Polímeros: Ciência e Tecnologia (Polimeros) 5th. issue, vol. 28, 2018

PolĂ­meros

Brazilian Polymer Association (ABPol)

VOLUME XXVIII - Issue V - Oct./Dec., 2018

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

P o l í m e r o s - I ss u e V - V o l u m e X X V I I I - 2 0 1 8 I n d e x e d i n : “ C h e m ic a l A b s t r a c t s ” — “ RA P RA A b s t r a c t s ” — “A l l - R u s s i a n I n s t i t u t e o f S ci e n c e ­T e c h n ic a l I n f o r m a t i o n ” — “ R e d d e R e v i s t a s C i e n t i f ic a s d e A m e r ic a L a t i n a y e l C a r i b e ” — “ L a t i n d e x ” — “ W e b o f S ci e n c e ”

and

Polímeros E d i t o r i a l C o u nci l Antonio Aprigio S. Curvelo (USP/IQSC) - President

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

Members Adhemar C. Ruvolo Filho (UFSCar/DQ) Ailton S. Gomes (UFRJ/IMA) Alain Dufresne (Grenoble INP/Pagora) Antonio Aprigio S. Curvelo (USP/IQSC) Bluma G. Soares (UFRJ/IMA) César Liberato Petzhold (UFRGS/IQ) Cristina T. Andrade (UFRJ/IMA) Edson R. Simielli (Simielli - Soluções em Polímeros) Edvani Curti Muniz (UEM/DQI) Elias Hage Jr. (UFSCar/DEMa) Eloisa B. Mano (UFRJ/IMA) João B. P. Soares (UAlberta/DCME) José Alexandrino de Sousa (UFSCar/DEMa) José António C. Gomes Covas (UMinho/IPC) José Carlos C. S. Pinto (UFRJ/COPPE) Júlio Harada (Harada Hajime Machado Consutoria Ltda) Laura H. de Carvalho (UFCG/DEMa) Luiz Antonio Pessan (UFSCar/DEMa) Luiz Henrique C. Mattoso (EMBRAPA) Marco-Aurelio De Paoli (UNICAMP/IQ) Osvaldo N. Oliveira Jr. (USP/IFSC) Paula Moldenaers (KU Leuven/CIT) Raquel S. Mauler (UFRGS/IQ) Regina Célia R. Nunes (UFRJ/IMA) Richard G. Weiss (GU/DeptChemistry) Rodrigo Lambert Oréfice (UFMG/DEMET) Sadhan C. Jana (UAKRON/DPE) Sebastião V. Canevarolo Jr. (UFSCar/DEMa) Silvio Manrich (UFSCar/DEMa)

A ss o ci at e E d i t o r s Adhemar C. Ruvolo Filho Alain Dufresne Bluma G. Soares César Liberato Petzhold José António C. Gomes Covas José Carlos C. S. Pinto Paula Moldenaers Richard G. Weiss Rodrigo Lambert Oréfice

Sadhan C. Jana

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

www.editoracubo.com.br

“Polímeros” is a publication of the Associação Brasileira de Polímeros São Paulo 994 St. São Carlos, SP, Brazil, 13560-340 Phone: +55 16 3374-3949 emails: abpol@abpol.org.br / revista@abpol.org.br http://www.abpol.org.br Date of publication: December 2018

Financial support:

Available online at: www.scielo.br

Polímeros / Associação Brasileira de Polímeros. vol. 1, nº 1 (1991) -.- São Carlos: ABPol, 1991Quarterly v. 28, nº 5 (Oct./Dec. 2018) ISSN 0104-1428 ISSN 1678-5169 (electronic version)

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

1. Polímeros. l. Associação Brasileira de Polímeros.

Polímeros, 28(5), 2018

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

Editorial Section News....................................................................................................................................................................................................E3 Agenda.................................................................................................................................................................................................E4 Funding Institutions.............................................................................................................................................................................E5 ABPol 30 Years.................................................................................................................................................................................... E6

O r i g in a l A r t ic l e Crystallization, thermal and mechanical behavior of oligosebacate plasticized poly(lactic acid) films Erika Martins Inácio, Maria Celiana Pinheiro Lima, Diego Holanda Saboya Souza, Lys Sirelli and Marcos Lopes Dias........................... 381

Sericin as compatibilizer in starch/ polyester blown films Patrícia Salomão Garcia, Franciele Rezende Barbosa Turbiani, Alessandra Machado Baron, Guilherme Luiz Brizola, Mariane Alves Tavares, Fabio Yamashita, Daniel Eiras and Maria Victória Eiras Grossmann..................................................................... 389

Influence of solvent used on oxidative polymerization of Poly(3-hexylthiophene) in their chemical properties Juliana de Castro Macêdo Fonsêca and Maria dos Prazeres Arruda da Silva Alves..................................................................................... 395

Use of chitosan in the remediation of water from purification of biodiesel Erivelton César Stroparo, Krissina Camilla Mollinari and Kely Viviane de Souza........................................................................................ 400

Synthesis, characterization and antibacterial activity of novel poly(silyl ether)s based on palm and soy oils Issam Ahmed Mohammed, Syed Shahabuddin, Rashmin Khanam and Rahman Saidur................................................................................. 406

Stability and rheological behavior of coconut oil-in-water emulsions formed by biopolymers Eliana da Silva Gulão, Clitor Junior Fernandes de Souza, Angélica Ribeiro da Costa, Maria Helena Miguez da Rocha-Leão and Edwin Elard Garcia-Rojas............................................................................................................................................................................... 413

Investigation on influence of stamp forming parameters on formability of thermoplastic composite Sugumar Suresh and Velukkudi Santhanam Senthil Kumar............................................................................................................................. 422

Preliminary analysis of N-vinylpyrrolidone based polymer gel dosimeter Juliana Rosada Dias, Thyago Fressatti Mangueira, Roseany de Vasconcelos Vieira Lopes, Maria José Araújo Sales and Artemis Marti Ceschin..................................................................................................................................................................................... 433

Quantification by FT-IR (UATR/NIRA) of NBR/SBR blends Joyce Baracho Azevedo, Lidia Mattos Silva Murakami, Ana Carolina Ferreira, Milton Faria Diniz, Leandro Mattos Silva and Rita de Cássia Lazzarini Dutra........................................................................................................................................................................ 440

PET glycolysis optimization using ionic liquid [Bmin]ZnCl3 as catalyst and kinetic evaluation

Carlos Vinícius Guimarães Silva, Eloi Alves da Silva Filho, Fabrício Uliana, Luciana Fernanda Rangel de Jesus, Carlos Vital Paixão de Melo, Rosangela Cristina Barthus, José Guilherme Aquino Rodrigues and Gabriela Vanini................................... 450

Core-shell magnetic particles obtained by seeded suspension polymerization of acrylic monomers Jacira Aparecida Castanharo, Ivana Lourenço de Mello Ferreira, Manoel Ribeiro da Silva and Marcos Antonio da Silva Costa............... 460

Preparation of gelatin beads treated with glucose and glycerol Débora Vieira Way, Márcio Nele and José Carlos Pinto................................................................................................................................. 468

Cover: Cover: ABPol 30 years.

Arts by Editora Cubo.

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Polímeros, 28(5), 2018

SABIC launches new ultra-high melt flow Polypropylene Resin for Nonwoven Fabrics SABIC launches an innovative new ultra-high melt flow polypropylene (PP) resin to enhance properties in melt-blown fibers for nonwoven fabrics. SABIC PP 514M12, the new product, will meet the needs of a wide range of potential end-uses in personal hygiene applications and other market segments.

The new product is expected to be commercially available by the end of 2018.

Designed on phthalate-free and odor-free technology, SABIC PP 514M12 material, offers very good processability for melt-blown fibers with high levels of drawability, spinnability and uniformity. The nonwovens developed to combine high barrier properties and absorption with breathability in thin and lightweight, high-performance webs of enhanced conformability and reduced material consumption.

SABIC PP 514M12 polymer is used to provide high purity and enhanced customer convenience over incumbent melt blown resins because of its phthalate-free, single-material technology.

The polymer resin is produced in regular pellet form for easy handling, storage, and use.

The new innovative polypropylene product for melt-blown fibers offers advanced material solutions to help manufacturers to push the limits of consumer safety and convenience, function, sustainability and cost control and at the same time meet strict hygiene and consumer protection standards.

SABIC PP 514M12 has the flexibility to meet specific customer’s application needs. The trial runs in collaboration with a dedicated machine manufacturer’s latest high-speed machine using production quantities of the new melt blown PP have shown very good processing and performance properties.

SABIC offers an extensive PP portfolio for a range of industry segments that include automotive, packaging, healthcare, home appliances and construction next to Personal Hygiene.

Its dedicated global segment organization offers polymer portfolio designed to cater needs of its customers for innovation, service and application development around the world.

Source: Plastics Insight - www.plasticsinsight.com

NSF awards two grants for polymer research Two recent grants awarded by the National Science Foundation will help scientists in the College of Natural Resources and Environment create new ways to use renewably sourced plant and wood polymers to tackle long-standing challenges in medical drug solubility and lignin utilization.

Kevin Edgar, professor in the Department of Sustainable Biomaterials and associate dean of Virginia Tech’s Graduate School, has been conducting research on the design of biodegradable, sustainably based polymers that can help enhance the abilities of orally administered drugs to reach the bloodstream. Edgar’s research, in a joint project with Lynne Taylor, professor of industrial and physical pharmacy at Purdue University, focuses on using polymers designed from cellulose,

the structural component of plants. The polymers work to prevent the crystallization of a drug’s molecules when it is in pill form and during transport through the gastrointestinal tract so that medication can effectively reach the bloodstream.

“The method that we use requires a specific mix of polymer and drug that ensures that the drug is so perfectly dispersed in the polymer that no two molecules of drug are next to each other,” said Edgar, who is also affiliated with Virginia Tech’s Macromolecules Innovation Institute. “Then the polymer has to be designed to release the drug within the gastrointestinal tract, which is mostly water.” The applications of Edgar’s research are wide-reaching. Many current medications have solubility issues; to ensure that enough medication reaches the bloodstream, patients are prescribed higher doses. The excess drugs that are not absorbed from a patient’s gastrointestinal tract have the potential to cause toxic side effects and carry the risk of negatively impacting water treatment systems when they pass through the body. Drugs currently in development that may cause toxicity due to these solubility issues could be used successfully with assistance from natural polymers, bringing powerful new drugs to patients.

The development of a new polymer that can increase bioavailability for a range of drugs has the potential to improve current medication regimens, minimize patient side effects, and reduce drug costs. Edgar and Taylor have already made strides in the field of polymer research to prevent drug crystallization, with 35 joint publications credited to their research groups.

Li Shuai, assistant professor in the Department of Sustainable Biomaterials, has been working to develop a new chemical process to replace current petroleum-reliant resins with a renewable material made from lignin, an organic polymer found in trees.

Lignin is a waste product of the paper pulping process and is typically burned as a low-value fuel. “Cellulose is the fiber that maintains the cell wall,” Shuai said. “If you just have cellulose fiber, a plant cannot stand very well. It’s like steel-reinforced concrete: you need both concrete and steel to maintain structure.

Lignin polymer is a kind of natural glue or adhesive that holds the cellulose fibers together.”

Shuai notes that the challenge of how to utilize lignin has existed since the pulping industry came into existence hundreds of years ago. He estimates that only 5 percent of lignin is currently developed into products, a number that he would like to see increase. His research proposes a new catalytic process that will enhance the reactivity of lignin products, making them a useful alternative for a variety of industrial products, from kitchen countertops to adhesives.

“The structure of lignin is very complicated; it’s very hard to utilize,” Shuai noted. “I’m trying to break down the polymer into single, small molecules, so that we can use them to make new polymers that will maintain their adhesive properties.” Lignin research holds the promise of replacing phenol formaldehyde resins, petroleum-based products that are widely used in manufacturing commercial products. Shuai hopes that finding a renewable alternative for this crucial resin will have additional positive effects on the environment by reducing the amount of lignin that reaches waste streams.

Source: EurekAlert! - www.eurekalert.org

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

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

February

June

17th Polyethylene Films Date: February 5-7, 2019 Location: Coral Springs, United States Website: www.ami.international/events/event?Code=C947 PLASTEC West Date: February 5-7, 2019 Location: Anaheim, United States Website: plastecwest.plasticstoday.com International Conference on Polymers and Plastics, Artificial Intelligence (ICPPAI 2019) Date: February 23-24, 2019 Location: Shanghai, China Website: irnest.org/icppai-feb-2019 1st International Symposium on Polymer Chemistry and Applications (SICPA-2019) Date: February 23 -25, 2019 Location: Taghit, Algeria Website: www.sicpa-dz.com Polymers for Fuel Cells, Energy Storage, and Conversion Date: February 24-27, 2019 Location: Pacific Grove, United States Website: polyacs.net/Workshops/19Fuel/home.html

11th Polyimides & High Performance Polymers Conference (STEPI11) Date: June 2-5, 2019 Location: Montpellier, France Website: stepi.umontpellier.fr Oil & Gas Polymer Engineering Date: June 4-5, 2019 Location: Houston, United States Website: www.ami.international/events/event?Code=C0981 Polymers: Gordon Research Seminar - Innovations in Design, Fabrication and Application of Polymeric Materials Date: June 8-9, 2019 Location: South Hadley, United States Website: www.grc.org/polymers-grs-conference/2019 Polymers: Gordon Research Conference Date: June 9-14, 2019 Location: South Hadley, United States Website: www.grc.org/polymers-conference/2019 PLASTEC East Date: June 9-14, 2019 Location: New York, United States Website: advancedmanufacturingnewyork.com/plastec 13th International Workshop on Polymer Reaction Engineering Date: June 11-14, 2019 Location: Hamburg, Germany Website: dechema.de/en/PRE2019.html 6th International Conference and Exhibition on Polymer Chemistry Date: June 12-13, 2019 Location: Montreal, Canada Polymer Foam Date: June 18-19, 2019 Location: Pittsburgh, United States Website: www.ami.international/events/event?Code=C0968

March Polymers in Footwear Date: March 5-6, 2019 Location: Woburn, United States Website: www.ami.international/events/event?Code=C971 4th International Conference on Polymer-Biopolymer Chemistry Date: March 14-15, 2019 Location: Amsterdam, Netherlands Website: polymer-biopolymer.euroscicon.com Plástico Brasil Date: March 25-29, 2019 Location: São Paulo, Brazil Website: www.plasticobrasil.com.br 4th Edition of International Conference and Exhibition on Polymer Chemistry Date: March 28-30, 2019 Location: Rome, Italy Website: polymerchemistry.euroscicon.com

April Fire Retardants in Plastics Date: April 2-3, 2019 Location: Pittsburgh, United States Website: www.ami.international/events/event?Code=C961 FEIPLASTIC Date: April 8-12, 2019 Location: São Paulo, Brazil Website: www.plasticobrasil.com.br

May 6th International Symposium Frontiers in Polymer Science Date: May 5-8, 2019 Location: Budapest, Hungary Website: www.elsevier.com/events/conferences/frontiers-inpolymer-science International Conference of the Polymer Processing Society (PPS-35) Date: May 26-30, 2019 Location: Çeşme-Izmir, Turkey Website: www.pps-35.org

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July Polymer Composites and High Performance Materials Date: July 22-25, 2019 Location: Sonoma, United States Website: polyacs.net/Workshops/19Composites/home.html

September 13th International Symposium on Ionic Polymerization (IP 2019) Date: September 8-13, 2019 Location: Beijing, China Website: iupac.org/event/international-symposium-on-ionicpolymerization-ip-19 International Rubber Conference (IRC 2019) Date: September 10-12, 2019 Location: London, United Kingdom Website: www.iom3.org/rubber-engineering-group/event/ international-rubber-conference-irc-2019

October 15th Congresso Brasileiro de Polímeros (15th CBPol) Date: October, 27-31, 2019 Location: Bento Gonçalves, Rio Grande do Sul, Brazil Website: www.cbpol.com.br

November 31st International Plastics & Rubber Machinery, Processing & Materials Exhibition Date: November 14-17, 2019 Location: Jakarta - Indonesia Website: www.plasticsandrubberindonesia.com Plastics & Rubber Vietnam Date: November 27-29, 2019 Location: Hanoi - Vietnam Website: plasticsvietnam.com Polímeros, 28(5), 2018

ABPol Associates Sponsoring Partners

Collective Members Master Polymers Ltda.

Nexo International Ltda.

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

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

PolĂ­meros, 28(5), 2018

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ISSN 1678-5169 (Online)



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

ABPol 30 Years Connecting the Brazilian Polymer Community Foundation On September 23, 1988, the Associação Brasileira de Polímeros, ABPol (Figure 1) was officially founded.

The idea to create an society to foster the polymer activities in Brazil arose in March 1988, through professors from the Polymer Group of the Materials Engineering Department of the Federal University of São Carlos (DEMa/UFSCar).

The idea spread throughout Brazil, being a point of discussion among university professors, professional

from industry and research centers, working in the polymer field. The society would be an autonomous and impartial organization, aimed to gather professionals in the polymer field, whose objectives would be to disseminate technical and scientific information through a Brazilian Technical Journal (to be created), and to promote and support national and international events as conferences, courses, meetings, etc.

Figure 1. (a) Foundation of the ABP - Associação Brasileira de Polímeros during the 1º Encontro Nacional da Associação Brasileira de Polímeros, (b) signature of the Foundation Act by Professor Eloisa Mano (she is still active up to now).

The “Associação”, as it comes up to be known, would have a different focus from those common at the time which were mainly focused in business, since the promotion of scientific congresses of high technical level and scientific journals were not at that moment a priority of the industrial sector. Another important point brought up was that it should not only bring together people working in companies and institutions, but also any professional interested in the polymer field. Having this aim, in June 1988 preparations for the founding of the Associação began, and an official ceremony took place at DEMa/UFSCar, since there was an group of people that would provide all necessary technical support to organize the event. Although up to that moment the Associação did not exist juridical, many companies support it sponsoring the event. After contacting other similar societies, a statute was written and later approved in assembly.

On September 23, 1988 (first spring day that year) with the presence of 145 people (Chart 1) the “1º Encontro Nacional da Associação Brasileira de Polímeros” (1º National Meeting of the Brazilian Polymer Association), the Foundation Act of ABP - Associação Brasileira de Polímeros, was announced (Figure 2). All participants present in this official ceremony,

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activity related to the polymer field were formally enrolled as founding members of ABPol. Many institutions supported the foundation of ABPol, and were considered “Founding Sponsors of ABPol”: Materials Engineering Department and Graduate Program in Sciences and Materials Engineering both from UFSCar, IBM Brazil Ltda., Polisul Petroquímica SA, Resana Petroquímica SA, Polialdem Petroquímica SA and Polipropileno SA. Many of these companies merged forming greater petrochemical companies today.

The original acronym chosen was ABP, but since there were already other societies with it, shortly afterwards it was renamed to ABPol (Figure 3) which stands up to now.

During the event, a roundtable discussion was held with a number of celebrities, including Professor Eloisa Mano, who with a pleasant, motivational and challenging speech, said: “... it is easy to create such a society, the hard part is maintain it, make it to grow, and achieve the set goals.”

On that day, the first Provisional Council of ABPol was elected, and then in a meeting same days afterwards the first provisional Board of Directors set (Chart 2).

Polímeros, 28(5), 2018

ABPol 30 Years Chart 1. Participants present in the 1º National Meeting of the Brazilian Polymer Association, initially named by ABP and later renamed as ABPol. Silvio Manrich Elias Hage Júnior Rosario E. Suman Bretas José Augusto Marcondes Agnelli Sebastião Vicente Canevarolo Jr. Abigail Lisbão Simal Rinaldo Gregório Filho José Alexandrino de Sousa Amadeu J. Logarezzi Luiz Antônio Pessan Sati Manrich Edson Simielli Aloísio Manso Silva Juan Raul Quijada Eloisa Biasotto Mano Ivo Bocatto Geraldo R. de Almeida Rubens Rela Filho Wilson Z. Franco Filho Giovanni Molinaro Luiz Carlos Roncaglione Wladimir Pedro Castanheiro Silvio José Marola Heloisa de Moraes Grimaldi Luiz Henrique Land Manier Marcus Luiz Pontarolli Roberto Klaus Huessner Luiz Adolfo Bascheira Mario Colin Fernando de Almeida Castro Odair Timi Luis Fernando D. Cassinelli Warney José Juns Áiala Luiz Carlos Martins Wagner Frollini Zabotto Nelson José Piccoli Antônio Celso Jiampaulo Ferraz Marcos Rogério de Souza Atílio Eduardo Reggiani Rose Mary Araújo Gondim Mariângela Palácio R. Sanches João Alioti Júnior

Polímeros, 28(5), 2018

Henrique Northfleet Neto Carlos Ventura D’Alkaine Eloy S. Alvarez André Victor Danc Edison Bittencourt Frahnz Hintermayer Flaisa Pinotti Zabotto Arnaldo Antônio Ditlef Jean Richard Dasnoy Marinho Hans Jurgen Kestenbach Sérgio Antônio Balbi Paulo Aparecido dos Santos Nádia Chaves Pereira de Souza Antônio Mário Donato Nelson Rondo Sérgio Paulo Campane Filho Antônio José Felix de Carvalho Marcelo Aparecido Chinelatto Carlos Koiti Kobayashi Hélio Kiyoiti Motooka Marco Antônio Simabuko Augusto César Lovo Roberto Araújo Moncorvo Zoé Cecília de Araujo Moncorvo Marino Francesco Gaiofatto Márcia Papa Ciminelli Luis Ernesto Roca Bruno Aparecido D. Silveira Nelson Fumio Kunieda Sérgio Monsanto de Paula Adhemar Ruvolo Filho Cláudio Bartholomeu de Barros Disnei Aparecido Lamas Maria da Conceição Geraldes Marcus Vinícius Caneppele Gil de Carvalho Paulo Roberto A. S. Branco Paulo Sérgio Braga de Souza Armando Braga de Souza Mário E. P. Reis Erika Kunieda José Roberto Bertolino

Marco Antônio Boix do Nascimento Eliezer Gibertoni Luiz Fernando Rodrigues Brano Luiz Gonzaga de Carvalho Geber D. Pedroza Walter Paschoalino Filho Sérgio Sanchez Gilmar A. S. Martins Alexandre A. R. de Pontes Etore Luis Della Barba, Milton Gonçalves Barbosa Roberto Nardinelli Filho Benedito Laércio de Camargo Lygia Ribeiro Gil Keiji Maeshiro Wladimir de Souza Moraes Paulo Sérgio Budin Éderson Catóia Ricardo Luis Duarte de Souza Luciano Rodrigues Nunes Walmir H. Wada Luiz Di Souza Roberto M. Mitsuoka Dilermando N. Travessa Adriana Scoton Antônio João Carlos Colmenedo Celso Morgon Aldo Sussumu Tanaka Antonio Pascoal Del’Arco Jr. Luis Segnini Pulitano Maria Cristina B. de Jesus João Carlos Girioli Altair Pupin Júnior Tomaz T. Ishikawa Maurizio Ferrante Nilson Casimiro Pereira Antônio Carlos Rosalini Maria Zanin Sebastião Elias Kuri Mori Yoshiro Jan Willem Orberg

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ABPol 30 Years

Figure 2. ABPol Foundation Act. E8

PolĂ­meros, 28(5), 2018

ABPol 30 Years

Figure 3. a) The original ABP logo, and b) the actual one of ABPol. Chart 2. Past and Present Presidents of ABPol since its foundation, and current Board of Directors and Council.

First provisional Board of Directors,

ABPol’s Past and Present Presidents Name

1988 to 1989

Silvio Manrich

President: Silvio Manrich (UFSCar) Vice-President: Jan W. Oberg (Resana)

Francisco J. X. de Carvalho Ailton de Souza Gomes Edson Roberto Simielli

Diretors: Edison Bittencourt (Unicamp) Eloy Alvarez (Proquigel)

Domingos Antonio Jafelice

Luiz Henrique Northfleet (UFRGS) Mário Colin (Ambalit)

Raquel S. Mauler

Paulo Roberto Branco(Royal Diamond Dielétricos S.A.)

Dellyo Ricardo S. Álvares

Sebastião V. Canevarolo Jr. (UFSCar) Zoé Cecília de Araújo Moncorvo (Pepasa)

Luiz Antonio Pessan José Donato Ambrósio

Mandate 1988 a 1989 1989 a 1991 1991 a 1993 1999 a 2001

Institution DEMa - UFSCar

1993 a 1995

CTA

1995 a 1997 1997 a 1999 2001 a 2003 2003 a 2005 2005 a 2007 2007 a 2009 2009 a 2011 2011 a 2013 2013 a 2015 2015 a 2017 2017 atual

IMA - UFRJ GE Plastics S.A. DSM IQ - UFRGS CENPES -PETROBRAS DEMa - UFSCar CCDM - UFSCar

Actual Board of Directors President: José Donato Ambrósio - (CCDM - UFSCar) Vice President: Marco-Aurélio De Paoli - (IQ - UNICamp) Executive Directors* Director of Innovation and Technology: Rodrigo Lambert Oréfice - (UFMG) Director of Publications: Cesar Liberato Petzhold - (IQ - UFRGS) Director of Technical Commissions: Derval dos Santos Rosa - (CECS - UFABC) Director of Regional Branches: Edvani Curti Muniz - (DQ - UEM) Event Director: Antonio José Felix de Carvalho - (EESC - USP) Director of Business Relations: Marco Antonio Cione - (BRASKEM) Technical Scientific Director: Adhemar Colla Ruvolo Filho - (DEMa - UFSCar) Directors of the Regional Branches Eastern Regional Director: Ana Lucia Nazareth da Silva - (IQ - UFRJ) Regional Directorate of Minas Gerais: Daniel Pasquini - (IQ-UFU) Northeast Regional Director: Josiane Dantas Viana Barbosa - (CIMATEC-SENAI) South Regional Director: Otavio Bianchi - (CCET - UCS) Fiscal Council Edson Noriyuki Ito - (DEMat - UFRN) Luiz Antonio Pessan - (DEMa - UFSCar) Valdir Soldi - (IBTeC-LC) * All Executive Directors belong to the ABPol’s Council

Polímeros, 28(5), 2018

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ABPol 30 Years Actual ABPol’s Council Members Edcleide Maria Araújo – (DEMa - UFCG) Élcio Hobi de Oliveira - dpUNION Elisabete Frollini – (IQSC – USP) Hélio Wiebeck – (POLI – USP) Julio Harada - Harada Hajime Machado Consultoria Ltda Laura Hecker de Carvalho – (UAEMa - UFCG Leonardo Bresciani Canto – (DEMa – UFSCar) Luis Fernando Dagnoni Cassinelli - Elabora Consultoria Luiz Henrique Catalani – (IQ – USP) Mara Zeni Andrade – (CCET- UCS) Marcos Esteves de Oliveira - ARLANXEO Rafael Barbosa Rodrigues - SABIC - Innovative Plastics Raquel Santos Mauler – (IQ – UFRGS) Sebastião Vicente Canevarolo Jr. – (DEMa –UFSCar) Sérgio Henrique Pezzin – (CCT/UDESC) Yêda Medeiros Bastos de Almeida – (DEQ - UFPE)

With the foundation and its registration in the Forum, meetings of the provisional Board of Directors and Council were held to outline the objectives and activities of ABPol. As ABPol did not yet have its headquarters, the everyday work was carried out in the residence of Prof.

Silvio Manrich, the first President of ABPol. However, in 1989, DEMa/UFSCar provided a small room inside the Polymers Laboratory to ABPol set its headquarters, and a full-time secretary was hired. Aiming to expand nationally its acceptance, a 2º Meeting of the Brazilian Polymer Association was organized and held on July 13‑14, 1989, with more than 300 participants. The place was carefully chosen at FIESP São Paulo – SP, a building at the financial heart of São Paulo, with sponsorship from CNPq, IBM, FIESP and Aprobad. The main theme of the meeting was “Polymers: Brazil’s situation in the global context”, and the objective was to map teaching and research institutions in Brazil. At this meeting, a general assembly was held to approve the Bye-Laws of ABPol. Sixteen teaching institutions presented their undergraduate and graduate teaching programs, their laboratorial infrastructure and research groups. Once consolidated as an institution, ABPol had two major challenges within

its main objectives as a national institution, which were to hold a national scientific and technological Congress and create a journal that would disseminate the research works undertaken in Brazil. In 1991 the 1º Congresso Brasileiro de Polímeros (1st CBPol, 1º Brazilian Polymer Congress) was held, and in the same year the first issue of the journal “Polímeros: Ciência e Tecnologia” was launched. The history of these two great achievements and the updated situation of them will be discussed later.

As commented by Silvio Manrich in the 20-year ABPol document, with the so-called Brazilian Financial Collor Plan in the early 90’s, which froze all the money citizens hold in the banks, corporations and non-profit institutions, such as ABPol, went through a deep financial crisis. This has taken ABPol to a zero-cash level for many months and forced it to stop its activities. However, thanks to many partners, soon afterwards ABPol could recover, by asking the support of the partners and the result was surprising, recalls Edson Simielli, president in that period. With the financial crisis over ABPol could restart its activities, the most pressing demand was to keep the finances and the payroll of the staff honored.

Some significant achievements in the ABPol’s history.

1988 – Foundation of ABPol during the 1st. Encontro Nacional da Associação Brasileira de Polímeros. São Carlos, SP. E10

1988 – Front page of the 1st Bulletin of ABPol, run in a series up to 6.

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ABPol 30 Years

1991 – 1st Congresso Brasileiro de Polímeros - 1st CBPol. São Paulo, SP.

1992 – Attendees present at the Seminário das Comissões Técnicas of ABPol, São Paulo, SP.

1993 – Opening ceremony of the 2nd Congresso Brasileiro de Polímeros - 2nd CBPol. Sao Paulo-SP.

1991 – Front page of the 1st issue of the journal Polímeros: Ciência e Tecnologia, showing the 1º Brazilian Polymer Congress logo.

1997 – Prof. Ailton Gomes, president of ABPol, receives the ABPol’s accreditation handed by the Brazilian Minister of Science and Technology - MCT as Sectorial Technology Entity for Polymers - ETS-Polymers.

1992 – 1st ABPol’s Headquarters (a rented house).

1999 – Creation of the two first Regional Branches of ABPol. Later on another two were created, covering almost all the Brazil’s country.

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ABPol 30 Years

2007 – ABPol acquire a house and set its own Headquarters in São Carlos, SP at São Paulo Street, 994.

2000 – 2nd ABPol’s Headquarters (rented upstairs room).

2017 – The ABPol’s Headquarters, after a complete renovation.

2006 – Attendees during the IUPAC/MACRO 2006, held in Rio de Janeiro, RJ, organized by ABPol.

2009 – 10th Congresso Brasileiro de Polímeros - 10th CBPol Foz do Iguaçu-PR, with more than 1,000 participants.

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2018 – ABPol’s scientific journal “Polímeros: Ciência e Tecnologia” gets internationalized by publishing all its content in English. The front headlines states “Polímeros, now only in English”.

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ABPol 30 Years

Reports from the Past and Present Presidents of ABPol. Silvio Manrich: 1988-1989, 1989-1991, 1991-1993 and 1999-2001 “ABPol was born from a “hallways talk” that some professors from the Materials Engineering Department of Federal University of São Carlos, DEMa/UFSCar had on a typical morning in March 1988. The name of the society was straightforward thought, it had to be ABP (later became ABPol), after all we had already running in the materials ​​ field the Brazilian Ceramics Association - ABC (founded in 1933) and the Brazilian Metal Association - ABM (founded in 1944). Coincidentally, the new Associação was also established in a year with two repeating digits, 1988, just like the other two. After the second major meeting of ABPol, in which the “First Elected Council” was also instaled for a two-year term office, they began the preparation for the two major conferences planned ahead. The first was 1º Congresso Brasileiro de Polímeros, 1st CBPol. Perhaps this was one of the most audacious act of the Associação, it was decided to hold the event at the Anhembi Convention Center, the major and most important conference center in São Paulo city. The 2nd CBPol was not different.

As the third Board of Directors took seat, they immediately had to decide, with help from the Council of Directors where to hold the second congress. Again the decision was to be held in the Anhembi Convention Center. This initially sounded like a bomb, because everybody knew the great effort was to hold the 1st CBPol. It was, however, an opportunity to definitively set the image of a “strong Association” in the country. In the 2nd CBPol, more support, peace of mind and more financial surpluses were obtained that sustained ABPol for some time. Thus over the years ABPol has truly become an Associação of polymer professionals, and CBPol has become the main technico‑scientific polymer conference in Brazil today.” (Adapted from “20 Anos Associando os Profissionais da Área de Polímeros”, Polímeros: Ciência e Tecnologia, vol. 18, nº 4, 2008, by Silvio Manrich in collaboration with Sebastião V. Canevarolo).

Francisco José Xavier de Carvalho: 1993-1995 From 1993 to 1995 I had the honor to preside over ABPol. In this period we tried to emphasize the interaction with the productive sector; with this approach we could make a strong link with the automobile industry, strengthening the aim of this sector in the use of composites based on polymers/natural fibers. As a result of these actions, Mercedes Benz and other industries starts sponsoring ABPol. Also within this approach were created the Inter-Laboratory Commissions, whose early work was also linked with the automobile industry. We also worked in the sanitation area when SABESP (water supply and sewer collector company for all São Paulo city), aware of the great leaking in the residential junctions was about to rule out the use of pipes made of polyethylene. ABPol held a seminar at SABESB and from that a technical committee was created with the participation of the polyethylene pipe industry, which elaborated a set of specifications of the materials and procedures for handling and installation that finally solved the problems. During our term, we organize the 2nd and 3th CBPol in 1993 and 1995 respectively. We also held the First Colóquio Internacional de Macromoleculares in Gramado and the Seminário Internacional de Fibras e Polímeros Naturais in São Paulo. I hope ABPol continue to succeed into integrating the polymer community, showing the path of scientific and technological development.

(Testimony by Francisco José Xavier de Carvalho for this publication).

Ailton de Souza Gomes: 1995-1997 “The main role of ABPol is to serve as a source of disclosure, consultation, training of personnel and promoter of events in the polymer sector in Brazil. In the previous administration ABPol sought to meet these goals by encouraging the Characterization Commissions, Recycling and Rheology and Processing, through the creation of Regional Branches in the South, in Rio de Janeiro and Bahia, in holding seminars, courses and the 4th Congresso Brasileiro de Polímeros and in the creation of ETS Polímeros. In the academic context, through the dissemination of technical-scientific articles in the journal and offer technical courses, seminars and organize national congresses. In the business sector, through activities in the sector, as well as training of technical personnel in new technologies, even inviting foreign guest specialists. The very much sought increase in the number of ABPol members will occur by encouraging the creation of new Regional Branches, such as in the Northeast and Minas Gerais, as well as by attracting undergraduate and graduated students. I believe that by the implementation of the ETS objectives, ABPol will consolidate itself as one of the most important technical-scientific associations in the country.” (extract from “ABPol 10 anos - Contribuições e Perspectivas”, Polímeros: Ciência e Tecnologia, vol. 8, nº 3, 1998, written by Ailton de Souza Gomes).

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ABPol 30 Years Edson Roberto Simieli: 1997-1999 The period from 1997 to 1999 was marked by many turbulences and uncertainties leading to an enormous financial difficulty. While on the one hand the future of ABPol seemed uncertain, on the other hand it awakened in all, individual members and sponsors alike, a deep feeling of continuing the initial mission the Associação was created. With great bravery and determination we overcome all obstacles and consolidate ABPol as the most important scientific Brazilian society in the polymer field. I should also highlight the negotiations with International Union of Pure and Applied Chemistry - IUPAC. Thanks to the efforts of councilors and directors at the time, together with the international committee, academic area and government agencies, we were able to make feasible and organize, for the first time in Latin America, the IUPAC World Polymer Congress – Macro2006, held in Rio de Janeiro city 2006. (Reported by Edson Roberto Simieli for this publication).

Domingos Antonio Jafelice: 2001–2003 and 2003-2005 In my two terms as President of ABPol (2000-2001 and 2002-2003), I had the great pleasure of celebrating and encouraging the coexistence and exchange of information among the Materials Science professionals of the Academy, Research Centers and Corporate/business Sector. In addition to consolidating the importance of CBPol, ABPol’s participation in national and international events, the publication of the journal Polímeros: Ciência e Tecnologia, I have the special memory of having, together with the members of the Council of Directors, the partners and sponsors, the challenge to expand the ABPol library. The number of titles published by ABPol in four years, surpassed in more than 100% the launches that have occurred since its foundation. At that time soon after the turn of the century, the Internet was incipient and e-book sounded like work of fiction. The quantitative and qualitative expansion of the library contributed to consolidate the ABPol’s image as a valued asset in society and a multiplier of sound knowledge in the polymer area, a sector at that time lacking in technical information for professionals working in this area in Brazil. (Reported by Domingos Antonio Jafelice for this publication).

Raquel Santos Mauler: 2005-2007 and 2007-2009 The Associação Brasileira de Polímeros - ABPol in its 30 years has always been very active and its differential is to bring together academia and the productive sector, always guaranteeing a balance in its deliberative agencies. For some years, I belonged to the Board of Directors of the Association and for four years I presided over it. For a society that survives from members’ annuities and sponsorships, times are never too easy. However, since its creation, ABPol has never stopped promoting the country’s main polymer event - CBPol, which is in its 15th edition, among many other events. My contribution was to continuing the objectives and actions that were already being under development, and also by others that were a differential at the time. During this period, Macro 2006 was held, one of the most important international conferences in the area and so difficult to get the privilege to organize it.

We began the electronic election process for the Council of Directors and promoted a profound administrative reform that culminated in ABPol acquiring its own headquarters. This reform was very difficult to be implemented but was fundamental to the survival of the society.

Today is gratifying for me to see, as a member of the polymer community, that after 30 years ABPol remains strong and fulfilling its role as focal point in the Brazilian polymer area. (Reported by Raquel Santos Mauler for this publication).

Dellyo Ricardo dos Santos Alvares: 2009-2011 and 2011-2013 In September 2018 ABPol completed 30 years of relevant services rendered to the polymer community in the country. I have great satisfaction to revisit my term as president of this society, remembering the great teamwork that continued the previous management, observing the institutional strengthening of ABPol, achieving a long-desired financial balance, growth and expansion of our regional branches, with highlighting the creation of the Regional Northeast, the fantastic work carried out in the technical commissions and courses offered and finally perhaps the most outstanding, by the international renown achieved in that period by the polymers magazine among other achievements. Finally, I would like to express my view that at this moment our country undergoes major transformations in the economic, political and social fields. I am also sure that we have responsibility and great challenges to be overcome with regard to the scientific and technological issue and especially in the field of polymers. On the other hand, I believe that the effort to succeed in this endeavor will only be achieved if it is undertaken collectively, if our community has a clear vision of the future and knows how to identify our major demands and is able to develop the most effective strategies to reach the E14

Polímeros, 28(5), 2018

ABPol 30 Years ultimate goal of building a better country. In this way, I am totally convinced that to participate actively and effectively in ABPol is an important means and opportunity for being recognized as one of the main and legitimate forums for the discussion and generation of ideas, projects and achievements of our polymer community. (Reported by Dellyo Ricardo dos Santos Alvares for this publication).

Luiz Antonio Pessan – 2013 – 2015 and 2015 - 2017 It was a great honor and satisfaction to hold the presidency of the Associação Brasileiro de Polímeros - ABPol for the periods 2013-2015 and 2015-2017. These years were very intense in activities organized by ABPol as the XIV Simpósio Latino Americano de Polímeros (XIV SLAP) / XII Congresso Iberoamericano de Polímeros (XII CIP) in Porto de Galinhas - PE (October / 2014), the 13th Congresso Brasileiro de Polímeros in the city of Natal - RN (October / 2015) and the 14th Congresso Brasileiro de Polímeros in the city of Águas de Lindóia - SP (October / 2017). In addition to organizing these important congresses, ABPol organized the Seminário das Comissões Técnicas of ABPol, Programas Interlaboratoriais, training courses and meeting of ABPol Regionals. An important activity in this period was the detailed survey and solving the financial situation of its scientific journal Polímeros: Ciência e Tecnologia. In 2017, a complete renovation of ABPol’s headquarters was carried out, which was once necessary. This renovation was finalized in mid-2017 and today ABPol has a practically new headquarters with a higher market value and that provides excellent conditions of use by ABPol employees, associates, members of the board of directors, Polímeros journal committee, and other users. We ended the periods in the presidency of ABPol quite satisfied by the team work with the Board and Secretariat of ABPol, for the events held and to put our ABPol in excellent financial condition and with a new headquarters. (Reporting

by Luiz Antonio Pessan for this publication).

José Donato Ambrósio - 2017 – Current President Today ABPol is a nationally consolidated Associação, and this is the result of the effort, dedication and selflessness of countless people over the last 30 years. We have our own Headquarters acquired thanks to a competent planning and management in the MACRO-2006 Congress of UIPAC. This Headquarters has been totally renovated by the previous Board of Directors, so that today we have a very pleasant environment to develop our activities.

In addition, ABPol has national recognition of professionals in the field, development institutions and the business community. However, much effort is required for it to fulfill its commitments in the most diverse plans, in the financial field, for example, fixed expenses are high and resources increasingly scarce due mainly to the critical economy Brazil is facing. It is necessary that ABPol plan its steps and remain connected with the entire Brazilian Polymer Community. For this, actions such as the construction of a new website for the association is already underway, surveys with the student and business community are also moving so that we can add more members and sponsors to ABPol. Another action under progress is the ABPol Statute, which is out-of-date and needs to be updated, revised and approved by the ABPol Assembly. Our journal Polímeros: Ciência e Tecnologia is doing very well, and with its internationalization the impact factor (IF) is steadily increasing. Our Regionals are beginning to maintain a consistency in their meetings, and this is very important from the regional point of view, which ends up reflecting nationally. Finally, I would like to comment on the 15th CBPol, which will be held in the Serra Gaúcha in the city of Bento Gonçalves - RS, for which we count on everyone’s participation. (Reporting by José Donato Ambrósio for this poblication).

The Congresso Brasiliero de Polímeros (CBPol) and other Congresses organized and supported by ABPol After the setting the First Elected Board of Directors for a two-year term, the preparations to the 1st Congresso Brasileiro de Polímeros (1st CBPol) started. It was decided that the Event would be held at Anhembi Convention Center in São Paulo, despite the high costs involved, and the short time of existence of ABPol. Thus, some rooms and the auditorium Elis Regina were rented for about 1,000 people, in addition to a large space for exhibitors.

The event was attended by professionals from all over the world, mainly from companies in São Paulo. A little less than 200 contributions were presented with 18 companies sponsoring and / or exhibiting at the event, in addition to the support of government funding agencies. Despite all Polímeros, 28(5), 2018

that the congress almost went bankrupted. At this event was launched the technical journal Polímeros: Ciência e Tecnologia. It should be noted, however, the great boldness of the Board of Directors and all those who participated in the organization of the 1st CBPol, because despite the difficulties in 1991, it was possible to create a remarkable Event for all Brazilian polymer community. As a result of this work after 28 years we will held next year in the Serra Gaúcha the 15th CBPol in Bento Gonçalves - RS. As quoted

by Professor Silvio Manrich in the text commemorating the 20 years of ABPol, published in the journal Polímeros: Ciência e Tecnologia, several directors and partners did much to leverage ABPol in its early years, among which we can mention Professors Elias Hage, José A. Sousa, José Agnelli, Luiz Pessan, Sebastião Canevarolo, Sati and Silvio Manrich from DEMa/UFSCar, as well as colleagues from other 15/E15

ABPol 30 Years universities, research centers and companies, such as Ailton Gomes, Fernanda Coutinho, Francisco Carvalho, Henrique Northfleet, Jan Orberg, Júlio Harada, Laura Hecker, Lúcia Mei, Mário Colin, Paulo Branco, Ricardo Baumhardt Neto, Zoé Moncorvo, among many others. The organization of the 2nd CBPol was another great challenge for the Associação, as the third Board of Directors were set chair they had to decide with the Council Board where the next congress would be held. Again the decision was set to be in Anhembi, as it was an opportunity to definitively fix the image of ABPol as an representative society of the polymer area in Brazil.

Despite the difficulties, there was great support from many institutions, was possible to hold a big event and still have a financial surplus that kept ABPol financially alive for some time afterwards. In this event, the number of papers increased, there were almost one thousand participants, among them many invited foreigners and those who came spontaneously. ABPol has always invited researchers of national and international renown for their plenary sessions and special presentations. Currently CBPol is formatted with seven plenary sessions, delivered by national and international speakers, and another two plenary sessions delivered by the newly recipients of the Prof. Eloisa Biassoto Mano Award in Research and the ABPol Polymer Technology Award. Chart 3 shows the fifteen Brazilian Polymer Congresses held so far.

In addition to the traditional CBPol, during these 30 years ABPol has organized and/or supported several national and international events in the polymer field. The largest Brazilian event that also covers the area of polymers is the Congresso Brasileiro de Ciência e Engenharia de Materiais (CBECIMat), which had its 23rd edition in 2018 in the city of Foz do Iguaçu-PR. As it is a very important event that covers the areas of polymers, metals, ceramics and composites, CBECiMat has had all the support of the three

Brazilian associations of materials, namely the Associação Brasileira de Cerâmica (ABCERAM), Associação Brasileira de Metalurgia, Materiais e Mineração (ABM) and the Associação Brasileira de Polímeros (ABPol). ABPol has contribute to host international events in Brazil, which is very important for the Brazilian polymer community to participate and maintain closer contact with renowned international researchers, fostering the exchange and easy update of the international developments in the polymer field. In the meeting in 1994 was approved by the Board of Directors of ABPol the organization of Simposio Latino-Americano de Polímeros SLAP e o Simposio Ibero-Americano de Polímeros SIAP and the International Macromolecular Colloquium. These approvals were taken after careful considerations that ABPol did not have the financial resources neither men-power to hold such big events, as pointed out Silvio Manrich. The good results coming out from these international events, encourage the president Edson Simielli in 1998 to agree fostering in Brazil the MACRO2006 International Symposium on Macromolecules of IUPAC. The acceptance from the IUPAC Board of Directors came after ABPol commit to fulfil all requirements set by IUPAC, and also thanks to contributors who represented Brazil in previous MACRO events as David Tabak (FioCruz - RJ), Roberto S. Fernando Freitas (UFMG - DEQ) and Sebastião Canevarolo Jr. (UFSCar - DEMa), besides the president Edson Simielli who was personally involved. In 2001 President Silvio Manrich signed the Letter of Commitment in the presence of Prof. Robert Gilbert (University of Queensland, Brisbane, Australia) chair of the IUPAC Macromolecules Division. Domingos Jafelice, who was president of ABPol from 2001-2005, also collaborated so that ABPol maintained the Brazilian annuities with IUPAC. Finally in 2006 in Rio de Janeiro-RJ, President

Chart 3. All Congresso Brasileiro de Polímeros (CBPol).

CONGRESSO BRASILEIRO DE POLÍMEROS - CBPol.

Edition Year General Chairmain 1st CBPol 1991 Sílvio Manrich 2nd CBPol 1993 Silvio Manrich 3rd CBPol 1995 Ailton S. Gomes 4th CBPol 1997 Sebastião V. Canevarolo Jr. 5th CBPol 1999 Ailton S. Gomes 6th CBPol 2001 Raquel S. Mauler 7th CBPol 2003 Roberto Fernando S. Freitas 8th CBPol 2005 Fernando Galembeck 9th CBPol 2007 Laura H. de Carvalho 10th CBPol 2009 Edvani Curti Muniz 11th CBPol 2011 Sebastião V. Canevarolo Jr. 12th CBPol 2013 Valdir Soldi 13th CBPol 2015 Rosângela C. Balaban 14th CBPol 2017 Antonio J. Félix de Carvalho 15th CBPol* 2019 Otávio Bianchi *15th CBPol will be held in October 27-31, 2019 in Bento Gonçalves - RS.

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Number of Participants 1000 850 500 500 460 570 554 700 750 1026 1031 977 707 622 To be held

Place São Paulo - SP São Paulo - SP Rio de Janeiro - RJ Salvador - BA Águas de Lindóia - SP Gramado – RS Belo Horizonte – MG Águas de Lindóia – SP Campina Grande – PB Foz do Iguaçu - PR Campos do Jordão - SP Florianópolis - SC Natal - RN Águas de Lindoia - SP Bento Gonçalves - RS

Polímeros, 28(5), 2018

ABPol 30 Years Raquel Mauler together with the chairman of the event Ailton S. Gomes brilliantly finalized this very important event, which had 1,120 participants. Not only ABPol got the merit to host a so important international event in the polymer world, but also could make enough extra cash to be able to by its own headquarters. The conscious work of the Council Board chaired by Raquel Mauler, and directors such as Edson F. Joaquim, Luiz A. Pessan and others had made this possible. Other important international congresses hosted

by ABPol, either by organizing, promoting or supporting are highlighted in Chart 4.

The journals “Polímeros: Ciência e Tecnologia” and “Materials Research” The launch of a scientific Brazilian polymer journal was the second major challenge for the Associação, mainly because this was done in the early years of ABPol existence. Figure 4 shows the evolution of the number of articles published by Polímeros: Ciência e Tecnologia since its starts up to now.

The launch of the journal was much discussed, doubts upon its financial viability, real interest in the public to publish in a newly started national journal and even if the quantity

Chart 4. International congresses and events hosted and/or supported by ABPol up to now.

• September 04-08, 1994 - SLAP / SIAP / IMC, Gramado - RS. • May 23, 1995 - Technical Lecture delivered during Brasilplast: “Software to Solve Problems in Polymer Processing” - Professor John Vlashopoulus and Dr. J. Vlcek. Sao Paulo-SP • October 4, 1996 - Seminar “Polymerization of Olefins with Metallocene Catalyst” - Prof. Dr. Walter Kaminsky.

• May 21, 1997 - 1st Workshop de Caracterização, Degradação e Reciclagem de Polímeros, São Paulo - SP. • August 6-9, 2000 - 2nd Seminário Brasileiro sobre Avanços em Processamento de Polímeros - coordination: Professor José Alexandrino de Sousa, Director of ABPol, São Carlos - SP. • November 26, 2002 - Seminar “Polímeros do Futuro: Tendências e Oportunidades”, São Paulo - SP. • March 11, 2003 - ABPol promoted a round of lectures during Brasilplast. São Paulo-SP. • September 12-15, 2004 - 5th International Symposium on Natural Polymers and Composites (ISNAPOL) and 8th Brazilian Symposium on the Chemistry of Lignins and other Wood Components, São Pedro - SP. • November 7-10, 2004 - PPS 2004 - Americas Regional Meeting, Florianópolis - SC. • April 10-13, 2005 - X International Macromolecular Colloquium, Gramado - RS. • July 16-21, 2006 - World Polymer Congress (Macro 2006), Rio de Janeiro, RJ. • April 22-25, 2007 - XI International Macromolecular Colloquium (IMC) and 6th International Symposium on Natural Polymers and Composites (ISNAPOL), Gramado - RS. • February 3, 2009 - One-Day International Workshop on Advanced Renewable Technology, São Paulo, SP. • April 14-15, 2011 - International Workshop on Innovation and Applications in Composite and Nanocomposite Materials (IWINM / 2011), São Paulo, SP. • April 18-20, 2011 - VI International Materials Symposium (MATERIALS 2011) and XV Meeting of SPM - Sociedade Portuguesa de Materiais, Guimarães, Portugal.

• April 25-29, 2011 - 3rd French Brazilian Meeting on Polymers (FBPOL2011), Florianópolis, SC. • March 13-14, 2012 - XX Simpósio Internacional sobre Tecnologias de Plásticos, São Paulo, SP. • October 12-16, 2014 - IV Simpósio Latino Americano de Polímeros (XIV SLAP) and XII Congresso Iberoamericano de Polímeros (XII CIP).

Porto de Galinhas - PE. • August 28-31, 2016 - 3rd Brazilian Conference on Composite Materials (BCCM-3), Gramado, RS.

Figure 4. Number of articles published per year by Polímeros: Ciência e Tecnologia, since its launch in 1991.

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ABPol 30 Years of good and publishable articles was enough. All of these worries indeed made sense at that time. However the polymer community, trusting in its partners and collaborators, and standing upon one of the ABPol’s original grand goals, having its own publishing media, embraced this cause. Initially each issue had six articles, most of them submitted by invitation from the editors, and some advertisements that sustained the first editions. Emanoel Fairbanks editor of the journal Plástico Moderno participated in meetings with ABPol and greatly contributed to the Associação, remembers Silvio Manrich. An article was published on the fifteen years of the journal “Polímeros: Ciência e Tecnologia” (Volume XV, No. 4, 2005 pages E4 to E17), recording the complete history of this journal its editors and committee members. It is worth mentioning the tireless editorial coordinators of the Editorial Committee, being the first Sebastião V. Canevarolo, followed

by José Alexandrino de Sousa, Antônio Aprígio Curvelo, Elias Hage Jr., Adhemar Colla Ruvolo Filho, Elisabete Frollini and currently Sebastião V. Canevarolo. An important participation was of Professor José Alexandrino de Sousa, who stamped the fate of this magazine helping to maintain since its launch the best possible quality of texts, photos, artwork, among the unforgettable trips to São Paulo in search for sponsorship for the journal and other events organized

by ABPol. It is always difficult to convince companies about the importance of a newly created society. But gradually, after having held the 1st CBPol and launching the journal, the roots start to grow and guaranteeing its sustainability.

In the beginning the journal was financially supported by the national funding agencies CNPq and CAPES, funding many projects submitted by the president of the Editorial Board or by its Editor-in-Chief. It was edited in printed form with four issues per year and the management of the article submission process was done in an online home made platform. All of this generated substantial costs that were not covered by the sponsoring coming from advertising.

From 2015 the financial situation worsened substantially and other alternatives were sought. Under the editorship of Profa. Elisabete Frolini the magazine migrate the management of articles to the SciELO online platform and discontinued its printed form. Another important step was the decision of publishing the articles written only in English. Currently, the journal is published only in English, in the virtual form, the articles are released via the internet for open and free download access. The submission process is done by the ScholarOne Manuscripts platform. This greatly favored its

internationalization, steadily increasing the impact factor to 0.7 in 2018 (Figure 5).

Today the journal is organized as follows: there is an Editorial Council with 26 members, its president is Professor Antonio Aprigio Curvelo. Under it there is the Editorial Committee composed by the Editor-in-Chief, currently is Professor Sebastião Canevarolo Jr. and 10 Associate Editors, with international representativeness (Brazil, France, Portugal, Belgium and United States), all of them also belonging to the Editorial Council (Chart 5). The current ABPol collaborator, Charles Fernandes de Souza, is the editorial assistant and organizes the proceedings of the authors, committee, consultants, publishing and electronic publishing company (SciELO). Submission of papers to the journal is open to the entire international polymer community. The authors follow the rules of the journal for writing articles, which can only be done in English. After the evaluation and approval by 3 peer-review, the manuscripts are accepted and published. Today the magazine has the contribution of 298 AdHoc reviewers. In its 28th volume can be found in the Web of Science database with ISSN: 0104-1428, is indexed in SciELO, Scopus, DOAJ, Chemical Abstracts, RAPRA Abstracts, All-Russian Institute of Science and Technical Information, Network of Scientific journals of Latin America and the Caribbean and Latindex.

ABPol also publishes in collaboration with other societies the journal “Materials Research - Ibero-American Magazine of Materials”, which is a journal published in English since its starts (Figure 6). The creation of a Brazilian journal dedicated to Materials Science and Engineering was discussed and approved during the 13th Congresso Brasileiro de Ciência e Engenharia de Materiais (CBECIMat) in 1998. We recall part of the editorial of the first published issue, written by Edgar D. Zanotto, its first Editor-in-Chief (Mat. Res. Vol.1 n.1 São Carlos Oct. 1998 - http://dx.doi. org/10.1590/S1516-14391998000100001): The idea was centered and debated at the “general meeting” of the 11th CBECIMAT - Congresso Brasileiro de Ciência e Engenharia de Materiais - in 1994 and later decided at the general meeting of the 12th CBECIMAT in 1996. After a long preparation process, we have the grateful to be accountable to the 13th CBECIMAT assembly in 1998, fulfilling the goal set by this community. It is important to emphasize that this enterprise only crystallized due to the enthusiasm and dedication of some members of the editorial staff, especially Fernando

Figure 5. Evolution of the Impact Factor IF of “Polímeros: Ciência e Tecnologia”.

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Polímeros, 28(5), 2018

ABPol 30 Years Chart 5. Current Editorial Committee and Council of “Polímeros: Ciência e Tecnologia”.

Editorial Committee Editor-in-Chief

Editorial Council President

• Sebastião V. Canevarolo Jr. (UFSCar/DEMa), São Carlos, SP, Brasil • Antonio Aprigio S. Curvelo (USP/IQSC), São Carlos, SP, Brasil Associated Editors

Members

• Adhemar C. Ruvolo Filho (UFSCar/DQ), São Carlos, SP, Brasil

• Adhemar C. Ruvolo Filho (UFSCar/DQ), São Carlos, SP, Brasil

• Alain Dufresne (Grenoble INP/Pagora), Saint Martin d’Heres, RA, France • Ailton S. Gomes (UFRJ/IMA), Rio de Janeiro, RJ, Brasil • Bluma G. Soares (UFRJ/IMA), Rio de Janeiro, SP, Brasil

• Alain Dufresne (Grenoble INP/Pagora), Saint Martin d’Heres, RA, France

• César Liberato Petzhold (UFRGS/IQ), Porto Alegre, RS, Brasil

• Bluma G. Soares (UFRJ/IMA), Rio de Janeiro, RJ, Brasil

• José António C. Gomes Covas (UMinho/IPC), Guimarães, RN, Portugal • César Liberato Petzhold (UFRGS/IQ), Porto Alegre, RS, Brasil • José Carlos C. S. Pinto (UFRJ/COPPE), Rio de Janeiro, SP, Brasil

• Cristina T. Andrade (UFRJ/IMA), Rio de Janeiro, SP, Brasil

• Richard G. Weiss (GU/DeptChemistry), Washington, DC, United States • Edson R. Simielli (Simielli - Soluções em Polímeros), Campinas, SP, Brasil • Paula Moldenaers (KU Leuven/CIT), Leuven, FB, Belgium

• Edvani Curti Muniz (UEM/DQI), Maringá, PR, Brasil

• Rodrigo Lambert Oréfice (UFMG/DEMET), Belo Horizonte, MG, Brasil • Elias Hage Jr. (UFSCar/DEMa), São Carlos, SP, Brasil • Sadhan C. Jana (UAKRON/DPE), Akron, OH, United States

• Eloisa B. Mano (UFRJ/IMA), Rio de Janeiro, RJ, Brasil • José Alexandrino de Sousa (UFSCar/DEMa), São Carlos, SP, Brasil • José António C. Gomes Covas (UMinho/IPC), Guimarães, RN Portugal • José Carlos C. S. Pinto (UFRJ/COPPE), Rio de Janeiro, RJ, Brasil • Júlio Harada (Harada Hajime Machado Consutoria Ltda), São Paulo, SP, Brasil • Luiz Antonio Pessan (UFSCar/DEMa), São Carlos, SP, Brasil • Luiz Henrique C. Mattoso (EMBRAPA), São Carlos, SP, Brasil • Marco-Aurelio De Paoli (UNICAMP/IQ), Campinas, SP, Brasil • Osvaldo N. Oliveira Jr. (USP/IFSC), São Carlos, SP, Brasil • Paula Moldenaers (KU Leuven/CIT), Leuven, FB, Belgium • Raquel S. Mauler (UFRGS/IQ), Porto alegre, RS, Brasil • Regina Célia R. Nunes (UFRJ/IMA), Rio de Janeiro, RJ, Brasil • Richard G. Weiss (GU/DeptChemistry), Washington, DC, United States • Rodrigo Lambert Oréfice (UFMG/DEMET), Belo Horizonte, MG, Brasil • Sadhan C. Jana (UAKRON/DPE), Akron, OH, United States • Sebastião V. Canevarolo Jr. (UFSCar/DEMa), São Carlos, SP, Brasil • Silvio Manrich (UFSCar/DEMa), São Carlos, SP, Brasil

Rizzo and José Carlos Bressiani. We should also extend our thanks to the three associations responsible for the journal: Associação Brasileira de Metalurgia, Materiais e Mineração - ABM, Associação Brasileira de Cerâmica - ABC and Associação Brasileira de Polímeros - ABPol, whose secretariats have helped us in the dissemination and management of signatures and financial resources. It should be noted that the management of the resources of Materials Research were made by ABPol until the year 2012, after that the finances have been administered by the journal itself.

Technical Committees and Interlaboratory Programs

Figure 6. Materials Research - Ibero-American Journal of Materials.

Polímeros, 28(5), 2018

For greater interaction with its partners and all polymers community, in 1992 the Board of Directors of ABPol create Technical Committees and appointed its Director Sebastião V. Canevarolo to outline the basic guidelines for their operation. The first Technical Committee created was in the area of Identification and Characterization of Polymers, whose first director was Sebastião Canevarolo 19/E19

ABPol 30 Years himself. Following other commissions were created, such as Plastic Recycling coordinated by Hélio Wiebeck and Rheology and Polymer Processing coordinated by Júlio Harada. These committees started meeting in São Paulo city every 3-4 months having technical and/or scientific invited lectures, to foster the networking and exchange of experience among professionals in the polymer field.

The needs to ​​create Technical Committees arose from meetings of ABPol’s directors with members of many industrial societies such as Sindicato da Industria de Resinas do Estado de São Paulo SIRESP, Associação Brasileira da Industria Química ABIQUIM, Associação Brasileira da Industria do Plastico ABIPLAST, Associação Brasileira da Industria de Máquinas ABIMAQ and Secretaria da Indústria do Estado de São Paulo. This networking greatly contributed to ABPol establishing its image in the industry, showing its importance within these societies, as well as within research funding agencies such as FAPESP and CNPq. With such a performance ABPol was recognized as an active society and taken as model in organizing congresses and journals.

Currently the meetings take place jointly among the three Committees, to launch, conduct and publically present the results of the Interlaboratory Programs. The participation in the meetings is open to the community, with its enrollment in the mailing list. The Interlaboratorial Programs (PI) promoted by ABPol is another very important activity for the industrial and research sectors in Brazil, since the IPs aim to guarantee the performance of laboratory equipment, and are fundamental tools to ensure the quality of the results obtained and their interpretation, both in the industrial and academic environment. The participation in IP of laboratories accredited by the Instituto Nacional de Metrologia, Qualidade e Tecnologia INMetro is compulsory, in which a minimal performance is requested in the renewal audits of the Laboratory scope. Not only accredited laboratories are encouraged to take part in IP, any laboratory that uses its equipment frequently for the most diverse applications are invited too. ABPol has always sought to be a pioneer in the launching of Interlaboratory Programs in Brazil, such as the Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Impact Strength, Thermogravimetry (TG) and Oxidative Induction Time (OIT). This pioneering is a direct response to the requests from the Brazilian polymer community. In this year 2018, ABPol is promoting the Ciclo de Programas Interlaboratoriais with five test methods: 3rd PI of Oxidative Induction Time - OIT - ASTM D3895, 2nd PI of Thermogravimetry (TG) - ISO 11358 and ASTM E1131, (ASTM E1252) and ASTM D1238 (ASTM E1252)

and ASTM D1238 (ASTM E1252), and the 8th PI of Melt Flow Index (ASTM D1238). Since 2013, the laboratory “Centro de Caracterização e Desenvolvimento de Materiais” (CCDM) of DEMa/UFSCar has collaborated with ABPol in the PIs by providing homogeneous samples and preparing the protocols for the tests. The ABPol Secretariat is responsible for the confidential identification of equipment and laboratories, as well as sending the samples and typing the results for statistical analysis of the results. Preliminary results are sent to the participants and discussed informally at a meeting promoted by ABPol, and after that the final results are consolidated in a final report. The Chart 6 shows all Interlaboratorial Programs carried out by ABPol since its first launch in 1993.

Short-Courses Other important activity ABPol has been offering throughout its 30 years ABPol to the Brazilian polymer community is offering short-courses presenting basic science and applied technology of commercial polymers, polymer blends and composites. In the last years the participants are mainly professionals of industries and research centers, but also researchers of Brazilian universities. Since 1989, ABPol has promoted 182 short-courses for more than 3,000 participants nationwide, training and updating professionals and students in the polymer field. Over the last decade, three short-courses have stood out due to the great demand from the polymer community, which are Injection Molding given by Júlio Harada, Polymer Degradation and Stabilization by Marco-Aurelio De Paoli and the Failure Analysis and Characterization of Polymers presented by a team of polymer specialists from CCDM/DEMa/UFSCar.

ABPol Partners Throughout these 30 years, the ABPol Partners have been the main financial sponsor and responsible for the maintenance and performance of the Associação throughout the Brazilian territory. The sponsoring types are divided into several categories of members. Individuals are ranked as Individual and Junior Members. Companies and teaching institutions are ranked as Collective and Educational Institution respectively, and finally the full partner as Sponsoring Partners (subdivided in Gold, Silver and Bronze).

Each category grant to the partners enrolled a particular set of benefits, listed in the ABPol’s website. The Associação

Chart 6. Interlaboratorial programs held by the Polymer Identification and Characterization Commission.

Year/Program 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 DSC 1 2 3 4 5 6 7 HDT 1 Impact 1 2 3 4 5 6 7 Creep 1 2 3 4 5 6 7 8 FTIR 1 2 3 4 5 6 7 8 9 OIT 1 2 3 Ash Content 1 2 TG 1 2 Stress-Strain 1 2 3 4 5

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Polímeros, 28(5), 2018

ABPol 30 Years is currently conducting a survey with each target audience (individual members, students and companies) to update their required facilities and benefits should ABPol provide to them. The current Executive Council is working to expand its number of members. One of the ways is making sure that they are being informed upon the benefits they have and so better attract them to become members. Some examples of membership facilities that are thought of are to make available a database with job opportunities, contests and exams at the national level for individual and student. To the partner companies, could be the provision of information such as consultation and dissemination of job opportunities, via consulting the database of Resumes of members, ease of access to environmental legislation and indication of researchers and Research Groups or Research Centers available in Brazil, particularly those leaving close to the region where the job in being offered. These and many other propositions are under debate by the Council members, which should be implemented shortly. It is important to mention that throughout its 30-year history, ABPol has given two honorary titles to their most respected members, Professor Eloisa Biasotto Mano of UFRJ-IMA, awarded in 2001 during the 6th CBPol in Gramado - RS and Professor Silvio Manrich of UFSCar-DEMa awarded in 2003 during the 7th CBPol in Belo Horizonte - MG.

Books As mentioned in the text commemorating the 20 years of ABPol, for many years ABPol’s advisors discussed the need for the society to offer its members access to the technical literature on polymers, and even considered​​ creating a library. The library was not built, instead flourished the initiative of encouraging professionals of the polymer area to publish technical polymer books written in Portuguese. In order to help potential authors into the process of publishing, ABPol signed an agreement with the publisher Editora Artliber. The potential authors submit the manuscript of the book to ABPol, which is evaluated by a Technico‑Scientific Committee of ABPol, and if approved, the manuscript is sent to the publisher for diagraming printing and commercialization. The publication is with no cost to the author, Artliber pays the authorial rights directly to the authors and a set percentage of the sales to ABPol that it has promoted. This agreement has ensured success to all partners, authors, ABPol and publisher. The process began in 2000 with the publication of the book “Aditivação de Polímeros” by Professor Marcello R. Rabello of the Federal University of Campina Grande (UFCG) in Paraíba and still holds. Today, ABPol offers 46 titles written in Portuguese to the benefit of its community.

Regional branches The Brazil’s great territorial extension reduces the chances for professional living and working in different part of the country to meet together, mainly in the case of they do not know each other. In order to minimize this problem ABPol created Regional Branches, providing a closer meeting point where the networking could be enhanced, in these regional groups the “Polymer World” Polímeros, 28(5), 2018

could be more frequently discussed, in seminars, meetings, courses all organized and held by local individuals. The first Regional was created covering the South part of Brazil e soon afterwards the East region, in addition to ABPol activities in the state of São Paulo. These regions were chosen because they have the highest density of professional and students in the universities, research institutions and companies that study, research and work in the polymer area. Subsequently, the Northeast Regional was created, bring together nine states of northeast of Brazil, which have a significant increase in the number of students and researchers from universities and companies. The fourth and most recently Regional ABPol has created was the Regional Minas Gerais. Professional living and working in the State of Minas Gerais were initially included in the East Regional, but due to the growing number of courses, companies and researchers, was wise to create another regional. Each regional have being very dynamic, a brief description of their activities are:

East Regional The East Regional was initially created in 1993 as a Delegacy, and later in 1999 it became a Regional. It covers the partners of the states of Rio de Janeiro and Espirito Santo. Its first Director was Elisabeth Omar R. da Rosa and the current Director is Ana Lucia Nazareth da Silva having as Vice-Director Ana Maria Furtado de Souza.

This Regional was created due to the importance of the State of Rio de Janeiro and particularly is capital city of Rio de Janeiro having a large number of universities and research institutions such as Universidade Federal do Rio de Janeiro UFRJ with its world famous Instituto de Macromoleculas Profa. Eloisa B. Mano IMA and Alberto Luiz Coimbra Institute for Graduate Studies and Research in Engineering (known as) COPPE, Universidade Estadual do Rio de Janeiro UERJ, Instituto Nacional de Tecnologia INT, Petrobrás, as well as a number of other companies, research centers and Federal Institutes. The neighbor State of Espirito Santo with its University and Federal Institute also belongs to this regional. The East Regional created and has being organizing the already traditional “Café com Polímeros” (Coffee break with Polymers) normally held in the IMA/UFRJ. The plan for 2019 is organize and host the first polymer meeting in Vitoria, capital of the Espirito Santo State.

South Regional The South Regional was initially created in 1996 also as a Delegacy, and later in 1999 it became a Regional.

It covers the states of Paraná, Santa Catarina and Rio Grande do Sul. The first Director was Telmo Ojeda and currently its Director is Otávio Bianchi having as Vice-Director Jose Ricardo Fajardo. As set by its members, the main objectives of South Regional is to seek the integration of the polymers community working in the various centers of activities in the south of Brazil, covering the areas of plastics, rubbers, paints and adhesives. It is understood that the best way to achieve this goal is organizing and hosting technical events such as courses, seminars and meetings, sharing technical 21/E21

ABPol 30 Years and scientific knowledge demanded by the professional of this region, providing periodic contact between academic professionals and researchers with common interests in the polymer area. The South Regional held the Workshop in “Polymers from Renewable Sources”.

Northeast Regional The Northeast Regional was created in 2011 and covers the states of Bahia, Sergipe, Alagoas, Pernambuco, Paraíba, Rio Grande do Norte, Ceará, Piauí and Maranhão. Its first Director was Rosangela Balaban and its Vice-Director Edson Noriyuki Ito. Its current Director is Josiane Dantas Viana Barbosa having as Vice-Director Tatianny Soares Alves. This Regional plays an important role helping the networking among professional from the great number of research groups present in this region. Every even year it holds the “Encontro Nordeste de Ciência e Tecnologia de Polímeros”, interposed with CBPol which happens every odd year. So far, four Meetings have been held in the cities of Natal-RN, Salvador-BA, Fortaleza-CE and recently again in Salvador from September 27-28, 2018, with the presence of 174 participantes.

Minas Gerais Regional The Minas Gerais Regional was created in 2016, separating from the East Regional, to attend more effectively the large number of education and research institutions, and companies set in Minas Gerais State. This state has a large territorial extension with a great number of people working with polymers. The State of Minas Gerais has 22 higher education institutions, including Federal Institutes of Technology and Federal Universities, which maintains 71 campuses throughout the state, three state institutions, as well as private and philanthropic colleges and universities.

Its current Director is Daniel Pasquini having as Vice‑Director Harumi Otaguro. On November 21-22, 2018, the Minas Gerais Regional will held the 2nd “Workshop Mineiro de Polímeros”.

ABPol Headquarters The Associação Brasileira de Polímeros is set in its own headquarters since 2007, acquired during the management of President Raquel Mauler, who fulfilled one of the society’s dream. It is a spacious house installed in a piece of land with more than 400 m2 having a typical twentieth century inner city architecture, with a large internal area with seven rooms (one meeting room, three rooms with built-in cabinets, a kitchen, two bathrooms) and a closed garage.

Such a facility allows it to hold activities such as courses and celebrations. In 2017, the Board of Directors presided over

by Luiz Antonio Pessan carried out a complete renovation of the headquarters, with maintenance of the roof, changing

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the carpet floor to porcelain tile, renewing the electrical instalations, replacing corroded iron windows, creating internally a second bathroom with disabled facilities, as well as a disabled access ramp, replacing the grill and front doors for greater protection of the patrimony and overall painting.

This has made ABPol Headquarters more suitable for the development of its everyday activities besides improving the assets that is the perennial part of the Associação.

Final comments from the actual President José Donato Ambrósio I would like to express the great pleasure of being in the presidency of ABPol in its 30 years of existence, no institution survives so long being recognized, and in an appropriate way, without any judicial or financial pendency. This is even more crucial in Brazil, with its frequent economical ups and downs, in moments of crisis Science and Technology, the main focuses of ABPol, are the first to be set aside and the last ones to enjoy the benefits when the Country gets back into growth. This was only and continues to be possible thanks to the efforts of the Members and Sponsors, the Organizing/Scientific Committees and the Exhibitors during the Congresso Brasileiro de Polímeros. It should also be mentioned the great support from the Brazilian funding agencies CNPq, CAPES, FAPESP and other stately run agencies funding the development of research set in other Brazilian States, particularly when the CBPol is held in these states. I would also like to thank all the employees who have served ABPol during this 30 years period, to all members of present and past Board of Directors who have guided ABPol, and its journal Polímeros: Ciência e Tecnologia, freely donating part of their time in favor to the Brazilian Polymer Community. Finally, I thank all those unknown people who collaborated and still are collaborating to the growth of our Associação and wish many years of existence to ABPol. Text prepared by José Donato Ambrósio from CCDM/DEMa/UFSCar and current President of ABPol, with the collaboration of Marco-Aurelio De Paoli in the section dealing with the journal Polímeros: Ciência e Tecnologia, as well as in addition to the ABPol employees Marcelo Perez Gomes and Charles Fernandes de Souza, for retrieving information and images in the archived ABPol documents. English reviewed by Sebastião Canevarolo.

This text was based on the article ABPol 20-years “20 Anos Associando os Profissionais da Área de Polímeros” published in Polímeros: Ciência e Tecnologia, vol. 18, nº 4, 2008, written by Silvio Manrich in collaboration with Sebastião V. Canevarolo. Referring again to this text was unavoidable, it was originally very well written and full of historical facts, which are already set in time.

Polímeros, 28(5), 2018

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.04917

Crystallization, thermal and mechanical behavior of oligosebacate plasticized poly(lactic acid) films Erika Martins Inácio1, Maria Celiana Pinheiro Lima2, Diego Holanda Saboya Souza1, Lys Sirelli1 and Marcos Lopes Dias1* 1

Instituto de Macromoléculas Professora Eloisa Mano – IMA, Universidade Federal do Rio de Janeiro – UFRJ, Rio de Janeiro, RJ, Brasil 2 Instituto Federal do Rio de Janeiro – IFRJ, Duque de Caxias, RJ, Brasil *mldias@ima.ufrj.br

Abstract The biodegradable aliphatic oligoester oligo(trimethylene separate) (OTS) was synthesized by polycondensation and used to plasticize poly(lactic acid) (PLA). Casting films of PLA and PLA/OTS with concentrations of 1, 5 and 10 wt.% were prepared, and these films were characterized by thermal analyses, crystallinity, rheology and mechanical tests.

DSC revealed the decrease in the Tg of PLA films with addition of the oligomer and a partial immiscibility. Addition of OTS to PLA slightly decrease the thermal stability as well as increase the degree of crystallinity of these films.

Dynamic-mechanical analyses of casting films showed that the PLA/OTS system presented lower storage modulus than PLA and mechanical test revealed an increased in the elongation at break for PLA films containing the oligoester.

The results make possible to conclude that the oligomer synthesized from bio-based monomers acts as a plasticizer of PLA increasing the PLA ductility.

Keywords: plasticization poly(lactic acid), oligoesters, trimethylene sebacate, cast films.

1. Introduction Thermoplastics have been increasingly used as packaging materials due to important properties like low density, high mechanical resistance and transparency. The use of conventional plastics has caused increasing concern in relation to the environmental impacts that these materials can generate, due to the degradation time, which can reach hundreds of years[1-4].

For this reason, the scientific community has searched new polymer materials that can decrease the impacts of fossil plastics, with focus in the biodegradable bioplastics[5].

Biodegradable plastics are materials in which the degradation occurs initially by the action of microorganisms, like bacteria, fungi and algae, transforming the polymer chains in carbon dioxide, methane, microbial cell components and other products[3]. Biodegradation processes can decrease the amount of plastic residue in the environment, since it reduces drastically the degradation time of these materials.

Nevertheless, for the biodegradation of a polymer to occur, it must be in an appropriate environment because, if not, biodegradation can equally take place in many years[6].

Aiming for green materials to substitute conventional plastics, different biodegradable plastics has been used, with emphasis in polymers from natural origin obtained by chemical synthesis or microbiological fermentations[4].

Poly(lactic acid) (PLA) is an important biodegradable polymer which can be synthesized by means of condensation of lactic acid or by ring opening polymerization of lactides that are lactic acid dimers. Due to its biodegradability, non‑toxicity and good biocompatibility and processability[7], PLA has

Polímeros, 28(5), 381-388, 2018

been largely investigated in studies that aim application as food packaging[8,9]. However, although it has high modulus, it is a fragile and brittle material, with a low elongation at break similarly to polystyrene[10].

To adequate PLA properties for packaging application and to improve its thermal and mechanical properties, particularly its flexural properties, this polymer is usually modified by copolymerization with other monomers or by plasticization[5,10-13].

Plasticization usually improves the processability of polymers, as well as increase the polymer flexibility and ductility in amorphous polymers. The efficiency is in general evaluated in terms of the decreasing in the glass transition temperature (Tg) and increasing of toughness, and it is dependent on polymer molar mass and amount of plasticizer[13].

The solubility parameter and the magnitude of polymer‑plasticizing interaction are usually used to evaluate the miscibility between the material components and are good elements to facilitate the selection of an effective plasticizer.

Thus, plasticizers are important non-volatile molecules which actuate modifying the intermolecular interactions between the polymer chains by preferential interactions with the macromolecular chains. These interactions change chain conformation, resulting in increasing of molecular mobility[10].

Aiming to investigate the efficiency of oligoester as PLA biodegradable plasticizers, a oligoester based on two

381/388 381

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

Inácio, E. M., Lima, M. C. P., Souza, D. H. S., Sirelli, L., & Dias, M. L. bio-based monomers, sebacic acid and trimethylene glycol was synthesized and added to a commercial PLA. So, in this paper the crystallization, thermal and mechanical behavior of these oligoester plasticized-PLA are reported.

2. Materials and Methods 2.1 Materials PLA Ingeo 4043D (Mn= 160.000 g/mol) film grade from NatureWorks LLC was used as received. Chloroform 99.8% (amilene stabilized) was furnished by Tedia Brazil.

Dimethylsebacate and trimethylenediol (propan-1,3-diol) Aldrich and zinc acetate from Spectrum were used as received.

2.2 Synthesis of oligosebacate The synthesis of the oligo(trimethylene sebacate) (OTS) was carried out by a bulk polycondensation of dimethylsebacate and trimethylenediol using zinc acetate as catalyst. The reaction took place in a single stage by using equimolar proportion of the monomers according to procedure previously described in the literature[14]. Thus, the monomers and catalyst (0.5 wt.%) were placed in a glass flask and heated to 200 °C. By using vacuum, methanol was progressively removed during 2 h. At the end of this time, the molten oligoester was poured into a glass surface to solidify.

2.3 Oligoester characterization The oligoester was analyzed by FTIR in a Varian Excalibur 3100 FT-IR by Attenuated Total Reflectance (ATR) in the range of 4000-400 cm-1. 1H NMR spectrum of OTS was obtained in a Varian NRM equipment model Mercury VX-300, using CDCl3 as solvent. The molecular weight was determined by GPC using a Shimadzu LC equipment with refractive index detector, chloroform as solvent and monodisperse polystyrene as calibration standard. The analyses were carried out in a flow rate of 1.0 mL/min, injection volume of 20 μm, at 25 °C. The number and weight average molar mass (Mn and Mw, respectively) and polydispersity (Mw/Mn) were determined by a Shimadzu software. Thermal transition temperatures were determined in a DSC Hitachi model 7020 in the temperature range from –80 to 100 °C at 10 °C/min. Samples were first heated, followed by a fast cooling (quenching) at 50 °C/min up to –80 °C and subsequently reheated at 10 °C/min.

2.4 Preparation of PLA films PLA films were prepared by casting from 10 wt./v% chloroform solutions. OTS was added to these solutions to attain the final concentration of 1, 5 and 10 wt.% in relation to PLA. The solutions containing PLA and OTS were casted over to 289 cm2 mold with 3 mm thickness and dried for

7 days. After this time, the films were dried under vacuum for more 24 h as attempt to eliminate the residual solvent.

2.5 Characterization of plasticized films PLA films were analyzed by TA DSC equipment under nitrogen atmosphere in the temperature range from 25 to 200 °C at 10 °C/min. Three heating runs were used to evaluate the polymer thermal transitions. The degree of crystallinity was calculated using the standard melting enthalpy reported

by Sarasua et al.[15] (106 J/g), considering the enthalpy of crystallization on heating and OTS weight fraction. Thermal stability was analyzed in a TA Thermoanalyser Q500 from 25 to 700 °C at 10 °C/min under nitrogen flow. X-ray diffraction were carried out in a diffractometer Rigaku Miniflex model using CuKα radiation (wavelength, 1.5418 Å) in the 2θ range 2° to 50°, 0.05° step/s at room temperature.

Rheological behavior of films containing 10 wt.% OTS was studied using a TA AR 2000 rheometer in the parallel plate geometry (diameter 25 mm) at 165 °C. Disc-like specimens with 2 cm diameter were used. Tests were carried out in the 10-1-102 Hz interval at 5% deformation to have the material response in the linear viscoelastic regime. DMA analysis were carried out in a TA DMA Q800 model, from –20 to 120 °C at 1 Hz frequency and heating rate of 3 °C/min.

Rectangular specimens with 13.0 × 7.0 × 0.15 mm were used and experiments were done in the tensile mode with a controlled force of 0.01 N. Films tensile tests were carried out in a EMIC DL-300 universal machine at 5 mm/min after conditioning the specimens at 23 °C for 48 h. Specimens were prepared according the ASTM D882-12 method for films.

3. Results and Discussions 3.1 Oligosebacate synthesis and characterization The oligo(trimethylene sebacate) (OTS) was obtained by polycondensation of dimethylsebacate and propan‑1,3-diol catalyzed by zinc acetate (Figure 1). The OTS presented white color and a wax-like aspect. FTIR was used to confirm its structure (Figure 2). From the figure, it is possible to observe the carbonyl characteristic absorption bands at 1727 cm-1 (C=O) and 1177 cm-1 (C-C(C=O)-O). The spectrum shows also absorption bands at 2926 and 2853 cm-1 attributed to asymmetric and symmetric methylene groups in the oligoester structure as well as bands at 1350-1150 cm-1 region characteristic of vibration of long chain esters. The spectrum presents a band at 3500 cm-1 attributed to O-H bonds of alcohols, related to the hydroxyl end groups[16].

GPC results revealed that the OTS has Mn= 2,920 g/mol, Mw= 6,120 g/mol and polydispersity Mw/Mn= 2.1. From a second DSC heating run, the oligomer showed a Tg at –22 °C and cold crystallization (Tcc) at 35 °C (ΔHcc = 0.43 J/g) with a melting transition (Tm) at 50 °C, indicating that it is a semi-crystalline material. On cooling, the OTS shows a

Figure 1. Reaction of transesterification to obtain oligo(trimethylene sebacate).

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Polímeros, 28(5), 381-388, 2018

Crystallization, thermal and mechanical behavior of oligosebacate plasticized poly(lactic acid) films

Figure 2. FTIR spectrum of OTS. Figure 3. DSC curves (3rd heating run) of PLA and PLA/OTS films.

crystallization temperature (Tc) at around 27 °C (ΔHc = 4 J/g).

In the literature, the reported sebacate polyester with structure closest to OTS is the poly(ethylene sebacate) with Mw= 10,000 g/mol that presented Tg = –30 °C Tm= 74 °C[14].

The thermal stability of OTS was evaluated by thermogravimetry. The OTS showed a bimodal weight loss DTG profile, with a first maximum degradation rate Tmax = 399 °C (TONSET = 336 °C), followed by a second small weight loss at high temperature (Tmax = 440 °C).

The stability of OTS was superior to that observed for the PLA used in this work.

3.2 Plasticized films of PLA Films of PLA containing OTS was analyzed by different physical methods to have insight on the influence of this additive on the main PLA properties and evaluate the plasticizing action of this oligomer.

3.2.1 Thermal transitions and crystallinity Main transitions of PLA and PLA/OTS films were identified by DSC. Table 1 resumes the values of melting transition temperature (Tm) and degree of crystallinity (Xc) obtained in the first heating run of DSC analyses which aims to evaluate the crystallization process during film formation by polymer solution evaporation. It is possible to observe that although the PLA casting film presented low crystallinity (Xc= 6%), PLA/OTS films showed Xc significantly higher than this PLA film (Xc from 33 to 37%). It is also shown that Xc increased slightly as OTS content increased. The degree of crystallinity of PLA/OTS films was even higher than that observed for PLA pellets. This higher crystallinity may be attributed to the presence of the oligoester which induces the polymer crystallization during solvent evaporation by increasing the mobility of polymer chains[17].

Figure 3 presents the curves related to a 3rd heating run of PLA films obtained after a controlled cooling at 10 °C/min from the melt. From these curves, it is possible to see that the Tm for PLA and PLA/OTS films is superior as compared to that of PLA pellets, which may be attributed to the increase of crystal perfection due to solvent interaction with polymer chains during film formation[17].

Polímeros, 28(5), 381-388, 2018

Table 1. Main thermal transitions and degree of crystallinity of PLA and PLA/OTS casting films obtained by Differential Scanning Calorimety (DSC).

Material PLA Pellets PLA(film) PLA/OTS

OTS (%)

Tma

Xca

0

(°C) 149

(%) 22

0 1 5 10

152 151 153 150

6 33 34 37

Tgb (°C)

Tmc

Tccc

58

(°C) 149

(°C) 124

60 57 55 53

152 152 152 152

127 129 128 128

Degree of crystallinity obtained of the curve of 1 st heating; Tg obtained of the curve of 2nd heating; cTransitions values obtained of the curve of the 3rd heating. a

b

It is possible to note that the curves of all PLA casting films obtained from the 3rd heating run showed the same profile with a glass transition, a cold crystallization and a melting transition. It is important to mention also that all curves presented a similar cold crystallization (Tcc) and melting transition (Tm) temperatures, i.e., Tm and Tcc remain practically constant as OTS content increased. It must be also mentioned that during the cooling at 10 °C/min employed before the 3rd heating, no crystallization peak was observed for these samples. However, the influence of the oligomer in the crystallization process can be supported by the Xc values observed in the first heating run that are higher than those from the third heating. This difference in Xc is related to the fact that the casting films were prepared and dried at room temperature. Thus, the films were crystallized slowly during solvent evaporation. So, in the first heating, Xc is higher while in the 3rd heating after a cooling at 10 °C/min it is lower, since at this cooling rate the time is not enough for adequate material crystallization[18].

Addition of OTS to PLA decreased the Tg and this decrease is enhanced as the concentration increased, indicating the plasticizing effect of the oligomer.

Figure 4 shows the behavior of Tg obtained experimentally and Tg predicted according the Fox Equation (Equation 1)[19] for PLA/OTS films containing 1, 5 and 10 wt.% of OTS. 383/388 383

Inácio, E. M., Lima, M. C. P., Souza, D. H. S., Sirelli, L., & Dias, M. L.

( )

( )

= 1/ Tg Wx / Tg x + W y / Tg y (1)

In this equation that is used to evaluate the miscibility of polymer blends[20], Wx e Wy are the molar fraction and TGx e TGy are the glass transition temperatures of each blend components. It is possible to observe that the results presented a linear behavior, with a line coming from the same point, since in the 1 wt.% PLA/OTS system, values of theoretical and experimental Tg are practically the same.

As OTS concentration increases, Tg values start to become far from each other. This result suggests a partial miscibility of OTS in PLA, since although it is clear the influence of the oligomer on the glass transition process by the reduction of the Tg of PLA, with increasing content of OTS, the theoretical values of Tg are not attained as expected for a completely miscible system.

3.2.2 Thermal stability Commercial PLA (pellets) presented a unique stage of weight loss with TONSET and Tmax of 336 and 358 °C, respectively. However, in the PLA films prepared by casting from chloroform solutions two stages of weight loss are noted: one with TONSET e Tmax around the same temperatures observed for PLA pellets, and another at lower temperatures (TONSET = 85 °C and Tmax= 102 °C). This first stage of weight loss is attributed to the presence of residual solvent in the films[21], due the know strong interaction between chlorine and carbonyl groups[22]. This interaction also explains why this temperature of weight loss attributed to the residual

solvent (85 °C) is superior to the boiling point of chloroform (60 °C). To prove this fact, the thermal stability of PLA films was compared with that of PLA extruded. The results presented in Table 2 support that this first stage of weight loss is due to residual solvent which is still present in the films even after vacuum treatment for 24 h.

Processing in the molten state can cause chain break and decrease in the molecular weight, influencing the results of thermal decomposition shown by TG analyses. In this work, films were prepared by casting, process that did not cause any molecular weight reduction. Thus, the different weight loss profiles observed and final amount of residues at 700 °C are due to the presence and content of the oligoplasticizer in the material. All the films showed two stages of weight loss, the first around 100 °C and the second at about 350 °C. For PLA pellet, only one stage was observed differently of the cast films, confirming that the first stage of weight loss is due to solvent loss. This weight loss is in the range of 7-11 wt.%, what indicate that a considerable amount of solvent remains in the polymer even after 24 h of vacuum treatment at room temperature. These films were not dried at more severe condition by heating to avoid annealing of the films, what would influence their crystallinity.

Considering the second stage of weight loss, a decrease in TONSET and Tmax takes place when the plasticizer is added to PLA. This decrease is easily seen when the Tmax of the non-additivated film is compared with the Tmax of the sample containing 10 wt.% of OTS. It is important to emphasize that the Tonset of the non-additivated film is higher than those shown for PLA/OTS films. This fact can be explained considering the influence of the oligoester soluble fraction in the polymer which must be homogeneous dispersed in the PLA matrix[12].

The OTS used in this work has Tmax = 400 °C, which is relatively close to PLA film (Tmax = 354.2 °C). This means that the DTG peak of the second decomposition stage is not only related to PLA, but also to OTS main degradation. Thus, it is possible to conclude that addition of OTS promotes a small reduction of thermal stability of the material.

3.2.3 Morphology by X-ray diffraction

Figure 4. OTS concentration versus theoretical and experimental glass transition temperature.

X-ray diffraction (XRD) was used to evaluate the influence of the oligoester on the crystallinity of the films.

Figure 5 shows the XRD curves of PLA and PLA/OTS films containing 1, 5 and 10 wt% OST. The XRD curve of the PLA film showed an amorphous halo, indicating low degree of crystallinity of this film. However, PLA/OTS films presented three crystalline reflections at 17, 19 and

Table 2. Evaluation of weight loss stages for PLA pellet, PLA extruded and PLA cast films.

PLA Sample Pellet Extruded Film PLA/OTS

384 384/388

OTS (%) 0 0 0 1 5 10

TONSET (°C) 85 87 89 96

Stage I Tmax (°C) 102 120 125 125

Weigh loss (%) 7.8 8.4 7.9 6.6

TONSET (°C) 336 329 332 329 324 329

Stage II Tmax (°C) 358 353 354 355 356 342

Residue at 700 °C (%) 0.9 1.8 0.4 0.3 0.7 1.2

Polímeros, 28(5), 381-388, 2018

Crystallization, thermal and mechanical behavior of oligosebacate plasticized poly(lactic acid) films

Figure 5. X ray diffraction curves of PLA and PLA/OTS films.

Figure 6. Storage modulus (G’) and loss modulus (G”) as a function of the frequency for PLA and PLA/OTS film containing 10 wt.% OTS.

23° indicating that these films are semi-crystalline materials.

According to Byun et al.[17], these reflections are characteristics of PLA casting films from chloroform. It is interesting to note that the intensity of the reflection at 23° increases linearly as OST content increases. This indicates that OTS seems to be inducing PLA crystallization. According to DSC data, OTS is only partially soluble in PLA at higher contents. No crystalline peak that could be attributed to OTS crystallization was observed. So, this increase in crystallinity seems to be related a nucleation effect of OTS insoluble phase that is probably in the amorphous state.

3.2.4 Rheological behavior Storage modulus (G’), loss modulus (G”) and complex viscosity (η*) as a function of frequency of PLA/OTS was evaluated at 165 °C to investigate the rheological behavior of these materials (Figures 6 and 7). The measurements were carried out at deformation of 5%, which is in the interval of linear viscoelasticity of high molecular weight of PLA without any additive[23,24].

Figure 6 shows the G’ and G” versus frequency curves for the PLA and PLA/OTS containing 10 wt.% of the oligomer. From the figure, one can observe that G’ decreased with addition of the oligoester as expected, being this effect practically the same along the region of low and high frequencies. The behavior of loss modulus G” versus frequency shows also a reduction of G” with the addition of the oligomer. In this case, the decrease of G” is more pronounced in frequencies lower than 10 Hz. The figure shows a transition from a fluid-like (G” > G’) to a solid-like (G’ > G”) between 5 and 20 Hz. The crossover frequency shifts to a higher value with the addition of OTS, indicating that the response becomes more fluid-like, as should be expected.

Figure 7 shows the curves of complex viscosity (η*) versus frequency for these two samples. Also for this rheological property, non-additivated PLA presents a higher value compared with the sample containing 10 wt.% OTS. This expected decrease in η* is due to oligoester molecules solubilization in the PLA matrix which reduces the melt Polímeros, 28(5), 381-388, 2018

Figure 7. Complex viscosity as function of frequency for PLA and PLA/OTS film containing 10 wt.% OTS.

viscosity[25]. This behavior is another indication of the plasticization effect of OTS over PLA during the processing.

3.2.5 Dynamic mechanical behavior Curves of storage modulus (E’) of PLA and PLA/OTS films obtained from dynamic mechanical analysis are presented in Figure 8. The curves show a typical behavior of thermoplastic polymers, with a drastic decay of E’ when approaching to PLA glass transition. After Tg, a plato can be identified. According to Huda et al.[26], this behavior observed for PLA casting films like elastomers, which presents amorphous and crystalline phases in their structure.

From the curves, it is possible to note that the modulus decreases when the content of OTS is increased in the films.

Values of storage modulus for these films in temperatures which are representatives for application condition, i.e. below and above Tg (–20, 0 and 60 °C), were selected and are presented in Table 3. From the table, by analyzing each temperature separately, it is possible to observe that a significant decrease in the storage modulus occurred at 385/388 385

Inácio, E. M., Lima, M. C. P., Souza, D. H. S., Sirelli, L., & Dias, M. L. –20 and 0 °C as the concentration of the oligomer increases.

For 60 °C, close to the glass transition temperature, a drastic reduction in the E’ took place. This behavior is expected since at Tg the system acquires high level of chain segmental mobility[26]. After 70 °C, an increase of E’is observed for PLA and PLA/OTS containing 1 wt.% OTS that can be attributed to thermal crystallization, meaning that these films had still amorphous materials capable of crystallizing.

of crystallinity according to DSC results. The thermal crystallization of PLA and PLA/OTS with 1 wt.% OTS was also detected by the loss modulus curves.

Figure 9 presents the loss modulus (E”) curves as a function of temperature for PLA and PLA/OTS with 1, 5 e 10 wt.% OTS, respectively. The curves presented the characteristic peak of relaxation phenomenon related to the glass-rubber transition. Values of Tg were obtained from the maximum of loss modulus peaks (Table 3). It is possible to observe that the Tg values obtained from the lost modulus peaks are lower than those observed from DSC (Table 1).

This difference can be related to the cyclic mechanical stress applied in tensile mode in addition to DMA heating, differently from DSC, which uses only thermal heating.

The intensity of these maximum peaks for casting films is related with the relaxation index inhibited by the crystalline phase of the films[26]. Thus, it is possible to observe the less intense peak for PLA/OTS 10 wt.% that has higher degree

3.2.6 Tensile properties

Figure 8. Storage modulus versus temperature for PLA and PLA/OTS films.

Although, it was observed a certain degree of haze in the films with higher content of OTS, no indication of the OTS phase separation could be detected from dynamic mechanical tests.

Tensile properties of PLA films containing OTS were evaluated according the ASTM D 882-12 method. Table 4 resumes the results of stress and strain at yield and at break for films with 1, 5 and 10 wt.% of OTS. According to literature[27], the young’s modulus should decrease with addition of the oligomer, since plasticizers reduce the intermolecular forces that actuate in the macromolecular chains, increasing material flexibility.

Although, a considerable experimental error was observed in the elastic modulus values (not presented in the table), the film containing 1 wt.% OTS showed a slightly increase of modulus. For the films with 5 and 10 wt.% OTS, the expected decrease in the elastic modulus was observed.

Figure 9. Loss modulus curves for PLA e PLA/OTS films.

Table 3. Storage modulus at –20, 0 and 60 °C and Tg obtained from loss modulus peak of PLA and PLA/OTS casting films.

Sample (casting film) PLA/OTS

E’ (MPa)

Tg

OTS (wt.%)

–20 °C

0 °C

60 °C

0 1 5 10

2711 2005 1661 1337

2639 2007 1693 1306

49 27 63 61

(°C)a 37 32 31 25

Deformation at maximum stress (%) 6±0 6±0 298 ± 11 261 ± 41

Ultimate stress

Elongation at break

Values obtained from peak maximum of E’.

a

Table 4. Tensile properties of PLA and PLA/OTS films obtained by casting.

Sample PLA PLA/OTS

386 386/388

OTS (wt.%)

Maximum Stress

0 1 5 10

26 ± 8 25 ± 2 22 ± 3 16 ± 2

(MPa)

(MPa)

(%)

14 ± 5 9±3 16 ± 2 21 ± 4

10 ± 4 263 ± 40 299 ± 10

Polímeros, 28(5), 381-388, 2018

Crystallization, thermal and mechanical behavior of oligosebacate plasticized poly(lactic acid) films for financial support and CAPES for the E.M. Inacio scholarship.

6. References

Figure 10. Tensile test specimens of (a) PLA before tensile test and after the test: (b) PLA, (c) PLA/ 5 wt.% OMT (d) PLA/ 10 wt.% OTS.

Addition of OTS to PLA films produced the expected effect of increasing the elongation at break and consequently the ductility of these films (Figure 10). The observed values of elongation at break of PLA/OTS films with 5 and 10 wt.% indicates a marked increase in the ductility of the films, which corroborate the plasticizing effect of OTS[27].

4. Conclusions A oligoester based on the bio-based monomers trimethylene glycol and sebacic acid (OTS) was synthesized and applied to PLA plasticization. According to thermal analyses studies, it was possible to demonstrate that the addition of this oligomer to the polyester decreases the glass transition temperature of the films, evidencing that OTS acts canceling polymer‑polymer interaction which allows to increase mobility of the amorphous phase. Nevertheless, a partial miscibility which decrease transparency was confirmed by the comparison of the expected theoretical and experimental Tg values. The oligomer also produced an unexpected increase of the degree of crystallinity of PLA films, contributing also for the decrease in their transparency.

PLA films containing OTS show lower storage moduli that decreased as the content of OTS increased. From mechanical tests, these PLA-OTS films presented an increase in the elongation at break, suggesting increase in the ductility.

By considering the results, it is evident the plasticizing effect of this oligomer on PLA.

5. Acknowledgements The authors are grateful to Conselho Nacional de Pesquisa Científica e Tecnológica – CNPq (Process 310917/2014-0) and FAPERJ (E-26/201.304/2014) Polímeros, 28(5), 381-388, 2018

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Received: July 12, 2017 Revised: Nov. 13, 2017 Accepted: Jan. 04, 2018

Polímeros, 28(5), 381-388, 2018

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.05117

Sericin as compatibilizer in starch/ polyester blown films Patrícia Salomão Garcia1,2, Franciele Rezende Barbosa Turbiani2, Alessandra Machado Baron2, Guilherme Luiz Brizola2, Mariane Alves Tavares2, Fabio Yamashita1, Daniel Eiras3 and Maria Victória Eiras Grossmann1* 1

Grupo de Pesquisa em Materiais Biodegradáveis – Polibiotec, Departamento de Ciência e Tecnologia de Alimentos, Universidade Estadual de Londrina – UEL, Londrina, PR, Brasil 2 Coordenação da Licenciatura em Química – COLIQ, Universidade Tecnológica Federal do Paraná, Câmpus de Apucarana – UTFPR, Apucarana, PR, Brasil 3 Departamento de Engenharia de Materiais, Universidade Federal de São Carlos – UFSCar, São Carlos, SP, Brasil * victoria@uel.br

Abstract This study investigated the effects of low concentrations of sericin (≤ 1.5 wt%) in starch- poly(butylene-adipate-co-terephthalate) (PBAT) films. The films were produced by blown extrusion and mechanical, barrier and structural properties were determined. Films containing 1.0 and 1.5 wt% sericin showed higher tensile strength (6.41 and 6.59 MPa) and Young’s modulus (90.88 and 132.71 MPa) compared with film without sericin (4.76 MPa and 18.64 MPa). When 0.5 wt% of sericin was used, the elongation was reduced by 62%. The addition of sericin in a concentration of 1.5% (w/w) decreased the water vapor permeability of films from 7.55 to 5.94 g (m s Pa)-1, likely due to the formation of a more homogeneous and compact matrix. Based on these results, a mechanism of action is proposed, whereby sericin acts at the interface of the polymers (starch and PBAT), reducing the interfacial tension and enhancing compatibility.

Keywords: biodegradable packaging, compatibilization, extrusion, poly(butylene- adipate-co-terephthalate).

1. Introduction The blending of starch with biodegradable polyesters is a well-known strategy to improve the mechanical and/or barrier properties of starch-based packaging materials.

Thus, mixtures with poly(butylene adipate co-terephthalate) (PBAT)[1-4], polylactic acid (PLA)[5,6], and poly(vinyl) alcohol (PVOH)[7], among others, have been studied. Due to the differences in polarity between starch (hydrophilic) and polyesters (hydrophobic), the use of a compatibilizer has been shown to be necessary. Compatibilizers act by reducing interfacial tension caused by differences in polarity, thereby improving the polymer compatibility. Consequently, barrier and/or mechanical properties of the materials are improved[1-3,8-11].

In previous studies, proteins have been added to starch for the manufacturing of packaging materials[12-15].

In these works, proteins were generally included at levels ranging from 10 to 50 wt%, as part of the polymer matrix.

The impact of these additions on the mechanical properties of the materials can be positive or negative, depending on the protein structure, concentration in the blend and processing conditions.

To the best of our knowledge, there are no studies on the use of protein at low concentrations (≤ 1.5 wt%) as an additive in starch/polyester blends. However, in preliminary tests, we observed that sericin (a silk protein) seems to present compatibilizer action in blends of starch/PBAT processed by extrusion. During processing, the denaturation of sericin

Polímeros, 28(5), 389-394, 2018

should occur, which unfolds its chains and improves its interaction with both starch and PBAT. Sericin is a protein extracted from the Bombyx mori silkworm. Sericin acts as a natural glue that fixes silk fibers (fibroin) together. During silk production, fibroin is recovered and sericin removed and discharged as a waste.

The molecular weight of sericin ranges from 24 to 400 kDa[16], and the predominant amino acids are serine (40%), glycine (16%), glutamic acid, aspartic acid, threonine, and tyrosine[17]. While fibroin is being studied as an interesting biocompatible material for tissue engineering, sericin is generally neglected.[18]. However, sericin could be used as an additive or adjuvant in polymer blends, thereby adding value and promoting a positive impact on the environment.

Thus, the objective of this work was to evaluate the role played by small amounts of sericin (≤ 1.5 wt%) in blown films of starch-PBAT and to propose a mechanism of action.

2. Materials and Methods 2.1 Materials The films were manufactured with cassava starch (23 wt% amylose and 13.3 wt% moisture), provided by Indemil (Paranavaí, Brazil); poly(butylene-adipate-co-terephthalate) PBAT (Ecoflex® S BX 7025, Basf, Ludwigshafen, Germany); glycerol (Dinamica, Diadema, Brazil), and sericin (extracted

389/394 389

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

Garcia, P. S., Turbiani, F. R. B., Baron, A. M., Brizola, G. L., Tavares, M. A., Yamashita, F., Eiras, D., & Grossmann, M. V. E. from silkworm cocoons (Bombyx mori), according with the methodology employed by Turbiani et al.[18].

2.2 Production of films The components of each formulation were manually mixed and extruded through a die with six 2-mm diameter holes in a laboratory twin-screw extruder (D-20, BGM, Taboão da Serra, Brazil) in order to obtain the pellets.

The screws had a 20 mm diameter (D) and L/D=35.

The screw speed was 100 rpm and the temperature profile was 90/120/120/120/120 °C at the five heating zones.

Then, the pellets were again extruded using a mono-screw extruder (EL-25, BGM, Taboão da Serra, Brazil) to obtain the blown films. The screw had D=25 mm and D/L=26.

The temperature profile was 90/120/120/130 °C at the four heating zones and 130 °C at the 50-mm film- blowing die, and the screw speed was 40 rpm. The control formulation (without sericin) contained 61, 26 and 13 (wt %) manioc starch, PBAT and glycerol, respectively. Preliminary tests suggested that sericin has a plasticizing effect. Additionally, these tests showed that sericin contents higher than 2 (wt%) may compromise the production and the properties of the films.

Therefore, three other formulations were tested containing 0.5, 1.0 and 1.5 sericin (wt%). These concentrations were deducted from those of glycerol to keep the concentration of plasticizer constant. The samples were coded as 0S, 0.5S, 1.0S and 1.5S, with the numbers representing the sericin concentration (wt%). The thickness of the films was determined as the average of five random measurements of each sample, using a digital micrometer (Mitutoyo, Illinois, USA).

2.6 Fourier transformed infrared spectroscopy (FT-IR) Previously cut films were dried for one week in a desiccator containing anhydrous CaCl2 (~ 0% RH). FT-IR spectra were obtained with an FT-IR spectrophotometer 640-IR model (Varian, São Paulo, Brazil) provided with a module of Attenuated Total Reflectance (ATR). The analyses covered the wave numbers from 4000 to 400 cm-1 with a resolution spectrum of 4 cm-1. Twelve scans were performed on each sample.

2.7 Dynamic Mechanical Analysis (DMA) A Dynamical Mechanical Analyzer (DMA - model Q800, TA Instruments, New Castle, USA) was used. The samples (previously conditioned at 53% RH for 7 days) were scanned from - 90 °C to 100 °C with heating rate of 3 °C /min and fixed frequency of 1 Hz. Glass transition temperatures (Tg) were obtained as the temperatures of the tan δ peaks.

2.8 Statistical analysis The data were analyzed using STATISTICA 7.0 software (StatSoft, Oklahoma) with analysis of variance (ANOVA) and Tukey test at a 5% significance level.

3. Results and Discussion All the films, both with and without sericin, presented good handleability, processability, flexibility and uniformity with smooth surfaces. The mean thickness ranged from 180.4 to 247.7 µm.

3.1 Films morphology-scanning electron microscopy (SEM)

The fractured surfaces of the films were assessed using an FEI Quanta 200 scanning electron microscope (FEI Company, Tokyo, Japan), which was operated at an acceleration voltage of 20 kV. The samples were cooled in liquid nitrogen and then broken (cryogenic fracture).

Before coating with a gold layer, the samples were stored at 25±2 °C in a desiccator with anhydrous CaCl2 (~0% RH) for 2 days. Images were taken at a magnification of 1600x.

As observed on the micrographs of film fracture (Figure 1), the absence of starch granules demonstrates the process was adequate, promoting the desired disruption of the granular structure. This disruption is essential to enable better starch interaction with glycerol and PBAT. All samples showed fibrillar structure, with oriented grips indicating the chain orientation promoted by the process. The addition of sericin at 1.0 and 1.5 (wt %) levels formed films with slightly more homogenous and compact structures, suggesting the matrices were more cohesive.

2.4 Mechanical properties

3.2 Mechanical properties

The tensile properties were determined using the texture analyzer model TATX2i (Stable MicroSystems, Surrey, England), according to the ASTM-D882-02 method[19]. The samples, previously conditioned at 53±2% RU (Mg(NO3)2 saturated solution) and 25±2 °C for 48 h, were cut (50 mm x 20 mm) along the longitudinal direction. The crosshead speed was set at 0.83 mm.s-1 (load cell of 50 kg), and the initial distance between the grips was 30 mm. Five replicates were evaluated.

The values of tensile strength, elongation at break and Young’s modulus are shown in Table 1. Increasing sericin concentration up to 1.0 (wt%) (1.0S) significantly (p ≤ 0.05) increased the tensile strength of the films. A further increase was not observed when sericin was added at the 1.5 (wt %) level (1.5S). The maximum value obtained (6.59 ± 0.28 MPa) was 36% greater than that of the film without sericin (4.76 ± 0.16 MPa).

On the other hand, the elongation was reduced by 62% with the inclusion of the lower level of sericin (sample 0.5S). Indeed, the elongation decreased even further with the increase of sericin concentration up to the maximum concentration tested. These effects also impacted the Young’s modulus, which increased with the increasing protein

2.3 Scanning Electron Microscopy (SEM)

2.5 Water Vapor Permeability (WVP) The ASTM E-96-00 method[20], modified as described in our previous work[1], was used. Tests were conducted in triplicate.

390 390/394

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Sericin as compatibilizer in starch/ polyester blown films

Figure 1. Electron micrographs of films (fractures) containing different levels of sericin.

Table 1. Mechanical properties and water vapor permeability of the films.

Sample 0S 0.5S 1.0S 1.5S

σ (MPa) 4.76 ± 0.16c 5.75 ± 0.16 b 6.41 ± 0.31a 6.59 ± 0.28a

ε (%) 252.22 ± 18.13a 95.49 ± 16.24b 83.05 ± 29.95b 45.79 ± 16.02c

E0 (MPa) 18.64 ± 2.44d 66.33 ± 4.54c 90.88 ± 10.58b 132.71 ± 12.97a

WVP (x10-11 g (m s Pa)-1) 7.55 ± 0.72a 6.80 ± 0.56ª,b 6.91 ± 0.67ª,b 5.94 ± 0.21b

σ: tensile strength; ε: elongation at break; E0: Young’s modulus; and WVP: water vapor permeability. Results expressed in (mean ± standard deviation). a,b Different letters in the same column indicate significant differences (p≤0.05) according to the Tukey’s test.

concentration, ultimately reaching a value 700% greater than 0S when 1.5 wt% sericin was added. Both results, decreased elongation and increased rigidity, indicated the molecular mobility of the starch and PBAT chains was reduced by the presence of sericin. Initially, one can understand this effect as similar to that produced when the plasticizer is reduced. Sericin levels were substituted at similar levels to glycerol; thus, if the plasticizing action of sericin was null or lower than that of glycerol, there would be a decrease in plasticizer level. However, this cannot be the only reason for the increase in stiffness of the films, as the reduction in glycerol was very small to justify this behavior.

Several authors have employed proteins in blends with starch for the manufacturing of films[12,13,15,21,22]. However, in these works, protein was incorporated at higher concentrations (10 to 50 wt%), thereby configuring the protein as another constituent of the polymer matrix. In these cases, the effects of the proteins on the mechanical properties of the films varied as a function of the structural configuration of the protein and of the characteristics of the starch; however, Polímeros, 28(5), 389-394, 2018

the tensile strength predominantly decreased, while the elongation of the starch films increased.

These results are contrary to those observed in our work, which show that sericin may be considered as an additive due to the low amounts used. Thus, we propose another mechanism of action by which the sericin, due to its amphoteric character, acts similarly to a surfactant agent. Thus, the side chains of amino acid residues with hydrophobic character (such as glycine) and hydrophilic character (such as serine, aspartate, and asparagine) interact with PBAT and starch, respectively. Then, once located in the interface between these polymers (Figure 2), sericin establishes molecular interactions with them, making the material more resistant and less flexible. In addition to being a plasticizer, sericin could act as a compatibilizer, contributing to greater dispersion and interaction between the starch-PBAT phases. This proposed mechanism explains the more homogenous and compact morphology (shown in Figure 1) and the higher values of tensile strength and Young’s modulus observed in samples 1.0S and 1.5S (Table 1).

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Garcia, P. S., Turbiani, F. R. B., Baron, A. M., Brizola, G. L., Tavares, M. A., Yamashita, F., Eiras, D., & Grossmann, M. V. E.

Figure 2. Scheme representing interactions between fragments of: (a) PBAT, (b) protein and (c) starch. R=side chains of amino acids residues.

Mariani et al.[23] added soy protein isolate (SPI) in blends of poly (3-caprolactone) and corn starch and observed an increase in tensile strength and elongation with 3.5 wt% SPI. However, when 11 wt% of SPI was added, no effect was observed. These results indicate that low concentrations of proteins could act as compatibilizers, although the authors did not explore this possibility.

3.3 Water Vapor Permeability (WVP) The films containing the highest level of sericin (1.5S) showed significantly lower WVP (5.94 x 10-11 g (m s Pa)-1) than the film without sericin (7.55 x 10-11 g (m s Pa)-1), as shown in Table 1. The more compact structure observed in the 1.5S sample (Figure 1) may have reduced the WVP. The amphiphilic composition of sericin may have contributed to a better interaction with starch and PBAT, forming a more tight material, which restricted the water diffusion.

Other authors[1-3,11] have shown that when compatibilizers are used in starch/polyester blends the result is always a more homogeneous and denser matrix due to improvement in the interfacial adhesion.

3.4 Fourier Transform Infrared Spectroscopy (FTIR) ATR-FTIR spectra of starch- PBAT- sericin films are shown in Figure 3. Characteristic bands previously observed by other researchers[1,2] in starch/PBAT blends are present in all samples, such as those at 3000-3500, 2800-2930 and 1715 cm-1, which is attributed to the OH- stretching, CH- stretching and absorption of carbonyl groups of esters, respectively.

The broadband at 3000-3500 cm-1 could also represent N-H stretching from sericin in samples containing this protein.[24,25] 392 392/394

As the concentration of sericin increased from 0 to 1.5 (wt%), a progressive reduction in the intensity of the absorption band at 3000- 3500 cm-1 was observed, indicating a hydrogen bonding interaction between sericin and starch and/or PBAT chains. This increase in hydrogen bonding could explain the action of sericin, which strengthens the material structure and thus explains the results of tensile strength and modulus.

At the same time, the hydroxyl groups of starch and carbonyl groups of PBAT, involved in the interactions with sericin, become unavailable to form hydrogen bonds with water, thereby explaining the decrease in WVP. In the samples 0.5S, 1.0S, and 1.5S, the characteristic bands of random coil structure of sericin at approximately 1650 cm-1 (C=O stretching, amide I) and 1520 cm-1 (N-H deformation, amide II)[26] were marginally observed, likely due to its low concentration.

The absorption band at 1715 cm-1 in the film without sericin (0S) is attributed to the stretching of the C=O groups[25] present in the PBAT structure. The progressive increase in the protein concentration in samples 0.5S, 1.0S, and 1.5S caused an increase in the number of amide bonds (-NH2C=O), which justifies the increases in the relative intensities of the absorption bands in this region. Additionally, the residues of the amino acids aspartate and asparagine, constituents of sericin, have carbonyl groups in the side chain, which could also contribute to the increase in absorption in the region 1700 -1750 cm-1.

The bands at 1025, 1110 and 1270 cm-1 are assigned to the stretching of the C-O bonds[1,25] present in starch, glycerol, PBAT and sericin. The intensity of the last two bands increased as more sericin was added to the films.

Polímeros, 28(5), 389-394, 2018

Sericin as compatibilizer in starch/ polyester blown films

Figure 3. FT-IR spectra of the films with different sericin concentrations.

Figure 4. Storage modulus and tan δ as a function of temperature.

3.5 Dynamic Mechanical Properties (DMA) The results of storage modulus (E´) and tan δ are shown in Figure 4. The E´values of samples decreased with the increase of temperature. Similar values of E´ were observed for all the samples at temperatures lower than -35 °C. Further increases in temperature showed higher storage moduli of the sample 1.5S compared with those of the other samples indicating lower chain mobility. Additionally, at temperatures higher than approximately 50 °C the E´values of samples 0.5S and 1.0S were lower than the observed for 0S. The tan δ curves showed three relaxations in all samples, indicating the presence of three partially miscible phases.

In the control sample (0S), these relaxations are located at -58 °C, -29 °C and 54 °C. According to Olivato et al.[27], these peaks represent the glass transition temperatures (Tg) of the glycerol, PBAT and starch-riches phases, respectively.

Samples containing sericin showed different behaviors depending on its concentration. While in 0.5S films the Tgs were similar to those of the control, in the 1.0S sample the Tg of the starch- rich phase was shifted to a higher temperature (63 °C). This result indicated the molecular mobility of the starch chains was reduced by the presence of sericin and Polímeros, 28(5), 389-394, 2018

could explain the increase in stiffness observed in Table 1.

Differently, the highest content of sericin (1.5S) shifted the tan δ peaks of the PBAT and starch- rich phases to lower temperatures (-35 and 50 °C, respectively), indicating a plasticizing effect. The wide range of chain lengths and chain branching of starch (indicated by the relatively broad tan δ peak) associated with the wide molar mass distribution of sericin can help to explain these results. The short chain segments of sericin could act as plasticizers improving the mobility of the polymer short chain segments, while the larger sericin segments could act as compatibilizers between polymers, increasing stiffness.

4. Conclusions The mechanical and barrier properties of blown films manufactured with blends of starch and PBAT were improved when low (≤1.5 wt%) concentrations of sericin were added. These effects, together with the formation of a more homogeneous and compact microstructure of films, allows one to hypothesize that sericin may have a compatibilizing action. Due its amphoteric character, sericin could be located at the interface between starch and PBAT, 393/394 393

Garcia, P. S., Turbiani, F. R. B., Baron, A. M., Brizola, G. L., Tavares, M. A., Yamashita, F., Eiras, D., & Grossmann, M. V. E. reducing the interfacial tension and enhancing compatibility.

Further studies should be performed with other proteins to extend the applicability of these conclusions.

5. Acknowledgements The authors would like to thank the laboratories of spectroscopy (ESPEC) and of microanalysis (LMEM) from the Universidade Estadual de Londrina (UEL) for the FTIR and SEM analyses and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial support.

6. References 1. Garcia, P. S., Grossmann, M. V. E., Shirai, M. A., Lazaretti, M. M., Yamashita, F., Muller, C. M. O., & Mali, S. (2014). Improving action of citric acid as compatibiliser in starch/polyester blown films. Industrial Crops and Products, 52, 305-312. http://dx.doi. org/10.1016/j.indcrop.2013.11.001.

2. 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.

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3. Ren, J., Fu, H., Ren, H., & Yuan, W. (2009). Preparation, characterization and properties of binary and ternary blends with thermoplastic starch, poly(lactic acid) and poly(butylene adipateco-terephthalate). Carbohydrate Polymers, 77(3), 576-582. http:// dx.doi.org/10.1016/j.carbpol.2009.01.024.

4. Thunwall, M., Kuthanova, 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.

5. Teixeira, E. M., Curvelo, A. A. S., Corrêa, A. C., Marconcini, J. M., Glenn, G. M., & Mattoso, L. H. C. (2012). Properties of thermoplastic starch from cassava bagasse and cassava starch and their blends with poly (lactic acid). Industrial Crops and Products, 37(1), 61-68. http://dx.doi.org/10.1016/j.indcrop.2011.11.036.

6. Shirai, M. A., Olivato, J. B., Demiate, I. M., Müller, C. M. O., Grossmann, M. V. E., & Yamashita, F. (2016). Poly(lactic acid)/thermoplastic starch sheets: effect of adipate esters on the morphological, mechanical and barrier properties. Polímeros: Ciência e Tecnologia, 26(1), 66-73. http://dx.doi.org/10.1590/01041428.2123.

7. Shi, R., Bi, J., Zhang, Z., Zhu, A., Chen, D., Zhou, X., Zhang, G. L., & Tian, W. (2008). The effect of citric acid on the structural properties and cytotoxicity of polyvinyl alcohol/starch films when molding at high temperature. Carbohydrate Polymers, 74(4), 763-770. http://dx.doi.org/10.1016/j.carbpol.2008.04.045.

8. Ma, X., Yu, J., & Zhao, A. (2006). Properties of biodegradable poly(propylene carbonate)/starch composites with succinic anhydride. Composites Science and Technology, 66(13), 23602366. http://dx.doi.org/10.1016/j.compscitech.2005.11.028.

9. Miranda, V. R., & Carvalho, A. J. F. (2011). Blendas compatíveis de amido termoplástico e polietileno de baixa densidade compatibilizadas com acido cítrico. Polímeros: Ciência e Tecnologia, 21(5), 353360. http://dx.doi.org/10.1590/S0104-14282011005000067.

10. Ning, W., Jiugao, Y., Xiaofei, M., & Ying, W. (2007). The influence of citric acid on the properties of thermoplastic starch/ linear low-density polyethylene blends. Carbohydrate Polymers, 67(3), 446-453. http://dx.doi.org/10.1016/j.carbpol.2006.06.014.

11. Raquez, J. M., Nabar, M. Y., Narayan, R., & Dubois, P. (2008). In situ compatibilization of maleated thermoplastic starch/polyester melt-blends by reactive extrusion. Polymer Engineering and Science, 48(9), 1747-1754. http://dx.doi.org/10.1002/pen.21136.

12. Al-Hassan, A. A., & Norziah, M. H. (2012). Starch-gelatin edible films: water vapour permeability and mechanical properties as 394 394/394

affected by plasticizers. Food Hydrocolloids, 26(1), 108-117. http://dx.doi.org/10.1016/j.foodhyd.2011.04.015.

13. Basiak, E., Lenart, A., & Debeaufort, F. (2017). Effects of carbohydrate/protein ratio on the microstructure and the barrier and sorption properties of wheat starch-whey protein blend edible films. Journal of the Science of Food and Agriculture, 97(3), 858-867. http://dx.doi.org/10.1002/jsfa.7807. PMid:27197704.

14. Corradini, E., Souto de Medeiros, E., Carvalho, A. J. F., Curvelo, A. A. S., & Mattoso, L. H. C. (2006). Mechanical and morphological characterization of starch/zein blends plasticized with glycerol.

Journal of Applied Polymer Science, 101(6), 4133-4139. http:// dx.doi.org/10.1002/app.23570.

15. Rocha, G. O., Farias, M. G., Carvalho, C. W. P., Ascheri, J. L. R., & Galdeano, M. C. (2014). Filmes compostos biodegradáveis a base de amido de mandioca e proteína de soja. Polímeros: Ciência e Tecnologia, 24(5), 587-595. http://dx.doi.org/10.1590/01041428.1355.

16. Cao, T. T., & Zhang, Y. Q. (2016). Processing and characterization of silk sericin from Bombyx mori and its application in biomaterials and biomedicines. Materials Science and Engineering C, 61(1), 940-952. http://dx.doi.org/10.1016/j.msec.2015.12.082.

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17. Takasu, Y., Yamada, H., & Tsubouchi, K. (2002). Isolation of three main sericin components from the cocoon of the silkworm, Bombyx mori. Bioscience, Biotechnology, and Biochemistry, 66(12), 2715-2718. http://dx.doi.org/10.1271/bbb.66.2715.

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18. Turbiani, F. R. B., Tomadon, J. Jr, Seixas, F. L., & Gimenes, M. L. (2011). Properties and structure of sericin films: effect of the cross linking degree. Chemical Engineering Transactions, 24, 1489-1494. http://dx.doi.org/10.3303/CET1124249.

19. American Society for Testing and Materials – ASTM. (2002).

Standard test method for tensile properties of thin plastic sheeting.

Philadelphia: ASTM. D-882-02 20. American Society for Testing and Materials – ASTM. (2000).

Standard test methods for water transmission of material.

Philadelphia: ASTM. E-96-00.

21. Fakhouri, F. M., Costa, D., Yamashita, F., Martelli, S. M., Jesus, R. C., Alganer, K., Collares-Queiroz, F. P., & Innocentini-Mei, L. H. (2013). Comparative study of processing methods for starch/ gelatin films. Carbohydrate Polymers, 95(2), 681-689. http:// dx.doi.org/10.1016/j.carbpol.2013.03.027. PMid:23648030.

22. Sun, Q., Sun, C., & Xiong, L. (2013). Mechanical, barrier and morphological properties of pea starch and peanut protein isolate blend films. Carbohydrate Polymers, 98(1), 630-637. http:// dx.doi.org/10.1016/j.carbpol.2013.06.040. PMid:23987392.

23. Mariani, P. D. S. C., Allganer, K., Oliveira, F. B., Cardoso, E. J. B. N., & Innocentini-Mei, L. H. (2009). Effect of soy protein isolate on the thermal, mechanical and morphological properties of poly (3-caprolactone) and corn starch blends. Polymer Testing, 28(8), 824-829. http://dx.doi.org/10.1016/j.polymertesting.2009.07.004.

24. Joshi, M., Gulrajani, M. L., & Bar, M. (2015). Novel cross-linked sericin films: characterization and properties. Journal of Applied Polymer Science, 132(5), n/a. http://dx.doi.org/10.1002/app.41400.

25. Pavia, D. L., Lampman, G. M., Kriz, G. S., & Vyvyan, J. R. (2009).

Introduction to spectroscopy. 4th edition, Belmont: Brooks/Cole.

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Preparation and characterization of electrospun nanofibers based on silk sericin powders. Journal of Materials Science, 48(10), 3731-3736. http://dx.doi.org/10.1007/s10853-013-7171-6.

27. Olivato, J. B., Nobrega, M. M., Müller, C. M. O., Shirai, M. A., Yamashita, F., & Grossmann, M. V. E. (2013). Mixture design applied for the study of the tartaric acid effect on starch/polyester films. Carbohydrate Polymers, 92(2), 1705-1710. http://dx.doi. org/10.1016/j.carbpol.2012.11.024. PMid:23399209.

Received: May 27, 2017 Revised: Nov. 13, 2017 Accepted: Nov. 14, 2017 Polímeros, 28(5), 389-394, 2018

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.15916

Influence of solvent used on oxidative polymerization of Poly(3-hexylthiophene) in their chemical properties Juliana de Castro Macêdo Fonsêca1* and Maria dos Prazeres Arruda da Silva Alves2 Unidade Acadêmica do Cabo de Santo Agostinho, Universidade Federal Rural de Pernambuco – UFRPE, Cabo de Santo Agostinho, PE, Brasil 2 Departamento de Química Fundamental, Universidade Federal de Pernambuco – UFPE, Recife, PE, Brasil 1

*juliana.fonseca@ufrpe.br

Abstract The aim of the study is to utilize the simplicity of oxidative polymerization with ferric chloride to originates poly(3-hexylthiophene) of lower molecular weight. So, the chloroform, in general used as solvent in this synthesis, was switched by dichloromethane. The obtained polymers were characterized by infrared spectroscopy (FTIR), ultra-violet visible spectroscopy (UV-Vis), gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) were used to evaluate the structure, conjugation length, molecular weight and regioregularity with the goal of comparing these properties with those of poly (3-hexylthiophene) synthesized in chloroform. Despite large difference observed in molecular weight of polymers obtained by chloroform and dichloromethane, no significant differences were observed of these polymers in regioregularity and conjugation length.

Keywords: ferric chloride, oxidative coupling, poly(3-alkylthiophene), poly(3-hexylthiophene).

1. Introduction Conjugated polymers are largely studied due to the combination of characteristics similar to semiconductors (electrical and optical properties) and low weight and processability of common polymers. Between these polymers, polythiophenes are one of the most studied polymer due to possibility of attach different functional groups into their backbone to originates different properties[1].

The insertion of alkylic chain on position 3 of thiophene ring brings to this polymer the possibility of being melted and solubilized[2]. These polymers can be applied in fabrication of electroluminescent devices, as light emission diode (LED), Field Effect Transistors (FET)[1], Polymer solar cells[3].

There are many synthetic methods for polymerization of 3-alkylthiophene by chemical synthesis, for instance Rieke, McCullough and GRIM methods[4-6]. The differential of these methods is that the obtaining polymers have low molecular weight and high content of regioregularity.

On the other hand, these methods need more than one step of reaction and special conditions of synthesis, such as temperature maintained lower than -5 °C or higher than 60 °C. The chemical synthesis with ferric chloride (FeCℓ3), although do not leads to high regioregularity polymers, is probably the most used chemical method of synthesis due to its simplicity and possibility of be applied in large scale. Almost all the polymerizations reactions of poly(3-alkylthiophene) by chemical oxidation with FeCℓ3 uses chloroform as solvent. This polymerization originates polymers with regioregularity about 70-80% and high molecular weight in relation to other methods[7]. In some applications, like those that need electron conduction, since the same regioregularity is maintained, polymers with lower molecular weight present the higher electron conduction.

Polímeros, 28(5), 395-399, 2018

The decrease of electron conduction, with the enhanced of molecular weight, was attributed in some studies to the decrease of cristallinity of these polymers[8-10].

The aim of this work is to utilize the simplicity of oxidative synthesis with FeCl3 to synthesize poly(3-hexylthiophene) (PHT) with low molecular weight. For this purpose, this synthesis will use dichloromethane as the reaction medium, since this is a solvent in which the PHT presents low solubility.

Although in literature there are reports of synthesis of poly(3-alkylthiophenes) using FeCl3 and dichloromethane as solvent[11], no description was made about which polymer of this class were polymerized and none characterization was made to compare the characteristics of the polymer obtained in dichloromethane in relation the same polymer obtained in conventional method (with chloroform). There is a variation on time of polymerization of polymers synthesized in dichloromethane, to ensure the characteristics observed between the poly(3-hexylthiophenes) synthesized in different solvents are related only to difference of solubility of the solvent used in polymerization, and no to the differences in reaction media. Was observed a large difference in relation to molecular weight of poly(3-hexylthiophene) synthesized in different solvents. No relevant differences were observed in relation to the conjugation length and regioregularity.

2. Materials and Methods 2.1 Experimental 3-hexylthiophene 99% of purity from sigma-aldrich and anhydrous ferric chloride (FeCℓ3) from BDH GPR, was used as received. Halogenated solvents chloroform

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

Fonsêca, J. C. M., & Alves, M. P. A. S. and dichloromethane (both P.A. from Vetec) was dried over phosphorus pentoxide (P4O10) under reflux, and then was used immediately after distilled. Acetone (P.A. Dinâmica) was used as received.

2.2 Polymer synthesis The synthesis was carried out at room temperature under nitrogen atmosphere in oven dried glassware. Polymers were obtained by oxidative coupling with anhydrous ferric chloride in dry chloroform or dichloromethane as follow.

A 3-hexylthiophene (12 mmol) was added in solution into a dispersion of ferric chloride (48 mmol) with 150 mL of solvent. After 16 hours (or 40 hours), the polymer was precipitated by methanol. The obtained polymer was the dissolved in chloroform and re-precipitated in methanol to be purified. The obtained polymer was dried in a vacuum oven.

2.3 Characterization FTIR spectra in the middle IR region in the range 4000‑400 cm−1 (128 scans at resolution 4 cm-1) were obtained on a Bruker ISF66 spectrometer by KBr pellet (pressed discs with 5000 kg/cm2 during 10 min) in a proportion of 0.7 mg of sample and 100 mg KBr. NMR spectra were recorded on a VARIAN UNMRS 400 MHz in CDCl3. The aromatic region of poly(3-hexylthiophene) in 1H NMR spectra, were deconvoluted using a Varian VnmrJ software and relatively integrated in order to measure the regioregularity of these polymers. UV-Vis spectra were recorded in Perkin Elmer Lambda 650 in THF solution. GPC was performed on a Viscotek TDA 032 equipped with light scattering and refractrometer index detectors and a column of Fluorinated divinylbenzene gel. The samples were prepared with concentrations ranging from 0.5 to 2 mg/mL of THF.

are present in all polymers[12]. In 824, 823 and 824 cm-1 the thiophene ring C–H out-of‑plane bend modes of PHTcl, PHTdcm16 and PHTdcm40 can be observed, respectively.

According to Zerbi et al.[13], a correlation between these band and backbone planarity can be made, being the bands at higher wave numbers (around 835 cm-1) related to a more twisted conformation, while the lower wave number (near 820 cm-1) is related to a more planar conformation. Once we could not find a significant difference in these bands, we can infer that the two solvents used under the adopted conditions in this study, did not influence in planarity for the obtained polymers.

3.2 Molecular weight In Table 1, the molecular weights of polymers are presented. It can be seen that the polymer synthesized in chloroform has higher molecular weight than polymers synthesized in dichloromethane, even when a large time of polymerization was applied. Differences were observed with relation to polidispersity, presenting the polymers synthesized in dichloromethane lower dispersion than polymer synthesized in chloroform.

As the solubility of a polymeric chain obey the relation of the attractive force between them and the cohesive force polymer/solvent, the lower molecular weight of polymers synthesized in dichloromethane compared to polymer prepared by the same conditions in chloroform may be related to the precipitation of polymeric chains in this solvent. In other words, assuming that the polymer has low solubility in the solvent used in the synthesis (dichloromethane), as

3. Results and Discussion Differences were observed in relation to reaction media of polymers obtained with different solvents. On chloroform synthesis, a dark black color was observed with presence of insoluble particles of FeCl3, while a dark green color is observed in dichloromethane synthesis and no observation of FeCl3 particles was made. Then, it could be seen that ferric chloride is partially solubilized in ferric chloride in concentration used (0.04 g/mL).

The polymerization yield after soxhlet extraction in acetone to removal of oligomers was of 73% for poly(3‑hexylthiophenes) synthesized in dichloromethane for 16 hours (PHTdcm16); 83% and 88% for poly(3‑hexylthiophenes) synthesized in dichloromethane for 40 hours (PHTdcm40) and poly(3‑hexylthiophenes) synthesized in chloroform for 16 hours (PHTcl), respectively.

3.1 Infrared absorption In Figure 1 are presented the infrared spectra of PHTcl; PHTdcm16 and PHTdcm40 polymers. In all spectra are present bands at 3055 cm-1 related to the stretching vibrations of C-H aromatic bonds, peaks near 2920 and 2850 cm-1 relative to symmetric and asymmetric vibrations of C-H linkages in alkylic chains, respectively. Near to 1510 and 1458 cm-1, the symmetric and asymmetric vibrations of thiophene rings (C=C bond) 396 396/399

Figure 1. FTIR spectra of (a) PHTcl; (b) PHTdcm16; (c) PHTdcm40.

Table 1. Molecular Weights and polydispesity of poly(3hexylthiophene) synthesized with chloroform for 16 hours (PHTcl) and poly(3-hexylthiophene) synthesized with dichloromethane for 16 and 40 hours, respectively (PHTdcm16 and PHTdcm40).

PHTcl PHTdcm16 PHTdcm40

Mn (KDa) 1300 200 282

Mw (KDa) 2700 378 500

Polidispesity 2.04 1.89 1.77

Polímeros, 28(5), 395-399, 2018

Influence of solvent used on oxidative polymerization of Poly(3-hexylthiophene) in their chemical properties the polymerization occurs the chain reaches a size greater than the solubility capacity of the reaction medium and then precipitates. Thus, the polymers obtained under these conditions should have a smaller chain size and therefore less number of repeating units than polymers synthesized in more soluble medium.

On the other hand, increasing polymerization in dichloromethane should not result in considerable improvements in the molecular weight of originated polymer. Thus, since the molecular weight of PHTdcm16 is higher than molecular weight of PHTdcm40, more than difference in solubility in synthesis in different solvents is observed.

The answer for the unusual molecular weight of the polymers obtained in dichloromethane may be related to the polymerization mechanism. The most accepted mechanism polymerization of poly(3-hexylthiophene) in ferric chloride is radicalar[14] in which the growth of polymeric chain occurs in two ways: insertion of on monomer per time or combination of oligomers in solution. Since chloroform and dichloromethane do not exhibit large differences in density, considerable differences in monomer diffusion in these solvents are unlikely to be observed. However, difference in polarity is observed between the two solvents used. The high polarity of dichloromethane in relation to chloroform promotes more cationic stabilization of the species, leaving the cationic species less reactive in relation to polymerization made in chloroform. This phenomenon can contribute to the low molecular weight presented by PHTdcm16 and PHTdcm40.

Another possible explanation to the variation of molecular weight is the difference of solubility of FeCl3 in these solvents. Was observed that ferric chloride is much more soluble in dichloromethane than chloroform. According to Niemi et al.[14], its necessary the presence of FeCl3 crystals to polymerization happen. So, the large number of ferric chloride crystals presents on reaction made in chloroform can be the reason for the large molecular weight on this polymer.

Most studies analyzing molecular weight of poly (alkyl thiophenes) use regioregular synthesis methods, such as McCullough and Rieke[15-17]. The polymers obtained by oxidative synthesis, using ferric chloride as oxidant agent, presents higher molecular weight and, therefore, cannot be compared with polymers synthesized by other methods.

shift. So, the regioregularity of poly(3‑alkylthiophenes) was obtained by integration of each of these peaks[18,19]. These regioregularity can be obtained by alkylic protons and 13C integration too, but these protons are less sensitive than aromatic ones, and in carbon spectra, the aromatic carbons for 100% regioregularity polymer originate 4 signals, while for less regioregular polymers, 12 different peaks can be observed[2]. The percentage of the four triade present on PHTcl, PHTdcm16 and PHTdcm40 can be observed on Table 2.

3.3 NMR The poly(3-alkylthiophenes) were analyzed by 1H NMR, and can be observed in these spectra the presence of peaks related to methylenic protons in the region of 0.8-3 ppm, and aromatic proton on interval of 6.98 to 7.05 ppm (Figure 2).

Since these polymers present asymmetric structure, the enchainment of 3-alkylthiophenes can originate three different configurations during polymerization. These configurations originate four different triads, which are HT-HT (head to tail - head to tail); HT-TT (head to tail tail to tail); HT-HH (head to tail – head to head); TT-HH (tail to tail - head to head), as can be seen on Figure 3.

Due to differences on chemical environments observed

by NMR, these triads are presented on aromatic proton interval (between 6.98 and 7.05), and each triad present a difference of approximately 0.02 ppm between chemical Polímeros, 28(5), 395-399, 2018

Figure 2. 1H-NMR spectra of (a) PHTcl; (b) PHTdcm16; (c) PHTdcm40 with expanded area corresponding to the region of aromatic hydrogens.

Figure 3. Scheme of possible poly(3-alkylthiophene) triads HT-HT, HT-TT, HT-HH and TT-HH. 397/399 397

Fonsêca, J. C. M., & Alves, M. P. A. S. The differences presented by HT-HT linkages between the PHTcl and PHTdcm16 are not very significant. So, can be inferred that the differences between reactional media, ferric chloride solubility and solvent polarity, do not affect the considerably the regioregularity of obtained polymers.

Otherwise, PHTdcm 40 presents a very low percentage of HT-HT linkages, and no explanation was found to this.

The regioregularity values obtained for PHTcl and PHTdcm16 are high in relation to values obtained in literatures for the same variables, as temperature of polymerization[20,21].

According to Amou et al.[22], the decrease of monomer concentration in polymerization, increase the regioregularity.

With a concentration of 1 mol monomer/L of solvent, the HT content is of 76% and this value increase to 88% when concentration decrease to 0.05 mol monomer/L. As the concentration of monomer used in our study is lower, 0.05 mol/L, then other studies, 0.066 mol/L[21,23], this is the possible explanation for higher regioregularity obtained.

3.4 UV-vis absorption The UV-vis absorption spectra in conjugated polymers, can give a measurement of the transition π - π*, and consequently, the conjugation length of the poly(3alkylthiophenes). This conjugation length depends mainly to regioregularity of polymer. In Figure 4 is observed UV-Vis absorption spectra of polymers synthesized in chloroform and dichloromethane. Higher wave length absorption is observed to PHTcl. Although only a little difference in percentage of HT-HT triads is observed between the PHTcl and PHTdcm16, the larger wave number absorption of PHTcl is relative to higher molecular weight presented by Table 2. Regioregularity of poly(3-hexylthiophene) synthesized in chloroform for 16 hours (PHTcl) and poly(3-hexylthiophene) synthesized with dichloromethane for 16 and 40 hours, respectively (PHTdcm16 and PHTdcm40).

PHTcl PHTdcm16 PHTdcm40

HT-HT (%) 76.6 71.6 43.4

HT-TT (%) 5.6 0.7 22.6

HT-HH (%) 10.4 -

TT-HH (%) 7.4 27.7 34.0

Figure 4. UV-vis absorption spectra of (a) PHTcl; (b) PHTdcm16; (c) PHTdcm40.

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this polymer. According to Jeffries-El and McCullough[6], the conjugation length of poly(3‑alkylthioiphenes) increase with the molecular weights. The values of maximum absorption for poly(3‑hexylthiophenes) are in accordance with the literature. For PHT for example, McCullough and Lowe[24] observed a maximum absorption of 436 nm for polymer obtained by oxidation with FeCl3.

In observations made by infrared spectra, polymeric chains of PHTcl is more planar than PHTdcm16 and PHTdcm40 chains. These results corroborate the observed by UV-Vis.

4. Conclusions Poly(3-hexylthiophene) was successful synthesized by oxidative polymerization with anhydrous ferric chloride, using dichloromethane as solvent. A large difference of molecular weight is observed by this polymer in relation to poly(3-hexylthiophene) synthesized by the same conditions, but using chloroform as solvent. Polymers synthesized in dichloromethane presents considerable lower molecular weight in relation to polymer synthesized in chloroform, and this diminution is observed in polydispersity too. This decrease can be related to differences in solvent polarity or solubility of ferric chloride. Despite the observed differences in molecular weight, no considerable variation is observed in the regioregularity of these polymers. The UV-Vis analyses show that PHTcl presents higher conjugation length than PHTdcm16 and PHTdcm40, which is expected because of the higher molecular weight found for PHTcl.

5. Acknowledgements The autors would like to thanks to FACEPE, CNPq and CAPES for financial support, Rosa Maria Souto Maior, for technical support and to members of central analítica – DQF/UFPE for samples characterization.

6. References 1. Perepichka, I. F., & Perepichka, D. F. (2009). Handbook of thiophene-based materials: applications in organic electronics and photonics. United Kingdom: John Willey & Sons. http:// dx.doi.org/10.1002/9780470745533.

2. Fichou, D. (1999). Handbook of oligo- and polythiophene.

United Kingdom: John Wiley & Sons.

3. Lanzi, M., Salatelli, E., Benelli, T., Caretti, D., Giorgini, L., & Di-Nicola, F. P. (2015). A regioregular polythiophene-fullerene for polymeric solar cells. Journal of Applied Polymer Science, 132(25), 42121. http://dx.doi.org/10.1002/app.42121.

4. Chen, T. A., & Rieke, R. D. (1992). The first regioregular head-to-tail poly(3-hexylthiophene-2,5-diyl) and a regiorandom isopolymer: nickel versus palladium catalysis of 2(5)-bromo5(2)-(bromozincio)-3-hexylthiophene polymerization. Journal of the American Chemical Society, 114(25), 10087-10088. http://dx.doi.org/10.1021/ja00051a066.

5. McCullough, R. D., Lowe, R. D., Jayaraman, M., & Anderson, D. L. (1993). Design, synthesis and control of conducting polymer architectures: structurally homogeneous poly(3alkylthiophene)s. The Journal of Organic Chemistry, 58(4), 904-912. http://dx.doi.org/10.1021/jo00056a024.

6. Jeffries-El, M., & McCullough, R. D. (2006). Regioregular polythiophenes. In T. J. Skotheim, & J. R. Reynolds (Eds.), Polímeros, 28(5), 395-399, 2018

Influence of solvent used on oxidative polymerization of Poly(3-hexylthiophene) in their chemical properties Conjugated polymers: theory, synthesis, properties and characterization (2nd ed., pp. 9-1). Boca Raton: CRC Press.

7. Loewe, R., Khersonsky, S. M., & McCullough, R. D. (1999).

A simple method to prepare head-to-tail coupled, regioregular poly(3-alkylthiophenes) using grignard metathesis. Advanced Materials, 11(3), 250-253. http://dx.doi.org/10.1002/(SICI)15214095(199903)11:3<250::AID-ADMA250>3.0.CO;2-J. 8. Ballantyne, A. M., Chen, L., Dane, J., Hammant, T., Braun, F. M., Heeney, M., Duffy, W., McCulloch, I., Bradley, D. D. C., & Nelson, J. (2008). The effect of poly(3-hexylthiophene) molecular weight on charge transport and the performance of polymer:fullerene solar cells. Advanced Functional Materials, 18(16), 2373-2380. http://dx.doi.org/10.1002/adfm.200800145.

9. Fumagalli, L., Binda, M., Natali, D., Sampietro, M., Salmoiraghi, E., & Di Gianvincenzo, P. (2008). Dependence of the mobility on charge carrier density and electric field in poly(3-hexylthiophene) based thin film transistors: Effect of molecular weight. Journal of Applied Physics, 104(8), 084513. http://dx.doi.org/10.1063/1.3003526.

10. Kim, Y. S., Lee, Y., Lee, W., Park, H., Han, S.-H., & Lee, S.H. (2010). Effects of molecular weight and polydispersity of poly(3-hexylthiophene) in bulk heterojunction polymer solar cells. Current Applied Physics, 10(1), 329-332. http://dx.doi. org/10.1016/j.cap.2009.06.021.

11. Wang, Y., Lucht, B. L., & Euler, W. B. (2002). Investigation of the oxidative coupling polymerization of 3-alkylthiophene with iron (III) chloride. Polymer Preprints, 43(20), 1160.

Retrieved in 2017, May 28, from http://copper.chm.uri.edu/ weuler/wang.pdf 12. Osterholm, J. E., Sunila, P., & Hjertberg, J. (1987). 13C CPMAS NMR and FTIR studies of polythiophene. Synthetic Metals, 18(1-3), 169-176. http://dx.doi.org/10.1016/03796779(87)90873-3.

13. Zerbi, G., Chierichetti, B., & Inganas, O. (1991). Thermochromism in polyalkylthiophenes: Molecular aspects from vibrational spectroscopy. The Journal of Chemical Physics, 94(6), 46464658. http://dx.doi.org/10.1063/1.460593.

14. Niemi, V. M., Knuuttila, P., Osterholm, J. E., & Korvola, J. (1992). Polymerization of 3-alkylthiophenes with FeCl3.

Polymer, 33(7), 1559-1562. http://dx.doi.org/10.1016/00323861(92)90138-M. 15. McCarley, T. D., Noble, DuBois, C. J., & McCarley, R. L. (2001). MALDI-MS Evaluation of poly(3-hexylthiophene) synthesized by chemical oxidation with FeCl3. Macromolecules, 34(23), 7999-8004. http://dx.doi.org/10.1021/ma002140z.

16. Zen, A., Pflaum, J., Hirschmann, S., Zhuang, W., Jaiser, F., Asawapirom, U., Rabe, J. P., Scherf, U., & Neher, D. (2004). Effect of molecular weight and anneling of poly (3-hexylthiophene)s on the performance of Organic Field

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Effect Transistors. Advanced Functional Materials, 14(8), 757-764. http://dx.doi.org/10.1002/adfm.200400017.

17. Joshi, S., Grigorian, S., Pietsch, U., Pingel, P., Zen, A., Neher, D., & Scherf, U. (2008). Thickness dependence of the crystalline structure and hole mobility in thin films of low molecular weight poly(3-hexylthiophene). Macromolecules, 41(18), 6800-6808. http://dx.doi.org/10.1021/ma702802x.

18. Maior, R. M. S., Hinkelmann, K., Eckert, H., & Wudl, F. (1990). Synthesis and characterization of two regiochemically defined poly(dialky1bithiophenes): a comparative study.

Macromolecules, 23(5), 1268-1279. http://dx.doi.org/10.1021/ ma00207a008.

19. Barbarella, G., Bongini, A., & Zambianchi, M. (1994).

Regiochemistry and conformation of poly(3-hexylthiophene) via the synthesis and the spectroscopic characterization of the model configurational triads. Macromolecules, 27(11), 30393045. http://dx.doi.org/10.1021/ma00089a022.

20. Nicho, M. E., Hernandez, F., Hu, H., Medrano, G., Guizado, M., & Guerrero, J. A. (2009). Physicochemical and morphological properties of spin-coated poly (3-alkylthiophene) thin films.

Solar Energy Materials and Solar Cells, 93(1), 37-40. http:// dx.doi.org/10.1016/j.solmat.2008.02.016.

21. Sivaraman, P., Mishra, S. P., Bhattacharrya, A. R., Thakur, A., Shashidhara, K., & Samui, A. B. (2012). Effect of regioregularity on specific capacitance of poly(3-hexylthiophene).

Electrochimica Acta, 69, 134-138. http://dx.doi.org/10.1016/j. electacta.2012.02.085.

22. Amou, S., Haba, O., Shirato, K., Hayakawa, T., Ueda, M., Takeuchi, K., & Asai, M. (1999). Head-to-tail regioregularity of poly(3-hexylthiophene) in oxidative coupling polymerization with FeCl3. Journal of Polymer Science. Part A, Polymer Chemistry, 37(13), 1943-1948. http://dx.doi.org/10.1002/(SICI)10990518(19990701)37:13<1943::AID-POLA7>3.0.CO;2-X. 23. Urien, M., Bailly, L., Vignau, L., Cloutet, E., de Cuendias, A., Wantz, G., Cramail, H., Hirsch, L., & Parneix, J.-P. (2008).

Effect of the regioregularity of poly(3-hexylthiophene) on the performances of organic photovoltaic devices. Polymer International, 57(5), 764-769. http://dx.doi.org/10.1002/pi.2407.

24. McCullough, R. D., & Lowe, R. D. (1992). Enhanced electrical conductivity in regioselectively synthesized poly(3alkylthiophenes). Journal of the Chemical Society, Chemical Communications, 0(1), 70-72. http://dx.doi.org/10.1039/ c39920000070.

Received: May 28, 2017 Revised: July 26, 2017 Accepted: Mar. 18, 2018

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.02416

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

Use of chitosan in the remediation of water from purification of biodiesel Erivelton César Stroparo1*, Krissina Camilla Mollinari1 and Kely Viviane de Souza1 Laboratório de Qualidade de Águas, Departamento de Engenharia Ambiental, Universidade Estadual do Centro Oeste – UNICENTRO, Irati, PR, Brasil

1

*stroparo.erivelton@gmail.com

Abstract This article evaluates the efficiency of the degradation of pollutants present in water from the purification of biodiesel, characterized by high content of chemical oxygen demand (COD), suspended solids (SS), oils and greases, methanol, soap, and glycerol. The treatment process proposed was of the photo-Fenton type using iron immobilized in chitosan.

The characterization of the material was performed according to degree of deacetylation (DD) and thermal stability (TG). The results revealed a DD of 66.5% and that the material undergoes decomposition in three temperature stages: 100; 150-350 and above 350 °C. The evaluated parameters were: COD, suspended solids, oils and greases, color and turbidity. After a 180-minutes long treatment, the removal percentage was 94.52, 70, 55, and 60% respectively. These results indicate that the photo-Fenton process can be an alternative for pre-treatment this type of effluent.

Keywords: biofuel, photo-degradation, transesterification, wastewater.

1. Introduction The dependency on oil and the pollution generated by its extraction, benefiting, transportation, and burning, are the great disadvantages of the use of this fuel, a fact that has been encouraging the search for alternative energy sources, especially renewable ones. Biodiesel, because it is derived from oil seeds and even animal fat, present itself as a viable alternative to the total or partial substitution of diesel fuel. It can be obtained in different processes such as cracking, transesterification or esterification, resulting in glycerin as co-product[1]. However, in order to comply with international quality standards, biodiesel needs purification, which is carried out via washing.

The process aims at the removal of impurity and contaminants (catalyst, excess of alcohol, soaps, oils, and greases and residual glycerol) in excess, by the addition of great volumes of water, which results in wastewater with a high organic load, a fact that gives it low biodegradability[2].

Therefore, this wastewater is harmful to the environment and cannot be discharged into systems of collection and transportation of sanitation wastewater or bodies of water without a proper treatment[3].

There are several technologies that are employed in the treatment of this type of wastewater, including biological, chemical, and physical processes[4]. Researchers mention coagulation, electro-coagulation, biological processes and adsorption, in addition to the use of integrated processes, once the treatment of residual water has been one of the main concerns in terms of environmental protection. In addition to these, Advanced Oxidation Processes (AOPs) have been proposed as alternative technologies for isolated or combined treatment of wastewater of several classes, including the one generated during the purification of biodiesel[2-5].

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In comparison to other APOs, the homogeneous Fenton process has been widely studied to degrade several compounds and/or improve the biodegradability of aqueous effluents, and it is relatively cheap and easy to operate[5].

In this process, hydrogen peroxide (H2O2) is catalyzed by ferrous ion (Fe2+) in order to generate hydroxyl radicals (•OH), according to Equation 1.

Fe2 + + H 2O2 → Fe3+ + •OH + OH −

k1 = 76 M / s

(1)

Highly reactive and non-selective hydroxyl radicals may, on their turn, react with the substances of interest.

Fe2+ ions can be regenerated through Equation 2, but the process is relatively slow[6].

Fe3+ + H 2O2 → Fe2 + + HO2 • + H + k2 = 0.001 − 0.01 M / s (2)

In order to reinforce the regeneration of ferrous ions, light (UV or Vis) is usually introduced into the system. In the presence of irradiation, ferrous ions can be regenerated and additional hydroxyl radicals will be introduced via Equation 3.

Fe ( OH )

2+

+ hν → Fe2 + + •OH (3)

Thus the efficiency of the process is enhanced, once that the catalytic cycle closes with the generation of 2 moles of hydroxyl radicals for each mole of initially decomposed H2O2.

In spite of its high oxidation efficiency, homogeneous Fenton process presents some major drawbacks: (i) the narrow pH interval, due to the fast precipitation of Fe(OH)3 with pH

Polímeros, 28(5), 400-405, 2018

Use of chitosan in the remediation of water from purification of biodiesel higher than 2.8 and, consequently an early termination of the reaction; (ii) the need to recover great amounts of iron sludge precipitating after the treatment; and (iii) the continuing of the treatment of the resulting sludge. Consequently, the global cost of the homogeneous photo-Fenton process is increased[6]. These factors limit the application of the homogeneous Fenton process, turning into an important drawback that restricts its use in great scale[7]. Therefore, efforts have been made to apply heterogeneous catalysts for the incorporation of iron species in several carriers, such as chitosan, for instance[5].

Chitosan, an amino polysaccharide polymer, is obtained by alkaline deacetylation of chitin and is comprised of glucosamine (deacetylation units) and randomly distributed N-acetyl-glucosamine units (acetylation units). It has been extensively used in fabric engineering and other biomedical applications because it is from natural origin, it is biodegradable, non-toxic, and bio-compatible, in addition to its susceptibility to chemical modifications[7]. These features make chitosan an interesting carrier for the immobilization of Fe2+/Fe3+ ions for later application in photo-Fenton-type processes, since its use for this end is not reported much.

Therefore, the present study aims at studying chitosan as a matrix for iron adsorption and its application in heterogeneous photo-Fenton process as a treatment for wastewater generated by biodiesel purification.

2. Materials and Methods 2.1 Materials Chitosan with 100-mesh granulometry, purchased from Polymar, a company located in the state of Ceará, Brazil, was used without prior treatment. All chemical products possessed analytic degree and were used without any additional purification and the solutions were prepared using deionized water.

2.2 Biodiesel production The conversion of soy oil into biodiesel was carried out via transesterification process in basic catalysis (KOH 3% m/v) and methyl route (methanol 30% v/v). The oil was heated to 60 °C, with KOH and methanol under stirring with a reactional time of 1 hour. The separation of biodiesel from its coproduct (glycerin) was carried out by decantation during 24 hours. Later, pure biodiesel (B100) was submitted to a purification process (washing) carried out in three stages, each one with the addition of a volume of water corresponding to that of biodiesel. The separation of the organic phase of the aqueous phase occurred by decantation.

2.3 Preparation of chitosan spheres Chitosan spheres were prepared from 5.0 g of the polymer dissolved into 100 mL of a 5% acetic acid solution (m/v). Next, the polymer solution was trickled on an NaOH 2.0 mol L-1 solution. After the formation of the spheres, they were left in the NaOH solution for 24 hours in order to complete precipitation. Later, they were washed using water until wash Polímeros, 28(5), 400-405, 2018

water reached neutrality, Next, the spheres were submitted to a reticulation reaction with 0.1% (v/v) glutaraldehyde during 24 hours and they were washed with water in order to remove excess of reticulating agent[8].

For iron sorption, known amounts of reticulated spheres were added to a 250 mL of an Fe2+ 200 mg L-1 at pH=3 solution, under orbital stirring (120 rpm). For determination re. mnant Fe2+ in solution was used the Phenanthroline method (Fe B-3500 - Standard Methods for the examination of water and wastewater)[9].

2.4 Determination of Deacetylation Degree (DD) of chitosan The amount of amino protonated groups was determined for the chitosan sample with and without reticulation, through potentiometric titration. In his method, 0.2 g of chitosan was added to a 0.3 mol L-1 HCl solution during 24 hours.

Next, the solution was titrated with a NaOH 0.2 mol L-1 solution. The percentage of amino groups was calculated using Equation 4. % NH 2 =

C NaOH × (V 2 − V 1) ×161 (4) m

Where: C = concentration of the NaOH solution in mol L-1; V1 and V2 the volumes used to neutralize the excess of HCl and to neutralize the sample of protonated chitosan, respectively; 161 corresponds to the value of molar mass of the monomeric unit of the chitosan; and m the mass of the sample (g).

2.5 Thermogravimetric Analysis (TGA) Thermal stability of the samples was evaluated via thermogravimetry, under an oxidation atmosphere employing a heating rate of 10 ºC min-1 (from room temperature up to 1000 ºC).

2.6 Treatment process Experiments were conducted in a 300 mL bench reactor equipped with water cooling, magnetic stirring system, and assisted by artificial radiation using a 125 W mercury vapor lamp inserted into the solution with the aid of a quartz bulb.

250 mL of biodiesel wash water was used in pH=7.3 (which is natural of wash water); 200 mg L-1 of H2O2 and mass of spheres of 1 g. Treatment time was 180 minutes.

2.7 Analytical procedures The analyses were carried out in triplicate. The pH of the solutions was determined using a Phtek- PHS-3E meter.

COD was measured using the closed reflux colorimetric method. H2O2 concentrations were spectrometrically determined using a modified methodology based on procedures described by literature[10]. Iron was evaluated using UV-vis spectroscopy, applying methodology based on complexation reaction between Fe2+ and o-phenanthroline. Determination of color, turbidity, SS, and oil and greases was carried out according to “Standard Methods” methodology[9].

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Stroparo, E. C., Mollinari, K. C., & Souza, K. V.

3. Results and Discussions 3.1 Determination of the degree of deacetylation of chitosan The degree of deacetylation is defined as the molar ratio of deacetylation in the C-2 position of the 2-acetamido-2-deoxy-d-glucopyranose unit in polysaccharides chains. DD is one of the most important parameters for identifying the quality of chitosan, because it influences several physical-chemical properties of the material, such as solubility, flocculation, and ability of chelation with metallic ions[11]. The greater the amount of amino groups, the greater is electrostatic repulsion among chains and, consequently, greater is solvation in water. Arbitrarily, when the deacetylation degree is greater than 40% the polymer is defined as chitosan[12].

Several methods have been described in the literature to determine DD, amongst them the most used are potentiometric titration[13], UV spectroscopy[12], infrared spectroscopy, mass spectroscopy[14] and nuclear magnetic resonance spectroscopy[. However, the best method[15] for

determining DD is still subject of studies. For these reasons, and taking into account the availability of equipment and ease of operation, potentiometric titration was the chosen method in this study. Figure 1 illustrates the profile of the curve obtained through potentiometric titration of the solution of pure chitosan.

It was possible to observe that the curve presents two inflexion points: the first is related to the neutralizing of excess of HCl in the solution and the second point refers to the neutralization of protonated amino groups[16]. The DD figure calculated using this method was 66.5%.

For comparison ends, in the literature DD figures were found ranging from 50.0 to 92.3%[17-19]. These variations are due to the source and the way of obtaining the polymer developed by the manufacturer.

Reticulated spheres with glutaraldehyde do not present amounts of protonated amino groups that are measurable by the method. Only an inflexion in the potentiometric titration curve was observed, referring to the consumption of NaOH necessary to neutralize add HCl, indicating the link of the glutaraldehyde by amino groups, as proposed in Figure 2.

This behavior was also observed by Torres et al.[13].

Taking into account and evaluating the two possibilities (reticulation and ramification), both may occur. However, after the reaction with glutaraldehyde, the spheres become insoluble in the acetic acid solution. Should only the formation of glutaraldehyde ramifications be favored, the resulting polymer would probably be more soluble than the precursor polymer, in the linear shape. Thus, it might be suggested that both processes have occurred, however the reticulation effect seems to be more effective.

3.2 Thermal Gravimetric Analysis (TGA) Figures 3 and 4 show the results obtained from thermal gravimetric analyses for pure and reticulated chitosan spheres (before and after the insertion of iron), respectively.

Figure 1. Curve of potentiometric titration of pure chitosan solution in HCl.

The profile shown in Figure 3, referring to pure chitosan, reveals that the polymer suffers decomposition in three

Figure 2. Proposal of interaction of glutaraldehyde by the -NH2 chitosan group.

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Polímeros, 28(5), 400-405, 2018

Use of chitosan in the remediation of water from purification of biodiesel temperature stages: the first, comprising temperatures below 100 ºC, is related to loss of water; in the second, between 150 and 350 °C, decomposition may be related to depolymerization of the material or to the deacetylation of acetamido groups from precursor chitin. The third stage, for temperatures above 350 ºC, may be attributed to the degradation of final residues of the biopolymer’s organic matter.

The thermogram of reticulated chitosan (Figure 4A) also revealed three bands of loss of mass, differentiating only in the feature that reticulated chitosan presented less stability, considering that greater mass was lost in the second band, at lower temperature, of up to 230 °C. The reticulation promoted by the reaction with glutaraldehyde should, in a first moment, promote an additional thermal stability to chitosan. This fact, however, was not observed when the data revealed by the thermograms was analyzed. This behavior may be justified due to the frailty of the imine (-HC=NH-) links formed after the reticulation. Multiple links, whether they are shared among carbon atoms or among nitrogen and carbon, as it is the case in point, are thermolabile links, especially if the effect of the temperature is added to the effect

of the oxidizing atmosphere. On the other hand, the thermal evaluation of the materials obtained after the insertion of iron in the structure of the polymer (Figure 4B) did not change the thermal profile of the reticulated chitosan, indicating that ion interactions did not change, neither favorably nor unfavorably, the behavior under the effect of the temperature of reticulated chitosan.

3.3 Sorption of iron in chitosan spheres By monitoring Fe2+ concentration in solution, it was possible to calculate the adsorption capacity by the spheres, expressed by (qe), the amount of adsorbed iron in the balance, through Equation 5. qe =

( C0 – Ceq ) ×V m

(5)

Where: qe= amount of Fe2+ sorbed (mg g-1); Co= initial concentration of iron (mg L-1); Ceq= concentration of iron in equilibrium (mg L-1); V= volume of the Fe2+ solution used (L); m= mass of chitosan beads used in the sorption process (g).

Figure 5 shows the adsorption capacity of chitosan spheres in function of time. It is possible to observe that balance was reached after 60 hours of contact. In this essay, a figure was obtained of approximately 36.0mg of adsorbed iron per gram of sample.

3.4 Treatment of biodiesel wash water by photo-Fenton process

Figure 3. Thermogram obtained for the sample of chitosan without reticulation.

The characteristics of biodiesel wash water have already been studied by several researchers and usually present high contents of COD, SS, oils, and grease[2].

The characterization of water from biodiesel B100 purification is presented in Table 1.

In regards to pH, data from literature show that residual waters from biodiesel purification present pH values ranging from 3.14 to 11.00[20-22]. This wide range in pH value may

Figure 4. Thermogram obtained for the chitosan sample after reticulation by glutaraldehyde (A) and after insertion of iron (B).

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Stroparo, E. C., Mollinari, K. C., & Souza, K. V. interfering in the natural balance of that aquatic ecosystem.

According to the EPA (Environmental Protection Agency), the quality of life within a mixing zone must be exempt of undesirable deposits and substances that produce changes in color, odor, and turbidity For SS and oils and greases, the decrease was 53 and 70% respectively. The color of the treated effluent presented a 55% decrease, presenting a value that is above the maximum allowed[24] this is probably due to the presence of residues from non-transesterified fatty acids.

Figure 5. Representation of the concentration of ferrous ions sorbed by reticulated chitosan spheres.

Table 1. Characterization of water from biodiesel B100 purification.

Parameter pH COD (mg L-1) Turbidity (UNT) SS (mg L-1) Oils and greases (mg L-1) Color (uC)

Water

Water

(Before treatment) 7.3 5,556.0±0.9 219.0±0.1 243.4±2.3 730.5 ±1.7 1,450.1±0.3

(After treatment) 6.5 333.3±0.6 87.6±0.1 114.4±1.6 219.1±0.9 652.5±0.5

influence significantly conventional treatments of residual water, such as those physical-chemical, for instance. However, when using heterogeneous photo-Fenton process, pH does not influence the treatment, since the proposal was the use of immobilized Fe2+,thus it is possible to carry out the treatment without the need for adjustments in pH value, which is an advantage of the process.

The COD of the effluent is elevated, possibly due to the presence of oils and greases and, especially, of glycerol residue. In different works, researchers analyzedanalyzed the COD of the raw effluent generated from biodiesel purification, corresponding to 7,500 mg L-1 and 29,595 mg L-1 respectively[4,23]. The difference between the figures found in the literature in this study refers to the type of raw material adopted in the process and the route employed.

An aquatic system that receives effluents presenting these levels of organic matter will result in the consumption of oxygen of the receiving body, and it might reach levels of total anoxia, depending on the type of bacteria in that environment, therefore the need is evident of treatment for this type of effluent.

With heterogeneous photo-Fenton process, after 180 minutes a 94% decrease of COD took place, however, since the initial figure was very high, this decrease was not enough for the final effluent to comply with discharge standards.

Regarding turbidity, it was observed to a 60% decrease, and the remaining turbidity might possibly be related to the presence of esters that form an emulsion that is difficult to remove. In spite of the fact that turbidity is not a direct indicator of risk to health, its increase in courses of water affects the light zone and, consequently, photosynthesis, 404 404/405

The results obtained for the studied parameters indicate that the isolated photo-Fenton process is not enough for the treatment of this type of effluent; however, the combination with biological and/or physical-chemical processes might be a promising alternative. Ramírez and collaborators[25] investigated the efficiency of an integrated process combining photo-Fenton with aerobic sequential batch reactor (SBR) for treatment of wastewater from an a biodiesel production plant. In this study, the homogeneous photo-Fenton process was applied, adjusting the pH of the wastewater to 2.3 and the treatment lasted 2 hours. The results express that the chemical oxidation process promoted a high potential of CDO removal, of approximately 90%. However, some problems have been pointed out, such as the cost of UV radiation and the difficulty of decomposing the sludge formed at the end of the biological treatment[25].

It should also be noted that H2O2 was monitored during the entire treatment process, and four additions of oxidizing agent were necessary, in a total of 800 mg L-1 over 180 minutes of treatment. Another important aspect to be taken into account is related to the chitosan matrix, which did not suffer decomposition during the treatment, a fact that was already expected, since the system is refrigerated and the temperature inside the reactor did not reach the temperature of material decomposition indicated by TGA analysis.

Lastly, it was observed that iron was not released from the matrix into the solution, which suggests a possibility of reusing the spheres.

4. Conclusions The production of biodiesel from soy oil results in a great amount of residual water with high levels of organic load, which needs to be treated efficiently in order to minimize its environmental impact. Several treatments are being studied for the treatment or pre-treatment of residual water from biodiesel and each one of them has both advantages and disadvantages.

This study has achieved the proposed goals, the chitosan matrix has revealed itself to be proper for its ability of Fe2+ ions sorption as well as stability in treatment conditions.

Isolated, photo-Fenton process did not present itself as being efficient. However, it might be indicated as pre-treatment for water from biodiesel purification, with a decrease of over 50%, at least in the parameters that were analyzed, and it has the advantage of the possibility of application of heterogeneous photo-Fenton process in any pH range.

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Use of chitosan in the remediation of water from purification of biodiesel

5. References 1. Okoye, P. U., & Hameed, B. H. (2015). Review on recent progress in catalytic carboxylation and acetylation of glycerol as a byproduct of biodiesel production. Renewable & Sustainable Energy Reviews, 53, 558-574. http://dx.doi.org/10.1016/j. rser.2015.08.064.

2. Daud, N. M., Sheikh Abdullah, S. R., Abu Hasan, H., & Yaakob, Z. (2015). Production of biodiesel and its wastewater treatment technologies: a review. Process Safety and Environmental Protection, 94, 487-508. http://dx.doi.org/10.1016/j.psep.2014.10.009.

3. Veljković, V. B., Stamenković, O. S., & Tasić, M. B. (2014).

Thewastewater treatment in the biodiesel production withalkalicatalyzed transesterification. Renewable & Sustainable Energy Reviews, 32, 40-60. http://dx.doi.org/10.1016/j.rser.2014.01.007.

4. Pitakpoolsil, W., & Hunsom, M. (2013). Adsorption of pollutants frombiodiesel wastewater using chitosan flakes. Journal of the Taiwan Institute of Chemical Engineers, 44(6), 963-971. http://dx.doi.org/10.1016/j.jtice.2013.02.009.

5. Gao, Y., Wang, Y., & Zhang, H. (2015). Removal of Rhodamine B with Fe-supported bentonite as heterogeneous photoFenton catalyst under visible irradiation. Applied Catalysis B: Environmental, 178, 29-36. http://dx.doi.org/10.1016/j. apcatb.2014.11.005.

6. Li, H., Li, Y., Xiang, L., Huang, Q., Qiu, J., Zhang, H., Sivaiah, M. V., Baron, F., Barrault, J., Petit, S., & Valange, S. (2015). Heterogeneous photo-Fenton decoloration of Orange II over Al-pillared Fe-smectite: Response surface approach, degradation pathway, and toxicity evaluation. Journal of Hazardous Materials, 287, 32-41. http://dx.doi.org/10.1016/j. jhazmat.2015.01.023. PMid:25621831.

7. Barndõk, H., Blanco, L., Hermosilla, D., & Blanco, A. (2016).

Heterogeneous photo-Fenton processes using zero valent iron microspheres for the treatment of wastewaters contaminated with 1,4-dioxane. Chemical Engineering Journal, 284, 112121. http://dx.doi.org/10.1016/j.cej.2015.08.097.

8. Souza, K. V., Zamora, P. G. P., & Zawadzki, S. F. (2010).

Esferas de quitosana/Fe na degradação do corante Azul QR19 por processos foto-Fenton utilizando luz artificial ou solar.

Polímeros: Ciência e Tecnologia, 20(3), 210-214. http://dx.doi. org/10.1590/S0104-14282010005000035.

9. Rice, E. W., Baird, R. B., Eaton, A. D., & Clesceri, L. S. (2012). Standard methods for the examination of water and wastewater, 22nd ed. Washington: American Public Health Association, American Water Works Association, Water Environment Federation.

10. Oliveira, M. C., Nogueira, R. F. P., Gomes, J. A., No., Jardim, W. F. (2001). Sistema de injeção em fluxo espectrofotométrico para monitorar peróxido de hidrogênio em processo de fotodegradação por reação foto-Fenton. Química Nova, 24(2), 188-190. http://dx.doi.org/10.1590/S0100-40422001000200007.

11. Wang, C., Yuan, F., Pan, J., Jiao, S., Jin, L., & Cai, H. (2014). A novel method for the determination of degree of deacetylation of chitosan by coulometric titration. International Journal of Biological Macromolecules, 70, 306-311. http://dx.doi. org/10.1016/j.ijbiomac.2014.07.007. PMid:25020083.

12. Tan, S. C., Khor, E., Tan, T. K., & Wong, S. M. (1998). The degree of deacetylation of chitosan: advocating the first derivate UV- spectrophotometry meted of determination. Talanta, 45(4), 713-719. http://dx.doi.org/10.1016/S0039-9140(97)00288-9.

PMid:18967053.

13. Torres, M. A., Vieira, R. S., Beppu, M. M., & Santana, C. C. (2005). Produção e caracterização de microesferas de quitosana modificadas quimicamente. Polímeros: Ciência e

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Tecnologia, 15(4), 306-312. http://dx.doi.org/10.1590/S010414282005000400016.

14. Duarte, M. L., Ferreira, M. C., Marvão, M. R., & Rocha, J. (2001). Determination of the degree of acetylation of chitin materials by 13C CP/MAS NMR spectroscopy. International Journal of Biological Macromolecules, 28(5), 359-363. http:// dx.doi.org/10.1016/S0141-8130(01)00134-9. PMid:11325422.

15. Lavertu, M., Xia, Z., Serreqi, N. A., Berrada, M., Rodrigues, A., Wang, D., Buschmann, M. D., & Gupta, A. (2003). A validated 1H NMR method for the determination of the degree of deacetylation of chitosan. Journal of Pharmaceutical and Biomedical Analysis, 32(6), 1149-1158. http://dx.doi.org/10.1016/ S0731-7085(03)00155-9. PMid:12907258.

16. Jiang, X., Chen, L., & Zhong, W. (2003). A new linear potentiometric titration method for the determination of deacetylation degree of chitosan. Carbohydrate Polymers, 54(4), 457-463. http://dx.doi.org/10.1016/j.carbpol.2003.05.004.

17. Jiang, D. S., Long, S. Y., Huang, J., Xiao, H. Y., & Zhou, J. Y. (2005). Immobilization of Pycnoporus sanguineus laccase on magnetic chitosan microspheres. Biochemical Engineering Journal, 25(1), 15-23. http://dx.doi.org/10.1016/j.bej.2005.03.007.

18. Yang, Y. M., Wang, J. W., & Tan, R. X. (2004). Immobilization of glucose oxidase on chitosan-SiO2 gel. Enzyme and Microbial Technology, 34(2), 126-131. http://dx.doi.org/10.1016/j. enzmictec.2003.09.007.

19. Lin, H., Wang, H., Xue, C., & Ye, M. (2002). Preparation of chitosan oligomers by immobilized papain. Enzyme and Microbial Technology, 31(5), 588-592. http://dx.doi.org/10.1016/ S0141-0229(02)00138-2.

20. Brito, J. F., Ferreira, L. O., Silva, J. P., & Ramalho, T. C. (2012).

Tratamento da água de purificação do biodiesel utilizando eletrofloculação. Quimica Nova, 35(4), 728-732. http://dx.doi. org/10.1590/S0100-40422012000400014.

21. Jaruwat, P., Kongjao, S., & Hunsom, M. (2010). Management of biodiesel wastewater by the combined processes of chemical recovery and electrochemical treatment. Energy Conversion and Management, 51(3), 531-537. http://dx.doi.org/10.1016/j. enconman.2009.10.018.

22. Siles, J. A., Martin, M. A., Chica, A. F., & Martin, A. (2010).

Anaerobic co-digestion of glycerol and wastewater derived from biodiesel manufacturing. Bioresource Technology, 101(16), 6315-6321. http://dx.doi.org/10.1016/j.biortech.2010.03.042.

PMid:20363620.

23. Grangeiro, R. V. T., Melo, M. A. R., Silva, E. V., Souza, A. G., & Toscano, I. A. S. (2014). Caracterização física, química e toxicológica da água de lavagem gerada na produção de biodiesel. Revista Verde de Agroecologia e Desenvolvimento Sustentável, 9(1), 78-83. Retrieved in 2016, February 22, from https://www.gvaa.com.br/revista/index.php/RVADS/article/ view/2632 24. Sperling, M. V. (2014). Introdução à qualidade das águas e ao tratamento de esgotos. Belo Horizonte: Editora UFMG. 25. Ramírez, X. M. V., Mejía, G. M. H., López, K. V. P., Vásquez, G. R., & Sepúlveda, J. M. M. (2012). Wastewater treatment from biodieselproduction via a coupled photo-Fenton – aerobic sequentialbatch reactor (SBR) system. Water Science and Technology, 66(4), 824-830. http://dx.doi.org/10.2166/ wst.2012.250. PMid:22766873.

Received: Mar. 09, 2016 Revised: Sept. 12, 2017 Accepted: Dec. 22, 2017

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.10317

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

Synthesis, characterization and antibacterial activity of novel poly(silyl ether)s based on palm and soy oils Issam Ahmed Mohammed1*, Syed Shahabuddin2*, Rashmin Khanam3 and Rahman Saidur2 Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia Research Centre for Nano-Materials and Energy Technology â&#x20AC;&#x201C; RCNMET, School of Science and Technology, Sunway University, Selangor Darul Ehsan, Malaysia 3 Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, New Delhi, India 1

2

*issam_usm@yahoo.com or issam@um.edu.my

Abstract In this research, palm oil and soy oil were used as a natural polyol to prepare novel poly(silyl ether)s. Palm oil and soy oil were first converted to monoglyceride by one step via alcoholysis process in the presence of 0.1% CaO as a catalyst. The monoglycerides were characterized by Fourier transform infrared spectrometer (FT-IR), nuclear magnetic resonance (NMR) and iodine test. The novel poly(silyl ether)s were prepared via polycondensation reaction between dimethyldichlorosilane with monoglycerides based on palm and soy oils, respectively. FT-IR, NMR and silicone-29 (29Si NMR) were used to confirm and determine the presence of silicone in the synthesized polymers.

Thermal behavior was studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).

Antibacterial activity of the polymers was screened against three different strains of bacteria, namely Escherichia coli E266, Staphylococcus aureus S276 and Salmonella choleeraesuis 10708.

Keywords: antibacterial, dimethydichlorosilane, palm oil, poly(silyl ethers), polyol, soy oil.

1. Introduction Currently, the consumption of polymeric materials such as plastics, resins, adhesives etc. has increased enormously throughout the world. Polymers and polymeric based materials have been used extensively for various applications and have become the essential part of scientific study and research[1,2].

Polymeric materials comprising of inorganic and metal elements have always been the focus of many researchers to harness the unique properties of such polymers. Poly(silyl ether)s, for instance, is a silicon containing polymer which epitomizes an important category of useful materials such as polymeric membranes[3], conducting polymers[4], plastics and elastomers[5-7], stimulus-sensitive materials and so on[8]. Silicon containing polymers, commonly known as polysiloxanes, have received much scientific consideration as a functional and high-performance polymeric materials owing to their significant flexibility at low temperatures and enhanced stability at high temperatures. Due to the presence of Si-O-Si skeleton within the polymeric matrix, polysiloxanes exhibits enhanced performance at high and low temperatures and have been used as elastomers and high performance plastics in various industrial applications[9].

Poly(silyl ether) is a polymer containing O-SiR2-O linkage in its main chain which is responsible for its unique properties such as high thermal stability, good mechanical properties, good processibility and low glass transition temperature[10,11]. Due to the non-toxicity of poly(silyl ether)s, most of these polymers find potential application in medical field such as an artificial skin to cover wounds, optical lenses and implants etc., as they are non-cytotoxic

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and there is no evidence of causing adverse effect on the human body. Additionally, the unique hydrolytic reactivity of poly(silyl ether)s makes them attractive in many other applications[12]. Therefore, it has been a material of immense interest in the preparation of polymers based on silicon with respect to evaluate their biological activity[13].

Environmental pollution has been a serious issues and various researches are dedicated to lower down the menace cause by various pollutants[14,15] including petroleum products. As it is known, most of the poly(silyl ether)s have been prepared via polycondensation reaction between dichlorodiorganosilanes with various diols which are usually derived from petroleum products[16-18]. The global warming and environmental issues have gained the interest of researchers in attempt to replace or reduce the petroleum sources by green, biodegradable and renewable sources. Vegetable oil with the major composition of triglycerides, and saturated and unsaturated fatty acids has gained significant scientific attention as natural resources for research and development works in substitution of petroleum sources as it is present abundantly and is an economic biological source[19,20].

Polyol derived from vegetable oils acts an important precursor in the polymer synthesis, and subsequently the polymerization is carried out with different raw materials to produce various types of polymers, such as alkyd-epoxy resin[21], hydrogels[22] polyurethanes[23-26], polyesters[27,28] and poly(alkyd urethane)s[29].

However, up to date, there is no research report on the synthesis of poly(silyl ether)s based on vegetable oils and

PolĂ­meros, 28(5), 406-412, 2018

Synthesis, characterization and antibacterial activity of novel poly(silyl ether)s based on palm and soy oils their bioactivities.We have reported a novel approach for the synthesis poly(silyl ether)s based on palm oil and soy oil for the first time. This article describes a one-step reaction of palm oil and soy oil with glycerol in the presence of catalyst to produce monoglycerides. These monoglycerides functions as polyols, and subsequently these polyols are reacted with dichlorodimethysilane to produce new poly(silyl ether)s.

The structures, properties and antibacterial activities of the polymer were investigated and discussed.

2. Experimental 2.1 Materials Palm and Soy oils were purchased from commercial sources, (Seri Murni Sdn.Bhd.) and (VJ AGGRO Sdn. Bhd.), respectively. Glycerol, dichlorodimethylsilane, pyridine, sodium thiosulfate, potassium iodide, dimethylformamide (DMF) and tetrahydrofuran (THF) were purchased from Aldrich-Sigma. All the chemicals were purchased and used without further purification except for pyridine which was distilled by using the standard method.

2.2 Synthesis of monoglycerides of soy and palm oils Briefly, 146.5 g of soy oil and 0.1% calcium oxide (based on oil) were placed in the reaction flask. 15.5 g glycerol was filled into the dropping funnel and fitted to the reactor flask. The reaction mixture was then heated at 235°C under vigorous stirring. For the first 5 minutes, nitrogen gas was allowed to flow swiftly, and later adjusted to one bubble per second throughout the experiment. The dropping funnel was then opened steadily until all glycerol was poured into the flask. The reaction mixture was kept under constant stirring for 4 hours. A sample of polymer solution was taken after regular interval using glass rod to test the solubility in ethanol. The reaction was assumed to be completed until the solution obtained has negative presence of emulsion or white spots in ethanol. Similar procedure was followed for the synthesis of monoglycerides of Palm Oil where 128 g of palm oil was used under analogous conditions as for soy oil monoglycerides. Scheme 1 illustrates the monoglycerides preparation.

of the work-up procedure was the same as described in the previous section for soy oil. Scheme 2 illustrates the poly(silyl ether)s preparation derived from monoglycerides.

2.5 Instrumentation FT-IR spectra was measured on a Perkin-Elmer 2000 FTIR with a potassium bromide (KBr) beam splitter. All spectra were collected between 4000 cm-1 to 400 cm-1. 1H NMR spectra were recorded by Bruker 500 MHz spectrometer, and the samples for monoglycerides and polymers were prepared at the concentration of 100 mg/ml in DMSO-d6 and CDCl3 as solvents, respectively. Viscosity was measured by HAAKE Rotary Viscometer using spindle 5 at a rotation speed of 105 rpm. Iodine value test was performed to determine the amount of unsaturated groups present in each synthesized poly(silyl ether) according to Lubrizol Standard AATM 112-01.

Thermal stability investigations were carried out using a Perkin Elmer TGA-6 under an inert N2 atmosphere at a heating rate of 10 °C/min. Then, 10 mg of dried sample were loaded inside the alumina crucible, and the weight changes were monitored from 30–800 °C. Differential Scanning Calorimetry (DSC) studies were carried out with a Perkin-Elmer Pyris Series 7 thermal analyzer at a heating rate of 10°C/min under an inert N2 atmosphere ranging from room temperature to 300°C.

Scheme 1. Synthetic route of the monoglycerides.

2.3 Synthesis of poly(silyl ether)s derived from soy oil 70 g (0.076 mol) of monoglyceride of soy oil was dissolved in 13.24 g of pyridine with continuous stirring under nitrogen atmosphere. 23.77 g of dichlorodimethylsilane was then transferred to a dropping funnel and added dropwise to the mixture. Then, the mixture was stirred at room temperature for 48 hours and afterwards the temperature was raised to 60°C for 3 hours. The reaction mixture was then poured into 50 ml of 10% HCl solution. The precipitate obtained was washed several times with methanol and acetone and dried at 60°C in a vacuum oven.

2.4 Synthesis of poly(silyl ether)s derived from palm oil 62.14 g (0.1258 mol) of monoglyceride of palm oil was dissolved in 12.84 g of pyridine with continuous stirring under nitrogen atmosphere. Then, 23.05 g of dichlorodimethylsilane was subsequently added dropwise to the mixture. The rest Polímeros, 28(5), 406-412, 2018

Scheme 2. Synthesis of the poly(silyl ether)s.

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Mohammed, I. A., Shahabuddin, S., Khanam, R., & Saidur, R.

Figure 1. FT-IR spectra for monoglyceride, dichlorodimethylsilane, poly(silyl ether)s based palm oil and soy oil.

3. Results and Discussion 3.1 Characterization of monoglycerides FT-IR spectra executed in the monoglycerides, dichlorodimethylsilane and poly(silyl ether)s are shown in Figure 1. For the oil monoglycerides, broad peak is observed at 3370.95 cm-1 which attributed to presence of the hydroxyl groups. A small peak appeared at 3090 cm-1 which may be due to CH=CH, whereas a sharp peak at 2922.93 cm-1 indicates the stretching of aliphatic C-H. Strong peak at 1737.21 cm-1 is attributed to the stretching of carbonyl C=O group. A characteristic Si-O peak appears in the IR spectrum of poly(silyl ether)s at around 1050-1080 which represents the presence of Si-O linkages in the synthesized polymers. In addition, other absorption peaks appeared at 1653.70 cm-1; 1239.62 cm-1 and 1047.14 cm-1 are assigned for the presence of C=C, C-O-C bond and C-C, respectively.

Figure 2. 1H NMR of soya oil monoglyceride.

The structures of monoglycerides (soy and palm) is further confirmed by 1H NMR analysis and the type of protons, and their splitting are illustrated in Figures 2 and 3, respectively.

The peaks for both the monoglycerides (palm and soy) are almost similar but only differ at the position 2.7 ppm for palm based monoglyceride and at 2.8 ppm for soy based monoglyceride. The spectra analysis confirmed the formation of polyols.

3.2 Characterization of poly(silyl ether)s The structural elucidations of the polymers are confirmed by spectroscopic analyses such as FT-IR, 1H and 29Si NMR. The FT-IR spectra of the polymers in Figure 1 showed the 408 408/412

Figure 3. 1H NMR of palm oil monoglyceride.

Polímeros, 28(5), 406-412, 2018

Synthesis, characterization and antibacterial activity of novel poly(silyl ether)s based on palm and soy oils appearance of new absorption bands at 1260 cm-1 and at 864 cm-1 which can be attributed to the O-Si-CH3. The disappearance of the absorption band at 3379 cm-1 for -OH group and the appearance of new peaks prove the completion of reaction and confirms the presence of O-Si-O in the backbone of the polymers. C=O group is easily recognized by a strong, sharp band at 1737 cm-1. Weak peaks at 3090 cm-1 and at 1653 cm-1 are assigned to CH=CH and C=C, respectively.

The 1H NMR for poly(silyl ether)s based on monoglycerides of palm oil, and soy oil are shown in Figures 4 and 5, respectively. The spectra are obtained with deuterochloroform (CDCl3) and without using tetramethylsilane (TMS) as the internal reference to avoid the overlap with protons of dimethylsilane based polymers. The 1H NMR spectrum in Figure. 4 showed a new peak appearing at 0.2 ppm, which is attributed to the dimethylsilyl (CH3)2-Si. The prominent triplet peak at 0.8 ppm is assigned to the proton at the terminal of a methyl group of fatty acid chains. Multiplet peaks at 1.2 ppm are due to the protons in methylene groups (-CH2). Proton attached to the carbonyl group (CH2-CO) centered at 2.35 ppm, whereas the proton of the vinylic groups (C=C-H) appeared at 5.35 ppm. Protons of CH-O, CH2-O and CH2-O-CO appeared at 4.15 ppm, 3.7 ppm and 4.16 ppm, respectively.

For the polymer based on monoglyceride of soy oil, it has a peak obvious at 2.75 ppm which cannot be seen on the spectrum of the palm oil based polymer (Figure 5).

This indicates that soy oil-based polymer has two double bonds, which give a clearer peak compared to palm oil, which has a smaller peak at the same position that indicates the presence of one double bond. It is well known that the linoleic in soy oil is responsible for the two double bonds while the oleic is responsible for one double bond for palm oil based polymer.

Furthermore, chemical structure of polymers is confirmed by 29Si NMR. As evident from Figures 6 and 7, there are several peaks in the range of -15 ppm to -25 ppm which proved the presence of a silicon element in both poly(silyl ether)s. The corresponding chemical shifts characterize types of the silicon bonding, for example, peaks at -19.08 and -19.11ppm are due to CH-O-Si for the polymers based on soy and palm oils, respectively. Other peaks at -21.53 and -21.88ppm are assigned to CH2-O-Si for the polymers based on soy and palm oils, respectively.

Whereas, the silicon in CH3-Si-CH3 for the polymers based on soy and palm oils are centered at -22.02 and -22.21ppm, respectively. From the spectroscopic analyses, we can confirm the successful synthesis of poly(silyl ether)s.

Figure 4. 1H NMR spectra of poly(silyl ethers) based palm oil.

Figure 5. 1H NMR spectra of poly(silyl ether)s based soy oil.

Figure 6. 29Si NMR of poly(silyl ether) derived from palm oil.

3.3 Properties of poly(silyl ether)s The viscosity of the poly(silyl ether) based on soy oil and palm oil were found to be 1137.8 cP 1140.7 cP at rotation of 105 rpm. The resistance of the flow for both the obtained polymers does not show much difference comparatively.

As well, the viscosity for both of monoglycerides, palm and soy oils is measured, and found to be respectively, 110.2 cP and 102.5 cP. It can be observed that the viscosity of the polymers is approximately 10 times then the viscosity of the monoglycerides which indicates the enormous increase in the molecular weights of the polymers, hereby signifying Polímeros, 28(5), 406-412, 2018

Figure 7. 29Si NMR of poly(silyl ether) derived from soy oil.

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Mohammed, I. A., Shahabuddin, S., Khanam, R., & Saidur, R. the efficacious synthesis of polymers. Thus, the higher the amount of cross linking, higher will be the formation of branched polymeric chains that led to additional binding effect and therefore enhances viscosity.

The iodine values analysis for poly(silyl ether)s is carried out by the procedure as described elsewhere 29. The results exhibited the degree of unsaturation in these polymers based on palm and soy oils is found to be 55.56 and 120.5, respectively. Based upon the Iodine test it can be inferred that soy oil derived polymer has more unsaturated bonds as compared to the palm oil derived polymer since the number of double bonds found in soy oil are more than the palm oil. This is due to the fact that soy oil consists of higher constituent of linoleic acid, which has two double bonds in its structure as compared to the palm oil. Therefore, the higher iodine value denotes the higher double bond content in the polymer composition.

The thermal analysis of poly(silyl ether)s based on palm oil and soy oil, was carried out using thermogravimetric analysis performed under a nitrogen atmosphere by heating samples from 35-800 °C with a ramp rate of 10 °C/min.

Figure 8 shows the TGA thermogram of the poly(silyl ether)s based on palm oil and soy oil . As is obvious from the TGA, the poly(silyl ether) based on soy oil, which is denoted the blue line, whereas poly(silyl ether) based on palm oil denoted by the red line undergoes two step degradation. As apparent from the TGA data, the thermal stability of these polymers is rather low and they began to degrade at a temperature below 250 °C. The low thermal stability of poly(silyl ether)s based on vegetable oils is due to the presence of long chain alkyl groups present in the main chain. Therefore, the initial degradation essentially starts from the long alkyl chain, and the second stage of degradation occurred due to the cleavage of Si-O linkage in the polymeric backbone.

It is evident from the Figure 8 and Table 1 that poly(silyl ether) based on soy oil at T10 is more stable than poly(silyl ether) based on palm oil. This observation can

be explained on the basis of the structure of soy oil based monoglyceride which possesses more double bonds, resulting strong intermolecular interactions, as compared to the poly(silyl ether) based on palm oil where the number of double bond is less in quantity. Similar observations have been reported on synthesis of polyurethanes based on soy and palm oils[23].

To study the thermal behavior and phase transitions of the synthesized polymers DSC analysis were carried out using Perkin-Elmer Pyris Series 7 thermal analyzer at a heating rate of 10°C/min under an inert N2 atmosphere ranging from room temperature to 300°C. As apparent from Figure 9, Poly(silyl ether)s based on palm oil and soy oil exhibited endothermic peaks at 176 °C and 82.9 °C and the glass transition temperatures was found to be 31.6 °C and 34.2 °C, respectively. The glass transition occurred due to the increase in the heat capacity (Cp) of the sample during heating, which is due to an enhancement in molecular motion of the polymeric chains[29]. It is suggested that the glass transition might be attributed to the long alkyl carboxyl groups present in the polymeric chain[23]. The DSC data again reveals that soy oil based poly(silyl ether) polymer is more thermally stable as compared with the palm oil based poly(silyl ether) polymer.

3.4 Antibacterial activity Antimicrobial test is usually carried to determine antimicrobial potential of the polymers and to know which microbe’s activity is hampered by presence of polymer. The standard used for these antimicrobial studies is Streptomycin with the concentration of 100mg/ ml. The test is performed by placing 6mm diameter of paper disc containing antibiotic and 6 mm diameter discs of polymer prepared by pressing the polymer using standard equipment onto the cultural agar plate with different strains of microbes. The microbe culture is standardized to 0.5 McFarland standard which is

Figure 9. DSC curves of poly(silyl ether)s based on (a) Soy Oil and (b) Palm Oil.

Figure 8. TGA curves of poly(silyl ether)s.

Table 1. Thermal decomposition temperature of poly(silyl ether)s.

Poly(silyl ether)s Palm Oil Soya Oil

410 410/412

Thermal decomposition temperature 10 wt % loss 20 wt % loss 192 215 256 290

Residue yield at 700 °C (%) 12 10

Polímeros, 28(5), 406-412, 2018

Synthesis, characterization and antibacterial activity of novel poly(silyl ether)s based on palm and soy oils Table 2. Antibacterial activity of poly(silyl ether)s.

Poly(silyl ether)s Palm Oil Soya Oil Standard

Salmonella Staphylococcus E. coli E266 choleraesuis aureus S276 10708 Diameter of Inhibition zones (mm) 4 5 24 15 34

approximately equals to 108cells per culture. Not more than 6 discs were placed on the same agar plate. Streptomycin is used as standard antibiotic for each bacterium. The plates were inverted and incubated at 30-37 °C for 16-24 hrs or until sufficient growth has occurred and after incubation, each plate is examined for antimicrobial activity. The diameters of the zones of complete inhibition (as judged by the unaided eye) are measured, including the diameter of the disc. Zones are measured to the nearest whole millimeter, using sliding calipers or a ruler, which is held at the back of the inverted petri plate.

Antibacterial activity were studied against three different bacteria and the results showed that the poly(silyl ether) based on soy oil exhibits poor resistance, whereas the poly(silyl ether) based on palm oil didn’t show any bioactivity.

The results of the antibacterial are presented in Table 2.

4. Conclusion Recently, vegetable oils have become one of the most important natural resources to synthesize polyol in order to replace the polyol based on petroleum sources. In summary, we present here a facile and distinctive route to synthesize the novel poly(silyl ether)s based on vegetable oils. The FT-IR, NMR and 29Si NMR spectroscopy studies confirmed the successful formation of novel poly(silyl ether)s polyols.

The low iodine value of monoglyceride based on palm oil indicates the higher saturation bond as compared to the monoglyceride of soy oil. From the viscosity data it was inferred that poly(silyl ether) based on palm oil possesses a higher viscosity as compared to the poly(silyl ether) based on soy oil. However, the thermal behavior showed lower stability than the poly(silyl ether) based on soy oil.

Antibacterial activity has been screened against different bacteria and showed that poly(silyl ether)s possesses very poor resistance as compared to the standard drug that used in this study.

5. Acknowledgements The authors would like to thank the University of Malaya (UM) and Sunway University for the research facilities and financial support through internal grant (INT-2018-SST-RCNMET-04).

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Received: Oct. 20, 2017 Revised: Feb. 27, 2018 Accepted: Apr. 15, 2018

Polímeros, 28(5), 406-412, 2018

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.08017

Stability and rheological behavior of coconut oil-in-water emulsions formed by biopolymers Eliana da Silva Gulão1,2, Clitor Junior Fernandes de Souza1,3, Angélica Ribeiro da Costa4, Maria Helena Miguez da Rocha-Leão2 and Edwin Elard Garcia-Rojas1,4* Programa de Pós-graduação em Ciência e Tecnologia de Alimentos – PPGCTA, Universidade Federal Rural de Rio de Janeiro – UFRRJ, Seropédica, RJ, Brasil 2 Departamento de Ciência de Alimentos, Instituto de Química, Universidade Federal do Rio de Janeiro – UFRJ, Rio de Janeiro, RJ, Brasil 3 Programa de Pós-graduação em Ciência e Tecnologia de Alimentos, Universidade Federal da Grande Dourados – UFGD, Dourados, MS, Brasil 4 Laboratório de Engenharia e Tecnologia Agroindustrial – LETA, Universidade Federal Fluminense – UFF, Volta Redonda, RJ, Brasil 1

*edwinr@id.uff.br

Abstract Proteins are frequently used as emulsifiers and stabilizers. In this work, two proteins with different isoelectric points were used: lactoferrin and ovalbumin. Solutions containing different proteins ratios, with different pH values, were stored for 7 days at 25 °C to analyze the system stability. Systems containing 3% w/v lactoferrin remained stable at all pH values studied, while systems containing 1% w/v ovalbumin remained stable only at a high pH value (8.0).

Emulsions containing a mixture of proteins remained stable at a pH between the isoelectric points of the two proteins, which was attributed to an electrostatic bond because of the opposite charges of proteins at this pH. During the analysis of rheological properties, it was possible to observe a non-Newtonian behavior of the emulsions, using the models of Carreau and Cross to describe the pseudoplastic behavior of suspensions. This study provides important information for the use of functional ingredients.

Keywords: emulsion stability, oil-in-water emulsion, polymers, emulsifiers.

1. Introduction Proteins are widely used as emulsifiers in foods. For this reason, the proteins have been widely studied to better understand the mechanisms involved in the stabilization of emulsion systems. The thick layer formed around the droplets as a consequence of protein adsorption prevents coalescence[1-4]. However, emulsions emulsified and/or stabilized with proteins are highly sensitive to stresses such as pH, ionic strength, and temperature[5-7].

Lactoferrin (Lf) is a glycoprotein obtained from milk, with a molecular weight of 80 kDa and an isoelectric point (pI) close to 8.0; its main feature is the ability of each molecule to bind to two iron ions[8]. For be located in several tissues is considered a multifunctional protein participating in different physiological processes, as: regulation of iron absorption in the gut, immune response, antioxidant property, anticancer and anti-inflammatory properties and protection to microbial infection[9]. Studies of emulsion stability using lactoferrin have shown that the protein has a great stabilizer capacity[10-12].

On the other hand, ovalbumin (OVA), the most abundant egg protein, is widely used in the food industry due to its ability to form gels with other polymers. It has a molecular weight of 42 kDa, is negatively charged at a neutral pH, and has an isoelectric point of approximately 4.8[13]. In strong electrostatic repulsion conditions (pH far from its pI and

Polímeros, 28(5), 413-421, 2018

at a low ionic strength), denatured ovalbumin forms linear, semi-flexible aggregates, while their level of branching considerably increased when the electrostatic repulsions are screened[14]. Recently, other researchers have studied the emulsifying properties of ovalbumin associated with gum arabic. In the first study, Niu et al.[15] studied the stability of emulsion w/o by complexes formed between egg albumin and arabic gum under stress conditions as changes in pH, ionic strength and heating, observing stability in acid pH conditions, in the absence of salt ions and upon heating, while in a second study, Niu et al.[16] studied the stability of emulsion w/o using the same complex, showing improved physical and oxidative stability in the ratio 1: 2 and, through the rheology, noted that this proportion provide systems more viscous with higher storage modulus.

Emulsions have been very suitable for encapsulating lipophilic components. These systems can be produced from natural ingredients with high nutritional quality using relatively simple processing operations, such as mixing and homogenization[2,17].

The physico-chemical properties of the formulation may influence the obtaining process, the type and stability of the system, as well as the phase behavior of the dispersion. The main phenomena involved in the O/W emulsion instability process

413/421 413

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

Gulão, E. S., Souza, C. J. F., Costa, A. R., Rocha-Leão, M. H. M., & Garcia-Rojas, E. E. are flocculation and coalescence. In flocculation occurs the reversible aggregation of droplets with maintenance of the interfacial film forming a two-dimensional network, whereas coalescence can be induced by thinning and rupturing the film between droplets, when two or more droplets of the dispersed phase approach each other with enough energy to melt and form a larger droplet[4-6].

Studies involving emulsions have increased due to the possible application of functional ingredients to the food, such as vegetable oils. Coconut oil is a vegetable oil obtained from fresh or mature coconut fruits by mechanical or natural processes, with or without the use of heat in the absence of chemical refining[18]. Its consumption is increasing, not only because of its pleasant taste but also because of its potential health benefits[19].

The aim of this work was to study the stability and rheological properties of model oil-in-water emulsions prepared with lactoferrin and ovalbumin as emulsifiers.

2. Materials and Methods 2.1 Materials Dehydrated lactoferrin (Bioferrin 2000, 95% w/w putity) was obtained from Glanbia Nutritionals (Fitchburg, WI, USA) and ovalbumin (A5503, 98% w/w purity) was obtained from Sigma-Aldrich (St. Louis, MO, USA). Unrefined coconut oil of the brand Copra (Brazil) was obtained from the local market. This study used analytical reagents and ultrapure water (Master P&D, Gehaka, Brazil) with a conductivity of 0.05 μS/cm.

2.2 Protein solution preparation Lf (3%, 2.25%, 1.5% and 0.75% w/v) and OVA (3%, 2.25%, 1.5% and 0.75% w/v) concentrations were prepared by previously solubilizing the proteins without pH adjustment in ultrapure water and agitating them with the aid of a magnetic stirrer (NT101, Novatecnica, Brazil) for approximately 3 hours. The solutions containing the mixture of the two proteins (3% Lf; 2.25% Lf-0.75% w/v OVA, 1.5% Lf-1.5% w/v OVA, 0.75% Lf-2.25% w/v OVA; 3% w/v OVA) were adjusted with HCl 0.5 mol/L or NaCl 0.25 mol/L to different pH values ​​(2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0) and shaken with the aid of a magnetic stirrer.

2.3 Emulsion preparation Emulsions were prepared by mixing 10% v/v of coconut oil with 90% v/v of the aqueous protein solution, with different ratios of protein and pH values as mentioned at section 2.2. The coconut oil was subjected to a 25 °C at a thermostatic bath with a precision of 0.05 °C (MPC-108A, Huber, Offenburg, Germany) to obtain it in liquid form.

The solutions were homogenized using an Ultra-Turrax T 10 Basic (Gehaka, Brazil) at 25 °C for 2 minutes at 13.000 rpm and were subsequently subjected to ultrasound for 3 minutes at 25 °C (Ultrasonic Processor, Hielscher, Germany) at a frequency of 30 kHz (100% amplitude and 0.5 cycles per minute).

414 414/421

2.4 Properties and stability of emulsions 2.4.1 Zeta-potential and droplet size measurements The Zeta-potential and droplet size distribution were obtained by dynamic light scattering (DLS) measurements on emulsions stored in quiescent conditions after 1 and 7 days an incubator (TE-424, Tecnal, São Paulo, Brazil) at 25 °C. The emulsions were diluted with deionized water to a pre-set pH value at a ratio of 1:200 v/v and were placed in capillary tubes, which were placed inside the equipment (Nano-ZS, Malvern Instruments, Malvern, UK). The samples were equilibrated for 1 minute in the instrument. Intensity-weighted z-average diameter was obtained from droplet size distribution.

2.4.2 Influence of temperature on the stability of emulsions Emulsions that demonstrated stability after the zeta potential and z-average diameter experiments were subjected to temperature variations (30 to 90 °C with a range of 10 °C) in a thermostatic bath with a precision of 0.05 °C (MPC-108A, Huber, Offenburg, Germany) and were maintained at each temperature for 20 minutes for further evaluation of the droplet diameter. Following the methodology proposed by Bengoechea et al.[20], emulsions were diluted with deionized water (1:200 v/v) with a pre-adjusted pH for analysis.

2.4.3 Rheological properties The rheological measurements of the emulsions were performed with a controlled stress rheometer (Thermo Scientific, Mars III Haake, Karlsruhe, Germany) using a cone-plate sensor (diameter 60 mm, angle 1°, gap 0.052 mm).

The temperature of the test was precisely controlled by a Peltier system on board, and a protection cover (solvent trap) was used to prevent the evaporation of water during analysis. All analyses were performed in duplicate, and the average time before the tests was 5 min. Steady shear tests were performed using a ramp shear rate from 0 to 500 s-1 at a fixed temperature of 25 °C. The models of Newton (1), Power Law (2), Herschel-Bukley (3), Cross (4) and Carreau (5) were tested to describe the flow behavior. τ = µ( γ ) (1) n = τ K ( γ ) (2) n τ = τ0 + K ( γ ) (3)

 η −η  ∞  η = η∞ +  0 (4)  1 + ( λγ )n   

  η0 − η∞ η = η∞ +    1 + ( λγ )2 

(

)

N 2

    (5)  

In these models, τ0, τ, λ, γ , μ, η, η0, η∞, K, n, and N represent the yield stress (Pa), shear stress (Pa), relaxation time (s), shear rate (s-1), viscosity (Pa⋅s), apparent viscosity (Pa⋅s), zero-shear rate of viscosity (Pa⋅s), infinite-shear rate of viscosity (Pa⋅s), consistency coefficient (Pa·sn), flow behavior index and potency index, respectively.

Polímeros, 28(5), 413-421, 2018

Stability and rheological behavior of coconut oil-in-water emulsions formed by biopolymers 2.4.4 Optical microscopy Emulsions containing 10% v/v of coconut oil were observed through an optical microscope (Eclipse E-200, Nikon, Japan) amplified 60x with coupled camera (Evolution VF, MediaCybernetics, USA). In order to compare, the five different formulations were evaluated in pH values i​​ n which they presented stability and instability, according to the zeta potential and z-average diameter results. The emulsions were diluted with deionized water with a pre-set pH value at a ratio of 1:200 v/v.

3. Results and Discussion 3.1 Properties and stability of emulsions 3.1.1 Influence of pH and ratio of biopolymers Initially, we evaluated the ζ-potential of each protein and mixtures containing 3% w/v Lf and 3% w/v OVA for comparison with their behavior in the emulsions, as seen in Figure 1A. It can be observed that Lf presented change in electric charge in the individual protein solution, occurring dislocation of negative charge in the pH 11.8 (-31.1) to positive at pH 1.8 (+16.45) with zero load point (pI) close to 8.0, as also reported in the literature[9]. OVA showed a similar behavior, suffering displacement of negative charge in the pH 11.7 (-26.3) to positive charge at pH 1.2 (+24.3) with zero load point near pH 5.0, in agreement with the data reported by Croguennec et al.[14]. The mixtures containing

3% Lf-3%OVA w/v showed negative charge (-20.96) at pH 11.7 to the positive charge (+20.2) in pH 1.18, with zero load point near pH 6.5, being among those of the original polymers. At this pH, Lf is positively charged and OVA negatively charged, which indicates the possible electrostatic bonding between proteins.

Figure 1B shows the results of the ζ-potential of emulsions with different protein proportions after the seventh day of their formation. Emulsions containing 3% Lf w/v showed behavior similar to that of aqueous proteins (Figure 1), having a positive charge from pH 1.7 to pH 8.0 and a point of zero charge near the pI of the protein. Emulsions containing 3% OVA w/v also showed behavior similar to that of the aqueous solution of the original polymer, with a zero load point near the pI protein (between 4.5 and 5.0).

The behavior of emulsions containing mixtures of both proteins, varied according to the relative amount of Lf and OVA used in the system.

It can be observed that all the emulsions showed a positive charge at low pH and a negative charge at higher pH values, with a zero load point between 5.0 and 6.2.

However, when the concentration of Lf was higher than that of OVA (2.25-0.75% w/v Lf-OVA), the zero-charge point (6.2) was close to pI of Lf. Conversely, when the concentration of OVA was higher than that of Lf (2.25-0.75% w/v OVA-Lf), the zero-charge point (5.0) was near to pI of OVA.

Figure 1. (A) Effect of pH on the zeta potential of the solutions containing 3% w/v Lf (●), 3% w/v OVA (○) and mixtures containing 3-3% w/v Lf:OVA (▼); Influence of pH on emulsions containing 10% v/v coconut oil at the seventh day after its formation on the zeta potential (B) and intensity-weighted z-average diameter at the seventh day after their formation (C), when: (●) 3% w/v Lf; (○) 2.25-0.75% w/v Lf:OVA; (▼) 1.5-1.5% w/v Lf:OVA; (∆) 2.25-0.75% w/v OVA:Lf; (■) 3% w/v OVA. Polímeros, 28(5), 413-421, 2018

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Gulão, E. S., Souza, C. J. F., Costa, A. R., Rocha-Leão, M. H. M., & Garcia-Rojas, E. E. Similar behavior was observed in emulsions containing lactoferrin and β-lactoglobulin[21,22]. The composition of the proteins also exerted a significant influence on the stability to aggregation of the droplets as a function of pH. In Figure 1C, it can be observed that the emulsions containing 3% w/v Lf remained stable from pH 2.0 to 8.0, with no aggregation of droplets (z-average diameter < 310 nm). The high stability of these emulsions can be attributed to a combination of electrostatic and steric repulsion between the droplets.

Presumably, Lf molecules are oriented at the oil-water interface so that the hydrophilic groups of protein point to the aqueous phase and provide a strong steric repulsion[6,21,22].

Visually, it can be observed that in emulsions formed with 3% w/v Lf at all the pH values, no phase separation was evidenced (Figure 2-I). For emulsions containing 3% w/w OVA, the stability to droplet aggregation was noticeably influenced by pH (Figure 2-II). It can be observed that at pH values from 2.0 to 6.0, a strong aggregation of droplets (z-average diameter > 1200 nm) occurred, but at higher pH values ​​(pH 7.0 to 8.0) the emulsions presented lower zeta-average diameter (z-average diameter < 702 nm).

The same occurred in the emulsions containing 2.25-0.75% Lf-OVA w/v (Figure 2-III), with less droplet aggregation at higher pH (6.0 to 8.0). This fact can be explained by those

emulsions having a greater electrostatic repulsion instead of steric repulsion between the oil droplets and ovalbumin molecules, leading to emulsion stability. Consequently, as particles tend to aggregate when the pH is below or near the pI of protein, an electrostatic repulsion is not strong enough to overcome the attraction forces between the molecules[23].

All emulsions containing mixtures of Lf and OVA showed an aggregation of molecules at low pH values, with the most stable being between pH 5.0 and 7.0, which are intermediate values between ​​ the isoelectric points of the proteins. These results suggest that Lf and OVA are capable of forming an interfacial complex that improves the stability of the emulsion aggregation. Based on the study

by Tokle et al.[21], who observed the stability of emulsions formed by lactoglobulin and lactoferrin, it can be suggested that the same model may be used for emulsions formed between Lf and OVA, assuming that the complex can be formed in different ways that lead to a variety of interfacial structures: Lf adsorbs the surface of the droplets, and then OVA adsorbs at the top, forming a multilayer; OVA adsorbs the surface of the droplets, and then Lf adsorbs at the top, forming a multilayer; Lf and OVA in solution form a complex, which is then adsorbed to the surfaces of droplets, forming a mixture layer; Lf and OVA are adsorbed to the surfaces of

Figure 2. Visual appearances of o/w emulsions containing 10% v/v coconut oil and solutions at the seventh days of quiescent storage after their formation, when: (I) 3% w/v Lf; (II) 3% w/v OVA; (III) 2.25-0.75% w/v OVA:Lf; (IV) 2.25-0.75% w/v Lf:OVA; (V) 1.5-1.5% w/v Lf:OVA, when (A) pH 2.0; (B) 3.0; (C) pH 4.0; (D) pH 5.0; (E) pH 6.0; (F) pH 7.0; and (G) pH 8.0.

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Polímeros, 28(5), 413-421, 2018

Stability and rheological behavior of coconut oil-in-water emulsions formed by biopolymers droplets, forming a mixture layer that may be a monolayer or a multilayer. In addition, among emulsions containing mixtures of proteins, those containing 2.25-0.75% OVA-Lf w/v (Figure 2-IV) at pH 7.0 showed the smallest droplet diameter (361 nm) and maintained a fully stable condition during the 7 days of storage. Although the emulsions containing only OVA were stable to gravitational separation (or creaming/or phase separation) at a pH values ranging from 7.0 to 8.0, when OVA (1.5% w/v) was mixed with Lf (1.5% w/v), the resultant emulsions showed no phase separation (or creaming/or gravitational separation) in the pH range 5.0-6.0 (Figure 2-V). This fact would be associated with lower z-average values (< 700 nm) (Figure 1C).

3.1.2 Influence of temperature Initially, all the samples containing only albumin (OVA 3% w/v) were adjusted to pH 8.0; the samples containing only lactoferrin (Lf 3% w/v) were adjusted to pH 7.0; and all the emulsions containing the protein mixtures were adjusted to pH 6.0, being the pH at which the emulsions showed higher stability at 25 °C. Emulsions containing 3% w/v Lf showed larger-diameter droplets, indicating an initiation of aggregation close to 60 °C, which is indicated as the first denaturation temperature of Lf[24]. Figure 3-I shows the droplet diameter of emulsions containing 3% w/v Lf (pH 7.0), 3% w/v OVA (pH 8.0) and mixtures with different proportions Lf:OVA and a pH between the isoelectric points of the proteins (6.0).

Upon reaching temperatures above 80 °C, aggregation of the molecules occurred, and an emulsion with a gel aspect appeared. Similar results were observed by Tokle et al.[21], indicating that although at this pH (far from its pI), a strong electrostatic repulsion occurs, hydrophobic bonds between protein and lipid droplets overcome the electrostatic repulsion of micelles, leading to approach and subsequent aggregation.

According to Croguennec et al.[14], when the denaturation temperature is reached, an exposure of nonpolar amino acid occurs, resulting in hydrophobic interactions.

In turn, emulsions containing 3% w/v OVA did not show aggregation at all temperatures studied, with larger-diameter droplets just above 80 °C but no visually observed aggregation (Figure 3 II-E). Samples containing mixtures of proteins (Figures 3II-B, 3 II-C and 3 II-D) presented behavior that varied with the concentration of

each biopolymer, but all showed instability and presented an aggregation of droplets between 60 and 70 °C. At these temperatures, it can be observed that the droplet diameter was higher in emulsions containing a higher concentration of lactoferrin (2.25-0.75% w/v Lf:OVA > 6.000 nm) and lower when the concentration of OVA was higher (2.25-0.75% w/v OVA:Lf, <4.000 nm), due to the greater instability of Lf at high temperatures. We can also observe that the emulsions containing mixtures showed higher droplet diameters at lower temperatures than did emulsions containing each protein isolate separately. Similar results were observed

by Tokle et al.[21] when studying the formation of emulsions from interactions between lactoferrin and β-lactoglobulin.

It can be suggested that a possible electrostatic interaction between the molecules and OVA/LF, with the pH is being between the pI of the two proteins, caused changes in the physical layers of the proteins involving the oil droplets.

The emulsion gelation occurs when the interfacial aggregates begin to overlap, and hardening occurs mainly due to the rearrangement of the network-like molecules on a scale of different lengths[25]. It is the result of chemical interactions (electrostatic and hydrophobic) between molecules of a single protein or from the combined interactions between protein molecules. The destabilization of the native protein tertiary structure increases their interactions at a level that ultimately causes the formation of a stable network[25,26].

3.1.3 Rheological properties The flow behavior of the emulsions prepared at pH where they exhibited the highest stability and the apparent viscosity vs. shear rate curves are shown in Figure 4.

The apparent viscosity of all the studied emulsions decreased with the increasing shear rate and exhibited non-Newtonian behavior. The Carreau and Cross models, which describe the pseudoplastic behavior of suspensions, were used to model the flow curves of the emulsions evaluated.

These models are useful for predicting apparent viscosity over a wide shear rate range[27], in contrast to the power law model that was also used in this work. The parameters obtained by these models are shown in Table 1. Many dispersed systems behave like a non-Newtonian fluid that presents three distinct regions during the flow: (i) at low shear rate, the apparent viscosity tends to reach a Newtonian

Figure 3. (I) Intensity-weighted z-average diameter for o/w emulsions containing 10% v/v of coconut oil subjected to thermal treatments at different temperatures. (●) 3% w/v Lf, pH 7.0; (○) 2.25-0.75% w/v Lf:OVA, pH 6.0; (▼) 1.5-1.5% w/v Lf-OVA, pH 6.0; (Δ) 2.25-0.75% w/v OVA:Lf, pH 6.0; (■) 3% w/v OVA, pH 8.0; (II) Photographs at bulk scale of o/w emulsions subjected to heating. (A) 3% w/v Lf, 80 °C; (B) 2.25-0.75% w/v Lf:OVA, 70 °C; (C) 1.5-1.5% w/v Lf-OVA, 70 °C; (D) 2.25-0.75% w/v OVA:Lf, 70 °C; and (E): 3% w/v OVA, 90 °C. Polímeros, 28(5), 413-421, 2018

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Figure 4. Apparent viscosity as a function of the shear rate of the o/w emulsions containing 10% v/v coconut oil, when: (●) 3% w/v Lf, pH 7.0; (○) 2.25-0.75% w/v Lf:OVA, pH 6.0; (▼) 1.5-1.5% w/v Lf:OVA, pH 6.0; (Δ) 2.25-0.75% w/v OVA-Lf, pH 6.0; (■) 3% w/v OVA, pH 8.0. Continuous lines represent the models fitted Carreau (A) and Cross (B) to the data.

Table 1. Adjustment parameters of flow curves of Carreau (Equation 5), Cross (Equation 4), and power law (Equation 2), models for the studied emulsions.

Sample 3% LF 2.25%LF-0.75OVA 1.5% LF-1.5% OVA 2.25%OVA-0.75%LF 3% OVA

η0 0.365 0.0219 0.0583 0.0278 0.2059

λ 0.873 0.2625 1.3629 0.5678 0.3870

Carreau N 0.683 0.5917 0.5016 0.5057 0.7175

η∞ 0.0015 0.0017 0.0013 0.0013 0.0014

R2 0.997 0.995 0.999 0.999 0.994

η0 0.4510 0.0170 0.1254 0.0369 0.1544

λ 1.6472 0.3123 5.5669 1.3349 0.4763

Cross n 1.3757 1.2556 1.0142 1.0407 1.4700

η∞ 0.0015 0.0017 0.0013 0.0013 0.0014

R2 0.997 0.995 0.999 0.999 0.994

Power Law K n R2 0.0886 0.1839 0.893 0.0085 0.7113 0.746 0.0061 0.7253 0.752 0.0066 0.7122 0.770 0.1555 0.0397 0.971

λ = relaxation time (s); η = apparent viscosity (Pa⋅s), η0 = zero-shear of viscosity (Pa⋅s); η∞ = infinite-shear rate of viscosity (Pa⋅s); K = consistency coefficient (Pa·sn); n = flow behavior index; N = potency index; R2 = correlation coefficient.

plateau where the viscosity is independent of the shear rate (zero shear viscosity (η0)[28]; (ii) at intermediate shear rates, pseudoplastic behavior is observed, with apparent viscosity decreasing with increasing shear rate; and (iii) again, the fluid behaves as Newtonian at high shear rate (infinite shear viscosity, η∞). Although not presenting the Newtonian flow regime at low shear rates, the models that best fit the data were Carreau and Cross, justified by the higher determination coefficient values ​​R2> 0.99. Due to the limitations of the equipment, only the obtained values ​​of shear rate rate above 4.0 s-1 are presented; therefore, it was not possible to observe the Newtonian flow regime at low shear rates.

Figure 4 shows the fit of these plotted models (Carreau and Cross) against the measured data.

The parameters analysis (Table 1) reveals that only the proteins used had influence on the Newtonian viscosity at low shear rates. The emulsions formulated with only Lf and OVA presented higher values ​​of η0. Higher values ​​of η0 suggest that stronger interactions occurred between proteins and oil droplets compared to Lf-OVA complexes[29]. It is also known that the protein surface coating (mg/m2) of Lf-stabilized emulsions, prepared at pH 7.0, is greater than emulsions stabilized with β-lactoglobulin, due to their higher molar mass[22]. When it comes to the pseudoplastic region, where the Power Law was maintained, the viscosity characteristic slope was also different for emulsions containing only the protein and those with the Lf-OVA complexes, and the N parameter (Carreau model) is related to this region’s slope.

The emulsions formed by the complexes presented lower values of ​​ N and this behavior is related to the increase of 418 418/421

the pseudoplastic character, reinforcing the interactions and the formation of an entanglement between the proteins in the emulsion. This pseudoplastic region may be associated with droplet flocculation, which increases the apparent dispersed phase volume and increases the formation of non-spherical aggregates[30]. In fact, the emulsions formed by the complexes showed greater droplet aggregation as shown in section 3.1.1, but did not account for stability of these emulsions. The time constant (λ) is related to the instability of the emulsions against creaming. Thus, emulsions exhibiting longer times showed greater stability due to strong droplet-droplet interactions[30].

The emulsion containing 1.5-1.5% w/v Lf:OVA presented the highest λ, and among the emulsions formed by the two proteins, also obtained a smaller z-average diameter, as can be seen in Figure 1C. It is possible to affirm that the emulsions containing only protein (Lf or OVA) presented greater resistance to the flow (> η0), but the formulations containing the two proteins presented a greater stability, requiring a higher shear stress to occur the break-up of the structure. For high shear rates, all emulsions presented infinite shear viscosity (η∞).

3.1.4 Optical microscopy Order to better observe the interaction effect between Lf and OVA on the stability of emulsions, images of all formulations at the pH values ​​were obtained on the optical microscope, where they were more stable or unstable, according to the results of zeta potential and droplet diameter, when: 3% w/v Lf, pH 7.0; 3% w/v Lf, pH 3.0; 3% w/v OVA, pH Polímeros, 28(5), 413-421, 2018

Stability and rheological behavior of coconut oil-in-water emulsions formed by biopolymers

Figure 5. Photomicrographs of o/w emulsions containing 10% v/v coconut oil at the seventh day of quiescent storage after their formation.

(A) 3% w/v Lf, pH 7.0; (B) 3% w/v Lf, pH 3.0; (C) 3% w/v OVA, pH 8.0; (D) 3% w/v OVA, pH 3.0; (E) 1.5% w/v Lf:OVA, pH 6.0; (F) 1.5% w/v Lf:OVA, pH 3.0; (G) 2.25-0.75% w/v Lf:OVA, pH 6.0; (H) 2.25-0.75% w/v Lf:OVA, pH 3.0; (I) 2.25-0.75% w/v OVA-Lf, pH 6.0; (J) 2.25-0.75% w/v OVA-Lf, pH 3.0.

8.0; 3% w/v OVA, pH 3.0; 1.5% w/v Lf:OVA, pH 6.0; 1.5% w/v Lf:OVA, pH 3.0; 2.25-0.75% w/v Lf:OVA, pH 6.0; 2.25-0.75% w/v Lf:OVA, pH 3.0; 2.25-0.75% w/v OVA-Lf, pH 6.0; 2.25-0.75% w/v OVA-Lf, pH 3.0. The results can be seen at Figure 5. It is noted that emulsions containing 3% w/v Lf were stable at pHs 7.0 and 3.0 (Figures 5A and 5B), which corroborated with previous results (Figure 1C), since the emulsions containing only Lf presented constant diameter of particle, from pH 2.0 to pH 8.0. The emulsions containing mixtures of Lf and OVA were more stable at pH values between ​​ the pI of the proteins, confirming previous results (Figures 1B and 1C).

It is noticed that emulsions at pH 6.0 containing ratios of 1.5% w/v Lf:OVA, (Figure 5E), 2.25-0.75% w/v Lf:OVA (Figure 5G) and 2.25-0.75% w/v OVA-Lf (Figure 5I), were stable. However, when the pH of same systems was adjusted to pH values below pI of proteins (3.0), the approximation of droplets was observed, causing aggregation and possibly flocculation, as there is no evidence of micelles disruption (Figures 5F, 5H and 5J). In this pH value, Lf and OVA presented positive charges as seen on zeta-potential results (Figure 1A), therefore, there is no electrostatic interaction and consequently no formation of electrostatic complexes that would allow the repulsion between droplets.

Emulsions containing 3% w/v OVA were stable at pH 8.0 (Figure 5C) and unstable at pH 3.0 (Figure 5D).

At pH 3.0, the emulsion coalescence could be observed, with the approaching and melting of droplets forming large aggregates. A similar phenomenon was observed when studying Polímeros, 28(5), 413-421, 2018

the stability of double w/o/w emulsions containing only WPI as emulsifier[31]. The authors attributed the emulsions coalescence to the formation of a thin polymer layer at the interface of the droplet, since the electrostatic complexes formed by the interaction between polymers can promote the formation of more resistant layers at the interface of the oil droplets, facilitating repulsion between droplets and supporting the stability of the system.

4. Conclusions This study demonstrated that the physicochemical properties of emulsions can be modulated by varying the ratio between two globular proteins with different isoelectric points: lactoferrin and ovalbumin. At pH values between ​​ isoelectric points, the proteins have opposing charges and can form electrostatic complexes. These complexes can alter the stability of the oil droplets relative to pH and temperature.

Although ovalbumin is able to stabilize the emulsions only at a restricted pH, the addiction of lactoferrin to the system provided stability to the emulsions in a higher pH range.

This approach may be useful for designing emulsion-based systems for use in functional foods and beverages.

5. Acknowledgements The authors acknowledge the financial support of Brazilian agencies CNPq and FAPERJ. 419/421 419

Gulão, E. S., Souza, C. J. F., Costa, A. R., Rocha-Leão, M. H. M., & Garcia-Rojas, E. E.

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11. Figueiredo, F. G., Mantovani, R. A., Consoli, L., Hubinger, M. D., & Cunha, R. L. (2017). Structural and emulsifying properties of sodium caseinate and lactoferrin influenced by ultrasound process. Food Hydrocolloids, 63(1), 178-188. http:// dx.doi.org/10.1016/j.foodhyd.2016.08.038.

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15. Niu, F., Zhou, J., Niu, D., Wang, C., Liu, Y., Su, Y., & Yang, Y. (2015). Synergistic effects of ovalbumin/gum arabic complexes on the stability of emulsions exposed to environmental stress.

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18. Villarino, B. J., Dy, L. M., & Lizada, M. C. C. (2007). Descriptive sensory evaluation of virgin coconut oil and refined, bleached and deodorized coconut oil. Lebensmittel-Wissenschaft + Technologie, 40(2), 193-199. http://dx.doi.org/10.1016/j. lwt.2005.11.007.

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Stability and rheological behavior of coconut oil-in-water emulsions formed by biopolymers 29. Murillo-Martínez, M. M., Pedroza-Islas, R., Lobato-Calleros, C., Martínez-Ferez, A., & Vernon-Carter, E. J. (2011). Designing W1/O/W2 double emulsions stabilized by proteine polysaccharide complexes for producing edible films: rheological, mechanical and water vapour properties. Food Hydrocolloids, 25(4), 577585. http://dx.doi.org/10.1016/j.foodhyd.2010.06.015.

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Received: Sept. 07, 2017 Revised: Apr. 13, 2018 Accepted: May 22, 2018

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.11717

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

Investigation on influence of stamp forming parameters on formability of thermoplastic composite Sugumar Suresh1* and Velukkudi Santhanam Senthil Kumar2 Velammal Engineering College, Mechanical Engineering, Anna University, Chennai, Tamil Nadu, India College of Engineering Guindy, Mechanical Engineering, Anna University, Chennai, Tamil Nadu, India

1

2

*deva.suresh78@gmail.com, vssk70@gmail.com

Abstract Advanced fabric reinforced polymer composites find extensive applications in aerospace and structural fields due to their high mechanical properties. A novel stamp forming technique finds extensive use in the hemispherical forming of thermoplastic composites. This study investigates the influence of stamp forming parameters on the formability of thermoplastic composite using Taguchi’s robust design and grey relational analysis. Taguchi’s orthogonal array was used for designing the forming experiments. Responses such as forming ratio and logarithmic thickness strain were considered for the assessment of sheet formability through single and multi-response optimization. Analysis of variance was used for the determination of the contribution of each parameter on formability and it was identified that the die temperature acts as a prominent factor, followed by blank holder force and blank temperature. The confirmation test was conducted at optimum parameter levels and the obtained experimental grade was seen within the confidence interval of the predicted value.

Keywords: thermoplastic composite, stamp forming, sheet formability, grey relational analysis, optimization.

1. Introduction At present, advanced glass fabric reinforced thermoplastic (GFRTP) composites are found as substitutes for metals and thermoset composites due to their better impact, corrosion-resistance and fracture toughness properties[1].

The major driver of growth for the fabric reinforced thermoplastic composite in aerospace, automotive and sporting goods industries is the increasing requirement of recyclable, lightweight, and environment friendly products[2].

The higher durability feature of thermoplastic composites made them better suitable for crash applications than the thermoset composites. For mass production, the final product which yields a potential thermoplastic composite, can possibly be melt-shaped for fast and programmed processing.

In thermoplastic composites, the advantages of stiff fibres are combined with those of the ductile thermoplastic matrix[3].

Currently, automotive industries are discovering novel and cost-effective processing technologies particularly in the field of press forming, tape laying and winding processes.

The type of matrix and reinforcing materials determines the processing methods to be used. The processing techniques that have surfaced recently have utilized these advanced fabric reinforced composites to form complex-shaped parts for large volume production[4]. Stamp forming is widely seen as a fastest technique involving the deformation of the solid sheet material. Stamp forming is not well suited for thermosetting composites, as the molecular structure of the thermoset does not permit the material flow. This stamp forming approach is very well established as ideal for the forming of woven fabric-reinforced thermoplastic composites.

As the temperature approaches the melting point of the

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matrix, the thermoplastic composites can be softened with the ability to flow to fit into the die cavity[5]. Instabilities like buckling and wrinkling may occur during the formation of the woven fabric-reinforced composites into dome shaped parts. The processing parameters which mostly control the forming characteristics of stamp formed components, require optimization for the purpose of controlling the occurrence of wrinkling and other defects[6].

Nurul Fazita et al.[7] studied the impact of parameters on the existence of deformations in fabric reinforced poly-lactic-acid polymer composites and identified that the hot tooling conditions would provide better-quality domes. They observed the larger significance of wrinkles in the wrap direction of the composite domes in contrast with the weft direction. The influence of four parameters on the degree of crystallinity, shear strength, and part thickness were evaluated by Lessard et al.[8]. They found a notable contribution on part consolidation made by the stamping pressure and mold temperature. The emphasis of Ma et al.[9] was on the progress of a new stamping method for fiber reinforced polymers and optimized the process parameters using Taguchi’s split-plot designs. The outcomes depicted the correlation between the processing parameters and the shear stress. Zhu et al.[10] noticed the shear distribution during the forming as the outcome of both the sheet orientation and the mold shape. They carried out experiments on the optimization for the holding force, mold shape, forming temperature, sheet orientation and stamping speed.

The influence of parameters on the formability of composites was investigated by Venkatesan and

Polímeros, 28(5), 422-432, 2018

Investigation on influence of stamp forming parameters on formability of thermoplastic composite Kalyanasundaram[11] who identified the preheat temperature as the most significant factor in controlling the formability of composites, followed by the blank holder force for achieving quality parts. Kalyanasundaram et al.[12] studied the forming behavior of fiber metal laminates using the design of experiments technique, for understanding the effects of process parameters. They have presented the changes in formability of the materials by the recrystallization behavior. Vanclooster et al.[13] evaluated the influence of parameters on the formation of wrinkling and spring back using the fractional factorial design. The conclusion was that a high preheat temperature, a high deep drawing speed, a medium blank holder pressure, a low tool temperature and the expansion of additional polypropylene between the layers prompted a wrinkle free and full-grown composite.

Lee et al.[14] did analysis of the impact of blank holding force on the shapes formed on non-crimp fabrics during the stamp forming process. Many researchers have done experimental and numerical formability analyses for woven fabric reinforced polymer composites[15-18].

Extensive knowledge has been developed for short/long fibre reinforced thermoplastic composites on the optimization and processing of product performance[19]. However, the development of continuous and woven fabric reinforced composites is still not up to the mark. In this study, the novel glass fabric reinforced polypropylene based thermoplastic composite is introduced to help analysis of its formability characteristics under double curvature dome forming.

The objective is to investigate the influence of stamp forming process parameters on the formability, using single response and multi-response optimization. Taguchi’s L9 orthogonal array (OA) experimental design has been employed in the conduct of forming experimental runs. The significant contribution of each parameter on sheet formability was determined using the analysis of variance. The confirmation test was carried out at optimum parameter levels for the validation of the results of analysis.

2. Experimentation 2.1 Proposed methodology The conventionally available manufacturing process for thermoplastic composites is stamp forming, which has proved to be an optimal method for producing products with higher rates. In this study, the stamp forming experiment was conducted on the basis of Taguchi’s L9 orthogonal array.

Taguchi technique uses a minimum number of experimental trials for finding effective solutions to the problems, by analyzing the entire process parameter space. Taguchi’s robust process design was used for solving the single response optimization problems. Grey Relational Analysis (GRA) which is an efficient technique for solving the multi-response problems[20], was implemented. GRA technique uses the grey relational coefficient and grey relational grade for optimizing the multi-response problems. The proposed methodology was analyzed using Minitab-17 software. The analysis identified the proposed multi-response optimization technique offering proof of being an optimal method for providing better formability characteristics during stamp forming of Polímeros, 28(5), 422-432, 2018

Figure 1. Process flow of the proposed methodology.

thermoplastics. Figure 1 is the process flow chart of the proposed methodology.

2.2 Selection of materials In this experimental work, an isotactic polypropylene (0.5mm film, ρ =0.905 g/cm3) reinforced with novel plain weave (Figure 2) glass fabric (265 g/m2, ρ =2.54 g/cm3, v f =19%) thermoplastic composite fabricated through hot compression molding using film stacking approach was used for the stamp forming process[21]. The (3-aminopropyl) trimethoxy silane and polypropylene grafted maleic anhydride[22] were used as the silane coupling agent and matrix compatibilizer, respectively for the purpose of improving the adhesion between the matrix and reinforcement.

The GFRTP laminate was 300×300×2.2 mm3 in size and the novel glass fabrics were stacked in [0-90]4 sequence in the laminate. Water jet cutting was used for cutting the 108mm diameter circular composite blanks, from the novel plain weave reinforced thermoplastic laminate. This is shown in Figure 3.

2.3 Stamp forming setup Stamp forming setup consists of a stamping die set, an oven which is used for heating the circular blank, a temperature controller unit used to monitor the heating of the steel die and the computer with data acquisition system[23].

The steel die and punch were attached on the 1000kN Universal Testing Machine (UTM). The punch which had a radius of 27.5 mm and the die of 30 mm radius with heating unit were connected to the upper base and lower base of UTM respectively, as shown in Figure 4. The hemispherical punch was used for the application of a uniform load in all directions of the circular blank.

2.4 Experimental design Taguchi’s design of experiments approach was implemented for reducing the number of experimental runs and enabling the design of the stamp forming experiments. Three important process parameters such as, Die Temperature (DT), Blank Temperature (BT) and Blank Holder Force (BHF) that could affect the formability behavior of composites, were considered for the investigation[21]. Each stamp forming parameter had three distinct levels. These are illustrated in Figure 5. The process parameters were chosen on the basis of findings seen in literatures[7,8,24,25].

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Suresh, S., & Senthil Kumar, V. S.

Figure 2. Novel plain weave glass fabric structure.

Figure 4. Stamping die set.

Figure 3. Circular composite blank.

Before taking up the stamp forming process, each circular blank was pre-heated to the definite blank temperature in the oven and then transferred to the steel die. Similarly, before the forming process, the die was heated using four heating rods to the definite temperature. This was monitored using a temperature controller unit. During the stamp forming process, the designed BHF has been acting gradually on the heated blank using four sets of springs. The hemispherical punch moving at the rate of 85mm/min, caused deformation of the heated blank into the double curvature die cavity.

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Figure 5. Process parameters and responses.

Following stamp forming, the stamp formed GFRTP component was taken from the steel die for formability analysis. The overall view of the works carried out in the present study is shown in Figure 6.

PolĂ­meros, 28(5), 422-432, 2018

Investigation on influence of stamp forming parameters on formability of thermoplastic composite

Figure 6. Photographic view of works carried out in the present study.

3. Results and Discussions 3.1 Performance characteristics for formability Deformations like in-plane shear, laminate buckling, transverse squeeze flow and matrix degradation that occurred in the blank required analysis for the enhancement of the composite sheet forming process. In this study, significant responses such as forming ratio and thickness strain were considered for the evaluation of the forming behavior of thermoplastic composites.

3.1.1 Forming Ratio (FR) In the case of hemispherical forming, the formability could be determined by considering the maximum extent of possible deformation allowed by the blank. The forming ratio has a significant contribution in the composite sheet forming process[7,26].

in Figure 6. The logarithmic thickness strain was calculated from the flange thickness for the evaluation of the variations in thickness that occurred in the profile. The calculation was done taking the natural logarithm of the ratio of the flange thickness (t) to the original blank thickness (to) using Equation 3[27].

(1)

t  Logarithmic thickness strain ( εt ) = ln   (3)  t0 

rdie 2 + h 2 (2) 2h

The forming experiments were carried out using Taguchi’s L9 Orthogonal array. The calculated values of the responses are given in Table 1.

= For min g Ratio

π ro2 ro2 Area of Blank = = Area of formed dome shape 2 π r 2rdome h h dome

rdome =

Figure 7. Schematic view of Dome shaped component.

Where, r0 - Radius of circular blank; rdome - Radius of dome surface; rdie - Radius of die opening; h - Height of dome surface.

The draw depth of GFRTP stamp formed component, as illustrated in Figure 7, was measured using a Coordinate measuring machine and was converted into the forming ratio using Equation 1. The radius of dome surface in Equation 1, has been calculated using Equation 2. The draw depth of stamp formed component was considered as the height of the dome surface for the purpose of calculating the forming ratio.

3.1.2 Logarithmic Thickness Strain (LTS) The flange thickness of GFRTP stamp formed component was measured using the Vision measuring system as shown Polímeros, 28(5), 422-432, 2018

3.2 Single response optimization Optimization of the stamp forming parameters with single objective function was carried out using the Taguchi’s robust process design which helps reducing the effects of noise factors by determining the best levels for the control factors.

Taguchi has designed three types of signal to noise ratios (S/N ratio), namely, larger-the-better, smaller-the-better and nominal-the-best on the basis of the nature of performance characteristics[28].

In this investigation, a smaller-the-better type S/N ratio has been considered for the minimization of the responses, namely, the forming ratio and log. thickness strain (absolute value). The S/N ratio for smaller-the-better type is given below.

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Suresh, S., & Senthil Kumar, V. S. parameters were set at 100ºC, 230ºC, and 8kN respectively for the log. thickness strain.

S 1 r 1 ratio = −10 log10 ∑ 2 (4) N r i =1 yi

3.2.1 Analysis of variance

Where, r = number of replications and yi = observed response value.

The purpose of analysis of variance (ANOVA) is to identify the most significant factor which would affect the performance characteristics. F-test was carried out for understanding the significance of the process parameters.

The factor with high F-value is greatly significant in the effect on the response of the process. The effects of forming parameters, namely, die temperature, blank temperature and blank holder force on the responses were analyzed using Minitab-17 software. The ANOVA details of the forming ratio and the log. thickness strain, were calculated and are presented in Table 3. The contribution of each parameter indicates the degree of influence of that parameter on the formability characteristics and is highlighted in Table 3.

The analysis shows clearly the die temperature as the most

The calculated experimental responses were converted to the S/N ratio using Equation 4. The values are presented in Table 1. Regardless of the objective function, a larger S/N ratio corresponds to better performance characteristics.

The average S/N ratio values of the forming ratio and the log. thickness strain for all the levels were calculated and are tabulated in Table 2. Based on the larger S/N ratio values, the optimal level setting was predicted as DT3BT1BHF1 and DT2BT3BHF3 for the forming ratio and log. thickness strain, respectively. The die temperature, blank temperature and the blank holder force were set at 170ºC, 170ºC, and 2kN respectively for the forming ratio; while the forming

Table 1. Taguchi’s L9 OA with process parameters, responses and S/N ratio.

Process parameters Exp. runs

Die Temp. (°C)

1 2 3 4 5 6 7 8 9

Blank Temp. (°C)

30 30 30 100 100 100 170 170 170

Process responses

S/N ratio

Blank Holder Force

FR

LTS

FR

LTS

(kN) 2 5 8 5 8 2 8 2 5

1.79 1.85 1.82 1.76 1.73 1.72 1.67 1.66 1.71

0.079 0.167 0.036 0.108 -0.047 0.070 -0.229 -0.116 -0.157

-5.057 -5.343 -5.201 -4.910 -4.761 -4.711 -4.454 -4.402 -4.660

22.087 15.543 28.942 19.361 26.647 23.073 12.809 18.747 16.072

170 200 230 170 200 230 170 200 230

FR – Forming Ratio, LTS – Logarithmic Thickness Strain.

Table 2. Response table for forming ratio and log. Thickness strain.

Process Parameter

Forming ratio BT -4.81 -4.84 -4.86 0.05 3 DT3BT1BHF1

DT -5.20 -4.79 -4.51 0.70 1

Level 1 Level 2 Level 3 Delta Rank Settings

BHF -4.72 -4.97 -4.81 0.25 2

DT 22.19 23.03 15.88 7.15 1

Log. thickness strain BT 18.09 20.31 22.70 4.61 3 DT2BT3BHF3

BHF 21.30 16.99 22.80 5.81 2

DT – Die Temperature, BT – Blank Temperature, BHF – Blank Holder Force.

Table 3. Analysis of variance for forming ratio and log. Thickness strain.

Factor

DoF

DT BT BHF Error Total

2 2 2 2 8

SS 0.73189 0.00378 0.09568 0.00025 0.83161

Forming ratio F MSS ratio 0.3659 2930 0.0019 15 0.0478 383 0.0001

Contribution (%) 88.01 0.46 11.51 0.03 100

SS 91.71 31.89 54.55 47.58 225.73

Log. thickness strain F MSS ratio 45.85 1.93 15.94 0.67 27.27 1.15 23.79

Contribution (%) 40.63 14.13 24.17 21.08 100

DoF – Degrees of Freedom, SS – Sum of Squares, MSS – Mean Sum of Squares, DT – Die Temperature, BT – Blank Temperature, BHF – Blank Holder Force.

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Polímeros, 28(5), 422-432, 2018

Investigation on influence of stamp forming parameters on formability of thermoplastic composite significant factor affecting the performance characteristics of the dome-shape formed components followed by the blank holder force and blank temperature for both the responses.

However, considerable variations on the percentage contribution of each parameter were noticed between the responses. This is highlighted in Table 3.

Where, ∆ 0i (k ) = x0 (k ) − xi (k ) the real value of the difference between x0 (k ) and xi (k ) , ς is distinguishing coefficient (0_1); ∆ min smallest value of ∆ oi ; and ∆ max largest value of ∆ oi .

Using Equation 7[30], the weighted grey relational grade ( g ) was calculated from the grey relational coefficients of the selected responses. = gi ∑ nk =1 wi (k )ξi (k ) (7)

3.3 Multi-response optimization

Where, n - number of responses, w - weight of the kth response.

As stated in the Literatures[30,31], the weights were assigned on the basis of the engineering or decision makers’ judgments. However, in a real case, it is still very difficult to define a particular weight for each of the responses. Hence, the weights are assigned on the basis of the significance of the responses[32]. In this investigation of composite sheet forming, the significance of the forming ratio response was seen as much higher than that of the log. thickness strain response. Henceforth, the weights for the responses were assigned as given in Table 4[28,33]. The grey relational coefficients of forming ratio and log. thickness strain and the weighted grey relational grades for the four cases were calculated and have been tabulated in Table 4.

The multi-response optimization problem could be transformed into a single response optimization problem with the grey relational grade as the objective function[29], using grey relational analysis. The S/N ratio values of the forming ratio and log. thickness strain of the stamp formed components, presented in Table 1, were analyzed for a study of the effects of the stamp forming parameters. Normalization is a transformation done on a single input data for the even distribution of data and scaling it into an acceptable range.

The S/N ratio values of the responses require normalization from zero to one for the purpose of optimizing the stamp forming process. The process of normalizing the responses is known as the grey relational generation, wherein both the responses (i.e.) forming ratio and log. thickness strain, should follow the smaller-the-better type problem that could be expressed as in Equation 5. xi ( k ) =

max yi ( k ) − yi ( k )

max yi ( k ) − min yi ( k )

3.3.1 Optimum level of factors Maximization of weighted grade leads to the better product quality. Hence, the effect of factor was estimated on the basis of the weighted grade. The average grey relational grade was calculated for each level of factors in the four cases.

Details are presented in Table 5, along with the optimum level of factors. The optimal forming parameters setting was predicted from the highest grey relational grade of the levels[29,34]. The response table (Table 5) shows the predicted optimal level setting for all four cases as DT3BT2BHF1. The die temperature, blank temperature and the blank holder force were set at 170ºC, 200ºC, and 2kN respectively.

(5)

Where, xi ( k ) is the grey relational generation, max yi ( k ) is the highest value of yi ( k ) for the kth response and min yi ( k ) is the lowest value of yi ( k ) for the kth response.

Using Equation 5, the S/N ratio of the responses were normalized. Details are presented in Table 4. Grey relational coefficient (GRC) ξi ( k ) was calculated on the basis of the normalized values for showing the relationship between the desired and the actual experimental values, using Equation 6.

An ideal sequence for the responses is x0 ( k ) at ( k = 1, 2,..).

3.3.2 Analysis of variance The ANOVA details of weighted grey relational grade for the four cases are presented in Tables 6 and 7.

The analysis clearly shows the die temperature as the most significant factor[8] followed by the blank holder force and blank temperature for all the four cases, in affecting the performance characteristics of dome-shape formed

∆ min + ς∆ max (6) ξi ( k ) = ∆ oi ( K ) + ς∆ max

Table 4. Normalized values, grey relational coefficients and weighted grades of the responses.

Exp. Runs 1 2 3 4 5 6 7 8 9

Normalized Values

Grey Relational Coefficient

FR

LTS

FR

LTS

0.288 0.000 0.095 0.486 0.637 0.688 0.947 1.000 0.739

0.778 0.320 1.000 0.628 0.944 0.607 0.000 0.587 0.371

0.413 0.333 0.356 0.493 0.579 0.616 0.904 1.000 0.657

0.692 0.424 1.000 0.573 0.899 0.560 0.333 0.548 0.443

0.6 x FR + 0.4 x LTS 0.528 0.369 0.622 0.518 0.700 0.657 0.673 0.819 0.565

Weighted Grey Relational Grades 0.7 x FR + 0.8 x FR + 0.9 x FR + 0.3 x LTS 0.2 x LTS 0.1 x LTS 0.500 0.473 0.446 0.360 0.351 0.342 0.559 0.496 0.434 0.509 0.499 0.490 0.667 0.634 0.601 0.644 0.631 0.617 0.730 0.787 0.844 0.864 0.910 0.955 0.585 0.605 0.626

FR – Forming Ratio, LTS – Logarithmic Thickness Strain.

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Suresh, S., & Senthil Kumar, V. S. Table 5. Response table for weighted grey relational grades (Cases: 1 to 4).

Cases Process Parameter Level 1 Level 2 Level 3 Delta Rank Settings

(0.6 x FR) + (0.4 x LTS)

(0.7 x FR) + (0.3 x LTS)

(0.8 x FR) + (0.2 x LTS)

(0.9 x FR) + (0.1 x LTS)

DT

BT

BHF

DT

BT

BHF

DT

BT

BHF

DT

BT

BHF

0.507 0.625 0.686 0.179 1

0.573 0.630 0.615 0.057 3 DT3BT2BHF1

0.668 0.484 0.665 0.184 2

0.473 0.607 0.727 0.253 1

0.580 0.631 0.596 0.051 3 DT3BT2BHF1

0.670 0.485 0.652 0.185 2

0.440 0.588 0.767 0.327 1

0.586 0.632 0.578 0.054 3 DT3BT2BHF1

0.671 0.485 0.639 0.186 2

0.407 0.569 0.808 0.401 1

0.593 0.633 0.559 0.074 3 DT3BT2BHF1

0.673 0.486 0.626 0.186 2

DT – Die Temperature, BT – Blank Temperature, BHF – Blank Holder Force, FR – Forming Ratio, LTS – Logarithmic Thickness Strain.

Table 6. Analysis of variance for weighted grey relational grades (Cases: 1 and 2).

Cases: 1 and 2 (0.6 x FR) + (0.4 x LTS) (0.7 x FR) + (0.3 x LTS) Factor DoF SS MSS F-ratio Contribution (%) SS MSS F-ratio Contribution (%) DT 2 0.04985 0.0249 4.34 37.42 0.09618 0.0481 12.07 56.35 BT 2 0.00516 0.0026 0.45 3.88 0.00404 0.0020 0.51 2.37 BHF 2 0.06673 0.0334 5.81 50.09 0.06251 0.0313 7.85 36.62 Error 2 0.01148 0.0057 8.62 0.00797 0.0040 4.67 Total 8 0.13323 100 0.17069 100 DoF – Degrees of Freedom, SS – Sum of Squares, MSS – Mean Sum of Squares, DT – Die Temperature, BT – Blank Temperature, BHF – Blank Holder Force, FR – Forming Ratio, LTS – Logarithmic Thickness Strain.

Table 7. Analysis of variance for weighted grey relational grades (Cases: 3 and 4).

Cases: 3 and 4 (0.8 x FR) + (0.2 x LTS) (0.9 x FR) + (0.1 x LTS) Factor DoF SS MSS F-ratio Contribution (%) SS MSS F-ratio Contribution (%) DT 2 0.16088 0.0804 24.51 69.47 0.24397 0.1220 33.53 77.23 BT 2 0.00504 0.0025 0.77 2.18 0.00816 0.0041 1.12 2.58 BHF 2 0.05910 0.0295 9.00 25.52 0.05650 0.0283 7.77 17.89 Error 2 0.00656 0.0033 2.83 0.00728 0.0036 2.30 Total 8 0.23158 100 0.31590 100 DoF – Degrees of Freedom, SS – Sum of Squares, MSS – Mean Sum of Squares, DT – Die Temperature, BT – Blank Temperature, BHF – Blank Holder Force, FR – Forming Ratio, LTS – Logarithmic Thickness Strain.

components. With increase in the weightage of forming ratio, the contribution of die temperature increased from 37.5% to 77.2%, whereas the contribution of blank holder force and blank temperature decreased from 50% to 17.9% and from 3.9% to 2.2% respectively.

3.4 Predicted optimum condition The optimum level of factors obtained on the basis of experiments was DT3BT2BHF1 for all the four cases of multi-response optimization. The grey relational grade was predicted for all the cases using Equation 8[34]. The average grey relational grade values of the factors at their optimum levels are taken from Table 5, in order to calculate the predicted grade value. The overall average grey relational grade (T) was calculated by averaging the grey relational grades of all the factors.

confirmation experiment run values of the grey relational grade for the four cases of multi-response optimization problems are listed in Table 8 along with the draw depth and flange thickness of the stamp formed components. As with multi-response optimization, the confirmation experiment was conducted for single response optimization problems and the details are presented in Table 8.

The confidence interval (C.I.) and effective sample size were calculated using Equations 9 and 10[35].

C.I . =

Where, Fα(1, df of error) is table F-value at given significance level, MSSERROR is mean sum of squares of error, neff is effective sample size

Grey Relational Grade ( predicted ) = DT3 = + BT2 + BHF1 − 2T (8) neff

3.4.1 Confirmation run The confirmation experiment was performed by setting the forming parameters at the optimum levels. The die temperature, the blank temperature and the blank holder force were set at 170ºC, 200ºC and 2kN respectively for all the four cases.

The results are presented in the Table 8. The predicted and 428 428/432

MSSerror Fα (1, df of error ) (9) neff

Total number of experimental runs = 1.286 (1 + Total DoF associated withitems used in (10) estimating the predicted mean grade)

Details of the 90% confidence interval of the predicted grade values are presented in Table 8. The experimental grade values of the multi-response optimization problems were seen lying well within the confidence interval of the corresponding predicted values, showing the good matching of the predicted grey relational grades with the experimental Polímeros, 28(5), 422-432, 2018

Investigation on influence of stamp forming parameters on formability of thermoplastic composite Table 8. Grey relational grade values of predicted and experimental runs.

Optimum setting

Predicted

Experimental grade

Confidence Interval

Draw depth (mm)

Flange thickness (mm)

Case 1

DT3BT2BHF1

grade 0.772

0.819

0.578 to 0.966

29.25

1.96

Case 2

DT3BT2BHF1

0.822

0.864

0.659 to 0.985

29.25

1.96

Case 3

DT3BT2BHF1

0.873

0.910

0.725 to 1.021

29.25

1.96

Case 4

DT3BT2BHF1

0.923

0.955

0.768 to 1.078

29.25

1.96

FR

DT3BT1BHF1

-4.40

-4.91

-4.43 to -4.37

28.89

1.98

LTS

DT2BT3BHF3

16.76

27.04

4.20 to 29.32

27.50

2.30

FR – Forming Ratio, LTS – Logarithmic Thickness Strain.

grey relational grades for the optimum process parameter setting. For the forming ratio, the experimental value was not seen lying within the C.I. of predicted values. Similarly, for log. thickness strain, the range of C.I. was very huge due to a high % error in the ANOVA results. Hence, the optimal settings of single response optimization problems did not provide the desired values.

3.4.2 Comparison between single and multi-response optimization In the case of the single response optimization, the optimal forming parameters setting were 170ºC, 170ºC, and 2kN respectively for the forming ratio and 100ºC, 230ºC, and 8kN respectively for the log. thickness strain. In the case of multi-response optimization, the optimal forming parameters setting were 170ºC, 200ºC, and 2kN respectively for all the four cases.

The draw depth (29.25 mm) and flange thickness (1.96 mm) of the stamp formed component obtained at the multi-response optimization problems were found to be better than the corresponding values of the single response optimization problems. The conclusion from the study is that the stamp formed components obtained have better performance characteristics in the multi-response optimization, instead of in a single response optimization.

Figure 8. Forming ratio of components for the various experimental runs.

3.5 Effects of process parameters on forming ratio The measured draw depth was transformed into meaningful performance characteristic such as the forming ratio for effective assessment of the forming behavior. The typical forming ratio for the maximum draw depth formed component was 1.62. This was obtained by considering the height of dome surface as equal to the radius of the die. Figure 8 is the plotting of the forming ratio of GFRTP components under various experimental runs. It reveals the achievement of the forming ratio closer to that of the typical value of 1.62 for the experimental runs no.7 to no.9. This observation indicates the components formed under high die temperature process conditions as attained the larger draw depth, closely approaching the typical forming ratio. This could be due to the reduced flow resistance for the blank as a result of low temperature difference between the heated blank and hot die.

The blanks formed under low BHF (experimental runs no.1, no.6 and no.8) achieved a reasonably good forming ratio but exhibited wrinkling around the flange and buckling in the dome bend area as shown in Figures 9 and 10[24]. The increase in rate of flow of the blank from the outer region of flange developed a severe strain on the blank elements due to the high circumferential compressive stress, which led to the formation of wrinkling at low BHF. However, the increase Polímeros, 28(5), 422-432, 2018

Figure 9. Wrinkles in GFRTP components.

Figure 10. Buckling & Overlap in GFRTP components.

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Suresh, S., & Senthil Kumar, V. S. in BHF caused a big reduction in the prevalence of defects, but with a slight reduction in the forming ratio. The increased flow resistance at high BHF simultaneously increased the radial tensile stress on the blank, which in turn regulated the flow of blank by controlling the circumferential stress and also minimized the occurrence of wrinkling.

at the faster rate and led to the formation of a severe wrinkling on the surface of components, which in turn increased the flange thickness.

The increase in blank temperature caused a significant reduction in the resin viscosity with simultaneous enhancement of the fluidity of the resin. However, the further increase in blank temperature led to the sticking of matrix resin on the punch and die surfaces which caused diminution in the surface quality of the components formed. The blanks formed under high blank temperature (experimental runs no.3, no.6 and no.9) were subjected to severe degradation as a result of the oxidation of matrix.

Fibre buckling was observed when the blank holder force acting on the blank fell below the circumferential compressive stress as shown in the microscopic image (Figure 12) of the specimen, at the flange portion. This in turn caused an increase in the flange thickness[25]. As elaborately discussed in the previous section, the components formed under low BHF showed a relatively high wrinkling than the high BHF components, as a result of high circumferential stress on the blank elements. The conclusion from the experimental results is that the flange thickness depends on the amount of temperature difference as well as the frictional force between the heated blank and the die.

3.6 Effects of process parameters on logarithmic thickness strain

4. Conclusion

The logarithmic thickness strain was used for the estimation of the amount of thinning and thickening that occurred on the flange portion of the stamp formed components.

The logarithmic thickness strain of GFRTP stamp formed components under various experimental runs has been plotted (Figure 11). Compared to the initial blank thickness, the components formed under high die temperature conditions were up to 22% thinner, whereas the low die temperature formed components were up to 16% thicker at the flange portion[8]. The reason is that the high temperature difference between the heated blank and die, made the blank to solidify

The focus of this experimental investigation was the influence of stamp forming parameters on the formability of thermoplastic composite using Taguchi based grey relational analysis for single and multi-response optimization problems.

The following conclusions are drawn: • The analysis helped the identification of die temperature acting as a prominent factor, followed by the blank holder force and blank temperature in controlling the performance characteristics of stamp formed components for both single and multi-response optimization problems; • Compared to single response optimization, Taguchi based multi-response optimization is found to be a very powerful tool for predicting the performance characteristics in the stamp forming of GFRTP composite; • The conclusion from the grey relational analysis is that the stamp formed components could be obtained with better performance characteristics at the die temperature of 170°C, blank temperature of 200°C and blank holder force of 2kN process condition;

Figure 11. Logarithmic thickness strain for the experimental runs.

• Stamp forming process produced the hemispherical components with the maximum draw depth of 29.25 mm and flange thickness of 1.96 mm, without much wrinkling and defects; • Confirmation test results helped the verification of optimum process parameter levels determined and the experimental grade obtained lies well within the confidence interval of the predicted value; • The increase in die temperature resulted the improvement in the forming ratio by reducing the flow resistance between the heated blank and die, but a decrease in the flange thickness of the components; • The increase in blank holder force caused a slight reduction in the forming ratio and the flange thickness but improved the quality of the profile obtained;

Figure 12. Microscopic image of the specimen at the flange.

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• The change in blank temperature has been identified as having an insignificant effect on the performance characteristics.

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Investigation on influence of stamp forming parameters on formability of thermoplastic composite

5. Acknowledgements The authors wish to thank Anna University and Velammal Engineering College, Chennai for the help rendered in preparing the laminates and conducting the stamp forming experiments.

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20. Jayaraman, P., & kumar, L. M. (2014). Multi-response optimization of machining parameters of turning AA6063 T6 aluminium alloy using grey relational analysis in Taguchi method. Procedia Engineering, 97, 197-204. http://dx.doi. org/10.1016/j.proeng.2014.12.242.

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28. Vijayan, S., Raju, R., & Rao, S. R. K. (2009). Friction stir welding of Alâ&#x20AC;&#x201C;Mg alloy: comparison of process parameter optimization between single and multi response using Taguchi methodology. International Journal of Applied Engineering Research, 4(5), 709-725. Retrieved in 2017, November 28, from https://www.ripublication.com/ijaerv4/ijaerv4n5_7.pdf 29. Haq, A. N., Marimuthu, P., & Jeyapaul, R. (2008). Multi response optimization of machining parameters of drilling Al/SiC metal matrix composite using grey relational analysis in the Taguchi method. International Journal of Advanced Manufacturing Technology, 37(3), 250-255. http://dx.doi. org/10.1007/s00170-007-0981-4.

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33. Sathiya, P., Aravindan, S., & Noorul Haq, A. (2006). Optimization for friction welding parameters with multiple performance characteristics. International Journal of Mechanics and Materials in Design, 3(4), 309-318. http://dx.doi.org/10.1007/ s10999-007-9037-z.

34. Vijayan, S., Raju, R., & Rao, S. K. (2010). Multiobjective optimization of friction stir welding process parameters on aluminum alloy AA 5083 using Taguchi-based grey relation analysis. Materials and Manufacturing Processes, 25(11), 1206-1212. http://dx.doi.org/10.1080/10426910903536782.

35. Panneerselvam, R. (2012). Design and analysis of experiments.

India: PHI Learning (P) Ltd. Received: Nov. 28, 2017 Revised: Mar. 18, 2018 Accepted: May 15, 2018

PolĂ­meros, 28(5), 422-432, 2018

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.01718

Preliminary analysis of N-vinylpyrrolidone based polymer gel dosimeter Juliana Rosada Dias1, Thyago Fressatti Mangueira1,2, Roseany de Vasconcelos Vieira Lopes3,4, Maria José Araújo Sales3 and Artemis Marti Ceschin1* 1

Departamento de Engenharia Elétrica, Faculdade de Tecnologia, Universidade de Brasília – UnB, Brasília, DF, Brasil 2 Departamento de Física, Universidade Católica de Brasília – UCB, Brasília, DF, Brasil 3 Instituto de Química, Universidade de Brasília – UnB, Brasília, DF, Brasil 4 Faculdade do Gama – FGA, Universidade de Brasília – UnB, Gama, DF, Brasil *artemis@pgea.unb.br

Abstract This paper aims to evaluate the dosimetric characteristics of modified VIPARnd for radiotherapy dosimetry using optical investigations. The absorbance spectrum of the irradiated gel dosimeter was evaluated optically with spectrophotometer techniques and with a CMOS imaging system. The useful dose range for the peak value and the relative area under the absorbance curve is 3-20 Gy. The dose-response curve for CMOS readout has an interval of linearity from 3-20 Gy. The modified VIPARnd developed has a good dose range and good temporal stability in the spectrophotometric analysis of the intervals studied. The CMOS readout is transportable, cheaper, easier to use and an excellent alternative for dosimetry.

Keywords: polymer gel dosimetry, optical analysis, N-vinylpyrrolidone, radiotherapy.

1. Introduction Recent technological advances in radiotherapy require quality assurance (QA) that needs accurate and precise dose verification. Dose measurement usually falls into two categories: absolute and relative. The reference dosimetry aims to produce accurate and consistent values ​​relative to the primary standards, this allows the comparison of results between centers. However, to ensure safe operation of the equipment in order to verify dose calculations and verify the dose administered in vivo, measurements are required in a range of conditions covering all aspects of clinical use, not only the conditions of reference. A possibility for measuring dose distributions is gel dosimetry[1,2].

The gel dosimeters are gelatine-matrix-based dosimetry system that avoids the diffusion problem.

In these three-dimensional dosimetry systems the gelatine matrix contains monomers that polymerize by free-radical induced chain reactions to form spatially fixed cross-linked networks[1]. Gel dosimeters are mostly composed of water, gelatin and small amounts of other compounds that provide tissue equivalency, upon irradiation, it polymerizes in an aqueous gelatinous matrix as a function of the absorbed radiation dose[1,3]. The gel dosimeters do not present angular dependence and have high resolution[2]. Currently, there are two types of gel dosimetry systems: Fricke and polymer gel dosimeters[1].

The Fricke dosimeter consists of ferrous sulfate in an aqueous gel solution. The irradiation induce oxidation and to conversion of ferrous ions to ferric ions modified NMR

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relaxation rates[1,4,5]. Fricke gel exhibits high ion diffusion that causes low spatial resolution. Currently, recent formulations of Fricke gel dosimeters based on PVA-GTA (Poly-vinil alcohol-glutaraldehyde) were developed[6]. These materials are not toxic and have a lower diffusion coefficient than the standards Fricke gels. The increase in GTA concentration is a viable method to reduce the diffusion of ions into the gel matrix[7]. The other type is polymer gel, which contains monomers dissolved in a gel matrix based on radiation induced polymerization and crosslinking of acrylic monomers[2,8].

The solution is polymerized due to free radicals produced by radiolysis. This alters the gel dosimeter physicochemical properties in proportion to the absorbed dose causing opacity.

There are different polymer gel compositions of which many were susceptible to atmospheric oxygen. Initially, the polymer gel dosimeters should be manufactured in an oxygen-free environment, because oxygen inhibits the radiation-induced polymerization[1,2].

In 2001, Fong et al. proposed the use of antioxidants to reduce the oxygen effect. Ascorbic acid (ASC) is used to bind oxygen contained within the gel matrix in a process initiated by copper sulfate, possibiliting the gel preparation at normal atmosphere conditions[9,10]. The polymer gel dosimetry was studied for different types of irradiation, such as gamma rays from cobalt sources used in external radiotherapy, high-energy x-rays and high-energy electron beams produced by clinical linear accelerators and brachytherapy sources[11].

Significant energy dependence was not found in studies of high-energy photon and high-energy electron beams[2,10,11].

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

Dias, J. R., Mangueira, T. F., Lopes, R. V. V., Sales, M. J. A., & Ceschin, A. M. Baras et al. reported an adequate spatial resolution for dosimetry of 192Ir HDR brachytherapy source[12]. Authors continued to investigate polymer gel dosimetry for treatments with high dose gradient, as with Intensity-Modulated Radiation Therapy (IMRT)[13,14], Intensity-Modulated Arc Therapy (IMAT)[15,16] and stereotactic radiosurgery (SRS)[17,18].

Polymer gel dosimeters have also been applied to proton[19,20] and neutron beams[21]. To evaluate the dose distribution in polymer gel dosimeters, many imaging modalities can be used. The opacity caused by radiation provides optical contrast in polymer gels[22,23,24]. Some researchers considered optical investigation to analyze different solution compositions and response to ionizing radiation[25,26,27]. The use of monomer N-vinylpyrrolidone (NVP) in gel dosimetry has been developed

by Pappas et al.[25] and was named VIPA. The VIPAR polymer gel consists of NVP, N,N’methylenebisacrylamide (BIS), gelatin and argon was used to remove oxygen. A new gel composition (VIPARnd) based on Pappas formulation described by Kozickic et al., 2007 has the NVP concentration doubled and copper sulphate and ascorbic acid added[28-30].

The concentration of monomers in gel solutions alters the dosimetric characteristics, like dose range, sensitivity and stability[31,32].

The purpose of this study is to evaluate basic dosimetric properties of this modified VIPARnd using infrared, UV-Vis spectrophotometer and a CMOS camera. The dose-response sensitivity, repeatability, reproducibility and post-irradiation temporal stability were investigated for a 6 MV photon beam used in radiotherapy.

the water molecule occurs is presents according to schematic shown in Figure 1[30].

The molecular product hydrogen is chemically inert and readily escapes, whereas the other molecular product hydrogen peroxide (H2O2), is retained in water and reacts with the reducing species (e•aq- and H•) to produce •OH and corresponding species. In pure water, after a time in a given radiation field, the concentration of hydrogen peroxide becomes steady. With g-ray radiation the concentration is low and there is very little decomposition[31].

The positive ion formed from the reaction (H2O+) can form the hydroxyl radical (OH•) when dissociating into the form H• and •OH. Hydrogen and hydroxyl radicals can also be formed through the excitation of the water molecule.

As a result of the radiolysis reactions we have a pair of H+ and OH- ions and a pair of free radicals H• and •OH[31].

In the reactions shown in 1, 2 and 3 (Figure 2) the breaks of the carbon double bond in BIS are caused by interaction with the hydrogen (H•) and hydroxyl (•OH) and electron-hydrated (e•aq-)[33].

In the NVP reactions with the free radicals produced by the radiolysis of the water can form the radicals shown in Figure 3[32].

The VIPARnd gel dosimeter is a hydrogel gelatin in which th10e monomers N-vinylpyrrolidone (NPV) and N, N’-methylenebisacrylamide (BIS) are dissolved. When the gel is irradiated the water molecules are ionized. From the possible reactions between NVP and BIS molecules as shown in Figure 4, several subsequent reactions can

2. Materials and Methods 2.1 Mechanism Radiolysis of water under high energy radiation has been extensively studied. Water is the compound at the highest concentration within the dosimeter solution and it is the molecule that to interact most likely with radiation[25].

Radiation (hv) causes ionization in water molecules, a phenomenon called radiolysis[28]. The processes of the radiolysis of pure water at where The initial breakdown in

Figure 1. Process of radiolysis of water[30-32].

Figure 2. Breaking possibilities of BIS molecules[33].

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Preliminary analysis of N-vinylpyrrolidone based polymer gel dosimeter occur by forming a series of chromonomer radicals in the solution. The gel dosimeter obtained in this work follows the mechanistic proposal presented in Figure 4.

cuvette was irradiated to show the air influence. Oxygen presence inhibits the radiation-induced polymerization.

2.2 Gel preparation

The gels were irradiated 24 hours after preparation with absolute doses of 3, 5, 10, 15, 20 and 50 Gy using a Varian 21 iX linear accelerator with 6MV photons at 5.0 cm of depth in a RW3 solid water phantom. The samples were removed from the refrigerator before irradiation to stabilize at room temperature (~22 °C). The irradiation was done with a field size of 10 × 10 cm2, SSD of 100 cm and a dose rate of 6 Gy/min. The dose was calculated at the center of the cuvette in order to have a homogenous dose distribution.

The modified VIPARnd was prepared using NVP (purity grade ≥99%, Sigma Aldrich), N,N’methylenebisacrylamide (BIS) (Sigma Aldrich), gelatin (Type A/300 bloom, Sigma Aldrich), CuSO4x5H2O (purity grade ≥99%) and ASC and ultra pure deionized water (Table 1). The procedure used to manufacture the solution was the same as described by Kozickic et al., 2007. BIS was dissolved in water heated below 50 °C, after gelatin was added. The solution temperature was cooled to 33 °C, the NVP, ASC and CuSO4.5H2O were added. The solution was stirred continuously during the entire mixing procedure.

The VIPARnd formula described by Kozicki et al.[28] exhibit high opacity with the absorbed dose. In the studied polymer gel the concentration of NVP and BIS was reduced aiming to optical analysis.

The cuvettes used as gel containers were closed with Parafilm foil and stored in a refrigerator (~6 °C) to solidify.

The cuvettes were made of glass with 10mm path-length.

Resulting gels were clear and transparent. The major difficulty is not having air bubbles at the top of the gel container.

The influence of bubbles is shown in Figure 5. This gel cuvette was placed upside down before the gel solidified, placing the air bubble on the closed end. After that, the

2.2 Characterization

Absorption spectra were measured for a wavelength range 280-480 nm using a Varian Cary 5000 UV-Vis spectrophotometer with temperature-controlled cuvettes, maintained at 22 °C. The baseline is the empty cuvette.

The absorbance measurements were carried out with 2 mm intervals between the highest dose to the lowest dose and lastly with the reference cuvette (0 Gy). For the analysis of temporal stability, the absorbance of doses 0, 5, 10 and 15 Gy was measured at three different post-irradiation times, 24 h, 192 h and 360 h.

A cheaper and simpler analysis method was also developed. The gel cuvettes were analyzed with an imaging system developed at 24h post-irradiation. This apparatus consisted of a medical light box, a CMOS camera and a MatLab routine. The cuvettes were placed on a medical Table 1. Gel composition.

Figure 3. Breaking N-vinylpyrrolidone (NVP) molecule without oxygen fixation[32].

Component Gelatin (300 Bloom)

Concentration 3.5% w/v

N,N’methylenebisacrylamide (BIS)

2% w/v

N-vinylpyrrolidone (NVP)

4% w/v

Ascorbic acid (ASC)

397 mM

Copper sulfate pentahydrate (CuSO4.5H2O)

32 mM

Pure Water

90.5% w/v

Figure 4. Proposal of possible reactions between molecules of N-vinylpyrrolidone (NVP) and N,N’methylenebisacrylamide (BIS)[30].

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Dias, J. R., Mangueira, T. F., Lopes, R. V. V., Sales, M. J. A., & Ceschin, A. M. light box and photographed, without flash and no filters on automatic mode. The CMOS camera was a Nikon Coolpix P510. The file image format is JPG and this file was read in a MatLab routine that converted it into only one matrix (gray scale image). For determining the gray scale, the routine analyzes a matrix of 9 × 9 at the cuvette center using mean pixel intensity.

3. Results and Discussions After being irradiated these chromonomers react with each other to form polymer chains. The radiation causes opacity in the dose absorbed in the gel, as can be seen in Figure 6a. After irradiation the dosimeters were put back

in the refrigerator for storage. The gel opacity reduces the pixel intensity as seen in Figure 6b.

High energy radiation produces ionization and excitation in polymer molecules. These energy-rich species undergo, dissociation, abstraction and addition reactions in a sequence, leading to chemical stability. As a result, a polymeric material may undergo cross linking reaction, leading to increase in the molecular weight or undergo chain scission reaction, leading to decrease in the molecular weight. Generally, both processes occur simultaneously but in given radiation conditions, one of them is the predominant process[24].

Due to the high fraction of cross-linking agents the final structure of the polymer is a three-dimensional network.

The degree of polymerization is directly proportional to the absorbed dose. And because of the gelatinous matrix the polymer aggregates cannot diffuse into the gel structure preserving the spatial information of the dose absorption[30].

The visible and ultraviolet absorption spectra of the gel with different doses are shown in Figure 7.

Figure 5. Air bubble in an irradiated modified VIPARnd gel cuvette.

Data shows that the modified VIPARnd had a maximum absorbance at 300-320 nm depending on the absorbed dose. The relative absorbance of peak values was obtained by subtracting the maximum absorbance of the reference cuvette with 0 Gy. This data has sigmoidal comportment (Figure 8). The linear regression of data are also reported in Figure. 8, showing good linearity of response in the dose range of 3-20 Gy, with R2 = 0.9780.

Figure 6. (a) Representes cuvettes of irradiated modified VIPARnd. The dose absorbed from left to right is 0, 3, 5, 10, 15, 20 and 50 Gy and (b) Image acquired by the imaging system developed. The dose absorbed from left to right is 0, 3, 5, 10, 15, 20 and 50 Gy.

Figure 7. Visible and Ultraviolet absorption spectra for modified VIPARnd at 24h after irradiation measured in Gray (Gy).

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Figure 8. The relative maximum UV-VIS absorbance as a function of absorbed dose. Error bars indicate the standard deviation of the relative maximum absorbance values measured in Gray (Gy).

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Preliminary analysis of N-vinylpyrrolidone based polymer gel dosimeter The absorbance values for UV-VIS spectra in Figure 4 increase for any wavelength with increasing dose, as is characteristic of opacity gel[26,34]. Therefore, the areas under the spectra were investigated by curve integrated as shown in Figure 9. The area values were obtained by subtracting the area of the reference cuvette with 0 Gy. The same sigmoidal comportment was observed, and the linear regression of data showing good linearity of response in the dose range of 3-20 Gy, with R2 = 0.9802.

The picture obtained by the imaging system developed was converted into gray scale and value of pixel was registered. The inverse of gray values (1/pixel value) was calculated and normalized by subtracting the value of the reference cuvette with 0 Gy. In Figure 10, the relative inverse of gray values (1/pixel value) obtained through a MatLab routine is reported versus dose. The plotted data show similar comportment of spectroscopy data analysis, and the linear regression of data showing good linearity of response in the dose range of 3-20 Gy, with R2 = 0.9849.

Figure 9. The relative area under the UV-VIS spectra as a function of absorbed dose. Error bars indicate the standard deviation of the relative area values measured in Gray (Gy).

Radiation causes gel opacity that can be detected by optical investigations. The aim of this paper was to analyze the modified VIPARnd using two different optical techniques, spectrophotometry and an CMOS imaging device. The dose-response for spectrophotometric data was analyzed for absorbance peak and area under absorbance curve. The inverse of pixel intensity in function of dose was analyzed for the CMOS imaging device.

Temporal variation of the relative peak absorbance to the modified VIPARnd at 24h, 192h and 360h post-irradiation with 0, 5, 10 and 15 Gy is plotted in Figure 11.

It was previously shown that the time between irradiation and gel readout doesn’t affect the system dose characteristics for N- vinylpyrrolidone based polymer gel[23]. The data remains practically constant for at least two weeks after irradiation.

The repeatability and reproducibility of gel response were 0.5% and 5% respectively.

4. Conclusions

Figure 10. Relative inverse gray value as a function of absorbed dose. Error bars indicate the standard deviation of the relative inverse gray values measured in Gray (Gy).

The interval of linearity for high-energy photon (6 MV) extends from 3 Gy up to 20 Gy for analyses using the spectrophotometric technique and from 3 Gy up to 20 Gy for data obtained with the imaging device developed. The data for the area under absorbance curve presented the highest sensitivity for dose-reponse.

Absorbance measurements with different post-irradiation time indicated a temporal stability for the gel dosimeter up to at least 360 h, though the spectra shape has varied with the absorbed dose and also over the time after irradiation.

However, the trends of the observed changes are similar, independently of the dosimeter composition.

The modified VIPARnd polymer gel presented could be helpful for dosimetry of beams used in radiotherapy.

The CMOS readout is a transportable, cheaper, easier to use and we suggest as future work the analysis of spatial resolution this setup for two-dimensional (2D) measurements as an alternative for dosimetry of small fields in radiotherapy.

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Figure 11. Variation of maximum UV-VIS absorbance at different times post-irradiation measured in Gray (Gy).

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Dias, J. R., Mangueira, T. F., Lopes, R. V. V., Sales, M. J. A., & Ceschin, A. M.

5. Acknowledgements The authors are grateful to CNPq for financial support, to the Instituto de Radioterapia de Taguatinga for their kind contribution in gel irradiation and to Professor DSc. Marek Kozicki for the discussions and helpful tips about gel preparation and air control.

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14. Gustavsson, H., Karlsson, A., Back, S. A. J., Olsson, L. E., Haraldsson, P., Engström, P., & Nyström, H. (2003). MAGICtype polymer gel for three-dimensional dosimetry: Intensitymodulated radiation therapy verification. Medical Physics, 30(6), 1264-1271. http://dx.doi.org/10.1118/1.1576392.

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16. Ceberg, S., Gagne, I., Gustafsson, H., Scherman, J. B., Korreman, S. S., Kjaer-Kristoffersen, F., Hilts, M., & Bäck, S. A. (2010). RapidArc treatment verification in 3D using polymer gel dosimetry and Monte Carlo simulation. Physics in Medicine and Biology, 55(17), 4885-4898. http://dx.doi. org/10.1088/0031-9155/55/17/001. PMid:20679702.

17. Watanabe, Y., Akimitsu, T., Hirokawa, Y., Mooij, R., & Perera, G. (2005). Evaluation of dose delivery accuracy of Gamma Knife by polymer gel dosimetry. Journal of Applied Clinical Medical Physics, 6(3), 133-142. http://dx.doi.org/10.1120/ jacmp.v6i3.2110. PMid:16143798.

18. Gopishankar, N., Watanabe, Y., & Subbiah, V. (2011). MRIbased polymer gel dosimetry for validating plans with multiple matrices in Gamma Knife stereotactic radiosurgery. Journal of Applied Clinical Medical Physics, 12(2), 133-145. http:// dx.doi.org/10.1120/jacmp.v12i2.3333. PMid:21587176.

19. Gustavsson, H., Bäck, S. A., Medin, J., Grusell, E., & Olsson, L. E. (2004). Linear energy transfer dependence of a normoxic polymer gel dosimeter investigated using proton beam absorbed dose measurements. Physics in Medicine and Biology, 49(17), 3847-3855. http://dx.doi.org/10.1088/0031-9155/49/17/002.

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20. Zeidan, O. A., Sriprisan, S. I., Lopatiuk-Tirpak, O., Kupelian, P. A., Meeks, S. L., Hsi, W. C. Z., Li, Z., Palta, J. R., & Maryanski, M. J. (2010). Dosimetric evaluation of a novel polymer gel dosimeter for proton therapy. Medical Physics, 37(5), 21452152. http://dx.doi.org/10.1118/1.3388869. PMid:20527548.

21. Mangueira, T. F., Silva, C. F., Coelho, P. R. P., & Campos, L. L. (2010). Gamma/neutron dose evaluation using Fricke gel and alanine gel dosimeters to be applied in boron neutron capture therapy. Applied Radiation and Isotopes, 68(4-5), 791-794. http://dx.doi.org/10.1016/j.apradiso.2010.01.027.

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26. Mattea, F., Romero, M. R., Vedelago, J., Quiroga, A., Valente, M., & Strumia, M. C. (2015). Molecular structure effects on the post irradiation diffusion in polymer gel dosimeters.

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27. Lotfy, S., Basfar, A. A., Moftah, B., & Al-Moussa, A. A. (2017). Comparative study of nuclear magnetic resonance and UV–visible spectroscopy dose-response of polymer gel based on N-(Isobutoxymethyl) acrylamid. Nuclear Instruments & Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms, 413, 42-50. http://dx.doi.org/10.1016/j. nimb.2017.09.033.

28. Kozicki, M., Maras, P., Rybka, K., Biegański, T., Kadłubowski, S., & Petrokokkinos, L. (2007). On the development of the VIPAR polymer gel dosimeter for three-dimensional dose measurements. Macromolecular Symposia, 254(1), 345-352. http://dx.doi.org/10.1002/masy.200750850.

29. Papoutsaki, M. V., Maris, T. G., Pappas, E., Papadakis, A. E., & Damilakis, J. (2013). Dosimetric characteristics of a new polymer gel and their dependence on post-preparation and post-

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irradiation time: Effect on X-ray beam profile measurements.

Physica Medica, 29(5), 453-460. http://dx.doi.org/10.1016/j. ejmp.2013.01.003. PMid:23375524.

30. Tauhata, L., Salati, I. P., Di Prinzio, R., & Di Prinzio, A. R. (2006). Radioproteção e dosimetria: fundamentos. Rio de Janeiro: IRD/CNEN. 31. Wang, Y., & Wang, H. (2009). The radiation-induced peroxidation of poly(N-vinylpyrrolidone) in an aqueous solution. Radiation Physics and Chemistry, 78(3), 234-237. http://dx.doi.org/10.1016/j.radphyschem.2008.11.005.

32. Hassouna, F., Therias, S., Mailhot, G., & Gardette, J. (2009).

Photooxidation of poly(N-vinylpyrrolidone) (PVP) in the solid state and in aqueous solution. Polymer Degradation & Stability, 94(12), 2257-2266. http://dx.doi.org/10.1016/j. polymdegradstab.2009.08.007.

33. Kozicki, M., Filipczak, K., & Rosiak, J. M. (2003). Reactions of hydroxyl radicals, H atoms and hydrated electrons with N-N’-methylenebisacrylamide in aqueous solution. A pulse radiolysis study. Radiation Physics and Chemistry, 68(5), 827-835. http://dx.doi.org/10.1016/S0969-806X(03)00311-6.

34. Tranter, G. E. (2017). UV–Visible Absorption Spectrometers. In J. Lindon, G. E. Tranter, D. Koppenaa (Eds.), Encyclopedia of spectroscopy and spectrometry (491-494). Oxford: Academic Press. http://dx.doi.org/10.1016/B978-0-12-409547-2.12689-7.

Received: Mar. 16, 2018 Revised: May 30, 2018 Accepted: June 09, 2018

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.00918

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

Quantification by FT-IR (UATR/NIRA) of NBR/SBR blends Joyce Baracho Azevedo1,2, Lidia Mattos Silva Murakami1,2, Ana Carolina Ferreira3, Milton Faria Diniz4, Leandro Mattos Silva5 and Rita de Cássia Lazzarini Dutra1* Instituto Tecnológico de Aeronáutica – ITA, São José dos Campos, SP, Brasil 2 Tenneco Automotive Brasil, Cotia, SP, Brasil 3 General Motors do Brasil – GM, São Caetano do Sul, SP, Brasil 4 Divisão de Química – AQI, Instituto de Aeronáutica e Espaço – IAE, São José dos Campos, SP, Brasil 5 Petroquímica Braskem S.A., Santo André, SP, Brasil 1

*ritacld@ita.br

Abstract Rubber blends are important materials in automotive industry, as well as in other sectors. However, there are implications when suitable use of a polymer in an artifact is not made. In the automotive area, for example, the use of an elastomer without the fuel resistance requirement would result in component degradation, potential fuel leakage, and danger of fire.

The use of polymer blends may be the solution to this problem. Fourier transform infrared spectroscopy (FT-IR) can be used for the knowledge of the polymer content of these blends. Then, FT-IR quantitative methodologies for determining acrylonitrile-butadiene copolymer (NBR) copolymer and butadiene-styrene copolymer (SBR) contents were developed by the transflectance accessory, NIRA, and the transmission mode, being the sample analyzed by transmission and universal attenuated total reflection (UATR) in the medium infrared (MIR). UATR and NIRA methodologies showed better accuracy. However, the MIR analysis showed a detection limit between 10-20% of NBR. Keywords: content, NBR, NIRA, SBR, UATR.

1. Introduction In contrast to the deceleration in the new polymers production, there is a growing interest in the processes research and development for the modification of existing polymers[1]. In this context, polymer blends are available for specific applications. According to the literature, the necessary condition is that the lower content of one of components must exceed at least 5%[2,3].

Blends are often used to improve properties of each polymer involved in the product, process and/or reduce cost.

There are many applications in several industries, such as aeronautics, naval, automotive, graphics, real estate, among others. Therefore, studies involving polymers and their blends are attractive, since the methodologies developed can be used in different sectors[1,4].

Butadiene-based copolymers are widely used in automotive industry. Among these, the SBR and NBR copolymers are outstanding. SBR plays a major role in the market due to its application in tires production. When SBR is used in conjunction with the BR-high cis butadiene homopolymer, excellent properties are obtained for application to tire tread.

Since year 2000, automobile and tire manufacturers have been concerned about the environment and which led them to invest in new cleaner synthetic processes for production of these elastomers. Butadiene is a monomer used in the manufacture of elastomers of great economic interest worldwide. According to their properties, the polymers are assigned to a specific type of use[5].

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There are several blends available in the world market, but for the purpose of this paper, the blend composed of NBR and SBR copolymers was selected based on its properties which are suitable on lowering costs by improving certain properties of NBR rubber, which has good chemical and oil resistance. However, these properties vary according to a considerable number of rubber products. Higher the acrylonitrile (AN) content, greater the oil resistance, however lower the flexibility. It is possible to use a NBR blend of high content AN with SBR rubber to obtain an oil resistance degree as such a NBR with low content of AN, with an overall economy in cost. NBR products with high AN content tends to shrink in contact with lubricating oils, in high temperature. The manufacture of NBR/SBR blends constitutes a solution for the final artifact achieve desired properties. SBR can also improve NBR processing[6].

In the automotive industry, NBR is usually applied in hoses that have direct contact with fuels or gases [5]. NBR is also used in the aerospace industry, as rocket motor thermal insulation[7]. It comes to our attention that the quality of the product delivered by the supplier might not meet the specification needed, consisting only by NBR. This may lead to detachments compromising the integrity of the rubber / propellant interface.

NBR rubber also benefits aeronautics industry on appliances as such hoses, seals, and self-sealing fuel and oil tanks. It is applied in the nuclear industry to make protective gloves. NBR property of withstanding a temperature range

Polímeros, 28(5), 440-449, 2018

Quantification by FT-IR (UATR/NIRA) of NBR/SBR blends of -40 to 108°C makes it the ideal material for aeronautical applications. Still, NBR can be applied to create molded products, adhesives, sealants, sponges, expanded foams and carpets[8].

A variation in polymerization, AN ratio to butadiene, processing properties and vulcanization are characteristics added in NBR / SBR blend by NBR rubber worth to mention.

The AN content is one of the main criteria to define the basic properties of an elastomer. Nitrile group polarity grants to elastomers resistance to oils and hydrocarbon-based solvents, flexibility and abrasion resistance[5]. In this paper, a NBR rubber with AN content of 37-41% was used according to NBR supplier. Additionally, a FT-IR methodology developed by the group[9] was applied to precisely acquire the AN value.

The AN content determination in NBR have been performed by FT-IR transmission with values reference obtained by Kjeldhal method[10], measuring contents up to around 40%. FT-IR transmission and reflection (UATR) techniques[9] were used for determining contents up to around 50%, with good results, indicating that UATR methodology presents better linear correlation and less analysis time.

One of the most common blend elastomer is the SBR responsible for nearly 40% of all synthetic rubber used in the world. According to data from 2007, approximately 2.4 million tons of SBR per year were already produced in the world[5]. SBR rubber characteristics depend on styrene content, which can vary between 10 and 85%. Formulations with low styrene content exhibit an elastomeric behavior, whereas those with high styrene content have a thermoplastic

nature[11]. SBR-1502 was object of this study, with 23.5% styrene, obtained by cold polymerization (10°C maximum) in emulsion of fatty and resinous soaps, coagulated in a salt / acid or acid system and stabilized with a non-smelly antioxidant.

SBR rubber has good mechanical properties, high resistance. Likewise, it has good resistance to abrasion, ozone and weathering, but regarding to oil resistance it presents a gap, making this mixture with NBR beneficial for both copolymers, dependent on the suitable application of the final artifact[12].

The property variations are dependent on the functional groups content of the polymers and also compounds present in the product composition. Therefore, the possibility of using blends to reach a specific application indicates the need for suitable characterization and/or quantification of these materials. Instrumental techniques, mainly Fourier transform infrared spectroscopy (FT-IR), associated or not with other techniques, is mentioned in the literature for this goal, including also studies of polymers used in the automotive and aerospace industry, such as NBR, SBR and their polymer blends[13-18].

Table 1 shows some studies. Although good results were achieved in these studies, some observations were made in this study, which served as a basis for the elaboration of the methodology currently developed.

It is observed that the MIR region is the most used, just as the technique obtaining FT-IR spectra is the conventional one, which means transmission and the use of other instrumental

Table 1. Main aspects cited by studies on polymers and their blends characterization.

Author Shield et al.[19]

Year 2003

Dutra et al.[17]

2004

Berridi et al.[20]

2006

Chakraborty et al.

2007

Lee et al.[21]

2007

[11]

Main conclusion FT-MIR Analysis (medium infrared) and FT-NIR (near infrared) were used to NBR/SBR determination. Obtaining modes: MIR - transmission and ATR/ NIR – optical fiber – NBR band – 2240 cm-1 and SBR – 1600 cm-1.

NIR range – 5443 - 6103 cm-1.

Methodology errors MIR – 4% and NIR – 2%.

NR/SBR blends were analyzed by FT-IR transmission/ controlled pyrolysis and TGA/DTG, with linear correlation 0.998 and methodology error 1.73%, within the accuracy limits of the equipment.

NR/SBR blends were analyzed by FT-IR transmission / pyrolysis in Bunsen burner and TGA/DTG. FT-IR was more effective in the determination.

Determination of acrylonitrile (AN) content in NBR gum (without additives) by FT-IR transmission/cast film, with reference values obtained by the Kjeldhal method, measuring contents up to around 40%.

NR, SBR and BR content determination in a ternary mixture of these elastomers by transmission/pyrolysis FT-IR in Bunsen burner, TGA, DSC and by gas chromatography and mass spectrometry coupling by pyrolysis (Py-GC / MS).

This last method was more precise, there was interference of one elastomer in the other, with the other techniques.

Polímeros, 28(5), 440-449, 2018

Coments Although the relative error of methodology was compared with methods as TGA (10%), a medium intensity band (1600 cm-1) was used for SBR, which may probably cause a greater error than if it were used at 700 cm-1, for lower contents of this polymer.

Controlled pyrolysis technique, while accurate, involves elaborate sample preparation and requires reasonable analysis time. Using thermal analysis technique to validate data, although more accurate, is more complex, depending on the rubbers degradation temperatures being adequate, that is the degradation of one rubber finish before the other begins.

Pyrolysis technique in Bunsen burner is less precise than the controlled one, however, relative bands were used.

There was no comment on methodology errors.

Cast film technique involves solvent use, elaborated sample preparation, and there may be interference associated with the solvent/polymer interaction, and requires reasonable analysis time. Validation by Kjeldhal or any other instrumental method, although more precise, implies knowledge of both techniques for elaboration of the calibration curve.

There was considerable variation in contents determination, especially by TGA and FT-IR, but it should also be considered that the use of coupling techniques requires specialists in both areas, in this case, chromatography and mass, for better results interpretation.

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Azevedo, J. B., Murakami, L. M. S., Ferreira, A. C., Diniz, M. F., Silva, L. M., & Dutra, R. C. L. Table 1. Continued...

Author Sanches et al.[9]

Year 2008

Harada[22]

2016

Ujianto et al.[23]

2017

Datta et al.[24]

2017

Main conclusion Determination of acrylonitrile (AN) content in NBR non-vulcanized/vulcanized by FT-IR transmission / pyrolysis in Bunsen burner and controlled, with solvent extraction and by UATR, as received, measuring contents up to around 50%. Techniques presented similar precision, but UATR was more adequate to the determination, due to the shorter analysis time and the smaller amount of sample used.

It focuses on rubber analysis techniques, such as infrared, TGA, Py-GC/MS, but in the FT-IR analysis the focus is on qualitative reflection analysis for component verification.

It focuses on FT-IR of NR

The quantitative part is also centered on the Py-GC/MS analysis. FT-IR is cited qualitatively.

Qualitative analysis, aiming at the evaluation of spectrometric changes, resulting from devulcanization.

Determination of NR, SBR and BR contents in ternary The vinylidene band at 885 cm-1, which would be more mixture by FT-IR and TGA. Bands 1375 (NR), 699 (SBR) characteristic of NR, could have been tested. and 738 (BR) cm-1 and relative bands were used in the FT-IR methodology.

techniques. However, it validates the FT-IR data and makes the methodology more complex and time-consuming.

Methodological errors are not generally compared. In this paper, it was proposed a FT-IR methodology in the MIR region, with data validation in the NIR region, by means of less conventional spectral modes, such as UATR and NIRA, compared to data obtained by transmission. The samples were prepared by pyrolysis in a Bunsen burner, with evaluation of FT-IR methodology error.

2. Materials and Methods 2.1 Samples Nine samples of NBR/SBR blends were prepared at Tenneco Automotive Brazil, with materials kindly provided by the company, in the proportions 10/90, 20/80, 30/70, 40/60, 50/50, 60/40, 70/30, 80/20, 90/10, according to the formulation found in Table 2.

2.1.1 Preparation of rubber samples The raw material was weighed on a precision scale and all components, except sulfur and accelerators, tetramethylthiuram disulfide (TMTD), (1,3-Dimethylbutyl)N’-phenyl-phenylenediamine (6PPD), N-(cyclohexylthio) phthalimide (PVI) and 4,4 Dithiomorpholine (DTDM), which were mixed in banbury of 2 liters per 240 seconds, with a pound pressure of 4 kgf/cm2, rotation of 70 rpm and initial temperature of 40°C, for production of master batch. It was processed into a roller form six times in a lab open mill with a rotation of 40 rpm. Later, the master batch was accelerated at banbury, with the rest of the weighted components (TMTD, 6PPD, PVI, DTDM and sulfur) for 120 seconds, with 4kgf/cm2 pound pressure, 70 rpm rotation and initial temperature of 40° C. Then the rubber was homogenized in roller form six times in an open mil lab with a rotation of 40 rpm and withdrawn into blanked.

For the preparation of vulcanized rubber sheet, a hydraulic press with vulcanization time of 6 min, plateaus temperature of 160°C and 150 kgf/cm2 of closing pressure was used.

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Coments UATR method was used to determine the AN content in the rubber used in this study.

2.2 Equipment of characterization/conditions 2.2.1 FT-IR analysis The samples were analyzed in Spectrum One PERKINELMER FT-IR spectrometer (MIR regions of 4000 to 400 cm-1 and NIR of 12000 to 4000 cm-1, 4 cm-1 resolutions, gain 1, 20 scans), being spectra obtained by transmission techniques (MIR and NIR) and reflection (MIR), using the UATR accessory, and in NIR region, also using the Frontier PERKINELMER FT-IR spectrometer, NIRA accessory, being all samples of different methodologies, prepared by pyrolysis in Bunsen burner.

In Bunsen’s pyrolysis, samples of each rubber blend were cut, extracted for 8 hours in a Soxhlet extractor, using methanol as solvent[25]. After solvent evaporation in the oven, it was put a quantity of about 0.5 g of sample in each pyrolysis tube. The tubes were flamed in Bunsen burner, at the same flame height (marked with the aid of an universal device and a claw to determine the same pyrolysis position).

For the transmission analysis, by pyrolysis, was used the 0.025mm spacer.

By reflection, using the UATR accessory, in the same way that was done in a recent study by Rigoli et al.[26], the pyrolysis samples were analyzed by placing them in contact with the diamond-coated zinc selenide crystal surface with 120N (Newton) torque application.

For MIR analysis, the nine NBR/SBR samples (composition already shown in Table 2), prepared by pyrolysis in Bunsen burner and analyzed by transmission and reflection (UATR), were used to prepare ANBR/ASBR x [NBR]/[SBR] analytical curve, aiming the NBR and SBR contents determination, through the relative band A 2237/A700.

This band is composed by analytical absorptions of stretching (υ) C ≡N of NBR (2237 cm-1) and bending (δ) C-H of SBR (700 cm-1). The baselines used were: 2275-2150 cm-1 (band 2237 cm-1) and 2150-590 cm-1 (band 700 cm-1), for transmission / pyrolysis methodology, and 2275-2180 cm-1 (band 2237 cm -1), 858-642 cm-1 (band 700 cm-1) for UATR methodology.

Polímeros, 28(5), 440-449, 2018

Quantification by FT-IR (UATR/NIRA) of NBR/SBR blends Table 2. NBR/SBR Blend Formulation System.

Components NBR

Functional group

SBR

900

800

700

600

Phr 500

400

300

200

100

100

200

300

400

500

600

700

800

900

Naphthenic Oil

45

Zinc Oxide Stearic Acid

ZnO

37 10

Carbon Black N550 Sulfur TMTD

C S

680 8 8

6PPD

18

PVI

5.5

DTDM

10

Paraffin wax

CnH 2n+2, n = around 50 – 75

For the NIR methodology, the same number of reference NBR / SBR samples, prepared by pyrolysis in Bunsen burner and analyzed by transmission, were used to prepare the analytical curve A4336/A4060 x [NBR]/[SBR]. The bands chosen are in the region of combination or overtones of fundamental bands. In the case of NBR/SBR blend, the band A4336 is probably attributed to the first overtone of stretching (υ) of C≡N group of NBR or of combination bands, and the A4060 to the second overtone of bending (δ) of SBR aromatic CH groups[19,27]. The baseline used was 4540-4000 cm-1 (bands 4336 and 4060 cm-1). For NIRA methodology, the same number of samples and the same analytical bands were used. The samples were also prepared by pyrolysis in Bunsen burner, and were analyzed by transflectance because they were in the liquid state[28]. The baseline used was 4780 to 4000 cm-1.

The data of all FT-IR/MIR and NIR methodologies, for each sample, represent the median of 5 values of analytical bands intensity chosen, being that the mean standard deviations (Equations 1 and 2) and the relative error (RD) Polímeros, 28(5), 440-449, 2018

20

(Equation 3) were calculated by non-parametric treatment in agreement with Hórak[29] and with the methodology adopted successfully in group quantitative studies for rubber and other materials[17,28,30]. ˆ σ ˆ µˆ = σ n

(1)

= σˆ K R × R (2)

Where, σ̂ is the mean standard deviation, n, the measurements number, R is the difference between the highest and the lowest values of absorbance. KR is the coefficient to calculate the standard deviation (σ̂) of a range of values, with KR = 0.430 for 5 experiments[29]. The RD of the measurements for each analyzed sample, given in %, was determined by Equation 3, where μ is the median value of A. The median of the relative errors represents the error of the methodology[17,28,30]. σˆ µˆ RD( %= ) µ ×100 (3) 443/449 443

Azevedo, J. B., Murakami, L. M. S., Ferreira, A. C., Diniz, M. F., Silva, L. M., & Dutra, R. C. L.

3. Results and Discussion

3.3 MIR/transmission analysis of NBR/SBR

3.1 FT-IR analysis

In Figure 1, are the MIR/transmission spectra of some NBR/SBR blends studied. It can be observed that the bands intensities A2237 and A700 increase and decrease according to the content of NBR and SBR, respectively, as expected by Lambert-Beer Law, for quantitative analyzes[32]. The data for elaboration of calibration curve are shown in Table 4 and Figure 2. To overcome liquid film thickness issues and to improve the data accuracy[32], mean values of relative band A2237/A700 were considered as a function of the relative NBR/SBR concentration.

In this topic the following were addressed: a) the determination by UATR of AN content of NBR used in the blends, according to methodology previously developed by the group[9], since only one range was furnished by the supplier. For SBR rubber, the determined value as reported by the supplier was used. These values were not used in the blends contents calculation, only used for the proper characterization of the raw materials used for the prediction of properties of blends, for future and specific applications. b) the determination of the NBR/SBR blends in two spectral regions, by different ways of obtaining spectra, aiming to evaluate the most suitable conditions for this type of analysis.

3.2 Determination by UATR of AN content of NBR used in the blend

From the calibration curve (Table 4), the following correlation (Equation 4 - R = 0.98, with 96% of the values explained by the methodology, R2 = 0.96) is proposed: = A2237 / A700

0.17 [ NBR ] / [ SBR ] + 0.14 (4)

To find the two elastomers contents of the unknown mixture, Equation 5 should also be used. This is valid for all the methodologies developed in this study.

In Table 3, the data for AN content in NBR calculation are inserted.

Table 3. UATR data for determination of AN in NBR.

Sample

NBR

A2237 0.040 0.039 0.040 0.040 0.040

A2237 (MEDIAN)

0.040

Mean standard deviation

RD(%)

Calculated acrylonitrile content[9] (%) (*)

0.001

2.5

30 ±1

Acrylonitrile content (%) range, reported

by NBR gum supplier (**) 37-41

(*) y = 0.0014 x – 0.002 – calibration curve, where y= median value of A2237[9]; (**) Only the range of AN content was reported by NBR (gum) supplier, without the determined value, nor what method was used. Therefore, the value considered for the material characterization was obtained, that is, 30 ± 1%, of medium AN content[31] by the FT-IR methodology, previously developed [9], which is accurate, that is, with the relative error around 2%, under the conditions used (UATR, sample analyzed as received). It is interesting to note that the content found is also used for applications aerospace[9], around 33%.

Figure 1. MIR/transmission spectra (Bunsen burner pyrolysis) of NBR/SBR blends, with AN and styrene bands, marked with n and s, respectively.

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Polímeros, 28(5), 440-449, 2018

Quantification by FT-IR (UATR/NIRA) of NBR/SBR blends Table 4. MIR/transmission data (Bunsen burner pyrolysis) for calibration curve elaboration and associated methodology errors.

NBR/SBR (Relative Concentration) 90 / 10

A2237/A700 Median 1.563

Mean standard deviation

RD %

0.013

0.83

(9.0) 80 / 20

0.984

0.007

0.71

(4.0) 70 / 30

0.608

0.004

0.66

(2.3) 60 / 40

0.394

0.011

2.79

(1.5) 50 / 50

0.401

0.024

5.99

(1.0) 40 / 60

0.239

0.010

4.18

(0.67) 30 / 70

0.142

0.007

4.93

(0.43) 20 / 80

0.108

0.007

6.48

(0.25) 10 / 90

0.067

0.010

14.93

(0.11)

bands A2237 and A700 increase and decrease according to the NBR and SBR content, respectively, as expected by the Lambert-Beer Law. The data for calibration curve elaboration are shown in Table 5 and Figure 4. In this methodology, A2237/A700 relative band was also used to improve the accuracy of the data.

From the calibration curve (Table 5), the following correlation (Equation 6 - R = 0.98, with 96% of the values explained by the methodology, R2 = 0.96) is proposed: Figure 2. MIR/transmission calibration curve A2237/A700 versus = A2237 / A700 relative concentration [NBR/SBR].

[ NBR ]

+ [ SBR ] = 100% (5)

The methodology error, which is relative errors median[28] calculated in Table 4, already mentioned, 4.18%, can be considered good, compared to the reference value[29], ≤ 2%, which is usually only found under fixed conditions, ideal for sample preparation, that is, in solution form and analyzed in closed cell, with thickness control.

The error falls to 2.79%, closer to the accuracy limit of the equipment, ≤ 2%, for optimal condition, if the contents of 10-20% of NBR are not considered, may suggest a limit of detection in this range, by this methodology, probably due to the low intensity of the AN band, for these levels.

3.4 MIR/UATR analysis of NBR/SBR In Figure 3, the MIR/UATR spectra of some studied NBR/SBR polymer blends are included. As for transmission MIR spectra, it can be observed that the intensities of Polímeros, 28(5), 440-449, 2018

0.05 [ NBR ] / [ SBR ] + 0.03 (6)

The methodology error, which is the median of the relative errors (Table 5), 3.41%, can be considered good compared to the reference value, ≤ 2%. The error falls to 2.09%, closer to the accuracy limit of the equipment, ≤ 2%, for optimal condition, if the contents of 10-20% of NBR are not considered, and may also suggest a limit of detection in this band, by this methodology, probably due to the low intensity of the AN band, for these levels.

3.5 NIR/transmission analysis of NBR/SBR In Figure 5, the NIR/transmission (pyrolysis in Bunsen burner) spectra of some NBR / SBR polymer blends studied are shown. As for MIR and UATR spectra, it can be observed that the intensities of the bands A4336 and A4060 increase and decrease according to the NBR and SBR content, respectively, as expected by the Lambert-Beer Law. In this methodology, the relative band A4336/A4060 was chosen to overcome liquid film thickness issues and to improve the data accuracy. Table 6 shows the values used, as well as their mean and relative deviations.

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Azevedo, J. B., Murakami, L. M. S., Ferreira, A. C., Diniz, M. F., Silva, L. M., & Dutra, R. C. L. Table 5. MIR/UATR data (Bunsen burner pyrolysis) for calibration curve elaboration and associated methodology errors.

NBR/SBR - (Relative Concentration) 90/10 (9.0) 80/20 (4.0) 70/30 (2.3) 60/40 (1.5) 50/50 (1.0) 40/60 (0.67) 30/70 (0.43) 20/80 (0.25) 10/90 (0.11)

A2237/A700 (Median)

Mean standard deviation

0.431 0.263 0.187 0.111 0.088 0.047 0.030 0.014 0.010

0.009 0.005 0.003 0.002 0.003 0.003 0.002 0.001 0.003

RD (%) 2.09 1.90 1.60 1.80 3.41 6.38 6.67 7.14 30.00

Figure 3. MIR/UATR spectra of NBR/SBR blends, with the AN and styrene bands, labeled with n and s, respectively.

limit, the linearity is not as good as that found for the MIR, transmission and UATR methodologies.

3.6 NIRA analysis of NBR/SBR

Figure 4. MIR/UATR calibration curve A2237/A700 versus relative concentration [NBR/SBR].

To improve the results of NIR methodology, using the reflection method, the samples were analyzed by transflectance in this region (NIRA). The analytical bands chosen were the same. Figures 7-8, Table 7 and Equation 8 shows the results obtained. The methodology error was 0.74% (Table 7), with good linearity R = 0.96, and 92% of the data found were explained by this methodology. The error is within the limits of equipment accuracy, ≤ 2%, and there is no evidence of limit of detection of low levels of NBR.

A4336 / A4060 0.30 [ NBR ] / [ SBR ] + 2.46 (8) Figure 6 shows the calibration curve of NIR / transmission = (Bunsen burner pyrolysis) A4336/A4060 versus [NBR]/[SBR] (% w/w). From the calibration curve (Table 6), the following To know the contents of unknown samples it is enough correlation (Equation 7 - R = 0.92, with 85% of the values found, to analyze 5 aliquots of the rubber and to use the suitable being explained by the developed methodology) is proposed: calibration curves established in the developed methodologies, depending on the region of the infrared available in the laboratory. For example, Table 8 shows the evaluation of = A4336 / A4060 0.26 [ NBR ] / [ SBR ] + 2.58 (7) the MIR methodologies developed by means of analysis of unknown concentration NBR / SBR sample.

The methodology error was 1.33% (Table 6). Although Although the test sample has been analyzed by the the error is within the limits of the equipment accuracy, ≤ 2%, there being no evidence of NBR low levels detection analyst, without the knowledge of its concentration, the 446 446/449

Polímeros, 28(5), 440-449, 2018

Quantification by FT-IR (UATR/NIRA) of NBR/SBR blends Table 6. NIR transmission data (Bunsen burner pyrolysis) for calibration curve elaboration and associated methodology errors.

NBR/SBR

A4336/A4060

(Relative Concentration) 90/10 (9.0) 80/20 (4.0) 70/30 (2.3) 60/40 (1.5) 50/50 (1.0) 40/60 (0.67) 30/70 (0.43) 20/80 (0.25) 10/90 (0.11)

(Median) 4.625 4.000 3.733 3.231 2.893 2.714 2.484 2.400 2.200

Mean standard deviation

RD (%)

0.058 0.160 0.043 0.045 0.025 0.036 0.059 0.025 0.030

1.25 4.00 1,15 1.39 0.86 1.33 2.38 1.04 1.36

Table 7. NIRA data (pyrolysis in Bunsen burner) for calibration curve elaboration and associated methodology errors.

NBR/SBR (Relative Concentration) 90/10 (9.0) 80/20 (4.0) 70/30 (2.3) 60/40 (1.5) 50/50 (1.0) 40/60 (0.67) 30/70 (0.43) 20/80 (0.25) 10/90 (0.11)

A4336/A4060 (Median)

Mean standard deviation

RD (%)

4.865 3.973 3.42 3.171 2.877 2.632 2.459 2.305 2.161

0.067 0.039 0.126 0.127 0.021 0.007 0.016 0.012 0.016

1.38 0.98 3.68 4.01 0.73 0.27 0.65 0.52 0.74

Table 8. Data of unknown NBR/SBR sample (X/Y) for validation of MIR methodologies developed.

NBR/SBR(nominal relative concentration)/ methodology Unknown sample (X/Y)/MIR/transmission

A2237/A700 0.569

A2237/A700

Calculated concentration

0.632

NBR = 74.29

(median)

0.592

RD (%) 2.53

SBR = 25.71

0.632 0.644 Unknown sample (X/Y)/ MIR/UATR

0.653 0.155 0.155

0.155

NBR = 71.43

5.81

SBR = 28.57

0.146 0.192 0.165

Figure 5. NIR transmission spectra (Bunsen burner pyrolysis) of NBR/SBR blends, with AN and styrene bands, labeled with n and s, respectively.

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Azevedo, J. B., Murakami, L. M. S., Ferreira, A. C., Diniz, M. F., Silva, L. M., & Dutra, R. C. L. methodology showed better correlation, with no limit of detection and with error around 1%, within the limits of the FT-IR spectrometer. Both methodologies MIR/NIR are fast, therefore useful as quality control in different industrial and research scenarios.

5. Acknowledgements This study was supported in part by the National Senior Visiting Professor Program (PVNS) from the Coordenação de Aperfeiçoamento Pessoal de Nível Superior (CAPES).

Figure 6. NIR calibration curve A 4436/A 4060 versus relative concentration [NBR/SBR].

Figure 7. NIRA Spectra (pyrolysis in Bunsen burner) of NBR/ SBR blends.

Figure 8. NIRA calibration curve A4436/A4060 versus relative concentration [NBR/SBR].

nominal value that should have been found would be around NBR70 / SBR30. Thus, both methodologies presented satisfactory values, with the best result for which UATR was used.

4. Conclusion Summarily, all MIR and NIR methodologies were useful for NBR and SBR contents determination in the analyzed blends. The best correlation in the MIR region was found for the UATR methodology (pyrolysis in Bunsen burner), although there may be a detection limit between 10-20% NBR and an error around 3%. In the NIR region, the NIRA 448 448/449

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19. Shield, S. R., & Ghebremeskel, G. M. (2003). Use of mid and near infrared techniques as tools for characterizing blends of copolymers of styrene–butadiene and acrylonitrile-butadiene.

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21. Lee, S. Y., Lee, W., Cho, S., Kim, I., & Ha, C. (2007). Quantitative analysis of unknown compositions in ternary polymer blends: a model study on NR/SBR/BR system. Journal of Analytical

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and Applied Pyrolysis, 78(1), 85-94. http://dx.doi.org/10.1016/j. jaap.2006.05.001.

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Received: Feb. 01, 2018 Revised: May 22, 2018 Accepted: June 20, 2018

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.00418

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

PET glycolysis optimization using ionic liquid [Bmin]ZnCl3 as catalyst and kinetic evaluation Carlos Vinícius Guimarães Silva1*, Eloi Alves da Silva Filho1, Fabrício Uliana1, Luciana Fernanda Rangel de Jesus1, Carlos Vital Paixão de Melo1, Rosangela Cristina Barthus1, José Guilherme Aquino Rodrigues2 and Gabriela Vanini3 Laboratório de Físico-Química, Departamento de Química, Centro de Ciências Exatas, Universidade Federal do Espírito Santo – UFES, Vitória, ES, Brasil 2 Laboratório de Eletroquímica e Eletroanalítica, Departamento de Química Inorgânica, Centro de Tecnologia, Instituto de Química, Universidade Federal do Rio de Janeiro – UFRJ, Rio de Janeiro, RJ, Brasil 3 Laboratório de Geoquímica Orgânica Molecular e Ambiental, Departamento de Química Inorgânica, Centro de Tecnologia, Instituto de Química, Universidade Federal do Rio de Janeiro – UFRJ, Rio de Janeiro, RJ, Brasil 1

*carlosviniciusgs@gmail.com

Abstract In the present work, the depolymerization of polyethylene terephthalate (PET) was performed by the method of glycolysis with ethylene glycol. The process was carried out using a factorial design in the Box-Behnken optimization model, using a response surface methodology (RSM) in which three factors (time, temperature and mass ratio of ethylene glycol) were studied in three levels of variation (- 1, 0, +1) with two replicates of the center point, totalizing 15 experiments for which the yield of bis (2-hydroxyethyl) terephthalate (BHET) monomers formed in the process was chosen as response. In parallel, the Arrhenius kinetic test was used to determine the apparent activation energy (Ea) for the 1-butyl-3-methylimidazole trichlorozincate ([Bmin]ZnCl3) - catalyst used in the depolymerization process.

The products of glycolysis obtained were characterized by spectroscopic techniques (FTIR), (1H and 13C NMR), thermal analyses (TGA) and (DSC) and Mass Spectrometry LC-MS/MS hybrid Quadrupole-Orbitrap.

Keywords: PET, glycolysis, ionic liquids, design of experiments, activation energy energy.

1. Introduction Poly(ethylene terephthalate) - popularly known as “polyester” in textile industry - a semicrystalline thermoplastic first developed and recognized in the England by scientists Whinfield and Dickson[1] through polycondensation reaction of terephthalic acid with ethylene glycol in 1941, has been widely used in various applications ranging from textile fibers (67%), blown injection packagings (24%), bioriented films (5%) and engineering polymers (4%). The success of this material is due to its excellent relationship between the mechanical and thermal properties and the low cost of production[2,3]. Its global consumption exceeded 54 million tons in 2010 and had an increase of about 4.5% per year between 2010 and 2015[4]. Due to this high consumption rate, recycling of this waste has become a major challenge for the conservation of resources and protection of the environment[5] since the material is responsible for 8% by weight and 12% by volume of solid waste in the world.

PET recycling not only contributes as a partial solution to the problem of solid waste but also as a source of raw material for some industries, assisting the conservation of high-cost petrochemical products through the use of terephthalic resins and polyurethanes and as coatings and other applications, which are of great importance[6]. It is observed that in the

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last years, the interest in PET recycling has been growing continuously because of ecological and economic concerns.

PET depolymerization occurs by three methods: hydrolysis, glycolysis, and methanolysis. Other processes such as ammonolysis and aminolysis have also been included for historical and practical reasons. Of all the chemical recycling processes, the most applied ones on a commercial scale are methanolysis and glycolysis for economic reasons[7]. The glycolysis reaction is described as the transesterification process between PET ester groups and a diol, usually ethylene glycol in excess to obtain the monomer bis-2-hydroxyethyl terephthalate (BHET). This product, in turn, can also be incorporated into the virgin material in the production of unsaturated polyesters, plastic masses, rigid or flexible polyurethanes, and other fine chemicals.

PET glycolysis has attracted much attention recently, but its reaction speed is very slow in the absence of catalysts.

Thus various types of catalysts have been explored for this reaction, such as metal acetates, metal chlorides, metal oxides, solid superacids, carbonates, sulfates and titanium phosphates[8,9]. These traditional catalysts are efficient, but some are oxidizing and many are harmful to the environment

Polímeros, 28(5), 450-459, 2018

PET glycolysis optimization using ionic liquid [Bmin]ZnCl3 as catalyst and kinetic evaluation and difficult to separate from the reaction mixture, which could influence the properties of the product[10].

Baliga and Wong[11] evaluated the depolymerization reaction at 190 °C with excess ethylene glycol (EG/PET = 1:4) in the presence of various metal acetates as catalysts: zinc, lead, manganese and cobalt, as typically used in transesterification reactions. In the experiment without a catalyst, a considerable amount of PET can be observed after 8 h reaction, showing the catalyst importance in the depolymerization process. In the catalyzed experiments, the glycolyzed products consisted of a mixture of BHET and some oligomers, being analyzed by hydroxyl number[12], showing a significant increase in the initial rate of depolymerization influenced by catalysts following the order: Zn2+> Pb2+> Mn2+> Co2+.

Kao et al.[13] investigated the efficiency of Na+, Mn2+, 2+ Co , Cu2+, Cu2+, Cu2+ and Zn2+ acetates as PET catalysts with ethylene glycol through differential scanning calorimetry (DSC) analysis of the products resulting from a high temperature and pressure reaction for 30 min, also using hydroxyl number measurements, which verified better results also for zinc.

According to Wang et al.[14] it was possible to obtain satisfactory results with 100% PET depolymerization by glycolysis in the presence of ethylene glycol with 71.2% bis-2-hydroxyethyl terephthalate monomer (BHET) formed in 8 hour reaction time, but the volume of catalyst consumed was high (approximately 20% wt.). The group also made comparisons of average molecular weight by capillary viscosimetry measurements[15] for PET reacting at temperatures between 160 and 180 °C. In 2011, Yue et al.[16] added to the studies the investigation of basic ionic liquids exhibiting excellent yields with a reaction time of 2 hours and 5% wt. catalysts. In 2013, members of the same group[17] studied the effect of ionic liquids combined with zinc and manganese chlorides as catalysts in the presence of Lewis and Brönsted acid sites in coordination with pyridine achieving 100% PET conversion and yields that reached 84.9% in monomer production (BHET). One of their goals was to reduce the amount of catalyst consumed, successfully reducing that value to 0.16% wt.[18]. Their new study in 2014[10] was based on novel compounds of metal‑dialkylimidazole ionic liquids. The reaction activity was tested with Cu, Al, Sn, Ni, Fe, Pb, Mn and Zn ions, confirming the efficacy of 1-butyl‑3‑methylimidazole combined with zinc chloride ([Bmim] ZnCl3) showing 97.9% in PET conversion and 83.3% yield of BHET produced. In the same year, Al Sabagh et al.[9] compared glycolysis under the effect of ionic liquids combined with copper and zinc acetates at a relatively high concentration (50%), giving better results for copper over a 2 h period. This result was compared to a kinetic study, finding the reaction constants for various temperatures, using this argument to find the activation energy for comparison. The resulting values were 56.4 kJ/mol and 53.8 kJ/mol for copper (II) and zinc, respectively.

The aim of this work is to optimize the performance of post-consumption polyethylene terephthalate glycolysis process as a function of the reaction parameters (time, temperature and mass ratio EG: PET) and to determine the apparent activation energy of catalyst trichlorozincate 1-butyl-3-methylimidazole ([Bmim] ZnCl3).

Polímeros, 28(5), 450-459, 2018

2. Materials and Methods 2.1 Materials 1-Butyl-3-methylimidazole chloride 98.0% HPLC (Sigma‑Aldrich); zinc anhydrous chloride P.A. ACS (Dynamika); dichloromethane 99.9% HPLC (Merck); ethylene glycol P.A. ACS (Neon).

2.2 Catalyst synthesis For the synthesis of 1-butyl-3-methylimidazole trichlorozincate ([Bmin]ZnCl3) a mixture of equimolar amounts of 1-butyl-3-methylimidazole chloride [(Bmin]Cl) (Sigma-Aldrich HPLC 98.0%), and zinc chloride (Dynamika P.A. ACS) was prepared under constant stirring for 24 h in excess dichloromethane (Merck HPLC 99.9%). Then the mixture was subjected to filtration and vacuum distillation of the liquid phase, according to the procedure described elsewhere[18].

2.3 Experimental procedure of PET glycolysis The 15 factorial experiments were carried out for the following variables: time, temperature and the solvent mass ratio (EG:PET), in random order for fixed amounts of approximately 5 g PET with 5% wt catalyst addition.

For each experiment, a reflux kit with heating jacket, a 150 mL two-neck round bottom flask (Uniglass), a condenser, capillary mercury thermometer (Incoterm) and mechanical stirrer were used.

For monomers separation, the reaction mixture was rapidly filtered with a steel screen to remove residual PET (Fraction A). Approximately 40 mL of ice-cold distilled water was added to the liquid phase in a 250 mL beaker with constant stirring until the system reached room temperature (25-30°C). The mixture was vacuum filtered with an ultrafine paper filter separating the solid phase (Fraction B), containing oligomers and dimers, followed by drying in an oven at 50°C for 6 h and the liquid phase composed mainly of monomers, excess ethylene glycol and catalyst. This was crystallized in the refrigerator for 24 h and subjected to vacuum filtration with ultrafine paper filter and oven drying at 50°C (Fraction C). All fractions were weighed on an analytical balance.

The yield of monomer fraction, the main product of the reaction is defined by Equation 1[9]: % BHET Yield =

WBHET / MWBHET x100 % WPETi / MWPET

(1)

where, WBHET is the weight of the monomer obtained by “fraction C”, WPETi the initial PET weight, MWBHET is the molar weight for the BHET monomer in the amount of 254 g⋅mol-1, and MWPET is molar weight to PET in the amount of 192 g·mol-1 per repeating unit.

2.4 Experiments design For accomplishment of glycolysis process, the optimization of response surface methodology with the Box-Behnken design[19,20]was carried out, aiming the monomer yield response optimization to 3 variables: reaction time, temperature and 451/459 451

Silva, C. V. G., Silva Filho, E. A., Uliana, F., Jesus, L. F. R., Melo, C. V. P., Barthus, R. C., Rodrigues, J. G. A., & Vanini, G. mass ratio between ethylene glycol/PET in 3 levels (1, 0, +1), allowing to verify the interaction between variables, where the number of experiments is given by Equation 2: N = k ² + k + cp

(2)

Where: “k” the number of variables and “cp” the number of experiments in the central point conditions, resulting in a total of 15 experiments in which 2 repetitions of the central point are included. The values for maximum and minimum levels were chosen with help of some other published studies since the system to be worked is already known.

In the summary, the levels of the variables are organized in Table 1.

The matrix defined by the Box-Behnken design for the realization of the sequence of experiments is given in Table 2:

2.5 Apparent activation energy New trials were performed on the same system at reflux, with about 2g of PET, 5% wt. catalyst (100 mg) [Bmin] ZnCl3 and 20 mL ethylene glycol (about 10:1 EG:PET).

The total of the 20 experiments were performed in total at varying intervals of time to temperatures of 170°C, 180°C, 190°C, and 197°C respectively. The residual PET mass was weighed to calculate the conversion rate for each reaction.

The conversion rate of PET in subproduct 3 is defined

by Equation 3[18]: % PET Conversion =

Wi − W f Wi

x100 %

(3)

Where: Wi represents the initial mass of PET and W f represents the mass of residual PET (non-depolymerized).

Table 1. Variables involved and their levels.

Variables Time (min) Temperature (°C) EG:PET (w/w)

-1 60 170 2

Coded levels 0 90 180 6

1 120 190 10

2.6 Characterization Infrared spectroscopy analysis was performed with Spectrum 400 FT-MIR / FT-NIR - Perkin Elmer, in attenuated total reflectance (ATR) mode, 16 scans, with a resolution of 4 cm-1, 1H-RMN and 13C-RMN spectroscopy were measured in a Varian 400 MHz at 9.4 T, 5 mm BroadBand1H/X/D NMR probe with chloroform-d (CDCl3) solution, chemical shifts (δ) in ppm relation to tetramethylsilane (TMS). Mass spectra were obtained in a Q-Extractive Plus (ThermoScientific) LC-MS/MS hybrid Quadrupole-Orbitrap. The samples were diluted in methanol 0.25 mg/mL solution (CH2OH); direct infusion in positive and negative mode using electrospray ionization source; spray voltage: -4 kV; sheath gas flow: 15; auxiliary gas flow: 0; capillary voltage: -70V; capillary temperature: 300 °C; tube lens: -120V. Thermal analyses were conducted with DSC Q200 (TA Instruments) and TG SDT Q600 (TA Instruments) controlled by software Universal V4.7; with approximately 5 mg of the sample at heating rates of 10ºC⋅min-1 with 50 mL/min N2 flow in the temperature range of -80 a 600°C for DSC and 20 a 600°C for TGA analysis.

3. Results and Discussions 3.1 Glycolysis products Residual PET was previously separated from the oligomer mixture (fraction B), which showed a white-green color in most experiments. Differential scanning calorimetry (DSC) comparisons of crystalline melt temperature were carried out (Figure 1), comparing samples from the initial PET fractions, and fractions of monomers (fraction C) and oligomers (fraction B). The BHET monomer fraction presented a melting temperature of 113.34°C (endothermic peak classified as crystalline melt) with a melting enthalpy of 134.6 J/g and the fraction of oligomers showed a temperature close to 110.38°C, but with a lower intensity, which justifies the presence of monomers also in fraction B, with an enthalpy value of 90.14 J/g. Fractions B and C differed adequately from the behavior of crushed PET sample which presented, according to the thermogram, the melting temperature of 249.37°C and enthalpy of 33.19 J/g.

Table 2. Box-Behnken planning matrix and experimental yields (%).

Entry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

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Run Order 11 6 3 15 10 8 14 7 5 1 12 2 9 4 13

-1 1 -1 1 -1 1 -1 1 0 0 0 0 0 0 0

B.B. Design -1 -1 1 1 0 0 0 0 -1 1 -1 1 0 0 0

0 0 0 0 -1 -1 1 1 -1 -1 1 1 0 0 0

Uncoded Conditions 60min / 170°C / 6:1 120min / 170°C / 6:1 60min / 190°C / 6:1 120min / 190°C / 6:1 60min / 180°C / 2:1 120min / 180°C / 2:1 60min / 180°C / 10:1 120min / 180°C / 10:1 90min / 170°C / 2:1 90min / 190°C / 2:1 90min / 170°C / 10:1 90min / 190°C / 10:1 90min / 180°C / 6:1 90min / 180°C / 6:1 90min / 180°C / 6:1

Yield (%) 0.6499 7.8490 18.9777 29.4154 15.0480 16.2325 1.5615 38.2821 0.1315 18.5935 0.7044 37.5753 16.1729 20.4950 18.1154

Polímeros, 28(5), 450-459, 2018

PET glycolysis optimization using ionic liquid [Bmin]ZnCl3 as catalyst and kinetic evaluation

Figure 1. Thermogram of DSC curves of PET and products.

From the thermogravimetric analysis (Figure 2), the first mass loss of 26.24% was observed, starting at 203.34°C for the sample of BHET monomers (fraction C) indicating its thermal degradation and the second loss of mass of 67.01% 400.39°C referring to the decomposition of PET produced by re-polymerisation in the heating ramp. For the oligomers sample (fraction B) there was degradation with the first mass loss of 22.97% at 198.10ºC and, similarly to the fraction of monomers, it also had a second mass loss of 66.98% referring to the formation of PET at high temperatures at 406.70ºC. All the results of thermal analyzes are listed in Table 3.

Analysing of the FTIR spectrum (Figure 3) it can be seen that all components have the same bands: 2957 and 2899 cm-1 (CHsp3), 1714 cm-1 (C = O) and 1407 cm-1 (CH aromatic), which implies they all present the same functional groups and differ only by the appearance of the band near 3437 cm-1 related to the hydroxyl group, present in monomers and oligomers, observed yet stronger in monomers.

Figure 2. Thermogram of TGA curves of PET and products.

The hydrogen NMR spectrum (Figure 4) shows the presence of four aromatic protons of benzene ring at 8.12 ppm.

The signals at 4.49 and 3.98 ppm are characteristic of the presence of methylene protons COO-CH2- and CH2OH respectively. A signal at 2.05 ppm points to the presence of hydroxyl protons. The Figure 4, also shows the presence of residual water signal at 1.60 ppm and the solvent CDCl3 at 7.26 ppm.

The 13C NMR signals are presented in Figure 5, where the signal is shifted related to carbonyl at 166 ppm. Aromatic carbons and methylenes are based on 133.83 and 129.67 ppm while CH2OH and -COO-CH2- are located at 67.02 and 61.26 ppm respectively. The formation of the bis-2-hydroxyethyl terephthalate monomer (BHET) is therefore confirmed by the proposed structure and their NMR spectrum show to be in agreement with the literature[21,22].

Mass spectrometry analysis with electrospray ionization (ESI-MS) in the positive mode (Figure 6) showed two peaks with high intensity confirming the presence of Polímeros, 28(5), 450-459, 2018

Figure 3. FTIR spectrum of PET and products.

bis‑2-hydroxyethyl terephthalate monomer (BHET) of [M + Na]+ = 277.07 m/z for [2M + Na]+ = 531 m/z due to the formation of non covalent dimer. The peak at [M + Na]+ = 469.11 m/z at low intensity is related to the presence of glycosylated dimer, and other low intensity peaks are related to fragmentations dimer uncoordinated [2M + Na]+ at 513 and 321 m/z respectively.

453/459 453

Silva, C. V. G., Silva Filho, E. A., Uliana, F., Jesus, L. F. R., Melo, C. V. P., Barthus, R. C., Rodrigues, J. G. A., & Vanini, G. Table 3. Values found by thermal analysis.

Melt Temperature ΔHº Melt Mass loss

Unreached PET 249.37 °C 33.19 J/g (1) 90~95% (390~400 °C)

Fraction B 110.38 °C 90.14 J/g (1) 22.97% (198 °C) (2) 66.98% (407 °C)

Fraction C 113.34 °C 134.6 J/g (1) 26.24% (204 °C) (2) 63.44% (400 °C)

Figure 4. 1H-NMR spectrum of BHET.

Figure 5. The13C-NMR spectrum of BHET. 454 454/459

Polímeros, 28(5), 450-459, 2018

PET glycolysis optimization using ionic liquid [Bmin]ZnCl3 as catalyst and kinetic evaluation

Figure 6. ESI(+)-MS spectrum of BHET.

3.2 Apparent activation energy PET depolymerization studies usually assume the process as having first-order kinetics[9,23]. The depolymerization reaction rate constant is proportional to the PET concentration (per repeating unit) and ethylene glycol (EG). So the equation can be written like this: d [ PET ] dt

= −k [ EG ][ PET ]

(4)

As in the reaction conditions ethylene glycol (EG) is in excess, the concentration of ethylene glycol is considered constant because the solvent mass is much higher than the mass of PET. It is therefore rewritten k [ EG ] as k ′,so: d [ PET ] dt

= −k ′ [ PET ]

(5)

[ PET ] is the concentration of PET per repetition unit: = [ PET ]

[ PET ]0 (1 − x )

dX = k '' (1 − x ) dt

(6) (7)

Where x is the conversion of PET. In this way, k '[ PET ] can be written as k '', which will be the pseudo 1st order rate constant. Integrating Equation 7, we have:  1  ln   = k '' t 1− x 

(8)

Applying Equation 8 as a function of glycolysis time, it is possible to find the rate constant k ‘in a graph ln (1/(1-x)) versus time, using the line slope. The coefficients of linear Polímeros, 28(5), 450-459, 2018

correlation (R2) were greater than 0.99 in the experiments for each studied temperature (Figure 7), the values for the constants k’ were 0.0909; 0.0775; 0.0139; 0.0024 and 0.0008 min-1 for the temperatures of 197, 190, 180, 170, and 160°C respectively.

Using the rate constants values it was possible to obtain the activation energy (Ea) from the ratio obtained from Equation 9: ln = k ln A −

Ea

RT

(9)

Where: “A” is a pre-exponential factor, “R” is the gas constant (8.314462 J∙K-1∙mol-1), and “T” is the temperature in Kelvin.

The apparent activation energy for the process of glycolysis with the catalyst [Bmin]ZnCl3, calculated on the straight line slope in Arrhenius plot (Figure 8) was 36.49 kJ/mol.

The calculated result of the apparent activation energy is well lower compared to the data reported in the literature (Table 4), the energy values 53.8 kJ/mol and 56.4 kJ/mol for 1-butyl-3- methylimidazole acetate combined with zinc and copper acetates respectively[9], 58.53 kJ/mol with 1-butyl-3-methylimidazole acetate[23], 79.3 kJ/mol with zinc and aluminum oxides mixture[24], 85 kJ/mol with zinc acetate[25], 92 kJ/mol with zinc (acetate and stereate) salts[26] and 108 kJ/mol without catalyst[25].

3.3 Design of experiments The Table 2, presents the trends in yield behavior for the formation of bis (2-hydroxyethyl) terephthalate (BHET) monomers as a function of simultaneous changes in variables and levels. The combination of the 15 experiments results in the optimization of the “% yield” response with statistical 455/459 455

Silva, C. V. G., Silva Filho, E. A., Uliana, F., Jesus, L. F. R., Melo, C. V. P., Barthus, R. C., Rodrigues, J. G. A., & Vanini, G. tests and in a surface chart known as Surface Response Methodology (MSR).

The regression model applied in optimization schedules with central points is usually a quadratic polynomial equation used to predict response as a function of independent variables. The equation can be expressed as: Y =β0 + ∑βi xi + ∑βii xi2 + ∑ ∑βij xi x j + ε i

i

i< j j

(10)

Where: Y is the expected response, β0 is a constant, βi , βii and βij are linear, quadratic and interactive coefficients respectively and ε is the model waste. The independent variables ( xi ) chosen in this case are time ( x1), temperature ( x2) and mass ratio EG: PET ( x3). The polynomial coefficients were estimated by the method of least squares regression[27] and the validation of the model made by analysis of variance (ANOVA). When applying the experimental data in Equation 10,

a mathematical relationship between “predicted yield” and independent variables (Equation 11) is found Yield ( BHET ) =18.2617 ±5.3778 + 6.9427 ±3.2932 x1 + 11.9034±3.2932 x2 + 3.5147 ±3.2932 x3 − 0.2544±4.8475 x12 − 3.7843±4.8475 x22 − 0.2262±4.8475 x32 + 0.8096±4.6573 x1x2 +

(11)

8.8840±4.6573 x1x3 + 4.6023±4.6573 x2 x3

For Equation 11 confidence intervals were assigned for each coefficient (β0, β1,β2 …β9 ), demonstrating interactions which are indeed significant in the reaction process by the t-test[28]. This observation is demonstrated in the graph (Figure 9) through tie-line indicating the coefficients statistical significance, where significant amounts deviate from the value 0. In significance order we have the coefficients corresponding to the effects of variables: temperature (b2), time (b1), EG dosage vs. time interaction: PET (b13) and finally the dosage EG: PET (b3).

The Figure 10a shows the experimental values based on the responses predicted by the model. It can be seen that there is a good agreement between experimental data and those responses predicted by the model of Equation 11.

This observation confirms the good model fit described in Table 5. The Figure 10b shows the behavior of the waste, i.e., the difference between experimental and predicted values. It is noted in this comparison between the expected response and the waste that they behave randomly with no default, showing good homoscedasticity (error variance is constant) and the relationship between variables is predominantly linear.

The F-test can be used to verify the regression significance.

If the calculated F is larger than the tabulated one, it indicates good regression and, consequently, the mathematical model satisfactorily represents the experiment[29]. Thus the obtained Figure 7. Line equations obtained for the argument ln (1/(1-x)) vs Time.

Figure 9. The coefficients and confidence intervals for t-student 95% (p-value<0.05) DF=2.

Figure 8. The Arrhenius plot for the catalyst [Bmin]ZnCl3.

Table 4. apparent activation energies for PET glycolysis studies.

Calculated (kJ/mol) 36.49

456 456/459

Ref.[9] 53.8

Ref.[9] 56.4

Ref.[23] 58.53

Ref.[24] 79.3

Ref.[25] 85

Ref.[26] 92

Ref.[25] 108

Polímeros, 28(5), 450-459, 2018

PET glycolysis optimization using ionic liquid [Bmin]ZnCl3 as catalyst and kinetic evaluation values were FCal.= 10.9087 > F9.5 = 4.77, concluding that the model is significantly correct. The residue distribution was carried out to prove the model’s statistical significance, verifying the lack of fit and the pure error. In this case, a calculated F smaller than the tabulated F indicates the absence of mismatch of the developed mathematical model[29]. Thus it was obtained an FCal. = 6.8466 <F 3.2 = 19.16 concluding that the model does not have lack of fit. Therefore, the developed model is well-adjusted to a 95% confidence level.

After ensuring the model suitability, the surface (3D) and contour (2D) graphs were plotted, referring to the following

parameters combinations: time vs temperature in 3 levels (-1, 0, 1) of ethylene glycol dosage in relation to PET (EG: PET), demonstrating the behavior of the two factors variation with a fixed (constant) variable for the income response, aiming to contribute to the illustration of the best experimental conditions for a high yield. The largest response is determined to find the maximum point within the area delimited by the levels of each factor. Figure 11 evaluates that the increase in yield is favored by increasing the three variable set to the maximum level, however Figure 11a shows a different trend, which demonstrates that the good

Figure 10. (a) Experimental yield vs predicted yield; (b) residues vs predicted yield.

Figure 11. Response surfaces to the (%) yields obtained from time and temperature at fixed EG:PET dosage: (a) 2:1 (-1); (b) 6:1 (0); (c) 10:1 (+1).

Polímeros, 28(5), 450-459, 2018

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Silva, C. V. G., Silva Filho, E. A., Uliana, F., Jesus, L. F. R., Melo, C. V. P., Barthus, R. C., Rodrigues, J. G. A., & Vanini, G. Table 5. Analysis of Variance (ANOVA) from Box-Behnken model.

Source of Variation

Square Sum (SS)

Regression (R) 2073.90 Residues (r) 105.6189 Lack of Fit (LoF) 96.2469 Pure Error (PE) 9.3718 Total 2179.52 % of explained variation (R2): 95.15 % maximum of explainable variation: 99.57

Degrees of Freedom (DF)

Mean Square (MS)

9 5 3 2 14

230.4336 21.1238 32.0823 4.6859

response (approximately 20%) in amounts of ethylene glycol -1 (2:1) is achieved with time by -1 (60 min), at maximum temperature (190°C).

From Figures 11b and 11c, it is seen that the behavior changes when, if there is an increase in asolvent, better yields are obtained by increasing the time from 0 (90 min) to +1 (120 min), at maximum temperature (190°C). Another point to be highlighted is that excess solvent favors obtaining the liquid phase (phase C) by filtration, reducing yield losses. Under the best conditions shown in Figure 11c, in a proportion of +1 ethylene glycol (10:1), the critical yield (peak point under these conditions) of approximately 50% is reached.

4. Conclusions The synthesis of the bis-(2-hydroxyethyl) terephthalate (BHET) monomers was performed satisfactorily and the possible difficulties in the fractions separation step were minimized by improving the formed crystals purity.

The choice of factors and reactional levels applied in Box-Behnken design was aided by articles in the field of experiments optimization, even though most of them dealing with univariate and poorly applied methods but that played an important role in this stage, which can be proved by the graph of the coefficients (Figure 9), showing considerable relevance to the effects on yield as a response.

The reaction process with [Bmin]ZnCl3 presented apparent activation energy of 36.49 kJ/mol lower than those already reported in the literature.

The ANOVA table showed significant values of R2 (95.15%), F test for regression (10.91) greater than the tabulated and a residue (6.85) smaller than the tabulated having good adequacy to quadratic model. The effects in order of statistical significance were the following variables: temperature, time, interaction time vs EG dosage:PET and dosage w/w of EG:PET. The generated graphs of response surface show a good region where yields greater than 50% yield are achieved in the conditions established with the increase of three variables together, which can be applied for further reactions depolymerization, since the monomer is not the only interest in the process, but the degradation of the starting material generating new chemical compounds represent a wide range of applications in the production of resin and derivatives.

458 458/459

FCal.

FTab.

(95%) 10.9087

(95%) 4.77

6.8466

19.16

5. Acknowledgements The authors gratefully thank CAPES for MS scholarship, laboratory (LAGOA/LADETEC–UFRJ) for LC-MS analysis and (NCQP-UFES) for FTIR, TGA/DSC, and NMR analyses.

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19. Montgomery, D. C. (2013). Design and analysis of experiments.

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20. Novaes, C. G., Yamaki, R. T., Paula, V. F., Nascimento, B. B., Jr., Barreto, J. A., Valasques, G. S., & Bezerra, M. A.

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(2017). Otimização de métodos analíticos usando metodologia de superfícies de resposta - Parte I: variáveis de processo.

Revista Virtual Quimica, 9(3), 1284-1215. http://dx.doi. org/10.21577/1984-6835.20170070.

21. Ernö, P., Bühlmann, P., Badertscher, M. (2009). Structure determination of organic compounds - tables of spectral data. Basel: Springer Nature Switzerland AG. http://dx.doi. org/10.1007/978-3-540-93810-1.

22. Breitmaier, E., & Voelter, W. (1990). Carbon 13 NMR spectroscopy: high-resolution methods and applications in organic chemistry and biochemistry. 3rd ed. New York: VCH. 23. Al-Sabagh, A. M., Yehia, F. Z., Eissa, A.-M. M. F., Moustafa, M. E., Eshaq, G., Rabie, A.-R. M., & ElMetwally, A. E. (2014).

Glycolysis of poly(ethylene terephthalate) catalyzed by the lewis base ionic liquid. Industrial & Engineering Chemistry Research, 53(48), 18443-18451. http://dx.doi.org/10.1021/ ie503677w.

24. Chen, F., Zhou, Q., Bu, R., Yang, F., & Li, W. (2015). Kinetics of poly(ethylene terephthalate) fiber glycolysis in ethylene glycol. Fibers and Polymers, 16(6), 1213-1219. http://dx.doi. org/10.1007/s12221-015-1213-4.

25. Chen, J.-W., Chen, L.-W., & Cheng, W.-H. (1999). Kinetics of glycolysis of polyethylene terephthalate with zinc catalyst.

Polymer International, 48(9), 885-888. http://dx.doi.org/10.1002/ (SICI)1097-0126(199909)48:9<885::AID-PI216>3.0.CO;2-T. 26. Campanelli, J. R., Kamal, M. R., & Cooper, D. G. (1994).

Kinetics of glycolysis of poly(ethylene terephthalate) melts.

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27. Liu, Q., Li, R., & Fang, T. (2015). Investigating and modeling PET methanolysis under supercritical conditions by response surface methodology approach. Chemical Engineering Journal, 270, 535-541. http://dx.doi.org/10.1016/j.cej.2015.02.039.

28. Pereira, E. R., Fo. (2015). Planejamento fatorial em química: maximizando a obtenção de resultados. São Carlos: EdUFSCar. 29. Barros, B., No., Scarminio, I. E., & Bruns, R. E. (2010). Como fazer experimentos: aplicações na ciência e na indústria, 4th ed. Porto Alegre: Bookman.

Received: Jan. 29, 2018 Revised: July 24, 2018 Accepted: July 26, 2018

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.10517

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

Core-shell magnetic particles obtained by seeded suspension polymerization of acrylic monomers Jacira Aparecida Castanharo1, Ivana Lourenço de Mello Ferreira1, Manoel Ribeiro da Silva2 and Marcos Antonio da Silva Costa1* Universidade do Estado do Rio de Janeiro – UERJ, Rio de Janeiro, RJ, Brasil 2 Universidade Federal de Itajubá – UNIFEI, Itajubá, MG, Brasil

1

*marcoscosta.iq.uerj@gmail.com

Abstract Core-shell magnetic polymer particles were synthesized by seeded suspension polymerization. The core was made of poly(methyl methacrylate-co-divinylbenzene) and a mixture of magnetite, maghemite and goethite (P(MMA-co-DVB)-M).

The shell was composed of poly(glycidyl methacrylate-co-divinylbenzene) (P(GMA-co-DVB)). These particles were characterized by infrared spectrometry (FTIR), thermal analysis (TG), scanning electron microscopy (SEM), dynamic light scattering (DLS) and vibrating sample magnetometry (VSM). The results showed the formation of core-shells with good magnetic properties (≈7.1 emu/g) and good thermal resistance (≈300 ºC). The light scattering experiments showed that the particle size of these materials changed from 5-90 microns (core) to 5-120 microns (core-shell). Scanning electron microscopic images were useful to show the formation of P(GMA-co-DVB) shells on P(MMA-co-DVB)-M cores. The materials synthesized in this work have potential to be modified and employed in magnetic separation processes in the biotech and environmental fields.

Keywords: magnetic polymer microspheres, core-shell, seeded suspension polymerization, biopolymers.

1. Introduction Core-shell magnetic polymer particles are typically prepared by a series of emulsion, dispersion or suspension polymerizations. Both core and shell domains can be composed of varied materials, including polymers, inorganic solids, and metals[1]. The core-shell model is becoming the most efficient way to use magnetic polymer particles as carriers and separators in the technological field. The magnetic nanoparticles can be shifted to the polymer core so they remain protected from the weather (e.g., oxidation) and to prevent leaching of nanoparticles during application, maintaining their magnetic properties during use cycles.

The surface properties are obtained by coating, allowing the integration of various functionalities to the final polymer particles. The core-shell synthesis is performed consecutively or sequenced in the presence of different monomers, where these seeded particles can be prepared in more than one polymerization stage or a single stage (in situ)[2,3]. Pinto et al. [4] synthetized core-shell polymer particles combined with suspension-emulsion polymerizations using styrene and employed lipase B from Candida Antarctica as support for immobilization. They described the performance of the biocatalysts as a function of the specific area, pore volume and average pore diameter of the supports. They observed that the average pore sizes did not affect the enzymatic activities in the analyzed range of pore sizes. They also observed that the increase of the specific area (and of the pore volume) led to higher enzyme loadings as well as an increase in the esterification activity. Besteti et al.[5] also combined suspension–emulsion polymerizations to produce

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polymer supports using styrene, methyl methacrylate, and cardanol as monomers. They reported that the obtained polymer particles presented the characteristic core–shell particle structure, with specific areas and average pore sizes. They also showed that the particles could be used successfully for immobilization of CALB, leading to immobilization efficiencies and enzyme activities better than the ones obtained with Accurel MP 1000 (commercial support for the immobilization of enzymes).

Ribeiro et al.[6] produced core-shell particles by seeded suspension polymerization by using polystyrene (PS) as polymer core, or seed, and methyl methacrylate (MMA) as the shell forming monomer. The TEM measurements revealed that the core-shell morphology consisted of PMMA clusters dispersed in the PS matrix. The synthesized core‑shell particles presented enhanced chemical resistance to cyclohexane compared to PS. Despite extensive work on the seeded polymerization technique, these materials do not have magnetic properties. Moreover, only one paper on magnetic core-shells synthesized by seeded suspension polymerization exists[7]. In this work[7], magnetic polymeric microspheres based on styrene (STY) and divinylbenzene (DVB) were synthesized in two steps. The addition method and the swelling time were varied. All methods tested to form the poly(styrene-co-divinylbenzene) shell produced particles with diameter larger than the core. The best results obtained used 48 hours of core swelling at 10 °C. Therefore, the objective of this study was to synthesize a magnetic polymer with core-shell morphology by suspension seeded

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Core-shell magnetic particles obtained by seeded suspension polymerization of acrylic monomers polymerization based on MMA (core) and GMA (shell) with lower swelling time and at room temperature. This material could have advantages, such as biocompatibility, protection of magnetic material within the core and shell characteristics that can be chemically modified to obtain tailor-made magnetic polymeric particles. For example, the epoxide group of the poly (glycidyl methacrylate) shell may undergo amination reaction for the introduction of amine groups, producing a material with application to the immunocapture of b-amyloid peptides [8], immunomagnetic separation of bone marrow cells[9], capture of epithelial cancer cells[10], etc. In the environmental area, these same materials could be used for removal of heavy metals[11] and dyes[12] from aqueous media.

2. Materials and Methods 2.1 Materials All monomers were commercial grade. Divinylbenzene (DVB) (Nitriflex, Rio de Janeiro, Brazil), methyl methacrylate (MMA) (Lanxess, Rio de Janeiro, Brasil) and glicidyl metacrylate (GMA) (Sigma, St. Louis, USA) were used as received. 2-2’-azo-bis-isobutyronitrile (AIBN) (Migquimica, São Paulo, Brazil) was used after purification in methanol PA (B’Herzog, Rio de Janeiro, Brazil). Poly(vinyl alcohol) (PVA 224) (Kuraray, Tokyo, Japan), sodium chloride (NaCl) (Vetec, Rio de Janeiro, Brazil), sodium dodecyl sulfate (SDS) (B’Herzog, Rio de Janeiro, Brazil), n-heptane (Vetec, Rio de Janeiro, Brazil) and toluene (Vetec, Rio de Janeiro, Brazil) were also used as received. The magnetic material was composed of magnetite, maghemite and goethite, as described in our previous paper[13].

2.2 Core-shell synthesis 2.2.1 First step The poly(methyl methacrylate-co-divinylbenzene)magnetic core (P(MMA-co-DVB)-M) was synthesized as described in our previous paper[13]. The organic phase (OP) was composed of 0.3 total mols (0.27 mols of MMA and 0.03 mols of DVB), 5% m.m. magnetic material, n-heptane (100% degree of dilution) and 2% m.m. AIBN. The aqueous phase (AP) was composed of 1% m.v. PVA and 1% m.v. NaCl. We performed a semi suspension of OP at 50 °C during 30 minutes at 700 rpm. After this step, the OP was added to the aqueous phase (volume ratio OP:AP = 1:4) and the suspension polymerization was conducted at 80 °C for 4 h.

2.2.2 Second step The shell was obtained by seeded polymerization, adapted from the literature[14,15]. This involved placing 0.5 g of the core (or seed) in a 500 mL three-necked flask.

Under stirring (200 rpm), the aqueous phase of the coating, containing PVA at 1% m.v. and SDS, was added to the reaction system. Next, half of the organic phase of the coating (GMA:DVB = 9:1) was added dropwise. The swelling occurred at room temperature for 1 h, 12 h or 24 h. After this time, the second part of the OPC was mixed with 1% m.m.

AIBN and added dropwise to the reaction. The suspension polymerization occurred for 4 h, at 70 °C, under stirring at 600 rpm. All solutions remained an ultrasonic bath for Polímeros, 28(5), 460-467, 2018

15 minutes before being used. We analyzed the swelling time, surfactant concentration (without sodium dodecyl sulfate - WSDS, with sodium dodecyl sulfate below the critical micelle concentration - BCMC and above it - ACMC) and mass ratios of seeds in shell monomers of 1:5 and 1:10.

All the synthesized materials were purified with a Soxhlet extractor, first with toluene and then with n-heptane, and dried at 60 °C. 2.3 Instrumentation and characterization The composition of the core-shells was analyzed by the FTIR ATR method (PerkinElmer Spectrum One spectrometer) in the range between 4000 cm-1 and 550 cm-1, where each spectrum was scanned at the resolution of 4 cm-1.

The VSM measurements (Lake Shore 7400 magnetometer) were performed on 0.05 g of sample, with a magnetic field between ±12 KG, at room temperature, during 10 minutes.

The morphology of the material was analyzed by SEM (FEI Inspect 550). Previously, the sample was placed on conductive tape and coated with a layer of gold to increase conductivity and protect against localized heating. The coated sample was loaded in the equipment to allow interaction with secondary electrons, under high vacuum and acceleration voltage of 20 kV. The particle size distribution of the seeds (cores) and the core-shells was determined by laser light scattering (Malvern, Mastersizer 2000). The samples were placed in the analyzer’s chamber containing a water and ethanol solution. The presence of a stirring system (1750 rpm) assured dispersion and homogenization of the particles in the medium. The samples were fed through the analyzer with the aid of a pump. The thermal degradation of the materials was checked by TG (TA Instruments, Q50 V6.4 Build 193), where about 10 mg of sample was placed in a platinum dish and heated under a nitrogen atmosphere with a flow rate of 100 mL/min, from 50 °C to 650 °C at a rate of 10 °C/min. The deviation of the tangent method for marking curves was used.

3. Results and Discussion Figure 1 shows the electronic micrographs of the core by SEM (Figure 1a and 1b). The surface of the core has compact and shapeless structures (Figure 1b). It is possible to visualize small agglomerated spherical particles inside the larger microsphere (Figure 1a). These morphological differences between the external surface and interior of microspheres are common features of crosslinked macroporous polymers synthesized by suspension polymerization. It is known that the diluent-copolymer affinity modifies the nuclear chains and the internuclear ones as well, and the use of a nonsolvating diluent (heptane) has a tendency to produce large pores.

The literature[16] explains that the nongel porosity occurs through channels between various spherical gel particles with smaller size bonded together, forming a larger microsphere, so the polymer domains are present as compact and formless structures. This agglomeration of microspheres inside the beads can cause an opaque appearance because of these structures. The greater compactness of polymeric areas on the surface than inside the microspheres has been attributed to compression due to the interfacial tension between the 461/467 461

Castanharo, J. A., Ferreira, I. L. M., Silva, M. R., & Costa, M. A. S. organic phase and the aqueous phase during the suspension polymerization[17].

Figure 2 and Figure 3 show the SEM results of the core-shell microspheres. Generally, comparison of the core-shell surfaces (Figure 2b, 3b, 3d and 3f) with the core surface (Figure 1b) reveals differences. While the surface of the core is compacted and has no defined shape, the surfaces of the core-shells have varying shapes, such as a film distributed along the full extent of the microsphere with very small structures adhered to the surface, including the presence of some bubbles. In general it was possible to produce a uniform coating and control the shell thickness.

The high magnification SEM images provided information about the change of the microspheres’ surfaces after the seeded polymerization process. This result is in accordance with the literature[1,15,18]. These surfaces are characteristic of non-porous shells. According to Lenzi et al.[19], when the core used as seed is washed and dried, the result, after the seeded suspension polymerization, is polymer particles that coalesce, while the swollen suspension particles lose their compartmentalized character. Chaudhuri and Paria[1] reported that these smooth surfaces as a coating can be obtained when the shell material is produced directly on the surface of the core by heterogeneous nucleation.

Figure 1. Scanning electron micrographs of the P(MMA-co-DVB)-M core: (a) x1,200 and (b) x20,000.

Figure 2. Scanning electron micrographs of the core shells synthesized with different swelling times: (a) and (b) 1 h, (c) 12 h, and (d) 24 h.

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Core-shell magnetic particles obtained by seeded suspension polymerization of acrylic monomers Figure 2 also shows micrographs of the core-shells synthesized with different swelling times: 1 h (Figure 2a and 2b), 12 h (Figure 2c) and 24 h (Figure 2d). The increase of swelling time (12 and 24 hours) caused fracturing of the materials.

During swelling, the core was under strong mechanical agitation for long periods, sufficient to cause collapse of the system. The core-shell synthesized after swelling for 1 h has a slightly rougher surface compared to the core (Figure 1b).

This indicates that the shell monomers were adsorbed and polymerized on the core surface.

The electron micrographs of core-shells synthesized with different amounts of SDS and with different seed: monomer ratios of the shell are shown in Figure 3.

The surfaces of the core shells are compared with magnification of 20,000 x in Figure 2b (WSDS), Figure 3b (BCMC) and Figures 3d and 3f (ACMC 1:5 and ACMC 1:10, respectively). There is a subtle difference between them, where nanostructures can be observed adhered to the microspheres.

These nanostructures tended to swell, forming a roughened film, with the increase of SDS content. The function of the surfactant is to decrease surface tension and monomer diffusion and prevent coalescence. Thus, the introduction of surfactant in the synthesis of core-shells caused greater concentration of monomer in the seed stage, but not in the aqueous phase, acting to reduce the amount of monomer dissolved in this phase. The appearance of the coatings was also different

Figure 3. Scanning electron micrographs of the core shells: (a) and (b) sodium dodecyl sulfate below the critical micelle concentration, with seed mass ratios of: OP = 1:5 (BCMC 1:5); (c) and (d) sodium dodecyl sulfate above the critical micelle concentration, with seed mass ratios of monomers - 1:5 (ACMC 1:5); (e) and (f) sodium dodecyl sulfate above the critical micelle mass ratios of seeds in shell monomers - 1:10 (ACMC 1:10).

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Castanharo, J. A., Ferreira, I. L. M., Silva, M. R., & Costa, M. A. S. depending on the critical micelle concentration (CMC) of SDS. Comparing Figures 3b and 3d (BCMC and ACMC, respectively), the images suggest a coating replete with small points in BCMC and small plates attached in ACMC. The increase of SDS above the CMC led to formation of a thin film on the microspheres, probably due to the existence of a large number of micelles arranged in solution and the lower surface tension in the reaction system.

The literature indicates that when the concentration of SDS is below the CMC (8.32x10 -3 mol/L), the secondary nucleation is minimized[20]. This effect was not observed in any of the core-shells synthesized with different SDS concentrations. In both cases, the core-shells were well dispersed throughout the sample. This was possible because we performed a swelling test in a beaker before the synthesis, to limit the quantity of monomers in the system and prevent the polymerization from occurring outside the area of the seeds.

Figure 3c and Figure 3e show the SEM micrographs of core shells, with SDS above the CMC and different mass ratios of seeds (ACMC 1:5 and ACMC 1:10) and their respective surfaces (Figures 3d and 3f) for comparative

purposes. In both core-shells, the surfaces are smooth, like plates attached to the surface. There is a report in the literature[1] that when synthesis involves purification and drying, the result is enclosures without pores. This is due to the occurrence of heterogeneous nucleation in this polymerization system, so the molecules of the shell polymers are produced directly on the surface of the core.

The ACMC core-shell with ratio of 1:10 (Figures 3e and 3f) has small bubbles on the shell surface and its coating appears to be more homogeneous than the ACMC core shell with ACMC 1:5 ratio (Figures 3c and 3d). The uptake of the shell monomers in all the systems studied resulted in rough and thin film on the surface of the cores.

Figure 4 shows the results of particle size determination of the core-shell. As can be seen in the study of different swelling times (Figure 4a), the core-shell with 1 h of swelling had particle size range shifted to larger values. This is strong evidence that core microspheres were swollen and the polymerization of GMA/DVB took place to form the shell.

Similar results have been found by other researchers[1,7].

In syntheses where the swelling time was longer, the displacement of the particle size was toward smaller sizes

Figure 4. Size and size distribution of the of the P(MMA-co-DVB)-M core and core-shells (a) swelling for different times: 1 h, 12 h and 24 h; (b) core-shell particles with different additions of surfactant: without sodium dodecyl sulfate (WSDS), sodium dodecyl sulfate below critical micelle concentration (BCMC), and sodium dodecyl sulfate above critical micelle concentration (ACMC) (mass ratios of seeds in shell monomers 1:5) and (c) core-shell particles with sodium dodecyl sulfate above critical micelle concentration and different mass ratios of seeds in shell monomers of 1:5 (ACMC 1:5) and 1:10 (ACMC 1:10) (obtained by dynamic light scattering).

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Core-shell magnetic particles obtained by seeded suspension polymerization of acrylic monomers for the core, showing that these reactions caused fracture of the microspheres, confirming the results observed the SEM images (Figure 2). Comparison of the core and core-shells showed an upward shift of the size range in all second polymerization systems (Figures 4b and 4c). These results also show that increasing the monomer concentration in the shell formation from 1:5 to 1:10 (ACMC) (Figure 4c) did not influence the particle size displacement. Similar results have also been reported by[21,22]. It is known that crosslinked polymers have limited swelling degree. It is possible that this characteristic influences the evolution of the particle size of the core-shell. Another limitation to the evolution of the core-shell particle size is the size of the core. One of the biggest challenges of synthesizing core-shells is related to control to assure uniform coating thickness[1].

The results of saturation magnetization of the synthesized core-shells with different concentrations of surfactant are shown in Figure 5a and with different shell monomer ratios in Figure 5b. At this stage, all the core shells showed good

response to the magnetic field (7.3-6.8 emu/g) and remanent magnetization (Mr) close to zero, indicating superparamagnetic behavior. The saturation magnetization also showed values below the core Ms value (7.5 emu/g). The small differences in the results indicate possible loss of the magnetic material adsorbed during the second polymerization. Another possibility for the reduction of the core shell Ms value is the presence of the polymer shell. Since this result is given in terms of mass, weight increase of the samples due to the incorporation of the P(GMA-co-DVB) to the P(MMA-co-DVB)-M core can also be considered. According to the literature, these results would enable use of these materials as ion-exchange resins with magnetic properties and Ms close to 8.0 emu/g, would be excellent to use these microspheres in catalytic processes as well[23,24].

The FTIR results obtained are shown in Figure 6. The axial asymmetrical deformation of the epoxide ring appears in the region of 906 cm-1. A report in the literature[25] about the ATR-FTIR technique indicates that besides the analysis of

Figure 5. Saturation magnetization curves of the of the P(MMA-co-DVB)-M core and core shells obtained: (a) core-shell particles with different additions of surfactant: without sodium dodecyl sulfate (WSDS), sodium dodecyl sulfate below critical micelle concentration (BCMC), and sodium dodecyl sulfate above critical micelle concentration (ACMC) (mass ratios of seeds in shell monomers OP = 1:5) and (b) core-shell particles with sodium dodecyl sulfate above critical micelle concentration and different mass ratios of seeds in shell monomers of 1:5 (ACMC 1:5) and 1:10 (ACMC 1:10).

Figure 6. FTIR spectra of the P(MMA-co-DVB)-M core and core-shell particles with sodium dodecyl sulfate above critical micelle concentration and different mass ratios of seeds in shell monomers of 1:5 (ACMC 1:5) and 1:10 (ACMC 1:10).

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5. Acknowledgements The authors thank Coordenação de Aperfeiçoamento de Pessoal do Nível Superior (CAPES) (Edital 04/CII-2008, REDE NANOBIOTEC – BRASIL) for financial support via the doctoral scholarship awarded through the project called “Nanobiotechnology for the development of polymer materials for applications in health and the environment”, Migquimica for AIBN donation, Nitriflex for donating the monomers, and Laboratório de Engenharia de Polimerização (ENGEPOL) of Instituto Alberto Luiz Coimbra de Pós‑Graduação e Pesquisa de Engenharia (COPPE-UFRJ) for dynamic light scattering analysis.

Figure 7. TG and DTG curves of the P(MMA-co-DVB)-M core and core-shell particles with sodium dodecyl sulfate above critical micelle concentration and different mass ratios of seeds in shell monomers of 1:5 (ACMC 1:5) and 1:10 (ACMC 1:10).

the interaction of matter with electromagnetic radiation in the infrared range, in many cases the technique can perform quantitative analysis, since the response to the signal obtained

by FTIR spectra can be related to the concentration of analyte in the sample. In the sample ACMC1:10, this band is more intense than in sample ACMC 1:5, so it is possible that the adsorption of GMA in this synthesis was more significant.

Figure 7 shows the thermal degradation curves of the core-shells synthesized with different concentrations of shell monomers. All the samples also showed a small weight loss between 100-200 °C, attributed to the presence of GMA trace amounts in the samples (their degradation temperature is around 180 °C). Above this temperature, only one thermal degradation stage (TONSET = 300 °C) occurred for the core-shell samples, indicating there was no change in the degradation profile according to the shell formation method. The results also show no significant change in TMAX values (about 397 ºC) of the core shells compared to the core.

This result can be explained by the fact the shell is a thin layer that probably did not affect the thermal degradation of the samples at this stage.

4. Conclusions It was possible to synthesize polymeric microspheres with core-shell morphology based on (P(MMA-co-DVB)-M) constituting the core and P(GMA-co-DVB) composing the shell. The core-shells obtained with stirring speed of 600 rpm had good magnetic properties (Ms ≈7.1 emu/g) and were free of hysteresis. The scanning electron microscopic images were efficient to show the formation of the shell on the polymeric core. The light scattering analysis showed the displacement of particle size distribution to larger sizes (5-90 µm (core) to 5-120 µm (core-shell)). The FTIR spectra also showed the incorporation of glycidyl methacrylate, corroborating the other results and confirming the formation of magnetic polymeric microspheres with core-shell morphology. Finally, there was no change in degradation profile in the core-shells according to the TG and DTG curves.

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Hemijska Industrija, 68(6), 685-699. http://dx.doi.org/10.2298/ HEMIND140127023S. 13. Castanharo, J. A., Ferreira, I. L. M., Silva, M. R., Costa, G. M., Oliveira, M. G., & Costa, M. A. S. (2015). Microesferas magnéticas à base de poli(metacrilato de metila-co-divinilbenzeno) obtidas por polimerização em suspensão. Polímeros: Ciência e Tecnologia, 25(2), 192-199. http://dx.doi.org/10.1590/01041428.1666.

14. Gonçalves, O. H., Machado, R. A., Araújo, P. H., & Asua, J. M. (2009). Secondary particle formation in seeded suspension polymerization. Polymer, 50(2), 375-381. http://dx.doi. org/10.1016/j.polymer.2008.11.006.

15. Lin, W., Biegler, L. T., & Jacobson, A. M. (2010). Modeling and optimization of a seeded suspension polymerization process. Chemical Engineering Science, 65(15), 4350-4362. http://dx.doi.org/10.1016/j.ces.2010.03.052.

16. Rabelo, D., & Coutinho, F. M. B. (1994). Porous structure formation and swelling properties of styrene-divinylbenzene copolymers. European Polymer Journal, 30(6), 675-682. http:// dx.doi.org/10.1016/0014-3057(94)90115-5.

17. Belfer, S., Egozy, Y., & Korngold, E. (1984). Resins containing extractants: morphology of polymers prepared by polymerization of vinyl monomers in the presence of uranium-selective extractants. Journal of Applied Polymer Science, 29(12), 3825-3836. http://dx.doi.org/10.1002/app.1984.070291216.

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18. Heydarpoor, S., Abbasi, F., Jalili, K., & Najafpour, M. (2015).

Synthesis of core-shell PS/PMMA expandable particles via seeded suspension polymerization. Journal of Polymer Research, 22(8), 151-161. http://dx.doi.org/10.1007/s10965-015-0789-0.

19. Lenzi, M. K., Silva, F. M., Lima, E. L., & Pinto, J. C. (2003).

Semibatch styrene suspension polymerization processes.

Journal of Applied Polymer Science, 89(11), 3031-3038. http:// dx.doi.org/10.1002/app.12443.

20. Daigle, J. C., & Claverie, J. P. (2008). A simple method for forming hybrid core-shell nanoparticles suspended in water. Journal of Nanomaterials, 1, 1-8. http://dx.doi.org/10.1155/2008/609184.

21. Liu, X., Fan, X. D., Tang, M. F., & Nie, Y. (2008). Synthesis and Characterization of Core-Shell Acrylate Based Latex and Study of Its Reactive Blends. International Journal of Molecular Sciences, 9(3), 342-354. http://dx.doi.org/10.3390/ ijms9030342. PMid:19325753.

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

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23. Lee, Y., Rho, J., & Jung, B. (2003). Preparation of magnetic ion-exchange resins by the suspension polymerization of styrene with magnetite. Journal of Applied Polymer Science, 89(8), 2058-2067. http://dx.doi.org/10.1002/app.12365.

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25. Conceição, V. N., Souza, L. M., Merlo, B. B., Filgueiras, P. R., Poppi, R. J., & Romã, W. (2014). Estudo do teste de Scott via técnicas espectroscópicas: um método alternativo para diferenciar cloridrato de cocaína e seus adulterantes. Quimica Nova, 37, 1538-1544. http://dx.doi.org/10.5935/0100-4042.20140240.

Received: Oct. 27, 2017 Revised: Apr. 06, 2018 Accepted: June 05, 2018

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.04317

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

Preparation of gelatin beads treated with glucose and glycerol Débora Vieira Way1, Márcio Nele2 and José Carlos Pinto1* Programa de Engenharia Química, Instituto Alberto Luiz Coimbra de Pós-graduação e Pesquisa em Engenharia – COPPE, Universidade Federal do Rio de Janeiro – UFRJ, Rio de Janeiro, RJ, Brasil 2 Departamento de Engenharia Química, Escola de Química – EQ, Universidade Federal do Rio de Janeiro – UFRJ, Rio de Janeiro, RJ, Brasil

1

*pinto@peq.coppe.ufrj.br

Abstract Gelatin is employed in pharmaceutical applications because of its biodegradability, biocompatibility and low toxicity.

However, it may be necessary to promote gelatin crosslinking in order to develop drug release systems and extend release times. SEC analyses are used here for the first time to monitor the evolution of molar mass distributions of gelatins during treatment with glycerol and glucose in dispersed media. Unambiguous experimental evidence of gelatin crosslinking in presence of sugars and glycerol has yet to be presented. SEC results indicate that average molar masses decrease during gelatin treatment, while FT-IR analyses indicate that gelatins are subject to structural modifications during processing, which can explain the decrease of gelatin solubility after treatment. The results presented here indicate the importance of using SEC techniques to monitor gelatin crosslinking, as they seemingly contradict previously published results that make use of indirect measures for this purpose.

Keywords: crosslinking, gelatin, size exclusion chromatography, SEC, molar mass distribution.

1. Introduction Gelatin is a generic name used to describe proteins produced from the chemical hydrolysis of collagen[1,2]. The fabrication procedure, usually known as “conditioning process”, can exert pronounced influence on the final properties of the obtained protein (or gelatin). Collagen can be hydrolyzed through alkali-conditioning or acid-conditioning, leading to type A (acid) or type B (basic) gelatins, presenting distinct isoelectric points[1-3]. The collagen structure comprises three alpha chains, which are coiled into a left-handed helix, originating the well-known triple-helix structure. When it is subjected to the conditioning process, the triple-helix is partially broken to form gelatin[1,4]. Gelatin is an inexpensive, biodegradable, biocompatible and non-toxic protein.

Because of this, its use as an encapsulating material has been extensively studied in pharmaceutical applications[1].

Drug encapsulation can offer various practical benefits for pharmaceutical applications, including masking of bad taste and odor of drugs, protection against photobleaching and oxidation, and development of controlled and/or targeted release of encapsulated bioactive molecules[5,6].

When hydrophilic polymers such as gelatin are used for drug encapsulation, it can be useful to crosslink the polymer chains in order to promote the decrease of the polymer solubility in body fluids and extend the release time of the drug[7]. (Although the term crosslinking can be used to describe different physico-chemical phenomena, in the present manuscript the term crosslinking is used to describe the formation of covalent chemical bonds among gelatin macromolecules with the mediation of smaller

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molecules, called crosslinking agents.) However, gelatin coating has also been proposed as an alternative to gelatin crosslinking[8]. Some of the most cited gelatin crosslinking agents are glutaraldehyde[9-11], formaldehyde[1,12,13], glyoxal[13,14] and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC)[15,16]. Nevertheless, all the previously cited compounds are toxic and therefore should be avoided when pharmaceutical applications are pursued.

In order to replace the reported toxic compounds for natural non-toxic gelatin crosslinking agents, some authors reported the use of genipin[17], dialdehyde starch[18] and polyphenol[17,19], for example. Many studies have also proposed the use of native and/or oxidized sugars, including dextran[20-22], fructose[23] and glucose[2,23]. In all the selected studies concerning the use of sugars, the crosslinking reaction time was usually small and in the range from 5 to 10 minutes[20-23]. Authors that report gelatin crosslinking usually do so by presenting indirect analytical data as drug release reduction[9,22] or as consumption of free amino groups[10,12,16] or also by presenting information of decrease in gelatin solubility[14,21,23]. These results do not undoubtedly prove the crosslinking reaction occurrence as the effects observed could also be caused by other side reactions. Nevertheless, some authors presented evidences of viscosity increase[13,20] or FT-IR (Fourier transform infrared spectroscopy) analyses[10,11] that could actually prove that reactions had happened in the reacting medium. However, despite the results reported in these studies, unambiguous experimental evidence of gelatin microparticle crosslinking

Polímeros, 28(5), 468-476, 2018

Preparation of gelatin beads treated with glucose and glycerol in presence of sugars (and glycerol) has never been presented, as formation of solid particles can be due to physico-chemical effects other than crosslinking, such as modification of chain composition and configuration.

Based on the previous discussion, in the present paper SEC (Size Exclusion Chromatography) analyses were used for the first time to monitor the evolution of molar mass distributions of gelatins, when these materials were treated with glycerol and glucose. Particularly, one must observe that molecular weight distributions can be very sensitive to occurrence of crosslinking reactions, as formation of a single average covalent bond between the existing macromolecules can cause the doubling of the average molecular weights.

Additionally, even when crosslinking takes place at high levels and leads to formation of insoluble material, the molecular weight distributions of the soluble fractions are expected to change considerably. For this reason, SEC analyses were performed to evaluate the importance of crosslinking reactions during thermal treatment of gelatin with glucose and glycerol.

2. Materials and Methods 2.1 Materials Pigskin gelatin (240-270 Bloom), PhEur gelatin, Sorbitan monooleate (SPAN 80) and D-(+)-Glucose ACS reagent were purchased from Sigma-Aldrich (Rio de Janeiro, Brazil) as pharmaceutical grades. Glycerol, acetone and sodium dodecyl sulfate (SDS) were obtained from VETEC (Rio de Janeiro, Brazil) with minimum purity of 99.5%. Sunflower oil was purchased from Liza (Rio de Janeiro, Brazil) as a nutritional grade. Doxycycline hyclate (99%) was purchased from Pharma Nostra (Goiás, Brazil). All reagents were used without further purification.

gelatin. The rest of the procedure was reproduced exactly as described above, but the reaction was conducted for only 20 minutes.

2.3 SEC analyses The chromatographic system comprised three OH-PAK SB-806 (Shodex, Japan) columns connected in series, a Phenomenex TS-430 separation module (Phenomenex, United States) and a Viscotek VE358 refractive index detector (Viscotek, United Kingdom). The running conditions and sample preparation procedures were defined in accordance with previously published material[26]. The mobile phase (18 g/L of SDS in Milli-Q water) was filtrated through 0.45 μm filters prior to use. Sample preparation consisted in dissolving 1 mg of samples of the produced gelatin particles in 1 mL of the SDS solution at room temperature. Before injection, all samples were filtrated through 0.22 μm syringe filters. It is important to emphasize that clear and transparent solutions were obtained in all cases. Samples of 200 μL were then injected into the SEC device and run for 80 min at flow rates of 0.5 mL/min at 40 °C. The equipment was calibrated with poly(styrene sulfonate) standards (American Polymer Standards Corporation, United States) ranging from 3420 to 2350000 Da.

2.4 FT-IR analyses FT-IR analyses were performed in a Thermo Nicolet 6700 FT-IR spectrometer (Nicolet, United States) equipped with a diamond Smart Orbit accessory for direct analyses of solid samples. The Smart Orbit accessory is shown in Figure 1. Infrared analyses were performed in the mid‑infrared region in total reflection mode with resolution of 4 cm-1 at room temperature. Spectral data were reported as averages of 128 scans.

2.2 Reactions Initially, glucose or glycerol was dissolved in 30 g of distilled water at 60 °C in a glass flask. Then, 3 g of gelatin were added into the flask and the mixture was kept under continuous magnetic stirring at 60 °C until solubilization of the protein and obtainment of a clear transparent solution.

The solution was then poured into a previously prepared mixture containing 120 g of sunflower oil and 6 g of SPAN 80, kept at the desired reaction temperature (50 °C or 60 °C), in order to avoid particle coalescence and allow for preparation of regular droplets of gelatin solution, as stabilized by SPAN.

The resulting reaction mixture was kept under vigorous magnetic stirring at 50 or 60 °C for 30 min and 2 mL aliquots were withdrawn at regular intervals of 5 minutes for further analyses. Operation conditions were selected in accordance with previously published references[23-25]. After the reaction step, the reaction medium was cooled down to 10 °C and then 30 ml of acetone were added into the reaction flask in order to promote the dehydration of the gelatin droplets and obtain gelatin particles. The product was then filtrated, washed with abundant amounts of acetone (for removal of residual oil and water) and kept in desiccators at room temperature to prevent absorption of water.

When doxycycline was used in the reactions, 1.5g was solubilized in water and heated to 60º before adding the Polímeros, 28(5), 468-476, 2018

Figure 1. Smart orbit accessory.

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3. Results and Discussions As gelatins may have distinct characteristics, it is important to characterize these materials before use because small differences between them may cause different behaviors during the reactions. Table 1 shows the detailed amino acid composition of the analyzed gelatins, as provided by Biosynthesis (Texas, United States). As one can see in Table 1, the analyzed gelatins were not very different in terms of amino acid compositions, although small composition changes can affect significantly the concentration of a particular functional group. Gelatins were also characterized by size exclusion chromatography (SEC), as shown in Figure 2, and by optical microscopy, as shown in Figure 3. Results indicate that the molar mass distributions of both gelatins were very similar, but that PhEur gelatin has smaller particle size distribution when compared to Pigskin gelatin. According to Dupont[26], gelatins can undergo hydrolysis upon aging, leading to increase of gelatin fractions of low molar mass, especially around 14,000 Da. However, as one can see in Figure 3, the original raw materials presented high average molar masses and small fractions of low molar masses, indicating that gelatins had not been subject to significant aging.

The pHs of aqueous solutions of PhEur and pigskin gelatin (0.1 g/mL) were measured in order to avoid reaction processing in the vicinities of the isoelectric points (IP). This precaution is necessary to allow for complete solubilization of gelatin in the aqueous phase. The results are shown in Table 2 and confirm that the analyzed gelatins belong to group A (acid gelatins) and are expected to dissolve in acidic media.

Table 3 presents the full set of gelatin treatment runs analyzed in the present manuscript. Runs were performed Table 1. Amino acid composition of the analyzed gelatins.

Aminoacid Hydroxyproline Aspartic acid and asparagine Serine Glutamic acid and glutamine Glycine Histidine Arginine Threonine Alanine Proline Cysteine Tyrosine Valine Methionine Lysine Isoleucine Leucine Phenylalanine Tryptophan

PhEur Gelatin Composition (mol%) 13.47 5.51

Pigskin Gelatin Composition (mol%) 12.84 5.25

2.82 10.11

2.78 9.72

21.18 1.32 8.67 1.86 8.60 13.14 0.00 0.65 2.09 0.71 3.93 1.23 2.82 1.99 0.00

21.51 1.33 8.84 1.85 8.54 13.96 0.00 0.86 1.68 0.91 3.97 1.13 2.75 2.08 0.00

Table 2. pH of aqueous gelatin solutions (0.1 g/mL).

Figure 2. Weight average molar mass distributions of the original gelatins before treatment.

Gelatin PhEur Pigskin

pH 5.76 5.51

Classification Type A

IP range* 7 to 9

*According to Gelatin Manufacturers Institute of America GMIA[3].

Figure 3. Optical micrographs of samples of the original PhEur (a) and Pigskin (b) gelatins.

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Polímeros, 28(5), 468-476, 2018

Preparation of gelatin beads treated with glucose and glycerol with distinct concentrations of crosslinking agents, distinct gelatins and at different reaction temperatures. Also, one reaction was performed with doxycycline (DOX), used as a model drug, to simulate a real condition in which a drug is encapsulated to observe the reaction behavior. The pHs of the prepared aqueous solutions were measured to ensure that pH values were significantly below the isoelectric points of the gelatins, as already discussed.

Figure 4 shows the evolution of the average molar masses of the analyzed samples in Run#1 to Run#7 and compares them to PhEur gelatin average molar mass before any kind of treatment. One can observe that for Run#1 the average molar masses decreased from 197000 g/mol to 153000 g/mol (approximately 22%) in the very beginning of the expected crosslinking process when compared to PhEur gelatin before the reaction, remaining essentially constant after 5 minutes of treatment. At this point, one must observe that the reaction time was assumed to start after preparation of the inverse suspension, so that it did not include the time required for preparation of the initial aqueous solution of gelatin, which took approximately 10 minutes. This explains the sudden decrease of the average molecular weights of treated gelatins when the reaction time was equal to zero, reflecting the fast modification of the gelatin properties during the preparation of the initial aqueous gelatin solution.

Based on Figure 4, it is possible to infer that glucose was not acting as a crosslinking agent at the analyzed conditions. More interestingly yet, similar trends were observed when additional amounts of glucose were used, as shown in Figure 4, although the average molar mass decrease reached 37%, 35% and 28% in Run#2, Run#3 and Run#4, respectively. More specifically, the average molar masses decreased from 197000 g/mol in PhEur gelatin to 123000 g/mol in Run#2, to 129000 g/mol in Run#3 and to 142000 g/mol in Run#4. Therefore, it seems plausible to admit that glucose was not acting as a crosslinking agent during gelatin treatment at the analyzed conditions, despite the previously reported data. This highlights the importance of using techniques that can actually prove the crosslinking occurrence other than indirect analytical methods, that can lead to misleading conclusions.

Similar results were obtained at different treatment temperatures and when glycerol was used as the crosslinking agent, as also illustrated in Figure 4. Moreover, the observed results were essentially the same when different molar

mass averages were used to observe the evolution of the molecular weights, due to the very similar molecular weight distributions of the analyzed samples. Particularly, published material reports the possible occurrence of spontaneous gelatin crosslinking after exposure to higher temperatures[27], which could not be confirmed in the temperature range of 50-60 °C at the analyzed conditions, as shown in Figure 4 for treatment temperature of 60 °C. Finally, Figure 4 shows that the weight average molar masses of the final products were very similar in all cases, indicating that the addition of glucose and glycerol to the reaction medium exerted little effect on the evolution of molar masses in the analyzed experiments.

Figure 5 exemplifies the molecular weight distribution of the produced gelatins and Figure 6 shows that it was possible to produce gelatin microparticles. Figure 6 also shows that the particles produced tend to form small aggregates that are probably formed after the drying procedure.

Despite the results presented in Figure 4, one point must be emphasized. The operation pressure of the SEC equipment increased steadily with the reaction time, indicating some sort of consistent structural change of the gelatin structure or formation of nanogel that could not be removed through filtration in all runs. This can be regarded as an indirect evidence of slight increase of molecular weights (that could not be detected through the SEC calibration curve) or of decrease of gelatin solubility due to modification of the macromolecular conformation and stereo configuration.

One must observe that gelatin is known to be a thixotropic

Figure 4. Evolution of weight average molar mass from Run#1 to Run#7.

Table 3. Operation conditions used in gelatin treatment experiments.

Run

Gelatin

Glycerol (%)

Glucose (%)

Doxycycline (g)

1 2 3 4 5 6 7 8 9

PhEur PhEur PhEur PhEur PhEur PhEur PhEur Pigskin PhEur

10 -

1 2 3 4 4 -

0.75

Temperature (ºC) 50 50 50 50 50 50 60 50 60

pH** 5.4 4.4 4.0 4.0 5.3 5.8 5.8 5.5 1.4

**pH was measured immediately after the complete solubilization of gelatin and before dispersion in sunflower oil.

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Figure 5. Molecular weight distributions of gelatin samples of the original material and of the final product of Run#1.

material [28], so that the viscosity of a gelatin solution is expected to change under stress, which can magnify pressure fluctuations of the SEC equipment associated with the modification of the gelatin structure.

Figure 7 shows FT-IR spectra of gelatin samples treated in absence of crosslinking agents. It can be noticed that the intensity of the band positioned at 3274 cm-1 increased considerably (in relation to the main peaks located at 3420 and 1700 cm-1) for the PhEur gelatin when glucose or glycerol were not used. This region is usually assigned for existence of amide A and amide B bonds, which are characteristic of peptide chains, as also reported in Table 4.

In order to observe more clearly the existence of bands related to amides I, II and III bonds, Figure 7 was enlarged, as shown in Figure 8, that also shows the relative increase of the bands that characterize the amides I, II and III bonds.

Hence, as chemical compounds were not added to the reaction medium in order to promote the formation of C=O or NH functional groups, it seems plausible to assume that structural modification of the gelatin occurs spontaneously during the thermal treatment at the analyzed conditions.

Susy and Byler[29] studied the IR deconvolution of amide I bands and related the observed changes to modifications of protein secondary structures. Based on these previous observations, the shape and position of the amide I band obtained in the present study probably corresponds to the α-helix conformation. Assuming that this is correct, as the intensity of the amide I band increases during the reaction treatment, it seems plausible to assume that the characteristic triple helix structure of collagen (which is partially destroyed when gelatin is produced) is still being affected by the thermal treatment process during the analyzed experiments.

This conjecture can also be supported by the available SEC analyses, as the decrease of average molar masses can possibly be related to the residual degradation of the triple helix structure and formation of the α-helix structure, as degradation of the triple helix structure would necessarily lead to the relative increase of the lower molecular weight fractions of analyzed samples.

Similar results could be obtained when glycerol and glucose were added to the reaction medium, as shown in Figures 9 and 10, reinforcing the assumption that these chemicals do not act as crosslinking agents during the gelatin treatment in the analyzed conditions. Particularly, 472 472/476

Figure 6. Optical micrograph of gelatin particles produced in Run#1.

Figure 7. FT-MIR spectra of gelatin samples treated in absence of crosslinking agents.

Figure 10 compares FT-IR results obtained after thermal treatment in presence of glucose with samples prepared through mixing of all reagents, as described in the previous section, but not submitted to thermal treatment. It can be noticed that mixing is not sufficient to promote the FT-IR changes described previously, indicating once more that the Polímeros, 28(5), 468-476, 2018

Preparation of gelatin beads treated with glucose and glycerol Table 4. Characteristic infrared bands of gelatins[30].

Identification 1 2 3 4

Frequencies 3300 cm-1 3100 cm-1 1700-1600 cm-1 1480-1575 cm-1 1229-1301 cm-1

Designation Amide A Amide B Amide I Amide II Amide III

Figure 8. Partial FT-MIR spectrum (1700 to 1000 cm-1).

Figure 9. FT-MIR spectra of gelatin samples treated with glycerol (Run#5).

thermal treatment leads to spontaneous modifications of the gelatin structure. Figure 11 shows that the observed FT-IR changes were similar for both analyzed gelatins, indicating that the observed FT-IR modifications did not depend on the particularly analyzed gelatin structure.

Based on the obtained results, it seems reasonable to assume that glucose and glycerol do not act as gelatin crosslinking agents at the analyzed conditions and that the modification of gelatin properties observed after thermal treatment is related mostly to the residual modification of the characteristic triple helix structure of collagen. It must be observed that modification of the gelatin structure is Polímeros, 28(5), 468-476, 2018

Vibrational mode NH stretching NH stretching Approximately 80% of the peptidic linkages C=O stretching CN stretching, NH bending CN stretching, NH bending

Figure 10. FT-MIR spectra of gelatin samples treated with glucose (Run#4).

Figure 11. FT-MIR spectra of gelatin samples treated with glucose (Run#4 and Run#8).

fast at the analyzed conditions, as the most significant modifications of the weight average molar masses take place in less than 10 minutes at the analyzed treatment conditions.

As a consequence, addition of glycerol and glucose to the reaction medium at the analyzed conditions do not improve significantly the properties of gelatin particles produced in oil suspensions.

Doxycycline (DOX) is a broad sprectrum antibiotic used both in human and animal treatment and, therefore, a drug of great interest for the Pharmaceutical industry[31,32]. As can be noted in Figure 12, that shows the chemical structure of doxycycline, it presents multiple acid and amine groups that 473/476 473

Way, D. V., Nele M., & Pinto, J. C. could possibly crosslink gelatin. Therefore, one more test was conducted using DOX to observe if it could engage in crosslinking reactions.

As shown in Figure 13, the decrease in the weight average molar mass in Run#9 right in the beginning of the reaction is less than 3% when compared to PhEur gelatin before any kind of treatment. Comparing this result to the previously reported reactions, in which the decreases in the average molar masses were in order of 30%, it seems plausible to admit that doxycycline may be interacting with gelatin.

Figure 12. Chemical structure of doxycycline.

Figure 13. Weigh average molar mass of pristine PhEur gelatin and weigh average molar masses of Runs #7 and #9 in the beginning of the reaction.

Besides, in Run#9 after 20 min of reaction, the decrease reached only 23% and as can be seen in Figure 14, the molar mass is broader than in Run#7 and slightly dislocated to higher molar masses. As the only difference between Run#7 and Run#9 is the use of doxycycline and the decrease observed in Run#7 was ~39%, two simultaneous fenomena may be occurring. The first one is observed by the decrease in molar mass and is associated to the structural modifications of gelatin already discussed. Besides, as doxycycline molar mass is only 545 g/mol, it seems likely to assume that the very discrete 3% decrease in the molar mass can not be associated to a simple interaction between gelatin and doxycycline. Therefore, the second fenomena observed is the increase in gelatin molar mass, that is probably caused by the crosslinking of gelatin by doxycycline.

Based on the obtained results, it can be concluded that the proposed SEC technique seems appropriate to monitor the evolution of molar mass distributions of gelatins.

Obtained SEC results indicated that the average molar masses decreased during the gelatin treatment and FT-IR (Fourier Transform Infrared Spectroscopy) analyses indicated that gelatins were subject to structural modifications during processing, which can eventually explain the decrease of gelatin solubility in water after treatment observed by other groups. Particularly, based on the obtained results it could be concluded that glucose and glycerol did not act as gelatin crosslinking agents at the analyzed conditions (temperatures ranging from 50 °C to 60 °C, maximum reaction times of 30 min, gelatin concentration of 10 wt%, crosslinking agent concentration below 10 wt% and pH values below 5.8), despite previous dats reported in the literature. Moreover, the modification of gelatin properties observed after thermal treatment was related mostly to the residual modification of the characteristic triple helix structure of collagen.

As a consequence, addition of glycerol and glucose to the reaction medium at the analyzed conditions did not improve significantly the properties of gelatin particles produced in oil suspensions. Therefore, the results presented in this paper emphasize the importance of using unambiguous experimental techniques to investigate gelatin crosslinking.

4. Conclusions A size exclusion chromatograph (SEC) procedure was proposed and successfully used to monitor the evolution of molar mass distributions of gelatins in aqueous solutions.

As observed at different conditions (temperatures ranging from 50 °C to 60 °C, maximum reaction times of 30 min, gelatin concentration of 10 wt%, crosslinking agent concentration below 10 wt% and pH values below 5.8), the use of glycerol and glucose did not allow for effective crosslinking of gelatin samples treated in inverse suspensions, as evaluated through SEC and despite previous reports based on indirect crosslinking characterization. Finally, doxycycline was shown to act as a crosslinking agent for gelatin.

5. Acknowledgements

Figure 14. SEC analysis of the final product of Run#7 and #9.

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The authors thank CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil) and FAPERJ (Fundação Carlos Chagas Filho de Amparo à Polímeros, 28(5), 468-476, 2018

Preparation of gelatin beads treated with glucose and glycerol Pesquisa do Estado do Rio de Janeiro, Brazil) for supporting this research and providing scholarships.

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Received: Apr. 28, 2017 Revised: June 16, 2018 Accepted: July 04, 2018

PolĂ­meros, 28(5), 468-476, 2018

PolĂ­meros

Brazilian Polymer Association (ABPol)

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