456, 012038. http://dx.doi.org/10.1088/17551315/456/1/012038. 19. Nathwani, D. (2018). Overview of AMR. In British Society for Antimicrobial Chemotherap (Ed.), Antimicrobial stewardship: from principles to practice (Chap. 1, pp. 12-26). UK: British Society for Antimicrobial Chemotherap. Retrieved in 2020, April 18, from http://www.bsac.org.uk/antimicrobialstewardshipebook/BSACAntimicrobialStewardship-FromPrinciplestoPractice-eBook.pdf 20. Almutairi, M. S., Zakaria, A. S., Ignasius, P. P., Al-Wabli, R. I., Joe, I. H., & Attia, M. I. (2018). Synthesis, spectroscopic investigations, DFT studies, molecular docking and antimicrobial potential of certain new indole-isatin molecular hybrids: experimental and theoretical approaches. Journal of Molecular Structure, 1153, 333-345. http://dx.doi.org/10.1016/j. molstruc.2017.10.025. 21. Hussain, S. S., HusseinAlwan, A., Abbas, M., & Tektook, N. K. (2019). Biochemical and molecular diagnosis of Escherichia coliand Pseudomonas aeruginosa isolated from UTI patients. In The First International Scientific Conference of Health and

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Medical Specialties (pp. 12-30). Iraq: Kut Technical Institute, Middle Technical Universty. Retrieved in 2020, April 18, from http://kti.mtu.edu.iq/conf/researches/3.pdf 22. Corey, B. W., Thompson, M. G., Hittle, L. E., Jacobs, A. C., Asafo-Adjei, E. A., Huggins, W. M., Melander, R. J., Melander, C., Ernst, R. K., & Zurawski, D. V. (2017). 1, 2, 4-triazolidine3-thiones have specific activity against Acinetobacter baumannii among common nosocomial pathogens. ACS Infectious Diseases, 3(1), 62-71. http://dx.doi.org/10.1021/acsinfecdis.6b00133. PMid:27764938. 23. Majeed, Z., Mansor, N., ismail, S., Mathialagan, R., & Man, Z. (2016). Gompertz kinetics of soil microbial biomass in response to lignin reinforcing of urea-crosslinked starch films. Procedia Engineering, 148, 553-560. http://dx.doi.org/10.1016/j. proeng.2016.06.510. Received: Apr. 17, 2020 Revised: July 19, 2020 Accepted: July 24, 2020

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.00920

Polymeric nanoemulsions enriched with Eucalyptus citriodora essential oil Flávia Oliveira Monteiro da Silva Abreu1* , Emanuela Feitoza Costa1, Mayrla Rocha Lima Cardial1 and Weibson Pinheiro Paz André2 Laboratório Química Analítica e Química Ambiental – LAQAM, Programa de Pós-graduação em Ciências Naturais – PPGCN, Universidade Estadual do Ceará – UECE, Fortaleza, CE, Brasil 2 Laboratório de Doenças Parasitárias – LABODOPAR, Programa de Pós-graduação em Ciências Veterinárias – PPGCV, Universidade Estadual do Ceará – UECE, Fortaleza, CE, Brasil

1

*flavia.monteiro@uece.br

Abstract Eucalyptus citriodora oil has a well-known antimicrobial activity, however, its volatility limits its therapeutic applicability. Oil-in-water chitosan-based nanoemulsions have been prepared using a high-energy method in variable conditions in order to produce a stable formulation with an effective antimicrobial action. Physical-chemical characterizations and antimicrobial activity were performed. Results showed that the nanoemulsions with stability over 60 days and encapsulation efficiency higher than 90% were the ones with higher surfactant content. An optimal formulation was produced with the longer chain surfactant, which impacted in a particle size of 489.2±0.25nm and encapsulation efficiency of 92.5±0.17%. This formulation showed sustained release over 72h according to zero order kinetics, where the drug diffusion is lower than the respective dissolution release rate. The bactericidal action of the tested formulations showed an expressive inhibition rate against S. typhimurium (73%), with potential for an effective release system for antimicrobial control. Keywords: chitosan, encapsulation, Eucalyptus citriodora. How to cite: Abreu, F. O. M. S., Costa, E. F., Cardial, M. R. L., & André, W. P. P. (2020). Polymeric nanoemulsions enriched with Eucalyptus citriodora essential oil. Polímeros: Ciência e Tecnologia, 30(2), e2020024. https://doi. org/10.1590/0104-1428.00920

1. Introduction The indiscriminate use of conventional antimicrobials has created resistant pathogens, which lead to the growth of severe infections and invasive diseases. Given this situation, research has been conducted in order to find alternative drugs. Plants are a rich source of pharmacologically interesting bioactive resources, and the antimicrobial potential of the Essential Oils (EO) has been explored in the last decade[1]. EOs are mixtures of chemical compounds that present aromatic structures of natural origin, where their constitution differs widely among plant species and is generally classified as terpenes, terpenoids and phenolic compounds[2]. Eucalyptus citriodora belongs to the Myrtaceae family, and these species are known for the characteristics of their essential oils. It is known that the E. citriodora essential oil (ECEO) has a wide spectrum of biological activities, including herbicidal[3,4], antifungal[5], insecticide[6], antioxidant[7,8], antimicrobial[9,10] properties. However, the storage of EOs is a critical matter due to their sensitivity to heat, humidity and air, being subject to hydrolysis, oxidation, dehydration and isomerization reactions[11-13]. Thus, the encapsulation of EOs is an important nanotechnological strategy to enable the use of such constituents, improving their physical-chemical stability and promoting protection against external factors[14-18].

Polímeros, 30(2), e2020024, 2020

Nanoemulsions (NEs) are useful alternatives in the encapsulation of EOs, enabling the improvement of physical-chemical stability, the modulation of release rates and bioavailability of such active principles, as it has been reported in recent studies[14-17]. The composition of the formulations, method and preparation conditions are intrinsically related, and it is necessary to conduct research to formulate more stable, efficient controlled release systems for the incorporation of active ingredients with antimicrobial action[12,14-18]. Chitosan (Cs) is a cationic biopolymer in acid conditions, and is formed of D-glucosamine and N-acetylD-glucosamine bound by β-glycosidic bonds (1-4), it is a deacetylation of chitin, which is present in the shell of crustaceans[19]. Several studies have been carried out to explore its potential in different types of encapsulation matrices, such as nanoparticle systems[19,20], nanogels[21,22], nanoliposomes[9,23] conventional emulsions[24,25] and Pickering emulsions[26,27]. The use of Chitosan in a encapsulation system can enhance the transport of drugs across the nasal membrane, increasing the permeability of the epithelial membrane and retaining a formulation for extended time periods due to its mucoadhesive properties[16,20]. The addition of an anionic crosslinker into the chitosan-surfactant-oil

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


Abreu, F. O. M. S., Costa, E. F., Cardial, M. R. L., & André, W. P. P. system may increase the nanoemulsion stability, in order to retain the oil inside the micelle for a longer time[14,20]. Although the effect of surfactant and oil relative content in nanoemulsions has been studied to some extent[19-22,25,26], the main limitation of nanoemulsion system is caused by droplet growth and phase separation after a short period of time, which compromises the applicability. In this study, chitosan nanoemulsions incorporated with ECEO were developed adding a ionic crosllinker, aiming to improve the physical-chemical stability, statistically correlating the formulations conditions with the nanoemulsion stability aiming for antimicrobial applications.

2. Materials and Methods 2.1 Materials The following materials were used: chitosan from shrimp (Cs) (Polymar, CE, 72% deacetylation degree, Mw = 3,3 x 105 g.mol-1), acetic acid (Dynamics). Nonionic surfactants Tween20® (T20) and Tween80® (T80) (Dynamics), Sodium Tripolyphosphate crosslinker agent (TPP) (Dynamics) and ECEO (FERQUIMA).

2.2 Preparation of nanoemulsion Eight oil-in-water nanoemulsions (O/W) were prepared by means of the high-speed homogeneization method, adapted from Ribeiro et al.[28], by varying the type of the surfactant, and the relative content of Cs, ECEO and surfactant in the nanoemulsion. First, the surfactant agent (Tween 80 or Tween 20®) was added to ECEO at a mass ratio of 1:2 or 1:4 and then subjected to a vortex stirring (model NI1059 - Vortex) at 1000 rpm for 2 min, forming the oil phase. The oil phase was added to the Cs solution (1% v/v in acetic acid) to form the nanoemulsions with a volume raio with the aid of a mechanical homogenizer Model ULTRA380 of the Ultrastirrer brand at 25.000 rpm over 2 min. The proportions 4:2 and 8:2 of the chitosan in relation to the ECEO were tested. A solution of ionic crosslinker agent TPP (0.5% m/v) was finally added in the system in the proportion chitosan:TPP 4:1 and 8:1 and then the mixture was kept under stirring for 1 min. About 200 ml of Nanoemulsions were produced, stored in close vials and kept in the refrigerator. A small portion of the nanoemulsions (10 ml) was frozen and then freeze-dried (L101, Liobras, Brazil) for FTIR and Scannin Electron Microscopy (SEM) analysis.

performed through ANOVA analysis in the Excel program (Microsoft 2013). The significance of the encapsulation parameters was verified using a confidence level of 95%, with a (p) value lower than 0.05.

2.4 Characterization of nanoemulsions A physical stability study was carried out 24 hours, 30 days and 60 days after the preparation of the formulations, in order to verify visual signs of creaming or phase separation, adapted from Mwang et al.[27] and Dickinson[29]. in closed vials, protected from light, kept at temperature of 26 °C. With the aid of a caliper, the thickness of the formed creaming was measured throughout the observation period. Creaming index (CI) was determined by measuring serum height (Hs) and total height (Ht) of an emulsion 1, 30 and 60 days after sample preparation, and calculated according to Equation 1[27]. CI ( %= )

The viscosity of the emulsions was measured on an Ostwald type glass viscometer, timing the flow time. The viscosities of the samples were obtained through the calculation described by Almeida et al.[30]. Particle size, polydispersity index (PDI) and zeta potential were determined after 30 days by dynamic light scattering using the Malvern Zetasizer equipment (Malvern Instruments, United Kingdom). The NE samples were dispersed in distilled water, forming a concentration of 0.1% (v/v) NE/water and left in agitation for 12 hours, to ensure full matrix dispersion in aqueous medium. The infrared spectra (FT-IR) were obtained using a Nicolet iS5 model spectrophotometer from Thermo Scientific. The samples were prepared in KBr tablets in the proportion 1:20 (m/m) (sample:KBr) and the spectra recorded in the range of 4000 to 400 cm-1, using 32 scans and 4 cm-1 resolution.

2.5 Scanning electronic and optical microscopy Morphological characterization was performed by SEM (Zeiss DSM, model 940A), using an accelerating voltage of 20kV and a magnification of 100-3000x. Samples were previously coated with platinum using a sputter coater (Electron Microscopy Sciences, Hatfield, PA, USA). Table 1. Experimental conditions of Chitosan NPs production with Eucalyptus citriodora essential oil (ECEO).

NE1

T20QOT421

Factor A Surfactant Type T20

NE2

T80QOT421

T80

4:2

4:1:1

NE3

T20QOT411

T20

8:2

4:1:1

NE4

T80QOT411

T80

8:2

4:1:1

NE5

T20QOT841

T20

4:2

8:1:1

NE6

T80QOT841

T80

4:2

8:1:1

NE7

T20QOT821

T20

8:2

8:1:1

NE8

T80QOT821

T80

8:2

8:1:1

Formulation code

2.3 Experimental design and statistical analysis A 23 replicate factorial design was performed to evaluate the influence of the factors in the efficiency of encapsulation of ECEO. Based on the literature and previous studies, the independent variables include the following factors: surfactant type (Tween 20 and 80, Factor A), quantitative ratio by chitosan and ECEO (4:2 and 8:2, factor B) and chitosan: surfactant ratio:TPP (4:1:1 and 8:1:1, Factor C). The dependent variables were the encapsulation efficiency of ECEO and viscosity. The factorial planning consisted of 8 experiments in replicate and the factors were evaluated at two different levels, low (-1) and high (+1), as described at Table 1. The statistical treatment of the data was 2/9

Hs ×100 (1) Ht

Factor B Factor C Cs:ECEO Cs:Surf:TPP Ratio Ratio 4:2 4:1:1

Factor A: Surfactant type: Tween 20 (-) and Tween 80 (+), Factor B: Cs:ECEO ratio: 4:2 (-) and 8:2 (+) and Factor C: Cs:Surfactant:Tripolyphosphate (TPP) ratio:4:1:1 (-) and 8:1:1 (+).

Polímeros, 30(2), e2020024, 2020


Polymeric nanoemulsions enriched with Eucalyptus citriodora essential oil Optical Microscopy was realized by placing 100 µL of nanoemulsions between two glass lamins in an optical microscope (Digital OPTON- 40,model TNB-01-D) using an objective lens with 40x. Photos were adquired using a Software ISCapture using a magnification of 400x.

2.6 Encapsulation efficiency assessment The quantity of encapsulated ECEO was adapted from Sugasini and Lokesh[31]. 1g of each nanoemulsion was sonicated for 10 minutes, diluted in ethanol (95%) in a 10 mL flask and centrifuged at 4000 rpm for 20 minutes. Subsequently, 1 mL of suspended material was removed and diluted with ethanol (96%) in a 5 mL flask and taken for reading in the Thermo Scientific Spectrophotometer (GENESYS 6 UV-Vis) at a wavelength of 214 nm. The Encapsulation Efficiency (EE%) was calculated according to Equation 2: Determined Oil Concentration  EE ( % = ) 100 ×   (2)  Total Theoretical Oil Concentration 

It was prepared in triplicate in a standart solution of 500 ppm of ECEO in ethanol 96% (Dinamic). Further dilutions were made to obtain concentrations of 250, 210, 170, 130, 90, 80, 70, 60, 50, 40, 30, 20 and 10 mg. L-1. The oil concentration was determined in the medium through a calibration curve, available in the Supplementary Material (Figure S1a), and represented by Equation 3: Y= 0.0024x + 0.0615

R2 = 0.998 (3)

2.7 Kinetic release profile The most stable formulations were submitted to in vitro release tests. 300 mg of each sample was added in dialysis membranes (10 KDa) in a beaker containing 10 mL of distilled water at pH=7. Neutral pH was chosen to study the release in aqueous media, an environment where microorganisms present higher viability of action[32]. Aliquots of 3 mL were taken from the system at 15-minute intervals, in the first hour, and each 1 hour up to 8 hours, and after 24h and 72h. After each measurement, the aliquot was returned to the release system. A UV-vis spectrophotometer reading was performed at a wavelength of 214 nm and the concentration in the aqueous medium was converted using the calibration curve in water represented by Equation 4, available in the Supplementary Material (Figure S1b). Y= 1.1631x + 0.0388

R2 = 0.981 (4)

2.8 Antimicrobial activity To standardize the technique and size of the inoculum, positive and negative gram bacteria were used, Sthaphylococcus aureus and Salmonella typhimurium, respectively, which were sown in 2 mL of the Tripticase Soy Agar (TSA) culture medium, after which they were placed in the incubator for 24 hours, before the test, for growing the microorganisms. An antimicrobial investigation was performed using the Müller Hinton agar diffusion method. The antimicrobial activity of NE was evaluated by using 100 µL of NE and 30 cgm of Chloramphenicol as positive control. A negative control was made mixing chitosan, tween and TPP solution using Polímeros, 30(2), e2020024, 2020

the same procedure as described for NE production, without the ECEO oil. Also, distilled water were used as negative control. The diameter of the inhibition zone was measured with a caliper up to the closest value of 0.1mm. The total area of the zone was calculated and subtracted from the disc area of the film and this difference in the area was reported as the inhibition zone.

3. Results and Discussions 3.1 Physico-chemical assessment of nanoemulsions The effect of storage time on droplet size nanoemulsion was determined within 24 hours, 30 days and 60 days. The solubility of essential oils in an aqueous solution is higher than that of lipids composed of medium or long chain fatty acids[20], therefore, nanoemulsions prepared from them are particularly prone to Ostwald maturation. During the analysis time, there was creaming formation for only two samples. The creaming rates in the respective time intervals of 24 hours, 30 days and 60 days are shown in Figure 1. In the evaluation of the stability of the systems, the analysis of variance (ANOVA) (available in Supplementary Material, Table S1), revealed that the only significant factor is factor C, which studies the influence of the relative ratio between Cs: Surf:TPP. Thus, we can state that for the stability of the micellar system, the ratio between the Cs wall material, surfactant and TPP must be maintained at the relative ratio (4:1:1). It is observed that the first four formulations (T20QOT421, T80QOT421, T20QOT411 and T80QOT411), which were produced with a Cs:Surf 4:1 and Cs:TPP 4:1 ratio were more stable than the others, regarding the creaming and separation, because they had a percentage of segregated volume lower than 1%, even after 60 days. During the interval of 24 hours, 30 and 60 days, the sample tests T20QOT841 and T20QOT821 were the only ones that presented a significant creaming formation, with values of 13.3% and 6.3%, respectively. These results were corroborated by the optical microscopy, where there was an increase of the droplets size in these formulations (available in Supplementary Material, Figure S2). It is observed that these samples were prepared with Tween 20 using a smaller amount of surfactant (Cs: Surf 8:1) and also lower TPP concentration, which lead to a relatively large emulsion droplets[27]. Phenomena related to the separation of phases of an emulsified system are linked to differences in density between the component phases of the system[29], thus, it is possible to infer that the use of Tween 20 may have favored

Figure 1. Creaming index at time intervals 24h, 30 and 60 days. 3/9


Abreu, F. O. M. S., Costa, E. F., Cardial, M. R. L., & André, W. P. P. creaming in the mentioned compositions, since it is denser (1.1 g.cm-3) than Tween 80 (1.07 g. cm-3). In the study of Mwangi et al.[27], they investigated the effects of Cs concentration in Pickering emulsions and found that the increase in chitosan concentration from 0.01 to 0.3% w/v decreased the creaming rates, making it possible to consider that the polymer delayed the movement of the droplets. Xiong et al.[25] evaluated the addition of Cs in ovalbumin emulsions and reported that the increase in chitosan concentration (0.3% m/m) in the system considerably increased stability and decreased the formation of creaming. Calero et al.[33] observed that concentrations below 0.5% m/m of Cs tended to a significant increase in viscosity, which they attributed to the occurrence of flocculation of oil droplets and formation of creaming.

3.2 Encapsulation efficiency, zeta potential and particle size Nanoemulsions presented considerable variation in the Encapsulation Efficiency values according to the reaction condition. Table 2 describes the values of Zeta Potential, Particle Size and Encapsulation Efficiency. The nanoemulsions presented a content of ECEO that varied between approximately from 55 to 92%. The variance analysis (ANOVA) revealed that the significant factors were the relative ratio Cs/ECEO (factor B) and the relative ratio between Cs/Surfactant (factor C). Thus, we can state that for the stability of the micellar system, a greater oil retention capacity is obtained when the ratio between the wall material and the surfactant is maintained in the quantity (4:1) (NE1, NE2, NE3 and NE4). In the same way, the wall material must be in an optimum ratio of 4:2 in relation to the ECEO (NE1, NE2). In fact, the NE1 and NE2 formulations presented the highest encapsulation efficiency: 91.1 and 92.5, respectively. The data obtained showed that formulations in these proportions favored the occurrence of hydrophobic interactions between the essential oil constituents and the proposed matrix, leading to greater incorporation of the active ingredient. In the study of Chitosan nanoparticles loaded with eugenol[34], the highest encapsulation efficiency was achieved using the proportion Cs:eugenol of 1:1 using Tween 60 as surfactant. In another study, Chitosan nanoparticles loaded with carvacrol showed an ideal proportion of Cs:carvacrol 1:1 for an encapsulation efficiency of 31.4±1.3%[35]. Regarding the effect of the variables on particle size, as shown in Table 2, nanoemulsions presented a droplet

diameter ranging from about 388 to 1271 nm, in agreement with the evaluated formulations. The ANOVA analysis revealed that the significant factors in particle size are factor A, which corresponds to the type of surfactant, and factor C, which studies the influence of the relative ratio between Cs:Surf:TPP. The relative amount of ECEO only showed significance when in interaction with the relative surfactant content. It was possible to show that a higher relative surfactant and higher TPP concentration amount in the formulation resulted in lower values of droplet diameters. Thus, we can state that the stability of the micellar system is achieved when Tween 80 is used with a higher relative amount and with higher relative amount of TPP (NE 2 and NE 4). When Tween 80 is used, smaller particle sizes are obtained, which means that there was less coalescence or lower degree of Ostwald maturation. At the same time, particles with increased size suffered from coalescence process, forming microemulsion instead of nanoemulsions, and caused an increase in the viscosity of the system[36]. Viscosity (η) is related to the colloidal stability of emulsified systems, where the lower the viscosity, the smaller the corresponding particle diameter, which in turn influences the inter-particle interactions[14]. The average viscosity of the NEs was 2.63 ±1.03 cP, and the formulations with relative content of Cs:Surf (4:1) presented significantly lower values of viscosity (NE1, NE2, NE3 and NE4), an indication of their stability. In this case, the effect related to a higher relative content of Tween in the formulation is observed, and there was a better solubilization of the oily phase to the surfactant. The surfactant was able to reduce the surface tension between the phases, influencing the reduction of the particle size, avoiding the coalescence process, and lower viscosity, consequently, promoting a single-phase system. The viscosity values as a function of the NE concentration are in Supplementary Material (Figure S3). Regarding the zeta potential, all NEs presented high potential values (Table 2). The reduction of this potential leads to the reduction of electrostatic repulsion, facilitating the aggregation of particles, and is therefore used as an indication of the stability of a dispersion[37]. These positive values are a characteristic of an excellent electronic stabilization and are related to the protonated amino groups of Cs, which coat the micelles. A schematic representation of the hypothetical structure for the micelle formed in the nanoemulsion are in Figure 2.

Table 2. Zeta Potential, Particle Size, Encapsulation Efficiency, Viscosity Results and Polidispersity Index (PDI). Formulation NE1 NE2 NE3 NE4 NE5 NE6 NE7 NE8

4/9

T20QOT421 T80QOT421 T20QOT411 T80QOT411 T20QOT841 T80QOT841 T20QOT821 T80QOT821

Zeta Potential (mV)

Particle Size (nm)

+50.8±1.6 +48.5±1.2 +52.8±1.3 +50.9±1.3 +44.9±2.2 +40.7±1.9 +31.0±2.7 +39.0±2.4

789±0.6 489±0.3 596±0.8 388±0.2 1248±1.2 921±0.9 1271±1.1 992±0.8

Encapsulation Efficiency (%) 91.1±0.3 92.5±0.2 83.2±0.1 90.7±0.7 73.9±1.1 69.3±0.9 66.1±0.8 55.5±0.8

Viscosity (cP) 2.2 ±0.70 1.4±0.04 1.2±0.05 1.8±0.62 3.4±0.92 3.3±0.97 3.8±1.00 3.9±1.01

PDI 0.535± 0.02 0.215 ± 0.03 0.436 ± 0.03 0.176 ± 0.01 0.684 ± 1.01 0.687 ± 1.03 0.656± 1.01 0.637± 1.00

Polímeros, 30(2), e2020024, 2020


Polymeric nanoemulsions enriched with Eucalyptus citriodora essential oil The micelle is formed by ECEO in the central nucleus, stabilized by the surfactant. Chitosan entangles with the surfactant through intermolecular forces, coating the micelle. Finally, TPP is added and crosslink partially the chitosan network in order to increase the stability of the micelle.

3.3 Antimicrobial activity of NE formulations Based on their higher stability, NE1, NE2, NE3 and NE4 were evaluated regarding their antimicrobial properties. Table 3 describes the antibacterial activity of nanoemulsions tested against S. aureus and S. typhimurim pathogens, where the chloramphenicol antibiotic was used as a positive control, distilled water and the NE1 Matrix and NE2 Matrix (without the ECEO oil) were used as a negative control. Table 3. Antimicrobial activity of NE1, NE2, NE3 and NE4 tested against S. aureus and S. typhimurim pathogens. Formulation Chloramphenicol OECO NE 1 Matrix NE 1 NE 2 Matrix NE 2 NE 3 NE 4

Inhibition Rate (%) S. Aureus S. Typhimurium 100 100 21.8±4.9 23.7±1 22.8±2.2 21.4±1.4 41.6±10.1 56.7±12.8 21.0±0.4 21.3±1.2 55.6±10.0 73.2±13.3 21.4±1.3 21.3±0.4 23.4±3.9 21.9±3.6

Figure 2. Schematic representation of the hypothetical structure for the micelle formed in the Cs-ECEO nanoemulsion.

NE1 and NE2 formulations showed an enhanced effect, with higher inhibitory activity when compared to the trial values with free ECEO, NE3, NE4 and the NE matrix. The NE1 formulation (T20QOT421) trial showed an inhibitory rate of 41.56% (10.37 mm) for S. aureus and 56.7% (13.61 mm) for S. typhimurium, versus the chloramphenicol inhibitory zone (25 mm). NE2 (T80QOT421) showed values of 55.6% for S. aureus (12.89 mm) and 73.32% (18.33 mm) for S. typhimurium. The OCEO free oil, which posses a known antimicrobial activity, with values of aproximately 27% and 31% of inihibition rate against S. aureus and S. typhimurium, respectively. On the other hand, NE3 and NE4 presented a discrete inhibition rate against S. aureus and S. typhymurium, with values close to those founded by NE matrices, around 21%. In this case, the antimicrobial activity is attributed to the chitosan matrix[38]. NE3 and NE4 presented lower ECEO content in the formulation in comparison with NE1 and NE2 (see Table 1), which probably caused the reduced effect. In this case, higher dosages would be required for NE3 and NE4 in order to achieve performance close to NE1 and NE2. In this case, this is a clear indication that the proposed emulsification system optimizes the dispersibility of EO in aqueous solution and its physical-chemical stability increased its antimicrobial activity[39] and affirming that gram-positive bacteria are sensitive to plant derivatives, although they are more resistant due to their thick cell wall of peptidoglycan. On the other hand, an expressive inhibition rate against S. typhimurium of NE2 (T80QOT421) with 73.32% can be observed, being able to confirm that the concentration and type of surfactant favored the interaction of encapsulated essential oil with water, making it more available in the action on lipopolysaccharide membranes and their hydrophilic clusters found in gram-negative bacteria. In addition, the physical-chemical stability of the NE2 (T80QOT421) sample, as well as its reactive condition was ideal for inhibition activity for the tested microorganisms. There are some reports in the literature that point to a strong search for evaluation of the antimicrobial activity of Eucalyptus plants and their various species[27,38-40]. The presence of E. globulus nanoemulsion incorporated with a relative content of 5% to chitosan films showed greater activity against S. aureus with an inhibition rate of 78.9%[38]. Based on the encapsulation efficiency results and the inhibition rate, NE1 and NE2 were further characterized regarding their physico-chemical properties.

3.3 Absorption spectroscopy in the infrared region (FT-IR)

Figure 3. FTIR spectra of Chitosan, ECEO, NE1 (T20QOT421) and NE2 (T80QOT421). Polímeros, 30(2), e2020024, 2020

Figure 3 shows the infrared spectra (FT-IR) of Cs, ECEO and NE1 and NE2. Chitosan presents amine groups, which display broad stretching vibrations at 3,427 cm-1. The Cs main vibration modes are asymmetrical and symmetrical bending amine vibrations in 1580 and 1417 cm-1. The bands in 1092 cm-1, 1089 cm-1 and 1093 cm-1 are related to the C-O-C stretching of Cs[41]. On the other hand, a broadband centered on 3,437 cm-1 is observed in the ECEO spectrum, referring to the O-H stretching modes of its alcoholic components, such as citronellol, isopulegol and neo-isopulegol[5]. These components are the main constituints of ECEO, as reported in the literature[42,43]. The strong-intensity narrow 5/9


Abreu, F. O. M. S., Costa, E. F., Cardial, M. R. L., & André, W. P. P. band observed in 1727 cm-1 and the medium-intensity band observed in 1454 cm-1 for ECEO can be attributed, respectively, to the stretching of C=O and bending of C-H citronellal stretching mode[42]. Despite the overlapping of the vibrational modes from Cs and ECEO around 3,400 cm-1, it was possible to observe the presence of citronellal component of the ECEO through the peaks in the region of 1727 and 1724 cm-1 in the NE1 (T20QOT421) and NE2 (T80QOT421) formulations. NE1 and NE2 also showed a small peak at 1450 cm-1, due to the =C-H scissoring band present in citronellal and absent in Cs spectra, indicating the presence of ECEO major components incorporated in the NEs.

Table 4. Determination coefficients (R2) for different kinetic models. NE1 T20QOT421 0.9403

NE2 T80QOT421 0.9391

K0 (h-1)

1.453

1.4351

R2

0.8607

0.739

K1 (h-1)

0.0212

0.00226

Model

Parameters

Zero order

R2

First order Higuchi KorsmeyerPeppas

R2

0.908

0.9348

KH (h-1/2)

0.0538

0.0547

R2

0.8177

0.8177

0.0144

0.0144

KKP (h ) -n

3.4 Morphology of nanoemulsions The micrographs obtained by MEV of the NE2 are represented in the Supplementary Material (Figure S4). It was possible to observe the presence of microspherical inclusions as discrete particles, aggregated to the polymeric network, visualized in Figure S4a and S4b. NE2 presented a porous characteristic, with microspherical micellar domains embedded in the polymeric network, possibly caused by the increase of emulsion droplet during freeze drying process. In fact, the formation of porous structures in nanoemulsions has been attributed by the formation of micellar vacuoles in the polymeric network[44,45]. The addition of a cryoprotectan agent has been reported in the literature in order to preserve structural integrity and improve the shelf-life of nanoemulsions[44].

3.5 Nanoemulsion in vitro release profile The ECEO release kinetics of NE 1 (T20QOT421) and NE 2 (T20QOT421) are shown in Figure 4. The NE1 (T20QOT421) and NE2 (T80QOT421) formulations presented a similar release profile, in which they were constant in the first hours and gradually increased after 20 hours of study, with a controlled release profile. After 30 hours, it showed a more prolonged release profile with approximately 50% of oil released, reaching above 95% after 72 hours of release. The release profile of the NEs was analyzed applying zero order, first order, Higuchi and Korsmeyer-Peppas kinetics[46]. Linear regression was used to calculate the values of the release constants (k) and the correlation coefficients (R2). Table  4 shows the correlation coefficients of the kinetic models for NE1 and NE2 samples. NE 1 and NE2 showed that the in vitro release of ECEO was best fitted in the zero order kinetic model, due to the higher correlation coefficient (R2). This model is based on the slow release of the active substance from the emulsion system that gradually tend to disaggregate and disintegrate in the dissolution medium, where the drug diffusion speed, from the inside to the outside of the matrix, is lower than the respective dissolution speed[47]. The release kinetics of the essential oil of Pimenta dioica presented a transport mechanism case II (zero order release kinetics) for chitosan/k carrageenan micro spheres (mass ratio 1:1) and a non-fickian release mechanism for chitosan/k-carrageenan micro spheres (1:0, 3:1 and 2:1). The release rate increased along with the chitosan content[48]. 6/9

Figure 4. Release kinetics of ECEO for NE 1 (T20QOT421) e NE 2 (T20QOT421)

4. Conclusions Chitosan Nanoemsulsions enriched with E. Citriodora were produced, and the studied parameters presented a direct influence on the stability. Nanoemulsions with higher stability were the ones using Cs:Tween:TPP 4:1:1 mass ratio, with and average particle size of 565 mm, stable agaist creaming over 60 days of storage, verified visualy and by optical microscopy. NE2 and NE1 presented the best set of properties, reaching an encapsulation efficiency value of 92.5% and significative inhibition rate against S. aureus and S. typhimurium., due to the chitosan: ECEO oil mass ratio of 4:2. Also, in these conditions, the type of surfactant influenced in relation to particle size, where Tween 80 provided smaller micellar sizes due to the enhanced solubilization of the oil phase, reducing the surface tension of the phases, implying directly in a lower particle size and lower viscosity. Kinetics showed a sustained release over three days, and the release profile best fitted were zero order kinetic model, corresponding to a slow release of the essential oil from the emulsion system that gradually disintegrate in the dissolution medium. Thus, we conclude that nanoemulsion of chitosan, tween and TPP enriched with E. citriodora were sucsecfully optimized with potential for an effective release system for antimicrobial control. Polímeros, 30(2), e2020024, 2020


Polymeric nanoemulsions enriched with Eucalyptus citriodora essential oil

5. Acknowledgements The authors thank Professor Dra. Roselayne Ferro Furtado de Sá from Embrapa Agroindustria Tropical for SEM analisys. This work was supported by the Conselho Nacional de Desenvolvimento Científico - CNPq [Projeto Universal 442965/2014-1].

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Abreu, F. O. M. S., Costa, E. F., Cardial, M. R. L., & André, W. P. P. 25. Xiong, W., Ren, C., Tian, M., Yang, X., Li, J., & Li, B. (2018). Emulsion stability and dilatational viscoelasticity of ovalbumin/chitosan complexes at the oil-in-water interface. Food Chemistry, 252, 181-188. http://dx.doi.org/10.1016/j. foodchem.2018.01.067. PMid:29478530. 26. Shah, B. R., Zhang, C., Li, Y., & Li, B. (2016). Bioaccessibility and antioxidant activity of curcumin after encapsulated by nano and Pickering emulsion based on chitosan-tripolyphosphate nanoparticles. Food Research International, 89(Pt 1), 399-407. http://dx.doi.org/10.1016/j.foodres.2016.08.022. PMid:28460931. 27. Mwangi, W. W., Ho, K. W., Tey, B. T., & Chan, E. S. (2016). Effects of environmental factors on the physical stability of pickering-emulsions stabilized by chitosan particles. Food Hydrocolloids, 60, 543-550. http://dx.doi.org/10.1016/j. foodhyd.2016.04.023. 28. Ribeiro, J. C., Ribeiro, W. L. C., Camurça-Vasconcelos, A. L. F., Macedo, I. T. F., Santos, J. M. L., Paula, H. C. B., AraújoFilho, J. V., Magalhães, R. D., & Bevilaqua, C. M. L. (2014). Efficacy of free and nanoencapsulated Eucalyptus citriodora essential oils on sheep gastrointestinal nematodes and toxicity for mice. Veterinary Parasitology, 204(3-4), 243-248. http:// dx.doi.org/10.1016/j.vetpar.2014.05.026. PMid:24929446. 29. Dickinson, E. (2009). Hydrocolloids as emulsifiers and emulsions stabilizers. Food Hydrocolloids, 23(6), 1473-1482. http://dx.doi.org/10.1016/j.foodhyd.2008.08.005. 30. Almeida, A. C. S., Silva, J. P. M., Siqueira, A., & Frejlich, J. (1995). Medida de viscosidade pelo método de Ostwald: um experimento didático. Revista Brasileira de Ensino de Física, 17, 279-283. Retrieved in 2020, January 18, from http://www. sbfisica.org.br/rbef/pdf/vol17a35.pdf 31. Sugasini, D., & Lokesh, B. R. (2017). Curcumin and linseed oil co-delivered in phospholipid nanoemulsions enhances the levels of docosahexaenoic acid in serum and tissue lipids of rats. Prostaglandins, Leukotrienes, and Essential Fatty Acids, 119, 45-52. http://dx.doi.org/10.1016/j.plefa.2017.03.007. PMid:28410669. 32. Almajano, M. P., Carbó, R., Delgado, M. E., & Gordon, M. H. (2007). Effect of pH on the antimicrobial activity and oxidative stability of oil-in-water emulsions containing caffeic acid. Journal of Food Science, 72(5), C258-C263. http://dx.doi. org/10.1111/j.1750-3841.2007.00387.x. PMid:17995712. 33. Calero, N., Muñoz, J., Cox, P. W., Heuer, A., & Guerrero, A. (2013). Influence of chitosan concentration on the stability, microstructure and rheological properties of O/W emulsions formulated with high-oleic sunflower oil and potato protein. Food Hydrocolloids, 30(1), 152-162. http://dx.doi.org/10.1016/j. foodhyd.2012.05.004. 34. Woranuch, S., & Yoksan, R. (2013). Eugenol-loaded chitosan nanoparticles: I. thermal stability improvement of eugenol through encapsulation. Carbohydrate Polymers, 96(2), 578-585. http:// dx.doi.org/10.1016/j.carbpol.2012.08.117. PMid:23768603. 35. Keawchaoon, L., & Yoksan, R. (2011). Preparation, characterization and in vitro release study of carvacrol-loaded chitosan nanoparticles. Colloids and Surfaces. B, Biointerfaces, 84(1), 163-171. http://dx.doi.org/10.1016/j.colsurfb.2010.12.031. PMid:21296562. 36. Sing, A. J. F., Graciaa, A., Lachaise, J., Brochette, P., & Salager, J. L. (1999). Interactions and coalescence of nanodroplets in translucent O/W emulsions. Colloids and Surfaces A, Physicochemical and Engineering Aspects, 152(1-2), 31-39. http://dx.doi.org/10.1016/S0927-7757(98)00622-0. 37. Katata-Seru, L., Lebepe, T. C., Aremu, O. S., & Bahadur, I. (2017). Application of Taguchi method to optimize garlic essential oil nanoemulsions. Journal of Molecular Liquids, 244, 279-284. http://dx.doi.org/10.1016/j.molliq.2017.09.007. 8/9

38. Hafsa, J., Smach, M. A., Ben Khedher, M. R., Charfeddine, B., Limem, K., Majdoub, H., & Rouatbi, S. (2016). Physical, antioxidant and antimicrobial properties of chitosan films containing Eucalyptus globulus essential oil. LebensmittelWissenschaft + Technologie, 68, 356-364. http://dx.doi. org/10.1016/j.lwt.2015.12.050. 39. Shakeri, A., Khakdan, F., Soheili, V., Sahebkar, A., Rassam, G., & Asili, J. (2014). Chemical composition, antibacterial activity, and cytotoxicity of essential oil from Nepeta ucrainica L. spp. kopetdaghensis. Industrial Crops and Products, 58, 315-321. http://dx.doi.org/10.1016/j.indcrop.2014.04.009. 40. Knezevic, P., Aleksic, V., Simin, N., Svircev, E., Petrovic, A., & Mimica-Dukic, N. (2016). Antimicrobial activity of Eucalyptus camaldulensis essential oils and their interactions with conventional antimicrobial agents against multi-drug resistant Acinetobacter baumannii. Journal of Ethnopharmacology, 178, 125-136. http://dx.doi.org/10.1016/j.jep.2015.12.008. PMid:26671210. 41. Tang, D. W., Yu, S. H., Ho, Y. C., Huang, B. Q., Tsai, G. J., Hsieh, H. Y., Sung, H. W., & Mi, F. L. (2013). Characterization of tea catechins-loaded nanoparticles prepared from chitosan and an edible polypeptide. Food Hydrocolloids, 30(1), 33-41. http://dx.doi.org/10.1016/j.foodhyd.2012.04.014. 42. Araújo-Filho, J. V., Ribeiro, W. L. C., André, W. P. P., Cavalcante, G. S., Guerra, M. C. M., Muniz, C. R., Macedo, I. T. F., Rondon, F. C. M., Bevilaqua, C. M. L., & Oliveira, L. M. B. (2018). Effects of Eucalyptus citriodora essential oil and its major component, citronellal, on Haemonchus contortus isolates susceptible and resistant to synthetic anthelmintics. Indrustial Cropsand Products, 124, 294-299. http://dx.doi. org/10.1016/j.indcrop.2018.07.059. 43. Farag, N. F., El-Ahmady, S. H., Abdelrahman, E. H., Naumann, A., Schulz, H., Azzam, S., & El-Kashoury, E. S. A. (2018). Characterization of essential oils from Myrtaceae species using ATR-IR vibrational spectroscopy coupled to chemometrics. Industrial Crops and Products, 124, 870-877. http://dx.doi. org/10.1016/j.indcrop.2018.07.066. 44. Morais, A. R. V., Alencar, É. N., Xavier, Jr., F. H., Oliveira, C. M., Marcelino, H. R., Barratt, G., Fessi, H., Egito, E. S. T., & Elaissari, A. (2016). Freeze-drying of emulsified systems: a review. International Journal of Pharmaceutics, 503(1-2), 102-114. http://dx.doi.org/10.1016/j.ijpharm.2016.02.047. PMid:26943974. 45. Fernandes, R. V. D. B., Borges, S. V., & Botrel, D. A. (2014). Gum arabic/starch/maltodextrin/inulin as wall materials on the microencapsulation of rosemary essential oil. Carbohydrate Polymers, 101, 524-532. http://dx.doi.org/10.1016/j. carbpol.2013.09.083. PMid:24299808. 46. Dash, S., Murthy, P. N., Nath, L., & Chowdhury, P. (2010). Kinetic modeling on drug release from controlled drug delivery systems. Acta Poloniae Pharmaceutica Drug Research, 67(3), 217-223. PMid:20524422. 47. Lopes, C. M., Lobo, J. M. S., & Costa, P. (2005). Formas farmacêuticas de liberação modificada: polímeros hidrifílicos. Revista Brasileira de Ciências Farmacêuticas, 41(2), 143-154. http://dx.doi.org/10.1590/S1516-93322005000200003. 48. Dima, C., Cotârlet, M., Alexe, P., & Dima, S. (2014). Reprint of “Microencapsulation of essential oil of pimento [Pimenta dioica (L) Merr.] by chitosan/k-carrageenan complex coacervation method”. Innovative Food Science & Emerging Technologies, 25, 97-105. http://dx.doi.org/10.1016/j.ifset.2014.07.008. Received: Jan. 18, 2020 Revised: July 28, 2020 Accepted: July 30, 2020 Polímeros, 30(2), e2020024, 2020


Polymeric nanoemulsions enriched with Eucalyptus citriodora essential oil

Supplementary Material Supplementary material accompanies this paper. Figure S1: Calibration curves (a) in Ethanol; (b) in water with surfactant. Table S1: ANOVA Statistic Results of influence on the parameters on Creaming. Figure S2: Optical Microscopy of Emulsion droplets for NEs a) NE1; b) NE2; c) NE3 and d) NE4 after 30 days (a, b, c, d) and after 60 days (a’, b’, c’ d’). Figure S3: Viscosity of NEs as a function of the concentration. Figure S4. Scanning Electron Microscopy surface images of NE 2 (T80QOT421) at different magnification a) 667x and b) 2670x. This material is available as part of the online article from http://www.scielo.br/po

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.02220

Advances and perspectives in the use of polymers in the environmental area: a specific case of PBS in bioremediation Priscilla Braga Antunes Bedor1* , Rosana Maria Juazeiro Caetano2, Fernando Gomes de Souza Júnior3 and Selma Gomes Ferreira Leite1 Laboratório de Microbiologia Industrial, Escola de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil 2 Unidade Multiusuário de Análises Ambientais, Instituto de Biologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil 3 Laboratório de Biopolímeros e Sensores, Instituto de Macromoléculas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil

1

*priscillabedor@eq.ufrj.br

Abstract Biodegradable polymers (e.g. poly(butylene succinate) - PBS) have been used in several sectors such as the environmental area, especially in bioremediation, in biological processes for conversion of pollutants into inorganic compounds. In this study, the foresight methodology for the use of biodegradable polymers, including PBS, reveals a publication rate of approximately 8.74 articles and 30.63 patents per year, between 2005 and 2019. However, the application of PBS, specifically, is still restricted to the environmental area, with only 3.0% of the 1484 works from this period. The results showed a more significant number of papers on the PBS application for synthesis, characterization, and application in the areas of Chemistry, Physics, and Pharmacy. In the area of bioremediation, only three studies related to PBS were found, revealing the lack of research and development to increase the contribution in the area of environmental recovery. Keywords: biodegradable polymer, biopolymer, bioremediation, foresight methodology, poly(butylene succinate). How to cite: Bedor, P. B. A., Caetano, R. M. J., Souza Júnior, F. G., & Leite, S. G. F. (2020). Advances and perspectives in the use of polymers in the environmental area: a specific case of PBS in bioremediation. Polímeros: Ciência e Tecnologia, 30(2), e2020023. https://doi.org/10.1590/0104-1428.02220

1. Introduction From Antiquity to the present days, the demand for oil and its derivatives has been growing largely due to the population increase, the urbanization of large centers, and the value of oil in the international market. The high consumption of these inputs implies their higher exploration and processing, which may result in damage to the environment due to its well drilling and extraction activities, refining and transportation to commercialization, and final disposal. Pollution may occur in the land, air, or water environments, although land and sea fuel leaks are best known to the population[1,2]. As an alternative to polymers derived from fossil fuels, biopolymers and biodegradable polymers are widely used, having great importance in the biomedical and drug areas, since they are obtained from natural resources, are biodegradable and present a high affinity with biological systems[3,4]. Its application in the environmental area is prevalent and has increased in the recent years. Therefore, the main objective of this work is to map the evolution of international studies and resulting publications in the environmental sector over a period of 15 years[5-8]. The mapping was done to addressing bioremediation, which has been a very prominent approach

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in the environmental area. This work was completed with a case study for PBS, a polymer that might be highlighted as promising for biostimulation exploration, one of the potential existing bioremediation techniques.

2. Biodegradable Polymers, Biopolymers, and Green Polymers: Definitions and Applications According to the IUPAC[9], biodegradable polymers are defined as susceptible to degradation by biological activity followed by a decrease in their molar mass. Biodegradable polymers are divided in bio-based or petrochemical-based polymers based on their origin[10]. Bio-based polymers are called biopolymers or “green polymers” since they are derived from renewable sources such as animals, plants, algae, and bacteria[11-13]. Biopolymers may to be obtained in different forms: (i) available in the natural environment in the form of polysaccharides (e.g. cellulose, alginate, chitin)[9,14], exopolysaccharides, and proteins (e.g. biofilms)[15]; (ii) from microbial production

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Bedor, P. B. A., Caetano, R. M. J., Souza Júnior, F. G. & Leite, S. G. F. or fermentation (e.g., PHB, PBS)[16,17], or (iii) chemically synthesized from biomass (e.g.PLA)[18]. Biopolymers have several advantages over petrochemical-based polymers, since they are obtained from renewable natural sources[19], have a low-cost extraction, and present characteristics of biocompatibility[20] and biodegradability[21]. Thus, biopolymers have been traditionally used in industrial activities related to food[22-24], biomedical[25], and pharmaceutical production[26,27], as well as applications in the environmental sector[28-30].

3. Biopolymers in the Environmental Area Most of the applications and environmental research present in the literature addresses bio-based biodegradable polymers. These polymers aim to improve processes such as emulsion stabilization[31], removal of contaminants from aqueous solutions[32], composition of coating materials for protecting active agents from the environment[33,34], and controlled release of active substances (e.g. drugs, fertilizers, and nutrients)[5,35,36]. The use of biopolymers is highlighted since most of the biopolymers obtained by fermentation are readily hydrolysable polyesters[37]. The hydrolysis of these biopolymers produces smaller molecules that are absorbed by microorganisms and are transformed into innocuous products such as water and carbon dioxide and converted into cellular biomass[38]. Studies have also been carried out about the ecotoxicological evaluation of the biodegradable polymers in the soil, as in the case of the polyesters poly(butyl adipate-co-terephtalate) (PBAT) and poly(lactic acid) (PLA)[28]. Studies in the literature have reported the use of biopolymers as essential factors in the processes of bioremediation, recovery of degraded environments, and remediation of heavy metals and petroleum derivatives through natural biopolymers, such as polypeptides and polysaccharides[28,39,40]. Studies about the processes of bioremediation of environmental contaminants[41] have evaluated formaldehyde bioremediation through the association of Aspergillus oryzae and poly(ε-caprolactone) (PCL). Other authors[42] used polyhydroxyalkanoate as a slow release system

for bioremediation of aquifers contaminated with chlorinated solvents, and[8] studied the use of poly(butylene succinate) (PBS) as a nutrient-releasing system in the biodegradation of petroleum by Pseudomonas aeruginosa. Some of the groups of polymers involved in the environmental area and some of its examples are shown in Figure 1. Polyesters[43-45], polyolefins[46,47], polyamides[48,49], and polysaccharides[28,50-52] may be obtained naturally or through industrial chemical processes and are used in the removal or reduction of pollutants, among other applications in the environmental area, considering the advantages and disadvantages of each one for these applications. The investigations on biopolymers seek efficient results about the biodegradability of these compounds, aiming to expand their application, which in recent years have apparently targeted bioremediation.

4. Bioremediation With the purpose of restoring the balance between the biotic and abiotic factors of the impacted environment, technologies were developed using living organisms (e.g. bacteria, fungi, and plants) or enzymes present in them, with the ability to degrade pollutants, therefore reducing their release in the affected area[53,54]. These technologies that make up bioremediation are environmental friendly, might be less expensive in some cases, and cause less impact to the environment when compared to technologies that use chemical and/or physical processes[55,56]. In addition, bioremediation emerges as an alternative that may be applied both in situ (affected site) and ex situ, with bench scale tests for process optimization and subsequent in situ application. Among the possibilities of bioremediation application are natural attenuation, phytoremediation, composting, biostimulation, and bioaugmentation, among others[57-59]. Frequently, for a better effectiveness of the bioremediation process, biopolymers are used as tools, either in direct removal, as an auxiliary matrix, or even as an organic source in the minimization of environmental pollutants. In the case of biostimulation or bioaugmentation by nutrient

Figure 1. Some classes of polymers applied in environmental area with their examples, advantages, and disadvantages. 2/10

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Advances and perspectives in the use of polymers in the environmental area: a specific case of PBS in bioremediation and microorganism addition, respectively, biopolymers are present as physical barriers that prevent the immediate release of the pollutant in the area to be remedied, increasing the efficiency of pollutant biodegradation[6]. Table 1 presents some works related to the application of different biopolymers in bioremediation in the last two years. Due to the impact of scientific advances on the above applications, there was an interest in searching for the most current works on the environmental area, with emphasis on bioremediation. For this purpose, the Foresight Methodology was adopted, as described in the next section.

5. Foresight Methodology The main objective of prospecting technology monitoring is to inform the academic community and decision makers about what has been developed in the medium and long

term in a certain field of expertise, based on what has been researched and carried out in a certain knowledge area. This helped to identify in which sectors certain products or techniques have a great potential of use or even of innovation[67]. In this work, macro and meso level analyses of biopolymers and, specifically, of PBS, were performed from data obtained from the Scopus database containing scientific articles. For the patent documents, the international Lens patent database was used. Their easy and free access to the academic community was the selection criteria for choosing these bases. The search strategy consisted of establishing a specific period between 2005 and 2019, in which there was an increase in the publication of patents worldwide. It should be noted that the survey did not include the current year, since there were not enough data for the entire 12-month

Table 1. Recent papers with polymer applications in bioremediation. Polymer applications in bioremediation Polymer Application Results Reference [40] Mixture of proteins and peptides Biopolymer-PFP (polystyrene foam The combination of an immobilized phase (non-toxic biopolymer) extracted from corn gluten meal pellet) system for the recovery of with a sorbing phase (recyclable polystyrene foam – PFP – and and hemp. heavy oil from a highly weathered non-toxic) reduced the hydrocarbons of a heavy oil-impacted soil. soil sample by 94% compared to control test with water (25%), biopolymer (52%) and PFP (58%) [60] Poly-γ-glutamic acid (γ-PGA) TCE-contaminated groundwater Approximately 99% of TCE (initial concentration ¼ 4.3 mg.L-1) bioremediation was degraded after 85 days [59] Rhamnolipid (Biosurfactant) Bioremediation of leaky marine The cell-free broth containing biosurfactants produced by environments by use of biosurfactant bacterial strains significantly desorbed crude oil in oil-polluted marine sediment. [61] Wood waste and biofilm Bioremediation of contaminated Biofilms of P. putida and B. cereus grown on wood waste soil by toluene pretreated with LPN-plasma led to 91% and 89% toluene degradation, respectively, whereas biofilms grown on untreated wood waste led to toluene degradation of 78% and 58%, respectively. [62] Modified lignocellulose sawdust Treatment of oil spills The total oil was removed from the microcosms after the biological treatment ranging from 65% to 80% after 5 days. Besides that, the Gas Chromatography (GC) analysis of the crude oil remaining in the culture medium showed that the isoparaffins biodegradation higher than n-paraffins in microcosms contain biosurfactant. [63] Cyclodextrins (CD) cyclic Wastewater treatment The bacteria/CD-F biocomposite has shown removal efficiency oligosaccharides of Ni(II), Cr(VI) and RB5 as 70 ± 0.2%, 58 ± 1.4% and 82 ± 0.8, respectively. The pollutants’ removal capabilities of the bacteria/CD-F was higher, compared to free bacteria, since bacteria can use CD as an extra carbon source that promotes their growth rate. [64] Rhamnolipid (Biosurfactant) Bioremediation of oil contaminated The degradation of total petroleum hydrocarbon (TPH) on soil rhamnolipid biosurfactant application at 1.5 g L−1 was found to be 86.1% and 80.5% in two soil samples containing 6800 ppm and 8500 ppm TPH, respectively. [65] (1→ 3)-α-D-glucans Bioremediation by removing heavy For economic reasons, L. edodes was selected because of the metals using biological material complicated, multi-stage and time-consuming cultivation processes of the other two species. Choosing the best biosorbent, the efficiency of glucan isolation was taken into consideration, showing metal removal percentages for Ni2 +, Cd2 +, Zn2 +, and Pb2 + equivalent to 13, 25, 14, and 50, respectively. [66] Immobilized laccase on calcium Enzymatic bioremediation of Ca-AIL and Cu-AIL exhibited 71% and 65.5% BPA degradation and copper alginate beads bisphenol A efficiency on 14 d. [56] Chitin Biotreatment system for mine- Chitin was used as metal ion sorbent and biostimulant of impacted water (river water impacted sulfate-reducing bacteria (SRB). The results indicated that by coal acid mine drainage – MIW) using shrimp shells as a chitin source, the removal of sulfate, iron, aluminum, and manganese ions in MIW were 99.75%, 99.04%, 98.47%, and 100%, respectively in 41 days.

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Bedor, P. B. A., Caetano, R. M. J., Souza Júnior, F. G. & Leite, S. G. F. period. The summaries and title of the patent and articles were investigated using the terms “biopolymers”, “green polymers”, “biodegradable polymers”, and “bioremediation”, with variations in the search field, using AND NOT to minimize duplication. The flowchart presenting the first steps of the foresight methodology may be seen in Figure 2. From a broader search on the Scopus database, considering the 15-year period, 17,147 scientific articles were found for biopolymers, 12,015 for biodegradable polymers, and 204 for green polymers. Based on these results, the five major areas of application are Chemistry, Materials Science, Engineering (including Chemical Engineering), Physics & Astronomy, and Biochemistry, Genetics & Molecular Biology. The environmental area represented 5.93% of the publications, considering the three categories of search. When the environmental bioremediation area is specified for biopolymers, biodegradable polymers, and green polymers, the number of publications declined to 199, 283 and 2, with a reduction of 98.84%, 97.65%, and 99.02%, respectively. However many of the publications belonged to the environmental area only due to the nature of the polymer, not because of its application. A broad search, such as that made for the articles was carried out on the Lens patent basis, resulting in 90,031 patents for biopolymers, 99,608 for biodegradable polymers, and 519 for green polymers, considering the same terms and search period. Likewise, the search for these terms related to bioremediation generated a total of 736 patents for biopolymers, 175 for biodegradable polymers, and 1 for green polymers, indicating a reduction of 99.18%, 99.82%, and 99.81%, respectively, and evidencing the small number of papers about polymers in this area, specifically. However, throughout this survey, the use of poly(butylene succinate) – PBS – appeared quite often (about 10% of citations). In this context, the PBS case study was encouraged.

The main objective of this article is to investigate the research on the application of biodegradable polymers, especially PBS, on bioremediation in an international context. In this case, the same foresight methodology was applied using the terms “poly(butylene succinate)” and “bioremediation” with variations in the search field, using AND NOT to minimize duplication. The second flowchart presenting the steps of foresight methodology about poly(butylene succinate) and its application is shown in Figure 3. When searching for the term “poly(butylene succinate),” the number of patents and academic articles showed a gradual increase over time, with 1,484 articles and 3,657 patents from 2005 to the end of 2019, as shown in Figure 4. The rate increase was calculated from the trend line and presented approximately 8.74 articles and 30.63 patents per year, with R2 of 0.9187 and 0.8252, respectively. The highest number of patents is due to the sum of patents applied and granted. It was also possible to identify an increase of approximately 96.19% in the number of articles and 98.97% in the number of patents for this biodegradable polymer in the established period, indicating a significant increase in PBS application in different areas of knowledge. In 2018,

6. A Specific Case: Poly(butylene succinate) – PBS The poly(butylene succinate) – PBS is considered a biodegradable polymer partially derived from biological (petrochemical) processes[68], as well as by the microbiological fermentation of renewable raw materials, such as glucose, xylose, and starch to obtain succinic acid and possibly a second monomer, 1,4-butanediol, from this acid or from petroleum derivatives[69,70]. PBS is obtained by the transesterification reaction of 1,4-butanediol with succinic acid, followed by a polycondensation step with an increase in the size of the polymer chain and water release from the system as vapor[70]. PBS has been used in synthesis studies and production of food packaging[71,72], biomedical[73,74] and pharmaceutical[75-78] products, but has gained prominence in the field of green chemistry as one of the most promising aliphatic polyesters due to its thermal properties, good processability, biodegradability, and easy application in composting[79-81]. Some authors[82,83] advocate the application of PBS in the environmental area, with research targeting the removal of excess nitrogenous nutrients in effluents, while[45] addressing the physical removal of petroleum from the environment through the use of PBS with magnetic particles. 4/10

Figure 2. Steps of the foresight methodology from polymers in general to the bioremediation application.

Figure 3. Steps of the foresight methodology to poly(butylene succinate) and its application on bioremediation. Polímeros, 30(2), e2020023, 2020


Advances and perspectives in the use of polymers in the environmental area: a specific case of PBS in bioremediation there was a decrease in the number of patents granted (320) compared to the previous two years, which showed values of 404 patents in 2017 and 467 of this type of production in 2016. In 2019, this value was already increasing again with 346 patents and an upward trend for the following years.

Figure 4. Annual distribution of patent publications and academic articles on poly(butylene succinate) between 2005 and 2019. The annual distributions of papers are represented by (■) and patents by (●).

The graph also reveals a stabilization in the publication of articles in the last 6 years, which might be regarded, in a more optimistic view, as an opportunity for more investigations about this polymer. Regarding the areas of application of the PBS, the ones with the highest number of patents and articles were: Physics (51.8%) and Materials Science (32.7%), both with a high number of papers focusing on the characterization of the materials. In the graphs shown in Figures 5a and 5b, the areas of application of the PBS were studied in the period between 2005 and 2019, which exhibited a high number of articles and patents (including granted and applied patents), according to the classification of the databases consulted. The analysis of these graphs revealed a low percentage of publications in the environmental area (3.0%), therefore suggesting a refinement of the search with the descriptors “poly(butylene succinate)” AND “bioremediation”, for a better understanding of this scenario. This last research yielded only 16 documents, and of the only two articles about the application of PBS in the environmental area, the one published in 2010[84] deals with the environmental biodegradation of synthetic polymers, while the one from 2018[8] evaluates the biodegradation of hydrocarbons with the use of the biodegradable already mentioned polymers. Patent prospecting revealed that of the 3,657 documents

Figure 5. Distribution of (a) academic papers and (b) patents on poly(butylene succinate) by application area for the period between 2005 and 2019. Polímeros, 30(2), e2020023, 2020

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Bedor, P. B. A., Caetano, R. M. J., Souza Júnior, F. G. & Leite, S. G. F. found for PBS use, only 11 were related in some way to bioremediation, although in the narrower search involving the CPC (Cooperative Patent Classification) classification, none of the patents found were directly related to bioremediation. The only links found were those related to surface coatings and composite synthesis. Based on the findings of the research in the area of biopolymers, the studies seek efficient results of the biodegradability of these compounds, aiming to expand their application, which in recent years apparently targets bioremediation, as shown in Figure 6. According to the research carried out in this study, in both bases analyzed, in the last 15 years there were few publications on the application of PBS in bioremediation, especially when the applied technique was biostimulation. The works with environmental application of PBS will be shown below. The effect of dissolved oxygen on heterotrophic denitrification using poly(butylene succinate) as a carbon source and biofilm carrier was investigated in a recent work[85] in which the researchers evaluated the process under aeration, low aeration, and anoxic conditions, all in static batch, for 96 hours. The best nitrate and total nitrogen removal rates were identified at 65 hours of experiment under aerated condition, with values of 37.44 ± 0.24 and 36.24 ± 0.48 g.m3d-1, respectively. The authors concluded that the costs of the denitrification process using PBS as carbon source and biofilm carrier might be significantly reduced. The use of this polymer might also prevent effluent pretreatment. Another study[82] evaluated the use of PBS as a biofilm carrier and carbon source for treatment of the wastewater from aquaculture recirculation systems (RAS) wastewater in two reactors with 0‰ salinity and 25‰ salinity, respectively. The authors found high denitrification rates 0.53 ± 0.19 kg NO3-N. m-3.d-1 (0‰ salinity) and 0.66 ± 0.12 kg NO3-N. m-3. d-1 (25‰ salinity) and the nitrite concentration was maintained below 1 mg.L-1 in PBS solid-phase packing reactors for real RAS wastewater treatment. The salinity (25‰) parameter exhibited a more stable nitrate removal efficiency when changing operating conditions, causing adverse effects such as nitrate dissimilation

to ammonia and the excess of dissolved organic carbon. The PBS degradation was demonstrated by SEM and FTIR analyses. The conclusion of the authors was that PBS showed great potential in the denitrification process, but needed further study on accurate carbon release for RAS practice. In another study using PBS for bioremediation of industrial wastewaters[86], the effect of other biodegradable polymers like poly(hydroxybutyrate valerate) (PHBV), and poly(caprolactone) (PCL) was also assessed on the swine wastewater denitrification process. In this study, the authors used the polymers as biofilm carriers and carbon source and found that systems containing PCL presented a high denitrification efficiency (higher than 95%) in 20 days. On the other hand, PBS presented low nitrate removal at 30 days of experiment, with the highest removals on days 11 and 23, with a concentration similar to the initial one (37 mg.L-1) after reaching the maximum value of 54.7 mg.L-1 on the 8th and 19th days. The biostimulation application was only addressed in a study carried out by a group[8], in which microparticles were obtained from the fusion of PBS with urea and subsequent radiation for the application in the biostimulation test of Pseudomonas aeruginosa in order to remove Total Petroleum Hydrocarbons (TPH) in bench scale tests. This study resulted in 35.8% oil removal with microparticles irradiated with 25kGy after 30 days of testing. Due to its physical characteristics and biodegradability[80,81,87,88], PBS is potentially useful in the environmental area, mainly by reducing or removing pollutants from the environment, avoiding the compromise of the biotic community of the area. The choice of biodegradable polymers such as PBS for bioremediation processes is important since its occasional addition to the environment in an attempt to reduce damage, also enables this biodegradable polymer to act as a carbon source to the local microbiota. Therefore, it does not remaining in the environment for a long period of time. Another advantage of using PBS in bioremediation is the possibility of obtaining it from the transesterification reaction of monomers that might be acquired by microbiological fermentation of renewable raw materials such as glucose, xylose, and starch to obtain succinic acid[69,70], therefore reducing the environmental impact yielded by the petrochemical sector.

Figure 6. Timeline with the advancement of biopolymer research, focusing on environmental and bioremediation in the last 15 years. 6/10

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Advances and perspectives in the use of polymers in the environmental area: a specific case of PBS in bioremediation

7. Conclusions

9. Acknowledgments

The results showed scientific articles and patents, mainly for biopolymers and biodegradable polymers, in the period of 15 years. Biopolymers presented 17,147 articles and 90,031 patents, while biodegradable polymers presented 12,015 articles and 99,608 patents. The search for the major applications of these polymers and green polymers revealed that the five major areas are Chemistry, Materials Science, Engineering (including Chemical Engineering), Physics & Astronomy, and Biochemistry, Genetics & Molecular Biology. The low percentage of works in the Environmental area (approximately 6%) encouraged a more specific search for bioremediation, which showed percentages of reduction higher than 97% in both documentary sources. The searches also revealed an upward trend on PBS use, with rates of 8.74 for articles and 30.63 for patents per year, although there is a stabilization in the number of articles in the last 6 years, a fact that might be seen as an opportunity for new publications. More studies were also identified regarding the application of PBS in the areas of Physics (51.8%) and Materials Science (32.7%) patent documents and articles, respectively. The use of this polymer was highlighted in processes of synthesis, characterization and application in the areas of chemistry, physics and pharmacy, mainly in the area of controlled release of medicines, which shows the potential application of this polymer in situations of absence of risk in different environments. However, for the main objective of this study and in the period evaluated, there was only 1 publication directly related to the use of PBS for bioremediation[8], indicating a lack of research in this area and this may be useful for unpublished work and for a greater contribution to environmental recovery that not only affects the environmental sector, but also socioeconomic sectors.

This study was partially funded by the Coordination for the Improvement of Higher Level Personnel - Brazil (CAPES – Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil) - Finance Code 001 and by the National Council for Scientific and Technological Development (CNPq – Conselho Nacional de Desenvolvimento Científico e Tecnológico).

8. Perspectives Petroleum is still the largest source of raw material for the production of synthetic polymers, making them expensive compared to those obtained from natural sources. Modern society presents many materials that are obtained from renewable sources and, in the wake of technology, several studies point out to the use of natural biodegradable polymers. Among them, poly(butylene succinate) (PBS) may be obtained from petrochemical products, fermentation agro-industrial waste, or from other renewable sources[89]. Although it presents both good processing and biodegradable properties, the widespread application of PBS is limited because it exhibits a highly linear chain structure that results in high crystallinity, high hydrophobicity, and low melt strength and viscosity[90]. Thus, the expansion of PBS use in several areas of application of biodegradable polymers depends on improvements in the processes of obtaining natural renewable sources in order to reduce the costs of the final product, as well as improvements in its thermomechanical properties. This is done by increasing molecular weight through polymer synthesis in the presence of effective catalysts; branching of the main chain; synthesis of co-polyesters; and addition of fillers, among other modifications[91], therefore representing a sector with great potential for new studies and publications. Polímeros, 30(2), e2020023, 2020

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Polímeros, 30(2), e2020023, 2020


Polímeros VOLUME XXX - Issue II - Apr./June, 2020

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Polímeros: Ciência e Tecnologia 2nd. issue, vol. 30, 2020  

The journal Polímeros: Ciência e Tecnologia is a quarterly publication of the Brazilian Polymer Association (Associação Brasileira de Políme...

Polímeros: Ciência e Tecnologia 2nd. issue, vol. 30, 2020  

The journal Polímeros: Ciência e Tecnologia is a quarterly publication of the Brazilian Polymer Association (Associação Brasileira de Políme...

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