Polímeros: Ciência e Tecnologia (Polimeros), vol.25, n.4, 2015

waters.com

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APC vs. GPC com padrão de poliestireno Mp = 510 30.00

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VOLUME XXV - N° 4 - JUL/AGO - 2015

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Editorial

http://dx.doi.org/10.1590/0104-1428.2504

Caros leitores

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Elisabete Frollini

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Abraços

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Os sucessivos congressos realizados pela ABPol têm confirmado a presença de uma sólida comunidade de pesquisadores desenvolvendo pesquisa na área de Polímeros no país, cuja manutenção e expansão estão ligadas, por exemplo, ao fortalecimento da pós-graduação e de programas de pós-doutorado no país. Esta comunidade vem perseguindo metas no sentido de se alinhar a centros de excelência em pesquisa internacionais, concentrando-se na geração de recurso humano capacitado, assim como na criação de uma infraestrutura dinâmica, para o que contam com o fundamental apoio de agências de fomento, fundações, fundos setoriais de ciência e tecnologia, assim como do setor privado.

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O progresso da pesquisa nesta área requisita disponibilidade de recurso humano altamente qualificado, assim como de uma infraestrutura dinâmica, ou seja, com capacidade de acompanhar os avanços que ocorrem em escala mundial.

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Neste ano a Associação Brasileira de Polímeros (ABPol) realiza o 13o Congresso Brasileiro de Polímeros (Natal, Rio Grande do Norte, 10 a 22 de outubro). Esta corresponde a uma das atividades desta Associação, que tem como parte dos objetivos a difusão de conhecimento e divulgação de resultados de pesquisas em andamento, visando o avanço da área de Materiais Poliméricos, a qual pode ser considerada como estratégica, em qualquer país.

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Polímeros, 25(4), 2015

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P o l í m e r o s - N º 4 - V o l u m e X X V - J u l / A g o - 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 ”

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Polímeros P r e s i d en t e

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Conselho Editorial

Comitê Editorial

Marco-Aurelio De Paoli (UNICAMP/IQ)

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Membros

do

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) 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)

Elisabete Frollini – Editora

Membros

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Comitê Editorial

Adhemar C. Ruvolo Filho Bluma G. Soares César Liberato Petzhold Glaura Goulart Silva José António C. Gomes Covas José Carlos C. S. Pinto Regina Célia R. Nunes Sebastião V. Canevarolo Jr.

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Produção

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Assessoria Editorial

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www.editoracubo.com.br

Tiragem 1.500 exemplares

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“Polímeros” é uma publicação da Associação Brasileira de Polímeros Rua São Paulo, nº 994 CP 490 - 13560-340 - São Carlos, SP, Brasil Fone/Fax: (16) 3374-3949 e-mails: abpol@abpol.org.br / revista@abpol.org.br http://www.abpol.org.br

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Data de publicação: Agosto 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 4 (jul/ago. 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

S e ç ã o T é cn i c a Using glycerol produced from biodiesel as a plasticiser in extruded biodegradable films

Polyurethane/Poly(2-(Diethyl Amino)Ethyl Methacrylate) blend for drug delivery applications María Gabriela Echeverría, Oscar Ricardo Pardini, María Valeria Debandi, Nora Judit François, Marta Edith Daraio and Javier Ignacio Amalvy............................................................................................................................................................................... 336

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Ana Paula Bilck, Carmen Maria Olivera Müller, Juliana Bonametti Olivato, Suzana Mali, Maria Victoria Eiras Grossmann and Fabio Yamashita........................................................................................................................................................................................ 331

Evaluation of chemical and mechanical resistance of virgin and recycled poly (ethylene terephthalate) and poly(methylene oxide) when applied as gravel pack in petroleum wells Alexandre Zacarias Ignácio Pereira and Marcia Cerqueira Delpech............................................................................................................. 344 Andrés Felipe Cordero, Milton Gómez and José Humberto Castillo.............................................................................................................. 351

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Polyphenolic resin synthesis: optimizing plantain peel biomass as heavy metal adsorbent Synthesis and characterization of new soluble polyamides from Acenaphtohydrazinomercaptotriazole diamine Hossein Mighani and Najmeh Kia................................................................................................................................................................... 356

Natural rubber latex: determination and interpretation of flow curves Harrison Lourenço Corrêa, Ana Maria Furtado de Sousa and Cristina Russi Guimarães Furtado.............................................................. 365 Gabriel Abreu Uehara, Marcos Pini França and Sebastiao Vicente Canevarolo Junior................................................................................ 371

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Recycling assessment of multilayer flexible packaging films using design of experiments Blends of ground tire rubber devulcanized by microwaves/HDPE - Part B: influence of clay addition Fabiula Danielli Bastos de Sousa, Júlia Rocha Gouveia, Pedro Mário Franco de Camargo Filho, Suel Eric Vidotti, Carlos Henrique Scuracchio, Leice Gonçalves Amurin and Ticiane Sanches Valera..................................................................................... 382

Improving the thermal properties of fluoroelastomer (Viton GF-600S) using acidic surface modified carbon nanotube Synthesis, characterization and thermal degradation of cross-linked polystyrene using the alkyne-functionalized esters as a crosslinker agent by click chemistry method

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Javad Heidarian, Aziz Hassan and Nor Mas Mira Abd Rahman.................................................................................................................... 392

Hakan Akat and Fehmi Saltan......................................................................................................................................................................... 402

Avaliação das propriedades mecânicas e morfológicas de compósitos de PEAD com pó de Pinus taeda e alumina calcinada Karine Grison, Taís Caroline Turella, Lisete Cristine Scienza e Ademir José Zattera.................................................................................... 408 Luciana Cunha Costa, Maria Aparecida Larrubiua Granado Moreira Rodrigues Mandu, Luiz Claudio de Santa Maria e Mônica Regina da Costa Marques................................................................................................................................................................ 414

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Resinas poliméricas reticuladas com ação biocida: atual estado da arte

Capa: 13º Congresso Brasileiro de Polímeros.

Elaboração artística Editora Cubo.

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I N F O R M E S

Colour-changing polymer tackles concussion diagnosis head on

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Diagnosing concussion is a difficult task, but scientists in the US have designed a tool that can highlight a potential injury with a polymer-based patch that changes colour depending on the level of impact. It is hoped the material could be integrated into protective headgear for athletes or soldiers.

Intense scrutiny is being levelled at sports organisations over the lack of protection that athletes have to defend them from a severe head injury. Although the safety culture is beginning to change in sports such as American football, medical professionals still face the difficult prospect of diagnosing a suspected concussion quickly in the high pressure environment of a sporting arena or stadium.

For Shu Yang from the University of Pennsylvania, the blurred line in diagnosing concussion raises an unsettling question both for researchers and doctors, who may not be sure whether a patient has suffered an injury. ‘To what extent should players or soldiers [be allowed to] go back to the battlefield or the playfield?’ Yang asked when speaking at the 250th ACS National Meeting & Exposition in Boston, US. Her concerns led her to seek a solution to the concussion diagnosis conundrum. Yang, along with colleagues at Villanova and Temple University, looked to structural colours in nature for ideas. ‘We take inspiration from opal, which is made from silica beads,’ says Yang. She goes on to explain that such materials take on particular colours depending on their internal microstructure, and changes in this structure can alter how light is diffracted.

But producing analogous crystals in the lab is incredibly expensive, so the team turned to flexible polymers instead. Yang and her colleagues used a light-sensitive epoxy named SU-8, melted it and poured it over a crystalline arrangement of opals.

Once the polymer had cooled and solidified, the opals were removed to produce a porous polymer network resembling a sponge.

‘Light coming towards this porous material gets reflected,’ says Yang. ‘It’s like the colour you see in iridescence in [a] soap bubble.’ The pores are acting as ‘inverse opals’, according to Yang.

By applying a force roughly equivalent to a typical football tackle using nanoindentation, Yang was able to see the porous patch changed colour. ‘If you have external force hitting this porous material, the pore size [and] shape will be changed,’ she explains. ‘So, this… will cause a structural change, [which] causes a colour change.’

Crucially this colour change is not reversed when the force is removed, making it ideal for protective equipment. ‘Once you remove the force, the material is permanently deformed,’ says Yang. It can also be tuned to accommodate for different coloured surfaces: E4

‘If we started with different nanoparticles, we can generate different initial colours, whether it’s a red, orange, green or purple.’

Yang acknowledges, however, that a commercial product may still be a long way off, but she is glad that technology will help in tackling the concussion issue head on. ‘There [are] a lot of things we need to do,’ she says. ‘From a protective point of view, at least we can use this to tell people what’s going on.’

Source: Royal Society of Chemistry

New polymer able to store energy at higher temperatures A team of researchers at the Pennsylvania State University has created a new polymer that is able to store energy at higher temperatures than conventional polymers without breaking down. The team describes how they created the polymer and why they believe it could be useful in many products. Harry Ploehn with the University of South Carolina offers a brief history of polymers created for use in electronics, in a News & Views piece in the same journal issue, and describes the work done by the team on this new effort–he also offers an opinion on the prospects for the newly development polymer.

As Ploehn notes, dielectric capacitors are used in wide variety of applications that require holding onto a charge and then offering a short burst of power when needed. In many applications dielectrics are made of polymers (because they are light, relatively easy to make and because defects can be easily controlled), but there are still some areas where they cannot be used because they cannot function correctly under temperature extremes—that prevents their use inside car engines, for example. In this new effort, the researchers have taken a new approach to creating a polymer that allows for use in extremely hot applications.

The new polymer was created by the team by adding nanometer-scale sheets of boron nitride to a conventional polymer, which testing showed increased its energy density by 400 percent (which means capacitors made using it could be smaller and thus lighter). And testing also showed the newly improved polymer was able to remain stable at temperatures as high as 300°C, and was able to withstand rigorous bending.

One drawback of the new polymer is that because it requires an extra step, its production costs would be higher than for conventional dielectric polymer capacitors, and there are also still questions about how easy it would be to prevent defects and whether it will stand up to long term wear and tear. If it proves to be resilient and a way can be found to drive down costs, it is likely, Ploehn believes, that the new polymer will have a bright future in applications ranging from hybrid cars to aerospace systems.

Source: Phys.org Polímeros, 25(4), 2015

January Plastics in Automotive Date: 14 January 2016 Local: Detroit - USA Website: www.plasticsnews.com/2015auto Thermoplastic Concentrates 2016 Date: 26-28 January 2016 Local: Florida - USA Website: http://www.amiplastics.com/events/event?Code=C697 Interplastica 2016 Date: 26-29 January 2016 Local: Moscow - Russia Website: http://www.interplastica.de/

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/

February

Guangzhou International Wood-Plastic Composites Fair 2016 Date: 13–16 May 2016 Local: Guangzhou - China Website: http://www.musuz.com/

Polymers in Photovoltaics 2016 Date: 2-3 February 2016 Local: Düsseldorf - Germany Website: http://www.amiplastics.com/events/event?Code=C703

International Workshop on Polymer Reaction Engineering Date: 17–20 May 2016 Local: Hamburg - Germany Website: http://events.dechema.de/events/en/pre2016.html

6th Annual Next Generation Bio-Based & Sustainable Chemicals Date: 3-5 February 2016 Local: New Orleans - USA Website: http://www.infocastinc.com/events/biobased-chemicals

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 West 2016 Date: 9-11 February 2016 Local: California - USA Website: http://plastecwest.plasticstoday.com/ SPE International Polyolefins Conference Date: 22-25 February 2016 Local: Texas - USA Website: https://www.spe-stx.org/conference.php

March Sustainable Plastics 2016 Date: 1-2 March 2016 Local: Cologne - Germany Website: http://www.amiplastics.com/events/event?Code=C706 Plastimagen 2016 Date: 8-11March 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/

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/

June 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 Organic Semiconductors Date: 22–25 September 2016 Local: Dubrovnik - Croatia Website: http://www.zingconferences.com/conferences/organicsemiconductors/

November Expoplast 2016 Date: November 30 - December 1, 2016 Local: Québec - Canada Website: http://expoplast.plasticstoday.com/

Polímeros, 25(4), 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(4), 2015

Associados da ABPol As nossas boas vindas...

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(4), 2015 E7

http://dx.doi.org/10.1590/0104-1428.1803

Using glycerol produced from biodiesel as a plasticiser in extruded biodegradable films Ana Paula Bilck1, Carmen Maria Olivera Müller1, Juliana Bonametti Olivato1*, Suzana Mali2, Maria Victoria Eiras Grossmann1 and Fabio Yamashita1 Departamento de Ciência e Tecnologia de Alimentos, Centro de Ciências Agrárias, Universidade Estadual de Londrina - UEL, Londrina, PR, Brazil 2 Departamento de Bioquímica e Biotecnologia, Centro de Ciência Exatas, Universidade Estadual de Londrina - UEL, Londrina, PR, Brazil

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*jubonametti@uel.br

Abstract The demand for renewably sourced biodegradable materials has increased the need to produce materials that combine appropriate functional properties at competitive costs. Thermoplastic starch and polyester blends are an interesting alternative to current materials due to the low cost of starch and the functional properties and processability of the resulting blends. Producing thermoplastic starch (TPS) requires using a plasticiser at concentrations between 20 and 30%wt (in relation to starch). Glycerol is the most common plasticiser due to its high plasticising capacity and thermal stability at processing temperatures. The objective of this study was to evaluate glycerol waste from the biodiesel industry, with different degrees of purification, as plasticisers for TPS / poly (butylene adipate-co-terephthalate) (PBAT) blends.

Different purities of glycerol produced films with similar mechanical, optical and barrier properties to those made with purified glycerol (99.7%). Therefore, crude glycerol is a renewable alternative plasticiser that reduces the cost of plasticisation by 6-fold.

Keywords: cassava starch, poly (butylene adipate-co-terephthalate), biopolymers, extrusion, biodegradable packaging.

1. Introduction The search for renewable energy sources that will ensure sustainable development has resulted in using biodiesel as an alternative fuel in the Brazilian energy matrix. Glycerol is the main by-product of biodiesel production and corresponds to approximately 10% of the total biodiesel production[1]. Brazil produced 1.2 billion litres of biodiesel in 2008 to supplement plain diesel at a 2% ratio, as required by law, resulting in the production of over 100 million litres of glycerol[2]. The crude glycerol obtained by the transesterification of triglycerides with alcohol has a low aggregate value due to the presence of impurities, such as water, methanol residues, sodium hydroxide, free fatty acids, fatty acid salts, esters, sulphur compounds, proteins and minerals[3].

The estimated glycerol production for 2013 is 488 million litres, and there are no current prospects to convert it into products with a greater aggregate value. The price of glycerol is related to its degree of refinement, ranging from US$167/ton for crude glycerol to US$267/ton for technical grade glycerine and US$1000/ton for bi-distilled glycerol.

The industrial use of glycerol is essential for the economic sustainability of the biodiesel industry in Brazil.

Glycerol is used as a plasticiser to produce starch-based biodegradable films. Starch and glycerol melt and flow at temperatures between 90 °C and 180 °C and under shear stress, producing thermoplastic starch that, allowing their use injection, extrusion and blowing equipment. Plasticisers create greater flexibility in the polymer structure by reducing the intermolecular forces and the glass transition temperature of the material, which increases the mobility of the polymer chains in the starch films. The required

Polímeros, 25(4), 331-335, 2015

proportion of starch and glycerol depends on the type of starch used. According to the literature[4-8] approximately 20-25 kg of glycerol are necessary to produce 100 kg of thermoplastic starch. The interactions between glycerol, starch and PBAT are mostly related to hydrogen bonds and the role of glycerol as plasticiser was already fully discussed by other researchers[6,9].

Thermoplastic starch materials have some drawbacks, such as poor water resistance and comparatively poor mechanical properties. However, these materials can be blended with synthetic co-polyester biodegradable polymers to help improve these shortcomings. Several researches were developed using thermoplastic starch and poly (butylene adipate-co-terephthalate) (PBAT) to produce biodegradable blends[10-12]. According several authors[13,14] is possible to obtain starch/PBAT films with good mechanical and barrier properties using around 40%wt of PBAT in the formulation.

The objective of this work was to test three grades of glycerol from biodiesel production to develop biodegradable films based in cassava starch/PBAT, obtained by blow extrusion.

2. Materials and Methods 2.1 Materials Three different grades of glycerol were obtained as by-products from biodiesel production (Meridional TCS Ind. e Com. de Oleos S.A, Brazil): crude glycerol (CG), technical grade glycerine (TGG) and bi-distilled glycerine

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Bilck, A. P., Müller, C. M. O., Olivato, J. B., Mali, S., Grossmann, M. V. E., & Yamashita, F. (BDG) (Table 1 and Figure 1) and were used as starch plasticisers. The biodegradable polymers tested were native cassava starch (Indemil, Brazil) and poly (butylene adipate‑co-terephthalate) (PBAT) from Basf (Germany), traded as Ecoflex 7011.

2.2 Film production The film was produced by blow extrusion using a pilot extruder (BGM EL-25 (São Paulo, Brazil)), which is made up of a 25 mm diameter screw, a 10-HP motor drive, four heating zones and an external cooling air ring with a 300- to 350-mm diameter.

The film was manufactured using a formulation based in our previous results[13-15] by mixing 40.0%wt PBAT, 46.6%wt cassava starch and 13.4%wt glycerol of three different types (Table 1). This mixture was extruded, pelleted and the resulting blend pellets were extruded twice and then processed to form a film by blow extrusion.

The formulations were named according the glycerol used as CG (crude glycerol), TGG (technical grade glycerine) and BDG (bi-distilled glycerine).

The maximum tensile strength (MPa), elongation at break (%) and Young’s or elasticity modulus (MPa) were assessed.

2.3.2 Water vapour permeability (WVP) The tests were conducted using the ASTM method E-96‑00[17], with some modifications. The film was previously conditioned at 53% RH and 25 °C for 48 hours, and each film sample was fixed in a circular opening of a permeation cell with a diameter of 60 mm2 sealed with silicone grease.

The interior of the cell was filled with a saturated magnesium chloride solution (33% RH) and was stored at 25 °C in a desiccator containing a saturated sodium nitrite solution to provide 64% RH. 2.3.3 Optical properties The films’ opacity was determined using a BYK Gardner colorimeter (D65 illuminant and visual angle of 10°). Sample opacity (Y) was calculated as the ratio between the opacity of the sample placed under a black pattern (YB) and the opacity of the sample placed under a white pattern (YW), according to the equation: Y = (Yb / Yw) × 100. Five samples of each formulation were tested.

2.3 Film characterisation

2.3.4 Contact angle measurement

2.3.1 Mechanical properties of the films

The contact angle was measured using a contact angle meter (Data Physics OCA-15, Germany). Images were captured through a high-resolution camera and were analysed using the Image Tool software. Film samples (40 mm × 20 mm) were fixed in a glass plate and placed at the base of the unit. A distilled water drop (5 μL) was placed on the film surface using a syringe. The measurements were performed at room temperature, and the contact angle was calculated as the average of five measurements after drop stabilisation.

The contact angle hysteresis was calculated by measuring the difference between the advancing and receding angles.

The mechanical properties of the films were obtained in a Stable Micro Systems texture analyser, model TA.TX2 plus (Stable Micro Systems, Surrey-England), according to the methodology established by the American Society for Testing and Material ASTM D882-00[16]. Ten repetitions of each film direction (transverse and longitudinal) were tested.

Table 1. Chemical composition of different glycerol from biodiesel production.

Composition Glycerol content (%) Moisture (%) Methanol content (%) Ashes (%) pH Density (g/mL) CIE-Lab Colour Parameters L a* b*

CG 80.71 10.83 0.014 5.62 6.0 1.25

TGG 81.90 11.50 0.024 5.90 6.0 1.26

34.8 2.7 15.9

42.7 –0.3 10

BDG > 99.7 < 0.3 * * * * 46.6 -0.1 1.0

CG = crude glycerol, TGG = technical grade glycerine, BDG = bi-distilled glycerine. *Data not provided by the manufacturer.

Figure 1. Crude glycerol (CG), technical grade glycerine (TGG) and bi-distilled glycerine (BDG) from biodiesel production.

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2.3.5 Statistical analysis The results of the mechanical and WVP tests were analysed using STATISTICA 7.0 software (Statsoft, Oklahoma), with analysis of variance (ANOVA) and Tukey’s test at a 5% significance level.

3. Results and Discussion 3.1 Mechanical properties The mechanical properties of the films produced with cassava starch, PBAT and the different types of glycerol are presented in Table 2.

The tensile strength of the films ranged from 4.9 ± 0.3 MPa to 6.4 ± 0.7 MPa, and there were no significant differences among the films produced with crude glycerol (CG), technical grade glycerine (TGG) and bi-distilled glycerine (BDG) in both longitudinal and transverse tensile tests. These results showed that the presence of some impurities in the crude glycerol did not influence the tensile strength of the films.

On the other hand, for the same formulation, the longitudinal tensile strength was significantly higher than the transverse tensile strength by approximately 11 to 24%, most likely due to the direction of the polymer chains’ alignment during the extrusion process. This anisotropic Polímeros , 25(4), 331-335, 2015

Using glycerol produced from biodiesel as a plasticiser in extruded biodegradable films Table 2. Mechanical properties of the films.

Sample CG TGG BDG

Tensile strength (MPa) L T 5.9a,A(±0.4) 5.3b,A(±0.3) 6.4a,A(±0.7) 5.0b,A(±0.5) 6.1a,A(±0.6) 4.9b,A(±0.3)

Elongation at break (%) L T 182.6a,A(±91) 71.7b,A(±26) 171.4a,A(±23) 52.9b,B(±12) 250.6a,A(±51) 81.1b,A(±21)

Young’s Modulus (MPa) L T 82.3b,AB(±36) 122.1a,A(±13) 114.5a,A(±28) 126.2a,A(±26) 48.5b,B(±12) 101.6a,A(±27)

Means with different letters in the same row indicate differences at the 0.05 level by Tukey’s test. A,B Means with different letters in the same column indicate differences at the 0.05 level by Tukey’s test. L = Longitudinal direction; T= Transverse direction.

a,b

behaviour for blown‑films is well-known and already studied in thermoplastic starch films[18]. Santana and Manrich[19] observed the same anisotropic behaviour for polypropylene/ polystyrene blown films. According to the authors, the tensile properties were influenced by the composition of the materials and process conditions.

Considering the elongation at break results, the samples were more extensible in the longitudinal direction than in the transverse direction (~3×) and were not significantly affected by the glycerol grade. This fact shows that the purity grade of the glycerol did not influence the plasticisation of the film, which can be explained by the different composition of the crude and distilled glycerol. Considering that crude glycerol has a lower concentration of the glycerine, due the presence of impurities, the composition of the impurities includes fatty acids as a result of the glycerol production from biodiesel. The fatty acids also acted as plasticisers[20] resulted in films with similar elongation at break than those with TGG and BDG. Similar results were observed

by Nobrega et al.[21].

The Young’s modulus showed that the samples were significantly more rigid in the transverse direction than in the longitudinal direction, varying between 10 and 90% difference.

Based in the mechanical properties, it is possible to observe that the crude glycerol (CG) can be used to produce starch/PBAT films with similar properties to those produced with BDG and TGG, without additional steps of purification.

This represents an important way to save resources and to promote the utilisation of a by-product of biodiesel industry.

3.2 Water vapour permeability (WVP) Considering the results presented at Table 3, the water vapour permeability of plasticised films did not differ significantly for CG, TGG and BDG glycerol; the permeability value varied from 2.13 x 10–6 to 3.49 × 10–6 g / m.Pa.day (Table 3). Based on these results, is possible to observe that the different types of glycerol did not interfere in the molecular mobility of the polymeric chains, i. e., the plasticiser effect was the same for all the samples, which is in according with the results of the mechanical properties.

In addition, the results showed that the impurities of the crude glycerol (CG) did not change the WVP of the films.

Previous researches[5,9] also evaluated the effect of the plasticisers, particularly glycerol, on the films and observed that greater proportions of glycerol contributed to the increase in WVP because it causes structural modifications in the polymeric network and increases the molecular mobility, which facilitates the diffusivity of water. In this work, however, no changes in WVP were recorded.

Polímeros, 25(4), 331-335, 2015

Table 3. Water vapour permeability (WVP) of the films.

Sample CG TGG BDG

Water vapour permeability (x106) (g/m.Pa.day) 2.47 a (±0.62) 2.13 a (±0.12) 3.49 a (±0.55)

Means with different letters indicate differences at the 0.05 level

by Tukey’s test. a,b

Other authors that studied blends of PBAT and thermoplastic starch, even with different proportions between these components, found similar results to those presented in this work. Bilck et al.[22] found WVP values of 4.22 × 10–6 g / m.Pa.day and Nobrega et al.[15] found 8.07 × 10–6 g / m.Pa.day, using a 33%-64% RH gradient across the film. Also Olivato et al.[23] evaluated the WVP in films of starch/PBAT (50:50) using 0-75% as RH gradient and reported values of 5.4 × 10–6 g /m.Pa.day for WVP.

3.3 Opacity The opacity ranged from 48.64% (TGG films) to 50.60% (BDG films) (Table 4). Despite the colour difference among the three different grades of glycerol (Table 1, Figure 1), there were no significant differences in the opacity among the films, which is an interesting result when the objective is the application of the film as food packaging.

The presented results (Table 4) agreed with the results reported by other authors, which obtained an opacity value around 50%, for thermoplastic starch film[24,25], and 34% for PBAT film[24]. Is important to point out that the results of this work for the blends starch/PBAT was intermediary when compared to the pure polymers, which were already expected.

3.4 Contact angle Table 5 shows the contact angle results and the Figure 2 shows photographs of the drop deposition on the surface of the films.

The CG and TGG films showed no significant differences in contact angle, indicating that these materials have similar smoothness. However, the BDG film had a contact angle lower than CG and TGG films, indicating a difference in surface energy. This behaviour could be associated with the glycerol composition; the BDG had approximately 25% more glycerol than the others (Table 1), and, consequently, had proportionally more plasticiser that created its higher hygroscopic surface. Other researchers reported that starch‑based films had increased hygroscopic characteristics with increased glycerol concentrations and associated this process with an increase in hydroxyl groups available to make hydrogen bonds with water[4,13-15].

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Bilck, A. P., Müller, C. M. O., Olivato, J. B., Mali, S., Grossmann, M. V. E., & Yamashita, F.

Figure 2. Images of the drop on the film surface.

Table 4. Opacity of the sample placed under a black pattern (YB), under a white pattern (YW) and opacity (%) of the films.

Film

Yw

Yb

Opacity (%)

CG TGG BDG

91.34a (± 0.44) 91.82a (± 0.28) 91.30a (± 0.28)

46.16a (± 0.97) 44.65a (± 2.13) 46.19a (± 1.14)

50.53a (± 1.29) 48.64a (± 2.44) 50.60a (± 1.30)

Means with different letters in the same column indicate differences at the 0.05 level by Tukey’s test. a,b

Table 5. Contact angle and hysteresis of the films.

Sample

CG TGG BDG

Contact angle 70.9 (± 2.5) b 68.4 (± 1.5) a,b 60.6 (± 3.7) a

Advancing angle 79.2 (± 3.4) 79.0 (± 1.6) 70.0 (± 2.4)

Receding angle 43.9 (± 3.1) 43.6 (± 1.7) 44.1(± 1.2)

Hysteresis 35.3 b 35.4 b 25.9 a

Means with different letters in the same column indicate differences at the 0.05 level by Tukey’s test. a,b

Białopiotrowicz[26] examined the contact angle in corn and potato starch films at different concentrations (2, 4, 6, 8, 10 and 12%wt) for different liquids (water, glycerol, formamide, ethylene glycol and diiodomethane poly(methyl methacrylate)) and reported that the contact angles decreased linearly with increasing starch concentration. According to the author, an increasing in starch concentration increased the water bound to the starch chains, thereby reducing the amount of water available at the surface.

Other researchers working with starch blends reported similar contact angle values to those found in this work.

Veiga-Santos et al.[27] reported contact angle values between 38.2° and 80.1° for cassava starch and xanthan gum blends.

Demirgöz et al.[28] used blends of corn starch with other polymers (ethylene-vinyl alcohol, cellulose acetate and ε-caprolactone) and observed contact angles between 39.9° and 73.6°.

4. Conclusion Different purities of glycerol from biodiesel production did not affect the mechanical and barrier properties when used to plasticise starch-based films. Therefore, crude glycerol could be used as an alternative plasticiser to reduce the cost of producing these polymer films.

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5. Acknowledgements The author’s thanks CNPq, CAPES and Fundação Araucária for the financial support given to this work.

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2. Freitas, S. M., & Nachiluk, K. (2009). Desempenho da Produção Brasileira de Biodiesel em 2008. Análises e Indicadores do Agronegócio, 4(2), 1-4. Retrieved in 09 June 09 2014, from http://www.iea.sp.gov.br/out/LerTexto.php?codTexto=10115 3. Thompson, J. C., & He, B. B. (2006). Characterization of crude glycerol from biodiesel production from multiple feedstocks.

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4. Müller, C. M. O., Yamashita, F., & Laurindo, J. B. (2008).

Evaluation of the effects of glycerol and sorbitol concentration and water activity on the water barrier properties of cassava starch films through a solubility approach. Carbohydrate Polymers, 72(1), 82-87. http://dx.doi.org/10.1016/j.carbpol.2007.07.026.

5. Galdeano, M. C., Mali, S., Grossmann, M. V. E., Yamashita, F., & García, M. A. (2009). Effects of plasticizers on the properties of oat starch films. Materials Science and Engineering C, 29(2), 532-538. http://dx.doi.org/10.1016/j.msec.2008.09.034.

6. Müller, C. M. O., Laurindo, J. B., & Yamashita, F. (2009).

Effect of cellulose fibers on the crystallinity and mechanical properties of starch-based films at different relative humidity values. Carbohydrate Polymers, 77(2), 293-299. http://dx.doi. org/10.1016/j.carbpol.2008.12.030.

7. Müller, C. M. O., Laurindo, J. B., & Yamashita, F. (2009). Effect of cellulose fibers addition on the mechanical properties and water vapor barrier of starch-based films. Food Hydrocolloids, 23(5), 1328-1333. http://dx.doi.org/10.1016/j.foodhyd.2008.09.002.

8. Pelissari, F. M., Grossmann, M. V. E., Yamashita, F., & Pineda, E. A. G. (2009). Antimicrobial, mechanical, and barrier properties of cassava starch-chitosan films incorporated with oregano essential oil. Journal of Agricultural and Food Chemistry, 57(16), 7499-7504. http://dx.doi.org/10.1021/jf9002363.

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9. Alves, V. D., Mali, S., Beleia, A. P., & Grossmann, M. V. E. (2007). Effect of glycerol and amylose enrichment on cassava starch film properties. Journal of Food Engineering, 78(3), 941-946. http://dx.doi.org/10.1016/j.jfoodeng.2005.12.007.

10. Kijchavengkul, T., Auras, R., Rubino, M., Ngouajio, M., & Fernandez, R. T. (2008). Assessment of aliphatic-aromatic Polímeros , 25(4), 331-335, 2015

Using glycerol produced from biodiesel as a plasticiser in extruded biodegradable films copolyester biodegradable mulch films. Part I: field study.

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11. Brandelero, R. H. H., Yamashita, F., & Grossmann, M. V. E. (2010). The effect of surfactant Tween 80 on the hydrophilicity, water vapor permeation, and the mechanical properties of cassava starch and poly(butylene adipate-co-terephthalate) (PBAT) blend films. Carbohydrate Polymers, 82(4), 11021109. http://dx.doi.org/10.1016/j.carbpol.2010.06.034.

12. Bilck, A. P., Roberto, S. R., Grossmann, M. V. E., & Yamashita, F. (2011). Efficacy of some biodegradable films as pre-harvest covering material for guava. Scientia Horticulturae, 130(1), 341-343. http://dx.doi.org/10.1016/j.scienta.2011.06.011.

13. Olivato, J. B., Grossmann, M. V. E., Yamashita, F., Eiras, D., & Pessan, L. A. (2012). Citric acid and maleic anhydride as compatibilizers in starch/poly(butylene adipate-co-terephthalate) blends by one-step reactive extrusion. Carbohydrate Polymers, 87(4), 2614-2618. http://dx.doi.org/10.1016/j.carbpol.2011.11.035.

14. Olivato, J. B., Grossmann, M. V. E., Bilck, A. P., & Yamashita, F. (2012). Effect of organic acids as additives on the performance of thermoplastic starch/polyester blown films. Carbohydrate Polymers, 90(1), 159-164. http://dx.doi.org/10.1016/j. carbpol.2012.05.009. PMid:24751025.

15. Nobrega, M. M., Olivato, J. B., Müller, C. M. O., & Yamashita, F. (2012). Biodegradable starch-based films containing saturated fatty acids: Thermal, infrared and Raman spectroscopic characterization. Polímeros: Ciência e Tecnologia, 22(5), 475480. http://dx.doi.org/10.1590/S0104-14282012005000068.

16 American Standard Testing Methods. (2002). D-882-02: standard test methods for tensile properties of thin plastic sheeting. Philadelphia: ASTM. Annual book.

17 American Standard Testing Methods. (2000). E-96-00: standard test methods for water vapor transmission of material.

Philadelphia: ASTM. Annual book.

18. Thunwall, M., Kuthanová, V., Boldizar, A., & Rigdahl, M. (2008). Film blowing of thermoplastic starch. Carbohydrate Polymers, 71(4), 583-590. http://dx.doi.org/10.1016/j. carbpol.2007.07.001.

19. Santana, R. M. C., & Manrich, S. (2005). Filmes tubulares de compósitos de termoplásticos pós-consumo: Análise térmica e mecânica. Polímeros: Ciência e Tecnologia, 15(3), 163-170. http://dx.doi.org/10.1590/S0104-14282005000300005.

20. Nobrega, M. M., Olivato, J. B., Grossmann, M. V. E., Bona, E., & Yamashita, F. (2012). Effects of the incorporation of saturated fatty acids on the mechanical and barrier properties

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of biodegradable films. Journal of Applied Polymer Science, 124(5), 3695-3703. http://dx.doi.org/10.1002/app.35250.

21. Nobrega, M. M., Olivato, J. B., Bilck, A. P., Grossmann, M. V. E., & Yamashita, F. (2012). Glycerol with different purity grades derived from biodiesel: Effect on the mechanical and viscoelastic properties of biodegradable strands and films.

Materials Science and Engineering C, 32(8), 2220-2222. http://dx.doi.org/10.1016/j.msec.2012.06.005.

22. Bilck, A. P., Grossmann, M. V. E., & Yamashita, F. (2010).

Biodegradable mulch films for strawberry production.

Polymer Testing, 29(4), 471-476. http://dx.doi.org/10.1016/j. polymertesting.2010.02.007.

23. Olivato, J. B., Grossmann, M. V. E., Yamashita, F., Nobrega, M. M., Scapin, M. R. S., Eiras, D., & Pessan, L. (2011).

Compatibilisation of starch/poly(butylene adipate coterephthalate) blends in blown films. International Journal of Food Science & Technology, 46(9), 1934-1939. http://dx.doi. org/10.1111/j.1365-2621.2011.02704.x.

24. Costa, D. L. M. G. (2008). Produção por extrusão de filmes de alto teor de amido termoplástico de mandioca com poli(butileno adipato co-tereftalato) (PBAT) (Masters dissertation). Universidade Estadual de Londrina, Londrina.

25. Melo, C., Garcia, P. S., Grossmann, M. V. E., Yamashita, F., Dall’Antônia, L. H., & Mali, S. (2011). Properties of extruded xanthan-starch-clay nanocomposite films. Brazilian Archives of Biology and Technology, 54(6), 1223-1233. http://dx.doi. org/10.1590/S1516-89132011000600019.

26. Białopiotrowicz, T. (2003). Wettability of starch gel films.

Food Hydrocolloids, 17(2), 141-147. http://dx.doi.org/10.1016/ S0268-005X(02)00046-2.

27. Veiga-Santos, P., Oliveira, L. M., Cereda, M. P., Alves, J., & Scamparini, A. R. P. (2005). Mechanical properties, hydrophilicity and water activity of starch-gum films: Effect of additives and deacetylated xanthan gum. Food Hydrocolloids, 19(2), 341-349. http://dx.doi.org/10.1016/j.foodhyd.2004.07.006.

28. Demirgöz, D., Elvira, C., Mano, J. F., Cunha, A. M., Piskin, E., & Reis, R. L. (2000). Chemical modification of starch based on biodegradable polymeric blends: effects on water uptake, degradation behavior and mechanical properties.

Polymer Degradation & Stability, 70(2), 161-170. http:// dx.doi.org/10.1016/S0141-3910(00)00102-6.

Received: June 09, 2014 Revised: Dec. 16, 2014 Accepted: Dec. 18, 2014

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http://dx.doi.org/10.1590/0104-1428.1716

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

Polyurethane/Poly(2-(Diethyl Amino)Ethyl Methacrylate) blend for drug delivery applications María Gabriela Echeverría1, Oscar Ricardo Pardini1,2,3, María Valeria Debandi4, Nora Judit François4, Marta Edith Daraio4 and Javier Ignacio Amalvy1,2,3,5,6* Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas - INIFTA, Centro Científico Tecnológico – CCT, Consejo Nacional de Investigaciones Científicas y Técnicas - CONICET, Universidad Nacional de La Plata - UNLP, La Plata, BA, Argentina 2 Comisión de investigaciones Científicas de la Provincia de Buenos Aires - CICPBA, La Plata, BA, Argentina 3 Centro de Investigación y Desarrollo en Tecnología de Pinturas - CIDEPINT, Comisión de Investigaciones Científicas de la Provincia de Buenos Aires – CICPBA, Centro Científico Tecnológico – CCT, Consejo Nacional de Investigaciones Científicas y Técnicas - CONICET, La Plata, BA, Argentina 4 Grupo de Aplicaciones de Materiales Biocompatibles, Facultad de Ingeniería, Universidad Nacional de Buenos Aires, Buenos Aires, Argentina 5 Cátedra de Materiales Poliméricos, Facultad de Ingeniería, Universidad Nacional de La Plata, La Plata, Argentina 6 CITEMA, Facultad Regional La Plata, Universidad Tecnológica Nacional, La Plata, Argentina 1

*jamalvy@inifta.unlp.edu.ar

Abstract A pH-sensitive blend of polyurethane (PU) and poly(2-(diethyl amino)ethyl methacrylate (PDEA) with good film‑forming capacity was prepared from the corresponding aqueous dispersions. The polymer matrix was first characterized by using FTIR, DSC, water vapor transmission and water swelling capacity at different pHs. The drug release profile of films was evaluated using a vertical Franz Cell and theophylline as model drug. The water swelling degree increases from 54 to 180% when the pH of the medium is changed from 6 to 2, demonstrating the pH-responsive behavior of the film. The in-vitro release studies indicate that an anomalous transport mechanism governs the theophylline release.

Keywords: polyurethanes, drug delivery systems, stimuli-sensitive polymers, swelling, theophylline.

1. Introduction Blending of polymers may improve the product performance by producing materials having the desired properties or by improving specific properties[1]. Blends have many applications, but in particular they are being proposed for using in drug delivery based on polymers[2-4]; or on composites[5]. pH-sensitive systems are a particular case and several materials were proposed for preparing them, including silica particles[6,7], other inorganic particles[8], polymeric blends[9-12], copolymers[13-15] and hybrid materials[16,17].

Within pH-responsive systems, poly(N-isopropylacrylamide) (PNIPAm) is perhaps the most studied polymer[18-22]. These are network-like systems that contain pH-dependent ionizable groups. A slight pH variation can modify the network electrical charge, controlling the interaction between chains and, hence, the polymer mesh dimensions.

In previous work, we have studied 2-(diethyl amino) ethyl methacrylate (PDEA) microgels as matrices for controlled release using theophylline as a model drug[23].

Different controlled release of theophylline systems were also studied[24-29]. A previous study of PDEA-based microgels[30] shows that they are soft and film forming in contrast to high Tg microgels. The latex-to-microgel transition was observed

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at around neutral pH, useful for human applications, and the swelling was found to be reversible[30]. However, depending on the environmental conditions, films formed from pure PDEA crosslinked microgels could be hard and brittle.

A simple way to modify this is by blending the PDEA with a good film-forming polymer like polyurethanes. Our group has been working for a long time with polyurethane systems including blends and hybrids[31]. Preliminary work changing the PU/PDEA ratio indicated that 50/50 is a promising composition in terms of film quality, and the characterization of such a blend and their release properties are the subject of the present paper.

2. Experimental 2.1 Materials Water was purified using a Millipore Simplicity System.

Theophylline (Th, C7H8N4O2, Mw = 180.17), was purchased from Droguería Saporiti (Buenos Aires, Argentina).

The 2-(diethylamino)ethyl methacrylate (DEA, Aldrich) and poly(propylene glycol)diacrylate (Aldrich) were treated with basic alumina in order to remove the inhibitor. Sodium dodecyl

Polímeros , 25(4), 336-343, 2015

Polyurethane/Poly(2-(Diethyl Amino)Ethyl Methacrylate) blend for drug delivery applications sulfate (Riedel-de Haën) and potassium persulfate (Anedra) were used as received. Poly(ethylene glycol) monomethyl ether methacylate macromonomer (Mn = 2,000; Mw/Mn = 1.10, steric stabilizer in the microgel synthesis) was supplied by Cognis Performance Chemicals (Hythe, UK) as a 50% wt. % aqueous solution. Doubly distilled de‑ionized water was used in every polymerization. Isophorone diisocyanate (Aldrich), 2-hydroxyethyl methacrylate (Aldrich), dibutyltin dilaurate (Aldrich), and triethylamine (U.V.E.) were of analytical grade and used as received. Polypropylene glycol 1000 (Voranol 2110, Dow) was dried and degassed at 80 °C at 1-2 mm Hg before use. Dimethylol propionic acid (Aldrich) was dried at 100 °C for 2 h in an oven.

Polyurethane (PU) was synthesized following a prepolymer mixing process by polyaddition of isophorone diisocyanate, polypropylene glycol, 2-hydroxyethyl methacrylate and 2,2-bis(hydroxymethyl)propionic acid[31]. Polymerization of PDEA was carried out according to previous work[30].

Films were prepared by mixing the required amount of both dispersions and casting them on a Teflon substrate by evaporating the water at 30 °C. Samples were thermally treated (cured) at 60 °C for 48 h to allow complete coalescence.

The model drug theophylline was incorporated into the dispersion at 0.1 wt. %. The final Th concentration in the film was 0.9 wt %.

2.2 Films characterization The FTIR spectra were measured in the transmission mode using a FTIR Nicolet 380 spectrometer. Theophylline spectrum was run as a KBr disk. The number of scans per experiment was 64. Spectra processing were performed using the software EZ Omnic.

DSC was performed using a Shimadzu DSC-60 instrument. Film samples were first heated to 120 °C at a rate of 30 °C.min–1 and cooled down at 30 °C.min–1 to -100 °C before scanning, to erase thermal history. Then the sample

was heated from –100 °C to 150 °C at 10 °C.min–1 and the sample was cooled down at 30 °C min–1 to -100 °C. A second heating was used for analysis and it was performed between - 100 °C and + 300 °C, at a heating rate of 10 °C.min–1.

A nitrogen gas purge was applied.

The thickness of films was measured using a digital thickness meter (Schwyz, type II) to the nearest 0.001 mm.

The water vapor transmission (WVT) through the films was determined using a modified ASTM E96-00 method[32].

The water vapor permeation cells and their use are described elsewhere[33].

The swelling kinetics of the materials was performed in a stainless steel basket, in aqueous media at 25 °C. At fixed intervals, the film was removed from the basket, dried out with tissue paper and weighed to the nearest 0.1 mg, in order to obtain the mass of the swollen film. Experiments were carried out by duplicate.

Theophylline release assessments of the films were performed as described before[33] using a Flat Ground Joint type Franz Cell (PermeGear, Inc., USA) and a membrane of cellulose (average pore diameter = 48 Å; Mw cut‑off = 12,000; Arthur Thomas CO., USA). The data were fitted only at short times (up to 6000 s) in order to preserve an almost ideal sink condition, which corresponds to a low drug concentration in the release medium.

3. Results and Discussion Scheme 1 shows the chemical structures of PU and PDEA polymers.

The observation of the FTIR spectrum of the blend indicates differences in the N-H stretching vibration and in the carbonyl region when compared with pure polymers.

Figure 1 shows the FTIR spectra of the PU (a), PDEA (b) and the PU/PDEA blend (50/50) (c) in the 3800 – 2600 cm–1

Scheme 1. Chemical structures of PU and PDEA. Polímeros, 25(4), 336-343, 2015

337

Echeverría, M. G., Pardini, O. R., Debandi, M. V., François, N. J., Daraio, M. E., & Amalvy, J. I. (Figure 1a) and 1800 – 1000 cm–1 (Figure 1b) regions where changes are observed.

The PU spectrum shows a strong absorption at 3331 cm–1 arising from H-bonded N–H. A shoulder is also observed in the 3650 – 3480 cm–1 region. The incorporation of PDEA component (Figure 1 spectrum c) increases the intensity of the shoulder and broadens the N-H band, especially on the high wavenumber side. The maximum of the N-H stretching vibration band shifts slightly to 3333 cm–1, indicating an increment of free N-H bonds and, therefore, a decrease of the H-bonds formed with the carbonyl groups of PU. In the C-H stretching region the contribution of the PDEA is observed as a shoulder at 2810 cm–1, but no shifts are observed (Figure 1 spectrum c).

In the C=O stretching region the band observed at 1716 cm–1 in the PU is attributed to H-bonded C=O. The band at 1729 cm–1 in the PDEA is assigned to the carbonyl stretching vibrations of the ester groups (Figure 1 spectrum b). The corresponding band in the blend is located at 1720 cm–1 (Figure 1 spectrum c).

Figure 1. FTIR spectra of PU (a), PDEA (b) and PU/PDEA blend (50/50) (c) in the 3800 – 2600 cm–1 (a) and 1800 – 100 cm–1 (b) ranges.

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In the C-O-C bands (stretching and bending) of the soft segments of PU (PPG), the band observed at 1240 cm–1 assigned to the asymmetrical stretching of C-O-C groups and the C-O stretching vibrations at 1109 cm–1 of the urethane and ether groups remain almost unchanged. The contribution of the ester group of PDEA is observed as a shoulder at 1150 cm–1. These features indicate some interaction of PU and PDEA polymer chains. This behavior is similar to those reported for PU/acrylic systems when increasing the acrylic content[34]. The observed changes were attributed to the breaking of the hydrogen bonding interactions in the PU and the formation of new H-bonds with the acrylic component[34].

Figure 2 shows the chemical structure and the FTIR spectrum of theophylline.

The main band of the FTIR spectra of theophylline in the high wavenumbers region is the N(7)-H stretching at 3448 cm–1[35]. A weak band observed at 3122 cm–1 is assigned to the C(8)-H stretching. In the low region below 2000 cm–1 the main bands are observed at 1717 cm–1 and 1668 cm–1 assigned to asymmetric and symmetric stretching vibrations of the C=O bonds and the band at 1568 cm–1 assigned to the C=N stretching vibrations. A weak band at 1610 cm–1 is assigned to the C=C stretching vibration[35].

Figure 3a shows the FTIR spectrum of the PU/PDEA (50:50) film and Figure 3b the film loaded with Th 0.9 wt. %.

The band of Th at 1668 cm–1 assigned to the carbonyl stretching vibration is observed at 1665 cm–1 in the polymer matrix, indicating a low degree of interaction through the formation of H-bonds between the N-H groups of PU and the carbonyl groups of the Th. The N-H stretching band at 3331 cm–1 shifted to 3342 cm–1 and was broader on the high wavenumbers side, while the shoulder at 3520 cm–1 increased in intensity due to the increment of free N-H, as a consequence of the interaction of Th with the carbonyl groups. The shoulder at 2810 cm–1 also increases the intensity with the incorporation of Th. The carbonyl stretching band of the PU/PDEA blend observed at 1720 cm–1 has slightly shifted to 1724 cm–1 after the incorporation of theophylline. Detailed comparisons of spectra show that the FTIR of the PU/PDEA containing Th

Figure 2. Chemical structure and FTIR spectrum of theophylline.

Polímeros , 25(4), 336-343, 2015

Polyurethane/Poly(2-(Diethyl Amino)Ethyl Methacrylate) blend for drug delivery applications differs considerably from the PU/PDEA spectrum. Figure 4 shows the spectral addition of PU and PDEA compared to the PU/PDEA blend loaded with Th. A close examination of both spectra of Figure 4 shows that spectral addition of PU and PDEA is more similar to the PU/PDEA blend loaded with Th than the PU/PDEA blend without Th (see Figure 3a). This suggests that the incorporation of theophylline molecules interrupts the interaction between PU and PDEA, probably because the interactions between the Th molecules and the polymer chains are stronger than the interactions that occur between the polymers themselves. A detailed analysis using spectra subtraction shows that the carbonyl group O(2) of theophylline is involved in the interaction, but bands involving N(7) and O(6) are almost unchanged after their incorporation into the polymeric blend.

Figure 5 show the DSC curves of the second heating for pure PU, pure PDEA and the PU/PDEA: 50/50 blend.

The pure PU curve (a) shows the typical transitions found in this type of polymer, the glass transition of the soft segments (Tgs) at around − 30 °C and the transition observed

at around 35 °C[34]. The curve of the pure cross-linked PDEA (b) shows two endotherms at 36 and 49 °C corresponding to the dissociation of the hydrophobic interaction indicating the existence of two main regions in the PDEA matrix[36].

The associated heat of the first endotherm is higher than the second one. The DSC of the 50:50 blend (c) shows transitions at 25 and 44 °C indicating that the blending changes the interactions and the two endotherms shifted to lower temperature, with a more substantial change for the low temperature endotherm. Figure 6 shows the DSC curves of the blend with and without Th. By including Th, the endotherms observed in the blend are almost at the same temperatures, indicating that Th interacts weakly with the PDEA part of the blend.

No DSC signal from Th was observed at higher temperature (TmTh = 274 °C), probably because of the low concentration of the model drug in the polymer matrix.

The water vapor transmission rate (WVT, g m–2 s–1) represents the steady water vapor flow normal to specific parallel surfaces and at certain temperature and humidity.

The weight gain of the permeation cells as a function of time showed a linear behavior. The slope of each curve was calculated by linear regression and the coefficient R2 was over 0.995 in all cases. The water vapor transmission rate (WVT, g m–2 s–1) was calculated from the slope of the straight line divided by the exposed area of the film

Figure 3. FTIR spectra of PU/PDEA (50/50) blend (a) and loaded blend with 0.9 wt. % of theophylline (b).

Figure 5. DSC curves of PU (a), PDEA (b) and PU/PDEA:50/50 blend (c).

Figure 4. FTIR spectral addition of PU + PDEA spectra (a) and FTIR spectrum of PU/PDEA blend (50/50) loaded with 0.9 wt. % of theophylline (b).

Polímeros, 25(4), 336-343, 2015

Figure 6. DSC curves of PU/PDEA blend (a) and PU/PDEA blend loaded with Th (b).

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Echeverría, M. G., Pardini, O. R., Debandi, M. V., François, N. J., Daraio, M. E., & Amalvy, J. I. (7.07x 10–4 m2). Permeance (g m–2 s–1 Pa–1) was computed as previously described[33]. The water vapor permeability is the arithmetic product of permeance and thickness.

These results (Table 1) could be compared with those obtained for films prepared from biopolymers, such as Scleroglucan. In that case we obtained higher values: 1.4 x 10–2 g s–1 m–2 for WVT and 5.2 x 10–6 g s–1 m–2 Pa–1 for permeance[33]. This relatively high transmission of water vapor can be explained by taking into account the profuse hydrophilic groups present in that polysaccharide.

The pure PU presents a low water permeability of about 8.0 x 10–9 g cm m–2 Pa–1 s–1 as determined in our laboratory.

In the present case the PDEA modifies the WVT of pure PU by introducing hydrophilic groups and as it has been described above, the microstructure of PU was altered with the presence of PDEA in the PU/PDEA blend causing an increase in the water permeability (0.232 g cm m–2 mmHg–1 day–1).

To analyze the film behavior during the swelling process, we calculated the mass swelling degree’s variation in time as follows[33]: (mt − m0 ) *100 m0

Dynamic swelling data were adjusted with a first order Equation 2[37]: = Qt Qmax (1 − e− k *t )

(2)

where Qmax is the maximum swelling degree (%), the equilibrium mass swelling ratio, and k is a swelling rate constant. For first-order kinetics, the rate of swelling at any time t is directly proportional to the water content that the hydrogel has to gain before the equilibrium of water content Qmax is reached. Figure 7 shows the water swelling behavior of PU/PDEA blend with time at pH 6 and 2.

We have demonstrated the pH-responsive behavior of these films by performing water swelling experiments at pH 6 and 2. In the presence of purified water, the equilibrium swelling degree Qmax was 54%, while at pH 2 Qmax reached a value of 180%. The same trend was verified measuring the film diameter, increasing 7.4% at pH 6 and 52% at pH 2.

The swelling data up to 80% of the maximum water uptake have been adjusted by the following empirical equation[38]: Qt= k´∗t m

(3)

where Qt is the swelling degree (%) at time t, mt is the mass of the swollen film at time t, m0 is the mass of the dry sample at time 0 and (mt − m0 ) is the weight of the water absorbed by the film at time t. The maximum value for Qt is defined as Qmax .

Here k’ is a constant incorporating characteristics of the macromolecular network system and the penetrating solvent, and m is the diffusional exponent, which is indicative of the transport mechanism.

Figure 8 shows the initial time variation of swelling degree at pH 6, and the fit to Equation 3. The m value of 0.51 indicates that until reaching 80% of the total swelling, the water uptake process is mainly diffusion controlled[39].

Figure 7. Time variation of the swelling degree at pH 6 (▲) and 2 (△) for a polyurethane/PDEA (50:50) film. Line represents the best fit to Equation 2. Error bars: ± standard deviation for duplicate measurements.

Figure 8. Time variation of the swelling degree up to 80% of the maximum water uptake at pH 6. Line represents the best fit to Equation 3, parameters: m = 0.51 and k’ = 13 min-m. Error bars: ± standard deviation for duplicate measurements.

Qt =

(1)

Table 1. Water Vapor Transmission (WVT) and Permeance of films. Temperature: 29 °C. RH: 86%.

Physical property WVT (g s–1 m–2) Permeance (g s–1 m–2 Pa–1)

Average and standard deviationa PU b PU/PDEA c –3 (2.20 ± 0.18) x 10–3 (1.37 ± 0.20) x 10 (4.02 ± 0.58) x 10–7 (6.50 ± 0.54) x 10–7

Obtained for 4 replicates. Average thickness of films: b(0.22 ± 0.01) mm. c(0.31 ± 0.04) mm.

a

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Polyurethane/Poly(2-(Diethyl Amino)Ethyl Methacrylate) blend for drug delivery applications For the initial swelling degrees (corresponding to the first 12 minutes) and taking into account that the constant m indicates Fickian behavior of water transport, the Equation 4 was used to estimate the diffusion coefficient D of water into the film[40,41]: 2 0.5 = Qt 2* Qmax ( D * t / π * L= ) K D * t 0.5

(4)

where L is the thickness of the dry film. Figure 9 shows the swelling degree vs. t0.5 and the fit to the Equation 4. The obtained value for KD was 13.3 min–0.5.

Taking into consideration the average film thickness L = 0.31 mm, Equation 4 leads to D = 7.55 x 10–7 cm2 s–1. This value is of the same order of magnitude as those obtained by Brazel and Peppas for two polymeric systems, poly(2-hydroxyethyl methacrylate-co-methylmethacrylate) (poly(HEMA-co-MMA)) and poly(vinyl alcohol) (PVA)[39].

Curves of Th concentration (Ct) released in the lower compartment of the vertical diffusion cell as a function of time (t) were plotted and the cumulative concentration of Th was adjusted to a power-law type relationship[42,43]:

Figure 9. Swelling degree obtained at pH 6 as a function of square root of time. Line represents the best fit to Equation 4 with parameter KD = 13.3 min-0.5. Error bars: ± standard deviation for duplicate measurements.

mt = k * t n (5) m∞

Here mt and m∞ are the cumulative amount of drug released after a time t and at infinite time, respectively, k is a constant related to kinetic behavior and experimental conditions and n is the exponent depending on the release process. Both m∞ and k were incorporated in a constant K , and Equation 6 was used to fit the data: Ct = K * t n (6)

where Ct is the molar concentration of Th in the receptor compartment at time t.

Figure 10 shows the cumulative concentration of theophylline (Th) as a function of release time for a polyurethane-PDEA (50:50) film. The polymeric matrix was loaded with Th 0.9 wt. % and the release was performed at pH 6.

Equation 6 describes the drug delivery kinetics and it is only valid for the first 60% of the fractional release. For thin disks when n is equal to 0.5 the drug is said to diffuse with Fickian behavior. For n = 1 the behavior is called Case II diffusion, controlled by the relaxation of the macromolecular chains. Finally, anomalous transport behavior, which is intermediate between Fickian and Case II, is known as non‑Fickian diffusion[31]. In our case the n value of 0.67 points to an anomalous drug transports. The Th-polymer interaction could modify the release kinetics. Hsiue et al. have studied the interaction of Th and an acrylic polymer (Eudragit L) and the effect on the release process[44]. They suggested interaction with the polymer via the C=O and C=N and they observed broadening and shifting of some FTIR bands.

They also found that the percentage of Th hydrogen bonding with the acrylic polymer decreases with the increase of Th concentration release. They studied concentrations as high as 30 wt. %. However at the responsive pH of the polymer the kinetics did not change very much.

Polímeros, 25(4), 336-343, 2015

Figure 10. Cumulative concentration of Th as a function of release time for a polyurethane/PDEA (50:50) film, loaded with theophylline 0.9% w/w. Line represents the best fit to Equation 6, parameters: n = 0.67 ; k =1.2 x 10-6 M.s-n.

4. Conclusions A blend of PDEA based hydrogel with polyurethane was prepared having good film forming properties and adequate for drug delivery applications. The blending of PDEA with PU modifies the interactions as revealed by the DSC and FTIR analysis. The water uptake process on such a blend is mainly diffusion controlled, but the release of the model drug theophylline in water follows an anomalous drug transport process. By changing the PDEA content it is expected to control permeation rates.

5. Acknowledgements We are grateful to ANPCyT (PICT 2011 - 0238), CICPBA and Universidad de Buenos Aires (Grant UBACyT 2011-2014) for their financial assistance.

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Received: Apr. 06, 2014 Revised: Jan. 19, 2015 Accepted: Feb. 09, 2015

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http://dx.doi.org/10.1590/0104-1428.1822

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

Evaluation of chemical and mechanical resistance of virgin and recycled poly (ethylene terephthalate) and poly(methylene oxide) when applied as gravel pack in petroleum wells Alexandre Zacarias Ignácio Pereira1* and Marcia Cerqueira Delpech2 Petróleo Brasileiro S.A. - PETROBRAS, Rio de Janeiro, RJ, Brazil Instituto de Química - IQ, Universidade do Estado do Rio de Janeiro - UERJ, Rio de Janeiro, RJ, Brazil 1

2

*alexandre.zip@petrobras.com.br

Abstract Nowadays more and more unexpected uses for common materials have been observed, especially when recycled polymers are concerned. In this work, the viability for application of virgin and recycled poly(ethylene terephthalate) (PETvir and PETrec, respectively) and also poly(methylene oxide) (PMO) as granular materials (gravel) for gravel packing in sand control systems for unconsolidated sandstone reservoirs was studied. Polymer samples were tested in conditions similar to those observed in Campos Basin sandstone formations, in Brazilian Southwest (70 °C and 24.1 MPa). Samples were individually confined in roller cells with chemicals used in formation treatment: hydrochloric acid, pentapotassic DTPA salt (chelant Trilon CK) and in a mixture of diesel, xylene and butyl glycol. Mass loss was measured and the changes in molecular mass verified by size exclusion chromatography (SEC). Physical shape and grain size distribution were verified by scanning electron microscopy (SEM) and sieving tests. The effects over the polymeric gravel pack confinement resistance and permeability were evaluated using an API permeability cell. PMO proved to have a limited use, whereas PETrec and PETvir samples were not significantly affected, suggesting the viability of applying that recycled polymer in gravel packing for sand control in petroleum wells.

Keywords: poly(ethylene terephthalate), recycled polymer, poly(methylene oxide), gravel pack, chemical resistance, sand control, oil well.

1. Introduction Polymers are highly versatile materials. In fact, their application is virtually unlimited, once the industry development is always facing new problems and, therefore, demanding new solutions that results in novel ways of using those substances. This is the case of the oil industry, where polymers can be found everywhere, from simple sealing rings to complex platform turrets. One of those new proposed applications is in oil well building, where conventional polymers, as poly(ethylene terephthalate) (PET) and poly(methylene oxide) (PMO) can find new unexpected uses as, for example, granular materials (gravel) in underground sand filters (gravel packs). Moreover, even recycled PET has the necessary characteristics to be used in the same way, once its properties were found to be similar to the virgin material, potentially opening a new front for polymer recycling[1].

Is important to notice that the main Brazilian oil fields are composed by mechanically fragile sandstone formations[2,3], meaning that all the wells installed in those fields need to be equipped with some kind of sand control system to prevent the contamination of the oil production with sand. Sand filters, composed of metallic screens and granular materials, are known as gravel packs[4-6] and have been the usual choice for the last two decades. Typically the granular gravel employed in those operations is basically an inorganic compound, such as sand, sintered ceramic or

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sintered bauxite. Despite their chemical resistance, those inorganic compounds have high density, which brings difficulties to install the gravel pack. Besides that, they cannot be shaped, have dispersed size distribution and are relatively costly, problems that can be overcome by replacing them by polymeric materials such PET or PMO. A previous work[1], where PET and PMO were exposed to seawater and petroleum environments, already has shown the good potential for those polymers as gravel packs. Nevertheless, an exposition of these polymers, to more aggressive media which simulates conditions that polymers would have to face when used for gravel packing oil producers or water injection wells, is still needed.

The purpose of this work is evaluate chemical and mechanical resistance of virgin and recycled PET and virgin PMO, when exposed to different aggressive liquid media, commonly used to treat formations, in a simulated oil well environment. Test parameters (temperature and pressure of the medium, as well as time of exposure to chemicals) were defined to match the observed treatment conditions.

The chemicals were chosen according to those employed in Campos Basin, in offshore Brazilian Southwest.

This work provides a systematic test pattern that compensates the lack of standard tests of the American Petroleum Institute (API) for polymeric materials to be applied as gravel pack in sand control systems.

Polímeros , 25(4), 344-350, 2015

Evaluation of chemical and mechanical resistance of virgin and recycled poly (ethylene terephthalate) and poly(methylene oxide) when applied as gravel pack in petroleum wells

2. Experimental 2.1 Materials Virgin and recycled poly(ethylene terephthalate) (PETvir and PETrec, respectively) were employed as received from Recipet Revalorização de Produtos LTDA, avoiding to introduce new process variables in the test. Poly(methylene oxide) (PMO) was supplied by ICO Polymers Global.

The products used in the chemical tests were: hydrochloric acid (HCl), from Vetec Química Fina Ltda.; chelating agent triamino diethylene penta potassium acetate (DTPA pentapotassium salt) (Trilon CK), from BASF do Brasil S.A.; and the solvents: 2-butoxyethanol (butyl glycol), from Oxiteno S.A., automotive diesel, from PETROBRAS S.A. and xylene, from Vetec Química Fina Ltda.

All polymer samples were characterized, prior to chemical exposure and after that, by size exclusion chromatography (SEC), scanning electron microscopy (SEM) and grains pack permeability, described hereafter.

2.2 Evaluation of the chemical resistance After characterization, polymer samples (PETvir, PETrec and PMO) were placed inside individual cells made of steel N316 and Hastelloy C276, prototypes developed by PETROBRAS[1]. Each cell, with capacity for 443 mL each, was filled with 300 g of the polymeric samples and the respective liquid medium. Test pressure and temperature (24.1 MPa and 70 °C) were chosen to match the hydrostatic and thermal conditions observed at formations located at 3.500 m depth, in Campus Basin, normally subjected to sand control. To avoid significant temperature and pressure variations during the tests, cells, polymer samples and liquids were heated to the test temperature (70 °C) prior to the confinement and the pressurization process. Pressure tests were made just before cells closing to verify sealing conditions. To prevent stagnation and intensify the contact of the polymer grains with the liquid medium cells were placed inside a roller oven and subjected to constant and uninterrupted axial rotation of 50 rpm at test temperature.

Each test was performed filling the cells with just one type of chemical product at a time: hydrochloric acid (HCl) 15%, DTPA penta potassium salt (Trilon CK) 10% and a mixture of diesel (45%), xylene (45%) and butyl glycol (10%).

Exposure periods were chosen considering the maximum exposure time expected during chemical treatments usually performed in wells[7,8]: 24 h for acid and solvents mixture and 96 h for Trilon CK. After the exposure period, the samples were washed with neutral detergent and running water onto a metal sieve of 250μm Mesh size (thin enough to avoid significant loss of polymer fragments) vacuum dried at 70 °C for 24 h, and then weighed.

subjected to agitation for 10 min in the sieve shaker, using the shaking intensity 9. The polymer mass retained in each sieve was measured by differential weighing.

2.3.2 Mechanical resistance of the polymeric gravel pack The mechanical strength of the polymeric gravel pack was evaluated using an API permeability cell[1], according to API standards for granular agents applied in gravel packing operations[9,10]. A thin layer of polymer grains was disposed in the cell and then compressed at 13.8 MPa and 70 °C simulating the confinement stress over a gravel pack system observed in oil wells. Mineral oil was flown through the grain layer to determine its permeability. The permeability behavior was taken as a measure of the polymeric gravel pack mechanical resistance to the oil well conditions.

2.3.3 Size exclusion chromatography (SEC) Number and weight average molecular mass and polydispersity values of PETvir, PETrec and PMO samples were determined employing size exclusion chromatography (SEC) technique. HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) was the solvent employed for sample solutions (0.1% m/v) and the mobile phase used in a chromatographer Waters 600 equipped with 2 columns Shodex HFIP 803 and 805, at 35 °C, at a flow rate of 1.0 mL/min.

Non-exposed samples were firstly analyzed. During the exposure to chemicals, samples were collected from the rolling cells and analyzed after the exposure period, in order to verify possible chemical degradation factors reflected in molecular weight and/or polydispersity.

2.3.4 Scanning electronic microscopy (SEM) Scanning electronic microscopy (SEM) observation was performed in a Jeol JSM 6460 LV microscope in a magnification range varying from 25 to 100x. Samples were coated with a 200Å gold-palladium in an Eduards SIX vacuum metallizer. All micrographs were taken at 25 mm, through secondary electron imaging, under an accelerating voltage of 20.0 keV.

3. Results and Discussion 3.1 Mass loss and granulometry

2.3.1 Granulometry

Table 1 shows that mass loss produced by chemical exposure was negligible in the case of exposure to solvents and Trilon CK[11-13], but the exposure to acid caused an appreciable mass loss in all samples[12-15]. A comparison with other conventional gravel pack materials revealed that both recycled and virgin PET, exhibited mass changes close to the observed for those products in similar tests with the same substances[9,10]. PMO, however, suffered a mass loss much higher than PET when exposed to HCl[16-18], resulting in mechanical integrity failure of its grains, proving, therefore, to be unacceptable for the proposed application.

The determination of the polymer samples particle size was performed in a sieve shaker Produtest, model 4062, equipped with six sieves, ranging from 2 to 14 Mesh (apertures from 4.75 to 1.20 mm) assembled vertically in decreasing Mesh size. Samples of 40 g were taken, before and after the chemical exposure. Samples were washed, dried and then

The granulometry results presented in the Figure 1 demonstrate that neither virgin nor recycled PET were significantly affected by the chemical exposure. PMO samples behave in the same way when exposed to solvents or Trilon CK. However, the exposure to HCl greatly compromised PMO mechanical integrity, so its grains could

2.3. Characterization

Polímeros, 25(4), 344-350, 2015

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Pereira, A. Z. I., & Delpech, M. C. not be measured after acid exposure. Virgin PET showed no significant variation in granulometric curve. The recycled polymer particle size, before and after the exposure tests, showed a more significant variation when compared to the virgin one, but the formation of fine fractions, resulting from grain fragmentation was not observed, indicating that the integrity of the recycled material was preserved. It is important to emphasize that the sieving tests are not accurate and, therefore, are not able to define small changes in the shape of the grains of tested polymers. Basically, it indicates relatively large changes in the size of analyzed particles.

Nevertheless, the absence of major changes or formation of fine fractions evidence that there was no relevant alteration in PET grains size, although PMO sample aspect indicates major polymer degradation. These observations are also supported by SEM results, presented below.

Table 1. Mass loss after chemical exposure at 24.1 MPa and 70 °C. Final Mass

Polymer

Chemicals

Initial Mass (g)

Virgin PET Recycled PET PMO Virgin PET Recycled PET PMO Virgin PET Recycled PET PMO

Organic Solvents

200 200

(g) 200.7 199.8

HCl

200 200 200

199.9 182.8 184.2

0.0 8.6 7.9

Trilon CK

200 200 200

72.1 199.3 199.8

64.0 0.3 0.1

200

198.3

0.8

Δm (%) 0.2 0.1

3.2 SEM SEM micrographs obtained before and after subjecting the polymers to chemical exposure under test conditions are presented in Figure 2. The images show, in detail, that there were no evident changes on the surface of the grains of both virgin and recycled PET, in all chemicals tested.

Considering the sensitivity of PET to hydrolysis in very acidic or alkaline media[11-14], the small attacks suffered by the recycled and virgin samples under test conditions can be attributed to the relatively low temperature in a short exposure period of time[13], both parameters derived from the observed operational oil well conditions[7].

SEM analysis strongly reinforces the potential application of this material as sand control agent, evidencing the suitability of the recycled compound in a very significant application.

PMO sample, in turn, was strongly attacked, with remarkable changes in the shape of grains, especially in the acid medium, in which smaller and brittle grains were generated induced by the degradation[16-18]. In oil wells, those particles can block the pores formed by the polymer grains package, thereby reducing its permeability and preventing hydrocarbon or water flow, which is totally undesirable for a sand control agent[5].

3.3 SEC Table 2 presents the values of number average (‾Mn), mass average (‾Mw) molecular mass and polydispersity index (‾Mw/¯Mn) obtained by size exclusion chromatography (SEC) for PET and PMO samples. Taking into account the sensitivity of the technique, the results showed that there were no marked changes, neither on the molecular mass

Figure 1. Granulometric curves for PET (virgin and recycled) and PMO samples after chemical exposure, at 24.1 MPa and 70 °C. 346

Polímeros , 25(4), 344-350, 2015

Evaluation of chemical and mechanical resistance of virgin and recycled poly (ethylene terephthalate) and poly(methylene oxide) when applied as gravel pack in petroleum wells

Figure 2. Micrographs obtained before chemical exposure ((a) PETvir (25x); (b) PETrec (30x); (c) PMO (35x)) and after chemical exposure at 24.1 MPa and 70 °C for 24 h to solvents; ((d) PETvirgin (27x); (e) PET rec (30x); (f) PMO (37x)); 96 h to Trilon CK 10%; ((g) PETvir (25x); (h) PETrec (30x); (i) PMO (35x)) and 24 h to HCl 15%; ((j) PETvir (27x); (k) PETrec (30x); (l) PMO (45x)).

Table 2. Number average (‾Mn), mass average (‾Mw) molecular mass and polydispersity index (‾Mw/¯Mn) of virgin and recycled PET samples, and PMO, before and after chemical exposure under test conditions.

Chemicals

PETvir

PETrec

PMO

‒Mn

‒Mw

‒Mw/‒Mn

‒Mn

‒Mw

‒Mw/‒Mn

‒Mn

‒Mw

‒Mw/‒Mn

As received

43900

81600

1.9

37900

61600

1.6

119902

259661

2.2

Trilon CK

38600

64900

1.7

36600

63000

1.7

138708

252964

1.8

HCl

42700

66600

1.6

40300

60900

1.5

values nor on the polydispersity of both virgin and recycled PET samples after chemical exposure.

PMO sample presented a similar behavior of PET when exposed to the Trilon CK solution but it was strongly Polímeros, 25(4), 344-350, 2015

Insoluble

attacked by HCl. As a consequence of the acid exposure, PMO grains became extremely brittle and insoluble in the SEC solvent (HFIP), preventing the realization of further chromatographic analysis. Strong acids produce hydrolytic 347

Pereira, A. Z. I., & Delpech, M. C. degradation of polyacetals like PMO, and the mechanism involves changes in the polymer surface[16-18] which can, at least in some extent, explain the observed effect over the solubility of PMO in HFIP. The hydrolysis caused by acid exposure on PMO is described in the literature[14,16] explaining the observed effects on PMO grains exposed to HCl. Further researches, necessary to completely explain the hydrolysis effect on the solubility of PMO in HFIP, exceed the scope of this study and, therefore, were not performed.

Although being a polymer susceptible to hydrolysis[13], PET samples experienced just smaller effects after exposure to both, alkaline and acid media.

3.4 Mechanical resistance of the polymeric gravel pack There are several ways of testing the mechanical properties of a thermoplastic, however, none of them better represent the mechanical stress to which it will be subjected, when applied as gravel pack, as the API test[9,10], designed specifically to simulate the confinement conditions observed in oil well environment. Differently from the hydrostatic pressure, simulated in the chemical tests, the forces are applied in just one direction, allowing the gravel pack deformation. If a continuous deformation is observed, the porosity created by the space among grains collapses and a progressive reduction in the permeability is observed[3,9,10].

In open hole gravel pack, those forces are produced by the tendency of the formation to close around the gravel pack due to mechanical accommodation[2].

The polymers were tested before and after chemical exposure, so the effects of conventional oil well chemical treatments over PMO, recycled PET and virgin PET mechanical properties could be observed. The initial variations, observed in the curves, were due to the plastic characteristics of the tested material that produces small changes in the thickness and porous structure of the polymer grain layer. The stabilization of grain layer can be seen in the pack thickness curve that presented a constant profile after a few minutes of test. A progressive reduction in the permeability or in the layer thickness would indicate poor mechanical resistance while stabilization in those polymeric gravel pack properties represents good resistance to the confinement conditions, and, therefore, suitability for the use in sand control systems.

The results indicated that all tested PET types maintain their mechanical resistance in acceptable levels, meaning that the chemical exposure did not attack those polymers significantly under the test conditions. Therefore, PET polymers prove to be adequate as sand control agent.

PMO, also, have shown good resistance to solvents and Trilon CK, but was not tested with HCl due to the high sensitivity to acid attack, observed in the previous assays.

The test results can be observed in Figures 3 and 4.

It is important to note that, although the mechanical test presents qualitative characteristics, permeability stabilization in acceptable levels is a good indication that the well environment will not produce significant collapse of the polymeric gravel pack pore structure, therefore, will not cause significant impairment to hydrocarbon production[3,9,10].

Figure 3. PMO, PETrec and PETvir gravel pack permeability tested under 70 °C and a confinement pressure of 13.8 MPa, before chemical exposure.

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Polímeros , 25(4), 344-350, 2015

Evaluation of chemical and mechanical resistance of virgin and recycled poly (ethylene terephthalate) and poly(methylene oxide) when applied as gravel pack in petroleum wells

Figure 4. PMO, PETrec and PETvir gravel pack permeability tested under 70 °C and a confinement pressure of 13.8 MPa, after chemical exposure to Trilon CK 10% for 96 hours and to solvents for 24 hours, at 70 °C and 24.1 MPa. PETrec and PETvir gravel pack permeability 24 hours of exposure to HCl 15% at 70 °C and 24.1 MPa. Polímeros, 25(4), 344-350, 2015

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Pereira, A. Z. I., & Delpech, M. C.

4. Conclusions In the test conditions, simulating those observed in Campos Basin Oil wells, no significant effects of chemical exposure were observed on the PET samples. The mass loss was insignificant, without noticeable changes in number average (‾Mn), mass average (‾Mw) molecular mass and polydispersity (‾Mn/¯Mw) of the tested samples.

Likewise, the permeability of PET gravel packs presented a stable behavior when subjected to compression at oil well conditions (API test), evidencing that the use of PET (virgin and recycled) as gravel pack is viable.

Although poly (methylene oxide) (PMO) presents desirable properties for sand control agent as well, the observed acid resistance is not acceptable for its application in oil well environment, unless if applied only in wells without perspectives of undergoing acid treatments. Therefore, in general terms, this polymer is not recommended to be used in sand control systems.

The conclusions of the previous work[1] were reinforced by the results obtained in the short term exposure tests, i.e., the new proposed use for recycled PET aggregates value to this material, since, as a sand control agent, there is no necessity of any additional treatment, besides the conventional recycling process[19-21]. That also improves PET recycling attractiveness in general, contributing to environment preservation.

5. Acknowledgements The authors wish to thank Petrobras for the permition to publish this work and also Centro de Pesquisas e Desenvolvimento Leopoldo Américo Miguez de Mello (CENPES/PETROBRAS) and Instituto de Química/ Universidade Federal do Rio de Janeiro (IQ/UFRJ) for the analysis.

6. References 1. Pereira, A. Z. I., & Delpech, M. C. (2012). Thermal and mechanical evaluation of the stability of recycled poly(ethylene terephthalate) applied as sand control agent in petroleum wells.

Polymer Degradation & Stability, 97(7), 1158-1163. http:// dx.doi.org/10.1016/j.polymdegradstab.2012.03.045.

2. Roegiers, J. C., & Thiercelin, M. C. (2000). Formation characterization: rock mechanics. In J. M. Economides, K. G. Nolte (Eds.), Reservoir stimulation (pp. 3.1-3.8). West Succex: John Wiley & Sons.

3. Tiab, D., & Donaldson, E. C. (2012). Petrophysics: theory and practice of measuring reservoir rock and fluid transport properties. Walthan: Gulf Publishing.

4. Carlson, J., Gurley, D., King, G., Price-Smith, C., & Waters, F. (1992). Sand control: why and how. Oilfield Review, 41-53.

Retrieved in 10 February 2014, from http://www.slb.com/~/ media/Files/resources/oilfield_review/ors92/1092/p41_53.pdf 5. Burton, R. C., Mackinley, W. M., Hodge, R. M., & Landrum, W. R. (1998). Evaluating completion damage in high-rate, gravel-packed wells. Society of Petroleum Engineers, 13(4), 259-265. Retrieved in 10 February 2014, from https://www. onepetro.org/journal-paper/SPE-52893-PA 6. Nguyen, P. D., & Norman, L. R. (2005). US Patent No 20050284631. Washington: U.S. Patent and Trademark Office.

7. Daher, J. S., Gomes, J. A. T., Rosario, F. F., Bezerra, M. C., Amorim, V. C. F., Dumas, G. E., & Oliveira, S. E. A. P. (2006). Field experience to assess efficiency of scale dissolver 350

treatment in a subsea deep water well. In SPE International Oilfield Scale Symposium. Aberdeen: Society of Petroleum Engineers. Retrieved in 10 February 2014, from https://www. onepetro.org/conference-paper/SPE-100653-MS 8. Pereira, A. Z. I., Calderon, A., Chagas, C. M., & Pinto, E. A. (2007). Recent advances in deepwater horizontal injector wells acidizing in Campos Basin. In European Formation Damage Conference. Scheveningen: Society of Petroleum Engineers.

Retrieved in 10 February 2014, from https://www.onepetro. org/conference-paper/SPE-107787-MS 9. American Petroleum Institute. (2008). API RP 19C: measurement of properties of proppants used in hydraulic fracturing and gravel-packing operations. Washington.

10. American Petroleum Institute. (2008). API RP 19D: measuring the long-term conductivity of proppants. Washington.

11. Namboori, C. G. G., & Haith, M. (1968). Steric effects in the basic hydrolysis of poly(ethylene terephthalate). Journal of Applied Polymer Science, 12(9), 1999-2005. http://dx.doi. org/10.1002/app.1968.070120901.

12. Mancini, S. D., & Zanin, M. (2002). Influência de meios reacionais na hidrólise de PET pós-consumo. Polímeros: Ciência e Tecnologia, 12(1), 34-40. http://dx.doi.org/10.1590/ S0104-14282002000100010.

13. van Schoors, L. V. (2007). Hydrolytic aging of polyester (polyethylene terephthalate) geotextiles: state of the art assessment. Bulletin des Laboratoires des Ponts et Chaussées, 270, 133-154. Retrieved in 10 February 2014, from http:// www.geotech-fr.org/sites/default/files/revues/blpc/BLPC%20 270-271%20pp%20133-154%20Vouyovitch.pdf 14. Yoshioka, T., Sato, T., & Okuwaki, A. (1994). Hydrolysis of waste PET by sulfuric acid at 150°C for a chemical recycling.

Journal of Applied Polymer Science, 52(9), 1353-1355. http:// dx.doi.org/10.1002/app.1994.070520919.

15. Yoshioka, T., Okayama, N., & Okuwaki, A. (1998). Kinetics of hydrolysis of PET powder in nitric acid by a modified shrinking-core model. Industrial & Engineering Chemistry Research, 37(2), 336-340. http://dx.doi.org/10.1021/ie970459a.

16. Ivanova, L. V., Pavlov, N. N., & Zaikov, G. Y. (1976).

Macrokinetic features of the degradation of polyoxymethylene blocks in aqueous solutions of mineral acids. Polymer Science URSS, 18(6), 1534-1542. http://dx.doi.org/10.1016/00323950(76)90353-1.

17. Pchelintsev, V. V., Sokolov, A. Yu., & Zaikov, G. E. (1988).

Kinetic principles and mechanisms of hydrolytic degradation of mono and polyacetals - A review. Polymer Degradation and Stability, 21(4), 285-310. http://dx.doi.org/10.1016/01413910(88)90017-1.

18. Kusy, R. P., & Whitley, J. Q. (2005). Degradation of plastic polyoxymethylene brackets and the subsequent release of toxic formaldehyde. American Journal of Orthodontics and Dentofacial Orthopedics, 127(4), 420-427. http://dx.doi. org/10.1016/j.ajodo.2004.01.023. PMid:15821686.

19. La Mantia, F. P., & Vinci, M. (1994). Recycling poly(ethyleneterephthalate). Polymer Degradation & Stability, 45(1), 121-125. http://dx.doi.org/10.1016/0141-3910(94)901872.

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

21. Associação Brasileira da Indústria do PET. (2014, May 15).

Retrieved in 10 February 2014, from http://www.abipet.org. br/index.html Received: June 27, 2014 Revised: Nov. 13, 2014 Accepted: Feb. 09, 2015 Polímeros , 25(4), 344-350, 2015

http://dx.doi.org/10.1590/0104-1428.1529

Polyphenolic resin synthesis: optimizing plantain peel biomass as heavy metal adsorbent Andrés Felipe Cordero1*, Milton Gómez1 and José Humberto Castillo2 Programa de Química, Universidad del Quindío, Armenia, Colombia 2 Programa de Física, Universidad del Quindío, Armenia, Colombia

1

*corderoqco@hotmail.com

Abstract Polyphenolic resol resins were obtained from an ethanolic extraction of green plantain peels (Musa paradisiaca) grown in Colombia. A synthesis was then performed by polycondensation in an alkaline pH solution in order to perform research on phenolic resin production with high mechanical performance. The polymers were characterized by DSC and TGA analyses and the resins showed a melting point of 94 °C and the typical properties of resol resins. Moreover, the synthesis was controlled using the infrared technique (FTIR) where different organic functional groups present in the polymers obtained are observed. The obtained resins were used as heavy metal adsorbents in which the content of those toxic agents is measured by Atomic Absorption Analysis (AA) indicating that these resins have a high retention affinity to Pb+2, Ni+2 and Cr+3 (79.01%, 98.48%, 94.14%, respectively) as determined by Freundlich isotherms.

Keywords: resol resins, differential scanning calorimetry, infrared spectroscopy, thermogravimetry, freundlich isotherms, toxic heavy metal adsorbents.

1. Introduction Nowadays, the majority of us see the contamination of water streams and the dumping of industrial, agricultural and domestic wastewater into natural resources as an increasingly growing global problem, which will continue to affect life on the planet. For this reason, it is necessary to implement methods and cleaning techniques to treat disposable waste and water supplies that affect our health. Different studies show that some materials that adsorb heavy metals have been investigated and prepared at low costs to replace the materials that have been used in a conventional way such as activated carbon and zeolites[1]. Besides, the different biosorption mechanisms that retain the heavy metals introduced into the environment as contaminants have been examined by analysis of adsorption isotherms. Meanwhile, agricultural waste material shows many advantages when used within the adsorption processes; for instance, low cost, high efficiency, chemical and biological residual reduction, easy regeneration of the adsorbents and a high selectivity towards selected cations[2]. The purpose of the present study is to provide enough thermal information about the different aspects of heavy metal adsorbents from green plantain peel (Musa paradisiaca) ethanolic extract to be used in the purification of wastewater, taking into account the high retention capacity and selectivity to heavy metals of these cheap materials according to isotherm analyses.

2. Experimental 2.1 Adsorbent resin synthesis The Bakelite adsorbents of resol types, supported on hydrolyzed Raw Ethanolic Extracts (REE) of green plantain peels, were prepared by polycondensation in alkaline

Polímeros, 25(4), 351-355, 2015

media, with formaldehyde addition in variable amounts as polymerization catalyst.

2.2 Thermal analysis by Differential Scanning Calorimetry (DSC) The thermal behavior of the samples was studied by means of DSC using 2920 MODULATED TA INSTRUMENTS equipment. The obtained samples from the different syntheses of the resol resins were scanned between -50 °C ≤ T ≤ 250 °C at a heating rate of 10 °C min-1 with a nitrogen flow rate of 50 mL min-1. Analyzed samples had weights between 2.5 mg and 4.86 mg.

2.3 Thermal analysis by Thermogravimetry (TGA) The TGA analyses are important because they determine the sample weight loss as a function of temperature, and were conducted using a TGA 2050 TA INSTRUMENT THERMOGRAVIMETRIC ANALYZER. Samples were heated at 10 °C min-1 under a nitrogen flow rate of 50mL min-1 from room temperature to 400 °C. Weights between 3.41 mg and 4.86 mg of each sample were analyzed.

2.4 Resol resins for heavy metal adsorption For the adsorption of toxic metals of interest, different criteria were considered regarding the homogenization method with the purpose of getting compatible results between them by the use of different statistic analyses and to establish an experimental procedure for the determination of the amount of cations retained by the resins. To do this, several heavy metal solutions were prepared to represent an initial concentration ([]0) from 12 ppm to 20 ppm, diluted from the standards of Pb+2, Ni+2 and Cr+3 for atomic absorption

351

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

Cordero, A. F., Gómez, M., & Castillo, J. H. with nitric acid at 1%. These solutions were used as the column feed (glass columns with 30 cm in length and a diameter of 1 cm), which consisted of a stationary phase of the resol resin where 6 g of this wet resin were introduced into the column. The eluent collected represented the final retained concentration ([]f). An acid digestion was made to the liquid obtained from the retention. Samples were diluted with 10 mL of distilled water and nitric acid at 1%. Finally, the solutions with []0 and []f were analyzed by means of Atomic Absorption (AA) in order to determine the actual composition and determine each column concentration gradient with the toxic cations determined.

2.5 Fourier-Transform Infrared Spectroscopy (FTIR) studies A Bruker FT-IR Spectrophotometer was used for recording the FT-IR spectrum in the region from 500 - 4000 cm-1 in order to observe the different organic functional groups present in the extracts and in the polymers obtained. Film samples were cut into small pieces (10 mm - 10 mm) and dehydrated in a desiccator containing silica gel for 3 weeks.

3. Results and Discussion 3.1 Thermal analysis of phenolic resins by Differential Scanning Calorimetry (DSC) The thermal event characterization of the resol resins was performed between -50 °C and 250 °C; different behaviors could be observed, which allow us, at the same time, to identify the different physical changes that occur in the polymer structure[3]. We have to remember that the resol resins are classified within thermo stable polymers which are degraded at high temperature at the melting point, since there is a polymorphic arrangement inside its crystalline structure, normal for a polymer belonging to a biological system, showing them a non uniform configuration[4].

This can be visualized in the thermogram (Figure 1) of the Bakelite Resol Standard (BRS) resin and the tannin resol

Figure 1. DSC thermogram of resol phenolic resins synthesized from extracts at different catalyst concentrations.

352

resin (T2) synthesized from plantain peels with the other resol resins using different catalyst concentrations (T1-T8), making it possible to compare all the thermal transitions.

First, for the BRS, there was a perfectly defined jellification phase at -0.71 °C, very similar to that shown in the T2 thermogram at -1.07 °C, where the crystals could adopt a uniform shape. This transition was followed by a polymeric calorific capacity rise due to glass point transition (Tg) within a temperature range from 6 °C to 12 °C in BRS and from 10 °C to 12 °C for to T2. When both polymers crystallized, the corresponding exothermal crystallization transition (Tc) could be visualized above the Tg, at 31.44 °C for both resins, where the two crystals have adopted defined crystalline structures. These depress shows that the polymer is probably able to crystallize[5].

If the heating of our polymer is raised above its Tc, we arrive to the final thermal transition, the melting point (Tm), that was defined above 94 °C. When such a temperature was reached, the resin crystals started to separate from one another and the chains left their arrangements leading to free movement. The melting point is a first order transition, which means that when the melting point is reached, the polymer temperature will not increase until all the crystals have melted. To summarize, we observed that the BRS and T2 resins showed very similar behaviors. The rest of the resins showed a typical amorphous structural behavior, because they did not exhibit the transitions of a hard plastic (typical of Bakelite) with its characteristic Tc and Tm, as was the case with the T1 resin. Even so, the other resins exhibited a thermo-plastic behavior since they did not show any degradation when reaching the melting point (Tm) and continued showing, when the isotherm was applied, the same transitions with different intensities (Table 1). This is possibly due to incomplete polymerization and, perhaps, due to intermolecular forces and steric effects inside the polymer being reduced[3].

3.2 Thermogravimetrical analysis (TGA) The weight losses of the different synthesized resins were analyzed by thermogravimetry[6]. This suggests, as a typical property of the phenolic resins, that the aforementioned polymers had a high stability when exposed to different heat scanning. Figure 2 shows the different thermal stability profiles of the obtained phenolic resins.

For the T2 resin, free water loss was observed at 60 °C since such a polymer, as well as the other resins, has a biological origin and, therefore, large free water amounts[7].

Besides, it is important to take into account that the majority of these structures exhibited a weight loss above 150 °C since it was pointed out before; these structures are possibly degraded if they are heated above the melting point temperature[8]. The BRS showed a particular behavior since water loss started at the beginning of the analysis, but weight remained relatively constant above 200 °C[8]. This may be due to the formation of a great quantity of water molecules during the condensation synthesis of the polymer and a high grade of polymerization and to the drying processes, which give the hard plastic a great thermal stability due to the formation of a great molecular network when having phenolic groups with reactive carbons towards substitution Polímeros , 25(4), 351-355, 2015

Polyphenolic resin synthesis: optimizing plantain peel biomass as heavy metal adsorbent Table 1. Temperature and enthalpy values for BRS and T2.

Resin

Tg (°C)

∆H1 (J/g)

Tc (°C)

∆H2 (J/g)

Tm (°C)

∆H3 (J/g)

BRS T2

6.42 10.25

0.11 0.001

31.44 31.42

40.68 55.94

94 94

285.6 1.67

Log

Figure 2. TGA analysis for the resol phenolic resins synthesized from extracts.

by formaldehyde[6]. It is most likely that this phenomenon does not occur in T2 since the monomer (polyphenolic metabolites) possesses high quantities of aromatic carbons substituted from their starting level which possibly limit the polymerization. The T1 resin showed greater stability due to the high grade of crystallinity that the amorphous polymers have. Despite the low grade of polymerization of the other resins, they could present an additional curing process due to extended heating[9].

3.3 Heavy metal adsorption determination In order to measure the adsorption, the cation quantity retained by the resol resins was determined by the atomic absorption technique. This technique proved that it could be used for this type of study[10]. The results are shown in the Table 2.

Thus, we obtained a retention percentage from the Polyphenolic Resin (PR) of 79.01% for the Pb+2, 98.48% for Ni+2 and 94.14% for Cr+3, these high percentage retention is possibly due by the different organic group present in the resin (amines, carbonyls, ethers, etc) while in Bakelite Resol Standard (BRS) only has hydroxyl groups for the metal retention. The determination of the Freundlich adsorption isotherms (Figure 3) was adapted to the experimental conditions in which a physical process was made. This process did not show changes in the molecular configuration when the cations had been adsorbed[11]. Freundlich’s model assumes that the sorbent surface is heterogeneous and the sorption positions have different affinities; where, the major affinity positions are filled at the beginning, and then the other spaces are periodically filled[11].

1

x n (1) =KCeq m Polímeros, 25(4), 351-355, 2015

x 1 =LogK+ LogCeq (2) m n

In the graphics of this mathematic model (Equation 1) the sorption of low metal concentration was illustrated since this profile does not assume saturation phenomena[12].

We took into account (Equation 2) of logarithmic linearity, which allowed us to calculate the K value that represents a constant of equilibrium that defined the capacity in terms of mg of adsorbed metals/g of adsorbent, and the 1=n value which is a constant referred to the affinity or adsorption energy between the adsorbent and the adsorbate[13].

According to previous results, the metals were adsorbed by the T2 phenolic resin, showing a high capacity to perform this work. However, it was observed that the T2 column had a high capacity to retain both Ni+2 and Cr+3 with maximums of 71.43 and 64.32, respectively (Table 3). The Pb+2 retention values were low since this heavy metal needs to be adsorbed in acidic conditions[14].

We could also observe that at high grades of polymerization, there are major amounts of hydroxyl, carbonyls and ether groups that have a possible, direct responsibility for this adsorption (Figure 3).

3.4 Fourier-Transform Infrared Spectroscopy (FTIR) analysis The FTIR spectra were very useful to determine functional groups present in the extracts and samples obtained. Figure 4 shows the different structural changes that raw materials suffered after being isolated from their vegetable matrixes or during the treatment as starting material for the phenolic resin synthesis.

As was observed, for the Raw Ethanolic Extract (REE), the corresponding signals at 3417 cm-1, 2927 cm-1 and 2854 cm-1 are typical of the carboxylic acid vibration due to its high content of gallic acid and to other similar structures like carbohydrates and coumarins with phenolic groups. At the same time, it was possible to confirm this evidence by the peak of symmetrical enlargement observed at 1731 cm-1, characteristic of the aromatic carboxylic acids possibly substituted by a methoxy or an acetate group or lactone groups. Also, the existence of polysubstituted aromatic groups was detected due to enlargement signals between 1400 cm-1 and 1600 cm-1 with medium intensity[15].

This is why we probably could find aromatic amides in the extracts, evidenced by the low intensity signals between 1000 cm-1 and 1200 cm-1 due to the probable absorption of a few groups at this frequency[16].

As mentioned above, there is a great variety of signals in the REE that can be attributed to many functional groups; at the same time, they can be present or absent after synthesis or fractionation steps. This is the case for T2 and BRS which were obtained by condensation with formaldehyde 353

Cordero, A. F., Gómez, M., & Castillo, J. H. Table 2. Cation concentrations adsorbed by the resin.

Cation sample Cr+3 Pb+2 Ni+2

Initial Concentration (mg/L) BRS PR 11.241 12.292 12.150 13.954 10.193 20.561

Average Final Concentration (mg/L) BRS PR 6.1324 0.7192 4.8875 2.9268 7.1956 0.3118

Cation Retention Percentage (%) BRS PR 45.446 94.149 59.773 79.025 29.406 98.483

does not appear. However, we can observe some absorption at 1100 cm-1 which could be attributed to the presence of compounds produced by the ether condensation process.

As a result, we can deduce that, possibly, phenolic resins with tannic and other similar monomers can be designed.

Figure 3. Freundlich isotherm adsorption for Cr+3, Ni+2, Pb+2.

Table 3. Obtained adsorption capacity (k) values and the affinity constant (1/n).

Resin Cr+3 Pb+2 Ni+2

Log k 0.172 1.663 1.783

K 64.32 44.23 71.43

1/n 0.743 0.645 1.098

When the crystal called PFE (Polyphenols Fractionated Extract) were isolated using Liquid Chromatography (LC), the corresponding spectral analysis led to these results: An intense signal in the 3400 cm-1 region, which indicates the presence of a benzoic acid structure[18,19]. This signal is accompanied by another weak signal around 2900cm-1.

In the same way as the other spectra, we could observe that the band at 1600 cm-1 may belong to the same substituted aromatic rings, where double bonds of 6 members have enlargement frequencies and annular tension at this wave number. The aromatic compounds have a fingerprint region, including the absorptions from 1000 cm-1 to 1200 cm-1[20].

These results confirm the pholyphenolic structures of the gallic acid type in the PFE.

4. Conclusions According to the DSC and TGA analyses, the phenolic resins have a great thermal stability. Nevertheless, the resin that had a similar profile as BRS was the T2 resin with polymorphic crystalline structure. It was evidenced when we observed that some polymers did not have a rigidity comparable with the other control resin (BRS) according to the profiles showed in the DSC and TGA thermograms.

Freundlich’s isotherms were utilized to determine the adsorption capacity coefficient of the resin, and the affinity adsorption efficiency was high for Cr+3 and Ni+2, while a medium efficiency was obtained for Pb+2. FTIR spectra revealed that our polymer was composed of polyphenols.

5. Acknowledgements Figure 4. FTIR spectra for the ethanolic extract analysis and the phenolic resins obtained.

under alkaline pH, showing a similar profile. An important absorption can be visualized at 3417 cm-1 accompanied by a very tenuous signal at 2927 cm-1 which indicates the presence of hydroxyl aromatic groups typical of carboxyl acid. In the same way, a deformation of the plane was observed at 1454 cm-1 that could indicate the presence of methylene groups (R-CH2-R), substituted by aromatic groups[17]. Surely, the signal at 1600 cm-1 corresponds to the polysubstituted aromatic rings. We can observe that if the resins are submitted to a curing process, the excess of formaldehyde would be reduced as the carbonyl group signal 354

The authors wish to thank Dr. Julian Andres Caballero Narvaez and Dr. Joaquin Angel Rodriguez for assistance with the manuscript. The development of the thermal analysis by Dr. Ruben Antonio Vargas Zapata and Dr. Jesus Roberto Castillo Chamorro for helpful discussions.

This work was supported by the University of Quindío and the University of Valley (Colombia).

6. References 1. Bailey, S. E., Olin, T. J., Bricka, R., & Adrian, D. (1999). A Review of Potentially Low-Cost Sorbents for Heavy Metals.

Water Research, 33(11), 2469-2479. http://dx.doi.org/10.1016/ S0043-1354(98)00475-8.

2. Sud, D., Mahajan, G., & Kaur, M. P. (2008). Agricultural waste material as potential adsorbent for sequestering heavy Polímeros , 25(4), 351-355, 2015

Polyphenolic resin synthesis: optimizing plantain peel biomass as heavy metal adsorbent metal ions from aqueous solutions - a review. Bioresource Technology, 99(14), 6017-6027. http://dx.doi.org/10.1016/j. biortech.2007.11.064. PMid:18280151.

3. Alonso, M., Oliet, M., Pérez, J., Rodríguez, F., & Echeverría, J. (2004). Determination of curing kinetic parameters of ligninphenolformaldehyde resol resins by several dynamic diferential scanning calorimetry methods. Thermochimica Acta, 419(1-2), 161-167. http://dx.doi.org/10.1016/j.tca.2004.02.004.

4. Tejado, A., Peña, C., Labidi, J., Echeverria, J. M., & Mondragon, I. (2007). Physico-chemical characterization of lignins from different sources for use in phenol-formaldehyde resin synthesis. Bioresource Technology, 98(8), 1655-1663. http:// dx.doi.org/10.1016/j.biortech.2006.05.042. PMid:16843657.

5. Domínguez, J., Alonso, M., Oliet, M., Rojo, E., & Rodríguez, F. (2010). Chemorheological study of the curing kinetics of a phenolic resol resin gelled. European Polymer Journal, 46(6), 1237-1243.

6. Wang, M., Leitch, M., & Charles, C. (2009). Synthesis of phenol-formaldehyde resol resins using organosolv pine lignins.

European Polymer Journal, 45(12), 3380-3388. http://dx.doi. org/10.1016/j.eurpolymj.2009.10.003.

7. Chen, Y., Chen, Z., Xiao, S., & Liu, H. (2008). A novel thermal degradation mechanism of phenol–formaldehyde type resins. Thermochimica Acta, 476(1-2), 39-43. http://dx.doi. org/10.1016/j.tca.2008.04.013.

8. Pérez, J., & Fernández, A. (2011). Thermal stability and pyrolysis kinetics of lignin-phenol-formaldehyde resins. Journal of Applied Polymer Science, 123(5), 3036-3045. http://dx.doi. org/10.1002/app.34817.

9. Zhao, Y., Yan, N., & Feng, M. (2013). Thermal degradation characteristics of phenol–formaldehyde resins derived from beetle infested pine barks. Thermochimica Acta, 555, 46-52. http://dx.doi.org/10.1016/j.tca.2012.12.002.

10. Silva, E. L., & Roldan, P. S. (2009). Simultaneous flow injection preconcentration of lead and cadmium using cloud point extraction and determination by atomic absorption spectrometry.

Journal of Hazardous Materials, 161(1), 142-147. http://dx.doi. org/10.1016/j.jhazmat.2008.03.100. PMid:18456398.

11. Coles, C., & Yong, N. (2005). Use of equilibrium and initial metal concentrations in determining freundlich isotherms for soils and sediments. Engineering Geology, 85(1-2), 19-25. http://dx.doi.org/10.1016/j.enggeo.2005.09.023.

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12. Mohan, D., & Pittman, C. U., Jr (2006). Activated carbons and low cost adsorbents for remediation of tri- and hexavalent chromium from water. Journal of Hazardous Materials, 137(2), 762-811. http://dx.doi.org/10.1016/j.jhazmat.2006.06.060.

PMid:16904258.

13. Chubar, N., Carvalho, J., & Correia, M. (2004). Heavy metals biosorption on cork biomass: effect of the pre-treatment. Colloids and Surfaces. A, Physicochemical and Engineering Aspects, 238(1-3), 51-58. http://dx.doi.org/10.1016/j.colsurfa.2004.01.039.

14. Kadirvelu, K., Thamaraiselvi, K., & Namasivayam, C. (2001).

Removal of heavy metals from industrial wastewaters by adsorption onto activated carbon prepared from an agricultural solid waste. Bioresource Technology, 76(1), 63-65.. http:// dx.doi.org/10.1016/S0960-8524(00)00072-9. PMid:11315812.

15. Zhao, Y., Yan, N., & Feng, M.(2013). Biobased phenol formaldehyde resins derived from beetle-infested pine barks: structure and composition. ACS Sustenable Chemistry and Engineering, 1(1), 91-101.

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

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

17. Huang, C. B., Jeng, R., Sain, M., Saville, B. A., & Hubbes, M. (2006). Production, characterization, and mechanical properties of starch modified by Ophiostoma spp. BioResources, 1(2), 257-269.

18. Kizil, R., Irudayaraj, J., & Seetharaman, K. (2002).

Characterization of irradiated starches by using FT-Raman and FTIR spectroscopy. Journal of Agricultural and Food Chemistry, 50(14), 3912-3918. http://dx.doi.org/10.1021/ jf011652p. PMid:12083858.

19. Krishnan, R., & Maru, G. (2006). Isolation and analyses of polymeric polyphenol fractions from black tea. Food Chemistry, 94(3), 331-340. http://dx.doi.org/10.1016/j.foodchem.2004.11.039.

20. Poljanšek, I., & Krajnc, M. (2005). Characterization of phenolformaldehyde prepolymer resins by in line FT-IR spectroscopy.

Acta Chimica Slovenica, 52(3), 238-244.

Received: Sept. 04, 2013 Revised: Oct. 17, 2014 Accepted: Feb. 09, 2015

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http://dx.doi.org/10.1590/0104-1428.1912

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

Synthesis and characterization of new soluble polyamides from Acenaphtohydrazinomercaptotriazole diamine Hossein Mighani1* and Najmeh Kia2 Department of Chemistry, Golestan University, Gorgan, Iran Department of Chemistry, Qaemshahr Branch, Islamic Azad University, Qaemshahr, Mazandaran, Iran 1

2

*h.mighani@gu.ac.ir

Abstract A diamine Acenaphtohydrazinomercaptotriazole (AHTD) was synthesized in one step from acenaphthoqinone and 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole. The diamin was characterized by FTIR, 1HNMR, 13CNMR and melting point. Diamin was used to prepare novel polyamides. The low temperature solution polycondensation of diamin with tow aromatic and tow aliphatic diacid chlorides afforded diamin-containing polyamides with inherent viscosities of 0.38–0.47 dl/g in DMF at 25 °C. The polyamides were generally soluble in a wide range of solvents such as dimethylformamide(DMF), N-Methylpyrolidone(NMP), tetrachloroethane (TCE), dimethylsulfoxide(DMSO) and H2SO4. Thermal analysis showed that these polyamides were practically crustily and with Tg under 100 °C. Keywords: polyamides, thermalstability, polycondensation, acenaphthoqinone.

1. Introduction Acenaphthoquinone is a quinone derived from acenaphthene.

It is insoluble in water, but soluble in alcohol. It is used as an intermediate for the manufacturing of dyes, pharmaceuticals and pesticides. It is also used in chemical research as a drug and therapeutic agent. Triazole derivatives have been reported as a class of useful heterocyclic compounds, and have found widespread applications in the fields of agrochemicals and pharmaceuticals[1,2]. We have synthetized a diamin that produced of reaction of acenaphtochinon with Triazole derivatives and is used for production of thermally stable polyamides. Polyamides are characterized as high temperature resistant materials with a favorable balance of other physical and chemical properties[3]. Aromatic polyamides have the poor process ability due to their insolubility in common organic solvents and extremely high glass transition or melt temperature. The synthesis of soluble polyamides without deteriorating their excellent properties[4-10]. DSC studies of some polyamides[11,12] were reported in literature. We successfully prepared aromatic polyamides[13], polyimides[14], polyesters, polyquinoxalines, from a number of new functional monomers[15]. Thermally stable polymers have received extensive interest due to the increasing demands for high temperature polymers as replacements for ceramics and metals in the automotive, aerospace, and microelectronics industries. Aromatic polyamides are one of the most important classes of high performance polymers, because they possess excellent mechanical properties, thermal stability, chemical resistance, and low flammability. However, they encounter processing difficulties due to limited solubility in organic solvents and high glass transition or melting temperatures. It is a result of chain stiffness and intermolecular hydrogen bonding between amide groups. In this article, we report the synthesis of polyamides by low temperature solution polycondensation of diamin with tow aromatic and tow aliphatic diacid chlorides such as terephthaloyldichloride

356

(TP), isophthaloyldichloride(IP), adipoylchloride(AP) and sebacoyldichloride (SC) . Physical properties of polymers including characterization, inherent viscosity, solubility, and thermal properties are also reported.

2. Experimental 2.1 Materials and instruments Acenaphthoqinone, 4-amino-3-hydrazino-5-mercapto1,2,4-triazole and other reagents and solvents were purchased from Fluka and used without purification. 1HNMR and 13 CNMR spectra were recorded on a 500 MHz Bruker Advance DRX instrument using DMSO-d6 as solvent and tetramethyl silane as an internal standard. FTIR 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 calorimetry (DSC) analysis were performed using Perkin-Elmer Pyris and Metler Tolledo 822e, respectively. Inherent viscosity (ηinh=Lnηrel/C) of polymers were determined for solution of 0.5 g/dl in NMP at 25 °C using an ubbelohde viscometer. Total sulfur was measured using Tanaka Model RX-360 SH.

3. Preparation of Monomers 3.1 Acenaphtohydrazinomercaptotriazoldiamine (AHTD) The 1,2-dihydro-acenaphtylene-1,2-dione (1.82 g, 10 mmol) was dissolved in 25ml of ethanol and 1ml of conc. HCl and then added to a suspension of 4-amino-3hydrazino-5-mercapto-1,2,4-triazole (2.92 g, 20 mmol) in 25 ml of ethanol and 5 ml water. The mixture was stirred for 10 h at reflux temperature. The orange solid was filtered off, washed with ethanol and water and dried in a vacuum

Polímeros , 25(4), 356-364, 2015

Synthesis and characterization of new soluble polyamides from Acenaphtohydrazinomercaptotriazole diamine oven at 70 °C. A orange solid product was obtained in a 65% yield which starts to melt at 260 °C. The chemical structure of diamine and its procedure is shown in Scheme 1.

4. Preparation of Polyamides 4.1 Polyacenaphtohydrazinomercaptotriazolterephthalate (PA1) A typical procedure for the preparation of polyamides is given in Scheme 2. A 100 ml two-necked flask equipped with a dropping funnel and gas inlet tube was charged with a mixture of AHTD (0.656 g, 2 mmol), 30 ml dimethylformamide

(DMF) and triethylamine (0.8 ml). 2 mmol Diacidchloride (DC) (such as terephthaloyl chloride, isophthaloyl chloride, adipoyl chloride and sebacoyl chloride) dissolved in 20 ml DMF was added dropwise to the stirred solution at 0 °C under N2. The mixture was subsequently stirred at ambient temperature for 5 h under N2, and then it was poured into cold water. The orange solid product was separated by filtration and washed with NaHCO3 solution. Then the solid product dried in vacuum oven at 70 °C. An orange solid product was obtained in a 86% yield which starts to melt at 280 °C.

5. Result and Discussion 5.1 IR, 1HNMR and Elemental Analysis of diamine(AHTD) The monomer, AHTD, was prepared according to the procedures which are given in the Scheme 1. IR, 1HNMR and the results of elemental analysis are given in Table 1.

These regions of the IR spectra in Figure 1 are of particular interest, the 3150-3446 cm–1 (NH and NH2 asymmetric and symmetric stretch), 2980 (C-H aromatic ring) 1638(C=N), 1590(C=C), 1585 cm–1 (NH2) and 908(C-S) and 1HNMR, 13 CNMR data in Figure 2 and Figure 3 with 1HNMR (CDCl3): δ(ppm) 12.7-12.9(NH), 7.78-8.3(CH aromatic), 5.7(NH2) and 1.1(SH) and 13CNMR(400, DMSO, d6, TMS) δ ppm: 118.87 (CAr), 125.24(CAr), 127.22 (CAr), 129.49 (CAr), 130.95 (CAr), 136.66 (CAr), 133.27(C=N) and 179.23(C-S)

Scheme 1. The procedure for the preparation of Diamine.

The polyamides were synthesized by direct polycondensation of aromatic and aliphatic diacidchlorides (Scheme 2) with

Scheme 2. The typical procedure for the preparation of polyamides.

Polímeros, 25(4), 356-364, 2015

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Mighani, H., & Kia, N. AHTD using triethylamine as catalyst. The reactions were carried out in DMF solution of the diacidchloride and AHTD in a nitrogen atmosphere and at room temperature.

The polymerizations proceeded in homogeneous solution

and the yields of the polyamides were quantitative.

The elemental analysis values of all the polyamides, Table 1, were generally in good agreement with the calculated values of proposed structures. As representative example,

Table 1. Spectra data, elemental analysis results and the yield of polyamides.

Substrate

IR (KBr, cm_1)

NMR (DMSO-d6, δ, ppm)

Elemental analysis Calc.

AHTD

PA1

PA2

PA3

PA4

3150-3446 cm–1 (NH and NH2 asymmetric and symmetric stretch), 2980 (C-H aromatic ring), 1638(C=N), 1590 (C=C), 908(C-S) 3430(N-H), 3100 (C-H aromatic), 1790 (C=O), 1631 (C=N), 1527(C=C aromatic), 910(C-S) 3300(N-H), 3117 (N-H), 2965 (C-H aromatic), 1636 (C=O), 1560 (C=N), 1508(C=C aromatic), 910(C-S) 3210(N-H), 3000 (C-H aromatic), 2800(C-H aliphatic) 1638 (C=O), 1590 (C=N), 1476(C=C aromatic), 910(C-S) 3430(N-H), 2900 (C-H aliphatic) 1636 (C=O), 1570(C=N), 1505(C=C aromatic), 910(C-S)

Found

C

H

N

C

H

N

12.7-12.9(NH), 7.78, 8.3(CH,Aromatic), 5.7(NH2), 1.1(SH)

43.84

3.19

38.35

44.12

3.25

37.92

12.7(NH), 7.8 - 8.8 (CH Aromatic), 1.1(SH)

50.70

2.82

29.57

51.02

2.98

28.98

12.7(NH), 7.8 - 8.8 (CH Aromatic), 1.1(SH)

50.70

2.82

29.57

51.32

3.02

28.83

12.8(NH), 7.1 - 8.4 (CH Aromatic), 1.9 – 2.1(CH2), 1.1(SH)

48.17

3.65

30.65

47.92

3.56

31.03

12.8(NH), 7.1 - 8.4 (CH Aromatic), 1.9 - 2.8(CH2), 1.1(SH)

51.65

4.64

27.81

51.89

4.35

28.12

Figure 1. IR spectra of diamine.

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Synthesis and characterization of new soluble polyamides from Acenaphtohydrazinomercaptotriazole diamine

Figure 2. 1HNMR spectra of diamine.

Figure 3. 13CNMR spectra of diamine.

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Mighani, H., & Kia, N. the complete elemental analysis of PA1 was as follows: C, 50.70% (51.02% calculated); H, 2.82% (3.21%); N, 29.57% (28.58%). The polyamides were also characterized by IR and NMR spectrometers. The presence of amide bands at ca. 3430 cm–1 (N-H stretching), 1790 cm–1 (C=O stretching), 1631 cm–1 (N-H bending and C-N stretching) and 910 cm–1 (C-S), in the IR spectra in Figure 4 for PA1 and amidic proton

at ca. 12.5 ppm in the NMR spectra of PA1 in Figure 5 confirmed the amidic structure of polymers.

The limiting viscosity number [η] of polyamides was determined for extracted and dried polymers in DMF, depending on the solubility of the polyamide. For the same or similar type of linear polymers the [η] value is proportional to the molecular mass. The inherent viscosities of polyamides (PA1-PA4), obtained in DMF were in the

Figure 4. FTIR spectra of PA1.

Figure 5. 1HNMR spectra of PA1.

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Polímeros , 25(4), 356-364, 2015

Synthesis and characterization of new soluble polyamides from Acenaphtohydrazinomercaptotriazole diamine range of 0.38–0.47 dl/g that revealed reasonable molecular weights. The limiting viscosity number [η] of aromatic polyamides is less than aliphatic polyamides.

One of the major objectives of this study was producing modified polyamides with improved solubility. The solubility of these polyamides was determined for the powdery samples in excess solvents and the results are listed in Table 2.

All the polyamides were readily soluble in common polar aprotic solvents without need for heating. Also, by heating they were soluble in a less efficient solvent such as THF. The good solubility behavior of most prepared polyamides can be explained through the enhancement of solubility induced by the side biphenyl groups of the diamine moiety.

The thermal behavior of polyamides was studied by DSC and TGA.. Thermal properties of the prepared polyamides were evaluated by means of DSC and TGA. Representative DSC

and TGA thermograms are shown in Figures 6, 7, 8 and 9 for two aromatic and aliphatic polyamides(PA2,PA3).

The DSC curves of Polyamides(PA2,PA3) were shown the glass transition temperature of these polymers at 65 °C and 55 °C and cristallinity temperature of both polymers at 251 °C and the melt temperature of polymers at 330 °C and 310 °C respectively. The DSC curves showed that the aliphatic polyamides have lower glass transition temperature such as aromatic polyamides and they have certainly melt temperature less than aromatic polyamides.

The thermal stability of polyamides was also evaluated

by TGA. The temperatures of the 10%, 25% and 50% weight loss and the remained polyamides at 600 °C in nitrogen atmosphere were given in Table 3.

Table 2. Solubility of polyamides.

Polym. code

NMP

DMF

DMSO

TCE

THF

H2SO4

HMPA

DMAC

Aceton

Ethanol

Methanol

CHCl3

AHTD PA1 PA2 PA3 PA4

+ + + + +

+ + + + +

+ + + + +

+ ± ± ± ±

+ + + + +

+ + + + +

+ + + ± ±

+ + + + +

+ -

+ ± ± ± ±

+ -

± ± ± ± ±

Soluble (+), partially soluble (±), insoluble (-) Solubility tested with 0.5 g of polymer in 100 ml of solvent. NMP=N-methylpyrolidone, DMF=dimethylformamide, DMSO=dimetylsolfoxide, TCE=tetrachloroethane, Py=pyridine, THF=tetrahydrofurane, HMPA=hexamethylenphosphoramide, DMAC=dimethylacetamide.

Figure 6 . DSC of PA2.

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Mighani, H., & Kia, N.

Figure 7 . DSC of PA3.

Figure 8 . TGA of PA2.

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Synthesis and characterization of new soluble polyamides from Acenaphtohydrazinomercaptotriazole diamine

Figure 9 . TGA of PA3.

Table 3. Thermal analysis, viscosity and yield of the polyamides.

Compound code

Tg

Tc

Tm

T10(°C)a

T25(°C)b

T50(°C)c

%Ch. Y. d

AHTD PA1 PA2 PA3 PA4

90 65 55 50

251 251 251 240

260 320 330 310 310

230 230 220 180

320 400 310 290

420 450 340

42 60 38 16

ηinh (dl/g)e 0.04 0.38 0.42 0.45 0.47

Tg Glasstransition Temperature. Tc cristallinity Temperature . Tm Melting temperature. a10% weight loss. b25% weight loss. c50% weight loss. d Char yield percent at 600 °C, obtained from TGA. eMeasured in DMF at 25 °C (c=0.5 g/dl).

All the polymers were stable up to 200 °C in nitrogen and show almost the same stability. We found that these polyamides did not show obvious weight losses until the temperature reached 200 °C in nitrogen, implying that no thermal decomposition occurred. However, as the temperature over 200 °C, the polymers showed a rapid thermal decomposition.

The 10% weight loss of all polymers was in temperature range of 180-230 °C. The 25% weight loss of all polymers was in temperature range of 290-320 °C. The 50% weight loss of all polymers was in temperature range of 340-450 °C. The polyamides (PA1,PA2) remained 42-60% of the original weight at 600 °C in nitrogen and the polyamides (PA3,PA4) remained over 16-38% of the original weight at 600 °C in nitrogen. Two of the polyamides(aliphatic) exhibited a more Polímeros, 25(4), 356-364, 2015

weight loss at the same temperature and they have a short char yield against aromatic polyamides.

6. Conclusion A series of polyamides were prepared from the reaction of two aromatic and two aliphatic diacid chlorides with a diamine AHTD. The molar ratio of diacid chloride to the AHTD was 2:2 and the reaction was carried out at ambient temperature for 5 h under N2 atmosphere. The polyamides were fully characterized and their thermal properties were studied. Two of the polyamides(aliphatic) exhibited a more weight loss at the same temperature and they have a short char yield against aromatic polyamides. The introduction of aromatic side groups in structure of the diamine resulted 363

Mighani, H., & Kia, N. in crystalline polyamides that the degree of crystallinity has a big influence on hardness, density, transparency and diffusion. The polyamides have very good solubility in aprotic solvents such as DMF and generally, the solubility of aromatic polyamides were better in selected solvents.

Aliphatic polyester hopes of higher inherent viscosity and thus had a higher molecular weight. The glass temperature of the aliphatic polyamides was lower than aromatic polyamides but unlike crystalline temperature and melting temperature are close together and the differences were not significant.

7. References 1. Maxwell, J. R., Wasdahl, D. A., Wolfson, A. C., & Stenberg, V. I. (1984). Synthesis of 5-aryl-2H-tetrazoles, 5-aryl-2Htetrazole-2-acetic acids, and [(4-phenyl-5-aryl-4H-1,2,4-triazol3-yl)thio]acetic acids as possible superoxide scavengers and antiinflammatory agents. Journal of Medicinal Chemistry, 27(12), 1565-1570. http://dx.doi.org/10.1021/jm00378a007.

PMid:6094808.

2. Vicentini, C. B., Manfrini, M., Veronese, A. C., & Guarneri, M. (1998). Synthesis of 4-(pyrazol-5-yl)-1,2,4-triazole-3-thiones.

Journal of Heterocyclic Chemistry, 35(1), 29-32. http://dx.doi. org/10.1002/jhet.5570350106.

3. Couderchet, M., Schmalfuß, J., & Böger, P. (1998). A specific and sensitive assay to quantify the herbicidal activity of chloroacetamides. Pesticide Science, 52(4), 381-387. http:// dx.doi.org/10.1002/(SICI)1096-9063(199804)52:4<381::AIDPS735>3.0.CO;2-8.

4. Cassidy, P. E. (1980). Thermally stable polymers. New York: Marcel Dekker.

5. Imai, Y., Maldar, N. N., & Kakimoto, M. (1984). Synthesis and characterization of soluble aromatic polyazomethines from 2,5-bis(4-aminophenyl)-3,4 diphenylthiophene and aromatic dialdehydes. Journal of Polymer Science: Polymer Chemistry Edition, 22(12), 3771-3778. http://dx.doi.org/10.1002/ pol.1984.170221214.

6. Liaw, D.-J., Uexama, N., & Havada, A. (2004). In N. Ueyama & A. Harada (Eds.), Macromolecules nanostructured materials (chap. 2.2, pp. 80). Berlin: Springer.

7. Liaw, D.-J. (2005). Optically high transparency and light color of organosoluble polyamides containing trifluoromethyl and kink diphenylmethylene linkage. Journal of Polymer Science.

364

Part A, Polymer Chemistry, 43(19), 4559-4569. http://dx.doi. org/10.1002/pola.20782.

8. Liaw, D.-J., Huang, C. C., & Chen, W. H. (2006). Color lightness and highly organosoluble fluorinated polyamides, polyimides and poly(amide–imide)s based on noncoplanar 2,2′-dimethyl-4,4′-biphenylene units. Polymer, 47(7), 23372348. http://dx.doi.org/10.1016/j.polymer.2006.01.028.

9. Wu, S.-C., & Shu, C. F. (2003). Synthesis and properties of soluble aromatic polyamides derived from 2,2′-bis(4carboxyphenoxy)-9,9′-spirobifluorene. Journal of Polymer Science. Part A, Polymer Chemistry, 41(8), 1160-1166. http:// dx.doi.org/10.1002/pola.10657.

10. Yang, C.-P., Hsiao, S.-H., & Lin, J.-H. (1992). New poly(amideimide)s syntheses. II. Soluble poly(amide-imide)s derived from 2,5-bis(4-aminophenyl)-3,4-diphenylthiophene and various N-(ω-carboxyalkyl)-trimellitimides, N-(carboxyphenyl) trimellitimides, or N,N″-bis(ω-carboxyalkyl)pyromellitimides.

Journal of Polymer Science. Part A, Polymer Chemistry, 30(9), 1865-1872. http://dx.doi.org/10.1002/pola.1992.080300909.

11. Siracusa, G., Pollicino, A., & Borrello, G. M. (1997). The preparation by a solid-solid interaction route of aromatic polyamide materials containing sulphone, ether and ketone linkages. Journal of Thermal Analysis and Calorimetry, 50(4), 633-646. http://dx.doi.org/10.1007/BF01979035.

12. Fujimura, T., Sarugaku, N., Tsuchiya, M., Ishimaru, K., & Kojima, T. (2001). Thermogravimetric Analysis of Aromatic Polyamides with Various Benzimidazolyl Contents. Journal of Thermal Analysis and Calorimetry, 64(2), 425-431. http:// dx.doi.org/10.1023/A:1011516804961.

13. Ghaemy, M., Mighani, H., & Alizadeh, R. (2011). Synthesis and characterization of Schiff-base-containing polyamides.

Chinese Journal of Polymer Science, 29(2), 148-155. http:// dx.doi.org/10.1007/s10118-010-1004-8.

14. Ghaemy, M., & Mighani, H. (2010). Synthesis and characterization of Schiff-base-containing polyimides. Journal of Applied Polymer Science, 118(5), 2496-2501. http://dx.doi.org/10.1002/ app.31178.

15. Ghaemy, M., Mighani, H., & Ziaei, P. (2009). Synthesis and characterization of novel organosoluble polyesters based on a DIOL with azaquinoxaline ring. Journal of Applied Polymer Science, 114(6), 3458-3463. http://dx.doi.org/10.1002/app.30726.

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

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http://dx.doi.org/10.1590/0104-1428.1947

Natural rubber latex: determination and interpretation of flow curves Harrison Lourenço Corrêa1,2*, Ana Maria Furtado de Sousa1 and Cristina Russi Guimarães Furtado1 1 Departamento de Processos Químicos, Instituto de Química, Universidade do Estado do Rio de Janeiro - UERJ, Rio de Janeiro, RJ, Brazil 2 Departamento de Engenharia Química, Instituto de Tecnologia, Universidade Federal Rural do Rio de Janeiro - UFRRJ, Seropédica, RJ, Brazil

*harrisoncorrea@ufrrj.br

Abstract As consumers become more demanding, the importance grows of guaranteeing the quality of products. The employment of reliable testing techniques that assure the origin and characteristics of the inputs used by industry is a key factor in this respect. In the rubber processing industry, the most commonly used characterization tests include determination of the total solids and dry rubber content, mechanical stability, odor, color and presence of volatile compounds, among others. For the most part, these tests are sufficient for the latex transformation industry. However, in situations where there is a need to know the behavior of latex in reaction to the mechanical forces of machines (mixers, pumps, etc.), other tests must be used. Rheological tests to determine viscoelastic data by means of plotting flow curves combined with the application of theoretical models can provide important details for characterization of different types of latex.

This article presents the protocol employed by the Rheology and Image Laboratory of Rio de Janeiro State University (UERJ) for the rheological study of Brazilian latex. The samples analyzed came from the state of São Paulo.

Keywords: latex, natural rubber, rheology.

1. Introduction Natural rubber latex (NRL) for industrial purposes is sold in concentrated form, with high dry rubber content (DRC), of 30 to 60%, depending on the productive process. Because it is a material resulting from plant physiology, natural latex needs a series of analyses to monitor and control its quality.

The testing protocols serve to ascertain the concentrations of certain components (levels of minerals, thiols, proteins, lipids, carbohydrates, etc.). The results of these tests are important indicators of rubber tree productivity[1]. Once the latex is extracted from the tree, these parameters must be adjusted to the processing needs of each industry. Therefore, it is necessary to employ preliminary processing stages, including concentration and addition of preservation agents (generally ammonia), before sending the material to the factory. Although ammonium hydroxide is the preferred preservation agent due to its low cost, others can be used to prevent coagulation of NRL, such as sodium sulfide, formalin and zinc oxide[2]. Many articles have studied the components of natural latex, including some addressing the diagnostic techniques[3-6]. The results presented are important to the extractive and productive segments of the rubber sector. Other lines of research into latex involve rheology.

This entails, for example, measuring the viscosity of the raw material (60% concentrated) in function of temperature variation, or more specifically, in function of shear rate[7].

These studies provide data on the material’s behavior when submitted to industrial processing conditions (agitation, pumping, evaporation, etc.) that are useful for manufacture of latex articles.

Polímeros, 25(4), 365-370, 2015

Although the diagnosis of the components of natural latex is consolidated, there is a lack of data in this material’s rheology. Determination of the best processing conditions requires data on how latex behaves as a Newtonian fluid, obtained from flow curves as well as application of mathematical models able to describe the flow behavior under various conditions. This article makes a contribution in this respect.

2. Materials and Methods We used NRL samples supplied by the company Colitex, located in the state of São Paulo, Brazil. These samples varied as to content of stabilizer added, and are called here low concentration (LC), 0.2% of NH4OH (w/w) and ‘normal’ concentration (NC), with concentration higher than 0.6% of NH4OH (w/w). Table 1 presents the properties of the NRL samples.

For the purpose of proposing a scientific method that can correlate the behavior of natural rubber latex to the needs of processing industries, we evaluated the flow curves for different samples obtained from industrial suppliers. For this, we employed an Anton Paar model MCR-301 coaxial cylinder rheometer equipped with a Peltier temperature control system. The latex samples were shaken manually for 10 seconds before being transferred to the measurement reservoir.

To determine the viscosity behavior of the samples in function of shear rate (s–1), they were submitted to a testing protocol involving definition of two shear rate ranges

365

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

Corrêa, H. L., Sousa, A. M. F., & Furtado, C. R. G. (10‑100 s–1 and 10-1000 s–1), so as to determine the limits of Newtonian behavior.

The temperatures of these assays were previously programmed at 25, 30 and 40 °C, based on the probable temperatures reached during the packing and transport of the raw material, according to the rheological testing conditions shown in Table 2.

3. Results and Discussion 3.1 Flow curves The samples were assigned alphanumeric codes in the form ‘XXX-FCXX’, where the first letter of the first group represents the origin of the sample (first letter of the company’s Table 1. Properties of the NRL samples.

Properties Total solids content (%) Dry rubber content (%) NH4OH (%, w/w) pH Color Odor Film color

LC Sample 59

NC Sample 61

60

60

0.2 10 White Slightly sweet No gray or blue

>0.6 11 White Slightly sweet No gray or blue

name) and the next two indicate the stabilizer concentration (LC – low concentration, 0.2% w/w; NC – concentration higher than 0.6% w/w), and the second group identifies the test (FC – flow curve) and temperature (25 / 30 / 40 °C).

To assess the repeatability of the tests, the samples were submitted to three runs (1, 2, 3), under the same conditions (temperature and shear range). Figures 1, 2 and 3 show the stress behavior (σ) in function of shear rate (ẏ) at the three temperatures, as well as the evolution of viscosity (η) in relation to shear rate.

From the overlap of all three curves generated by the tests (runs 1, 2, 3), it can be perceived that the method applied combined with careful preparation of the samples (agitation, conditioning, weighing and transfer) and equipment calibration produced repeatable results for the conditions employed.

Analysis of the curves (b) of Figures 1-3 shows that regardless of the temperature, the samples behaved as Newtonian fluids at low shear rates. The viscosity of the natural latex rubber samples declined with increasing shear rate because of the pseudoplastic behavior.

Figures 4, 5 and 6, showing the flow curves of the samples with concentration of NH4OH higher than 0.6% (w/w), indicate similar behavior: a decrease in viscosity with rising shear rate, defined limit of the Newtonian fluid region and repeatability of the results.

3.2 Application of the models to the experimental data Table 2. Rheological testing conditions for determination of the flow curves.

Parameters Total testing time (s) Testing temperatures (°C) Shear ranges (s–1)

Parameters applied in the tests 930 25 / 30 / 40 10 to 100 / 10 to 1000

Predicting the behavior of fluids when subjected to mechanical forces is always useful to determine the best processing parameters, especially in the case of polymer materials. In this respect, the use of mathematical models able to reproduce the observed phenomenon is essential to the productive sector to enable adjustment of the data

Figure 1. Flow curves (25 °C) for the natural latex sample supplied by Colitex (0.2% NH4OH, w/w): (a) strain versus shear rate; (b) viscosity versus shear rate.

Figure 2. Flow curves (30 °C) for the natural latex sample supplied by Colitex (0.2% NH4OH, w/w): (a) strain versus shear rate; (b) viscosity versus shear rate.

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Polímeros , 25(4), 365-370, 2015

Natural rubber latex: determination and interpretation of flow curves obtained from laboratory tests to the real processing conditions (industrial scale).

Analysis of Figures 1b-6b allows concluding that the samples investigated behaved as non-Newtonian fluids. More

specifically, they behaved as pseudoplastic (shear thinning) fluids, since the viscosity decreased with increasing shear rate. However, a more attentive observer might question the non-Newtonian behavior of the samples, since the curves of

Figure 3. Flow curves (40 °C) for the natural latex sample supplied by Colitex (0.2% NH4OH, w/w): (a) strain versus shear rate; (b) viscosity versus shear rate.

Figure 4. Flow curves (25 °C) for the natural latex sample supplied by Colitex (>0.6% NH4OH, w/w): (a) strain versus shear rate; (b) viscosity versus shear rate.

Figure 5. Flow curves (30 °C) for the natural latex sample supplied by Colitex (>0.6% NH4OH, w/w): (a) strain versus shear rate; (b) viscosity versus shear rate.

Figure 6. Flow curves (40 °C) for the natural latex sample supplied by Colitex (>0.6% NH4OH, w/w): (a) strain versus shear rate; (b) viscosity versus shear rate.

Polímeros, 25(4), 365-370, 2015

367

Corrêa, H. L., Sousa, A. M. F., & Furtado, C. R. G. σ x ẏ (Figures 1a-6a) at first were linear (suggesting ideal, and hence Newtonian, behavior). In this case, the shear rate range used (0 to 100 s–1) might have been too low to reveal the non-Newtonian domain of the latexes. However, the tests carried out up to higher rates (10 to 1000 s–1) confirmed the behavior originally noted: linear σ x ẏ curves, suggesting probable Newtonian behavior, as can be seen in Figure 7a.

At high shear rate, the sample yet keeps the non-Newtonian behavior, as noted by Figure 7b.

Table 3 shows the initial and final viscosity values obtained after applying shear rates between 10 and 100 s–1.

For all the temperatures analyzed, the application of shear stresses in the range of 10 to 100 s–1 on the NRL samples caused a reduction of over 30% in the initial viscosity, independent of the preservative concentration.

Table 4 shows the mean viscosities of the NRL samples (ηm) at each temperature.

Table 3. Initial (ηo) and final viscosity (ηf) corresponding to shear rates of 10 s–1 and 100 s–1, respectively, for different NRL samples at temperatures of 25, 30 and 40 °C. Samples CNCFC25 CNCFC30 CNCFC40 CLCFC25 CLCFC30 CLCFC40

Initial viscosity, Pa.s (ηo) 0.0787

Final viscosity, Pa.s (ηf) 0.0507

0.0671

0.0446

34

0.0498

0.0332

33

0.0776

0.0471

39

0.0651

0.0415

36

0.0504

0.0333

34

Reduction (%) 36

Table 4. Mean viscosities obtained at temperatures of 25, 30 and 40 °C. Samples CNC-FC25 CNC-FC30 CNC-FC40 CLC-FC25 CLC-FC30 CLC-FC40

Mean viscosity (Pa.s) 0.0629 0.0543 0.0401 0.0603 0.0520 0.0408

An increase of 15 °C in the testing temperature promoted reductions in viscosity of 36% and 32% for samples CNC and CLC, respectively, near the reduction attained by the application of mechanical force.

The non-ideal behavior of the samples can be confirmed by the rheological models applied to the experimental data and their respective correlation coefficients.

3.2.1 Model applied to Newtonian fluids As seen previously, in fluids with ideal behavior the fluid’s resistance to deformation is directly proportional to the shear rate applied, according to Equation 1[8]. η=

σ (1) y

From the previous discussion, the dispersion of the experimental data can suggest ideal behavior of the latex samples. Figures 8-13 show the empirical data fitted to the model of Equation 1 (red line).

The curves fitted according to Equation 1 show decreasing viscosity (which is predicable) of the latex samples with 0.2% of NH4OH as stabilizer, with correlation coefficients (R2) between 0.9568 and 0.9694. These coefficients, which can vary from 0 to 1, are essential to verify the concordance between the empirical data and the behavior proposed by the model. The nearer the coefficient is to 1, the better the fit[9], so that more accurate predictions of y can be made from the known values of x[10].

3.2.2 Model applied to non-Newtonian fluids (power law) Within a determined shear rate range, some fluids can present very distinct regions in the graph of η x ẏ.

For the typical rheogram (curve obtained by plotting shear rate x viscosity)[11], there is a model able to represent the curve in the entire region. This model is called the Cross model, in homage to the noted rheologist Malcolm Cross[8], is expressed by Equation 2. η −ηo 1 = (2) η0 −η∞ 1 + ( K .y)  m

Where K is the time dimension and m is a dimensionless constant, associated with the pseudoplastic nature of the fluid. The nearer to 1 this constant is, the more pseudoplastic the material will be, while the nearer it is to 0, the more Newtonian the fluid’s behavior will be.

Figure 7. Flow curves (40 °C) for the natural latex sample supplied by Colitex (>0.6% NH4OH, w/w): (a) stress versus shear rate (10 to 1000 s–1); (b) viscosity versus shear rate.

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Polímeros , 25(4), 365-370, 2015

Natural rubber latex: determination and interpretation of flow curves

Figure 8. Flow curve (25 °C) for the natural latex sample supplied

by Colitex (0.2% NH4OH, w/w) fitted to Equations 1 (linear) and 3 (power).

Figure 9. Flow curve (30 °C) for the natural latex sample supplied

by Colitex (0.2% NH4OH, w/w) fitted to Equations 1 (linear) and 3 (power).

Figure 10. Flow curve (40 °C) for the natural latex sample supplied

by Colitex (0.2% NH4OH, w/w) fitted to Equations 1 (linear) and 3 (power).

Figure 11. Flow curve (25 °C) for the natural latex sample supplied

by Colitex (>0.6% NH4OH, w/w) fitted to Equations 1 (linear) and 3 (power).

However, by making some assumptions, such as: ηo >> η∞, K.ẏ >> 1 and small η∞ (which can be verified from Figures 1b-6b), Equation 2 can be developed as follows: η 1 η − η0 =0m . m (2.1) K

η = = η

η0 + 

η0 1 (2.2) .

K m y m

η0 . 1 + 

y

1 1  (2.3) .  K m y m 

By replacing the variables K and m with the variables k and n, the Ostwald-de Waele equation is obtained (Equation 3), also called the power law[8,11-13].

Figure 12. Flow curve (30 °C) for the natural latex sample supplied

by Colitex (>0.6% NH4OH, w/w) fitted to Equations 1 (linear) and 3 (power).

η = k .y n −1 (3)

Or σ = k .y n (4)

Where k is the flow consistency index and n is the power law index (or flow behavior index). In this case, as m approaches (n-1), the new index will indicate more nearly Newtonian behavior the closer the value of n is to 1[8,11,12].

From this standpoint, based on the assumption that the fluid is non-Newtonian and hence, with the experimental data arranged according to the tendency described by the power law, Figures 8-10 and Figures 11-13 show the respective adjustments by the model described in Equation 3 (green line) for the samples with 0.2% of NH4OH and concentration higher than 0.6% for the same stabilizer, respectively.

Polímeros, 25(4), 365-370, 2015

Figure 13. Flow curve (40 °C) for the natural latex sample supplied

by Colitex (>0.6% NH4OH, w/w) fitted to Equations 1 (linear) and 3 (power).

The correlation coefficients of the curves plotted according to the Ostwald-de Waele model for the latex samples with low preservative concentration, at all three temperatures analyzed, are very near 1 (0.999), showing that the power law is able to adequately represent the experimental data.

The coefficients of m, greater than 0.7, reinforce the non‑Newtonian behavior of the samples analyzed[8].

369

Corrêa, H. L., Sousa, A. M. F., & Furtado, C. R. G. Just as for the samples with low preservative concentration (0.2% of NH4OH, w/w), the experimental data obtained from the rheological tests for the latex samples containing a NH4OH concentration >0.6% (w/w) better fit the Ostwald‑de Waele model. In comparison with the fits provided by the Newtonian model, the power law allowed more precise convergence of the experimental data, with correlation coefficients of 0.999. The values of m obtained (greater than 0.8) reaffirm the non-ideal behavior of the samples analyzed.

The application of the Ostwald-de Waele model (power law) to the empirical data and their subsequent convergence allows inferring that reduced viscosity of the samples with rising shear rate indicates non-ideal behavior, already starting at shear rates between 0 and 100 s–1.

4. Conclusions The results presented here show that the application of thermal or mechanical energy is sufficient to reduce the viscosities to similar levels, by around 35%. In this case, increases in temperature of 15 °C resulted in viscosities near those observed when the samples were submitted to shear stresses of 100 s–1.

Mathematical modeling is an essential tool for analysis and discussion of the rheological behavior of natural rubber latex, allowing a more precise investigation of its pseudoplastic behavior based on flow curves. The increase in temperature promoted a reduction of the average viscosity of the latex samples, and when this was analyzed employing shear stress and shear rate data, the power law best represented the behavior, even for shear rates between 0 and 100 s–1.

It was observed that the shear rate around 60 s–1 is the limit between the Newtonian and non-Newtonian behavior at all temperatures studied.

5. Acknowledgements The authors are grateful for Colitex by supply of natural rubber latex.

6. References 1. American Standard Testing for Materials - ASTM. (2010).

ASTM D1076: Standard specification for rubber-concentrated, ammonia preserved, creamed and centrifuged natural latex.

West Conshohocken.

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2. Jawjit, W., Pavasant, P., & Kroeze, C. (2015). Evaluating environmental performance of concentrated latex production in Thailand. Journal of Cleaner Production, 98, 84-91. http:// dx.doi.org/10.1016/j.jclepro.2013.11.016.

3. Siler, D. J., & Cornish, K. (1995). Measurement of protein in natural rubber latex. Analytical Biochemistry, 229(2), 278-281. http://dx.doi.org/10.1006/abio.1995.1413. PMid:7485983.

4. Bonfils, F., Ehabe, E. E., Aymard, C., Vaysse, L., & SainteBeuve, J. (2007). Enhanced solvent extraction of polar lipids associated with rubber particles from Hevea brasiliensis.

Journal of Phytochemical Analysis, 18(2), 103-108. http:// dx.doi.org/10.1002/pca.956. PMid:17439009.

5. Liengprayoon, S., Bonfils, F., Sainte-beuve, J., Sriroth, K., Dubreucq, E., & Vaysse, L. (2008). Development of a new procedure for lipid extraction from hevea brasiliensis natural rubber. European Journal of Lipid Science and Technology, 110(6), 563-569. http://dx.doi.org/10.1002/ejlt.200700287.

6. Sansatsadeekul, J., Sakdapipanich, J., & Rojruthai, P. (2011).

Characterization of associated proteins and phospholipids in natural rubber latex. Journal of Bioscience and Bioengineering, 111(6), 628-634. http://dx.doi.org/10.1016/j.jbiosc.2011.01.013.

PMid:21354367.

7. Jatuporn, S. (2006). Rheological properties of natural rubber latex (Master’s thesis). Suranaree University of Technology, Thailand.

8. Barnes, H. (2000). A handbook of elementary rheology.

Aberystwyth: Cambrian Printers.

9. D’Urso, P., & Santoro, A. (2006). Goodness of fit and variable selection in the fuzzy multiple linear regression. Fuzzy Sets and Systems, 157(19), 2627-2647. http://dx.doi.org/10.1016/j. fss.2005.03.015.

10. Brown, A. M. (2001). A step-by-step guide to non-linear regression analysis of experimental data using a Microsoft Excel spreadsheet. Computer Methods and Programs in Biomedicine, 65(3), 191-200. http://dx.doi.org/10.1016/ S0169-2607(00)00124-3. PMid:11339981.

11. Perry, R., Green, D., & Maloney, J. (1999). Perry’s chemical engineers’ handbook. United States: McGraw-Hill.

12. Macosko, C. (1994). Rheology, principles, measurements and applications. United States: Wiley-VCH. 13. Sorbie, K., Clifford, P., & Jones, E. (1989). The rheology of pseudoplastic fluids in porous media using network modeling.

Journal of Colloid and Interface Science, 130(2), 508-534. http://dx.doi.org/10.1016/0021-9797(89)90128-8.

Received: Oct. 06, 2014 Revised: Mar. 16, 2015 Accepted: Mar. 23, 2015

Polímeros , 25(4), 365-370, 2015

http://dx.doi.org/10.1590/0104-1428.1965

Recycling assessment of multilayer flexible packaging films using design of experiments Gabriel Abreu Uehara1*, Marcos Pini França2 and Sebastiao Vicente Canevarolo Junior1 Departamento de Engenharia de Materiais, Universidade Federal de São Carlos - UFSCar, São Carlos, SP, Brazil 2 Dow Brasil S.A., São Paulo, SP, Brazil

1

*gabrieluehara@live.com

Abstract The viability of recycling post-industrial packaging waste, compounded from multilayer laminated PET-PE films, for production of polymer blends with good physico-mechanical performance is analyzed. Initially, several PET-PE model-blends were prepared from fresh polymers and were compounded with different formulations, based on design of experiments (DOE). Polymer compatibilizers based on maleic anhydride (PE-g-MA) and glycidyl methacrylate (E-GMA) have been used to promote the compatibilization reaction. The physico-mechanical properties of the model‑blends were evaluated by response surface methodology (RSM). Finally, the post-industrial waste was compounded with the same concentration of compatibilizers in the previous set of model-blends. The DOE methodology showed to be a useful tool for assessing the recycling, since it helped to produce recycled materials with acceptable physico-mechanical properties. Between both compatibilizers studied, PE-g-MA showed to be the best additive for compatibilization due to the presence of a polyamide component in the waste, which undergoes a kinetically favorable compatibilization reaction.

Keywords: DOE, multilayer flexible packaging films, polymer blends, recycling, response surface methodology.

1. Introduction Plastics are versatile materials that are present in all aspects of the modern life, providing goods and services that no other material would be able to provide. However, the accumulation of plastics in the environment has become a significant problem[1]. An ideal solution would be the recovery and the recycling of those materials, prolonging its life cycle and reducing environmental issues. Moreover, the majority of plastics still are based on oil feedstock, a non-renewable source of raw materials. Hence, recycling of post-industrial and post-consumer plastics has been spread rapidly among the industry[2].

In most underdeveloped and emerging countries, socio-economic issues and the low aggregated value of the recycled materials lead to a poor recyclability index.

The low aggregated value is caused by the low quality of the recycled materials available on the market, which prevents its use in applications with strict specifications.

The recycled materials are generally compounded from a mixture of incompatible polymers[3]. This often results in products with lower quality and with variable consistency.

Paradoxically, flexible packaging have increasingly been designed with multilayer films based on immiscible materials (PE, PET, nylon) in order to reach products with an adequate performance with an acceptable cost. This implies the production of great amounts of multilayer film waste with functional materials but with low capacity of reuse, leading to a holdback for the companies that have to face tougher environmental laws. One typical example is the Brazilian National Solid Waste Policy (NSWP), a new law implemented in 2010 which the main goal is to decrease the total volume of solid waste produced nationally. The NSWP establishes

Polímeros, 25(4), 371-381, 2015

principles, objectives, guidelines, goals and actions in order to provide a better management of the several types of solid waste, increasing sustainability from the local level to the national level. This shall contribute even more for the utilization of recycled polymers, such as thermoplastics, but still represents a great challenge due to the low capacity of reuse of multilayer films as mentioned before.

With the objective to collaborate with the resolution of this dilemma, several studies on recycling methods have been proposed[2-4]. Previous works have already shown that the use of polymer compatibilizers like polyethylene grafted with maleic anhydride[5,6] or glycidyl methacrylate[6,7] can enhance significantly the physico-mechanical properties of PET/PE blends. However, the great majority of these studies have been developed in a very limited way, considering the use of PET that was originated from different applications[8] rather than flexible packaging, and also utilizing compatibilizers with an unknown composition[9]. As discussed, multilayer flexible packaging can be made with a gamma of different polymers with different physico-chemical properties, particularly polarity. Hence, compatibilization methods[10] shall be developed in order to improve the adhesion between the components, enhancing the final properties for recycled materials. Moreover, there is a lack of literature regarding a complete scanning of the composition range on the properties of PET/PE systems based on multilayer packaging films. These needs take us to the main objective of this paper which was to build up PET/PE model blends, two of the main common polymers applied in the flexible packaging industry, in order to improve the performance of recycled scraps of multilayer packaging films. Thereby, these

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Uehara, G. A., França, M. P., & Canevarolo, S. V., Jr. models can be used to provide tailored properties based on a physico-mechanical screening of PET/PE blends, using design of experiments (DOE) and multivariate data analysis.

2. Materials and Methods 2.1 Materials The resins used for compounding the PET/PE model blends were a commercial virgin LLDPE (hereinafter denominated “PE”) trade name Dowlex™ 2050B, supplied

by Dow Brasil S.A. and Polyethylene Terephthalate (PET) grade Cleartuf Turbo™, supplied by M&G Polímeros.

Two different types of commercial compatibilizers were used: a random copolymer of ethylene-glycidyl methacrylate (E-GMA), trade name Lotader™ AX8840, supplied by Arkema and a copolymer of ethylene-α-olefin grafted with maleic anhydride (PE-g-MA), trade name Amplify™ GR216, supplied by Dow Brasil S.A. The multilayer PET/PE films are commercial scraps of stand-up pouches, sent directly by the cosmetic industry, free of contamination and in the form of cut films.

2.2 Melt processing For the model blends, PET pellets were carefully dried before use in a vacuum oven at 160 °C during 5h. Adequate quantities of the components were weighted and the melt blended formulations were processed in a Werner & Pfleiderer ZSK30 co-rotating twin-screw extruder. The temperature profile, kept constant throughout the experiments was 240‑260-260-260-260-210 °C. The melt strands were cooled down, pelletized, and kept for at least 24h resting at room temperature, in sealed plastic bags before the injection molding of specimens.

2.3 Design of experiments (DOE) and reprocessing of multilayer waste films The compatibilization study and the subsequent analysis of physico-mechanical behavior were made considering statistical tools by means of a 22 full factorial central point DOE. The factors analyzed were (a) the concentration of the compatibilizers (E-GMA and PE-g-MA) and (b) the PET/PE weight ratio. Table 1 illustrates the first DOE chosen.

In order to improve the sensibility of the model, the 22 full factorial DOE was expanded to a central composite design, which further provides a screen of the physico-mechanical behavior by means of the response surface methodology (RSM). The expansion is shown in Figure 1, which compares

both DOE. Figure 1b shows the four additional points (experiments) obtained by rotating the initial planning by a factor of , defined as “α rotability parameter”[11].

Table 2 illustrates the additional points in the design of experiments, after this expansion.

The last four runs (i.e., extrusion 8 to 11) are the edges of the rotated square in Figure 1, creating a star-like design. Since two compatibilizers were used, a total of (11 extrusions)×(2 additives)= 22 runs of compatibilized blends were needed. Additionally, 3 uncompatibilized blends with ratios of 25/75, 50/50 and 75/25 were also processed for comparison and assessment of the compatibilizer’s performance. The pristine polymers (PE and PET) were also processed in the same way, totalizing 27 runs.

Models of PET/PE physico-mechanical properties were constructed using Statistica 7 software. A practical test was performed utilizing those models in order to evaluate the viability of recycling the waste of multilayer flexible packaging films. The multilayer waste films were shredded in smaller pieces in a laboratory knives mill (brand Primotécnica), dried in a vacuum oven at 80 °C during 5h to avoid hydrolysis of PET component during the reprocessing. The shredded multilayer waste was fed into the Werner & Pfleiderer ZSK30 extruder by means of a K-tron gravimetric feeder to be melt blended with the compatibilizers, keeping all the previous processing conditions constant. The content of each compatibilizer was varied widely (0, 3, 5, 10 and 15 weight % (hereinafter just w%)). The melt strands of the compatibilized waste was cooled down, pelletized, and kept at least 24h resting at room temperature, in sealed plastic bags before injection molding.

2.4 Mechanical analysis The tensile test was done at room temperature in an Instron universal test machine, model 5569, according to ASTM D-638, at a constant pulling rate of 50 mm/min.

The Izod impact test was done at room temperatures in a Ceast pendulum type machine (hammer of 4J), model 6545, following the standard ASTM D-256. The specimens were previously notched according to the same standard, kept in a room with controlled humidity and temperature at least 24h before the test was carried out.

2.5 Thermal characterization of the post-industrial scraps Thermal curves of the post-industrial multilayer waste was taken in a differential scanning calorimeter, DSC-Q2000 from TA Instrument, tested in a nitrogen atmosphere of

Table 1. Design of experiments: 22 full factorial with central point.

Experiment Extrusion 1 2 3 4 5 6 7

372

PET/PE –1 +1 –1 +1 0 0 0

Codification Compatibilizer –1 –1 +1 +1 0 0 0

Variables PET/PE (wt%) 25/75 75/25 25/75 75/25 50/50 50/50 50/50

Compatib. (wt%) 5 5 15 15 10 10 10

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Recycling assessment of multilayer flexible packaging films using design of experiments

Figure 1. Diagram of the (a) 22 full factorial design with central point and its rotation to get (b) a central composite design.

Table 2. Design of experiments: central composite (star-like design).

Experiment Extrusion No. 1 2 3 4 5 6 7 8

PET/PE –1 +1 –1 +1 0 0 0

9

+ 2

10 11

Codification Compatibilizer –1 –1 +1 +1 0 0 0 0

Compatib. (wt%) 5 5 15 15 10 10 10 10

0

85/15

10

0

− 2

50/50

3

0

+ 2

50/50

17

− 2

50 mL/min, at a heating rate of 10 °C/min up to 280 °C, held for 5 minutes and cooled at the same heating rate until 30 °C. A total of seven DSC runs regarding random samples collected from the waste sent by the manufacturer was performed. In order to obtain an approximate value of the scraps composition, a PET/PE calibration curve was made with some of the blends composition that was previously extruded. The chosen compositions for fitting the calibration curve were: pristine PET, pristine PE, and three uncompatibilized blends thereof (25/75, 50/50 and 75/25).

3. Results and Discussions 3.1 Mechanical behavior of uncompatibilized PET/PE blends Figure 2 shows the mechanical behavior of uncompatibilized blends during tensile testing. In general, immiscible blends show a two phase morphology, which consists of a continuous matrix and a droplet-like dispersed phase[12,13]. This is most Polímeros, 25(4), 371-381, 2015

Variables PET/PE (wt%) 25/75 75/25 25/75 75/25 50/50 50/50 50/50 15/85

often when the blend composition is beyond the phase inversion region. The final morphology is dependent on several parameters such as: processing conditions, PET/PE ratio, temperature of crystallization of the individual components and the viscosity ratio. Additionally, the components may crystallize at different times and in different manners, leading to different morphologies and hence different properties[10].

As seen in Figure 2a, the addition of PE decreases the yield strength of the blend. This can be explained by the fact that PET is tougher than PE with much higher yield strength.

Therefore, the addition of a soft polyolefin dispersed phase into a matrix of the rigid polyester reduces the volumetric presence of the PET in the transversal section of the specimen, decreasing yield strength value of the blend. When PE builds up the matrix, the addition of rigid particles of PET tends to slowly enhance the yield strength behavior of the blend. These results are related with the model of two-phase systems proposed by Uemura and Takayanagi[14]. A secondary effect is the reduction of the crystallization rate and the 373

Uehara, G. A., França, M. P., & Canevarolo, S. V., Jr.

Figure 2. (a) Yield Strength and (b) Elongation at Yield of uncompatibilized PET/PE blends as a function of the blend’s composition.

degree of crystallinity of PET by blending. This is likely due to the expense of energy required by the crystallizing growth front to reject and deform the polyolefin dispersed molten droplets, which can cause a marked depression of the spherulite growth rate[15]. Figure 2b shows a deleterious effect (minimum point) of the blending in the elongation at yield of the blend which is in good agreement with the results obtained by Boutevin et al.[7].

Figure 3 shows the Izod impact strength of the pristine polymers, PE and PET, and the uncompatibilized blends.

There is a deleterious effect when both polymers are blended without compatibilizers, including some compositions which show their impact strength lower than the individual components. In fact, there is a minimum value around PET/PE 50/50 composition, which is likely due to the formation of a co-continuous phase which both components form the matrix phase.

Blending is a process often used to provide tailored product properties for a specific application. However, this situation is more complex when applied to immiscible polymers, since the desired properties are not achieved readily. One possible solution is the use of compatibilizers.

Theses additives are responsible for enhancing the phase dispersion and stability, in the same way they improve the adhesion between the phases[16]. Compatibilizers also affect both phase morphology and the crystallization behavior of the blend’s components. Therefore, since these factors are closely related to the final properties of the product, it is worth to study the effects of compatibilizers onto physico‑mechanical behavior of the blends.

3.2 Mechanical behavior of compatibilized PET/PE blends with PE-g-MA Figure 4 shows the yield strength predicted means of PET/PE blends compatibilized with PE-g-MA. Overall, the yield strength is predicted to increase with the increase of the PET phase. According to Table 3, the effect due to the PET content (%PET) is approximately 7.4. This means that 374

Figure 3. Izod impact strength of PET/PE blends as a function of the blend’s composition.

when the PET content climbs from 25 to 75w%, the yield strength increases by 7.4 MPa on average. Similarly, also according to Table 3, when the compatibilizer concentration is increased from 5 to 15w%, there is a 2.2 MPa reduction of yield strength on average.

Figure 5 shows the Pareto chart for the Young modulus, E. The variable % PE-g-MA had an effect of -0.16, meaning that if the content of PE-g-MA is increased from 5 to 15%, the modulus of elasticity would decrease 0.16 GPa on average. This is due to the fact that the compatibilizer has an elastomeric behavior which reduces the elastic modulus.

Moreover, the anhydride groups of PE-g-MA can react with the PET hydroxyl end groups, promoting a chemical anchoring between the polyester and the compatibilizer as indicated by Figure 6[17]. Additionally, the polyolefin phase of PE-g-MA is miscible with the PE component, forming a physical anchoring.

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Recycling assessment of multilayer flexible packaging films using design of experiments Table 3. Simulated effects (principal and 2-order) of the Yield Strength of PET/PE blends compatibilized with PE-g-MA. Codified Extrusion No. 1 2 3 4 5 6 7

PET/PE Ratio –1 1 –1 1 0 0 0

Real

Comp.

PET/PE Ratio

% Comp.

–1 –1 1 1 0 0 0

25 75 25 75 50 50 50

5 5 15 15 10 10 10

Answer Yield Strength (MPa) 22.0 33.7 24.1 27.2 24.2 23.8 25.4 Sum Simulated Effects

Effects 1

2

12

–22.0 33.7 –24.1 27.2 0 0 0 14.8 7.4

–22.0 –33.7 24.1 27.2 0 0 0 –4.4 –2.2

22.0 –33.7 –24.1 27.2 0 0 0 –8.6 –4.3

3.3 Mechanical behavior of compatibilized PET/PE blends with E-GMA random copolymer

Figure 4. Predicted Means for Yield Strength (in MPa) with two factors at two levels. The model includes: main effects and 2-way interaction. Errors estimated based on a 95% confidence interval.

Figure 5. Pareto’s Chart of Effects of Young Modulus (GPa) of PET/PE blends compatibilized with PE-g-MA.

Figure 7 shows the average predicted Yield Strength for PET/PE blends compatibilized with E-GMA random copolymer. Overall, as in the previous case of PE-g-MA compatibilization, the Yield Strength is predicted to increase with the increase of the PET component, as also predicted by Table 4. Conversely, when the compatibilizer concentration is increased from 5 to 15w%, the Yield Strength increases approximately 7.3 MPa on average. This result is the opposite from that obtained when the PE-g-MA compatibilizer was used.

The Young modulus was also assessed using the Pareto’s Chart shown in Figure 8. As expected, the increase of PET content increases the Young Modulus, E. On the other hand, the compatibilization using E-GMA random copolymer reduces the elastic modulus. However, this reduction when compared with the one produced by the PE-g-MA grafted copolymer is only half of the value. This is likely due to the different kind of structure that both compatibilizers have.

PE-g-MA has an elastomeric behavior, reducing even more the values of Young modulus.

In terms of chemical reactivity, the epoxy group in E-GMA can undergo reactions with both reactive hydroxyl and carboxyl end groups of PET. The presence of a copolymer that has mutual affinity between the polyester and the polyolefin phase promotes the reduction of the size of second phase particles, increasing the adhesion between the two phases. However, the use of copolymers containing GMA groups always increases the viscosity[4]. This is attributed to the formation of crosslinking during the blending, as illustrated by Figure 9.

The aforementioned reactions occur simultaneously, giving rise to complex macromolecular structures, impacting directly on mechanical properties of the blends compatibilized with E-GMA, as detailed in the further sections.

3.4 Experimental expansion: tensile properties of PET/PE model blends

Figure 6. Chemical reaction between the hydroxyl end groups of the PET with the maleic anhydride groups of the PE-g-MA compatibilizer grafted copolymer.

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Figure 10 shows the effect of PET/PE ratio and concentration of compatibilizers on the elongation at break of the blends. The blends compatibilized with PE-g-MA (Figure 10a) showed higher elongation at break mainly when both concentration of PE and compatibilizer were kept high. With E-GMA, this behavior was noticed regarding 375

Uehara, G. A., França, M. P., & Canevarolo, S. V., Jr. higher amounts of PET instead of PE. This is likely due to the possibility of chain extension arising from the reaction between PET end groups and GMA, which increase the probability of entanglements along PET macromolecules.

As consequence, the macromolecules will offer more resistance to uncoil, enhancing then the elongation at break of the blend.

As discussed before, the GMA reaction with both PET end groups had been reported extensively in the literature[6,18-20]. The PE-g-MA grafted copolymer has a much lower number of maleic anhydride groups per polyethylene chain, lowering the probability of chain extension in the case of blends compatibilized with PE-g-MA grafted copolymer.

Instead, the α-olefin phase of the compatibilizer establishes physical interaction with the PE phase, generating physical anchoring due to the miscibility between the components, explaining the higher elongations noticed when the PE was the matrix phase. Figure 11 shows that PE-g-MA is a better compatibilizer considering the elongation at yield behavior.

E-GMA also developed a good response, particularly in the region of higher content of compatibilizer and high PET/PE ratio.

3.5 Experimental expansion: izod impact strength of PET/PE model blends

Figure 7. Predicted Means of Yield Strength (in MPa) with two factors at two levels. The model includes: main effects and 2-way interaction. Errors estimated based on a 95% confidence interval.

Figure 8. Pareto’s chart of effects for Young modulus (GPa) of PET/PE blends compatibilized with E-GMA random copolymer.

Better impact properties could be achieved using low to medium amounts of compatibilizers. Figure 12 shows the effect of addition of 5 and 15w% PE-g-MA and E-GMA onto the Izod impact strength of the blends, as function of the PET/PE ratio.

In both PET/PE compositions, there’s a clear tendency of enhancement of the impact properties when utilizing the compatibilizers. However, a more pronounced effect was evidenced at 25/75w% PET/PE composition (Figure 12a), where the energies were shifted from 8.1 kJ/m2 (uncompatibilized) to 60.4 and 83.1 kJ/m2 for PE-g-MA and E-GMA, respectively.

This represents an enhancement of 645% and 926% in the impact strength values (with respect to the uncompatibilized blends). This seems to be a paramount result, since it could be obtained regarding lower amounts of compatibilizers (5w%). Overall, higher amounts of the compatibilizers seem to increase even more the impact strength (Figure 12b).

Surprisingly, the addition of 15w% of PE-g-MA seems to produce compatibilized blends with equivalent performance than those blends compatibilized with 15w% of E-GMA. This unexpected result is likely to be attributed to the higher reactive content of E-GMA, which has 8w% of glycidyl groups, against approximately 1w% of maleic anhydride in the case of PE-g-MA. The more concentrated the compatibilizer, the higher the chance of occurring parallel reactions, such as crosslinking, as previously indicated in Figure 9, which is detrimental from the physico-mechanical point of view.

Table 4. Simulated effects (principal and 2-order) of the Yield Strength for PET/PE blends compatibilized with E-GMA random copolymer.

Extrusion No. 1 2 3 4 5 6 7

376

Codified PET/PE Ratio –1 1 –1 1 0 0 0

Real Comp.

–1 –1 1 1 0 0 0

PET/PE

Comp.

Ratio 25 75 25 75 50 50 50

(%) 5 5 15 15 10 10 10

Answer Yield Strength (MPa) 22.0 24.0 21.7 39.1 21.4 20.9 23.2 Sum Simulated Effects

Effects 1

2

12

–22.0 24.0 –21.7 39.1 0 0 0 19.3 9.6

–22.0 –24.0 21.7 39.1 0 0 0 14.7 7.3

22.0 –24.0 –21.7 39.1 0 0 0 15.5 7.7

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Figure 9. Chemical reaction between PET end groups with E-GMA and the subsequent formation of crosslinking. (a) Chain extension with OH end group and crosslinking (b) chain extension with COOH end group and crosslinking.

Figure 10. Response surfaces of Elongation at Break as a function of PET/PE ratio, type and concentration of compatibilizer. Blends with (a) PE-g-MA and (b) E-GMA.

Figure 11. Response surfaces of Elongation at Yield as function of PET/PE ratio, type and concentration of compatibilizer. Blends with (a) PE-g-MA and (b) E-GMA. PolĂ­meros, 25(4), 371-381, 2015

377

Uehara, G. A., França, M. P., & Canevarolo, S. V., Jr. On the other hand, PE-g-MA cannot undergo crosslinking due to the reactivity of the anhydride (cyclic acid) ring, which will only react with the hydroxyl end groups of PET. In other words, the occurrence of parallel reactions as in the case of E-GMA might influence negatively the effectiveness of the compatibilization reaction when used in higher concentrations. This shall explain why E-GMA didn’t have a superior performance than PE-g-MA when utilized at higher concentrations (15w%) at 25/75 PET/PE composition.

Despite of being well represented with bar graphs, the values of impact strength could be better visualized utilizing RSM, which provides a multivariate data analysis. The regression coefficients for both models are shown in Equation 1 and 2, where corresponds the amount of PET (in w%), corresponds to the concentration of compatibilizer (in w%) and is the Izod impact strength (in kJ/m2). The response surfaces of the models are also represented in Figure 13.

z= −4.32 x + 0.037 x 2 − 0.45 y + 0.16 y 2 − (1)

0.055 xy + 135.4

z= −5.08 x + 0.038 x 2 − 4.48 y + 0.27 y 2 + 186.2 (2)

Overall, Figure 13 shows that both compatibilizers had similar surfaces. E-GMA seems to be slightly more effective at higher amounts of PET. On the other hand, at higher amounts of PE, both E-GMA and PE-g-MA seems to have similar behavior, especially for higher amounts of compatibilizers.

Both surfaces exhibit a point of minimum somewhere around the co-continuous region (50/50). According to Equation 1, the blends compatibilized with PE-g-MA are expected to have a minimum point in the region around PET/PE 65/35 with 10w% of the compatibilizer. Similarly, Equation 2 foresees that a minimum point is expected somewhere around 70/30 with 8w% of E-GMA. The main conclusion is that both regions should be avoided, since it yields the lowest values of Izod impact strength.

Figure 12. Izod impact strength of PET/PE blends (relative concentrations as shown) compatibilized with (a) 5w% and (b) 15w% of each compatibilizer. Uncompatibilized blend is also shown for comparison.

Figure 13. Response surfaces of Izod impact strength as function of PET/PE ratio and % compatibilizer. (a) Blends compatibilized with PE-g-MA and (b) blends compatibilized with E-GMA. 378

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Recycling assessment of multilayer flexible packaging films using design of experiments 3.6 Thermal characterization of the post-industrial multilayer flexible packaging films Figure 14 shows a thermal cycling of the multilayer scrap sample. The two characteristic peaks around 130 °C and 250 °C are attributed, respectively, to the fusion of PE and PET components. An endotherm peak around 110 °C was also detected, which is attributed to the peak of fusion of the adhesives, commonly made of LDPE. Unexpectedly, an endotherm peak around 210 °C was also detected, which is attributed to a minor content of a Nylon-6 component that ought to be acting as a barrier material in the package.

Considering that the nylon present in the structure will play the same role as PET during the compatibilization reaction (i.e., both of them will react with the compatibilizers, although at different rates), it is possible to use the calibration curve that had been constructed to estimate the total “reactive” fraction (PET+Nylon) present in the structure. The calibration curve obtained was with R2 equal to 0,998. Replacing the population mean value of 0.23 (i.e., the normalized value of ΔHPET/(ΔHnylon + ΔHPET + ΔHPE)) led to a value equal to

Figure 14. Thermal cycling of post-industrial multilayer flexible packaging film recorded in a DSC.

22.5, meaning that the multilayer film contains approximately 22.5w% of reactive content (PET+Nylon) and 77.5w% of PE. According to the manufacturer, the real composition of the multilayer plastic films is of 70w% of PE, 10w% of PET, 10w% of Nylon-6 and the remainder is divided between adhesives and ink. Therefore, our estimation is quite similar to the real composition. Based on this, it was possible to estimate which PET/PE composition our model was situated before the reprocessing of the multilayer waste was done.

3.7 Reprocessing of the post-industrial multilayer flexible packaging film waste: mechanical properties of the compatibilized scraps Figure 15 shows the behavior of the compatibilized scraps under tensile testing when the specimens reach the rupture.

The breaking strength tends to increase with the increase of PE-g-MA content, while remain almost constant for the scraps compatibilized with E-GMA. On the other hand, elongation at break increased significantly for the scraps compatibilized with PE-g-MA. The better performance of PE-g-MA is attributed to the presence of the nylon component in the multilayer film waste. As evidenced by Macosko et al.[16], the amine terminal groups of nylon undergo a very fast reaction ( around 103 kg/mol.min) with the succinic rings of maleic anhydride. This reaction, that has also been reported by Hage and Pessan[21], leads to imide formation.

In contrast, the reaction between amines and epoxy rings of GMA could also occur, but at a very lower rate ( kg/mol.min).

In other words, the reaction between PE-g-MA and nylon occurs preferentially, rather than with E-GMA, meaning that PE‑g-MA will firstly compatibilize the nylon component and subsequently the PET component. When the PE-g-MA content is low (3 or 5w%), the compatibilization reaction will take place preferentially with nylon, remaining PET component uncompatibilized, resulting in poor mechanical properties. On the other hand, higher amounts of PE-g-MA will compatibilize both nylon and PET components. This explains why Figure 15b gave rise to a sudden climb when switching from 5 to 10w% of PE-g-MA.

Figure 15. Physico-mechanical behavior for pure and compatibilized multilayer film waste. (a) Breaking strength and (b) Elongation at break.

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Uehara, G. A., França, M. P., & Canevarolo, S. V., Jr.

Figure 16. Physico-mechanical behavior for pure and compatibilized multilayer film waste. (a) Young Modulus, E and (b) Izod impact strength.

The same argument is valid for E-GMA, except that for this case the glycidyl groups are going to react preferentially with COOH end groups of PET[22]. If E-GMA is present in sufficient amounts, the competition of the reactions between nylon, GMA and PET end groups could be overcome. This behavior is also shown in Figure 15b when the content of E-GMA is switched from lower to higher amounts. However, the crosslinking effect of GMA has to be taken into account, which is depreciative for mechanical properties, explaining why E-GMA didn’t show equivalent performance than PE-g-MA. Figure 16a shows the Young Modulus, E for the compatibilized scraps. Overall, the reduction of Young modulus seems to be slightly more pronounced for the scraps compatibilized with PE-g-MA. This result seems to be following good agreement with the Pareto chart analysis shown previously (Figure 5 and 8), where the model foresees that PE-g-MA was responsible for a superior decrease of Young modulus.

Figure 16b shows the results of Izod impact strength for the compatibilized film waste. Once again, the material compatibilized with PE-g-MA showed a superior performance due to the presence of the polyamide component, which provides a synergic effect that assists the compatibilization reaction with PE-g-MA. Similar effect has also been reported

by Araújo et al.[23], where only the blend compatibilized with maleic anhydride showed super-toughness at room temperature.

4. Conclusions The design of experiments guided the construction of PET/PE model-blends, which were used to screen their physico-mechanical behavior. These models were also used to evaluate the recycling potential of multilayer flexible packaging films that are essentially made of PET/PE components.

380

The compatibilized model-blends showed higher values of elongation at break with the increase of the concentration of the compatibilizers. However, PE-g-MA seems to be more effective for blends with a lower PET/PE ratio (i.e., matrix of PE), while E-GMA presented better properties at higher PET content. The same trend is present when a screening of the elongation at yield was made.

The impact test performed for the model-blends suggests that both compatibilizers have a more pronounced effect when dealing with lower PET/PE ratios. However, the use of higher concentrations of E-GMA did not bring a proportional enhancement of impact strength, due to the possible formation of crosslinking during the compatibilization reaction.

The recycled blends made of compatibilized multilayer film waste presented an acceptable physico-mechanical performance, mainly when medium to high compatibilizers content were used. Among the two additives studied, PE-g-MA seemed to be a better compatibilizer for the scraps. This is attributed to a synergic effect between maleic anhydride groups present in the compatibilizer with amine groups of the nylon-6 component in the film waste, which undergo a kinetically favorable reaction of compatibilization.

Overall, the use of polymer compatibilizers have shown to be a useful method for recycling the multilayer structure based in immiscible polymers, creating a sustainable solution for an environmental problem. However, despite of presenting good physico-mechanical properties, care must be taken when analyzing the viability of recycling the compatibilized film waste under an economic perspective. The use of higher amounts of compatibilizer (as in the case of 10 or 15w%) is not a common practice among the recycling industry, due to the high costs of the compatibilizers. Nevertheless, under a scientific approach, the recycling of the multilayer films waste was found to be feasible.

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5. Acknowledgements The authors thank Dow Brasil for accepting publishing this paper, Dow Brasil, M&G Polímeros and Arkema for donation of the raw materials, G.A.U. and S.V.C. also thanks CNPq for the financial support.

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4. Coltelli, M. B., Savi, S., Aglietto, M., & Ciardelli, F. (2009). A chemical view onto post-consumer poly(Ethylene Terephthalate) valorization through reactive blending with functionalized polyolefins. Polymer Science, Series A, 51(11-12), 1249-1261. http://dx.doi.org/10.1134/S0965545X09110108.

5. Chiu, H. T., & Hsiao, Y. K. (2006). Compatibilization of poly(ethyleneterephthalate)/polypropylene blends with maleic anhydride grafted polyethylene-octene elastomer. Journal of Polymer Research, 13(2), 153-160. http://dx.doi.org/10.1007/ s10965-005-9020-z.

6. Kalfoglou, N. K., Skafidas, D. S., & Kallitsis, J. K. (1995).

Comparison of compatibilizer effectiveness for PET/ HDPE blends. Polymer, 36(23), 4453-4462. http://dx.doi. org/10.1016/0032-3861(95)96853-Z. 7. Boutevin, B., Lusinchi, J. M., Pietrasanta, Y., & Robin, J. J. (1996). Improving poly(ethylene terephthalate) high-density polyethylene blends by using graft copolymers. Polymer Engineering and Science, 36(6), 879-884. http://dx.doi. org/10.1002/pen.10475.

8. Lopes, C. M. A., Goncalves, M. D. C., & Felisberti, M. I. (2007). Blends of poly(ethylene terephthalate) and low density polyethylene containing aluminium: a material obtained from packaging recycling. Journal of Applied Polymer Science, 106(4), 2524-2535. http://dx.doi.org/10.1002/app.26769.

9. Bartoli, F., Bruni, C., Coltelli, M. B., Castelvetro, V., & Ciardelli, F. (2012). Conversion of post-industrial pet-pe scraps into compatibilized plastic blends for new applications.

In 6th International Conference on Times of Polymers (TOP) and Composites (pp. 160-162). Ischia: American Institute of Physics.

10. Utracki, L. A. (2002). Polymer blends handbook. Netherlands: Kluwer Academic Publishers.

11. Neto, B. B., Scarminio, I. S., & Bruns, R. E. (2010). Como fazer experimentos: pesquisa e desenvolvimento na ciência e na indústria. Porto Alegre: Bookman.

12. Sundararaj, U., & Macosko, C. W. (1995). Drop breakup and coalescence in polymer blends: the effects of concentration

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and compatibilization. Macromolecules, 28(8), 2647-2657. http://dx.doi.org/10.1021/ma00112a009.

13. Harrats, C., Thomas, S., & Groeninckx, G. (2006). Micro and nanostructured multiphase polymer blend systems. United States: CCR Press.

14. Uemura, S., & Takayanagi, M. (1966). Application of the theory of elasticity and viscosity of two-phase systems to polymer blends. Journal of Applied Polymer Science, 10(1), 113-125. http://dx.doi.org/10.1002/app.1966.070100109.

15. Martuscelli, E. (1984). Influence of composition, crystallization conditions and melt phase-structure on solid morphology, kinetics of crystallization and thermal-behavior of binary polymer polymer blends. Polymer Engineering and Science, 24(8), 563-586. http://dx.doi.org/10.1002/pen.760240809.

16. Macosko, C. W., Jeon, H. K., & Hoye, T. R. (2005). Reactions at polymer-polymer interfaces for blend compatibilization.

Progress in Polymer Science, 30(8-9), 939-947. http://dx.doi. org/10.1016/j.progpolymsci.2005.06.003.

17. Lusinchi, J. M., Boutevin, B., Torres, N., & Robin, J. J. (2001). In situ compatibilization of HDPE/PET blends.

Journal of Applied Polymer Science, 79(5), 874-880. http:// dx.doi.org/10.1002/1097-4628(20010131)79:5<874::AIDAPP120>3.0.CO;2-B. 18. Carvalho, G. B., & Souza, J. A. (2009). Compatibilização reativa e tenacificação em blendas poliméricas de PET reciclado com elastômeros olefínicos. In Anais do 10º Congresso Brasileiro de Polímeros (pp. 1-10). Foz do Iguaçu: Associação Brasileira de Polímeros.

19. Yildirim, E., & Yurtsever, M. A. (2012). A comparative study on the efficiencies of polyethylene compatibilizers by using theoretical methods. Journal of Polymer Research, 19(2), 1-12. http://dx.doi.org/10.1007/s10965-011-9771-7.

20. Tedesco, A., Krey, P. F., Barbosa, R. V., & Mauler, R. S. (2002).

Effect of the type of nylon chain-end on the compatibilization of PP/PP-GMA/nylon 6 blends. Polymer International, 51(2), 105-110.

21. Becker, D., Porcel, F., Hage, E., Jr., & Pessan, L. A. (2008).

The Influence of the compatibilizer characteristics on the interfacial characteristics and phase morphology of aPA/ SAN blends. Polymer Bulletin, 61(3), 353-362. http://dx.doi. org/10.1007/s00289-008-0956-0.

22. Orr, C. A., Cernohous, J. J., Guegan, P., Hirao, A., Jeon, H. K., & Macosko, C. W. (2001). Homogeneous reactive coupling of terminally functional polymers. Polymer, 42(19), 8171-8178. http://dx.doi.org/10.1016/S0032-3861(01)00329-9.

23. Araújo, E., Hage, E., Jr., & Carvalho, A. (2003). Compatibilization of Polyamide 6/ABS Blends using MMA-GMA and MMAMA Reactive Acrylic Copolymers. Part 1. Rheological and Mechanical Properties of Blends. Polímeros: Ciência e Tecnologia, 13(3), 205-211. http://dx.doi.org/10.1590/S010414282003000300011.

Received: Oct. 14, 2014 Revised: Feb. 27, 2015 Accepted: Mar. 06, 2015

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http://dx.doi.org/10.1590/0104-1428.1955

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

Blends of ground tire rubber devulcanized by microwaves/ HDPE - Part B: influence of clay addition Fabiula Danielli Bastos de Sousa1*, Júlia Rocha Gouveia1, Pedro Mário Franco de Camargo Filho1, Suel Eric Vidotti1, Carlos Henrique Scuracchio1, Leice Gonçalves Amurin2 and Ticiane Sanches Valera2 Centro de Engenharia, Modelagem e Ciências Sociais Aplicadas - CECS, Universidade Federal do ABC/UFABC, Santo André, SP, Brazil 2 Departamento de Engenharia Metalúrgica e de Materiais, Escola Politécnica, Universidade de São Paulo - USP, São Paulo, SP, Brazil

1

*fabiuladesousa@gmail.com

Abstract The main objective of this work is to study the influence of clay addition on dynamically revulcanized blends of Ground Tire Rubber (GTR)/High Density Polyethylene (HDPE). GTR was previously devulcanized in a system comprised of a conventional microwave oven adapted with a motorized stirring, with a fixed microwave power and at various exposure times. The influence of clay addition on the final properties of the blends was evaluated in terms of mechanical, viscoelastic, thermal and rheological properties, with morphology being also analyzed. The results depict that the clay can modify the rheological behavior of the GTR phase, in addition to the thermal and mechanical properties of some blends.

Keywords: clay, recycling, GTR, devulcanization, HDPE.

1. Introduction The reuse, recycling and recovery of waste cross-linked rubber are of great scientific and technological interest.

Rubber requires a long period to degrade naturally due to its cross-linked structure and the presence of stabilizers and other additives[1,2], what consequently reduce its processability[3,4].

Many efforts have been made regarding the preparation and characterization of polymer blends containing GTR and various thermoplastics, as a recycling alternative[5,6].

The properties of these materials depend on the concentration of the recycled material, as well as the adhesion between the phases[7,8]. On the other hand, the adhesion between GTR and the polymer matrix is usually very weak as consequence of the three-dimensional structure generated by cross-linkings, in the case of blends in which the GTR is just ground[9-11].

Cañavate et al.[6] report that the lack of adhesion between phases is a consequence of the large particle size of GTR, superficial characteristics and cross-linked structure, which hamper its adsorption by the thermoplastic matrix molecules. In the production of thermoplastic vulcanized blends (TPVs) containing recycled rubbers, the addition of a virgin rubber or the promotion of the rubber devulcanization (at least partial) are pre-requisites to obtain resultant good mechanical properties[12]. The poor adhesion between the phases and the large particle size of the rubber phase facilitate the propagation of cracks and lead to a pronounced decline of the mechanical properties of the blends[13].

In order to improve the properties of blends containing recycled rubbers, some authors devulcanize the rubber phase[3,9,14-18], or add functional fillers[19-33]. Besides, it is well known that dynamic vulcanization notoriously increases the adhesion and interaction between the phases.

Devulcanization provides to the vulcanized rubber the ability to flow and to be remolded[34]. So, during the processing of the blend, it acts by increasing the break-up ability and contributes to the refinement of the morphology[35].

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In recent years, a new type of polymer material has emerged: polymeric blends reinforced with nanofillers as organically modified clays. This new type of high performance material combines the advantages of polymeric blends and nanocomposites, by using small concentrations of nanofillers.

In many cases, the nanofillers act as compatibilizing agent, decreasing the interfacial tension and promoting greater particle breakage during processing, thus decreasing the coalescence of the particles and increasing the morphology refinement[36].

In this work, the influence of clay addition in the blends GTR devulcanized by microwaves/HDPE is investigated.

The results show that the presence of clay in the blends can influence mechanical, thermal and rheological properties of some blends.

2. Experimental 2.1 Materials HDPE IA-59, a grade for injection molding, was kindly supplied by Braskem (MFI = 7.3 g/10 min). Ground waste truck tire (GTR) separated from non elastomeric components, rubber accelerator N-tert-butyl-2-benzothiazole sulfenamide (TBBS) and sulfur were kindly supplied by Pirelli Pneus Ltda. Organically modified montmorillonite Cloisite 20A was kindly supplied by Bentonit União Nordeste.

2.2 Devulcanization of GTR and mixture with vulcanization additives GTR was devulcanized in a system comprised of a conventional microwave oven adapted with a motorized stirring system with speed control. The devulcanization process was done by using the maximum power of the oven,

Polímeros , 25(4), 382-391, 2015

Blends of ground tire rubber devulcanized by microwaves/HDPE - Part B: influence of clay addition i.e. 820W. The time at which the material was exposed to microwaves varied from 1 to 5 minutes and also 2-2, 2-2‑2, and 3-3, where the numbers represent the exposure time to microwaves (minutes) and the hyphen corresponds to an interval of 10 minutes between consecutive treatments, under stirring with the oven switched off.

The devulcanized GTR was mixed with the vulcanization additives by using a laboratory two roll mill PRENMAR for approximately 6 minutes at room temperature. To promote the dynamic revulcanization during the processing with the thermoplastic, 1 phr of accelerator TBBS and 1 phr of sulfur were added.

were performed in Single Cantilever mode, frequency of 1 Hz, temperature ranging from –100 to 140 °C and heating rate of 3 °C/min.

2.3 Preparation of the blends

Due to the large number of results, the work was divided into two parts. The part A covers more specifically the influence of the devulcanization of GTR on the properties of the blends, whereas part B is related to the influence of clay on their properties. Some results of the blends without clay are replicated from part A[35] in order to deepen the analysis of the results.

The blends were prepared in an internal mixer coupled to a torque Rheometer Polylab 900 at 160 °C and 80 rpm for 15 minutes. The compositions and nomenclature used for the blends are described in the Table 1. All the blends have 5 wt% of clay Cloisite 20A in relation to the HDPE phase.

2.4 Characterization Thermal properties of the HDPE phase were analyzed

by Differential Scanning Calorimetry (DSC) in a DP Union DSC Q200 under nitrogen atmosphere. The samples were heated from room temperature to 190 °C and were held at this temperature for 3 min to erase their thermal history and destroy the HDPE crystalline nuclei. They were then cooled to –90 °C and were subsequently heated to 200 °C. All the steps were performed at a rate of 10 °C/min.

Mechanical properties of the blends were analyzed by tensile tests in an Instron Universal Testing Machine 3369 with a 10 kN load cell at a crosshead speed of 50 mm/min. The samples were prepared in the shape of plates by compression molding at 160 °C in a hydraulic press, and then the blends were cut into dumbbell shaped tensile test according to ASTM D412, type IV. Rheological properties of the blends were analyzed by small amplitude oscillatory rheometry in frequency sweep mode, by using a parallel plate rheometer Anton Paar CTD450 (diameter 25 mm, gap 1.3 mm, 0.5 % strain for the viscoelastic linear response at 170 °C under inert atmosphere).

Dynamic mechanical properties of the blends were analyzed by using a DMA Q800 TA Instruments. The analyses

A Jeol JMS-6701F Scanning Electron Microscope was used to observe the morphology of the blends. Working distances of each sample are shown in the respective micrographs.

The samples were firstly pressed in a hydraulic press, cut, fractured just after being immersed in liquid nitrogen and then coated with gold by using a sputter coater.

3. Results and Discussion

3.1 Processing behavior of the blends The literature presents some works in which dynamic vulcanization is analyzed during processing into internal mixer[22,37-44], as performed on this work. In this particular case, the influence of a clay addition in the dynamic revulcanization reaction is analyzed.

During the mixing, just after the addition of the matrix phase and as soon as the torque measured by the equipment was stabilized, GTR (containing or not vulcanization additives) was added into the mixer, what permitted the analysis of the dynamic revulcanization behavior of the blends, which is reported in the Table 2. HDPE and clay were mixed manually before the introduction into the mixer. The MFinal values represent the torque measured by the equipment at the end of the mixing process.

CRA (Cure Rate Average) values were calculated according to Equation 1[45]: CRA =

1 (1) t90 − ts1

where t90 is the optimum cure time and ts1 the scorch time.

The value is proportional to the average slope of torque

Table 1. Nomenclatures and compositions of the blends produced in this work. In the blends nomenclature, “+20A” is used to represent the presence of the clay Cloisite 20A. Nomenclature 80GTR0/20HDPE+20A 80GTR0+ad/20HDPE+20A 80GTR1+ad/20HDPE+20A 80GTR2+ad/20HDPE+20A 80GTR3+ad/20HDPE+20A 80GTR4+ad/20HDPE+20A 80GTR5+ad/20HDPE+20A 80GTR2-2+ad/20HDPE+20A 80GTR2-2-2+ad/20HDPE+20A 80GTR3-3+ad/20HDPE+20A

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GTR amount (wt%) 80 80 80 80 80 80 80 80 80 80

HDPE amount (wt%) 20 20 20 20 20 20 20 20 20 20

Devulcanization time of GTR (min) — — 1 2 3 4 5 2-2 2-2-2 3-3

Presence of vulcanization additives — Yes Yes Yes Yes Yes Yes Yes Yes Yes

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de Sousa, F. D. B., Gouveia, J. R., Camargo, P. M. F., Fo., Vidotti, S. E., Scuracchio, C. H., Amurin, L. G., & Valera, T. S. Table 2. Dynamic revulcanization behavior of the blends containing clay. The results of the blends without clay are replicated from de Sousa et al.[35].

Blend 80GTR0/20HDPE+20A 80GTR0+ad/20HDPE+20A 80GTR1+ad/20HDPE+20A 80GTR2+ad/20HDPE+20A 80GTR3+ad/20HDPE+20A 80GTR4+ad/20HDPE+20A 80GTR5+ad/20HDPE+20A 80GTR2-2+ad/20HDPE+20A 80GTR2-2-2+ad/20HDPE+20A 80GTR3-3+ad/20HDPE+20A 80GTR0/20HDPE 80GTR0+ad/20HDPE 80GTR1+ad/20HDPE 80GTR2+ad/20HDPE 80GTR3+ad/20HDPE 80GTR4+ad/20HDPE 80GTR5+ad/20HDPE 80GTR2-2+ad/20HDPE 80GTR2-2-2+ad/20HDPE 80GTR3-3+ad/20HDPE

t90 (min)

ts1 (min)

CRA (min–1)

1.03 0.78 1.00 0.75 0.95 1.11 0.95 0.80 1.10

0.52 0.45 0.50 0.45 0.45 0.65 0.71 0.52 0.85

1.96 3.03 2.00 3.33 2.00 2.17 4.17 3.57 4.00

1.17 0.95 0.65 1.15 1.13 1.01 0.80 0.75 1.05

0.75 0.75 0.48 0.95 0.72 0.68 0.45 0.50 0.68

2.38 5.00 5.88 5.00 2.44 3.03 2.86 4.00 2.70

versus time curve or, in other words, it is proportional to the rubber revulcanization speed[35].

In general, but with some exceptions, the presence of clay did not influence t90, ts1 and CRA values, possibly due to the low amount of clay in the blends. No significant differences were observed between the values of the final viscosities of the blends whether or not containing clay.

In addition and as reported previously[35], t90 and ts1 values of the blends were much smaller than the values of the neat rubber obtained by using a rheometer. CRA values were consequently higher in comparison to the neat rubber, showing that the dynamic revulcanization reaction occurred with higher rate. It is attributed possibly to high shear rates generated within the internal mixer during processing.

3.2 Oscillatory rheometry The storage modulus (G’) and complex viscosity (η*) of the blends, in function of the frequency, are summarized in the Figure 1.

In order to facilitate the analysis of the results, G’ values at the minimum and maximum frequencies of the blends are summarized in the Table 3.

According to the Figure 1, the complex viscosity decreased as the frequency increased, which clearly shows the pseudoplastic behavior of the blends, assuming the Cox Merz rule[46-51]. No significant differences were observed between the blends in relation to the exposure time of GTR to microwaves, and also whether or not[35] containing clay.

Dynamic revulcanization increased G’ values at minimum frequency.

G’ values could be influenced by cross-linking density[52] and/or blend morphology[42,43], being that the morphology refinement and compatibility between the phases tend to increase the G’ values. According to SEM micrographs, no 384

MFinal (dN.m) 108.00 105.00 109.00 110.00 97.70 95.70 73.80 102.00 97.00 53.40 107.00 108.00 106.00 111.00 92.50 93.90 63.10 103.00 96.20 54.30

conclusion about the morphology refinement of the blends can be made, but the mechanical properties results depict the poor adhesion between the phases, being that a possible particle detachment from the matrix occurs when applied an external stress. So, G’ values are expected result from morphology and cross-linking density in the present work.

The blends containing GTR exposed to microwaves for long periods of time presented flattening of the curve G’ towards the same blends without clay. According to the literature[47,51,53], flattening of the curve G’ is due to the three-dimensional network formation. In nanocomposites, this behavior is observed in systems with intercalated and/ or exfoliated structures, and this is known as pseudosolid behavior[54]. So, the presence of clay in these blends somehow helped the formation of this network, and the clay lamellae probably presented intercalated and/or exfoliated structures.

3.3 Dynamic mechanical properties The temperature dependence of tan δ of the blends is shown in the Figure 2.

According to the Figure 2 and as depicted in our previous work[35], there are two transitions related to the phases of the blends: around –30 °C refers to the glass transition (Tg) of the GTR and the other refers to α transition of the HDPE phase (Tα) around 100 °C. The existence of two distinct transitions proves the immiscible character of the blends, and the presence of clay on the blends seems not to alter this character. It can also be observed that there is a trend towards the reduction of the area under the peak related to GTR transition, as well as the reduction of the height of the same peak, which is due to mobility restriction generated by the cross-linkings of this phase[48,55,56]. The presence of clay did not alter significantly this behavior.

Tg values of the devulcanized rubber and rubber phases of the blends (containing or not clay) were obtained from Polímeros , 25(4), 382-391, 2015

Blends of ground tire rubber devulcanized by microwaves/HDPE - Part B: influence of clay addition

Figure 1. G’ and η* versus frequency of the blends. The curves were separated for better visualization and analysis of results. The results of the blends without clay are replicated from de Sousa et al.[35].

Table 3. G’ (Pa) at the minimum and maximum frequencies of the blends.

Blend 80GTR0/20HDPE+20A 80GTR0+ad/20HDPE+20A 80GTR1+ad/20HDPE+20A 80GTR2+ad/20HDPE+20A 80GTR3+ad/20HDPE+20A 80GTR4+ad/20HDPE+20A 80GTR5+ad/20HDPE+20A 80GTR2-2+ad/20HDPE+20A 80GTR2-2-2+ad/20HDPE+20A 80GTR3-3+ad/20HDPE+20A

G’ (Pa) at 0.01 rad/s 9.4x104 2.52x105 1.92x105 2.50x105 1.59x105 2.20x105 1.99x105 2.07x105 2.33x105 1.34x105

G’ (Pa) at 300 rad/s 4.11x105 6.60x105 5.18x105 6.79x105 4.25x105 6.45x105 5.98x105 5.56x105 7.48x105 4.03x105

the maximum peaks of the curves tan δ versus temperature.

These values are presented in the Figure 3.

like a vulcanized one. The clay seems not have influenced the dynamic revulcanization reaction of rubber phase.

According to the Figure 3, three zones of distinct Tg behaviors can be determined. They were divided into continuous, dotted and dashed line zones, which are described below.

Dashed line zones: the final temperature of the GTRs after the time of exposure to microwaves was apparently enough to generate high degree of devulcanization in the sample. During processing of the blends, due to the devulcanization degree reached by the elastomeric phase of the samples, the rubber chains acquired some mobility, demonstrated by the increase in the Tg values. In other words, the devulcanization level of the elastomeric phase influenced the dynamic revulcanization reaction, changing the Tg value of this phase.

Continuous line zone: GTR was not exposed to microwaves.

Even knowing that the clay was added first with the HDPE into the mixer, somehow it seems to act in the elastomer phase of blends containing GTR without being exposed to microwaves and without additives of vulcanization.

Dotted line zones: the final temperature of GTRs after the time of exposure to microwaves probably was not enough to provide high degree of devulcanization in the samples.

Due to the low degree of devulcanization, there was not a significant change in Tg of the rubber, which behaved just Polímeros, 25(4), 382-391, 2015

3.4 Thermal properties by DSC The results of the DSC from the second heating cycle of the blends are summarized in the Table 4. The crystallization degree was calculated according to Equation 2[57]: 385

de Sousa, F. D. B., Gouveia, J. R., Camargo, P. M. F., Fo., Vidotti, S. E., Scuracchio, C. H., Amurin, L. G., & Valera, T. S.

Figure 2. Tan δ versus temperature of the blends. The curves were separated for better visualization and analysis of results. The results of the blends without clay are replicated from de Sousa et al.[35].

According to previous work[35], the crystallization degree of the HDPE phase was affected by the presence of the rubber, since the crystallization degrees of the HDPE phase were higher than the neat HDPE. It seems that the presence of clay did not influence significantly on the results. Only the blends 80GTR0+ad/20HDPE+20A, 80GTR2+ad/20HDPE+20A and 80GTR4+ad/20HDPE+20A presented higher crystallization degrees compared to the same blends without clay[35].

The increase of the crystallization degree of these blends probably influenced its mechanical properties, since the elongation at break of the blends 80GTR0+ad/20HDPE+20A and 80GTR2+ad/20HDPE+20A was lower than the same property of these blends without clay.

Figure 3. Tg values of the devulcanized rubber and rubber phases of the blends as determined by DMA.

 ∆H  χc = m .100 (2) ( ∆H m100 .WHDPE )  

where χc is the crystallization degree, ∆H m is the enthalpy of melting (J/g), ∆H m100 is the enthalpy of melting of the HDPE 100% crystalline (293 J/g)[58] and WHDPE is the mass fraction of HDPE in blend.

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HDPE crystallinity was more sensitive to differences in the flow of GTR generated by its exposure to microwaves than by the clay addition, as consequence of changes in the number and average size of spherulites induced by the presence of rubber domains[59].

3.5 SEM SEM micrographs of some blends are presented in the Figure 4.

According to SEM micrographs and as also observed previously[35], no conclusions can be made concerning the morphology refinement because it is not possible to distinguish between the phases from the presented SEM Polímeros , 25(4), 382-391, 2015

Blends of ground tire rubber devulcanized by microwaves/HDPE - Part B: influence of clay addition Table 4. Values of melting temperature, enthalpy of melting (ΔHm) and crystallization degree (χc) of the HDPE phase of the blends.

The results of the blends without clay are replicated from de Sousa et al.[35].

Sample HDPE 80GTR0/20HDPE+20A 80GTR0+ad/20HDPE+20A 80GTR1+ad/20HDPE+20A 80GTR2+ad/20HDPE+20A 80GTR3+ad/20HDPE+20A 80GTR4+ad/20HDPE+20A 80GTR5+ad/20HDPE+20A 80GTR2-2+ad/20HDPE+20A 80GTR2-2-2+ad/20HDPE+20A 80GTR3-3+ad/20HDPE+20A

Tm (°C) 141.74 135.34 133.71 133.57 132.56 133.79 135.24 136.47 133.81 134.50 134.77

ΔHm (J/g) 183.72 48.96 36.41 37.76 41.21 36.72 52.59 49.94 41.72 47.58 43.25

χC (%) 62.70 83.55 65.40 67.83 74.03 65.96 89.75 85.23 74.94 81.20 78.62

Sample 80GTR0/20HDPE 80GTR0+ad/20HDPE 80GTR1+ad/20HDPE 80GTR2+ad/20HDPE 80GTR3+ad/20HDPE 80GTR4+ad/20HDPE 80GTR5+ad/20HDPE 80GTR2-2+ad/20HDPE 80GTR2-2-2+ad/20HDPE 80GTR3-3+ad/20HDPE

Tm (°C)

ΔHm (J/g)

χC (%)

134.86 132.12 133.93 133.53 133.14 133.81 135.79 133.46 136.65 133.77

52.84 33.57 41.38 40.43 51.29 39.02 52.03 51.75 54.56 46.66

90.17 57.29 70.61 68.99 87.52 66.59 88.79 88.30 93.10 79.63

Figure 4. SEM micrographs of the blends: (a) 80GTR0/20HDPE+20A; (b) 80GTR0+ad/20HDPE+20A; (c) 80GTR3+ad/20HDPE+20A; (d) 80GTR4+ad/20HDPE+20A; (e) 80GTR2-2+ad/20HDPE+20A; (f) 80GTR3-3+ad/20HDPE+20A. Polímeros, 25(4), 382-391, 2015

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de Sousa, F. D. B., Gouveia, J. R., Camargo, P. M. F., Fo., Vidotti, S. E., Scuracchio, C. H., Amurin, L. G., & Valera, T. S. micrographs. It could be observed that the blends containing GTR with longer exposure times to microwaves presented a less coarse surface in comparison to the other blends (detail: area inside the circle in the Figures 4d and 4e), result of a lower fracture resistance to the external force applied on the blends. This tendency was also observed in the results of mechanical properties of the blends (see section 3.6).

It seems that the presence of clay somehow improved the interaction between the phases, as described by the discrete increase on the G’ values of some blends containing clay.

However no significant differences between the SEM micrographs could be observed.

3.6 Mechanical properties The main results of the tensile tests of the blends whether or not containing clay are presented in the Figure 5.

The Young’s modulus values increased with the increase of the exposure time of GTR to microwaves, with the exception of the blend 80GTR2+ad/20HDPE+20A. In the blends containing clay with GTR exposed to higher exposure times

to microwaves, the Young’s modulus values were higher than the blends without clay showing the reinforcement effect of the clays in the blends or, in other words, the stiffness increasing of the blends[60,61]. According to Braga et al.[54], the increase on this value due to the addition of a clay in the blend could be attributed to the greatest degree of clay dispersion in the matrix, as also observed in the oscillatory rheometry results. Still about the Young’s modulus of the blends containing clay, it could be observed that the blends showing the highest values were the ones with the highest crystallization degree values. Also according to Hills[62], the vulcanization process increases the stiffness of the elastomeric chains due to the cross-linking formation, contributing to the increase of the Young’s modulus value. These values follow the trend of Tg value increasing as the exposure time of GTR to microwaves increased, so the increase of the cross-linking density could also be the responsible for the Young’s modulus increasing.

Stress at break and tensile strength values decreased as the exposure time of GTR to microwaves got higher.

Regarding the Tg values of the elastomeric phase (section 3.3),

Figure 5. Young’s modulus (a), stress at break (b), tensile strength (c), and elongation at break (d) in function of the exposure time to microwaves of the GTR, of the blends 80GTR/20HDPE containing or not clay.

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Blends of ground tire rubber devulcanized by microwaves/HDPE - Part B: influence of clay addition it increased with the exposure time of GTR to microwaves.

As the Tg is related to the cross-linking density, this means that probably there was an increase of the cross-linking density. The tensile strength behavior is probably due to the reinforcement effect of clay. There was not a significant change in the elongation at break of the blends with the clay addition.

In general, the mechanical properties of the blends containing clay are not so good, especially the results of elongation at break, probably due to the poor adhesion between the phases[13,14,60,63]. According to the presented results, adhesion between the phases was not sufficient to promote good stress transference, resulting in the deterioration of the mechanical properties results.

As observed in the previous work[35], one of the qualifying standards for a blend to be deemed as a TPV is to present typical elastomeric elongation, which has also not been verified in the results obtained, even after adding a nanometer filler like an organically modified clay. Thus, these blends are composed by 80% of a recycled material (GTR), what may have decreased its mechanical properties.

4. Conclusions The properties of dynamically revulcanized blends containing HDPE and GTR devulcanized by microwaves were studied as function of clay addition, and different techniques were adopted.

According to the torque development during the mixing process, the presence of clay did not modify significantly the dynamic revulcanization reaction rate of the blends.

The oscillatory rheometry results demonstrated that the lack of adhesion between the phases influenced the rheological properties of the blends, and some of them presented pseudosolid behavior. The dynamic mechanical properties depicted that there were differences in the Tg values of the elastomeric phase, depending on the exposure time to microwaves. No conclusion about the morphology refinement of the blends could be made based on the SEM micrographs, but a less coarse surface of the blends containing GTR exposed to microwaves for longer periods was observed. According to mechanical properties results, the poor adhesion between the phases probably resulted in the deterioration of these properties. In contrast, clay seems to increase the stiffness of the blends containing GTR exposed to microwaves for longer periods due to the increase of the Young’s modulus.

Summarizing, the presence of clay altered the rheological behavior, thermal and mechanical properties of some blends.

The addition of clay may be a way to improve the properties of dynamically revulcanized blends containing recycled rubber as a whole.

5. Acknowledgements The authors would like to thank Braskem, Pirelli and Bentonit União Nordeste for the material donation, FAPESP (process number 2010/15799-6) and CNPq (process number 201891/2011-5) for the financial support.

Polímeros, 25(4), 382-391, 2015

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Received: Oct. 07, 2014 Revised: Mar. 05, 2015 Accepted: Apr. 22, 2015

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S C I E N T I F I C T E C H N I C A L

Improving the thermal properties of fluoroelastomer (Viton GF-600S) using acidic surface modified carbon nanotube Javad Heidarian1,2*, Aziz Hassan1 and Nor Mas Mira Abd Rahman1 Polymer and Composite Materials Research Laboratory, Department of Chemistry, University of Malaya - UM, Kuala Lumpur, Malaysia 2 Polymer and Science Technology Division, Research Institute of Petroleum Industry - RIPI, Tehran, Iran 1

*heidarianj@um.edu.my; heidarianj@yahoo.com

Abstract Acid surface modified carbon nanotube (MCNT)-, Carbon nanotube (CNT)-filled fluoroelastomer (FE) and unfilled-FE were prepared (MCNT/FE, CNT/FE and FE). The compounds were subjected to thermogravimetric analysis (TGA) and heat air aging, and characterized by Energy Dispersive X-Ray (EDX). Results showed that MCNT improved the thermal properties of FE, resulting in a larger amount of FE and char remaining in the temperature range of 400-900 °C relative to unfilled FE and CNT/FE. The MCNT/FE TGA curve shifted towards higher temperatures compared to CNT/FE and FE. The same results also revealed that higher percentages of FE were undegraded or less degraded especially near MCNT in the temperature range of 400-540 °C. Energy Dispersive X-Ray (EDX) results indicated that the percentage of carbon and fluorine in the residue of TGA scans, up to 560 °C, of MCNT/FE were the same as CNT/FE, and were higher than FE. EDX results of TGA residue (run up to 900 °C) showed that most of the undegraded FE, which was not degraded at temperatures below 560 °C, was degraded from 560 °C to 900 °C in both MCNT/FE and CNT/FE, with the char in MCNT/FE being more than that in CNT/FE. EDX analysis of thermal aged specimens under air showed that, with increasing aging time, a greater percentage of C, O and F was lost from the surface of filler/FE and FE. The order of element loss after 24 hour aging time was: MCNT/FE > FE > CNT/FE. Keywords: nanocomposites, fluoroelastomer, acidic surface modified, carbon nanotube, thermal properties, thermal aging.

1. Introduction Viton is a synthetic rubber and fluoroelastomer (FE).

Viton GF-600S is a terpolymer of hexafluoro-propylene, vinylidene fluoride and tetra-fluoroethylene with a cure site monomer. It is a peroxide cure, 70% fluorine FE[1,2].

Normally, in the formulation of FE, carbon black (CB) is used. Replacing CB with surface modified CNT (MCNT) is expected to improve the thermal properties of FE, which is very effective in making O-rings especially for the oil and gas industries[3-5]. MCNT is also expected to improve thermo-oxidative degradation resistance of FE composites when subjected to thermal aging conditioning in air.

MCNT improves the properties of fluoropolymers, such as crystallinity, electrical response, mechanical properties, viscoelastic behavior, etc, and therefore their thermal stability.

This finding has been reported by a number of researchers and examples of literatures and the reasons for the changes in these properties are mentioned bellow.

It has been reported[3] that the use of multi-walled carbon nanotubes (MWCNTs)-embedded in fluorinated rubber leads to a rubber nanocomposite with cellulation structure.

This structure possesses improved thermal resistance.

Pham et al.[4] observed that with increased MWCNT loading in FE/MWCNTs nanocomposites, there is a steady increase in the decomposition temperature. Interactions between CNT and fluropolymers and the effect of surface area of CNT on the active interfacial area between them were investigated by a number of researchers, for examples:

392

A strong interaction between fluoropolymers and CNT was reported by He et al.[6]. The high aspect ratio of nanotubes also leads to a great increase in the active interfacial area between CNT and the fluoropolymer chain as reported by Chae et al.[7]. An energetic relationship between the surface of CNT and fluoropolymer has been reported by Levi et al.[8].

CNT can change the mechanical and thermo-mechanical properties of polyvinilydienefluoride (PVDF)[9-11] or the mechanical properties of polytetrafluoroethylene (PTFE) [12,13] . CNT can also change the degree of crystallinity of fluoropolymers and, therefore, their properties[14-16].

Sementsov et al.[13] reported that in nanocomposites of PTFE and MWCNT, the concentration and nature of oxygen containing MWCNT surface groups influences the strength parameters of the composite material. Wen et al.[17] prepared (PVDF)/MWCNTs nanocomposites and studied the melt viscoelastic behavior of the composites. The results showed that PVDF/MWCNTs-g-OH (OH grafted) nanocomposites exhibit more significant solid-like behavior than PVDF/MWCNTs nanocomposites. Huang et al.[16] showed that the interfacial interaction between the single walled carbon nanotubes (with hydroxyl groups) and PVDF has an effect on inducing crystallinity. The thermal stability of the PTFE composites is also enhanced by the presence of CNT as reported by Park et al.[18]. The temperatures recorded at maximum decomposition rate were affected by the type of surface modification of MWCNT. The thermograms

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Improving the thermal properties of fluoroelastomer (Viton GF-600S) using acidic surface modified carbon nanotube for PTFE/MWCNT composites also shifted towards high temperatures.

Carabineiro et al.[19,20] prepared CNT/PVDF composites using modified CNT samples. According to their research results, surface modifications of MWCNTs had an effect on the electrical response and the degree of crystallinity of the CNT/PVDF nanocomposites. Similarly, Xu and Yang[21] prepared FE/MWCNT composite films using different surface modified CNTs. The better mechanical properties of CF4 plasma-modified CNT (FCNTs) composites over other studied CNTs is due to the better dispersion and enhanced chemical compatibility from introducing electron-rich fluorine atoms and also from hydrogen bonding.

The effect of thermal aging conditioning on FE in air and/or other environments were also verified by researchers.

For example: the physical and chemical changes associated with degradation on the surface, near the surface and bulk of the FE seals in engine oil and additives were investigated by Smith et al.[22]. Degradation of these materials was reported to be limited to the near surface region of the samples to a depth of less than approximately 50 μm. The process resulted in the release of either F2 or HF. Research on the verification of the effect of MCNT on the amount of residues in TGA runs of MCNT/FE nanocomposites is rather rare. In addition, comparison of the amount of residue in TGA runs of MCNT/FE, CNT/FE and FE detailing elemental composition is seldom published.

Therefore, this investigation is unique in the sense that knowledge of the amount of residue and the composition of the elements in the residue gives an insight into the ability of MCNT to improve the thermal stability of CNT/FE and FE composites. Furthermore, the presence of elemental fluorine on the surface of MCNT/FE aged in air indicates whether MCNT can improve the resistance of the nanocomposites to thermo-oxidative degradation or not.

In the present work, MCNT was used as a filler for Viton GF-600S with the aim of improving the thermal stability and thermal aging resistance of FE. The thermal properties of the composites MCNT/FE were assessed by Thermogravimetric Analysis (TGA) and compared vis‑à‑vis those of CNT filled and unfilled FE composites in our previous work[23]. Energy Dispersive X-Ray (EDX) was also used to characterize the elemental composition of the undegraded FE and char after TGA runs at temperatures below 900 °C. This was to ascertain whether the incorporation of MCNT could preserve more of the undegraded FE and char compared to CNT/FE or unfilled FE. EDX was also employed to verify the amount of Zn in the residue and to confirm a possible reaction with MCNT. Thermal aging conditioning in air together with EDX was also conducted to investigate the elemental composition of the surfaces of MCNT/FE as a function of aging time.

2. Experimental 2.1 Materials and compounding procedure The materials used were Viton GF-600S fluoroelastomer, FE; organic peroxide, Luperox 101 XL-45; acid surface modified carbon nanotube MCNT (TNMC8, -COOH Content:0.49wt%), carbon nanotube CNT (TNM8) both with an outside Polímeros, 25(4), 392-401, 2015

diameter > 50 nm, inside diameter:5-15nm, purity > 95%, and length 10-20 μm; zinc oxide; and triallylisocyanurate, TAIC supplied by ERIKS Sdn. Bhd. (Malaysia), Arkema Sdn. Bhd. (Malaysia), Chengdu Organic Chemicals Co. Ltd. (Chinese Academy of Sciences, China), Texchem Materials Sdn. Bhd. (Malaysia) and Liu Yang San Ji Chemical Trade Co. Ltd. (China) respectively. Three formulations were compounded, MCNT filled FE (MCNT/FE), CNT filled FE (CNT/FE) and unfilled FE (FE). The amounts of FE, organic peroxide, zinc oxide and TAIC in these compounds were 70.0, 2.1, 2.1 and 2.1 g respectively. For MCNT/FE and CNT/FE, 7.0 g filler was used.

Mixing FE with additives was done using a laboratory scale two roll mill with a roll temperature of 48°C. FE in the above mentioned composition was supplied to the open roll. A uniform band was formed while three rolling cuts from each side of the mill were made, so that the polymer would be uniform and sufficiently warmed up. In the next stage, pre-blended ZnO and TAIC were added uniformly into the gum and three rolling cuts from each side of the mill were made. After setting the roll distance to 1.1 mm, MCNT was then fed in. The compound was then tightly milled ten times. The roll distance was then adjusted to 1.1 mm, and the peroxide was added and, after the final five to six rolled up end passes, the mixture was supplied to the open roll and sheeted. After 24 hours, re-milling was done with a roll temperature of 26 °C. A similar procedure was used for CNT/FE and FE.

2.2 Curing and post curing Curing of the FE compound was done in molds (15 cm × 15 cm × 1 mm and 18 cm × 18 cm × 2 mm) in a heated press, at 177 °C under a pressure of 10 MPa for 7 min. The post curing was done in an oven at 232 °C for two hours. The conditions for curing and post curing were recommended by the supplier.

2.3 Thermal gravimetric analysis (TGA) 25-35 mg of post-cured sample was subjected to TGA runs from room temperature to 900 °C. This was carried out on a Perkin-Elmer thermal analysis system, model Pyris Diamond TG/DTA, at a scan rate of 20 °C.min–1 and under nitrogen atmosphere of 20 ml.min–1. In addition, TGA runs from room temperature to 560 °C were carried out under the same conditions and then cooled to room temperature at a scan rate of 100°C.min-1. The same procedure was repeated with the temperature raised to 900 °C. The specimens were designated according to temperature, for example MCNT/FE-560 °C, where the temperature after the specimen designation is the highest temperature of the TGA run. The same procedure was applied for 3.5-5 mg of pure MCNT.

2.4 Thermal aging Thermal aging was carried out according to ASTM D-573 for 24, 48 and 72 hours at 250 °C. The samples (5 mm × 5 mm × 2 mm) were named FE, FE-24, FE-48 and FE-72, where the numbers following FE indicate the aging time in hours. Similar types of abbreviation were used for the MCNT/FE and CNT/FE aged samples.

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Heidarian, J., Hassan A., & Rahman, N. M. M. A. 2.5 Energy Dispersive X-Ray (EDX) and Field Emission Scanning Electron Microscopy (FESEM) image analyses EDX analysis was conducted using FESEM Philip XL-40 (UK) coupled with EDX. The residue obtained from the heating-cooling TGA scans was first applied on an aluminum stub using double sided copper tape (3M Company), then coated with gold for EDX elemental analysis to determine the elements of C, O, F, Si, Ca and Zn. Elemental compositions of the surfaces of the aged and unaged samples were obtained using EDX. Un-aged and aged samples, 5 mm × 5 mm × 2 mm in dimension, from the molded post cured FE, CNT/FE and MCNT/FE rubber sheets were used for EDX analysis. The major elements characterized were C, O, F and Si. The surface images for some of the samples were obtained by FESEM. In FESEM imaging of MCNT/FE, the razor cut (cross-section) surface was used. Specimens for EDX and FESEM imaging analysis were applied on a copper tape and gold coated as mentioned above. However, for FESEM images of residues obtained from MCNT/FE-560 °C and MCNT/FE-900 °C, no gold coating was used.

thermally stable than FE in CNT/FE under N2. Furthermore in MCNT/FE, FE near MCNT is considerably more thermally stable than FE in the bulk. FE near MCNT in MCNT/FE to a larger extent is more thermally stable than both FE near CNT and also FE in the bulk in CNT/FE. It can be concluded that a highly filled FE with MCNT will have a high percentage of FE near or attached to MCNT, which can have thermal stabilities up to 540 °C. Therefore

3. Results and Discussion 3.1 TGA Figure 1 shows the TGA thermograms of MCNT, FE, MCNT/FE and CNT/FE. The extracted data from these plots are presented in Table 1. In Table 1, Tonset, T5%, T10% and T50% are the onset temperature at which the compound started to lose weight (degrade), and temperatures at which the compound lost 5%, 10% and 50% weight respectively.

Tonset, T5%, T10% and T50% increased for MCNT/FE compared to CNT/FE and FE. As can be seen from Figure 1 the MCNT/FE curve shifted towards higher temperatures and the thermal stability improved compared to CNT/FE. Figure 2 shows the amount of this temperature (thermal stability) shift versus weight%. Figure 2 shows that for the weight% of 100 to 40% the amount of thermal stability shift is almost constant (≈10 °C). However, for weight% between ≈20 to 40% the thermal stability shift increases suddenly (≈20ºC). This increase in thermal stability shift indicates that in this weight% range compared to the 100 to 40 weight% range, FE in MCNT/FE showed more thermal stability improvement relative to FE in CNT/FE. Pham et al.[4], used a SEM micrograph of the ash residue collected after 90% degradation of the compound and showed that less or partial degradation of the polymer chains attached to the nanotubes occurred whereas extensive degradation occurred in the bulk. Therefore, the higher thermal stability shift for weight% between ≈20 to 40% represents the part of FE which is near or attached to MCNT. All of the above mentioned results show that FE in MCNT/FE is more

Figure 1. Heat and cool TGA curves of pure MCNT, FE and filler/FE: (a) zoomed and (b) unzoomed.

Table 1. TGA thermal properties of FE, filler/FE and pure filler.

Specimen

TOnset (°C)

T5% (°C)

T10% (°C)

T50% (°C)

FE CNT/FE MCNT/FE MCNT CNT

423.4 421.1 433.1 627.7 594.5

442.6 446.2 457.7 693.6 640.2

470.7 475.4 485.4 748.4 692.9

497.8 505.1 513.7 -

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Figure 2. Thermal stability shift curve calculated from TGA curves of FE and filler/FE. Polímeros , 25(4), 392-401, 2015

Improving the thermal properties of fluoroelastomer (Viton GF-600S) using acidic surface modified carbon nanotube it is predicted that a highly filled FE with MCNT can stay up to 540 °C. Figure 2 also shows the amount of this thermal stability shift versus weight% for MCNT/FE relative to FE. Again the MCNT/FE curve shifted towards higher temperatures and the thermal stability improved compared to FE. Figure 2 shows that, for the weight% of 100 to 50%, the amount of thermal stability shift is almost constant (≈13-15 °C). However for weight% between ≈20 to 50% the thermal stability shift increases gradually (≈15-33 °C). This increase in thermal stability shift shows that in this weight% range compared to the 100 to 50 weight% range, FE in MCNT/FE has more thermal stability improvement relative to FE in unfilled FE. Once more, based on Pham et al.[4] work and the above results it can be concluded that greater thermal stability shift for weight% between ≈20 to 50% will be for the part of FE which is near or attached to MCNT. All of the above mentioned results show that FE in MCNT/FE is more thermally stable than FE in unfilled FE under N2. Furthermore in MCNT/FE, FE near MCNT is considerably more thermally stable than FE in the bulk. FE near MCNT in MCNT/FE to a large extent is more thermally stable than FE in unfilled FE. By comparing the thermal stability improvement of FE in MCNT/FE and CNT/FE, both relative to FE in unfilled FE, it can be seen that for all weights% (100 to ≈20%) the thermal stability improvement of FE in MCNT/FE is considerably more than that of CNT/FE. 3.1.1 TGA: weight of residual Figure 1 also shows that with the incorporation of MCNT, a greater amount of the FE remained and produced char preserve in the temperature range of 400-540 °C compared to CNT/FE and FE. This amount was calculated as follows.

Table 2. The percentage of filler remaining in pure filler and filler/FE at different temperatures.

Temperature (°C) 520 530 540 560 600 650 700 800 875

MCNT 100.00 99.94 99.87 99.67 99.04 97.21 94.39 82.52 74.15

MCNT/FE 8.40 8.39 8.39 8.37 8.32 8.17 7.93 6.93 6.23

CNT 100.00 100.00 99.70 99.30 97.90 94.50 89.30 66.60 54.80

CNT/FE 8.4 8.4 8.4 8.3 8.2 7.3 7.5 5.6 4.6

The percentage of “MCNT remaining” within the nanocomposite can be calculated by multiplying the percentage of MCNT obtained from the TGA data of pure MCNT at that temperature by 8.4 (the initial percentage of MCNT in FE). These amounts are shown in Table 2. From Figure 1 and Table 2, it can be seen that pure MCNT lost less weight at temperatures up to 900 °C than pure CNT. Again, in the TGA of the nanocomposite, at each temperature, the percentage of “undegraded FE + char + mineral additives” can be calculated by subtracting the percentage of “MCNT remaining” in the nanocomposite (Table 2) from the percentage of nanocomposite remaining in the TGA curve extrapolated in Figure 1 at that temperature. The results of these calculations are shown in Table 3. This amount, minus the initial mineral filler (2.5%), gives the percentage of “undegraded FE + char” as recorded in the same table.

The same calculations were done for CNT/FE. However, in Table 3 the possible reactions of fillers at high temperatures are not considered.

The results in Table 3 support the finding that, in MCNT/FE, a greater amount of FE remained and produced char preserve, particularly in the temperature range of 520‑540 °C, compared to CNT/FE and FE. Therefore, the presence of MCNT enhances the thermal stability of FE, resulting in a higher percentage of the nanocomposite remaining undegraded at higher temperatures compared to CNT in FE or unfilled FE. Besides, in MCNT/FE and CNT/FE, most of the char was stable up to 900 °C. 3.1.2 EDX analysis: residual elemental The composition of the residue from the heating‑cooling TGA run cycle, as mentioned in the experimental section, was characterized by EDX. The TGA curves of the samples are shown in Figure 3. In the heating-cooling run, the cooling was done with the highest possible cooling rate in order to prevent further degradation and to keep the same composition of the remaining materials at 560 °C and at 900 °C upon cooling. Table 4 shows the elemental compositions of the residues in heating-cooling TGA runs for the compounds under study which were extracted from the EDX results (Figures 4 and 5). Figures 4 and 5 also show FESEM images of MCNT/FE-560 °C and MCNT/FE-900 °C residues respectively.

From Figure 3 it can be seen that, at low temperatures, after a cooling scan of the MCNT/FE-560 °C sample, 19.18% of the nanocomposite remained. If this amount

Table 3. The percentage of “undegraded FE + char + mineral additives” and “undegraded FE + Char” remained in the compounds at different temperatures.

Temperature (°C) 520 530 540 560 600 650 700 800 875

“undegraded FE + char + mineral additives” FE MCNT/FE CNT/FE 30.58 12.56 17.63 11.58 12.19 10.88 10.54 10.48 7.90 9.65 9.68 7.00 8.84 9.52 6.10 8.24 8.32 4.90 7.65 8.32 4.30 7.30 8.32

Polímeros, 25(4), 392-401, 2015

“undegraded FE + Char” MCNT/FE CNT/FE 28.08 10.06 15.13 9.08 9.69 8.38 8.04 7.98 7.15 7.18 6.34 7.02 5.74 5.82 5.15 5.82 4.80 5.82

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Heidarian, J., Hassan A., & Rahman, N. M. M. A. is multiplied by weight% of each element in Table 4, the weight% of that element based on the initial nanocomposite can be obtained. The same procedure was carried out for all

specimens. The results of these calculations are presented in Table 5.

These results show that the percentage of carbon and fluorine in the residue of the TGA scan of MCNT/FE-560 °C are the same as CNT/FE-560 °C. This proves that MCNT is able to preserve the same amount of FE from degradation compared to the samples containing CNT at this temperature.

Similarly, based on the EDX results and considering the work of Pham et al.[4] as mentioned earlier, it can be seen that FE attached to or near MCNT at the higher temperature range exhibits a lower degradation tendency. Considering this and the fact that more carbon and fluorine remained in this nanocomposite residue after the TGA run, it can also be concluded that a greater amount of the FE remained undegraded or less degraded especially near MCNT. The amount of remaining fluorine represents the undegraded FE.

Figure 3. Heat and cool TGA curves of FE and filler/FE up to 560 °C.

These results also show that the percentage of carbon and fluorine in the residue of the TGA scan of MCNT/FE-560 °C is higher compared to FE-560 °C. This proves that MCNT is able to preserve more FE from degradation compared to the samples containing unfilled FE.

Figure 4. EDX spectra (a) and FESEM image (b) of MCNT/FE-560 °C.

Figure 5. EDX spectra (a) and FESEM image (b) of MCNT/FE-900 °C.

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Improving the thermal properties of fluoroelastomer (Viton GF-600S) using acidic surface modified carbon nanotube Table 4. The weight% (Wt%) and Atomic% (At%) composition of the remaining composites in TGA runs.

Element C O F Si Ca Zn Total

FE-560°C Wt % At % 27.16 50.48 14.00 19.53 11.07 13.01 3.05 1.70 44.72 15.28 100 100

MCNT/FE-560°C Wt % At % 69.78 84.46 5.34 4.86 9.11 6.97 1.45 0.53 14.32 3.18 100 100

CNT/FE-560°C Wt % At % 68.98 80.89 10.05 8.85 10.45 7.75 0.46 0.23 0.83 0.29 9.23 1.99 100 80.89

MCNT/FE-900°C Wt % At % 83.87 92.01 6.14 5.06 1.55 1.07 1.20 0.40 7.23 1.46 100 100

CNT/FE-900°C Wt % At % 65.42 83.62 8.95 8.59 2.54 2.05 2.11 0.81 20.98 4.93 100 100

Table 5. Amount of element remained based on initial weight of compound.

Element C F Zn Ca Si

FE-560°C 3.42 0.85 2.08 0.27 -

MCNT/FE-560°C 13.38 1.75 2.75 0.28 -

3.1.3 EDX analysis: undegraded FE and char At 560 °C, the “undegraded FE + char” for MCNT/FE-560 °C can also be calculated by subtracting the percentage of “MCNT remaining” in the nanocomposite (Table 2) from the percentage of “C + F” in the EDX analysis at 560 °C. Thus, the percentage of “undegraded FE + char” for MCNT/FE-560 °C is 6.76 and for CNT/FE-560 °C is 6.98%, again showing the same percentage of “undegraded FE + char” as in the case of using MCNT or CNT as filler for FE. Table 5 also shows that when MCNT/FE-900 °C and CNT/FE-900 °C were run up to 900 °C, much less fluorine and carbon remained compared to MCNT/FE-560 °C and CNT/FE-560 °C respectively. These results indicate that most of the undegraded FE at temperatures below 560 °C was degraded from 560 °C up to 900 °C in both MCNT/FE and CNT/FE. At 900 °C, the “char” for MCNT/FE-900 °C can also be calculated by subtracting the percentage of “MCNT remaining” in the nanocomposite (Table 2) from the percentage of “C + F” in EDX analysis at 900 °C. Thus, the percentage of “char” for MCNT/FE-900 °C is 3.29% and for CNT/FE-900 °C is 1.9%, showing more “char” remained in the case of using MCNT as the filler for FE compared to CNT. Therefore, it can be suggested that in MCNT/FE, more char is stable up to 900 °C compared to CNT/FE. Comparison of Zn% in CNT/FE-560 °C and CNT/FE-900 °C (Table 5) shows that the amount of Zn in CNT/FE was almost unchanged and did not undergo any reaction up to 900 °C. On the other hand, the Zn% in MCNT/FE-560 °C and MCNT/FE-900 °C shows that a certain amount disappeared up to 900 °C. This is due to the reaction of ZnO with carbon at high temperatures, producing vaporized Zn. This reaction of ZnO and C at high temperatures was reported by Gokon et al.[24].

3.2 Verifying thermal stability in FE composites The increased decomposition temperatures caused by using MCNT in FE are due to several reasons, some of which are the same as those mentioned for CNT in FE[4]. Firstly, Polímeros, 25(4), 392-401, 2015

Element remained (%) CNT/FE-560°C MCNT/FE-900°C 13.13 10.69 2.00 0.20 1.76 0.92 0.16 0.15 0.09 -

CNT/FE-900°C 6.26 0.24 2.00 0.20 -

the presence of MCNT in FE makes the active centers of the FE main chains inactive, preventing degradation, therefore saving FE that is nearer to the MCNT surface. Secondly, the interactions between MCNT and FE result in increased physical and chemical cross-linking points which prevent the degradation of the polymer chains. Besides, considering that the degradation of FE is a radical chain reaction, it is therefore susceptible to inhibition by reagents capable of trapping such radicals. Furthermore, the antioxidant nature of MCNT, attributed to its high electron affinity (≈ 2.65 eV), enables it to act as a radical scavenger. Consequently, MCNT helps to trap radicals and inhibits the degradation of FE nearer to it. Moreover, Endo et al.[3] reasoned that the thermal stability of FE near MCNT is due to the presence of bounded rubber to MCNT and concluded that this structure could prevent the decomposition of rubber at high temperatures by resisting molecular mobility.

Wang et al.[25] reported that in PVDF/SiO2- grapheme oxide (GO) composites there is a strong interaction between many of the functional groups in the GO and PVDF chains.

In particular, the C-F bond in PVDF and carboxyl or hydroxyl groups of grapheme oxides (GO) in the PVDF/SiO2-GO composites form hydrogen bonds, and this supports the enhancement of interfacial interaction. The same hydrogen bonding can be formed between functional groups in MCNT and C-F of FE. Ma and Larsen[26] also reported that nitric acid treated single wall nanotubes (SWNT) compared to untreated MWNT have better physical surface affinities with PVDF. The same compatibility can be mentioned here between MCNT and FE compared to CNT and FE. Therefore, there is a strong interaction, which is from the hydrogen bonding and compatibility described above, between MCNT and FE, and these interactions are not present between CNT and FE. More interactions between MCNT and FE compared to CNT and FE result in increased physical and chemical cross-linking points, which prevents more degradation of the polymer chains in the case of MCNT/FE. Furthermore, these interactions will increase the amount of bounded rubber to MCNT in MCNT/FE compared to CNT in CNT/FE and, 397

Heidarian, J., Hassan A., & Rahman, N. M. M. A. as explained above, more bounded rubber will increase the thermal stability in the case of MCNT/FE.

3.3 Effect of thermal aging on residual elemental composition Figure 6 illustrates representative figures of EDX obtained for aged and un-aged samples. The elemental weight percent extracted from these figures is presented in Table 6. This table shows the surface composition of the composites before and after aging. The major elements in the composites are C, O, F and Si. The initial loss in element is defined as the percentage lost due to aging for different periods of time. The percentage loss can be calculated as follows: For 100 g of un-aged FE (Table 6), there were 34.26, 4.99, 59.82 and 0.92 g of C, O, F and Si respectively.

After 72 hours of aging, if Crem, Orem, and Frem g of C, O and F respectively remained and Clos, Olos and Flos g of C, O and F respectively were lost. Then;

with CNT/FE was observed. However, as the aging time increased, there was a drastic increase in percentage loss.

FE underwent thermal oxidation and dehydrofluorination during hot air aging[27]. Due to the dehydrofluorination reaction, HF was produced[27] and the carboxylic acidic groups on the surface of MCNT reacted with HF. Wang et al.[28] reported a similar reaction between dispersed graphene oxide (GO) and hydrofluoric acid (HF) during the synthesis of fluorinated grapheme sheets (FGS). The authors mentioned that fluorine was grafted onto the basal plane of graphene.

Furthermore, the oxygen-containing groups in GO played a major role in FGS formation, and the fluorination degree could be easily controlled by varying the reaction temperature, times and amounts of HF. They also stated that fluorination

Crem + Clos = 34.26 g ;

Orem + Olos = 4.99 g and (1) Frem + Flos = 59.82 g

Since Si is not lost during aging, the amount of Si after 72 hours of aging is 0.92 g. If T is the total weight of the remaining elements, then; T = Crem + Orem + Frem + 0.92 g After 72 hours of aging, the weight percentage of Si

is 2.32% (Table 6), therefore;

0.92 = 0.0232 , and thus T

T = 39.66 g. Using T and the percentage of C (Table 6), after 72 hours of aging (30.89%), Crem can be calculated as, 0.3089 = Crem . Thus, Crem = 0.3089 x 39.66 = 12.25 g.

T

Clos = 34.26 – Crem = 22.01 g. Therefore, the percentage of Clos is, Clos (%) =

Wt.ofClos x100(%) = Wt.ofinitialC

22.01 x100(%) = 64.24% 34.26

(2)

This means 64.24% of the initial C was removed from the surface after 72 hours of aging at 250 °C. The same calculations were done for F and O in all other aged composites. The results of these calculations are presented in Table 7. These results show that for each composite, with increasing aging time, the percentage loss of C, O and F increased. This is because, as the aging time increased, more degradation including dehydrofluorination, defluorination and carbon oxygen reactions occurred especially at the surface[27]. The results also show that at each aging time, for CNT/FE the loss of elements was lower than for MCNT/FE. Therefore, CNT can preserve a larger portion of the elastomer surface from degradation compared to MCNT. For CNT/FE, up to 24 hours of aging, the initial percentage loss of each element slightly increased. Nevertheless, as the aging time increased, even a decrease in percentage loss was observed. This means that the slight degradation happened mainly in the first 24 hours and did not increase after that.

For MCNT/FE, up to 24 hours of aging, the same trend as 398

Figure 6. EDX spectra of (a) MCNT/FE and (b) MCNT/FE-72.

Polímeros , 25(4), 392-401, 2015

Improving the thermal properties of fluoroelastomer (Viton GF-600S) using acidic surface modified carbon nanotube Table 6. The surface composition of the composites before and after aging, obtained by EDX. Element C O F Si Total Element C O F Si Total Element C O F Si Total

Wt %

At %

Wt %

FE 34.26 44.95 4.99 4.92 59.82 49.62 0.92 0.52 100 100 MCNT/FE 34.06 44.64 6.41 06.31 58.5 48.48 1.02 0.57 100.00 100.00 CNT/FE 35.43 46.32 3.60 3.53 59.99 49.60 0.98 0.55 100 100

At %

Wt %

FE-24 -

-

MCNT/FE-24 30.46 40.63 7.36 7.37 60.51 51.04 1.68 0.96 100.00 100.00 CNT/FE-24 36.75 47.92 2.79 2.70 58.56 48.32 1.91 1.07 100 100

occurred at the original sp3 C sites in GO, that is, the C sites connected with the oxygen-containing groups. In the case of MCNT/FE, this reaction caused increased degradation particularly at aging times higher than 24 hours, leading to more loss of F and C from the surface compared to CNT/FE. Comparing the results of FE and MCNT/FE at aging times longer than 24 hours, it can also be seen that for FE without MCNT, the loss of elements was lower than for FE with MCNT. This could be due to the same reasons as those given above in the comparison of MCNT/FE and CNT/FE. The reasons adduced for the saving of a higher percentage of undegraded FE and char in the TGA runs are also valid for the thermal aging of MCNT/FE in the first 24 hours.

Besides, the antioxidant nature of MCNT enables it to act as a radical scavenger[4] especially for the oxide radicals produced due to the presence of air. This also helps to trap radicals, thereby inhibiting the degradation of nearby MCNT, and results in an increased percentage of undegraded FE.

At %

Wt %

At %

FE-48

FE-72

30.65 41.04 3.94 3.96 64.02 54.20 1.40 0.80 100 100 MCNT/FE-48 31.46 42.11 7.07 7.10 56.99 48.23 4.48 2.56 100.00 100.00 CNT/FE-48 31.99 42.60 3.53 3.53 62.92 52.98 1.56 0.89 100 100

30.89 41.37 04.75 04.78 62.03 52.52 2.32 1.33 100 100 MCNT/FE-72 26.58 36.95 12.95 13.51 47.77 41.99 12.69 7.55 100.00 100.00 CNT/FE-72 30.90 41.39 3.69 3.71 63.63 53.89 1.78 1.02 100 100

Table 7. Initial element loss percentage after aging compared to un-aged samples.

Element C O F Si Element C O F Si Element C O F Si

Initial Element loss% FE-24 FE-48 FE-72 41.21 64.25 48.11 62.25 29.67 58.88 0 0 MCNT/FE-24 MCNT/FE-48 MCNT/FE-72 45.70 78.97 93.73 30.29 74.89 83.76 37.20 77.82 93.44 0 0 0 CNT/FE-24 CNT/FE-48 CNT/FE-72 46.73 43.28 51.98 60.19 38.40 43.57 49.86 34.11 41.60 0 0 0

A considerable depletion of F and C on the surface and to a depth of around 10-15 μm of the cross-section of the CB/FE seals aged in oil containing amine based dispersant at 150 °C was also reported by Smith et al.[22]. They also reported the catalytic effect of amine on the degradation of FE. The authors reported that polytetrafluoroethylene (PTFE) also began to soften and release F at around 200-220 °C. This may explain the apparent susceptibility to heating in air shown by elastomers with a high TFE content. A drastic decrease in C and F due to thermal aging in air at 200 °C from the surface of CB/FE (up to a depth of 5 nm) was also reported by Wang et al.[27].

Figure 7 shows the FESEM image of MCNT/FE razor cut surfaces. The very good distribution and dispersion of MCNT in FE can be seen in this figure.

3.4 Other works on FE and fillers/FE In our before study[29], we verified the crystalinity of some of the above mentioned FE and fillers/FE, by Dynamic mechanical analysis (DMA), Differential Scanning Calorimetry Polímeros, 25(4), 392-401, 2015

Figure 7. FESEM image of MCNT/FE (the razor cut cross section surface).

(DSC) and X-ray diffraction (XRD). Verifying thermal properties of fluoroelastomer using carbon nanotubes in presence of air and under nitrogen flow is the other study[30].

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Heidarian, J., Hassan A., & Rahman, N. M. M. A.

4. Conclusions TGA shows that the thermal stability of FE in a N2 atmosphere increased with the presence of MCNT relative to when either CNT was used or while FE was unfilled. A higher percentage of this composite in the form of undegraded FE or char remained within the temperature range of 400‑900 °C compared to CNT/FE or FE. The MCNT/FE TGA curve shifted towards higher temperatures compared to CNT/FE or FE. The same results also revealed that a higher percentage of FE was undegraded or less degraded especially near MCNT in the temperature range of 400-540 °C. EDX analysis shows that the percentage of carbon and fluorine in the residue of TGA runs up to 560 °C of MCNT/FE was the same as CNT/FE and higher than that of FE. EDX of the residue of TGA runs up to 900 °C shows that most of the undegraded FE which was not degraded at temperatures up to 560 °C was degraded from 560° up to 900 °C in both MCNT/FE and CNT/FE. However, the char in MCNT/FE was more than that in CNT/FE at 900 °C. The EDX results of aged specimens under air indicate that the percentage of C, F and O lost on the surface of filler/FE and FE increased with increasing aging time.

Again, at 24 hour aging time, MCNT preserved a higher percentage of these elements compared to CNT. The order of percentage loss in elements after 24 hour aging time was MCNT/FE > FE > CNT/FE.

5. Acknowledgements We thank the University of Malaya as the work reported in this paper was funded under the grant numbers UMRG (RG322-15AFR) and BKP (BK005-2014).

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19. Carabineiro, S. A., Pereira, M. F., Pereira, J. N., Caparros, C., Sencadas, V., & Lanceros-Mendez, S. (2011). Effect of the carbon nanotube surface characteristics on the conductivity and dielectric constant of carbon nanotube/poly(vinylidene fluoride) composites. Nanoscale Research Letters, 6(1), 302. http://dx.doi.org/10.1186/1556-276X-6-302. PMid:21711832.

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The effect of nanotube surface oxidation on the electrical Polímeros , 25(4), 392-401, 2015

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24. Gokon, N., Hasegawa, N., Kaneko, H., Aoki, H., Tamaura, Y., & Kitamura, M. (2003). Photocatalytic effect of ZnO on carbon gasification with CO2 for high temperature solar thermochemistry. Solar Energy Materials and Solar Cells, 80(3), 335-341. http://dx.doi.org/10.1016/j.solmat.2003.08.016.

25. Wang, J., Chen, P., Chen, L., Wang, K., Deng, H., Chen, F., Zhang, Q., & Fu, Q. (2012). Preparation and properties of poly (vinylidene fluoride) nanocomposites blended with graphene oxide coated silica hybrids. Express Polymer Letters, 6(4), 299-307. http://dx.doi.org/10.3144/expresspolymlett.2012.33.

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26. Ma, J., & Larsen, R. M. (2012). Use of Hansen solubility parameters to predict dispersion and strain transfer of functionalized single-walled carbon nanotubes in poly(vinylidene fluoride) composites. Journal of Thermoplastic Composite Materials, 27(6), 801-815. http://dx.doi.org/10.1177/0892705712455036.

27. Wang, Y., Liu, L., Luo, Y., & Jia, D. (2009). Aging behavior and thermal degradation of fluoroelastomer reactive blends with poly-phenol hydroxy EPDM. Polymer Degradation & Stability, 94(3), 443-449. http://dx.doi.org/10.1016/j. polymdegradstab.2008.11.007.

28. Wang, Z., Wang, J., Li, Z., Gong, P., Liu, X., Zhang, L., Ren, J., Wang, H., & Yang, S. (2012). Synthesis of fluorinated graphene with tunable degree of fluorination. Carbon, 50(15), 5403-5410. http://dx.doi.org/10.1016/j.carbon.2012.07.026.

29. Heidarian, J., & Hassan, A. (2014). Microstructural and thermal properties of fluoroelastomer/carbon nanotube composites.

Composites. Part B, Engineering, 58, 166-174. http://dx.doi. org/10.1016/j.compositesb.2013.10.054.

30. Heidarian, J., & Hassan, A. (2015). Improving thermal properties of fluoroelastomer using carbon nanotubes in presence of air and under nitrogen flow. Asian Journal of Chemistry, 27(4), 1235-1239. http://dx.doi.org/10.14233/ajchem.2015.17200.

Received: Dec. 27, 2014 Accepted: Apr. 29, 2015

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

Synthesis, characterization and thermal degradation of cross-linked polystyrene using the alkyne-functionalized esters as a cross-linker agent by click chemistry method Hakan Akat1* and Fehmi Saltan1,2 Department of Chemistry, Faculty of Science, Ege University, Bornova, Izmir, Turkey 2 Department of Chemistry, Faculty of Science, Çankırı Karatekin University, Merkez, Çankırı, Turkey

1

*hakan.akat@ege.edu.tr

Abstract In this study, it has been demonstrated that cross-linked polystyrene (CPS) was successfully prepared by using click chemistry. For this purpose, firstly, poly (styrene-co-4 chloromethylstyrene) with 4-chloromethylstyrene was synthesized. Secondly, alkyne-functionalized esters (dipropargyl adipate, dipropargyl succinate) were obtained using propargyl alcohol, adipoyl chloride and succinyl chloride. Azide-functionalized polystrene (PS-N3) and dipropargyl adipate (or dipropargyl succinate) were reacted in N,N-dimethylformamide for 24 h at room temperature to give CPS. The synthesized polymer and compounds were characterized by nuclear magnetic resonance (1H-NMR), gel permeation chromatography (GPC), fourier transform infrared spectroscopy (FT-IR) and thermogravimetric (TG/DTG) analysis.

The surface properties were investigated by Scanning Electron Micrography (SEM).

Keywords: polystyrene, cross-linked polymers, click chemistry, thermal degradation.

1. Introduction In last years, polystyrene (PS) has managed to become one of the world’s most widely used polymers. PS is one of the three standard plastics (polyolefins, poly(vinyl chloride), and PS), and PS can be applied in many fields, such as the packaging of electrical equipment, apparatus, instruments, and foods, thermal insulation materials for buildings and cold storage, and disposable dinner service[1]. However polystyrene do not offer the properties associated with thermoset polymers, and hence its applications are limited. Cross-linking of polystyrene is one approach to improve the properties and consequently to access the demanding regimes of high-tech applications. Crosslinked polystyrene (CPS) have excellent mechanical properties and good chemical stability. Their excellent performances provide wide applications as packing materials for liquid chromatography[2-5], as ion-exchange resins[6,7] and as imprinted adsorbents for the selective separation of hazardous organic compounds[8,9]. Cross-linking of PS is readily achieved by the incorporation of a multifunctional monomer during the polymerization process[10-15]. High-energy radiation or photochemical irradiation has been used, but in addition to the cross-linking both methods may also involve chain scission that can result in polymer degradation or the introduction of unwanted impurities. Alternative thermal methods for the formulation of thermosetting materials usually involve Diels-Alder and click chemistry reactions which may suffer from the reversibility[16-17]. Yagci et al.[15] synthesized polystyrene using click chemistry method.

Other methods involves classical cross linker agent as DVB in literature. In our study, we introduce new strategy using both click chemistry method and new crosslinker agents (alkyne-functionalized esters).

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2. Experimental 2.1 Materials Styrene (S, 99%, Sigma-Aldrich Company, USA) and 4-chloromethylstyrene (CMS, ca. 60/40 meta/para isomer mixture, 97%, Sigma-Aldrich Company, USA) were distilled under reduced pressure before use. 2,2 Azobis(isobutyronitrile) (AIBN, 98%, Sigma-Aldrich Company, USA) was recrystallized from ethanol. Other solvents were purified by conventional procedures. Triethylamine (98%, Sigma‑Aldrich Company, USA) and dichloromethane (99.9%, HPLC grade, Sigma-Aldrich Company, USA) were distilled from CaH2. Noxyl- free radical (TEMPO, 99%, Sigma-Aldrich Company, USA) was used as received Ethylenediaminetetraacetic acid (EDTA, 99%, Sigma‑Aldrich Company, USA) N,N-dimethylformamide (DMF 99%, Sigma-Aldrich Company, USA). Propargyl alcohol (99%, Sigma-Aldrich Company, USA) were used without any purification. Pyridine (anhydrous, 98%, Sigma-Aldrich Company, USA). Adipoyl chloride (98%, Sigma-Aldrich Company, USA). Succinyl chloride (95%, Sigma-Aldrich Company, USA). 2,2’-bipyridine (reagent plus >99%, Sigma-Aldrich Company, USA). Copper(I) bromide(98%, Sigma-Aldrich Company, USA). Hydrochloric acid (ACS reagent, 37%, Sigma-Aldrich Company, USA).

2.2 Instrumentation 1 H-NMR (NMR, nuclear magnetic resonance) measurements were recorded in CDCl3 (deuterium chloroform) with Si(CH3)4 as internal standard, using Varian AS-400 (400 MHz) instrument. Fourier transform infrared spectroscopy (FTIR) spectra were recorded on a PerkinElmer FTIR Spectrum

Polímeros , 25(4), 402-407, 2015

Synthesis, characterization and thermal degradation of cross-linked polystyrene using the alkyne-functionalized esters as a cross-linker agent by click chemistry method FTIR T% (cm–1): 3294 (HC≡ CH), 2920 (-CH2-), 2126 (≡C-H), 1736 (-C=O), 1259 (-C-O-) 1H-NMR (CDCl3, 400 MHz, 25 °C, TMS): δ=1.76 (m, 4H, CH2), 2.45 (m, 4H, CH2-CO), 2.55 (t, 2H, ≡C-H), 4.72 (d, 4H, O-CH2) ppm.

DPS:yield of 65%. FTIR T% (cm-1): 3289 (HC≡ CH), 2920 (-CH2-), 2128 (≡C-H), 1724 (-C=O), 1242 (-C-O-) 1H-NMR (CDCl3, 400 MHz, 25 °C, TMS): δ = 2.50 (m, 4H, CH2-CO), 4.40(d, 4H, O-CH2), 2.20 (t, 2H, ≡C-H).

One-B spectrometer. Molecular weights were determined by gel permeation chromatography (GPC) instrument equipped with a Waters styragel column (HR series 2, 3, 5E) with THF as the eluent at a flow rate of 0.3 mL/min and a Waters 410 differential refractometer detector.

TG measurements of powders polymer samples were obtained on PerkinElmer Diamond TA/TGA from 25 to 1000 °C and heating rate of 10 °C/min under constant flow rate of 100 mL/min of nitrogen atmosphere. The sample weights for all the experiments were taken in the range of 8–10 mg. All SEM images were obtained by using a field emission scanning electron microscope Zeiss FE-SEM Supra 25 microscope under high vacuum at a voltage of 15.0 kV with a working distance of 6.0 mm.

2.6 Preparation of the crosslinked polystyrene by using DPA(C-PSA) and DPS(C-PSS) In a flask, PS-N3, DPA (or DPS), copper (I) bromide, 2, 2’-bipyridine and dry DMF were added. The flask was capped with a septum and purged with dry nitrogen for 10 min.

The mixture was stirred overnight at room temperature. After removing the catalyst by EDTA, functionalized polymer was precipitated in methanol (200 mL), filtered, and dried under vacuum overnight with a yield of 70% (mol feed ratios are seen Table 1).

2.3 Synthesis of poly(styrene-co-chloromethylstyrene) Poly(styrene-co-4-chloromethylstyrene) (P(S-co-CMS)) was synthesized as described previously[18].

2.4 Synthesis of polystyrene azide (PS-N3)[19]

3. Result and Discussion

A typical procedure for the preparation of PS-N3 from 10 mol % CMS containing P(S-co-CMS) is as follows: P(S‑co-CMS) (1.0 g, 1.04 ×10–4 mol) was dissolved in DMF, and NaN3 (0.07 g, 1.01 ×10–3 mol) was added. The resulting solution was allowed to stir at 25 °C overnight and precipitated in excess methanol/water mixture (1/1 by volume). 1H NMR (CDCl3): δ ppm) 7.40–6.20 (b, 9H), 4.25 (s, 2H) FTIR T% (cm_1): 3060, 2924, 2096, 1681, 1601, 1492, 1453, 757, 698. Mn: 3500 g/mol PDI: 1.50.

In our study, we first synthesized (P(S-co-CMS)) and P-N3.

Following experiment was carried out for alkyne‑functionalized esters (DPA and DPS). DPA and DPS were used to obtain cross-linked polystyrene. CPS was synthesized via click chemistry (Scheme 1). Chemical structure of both esters and polymers were identified by several techniques such as FT-IR, NMR, GPC, TG, DTG and SEM. The FT-IR spectra of DPA;PS-N3;C-PSA65%;C-PSA12% and DPS;PS-N3;C-PSS65%;C-PSS12% are shown in Figure 1 and Figure 2, respectively. According to this FT-IR spectra, appearance of the -N3 stretching is clear at 2096 cm–1 and it is notable that spectra of ADP and DPS show -HC≡ CH- ; ≡C-H- peaks at around 3290;2120 cm-1. After cross-linked reaction between DPA(or DPS) and PS-N3, disappearance of –N3 and alkyne peaks can be seen. These FT-IR data show successful of PS-N3, CPS, DPA and DPS synthesis.

On the other hand, they are also supported by 1H-NMR. From the 1H NMR spectra of synthesized DPA and DPS, it is observed that -C≡H protons signals at 2.40 and 2.20 ppm, respectively. O-CH2 protons are observed at 4.72(DPA) and 4.40(DPS) ppm. -CH2-CO protons can be seen at 2.45 ppm and 2.50 ppm.

Thermal behaviour and thermal stability of the synthesized CPS is investigated by TG measurement. TG curves and the corresponding derivative curves (DTG) for cross-linked polystrene are shown in Figure 3 and Figure 4, respectively.

The derivative of the thermogram with respect to temperature,

2.5 Synthesis of dipropargyl adipate (DPA, diprop-2-ynyl adipate) and dipropargyl succinate (DPS, diprop-2-ynyl succinate) Propargyl alcohol (2.01 g, 0.036 mol), pyridine (2.69 g, 0.034 mol), and dry dichloromethane (20 mL) were charged to a 50 mL round-bottom flask. The resulting solution was maintained at 0 °C by means of a salt-ice bath.

A solution of adipoyl chloride (2.63 g, 0.017 mol) or succinyl chloride (3.11 g, 0.017 mol) in 5 mL of dry dichloroethane was added dropwise over 30 min. The solution was stirred overnight at room temperature and then transferred to a 250 mL separatory funnel with the aid of a small amount of dichloromethane. The dichloromethane solution was washed with water (2×25 mL), 5% HCl (20 mL), and saturated sodium bicarbonate solution (25 mL). The dichloromethane solution was dried over MgSO4 and the mixture was filtered.

Organic phase was removed by evaporator. The products were dried under vacuum overnight. DPA: yield of 70%.

Table 1. Mol feed ratio of synthesized cross-linked polymers.

Compound (C) DPA DPS Compound (C) DPA DPS

CuBr

bipyridine

6.6×10–4 mol 0.094 g 3.3×10–4 mol 0.0473g

1.3×10–3 mol 0.2 g 6.6×10–4 mol 0.10g

65% Azide Containing PS C

CuBr

bipyridine

0.3×10–4 mol 0.042 g 0.3×10–4 mol 0.042 g

0.6×10–4 mol 0.093g 0.6×10–4 mol 0.093g

Polímeros, 25(4), 402-407, 2015

PS-N3

4.12×10–4 mol 0.092g 3.3×10–4 mol 0.1 g 2,10×10–4 mol 0.041g 1.68×10–4 mol 0.05g 12% Azide Containing PS C PS-N3 1.87×10–4 mol 0.041g 1.87×10–4 mol 0.036g

1.5×10–4 mol 0.05g 1.5×10–4 mol 0.05g

DMF 5 ml 5ml DMF 5 ml 5ml

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Akat, H., & Saltan, F.

Scheme 1. General procedure for the synthesis of alkyne functionalized ester containing CPS via click chemistry.

also known as a differential thermogram or DTG, indeed shows the maximum rate of polymer decomposition (Tmax). TG thermogram under N2 atmosphere revealed that C-PSA65% and C-PSS65% degradation takes place in three stages, C-PSA12% and C-PSS12% degradation takes place in two stages.

The first stage for the C-PSA65% being at a temperature around 312 °C that corresponds to a very small mass loss 404

of about 10%. The second occurs at about 378 °C that corresponds to mass loss of about 25% and the last stage occurs at about 600 °C that corresponds to mass loss of about 50%. C-PSA12% has two main decomposition stages. First one appears to begin around 291 °C and stop around 414 °C. The second one appears to begin around 390 °C and stop around 526 °C. The remaining mass without degradation of C-PSA65% is higher than C-PSA12%. When compared to Polímeros , 25(4), 402-407, 2015

Synthesis, characterization and thermal degradation of cross-linked polystyrene using the alkyne-functionalized esters as a cross-linker agent by click chemistry method

Figure 1. Comparison of FT-IR spectra of DPA;PS-N3;C-PSA65%;C-PSA12%.

Figure 2. Comparison of FT-IR spectra of DPS;PS-N3;C-PSS65%;C-PSS12%.

PolĂ­meros, 25(4), 402-407, 2015

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Akat, H., & Saltan, F.

Figure 3. Comparison of TG curves of PSS65%;C-PSS12% and C-PSA65%;C-PSA12%.

Figure 4. Comparison of DTG curves of C-PSA65%;C-PSA12% and PSS65%;C-PSS12%.

C-PSS65% and C-PSS12%, it is observed that C-PSS65% more stable then C-PSS12%.

The first, second and third degradation stages of C-PSS65% begin 225, 296, 396 °C and the mass loss is about 10%, 20% and 75%, respectively. C-PSS12% curves show two degradation stages which temperatures are 220 oC and 412 oC. When thermal degradation curves of polystyrene compared with crosslinked polystyrene, the char yield of the thermally cured polystyrene was about 40% and much higher than PS (0.0%) in literature[15,20-22]. We also observed that thermal stability of CPS increases with the chain length of alkyne functionalized esters used (All Tmax values are shown in Table 2).

Table 3 displays the SEM micrographs obtained before and after cross-linked PS-N3/DPA/DPS. The SEM microphotographs of PS-N3 show that, most of the microspheres are unregularly spherical, and the interface is clear and smooth. The average particle size is between 1500μm-680 nm in diameter. The SEM images of various crosslinked PS, it could be visualized that no inert layer was formed on the surfaces of the C-PSS and C-PSA after cross-linked between PS-N3 and alkyne functionalized esters. The images also indicate an increase in compact 406

Table 2. Tmax values of the synthesized cross-linked polystyrene.

CPS N3% Tmax(oC)

C-PSS

C-PSA

12 225 412 -

65 235 320 421

12 351 423 -

65 335 387 629

Table 3. SEM micrographs of PS-N3, C-PSA65%;C-PSA12% and C-PSS65%-C-PSS12%.

Azid%

Sem micrographs of PS-N3

Sem micrographs of CPS after crosslinked C-PSA C-PSS

packing with increasing DPA or DPS content, suggesting the formation of a rigid interpenetrating network formation and increased crosslinking.

4. Conclusions In conclusion, we introduce an effective strategy to synthesize a novel cross-linked polystyrene(C-PS) by using click chemistry. The Cross-linking reaction was Polímeros , 25(4), 402-407, 2015

Synthesis, characterization and thermal degradation of cross-linked polystyrene using the alkyne-functionalized esters as a cross-linker agent by click chemistry method carried out under the condition of low temperature and we used the synthesized alkyne-functionalized esters as a cross-linker. According to data obtained from TG and DTG curves, chain length of alkyne functionalized esters plays important role for thermal stability and in char yield . PS cured in this way exhibited much more thermal stability than those of structurally similar cross-linked polymers. Surface morphologies of CPS changed when used cross‑linker (DPA or DPS) of different chain lengths.

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Crosslinked polystyrene beads modified with polar groups for the separation of aromatic/aliphatic hydrocarbons. Journal of Applied Polymer Science, 131(8), 40156-40162. http://dx.doi. org/10.1002/app.40156.

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10. Archibald, T. G., Malik, A. A., Baum, K., & Unroe, M. R. (1991). Thermally stable acetylenic adamantane polymers.

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11. Bellenger, V., Verdu, J., & Morel, E. (1989). Structure-properties relationships for densely cross-linked epoxide-amine systems based on epoxide or amine mixtures. Journal of Materials Science, 24(1), 63-68. http://dx.doi.org/10.1007/BF00660933.

12. Douglas, W. E., & Overend, A. S. (1991). Curing reactions in acetylene terminated resins—I. Uncatalyzed cure of arylpropargyl ether terminated monomers. European Polymer Journal, 27(11), 1279-1287. http://dx.doi.org/10.1016/00143057(91)90066-W. 13. Kirchhoff, R. A., Bruza, K., Carriere, C., & Rondan, N. (1992).

Makromolekulare Chemie. Macromolecular Symposia, 5455(1), 531-534. http://dx.doi.org/10.1002/masy.19920540140.

14. Morel, E., Bellenger, V., Bocquet, M., & Verdu, J. (1989).

Structure-properties relationships for densely cross-linked epoxide-amine systems based on epoxide or amine mixtures.

Journal of Materials Science, 24(1), 69-75. http://dx.doi. org/10.1007/BF00660934.

15. Yagci, Y., Kiskan, B., Gacal, B., & Ergin, M. (2007). Thermally curable polystyrene via click chemistry. Macromolecules, 40(13), 4724-4727. http://dx.doi.org/10.1021/ma070549j.

16. Wang, Y. X., & Ishida, H. (1999). Cationic ring-opening polymerization of benzoxazines. Polymer, 40(16), 4563-4570. http://dx.doi.org/10.1016/S0032-3861(99)00074-9.

17. Kasapoglu, F., Cianga, I., Yagci, Y., & Takeichi, T. (2003).

Photoinitiated cationic polymerization of monofunctional benzoxazine. Journal of Polymer Science. Part A, Polymer Chemistry, 41(21), 3320-3328. http://dx.doi.org/10.1002/ pola.10913.

18. Gacal, B., Akat, H., Balta, D. K., Arsu, N., & Yagci, Y. (2008).

Synthesis and characterization of polymeric thioxanthone photoinitatiors via double click reactions. Macromolecules, 41(7), 2401-2405. http://dx.doi.org/10.1021/ma702502h.

19. Yildirim, Y., Dogan, B., Muğlali, S., Saltan, F., Ozkan, M., & Akat, H. (2012). Synthesis, characterization, and thermal degradation kinetic of polystyrene-g-polycaprolactone. Journal of Applied Polymer Science, 126(4), 1236-1246. http://dx.doi. org/10.1002/app.36888.

20. Malhotra, S. L., Hesse, J., & Blanchard, L. P. (1975). Thermal decomposition of polystyrene. Polymer, 16(2), 81-93. http:// dx.doi.org/10.1016/0032-3861(75)90133-0.

21. Sivalingam, G., & Madras, G. (2003). Thermal degradation of poly (ε-caprolactone). Polymer Degradation & Stability, 80(1), 11-16. http://dx.doi.org/10.1016/S0141-3910(02)00376-2.

22. McNeill, I. C., Zulfiqar, M., & Kousar, T. A. (1990). Detailed investigation of the products of the thermal degradation of polystyrene. Polymer Degradation & Stability, 28(2), 131151. http://dx.doi.org/10.1016/0141-3910(90)90002-O. Received: Oct. 03, 2014 Revised: Feb. 26, 2015 Accepted: Mar. 20, 2015

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http://dx.doi.org/10.1590/0104-1428.1852

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Avaliação das propriedades mecânicas e morfológicas de compósitos de PEAD com pó de Pinus taeda e alumina calcinada Evaluation of the mechanical and morphological properties of HDPE composites with powdered Pinus taeda and calcined alumina Karine Grison1, Taís Caroline Turella1, Lisete Cristine Scienza2 e Ademir José Zattera1* 1

Programa de Pós-Graduação em Engenharia de Processos e Tecnologias, Universidade de Caxias do Sul - UCS, Caxias do Sul, RS, Brasil 2 Departamento de Materiais, Universidade Federal do Rio Grande do Sul - UFRGS, Porto Alegre, RS, Brasil *ajzattera@terra.com.br

Resumo Neste estudo foram desenvolvidos compósitos utilizando PEAD, pó de madeira (Pinus taeda), alumina calcinada e dois diferentes tipos de agentes compatibilizantes para avaliação das propriedades morfológicas e mecânicas dos mesmos. Para aumentar a interação entre a matriz polimérica e o pó de madeira foram utilizados 2% de polietileno graftizado com anidrido maleico em todas as formulações. Para efeito comparativo foi desenvolvida uma formulação com viniltrietoxisilano como compatibilizante para a alumina calcinada. O teor de cargas variou de 4% a 33% para os compósitos de carga única e mantiveram o percentual de 28% para os compósitos com as duas cargas. A interação entre a matriz polimérica e as cargas, proporcionada pelo agente compatibilizante anidrido maleico, foi observada nas micrografias da interface da matriz/carga. A utilização do silano não proporcionou efeito adicional nas propriedades mecânicas dos compósitos. Os compósitos isentos de alumina apresentaram maior resistência à tração, porém na resistência à flexão a presença da alumina contribuiu para o aumento desta propriedade provavelmente devido à pequena interação existente entre a interface do seu grão e a matriz polimérica.

Palavras-chave: compósito, PEAD, pó de madeira, alumina calcinada, anidrido maleico.

Abstract This work aims at the evaluation of morphological and mechanical properties of HDPE composites developed with wood flour (Pinus taeda), calcined alumina and two different types of compatibilizing agents. In order to improve the interaction between the polymer matrix and wood flour 2% maleic anhydride-grafted polyethylene was used in all formulations. For comparison a formulation with triethoxyvinylsilane as compatibilizer for the calcined alumina was developed. The filler content ranged from 4% to 33% for the single filler composite while the percentage of 28% was kept as such for the two-fillers composites. The interaction between the polymer matrix and fillers, provided by the maleic anhydride compatibilizer agent, could be observed in the micrographs of the matrix / filler interface. The silane did not improve the mechanical properties of the composite. Free alumina composites showed higher tensile strength, but concerning flexural strength the presence of alumina contributed to increased values in this property. This was probably caused by the reduced interaction between the interface of its grain and the polymer matrix.

Keywords: composite, HDPE, wood flour, calcined alumina, maleic anhydride.

1. Introdução Os materiais compósitos são uma alternativa em substituição aos materiais utilizados em setores que abrangem desde a construção civil à indústria automobilística, aliando propriedades como baixa densidade, boas propriedades mecânicas, facilidade de moldagem e elevada resistência

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à corrosão e à fadiga[1,2]. Sua utilização pode ser voltada à redução do custo do produto final e/ou à melhora em alguma propriedade específica como: mecânica, térmica, acústica, elétrica ou ótica, fazendo com que os materiais compósitos ganhem especial destaque na indústria[3,4].

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Avaliação das propriedades mecânicas e morfológicas de compósitos de PEAD com pó de Pinus taeda e alumina calcinada Em materiais compósitos são empregados polímeros, cerâmicas e metais como matriz e utilizam-se fibras/pós vegetais ou minerais, como fase dispersa[5-8]. Quando os polímeros são utilizados como matriz os mais usuais são o polietileno de baixa e alta densidade (PEBD e PEAD), o polipropileno (PP), o policloreto de vinila (PVC), o poliestireno (PS), o acrilonitrila-butadieno-estireno (ABS) e o nylon (PA)[9,10].

2. Materiais e Métodos 2.1 Materiais O polietileno de alta densidade (PEAD) grade ES 6004, fornecido pela Braskem, possui índice de fluidez de 0,35 g/10 min (190 °C/2,16 kg) e densidade 0,96 g/cm3.

O agente compatibilizante utilizado para a carga vegetal foi o polietileno de alta densidade graftizado com anidrido maleico (PE-g-MA), especificação 3029 Polybond, da Chemtura; e para a carga mineral o agente compatibilizante viniltrietoxisilano (VTES), 97% de pureza, da empresa Sigma-Aldrich. As tábuas de Pinus taeda foram fornecidas por uma empresa do ramo de materiais de construção de Caxias do Sul e a alumina calcinada A-2 foi fornecida pela empresa Alcoa S/A, possuindo 99,2% de Al2O3 e alto grau de hidrofobicidade.

Entre as cargas utilizadas para conferir um melhor desempenho às propriedades dos compósitos estão as de natureza mineral (carbonatos, silicatos, argilas e outras)[11], ou vegetal (sisal, juta, algodão, madeira e outras). A carga natural vegetal possui a vantagem de ser uma fonte renovável, contudo poderá apresentar variações em suas propriedades químicas devido às condições climáticas e regionais onde se dá o cultivo e também ao processamento das mesmas[12]. Sua polaridade dificulta a interação destes com a matriz polimérica apolar, sendo necessário o uso de agentes compatibilizantes aumentando a área interfacial entre matriz/carga objetivando melhorias significativas nas propriedades do compósito[13]. As propriedades de resistência à tração, flexão e módulo de elasticidade podem atingir valores superiores com o uso de agente compatibilizante[14,15] e com a seleção correta do tipo e do percentual de carga vegetal[16]. Alguns dos compatibilizantes mais utilizados em compósito termoplástico com carga vegetal são os baseados em anidrido maleico, silanos ou peróxidos de polietileno, promovendo uma boa adesividade interfacial entre as fibras e a matriz[13,17].

2.2 Preparação das amostras As tábuas de Pinus taeda foram serradas, moídas em moinho de facas e classificadas utilizando as peneiras (Escala Tyler) com malhas 35, 48, 65, 100 e 150. Posteriormente foram misturadas às formulações em percentuais de 14, 19, 24 e 33%, sendo cada percentual elaborado com a proporção granulométrica apresentada na Tabela 1. A alumina foi tratada com 0,5% de VTES em solução 95% de etanol e agitada por 2 horas. A amostra permaneceu em repouso por 16 horas.

Após a remoção do sobrenadante a alumina tratada foi seca em estufa por 5 horas a 90 °C antes de ser adicionada às formulações nos percentuais de 4, 9, 14 e 33% (m/m) e o percentual dos grãos obtidos na classificação granulométrica encontra-se na Tabela 2.

As Tabelas 3 e 4 apresentam as formulações de compósitos desenvolvidas. As amostras foram secas em estufa por 24 horas, a 80 °C e processadas em extrusora duplarrosca marca MH Equipamentos L/D 32, com rosca

Para este trabalho utilizaram-se PEAD, pó de Pinus taeda, alumina calcinada, anidrido maleico graftizado e viniltrietoxisilano com o objetivo de avaliar a influência dos diferentes percentuais de carga vegetal e mineral nos compósitos e o efeito dos agentes de acoplamento nas propriedades mecânicas dos compósitos.

Tabela 1. Percentual das diferentes granulometrias de pó de Pinus taeda utilizadas nas formulações dos compósitos confeccionados com pó de madeira.

Malha % usado

48 36

65 36

100 14

150 14

Tabela 2. Percentual das diferentes granulometrias de alumina utilizadas nas formulações dos compósitos.

Tyler massa (g) % em massa

+65/-100 0 0

+100/-150 0,33 16,33

+150/-200 1,07 52,39

+200/-270 0,53 26,17

+270/-fundo 0,06 2,85

+Fundo 0,05 2,26

Tabela 3. Percentuais dos componentes utilizados nas formulações dos compósitos de carga única.

Materiais* PEAD PE-g-MA (MA) VTES (S) Pó de madeira (M) Alumina (A)

9A 91 0 0 0 9

9A/2MA 89 2 0 0 9

9A/0,5S 90 0 0,5 0 9

14M/2MA 84 2 0 14 0

14A/2MA 84 2 0 0 14

33M/2MA 65 2 0 33 0

33A/2MA 65 2 0 0 33

*Valores expressos em % em massa. A simbologia adotada refere-se a quantidade e natureza do material adicionado. Ex: 9A/2MA significa 9% de alumina e 2% de anidrido maleico.

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Grison, K., Turella, T. C., Scienza, L. C., & Zattera, A. J. Tabela 4. Percentuais dos componentes utilizados nas formulações dos compósitos com duas cargas.

Materiais* PEAD PE-g-MA (MA) Pó de madeira (M) Alumina (A)

24M/4A/2MA 70 2 24 4

Compósitos 19M/9A/2MA 70 2 19 9

14M/14A/2MA 70 2 14 14

*Valores expressos em % em massa.

de 20 mm, utilizando o perfil de temperatura de 145 °C, 170 °C, 180 °C, 180 °C, 178 °C, 165 °C, 180 °C, 185 °C e 185 °C da alimentação até a matriz, e com velocidade de rosca de 200 rpm. As amostras obtidas da extrusão foram secas em estufa por 24 horas, a 80 °C e posteriormente foram injetados os corpos de prova para ensaios numa injetora Himaco, modelo LHS 150-80, utilizando-se perfil de temperatura de 190 °C, 180 °C e 170 °C e velocidade de rosca de 60 rpm na injetora.

2.3 Caracterização A avaliação morfológica dos compósitos e das matériasprimas foi realizada com um microscópio eletrônico de varredura da marca Shimadzu, modelo SSX-550 Superscan.

Os corpos de prova utilizados foram fraturados criogenicamente e recobertos com uma fina camada de ouro antes da análise.

Para os ensaios mecânicos foi utilizada uma máquina universal de ensaio EMIC DL 2000, segundo a norma ASTM D 638:10 para o ensaio de resistência à tração, com velocidade de 10 mm.min-1. Os ensaios de flexão foram realizados conforme a norma ASTM D 790:10, utilizando-se célula de carga de 100 kgf e velocidade de 1,5 mm.min–1. O ensaio de impacto IZOD, com entalhe, pêndulo de 1 J e velocidade de 3,5 m.s-1 foi realizado em equipamento da CEAST, modelo Resil 25, conforme a norma ASTM D 256:10.

3. Resultados e Discussões 3.1 Microscopia Eletrônica de Varredura (MEV) Na Figura 1a visualiza-se uma boa adesão na interface madeira/PEAD para o compósito com 33% de pó de madeira, que influencia de forma positiva nas propriedades mecânicas. Pela análise da Figura 1b pode-se visualizar um grão de alumina e seu interior, formado por um aglomerado de inúmeras partículas de alumina. Observa-se que na Figura 1c o interior das partículas não apresenta a presença da matriz polimérica tornando o grão um ponto frágil na estrutura do compósito.

A Figura 2 mostra as micrografias da região fraturada para os compósitos contendo duas cargas (pó de madeira e alumina) em matriz de PEAD modificada com anidrido maleico.

Na Figura 2a e b observa-se a boa adesão interfacial entre a matriz de PEAD e a fase dispersa de madeira.

A análise da figura mostra que não houve descolamento na área interfacial matriz/madeira e ocorreu o rompimento da partícula da madeira próximo à superfície da matriz, corroborando a afirmação da boa adesão da carga à matriz.

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Figura 1. Micrografias da região fraturada (a) e (b) com aumento de 1000x para os compósitos de fase única utilizando percentual de 33%, e PEAD-g-MA como compatibilizante e micrografia (c) com aumento de 6000x para o interior do grão de alumina.

Na Figura 2c visualiza-se ambas as cargas na mesma região de análise do microscópio. Observa-se que a matriz polimérica envolve a madeira (m) e interpenetra em suas camadas, isto não se percebe com a alumina (a), onde a matriz encontra-se somente no entorno de seu grão. Esta baixa interação observada pode influenciar negativamente nas propriedades mecânicas do compósito pelo fato de não haver adesividade interna entre as partículas de alumina que constituem o grão.

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Avaliação das propriedades mecânicas e morfológicas de compósitos de PEAD com pó de Pinus taeda e alumina calcinada As amostras contendo pó de madeira apresentaram valores de resistência à tração superior ao valor do PEAD virgem, o que pode indicar uma boa interação da madeira com o polímero proporcionado pela adição do agente compatibilizante MA[17]. O maior teor de madeira (33%) aliado à boa interação madeira/HDPE, conforme visto nas micrografias anteriores (Figuras 1a e 2a), auxilia na dissipação da energia da matriz para a carga, aumentando o valor da propriedade de resistência à tração em 52% neste compósito.

A amostra que apresentou o melhor desempenho foi o compósito com 33% de madeira (formulação 33M/2MA), houve um aumento da propriedade de resistência à tração e do módulo elástico. Por outro lado, a adição da alumina ocasiona uma diminuição das propriedades mecânicas devido a pouca interação entre as pequenas partículas que formam o grão de alumina observado na Figura 1c. Verifica-se um aumento gradual na resistência à tração à medida que se aumenta o percentual de pó de madeira utilizado nas amostras, o que corrobora o fato da madeira agir como um reforço distribuindo as tensões exercidas sobre a matriz[3] e à boa interação com a matriz polimérica observadas nas Figuras 1 e 2.

3.3 Resistência à flexão

Figura 2. Micrografias para os compósitos utilizando duas fases dispersas e matriz de PEAD modificado com o agente compatibilizante PEAD-g-MA. Onde a é alumina e mé madeira.

Analisando os resultados da Tabela 6 pode-se realizar um comparativo do desempenho entre as formulações de compósitos utilizando anidrido maleico (9A/2MA) e de compósitos utilizando silano (9A/0,5S) no ensaio de resistência à flexão.

Nesta comparação observou-se um desempenho superior para os compósitos com anidrido maleico. A partir da análise do desempenho dos agentes compatibilizantes contidos nas Tabelas 4 e 5, observou-se que, para as formulações de compósitos utilizados neste trabalho, o agente compatibilizante mais indicado foi o anidrido maleico. Este melhor desempenho do anidrido maleico pode ser explicado pelas reações desencadeadas pelo agente de acoplamento na interface madeira/matriz quando grupos hidroxila (OH) da celulose reagem com o anidrido proporcionando maior ancoragem ao polímero e menor ação hidrofílica por parte da madeira[1,17].

A formulação de compósito que obteve o melhor desempenho quanto às propriedades de resistência à flexão foi a amostra contendo 24% de madeira e 4% de alumina (24M/4A/2MA), onde a menor quantidade de alumina consegue distribuir-se de maneira mais homogênea na matriz, posicionando-se nos espaços existentes entre uma partícula de madeira e outra conforme visualiza-se na Figura 2d.

Os compósitos contendo somente alumina obtiveram os menores valores para a resistência à flexão, confirmando que foi visualizado na micrografia do aglomerado de alumina que apresenta seu interior fragilizado, sem interação com a matriz polimérica, Figura 2c.

3.2 Resistência à tração

3.4 Resistência ao impacto

Analisando a Tabela 5 observou-se que nas amostras 9A/2MA e 9A/0,5S não houve alteração significativa nos valores para a resistência à tração com o uso de diferentes agentes compatibilizantes. Por outro lado houve um acréscimo das propriedades mecânicas com o uso dos agentes compatibilizantes em relação ao PEAD.

Através da análise dos resultados contidos na Tabela 7, comparando-se as amostras utilizando alumina e agentes compatibilizantes distintos, observou-se que o uso do agente compatibilizante anidrido maleico (MA) obteve resultado superior ao agente compatibilizante à base de silano (S).

Nos compósitos constatou-se que a adição de alumina e/ou

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Grison, K., Turella, T. C., Scienza, L. C., & Zattera, A. J. Tabela 5. Propriedades mecânicas de resistência à tração para as diferentes formulações de compósitos e PEAD. Amostra PEAD PEAD/2MA 9A/2MA 9A/0,5S 14M/2MA 14A/2MA 33M/2MA 33A/2MA 24M/4A/2MA 19M/9A/2MA 14M/14A/2MA

Resistência à Tração (MPa) 21,43 ± 0,52 21,21 ± 0,30 23,24 ± 0,43 22,98 ± 0,76 27,16 ± 0,35 22,89 ± 0,39 32,39 ± 0,69 22,23 ± 0,44 30,22 ± 0,51 28,84 ± 0,46 27,10 ± 0,33

Deformação (%) 19,61 ± 1,11 15,73 ± 0,40 18,84 ± 0,79 18,03 ± 0,54 16,19 ± 0,43 18,09 ± 0,32 9,48 ± 0,44 13,63 ± 0,45 12,03 ± 0,35 12,35 ± 0,26 12,34 ± 0,23

Módulo Elástico (MPa) 507,90 ± 26,74 510,10 ± 8,40 562,60 ± 18,58 600,90 ± 28,78 699,90 ± 22,95 594,60 ± 17,70 1003,00 ± 30,42 791,20 ± 29,95 829,00 ± 27,64 822,90 ± 22,16 835,20 ± 20,78

Tabela 6. Propriedade mecânica de resistência à flexão para os compósitos e PEAD. Amostra PEAD PEAD/2MA 9A/2MA 9A/0,5S 14M/2MA 14A/2MA 33M/2MA 33A/2MA 24M/4A/2MA 19M/9A/2MA 14M/14A/2MA

Resistência à Flexão (MPa) 16,63 ± 0,84 16,77 ± 0,60 17,72 ± 1,49 14,63 ± 1,79 28,25 ± 0,93 20,97 ± 0,63 25,92 ± 2,04 16,25 ± 0,39 32,80 ± 0,84 29,57 ± 1,33 30,02 ± 0,42

Tabela 7. Propriedade mecânica de resistência ao impacto para os compósitos e o PEAD virgem.

Amostra PEAD PEAD/2MA 9A/2MA 9A/0,5S 14M/2MA 14A/2MA 33M/2MA 33A/2MA 24M/4A/2MA 19M/9A/2MA 14M/14A/2MA

Resistência ao Impacto (J/m) NÃO ROMPEU * NÃO ROMPEU * 154,92 ± 6,78 92,22 ± 18,71 111,62 ± 4,67 119,52 ± 2,80 71,12 ± 5,42 77,26 ± 3,34 78,30 ±4,71 77,61 ± 4,67 76,28 ± 4,03

*Utilizando-se martelo de 1J.

pó de madeira ocasiona uma redução da resistência ao impacto, independente do teor utilizado. Estes resultados inferiores foram atribuídos à menor mobilidade molecular obtida à medida que aumenta-se o percentual das cargas nas formulações dos compósitos[18].

Com relação à incorporação de pó de madeira em polímero termoplásticos, a redução da resistência ao impacto em relação ao polímero puro e o aumento da resistência à tração também foram constatados por outros pesquisadores[19], sendo sugerido que este último efeito possa estar relacionado à característica da estrutura química da celulose, cuja macromolécula possui fortes interações de ligações de hidrogênio.

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Deformação (%) 6,85 ± 0,38 6,51 ± 0,40 6,80 ± 0,19 7,11 ± 0,99 6,54 ± 0,67 6,74 ± 0,16 6,42 ± 0,24 6,96 ± 0,48 6,09 ± 0,37 6,30 ± 0,20 6,55 ± 0,28

Módulo Elástico (MPa) 668,00 ± 121,20 642,30 ± 42,00 714,30 ± 72,12 519,20 ± 157,10 1344,00 ± 75,52 931,20 ± 68,40 1181,00 ± 153,90 644,30 ± 29,47 1761,00 ± 89,40 1674,00 ± 155,60 1642,00 ± 53,70

Os melhores resultados nos ensaios mecânicos observados com o uso do PEAD-g-MA, como agente de acoplamento para o pó de madeira na matriz polimérica, mostram que a presença de grupamentos de anidrido maleico no PEAD‑g-MA auxiliam na interação das cadeias do polímero e celulose, contribuindo para uma melhor adesão entre a carga e a matriz[20].

4. Conclusão Através da análise morfológica foi constatada a existência de espaços vazios entre as partículas que constituem o grão de alumina, o que origina pontos frágeis quando incorporados à matriz polimérica. A superfície externa do grão apresentou boa adesão à matriz quando usado o compatibilizante anidrido maleico, o que contribuiu na propriedade de flexão para o compósito que utilizou o menor percentual de alumina 24M/4A/2MA. Os resultados obtidos mostraram que os compósitos que contêm na sua formulação o agente compatibilizante à base de anidrido maleico possuem boas propriedades mecânicas, com valores superiores as do polímero puro bem como as dos demais compósitos contendo silano como agente compatibilizante.

O melhor resultado para a resistência à tração foi obtido com o compósito com a formulação 33M/2MA e para a resistência à flexão foi obtido com o compósito de formulação 24M/4A/2MA, demonstrando que a alumina influi negativamente nos esforços de tração, mas proporciona maior rigidez ao material, aumentando sua resistência à flexão. Para a resistência ao impacto observou-se que o aumento de carga Polímeros , 25(4), 408-413, 2015

Avaliação das propriedades mecânicas e morfológicas de compósitos de PEAD com pó de Pinus taeda e alumina calcinada de madeira e/ou alumina ocasiona uma menor resistência ao impacto, possivelmente devido à menor mobilidade das cadeias poliméricas com a presença das cargas e à estrutura química da celulose com suas fortes ligações de hidrogênio.

A adição de cargas reduz a resistência ao impacto do PEAD devido às restrições impostas à mobilidade molecular do polímero. Novamente o uso do anidrido maleico proporcionou um melhor resultado em relação ao silano.

Fica evidente o efeito do pó de madeira de Pinus taeda, uma carga de fonte natural e renovável, na melhoria das propriedades mecânicas dos compósitos poliméricos em relação ao polímero puro.

5. Referências 1. Jawaid, M., & Abdul Khalil, H. P. S. (2011). Cellulosic/ synthetic fibre reinforced polymer hybrid composites: A review. Carbohydrate Polymers, 86(1), 1-18. http://dx.doi. org/10.1016/j.carbpol.2011.04.043.

2. Cândido, G. M., Rezende, M. C., Donadon, M. V., & Almeida, S. F. M. (2012). Fractografia de compósito estrutural aeronáutico submetido à caracterização de tenacidade à fratura interlaminar em modo I. Polímeros: Ciência e Tecnologia, 22(1), 41-53. http://dx.doi.org/10.1590/S0104-14282012005000019.

3. Ku, H., Wang, H., Pattarachaiyakoop, N., & Trada, M. (2011).

A review on the tensile properties of natural fiber reinforced polymer composites. Composites Part B: Engineering, 42(4), 856-873. http://dx.doi.org/10.1016/j.compositesb.2011.01.010.

4. Pöllänen, M., Suvanto, M., & Pakkanen, T. T. (2013). Cellulose reinforced high density polyethylene composites - morphology, mechanical and thermal expansion properties. Composites Science and Technology, 76, 21-28. http://dx.doi.org/10.1016/j. compscitech.2012.12.013.

5. Zimmermann, M. V. G., Turella, T. C., Zattera, A. J., & Santana, R. M. C. (2014). Influência do tratamento químico da fibra de bananeira em compósitos de poli(etileno-co-acetato de vinila) com e sem agente de expansão. Polímeros: Ciência e Tecnologia, 24(1), 58-64. http://dx.doi.org/10.4322/polimeros.2013.071.

6. Hablitzel, M. P., Garcia, D. E., & Hotza, D. (2011). Interfaces fracas em compósitos de matriz cerâmica de alumina/alumina.

Revista Matéria, 16(3), 788-794. http://dx.doi.org/10.1590/ S1517-70762011000300006.

7. Gregolin, E. N., Goldenstein, H., Gonçalves, M., & Santos, R. G. (2002). Aluminium matrix composites reinforced with co-continuous interlaced phases aluminium-alumina needles.

Materials Research, 5(3), 337-342. http://dx.doi.org/10.1590/ S1516-14392002000300019.

8. Vieira, L. E., Jr., Rodrigues, J. B., No., Hotza, D., Klein, A. N. (2009). Compósitos de matriz metálica reforçados pela dispersão de partículas cerâmicas produzidos por mecanossíntese: uma revisão. Exacta, 7(2), 195-204. http://dx.doi.org/10.5585/ exacta.v7i2.1626.

9. Valente, M., Sarasini, F., Marra, F., Tirillo, J., & Pulci, G. (2011). Hybrid recycled glass fiber/wood flour thermoplastic composites: manufacturing and mechanical characterization.

Composites Part A: Applied and Manufacturing, 42(6), 649657. http://dx.doi.org/10.1016/j.compositesa.2011.02.004.

Polímeros, 25(4), 408-413, 2015

10. Deka, B. K., & Maji, T. K. (2011). Study on the properties of nanocomposite based on high density polyethylene, polypropylene, polyvinyl chloride and wood. Composites Part A: Applied and Manufacturing, 42(6), 686-693. http:// dx.doi.org/10.1016/j.compositesa.2011.02.009.

11. Mareri, P., Bastide, S., Binda, N., & Crespy, A. (1998). Mechanical behavior of polypropylene composites containing fine mineral filler: effect of filler surface treatment. Composites Science and Technology, 58(5), 747-752. http://dx.doi.org/10.1016/ S0266-3538(97)00156-5.

12. John, M. J., & Thomas, S. (2008). Biofibres and biocomposites.

Carbohydrate Polymers, 71(3), 343-364. http://dx.doi. org/10.1016/j.carbpol.2007.05.040.

13. Xie, Y., Hill, C. A. S., Xiao, Z., Militz, H., & Mai, C. (2010).

Silane coupling agents used for natural fiber/polymer composites: a review. Composites Part A: Applied and Manufacturing, 41(7), 806-819. http://dx.doi.org/10.1016/j.compositesa.2010.03.005.

14. Silva, L. J., Panzera, T. H., Velloso, V. R., Christoforo, A. L., & Scarpa, F. (2012). Hybrid polymeric composites reinforced with sisal fibres and silica microparticles. Composites Part B: Engineering, 43(8), 3436-3444. http://dx.doi.org/10.1016/j. compositesb.2012.01.026.

15. Faruk, O., & Matuana, L. M. (2008). Nanoclay reinforced HDPE as a matrix for wood-plastic composites. Composites Science and Technology, 68(9), 2073-2077. http://dx.doi. org/10.1016/j.compscitech.2008.03.004.

16. Fabiyi, J. S., & McDonald, A. G. (2010). Effect of wood species on property and weathing performance of wood plastic composites.

Composites Part A: Applied and Manufacturing, 41(10), 14341440. http://dx.doi.org/10.1016/j.compositesa.2010.06.004.

17. Kabir, M. M., Wang, H., Lau, K. T., & Cardona, F. (2012).

Chemical treatments on plant-based natural fibre reinforced polymer composites: An overview. Composites Part B: Engineering, 43(7), 2883-2892. http://dx.doi.org/10.1016/j. compositesb.2012.04.053.

18. Correa, C. A., Fonseca, C. N. P., Neves, S., Razzino, C. A., & Hage, E., Jr. (2003). Compósitos termoplásticos com madeira.

Polímeros: Ciência e Tecnologia, 13(3), 154-165. http://dx.doi. org/10.1590/S0104-14282003000300005.

19. Vianna, W. L., Correa, C. A., & Razzino, C. A. (2004). Efeitos do tipo de poliestireno de alto impacto nas propriedades de compósitos termoplásticos com farinha de resíduo de madeira.

Polímeros: Ciência e Tecnologia, 14(5), 339-348. http://dx.doi. org/10.1590/S0104-14282004000500012.

20. Redighieri, K. I., & Costa, D. A. (2008). Compósitos de polietileno reciclado e partículas de madeira de reflorestamento tratadas dom polietileno modificado. Polímeros: Ciência e Tecnologia, 18(1), 5-11. http://dx.doi.org/10.1590/S010414282008000100006.

Enviado: Jul. 19, 2014 Revisado: Set. 25, 2014 Aceito: Fev. 13, 2015

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http://dx.doi.org/10.1590/0104-14281739

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

Resinas poliméricas reticuladas com ação biocida: atual estado da arte Crosslinked polymer resins with biocide action: state-of-the-art Luciana Cunha Costa1, Maria Aparecida Larrubiua Granado Moreira Rodrigues Mandu2, Luiz Claudio de Santa Maria2 e Mônica Regina da Costa Marques2* 1

Centro Setorial de Ciências Biológicas e da Saúde, Centro Universitário Estadual da Zona Oeste - UEZO, Rio de Janeiro, RJ, Brasil 2 Departamento de Química Orgânica, Instituto de Química, Universidade do Estado do Rio de Janeiro UERJ, Rio de Janeiro, RJ, Brasil *monicamarques@uerj.br

Resumo Copolímeros reticulados à base de divinilbenzeno vêm sendo extensivamente empregados como suportes de catalisadores e complexantes de íons metálicos, adsorventes de compostos orgânicos e fases estacionárias em separações cromatográficas. A introdução de grupos biocidas a estes materiais é relatada em patentes desde a década de 1970, contudo apenas a partir do ano 2000 estes copolímeros passaram a ser aplicados também como suportes para grupos biocidas. A presente revisão apresenta as principais combinações de suportes poliméricos e grupos biocidas estudados com o objetivo de preparar resinas biocidas reticuladas. Procura-se estabelecer relação entre as características dessas resinas e seu mecanismo de ação biocida.

Palavras-chave: agentes antimicrobianos imobilizados em polímeros, biocida, copolímeros de estireno-divinilbenzeno, resinas poliméricas.

Abstract Crosslinked copolymers of divinylbenzene have been extensively employed as supports for catalysts and chelating groups of metal ions, adsorbents of organic compounds and stationary phases for chromatography separations. The use of these copolymers as support for biocidal groups is reported in patents since the 1970s, but only after 2000 were these copolymers also applied as supports for biocidal groups. This paper describes the main combinations of polymeric supports and biocide groups employed in biocide polymer resins. The relationship between the characteristics of these resins and their mechanism of action is also established in this work.

Keywords: antimicrobial agents immobilized on polymers, biocide, styrene-divinylbenzene copolymers, polymeric resins.

1. Introdução A contaminação por micro-organismos pode causar sérias complicações para o homem, particularmente se estiver em equipamentos médicos, cirúrgicos, odontológicos, medicamentos, produtos de higiene e de cuidados com a saúde, sistemas de purificação de água, tecidos, embalagens e estocagem de alimentos[1,2].

Uma maneira de combater as atividades microbianas negativas é através de agentes biocidas. “Biocida” é um termo genérico utilizado para se referir aos compostos dotados da capacidade de inibir o crescimento ou matar determinados micro-organismos. A aplicação desta classe de materiais é muito ampla, podendo ser utilizados nos mais diversos produtos e processos, e por isso outros termos são utilizados

414

para diferenciá-los entre si: antibióticos, antissépticos, desinfetantes e conservantes[3].

Percebe-se que há uma confusão conceitual quanto à atividade do agente antimicrobiano. O termo biocida só deve ser utilizado quando ocorrer a destruição significativa dos micro-organismos e o termo bioestático ou bacteriostático quando ocorrer a inibição do crescimento dos micro‑organismos, sem que no entanto estes sejam destruídos[4,5]. Os agentes biocidas podem exercer efeitos tanto bacteriostáticos quanto bactericidas. Os mecanismos de ação responsáveis por esses efeitos podem diferir. Efeitos bacteriostáticos são geralmente considerados quando causam algum dano metabólico que é reversível pela remoção ou neutralização do agente,

Polímeros , 25(4), 414-423, 2015

Resinas poliméricas reticuladas com ação biocida: atual estado da arte enquanto que a ação bactericida resulta de danos irreparáveis e irreversíveis à estrutura ou função vital celular[5].

A escolha do grupo biocida adequado deve levar em consideração a natureza da bactéria e o provável mecanismo de ação deste agente. As bactérias do grupo coliforme, por serem gram-negativas, apresentam além da membrana citoplasmática uma camada adicional constituída de lipopolissacarídeos que confere a elas uma maior integridade estrutural. Esta camada adicional é uma barreira para a atuação direta de agentes biocidas. Nestes casos, a membrana citoplasmática normalmente é o local predisposto a ataque de agentes biocidas. Uma vez que, é na membrana citoplasmática das células gram-negativas e gram-positivas que ocorrem as interações balanceadas entre os fosfolipídeos e as proteínas enzimáticas e estruturais.

Esta situação de equilíbrio garante uma impermeabilidade controlada e a organização topológica pela qual a homeostase intracelular e o transporte e metabolismo vetorial são mantidos. O citoplasma também é um local muito importante, onde ocorrem muitos processos catabólicos e anabólicos, contudo por ser mais externa a membrana é mais sujeita à ação de bactericidas[6].

Agentes antimicrobianos de baixa massa molecular são comumente usados na esterilização de água e solo e na preservação de alimentos[7]. Estes agentes, de forma geral, apresentam muitas desvantagens tais como a toxicidade residual e capacidade antimicrobiana de curto prazo devido à dificuldade no controle da taxa de difusão[6-8]. O método de cloração da água, por exemplo, leva a formação de compostos orgânicos clorados, tais como trialometanos (THM), quando da reação do cloro. Diversos estudos apontam que esses compostos são carcinogênicos[9].

O ozônio também é outro agente de baixa massa molecular muito utilizado. Este composto apresenta como principal desvantagem a sua instabilidade, o que dificulta o seu transporte e armazenamento, exigindo que seja gerado in situ por meio de um processo dispendioso[10-14].

Como a toxidade residual é elevada mesmo quando estes agentes antimicrobianos de baixa massa molecular são usados na quantidade adequada[7,15], uma série de polímeros antimicrobianos vem sendo desenvolvidos visando minimizar este problema.

Dentre as formas de preparação de polímeros antimicrobianos está a introdução de grupos bactericidas em suportes poliméricos e dentre os suportes poliméricos estudados encontram-se os copolímeros reticulados à base de divinilbenzeno. A imobilização de grupos bactericidas em copolímeros de divinilbenzeno, visando a preparação de resinas biocidas reticuladas, vêm atraindo cada vez mais a atenção dos pesquisadores. Entretanto, não são encontrados na literatura trabalhos de revisão que versam especificamente sobre o desenvolvimento destas resinas. Por este motivo, este trabalho de revisão apresenta as principais metodologias adotadas para a preparação de resinas biocidas reticuladas e procura estabelecer uma correlação entre o mecanismo de ação das resinas poliméricas biocidas e as características dos micro-organismos estudados.

Polímeros, 25(4), 414-423, 2015

2. Polímeros Reticulados com Atividade Biocida De acordo com Kenawy[7], um polímero antimicrobiano ideal deve possuir como características principais os seguintes parâmetros: síntese fácil e economicamente viável; estabilidade em longo prazo para uso e armazenagem na temperatura da aplicação pretendida; insolubilidade em água para aplicação em processos de desinfecção de água; não se decompor e/ou emitir produtos tóxicos; possibilidade de ser regenerado quando perder sua atividade; e ser biocida para um amplo espectro de micro-organismos patogênicos em curtos tempos de contato. Infelizmente, muitas destas características não têm sido estudadas pelos pesquisadores que se propõem a desenvolver novos polímeros antimicrobianos. A avaliação do tempo de vida útil dos polímeros, por exemplo, tem sido negligenciada em muitos trabalhos e o estudo da ação biocida limita-se quase sempre ao emprego de Escherichia coli e de bactérias gram-positivas como Staphylococcusaureus, não sendo avaliadas outras espécies de micro-organismos como vírus e fungos[15].

De acordo com Siedenbiedel e Tiller[16], polímeros antimicrobianos podem se dividir em três grupos: - os polímeros biocidas (biocidal polymer): são preparados pela introdução de grupos biocidas a estruturas poliméricas preparadas previamente (suportes); - os biocidas poliméricos (polymeric biocide): são polímeros cujas unidades repetitivas (meros) possuem ação biocida; e - polímeros que liberam biocidas (biocide-releasing polymers): são materiais nos quais a porção polimérica atua meramente como carreadora do biocida[16].

Embora esta distinção sugerida por Siedenbiedel e Tiller[16] seja muito importante, a maioria dos pesquisadores não a utiliza, tratando diferentes materiais simplesmente como polímeros biocidas.

Resinas poliméricas vêm sendo extensamente avaliadas como suportes, sobretudo para catalisadores[17-23] e complexantes de íons metálicos[24-31]. A aplicação desses materiais como suportes para agentes biocidas tem sido relatada em diversas patentes desde a década de 70[10,32-44]. Na maioria destas patentes é descrita a preparação de complexos de transferência de carga com iodo imobilizados em resinas poliméricas reticuladas à base de estireno-divinilbenzeno (Sty-DVB). Estes materiais são indicados em processos de desinfecção de água e de fluidos biológicos. Entretanto, só a partir do ano 2000, foi que estes materiais começaram a ser extensivamente aplicados como suportes para grupos biocidas, introduzindo um novo campo de aplicação para copolímeros reticulados.

Outros suportes poliméricos mais hidrofílicos, como por exemplo, copolímeros de ácido metacrílico[45] e poli(metacrilato de glicidila)[15] também estão sendo modificados com grupos que possuem atividades biocidas. A principal vantagem para emprego destes suportes está relacionada a sua maior capacidade de inchamento em água, meio em que os micro‑organismos normalmente se encontram.

O desinteresse por estes materiais é normalmente justificado pelo maior custo, em relação aos clássicos copolímeros 415

Costa, L. C., Mandu, M. A. L. G. M. R., Santa Maria, L. C., & Marques, M. R. C. Sty-DVB. Não foram encontrados estudos comparativos de avaliação da ação biocida de copolímeros de diferentes graus de hidrofilicidade funcionalizados com os mesmos grupos biocidas. Estudos desta natureza seriam importantes para dimensionar o efeito do grau de hidrofilicidade dos suportes sobre a eficiência biocida das resinas.

Os agentes biocidas normalmente introduzidos aos substratos poliméricos derivam de uma variedade de classes químicas (Tabela 1). Dentre os grupos biocidas mais estudados, destacam-se os sais de amônio e fosfônio quaternários [1,7,8,11,12,16,46-62], os complexos de transferência de carga envolvendo grupos amônio quaternário e iodo [10,12,13,32-44,47,63-66], as N-haloaminas[7,47,67-76], derivados de fenóis e ácido benzóico[50,77,78], sulfoderivados[46,47,79-81]. Além destes grupos, é comum também a introdução de compostos inorgânicos antimicrobianos aos polímeros, especialmente nanopartículas de prata[9,47,82-84]. A escolha destes agentes biocidas é normalmente feita com base em um conhecimento prévio da ação germicida ou bacteriostática dos compostos de baixa massa molecular[10].

Polieletrólitos catiônicos ou poliquats incluem os polímeros contendo grupos amônio, fosfônio, piridínio, anilínio, amidínio, guanidínio, tiourônio, imidazólio, diazônio, carbênio e sulfônico, dentre outros[82]. Os polímeros contendo grupos amônio, fosfônio e piridínio são indiscutivelmente os biocidas poliméricos mais explorados na literatura[47].

A ação biocida dos outros grupos catiônicos tem sido pouco explorada[1,7,12,15,16,47-62]. O mecanismo mais aceito de ação biocida dos polímeros poliquats é baseado na interação destrutiva entre os grupos quaternários e a parede celular e/ou membrana citoplasmática. O polímero contendo

estes grupos é atraído pelos fosfolipídios, constituintes da membrana celular, carregados negativamente. As camadas de fosfolipídios são então redistribuídas através da interação com o material bactericida que possuem múltiplos centros carregados positivamente; em função disso ocorre um deslocamento dos fosfolipídios e desorganização da arquitetura da membrana, provocando a liberação de constituintes celulares e consequentemente morte da bactéria[2,16,46,47,49,52,54,59].

Em diversos trabalhos que tratam do desenvolvimento de resinas poliquats é feita a avaliação da influência do comprimento da cadeia alquil quaternário sobre a eficiência biocida do produto[46,50,51,53-57,59,60]. Como exemplo deste tipo de estudo é possível citar o trabalho de Jiang e colaboradores[56].

Estes autores prepararam uma série de resinas contendo grupos amônio quaternário fazendo a graftização de aminas terciárias trietilamina, tripropilamina, tributilamina e trioctilamina a um copolímero Sty-DVB clorometilado. A atividade antimicrobiana das resinas foi avaliada contra a bactéria gram-positiva S. aureus por meio de ensaios em batelada.

O polímero graftizado com trioctilamina apresentou maior eficiência bactericida seguida por tributilamina, tripropilamina e trietilamina. Os autores sugerem que o aumento do tamanho da cadeia substituinte gera um aumento da hidrofobicidade do polímero e consequentemente favorece a interação com a membrana citoplasmática causando a morte da bactéria.

Em um estudo semelhante, Lu e colaboradores[50] realizaram uma comparação entre a capacidade biocida de monômeros funcionalizados com sais de amônio e fosfônio quaternário e polímeros preparados a partir da polimerização destes monômeros. Este tipo de comparação não é comum na literatura, talvez porque julga-se que um

Tabela 1. Estrutura dos polímeros biocidas comumente estudados[10,47,67,77].

Grupo biocida Complexos de transferência de carga com iodo

Atividade Inibem a função das proteínas e são um forte agente oxidante.

Ref.

Fenóis

Rompem a membrana plasmática e desnaturam as enzimas

[47,48]

N-haloaminas

Os halogênios agem juntamente com os componentes orgânicos da molécula alterando os componentes celulares.

[47]

Sais de amônio quaternário

A interação destrutiva entre os grupos quaternários e os fosfolipídios das membranas celulares causam a ruptura da membrana celular

[2,49]

Sais fosfônio quaternário

416

Estrutura

[10,47]

[2,49]

Polímeros , 25(4), 414-423, 2015

Resinas poliméricas reticuladas com ação biocida: atual estado da arte biocida polimérico tenha sempre menor capacidade que um monômero biocida, por conta do impedimento estérico que o polímero oferece para o contato com as bactérias ou a difusão do agente biocida no meio. No estudo de Lu e colaboradores[50] os monômeros sais de amônio quaternário foram sintetizados pela quaternização de metacrilato de dimetilaminoetila (DMAEMA) com diferentes haletos orgânicos: cloreto de benzila (BC), brometo de butila (BB), brometo de dodecila (DB) e brometo de hexadecila (HB).

A homopolimerização destes monômeros modificados gerou os biocidas denominados DMAEMA-BC, DMAEMA-BB, DMAEMA-DB e DMAEMA-HB respectivamente. A ação biocida dos monômeros e polímeros amônio quaternário aumentou com o aumento da cadeia carbônica. Os autores também comprovaram que os polímeros DMAEMA-BC e DMAEMA-BB, preparados a partir da quaternização de DMAEMA com os haletos de alquila de cadeia menor (cloreto de benzila e brometo de butila, respectivamente), apresentaram maior eficiência biocida que os monômeros quaternizados precursores. Já os polímeros DMAEMA‑DB e DMAEMA-HB, quaternizados com os haletos de alquila de cadeia maior (brometo de dodecila e brometo de hexadecila, respectivamente), mostraram menor ação biocida que os monômeros de origem. Os autores não fornecem explicações para estes dados.

A capacidade desinfetante de iodo e de seus derivados é reportada por diferentes autores, assim como o uso de materiais catiônicos com propriedades bactericidas[10-13,32-44,63-66]. O iodo é conhecido como agente antimicrobiano, pois apresenta facilidade em penetrar na parede celular dos micro-organismos, inibindo a sua síntese vital. É bem conhecido que moléculas de piridina (Py) reagem com iodo formando um complexo molecular estável do tipo n-s, denominado complexo de transferência de carga (CTC). O iodo apresenta uma forte tendência a formar estes complexos mesmo com doadores fracos. Tais complexos usualmente apresentam contribuição de estruturas carregadas e, frequentemente, I3– e I5– resultam destas interações[10]. Devido à facilidade de ancorar o iodo em copolímeros contendo grupos amônio quaternário, o interesse no uso do iodo como desinfetante tem aumentado muito nos últimos anos[10,12,13,64,65].

Em estudos realizados por Jandrey e colaboradores[10,64,65] foi avaliada a influência da composição monomérica do copolímero de 2-vinilpiridina-estireno-divinilbenzeno (2-Vpy‑Sty-DVB) sobre a ação biocida dos complexos de transferência de carga entre o iodo e o nitrogênio da 2-Vpy. Três copolímeros com razões molares entre os monômeros 2-Vpy-Sty-DVB de 70/00/30; 70/10/20 e 70/20/10, respectivamente, foram preparados e impregnados com iodo. Todos os materiais sintetizados neste trabalho foram testados contra suspensão de E. coli, em diferentes concentrações iniciais de célula bacterianas (103 a 107 células mL–1). Os copolímeros não modificados não apresentaram atividade bactericida, enquanto que os seus respectivos complexos poliméricos com iodo apresentaram excelente atividade bactericida. Para esses copolímeros, os pesquisadores sugerem que o mecanismo de ação bactericida envolva interações entre os complexos de transferência de carga e a parede celular negativamente carregada das células de E. coli[10,64,65].

De acordo com o mecanismo de ação, as resinas biocidas podem ser classificadas em desinfetantes poliméricos Polímeros, 25(4), 414-423, 2015

insolúveis de contato (IPCD, do inglês, Insoluble Polymeric Contact Disinfectants) e desinfetantes de liberação de demanda (DRD, do inglês, Demand Release Disinfectants)[10].

As resinas poliméricas que apresentam atividade biocida pelo contato são principalmente resinas de troca aniônica, incluindo as resinas com grupo amônio e fosfônio quaternário.

Nesse caso, acredita-se que a interação entre os microorganismos e o polímero desinfetante ocorra através da carga negativa presente na superfície celular e as cargas positivas na superfície dos polímeros[9,46]. Por outro lado, as resinas do tipo DRD liberam o agente biocida que é difundido após o contato do polímero com o meio e interage com os micro-organismos. Comumente neste caso, o agente biocida encontra-se na forma de contra-íon ou composto de baixa massa molecular disperso na matriz polimérica[47,48].

A capacidade antibacteriana dos IPCD está estritamente relacionada à acessibilidade da solução contaminada aos grupos biocidas presentes na matriz polimérica, enquanto para os polímeros DRD a eficiência está relacionada a capacidade de difusão do agente antimicrobiano no meio.

Tanto o acesso das bactérias aos agentes biocidas quanto à difusão destes agentes biocidas são controlados pelas características morfológicas do suporte[10,12].

Valle e colaboradores[12,13] estudaram copolímeros à base de 2Vpy, na razão molar 2-Vpy-Sty-DVB de 70/10/20, mas variando a composição da mistura diluente: tolueno/n-heptano = 50/50 e 70/30, obtendo dessa forma, polímeros com morfologiasvariadas. Estes copolímeros foram quaternizados com iodeto de metila e acrilonitrila e posteriormente impregnados com iodo. O fator morfológico que contribuiu mais significativamente para a atividade biocida dos produtos finais foi a capacidade de inchamento em meio aquoso. Os copolímeros não modificados não apresentaram ação bactericida significativa contra E. coli, entretanto os copolímeros quaternizados com iodeto de metila ou acrilonitrila mostraram uma pequena ação biocida.

O copolímero de menor porosidade, aquele preparado com composição diluente 50/50, com maior capacidade inchamento em água e quaternizado com iodeto de metila foi o mais ativo (superior a 17% para todas as concentrações de E. Coli testadas -103-107 células mL–1). A incorporação de iodo aos copolímeros quaternizados forneceu materiais com elevada atividade biocida. Os testes de estabilidade demonstraram que estes copolímeros impregnados com iodo são agentes de liberação de demanda (DRD). A maior parte desses copolímeros liberou iodo no meio capaz de matar as células E. coli. Contudo, esse fato não pode ser encarado como prejudicial à proposta do material sintetizado, uma vez que a concentração de iodo liberada no meio era ínfima e ocorreu de forma gradativa[12,13].

Os trabalhos de Jandrey e colaboradores[10,64,65], Valle e colaboradores[12,13] são interessantes porque procuram estabelecer uma relação entre a eficiência das resinas biocidas e as características de porosidade dos suportes poliméricos precursores. Como já comentado, a capacidade antibacteriana das resinas poliméricas são dependentes não apenas das características físico químicas dos grupos biocidas, mas também das características morfológicas do suporte polimérico que suporta estes grupos. A maioria dos trabalhos que tratam do desenvolvimento de polímeros biocidas se limita a desenvolver uma metodologia para a 417

Costa, L. C., Mandu, M. A. L. G. M. R., Santa Maria, L. C., & Marques, M. R. C. preparação do polímero e avaliação da capacidade biocida.

A relação entre as características morfológicas dos suportes poliméricos e a capacidade biocida das resinas é na maioria das vezes negligenciada[24,30].

O grupo N-haloamina é outro grupo muito estudado e que tem se mostrado eficiente contra uma grande variedade de micro-organismos tais como vírus, bactérias, fungos e leveduras[7,48,68]. N-haloaminas são definidos como compostos contendo uma ou mais ligações covalentes nitrogênio‑halogênio, formadas pela cloração de grupos imida, amida ou amina[48].

A introdução destes grupos a suportes poliméricos é comumente realizada a partir da reação desses suportes com anéis heterocíclicos de 5 e 6 membros contendo grupos funcionais amida e imida, seguida de halogenação[7,48,68].

O mecanismo de ação biocida proposto para polímeros contendo grupos N-haloamina é baseado no contato entre os grupos funcionais e o micro‑organismo, o que resulta na liberação do halogênio e morte do micro-organismo[51].

Uma das principais vantagens para a sua aplicação tem sido a sua estabilidade ao pH do meio. O grupo N-haloamina

Figura 1. Estrutura química dos monômeros vinílicos de hidantoína 3-alil-5,5-dimetil-hidantoína (ADMH) e 3-(4’-vinilbenzil)‑5,5-dimetil-hidantoína (VBDMH)[76].

é muito estável, não se decompõem em água para formar produtos tóxicos e não libera halogênio no meio até que ocorra o contato com o micro-organismo[7,11,47,69].

Sun e Sun[76] introduziram grupos N-haloamina a copolímeros de Sty-DVB fazendo a copolimerização de Sty e DVB com os monômeros vinílicos de hidantoína: 3-alil‑5,5‑dimetil‑hidantoína (ADMH) e 3-(4’-vinilbenzil)‑5,5‑dimetil-hidantoína (VBDMH) (Figura 1). Os copolímeros obtidos foram tratados com uma solução de cloro com o objetivo de transformar os grupos hidantoína em N-haloamina. As propriedades biocidas dos derivados N-haloamina foram examinadas contra bactérias gram-negativa e gram-positiva, E. coli e S. aureus, respectivamente. Pelos resultados obtidos, os autores observaram maior atividade biocida contra E. coli, para ambos os derivados N-haloamina, oque foi justificado em função das diferenças estruturais das membranas citoplasmática das bactérias[76].

O grupamento fenólico também é conhecidamente considerado como um agente biocida contra uma série de micro-organismos. Estes compostos danificam as membranas celulares e ocasionam a liberação dos constituintes intracelulares ou causam coagulação intracelular dos constituintes citoplasmáticos, provocando à morte da célula[47].

Jeong e colaboradores[78] estudaram a atividade biocida dos produtos de reação de copolímeros alternados de estireno‑anidrido maleico (SMA) com 4- aminofenol (AP) contra as bactérias gram-negativa e gram-positiva E. coli e S. aureus, respectivamente (Figura 2). Tanto o copolímero modificado SMA-AP quanto o reagente 4-aminofenol mostraram fortes atividades bactericidas contra os dois tipos de bactérias. A atividade do copolímero contra E. coli foi ligeiramente mais baixa que contra S. aureus, sugerindo que o polímero pode ter limitações de difusão através da parede celular das bactérias gram-negativas. Além disso, o reagente 4-aminofenol apresentou maior ação biocida que o polímero SMA-AP, o que foi atribuído a sua maior facilidade de difusão através das paredes celulares das bactérias[78].

Resinas poliméricas contendo grupos sulforados vêm sendo extensamente avaliadas em relação à capacidade complexante de íons metálicos[23,30]. Embora os sulfoderivados possuam conhecida ação biocida, a capacidade biocida de

Figura 2. Reação entre copolímeros alternados de estireno-anidrido maleico (SMA) com 4- aminofenol (AP) visando a preparação do copolímero modificado SMA-AP[78].

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Polímeros , 25(4), 414-423, 2015

Resinas poliméricas reticuladas com ação biocida: atual estado da arte resinas contendo estes grupos ainda é muito pouco explorada na literatura. O desenvolvimento de resinas com essa dupla funcionalidade, capacidade complexante de íons metálicos e ação biocida é extremamente interessante do ponto de vista ecológico e ambiental.

Recentemente Souza e colaboradores[79] incorporaram grupos sulfofosforila a um copolímero à base de Sty-DVB a partir da fosforilação destes copolímeros com PCl3/AlCl3 seguida de reação com CS2 em meio básico (Figura 3). Essas resinas tiveram sua ação biocida avaliadas contra suspensões de E. Coli nas concentrações de 103-107 células/mL. Tanto o produto da primeira etapa (fosforilação) quanto da segunda etapa (formação do grupamento sulfofosforila) apresentaram ação biocida em torno de 100% até a concentração de 105, a partir dessa concentração o material sulfofosforilado apresentou uma eficiência em torno de 80% enquanto o fosforilado caiu para 20%[79].

Costa e colaboradores[80] avaliaram a capacidade biocida de uma resina polimérica hiperreticulada contendo grupos ditiocarbamato. A resina hiperreticulada utilizada neste trabalho foi a resina comercial MN-250 produzida pela Purolite SRL. A preparação da resina ditiocarbamato seguiu a metodologia clássica baseada na nitração dos anéis benzênicos, redução dos grupos nitro e reação dos grupos amino com dissulfeto de carbono. Os produtos dessas reações foram submetidos à avaliação da capacidade bactericida contra suspensão de E. coli nas concentrações de 103-107 células/mL. A resina comercial e os produtos das reações de nitração e redução não apresentaram ação biocida para nenhuma das concentrações de E. Coli avaliadas.

Já a resina contendo grupos ditiocarbamato mostrou ação biocida significativa para todas as concentrações de E. Coli estudadas, sendo que para a concentração de 103 células/mL a ação biocida foi de 92%[80].

Também tem sido estudada a capacidade biocida de compósitos e nanocompósitos metálicos preparados a partir da introdução de partículas metálicas a resinas reticuladas à base de DVB[85-87]. Os estudos de nanomateriais bactericidas são particularmente oportunos considerando o recente aumento de novas linhagens de bactérias resistentes aos mais potentes antibióticos e as potencialidades das partículas em escala manométricas[88].

Dentre os agentes antimicrobianos inorgânicos, a prata tem sido empregada mais extensivamente[47,86]. Embora a ação biocida da prata seja muito bem conhecida, o seu mecanismo de atuação bactericida é somente entendido parcialmente[87]. Muitos estudos têm sugerido que o mecanismode atuação bactericida envolva a interação dos íons prata com macromoléculas biológicas. Íons prata trocam o H+ dos grupos sulfidrila e tiol, inativando as proteínas, diminuindo a permeabilidade da membrana e causando a morte da célula. Outros estudos têm mostrado mudanças estruturais evidentes na membrana celular, bem como a

formação de pequenos grânulos com densidade eletrônica formados pela prata e o enxofre[50] Santa Maria e colaboradores[84] prepararam nanocompósitos de prata fazendo a incorporação de nanopartículas de prata a duas resinas comerciais:Amberlyst15WET; e LewatittVPOC1800, ambas resinas sulfônicas, porém com características de porosidade diferenciadas: a primeira macroporosa; e a segunda do tipo gel. A incorporação de nanopartículas de prata às resinas foi feita através de impregnação inicial de íons Ag+ (tratamento das resinas sulfônicas com AgNO3) seguida de redução com NH4OH na presença de agente protetor (solução gelatina-hidroxietilcelulose). Os compósitos obtidos foram avaliados quanto a sua atividade bactericida contra E. colinas concentrações entre 103 a 107 celulas mL–1.

As atividades bactericidas de todos os compósitos de prata foram significativas, indicando que este metal realmente é eficaz como agente antimicrobiano. De uma forma geral, a atividade biocida decresceuem função do aumento da concentração de bactérias. Esse fato possivelmente pode ser atribuído à saturação do copolímero, já que as soluções foram eluídas sempre na mesma coluna recheada com a resina impregnada com prata. Isto significa que até a eluição da concentração 107 célulasmL–1 de E.coli, mais de 1015 células já haviam passado pela coluna e devem ter formado um biofilme ao redor das pérolas que prejudicaram a interação da prata com novas bactérias[84].

Gangadharan e colaboradores[45] também estudaram a ação biocida de resinas impregnadas com prata, mas introduziram nanopartículas de prata a um copolímero de ácido metacrílico reticulado com DVB. A introdução das nanoparticulas de prata foi feita através de tratamento dos copolímeros com solução de AgNO3 seguida de redução química com boroidreto de sódio. O compósito obtido foi avaliado quanto a sua atividade bactericida empregando o teste de zona de inibição contra duas bactérias gram‑ negativas (E. coli e Pseudomonas aeruginosa) e duas gram-positivas (S. aureus eBacillus subtilis). Para todas as bactérias houve presença de um halo de inibição, indicando poder bactericida[45].

As propriedades bactericidas da prata, em adição às características dos polímeros como resistência mecânica e baixa massa específica, fornecem atributos únicos as resinas impregnadas com nanopartículas de prata, que garantem vantagens em relação às técnicas atualmente utilizadas para desinfetar a água[84,87]. Contudo, torna-se importante avaliar a toxicidade deste metal tanto para o meio ambiente quanto para o ser humano, além da avaliação da estabilidade dessas resinas, se ocorre uma possível lixiviação do metal introduzido na matriz polimérica[10,12,13,64,65,87]. Sendo partículas extremamente pequenas, as nanopartículas de prata devem possuir uma capacidade de deslocamento por todo o meio ambiente considerável, o que as tornam disponíveis tanto na atmosfera, no meio aquático, bem como no solo[88,89]. Assim, são necessárias mais informações acerca da sua toxicidade e determinação dos níveis seguros de exposição, para que

Figura 3. Rota para a introdução de grupos sulfofosforila a copolímeros Sty-DVB[79].

Polímeros, 25(4), 414-423, 2015

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Costa, L. C., Mandu, M. A. L. G. M. R., Santa Maria, L. C., & Marques, M. R. C. as resinas impregnadas com nanopartículas de prata possam ser utilizadas no tratamento de águas.

A maioria dos trabalhos que estuda a ação biocida de resinas poliméricas avalia a ação bacteriológica destes materiais por meio de testes de halo de inibição e/ou ensaios em batelada. Os estudos que utilizam ensaios em batelada como método de avaliação biocida quase sempre não exploram variações de massa de resina, tempo de contato e concentração de bactérias no meio. Estes dados são de grande importância para efeitos de comparação da ação biocida dessas resinas e auxiliam no desenvolvimento de novos materiais mais eficientes.

Por se tratarem de materiais infusíveis e insolúveis, as resinas biocidas e nanocompósitos biocidas podem ser utilizados em processo de colunas, e estas colunas podem ser reutilizadas após uma simples regeneração. Dessa forma, o elevado custo inicial do material é recuperado em curto prazo, fazendo com que a relação custo/benefício deste processo de tratamento de águas seja economicamente viável[14]. Os estudos em coluna são muito pouco explorados na literatura, entretanto alguns dados obtidos a partir destes estudos, tais como, ponto de ruptura, capacidade de trabalho, são extremamente importantes do ponto de vista de aplicação das resinas biocidas em macro escala.

3. Conclusões Resinas biocidas preparadas a partir da introdução de grupos biocidas a suportes poliméricos reticulados apresentam grande potencial para tratamento de águas contaminadas com micro-organismos patogênicos. Dentre os grupos biocidas incorporados às resinas poliméricas percebe-se que há um grande interesse pelos grupos amônio e fosfônio quaternário, grupos N-haloamina e nanocompósitos de prata. A capacidade biocida de resinas contendo grupos sulfurados ou outras nanopartículas metálicas têm sido ainda pouco explorada na literatura, embora muitos desses compostos possuam conhecida ação biocida. Sabe-se que as propriedades antibacterianas das resinas biocidas estão relacionadas não só com a capacidade bactericida dos grupos, mas também com a distribuição adequada desses grupos ativos na superfície da rede polimérica. Por este motivo, é de grande relevância o estudo para obter suportes poliméricos com estrutura físico‑química que favoreça o contato com os micro-organismos ou a difusão do biocida no meio. Há alguns trabalhos na literatura que tem se esforçado neste sentido, procurando estabelecer relações entre as características morfológicas dos suportes poliméricos e a capacidade biocida das resinas produzidas a partir destes suportes. Contudo, são necessários estudos mais detalhados de influência do grau de porosidade e capacidade de inchamento dos suportes poliméricos sobre a capacidade biocida das resinas.

4. Agradecimentos Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) e Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) pelo apoio financeiro.

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Enviado: Abr. 07, 2014 Revisado: Abr. 06, 2015 Aceito: Abr. 24, 2015

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