Polímeros: Ciência e Tecnologia (Polimeros), vol.25, n.5, 2015

Novos Avanços em Hostaform® POM Soluções inovadoras para ambientes exigentes

HOSTAFORM POM SÉRIE XGC – ACOPLAMENTO DE ALTO DESEMPENHO

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Ampliação do leque de atuação

Ideal para tubos

• Alta resistencia à fadiga • Elevada resistência à tração e rigidez • Baixa absorção de umidade • Alta resistência ao desgaste • Excelente estabilidade térmica • Excelente resistência química a solventes • Alta Estabilidade em temperaturas

• Alta estabilidade dimensional • Baixo teor de extraíveis quando

HOSTAFORM POM LPT – SÉRIE DE BAIXA PERMEAÇÃO

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Robustez mecânica

• Excelente impacto aliado à baixa permeabilidade de volateis, atendendo às regulamentações EPA/CARB • Fácil utilização em soluções monocamada • Comprovada resistência em longos períodos de exposição em combustíveis • Propriedades de barreira inerentes à resina POM

comparado às poliamidas

• Ampla resistência química • Baixa absorção de umidade • Exclusiva propriedade elástico mecânica

• Excelente tenacidade e resiliência VOLUME XXV - N° 5 - SET/OUT - 2015

elevadas, garantindo manutenção das propriedades no longo prazo

Polímeros

A Celanese amplia o leque de opções para as mais diversas aplicações com o lançamento de novos grades no portfolio de Hostaform POM.

• Melhor relação rigidez e resistência • Superior resistência mecânica na linha de solda fria

• Maior estabilidade térmica • Elevada resistência ao impacto charpy com entalhe

• Melhor integridade na linha de emenda

• Elevada temperatura de deflexão térmica (HDT)

• Elevada resistência química

Celanese, Alameda Ministro Rocha Azevedo, 38 conj. 102/604 – São Paulo/SP – Brasil CEP 01410-000 Telefone: (11) 31473360/3370, contato@celanese.com © 2014 Celanese ou suas afiliadas. Todos os direitos reservados.

Celanese ®, design registrado C-ball e todas as outras marcas comerciais aqui identificadas com ®, TM, SM, salvo indicação em contrário, são marcas comerciais da Celanese ou suas afiliadas.

(18 a 22 de outubro de 2015)

Para maiores informações visite: celanese.com/engineered-materials

Celanese Impact Performance Ad.indd 1

Matéria sobre o 13º CBPOL

3/31/14 1:39 PM

Technyl® está mais forte do que nunca Technyl® é uma linha completa de plásticos de engenharia de alto desempenho para aplicações automotivas e de transportes, construção e energia, bens de consumo e equipamentos industriais.

Conheça o Technyl Force®, a nossa nova oferta de produtos e serviços.

O mundo traz desafios. Nós respondemos com inovação.

Saiba mais: www.technyl.com

http://dx.doi.org/10.1590/0104-1428.2505

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Editorial

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Mudanças na Polímeros A partir do próximo número da Polímeros passaremos a contar com o Prof. Sebastião Canevarolo como editor da revista e com a participação no Comitê Editorial do Prof. Covas da Universidade do Minho, Portugal, e do Prof. João B.P. Soares da University of Alberta, Canadá. O Prof. Adhemar Ruvolo atuará ainda como editor interino até julho de O novo editor assume após o término do mandato de quatro anos da Profa. Elisabete Frollini. O Conselho Editorial

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2016, auxiliando o Prof. Canevarolo. agradece o trabalho da Profa. Elisabete, que atuou firmemente como editora e promoveu, juntamente com o Comitê Editorial, muitas melhorias importantes na revista, sendo elas: a mudança do formato da versão impressa, a criação do template, a implementação da predominância de artigos em inglês, o site em inglês e o início do processo de migração A decisão do Comitê Editorial pela predominância de artigos em inglês visava a maior internacionalização de nossa

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do sistema de submissão para a plataforma ScholarOne. revista e resultou em um aumento considerável nos acessos aos artigos por pessoas do exterior. Como consequência disso, o Conselho Editorial, em sua reunião durante o CBPol, oficializou a decisão da revista passar, a partir de outubro de 2015, a processar somente os artigos redigidos em inglês e no formato do template. Além disso, já em janeiro de 2016 publicado todos os artigos em português que foram submetidos/aceitos até setembro de 2015, passando então a ter uma

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deveremos estar recebendo todas as submissões pelo site da revista na plataforma ScholarOne. Esperamos em 2016 ter revista inteiramente em inglês. Todas essas medidas visam atender os padrões exigidos pela plataforma ScholarOne e, naturalmente, melhorar ainda mais o nível técnico/científico da Polímeros.

Em 2015 a revista teve apoio financeiro direto somente do CNPq e indireto da FAPERGS, o que causou uma redução última reunião, autorizaram o uso de fundos próprios da associação para a finalização dos números de 2015. Além disso,

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considerável nos recursos disponíveis para a revista. Como consequência disso, a Diretoria e Conselho da ABPol, em sua a Diretoria e Conselho da ABPol decidiram, e o Conselho Editorial referendou, que a revista deixasse de ser impressa, passando a ser acessada exclusivamente pela internet. Com isso reduziremos consideravelmente os custos da revista e aumentaremos a sua visibilidade. Em futuro próximo os sócios da ABPol receberão os números da revista na forma Apesar dessas medidas, a saúde financeira da Polímeros ainda é uma incógnita para 2016

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Professor Marco-Aurelio De Paoli Presidente do Conselho Editorial

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de uma mensagem eletrônica, com o expediente e o índice dos trabalhos com um link para cada artigo em versão pdf.

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Polímeros, 25(5), 2015

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P o l í m e r o s - N º 5 - V o l u m e X X V - S e t / O u t - 2 0 1 5 - ISS N 0 1 0 4 - 1 4 2 8

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I n d e x a d a : “ 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 ” — “ I S I W e b o f K n o w l e d g e , W e b o f S ci e n c e ”

and

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Polímeros P r e s i d en t e

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Conselho Editorial

Marco-Aurelio De Paoli (UNICAMP/IQ)

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Membros

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Conselho Editorial

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Adhemar C. Ruvolo Filho (UFSCar/DQ) Ailton S. Gomes (UFRJ/IMA) 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) Elias Hage Jr. (UFSCar/DEMa) Elisabete Frollini (USP/IQSC) Eloisa B. Mano (UFRJ/IMA) Glaura Goulart Silva (UFMG/DQ) 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) Osvaldo N. Oliveira Jr. (USP/IFSC) Raquel S. Mauler (UFRGS/IQ) Regina Célia R. Nunes (UFRJ/IMA) Rodrigo Lambert Oréfice (UFMG/DEMET) Sebastião V. Canevarolo Jr. (UFSCar/DEMa) Silvio Manrich (UFSCar/DEMa)

Comitê Editorial Sebastião V. Canevarolo Jr. – Editor

Membros

do

Comitê Editorial

Adhemar C. Ruvolo Filho Bluma G. Soares César Liberato Petzhold Glaura Goulart Silva João B. P. Soares José António C. Gomes Covas José Carlos C. S. Pinto Regina Célia R. Nunes

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Produção

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Assessoria Editorial

www.editoracubo.com.br

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“Polímeros” é uma publicação da Associação Brasileira de Polímeros Rua São Paulo, nº 994 13560-340 - São Carlos, SP, Brasil Fone/Fax: (16) 3374-3949

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e-mails: abpol@abpol.org.br / revista@abpol.org.br http://www.abpol.org.br Data de publicação: Outubro de 2015

Apoio:

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Polímeros / Associação Brasileira de Polímeros. vol. 1, nº 1 (1991) -.- São Carlos: ABPol, 1991Versão eletrônica disponível no site: www.scielo.br

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Bimestral v. 25, nº 5 (set./out. 2015) ISSN 0104-1428

Site da Revista “Polímeros”: www.revistapolimeros.org.br

1. Polímeros. l. Associação Brasileira de Polímeros.

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Polímeros Seção Editorial

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Editorial................................................................................................................................................................................................E1 Informes & Notícias ............................................................................................................................................................................E4 Calendário de Eventos ........................................................................................................................................................................E5 Associados...........................................................................................................................................................................................E6 Matéria.................................................................................................................................................................................................E8

S e ç ã o T é cn i c a Influence of the polymeric coating thickness on the electrochemical performance of Carbon Fiber/PAni composites

Binary mixture micellar systems of F127 and P123 for griseofulvin solubilisation

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Carla Polo Fonseca, Dalva Alves de Lima Almeida, Mayara Camila Duarte de Oliveira, Maurício Ribeiro Baldan and Neidenei Gomes Ferreira.......................................................................................................................................................................... 425 Lillian Maria Uchôa Dutra, Maria Elenir Nobre Pinho Ribeiro, Igor Marques Cavalcante, Débora Hellen Almeida de Brito, Luana de Moraes Semião, Raquel Freitas da Silva, Pierre Basílio Almeida Fechine, Stephen George Yeates and Nágila Maria Pontes Silva Ricardo.......................................................................................................................................................... 433

The effects of porosity in friction performance of brake pad using waste tire dust Synthesis and characterization of novel polyester containing Schiff-base unit

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Ibrahim Mutlu, Ilker Sugözü and Ahmet Keskin.............................................................................................................................................. 440 Hossein Mighani, Ehsan Fathollahi and Moosa Ghaemy............................................................................................................................... 447

Rheological, mechanical and morphological properties of poly(methyl methacrylate)/poly(ethylene terephthalate) blend with dual reactive interfacial compatibilization Juciklécia da Silva Reinaldo, Maria Carolina Burgos Costa do Nascimento, Edson Noriyuki Ito and Elias Hage Junior............................ 451 Harley Moraes Martins, Juacyara Carbonelli Campos, Maria José de Oliveira Cavalcanti Guimarães and Ana Lúcia Nazareth da Silva..... 461

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Influence of lubricant oil residual fraction on recycled high density polyethylene properties and plastic packaging reverse logistics proposal High shear dispersion of tracers in polyolefins for improving their detection Valérie Massardier, Molka Louizi, Elisabeth Maris and Daniel Froelich....................................................................................................... 466

High density polyethylene and zirconium phosphate nanocomposites Adan Santos Lino, Luis Claudio Mendes, Daniela de França da Silva and Olaf Malm................................................................................. 477 Rayson de Jesus Araújo, Isaias Damasceno da Conceição, Laura Hecker de Carvalho, Tatianny Soares Alves e Renata Barbosa............. 483

Desenvolvimento e caracterização de filmes compósitos de quitosana e zeólitas com prata

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Influência da argila vermiculita brasileira na biodegradação de filmes de PHB

Patricia Hissae Yassue-Cordeiro, Cassio Henrique Zandonai, Classius Ferreira da Silva e Nádia Regina Carmargo Fernandes-Machado.... 492

Synthesis and characterization of poly(S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate) by electrochemical polymerization Ha Tran Nguyen and Le-Thu Thi Nguyen........................................................................................................................................................ 503 Naret Intawong, Sittichai Udomsom, Konnatee Sugtakchan and Watcharin Sitticharoen............................................................................... 508

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Influence of flow pattern development at die entrance and inside annular die on extrudate swell behavior of NR compound

Capa: Logo 13º Congresso Brasileiro de Polímeros.

Elaboração artística Editora Cubo.

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I N F O R M E S

Improved polymer membranes may simplify desalination, reduce cost

E N O T Í C I A S

With worries about a worldwide water crisis looming, the process of turning salty water into drinking water, long regarded as expensive, is looking up. A University of Virginia engineering professor is exploring ways to improve polymer membranes to make desalination simpler and less expensive.

Geoffrey M. Geise, an assistant professor in the Department of Chemical Engineering, believes the membranes can also be used to help create and store clean energy.

“Membranes purify water by blocking, to a large extent, salt and/or contaminants from passing through,” Geise said. “The desalination membranes that we study work by allowing water molecules to move more rapidly through the polymer compared to salt, resulting in less salt on the product side of the membrane.”

In general, salt dissociates into ions that pick up and hold onto water molecules in a way that makes a hydrated ion larger than a single water molecule. Water moves faster through the membrane compared to the salt (or ions) because it is smaller than the hydrated ions. Additionally, ions are less energetically favored in the membrane phase compared to the water phase, resulting in a situation where ions prefer to stay out of the polymer, which also results in effectively slower salt transport compared to water. By changing the polymer chemistry, Geise’s team is trying to maximize the separation efficiency based on these mechanisms.

While water and energy research are being conducted in many places around the world, Geise thinks his group has an edge.

“I believe our team at UVA brings a unique combination of experimental and computational research capabilities that will make it a leader in this area,” he said. “We can apply these same principles to other contaminants or pollutants, but a key challenge is understanding how to fine-tune material chemistry to maximize the selectivity of the polymer. That would make water purification as efficient as possible.”

A polymer is a material made up of large macromolecules that are chains of much smaller repeat units. Changing the chemical nature of the repeat units changes the properties of the overall polymer.

A polymer membrane is a film of solid polymer that is designed to generally act as a barrier.

“In our work, we deal with semi-permeable membranes that are designed to act as a barrier against transport of certain molecules while allowing transport of other molecules,” Geise said.

Geise said he and the researchers in his laboratory are working on developing a better understanding of how to minimize the amount of salt, or ions, that travel through membranes without affecting the amount of water that passes through. He said they can adjust E4

the polymer structure to control the speed of salt movement compared to the speed of water movement through the polymer.

“If salt diffuses much slower than water, then desalination occurs,” he said.

But the researchers can also restrict salt passage by blocking the salt from entering the membrane in the first place. This can be done by designing a polymer such that salt strongly prefers to remain in the salty water feed solution, as opposed to entering the membrane and moving through it to the product solution.

“If the salt never gets into the membrane, it cannot move through the membrane and desalination occurs,” Geise said.

More than half of existing desalination technologies on the market rely on reverse osmosis membranes, where water is pressurized on the feed side of the membrane, and this pressure causes water to move through the polymer. Other technologies, such as electrodialysis, require electrical energy to drive the separation.

“By making membranes that are more selective, we can reduce energy consumption by reducing pressure requirements for reverse osmosis or electrical energy requirements for electrodialysis,” Geise said.

Geise’s research not only looks at water desalination, but also explores how to generate clean energy using similar membranes. Many of the energy generation and storage applications with which Geise is working, however, are part of emerging technologies that are not widely used today.

The emerging energy generation technology “reverse electrodialysis” turns the electrodialysis process around and uses differences in salt concentrations on either side of a membrane to generate electrical power.

“In energy-storage technologies, such as flow batteries, membranes are used to separate the different compartments of the battery while still allowing ions to pass through the membrane in order to enable the battery to work,” Geise said. “In batteries and energy generation, unlike desalination, we typically want to enable ions to move through the membrane while effectively blocking transport of other components of the system.”

The worldwide need for increased access to purified water and clean energy drives his research, Geise said.

“Membranes enable many technologies in this area, and improved membranes will contribute to more efficient water purification and enhanced renewable energy resources,” he said.

Source: University of Virginia Polímeros, 25(5), 2015

March

June

Sustainable Plastics 2016 Date: 1-2 March 2016 Local: Cologne - Germany Website: http://www.amiplastics.com/events/event?Code=C706

Polymer Compounding for Innovations in Plastics Industry Date: 7–9 June 2016 Local: Newark - USA Website: http://www.compoundingconference.com/

PackPlus South 2016 Date: 2-5 March 2016 Local: Hyderabad - India Website: http://www.packplussouth.in/

COMPLAST Kenya Plast 2016 Date: 8–10 June 2016 Local: Nairobi - Kenia Website: http://www.kenyaplast.in/

Plastimagen 2016 Date: 8-11 March 2016 Local: Ciudad de México - México Website: http://www.plastimagen.com.mx/en KOPLAS 2015 Date: 10-14 March 2016 Local: Goyang - Korea Website: http://www.koplas.com/ International Plastics Showcase Date: 23-27 March 2016 Local: Florida - USA Website: http://npe.org/ Science & Engineering Of Polymeric Materials – SEPM 2016 Date: 24-27 March 2016 Local: Monastir - Tunisia Website: http://www.sctunisie.org/sepm2016/

April PlastShow 2016 Date: 12-15 April 2016 Local: São Paulo - SP Website: http://www.arandanet.com.br/eventos2016/plastshow PLASTEC New England Date: 13-14 April 2016 Local: Massachusetts - USA Website: http://plastec-new-england.plasticstoday.com/ POLLUTEC BRASIL Date: 12-14 April 2016 Local: São Paulo - SP Website: http://www.pollutec-brasil.com/

May ExpoPlast Perú 2016 Date: 3–6 May 2016 Local: Lima- Peru Website: http://www.expoplastperu.com/ Guangzhou International Wood-Plastic Composites Fair 2016 Date: 13–16 May 2016 Local: Guangzhou - China Website: http://www.musuz.com/ International Workshop on Polymer Reaction Engineering Date: 17–20 May 2016 Local: Hamburg - Germany Website: http://events.dechema.de/events/en/pre2016.html 26th Annual Conference on Recent Advances in Flame Retardancy of Polymeric Materials Date: 17–20 May 2016 Local: Connecticut - USA Website: www.bccresearch.com/conference/flame

PLASTEC East Date: 14–16 June 2016 Local: New York - USA Website: http://plastec-east.plasticstoday.com/

July 80th Prague Meeting on Macromolecules - Self-Organizaion in the World of Polymers Date: 10–14 July 2016 Local: Prague - Czech Republic Website: http://www.imc.cas.cz/sympo/80pmm/ Argenplás 2016 Date: 13–16 July 2016 Local: Buenos Aires - Argentina Website: http://www.argenplas.com.ar/

August Interplast 2016 Date: 16–19 August 2016 Local: Joinville - SC Website: www.messebrasil.com.br

September Polycondensation 2016 Date: 11–15 September 2016 Local: Moscow / St Petersburg - Russian Website: http://www.polycondensation2016.ac.ru/index.php/en/ Organic Semiconductors Date: 22–25 September 2016 Local: Dubrovnik - Croatia Website: http://www.zingconferences.com/conferences/organicsemiconductors/

October Polymeric Implants & Catheters in Medical Devices Date: 4–6 October 2016 Local: Las Vegas - USA Website: http://www.mediplastconference.com/

November Polymer Foam – 2016 Date: 8–10 November 2016 Local: Cologne - Germany Website http://www.amiplastics.com/events/event?Code=C752 Expoplast 2016 Date: November 30 - December 1, 2016 Local: Québec - Canada Website: http://expoplast.plasticstoday.com/

Polímeros, 25(5), 2015 E5

Associados da ABPol Patrocinadores

Instituições UFSCar/ Departamento de Engenharia de Materiais, SP SENAI/ Serviço Nacional de Aprendizagem Industrial Mario Amato, SP UFRN/ Universidade Federal do Rio Grande do Norte, RN

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Polímeros, 25(5), 2015

Associados da ABPol As nossas boas vindas...

Ao novo Sócio Patrocinador Afinko Soluções em Polímeros Ltda Agradecemos o valioso apoio!

Luiz Antonio Pessan Presidente

Coletivos A. Schulman Plásticos do Brasil Ltda.

Aditive Plásticos Ltda.

Avamplas – Polímeros da Amazônia Ltda.

CBE – Grupo Unigel Colorfix Itamaster Indústria de Masterbatches Ltda.

Cromex S/A Cytec Comércio de Materiais Compostos e Produtos Químicos do Brasil Ltda.

Fastplas Automotive Ltda.

Formax Quimiplan Componentes para Calçados Ltda.

Fundação CPqD - Centro de Pesquisa e Desenvolvimento em Telecomunicações Imp. e Export. de Medidores Polimate Ltda.

Innova S/A Instituto de Aeronáutica e Espaço/AQI Jaguar Ind. e Com. de Plásticos Ltda Johnson & Johnson do Brasil Ind. Com. Prod. para Saúde Ltda.

Master Polymers Ltda.

Milliken do Brasil Comércio Ltda.

MMS-SP Indústria e Comércio de Plásticos Ltda.

Nexo International Ltda.

Nitriflex S/A Ind. e Com. Politiplastic Politi-ME. Premix Brasil Resinas Ltda.

QP - Químicos e Plásticos Ltda.

Radici Plastics Ltda.

Replas Comércio de Termoplásticos Ltda.

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

Polímeros, 25(5), 2015 E7

13º Congresso Brasileiro de Polímeros – 13º CBPol Natal – RN, 18 a 22 de Outubro de 2015 Rosangela de Carvalho Balaban Coordenadora geral do 13º CBPol A 13ª edição do Congresso Brasileiro de Polímeros – CBPol foi realizada no Centro de Convenções de Natal, localizado em uma área privilegiada de Natal, na Via Costeira, dentro do Parque das Dunas, em Ponta Negra.

As atividades do congresso tiveram início já na manhã do dia 18 de outubro, quando foram oferecidos quatro minicursos aos congressistas, que tiveram duração de oito horas cada um e foram ministrados integralmente ao longo da manhã e tarde do primeiro dia do evento. A Tabela 1 reúne as informações dos minicursos.

Tabela 1. Minicursos no 13º CBPol. Título do minicurso Técnicas microscópicas de caracterização de blendas e nanocompósitos poliméricos Utilização de matérias-primas renováveis na área de polímeros Polímeros na produção de petróleo Atualizações em tecnologia da borracha

Docente Edson Noriyuki Ito – DEMat/UFRN José Manoel Marconcini CNPDIA/EMBRAPA Carlos Nagib Khalil – CENPES/ Petrobras Regina Celia Reis Nunes – IMA/ UFRJ

A solenidade de abertura do 13º CBPol (Figura 1) aconteceu oficialmente às 19h:30 do dia 18 de outubro, no auditório do Pavilhão Morton Mariz do Centro de Convenções de Natal, contando com a presença do Presidente da ABPol, Prof. Dr. Luiz Antonio Pessan; a Profa. Dra. Rosangela de Carvalho Balaban, Coordenadora geral do 13º CBPol; o Prof. Dr. José Daniel Diniz Melo, Vice-Reitor da UFRN; o Prof. Dr. Marco Aurélio De Paoli, Presidente da Comissão do Prêmio ABPol Profa. Eloisa Mano; o Prof. Dr. José Donato Ambrósio, Presidente da Comissão do Prêmio ABPol de tecnologia; o Prof. Dr. Edvani Curti Muniz, Coordenador do comitê científico do 13º CBPol e o Prof. Dr. Edson Noriyuki Ito, Vice‑coordenador do 13º CBPol. Inicialmente, houve a apresentação musical do grupo Harmonium. Em seguida, a mesa de abertura do evento foi constituída (Figura 2). Na sequência, houve o pronunciamento do Presidente da ABPol, Prof. Dr. Luiz Antonio Pessan; da Profa. Dra. Rosangela de Carvalho Balaban, Coordenadora geral do 13º CBPol e do Prof. Dr. José Daniel Diniz Melo, Vice-Reitor da UFRN. Dando continuidade à cerimônia, o Prof. Luiz Antonio Pessan convidou o Prof. Dr. Marco-Aurélio De Paoli para presidir a cerimônia de premiação da ganhadora do Prêmio ABPol Profa Eloisa Mano, a Profa. Dra. Raquel Santos Mauler (Figura 3). Em seguida, o Prof. Dr. José Donato Ambrósio foi convidado a presidir a cerimônia de premiação do ganhador do Prêmio ABPol de Tecnologia, o Dr. Dellyo Ricardo Santos Alvares (Figura 4). Foram também homenageados com placa pela contribuição à ABPol a Coordenadora Geral do evento (Figura 5) e o Vice-coordenador (Figura 6). Ao final, um mini jantar foi oferecido no foyer do Centro de Convenções (Figura 7).

Figura 1. Solenidade de abertura do 13º CBPol.

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Polímeros , 25(5), 2015

13º Congresso Brasileiro de Polímeros – 13º CBPol Natal – RN, 18 a 22 de Outubro de 2015

Figura 2. Formação da mesa diretora. Da esquerda para a direita: Prof. Dr. Edvani Curti - Coordenador do comitê científico do 13º CBPol; Prof. Dr. José Donato Ambrósio, Presidente da Comissão do Prêmio ABPol de Tecnologia; Prof. Dr. José Daniel Diniz Melo, Vice-Reitor da UFRN; Prof. Dr. Luiz Antonio Pessan, Presidente da ABPol; Prof. Dr. Marco Aurélio De Paoli, Presidente da comissão do prêmio ABPol Profa. Eloisa Mano; Profa. Dra. Rosangela de Carvalho Balaban, Coordenadora geral do 13º CBPol; Prof. Dr. Edson Noriyuki Ito, Vice-coordenador do 13º CBPol.

Figura 3. Entrega do Prêmio ABPol Profa. Eloisa Mano à Profa. Raquel Santos Mauler.

Figura 4. Entrega do prêmio ABPol de Tecnologia ao Dr. Dellyo Ricardo Santos Alvares.

Nesta edição do CBPol, foram apresentadas 9 conferências plenárias, ministradas por renomados pesquisadores brasileiros e estrangeiros (Tabela 2). Dos 1.038 trabalhos recebidos, 1.004 foram aprovados. Desse total, 30 foram selecionados para apresentação por experientes pesquisadores, com duração de 30 min. Os demais trabalhos foram indicados para apresentação em sessões orais durante 20 min ou em sessões de pôsteres com duração de 90 min, de acordo com a avaliação da comissão científica, coordenada pelo Prof. Dr. Edvani Curti Muniz e constituída por 18 coordenadores de área e 243 avaliadores. Doze empresas estiveram presentes ao longo de todo o evento apresentando em seus stands os novos produtos/equipamentos e ministrando palestras técnicas.

Em mesa redonda, coordenada pelo Prof. Marco-Aurélio De Paoli (IQ-UNICAMP), foi discutido o tema “Construção e disseminação de ética em pesquisa, desenvolvimento e inovação”, com a participação dos convidados Prof. Valdir Soldi Polímeros, 25(5), 2015

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Balaban, R. C.

Figura 5. Entrega de homenagem à Coordenadora do evento, Profa. Rosangela de Carvalho Balaban, pela contribuição à ABPol.

Figura 6. Entrega de homenagem ao Vice-coordenador do evento, Prof. Edson Noriyuki Ito, pela contribuição à ABPol.

Figura 7. Mini jantar após solenidade de abertura do 13º CBPol.

(IQ-UFSC), Prof. Carlos Arthur Ferreira (DEMAT-UFRGS) e o Prof. Luis Claudio Mendes (IMA-UFRJ). O assunto despertou bastante interesse dos congressistas, que participaram fazendo perguntas e emitindo opiniões.

O jantar de confraternização aconteceu no Imirá Plaza Hotel, localizado na Via Costeira, onde estiveram presentes 400 congressistas. Foi mais um momento de grande descontração e alegria, quando os participantes puderam usufruir da brisa do mar de Ponta Negra e conversar animadamente com os amigos reencontrados.

A programação do 13º CBPol procurou intensificar a discussão de temas de grande importância atual na área de materiais poliméricos, tais como: Aditivos e formulação; Biopolímeros e polímeros biodegradáveis; Blendas poliméricas; Borrachas e elastômeros; Compósitos e nanocompósitos poliméricos; Correlação estrutura e propriedades nos polímeros; Degradação e estabilização de polímeros; Membranas e barreiras poliméricas; Mercado e desenvolvimento tecnológico; Modelagem e simulação no processamento; Modificação de polímeros; Polímeros para a indústria do petróleo e gás natural; Polímeros para a indústria biomédica e farmacêutica; Polímeros para eletroeletrônica, semicondutores, aplicações magnéticas; Reologia E10

Polímeros , 25(5), 2015

13º Congresso Brasileiro de Polímeros – 13º CBPol Natal – RN, 18 a 22 de Outubro de 2015 Tabela 2. Conferências plenárias no 13º CBPol. Título da conferência

Conferencista Profa. Raquel Santos Mauler

Nanocompósito polimérico: Uma visão química Tecnologia - Viagem muito além do Horizonte Energia - Enorme desafio e a força motriz no século XXI Polióis vegetais: matéria-prima versátil para preparação de polímeros

Instituto de Química, Universidade Federal do Rio Grande do Sul (UFRGS) Dr. Dellyo Ricardo Santos Alvares CENPES/Petrobras Prof. Cesar Liberato Petzhold Instituto de Química, Universidade Federal do Rio Grande do Sul (UFRGS)

Hidrogéis à base de polímeros naturais em aplicações biomédicas

Prof. João F. Mano Departamento de Engenharia de Polímeros, Escola de Engenharia da Universidade do Minho, Guimarães, Portugal

Análise do comportamento à fluência de polímeros e compósitos poliméricos submetidos a envelhecimento por ação de fluidos

Prof. José Roberto Moraes d´Almeida Departamento de Engenharia de Materiais, Pontifícia Universidade Católica do Rio de Janeiro

Uso de recursos naturais no desenvolvimento de compósitos poliméricos: possibilidades e limitações Macromolecular 1D crystalline nano-arrays for hierarchical structures and functional material Nanostructured biomaterials from polysaccharides: applications and opportunities

Profa. Laura Hecker de Carvalho Departamento de Engenharia de Materiais, Universidade Federal de Campina Grande Prof. You-Lo Hsieh College of Agricultural and Environmental Sciences, University of California, Davis, USA Prof. Matt Kipper Department of Chemical and Biological Engineering, Colorado State University, Fort Collins, USA Prof. Jinwen Zhang

New perspectives of vegetable oils as feedstocks for high performance polymers

School of Mechanical and Materials Engineering & Composite Materials & Engineering Center, Washington State University, Pullman, USA

Figura 8. Número de trabalhos submetidos nas diferentes áreas dos materiais poliméricos: (1) Aditivos e formulação; (2) Biopolímeros e polímeros biodegradáveis; (3) Blendas poliméricas; (4) Borrachas e elastômeros; (5) Compósitos e nanocompósitos poliméricos; (6) Correlação estrutura e propriedades nos polímeros; (7) Degradação e estabilização de polímeros; (8) Membranas e barreiras poliméricas; (9) Mercado e desenvolvimento tecnológico; (10) Modelagem e simulação no processamento; (11) Modificação de polímeros; (12) Polímeros para a indústria do petróleo e gás natural; (13) Polímeros para a indústria biomédica e farmacêutica; (14) Polímeros para eletroeletrônica, semicondutores, aplicações magnéticas; (15) Reologia e processamento de polímeros; (16) Síntese de polímeros; Reciclagem de polímeros; (17) Técnicas experimentais convencionais e avançadas de caracterização e (18) Outras áreas.

Polímeros, 25(5), 2015

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Balaban, R. C.

Figura 9. Número de trabalhos apresentados no 13º CBPol oriundos das diferentes regiões federativas do Brasil.

Tabela 3. Estudantes premiados no 13º CBPol. Vanessa Silva de Lima (iniciação científica) Título do trabalho: Modificação de goma de cajueiro com acrilamida assistida por ultrassom e uso desta no tratamento de águas Instituição: UFRGS Prêmios Wiley

Coautores: Jalma Maria Klein, Rosmary Nichele Brandalise, Maria Madalena de Camargo Forte Alex Otávio Sanches (doutorado) Título do trabalho: Efeito sinergético em compósitos trifásicos de poliuretano/PZT/negro de fumo Instituição: UNESP Coautores: Darcy Hiroe Fujii Kanda, Luiz Francisco Malmonge, Michael Jones Silva, José Antonio Malmonge Raiza Freitas de Oliveira (iniciação científica) Título do trabalho: Análise da degradação de polipropileno sob múltiplas extrusões Instituição: UFRN Coautores: Erik dos Santos Silva, Adriano Lincoln Albuquerque Mattos, José Kaio Max Alves do Rêgo, José Heriberto Oliveira Nascimento, Edson Noriyuki Ito Bruno Felipe Bergel (mestrado)

Prêmios ABPol

Título do trabalho: Influência da estocagem em diferentes condições de umidade nas propriedades físicas e mecânicas de embalagens expandidas biodegradáveis de amido de: batata, mandioca e milho Instituição: UFRGS Coautores: Mariana Oliveira Engel, Ruth Marlene Campomanes Santana Marcelo Ferreira Leão de Oliveira (doutorado) Título do trabalho: Avaliação das propriedades térmicas dos nanocompósitos de ecobras e vermiculita modificada com sal alquil fosfonio Instituição: UERJ Coautores: Fernanda Cristina Fernandes Braga, Marcia Gomes Oliveira, Marcia Christina Amorim Moreira Leite

e processamento de polímeros; Síntese de polímeros; Reciclagem de polímeros; Técnicas experimentais convencionais e avançadas de caracterização. A Figura 8 mostra o número de trabalhos submetidos ao 13º CBPol nessas diferentes áreas, indicando mais uma vez a predominância das áreas “Compósitos e nanocompósitos poliméricos” e “Biopolímeros e polímeros biodegradáveis”, o que pode ser interpretado como reflexo da busca por materiais de propriedades melhoradas e versáteis, assim como a grande preocupação com a utilização de materiais de baixo impacto ambiental.

O número de trabalhos recebidos por cada região federativa é mostrado na Figura 9. Os dados indicam um significativo crescimento da participação da região nordeste e que ainda há poucos trabalhos desenvolvidos na área de polímeros na região norte e centro-oeste. Esses indicadores podem ser úteis para as regionais da ABPol constituídas recentemente, no sentido de promoverem a aproximação dos colegas pesquisadores que se encontram “ilhados” nas regiões norte e centro-oeste.

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Polímeros , 25(5), 2015

13º Congresso Brasileiro de Polímeros – 13º CBPol Natal – RN, 18 a 22 de Outubro de 2015 Tabela 4. Estudantes agraciados com menção honrosa.

Gabriel Abelha Carrijo Gonçalves (iniciação científica) Título do trabalho: O efeito do tratamento alcalino nas propriedades mecânicas da fibra de coco verde Instituição: UESC Coautor: Celso Carlino Maria Fornari Junior Querem Apuque Felix de Andrade (mestrado) Título do trabalho: Efeito de tratamento térmico sobe o índice de sensibilidade ao entalhe (ISE) da blenda PMMA/PETrec Instituição: UFRN Coautores: Wanderson Santana da Silva, Edson Noriyuki Ito Ricardy L. P. Mesquita (mestrado) Título do trabalho: Síntese de nanopartículas de prata por ultrassom utilizando galactomanana de Fava Danta Instituição: UFC Menções honrosas

Coautores: Judith Pessoa de Andrade Feitosa, Pablyana Rodrigues da Cunha Vinicius de Macedo (mestrado) Título do trabalho: Análise morfológica de espumas flexíveis de poliuretano com adição de celulose de pinus Instituição: UCS Coautores: Matheus Vinicius Gregory Zimmermann, Lisete Cristine Scienza, Ademir José Zattera Ana Paula Bispo Gonçalves (doutorado) Título do trabalho: Caracterização térmica e estrutural de compósitos de PET reciclado/PEAD reforçados com fibras de bananeira roxa Instituição: UFBA Coautores: Danilo Hansen Guimarães, Cleidiene Souza Miranda, Nadia Mamede José Giovani Pavoski (doutorado) Título do trabalho: Estudo da utilização de óxido e óxido reduzido de grafite como suporte na polimerização de etileno Instituição: UFRGS Coautores: Thuany Maraschin, Marcéo Auler Milani, Raul Quijada, Nara Regina de Souza Basso, Griselda Barrera Galland

Aos melhores trabalhos apresentados por alunos de graduação, mestrado e doutorado, foram concedidos prêmios oferecidos pela WILEY e ABPol e menções honrosas, tomando por base a sua contribuição técnico-científica, a qualidade da apresentação e o domínio do conteúdo demonstrado pelo aluno. Nesta edição do CBPol, a avaliação dos trabalhos visando a premiação foi iniciada já na fase de submissão, quando foi solicitado aos autores que indicassem em seu resumo a categoria de cada aluno (IC, M, D) e quem seria o apresentador. Com base nessas informações e pela qualidade do resumo, vários trabalhos foram sinalizados pelos avaliadores. Entretanto, nova análise foi feita durante a apresentação pelo aluno no evento, considerando a qualidade da apresentação e o domínio do conteúdo demonstrado. As Tabelas 3 e 4 apresentam os alunos agraciados com os prêmios Wiley e ABPol e os que receberam menção honrosa, respectivamente.

No encerramento do evento, após a divulgação dos estudantes premiados, o presidente da ABPol, Prof. Luiz A. Pessan, deu posse à nova diretoria da ABPol para o biênio 2015-2017 e fez um breve relato dos resultados do 13º CBPol, constatando com grande satisfação o sucesso do congresso.

O sucesso na realização de um evento do porte do CBPol só é possível pelo trabalho voluntário intenso e dedicação de muitas pessoas. Sem a colaboração de todos os associados que participaram das diversas comissões, desde a organização até a premiação dos melhores trabalhos, não seria possível alcançarmos o sucesso que felizmente alcançamos. Dessa forma, agradecemos imensamente todo o trabalho realizado por essas pessoas. Agradecemos também a presença dos expositores e patrocinadores (Altmann, Nova Analítica, Anton Paar, AX Plásticos, Bruker, dp Union, Flowscience, Hitachi, Instron, Netzsch, Perkin Elmer, Polimate, ReoTerm, TA Instruments, Waters, Wiley) que ajudaram a abrilhantar ainda mais o evento, assim como o apoio financeiro recebido da CAPES, CNPq e FAPESP e o apoio institucional da UFRN. A todos, o nosso muito obrigada. Tornamos público também os nossos sinceros agradecimentos à equipe que atua na secretaria da ABPol (Marcelo, Ana e Charles) e que trabalhou intensamente nos últimos meses para garantir que o melhor fosse apresentado aos colegas congressistas. Por último, agradecemos à diretoria da ABPol pela confiança que nos foi depositada para a realização de um evento de tamanha relevância técnico-científica para o país.

Obrigada a todos que partilharam conosco o 13º CBPol e até breve, no 14º CBPol, em São Paulo!

Polímeros, 25(5), 2015

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http://dx.doi.org/10.1590/0104-1428.1804

Influence of the polymeric coating thickness on the electrochemical performance of Carbon Fiber/PAni composites Carla Polo Fonseca1, Dalva Alves de Lima Almeida1*, Mayara Camila Duarte de Oliveira1, Maurício Ribeiro Baldan1 and Neidenei Gomes Ferreira1 Laboratório Associado de Sensores e Materiais, Instituto Nacional de Pesquisas Espaciais - INPE, São José dos Campos, SP, Brazil

1

*dalva.dri@gmail.com

Abstract Carbon fiber/polyaniline composites (CF/PAni) were synthesized at three different deposition time of 30, 60 and 90 min by oxidative polymerization. The composite materials were morphologically and physically characterized by scanning electron microscopy and by Raman spectroscopy, respectively. Their electrochemical responses were analyzed by cyclic voltammetry, by galvanostatic test, and by electrochemical impedance spectroscopy. The influence of the PAni layer thickness deposited on carbon fibers for the composite formation as well as for their electrochemical properties was discussed. The CF/PAni-30 showed a nanometric thickness with more homogeneous morphology compared to those formed in deposition times of 60 and 90 min. It also showed, from the electrochemical impedance spectroscopy measurements, the lowest charge transfer resistance value associated to the its highest value for the double-layer capacitance of 180 Fg-1 making it a very strong candidate as a supercapacitor electrode.

Keywords: carbon fiber, polyaniline, composite, supercapacitors.

1. Introduction The development of new materials has been required concerning the application on modern and alternative devices associated to the world energy problem. This problem is not only related to energy shortages, but also to energy sources to minimize the environmental impact[1]. In this context, supercapacitors have played an outstanding role in research energy groups, with new promising approaches to produce renewable energy sources besides reducing environmental problems. Supercapacitors and batteries are considered as energy storage devices of equal significance, due to their complementary modes of operation. However, there are distinctions between them with respect to charge storage mechanisms. In the case of supercapacitors there are two possible mechanisms for energy storage: (1) firstly, by the accumulation of charge on the surfaces of the active material, where this process occurs by the electrostatic charge accommodation at the electrical double-layer, through the adsorption of the electrolyte ions on the surfaces of electrically stimulated carbon-based materials; (2) secondly, by the fast and reversible redox or Faradaic reactions during the oxidation/reduction process, where the devices are called as pseudocapacitors, whose electrodes are made up by transition metal-oxides, hydroxides, and/or conducting polymers oxides or conducting polymers,[2-6].

Recently, supercapacitors have played an increasingly important role in applications such as the auxiliary power source in combination with battery electric and hybrid vehicles[6], because they exhibit power densities which are about ten times higher than those of batteries, showing excellent cycling stability even after hundreds of thousands of charge/discharge cycles. Other applications which include their use are: short-time power source for mobile electronic

Polímeros, 25(5), 425-432, 2015

devices, backup power sources for computer memory, cell phones[7], laser pulse, etc.,[2,8] which are highly time dependent[3].

Various materials have been studied for applications in supercapacitor such as: (i) carbon; (ii) transition metal oxides, ruthenium and iridium; and (iii) conducting polymers. Among them, conducting polymers are one of the most studied due to their characteristics, such as high electrical conductivity, electrochemical reversibility, low weight, and stability in the air[2-7]. Particularly, cconducting polymers such as polyaniline (PAni)[9,10], polypyrrole[11,12], poly(ethylenedioxythiophene) polythiophene[4] have appeared as the most cited in literature.

In this context, PAni is a very promising candidate for practical applications due to its reversible control of electrical properties by both charge–transfer doping and protonation, good processability, environmental stability, and low cost.

A major inconvenience in the application of conducting polymers as electrodes in power devices is related to their low stability during cycling, due to the volume changes of the films with the doping/undoping process. This process causes dilatation/reduction on the film volume, breaking its morphology, and, consequently, harming its conductive properties. This stress, which happens during the charge/discharge process of the conducting polymer, occurs mainly when it is polymerized as random form, i.e. with a large amount of crosslinking. To reduce this effect, many authors have used a matrix that serves as a template during the polymer growth[13,14]. In this case, the carbonaceous materials have proved to be a great material to orient the conducting polymer polymerization, such as carbon nanotube, carbon fibers and others.

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

Fonseca, C. P., Almeida, D. A. L., Oliveira, M. C. D., Baldan, M. R. & Ferreira, N. G. The synthesis of conducting polymer on carbonaceous material has been cited in the literature by reporting the improvement of its electrical conductivity as well as its mechanical properties in comparison to those of the original polymer matrix[15-21]. Recently, the use of porous carbon, carbon nanotubes, or even graphene as a nano-architectural template for synthesis of nano-sized PAni has been reported to enable exceptional conductive properties and to mitigate the cycle degradation issues caused by PAni mechanical problems[14,21]. Taking into consideration the above revision, this work presents the PAni deposition on CF through a chemical polymerization at different deposition times of 30, 60 and 90 min leading to different mass of the conducting polymers on CF matrix. The CF/ PAni composites were morphologically and physically characterized by scanning electron microscopy and the Raman spectroscopy, respectively.

Their electrochemical responses were analyzed by cyclic voltammetry (CV), galvanostatic test, and electrochemical impedance spectroscopy (EIS) measurements.

Taking into account the techniques mentioned above, the EIS is considered a major one because it provides important information about the electrode interface reactions.

The impedance response of electrodes rarely shows the ideal response except for single electrochemical reactions.

In the case of materials with heterogeneous surfaces such as composites, the CPE defines inhomogeneity of the surface in the electrochemical EIS experiments and it is reasonable to expect that a better fit for real system is obtained by using CPE[22,23]. The impedance of the constant phase elements is a power-law dependent interfacial capacity defined in Equation 1 as: ZCPE = 1

Q ( jω)

n

(1)

where Q is the frequency independent constant relating to the surface electro active properties, ω is the radial frequency, the exponent n arises from the slope and its value may change in the range -1≤ n ≤ 1, which it is estimated from the slope plot of log Z vs. log ω . When n = 0, the CPE behaves as a pure resistor. When n=1 CPE behaves as a pure capacitor and Q has units of a capacitance, and represents the capacity of the interface. When n=-1 CPE behaves as an inductor; while n=0.5 corresponds to Warburg impedance (Zw), which is associated with the domain of the mass transport control arising from the ions diffusion from the electrode/electrolyte interface. Generally, the CPE has been associated to several factors, such as the morphology of the electrode, the presence of the porous, the roughness of polycrystalline material, and the distribution of the relaxation time due to the heterogeneities existing at the electrode/electrolyte interface[24]. From the analysis of these elements, it is possible to investigate the electrochemical behaviour of the electrodes and their applicability.

2. Experimental The CFs were cut in the size of 2×1 cm and weighted. Six samples were prepared for each synthesis, simultaneously.

The fibers were fixed at platinum wire and placed in a solution containing purified aniline (Aldrich) by simple 426

distillation (three times) (12.6 mmol L–1) and 1.0 mol L–1 HCl, 3.0 mol L–1 NaCl and cooled to –10 °C using an ice bath.

Another solution containing 1.0 mol L–1 HCl, 3.0 mol L–1 NaCl and 0.03 mol L–1 ammonium persulfate, (NH4)2S2O8, was added to the aniline solution at different deposition times of the 30, 60 and 90 min at –10 °C with vigorous stirring.

The CF/PAni composites were named as CF/PAni-30, CF/PAni-60, and CF/PAni-90 for samples with deposition times of 30, 60, and 90 min, respectively. The composites were washed successively with 1.0 mol L–1 HCl, obtaining the conduction sate of the PAni (emeraldine), and deionized water and ethanol several times until the filtrate became colorless. All samples were dried under vacuum for 24 h.

After completely dried, the samples were weighed using an analytical balance.

The PAni powder was also synthesized by chemical polymerization using the same solutions of the composites to produce the PAni electrode. The oxidizing agent solution was added with vigorous stirring for 90 min. The precipitate was collected by filtration, and then washed with 1 mol L–1 HCl, obtaining the conducting state of the PAni (emeraldine).

The PAni electrode was prepared by mixing the PAni powder (90% wt.) with poly vinylidene fluoride (PVDF) (10% wt.

MW = 105 g mol–1) in N.N.-dimethyl acetamide. The films were obtained by painting the platinum electrode. Prior to the use, the electrodes were dried at room temperature for 72 h.

The morphological characterization was carried out by scanning electron microscopy (SEM) JEOL model JSM‑5900LV. The Raman spectra were recorded using a micro - Raman scattering spectroscopy (Renishaw microscope system 2000) in backscattering configuration at room temperature employing 514.5 nm Ar ion laser.

The composite electrodes were characterized by cyclic voltammetry, by chronopotenciometry, and by electrochemical impedance spectroscopy experiments in the 1.0 mol L−1 H2SO4 solution. The cyclic voltammograms were acquired in a potential scan of the –0.1 ≤ E ≤ 0.78 V vs. Ag/AgCl with several scan rates (1, 5, 10, 25, 50, 75 and 100mV/s).

The charge-discharge curves were obtained at three different current densities (±0.50, ±0.75 and 1 ± 1mA cm–2) within the potential window –0.1V-0.75V vs Ag/AgCl. All the impedance spectra were recorded at an open circuit potential.

The impedance spectra were recorded by applying the ac amplitude of 10 mV and the data were collected in the frequency range from 105 to 10–3 Hz. The impedance data were analyzed using the Boukamp’s fitting program[23,24].

All the electrochemical data were obtained with an AUTOLAB – PGSTAT30 potentiostat system.

3. Results and Discussion The SEM images of CF, of PAni powder, and of CF/PAni composites are shown in Figure 1. The average diameter of the CF (Figure 1a) was estimated at about 10 µm and presented a smooth surface, free of cracking.

Moreover, the PAni morphology was composed of plates and clusters with foam aspect, Figure 1b. All the composites prepared by chemical polymerization presented a similar and well‑dispersed carbon fiber uniformly enwrapped by the PAni, Figure 1c-h.

Polímeros, 25(5), 425-432, 2015

Influence of the polymeric coating thickness on the electrochemical performance of Carbon Fiber/PAni composites

Figure 1. SEM images of (a) CF, (b) PAni powder, (c,d) CF/PAni - 30, (e,f) CF/PAni - 60, and (g,h) CF/PAni - 90.

PolĂ­meros, 25(5), 425-432, 2015

427

Fonseca, C. P., Almeida, D. A. L., Oliveira, M. C. D., Baldan, M. R. & Ferreira, N. G. This complete coverage by the PAni on the CF is related to the Van der Waals interaction between CFs and the PAni by effective interaction between the π- bonds of the aromatic ring of PAni and CF. This interaction facilitates the growth of a homogeneous conductive polymer on the carbon fiber, due to the electronic conductivity increase provided by CF. The PAni thickness increase on the carbon fiber was observed as the deposition time increased. For CF/PAni-30, a homogeneous coating of the nanometer thickness (84 nm) appeared covering the entire CF surface. Nonetheless, for composites deposited for 60 and 90 min, the presence of agglomerates among the carbon fibers also occurred.

The thickness values of CF/PAni-60 and CF/PAni- 90 were around 0.28 and 1.32 µm, respectively. This is an indication of their nanometric characteristics loss.

CF/PAni composites, carbon fiber, and PAni powder were also characterized by Raman spectroscopy as shown in Figure 2. Raman spectroscopy provides an extremely useful tool to characterize PAni. With this technique it is possible to obtain the structural information, the oxidation state, the doping, the crosslinking as well as the chain conformation of the polymeric compounds[22,23,25]. Figure 2 shows the Raman features for: (a) CF,(b) PAni powder, (c), CF/PAni –30, (d) CF/PAni –60, and (e) CF/PAni-90.

The spectrum (a) refers to CF electrode with a profile graphite-like material[26,27], showing two bands: D (~1352 cm−1), G (~1582 cm−1). Nonetheless, the spectrum (a) is compatible with PAN-based CF, i.e., it is the structure of the carbon fibers obtained from polyacrylonitrile precursor graphitized at temperatures around 1000 °C[27-29], as expected. For all composites analyzed, the spectra are dominated by the PAni spectrum and exhibit characteristic bands of conducting species, mainly CF/PAni-30. The C-N+ band, which is characteristic of emeraldine salt was associated to the splitting in 1320-1370 cm–1[30]. Nascimento et al. have associated the bands around 1324-1375 cm–1 to C-N+ of polarons having different conjugation lengths[31]. In general, the CF/PAni composite spectra were dominated by the PAni behavior

indicating a good coating of the conducting polymer on the carbon fibers for the three kinds of composites studied.

Considering the spectra region from 1100 to 1210 cm–1, all spectra show the band at 1160 cm-1 that correspond to the C-H bending. This band is commonly characterized by the high degree of the PAni oxidation. In addition, for CF/PAni-30 composite, the spectrum is quite different and presents the bands at 1630 cm-1 and at 575 cm–1, which may be associated with the deformation of cross-linkages with a phenazine configuration. These bands were not verified for CF/PAni-60 and CF/PAni-90. Moreover, for these composites, the presence of a strong band at 1480 cm–1 is observed and associated to the C=N stretching in quinoid segments.

Also, the peak at 1220 cm–1 is ascribed to C-N stretching in the benzoid segments. In the range from 1500 cm–1 to 1650 cm–1 different C-C stretching bands may be assigned to the quinone, phenyl and to semi-quinone structure[32,33].

The electrochemical performance of CF, PAni powder, and CF/PAni composites was analyzed by cyclic voltammetry.

Figure 3 shows the cyclic voltamograms of all materials, normalized by the mass of each sample. The cycle performance was not investigated over 0.78 V vs. Ag/AgCl to avoid the PAni degradation. The results show that the CF has a purely capacitive profile assigned to its electric double layer formation (Figure 3 inset). At lower potentials, the reduction process of hydrogen can be observed.

The cyclic voltammetry of the PAni powder shows a poorly defined single redox peak, which has been assigned to the conversion of leucoemeraldine/emeraldine states[32].

The emeraldine/pernigraniline transition was not observed in the cyclic voltammogram of Figure 3. Probably, during the PAni electrode formation, the agglomerates were not totally separated making the visualization of other redox couples difficult. Besides, the cyclic voltamograms were performed in the range of potential below the emeraldine/ pernigraniline transition to prevent the PAni overoxidation.

For CF/PAni –30, cyclic voltammograms showed peaks attributed to different oxidation states of PAni. The redox peaks, at a and at a’ are assigned to the conversion of leucoemeraldine/emeraldine states at 0.27 and at 0.07V vs. Ag/AgCl, and the beginning of the b and b’ peaks are related to the conversion between esmeraldine/pernigraniline.

Figure 2. Raman spectra of (a) CF, (b) PAni powder, (c) CF/PAni - 30, (d) CF/PAni - 60, and (e) CF/PAni - 90.

Figure 3. Cyclic voltamograms normalized by the mass of CF, PAni powder, CF/PAni-30, CF/PAni-60, and CF/PAni-90 composites.

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Polímeros, 25(5), 425-432, 2015

Influence of the polymeric coating thickness on the electrochemical performance of Carbon Fiber/PAni composites Intermediate peaks were noticed in the region of 0.4 and 0.6 V vs. Ag/AgCl (c / c` and d / d ‘) which have been attributed to the benzoquinone / hydroquinone (BQ/HQ) pair and to the redox reaction of ortho-aminophenol (PAP) and benzoquinoline (IQ), respectively[34]. These processes were related to the PAni degradation.

The PAni redox pairs were not observed for the voltammograms of CF/PAni-60 and CF/PAni-90 due to the presence of the capacitive charging development.

This process is characterized by the rectangular format of the voltammograms[24]. This fact can be attributed to the increase of the deposition time that causes a disorder in the polymer chains during the PAni film growth and may prevent the faradic processes. CF/PAni-30 composite has the lowest amount of conductive polymer mass, and it presented the highest charge storage capacity. This fact could be related to the close contact of the PAni layer with the carbon fiber facilitating the faradic transport and the capacitive charge across the composite bulk.

The cyclic voltammograms for CF/PAni-30 and for CF/PAni-60 composites at different scan rates are shown in Figures 4 and 5, respectively. For both electrodes an increase in the peak current (ip) as well as a peak current shift as a function of the scan rate increase were observed. Nonetheless, it is important to point out that for CF/PAni-60 at scan rates higher than 75 mV.s–1 the peak currents disappeared and the redox process was not evident. Similar behavior was observed for CF/PAni –90 composite in the whole range of scan rate studied (not shown) as a reversibility loss.

Firstly, the electrochemical reversibility was evaluated by the ratio between the anodic and the cathodic charges (qa/qc). For a reversible system, the qa/qc must be equal to 1 and it is independent of the scan rate. The CF/PAni-30 composite showed an excellent electrochemical reversibility presenting a qa/qc ratio close to 1 even at high scan ratios.

The qa/qc ratio showed a decrease from 1 to 0.85 at 75 mVs–1 for the CF/PAni-60 composite. In addition, for CF/PAni-30 and CF/PAni-60- composites the anodic peak shifted to a more negative potential while the cathodic peak shifted to a more positive potential, as expected for quasi‑reversible systems[35]. However, it was observed that for the same scan rate ΔEp is larger for CF/PAni-60 than that for CF/PAni‑30.

This means that not all ions, which were inserted in the CF/PAni –60 at electroactive sites during the charge process, came out for the discharge process leading to a slower kinetics for this electrode.

The deformations observed in the voltammograms, mainly for scan rate higher than 50 mVs–1, can be associated to the electroactivity of these materials and, therefore, to the conformation of polymer chains during the polymerization process. Particularly, for CF/PAni-30 composite, its lowest voltammogram deformation is associated to its strong electroactivity. This behavior may be explained taking into account the high uniformity of its polymeric layer (Figure 1c) also associated to its high conductivity confirmed by the Raman features that are very similar to those of the PAni powder (Figure 2b).

The electrochemical characteristics of these materials, taking into account their electrode/electrolyte interfaces, were also investigated by electrochemical impedance spectroscopy Polímeros, 25(5), 425-432, 2015

(EIS) at an open circuit potential. The EIS of CF, PAni, and CF/PAni composites were obtained in the range from 10–3 to 105 Hz. The spectra presented in Figure 6 show the electrolytic properties at high frequency region while at mid

Figure 4. Cyclic voltammograms for CF/PAni-30 composite at different scan rates.

Figure 5. Cyclic voltammograms for CF/PAni-60 composite at different scan rates.

Figure 6. EIS measurements of CF, PAni, and CF/PAni composites.

429

Fonseca, C. P., Almeida, D. A. L., Oliveira, M. C. D., Baldan, M. R. & Ferreira, N. G. frequency region the impedance response is associated with the electrode/electrolyte interface. The semicircle intersections with the real axis (Z’) at high and at mid frequencies allow finding out the electrolyte and charge transfer resistances (Re and Rct), respectively.

is formed between the CF and PAni for deposition time of 30 min. Also, we can see that the double layer capacitance values for all composites were much higher than those obtained by their pure components, showing the synergism of this synthesis[37].

In the low frequency regime, two different regions may occur. In the first region, the impedance response, ideally at 45° straight line (Warburg impedance), represents the mass transfer parameters of the electrochemical doping process. In this region, the impedance is controlled by the counter-ions diffusion inside the composite electrode[36].

In the second region, the mass transport is limited, and the charge accumulation is favored indicating a pure capacitor behavior. In this case, the diffusion layer involves the entire electrode thickness. Particularly, the response (ideally at 90° straight line) shows that CF/PAni composites resemble a pure capacitor.

A complementary analysis of the superior response of CF/PAni-30 electrode can also be observed in Figure 9 by the evaluated diffusion coefficient for PAni and for CF/PAni composite electrodes, from EIS measurements. The diffusion coefficient drastically increased when PAni is in the composite form also varying as a function of the polymer thickness with its maximum for the CF/PAni-30 electrode.

In order to analyse EIS results, the data were fitted using the equivalent circuit shown in Figure 7, where RE and RCT are the electrolyte and the charge-transfer resistances.

The CPE1, the CPE2, and the CPE3 are the constant phase elements[36]. The CPE was introduced as a replacement for the capacity in EIS measurements and are commonly used.

The CF/PAni composites showed good symmetry between the charge/discharge processes. For the electrodes of pure components, i.e. CF and PAni, we can observe that the time of the charge/discharge process is much shorter than those observed for the composite electrodes.

The specific capacitance of CF, PAni, and CF/PAni composites were obtained using galvanostatic charging– discharging cycling of the electrodes for three different current densities. These results are shown in Figure 10 for current density of ±1.0 mA.

The fitting results based on the proposed equivalent circuit of Rct and Cdl values are shown in Figure 8. We can clearly observe that the PAni insertion on the CF drastically decreased the Rct value getting too close to the Rct value of PAni powder. The Rct value for CF/PAni-30 was lower than those for CF/PAni-60 and CF/PAni-90 composites. This result also supports the hypothesis that a more cohesive interface

Figure 7. Equivalent circuit used to fit the EIS data for CF, PAni powder, and CF/PAni composites.

Figure 8. Variation of the specific capacitance according chargetransfer resistance.

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Figure 9. Diffusion coefficient for PAni and for CF/PAni composite electrodes.

Figure 10. Charge and discharge curves of CF, PAni powder, CF/PAni - 30, CF/PAni - 60, and CF/PAni - 90.

Polímeros, 25(5), 425-432, 2015

Influence of the polymeric coating thickness on the electrochemical performance of Carbon Fiber/PAni composites case of the CF/PAni-30 composite, promoting a decrease in the charge transfer resistance, making its charge/discharge process faster and more effective.

5. Acknowledgements This work was supported by the CNPq proc number 150663/2010-2 and FAPESP proc number 2009/17584-0.

6. References

Figure 11. Specific Capacitance of of CF, PAni powder, CF/PAni - 30, CF/PAni - 60, and CF/PAni – 90 obtained from charge and discharge curves.

The specific capacitance values (Figure 11) can be calculated according to the following relationship in Equation 2: Csp = it

∆Vm

(2)

where Csp is the specific capacitance [Fg–1], I is the charge/ discharge current, t is the charge/discharge time, ΔV is the voltage difference between the upper and the lower potential limits, and m is the mass of active material. The CF and the PAni electrodes showed lower specific capacitance values than those for the composite electrodes (CspCF = 4.77 and CspPAni = 20.14 Fg–1). In addition, as observed in the cyclic voltammetry, the highest specific capacitance was obtained for CF/PAni- 30 composite, (∼Csp=180 Fg–1), making it a very strong candidate as supercapacitor electrode.

4. Conclusion The CF/PAni composites from chemical synthesis process, at different deposition times, were obtained and characterized with success. From SEM analyses, CF/PAni-60 and CF/PAni –90 composites showed a micrometric thickness with polymeric clusters among the fibers. However, for CF/PAni-30 composite a nanometric thickness with a homogeneous morphology was obtained. The Raman spectra showed that the CF/PAni-30 composite seems to be more conductive than the other composites due to its more similar features to that for PAni itself. This fact was evidenced by the radical cation band, quite pronounced in this material. From cyclic voltammetry, it was possible to verify the highest electroactivity of the CF/PAni-30, due to its best electrochemical reversibility in the whole range of scan rates analyzed. This fact was confirmed by the EIS results, where CF/PAni-30 composite depicted the lowest charge transfer resistance value associated to its highest values for the double layer capacitance and for the diffusion coefficient. Furthermore, the charge/discharge testing showed a specific capacitance around 180 Fg–1 for the CF/PAni-30 composite. These results showed that an effective coverage of PAni film on CF matrix occurred in the Polímeros, 25(5), 425-432, 2015

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Received: Nov. 13, 2014 Revised: Mar. 02, 2015 Accepted: Apr. 29, 2015

Polímeros, 25(5), 425-432, 2015

http://dx.doi.org/10.1590/0104-1428.1831

Binary mixture micellar systems of F127 and P123 for griseofulvin solubilisation Lillian Maria Uchôa Dutra1*, Maria Elenir Nobre Pinho Ribeiro1, Igor Marques Cavalcante1, Débora Hellen Almeida de Brito1, Luana de Moraes Semião1, Raquel Freitas da Silva1, Pierre Basílio Almeida Fechine2, Stephen George Yeates3 and Nágila Maria Pontes Silva Ricardo1 Laboratory of Polymers and Materials Innovation, Department of Organic and Inorganic Chemistry, Universidade Federal do Ceará - UFC, Fortaleza, CE, Brazil 2 Group Chemistry of Advanced Materials, Departament of Physical, Chemical and Analytic Chemistry, Universidade Federal do Ceará - UFC, Fortaleza, CE, Brazil 3 Organic Materials Innovation Centre, School of Pharmacy and Pharmaceutical Sciences, University of Manchester, Manchester M13 9PL, United Kingdom 1

*lmudutra@hotmail.com

Abstract Pluronics molecules self-assemble in aqueous solution providing a core/shell architecture that improves the solubility of hydrophobic drugs. Binary mixtures of Pluronics have been studied as drug nanocarriers in order to combine their advantages, like high colloidal stability, small particle size and good solubilisation capacity (Scp). In this work we studied Pluronics binary mixture, P123 and F127, as nanocarriers of the hydrophobic drug griseofulvin. P123 (E21P67E21) shows a relative good Scp, whereas F127 (E98P67E98) shows a good colloidal stability. According to data, these binary mixtures form stables nano-sized comicelles in aqueous solution. The Scp of the P123/F127 systems at 25 and 37 °C was monitored by UV/Visible spectroscopy, showing good results at both temperatures, as would be expected, since P123/F127 have similar length hydrophobic block. Hydrophobic-dependence and temperature-responsive of the systems were evaluated by CMC, particle size and colloidal stability. Hence, stables P123/F127 comicelles may have potencial as hydrophobic drug delivery.

Keywords: binary mixtures, griseofulvin, Pluronics.

1. Introduction The use of block copolymers in pharmaceutical science and industry has a long history. In this context, self-assembly copolymer surfactants have been used as solubilizing and stabilizing agents of poorly water soluble drugs in pharmaceutical formulations[1-5]. These polymers form micelles in aqueous solution with a core/shell architecture, where the hydrophobic core is segregated from the aqueous exterior by a hydrophilic shell, which provide themselves an effective drug carrier[3,6-9].

Among these systems, amphiphilic triblock copolymers formed by poly(ethylene oxide) (E) and poly(propylene oxide) (P) blocks with an EMPNEM arrangement (where “m” and “n” denote the monomers units) have been studied.

They are known as Pluronics, and have been investigated due to several reasons. In aqueous solution their amphiphilic molecules self-assemble in micelles, where P segments comprise a hydrophobic core as a nanoenvironment for the incorporation of hydrophobic drugs, which may increase the drug stability. Their hydrophilic block E, forming the corona, prevents aggregation, protein adsorption and recognition by the reticulo endothelial system (RES) that increases their blood time circulation[5,7,9]. These copolymers in aqueous solution form micelles or physical gels, and this behavior will be dependenton their concentration and temperature in the system. At concentrations above the critical micelle concentration (CMC) and at temperatures above the critical

Polímeros, 25(5), 433-439, 2015

micelle temperature (CMT), the block copolymer molecules can self-assemble into micelles in aqueous solutions. At higher concentrations, the closed packing of micelles results in the formation of gel-like ordered structures. Thus, Pluronics solutions are capable of exhibiting thermally reversible gelation behavior[4,10,11].

These micelles can show spherical, cylindrical or lamellar morphology. This depends on the relative length of both blocks, which changes the hydrophilic–lipophilic balance (HLB) of block copolymers[7,8,10,11]. Due to their small particle size (<100 nm) these systems exhibit many advantages such as targeting ability, long circulation time and easy production on effective delivery of drugs. Incorporation of low molecular mass drugs into Pluronic micelles can increase their solubility and stability and improve their pharmacokinetics and biodistribution[7-9,11-13].

Lee et al.[8] reported that some binary mixtures of Pluronics like L121/F127 show cooperative aggregation, however, these kind of systems need extra energy input such as heating and ultrasonication to form stable nano-sized particles. Therewith, Lee et al.[8]studied binary mixtures with similar length of hydrophobic block which these EMPNEM copolymers are chosen as nanocarriers for encapsulation of hydrophobic drugs in order to combine the advantages in their physicochemical properties such as a high colloidal

433

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

Dutra, L. M. U., Ribeiro, M. E. N. P., Cavalcante, I. M., Brito, D. H. A., Semião, L. M., Silva, R. F., Fechine, P. B. A., Yeates, S. G., & Ricardo, N. M. P. S. stability, formation of small particle size, good solubilisation capacity and thermally reversible gelation behavior[8,10,11].

In this study we have focused on the solubilisation capacity (SCP) between Pluronics with similar length of hydrophobic block, P123 (E21P67E21) and F127 (E98P67E98), by the usual quantification technique ofUV/Visible spectroscopy[1,14,15]. Although the hydrophobic griseofulvin was used as a standard drug to compare the values of SCP of the copolymers and their mixture, recently, griseofulvin has been attracting considerable interest as a potential anticancer drug, that shows low toxicity and efficacy to kill cancer cells[6,8,16,17]. In addition, studies such as micellar properties, i.e., critical micelle concentration (CMC) and particle size as micelle hydrodynamic diameter (DH), are necessaries to confirm their values of SCP, and verified their stability as hydrophobic drug deliveries at body temperature[1,10,11,13,18].

2. Materials and Methods 2.1 Materials The copolymers E98P67E98(F127) and E21P67E21 (P123) (E = ethylene oxide and P = propylene oxide), commercially available as Pluronics (Figure 1a), were purchased from BASF but supplied by Uniquema and used as received. Values​​ of molecular characteristics were measured by gel permeation chromatography (GPC) using N, N-dimethylacetamide as solvent 70 °C, and these results were published in a previous study by Chaibundit et al.[11] (Table 1). The fluorescent dye, DPH (1,6-diphenyl-1,3,5-hexatriene), was supplied by

Figure 1. (a) Chemical structure of EMPNEM and; (b) Chemical structure of griseofulvin.

Table 1. Molecular characteristics of the copolymers P123 (E21P67E21) and F127 (E98P67E98), data published by Chaibunditetal[11] and Oh et al.[13].

E21P67E21

Mna (g mol-1) 5.75

E98P67E98

12.5

Copolymer

% Eb

Mw/Mn

32

1.10

Mwc (g mol–1) 6.6

69

1.20

15

HLBd 8 22

Average molecular weight[11]. bHydrophilic portion of copolymer[11].

Number average molecular weight, calculeted from Mnand Mw/Mn[11]. dHydrophilic–lipophilic balance[13]. a c

434

Biochemika, and griseofulvin (weight average of 352,8 g mol–1, Figure 1b) was supplied by Sigma-Aldrich (Poole Dorset, UK). All the other materials used were of analytical grade.

2.2 Binary mixtures PluronicsP123 and F127 mixed systems were prepared by two distinct methods: polymer/solution w/w and w/v.

For the solubilisation and size particle procedures each mixture was prepared weighing the copolymers and dissolving them in Milli-Q water to the desired concentration of 1% (w/w), where the weight percentages of P123 in the mixture were 30, 50 and 70%, and, in what follows, the mixtures are referred to as PF 30, PF 50 and PF 70. In the critical micelle concentration experiment, stock solutions of the binary mixtures PF 30, PF 50 and PF 70 (1%, w/v) were prepared by dissolving the copolymers in Milli- Q, allowed to stir for at least 14h, and then stored at 4 °C overnight.

The solutions were transferred to room temperature (25 °C) and kept for more than 1 h before further dilutions.

2.3 Critical micelle concentration (CMC) Various methods are used to determine the CMC of surfactants. These methods (e.g. dye solubilisation and surface tension) measure properties that show an abrupt change when the surfactant molecules begin to micellize as its concentration changes. As the surfactant concentration increases and it begins to micellize, the hydrophobic dye starts to migrate from the polar aqueous medium into the unpolar core of the micelles. In this hydrophobic environment, the intensity of the dye absorbance increases abruptly. The determination of CMC of the copolymers and their mixtures was performed through the method of dye solubilisation, using a Hitachi Spectrophotometer U-2000.

The hydrophobic dye 1,6-diphenyl-1,3,5-hexatriene (DPH) was used as a probe to determine micelles formation. DPH was dissolved in methanol (0.4 mM) in the dark, and added to the solutions of the copolymers in the ratio of 1:100 (30μL DPH:3ml solution). Thus, solutions of copolymers (ranging from 0.0001-1%) in methanol and 0.004mM DPH were obtained. The absorbance wavelength used for the DPH was 356nm.The absorbance measurements of the samples were taken around 3 and 24h after the addition of DPH. During all the process the solutions containing DPH were kept in the dark. These studies were performed at 25 and 37 °C. Plots of absorbance against log C (wt. %) were used to determine the onset of micellization[10].

2.4 Solubilisation The method used for the solubilisation of griseofulvinwas the “shake flask” method, adapted from Aliabadi and Lavasanifar[15]. Copolymers and their mixtures were dissolved in Milli-Q water (1% w/w). Then, a portion of drug (w ≈ 10 mg) was added to an aliquot of copolymer solution (10 mL). The system was slowly stirred at 25 °C (± 0.1 °C) for 4 days in a thermostatic bath. After that, 3 mL of supernatant were filtered (0.45 μm Millipore) to remove any non-solubilized drug. Aliquots of the filtered samples were diluted with methanol (10x) and the drug concentration was monitored by UV/Visible spectroscopy at 292 nm, using a calibration curve based on Beer’s law.

Polímeros, 25(5), 433-439, 2015

Binary mixture micellar systems of F127 and P123 for griseofulvin solubilisation For more 4 days, the remaining supernatant (7 mL) was stirred at 37 °C (± 0.1 °C), and then, the same procedure was performed. All measurements were made in triplicate.

2.5 Micelle size DLS technique is based on the Brownian motion, where the time-dependent fluctuations in the intensity of scattered light from a suspension of particles undergoing random.

Analysis of these intensity fluctuations allows for obtain the diffusion coefficients, and by aid of Stokes- Einstein equation can determine the particle size, i.e., hydrodynamic diameter or radius (DH or rH). Using the equipment Nano Zetasizer, Malvern Zetasizer Nano ZS (ZEN 3500) the DH of triblock copolymers P123, F127 and their mixtures PF 30, 50 and 70, with and without drug, were determined at 25 and 37 °C. The measurements were made using the filtered aliquots from the solubilisation procedure. The systems were investigated using 30 scans with 30 s acquisition time allowed for each scan. All the measurements were made in triplicate[11,18].

3. Results and Discussion 3.1 Critical micelle concentration (CMC) The CMC, the fraction of molecules in micellar form, and the size and the aggregation number of the micelles, as well as the temperature dependence of these parameters, are of great interest for aqueous EMPNEM block copolymer micellar solutions. As observed by Alexandridis et al.[10], it becomes necessary to study the systematic formation of the micelles of these block copolymers, determining the micellization origin and the effects of hydrophilic (E) and hydrophobic (P) block in this parameter[10]. DPH solubilisation method, using UV/Visible spectroscopy, was performed by Alexandridis et al.[10] to study the micellization of different Pluronics indicated that the optimum wavelength of DPH absorbance is 356 nm[10]. The CMC can be determined from the plots of DPH absorbance versus log C (wt. %): the concentration where an abrupt increase of absorbance occurs is the CMC (Figure 2a).

Micelle formation of P123, F127 and their mixtures in aqueous solutions was monitored by UV/Visible using DPH as a dye probe. The CMC values were determined at 25 °C, once this is the temperature of preparation and storage of some commercial drug formulations, and at 37 °C, the body temperature. Copolymers used as solubilizing agents should be mostly micellized in dilute aqueous solution. Low CMC values of surfactants are interesting for drug solubilisation because they provide high stability of their micelles in solutions upon dilution in the blood[7,12,18,19].

Figure 2b shows CMC values of P123, F127 and their mixtures at 25 and 37 °C. The results were expressed as weight percentage of polymer in solution (wt. %), since this is the usual way to evaluate the efficiency of surfactants for commercial applications[18]. According to Tadros[20], temperature acts differently on the solubility of the different types of surfactants. It was observed that those surfactants that have altered solubility with increasing temperature would have the same behavior in relation to their CMC, since the surfactant solubility interferes in their CMC. Polímeros, 25(5), 433-439, 2015

Figure 2. (a) Plots of absorbance of DPH versus log C (wt. %) of P123, F127 and the mixture PF 50 at 25 °C; (b) Effect of temperature at CMC of copolymers P123, F127 and their mixtures, PF 30, 50 and 70.

In general, the CMC of nonionic copolymers undergoes reduction as the temperature increases[10]. Increasing temperature decreases the CMC, in which the polymer becomes more hydrophobic due to micellar growth, and this effects on the polarity of the polymer decreases, as the temperature rises up, due to the dehydration of the E chains[11,21].The CMCs of all systems studied in this work at 37 °C are lower than at 25 °C (Figure 2b), consistent with the studies reported by Tadros[20] for nonionic surfactants and by Alexandridis et al.[10] for EMPNEM block copolymers[10,20].

Attwood et al.[18] reported that, within a series of Pluronics, CMC values are affected by variation of E-block length. Although the effect of poly(ethylene oxide) (E) on the CMC is less pronounced than that of poly(propylene oxide) (P), the EMPNEM CMC becomes dependent of the number of E units when two copolymers have the same hydrophobic block length. This would indicate that the micelle formation becomes more difficult than more hydrophilic the molecules[10,18].The higher is the hydrophobic character of the copolymer the lower will be its CMC, since micellization reduces its unfavorable interactions with water.

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Dutra, L. M. U., Ribeiro, M. E. N. P., Cavalcante, I. M., Brito, D. H. A., Semião, L. M., Silva, R. F., Fechine, P. B. A., Yeates, S. G., & Ricardo, N. M. P. S. Hence, the results obtained in this work to the copolymers P123 and F127 were 0.055 and 0.357mM at 25 °C, and 0.006 and 0.048 mM at 37 °C, respectively, consistent with the values published by Alexandrids et al.[9] and Attwood and Booth[22]. Thus, we can observe that the CMC of F127 is higher than that of P123, once the hydrophilic block (E) of F127 is five times larger than that of P123[18].

The mixtures kept the profile of the temperature dependence of the copolymers alone (Figure 2b). The CMC values for the mixtures at 25 and 37 °C were found to be intermediate compared to those found for the pure copolymers. We could observe that as P123 ratio in the mixtures increases, CMC decreases, once P123 has a lower CMC than F127. For example, the CMC value found for PF 30 was 0.027wt. %, while for PF 70 was 0.018wt.% at 37 °C. The low CMC values of these systems at 37°C bring to these mixtures promising pharmacological applications once the micelles could remain stable even upon dilution in the blood[7,8,11,13,15,18,23].

micellization and stability and high solubilisation capacity (SCP).The encapsulation efficiency can be measured by compatibility of the micelle core with the drug, and this

3.2 Micelle size Generally, so that the efficiency of the encapsulated active be long during its circulation in blood, the micelles should be small enough to evade detection and destruction by the reticular endothelial system[12].

In studies by Chaibundit et al.[11] it was observed that binary mixtures of Pluronics, which have the same hydrophobic block length, formed stables comicelles in diluted aqueous solution, and these mixtures showed a single narrow distribution and small particles at room and body temperature[10,11]. In studies by Wei et al.[12] this behavior was observed for the mixtures between P123 and F127 solubilizing the drug Paclitaxel. These micelles showed hydrodynamic diameter (DH) ranging from 20 to 30 nm and polydispersivity index between 0.14 and 0.23.

In our study, P123/F127 micelles showed unimodal size distribution and average micelle size, proving comicelles formation to the same mixtures loading griseofulvin drug.

DH values of the systems F127, P123 and their mixtures PF 30, 50 and 70, without (Figure 3a) and with (Figure 3b) griseofulvin, at 25 and 37 °C are shown in Figure 3. The DH of copolymer F127 is larger than that of P123, since F127 has a hydrophilic chain length of poly(oxyethylene) bigger than P123.

The encapsulated drug, griseofulvin, had virtually no influence on the hydrodynamic radius (rH) of micelles of P123 and F127, considering the standard deviation of the analyses (Figure 4). However, this increase might nevertheless reflects a certain increase in the hydrophobic micelle core size because of griseofulvin solubilisation[12].

The difference of rH for the systems P123 and F127, with and without encapsulated drug, is between 1 and 3 nm, and for their mixtures this difference is even smaller, as seen

by Wei et al.[12]. Therefore, micelles of binary mixtures of Pluronics form particles smaller than 200 nm, which is a great advantage for use in pharmacological applications[8,12].

Figure 3. Hydrodynamic diameter (DH) of copolymers systems at 1% w/v at 25 and 37 °C: (a) without griseofulvin; and (b) with griseofulvin.

3.3 Solubilisation We have appointed important characteristics to be sought in a micellar system for drug delivery, such as small micelle size and a low CMC, giving a high extent of 436

Figure 4. Effect of encapsulated drug on rH of the systems at 25 °C. Polímeros, 25(5), 433-439, 2015

Binary mixture micellar systems of F127 and P123 for griseofulvin solubilisation interaction controls the rate of uptake and release of the active[5,22].

Values of SCP of the copolymer solutions for griseofulvin were obtained by UV/Visible spectroscopy, and these results are reported in milligrams of solubilized drug per gram of copolymer in solution (S mg.g–1), after correction for the solubility of griseofulvin in water (S0 mg.dL–1), SCP = S - S0,[6,14,22,24].The values of S0 for griseofulvin were 1.34 and 1.83 mg.dL–1 at 25 and 37 °C, respectively, similar to those reported by Ribeiro et al.[24], and the values of SCP (mg/g) obtained for F127, P123 and their mixtures, PF 30, 50 and 70, are showed in Figure 5.

Bearing in mind earlier studies by Attwood and Booth[22] and Crothers et al.[1], we have used griseofulvin as a standard aromatic drug for comparing the SCP of micellar solutions of different block copolymers. Solubilisation capacity data published by Attwood and Booth[22] to P123 and F127, 3.0 and 2.2 mg g–1, were similar with our results, considering the standard deviation of samples, using the same method and temperature[22].

As it would be expected from this discussion, the solubilisation capacity of EMPNEM diluted solutions, with hydrophobic P blocks, showed low values when compared with values of other types of copoly(oxyalkylenes)[1,22,24].

However, Lee et al.[8] studied the SCP and aqueous stability of copolymers of EMPNEM type, analyzing their HLB (hydrophilic/lipophilic balance), and observed that the solubility of the drug in these nano-colloidal systems do not just depend on hydrophobicity of the block, but also on the length of the hydrophilic block[8]. We observed that our SCPvalue of P123 was higher than that of F127: 3.5 and 1.5 mg/g at 25 °C, respectively (Figure 5). According to Jindal and Mehta[5], the HLB values for the copolymers P123 and F127 are 8 and 22, respectively, which the higher the HLB, the higher hydrophilicity, and these balance values are an indicative that the encapsulation efficiency of P123 for hydrophobic drugs would be better than that of F127[5,21].

Lee et al.[8] studied the direct effect of the hydrophilic– lipophilic balance in the kinetic and thermodynamic stability of micelles in binary mixtures of Pluronics. In their studies the L121 (HLB = 2) showed less aqueous stability and previous precipitation at diluted solutions, when added hydrophilic triblocks EMPNEM with the same hydrophobic P portion and with long hydrophilic chain, was observed an increase on aqueous stability.

According to Lee et al.[8] P123 with a low CMC increased the thermodynamic stability due to tight hydrophobic interactions with hydrophobic blocks, while the Pluronic with long hydrophilic chain, like F127, increased kinetic stability due to steric hindrance for micelle aggregation[8].

These results suggest that Pluronics with relatively low HLB increase the thermodynamic stability, but do not affect the kinetic stability. This way, incorporating long PEO chains into micelles to prevent secondary micellar aggregation by steric hindrance, forming a kinetically stable dispersion[8].

The mixing of P123 and F127 is studied in this work to overcome the limitations of low solubilisation capacity and combine the advantages of high stability of Pluronics.

Further analyzing our values of SCP for griseofulvin in the binary mixtures, PF 30, 50 and 70, we observed that increasing Polímeros, 25(5), 433-439, 2015

P123 levels in PF mixtures increase the solubilisation of griseofulvin.

These results were expected, as discussed by Lee et al.[8] and Kulthe et al.[19], which the Pluronics mixtures are good solubilising agents of hydrophobic drugs, where the increase in the encapsulated efficiency by the micelles it was observed for mixtures which had a higher ratio of hydrophobic polymer. Supporting our values of SCP to PF mixtures where this behavior still keep the high solubilisation capacity to mixtures that have higher rates of P123[8,19,21].

In studies with a series of EMPNEM copolymers was observed the influence of temperature on solubilisation capacity[21]. In our studies, SCP at 25 °C is lower than at 37 °C (see Figure 5). According to Kadam et al.[21], this behavior can be explained by the increase in thermal vibrations of the monomers in the micelles, resulting in an increase in the space available for solubilisation of the drug into the micelle, in addition to the increased griseofulvin solubility in water, varying for high temperature[11,21].

This increase in SCP with the increase of temperature can be better understood through the micelle-water partition coefficient, calculated by a thermodynamic point of view.

The solubilisation can be considered as a normal partitioning of the drug between micelle and aqueous phases and the partition coefficient is the ratio of the drug concentration in the micelle to that in water for a particular surfactant concentration (P = SCP/SO). The standard free energy of solubilisation is ΔGS°= - RT ln P, where R is the universal gas constant, T is the temperature in Kelvin scale, and P is the partition coefficient between the micelle and the aqueous phase[6]. Table 2 shows the influence of temperature on the partition coefficient of griseofulvin.

Figure 5. Solubilisation capacity (SCP) of griseofulvin in 1 wt. % solutions of P123, F127 and their binary mixtures, PF 30, 50 and 70, at 25 and 37 °C. Table 2. Partition coefficient and Gibbs free energy at 25 and 37 °C for all the systems.

Systems F127 PF 30 PF 50 PF 70 P123

25 °C ln P 0.1245 0.3321 0.7335 0.4498 0.9565

ΔGs° (kJ mol–1) –0.3085 –0.8228 –18,175 –11,146 –23,697

37 °C ln P 0.1518 0.5048 0.6590 0.6386 0.9507

ΔGs° (kJ mol–1) –0.3912 –13,010 –16,986 –16,460 –24,502

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Dutra, L. M. U., Ribeiro, M. E. N. P., Cavalcante, I. M., Brito, D. H. A., Semião, L. M., Silva, R. F., Fechine, P. B. A., Yeates, S. G., & Ricardo, N. M. P. S. As observed by Kadam et al.[6] in their studies using Pluronics for solubilisation of carbamazepine, our results show the free energy of solubilisation is negative in all systems, including the PF mixtures, and becomes more negative with the temperature increase. This way the spontaneous griseofulvin solubilisation in the aqueous solutions of these copolymers is manifested by the negative values of ΔGS°. Increasing temperature decreases ΔGS°, what favors its spontaneous solubilisation, since increases the drug/unimer ratio, i.e., the higher number of drug molecules can be accommodated into micelles[6,10].

4. Conclusions These series of block copolymers EMPNEM are frequently used as solubilizing agents for water poorly soluble drugs.

In this paper, we have investigated the solubilisation of a hydrophobic drug, griseofulvin, in the binary mixtures of Pluronics P123 with F127 that self-assemble forming comicelles in dilute aqueous solution.

The CMC values for the mixtures at 25 and 37 °C were found to be intermediate compared to those of the pure copolymers. The low CMC values of these systems at 37 °C indicate that their micelles could remain stable even upon dilution in the blood, increasing the circulation time of the drug in the blood. In the studies of particle size, the binary systems showed a single narrow distributionin with a particle size ranging from 20 to 30 nm at room and body temperature, an advantage for pharmacological applications.

Pluronics P123 and F127 binary mixtures showed a spontaneous solubilisation of griseolfulvin and could be useful in its pharmacological formulations, since they combine the properties of F127, thermodynamic stability, with the better solubilisation capacities of P123. By a thermodynamic point of view the increase of the temperature from 25 to 37 °C promotes greater spontaneity and stability to these systems in aqueous solution. Therefore, Pluronic comicelles can increase drug solubility and stability, making them interesting drug nanocarriers candidates to pharmacological applications.

5. Acknowledgements This work was financially supported by Brazilian Agencies, Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação Cearense de Apoio ao Desenvolvimento Científico e Tecnológico (FUNCAP) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).

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Received: July 08, 2014 Revised: Mar. 24, 2015 Accepted: Apr. 22, 2015

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http://dx.doi.org/10.1590/0104-1428.1860

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

The effects of porosity in friction performance of brake pad using waste tire dust Ibrahim Mutlu1*, Ilker Sugözü2 and Ahmet Keskin3 Technology Faculty, Afyon Kocatepe University, Afyonkarahisar, Turkey 2 Tarsus Technology Faculty, Mersin University, Mersin, Turkey 3 Bolu Vocational School, Abant Izzet Baysal University, Bolu, Turkey

1

*ibrahimmutlu@aku.edu.tr

Abstract This research is focused on the effect of porosity on the friction-wear properties of automotive brake pads. Waste Tire Dust (WTD) was used as a new friction material in brake pads. Newly formulated brake pad materials with five different components have been produced by conventional techniques. In the experimental studies, the change of the friction coefficient, the temperature of the friction surface, the specific wear rate, and the hardness, density and porosity were measured. In addition, the micro-structural characterizations of brake pads are determined using Scanning Electron Microscopy (SEM). The mean coefficient of friction, porosity and specific wear are increased due to a WTD rate increases, on the other hand, hardness and density are decreased. As a result, WTD can be considered as an alternative to revalorize this kind of waste products in the brake pads and the amount of porosity of the brake pad affected the friction coefficient and wear behavior of the pad.

Keywords: brake pad, composite materials, friction, porosity, waste tire.

1. Introduction Automotive friction materials have been formulated for about one century[1]. Nowadays, formulated automotive friction materials are generally multi-component systems that comprise more than 10 components, in order to achieve the desired friction properties[2,3]. A characteristic friction material is a multi-component polymer matrix composite with a formulation often developed empirically[4]. Brake pads used in automotive brakes are generally made of many components. These are classified into four major categories binder, fibers, friction modifiers and fillers all of which are based on the major function they perform apart from controlling friction and wear performance[5]. Brakes are exposed to large thermal stresses during routine braking and extraordinary thermal stresses during hard braking. Unfortunately, the manufacturing process inevitably produces a wide range of variations in both microstructure and defect population, such as porosity, intermetallic particles, and trapped oxide films, which are all detrimental to the mechanical properties, in particular, the fatigue behavior[6].

In recent years, as other fibers have taken the place of asbestos, the porosity of brake pads has come to be an important constituent of these composite materials. Porosity is involved in the transmission of heat from friction as well as in the sound produced during braking and it helps vent the decomposition gases that sometimes produce a fading effect during a very sudden braking. A spatial characterization of porosity is vital to controlling the structuring of brake pad materials as they are produced[7]. The current trend in the research field is the utilization of industrial or agricultural wastes as a source of raw materials for composite development[8]. This will provide more economical benefit and also environmental

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preservation. Moreover, many factors should be considered when developing brake materials to fulfill requirements such as, a stable friction coefficient and a lower wear rate at various operating speeds, pressures, temperatures, and environmental conditions in the automotive sectors[9-11].

Tire accumulation is a growing worldwide problem because it is recalcitrant to the environment. Every year about 800 million tires are rejected, and this amount is increasing by 2% each year[12]. Different strategies have been proposed to eliminate rubber wastes including incineration with energy recovery or grinding them down to be used as modifiers for different materials[13]. Sintering of rubber is another possibility of recycling tires. This process requires only the application of heat and pressure to achieve cross-linked rubber with good mechanical properties[14]. No information is available in the literature on the use of Waste Tire Dust (WTD) for the formulation of new brake pad materials. Therefore, brake pad materials have been formulated with the aim of using WTD as a new industrial waste material for automotive friction materials. In the experimental studies, the change of friction coefficient, the amount of wear, density, hardness and porosity were measured. In addition, micro‑structural characterizations of braking pads were looked at by using a SEM. The results revealed that WTD can in fact be used for friction materials in the brake lining pad. This study has been undertaken to investigate the effects of porosity on automotive brake pads from 5% to 15% by the weight of waste tire dust. In addition, it was investigated the relationship between wear behavior, porosity and friction characteristics of the pad was investigated.

Polímeros, 25(5), 440-446, 2015

The effects of porosity in friction performance of brake pad using waste tire dust

2. Materials and Methods 2.1 Materials, formulations and specimen preparation In this study, a new automotive brake friction material was developed by using additive WTD. WTD is obtained from the waste tires of automobile via grinding in Turkey.

Five different specimens were produced. These specimens contain WTD, phenolic resin, copper particles, aluminum oxide, graphite, brass particles, cashew and barite. An analytical balance was used to weigh the components. Friction material specimens were produced by a conventional procedure for a dry formulation following dry-mixing, pre-forming and hot pressing. These components were then mixed for 10 minutes using a commercial blender. The final mixture was loaded into an inch square (small specimens) mold for pre-forming under pressing at a pressure of 9.8 MPa. Pre-formed specimens were put in hot pressing mold at a pressure of 14.7 MPa and 180 °C for 15 minutes. During the hot pressing process, pressure was released several times to release the gases that evolved from the cross linking reaction (poly condensation) of the phenolic resin. Detailed conditions for each manufacturing step can be found in the author’s other study[15]. The percentages of the phenolic resin, copper particles, aluminum oxide, graphite, brass particles and cashew didn’t change in five different specimens. On the other hand, the percentages of the barite and WTD changed inversely proportional to each other. The composition of the friction materials studied in this work is shown in Table 1.

2.2 Test and analysis In this study, the performance of WTD on brake friction characteristics was examined. The friction coefficient‑temperature-time graphs and the mean coefficient of friction were obtained to identify the friction characteristic.

In order to define friction coefficients of automotive brake pad under different temperatures, a test device was used.

Figure 1 shows the disc test equipment used in this study.

Using a real brake disc type tester, the friction coefficient characteristics of the pad next to the disc made of cast iron were investigated by changing the pad. The test specimen was mounted on the hydraulic pressure and pressed against the flat surface of the rotating disc. Before performing the friction coefficient test, the surfaces of the test specimens and the cast iron discs were ground with 320-grid sandpaper. The normal load was varied to achieve a constant friction force. Braking tests were carried out under 1.05 MPa pressure, 6 m/s velocity and at temperatures from 50 to 400 °C for 500 seconds. An electrical heater was used in order to achieve a 400 °C friction surface temperature.

The temperature and friction coefficient values were stored in a databank. The tests were repeated three times for each specimen. Friction coefficient-temperature-time graphs are obtained to identify the effect of these variables. The friction coefficient of surface of the friction material pairs needs to be high and stable. The friction coefficient was calculated by measuring normal and tangential pressures throughout a 500 second test. It is expressed as a mean value of entire braking dependence during the friction coefficient test. Wear rate was calculated as the specific weight loss of specimens during the tests. Specific wear rate is determined by the mass method following the Turkish Standard (TS 555)[16] Polímeros, 25(5), 440-446, 2015

Table 1. The components of specimens (weight %).

Specimens Code WTD1 Phenolic Resin 20 Cu Particles 15 Al2O3 5 Graphite 5 Brass Particles 2.5 Cashew 10 Barite 37.5 WTD 5 Total 100

WTD2 20 15 5 5 2.5 10 35 7.5 100

WTD3 20 15 5 5 2.5 10 32.5 10 100

WTD4 20 15 5 5 2.5 10 30 12.5 100

WTD5 20 15 5 5 2.5 10 27.5 15 100

Figure 1. The disc test equipment used in this study.

and British Standard (BS AU142)[17] and was calculated by the following equation: V=

m1 − m2 (1) Lf m ρ

where, V is specific to wear (mm3/MJ), m1 is the mass of brake pad before testing (kg), m2 is the mass of brake pad after testing (kg), L is the friction distance calculated by using the number of revolution and radius of the disc (m), fm is the average friction force (N), ρ is the density of brake pad (kg/mm3).

The friction surfaces of the specimens were characterized using SEM (LEO 1430VP). The specimen surfaces for the SEM observations were always coated with carbon. The density of the specimen was determined by weighing the specimen on a digital scale and measuring their volume by the liquid displacement method. Hardness testing was carried out on a Brinell hardness testing machine using a 62.5 kgf load and 5 mm steel ball to determine the hardness variation as a function of braking pad compositions. The surface of the specimens was carefully prepared and each specimen was tested after production of each braking pad. At least five indentations were made from the center to the edge of the specimens to obtain an accurate value of the hardness for each specimen and an average value was obtained. Experimental scatter was at most ± 2 HB. Therefore, it was concluded that the braking pads were homogeneous. Porosity was also measured for WTD containing specimens. Porosity is calculated by using the following Equation 2: = Φ

W3 − W1 ×100 (2) W3 − W2 441

Mutlu, I., Sugözü, I., & Keskin, A. where, Φ is porosity(%), W1 is the dry weight of specimens (g), W2 is the specimens soaked in water for 48 hours in water weight(g), W3 is the weight of the specimens after waiting 48 hours in water specimens(g).

3. Results and Discussion 3.1 Friction performance The coefficient of friction (μ) varied significantly in the initial stage of testing. This can be attributed to the fact that the size of the contact area increased and the friction layer developed on the surface. The variations of μ with its respective test time are depicted in Figure 2. As seen in the figure, the friction coefficients show different features depending on the content.

It is seen in this figure that μ initially increased in all specimens, then slowly decreased. There is an increase in μ between 0th-100th second which degrades slightly after the 100th second where μ kept almost constant in WTD1, WTD4 and WTD5 coded specimens. Such an increase can often be attributed to the adhesion of metal chips in the brake pad to the friction surface of the cast iron disc.

The observed amount of change in the friction coefficient is usually a sign of unstable and aggressive friction. Some vibration and noise were observed approximately until the 100th second of testing. This vibration was typically observed at the beginning of the test before the development of the stable friction layer. After the 100th second this degradation somewhat slowed with slight fluctuations. Till the 450th second, as a result of friction, a temperature of 300-350 °C is achieved on the friction surface. WTD2 and WTD3 coded specimens show a fluctuation in μ from the 100th second to the 400th second. It shows a rapid decrease and a rapid increase in μ.

The increase in μ occurs when metallic materials inside brake pads rub against cast iron brake disc surface. However, due to friction wear detachments occur. As a consequence, μ starts to decrease. Later, this behavior repeats with the newly formed friction surface. This situation is fluctuating, and undesirable. These specimens include 7.5% and 10% WTD, and μ is decreased from 0.47 to 0.40 in a short time.

A rapid increase or decrease in μ has led to a rapid increase in temperature on the surface of friction. On the other hand, the μ for the WTD1, WTD4, and WTD5 specimens increase

Figure 2. The change of friction coefficient as a function of time for specimens.

442

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The effects of porosity in friction performance of brake pad using waste tire dust at the beginning of test and a small decrease is observed after 100-150 seconds.

bulk. The presence of a well-developed friction layer on the friction surface as well as its morphology is easily visible.

It is seen from this figure that the friction coefficient gradually increases in all specimens up to 150 °C. It shows a variable behavior between the temperatures of 150 °C and 350 °C. It is found that μ decreases with increasing testing temperature. Generally, μ decreases between 350 °C and 400 °C due to softening of phenolic resin. As a result, fading occurs during the brake action. Furthermore, with the increasing temperatures, the components in the braking pad affected each other due to the faster diffusion. This phenomenon is called thermal fade[18,19]. The friction behavior of specimens coded WTD1, WTD4 and WTD5 are consistent with each other. Therefore, if a higher μ is desired, WTD can be used 5, 12.5, and 15% as an additive. WTD1, WTD4 and WTD5 coded specimens can be suggested as better material for brake pads than the others. In addition, a more stabilized μ is obtained with these specimens.

As seen from the micrographs, some particles in the rubbed surfaces of pads are detached from the body and created macro-voids in addition to the micro-voids as shown in Figure 3, WTD3, WTD4, and WTD5. In pads, particle–matrix detaching and cracking are observed due to softening and charring of matrix resin as can be seen in Figure 3, WTD3 and WTD4. It is also clear from Figure 3 that the component are homogeneously distributed in the matrix and, therefore, very few micro voids are observed in the structure. It is known that[20] if the metal-component coherent surface is larger, friction and wear will increase.

It is also observed that Al2O3 particles are distributed in a quite homogeneous manner and therefore they can possibly remain effective on the friction surface. The worn metallic particles imply that they actively participated in friction during braking test. The macro voids are formed as a result of falling of the metallic particles during the friction process. In addition, micro voids were observed on the surface (Figure 3, WTD3 and WTD4). Figure 3 shows the wear debris of all specimens. The abrasive effect of the detached particles further increases wear rate (Figure 3, WTD3, WTD4 and WTD5)[21,22].

In WTD1, WTD4 and WTD5 coded specimens, after μ first increases, it maintains a constant value with slight fluctuations. This can be explained as follows: Because of heating due to friction, the micro-structural changes in the brake pad are finished and thus a constant μ is able to be maintained. μ of WTD1 specimen has risen slowly, but μ of other specimens has risen quickly. These results are consistent with the behavior of friction coefficient of all of specimens. These specimens have almost a similar average μ value between 0.39 and 0.44. Therefore, if a μ value between 0.40 and 0.45 is desired, WTD can be used in brake pads with 12.5 and 15% weight as additive. For higher μ values, adjusting the rate of WTD can be recommended.

Furthermore, if stability is desired in μ, WTD5 coded specimen is suggested as better material for brake pads when compared to others (Table 2).

3.2 Character of friction surfaces SEM micrographs of braking pads using WTD after the braking test for frictional surface including the information about the friction layer are shown in Figure 3. These figures show the worn surfaces of all specimens tested at sliding speed of 6 m/s. It is seen from these figures that a homogeneous microstructure is observed in the frictional surfaces. The friction process is characterized by the development of friction debris. Such debris adheres to the friction surface and forms a friction layer easily visible by an inspection of the specimen surface after the friction test.

Systematic analysis of the surface of the composite materials indicated that the friction process dominantly occurred on the friction layer which eventually covered the top of the

Similarly, WTD is well spread out over the braking pad and hence larger micro-voids occur in the specimens, having a higher rate of WTD particles as seen in Figure 3, WTD4 and WTD5. The micrographs reveal that the higher the rate of WTD content, the coarser the particles of the resulting wear debris are, indicating severe wear (Figure 3, WTD3, WTD4 and WTD5). Typical wear debris consists of sheared-deformed polymer matrix containing small detached participles; the wear powder of the metallic counterpart. The particles can either be lost from the contact zone immediately after being detached from the composite surface, or remain there for a while as transferred and back-transferred layers[22].

As can be seen from Figure 3, WTD1 and WTD2, the friction layer is not continuous. A thick friction layer is developed on the surface after testing. Such a layer is developed predominantly in scratches which were filled with friction debris. The “uncovered areas” were dominantly associated with the presence of graphite on the surface.

Graphite is characterized by its lubricating properties, and a low adherence of the friction layer can result. It can be clearly seen that friction layers have been formed in the specimens. Larger “uncovered” areas were observed during the testing. An image analysis of the friction surface revealed that the uncovered areas did not correspond to the content of graphite in the bulk (Figure 3, WTD3 and WTD5). On the other hand, the amount of surface covered by deformed

Table 2. Typical characteristics of the brake pad used in this study.

Specimen code WTD1 WTD2 WTD3 WTD4 WTD5

Mean coefficient of friction 0.40764 0.39601 0.42259 0.42899 0.44123

Polímeros, 25(5), 440-446, 2015

Standard deviation 0.08024 0.06676 0.066897 0.06754 0.06926

Specific wear

Hardness

Density

Porosity

(g/mm2) 0.21 × 10–6 0.22 × 10–6 0.24 × 10–6 0.26 × 10–6 0.31 × 10–6

(HRB) 25.3 26.8 26.5 21.5 20.9

(g/cm3) 2.170 1.678 1.704 1.739 1.709

(%) 6.578947 9.333333 15.28571 17.66667 18.3

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Mutlu, I., Sugözü, I., & Keskin, A.

Figure 3. SEM micrographs of brake pad specimens.

metallic particles increases with increased temperature, as apparent in Figure 3, WTD3 and WTD4. This tendency is clearly related to the ability of metallic particles to be easily smeared over the surface with increased temperature.

The friction layer adheres well to deform metallic particles.

An active friction surface layer developed in all specimens due to a homogenous distribution of components (Figure 3).

While macro-voids exist in WTD4 and WTD5 specimens, these specimen components’ WTD rate 12.5 and 15% demonstrate a homogenous distribution (Figure 3, WTD4 and WTD5). In WTD3, WTD4 and WTD5 specimens, since the components actively participate when there is 444

in friction, some particles detach from the bulk and thus macro-voids are observed. On the other hand, micro-voids are observed in WTD1, WTD2 and WTD3 specimens due to the homogenous distribution of components (Figure 3).

3.3 Density, hardness and porosity of brake pad materials Table 2 presents the density, hardness, porosity, the mean coefficient of friction, the standard deviation of coefficient of friction and specific wear of the specimen during the tests for 500 seconds. A density measurement test was carried out on a laboratory scale to examine the density of the material.

Polímeros, 25(5), 440-446, 2015

The effects of porosity in friction performance of brake pad using waste tire dust Density depends upon the components in the pad material.

A metallic element has a higher density than an organic element. Friction elements often exist as a combination of various elements. The results shown in Table 2 are the average density of three readings for each formulation.

It is seen from Table 2 that WTD1 coded specimen has the highest density with the value of 2.170 g/cm3. It includes 37.5% barite, which is a heavy dust material used as a filled friction material. The higher the barite rate, the higher the density is.

The mass of the specimens was measured before and after the friction test, and wear rates were calculated as a mean value of the weight reduction in the three specimens.

As can be seen from Table 2, the mean coefficients of friction and the standard deviation of these specimens are very close to each other. The μ achieved in specimens WTD3, WTD4 and WTD5 are approximately 0.42-0.44 and higher, which are considered to be very good when compared to coefficients of friction achieved in current brake pads.

The mean coefficients of friction are higher in addition; the standard deviation is higher in the WTD4 and WTD5 specimens. In addition, the standard deviation is higher in the specimen where the mean coefficient of friction is average in the WTD1 specimen. Finally, less wear is observed on the specimens where the additive WTD material rate is WTD1 or WTD2, compared to the other specimens. But its mean coefficient of friction is lower than one of WTD3, WTD4 and WTD5. Therefore, the WTD material positively contributes to the mean coefficient of friction in brake pads and positively contributes to the wear resistance in brake pads. The detected roughness is very similar for all testing conditions regardless of the testing temperature and pressure applied. This indicates that chemical changes on the surface, rather than varying roughness, is responsible for performance changes.

The highest hardness is observed in WTD2 coded specimen. It has 7.5% WTD. Based on previous experiments, a WTD rate between 5-10% has a positive effect on hardness whereas a WTD rate greater than 12.5% has negative effect on hardness. 12.5% and 15% WTD rate specimens have the lowest hardness and the highest specific wear. Table 2 shows the variation in specific wear rates with increasing WTD rate for all specimens investigated. The specific wear rate is increased with increasing WTD rate as expected.

Table 2 shows the porosity test results for all formulations of brake pad materials. Porosity, a gross measure of the pore structure, gives the fraction of the total volume that is void[23].

Porosity has an important role in automotive brake pad materials since the function of porosity is to absorb energy and heat. This is a very important for the effectiveness of the brake system. Brake pads should have a certain amount of porosity to minimize the effect of water and oil on the friction coefficient. Increasing porosity by more than 10% could reduce the brake noise[11,24]. It was generally observed in our study that the specimens with high porosity tend to exhibit high friction coefficient (Table 2). The shape of the pore is highly variable, as can be recognized by observation of the micrographs. SEM allows for the observation of the surface pore structure. From the porosity results as shown in Table 2, it can be seen that two brake pad formulations, 5 and 7.5% of WTD specimens, show a lower percentage Polímeros, 25(5), 440-446, 2015

of porosity compared to other specimens. WTD1 has a porosity of 6.58%. On increasing WTD is found to have increased porosity of about 17.67% to 18.3%.

4. Conclusions In this study, WTD was added to the composite and specimens were successfully obtained by a conventional manufacturing method. The effect of the WTD content on the friction and wear behavior of brake pad automotive was experimentally analyzed. The results of friction test showed that WTD can substantially improve properties of friction materials. The performance of such materials may be enhanced by improving the adhesion between both co-components. WTD may be improved by choosing an adequate compatibilizing agent. The use of a low cost compatibilizing agent will be the subject of future studies.

From the friction and wear tests, the following conclusions were reached. The coefficient of friction was found to decrease with an increasing friction surface temperature up to 300 °C. Also the standard deviation was very small, which means that the material has a stable friction characteristic.

The standard deviation was in the acceptable range for all specimens. The specific wearing rate of friction materials with WTD relatively increased but these increases are in the acceptable range for all specimens. Some micro-voids and micro-cracks were observed on the worn surface. No direct proportionality between mean coefficients of friction and the standard deviation and wear resistance could be found due to the complexity of composite structure.

The highest friction coefficient was obtained with the specimen having 15% WTD rate. The smaller value was obtained with specimen having 5%, 7.5% WTD rate.

The specimens with 7.5%, 10% and 12.5% WTD rate had more stable friction coefficient than other specimens. While the specimens with 10-15% WTD rate had higher friction coefficients, their wear rate was considerably higher than that of others specimens. The 5% WTD rate had higher density and lower porosity compared to other specimens.

Porosity of WTD in brake pads was high which is an important factor for friction material. Thus WTD added brake pad composites can be considered as potential candidate.

Bulk density and hardness is reduced by adding WTD. As a result of the experiments the structural and chemical composition of the friction layer generated on the friction surface significantly differed from the bulk. It is apparent that no simple relationship exists between composition of the friction layer and bulk material formulation.

Acknowledgements This research is funded by the Scientific & Technological Research Council of TURKEY (TÜBİTAK) (Grant Reference No: 106M006). The authors wish to acknowledge the TÜBİTAK and our partner organizations for their support.

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Tatung University, Taiwan. Retrieved in 29 March 2015, from http://ethesys.lib.ttu.edu.tw/ETD-db/ETD-search/ view_etd?URN=etd-0805104-170550 24. Jaafar, T. R., Selamat, M. S., & Kasiran, R. (2012). Selection of best formulation for semi-metallic brake friction materials development. Powder Metallurgy, 1-30. Retrieved in 29 March 2015, from www.intechopen.com/download/pdf/28435 Received: Aug. 07, 2014 Revised: Apr. 03, 2015 Accepted: May 25, 2015

Polímeros, 25(5), 440-446, 2015

http://dx.doi.org/10.1590/0104-1428.1911

Synthesis and characterization of novel polyester containing Schiff-base unit Hossein Mighani1*, Ehsan Fathollahi1 and Moosa Ghaemy2 Laboratory of Polymer Chemistry, Department of Chemistry, Faculty of Science, Golestan University, Gorgan, Iran 2 Faculty of Chemistry, Mazandaran University, Babolsar, Iran

1

*h.mighani@gu.ac.ir

Abstract A new Schiff base type of polyester containing 2,2-dimethyl-1,3-diaminopropane was prepared by solution polycondensation of 1,4-benzenedicarbonyl dichloride with Bis(4-hydroxybenzilaldehid)-2,2-dimethyl-1,3-propildiimine (H 2HB2P) which is derived from a 2,2-dimethyl-1,3-diaminopropane Schiff base reacted with a 4-hydroxybenzaldehyde monomer.

The monomer and the polyester were characterized by FTIR, 1HNMR, and elemental analysis. The prepared polyester showed inherent viscosity of 0.29 dl/g in NMP at 25 °C, indicating their moderate molecular weight. The Polyester was completely soluble in aprotic polar solvents such as N-methylpyrolidone (NMP), dimethylformamide (DMF), Dimethyl Acetamid (DMAC), dimthylsulfoxide (DMSO). TGA determined the 10% weight loss temperature (T10) at 280 °C and residual weight at 600 °C ca. 41% under nitrogen atmosphere.

Keywords: polyester, Schiff base, 2, 2-dimethyl-1, 3-diaminopropane, thermal stability.

1. Introduction

2. Experimental

Polymers have received significant attention due to their lightness and favorable physical and chemical properties. Amongst polymers, polyesters have been the subject of numerous commercial applications. This in turn, has attracted a plethora of researches and studies in the synthesis of polyesters from diols and diacid chlorides by condensation polymerizations[1,2]. Synthesis of polymers with conjugative bonds including –C=N– and–C=C– in the main chain has grabbed researcher’s interests for many years[3-8]. Generally, Schiff base bonds confers appropriate features such as; thermal stability, conductivity, liquid crystal properties and chelating effects to polymers[9,10]. Nowadays, polyesters with Schiff base units have been an interesting area for researchers due to the particular properties. Aromatic structures in this class of polymers have a high thermal stability[11]. Aromatic polymers with Schiff base units have a high thermal stability, they suffer from low solubility. To solve this problem, many efforts were triggered toward increasing the solubility[12,13]. Substituting flexible groups along the main chain of polyesters with Schiff base units is of strategies to enhance the solubility in organic solvents[14].

In this paper for the first time we investigate the synthesis and characterization of polyester containing Schiff base unit with high solubility by solution polymerization of bis(4-hydroxybenzaldehyde)- 2,2 dimethyl-1,3-propyl diamin(H2HB2P) with terephthaloyl dichloride. Monomer and resultant polymer was characterized by FT-IR, 1HNMR and CHNS. Also the inherent viscosity, solubility and thermal stability of the polymer were studied.

2.1 Materials and instruments

Polímeros, 25(5), 447-450, 2015

2, 2-dimethyl-1, 3-diaminopropane, 4-hydroxybenzaldehyde, terephthaloyl dichloride and solvents were purchased from Fluka and used without further purification. 1HNMR spectra were recorded on a 500 MHz Bruker Advance DRX instrument using DMSO-d6 as solvent and tetramethylsilane as an internal standard. FT-IR spectra were recorded using a Bruker Vector 22 spectrometer on KBr pellets. The CHN‑600 Leco analyzer was used for elemental analysis. Thermal gravimetric analysis (TGA) and differential scanning calorimetery (DSC) were performed using Perkin-Elmer Pyris and MetlerTolledo 822e, respectively. Inherent viscosity ([η]inh = lnηrel/c, at a concentration of 0.5 g/dl) was measured with an Ubbelhode suspended-level viscometer at 25 °C in NMP solution.

2.2 Pre-treatment of monomer In a 250 mL round bottom flask equipped with a magnetic stirring, 4-hydroxybenzaldehyde (3.15 g, 26 mmol) dissolved in a mixture of 40 mL methanol, 1 mL of conc. HCl was added. A solution of 2, 2-dimethyl-1, 3-diaminopropane (1.32 g, 13 mmol) in 30 mL of methanol and few drops were added to the flask. The mixture was stirred for 5 h under reflux condition. After cooling the reaction, The precipitated product, Bis (4-hydroxybenzilaldehid)-2, 2-dimethyl-1,3-propildiimine (H2HB2P) (Scheme 1), was collected by filtration, washed with ethanol and dried in a vacuum oven at 70 °C for 3 h. A yellow product was obtained in 65% yield with a melting point of 186 °C. IR (KBr) (δmax cm–1): 3205 (OH), 1649 (CN), 1585 (C=CAr).

1 HNMR (400, DMSO, d6, TMS) δ ppm: 9.86 (1H, S, OH),

447

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

Mighani, H., Fathollahi, E., & Ghaemy, M.

Scheme 1. Synthesis of H2HB2P.

8.16 (1H, S, NH), 0.93-1.04 (6H, t, CHmethyl), 3.42-3.56 (4H, C, CHmethylene).

2.3 Preparation of polyester In a two-necked flask 100 mL equipped with a dropping funnel and gas inlet tube was charged with a mixture of Bis(4-hydroxybenzilaldehid)-2,2-dimethyl-1,3-propildiimine (0.62 g, 2 mmol), 20 mL dimethylformamide (DMF) and triethylamine (0.8 mL). 1, 4-benzenedicarbonyl dichloride (0.40 g, 2 mmol) dissolved in 10 mL DMF was added drop wise to the stirred solution at 0 °C under N2 atmosphere.

The mixture was subsequently stirred at ambient temperature for 5 h under N2 and then it was poured into cold water.

The yellow solid product was separated by filtration and washed with NaHCO3 solution. Then polymer washed with methanol, and dried under reduced pressure at 80 °C for 24 h.Yield 60%, IR (KBr) (δmax cm–1): 1736 (C=O), 1210 and 1270 (C-O), 1598 (C=C), 1660 (C=N). 1HNMR (400, DMSO, d6, TMS) δ ppm: 0.93-1.06 (6H, CHmethyl), 3.36-3.52 (4H, CHmethylene), 7.40-8.39 (12H, CHAr), 8.40 (2H, CH=N). Anal.Cald. for [C27H24N2O4]: C, 73.64; H, 5.45; N, 6.36. Found: C, 74.54; H, 5.22; N, 7.06.

Figure 1. 1HNMR of H2HB2P.

3. Result and Discussion Scheme 1 depicts route for synthesis of monomer (H2HB2P).

The band at 3205 cm–1 is associated to OH, while the band at 1649 cm–1 can be attributed to the imine group(N=C).

The absorption peak at 1585 cm-1 is characteristic of double bond group (C=C). The Figure 1, 1HNMR spectra showed the OH protons in 9.86 ppm, the peak at around 8.16 ppm is assigned to NH, and methyl peak is observed in 1.04-0.93 ppm and the peak from 3.42-3.47 ppm is characteristic of methylene.

Polyester is synthesized by polymerization of H2HB2P with terephthaloyl dichloride in the presence of triethylamine.

Reaction was carried out in DMF as H2HB2P solvent and terephthaloyl dichloride in nitrogen atmosphere at room temperature. The result of elemental analysis is closely similar to calculated percentages. Elemental percentages are obtained as follows: C, 74.54% (73.64% calculated); H, 5.22% (5.45%); N, 7.06% (6.36%). Polyester was also characterized with 1HNMR and IR Spectroscopy. In Figure 2, showed IR spectra peaks; the peak at 1736 cm–1 is associated to (stretch C=O), and the peak at 1660 cm–1 is characteristic of (N=C) and the peak at 1598 cm–1 is related to (stretch C=C).

1 HNMR spectra of the representative polyester, in Figure 3, showed signals at 8.40 ppm due to the proton of azomethine, at 7.40-8.39 ppm related to the protons of aromatic groups, the protons of methyl at 0.93-1.06 ppm and in the regions 448

Figure 2. IR of polyester.

Figure 3. 1HNMR of polyester.

of 3.36-3.52 ppm corresponding to aromatic protons and water proton. The inherent viscosity [η] of polymer was measured in NMP, equal to 0.29 dl/g. It is well established that viscosity has direct relation with molecular weight therefore polyester possess a reasonable molecular weight.

Polyester was dissolved easily in NMP, DMF, DMAC and Polímeros, 25(5), 447-450, 2015

Synthesis and characterization of novel polyester containing Schiff-base unit Table 1. The physical and thermal properties of polyester.

Yield (%)

ηainh(dl/g)

Tgb (◦C)

T10%c(◦C)

T20%d(◦C)

Rw(%)e

60

0.29

174

268

341

41.4

Detected in NMP with a concentration of 0.5 g/dl at 25 °C. bDetected by DSC at a heating rate of 10 °C /min in N2. c10% weight loss temperature (Determined by TGA at a scan rate of 10 °C /min in N2). d20% weight loss temperature (Determined by TGA at a scan rate of 10 °C /min in N2). e Residual weight (%) when heated to 600 °C (Determined by TGA at a scan rate of 10 °C /min in N2).

a

6. References

Figure 4. TGA of polyester.

DMSO at room temperature. It is hypothesized that this is because aliphatic structure of H2HB2P monomer enhance the flexibility of polymer. The polyester was insoluble in acetone and methanol. Thermal stability of polyester was investigated with TGA and DSC instruments. Differential scanning calorimeter (DSC) analysis was performed at a heating rate of 10 °C/ min. The scanning of polymer was carried out over 300 °C. The glass transition temperature was recorded about 170 °C. As anticipated, the Tg value of this polyester depended on the structure of the diol aliphatic part employed. Thermal stability was carried out in nitrogen atmosphere. Polymer showed 10 percent weight loss over 270 °C and 50 percent weight loss over 400 °C. 41.4% of the polymer remained unchanged around 600 °C (Figure 4).

Physical and thermal properties were shown in Table 1.

4. Conclusion Polyester was prepared from H2HB2P diol and terephthaloyl dichloride. With molar ratio of diol to diacid chloride 2:2 the polymerization was performed at room temperature under N2 atmosphere within 5 hours. Polyester was prepared, characterized and its thermal stability was investigated.

The presence of aliphatic group increased the flexibility of diol and as a result enhanced the solubility of polyester.

The poyester has a 10 percent weight loss at 268 and 20% weight loss at 341 °C and a residual weight (41.4%) at 600 °C. The polyester has a glass transition temperature at 174 °C and it showed that the polyester is a thermally stable material. The inherent viscosity of polyester is 0.29 dl/g and showed a high molecular weight for polymer.

5. Acknowledgements We acknowledge Golestan University (GU) for partial support of this work and mazandaran University (UMZ) for NMR spectral analysis.

Polímeros, 25(5), 447-450, 2015

1. Kricheldorf, H. R., Struve, O., & Schwarz, G. (1996). Whiskers: 13. Polyesters based on 4, 4′-biphenyldiol and biphenyl- 4, 4′-dicarboxylic acid. Polymer, 37(19), 4311-4320. http://dx.doi. org/10.1016/0032-3861(96)00260-1.

2. Ludwig, H. (1971). Polyester fibers, chemistry and technology.

New York: John Wiley.

3. Yang, J., Sun, W. L., Jiang, H. J., & Shen, Z. Q. (2005).

Synthesis and properties of two novel poly (Schiff base)s and their rare-earth complexes. Polymer, 46(23), 10478-10483. http://dx.doi.org/10.1016/j.polymer.2005.08.037.

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6. Shi, S. Y., Li, Z., & Wang, J. (2007). Synthesis and characterization of some novel conjugated polyoxadiazoles with Schiff base structure. Journal of Polymer Research, 14(4), 305-312. http:// dx.doi.org/10.1007/s10965-007-9111-0.

7. Khuhawar, M. Y., Mughal, M. A., & Channar, A. H. (2004).

Synthesis and characterization of some new Schiff base polymers. European Polymer Journal, 40(4), 805-809. http:// dx.doi.org/10.1016/j.eurpolymj.2003.11.020.

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9. Coskun, Y., Cirpan, A., & Toppare, L. (2004). Conducting polymers of terepthalic acid bis-(2-thiophen-3-yl-ethyl) ester and their electrochromic properties. Polymer, 45(15), 49894995. http://dx.doi.org/10.1016/j.polymer.2004.05.038.

10. Li, X. G., Zhou, H. J., & Huang, M. R. (2005). Synthesis and properties of a functional copolymer from N-ethylaniline and aniline by an emulsion polymerization. Polymer, 46(5), 1523-1533. http://dx.doi.org/10.1016/j.polymer.2004.12.021.

11. Deng, F., He, W., Luyt, A. S., & Jiang, Y. Y. (2011). Synthesis and properties of a novel polyester containing bithiazole. Chinese Chemical Letters, 22(1), 109-113. http://dx.doi.org/10.1016/j. cclet.2010.09.019.

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Received: Aug. 31, 2014 Revised: Jan. 18, 2015 Accepted: Feb. 26, 2015

PolĂ­meros, 25(5), 447-450, 2015

http://dx.doi.org/10.1590/0104-1428.1924

Rheological, mechanical and morphological properties of poly(methyl methacrylate)/poly(ethylene terephthalate) blend with dual reactive interfacial compatibilization Juciklécia da Silva Reinaldo1, Maria Carolina Burgos Costa do Nascimento1, Edson Noriyuki Ito1* and Elias Hage Junior2 Departamento de Engenharia de Materiais, Universidade Federal do Rio Grande do Norte - UFRN, Natal, RN, Brazil 2 Departamento de Engenharia de Materiais, Universidade Federal de São Carlos - UFSCar, São Carlos, SP, Brazil

1

*ito@ufrnet.br

Abstract In this work, the rheological, mechanical and morphological behavior of immiscible blend poly (methyl methacrylate) with elastomeric particles (PMMAelast) and post-consumer poly (ethylene terephthalate) (PET) with and without the use of the interfacial compatibilizer poly (methyl methacrylate-co-glycidyl methacrylate-co-ethyl acrylate) (MGE) was studied. The significant increase in torque presented in rheological analyses has shown a indication of chemical reactions between the epoxy group of MGE with end groups of PET chains and also with the elastomeric phase of PMMAelast.

The increased concentration of PET yielded an increase in maximum strength and elasticity modulus and a decrease in elongation at break. The PMMAelast/PET binary blend (50/50 wt%) and PMMAelast/PET/MGE compatibilized blend (65/30/5 wt%) showed pronounced results in elongation at break compared to PMMAelast, whereas, in the first results were due to the evidence of a co-continuous morphological structure and in the second, due to the efficiency of the dual reactive interfacial compatibilization of PMMAelast/PET blends. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses showed that PMMAelast/PET/MGE blends exhibit complex phase morphology due to the presence of elastomeric particles in the PMMAelast copolymer and in the use of MGE terpolymer.

Keywords: PMMA copolymer, post-consumer PET, morphology, reactive extrusion.

1. Introduction Polymer blends seem to be a viable alternative to obtain new polymeric materials with properties usually not found in a single polymer. The interest both academic and industrial to produce and refine new materials through the mechanical mixing of commercially available polymers has grown significantly each day. This approach is relatively simple and commercially attractive compared to the synthesis of new polymers[1-3].

Poly (methyl methacrylate) (PMMA) is a polymer belonging to the class of methacrylates and shows many possibilities for technological applications. Due to its amorphous structure, PMMA is a transparent material that exhibits good optical properties[4-6]. It is widely used in applications replacing glass, which require transparency and good resistance. However, PMMA is brittle at room temperature with low elongation at break and low impact strength. A very common method to promote improvements in the mechanical properties of PMMA is its toughening with elastomers[7-12].

The addition of elastomers in PMMA become the polymer opaque and lose transparency, one of its most important characteristics of this material. A solution to this problem is the addition of MBS copolymers (methyl methacrylatebutadiene-styrene) or MABS (methyl methacrylateacrylonitrile-butadiene-styrene), which do ot change the

Polímeros, 25(5), 451-460, 2015

PMMA transparency because the refraction index of these elastomers is close to the PMMA. Studies in literature show that the addition of MBS to PMMA does not change its transparency and improves its mechanical properties, especially elongation at break and impact strength[7,13-17].

PET is a polymer belonging to the group of polyesters, produced by the condensation reaction between terephthalic acid and ethylene glycol. This polymer can be found in different percentage of crystallinity: in the amorphous form (transparent), partially crystalline and oriented (translucent) or with a high degree of crystallinity (opaque). Due to its good mechanical performance, chemical resistance, transparency, processability and reasonable thermal stability, PET has ideal characteristics for the manufacture of a wide variety of products in the packaging sector such as soft drinks, water, juices, edible oils, etc., in addition to durable items used in electronics and automobiles[6,18-21].

Bottle grade PET (PETG) has 2% by weight of terephthalic acid replaced by isophthalic acid, and this structural change hinders crystallization, retarding it sufficiently so that the maximum degree of crystallinity during stretching in the blow molding process does not exceed 35%, providing a semi-crystalline, transparent and resistant product. The PETG was developed to replace glass[22].

451

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

Reinaldo, J. S., Nascimento, M. C. B. C., Ito, E. N., & Hage, E., Jr. One of the major problems of society is the post‑consumer waste. PET is a plastic material widely found in garbage, which takes over 100 years to degrade in the environment[23-26].

A viable alternative for the recycling of plastic materials with higher added value, such as PET used as soft drink bottles is the development of polymer blends. PMMA/PET blend can be a form of conscious reuse of post-consumer PET, decreasing the accumulation of this material in landfills and helping the environment[27].

PMMA/PET blends are mainly use in electrical and automotive applications, which require materials with good dimensional stability especially for electronic circuit equipment. PET is a material with good dimensional stability in the temperature range from 0 to 100 °C[6], its use in mixtures promotes improvements in the PMMA properties, which is an amorphous polymer that may exhibit variations in its dimensional stability. Furthermore, it can also reduce production costs by replacing part of virgin PMMA resin by post-consumer PET[27,28].

Most immiscible blends have unstable phase morphology and often lower properties compared to pure polymers, requiring the addition of an interfacial compatibilizer.

The use of compatibilizers in these immiscible systems must accomplish: (i) optimization of the interfacial tension, i.e., the degree of dispersion; ii) stabilize the morphology against high stresses during forming, and (iii) enhance adhesion between the phases in the solid state[29-31].

Studies in literature with poly (butylene terephthalate) (PBT) and poly (styrene-co-acrylonitrile) (SAN) blends[32,33] have shown that poly (methyl methacrylate-co-glycidyl methacrylate-co -ethyl acrylate) (MGE) is an efficient compatibilizer for the PBT/SAN system. These studies showed that MGE has miscibility with SAN copolymer according to the acrylonitrile concentration in the SAN, and also there is a chemical reaction of end groups of the carboxylic and hydroxyl chains of PBT. Torque rheometry provides, by monitoring torque as a function of time, evidence of the occurrence of chemical reactions between components of the polymer blend.

And also interfacial compatibilizer, which increase the torque, promote a chemical reactions with in situ formation of a copolymer (reactive extrusion) during processing of the polymer blend[34-36].

In the work developed by Ito et al.[37], the torque rheometry results showed no increase in torque with the addition of compatibilizer MGE to the PMMAhomo/silica/MGE composition (96/2/2 wt%) when compared with the torque value of pure PMMAhomo. On the other hand, the PMMAelast/silica/MGE composition (96/2/2 wt%) showed a significant increase in torque compared to pure PMMAelast, indicating that there was no reaction between MGE and silica. Thus, the occurrence of reactions between PMMAelast and MGE was verified.

Studies conducted by Dewangan and Jagtap[38] showed that the addition of PtBA-b-PMMA compatibilizer, which has acidic functional groups that react with end groups of hydroxyl chains present in PET, synergistically affects the mechanical properties of the PMMA/PET binary blend.

Dantas[39] showed that the increase of PET percentage as dispersed phase in the PMMAhomo/PET binary blend caused a significant increase in the average diameter of the 452

dispersed phase. In relation to the use of MGE compatibilizer, it was observed that there was a reduction in the average diameters of the dispersed phase for compositions with the same percentage of PET. Due to the incompatibility and immiscibility of the PMMA/PET binary blend, it is necessary to use a compatibilizer to improve the properties of this blend. Therefore, the aim of this study was to correlate the rheological, mechanical and morphological properties of poly (methyl methacrylate) copolymerized with elastomer and post-consumer poly (ethylene terephthalate) binary blend with and without the use of compatibilizer MGE until to phase inversion.

2. Experimental 2.1 Materials This study used two types of poly (methyl methacrylate) (PMMA): poly (methyl methacrylate) homopolymer (PMMAhomo) (ECL-DH); poly (methyl methacrylate) copolymerized with elastomeric particles (PMMAelast) (ECP800); both acquired from Unigel SA with melt flow indexes of 1.2 and 3.8 g/10 min (standard ASTM D1238, 230 °C/3.8 kg, obtained from the supplier), respectively. Poly (ethylene terephthalate) (PET) was obtained from soft drink bottles with melt flow index of 15 g/10 min (standard ASTM D1238, 250 °C/2.16 kg, measured by the authors). Poly (methyl methacrylate-coglycidyl methacrylate-co-ethyl acrylate) (MGE), used as compatibilizer, was synthesized in laboratory according to methodology described in literature[32,33].

The formulations of polymer blends used for rheological, mechanical and morphological characterization, and solvents used for the extraction of phase in the morphology of the PMMAelast/PET binary blends and PMMAelast/PET/MGE compatibilized blends are showed in Table 1.

2.2 Rheological characterization Table 1 shows the polymer blends used in the characterization of the rheological behavior of mixtures that were performed using a PolyLab Haake torque rheometer model Reomix 600, rotation speed of 100 rpm, temperature of 240 °C, mixing chamber of 69 cm3 with 70% of filled volume, and processing time of 15 minutes.

2.3 Extrusion and injection molding processing The compositions of polymer blends used in the characterization of the mechanical and morphological behaviors are shown in Table 1. The mixtures were prepared in a co‑rotating twin screw extruder from company AX Plásticos Máquinas Técnicas LTDA, D = 16 mm and L/D = 40, using a temperature profile of 102/160/190/210/220/230/220/210 °C from the feeding zone to the matrix. The materials were added into the feed hopper at 80 rpm and screw rotation speed of 220 rpm. After extrusion, the formulations of polymer blends were granulated and dried in a circulating air oven (at 60 °C for 12 hours) and then in vacuum (at 60 °C for 12 hours).

The molding of test specimens for tensile strength analysis (ASTM D638-01) was performed in an Arburg injection molding machine, model 270V, with temperature profile Polímeros, 25(5), 451-460, 2015

Rheological, mechanical and morphological properties of poly(methyl methacrylate)/poly(ethylene terephthalate) blend with dual reactive interfacial compatibilization of 230/240/240/250/250 °C, molding temperature of 50 °C and cooling time equal to 50s.

2.4 Mechanical characterization Uniaxial tensile tests were performed in a Shimadzu universal testing machine model AG - 300 kN, speed of 1mm.min–1 up to 0.5% and strain of 5mim.min–1 until failure. For calculation of the elasticity modulus, speed of 1 mm.min–1 was used, using segment mode between 0.05 and 0.25% of strain.

2.5 Morphological characterization 2.5.1 Scanning electron microscopy Samples were cryo-fractured in liquid nitrogen and then phase extraction was performed with chloroform and a phenol/1,1,2,2-tetrachloroethane solution (60/40 wt%) (Table 1) under mechanical stirring in ultrasound for 5 and 15 minutes. Samples were placed on SEM specific support and metallized with a thin gold layer. Morphological analyses were performed using a Philips scanning electron microscope model XL-30 FEG. 2.5.2 Transmission electron microscopy Samples collected from the center of the tensile specimen were cataloged and prepared by reducing the sample cross‑sectional area (trimming) and sizing the sample tip to be cryo-ultramicrotomized in the trapezoidal form, which provides better stress distribution in the cutting of films, with surface area of approximately 0.5 mm2.

Then, samples were sectioned on a Leica ultramicrotome model Reichert Ultracut S using a diamond knife (Diatome CryoHisto 45º), temperature of –60 °C cooled with liquid Table 1. Formulations of polymer blends used for rheological, mechanical and morphological characterization, and solvents used in function of the morphologies.

Rheological Materials

Studies (wt%)

Mechanical and Solvents Morphological

PMMAelast

100

(wt%) 100

*1 and *2

PMMAhomo

100

-

-

PET

100

100

-

MGE

100

-

-

PMMAelast/MGE

95/5

-

-

PMMAhomo/MGE

95/5

-

-

PMMAelast/PET

95/5

95/5

*2

PMMAelast/PET

85/15

85/15

*2

PMMAelast/PET

70/30

70/30

*1

PMMAelast/PET

50/50

50/50

*1

PMMAelast/PET

30/70

30/70

*1

PMMAelast/PET/MGE

80/15/5

80/15/5

*2

PMMAelast/PET/MGE

65/30/5

65/30/5

*1 and *2

*1 - Chloroform (solvent to PMMAhomo and elastomeric particles). *2 - Phenol / 1,1,2,2-tetrachloroethane (60/40 wt%) (solvent to PET and elastomeric particles).

Polímeros, 25(5), 451-460, 2015

nitrogen to avoid deformation of the original microstructure, cutting rate of 0.2 mm.s –1 and sample thickness of 25 nm.

The sliced samples were exposed to ruthenium tetroxide vapor (RuO4) for 4 hours for the incorporation of atoms of high atomic number into the PET phase and to generate a contrast between domains of the dispersed phase in relation to the continuous phase. Morphological analyses, obtained by TEM, were carried out with a Philips model CM120, using voltage of 120kV. Subsequently, Image Pro Plus software version 4.5 (Media Cybernetics) was used to determine the average diameter of particles based on photomicrographs obtained.

3. Results and Discussion 3.1 Rheological characterization The analysis of the reactivity of pure polymers (PMMAhomo, PMMAelast and PET) with the interfacial compatibilizer (MGE) as a function of the torque variation was analyzed in a torque rheometer.

Figure 1 presents the results of the torque versus time for pure polymers (PMMAelast and PET) and PMMAelast/MGE (95/5 wt%) and PET/MGE (95/5 wt%) mixtures. A significant increase in the torque value, both for PMMAelast and PET with the addition MGE was observed. The increase in the torque value of PET is related to the reaction that occurs between the epoxy group of MGE and the carboxyl and hydroxyl groups present at the end of the PET chain, whose results are found in literature on studies conducted in reactive compatibilization with poly (butylene terephthalate) (PBT), which has structure similar to PET[32,33].

Figure 2 shows the analysis of PMMAhomo/MGE and PMMAhomo/MGE mixtures (95/5 wt%), which analysis aim to investigate the increased torque in the PMMAelast/MGE mixture presented in Figure 1. The PMMAhomo/MGE mixture showed no significant increase in torque compared to PMMAhomo, thus there is indication that the reactivity between PMMAelast and MGE is a function of the reactivity of the elastomeric particles of PMMA with the epoxy group of MGE.

Figure 1. Torque versus time curves for PMMA elast, PET, PMMAelast/MGE (95/5) and PET/MGE (95/5).

453

Reinaldo, J. S., Nascimento, M. C. B. C., Ito, E. N., & Hage, E., Jr. An illustrative representation of reactions occurring during the mixing of the PMMAelast/PET/MGE blend is showed in Figure 3. The epoxy group of MGE[32,33] reacts with end-chain groups (carboxyl and hydroxyl) of PET, and the increased torque of the PMMAelast/MGE mixture is related to the possible reaction of the epoxy group of MGE with elastomeric particles of PMMA. The PMMAelast is composed of homopolymer PMMA and copolymer PMMA with elastomeric particles (PMMAcopo). Thus, there is a possibility of reactivity of MGE with PMMAelast and with PET, forming the complex interfacial structure PET‑g‑MGE-g-PMMAelast.

The torque vs. time curves for pure polymers and for binary blends in Figure 4 show that the PMMAelast had higher torque compared to PET, thus the increased percentage of PET in the binary blend leads to a proportional reduction of the torque value, i.e., reducing the viscosity of this mixture.

Figure 5 presents an increase in torque as a function of the addition of MGE to the binary blend with 30 to 15% by weight of dispersed phase PET. The results showed that the addition of MGE increases the torque of the PMMAelast/PET blend, where the first torque increase peak (not shown on graph) is due to the addition of the solid material before the softening and melting as a function of time and temperature.

The second peak in the torque versus time curve that is displayed in the compatibilized blends is an indication of the dual reactivity of MGE with PMMAelast and PET.

3.2 Mechanical characterization The mechanical properties of pure polymers (PMMAelast and PET) and of PMMAelast/PET binary blends with and without the use of compatibilizing agent MGE are showed in Table 2 and Figure 6.

The PMMAelast used in this study showed better elongation at break properties compared to commercial types of PMMA[39], due to the modification of the mechanical properties (toughening mechanisms[7-10]) caused by elastomeric particles.

The results of maximum strength and elastic modulus (Table 2 and Figure 6) showed that these properties increase as a function of the PET concentration in the binary blend and also due to the use of MGE. The addition of PET as a dispersed phase reduced the elongation at break in the PMMAelast/PET blend. However, in the blend with 30 wt% of PET compatibilized with 5 wt% of MGE, and in the binary blend with 50 wt% of PET, increase in this property (synergism) how has been observed in Figure 6c. These results indicate an efficient interfacial compatibilization by reducing the size of the dispersed phase, and co-continuous morphology, respectively.

Figure 4. Torque versus time curves for pure polymers (PMMAelast and PET) and for binary blends (PMMAelast/PET).

Figure 2. Torque versus time curves for PMMA homo , PMMAhomo/MGE (95/5) and MGE.

Figure 3. Illustrative representation of the reaction of MGE with end-chain groups of PET with the elastomeric phase of copolymer PMMA (PMMAelast = PMMAhomo + PMMAcopo).

454

Figure 5. Torque versus time curves for PMMA elast /PET binary blends: (70/30) and (85/15) and PMMAelast/PET/MGE compatibilized blends: (65/30/5) and (80/5/15).

Polímeros, 25(5), 451-460, 2015

Rheological, mechanical and morphological properties of poly(methyl methacrylate)/poly(ethylene terephthalate) blend with dual reactive interfacial compatibilization

Figure 6. Mechanical properties of the PMMAelast/PET binary blends in function of the PET concentration. (a) Tensile strength; (b) Elastic modulus; and (c) Elongation at rupture.

Table 2. Mechanical properties of pure polymers (PMMAelast and PET) and PMMA/PET and PMMA/PET/MGE blends.

Composition

Tensile strength

(wt%) PMMAelast (100) PET (100) PMMAelast/PET (95/5) PMMAelast/PET (85/15) PMMAelast/PET (70/30) PMMAelast/PET (50/50) PMMAelast/PET (30/70) PMMAelast/PET/MGE (80/15/5) PMMAelast/PET/MGE (65/30/5)

(MPa) 34.9 ± 0.6 51.8 ± 0.7 35.1 ± 0.2 36.5 ± 1.2 41.5 ± 0.1 44.4 ± 1.3 52.4 ± 0.8 37.4 ± 0.1 39.2 ± 0.2

Regarding to the blends with 15 wt% of PET in Figure 6c, no significant increase in the elongation at break was observed. The compatibilization agents used and the weight percentage of PET are not enough to promoted the synergism in the PMMAelast/PET blends.

3.3 Morphological characterization 3.3.1 Scanning electron microscopy Specific solvents can be used for phase extraction in polymer blends, allowing observing the morphology of the dispersed phase by electron microscopy techniques.

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Elastic modulus (GPa) 1.4 ± 0.1 2 ± 0.0 1.4 ± 0.1 1.6 ± 0.1 1.7 ± 0.0 1.9 ± 0.0 2.2 ± 0.1 1.7 ± 0.1 1.8 ± 0.1

Elongation at rupture (%) 51.6 ± 1.0 18.5 ± 3.4 44.1 ± 3.1 38.4 ± 1.0 46.0 ± 7.8 104.2 ± 9.1 12.9 ± 3.5 39.9 ± 2.1 81.6 ± 4.7

Chloroform is solvent of the PMMA and the phenol/1,1,2,2tetrachloroethane solution (60/40 wt%) solubilizes the PET[40]; thus, these solvents can be used to extract phases present in the PMMAelast/PET mixture.

Figure 7 shows the morphology of PMMAelast obtained after the extraction of phases using two solvents: chloroform and phenol/1,1,2,2-tetrachloroethane solution. Preliminary tests with chloroform showed that there is complete solubilization of PMMAelast after 10 minutes under ultrasonic agitation.

A structure of spherical voids are formed after 5 minutes of immersion of PMMAelast in chloroform (Figure 7a), 455

Reinaldo, J. S., Nascimento, M. C. B. C., Ito, E. N., & Hage, E., Jr.

Figure 7. PMMAelast morphology: (a) solubilization with chloroform for 5 minutes, (b) solubilization with phenol/1,1,2,2-tetrachloroethane solution (60/40% wt) for 15 minutes.

Figure 8. Morphology of PMMAelast/PET and PMMAelast/PET/MGE blends: (a) (70/30), (b) (65/30/5) (c) (50/50) (d) (30/70) using chloroform for 15 minutes.

456

PolĂ­meros, 25(5), 451-460, 2015

Rheological, mechanical and morphological properties of poly(methyl methacrylate)/poly(ethylene terephthalate) blend with dual reactive interfacial compatibilization which was an indication of preferential solubilization of elastomeric particles.

In Figure 7b, the phenol/1,1,2,2-tetrachloroethane solution was used as solvent with the aim of showing that the solution does not react with the PMMA structure.

However, the morphology of fibrillar dispersed phase was verified, which appears after the immersion of PMMAelast in the phenol/1,1,2,2-tetrachloroethane solution. This result corroborates the illustrative representation of Figure 3, where PMMAelast is composed of homopolymer PMMA (PMMAhomo) and copolymer PMMA with elastomeric particles (PMMAcopo). Therefore, the solvent is preferably solubilized with elastomeric particles, extracting PMMAcopo and remaining the PMMAhomo phase, corresponding to the fibrillar phase shown in Figure 7b.

In Figure 8a, apparently, there was a collapse of the disperse phase PET due to the extraction of the major phase of the PMMAelast/PET blend. The morphology with the formation of spherical voids (Figure 8b) is an indication of extraction of elastomeric particles, keeping the structure of the PMMAelast/PET blend as a function of the reactive compatibilization, corroborating synergism results observed in the elongation at break for this PMMAelast/PET/MGE blend (65/30/5 wt%). The comparative analysis of the morphology of the binary blend (Figure 8a) with the same composition as the compatibilized blend (Figure 8b) showed a reduction in the size of the dispersed phase PET, increasing the surface area of PET particles and increasing the interaction with the PMMA matrix and thus increasing the matrix stability against the attack of solvents.

In Figure 8, chloroform is used as solvent for PMMAelast/PET and PMMAelast/PET/MGE blends. Preliminary test has confirmed that chloroform did not solubilize PET, so the voids shown in Figures 8a-d correspond to the PMMA phase, which was extracted with chloroform.

In PMMAelast/PET binary blends with 50 wt% of dispersed phase (Figure 8c), a co-continuous morphology was observed, which was confirmed by the synergism found in its mechanical properties when compared to the other blends before and after phase inversion.

Figure 9. Morphology of PMMAelast/PET and PMMAelast/PET/MGE blends (a) (95/5) (b) (85/15) (c) (65/30/5) and (d) (80/15/5) using phenol/1,1,2,2-tetrachloroethane solvent for 15 minutes.

Polímeros, 25(5), 451-460, 2015

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Reinaldo, J. S., Nascimento, M. C. B. C., Ito, E. N., & Hage, E., Jr.

Figure 10. Morphology of PMMAelast/PET and PMMAelast/PET/MGE blends: (a) (70/30) and (b) (65/30/5) stained with RuO4 and obtained

by TEM.

The photomicrograph of Figure 8d shows a surface with voids of irregular shapes, these voids were generated by extraction of the PMMAelast dispersed phase in the PET matrix. This morphology also corroborated with the result of mechanical behavior, as the drastic reduction in the elongation at break, increase in the maximum strength, and elastic modulus, how a function of the PET matrix.

Figures 9a and 9b show that the phenol/1,1,2,2tetrachloroethane solution favored the extraction of the elastomeric particles and the PET. The fibrillar morphology shown by this composition corresponds to PMMAhomo.

For compatibilized blends (Figure 9c and 9d), the morphology was not sufficiently revealed. The MGE terpolymer reacts with PMMAelast and PET simultaneously, hindering the extraction of phase with the phenol/1,1,2,2 tetrachloroethane solution in PMMAelast/PET/MGE blends.

3.3.2 Transmission electron microscopy In Figure 10, it was observed that the PMMAelast/PET blend showed a complex morphology, where the elastomeric particles of PMMAelast appear in spherical shape and PET phase with the dark regions into the PMMA matrix.

The average diameter of elastomeric particles measured in Figure 10a and 10b are 300 ± 20 nm and 290 ± 20 nm, respectively. These results confirm that elastomeric particles do not undergo changes in size with the addition of the compatibilizer. If the PMMAelast was a polymer blend, the interaction between MGE and elastomeric particles would favor the reduction of the average diameters of these particles.

These results corroborate with the morphologies shown by the extraction phase obtained by SEM (Figure 7, 8 and 9) for the PMMAelast/PET blend and by illustrative proposal shown in Figure 3.

4. Conclusions The study of the rheological, morphological and mechanical behavior of immiscible and incompatible polymer blends constituted with poly (methyl methacrylate) with elastomeric particle and post-consumer poly (ethylene terephthalate) 458

(PMMAelast/PET) showed that these properties are directly correlated and vary depending on the composition and addition of the compatibilizer.

The addition of MGE terpolymer to the PMMAelast/PET blend increased the torque of both polymers, as shown in the rheological results. Thus, MGE reacts with PMMAelast and PET, corroborating with the changes in the PMMAelast/PET blends properties.

The results of the elongation at break in the mechanical tests were conclusive to evidence the co-continuous morphology in the PMMAelast/PET blend (50/50 wt%), and also to show the effectiveness of the dual reactive compatibilization in the blend with 30 wt% of PET dispersed phase with 5wt% of MGE. The morphological study using solvents aided in the visualization of spherical particles in the elastomeric phase of PMMAelast, and showed that the PMMAelast is composed of a PMMAhomo phase and another PMMAcopo phase.

It was concluded that the PMMAelast/PET blend compatibilized by MGE terpolymer has complex morphology that can be better understood in this work.

5. Acknowledgements The authors would like to thank company Unigel for providing poly (methyl methacrylate) used in this work.

To Brazilian funding agencies REUNI-CAPES, CNPq and FINEP for financial support and infrastructure.

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Received: Sept. 12, 2014 Revised: Feb. 27, 2015 Accepted: Mar. 30, 2015

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http://dx.doi.org/10.1590/0104-1428.1934

Influence of lubricant oil residual fraction on recycled high density polyethylene properties and plastic packaging reverse logistics proposal Harley Moraes Martins1, Juacyara Carbonelli Campos2, Maria José de Oliveira Cavalcanti Guimarães2* and Ana Lúcia Nazareth da Silva3 Instituto Federal do Rio de Janeiro - IFRJ, Arraial do Cabo, RJ, Brazil Departamento de Processos Orgânicos, Escola de Química, Universidade Federal do Rio de Janeiro - UFRJ, Rio de Janeiro, RJ, Brazil 3 Instituto de Macromoléculas Professora Eloisa Mano - IMA, Universidade Federal do Rio de Janeiro - UFRJ, Rio de Janeiro, RJ, Brazil 1

2

*mjg@eq.ufrj.br

Abstract To recycle post-consumer HDPE contaminated with waste lubricating oils, companies include prior washing and drying in the process. This consumes large amounts of water and energy, generates significant effluent requiring treatment.

This study assesses lubricating oil influence on HDPE properties to evaluate the feasibility of its direct mechanical recycling without washing. The current lubricating oil packaging reverse logistics in Rio de Janeiro municipality is also analyzed. HDPE bottle samples were processed with seven oil contents ranging from 1.6-29.4 (wt%). The results indicated the possibility to reprocess the polymer with oily residue not exceeding 3.2%. At higher levels, the external oil lubricating action affects the plastic matrix processing in the extruder and injection, and the recycled material has a burnt oil odor and free oil on the surface. Small residual oil amounts retain the plastic properties comparable to the washed recycled polymer and exhibited benefits associated with the oil plasticizer action. However, oil presence above 7.7% significantly changes the properties and reduces the elasticity and flexural modulus and the plastic matrix crystallinity.

Keywords: HDPE, lubricant oils, properties, reverse logistics.

1. Introduction Plastic materials are presented as the ideal solution for diverse industry segments. The possibilities related to easy molding and handling, durability, low weight, among other characteristics, have consecrated their replacement of other materials. HDPE is a type of plastic present in almost all economic sectors[1], but it is precisely the packaging sector that has highlighted its large capacity to adapt to different types of use[2].

The packaging industry is almost completely dominated by this material type. As in the food industry, cosmetics, soft drinks and many others, the producers of lubricating oil producers also have opted for polymeric materials. In Brazil, about 2% of plastic container sold products are lubricating oils[3]. In this case, the thermoplastic body of the bottle is high density polyethylene - HDPE. Lubricating oils pose an environmental contamination risk and classified as hazardous waste, according to the Brazilian standard NBR 10004/04[4]. The base oil and its additives cause impacts by various pathways: soil, water bodies and air. Lei and Wu[5] stated that a gallon of oil has the potential to contaminate up to one million gallons of drinking water.

Similar to oil, post-consumer automotive lubricant packaging poses an environmental contamination risk, because significant amounts of oil and additives remain in their interior[2,6]. Furthermore, the residual lubricant is

Polímeros, 25(5), 461-465, 2015

hard to remove in the package washing process commonly used in Brazil[7] magnifying the logistic difficulties and economic viability. The oil and its additives impose a toxicity characteristic to the used packaging and makes it a hazardous waste[8]. As such, the measures associated with the contaminated packaging temporary storage, transport and treatment/disposal must conform to strict controls.

These appear in the Brazilian environmental laws (federal, state and municipal) and technical standards, such as ABNT NBR 12.235/92, which deals with hazardous waste storage, ABNT NBR 13.221/10 and ABNT NBR 7500/13, which set guidelines for dangerous products and waste transportation, among others.

In the United States, 20 million gallons of waste oil are disposed into the environment each year and such post‑consumer plastic packaging with oily residue is not accepted in most of the country’s recycling programs[5].

Besides the residual oil important environmental impact in the studied waste classification regarding their potential and logistics system, the oily fraction presence directly affects recycling process operational aspects.

The post-consumed packaging oily presence makes recycling difficult, as it increases the material melt index, and exudes when extruded and after processing. The oily residue affects the recycled artifacts quality causing their deformity. Additionally, processing temperatures above 200 °C

461

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

Martins, H. M., Campos, J. C., Guimarães, M. J. O. C., & Silva, A. L. N. can lead to oily residue thermal degradation, conveying a strong burnt oil odor to recycled plastic[9].

Mechanical plastic recycling is deployed on a large scale in Brazil. Packs with oily residue make mechanical recycling more difficult due to the required decontamination steps[5].

The conventional cleaning processes include significant water and energy consumption reducing the feasibility of lubricant bottle recycling[10]. Therefore, an environmentally and economically feasible oily residue cleaning method is a challenge.

Martins studied the influence of variables such as temperature and bottle position in the HDPE post-consumer lubricant packaging decontamination process by gravitational flow. This focused on the oil collector apparatus structural characteristics and proposed practices to maximize oily waste removal and minimize energy consumption[11].

The technical literature presents various cleaning techniques with aqueous and non-aqueous solvents as well with supercritical fluids, as a package pre-recycle treatment step. However, all techniques are considered expensive, and generate additional waste, preventing reverse logistics of such wastes[5].

This study aims to simplify the automotive lubricant plastic packaging conventional mechanical recycling process by excluding the associated decontamination steps (washing, drying and effluent treatment). The study evaluates HDPE packaging mechanical and thermal properties having been reprocessed with different lubricating oil amounts to establish the limits for direct recycling (without washing).

Furthermore, the study also shows the feasibility process for an efficient reverse logistics.

2. Experimental 2.1 HDPE post-consumer bottle processing Cleaned and dried lubricating oil bottles were collected from gas stations and then fragmented in a mill, Primotécnica model Knives Mill LP 1003 5HP. 600g of fragmented bottles were blended with known amounts of semisynthetic BR LUBRAX TECHNO lubricating oil (SAE 15W / 40 Flash Point 236 °C Viscosity index 133) (Table 1).

It is important to emphasize that samples prepared with post-consumer HDPE packaging with different lubricating oil content were representative of results obtained in field research made in 56 gas stations in Rio de Janeiro State Municipality[11]. The values of 1.6%, 2.4% and 3.2% Table 1. Recycled HDPE/ lubricating oil compositions.

Composition H0* H1 H2 H3 H4 H5 H6 H7

Oil mass (g) 0 10 15 20 50 100 200 250

Oil Content (wt%) 0 1.6 2.4 3.2 7.7 14.3 25.0 29.4

* Virgin lubricating oil bottle from COSAN supplier.

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simulate residual oil supply drainages of 90%, 92% and 95%, respectively. Values of 7.7% and 14.3% correspond respectively to minimum and average oil remaining values​​ after drainage found in the field research. Contents of 25% and 29.4% correspond to residue supply, according to the literature[5] and residue supply average value according to field research in 56 gas stations.

The compositions were processed in a twin-screw co-rotating extruder (TeckTril, model DCT-20) with 20 mm diameter and a 36 length to diameter (L/D ratio).The temperature profile was 90 °C /140 °C /160 °C /160 °C /170 °C /170 °C /180 °C /190 °C /200 °C /210 °C. The sample feed rate in the extruder was 30rpm and the rotational screw speed was 200 rpm. The extruded filaments were immediately quenched in water at the die exit and later pelletized in a granulator and then dried in the oven at 60 °C. Injected samples were obtained with a linear screw temperature profile between 170 °C and 210 °C from the rear to the injection nozzle with a mold temperature of 30 °C. The injection and back pressures were 1400 bar and 450 bar, respectively, and the injection speed was 26 cm3/s. An Arburg 270S machine produced Type I samples, according to ASTM D638.

The compositions were characterized regarding the melt flow index (ASTM D1238-13) in a Dynisco Instruments model LMI 4000, at 190 °C/2,16 kg. The mechanical properties (tensile: ASTM D638-10, flexural: ASTM D790‑10, procedure A) were determined in an EMIC Universal Testing machine with speeds of 25 mm / min (tensile) and 14 mm / min (flexural).

The impact tests, Izod method with notch were conducted according to ASTM D256-10 in CEAST equipment with a 2J pendulum. The differential scanning calorimetric (DSC) analyses were performed on a TA Instruments model Q1000 in the temperature range from 30 °C to 200 °C, heating rate of 10 °C / min under nitrogen flow of 30 ml / min.

The crystallinity degree was determined using the enthalpy of fusion of 100% crystalline HDPE which is 293 J / g.

3. Results and Discussion The processing was easily performed with oil content compositions up to 2.4 wt%. For higher oil content compositions, the processing became more difficult. This behavior probably occurred due to the friction reduction between the polymer melt and extruder screw.

During the shearing that occurs in processing, the lubricant molecules can migrate, being deposited on the machine walls / screw, with a release film formation between the extruder and the polymeric mass causing the polymer melt slip[12] . The same behavior was observed during the injection process in the sample production for characterization tests. Table 2 shows the results of the melt flow index of post-consumer HDPE bottle obtained with different lubricating oil amounts.

A moderate increase in MFI values can be observed compared to a virgin lubricating oil bottle, while in H5, H6 and H7 samples, significant MFI values modification occurred, exceeding a 100% oil content increase from 14.3%. This fact prevents any potential recycling processes, and directly affects the blow molding process due to the difficulties associated with the “parison” formation.

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Influence of lubricant oil residual fraction on recycled high density polyethylene properties and plastic packaging reverse logistics proposal The residual oil influence in the recycled HDPE mechanical properties is displayed in Tables 3 and 4. Based on the samples tensile and flexural tests results, it appears the measured parameter values (elastic and flexural modulus) were progressively reduced as the oil content increased.

This behavior strengthens the interpretation that the lubricating oil has a plasticizing effect on the polymeric matrix.

Plasticizers are inserted between the resin macromolecules, favoring slippage and molecular mobility, affecting the mechanical properties[13,14]. The plasticizing effect is associated in general with an increase in elongation and a tensile strength and elastic modulus decrease[12].

In tests (tensile and flexural), reductions in modules and the stress yield had greater impact on the oil content samples equal to or higher than 7.7%. The variation has exceeded 76% in the relation between the Young modulus case for a sample with 29.4% of oil in comparison with the pure material value.

Considering these results and potential recycled HDPE applications, it is possible to conclude that direct packaging processing with oily residue levels equal to or higher than Table 2. Melt flow index of recycled post-consumer HDPE / Lubricating oil bottles.

Sample H0 H1 H2 H3 H4 H5 H6 H7

Oil Content (wt.%) 0 1.6 2.4 3.2 7.7 14.3 25.0 29.4

MFI (g/10min) 0.32 ± 0.08 0.37 ± 0.08 0.37 ± 0.02 0.41 ± 0.06 0.48 ± 0.09 0.70 ± 0.05 1.02 ± 0.09 1.34 ± 0.18

the composition represented by H4 could produce much lower stiffness resins than those commonly used in the market, compromising their marketing and use. Candian studied recycled HDPE use and set the limit of 547 MPa for Young’s modulus for structural applications[15]. The H0 control sample reached this value as also the compositions H1, H2 and H3. The other compositions (H4, H5, H6 and H7) presented values below ​​ 453 MPa for this parameter.

As previously mentioned, the technical literature has few evaluations of HDPE lubricating oil bottle applicability.

Only a patent was found presenting a method to produce composites based on recycling HDPE containers contaminated with lubricating oil (around 3 wt.%) and cellulosic fibers, to improve its mechanical properties[5].

The impact resistance values of various compositions are shown in Table 5. The experimental data shows the impact resistance slightly increased in the H4 sample, and was more pronounced in the H5, H6 and H7 samples. The H6 and H7 samples did not break under the test conditions.

The impact resistance increase, especially in samples with oil content equal to or higher than the H5 sample, proved the oil plasticizing action, which increases the polymer matrix free volume and leads to an increase in the material’s ability to absorb energy[12].

Table 6 displays the results for melting temperature (Tm), enthalpy of fusion (ΔHm) and crystallinity degree (Xm) of seven compositions of recycled HDPE / lubricating oil bottles.

When comparing the results for each HPDE sample, a reduction trend can be seen in the Tm value with increasing oil content. The Tm value decrease confirmed the lubricating oil plasticizing effect. The plasticizers increase the macromolecules mobility and reduce their melt temperatures. Thus, the Tm

Table 3. Tensile and impact strength data of recycled HDPE / Lubricating oil bottles.

Sample

Oil Content (wt%)

Young Modulus

0 1.6 2.4 3.2 7.7 14.3 25.0 29.4

(MPa) 750 (± 21.4) 671 (± 6.1) 623 (±15.1) 599 (± 26.0) 435 (± 9.3) 315 (±11.9) 200 (±10.3) 178 (±10.9)

H0 H1 H2 H3 H4 H5 H6 H7

Stress at Yield (MPa) 22.0 (± 0.5) 21.5 (± 0.2) 20.9 (± 0.3) 20.6 (± 0.3) 18.4 (± 0.3) 15.8 (± 0.4) 12.2 (± 0.3) 11.4 (± 0.4)

Impact Resistence (J/m) 156.1 (± 5.4) 155.3 (± 2.6) 155.4 (± 7.4) 155.5 (± 3.4) 159.1 (± 4.8) 179.8 (± 6.2) ND* ND*

* Not determined under the studied test conditions.

Table 4. Parameters of Flexural Tests of Recycled HDPE / Lubricating oil Bottles.

Sample H0 H1 H2 H3 H4 H5 H6 H7

Polímeros, 25(5), 461-465, 2015

Oil Content (wt%) 0 1.6 2.4 3.2 7.7 14.3 25.0 29.4

Flexural Modulus (MPa) 711.5 (±17.6) 666.0 (±13.4) 661.6 (±5.7) 573.9 (±5.2) 482.3 (±16.4) 416.0 (±23.1) 317.5 (±13.5) 310.7 (±4.3)

Flexural Offset Yield Strength (MPa) 22.03 (± 0.5) 20.91 (± 0.8) 20.51 (± 0.1) 18.58 (± 0.3) 16.81 (± 0.6) 14.48 (± 0.7) 10.70 (± 0.4) 9.50 (± 0.3)

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Martins, H. M., Campos, J. C., Guimarães, M. J. O. C., & Silva, A. L. N. Table 5. Impact resistance data of recycled HDPE / Lubricating oil bottles.

Sample H0 H1 H2 H3 H4 H5 H6 H7

Oil Content (wt%) 0 1.6 2.4 3.2 7.7 14.3 25.0 29.4

Impact Resistence (J/m) 156.1 (± 5.4) 155.3 (± 2.6) 155.4 (± 7.4) 155.5 (± 3.4) 159.1 (± 4.8) 179.8 (± 6.2) ND* ND*

* Not determined under the studied test conditions.

Table 6. Thermal parameters of recycled HDPE/ Lubricating oil bottles.

Sample H0 H1 H2 H3 H4 H5 H6 H7

Oil Content (wt.%) 0 1.6 2.4 3.2 7.7 14.3 25.0 29.4

Tm (°C)

ΔHm (J/g)

Xm (%)

132.4 132.0 131.9 131.2 131.2 130.3 129.9 127.1

209.2 202.7 191.0 187.0 166.6 160.5 153.9 135.5

71.4 69.2 65.2 63.8 56.9 54.8 52.5 46.2

value reduction with increased oil content was interpreted as the molecular fraction interference of lubricating oil dispersed in the polymer matrix. The polymer crystalline phase high molecular motion leads to less perfect crystals and a lower crystallinity degree, facilitating an easier melt process[16].

The thermal analysis results, in particular the clear reduction trend in the samples’ crystallinity degree with increased oil content, were in accordance with the mechanical tests results. The crystallinity degree reduction causes an elastic modulus decrease and an increase in the material ductility[17].

3.1 Analysis of current reverse logistics of lubricating oil plastic packaging Field research conducted by Martins[11,18] demonstrated that, despite compulsory federal law requirements, the reverse logistics system of automotive lubricant plastic bottles practiced in Rio de Janeiro municipality has significant shortcomings with regard mainly to systematic oily fraction separation from the plastic waste and bottle temporary storage, with direct consequences on the recycling process viability, cost and safe transportation. Field research evidence was collected and proves the only reverse logistics program of this waste type operating in Brazil (Jogue Limpo), presents several operational and logistical problems with direct economic impact and environmental feasibility of the system.

The actual system of logistics considers the lubricating oil bottle transportation without residual oil removal or, in the best case, the post-consumer bottles are taken to an oil collector apparatus, commonly called “dripping”, for the gravitational drainage of the waste. The mobile oil collector is a metallic funnel with a small inclination to the 464

horizontal. This structure contributes to poor drainage done at collection points: the bottles remain in the apparatus, often “laying” or very slightly inclined and, consequently, with little oil drainage effect. Furthermore, the lack of definitions - practice currently developed – such as the minimum draining time and the best bottle position during the residual oil gravitational separation process and also the lack of suitable bottle protection media also provoke waste disposal losses.

In the case of post-consumer lubricating oil bottles with oily residue, companies include washing and drying steps which consume large amounts of water and energy, as well as generating significant effluents to be treated. In addition, the excessive residual oil presence hampers the recycling process, causing deformity and a burnt oil odor in the final artifact. These factors have made the activity unfeasible for some recyclers. To recycle such waste and be attractive to entrepreneurs, an effective collection system is necessary, associated with the plastic waste separation from oil contaminant.

Barriers associated with the plastic bottle transport system indicate bottle fragmentation at the lubricating oil point of sale can bring several logistical, environmental and economic benefits associated with the increased material bulk density, for example, a significant collecting trip reduction and smaller material temporary storage area.

Finally, the analyses indicate the urgency to reengineer the reverse logistics system and to suggest the deployment of lubricant packaging decontamination in more appropriate gravitational drainage equipment; fragmentation at the generator point to facilitate material storage and transportation and direct polymer recycling without the washing step.

4. Conclusions Direct mechanical recycling (without washing) of post‑consumer lubricating oil bottles is an alternative to increase the feasibility of this waste type reverse logistics.

For this technology to be technically and economically feasible, a methodology is necessary to effectively remove the residual oily fraction from the bottles, for the final waste not to compromise the reprocessing, and especially not significantly alter the recycled plastic properties.

Reprocessing HDPE post consumer bottles is feasible with lubricating oil content up to 3.2%. In larger quantities, the lubricant oil external action affects the plastic matrix processing in the extrusion and injection processes, and the recycled material presents a burnt oil odor and free oil on the surface. The HDPE properties with small processed lubricant oil amounts are comparable to the recycled polymer after decontamination by washing, without ​​ any prejudice related to the automotive oil plasticizing action.

However, the presence of more than 7.7% of lubricant oil alter the recycled HDPE properties, significantly reducing, for example, the elasticity modulus (flexural and tensile), and the plastic matrix crystallinity degree.

5. Acknowledgements The authors thank FAPERJ (EXTPESQ Project - 2012E-26/111 531/2012) for their financial support.

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Influence of lubricant oil residual fraction on recycled high density polyethylene properties and plastic packaging reverse logistics proposal

6. References 1. Associação Brasileira da Indústria Química - COPLAST/ ABIQUIM. (2014, January). São Paulo. Retrieved in 8 January 2014, from http://www.abiquim.org.br/resinastermoplasticas/ default.asp 2. Xavier, L. H., Cardoso, R., Matos, R. M., & Adissi, P. J. (2006).

Legislação ambiental sobre destinação de resíduos sólidos: o caso das embalagens plásticas pós-consumo. In XIII Simpósio de Engenharia de Produção (pp. 1-11). Bauru: UNESP. 3. Programa Jogue Limpo. (2014, March). Retrieved in 3 March 2014, from http://www.programajoguelimpo.com.br/index. php 4. Brasil. Ministério do Meio Ambiente - MMA. (2013). Relatório do Ministério do Meio Ambiente para o Conselho Nacional do Meio Ambiente (CONAMA). Óleo lubrificante usado ou contaminado. Brasília. Retrieved in 7 March 2014, from http://www.mma.gov.br/port/conama/processos/174D441A/ Apres_OLUC_Zilda.pdf 5. Lei, Y., & Wu, Q. (2009). WO 2009/079273 A2. Composites made of thermoplastic polymers, residual oil, and cellulosic fibers. Retrieved in 23 January 2014, from http://www.google. com/patents/WO2009079273A2?cl=en 6. Brasil. Ministério do Meio Ambiente - MMA. (2011). Plano nacional de resíduos sólidos: versão preliminar. Brasília.

Retrieved in 12 February 2014, from http://www.mma.gov.br/ estruturas/253/_publicacao/253_publicacao02022012041757. pdf 7. Kishi, S. A. S. (2008). Conheça a reciclagem de embalagens de óleo lubrificante. Revista das Águas, 2(5). Retrieved in 15 March 2014, from http://midia.pgr.mpf.gov.br/4ccr/sitegtaguas/ sitegtaguas_5/reciclagem.html 8. Federação das Indústrias do Estado de São Paulo - FIESP. (2007). Reciclagem de embalagens plásticas usadas contendo óleo lubrificante. São Paulo: FIESP. Retrieved in 13 November 2013, from http://www.fiesp.com.br/indices-pesquisas-epublicacoes/reciclagem-de-embalagens-plasticas-usadascontendo-oleos-lubrificantes-2007/

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9. Pires, A. S. (2004). Reciclagem de frascos plásticos de postos de gasolina. Rio de Janeiro: Núcleo Interdisciplinar de Estudos Ambientais e Desenvolvimento - NIEAD/UFRJ. 10. Martins, H. M. (2005). A destinação final das embalagens de óleo lubrificante: o caso do Programa Jogue Limpo (Master’s dissertation). Universidade Estadual do Rio de Janeiro, Rio de Janeiro.

11. Martins, H. M. (2014). Análise do cenário atual e desenvolvimento de metodologia para otimização da logística reversa de embalagens de lubrificantes automotivos pós-consumo (Doctoral thesis).

Universidade Federal do Rio de Janeiro, Rio de Janeiro.

12. Rabello, M. S. (2000). Aditivação de polímeros. São Paulo: Artliber.

13. De Paoli, M. A. (2008). Degradação e estabilização de polímeros. São Paulo: Artliber.

14. Parente, R. A., & Pinheiro, L. M. (2008). Plásticos reciclados para elementos estruturais. Cadernos de Engenharia de Estruturas, 10(47), 75-95. Retrieved in 20 April 2014, from http://www. set.eesc.usp.br/cadernos/nova_versao/pdf/cee47_75.pdf 15. Canadian, L. M. (2007). Estudo do polietileno de alta densidade reciclado para uso em elementos estruturais (Master’s dissertation). Universidade de São Paulo, São Carlos.

16. Santos, A. S. F., Freire, F. H. O., Costa, B. L. N., & Manrich, S. (2012). Sacolas plásticas: destinações sustentáveis e alternativas de substituição. Polímeros: Ciência e Tecnologia, 22(3), 228237. http://dx.doi.org/10.1590/S0104-14282012005000036.

17. Pradella, J. G. C., Terence, M. C., Miranda, L. F., & Pereira, N. C. (2010). Estudo das propriedades mecânicas e térmicas do polímero poli-3-hidroxibutirato (PHB) e de compósitos PHB/pó de madeira. Polímeros: Ciência e Tecnologia, 20(1), 65-71. http://dx.doi.org/10.1590/S0104-14282010005000011.

18. Martins, H. M., Nascentes, A. L., Guimarães, M. J. O. C., & Campos, J. C. (2015). Management of lube oil container: a review. Revista Teccen, 6(1), 13-19. Retrieved in 20 April 2015, from http://www.uss.br/pages/revistas/revistateccen/V6N12015/ pdf/002-Gerenciamento_de_embalagens_de_lubrificantes.pdf Received: Sept. 19, 2014 Revised: May 12, 2015 Accepted: June 19, 2015

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http://dx.doi.org/10.1590/0104-1428.1974

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High shear dispersion of tracers in polyolefins for improving their detection Valérie Massardier1*, Molka Louizi1, Elisabeth Maris2 and Daniel Froelich2 UMR 5223 Ingénierie des Matériaux Polymères, Centre National de la Recherche Scientifique – CNRS, Institut National des Sciences Appliquées de Lyon – INSA Lyon, Villeurbanne, France 2 Laboratoire Conception Produit Innovation, Chambéry, Arts et Métiers ParisTech, Savoie Technolac, Le Bourget du Lac, France

1

*valerie.massardier@insa-lyon.fr

Abstract An efficient recycling of end-of-life products is of crucial interest from an economical and ecological point of view.

However, the near infrared spectroscopy often used for the optic sorting processes is limited because of the absorption of carbon black present in black plastics and as it only sorts as a function of chemical formulas. The tracing technology developed in this study is based on the dispersion of lanthanide complexes particles into polymers to give them a code that can be related to their formulation and viscosity that are important parameters for their re-processing. As the success of this technology is conditioned by achieving a fine dispersion of the tracer particles, we also focus on accomplishing a fine dispersion of tracer particles by using a high shear process. Processing under high shear rate (N= 800 rpm) has proved to play a determining role in dispersing finely and homogenously tracer particles within PP matrix. Thanks to the good quality of dispersion, the detection of three tracers at a level of 0.1 wt% has been successfully achieved, even in black matrices for an acquisition time of 10 ms.

Keywords: tracers, polyolefins, automated sorting, UV fluorescence, high shear extrusion, recyclability.

1. Introduction The plastics success is owing to their attractive performances, inexpensive, durable materials, lightweight, recyclable, as well as adjustable properties depending on their formulation[1]. Polyolefins[2] represent a very important family of polymers, constituting more than a third of the total plastics demand in Europe.

Recycling of post-consumer products requires their sorting that is often based on sink and float separation.

This technique allows the separation of shredded plastics according to their densities[3] but is not very efficient for separating plastics and formulations that have very close densities, such as HDPE, LDPE, PP, etc.

In addition to the existing automated sorting systems mentioned above, tracing technologies based on tracer systems can be used to refine the sorting of end-of-life products, especially those having close densities or black ones. The tracer signature is also relevant to increase the selective sorting of end-of-life products by providing a signature for polymer type and grade in complex mixtures.

Tracing technologies consist in adding small amounts of tracer into plastics during the compounding process. The tracer is expected to emit a signature detectable by either magnetic or NIR detectors, UV, X-ray fluorescencespectrometry, etc. Several studies have been conducted to apply and evaluate the efficiency of tracing technologies.

In the earlier 90’s, Ahmad[4] and Simmons et al.[5] have used a tracer system to ensure a high speed positive sorting of plastic bottles. By combining three fluorescent tracers dispersed in polymers, it was possible to detect their signature

by UV-spectroscopy and thus identify PEHD bottles. This

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technique was also successfully applied for identification of HDPE, LDPE, PP, EVA, PVC and PET polymers. In addition, the chosen tracers were compatible and chemically non-reactive with the matrices, did not affect the plastics transparency but were poorly detected in black plastics. In their study, Corbett et al.[6] have also shown the efficiency of UV-spectroscopy to detect luminescent phosphor based molecules in white polymers for the separation of waste polymers. Other researches[7,8] have confirmed the effectiveness of tracing technologies for enhancing the sorting of shredded wastes by simple use of flame retardants (FR) as tracers and identifying them by X-ray fluorescence spectrometry (XRF). Moreover, the near-infrared technique (NIR) can be used to detect the fluorescence of tracers based on rare earths with concentrations ranging from 0.001 to 1 ppm in polymers. However, this method has shown its limitation to detect a signal when the matrix is black because the carbon black used as colorant significantly absorbs all of the rays in the NIR[9].

All the above tracing techniques based on optical spectrometry have reached their limits for the tracer detection in black plastics. In fact, carbon black strongly absorbs in the ultraviolet, visible and near infrared regions and thus reduces the tracer detection. To overcome these technological limitations, Froelich et al.[10] have proposed a comparative study on the advantages and limits of spectrometric techniques (Table 1) used for the detection of tracer systems. As a result of this study, they pointed out that the priority candidate polymers for tracing are those recognized as difficult to sort with the existing physico-chemical or optical sorting technologies.

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High shear dispersion of tracers in polyolefins for improving their detection Table 1. A comparative study of the detection techniques used for detecting a tracer system[10].

Detection technique High speed identification.

Limits Higher quantities of tracer for dark plastics than for white.

Tracer concentration: (30-100 ppm)

Fluorescence of the polymer matrix.

Near Infrared

High speed identification.

Mid Infrared XRF

Tracers’ identification in dark plastics.

Tracers’ identification in dark plastics.

Clean surface detection.

Unsuitable for the identification of tracers in dark plastics.

Unsuitable for high-speed identification.

(X-ray fluorescence)

High speed identification. Volume detection.

Magnetic detection

Sensitivity lack with the additives contained in plastics. Proven Only useful for binary discrimination. and established technology.

Requirement of high quantity of tracers.

UV

Advantages

They are essentially polymers that are dark-colored and have the same densities. Bezati et al.[11-14] have shown that the X-ray fluorescence allows the detection of few tracers, while the magnetic detection is applied for the detection of only one tracer. Furthermore, the X-ray fluorescence detection which is a volume detection, can be a reliable method for high speed identification and sorting of black plastics into different families and grades. Moreover, the tracers adapted for the XRF detection process are the elements belonging to Mendeleyev’s Periodic Table (Yttrium (Y), Cerium (Ce), etc.) and with concentration levels of about 500 ppm or less. Nevertheless, the drawback of this study is that the choice of tracers is limited by Mendeleyev’s Periodic Table elements which are neither present in polymers nor in their additives.

The choice of tracers with UV signal seems to be more opened and Lambert and Hachin[15,16], Maris et al.[17] have shown that tracers (T1 and T2), at percentages lower than 250 ppm were detected in white and black colored PP and ABS by UV fluorescence spectrometry as the identification technique, even after ageing standard tests.

The idea of tracing polymers for recycling seems to have potential benefits, especially to increase not only selective sorting of black colored polymers but also sorting as a function of viscosity and composition. As regards the criteria for the choice of tracers, they must be stable at processing temperatures (extrusion or injection molding conditions), non reactive, non-hazardous, non-toxic to the environment and human life, stable at climatic conditions in particular to UV radiations, non-expensive (with cost less than 0.06 €/kg) to facilitate their implementation in the industrial process. In addition, with regard to their detectability, tracers must have strong signal intensity, low fluorescence lifetime and well distinguished peaks to avoid overlap with other elements even in the presence of pigments and carbon black. Regarding the detection system, it must have a high detection rate per second, be able to identify rapidly tracers contained in grinded plastics (black or white) with sizes of about 20 mm, singly or in any combination at very high speeds (10 ms).

The quality of detection is strongly related to the dispersion of tracers that often depends on the choices of extrusion parameters (screw profile and speed, etc). As regards the influence of twin-screw extrusion conditions, measurable Polímeros, 25(5), 466-476, 2015

Number of tracers limited by the Mendeleyev’s Periodic Table

extrusion characteristics were found to be of critical importance to find relationships between extrusion process, morphology development and finally polymer blends properties. In this field, different pioneering works have been carried out few years ago in twin screw extruders[18,19]. Recently, high shear processes[20-23] have proved to be an effective way for polymer blending. For example, high screw speed can give rise to the development of nanostructured blends with properties impossible to reach with classical processing techniques (twin-screw extruder, internal mixer, etc.). Concerning high shear extrusion, Louizi et al.[24,25] and Bouaziz et al.[26] have recently shown that the final morphology of polymer blends is significantly influenced by extrusion parameters such as mean residence time and screw rotation speed.

Moreover, the specific mechanical energy “SME”, which characterizes the extrusion process (with parameters such as torque, temperature, rotation speed, and throughput), can be correlated with the quality of the final product.

As outlined above, processing under high shear flow can provide strong shear stress on an extruded material by simple adjustment of screw rotation speeds, and thus improve the fragmentation and dispersion of tracer particles in polymer blends. Therefore, in this study, we investigate the effect of extrusion (variation of speed for a screw profile dedicated to dispersion of fillers) on the morphological development, thermal, mechanical as well as optical properties of a traced polyolefin formulation.

2. Experimental Part 2.1 Materials The materials investigated in this study are commercial grades used in the automotive and electrical & electronic fields: i) PP108MF97 is a white high impact polypropylene, also named (PP108 MF 97), manufactured by Sabic, made of 78 wt % isotactic PP and 22 wt % ethylene-propylene-rubber random copolymer (EPR), does not contain carbon black, its melt flow index MFI is 10 g/10 min under 2.16 kg at 230°C and its specific gravity equals 0.915 g/cm3; ii) BMU 133 is a black polypropylene copolymer provided by Exxon Mobil Chemicals. It contains 10% mineral filled elastomer, shows a melt flow index MFI = 15 g/10 min under 2.16 kg at 230°C and a specific gravity of 0.970 g/cm3.

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Massardier, V., Louizi, M., Maris, E., & Froelich, D. Three fluorescent tracers (T1, T2 and T3) were tested and belong to the inorganic family of the lanthanide complexes. T1 is an aluminium barium magnesium oxide, T2 is a doped aluminium and barium oxide, T3 is a doped vanadium trioxide. These tracers do not chemically react with the materials and were provided by the start up Tracing Technologies. They are thermally stable at high temperatures, compatible with the REACH regulations.

Their essential feature is that when they are excited with a UV source between 300 and 400 nm, they fluoresce in the visible light spectrum.

2.2 Preparation of traced blends All traced blends are prepared with a co-rotating twin screw-extruder (TSE) Leistritz ZSE 18 HP. The screw profile, with a screw diameter of 18 mm and a L/D ratio of 60, used for all the experiments is illustrated in Figure 1.

The originality of this extruder lies on reaching high shear rates on extruded blends by adjusting the screw rotation speed. In addition, this technique has proven to be a key to the preparation of well-dispersed silica nanofillers within polypropylene matrix. We extrapolate these results to achieve a fine dispersion of tracers within PP matrix. Indeed, a good dispersion of the tracer is required for a good detection by UV spectrometry. The chosen rotation speeds are set to 300, 800 and 1200 rpm. These screw rotation speeds from 300 to 1200 rotations per minute correspond to shear rates ranging from 220 to 750 s–1 calculated thanks to Ludovic software[27]. The extrusion temperature and the feed rate (Q) are 200°C and 3 kg/h, respectively. The tracer concentration in all samples is 0.1% by weight. For each processing condition, the mean residence time is evaluated by adding one coloured pellet into the hopper. The melt temperature at the die exit is measured by introducing a thermocouple into the bulk extrudate (Table 2). These experimental parameters are determined in order to find a relationship between the extrusion process and the final properties of traced blends.

Table 2. Experimental processing parameters.

Screw speed (rpm) 100 800 1200

Maximal shear rate

Melt temperature

(s–1) 140 500 750

(°C) 210 231 252

Mean residence time (s) 85 55 48

At the die exit of the extruder, the extrudates are pelletized and then moulded at 200°C through a Battenfeld 350 PLUS injection moulding machine. Standard tensile and rectangular bars are produced for mechanical tests.

2.3 Characterization of tracers’ dispersion and structure The structure of tracers and their dispersion in the selected polymers were investigated by Scanning Electron Microscopy (SEM) using a Hitachi S800 model at an accelerating voltage of 30 kV. Prior to observations, samples were cryo-fractured in liquid nitrogen to avoid any plastic deformation.

2.4 Mechanical tests Tensile tests of the prepared blends were determined by means of an Instron machine MTS 2/M tester, at a crosshead speed of 30 mm/min at room temperature. Impact tests were performed by means of a Zwick D7900 Type 5102-100/00 instrument in compliance with standard ISO 179 on notched specimens conditioned at –22°C for 48h. All the reported values are averages of ten experimental results to check reproducibility.

2.5 Thermal properties The thermal properties of blends before and after UV irradiation were carried out by differential scanning calorimetry using DSC Q10 of TA instruments. To perform these tests, samples were cut into pellets and placed in aluminium pans. A scan was performed from 10 to 200°C, further maintained for 2 min at 200°C to erase the thermal history of the blends and then cooled down from 200°C to 10°C. The heating and cooling rate was fixed at 10°C/min.

The degree of crystallinity, χC, was calculated considering a melting enthalpy of 209 J/g for a 100% crystalline polypropylene.

2.6 Detection of tracer signature by UV fluorescence spectrometry The detection of the tracers’signal for the traced blends was performed by UV fluorescence spectrometry.

The laboratory apparatus used is a UV fluorescence spectrometer Horiba Jobin Yvon type Fluomax. A 150 W Xenon lamp emits photons with broad energy spectrum in the range [250-900 nm] (Figure 2). The photons reach the excitation monochromator which selectively transmits light

Figure 1. Screw configuration of the co-rotating high shear extruder.

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Polímeros, 25(5), 466-476, 2015

High shear dispersion of tracers in polyolefins for improving their detection of a wavelength in a band centered on the specified excitation wavelength. The light is reflected at specific angle to the sample and then transmitted to emission monochromator.

The photomultiplier signal amplifies the signal and accounts the number of photons in count per second.

Grating, sensor mirrors lenses, beam splitters have a response that depends on the wavelength and must be subtracted to the signal. The acquisition of a corrected spectrum is necessary to characterize a new component and for quantum yield measurements. The excitation spectrum is between 240 and 600 nm and the emission spectrum between 290 and 850 nm.

The number of photons emitted is counted and averaged for each wavelength referring to the integration time (IT).

Part of the signal is due to noise (dark count: distortion of the detector signal) and is substracted. Arbitrary unit is used for the intensity measurement.

The experimental features are excitation wavelength: 325 nm, integration time: 0.1 s, excitation/emission

monochromator slit i) for black polymer: 0.59 mm/0.23 mm, ii) for white polymers: 0.23 mm/0.04 mm.

In order to validate the UV-ray fluorescence measurements, the criteria that must be taken into account are the following: eliminate the Rayleigh scattering with a filter, search for a linearity perimeter between the intensity of the signal and concentration, validate an excitation wavelength allowing discrimination between the fluorescence of the tracers and that of the matrix. Finally, the intensity of the tracer’s fluorescence signal must be greater than three times the one of the white matrix signal standard deviation in order to be validated.

Moreover, the features of the fluorescence emission are the intensity and the relative standard deviation (RSD).

The intensity of tracer signal must be significantly higher than the signal of the instrument and the polymer fluorescence.

The relative standard deviation (RSD) gives information about the dispersion of the tracers for the same average surface analyses.

Since the UV spectroscopy is a surface detection method, 20 measurements are carried out on the exposed surface.

3. Results and Discussions 3.1 Characterization of the dispersion and structure of T3 tracer

Figure 2. Scheme of the spectrometer. The source (a) is a Xe lamp of 150 W, emitting from 240 to 850 nm. The beam enters an excitation monochromator (b) and exits as a UV monochromatic light. The beam reaches the sample with a 60 degree incidence angle. The reflected light on the sample (c) is composed of fluorescence lines and Rayleigh scattering. Then, a high-pass filter with a 370 nm cut-off wavelength is added before an emission monochromator (b’) and a photomultiplier (e).

After validating the detection of fluorescent tracers by using UV-fluorescence spectrometry, it is another aim of this study to achieve a fine and homogenous dispersion of tracers within two PP matrices. Indeed, an efficient dispersion of tracer particles is of great importance since it may not only improve their detection but also lead to enhanced mechanical properties of traced blends[14,28].

Before proceeding to the characterization of tracer’s dispersion, in the first instance, it was appropriate to examine the structure of T3 tracer which was delivered in micrometer powder. A concise analysis was carried out by Scanning Electron Microscopy (SEM) to evaluate its structure.

As clearly seen from SEM micrographs taken at different magnifications (Figure 3), the T3 powder is organized

Figure 3. SEM image of the micrometric T3 tracer as received.

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Massardier, V., Louizi, M., Maris, E., & Froelich, D. in form of sticks which aggregate together to form large agglomerates. In order to separate these agglomerates into finer particles, it is necessary to apply strong forces. That is why a high-shear extruder is used for preparing traced blends. This recent generation of extruder is of scientific importance and possesses a profound prospect in industrial applications: it facilitates the dispersion of fillers in matrices thanks to strong shear forces by simply adjusting the screw rotation speed without any additive[29,30].

To highlight the high shear effect, the micrographs displayed in Figure 4a and b depict the morphologies of traced blends ((PP108 MF 97-T3-0.1) and (BMU133-T3-0.1)) as a function of the screw speed, respectively 100 rpm (a) and 800 rpm (b).

For the traced blends (PP108 MF97-T3-0.1) processed under low shear rate (100 rpm), numerous agglomerates of T3 tracer are seen on SEM micrographs (Figure 4a) with sizes ranging from 2 to 5 µm inducing agglomeration problems as well as heterogeneous distribution. This can be ascribed to the inadequacy of the applied shear rate (i.e. 220 s–1) during compounding to break agglomerates into finer ones. Interestingly, by increasing the screw rotation speed up to 800 rpm, the size of tracer agglomerates is reduced to less than 80 nm and a homogeneous dispersion of these

particles is achieved, leading to decreased distances between particles. (Figure 4b). This finer dispersion is due to the high shear stresses (from 220 to 550 s–1) applied on the tracer agglomerates and resulting in their division into finer ones within PP matrices. Such an effect was recently observed by other authors[31,32]. They showed that the rotation speed increase, which mainly controls the shear conditions during extrusion, has a high influence on the dispersion of fillers.

As regards the black colored traced polymer (BMU133-T3-0.1), it is not easy to distinguish tracers in form of particles or agglomerates. Apparently, the presence of other additives such as mineral fillers and carbon black contained in BMU 133 polymer can mask the T3 tracer.

3.2 Mechanical properties By means of SEM observations, it is shown that the increase of screw speed greatly impacts the dispersion of tracer particles within the polyolefin matrices; consequently, the mechanical properties should also be influenced. Indeed, a homogenous and fine dispersion of fillers induces an improvement of the mechanical properties of materials, such as poor dispersion as well as presence of agglomerates that lead to structural defects. To evaluate the effect of adding tracers on the mechanical properties of traced polymers as a

Figure 4. Morphologies of PP108 MF 97-T3- 0.1 traced blends extruded at (a) 100 rpm and (b) 800 rpm.

Table 3. Mechanical properties of PP108 MF 97 and BMU 133 polymers as received and their traced blends processed at various screw speeds.

Samples PP108 MF 97-reference (W) PP108 MF 97-T3- 0.1 (100 rpm) PP108 MF 97-T3- 0.1 (800 rpm) PP108 MF 97-T3- 0.1 (1200 rpm) BMU133-reference (B) BMU133-T3- 0.1 (100 rpm) BMU133-T3- 0.1 (800 rpm) BMU133-T3- 0.1 (1200 rpm) BMU133-T2- 0.1 (100 rpm) BMU133-T2- 0.1 (800 rpm) BMU133-T2- 0.1 (1200 rpm)

E

σm

εb

(MPa) 450± 10 470±10 440±08 280±04 420±10 453±05 410±08 283±07 461±04 430±08 245±02

(MPa) 20 ±10 19 ±05 20 ±06 19 ±04 13±03 12±05 13±06 12±02 12±01 13±08 11±05

(%) 530± 04 480± 10 570± 05 410±10 187±10 106±20 251±10 145±10 136±03 224±02 132±08

Impact Strength (kJ/m2) 8±01 6±02 14±01 9±01 7±01 6±01 12±01 8±01 7±02 11±02 6±01

W: white polymer; B: black polymer.

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High shear dispersion of tracers in polyolefins for improving their detection function of screw rotation speeds (100, 800 and 1200 rpm), tensile stress (σm), tensile modulus (E), elongation at break (εb) and impact strength are investigated and summarized in Table 3.

As reported in Table 3, on one hand, the addition of tracer particles to the selected polymers induces a slight increase of Young’s modulus from 20 to 40 MPa, compared to PP matrix. This increase is not significantly important and can be induced by the reinforcing effect of tracer particles.

Furthermore, the elongation at break decreases for all traced polymers processed at 100 rpm. This decrease must be related to the extended agglomeration of tracer particles as observed earlier in Figure 4. These tracer agglomerates can act as stress concentrators, initiate the specimen fracture and cause mechanical failure points. On the other hand, it can be observed that by increasing the screw speed up to 800 rpm, the elongation at break and impact strength values of traced formulations are close to the ones of the polymers as received, as extrusion at screw speed of 800 rpm significantly increases the mechanical properties of neat PP/EPR[23]. Similarly, Louizi et al.[25] have shown that the increase of screw speed leads to higher mechanical energy (SME), which quantifies the level of energy transferred to the blends by mechanical input during extrusion[24,33].

They have shown that the breakup of agglomerates (such

as silica ones) in a PP matrix is favoured by high shear rates and results in a greater dispersion of the fillers.

For polymer blends, Teyssandier et al.[23] have observed improved elongation at break and impact strength values for polyamide 12 (PA12)/plasticized starch blends processed at high-shear rates. This improvement is attributed to very fine dispersion of starch particles in the PA12 matrix.

Nonetheless, all the traced blends processed at 1200 rpm reveal a noticeable reduction in mechanical properties owing to the degradation of the PP polymer chains resulting from all the thermal and mechanical history experienced by the polymer blends during the process[34,35].

Obviously, by examining the experimental processing parameters reported in Table 2, it can be noted that the increase of the screw speed from 800 to 1200 rpm induces self heating leading to a sharp increase of the extruder exit temperature from 232 to 252°C as well as a slight decrease in mixing time from 55 to 48 s. Thus, processing under high shear rate (800 rpm) plays a determining role in dispersing finely and homogenously the tracer particles within PP matrix; this is fundamental for the conservation or even enhancement of the mechanical properties of the traced blends.

Figure 5. Crystallization (a) and melting (b) peaks of BMU 133 with T3 tracer.

Table 4. Thermal properties and crystallinity degrees (obtained by DSC and TGA) of PP108 MF 97 and BMU 133 polymers as received and their traced blends processed at various screw speeds.

Samples PP108 MF 97-reference (W) PP108 MF 97-T3-0.1-100 rpm PP108 MF 97-T3-0.1-800 rpm PP108 MF 97-T3- 0.1-1200 rpm BMU133-reference (B) BMU133-T3- 0.1-100 rpm BMU133-T3-0.1-800 rpm BMU133-T3-0.1-1200 rpm BMU133-reference (B) BMU133-T2- 0.1-100 rpm BMU133-T2- 0.1-800 rpm BMU133-T2-0.1-1200 rpm

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Tm

∆Hf

Tc

ΔHc

Xc

(°C)

(J/g PP)

(°C)

(J/g PP)

(%)

167.5 168.1 167.8 166.7 168.2 167.5 167.1 167.4 168.2 168.4 167.2 168.5

53.3 55.2 58.3 55.8 51.2 53.7 55.2 54.4 51.2 55.8 57.1 54.8

132.3 131.7 132.3 132.5 124 125 124 124 124 124 124 123

58.8 60.7 63.4 62.2 57.1 59.3 62.4 59.1 57.1 60.3 63.2 58.3

25.5 26.4 27.8 26.7 24.5 25.7 26.5 26.0 24.5 26.6 27.3 26.2

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Massardier, V., Louizi, M., Maris, E., & Froelich, D. 3.3 Thermal properties The effect of adding T3 and T2 tracers on the thermal properties of traced blends processed at various screw speeds were analyzed by differential scanning calorimetry (DSC) and thermogravimetric analyses under nitrogen (Figure 5 and 6). Table 4 summarizes the results, listing the melting/crystallization temperatures as well as crystallization/ melting enthalpies of traced blends. In addition, the temperature at maximum weight loss (Tmax) which is defined at the peak of the derivative of the TGA curves has been measured (Table 4). Whatever the screw rotation, the addition of tracer particles at a concentration of 0.1% to the black or white PP matrix does neither affect their melting nor their crystallization temperatures.

Nevertheless, at N=800 rpm, the tracer particles seem to increase slightly the crystallinity degree of PP, which suggests that added particles may behave like centers of germination and nucleation. Such a behavior was already observed by Liu et al.[36] who found that fine powders of rare earth oxides may act as nucleators and influence the growth rate of polypropylene spherulites. The study of Xiaomin et al.[37] shows that the addition of 1 wt % of yttrium oxide (Y2O3) as a tracer acts as a nucleating agent and increases the crystallinity degree of the investigated polymer. However, recently, Bezati et al.[11,14] have shown that the dispersion of 0.1% cerium oxide to a PP matrix, under classical extrusion conditions, does not influence the thermal properties.

Thus, extrusion at a high screw speed of 800 rpm (Table 4) seems to improve the dispersion of our fillers that can act as nucleating agents able to increase the cristallinity degree.

However, TGA reveals that the variation of screw rotation does not affect the thermal stability of the traced blends (Figure 6).

3.4 Detection of tracers using UV-fluorescence spectrometry The first objective is to show the three fluorescent tracers are detected in both white and black polyolefin matrices.

The excitation wavelength is the same for each tracer.

The three fluorescence emission wavelengthes correspond to green, blue and red colours (Figure 7). Fluorescence emission spectrum of T3 displays several peaks characteristic of rare earth complexes with peak width of about 5 nm at its base. T1 and T3 tracers both display one peak with peak width of about respectively 50 and 100 nm at their base.

The fluorescence lifetime is of about 10-3 s for lanthanide complexes and of about only 10-9 s for organic tracers.

The commercial tracers (T1, T2 and T3) were primarily selected on the basis of their good excitation wavelength in the [310-370 nm] spectral band range as well as of their fluorescence emission band signatures in the visible band range of the spectrum. As shown in the spectra, the signature of each tracer, at concentration rates of 0.1wt%, is clearly visible and distinguishable from the “background” sample.

It seems that the signal of the T3 tracer is more intense than those of T1 and T2 tracers. The T3 tracer is very interesting for the rest of the study because, as its signal intensity is the most important, it can be added to the polymer matrix in less than 1000 ppm, down to 30 ppm as was already verified by laboratory equipments. In what follows, we have focused the experiments on blends with T3 and T2 tracers at 1000 ppm concentration to analyze their influence on the final properties of traced blends. As T3 does, tracers can display several peaks, which can facilitate their detection.

Inorganic tracers often present finer peaks than inorganic ones, which are more easily distinguishable from the polymer fluorescence peaks.

Figure 6. TGA curves of PP108 MF 97-T3-0.1 traced blends processed at different screw speeds (100, 800 and 1200 rpm).

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High shear dispersion of tracers in polyolefins for improving their detection Table 5b. Measured values of UV-detection of traced black blends containing T3 or T2 tracers (BMU 133-T2-0.1 and BMU 133-T30.1) processed at 800 rpm.

Traced blends (800 rpm) Average Fluorescence intensity (AFI) Standard deviation (SD) Relative standard deviation (RSD)

BMU133-T2-0.1

BMU133-T3-0.1

1.9 E+06

1.1 E+06

4.1 E+05

2.6 E+05

21%

22%

N = 800 and 1200 rpm displays lower relative standard deviation for the measurements of fluorescence intensity compared to the traced blends processed at 100 rpm. This is ascribed to the fine dispersion of tracer particles within the PP matrix obtained when processing at high shear rates. As the conservation of mechanical properties and good detection of tracers are two necessary conditions for the success of the tracing technology, in what follows, the UV-detection is achieved only for samples processed at 800 rpm. In fact, the processed samples at 1200 rpm show failures in mechanical properties (Table 3).

As 800 rpm is a good compromise for both detection and maintenance of mechanical properties, the BMU 133 based black formulation has been processed at this rate and the detection of both T2 and T3 is good.

Figure 7. Spectra of virgin black BMU 133 with T1, T2, T3 tracers at concentrations of 1000 ppm.

Table 5a. Measured values of UV-detection of traced white blends (PP108 MF 97-T3) processed at various screw speeds.

Traced blends PP108 MF 97-T3-0.1-100 rpm PP108 MF 97 -T3-0.1-800 rpm PP108 MF 97-T3-0.1-1200 rpm

AFI1 4.8 E+07

SD2 9.3E+06

RSD3 19%

5.8 E+07

8.1E+06

14%

6.1 E+07

8.5E+06

14%

1: Average Fluorescence Intensity. 2: Standard Deviation. 3: Relative Standard Deviation.

3.5 Study of the relation between dispersion and detection of tracers Since the shear rate exerted during melt mixing has shown a significant influence on the dispersion as well as on the distribution of tracer particles, the average fluorescence intensity should also be enhanced. From Table 5a, it can be observed that the processing of traced blends at Polímeros, 25(5), 466-476, 2015

As clearly shown in Table 5b, the average fluorescence signal of black traced blends is less intense than for white ones.

The signal is attenuated by the presence of carbon black, but the signal/noise ratio is sufficiently high for the detection to be positive. It is worth noting that the dispersion of 0.1 wt% of T2 or T3 tracer in the PP copolymer containing 1 wt% of carbon black is more difficult to accomplish compared to the white PP because of lower fluidity of the black colored formulation. When processing at 800 rpm, the relative standard deviation of fluorescence intensity of BMU 133-T2-0.1 and BMU133-T2-0.1 is higher (respectively around 21% and 24%) compared to the white PP108MF97-T3-0.1 (14%).

4. Conclusion Based on this research, high shear process (800 rpm) has proved to play a determining role in dispersing finely and homogenously tracer particles within PP matrix.

Such an effect is fundamental for the conservation of mechanical properties of traced blends and for enhancing the detection of tracers. Interestingly, it appears that the concept of tracing polymers could be a key for the high speed identification and automated on-line sorting of black plastics into different families and grades. The detection of three tracers (T1, T2 and T3) at a level of 0.1 wt% in black matrices was successfully achieved through the use of UV-ray fluorescence spectrometry. In conclusion, this research contributes to the improvement of the recyclability of white and black-coloured polymers and can be applied also for polymers having similar densities. Furthermore, it can be used as a guideline for tracing polymers to increase the rate of automatic sorting.

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5. Acknowledgements The authors would like to thank the National Research Agency (ANR) for its contribution to the funding of this work and for providing industrial orientations and scientific supervision to the research. Authors also wish to acknowledge P. Alcouffe and the ‘‘Centre de Microstructures et d’analyses, plateforme Lyon 1” of the University Lyon 1 for his assistance in the SEM characterization and valuable discussions.

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Received: Nov. 12, 2014 Revised: Apr. 09, 2015 Accepted: May 25, 2015

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Abbreviations

ABS: Acrylonitrile Butadiene Styrene resins

DSC: Differential Scanning Calorimetry

EVA: Ethyl Vinyl Acetate copolymer

FR: Flame Retardant

LDPE: Low Density Polyethylene

HDPE: High Density Polyethylene

NIR: Near Infra Red

PET: Poly(ethylene terephtalate)

PP: Polypropylene

PS: Polystyrene

PVC: Poly(Vinyl Chloride)

RSD: Relative Standard Deviation

SEM: Scanning Electron Microscopy

UV: Ultra Violet

χC: Crystallisation Degree

476

XRF: X-Ray Fluorescence

Polímeros, 25(5), 466-476, 2015

http://dx.doi.org/10.1590/0104-1428.2030

High density polyethylene and zirconium phosphate nanocomposites Adan Santos Lino1, Luis Claudio Mendes2*, Daniela de França da Silva2 and Olaf Malm1 Laboratório de Radioisótopos Eduardo Penna Franca, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro – UFRJ, Rio de Janeiro, RJ, Brazil 2 Instituto de Macromoléculas Professora Eloisa Mano, Universidade Federal do Rio de Janeiro – UFRJ, Rio de Janeiro, RJ, Brazil

1

*lcmendes@ima.ufrj.br

Abstract Nanocomposite based on high density polyethylene (HDPE) and layered zirconium phosphate organically modified with octadecylamine (ZrPOct) was obtained through melt processing. The ZrPOct was synthesized by precipitation and modified by suspension and sonication procedures. The initial and maximum degradation temperatures (Tonset and Tmax) were increased. A slight decrease of crystallinity degree was detected. Reduction of elastic modulus and elongation at break were noticed. The lamellar spacing was increased (3.3 times higher). The storage modulus decreased and low field nuclear magnetic resonance (LFNMR) revealed an increasing of molecular mobility. The presence of octadecylamine enhanced the entrance of HDPE in the ZrPOct galleries. Several characteristics of HDPE were changed indicating that intercalation was successful. All results indicated that partially intercalated and/or exfoliated nanocomposite was achieved.

Keywords: nanocomposite, HDPE, layered zirconium phosphate.

1. Introduction Over the past two decades great advances in nanotechnology emerged, which is considered a promissing technology of the 21st century. Great potential for innovations that increase the economic prosperity and sustainable development are expected[1,2]. Recent study indicates that nanocomposites occur naturally through synergistic effect as found in nacre (the outer layer of pearls) consisted of proteins, polysaccharides and nanometric layers of calcium carbonate (CaCO3). To produce advanced materials, researchers are investigating and trying to adjust natural composites to their level of structural control and properties[3]. The addition of fillers enhances mechanical, thermal and barrier properties of the composites[4,5]. Synthetic nanocomposites have been prepared with various polymers and montmorillonite (MMT) is the most common filler used. In turn, the use of layered zirconium phosphate (ZrP), an inorganic and synthetic filler, in the formation of a nanocomposite results in a material with higher aspect ratio, purity and surface energy advantages in relation to MMT[6,7].

The polyethylene family is diversified. High density polyethylene (HDPE) and linear low density polyethylene (LLDPE) are marked members. Although they are produced by Ziegler-Natta and metalocenic catalyst they are homopolymer and copolymer, respectively. HDPE is a homopolymer obtained by coordination polymerization of ethylene gas. Its polymeric chains are linear and constituted by the catenation of ethylene mers. LLDPE is a copolymer obtained by coordination polymerization of ethylene gas with an alpha-olefin (propylene, butane, hexane, etc). It is considered a branched polymer once its polymeric chains are constituted by mers of ethylene and mers of alpha-olefin (propylene is commercially more common). As a consequence

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of those branching in LLDPE, its properties differ a lot from those presented by HDPE For instance, the density, degree of crystallinity, melting temperature and Young’s modulus are quite different[8]. High-density polyethylene (HDPE) is a semicrystalline polymer with many advantages – low density, strong tenacity, high resistance to impact, abrasion and corrosion. Additionally, inertia to the majority of chemicals, low toxicity and long lifetime contribute for large industrial applications[9]. Nanoparticles of silicalite-1 were used with HDPE. Rheological and physical properties were investigated. The authors observed slight effect on the melting temperature, onset degradation temperature and decreasing of intensity of HDPE diffraction peaks[10]. It was found that ultrasonic treatment enhanced the intercalation of HDPE into lattice layers of clay by increasing d-spacing up to 50%[11]. Impact strength, modulus, and flexural strength of HDPE/exfoliated graphite nanocomposites were compared to others types of reinforcement (glass fibers and carbon black). Polymer nanocomposites from HDPE/exfoliated graphite were equivalent in flexural stiffness and strength to HDPE composites reinforced with glass fibers and carbon black[12]. Synergistic effect introduced by nanoparticles of nano-CaCO3 and OMMT in HDPE was reported[13,14] inferred that a higher degree of exfoliation for nanosized clay particles is key to enhancing the rheological, mechanical, and flame retarding properties even when small amounts of clay (less than 1%) are used.

Considering that it was not found scientific article related to nanocomposite of HDPE and zirconium phosphate modified with long-chain amine, the aim of this work was to investigate the influence of the intercalation of octadecylamine inside ZrP galleries on the HDPE characteristics. Through

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Lino, A. S., Mendes, L. C., Silva, D. F., & Malm, O. thermal, crystallographic, thermo-mechanical, tensile and molecular mobility analyses the formation of intercalated and/or exfoliated nanocomposite was evaluated.

2. Materials and Methods 2.1 Materials High-density polyethylene (HDPE) – melt flow index of 0.35 g/10 min and density of 0.960 g/cm3 – was provided by Braskem (Triunfo, RS, Brazil). Phosphoric acid, zirconium oxychloride and octadecylamine were purchased (Aldrich Co.).

2.2 Synthesis of layered zirconium phosphate The ZrP was synthesized by direct precipitation method[15]. An 12M phosphoric acid solution (H3PO4) and zirconium oxychloride were mixed in the proportion of P/Zr = 18. The system was kept under agitation and reflux at 110 °C, for 24 hours. After that, the resulting material was centrifuged (3400 rpm for 30 min) and washed successively with deionized water in order to obtain neutral pH and absence of chloride[16-18]. The resulting solid was placed in a freezer at –80 °C for 24 hours and then submitted to lyophilization for 4 days.

2.3 Modification of the layered zirconium phosphate The ZrP was modified by intercalation of amine according to the experimental procedure[19,20]. A certain amount of α-ZrP and a solution of octadecylamine (2:1 alcohol/water) were mixed at an amine/α-ZrP molar ratio of 1.5. The product was centrifuged and washed successively with alcohol to remove the excess of amine. As before, the resulting solid was placed in a freezer at –80 °C for 24 hours and then submitted to lyophilization for 4 days. The final product was labeled as ZrPOct.

2.4 Preparation of nanocomposites Nanocomposites of HDPE and layered zirconium phosphates – neat and organically modified with octadecylamine – with a fixed phosphate percentage of 2% w/w, were processed in a counter-rotating twin-screw extruder. The extruder was adjusted to operate at 100 rpm and temperature profile of 160 °C (input) and 170 °C, 180 °C and 190 °C (output), conditions recommended by the polymer manufacturer. The extrudate was cooled and granulated. In order to homogenize the nanocomposite, the material was reprocessed under the same conditions. In order to characterize the material, thin plates was processed in Carver press at 210 °C, with load of 5000 kg for 7 minutes.

2.5 Characterization 2.5.1 Low field nuclear resonance magnetic (LFNMR) The relaxation time of the HDPE and nanocomposites, H low-field nuclear magnetic resonance (1HLFNMR) analysis was carried out in a Maran Ultra 23 low-field NMR device.

The relaxation time (T1) was measured in time intervals of 10 seconds and 20 points, at 27 °C. The result was expressed in terms of domain curves.

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2.5.2 Dynamic-mechanical analysis (DMA) Dynamic-mechanical analysis (DMA) was carried out in a TA Instruments Q800 instrument, using rectangular specimens with dimensions of 8x 1x 0.1 cm, scanning from –150 to 100 °C, heating rate of 2 °C/min and frequency of 1 Hz, in the single-cantilever mode. The storage modulus (E’), the loss modulus (E’) and loss tangent (tanδ) were determined.

2.5.3 Wide angle X-ray diffraction (WAXD) The WAXD was performed in a Rigaku Miniflex diffractometer, employing CuKα radiation with wavelength of 1.5418Å and Ni filter, at a voltage of 30kV and current of 15mA, with 2θ between 2-35°. From the diffractograms it was identified the crystallographic planes and calculated the interlamellar spacing, using Bragg’s equation.

2.5.4 Thermogravimetry (TGA) The thermal stability was evaluated in a TA Instruments Q500 thermogravimetric analyzer. The thermogravimetric curves were obtained between 30 and 700 °C, at 10 °C/min, under a nitrogen atmosphere. The temperatures of initial, maximum and final degradation (TINICIAl, TMAX and TFINAL) were determined as well the residue.

2.5.5 Differential scanning calorimetry (DSC) The calorimetric properties were proceeded using a TA Instruments Q1000 differential scanning calorimeter (DSC). Three thermal cycles were applied. At first, the sample was heated from 40 to 200 °C at 10 °C/min under a nitrogen atmosphere and then kept for 2 minutes in order to eliminate the thermal history. Following, it was cooled to 40 °C at 10 °C/min. Finally, a second heating cycle was carried out under the same conditions as the first. The melting temperature (TM) was measured considering the curve plotted from the second heating cycle. The crystallization temperature (TC) was determined when possible. The melting enthalpy (ΔHM) was used to calculate the crystallinity degree (XC), considering the melting enthalpy of the 100% crystalline HDPE (290 J.g–1) and corrected regarding the HDPE content.

2.5.6 Tensile measurements Stress-strain test was performed by using an Instron model 5569 universal testing system, according to the ASTM D 638 with a 10-kN load cell and testing velocity of 10 mm/min.

The parameters assessed were the elastic modulus, stress and elongation at break and stress and elongation at yield.

The results were expressed considering the mean of five test specimens.

2.5.7 Flowability The effect of the zirconium phosphate nanoparticles on the HDPE melt flow rate (MFR) was analyzed using a Dynisco plastometer following the ASTM D 1238, at 190 °C, 2.16 kg and melt time of 240 seconds.

3. Results and Discussions 3.1 Hydrogen low field nuclear magnetic resonance Hydrogen NMR allows obtaining information on sample organization, heterogeneity and particle dispersion.

The relaxation data are important to understand the changes in Polímeros, 25(5), 477-482, 2015

High density polyethylene and zirconium phosphate nanocomposites the molecular structural organization and molecular dynamic of nanocomposites. Solid-state 1HNMR spectroscopy is sensitive enough to assess the different chain mobilities in polyethylene[21]. Semicrystalline polyethylene is composed of domains with widely different polymer chain mobilities.

In the crystalline domain, the chains are highly ordered and can only be reoriented very slowly. In contrast, in noncrystalline domains the polymer chains have high mobility. Table 1 shows the T1H values and the respective % of domain for the samples. For all the materials, it was not observed notorious displacement of peaks. Figure 1 shows the domain curves of the HDPE and composites. The relaxation curve of the HDPE revealed two domains. At relaxation times shorter than 400,000 s, one of them appeared, attributed to the chain mobility in the amorphous phase, while a second peak was detected at higher relaxation times concerning the rigid region – amorphous chains constricted among HDPE lamellae and crystalline phase – the latter normally being responsible for controlling relaxation process. The absence of relaxation times related to the filler in the composite domain curves is an important indication that good dispersion and filler/ polymer interaction has occurred, according to Tavares et al.

[22] and Mendes et al.[23].

Figure 1. 1HLFNMR domain curves of HDPE and composites.

3.2 Dynamic-mechanical test The tanδ curves (Figure 2) and Table 2 showed that the addition of ZrP – modified or not – promoted no influence in glass transition temperature (Tg) of the polymer. It was also observed a decrease in storage and loss modulus.

Octadecylamine or stearylamine [CH3-(CH2)17-NH2] is a long chain amine produced from the chemical reduction of stearic acid. Its chemical structure possesses a hydrocarbon chain with seventeen methylene groups. The HDPE polymer chain is constituted by catenation of thousands ethylene groups (two consecutive methylene groups bonded).

The presence of methylene groups in the chemical structure of both should provide strong interaction between HDPE and octadecylamine. It is worth to explain the role of the octadecylamine as modifier of the zirconium phosphate (ZrP) structure. The ZrP is a lamellar crystalline inorganic material which has poor interaction with polymers (organic material). For improving the interaction of ZrP with polyolefins its lamellar structure was organically modified with octadecylamine through acid/base reaction. The presence of octadecylamine between the galleries of ZrP resulted in the lamellae separation – d-spacing of ZrP was increased – and enhanced its organophilic characteristics. Such chemical modification facilitates the entrance of HDPE chains inside of the ZrPOct galleries. Due to the chemical structural similarity with HDPE chains the octadecylamine played a role as plasticizing for polyolefin resulting in decreasing of HDPE storage modulus (E’).

3.3 WAXD Figures 3, 4 and 5 show the diffractograms and Table 3 presents diffraction angle and d-spacing of the materials.

HDPE diffraction angles occurred at 2θ=22.21º and 2θ=24.52º as reported in literature[24]. The diffraction angle equivalent to basal spacing of the ZrP occurred at 2θ=12° with an interlamellar distance of 7.32 Å. In HDPE/ZrP, the diffraction angle of ZrP remained constant but the Polímeros, 25(5), 477-482, 2015

Figure 2. Tan Delta curves of the materials.

Table 1. NMR data of HDPE and composites.

Sample

T1H (ms)

T1H Domain (%)

19.68 388.13 16.60 356.43 21.43 356.43

12.46 87.54 12.50 87.50 13.00 87.00

HDPE HDPE/ZrP HDPE/ZrPOct

Table 2. DMA data of HDPE and composites.

Sample Tg (°C) Loss Modulus (E”) at Tg point (MPa) Storage Modulus (E’) at Tg point (MPa) Tanδ

HDPE –102

HDPE/ZrP –102

HDPE/ZrPOct –102

267

235

219

4690

4104

3915

0.057

0.057

0.056

interlamellar spacing decreased (d=7.25 Å) attributed to loss of water in the interlamellar layer by Costantino et al.[6].

In the presence of HDPE, the diffraction angle of ZrPOct decreased from 4.1 to 3.9° while the interlamellar spacing increased from 21.55 to 23.88 Å. It was also observed a slight shift of the HDPE diffraction planes to small angles 479

Lino, A. S., Mendes, L. C., Silva, D. F., & Malm, O. (from 22.21 to 21.7º and 24.52 to 23.9º. The changes could be attributed to the intercalation of the HDPE along the ZrPOct interlamellar layers. It can deduce that partially intercalated and/or exfoliated nanocomposite was achieved.

3.4 Thermogravimetry Table 4 shows the TGA data of the materials. The TONSET, TMAX and TFINAL of HDPE and HDPE/ZrP were very similar indicating that a microcomposite was produced. It is currently disseminate that the increasing of thermal stability in polymeric nanocomposites is attributed to layered filler. The lamellae – intercalated or exfoliated – act as barrier to the release of volatile products during degradation[15,25]. All thermal properties were higher for HDPE/ZrPOct indicating that a partially and/or exfoliated nanocomposite was produced.

3.5 Differential scanning calorimetry

Figure 3. WAXD diffractograms of the ZrP and ZrPOct fillers.

The calorimetric data in Table 5 showed that TC, TM and XC of HDPE and HDPE/ZrP were very close. Tm and Xc of HDPE/ZrPOct attained values slightly lower. Particularly, the HDPE degree of crystallinity was reduced as function of octadecylamine linked into the phosphate lamellae.

As mentioned, the amine acted as plasticizing agent of HDPE chain and retarded its crystallization process. It is again evidenced that partially and/or exfoliated nanocomposite was achieved.

3.6 Mechanical measurements Mechanical properties are arranged in Table 6. The elastic modulus increased for HDPE/ZrP and a decreasing was observed for HDPE/ZrPOct. The filler was responsible for decreasing of modulus and also the slight increasing of elongation at break as compared to HDPE/ZrP. The decrease of the Young modulus of the produced nanocomposite probably is also associated to the lower degree of crystallinity, as observed in DSC analysis. Then, it is valid to deduce that a partially and/or exfoliated nanocomposite was produced for HDPE/ZrOct. A decreasing of stress and elongation at break was presented for HDPE/ZrP and HDPE/ZrPOct. Two types of material were produced as function of the type of filler.

In the HDPE/ZrP, the ZrP acted as reinforcement of HDPE and it is deduced that a microcomposite was achieved[26].

Figure 4. WAXD diffractograms of the HDPE and composite HDPE/ZrP.

Table 3. 2θ values and interlayer distances of the materials.

Sample

2 θ (degrees)

d001(Å)

12.00 12.17 4.10 3.90

7.32 7.25 21.55 23.88

ZrP HDPE/ZrP ZrPOct HDPE/ZrPOct

Table 4. TGA data of the materials.

Sample

Tonset (°C)

Tmáx (°C)

HDPE HDPE/ZrP HDPE/ZrPOct

261 270 306

453 453 470

Tfinal (°C) Residue (%) 473 473 486

4.7 3.1 3.1

Table 5. Calorimetric properties of the materials.

Figure 5. WAXD diffractograms of the HDPE and composite HDPE/ZrPOct. 480

Sample

Tc (°C)

Tm (°C)

ΔHa (J/g)

Xc (%)

HDPE HDPE/ZrP HDPE/ZrPOct

115 116 116

134 134 133

208 208 201

72 72 69

Tc= crystallization temperature; Tm= melting temperature in the 2nd heating; ΔHa= melting enthalpy; Xc= degree of crystallinity.

Polímeros, 25(5), 477-482, 2015

High density polyethylene and zirconium phosphate nanocomposites Table 6. Mechanical properties of the materials.

Property/Sample Elongation at break (%) Stress at break (MPa) Elastic modulus (MPa) Elongation at yield (%) Stress at yield (MPa)

HDPE

HDPE/ZrP

HDPE/ ZrPOct

1043±224

216±82

393±81

17.5±0.7 672±33 13.8±0.25 25.6±0.1

14.5±0.9 733±19 12.6±0.60 25.5±0.3

15.4±2.2 623±28 14.4±0.70 26.0±0.7

Table 7. MFR of the materials.

Sample HDPE HDPE/ZrP HDPE/ZrPOct

MFR (g/10min) 0.33±0.03 0.28±0.02 0.27±0.02

For HDPE/ZrPOct the octadecylamine inside of ZrPOct developed a role as plasticizing agent of HDPE. It was responsible for decreasing of modulus and also the slight increasing of elongation at break as compared to HDPE/ZrP. Then, it is valid to to deduce that a partially and/or exfoliated nanocomposite was produced for HDPE/ ZrPOct.

3.7 Melt flow rate MFR values are presented in Table 7. The MFR showed tendency to decrease for HDPE/ZrP and HDPE/ZrPOct. Similar to happen in microcomposites, the fillers provide resistance to flowability of HDPE[27]. The lowest value was found to HDPE/ZrPOct due to the entrance of HDPE chain inside de ZrPOct lamellae. It induced to suppose that a partially and/or exfoliated nanocomposite was reached.

The findings corroborated to those in WAXD and mechanical measurements.

4. Conclusions Alpha-zirconium phosphate was synthesized and modified with octadecylamine in order to produce nanocomposite based on HDPE. According to some conventional characterization techniques of polymers (DSC, TGA, WAXD, MFR, tensile‑deformation) HDPE/ZrP behave as a microcomposite.

On the contrary, presence of octadecylamine as intercalation agent of ZrP allowed the increasing of its interlamellar spacing. Also facilitate the entrance of the HDPE chain along the filler galleries. This produced changes in the HDPE behavior. Decreasing of the (d001) diffraction angle, elastic modulus, degree of crystallinity besides increasing of the interlamellar spacing and thermal stability lead to induce that a partially and/or exfoliated nanocomposite was reached.

5. Acknowledgements This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) e Universidade Federal do Rio de Janeiro (UFRJ). We thank the Instituto de Radioisótopos da UFRJ for drying the lamellar phosphates.

Polímeros, 25(5), 477-482, 2015

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Polímeros: Ciência e Tecnologia, 4(3), 33-37. Retrieved in 12 December 2014, from http://www.revistapolimeros.org.br/ PDF/v4n3/v4n3a03.pdf Received: Dec. 12, 2014 Revised: Apr. 08, 2015 Accepted: July 07, 2015

Polímeros, 25(5), 477-482, 2015

http://dx.doi.org/10.1590/0104-1428.2031

Influência da argila vermiculita brasileira na biodegradação de filmes de PHB Influence of brazilian vermiculite clay in biodegradation of PHB films Rayson de Jesus Araújo1, Isaias Damasceno da Conceição1, Laura Hecker de Carvalho2, Tatianny Soares Alves3 e Renata Barbosa3* Departamento de Engenharia Mecânica, Universidade Federal do Piauí - UFPI, Teresina, PI, Brasil Programa de Pós-graduação em Ciência e Engenharia de Materiais, Universidade Federal de Campina Grande - UFCG, Campina Grande, PB, Brasil 3 Programa de Pós-graduação em Ciência dos Materiais, Universidade Federal do Piauí - UFPI, Campus Universitário Ministro Petrônio Portella, Teresina, PI, Brasil 1

2

*rrenatabarbosa@yahoo.com

Resumo Este trabalho teve como objetivo preparar e avaliar filmes PHB/vermiculita natural e modificada nas quantidades em peso de 1%, 3% e 6% através dos métodos intercalação por fusão e intercalação por solução. Os bionanocompósitos obtidos pelo método intercalação por fusão foram preparados em uma extrusora monorosca e posteriormente os filmes foram moldados via compressão. Na preparação dos filmes por solução, os sistemas foram submetidos à agitação e aquecimento a 80 °C. Os sistemas foram avaliados por difração de raios-X e o comportamento de biodegradação foi avaliado de acordo com a norma ASTM G 160-03. O acompanhamento da biodegradação foi realizado por meio de inspeção visual e perda de massa. Observou-se que o percentual de argila e o método de obtenção dos filmes influenciaram na estrutura formada e na biodegradação dos sistemas.

Palavras-chave: polímeros biodegradáveis, argila vermiculita, ensaio de biodegradação, bionanocompósitos.

Abstract This study aimed to prepare and to evaluate natural and modified PHB /vermiculite films in quantities of 1%, 3% and 6% by weight, through melt intercalation and solution intercalation methods. The bionanocomposites in the form of thin films, obtained by the melt intercalation method, were prepared in a single screw extruder and then molded via compression. In the preparation of the films by solution method, the systems were stirred and heated at 80 °C in the presence of the chloroform solvent. The systems were evaluated by X-ray diffraction and the degradation behavior was evaluated according to ASTM G 160-03, by visual inspection and through weight loss. It was observed that the percentage of clay and the method of obtaining of the films influenced in the structure and biodegradability of the systems.

Keywords: biodegradable polymers, vermiculite clay, biodegradation test, bionanocomposites.

1. Introdução O uso de plásticos sintéticos convencionais, polímeros derivados do petróleo, como material de embalagem é elevado, principalmente por sua disponibilidade, baixo custo e características funcionais, destacando-se as boas propriedades mecânicas, barreira aos gases e compostos aromáticos, e a facilidade de selagem térmica. No entanto, apesar das grandes vantagens dos plásticos sintéticos, seu uso crescente gera preocupação devido a problemas de contaminação ambiental decorrentes do descarte, uma vez que não são biodegradáveis e sua reciclagem consome grandes quantidades de energia térmica. O interesse de manter, ou melhorar, a qualidade dos produtos embalados e, ao mesmo tempo, reduzir o desperdício de embalagens, têm

Polímeros, 25(5), 483-491, 2015

incentivado a exploração de novos materiais de embalagens, como os filmes biodegradáveis formados de matérias-primas oriundas de recursos renováveis[1].

O uso de polímeros biodegradáveis destinados em especial para aplicações em embalagens alimentícias está aumentando consideravelmente, no intuito de reduzir a utilização de recursos não-renováveis e, com isso, impedir também o acúmulo de resíduos plásticos no meio ambiente.

Em paralelo, a indústria de embalagens vem exigindo o desenvolvimento de novas misturas/formulações, processamentos mais simples e diminuição de custo no uso de suas tecnologias[2]. Ao mesmo tempo dessas preocupações

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Araújo, R. J., Conceição, I. D., Carvalho, L. H., Alves, T. S., & Barbosa, R. anteriormente citadas, o consumidor também exige: alta qualidade do alimento e data de validade mais prolongada, além disso, que a embalagem seja transparente para facilitar a visualização do alimento e resistente quanto a contaminação, umidade e oxidação[3].

Os problemas decorrentes da poluição ambiental gerada pelo lixo plástico têm levado a comunidade científica a refletir sobre possíveis alternativas para o problema. Para o gerenciamento da enorme quantidade de lixo plástico produzido pela sociedade, a biodegradação é uma das alternativas que tem sido proposta e atualmente têm sido alçada a uma posição de destaque. A biodegradação consiste na degradação dos materiais poliméricos através da ação de organismos vivos[4].

A American Society for Testingand Materials (ASTM) tem proposto vários métodos de análise e acompanhamento da biodegradação dos polímeros, que consistem em ensaios de biodegradabilidade em exposição a microrganismos por meio de compostos em ambientes aeróbicos e anaeróbicos.

Dentre os métodos propostos pela ASTM se destaca a norma ASTM G 160-03[5] que avalia a susceptibilidade microbiológica de um material não metálico quando em contato com o ambiente natural do solo, e assim, o presente trabalho fundamenta-se nesta norma para a realização da avaliação da biodegradação dos filmes biodegradáveis.

O interesse pelos polímeros biodegradáveis na área de pesquisas científicas manifesta-se pelas propriedades semelhantes que eles possuem em relação aos plásticos convencionais[6].

Assim, existem vários tipos de polímeros biodegradáveis, destacando-se principalmente, o Polihidroxibutirato (PHB) que é produzido naturalmente por bactérias a partir de fontes renováveis de energia, e são biodegradados em alguns meses por uma enorme quantidade de bactérias e fungos presentes na natureza[7]. Porém, por ser produzido por um processo de fermentação bacteriana, ainda é um processo relativamente caro[8].

Os altos custos para produzir o polihidroxibutirato têm levado as empresas a incorporar materiais inorgânicos, como certos tipos de argilas no processo de fabricação, a fim de reduzir esses custos e para melhorar as propriedades do produto final, tornando-o mais competitivo em relação aos plásticos convencionais. Dentre as argilas utilizadas, a vermiculita se destaca por causa de sua propriedade de expandir-se a elevadas temperaturas, tornando-se um material leve, além de que, pode ser encontrada em abundância em algumas regiões no Brasil[9].

O uso de nanocompósitos pode ser uma boa solução tecnológica para melhorar as deficientes propriedades dos materiais para fins de embalagens. As nanopartículas desejadas devem ser recicladas e biodegradáveis[3]. A incorporação da argila vermiculita ao polihidroxibutirato (PHB) proporciona a formação de bionanocompósitos poliméricos. Em geral, os materiais inorgânicos não apresentam uma boa interação com os polímeros orgânicos, assim faz-se necessária a modificação desses materiais inorgânicos, tornando-os organofílicos, para que haja uma melhor interação polímero/argila e dessa maneira melhorar as propriedades dos bionanocompósitos poliméricos[10].

Os bionanocompósitos poliméricos podem ser obtidos através de quatro métodos: Polimerização in situ, intercalação 484

por solução, método sol-gel e intercalação no estado fundido[11].

O método intercalação no estado fundido, é um método rápido utilizado para obtenção dos nanocompósitos, não necessita da utilização de solventes nocivos ao meio ambiente e à saúde, e o processamento ocorre com o mínimo prejuízo para as propriedades do PHB. No método intercalação por solução permite observar o grau de inchamento da argila num determinado solvente.

Levando em consideração os fatores acima expostos, este artigo tem como objetivo principal avaliar a biodegradação de filmes biodegradáveis PHB/argila vermiculita natural e modificada de acordo com a norma ASTM G 160-03.

Os filmes foram obtidos pelos métodos intercalação por fusão e intercalação por solução e, posteriormente, caracterizados por difração de raios-X. O acompanhamento da biodegradação foi realizado por inspeção visual e por perda de massa.

2. Experimental 2.1 Materiais O Polihidroxibutirato (PHB) foi fornecido pela PHB Industrial S/A, São Paulo; a argila pela Mineração Pedra Lavrada, Santa Luzia - PB e o sal de amônio utilizado foi o Praepagen WB® (cloreto de estearildimetil amônio), fornecido pela Clariant, Recife - PE. O clorofórmio utilizado no método intercalação por solução foi fabricado pela Dinâmica Química Contemporânea Ltda. O solo utilizado no teste de biodegradação foi um composto orgânico comercial a base de esterco bovino e de galinha.

2.2 Processo de organofilização da argila O processo de organofilização consistiu no preparo de dispersões contendo concentrações de água destilada, argila e o sal de amônio, conforme métodos propostos por Barbosa et al.[12] e Mesquita[13].

2.3 Método intercalação por fusão Os sistemas foram preparados em uma extrusora monorosca modelo AX-16 da AX Plásticos sob temperaturas variando entre 160 °C, 165 °C e 175 °C, da primeira para a terceira zona, respectivamente, e velocidade de rosca de 50 rpm. Para a obtenção dos filmes biodegradáveis, todos os sistemas foram moldados por compressão em uma prensa hidraúlica MH-08-MN da MH Equipamentos Ltda, sob as seguintes condições: temperatura de 180 °C, carga aplicada de 4 - 4,5 toneladas e durante 20 segundos.

O teste de biodegradação em solo simulado foi realizado segundo a norma ASTM G 160-03[5], por um período de 60 dias. Neste ensaio foram analisados os filmes de PHB puro, os filmes de PHB/Argila Natural (1%, 3% e 6%) e os filmes de PHB/Argila Organofílica (1%, 3% e 6%).

Inicialmente, o solo fértil utilizado no ensaio de biodegradação foi preparado durante uma semana com o acompanhamento do pH e umidade, com o intuito de padronizar as variáveis existentes antes do ensaio de biodegradação, e assim, torná‑lo adequado para o início do ensaio.

Os filmes foram confeccionados com dimensões de 50 mm × 50 mm, conforme a norma ASTM G 160-03 e todas as amostras foram pesadas e identificadas com Polímeros, 25(5), 483-491, 2015

Influência da argila vermiculita brasileira na biodegradação de filmes de PHB o auxílio de fio de naylon e etiquetadas e logo após, enterradas verticalmente para retiradas nos períodos de 15, 30, 45 e 60 dias. Os sistemas foram avaliados em triplicata.

Não foram reportados resultados na 4ª retirada (60 dias), devido o elevado nível de biodegradação, impossibilitando o manuseio com as amostras e consequentemente, gerando imprecisão das medidas.

No intuito de visualizar as modificações macroscópicas foram registradas imagens dos bionanocompósitos com o auxílio de uma câmera digital Sony Cyber-shot DSC-W350 14.0 Megapixels.

Os sistemas foram colocados em uma estufa a uma temperatura de 30 °C (±2 °C) e umidade entre 75 a 95%.

Os testes de pH e umidade foram realizados quinzenalmente para controle das condições ambientais e da qualidade do solo para o ensaio. A água perdida durante o ensaio, devido à evaporação, foi reposta semanalmente, com o auxílio de um borrifador.

2.4 Método intercalação por solução Para a preparação dos filmes pelo método intercalação por solução, o PHB foi previamente peneirado e seco em estufa a 70 °C por 24 horas. Após esse tempo, foi adicionado o solvente e a solução foi agitada para ocorrer o inchamento do polímero. Em seguida, a solução foi submetida à agitação e aquecimento a 80 °C durante 3 horas. Para reduzir a perda do solvente por vaporização, foi montado um sistema de condensação, através de um condensador modelo Allihn.

Para a formação dos filmes de PHB puro e para os filmes dos bionanocompósitos nos percentuais de 1, 3 e 6% de argila vermiculita modificada ou natural, as referidas soluções foram vertidas em placas de mármores, espalhando-se livremente, e em seguida, os filmes foram retirados das placas.

3. Resultados e Discussão 3.1 Difração de raios-X (DRX): intercalação por fusão e intercalação por solução As análises de difração de raios-X foram realizadas na argila organofílica e nos filmes dos bionanocompósitos, a fim de investigar a dispersão das cadeias da argila na matriz polimérica, além de comparar a cristalinidade dos sistemas.

A Figura 1 apresenta os difratogramas da argila vermiculita organofílica (Org) e dos filmes dos bionacompósitos obtidos pela técnica de intercalação por fusão na presença da argila sem modificação (FPHB NAT 1%, FPHB NAT 3% e FPHB NAT 6%), e dos sistemas na presença da argila organofilizada (FPHB ORG 1%, FPHB ORG 3% e FPHB ORG 6%). E a Figura 2 apresenta os difratogramas da argila organofílica (Org) e dos filmes dos bionacompósitos obtidos pela técnica de intercalação por solução na presença da argila sem modificação (SPHB NAT 1%, SPHB NAT 3% e SPHB NAT 6%), e na presença da argila organofilizada (SPHB ORG 1%, SPHB ORG 3% e SPHB ORG 6%).

A argila organofílica (ORG) apresentou espaçamentos basais (d001=45,50 Ǻ, d002=37,72 Ǻ e d003=18,62 Ǻ), possivelmente devido a alguma quantidade de argila não intercalada[14]. Uma explicação seria que o aparecimento de vários espaçamentos basais durante a intercalação parece

O teste de biodegradação dos sistemas também foi realizado segundo a norma ASTM G160-03[5]. Os sistemas foram colocados em um ambiente fechado e mantidos a uma temperatura de 24 °C (±2 °C) e umidade entre 85 e 95%.

Os testes de pH e umidade do solo, foram realizados a cada retirada de amostras para controle das condições do ambiente e do solo para o ensaio. Devido à perda de umidade foi inserido um umidificador, a fim de aumentar a ventilação e circulação de ar no ambiente.

As amostras com dimensões de 50 × 50 mm foram pesadas, identificadas e em seguida enterradas/acondicionadas em solo preparado. Ao final de cada retirada as amostras foram limpas e secas a 23 °C. Os sistemas foram acompanhados quanto à perda de massa e aspecto visual durante 24 dias.

Esse período foi dividido em três retiradas: 06, 12 e 24 dias.

2.5 Difração de raios-X (DRX) Todos os sistemas antes de serem submetidos aos testes de biodegradação foram caracterizados por difração de raios-X em um difratômetro da marca Shimadzu XDR 6000, operando na faixa angular (2θ) entre 1,5° a 30°, utilizando Kα de Cu como radiação incidente, a tensão realizada foi de 40 Kv, corrente 30 mA e passo 0,02° .A varredura foi realizada na superfície dos filme dos bionancompósitos (50 × 50mm) Polímeros, 25(5), 483-491, 2015

Figura 1. Difratogramas da argila organofílica e dos bionanocompósitos obtidos via intercalação por fusão.

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Araújo, R. J., Conceição, I. D., Carvalho, L. H., Alves, T. S., & Barbosa, R. via fusão. Esse comportamento não era esperado para os sistemas produzidos via intercalação por solução, já que a preparação dos mesmos é provida apenas de uma agitação mecânica pouco agressiva, e consequentemente, refletindo numa baixa dispersão da carga, enquanto os sistemas preparados via fusão era esperado uma melhor dispersão, devido ao maior cisalhamento presente na preparação dos bionanocompósitos.

Os difratogramas dos bionanocompósitos obtidos pela técnica de intercalação por fusão (Figura 1) mostraram que as caracteristicas dos picos de PHB foram mantidas[20,21]. Este fato sugere que a estrutura cristalina de PHB não é alterada pela presença das argilas e pelo tipo de processamento[16]. Foi observado comportamento diferente para os bionanocompósitos obtidos pela técnica de intercalação por solução (Figura 2), onde os picos referentes ao PHB apresentaram uma diminuição dos picos ou quase o desaparecimento, fato atribuído a forma de preparo do filme (casting), gerando aspecto mais rugoso e aparência menos homogênea.

3.2 Inspeção visual: método intercalação por fusão

Figura 2. Difratogramas da argila organofílica e dos bionanocompósitos obtidos via intercalação por solução.

está associado à não uniformidade da distribuição dos íons de sódio entre as camadas do argilomineral e a troca seletiva do sódio pelo cátion do sal[15]. Isto provocaria a formação de arranjos diferentes do sal ao longo da superfície do material, com suas moléculas formando camadas laterais, simples ou duplas em algumas regiões, e arranjos estendidos parafínicos, em camada simples ou dupla[16].

Os picos de difração referente as distância interplanar basal da argila foram observados na região de baixo ângulo dos difratogramas para os bionanocompósitos via fusão e por via solução. Para os sistemas preparados pela técnica de intercalação por fusão, contendo argila sem modificação, poucas mudanças aconteceram na estrutura interlamelar da argila, indicando aspecto de um microcompósito. Já para os sistemas a base de argila organofílica, aparentemente ocorreu uma maior intercalação do polímero entre as lamelas da argila, uma vez os picos da argila foram deslocados para ângulos menores e consequentemente, aumentando a distância interplanar basal, indicando a formação de prováveis estruturas intercaladas com tendência à esfoliação[17-19].

Para os sistemas preparados via solução com argila sem modificação, também foram observadas mudanças significativas no padrão de difração, independente do teor de carga adicionado. Enquanto que a presença da argila organofilizada reduziu a intensidade dos picos, de maneira até mais intensa quando comparados aos sistemas preparados 486

A inspeção visual realizou-se por meio de registros de imagens dos filmes após as retiradas, em que é possível verificar as regiões atacadas por fungos e bactérias pela coloração microbiana. Os registros foram analisados antes de entrarem em contato com o solo e ao término de cada período.

Observa-se de uma maneira geral o mesmo perfil de degradação para os filmes preparados pela técnica de intercalação por fusão, independente do tipo de argila (natural ou organofílica). Os sistemas apresentaram manchas esbranquiçadas em toda sua extensão. Resultados semelhantes foram observados por Vanin et al.[22], sendo possível perceber que os microorganismos aderiram à superfície dos filmes biodegradáveis e que as manchas se tornam mais acentuadas com os maiores tempos de exposição. A Figura 3 ilustra o aspecto visual dos sistemas PHB Puro, PHB Nat 1% e PHB Org 1% antes do teste, e para a 1ª, 2ª e 3ª retiradas. É possível observar através das fotografias que os filmes sofreram alterações em sua superfície, conhecidamente segundo Flemming[23], como biodeterioração, que corresponde a um processo interfacial em que os microrganismos atacam e colonizam a superfície do polímero causando modificações superficiais por deposição de material extracelular excretado por eles, acúmulo de água, penetração na matriz com filamentos microbianos, e excreção de pigmentos microbianos lipofílicos que colorem o polímero.

A aparência dos filmes corrobora com os valores de perda de massa que posteriormente serão apresentados, onde verificou-se que os sistemas na presença da argila vermiculita modificada apresentaram menores índices de perda de massa, ou seja, a argila modificada atuou como uma barreira protetora a biodegradação e, consequentemente, apresentando aparência menos desintegrada.

3.3 Inspeção visual: método intercalação por solução A Figura 4 ilustra a aparência dos filmes após a 2° retirada (índice 2) e após a 3° retirada (índice 3), (a) PHB puro, (b, c, d) PHB NAT 1%, 3% e 6% (respectivamente), (e, f, g) PHB ORG 1%, 3% e 6%, respectivamente. Observam-se Polímeros, 25(5), 483-491, 2015

Influência da argila vermiculita brasileira na biodegradação de filmes de PHB

Figura 3. Fotografias dos filmes biodegradáveis PHB Puro, PHB Nat 1% e PHB Org 1% em diferentes tempos em contato com o solo.

Figura 4. Fotografias dos filmes após a 2° retirada (índice 2) e após a 3° retirada (índice 3), (a) PHB puro, (b, c, d) PHB NAT 1%, 3% e 6% (respectivamente); (e, f, g) PHB ORG 1%, 3% e 6% (respectivamente).

Polímeros, 25(5), 483-491, 2015

487

Araújo, R. J., Conceição, I. D., Carvalho, L. H., Alves, T. S., & Barbosa, R. no aspecto nos filmes na segunda retirada, pouco ataque de microrganismos, estando com aparência quase intacta. É possível que, devido ao pouco tempo (12 dias) e a temperatura de 24 °C, os microrganismos tiveram dificuldades para se desenvolverem. Já para os filmes na terceira retirada podemos observar áreas atacadas por microrganismos, com destaque para (b3) PHB NAT 1%, (d3) PHB NAT 6% e (f3) PHB ORG 3% que foram os mais biodegradados, devido maior tempo de exposição ao solo (24 dias). Esse comportamento corroborá com os resultados de perda de massa que serão apresentandos posteriomente.

Como as regiões amorfas degradam mais rapidamente em relação às regiões cristalinas, podemos afirmar que, com a incorporação dos sais na argila, provavelmente melhorou o empacotamento nas cadeias da argila com PHB, ficando assim menos suscetível aos ataques de microrganismos.

De maneira geral, o aspecto visual dos filmes obtidos pelos dois métodos apresentou o mesmo perfil de ataque, independente da concentração de argila, apresentando manchas esbranquiçadas em toda sua extensão. E ainda, ocorreu o aparecimento de manchas escuras em alguns filmes, comprovando a presença dos microrganismos após a realização do ensaio de biodegradação.

o PHB Puro e o PHB Org 1% apresentaram perda de massa de 48,98% e 42,57%, respectivamente.

A Tabela 2 e a Figura 6 apresentam os valores médios para a perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 3% e PHB Org 3% para os mesmos períodos de retiradas mencionados anteriormente. Verifica-se que o PHB Nat 3% apresentou maior perda de massa com 60,89%, enquanto o PHB Puro e o PHB Org 3% apresentaram perda de massa de 48,98% e 24,99%, respectivamente, para os 45 dias de exposição.

A Tabela 3 e a Figura 7 apresentam os valores médios para a perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 6% e PHB Org 6% para os mesmos períodos de retiradas. Percebe-se que o PHB Org 6% apresentou maior perda de massa, para a 1ª e 2ª retirada, enquanto o PHB Puro e o PHB Nat 6% apresentaram perda de massa de 48,98% e 46,36%, respectivamente para 45 dias de exposição ao solo simulado.

A Tabela 1 e a Figura 5 apresentam os valores médios para a perda de massa dos filmes biodegradáveis de PHB Puro, PHB Nat 1% e PHB Org 1% na 1ª, 2ª e 3ª retiradas, correspondendo a 15, 30 e 45 dias de exposição ao solo.

Observa-se que conforme aumenta o tempo em contato com o solo a quantidade de perda de massa do material é maior. Resultados semelhantes foram observados por Casarin et al.[24]. Para 45 dias de exposição, o sistema PHB Nat 1% apresentou maior perda de massa 89,75%, enquanto

Observa-se que os filmes obtidos pelo método intercalação por fusão, na presença e na variação do percentual da argila organofílica, levaram a menores índices de perda de massa, ou seja a argila modificada atuou como uma barreira protetora a biodegradação. A argila organofílica tem duas funções opostas na estabilidade dos bionanocompósitos polímero/argila: uma, é o efeito de barreira exercido pela argila, que pode melhorar a estabilidade a biodegradação e a outra, é o efeito catalítico da argila que pode acarretar a degradação da matriz polimérica diminuindo a estabilidade.

Quando se adicionou pequena fração de argila organofílica na matriz polimérica a dispersão foi favorecida, mas com a adição de níveis elevados dessa argila, o efeito catalítico é predominante e a estabilidade do bionanocompósito foi diminuída[25]. Este mesmo comportamento foi observado para o sistema PHB ORG 6%.

Tabela 1. Perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 1% e PHB Org 1% para diferentes tempos em contato com o solo.

Tabela 2. Percentual da perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 3% e PHB Org 3% em diferentes tempos em contato com o solo.

3.4 Perda de massa: método intercalação por fusão

Amostras PHB PURO PHB NAT 1% PHB ORG 1%

15 dias (%) 1,48 3,46 1,34

30 dias (%) 24,00 34,60 11,25

45 dias (%) 48,98 89,75 42,57

Figura 5. Percentual da perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 1% e PHB Org 1% para diferentes tempos em contato com o solo.

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Amostras PHB PURO PHB NAT 3% PHB ORG 3%

15 dias (%) 1,48 6,21 1,16

30 dias (%) 24,00 20,48 20,70

45 dias (%) 48,98 60,89 24,99

Figura 6. Percentual da perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 3% e PHB Org 3% em diferentes tempos em contato com o solo.

Polímeros, 25(5), 483-491, 2015

Influência da argila vermiculita brasileira na biodegradação de filmes de PHB Tabela 3. Percentual da perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 6% e PHB Org 6% em diferentes tempos em contato com o solo.

Amostras PHB PURO PHB NAT 6% PHB ORG 6%

15 dias (%) 1,48 1,20 5,44

30 dias (%) 24,00 11,25 37,22

45 dias (%) 48,98 46,36 40,46

Figura 7. Variação percentual da perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 6% e PHB Org 6% em diferentes tempos em contato com o solo.

Outra hipótese, é que durante a fase inicial de desintegração, as cadeias de alto peso molecular de PHB são hidrolisadas formando cadeias de baixo peso molecular.

Esta reação pode ser retardada em sistemas contendo argilas organofílicas, que impedem o movimento e a difusão na maior parte do filme[26]. Já para os sistemas contendo argilas não modificadas, foi observada uma maior perda de massa, este fato é explicado devido à presença de sítios ácidos de Lewis nas camadas da argila inorgânica, ou pela presença de água residual e a própria natureza hidrofílica, assim favorecendo a biodegradação[16].

Tabela 4. Perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 1% e PHB Org 1% para diferentes tempos em contato com o solo.

Amostras PHB PURO PHB NAT 1% PHB ORG 1%

06 dias (%) 0,98 0,19 0,23

12 dias (%) 1,07 1,55 0,94

24 dias (%) 10,92 19,26 6,62

Figura 8. Percentual da perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 1% e PHB Org 1% para diferentes tempos em contato com o solo.

Tabela 5. Perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 3% e PHB Org 3% para diferentes tempos em contato com o solo.

Amostras PHB PURO PHB NAT 3% PHB ORG 3%

06 dias (%) 0,98 0,07 0,46

12 dias (%) 1,07 1,22 0,81

24 dias (%) 10,92 3,88 16,23

Os maiores percentuais de perda de massa observados para os sistemas na presença de argila organofílica podem também estar relacionado ao baixo potencial de ação fungicida no sal quaternário de amônio presente na estrutura da argila vermiculita. Os compostos quaternário de amônio são agentes tensoativos catiônicos com boa atividade germicida[27].

3.5 Perda de massa: método intercalação por solução A Tabela 4 e a Figura 8 apresentam os valores médios para a perda de massa dos filmes biodegradáveis de PHB Puro, PHB Nat 1% e PHB Org 1% na 1ª, 2ª e 3ª retiradas, correspondendo a 06, 12 e 24 dias de exposição ao solo.

Figura 9. Percentual da perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 3% e PHB Org 3% para diferentes tempos em contato com o solo.

Observa-se o sistema PHB Nat 1% para 24 dias de exposição apresentou maior perda de massa 19,26%, enquanto o PHB Puro e o PHB Org 1% apresentaram perda de massa de 10,92% e 6,62%, respectivamente.

enquanto o PHB Puro e o PHB Nat 3% apresentaram perda de massa de 10,92% e 3,88%, respectivamente.

A Tabela 5 e a Figura 9 apresentam os valores médios para a perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 3% e PHB Org 3% para os mesmos períodos de retiradas mencionados anteriormente. Verifica-se que o PHB Org 3% apresentou maior perda de massa com 16,23%, Polímeros, 25(5), 483-491, 2015

A Tabela 6 e a Figura 10 apresentam os valores médios para a perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 6% e PHB Org 6% para os mesmos períodos de retiradas. Percebe-se que o PHB Nat 6% apresentou maior perda de massa com 23,33%, enquanto o PHB Puro e o PHB Org 6% apresentaram perda de massa de 10,92% e 2,26%, respectivamente para 24 dias de exposição ao solo simulado.

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Araújo, R. J., Conceição, I. D., Carvalho, L. H., Alves, T. S., & Barbosa, R. Tabela 6. Perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 6% e PHB Org 6% para diferentes tempos em contato com o solo.

Amostras PHB PURO PHB NAT 6% PHB ORG 6%

06 dias (%) 0,98 0,10 0,12

12 dias (%) 1,07 3,77 0,42

24 dias (%) 10,92 22,33 2,26

de vermiculita organofílica ficaram pouco evidentes os ataques de microrganismos.

5. Agradecimentos Os autores agradecem a FAPEPI e ao CNPq pelo apoio financeiro para a realização deste trabalho. Ao Laboratório Interdisciplinar de Materiais Avançados/CCN/UFPI e a UFCG pela concessão do espaço para a realização do procedimento experimental e a PHB industrial pela doação da matriz polimérica.

6. Referências

Figura 10. Percentual da perda de massa dos filmes biodegradáveis PHB Puro, PHB Nat 6% e PHB Org 6% para diferentes tempos em contato com o solo.

Para os sistemas obtidos pelo método via intercalação por solução, foi observado o mesmo comportamento dos filmes obtidos via fusão, ou seja, a presença e a variação do percentual da argila organofílica, promoveram a índices menores de perda de massa, ou seja a argila modificada também atuou como uma barreira protetora a biodegradação e ação fungicida. Com exceção do sistema com 3% de argila organofílica.

4. Conclusões Neste trabalho foi analisada a biodegradação dos filmes PHB Puro, e dos sistemas com 1, 3 e 6% de argila natural e modificada. A diferença nas estruturas dos bionanocompósitos é influenciada pelo método de obtenção, via intercalação por fusão ou solução. Os sistemas foram avaliados de acordo com a norma ASTM G 160-03. Foi observado para todas as amostras, conforme aumenta o tempo em contato com o solo, aumenta também a quantidade de perda de massa do material.

O ensaio de biodegradação mostrou-se viável, visto que é um processo adequado, ou seja, os microrganismos estão em ambiente propício para seu desenvolvimento e nutrição.

Nos resultados obtidos pelo método intercalação por fusão, o filme biodegradável PHB Nat 1% apresentou a maior perda de massa, com 89,75%, em relação aos outros filmes submetidos ao ensaio de biodegradação. Assim, observa-se que o percentual de argila vermiculita natural e os períodos de retiradas influenciaram na deterioração do material. Pelo método intercação por solução, podemos afirmar que as composições de PHB com vermiculita natural foram as mais atacadas por microrganismos, com destaque para a composição PHB Nat 6%. Já para os filmes 490

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Enviado: Dez. 14, 2014 Revisado: Jan. 13, 2015 Aceito: Maio 04, 2015

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http://dx.doi.org/10.1590/0104-1428.2059

T Desenvolvimento e caracterização de filmes compósitos de quitosana e zeólitas com prata T Development and characterization of chitosan/silver T zeolites composite films T Patricia Hissae Yassue-Cordeiro , Cassio Henrique Zandonai , Classius Ferreira da Silva e T Nádia Regina Carmargo Fernandes-Machado * T Laboratório de Catálise, Departamento de Engenharia Química, Universidade Estadual de Maringá – UEM, Maringá, PR, Brasil T Laboratório de Biotecnologia e Produtos Naturais, Departamento de Ciências Exatas e da Terra, Universidade Federal de São Paulo – UNIFESP, Diadema, SP, Brasil T T Resumo foram submetidas à troca iônica ou impregnação com prata e posteriormente adicionadas em filmes de quitosana T Zeólitas para a confecção de curativos para queimaduras. As zeólitas foram avaliadas por Ressonância magnética nuclear Fluorescência de raios X por reflexão total (TXRF), Microscopia eletrônica de varredura (MEV). Os filmes T (RMN), poliméricos foram analisados com relação às suas propriedades mecânicas, permeabilidade ao vapor d’água (PVA) e de prata. Observou-se que o procedimento de troca iônica não alterou a morfologia das zeólitas de partida.

T liberação Grumos de zeólita foram observados nas micrografias dos filmes e estes influenciaram nas propriedades mecânicas devido à desorganizaçao local no empacotamento das cadeiras poliméricas da quitosana. A metodologia de troca iônica impregnação influenciou diretamente na quantidade de prata presente superficialmente na zeólita e consequentemente T oualterou o perfil de liberação de prata em uma solução simulada de exudato de ferida. Os modelos cinéticos sugeriram T que a liberação da prata não foi essencialmente regulada pela lei de difusão de Fick.

T Palavras-chave: impregnação, troca-iônica, curativos para queimados, zeólita Y. T Abstract were subjected to ion exchange or impregnation with silver and added to chitosan films for producing burns T Zeolites dressings. Zeolites were characterized by nuclear magnetic resonance (NMR), total reflection X-ray fluorescence (TXRF), scanning electron microscopy (SEM). The polymer films were analyzed with respect to their mechanical properties, T water vapor permeability (WVP), and release of silver. It was observed that the ion exchange did not modify the morphology of the starting zeolite. Clusters of zeolite were observed in the micrographs of the films and they influenced mechanical properties due to local disruption in the packing of the polymer chains of chitosan. The methodology of T the ion exchange or impregnation directly influenced the amount of silver present in the zeolite surface and consequently 1

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*nadia@deq.uem.br

changed the silver release profile in an of simulated exudate fluid. The kinetic models suggested that the release of the silver was not primarily governed by Fick’s law of diffusion.

Keywords: impregnation, ion-exchange, burn dressings, type Y zeolite.

1. Introdução Os cremes tópicos de sufadiazina de prata têm sido longamente utilizados como principal gerenciador de feridas em pacientes com sérias queimaduras que são especialmente suscetíveis a infecções. No entanto, as desvantagens em seus usos incluem manchas na pele e toxicidade, além de necessitar frequente remoção e reaplicação da sulfadiazina de prata, ocasionando pseudo-cicatrizes, dor e trauma no paciente queimado[1]. Nesta perspectiva, uma alternativa é a utilização de curativos à base de filmes de biopolímeros, como, por exemplo, a quitosana. A própria estrutura química

492

da quitosana, similar à estrutura do ácido hialurônico, reforça a indicação do uso deste biopolímero como agente cicatrizador e reparador de feridas e de queimaduras, pois, a quitosana é capaz de aumentar as funções de células inflamatórias como os leucócitos polimorfonucleares e macrófagos, promovendo organização celular e atuando no reparo de feridas amplas, além de ser um agente antimicrobiano eficaz contra bactérias gram-positivas e negativas[2,3]. Devido a estas propriedades, a quitosana pode ser moldada na forma de filmes ou membranas para ser utilizada como curativos de

Polímeros, 25(5), 492-502, 2015

Desenvolvimento e caracterização de filmes compósitos de quitosana e zeólitas com prata feridas e de queimaduras ou como molde para enxerto de pele, agente hemostático e material para sutura cirúrgico[4].

Uma vantagem de se utilizar um biopolímero é que este pode ser utilizado como um filme onde podem ser incorporadas zeólitas trocadas com prata para a liberação controlada dos íons prata diretamente na ferida e na proporção necessária para atuar contra bactérias e promover a rápida cicatrização.

Assim, um curativo ideal, pode combinar as propriedades da quitosana com as propriedades antimicrobianas da prata com liberação controlada através do auxílio de uma zeólita obtendo um curativo com propriedades excelentes de aceleração da cicatrização, propriedades antifúngicas, antibacterianas e ainda recobrimento da área lesionada sem ocasionar ao paciente dor e desconforto.

Estruturamente, as zeólitas são polímeros cristalinos baseados em um arranjo tridimensional de tetraedros TO4 (SiO4 ou AlO4–) ligados por átomos de oxigênio para formar subunidades e enormes redes constituídas por blocos idênticos. Os tetraedros se arranjam em anéis que por sua vez são combinados para formar canais e cavidades regulares e uniformes[5].

Muitos autores estudaram zeólitas trocadas com prata a fim de se verificar o mecanismo de liberação da prata para o meio e sua consequente atividade antimicrobiana contra muitas estirpes como, por exemplo, Escherichia coli, Staphylococcus aureus e Pseudomonas aeruginosa[6-8].

Muitos estudos foram realizados adicionando zeólitas trocadas com prata em filmes poliméricos para aplicação como embalagens ativas para alimentos ou para curativos, como por exemplo, zeólitas com prata adicionadas em filmes de polietileno[9] e polipropileno[10]. No entanto, a incorporação de zeólitas trocadas com prata adicionadas em filmes poliméricos de quitosana para a obtenção de um curativo ideal ainda não foi muito investigado.

Neste contexto, o objetivo deste trabalho foi o desenvolvimento de novos materiais poliméricos com Ag-zeólita para a substituição do curativo convencional de sulfadiazina de prata no tratamento de queimaduras.

A incorporação da prata nas zeólitas foi realizada por duas metodologias diferentes, troca iônica e impregnação úmida a fim de avaliar os efeitos dos dois diferentes métodos nas características físico-química dos materiais finais sintetizados.

2. Materiais e Métodos 2.1 Materiais A zeólita de partida utilizada neste trabalho foi a NaY, cedida pela Fábrica Carioca de Catalisadores (FCC).

Como sal precursor antibacteriano foi utilizado o nitrato de prata P.A. (AgNO3) da marca Nuclear. Para a síntese dos filmes poliméricos foi utilizada quitosana com grau de desacetilação igual a 82%, produzida pela empresa Polymar (Fortaleza, Brasil).

2.2 Procedimento de troca iônica e impregnação A troca iônica foi realizada em batelada segundo o procedimento proposto por Silva e Fernandes-Machado[11].

Solubilizou-se o nitrato de prata em quantidade necessária para produzir o catalisador no teor desejado de fase ativa de Polímeros, 25(5), 492-502, 2015

5% em água deionizada, na qual a razão Ag+/Na+ foi igual a 2. As condições para a realização da troca-iônica foram: pH entre 5 e 6, temperatura de 80 °C, agitação branda e tempo de troca de 30 min. Após, seco em estufa a 100 °C por 12 h, sendo o material resultante denominado de AgY-TI. A zeólita impregnada com prata foi obtida solubilizando‑se o nitrato de prata (quantidade necessária para produzir o catalisador no teor desejado de fase ativa 5%) em água.

A suspensão obtida foi transferida para um evaporador rotativo e mantido sobre vácuo a 80 °C até que todo o conteúdo de água evaporasse. Secou-se em estufa a 100 °C por 12 h com a finalidade de retirar qualquer quantidade de água remanescente. O material foi calcinado a 773K por 5 h (rampa de aquecimento de 3 K/min.). Esta amostra foi denominada de AgY-I.

2.3 Preparo dos filmes poliméricos A quitosana em pó foi solubilizada em solução aquosa contendo ácido acético adicionado em quantidade estequiométrica mais 50% em excesso, baseada no grau de desacetilação e massa de amostra, sendo mantida sobre agitação magnética durante 2 h. Como agente plastificante foi utilizado glicerol 25% (g de glicerol/g massa seca de quitosana). A solução de quitosana contendo zeólita foi preparada de maneira similar à apresentada anteriormente, porém, adicionou-se 0,2% de zeólita em relação à massa total de solução (m/m) juntamente com o glicerol e homogeneizou-se a solução resultante sob agitação mecânica vigorosa a 1500 rpm por 2 h. Os filmes foram preparados dispersando a solução em placas de Petri de polietileno, estas submetidas à secagem em estufa com circulação forçada de ar à 37 °C por 24 h (Tecnal, Brasil).

2.4 Caracterização 2.4.1 Ressonância Magnética Nuclear (RMN) Para a determinação da razão Si/Al estrutural da zeólita NaY foi realizada a análise de ressonância magnética nuclear (RMN). Os experimentos de RMN no estado sólido foram realizados em equipamento Varian, modelo Mercury plus 300, na qual operou a 59,6132 MHz para a frequência do núcleo de 29Si e 78,186 MHz para o núcleo de 27Al, equipado com sonda de sólidos CP/MAS 7 mm.

2.4.2 Fluorescência de raios X por reflexão total (TXTF) A análise de fluorescência de raios X por reflexão total (TXRF) foi utilizada para a determinação da quantidade de prata nas zeólitas após o procedimento de troca iônica e impregnação utilizando o equipamento S2 PICOFOX. As amostras foram previamente preparadas e fixadas em refletores de quartzo, os quais foram irradiados por 800 s sob reflexão total por um feixe de raios X de 20 keV, extraído da fonte radioativa de Molibdênio, para determinação da concentração de prata presente nas amostras.

2.4.3 Microscopia Eletrônica de Varredura (MEV) As micrografias das amostras zeolíticas foram obtidas por meio de um microscópio eletrônico de varredura (Shimadzu SS-550). A avaliação da estrutura final dos filmes de quitosana pura ou com Ag-zeólitas foi realizada sobre a superfície longitudinal e na área transversal de 493

Yassue-Cordeiro, P. H., Zandonai, C. H., Silva, C. F., & Fernandes-Machado, N. R. C. ruptura, após fratura criogênica utilizando nitrogênio líquido.

Foi utilizado um microscópio eletrônico de varredura 440i (LEO Electron Microscopy Ltda.).

2.4.4 Difração de Raios-X (DRX) As análises de difração de raios X dos filmes poliméricos e das zeólitas foram realizadas utilizando um difratômetro Bruker D8 Advance. Utilizou-se uma fonte de radiação de emissão de cobre (CuKα, 0,24°/min na varredura, 40 kV e 50 mA) e varredura de 2θ variando na faixa 4 a 50°.

Para identificação das fases presentes foi utilizado o banco de dados do software JCPDS. 2.4.5 Propriedades mecânicas As propriedades mecânicas foram medidas baseadas na metodologia padronizada ASTM D-882[12] utilizando um texturômetro TA.XT2 (Stable Microsystems, Inglaterra).

Através desta análise foram determinados a porcentagem de elongação, módulo de Young e tensão de ruptura.

2.4.6 Permeação ao vapor d’água (PVA) Para a determinação da permeação ao vapor d’água (PVA) utilizou-se o método padronizado ASTM E96-95[13]. O filme foi fixado em frascos contendo sílica e acondicionados em dessecador com UR controlada igual a 75%. O ganho de massa dos frascos foi acompanhado durante 40 h. Foram realizadas 5 repetições para cada filme.

2.4.7 Cinética de liberação da prata in vitro O perfil de liberação de prata dos filmes foi realizado em solução simulada de exsudato de ferida. Esta solução contém 142 mmol/L de íons sódio e 2,5 mmol/L de íons cálcio que representa as concentrações de sais observadas nos fluidos das feridas e do soro. A prata liberada deste meio foi analisada por espectroscopia de absorção atômica (SpectrAA modelo 50B- VARIAN) utilizando lâmpada de cátodo oco (λ = 328 nm) e uma mistura de ar e acetileno.

2.4.8 Análise estatística Foram realizadas análises estatísticas utilizando-se o software livre Action (2014). As diferenças significativas entre as médias foram analisadas utilizando o Teste de Tukey, com nível de significância p ≤ 0,05.

3. Resultados e Discussão Utilizando os princípios da deconvolução de Euler e com o auxílio do software OriginPro foi possível decompor precisamente os quatro picos coordenados da Figura 1a, a fim de quantificar e identificar estruturalmente diferentes ambientes do silício, e com isso determinar a razão silício/alumínio estrutural. Assim, o espectro de RMN de 29Si da zeólita NaY revelou a presença dos ambientes Si(3Al), Si(2Al), Si(1Al) e Si(0Al), referentes a –89,27; –93,77; –99,10; e –104,61 ppm, respectivamente, como encontrado na literatura[5,14].

A razão molar de Si/Al estrutural determinada foi de 2,54.

Este valor está coerente com o relatado por Weitkamp e Puppe[15] o qual a razão Si/Al deve estar compreendida na faixa de 1,5 a 3. Quanto aos espectros de MAS-RMN de 27 Al (Figura 1b) da amostra NaY, observa-se uma linha de ressonância em 59,02 ppm, correspondendo ao sinal 494

Figura 1. Espectros de RMN de (a) 29Si e (b) 27Al.

das espécies de alumínio tetraédrico. A ausência de pico referente a alumínio octaédrico, sinal aproximadamente em 0 ppm, indica a inexistência de alumínio extra rede, resultados também obtidos por Guerra et al.[16].

A porcentagem mássica de prata obtida por TXRF foi de 20,25% para a amostra AgY-TI, o que representa 44% de sódio trocado e 7,99% para a amostra AgY-I, indicando que houve uma impregnação de cerca de 60% a mais de prata. Esse excesso de prata pode ser explicado pela alta higroscopicidade da zeólita, que sem um extremo cuidado de secagem prévia e tempo de pesagem, leva a um material com teor de umidade não desejado. Para a troca iônica, o nitrato de prata (5%) foi solubilizado em água deionizada com uma razão Ag+/Na+ igual a 2. A solução de nitrato de prata e zeólita foi filtrada e lavada 3 vezes, sendo que a primeira lavagem consistiu-se de 70% do volume da suspensão de troca iônica em água deionizada além da mesma quantidade de sal utilizada na troca. Em função do pequeno raio iônico da prata, durante a lavagem houve troca iônica, por isso a quantidade de prata é quatro vezes maior do que a quantidade estequiométrica supostamente necessária para a troca de todo o sódio da zeólita, justificando o alto teor obtido pela análise de TXRF. Polímeros, 25(5), 492-502, 2015

Desenvolvimento e caracterização de filmes compósitos de quitosana e zeólitas com prata Os picos característicos de zeólita FAU (Figura 2) em 2θ = 6,24°, 15,70°, 23,69°, 27,08° e 31,43° são atribuídos, respectivamente, aos planos cristalográficos [111], [331], [622], [624], [804] e foram observados tanto na zeólita de partida (NaY) como nas amostras submetidas aos procedimentos de troca iônica (AgY-TI) e impregnação (AgY-I).

A semelhança entre os diagramas das zeólitas de partida e as modificadas após o processo de troca com prata ou impregnação revela que estes processos não promovem qualquer modificação estrutural na zeólita[7,9,17-20]. Não foram encontrados os picos característicos da prata metálica em 2θ = 38,21°, 44,51°, 64,51° e 77,51°. Esse resultado indica uma boa troca iônica na amostra AgY-TI e que durante a calcinação não houve formação de aglomerados de Ag2O. Já na amostra impregnada, o baixo teor de prata e a alta dispersão dos critalitos explica sua não identificação.

Inúmeros autores incorporaram diversos teores de prata na estrutura zeolítica por diversas metodologias diferentes e muitos deles também não verificaram a presença de cristais de prata em seus diagramas[7-9,19,21-23].

Sabendo-se que a região de 2θ entre 10° e 20° é relacionada com a localidade dos cátions na estrutura zeolítica, observa‑se então, que em todas as amostras, houve uma redução da maior parte dos picos característicos, indicando uma redistribuição dos cátions de balanceamento de carga na estrutura interna da zeólita[7,18,24].

A Figura 3 ilustra a comparação entre os filmes de quitosana pura, filmes de quitosana com zeólita incorporada e a zeólita.

Observa-se que a incorporação de material zeolítico na matriz polimérica dos filmes promove o aparecimento de picos característicos das zeólitas nos diagramas dos filmes sintetizados.

A cristalinidade relativa da quitosana nos filmes com AgY-TI e AgY-I foi comparada com o filme de quitosana puro, o qual foi definido como sendo de 100%, utilizando a metodologia baseada no método ASTM D-3906-80[25].

Para comparação foram utilizados dois picos de difração característicos da quitosana, localizados em 2θ=11,4° e

Figura 2. Diagramas de DRX da zeólitas AgY-TI, AgY-I e NaY. Polímeros, 25(5), 492-502, 2015

20,1°, referentes ao cristal I (a = 7.76A°, b = 10.91A° e c = 10.30A°) e cristal II (a = 4.4A°, b = 10.0A° e c = 10.3A°), respectivamente, ambos ortorrômbicos[26].

Houve diminuição das intensidades relativas dos picos característicos da quitosana após a incorporação de zeólita, sendo de 51,65% e 82,49% para as amostras AgY-TI e AgY-I, respectivamente. A presença de zeólitas no filme interferiu no empacotamento ordenado das cadeias de quitosana tanto por efeitos estéricos como também pela formação de ligações de hidrogênio entre os grupos –OH superficiais das zeólitas e grupos –NH2 e –OH da quitosana, resultando na diminuição da cristalinidade da quitosana para ambas as amostras e o aparecimento de picos característicos de zeólita nos filmes sintetizados[27].

A Figura 4 ilustra as micrografias da zeólita NaY antes e após o procedimento de troca iônica e impregnação com nitrato de prata.

Pode-se observar que o procedimento de troca iônica e de impregnação não modifica a morfologia da zeólita de partida. O tipo de procedimento adotado não altera o

Figura 3. Diagramas dos filmes poliméricos de quitosana pura, zeólita e filme com zeólita para as amostras (a) AgY-TI e (b) AgY-I. 495

Yassue-Cordeiro, P. H., Zandonai, C. H., Silva, C. F., & Fernandes-Machado, N. R. C.

Figura 4. Micrografias das zeólitas (a) NaY, (b) AgY-TI e (c) AgY-I. (aumento de 10.000x).

tamanho médio do grão apresentando tamanho de partícula médio entre 0,77 e 0,80 µm. Esse resultado corrobora com o de DRX, pois não foram encontrados aglomerados que poderiam ser atribuídos à prata.

Outros autores também observaram que zeólitas com e sem prata apresentam aparência muito similar, formas poliédricas regulares e o mesmo tamanho de partícula[9,17,23].

496

As micrografias obtidas por microscopia eletrônica de varredura (MEV) da superfície dos filmes poliméricos com aumento de 500 vezes (micrografia da esquerda) e da seção transversal (micrografia da direita) das mesmas com um aumento de 3000 vezes são apresentadas na Figura 5.

Observa-se que o filme de quitosana pura (Figura 5) apresentou-se como uma matriz compacta, sem defeitos apreciáveis e ausência de macroporos, resultados estes também condizentes com os obtidos por outros autores[28-32].

A partir da micrografia da seção transversal dos filmes com zeólitas (Figura 5b e Figura 5c), observou-se que em todas as amostras houve alguma aglomeração das partículas de zeólita, indicando que os diâmetros das partículas eram demasiadamente grandes, e provável sedimentação das mesmas. Assim, ocorreu a separação de fases da zeólita e da quitosana, formando um filme compósito que se constituiu de duas fases bem distintas, uma orgânica de quitosana e uma inorgânica de zeólita. Wang et al.[30] também incorporaram zeólita beta em filmes de quitosana e verificaram que para partículas com diâmetro entre 3 e 5 µm pode haver a sedimentação da zeólita, o que influencia diretamente nas propriedades de barreira e superficiais dos filmes poliméricos.

Na Tabela 1 são apresentadas as propriedades mecânicas obtidas para os filmes poliméricos sintetizados neste trabalho.

A incorporação de zeólita NaY e zeólita impregnada (AgY-I) não alterou significativamente o módulo de Young e a tensão de ruptura quando comparado com o filme de quitosana pura, diferentemente do obtido pela amostra submetida ao procedimento de troca iônica, na qual apresentou diferença significativa quando comparada com as outras amostras deste estudo.

Como observado na análise de TXRF, a zeólita AgY-I apresentou uma porcentagem de prata muito menor do que a amostra AgY-TI, indicando que a presença de uma maior quantidade de prata pode influenciar significativamente nas propriedades mecânicas dos filmes provavelmente devido às interações eletrostáticas entre os polímeros/zeólitas/prata metálica, restringindo a mobilidade das cadeias poliméricas[26,33].

A diminuição da porcentagem e elongação para todos os filmes poliméricos com zeólita quando comparado com o filme de quitosana pura pode ser devido à presença de grumos de zeólita, nos quais causaram uma desorganização local no empacotamento das cadeiras poliméricas da quitosana fazendo com que a estrutura polimérica se rompesse mais facilmente próximos aos pontos onde os grumos de zeólita se encontram inseridos. Os grumos de zeólita podem ser observados nas micrografias transversais dos filmes poliméricos com zeólita. Também pela análise de MEV dos filmes sintetizados (Figura 5b e Figura 5c), observa-se a presença de pequenas fissuras em todos os filmes com zeólitas. Como na micrografia da seção transversal estas não se encontram presentes nos filmes de quitosana pura, sugere-se que nos demais filmes a presença destas fissuras e falhas facilitam o rompimento do filme reduzindo consequentemente a porcentagem de elongação.

A presença de glicerol nos filmes poliméricos resultou em filmes com melhor maleabilidade (menor módulo de Young) e melhor flexibilidade (maior porcentagem de elongação) do que os filmes confeccionados por Santos et al.[34] que Polímeros, 25(5), 492-502, 2015

Desenvolvimento e caracterização de filmes compósitos de quitosana e zeólitas com prata

Figura 5. Micrografias dos filmes, à esquerda imagem da superfície longitudinal e à direita imagem da área transversal de ruptura.

adicionaram zeólita ZSM-5 em filmes de quitosana sem a presença de glicerol. Fiori et al.[35] também observaram que a adição de plastificantes melhorou a flexibilidade do filmes de quitosana e que a adição de argila bentonita na matriz polimérica resultou em um filme mais resistente.

Na Tabela 2 são apresentadas os valores para a taxa de permeação ao vapor de água (TPVA) e a permeação ao vapor Polímeros, 25(5), 492-502, 2015

de água (PVA) dos filmes de quitosana. Não se observou diferença significativa entre os filmes de quitosana pura e os com zeólitas.

A pele humana normal possui permeabilidade ao vapor d’água (PVA) de 0,204 ±0,012 g/10 cm2/24 h, ou seja, a pele perde 0,204 g de água em uma área de 10 cm2 durante 24 h.

Para a pele com lesão por queimaduras de primeiro grau ou 497

Yassue-Cordeiro, P. H., Zandonai, C. H., Silva, C. F., & Fernandes-Machado, N. R. C. Tabela 1. Propriedades mecânicas dos filmes poliméricos.

Filme de quitosana Pura (sem zeólita) NaY AgY-TI AgY-I

Módulo de Young (MPa)* 4,17±0,97ª 5,36±0,99ª 11,00±0,81b 5,07±0,39ª

Tensão de ruptura (MPa)* 13,26±0,71ª 14,87±1,91ª 27,83±1,18b 15,39±2,08a

Porcentagem de elongação (%)* 19,60±0,38a 12,52±1,32c 8,94±1,70b 10,35±2,45b

*Diferentes sobrescritos na mesma coluna indicam diferenças significativas entre as formulações (p < 0,05).

Tabela 2. Taxa de permeação ao vapor d’água.

Filme de Quitosana Pura (sem zeólita) AgY-TI AgY-I NaY

TPVA (g/10cm2.24h)* 0,46 ± 0,03ª 0,49 ± 0,03ª 0,50 ± 0,01ª 0,49 ± 0,05ª

PVA (10-11 g/m.s.Pa)* 8,33 ± 0,46ª 8,46 ± 0,42ª 9,26 ± 0,02ª 9,17 ± 0,81ª

*Diferentes sobrescritos na mesma coluna indicam diferenças significativas entre as formulações (p < 0,05).

quando a ferida está formando o tecido de granulação, as permeabilidades são 0,279±0,026 e 5,138±0,202 g/10 cm2/24 h, respectivamente[36]. Em relação à permeabilidade ao vapor d’água de um curativo ideal[37,38], este deve possuir permeabilidade ao vapor d’água de 1,200 g/10 cm2/24 h enquanto que para Wu et al.[39] e Mi et al.[40] o ideal é de 2,500 g/10 cm2/24 h.

Kim et al.[41] encontraram valores de permeabilidade de 1,938 a 2,212 g/10 cm2/24 h, enquanto outros autores encontraram permeabilidades mais baixas semelhantes ao obtido neste trabalho, como Wang et al.[42] e Remuñán-López e Bodmeier[43] que obtiveram, 0,560-0,658 g/10 cm2/24 h e 0,288-1,008 g/10 cm2/24h, respectivamente.

Os valores de TPVA dos filmes sintetizados variaram entre 0,46 e 0,50 g/10cm2/24h e também não mostraram diferença significativa entre eles. Observa-se que muitos curativos disponíveis comercialmente apresentam valores ainda mais baixos variando entre 0,1360 e 0,476 g/10cm2/24h para os curativos Comfeel, Dermiflex, Granuflex E, IntraSite, Restore Cx, Tegasorb e Bioclusive[44].

A Figura 6 apresenta os perfis de liberação de prata a partir dos filmes poliméricos sintetizados.

O filme com AgY-TI apresentou uma taxa de liberação de prata maior do que o filme com AgY-I. Este fato é decorrente da maior concentração de prata na zeólita AgY-TI observada pela análise elementar de TXRF. Boschetto et al.[9] observaram também que quanto maior a quantidade de prata na superfície da zeólita, maior é a quantidade de prata lixiviada a partir de filmes de poliestireno.

Observa-se que a quantidade de prata liberada é muito baixa, o que poderia ser um fato positivo em relação à sua citotoxicidade e mesmo após dois dias de liberação ainda estava ocorrendo a liberação da prata, isto é, a quantidade de prata liberada ainda não havia se tornado constante para a amostra na qual a prata havia sido incorporada à zeólita pelo procedimento de troca iônica, AgY-TI. Para a zeólita impregnada com prata, já se esperava uma menor concentração de prata na solução, justamente porque o procedimento de impregnação visa a fixação da prata no suporte através da decomposição do sal AgNO3.

Todos os filmes sintetizados apresentaram uma liberação de prata menor que 1 ppm. No entanto, Walker et al.[45] 498

Figura 6. Perfis de liberação da prata a partir dos filmes poliméricos.

verificaram que os curativos comerciais Ancticoat e Aquacel-Ag Hydrofiber lixiviam 55 e 1 ppm de Ag+, respectivamente. Ou seja, Aquacel-Ag Hydrofiber libera tão pouca prata quanto os filmes sintetizados neste trabalho.

No entanto, a baixa concentração de prata obtida também foi verificada por outros autores que realizaram o experimento tanto em salmoura como em fluido exsudato de ferimento e observaram que as concentrações de prata iônica caem para 1 ppm em todos os casos[45,46].

Em termos de perfil de liberação, o filme polimérico com AgY-I apresentou um perfil de saturação, ou seja, a quantidade máxima de prata liberada é atingida em cerca de 0,25 ppm, onde é provável que toda a prata passível de liberação já tenha sido liberada. Por outro lado, a AgY‑TI não atinge esta saturação, apresentando um perfil de liberação lento, o que é bastante desejável já que a prata pode ser citotóxica quando liberada no leito de queimadura em grandes quantidades rapidamente.

Optou-se por realizar esta análise em solução simulada de exsudato de ferida por ser uma solução mais próxima da situação real encontrada em uma queimadura mesmo sabendo Polímeros, 25(5), 492-502, 2015

Desenvolvimento e caracterização de filmes compósitos de quitosana e zeólitas com prata que íons cloreto nesta solução podem inibir parcialmente os íons prata. O teste não foi realizado em água deionizada, pois, segundo Matsumura et al.[47] nenhuma quantidade de prata considerável foi detectada, não simulando uma condição real, pois não há troca iônica para liberar a prata presente na estrutura da zeólita.

Os dados experimentais obtidos nos ensaios de liberação de prata a partir dos filmes poliméricos são apresentados na Figura 7 e foram ajustados a vários modelos matemáticos visando analisar o comportamento cinético do sistema.

Os modelos utilizados (Tabela 3) foram Higuchi[48], primeira ordem[49], Korsmeyer et al.[50], Peppas e Sahlin[51].

Os ajustes dos quatro modelos propostos foram realizados utilizando o programa OriginPro e a escolha do melhor modelo ajustado foi realizada baseada no método de análise do coeficiente de correlação R2.

A Figura 7 apresenta os ajustes dos modelos cinéticos para os filmes com AgY-I e AgY-TI, respectivamente, e a Tabela 4 apresenta os parâmetros cinéticos obtidos bem como o coeficiente de correlação de cada modelo.

Os dados experimentais não se ajustaram ao modelo cinético de Higuchi[48] (Equação 1) pelos baixos valores de R2 obtidos. Este modelo apresenta fortes limitações na

interpretação dos mecanismos de liberação controlada, justamente por ser melhor aplicável em filmes poliméricos pouco solúveis e/ou que não apresentam capacidade de intumescimento[52,53], fatos não observados nos filmes sintetizados neste trabalho.

Apesar do coeficiente de correlação obtido pelo modelo de primeira ordem[49] (Tabela 4) ter sido muito maior do que aquele obtido pelo modelo de Higuchi[48], o modelo de primeira ordem não descreve a dissolução do agente ativo que está preso entre as cadeias poliméricas da quitosana, representando apenas o comportamento da droga que se encontra na superfície do filme, sendo característica de um processo de dissolução instantânea[54].

O mecanismo proposto por Korsmeyer et al.[50] (Equação 3) é utilizado quando o mecanismo controlador de liberação da droga não é conhecido ou quando há a combinação dos seguintes processos regidos independentemente: transporte do fármaco no interior da matriz (difusão Fickiana) e transição de um estado semirrígido a outro mais flexível, decorrente dos fenômenos de inchamento/relaxamento do filme. Segundo Peppas[55], para esse modelo, quando n for igual a 0,5 a liberação é controlada pela difusão. Quando n é igual a 1, o mecanismo controlador é o intumescimento, correspondente à cinética de ordem zero. Para 0,5 < n < 1, a liberação se dá por sobreposição dos dois fenômenos citados Tabela 3. Modelos cinéticos para liberação de fármacos.

Modelo

Equação

Higuchi[48]

Primeira ordem[49]

Korsmeyer[50]

Qt = Kh t Q∞

(1)

Q  ln  t  = K1t  Q∞ 

(2)

Qt = K 2t n Q∞

(3)

= Q K3t m + K 4t 2m

Peppas e Sahlin[51]

(4)

Tabela 4. Parâmetros dos modelos ajustados.

Modelo

Primeira ordem[49]

Korsmeyer[50]

Parâmetros

Filme com

Filme com

Cs (mg/mL) K1

AgY-I 1,4907 0,2453

AgY-TI NA NA

R2 K2

0,9206

NA

0,2176

0,1291

n

0,0529

0,1470

R K3

0,9319

0,8036

0,1602

0,1034

K4

0,0580

0,0274

m

0,0406

0,1130

2

0,9319

0,8785

2

Peppas e Sahlin[51]

R Figura 7. Ajuste dos modelos cinéticos para os filmes com (a) AgY-I e (b) AgY-TI. Polímeros, 25(5), 492-502, 2015

NA indica que o modelo não se ajustou, ou seja, o coeficiente de correlação (R2) obtido foi muito pequeno.

499

Yassue-Cordeiro, P. H., Zandonai, C. H., Silva, C. F., & Fernandes-Machado, N. R. C. ou transporte anômalo. Os dados utilizados para a estimação do parâmetro n devem ser obrigatoriamente Qt / Q∞ < 0, 6 .

Ajustando os dados experimentais ao modelo de Korsmeyer et al.[50], os valores encontrados para o parâmetro n foram ambos menores do que 0,5 indicando que o mecanismo de liberação não se deve primordialmente à difusão[55]. Valores de n menores do que 0,5 são atribuídas a não-homogeneização das partículas de tendência irregular, dificultando a liberação do fármaco por difusão controlada pela Lei de Fick[56].

Com base na Figura 7, observa-se que o modelo proposto por Peppas e Sahlin[51] resultou em uma curva idêntica ao modelo proposto por Korsmeyer et al.[50] para ambas as amostras. Este fato é devido ao baixo valor da constante K4, indicando que a contribuição dos fenômenos de erosão e relaxamento são desprezíveis em ambos os filmes sintetizados neste trabalho. Assim, o modelo cinético proposto por Peppas e Sahlin[51] também apresentou o expoente que caracteriza a cinética de liberação (m) abaixo de 0,5, o que corrobora com os resultados obtidos pelo modelo de Korsmeyer et al.[50] indicando que a liberação da prata a partir da zeólita e do filme de quitosana não é primordialmente governada pelo mecanismo de difusão.

Neste trabalho, liberação da prata pode ter sido dificultada por esta estar presente no filme polimérico provavelmente na forma de nanopartículas de prata e estas ficarem presas (“entrapped”) no filme, justificando a dificuldade da dissolução e difusão da prata para a solução simulada de exsudato de ferida.

O uso do par quitosana/prata pode levar indiretamente à formação de nanopartículas de prata pelo método clássico de produção de nanopartículas[57,58]. Neste método, agentes redutores são utilizados para reduzir os íons de prata em solução aquosa produzindo prata coloidal. Inicialmente, a redução de íons de prata (Ag+) conduz à formação de átomos de prata (Ag0), a qual é seguida por uma aglomeração. Estes aglomerados, eventualmente, conduzem à formação das nanopartículas coloidais de prata[57,59]. Devido esta aglomeração, um agente de estabilização é utilizado no processo de síntese para evitar a agregação das nanopartículas e para controlar o tamanho do produto final[60]. Estes estabilizadores desempenham um papel importante para controlar a formação de nanopartículas, bem como a sua estabilidade. A quitosana pode ser utilizada tanto como agente redutor como agente estabilizador para este fim, durante a síntese de nanopartículas de prata[58].

Mesmo não sendo a proposta do trabalho, a formação de nanopartículas de prata no filme polimérico de quitosana pode ser visto como um fator positivo, uma vez que partículas do tamanho nano potencializam a atividade antimicrobiana[61,62].

Assim, tanto as nanopartículas de prata como os íons prata lixiviados a partir dos filmes poliméricos inibem microorganismos patogênicos sinergicamente.

Por mais que a hipótese de formação de nanopartículas seja válida e coerente, esta hipótese deve ser firmemente averiguada.

4. Conclusões Os filmes poliméricos de quitosana com Ag-zeólita mostram-se como materiais potenciais e inovadores para o 500

desenvolvimento de um novo curativo. O processo de troca iônica ou impregnação não modifica a morfologia das zeólitas de partida, fato este constatado pelas análises de DRX e por MEV. Os filmes com Ag-zeólitas apresentaram-se mais opacos, com aglomerações de zeólitas na superfície do filme e mais rígidos, alterações que puderam ser observadas nas análises de MEV e de propriedades mecânicas, respectivamente.

A amostra AgY-TI não atinge um perfil de saturação de liberação de prata, apresentando um perfil de liberação lento, o que é bastante desejável já que a prata pode ser citotóxica, ressaltando o bom desempenho da utilização de zeólita em termos de liberação controlada de prata no meio. A hipótese de formação de nanopartículas justifica a baixa liberação de prata na solução simulada de exsudato de ferida e por meio de modelos matemáticos cinéticos foi constatado que a liberação de prata a partir da zeólita/filme polimérico não é governada primordialmente pelo mecanismo de difusão fickiano.

5. Agradecimentos À CAPES pela bolsa de mestrado concedida à Patrícia Yassue Cordeiro.

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Enviado: Jan. 12, 2015 Revisado: Abr. 08, 2015 Aceito: Jun. 01, 2015

Polímeros, 25(5), 492-502, 2015

http://dx.doi.org/10.1590/0104-1428.2208

Synthesis and characterization of poly(S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate) by electrochemical polymerization Ha Tran Nguyen1,2* and Le-Thu Thi Nguyen1 Faculty of Materials Technology, Ho Chi Minh City University of Technology, Vietnam National University, Ho Chi Minh City, Vietnam 2 Materials Technology Key Laboratory, Vietnam National University, Ho Chi Minh City, Vietnam 1

*nguyentranha@hcmut.edu.vn

Abstract A novel monomer of S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate (MTE) were synthesized via esterification reaction between 2-(thiophen-3-yl)acetic and ethane-1,2-dithiol in the presence of dicyclohexyl-carbodiimide (DCC) and N,N’-dimethylpyridin-4-amine (4-DMAP) as catalytic system. The structure of monomer was characterized via MS, 1H-NMR and 13C-NMR spectroscopies. The electrochemical polymerization of MTE monomer was performed in acetonitrile using lithium perchlorate (LiClO4) as electrolyte agent. The obtained polymer film (PMTE) was characterized via cyclic voltammetry and it exhibited the main oxidation peaks centered at +2V. Keywords: polythiophene, electrochemical polymerization, cyclic voltammograms.

1. Introduction Since the discovery of oxidized polyacetylene that could achieve a very high electrical conductivity, the field of conducting polymers has developed enormously. Nowadays there are many classes of conducting polymers including polyacetylene, polypyrrole, polyaniline, polythiophene and their derivatives. Due to their extremely high conductivity, which results from the delocalization of electrons along the polymer backbone, they are termed “synthetic metals”.

Besides their notable conductivity, these materials also exhibit interesting optical properties which show dramatic color shifts in response to changes in solvent, temperature, applied potential, and binding to other molecules. Both the changes in conductivity and color of conjugated polymers are induced by twisting of the polymer backbone and disrupting conjugation, making them attractive for their use as responsive electrical and optical devices[1-4].

Among the numerous polymers which have been developed and researched over the several decades, polythiophenes and their derivatives are one of the most interesting classes of conjugated polymers that exhibit advantageous characteristics such as high electrical conductivity, good environmentally and thermally stability[5]. The applications of these conducting polymers include non-linear optical devices, polymer light emitting diodes, sensors, organic field effect transistors, organic solar cells, and electrochromic devices[6-12]. However, polythiophene has the disadvantage of being insoluble, and hence of being difficult to be processed.

Instead, substituted polythiophenes with aliphatic or polar substituents are often used for improving the solubility. Base on that viewpoint, the synthesis of new thiophene derivatives through substitution to the 3 and/or 4 position has opened to exciting new materials with enhanced performances.

Polímeros, 25(5), 503-507, 2015

For example, incorporation of flexible pendant chains into the backbone improves the processability and solubility, and could also results in polymers having a low oxidation potential and moderate band gap with good stability in the oxidized state. Some other types of substituents reveal thermalchromic, photoluminence behaviors and electrochromic properties[13-15].

In recent years, much attention has been paid to gold nanoparticles due to their potential applications in nanotechnology, such as in single electron transistors or nonlinear optical devices[16,17]. Gold-thiol self-assembled monolayers (SAMs) have been widely studied[18-20] because it has high molar absorptivity in the visible region, making them useful for a variety of applications as nanoelectronics, catalysis, molecular recognition systems and developing new optical analytical methods. Therefore, this study aims to synthesize new conducting thiophene-based monomer containing functional thiol group based on S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate (MTE). Then, the polymerization of the synthesized monomers was also investigated via electrochemical polymerization technique.

2. Materials and Methods 2.1 Materials 2-(thiophen-3-yl)acetic, 1,2-Ethanedithiol, dicyclohexylcarbodiimide (DCC), N,N’-dimethylpyridin-4-amine (4-DMAP) and dimethylene chloride, lithium perchlorate (LiClO4), Acetonnitril, were purchased from Aldrich.

Sodium bicarbonate and chlorohydric acid were purchased from Daejung.

503

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

Nguyen, H. T., & Nguyen, L.-T. T. 2.2 Characterization

2.4 Electrochemical polymerization

H NMR and C NMR spectra were recorded in deuterated chloroform (CDCl3) with TMS as an internal reference, on a Bruker Avance 300 MHz The cyclic voltammograms were recorded to investigate the electroactivity of the polymer and the oxidation-reduction peak behaviour of the monomer. Acetonnitril (ACN)/lithium perchlorate (LiClO4) was used as a solvent-electrolyte couple.

The CV system consists of a potentiostat, a XY recorder, a CV cell containing Pt or Au foil working and counter electrodes, and a Ag/Ag+ reference electrode. The measurements were performed at room temperature under nitrogen atmosphere.

Electrodepositions were performed via cyclic voltammetry to study the redox behavior of the monomer and the oxidation stability of the polymer film.

All electrochemical experiments were carried out in a usual, one-compartment cell with a Ag/Ag+ (in aqueous saturation of potassium chloride) reference electrode (RE) and a platinum wire counter electrode (CE).

Electrodeposition of the MTE monomer was firstly examined by cyclic voltammetry to optimize the polymerization condition. The experiment was performed on a Pt disc electrode (surface area of 0.03 cm2) from 0.05 M monomer solution in acetonniltrile (ACN) containing 0.05 M LiClO4 by using a potentiostat (parstat 2263).

The obtained the polymer films were rinsed with acetonnitrile (ACN), and were placed into the monomer‑free solutions of 0.05 M LiClO4 in ACN for further electrodeposition measurements, which were conducted potentiostatically at 2.0 V.

1

13

2.3 Synthesis of S-3-mercaptopropyl 2-(thiophen-3-yl) ethanethioate An amount of 2-(thiophen-3-yl)acetic (1 g, 7.03 mmol), 1,2-ethanedithiol (0.66 g, 7.03 mmol), and 4-DMAP (0.214 g, 1.75 mmol) was dissolved in 80 ml of dimethylene chloride in a three necked round –bottomed flask. The solution was heated to 60 °C while stirring continuously under nitrogen. An amount of DCC (2.89 g, 14.06 mmol) in 20 ml methylenedichloride was slowly added into the solution.

After 9 hours, the solution was filtered and the filtrate was washed with Na2CO3 repeatedly and dried over Mg2SO4.

The solvent was removed under reduce pressure to obtain a yellow oil. The crude product was purified via a silica column using methylenchloride/methanol (60:1 v/v) as an eluent to yield the pure product as a yellow oil. 1H NMR (300 MHz, CDCl3), δ (ppm): 7.33 (s, 1H), 7.20 (s, 1H), 7.07 (s, 1H), 3.86 (s, 2H), 2.92 (m, 2H), 1.87 (m, 2H), 1.56 (s, 1H).

13 C NMR (75.5MHz, CDCl3), δ (ppm) 196.7, 133.4, 128.8, 126.05, 123.77, 44.92, 37.54, 28.15. MS m/z (M+): 232.

3. Results and Discussions 3.1 Synthesis of S-2-mercaptoethyl 2-(thiophen-3-yl) ethanethioate (MTE) The mechanism of the reaction between 2-(thiophen‑3‑yl) acetic and ethane-1,2-dithiol is described in Scheme 1.

3-thiophene acetic acid reacts with DCC to form N,N’‑dicyclohexylcarbamimidic 3-thiophene acetic acid anhydride which again reacts with another 3-thiophene acetic acid to create 3-thiophene acetic acid anhydride and release 1,3-dicyclohexylurea (DCU). Then 3-thiophene acetic acid

Scheme 1. Synthesis of S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate monomer.

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Polímeros, 25(5), 503-507, 2015

Synthesis and characterization of poly(S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate) by electrochemical polymerization anhydride reacted with 4-DMAP to form an acylpyridinium species. A Nucleophilic substitution appeared on the acyl group by ethane-1,2-dithiol to provide the thioester.

The chemical structure of the synthesized S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate monomer was confirmed by

H-NMR and 13C-NMR spectroscopies (Figures 1 and 2).

The 1H NMR spectrum shows all charateritic peaks that corresponding to the chemical strucure of monomer, a peak was abserved at 1.56 ppm which contributed to the thiol end group of monomer, and the peaks appear from 7.0-7.4 ppm 1

Figure 1. 1H-NMR of S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate.

Figure 2. 13C-NMR of S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate.

Polímeros, 25(5), 503-507, 2015

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Nguyen, H. T., & Nguyen, L.-T. T. that corresponding to protons in thiophene ring. The chemical structure of S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate monomer was confirmed via 13C-NMR which exhibited a peak at 196 ppm corresponding to the thioate group which indicating the formation of a thioester compound.

3.2 Electropolymerization The electrochemical polymerization of the S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate (MTE) monomer was successfully achieved shown in Figure 3 that performed in acetonniltrile (ACN) solution containing 0.05 M LiClO4, with a Pt disc electrode (surface area of 0.03 cm2) and using of 0.05 M of MTE monomer solution. The Figure 3 revealed an oxiadation peak at 2.1V and a reduction peak at 1.1V of monomer, respectively. The film thickness was increasing according to the increasing of scans, denoting the formation of a continuous film on the WE electrode.

After electropolymerization of the S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate monomer, the resulting polymer film were continuously measured for oxidative stability by cyclic voltametry in the monomer-free solution in the potential range of 0 to 2.5 V at different scan rates.

The obtained polymer films were rinsed several times with acetonnitril (ACN) after electropolymerization process.

Following, the polymer film were placed into the monomer‑free solutions of 0.05 M LiClO4 in ACN for characterization.

The cyclic voltammogram of polymer film (Figure 4) shows an oxidation peak at 2.1 V on Pt electrode which contributed to the oxidation peaks of poly(S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate). The film of PMTE was very stable during the redox process. Furthermore, the PMTE film showed the same redox potential peaks in its cyclic voltammogram after being stored at room temperature for four months, denoting a good stability of PMTE.

4. Conclusions In this study, a novel monomer S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate (MTE) which has a thiol end group was successfully synthesized via esterification of 3-thiophene acetic acid and ethane-1,2-dithiol using DCC and 4-DMAP as catalytic systems. The monomer was found to form electroactive polymer films on the working electrodes, and the polymer films exhibit good stability, reversible behavior and an oxidation potential of 2.1 V.

5. Acknowledgements This research was fully supported by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number “104.02-2013.18”.

6. References

Figure 3. Cyclic voltammograms of S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate in acetonnitril.

Figure 4. Cyclic voltammograms of Poly(S-2-mercaptoethyl 2-(thiophen-3-yl)ethanethioate).

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1. McCullough, R. D., Tristram-Nagle, S., Williams, S. P., Lowe, R. D., & Jayaraman, M. (1993). Self-orienting head-to-tail poly(3-alkylthiophenes): new insights on structure-property relationships in conducting polymers. Journal of the American Chemical Society, 115(11), 4910-4911. http://dx.doi.org/10.1021/ ja00064a070.

2. Chen, T. A., Wu, X., & Rieke, R. D. (1995). Regiocontrolled synthesis of Poly(3-alkylthiophenes) mediated by rieke zinc: their characterization and solid-state properties. Journal of the American Chemical Society, 117(1), 233-244. http://dx.doi. org/10.1021/ja00106a027.

3. Bao, Z., Dodabalapur, A., & Lovinger, A. J. (1996). Soluble and processable regioregular poly(3-hexylthiophene) for thin film field-effect transistor applications with high mobility.

Applied Physics Letters, 69(26), 4108-4110. http://dx.doi. org/10.1063/1.117834.

4. Greene, R. L., Street, G. B., & Suter, L. J. (1975). Superconductivity in polysulfur nitride (SN)x. Physical Review Letters, 34(10), 577-579. http://dx.doi.org/10.1103/PhysRevLett.34.577.

5. MacDiarmid, A. G. (2001). Nobel lecture: “synthetic metals”: a novel role for organic polymers. Reviews of Modern Physics, 73(3), 701-712. http://dx.doi.org/10.1103/RevModPhys.73.701.

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7. Yu, G., Wang, J., McElvain, J., & Heeger, A. J. (1998). Largearea, full-color image sensors made with semiconducting polymers. Advanced Materials, 10(17), 1431-1434. http://dx.doi. org/10.1002/(SICI)1521-4095(199812)10:17<1431::AIDADMA1431>3.0.CO;2-4.

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Reactive groups on polymer-covered electrodes. 2. functionalized thiophene polymers by electrochemical polymerization and their application as polymeric reagents. Macromolecules, 28(16), 5575-5580. http://dx.doi.org/10.1021/ma00120a023.

9. Tsumura, A., Koezuka, H., & Ando, T. (1986). Macromolecular electronic device: field-effect transistor with a polythiophene thin film. Applied Physics Letters, 49(18), 1210-1212. http:// dx.doi.org/10.1063/1.97417.

10. Argun, A. A., Cirpan, C., & Reynolds, J. R. (2003). The first truly all-polymer electrochromic devices. Advanced Materials, 10(16), 1338-1341. http://dx.doi.org/10.1002/adma.200305038.

11. Huynh, W. U., Dittmer, J. J., & Alivisatos, A. P. (2002). Hybrid nanorod-polymer solar cells. Science, 295(5564), 2425-2427. http://dx.doi.org/10.1126/science.1069156. PMid:11923531.

12. Arias, A. C., MacKenzie, J. D., McCulloch, I., Rivnay, J., & Salleo, A. (2010). Materials and applications for large area electronics: solution-based approaches. Chemical Reviews, 110(1), 3-24. http://dx.doi.org/10.1021/cr900150b. PMid:20070114.

13. Ertas, M., Cırpan, A., & Toppare, L. (2004). Synthesis and characterization of conducting copolymers of succinic acid bis-(4-pyrrol-1-yl-phenyl) ester and their electrochromic properties. Synthetic Metals, 143(1), 49-58. http://dx.doi. org/10.1016/j.synthmet.2003.10.018.

14. Pang, Y., Li, X., Ding, H., Shi, G., & Jin, L. (2007).

Electropolymerization of high quality electrochromic poly(3-alkyl-thiophene)s via a room temperature ionic liquid. Electrochimica Acta, 52(20), 6172-6177. http://dx.doi. org/10.1016/j.electacta.2007.04.015.

15. Groenendaal, L., Jonas, F., Freitag, D., Pielartzik, H., & Reynolds, J. R. (2000). Poly(3,4-ethylenedioxythiophene) and

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its derivatives: past, present, and future. Advanced Materials, 12(7), 481-494. http://dx.doi.org/10.1002/(SICI)15214095(200004)12:7<481::AID-ADMA481>3.0.CO;2-C. 16. Novak, J. P., Brousseau, L. C., Vance, F. W., Johnson, R. C., Lemon, B. I., Hupp, J. T., & Feldheim, D. L. (2000). Nonlinear optical properties of molecularly bridged gold nanoparticle arrays. Journal of the American Chemical Society, 122(48), 12029-12030. http://dx.doi.org/10.1021/ja003129h.

17. Vericat, C., Vela, M. E., Benitez, G., Carro, P., & Salvarezza, R. C. (2010). Self-assembled monolayers of thiols and dithiols on gold: new challenges for a well-known system. Chemical Society Reviews, 39(5), 1805-1834. http://dx.doi.org/10.1039/ b907301a. PMid:20419220.

18. Nakamura, T., Kondoh, H., Matsumoto, M., & Nozoye, H. (1999). Recognition properties of the nano-ordered structures of bis(mercaptomethyl)terthiophene monolayers on Au (111).

Synthetic Metals, 103(1-3), 2143-2144. http://dx.doi.org/10.1016/ S0379-6779(98)00602-X. 19. Muglali, M. I., Erbe, A., Chen, Y., Barth, C., Koelsch, P., & Rohwerder, M. (2013). Modulation of electrochemical hydrogen evolution rate by araliphatic thiol monolayers on gold. Electrochimica Acta, 90, 17-26. http://dx.doi.org/10.1016/j. electacta.2012.11.116. PMid:24235778.

20. Civit, L., Fragoso, A., & O’Sullivan, C. K. (2010). Thermal stability of diazonium derived and thiol-derived layers on gold for application in genosensors. Electrochemistry Communications, 12(8), 1045-1048. http://dx.doi.org/10.1016/j. elecom.2010.05.020.

Received: May 01, 2015 Accepted: Jun. 19, 2015

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http://dx.doi.org/10.1590/0104-1428.2021

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

Influence of flow pattern development at die entrance and inside annular die on extrudate swell behavior of NR compound Naret Intawong1*, Sittichai Udomsom1, Konnatee Sugtakchan1 and Watcharin Sitticharoen1 Department of Industrial Engineering, Faculty of Engineering, Rajamangala University of Technology Lanna, 128 Huay Kaew Road, Chiang Mai, 50300, Thailand

1

*naret_i@yahoo.com

Abstract This research studies influence of the flow pattern at annular die entrance through the inside of annular die flow channel of capillary rheometer on the swell behavior of NR compound. The annular die used in this research was specifically designed to create the specific pattern of Vortex Flow at Die Entrance (VFE) of NR compound. Results of the study showed that the thickness swell ratio was higher than diameter swell ratio by an average of 20% at every die gap size.

It was also found that the VFE flow pattern had direct significant influence on the swell behavior of NR compound while extrudating through annular die. Results from the study of the flow pattern could be used to explain why the thickness swell ratio is higher than the diameter swell ratio in every test condition.

Keywords: capillary rheometer, annular die, diameter swell ratio, thickness swell ratio, NR compound.

1. Introduction In polymer extrusion process, a device called annular die is used for most shaping of polymer products, such as in pipe extrusion process, extrusion blow moulding process, and blow film extrusion process. It is widely known that, for melt polymer extrudated through annular die, the size of polymer parison will expand both in diameter and thickness dimensions[1]. This is an important variable that production engineers must pay attention to, in order to control quality and size of polymer products. The products’ expansions in two dimensions are called diameter swell ratio and thickness swell ratio, respectively. In general, this occurrence could be explained in terms of elastic recovery and resident time, and the complex flow occurrences, due to the design of annular die[2,3].

Evidences from existing research show that important variable that influences the swell behavior of melt polymer after extrudated from the die is, in fact, the complex flow pattern of melt polymer at the die entrance which, in turn, resulting from the die design. Song et al.[4] studied the flow patterns of NR, SBR and EPDM in a barrel of capillary rheometer, using a wide range of die designs. They found that the radial flow simply moved inward to the capillary die as the ram moved down the barrel. So, no secondary flows occurred. Wood et al.[5] studied the flow pattern of natural rubber compound in different types of capillary rheometer, using colored layer technique. The experimental results show that velocity profiles and flow pattern are important variables in determining the flow properties of polymer.

Eggen and Hinrichsen[6] had investigated the effect of die entrance angle and die length on extrudate swell and the onset of extrudate distortion in capillary extrusion. They found that the elongation component at the entrance region mainly influenced the extrudate distortion. Sombatsompop and Dangtungee[7,8] both studied the effect of die/barrel system

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design on flow visualization and die swell of NR in a capillary rheometer, using colored layer technique. They found that the amount of natural rubber compound’s swell was influenced by pressure drop and complex flow pattern at the die entrance. In the most recent study of Intawong et al.[9], they studied the flow pattern and extrudate swell properties of Natural Rubber (NR) compound in a capillary rheometer, using two types of annular die: convergent annular die and divergent annular die. Their experimental results show that the thickness swell was higher than the diameter swell in every test condition. This difference could be explained by analysis of the complex flow pattern at the die entrance.

All the research mentioned above show the application of knowledge from studies about the development of flow pattern in melt polymer to explain the swell property of melt polymer while extrudating through the die. However, all these research are limited only to the development of flow pattern inside the barrel. Therefore, this research presents a continuing study from the research of Intawong et al.[9], by applying its results to demonstrate a direct influence of Vortex Flow at Die Entrance, which further develops into the die’s flow channel, on the swell behavior of melt polymer while extrudating through annular die, especially on the thickness swell ratio.

2. Experimental 2.1 Materials All of the tests used natural rubber (NR: STR 5L), supplied from PAN INNOVATION LIMITED (Thailand).

The materials were compounded in accordance with experimental procedure from the previous work of Intawong et al.[9].

The compound was divided into two separate parts: white

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Influence of flow pattern development at die entrance and inside annular die on extrudate swell behavior of NR compound pigmented NR compound (white color of NR+ Titanium Oxide compound) and unpigmented NR compound (brown color of NR compound).

2.2 Experimental technique and apparatus The experimental technique used for the study of the flow pattern of extrudated NR compound was colored layer technique. Details of the technique had already been published in the previous work of Intawong et al.[9], which reported an interesting result that the development of Vortex Flow at Die Entrance (VFE) had direct influence on the swell behavior of NR compound after extrudating through annular die. In order to get more insight into this occurrence, this research presents a new design of annular die that creates only the VFE flow pattern in the flow system. It also shows an obvious development of the flow pattern at the entrance through the flow channel of annular die. Results of the study could explain effect of VFE on the flow properties and the swell behavior of NR compound, without interference from the Vortex Flow at Wall (VFW) flow pattern. Details of the design in Figure 1 show that the annular die consists of 3 main parts: Die body #1, mandrel, and Die body #2, respectively.

Figure 1a shows that Die body #1 has an outer diameter of 36mm, with 4 holes of 14.5mm diameter for flow channel of melt polymer. Moreover, the top part of Die body #1 also has an annex (extended part) called a “Simulated obstructions” that features a cylindrical shape with 10 mm diameter and 6 mm height. This simulated obstruction is important in being a determiner and controller of NR compound’s flow direction to create the VFE flow pattern before going through flow channels of the annular die. It simulates flow condition of melt polymer flowing through a mandrel in a real production process. The mandrel part is designed to be centrally assembled to the bottom of Die body #1. Its diameter (a) could be changed to 2mm, 3mm, and 4mm, respectively. Both Die body #1 and mandrel are assembled with Die body #2 which has an outer diameter of 40mm and a constant flow channel of 6mm in diameter and 65mm in length. Thus, there are die gaps of 1mm, 1.5mm, and 2mm, respectively. Figure 1b shows a cross-section of annular die

that is assembled to a split barrel of the capillary rheometer, where the annular die is centrally fixed at the bottom of the barrel with a Die holder. In addition, a pressure transducer (Dynisco, Model PT460E-2CB-6, Franklin, MA)[10,11] is also installed on the 5mm top of the die entrance, in order to measure die entrance pressure drop, which will be further used to study the rheological properties.

2.3 Measurement of flow properties The wall shear stress (τW) and the apparent wall shear rate ( γ •w ) were determined using Equation 1 and Equation 2, respectively[12].

H ∆P τw = ent 2L

(1)

γ •w = − (1 n + 2 ) 2ν H

(2)

Where H = Die gap, ΔPENT = entrance pressure drop, L= Die land length, ν = average velocity, as defined by a piston speed of the capillary rheometer, and n = Power-law index.

In this work, the apparent wall shear rates were varied from 1 s–1 to 2.5 s–1.

2.4 Measurements of extrudate swell ratio The diameter swell ratio (BD) and the thickness swell ratio (BT) of NR compound were calculated from Equation 3 and Equation 4, respectively[13].

BD =

BT =

Dp

Do hp ho

(3)

(4)

Where DP = parison’s diameter, DO = outside diameter of the annular die, hP = parison’s thickness, and hO = die gap of the annular die.

Figure 1. (a) Die design; (b) a schematic cross-section of the annular die in a capillary rheometer.

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Intawong, N., Udomsom, S., Sugtakchan, K., & Sitticharoen, W.

3. Results and Discussion 3.1 Flow pattern development in the barrel Figure 2a-c shows development of the flow pattern of NR compound occurred inside the barrel of capillary rheometer in a form of Axial Flow (AF)[9,14], at the piston extrudate rates of 25mm to 100mm with 1.5 s–1 apparent wall shear rate.

This resulted from using a die with die gaps of 1mm, 1.5mm, and 2mm, respectively. It was found that the development of Axial Flow pattern showed continuous development of the melt layer velocity throughout all extrudate rates.

In general, there are shear flow pattern and parabolic-like

pattern with low melt velocity at the wall, and the highest velocity at the center of the barrel. These experimental results correspond with results from the previous study of Intawong et al.[9], as expected.

Regarding the effect of die gap size on the development of Axial Flow pattern of NR compound, it was found that reduction of the die gap size made the AF melt velocity increased significantly. This was confirmed by experimental results that counted number of NR compound layer with the AF flow left in the barrel of each die gap size, as shown in Figure 3. Results indicated that the number of NR compound layer linearly decreased continuously when the extrudate rate was increased in every die gap size. At the same extrudate rate, it was found that the number of NR compound layer left in the barrel decreased with the decrease of die gap size. This implied that the melt velocity of NR compound in the barrel increased as well. For instance, at the extrudate rate of 50mm, the number of NR layer decreased from 10 to 9 and 8 layers when the die gap size reduced from 2mm to 1.5mm and 1mm, respectively. That is, it increased by an average of 5% for every 0.5mm reduction of die gap size. This implied that the AF melt velocity of NR compound increased by 5% for every 0.5mm reduction of die gap size as well.

This resulted from the effect of adjusting balance of volumetric flow rate while the NR compound flew into the annular die channel, as could be explained by Equation 5[15].

Q = vA (5)

Where A is a cross-sectional area of annular die channel, v is an average velocity of NR compound, and Q is a volumetric flow rate of NR compound.

It can be seen that the size of die gap is reduced by decreasing the cross-sectional area of annular die channel (A) while the total volumetric flow rate of NR compound after extrudating from the die remains the same, due to a constant extrusion rate or apparent wall shear rate. Therefore, the NR compound flowing through the barrel into the annular die channel is accelerated (v), in order to adjust the balance of Volumetric flow rate to remain constant[16].

Figure 2. Flow patterns of NR compound in the barrels of capillary rheometer with different piston displacements [25mm, 50mm, 75mm and 100mm] and shear rate of 1.5 s–1. (a) die gap = 1mm; (b) die gap = 1.5mm; and (c) die gap = 2mm.

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Figure 3. Number of NR compound layer left in the barrel of capillary rheometer with the die gap of 1mm, 2mm and 3mm and at the piston displacements of 25mm, 50mm, 75mm and 100mm.

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Influence of flow pattern development at die entrance and inside annular die on extrudate swell behavior of NR compound 3.2 Flow pattern development in annular die This section describes an analysis of the Radial Flow (RF) flow pattern at the die entrance which occurred after the AF mentioned above. This will provide more insight into the development of flow pattern from the barrel into the annular die channel. This will also lead to a clearer explanation of the swell behavior of melt polymer flowing through the annular die. Figure 4a-c shows the flow pattern development of NR compound while flowing from the barrel into the annular die channel, which are selected from

experimental results at the shear rate of 1.5 s–1, die gap of 2mm, and the extrudate rate of 50mm to 75mm. The flow pattern development of NR compound was detected by tracking the movement of Layer A, Layer B and Layer C from the barrel into the annular die, respectively.

In Figure 4a, Layer A is shown in a brown line at the top of the layer, which is developing its flow pattern from AF to RF. Layer B shown in a white line below begins to flow into the annular die channel along the surface of artificial blockage in a form of VFE. Both ends of this rubber layer begin to enter into the center of the annular die channel.

Layer C which is the final flow layer of NR Compound is shown in a brown line flowing completely into the annular die channel. Development of the flow pattern occurs continuously with the extrudate rate, as shown in Figure 4b.

Layer A begins to enter the annular die channel while Layer B begins to replace Layer C, as can be seen that all the NR layers inside the annular die channel change from brown to white. In the final stage of flow pattern development in Figure 4c, Layer A replaces Layer B completely again, as can be seen that all the NR Compound inside the annular die channel changes from white to brown.

The flow pattern mentioned above develops continuously while the NR compound was extrudated through the annular die, and the molecular chain of NR compound was aligned (molecular orientations) in the same direction as the flow.

The important occurrence throughout the flow is, while there is replacement between layers, every layer is forced to flow along the surface of both simulate obstructions at the top and the mandrel, which is a very long distance.

As a result, there is more stretching of molecular chain of NR compound at the inner layer than at the outer layer, as shown in Figure 5. Therefore, there is accumulation of elastic storage energy at the inner wall of NR compound layer.

After exiting the annular die, the inner layer will become the wall of parison that will be influenced by an emission of elastic energy accumulated throughout the flow. As a result, the expansion in thickness is more pronounced than the expansion in diameter. This swell behavior is also found in this research and will be further explained in details.

Figure 4. (a) The first stage of flow pattern development of NR compound Layer A, Layer B, and Layer C; (b) the replacement of Layer A to Layer B and Layer B to Layer C; (c) the final stage of flow pattern development by NR compound Layer A replaced by Layer B completely.

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Figure 5. A schematic molecular orientations drawing of the NR compound in the inner layer zone and outer layer zone of an annular die channel.

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Intawong, N., Udomsom, S., Sugtakchan, K., & Sitticharoen, W. 3.3 Extrudate swell ratio behavior of NR compound The flow pattern development of NR compound from the barrel into the annular die channel mentioned above has an obvious direct effect on the swell behavior of NR compound extrudated through annular die of every size, as shown in Figure 6. In general, it is found that the thickness swell and the diameter swell of NR compound increase with the increase of apparent shear rate in every test condition.

This is because the increase of apparent shear rate is like the increase of force on NR compound while flowing into the annular die. This force occurs in a form of an apparent shear stress that increases with the increase of apparent shear rate, as shown in Figure 7. The increase of apparent shear stress indicates that there is increasing accumulation of elastic storage energy of NR compound while exiting the annular die. Thus, there is emission of energy which affects the swell of NR compound parison that increases in both dimensions.

When comparing the swell behavior of NR compound between the thickness swell ratio and the diameter swell, it

Figure 6. Diameter swell and thickness swell of NR compound flowed from the annular die with different die gap of 1mm, 1.5mm and 2mm.

Figure 7. Flow curves of NR compound with the die gap of 1mm, 1.5mm, and 2mm.

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was found that the thickness swell ratio was higher than the diameter swell ratio in every test condition. This corresponds with the research finding[9] which found that the thickness swell ratio of NR compound extrudated through every size of die gap was in a range of 2-2.5, while the diameter swell ratio was lower in a range of 1.6-1.9. In other words, it could be said that the thickness swell ratio was higher than the diameter swell ratio by about 20% in every size of die gap. This could be explained by the theory of accumulated elastic energy of NR compound while flowing in the annular die channel, together with evidences of the flow pattern development of NR compound described in the above section. That is, while flowing into the annular die channel, the molecular chain at the inner layer of NR compound (the part that will become the thickness of NR parison) tends to be stretched more than other layers. This can be seen from flow direction of the layer that is forced to flow along the surface of the simulate obstructions before entering the annular die channel, and it is stretched again at the mandrel’s surface. Consequently, this NR compound layer is forced by a shear stress more than other layers, and the force is also accumulated as elastic storage energy more than in other layers. Therefore, there is more emission of elastic energy at the inner layer of NR compound and, hence, more pronounced in the higher thickness swell ratio.

This explanation may contradict with the Deborah number (Ndep) theory which is used to explain the swell behavior of melt polymer in many other research[7,8]. This theory explains that the longer resident time of polymer in extrudate system with a long flowing distance causes the occurrence of molecular relaxation which reduces the shear stress; thus, the swell ratio decreases after exiting the die. However, findings of this research indicate differently. In particular, the inner layer of NR compound that has longer flowing distance than other layers tends to have a higher swell ratio.

With this finding, it is believed that the length of resident time do have certain effect on the swell behavior, but less than the influence of shear stress on the surfaces of simulate obstructions and mandrel. This explanation corresponds with the research of Mu et al.[17] who studied shear stress distributions of melt polymer in annular die using FES/BPNN/ NSGA-II mathematical model and found that the shear stress distributed densely at the mandrel’s surface. The experimental result about the effect of die gap on both thickness and diameter swell behaviors of NR compound is another piece of evidences that supports the above explanation. It can be seen that both thickness swell and diameter swell of NR compound increase in relation to the decrease of die gap’s size. This especially affects the thickness swell ratio more than the diameter swell ratio. It is also found that, at the same apparent wall shear rate, the thickness swell tends to increase in relation to the decrease of die gap’s size. This is because the size of die gap is decreased by the increasing mandrel’s diameter (a), which also increases the surface area of mandrel. The increasing area of mandrel’s surface leads to the increase of shear stress on the molecular chain of NR compound’s inner layer. After exiting the annular die, the thickness swell is found to increase in relation to the decrease of die gap’s size. For example, at the apparent wall shear rate of 1.5 s–1, it was found that the thickness swell ratio increased from 2.11 to 2.23 and 2.36, in relation Polímeros, 25(5), 508-513, 2015

Influence of flow pattern development at die entrance and inside annular die on extrudate swell behavior of NR compound to the decrease of die gap from 2mm to 1.5mm and 1mm, respectively. In other words, the average increase is about 7% for every 0.5mm decrease of die gap at every apparent wall shear rate. On the other hand, the diameter swell ratio also tends to increase in relation to the decrease of die gap, but only at an average of 3% for every 0.5mm decrease of die gap, at every apparent wall shear rate. This is because the NR compound that will become the outer diameter of parison is the outside layer of the wall of annular die that seems to be influenced by less amount of shear stress. This is because the surface area of the outer diameter of annular die wall does not change from its constant outer diameter of 6mm in every test condition.

4. Conclusion This research presents the study of the effects of the flow pattern of NR compound at the annular die entrance through the annular die flow channel on the swell behavior of NR compound in capillary rheometer. Results of the study explain the influence of the Vortex Flow at Die Entrance (VFE) flow pattern on the swell behavior of NR compound while extrudating through annular die, especially of the thickness swell ratio. That is, the thickness swell ratio is higher than the diameter swell ratio by an average of 20% in every die gap’s size. This could be explained from the fact that the VFE flow pattern at annular die entrance causes more stretching of the molecular chain and more accumulation of elastic storage energy at the NR’s inner layer, which will later become thickness of NR parison, than in the NR’s outer layer while flowing inside the annular die flow channel.

5. Acknowledgements The authors would like to thank the “Upgrading Theses into Research Publications, Creation, and Academic Service for Community Project” (HRG: Hands-on Research Group) of Rajamangala University of Technology Lanna (RMUTL) for financial support throughout this work.

6. References 1. Cogswell, F. N. (1981). Polymer melt rheology. London: George Godwin.

2. Garcia-Rejon, A., & Dealy, J. M. (1982). Swell of extrudate from an annular die. Polymer Engineering and Science, 22(3), 158-165. http://dx.doi.org/10.1002/pen.760220305.

3. Wagner, A. H., & Kalyon, D. M. (1996). Parison formation and inflation behavior of polyamide-6 during extrusion blow molding. Polymer Engineering and Science, 36(14), 1897-1906. http://dx.doi.org/10.1002/pen.10586.

4. Song, H. J., White, J. L., Min, K., Nakajima, N., & Weissert, F. C. (1988). Rheological properties, extrudate swell, and die entry extrusion flow marker experiments for rubber-carbon black compounds. Advances in Polymer Technology, 8(4), 431-449. http://dx.doi.org/10.1002/adv.1988.060080407.

5. Wood, A. K., Read, A. G., & Lovegrove, J. G. A. (1989). The effects of rheometer design in the measurement of the flow properties of polymer melts. Plastics and Rubber Processing and Applications, 12(1), 15-20.

Polímeros, 25(5), 508-513, 2015

6. Eggen, S., & Hinrichsen, E. (1996). Swell and distortions of high-density polyethylene extruded through capillary dies.

Polymer Engineering and Science, 36(3), 410-424. http:// dx.doi.org/10.1002/pen.10428.

7. Sombatsompop, N., & Dangtungee, R. (2001). Effect of die design on flow visualization and die swell of NR in a capillary rheometer. Journal of Materials Science Letters, 20(15), 14051408. http://dx.doi.org/10.1023/A:1011695527853.

8. Sombatsompop, N., & Dangtungee, R. (2001). Flow visualization and extrudate swell of natural rubber in a capillary rheometer: effect of die/barrel system. Journal of Applied Polymer Science, 82(10), 2525-2533. http://dx.doi.org/10.1002/app.2103.

9. Intawong, N-T., Wiratket, A., & Meechue, P. (2014). Flow visualization & extrudate swell behavior of natural rubber compound in annular die capillary rheometer. Polímeros: Ciência e Tecnologia, 24(4), 434-440. http://dx.doi.org/10.1590/01041428.1696.

10. Intawong, N.-T., Darajang, A., Udomsom, S., Yoochooshai, T., & Kantala, C. (2014). An annular rotating-die technique in extrusion process: effect of mandrel rotating speed on entrance pressure drop and flow properties of molten HDPE. International Journal of Plastics Technology, 18(2), 241-251. http://dx.doi.org/10.1007/s12588-014-9080-1.

11. Intawong, N.-T., Wongchaleo, C., & Sombatsompop, N. (2008).

Rheological properties, flow visualization and extrudate swell of NR compound by rotating-die rheometer. Polymer Engineering and Science, 48(6), 1191-1198. http://dx.doi. org/10.1002/pen.21074.

12. Winter, H. H., & Fritz, H. G. (1986). Design of dies for the extrusion of sheets and annular parisons: the distribution problem. Polymer Engineering and Science, 26(8), 543-553. http://dx.doi.org/10.1002/pen.760260805.

13. Koopmans, R. J. (1992). Extrudate swell of high density polyethylene. Part III: extrusion blow molding die geometry effects. Polymer Engineering and Science, 32(23), 1755-1764. http://dx.doi.org/10.1002/pen.760322304.

14. Intawong, N.-T., Kantala, C., Lotaisong, W., & Sombatsompop, N. (2011). A die rotating system for moderations of extrusion load and pressure drop profiles for molten PP and wood/ polypropylene composites in extrusion processes. Journal of Applied Polymer Science, 120(2), 1006-1016. http://dx.doi. org/10.1002/app.33209.

15. Diraddo, R. W., & Garcia-Rejon, A. (1992). Noncontact measurement of parison thickness profiles affected by swell and sag in continuous extrusion blow molding. Polymer Engineering and Science, 32(19), 1401-1410. http://dx.doi. org/10.1002/pen.760321902.

16. Intawong, N.-T., Darajang, A., Udomsom, T., Yoochooshai, S., & Kantala, C. (2014). An annular rotating-die technique in extrusion process: effect of mandrel rotating speed on extrudate swell behavior of HDPE parison. International Polymer Processing, 29(5), 607-615. http://dx.doi.org/10.3139/217.2930.

17. Mu, Y., Zhao, G., Wu, X., & Zhang, C. (2010). An optimization strategy for die design in the low-density polyethylene annular extrusion process based on FES/BPNN/NSGA-II. International Journal of Advanced Manufacturing Technology, 50(5-8), 517-532. http://dx.doi.org/10.1007/s00170-010-2556-z.

Received: Dec. 10, 2014 Revised: May 06, 2015 Accepted: June 01, 2015

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