Polímeros: Ciência e Tecnologia (Polimeros) 2nd. issue, vol. 29, 2019

Polímeros VOLUME XXIX - Issue II - Apr./June, 2019

São Paulo 994 St. São Carlos, SP, Brazil, 13560-340 Phone: +55 16 3374-3949 Email: abpol@abpol.com.br 2019

UBE lança ETERNATHANE®, pré-polímeros de poliuretano à base de policarbonato-diol para elastômeros de alto desempenho e durabilidade A UBE é uma indústria multinacional Japonesa que atua nos setores de químicos, máquinas, fármacos, energia e construção. Com escritórios ao redor do mundo e fábricas no Japão, Tailândia e Espanha, há um destaque na produção de caprolactama, poliamidas, fertilizantes e produtos químicos nos.

O poliuretano para elastômeros tornou-se cada vez mais soosticado para atender às exigências do mercado atual. Neste contexto, a UBE desenvolveu o ETERNACOLL® e o ETERNATHANE®, uma grande plataforma de soluções que oferecem possibilidades personalizáveis aos materiais de poliuretano, bem como retenção de desempenho superior e a longo prazo, como estabilidade térmica, resistência a óleo, estabilidade hidrolítica, resistência à intempéries e resistência química.

retenção das propriedades mecânicas após exposição a altas temperaturas

redução da absorção de água

retenção das propriedades originais após severa agressão hidrolííca e química

redução da perda de volume quando exposto à abrasão extrema

Os pré-polímeros de poliuretano ETERNATHANE®, à base de policarbonato-dióis ETERNACOLL® e terminados em isocianatos, são aplicados em elastômeros de alto desempenho. Através do aprimoramento das propriedades de resistência mecânica, química e térmica dos poliuretanos tradicionais, os novos elastômeros obtidos podem ser aplicados a novos usos e funções não disponíveis até o momento para novos mercados e clientes, tais como: petróleo e mineração, revestimento de rolos, membranas elastoméricas, pisos, elastômeros fundidos, TPU, rodas e pneus, compostos de poliuretano, selantes, eletrônicos e encapsulamento, entre outros. poliu

https://www.ube.com/contents/pcd/index.html

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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 I X - 2 0 1 9 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 Antonio Aprigio S. Curvelo (USP/IQSC) - President

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

Members Adhemar C. Ruvolo Filho (UFSCar/DQ) Ailton S. Gomes (UFRJ/IMA) Alain Dufresne (Grenoble INP/Pagora) Antonio Aprigio S. Curvelo (USP/IQSC) 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) Eloisa B. Mano (UFRJ/IMA) João B. P. Soares (UAlberta/DCME) 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) Laura H. de Carvalho (UFCG/DEMa) Luiz Antonio Pessan (UFSCar/DEMa) Luiz Henrique C. Mattoso (EMBRAPA) 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) Sadhan C. Jana (UAKRON/DPE) 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

Sadhan C. Jana

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 2019

Financial support:

Available online at: www.scielo.br

Polímeros / Associação Brasileira de Polímeros. vol. 1, nº 1 (1991) -.- São Carlos: ABPol, 1991Quarterly v. 29, nº 2 (Apr./June 2019) ISSN 0104-1428 ISSN 1678-5169 (electronic version)

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

1. Polímeros. l. Associação Brasileira de Polímeros.

Polímeros, 29(2), 2019

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

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

S h o r t C o m m u nic at i o ns Morphological structure and crystallinity of ‘Rainha’ sweet potato starch by heat–moisture treatment Mônica Tejo Cavalcanti, Natália Silva de Farias, Albanete da Nóbrega Cavalcante, Mônica Correia Gonçalves, Adriano Sant’Ana Silva and Roberlúcia Araújo Candeia................................................................................................................................ 1-4

Selecting chemicals for separation of ABS and HIPS in WEEE by froth flotation Solange Kazue Utimura, Arthur Pinto Chaves, Jorge Alberto Soares Tenório and Denise Crocce Romano Espinosa................................... 1-4

O r i g in a l A r t ic l e Obtaining and characterizing dental hybrid composites with clay or silica nanoparticles and boron-aluminum-silicate glass microparticles Lívia Rodrigues de Menezes and Emerson Oliveira da Silva .......................................................................................................................... 1-6

Evaluation of degradation of furanic polyamides synthesized with different solvents Cláudia Moreira da Fontoura, Vinicios Pistor, Raquel Santos Mauler ........................................................................................................... 1-6

Factorial design to obtain magnetized poly(ethyl acrylate‑co-divinylbenzene) Kelly Lúcia Nazareth Pinho de Aguiar, Kaio Alves Brayner Pereira, Marcelo Sierpe Pedrosa and Márcia Angélica Fernandes e Silva Neves........................................................................................................................................................ 1-8

Presence of iron in polymers extruded with corrosive contaminants or abrasive fillers Marcos Fernado Franco, Renan Gadioli and Marco Aurelio De Paoli ........................................................................................................... 1-6

Compatibility and characterization of Bio-PE/PCL blends Elieber Barros Bezerra, Danyelle Campos de França, Dayanne Diniz de Souza Morais, Ingridy Dayane dos Santo Silva, Danilo Diniz Siqueira, Edcleide Maria Araújo and Renate Maria Ramos Wellen........................................................................................ 1-15

Thermal radical polymerization of Bis(methacrylamide)s Stéfani Becker Rodrigues, Fabrício Mezzomo Collares, Douglas Gamba, Vicente Castelo Branco Leitune and Cesar Liberato Petzhold ................................................................................................................................................................................... 1-7

Study on mechanical & thermal properties of PCL blended graphene biocomposites Dinesh Kumar, Ganesh Babu and Sai Krishnan .............................................................................................................................................. 1-9

The influence of fiber size on the behavior of the araucaria pine nut shell/PU composite Giuliana Ribeiro Protzek, Washington Luiz Esteves Magalhães, Paulo Rodrigo Stival Bittencourt, Salvador Claro Neto, Rodrigo Lupinacci Villanova, Elaine Cristina Azevedo ................................................................................................................................... 1-9

Tribology of natural Poly-Ether-Ether-Ketone (PEEK) under transmission oil lubrication Thiago Fontoura de Andrade, Helio Wiebeck and Amilton Sinatora................................................................................................................ 1-9

Synthesis and characterization of amphiphilic block copolymers by transesterification for nanoparticle production André Rocha Monteiro Dias, Beatriz Nogueira Messias de Miranda, Houari Cobas-Gomez, João Guilherme Rocha Poço, Mario Ricardo Gongora Rubio and Adriano Marim de Oliveira .................................................................................................................. 1-12

Thermal, dielectric and catalytic behavior of palladium doped PVC films Ganesh Shimoga, Eun-Jae Shin and Sang-Youn Kim ...................................................................................................................................... 1-9

Castor polyurethane used as osteosynthesis plates: microstructural and thermal analysis Francisco Norberto de Moura Neto, Ana Cristina Vasconcelos Fialho, Walter Leal de Moura, Adriana Gadelha Ferreira Rosa, José Milton Elias de Matos, Fernando da Silva Reis, Milton Thélio de Albuquerque Mendes and Elton Santos Dias Sales.......................... 1-8

R e vi e w A r t ic l e Bio-based additives for thermoplastics Marco Aurelio De Paoli and Walter Ruggeri Waldman................................................................................................................................. 1-12

Cover: Typical disc surface roughness measurements for three test repetitions; (a) turning.

Arts by Editora Cubo.

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Polímeros, 29(2), 2019

Borealis Presents New Recycling Technology and Improved Recyclate Borealis, a leading provider of innovative solutions in the fields of polyolefins, base chemicals and fertilizers, announces the introduction of a new plastics recycling technology, Borcycle™.

This evolving technology will be used to produce high-quality compounds made of recycled polyolefins (rPO) such as the newly-launched Borcycle™ MF1981SY, an rPO with over 80% recycled content intended for use in visible appliance parts. Borealis also announces a series of significant material improvements to existing recyclates in the established Purpolen™ brand portfolio. These market launches and product improvements are important technology advancements and thus accelerate the transformation to a circular economy of plastics. Borealis and its wholly-owned subsidiary, mtm plastics, will showcase the new Borcycle technology and recyclate innovations at the K 2019 in October. Borealis is leading the industry by applying its Visioneering Philosophy™ to the development and implementation of novel polyolefins-based solutions that enable plastics reuse, recycling, and recovery, and by designing for circularity. These wide-ranging activities are gathered under the symbolic roof of EverMinds™, the Borealis platform dedicated to promoting a more circular mind-set in the industry. By capitalising on its profound expertise in virgin polyolefins and collaborating with value chain partners, Borealis keeps discovering new opportunities for business growth within the circular economy.

The new technology, Borcycle, transforms polyolefin‑based waste streams into recyclate pellet. As a transformative technology, it complements the existing Borealis virgin polyolefins portfolio with a range of pioneering, circular solutions. It unites state‑of‑the‑art technology with the profound Borealis polymer expertise gained over decades. As a scalable and modular technology, Borcycle has been developed to meet growing market demand for high-quality recyclate. Leading appliance brand owners, for one, have pledged to increase the amount of recycled plastics in their goods. Yet until recently, producers have not been able to rely on a consistent supply of high-quality recyclate. The Borcycle technology will help address this challenge. Compounds made using the Borcycle technology deliver high performance, add value and offer versatility.

Producers and brand owners in a range of industries will profit from the availability of high-quality recyclate that helps them meet environmental and regulatory challenges. “Advancing technology is crucial if our aim is to implement value-creating solutions in the circular sphere,” claims Maurits van Tol, Borealis Senior Vice President, Innovation, Technology & Circular Economy Solutions. “‘Building tomorrow together’ means innovating, collaborating, focussing on the customer, and above all – taking action. The launch of our new recycling technology Borcycle is tangible proof of our commitment to achieving plastics circularity.”

Recyclates from mtm save approximately 30% of CO2 emissions compared to virgin materials. A number of significant improvements have been made to existing recyclate grades in the Purpolen portfolio. “Mechanical recycling is presently a most eco-efficient method to implement the principles of the circular economy,” explains Guenter Stephan, Head of Mechanical

Recycling, Borealis Circular Economy Solutions. “Borealis and mtm plastics are leveraging their respective areas of expertise to make significant progress in achieving polyolefin circularity by upscaling recycling output and ensuring the reliable supply of high-quality plastics recyclate for European producers, in particular.”

Source: Borealis AG - www.borealisgroup.com

Bottlebrush Polymers: A Green Strategy for Purifying Natural Gas Natural gas and biogas have become increasingly popular sources of energy in recent years thanks to a cleaner and more efficient combustion process compared to coal and oil.

However, the presence of contaminants, such as carbon dioxide, means it must first be purified before it can be burned as fuel.

Unfortunately, traditional processes used to purify natural gas typically involve the use of toxic solvents and are extremely energy-intensive.

Now, researchers at the Massachusetts Institute of Technology (MIT) describe a new type of polymer membrane that can dramatically improve the efficiency of natural gas purification while reducing its environmental impact.

The membrane is capable of processing natural gas much more quickly than conventional materials, according to graduate student Yuan He. “Our design can process a lot more natural gas, removing a lot more carbon dioxide in a shorter amount of time,” he says. “Existing membranes are typically made using linear strands of polymer,” says Professor Zachary Smith, the project lead. “These are long-chain polymers, which look like cooked spaghetti noodles at a molecular level,” he says.

“You can make these cooked spaghetti noodles more rigid, and in so doing, you create spaces between the noodles that change the packing structure and the spacing through which molecules can permeate.”

Such materials are not sufficiently porous to allow carbon dioxide molecules to permeate through them at a fast enough rate to compete with existing purification processes. Instead of using long chains of polymers, Smith and his team have designed membranes in which the strands look like hairbrushes, with tiny bristles on each strand that allow the polymers to separate gases much more effectively. “We have a new design strategy where we can tune the bristles on the hairbrush, which allows us to precisely and systematically tune the material,” Smith says.

“In doing so, we can create precise subnanometer spacings, and enable the types of interactions that we need to create selective and highly permeable membranes.”

In experiments, the membrane was able to withstand unprecedented carbon dioxide feed pressures of up to 51 bar without suffering plasticization. This compares to around 34 bar for the best-performing materials. The membrane is also 2,000 -7,000 times more permeable than traditional membranes.

Since the side-chains, or “bristles,” can be predesigned before being polymerized, it is much easier to incorporate a range of functions into the polymer. The researchers are now planning to carry out a systematic study of the chemistry and structure of the brushes in order to investigate how this affects their performance.

Source: Advanced Science News - www.advancedsciencenews.com

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N N N N N N N N N N N N N

A A A A A A A A A A A A A A A A A A A A A

October

February

Conference Arab Rubber Expo 2019 Date: October 9-10, 2019 Location: Sharjah, United Arab Emirates Website: http://www.rubber-expo.com K 2019 Trade fair for plastics and rubber Date: October 16-23, 2019 Location: Dusseldorf, Germany Website: https://www.k-online.com/ 3rd International Conference on Metal Organic Frameworks and Porous Polymers Date: October, 27-30, 2019 Location: Paris, France Website: https://euromof2019.sciencesconf.org/ 15th Congresso Brasileiro de Polímeros (15th CBPol) Date: October, 27-31, 2019 Location: Bento Gonçalves, Rio Grande do Sul, Brazil Website: http://www.cbpol.com.br/ Materials + 3D Printing 2019 Date: October 31 - November 01, 2019 Location: Houston, Texas, United States Website: www.poly3d.org

2nd International Conference on Plastic and Polymers, Robotics, Applied Sciences, Design Engineering & Artificial Intelligence Date: February 17-18, 2020 Location: Kuala Lumpur, Malaysia Website: https://aet-forum.com/prada-feb-2020/ Layered Polymeric Systems Date: February 23-26, 2020 Location: Windsor, United States Website: www.polyacs.net/20lps 3rd World Congress on Bio-Polymers and Polymer Chemistry Date: February 24-25, 2020 Location: Rome, Italy Website: http://polymerchemistrycongress.alliedacademies.com/

November 10th International Conference on Biopolymers and Polymer Sciences Date: November 18-19, 2019 Location: Helsinki, Finland Website: https://biopolymers.materialsconferences.com/ Frontiers in Polymer Chemistry and Biopolymers Date: November 18-19, 2019 Location: Rome, Italy Website: https://www.longdom.com/polymerchemistry PPS Europe-Africa 2019 Regional Conference Date: November 18-21, 2019 Location: Pretoria, South Africa Website: https://www.pps2019.com/ Plastics & Rubber Vietnam Date: November 27-29, 2019 Location: Hanoi, Vietnam Website: https://www.plasticsvietnam.com/

December Annual Congress on Polymer Chemistry Date: December 02-03, 2019 Location: Tokyo, Japan Website: https://polymer.chemistryconferences.org/ Conference Latex Expo 2019 Date: December 4-5, 2019 Location: Chennai, India Website: http://www.latex-expo.com/ 16th Pacific Polymer Conference (PPC16) Date: December 8-12, 2019 Location: Singapore City, Singapore Website: http://www.pacificpolymer.org/public.asp?page=home.html 2nd International Conference on Polymerization Catalysis, Flexible Polymer and Nanotechnology Date: December 16-17, 2019 Location: Dubai, United Arab Emirates Website: https://polymer-catalysis.conferenceseries.com/ 6th World Congress on Smart Materials and Polymer Technology Date: December 16-17, 2019 Location: Dubai, United Arab Emirates Website: https://smart.materialsconferences.com/

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Mach 14th Expo Plasticos Date: March 110-13, 2020 Location: Guadalajara, Mexico Website: http://expoplasticos.com.mx/2020 5th International Conference and Exhibition on Polymer Chemistry Date: March 23-24, 2020 Location: London, United Kingdom Website: polymerchemistry.euroscicon.com

May Sustainable Polymers Date: May 17-20, 2020 Location: Safety Harbor, United States Website: www.polyacs.net/20sustainablepolymers 36th International Conference of the Polymer Processing Society (PPS-36) Date: May 31- June 4, 2020 Location: Montreal, Canada Website: www.polymtl.ca/pps-36/en

June Fluoropolymer Date: June 28 – July 1, 2020 Location: Denver, United States Website: www.polyacs.net/20fluoropolymer

July 48th World Polymer Congress (IUPAC - MACRO2020) Date: July 5-9, 2020 Location: Jeju Island, South Korea Website: www.macro2020.org Frontiers of Polymer Colloids (FPCOL 2020) Date: July 12-16, 2020 Location: Prague, Czech Republic Website: www.imc.cas.cz/sympo/84pmm

August Interplast Date: August 11-14, 2020 Location: Joinville, Brazil Website: www.interplast.com.br

September 9th International Conference on Fracture of Polymers, Composites and Adhesives Date: September 6–10, 2020 Location: Les Diablerets, Switzerland Website: www.elsevier.com/events/conferences/esistc4conference

Polímeros, 29(2), 2019

ABPol Associates Sponsoring Partners

Collective Members Master Polymers Ltda.

Nexo International Ltda.

Nitriflex S/A Ind. e Com. Radici Plastics Ltda.

Uniflon - Fluoromasters Polimeros Ind .Com. Imp. Export.Ltda

PolĂ­meros, 29(2), 2019

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.03917

Morphological structure and crystallinity of ‘Rainha’ sweet potato starch by heat–moisture treatment Mônica Tejo Cavalcanti1* , Natália Silva de Farias2, Albanete da Nóbrega Cavalcante1, Mônica Correia Gonçalves1, Adriano Sant’Ana Silva1 and Roberlúcia Araújo Candeia1 Unidade Acadêmica de Tecnologia de Alimentos, Centro de Ciências e Tecnologia Agroalimentar, Universidade Federal de Campina Grande – UFCG, Pombal, PB, Brasil 2 Programa de Pós-graduação em Ciência dos Alimentos, Universidade Federal de Santa Catarina – UFSC, Florianópolis, SC, Brasil 1

*monicatejoc@yahoo.com.br

Abstract Heat-moisture treatment is type of physical modification that which cause changes in the technological characteristics of the starch. One of the sources of starch that presents potential of use of this treatment is sweet potato of the variety ‘Rainha’ (Ipomoea batatas). Therefore, the objective of this work was extract the sweet potato starch, apply the heat‑moisture treatment in different relative humidity conditions (15, 20, and 25%), and characterize the starches as to water absorption capacity, morphology and crystallinity. Starch extracted from sweet potato resulted in a product of high purity. All modified starches showed a higher water absorption capacity when compared to native starch.

The morphology of the starch granules remained unchanged after the modification and the same was observed with respect to the crystallinity. However, modified 15% moisture starch showed significant changes in the amylose content, water absorption, and crystallinity, these characteristics extend the use of this starch, for use in foods.

Keywords: physical modification, tubercle, quality.

How to cite: Cavalcanti, M. T., Farias, N. S., Cavalcante, A. N., Gonçalves, M. C., Silva, A. S., & Candeia, R. A. (2019).

Morphological structure and crystallinity of ‘Rainha’ sweet potato starch by heat-moisture treatment. Polímeros: Ciência e Tecnologia, 29(2), e2019016. https://doi.org/10.1590/0104-1428.03917

1. Introduction The sweet potato (Ipomoea batatas) belongs to the Convolvulacea family and is an easily-adaptable rustic tuberous vegetable tolerant to dry seasons. It is a relatively low cost production crop of great economic and social importance in developing countries[1].

Starch is the main component of this root and corresponds to about 50-80% of dry matter, consisting of amylose and amylopectin in different proportions. The process of extracting this carbohydrate is of great interest to the food, pharmaceutical and chemical industry, because it presents physicochemical characteristics as, solubility, swelling power, pasting property, thermal, among others[2].

In its native form, starch often does not possess appropriate physicochemical properties for some types of processing. In this sense, the modifications of starches from alternative sources provide the amplification of use and favor the commercialization of starch.

Among the types of modifications, the physical modification by heat-moisture treatment has been highlighted with the advantage that the obtained starch is considered a natural and highly safe material[3]. Huang et al.[4] verified that this method applied to sweet potatoes promoted significant changes in increasing paste temperature and starch content, and decrease in viscosity and relative crystallinity.

Polímeros, 29(2), e2019016, 2019

Based on this approach, the objective of the study was to evaluate morphological and structural characteristics, water absorption capacity, as well as the physicochemical characteristics of ‘Rainha Branca’ sweet potato starch subjected to heat-moisture treatments.

2. Materials and Methods 2.1 Starch extraction Medium-sized ‘Rainha Branca’ sweet potatoes were purchased in the city of Campina Grande, Paraíba, Brazil. Starch was obtained by the method described by Adebowale et al.[5] with adaptations. The potatoes were ground with distilled water in a ratio of 1:2 (w/v). The mixture was filtered (70 mesh) and the filtrate was allowed to stand at 5°C for 8h. The supernatant was discarded and the starch was dried in air circulating oven at 40°C until final moisture of 13%.

2.2 Physicochemical characterization Sweet potato starch was evaluated for water content using an Infrared Moisture Analyser until constant weight (brand Marte, ID 200), ash, protein content and lipid content were determined using the AACC[6] method, the results were expressed as dry basis (%, db). Total

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Cavalcanti, M. T., Farias, N. S., Cavalcante, A. N., Gonçalves, M. C., Silva, A. S., & Candeia, R. A. carbohydrate content including fiber was calculated by difference. Apparent amylose content from starch was determined according to the methodology described by Martinez & Cuervas[7].

2.3 Modification of starch Starch modification by heat–moisture treatment (HMT) was carried out according to the method described by Hormdok & Noomhorm[8], where, the obtained starch had its water content adjusted to 15 (HMT15), 20 (HMT20) and 25% (HMT25) for posterior heat treatment.

2.4 Water and oil absorption capacity Water and oil absorption capacity were determined according to the method of Beuchat[9] at 25 ° C.

2.5 Morphological characterization The morphological evaluation was performed by a JEOL JSM 5800LV Scanning Electron Microscope (SEM) with 3kV. The determination of particle size was performed based on micrographs with a magnification of 2000x using ImageJ software.

Structural characterization was performed by X-ray diffraction in a SHIMADZU X-ray diffractometer (XRD 6100) with an angular sweep of 10°<2ɵ<50° in the Bragg‑Brentano assembly ɵ-2 system using Cu (kα1) radiation, a sweep scan of 0.02 (2ɵ), and 0.6 second interval for each sample.

The crystallographic phases of the samples and the standard JCPDS plots representing them were determined by the X-ray diffraction curves.

2.6 Statistical analysis The data starch water absorption capacity were submitted to analysis of variance ANOVA and the Tukey test (p ≤ 0.05), using Software Assistat 7.7

3. Results and Discussion 3.1 Physicochemical characterization The starch extracted from ‘Rainha’ sweet potatoes has its own characteristics, with low levels of minor constituents such as ash (0.36%, db), lipids (0.37%, db) and proteins (0.07%, db). The starch presented good quality and efficacy in the implemented extraction process, with carbohydrate content (sugars plus fibers) of about 85.57%.

As described in the literature, sweet potato starch is considered to have high amylose content and to have influence on starch properties[10]. When comparing the apparent amylose content in the native starch (30.39%, db) and those physically modified, we observed that the modified starch at 15% moisture presented lower values (28.85%, db) than other samples (HMT20 of 33.97% db, HMT25 of 31.19% db), which can be the result of additional interactions between the amylose-amylose and amylose-amylpectine chains which modify the starch matrix making the amylose more insoluble and unavailable for quantification[11] .

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3.2 Water and oil absorption capacity Sweet potato starch presented low water absorption capacity (WAC), however, the modified starch presented higher values of starch compared to the native, where: 0.76 (± 0.04) g/100g in the native starch; 0.95 (± 0.02) g/100g in the HMT15; 0.96 (± 0.02) g/100g in HMT20; and 0.85 (± 0.01) g/100g in HMT25. Similar behavior was observed regarding oil absorption capacity (OAC), where the modified starches presented higher values of starch, being 1.01 (± 0.02) g/100g in the native starch; 1.22 (± 0.07) g/100g in the HMT15; 1.23 (± 0.02) g/100g in the HMT20; and 1.34 (± 0.05) g/100g in the HMT25. Starch with low water absorption capacity is indicated as an ingredient in products that require both low retention of water and fat, improving characteristics such as product crunchiness.

3.3 Morphological characterization The size of the starch granules is an important parameter that affects their physicochemical properties and applications.

Micrographs of the starch (Figure 1) show surface roughness and few cracks/fissures in modified starches in comparison to original starch. However, all starch types presented ellipsoidal and rounded granules, with noticeable agglutination tendency in starches modified by heat-moisture treatment.

The ‘Rainha’ sweet potato native starch sample presented ellipsoidal granules and a smooth surface, with the granules size corresponding to about 5.51 μm. A small increase in particle size by 6.84 and 5.51 μm was observed for the morphologies of the granules corresponding to modified starches at 15% RM (HMT15) and 25% RM (HMT25), except for the sample of 20% RM (HMT20) that was smaller with 5.00 μm. Average particle size may be related to the amylose content, considering that the HMT 20 treatment had the highest amylose content.

Because starch granules are partially crystalline, they are defined based on the interplanar spaces and the relative intensity of the X-ray diffraction lines. Peak regions observed for sweet potato starch are characteristic of standard type A chains, which assume short to medium starch chain lengths (Figure 2).

The ratio of the starch crystallinity state (amorphous/ crystalline) is very important to understand its stability and application. The diffraction curve allows us to identify these characteristics, in addition to establishing the starch classification, which according to Yu et al.[12] and Zeng et al.[13] can be classified as type A, B, C and V starch. According to these authors, type A starch is a typical cereal starch, Type B is associated with tuberoses or amylose rich materials, and Type C starch resembles pea starch and various bean starches. Moreover, Type C can be considered as a mixture of the XRD patterns of starches A and B. Type V starch is a type of crystalline starch typical of complexes formed between amylose and lipid.

The starchs were characterized as Type A due to the presence of XRD curves at reflection points 2Ɵ = 10, 11, 15, 18 and 23°. The amylose content found in the starches corroborates with the crystallinity results, once, ranged from 28.85 to 33.97% indicating low content.

Polímeros, 29(2), e2019016, 2019

Morphological structure and crystallinity of ‘Rainha’ sweet potato starch by heat–moisture treatment

Figure 1. Micrographs of native starch granules and modified starch at 15% RH (HMT15), 20% RH (HMT20) and 25% RH (HMT25) of ‘Rainha Branca’ sweet potato, 2000x magnitude.

sample presented larger particle size with less agglutination.

This result can be explained because the modified sample at 15% relative moisture has lower amylose content, increasing its crystallinity.

4. Conclusions The extraction of sweet potato starch results in a product of high purity and good quality. The heat–moisture treatment caused morphological changes and water absorption capacity.

Modified 15% moisture starch presented considerable characteristics for use in fried food products as texture enhancers.

Figure 2. X-ray diffraction curves of native starch and modified starch at 15% RH (HMT15), 20% RH (HMT20) and 25% RH (HMT25) of ‘Rainha Branca’ sweet potato.

Waramboi et al.[14] conducted characterization studies of sweet potatoes from New Guinea and Australia, and found that sweet potatoes obtained a type A crystallinity pattern and peak values of 15; 17; 17.9 and 22.8º for 2Ɵ; values similar to those found in this study.

Based on the crystallinity values of the modified starches, the increase of the crystallite in relation to the original starch (7.37%) can be verified. However, the HMT 15 stood out from the others, obtaining 8.43% crystallinity.

This parameter corroborates with the results of the micrographs (Figure 1), which illustrates the difference in the morphology of the granule, considering that the 15% RM Polímeros, 29(2), e2019016, 2019

5. References 1. Nunes, M. U. C., Jesus, A. F., Lima, I. S., Santos, L. S., & Cruz, D. P. (2012). Produtividade de genótipos de batata-doce com diferentes colorações de raízes em cultivo orgânico.

Horticultura Brasileira, 30(2), S5542-S5548. Retrieved in 2017, June 17, from https://www.alice.cnptia.embrapa.br/ alice/bitstream/doc/949283/1/Produtividade.pdf 2. Zhu, F., Yang, X., Cai, Y., Bertoft, E., & Corke, H. (2011).

Physicochemical properties of sweetpotato starch. Starch, 63(5), 249-259. http://dx.doi.org/10.1002/star.201000134.

3. Bemiller, J. N. (1997). Starch modification: challenges and prospects. Starch, 49(4), 127-131. http://dx.doi.org/10.1002/ star.19970490402.

4. Huang, T.-T., Zhou, D.-N, Jin, Z.-Y., Xu, X.-M., & Chen, H.-Q. (2016). Effect of repeated heat-moisture treatments on digestibility, physicochemical and structural properties of 3/4

Cavalcanti, M. T., Farias, N. S., Cavalcante, A. N., Gonçalves, M. C., Silva, A. S., & Candeia, R. A. sweet potato starch. Food Hydrocolloids, 54(Part A), 202-210. http://dx.doi.org/10.1016/j.foodhyd.2015.10.002.

5. Adebowale, K. O., Olu-Owolabi, B. I., Olayinka, O. O., & Lawal, O. S. (2005). Effect of heat–moisture treatment and annealing on physicochemical properties of red sorghum starch.

African Journal of Biotechnology, 4(9), 928-933. Retrieved in 2017, June 17, from https://www.ajol.info/index.php/ajb/ article/view/71104 6. American Association of Cereal Chemists – AACC. (1995).

Approved methods (8th ed.). Saint Paul: AACC. 7. Martinez, C., & Cuervas, F. (1989). Evaluación de lacalidadculinaria y molineradel arroz. Guia de estudo para ser usada como complemento de launidadauditutorial sobre elmismo tema (3. ed., 73 p.). Cali: CIAT. Retrieved in 2017, June 17, from http://hdl.handle.net/10568/54016 8. Hormdok, R., & Noomhorm, A. (2007). Hydrothermal treatments of rice starch for improvement of rice noodle quality.

Lebensmittel Wissenchaft und Tecnologie, 40(10), 1723-1731. http://dx.doi.org/10.1016/j.lwt.2006.12.017.

9. Beuchat, L. R. (1977). Functional and electrophoretic characteristic of succinylated peanut flour proteins. Journal Agriculture Chemistry, 25(2), 258-260. http://dx.doi.org/10.1021/ jf60210a044.

10. Feng, W., Zhang, W., Wang, H., Ma, L., Miao, D., Liu, Z., Xue, Y., Deng, H., & Yu, L. (2015). Analysis of phosphorylation sites

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on autophagy proteins. Protein & Cell, 6(9), 698-701. http:// dx.doi.org/10.1007/s13238-015-0166-0. PMid:26081468.

11. Kaur, M., & Singh, S. (2019). Influence of heat-moisture treatment (HMT) on physicochemical and functional properties of starches from different Indian oat (Avena sativa L.) cultivars.

International Journal of Biological Macromolecules, 122, 312-319. http://dx.doi.org/10.1016/j.ijbiomac.2018.10.197.

PMid:30385334.

12. Yu, L., Zhai, H., Chen, W., He, S., & Liu, Q. (2013). Cloning and functional analysis of lycopene ε-Cyclase (IbLCYe) gene from sweetpotato, Ipomoea batatas(L.)Lam. Journal of Integrative Agriculture, 12(5), 773-780. http://dx.doi.org/10.1016/S20953119(13)60299-3.

13. Zeng, J., Li, G., Gao, H., & Ru, Z. (2011). Comparison of A and B starch granules from three wheat varieties. Molecules (Basel, Switzerland), 16(12), 10570-10591. http://dx.doi. org/10.3390/molecules161210570. PMid:22183883.

14. Waramboi, J. G., Dennien, S., Gidley, M. J., & Sopade, P. A. (2011). Characterisation of sweet potato from Papua New Guinea and Australia: physicochemical, pasting and gelatinisation properties. Food Chemistry, 126(4), 1759-1770. http://dx.doi. org/10.1016/j.foodchem.2010.12.077. PMid:25213955.

Received: June 17, 2017 Revised: Jan. 28, 2019 Accepted: Apr. 09, 2019

Polímeros, 29(2), e2019016, 2019

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.05718

Selecting chemicals for separation of ABS and HIPS in WEEE by froth flotation Solange Kazue Utimura1* , Arthur Pinto Chaves2, Jorge Alberto Soares Tenório1 and Denise Crocce Romano Espinosa1 Laboratório de Reciclagem, Tratamento de Resíduos e Metalurgia Extrativa – LAREX, Departamento de Engenharia Química – PQI, Escola Politécnica, Universidade de São Paulo – USP, São Paulo, SP, Brasil 2 Laboratório de Tratamento de Minérios e Resíduos Industriais – LTM, Departamento de Engenharia de Minas e de Petróleo – PMI, Escola Politécnica, Universidade de São Paulo – USP, São Paulo, SP, Brasil

1

*solange.utimura@usp.br

Abstract The feasibility of using common chemicals to separate plastics from waste electrical and electronic equipment (WEEE) by froth flotation is investigated. Plastic waste is one of the WEEE polluters and a separation is necessary to recycle it.

The most common plastics in electronic industries are acrylonitrile-butadiene-styrene (ABS) and high impact polystyrene (HIPS). These plastics are difficult to separate due to the similar specific weights and to both being repellent to water.

Froth flotation allows for separating particles by the differences in their surface characteristics by selective wetting agents. The common chemicals are ethanol and acetic acid to depress the plastics. The process with 20% weight of ethanol was able to produce a recovery concentrate of HIPS with 98% and ABS with 96%. The process with 40% weight of acetic acid produces a recovery concentrate of HIPS with 96% and ABS with 83%.

Keywords: WEEE, froth flotation, plastics separation, plastics recovery.

How to cite: Utimura, S. K., Chaves, A. P., Tenório, J. A. S., & Espinosa, D. C. R. (2019). Selecting chemicals for separation of ABS and HIPS in WEEE by froth flotation. Polímeros: Ciência e Tecnologia, 29(2), e2019017. https:// doi.org/10.1590/0104-1428.05718

1. Introduction Brazil is the second major producer of electronic waste (e-waste) in the Americas, with 1.5 Mt per year, which is around 7.1 kg/inh; yet only 13% of e-waste is treated appropriately. The global amount of e-waste generation in 2016 was arounf 44.7 Mt and the amount of e-waste is expected to grow to 52.2 Mt in 2021[1].

E-waste is referred to as WEEE, electrical and electronic scrap from a wide range of products (computers, cell phones, laptops, TVs) with different components (batteries, LCD-TVs, lamps, printed circuit boards). WEEE involves valuable materials, including metals, plastics and glass.

The opportunities for dismantling these materials make them an interesting business with a potential for reuse and recycling[2].

WEEE demands specific equipment to dismantle, shred, process and extract the materials. These materials, such as plastics components, can be recycled for producing a new products. The advantages of recycling WEEE are conserving natural resources, preserving landfill space, reducing pollution and saving energy[3].

The selective separation of plastic waste is an important step because these types of plastics should not be put together in the recycling operation reprocess. Contamination with other polymers with different melting points can limit the quality of plastic waste and cause some complications in

Polímeros, 29(2), e2019017, 2019

physical properties, such as polymer-polymer incompatibility, discoloration and degradation products[4].

A major difficulty in separating mixed plastics, is the natural hydrophobicity that is a feature of most plastics.

Plastics have a floating property, caused by their non-wetting characteristic, and the selective wetting of one element is necessary for the separation process[5]. Different studies on plastic waste separation have used different methods and an efficient alternative is a mineral processing technique denominated froth flotation. The application of the flotation technique to plastic separation correlates properties, such as low surface energy and low density[6].

Froth flotation was established for ore separation[7].

To apply this technique to plastic separation an appropriate chemical has to be added to selectively change the surface properties. The challenges in plastics flotation consist in selectively changing the surface characteristics from hydrophobic to hydrophilic properties[8].

Many studies demonstrated that froth flotation technique has advantages in sorting mixture plastics. For example, Thanh Truc et al.[9] revealed the combination of ZnO and microwave treatment for the selective separation of ABS and HIPS from WEEE by froth flotation. Recently, Guo et al.[3] separated ABS and PS from WEEE when using sodium hypochlorite as an aid of froth flotation.

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S S S S S S S S S S S S S S S S S S S S

Utimura, S. K., Chaves, A. P., Tenório, J. A. S., & Espinosa, D. C. R. The purpose of this study was to separate the most common plastics content in WEEE as ABS and HIPS by the froth flotation and using attractive and common chemicals such as ethanol and acetic acid to make the plastic recycling process viable.

2. Materials and Methods 2.1 Plastic waste preparation WEEE was collected from a recycling unit in a WEEE re-use center at the Universidade de São Paulo (USP – Brazil).

The process starts by dismantling and separating the cables, plastics, metals and glass. The procedure used to identify the plastic was based on the resin identification code (RIC) of the Society of the Plastic Industry. The plastics used for the experiments were of different colors to visually analyze the concentrate samples manually at the end of their respective tests. The ABS and HIPS were shredded by a knife shredder (RONE FA2305) and separated into size fractions: 5.66; 2.83; 2.00; 1.00; 0.50 and 0.30 mm.

2.2 Froth flotation experiment The samples used for froth flotation consisted of a mixture of 10 g of each plastic (ABS and HIPS) of the same sieve size. The reagent was used as a solution of ethanol P.A. (99.5% purity by CAAL) at different concentrations as well as the solution of acetic acid P.A. (99.7% purity

by CAAL).

The flotation tests were conducted in a glass column of 1,050 mm in height and 80 mm in diameter with a volumetric capacity of 3 dm3. The bottom of the flotation column was fitted with a ceramic sparger plate (10-16-μm pore diameter) that was used to produce gas bubbles with compressed air (3.0 dm3/min). The sample was fed on top of the column that was a mixture of flotation fluid and gas.

The hydrophilic particles were removed from the bottom (depressed plastics) and hydrophobic particles overflowed the flotation column[3].

No additional frother was required and a 5-minute conditioning time was used. The floated plastics were mechanically removed after 10-minute flotation period.

The floating and depressed plastics were collected respectively and dried under 50 °C to calculate depressing and floating rates.

separation depends on the plastics mixture type, the different hydrophobity grade, the size, density, shape of the particle and the particle weight[3,10].

3.1 Flotation with an aqueous ethanol solution The flotation reagent used for the tests consists of an ethanol aqueous solutions at different concentrations to control the surface tension. Selective wetting can be obtained by decreasing the surface tension of the flotation reagent in values whereby one plastic remains hydrophobic while another plastic changes into hydrophilic surface[11].

Figures 1 and 2 show the flotation experiments in aqueous ethanol solution at different concentrations with particle size between 2.00 to 2.83 mm. The flotation “recovery” refers to the amount of plastic that could be separated in percentage of mass. The curves were obtained in duplicate and the results were reproducible.

The mixture of ABS and HIPS in flotation experiments consists in 10 g of each plastic type of the same sieve size.

Figure 1 shows the aqueous solution of ethanol at 20% wt.

The recovery of ABS was 96% or collected 9.6 g of ABS that depressed in the column. The ABS purity was 98% with ethanol at 20% wt., or of the total depressed plastic, 98% was ABS. Figure 2 shows that at 20% wt. ethanol concentration, the recovery of HIPS was 98% or 9.8 g of floated HIPS. The HIPS purity was 96% with ethanol concentration at 20% wt., or of the total float plastic, 96% was HIPS. No additional frother was required because ethanol increased the formation of small air bubbles and improved the flotation of particles. The formation

Figure 1. Flotation recovery and purity of ABS as a function of ethanol concentration. Error bars show +/- standard deviation.

3. Results and Discussions The work was started by running flotation experiments on shredded WEEE plastics with a suitable range of particle size between 2.00 and 2.83 mm.

The appropriate range of plastic size can be 2.00 and 6.00 mm and influences on the floatability in selective separation of plastics. The plastic particles larger than 6 mm are more difficulty to float due the average of the specific gravity from the bubble-particle aggregate that is lower than the specific weight of the flotation medium. The particle size smaller than 1 mm increases the specific surface area and decreases the selectivity. The efficiency of the plastics 2/4

Figure 2. Flotation recovery and purity of HIPS as a function of ethanol concentration. Error bars show +/- standard deviation.

Polímeros, 29(2), e2019017, 2019

Selecting chemicals for separation of ABS and HIPS in WEEE by froth flotation of the froth layer on the surface pulp happens when the air bubbles occur through the pulp due the portion of chemical molecules[12].

3.2 Flotation with an aqueous acetic acid solution Figure 3 and 4 show the flotation experiments according the aqueous solution of acetic acid at different concentrations with particle size between 2.00 and 2.83 mm. The “recovery” refers to the amount of plastic that could be separated in percentage of mass. The curves were obtained in duplicate and the results were reproducible.

The ABS/HIPS samples used for the froth flotation tests, which consisted of 10 g of each plastic type of the same sieve size. Figure 3 shows the aqueous solution of acetic acid at 40% wt. The recovery of ABS was 83% or collected 8.3 g of ABS that depressed in the column. The ABS purity was 96% with acetic acid at 40% wt., or of the total depressed plastic, 96% was ABS. Figure 4 shows that at 40% of acetic acid concentration, the recovery of HIPS was 96% or 9.6 g of HIPS floated. The HIPS purity was 86% with 40% of acetic acid concentration (40% wt.) or of the total float plastic, 86% was HIPS. Therefore, the flotation range used in these experiments was based on selectivity and achieved by reducing the surface tension of the liquid with ethanol and acetic acid aqueous solutions. The concentrations of ethanol and acetic acid control the surface tension of the flotation medium.

The aqueous solutions of ethanol at 20% wt. and 40% wt. acetic acid were used to allow the separation of the ABS that depressed and the HIPS that floated.

Figure 3. Flotation recovery and purity of ABS as a function of acetic acid concentration. Error bars show +/- standard deviation.

Figure 4. Flotation recovery and purity of HIPS as a function of acetic acid concentration. Error bars show +/- standard deviation.

Polímeros, 29(2), e2019017, 2019

4. Conclusions Froth flotation is a mineral process technique in which hydrophobic particles are selectively separated from the froth. The hydrophobic particles float and are separated from the hydrophilic particles, which are depressed into the solution. In this froth flotation process, it is possible to separate ABS and HIPS from WEEE. The separation of ABS and HIPS is reached by the use of surface tension control and by adjusting the experimental conditions that induce the selective flotation.

The experimental work used ethanol and acetic acid to depress plastics and yielded good results. The concentration of ethanol and acetic acid control the surface tension and the aqueous solutions of ethanol at 20% wt. concentration and 40% wt. acetic acid were found to allow the separation of the ABS that depressed and the HIPS that floated.

5. Acknowledgments The authors are grateful for the financial support provided by CNPq (The Brazilian National Council for Scientific and Technological Development) and Fapesp (The State of São Paulo Research Foundation), Thematic Project 2012/51871-9 for this work.

6. References 1. Baldé, C. P., Forti, V., Gray, V., Kuehr, R., & Stegmann, P. (2017). The global E-waste monitor 2017: quantities, flows, and resources. Vienna: UNU, ITU, ISWA. 2. Suresh, S. S., Bonda, S., Mohanty, S., & Nayak, S. K. (2018).

A review on computer waste with its special insight to toxic elements, segregation and recycling techniques. Process Safety and Environmental Protection, 116, 477-493. http://dx.doi. org/10.1016/j.psep.2018.03.003.

3. Guo, C., Zou, Q., Wang, J., Wang, H., Chen, S., & Zhong, Y. (2018). Application of surface modification using sodium hypochlorite for helping flotation separation of acrylonitrilebutadiene-styrene and polystyrene plastics of WEEE. Waste Management (New York, N.Y.), 82, 167-176. http://dx.doi. org/10.1016/j.wasman.2018.10.031. PMid:30509579.

4. Wang, H., Wang, J., Zou, Q., Liu, W., Wang, C., & Huang, W. (2018). Surface treatment using potassium ferrate for separation of polycarbonate and polystyrene waste plastics by froth flotation. Applied Surface, 448, 219-229. http://dx.doi. org/10.1016/j.apsusc.2018.04.091.

5. Negari, M. S., Ostad Movahed, S., & Ahmadpour, A. (2018).

Separation of polyvinylchloride (PVC), polystyrene (PS) and polyethylene terephthalate (PET) granules using various chemical agentes by flotation technique. Separation and Publication Technology, 194, 368-376. http://dx.doi.org/10.1016/j. seppur.2017.11.062.

6. Thakur, S., Verma, A., Sharma, B., Chaudhary, J., Tamulevicius, S., & Thakur, V. K. (2018). Recent developments in recycling of polystyrene based plastics. Green and Sustainable Chemistry, 13, 32-38. http://dx.doi.org/10.1016/j.cogsc.2018.03.011.

7. Braga, P. F. A., Chaves, A. P., Luz, A. B., & França, S. C. A. (2014).

The use of dextrin in purification by flotation of molybdenite concentrates. International Journal of Mineral Processing, 127, 23-27. http://dx.doi.org/10.1016/j.minpro.2013.12.007.

8. Wang, J., Wang, H., Wang, C., Zhang, L., Wang, T., & Zheng, L. (2017). A novel process for separation of hazardous poly(vinyl chloride) from mixed plastic wastes by froth flotation. Waste 3/4

Utimura, S. K., Chaves, A. P., TenĂłrio, J. A. S., & Espinosa, D. C. R. Management (New York, N.Y.), 69, 59-65. http://dx.doi. org/10.1016/j.wasman.2017.07.049. PMid:28801216.

9. Thanh Truc, N. T., & Lee, B.-K. (2017). Selective separation of ABS/PC containing BFRs from ABSs mixture of WEEE by developing hydrophilicity with ZnO coating under microwave treatment. Journal of Hazardous Materials, 329, 84-91. http:// dx.doi.org/10.1016/j.jhazmat.2017.01.027. PMid:28126573.

10. Pita, F., & Castilho, A. (2017). Separation of plastics by froth flotation. The role of size, shape and density of the particles.

Waste Management (New York, N.Y.), 60, 91-99. http://dx.doi. org/10.1016/j.wasman.2016.07.041. PMid:27478025.

11. Chen, S., Zhang, Y., Guo, C., Zhong, Y., Wang, K., & Wang, H. (2019). Separation of polyvinyl chloride from

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waste plastic mixture by froth flotation after surface modification with sodium persulfate. Journal of Cleaner Production, 218, 167-172. http://dx.doi.org/10.1016/j. jclepro.2019.01.280.

12. Truc, N. T. T., & Lee, B. K. (2017). Combining ZnO/microwave treatment for changing wettability of WEEE styrene plastics (ABS and HIPS) and their selective separation by froth flotation.

Applied Surface, 420, 746-752. http://dx.doi.org/10.1016/j. apsusc.2017.04.075.

Received: Dec. 03, 2018 Revised: Feb. 28, 2019 Accepted: Mar. 01, 2019

PolĂ­meros, 29(2), e2019017, 2019

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.01416

Obtaining and characterizing dental hybrid composites with clay or silica nanoparticles and boron-aluminum-silicate glass microparticles Lívia Rodrigues de Menezes1 and Emerson Oliveira da Silva1*  Instituto de Macromoléculas Professora Eloisa Mano, Universidade Federal do Rio de Janeiro – UFRJ, Rio de Janeiro, RJ, Brasil

1

*eos@ima.ufrj.br

Abstract The aim of the present work was the obtaining and characterization of dental hybrid composites using nanoparticles (clay or silica) and boron-aluminum-silicate microparticles. We evaluated the dispersion of the nanofillers when changing their loading among 2.5%, 5%, 10% and 25% wt. Were tested, in the above quantities, four different types of nanofillers, two nanosilicas and two nanoclays The remainder of the inorganic phase, up to a total loading of 75% wt, was given by the boron-aluminum-silicate microparticles. The systems were characterized by XRD, TGA, LF-NMR, and . FTIR was used to determine the degree of conversion. The XRD and LF-NMR showed that the composites with 2.5% of clays, contained an exfoliated profile, and the groups with higher amounts of clay showed intercalated areas or the agglomeration of these particles. Furthermore, the silicas were agglomerated in all groups. The thermal resistance of the material was not affected by the silicas, but improved when using 2.5% of nanoclays. On the other hand, the addition of these particles caused the reduction of the degree of conversion of the systems.

Keywords: acrylate matrixes, hybrid composites, organoclays, silicas.

How to cite: Menezes, L. R., & Silva, E. O. (2019). Obtaining and characterizing dental hybrid composites with clay or silica nanoparticles and boron-aluminum-silicate glass microparticles. Polímeros: Ciência e Tecnologia, 29(2), e2019018. http://dx.doi.org/10.1590/0104-1428.01416

1. Introduction The quality of dental restorative composites have been steadily increasing in recent years[1,2]. Dental composites usually consist of a polymer matrix with silanized filler and a photo-initiator system, with small amounts of photo-stabilizer and inhibitor, this composition represents a standard case of traditional design. The main monomers used in these materials are dimethacrylates, which include bisphenol A glycerolate dimethacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA) and urethane dimethacrylate (UDMA)[1-3].

Adjustment of the filler amount and size is very important with respect to composition because this affects the overall properties of these materials. The field of nanotechnology involves materials in the 1-100 nm size range, should be it has brought new practices and including the use of many nanofillers[4,5]. In dental composites, silica nanofillers, due to their high surface area and spherical form, cause a large increase in stiffness and decrease in roughness, however, the spherical and tiny shape leads to the formation of a high charge-charge interaction[6,7], becoming more difficult to disperse than other fillers.

These materials require a high amounts of fillers for it to have a suitable viscosity to be sculpted. In this way the using of nanoparticles can cause difficulties of dispersion due to the high number of particles existing in a small mass

Polímeros, 29(2), e2019018, 2019

of fillers and due their higher surface energy[8], encouraging the obtaining of hybrid composites with a combination of micro and nanoparticles. In resin composites is very common the use of glass particles with high atomic numbers, such as barium, strontium, and zirconium[9].

Clay–polymer systems can have many morphologies, which include: (1) agglomerated particles, where the layers remain joined and polymer chains only interact with the surface layers; (2) intercalated, when the polymer chain is intercalated between the host platelets; and (3) exfoliated, when the silicate platelets are isotropically dispersed in a continuous polymer matrix. The best enhancements in physical properties can be achieved with the exfoliated topology[10,11].

Montmorillonite is a 2:1 phyllosilicate. Its crystalline structure consists of an aluminum hydroxide octahedral sheet sandwiched between two tetrahedral silicate layers[12].

Due to the organophilicity of the polymers, it is necessary to modify the clay surface with cationic surfactants such as alkylammonium or alkylphosphonium, forming the organoclay and providing expansion between the layers, facilitating the entry of the polymer chains within these. This is a key step to dispersion of these fillers in the polymer matrix[11]. In this way, these materials are of great interest in composite resin research, due to their reduced dimension, which increases

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Menezes, L. R., & Silva, E. O. the contact surface between matrix and fillers. In this field, nanoclay fillers are important and have been a subject of research in recent years due to the significant improvements small increments in these loadings can promote in the physicochemical properties of polymer composites[13,14].

The aim of the present work was the obtaining and characterization of dental hybrid composites using montmorillonite clay and silica nanoparticles and boron‑aluminum-silicate microparticles.

2. Materials and Methods 2.1 Materials A standardized resin matrix was used containing a mixture of Bis-GMA, UDMA and TEGDMA in the proportion 35:40:25wt% between them, associated with a camphorquinone (CQ) system-based as photoinitiator.

We used as the nanofillers one of the following four types: two organically modified clays (Viscogel B8 and Dellite 67G), a hydrophilic silica (Aerosil 200) with 12 nm diameter, an organomodified silica (Aerosil R972) with 16 nm diameter and a boron-aluminum-silicate glass with 4 μm diameter. In the case of both clay their lamellas present a diameter between 100 and 200 nm and 1 nm thickness.

In the all groups, the total filler loading was 75% wt.

The nanofiller‑only loading varied among 2.5%, 5%, 10% and 25% wt, the remainder (72.5%, 70%, 65%, 50% wt, respectively) being the loading of microfillers.

All the mixtures were formulated to contain a standard loading of inorganic pigments based on metal oxide so that these experimental composites would match the A3 dentin color pattern on the Vita scale[15]. In all preparations, the matrix used belonged to the same production batch, thus avoiding possible changes in composition. The clays and hydrophobic silica were surface modified, while the hydrophilic silica had no modification. Both clays have been modified by Bis(Hydrogenated Tallow Alkyl) Dimethyl Ammonium.

But Dellite 67G has high content of modifier, and Viscogel B8 has 10% of 2-propanol. The hydrophobic silica, in turn, was modified by dimethyldichlorosilane (DDS). The surface modification of all fillers was maded by the manufacturer.

The use of microparticles was necessary for the dental resins because these materials are worked at very high filler loadings due to the need for to the resin to have high viscosity to enable modeling the restoration. This way, the presence of a mix with nano and microparticulated fillers in the dental resins led to obtaining hybrid composites.

2.2 Methods The silicas and clay nanoparticles were combined with barium-alumino-silicate micrometer fillers glass (~ 4μm).

The proportion of filler/matrix was 75:25 wt/wt. Within the nanofiller, the load percentages were 2.5%, 5%, 10% and 25% in relation to the microfillers. The matrix/filler proportion was similar in all groups, with the only change being the relative amount of microfillers and nanoparticles.

The filler and matrix were mixed by a FlackTek DAC 150 SpeedMixer™ (Landrum, SC, USA), according to the following method: initially the nanofillers of each group were added to the matrix, after which the systems were 2/6

mixed in five cycles of five minutes each at increasing speeds of 1400, 1600, 2000, 2200 and 2400 rpm. Then, the microparticles were added to the mixture and subjected to the same mixing cycle, followed by two cycles of vacuum mixing (by manual rotation) for elimination of air bubbles that had been formed during mixing. The nanofillers were first added to the matrix in order to avoid high viscosity of the medium, which would hinder the dispersal of the particles.

X-ray diffraction The exfoliation of nanoclay particles in resin and the crystallinity of silicas were analyzed by X-ray diffraction (XRD). The diffraction studies were performed with a Rigaku Ultima IV X-ray diffractometer (Tokyo, Japan) (CuKα irradiation, 40 kV, 20 mA) in the range of 2θ = 1 to 80°.

Thermogravimetric analysis The thermogravimetric analysis (TGA) was performed on a Q50 thermobalance from TA Instruments, Inc. The samples with 15 mg were heated from 30 to 700°C, at a rate of 10°C/min, under nitrogen flow.

Degree of conversion The degree of conversion (DC) of the systems was determined with Fourier transform infrared spectroscopy (FTIR: Spectrum 100 Optica; PerkinElmer, MA, USA), containing an attenuated total reflectance apparatus with a ZnSe crystal (Pike Technologies, Madison, WI, USA).

The test was performed in the polymerized and unpolymerized samples and the DC was calculated using the band ratios of 1638 cm−1 and 1608 cm−1. The analysis was performed in 5 different samples from each group evaluated (N = 5) in order to determine the statistical dispersions of the values.

Low-field nuclear magnetic resonance To determine the relaxation measurements, a Maran Ultra low-field NMR (Resonance Instruments, Oxford, UK) was used, operating with the hydrogen nucleus at 23 MHz. Proton spin–lattice relaxation times were determined by inversion‑recovery pulse sequence (180°–τ–90°) using 20 data points, with 4 scans for each and a range of τ varying from 0.1 to 5000 ms, with 10 s of recycle delay and 90° pulse of 4.5 μs, calibrated automatically by the instrument’s software.

3. Results The silicas characterization using X-ray diffraction (Figure 1) revealed an unorganized structure characterized by the presence of an amorphous halo centered at 2θ = 22.35° for the hydrophobic silica (Aerosil R972) and at 2θ = 24.35° for the hydrophilic silica (Aerosil 200) presented two diffraction peaks. The broad diffraction peaks from silicas indicate the predominantly amorphous structure.

The diffractograms of the clays exhibit the characteristic peaks of montmorillonite structures. The peak d001 of both clays are very close to 2θ= 2o indicating their already high interlamellar spacing due to the presence of the surface modifier. In the clays’ diffractograms (Figure 2), the basal spacing was determined by applying Bragg’s equation: nλ = 2 sin θ to d (001) peak. The calculations showed that Polímeros, 29(2), e2019018, 2019

Obtaining and characterizing dental hybrid composites with clay or silica nanoparticles and boron-aluminum-silicate glass microparticles the basal spacing of the Dellite 67G and Viscogel B8 are 31.6 Å and 36.8 Å, respectively.

The composites diffractograms also revealed that the samples containing 5%-25% of both clays presented agglomerated systems because the peak d(001) stayed in a similar position as the pure clay. On the other hand in groups containing 2.5% of both clays, the d(001) peak disappeared, this result can reflecting the exfoliation of the clays in these systems, or even an increase in spacing between platelets greater than the limit of diffractometer detection (44 Å).

The initial degradation temperatures of all tested materials (Table 1) indicate that the silicas caused no significant changes in the thermal profile of the resins at any tested loadings, which may be related to the filler agglomeration.

The clays, in turn, increased the thermal resistance of the material when used at 2.5% and reduced this resistance at the other loadings tested. This behavior indicates that the

less concentrated group presents better particle dispersion and the other clay loadings caused a more crowded profile.

From analysis of Low Field Nuclear Magnetic Resonance (LF-NMR), the longitudinal relaxation time of hydrogen (T1H) values (Table 2) indicate that the Viscogel 67G and Dellite B8, when added to the system at a loading of 2.5%, caused a significant decrease in the spin-relaxation time of the hydrogen nucleus network, proving the formation of a composite with a high degree of exfoliation. The silicas, in turn, caused no significant change in the relaxation times compared with the control group (0% of nanofillers).

The results of DC obtained from the FTIR spectra (Table 3), showed that the degree of conversion of the evaluated resins comprised between 40.72% and 27.38%.

As well it showed that the increase of nanoparticles in the system caused the reduction of the degree of conversion of these systems.

Figure 1. XRD patterns of (a) Aerosil R972 and (b) Aerosil 200.

Figure 2. XRD patterns of nanoclays (a) Dellite 67G (b) Viscogel B8.

Table 1. Initial degradation temperatures of all tested materials.

Filler Dellite 67G Viscogel B8 Aerosil 200 Aerosil R972

0% 369 369 369 369

Polímeros, 29(2), e2019018, 2019

2.5% 379 377 369 366

Initial degradation temperature (°C) 5% 10% 351 333 362 346 364 369 370 367

25% 332 343 367 369

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Menezes, L. R., & Silva, E. O. Table 2. T1H values of all tested materials.

Filler Dellite 67G Viscogel B8 Aerosil 200 Aerosil R972

T1H values (ms)

0% 62 62 62 62

2.5% 15 15 60 59

5% 45 42 63 59

10% 42 46 61 62

25% 45 54 61 60

Table 3. Degree of conversion of all tested materials.

Filler Dellite 67G Viscogel B8 Aerosil 200 Aerosil R972

0% 44 ± 3 A 44 ± 3 A 44 ± 3 A 44 ± 3 A

2.5% 38 ± 3 B 41 ± 3 AB 37 ± 2 B 41 ± 4 AB

Degree of Conversion 5% 31 ± 2 C 34 ± 2 C 38 ± 3 B 39 ± 2 B

10% 29 ± 3 CD 32 ± 2 C 31 ± 1 C 39 ± 3 B

25% 28 ± 2 D 27 ± 3 D 29 ± 3 CD 33 ± 1 C

Means followed by different letters differ from each other by Tukey Test (p≤0.05).

4. Discussion The diffractograms of the resins with both clays (Figure 3) revealed the absence of exfoliation in groups containing 5%, 10% and 25% of these fillers. In the group with 2.5%, there was no peak d (001). This can be interpreted as reflecting an increase in the interlayer spacing to over 44 Å, being beyond the detection limit of the equipment. In this case, the system can be intercalated or exfoliated, requiring another technique to evaluate its configuration.

The dispersion of silicas can not be determined by XRD analysis becase these fillers have spherical shape, because of these the silicas dispersion was determined by NMR analysis. Based on the XRD results, it can be determined that the increase in clay loading led to a decrease in the dispersibility of these fillers, this behavior has been reported in previous studies[16,17]. This lower dispersion of clay is the cause of the increase in viscosity of these nanofillers, rather than their bare increase of loading. Another possibility relates to the increase of the number of particles in the system that generates a physical impediment to their dispersion, since there is limited space for a greater possibility of reunion and consequent agglomeration of these particles in more concentrated systems[16,17].

The change observed in the groups with nanoclays is due to the type of distribution of these particles in the system. The increased temperature required for weight loss in the groups with lower clay loadings indicates that this system is exfoliated, corroborating the diffraction results.

Similar studies have shown that this behavior results when these fillers are exfoliated. This fact can be attributed to the ability of layered structures to reduce the flow of gases within the material, and in this way, the heat flow[18,19]. In the other groups, in turn, there was a reduction in the mass loss temperature, which probably occurred because of the degradation of organic modifier present in these minerals, something that occurs when these fillers are agglomerated in a polymer system[20,21].

Thus, the LF-NMR analysis is in agreement with the results obtained by XRD, since the relaxation times also 4/6

show a possible exfoliated profile in mixtures containing 2.5% clay and the absence this at other loadings of these fillers. Similarly, the XRD showed that with loadings of 5% and 10%, secondary peaks appeared at angles smaller than the basal peaks. This finding, combined with the relaxation time reduction, confirms the presence of part of these fillers in the intercalated topology.

The reduction of relaxation times in the exfoliated configuration occurs because the clays used in the experiment were members of groups of montmorillonites characterized by high iron loadings. This compound causes a resonance effect, called a paramagnetic effect, which causes a change of the magnetic field reducing the relaxation periods of hydrogen nuclei of the polymer chains around the particles.

Thus, exfoliated systems, because of their better dispersion, have more polymer chains under the influence of the paramagnetic effect. This causes a decrease in relaxation time, which is observed by LF-NMR[22,23].

The explanations of this phenomenon are based on the presence of polymer chains around the clay layers, which brings the hydrogen nuclei of the paramagnetic metals that make up the clay layers nearer together. These metals act as relaxation agents, causing a decrease in the T1H interval[22,23].

In silica groups, the interaction between fillers and matrix reduces the mobility of the chains[24]. Thus, a decrease in relaxation time can be expected. However, as previously noted, these fillers are agglomerated in the system. The cluster formation decreases the interaction between the nanoparticles and matrix, thus reducing the effect on relaxation time.

The results showed that addition of nanoparticles lead to reduction of DC for the evaluated systems. This behavior has been previously reported in other studies with different nanoparticles. The reduction of polymerization conversion in these cases stems from the increase in viscosity of the system[25], which hinders the movement of its constituent during the polymerization, as well as, by the interaction of the nanoparticles with the light that can act as agents of the absorption and scattering of light, making the photoinitiation process less effective[26].

Polímeros, 29(2), e2019018, 2019

Obtaining and characterizing dental hybrid composites with clay or silica nanoparticles and boron-aluminum-silicate glass microparticles

Figure 3. XRD patterns of (a) composites with nanoclay Dellite 67G, (b) composites with nanoclay Viscogel B8.

5. Conclusions Based on the results, it can be concluded that: - The groups with organoclay loading of 2.5% produced exfoliated material, a fact proven by the findings of the XRD and LF- NMR techniques; - The clay fillers, when their loading was increased up to 5% and 10%, resulted into hybrid systems (partially exfoliated, partially agglomerated) and the groups with higher amounts of these fillers showed an agglomerated profile; - All the groups containing silicas (hydrophobic and hydrophilic), were agglomerated and shows a poor dispersion when compared to the clays; - The thermal resistance of the material was not affected by the fillers of Aerosil 200 and Aerosil R972, but improved when using 2.5% Dellite 67G and 2.5% Viscogel B8 and reduced with the addition of particles in the latter two groups of 5%, 10% and 25%; - As the nanoparticles are added in the systems there is a gradual reduction of the composite DC indicating that the presence of these damages the polymerization process of the dental resins.

6. Acknowledgements Authors thanks Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES, Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq and Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro - FAPERJ for financial support.

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22. Tavares, M. I. B., Nogueira, R. F., Gil, R. A. S., Preto, M., Silva, E. O., Silva, M. B. R., & Miguez, E. (2007). Polypropylene– clay nanocomposite structure probed by H NMR relaxometry.

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26. Carreno, N. L. V., Oliveira, T. C. S., Piva, E., Leal, F. B., Lima, G. S., Monks, M. D., Raubach, C. W., & Ogliari, F. A. (2012). YbF 3 / SiO 2 Fillers as Radiopacifiers in a Dental Adhesive Resin. Nano-Micro Letters, 4(3), 189-196. http:// dx.doi.org/10.1007/BF03353713.

Received: Feb. 22, 2016 Revised: May 31, 2017 Accepted: June 01, 2017

Polímeros, 29(2), e2019018, 2019

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.08917

Evaluation of degradation of furanic polyamides synthesized with different solvents Cláudia Moreira da Fontoura1, Vinicios Pistor1, Raquel Santos Mauler1*  Programa de Pós-graduação em Química – PPGQ, Instituto de Química – IQ, Universidade Federal do Rio Grande do Sul – UFRGS, Porto Alegre, RS, Brasil

1

*raquel.mauler@ufrgs.br

Abstract Aromatic polyamides have properties of industrial relevance. However, the industrial and technological advancement has followed the trend of sustainability by seeking renewable source materials. In this work, polyamides were synthetized using 2,5-furandicarboxylic acid with p-phenylene diamine, triphenyl phosphite and two solvents (NMP and DMAc).

To evaluate the influence of solvents on the reaction, a kinetic study of degradation was carried out by thermogravimetric analysis (TGA), X-ray diffraction (XRD) and viscometric analysis. The viscosity value was in the range 70-80 mL/g.

The TGA showed a higher thermal stability and activation energy for sample prepared with DMAc than the NMP. The XRD analysis showed that the PAFDMAc presents more defined crystalline forms due to its higher solvation capability.

The crystalline form can be correlated with the differences of Ea, because the crystalline orientation and the number of hydrogens bonds in sample PAFNMP may be lower than the structure attributed to PAFDMAc. Keywords: furanic polyamides, solvents, synthesis, kinetic degradation, crystallinity.

How to cite: Fontoura, C. M., Pistor, V., & Mauler, R. S. (2019). Evaluation of degradation of furanic polyamides synthesized with different solvents. Polímeros: Ciência e Tecnologia, 29(1), e20190019. https://doi.org/10.1590/0104-1428.08917

1. Introduction Aromatic polyamides are materials that exhibit an exceptionally rigid molecular structure characterized by high melting temperatures, low flammability, excellent tensile and impact strengths and differential thermal stability[1,2].

These properties are particularly manifested when all of the aromatic groups are linked in the para position[3].

Commercial aramids, mostly in the form of fibers, are used as reinforcement for thermal and ballistic protection[4].

With the foreseeable depletion of fossil resources, the rising price of raw materials, as well as environmental problems resulting from CO2 emissions, there is increasing interest in the development of technologies for the utilization of renewable biomass[5]. The main power source originates from vegetal biomass, such as cellulose, glucose and fructose, which can be converted to compounds derived from furan[6-8]. The 5-hydroxymethylfurfural (HMF) is one of the most promising furan derivatives for the chemical industry because it is a starting point in the production of other furan compounds used in industrial applications[9], such as 2,5-furandicarboxylic acid (FDCA). FDCA has great potential as a monomer in the synthesis of polyamides from direct polycondensation of the components in the presence of phosphorous-containing derivatives[10]. The direct polycondensation method produces the best results in terms of structural regularity, high molecular weight and high thermal stability[11,12].

According to Odian[13], during the polycondensation process, the solvents utilized can affect the polymerization

Polímeros, 29(2), e20190019, 2019

rates and the molecular weights as a result of preferential solvation of the reactants. Polar solvents enhance the rate of a polymerization because the transition state is more polar than the reactants. Therefore, the progress of a polymerization can be dramatically affected by specific interactions of a solvent with the functional groups of the reactants. The reactivity of a functional group can be altered by specific interactions with the solvent[13]. Results have shown that the best system for the polymerization of solvation have positive effects on the study of the kinetics of polyamide degradation. According to Gu et al.[14], the investigation of the kinetics and the mechanism of thermal degradation of new semi-aromatic polyamides containing a benzoxazole unit (BO6) must be fully understood for its successful use in manufacturing and elevated temperature applications. Thermogravimetric analysis (TGA) has been widely used to determine the kinetic parameters of the degradation process, such as activation energy (EA) using the Flynn-Wall-Ozawa (FWO) method[15,16]. The present study aims to evaluate the relationship between the thermal stability and the crystallinity of furanic polyamides synthesized with different solvents.

2. Materials Triphenyl phosphite (TPP) was purchased from Aldrich Co. Ltd. (Milwaukee, Wisconsin, US), 2,5-furandicarboxylic acid (FDCA) was purchased from Satachem Co. Ltd. (Minhang Shanghai, China) and dried under vacuum at

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

Fontoura, C. M., Pistor, V., & Mauler, R. S. 80 °C for 8 h, p-phenylene diamine (PPD) was purchased from Acros Organics (Geel, Belgium) and used without further purification. N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc) were purchased from Vetec Ltd. (Duque de Caxias, Rio de Janeiro, Brazil) and purified by distillation at reduced pressure. Lithium chloride was purchased from Vetec Ltd. (Duque de Caxias, Rio de Janeiro, Brazil) and dried under vacuum at 100 °C for 8 h.

The ethanol was purchased from Synth (Diadema, São Paulo, Brazil).

3.4 Thermogravimetric analysis The TGA analyses were performed on a Q50 (TA Instruments) under an atmosphere of N2 (40 mLmin-1) at different heating rates (5, 10, 20, and 40 °C.min-1). The mass used for the analyses was 10mg. These results were used to estimate the kinetic parameters of degradation. The apparent activation energy (EA) of degradation was determined using the Flynn‑Wall-Ozawa (FWO) method. The FWO is an isoconversional method and is described by the Equation 1. = ln β ln

3. Methods 3.1 Synthesis of furanic polyamide For the synthesis of furanic polyamide, 3.12 g (20 mmol) of FDCA, 2.16 g (20 mmol) of PPD and 1.2 g of LiCl were dissolved in 30.00 mL of NMP or DMAc. An aliquot of 12.00 mL (44 mmol) of TPP was pipetted into the solution to promote the condensation of the reaction. The reactants were mixed in a 250 mL glass reactor under mechanical stirring (300 rpm). The reaction was conducted under nitrogen to create an inert atmosphere and heated to 130 °C for 8 h. After 1 h, reduced pressure was applied to force the withdrawal of the water formed during the reaction[17].

After completion of the reaction, and the system returned to room temperature, the sample was poured into a beaker with ethanol for washing, forming a precipitate that was subsequently filtered under reduced pressure in a Buchner funnel coupled to a Kitasato flask. Finally, the sample was dried in a vacuum oven at 80 °C for 24 h. The conversion of the synthesized polyamides was approximately 90%. 1H NMR (300 MHz, DMSO-d6): δ (ppm) 10.55 (s, 1H - hydroxyl), 7.94 (s, 1H - amide), 7.85 (s, 1H - furane), 7.79 (s, 1H - furane), 7.71 (d, 1H - benzene), 7.66 (dd, 1H - benzene), 7.60 (d, 1H - benzene), 7.52-7.36 (m, 1H - benzene), 3.66 (s, 2H - amine).

3.2 Intrinsic viscosity The viscosities of polyamides were determined from solutions with concentration between 0.0005 and 0.003 g.mL-1 in sulfuric acid 98% at 30 ± 0.1 °C. The viscometer used was the Cannon-Fenske n° 520 20, capillary 1.01 mm.

The results were obtained by graphical extrapolation using the Huggins equation (ƞred. vs C).

3.3 X-ray diffraction X-ray diffractograms (XRD) were collected in powder form with monochromatic CuKa radiation (λ = 0.15418 nm) using a sample holder mounted on a Siemens D500. Intensities were measured in the range of 5° < 2θ < 50°, typically with scan steps of 0.05° and 2s step-1 (1.5min-1).

AEa E − 5.330 − 1.052 a RT g (α ( T ) ) R

(1)

Where g(α(T)) is a function of the degradation process, EA is the activation energy, R is the gas constant, A is the pre-exponential factor, β is the heating rate and T is the temperature. According to this method, the rate of reaction is dependent only of the temperature. Considering the temperature dependence, isolating the log β vs T for different heating rates a linear behavior can be observed and the EA can be obtained by the angular coefficient of the strain line[15,16,18].

The estimation of the EA values and the statistical error of the fits were determined according the ASTM E 1641–07 and ASTM E 698 – 05.

4. Results and Discussions 4.1 Polymer synthesis In the polycondensation of polyamides, the phosphite group is employed as a condensing agent, which is consumed over the course of the reaction because it is the main agent responsible for the conversion. For each mole of the amine group to react, one mole of the phosphite group[19] must be present. The addition of the inorganic salts increases both the solubility of the polymers in the average reaction and their viscosity, which consequently leads to higher yields and molecular weights of the polyamides. Scheme 1 illustrates the general reaction pathway for this synthesis.

During the polycondensation process, a polar aprotic solvent is added to solubilize the part of the non-polar chain, whereas inorganic salts, such as LiCl, are used to interact with the polar portion, increasing the solubility of the polymer in the solution and diminishing the strength of the interchain hydrogen bonds. Solvents that have been proven effective for this method are N-methylamides, particularly NMP and DMAc. The progress of the reaction was followed by the evolution of the polymer yield and the intrinsic viscosity in the determined reaction time.

The intrinsic viscosity can be attributed to the hydrodynamic volume by the interaction of hydrogen bonds associated with increased symmetry and efficient packing of the polymer chains[20]. The viscosities of PAFDMAc and PAFNMP were estimated at 74 and 77 mL/g, respectively. This is a

Scheme 1. Synthesis of polyamides using triphenyl phosphite (TPP).

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Polímeros, 29(2), e20190019, 2019

Evaluation of degradation of furanic polyamides synthesized with different solvents factor that is directly related to the molecular weight of the aromatic polyamides.

The solvents in this reaction were added in order to determine the best synthesis conditions. The choice of solvent is important because of the solubility of the polymer during the reaction favors the polycondensation.

From this evaluation, it is clear that the progress of the polymerization can be directly affected by specific interactions of the solvent with the functional groups of the reactants, ie, the reactivity of the functional group may be modified by the interaction with the solvent[13]. In order to understand the importance of solvation on the final result, a polymerization was carried out to study the degradation kinetics of furânicas polyamides in order to check the relationship between the thermal stability of microstructure and polyamides.

such as the isoconversional method of Flynn-Wall-Ozawa (FWO)[18]. Figure 3 shows the linear fit by the FWO method.

The range of linear fit is between α = 0.05 – 0.8. The linear fits are determined with a confidence interval of 95% and the correlation coefficients (r) were, for all fits, between 0.9985 – 0.1000. EA is obtained by the slope of the straight line of the fit (slope=EA/R) and the results are showed in Figure 4.

4.2 Degradation behavior Polyamides were characterized in relation to their thermal properties. These properties are directly associated with the intermolecular forces of the chains and the molecular weight of the polymer. Strong intermolecular interactions increase the thermal stability of the polyamide, facilitating packing of the polymer chains. The higher packaging causes high rigidity of the chains which prevent their mobility, hindering from obtaining a glass transition temperature and consequently determination of the degree of crystallinity due to its structural characteristics.

Figure 1 shows the thermogravimetric analysis. Three degradation stages were observed in the range of 50-100°C, 150-250°C and 300-600°C, respectively. The first range is associated with the solvent or water residues because of the higher concentration of hydrogen bond, e.g., among the amide and H2O groups. The second range of degradation may be correlated with the monomers that did not reacted, forming dimers and trimers. The third range of degradation is principally associated with the polymer backbone[21]. For the polyamide synthesized using NMP the percentage of polymer degraded in the third range was 33% and for the use of DMAc was 28% of weight. The residual mass was 60% and 33% to PAFDMAc and PAFNMP samples, respectively. The percentage of polymer maybe not correlated with the conversion of polymer in the synthesis because the thermogravimetric curves are a sum of physical and chemical phenomena, which occur randomly. However, the difference observed between the temperature ranges of the third degradation phenomena suggests that the solvents used cause differences in the microstructure of the polyamides, e.g., molecular packing. Moreover, the XRD analysis showed differences in the crystal formation. Just as Kevlar, the furanic polyamide does not present a precise melting point and because of this the temperature is higher and the degradation is difficulted by differences in the crystal formation.

Figure 2 illustrates the third range of degradation (300‑600°C) at 5, 10, 20 and 40 °Cmin-1. This range of degradation was selected to study because it represents the chain backbone. The progress of the degradation reaction (α) is determined only in this region and the α values between 0 - 1 correspond to this range degradation. The increase in the heating rate shifts the degradation to higher temperatures.

This linear shift allows application of the kinetic methods Polímeros, 29(2), e20190019, 2019

Figure 1. TGA analysis obtained for the PAF studied (β =10°C min-1).

Figure 2. TGA analysis obtained to the PAFDMAc sample at different heating rates.

Figure 3. FWO fits obtained to the PAFDMAc sample.

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Fontoura, C. M., Pistor, V., & Mauler, R. S. Through the temperature range of 300 – 600 °C used to determining EA were observed values between 178 – 238 kJmol-1 and 301 – 357 kJmol-1 for PAFNMP and PAFDMAc samples, respectively. For some PA studied, in the literature the EA shows values next to the obtained with NMP. For example, Herrera et al.[22] showed values of 162, 91 and 164 kJmol-1 to PA6, PA66 and PA612, respectively (values​​

in the range between 250-475 °C). Gu et al.[14] obtained a EA of 197 kJmol-1 for a semi-aromatic polyamide containing benzoxazole at ≈ 425°C and Amintowlieh et al.[23] obtained 201 kJmol-1 for a PA6 at 437 °C. These values are expected for non-aromatic PA and the variations among them are due to the variation of the crystalline degree and the concentration of amide groups per repetitive unit. Expected values ​​for an aromatic polyamide such as Kevlar are in the range 300 kJmol-1 and 200 kJmol-1 under dry nitrogen and air atmospheres, respectively[24]. The differences of EA may be due to the crystal orientation and the number of hydrogen bonds present in the microstructure of each polyamide, which could be less for use of NMP because more difficulty on its solvation effect.

4.3 Crystallinity characterization

Figure 4. Evolution of the EA in the third stage of degradation correlated with the backbone chains of the PAF.

Figure 5. X-ray diffraction diagram of the polymers.

The crystallinity of the aromatic polyamides, shown in Figure 5, can be evaluated by measurements of X-ray diffraction in the range of 2θ = 20 to 35°, showing, in most cases, two diffraction peaks attributed to crystallographic planes (200) and (110). These peaks are described as the carbonaceous interlayer[25]. The value of 2θ of the plane (200) is related to the distance between adjacent layers which interact primarily by van der Waals forces and to some extent by π-electron overlap. The value of 2θ at the crystal plane (110) is, however, related to the distance between adjacent polymer chains along the crystallographic (110), (110), (110) and (110) planes, which are characterized by an evident concentration of intermolecular interactions[26].

The PAF DMAc exhibits two diffraction peaks at 2θ ≈ 23° and 24° attributed to the (200) and (110) diffraction planes, respectively, indicating a semi crystalline form using solvent DMAc. The narrow diffraction peaks suggest a more ordered crystalline form. This XRD pattern indicates the presence of a semi crystalline state that formed during the polycondensation[27].

PAFNMP showed a broad halo at approximately 2θ ≈ 25°, indicating an amorphous polymer, which is most likely a result of the less organized structure caused by poor solvation. This amorphous form suggested by the wider diffraction peaks[28] could be explained by the decrease of intermolecular forces of the aromatic polyamides[29], promoting distortion of the polymer chain, hindering regular chain packing.

Figure 6 illustrates the probable structure of PAFNMP, suggesting less interaction between the layers compared

Figure 6. Draw illustrates of the lamellar orientation correlated with the polyamides with the different solvents.

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Polímeros, 29(2), e20190019, 2019

Evaluation of degradation of furanic polyamides synthesized with different solvents to the structure attributed to PAFDMAc. In this case, greater lamellar interaction is formed because of the larger number of hydrogen bonds. The behavior of these structures may also be related to the crystallinity of the polyamides as well as the XRD analyses presented.

PAFDMAc exhibits more defined crystalline forms because of the higher solvation power of DMAc[30]. The interaction forces between the polyamide chains also increase the interactions between the lamellae, facilitating the formation of hydrogen bonds between the carbonyl and amine groups, and the forces involved in aromatic stacking.

The reactivity of the functional group can be altered by specific interaction with the solvent. These results have shown that better solvating systems have an effect on the degradation of polyamides. Thus, the more defined crystalline forms suggest that the use of DMAc as solvent may be favorable because of its greater degree of freedom and its less steric hindrance compared to the NMP solvent, allowing a greater packaging of the polymer during the synthesis, as well as better thermal properties. The influence of the solvent is given by the dielectric constant of 38.85 for DMAc compared to 32.55 for NMP, facilitating the solvation of the system and subsequently increasing the crystal formation in the chain[31,32].

5. Conclusions Furanic polyamides were synthesized using 2,5-furandicarboxylic acid (FDCA) obtained by the oxidation of HMF (hydroxymethylfurfural) with p-phenylene diamine (PPD) and triphenyl phosphite (TPP). Two different solvents, NMP (N-methyl-2-pyrrolidone) and DMAc (N,N-dimethylacetamide), were employed to evaluate the solvation effect on the resulting microstructures and degradation characteristics. The TGA analysis showed higher thermal stability for the PAF synthesized with DMAc than NMP suggests that the solvents used cause differences in the microstructure of the polyamides. The activation energy was higher using DMAc corroborating the higher thermal stability. The XRD analysis showed higher ordered crystalline structure to the PAFDMAc than PAFNMP and this difference was attributed to the concentration of hydrogen bonds between layers. The more defined crystalline forms suggest that the use of DMAc as a solvent may be favorable because of its higher degree of freedom and lower steric hindrance compared to NMP, allowing for greater packing of the polymer during the synthesis.

6. Acknowledgements The authors gratefully acknowledged the Brazilian National Counsel of Technological and Scientific Development – CNPq and PRONEX/FAPERGS and Financing Agency for Studies and Projects (FINEP) and Braskem S.A. for the financial and technical support.

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8. Gopalakrishnan, P., Narayan-Sarathy, S., Ghosh, T., Mahajan, K., & Belgacem, M. N. (2014). Synthesis and characterization of bio-based furanic polyesters. Journal of Polymer Research, 21(1), 340. http://dx.doi.org/10.1007/s10965-013-0340-0.

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Thermal characterization of oil extracted from ethylene–propylene– diene terpolymer residues (EPDM-r). Thermochimica Acta, 510(1-2), 93-96. http://dx.doi.org/10.1016/j.tca.2010.06.028.

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Polyamide 6 – wheat straw composites: degradation kinetics.

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Preparation of Kevlar-derived carbon fibers and their anodic performances in Li secondary batteries. Carbon, 39(11), 16191625. http://dx.doi.org/10.1016/S0008-6223(00)00298-0.

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26. Shubha, M., Parimala, H. V., & Vijayan, K. (1991). Kevlar 49 fibres: correlation between tensile strength and X-ray diffraction peak position. Journal of Materials Science Letters, 10(23), 1377-1378. http://dx.doi.org/10.1007/BF00735683.

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New York: CRC Press.

Received: Sept. 26, 2017 Revised: Sept. 19, 2018 Accepted: Nov. 04, 2018

Polímeros, 29(2), e20190019, 2019

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.04118

Factorial design to obtain magnetized poly(ethyl acrylate‑co-divinylbenzene) Kelly Lúcia Nazareth Pinho de Aguiar1* , Kaio Alves Brayner Pereira1, Marcelo Sierpe Pedrosa1 and Márcia Angélica Fernandes e Silva Neves1 Instituto Federal de Educação, Ciência e Tecnologia do Rio de Janeiro – IFRJ, Nilópolis, RJ, Brasil

1

*kelly.pinhoo@gmail.com

Abstract Magnetized polymers are produced by incorporating magnetic particles in a polymeric matrix. This article describes the use of the suspension polymerization technique using ethyl acrylate and divinylbenzene as monomers, in the presence of heptane and/or toluene as diluent, initiated by free radicals. To produce the polymer, we first performed fractional factorial planning to help visualize the factors that could influence the results, to verify the action of different responses simultaneously. Five factors were evaluated that influence the production of the polymer and incorporation of iron in the matrix. Infrared spectroscopy, X-ray fluorescence, magnetic force testing and scanning electron microscopy were used to characterize the samples. The results indicated the positive influence of the quantity of the polymerization initiator on the yield of the process and the negative effect of the content of divinylbenzene on the incorporation of iron in the matrix and on the magnetic force.

Keywords: magnetized polymer, factorial design, suspension polymerization.

How to cite: Aguiar, K. L. N. P., Pereira, K. A. B., Pedrosa, M. S., & Neves, M. A. F. S. (2019). Factorial design to obtain magnetized poly(ethyl acrylate-co-divinylbenzene). Polímeros: Ciência e Tecnologia, 29(2), e2019020. https:// doi.org/10.1590/0104-1428.04118

1. Introduction Magnetized polymer spheres, also called magnetized resins, are obtained by incorporating magnetic particles in a polymeric resin. These resins have attracted strong interest in the field of research and development, due to their excellent potential for application in environmental remediation, to remove pollutants from affected sites.

After their functionalization, they can act by adsorbing a contaminant and then be removed by filtration or application of an external magnet[1].

These structures can be produced by various polymerization techniques. Suspension polymerization is the most common to generate magnetic spheres, due to the facility of separating the product from the reaction medium, the low level of impurities and the consistency of the spherical particles produced[2,3].

Because of the large number of factors that can influence the process of making polymers, and consequently the diverse characteristics of the resulting products, it is very important to plan the experiments to obtain the largest quantity of relevant data with the smallest number of reactions possible.

Among the types of experimental optimization, a multivariate method called factorial planning stands out, whereby it is possible to evaluate the responses of two or more variables simultaneously and determine which are most relevant[4,5].

The synthesis of magnetic microspheres using monomers such as methyl methacrylate crosslinked with divinylbenzene has been reported[6-9]. To date, no results of magnetized resins

Polímeros, 29(2), e2019020, 2019

have been found with the use of ethyl acrylate monomer and showing the influence of the experimental factors. This article describes the production of a magnetized form of the resin poly(ethyl acrylate-co-divinylbenzene) and evaluates the factors that influence the main characteristics of this polymer, by applying a factorial experimental design with five factors, to determine the more relevant experimental factors in the characteristics of the material for further optimization.

The structural characteristics were assessed by infrared spectroscopy, while the morphology was evaluated by scanning electron microscopy. The content of iron incorporated was detected by the X-ray fluorescence technique. Finally, the magnetic force was measured by a method developed by the Laboratory of Biopolymers and Sensors of the Institute of Macromolecules of Rio de Janeiro Federal University (LaBioS/IMA-UFRJ).

2. Materials and Methods for Preparation of Magnetized Poly(ethyl acrylate-co-divinylbenzene) 2.1 Materials Divinylbenzene (DVB) (Nitriflex S/A, Brazil) was washed with 5% aqueous sodium hydroxide to remove inhibitors.

Ethyl acrylate (Vetta Química LTDA, Brazil), benzoyl peroxide (BPO) (Vetec Química Fina LTDA, Brazil), toluene (TOL) (Vetec Química Fina LTDA, Brazil), heptane (HEP)

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

Aguiar, K. L. N. P., Pereira, K. A. B., Pedrosa, M. S., & Neves, M. A. F. S. (Vetec Química Fina LTDA, Brazil), glycerin (bidistilled glycerin, USP 99.5%, purchased from Audaz), poly(vinyl alcohol) (PVA) (Mowiol 18-88 from Sigma‑Aldrich, Brazil) and maghemite (particle size = 12 nm) were used as received.

2.2 Preparation of the magnetized poly(ethyl acrylate‑co-divinylbenzene) The magnetized poly(ethyl acrylate-co-divinylbenzene) was obtained by suspension polymerization, using a Syrris Atlas Sodium reactor with temperature control and overhead stirring. The continuous medium was composed of water or a mixture of water and glycerin (1:1 or 3:1), and the suspension agent was PVA, with variable concentrations as established in the experimental factorial design. This phase was kept under magnetic stirring at 70 °C until total dissolution of the suspension agent. The total volume of the continuous medium was four times that of the organic phase.

The organic phase was prepared in a round-bottom flask in the Atlas Sodium system by adding ethyl acrylate, DVB as crosslinker, varying the concentration from 20 to 40% by molar mass, and BPO as polymerization initiator, varying its concentration from 1% to 10% in relation to the total number of mols of the monomer. The diluent was TOL, HEP or a mixture of TOL:HEP in 1:1 proportion, while maghemite (5% by mass of the monomers) was used to incorporate iron in the polymeric matrix. The quantities used to prepare the organic phase were determined in the experimental factorial design, reported in Table 1, where the total amount of monomers employed was 0.1 mol. This phase was kept under stirring at 400 rpm and 50 °C for one hour, to improve the affinity of the maghemite with the organic phase and enable greater incorporation of iron in the polymer produced.

The aqueous phase was added to the round-bottom flask containing the organic phase and the temperature of the

system was increased to 70 °C while maintaining magnetic stirring of 400 rpm. The polymerization in suspension lasted 24 hours.

At the end of the process, the poly(ethyl acrylateco‑divinylbenzene) was removed from the flask and purified with water, ethanol and methanol.

2.3 Experimental factorial design Fractional factorial planning was carried out to ascertain the most important variables to maximize the yield, iron content and magnetic force of the poly(acrylate-co-divinylbenzene) obtained by the suspension polymerization in the presence of maghemite.

In this experimental design, the influence of five factors was evaluated, namely: percentages of poly(vinyl alcohol) (PVA), divinylbenzene (DVB), benzoyl peroxide (BPO), diluents and the composition of the continuous medium.

With these factors, the number of experiments was calculated according to Equation 1: Calculation of the number of experiments in the fractional design[10].

1 1 4 2n −= 25 −= 2= 16

(1)

For better reliability of the method, we used the central point condition in triplicate, for a total of 19 experiments.

The experimental conditions of each polymerization reaction are reported in Table 1. The factorial design described in this work was created by the Design-Ease10 software, to obtain the following response data: yield, iron content and magnetic force.

The fractional factorial design used in this work can confound some effects at a lower hierarchical level (confounding or aliasing), as shown in Table 2. Therefore, it was necessary to evaluate the primary effects to verify if

Table 1. Factorial design to produce poly(ethyl acrylate-co-divinylbenzene).

CODE R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 R16 R17 R18 R19

A = PVA (%) 0.5 5 0.5 0.5 5 0.5 5 5 0.5 5 5 2.75 5 0.5 0.5 0.5 5 2.75 2.75

B = DVB (%) 20 20 20 40 40 40 20 20 40 40 40 30 40 40 20 20 20 30 30

C = BPO (%) 1 1 10 1 10 1 10 1 10 1 1 5.5 10 10 10 1 10 5.5 5.5

D = HEP/TOL (%) 0/100 100/0 100/0 0/100 100/0 100/0 100/0 0/100 0/100 100/0 0/100 50/50 0/100 100/0 0/100 100/0 0/100 50/50 50/50

E = GLYC/Water (%) 50/50 50/50 50/50 0/100 50/50 50/50 0/100 0/100 50/50 0/100 50/50 25/75 0/100 0/100 0/100 0/100 50/50 25/75 25/75

PVA = Poly(vinyl alcohol); DVB = Divinylbenzene; BPO = Benzoyl peroxide; HEP/TOL = Heptane/Toluene; GLYC = Glycerin.

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Factorial design to obtain magnetized poly(ethyl acrylate-co-divinylbenzene) Table 2. Possible aliasing of the fractional factorial design.

Effects A B C D E AB AC AD AE BC BD BE CD CE DE

Aliasing effects* A B C D E AB + CDE AC + BDE AD + BCE AE + BCD BC + ADE BD + ACE BE + ACD CD + ABE CE + ABD DE + ABC

*Some parameters cannot be estimated independently.

any of these alone were significant, and then to ascertain the correct synergistic effect.

The application of a factorial design allows visualizing the positive and negative, primary and synergistic effects that influence the responses under analysis. To allow better visualization of these results, we used Pareto charts, where each factor is quantified according to its contribution to the problem and ranked in decreasing order of influence, to enable identification of the most important effects[10].

To evaluate the statistical significance of the results, we calculated the p-value, also called the descriptive level of p-level, which estimates the degree of the null hypothesis (Ho) for a model to be discarded[11,12]. It can thus be considered a reliability index of the model obtained. The p-value depends directly on a determined sample, supplying a measure of the strength of the results obtained by the test, in comparison with simple rejection or not of the null hypothesis. In statistics, this type of hypothesis generally states there is no relationship between two measured phenomena[13]. Technically speaking, the smaller the p-value of a determined result is, the stronger the evidence is against the null hypothesis, making the data obtained more reliable in indicating that the relationship is true between the parameters analyzed in the sample and the results representing the entire population[12]. In this framework, p-values lower than 0.01 are considered very reliable, while 0.01≤ p < 0.05 indicates moderate reliability, 0.05 ≤ p < 0.10 denotes weak reliability, and p ≥ 0.10 is considered not significant[5].

2.4 Characterization Fourier-transform infrared spectroscopy (FTIR) was used for structural analysis of the polymers, using a Nicolet iS5 spectroscope from Thermo Fisher Scientific, with potassium bromide (KBr) pellets, 32 scans per sample and 4 cm-1 resolution. Scanning electron microscopy was employed to study the morphological characteristics, using a Phenom ProX SEM with a magnetic particle sample holder, setting the acceleration voltage to 10 kV. A Rigaku REX CG energy dispersive X-ray fluorescence spectrometer was used to Polímeros, 29(2), e2019020, 2019

quantify the iron incorporated in the polymeric matrix.

Finally, the magnetic force was measured with an apparatus developed by the research group of the LaBioS/IMA-UFRJ, using a method to determine the magnetic force in function of the magnetic field generated in the sample. This system is composed of an electromagnet; a Teflon sample holder with volume of 1.76 cm3; a Shimadzu AY22 analytical balance; an ICEL PS4100 power source; a TLMP-HALL-02 Gaussmeter; and an ICEL MD-6450 ammeter[2].

3. Results and Discussion The polymers obtained from copolymerization of ethyl acrylate and divinylbenzene were characterized by FTIR. Since all the polymers produced presented the same spectrum only one of them is shown here, in Figure 1.

By reference against the bands characteristic of the infrared absorption of the groups present in the poly(ethyl acrylate-co-divinylbenzene), it was possible to analyze the bands depicted in Figure 1 and characterize the product obtained from the polymerization process. The band at 2977 cm-1 denotes the C-H axial deformation of aromatics, and is partly superimposed on the C-H axial deformation band of the aliphatics at 2932 cm-1 . The band at 1734 cm-1 can be attributed to the C=0 axial deformation of ester, while the bands at 1604 cm-1, 1473 cm-1 and 1448 cm-1 denote the C=C axial deformations of aromatic nuclei and the band at 1155 cm-1 is characteristic of the C–O axial deformation of ester[14].

Figure 2 presents the scanning electron microscopic images with 1000x magnification, where the bright white parts are the iron particles incorporated in the polymeric matrix.

The SEM images reveal the morphology of the magnetized resins, which did not exhibit a particular pattern. Some of the particles were spherical, others were fragmented and some were grouped in large agglomerates. These observations can be explained by the PVA content. It was verified that when a low PVA content is used, there is no suspension stability, forming brittle particles (Figure 2c). On the other hand, a high content of PVA provided the formation of agglomerate (Figure 2a and 2b). The center point of PVA content showed the best stabilization. These micrographs represent all the resins synthesized in this work.

The yields, iron content incorporated and magnetic force obtained from the polymerization reactions are reported in Table 3.

3.1 Yields The Pareto chart obtained from the data on the polymerization yield (Table 3) revealed the most important factors regarding the response to the parameters, as seen in Figure 3.

The most important factor for the yield from the polymerization of poly(ethyl acrylate-co-divinylbenzene) was the quantity of initiator used in the process. Since this effect was positive, we can conclude that the yield increased with higher concentration of BPO in the reaction medium. With large quantities of BPO, thermal decomposition generates large quantities of free radicals, which attack the monomer 3/8

Aguiar, K. L. N. P., Pereira, K. A. B., Pedrosa, M. S., & Neves, M. A. F. S.

Figure 1. FTIR spectrum of poly(ethyl acrylate-co-divinylbenzene).

Figure 2. (a) R10; (b) R11; (c) R16; (d) R18.

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Factorial design to obtain magnetized poly(ethyl acrylate-co-divinylbenzene) molecules, breaking the double bonds and starting the polymerization reaction. Therefore, the reaction is completed in less time due to the larger number of initiator species at the start of the polymerization process, thus increasing resin yield. As explained by Coutinho and Oliveira, the reaction kinetics shows that the polymerization speed is directly proportional to the concentration of monomers and the square root of the initiator concentration[15].

Figure 3 shows that the second leading factor for yield of the process is AD synergy, i.e., the association of the suspension agent (PVA) and the diluent (heptane), acting

Table 3. Yields, iron content incorporated and magnetic force obtained from the polymerization reactions.

Code

Yield

Iron Content

Magnetic

(%) 77.3 66.9 95.9 68.2 95.1 79.3 82.9 81.4 96.1 81.0 83.6 94.0 96.5 98.8 76.4 83.8 88.9 91.4 92.4

(% weight) 1.280 ± 0.000 0.916 ± 0.001 1.980 ± 0.000 0.165 ± 0.001 0.589 ± 0.001 0.560 ± 0.001 1.187 ± 0.006 1.117 ± 0.006 0.998 ± 0.003 0.392 ± 0.001 0.244 ± 0.001 1.903 ± 0.006 0.838 ± 0.001 1.600 ± 0.000 0.402 ± 0.002 1.987 ± 0.006 1.670 ± 0.000 1.210 ± 0.000 1.370 ± 0.000

Force (G/A) 18.01 18.99 22.50 4.35 12.74 5.06 11.02 20.28 15.89 14.99 12.66 15.42 14.52 2.55 4.83 12.14 16.39 10.07 16.33

R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 R16 R17 R18 R19 G/A = Gauss/Ampere.

negatively on the yield, but the primary effects A and D do not have significant influences, leading to the conclusion of confounding with the alias BCE, i.e., the synergy among the crosslinker DVB (B), the polymerization initiator BPO (C) and the addition of glycerin in the continuous medium (E), since the primary parameters B and C are highly significant.

The associated action of these three factors can be observed and better understood in Figure 4.

Figure 4 shows that the yield tends to rise with higher concentrations of BPO and DVB with the use of a continuous medium formed by 50% glycerin, revealing the synergistic effect of these three factors. In this situation, the polymerization reaction appears to start faster and the polymer formed seems to contain more crosslinks, so that glycerin molecules can be trapped in the crosslinks, increasing the mass of the poly(ethyl acrylate-co-divinylbenzene), and thus the yield of the suspension polymerization. However, this hypothesis requires additional analyses for confirmation.

The third most important factor for the yield is the concentration of DVB, with a positive effect for this response. This behavior can be explained by the increase of the crosslinks in the polymer chain, forming more resistant resins, making the particles more integral and avoiding loss of the polymer in the purification step.

The last factor with a significant contribution is the synergy between the BC factors, i.e., the cooperative action between the quantity of crosslinker (DVB) and the polymerization initiator (BPO), with a positive effect, Therefore, larger quantities of DVB and BPO also make the yield increase.

The contribution generated by each factor expressed as a percentage was also estimated. Only the factors C, BCE, B and BC made significant contributions, respectively of 43.95%, 15.27%, 7.51% and 5.82%. These parameters with strong influence on the results obtained have a good level of significance, with C and BCE being very reliable, B reliable, and BC relatively less reliable (Table 4).

Figure 3. Pareto chart of yield data.

Figure 4. 3D surface for the influence of the alias BCE (Divinylbenzene, Benzoyl peroxide and Glycerin) on the yield of poly(ethyl acrylate-co-divinylbenzene).

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Aguiar, K. L. N. P., Pereira, K. A. B., Pedrosa, M. S., & Neves, M. A. F. S. Table 4. Percentage of contribution of the effects that influence the polymerization yield.

Factor A - % PVA B - %DVB C - %BPO D -%Heptane E - %Glycerin AB AC AD (alias BCE) AE BC BD BE CD CE DE

Effect 0.062 5.64 13.64 1.91 1.76 3.39 -1.01 -8.04 -3.59 4.96 0.54 0.64 1.79 3.59 -4.09

% Contribution 9.232E-004 7.51 43.95 0.86 0.73 2.71 0.24 15.27 3.04 5.82 0.068 0.096 0.76 3.04 3.95

P-value* 0.0371 0.0001 0.1821 0.0062 0.1596 0.0610 0.1596 0.1137

*P-value = P-value is considered a reliability index of the model obtained, thus p-values lower than 0.01 are considered very reliable, while 0.01 ≤ p < 0.05 indicates moderate reliability, 0.05 ≤ p < 0.10 denotes weak reliability and p ≥ 0.10 is considered not significant; PVA = Poly(vinyl alcohol); DVB = Divinylbenzene; BPO = Benzoyl peroxide; BCE = synergy among Divinylbenzene (B), Benzoyl peroxide (C) and Glycerin (E).

3.2 Iron content in the magnetized resins X-ray fluorescence was used to evaluate this parameter, where each sample was analyzed in triplicate, to obtain the mean of the three values, expressed as a percentage by weight. The results are reported in Table 3.

For this response, the effect with the greatest influence on the iron incorporation in the polymer matrix is factor B, i.e., the concentration of divinylbenzene used in the polymerization. This effect is negative, so the level of iron in the magnetized poly(ethyl acrylate-co-divinylbenzene) increased with lower concentration of DVB in the reaction medium. This indicates that greater crosslinking of the polymer tends to reduce the incorporation of iron in the matrix (Figure 5).

The second most important factor is the synergy of the AD factors, i.e., the associated action of the suspension agent (PVA) and heptane as diluent. This has a negative effect, so the content of iron in the matrix increases with decreasing quantity of PVA and substitution of heptane by toluene for the polymerization.

Figure 5. Pareto chart of the iron content incorporated in the poly(ethyl acrylate-co-divinylbenzene).

Table 5. Contribution percentages of the effects that influence the content of iron incorporated in the resins.

Factor A - %PVA B - %DVB C - %BPO D -%Heptane E - %Glycerin AB AC AD AE BC BD BE CD CE DE

Effect -0.25 -0.64 0.33 0.31 0.069 -0.063 0.078 -0.51 -0.097 0.34 -0.088 -0.22 0.050 0.23 -0.35

% Contribution 4.03 26.27 6.70 6.17 0.30 0.25 0.39 16.37 0.60 7.35 0.49 3.05 0.16 3.55 7.89

P-value* 0.2478 0.0171 0.1500 0.1645 0.7397 0.7048 0.0419 0.6390 0.1348 0.6706 0.3080 0.2804 0.1272

*P-value = P-value is considered a reliability index of the model obtained, thus p-values lower than 0.01 are considered very reliable, while 0.01≤ p < 0.05 indicates moderate reliability, 0.05 ≤ p < 0.10 denotes weak reliability and p ≥ 0.10 is considered not significant.

3.3 Magnetic force

It can be observed that the factor with the greatest influence on the magnetic force of this polymer is the quantity of divinylbenzene (B), with a negative effect, meaning that the magnetic force of the poly(ethyl acrylate‑co-divinylbenzene) increases with decrease of the DVB concentration used for the polymerization. This occurs because a larger quantity of the crosslinker increases the number of crosslinks, diminishing the incorporation of iron inside the polymer matrix, and hence its magnetic force.

The magnetic force values exerted by the poly(ethyl acrylate-co-divinylbenzene) when exposed to a magnetic field are presented in Table 3. From these results, we obtained the Pareto chart shown in the Figure 6.

The second most important factor for this parameter is the AE synergy, i.e., the associated action between the suspension agent PVA and the glycerin added in the continuous medium. This synergistic effect is negative regarding the

According to the p-value, only these two effects are significant, because the values are below 0.05. Table 5 reports the percentage contribution of each of the factors, with highlight on the factors B and AD with 26.27% and 16.37%, respectively.

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Polímeros, 29(2), e2019020, 2019

Factorial design to obtain magnetized poly(ethyl acrylate-co-divinylbenzene) Table 6. Contribution percentages of the effects that influence the magnetic force of the resins.

Factor A - %PVA B - %DVB C - %BPO D -%Heptane E - %Glycerin AB AC AD AE BC BD BE CD CE DE

Figure 6. Pareto chart of the magnetic force exerted by the magnetized poly(ethyl acrylate-co-divinylbenzene).

resin’s magnetic force, so a higher content of PVA as the aqueous phase containing glycerin causes a reduction of the magnetic force. When this situation occurs, the viscosity of the reaction medium increases considerably, since the PVA also acts as a thickener, probably exceeding the ideal value for good incorporation of iron, thus increasing the magnetic force.

However, when the factors PVA and continuous medium are not associated, they have important positive effects.

In this way, the third most relevant factor for the magnetic force is the content of glycerin in the aqueous phase.

This occurs because the viscosity of the reaction medium increases, facilitating incorporation of iron in the matrix, and consequently increasing the magnetic force, but without exceeding the ideal level. Factor A (PVA) appears in fourth place when the continuous medium is composed of water alone, which also raises the viscosity of the reaction medium and favors the increase of the magnetic force.

Another important factor is the CE synergy, i.e., the combined action of the polymerization initiator BPO (C) and the presence of glycerin (E) in the continuous medium, acting with a positive effect. Therefore, the magnetic force of the poly(ethyl acrylate-co-divinylbenzene) increases when it is produced with faster reactions and in a more viscous medium.

The factors B, AE, E, A and CE have the greatest contribution percentages for the magnetic force parameter, as reported in Table 6, at 16.16%, 13.34%, 13.30%, 12.39% and 9.44%, respectively.

The p-values indicate that the factors B, AE, E and A are highly significant, with chances of being correct of 98.0%, 96.95%, 96.92% and 96.44%. The synergistic factor CE has significance considered reasonable, with p-value above 0.050, meaning a 94.05% chance of being the real value, and also of being considered true for the results obtained in the magnetic force analyses.

Polímeros, 29(2), e2019020, 2019

Effect 4.53 -5.18 -0.76 -0.87 4.70 2.23 -2.31 -0.66 -4.70 2.92 -2.15 -2.21 0.16 3.95 -0.048

% Contribution 12.39 16.16 0.34 0.45 13.30 3.01 3.21 0.26 13.34 5.13 2.80 2.95 0.016 9.44 1.361E-003

P-value* 0.0356 0.0200 0.0308 0.2547 0.2402 0.0305 0.1466 0.2709 0.2592 0.0595 -

*P-value = P-value is considered a reliability index of the model obtained, thus p-values lower than 0.01 are considered very reliable, while 0.01≤ p < 0.05 indicates moderate reliability, 0.05 ≤ p < 0.10 denotes weak reliability and p ≥ 0.10 is considered not significant.

4. Conclusions The results show that the quantity of the polymerization initiator BPO is the most important factor for the yield of poly(ethyl acrylate-co-divinylbenzene), since it attained yield greater than 90% when the BPO concentrations were highest. The quantity of divinylbenzene presented a negative effect in relation to the magnetic force of the resins obtained, and was the main factor found in this work in relation to both responses. Therefore, it was possible to choose the best conditions to obtain magnetized resins with use of the factorial design developed, from the resin denoted as R3, i.e., 0.5% PVA, 20% DVB, 10% BPO, 100% heptane and 50% glycerin, due to the high yield, high iron content and strong magnetic force.

The experimental conditions of the reaction R3 can be used as reference to optimize the magnetization process of poly(ethyl acrylate-co-divinylbenzene) resin in terms of the most important factors.

5. Acknowledgements To IFRJ, Nilópolis Campus, and CNPq for financing.

6. References 1. Costa, R. C., & Souza, F. G., Jr. (2014). Preparo de nanocompósitos de maghemita e polianilina assistido por ultrassom. Polímeros: Ciência e Tecnologia, 24(2), 243-249. http://dx.doi.org/10.4322/ polimeros.2014.035.

2. Castanharo, J. A., Ferreira, I. L. M., Costa, M. A. S., Silva, M. R., Costa, G. M., & Oliveira, M. G. (2015). Microesferas magnéticas à base de poli(metacrilato de metila-co-divinilbenzeno) obtidas por polimerização em suspensão. Polímeros: Ciência e Tecnologia, 25(2), 192-199. http://dx.doi.org/10.1590/01041428.1666.

3. Mano, E. B., & Mendes, L. C. (1999). Introdução a polímeros.

São Paulo: Blucher.

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Aguiar, K. L. N. P., Pereira, K. A. B., Pedrosa, M. S., & Neves, M. A. F. S. 4. Cunico, M. W. M., Cunico, M. M., Miguel, O. G., Zawadzki, S. F., Peralta-Zamora, P., & Volpato, N. (2008). Planejamento fatorial: uma estatística valiosa para a definição de parâmetros experimentais empregados na pesquisa científica. Visão Acadêmica, 9(1), 23-32. http://dx.doi.org/10.5380/acd.v9i1.14635.

5. Pereira, E. R., Fo. (2015). Planejamento fatorial em química: maximizando a obtenção de resultados. São Carlos: EdUFSCar. 6. Costa, C. N., Costa, M. A. S., Maria, L. C. S., Silva, M. R., Souza, F. G., Jr., & Michel, R. (2012). Síntese e caracterização de copolímeros à base de metacrilato de metila e divinilbenzeno com propriedades magnéticas. Polímeros: Ciência e Tecnologia, 22(3), 260-266. http://dx.doi.org/10.1590/S0104-14282012005000042.

7. Tai, Y., Wang, L., Gao, J., Amer, W. A., Ding, W., & Yu, H. (2011). Synthesis of Fe3O4@poly(methylmethacrylate-codivinylbenzene) magnetic porous microspheres and their application in the separation of phenol from aqueous solutions.

Journal of Colloid and Interface Science, 360(2), 731-738. http://dx.doi.org/10.1016/j.jcis.2011.04.096. PMid:21601864.

8. Lan, F., Liu, K.-X., Jiang, W., Zeng, X.-B., Wu, Y., & Gu, Z.-W. (2011). Facile synthesis of monodisperse superparamagnetic Fe3O4/PMMA composite nanospheres with high magnetization.

Nanotechnology, 22(22), 225604. http://dx.doi.org/10.1088/09574484/22/22/225604. PMid:21454944.

9. Chen, M., Lin, Z., & Qian, H. (2008). Preparation of thiophilic paramagnetic adsorbent for separation of antibodies. Chinese Chemical Letters, 19(12), 1495-1498. http://dx.doi.org/10.1016/j. cclet.2008.09.050.

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10. Lins, B. F. E. (1993). Ferramentas básicas da qualidade. Ciência da Informação, 22(2), 181-185. http://dx.doi.org/10.18225/ ci.inf.v22i2.502.

11. Paes, A. T. (1998). Itens essenciais em bioestatística. Arquivos Brasileiros de Cardiologia, 71(4), 575-580. http://dx.doi. org/10.1590/S0066-782X1998001000003. PMid:10347932.

12. Reis, M. M. (2017). Conceitos elementares de estatística.

Florianópolis: Departamento de Informática e Estatística, Universidade Federal de Santa Catarina. Retrieved in 2017, July 11, from http://www.inf.ufsc.br/~marcelo.menezes.reis/ intro.html.0020 13. Arsham, H. (1988). Kuiper’s P-value as a measuring tool and decision procedure for the goodness-of-fit test.

Journal of Applied Statistics, 15(2), 131-135. http://dx.doi. org/10.1080/02664768800000020.

14. Silverstein, R. M., & Webster, F. X. (2000). Identificação espectrométrica de compostos orgânicos (6. ed.). Rio de Janeiro: Livros Técnicos e Científicos.

15. Coutinho, F. M. B., & Oliveira, C. M. F. (2006). Reações de polymerization em cadeia: mecanismo e cinética. Rio de Janeiro: Interciência.

Received: June 04, 2018 Revised: Sept. 13, 2018 Accepted: Dec. 10, 2018

Polímeros, 29(2), e2019020, 2019

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.10017

Presence of iron in polymers extruded with corrosive contaminants or abrasive fillers Marcos Fernado Franco1, Renan Gadioli1 and Marco Aurelio De Paoli1*  1

Laboratório de Processamento de Polímeros, Instituto de Química, Universidade Estadual de Campinas – UNICAMP, Campinas, SP, Brasil *madpaoli@unicamp.br

Abstract Off-site measurements of the dimensions of extruder screws are used to monitor their wear. This wear causes the presence of metals in the processed polymer. We detected the presence of iron in polymers processed with corrosive contaminants or abrasive fillers. To this end we processed poly(ethylene terephthalate), PET, pure or contaminated with poly(vinyl chloride), PVC, and other thermoplastics reinforced with glass fibers, talc or vegetal fibers, and analyzed the metals in the processed materials by X-ray fluorescence spectroscopy. We show that iron dispersed in the polymer melt is generated by corrosion from the PET contaminated with PVC and by erosion from abrasive fillers. The contents of iron in the extruded polymers clearly indicate equipment wear. This contaminant acts as a polymer pro-degradant, decreasing its lifetime. Additionally, we show that the lower concentration of iron for composites with vegetal fibers indicates a lower abrasion in comparison to talc and glass fibers.

Keywords: extrusion, fibers, fillers, iron contamination, talc.

How to cite: Franco, M. F., Gadioli, R., & De Paoli, M. A. (2019). Presence of iron in polymers extruded with corrosive contaminants or abrasive fillers. Polímeros: Ciência e Tecnologia, 29(2), e2019021. https://doi.org/10.1590/01041428.10017

1. Introduction Low-carbon steel is a raw material used for mixer rotors, extruder screws and barrels. For extruder screws, hardfacings welded to the tops of flights provide additional wear resistance[1]. The presence of harder materials (i.e., pigments, like TiO2, or fillers, like talc or short glass fibers) in the polymer formulation is the main cause of wear in these tools[2]. Erosion by chemical attack on the metal surfaces may also cause wear[3]. On a longer time scale, polymer formulations with less abrasive components, like vegetal fibers, also wear the equipment. Worn flights of conveying elements and worn tips of kneading elements reduce mixing efficiency. Increasing screw speed may compensate efficiency reduction but it accelerates wear. Measuring, controlling and replacing or repairing extruder screws or mixer rotors, after a certain degree of wear, is therefore routine in every polymer processing plant. However, to our knowledge, there are no reports on the final destination of the metals removed from the processing equipment. In all cases, iron is the metallic element predominantly removed from the tool. Since metals and their oxides are not volatile, this contaminant migrates towards the polymer melt, remaining in the bulk of the processed material during its entire life.

Among the various impurities that affect the degradation of polymeric materials, impurities containing transition metals often show the most pronounced effect[4].

Poly(ethylene terephthalate), PET, is processed by extrusion for recycling[5]. Prior to processing, it is separated and cleaned. However, due to the similarity in density with

Polímeros, 29(2), e2019021, 2019

poly(vinyl chloride), PVC, this contamination is frequently present. PVC undergoes thermal degradation at the processing temperature for PET recycling (240-280 °C), yielding hydrochloric acid, HCl[6,7]. This contamination causes the hydrolytic degradation of PET and may cause corrosion of the screws and barrel of the extruder[3]. The determination of iron in recycled PET can be useful to indicate the extent of previous contamination of the raw material with PVC. Metal contamination in polymers may lead to the pronounced acceleration of oxidation reactions. Goss et al.[8] demonstrated that catalyst residue, in concentrations between 0.2 and 4.1 g per 1000 kg, accelerates degradation in polypropylene, PP. Another study, involving different transition metals and polyethylenes (low, high density, linear and ultra-high molecular weight), ranks iron as the second most reactive metal for polyolefin oxidation[9]. Other authors reported that iron (III) decomposes the antioxidant additive in the oven aging of PP[10]. It was also demonstrated that iron-based oxygen scavengers affect the thermo‑mechanical degradation of PP in multiple extrusions[11]. For ABS, the chemically reactive comonomer is butadiene and the effect of Iron(III) chloride on the degradation of polybutadiene was reported[12]. Additionally, the catalytic activity of transition metal oxides, including iron oxide, towards oxidation reactions is well known[13]. Thus, tracking iron in processed polymers is important to assess machine wear, to estimate the extent of metal deactivators needed to compensate its prodegradant effect and to improve the lifetime of the processed polymer.

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

Franco, M. F., Gadioli, R., & De Paoli, M. A. The aim of this work is therefore to confirm the presence of iron in polymers processed in a mixer and a single screw extruder. First, by processing PET contaminated with PVC, simulating the effects of the thermo-mechanical PET recycling process. Second, by determining the iron concentrations in different thermoplastic polymers processed with abrasive fillers and comparing them to the pure materials.

HDPE, all in the pure form and reinforced with 20 or 30 wt.% of short glass fibers (SABIC, Campinas, Brazil) and PP, pure (Braskem, Triunfo) and reinforced with 20 wt.% of short glass fibers and 10 wt.% talc (Borealis, Itatiba, Brazil).

Composites reinforced with cellulose fibers were processed and obtained as described in previous works: PP [14], HDPE [15] and PA-6[16].

2.2 Processing

2. Materials and Methods

2.2.1 Internal mixer

2.1 Materials

We used, in the form of pellets, poly(acrylonitrile-cobutadiene-co-styrene), ABS, poly(butylene terephthalate), PBT, polyamide-6, PA-6, and high-density polyethylene,

The samples were processed in an internal mixer Haake Rheomix with counter-rotating rotors connected to a torque rheometer Haake Rheocord 90. They were prepared using a previously dried, fixed amount of 50.0 g of PET-btg.

In each experiment, PVC-btg was added to the mixing chamber in quantities ranging from 0.0 to 81.5 μg, with a 5.0 μg increase for each processing. The mixing conditions were 250 °C and 50 rpm for 5 min with closed and locked mixing chamber[17]. The concentrations were higher than those set for extrusion due to limitations of weighing lower quantities in the µg range. The results are presented for the four selected samples shown in Table 2.

Table 1. PET-btg specifications provided by the producer.

2.2.2 Extruder

Pellets of commercial virgin bottle-grade PET (PET-btg, Solvay, Poços de Caldas, Brazil), Table 1, and bottle-grade PVC (PVC-btg), from bottles purchased locally, were used.

Prior to processing, PET-btg pellets were dried in a vacuum oven at 160 °C and 27 kPa for 6 h and stored in a desiccator with silica under a vacuum. Chips from milled PVC bottles were mixed with PET-btg in the proportions indicated below.

Characteristic

Specification

Method

Unit

Intrinsic viscosity Density Residual Acetaldehyde Crystallinity (density) Chips Weight Humidity Melting Temperature Color: L

0.80 ± 0.03 > 1.39 <3 > 48 1.5 < 0.4 240 ± 5 79 ± 3

ASTM D 2857 ASTM D 1505 ASTM D 4526 PD-12021# PD-12029# PD-12012# ASTM D 3418 ASTM D 1925

dL g-1 g cm-3 ppm % g/100 Chips wt.% °C CIE

# Methodology used by the producer.

Table 2. PVC mass and concentration as a contaminant for samples processed in the internal mixer.

Samples M1 M2 M3 M4

PVC-btg mass (μg) 0.0 30.4 ± 0.2 52.5 ± 0.5 59.1 ± 0.4

PVC concentration (mg kg-1) 0.000 0.61 ± 0.02 1.05 ± 0.05 1.12 ± 0.04

Table 3. PVC-btg mass and concentration as a contaminant of 2.0 kg of PET-btg. Samples processed in the extruder.

Sample PVC-btg mass (μg) PVC-btg concentration (mg kg-1) E1 30.00 ± 0.04 0.015 ± 0.04 E2 70.00 ± 0.02 0.035 ± 0.02 E3 110.00 ± 0.03 0.055 ± 0.03 E4 120.00 ± 0.10 0.060 ± 0.01

PVC-btg was mixed as a contaminant to a previously dried, fixed amount of 2.0 kg of PET-btg, Table 3, and the samples were processed in the single screw extruder Wortex WEX30 (Campinas, Brazil), L/D = 30, D = 32 mm with five heating zones. A monofilament Maddock mixing screw was used at a rotation speed of 100 rpm[18]. The temperature profiles are presented in Table 4. The strands cooled in a water tank were cut in the form of pellets and dried for 4 h in an oven at 100 °C. The same extruder was used to reprocess ABS, PBT, PA-6, PP and HDPE reinforced with glass fibers or talc using a double filament screw with a mixing element at zone 3 and rotation speed of 50 rpm. The temperature profiles are presented in Table 4. All samples were reprocessed five times, with strand cutting and drying at each processing cycle.

2.3 X-ray fluorescence, XRF, analyses PET samples were analyzed in triplicate in a Shimadzu EDX 700 benchtop EDXRF X-ray analyzer, with an X-ray rhodium tube and a Si/Li semiconductor detector, and irradiated at ambient conditions for 500 s. Other conditions were: 25% Si/Li dead time, 10 mm-collimated beam, 50 kV voltage and 10 µA current applied to the Rh tube. The energy range was 0 to 40.96 keV, with a 0.02 keV resolution[19].

For the samples reinforced with glass fibers, cellulose fibers or talc, we cut sections of three regions of the processed

Table 4. Temperature profiles (°C) used for extrusion: numbers in the samples correspond to the concentration of glass fibers, GF, or talc, T. Z refers to the extruder heating zones.

Sample Z1-Rear Z2 Z3 Z4 Z5-Nozzle

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PET 220 260 275 280 280

PET/PVC 220 260 275 280 280

ABS20GF 210 230 250 280 270

PBT30GF 220 240 250 265 260

PA30GF 220 260 280 290 275

PE30GF 195 210 220 235 225

PP20GF10T 170 220 230 250 240

Polímeros, 29(2), e2019021, 2019

Presence of iron in polymers extruded with corrosive contaminants or abrasive fillers strand, pressed at 220 °C to produce films of 1.0 cm2. Films were also obtained in triplicate from pellets of the pure polymers. These films were quantitatively analyzed in a Shimadzu XRF1800 sequential analyzer.

3. Results and Discussions Processing in an extruder or an internal mixer implies high shear rates[20,21]. The removal of metal from the equipment to the resin through friction, shear and/or chemical attack by some degrading product generated during processing is likely to occur. Using XRF analysis and by comparing a processed with a non-processed sample, it is possible to demonstrate this metal migration from the processing equipment to the polymer sample[22].

3.1 PET contaminated with PVC Figure 1 shows a comparison of the XRF spectra of PET-btg samples, before, virgin PET, and after processing, M1, in the twin-rotor internal mixer. The presence of a signal in the iron region of the spectrum of the processed sample indicates migration of eroded iron from mixer (chamber or rotors) to the polymer melt. Other metals detected, e.g., cobalt, are catalyst residues from polymer production or from additives[23].

The XRF spectrum of PET-btg contaminated with PVC shows several metals, detected both in pure processed PET and in processed PVC-contaminated PET, as shown in Figure 2. The insert in Figure 2 shows that the concentration of iron increases proportionally to the concentration of the contaminant. In Figure 3, we compare the XRF spectrum of the non-processed PVC sample, used as a contaminant, and of the rotor of the internal mixer. Strong peaks between 16 and 26 keV, in Figures 1, 2, and 4, are related to C, H and O, present in large concentrations in the samples. The absence of metals in non-processed PVC and the coincidence of the metals present in the mixer rotor and in the processed and contaminated PET-btg samples, clearly shows that the metals detected came from the processing equipment. The increase in iron concentration as a function of PVC contamination also suggests that the hydrochloric acid produced in the thermo-mechanical degradation of the contaminant erodes the metal from the processing equipment.

The samples processed in the extruder present a similar behavior. Figure 4 shows the XRF spectra of these samples and the insert emphasizes the presence of metals and the relative increase in iron concentration as a function of PVC contamination. In Figure 4, it is possible to note that Mn is also extracted from the extruder screw or barrel, but was not present in the samples processed in the internal mixer.

Figure 1. XRF spectra for the virgin PET-btg and M1 sample processed in the internal mixer. The insert shows a magnification of the signals assigned to iron.

Figure 2. XRF spectra for non-processed virgin PET-btg, mixer processed pure PET-btg, M1, and for samples processed in the mixer with increasing concentrations of PVC contamination, M2-M4, see Table 4. The insert shows a magnification of the signals assigned to iron.

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Franco, M. F., Gadioli, R., & De Paoli, M. A. The sizes of the screw and barrel of the extruder precluded the measurement of their XRF spectra, to confirm the origin of this metal.

3.2 Polymers with fillers

Figure 3. XRF spectra of a rotor of the internal mixer, full line, and a commercial non-processed PVC sample, dotted line.

In Figure 5, we compare the concentration of iron in pure PBT and ABS with the same polymers reinforced with 30 and 20 wt.% of glass fibers, respectively. Samples marked P1 to P5 correspond to reinforced polymers reprocessed for one to five cycles, in a single screw extruder. Initially it is noteworthy that the glass fiber reinforced polymers exhibit a much higher concentration of iron, eroded from the extruder (screw of barrel) during its large-scale production in the processing plant, in comparison to the pure sample. This is clear evidence that the wear of the processing equipment disperse metals in the polymers. Figures 5a and b also show that PBT produced with 30 wt.% of glass fibers has twice the concentration of iron as ABS produced with 20 wt.% of the same filler, further confirming the abrasiveness of the glass fibers to the processing equipment. Figure 5 also shows that reprocessing these reinforced polymers for five

Figure 4. XRF spectra for PVC-contaminated PET samples processed in the extruder. Left insert: magnification of the spectral region for metals (6-8 keV). Right insert: magnification of the signals assigned to iron (6.2-6.6 keV) for samples E1-E4 (see Table 3).

Figure 5. Plots of the Fe content as a function of material: PURE = pure sample, P0, P1, P2, P3, P4 and P5 are the number of reprocessing times of the samples reinforced with glass fibers. (a) PBT pure and reinforced with 30 wt.% of glass fibers and (b) ABS pure and reinforced with 20 wt.% of glass fibers.

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Presence of iron in polymers extruded with corrosive contaminants or abrasive fillers

Figure 6. Plots of the Fe content as a function of material: CF = cellulose fiber, PURE = pure sample and P0, P1, P2, P3, P4 and P5 are the number of reprocessing cycles of the samples reinforced with the abrasive fillers. (a) PA-6 with 30 and 40 wt.% of CF, pure and with 30 wt.% of glass fibers; (b) HDPE with 30 and 40 wt.% of CF, pure and with 30 wt.% of glass fibers and (c) PP with 30 wt.% of CF, pure and with 20 wt.% of glass fibers and 10 wt.% of talc.

cycles, in a single screw extruder, does not significantly affect the concentration of iron in the product. The abrasive filler, dispersed in the polymer in the first extrusion, causes no further erosion in the recycling steps because it is coated with the polymer and has low contact with the processing machine parts.

In Figures 6a and b, we compare the concentration of iron in PA-6 and pure HDPE, reinforced with 30 wt.% of glass fibers or reinforced with cellulose fibers (30 and 40 wt.%).

Figure 6c compares the iron concentration in pure PP, reinforced with 30 wt.% of cellulose fibers and reinforced with 20 wt.% of glass fibers and 10 wt.% of talc. For these three polymers, we also observe an increase in iron concentration comparing the pure and the reinforced polymer. However, for PA-6 reinforced with glass fibers (P0 in Figure 6a) the relative concentration of iron is two times higher in comparison to HDPE and PP also reinforced with glass fibers (P0 in Figure 6b and 6c), probably due to the rheology of the polyamide, because they were prepared in the same equipment with the same screw design. For all polymers, the reinforcement with glass fibers or glass fibers and talc causes a significantly higher iron concentration Polímeros, 29(2), e2019021, 2019

in comparison to cellulose fibers. This lower iron content indirectly demonstrates that cellulose fibers are less abrasive to the processing equipment, which poses an additional advantage in using vegetal fibers in substitution to glass fibers on certain applications. Reprocessing of the glass fiber reinforced polymers for five cycles did not cause any significant variations in the iron content.

Atmospheric oxygen oxidizes metallic iron to produce oxides. However, we did not determine the type of iron oxide dispersed in the polymers. Previous work with talc-reinforced PP contaminated with iron oxide demonstrates that this impurity accelerates the polymer degradation reactions[24].

The iron detected in this work remains dispersed in the polymers during its use and may accelerate the polymer degradation reactions.

4. Conclusions We used X-ray fluorescence spectroscopy to demonstrate migration to the polymer melt of metals, with emphasis on iron, resulting from the wear of mixer rotors and extruder screws during melt processing of PET pure or contaminated 5/6

Franco, M. F., Gadioli, R., & De Paoli, M. A. with PVC. The iron concentration depends on the presence of the corrosive contaminant. We also demonstrated the presence of iron in other thermoplastics processed with abrasive reinforcing fillers like glass fibers, talc or vegetal fibers. The last being the less aggressive fillers.

Additionally, we propose the determination of the concentration of metals in extruded polymers as an easy and simple approach to follow equipment wear, thus avoiding disassembling screws and barrels for inspection and measurement off site.

5. Acknowledgements The authors thank Braskem (Triunfo, Brazil), SABIC (Campinas, Brazil) and Borealis (Itatiba, Brazil) for supplying the materials. We also thank Prof. Elias A.G. Zagatto for suggestions. Work financed by São Paulo Research Foundation, FAPESP (grant number 2010/17804‑7).

6. References 1. Griskey, R. G. (1995). Polymer process engineering: a modern approach (pp. 278-310). London: Chapman and Hall. http:// dx.doi.org/10.1007/978-94-011-0581-1_7.

2. Reifenhäuser Reiloy. (2015). Barrel and screw handbook (10th ed., pp. 35-36). Reiloy: Reifenhäuser Gruppe.

3. Reifenhäuser Reiloy. (2015). Barrel and screw handbook (10th ed., pp. 36-37). Reiloy: Reifenhäuser Gruppe.

4. Osawa, Z. (1988). Role of metals and metal-deactivators in polymer degradation. Polymer Degradation & Stability, 20(3-4), 203-236. http://dx.doi.org/10.1016/0141-3910(88)90070-5.

5. Assadi, R., Colin, X., & Verdu, J. (2004). Irreversible structural changes during PET recycling by extrusion. Polymer, 45(13), 4403-4412. http://dx.doi.org/10.1016/j.polymer.2004.04.029.

6. Awaja, F., & Pavel, D. (2005). Recycling of PET. European Polymer Journal, 41(7), 1453-1477. http://dx.doi.org/10.1016/j. eurpolymj.2005.02.005.

7. Hjertberg, T., & Sörvik, E. M. (1984). Thermal Degradation of PVC. In E. D. Owen (Ed.), Degradation and stabilization of PVC (pp. 21-80). Essex: Elsevier Applied Science Publishers. http://dx.doi.org/10.1007/978-94-009-5618-6_2.

8. Goss, B. G. S., Nakatani, H., George, G. A., & Terano, M. (2003). Catalyst residue effects on the heterogeneous oxidation of polypropylene. Polymer Degradation & Stability, 82(1), 119-126. http://dx.doi.org/10.1016/S0141-3910(03)00172-1.

9. Gorghiu, L. M., Jipa, S., Zaharescu, T., Setnescu, R., & Mihalcea, I. (2004). The effect of metals on thermal degradation of polyethylenes. Polymer Degradation & Stability, 84(1), 7-11. http://dx.doi.org/10.1016/S0141-3910(03)00265-9.

10. Chirinos-Padrón, A. J., Hernández, P. H., & Sufirez, F. A. (1988). Influence of metal ions on antioxidant behaviour in polypropylene. Polymer Degradation & Stability, 20(3-4), 237-255. http://dx.doi.org/10.1016/0141-3910(88)90071-7.

11. Lehner, M., Schlemmer, D., & Sängerlaub, S. (2015). Recycling of blends made of polypropylene and an iron-based oxygen scavenger - Influence of multiple extrusions on the polymer stability and the oxygen absorption capacity. Polymer Degradation & Stability, 122(12), 122-132. http://dx.doi.org/10.1016/j. polymdegradstab.2015.10.020.

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12. Dragunski, D. C., Freitas, A. R., Rubira, A. F., & Muniz, E. C. (2000). Influence of iron(III) chloride on the degradation of polyisoprene and polybutadiene. Polymer Degradation & Stability, 67(2), 239-247. http://dx.doi.org/10.1016/S01413910(99)00119-6.

13. Haber, F., & Weiss, J. (1932). Über die Katalyse des Hydroperoxydes. Naturwissenschaft, 20(51), 948-950. http:// dx.doi.org/10.1007/BF01504715.

14. Gadioli, R., Morais, J. A., Waldman, W. R., & De Paoli, M. A. (2014). The role of lignin in polypropylene composites with semi-bleached cellulose fibers: mechanical properties and its activity as antioxidant. Polymer Degradation & Stability, 108(10), 23-34. http://dx.doi.org/10.1016/j.polymdegradstab.2014.06.005.

15. Guilhen, A., Gadioli, R., Fernandes, F. C., Waldman, W. R., & Aurelio De Paoli, M. (2017). High density polyethylene biocomposites reinforced with cellulose fibers and using lignin as antioxidant. Journal of Applied Polymer Science, 134(35), 45219. http://dx.doi.org/10.1002/app.45219.

16. Fernandes, F. C., Gadioli, R., Yassitepe, E., & De Paoli, M.-A. (2017). Polyamide-6 composites reinforced with bleached or semi-bleached cellulose fibers and fabricated by extrusion.

Polymer Composites, 38(2), 299-308. http://dx.doi.org/10.1002/ pc.23587.

17. Romão, W., Franco, M. F., Iglesias, A. H., Sanvido, G. B., Maretto, D. A., Gozzo, F. C., Poppi, R. J., Eberlin, M. N., & De Paoli, M. A. (2010). Fingerprinting of bottle-grade poly(ethylene terephthalate) via matrix-assisted laser desorption/ionization mass spectrometry. Polymer Degradation & Stability, 95(4), 666671. http://dx.doi.org/10.1016/j.polymdegradstab.2009.11.046.

18. Spinacé, M. A. S., Lucato, M. U., Ferrão, M. F., Davanzo, C. U., & De Paoli, M. A. (2006). Determination of intrinsic viscosity of poly(ethylene terephthalate) using infrared spectroscopy and multivariate calibration method. Talanta, 69(3), 643-649. http:// dx.doi.org/10.1016/j.talanta.2005.10.035. PMid:18970616.

19. Romão, W., Franco, M. F., Bueno, M. I. M. S., Eberlin, M. N., & De Paoli, M. A. (2010). Analysing metals in bottlegrade poly(ethylene terephthalate) by X-ray fluorescence spectrometry. Journal of Applied Polymer Science, 117(5), 2993-3000. http://dx.doi.org/10.1002/app.32232.

20. Macosko, C. W. (1994). Rheology principles, measurements, and applications. New York: VCH Publishers.

21. Cruz, S. A., Farah, M., Zanin, M., & Bretas, R. E. S. (2008).

Evaluation of rheological properties of virgin HDPE/recycled HDPE blends. Polímeros: Ciência e Tecnologia, 18(2), 144151. http://dx.doi.org/10.1590/S0104-14282008000200012.

22. Ferg, E. E., & Rust, N. (2007). The effect of Pb and other elements found in recycled polypropylene on the manufacturing of lead-acid battery cases. Polymer Testing, 26(8), 1001-1014. http://dx.doi.org/10.1016/j.polymertesting.2007.07.001.

23. Pawlak, A., Pluta, M., Morawiec, J., Galeski, A., & Pracella, M. (2000). Characterization of scrap poly(ethylene terephthalate).

European Polymer Journal, 36(9), 1875-1884. http://dx.doi. org/10.1016/S0014-3057(99)00261-X. 24. Nakatani, H., Shibata, H., Miyazaki, K., Yonezawa, T., Takeda, H., Azuma, Y., & Watanabe, S. (2010). Studies on heterogeneous degradation of polypropylene/talc composite: effect of iron impurity on the degradation behavior. Journal of Applied Polymer Science, 115(1), 167-173. http://dx.doi. org/10.1002/app.31010.

Received: Oct. 19, 2017 Revised: Nov. 13, 2018 Accepted: Feb. 20, 2019

Polímeros, 29(2), e2019021, 2019

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.02518

Compatibility and characterization of Bio-PE/PCL blends Elieber Barros Bezerra1, Danyelle Campos de França1, Dayanne Diniz de Souza Morais1, Ingridy Dayane dos Santo Silva2, Danilo Diniz Siqueira1, Edcleide Maria Araújo1*  and Renate Maria Ramos Wellen2 Departamento de Engenharia de Materiais, Universidade Federal de Campina Grande – UFCG, Campina Grande, PB, Brasil 2 Departamento de Engenharia de Materiais, Universidade Federal da Paraíba – UFPB, João Pessoa, PB, Brasil

1

*edcleide.araujo@ufcg.edu.br

Abstract In this work, blends based on environmentally friend polymers such as Biopolyethylene (Bio-PE), Polycaprolactone (PCL) and Polyethylene graft maleic anhydride (PEgMA) added as compatibilizer agent were produced by conventional extrusion, aiming to produce bio-blends with synergic properties at low processing cost, being at same time non‑polluting and therefore contributing to the environment preservation. Differential scanning calorimetry (DSC) showed that blending does not significantly interfere on the melting and crystallization behaviors of neat polymers, suggesting being low miscibility compounds. Mechanical properties were observed changing with blend composition as the impact strength significantly increased reaching values higher than 130% when compared to neat Bio-PE. Scanning electron microscopy (SEM) images showed honeycomb morphology in Bio-PE/PCL blends, and the addition of PEgMA decreased the coalescence contributing to obtain more stable and synergic compounds. Bio-PE/PCL/PEgMA at 80/20/10 contents presented the best properties and may be used for packaging materials (food containers, film wrapping), and hygiene products.

Keywords: Bio-PE, PCL, thermal behavior, mechanical properties, morphology.

How to cite: Bezerra, E. B., França, D. C., Morais, D. D. S., Silva, I. D. S., Siqueira, D. D., Araújo, E. M., & Wellen, R. M. R. (2019). Compatibility and characterization of Bio-PE/PCL blends. Polímeros: Ciência e Tecnologia, 29(2), e2019022. https://doi.org/10.1590/0104-1428.02518

1. Introduction Currently petroleum-based polymer products are still dominant in the world market due to their excellent mechanical and thermal properties, as well as to their great versatility in several applications, providing an amount of approximately 300 million tons of plastic products produced by the end of this year. However, given the characteristic of nonbiodegradability and durability of some polymers as polyolefins, polyamides, polyesters and so on, a serious environmental problem follows the contemporary man with potential damage to nature, especially in the populous urban centers[1-4].

Therefore, the society has been asking the industrial sector for adopting “ecologically acceptable” policies, such as the rational use of natural resources, mainly in the production of materials for the productive sectors. Focused on this subject polymer scientists have suggested as an alternative to the use of polymers derived from fossil sources the production of biopolymers (polymers produced from renewable sources) and biodegradable (polymers able to naturally degrade in the environment) ones[5-7].

The use of biodegradable polymers appear as a possible and fast solution to reduce environmental pollution, they can be produced from renewable resources such as maize, sugar

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cane, cellulose and chitin, for instance, additionally they present shorter life cycle compared to the non-biodegradable ones (as polypropylene (PP), poly(ethylene terephthalate) (PET), nylons and so on) and when discarded they produce compounds not harmefull to the environment, as the case of poly(hydroxibutyrate) (PHB), PCL, poly(butylene adipate‑co‐terephthalate) (PBAT) for instance[7].

Additionally, the use of “green” polymers, such as biopolyethylene (Bio-PE), produced from ethanol (from sugarcane), although not biodegradable, maintains the neutral balance of carbon dioxide (CO2) in the natural environment. The CO2 captured from the atmosphere by the biomass, when later released to the atmosphere by the combustion, is captured again by the sugarcane trough the photosynthesis process in the next harvest[7-10].

Another alternative to this scenario would be the use of environmentally degradable polymers, which have the advantage of being stable over their useful life and being degraded in a short time after disposal in the environment; PCL is one of these polymers that has aroused interest in the substitution of conventional polymers since it is a fully biodegradable hydroxycarbonic acid based on polyester.

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

Bezerra, E. B., França, D. C., Morais, D. D. S., Silva, I. D. S., Siqueira, D. D., Araújo, E. M., & Wellen, R. M. R. Moreover, it has good properties and also compatibility with other materials[11-17].

Research in polymer blends involving these two classes of polymers appears as a viable alternative to the process of developing ecologically friend materials. In addition, studies of polymer blends are an alternative to obtain materials with properties that, in general, are not found in a neat resin[18,19].

Therefore, the objective of this work is to develop polymer blends based on environmentally friend polymers (Bio-PE and PCL) with different compositions; Bio-PE/PCL/PEgMA blends were also produced aiming the tenacification and compatibilization of Bio-PE upon addition of PEgMA, which has PE and MA segments,which are able to react with Bio-PE and PCL end groups. These blends were characterized by differential scanning calorimetry (DSC), heat deflection temperature (HDT), mechanical tensile and impact strength tests, scanning electron microscopy (SEM) and contact angle measurement.

2. Materials and Methods 2.1 Materials High Density Polyethylene (Bio-PE), I’m green SHC7260, Braskem. Polymer produced from sugarcane.

Minimum carbon content from renewable source of 94%.

Density 0.959 g/cm3, MIF = 7.2 g/10 min (190°C/2.16 kg).

Polycaprolactone (PCL), Capa 6500, MIF = 28 g/10min (160°C/2.16 kg) and elongation up to 800%, purchased from Perstorp Winning Formulas. Polyethylene grafted with 1.5‑1.7% Maleic Anhydride (PEgMA) Polybond 3029, purchased from Addivant. Density 0.95 g/cm3, MIF = 4.0 g/10min (190°C/2.16 kg) and melt temperature (Tm) = 130°C. These parameters were collected from the resin datasheets, which are inserted in Appendix 1 with HDPE, PCL and PE-gMA Datasheets, respectively.

2.2 Methods Polymer blending carried out in a modular, interpenetrating, twin screw extruder with L/D ratio of 40, model ZSK 18 mm, Werner-Pfleiderer, Coperion (Wesseling, Rhein-Erft-Kreis, Germany). Prior to extrusion, the raw materials were manually mixed to promote further homogenization. For all blends, the following extrusion parameters were used: feed rate of 5 kg/h; screw speed of 250 rpm; temperature profile in the extruder zones 200°C in all zones. The output material was granulated and oven dried under vacuum at 40°C for 24h.

The compositions of the extruded blends and their codes are shown in Table 1.

Figure 1 shows the screw used during the extrusion.

The screw configuration has mixing sections with dispersive and distributive elements. The main feed zone of premixed

materials is indicated in Figure 1 with the down arrow.

The upward-facing arrows are degassing points (vents).

After extrusion, injected specimens were molded according to ASTM standards D 638, D256 and D648, for tensile, impact and HDT experiments, respectively. An Arburg Injector, Model Allrounder 270C Golden Edition (Loßburg, Baden-Württemberg, Germany), was used, operating at 180°C, with mold at 20°C. Blends, neat Bio-PE and PCL were subjected to the same injection parameters. An average of 10 specimens was used for each investigated composition.

2.3 Characterizations 2.3.1 Differential Scanning Calorimetry (DSC) DSC analyzes were performed using a TA Instrument DSC-Q20 (New Castle, Delawere, EUA). The temperature program used was: heating from 20°C to 250°C, cooling to 10°C, reheating to 250°C, at a heating/cooling rate of 10°C/min, under inert environment with nitrogen flow of 50 mL/min. The samples tested weighed approximately 3.5 mg.

2.3.2 Heat Deflection Temperature (HDT) HDT was determined according to ASTM D 648, in a Ceast equipment (Norwood, Massachusetts, EUA), model HDT 6 VICAT/N 6921.000, with a tension of 455 kPa, heating rate of 120°C/h (method A). The temperature was determined after the sample deflecting 0.25 mm. Series of five injected samples were tested and the HDT, with its respective standard deviation, is reported.

2.3.3 Mechanical test The tensile tests were performed according to ASTM D 638. Properties as elastic modulus, tensile strength and elongation at break were measured. The tests were performed in a universal EMIC equipment (Curitiba, Paraná, Brazil), model DL10000, using a 100 kgf load cell, with deformation rate of 50 mm/min, operating at room temperature (~23°C).

The results presented are an average of 10 specimens tested.

Table 1. Compositions of Bio-PE, PCL, Bio-PE/PCL and Bio-PE/ PCL/PEgMA blends.

Compounds Bio-PE (%) Bio-PE 100 Bio-PE/PCL 90 Bio-PE/PCL/PEgMA 90 Bio-PE/PCL 80 Bio-PE/PCL/PEgMA 80 Bio-PE/PCL 70 Bio-PE/PCL/PEgMA 70 PCL -

PCL (%) 10 10 20 20 30 30 100

PEgMA (phr) 10 10 10 -

Figure 1. Schematic representation of the screw configuration used during the extrusion.

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Compatibility and characterization of Bio-PE/PCL blends 2.3.4 Mechanical impact strength test

3. Results and Discussions

The IZOD impact strength tests were performed on notched specimens, using a Resil 5.5 equipment from Ceast (Norwood, Massachusetts, EUA) and a pendulum of 2.75 J, according to ASTM D 256, at room temperature (~23oC).

The results reported were obtained from an average of 10 specimens.

3.1 Differential Scanning Calorimetry (DSC)

2.3.5 Scanning Electron Microscopy (SEM) SEM analyzes were obtained on the Tescan Vega 3 equipment (South Moravia, Brno, Czech Republic) with a voltage of 30 kV under high vacuum, images were captured on the fracture surface of the fractured impact specimen.

The fracture surfaces of the samples were gold-covered (Shimadzu Metallic-IC-50, using a current of 4mA for a period of 3 minutes) in order to avoid negative charge accumulation. The average diameters of dispersed phases were computed using the Tesca See 3 software.

2.3.6 Contact angle measurement The contact angle analysis to determine the hydrophilicity of the blends was performed by distilled water drop method through a Phoenix-i model of the Electro Optics - SEO Surface (Saneop-ro, Namwon, South Korea). This analysis was done on the surface of the injection molded specimens.

An analysis was performed from 20 photos, using an interval of 10 seconds, totaling 200s.

Understanding how the addition of PCL and PEgMA affect the morphology of Bio-PE is especially important because the resulting crystalline structure will influence the chemical as well as physical properties of the blends; to reach this aim DSC was employed, these scans are presented in Figure 2, and parameters determined from them are presented in Tables A1-A4 of Appendix 2 .

DSC scans of Figure 2 (Top) present the exothermic peaks relative to melt crystallization of Bio-PE and PCL. The addition of PCL slightly changed the crystallization of Bio-PE, which has a crystallization range between 106.04°C and 119.19°C; the exothermic crystallization peak of PCL in the blends was observed between 32.91 and 42.48°C. Bio-PE has a degree of crystallinity ΔXc ~ 14.50% and PCL between 4.75-8.65%; these data are in the literature range as published by Fel et al.[20] for (high density polyethylene) HDPE and by Antunes & Felisberti[21] for PCL. The crystallization rates and τ1/2 (time to reach 50% of crystallinity) of Bio‑PE and PCL were subtly modified in the blends, as shown in Figures A4 and A5. These behaviors suggest the low miscibility of Bio-PE/PCL system, with respective crystalline phases, i.e. Bio-PE and PCL, crystallizing as separate phases, nevertheless phase segregation was not verified as further on presented in SEM images (Figure 3) where Bio-PE is the matrix and PCL the dispersed phase, nevertheless

Figure 2. Top: DSC scans of Bio-PE, PCL, Bio-PE/PCL and Bio-PE/PCL/PEgMA compounds acquired during cooling. Bottom: DSC scans of Bio-PE, PCL, Bio-PE/PCL and Bio-PE/PCL/PEgMA compounds acquired during the second heating.

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Bezerra, E. B., França, D. C., Morais, D. D. S., Silva, I. D. S., Siqueira, D. D., Araújo, E. M., & Wellen, R. M. R. upon addition of PEgMA the particle sizes decreased as an indication of chemical interactions between Bio-PE/PCL and PEgMA, conducting to the blends compatibilization[22].

DSC scans acquired during the second heating are presented in Figure 2 (bottom), two endothermic peaks are

observed, in the lower temperature region 47.57-62.05°C and in higher temperatures 106.41-138.46°C, associate with the fusion of PCL and Bio-PE, respectively. Similarly to that observed during the melt crystallization, the melting behavior of Bio-PE was not altered in the blends, with the

Figure 3. SEM images of fractured surface of: Bio-PE (a, b); PCL (c, d); Bio-PE/PCL (90/10) (e, f); Bio-PE/PCL (80/20) (g, h); Bio-PE/PCL (70/30) (i, j); Bio-PE/PCL/PEgMA (90/10/10 phr) (k, l); PE/PCL/PEgMA (80/20/10 phr) (m, n); PE/PCL/PEgMA (70/30/10 phr) (o, p).

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Compatibility and characterization of Bio-PE/PCL blends degree of crystallinity ΔXc: 13.27-18.28%. The parameters computed from these scans are found in Tables A1-A4 and in Figures A6 and A7 of Appendix 2 and 3.

The Molten Fraction plots presented a sigmoidal shape characteristic of phase transformation in polymers without discontinuities, behavior similar to that observed during crystallization from the melt (Relative Crystallinity); these curves are presented in Appendix 3, Figures A8-A11.

The melting rates of PCL and Bio-PE increased in the blends with values between 30-50% higher than in the neat resins, which can be understood as a facilitated melting process, thus providing a processing with less energy consuming and possibly cheaper[23,24].

3.2 Heat Deflection Temperature (HDT) Table 2 shows HDT of Bio-PE, Bio-PE/PCL and Bio-PE/PCL/PEgMA blends. Addition of PCL to Bio-PE promoted a slight decrease in the HDT of Bio-PE/PCL blends, being a reduction of approximately 3.9% for Bio‑PE/PCL blend (90/10); 9.3% for 80/20 and 12.6% for 70/30 blend.

This decrease is most like due to the high flexibility, low melting temperature (≈ 60°C) and low glass transition (≈ -60°C) of PCL[25]. These results are in agreement with the data obtained by DSC. The addition of PEgMA to Bio-PE/PCL provided distinct results for the different concentrations of PCL. It is verified for Bio-PE/PCL/PEgMA (90/10/10 phr and 70/30/10 phr) a similar behavior to that presented by their respective binary blends. For the compound 80/20/10 phr, an increase in HDT compared to Bio-PE is observed, this increase being approximately 3.4%, results suggest in this concentration the effect of PEgMA is optimized in terms of higher heat deflexion temperature stability.

Table 2. Heat deflection temperature (HDT) of Bio-PE, PCL, Bio-PE/PCL and Bio-PE/PCL/PEgMA blends.

Composition Bio-PE Bio-PE/PCL (90/10) Bio-PE/PCL/PEgMA (90/10/10 phr) Bio-PE/PCL (80/20) Bio-PE/PCL/PEgMA (80/20/10 phr) Bio-PE/PCL (70/30) Bio-PE/PCL/PEgMA (70/30/10 phr) PCL

HDT (°C) 66.8±1.5 64.2±0.7 64.5±0.4 60.6±1.0 69.1±0.2 58.4±0.5 58.9±0.8 51.3±0.7

In general, the individual contribution of each component and the morphology generated by the phases in polymer blends are the most important characteristics concerned with its performance. Generally, the continuous phase provides greater contribution to the HDT of the blends, as also reported

by Ferreira et al.[26] and Luna et al.[27]. Subsequently, the morphology of blends will be examined by SEM, where these results can be better elucidated.

3.3 Mechanical tests – tensile strength Table 3 presents the results for Elastic Modulus, Tensile Strength and Elongation at Break of the investigated compounds in this work.

From the data shown in Table 3, it is possible to infer that Bio-PE and PCL have high elongation at break, that is, both are able of undergoing large deformations[28,29].

Analyzing the effect of PCL addition on Bio-PE/PCL blends, it was observed that increasing PCL content did not promote a significant change in the Elastic Modulus nor in the Tensile Strength data. In general, the stiffness of immiscible blends may be related with the competitive effect between the performance of the interface and the stiff polymer content that presents higher stiffness (modulus), as reported by Machado et al.[30], Rosa et al.[31], Moura et al.[32] and Silva[33]. In the present work, despite the fact the Bio-PE/PCL blends are immiscible, their mechanical behavior was not negatively affected, by the contrary, the Elastic Modulus of Bio-PE/PCL was observed being ~5% higher than neat Bio-PE, producing a synergic performance.

In relation to the addition of PEgMA, it did not result in higher changes in the Elastic Modulus with observed decreases between 8-15%, on the other hand, the Elongation at Break of Bio-PE/PCL/PEgMA blends showed increases higher than 70% in relation to Bio-PE/PCL blends. These results are linked to the morphological effect among the phases, despite the immiscible character (as observed by DSC scans Figure 2, SEM images Figure 3, Table A1-A4 and Figures A6-A7 of Appendix 2 and 3), in the amorphous phases of both polymers, secondary interactions are possible to occur, additionally PEgMA contributes to better mechanical performance. SEM images captured with the aim of a better enlightenment, and shown further on[30,33,34], suggest the Elongation at Break of Bio-PE/PCL blends, being the ternary systems with addition of the functionalized copolymer PEgMA improved (higher), which can be resulted from the reaction between maleic anhydride with the hydroxyl (OH)

Table 3. Tensile properties of Bio-PE, PCL, Bio-PE/PCL and Bio-PE/PCL/PEgMA blends.

Composition Bio-PE Bio-PE/PCL (90/10) Bio-PE/PCL/PEgMA (90/10/10 phr) Bio-PE/PCL (80/20) Bio-PE/PCL/PEgMA (80/20/10 phr) Bio-PE/PCL (70/30) Bio-PE/PCL/PEgMA (70/30/10 phr) PCL

Elastic modulus (MPa) 445.2±20.3 467.6±15.9 412.8±11.9 465.4±6.9 430.8±10.1 426.2±6.6 365.3±10.1 238.5±16.5

Tensile strength (MPa) 22.9±0.4 23.6±0.3 23.2±0.4 23.7±0.3 23.0±0.5 23.3±0.2 21.5±0.2 18.8 ± 0.3

Elongation at break (%) 531.3±26.6 252.5±20.6 425.9±34.6 Not determined* 475.1±15.4 13.8±0.9 Not determined* > 580**

*After cold drawing and neck propagation, the specimens showed formation of fibrils and the equipment was unable to record the rupture; **Specimen did not break during the test.

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Bezerra, E. B., França, D. C., Morais, D. D. S., Silva, I. D. S., Siqueira, D. D., Araújo, E. M., & Wellen, R. M. R. end groups of PCL that may be taken place providing an interface with higher performance, behaviors which can be inferred from decreases in dispersed phase as showed in Figure 3 and Table 4 by dispersed phase’s average diameter measurements[24,25,35-40].

3.4 Impact strength Table 5 shows the Impact Strength results of Bio‑PE, PCL, Bio-PE/PCL and Bio-PE/PCL/PEgMA blends.

It is verified that addition of 10% PCL did not promote a significant variation in the impact strength of Bio-PE. On the other hand, blends with 20% and 30% PCL showed higher impact strength with increases of 88.2% for Bio-PE/PCL (80/20) and 83.2% for Bio-PE/PCL (70/30). This increase may be related to the PCL effect that presents elastomeric characteristics, being able to act as a properly impact modifier, thus promoting a significant improvement in the energy absorption mechanisms of the produced blends in this work[33,38,41]. The addition of PEgMA also contributed to increase the impact strength, where increases of 133.2% for Bio-PE/PCL/PEgMA (80/20/10 phr) and 100.3% for Bio-PE/PCL/PEgMA (70/30/10 phr) were reached. This behavior can be attributed to the higher amount of linkages between Bio-PE/PCL phases promoted by the reaction trough maleic anhydride and hydroxyl groups of PCL, as well as the compatibility of PEgMA with Bio-PE, which efficiently drives the tension transfer mechanisms between the phases (Bio-PE matrix and PCL dispersed phase, see SEM images)[24,33,38].

3.5 Scanning Electron Microscopy (SEM) Figure 3 presents SEM images of Bio-PE, PCL and Bio-PE/PCL and Bio-PE/PCL/PEgMA blends, these images were captured on the fractured surface of the specimens after impact experiments.

In Figure 3a-d is observed the surfaces of Bio-PE and PCL with characteristics of ductile fracture evidencing the elastic deformation followed by the plastic one, these images corroborate the previous results obtained with mechanical Table 4. Average diameter for the dispersed phase of Bio-PE/PCL blends.

Composition Bio-PE/PCL (90/10) Bio-PE/PCL (80/20) Bio-PE/PCL (70/30)

Average Diameter (µm) 1.2±0.1 2.0±0.1 2.8±0.2

Table 5. Impact Strength of Bio-PE, PCL, Bio-PE/PCL and Bio‑PE/PCL/PEgMA blends.

Composition Bio-PE Bio-PE/PCL (90/10) Bio-PE/PCL/PEgMA (90/10/10 phr) Bio-PE/PCL (80/20) Bio-PE/PCL/PEgMA (80/20/10 phr) Bio-PE/PCL (70/30) Bio-PE/PCL/PEgMA (70/30/10 phr) PCL

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Impact strength (J/m) 34.0±1.0 36.5±3.1 36.0±1.9 64.0±2.9 79.3±2.8 62.3±3.8 68.1±5.0 178.5±4.4

tests where deformations higher than 500% were reached for the neat polymers.

SEM images of 90/10, 80/20 and 70/30 Bio-PE/PCL blends, respectively, are shown in Figure 3e-j. These SEMs present a honeycomb morphology[42], and suggest low interfacial adhesion.

The increase of PCL content into Bio-PE/PCL blends conducted to an increase in the mean diameter of the dispersed phase, (see results in Table 4), leading to the coalescence between PCL domains, which are indicated by the red arrows in Figure 3. In addition, a larger number of PCL domains in Bio-PE/PCL 70/30 were pull out from Bio-PE matrix[43,44], these results agree with those shown in the DSC analyzes and with mechanical properties, where low miscibility was observed.

The effect of PEgMA on the phase behavior of Bio‑PE/PCL blends is also shown in Figure 3k-p.

For Bio‑PE/PCL/PEgMA 90/10/10 and 80/20/10 blends is verified a very similar morphology to that of Bio-PE. These images show a homogeneous morphology, and it is difficult to make distinction between the dispersed PCL phase from the Bio-PE matrix. This effect may occur due to the interaction and ability of the compatibillizer (PEgMA) to remain at the interface, promoting a reduction of the interfacial energy and avoiding the domain coalescence, this would be the driving force for the improvement in the impact strength as well as for the increase in the elongation at break as previously presented in mechanical results[45,46].

For the Bio-PE/PCL/PEgMa 70/30/10 blend, Figure 3o, p is observed a morphology similar to that of Bio-PE/PCL 70/30 blend. However, a smaller amount of domains are verified on the fracture surface in relation to the binary blend. At this concentration, the compatibillizer was shown to be less effective compared to the compositions Bio-PE/PCL/PEgMA 90/10/10 and 80/20/10. As also presented in Table 4 the dispersed phase’s average dimater increases with PCL content in binary blends and decreases upon addition of PEgMA, trend observed for Bio-PE/PCL 90/10/10 and 80/20/10, for the blend 70/30/10 the trend change and coalescence increases, suggesting solubility limit barrier was reached.

Summing up, the incorporation of PEgMA provided a better adhesion between the phases, contributing to the homogeneity of the blends in relation to the non-compatibillized ones, i.e., PEgMA led to the morphology stabilization of the blends[32,44,46,47]. It is suggested the addition of PEgMA increases interfacial adhesion due to the chemical interaction between the hydroxyl group of PCL and the maleic anhydride groups, as previously reported by Bezerra et al.[24].

3.6 Contact angle The contact angle measurement allows evaluating the hydrophilicity and hydrophobicity of the polymer blend surfaces, where this means the interaction energy between the surface and the used liquid. The collected data for the contact angle demonstrates the increased degree of blend surface interaction with water, indicating an increase in its hydrophilic character with the increase of PCL content, which is expected since PCL is the most hydrophilic polymer[48-50].

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Compatibility and characterization of Bio-PE/PCL blends

5. Acknowledgements The authors thank Addivant for the functionalized copolymers; Labmat (Laboratory of Materials Engineering/CCT/UFCG) for experiments, to MCTI/CNPq, CAPES/PNPD and CAPES, for the financial support.

6. References

Figure 4. Contact angle of Bio-PE, PCL, Bio-PE/PCL and Bio-PE/PCL/PEgMA blends.

Figure 4 shows the data of contact angle for Bio-PE, PCL, Bio-PE/PCL and Bio-PE/PCL/PEgMA blends, at different times, and Table A5 (Appendix 4) presents the average data with the standard deviation included. For the Bio-PE/PCL blends with 10% and 20% of PCL the contact angle is observed reducing 15.7% and 15%, respectively.

For Bio-PE/PCL blend (70/30) the contact angle increased 5.5% related to Bio-PE, as previously observed in Figure 3 and Table 4 at this composition coalescence of PCL dispersed particles took place decreasing the contact area of PCL phase and possibly providing a lower contact angle as presented in Figure 4.

For Bio-PE/PCL/PEgMA blends, i.e., 90/10/10 and 80/20/10, it was observed that addition of PEgMA promoted stabilization of the contact angle; meanwhile an increase of this parameter was verified for the composition 70/30/10.

As previously reported, this is probably due to the occurrence of reactions between the maleic anhydride group and hydroxyl groups of PCL, decreasing the disperse particle size and improving the the system compatilization[24].

4. Conclusions Processing of Bio-PE/PCL and Bio-PE/PCL/PEgMA blends does lightly interfere in the crystallization and melting events of neat polymers suggesting being mixtures with low miscibility. From HDT data reduced values were observed for the binary blends, meanwhile PEgMA provided subtle increase. Contact angle measurements indicate an increase in the blend’s hydrophilic character increasing PCL content.

Addition of PCL to Bio-PE reduced the elastic modulus, increased the elongation at break and impact strength, allowing a control of these properties by changing the blend composition. Impact Strength of compatibilized blends significantly increased when compared to neat Bio-PE being 113.2% higher for Bio-PE/PCL/PEgMA. Addition of PEgMA decreases the phase coalescence conducting to a more stable compounds as evidenced by SEM images.

Summing up Bio-PE/PCL/PEgMA (80/20/10) is thermally stable presenting better homogeneity with higher HDT and Impact strength.

Polímeros, 29(2), e2019022, 2019

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Received: Mar. 20, 2018 Revised: Jan. 06, 2019 Accepted: Feb. 20, 2019

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Bezerra, E. B., França, D. C., Morais, D. D. S., Silva, I. D. S., Siqueira, D. D., Araújo, E. M., & Wellen, R. M. R. Appendix 1. Datasheets.

Figure A1. Datasheets – HDPE.

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Figure A2. Datasheets – PCL.

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Bezerra, E. B., França, D. C., Morais, D. D. S., Silva, I. D. S., Siqueira, D. D., Araújo, E. M., & Wellen, R. M. R.

Figure A3. Datasheets – PEgMA.

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Compatibility and characterization of Bio-PE/PCL blends Appendix 2 . DSC Results - Tables.

Table A1. DSC data for Bio-PE collected during the cooling – Melt Crystallization Event.

Compounds (%) Bio-PE PCL Bio-PE/PCL (70/30) Bio-PE/PCL (80/20) Bio-PE/PCL (90/10) Bio-PE/PCL/PEgMA (70/30/10Pcr) Bio-PE/PCL/PEgMA (80/20/10Pcr) Bio-PE/PCL/PEgMA (90/10/10Pcr)

T0.1%

(°C) 119.19 119.70 119.46 119.38 119.35 119.39 119.36

T50%

First Peak–BioPE T99.9%

(°C) 115.31 116.66 115.91 116.07 116.13 116.59 116.03

(°C) 106.04 107.52 107.46 107.12 107.52 107.34 105.39

Tmp

cmax

t½

∆Hm

Xc

(°C) 115.37-116.90 116.03 116.15 116.42 116.84 116.49

(min−1) 1.7756 2.5037 2.1497 2.2896 2.3361 2.2740 1.7684

(min) 0.49 0.39 0.45 0.43 0.41 0.37 0.42

(J/g) 37.88 42.49 38.24 49.55 43.27 43.86 46.38

(%) 12.93 14.50 13.05 16.91 14.77 14.97 15.83

Table A2. DSC data for PCL collected during the cooling – Melt Crystallization Event.

Compounds (%) Bio-PE PCL Bio-PE/PCL (70/30) Bio-PE/PCL (80/20) Bio-PE/PCL (90/10) Bio-PE/PCL/PEgMA (70/30/10Pcr) Bio-PE/PCL/PEgMA (80/20/10Pcr) Bio-PE/PCL/PEgMA (90/10/10Pcr)

T0.1%

(°C) 34.42 42.48 43.79 42.61 44.42 45.17 44.80

Second Peak –PCL T50% T99.9% Tmp

(°C) 29.79 37.22 38.80 38.75 39.47 41.27 41.64

(°C) 23.79 32.91 34.48 35.18 34.16 37.24 38.47

(°C) 29.77 36.85 37.96 39.86 41.39 41.79

cmax

t½

∆Hm

Xc

(min−1) 2.1030 2.2325 1.8600 2.0444 1.6427 2.1896 2.5397

(min) 0.49 0.54 0.50 0.39 0.50 0.39 0.32

(J/g) 21.58 11.02 8.05 6.62 8.95 6.99 5.33

(%) 15.47 7.90 5.77 4.75 6.42 5.01 3.82

Table A3. DSC data for PCL collected during the second heating – Fusion Event.

Compounds (%) Bio-PE PCL Bio-PE/PCL (70/30) Bio-PE/PCL (80/20) Bio-PE/PCL (90/10) Bio-PE/PCL/PEgMA (70/30/10Pcr) Bio-PE/PCL/PEgMA (80/20/10Pcr) Bio-PE/PCL/PEgMA (90/10/10Pcr)

T0.1%

(°C) 46.57 47.87 48.32 51.75 46.36 48.63 51.14

T50%

(°C) 56.78 55.08 55.39 55.63 55.14 55.33 55.61

FirstPeak –PCL T99.9% (°C) 62.05 57.93 58.47 58.11 59.13 58.52 58.02

Tmp

cmax

t½

∆Hm

Xc

(°C) 57.19 55.65 56.05 56.03 56.02 56.19 56.26

(min−1) 1.7776 2.9497 2.6811 3.1103 2.4021 2.5409 2.8503

(min) 1.04 0.73 0.71 0.39 0.89 0.67 0.45

(J/g) 19.74 11.03 9.81 9.26 11.62 10.32 7.08

(%) 14.15 7.90 7.03 6.63 8.33 7.40 5.07

Table A4. DSC data for Bio-PE collected during the second heating – Fusion Event.

Compounds (%) Bio-PE PCL Bio-PE/PCL (70/30) Bio-PE/PCL (80/20) Bio-PE/PCL (90/10) Bio-PE/PCL/PEgMA (70/30/10Pcr) Bio-PE/PCL/PEgMA (80/20/10Pcr) Bio-PE/PCL/PEgMA (90/10/10Pcr)

Polímeros, 29(2), e2019022, 2019

T0.1%

(°C) 106.41 110.55 110.98 110.06 110.25 106.97 106.98

Second Peak –BioPE T50% T99.9% Tmp

(°C) 131.18 129.88 130.54 130.96 129.82 129.75 130.72

(°C) 138.46 135.55 136.80 137.04 135.87 136.01 137.58

(°C) 133.47 131.76 132.46 133.05 131.86 131.77 132.88

cmax

t½

∆Hm

Xc

(min−1) 1.0994 1.5131 1.2590 1.4486 1.4086 1.2183 1.0978

(min) 2.53 1.97 2.00 2.13 1.99 2.32 2.41

(J/g) 41.46 47.05 41.28 53.58 47.68 48.33 49.52

(%) 14.15 16.06 14.09 18.29 16.27 16.50 16.90

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Bezerra, E. B., França, D. C., Morais, D. D. S., Silva, I. D. S., Siqueira, D. D., Araújo, E. M., & Wellen, R. M. R. Appendix 3. DSC parameters Figures A4-A11.

Figure A4. Crystallization Rate of Bio-PE in the investigated compounds.

Figure A5. Crystallization Rate of PCL in the investigated compounds.

Figure A8. Relative Crystallinity of Bio-PE in the investigated compounds.

Figure A9. Relative Crystallinity of PCL in the investigated compounds.

Figure A6. Melting Rate of Bio-PE in the investigated compounds.

Figure A10. Molten Fraction of Bio-PE in the investigated compounds.

Figure A7. Melting Rate of PCL in the investigated compounds.

Figure A11. Molten Fraction of PCL in the investigated compounds.

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Polímeros, 29(2), e2019022, 2019

Compatibility and characterization of Bio-PE/PCL blends Appendix 4. Contact angle average data with the standard deviation.

Table A5. Average contact angle with its respective standard deviation.

Composition Bio-PE (100) Bio-PE/PCL (90/10) Bio-PE/PCL (80/20) Bio-PE/PCL (70/30) Bio-PE/PCL/PEgMA (90/10/10) Bio-PE/PCL/PEgMA (80/20/10) Bio-PE/PCL/PEgMA (70/30/10) PCL (100)

Polímeros, 29(2), e2019022, 2019

Contact angle 71.5±0.7 60.3±0.7 60.7±1.1 75.3±1.9 68.8±1.2 69.8±0.8 77.8±2.0 61.2±1.1

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.03218

Thermal radical polymerization of Bis(methacrylamide)s Stéfani Becker Rodrigues1, Fabrício Mezzomo Collares1, Douglas Gamba2, Vicente Castelo Branco Leitune1 and Cesar Liberato Petzhold2*  Laboratório de Materiais Dentários, Faculdade de Odontologia, Universidade Federal do Rio Grande do Sul – UFRGS, Porto Alegre, RS, Brasil 2 Departamento de Química Orgânica, Instituto de Química, Universidade Federal do Rio Grande do Sul – UFRGS, Porto Alegre, RS, Brasil 1

*petzhold@iq.ufrgs.br

Abstract Methacrylamides monomers for dental applications were synthesized using a one-step procedure starting from methacrylic anhydride and the respective diamine: N,N’-(propane-1,3-diyl)-bis(N-ethyl-2-methylacrylamide) (1), N,N’(butane-1,4-diyl)-bis(2-methacrylamide) (2), N,N’-(octane-1,8-diyl-)bis(2-methylacrylamide) (3) and N,N’-(1,4-phenylene)bis(2-methylacrylamide) (4). The structures were confirmed by 1H NMR, 13C NMR, FTIR-ATR and UHPLC-QTOF-MS. Thermal polymerization kinetics was investigated by modulated DSC for monomers (2), (3) and (4) using heating rates of 1, 2, 3 and 5 °C min-1. All IR spectra showed the C=C axial deformation at 1610 cm-1, in 1H NMR spectra the olefinic hydrogens were observed at 5.3 an 5.8 ppm and in 13C NMR, the vinylic carbons at 120 and 140 ppm. The exact m/z values were: 267.2068, 225.1595, 281.2222 and 245.1283 for monomers (1), (2), (3) and (4), respectively. The activation energy was: -182.7; -165.8 and -156.7 kJ mol-1 for monomers (2), (3) and (4), respectively. Monomers are promising candidates for use as hydrolytic stable adhesive systems for dental applications.

Keywords: adhesives, monomers, kinetics, differential scanning calorimetry (DSC), synthesis.

How to cite: Rodrigues, S. B., Collares, F. M., Gamba, D., Leitune, V. C. B., & Petzhold, C. L. (2019). Thermal radical polymerization of Bis(methacrylamide)s. Polímeros: Ciência e Tecnologia, 29(2), e2019023. https://doi.org/10.1590/0104-1428.03218

1. Introduction Dental hard tissues (enamel and dentin) achieve a strong bond with restoratives polymers by means of dental adhesives. These dental adhesives are compounds of hydrophilic and hydrophobic monomers, photoinitiators and solvents[1]. Crosslinking dimethacrylates and acrylates are the most commonly monomers used in adhesives due to improvement of polymerization reactivity and material properties[2-4]. The long-term durability of adhesive/dentin interface depends on the functional monomers and polymer chain integrity[5,6]. However, the methacrylate monomers present low hydrolytic stability mainly in acid environments as in single-bottle adhesive[7-9].

In this respect, methacrylamides and acrylamides were synthesized due to the hydrolytic stable amide group instead of an ester group, and also to their similarity to the amino acids as collagen fibrils that could facilitate hydrogen bond between collagen and amide groups[9-15].

Bis(acrylamide)s and bis(methacrylamide)s have been synthesized via acryloyl chloride or methacryloyl chloride with diamines resulting sometimes in solid monomers, with a very low solubility in organic solvents and difficult purification[16-22]. In this context, suitable liquid bis-(acrylamide) s N,N’-diethyl‑1,3‑bis(acrylamido)propane (DEAAP), N,N’-dimethyl-1,3-bis(acrylamido)propane (DMAAP), and N,N’-dimethyl-1,6-bis(acrylamido)hexane (DMAAH) were

Polímeros, 29(2), e2019023, 2019

synthesized as substitute to methacrylates commonly used in adhesive systems such as TEGDMA (triethylene glycol dimethacrylate) or HEMA (2-hydroxyethyl methacrylate) and improving hydrolytic stability of dental adhesives[16,23,24].

Monomers with reactivity, obtained with good yields and synthesized by one-step synthetic route are important to development of simplified dental adhesives. Thus, the aim of this study is the synthesis of hydrolytically stable bis(methacrylamide) monomers for dental applications by one-step synthetic route and the investigation their kinetic thermal polymerization by DSC using Kissinger methodology[23].

2. Materials and Methods 2.1 Materials N,N′-diethyl-1,3-propanediamine, methacrylic anhydride and 4-(dimethylamino)pyridine were purchased from Sigma-Aldrich and used without any further purification.

1,8-diaminooctane, 1,4-diaminobutane and p-phenylenediamine were purchased from Alfa Aesar and also used without any further purification. Triethylamine and solvents as dichloromethane, tetrahydrofuran, hexane and ethyl acetate were purchased from local suppliers. Dichloromethane was dried by refluxing with calcium hydride and further

1/7

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

Rodrigues, S. B., Collares, F. M., Gamba, D., Leitune, V. C. B., & Petzhold, C. L. distillation under N2 atmosphere. Column chromatography was performed using Silica gel Si 70 – 230 Mesh (supplied

by Sigma Aldrich) as stationary phase.

2.2 Monomer synthesis Synthesis of N,N’-(propane-1,3-diyl)-bis(N-ethyl-2methylacrylamide) (1) To a solution of N,N′-diethyl-1,3-propanediamine (0.5 g; 3.84 mmol), triethylamine (1.5 eq.) and 4-(dimethylamino) pyridine (5 mol%) in 12 mL of anhydrous dichloromethane, a solution of methacrylic anhydride (1.5 eq.) in 12 mL of anhydrous dichloromethane was added dropwise in an ice bath. After 16 hours at room temperature, 6 mL of water was added and the solution was extracted with dichloromethane (3 x 5 mL). After drying the organic phase with anhydrous Na2SO4, the solvent was removed in rotatory evaporator.

The crude product was purified by column chromatography, eluting with hexane:ethyl acetate (70:30) to give monomer (1) as yellow viscous oil. Yield: 50 %. 1H NMR (400 MHz, CDCl3) δ (ppm): 5.10 (s, 2H); 5.01 (s, 2H), 3.51 – 3.25 (m, 8H); 1.97 (m, 6H); 1.85 (m, 2H); 1.15 (t, J = 7.1 Hz, 6H). 13C NMR (100 MHz, CDCl3) δ (ppm): 172.5 (2); 141.1 (2); 114.3 (2); 114.3 (2); 43.1 (2); 41.4 (2); 27.6 (2); 20.6 (2); 14.3 (2).

(2)

Synthesis of N,N’-(butane-1,4-diyl)-bis(2-methacrylamide)

A solution of methacrylic anhydride (2.1 eq.) of dry dichloromethane (10 mL) was added dropwise to a solution of 1,4-diaminobutane (0.510 g; 57.72 mmol) and triethylamine (2.1 eq.) in dry dichloromethane (30 mL) in an ice bath. After stirring 16 hours at room temperature, water (10 mL) was added to the reaction and the aqueous phase was extracted with dichloromethane (3 x 10 mL).

After drying the organic phase with anhydrous Na2SO4 the solvent was evaporated. The crude product was purified by precipitation in hexane to afford monomer (2) as a white solid. Yield: 61 %. 1H NMR (400 MHz, CDCl3) δ (ppm): 6.27 (s, 2H); 5.69 (s, 2H); 5.32 (s, 2H); 3.34 (q, J = 6.2 Hz, 4H); 1.96 (s, 6H); 1.60 (m, 4H). 13C NMR (100 MHz, CDCl3) δ (ppm): 168.7 (2); 140 (2); 119.4 (2); 39.2 (2); 26.9 (2); 18.7 (2). Mp: 127.4 °C. (3)

Synthesis of N,N’-(octane-1,8-diyl-)-bis(2-methylacrylamide)

A solution of methacrylic anhydride (2.5 eq.) in dry dichloromethane (10 mL) was added dropwise to a solution of 1,8-diaminooctane (0.510 g; 3.46 mmol) and triethylamine (3.5 eq.) in 30 mL of dry dichloromethane in an ice bath. After stirring 16 hours at room temperature, water (10 mL) was added to the reaction and the aqueous phase was extracted with dichloromethane (3 x 10 mL). After drying the organic phase in anhydrous Na2SO4 the solvent was removed in rotatory evaporator. The crude product was purified by precipitation in hexane to afford monomer (3) as a white solid. Yield: 48 %. 1H NMR (400 MHz, CDCl3) δ (ppm): 6.05 (s, 2H); 5.67 (s, 2H); 5.30 (s, 2H); 3.28 (q, J = 6.8 Hz, 4H); 1.96 (s, 6H); 1.53 (qt, J = 6.8 Hz, 4H); 1.32 (m, 8H).

13 C NMR (100 MHz, CDCl3) δ (ppm): 168.5 (2); 140.3 (2); 119.1 (2); 39.7 (2); 29.5 (2); 29.1 (2); 26.8 (2); 18.7 (2).

Mp: 109.2 °C. 2/7

(4)

Synthesis of N,N’-(1,4-phenylene)-bis(2-methylacrylamide)

To a solution of p-phenylenediamine (0.515 g; 4.62 mmol) and triethylamine (3.5 eq.) in 30 mL of anhydrous dichloromethane, was added dropwise a solution of methacrylic anhydride (3.5 eq.) in anhydrous dichloromethane (10 mL) in an ice bath for 30 minutes. After stirring 16 hours at room temperature, water (15 mL) was added and the solution was extracted with tetrahydrofuran (3 x 10 mL). The organic phase was dried under anhydrous Na2SO4 and the solvent was removed in rotatory evaporator. The crude product was purified by precipitation in hexane to afford the monomer (4) as a white solid. Yield: 31 %. 1H NMR (400 MHz, DMSO-d6) δ (ppm): 9.73 (s, 2H); 7.61 (s, 4H); 5.79 (s, 2H); 5.49 (s, 2H); 1.95 (s, 6H). 13C NMR (100 MHz, DMSO-d6) δ (ppm): 166.5 (2); 140.4 (2); 134.7 (2); 120.4 (4); 119.7 (2); 18.8 (2). Mp: 246.5 °C.

2.3 Monomer characterization 2.3.1 Nuclear Magnetic Resonance (NMR) NMR measurements were recorded on a Bio Spin GmbH (Bruker Biospin, Rheinstetten, Germany), 1H: 400 MHz, 13 C: 100 MHz, in CDCl3 using tetramethylsilane (TMS) as standard or DMSO-d6. The multiplicities were attributed as: s = singlet; d = doublet; t = triplet; q = quartet; qt = quintuplet; dd = double dublet; ddd = double double dublet e m= multiplet.

The hydrogen assignments were attributed based on relative integral and coupling constant (J) in Hertz (Hz).

2.3.2 Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) ATR-FTIR measurements were performed in the Bruker Alpha FTIR Spectrometer (Bruker Optics, Ettlingen, Germany). The monomers were dispensed over a diamond crystal of Attenuated Total Reflectance (ATR) accessory.

A total of 64 scans were collected from 400 cm-1 to 4000 cm-1 at 4 cm-1 resolution.

2.3.3 Ultra-High Liquid Chromatography Quadrupole Time of Flight Mass Spectrometry (UHPLC-QTOF-MS) High-resolution mass spectra were obtained with a Q-TOF Micro instrument (Impact II, Bruker,) in electrospray ionization positive (ES+) mode. A Q-TOF system was used to separate the analytes of interest. Shim-pack XR-ODS III column (50 mm X 2 mm X 1.6 µm) was used to separate the analytes in isocratic mode with the mobile phase 40 % acetonitrile (0.1 % formic acid): 60 % water (0.1 % formic acid) (LC, Nexera x2, Shimadzu, Tokyo, Japan). The flow rate was 0.4 mL min-1 and column temperature was 35 °C. The optimal MS parameters were as following: capillary voltage 4500 V, source temperature 200 °C, end plate offset voltage 500 V, mass range (m/z) of 60-800 and calibration with sodium formate.

2.3.4 Thermal polymerization kinetics The polymerization kinetics of monomers (2), (3) and (4) were investigated using modulated differential scanning calorimetry technique (MDSC, Q2000, TA Instruments).

Three samples were analyzed with temperature range of 0–300 °C using an aluminum pan, at different heating rates Polímeros, 29(2), e2019023, 2019

Thermal radical polymerization of Bis(methacrylamide)s (1, 2, 3 and 5 °C min−1), with 100 s of period, amplitude of ± 1.0 °C, under nitrogen atmosphere with flow rate of 50 mL min−1 and with sample weight about 2.0 mg.

The maximum temperature peak obtained from nonreverse curve was used to determine the activation energy of the polymerization according to Kissinger methodology[24].

3. Results and Discussions 3.1 Synthesis and characterization of monomers Bis(methacrylamide)s were prepared in one-step reaction between methacrylic anhydride and diamines as showed in Scheme 1.

Scheme 1. Bis(methacrylamide)s synthesis.

The following monomers were synthesized with yields higher than 30 %: N,N’-(propane-1,3-diyl) bis(N‑ethyl‑2-methylacrylamide) (1), N,N’-(butane‑1,4‑diyl) bis(2-methacrylamide) (2), N,N’-(octane-1,8-diyl) bis(2‑methylacrylamide) (3) and N,N’-(1,4 phenylene) bis(2‑methylacrylamide) (4). As expected, monomer (1) having an ethyl substituent at nitrogen atom (N,N‑dialkylamide) was liquid, while monomers (2), (3) and (4) were white solids.

The C=C double bond axial deformation of monomers was detectable in the IR spectrum at 1610 cm-1, while C=O stretching appeared at 1660 cm-1, N-H at 3300 cm-1 and C-N at 1520 cm-1, confirming the synthesis of monomers (Figure S1, Supplementary Material). The signals of olefinic hydrogens of the compounds were detected by 1 H NMR at 5.3 and 5.8 ppm, while the sp2-hybridized C-atoms of the acrylamide double bonds were observed at 120 and 140 ppm in the 13C NMR spectra. Complete assignments of the monomers structures were given in Figure S2 (Supplementary Material). The exact m/z value of each monomer was determined by UHPLC-QTOF-MS, and the structure confirmed by comparison with theoretical isotopic profile, Table 1 and Figure S3 (Supplementary Material). Error values lower than 1.2 ppm (corresponding to a 20 mDa) and mSigma values ranged from 3.4 to 17.2 for the synthesized monomers were obtained. According to the manufacturer the err value below 5 ppm and mSigma below 20 is considered acceptable results.

Table 1. Exact m/z value for the synthesized monomers.

Monomer (1)

m/z (g/mol) 267.2068

err (ppm) 0.2

(2)

225.1595

1.2

(3)

281.2222

0.6

(4)

245.1283

0.6

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Molecular Structure

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Rodrigues, S. B., Collares, F. M., Gamba, D., Leitune, V. C. B., & Petzhold, C. L. 3.2 Thermal polymerization of the monomers Differential scanning calorimetry (DSC) is the most used thermal analysis technique in material sciences because of its ability to provide detailed information about both the physical and energetic properties of a substance and/or formulation. However, conventional DSC was not used in this study due to shortcomings with respect to weak transitions and overlapping events, which could be solved by the use of the more sophisticated modulated DSC (mDSC). In Figure 1 is showed the reverse, nonreverse and total heat flow of monomer (2) at a heating rate of 5 °C min-1. Total heat flow presented an endothermic event (related to monomer melting) followed by an exothermic event corresponding to the thermal polymerization. Using modulated DSC both events could be well separated, allowing the determination of the melting peak in the reverse heat flow and the polymerization enthalpy in the nonreverse heat flow (Table 2).

Unexpectedly, no exothermic event corresponding to the thermal polymerization was observed in DSC for the monomer (1) N,N’-(propane-1,3-diyl)bis(N-ethyl-2-methylacrylamide) in the investigated temperature range. To verify the monomer photochemical polymerization 1 mol % of camphorquinone

(CQ) and 1 mol % of ethyl 4-dimethylaminobenzoate (EDAB) were added and was investigated by PhotoDSC[23] (see Supplementary Material for experimental conditions).

Even after 600 s of photopolymerization the polymerization not occurred. It is known from the literature that N-disubstituted methacrylamides show a very low reactivity in radical homopolymerization, which can be explained on the basis of steric effects of the substituents of the amide group[25].

This behavior was not observed neither for N,N-disubstituted bis(acrylamide) nor for N-substituted bis(methacrylamide) that were commonly used in hydrolytically stable dental adhesive formulations[16]. Monomers (2), (3) and (4) are N-substituted bis(methacrylamide) and polymerized by radical thermal auto initiation (Table 2).

Different chemical structure of monomers resulted in activation energy (Ea) between -156.7 kJ mol-1 for monomer (4) to -182.7 kJ mol-1 for monomer (2). The presence of phenyl ring in monomer (4) makes the double bond more electron-deficient and more susceptible to polymerize (lower activation energy). The more flexible structure of monomer (3) also favors the polymerization reaction and the Ea is lower than monomer (2). No glass transition temperature could be observed in the second heating curve.

Figure 1. MDSC curves of monomer (2) at a heating rate of 5 °C min-1 with 100 s of period, amplitude of ± 1.0 °C. Table 2. Results of thermal kinetics, temperature maximum (Tmax) according with heating rate, activation energy (Ea – kJ mol-1) and correlation constant (R2) of monomers (M).

M (2) (3) (4)

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Tmax (°C) 1 °C min-1 119.31 114.2 259.0

2 °C min-1 121.5 113.2 273.0

Ea

3 °C min-1 122.5 118.0 268.3

5 °C min-1 129.4 122.6 260.4

kJ mol-1 182.7 165.8 156.7

R2 0.83 0.72 0.64

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Thermal radical polymerization of Bis(methacrylamide)s

4. Conclusions The synthetic route used in this study resulted in solid and liquid monomers with yields higher than 30 %. Moreover, the monomer (1) showed appropriate color and viscosity to dental adhesive application, but during characterization did not polymerized due to steric effects. The investigation of the thermal polymerization of monomers (2), (3) and (4) was obtained only by mDSC due to separation of cure and melting peaks and the monomer 4 showed the higher reactivity.

5. Acknowledgements The authors gratefully acknowledge CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for the scholarship (S.B.R.), Julio C.P. Vaghetti from LAMAT (Laboratório Multiusuário de Análise Térmica) for mDSC analyses and Alexsandro Dallegrave for the UHPLC-QTOF-MS analyses. The authors declare no potential conflicts of interest with respect to the authorship and/or publication of this study. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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14. Derbanne, M. A., Besse, V., Le Goff, S., Sadoun, M., & Pham, T.-N. (2013). Hydrolytically stable acidic monomers used in two steps self-etch adhesives. Polymer Degradation & Stability, 98(9), 1688-1698. http://dx.doi.org/10.1016/j. polymdegradstab.2013.06.006.

15. Klee, J. E., & Lehmann, U. (2009). N-alkyl-N-(phosphonoethyl) substituted (meth)acrylamides - new adhesive monomers for self-etching self-priming one part dental adhesive. Beilstein Journal of Organic Chemistry, 5(72), 1-9. http://dx.doi. org/10.3762/bjoc.5.72. PMid:20300456.

16. Moszner, N., Zeuner, F., Angermann, J., Fischer, U., & Rheinberger, V. (2003). Monomers for adhesive polymers, 4: synthesis and radical polymerization of hydrolytically stable crosslinking monomers. Macromolecular Materials and Engineering, 288(8), 621-628. http://dx.doi.org/10.1002/ mame.200350003.

17. Lichkus, A. M., Jin, X., Renn, C., Elsner, O., Szillat, F., Klee, J. E., Weber, C., Walz, U., & Scheufler, C. A. (2017). EP Patent No 3.231.411. Paris: European Patent Office.

18. Moszner, N., Lamparth, I., Bock, T., Fischer, U. K., Salz, U., Rheinberger, V., & Liska, R. (2013). International Patent No 2.013.034.777 A2. Hamburg: Patent Cooperation Treaty.

19. Gong, C., Wong, K.-L., & Lam, M. H. W. (2008). Photoresponsive molecularly imprinted hydrogels for the photoregulated release and uptake of pharmaceuticals in the aqueous media. Chemistry of Materials, 20(4), 1353-1358. http://dx.doi.org/10.1021/ cm7019526.

20. Azodi-Deilami, S., Abdouss, M., Kordestani, D., & Shariatinia, Z. (2014). Preparation of N,N-p-phenylene bismethacryl amide as a novel cross-link agent for synthesis and characterization of the core–shell magnetic molecularly imprinted polymer nanoparticles. Journal of Materials Science. Materials in Medicine, 25(3), 645-656. http://dx.doi.org/10.1007/s10856013-5118-8. PMid:24338334.

21. Salz, U., Zimmermann, J., Zeuner, F., & Moszner, N. (2005).

Hydrolytic stability of self-etching adhesive systems. The Journal of Adhesive Dentistry, 7(2), 107-116. http://dx.doi. org/10.3290/j.jad.a10282. PMid:16052759.

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Rodrigues, S. B., Collares, F. M., Gamba, D., Leitune, V. C. B., & Petzhold, C. L. 22. Tauscher, S., Angermann, J., Catel, Y., & Moszner, N. (2017).

Evaluation of alternative monomers to HEMA for dental applications. Dental Materials, 33(7), 857-865. http://dx.doi. org/10.1016/j.dental.2017.04.023. PMid:28528931.

23. Rodrigues, S. B., Collares, F. M., Leitune, V. C., Schneider, L. F., Ogliari, F. A., Petzhold, C. L., & Samuel, S. M. W. (2016).

Influence of hydroxyethyl acrylamide addition to dental adhesive resin. Dental Materials, 31(12), 1579-1586. http:// dx.doi.org/10.1016/j.dental.2015.10.005. PMid:26549355.

24. Huang, C., Mei, X., Cheng, Y., Li, Y., & Zhu, X. (2014). A model-free method for evaluating theoretical error of Kissinger

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equation. Journal of Thermal Analysis and Calorimetry, 116(3), 1153-1157. http://dx.doi.org/10.1007/s10973-013-3624-z.

25. Otsu, T., Inoue, M., Yamada, B., & Mori, T. (1975). Structure and reactivity of vinyl monomers: radical reactivities of N-substituted acrylamides and methacrylamides. Journal of Polymer Science. Part C, Polymer Letters, 13(8), 505-510. http://dx.doi.org/10.1002/pol.1975.130130811.

Received: May 28, 2018 Revised: Jan. 21, 2019 Accepted: Mar. 15, 2019

PolĂ­meros, 29(2), e2019023, 2019

Thermal radical polymerization of Bis(methacrylamide)s

Supplementary Material Supplementary material accompanies this paper.

Figure S1. IR spectra of monomers (1), (2), (3) and (4).

Figure S2. 1H NMR and 13C NMR of monomers (1), (2), (3) and (4).

Figure S3. Mass spectra of monomers (1), (2), (3) and (4) and theoretical isotopic profile.

This material is available as part of the online article from http://www.scielo.br/po

PolĂ­meros, 29(2), e2019023, 2019

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.05318

Study on mechanical & thermal properties of PCL blended graphene biocomposites Dinesh Kumar1, Ganesh Babu2 and Sai Krishnan3*  Mechanical Department, Jain University, Bangalore, Karnataka, Índia Mechatronics Department, Tishk Inernational University, Erbil, Iraqi Kurdistan, Iraq 3 Mechanical Department, Rajalakshmi Institute of Technology, Chennai, Tamil Nadu, Índia 1

2

*g.saikrishnan@gmail.com

Abstract Graphene is a new carbon based nonmaterial that attracts the technology and constitutes one of the great promises for nanotechnology applications in a near feature. It’s having versatile intrinsic mechanical, thermal and electrical properties.

By Incorporation of small amount of graphene fillers into polymer matrix can create attractive bio composites with different morphological and functional properties. The development of biomaterials with special properties is a requirement in biomedical research, particularly in biomedical application. The aim of this work was to develop biocompatible, usable bio composites for biomedical applications using graphene as filler. Recent research evidenced that grapheme-polymer bio composites are promising materials with applications ranging from transportation, biomedical systems, sensors, electrodes for solar panels and EMI.Chemically converted graphene (CCG) solution were prepared through reduction of GO, and Polycaprolactone (PCl), a synthetic biodegradable and biocompatible aliphatic polyester also a suitable for developing biocomposites.

Keywords: graphene, polymer biocomposites, polycaprolactone, biocompatible.

How to cite: Kumar, D., Babu, G., & Krishnan, S. (2019). Study on mechanical & thermal properties of PCL blended graphene biocomposites. Polímeros: Ciência e Tecnologia, 29(2), e2019024. https://doi.org/10.1590/0104-1428.05318

1. Introduction Biodegradable and/or Biocompatible materials have attracted the attention of researchers for many years. With the development of biomedical science, biomaterials have been recognized as an increasingly important area of research. In the biomedical field, a biomaterial can be defined as a material intended to interface with biological systems to evaluate, treat, augment or replace any tissue, organ or function of the body[1]. In the past twenty years, significant advancements have occurred in the area of biomaterials. Exhibiting remarkable biodegradability and biocompatibility, biomaterials such as poly(L-lactide) and polycaprolactone have been used extensively in a variety of biomedical applications, namely drug delivery systems, bone fixation devices, vascular grafts, gene delivery systems and tissue engineering[2]. In view of the diversity and complexity of the applications, a wide range of biomaterials need to be developed to properly meet the requirements of each particular biomedical application. This requirement is the primary motivation in the development of biocomposites which are usually composed of a biodegradable matrix and a reinforcing filler[3]. The structure and properties of the polymers can be optimized by the addition of fillers, and hence a wide range of biomaterials with diverse mechanical and biological properties can be developed. Biodegradable polymers can be categorized in different ways. From a degradation viewpoint, biomaterials can be categorized into two classes, biodegradable and nonbiodegradable.

Polímeros, 29(2), e2019024, 2019

However, categorizing biopolymers based on their origin into natural and synthetic is the most common way of categorizing those[4]. Natural biopolymers appear to be the most appropriate option for biomedical applications because of their excellent biocompatibility, their biodegradability through enzymatic or hydrolytic mechanisms and their great ability to copy native cellular environments. However, some fundamental disadvantages of natural biopolymers, namely the possibility of viral infections, antigenicity and variation in properties of different batches, are a major obstacle in fully employing them in biomedical applications[5]. Biometrics can also be functioned to meet specific requirements based on their final applications. The functional groups can be introduced either to the monomers or the polymer chains of the polymer. Polysaccharides and proteins are typical natural biopolymers used for biomedical applications[6].

Polysaccharides are high molecular weight polymeric carbohydrates composed of one or more monosaccharide repeating units[7]. Wide availability, low cost, diversity in structure and the presence of reactive functional groups in the polymer chain are some of the advantages of using polysaccharides for biomedical applications[8,9]. Proteins are high molecular weight polymers consisting repeating of units of amino acids linked together via peptide linkages. An attractive property of these natural polymers, polysaccharides in particular, is their great swellability that makes them ideal candidates for developing hydrogels[10,11].

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

Kumar, D., Babu, G., & Krishnan, S. It should be possible to overcome many of the problems associated with natural polymers and develop materials for specific applications through specific synthesis of polymers.

Synthetic materials possess more predictable behavior and batch-to-batch uniformity compared to natural polymers aliphatic polyesters, that are representative of the synthetic biodegradable polymers, are the most commonly used synthetic materials for biomedical applications. Polycaprolactone (PCl) is biodegradable semi-crystalline polyester with some unique properties that make it the material of choice for biomedical fields[12]. It has a low melting point (55-60 °C), dissolves in a wide range of organic solvents and is able to form miscible blends with different type of polymers[13].

All these properties make it a highly processable material suitable for biomedical applications. Furthermore, it can be easily synthesized from ε- caprolactone, a relatively inexpensive monomeric unit. There are two approaches to synthesize PCl: the condensation of 6-hydroxycaproic (6-hydroxyhexanoic) acid and the Ring-Opening Polymerization (ROP) of ε-caprolactone[14]. ROP is the preferred method as it provides the possibility of synthesizing the polymer with a higher molecular weight and a lower polydispersity[15]. PCl is extensively investigated in drug delivery applications and numerous micro- and nano-sized drug delivery vehicles are developed from PCl[16]. PCl shows great compatibility with many organic materials and polymers so it can be used as compatibilizers in many polymer formulations[17,18]. A wide range of biomaterials has already been used in developing structures for biomedical applications. However, it is hard to find a polymer that meets all the requirements for developing the perfect material for biomedical applications. As a result, researchers have developed biocomposites that are typically composed of a biodegradable matrix and filler, which is used to compensate for the deficiencies of the matrix[19].

Nano-clays, hydroxyapatite and carbonaceous materials are the major fillers that have widely been used in to improve

the properties of biomaterials[20,21]. Carbonaceous materials such as carbon nanotubes (CNT), fullerenes, graphite, and graphene oxide (GO) and graphene have recently attracted the attention of researchers as composite fillers for biomedical applications. The building block of carbonaceous materials is a layer of sp2 hybridized carbon atoms covalently bonded in a honeycomb lattice known as graphene[22]. Carbonaceous materials show excellent electrical, mechanical, and thermal properties that make them ideal fillers to develop materials of high performance for biomedical applications.

2 Prior Art Several studies seek to improve the mechanical properties of biodegradable polymers using hydroxyapatite[23-25], however, the improvements were not large enough to meet the criteria for bone engineering field[26,27]. Clay silicates have also been incorporated into polymers to improve their mechanical propertie[28-30], however, it is hard to make a homogenous dispersion from clay silicates as the particles tend to agglomerate inside the polymer matrix due to their highly hydrophilic nature. High conductivity of the graphene attracted the attention of researchers at that time, however, research on graphene moved slowly as synthesis of this nanosheet was found to be experimentally difficult[31]. Different approaches were taken to synthesize this 2D carbon structure, including the same methods used for developing CNTs, but none of them were able to prepare a high quality graphene.

Green and Hersam[32] reported the preparation of stable graphene dispersion by using the bile salt sodium cholate.

In this work, graphene flakes with controlled thicknesses could be isolated in suspension using density gradient ultracentrifugation (Figure 1). The synthesized graphene dispersion contained monolayer graphene sheets with thicknesses varying between 1 to >2nm. However, the graphene concentration of the dispersion was quite low

Figure 1. Schematic illustration of the graphene exfoliation process. Combination of graphite and sodium cholate are exfoliated to few‑layer graphene.

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Polímeros, 29(2), e2019024, 2019

Study on mechanical & thermal properties of PCL blended graphene biocomposites (90 μg ml−1), making this graphene dispersion an impractical choice for developing composites.

Other metal surfaces such as Ru, Ir, Ni, Co and Pt have also been used as substrates for producing graphene layers following the same method. The details are discussed in a review by Wintterlin and Bocquet[33]. Lack of control over the graphene thickness and non-uniform growth of single layer graphene[34] are the major issues that limit the real application of CVD method.

Wang et al.[35] prepared PCl-GO composites via in situ polymerization (Figure 2). GO was synthesized following the Hummers method. The tensile strength and elongation at break of the synthesized pure PCl is reported as 3 MPa and 140% respectively, and 7 MPa, 80% on addition of GO. The improvement in the tensile strength is indicative of the reinforcing effect of the GO on PCl.

3. Materials and Methods 3.1 Materials ε-Caprolactone (97%), N,N-dimethylformamide (DMF), N,N′-dicyclohexylcarbodiimide (DCC), 4-dimethylaminopyridine (DMAP), 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide

hydrochloride (EDC), N-hydroxysuccinimide (NHS), Methanol, dichloromethane, (3-aminopropyl)triethoxysilane 99%, tin 2-ethylhexanoate (95%), polycaprolactone(PCl) (Mn 80,000), methacrylic anhydride, hydrazine monohydrate (N2H4 64-65%, reagent grade, 98%), phosphorus pentoxide (P2O5), DL-lactic acid, (80-85% aqueous solution), Graphite powder and triethylamine were purchased and used as received. Milli-Q water with a resistivity of 18.2 mΩcm−1 was used in all preparations.

3.2 Material synthesis 3.2.1 Preparation of graphene oxide and chemically converted graphene Stable dispersions of CCG in DMF (0.5 mg ml−1) were prepared by sonicating CCG flakes, first synthesised from GO, in DMF (Figure 3 and Figure 4) using the procedure developed by Dr. Gambhir. GO was produced from natural graphite powder using a modified Hummers’ method and then the GO was reduced to CCG using hydrazine (NH2NH2) following Dan δi’s method. The aqueous CCG dispersion was further reduced using excess quantities of hydrazine followed by acidification to agglomerate and precipitate the CCG flakes from the aqueous dispersion. In the next step, the CCG flakes were filtered, washed and dried to give graphene powder. The dry graphene powder was then added to DMF followed by addition of triethylamine (N (CH2H5)3), that helps the homogenous dispersion of CCG, and the mixture was sonicated with continuous cooling under a dry nitrogen purge for up to 5 hours. The procedure resulted in a stable homogeneous dispersion of CCG in DMF with a CCG concentration of 0.5 mg ml-1.

3.2.2 Preparation of graphene/PCI composites through mixing and covalent attachment method

Figure 2. Grafting of PCl onto graphene sheets via in-situ polymerization of PCl.

In this section, we investigated the possibility of developing graphene/PCl composites using two approaches, the mixing method and the covalent attachment method.

The composites were prepared with different graphene contents that are 0.1, 0.5,1, 5 and 10 wt. %. The composites are labelled according to their preparation method and the

Figure 3. Synthesis of DMF-disperse CCG. Polímeros, 29(2), e2019024, 2019

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Kumar, D., Babu, G., & Krishnan, S.

Figure 4. Preparation of PCl-CCG composites through mixing and covalent attachment methods.

weight percentage of their graphene content. All prepared samples are listed in Table 1. The labels mixPCl-CCG x% and cPCl-CCG x% represent the composites prepared though the mixing and covalent attachment methods respectively.

The x is the weight percentage of the graphene content in the composites, e.g. cPCl-CCG 5% represents the covalently linked composite with 5 wt. % graphene content.

Graphene/PCl binary mixtures (mixPCl–CCGs) were prepared by mixing PCl in an appropriate amount of a 0.5 mg ml−1 DMF-dispersed graphene at 75 °C for 3 h, whilst in the preparation of covalently linked graphene/PCl composites (cPCl–CCGs) the mixture of PCland graphene was followed by the addition of N,N′-dicyclohexylcarbodiimide (DCC) as coupling agent and 4-dimethylaminopyridine (DMAP) as catalyst. In the mixing method, no strong link is formed between the graphene sheets and polymer chains, and the graphene sheets are entangled with the polymer chains. On the other hand, in the covalent attachment method, the polymer chains get covalently linked to the peripheral carboxyl groups of the graphene sheets by esterification in the presence of DCC and DMAP. Covalent linkages between graphene sheets and polymer chains can make the material stronger and even tougher. Addition of polymer to graphene dispersions has always been the main challenge in the process of composite preparation. The polymer should be added to the graphene dispersion slowly to avoid agglomeration and disturbance of the graphene dispersion. The other challenge was to find the optimum matrix/filler ratio. It was immediately apparent that the resulting black graphene/PCl composites became less flexible with increasing graphene content.

The addition of graphene was found to improve the tensile strength and conductivity of the polymer as found in the characterization sections below, however exceeding 5 wt.% graphene content made composite too brittle to handle for many of the characterizations. Consequently, no samples were prepared with more than 10% graphene.

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Table 1. PCl samples with different graphene concentrations prepared via mixing and covalent attachment methods.

PreparationMethod Mixed

Covalent Attachment

Graphene contents (Wt. %) 0

Sample labels PCL

0.1

mixCL-CCG 0.1%

0.5

mixCL-CCG 0.5%

1

mixCL-CCG 1%

5

mixCL-CCG 5%

10 0

mixCL-CCG 10% PCL

0.1

mixCL-CCG 0.1%

0.5

mixCL-CCG 0.5%

1

mixCL-CCG 1%

5

mixCL-CCG 5%

10

mixCL-CCG 10%

4. Results and Discussion 4.1 Stability and particle size of the dispersions A Malvern Zetasizer was used to monitor the stability of aqueous and DMFdispersed CCG dispersions and to measure the particle size of GO, aqueous and DMF‑dispersed CCG dispersions. For the experiments, 1 ml of the dispersions was diluted and transferred into a quartz cuvette for Zeta potential test. The zeta potential of the aqueous and DMF-dispersed CCG was found to be -39 mV and -31 mV respectively (Figure 5a). The zeta potential for both samples is < -30 mV and they remain stable for up to 100 days indicating good stability of the dispersions. The average size of the sheets as estimated by Zetasizer in the GO and CCG dispersions is similar, varying between 436 to 464 nm with the GO dispersion containing slightly larger sheets Figure 5b.

Polímeros, 29(2), e2019024, 2019

Study on mechanical & thermal properties of PCL blended graphene biocomposites The results indicate that the longer sonication time used for dispersing graphenenanosheets in DMF has not affected the average size of graphene sheets in DMF dispersion.

4.2 SEM images of aqueous and DMF dispersed CCG To prepare the SEM samples, one drop of each CCG dispersion was deposited on a silanized silicon wafer and the solvent was evaporated overnight. SEM images show on Figure 6 that both aqueous and DMF-dispersed graphene samples contain graphene sheets in different sizes. The dispersions contain very small graphene sheets (<100nm) due to fragmentation occurring during sonication.

The size of the larger sheets varies between 100 to 500 nm.

4.3 X-ray Diffraction X-ray Diffraction (XRD) is a useful technique to obtain information about the structure, crystallinity, orientation of crystallites and phase composition in crystalline and semi‑crystalline materials. The peaks in an XRD pattern correspond to diffractions from the crystallographic planes, by which the interplanar distances of the crystalline material

can be calculated X-ray diffraction (XRD) spectra of graphite GO and DMF-dispersed CCG are illustrated in Figure 7.

The samples were prepared either using a powder (graphite) or through depositing 500 μl of the relevant dispersion on a quartz substrate, followed by evaporating the solvent at room temperature and the spectra collected Graphite shows a strong peak at around 26.7o that is typical of well-ordered graphene crystal planes in graphitic systems. This peak corresponds to an interlayer distance (d-spacing) of 3.34 Å. After oxidation to GO, the peak in graphite is replaced with a new intense diffraction peak at about 10.6o (d-spacing of about 8.35 Å) in GO. The increase in d-spacing of GO is attributed to the intercalation of water molecules between two layers as well as hydrophobic nature of GOAfter chemical reduction, CCG displays a weak and broad x-ray diffraction peak at around 20 ~ 24o, corresponding to a d-spacing of about 3.69 Å.

The decrease in the average interlayer spacing in the CCG sample is attributed to deoxygenation and reduction in the basal defects of GO.The interlayer spacing of the peak in CCG is close to the d-spacing peak value of graphite, but the CCG peak is broad, representing the formation of much more disordered graphene sheets compared to graphite

Figure 5. (a) Dispersion stability of CCG samples and (b) average particle size of GO and CCG samples.

Figure 6. Scanning electron microscopy of (a) aqueous CCG, (b) DMF-dispersed CCG. Polímeros, 29(2), e2019024, 2019

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Kumar, D., Babu, G., & Krishnan, S. 4.4 Characterization of graphene/PCl composites 4.4.1 Thermogravimetric analysis TGA was used to help understand the composition of the composites through characterizing the thermal properties of the PCl and PCl-CCG composites. TGA datawere obtained by heating 10mg of samples to above 900 °C under nitrogen at a rate of 5 °C min −1. Figure 8 shows the thermal behaviour of pristine PCl as well as cPCl-CCG and mix PCl-CCG composites with 0.1, 0.5, 1 and 5 wt. % graphene contents.

Based on the results, the addition of graphene, whether in a binary mixture or a covalently linked composite, has very little effect on the decomposition temperature of polycaprolactone.

All samples show thermal stability up to 380 °C and the decomposing rapid decomposition, which is assigned to the degradation of the polymer chains. The residual weight after full decomposition of the polymer can be assigned to the graphene content as CCG weight losses are minimal in this temperature range.

The graphene percentage calculated from TGA analysis of the Composites prepared by the covalent attachment method (cPCl-CCG) is consistent with the percentage of graphene added to the reaction initially and indicates

good Attachment of the polymer. However, the graphene percentage in the mixtures (mixPCl-CCG) is very different to that added to the reaction mixture. This is Consistent with the observation of polymer being washed out of the composite during precipitation.

4.4.2 Differential scanning calorimetry The correlation between the heat flow and the temperatures of the materials can be studied by using differential scanning calorimetry (DSC). DSC test was done on pristine PCl, cPCl‑CCG and mixPCl-CCG composites with 0.1, 1 and 5 wt. % graphene contents. The samples (5-8 mg) were first dried in vacuum oven overnight to remove the solvents residues, and then they were presealed into aluminum pans for the tests. The melting point of PCl was found to be around 57 °C. DSC curves showed that the addition of graphene to polycaprolactone either covalently or as a mixture did not significantly affect the melting point of the PCl composites, which remains at 55‑60 °C (Figure 9). Addition of graphene was found to have increasing effect on the crystallization temperature for all of the composites. On addition of just 0.1 wt.%graphene the crystallization point increases massively from 19 °C in pristine PCl to 33 °C. This phenomenon can

Figure 7. X-ray diffraction patterns of graphite, GO and DMF-dispersed CCG.

Figure 8. Thermogravimetric curves of (a) cPCl-CCG and (b) mixPCl-CCG composites with different graphene contents. The residual weight after full decomposition of the polymer represents the actual amount of graphene in composites.

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Study on mechanical & thermal properties of PCL blended graphene biocomposites be attributed to the nucleating effect of graphene on PCl crystallization. Increasing the addition of graphene further increases the crystallization temperature and broadens the crystalization peak, indicating confined mobility of polymer chains and suppression of the crystal structure in

Figure 9. Differential scanning calorimetry curve of cPCl-CCG composites. The addition of graphene generally has little effect on the melt temperature, but increases the crystallization temperature of the composites.

the composite. The crystallization temperature reaches 35 °C in PCl composites with 5 wt. % graphenecontent.

4.4.3 Mechanical properties Tensile testing was performed to investigate the effect of CCG on the mechanical properties of PCl. Typical stress–strain curves of PCl and PCl composites are shown in Figure 10, and the detailed data of the mechanical properties are listed in Table 2. To prepare samples for mechanical properties tests, the samples were hot pressed at 100 °C to obtain a 0.1 mm thick film. Then the film was cut into strips with a width of 3 mm and a length of 20 mm. Pure PCl shows the typical stress-strain curves of ductile materials started with linear deformation behaviour up to the yield point, which is considered the upper limit of elasticity, followed by a plastic response that is irreversible.

The addition of graphene has not changed the ductility of the composites even at higher graphene contents, indicating a good level of graphene dispersion in the polymer matrix even in the composites prepared by mixing method. The pure PCl showed a high strain at break up to 1200%, but had low tensile yield strength and Young’s modulus of around 10 MPa and 94 MPa respectively. In general, the addition of graphene improves the strength of the composites, but decreases the elongation at break as the interaction between graphene and the matrix restricts the movement of the polymer chains. Figure 10 shows the increase in tensile

Figure 10. Stress-Strain curves of (a) cPCl-CCG and (b) mixPCl-CCG composites showing the large increase in tensile strengths and reductions in elongation at break.

Table 2. Mechanical properties of PCl, covalently-linked cPCl-CCG and mixPCl- CCG. Preparation Method Polycaprolactone Covalent

Graphene

Tensile Yield

Contents(wt.%) 0 0.1

(Mpa) 10±0.2 10±0.4

0.5 1 Mixture

Polímeros, 29(2), e2019024, 2019

Youngs Modulus (Mpa)

Elongation at Break (%)

94±12 90±4

1212±86 842±57

13±0.2

199±14

788±38

16±0.2

236±6

286±18

5 0.1

17±0.8 13.4±0.3

259±22 260±26

166±12 321±53

0.5

14.5±0.6

219±12

282±28

1

15±0.9

277±23

69.5±11

5

20±0.3

359±7

48.4±12

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Kumar, D., Babu, G., & Krishnan, S. yield strength in both covalently linked and mixed method materials. Incovalently attached composites, the addition of just 0.5 wt. % graphene increased tensile yield stress by almost 30% and doubled it on addition of 5%. Similarly the Young’s modulus increases from 94 MPa in pristine PCl to 199 MPa to 259 Mpa across the same range.

5. Conclusion The main aim of this project was to develop biocompatible, processablebiocomposites for biomedical applications.

Chemically converted graphene (CCG) as a dispersion (aqueous or DMF-dispersed CCG) was used as the main filler in this work due to its excellent properties and its potential to enhance the mechanical and electrical properties of the polymers. Two approaches were taken to synthesize composites, a mixing method in which the polymer was mixed with the CCG dispersion (mixPCl-CCG) and a covalent attachment method whereby the polymer chains were covalently linked to CCG sheets (cPCl-CCG). The homogeneous dispersions of CCG in cPCl-CCG composites led to the development of composites with much better flexibility compared to mixPCl‑CCG samples. The addition of 0.5 wt.% CCG increased the tensile strength and Young’s modulus by more than 70% and 170% respectively. The conductivity of PCl was also improved by around 12 orders of magnitude on addition of 5 wt. % CCG in mixPCl- CCG composites.

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Received: June 04, 2018 Revised: Sept. 13, 2018 Accepted: Dec. 10, 2018

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.01218

The influence of fiber size on the behavior of the araucaria pine nut shell/PU composite Giuliana Ribeiro Protzek1, Washington Luiz Esteves Magalhães2, Paulo Rodrigo Stival Bittencourt3, Salvador Claro Neto4, Rodrigo Lupinacci Villanova5, Elaine Cristina Azevedo1*  Programa de Pós-graduação em Engenharia Mecânica e de Materiais, Universidade Tecnológica Federal do Paraná – UTFPR, Curitiba, PR, Brasil 2 Laboratório de Tecnologia da Madeira, Embrapa Florestas, Colombo, PR, Brasil 3 Departamento Acadêmico de Química, Universidade Tecnológica Federal do Paraná – UTFPR, Medianeira, PR, Brasil 4 Instituto de Química de São Carlos, Universidade de São Paulo – USP, São Carlos, SP, Brasil 5 Departamento Acadêmico de Mecânica, Universidade Tecnológica Federal do Paraná – UTFPR, Curitiba, PR, Brasil

1

*helunica@yahoo.com.br

Abstract The use of araucaria pine nut shell in polymer composites may increase the pine nut value and help protec araucaria (Araucaria angustifolia) itself, which is an endangered species. The aim of this work is to study the influence of the size of pine nut shell fiber on the mechanical properties of composites made of this shell and polyurethane derived from castor oil. Composites with different polyurethane contents were manufactured with dried untreated pine nut shell sieved through 30 and 50 mesh sieves (0.6 and 0.3 mm, respectively). Composites were shaped by mechanical mixing of the components followed by hot pressing. Properties such as density, water absorption, and flexural strength were measured. Specimens were also characterized by SEM, FTIR, and TGA. The flexural strength of PU/0.3mm pine nut shell composites with 30% PU (wt%) was 57.7 MPa, and their water absorption was 7.37% after 24 hours of immersion.

Keywords: araucaria pine nut shell, composite, castor oil, polyurethane, mechanical properties.

How to cite: Protzek, G. R., Magalhães, W. L. E., Bittencourt, P. R. S., Claro Neto, S.,Villanova, R. L., & Azevedo, E. C. (2019). The influence of fiber size on the behavior of the araucaria pine nut shell/PU composite. Polímeros: Ciência e Tecnologia, 29(2), e2019025. https://doi.org/10.1590/0104-1428.01218

1. Introduction The development of products with low cost, reduced energy consumption and life cycle sustainability is driven by the worldwide concern with the environment and human health[1-3]. Biodegradable composites are environmentally friendly [1], can be made from renewable sources, and degraded by the action of microorganisms[2,4].

Composites made of biodegradable polymers and reinforced by natural fibers are an attractive option, since these fibers have some advantages when compared to synthetic ones, such as lower density, lower cost, and lower abrasivity during manufacturing. Besides, natural fibers are derived from renewable sources, are not toxic, and do not cause environmental impacts[1,5-7].

Fernandes et al.[8] analyzed the influence of silica nanoparticles on the compatibility between sisal fibers and high density polyethylene. They observed that thermal properties of HDPE did not change because of the presence of sisal fibers and silica nanoparticles in the composite.

The different chemical treatments in sisal fibers and the presence of silica nanoparticles resulted in improved

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mechanical properties and water uptake decrease in the composites, when comparing to HDPE. Spadetti et al.[9] investigated thermal and mechanical properties of composites made of both virgin and recycled polypropylene reinforced with cellulose fiber. The results showed that recycled polypropylene composites with 30% (wt%) cellulose fibers and virgin polypropylene composites with 20% (wt%) of cellulose fibers had a significant increase in storage modulus values (E’) and degree of crystallinity (χc), indicating a higher mechanical strength in these composites. However, the stiffness specimens of the material with 40% (wt%) of cellulose fibers decreased. These results were confirmed by SEM, where some agglomeration of the cellulose fibers within the matrix was observed. Both glass transition temperature (Tg) and crystalline melting temperature (Tm) of composites did not change.

Mano et al.[10] studied the morphological, mechanical, and thermal properties of composites made of polypropylene reinforced with curaua fibers treated with maleic anhydride grafted polypropylene. The use of PP-g-MA as a compatibilizer significantly increased fiber/matrix adhesion; however,

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

Protzek, G. R., Magalhães, W. L. E., Bittencourt, P. R. S., Claro Neto, S.,Villanova, R. L., & Azevedo, E. C. mechanical properties were only slightly improved when comparing to composites produced without compatibilizer.

Beltrami et al.[4] studied the morphological, mechanical, and thermal properties of composites made of PHBV and curaua fibers with alkaline treatment. Results indicate that the alkaline treatment improved the adhesion of the fibers to the matrix, which significantly improved the mechanical properties of the composites. However, NaOH concentrations of NaOH different from 5% may have a deleterious effect on the mechanical properties of the fibers and composites.

Mei & Oliveira[7] studied the morphological, mechanical and thermal properties and the biodegradability of composites containing chemically treated coffee grounds and poly(ε‑caprolactone). Thermal analysis showed that the addition of coffee grounds increased the maximum peak of thermal degradation by 10°C when compared to pure polymer. Biodegradability was higher for specimens containing acetylated coffee grounds.

Load transfer from the polymer matrix to the fibers greatly depends on the matrix-fiber interaction[4]. Natural fibers are hydrophilic, while most polymer matrixes are hydrophobic[8,11]. As a result, the adhesion between those materials is compromised, decreasing the mechanical properties of the composite[5,6]. One possible way to improve such interaction if by modifying the surface of the fibers by means of physical[12,13] or chemical methods[4,5,7].

Polyurethane derived from castor oil is a biodegradable polymer produced from renewable sources, and it is harmless to human health and to the environment, since no volatile organic compounds are liberated in its synthesis[6,14,15].

During polyurethane polymerization in the presence of vegetable fibers, crosslinks may result from the reaction of active hydrogens from hydroxyl or carboxyl groups from lignin and PU free isocyanate. Such reactions may improve matrix-fiber interaction, leading to better load transfer and enhanced mechanical properties. This is the reason no previous treatments on the fibers and no coupling agents are needed in this type of composites[11,16].

Marinho et al.[15] studied physical and thermal properties of composites made of PU based on castor oil and bamboo particles without any previous treatment. This approach minimizes the negative impact to the environment, since a solvente free polymer is obtained. The association of PU and bamboo particles produced the expected effects, including a decrease in moisture content, swelling and water absorption of bamboo as PU content increased.

Zau et al.[17] analyzed the chemical, physical and mechanical properties of agglomerated panels made of cumaru wood residues with PU derived from castor oil.

They produced panels with different amounts of residues (1000, 1300, 1500 g) and resin content (10, 12.5 and 15%).

Higher mechanical properties were achieved for panels with 1500g of residue and 15% of resin, and the values exceed the minimum specified by the NBR 14810-3 (2006), confirming their potential in producing particleboards.

Araucaria angustifolia is a tree from southern Brazil[18].

It is an endangered species, and there are legal restrictions concerning the use of its wood; therefore, incentives are given to the commercialization of its seed, the pine nut[19].

Pine nut is a nutritious food, containing mainly starch and 2/9

low amounts of sugars and lipids in its composition[20].

About 700 tons/year of pine nut shell residue are disposed of in south Brazil[21]. The use of this pine nut shell in polymer composites can reduce the amount of discarded material in the environment and increase its value. Araucaria angustifolia is an endangered species, mainly because of illegal exploitation and commercialization of its wood.

The use of pine nut shell may help to preserve the trees, since it can be a source of income and avoid cutting down trees. Composites made with pine nut shell can be used in handicrafts and furniture, replacing MDF, which has a significant impact on the environment.

The aim of this work is to evaluate the effect of pine nut shell size on mechanical, physical, and thermal properties of composites made of castor oil polyurethane and pine nut shell. Two different sizes of pine nut shell were used, i.e., those passing through 30 and 50 mesh (0.6 and 0.3 mm sieve opening), and the composites were produced with varying amounts of PU by means of mechanical mixing and hot pressing. Several characterization tests were carried out, namely: volumetric density, water absorption, flexural strength, thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM).

2. Materials and Methods 2.1. Materials Castor oil-based PU resins employed in this work were developed by the Group of Analytic Chemistry and Technology of Polymers – USP . Polyurethane is a bi-component resin obtained by the reaction of a polyol and an isocianate terminated pre-polymer. Currently, both pre-polymer and polyol are produced by Cequil, from Araraguara-SP, Brazil. The pre-polymer used is based on the diphenylmethanodiisocyanate (MDI). Polyols are polyesters derivate from castor oil with different amount of functional hydroxyl groups. The pre-polymer was synthesized from diphenylmethanediisocyanate (MDI) and prepolymerized with polyols, also derived from castor oil, keeping a percentage of free isocyanate for later reaction.

PU Polibond is athermoset adhesive. Polymer preparation was made according to the supplier instructions. Pine nut shell was donated by Embrapa Florestas, from Colombo‑PR, Brazil. The shell was crushed in a knife mill suited for grains and dry materials. Crushed shells were classified through 30 and 50 mesh sieves (0.6 and 0.3 mm aperture), dried at 100°C for 24 hours and kept in a desiccator until used No chemical or physical treatments were performed in the fibers.

2.2. Composites production Composites with 50%, 60%, and 70% of pine nut shell (wt%) were produced by mixing the pine nut shell to the castor oil polyurethane in a MH-100 series 6069 mixer (MH Equipamentos) 3200 rpm for 20s . The mixture was shaped in a hot press (Marconi Equipamentos, model MA 098/AR15, under 6 MPa pressure at 70°C for 20 minutes, which was sufficient to allow the system to cure.

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The influence of fiber size on the behavior of the araucaria pine nut shell/PU composite 2.3. Characterization of composites The density of the composites was measured according to EN 323:2002 Standard, and the water absorption was determined according to EN 317: 2002 Standard. Tests were conducted at a room temperature. Five specimens of each composite were cut from a plate, as 50X50 mm samples with unsealed borders. The initial thickness (the thickness is measured close to the center of the specimen) was measured and the samples were weighted before being submerged in distilled water for 2 h. After immersion, the water on the surface of the samples was removed, and the samples were immediately weighed, measured, and immersed in water again. After 22 h they were removed, pat dried, measured and weighted again.

Flexural tests were performed according to the ASTM D790-03 standard in an EMIC DL10000 universal tester, with load cell of 20 kN and test speed of 5mm/min.

Scanning Electron Microscopy was performed in a Zeiss microscope, model EVO MA 15. Specimens were gold sputtered prior to observation. SEM was used to investigate the surface of fibers after drying and the fracture surface of the composites after flexural test.

Thermogravimetric analyses (TGA) were carried out in a Perkin Elmer STA 6000 thermo scale, and the following parameters were used: Specimen mass: 5.0 to 10.0 mg; Temperature range 30 °C to 800 °C; Heating rate 10 C/min; Flow of N2 atmosphere 100 mL/min.

FITR analyses were carried out in a Varian infrared spectrometer model 640-IR, equipped with a diamond ATR accessory from PIKE, with a resolution of 4 cm-1.

A Shimadzu X-ray diffractometer, model XRD-700, with Cu Kα radiation, operating at 40 kV and 20 mA was used to analyze the crystallinity of the specimens. The degree of crystallinity was determined by the technique proposed

by Hermans and described by Poletto[22].

3. Results and Discussions 3.1. Density measurements The density of the composites is shown in Table 1.

It ranged from 1155.50 to 1214.08 kg/m3. According to Brasil et al.[23], the density of the pine nut shell powder is 180 kg/m3. PU density is 1090 kg/m3 and pine nut shell is 900 kg/m3.

The density of the composite with the addition of pine nut shell powder is greater than the density of PU alone.

According to the rule of mixtures, the density of the composite should be lower than the PU. Bubbles are generated during the production of PU because of the reaction of isocyanate with air humidity, as observed by Merlini et al.[16] and Marinho[15]. However, it was possible to obtain a slightly better densification of the composites because of the high speed (3200 rpm) of the mechanical mixing process, since the fine powder of the pine nut shell occupied the spaces of the bubbles generated in the polymerization process, thus allowing the incorporation of 70% of particles of 0.3 mm.

The standard technique used to produce composites with thermoset matrix is manual mixing of the components followed by pressing. The technique employed in this work, i.e., mechanical mixing, allowed a greater incorporation of fine particles within the polymer matrix, increasing the density of the material when compared to neat PU.

3.2. Water absorption determination The results obtained from the water absorption test for 2 and 24 hours for the composites with different fiber particle sizes are shown in Figure 1.

Our data indicate that water absorption increases with time, fiber content and decreasing particle size. This is to be expected since water absorption is attributed to the lignocellulosic component. So, water uptake should increase with the amount of fiber and its surface area. Even though the standard used in this work suggest that water uptake measurements should be made after 2h and 24h of immersion, we performed measurements up to saturation, as the ASTM D570 standard suggests. We observed that composites absorb water rapidly within the first 24 hours, and after that, a saturation level of 12.5% is reached for a sample with 50% PU, and no further water uptake is observed, even after 15 days of immersion.

Composites with 0.6 mm and 0.3 mm fibers and 50% PU showed the lowest water absorption in 2 and 24 hours immersion, and this is attributed to the higher amount of PU of these composites.

The data shown in Table 1 indicates that independent of the amount of fiber and its size, the density vary slightly, and increases a little when compared to the PU. Table 1. Composites density.

Sieve 0.6 0.6 0.6 0.3 0.3 0.3

PU (wt%) 100 30 40 50 30 40 50

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Density (Kg/m3) 1090.00±0.03 1194.31±24.66 1155.50±57.30 1155.63±14.15 1200.64±21.80 1213.78±15.45 1184.55±29.31

Figure 1. Water absorption test results. 2 and 24 hours of test for composites with 0.6 mm (#30) and 0.3 mm (#50) fibers.

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Protzek, G. R., Magalhães, W. L. E., Bittencourt, P. R. S., Claro Neto, S.,Villanova, R. L., & Azevedo, E. C. Water absorption is lower for the composites made with 0.6 mm fiber. Bigger fibers have less surface area, resulting in less water absorption. Composites made of 0.3 mm fiber and 40% PU and 50% PU showed very similar water absorption values.

Water absorption occurs only by the pine nut shell particles, because PU does not absorb water[15]. The values obtained indicate that the fibers were covered by PU efficiently regardless of the amount and granulometry of the fibers used and this is attributed to the mixing technique employed here. Marinho[15] has studied the water absorption of manually mixed PU and bamboo composites using the same PU employed here and obtained water uptake values of of 22.9% for composites made with 80% (wt%) of 2.7 mm bamboo fibers Measurements were made according to the ASTM D570 standard at room temperature.

3.3. Flexural strength measurements The flexural strength of the composites is shown in Figure 2. The flexural strength of PU is 42 MPa[11], and the highest flexural resistance was obtained for the composite made with 0.3 mm pine nut shell and 30% PU. When compared to PU, the increase in flexural strength was 27%.

The data shown in Figure 2 indicate that the flexural strength of the composites increases with increasing fiber content and decreasing filler particle size. This is associated with improved packing of finer fibers, as shown in Figure 3.

Vasco et al.[11] and Merlini et al.[16] observed that an interaction between hydroxyl groups from the fibers and PU isocyanate occurs, promoting chemical adhesion between the polymer matrix and the reinforcement. Smaller fibers favor packing, distribution and homogenization of the reinforcement within the matrix, resulting in better adhesion between materials[24].

The fibers were not treated to improve the interface with the PU, and even so displayed higher flexural strength values than those of other composites made with natural fibers, such as the composite developed by Zau et al.[17], that found flexural strength of 14 MPa for composites made with 85% sugarcane bagasse and castor oil polyurethane adhesive-based particulate. This shows that the mixing technique is efficient for the production of fine particulate composites with larger amounts than usual.

3.4. SEM The micrographs of the fracture surfaces after three‑point flexural test of composites made with 0.6 mm pine nut shell and 30% and 50% PU are shown in Figures 4a and 4b, respectively. In Figure 4a, a good fiber-matrix interface can be observed, as well as the presence of voids resulting from the fibers that were detached from the matrix during the tests. The fracture of the PU matrix and the presence of bubbles can also be observed.

For the composite with 50% PU (Figure 4b), the good fiber-matrix interface, as well as the voids from detached fibers, can also be observed. PU displayed brittle fracture, as demonstrated by the mirror-like areas close to stress concentrators such as bubbles and impurities of the surface of the fiber. The reduction in the composite mechanical strength could also be attributed to these characteristics.

Figure 2. Flexural strength of the composites.

Figures 5a and 5b show the fracture surfaces after bending test of composites made with 0.3 mm pine nut shell and 30% PU and 50% PU, respectively. In Figure 5a, it is not possible to observe the presence of voids or holes

Figure 3. SEM micrographs of 0.6 mm (a) and 0.3 mm (b) particles.

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The influence of fiber size on the behavior of the araucaria pine nut shell/PU composite

Figure 4. SEM microgaphs of the fracture surfasse of 0.6 mm composites: (a) 30%PU, (b) 50%PU.

Figure 5. SEM microgaphs of the fracture surfasse of 0.3 mm composites: (a) 30%PU, (b) 50%PU.

in the fiber-matrix interface, indicating that the fibers were well covered by the polymer and some chemical interaction between the components might have occurred.

This increases the adhesion between fibers and polymer, improving mechanical properties by means of a better distribution of mechanical loads. Some small bubbles can also be observed throughout the composite. In Figure 5b, the interaction between the fibers and the matrix can be observed, was well as the presence of voids resulting from fiber detachment. PU fracture is brittle, and there are bubbles all over the matrix. Although the homogenization technique has been efficient to promote the incorporation of the fiber into the matrix, it does not avoid the formation of small bubbles, which are inherent to the PU production process.

3.5. TGA The results from the thermogravimetric analyses for PU and pine nut shell are shown in Figures 6a and 6b, respectively.

Two distinct events can be observed for the PU, the first one occurring between 250°C and 350°C with a mass Polímeros, 29(2), e2019025, 2019

loss of 40%. In this temperature range, the urethane bonds are broken[25]. The second event takes place between 350°C and 500°C with a mass loss of 60%, and this is attributed to the decomposition of the ester bonds present in polyol[26].

Regarding the pine nut shell, an initial mass loss event at 30°C is observed, which is associated with the loss of absorbed water, typical of lignocellulosic materials[7]. In the range from 170°C to 295°C, there is another mass loss event related to the degradation of hemicellulose[5]. From 295°C to 330°C, cellulose degrades[27], while lignin degrades between 330 and 500°C[28]. The remaining 27% of mass can be considered carbonaceous residues.

In Figure 7, the TGA and DTG curves of 30 mesh and 50 mesh composites are shown. From the figure, it is possible to observe that the thermal stability of the composites lies between those of PU and pine nut shell. The first event occurs between 50°C to 150°C, and it is related to the presence of water [11]. The next event occurred between 150°C and 394°C and might have happened because of the degradation of the pine nut shell. The third event occurs form 394°C to 500°C and is probably related the degradation of the PU. 5/9

Protzek, G. R., Magalhães, W. L. E., Bittencourt, P. R. S., Claro Neto, S.,Villanova, R. L., & Azevedo, E. C.

Figure 6. Thermogravimetric data for (a) PU and (b) pine nut shell.

Figure 7. (a) TG and (b) DTG curves of 0.6 mm (#30) and 0.3 mm (#50) composites.

Particle size does not influence the thermogravimetry of the composites. The initial mass loss of the composites occurs around 150 °C, which is expected, since the thermal stability of the fibers of pine nut shell is around 170 °C.

3.6. FTIR FTIR spectrograms of PU and pine nut shell are shown in Figure 8. For PU, an O-H band is observed at 3320 cm-1.

The bands at 2920 and 2850 cm-1are associated with C-H symmetrical and asymmetrical stretching[27]. The isocyanate band is located at 2270 cm-1 [16], and the urethane bands at 1700, 1596, and 1520 cm-1 are related to the C=O and N-H stretching, and they tend to increase with the crosslinking of the polyurethane chains[16,29].

For the pine nut shell, a band at 3340 cm-1 associated to lignin phenols and cellulose and hemicellulose hydroxyls can be observed[30].

The band at 2930 cm-1 is related to the C-H bond stretching present in cellulose and hemicellulose[5]. The peak at 1610 cm-1 is related to C=O carbonyl bonds of the lignin[16], while the peak at 1024 cm-1 corresponds to the C-H aromatic group and to the stretching of primary alcohols of lignin[5].

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The spectrograms of 0.6 mm and 0.3 mm composites are shown in Figure 9a and Figure 9b respectively. There was a reduction in the intensity of the NCO and OH peaks of the composites. Such reduction might indicate a chemical affinity between O-H and N-C-O groups of the materials which the composites are made of.

3.7. XRD The XRD diffractograms of PU, pine nut shell fibers, and composites (both 0.6 and 0.3) are shown if Figure 10.

Polyurethane results from the chemical reaction between an isocyanate and a hydroxyl group. In this polymerization, a compound containing two or more isocyanate groups per molecule reacts with a polyol or a polyfunctional alcohol. Any changes in the polyol and pre-polymer ratio (–NCO/–OH) cause substantial morphological changes in the PU chains, leading to modifications in mechanical properties of the material. The degree of crosslinking is controlled by the isocyanate group (–NCO) of the pre-polymer and by the hydroxyl group of the polyol, and, in the composites with pine nut shell, a reation with the OH of the pine nut shell particles also occurs.

Polímeros, 29(2), e2019025, 2019

The influence of fiber size on the behavior of the araucaria pine nut shell/PU composite

Figure 8. FTIR spectra of (a) PU and (b) pine nut shell.

As demonstrated in Figure 10, the diffraction profiles show an amorphous broad shoulder, diffused diffraction with a maximum at 2θ = 20°. It is likely that some soft segment-hard segment phase mixing could occur in the system disturbing the soft segment crystallization[26,29].

This may account for the broader diffraction peaks shown in the diffracttograms. For ordinary synthetic polymers, the nonuniformity of the molecules makes it impossible to form perfect single crystals. As a result, amorphous and crystalline phases are present in a real polymers, and these entities have complex organization.

In the pine nut shell diffractograms, peaks at 16° and 22° are observed, corresponding to the amorphous and crystalline regions of cellulose, respectively[31]. Such behavior is similar to semicrystalline structures.

The degree of crystallinity of the composites are shown in Table 2, The determination of the amorphous to crystalline percentage was obtained from peak area ratios. It can be

Figure 9. FTIR spectra of PU and composites: (a) 0.6 mm and (b) 0.3 mm.

Figure 10. XRD diffractograms of PU, pine nut shell fibers, and composites: (a) 0.6 mm (#30) and (b) 0.3 mm (#50).

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Protzek, G. R., Magalhães, W. L. E., Bittencourt, P. R. S., Claro Neto, S.,Villanova, R. L., & Azevedo, E. C. Table 2. Degree of crystallinity.

Sieve

PU (%)

Xc (%)

0.6 0.6 0.6 0.6 0.3 0.3 0.3 0.3 -

0 30 40 50 0 30 40 50 100

36 32 34 31 36 32 32 32 31

observed that the composites display a small increase of crystallinity when compared to neat PU, indicating that structural changes occurred during the production process.

The results indicate that filler particle size does not affect the degree of crystallinity.

4. Conclusions The aim of this work was to investigate the mechanical, physical and thermal properties of properties of PU/pine nut shell composites as a function of fiber content and granulometry. Density was higher for composites made with finer fibers, and water absorption increased with time, fiber content and decreasing particle size. Flexural strength was higher for composites with higher amount of fibers and smaller sizes. A good fiber-matrix interface, as well as the presence of micro bubbles, which are inherent of the PU production process, was shown by the SEM micrographs.

TGA analyses showed that PU and all composites were thermally stable up to 150°. The reduction in the intensity of the NCO and OH peaks observed in FTIR analyses indicates reaction between these groups. The results indicate that the composite degree of crystallinity was not affected byfiller particle size.

5. Acknowledgements The authors would like to thank CAPES, FAPESP, Fundação Araucária, and CNPQ for financial support, CEQUIL for donating the PU used in this work, Embrapa Florestas for the equipments and for donating the pine nut shell, Centro Multiusuário de Caracterização de Materiais from UFPR-CT for the SEM analyses, DAQUI from Campus Medianeira of UTFPR, and LAMAQ from Campus Curitiba/Ecoville for the equipments.

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14. Azevedo, E. C., Nascimento, E. M., Chierice, G. O., Claro, S., No., & Lepienski, C. M. (2013). UV and gamma irradiation effects on surface properties of polyurethane derivate from castor oil. Polímeros Ciência e Tecnologia, 23(3), 305-311. http://dx.doi.org/10.4322/polimeros.2013.087.

15. Marinho, N. P., Nascimento, E. M., Nisgoski, S., Magalhães, W. L. E., & Neto, C. S., & Azevedo, E. C. (2013). Caracterização física e térmica de compósito de poliuretano derivado de óleo de mamona associado com partículas de bambu. Polímeros: Ciência e Tecnologia, 23(2), 201-205. https://doi.org//10.4322/ S0104-14282013005000007.

16. Merlini, C., Soldi, V., & Barra, G. M. O. O. (2011). Influence of fiber surface treatment and length on physico-chemical Polímeros, 29(2), e2019025, 2019

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17. Zau, M. D. L., Vasconcelos, R. P., Giacon, V. M., & Lahr, F. A. R. (2014). Avaliação das propriedades química, física e mecânica de painéis aglomerados produzidos com resíduo de madeira da Amazônia - Cumaru (Dipteryx Odorata) e resina poliuretana à base de óleo de mamona. Polímeros: Ciência e Tecnologia, 24(6), 726-732. http://dx.doi.org/10.1590/01041428.1594.

18. Orellana, E., Figueiredo, A., Fo., Péllico, S., No., & Vanclay, J. K. (2017). A distance-independent individual-tree growth model to simulate management regimes in native Araucaria forests. Journal of Forest Research, 22(1), 30-35. http://dx.doi. org/10.1080/13416979.2016.1258961.

19. Fichino, B. S., Pivello, V. R., & Santos, R. F. (2017). Trade-offs among ecosystem services under different pinion harvesting intensities in Brazilian Araucaria Forests. The International Journal of Biodiversity Science, Ecosystem Services & Management, 13(1), 139-149. http://dx.doi.org/10.1080/215 13732.2016.1275811.

20. Boff Zortéa-Guidolin, M. E., Piler de Carvalho, C. W., Bueno de Godoy, R. C., Mottin Demiate, I., & Paula Scheer, A. (2017).

Influence of extrusion cooking on in vitro digestibility, physical and sensory properties of brazilian pine seeds flour (Araucaria Angustifolia). Journal of Food Science, 82(4), 977-984. http:// dx.doi.org/10.1111/1750-3841.13686. PMid:28339105.

21. Lima, E. C., Royer, B., Vaghetti, J. C. P., Brasil, J. L., Simon, N. M., Santos, A. A., Jr., Pavan, F. A., Dias, S. L. P., Benvenutti, E. V., & Silva, E. A. (2007). Adsorption of Cu(II) on Araucaria angustifolia wastes: determination of the optimal conditions by statistic design of experiments. Journal of Hazardous Materials, 140(1-2), 211-220. http://dx.doi.org/10.1016/j. jhazmat.2006.06.073. PMid:16876938.

22. Poletto, M., Zattera, A. J., Forte, M. M. C., & Santana, R. M. C. (2012). Thermal decomposition of wood: Influence of wood components and cellulose crystallite size. Bioresource Technology, 109, 148-153. http://dx.doi.org/10.1016/j. biortech.2011.11.122. PMid:22306076.

23. Brasil, J. L., Ev, R. R., Milcharek, C. D., Martins, L. C., Pavan, F. A., Santos, A. A., Jr., Dias, S. L., Dupont, J., Zapata Noreña, C. P., & Lima, E. C. (2006). Statistical design of experiments as a tool for optimizing the batch conditions to Cr(VI) biosorption on Araucaria angustifolia wastes. Journal of Hazardous Materials, 133(1-3), 143-153. http://dx.doi. org/10.1016/j.jhazmat.2005.10.002. PMid:16297543.

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24. Ahmed Sbia, L., Peyvandi, A., Soroushian, P., Balachandra, A. M., & Sobolev, K. (2015). Evaluation of modified-graphite nanomaterials in concrete nanocomposite based on packing density principles. Construction & Building Materials, 76, 413-422. http://dx.doi.org/10.1016/j.conbuildmat.2014.12.019.

25. Azevedo, E. C., Claro, S., No., Chierice, G. O., & Lepienski, C. M. (2009). Aplicação de indentação instrumentada na caracterização mecânica de poliuretana derivada de óleo de mamona. Polímeros: Ciência e Tecnologia, 19(4), 336-343. http://dx.doi.org/10.1590/S0104-14282009000400014.

26. Azevedo, E. C., Chierice, G. O., Claro, S., No., Soboll, D. S., Nascimento, E. M., & Lepienski, C. M. (2011). Gamma radiation effects on mechanical properties and morphology of a polyurethane derivate from castor oil. Radiation Effects and Defects in Solids, 166(3), 208-214. http://dx.doi.org/10.

1080/10420150.2010.525235.

27. Ornaghi, H. l., Jr., Moraes, Á. G. D. O., Polletto, M., Zattera, A. J., & Amico, S. C. (2016). Chemical composition, tensile properties and structural characterization of buriti fiber.

Cellulose Chemistry and Technology, 50(1), 15-22. Retrieved in 2018, April 10, from http://www.cellulosechemtechnol.ro/ pdf/CCT1(2016)/p.15-22.pdf 28. Li, X., Lei, B., Lin, Z., Huang, L., Tan, S., & Cai, X. (2014).

The utilization of bamboo charcoal enhances wood plastic composites with excellent mechanical and thermal properties.

Materials & Design, 53, 419-424. http://dx.doi.org/10.1016/j. matdes.2013.07.028.

29. Trovati, G., Sanches, E. A., Neto, S. C., Mascarenhas, Y. P., & Chierice, G. O. (2010). Characterization of polyurethane resins by FTIR, TGA, and XRD. Journal of Applied Polymer Science, 115(1), 263-268. http://dx.doi.org/10.1002/app.31096.

30. Luo, Z., Li, P., Cai, D., Chen, Q., Qin, P., Tan, T., & Cao, H. (2017). Comparison of performances of corn fiber plastic composites made from different parts of corn stalk. Industrial Crops and Products, 95, 521-527. http://dx.doi.org/10.1016/j. indcrop.2016.11.005.

31. Obi Reddy, K., Uma Maheswari, C., Shukla, M., Song, J. I., & Varada Rajulu, A. (2013). Tensile and structural characterization of alkali treated Borassus fruit fine fibers. Composites. Part B, Engineering, 44(1), 433-438. http://dx.doi.org/10.1016/j. compositesb.2012.04.075.

Received: Apr. 10, 2018 Revised: Feb. 12, 2019 Accepted: Apr. 04, 2019

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.14416

Tribology of natural Poly-Ether-Ether-Ketone (PEEK) under transmission oil lubrication Thiago Fontoura de Andrade1* , Helio Wiebeck2 and Amilton Sinatora3,4 Research and Development, Punch Powertrain, Sint-Truiden, Belgium Departamento de Engenharia Metalúrgica e de Materiais, Escola Politécnica, Universidade de São Paulo – USP, São Paulo, SP, Brasil 3 Laboratório de Fenômenos de Superfície – LFS, Departamento de Engenharia Mecânica, Escola Politécnica, Universidade de São Paulo – USP, São Paulo, SP, Brasil 4 Instituto Tecnológico Vale, Vale S.A., Ouro Preto, MG, Brasil 1

2

*thiago.andrade@punchpowertrain.com

Abstract High performance polymeric materials such as poly-ether-ether-ketone (PEEK) are increasingly being used for challenging tribological applications in order to replace metal parts in vehicle engines and transmissions. The tribology of natural PEEK, under oil-lubricated conditions, was studied for different metal counterbody finishes. Two different finishing processes were selected for this study: turning and polishing. The test system used was a tri-pin on disc, with pins made of PEEK and counterbodies made of steel, and then dipped in ATF Dexron VI oil. The conclusion was that the wear rate generated by turning was about seven times as high as the wear rate generated by polishing. The friction coefficient displayed a direct correlation with the lubrication regime, and the level of counterbody roughness. On average, the friction coefficient on the hydrodynamic regime for polishing was more than 3 times lower than the friction coefficient in the boundary regime for turning.

Keywords: tribology, PEEK, roughness, wear, friction.

How to cite: Andrade, T. F., Wiebeck, H., & Sinatora, A. (2019). Tribology of natural Poly-Ether-Ether-Ketone (PEEK) under transmission oil lubrication. Polímeros: Ciência e Tecnologia, 29(2), e2019026. https://doi.org/10.1590/01041428.14416

1. Introduction Poly(ether-ether-ketone) (PEEK) is a semicrystalline polymer, first mentioned in the literature in the early 1980’s[1]. It has high melt and glass transition temperatures (Tm = 340 °C, Tg= 143 °C), high mechanical properties, excellent chemical resistance and melt and machining processability[2]. Furthermore, PEEK is known for its excellent tribological properties[3].

PEEK provides advantages such as relatively low friction and low wear rate for many tribological applications[4]. Many investigations on the friction and wear properties of PEEK, and its composites, have been performed. Cirino et al.[5] reported PEEK behavior to abrasive wear; Voss et al.[6] investigated the behavior of sliding and abrasive wear at room temperature, and Friedrich et al.[7] examined the effect of counterpart roughness and temperature in relation to PEEK friction and wear.

Most tribological studies related to PEEK friction and wear in the literature were performed exclusively on dry environments[7-11]. However, it has been established that, in general, the interfacial environment considerably changes the effects of friction in polymers.

Zeng et al.[10] pointed out both the beneficial and harmful effects of water on the friction and wear performance of

Polímeros, 29(2), e2019026, 2019

reinforced polymers. Water inhibits buildup of transfer film; it may also penetrate and corrode the fiber-matrix interface.

On the other hand, the role of water in decreasing frictional heat and reducing contact temperature was considerably pronounced, thus preserving the properties of the polymer such as stiffness, fatigue life and strength of the contact surface. The second beneficial effect of water is that it removes debris from the frictional region, thereby reducing abrasive wear, and ultimately improving the effect of carbon fiber polishing of the counterbody, in order to reduce surface roughness and wear.

However, the tribological behavior of PEEK under lubrication, with diesel and motor or transmission oil, has rarely been reported. Zhang et al.[12] have studied the frictional and wear properties of pure PEEK and PEEK composites immersed in diesel and motor oil submitted to sliding against steel counterbodies. It has been shown that, in mixed and boundary lubrication regimes, the structure of the materials tested significantly affected tribological performance. The addition of diesel reduced friction and wear rates of pure PEEK. In the case of PEEK composites containing carbon fiber, ceramic particles and solid lubricants, addition of 2uL/​​h diesel significantly increased friction and

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

Andrade, T. F., Wiebeck, H., & Sinatora, A. wear, as it inhibited buildup of high-performance transfer film. However, an increased flow of diesel gradually decreases friction and wear. In tests conducted with motor oil, the Stribeck curve demonstrates that, increments in sliding speed result in increased hydrodynamic action, thereby diminishing the friction coefficient. Another effect observed under this condition was a reduction or inhibition in counterbody film transfer buildup.

In view of the lack of studies about the wear morphology and friction behavior of PEEK under oil lubrication, the objective of the present work was to evaluate the friction and wear behavior of natural PEEK in lubricated environments, and with different levels of metal counterbody roughness.

2. Materials and Methods 2.1 Friction test Polymer behavior regarding friction and wear was analyzed using a three-pin on metal disc tribometer sliding unidirectionally (Figure 1). The three-point contact was used to provide greater rotation speed stability in the test.

The tribological results obtained from three-pin on disc test machines are generally different from those obtained from single-pin test machines. Single-pin tests tend to display stick-slip and preferential wear of pin edges. Three-pin on disc systems are particularly more suitable for the study of roughness on wear as they maintain contact surface fairly constant, after initial running-in[10].

The present study was conducted using Victrex 151G-type PEEK[11]. 5-mm-diameter pins were injected, per ASTM G99-04[13], at a temperature of approximately 380 °C. The friction surface was smoothly polished for 3 minutes using 0.5-µm sandpaper in order to reduce remnant rough edges from injection molding, and to correct friction surface flatness. The counterbody consists of a disc, made of SAE 8620 steel, submitted to carburizing, quenching and tempering to a surface hardness range of 58-63 HRC.

After heat treatment, the counterbody surface was finished by means of two different processes: turning and polishing.

The test was conducted with all pins completely immersed in ATF Dextron VI oil, at a temperature of 85 ± 5 °C inside the test chamber. The dynamic viscosity at 30 °C and 85 °C was 36.3 cP and 6.35 cP respectively. For each test, all three pins were replaced. The pins were positioned 120° apart, and then moved on the same track. Normal force was applied via a piezo-actuator on a servo‑controlled mechanism.

The capacitive sensor enabled continuous monitoring and comparison of the normal and nominal force of approximately 118 N (equivalent to an apparent contact pressure of 2 MPa), so that any variations could be immediately corrected.

Rotational speed was 125 rad/s, which corresponds to a linear speed of 2 m/s, also kept constant throughout the test. Test duration was determined after evaluation of wear for different sliding periods until the wear rate remained constant. As a result, we adopted a 120-minute period.

All tests were repeated at least three times.

2.2 Assessment of Wear The specific wear rate (WS) expressed by Equation 1 was calculated via material mass loss (Δm), by measuring the difference in pin mass before and after the test, divided by the load (F), sliding distance (L) and material density (ρ).

Ws =

∆m FL ρ

 mm3     Nm 

(1)

2.3 Roughness measurements A white light interferometer (Zygo Nexview) was used to measure roughness. Figure 2 shows the typical topography of each finishing studied. The mean linear roughness parameters are shown in Table 1. These parameters were calculated perpendicular to the sliding direction. Four measurements were carried out for each sample, 90° apart.

Figure 1. Diagram of tri-pin on disc apparatus.

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Figure 3. Friction surface of the natural PEEK pin before testing.

Figure 2. Typical disc surface roughness measurements for three test repetitions; (a) turning and (b) polishing.

Table 1. Values for surface roughness for each steel counterbody finishing: roughness average (Ra), root mean square (RMS), and total roughness (Rz).

Figure 4. Aspect of a sample of natural PEEK before the test, with abrasion wear marks across the friction surface of the pin.

Finishing Process Ra (µm) RMS (µm) Rz (µm) Turning 1.264 ± 0.010 1.477 ± 0.013 6.340 ± 0.149 Polishing 0.048 ± 0.003 0.063 ± 0.004 0.575 ± 0.096

2.4 Microscopic characterization of wear properties After gold sputtering, the frictional surfaces were examined via scanning electron microscopy (SEM), on a FEI Inspect F50 microscope. Energy dispersive X-ray analysis (EDX) was also used in SEM investigations in order to check whether particles were embedded in the friction surfaces.

3. Results and Discussion 3.1 Friction surface characterization before test Pins made of natural PEEK were submitted to mechanical polishing, and their surfaces were characterized as shown in Figures 3-5. Figure 3 shows a 50-x magnification of the pin friction surface, after being prepared for the test. Figure 4 and 5 show the friction surface via scanning electron microscopy.

The injection molded pins were polished to eliminate Polímeros, 29(2), e2019026, 2019

Figure 5. Contaminants from the polishing system circled in red.

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Andrade, T. F., Wiebeck, H., & Sinatora, A. burrs, but this process caused some abrasion marks due to contaminants in the polishing system. Such contaminants were identified, via EDX, as potassium chloride, as shown in Figure 6. The surface topography condition before the wear tests is important in order to avoid misinterpretation of the wear mode after sliding.

3.2 Wear mechanism of the pair PEEK/polishing counterbody In order to determine the predominant wear mechanism, worn surfaces were analyzed via SEM. After sliding against the polished counterbody, the PEEK pin displayed no apparent sliding marks. Figure 7 shows wear morphology after 120 minutes. Figure 7 b) and c) show the rounded edges of grooves formed during the preparation of the sample, and round-shaped debris. As the general aspect of the friction surface was very similar before and after the tests, it was not possible to identify sliding direction. This is evidence of hydrodynamic lubrication regime for most of the duration of the test. Apparently, the debris originated from the edges of the existing grooves. It could be hypothesized that the debris were formed by fatigue, probably caused by the oil film flowing between the sliding tribological pair[12]. Another possible explanation would be that, while sliding, the groove edges at the pin surface collided with counterbody asperities, despite oil film separation of the surfaces. The repeated collisions caused fatigue and the corresponding edges were ultimately eliminated from the matrix. Thus, debris and fractured regions or holes formed in the worn surface (Figure 7c and d). The debris can contribute to abrasion of the pins in the following sliding process, and be incorporated into the polymer bulk once again, or be transferred to the counterbody[12].

3.3 Wear mechanism of the pair PEEK/Turning counterbody Counterbody surface roughness, produced by the turning finishing, changed the tribological behavior of natural PEEK. The test of the PEEK pin against turned steel surface was

conducted under the same pressure and speed as the test with the polished disc. Figure 8 shows the wear morphology of the pin, at different magnifications, analyzed via SEM, after the 120-minute test, under oil lubrication. Figure 8a) shows how the metal counterbody abraded the plastic pin, forming its topography on the plastic friction surface. This indicates direct pin/disc contact, and a continuous wear process.

Figure 8b) displays peaks and valleys on the friction surface of the pin, similar to counterbody topography. Yellow arrows show shallow pits formed by fatigue. The surface observed in Figure 8c) and d) indicates the presence of microgrooves combined with wear morphology similar to aligned ripples or wavy folds, repeatedly formed, and perpendicular to the sliding direction. This demonstrates the viscoelastic behavior of natural PEEK[14]. When the pin touches the rigid asperities of the steel counterbody, and slips, under pressure and speed conditions, the molecules of the polymer are deformed and tend to align in the direction of the deformation. The alignment and relative movement between the amorphous portion of polymer molecules, and the accommodation by the deformation mechanism, results in a low elastic modulus; 3.7 GPa, typical for natural PEEK[10,15]. In solid contact with a rough surface, the low modulus of elasticity has two effects. The first effect is that the true area of contact is very close to the apparent contact area. The second is a considerable tangential movement, parallel to the sliding direction, without excessive release of wear debris[16]. This sliding mechanism works on the principle that a large portion of the polymer surface is strongly connected to the opposing surface. This connection takes place due to Van de Waals forces and hydrogen bonds[17]. The formation and rupture of such bonds control the friction adhesion component. This process is known as “stick-slip”, and due to adhesion forces at the surface, there is no relative movement between the bonded surfaces, even when the tangential movement is sufficient to break the metal / polymer connection, leading to development of ripples or wavy folds wear patterns[18,19]. Such surface characteristics occur under the boundary lubrication regime. The findings suggest that the wear mechanism is a

Figure 6. Potassium chloride contamination, as seen in Figure 4, identified by EDS. 4/9

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Tribology of natural Poly-Ether-Ether-Ketone (PEEK) under transmission oil lubrication

Figure 7. Morphology of natural PEEK pin wear tested against a polished counterbody. a) friction surface similar to the pre-test state; b) grooves produced during sample preparation; c) Yellow arrows point to fractures where debris formed; d) rounded debris are shown by green arrows. Red arrows point to holes on the friction surface.

combination of adhesion and abrasion[9,20]. Another factor that increases the adhesive / abrasive wear component is the presence of massive amounts of chip-type debris, generated at the very tip of the sliding pin, as shown by the yellow arrows in Figure 9. The wear mechanism that creates this type of debris can be defined as “transfer mode”, in which the interfacial bonding between the sliding pair is stronger than the cohesive strength of PEEK[21]. In this case, PEEK can be gradually transferred to the surface of the metal disc. Then, the material accumulated on the surface of the counterbody is removed in the form of flakes[12].

Zhang et al.[22] studied the effect of lubrication with diesel oil in natural PEEK and found that, under dry sliding, parallel grooves tend to form in the sliding direction; therefore, the abrasion mechanism by metal asperities is important.

However, wear morphology changes when the tribosystems are lubricated with diesel oil. Fewer grooves are formed on the surface of the PEEK pin during boundary lubrication.

Polímeros, 29(2), e2019026, 2019

This indicates that when diesel oil is present in the wear track, the effect of abrasion is attenuated, compared to dry sliding condition. On the other hand, the addition of diesel oil, as well as the use of ATF Dexron VI Oil, marked the onset of ripple-type wear patterns. The increased amount of diesel oil also incremented the number of ripple-type patterns.

It is believed that these types of wear patterns occur when the adhesion component is greater than abrasion, under a boundary lubrication regime[23,24].

3.4 Wear rate and friction coefficient To illustrate the contrast between polishing and turning, Figure 10 shows the values of specific wear rates as a function of metal disc roughness. For measurements made with natural PEEK, wear rates were approximately seven times higher for turning (2.664 ± 0.708 x 10-7mm3/Nm) than for polishing finishing (0.411 ± 0.242 × 10-7mm3/Nm).

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Andrade, T. F., Wiebeck, H., & Sinatora, A.

Figure 8. Morphology of a pin made of natural PEEK worn against turned counterbody. The white arrows indicate the sliding direction; a) Grooves generated by harder asperities of the counterbody; b) The yellow arrows indicate shallow pits formed by fatigue, c) Presence of vertical ripple-type patterns towards the slip direction; d) The red arrows show the morphology and the repetitive pattern of the ripples.

Figure 9. Surface of a pin made of natural PEEK tested against turning disc. Yellow arrows indicate the debris produced by material displacement caused by the tangential force during sliding.

The white arrow shows sliding direction.

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This result reflects the wear mechanism observed in scanning electron microscopy. When rubbed against the polished surface, natural PEEK produced less debris, formed by fatigue, probably due to the action of the oil film flux between the tribological pair during sliding. The turned surface produced much more debris due to cohesive wear abrasion and adhesion, which produced a higher specific wear rate than the polished surface.

Figure 11 shows the behavior of the friction coefficient of PEEK as a function of test time for turning and polishing.

The average friction coefficient for turning was 0.121 ± 0.009, whereas for polishing it was approximately 0.0347 ± 0.003.

In general, it was possible to ascertain that the friction coefficient increases as surface roughness increases. Greenwood and Williamson[25] initially proposed that when two surfaces slide over each other, friction comes from the shear stress generated by plowing caused by counterpart asperities.

In the case of the turned surface, clearly there was contact between the pin and disc; however, for the polishing finish, there is evidence that an oil film separated the tribological pair. Thus, the friction coefficient measured derives primarily from the viscous shear flow of the lubricant.

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Tribology of natural Poly-Ether-Ether-Ketone (PEEK) under transmission oil lubrication For the polymer-metal contact, friction can be attributed to two sources: deformation, which involves relatively large energy dissipation around the contact area of ​​the polymer, and adhesion at the friction surface between

Figure 10. Effect of counterbody roughness on specific wear rate of the pin made of natural PEEK.

the metal and the polymer[17]. The friction coefficient of PEEK/turning disc above 0.14, obtained at the start of the test, may be due to strong contribution of the adhesion mechanism of PEEK, which was highly deformed by the asperities on the turning disc. The high loss of hysteresis and internal energy dissipation can account for the high friction coefficient in the natural PEEK condition. This is confirmed by evidence of adhesive wear (wavy folds) observed in wear morphology[12]. During the test, when the pins were wearing out, the friction coefficient decreased due to increased contact area, and reduction of the adhesive wear component through a decrease in the pressure applied. This resulted in improved lubrication, with a friction coefficient of 0.12, after 90 minutes. Another factor that could have led to a reduced friction coefficient was the buildup of a tribofilm on the counterbody friction track. This occurs when the shear plane is changed from the steel surface to the polymer layer formed on the metal surface[12]. The tribofilm is produced as a result of a PEEK film being transferred to the counterbody through tribochemical reactions, such as the formation of organometallic compounds[26]. However, scanning electron microscopy did not show such tribofilm.

Figure 12 shows the surface of a turned counterbody analyzed via backscattered electron technique. The characterization

Figure 11. Results of friction tests conducted for the two different finishes studied regarding PEEK. a) turning and b) polishing.

Figure 12. Steel counterbody surface analyzed by electron backscatter technique; a) 30-x magnification; b) 1,000-x magnification.

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Andrade, T. F., Wiebeck, H., & Sinatora, A. of a tribofilm structure is complex because the film is extremely thin. Scherge et al.[27] measured the PA 46 transfer film layer formed on the metal counterbody, after sliding in a lubricated environment, through autoradiography and X-rays photoelectron spectroscopy. The key indicator to measure the thickness of the polymer film was the concentration of nitrogen that helped determine a 160-nm layer. The polymer chain of PEEK does not include nitrogen, but the concentrations of oxygen and carbon can be used in a future study.

4. Conclusions Natural PEEK showed great potential for application in vehicle powertrain parts in oil-lubricated environments.

The wear rate for both finishes tested is below 10-6 mm3/Nm, which enables the use of Natural PEEK for engineering applications. The results obtained with natural PEEK under sliding wear condition, for polished and turned counterbody finishings, can be summarized as follows: • The wear mechanism for the PEEK pin was fatigue of groove edges while sliding against a polished counterbody.

On the other hand, the wear mechanism seen for the PEEK pin/turned counterbody pair was a combination of abrasion and adhesion.

• The wear rate was seven times higher for turning than for polishing under the conditions tested.

• The friction coefficient for turning was more than 3 times that of polishing.

• The lubrication regime for the PEEK/polished counterbody pair was hydrodynamic, whereas for the PEEK/turned counterbody it was boundary.

5. Acknowledgements The authors wish to thank Mr. Ricardo Elhke and Mr. Kida Kazuhiro from Victrex for kindly supplying the polymeric material, as well as the test benches, and for their invaluable technical input.

6. References 1. Attwood, T. E., Dawson, P. C., Freeman, J. L., Hoy, L. R. J., Rose, J. B., & Staniland, P. (1981). Synthesis and properties of polyaryletherketones. Polymer, 22(8), 1096-1103. http:// dx.doi.org/10.1016/0032-3861(81)90299-8.

2. Gutiérrez, J. C., Rubio, J. C. C., & Faria, E. (2014). Usinabilidade de materiais compósitos poliméricos para aplicações automotivas.

Polímeros. Ciência e Tecnologia, 24(6), 711-719.

3. Friedrich, K., Karger-Kocsis, J., & Lu, Z. (1991). Effects of steel counterface roughness and temperature on the friction and wear of PEEK composites under dry sliding conditions.

Wear, 148(2), 235-247. http://dx.doi.org/10.1016/00431648(91)90287-5.

4. Ramachandra, S., & Ovaert, T. C. (1997). The effect of controlled surface topoghaphical features on the unlubricated transfer nad wear of PEEK. Wear, 206(1-2), 94-99. http:// dx.doi.org/10.1016/S0043-1648(96)07354-1.

5. Cirino, M., Friedrich, K., & Pipes, R. (1988). Evaluation of polymer composites for sliding abrasive wear applications.

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Composites, 19(5), 383-392. http://dx.doi.org/10.1016/00104361(88)90126-7.

6. Voss, H., & Friedrich, K. (1987). On the wear behaviour of short frbre-reinforced PEEK composite. Wear, 116(1), 1-18. http://dx.doi.org/10.1016/0043-1648(87)90262-6.

7. Friedrich, K., Karger-Kocsis, J., & Lu, Z. (1991). Effects of steel counterface roughness and temperature on the friction and wear of PEEK composites under dry sliding conditions.

Wear, 148(2), 235-247. http://dx.doi.org/10.1016/00431648(91)90287-5.

8. Lu, Z. P., & Friedrich, K. (1995). On sliding friction and wear of PEEK and its composites. Wear, 181-183(2), 624-631.

9. Ma, N., Lin, G. M., Xie, G. Y., Sui, G. X., & Yang, R. (2012).

Tribological behavior of polyetheretherketone composites containing short carbon fibers and potassium titanate whiskers in dry sliding against steel. Journal of Applied Polymer Science, 123(2), 740-748. http://dx.doi.org/10.1002/app.34502.

10. Zeng, H., He, G., & Yang, G. (1987). Friction and wear of poly(phenylene sulphide) and its carbon fibre composites: I unlubricated. Wear, 116(1), 59-68. http://dx.doi.org/10.1016/00431648(87)90267-5.

11. Wang, Q., Xu, Q. J., Shen, W., & Xue, Q. (1997). The effect of nanometer SiC filler on the tribological behavior of PEEK. Wear, 209(1-2), 316-321. http://dx.doi.org/10.1016/S00431648(97)00015-X. 12. Zhang, G., Wetzel, B., & Wang, Q. (2015). Tribological behavior of PEEK-based materials under mixed and boundary lubrication conditions. Tribology International, 88, 153-161. http://dx.doi.org/10.1016/j.triboint.2015.03.021.

13. Zhang, G., Yu, H., Zhang, C., Liao, H., & Coddet, C. (2008).

Temperature dependence of the tribological mechanisms of amorphous PEEK (polyetheretherketone) under dry sliding conditions. Acta Materialia, 56(10), 2182-2190. http://dx.doi. org/10.1016/j.actamat.2008.01.018.

14. Victrex. (2014). Materials properties guide. Lancashire: Victrex PLC. Retrieved in 2017, March 10, from http://www.victrex. com.

15. American Society for Testing and Materials – ASTM (2004).

ASTM G-99 04: standard test method for wear testing with pin-on-disk apparatus metals test methods and analytical procedure (Vol. 03.02; Section 3). West Conshohocken: ASTM 16. Elliott, D. M., Fisher, J., & Clark, D. T. (1998). Effect of counterface surface roughness and its evolution on the wear and friction of PEEK and PEEK-bonded carbon fibre composites on stainless steel. Wear, 217(2), 288-296. http:// dx.doi.org/10.1016/S0043-1648(98)00148-3.

17. Zhang, G., Zhang, C., Nardin, P., Li, W. Y., Liao, H., & Coddet, C. (2008). Effects of sliding velocity and applied load on the tribological mechanism of amorphous poly-ethr-ethr-ketone (PEEK). Tribology International, 41(2), 79-86. http://dx.doi. org/10.1016/j.triboint.2007.05.002.

18. Stachowiak, G. W., & Batchelor, A. W. (2005). Engineering tribology. Amsterdam: Elsevier.

19. Friedrich, K. (1986). Mild wear of rubber-based compounds.

In K. Friedrich (Ed.), Friction and wear of polymer composites (pp. 289-327). Amsterdam: Elsevier.

20. Schallamach, A. (1971). How does rubber slide? Wear, 17(4), 301-312. http://dx.doi.org/10.1016/0043-1648(71)90033-0.

21. Buckley, D. H. (1981). Surface effects in adhesion, friction, wear and lubrication. Amsterdam: Elsevier.

22. Zhang, G., & Schlarb, A. K. (2009). Correlation of the tribological behaviors with the mechanical properties of poly-ether-etherketones (PEEKs) with different molecular weights and their fiber filled composites. Wear, 266(1-2), 337-344. http://dx.doi. org/10.1016/j.wear.2008.07.004.

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Tribology of natural Poly-Ether-Ether-Ketone (PEEK) under transmission oil lubrication 23. Aharoni, S. M. (1973). The wear of polymers by roll formation.

Wear, 25(3), 309-327. http://dx.doi.org/10.1016/00431648(73)90002-1.

24. Myshkin, N. K., Petrokovets, M. I., & Kovalev, A. V. (2005).

Tribology of polymers: adhesion, friction, wear and mass transfer. Tribology International, 38(11-12), 910-921. http:// dx.doi.org/10.1016/j.triboint.2005.07.016.

25. Greenwood, J. A., & Williamson, J. B. P. (1966). Contact of nominally flat surfaces. Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, 295(1442), 300-319. http://dx.doi.org/10.1098/rspa.1966.0242.

26. Tamura, J., Clarke, I. C., Kawanabe, K., Akagi, M., Good, V. D., Williams, P. A., Masaoka, T., Schroeder, D., & Oonishi,

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H. (2002). Micro-wear patterns on UHMWPE tibial inserts in total knee joint simulation. Journal of Biomedical Materials Research, 61(2), 218-225. http://dx.doi.org/10.1002/jbm.10027.

PMid:12007202.

27. Scherge, M., Kramlich, J., BĂśttcher, R., & Hoppe, T. (2013).

Running-in due to material transfer of lubricated steel/PA46 (aliphatic polyamide) contacts. Wear, 301(1-2), 758-762. http:// dx.doi.org/10.1016/j.wear.2012.11.035.

Received: Mar. 10, 2017 Revised: Sept. 25, 2017 Accepted: Nov. 16, 2017

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.02918

Synthesis and characterization of amphiphilic block copolymers by transesterification for nanoparticle production André Rocha Monteiro Dias1, Beatriz Nogueira Messias de Miranda1, Houari Cobas-Gomez2, João Guilherme Rocha Poço3, Mario Ricardo Gongora Rubio1 and Adriano Marim de Oliveira1*  Núcleo de Bionanomanufatura – BIONANO, Instituto de Pesquisas Tecnológicas do Estado de São Paulo – IPT, São Paulo, SP, Brasil 2 SCINNTECH, São Paulo, SP, Brasil 3 Departamento de Engenharia Química – DEQ, Centro Universitário da Fundação Educacional Inaciana – FEI, São Bernardo do Campo, SP, Brasil

1

*amarim@ipt.br

Abstract Poly(ε-caprolactone)-block-poly(ethylene glycol)-poly(ε-caprolactone) (PCL-PEG-PCL, triblock) and Poly(ε-caprolactone)block-(poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide)-poly (ε-caprolactone) (PCL‑PEO-PPO‑PEO‑PCL, pentablock) copolymers were synthesized by transesterification with reduction of PCL molecular mass, enabling fewer reactions, lower temperatures, and eliminating extensive purification steps. Free hydrophilic groups were removed from the samples by selective precipitation, and 1H-NMR, FTIR, GPC and DSC analyses characterized the structure and properties of the resulting copolymers. The detection of remaining hydrophilic groups indicates the formation of the amphiphilic block copolymers (BCPs). Further, we obtained polymeric nanoparticles with monodisperse size distribution profiles by nano-precipitation from both the triblock and the pentablock copolymers using a microfluidic device, resulting 144.6 and 188.9 nm size and 0.093 and 0.102 nm polydispersity index, respectively. The nanoparticle assembly depends on the copolymer composition, and the possibility of nanoparticle assembly corroborates to the block structure of the copolymers, and the success of this synthesis route to obtain BCPs. Keywords: copolymers, Pluronic F127, Poly(ε-caprolactone), Poly(ethylene glycol), transesterification.

How to cite: Dias, A. R. M., Miranda, B. N. M., Cobas-Gomez, H., Poço, J. G. R., Rubio, M. R. G., & Oliveira, A. M. (2019). Synthesis and characterization of amphiphilic block copolymers by transesterification for nanoparticle production. Polímeros: Ciência e Tecnologia, 29(2), e2019027. https://doi.org/10.1590/0104-1428.02918

1. Introduction Over the past decades, poorly water-soluble compounds have shown their potential as drug candidates[1]. Unfortunately, despite the extensive development and applicability of these hydrophobic therapeutic agents, efficient delivery is often a challenge. Due to their frequently low molecular weight, rapid clearance occurs within the body, and the use of high doses is needed to compensate for its clearance and achieve therapeutic doses. Also, their organ and tissue distribution are often nonspecific, which enhances the probability of its accumulation in healthy tissues, enhancing toxicity and undesirable side effects, obviating the need for delivery alternatives[2].

Among numerous available strategies to achieve trigger-release, the use of block copolymer systems has proven effectiveness[3-5]. Its diversity and versatility meet the need for more continuous therapeutic drug effect, enabling the transport and release of the active agent at specific sites, specific times or after a specific stimulus, increasing efficiency and minimizing side effects[6-8]. Moreover, its

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mechanical and physicochemical properties, in general, can be changed and improved by simple manipulation of the amphiphilic block and its ratio. Such characteristic together with the production of self-assembled structures, commercial availability, biocompatibility, biodegradability, ease of synthesis and the ability to stabilize hydrophobic compounds that are otherwise insoluble in an aqueous environment make block copolymers an exciting class of materials with countless applications, including medicine.

Therefore, the use of block copolymers in controlled drug delivery foments the research of the different amphiphilic copolymers combinations and different synthesis routes.

A mandatory characteristic regarding drug carriers based on block copolymers are the biocompatibility and the biodegradability of the polymeric building blocks. Among amphiphilic copolymers, poly (ethylene glycol) (PEG) and some poloxamers (poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide), PEO−PPO−PEO) such as Pluronic F127 (F127) are known to provide interesting surface

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

Dias, A. R. M., Miranda, B. N. M., Cobas-Gomez, H., Poço, J. G. R., Rubio, M. R. G. & Oliveira, A. M. properties to the nanocarrier, are commercially available, biodegradable and are safe for internal use, what make them interesting for scientific and technological purposes[9]. Among the hydrophobic ones, poly (ε-caprolactone) (PCL) holds unique properties such as biodegradation within the body due to hydrolysis of its ester bonds. Moreover, PCL is an important starting point for building advanced polymer architectures[10].

For instance, ε-caprolactone (ε-CL) polymerization can be achieved by direct condensation, and by the use of anionic, cationic and nonionic-nucleophile initiators. However, block copolymers synthesis, in special the ones associated to PCL, often relies on ring-opening polymerization (ROP) routes that frequently depend upon high polymerization temperatures; long polymerization time; and multiple and extensive reaction steps, exemplified ROP reactions are shown in Table 1.

As an alternative, transesterification reaction has been used to obtain polymers with a narrow distribution of molecular weights and functionalized, i.e., with hydroxyl sides (diol polymers). The use of this process enables the production of hydroxyl telechelic polymers that can, for instance, be used to obtain block copolymers or to insert signaling structures. Several studies were conducted to obtain polymers with narrow molecular weight distribution and hydroxyl terminations through trans-esterification for block polymers production[24-28].

A reduction in the use of toxic reagents, reaction time, and steps lead to an increase in efficiency in the synthesis process, not requiring extensive purification steps. Therefore, in this paper, the poly(ε-caprolactone)-block-poly(ethylene glycol)-poly(ε-caprolactone) (PCL-PEG-PCL, triblock)

and the poly(ε-caprolactone)-block-(poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide)-poly (ε-caprolactone) (PCL-PEO-PPO-PEO-PCL, pentablock) copolymers are synthesized by transesterification with reduction of PCL molecular weight, in the presence of Pluronic F-127 or PEG. The resulting copolymers were characterized by gel permeation chromatography (GPC), 1H nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). This procedure represents an easy and low-cost way to obtain block copolymers with a degree of blockiness different from those previously reported[9,29,30].

Additionally, this paper also shows some interesting results of using synthesized block copolymer as building units for active pharmaceutical compounds nanocapsules synthesis by the microfluidic route employing nanoprecipitation strategy. It was used a homemade microfluidic device for nanoprecipitation, which is a development of the nanonization technique used for nanoparticle generation in fields like drug formulation and chemistry, among others[31-37].

2. Materials and Methods 2.1 Materials Pluronic F-127 (MwF127 is 12,600 g·mol-1) was purchased from Viabrasil, polycaprolactone 80,000 g·mol-1 (PCL) from Sigma-Aldrich, poly(ethylene glycol) (PEG, MwPEG 6,000 g·mol-1) from Synth, Diadema, Brazil and p-toluene sulfonic acid, PA, from Anidrol for block copolymer synthesis. All used solvents

Table 1. Literature review - ROP reactions.

Functional reactant ending groups

Catalyst

OH

Sn(Oct)2

Reference

[11-17]

NH2

[18]

Epoxy

[19]

Br

[20]

Triple bond

Ítrium complex

Sangers solvent

[21]

[22]

Nd(BH4)3(THF)3

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Reaction

[23]

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Synthesis and characterization of amphiphilic block copolymers by transesterification for nanoparticle production and salts were from Dinâmica Química Contemporânea Ltda, Diadema, Brazil.

2.2 Synthesis methods of block copolymers A Dean Stark apparatus setup was used for all reactions.

It consists of a 500 mL round bottom flask, reflux condenser, heating mantle with magnetic stirring and thermometer with sodium sulfate as drying material. An adaptation of a literature procedure enabeled the preparation of PCL‑F127‑PCL and PCL-PEG-PCL[26]. The initial polymers and the catalyst 4-toluenesulfonic acid (p-TSA) were dissolved in 150 mL of toluene. The mixture was kept under reflux at 110 °C. Table 2 shows all specific quantities, together with the reactions times. Reactions C and D were kept stirring for 2 hours before reflux. The solute concentration at the beginning of the reaction was between 25-50 mg·mL-1.

After cooling to room temperature, the remaining solvent in the sample was removed using a rotatory evaporator.

Then, the content was dissolved in 5 mL of dichloromethane (DCM). The amphiphilic block copolymer was isolated from hydrophilic polymers by selective precipitation with 50 mL of cold ethanol, under magnetic stirring. Finally, the material was dried at 40 °C for 24 hours.

2.3 Purification of block copolymers The produced amphiphilic block copolymers were recovered by selective precipitation method with cold ethanol as non‑solvent for hydrophobic blocks, under magnetic stirring. The material was dried at 40 °C for 24 hours. The block diagram illustrates this procedure, shown in Figure 1.

2.4 Characterization of block copolymers 2.4.1 Determination of molecular weight by Gel Permeation Chromatography (GPC) Viscotek TDAmax equipment, 2X Viscogel column and refractive index detector were used for GPC analysis, and a method was validated according to a standard procedure based on the comparison of chromatographic profiles of mixtures of different molecular weight polystyrene (PS) standards. Briefly, tetrahydrofuran (THF) at 0.5 mL·min-1 flow rate was used as the chromatography eluent and 35 °C as the column’s and detector’s temperature. The sample was dissolved in THF (10 mg·mL-1) and 100 μL of this solution was injected into the chromatography column for conducting the GPC analysis.

2.4.2 Hydrogen Nuclear Magnetic Resonance Analysis (1H NMR) Agilent 400 MR spectrometer conducted the 1H NMR measurements at a frequency of 400 MHz at 25 °C. Approximately 7 mg of each sample was dissolved in 600 μL of deuterochloroform (CDCl3), containing 0.05% of tetramethylsilane (TMS) to reference the chemical shift.

The values of the molar masses were estimated as follows: the value of 195 protons was attributed to the characteristic signal of propylene glycol methyl in 1.13 ppm of F127, from the molar mass value provided by the manufacturer.

Integrations of other signs provided the other amounts of protons. The molar mass of the block copolymer was obtained by the sum of the molar mass F127 (12,600 g·mol-1) plus the mass of PCL incorporated, according to Equation 1.

The PCL mole number was obtained by Equation 2.

M = ( cba )

12.600g n ( cl ) * 114g (1) + mol mol

n ( cl ) = 195 *

∫ 4 ppm 2

(2)

Where: M (cba) = molar mass of amphiphilic block copolymer (g.mol-1). n (cl) = number of mols of caprolactone (mol).

2.4.3 Attenuated total reflectance with Fourier transform infrared (ATR - FTIR) The IR spectra were obtained for solid samples using a Nicolet 6700 FT-IR spectrometer fitted with ATR, in the range of 4000 to 700 cm-1 and 128 accumulations. The Smart OMNI software was used for data processing.

2.4.4 Differential Scanning Calorimetry Analysis (DSC) Figure 1. Bock diagram representing the production and purification methods used. *Only for reactions C and D.

The samples were prepared using a sealed aluminum pan and analyzed by Shimadzu DSC-60. Three temperature ramps were done as follows: -80 °C to 120 °C; 120 °C to

Table 2. Compositions and reaction times of the PCL/F127/PCL pentablock and PCL/PEG/PCL triblock copolymers synthesis.

Reaction A B C D

F127/PCL (m/m) 0.63 2 −

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PEG/PCL (m/m) 0.63 − − 2

p-TSA (wt. %) 2.5 1.5 7 7

Reaction time (h) 18 18 4 4

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Dias, A. R. M., Miranda, B. N. M., Cobas-Gomez, H., Poço, J. G. R., Rubio, M. R. G. & Oliveira, A. M. -80 °C; and -80 °C to 120 °C; all at 10 °C·min-1 heating and cooling rates and with 50 mL·min-1 nitrogen gas flow.

2.5 Block copolymer nanocapsule synthesis and characterization 2.5.1 Microfluidic device For nanocapsule synthesis, in-flow nanoprecipitation technique was used. In this technique, block copolymers and active pharmaceutical compound were dissolved using acetone to obtain an organic solution. This solution is placed in contact with an antisolvent flow inside the microfluidic device. High material concentration regions are created due to the solvent diffusion from the organic phase into the antisolvent flow. At these regions the material is no longer soluble in the solvent - antisolvent mixture, increasing its concentration. When a material concentration exceeds a critical level, spontaneous nucleation takes place, generating nanoparticles[38, 39].

For implementing the nanoprecipitation strategy using microfluidics techniques, a 3D flow focalization homemade LTCC (Low Temperature Co-fired Ceramic) microfluidic device was fabricated, Figure 2a. The device consists in an organic phase input, dissolved material, DM, (Hydraulic Diameter DH = 214.6 µm), the anti-solvent (AS) inputs and the nanoprecipitation channel (NPC) (DH = 772 µm and length 6.5 mm). The DM and NPC channels are centered.

The four AS inputs have an input angle of 45º to the NPC

direction. Device inputs geometry makes possible the 3D flow focalization which highly improves the nanoprecipitation process due to a better solvent diffusion process from the dissolved material flow stream to the surrounding antisolvent flow[39,41].

Microfluidic device fabrication employed the typical LTCC process[40]. DuPont green LTCC ceramic tapes 951P2 and 951PX were used. Layers were fabricated using a prototyping machine equipped with an ultraviolet laser (355 nm wavelength), model LPKF Protolaser U3 (LPKF Laser & Electronics AG). One step thermo-compression lamination process was performed by means of a uniaxial laminator with a pressure of 11.8 MPa at 70 °C (hydraulic press machine, model MA098/A30, Marconi). Previous to the lamination process, the aligned sheets were baked at 60 °C for 20 min. For sintering we used a muffle furnace (EDG Equipment, model EDG10P-S), in a two-stage profile: first, heating the device at 450 °C for 30 min. and in sequence, sintering at 850 °C per 30 min.

The input and output brass fluidic interconnection tubes were glued to the ceramics using a high-temperature epoxy (EPO-TEK 353ND). For the gluing process, a hot plate at 150 °C for 2 min was used. The fabricated 3D flow focalization microfluidic device is showed in Figure 2b).

2.5.2 Sample preparation Organic phase fluid dissolved material was prepared from 1 g of synthesized pentablock PCL-F127-PCL copolymers and 100 mg of Hydrocortisone Acetate and mixed in 20 mL of Acetone (Sigma Aldrich) until complete dissolution. As Antisolvent (AS) fluid material we used 100 mL of purified DI water (Aqueous phase). A Milli-Q system (Millipore Corporation, USA) was employed to obtain the purified water.

For pumping the DM and AS into the microfluidic device at the desired flow rate (QDM and QAS, respectively) two syringe pumps (PHD 4400, Harvard Apparatus) were used.

2.5.3 Dynamic Light Scattering (DLS) DLS analyses were carried out using a laser particle analyzer (Zetasizer Nano ZS, Malvern Instruments) using the manufacturer’s software as the calculation method, in water. DLS measurements were based on 3 repetitions of 70 accumulation times. Samples were analyzed at 25 °C with a scattering angle of 90° and at 633 nm, based on a dispersant refractive index (RI) of 1.33, a viscosity of 0.89 and a dielectric constant of 78.3.

3. Results and Discussions 3.1 Synthesis and Characterization of PCL/F127/PCL and PCL/PEG/PCL block Copolymers

Figure 2. 3D Hydrodynamic focalization microfluidic device. a) Micro channels geometry; b) Manufactured microfluidic device.

Anti-solvent = Organic Phase; Dissolved Material = Aqueous Phase. Adapted from Cobas-Gomez[39] and Cobas-Gomez et al.[40].

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PCL/PEG/PCL triblock (reactions A and D) and PCL/F127/PCL pentablock (reactions B and C) copolymers were successfully synthesized by transesterification (Table 2). 1H-NMR spectrums were recorded to confirm the structure of the copolymers. In the spectra of the triblock produced by reactions A and D, shown in Figures 3b and c, the peaks at 3.64 ppm were attributed to the ethylene protons of the PEG ethylene glycol units Polímeros, 29(2), e2019027, 2019

Synthesis and characterization of amphiphilic block copolymers by transesterification for nanoparticle production (a, b). Peaks of ethylene glycol units were also found in the spectra of pentablock PCL/F127/PCL produced by reactions B and C, and attributed to the F127 units (a, b), shown in Figures 4b and c. Due to the high molecular weight of the analyzed copolymers, only a weak 1H-NMR signal at 4.23 ppm is seen from terminal ethylene units of PEG, but it was still characterized for all samples, as shown in Supplementary Material S1-S4. In Figures 4b and c, the very weak peak at 1.14 ppm was identified as the methyl protons of the F127 unit (c), and was not identified in the PEG copolymer due to the absence of methyl protons in the PEG copolymer structure, shown in Figure 3a. Peaks

at 1.38, 1.65, 2.31, and 4.06 ppm were assigned to the methylene protons in PCL units (identified as f, e, d, g, respectively), and therefore present in all copolymer products, both tri and pentablocks due to the existence of PEG units, which is very similar to the literature reported spectrum. In particular, the weak 4.06 ppm peak correlates to the methylene protons of a PEG and F127 end units that are connected with PCL blocks[42]. It is important to remind that free F127 and PEG groups were isolated from free PCL and freshly prepared block copolymers by selective precipitation using ethanol. Therefore, we can assume that only PCL-linked hydrophilic blocks are present

Figure 3. BCP formula (a) and 1H-NMR spectrum of PCL/PEG/PCL triblock copolymer, reactions A (b) and D (c), respectively.

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Figure 4. BCP formula (a) and 1H-NMR spectrum of pentablock PCL/F127/PCL pentablock copolymer, reactions B (b) and C (c), respectively.

in the precipitate. This assumption enables the MwNMR of the PCL/F127/PCL copolymers and the PEG/PCL block ratios calculation by comparing the PCL 4.06 ppm and the PEG or F127 3.64 ppm integrated peaks[29, 43].

From GPC traces (shown in Figure 5), shifts in profile and retention volumes are seen. The chromatogram of the physical mixture of PCL and F127 is shown in Figure 5a, and the peak at a retention volume of 25.19 mL was attributed 6/12

to PCL, due to its higher molecular weight, while the higher retention volume signal, of 28.17 mL, was attributed to F127. The profile of this chromatogram can be compared to the ones on Figures 5c and d that shows the GPC curves of pentablock copolymers produced in reactions B and C, respectively. Although the product’s curve is not unimodal, a shift in profile and retention volumes is observed for both cases. Considering that most of the non-reacted hydrophilic Polímeros, 29(2), e2019027, 2019

Synthesis and characterization of amphiphilic block copolymers by transesterification for nanoparticle production blocks were removed from the copolymer sample by selective precipitation, it is presumable that only the ones linked to PCL are left. Moreover, the peak shift to the right of the chromatogram seen when comparing Figures 4a physical mixture and c) or d) pentablock copolymer samples can be

explained by a decrease in the PCL molar masses, which leads to its linkage to hydrophilic blocks. The same can be extended to the triblock copolymer produced in reaction D, shown in Figure 5e, and using PEG instead of F127 (which chromatogram is shown in Figure 5b). Consistency in the data can be observed when compared to NMR and FTIR results shown in Table 3, in special for lower molar masses.

(Chromatographic profiles of mixtures of different molecular weight polystyrene (PS) standards and MW curve are shown in Supplementary Material S5-S6).

The Figures 6a and b show FTIR spectra for reactions A and B, tri and pentablock copolymers. These results were interpreted considering the polyester and polyether characteristic signals, which are attributed to 1,724 cm-1 and 1,108 cm-1, respectively. The absorption band at 1,724 cm-1 is attributed to the characteristic polyester C=O stretching vibrations of the ester carbonyl group from PCL, while 1,108 cm-1 can be attributed to C−O−C stretching vibrations of the repeated −OCH2CH2 groups of PEG (or F127). Once the reaction products were purified by selective precipitation using ethanol, free PEG and F127 were removed from the sample, and still, the presence of both groups in the sample was confirmed by FTIR, indicating block copolymer formation.

Curves that relate the peaks 1,108 cm-1 and 1,724 cm-1 ratio value (I1108 / I1724 ratio) with its molecular weights were obtained using the specific molar mass values previously acquired from 1H-NMR spectra and GPC chromatograms.

Different curves were prepared for samples using F127 and PEG as the hydrophilic block (pure PCL and F127 spectrum as well as curves for PCL/PEG/PCL and PCL/F127/PCL are shown in Supplementary Material S7-S9). This way, according to the obtained I1108 / I1724 ratio, we could presume the MFTIR for each sample, as shown in Table 3.

The results obtained by FTIR-ATR are consistent with those obtained by NMR and GPC, therefore, indicating the formation of the block copolymers products.

Thermal analyses were performed on the PCL and F127 reagents and compared to the results obtained for the sample from Reaction B (PCL/F127/PCL). Both the melting temperature and the crystallinity degree (analyzed by the enthalpy of fusion) of the polymer sample displayed a decrease when compared to individual components.

This can be explained by the PCL´s molar mass reduction.

The obtained melting point and enthalpy of fusion are presented in Table 4 (graphs are shown in Supplementary Information S11-S13).

Table 3. Molecular weights (g mol-1) of the PCL/PEG/PCL triblock (reactions A and D) and PCL/F127/PCL (reactions C and D) pentablock copolymers.

Sample

MFTIRa

MNMRb

MGPCc

A B C D

25.052 30.679 16.683 8.602

36.923 30.717 17.046 8.186

17.252 16.341 7.916

Calculated according to the I1108 / I1724 ratio of the FTIR-ATR peaks.

Number-average molecular weight calculated from 1H NMR Spectrum. c Number-average molecular weight measured by GPC (calibrated with polystyrene standards). a

Figure 5. GPC curves of (a) physical mixture of PCL and F127; (b) pure PEG; the block copolymer product after the trans esterification reactions (c) B; (d) C; and (e) D. Polímeros, 29(2), e2019027, 2019

b

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Figure 6. Sample FTIR spectrum of PCL/PEG/PCL triblock copolymer from reaction A and PCL/F127/PCL pentablock copolymer from reaction B. Marked peaks are attributed to polyester and polyether characteristic signals.

Table 4. Table of results from DSC curves of PCL, F127 and amphiphilic block copolymer product from Reaction B. Material PCL F127 Reaction B

Melting Point (°C) 59.05 58.06 44.76 53.64

Enthalpy of fusion (J·g-1) -54.33 -99.84 -8.54 -31.94

3.2 Influence of the hydrophilic block on copolymer formation The influence of the hydrophilic block´s size on the copolymer formation was analyzed. As a matter of comparison, the same procedure used for producing a pentabock copolymer (Reaction C, containing F127) was used for producing a triblock copolymer (Reaction D), containing only PEG as a hydrophilic block, as shown in Table 3. The Pluronic F127 is a poloxamer that has 2 polyethylene oxide, PEG, groups on the outside and polypropylene oxide, PPO, as the inner block. The same mass ratio F127/PCL and PEG/PCL was used, remembering that MwF127 is 12,600 g·mol-1 and MwPEG 8/12

is 6,000 g·mol-1. 1H-NMR, GPC, and FTIR analysis were promoted (as shown in Figures 3-5 and Supplementary Material S14-S15), all the FTIR and 1H-NMR results indicated that the PCL-PEG-PCL copolymers were formed successfully, and the amount of PCL incorporated could be calculated, resulting 4,446 g·mol-1 e 2,166 g·mol-1 for reactions C and D, respectively. According to this result, there is a direct relationship between each hydrophilic block Mw and the amount of incorporated PCL, indicating similar reactivity among the terminal hydroxyl groups.

3.3 Synthesis of amphiphilic block copolymers particles using microfluidics Triblock copolymer particles were successfully obtained using a microfluidic device as described before. A value of 144.6 nm with a polydispersity index of 0.093 was obtained for block copolymer from Reaction A, indicating the formation of particles with nanometric dimensions and low polydispersity. The occurrence of nanoparticle corroborates with the PEG – PCL biding since the simple physical mixing of these materials would not permit the particle formation.

Polímeros, 29(2), e2019027, 2019

Synthesis and characterization of amphiphilic block copolymers by transesterification for nanoparticle production Table 5. Table of results from block copolymer capsules synthesis using the microfluidic device. Adapted from Cobas-Gomez et al.,[40] The total flow rate (QT) is defined as the sum of QDM and QAS, and the flow rate ratio (RQ) defined as the ratio between QAS and QDM. RQ 1.3 10 1.3 10 6.26

QT (aqueous + organic flow rate; mL·min-1) 1 1 7.5 7.5 4.64

Particle size (nm)

PDI

459.1 287.8 355.5 188.9 233.4

0.235 0.228 0.206 0.102 0.188

QT = QDM + QAS. RQ = QAS/QDM.

Figure 7. Particle size distribution of PCL/PEG/PCL nanoparticles produced with Sample A and microfluidic device, using Flow rate ratio, RQ = 10 and Total flow rate, QT = 7.5 mL·min-1.

The pentablock copolymer obtained by Reaction B was used as the polymeric carrier for a pharmaceutical compound. The experiment variables were the total flow rate (QT) defined as the sum of QDM and QAS, and the flow rate ratio (RQ) defined as the ratio between QAS and QDM. A factorial experiment planning approach was used to set the variables values. The experiment parameters and results are presented in Table 5. Results showed sub-micron and nanocapsules with sizes ranging from 459.1 nm to 188.9 nm.

The polydispersity index remains lower than 0.235 which implies a narrow particle size distribution. A monodisperse particle size distribution profile (Size = 188.9 nm and PDI = 0.102) was observed for the sample obtained with experimental parameters RQ = 10 and QT = 7.5 mL·min-1, and the distribution performed with the previously mentioned sample is shown in Figure 7.

Therefore, the use of both triblock and pentablock copolymers produced by transesterification reactions enabled nanoparticle production by the use of a microfluidic preparation.

4. Conclusions This study demonstrates the use of transesterification with polyester molecular weight reduction as a versatile and straightforward approach for obtaining amphiphilic block copolymers. Concerning the FTIR-ATR, 1H NMR, and GPC results and assuming that the majority of free hydrophilic Polímeros, 29(2), e2019027, 2019

groups were removed from the analyzed sample by selective precipitation with ethanol, it is clear that polyester and polyether groups are presented in the product indicating the formation of the amphiphilic block copolymers. The results obtained for the molecular weights are consistent among the different techniques and also close to the theoretical values.

For the thermal analysis results, there was a decrease in both melting temperature and enthalpy of fusion. Since these parameters are related to the crystallinity and, consequently, the samples’ molecular weight, these decreases indicate the PCL molar mass reduction, an increase in biodegradability and proves the successful synthesis of amphiphilic block copolymers. Moreover, polymeric nanoparticles with sizes ranging from 459.1 nm down to 188.9 nm were successfully produced with a narrow polydispersity (0.235 down to 0.102) by nano-precipitation using a microfluidic device. The fact that particles have been produced with the product of the transesterification reactions already proves the synthesis of amphiphilic block copolymers since non-linked blocks would not enable particle production. We believe that this production technique is of extreme value for the reduction in the use of toxic reagents, and the simplification of block copolymers synthesis. Finally, the possibility of using a wide molecular weight range of polyesters, avoiding cyclization steps and molecular weight reduction, together with the advancing of nano theraphy will provide further knowledge and possible new carriers for disease treatment and diagnostic.

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5. Acknowledgments We acknowledge the Institute for Technological Research, IPT, and the Institute for Technological Research Foundation, FIPT, for infrastructure and A.R.M.D. and B.N.M.M. funds; the Centro Universitário da FEI for the support; and the Coordination for the Improvement of Higher Level Personnel, CAPES, for the support.

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Supplementary Material Supplementary material accompanies this paper: Figure S1. Sample amplified region of 1H-NMR spectrum of Reaction A. Figure S2. Sample amplified region of 1H-NMR spectrum of Reaction B. Figure S3. Sample amplified region of 1H-NMR spectrum of Reaction C. Figure S4. Sample amplified region of 1H-NMR spectrum of Reaction D. Figure S5. Standard polystyrene chromatograms.

Figure S6. GPC standard curve for molecular weight.

Figure S7. Sample FTIR spectrum of PCL. Figure S8. Sample FTIR spectrum of F127.

Figure S9. Molar mass curve based on FTIR data for reactions with F127.

Figure S10. Molar mass curve based on FTIR data for reactions with PEG. Figure S11. DSC curve of PCL. Figure S12. DSC curve of F127.

Figure S13. Sample DSC curve of reaction B. Figure S14. Sample FTIR spectrum of Reaction C. Figure S15. Sample FTIR spectrum of Reaction D. This material is available as part of the online article from http://www.scielo.br/po

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Polímeros, 29(2), e2019027, 2019

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.08718

Thermal, dielectric and catalytic behavior of palladium doped PVC films Ganesh Shimoga1, Eun-Jae Shin1 and Sang-Youn Kim1*  1

Interaction Laboratory of Advanced Technology Research Center, Korea University of Technology and Education, Byeongcheon-myeon, Cheonan City, South Korea *sykim@koreatech.ac.kr

Abstract The present paper discusses the aspects of synthesizing palladium (Pd) doped (Pd+2 and Pd0) poly(vinyl chloride) (PVC) using simple solution cast technique. The Pd loading to PVC was altered from 2.5% to 10.0% and the material properties were studied using UV-Visible spectroscopy (UV-Vis), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX) and Field Emission Scanning Electron Microscopy (FE-SEM). Thermal behavior of all the samples were studied using thermogravimetric analysis (TGA) and Broido’s method was employed to analyse the kinetic parameters involved in different degradation steps. All the composite films were sandwitched between disk shape gold electrodes; electrical contacts were established to study the dielectric properties. The influence of Pd loading on the dielectric properties of PVC were examined. Finally, the catalytic properties of Pd0 composites were studied using standard model reduction reaction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of aqueous sodium borohydride and reported.

Keywords: dielectric, heterogeneous catalysis, palladium nanocomposites, poly(vinyl chloride), thermal analysis.

How to cite: Shimoga, G., Shin, E.-J., & Kim, S.-Y. (2019). Thermal, dielectric and catalytic behavior of palladium doped PVC films. Polímeros: Ciência e Tecnologia, 29(2), e2019028. https://doi.org/10.1590/0104-1428.08718

1. Introduction Efforts to develop composite materials in order to achieve exceptional characteristics different from the individual components have been in practice from decades by scientific community[1,2]. Polymer metal composites/nanocomposites have been spread their interest as catalysts in modern organic synthesis[3], they have been widely used in aerospace and automobile industry, their properties are still being researched by tuning in electronic, sensors and catalytic applications[4-6].

Recent developments in solid ionic conductors, polymer electrolytes and intercalation materials have drawn keen interest from the researchers working in the field of plastic crystal ionic batteries, solid state galvanic cells and interfacial responsive sensory/electrical equipments[7-9]. In addition, the involvement of interfaces with metal composites play an important role in the regulation of composite properties[10].

Most of the thermoplastic polymers have widely been used in various fields from sensors to electrical equipment design due to their lightweight, ease of fabrication, exceptional processability, durability, and relatively low cost. Incorporation of various metallic oxides with thermoplastic polymers as polymer matrix have drawn profound applications in the removal of organic pollutants from water[11] and some of the metal doped polymers are used as matrix materials for ferroelectric composites[12].

Poly(vinyl chloride) (PVC) is one of the most commertially used thermosoftening plastic that have wide range of applications as fire retardants, corrosion resistance and electrical insulators. The miscibility and compatability of PVC with wide variety of organic/inorganic materials

Polímeros, 29(2), e2019028, 2019

have been observed in differing mechanical and electrical properties from rigid to flexible compounds. Recently, the applications of reinforced PVC composites are preceded to new directions in the field of polymer science and technology[13]. Dieletric performances of PVC incorporated with ground tire rubber (GTR), calcium copper titanate, zinc additives, piezoelectric lead zirconatetitanate, silica nanocomposites, graphite, and mica were studied extensively for its optoelectrical applications[14-27].

Due to remarkable catalytic activity of palladium nanoparticles (PdNPs), various bimetallic combinations of PdNPs with gold, nickel and other transitional metals, and also with supramolecules have paid much attention in the reduction of nitrophenol reduction reactions[28-30].

To best of our knowledge, no systematic practical research has been reported so far on the Pd doped PVC films for heterogeneous catalytic applications. In this present work, we made a successful attempt to fabricate Pd doped PVC films and subsequent reduction of the films by ecofriendly trisodium citrate dihydrate solution. The doping of Pd in PVC matrix was varied from 2.5 to 10.0 % (Stochiometric weight %) and thermal degradation of Pd-PVC films were systematically characterized using TGA and sensitive graphical Broido’d method[31] to calculate the thermodynammical parameters of each degradation steps. The variation of dielectric properties (dielectric constant and loss factor) were measured using impedance analyzer. Morphology was examined using FE‑SEM and catalytic performances for the reduction of 4-NP to 4-AP in presence of sodium borohydride was reported.

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

Shimoga, G., Shin, E.-J. & Kim, S.-Y. The rate constant of the catalytic degradation of 4-NP was calculated and it falls in the pseudo first order by using the Equation (2):

2. Materials and Methods 2.1 Materials Palladium chloride, poly(vinyl chloride) (Mw ~233000), and trisodium citrate dihydrate were procured from Sigma Aldrich, Seoul, South Korea. All the other chemicals and solvents are of reagent grade and used without any further purification. HPLC grade water was used throughout the study.

2.2 Synthesis of Pd-PVC and PNC-PVC composite films PVC films were doped with palladium (II) chloride (PdCl2) in various concentrations, prepared at room temperature by simple solution cast method. The desired concentration of palladium chloride solutions (2.5, 5.0, 7.5 and 10.0 weight %) were prepared by using ice cold distilled water (800 ¾L).

PVC (1g) was dissolved in 20 mL tetrahydrofuran (THF) at room temperature (22 °C), a known amount PdCl2 solutions were loaded into the PVC solutions separately. The solution was stirred for 24 h at room temperature and the resulting homogeneous solution was cast onto a glass plate with the aid of a casting knife. The thin films were allowed to dry at room temperature for 72 h and vacuum dried at 50 °C for 15 h, the completely dried films were subsequently peeled off. The stoichiometric mass ratio of PdCl2 with respect to PVC was varied as 0.0, 2.5, 5.0, 7.5 and 10.0, and the resulting thin films were designated as PVC, Pd-PVC-2.5, Pd-PVC-5.0, Pd-PVC-7.5 and Pd-PVC-10.0, respectively.

The thickness of the thin films was measured at different points using peacock dial thickness gauge (Model G, Ozaki MFG. Co. Ltd., Japan) with an accuracy of ¹2 ¾m and the average thickness was considered for calculation. The thickness of the membranes was found to be 345 ¹ 2 ¾m.

The Pd+2 doped PVC films (Pd-PVC-2.5, Pdâ&#x20AC;&#x2018;PVC-5.0, Pd-PVC-7.5 and Pd-PVC-10.0) were cut in to the dimensions of 250 mm x 250 mm and suspended in 50Â mL of 1 mM solution of trisodium citrate solution for 1 h with gentle stirring.

The obtained composite films were washed repeatedly with distilled water, gently wiped with clothing tissue paper and vacuum dried at 50 °C for 15 h. The resulting Pd nanocomposite PVC films were designated as PNC-PVC-2.5, PNC-PVC-5.0, PNC-PVC-7.5 and PNC-PVC-10.0, respectively.

2.3 Catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) Catalytic performance of PNC-PVC-10.0 was evaluated for the model reduction reaction of 4-NP to 4-AP in a standard 10 mL quartz cell. Typically, 10 mL of aqueous 4-NP (0.1 mM) solution was mixed with 0.05 g of PNCâ&#x20AC;&#x2018;PVC-10.0, followed by the addition of 5 mL aqueous NaBH4 solution (50 mM), and the time dependent UV-vis absorption spectra was recorded by VARIANEL08043361 UV- vis spectrophotometer (Varian, USA). The conversion of 4-NP to 4-AP was monitored every 4 min interval in a scanning range from 250 to 600 nm at room temperature (22 °C).

The percentage catalytic efficiency of the catalyst in the reduction of 4-NP into 4-AP was calculated by the following Equation (1): Percentage ( % ) conversion =

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C0 â&#x2C6;&#x2019; C t Ă&#x2014;100 C0

(1)

C  ln  0  = kt  Ct 

(2)

where C t is the concentration of 4-NP measured at time t, C0 is the initial concentration of 4-NP measured at time zero.

2.4 Characterization of Pd doped PVC films Pd doped PVC films were investigated using solid state electronic absorption spectra on a Perkin-Elmer UV-Vis spectrometer, model UV/VIS-35 (PerkinElmer, Inc., MA, USA). To understand the doping effect of Pd+2 and PdNPs content in PVC, thin films were subjected to powder X-ray diffraction study using Bruckerâ&#x20AC;&#x2122;s D-8 advanced X-ray diffractometer. The X-ray source was Ni filtered Cu KÎą radiation. The diffraction was scanned in the reflection mode at an angle 2θ over a range of 5 to 90° at a constant speed of 8°/min. Similarly, the surface morphology of PNC-PVC were analyzed by using Ultra-High-Resolution Field-Emission Scanning Electron Microscope (FESEM, FEI, & Nova NanoSEM450) instrument operating at 25 kV. Thermal stability of PVC silver nanocomposites were investigated using thermogravimetric analyzer (Q500, TA instruments, DE, USA) in the range from 25 °C to 600 °C in a 50 mL/min flow of N2 gas at a heating rate of 10 °C/min.

Pd-PVC and PNC-PVC films were subjected to the dielectric measurements; films were sandwiched between two electrodes (gold plated) and analysed by impedance analyzer, model HIOKI 3352-50 HiTESTER Version 2.3. The electrical contacts were checked to verify the ohmic connection.

The measurements were carried out at room temperature in between the 50 Hzâ&#x20AC;&#x201C;5 MHz. The dielectric constant (đ?&#x153;&#x20AC;â&#x20AC;&#x2122;) was calculated using Equation (3) and dielectric loss (tan δ) was calculated using Equation (4).

( Cp d )

Îľ' =

(3)

Îľ"

Îľ'

(4)

( ξο A )

tan δ =

where â&#x20AC;&#x2DC;đ?&#x2018;&#x2018;â&#x20AC;&#x2122; is the thickness of the polymer film and â&#x20AC;&#x2DC;đ??´â&#x20AC;&#x2122; is the cross-section area, â&#x20AC;&#x2DC;ξοâ&#x20AC;&#x2122; is the permittivity of the free space, â&#x20AC;&#x2DC;Îľ "â&#x20AC;&#x2122; and â&#x20AC;&#x2DC;Îľ 'â&#x20AC;&#x2122; is the permittivity (imaginary part) and permittivity (real part) of the material respectively. All these measurements were performed under dynamic vacuum.

3. Results and Discussions 3.1 Synthesis and Characterization of Pd-PVC and PNCâ&#x20AC;&#x2018;PVC composite films Pd doped PVC with different PdCl2 loading was fabricated at room temperature by adopting solution casting methodology. The desired PdCl2 was dissolved in 800 ÂľL of ice cold distilled water and added dropwise to the stirring PVC solution in tetrahydrofuran (THF) solvent. Pd+2 doped PVC films were chemically reduced using ecofriendly reducing agent, aqueous solution of trisodium citrate (1 mM), and PolĂ­meros, 29(2), e2019028, 2019

Thermal, dielectric and catalytic behavior of palladium doped PVC films repeatedly washed with water and vaccum dried at 50 °C prior to characterization. Figure 1 displays the portrait of Pd+2 doped PVC film with 10 weight % of PdCl2 to PVC and its respective chemically reduced form (PNC-PVC-10.0).

Solid state UV-Vis spectra of Pd-PVC-10.0 and PNC‑PVC-10.0 films were displayed in Figure 2 (a), the spectra confirms the characteristic broad continuous absorption. Pd-PVC-10.0 showed a broad peak around 400 nm due to the absorption of Pd+2 ions. For the reduced

sample (PNC-PVC-10.0), the peak at 417 nm was absent, indicating a complete reduction of Pd+2 ions to PdNPs. Figure 2 (b) shows the XRD pattern of PVC, Pd-PVC-10.0 and PNC-PVC-10.0. The diffraction peaks of PVC locate at 17.2° and 24.5°, which was the amorphous characteristic pattern of PVC. The crystalline nature of the PdNPs was confirmed for PNC-PVC-10.0 by the arrival of characteristic 2θ values at 40.1°, 46.2° and 67.3° corresponding to (111), (200) and (220) reflections from planes of the (face-centered cubic) fcc lattice respectively. Also, characteristic crystal planes of (311) and (222) respectively observed at 81.2° and 86.1°.

The FE-SEM and EDX spectrum of PNC-PVC-10.0 was displayed in Figure 3 (a) and (b) respectively, The morphology shown in Figure 3 (a) from which the average size of the PdNPs is found to be less than 100 nm with roughly spherical morphology. Elemental composition analysis

by EDX presented in Figure 3 (b), which shows strongest signal near to 2.8 to 3 keV, which is the typical absorption pattern of metallic nanocrystalline Pd surface on PVC, also strongest signals for carbon and chlorine atoms of PVC were obtained, indicating the presence of PdNPs in PVC matrix.

Figure 1. Snapshot of (a) Pd-PVC-10 film, (b) PNC-PVC-10.0 film.

The TG plots of PVC, Pd-PVC and PNC-PVC were displayed in Figure 4, it was observed that the thermogram of PVC, Pd-PVC and PNC-PVC showed two major degradation steps with onset decomposition at 240 °C. The initial weight

Figure 2. (a) Solid state UV-Vis spectra of Pd-PVC-2.5 and PNC-PVC films, (b) XRD pattern of PVC, Pd-PVC-10.0 and PNC-PVC-10.0 films.

Figure 3. (a) FE-SEM micrograph of PNC-PVC-10.0. (b) EDX Spectrum of PNC-PVC-10.0.

Polímeros, 29(2), e2019028, 2019

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Shimoga, G., Shin, E.-J. & Kim, S.-Y. loss step started at around 240â&#x20AC;&#x201C;340 °C was attributed to the dehydrochlorination in the PVC chains, leading to the formation of long polyene sequences in PVC chains[32].

Second degradation step is in the range of 410â&#x20AC;&#x201C;460 °C can be attributed for the degradation of main PVC chains with conjugated double bands resulted from dehydrochlorination.

It is observed that PNC-PVC films are moderately stable than Pd-PVC films, this is due to the availability of large number of Cl- ions in Pd-PVC films.

The free volume space in Pd-PVC was concealed by Cl- ions by doping PdCl2 to PVC, which endures the faster

degradation compared with PVC films. The chemical reduction of Pd-PVC films generates PdNPs on the surface of PVC, which slightly upsurges the stability of PNC-PVC compared to Pd-PVC material. Broido has developed a model and the activation energy associated with each stage of decomposition was evaluated by this method in order to find the kinetic and thermodynamic parameters for the each degradation step[31].

Plots of â&#x2C6;&#x2019;ln(ln(â&#x2C6;&#x2019;1/đ?&#x2018;Ś)) versus 1/đ?&#x2018;&#x2021; were developed for the decomposition segments of Pd-PVC and PNC-PVC films (Figure 5). From the plots, the activation energy (đ??¸đ?&#x2018;&#x17D;) and

Figure 4. (a) TG plot of PVC and Pd-PVC films, (b) TG plot of PVC and PNC-PVC films at a heating rate of 10 °C/min under a nitrogen atmosphere.

Figure 5. (a) Plots of â&#x20AC;&#x201C;Ln(ln(-1/y)) vs 1/TĂ&#x2014;10-3 for the first decomposition step of Pd-PVC films in the range 240 â&#x20AC;&#x201C; 340 °C, (b) for the decomposition step of Pd-PVC films in the range 410 â&#x20AC;&#x201C; 460 °C, (c) for the first decomposition step of PNC-PVC films in the range 240 â&#x20AC;&#x201C; 340 °C, (d) for the decomposition step PNC-PVC films in the range 410 â&#x20AC;&#x201C; 460 °C. 4/9

PolĂ­meros, 29(2), e2019028, 2019

Thermal, dielectric and catalytic behavior of palladium doped PVC films frequency factor (lnđ??´) were evaluated. The enthalpy (Î&#x201D;đ??ť), entropy (Î&#x201D;đ?&#x2018;&#x2020;), and free energy (Î&#x201D;đ??ş) have been calculated using standard equations and are summarized in Tables 1, Tables 2, Tables 3 and Table 4.

From the Table 1 and 2, indicated activation energies for Pd-PVC-5.0 was higher compared to Pd-PVC-2.5, Pd-PVC-7.5 and Pd-PVC-10.0, signposting that the decomposition step is faster in case of all Pd-PVC films except Pd-PVC-5.0.

This is because, higher the doping % of PdCl2, increases the content of Cl- ions in the PVC matrix, which in turn increses the rate of degradation step. However, the balance between Pd+2 and Cl- ions stabilizes the Pd-PVC-5.0 in maintaining the slow and moderate degradation rate in both the major degradation steps. The results of activation energies from Table 3 and 4 indicates that, PNC-PVC-10.0 undergoes degradation in a faster rate compared to all other PNCâ&#x20AC;&#x2018;PVC

materials, this can be explained on the effect caused by the chemical reduction of Pd-PVC films. The chemical reduction of Pd-PVC films, results in the growth of PdNPs on the PVC surface rather than the bulk PVC material, signposting the observation of higher activation energy values in case of PNC-PVC-2.5 and PNC-PVC-5.0 compared to PNC-PVC-7.5 and PNCâ&#x20AC;&#x2018;PVC-10.0, this is because of the developed PdNPs on the PVC surface which stabilizes the rate of degradation step, the rate of degradation is also toggles between the presence of Pd+2 and Cl- ions inside the bullk of PVC. So, higher the content of Pd+2 and Cl- in PNC-PVC-7.5 and PNC-PVC-10.0 results in the faster degradation therein.

The variation of dielectric constant and dielectric loss as a function of log (frequency) at room temperature for Pd-PVC and PNC-PVC films were displayed in Figure 6. From the

Table 1. Kinetic and thermodynamic parameters of PVC and Pd-PVC at the decomposition range 240 â&#x20AC;&#x201C; 340 °C. Title PVC Pd-PVC-2.5 Pd-PVC-5.0 Pd-PVC-7.5 Pd-PVC-10.0

Ea (kJ/mol) Ă&#x2014; 10-3 16.020 13.753 14.077 13.126 13.179

lnA -6.557 -6.823 -6.789 -6.932 -6.926

â&#x2C6;&#x2020;H

â&#x2C6;&#x2020;S

â&#x2C6;&#x2020;G

(kJ/mol)

(kJ/K)

(kJ/mol)

-4.665 -4.668 -4.667 -4.668 -4.668

-160.350 -159.207 -159.534 -159.798 -159.821

90.292 89.648 89.832 89.981 89.994

Table 2. Kinetic and thermodynamic parameters of PVC and Pd-PVC at the decomposition range 410 â&#x20AC;&#x201C; 460 °C. Title PVC Pd-PVC-2.5 Pd-PVC-5.0 Pd-PVC-7.5 Pd-PVC-10.0

Ea (kJ/mol) x 10-3 20.927 20.927 24.642 22.789 22.470

lnA -5.696 -5.695 -5.208 -5.444 -5.486

â&#x2C6;&#x2020;H

â&#x2C6;&#x2020;S

â&#x2C6;&#x2020;G

(kJ/mol)

(kJ/K)

(kJ/mol)

-5.865 -5.865 -5.861 -5.863 -5.864

-161.688 -161.663 -161.486 -161.493 -161.508

114.475 114.457 114.332 114.336 114.347

Table 3. Kinetic and thermodynamic parameters of PVC and PNC-PVC at the decomposition range 240 â&#x20AC;&#x201C; 340 °C. Title PVC PNC-PVC-2.5 PNC-PVC-5.0 PNC-PVC-7.5 PNC-PVC-10.0

Ea (kJ/mol) Ă&#x2014; 10-3 16.013 16.019 15.702 15.562 14.689

lnA -6.558 -6.540 -6.571 -6.599 -6.712

â&#x2C6;&#x2020;H

â&#x2C6;&#x2020;S

â&#x2C6;&#x2020;G

(kJ/mol)

(kJ/K)

(kJ/mol)

-4.665 -4.665 -4.665 -4.665 -4.666

-160.358 -159.863 -159.560 -159.863 -159.736

90.283 90.004 89.833 89.989 89.932

Table 4. Kinetic and thermodynamic parameters of PVC and PNC-PVC at the decomposition range 410 â&#x20AC;&#x201C; 460 °C. Title PVC PNC-PVC-2.5 PNC-PVC-5.0 PNC-PVC-7.5 PNC-PVC-10.0

Ea (kJ/mol) Ă&#x2014; 10-3 20.927 23.093 23.609 20.485 17.643

PolĂ­meros, 29(2), e2019028, 2019

lnA -5.696 -5.403 -5.337 -5.753 -6.158

â&#x2C6;&#x2020;H

â&#x2C6;&#x2020;S

â&#x2C6;&#x2020;G

(kJ/mol)

(kJ/K)

(kJ/mol)

-5.865 -5.863 -5.863 -5.866 -5.866

-161.688 -161.450 -161.448 -161.656 -161.984

114.475 114.306 114.305 114.452 114.685

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Shimoga, G., Shin, E.-J. & Kim, S.-Y.

Figure 6. Room temperature dielectric constant variation of (a) Pd-PVC, (b) PNC-PVC films, dielectric loss variation of (c) Pd-PVC (d) PNC-PVC films with log frequency.

Figure 6 (a) plot it is evident that, there is a marginal decrease in the dielectric constant over the measured frequency range with respect to increase in the Pd+2 loading was observed.

The dielectric constant increased with Pd+2 loading and reached an optimum value of 2.6 at 5% loading. The rate of decrease is larger at higher frequency region indicating quasi-DC (QDC) behavior[33]. As the frequency increases, pace maintenance and the orientation of dipolar groups with alternating field seems to be difficult, resulting in a continuously decreasing dielectric constant with increase of Pd+2 doping to PVC. From Figure 6 (b), we can notify further decrease of dielectric constant for PNC-PVC films, this is because the Pd+2 ions are chemically reduced to Pd0 on the surface of PVC, resulting not much contribution to the dielectric constant. The decrease in the dielectric constant can also be plained by the restriction of polarization mechanisms in the bulk of the material. Also, the density of dopant ions (Pd+2, Cl- and Pd0) in PVC matrix[34].

From Figure 6 (c) and (d), it was noted that loss factor of Pd-PVC and PNC-PVC films decreases with increase in frequency. There is a marginal increase in the dielectric loss with doping of Pd+2. Since, the presence of charge carriers in the PVC matrix increases by the sequential doping of Pd+2, increases the dissipation factor was observed. For 2.5% 6/9

doping of Pd+2, the dissipation factor was below 0.5 at lower frequencies. A slight PVC chain entanglements and less hinderence for the movement of charge carriers were observed, resulting in minor increase in the loss factor on Pd+2 doping. In case of PNC-PVC, due to unavailability of Pd+2 ions at the PVC surface due to chemical reduction, PdNPs might hinder the movement of charge in the material causing slight decrease in tan δ component. Overall the loss factor is within the range of 0.25 to 0.3 for all the composite films at 1 Hz.

3.2 Catalytic activity The model reduction reaction of 4-NP to 4-AP in the presence of aqueous NaBH4 was studied in presence of catalyst PNC-PVC-10.0. Before starting the reduction reaction, the UV-Vis absorbance spectrum of 4-NP solution with NaBH4 solution was recorded. The UV-Vis spectrum shows the λmax of 400 nm for 4-NP, in presence of catalyst PNC-PVC-10.0, arrival of another peak at λmax of 300 nm was observed due to the formation of 4-AP. The complete conversion of 4-NP to 4-AP was observed after 20 min.

The reduction of 4-NP to 4-AP in the presence of NaBH4 as a model reaction was depicted in Figure 7 (a).

The apparent rate constant (kapp) and correlation constants (R2) for PNC-PVC-10.0 were calculated using linear plots of Polímeros, 29(2), e2019028, 2019

Thermal, dielectric and catalytic behavior of palladium doped PVC films

Figure 7. (a) Time dependant UV-Vis spectra representing the catalytic reduction of 4-NP into 4-AP, (b) linear plot of –ln(At/Ao) versus reduction time (t) for PNC-PVC-10.0 catalyst.

Table 5. Catalytic reduction of 4-NP to 4-AP using PNC-PVC-10.0 catalyst.

Time (min) 0 4 8 12 16 20

% Conversion of 4-NP to 4-AP 0 4.407 18.327 27.443 88.133 94.273

–ln(At/Ao) versus reduction time (t) was shown in Figure 7 (b).

The percentage conversion of 4-NP to 4-AP with respect to reduction time (t) by PNC-PVC-10.0 catalyst was reported in Table 5, the apparent rate constant (kapp) calculated for the reaction was 2.371 x 10-3 sec-1.

The catalytic reduction was carried out in a closed 50 mL glass vial. Typically, 100 mg of finely chopped (1 mm x 10 mm) PNC-PVC-10.0 films were inserted into the mixture of 10 mL of 0.1 mM aqueous 4-NP and 5 mL of 50 mM aqueous NaBH4 solution, the rate of reaction drastically changes, the intense yellow color the reaction mixture (aqueous 4-NP and NaBH4 solution) was diminished to colorless in 20 min (Table 5). The catalytic reduction reaction was monitored by time dependant UV-visible spectrophotometer. The mechanism involved in the reduction groups to convert it into amino (-NH2) groups. The electron transfer from donor (BH4̄ ions) to acceptor (4-NP ions) was facilitated by PNC-PVC-10.0 (heterogeneous solid catalyst).

PNC-PVC-10.0 shows considerable catalytic performances with exhibited apparent rate constant (kapp) 2.371 × 10-3 sec-1 which was significantly higher than 1.5 × 10-3 sec-1 reported for polystyrene based thermosensitive microgel encapsulated PdNPs reported by Mei et al.[35].

Recently, Zhang et al.[36] in 2017, reported the catalytic activities of bimetallic Pt@Pd alloy cubic nanocomposites with reported kAPP 2.0 x 10-3 sec-1. The kAPP value reported

by Adekoya et al.[37] for polyol based nanobimettalic Ag/Pd Polyvinyl pyrollidone composites was 1.9 × 10-3 sec-1 at 90 °C. Esumi et al.[38] reported palladium nanocomposites of Polímeros, 29(2), e2019028, 2019

poly(amidoamine)s dendrimer kAPP value of 17.9 × 10-4 sec-1.

The kAPP value reported here for PNC-PVC-10.0 was considerably close to the value 2.4 × 10-3 sec-1 for 17 weight % PdNPs deposited on citrate-functionalized graphene oxide[39].

4. Conclusions A simple solution casting technique was adopted to fabricate palladium doped PVC composites from 2.5 to 10.0% (stochiometric). The thermal stability of all the materials were studied using TGA, using sensitive graphical Broido’s method to evaluate thermodynamical parameters at each stage of thermal degradation steps. The PdNPs in the PVC matrix was confirmed by UV-Vis, XRD, EDX. The PdNPs in PNC-PVC-10.0 were studied using FE-SEM and it was found that PdNPs were uniformly distributed with size less than 100 nm. EDX elemental composition of PNC‑PVC at any place of the film clears the uniform distribution of PdNPs. It was found that dielectric constant and loss factor for all the composites were marginally increased with Pd doping to PVC films. Since, Pd based self healing coatings are very familiar as anti-corrosion interfaces in automotive and aerospace engineering applications, proper tuning of noble metals and Pd coatings can be a useful candidate for electronic applications[40]. The article also highlights the catalytic performances of PNC-PVC-10.0 for a model reduction reaction of 4-NP using aqueous NaBH4 solution. The calculated apparent rate constant (kapp) was 2.371 × 10-3 sec-1 at room temperature, the correlation coefficient (R2) was found to be 0.956 for PNC-PVC-10.0.

Our results demonstrates that these PNC-PVC films are ideal materials as heterogeneous catalysts and prove their potential applications as nanocatalysts in industrial catalysis.

5. Acknowledgements This work was supported by the Technology Innovation Program (10077367, Development of a film-type transparent /stretchable 3D touch sensor /haptic actuator combined module and advanced UI/UX) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea).

This work was also supported by Priority Research Centers 7/9

Shimoga, G., Shin, E.-J. & Kim, S.-Y. Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF‑2018R1A6A1A03025526). Thanks for Cooperative Equipment Center at KoreaTech for assistance with UV-Vis, TGA, XRD and FESEM analysis.

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38. Esumi, K., Isono, R., & Yoshimura, T. (2004). Preparation of PAMAM− and PPI−Metal (Silver, Platinum, and Palladium) nanocomposites and their catalytic activities for reduction of 4-Nitrophenol. Langmuir, 20(1), 237-243. http://dx.doi. org/10.1021/la035440t. PMid:15745027.

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Received: Dec. 18, 2018 Revised: Feb. 03, 2019 Accepted: Feb. 18, 2019

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.02418

Castor polyurethane used as osteosynthesis plates: microstructural and thermal analysis Francisco Norberto de Moura Neto1, Ana Cristina Vasconcelos Fialho1* , Walter Leal de Moura1, Adriana Gadelha Ferreira Rosa1, José Milton Elias de Matos2, Fernando da Silva Reis2, Milton Thélio de Albuquerque Mendes2 and Elton Santos Dias Sales3 Departamento de Patologia e Clínica Odontológica, Universidade Federal do Piauí – UFPI, Teresina, PI, Brasil 2 Fismat, Departamento de Química, Universidade Federal do Piauí – UFPI, Teresina, PI, Brasil 3 Laboratório de Engenharia de Materiais, Programa de Pós-graduação, Departamento de Engenharia de Materiais, Instituto Federal do Piauí – IFPI, Teresina, PI, Brasil 1

*anacrisvf@gmail.com

Abstract Bone fractures to be corrected need stabilization of their extremities, which is achieved with the use of plates and screws. This research aimed to produce castor bean polyurethane (Ricinus communis), to make resorbable plate, structural and thermal analysis. The production was made by the glycerolysis of the triglycerides present in the oil, after addition of polyol/glycerol and hexamethylene diisocyanate (HDI) to form urethane structures, with and without addition of hydroxyapatite. The characterization was by FTIR spectroscopy, scanning electron microscopy (SEM), X-ray diffraction, differential scanning calorimetry and thermogravimetry. Plates with dimensions of 40 mm X 10 mm X 2 mm were obtained. The SEM showed flat and homogeneous surface. DRX analysis showed the semi-crystallinity of the biomaterial. Glass transition and thermal stability up to 50 °C were observed, followed by thermal decomposition up to 450 °C. The produced polyurethane showed it is possible to be applied in the manufacture of plate.

Keywords: maxillofacial surgery, fracture fixation, bone fractures, biocompatible materials, castor oil.

How to cite: Moura Neto, F. N., Fialho, A. C. V., Moura, W. L., Rosa, A. G. F., Matos, J. M. E., Reis, F. S., Mendes, M. T. A., & Sales, E. S. D. (2019). Castor polyurethane used as osteosynthesis plates: microstructural and thermal analysis. Polímeros: Ciência e Tecnologia, 29(2), e2019029. https://doi.org/10.1590/0104-1428.02418

1. Introduction The technique of functionally stable fixation of bone fractures consists of stabilizing the segments with plates and screws in direct contact with the structure, allowing new ossification. Titanium is the most used material because it is bioinert and possesses high mechanical resistance, allowing the bone to exert its function during the repair process, even with the occurrence of micromovements between the fragments[1].

Some problems are associated with the use of titanium plates. Interference in imaging tests, bone atrophy, pain, cold hypersensitivity and impairment of bone growth in children are the most cited. Due to being more rigid, the metallic material absorbs most of the incident forces, which may lead to reduction of bone density (stress-shielding phenomenon).

There is still no consensus on the need for additional surgical intervention for the removal of the metallic material after the consolidation of the fracture[2].

Polymers and composites, like hydroxyapatite/polymer properties, represent an alternative for the treatment of facial fractures because they have elastic modulus close to the bone and they are resorbable. The metabolism of these devices

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takes place in a concomitant period bone union, without leaving any by-products in the body. Resorbable plates and screws still present problems such as low mechanical resistance and inadequate design compared to titanium; besides the induction of inflammatory response during the hydrolysis of its molecules[3].

Copolymers of polylactic acid (PLA) and polyglycolic acid (PGA), unstable polyesters in wet conditions are the most widely used biodegradable devices[4,5]. The polymer derived from castor oil (Ricinus communis) was released for medical and dental use by the Ministry of Health in 1999 and also the Food and Drug Administration (FDA) in 2003.

Because it is both biocompatible and osteoconductive, it allows the growth of connective tissue and bone within its pores and assists in the stability of the surgical apparatus[1].

To improve the osteoconductivity of the polymer, bioactive ceramics, such as hydroxyapatite, have been combined to produce polymer composite due to their similar chemical structure with human bone tissue. Hydroxyapatite is the main inorganic component of the tissues of vertebrates and artificially synthesized as bioactive (osteoconductivite) and it also has the ability to encourage bone growth[1-5].

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

Moura Neto, F. N., Fialho, A. C. V., Moura, W. L., Rosa, A. G. F., Matos, J. M. E., Reis, F. S., Mendes, M. T. A., & Sales, E. S. D. The biocompatibility of resorbable polymers for fracture fixation is well established, but most of them hold high prices. The applicability of a biomaterial in the medical and dental area depends on its mechanical characteristics, biodegradation and microstructure features[6]. The study of castor oil polymer and hydroxyapatite/castor oil composite, a bone analog model, is justified by the possibility of local production of a resorbable biomaterial as an alternative in the treatment of facial fractures, with lower cost for use in the public service and also in pediatric patients. The purpose of this work was to develop polyurethane obtained by the chemical processing of castor oil and describe its microstructure and thermal characteristics for the production of resorbable plate for fixation of bone fractures.

mixture was placed in a rectangular shaped container, closed by a device (cover) and fastened with screws. The mold was pressed for completion of the polymerization reaction.

2. Materials and Methods

2.6 Scanning Electron Microscopy (SEM)

2.1 Synthesis of the biocomposite from castor oil

To perform Electron Microscopy, it was used FEI Quanta 250 FEG-equipment. Since it was a polymeric material, surface preparation was necessary. All samples were fractured in liquid nitrogen and coated with a gold layer to obtain better conductivity. A piece was deposited in the aluminum substrates. For this purpose, the samples were coated with gold in order to avoid the accumulation of charges that repel the incident electron beam. The micrographs served to observe the morphology and particle size of polyurethane[7,8].

The experiment was carried out at the Materials Physics Laboratory of the Federal University of Piauí (FISMAT‑UFPI). All samples of castor oil, extracted from the seeds of the Ricinus communis plant, had a production and quality certification; and they were initially analyzed for acidity, iodine, peroxide index, viscosity, and density; to confirm the physicochemical specifications provided by the manufacturer.

2.2 Oil catalysis and production of monoacylglycerol The initial stage for the production of biopolymer was the glycerolysis reaction of the triglycerides present in the castor oil structure, after addition of polyol (glycerol).

To achieve this, an amount of the oil (40 g) was weighed and mixed to glycerol (7.9 g) to give a suitable molar ratio.

After stirring, the catalyst Lithium Hydroxide (LiOH, 0.02 g) was added. The mixture was then placed in a round bottom flask for magnetic stirring and reaction mixture in a suitable atmosphere, with controlled time (5h) and temperature (140 °C); until obtaining monoacylglycerol (MAG), a resin with a gelatinous appearance.

2.3 Synthesis of hydroxyapatite (HA) Calcium hydroxide [Ca(OH)2, 1.5 g] and ammonium phosphate [(NH4)3PO4, 1,6 g] were initially added, which in aqueous solution they formed a characteristic white suspension. The solution was stirred for a predetermined time (2:30 h), then it was oven dried at 120 °C for 12 h, then centrifuged and washed. Finally, it was placed to dry at 300 °C for 6h.

2.4 Preparation of polyurethane The synthesized monoacylglycerol (which has the structure of a polyol) was mixed with Hexamethylene Diisocyanate (HDI), with a suitable stoichiometric ratio. The mixture was placed in a volumetric flask and heated to 95 °C with constant stirring in a controlled environment. After that, hydroxyapatite was added to obtain a concentration of 3% by mass, relative to the mass of the monoacylglycerol. After homogenization, the mixture was collected and stored in a suitable container. During the final phase of the polyurethane reaction, when the material reaches the “gel point”, the 2/8

2.5 Spectroscopic analysis in the infrared region (FTIR) The FTIR spectra of the synthesized monoacylglycerol and polyurethane samples were obtained in a Thermo Fisher SCIENTIFIC Nicolet iS5 spectrophotometer with purge pump and wavelength between 400 cm-1 and 4000 cm-1, 128 accumulated scans, 4 cm-1 resolution, in ATR, in Transmittance module. The method was used to verify the conclusion of the curing reaction of polyurethane and the presence of free isocyanate functional groups (NCO) after the reaction[7].

2.7 X-ray Diffraction Analysis (XRD) Polyurethane samples were analyzed for their microstructure by means of X-ray diffraction (XRD), Labx - XDR 600 equipment from Shimadzu with Cu-Kα radiation (λ = 1.5406 Å), 2θ in the range between 50° to 750°, scan rate of 2° / min and total exposure time of 40 minutes.

The objective was to identify the crystalline peaks, the crystalline and amorphous phases and also calculate the parameters of the crystalline network of the biomaterial[9].

2.8 Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) The DSC curve was obtained from TA Instruments; model Q2000, with temperature range between -150 °C and 600 °C. The TG curve was obtained in Q50, TA Instruments, with a temperature range between 25 °C and 1200 °C; both under nitrogen atmosphere, heating rate of 10 °/min and sample of 10 mg. The DSC technique was used to determine the temperature transitions of the physical state of the polyurethane. Thermogravimetry was used to study the stability range and thermal decomposition mechanisms of the material[7-9].

2.9 Descriptive Statistics Five samples of the monoacylglycerol and polyurethane obtained were analyzed by means of FTIR spectroscopy, and five polyurethane samples were evaluated by MEV, XRD, DSC, and TG. It was conducted a descriptive analysis of the following parameters: formation of the monoacylglycerol and polyurethane structure; characteristics of crystallinity and conformation of the molecules; in addition to the glass transition temperature, melting temperature, and the degradation onset temperature.

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Castor polyurethane used as osteosynthesis plates: microstructural and thermal analysis

3. Results and Discussion 3.1 Castor oil catalysis and physicochemical characterization Castor oil presents in its composition 89.5% to 90% triglyceride ricinoleic acid (12-hydroxy-cis-9-octadecenoic acid), whose molecular formula is C17H32OHCOOH. In the ester bonds of the triglyceride (1st carbon) reactions of hydrolysis, esterification, alcoholysis and, halogenation can occur (Figure 1)[9-12].

In the present study, the glycerolysis pathway of the triglycerides present in the oil was used (Figure 2).

The alkoxide is an active radical formed by the reaction of glycerol with lithium hydroxide (catalyst) (A). The C=O (carbonyl) bond of the triglyceride undergoes nucleophilic attack by alkoxide, forming a tetrahedral intermediate. After

rearrangement of this intermediate, a monoalcohol ester and the anion are formed, which, upon deprotonation of the conjugate acid from the base formed in the reaction, it regenerates lithium hydroxide and produces a diglyceride (B). Similar reactions occur with diglycerides, with formation of monoacylglycerol (MAG) (C)[13].

3.2 Formation and preparation of polyurethane plates A urethane structure is the result of the chemical reaction between an isocyanate group and a hydroxyl radical.The synthesis of a high molar mass polyurethane (Figure 3) occurs when isocyanate groups react with a polyfunctional alcohol (hydroxylated polymer or polyol).

In this research, the Hexamethylene Diisocyanate (HDI) was used, molecular formula C8H12O2N2 and molecular structure OCN-(CH2)6‑NCO. Although less reactive, HDI

Figure 1. Scheme of chemical structure of ricinoleic acid, the primary component of castor oil.

Figure 2. Scheme of catalysis of the triglyceride present in castor oil. (A): obtainment of the alkoxide as the catalyst; (B): breakdown of the triglyceride molecule; (C): molecules of monoglyceride and diglyceride were formed.

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Moura Neto, F. N., Fialho, A. C. V., Moura, W. L., Rosa, A. G. F., Matos, J. M. E., Reis, F. S., Mendes, M. T. A., & Sales, E. S. D.

Figure 3. Scheme of mechanism proposed for the reaction between monoglyceride and Hexamethylene Diisocyanate (HDI), with the formation of castor oil polyurethane.

is less volatile and less toxic because the composition does not have benzene[13,14].

The reaction begins with the attack of the nucleophilic center of the MAG (monoacylglycerol) on the electrophilic carbon of the carbonyl group (C = O) of the isocyanate; the proton is simultaneously transferred to the nitrogen atom.

A urethane structure is formed when the hydrogen atom of the hydroxyl group present in the MAG binds to the nitrogen atom of the isocyanate group. The mechanism repeats until the formation of the polyurethane structure[13].

During the final reaction of polyurethanes, curing agents, blowing agents, catalysts and fillers may be incorporated.

Hydroxyapatite is a biocompatible and osteoconductive material, serving as a structure for the migration of osteoprogenitor cells[8-10]. The last step to obtain the composite was conducted through the addition of hydroxyapatite.

The mixture was stored in a suitable container in order to wait for curing time of the material. Samples of the pure polyurethane and proportion of hydroxyapatite at 3% by mass were obtained (Figure 4).

Figure 4. Photography of polyurethane castor oil (COP) resorbable plates, with dimensions of 40 mm × 10 mm × 2 mm.

3.3 Analysis by infrared spectroscopy (FTIR) Figure 5 shows the FTIR spectrum for the monoacylglycerol obtained from castor oil. The main absorption bands and their functional groups are highlighted.

The absorption region between 3300 and 3250 cm–1is related to drawability of the OH group; the absorption bands between 3000 and 2750 cm–1are characteristics of the stretching mode of the CH, CH2 and CH3 groups; the 1750 cm–1region is characteristic of carbonyl stretch (C=O); the absorption bands between 1500 and 1250 cm–1is characteristic of the deformation of the CH2 and CH3 groups; 4/8

Figure 5. FTIR spectrum of monoglyceride molecules.

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Castor polyurethane used as osteosynthesis plates: microstructural and thermal analysis the absorption bands between 1250 and 1150 cm–1refer to the C-O and C-C bonds; the band region at 1100 cm–1is also characteristic of the stretching of C-O bonds and ester (-C-O-C-) group; finally, “wag” vibrations and asymmetric angular deformation of the CH and CH2groups are observed in the bands at 750 cm-1 [15-18].

The FTIR analysis performed on the polyurethane samples obtained by the chemical processing of castor oil with addition of 3% hydroxyapatite (HA) is shown in Figure 6. It is possible to observe the regions that prove the formation of the polymer.

The absorption band at 3315 cm-1 is characteristic of the N-H urethane bond. The regions of 2939 cm-1 and 2852 cm-1 are asymmetric and symmetrical stretching characteristics of CH3, respectively[15,16]. According to Pradhan and Nayak[9], these regions are characteristics of the stretching of the CH2 and CH3 groups. The carbonyl stretching band (C=O) was shifted to 1730 cm-1. The 1530 cm-1 region is characteristic of the amide NH deformation in the groups. The formation of polyurethane is also indicated by the absence of band in the region of absorption between 2350 and 2100 cm-1, relative to the N=C=O group, indicating no free isocyanate functional groups[17-19].

Figure 6. FTIR spectrum of castor oil polyurethane with addition of 3% HA.

3.4 Scanning Electron Microscopy (SEM) Figure 7 shows the microstructural analysis by Electron Microscopy of the polyurethane derived from castor oil without addition of hydroxyapatite. Flat and homogeneous surface, with evenly distributed protrusions and depressions; besides clearer granular structures suggestive of artifacts by residual material was observed.

The surface characteristics corroborate with the results obtained by Monteiro et al.[20], who analyzed the ultrastructure of polyurethane and membranes for bone regeneration, and it was observed a flat and homogeneous surface, protrusions and depressions with an irregular outline, besides granular structures of various sizes. Nacer et al.[6] and Marano and Tincani[21] state that the porous surface of the castor oil polymer promotes bone migration and deposition, behaving as a passive structure that allows osteoconduction.

The synthesized hydroxyapatite powder showed homogeneous spherical granular surface appearance, with granules sometimes agglomerated, sometimes spaced apart. Costa et al.[22] also analyzed the microstructure of HA in SEM and it was observed granular surface and also the presence of pores, which are important characteristics for biomedical applications, since they favor the adhesion between the neoformed bone tissue and the synthetic apatite.

Figure 8 shows the microphotograph of polyurethane with addition of 3% HA. According to Pradhan and Nayak[9], the gray regions indicate the polymer matrix and the bright spots indicate the distribution of hydroxyapatite particles.

Polymers with modulus of elasticity similar to that of bone structure allow a better distribution of forces between bone and implant. Bioactive ceramics such as hydroxyapatite have limited individual use because of the low fracture toughness. The HA/polymer composite structure resembles natural bone tissue, increasing the surface area, harboring cells and contributing to the production of organic matrix within the implant[23,24].

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Figure 7. SEM image (2000x). Polymer with flat and regular surface; artifacts.

Figure 8. Microphotograph (500x) of the biopolymer with 3% HA, showing bright scattered appearance related to the filler.

However, Alves et al.[25] mechanically evaluated the 70% polyhydroxybutyrate and 30% hydroxyapatite composite in the form of plate for bone fixation, and it was observed that the addition of HA in the polymer matrix caused reduction in the mechanical strength of the composites, because the particles acted as distributed defects in the organic matrix.

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Moura Neto, F. N., Fialho, A. C. V., Moura, W. L., Rosa, A. G. F., Matos, J. M. E., Reis, F. S., Mendes, M. T. A., & Sales, E. S. D. 3.5 X-ray diffraction (XRD) Figure 9 shows the Bragg-Brentano profile of the samples of the polymer with addition of 3% HA. Diffraction peaks around 195.2º are characteristic of semi-crystalline materials. The orderly packaging of the molecular chains is one of the main aspects of the crystallinity of a polymer.

Lack of chain alignment during solidification results in an amorphous region[9,26].

The degree of crystallinity also depends on the number of branches present and also the rate of cooling. The crystallinity of a biomaterial influences its in vivo performance by affecting reabsorption and its mechanical properties. It is known that amorphous regions are reabsorbed more rapidly and materials with more organized structure generally have a slower rate of resorption[27,28].

Lin et al.[17] introduced acetylated cellulose nanocrystals in the castor oil polyurethane formulation in order to strengthen the material. After analysis by X-ray diffraction, it was observed that for the concentrations of 5 and 10% by weight of cellulose there was no change in the reflection planes in relation to the pure polymer. Only with increasing charge concentration to 15 and 25%, characteristic crystallinity diffraction peaks were observed.

The molecules of the polymers are generally semicrystalline, dispersed within the remaining amorphous material.

The volumetric biodegradation of polyurethanes occurs by diffusion of water through amorphous regions, hydrolysis of ester linkages of the main chain and decrease in volume and molar mass when the polymer begins to fragment.

Degradation products containing carboxyl induce further degradation by autocatalysis. Then, the hydrolysis of the crystalline regions, enzymatic attack and the metabolism of the fragments occur[27,29-31]. The observed microstructure and crystalline aspects suggest that the biodegradation of polymers produced after coming into contact with body fluids under physiological conditions will occur through the volumetric erosion mechanism.

Figure 9. Diffractogram of Biopolymer with 3% hydroxyapatite, with a crystallinity peak around 195.2º which characterizes the semi-crystallinity of the material.

Figure 10. DSC curve of castor oil polyurethane with 3% hydroxyapatite.

3.6 Differential Scanning Calorimetry (DSC) and Thermogravimetry (TG) The Figure 10 (DSC) shows the heat energy flux associated with the transitions in the material as a function of temperature, and the Figure 11 (TG) shows the mass variation of polyurethane as a function of temperature; both obtained under the same experimental conditions. It is essential to compare the DSC and TG curves simultaneously since the first one detects events associated or not with mass loss, while TG indicates only thermal events related to material mass changes[7]. Thermal events of physical state change can be attributed from the DSC curve, provided that in the same temperature range of the TG curve no mass loss events are observed[8,9].

The temperature range of 50 °C was attributed to the glass transition of the polymer produced, since the baseline displacement in the endothermic direction was observed in Figure 10 (DSC), without significant mass loss in TG (Figure 11). This glass transition range, without peaks characteristic of phase transformations such as melting or recrystallization indicates the predominance of the 6/8

Figure 11. TG curve of castor oil polyurethane with 3% hydroxyapatite.

amorphous phase in the biomaterial[7,8].The other energy flux peaks in DSC coincide with mass loss events in TG. It is possible to observe two endothermic peaks at approximately 120 and 230 °C; and exothermic peaks between 250 and 300 °C, between 400 and 450 °C and above 450 °C (DSC); all accompanied by mass loss.

Polyurethanes generally decompose into two or three events due to structural differences[15,16].The biomaterial showed thermal stability up to 50 °C, from which two thermal Polímeros, 29(2), e2019029, 2019

Castor polyurethane used as osteosynthesis plates: microstructural and thermal analysis decomposition peaks and reduction of the initial sample mass were observed, which one peak was in the range of 200 to 250 °C and another peak was in the 350 °C temperature range (Figure 11). It is verified that the degradation process occurred in different stages.

Between 50 and 200 °C, the loss of approximately 10% of the initial mass resulted from the physical degradation of smaller groups, evaporation of solvent molecules and volatile organic compounds from the sample[16-26]. Between 200 and 300 °C, the loss of 50% of the mass occurred. This step involves the decomposition of unsaturated fatty acids; dissociation of polyurethane into isocyanates and alcohol, breaking of biuret, allophanate, ester and urethane linkages; dissociation of polyurethane into isocyanates and alcohol, break of biuret bonds, allophanate, ester and urethane linkages; and the formation of transition components such as amines and carbon dioxide[16-26].

The remainder of the mass was lost between 300 and 450 °C and above 450 °C. These stages are characterized by the remaining degradation of the polyol, decomposition of the major functional polyurethane groups and also of the flexible parts of the chain,dehydrogenation of alkyl groups present in monoacylglycerol; and thermolysis of the organic residues from previous steps, scission of carbon-carbon bonds and additional oxidation of the crosslinked network, respectively[10,15,26].

All the characterizations performed reached the necessary requirements for the production of a bioabsorbable plate.

Considering that plates for fixation of bone fractures ought to allow adequate reduction of fracture, alignment of the ends of the bone fragments and bone repair with the bone callus formation and bone remodeling.The biodegradation should occur during the process of bone repair, not yet determined, and it is related to contact of the plates with body fluids, temperature and movement of the anatomical area.

The characteristics of the material such as crystallinity and geometric shape are considered important for biodegradation process[4,24,32].

4. Conclusions Polyurethane in the form of resorbable plate for fixation of bone fractures was obtained by the chemical processing of castor oil.Absorption bands characteristic of the OH and carbonyl groups (C=O) were evidenced by the FTIR analysis of the monoacylglycerol obtained. FTIR analysis of polyurethane with 3% HA showed regions demonstrating the formation of the polymer.

SEM analysis showed flat and homogeneous surface of polyurethane and shiny aspects of the filler material (hydroxyapatite). Characteristics of semicrystalline polymers were observed in X-ray diffraction analysis. The suggested degradation mechanism was of the volumetric type.

After analysis in Differential Scanning Calorimetry (DSC) and Thermogravimetry (TGA), the temperature range of 50 °C was attributed to the glass transition and thermal stability of the polymer produced, from which mass reduction and two thermal decomposition peaks were observed. These results demonstrate the possibility of applying the biopolymer under physiological conditions.

Polímeros, 29(2), e2019029, 2019

Mechanical assays will be conducted in order to evaluate the influence of the addition of hydroxyapatite and the plasticizer polyethylene glycol (PEG) as a way to increase the strength and the elastic modulus of polyurethane during application in the functionally stable fixation technique.

5. Acknowledgments The authors would like to thank the Piauí Research Support Foundation – FAPEPI (process EFP 00012113 of W. L, Moura), and CNPq (process 310769/2014-0 and 310769/2014-0 of J. M. E. Matos). The authors declare that they have no conflict of interest

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Behavior study of the doped castor bean polymer rod with bioactive glass and hidroxyapatite in mice fêmur medullary canal. Acta Cirurgica Brasileira, 32(2), 116-124. http://dx.doi. org/10.1590/s0102-865020170204. PMid:28300879.

13. Król, P. (2007). Synthesis methods, chemical structures and phase structures of linear polyurethanes. Properties and applications of linear polyurethanes in polyurethane elastomers, copolymers and ionomers. Progress in Materials Science, 52(6), 915-1015. http://dx.doi.org/10.1016/j.pmatsci.2006.11.001.

14. Dave, V., & Patel, H. S. (2017). Synthesis and characterization of interpenetrating polymer networks from transesterified castor oil based polyurethane and polystyrene. Journal of Saudi Chemical Society, 21(1), 18-24. http://dx.doi.org/10.1016/j. jscs.2013.08.001.

15. Sathiskumar, P. S., & Madras, G. (2011). Synthesis, characterization, degradation of biodegradable castor oil based polyesters.

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16. Zhang, L., Zhang, M., Hu, L., & Zhou, Y. (2014). Synthesis of rigid polyurethane foams with castor oil-based flame retardant polyols. Industrial Crops and Products, 52(1), 380-388. http:// dx.doi.org/10.1016/j.indcrop.2013.10.043.

17. Lin, S., Huang, J., Chang, P. R., Wei, S., Xu, Y., & Zhang, Q. (2013). Structure and mechanical properties of new biomassbased nanocomposite: castor oil-based polyurethane reinforced with acetylated cellulose nanocrystal. Carbohydrate Polymers, 95(1), 91-99. http://dx.doi.org/10.1016/j.carbpol.2013.02.023.

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18. Hejna, A., Kirpluks, M., Kosmela, P., Cabulis, U., Haponiuk, J., & Piszczyk, Ł. (2017). The influence of crude glycerol and castor oil-based polyol on thestructure and performance of rigid polyurethane-polyisocyanurate foams. Industrial Crops and Products, 95(1), 113-125. http://dx.doi.org/10.1016/j. indcrop.2016.10.023.

19. Mutlu, H., & Meier, M. A. R. (2010). Castor oil as a renewable resource for the chemical industry. European Journal of Lipid Science and Technology, 112(1), 10-30. http://dx.doi. org/10.1002/ejlt.200900138.

20. Monteiro, A. S. F., Macedo, L. G. S., Macedo, N. L., & Balducci, I. (2010). Polyurethane and PTFE membranes for guided bone regeneration: histopathological and ultrastructural evaluation. Medicina Oral, Patologia Oral y Cirugia Bucal, 15(2), e401-406. http://dx.doi.org/10.4317/medoral.15.e401.

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22. Costa, A. C. F. M., Lima, M. G., Lima, L. H. M. A., Cordeiro, V. V., Viana, K. M. S., Souza, C. V., & Lira, H. L. (2009).

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25. Alves, E. G. L., Rezende, C. M. F., Oliveira, H. P., Borges, N. F., Mantovani, P. F., & Lara, J. S. (2010). Avaliação mecânica da placa de compósito de poli-hidroxibutirato e hidroxiapatita em modelos ósseos de gato. Arquivo Brasileiro de Medicina Veterinária e Zootecnia, 62(6), 1367-1374. http://dx.doi. org/10.1590/S0102-09352010000600011.

26. Cangemi, J. M., Santos, A. M., Claro Neto, S., & Chierice, G. O. (2008). Biodegradation of polyurethane derived from castor oil. Polímeros, 18(3), 201-206. http://dx.doi.org/10.1590/ S0104-14282008000300004.

27. Callister, W. D. Jr. (2002). Ciência e engenharia de materiais: uma introdução. Rio de Janeiro: LTC. 28. Dubois, L., Steenen, S. A., Gooris, P. J. J., Bos, R. R. M., & Becking, A. G. (2016). Controversies in orbital reconstructionIII. Biomaterials for orbital reconstruction: a review with clinical recommendations. International Journal of Oral and Maxillofacial Surgery, 45(1), 41-50. http://dx.doi.org/10.1016/j. ijom.2015.06.024. PMid:26250602.

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31. Reis, E. C. C., Borges, A. P. B., Oliveira, P. M., Bicalho, S. M. C. M., Reis, A. M., & Silva, C. L. (2012). Desenvolvimento e caracterização de membranas rígidas, osteocondutoras e reabsorvíveis de polihidroxibutirato e hidroxiapatita para regeneração periodontal. Polímeros: Ciência e Tecnologia, 22(1), 73-79. http://dx.doi.org/10.1590/S0104-14282012005000007.

32. Kanno, T., Sukegawa, S., Furuki, Y., Nariai, Y., & Sekine, J. (2018). Overview of innovative advances in bioresorbable plate systems for oral and maxillofacial surgery. Japanese Dental Science Review, 54(3), 127-138. http://dx.doi.org/10.1016/j. jdsr.2018.03.003. PMid:30128060.

Received: June 20, 2018 Revised: Nov. 26, 2018 Accepted: Mar. 08, 2019

Polímeros, 29(2), e2019029, 2019

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.06318

Bio-based additives for thermoplastics Marco Aurelio De Paoli1*  and Walter Ruggeri Waldman2 Laboratório de Processamento de Polímeros, Instituto de Química, Universidade Estadual de Campinas – UNICAMP, Campinas, SP, Brasil 2 Centro de Ciências e Tecnologias para Sustentabilidade, Universidade Federal de São Carlos – UFSCar, Campus de Sorocaba, Sorocaba, SP, Brasil 1

*madpaoli@unicamp.br

Abstract Presently, there are significant research efforts being undertaken to produce bio-based chemicals in a cost-effective way. The polymer chemists and engineers are no exception to this. Additives for polymers correspond to a large section of the plastics market and bio-based products can substitute many of them. The scientific literature has a large number of publications focusing on the preparation and testing of bio-based polymer additives; however, the small number of products that reach the market, which are bio-based, does not reflect this. In terms of the global market, the environmentally friendly appeal of bio-based additives alone is not sufficient; the bio-based product must have similar or better performance than the oil-based and be comparable or lower in cost than the existing products. In this review, we focus on bio-based polymer additives that have already reached the market or have a real possibility of reaching the market in a cost-effective way.

Keywords: thermoplastics, bio-based, additives, renewable, environmentally friendly.

How to cite: De Paoli, M. A., & Waldman, W. R. (2019). Bio-based additives for thermoplastics. Polímeros: Ciência e Tecnologia, 29(2), e2019030. https://doi.org/10.1590/0104-1428.06318

1. Introduction In the early days of polymer production, the majority of raw materials used by the industry were obtained from renewable resources or mining. With the development and growth of the petrochemical industry, raw materials derived from commodities obtained from petrol became dominant. Now, almost two centuries later, this trend is reversing. Environmental concern and cost are the main causes of this reversion and bio-based polymers and additives are reaching the market. However, the mere fact that a raw material is bio-based (or renewable) does not enable its use by industry. Large-scale production, reproducible properties, and a competitive cost in relation to its routinely used oil-based counterpart are important variables to take into account. Additionally, being a bio‑based (or renewable) material does not means that it is non-toxic (snake venom is natural and renewable!) or non-harmful to the environment.

There is a very large number of publications related to bio-based additives for polymers; however, as highlighted above, there is a long way from the lab bench to the polymer market, and cost effectiveness is the largest barrier to be crossed. There are reviews discussing academic works on different kinds of bio‑based polymer additives, but this review will focus on the bio-based additives that are already in the market or may reach it in a short time scale.

Polímeros, 29(2), e2019030, 2019

Polymers have additives added to adjust their final properties and performance for a particular application and/or to facilitate their processing. Additives represent a small percentage by weight of the formulation, but they have a strong impact on the final cost of a plastic product.

Exceptions are plasticizers, which have a low cost and may be present in poly(vinyl chloride), PVC, at concentrations as high as 50 % in weight (wt. %).

Reinforcing agents are one class of additives used specifically to modify the mechanical properties of a thermoplastic. Improvement of the tensile and flexural strengths are the aims in using these additives. Presently, the most commonly used reinforcing agents are glass fibers, talc, carbon fibers and nanosized chemically modified clays.

However, there is a growing trend for substituting these for vegetal fibers in some specific applications.

In this review, the term bio-based is used for a chemical species “[…] composed or derived in whole or in part of biological products issued from biomass (including plant, animal, and marine or forestry materials)”[1:377-410]. In the case of polymer additives, it is also important to consider the production scale, as well as the existing and/or potential market. A bio-based additive may fit into the above-mentioned definition, but it also has to be industrially produced, distributed, and sold, or have the potential to reach the market in a reasonable timescale. In general, the data available on bio-based additives is scarce and patents protect detailed

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R R R R R R R R R R R R R R

De Paoli, M. A., & Waldman, W. R. chemical information of commercial products. An interesting remark regarding the current status of bio-based additives is that during the review process of the manuscript, after the requests from the reviewers, we checked the links of the products we have scanned for the first submission, and some products were no longer available two months later.

This is a hint of how much this market is volatile and has yet to mature to achieve a consolidated status.

To the best of our knowledge, the bio-based additives used nowadays, produced from renewable resources, are plasticizers, colorants, biocides/antimicrobial agents, antistatic agents, antifogging agents, lubricants, flame retardants/smoke suppressants, and stabilizers (antioxidants, photostabilizers, and acid scavengers).

In this review, we focus on bio-based additives and reinforcement agents used for thermoplastics and commercially available or with potential to enter the market.

1.1 Plasticizers These additives are used to improve the flexibility of thermoplastics by reducing the intermolecular interactions.

Therefore, they lower the glass transition and the melting temperatures of the polymer. Thermoplastics use plasticizers extensively, reaching concentrations as high as 50 wt. %.

The plasticizers market, including bio-based ones, will be worth US$ 19,367 million dollars by 2019[2]. The global bio plasticizers market was valued at approximately USD 836 million in 2017 and is expected to generate revenue of USD 1,657 million by 2024[3].

Early phthalate-based plasticizers corresponded to 85 % of the total plasticizers market. In the last decade, due to toxicity concerns, their application was restricted and terephthalate and bio-based plasticizers appeared on the market.

The raw materials used for production of bio-based plasticizers are soybean oil, linseed oil, palm oil, sunflower oil, and castor oil. These polyunsaturated vegetable oils have high numbers of carbon–carbon double bonds available for epoxidation and are used as precursors to epoxidized oil products[4]. Usually, a peroxide or a peroxyacid is used to add an oxygen atom and convert the –C=C– bond to an epoxide group[5]. The epoxidized vegetable oils act as plasticizers, e.g. reducing the interactions between the electropositive and electronegative groups

of PVC. The carbonyls of the ester groups interact with the electropositive hydrogen atoms and the hydrocarbon tails interact with the electronegative chlorine atoms.

Additionally, the epoxide groups are more reactive than carbon–carbon double bonds, thus providing the additional advantage of acting as a good acid scavenger[6]. Thus, for PVC, they have the additional characteristic of acting as a stabilizer. Recent studies have shown that epoxidized sunflower oil is also a good plasticizer and stabilizer for PVC, pure or combined with other plasticizers[7].

An additional advantage for the use of epoxidized oils as additives in polymers is that, they can act as stabilizers where the mechanism of degradation comprises evolution of acid substances, like HCl, the main by-product of the PVC degradation.

The lower cost of soybean oil, in comparison to other vegetable oils, makes epoxidized soybean oil the most commonly used bio-based plasticizer in the food packaging market. Overall, the global bio-plasticizers market finds applications in food packaging, medical devices, consumer goods, toys, wire/cables, and the construction and automotive industries. For the automotive industry, epoxidized vegetable oils have the additional advantage of producing less VOC (volatile organic compounds) in comparison to phthalate‑based plasticizers.

The cost of bio-based plasticizers, compared with phthalate-based ones, is a key challenge faced by the bio‑based plasticizers market. The present number of commercial bio-based plasticizer products on the market are epoxidized soybean oil (26), citrates (13), sebacates (9), epoxidized linseed oil (6), and adipates (5)[8].

Bio-based plasticizers are widely used as additives in PVC resins for the production of cables, flooring, wire jacketing, food containers, automobile parts, etc. The use of bio-based plasticizers for wire applications can enable manufacturers to reduce carbon gas emissions by up to 40 %.

These bio-plasticizers, when used for cable manufacturing, offer various advantages in terms of electrical and temperature performance compared with traditional plasticizers[9]. Table 1 exemplifies a group of bio-based plasticizers currently in the market.

In the near future, one can envisage a tendency to ban petrol-based plasticizers and use exclusively bio-based plasticizers.

Table 1. Examples of bio-based plasticizers currently in the market.

Trade name Plasthall

Composition Manufacturer Renewable esters with long Hallstar (USA) carbon chain.

Comments According to the producer, the esters are polymeric, not only the molecules. A low leaching is expected.

Refs.

Vikoflex

Epoxidized vegetable oils Arkema (France)

Main market aspect is the reliability on the oxirane (epoxide ring) content.

[11]

JayflexTM

Adipate

Exxon Mobil (USA)

Used for low-temperature purposes and typically not alone, but in blends with phthalates, not replacing, but reducing the use of phthalates.

[12]

Morflex

Dibutyl Sebacate

Vertellus (USA)

Used for low-temperature applications, like packaging films for refrigerated food.

[13]

Reflex™

Soybean oil derivatives

PolyOne (USA)

-

[14]

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[10]

Polímeros, 29(2), e2019030, 2019

Bio-based additives for thermoplastics 1.2 Colorants Humankind has used colorants since the first cavemen painted the walls of their caverns. The methods for production of colorants and lightfast colorants was, for many centuries, a valuable secret. Iron blue, for example, is reported as the first colorant produced on the industrial scale after 1724[15].

The English and German chemical industries were born and flourished in the 19th century, producing dyes and pigments.

Colorants based on lead, cadmium, and chromium were dominant for industrial applications until the second half of the 20th century. With the birth of the environmental movement in the 1970s and the growing awareness of the environmental impacts of human activities, inorganic dyes appeared on the environmentalists’ radar, and their toxic effects led to movements banning them from the 1980s onwards[16].

Routinely, the word pigment is used for color agents; however, the term colorant used here is more adequate as it comprises both dyes and pigments. Colorants for thermoplastics are classified in two categories: pigments – when the colorant does not dissolve in the polymeric matrix, and dyes – when the colorant dissolves into solution with the polymers. Pigments can be inorganic, mostly metal oxides and sulfides, or organic, such as phthalocyanines or carbon black. Dyes are mostly organic, and the main classes are the anthraquinones and perinones. Although some anthraquinones are found in nature, their industrial production is based on the oxidation of anthracene. Organic colorants derived from anthraquinone, like Alizarin[17] and Carminic acid, have in common a thermally stable polyaromatic and conjugated chemical structure, Figure 1, which can resist thermal stress during processing. Bio-based colorants are not stable under this kind of stress. Because of this, bio-based colorants like indigoids, carotenoids, quininoids, among others, mostly find application in the field of textile fibers, which are less thermally stressed during their processing. We will not discuss this matter further as the focus of this review is thermoplastics, but we refer the reader to a comprehensive review on this subject[18].

Despite the efforts to study these alternative additives[19], we did find only one industrially produced bio-based colorant

Figure 1. Chemical representations of anthraquinone (top) and two of the anthraquinone-based colorants, Alizarin (bottom left) and Carminic acid (bottom right).

(Table 2) for use in thermoplastics. The manufacturer did not disclose the bio-based ingredient; however, it did provide the certification for biodegradability and compostability.

1.3 Biocides/antimicrobial agents Historically, humankind has used substances to prevent bacterial infection for millennia, even though the existence of microorganisms, such as bacteria and fungi was not known.

One example is the biocidal or antimicrobial action of the essential oils present in most spices, including pepper and oregano[21]. This explains why poor sanitary conditions are often associated with spicy foods. Additionally, a large number of essential oils tested positive as active antimicrobial agents for food packaging[22].

The term antimicrobial, used here, is more general and adequate than biocide. Biocide means “any chemical substance that destroys life” (bio = life and cide = kill, destroy), whereas antimicrobial limits its action to microorganisms. This class of additives, antimicrobial agents, comprises algaecides, antifouling agents, fungicides, bactericides, and bacteriostats.

The main areas of application of these additives are textiles, food packaging, and medical appliances. Marine applications are the main use for antifouling agents and these additives will not be discussed here.

Persistence is the main technical issue with the use of antimicrobial agents in polymers and, in general, inorganic compounds or metallic silver are used. However, silver or nanosized silver are harmful to the environment after lixiviation from the polymer. Other alternatives are thiazole derivatives and halogenated compounds. There is little mention in the literature of bio-based commercial products of this class.

Chitosan, a hydrophilic polysaccharide derived from chitin, is the main constituent of the outer skeleton of insects and crustaceans, such as shrimp, crab, and lobster[23]. It shows a broad antimicrobial spectrum to which gram-negative, gram‑positive bacteria, and fungi are highly susceptible. In the case of fungi, it shows fungistatic properties[24]. There are many studies about the minimum inhibitory concentration (MIC) for chitin, chitosan, their derivatives, or combinations thereof, with different results for different microorganisms. MIC is the lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism after overnight incubation. A summary of this property for chitosan is available in the literature[25]. To have the antimicrobial material available for microorganisms, the chitosan should be at the outer layer of the polymer matrix and migration to the bulk should be avoided. Chitosan can be used in polymer blends prepared by reactive extrusion or as an antimicrobial coating in film packaging[26]. Despite the availability of this bio-based raw material and knowledge

Table 2. Example of bio-based colorant currently in the market.

Trade name OnColor

Composition TiO2 and other allegedly bio-based and compostable compounds.

Polímeros, 29(2), e2019030, 2019

Manufacturer PolyOne (USA)

Comments Ref. Despite the comments on the website, the MSDS sheets only describes [20] TiO2, explaining that there are no additional ingredients that are classified as hazardous for health or environment

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De Paoli, M. A., & Waldman, W. R. of its antimicrobial activity, for thermoplastics there is no commercial product on the market based on this material.

Presently, there are a few commercial bio-based antimicrobials[27], shown below:

Gaia AB 504 Antimicrobial is an organic concentrate produced from citrus extracts that controls or retards the growth of bacteria, fungus, and algae in plastic molded parts.

Gaia Byoprotec is a proprietary blend of various organic products consisting of citric acid, citrus extract, and a blend of unique quaternary proprietary ammonium chloride salts.

Propolis offers antiseptic, antibiotic, antifungal, and even antiviral properties. Propolis starts as a sticky resinous sap, which seeps from the buds of certain trees and oozes from the bark of others. It tested positive for biocide action in natural rubber vulcanizates[28].

The potential future markets for bio-based antimicrobian additives are in biodegradable or edible food packaging or films for food packaging and medical appliances. Table 3 exemplifies bio-based antimicrobian additives (commercially named biocides), currently in the market.

1.4 Antistatic agents and antifogging agents Conventional polymers are insulators and static electricity can occur on the surface of polymer films. Antistatic agents are additives included in their formulation to generate electric conductivity on the surface of the polymer films and dissipate the static electricity.

surface on the film. A bio-based additive used for this purpose is Erucamide, cis-13-docosenoamide, derived from cis-13-docosenoic acid, Figure 2, obtained from canola and rapeseed oils[30]. Erucamide also can act as lubricant and slip agent, due to its low molar mass chain, which has an effect on free volume, fostering the movement of the polymer chains.

Glycerol monostearate is also used as an antistatic and antislipping agent in polymer films. It is produced by the esterification of stearic acid (octadecanoic acid) with glycerol.

Stearic acid and glycerol are bio-based raw materials. Stearic acid is obtained from fats and oils by the saponification of their triglycerides by using hot water (about 100 °C).

The resulting mixture is distilled to separate the pure form of the acid[22]. Glycerol is also obtained from vegetal species and is the major byproduct from the production of biodiesel.

Conductive carbon black is the most commonly used conductive filler, which imparts bulk electric conductivity to polymers. Depending on the source of carbon black, it could be classified as bio-based; however, its main industrial production route is oil-based.

Fogging occurs on the surface of transparent polymer films through the formation of a layer of water microdroplets.

This layer drastically reduces the light transmittance of the film. In packaging and greenhouse coverings, transparency of the films is important and fogging has to be precluded.

Antifogging agents act on the film surface and have a

Antistatic agents also act as antislipping agents because prevention of static electricity also prevents slipping of the films. Electric conductivity in polymeric devices is also necessary in components in different industrial machineries, because these machines must be grounded to avoid electric discharges, which may cause fire or explosions. The same property is necessary for the soles of shoes used by workers in environments with organic flammable vapors and in packaging electronic devices.

Conducting fillers are present in the formulation of these polymeric devices to provide bulk electric conductivity and avoid accidents.

In the case of films, the antistatic agent acts on the surface of the polymer. Hydrophilic end groups in the additive long‑chain molecule aid its diffusion into the hydrophobic media of polymers. After diffusion to the surface, the hydrophilic end of the molecule interacts with water molecules in the atmosphere, creating a dissipative

Figure 2. Chemical representations of the raw material Erucic acid (top) and the antistatic agent Erucamide (bottom).

Table 3. Examples of bio-based biocides currently in the market.

Trade name Gaia AB 504/505

Composition Manufacturer Derivatives from citrus extracts Phoenixplastics (USA)

Gaia Byoprotec

Citric acid, citrus extracts Phoenixplastics (USA) and quaternary ammonium chloride salts

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Comments 504: Specified for rotational molding.

505: Specified for extrusion and injection Blown film, injection molding and extrusion.

Refs.

[29]

[29]

Polímeros, 29(2), e2019030, 2019

Bio-based additives for thermoplastics mechanism of action very similar to antistatic agents.

The hydrophilic end of the long hydrocarbon molecule migrates to the surface of the hydrophobic film. This hydrophilic end interacts with the water microdroplets and increases the water contact angle with the film surface, restoring transparency. The above-mentioned bio-based glycerol esters are also used as antifogging agents.

Sorbitan esters are molecules with a hydrophobic chain and a hydrophilic end; they are industrially used as antifogging agents, Figure 3. Sorbitan is produced by the dehydration of sorbitol, which can be obtained from cellulose[31].

The dehydration reaction usually produces sorbitan as a mixture of five- and six-membered cyclic ethers (1,4-anhydrosorbitol, 1,5-anhydrosorbitol, and 1,4,3,6-dianhydrosorbitol) and the five-membered 1,4-anhydrosorbitol form is the main product[32]. The antifogging agents are sorbitan monostearate and sorbitan monolaurate, which are obtained by the esterification of sorbitol with stearic and lauric acids, respectively. Practically all antifogging agents available on the market are bio-based; however, to the best of our knowledge, there are no oil-based antifogging agents.

Table 4 exemplifies bio-based antistatic and antifogging agents, currently in the market.

1.5 Lubricants Lubricants change the rheology of the polymer melt in a desired way. They improve the flow of the polymer melt during processing by extrusion or rotomolding, reducing the effect of shear and the residence time. Besides affecting the rheology, they have other beneficial effects on the properties of the finished articles. They are considered as a processing aid and the reduction of the residence time reduces thermal

Figure 3. Chemical representation of a generic sorbitan ester and three possible substituents used in antifogging additives.

and mechanical degradation of the polymer[36]. In many cases, the lubricant permits the output of the extrusion process to be maintained by using a lower temperature profile, reducing thermal degradation of the polymer. They can be internal or external, depending on their interaction with the polymer used.

PVC, for example, is not processed without lubricants.

For this polymer, polar lubricant molecules act as an internal lubricant, whereas nonpolar molecules are external lubricants.

For nonpolar polyolefins, the lubricants have opposite effects.

The bio-based lubricants are waxes derived from fatty acids (stearic and palmitic acids) produced from animal resources, such as beef tallow. Tallow is a rendered form of beef or mutton fat, and is primarily made up of triglycerides.

It is solid at room temperature and can be stored for extended periods in an airtight container to prevent oxidation without the need for refrigeration. It is common for commercial tallow to contain fat derived from different animals.

Fats and oils are the raw materials used to produce stearic acid (octadecanoic acid) by the saponification of triglycerides by using hot water (ca. 100 °C). The resulting mixture is distilled to obtain the purified products[22].

Commercial stearic acid is often a mixture of stearic and palmitic (hexadecanoic) acids, although purified stearic acid is available. Fats and oils rich in stearic acid are more abundant in animal fat (up to 30 %) than in vegetable fat (typically < 5 %). The important exceptions are cocoa and shea butter, where the stearic acid content (as a triglyceride) is 28-45 %[37].

The mixture of stearic and palmitic acid, called fatty acids, is directly used as a lubricant in polymer processing by extrusion or calendaring. This mixture is sold under different trade names[38]. To comply with market and governmental rules, the source of the fatty acids can be animal or vegetal (for vegano, kosher, or halal food packaging, e.g.) and must be indicated by the producer.

Fatty acid esters of glycerol or ethanol can be also included as bio-based, depending on their source. Glycerol is a byproduct of biodiesel production plants and ethanol is produced from different vegetal species, such as sugar cane or corn. Fatty acid salts, such as sodium and calcium stearates, are also bio-based because they are produced by reacting stearic acid with the corresponding base. These salts are external lubricants for polyolefins and act as acid scavengers for polyolefins and stabilizers for PVC. Table 5 exemplifies bio-based lubricants currently available in the market.

Table 4. Examples of bio-based antistatic and antifogging agents currently in the market.

Trade name Rikemal and Rikemaster Atmer™ 129 Atmer™ 154 Atmer™ 110/116

Composition Fatty acid esters and organic acid esters of monoglycerides vegetable derived glycerol ester Alkoxylated fatty acid ester Ethoxylated sorbitan ester

Manufacturer Riken (Japan) Croda (UK) Croda (UK) Croda (UK)

Comments

Refs.

[33] [34] [34]

Used for PET

[35]

Table 5. Examples of bio-based lubricants currently in the market.

Trade name Atmer™ 1013 Crodamide™ ER Crodamide™ EBO

Composition Glycerol ester Erucamide Ethylene-bis-oleamide

Polímeros, 29(2), e2019030, 2019

Manufacturer Croda (UK) Croda (UK) Croda (UK)

Comments Applied in expanded polyethylene Applied in polyolefin films Applied for wood plastic composites

Refs.

[39] [40] [41]

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De Paoli, M. A., & Waldman, W. R. 1.6 Flame-retardants/smoke suppressants Historically, one of the first uses for flame-retardants was in the ancient wars, where in the first century BC Roman siege towers were coated with clay reinforced with hair to avoid being burned during the handling or the launching of flaming arrows. Gay-Lussac also participated in the early development of flame retardants with the invention of a fabric for theater curtains, which was treated with a mixture of ammonium phosphate, ammonium chloride, and borax[42]. The modern age of flame-retardants started during World War II, with the demand for airplane canvas to be waterproof and resist fire at the same time. In this context, the first halogenated flame retardant was born: chlorinated paraffin, mixed with antimony oxide and a binder[43].

Polymers are a source of concern in our modern daily life because they are a good fuel for fire in the cases of furniture, homes, cars, or airplanes. Presently, the efficient flame-retardants commercially available are hydrated metal hydroxides associated with halogenated compounds.

Despite that, environmental concerns about the toxicity of halogenated flame retardants (HFR) are increasing to the point of having a collective statement from 150 scientists against their use, called the San Antonio Statement[44].

Together with the environmental concern, the demand for a less toxic alternative drives the research for bio-based flame-retardants.

The mechanism of burning for polymers consists initially of melting and thermal or thermo-oxidative degradation of the melt. Volatiles are formed during degradation and, in contact with heat and oxygen, they start a combustion process, generating the flames and heat for the self-sustenance of the process. This process keeps going until one of the “heat – fuel – oxygen” triad is missing. The nature of the polymer can also influence the dynamics of a fire. Thermoplastics can flow and drip during burning, creating a vector for fire spreading, whereas thermosets emit their volatiles directly from the surface while in the solid state, not contributing to fire propagation. Other polymers, like PVC for example, emit toxic gases during burning with hazardous side effects.

The strategy to control or retard the burning of polymers interferes with the heat release or provides a way to decrease the concentration of oxygen in the surroundings of the flame.

For this purpose, additives make use of one or more of the strategies below: 1) reduction of the heat released in the gaseous phase and by scavenging reactive radicals; 2) decomposition of thermally released water or carbon dioxide in an endothermic reaction, cooling the system while decreasing the oxygen concentration; 3) use of a char-forming reaction that thermally insulates the substrate, decreasing the propagation of flames in the solid phase under the char and precluding access of oxygen and dispersion of gases to the environment.

One of the concerns regarding flame-retardants currently in use is their toxicity to human health and the environment.

Char-forming materials are an alternative and in the scientific literature, there are works with lignin as a char-forming material, which has some additional advantages such as acting as a stabilizer and reinforcing agent[45,46]. Despite these properties, there is no commercial product based on lignin using these features. However, there are recent initiatives developed for industry[47], where lignin is covalently bonded to phosphates to avoid phase separation, which limits the flame-retardation effect.

Great Lakes commercializes the product Kronitex™TCP, which is a triaryl phosphate derived from natural cresol, obtained from coal tar[48]. Despite the criticism around coal production, cresols are considered renewable as they can also be produced from vegetable coal. Another flame-retardant on the market, which are not oil-based and could be considered as being close to the concept of renewability, are nanoclays, such as montmorillonite or bentonite[49]. These form a layer of oxides during burning, promote thermal insulation, and form an oxygen diffusion barrier layer.

Some bio-based molecules such as DNA (deoxyribonucleic acid) and phytic acid have been considered for this application, and have achieved good results as flame-retardants[50]. This is due to the high concentration of phosphor in these compounds.

Despite the significant amount of research using bio-based substances as flame-retardants, highlighted by Dubois and co-workers in a recently published review[36], they are not on the market because they are not yet economically viable[51].

Table 6 shows one type of flame-retardant, which can be cited as bio-based, and available in the market.

1.7 Stabilizers Stabilizers are a class of polymer additives comprising primary and secondary antioxidants, photostabilizers, and acid scavengers. Primary antioxidants act as free radical scavengers and secondary antioxidants decompose the hydroperoxide groups formed upon oxidation. Photostabilizers act by different mechanisms, such as UV light absorption, excited state quenchers, filters, or free radical suppression by species generated after UV irradiation. Acid scavengers, or anti-acids, suppress the acid species formed upon decomposition of the polymer (in the case of PVC), acid impurities, or catalyst residues[52].

Primary antioxidants are hindered phenol species with different substituents in the para position of the aromatic ring. The term “hindered phenol” means a 2,6-bis-tert-butyl substituted phenolic ring, Figure 4. A substituent in the para position, in relation to the hydroxylic group, determines the diffusivity of the additive in the polymer matrix. Hindered phenols, such as vitamin E, are also chemical species that act as free radical scavengers, which are used as antioxidants by living organisms[53]. Vitamin E is also a commercial antioxidant for polymer films and for polymeric surgical implants[54,55].

Table 6. Examples of bio-based flame-retardants currently in the market.

Trade name Kronitex™TCP

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Composition Manufacturer Naturally derived cresol based tricresyl Great Lakes (USA) phosphate

Comments Despite cresols are obtained from naturally occurring coal tar, they are not considered bio-based.

Ref [48]

Polímeros, 29(2), e2019030, 2019

Bio-based additives for thermoplastics Bio-based phenolic compounds can have, in principle, activity as antioxidants for polymers; however, bio-based materials are a mixture of chemical species. The purification of these mixtures has a strong impact on the final cost and it is more favorable to use them as a mixture. Cashew nut shell oil is a mixture of meta-alkylphenols with variable degrees of unsaturation. Its technical grade shows antioxidant activity towards the thermal degradation of poly(cis-isoprene)[56].

Lignin is the second most abundant polymer on our planet and is a component of vegetal species. It is obtained as a byproduct of cellulose and paper plants and has a high availability at a low price. Lignin has a cross-linked structure containing different hindered phenol structures. Two of these phenols are the 2-methoxy-substituted guaiacyl groups and the 2,6-methoxy-substituted siringyl groups. The chemical structure of lignin, and the siringyl/guaiacyl group ratio, depends on the vegetal species from which it is extracted.

The higher this ratio is, the better is its antioxidant activity.

By using this strategy, previous works have demonstrated that lignin extracted from sugar cane bagasse has an antioxidant activity for polybutadiene[57] and styrene-butadiene rubbers[58]. The lignin extracted from Eucaliptus grandis, used to produce cellulose by the pulp and paper industry, had its siringyl/guaiacyl ratio determined as 2.1 to 2.5[59,60].

Formulations containing this lignin showed antioxidant activity for pure polymers and cellulose fiber composites with polypropylene,[61] polyethylene,[62] and polyamide-6[63].

In the case of polypropylene, aged formulations containing lignin maintained their properties for a longer period in comparison to formulations aged with a non-bio-based antioxidant[61].

Figure 4. Chemical representations of a hindered phenol (top) and vitamin E (bottom).

The oil-based antioxidants used for rubber and elastomers are aromatic amines, and the same strategy used with bio‑based phenols was applied by Abad et al.[64] to stabilize rubber with amino acids. In this work, cystine, tyrosine, asparagine phenyl alanine, and alanine showed antioxidant activity for vulcanized natural rubber.

The most common secondary antioxidants used for polymers are phosphites, like e.g. tris-nonylphenylphosphite and tris-1,3-di-tert-butylphenylphosphite. To the best of our knowledge, presently there are no bio-based secondary antioxidants on the market; however, they were used in a synergistic association with lignin to stabilize polyethylene[62].

UV absorbers are molecules that form a thermodynamically unstable species by the absorption of UV light, returning in the dark to the initial ground state form. One example is 2-hydroxybenzophenone, which forms an enol when irradiated. The enol form decays to the more thermodynamically stable ketone form, regenerating the stabilizer molecule. This mechanism is known as the keto – enol tautomerization mechanism.

This simple mechanism may occur in nature, but no bio-based hydroxybenzophenone products exist on the market. Additive producers suggest the use of stearates as light stabilizers for PVC; however, they really act as acid scavengers, deactivating the HCl formed upon photodegradation of this polymer. Lignin was reported as a light stabilizer for rubbers, acting as a filter for UV light, similarly to carbon black[43]. Another class of commercial photostabilizer are the hindered amines, HALS, which suppress free radicals when irradiated with UV light. In this class, bis(2,2,6,6-tetramethyl-4piperidyl) sebacate (Caplig 770™) is a bio-based HALS, produced from sebacic acid, Table 7. Castor oil is the raw material used to produce sebacic acid, by using sodium hydroxide, sulfuric acid, and catalysts including zinc oxide and phenol.

Acid scavengers, or anti-acids, can be ester salts, such as calcium, zinc, or magnesium stearate. Stearic acid is reacted with calcium, zinc, or magnesium hydroxides to produce these salts. The main source of stearic acid is animal fat, where it is present in large concentrations.

This origin permits their inclusion as bio-based materials.

Use of calcium and zinc stearates as stabilizers, that is, acid suppressors, for PVC and polyolefins is common practice by the industry. Use as a lubricant for polyolefin processing is another application of these salts. On the commercial market, we find the bio‑based Struktol TPW 426, which is a blend of fatty acid derivatives recommended for use with PVC[65].

Table 7. Examples of bio-based stabilizers currently in the market.

Trade name Riken E-Oil Series Struktol TPW 426

Composition Tocoferol derivative Blend of fatty acids derivatives

Caplig 770™

Plant based sebacate

Polímeros, 29(2), e2019030, 2019

Manufacturer

Comments Used in plastic for food packaging Struktol (USA) Also works as a compatibilizer in composites Nanjing Capatue Chemical Co Similar to HALS (China)

Refs.

[66] [65]

[67]

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De Paoli, M. A., & Waldman, W. R. 1.8 Reinforcing agents These additives tailor the mechanical properties of thermoplastic polymers, making them fit a specific application with controlled tensile and/or flexural properties. These reinforced materials are called “composites” because they consist of two heterogeneous phases: the polymer and the solid particles of the reinforcing agent. Presently, the most commonly used reinforcing agents are talc and short glass fibers. The predicted market shares are US$ 3.29 billion dollars for talc in 2021 and US$ 2.7 billion dollars for glass fibers in 2022[68]. These reinforcing agents produce excellent mechanical and thermal properties; however, they have a high density and are abrasive to the processing equipment[69]. Additionally, mechanical recycling of these composites is energy consuming and not cost effective for industrial purposes[70].

Substitution of the above-mentioned additives for vegetal fibers is common and depends on the development of the adequate processing method, which is frequently through extrusion with a twin-screw extruder. Their main advantage is the lower density, which reduces the weight of the final product; however, vegetal fibers thermally decompose at ca. 200 oC and most thermoplastics are processed above this temperature. In addition, the high shear ratio in a twin-screw extruder reduces the aspect ratio of vegetal fibers. Thus, the development of an adequate processing method is not trivial. An additional advantage of vegetal fibers is their lower abrasivity to the processing equipment[53].

The challenges in using vegetal fibers are the low thermal degradation temperature, availability, cost, and properties reproducibility. Due to the hydrophilic characteristics of vegetal fibers, in contrast to the hydrophobicity of polyolefins, a compatibilizing agent is also necessary. Despite these challenges, there is a plethora of patents and publications reporting the use of vegetal fibers as reinforcing agents for thermoplastics. The most commonly cited fibers are cellulose, silk, hemp, pineapple leaf, sisal, and curaua (the last three are bromeliaceae with long leaves)[71]. The choice depends on the regional availability and cost.

Among these vegetal fibers, curaua fibers have mechanical properties similar to glass fibers. Their composites with polypropylene[72], high-density polyethylene[73], and polyamide-6[74] can substitute their glass fiber counterparts in several applications. It was used by the automotive industry in the past but, unfortunately, the production of curaua fibers is limited and their price is not competitive in relation to glass fibers.

Hemp fibers have been extensively used throughout history. For centuries, ropes, sails, and textiles were made with hemp fibers. Presently, some car industries use hemp for composites with thermosets; however, textiles are the main market application for these fibers.

India and Brazil produce sisal fibers on a large scale for many different applications. Sisal fiber is a lignocellulosic material produced with reproducible properties. The long fibers extracted from the leaves (1.0 to 1.5 m long) of the sisal plant are milled and dried before being fed into the extruder to disperse in the thermoplastic. Their low density precludes the use of gravimetric dosimeters and other feeding techniques are used. Composites of polypropylene or high-density polyethylene with 30 wt. % of sisal fibers have tensile and flexural properties comparable to those using glass fibers[75]. Presently, other markets are more financially attractive for sisal fibers in comparison to polymer reinforcement.

Cellulose is the most abundant polymer in the world; it is present in all vegetal species. The mechanical properties and degree of crystallinity of the cellulose fibers depend on the vegetal species from which they are extracted[76].

The pulp and paper industries choose selected species of wood to produce cellulose fibers on a large scale with reproducible properties. In terms of availability and cost, cellulose fibers are the most favorable bio-based fibers to use in reinforced composites of thermoplastics. Oksman and co-workers published a series of reports on the preparation of polypropylene composites reinforced with cellulose fibers by using a twin-screw extruder[77,78]. Their low density is an advantage, but difficulties in feeding the extruder were also encountered. Pelletizing the cellulose fibers was the solution employed to avoid this[79]. Our group developed composites of cellulose fibers with high-density polyethylene (HDPE)[48] and polyamide-6[49]. For HDPE, a maleated polyethylene was used as compatibilizer. For polypropylene, the association of the cellulose fibers with lignin improved the stability and mechanical properties in comparison to using bleached cellulose fibers[80]. As long as paper is the main market for the cellulose and pulp industries, there will be low investment in using it for thermoplastic composites.

The same applies to nanocellulose; however, we cite one commercial product in Table 8.

In the future, we predict that this trend will revert and bio-based reinforcing agents will gradually substitute glass fiber and talc for most applications. Additionally, they will facilitate the thermal recycling of thermoplastic composites for energy production.

Table 8. Examples of bio-based reinforcing agents currently in the market.

Trade name DuraSense™

Composition Wood fiber composites

NeCycle™ powerRibs™ UBQ™

Cellulose resin bonded with cardanol NEC (Japan) Natural fiber composite Bcomp (Switzerland) reinforcement grid bio-based thermoplastic composite UBQ (Israel)

Nano Cellulose

Cellulose nanofibers

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Manufacturer Stora Enso (Finland/Sweden)

Green Science Alliance (Japan)

Comments Refs.

[81] The DuraSense family ranges the proportion of wood fibers (30-60%) and the nature of the polymers (fossil- or bio-based) [82]

Can be used both in thermoplastics or thermosets The biomass is extracted mainly from unsorted municipal solid waste

[83]

[84]

[85,86]

Polímeros, 29(2), e2019030, 2019

Bio-based additives for thermoplastics

2. Conclusions In this review, we focused on bio-based additives that are produced and marketed, or have the potential, for use by industry. We note that there is a global tendency to substitute oil-based for bio-based raw materials and, as seen above, the polymer additives industry is following this trend, aiming to reduce environmental impact with no changes in performance and no impact on the final cost of their products. This trend will certainly benefit the environment and customers. There is a large number of publications focusing on the characterization and use of bio-based additives; however, a limited number of these products are produced (even in pilot plant scale), or have reached the market. The limitations on marketability are mainly due to cost and availability.

As a final remark, it is common knowledge of the researchers on bio-based additives for thermoplastics to focus mainly on the relationships between composition and final properties of the materials. While we consider that basic science is of paramount importance for technological development, it is striking that the vast majority of the works that seek technological solutions do not present their results along with a cost analysis and/or considerations regarding logistics. We believe that much of this gap comes from the lack of familiarity with the fundamental practices for patenting and licensing of a process or product to the productive sector. As a final suggestion, we recommend, as a way to fill this gap, the development of partnerships with the productive sector, both in the additives industry and in the agricultural sector, for the development of economically and logistically feasible solutions.

3. Acknowledgements MAP acknowledges a Senior Researcher fellowship from CNPq and WRW the São Paulo Research Foundation (FAPESP) for the grant 2016/24936-3.

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Characterization and thermal stability of poly(vinylchloride) plasticized with epoxidized soybean oil for food packaging.

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12/12

compositesworld.com/news/green-science-alliance-co-ltdmanufactures-new-nano-cellulose-composites Received: Oct. 02, 2018 Revised: Feb. 28, 2019 Accepted: Mar. 01, 2019

PolĂ­meros, 29(2), e2019030, 2019

UBE lança ETERNATHANE®, pré-polímeros de poliuretano à base de policarbonato-diol para elastômeros de alto desempenho e durabilidade A UBE é uma indústria multinacional Japonesa que atua nos setores de químicos, máquinas, fármacos, energia e construção. Com escritórios ao redor do mundo e fábricas no Japão, Tailândia e Espanha, há um destaque na produção de caprolactama, poliamidas, fertilizantes e produtos químicos nos.

O poliuretano para elastômeros tornou-se cada vez mais soosticado para atender às exigências do mercado atual. Neste contexto, a UBE desenvolveu o ETERNACOLL® e o ETERNATHANE®, uma grande plataforma de soluções que oferecem possibilidades personalizáveis aos materiais de poliuretano, bem como retenção de desempenho superior e a longo prazo, como estabilidade térmica, resistência a óleo, estabilidade hidrolítica, resistência à intempéries e resistência química.

retenção das propriedades mecânicas após exposição a altas temperaturas

redução da absorção de água

retenção das propriedades originais após severa agressão hidrolííca e química

redução da perda de volume quando exposto à abrasão extrema

Os pré-polímeros de poliuretano ETERNATHANE®, à base de policarbonato-dióis ETERNACOLL® e terminados em isocianatos, são aplicados em elastômeros de alto desempenho. Através do aprimoramento das propriedades de resistência mecânica, química e térmica dos poliuretanos tradicionais, os novos elastômeros obtidos podem ser aplicados a novos usos e funções não disponíveis até o momento para novos mercados e clientes, tais como: petróleo e mineração, revestimento de rolos, membranas elastoméricas, pisos, elastômeros fundidos, TPU, rodas e pneus, compostos de poliuretano, selantes, eletrônicos e encapsulamento, entre outros. poliu

https://www.ube.com/contents/pcd/index.html

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Polímeros VOLUME XXIX - Issue II - Apr./June, 2019

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