Polímeros: Ciência e Tecnologia (Polimeros)4th. issue, vol. 28, 2018

Polímeros VOLUME XXVIII - Issue IV - Aug./Sept., 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 I 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

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“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: September 2018

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Polímeros / Associação Brasileira de Polímeros. vol. 1, nº 1 (1991) -.- São Carlos: ABPol, 1991Quarterly v. 28, nº 4 (Aug./Sept. 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(4), 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 Funding Institutions.............................................................................................................................................................................E4 Agenda.................................................................................................................................................................................................E5

O r i g in a l A r t ic l e Non-isothermal decomposition kinetics of conductive polyaniline and its derivatives William Ferreira Alves, José Antonio Malmonge, Luiz Henrique Capparelli Mattoso and Eliton Souto de Medeiros................................... 285

Nafion/sulfonated poly(indene) polyelectrolyte membranes for fuel cell application Jeanne Leticia da Silva Marques, Ana Paula Soares Zanatta, Mariska Hattenberger and Maria Madalena de Camargo Forte.................. 293

Evaluation of the application of cashew gum as an excipient to produce tablets Ana Paula de Sá Pinto, Kattya Giselle de Holanda e Silva and Claudia Regina Elias Mansur..................................................................... 302

Influence of Moringa oleifera derivates in blends of PBAT/PLA with LDPE Cristiane Medina Finzi-Quintão, Kátia Monteiro Novack, Ana Cláudia Bernardes-Silva, Thais Dhayane Silva, Lucas Emiliano Souza Moreira and Luiza Eduarda Moraes Braga............................................................................................................... 309

Extraction, chemical modification by octenyl succinic and characterization of cyperus esculentus starch Jonas Costa Neto, Roseli da Silva, Priscilla Amaral, Maria Rocha Leão, Taísa Gomes and Gizele Sant’Ana.............................................. 319

Synthesis of flexible polyurethane foams by the partial substitution of polyol by steatite Plínio César de Carvalho Pinto, Virginia Ribeiro da Silva, Maria Irene Yoshida and Marcone Augusto Leal de Oliveira........................... 323

Orange essential oil as antimicrobial additives in poly(vinyl chloride) films Carla Fabiana da Silva, Flávia Suellen Melo de Oliveira, Viviane Fonseca Caetano, Glória Maria Vinhas and Samara Alvachian Cardoso...................................................................................................................................................................... 332

Sheath-core bicomponent fiber characterization by FT-IR and other analytical methodologies Marcia Murakoshi Takematsu, Milton Faria Diniz, Elizabeth da Costa Mattos and Rita de Cássia Lazzarini Dutra................................... 339

Evaluation of hydrolytic degradation of bionanocomposites through fourier transform infrared spectroscopy Raquel do Nascimento Silva, Thainá Araújo de Oliveira, Isaias Damasceno da Conceição, Luis Miguel Araque, Tatianny Soares Alves and Renata Barbosa.................................................................................................................................................... 348

Effect of addition of clay minerals on the properties of epoxy/polyester powder coatings Natanael Relosi, Oscar Almeida Neuwald, Ademir José Zattera, Diego Piazza, Sandra Raquel Kunst and Eliena Jonko Birriel................ 355

Preparation and characterization of composites from copolymer styrene-butadiene and chicken feathers Maria Leonor Mendez-Hernandez, Beatriz Adriana Salazar-Cruz, Jose Luis Rivera-Armenta, Ivan Alziri Estrada-Moreno and Maria Yolanda Chavez-Cinco................................................................................................................................................................... 368

Effect of carboxymethylcellulose on colloidal properties of calcite suspensions in drilling fluids Keila Regina Santana Fagundes, Railson Carlos da Souza Luz, Fabio Pereira Fagundes and Rosangela de Carvalho Balaban................. 373

Cover: Composite images obtained by polarized light optical microscopy (pg 328).

Arts by Editora Cubo.

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Polímeros, 28(4), 2018

100 percent biobased, transparent, and thermally stable polyamide The natural substance 3-carene is a component of turpentine oil, a waste stream of the production of cellulose from wood.

Up to now, this by-product has been incinerated for the most part. Fraunhofer researchers are using new catalytic processes to convert 3-carene into building blocks for biobased plastics.

The new polyamides are not only transparent, but also have a high thermal stability. Plastics are a useful alternative to glass or metal for a wide range of applications. Polyamides play an important role in the manufacture of high-quality structural components, as they are not only impact- and abrasion-resistant, but also resistant to many chemicals and solvents. Today, polyamides are mainly produced from crude oil.

The Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB is investigating a sustainable alternative for the production of new high-performance plastics from terpenes found in resin-rich wood. The natural substances are available from conifers such as pine, larch or spruce. In the production of pulp, in which wood is broken down to separate the cellulose fibers, the terpenes are isolated in large quantities as a by-product, turpentine oil. In the joint project “TerPa – Terpenes as building blocks for biobased polyamides”, researchers at the Straubing BioCat branch of Fraunhofer IGB have now succeeded in optimizing the synthesis of lactams from the terpene 3-carene and converting them into a scalable, competitive process on a potentially industrial scale. Lactams are building blocks for the production of polyamides. The Straubing experts could already show that terpenes such as α-pinene, limonene and 3-carene are suitable raw materials for the synthesis of biobased lactams.

The conversion of 3-carene to the corresponding lactam requires four successive chemical steps. The special feature of the patent pending Straubing solution is that the conversions can take place as a “one-pot reaction sequence” in a single reactor – purification of the intermediate products is not required.

“We have achieved this by carefully selecting the catalysts and reaction conditions – and it saves time and money,” Paul Stockmann explains, who developed and optimized the promising process. “Even on a laboratory scale, our process delivers more than 100 grams of diastereomerically pure lactam monomer per production run. This quantity is quite sufficient for initial investigations of the production and evaluation of the new plastics,” Stockmann said. Another advantage: No toxic or environmentally hazardous chemicals are required for the synthesis of the lactam.

Nevertheless, that is not all. Due to the special chemical structure of 3-carene, the side chains of the natural compound inhibit the crystallization of the resulting polymer. “Our biobased polymers are therefore predominantly ‘amorphous’ and thus transparent which is very unusual for biobased polyamides,” says Dr. Harald Strittmatter, who heads the project at the BioCat branch in Straubing. This makes the new polyamides suitable as protective shields, for example in visors or ski goggles. They can also be produced with considerably less energy input than

petroleum‑based transparent polyamides. In contrast to other bioplastics, which are mainly produced from corn, wheat or potato starch, biobased polyamides do not compete with food production.

Rather, they add value to a waste stream that, so far, has been burned for energy production. Another advantage: The new biobased polyamides also have excellent thermal properties.

“The glass transition point of our polyamides is 110°C. They can therefore also be at permanently high temperatures, for example as components in the engine compartment of motor vehicles,” Strittmatter says. It is true that polyamides made from fossil resources have similarly temperature properties. However, due to their aromatic domains – which do not occur in the 3-carene based polyamides – they discolor over time under the influence of UV light, limiting their potential for outdoor applications.

Source: Phys.org - phys.org

Global Engineering Plastics Market 2018-2023 - Key Players are BASF, DowDuPont, SABIC, Shin‑Etsu Chemical and PolyOne The “Engineering Plastics Market up to 2023” report has been added to ResearchAndMarkets.com’s offering. Growing usage in applications such as automotive & transportation, electricals & electronics, consumer appliances, industrial & machinery, packaging, and other applications (construction and medical among many others) is fostering the engineering plastics market growth. The companies are indulged in R&D activities to innovate and develop new products, which can open new paths of applications.

Asia Pacific is the emerging region and also has a significant share in the global engineering plastics market. Other than Asia Pacific, South America, Middle-East, and developing countries of Europe have been witnessing substantial growth scenarios for engineering plastics. China and India are driving the demand for engineering plastics in the Asia Pacific region due to regional growth along with huge base of automobile manufacturers, increasing demand for packaging solutions from various applications industries, existence of electrical & electronics manufacturers, and increasing industrial establishment for metal fabrication. In developing regions, growing purchase power is leading the economic growth.

Globally, Asia Pacific is the largest engineering plastic market, primarily due to the presence of export-oriented manufacturing capacities and intense domestic demand from various end-user industries. The increase in manufacturing industries is further driving the market growth in the region.

The anticipated economic stability in Europe is expected to boost its manufacturing sector, complementing the growth of the engineering plastics market. North America is likely to remain the key region with a significant contribution from the US. Few of the prominent companies operating in the engineering plastics market are BASF SE, DowDuPont Inc., SABIC, Shin‑Etsu Chemical Corp., and PolyOne Corp.

Source: PR Newswire Association LLC - www.prnewswire.com

Polímeros, 28(4), 2018 E3

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

January

May

7th Future of Polyolefins Summit Date: January 16-19, 2019 Location: Antwerp, Belgium Website: www.wplgroup.com/aci/event/polyolefins-conference 6th Maximizing Propylene Yields Date: January 23-24, 2019 Location: Barcelona, Spain Website: www.wplgroup.com/aci/event/maximising-propyleneyields 22nd Thermoplastic Concentrates Date: January 29-31, 2019 Location: Coral Springs, United States Website: www.ami.international/events/event?Code=C0937

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

February 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

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

E4

June 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 Polymer Foam Date: June 18-19, 2019 Location: Pittsburgh, United States Website: www.ami.international/events/event?Code=C0968

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

Polímeros, 28(4), 2018

ABPol Associates Sponsoring Partners

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Polímeros, 28(4), 2018

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.03116

Non-isothermal decomposition kinetics of conductive polyaniline and its derivatives William Ferreira Alves1, José Antonio Malmonge2, Luiz Henrique Capparelli Mattoso3 and Eliton Souto de Medeiros4* Universidade Federal do Acre – UFAC, Campus Floresta, Cruzeiro do Sul, AC, Brasil Departamento de Física e Química – DFQ, Universidade Estadual Paulista “Júlio de Mesquita Filho” – UNESP, Campus de Ilha Solteira, Ilha Solteira, SP, Brasil 3 Laboratório de Nanotecnologia para o Agronegócio – LNNA, Centro Nacional de Pesquisa e Desenvolvimento de Instrumentação Agropecuária – CNPDIA, Empresa Brasileira de Pesquisa Agropecuária – EMBRAPA, São Carlos, SP, Brasil 4 Laboratório de Materiais e Biossistemas – LAMAB, Universidade Federal da Paraíba – UFPB, João Pessoa, PB, Brasil 1

2

*eliton@ct.ufpb.br

Abstract The non-isothermal decomposition kinetics of conductive polyaniline (PANI) and its derivatives, poly(o-methoxyaniline) (POMA) and poly(o-ethoxyaniline) (POEA), was investigated by thermogravimetric analysis (TGA), under inert and oxidative atmospheres, using Flynn-Wall-Ozawa’s approach to assess the kinetic parameters of the decomposition process. The order of reaction was found to be dependent on the degree of conversion indicating that both the early and the later stages of polymer degradation were next the zero or pseudo zero order kinetics, whereas the intermediate stages follow a first order kinetics. The activation energy was found to be dependent on both the degree of conversion and PANI derivative. Activation energy values vary from 125 to 250 kJ/mol, to decompositions carried out under nitrogen, and 75 to 120 kJ/mol to oxidative atmosphere. Parent PANI presented the best thermal stability and suggesting that thermal stability is also influenced by derivatization and type of atmosphere used.

Keywords: PANI, POEA, POMA, thermal decomposition, Flynn-Wall-Ozawa’s approach.

1. Introduction Polyaniline (PANI) and its derivatives poly(o-methoxyaniline) (POMA) and poly(o-methoxyaniline) (POEA) have been intensively studied due to their electrical and optical properties, low cost, good processability and a broad range of applications ranging from sensors and biosensor to smart windows and nanodevices[1,2]. More recently, the development of PANI nanostructures has opened up a new range of potential applications, due to their high surface area, controllable electrical conductivity, and ease of preparation[3]. Several authors are extensively studied the use of PANI nanofibers in the manufacture of electronic devices such as gas sensors, super capacitors and biomedical applications[4-6].

Regarding PANI thermal behavior, it is known that the conducting state presents a three-step decomposition process, where the first step is attributed to water evaporation, the second to loss of the dopant and the third to breaking of carbon backbone in the polymer, while the insulating state of PANI (emeraldine base) displays two peaks: one at low temperature attributed to water loss and the second at higher temperatures, attributed to polymer decomposition[7-11].

Additionally, PANI powders and films have been studied

by Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) to evaluate its thermal

Polímeros, 28(4), 285-292, 2018

properties. However, there are few studies related to the thermal behavior of PANI derivatives in emeraldine base form.

Thermal analysis of conducting polymers is of great interest to determine their thermal behavior in various technological applications, since it provides important information on the effect of morphological and structural changes such as cross-linking and functionalization.

This method has been largely used in the study of curing and degradation of polymers and decomposition of several other substances[12-17]. Improvements in the determination of the kinetic triplet – activation energy, pre-exponential factor and order of rection – has been proposed by several other authors, including more accurate solutions for the the temperature integral. A critical evaluation of the isoconventional methods has been reviewed in the literature[17].

In this work, polyaniline (PANI) and its derivatives, poly(o-metoxyaniline), POMA, and poly(etoxyaniline), POEA, were analyzed by thermogravimetric analysis (TGA) and their kinetics of thermal decomposition was studied

by Flynn–Wall–Ozawa’s approach to access the kinetics triplet (activation energy, pre-exponential factor and order of reaction) in order to compare the thermal behavior of PANI with its POEA and POMA derivatives.

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

Alves, W. F., Malmonge, J. A., Mattoso, L. H. C., & Medeiros, E. S.

2. Materials and Methods 2.1 Materials Polyaniline (PANI), poly(o-methoxyaniline) (POMA) and poly(o-ethoxyaniline) (POEA) were chemically synthesized according to the method described in the literature[10,11].

Briefly, the monomers of conducting polymers were dissolved in an acidic solution (HCl 1,0 M) separately and cooled to low temperature (0-2 °C). After cooling period, the solution containing the oxidant ((NH4)2S2O8) was poured in the acidic solution with the monomers. After 2 hours of reaction time, for the formation of the polyaniline, and 4 hours, for the formation of the derivatives, all polymers in the doped state (emeraldine salt, ES) were filtered, rinsed with distilled water and dried. Dedoping was performed by treatment with a 0.1 M ammonium hydroxide aqueous solution for 16 hours at a room temperature (~25 °C) to convert these polymers to the emeraldine base form (EB). Then they were filtered and transferred to a desiccator to dry under vacuum for 24 hours at a room temperature (~25oC) prior to thermal analyses.

2.2 Flinn-Wall-Ozawa’s approach A model Q 600 TA Instruments TGA was used to investigate the kinetics of thermal decomposition of the polymers, which was carried out in a platinum crucible.

About 10 mg of the conducting polymers were run using dynamic scans from 25 to 900 °C, at constant heating rates of 10, 20, 30 and 40oC/min under nitrogen and synthetic air atmospheres, at a flow rate of 50 mL/min.

In order to obtain the kinetic parameters of polymer degradation, thermogravimetric curves were analyzed according to Flynn–Wall–Ozawa’s approach using the methodology described in our previous works on rubber decomposition[12]. Briefly, when a polymeric material undergoes thermal decomposition according to the reaction aA (s) → bB(s) + cC(g) , if the decomposition starts at a temperature (T0) and is carried out at a linear increasing in temperature (T=T0+βt), where β is the constant heating rate (β = dT ), the thermal decomposition events can be dt

described by the following expression[13-16]: E  AE  = ln β ln  − ln( F (α)) (1)  − 5.3305 − 1.0516 R RT  

where, α is the fraction of the polymer that undergoes decomposition or the conversion degree, A is the pre-exponential factor, E is the activation energy of the degradation process, R is the gas constant and F(α) is a power series expansion.

Therefore, for a constant degree of conversion (α=constant), a plot of ln(β) versus 1/T, obtained from TGA curves, recorded at several constant heating rates (β), should result in a straight line whose slope is approximately –1.0516E/R. The reaction order can be determined by an extension of Avrami’s theory to describe non-isothermal as: ln{− ln[1 − α(T= )]} ln( A) −

E − n ln(β) (2) RT

Hence, a plot of ln[-ln(1-α(T ))] versus ln(β), which is obtained at the same temperature from a number of isotherms taken at different heating rates, should yield straight lines whose slope is reaction order or the Flynn-Wall-Ozawa’s exponent (n)[18-20]:

3. Results and Discussions Thermogravimetric curves of PANI, POMA and POEA at the heating rate of 10oC/min under nitrogen (a) and oxidative atmosphere (c) are shown in Figure 1. It can be observed in Figure 1a, as expected, that the onset of the thermal decomposition of PANI under nitrogen atmosphere occurs at 473°C and about 49.2% of residue is formed at 700°C; for POMA and POEA, the thermal decomposition starts, respectively, at 362 and 337°C, with 51.0 and 41.7% residue at 700°C. Figure 1b shows that PANI decomposition under oxidative atmosphere starts at 411°C with practically no residue after 650 °C; POMA and POEA had, respectively, onsets of decomposition at 283 and 289°C and, similarly to PANI, no residue after 650oC. The decomposition path of the samples under nitrogen and the oxidative atmosphere are different. While, under nitrogen atmosphere, degradation shows an ordinary path with 41.7% residue due to the protective atmosphere that causes a controlled degradation, the oxidative atmosphere, after the onset of degradation, had an almost sharp decrease in weight beause the presence of oxygen molecules combine with some of the degradation products to form volatiles such as carbon mono and dioxide decreasing considerably the amount of residues after 650°C.

Figure 1. Thermogravimetric curves showing the stepwise degradation of conducting PANI (Polyaniline) and its derivatives POEA (Poly(o-ethoxyaniline)) and POMA (Poly(o-methoxyaniline)) under: (a) nitrogen and (b) oxidative atmosphere at a heating rate of 10oC/min.

286 286/292

Polímeros, 28(4), 285-292, 2018

Non-isothermal decomposition kinetics of conductive polyaniline and its derivatives Comparing the onset temperatures under nitrogen and oxygen, PANI presents highest onset temperature, indicating therefore the highest thermal stability among its derivatives.

This might have taken place probably due to the high density of hydrogen bond between chains, which is a drawback in PANI dissolution, and because PANI has no alkyl group (eg methoxy and ethoxy) which facilitates the cross-linking reaction in pristine PANI, while in its derivatives these alkyl groups prevent cross-linking (due to steric hindrance) from taking place during heating[19]. Therefore, as the temperature increases, cross-links between PANI takes place between chains to form a more thermally stable structures[20,21].

The kinetics of thermal decomposition of conducting polymers was studied by thermogravimetry at different heating rates, and the kinetic parameters were calculated using the method Flynn-Wall-Ozawa[22-26]. The weight loss as a function of the temperature for the heating rates of 10, 20, 30 and 40°C/min is shown in Figure 2.

Figure 2 shows that for both the atmospheres (inert and oxidative) an increase in heating rate caused the decay curves to shift to higher temperatures, and profiles of the curves of thermal decomposition of conducting polymers have the same behavior, which is a consequence of the events having

Figure 2. Thermogravimetric curves of PANI (Polyaniline) and its derivatives POEA (Poly(o-ethoxyaniline)) and POMA (Poly(o-methoxyaniline)) under nitrogen atmosphere (a, c, e) and oxidative (b, d, f) atmosphere at the decomposition rates of 10, 20 30 and 40 ° C/min.

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Alves, W. F., Malmonge, J. A., Mattoso, L. H. C., & Medeiros, E. S. less time to take place as well as poorer heat diffusion into the samples, a well-known fact in TGA analysis of polymers.

From Equation 1, it was possible to calculate the activation energy over the entire range of decomposition of conducting polymers under both nitrogen and synthetic air atmospheres. Taking the ln [-ln (1-a (T))] vs ln (b), the slope, the activation energy Ea was calculated and the y-axis intercept used to determines the pre-exponential factor A as described earlier and shown in Figure 3.

Figure 3a, b shows a plot of the activation energy as a function of weight loss PANI, POMA and POEA in nitrogen and oxygen atmospheres. In general, PANI displayed a somewhat higher energy of activation for degradation in both atmospheres as compared to POMA and POEA. These results are in agreement with the results of the onset of thermal decomposition of PANI as already discussed.

Moreover, comparing the effect of the atmospheres on Ea values, one can observe that the activation energy values under nitrogen are slightly higher than under oxidative atmosphere. This happened because the presence of oxygen is known to catalyze the thermal decomposition of polymers. Moreover, along the degradation pathway, in the active pyrolysis region of the curve, the activation energy under oxygen remained almost constant while for nitrogen it started to increase after 40% conversion. This might have happened because of the formation of cross-linked structures, at higher extent to PANI and lower to POMA and POEA, which resulted in a more thermally stable structure.

Wang et al.[21], synthesized and characterized the thermal property of polyanilina with ZrO2, forming the composite NIBP/ZrO2, comparing the Ea, using Ozawa-Flynn-Wall.

The authors found that the Ea of PANI, in air atmosphere was below 100 kJ.mol-1, while the PANI/ZrO2 presented Ea values above 100 kJ.mol-1. These results are also in the same range of values found by Corradini et al.[26] who compared the thermal stability of various types of cotton using Ozawa’s model, in determining the activation energy for white cotton fibers.

Tables 1 and 2 show the pre-exponential values of thermal decomposition for PANI, POEA and POMA, respectively, under inert and oxidative atmosphere.

It can be also observed in Table 1 that the values of the pre-exponential factors for PANI, POMA and POEA as a function of the extent of thermal decomposition from 10 to 90% did not show any significant differences when comparing between the polymers. However, comparing nitrogen or oxygen atmospheres, ln(A) values were significantly lower to oxygen than to nitrogen. For the values of pre-exponential factors under oxidative atmosphere, there is a decrease in ln(A) with increasing mass loss, especially in the range between 10 and 50%. These differences can be explained by the fact that under nitrogen atmosphere the active pyrolysis region occurs oven a narrower range of temperature than under oxygen as can be seen in DTG curves (Figure 4).

This behavior (Figure 4) is due to the fact that under protective (inert) atmosphere the degradation steps are fewer

Figure 3. Curve vs. Ea. α (T) of conducting PANI (Polyaniline) and its derivatives POEA (Poly(o-ethoxyaniline)) and POMA (Poly(o-methoxyaniline)) in the atmosphere (a) nitrogen and (b) oxygen.

Table 1. Table of values pre-exponential factor of conducting polymers under nitrogen atmosphere. α (%) 10 15 20 25 30 35 40 45 50

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PANI (Polyaniline) 26.82 ± 1.98 25.47 ± 2.09 24.96 ± 2.30 24.87 ± 2.36 25.30 ±2.37 25.32 ± 2.80 25.97 ±2.74 26.50 ± 3.10 37.72 ± 8.84

ln (A) POMA (Poly(o-methoxyaniline)) 26.31 ±2.52 26.87 ± 1.95 27.47 ± 2.17 27.91 ± 2.22 27.40 ± 2.27 26.15 ± 3.30 24.48 ± 3.15 23.37 ± 4.77 25.19 ± 8.19

POEA (Poly(o-ethoxyaniline)) 27.00 ± 1.60 26.63 ±1.63 26.87 ± 1.66 27.05 ± 1.93 27.24 ± 1.82 27.12 ± 2.09 30.72 ± 2.10 30.70 ± 2.09 30.51 ± 3.20

Polímeros, 28(4), 285-292, 2018

Non-isothermal decomposition kinetics of conductive polyaniline and its derivatives Table 2. Pre-exponential factor of the conducting polymers under synthetic air atmosphere. α (%) 10 20 30 40 50 60 70 80 90

PANI (Polyaniline) 23.25 ± 2.25 19.67 ± 1.79 18.66 ± 1.80 18.11 ± 1.48 12.22 ± 1.52 16.30 ± 1.35 15.57 ± 1.31 15.34 ± 1.24 15.60 ± 1.15

ln (A) POMA (Poly(o-methoxyaniline)) 22.90 ±1.57 20.37 ± 1.57 17.77 ± 1.36 17.72 ± 1.27 18.03 ± 1.25 17.58 ± 1.36 16.98 ± 1.42 16.38 ± 1.38 16.57 ± 1.27

POEA (Poly(o-ethoxyaniline)) 20.12 ± 0.98 16.92 ±0.38 15.71 ± 0.17 15.57 ± 0.10 15.31 ± 0.26 14.64 ± 0.61 14.12 ± 0.70 13.92 ± 0.98 13.68 ± 0.82

Figure 4. First derivative thermogravimetric (DTG) curves as a function of the heating rates for PANI (Polyaniline) and its derivatives POEA (Poly(o-ethoxyaniline)) and POMA (Poly(o-methoxyaniline)) under nitrogen (a, c, e) and oxidative (b, d, f) atmosphere.

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Alves, W. F., Malmonge, J. A., Mattoso, L. H. C., & Medeiros, E. S. and more uniform, without many side reactions. On the other hand, the presence of oxygen, as already pointed out, catalyzes the oxidative degradation giving rise to a multi-step degradation (Figure 5), with several reactions occurring simultaneously, and thus producing a series of intermediary compounds that degrade over a broader range of temperature. As the temperature increases, the random break the bonds along polymer backbone gives rise to the formation of free radicals that attack other polymer chains, forming radicals and, ultimately, intermediary compounds.

The order of decomposition reaction, n, of conducting polymers was obtained from the slope of ln[-ln (1- α (T))] vs ln (β), as shown in Figure 6.

It is observed in Figure 6 that the order of reaction (n) varied with the temperature for both atmospheres. A noteworthy observation is the overall shape of the n versus temperature curve.

It has a bell-shaped form to all polymers under nitrogen as a consequence of a more uniform and controlled decomposition similarly to other polymers such as rubbers[27,28]. However,

Figure 5. Scheme of general degradation of polymers by oxidation[27].

shape of the n versus temperature curve of the decomposition of PANI, POEA and POMA under oxygen is very different due to the multi-step degradation abovementioned.

The decomposition the kinetic models described by Coats and Redfern[29], Broido[30] and Horowitz and Metzger[31], the determination of kinetic parameters, are accomplished by considering the reaction order to be equal to 1 throughout decomposition range. According to the results obtained here, it was observed that reaction order varies between 0 and 1.1 instead of being constant. These values indicate that a complex decomposition process is taking place.

While it is more predictable and uniform to reactions under nitrogen atmosphere, the presence of oxygen in the oxidative decomposition makes the reaction mechanisms more complex with oxygen intermediating and catalyzing side reactions as the temperature increases.

4. Conclusions The kinetics of decomposition of PANI, POEA and POMA was carried out using the Flynn-Wall-Ozawa method access the decomposition triplet (energy of activation, pre-exponential factor and reaction order) under oxidative and inert atmospheres. It was observed that PANI showed a higher activation energies than POMA and POEA. The lower values Ea for POMA and POEA could be due to alkyl groups that decrease cross-linking formation thus decreasing the thermal stability of these polymers. There were no significant differences in pre-exponential parameters of conducting polymers when comparing among these polymers.

However, the order of degradation reaction, which varied from ca. 0 to 1.1 was very dependent on the atmosphere.

This behavior was thus attributed to the presence of oxygen that makes the oxidative degradation more complex than under nitrogen. In general, there was a trend for PANI to be the most thermally stable polymer among them.

Figure 6. Flinn-Wall-Ozawa exponent (n) versus temperature for PANI (Polyaniline) and its derivatives POEA (Poly(o-ethoxyaniline)) and POMA (Poly(o-methoxyaniline)) under (a) nitrogen and (b) oxygen atmosphere.

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Non-isothermal decomposition kinetics of conductive polyaniline and its derivatives

5. Acknowledgements The authors acknowledge the financial support given

by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação de Amparo à Pesquisa do Estado do Acre (FAPAC).

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Received: July 17, 2016 Revised: Feb. 17, 2017 Accepted: Mar. 19, 2017

PolĂ­meros, 28(4), 285-292, 2018

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.02717

Nafion/sulfonated poly(indene) polyelectrolyte membranes for fuel cell application Jeanne Leticia da Silva Marques1, Ana Paula Soares Zanatta1, Mariska Hattenberger1 and Maria Madalena de Camargo Forte1* Laboratório de Materiais Poliméricos – LaPol, Escola de Engenharia – EE, Universidade Federal do Rio Grande do Sul – UFRGS, Porto Alegre, RS, Brasil

1

*mmcforte@ufrgs.br

Abstract Sulfonated poly(indene) (SPInd), with 35% and 45% degree of sulfonation, was blended with Nafion to prepare blended membranes with 10, 15 and 20 wt.% of SPInd. Membranes were evaluated by infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy and X-ray diffraction. Water uptake (WU), ion exchange capacity (IEC) and through-plane proton conductivity were measured. The membranes presented similar thermal stability to Nafion. WU was slightly higher for Nafion/SPInd membranes (19-21% at RT and 40-44% at 90 °C) compared with recast Nafion (16% and 34%, respectively), and IEC values showed a similar trend. Blended Nafion membranes had increased proton conductivity of 2.41 x 10-2 and 2.37 x 10-2 Scm-1 (20 wt. % of SPInd 35% and 45%, respectively), compared with 1.16 x 10-2 Scm-1 for recast Nafion. The results show that the addition of SPInd to Nafion is a potential route towards improving the performance of Nafion in proton conductivity for use in fuel cells devices.

Keywords: blended membrane, Nafion, proton exchange membrane, sulfonated poly(indene).

1. Introduction Fuel cell technology has emerged in recent years as a keystone for future energy supply. Notably, proton exchange membrane fuel cells (PEMFCs), with high efficiency and high power density, are well suited to a variety of applications, including residential power generation, transport (mainly automobile industry) and portable electronics. Hydrogen powered vehicles using Polymer Electrolyte Membrane Fuel Cells (PEMFCs) have been demonstrated by a number of auto manufacturers and hydrogen powered buses are in service in several cities[1-3]. Basically, a PEMFC electrochemically converts hydrogen and oxygen into electrical power, heat, and water. In PEMFCs, the proton exchange membrane (PEM) conducts protons from the anode to the cathode, acts as a barrier to the fuel and separates the electrodes. Although PEMFCs offer several advantages, including the possibility of using renewable fuels and having minimal environmental impact, there are also several key shortcomings with current PEMs that hinder fuel cell efficiency. These shortcomings include low proton conductivity at higher temperatures, poor water management and high fuel crossover[4,5].

Currently, the most popular PEMs used in fuel cells devices are Nafion membranes. The commercial polymer consists of a perfluorosulfonic acid-polytetrafluoroethylene ethylene (PFSA-PTFE) copolymer, with a tetrafluoroethylene backbone and perfluorinated vinyl ether side chains terminated with sulfonic acid groups. Nafion membranes are still quite expensive for large-scale application in PEMFCs[6,7] and although they offer high proton conductivity and good chemical, thermal, mechanical stability, an ideal PEM must be of low cost. Typically, they have micro- or nanophase

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morphological structure comprised of a hydrophobic matrix and interconnected hydrophilic ionic clusters, called ionic channels[8]. Proton conduction occurs via the ionic channels in the hydrated membrane and has a strong dependence on the water content as well as the operating temperature, usually between 80 °C and 100 °C[9]. Nafion continues to be at the focus of research due to the superior performance, and hence, Nafion composites containing other polymers or inorganic compounds have been widely studied[8-10]. Great efforts have been made to prepare the composite membranes based on Nafion to improve the performance and reduce the cost of the membranes used for FCs. Liyanage et al. reported that Nafion membranes modified with sulfonated organosilicon dendrimers exhibited less swelling (despite a high number of sulfonic acid groups), and higher ion exchange capacity and water retention[10]. Liu et al.[11] reported that Nafion membranes with 0.05 wt.% of functionalized multiwalled carbon nanotubes (MWCNTs) showed a 1.5-fold increase in mechanical strength and a five-fold increase in proton conductivity.

In this work, membrane blends were produced to be applied in PEMFCs using hydrogen as fuel. Nafion was modified with sulfonated poly(indene) (SPInd) using a simple, inexpensive process, aiming to improve the membrane water content, while maintaining good proton conductivity. SPInd was obtained through the sulfonation of poly(indene) with chlorosulfonic acid, previously reported by our group as a potential polymer electrolyte[12]. The SPInd has a thermally stable cyclic backbone with sulfonic groups attached to phenylene groups, making it hydrophilic. Nafion/SPInd

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

Marques, J. L. S., Zanatta, A. P. S., Hattenberger, M., & Forte, M. M. C. membranes were prepared by solution casting, using different contents of SPInd with sulfonation degrees of both 35% and 45%. The thermal, physicochemical and morphological characteristics of these membranes were investigated.

2. Materials and Methods 2.1 Materials Chlorosulfonic acid (ClSO3H; ≥ 98%) was purchased from Merck. 1, 2-dichloroethane (DCE, 99%), n-hexane (95%) and ethanol (96%) were purchased from Neon.

Dimethylacetamide (DMAc; PA) was purchased from Sigma Aldrich. All reagents were used as received. The Nafion solution (LiquionTM; 1100 EW, 15 wt. %) was purchased from Ion Power, Inc. Poly(indene) (PInd) (Mn = 45,000 g.mol-1) was synthesized by cationic polymerization of indene as described in a previous article published by our group[13].

2.2 Poly(indene) sulfonation The sulfonated poly(indene) (SPInd) was obtained by the sulfonation of PInd with chlorosulfonic acid.

PInd (10g/0.086 mol) was dissolved in DCE (60 ml), under stirring, in a four-necked flask and then cooled at -2 °C. Chlorosulfonic acid (0.029 or 0.036 mol) was dissolved in DCE (10 ml) and was added dropwise in the PInd solution.

The reactant mixture was stirred at 500 rpm for 2 h at -2 °C. The reaction was stopped by adding ethanol and the product was filtered and washed with hexane until the pH was between 6 and 7. The sulfonated poly(indene) (SPInd) was dried at 60 °C for 24 h, and kept in a desiccator in the dark.

Two samples of SPInd, with degree of sulfonation (DS) of 35% (SPInd35) and 45% (SPInd45), were prepared and both had a brownish color.

2.3 Membrane preparation Nafion (15 wt. %) and SPInd (20 wt. %) were dissolved separately in DMAc at room temperature. Pre-determined volumes of SPInd and Nafion solutions were mixed under stirring at room temperature. The recast Nafion and Nafion/SPInd membranes were obtained by pouring the DMAc solutions onto a glass Petri dish and evaporating the solvent under vacuum at 60 °C for 24 h. The membranes were removed from the Petri dishes by immersing them in water. Flexible and transparent yellowish membranes were obtained and after being dried at 140 °C for 2 h, the thicknesses were around 280 ± 30 µm. Blended Nafion/SPInd membranes were prepared with 10, 15 and 20 wt. % of SPInd. More than 20% of SPInd lead to poor miscibility and water-soluble domains in the membrane. The Nafion/SPInd membranes were dipped in a 3 wt. % H2O2 solution at 80 °C for 1 h to oxidize the organic impurities. The membranes were immersed in DI water for 1 h and then activated with a 0.5M H2SO4 solution at 80 °C for 1 h. Finally, the membranes were rinsed with DI water until a neutral pH was measured in the water. All membranes were stored in DI water, at room temperature and in the dark until use.

was performed with KBr pellet over the wavelength range of 400-4000 cm−1.

2.5 Thermal properties of the membranes Thermogravimetric analysis (TGA) of the membranes was performed on a Shimadzu TGA-50 analyzer raising the temperature from 25 °C to 800 °C at a heating rate of 20 °C min−1, under nitrogen atmosphere. Prior to analysis, the membranes were heated at 110 °C for 3 h in an oven to remove the moisture. Calorimetric analysis of the membranes was evaluated using a differential scanning calorimeter (DSC) (TA Instruments model 2910) raising the temperature from 40 °C to 240 °C at a heating rate of 10 °C min−1, under nitrogen atmosphere. The membranes were heated to 120 °C and kept at this temperature for 5 min to eliminate the water, cooled to 20 °C, and then re-heated to 200 °C (second run).

The second endothermic curve was analyzed.

2.6 SEM and XRD analysis The morphology of the cross-sectional area of the membranes was examined using a Jeol JSM 6060 field emission scanning electron microscope (SEM). The cryogenic fracture surface of the specimens was sputter coated with Au for 120 s. X-ray diffraction (XRD) analysis of the membranes was performed on a Philips diffractometer (X-Pert MPD) using a Cu Kα X-ray source (wavelength λ = 1.54056 Å) and a 2θ range of 5° to 50° with a scanning rate of 3° min-1 and scanning step of 0.05°/s, at 40mA and 40 kV. Before the measurements were taken, the membrane specimens were fixed on a glass sample holder and equilibrated under room temperature/pressure conditions for 24h.

2.7 Water uptake and ion exchange capacity of the membranes The membranes were dried under vacuum at 80 °C until a constant weight (Wdry) was obtained. Pre-weighed dry membrane specimens of 2 cm2 were soaked in deionized water at room temperature for 24 h and then heated to 90 °C. After 1 h the specimens were cooled to room temperature, removed from the water, wiped with tissue paper and weighed (Wwet). The water uptake of the membranes was determined by correlating the weight differences of the hydrated (Wwet) and dry (Wdry) membrane according to Equation 1.

Water Uptake =

Wwet − Wdry x100% (1) Wdry

The ion exchange capacity (IEC) of the membranes, expressed in mequiv. g−1, was determined using acid-base titration. The membrane specimens (2 cm2), dried under vacuum at 80 °C to a constant weight, were soaked in a 1 M NaCl solution and equilibrated for at least 24 h to allow exchange between the H+ and Na+ ions. Aliquots of the solution, in duplicate, were titrated with a 0.01 M NaOH solution to determine the HCl concentration in the medium.

The IEC was calculated as the milliequivalents of sulfonic groups per gram of dried sample.

2.4 Fourier Transform Infrared Spectroscopy (FT-IR)

2.8 Proton conductivity

The membranes were analyzed using a Perkin Elmer FT-IR spectrometer (Spectrum 1000) to identify the main groups present in the blended membranes. The analysis

The proton conductivity of the membrane specimens was measured in the transversal direction in a proton conductivity cell, immersed in deionized water at room temperature.

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Nafion/sulfonated poly(indene) polyelectrolyte membranes for fuel cell application The stainless-steel electrode of the cell, with an area of 1.77cm2, was connected to an AC impedance analyzer (PGSTAT 30/FRA 2, Autolab). In the frequency response analysis (FRA) software, an oscillation potential of 10 mV, from 1 MHz to 1 Hz, was used. The proton conductivity (σ) was calculated by applying Equation 2: σ=

l (2) RA

where: σ is the proton conductivity (S/cm), l is the thickness of the membrane (cm) or the distance between the electrodes, R is the ohmic resistance of the membrane (Ω), obtained by impedance analysis, and A is the cross-sectional area of the membrane (cm2). The membrane thickness was determined with a Byko-test 7500 (BYK GARDNER) gage. The resistance (R) was obtained at the high frequency intercept on the real axis (Z’) of the impedance spectrum.

3. Results and Discussions Poly(indene) (PInd) has a repeating unit comprised of a five-membered ring with an aromatic ring attached to it, which easily undergoes electrophilic substitution with a sulfonic acid (-SO3H) group. Sulfonated poly(indene) (SPInd) shows thermal stability up to 200 ºC and good proton conductivity[12].

SPInd with DS 35 or 45% (SPInd35 and SPInd45, respectively) was used to prepare blended Nafion/SPInd membranes with 10, 15 or 20 wt.% SPInd. Figure 1 shows the FT-IR spectra for the SPInd35, recast Nafion and Nafion/SPInd35 membranes. All spectra show abroad band at 3450 cm-1 arising from the -OH vibration of water linked to the hydrophilic -SO3H groups[14]. On the SPInd spectrum the aromatic C-C band is split into two peaks, at 1470cm−1and 1493cm−1, due to the presence of sulfonated and non-sulfonated rings. The absorption peak at 1022cm−1 was associated with the S=O stretching vibration. The absorption peaks at 1080cm−1 and 1250cm−1 were associated with the symmetrical O=S=O stretching vibration, and the asymmetric stretching vibration of the sulfonic groups, respectively. The absorption at 1650cm−1 was attributed to the backbone carbonyl-stretching band[15].

The spectrum also showed peaks at 1200cm−1 and 1144cm−1 associated with the asymmetric and symmetric F-C-F stretching vibrations, respectively. The bands at 1410cm−1 and 850cm−1 correspond to S=O and S-OH stretching of the SO3H group and the band at 1052cm−1 was related to the symmetric SO3− stretching vibration[16]. For comparison, the FT-IR and NMR spectra for PInd and SPInd20 were reported in previous publications from our group[12,13].

Figure 2 shows the thermogravimetric (TG) and derivative (DTG) curves of recast Nafion and blended Nafion/SPInd membranes. A modification of the Nafion degradation curve profile is observed due to the SPInd incorporation in the membrane and a lower chain degradation maximum temperature. The membranes degradation under nitrogen may be analyzed in relation to three distinct temperature ranges: (I) 50 to 200 °C due to a gradual loss of water; (II) 200 to 425 °C due to the desulfonation process and side chain decomposition; (III) 425 to 600 °C due to the PTFE and SPInd backbone degradation. The apex temperature (Tmax) in each range and the correspondent mass loss, as well as the residue at 800 °C are shown in Table 1. The water content of the membranes depends on the water uptake and linked water retained in it. The water mass loss of the Nafion blended membranes remained at the same order of magnitude, since previously the analyses were heated in an oven at 110 °C for 3 h. The water content in the Nafion/SPInd membranes is higher than in recast Nafion due to a higher content of -SO3H group in the membrane.

The high mass loss of the Nafion/SPInd45-10 can be due to a non-homogeneous specimen.

The high mass loss of the blended membranes in the range II is a consequence of the higher decomposition of -SO3H groups[17,18] present in these membranes. In the range III, the lower mass loss of the blended membranes is because the SPInd has an aromatic hydrocarbon main chain that undergoes carbonization during the -SO3H groups decomposition. This process is corroborated by a higher residue content at 800 °C. The low residue (0.6%) of recast-Nafion at 800 °C indicates a better oxidation and degradation process of a fluorocarbon backbone compared to an aromatic one. Usually hydrocarbons with an aromatic or

Figure 1. FT-IR spectra of recast Nafion, SPInd35 and Nafion/SPInd35 membranes.

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Marques, J. L. S., Zanatta, A. P. S., Hattenberger, M., & Forte, M. M. C.

Figure 2. TG and DTG curves of Nafion/SPInd35 (a,b) and Nafion/SPInd45 (c,d) membranes comparatively to recast Nafion.

Table 1. Maximum temperature and mass loss in the degradation ranges and residue at 800 ºC of recast and blended Nafion/SPInd membranes.

I Membrane Recast Nafion Nafion/SPInd35-10 Nafion/SPInd35-15 Nafion/SPInd35-20 Nafion/SPInd45-10 Nafion/SPInd45-15 Nafion/SPInd45-20

Tmax

II

T<200 °C Mass loss

(°C) No observed 86 85 85 85 87 82

(%) 1.6 4.6 4.0 4.9 6.5 4.4 4.5

(°C) 350 379 379 370 380 376 362

cyclic backbone undergo ring condensation and carbonization at high temperature and inert conditions resulting in high residue content (2.5-7.6%).

Figure 3 shows endothermic curves of the second DSC run for recast and blended Nafion membranes in the range of 40 to 240 °C, after annealing at 120 °C (1st run) for 5 min to eliminate the water. The short broad endothermic peak with the apex at around 160 °C is due water evaporation and 296 296/301

III

200 to 425 °C Tmax Mass loss (%) 10.4 20.5 20.4 18.2 19.9 19.4 16.5

Residue

425 to 600 °C Tmax Mass loss

(°C) 512 498 504 509 472 506 512

(%) 87.4 70.2 70.0 69.3 71.1 71.9 73.7

at 800 °C (%) 0.6 4.7 5.6 7.6 2.5 4.3 5.3

shows that the membranes have water molecules strongly bound into -SO3H groups. Thus, the membranes contain some highly stable hydrophilic clusters. The SPInd content seems to have a variable effect on the endothermic peak and apex temperature, which may result from variations in the dryness of the sample analyzed. It was observed that the membranes can retain water molecules even when maintained at temperatures higher than 100 °C. Polímeros, 28(4), 293-301, 2018

Nafion/sulfonated poly(indene) polyelectrolyte membranes for fuel cell application Similarly, to Nafion, SPInd is polymer with hydrophobic and hydrophilic domains, and when these polymers are blended chain molecules are reorganized per the affinity of domains. Water uptake plays an important role in the proton

Figure 3. Second run DSC endothermic curves of recast and blended Nafion/SPInd membranes.

transport and mechanical properties of a polymer electrolyte membrane (PEM)[19]. At temperatures below 100 °C, the water molecules facilitate the proton movement through the PEM membrane. The translocation of protons occurs via chemical exchange through a mechanism involving the reorganization of the hydrogen bonded water network, which provides sufficient ionic diffusivity[20]. Thus, an adequate level of water molecules is necessary to maintain a good level of proton conductivity. On the other hand, the water content should be optimized to ensure low fuel permeability.

The presence of sulfonic acid groups (-SO3H), further increased by the SPInd polymer, makes the hydrocarbon resin hydrophilic. Due to the interaction with water molecules via intermolecular hydrogen bonding, the hydrophilic channel volume and the size of the ionic domains in the microstructure is enhanced[21]. The performance of the membrane is also dependent on its morphological structure and hydrophilic and hydrophobic phase segregation, both of which strongly affect the proton conductivity of the membrane. Figure 4 shows SEM micrographs of the cross-sectional fractured surfaces of the membranes prepared with 10 to 20% of SPInd35 (a-c), 10 and 15% of SPInd45 (d and e), and recast Nafion (f). Comparison of Nafion/SPInd35-15 and

Figure 4. SEM images of the fractured surfaces of the blended membranes with 10 (a), 15 (b) and 20 wt. % (c) of SPInd35; and 10 (d) and 15 wt. % (e) of SPInd45; and recast Nafion (f).

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Marques, J. L. S., Zanatta, A. P. S., Hattenberger, M., & Forte, M. M. C. Nafion/SPInd45-15 (b and e) shows that phase segregation occurred for the membranes when SPInd with a lower degree of sulfonation was used. It is apparent that if the SPInd contains fewer polar groups that the affinity with the perfluorosulfonated polymer is lower, evidenced by the formation of particles in the fractured surface (a-c).

A slightly higher degree of sulfonation (SPInd45) changes the polymer polarity and a more compatible blend with the perfluorosulfonated polymer was possible. It can be seen in Figures 4d,e that the blended Nafion/SPInd morphology resembled recast Nafion (f). Thus, the dispersion of SPInd45 in the Nafion matrix produced a more homogeneous blend with no aggregation or domains of the sulfonated polymer.

Blended Nafion/SPInd membranes resulted in uniform membranes but some fragile while handling.

Figure 5 shows the XRD spectra for the recast and blended Nafion/SPInd membranes. Nafion membranes are made from the copolymers of long branching perfluoro sulfonic acid monomers (PFSA) and long sequences of tetrafluoroethylene (PTFE) that may crystallize and presents a weak XRD reflection at 2θ equal to 18° due to the (1 0 0) plane. The peak at 2θ of 39° is of the order of the distance between the nearest neighboring CF2 units[22]. The recast Nafion and blended Nafion/SPInd membranes showed the characteristic XRD reflection at 2θ (=18°), superimposed as a shoulder on a large amorphous halo. For blended membranes, the full width at half maximum (FWHM) decreased with an increase in the SPInd content, due to the degree of crystallite perfection which gradually improved[23]. The XRD peak pattern profile variation shows that the structure in the membranes was slightly changed by the introduction of SPInd. The shift in the peak to a higher 2θ angle indicates that the inter-planar spacing in the blended membrane was reduced with the introduction of the SPInd relative to that of the recast Nafion. By applying Bragg’s law (λ=2d sin θ), it was estimated that the distance between the planes of the recast Nafion (0.520 nm) was slightly reduced to 0.506 nm and 0.499 nm for Nafion/SPInd35 and Nafion/SPInd45, respectively. A similar trend was observed by Rhee et al. for Nafion/sulfonated montmorillonite composite membranes[24].

Figure 6 shows the water uptake of the Nafion/SPInd membranes after being soaked in water at room temperature (30 °C). The SPInd increased the membrane water uptake due to increased sulfonic acid content, compared to the pristine Nafion membrane. Water uptake for SPInd35 was slightly higher than for SPInd45. Whereas the sulfonation degree (SD) of 45% was determinant for a morphology more like to the Nafion, SD of 35% or 45% did not have significance on water uptake at room temperature.

Figure 7 shows the Nafion/SPInd membranes’ water uptake as a function of temperature. At room temperature, the water uptake of the blended membranes was of 19 to 21%, compared to 16% for the recast Nafion. As expected, water uptake increased with the temperature increasing, and as higher the temperature more significant was the sulfonation degree and SPInd content, due to a higher concentration of -SO3H groups in the membranes[13]. At 90 °C, the water uptake of the membranes Nafion/SPInd35 and Nafion/SPInd45 increased to 40-44% and 38-43%, respectively.

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In agreement with these results, Amjadi et al. reported similar trends for the water uptake of composite membranes prepared from Nafion and SiO2[25]. It was reported that water sorption of Nafion membranes increases with temperature due to an increase in the specific volume, and as well as a

Figure 5. XRD spectra of recast and Nafion/SPInd membranes.

Figure 6. Water uptake at room temperature of recast and blended Nafion/SPInd membranes as a function of SPInd content.

Figure 7. Water uptake of the Nafion/SPInd membranes as a function of temperature.

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Nafion/sulfonated poly(indene) polyelectrolyte membranes for fuel cell application drop-in Young’s Modulus[26,27]. In amorphous polymers, the free volume has great influence in the specific volume mainly in temperatures closer and above the polymer glass transition (Tg). Higher free volume allows greater water sorption.

The Nafion’s Tg is around 120 °C and the SPInd’s Tg is above 200 °C[11]. In the glass state, the free volume remains constant and increases as the temperature approaches to Tg’s interval. The increasing of Nafion water uptake with the temperature is linear and is driven by the increase of the free volume fraction or specific volume below the Tg. The water uptake of the blended Nafion/SPInd besides the Nafion free volume contribution is influenced by the -SO3H concentration in the membrane. There is no contribution of the free volume fraction of the SPInd since the highest temperature evaluated is quite far of its Tg. It is known that higher temperatures facilitate the fuel cross-over through the free volume of a membrane. Thus, hypothetically the SPInd domains with high Tg may help to depress the cross-over in the blended Nafion/SPInd membrane.

Values obtained for the membrane ion exchange capacity (IEC) as a function of SPInd content can be seen in Figure 8.

The IEC value for recast Nafion was 0.93 mequiv.g−1 and the membrane IEC increased as the SPInd content was increased.

Moreover, the Nafion/SPInd membranes showed higher IEC values with increasing DS (1.05 and 1.10 mequiv.g−1 for Nafion/SPInd35-20 and Nafion/SPInd45-20, respectively.

However, it should be noted that the IEC for membranes with the same concentration of SPInd, but different DS values was not significant, indicating that the 10% variation in the DS caused no significant change in the ion exchange capacity. The water uptake values mirror this finding to some extent, as the SPInd with the higher DS did not result higher WU values.

The electrochemical experiments for conductivity measurements at 100% RH at room temperature were carried out with membranes soaked for seven days in DI water.

The Nyquist plots of the Nafion/SPInd35 and Nafion/SPInd45 membranes shown in Figures 9a,b, respectively, exemplify as the membrane ohmic resistance was taken.

The inset in both figures shows an enlargement of the high frequency area of the plot, in which by convention, the membrane ohmic resistance is taken to be represented by the high frequency intercept of the modeled Nyquist plot to the real axis (Z’)[28,29]. The ionic conductivity and thickness of the recast and blended Nafion membranes are indicated in Table 2. Blended Nafion/SPInd membranes had higher conductivity, which increased as the SPInd content increased, when compared with Nafion. The highest ionic conductivities (2.41x10-2 and 2.37x10-2 S cm−1) were observed for Nafion/SPInd35-20 and Nafion/SPInd45-20, respectively.

Thus, the proton conductivity increases as the SPInd content increases. As found in other measurements, the DS did not result in significantly different values. The maximum sulfonation degree of SPInd and percentage in the blend Table 2. Thickness, resistance and conductivity of recast and blended Nafion membranes.

Figure 8. Ion exchange capacity of the Nafion/SPInd membranes as a function of the SPInd35 and SPInd45 content.

Membrane Recast Nafion Nafion/SPInd35-10 Nafion/SPInd35-15 Nafion/SPInd35-20 Nafion/SPInd45-10 Nafion/SPInd45-15 Nafion/SPInd45-20

l (µm) 255 300 269 294 302 307 281

R (Ω) 1.24 0.78 0.65 0.69 0.98 0.81 0.67

δ (x10-2 S cm-1) 1.16 2.17 2.34 2.41 1.74 2.14 2.37

Figure 9. Nyquist plots of the Nafion/SPInd35 (a) and Nafion/SPInd45 (b) membranes.

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Marques, J. L. S., Zanatta, A. P. S., Hattenberger, M., & Forte, M. M. C. is only limited by the SPInd water solubility. Sulfonation degree higher than 45% turn the SPInd totally water soluble, and higher percentage of it in the blend harder the sample solubility in the Nafion matrix.

Proton transport in the membrane relies on the presence of well-connected hydrophilic channels through the membrane, thus the water uptake and morphology of the membrane are crucial factors between others. The sulfonic groups of the SPInd positively contributed to the increased water uptake that enhanced this hydrated pathway. Increased water content in membranes is thought to lead to increased structural diffusion of water resulting in higher proton conductivity[30]. Furthermore, swelling of the ionic domains of the Nafion and SPInd improves the channel connectivity and extension through the membrane. Finally, the addition of extra sulfonated functional groups (-SO3H) via the SPInd blending provided additional protons to the hydrophilic channels, leading to increased transport via the high water content ((H2O)n.H+). Investigation of the mechanical stability, proton conductivity at increased temperature and single cell performance is required, and under way in our group.

4. Conclusions Blended Nafion/SPInd membranes could be prepared by casting from DMAc solution. Sulfonation degree higher than 45% turn the SPInd totally water soluble, and higher percentage of it in the blend harder the sample solubility in the Nafion matrix. Blended Nafion/SPInd membranes resulted in uniform membranes but some fragile while handling, however showed good proton conductivity.

The SPInd slightly increased the water uptake of blended Nafion membranes and the ion exchange capacity at room temperature, and as expected, water uptake increased with the temperature. The higher the temperature more significative the sulfonation degree and the SPInd content were, due to a higher concentration of -SO3H groups in the membranes, while maintaining good thermal properties. The membrane water uptake reduction can be related to the decreasing of free volume in the Nafion matrix and presence of hydrophobic SPInd domains in the blended Nafion/SPInd membranes.

The ionic conductivity of the blended membranes was slightly higher compared with the recast-Nafion membrane prepared under the same conditions. Increased water content in membranes is thought to lead to increased structural diffusion of water resulting in higher proton conductivity.

Proton transport in the membrane relies on the presence of well-connected hydrophilic channels through the membrane, thus the water uptake and morphology of the membrane are crucial factors between others. The sulfonic groups of the SPInd positively contributed to the increased water uptake that enhanced this hydrated pathway. The maintaining IEC and proton conductivity values observed for the blended Nafion/SPInd membranes, indicate promising potential for fuel cell application. Thus, Nafion membranes can be modified with SPInd, a lowest cost polymer, by replacing part of it without loss of conductivity and efficiency.

5. Acknowledgements The financial support from the Brazilian funding agencies Coordination for the Improvement of Higher Education Personnel (CAPES), National Council for 300 300/301

Scientific and Technological Development (CNPq), and Financier of Studies and Projects (FINEP) are greatly acknowledge.

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Received: Mar. 21, 2017 Revised: Aug. 03, 2017 Accepted: Oct. 22, 2017

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.04117

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

Evaluation of the application of cashew gum as an excipient to produce tablets Ana Paula de Sá Pinto1, Kattya Giselle de Holanda e Silva2 and Claudia Regina Elias Mansur1,3* Laboratório de Macromoléculas e Colóides na Indústria do Petróleo, Instituto de Macromoléculas – IMA, Universidade Federal do Rio de Janeiro – UFRJ, Rio de Janeiro, RJ, Brasil 2 Laboratório de Sistemas Híbridos, Faculdade de Farmácia, Universidade Federal do Rio de Janeiro – UFRJ, Rio de Janeiro, RJ, Brasil 3 Programa de Engenharia de Materiais e Metalurgia, Centro de Tecnologia, Instituto Alberto Luiz Coimbra de Pós-graduação e Pesquisa de Engenharia – COPPE, Universidade Federal do Rio de Janeiro – UFRJ, Rio de Janeiro, RJ, Brasil 1

*celias@ima.ufrj.br

Abstract Cashew gum is extracted from the exudate of the giant cashew tree (Anacardium occidentale L.). The objective of this work was to study the extraction and purification of cashew gum through experiments to characterize its structures and physicochemical and thermal properties, and to evaluate its use as a pharmaceutical excipient. The characterization of the materials was performed by infrared spectroscopy, thermogravimetric analysis and rheological studies of powder.

Analysis of the material showed that it has reasonable flow characteristics and compressibility, allowing the use as diluent of tablets. Tablets were produced with a cashew gum isolated and purified by the direct compression method, and it was shown that the tablets produced with the purified cashew gum obtained better mechanical properties (hardness and friability) and less disintegration time than tablets made with gum of cashew isolated, suggesting the use of purified cashew gum as a diluent for this type of pharmaceutical form.

Keywords: cashew gum, pharmaceutical excipient, direct compression, characterization, tablets.

1. Introduction The International Pharmaceutical Excipients Council defines excipients as substances composing pharmaceutical preparations that, although therapeutically inert or inactive, are necessary for their manufacture[1].

Tablets are one of the main forms for oral administration of solid drugs. They are easy to administer and can contain one or multiple drugs. They are prepared with pharmaceutical excipients that facilitate compression during manufacture and guarantee suitable mechanical properties for disintegration and drug release within the body[2]. They can be produced by compression of powders obtained by wet or dry granulation or by direct compression. In the direct compression method, the mixture of powders is compressed without a prior granulation step, reducing the number of steps on the production line and hence the time and cost[3].

The cashew gum from Northeastern Brazil is characterized as a branched heteropolysaccharide acid, which after hydrolysis is basically composed of β-D-galactose (72%), D-glucose (14%), arabinose (4.6%), rhamnose (3.2%) and glucuronic acid (4.7%)[4]. Cashew gum has been studied by various researchers in a wide range of fields, including the pharmaceutical sector. In this respect, this substance has been investigated for the formation of hydrogels, tablet fillers, mucoadhesive propertis, micro and nanoparticles for controlled drug release[5-8].

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Specifically, for production of tablets, cashew gum has been studied as a binder, drug release promoter and former of coating films. All the studies reported in the literature have used the wet granulation method to prepare tablets[6,9-11].

Also, no work has investigated the use of this excipient material as a diluent for tablets.

Another factor that deserves mention is the need to standardize the method to obtain any raw material, to assure its quality and safety, especially for medicinal use[1]. Previous studies of cashew gum have applied various methods to obtain this material, so there is as yet no standardized method for its extraction. Therefore, the objective of this study was to investigate the variables related to the extraction and purification of cashew gum, as well as the possibility of its use as a diluent excipient for production of tablets by the direct compression method.

2. Materials and Methods We used the following materials: cashew gum exudate, collected in the municipality of Severiano Melo, Rio Grande do Norte, Brazil; hydrated ethyl alcohol (95.54° GL); sodium chloride (NaCl) reagent grade, sodium hydroxide reagent grade; and spectroscopic potassium bromide (KBr), all acquired from Vetec Química Fina (Brazil).

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Evaluation of the application of cashew gum as an excipient to produce tablets 2.1 Extraction and purification of cashew gum The following factors were assessed in this respect: sodium chloride (NaCl) concentration; cashew tree exudate concentration in proportion to ethanol 95.54°GL; and number of purification steps.

2.1.1 Determination of the best NaCl concentration Initially the best salt content was evaluated for subsequent use in planning the experiments to evaluate the other factors (concentrations of gum and ethanol). To assess the influence of NaCl concentration, four aqueous solutions were prepared containing 10%w/v of unprocessed (in natura) gum (exudate), which were submitted to magnetic stirring for 24 hours. After this period, the pH of each solution was adjusted to pH 7 with sodium hydroxide 1 M (NaOH). Then, in each 100 mL of gum solution, varied quantities of NaCl were added (3, 5, 7 and 9 g), to obtain solutions called gum-NaCl 3%, 5%, 7% and 9%w/v. These were stirred until the salt was completely dissolved. Then the solutions were centrifuged to remove sand and other solids. The resulting solutions were filtered through a sintered disk funnel with porosity 1. The gum was extracted by precipitation using ethanol 95.54 °GL as non-solvent agent, in the ratio of 4:1 (ethanol:gum solution). After precipitation, the mixture was again centrifuged to separate the precipitate from the hydroalcoholic solution.

The precipitate was frozen and lyophilized and then ground with a mortar to obtain a powder. The isolated cashew gum (ICG) was then purified, by repeating the same routine as in the first step, but without adjusting the pH and adding salt. The amount of salt that will be used in the next steps will be chosen according to the evaluation of the yield obtained at the end of the purification process verified in this topic.

After the purification, the cashew gum (CG) was washed to remove a possible excess salt, as described below (performed in duplicate).

In each centrifuge tube (1, 2 and 3), 2 g of sample (ground CG) and 20 mL of ethanol were added. The tubes were shaken to assure contact of the ethanol with the gum particles. Then the tubes were spun at 4,000 rpm for 5 min.

For tube 1 this process was performed once only. For tube 2, the ethanol was discarded and 20 mL of fresh ethanol was added, followed by the same centrifuging, for two washing steps. For tube 3, the same process was repeated a third time, to complete three washing steps. At the end of the process, the remaining material in each tube after discarding the ethanol (supernatant) was frozen with liquid nitrogen and lyophilized until complete drying of the sample (24 hours). All the samples were ground, and identified as: tube 1- PCGW1, with one washing; tube 2- PCGW2, with two washings; and tube 3- PCGW3, with three washings.

At the end, each sample was ground in an analytic mill (model IKA®-WORKS A11 basic) for 2 minutes.

The resulting isolated and purified gum powders were analyzed by thermogravimetry (TGA) in a TA Instruments TGA Q500 analyzer, using a heating rate of 10 °C/min in a range between 0° and 700 °C, under an inert nitrogen atmosphere.

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2.1.2 22 Factorial design with center point repetitions to study the extraction of cashew gum The influence of the exudate and ethanol concentrations on the extraction yield was studied using a 22 factorial design.

For this purpose, cashew tree exudate solutions were prepared in distilled water at concentrations of 5, 7.5 and 10%w/v (low, level and high level, respectively) at pH 7. Then NaCl was added to reach a salt concentration of 7%w/v in the samples, which were centrifuged and then filtered through a sintered glass disk funnel. The filtrate was submitted to precipitation with ethanol at proportions of ethanol:CG solution of 4:1, 6:1 and 8:1 (low, level and high level, respectively).

Based on the results of the tests described above, it was necessary to perform complementary experiments, varying the exudate concentration (4.0 to 10.0%w/v) while keeping the ethanol proportion constant (4:1), to try to obtain the best results.

2.1.3 Obtaining purified cashew gum The purified cashew gum (PCG), used in the other steps, was obtained under the following extraction and purification conditions, selected based on the factorial experiments described above: NaCl concentration of 7% p/v; exudate concentration in solution of 7.0% p/v; ethanol:exudate solution ratio of 4:1; and three extraction steps, one for isolation and two for purification.

To check whether the number of extraction steps had an influence on the removal of impurities from the gum, a second purification step was performed with the gum sample obtained after the first purification step, following the same procedures as in the first step.

2.2 Fourier-Transform Infrared absorption spectroscopic analysis The chemical structure of the cashew gum was characterized by spectroscopy in the mid-infrared region of 4000 to 400 cm-1, in a Varian Excalibur spectroscope.

The spectra were obtained by mixing the material with potassium bromide (KBr) in pellet form, using 50 scans and resolution of 2 cm-1.

2.3 Thermogravimetric analysis The TGA of the purified gum was performed with a TA Instruments TGA Q500 analyzer, using a heating rate of 10 °C/min in the range from 0 °C to 700 °C under an inert nitrogen atmosphere.

2.4 Rheological testing of the powder The rheological tests of the purified cashew gum powder involved measuring the average particle size, along with the angle of repose and the bulk (or apparent) and tapped (or compacted) densities, to determine the flow properties.

These density values were used to determine the Carr index and Hausner ratio.

2.4.1 Determination of the average particle size For the verification of the average particle size, the apparatus “Bertel electromagnetic stirrer 110/220v with 6 screens” was used by means of the granulometric analysis described in Agência Nacional de Vigilância Sanitária[12].

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Pinto, A. P. S., Silva, K. G. H., & Mansur, C. R. E. 2.4.2 Angle of repose, Carr index and Hausner ratio and Flow properties The angle of repose was determined according to the method described by Aulton[13]. The Carr index and the Hausner ratio were obtained by using the density values of the gum samples, following the method described by British Pharmacopeia[14]. These parameters for the purified gum powder were compared with those values published in British Pharmacopeia [14] to indicate the flow properties.

2.5 Production of tablets After the tests of the purified powers, tablets were produced and their properties were evaluated by the method described below.

2.5.1 Preparation of the tablets The tablets were prepared by direct compression of the purified powder. For each tablet, a powder mass of approximately 350 mg was weighed and compressed manually in a Lemaq LM-1 Monopress, with single punch and using a spherical matrix having diameter of 13 mm, applying 3 metric tons of pressure.

2.5.2 Evaluation of average weight and mechanical strength The tests to determine the average weight and mechanical strength (hardness and friability) and disintegration period were performed according to the method described Agência Nacional de Vigilância Sanitária[12].

3. Results and Discussions 3.1 Extraction and purification of cashew gum The purpose of studying the method of extraction and purification of the cashew gum was to ascertain the factors that influence the yield and degree of purity. These factors were chosen due to their relevance, as presented in previous articles[4,15-17], according to which it is necessary to establish a reproducible method of extraction and purification of this material.

Initially, it was analyzed the effect of the concentration of NaCl in the aqueous solution prepared to dissolve the cashew tree exudate. Besides, the experiments was conduced to assess the influence of initial exudate mass and proportion of ethanol used to extract and purify the gum.

obtain a gum with higher solubility, particle size uniformity and high degree of purity.

3.1.2 22 factorial experiments to evaluate the cashew gum extraction conditions Table 1 shows the yields in the 22 factorial experiments, with three repetitions at the center point.

As shown by Table 1, the highest yields were obtained in experiments 1 and 3, where the exudate concentration was low level and the ethanol concentration was at both levels. This suggests that the gum concentration has a significant influence on the extraction yield. To corroborate this hypothesis, we performed statistical analysis using the Statisca 7.0 program to analyze the results shown in Table 2.

Table 2 and Figure 1 report the values of the coefficients associated with the two independent variables, along with their interaction. Only the exudate concentration had a significant influence, since the p-value obtained is lower than 0.05.

Table 1. Results of the factorial design 22.

Samples 1 2 3 4 5 6 7

Concentration exudate(%) -1 1 -1 1 0 0 0

Ethanol:Solution exudate -1 -1 1 1 0 0 0

Yield (%) 75.64 66.61 76.48 64.54 71.68 70.69 70.59

Table 2. Regression coefficients.

Regression Coefficient value P

β0

β1

β2

β12

70.89 -5.24 -0.31 -0.73 0.00001 0.003289 0.411646 0.137846

Model adjustment missing 0.744946

3.1.1 Determination of the best NaCl concentration According to Costa et al.[15], the addition of NaCl in excess in a previously neutralized aqueous solution of cashew gum enables the substitution of the cations possibly contained in the exudate (K+, Ca2+, Mg2+, Fe3+) by Na+, favoring its transformation into sodium salt. This transformation is reflected in an increase of the gum’s solubility in aqueous solutions: at NaCl concentrations of 3, 5, 7 and 9% the final yield was 58.16, 63.93, 75.56 and 76.10%, respectively.

As can be seen, higher NaCl concentrations promoted increased solubility of the solutions containing the exudate, leading to higher final yield of the process.

To validade the method of extracting the cashew gum (CG) was employed the NaCl concentration of 7% w/v to 304 304/308

Figure 1. Diagram of Pareto for each independent factor and interaction in factorial design 22. According to the figure, only the concentration of the gum is a significant factor to the process.

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Evaluation of the application of cashew gum as an excipient to produce tablets As shown in Table 2, of the variables analyzed, only gum concentration presented a statistically significant influence.

The negative value of the associated regression coefficient (β1) indicates it is best to work with the lowest concentration and that neither the ethanol concentration nor the interaction between the resin and ethanol concentrations was statistically significant. However, the value near zero of the regression coefficient (β2) associated with the ethanol concentration also indicates it is better to work with the medium ethanol concentration or with the lowest concentration value.

Based on the general mathematical model represented in Equation 1 for the 22 factorial design, it is possible to write a predictive model obtained from analysis of the experimental results, as presented in Equation 2.

Y = β0 − β1 X1 − β2 X 2 − β12 X1 X 2 (1) = Y 70.89 − 5.24 X1 (2)

After verifying the significant influence of gum concentration, we performed complementary experiments varying this concentration and keeping the ethanol:solution ratio constant at 4:1. Figure 2 shows the results with gum concentrations from 4% to 10% w/v.

3.3 Thermogravimetric analysis Table 3 presents the temperatures of each degradation stage of the samples: isolated cashew gum (ICG), purified cashew gum (PCG), purified cashew gum with one washing step (PCGW1), purified cashew gum with two washing steps (PCGW2), and purified cashew gum with three washing steps (PCGW3); as well as the percentage of residual mass of each sample. According to this table, sample ICG had one degradation stage more than the other samples, at a temperature of 180.85 °C. The existence of this additional degradation stage shows that the method used to purify the CG was effective, by removing contamination by plant matter from the gum’s sugars, Mothé and Rao[18]. The thermographs of the purified CG samples contain three degradation peaks, the first at 48.23 °C, referring to the loss of water, and the second and third, at 232.29 °C and 295.85 °C, respectively, showing that the decomposition of the polysaccharides of this gum occurs in two stages, confirming the finding reported by Mothé and Rao[18].

To check whether sample PCG was free of possible excess NaCl added during the purification process, we performed

The results shown in Figure 2 indicate that the greatest purified gum yield was obtained at an exudate concentration in the solution of 7% w/v. The inflection point of the curve of concentration vs. yield represented in Figure 2 is 7%.

As of this concentration, the yield of the CG extraction process started to decline, indicating a saturation point of the system exists.

3.2 Fourier -Transform Infrared Spectroscopy (FTIR) The FTIR spectrum presented in Figure 3 has two cashew gum bands, as described in the literature Silva et al.[17].

The following bands can be observed: an intense band in the range from 3398 to 3392 cm-1, which can be attributed to the stretching vibration of the hydroxyl – OH group, typical of polysaccharides; a small band from 2927 to 2928 cm-1, referring to the stretching vibration of the C-H groups, related to the monosaccharide galactose; a band from 1643 to 1613 cm-1, which can be attributed to the O-H group from the scissoring vibration of water molecules of residual carboxyl groups of glucuronic acid; and a broad and intense band from 1078 to 1080 cm-1, referring to the stretching of the C-O-C group from the glycosidic bonds of the sugars and stretching and bending vibrations of the O-H bond of the pyranoside sugars present in the chain of this gum.

Figure 2. Study the yield of cashew gum. The 7% concentration is inflection point, where the maximum yield of the curve occurs.

Figure 3. FTIR (KBr) spectrum GC purified.

Table 3. Thermogravimetric analysis.

Samples

Temperature of the first degradation stage (°C)

ICG PCG PCGW1 PCGW2 PCGW3

53.81 48.23 49.25 50.55 48.05

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Temperature in the second degradation stage (°C) 180.85 -

Temperature of the third degradation stage (°C) 227.36 232.29 228.29 227.92 228.99

Temperature of the fourth degradation stage (°C) 292.51 295.85 292.81 292.28 291.20

Residual percentage (%) 19.56 21.02 20.57 19.93 19.78

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Pinto, A. P. S., Silva, K. G. H., & Mansur, C. R. E. three washing steps of the PCG. The thermographs referring to samples PCGW1, PCGW2 and PCGW3 show that it is not necessary to perform washing steps of the PCG, since there were no significant changes in the residual mass percentages at the end for each sample.

3.4 Rheological properties of the powder The following rheological properties of the cashew gum samples were evaluated: average particle size, by granulometry; and compressibility and flow of the isolated and purified gum samples, by measuring the bulk (or apparent) density, tapped (or compacted) density and angle of repose.

3.4.1 Determination of the average particle size The results of this experiment showed that the purified CG sample has varied particle size distribution, as can be observed in Figure 4, which reports the percentages of mass retained in the sieves with different mesh sizes. According to Agência Nacional de Vigilância Sanitária[12], the powder samples had semi-fine profile, because all the particles passed through the 355 µm mesh sieve and at most 40% passed through the 180 µm mesh. We found that the average size of the purified CG particles was 253.64 µm, which can be considered a relatively small size.

3.4.2 Angle of repose Another parameter of the flow behavior of a powder is the angle of repose, which is a measure of the powder’s ability of flow through an orifice in a flat surface. It is considered a direct measure[19-21]. This is an easy flow measure to obtain because it only requires determining the angle formed between the side of a stationary pile of powdered material and the horizontal. The higher the angle of repose, the more cohesive the powder is.

The static angle of repose was 38º (base radius= 7 cm and height= 5.5 cm) for the purified gum. This value suggests the sample in question has a reasonable flow property, as described in Hausner[22]. The better angle of the purified gum can be related to its smaller average particle size, resulting

in a greater surface area and commensurately stronger cohesion among the particles.

3.4.3 Carr index and Hausner ratio The Carr index and Hausner ratio are similar parameters, also used to assess the flow properties of powdered materials, related to the degree of particle interaction and the compressibility of the sample. They are both based on measurement of the bulk (or apparent) density and tapped (or compacted) density[14,22-24].

The Carr index and Hausner ratio were found by applying the formulas mentioned previously. The values were 19.69 and 1.24 for the Carr index and Hausner ratio of the purified CG, respectively.

3.4.4 Flow properties of the cashew gum powders Knowledge of the flow properties of powders is one of the main objectives of the pre-formulation tests conducted during the development of a product, since this parameter affects the quality of solid pharmaceutical preparations, such as tablets and capsules. This parameter is generally determined before testing the compression of tablets or filling of gelatin capsules. Low fluidity of the raw material can negatively affect hardness, friability and content uniformity of tablets[15].

The flow characteristics of powders can be determined by various techniques, such as measuring the angle of repose and calculating the Carr index and Hausner ratio.

These tests allow assessing the interactions of the particles, since their size, size distribution and morphology affect the flow parameters of the material. Particles with large surface areas in relation to volume (smaller particles) and those with irregular surfaces Interact more readily due to electrostatic and friction forces, increasing the flow resistance and diminishing the flow. Small particles with low density and irregular morphology generally have worse flow properties than larger spherical particles with high density[25,26].

Based on the Carr index and Hausner ratio values in correlation with the flow characteristics stipulated in British Pharmacopeia[14], the purified cashew gum has intermediate flow resistance, so it might or might not impair the feed to the compression machine and negatively affect the average weight and hardness of the tablets. However, the angle of repose results showed that the flow characteristics were reasonable. Taken together, the Hausner ratio, Carr index and angle of repose values show that the only negative aspect of the purified cashew gum powder is the relatively high cohesion between particles, suggesting the use of slip agents to improve the flow in the compression machine feeders.

Sliding and lubricating agents are normally used when producing tablets, even for materials with good flow properties, so this is not a limiting factor of the use of cashew gum as a diluent for tablets produced by direct compression.

3.5 Tablets

Figure 4. Percentage of mass Purified CG retained in different sizes of mesh sieves. The powder samples had semi-fine profile.

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Cashew gum has been investigated by several researchers as an excipient for production of tablets by the wet granulation method. In these works, the cashew gum served as a binding agent of the excipients of the active ingredients, as well as to form films to coat tablets[6,10-13].

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Evaluation of the application of cashew gum as an excipient to produce tablets 3.5.2.3 Disintegration test

Figure 5. Tablets of purified cashew gum. (A) Powder purified gum; (B) Purified gum tablet.

Figure 5 contains an image of the tablets produced in this study from the purified cashew gum. It is noteworthy that this material in the experimental condition used was suitable for compression.

The tablet pre-formulation tests recommended by the Brazilian Pharmacopoeia are summarized next.

3.5.1 Evaluation of average weight According to Agência Nacional de Vigilância Sanitária[12], the acceptable limits of variation for uncoated tablets with average weight of 250 mg or more is ± 5%. The tablets were prepared aiming to obtain a final lot with average weight of 350 mg. The results obtained showed that the average weight was well within the acceptable tolerance, since it was 352 mg, a positive variation of approximately 0.6%.

3.5.2 Determination of the mechanical strength of the tablets The mechanical strength of the tablets prepared with the isolated and purified cashew gum samples was determined by measuring the hardness and friability.

3.5.2.1 Hardness test This test is applied mainly to uncoated tablets, allowing assessment of the resistance to crushing or breakage by radial pressure, by simulating falls during manufacture, packaging or transport. The hardness of a tablet is proportional to its compression strength and inversely proportional to its porosity.

According to Agência Nacional de Vigilância Sanitária[12], the minimum hardness acceptable for a tablet is 30 N, or approximately 3 kgf. In this study, we evaluated the hardness of 10 tablets made from isolated and purified cashew gum, finding an average hardness of 6.4 kgf and 6.8 kgf respectevely, higher than the minimum threshold set by Agência Nacional de Vigilância Sanitária[12]. It should be stressed that the hardness must be sufficiently high to keep the tablets from breaking during production and transport (3kgf), but not so high as to impair their disintegration in the gastrointestinal tract.

3.5.2.2 Friability test This test is only applied to uncoated tablets, to determine the resistance to abrasion when subjected to the mechanical action of the measurement device. The percentage of mass loss of the purified gum tablets (0.17%) and isolated gum tablets (0.75%) was far below the maximum limit stipulated

by Agência Nacional de Vigilância Sanitária[12] of 1.5%.

None of the tablets cracked or presented fissures at the end of this test.

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According to Agência Nacional de Vigilância Sanitária[12], a material in this test should disintegrate 30 minutes, meaning that after this interval, no residue of the units tested (capsules or tablets) should remain in the device’s metal screen, except insoluble fragments of tablet coatings or capsule films. Units that are transformed into a pasty mass are also considered disintegrated, provided they do not have a palpable core.

The disintegration process of the isolated cashew gum occurred in 30 minutes, limited maximum estimated by Agência Nacional de Vigilância Sanitária[12]. It is possible to notice that part of the material was soluble in the disintegration water and a large amount of particles was dispersed in the medium, confirming the not complete solubility of all the material isolated in the method of obtaining the cashew gum. However, the disintegration time of the CGP was 10 minutes, ie, three times less than the gum disintegration of the ICG, showing that the purification process favors a solubility of the material and removes insoluble particles from the disintegration process.

Based on the results of this study, we can recommend the use of purified cashew gum as a diluent to make tablets, due to its high solubility in water and low disintegration time.

4. Conclusions To obtain higher yields in the cashew gum extraction process, it was established: exudate concentration in water of 7%, ethanol ratio: 4: 1, 7 g NaCl solution in 100 ml 7% gum solution and two extraction steps (isolation and purification).

The result of the FTIR proved the characteristic bands of cashew gum and the thermograms proved the purity of the material.

The flow properties of purified cashew gum were found to be reasonable, providing suitable conditions for the use of such material as a diluent of tablets obtained by direct compression, as evidenced by the pharmacopoeial tests performed on tablets in this work.

Therefore, the characterization tests take as a whole show that this gum can be a promising source of raw material in Brazil, especially in light of the abundance of Anacardium occidentale trees. Therefore, new studies should be conducted to adjust the properties of the gum, to add further support to the hypothesis that this gum can be used industrially in the pharmaceutical, food and cosmetics sectors.

5. Acknowledgements We thank the Office to Improve University Personnel (CAPES), of the Ministry of Education and the National Council for Scientific and Technological Development (CNPq) and FAPERJ - Carlos Chagas Filho Foundation for Research Support of Rio de Janeiro.

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Evaluation of Anacardium occidentale gum as gelling agent in aceclofenac gel. International Journal of Pharm Tech Research, 1(3), 695-704. Retrieved in 2016, May 6, from http://sphinxsai. com/PTVOL3/PT=48,%20RAVIKUMAR%20(695-704).pdf 17. Silva, D. A., Maciel, J. S., Feitosa, J. P. A., Paula, H. C. B., & De Paula, R. C. M. (2010). Polysaccharide-based nanoparticles formation by polyeletrolyte complexation of carboxymethylated cashew gum and chitosan. Journal of Materials Science, 45(20), 5605-5610. http://dx.doi.org/10.1007/s10853-010-4625-y.

18. Mothé, C. G., & Rao, M. A. (2000). Thermal behavior of gum arabic in comparison with cashew gum. Thermochimica Acta, 357, 9-13. http://dx.doi.org/10.1016/S0040-6031(00)00358-0.

19. Geldart, D., Abdullah, E. C., Hassanpour, A., Nwoke, L. C., & Wouters, I. (2006). Characterization of powder flowability using measurement of angle of repose. China Particuology, 4(3-4), 104-107. http://dx.doi.org/10.1016/S1672-2515(07)60247-4.

20. Fu, X., Huck, D., Makein, L., Armstrong, B., Willen, U., & Freeman, T. (2012). Effect of particle shape and size on flow properties of lactose powders. Particuology, 10(2), 203-208. http://dx.doi.org/10.1016/j.partic.2011.11.003.

21. Jallo, L. J., Ghoroi, C., Gurumurthy, L., Patel, U., & Davé, R. N. (2012). Improvement of flow and bulk density of pharmaceutical powders using surface modification. International Journal of Pharmaceutics, 423(2), 213-225. http://dx.doi.org/10.1016/j. ijpharm.2011.12.012. PMid:22197769.

22. Hausner, H. H. (1967). Friction conditions in a mass of metal powder. International Journal of Powder Metallurgy, 3(4), 7-13. Retrieved in 2016, May 6, from https://www.osti.gov/ biblio/4566075 23. Carr, R. L. (1965). Classifying flow properties of solids.

Chemical Engineering (Albany, N.Y.), 72(3), 69-72., Retrieved in 2016, May 6, from http://en.journals.sid.ir/ViewPaper. aspx?ID=232696 24. Guo, A., Beddow, J. K., & Vetter, A. F. (1985). A simple relationship between particle shape effects and density, flow rate and Hausner ratio. Powder Technology, 43(3), 279-284. http://dx.doi.org/10.1016/0032-5910(85)80009-7.

25. Morin, G., & Briens, L. (2013). The effect of lubricants on powder flowability for pharmaceutical application. AAPS PharmSciTech, 14(3), 1158-1168. http://dx.doi.org/10.1208/ s12249-013-0007-5. PMid:23897035.

26. Shah, R. B., Tawakkul, M. A., & Khan, M. A. (2008). Comparative evaluation of flow for pharmaceutical powders and granules.

AAPS PharmSciTech, 9(1), 250-258. http://dx.doi.org/10.1208/ s12249-008-9046-8. PMid:18446489.

Received: May 31, 2017 Revised: Oct. 11, 2017 Accepted: Dec. 14, 2017

Polímeros, 28(4), 302-308, 2018

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.05717

Influence of Moringa oleifera derivates in blends of PBAT/PLA with LDPE Cristiane Medina Finzi-Quintão1*, Kátia Monteiro Novack1,2, Ana Cláudia Bernardes-Silva1,3, Thais Dhayane Silva2, Lucas Emiliano Souza Moreira2 and Luiza Eduarda Moraes Braga2 Programa de Pós-graduação em Engenharia de Materiais, Rede Temática em Engenharia de Materiais – REDEMAT, Escola de Minas, Universidade Federal de Ouro Preto – UFOP, Ouro Preto, MG, Brasil 2 Departamento de Química, Universidade Federal de Ouro Preto – UFOP, Campus Morro do Cruzeiro, Ouro Preto, MG, Brasil 3 Departamento de Química, Biotecnologia e Engenharia de Bioprocessos, Universidade Federal de São João del-Rei – UFSJ, Campus Alto Paraopeba, Ouro Branco, MG, Brasil

1

*finzi@ufsj.edu.br

Abstract There are few studies about Moringa oleifera derivates in polymer developments where vegetable oil was used as a plasticizer and a biodegrading agent. The polymerization of moringa oil (MO) was carried out assisted by microwaves without catalysts presence. There aren’t studies about the polymerization of MO using microwaves technology.

Moringa’s oil and its polymer (PMO) were used as a biodegrading agent for mixtures of low density polyethylene (LDPE) with poly(butylene adipate-co-terephthalate)/poly(lactic acid) (PBAT/PLA). The mixtures producted films that were characterized and submitted to biodegradation analysis in order to discuss the influence of moringa components.

Results showed that both moringa components improved thermal properties and reduced the crystalline phase of the mixture. The addition of PMO had improved the biodegradation capacity up to five times while MO had improved it up to three times. The results showed the greatest influence of moringa components on biodegradation of mixtures with cited polymers.

Keywords: biodegradation, biopolymers, microwaves, Moringa oleifera.

1. Introduction Conventional polymers such as low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP) and others are classified as bioinert materials. They have a long life time and can represent an environmental problem due to their difficult discard. The use of biodegradable polymers represent a way to reduce the amount of plastic waste disposed in landfill[1].

In USA, the biodegradable bags certified by the U.S Composting Council are being used in San Francisco for transportation of compostable materials. In Brazil, the biodegradable bags are being used without certification and blended with high density polyethylene. The mixture of biodegradable polymers and conventional polymers produce a plastic with low degradability behavior. This plastic needs the presence of additives to improve mechanical properties lost due to the mixture.

The biopolymers as (poly(ε-caprolactone) (PCL), polyhidroxybutirate (PBH), poly(lactic acid) (PLA) and poly(butylene - adipate - co - terephthalate) (PBAT) are hetero-chain polymer. They can be used as a substitute for conventional polymers in production of plastic bags, medicinal products, food packages and others. The backbones of hetero-chain polymers have atoms such as oxygen and nitrogen and these atoms make the polymer susceptible to hydrolysis and biodegradation process[2].

Polímeros, 28(4), 309-318, 2018

PLA is a biopolymer that has been attracting attention due to its stiffness, biodegradation and biocompatibility[3,4].

PBAT is an aliphatic aromatic copolyester, biodegradable, hydrophobic, flexible, it presents a better processability than other biopolymers and similar mechanical properties to polyethylene[5]. The purpose of the mixture of PBAT and PLA was to obtain a cheaper polymer, with better mechanical properties than PLA and with high biodegradation behavior.

The biodegradation can occur by two simultaneous processes: enzymatic degradation and water induced hydrolysis. Some plastics (e.g PLA) will not biodegrade without prior hydrolysis[2]. The highest rate of hydrolysis means a better and faster biodegradation due to the better microbe’s attack to the carbon backbone.

Some polymer mixtures are immiscible and need to be compatibilized aiming the optimization of the interfacial tension and the increase of the adhesion between the phases when in solid state[6]. In mixtures of LDPE with PLA, the use of compatibilizers reduces the material cost and improves the toughness, increasing the deformability and reducing the tensile strength in comparison with PLA[3,6]. Plasticizers exchange the intermolecular bonds among polymer chains and improve the conformational changes, that can result in an increase in the deformability. The plasticized polymers present a reduction on their glass transition and processing

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

Finzi-Quintão, C. M., Novack, K. M., Bernardes-Silva, A. C., Silva, T. D., Moreira, L. E. S., & Braga, L. E. M. temperature, which enables the melt processing[7]. Plasticizers can also reduce the stiffness of polymers, increase the elongation and tear strength and change thermal characteristics reducing the processing temperature[7].

Vegetable oils (VOs) such as castor, buriti, palm and M. oleifera oils were blended with some conventional polymers to improve the processability of them[8-14]. They are composed by triglycerides (esters of glycerol) with three long chain fatty acids that vary depending on the source of the oil. The most common fatty acids are oleic acid (C18:1), linoleic acid (C18:2) and linolenic acid (C18:3) but the number of double bonds varies for different oils[15-18].

According to literature, several routes can synthesize VOs based polyols[8,11], but the most used one is the epoxidation of the double bonds followed by the reaction of the epoxy groups with ring opening reagents. Epoxidized VOs are used as plasticizers for polymers as LDPE, PP, PS and PVC[17,19], due to the presence of olefinic chains on fatty acids[7].

Meanwhile, there are few studies that investigated if the vegetable oil, in natura, presents characteristics of plasticizer or compatibilizer, aiming to improve the biodegradation properties and to enhance the mechanical properties of polymers.

In literature, the mass proportion of vegetable oil used in mixtures of polymers as additive for commodities is up to 3% due to the loss of mechanical properties. In this manuscript, the mass concentration of the vegetable oil or the mass concentration of its polymer is up to 15% in order to restore the mechanical properties lost with the mixture of disposal polymers. The results for MO showed that it decreased the crystallinity of the mixture of PE with PB (named PEPB) and improved the thermal stability and the biodegradation. The tests of respirometry showed significant improvement in the biodegradation capacity of PEPB, in comparison to previous studies for the film without oil.

Meanwhile, the use of PMO showed the increase of 80% of biodegradation capacity comparing to the mixture PEPB and 35% in comparison to similar mixture of MO with PEPB. Thermal properties are similar for both moringa components but the microscopy and biodegradation tests showed that MO presents a plasticizer behavior and PMO is a compatibilizer between commercial plastics.

2. Materials and Methods 2.1 Moringa oleifera compounds

The Moringa oleifera oil was extracted from seeds of a small tree native to northern India called Moringa oleifera Lam which belongs to the Moringaceae family. MO presents a high nutritional importance due to the presence of important nutrients and antinutrients: minerals, vitamins, tannins, fibers and fatty acids[20,21]. The seed of M. oleifera is composed by 38% in mass of fatty acids like oleic acid (63.4%), linoleic acid (3.1%), palmitic acid (8.4%) and stearic acid (8%)[18,22,23].

Oleic acid fatty has high stability due to its low unsaturation and this fact favors the polymerization process[24].

Moringa oleifera oil was extracted by seeds during 8 hours in Soxhlet extractor.

Henri Dou et al. verified the researches and developments about M. oleifera Lam and showed that there are 356 patents, 267 references on Medline and 552 references on Web science between 2010 and 2015. They are about nutrition, water treatment, moringa leaf extract and medicine effects[22,25,26].

LDPE was obtained from food bags and the PBAT/PLA from market bags. The samples were produced by the mixture of MO or PMO with cited polymers in specific proportions up to 10 g in presence of 100 mL of xylene. The system was heated up to 110 °C with manual stirring during 1 min every 10 minutes. After 120 minutes, the heating was stopped and the mixture was stirred until the extra solvent was dried. Those mixtures were dried at room temperature for 36 hours or until complete solvent evaporation. Dried blends were pressed in a hot press machine at 2.5 ton, during 5 minutes and 150 °C.

In this study, the polymer of moringa oil (PMO) was obtained using microwaves irradiation without catalyzers presence. The use of microwave (MW) technology in the organic synthesis is widely described in literature[17,26-29] due to its advantages, such as safety, speed, effectiveness and rate enhancement by selective heating. Polymerization under microwaves irradiation is becoming common for synthesis of polyesters, biodegradable polymers and open ring[27,30].

According to literature, the kinetics of reactions using microwaves is better than the conventional heating[17,23,31].

The Brazilian plastic bags are produced by mixtures of 50% of biodegradable polymer (PBAT/PLA) with 50% of high-density polyethylene (HDPE). The biodegradable polymer used to produce market bags is compostable and its discarded in landfills, dumping ground or in environmental impair the expect biodegradation behavior. The aim of this study was to investigate the behavior of M. oleifera oil (MO) and its polymer (PMO) obtained by MW, in mixtures of disposal plastics as LPDE (named PE) with PBAT/PLA (named PB), improving the biodegradation behavior without a loss in the mechanical properties.

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Moringa oleifera polymer was obtained by polymerization of moringa oil assisted by microwaves irradiation.

The polymerization was carried out in a microwave domestic oven with 0.85 kW of potency. 50 mL of MO were polymerized in a becker of 100 mL during 1 hour every day up to 16 days.

2.2 Films preparing

The controller film was composed by 2.5 g of PE with 2.5 g of PB. The highest presence of moringa components was investigated during the preparation of the samples.

In this work 10 samples ar used to explain MO and PMO influence in mixtures of PE with PLA/PBAT. The mixture of 50 wt% of PE with 50 wt% of PB was named PEPB. The mixtures of MO with PE and PB produced the samples: M5-45-50, M10-40-50, M15-35-50, M20-40-40, M30-30-40.

The mixtures of PMO with PE and PB produced the samples: P5-45-50, P10-40-50, P15-35-50, P20-40-40, P30-30-40.

2.3 Characterization Thermal Gravimetric Analysis (TGA) was carried out in a TA Instruments, SDT 2960 Simultaneous DTA-TGA model, at 20 °C/min, in inert (N2) atmosphere, interval: 0-700 °C. Polímeros, 28(4), 309-318, 2018

Influence of Moringa oleifera derivates in blends of PBAT/PLA with LDPE Gel Permeation Chromatography (GPC) was carried out in a Shimadzu LC-20AD Model, solvent: THF, column: 1 Waters linear e 1 Shimadzu GPC 803, flow: 1.0 mL.min-1, injection: 20 µL, conc.: 0.2% (p/v).

Fourier Transform Infrared Spectroscopy (FTIR) analysis was carried out in a FT-IR System Spectrum GX/Perkin Elmer.

Scanning Electron Microscope (SEM): was carried out in an Scanning Electron Microscopy Vega 3 TESCAN, HV: 25.0kV, det: SE, SEM MAG: 100x – 4 kx.

Wide Angle X-Ray Diffraction (WAXD) was carried out in an EDX-720/800HS Energy Dispersive X-Ray Fluorescence Spectrometer. WXRD diffractograms were obtained with Cu radiation (k=1,541å) at 40 kV and 20 mA. The analysis was made at 20 °C and at angles between 5-60o, with a step of 0.025° and rate of 1°/min. The relative crystallinity was determined by the equation Xc=Ap/Ap+Ab, where Xc is the relative crystallinity, Ap is the crystallinity of WXRD and Ab is the amorphous area.

Tensile strength test (TST) was carried out in an EMIC DL-2000, Trd18, cross-head speed: 500 mm/min, load: 200 kgf. ASTM - D1708-13.

The biodegradation analyses were carried out according to NBR14283-199, which specifies the procedures to use Bartha Respirometer (Figure 1). According to NBR, 0.6g of sample was buried in 50g of compostable soil (Figure 1F), under controlled temperature (28 °C), free CO2 ambient,

during 9 weeks. CO2 production due to biodegradation was quantified every day with the titration of KOH (Figure 1E) converted in K2CO3.

Soil and sample are conditioned in the vessel without addition of water (Figure 1F) or contact with operator. After 19 weeks, the weight and samples morphology were analyzed.

The experimental system was composed by one Bartha Resp. without sample, three Bartha Resp. with controller sample, and three Bartha Resp. with the study sample disposed in temperature controlled ambient (28 °C).

3. Results and Discussions 3.1 GPC According to GPC analysis, MO has a molecular weight near to 1214 g.mol-1. After polymerization assisted by microwaves, GPC showed that PMO is composed of a mixture of components with 16% upper to 285,000 g.mol-1, 4% of molecular weight near to 1,229 g.mol-1 and 80% of high molecular weight near to 54, 937 g.mol-1 what indicates the oil polymerization.

3.2 FTIR Figure 2 exhibits the difference of IR spectra of M. oleifera oil and polymer. MO spectrum identified the absorption band at 3474 cm-1, which refers to hydroxyl groups formed by triglycerides hydrolysis. The thermal polymerization reduced the absorption band intensity due to the water loss.

The absorption band at 3004-3009 cm-1 is typical of fatty acids as oleic acid and indicates the cis stretching of double bond (=C-H)[32-37]. This absorption band isn’t present in PMO IV which confirms the breakage of the double bonds during polymerization process. The thermal polymerization was confirmed also by the loss of the double bond (C=C) identified at 1640 cm-1 of MO spectrum.

Mixtures with MO exhibit O-H group shifted from 3474 cm-1 to 3730 cm-1 caused by the triglycerides hydrolysis of oil. The absorption band at 1744 cm-1 that identifies the carbonyl of esters of PEPB. IR spectrum of MO samples exhibits the absorption band at 3004 cm-1 which confirm the presence of oleic acid, indicating the compatibility of the MO with PEPB.

Figure 1. Bartha Respirometer. (A - cannula cap; B - Cannula (∅i between 1 mm and 2 mm) with cannon Luer; C - Rubber Stopper; D - Side arm (∅ 40 mm ~ H ~ 100mm); E - KOH solution; F - Solo; G - Erlenmeyer flask (250 mL); H - Valve; I - support (glass or cotton wool); J - ascarita filter (∅ 15 mm ~ H ~ 40mm).

Font: NBR14283-199.

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Figure 2. IR spectra of M. oleifera oil and M. oleifera polymer.

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Finzi-Quintão, C. M., Novack, K. M., Bernardes-Silva, A. C., Silva, T. D., Moreira, L. E. S., & Braga, L. E. M. IR spectrum of samples as P5-35-50 hasn’t shown the presence of O-H group at 3720 cm-1 caused by the triglycerides hydrolysis of oil. The spectrum of P10-40-50 showed the shift of C=O (PEPB) stretching of ester at 1744 cm-1 in to the carbonyl stretching of carboxylic acids at 1710 cm-1, indicating the influence of PMO in PEPB. The P15-35-50 spectra exhibit O-H group at 3712 cm-1 even as the presence of oleic acid residue at 3009 cm-1. The absorption band between 1400- 1300 cm-1 related to C-O of carboxyl acids disappeared and the spectrum showed bands at 1268 cm-1 and 1250 cm-1related to C-O of aromatic ethers of PBAT structure. PBAT absorption band appears at 1270 cm-1 and 1248 cm-1 by C-O of aromatic ester groups. The C-O of PLA appears at 1028 cm-1 of vinyl ether group. The C-H wagging vibrations were found at 795 cm-1 for three adjacent hydrogens and 750 cm-1 for four adjacent hydrogens.

3.3 Thermal analysis The Thermal Gravimetric analysis (TG) of samples and their original components showed that PEPB enhanced the thermal stability when MO was added into the mixtures chains (Figure 3).

M15-35-50 and M20-40-40 present a different stage of degradation and a higher thermal stability (Figure 3).

As the M20-40-40 sample exuded during the hot press, M15-35-50 was used as a study sample. TG curves of M15-35-50 show two stages of degradation, the first stage

occurring between 124 °C and 436 °C in which it lost approximately 63% of mass, and the second stage, with a loss of approximately 31%. TG results confirms that there is a limit on the amount of oil to be added to the mixture of PEPB, which occurs during the hot press process. In fact, samples with MO concentration higher than 20% also exuded during hot press and are considered unworkable.

TG curves of PMO samples showed a complex thermal degradation behavior which increased the thermal stability of PEPB (Figure 3). P5-40-50 and P15-35-50 samples exhibit higher thermal stability than P10-40-50, so P15-35-50 was used as a study sample.

Derivative Thermal Gravimetric analysis (DTG) of M15-35-50 determine the degradation temperature of mixture components. PLA degradation was identified at 351.5 °C, PBAT at 377.8 °C, MO at 391.2 °C and LDPE at 483,8 °C. In fact, DTG curve of M15-35-50 indicates a compatibilizer behavior for moringa oil.

DTG curve of P15-35-50 showed higher thermal stability and complex thermal degradation behaviour (Figure 4).

The temperature at 122.65 °C represents the water loss of PB and PMO. The main degradation stage is divided in two temperatures, first at 393.7 °C due to PMO and second at 399 °C due to the interacting of PMO with the PB crystalline phase. The secondary degradation stage indicated relationship between the blend components. The interaction of PMO with the PB amorphous phase exhibit degradation temperature at

Figure 3. Comparative TG curves in inert atmosphere for samples with MO and PMO.

Figure 4. DTG comparative curves of M15-35-50, P15-35-50, MO, PMO and PEPB. 312 312/318

Polímeros, 28(4), 309-318, 2018

Influence of Moringa oleifera derivates in blends of PBAT/PLA with LDPE 340 °C and for PMO interacting with PE the degradations temperatures were identified at 472 °C and 482 °C. Differential temperature curve (DTA) indicated two major stages for change of phase of mixtures. DTA curves for M15-35-50 and P115-35-50 showed the change of phase near to 126 °C, which refers to polyethylene (Figure 5).

PB phase was exhibited in MO15-35-50 by PBAT/PLA near to 396 oC, PBAT at 436 °C, PBAT/PE at 484.6 °C and LDPE at 499,6 oC (Figure 5). P15-35-50 exhibit PB, at 406.9 °C referring to PBAT and 491.7 °C referring to relationship of PBAT/LDPE (Figure 5). The PLA and PMO temperatures weren’t explicit in DTA curve of P15-35-50, but the two defined stages indicate their interaction with PMO and PBAT, the plasticizer behavior of PMO.

3.4 Wide X-ray diffractogram The x-ray diffractograms of MO and PMO exhibit similar amorphous behavior (Figure 6). The PMO hasn’t presented any organization that indicates the increase or loss of crystallinity after thermal polymerization.

Diffractogram of PEPB (Figure 7) identified a semi crystalline material with characteristic peaks of LDPE and relative crystallinity of 55%. Peaks at 20.60 and 23.2° are typical in crystalline phase of PBAT, the peak 29.6° is related to PBT (butylene terephthalate) crystals and the peak 16.7°

is related to the crystalline phase of PLA. LDPE presents characteristic peaks identified at 2ϴ=21.5° and other at 2ϴ=23.75° (Figure 8)[38,39].

Diffractograms of M5-45-50 and PEPB exhibit peaks close to 21.8° and PEPB lost up to 4% of its crystallinity.

The increasing of oil in mixture PEPB changed the main peak for 19.6°, close to MO characteristic peak and it exhibits a peak in 17.9°, close to the peak of the crystalline phase of PLA, which returns the relative crystallinity of 55% for PEPB. In M15-35-50, the relative crystallinity was reduced to 47% but the characteristic peaks of LPED in 21.68° and 24.03° were better defined than in the others samples.

The addition of PMO in mixture PEPB increased the base of the main peak at 21o besides duplicated it (Figure 8).

The intensity of second peak reduces from P5-45-50 to P15-35-50 while the base was increased. The diffractogram indicated that the amorphous phase of PMO interacted with the crystalline phase of PE from PEPB, reducing the crystallinity and increasing the processability.

3.5 Mechanical tests Table 1 shows that mixture PEPB reduces the elongation and elastic modulus of LDPE and PBAT/PLA. from 450% of LDPE to 15% of PEPB. PB tensile stress was reduced from 43 MPA to 8.9 MPA and elastic modulus reduced

Figure 5. DTA comparative curves of M15-35-50, P15-35-50, MO, PMO and PEPB.

Figure 6. Diffractograms of M. oleifera oil and M. oleifera polymer.

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Finzi-QuintĂŁo, C. M., Novack, K. M., Bernardes-Silva, A. C., Silva, T. D., Moreira, L. E. S., & Braga, L. E. M.

Figure 7. Diffractograms of samples with moringa oil.

Figure 8. Diffractograms of moringa polymer.

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Influence of Moringa oleifera derivates in blends of PBAT/PLA with LDPE 50% for PE. The mixture PEPB presents worse mechanical properties than LDPE and PBAT/PLA. The addition of moringa components in mixture of PEPB increase the rupture force from 0.85 Kgf to 1.05 Kgf of MO and to 1.30 Kgf of PMO. MO addition improves the ductility of PEPB and reduces elastic modulus. PMO improved the processability when reducing the stiffness of PEPB (elastic modulus) which had improved the ductility. PMO turned tensile stretch of P15-35-50 similar to PE and increased the percent elongation. PMO addition improved the mechanical properties loss with the mixture of polymers more than MO.

3.6 Biodegradation tests MO15-35-50 and P15-35-50 were selected for analysis due to present the higher concentration of moringa components without problems like exudation and better

results in thermal analysis. Previous studies about PB’s degradation in Bartha Respirometer (Figure 1) showed a mass loss of approximately 30%, but with a lower carbon production[40]. The biodegradation of the samples in Bartha Respirometer showed that the process of assimilation of carbon exhibit a higher effectiveness comparing to the one with no presence of moringa oil. The samples lost 8% of mass but the biodegradation indicates the production of 3.541 mg of carbon biodegraded.

The mixture PEPB with MO improves the thermal resistance and the biodegradation behavior. The micrographs before biodegradation (Figure 9) showed a homogeneous form and after biodegradation showed a spongy form (Figure 10) due to the microorganism attack.

The biodegradability analysis with Bartha Respirometer verified the biodegradation capacity of samples using a

Table 1. Results of Tensile stretch test.

Tensile stress (MPa) Elastic modulus (Mpa) Elongation (%)

PE* 10 ± 0.8 220 ± 10.5 450 ± 22.1

PB* 44.3 ± 8.5 630 ± 23.5 285 ± 8.7

PEPB 8.9 ± 2.3 103.1 ± 5.4 15 ± 2.7

M15 9.1 ± 2.1 33.1 ± 5.2 22 ± 3.4

P15 9.7 ± 1.8 51.3 ± 4.2 19 ± 2.7

*BASF Report for films at 50 μm. PE (polyethylene); PB (biodegradable polymer); PEPB (mixture 1:1 of PE and PB); M15 (sample M15‑35‑50); P15 (sample P15-35-50).

Figure 9. Micrography of M15-35-50 before biodegradation using Bartha Respirometer.

Figure 10. Micrography of M15-35-50 after biodegradation using Bartha Respirometer.

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Finzi-Quintão, C. M., Novack, K. M., Bernardes-Silva, A. C., Silva, T. D., Moreira, L. E. S., & Braga, L. E. M.

Figure 11. Micrography of P15-35-50 before biodegradation using Bartha Respirometer.

Figure 12. Micrography of P15-35-50 after biodegradation using Bartha Respirometer.

controlled atmosphere to quantify the CO2 produced during the process. The results of tests with PEPB, and its mixtures, with MO and PMO verified that films with MO and PMO exhibit enhance of the biodegradation capacity of mixture with PEPB. In analysis with P15-35-50, after 9 weeks, the mixture PEPB produced 15 mg of CO2, the sample produced 71 mg of CO2 and the sample M15-35-50 produced 23 mg of CO2. After 17 weeks, P15-35-50 produced 113 mg of CO2, M15-35-50 produced 44 mg and PEPB produced 33 mg of CO2. The free test of biodegradation showed that P15-35-50 lost 51% of its weight while M15-35-50 lost 38% of it.

P15-35-50 before the biodegradation process (Figure 11) showed an uniform surface. After Bartha Respirometer tests, the sample showed structures similar to fibers (Figure 12) which indicated the compatibilizer behavior of PMO in PEPB mixture.

4. Conclusions The best film resultant from the mixtures of MO/ PMO, LDPE and PB exhibits proportions of 15% in mass of moringa components, 35% in mass of PE and 50% in mass of PB. The polymer produced from the oil of Moringa oleifera increased its thermal stability for the samples 316 316/318

with 15%. The P15-35-50 sample has the best composition and a higher thermal stability. The sample P15‑5-50 showed the increase of 80% of biodegradation capacity comparing to the mixture PEPB and 35% in comparison to a similar mixture of MO with PEPB. Both M15-35-50 and P15-35-50 weren’t fragmented even losing mass after the biodegradation tests, which indicates that fragmentation stage didn’t occur. In sample M15-35-50, the spongy form after biodegradation test indicates the plasticizer behavior of moringa oil. The presence of fibers in biodegradation test of P15-35-50 indicated a compatibilizer behavior of moringa polymer. The addition of moringa oil improved the biodegradation capacity up to 31% and the thermal resistance up to 10%. Also, it increased the ductility of the mixture of LDPE with PLA/PBAT, but some loss in the tensile stretch. On the other hand, the moringa polymer addition improved the biodegradation capacity up to 81%, the same thermal resistance of oil addition, while increasing the ductility and the tensile stretch, to higher values than PEPB and MO films.

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23. Mekewi, M. A., Ramadan, A. M., ElDarse, F. M., Abdel Rehim, M. H., Mosa, N. A., & Ibrahim, M. A. (2017). Preparation and characterization of polyurethane plasticizer for flexible packaging applications: natural oils affirmed access. Egyptian Journal of Petroleum, 6(1), 9-15. http://dx.doi.org/10.1016/j. ejpe.2016.02.002.

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26. Nguyen, N. T., Greenhalgh, E., Kamaruddin, M. J., El harfi, J., Carmichael, K., Dimitrakis, G., Kingman, S. W., Robinson, J. P., & Irvine, D. J. (2014). Understanding the acceleration in the ring-opening of lactones delivered by microwave heating.

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32. Schlemmer, D., Sales, M. J. A., & Resck, I. S. (2009).

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37. Vlachos, N., Skopelitis, Y., Psaroudaki, M., Konstantinidou, V., Chatzilazarou, A., & Tegou, E. (2006). Applications of Fourier transform-infrared spectroscopy to edible oils. Analytica Chimica Acta, 573-574, 459-465. http://dx.doi.org/10.1016/j. aca.2006.05.034. PMid:17723561.

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Received: May 31, 2017 Revised: Oct. 24, 2017 Accepted: Oct. 29, 2017

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.01217

Extraction, chemical modification by octenyl succinic and characterization of cyperus esculentus starch Jonas Costa Neto1*, Roseli da Silva1, Priscilla Amaral1, Maria Rocha Leão1, Taísa Gomes2 and Gizele Sant’Ana3 Departamento de Engenharia Bioquímica, Universidade Federal do Rio de Janeiro – UFRJ, Rio de Janeiro, RJ, Brasil 2 Departamento de Tecnologia de Alimentos, Instituto Federal do Maranhão – IFMA, São Luis, MA, Brasil 3 Departamento de Tecnologia de Processos Bioquímicos, Universidade Estadual do Rio de Janeiro – UERJ, Rio de Janeiro, RJ, Brasil 1

*jonasneto@ifma.edu.br

Abstract The purpose of this study was to characterize, isolate and chemically modify tiger nut (Cyperus sculentus L.) starch with octenyl succinic anhydride. The efficiency of the chemical modification was 0.04. Chemical composition, particle morphology (SEM), particle size, X-ray diffraction, infrared analysis, thermogravimetric analysis, differential scanning calorimetry and swelling and solubility power were determined for characterization of the native and modified starch.

Both showed similar chemical composition and amylose and amylopectin contents, as well as absorption spectra in the infrared region without modification of the molecular structure and A-type crystalline pattern. The particles of both had an oval and spherical shape. The modified starch was more resistant to temperature and the gelatinization process occurred at 67.52 °C. These results suggest that tiger nut starch has a great industrial potential.

Keywords: functional properties, octenyl succinic anhydride, tiger nuts starch.

1. Introduction Starch is the main reserve substance in higher plants, supplying 70 to 80% of the calories consumed by man.

It is a polysaccharide composed of repeating units of D-glucopyranose, in which D-glucose units are linked by α-1,4 bonds. This natural polymer consists basically of two macromolecules: amylose (15-30%) and amylopectin (85-70%)[1-3].

The starch market has been growing and improving in recent years, leading to the search for products with specific characteristics that meet the requirements of these industries[4]. The production of modified starches is an alternative that has been developed with the objective of overcoming one or more limitations of native starches, and thus increase the usefulness of this polymer in industrial applications[5]. The reasons for these modifications involve decreasing the retrogradation and tendency of the pastes to form gels, conferring stability in cooling and thawing processes, improving the texture of the pastes or gels and the formation of films, adding hydrophobic groups and introducing emulsifying power[6]. One of the chemical modification techniques is the treatment of native starches with octenyl succinic anhydride (OSA starches), whose modification provides an amphiphilic character to the starch molecule and, consequently, surface active properties[7].

Tiger nut (Cyperus esculentus), also called chufa or “junça”, belonging to the Cyperaceae family, is cultivated especially in sandy soils[8]. The plant originates in East Africa and its use is very old. It is a very nutritious tuber, being

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characterized mainly by the high presence of carbohydrates and oils, which represent around 24.5% of its total composition[9].

The objective of this study was to characterize native starch isolated from tubers of Cyperus esculentus, and modify it chemically by means of esterification reactions with octenyl succinic anhydride (OSA).

2. Materials and Methods 2.1 Tiger nut starch extraction and chemical modification.

For extracting the tiger nut starch, a sanitization of the tubers was carried out with 10% solution of sodium hypochlorite, followed by milling thereof, by means of a mill type Willye (TE - 680), being previously dried at 50 °C for 48 h. The extraction process was performed according to the procedure described by Guraya et al. (2004)[10].

Starch succinylation was carried out in alkaline medium according to the procedure described by Song et al. (2006)[11].

The efficiency of the reaction was performed by determining the degree of substitution according to the procedure of Kweon et al. (2001)[6].

2.2 Granule morphology by Scanning Electron Microscopy. (SEM) The observation of the starch granule morphology was carried out under scanning electron microscope (Hitachi S5200).

The powder sample was placed on an aluminum surface and

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

Costa Neto, J., Silva, R., Amaral, P., Leão, M. R., Gomes, T., & Sant’Ana, G. covered with gold/palladium (40/60) with an acceleration potential of 20.00 kV.

2.3 X-ray Diffraction analysis. (XRD) The structural characterization of the starch was performed by an X-ray diffraction equipment (Siemens D5000) at room temperature. The samples were packed in aluminum cells and illuminated by 40mA, 45kV CuKα radiation (λ = 1.54056Å). The samples were scanned in the range of 2θ diffraction angles between 5° and 40

2.4 Particle size analysis.

The particle size distribution was obtained using a laser diffraction apparatus (Beckman Coulter LS 13 320) with the sample suspended in water at 20 °C.

2.5 Differential Scanning Calorimetry analysis. (DSC) The DSC curves were obtained using the NETZSCH STA 409 Pc Luxx equipment, under the following experimental conditions: dynamic nitrogen atmosphere with flow rate of 60 ml/min; heating rate of 10 °C/min, in a range of 40 °C to 250 °C; partially closed aluminum capsule and sample mass around 4.0 mg.

2.6 Analytical methods The physicochemical analyses of the native and modified starch were performed according to the methods described

by AOAC (1997)[12]. The analyzed parameters were: protein, carbohydrate, lipid, moisture, amylose and ash.

3 Results and Discussion 3.1 Tiger nut starch extraction and composition.

The isolation of the tiger nut starch was relatively easy, as there was no interference of other compounds, mainly protein and lipid, on its extraction yield. The yield observed

for the tiger nut starch extraction was 33.5%[4]. The efficiency of the reaction was performed by determining the degree of substitution (0,04)[13]. It is observed in Table 1 that native and modified tiger nut starch presented lower values ​​of moisture, ashes, protein and lipid when compared to the values obtained ​​ for dry matter. Native tiger nut starch and modified showed higher levels of amylopectin (83.9%; 83,0%)[2,11]

3.2 Morphology and particle size of native and modified starch According to Figure 1, it can be seen that the native tiger nut starch and modified granules had a smooth surface with no grooves and, for the most part, oval shapes[14,15].

According to the particle size distribution analysis, the native tiger nut starch presented an average size of 0.182 μm and the modified starch had an average size of 0.156 μm as shown in Figure 2[15].

3.3 X-ray Diffraction (XRD) of native and modified starch According to Figure 3, corresponding to the diffractograms of the native and modified tiger nut starch, it was possible to notice that in both samples, the strongest peaks observed Table 1. Chemical composition of the native and modified tiger nuts starch and tiger nut.

Native Modified Starch Starch Moisture 0.037±0.003 0.033±0.002 Ash 0.15±0.01 0.26±0.01 Protein 4.04±0.14 4.75±0.11 Lipid 8.41±0.51 4.04±0.21 Total carbohydrate 87.4±0.12 91.0±0.09 Amylose 16.100±0.003 17.000±0.001 Amylopectin 83.900±0.002 83.000±0.002 Compounds (%)

Tiger nut 33.50±0.02 1.03±0.01 6.30±0.01 15.70±0.01 46.54±0.02 * *

*Not analysed; (±) standard deviation.

Figure 1. Scanning electron micrographs of starch granules obtained from the native and modified tiger nut starch. (a) native starch 2400x; (b) modified starch 2400x.

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Extraction, chemical modification by octenyl succinic and characterization of cyperus esculentus starch

Figure 2. Particle size distribution of tiger nut starch granules. (a) native starch; (b) modifed starch. The line indicates the cumulative distribution of particles.

Figure 3. X-ray diffraction spectra of the native and modified tiger nut starch.

Figure 4. DSC thermographs of native and modified tiger nut starch.

occurred approximately at 15°, 17°, 18° and 23° 2θ, a fact that characterizes this starch as A-type crystalline pattern[16-19].

4. Acknowledgements

3.4 Differential Scanning Calorimetry (DSC) of native and modified tiger nut starch The curves obtained for the native and modified starch, presented in Figure 4, were performed with the aim to evaluate, mainly, the gelatinization process thereof.

For the native starch, two endothermic peaks occurred: the first one was in the range of 62.27-75.55 °C (ΔH = 228.86 J.g-1), with maximum at 67.52 °C, related to the gelatinization process of the starch. For the modified starch, only one endothermic peak was observed, occurring in the range of 104.76-117.65 °C (ΔH = 714.28 J.g-1), with maximum at 108.28 °C, related to the melting process of the modified starch.

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This work was financed by CAPES and CNPq. The authors are grateful to the Universidade Federal do Rio de Janeiro, Instituto Federal do for the help given to perform the experimental part.

5. Conclusion This study explored the physicochemical properties of native and modified starch isolated from tubers of tiger nut (Cyperus esculentus) with respect to their likely potential for the industry as a whole. In addition, the satisfactory modification of tiger nut starch increased the possibilities of use by the industry, as it was shown to be more resistant to temperature as observed by DSC. These facts can raise 321/322 321

Costa Neto, J., Silva, R., Amaral, P., Leão, M. R., Gomes, T., & Sant’Ana, G. the importance of the polymer of this tuber as an alternative source of starch, since in Brazil, the tiger nut is constantly eliminated because it is an allelopathic weed.

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19. Zavareze, E. R., El Hal Al, S. L. M., Pereira, J. M., Radünz, A. L., Elias, M. C., & Dias, A. R. G. (2009). Caracterização química e rendimento de extração de amido de arroz com diferentes teores de amylose. Brazilian Journal of Food Technology, 1, 24-30. Retrieved in 2017, 08, 15 , from http://bjft.ital.sp.gov. br/artigos/especiais/especial_2009/v11_edesp_06.pdf Received: Mar. 22, 2017 Accepted: Dec. 21, 2017

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.10417

Synthesis of flexible polyurethane foams by the partial substitution of polyol by steatite Plínio César de Carvalho Pinto1*, Virginia Ribeiro da Silva2, Maria Irene Yoshida1 and Marcone Augusto Leal de Oliveira3 Departamento de Química, Universidade Federal de Minas Gerais – UFMG, Belo Horizonte, MG, Brasil 2 Laboratório de Química de Nanoestruturas de Carbono, Centro de Desenvolvimento da Tecnologia Nuclear – CDTN, Belo Horizonte, MG, Brasil 3 Departamento de Química, Universidade Federal de Juiz de Fora – UFJF, Juiz de Fora, MG, Brasil

1

*plinioccp@yahoo.com.br

Abstract This work describes the synthesis of composites steatite/flexible polyurethane by replacing 4.5 wt. % of polyol with steatite rock powder. We evaluated two mechanical properties of composites (comfort factor and support factor) for various formulations based on a fractional factorial design. The new synthesized composites showed higher support factor, greater comfort factor, and lower cost, compared to conventional flexible polyurethane foams. There is not a significant change in the chemical composition of the foams, due to substitution of 4.5 wt. % polyol by steatite. However, there was a decrease in cell size and greater interaction between the hard segments of the composite.

Keywords: composites, foam, steatite, mechanical properties, polyurethanes.

1. Introduction The polyurethane is a polymer which does not contain monomer unit, but is predominantly formed by urethane linkages (-HN-CO-O-). It is produced by the simultaneous reactions between an isocyanate with a polyether polyol (polimerization), Figure 1, and water (blowing), Figure 2.

They are also placed in the formulation other reagents, such as catalysts, blowing agents, fillers, flame retardants and pigments[1,2].

In a few minutes, a liquid mixture of low molecular weight reactants polymerize to form a solid, the supramolecular material formed by open cells, high permeability to gases, low density and with a phase separated morphology[3].

The foams are composed of a polymeric solid phase and a air gaseous phase[4]. The solid phase has a heterogeneous separation (micro scale), often accompanied by the mixture of crystalline hard segments and amorphous soft domains[5].

The hard segments are formed by substituted ureas and urethanes, which can interact, by hydrogen bonds, due to the polar nature these bonds. The flexible domains are formed by the polyether polyol or polyester chain[4-6]. These hard segments are covalently bonded to the polyol domains by urethane linkages[7-8].

The reversible deformation, excellent light weight, strength/weight ratio performance, comfort protection, thermal and acoustic insulating and other positive aspects of this polymeric material are the biggest selling group of polyurethanes[9-11]. The flexible foams find wide application in furniture, mattresses, upholstery, automotive seats and packing systems[12-13]. However, flexible polyurethane foam

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presents some undesirable features such as low thermal stability and low mechanical strengths[14].

In this paper, we proposed the use of powdered rock steatite from Pedras Congonhas Ltd., Nova Lima, Brazil, an inorganic filler rich in talc, partially replacing the polyol in the production of flexible polyurethane foams in order to reduce costs and improve the mechanical properties of the polymer, such as support factor and comfort factor. Support factor measured by compression modulus is perhaps the most important function of flexible polyurethane foam.

Foam’s ability to provide support has a direct effect on other key properties such as comfort and durability. It is valid measurement of foam’s cushioning ability. It also means that the foam is capable of distributing the weight of the person for maximum comfort[15]. The comfort factor is the property that measures the foams firmness. It is the ratio of the force required for an indentation disk compress the sample to 65% of its original thickness divided by the force required for an indentation disk compress the sample to 25% of its original thickness.

The mineral talc is widely used as filler in paper industry, paints, cosmetics, pharmaceuticals, refractories, ceramics, pesticides, lubricants, food industry and accident prevention, due to its properties, low hardness, whiteness, low electrical and thermal conductivity, chemical resistance and adsorption of organic substances[16-19]. Talc is also used as filler in composites, in order to improve the compound mechanical characteristics, increasing the nucleation of the polymer and the dimensional stability of the final product[19].

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Pinto, P. C. C., Silva, V. R., Yoshida, M. I., & Oliveira, M. A. L. 2.4 Analysis of mechanical properties of the foams

Figure 1. Polimerization reaction of polyurethane.

The support factor of foams measured by compression modulus was determined in a universal testing machine EMIC DL-3000, according to Brazilian standard NBR 8910:2003 (ASTM D3574 - Test C), Figure 3(a). The comfort factor determined by the indentation force deflection is determined on the same machine, according to Brazilian standard NBR 9176:2003 (ASTM D3574 - Test B1), Figure 3(b).

2.5 Chemical and physical characterization of steatite Figure 2. Blowing reaction of flexible polyurethane.

2. Materials and Methods 2.1 Materials The production of flexible polyurethane composites used: polyether polyol Voranol 4730 Dow Chemical (polymer of ethylene oxide/propylene oxide), toluene diisocyanate Voranate T 80 Dow Chemical (80/20 blend of toluene diisocyanate isomers 2,4 and 2,6, respectively), amine catalyst Aricat AA 805 Arinos Chemistry (mixture of N, N-diethylethanolamine and 2,2’-oxydiethanol), tin catalyst Liocat 29 Miracema-Nuodex (bis (2-ethylhexanoate) tin (II)), surfactant Niax L-540 GE Silicones (composition protected by patent) and distilled water as blowing agent.

2.2 Sample preparation of steatite A steatite rock sample of Mustards Mine, New Lima, Brazil was milled for 5 min in a ring mill and sieved by mechanical stirring for 12 h. The entire sample had a size smaller than 100 mesh (< 149 µm).

2.3 Synthesis of flexible polyurethane composites In a 300 mL polypropylene cup were added: distilled water, surfactant, amine catalyst and polyol. It was stirred at 2000 rpm for 1 minute by a mechanical stirrer. Steatite was added and stirred for 1 min. Was added to the tin catalyst, stirring up again for 30 seconds. Was added toluene diisocyanate, stirring for a further 6 seconds and transferred the mixture to a wooden cubic box of 10 cm edge (template).

After 24 h, the foams were removed from the molds and stored to prevent the incidence of sun, wind and humidity for at least three days, for the healing. Flexible polyurethane composites were synthesized in random order by drawing lots.

The formulations varied according to a fractional factorial design type 2V5-1(fifth order) with five factors (variables): steatite and polyol, isocyanate, amine catalyst, tin catalyst and silicone; two levels (concentration): low -1, high +1; and triplicate central point generating relationship I = 12345.

This type of fractional design is of interest because the main effects will be confused with fourth order interactions (low significance), and there is no confusion between the second order interactions[20]. The water used as blowing agent was kept fixed concentration of 3.2 wt. % to have the same density foams. The responses considered for the design were foam comfort factor and support factor. The triplicate in central point (experiments 17, 18 and 19) was used to calculate the experimental error and the significance of effects.

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The steatite is dried in an oven at a temperature of 110 °C to a constant mass. The loss of mass due to drying is considered to be water. XRD patterns were collected with a Siemens D5000 instrument using a Ni-filtered Cu Kα radiation (λ = 1.5418 Å) and a graphite monochromator in the diffracted beam. A scan rate of 1° min-1 was applied to record a pattern in the 2θ range of 5° - 80°. The XRD lines were encountered in JCPDS (Joint Committee on Powder Diffraction Standard). The chemical composition of steatite was determined using a Shimadzu EDX-720 Energy Dispersive X-ray Fluorescence Spectrometer.

The following operating conditions were selected: voltage of 15 kV tube (Na-Sc) and 50 kV (Ti-U) with current in the tube 188 and 37 μA, respectively; in vacuum and detector Si(Li) cooled with liquid nitrogen. The quantitative method used for counting of hydroxil groups was the acetylation of a known mass sample with acetic anhydride in excess, in the presence of pyridine as solvent and imidazole as catalyst[21]. The Figure 4 shows the acetylation reaction of hydroxyl containing minerals.

Infrared spectra were obtained from a Perkin-Elmer Spectrum RX FT-IR spectrometer, using KBr disks in the 4000-400 cm-1 region with 64 scans and 4 cm-1 of spectral resolution. Thermogravimetry (TG) and Differential Thermal Analysis (DTA) were carried out by DTG-60 Shimadsu instrument at temperatures ranging from ambient to 650 °C with a heating rate of 10 °C min-1 in air flow of 100 mL min-1.

2.6 Chemical and physical characterization of foams It used the same conditions for the thermal analysis and infrared spectroscopy of steatite. However, infrared spectra were obtained using ATR (Attenuated Total Reflectance) configuration. In a scanning electron microscope JEOL JSM-6360LV, operating in high vacuum, images of the polymer fracture surfaces were obtained by backscattered electron. The identification of mineral or polymer phase was carried out by a EDS (Energy Dispersive Spectrometry) probe. A foam cube with edge 1 cm was metallized with gold to conduction electrons. The foams were sliced into 1 mm thick strips, with the aid of scissors and fixed on a glass slides with adhesive tape. Those glass slides were examined with a microscope Carl Zeiss Model Axioskop 40 under 25x magnification (2.5x objective and 10x eyepiece) and photographed with a coupled digital Canon camera.

3. Results and Discussions 3.1 Chemical and physical characterization of steatite It is considered in this work that a portion of the polyol may be replaced by hydroxyl-containing minerals, in order to modify the mechanical properties of flexible polyurethane Polímeros, 28(4), 323-331, 2018

Synthesis of flexible polyurethane foams by the partial substitution of polyol by steatite foams. Therefore, the characterization of the steatite was performed to identify its chemical properties and also know their influence in the synthesis of polymeric composite.

The Table 1 shows the chemical composition of steatite.

The Figure 5 shows X ray diffraction pattern and infrared spectra of the steatite.

The X-ray diffraction pattern of steatite allow us to identify the rock as composed mainly of the minerals talc Mg3Si4O10(OH)2, clinochlore Mg5Al2Si3O10(OH)8 and actinolite Ca2Mg5Si8O22(OH)2. Infrared spectra of the steatite show bands that are mainly found in vibrational modes for talc phase.

This indicates that it is the mineral in highest concentration in the rock. This conclusion is supported by the presence of

two very fine bands at 3677 cm-1 and 3661 cm-1 related to the OH stretching mode of talc. The enlargement of the band at 1014 cm-1 and the shoulder observed at 951 cm-1 are indicative of the presence of clinochlore. The band at 951 cm-1 is a high intensity clinochlore mode, not observed for talc[22,23].

The band at 756 cm-1 may be attributed to actinolite, related to the symmetric stretching mode of Si‑O-Si[24]. Talc is a tri‑octahedral layered mineral with each hydroxyl group linked to three octahedral cations. According to the nature of these cations, there are different frequencies for the OH stretching mode. The band found in the spectrum at 3677 cm-1 can be assigned to υ Mg3O-H mode[25]. The band at 3661 cm-1 is assigned to υ Mg2FeO-H mode[25], at 3460 cm-1 to υ O-H mode of adsorbed water on the surface[26], at 1014 cm-1 to υas Si-O-Si mode[22], at 670 cm-1 to υs Si-O-Si mode[22] and the band at 463 cm-1 is assigned to out of phase translational mode of hydroxyl group with others oxygens[27,28].

Therefore, based on the results of X ray diffraction and infrared spectroscopy, it follows that the hydroxyls are on a chemical environment according to the Figure 6[29], which will react with isocianate in the polymer synthesis.

Figure 3. Mechanical test of foams Compression Modulus (a) and Indentation Force Deflection (b).

The reactivity of the hydroxyl groups present in the steatite mineral was verified by hydroxyl counting methodology for polyols used in polyurethane synthesis. The steatite features 20 mg KOH/g, while the polyol used in flexible polyurethane synthesis feature 34-56 mg KOH/g[30]. In addition to this lower reactivity, the steatite presents the hydroxyl strongly linked to Mg2+ ions and Fe2+ in the crystal structure of the mineral. Therefore, the hydroxyls of steatite are in a compact and rigid structure, while the hydroxyl groups of the polyol are a flexible polymer backbone, Figure 7.

Table 1. Chemical composition of steatite sample.

Figure 4. Acetylation reaction of the mineral OH.

Oxides MgO SiO2 Al2O3 CaO Fe2O3

(wt. %) 30.7 49.6 2.3 1.2 8.8

Oxides K2O Na2O Cr2O3 MnO NiO

(wt. %) 0.1 0.1 0.5 0.1 0.1

Figure 5. X ray diffraction pattern (a) and infrared spectra (b) of the steatite sample.

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Pinto, P. C. C., Silva, V. R., Yoshida, M. I., & Oliveira, M. A. L. Therefore, steatite minerals may also react with the isocyanate for the production of flexible polyurethane foams, Figure 8.

In the Figure 8 it can be seen that 2,4-toluene diisocyanate is reacted with the mineral and allows the traditional polymerization (isocyanate more polyol) on the surface of

the mineral. Furthermore, minerals may be connected by covalent chemical bonds (urethane).

The humidity of steatite is 0.1 wt. %. This value is very low, so it will not contribute significantly to the reaction with TDI in the synthesis of composites. The water could affect the expansion reaction and change the properties of the composite according to the Figure 2.

The steatite thermal analysis is shown in Figure 9.

Thermogravimetry of the steatite sample shows two caracteristic mass loss. The first mass loss of 3.5 wt. %, which starts at 532 °C ending at 840 °C, is related to dehydration of amphibole (actinolite) and clinochlore[31]. The second mass loss of 1.2 wt. % starts at 852 °C is related to dehydration of talc, which begins above 850 °C[32-34]. The decomposition of talc is described by the following Reaction 1[31]: Mg3Si4O10 ( OH )2 (talc ) → 3 MgSiO3 ( enstatite ) + SiO2 (cristobalite) + H 2O (1)

Figure 6. Talc chemical structure.

Therefore, steatite heating at high temperature promotes the release of water, which could be an interesting feature as flame retardant[10-13]. This could hamper the composite burning in commercial applications where this property is required. However, it has not been studied.

3.2 Foams mechanical properties

Figure 7. Representation of the polyol monomer unit.

According to a statistical analysis of Table 2, the variables isocyanate and tin catalyst have a significant effect on the foam support factor, as well as the interaction between

Figure 8. Reaction between the diisocyanate and the OH group of the mineral.

Figure 9. Steatite thermal analysis (TG and DTA).

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Synthesis of flexible polyurethane foams by the partial substitution of polyol by steatite them. Tests 1, 2, 9 and 10 of Table 2 show that the two variables being in the lower level (isocyanate index: 105; tin catalyst: 0.1) generates a null response (zero) for comfort, within the range of 95% confidence for the experimental region investigated. In practice, the foam had a physical and structural defect known as crack, which prevented the realization of mechanical test. This occurred because in tests, the low concentration of isocyanate and tin catalyst did not favor the polymerization reaction. The reduction in the concentration of the reagent and catalyst displaced the equilibrium of the reaction in the direction of formation of the reactants (Figure 1). Complications arise due to the simultaneous and therefore competitive nature of the reactions of the blowing and gelation and the effect of formulation and process variability on the activation energy of these reactions[35]. The variable polyol + steatite have a significant effect on the foam support factor. Table 2 shows that increasing the amount of steatite causes an increase in support factor or hardness of the foam. Example: Test 3 compared to Test 4; Test 5 compared to Test 6, successively.

The increased amount of isocyanate and tin catalyst also increases the hardness of the foam by increasing both the urea phase content and the phase connections between the polyol domain and the urea segments in the polymer chain[2,7,36].

The interaction between the variables polyol + steatite and isocyanate is positive and not significant. Table 2 shows that increasing the levels of two variables (polyol + steatite: changing from 100.00 to 95.50 of polyol and 0.00 to 4.50 of steatite ; isocyanate index: changing from 105 to 125) simultaneously increases the foam hardness. The interaction between isocyanate and tin catalyst is negative and significant within the range of 95% confidence for the experimental region investigated. The variable silicone showed no significant effect on the properties analyzed, since the silicone acts only as a surfactant to lower surface tension, emulsify incompatible formulation ingredients, promote generation

of bubbles during mixing, and stabilize cell window[36,37].

This fact confirms that the fractional factorial design used can be considered satisfactory since the variable silicone was considered little significant, within the experimental range investigated. Also, the amine, which balances and controls the expansion reaction and gelification, showed no significant effect on the mechanical properties of the formulations studied. As the 3rd order interactions (three variables) or higher orders among variables, as a rule, are not significant, these were not considered for analysis.

3.3 Characterization of flexible polyurethane composites In the Figure 10 we can see that the polymer (dark mass) is formed with mineral adhered to its surface, Figure 10 (a, b and c).

The polymer may also coat the mineral, according to the side section seen in Figure 10 (e). The mineral (white particle) is a magnesium silicate confirmed by EDS spectrum Figure 10 (d). This was expected, since talc Mg3Si4O10(OH)2 is the main mineral of steatite. These observations suggest that there is a chemical interaction between the mineral and the polymer, which was identified by infrared spectroscopy.

The Figure 11 shows the composite images obtained by polarized light optical microscopy.

The foams of the tests 5 and 6 have similar formulations.

The difference is that the foam 5 has 100% polyol and a minimum amount of silicone. While the foam 6 has 95.5 wt. % polyol, 4.5 wt. % of steatite and the maximum amount of silicone. It is noted that foam 6 has smaller cells and more interconnected. We observed the same when comparing foams of tests 7 and 8. They are foams with the best overall properties. As silicon shown not to influence significantly the physical properties of the foams, we attribute this morphological difference between foams for replacement of the polyol by steatite. The smaller number of hydroxyls of steatite increases the isocyanate index

Table 2. Matrix for the fractional factorial design 2V5-1 to study the mechanical properties of flexible polyurethane composites with answers.

Tests 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Polyol + steatite (%) 100.00 + 0.00 95.50 + 4.50 100.00 + 0.00 95.50 + 4.50 100.00 + 0.00 95.50 + 4.50 100.00 + 0.00 95.50 + 4.50 100.00 + 0.00 95.50 + 4.50 100.00 + 0.00 95.50 + 4.50 100.00 + 0.00 95.50 + 4.50 100.00 + 0.00 95.50 + 4.50 97.75 + 2.25 97.75 + 2.25 97.75 + 2.25

Isocyanate index 105 105 125 125 105 105 125 125 105 105 125 125 105 105 125 125 115 115 115

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Factors Tin catalyst (%) 0.1 0.1 0.1 0.1 0.2 0.2 0.2 0.2 0.1 0.1 0.1 0.1 0.2 0.2 0.2 0.2 0.15 0.15 0.15

Amine catalyst (%) 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.8 0.8 0.8

Silicone (%) 0.8 0.6 0.6 0.8 0.6 0.8 0.8 0.6 0.6 0.8 0.8 0.6 0.8 0.6 0.6 0.8 0.7 0.7 0.7

Answers Comfort factor Support factor (arb. unit) (kPa mm-2) 0.00 0.00 0.00 0.00 2.55 3.72 2.83 4.91 2.46 3.74 2.48 3.38 2.54 4.10 2.66 4.87 0.00 0.00 0.00 0.00 2.73 3.50 3.04 4.61 2.41 3.12 2.57 4.30 2.65 3.89 2.70 4.56 2.75 4.31 2.49 4.34 2.47 4.13

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Figure 10. Composite images (a, b, c and e) obtained by scanning electron microscopy and EDS spectrum (d) of mineral particle (whiter particle).

Figure 11. Composite images obtained by polarized light optical microscopy. Test 5 foam of the Table 2 seen in the microscope without crossed nicols (a) and under crossed nicols (b). Test 6 foam of the Table 2 seen in the microscope without crossed nicols (c) and under crossed nicols (d).

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Synthesis of flexible polyurethane foams by the partial substitution of polyol by steatite promoting a greater amount of cross-linking (hard segments interconnected in a network) in the polymer chain[36,38]. Also, the polymer chain of the polyol contributes to the size of the polyurethane chain. In contrast, polyurethane grows on the surface of steatite, which serves as a center of nucleation and an additional point of cross-linking[2].

Infrared spectrum of Figure 12 shows the bands related to the vibrational transition modes of the chemical groups of the polyurethane, demonstrating that the conversion of reactants to products has been successfully performed in the synthesis process. The band at 3288 cm-1 attributed to νN-H of urethane, 2970 cm-1 attributed to νC-H of CH3, 2930 cm-1 attributed to νC-H of CH2, 1724 cm-1 attributed to νC=O of urethane and primary amide without hydrogen bond, 1716 cm-1 attributed to νC=O of urethane and primary amide with hydrogen bond, 1640 cm-1 attributed to νC=O of urea, 1598 cm-1 attributed to νC=C of aromatic ring, 1540 cm-1 attributed to νC-N and δNH of secondary amide, 1456 cm-1 attributed to δCH on the plan of CH2, 1418 cm-1 attributed to νC-C of aromatic ring, 1372 cm-1 attributed to δCH off-plan of CH2, 1094 cm-1 attributed to νC-O-C of aliphatic ether. The bands between 900-650 cm-1 are assigned to the aromatic ring deformation modes[39-42].

The band 1640 cm-1 attributed to νC=O of urea reflects the rigid segments of the foam. The hydrogen bond between the carbonyl corresponds to interaction between the rigid segments[42]. Therefore, the greater the intensity of the absorption band at 1640 cm-1, the greater the interaction between hard segments and, consequently, the greater the

degree of separation of microphases (hard and soft segments) in the foam. Analyzing the absorption intensity of the band at 1640 cm-1 of normalized infrared spectrum for all foams, it is noted that foams with steatite have higher intensities than foams without the addition of steatite. Therefore, the increase of the hardness and the comfort factor of the foams by addition of steatite, is due to increased interaction between hard segments. These hydrogen bonds strengthen the phase connectivity and provide the hard urea segments with additional disruption choices under compression, which promotes chain slippage and mobility[7]. There is no significant difference in the chemical composition of the foams with 4.5 wt % or 0.0 wt. % of the steatite, according to their infrared spectra.

According to the Figure 13, the flexible polyurethane foams have three exothermic weight losses between 200 °C and 400 °C (DTA curve in blue identifying the exothermic peaks and the DTG curve in black identifying the mass variation), corresponding to approximately 88 wt. %. The polyurethane heating causes its degradation into smaller nitrogen compounds such as hydrogen cyanide, acetonitrile, acrylonitrile, propionitrile, pyrrole, pyridine, aniline, benzonitrile, quinoline and phenyl isocyanate[43].

It occurs the breakdown of urethane linkages above 200 °C, and subsequently decompressing polyether chain between 250-320 °C. At higher temperatures (around 375 °C), the polyether bonds are broken[44]. The last stage is the breakdown of the carbon chain[45]. Above 400 °C occurs final polymer degradation[11,46]. The foam 6 has a final residue of

Figure 12. Infrared spectrum of the foams 5 and 6.

Figure 13. Thermal analysis of the foams 5 and 6.

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Pinto, P. C. C., Silva, V. R., Yoshida, M. I., & Oliveira, M. A. L. 4 wt. %, due to the presence in the formulation of steatite.

The foam 5 has no final residue, it is totally degraded by heating to 600 °C. Therefore, foams having steatite has a higher ash content than traditional foams. In general, the thermal behavior of the foams during the heating does not change significantly, due to substitution of 4.5 wt. % polyol by steatite. Thus, there is not a significant change in the chemical composition of the foam, due to addition of steatite.

4. Conclusions The steatite rock is composed of attractive minerals for use in polyurethane synthesis, since it presents reactive hydroxyl and chemical properties useful as high thermal stability. The composites steatite/flexible polyurethane presented in relation to conventional foams, improvement in mechanical properties analyzed: comfort factor and support factor. Thus, foams with steatite are cheaper, have greater load support and increased comfort. There is not a significant change in the chemical composition of the foams, due to substitution of 4.5 wt. % polyol by steatite.

However, there was a decrease in cell size and greater interaction between the hard segments of the composite.

The fractional factorial design showed be very useful and effective to test flexible polyurethane formulations. It enabled the study of the influence of each formulation component on the foams mechanical properties, as well as the influence of interactions between them. Sum up, the multivariate approach, in contrast of the univariate one, presents more comprehensive understanding of the investigated system through simultaneous evaluation of variables combined with a reduced number of experiments, that results in lower spending of reagents and laboratory time.

5. Acknowledgements Thanks to CNPq and Pedras Congonhas Ltd. for financial support.

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34. Balek, V., Pérez-Maqueda, L. A., Poyato, J., Cerný, Z., Ramírez-Valle, V., Buntseva, I. M., & Pérez-Rodríguez, J. L. (2007). Effect of grinding on thermal reactivity of ceramic

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36. Kaushiva, B. D., McCartney, S. R., Rossmy, G. R., & Wilkes, G. L. (2000). Surfactant level influences on structure and properties of flexible slabstock polyurethane foams. Polymer, 41(1), 285-310. http://dx.doi.org/10.1016/S0032-3861(99)00135-4.

37. Zhang, X. D., Macosko, C. W., Davis, H. T., Nikolov, A. D., & Wasan, D. T. (1999). Role of silicone surfactant in flexible polyurethane foam. Journal of Colloid and Interface Science, 215(2), 270-279. http://dx.doi.org/10.1006/jcis.1999.6233.

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39. Tu, Y.C., Suppes, G. J., & Hsieh, F.H. (2009). Thermal and mechanical behavior of flexible polyurethane-molded plastic films and water-blown foams with epoxidized soybean oil.

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40. Ludwick, A., Aglan, H., Abdalla, M. O., & Calhoun, M. (2008).

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41. Barbosa, L. C. A. (2007). Espectroscopia no Infravermelho na caracterização de compostos orgânicos. Viçosa: Editora UFV. 42. Zhao, P. Z., Wang, Y. S., Zhu, J. H., Hua, X. Y., & Wen, Q. Z. (2008). Characterization of graded polyurethane elastomer

by FTIR. Science in China. Series B, Chemistry, 51(1), 58-61. http://dx.doi.org/10.1007/s11426-007-0093-x.

43. Herrera, M., Matuschek, G., & Kettrup, A. (2002). Thermal degradation of thermoplastic polyurethane elastomers (TPU) based on MDI. Polymer Degradation & Stability, 78(2), 323331. http://dx.doi.org/10.1016/S0141-3910(02)00181-7.

44. Ravey, M., & Pearce, E. M. (1997). Flexible polyurethane foam I. Thermal decomposition of a polyether-based, water-blown commercial type of flexible polyurethane foam. Journal of Applied Polymer Science, 63(1), 47-74. http://dx.doi.org/10.1002/ (SICI)1097-4628(19970103)63:1<47::AID-APP7>3.0.CO;2-S. 45. Spirckel, M., Regnier, N., Mortaigne, B., Youssef, B., & Bunel, C. (2002). Thermal degradation and fire performance of new phosphonate polyurethanes. Polymer Degradation & Stability, 78(2), 211-218. http://dx.doi.org/10.1016/S01413910(02)00135-0.

46. Allan, D., Daly, J., & Liggat, J. J. (2013). Thermal volatilisation analysis of TDI-based flexible polyurethane foam. Polymer Degradation & Stability, 98(2), 535-541. http://dx.doi. org/10.1016/j.polymdegradstab.2012.12.002.

Received: Dec. 20, 2017 Revised: Jan. 28, 2018 Accepted: Feb. 05, 2018

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.16216

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

Orange essential oil as antimicrobial additives in poly(vinyl chloride) films Carla Fabiana da Silva1, Flávia Suellen Melo de Oliveira2, Viviane Fonseca Caetano2, Glória Maria Vinhas2* and Samara Alvachian Cardoso2 Laboratório de Análises Físico-Química de Alimentos, Departamento de Ciências Domésticas, Universidade Federal Rural de Pernambuco – UFPE, Recife, PE, Brasil 2 Laboratório de Materiais Poliméricos e Caracterização, Departamento de Engenharia Química, Universidade Federal de Pernambuco – UFPE, Recife, PE, Brasil 1

*gmvinhas@yahoo.com.br

Abstract In this work were developed and evaluated films of poly(vinyl chloride)-PVC additivated with orange essential oil – OEO. These films were evaluated with FT-IR spectroscopy; mechanical tests; migration OEO in simulants; and determination of stability after sterilization by gamma radiation at a dose of 25 kGy. The OEO was assessed with GC-MS and analysis of antimicrobial activity. The films were prepared by the casting solution technique. The essential oil concentrations in PVC were 2%, 10% and 30% (w/w). The results showed that the OEO was incorporated into the polymer matrix and that this oil had antimicrobial activity against the bacteria E. coli and S. aureus. The migration of OEO in the films occurred with all simulants. The incorporation of OEO in the films also made them more flexible. It was also found that additive with 30% w/w OEO provides a protective effect for the polymer after sterilization by gamma radiation.

Keywords: antimicrobial activity, mechanical tests, migration, orange essential oil, poly(vinyl chloride).

1. Introduction Food packaging has improved over the years in order to match the demands of modern society[1]. The search for alternative in packaging systems has been carried out to preserve the quality of food and prolong its commercial validity[2]. Among these systems is antimicrobial packaging, acting by the slow migration of active agents incorporated into the polymeric matrix to the surface of the food[3,4].

One possibility for the formulation of antimicrobial packaging is to use an additive with essential oils (EOs).

EOs are liquid mixtures of volatile compounds extracted from leaves, flowers, stems, roots, seeds or fruit peel that have attracted interest of the food industry for their antimicrobial nature[5-8]. This antimicrobial action is due to the presence of components that have the ability to alter the permeability of the outer membrane of micro‑organisms and/or inhibit important enzymes for their growth and survival[9].

An alternative to this kind of antimicrobial packaging would be the combination of poly(vinyl chloride) (PVC) with essential oil. PVC is one of the most consumed thermoplastics in the world, with good cost-benefit and the ability to incorporate diverse types of additives, besides being recyclable, non-toxic and inert[10-13]. PVC is a rigid polymer. This rigidity is attributed the forces of Van der Waals dipole-dipole caused by the hydrogen and chlorine attached to the same carbon atom[12]. The additives incorporated in the PVC can change their characteristics, such as the decrease in the rigidity or transparency; to promote greater resistance

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to weathering conditions; to promote antimicrobial action; and combined changes[13-15].

A potential antimicrobial agent is the orange essential oil (OEO). This oil has d-limonene as its main antimicrobial agent. This is a monocyclic monoterpene extracted from citrus peel, easily absorbed into the polymer matrix; and has intense antimicrobial activity, making it attractive for the food packaging industry[14]. Furthermore, the extraction of essential oil orange can be considered a sustainable raw material, as the shell of the citrus fruit is considered a loss to the industry of fruit juice[16,17]. In the literature reporting PVC added with substances that have the function of stabilizers, plasticizers or viscosity increasing agent, such inseed oil and gum rosin[18]. Also, works are reported of limonene added to other polymers, such as PLA[14,19,20], blends of PHB/PLA[21,22], starch‑sodium caseinate blend films[23] and chitosan films[14,24,25]. In literature also are reported workes that used other essential oils with polymers, such as gelatin films with citrus oils[26], chitosan films with cinnamon oil[27]; films from soy protein with cinnamon oil[28], k-carrageenan film with savory oil[29], chitosan films with basil[30], films from whey protein with oregano oil[31] and chitosan films with Zataria oil multiflora[32].

This study were developed and evaluated PVC films additivated with orange essential oil aiming towards the application to antimicrobial packaging for the food industry.

The additive with this EO permits a greater interaction of the packaging with the food an important differential compared to conventional packaging.

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Orange essential oil as antimicrobial additives in poly(vinyl chloride) films

2. Materials and Methods 2.1 Materials The orange essential oil (OEO) with specific density of 0.8420 g/mL was donated by AGROTERRENAS Company (São Paulo - BR) and the polymer was donated by TELETRON (Pernambuco - BR). The solvent tetrahydrofuran (THF) used from Sigma Aldrich.Text paragraph within a first subsection.

2.2 Characterization of the OEO by GC-MS Characterization of the essential oil was performed with a gas chromatography mass spectrometry (GC-MS) system from Thermo Scientific. The chromatograph was a Trace 1300 model. The mass spectrometer was the ISQ Single Quadrupole system. The temperature parameters were used were: GC oven ramp 60 °C for 3 min (10 °C/min to 300 °C) and 300 °C for 15 min; injector temperature 270 °C; MS temperature of the transfer line 280 °C; and MS source temperature of 250 °C ions.

2.3 Production of polymer films The films were produced by the solution casting method with 1.5g of PVC and 50 mL of THF[33]. The PVC films were prepared by additivating with orange essential oil in different amounts (0, 2, 10 and 30% w/w). The orange essential oil was added to the polymer according to the methodology adopted by Morelli et al.[34]. The glass Petri dishes used in the solvent evaporation step had the following dimensions: 15.0 × 2.0 cm. The PVC films and PVC additivated with OEL had an average thickness of (0.083 + 0.015) mm.

sealed and placed in a hot air oven at 40 °C. The migration periods were monitored at 0, 36, 84 and 162 hours.

2.7 Antimicrobial activity of OEL The activity of the orange essential oil was investigated by disk diffusion assay with medium Plate Count Agar (PCA)[36].

Filter paper disks of 2 cm diameter were utilized, having been sterilized by UV irradiation for 10 min (each side for 5 min).

Aliquots of 0.5 mL of S. aureus (ATCC 6538) and E. coli (ATCC 8739) in the order of 107 CFU/mL, were quantified by turbidity on the Mcfarland comparison scale. They were inoculated into the PCA by the pour plate method.

After solidification of the PCA, these were placed on discs immersed with orange essential oil, in the center of the petri dish. The plates were incubated at 35 °C for 48h.

2.8 Radiolytic sterilization of films The films were exposed to gamma radiation with a Gammacell (GC)-220 Cobalt-60 irradiator at a dose of 25 kGy. This dose is also used to sterilize the food packaging[37].

2.9 Statistical analysis All data were analyzed by One-way analysis of variance (ANOVA) using Duncan’s test for comparison between the means (p <0.05). The statistical analyses were performed with STATISTICA 7.0 software.

3. Results and Discussion 3.1 GC-MS of orange essential oil

Mid-infrared (MIR) spectra of the films were acquired in a Tensor 27 spectrometer (Bruker) with an Attenuated Total Reflectance-ATR accessory. The spectra of the films were recorded under the following conditions: mid-infrared region 4000-400 cm-1, resolution of 4 cm-1 and 16 scans.

The GC-MS analysis identified over 150 constituents present in the OEO. Figure 1 highlights main constituents, representing 89.78% of the oil composition.

Figure 1 shows the major components of the OEO were p-Mentha-1(7),3-dieno (1), D-Limoneno (2), Linalol (3), Decanal (4), n-Hexadecanoic acid (5) and cis-13‑Octadecenoic acid (6). These compounds are classified as terpenes, alcohol, aldehyde and carboxylic acids and their molecular structures are summarized in Table 1, with their respective retention times (RT) and peak areas.

The most known for their antimicrobial compounds are the phenols, terpenes and aldehydes. These act by altering the concentration of fatty acids in the microbial cell membrane, causing damage to its structure[38].

D-limonene was expected as the major constituent as described in the literature on Citrus oils[39]. Other authors who studied Citrus oils quantified 84.7% in grapefruit oil, 94.51% in orange oil and 60.0% in lemon oil[40-42].

2.6 Migration test

3.2 Mid-infrared spectra (FTIR) of PVC/OEO films

To follow the migration of orange essential oil, we used mid-infrared spectroscopy, using the attenuated total reflection technique (ATR)[4]. The conditions chosen were: spectral range 1670 to 1616 cm-1; resolution of 4 cm-1; and 16 scans. Samples of scale films (30x10) mm were used in the migration tests. To perform the test, the samples were immersed in food simulants: distilled water, olive oil and 10% ethanol. Each film sample was immersed in 6 mL of simulant,

Figure 2 shows the FTIR spectra obtained in the mid‑infrared region of orange essential oil, pure PVC film and PVC films additivated with 2, 10 and 30% w/w of orange essential oil. In this figure the main bands have been identified in accordance with the literature, found in pure PVC film which are 2911, 1249, 957, 837 and 616 cm-1 related to the CH stretching, CH rocking, trans CH wagging C-Cl stretching and cis CH wagging, respectively[43]. In PVC

2.4 Mechanical properties Mechanical tests were carried out in a universal tensile testing instrument, DL-500MF brand model EMIC, in accordance with the ASTM D882-12 standard[35]. Assays were conducted at room temperature without humidity control. Assays were performed under the following conditions: load cell of 500 N; jaw speed of 100 mm/min; initial distance between the jaws 40 mm; and dimension of the specimen (20 × 50) mm. For each film composition, there were 9 replicates.

2.5 Mid-infrared spectra acquisition (FTIR)

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Silva, C. F., Oliveira, F. S. M., Caetano, V. F., Vinhas, G. M., & Cardoso, S. A.

Figure 1. GC-MS chromatogram of orange essential oil (OEO).

Table 1. Major components orange essential oil determined by GC-MS. Number 1 2 3 4 5 6

Component p-Mentha-1(7), 3-diene Limonene Linalol Decanal n-Hexadecanoic acid cis-13-Octadecenoic acid

Retention time (RT) (min) 6.80 7.07 8.82 10.64 19.71 21.41

Figure 2. FTIR spectra of the orange essential oil (OEO), pure poly(vinyl chloride) film (PVC) and poly(vinyl chloride) films additivated with 2, 10 and 30% of w/w of orange essential oil (PVC/2%OEO, PVC/10%OEO and PVC/30%OEO, respectively).

films additivated with orange essential oil, a 1644 cm-1 peak band is observed. This band gives evidence of the presence of orange essential oil which is identified as the stretch of the C = C bond. This band is present in orange essential oil, but it is not present in the PVC FTIR spectrum, so this band can be used for purposes of evaluating oil migration in a food simulant environment. In Figure 3 there is a 1670‑1616 cm-1 region in the spectra of films evaluated.

As can be seen in Figure 3, the increased peak of the band is due to the increase in the percentage of oil.

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Peak area (%) 1.98 79.97 1.11 0.93 1.84 3.95

Figure 3. FTIR spectra of the orange essential oil (OEO), pure poly(vinyl chloride) film (PVC) and poly(vinyl chloride) films additivated with 2, 10 and 30% of w/w of orange essential oil (PVC/2%OEO, PVC/10%OEO and PVC/30%OEO, respectively) in the region of 1616-1670 cm-1.

3.3 Migration test of the orange essential oil For migration analysis, samples of PVC films were evaluated. These PVC films were additivated with 2%, 10% and 30% w/w of OEO exposed to the following chemical agents: 10% ethanol, olive oil and water. These media simulate alcoholic foods (ethanol), greasy food (olive oil) and aqueous non-acid foods (pH > 4.5) (water), as established

by Resolution Nº. 32 of the Common Market Group, MERCOSUR (2010)[44].The acquisition of the spectra was carried out in periods of 0, 36, 84 and 162 hours. Figure 4 Polímeros, 28(4), 332-338, 2018

Orange essential oil as antimicrobial additives in poly(vinyl chloride) films shows the spectra of PVC samples additivated with 2% w/w of OEO. The essential oil migration to the film surface can be observed by the decrease in peak at the 1644 cm-1 band.

Figure 4 shows a decrease in the intensity of the peak at periods of 36, 84 and 162 hours. This migration is justified by the diffusion mechanism that is strongly influenced by interactions occurring between the media and the packaging material[45].

Figure 5 illustrates the spectra of PVC samples with 30% w/w of OEO. Figure 5a shows that OEO migration in the ethanol simulant occurs gradually over the period.

Figure 5b shows migration in the simulant olive oil with higher speed, being completed in the first 36 h. Figure 5c shows OEO migration at a slower speed, as can be verified by the intensity of the peak at 1644 cm-1.

The migration of orange essential oil in the simulant olive oil occurred with higher speed due to the affinity and solubility between them. The diffusion of the active agent

and its solubility of the polymer is extremely important to define the basic conditions for their use. The diffusion behavior of chemicals incorporated in the polymers is a very complex process and depends on several parameters, such as the concentration of substances in the packing, nature of the food, temperature and the period of time during which the contact lasts[46]. In the literature, there are studies that have evaluated the migration of limonene in other polymers.

Authors evaluated the diffusion of limonene in low-density polyethylene film[47].They found that limonene diffusion velocity in the polymer was low due to the morphological differences in the polymer.

3.4 Antimicrobial activity of OEL Figures 6a and 6b illustrate the antimicrobial test through the zone of inhibition for S. aureus (Gram positive) and E. coli (Gram-negative). It can be seen that these figures the zone of inhibition showed antimicrobial activity for the bacteria tested in the oil. Diameters of the inhibition halos shown in Figures 6a and 6b were 21,6 mm and 38,5 mm, respectively. The antimicrobial activity of orange essential oil has also been observed by other authors[48,49].

3.5 Mechanical properties

Figure 4. Migration in pure poly(vinyl chloride) film (PVC) and poly(vinyl chloride) film additivated with 2% of w/w of orange essential oil (PVC/OEO) in the simulants: (a) ethanol; (b) olive; and (c) water by Infrared.

Figure 5. Migration in pure poly(vinyl chloride) film (PVC) and poly(vinyl chloride) film additivated with 30% of w/w of orange essential oil (PVC/OEO) in the simulants: (a) ethanol; (b) olive; and (c) water by Infrared.

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Table 2 shows the results of tensile tests for mechanical properties, using Young’s modulus, percentage elongation at break and tensile strength of PVC films, PVC/2%OEO, PVC/10%OEO and PVC/30%OEO. The mean values of the mechanical properties obtained through the mechanical tests were compared statistically with Duncan’s test at a significance level of 5% (p <0.05). We verified that there was a reduction of the values of Young’s modulus for the additive with 30% w/w of OEO. For the percentage elongation at break, the values presented no statistical differences for the level of significance of 5%. For maximum stress, significant changes were observed from the additive with 10% w/w of OEO. Table 3 shows the results of tensile tests for Young’s modulus, percentage elongation at break and tensile strength of PVC films, PVC/2% OEO, PVC/10% OEO and PVC/30% OEO after exposure to gamma radiation. The mean values of the mechanical properties were compared statistically

by Duncan’s test at a significance level of 5% (p <0.05).

This verified that there were no significant changes in the values of Young’s modulus. For the percentage elongation at break, there was a decrease in value of this property with the additive at 30% w/w of OEO.

Figure 6. Antimicrobial test through the zone of inhibition: (a) S. aureus (Gram positive); (b) E. coli (Gram-negative).

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Silva, C. F., Oliveira, F. S. M., Caetano, V. F., Vinhas, G. M., & Cardoso, S. A. Table 2. Average values obtained for the mechanical properties tensile strength, percentage elongation at break and Young’s modulus in pure poly(vinyl chloride) film (PVC) and poly(vinyl chloride) films additivated with 2, 10 and 30% of w/w of orange essential oil (PVC/2%OEO, PVC/10%OEO and PVC/30%OEO, respectively).

Samples PVC/2%OEO PVC/10%OEO PVC/30%OEO PVC

Young’s Modulus (MPa)* 1224.00 ± 28.83a 1153.00 ± 143.28a 755.93 ± 37.46b 1275.00 ± 77.79a

Elongation-at-break (%)* 5.628 ± 0.197a 6.056 ± 0.030a 6.018 ± 0.726a 5.901 ± 0.344a

Maximum Tensile(MPa)* 42.150 ± 1.451a 31.505 ± 1.278b 33.410 ± 2.272b 43.580 ± 0.850a

*Values are presented as means ± standard deviation. Different letters in the same column indicate significant differences (p < 0.05).

Table 3. Average values obtained for the mechanical properties tensile strength, percentage elongation at break and Young’s modulus of the irradiated samples in pure poly(vinyl chloride) film (PVC) and poly(vinyl chloride) films additivated with 2, 10 and 30% of w/w of orange essential oil (PVC/2%OEO, PVC/10%OEO and PVC/30%OEO, respectively).

Samples PVC/2%OEO PVC/10%OEO PVC/30%OEO PVC

Young’s Modulus (MPa)* 0.083 ± 0.006a 0.076 ± 0.025a 0.089 ± 0.029a 0.076 ± 0.011a

Elongation-at-break (%)* 1059.77 ± 112.18a 941.65 ± 89.76a 738.17 ± 10.01b 947.72 ± 44.19a

Maximum Tensile (MPa)* 6.232 ± 0.090a 6.062 ± 0.192a 5.770 ± 0.575ab 5.476 ± 0.169b

*Values are presented as means ± standard deviation. Different letters in the same column indicate significant differences (p < 0.05).

Comparing the mean values for each property before and after gamma radiation, we observed that there was a reduction in all parameters for each PVC film with oil additives. Similar result was observed in the work done by Landgraf[37].The author affirms that although sterilization by gamma radiation at 25 kGy dose inactivates the antimicrobial agent, the highly reactive species generated in the irradiation process can have undesirable effects on packaging materials, degrading the polymer may lower its resistance, change the color and transparency.

A comparison of the reduction obtained before and after the sterilization process showed that the Young’s modulus of the control film decreased by 25.67%, while for the films with 30% OEO this reduction was only 2.35%.

For elongation, these reductions were 7.20% and 4.12%, respectively for the film control and 30% OEO. For maximum stress, there was a reduction of 1.23% for the films with 30% OEO and an increase of 11.17% for the control film.

These results indicate that irradiation affects in the PVC film is more intense in the PVC film without OEO, while in the presence of 30% w/w of OEO these changes were minimal.Accordingto Uzeli (2013), packaging properties should be maintained after sterilization[50]. Thus, PVC films with 30% orange oil meets this requirement.

Table 3 also shows that the flexibility in PVC film with oil increased after sterilization by gamma radiation. This is important for packaging, since flexibility is a desirable property for this polymer.

4. Conclusions OEO presented antimicrobial activity to E. coli and S. aureus, two microorganism pathogens of great relevance to food area. Through the results of the migration test, it was found that the OEO migration speed for each food simulant is related to the amount of additive used in the active film.

The higher the percentage of additives, the most essential oil migration speed to the surface of the film. The mechanical 336 336/338

properties demonstrated that in the presence of OEO, the PVC films were more flexible, even after being irradiated with gamma radiation. The results from the mechanical and migration properties showed that orange essential oil is promising for use in antimicrobial packages, because the essential oil is an antimicrobial agent that migrates to the surface of the film in food simulants and also contributes to improve flexibility of the film.

5. Acknowledgements The authors thank the Fundação de Amparo Ciência e Tecnologia do Estado de Pernambuco (FACEPE) for the provided scholarship.The materials donated by companies AGROTERRENAS Company and TELETRON. The English text of this paper was revised by Sidney Pratt, Canadian, MAT (The Johns Hopkins University), RSAdip - TESL (Cambridge University).

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Received: Jan. 23, 2017 Revised: July 04, 2017 Accepted: Jan. 23, 2018

Polímeros, 28(4), 332-338, 2018

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.09016

Sheath-core bicomponent fiber characterization by FT-IR and other analytical methodologies Marcia Murakoshi Takematsu1, Milton Faria Diniz2, Elizabeth da Costa Mattos1,2 and Rita de Cássia Lazzarini Dutra1* Instituto Tecnológico de Aeronáutica – ITA, São José dos Campos, SP, Brasil Instituto de Aeronáutica e Espaço – IAE, Divisão de Química – AQI, São José dos Campos, SP, Brasil 1

2

*ritacld@ita.br

Abstract The bicomponent fibers are a special class of fibers that consolidate two polymers in only one fiber in order to explore individual properties of each polymer and can be designed in a spatial configuration that allows the enhancement in application of this material. Thereby, an appropriate characterization of bicomponent fibers is very valuable to process monitoring, quality control and forensic investigation. The sheath-core bicomponent fiber composed by polyethylene (PE), polypropylene (PP) and titanium dioxide (TiO2) was analyzed by Fourier transform infrared (FT-IR) spectroscopy and other analytical methodologies. Results obtained by FT-IR using modern accessories showed efficiency to characterize the polymers of sheath (PE) and core (PP), moreover these polymers were confirmed by DSC (Differential Scanning Calorimetry). The morphology and elemental composition were also studied by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS). The thermogravimetric analysis (TGA) and colorimetric analysis allowed characterize and quantify the concentration of TiO2.

Keywords: bicomponent fiber, characterization, FT-IR, polyethylene, polypropylene.

1. Introduction The bicomponent fiber is produced to explore properties nonexistent in the fiber constituted by a unique polymer and is developed in order to achieve better results in these criteria: luster, resistance, dyeing, shrinkage, and stability of the fiber. The spatial configuration of two components of fiber consists usually of two types: side by side and sheath-core. In the first configuration, two components are divided lengthwise in two or more different regions and, the second type, one component is in the core of fiber and another one around the core and is called sheath[1]. These fibers are also known as “composite”, “conjugate”, and “hetero” fibers and, nowadays, the majority of bicomponent fibers commercially produced is sheath-core which assumes different spatial configurations depending on core position [2].

Dasdemir et al.[2] also describes that the major application of these fibers is in nonwoven area and one of purpose of use includes the increase of flexibility and strength, improvement of melting process, cost reduction and enhancement in surface properties of material.

Andrzejewski, et al.[3] studied a new concept of bicomponent fibers as a base material for self-reinforced composite. The objective of this study was to explore the different thermal properties performed by bicomponent fibers when they are processed by different techniques, such as extrusion and injection molding.

The fibers are the main components of nonwoven and have performed an important role in mechanical properties[4]. There are also additives able to modify the fibers to communicate and improve desirable properties

Polímeros, 28(4), 339-347, 2018

or reduce and remove some unwelcome attributes to final product. One example of modification is the use of delustrant component which reduces the brightness as long as intensify the opacity of fiber. With this purpose, TiO2 can be incorporated as a concentrated suspension in the solid polymer before extrusion reducing significantly the transparence of fiber[5]. This present study was conducted to characterize the sheath-core bicomponent fibers constituted by thermoplastic polymers (PE/PP) and TiO2.

According to Demirci et al.[4], the sheath-core bicomponent fibers have the sheath constitution a material with lower melting point than core material. In bicomponent fibers, PE is frequently used in the sheath whereas PP, polyamide 6 (PA6) and polyester, such as polyethylene terephthalate (PET) are the polymers most often used as core material.

The polymers used in the core have usually the highest values of elasticity module than the sheath material and the transversal area of core is larger than the sheath.

One important polymer of great industrial importance is PE that is very used in the sheath because this polymer has played a good interfacial stability in bicomponent melt spun process due its thermal expansion and behavior very characteristic of PE[2]. Since 1950, the HDPE (high density polyethylene) is considered for perform superior mechanical properties in extrusion of melt fibers however the application of PP fibers in the nonwoven sector, particularly in medical and hygiene areas, had risen more recently[5].

The most important polymer used in the world is the PP. However, PP presents hydrophobicity, poor biocompatibility

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

Takematsu, M. M., Diniz, M. F., Mattos, E. C., & Dutra, R. C. L. and the low reactivity in the surface restricts its application.

Many physical and chemical surface treatments were developed in order to turn the surface more reactive, such as: blending, surface coating, plasma treatment, gamma ray, UV (ultraviolet), ozonation treatment and chemical grafting[6].

The different characteristics of materials used in bicomponent fibers composition and the importance of appropriate manufacturing to attend the required properties to final product, address to an ideal characterization of the components to verify the real composition and, significantly, the spatial configuration of fibers.

Other application of bicomponent fibers consists in the enhancement of the structure of disposable hygienic absorbent products, such as disposable diapers, especially in a layer that has property of liquid permeation. As the absorbent layer is typically made from an absorbent material that includes natural fibers such as cellulose, fluff pulp fibers, cotton fibers, and rayon fibers, and a super absorbent polymer (SAP), after liquid is absorbed into the absorbent layer, the absorbent material of the absorbent layer tends to expand and become heavy causing an uncomfortable feeling in user. In order to perform a supportive structure to fix the absorbent material in place, the synthetic fibers are incorporated into the absorbent layer[7].

Several analytical techniques are applied to study these fibers. Meleiro and García-Ruiz[8] conducted spectroscopic techniques in order to identify and compare different textile fibers with aim in forensic field. Microspectrophotometry in the ultraviolet-visible range and Raman spectroscopy were the main techniques studied in this scientific paper.

They mentioned that UV-Vis microspectrophotometry is the first recommended technique, which is principally used to study the color of the fibers. Moreover, FT-IR spectroscopy is the recommended tool to determine the fiber nature that can be combined with Raman as a complementary technique to get a comprehensive analysis of textile fibers. Others analytical methodologies are emerging to the analysis of fibers traces, such as infrared (IR) chemical imaging spectroscopy and X-ray fluorescence spectroscopy[8].

Based on the combination of techniques, this present study is focused on characterize a bicomponent fiber by FT-IR spectroscopy associated with others different methodologies with purpose to contribute with new methodologies to forensic field, polymer and fiber characterization.

The FT-IR spectroscopy consists in one of many analytical tools that have been performed to characterize blends, especially when two polymers are in separate and distinct phases it is possible to assume that there are two different materials that not interact in IR spectrum, except in a possible interaction between the two phases. In the last case, the IR spectrum shows the bands derived of miscibility of polymers; on the contrary, it is feasible to determine the two polymers analyzing the blend by this technique[9].

Prati et al.[10] studied IR spectra obtained by FT-IR microscopy which allies the images to analytical features of FT-IR spectrophotometer. FT-IR microscopy can be used in reflection and transmission modes. The ATR (attenuated total reflectance) objective is generally considered one of the more reliable methods to analyze cross sectional areas, due to the fact of register similar spectra collected by 340 340/347

transmission mode. There are two precautions to be taken when this FT-IR technique is used: the contact between the crystal and sample should be suitable and, as the sample can slide on the crystal, it is necessary to verify if the area to be analyzed do not move during the spectrum register.

Flynn et al.[1] concluded that IR chemical imaging with sample preparation using DAC (diamond Anvil cell) accessory and ATR microscopy provides the spatial configuration of bicomponent fibers and chemical information of each polymer that composes the fibers as well if it is possible to detect the spectral differences between the two presented components, once depending on the size of fiber diameter, the ATR microscopy does not allow spectral resolution to differ the polymers. For this reason, there are restrictions regarding to the ATR microscopy mode.

In this present study, three non-destructive FT-IR techniques were performed given that two by transmission mode (with and without microscope), PAS (photoacoustic spectroscopy) and reflection mode which consists of DRIFT (diffuse reflectance infrared Fourier transform) and UATR (universal attenuated total reflectance) in order to investigate the surface and core of bicomponent fiber. Basically, the study was conducted employing: SEM images to characterize the sheath-core configuration and width of each layer; thermal analysis to determine mass loss during thermal degradation; FT-IR and ultraviolet and visible (UV-VIS) spectroscopy to characterize known components. Related to inorganic content, TiO2, analysis by FT-IR transmission mode of fiber calcination residue were carried out with purpose of identify the type of TiO2 crystal added to polymer of the bicomponent fiber studied in this paper. Additionally to this, the bicomponent fibers were also studied by EDS to understand in which part of sheath-core bicomponent fiber the titanium was incremented and other pyrolysis reaction of inorganic residue with potassium pyrosulfate with after color reaction with hydrogen peroxide was also performed to confirm the presence of titanium and to quantify this residue.

2. Materials and Methods 2.1 Sample The bicomponent fiber 3 denier PE/PP supplied by Far Eastern New Century Corporation (Taiwan) was used.

The composition of this material is known: PE, PP, blue dye and TiO2. As the dye has minimum concentration in the fiber, this additive was not part of the scope of this study.

2.2 Equipment/experimental conditions/methodologies 2.2.1 SEM / EDS The samples were analyzed using FEI Quanta600 FEG. The images were acquired in SE (secondary electron) mode and different magnifications were applied (500x and 9500x). The EDS analysis with an acceleration tension of 15kV was used in backscattering mode. The samples were fractured after freezing in liquid nitrogen and the sputtering with platinum was prepared before mounted on SEM stub.

The intention of this experiment was to analyze qualitatively the sample to study the elemental composition in each part of fiber and define the cross-sectional area to understand the type of bicomponent fiber. Moreover, the SEM technique Polímeros, 28(4), 339-347, 2018

Sheath-core bicomponent fiber characterization by FT-IR and other analytical methodologies allows to measure each part of bicomponent fiber and this resource was also taken in one fiber to understand mainly the width of surface layer, once the sample was studied by FT-IR surface modes: UATR and PAS. 2.2.2 DSC The fiber sample was analyzed by equipment of PerkinElmer DSC 6000 and about 1.5 mg of sample was introduced into aluminum pan and then tightly sealed.

One empty aluminum pan was used as a reference. With continuous nitrogen (N2) flow, the pans were heated until 200 °C at 10 °C/min and then cooling step was conducted at 20 °C/min until -40 °C, to arrange the crystals. After cooling, the second curve of melting was evaluated by new heating until 200 °C at 10 °C/min. The apparatus calibration was carried out with indium and zinc as standards. As the first heating step presents the shape memory, the polymer melting temperatures (Tm) were taken from the second heating curve.

2.2.3 TGA Pyris 1 TGA model (PerkinElmer) was used to determine the content of inorganic residue in the sample. About 3.0 mg of sample was weighed in the platinum crucible and heated until 800 °C with a continuous N2 flow at 20 °C/min; then the atmosphere was shifted to synthetic air until 1000 °C at the same rate and the final temperature was hold for 2 minutes.

The apparatus calibration was carried out with iron and nickel as standards.

2.2.4 Determination of TiO2 through ultraviolet-visible (UV-VIS) spectroscopy 8453 model UV-VIS spectrophotometer (Agilent) was used to determine the absorbance at 410 nm using 1cm quartz cuvette. The sample was carbonized in Bunsen burner until form a black residue and it was taken to a muffle furnace at 800 °C for 3 hours. The white residue formed after 800 °C was pyrolyzed with potassium pyrosulfate in Bunsen burner until complete the reaction. The solid formed was dissolved with sulfuric acid 50% in water and the reaction with 30% hydrogen peroxide (H2O2) was performed to achieve the yellow color to identify and quantify the titanium present in TiO2.

2.2.5 FT-IR spectroscopy The transmission, reflection and photoacoustic modes were analyzed by Spectrum One. PAS mode (300 model supplied by MTEC, Inc.) and FT-IR microscope (FT-IR MIC) in transmission mode were conducted in Spectrum 2000 and AutoIMAGE PerkinElmer microscope, the both equipment were supplied by PerkinElmer.

PAS and reflection modes consist in FT-IR surface techniques whereas in transmission mode the IR beam pass through the sample and the spectrum represents all material that compose the sample. The reflection accessories used were: UATR and DRIFT. UATR consists of a composite Zn-Se diamond crystal that allows collect the spectra directly from the surface sample without any special preparation. The UATR spectra were collected over the range 4000 – 550 cm-1 (MIR- middle infrared region), gain 1 and 20 scans at resolution of 4 cm-1. The background scan was obtained before the initiate the sample analysis and it was acquired without any material in contact with the crystal maintained dry and clean.

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On the other hand, the reference material used to perform the background scan of DRIFT and PAS accessories were, respectively, calibration mirror and carbon black (supplied by MTEC Photoacoustic, Inc.). DRIFT spectra were collected over the range 4000 – 400 cm-1, gain 1, 20% energy, 20 scans at resolution of 4 cm-1. PAS spectra were collected over the range 4000 – 600 cm-1, gain 1, 32 scans at resolution of 4 cm-1, using helium gas as purge gas, mirror velocities to obtain the spectra: 0.05 and 1.00 cm/s. Transmission spectra were collected over the range 4000 – 400 cm-1, gain 1, 20 scans at resolution of 4 cm-1.

The conditions of FT-IR MIC in transmission mode were range 4000 – 700 cm-1 and 20 scans at resolution of 4 cm-1.

The samples were prepared according to required preparation of each technique as following described: • Transmission mode: this technique was used to identify the inorganic residue of sample. The fiber, as received, was prepared to be analyzed by transmission mode in this proportion 1:400 mg KBr pellet. The calcination of bicomponent fiber in muffle furnace was conducted before the preparation of KBr pellet (0.6:400 mg KBr).

Moreover, the casting film was prepared dissolving about 20 mg of sample previously in 20 mL toluene (lightly heated) and then the thin film was formed by evaporation of solvent in a watch glass.

• UATR mode: the area of crystal that had contact with the sample was approximately 2 mm of diameter. The sample area was visually selected and the pressure about 120N was applied on the sample to ensure a good contact between the sample and incident IR beam, preventing loss of IR incident radiation.

• FT-IR MIC transmission mode: for transmission analysis using microscope, some fibers were disposed very straight in a support with a window to IR beam pass through the sample and acquire the IR spectrum.

Background was collected adjacent to the sample through the air.

• DRIFT mode: the sample was tested directly in DRIFT mode using the macro sample support.

• PAS mode: the sample was also tested directly in this mode.

3. Results and Discussions 3.1 Morphology and elemental identification of fibers by SEM/EDS The fibers were analyzed related to morphology and elemental identification as shown in Figure 1. The EDS detector coupled to SEM was used with objective to identify the chemical elements present in the layers of sample. A high accelerating voltage (generally higher than 10 kV) is required to excite the electrons of interest elements. This detector is largely used in material which composition has many elements[11]. Previous studies including SEM analysis of bicomponent fibers focused only in physical structure of the material[1-3].

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Takematsu, M. M., Diniz, M. F., Mattos, E. C., & Dutra, R. C. L. As from images obtained by aggregated fibers (Figure 1a) and the cross-sectional fiber it was possible to classify as sheath-core because two layers are evidenced by Figure 1b, in which there is an inner layer with approximately 16.78 µm of diameter (core) with another one surrounded all inner layer with approximately 3.72 µm of width (sheath) in a cylindrical format. In order to investigate the chemical composition in the core and sheath, the EDS spectra were collected in backscattering mode and then the elemental analysis was performed in two points in which the beam is irradiated on a chosen area within the field of view. In the region 1 (core), it was observed only presence of carbon (C) as shown image Figure 1c; however, in region 2 (sheath) carbon (C), oxygen (O) and titanium (Ti) were identified according to Figure 1d. This technique SEM/EDS was also used in a recent paper to characterize iron as Fe3O4 nanoparticles present in bicomponent nanofibers composite[12].

By EDS analysis it is possible to assure the presence of Ti and O in the sheath of bicomponent fibers indicating an increment of the additive TiO2 in the outside of fiber to give more opacity to material[5]. Nevertheless, more two studies were conducted to characterize and quantify this oxide in these fibers by colorimetric and thermal gravimetric methodologies. Otherwise, by FT-IR it was possible to characterize this inorganic additive by spectrum of calcinated residue. Once the EDS technique is dedicated to elemental

analysis, the polymers that compose the bicomponent fiber can not be distinguished by this technique. For this reason, this study has proposed DSC analysis to find out the melting point of polymers and additional methodologies developed

by FT-IR were performed with the purpose to enrich the characterization of polymers that compose each layer of bicomponent fiber.

3.2 DSC analysis The polymers Tm was taken by second heating curve and this curve can be observed in Figure 2. The thermogram indicates two melting peaks in the second curve at 128 °C and 162 °C suggesting that the composition of the samples is based on PE and PP, once the Tm of each polymer is according to the literature[13]. As from these results, it is possible to suggest that the composition of sample is PE and PP, as mentioned by supplier. However, more studies are necessary to confirm this characterization and further understand what polymer is related to sheath and core.

In order to achieve these objectives, these studies were performed by FT-IR.

3.3 TGA analysis This thermal analysis allowed investigating the content of material composition, such as: volatiles components: 0.135% until 300 °C; polymeric degradation:

Figure 1. SEM images and EDS spectra of 3 denier PE/PP bicomponent fiber: (a) SEM micrograph of fibers; (b) SEM micrograph of individual fiber cross section with width of core and sheath; (c) EDS spectrum of region 1(core); (d) EDS spectrum of region 2 (sheath).

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Sheath-core bicomponent fiber characterization by FT-IR and other analytical methodologies 3.4 Characterization and quantification by colorimetric reaction The colorimetric technique allows evaluating the reaction of ion Ti+4 with H2O2 in sulfuric acid solution and evaluated by a calibration curve which obeys Lambert-Beer law (Lopes-Mollinero et al.)[14]. The result achieved by this colorimetric reaction and the intensity of color read in UV-VIS spectrophotometer was 1.81% of TiO2. This data corroborated the value recorded in TGA analysis and confirmed presence of Ti+4.

3.5 FT-IR characterization

Figure 2. DSC thermogram of 3 denier PE/PP bicomponent fiber (nitrogen, second heating).

Figure 3. TGA curve of 3 denier PE/PP bicomponent fiber (nitrogen, 20°C/min, until 800 °C; synthetic air, 20 °C/min, 800 °C – 1000 °C and 2 minutes at 1000 °C).

98.067%, 300 °C – 1000 °C and inorganic residue: 1.866%, at 1000 °C (Figure 3). The low concentration of volatiles and presence of additives used to facilitate the processing of material and modify the physical chemical properties of final product, normally, consist in organic solvents that degrade and volatilize before PE and PP degradation.

These polymers initiate the thermal degradation at the same range of temperature when submitted to TGA analysis, so it is not possible to verify using this technique the composition in % of each polymer contained in the fiber. On the other hand, it is possible to verify that there is an inorganic residue present in the fiber composition, which means that, can be the TiO2, a solid reagent very useful as filler in polymeric blends with properties to reduce transparency and turn the material more opaque as mentioned previously. In order to evaluate if this residue is TiO2, a typical analysis by pyrolysis with potassium pyrosulfate and posterior reaction with H2O2 was carried out.

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Currently, there are available many modes to obtain FT-IR spectrum and some of them were chosen to investigate if a particular mode can be correlated with the measures obtained by SEM. In this manner, the characteristics of surface analysis by DRIFT, UATR and PAS were discussed especially addressing the sheath layer to enhance the understanding some results found using other analytical techniques. The FT-IR transmission mode was also aim of this present study by pellet and casting film and using microscope.

Transmission mode: the transmission mode used in FT-IR with KBr pellet sample preparation consists in the simplest and more used in routine analysis of solid samples. Basically, the IR beam pass through the sample and the spectrum reveals the components of inner and surface sample, evidencing normally the material in major concentration. The use of KBr pellets has been avoided in a routine because demands time and the quality of preparation are very significant to achieve a good spectrum due the bands of humidity coming from hygroscopic property of KBr[15]. The 3 denier PE/PP bicomponent fiber was prepared with KBr (1:400 mg) forming a pellet (Figure 4) and a thin film was also evaluated by transmission mode after dissolving the fiber in toluene lightly heated forming a casting film (Figure 5).

According to Figure 4, the transmission mode FT-IR spectrum of pellet defined mainly IR absorption bands related to PE and oxide: in 1470 cm-1 and 718 cm-1 (PE) and 500 cm-1 (oxide), marked with black stars. On the other hand, the spectrum of casting film by transmission (Figure 5) was crucial to define the presence of PP (marked with black stars, bands 1376, 1167, 997, 973 cm-1) in the fiber since this polymer was not evidenced by pellet. In this case, the PE was also better defined and marked with red stars. These two sample preparations were chosen to attend the first classic mode to evaluate any material by FT-IR and compare this mode with other modern modes that provided more information about the composition of core and sheath, once the transmission mode is not selective to surface and analyze the sample as a whole. The importance to introduce the pellet was identified the oxide presence and the casting film allows to define the polymeric composition in the fiber.

In the Figure 4, the absorption bands in 3434 and 1631 cm-1 are due the moisture present in the pellet. However, it was noticed that this sample is very difficult to grind and, for consequence, the pellet formed is not homogenous due the difficult incorporation of it in the salt. This analysis suggested the presence of only one polymer in the fiber, 343/347 343

Takematsu, M. M., Diniz, M. F., Mattos, E. C., & Dutra, R. C. L. PE. Since this technique has the drawback of moisture presence and difficulty to prepare a good pellet to analyze, other studies with different FT-IR techniques and accessories were carried out to drive this study to FT-IR analysis more reliable and feasible characterizing the composition of this bicomponent fiber.

Meanwhile, before starting the use of reflection and PAS techniques to analyze the polymers, the transmission mode using KBr pellet was also performed to verify the composition of the calcined residue of bicomponent fiber (Figure 6). It is possible to observe the presence of large bands at 671, 500 and 422 cm-1, marked with black stars, that constitute characteristic bands of metallic oxide, as reference spectrum of TiO2, according to Hummel[16]. The spectrum shown in Figure 6 was compared to the Hummel [16] reference spectrum that mentions two types of TiO2 crystals: rutile and anatase, spectrum number 5438 and 5439, respectively.

Although the spectrum obtained from sample calcination presents the characteristic bands of anatase and rutile crystal formation, the bands present more similarity to anatase crystal. According to Chen et al.[17], TiO2 consists in a multicrystal substance and the crystalline structures include brookite, anatase and rutile. Anatase and rutile are the structures more common to be used and they form crystalline structures in a tetragonal format and the rutile density is higher than anatase.

Valentim, Tavares & Silva[18] studied the effect of TiO2 addition in ethylene and vinyl acetate copolymer and characterized this mineral by transmission under KBr pellets.

The result obtained in their study showed IR absorption bands in the same region of bands showed in Figure 6, as expected: about 669-555 cm-1 (regarding to Ti-O-Ti), and a band at 3450 cm-1, which the authors attributed to hydroxyl group present in the oxide surface or moisture of pellet.

In this current study, this last band was also observed and the authors preferred to attribute it just to the presence of moisture, since there was observed a band at 1640 cm-1 which is also attributed to residue of water in the pellet. According to literature[15] the transmission mode is not applicable to surface analysis of oxide.

FT-IR MIC transmission mode: this analytical technique uses a combination of FT-IR spectrometer with a microscope and is considered an important forensic tool that detects and identifies the fibers. FLYNN et al. evaluated the application of infrared chemical imaging to analysis of bicomponent fibers and they discussed about transmission and ATR mode using FT-IR MIC, given that ATR mode is more dedicated to surface analysis and transmission mode elucidates the sheath and core components by the spectrum combination of the both parts of bicomponent fibers[1]. This present study investigated the sample by FT-IR MIC transmission mode in order to compare the results obtained using FT-IR MIC to casting film spectrum. Indeed, the result obtained by FT-IR MIC transmission mode as shown in Figure 7 corroborates the information reported by FLYNN et al. about this specific mode, because the sample spectrum yielded a combined spectrum of sheath and core components. Furthermore, it is possible to assure that this analysis showed sensitivity similar of spectrum obtained by formation of casting film, once the bands related to PE and PP were very well defined 344 344/347

Figure 4. Transmission FT-IR spectrum of 3 denier PE/PP bicomponent fiber, as received, KBr pellet (1:400 mg). *Bands related to PE (1470 cm-1 and 718 cm-1) and to oxide (500 cm-1).

Figure 5. Transmission FT-IR spectrum of 3 denier PE/PP bicomponent fiber, after toluene treatment, casting film. Bands related to PE (red star) and Bands related to PP (black star).

Figure 6. Transmission FT-IR spectrum of calcined residue of bicomponent fiber 3 denier PE/PP, KBr pellet (1:400mg). *Bands related to TiO2.

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Sheath-core bicomponent fiber characterization by FT-IR and other analytical methodologies and interference fringing, normally expected to transmission analysis using microscope, was not observed.

For this reason, the spectrum recognized PE (marked with red stars) and PP (marked with black stars) as the IR beam passed through the sheath and core of sample, as shown in Figure 7.

Reflection mode by DRIFT: Differently of transmission mode that use KBr pellet, the reflection mode by DRIFT do not require sample preparation, therefore the sample is analyzed directly by this technique without any treatment.

Moreover, the main benefit of this technique is based on the intensification of non-fundamental bands (combination bands and overtones). So, a spectrum more completed of sample can be acquired by DRIFT mode, when compared to transmission mode providing more information about the sample[19]. However, as the interpretation of overtones and combination bands is not easy, the presence of these bands can cause a disturbance the process of spectrum interpretation. Generally, DRIFT spectra evidence surface coating and inner composition showing, in some spectra, large bands. In this case, the spectrum presented well-defined bands suggesting that the IR beam passed through by the surface in a depth with more 3 µm, according to results obtained by SEM images. The DRIFT spectrum shown in Figure 8, evidenced with excellent resolution, the presence of PE (duplet about 720 and 730 cm-1, marked with red star) and PP (1167, 997, 973, 841 cm-1, marked with black stars).

As from this data, it is possible to confirm the presence of PP in the sample as supplier information, but it is unknown what polymer consists in the sheath and core by this spectrum.

Furthermore, the spectrum also evidenced the presence of TiO2 once there was observed a large absorption band at 555 cm-1. The DRIFT analysis allowed to check the presence of PE, PP and TiO2 and consists in a good technique to analyze globally the fibers. For this reason, DRIFT definitely is not considered a selective technique.

UATR reflection mode: the UATR reflection mode was used by Noureddine et al.[20] in studies of chemical coating in woven samples. This is considered a surface and non-destructive technique that use a zinc selenide crystal with diamond to analyze the surface material pressuring the sample against the crystal to assure that it has a good contact with the surface of sample and the incident IR beam, preventing loss of beam irradiation. As DRIFT technique, UATR does not require sample preparation and the sample can be analyzed directly. With the purpose to investigate the surface or the sheath of the bicomponent fibers, the result found of sample presented a typical spectrum of PE being observed characteristic bands of PE: 1470 cm-1 e 729 cm-1, marked with red stars. This result allows concluding that this polymer composes the sheath of fiber (Figure 9), once this technique examines the superficial part of the sample.

According to data sheet of FT-IR equipment supplier, the zinc selenide and diamond crystal has 2.0 µm of IR beam penetration depth. Once the image (b) of Figure 1 (SEM) showed the width of external layer measures about 3.7 µm, it is clear that the IR beam penetrates the external side of fiber and did not reach the core of fiber, for this reason, the measures obtained by SEM were important to comprehend this surface mode and the spectrum resulted by UATR has corroborated the information described by equipment supplier.

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Figure 7. FT-IR MIC transmission mode spectrum. Bands related to PE (red star) and bands related to PP (black star).

Figure 8. DRIFT spectrum of 3 denier PE/PP bicomponent fiber, as received. Bands related to PE (red star) and bands related to PP (black star).

Figure 9. UATR spectrum of 3 denier PE/PP bicomponent fiber, as received. Bands related to PE (red star).

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Takematsu, M. M., Diniz, M. F., Mattos, E. C., & Dutra, R. C. L. In other words, UATR technique showed more selectivity to evaluate the PE in bicomponent fiber and confirm the presence of this polymer in the sheath.

PAS mode: the PAS mode is recognized as a near-surface and non-destructive analytical technique. This technique is based on the direct measure of absorbed energy by samples through a photoacoustic signal less susceptible to light scattering of particles present in the material[21,22]. The IR beam is absorbed by sample creating an induced heating due the absorption which provide a thermal expansion modifying the pressurization of inert gas present within the chamber and transforming this alteration of pressure in a photoacoustic signal detected by one microphone and then a spectrum is generated by a computer system. PAS represents a good technique to perform dark samples once as higher the rate of IR absorption better will be the photoacoustic signal[23].

Faster mirror velocities yield lower-intensity signals because the thermal diffuse depth decreases[24]. For this reason, more superficial layer has better resolution with increase of mirror velocity. The spectrum obtained of bicomponent fibers using PAS technique also include 100% PE and 100% PP materials used as standard (Figure 10). The image suggests that at slow velocity (0.05 cm/s) it is possible to observe the presence of PP, characteristics bands marked with black stars, corroborating the result found by DRIFT mode. Moreover, when the 1.00 cm/s is applied, the superficial layer is more evidenced and the spectra obtained are typical of PE, characteristics bands marked with red stars, as reported in UATR mode.

Based on these results, a comprehensive study for characterization of bicomponent fiber can be summarized by a representative figure (Figure 11) which compiles the analytical methodologies used to determine the respective polymer and oxide that composed each part of fiber (sheath and core).

4. Conclusions This present study started the elucidative process of 3 denier PE/PP bicomponent fiber with an analysis of imaging able to obtain a spatial configuration of fiber that clearly defined the fiber as the sheath-core structure.

The EDS analysis was fundamental to prove that TiO2 was added in PE bulk to compose the sheath. A non-destructive technique, the FT-IR analyses were essential to characterize each part of sample using modern accessories and, from the results obtained in this study, FT-IR spectroscopy can be considered the most important analytical technique to elucidate the polymer composition of each section of sheath-core bicomponent fibers. Once this study was focused on using different modes of FT-IR, it was possible to conclude that the feasible techniques to analyze the polymers of sheath (PE) and core (PP) structures were UATR and PAS. UATR was able to identify the component of more external layer and PAS revealed the components of both sheath and core, using different velocities. Other modes as transmission and DRIFT confirmed the presence of PE and PP in the whole fiber. Overall, this study provided a sequence of analytical methodologies that can be very helpful to understand since the spatial configuration until the real composition of sheath-core bicomponent fibers.

This study disclosed about the important role of FT-IR spectroscopy to elucidate the composition of sheath-core structure along with other analytical methods such as: SEM/EDS and DSC. Colorimetric assay was also conducted to confirm the presence of titanium detected by the EDS spectrum and the concentration of this inorganic residue found by TGA.

5. Acknowledgements Figure 10. PAS spectrum: (a) 3 denier PE/PP bicomponent fiber, as received, velocity = 0.05 cm/s; (b) 100% PP material – Velocity = 0.05 cm/s; (c) 3 denier PE/PP bicomponent fiber, as received, velocity = 1.00 cm/s; (d) 100% PE material – velocity = 0.05 cm/s. Bands related to PE (red star) and bands related to PP (black star).

This study was supported in part by the National Senior Visiting Professor Program (PVNS) from the Coordenação de Aperfeiçoamento Pessoal de Nível Superior (CAPES).

The authors also would like to thank Fabio Eduardo Rangel for the support and collaboration in this study.

6. References

Figure 11. Representative figure of 3 denier PE/PP bicomponent fiber showing the cross section of fiber and analytical techniques used to characterize PE, PP and TiO2 in each bicomponent fiber section.

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Received: Mar. 08, 2016 Revised: July 06, 2016 Accepted: Sept. 08, 2016

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.09217

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

Evaluation of hydrolytic degradation of bionanocomposites through fourier transform infrared spectroscopy Raquel do Nascimento Silva1, Thainá Araújo de Oliveira1, Isaias Damasceno da Conceição1, Luis Miguel Araque1, Tatianny Soares Alves1,2 and Renata Barbosa1,2* Grupo de Pesquisa Polímeros e Materiais Conjugados, Programa de Pós-graduação em Ciência e Engenharia dos Materiais, Universidade Federal do Piauí – UFPI, Teresina, PI, Brasil 2 Graduação em Engenharia de Materiais, Centro de Tecnologia, Universidade Federal do Piauí – UFPI, Teresina, PI, Brasil 1

*rrenatabarbosa@yahoo.com

Abstract Studies about in vitro biodegradation of polymers have grown considerably due to the wide application of biodegradable polymers in biomedical areas. The objective of this study was to prepare bionanocomposites films of PHB, PEG, and organoclays by solution intercalation, and to evaluate the morphology, structure, hydrolytic degradation through FTIR and the calculation of carbonyl content. The results showed that bionanocomposites displayed intermediated dispersion of the filler, the polymer chains were intercalated into the organoclay layers and was observed some degree of exfoliation.

There was an influence of PEG and of the clay on the degradation of the polymer, this fact was observed due to the decrease in the intensity of PHB carbonyl band in the region around 1275 cm-1, affecting the amorphous and crystalline regions of the polymer. This reduction can be associated with the increase in hydrophilicity of the polymer caused by the presence of the PEG and clay, suggesting the possibility of increasing the biodegradability of the pure polymer.

In future research, there will be made characterizations to know if these materials can be used in medical devices.

Keywords: biodegradation, bionanocomposites, hydrolytic degradation, polyhydroxybutyrate.

1. Introduction The search for materials obtained from renewable sources has led to the growing interest in the use of biodegradable polymers, which can be used in several areas of society, i.e. the biomedical area. The most known and important biodegradable polymers are the aliphatic polyesters, poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(caprolactone) (PCL) and poly(hydroxybutyrate) (PHB)[1]. The main reasons for using these polymers in medical areas are their biocompatibility[2].

Among biodegradable polymers PHB can be highlighted, a polymer produced naturally by bacteria from renewable energy sources that can be biodegraded in nature[3].

However, PHB presents some disadvantages, for instance, narrow processability window and poor mechanical and barrier properties. In order to improve PHB properties, some modifications have been made, for example, blend and composite formation[4]. Fillers with dimensions on the range of nanometers have been widely investigated; since polymer’s properties are greatly improved with just a low content of the filler. Clays are layered silicate minerals, such as montmorillonite that has high availability, versatility, low cost, which have minimal adverse effects on the environment and human health. The individual clay particle presents a platelet structure, with a thickness of approximately 1 nm and lateral dimensions up to 1 µm. In composites, the nanoclays reinforcing efficiency, good barrier properties, and improved dimensional and thermal stability are strongly related to their aspect ratio and large surface area[5,6].

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Furthermore, the addition of a plasticizer can improve PHB properties, increasing its thermal stability and representing an effective way to develop a new material with desired properties[7,8]. In this sense, poly (ethylene) glycol (PEG) is a flexible and biocompatible polyester widely used to modify hydrophobic polymers and to form amphiphilic block copolymers[9]. PEG is non-toxic, soluble in water and inorganic solvents, chemically stable and inert in acidic and alkaline media. Additionally, it is widely used in different pharmaceutical, food, and cosmetic formulations[10,11].

The use of polymeric materials for diverse applications has increased since the synthetic polymers were discovered.

In the case of biomedical applications, the use biodegradable polymers and bionanocomposites have been the great importance since they are widely used in the formation of implants, the manufacture of capsules for controlled drug delivery, and the develop of scaffolds for engineering tissue, among other applications. For biomedical application, polymers and bionanocomposites have to satisfy specific requirements such as compatibility and appropriate mechanical properties.

Also, degradation products must be readily metabolized and excreted by the body without toxicity[12,13].

Thus, the present work had the objective of developing pure PHB and PHB/PEG/Organoclay bionanocomposite films in different compositions through the solution intercalation method. Subsequently, there were evaluated the systems morphology by optical microscopy, structure by X-ray diffraction analysis, hydrolytic degradation, and carbonyl

Polímeros, 28(4), 348-354, 2018

Evaluation of hydrolytic degradation of bionanocomposites through fourier transform infrared spectroscopy content by Fourier Transform Infrared Spectroscopy, to evaluate the degradation state.

2. Materials and Methods 2.1 Materials PHB as a yellowish powder with a high degree of purity of over 99.5% was supplied by PHB Industrial S/A, and it is biosynthesized by aerobic fermentation and extraction purification through a natural solvent. Mineração Pedra Lavrada (Paraiba) provided the expanded vermiculite clay for the development of this research. Poly (ethylene) glycol (PEG) and the chloroform solvent were purchased from Synth Ltda. The stearyl dimethyl ammonium chloride salt (Praepagen WB®) was purchased from Clariant do Brasil.

2.2 Chemical Modification Process of Vermiculite Clay (VMT) The organofilization of the VMT clay was performed according to procedures followed by Barbosa et al.[14] and Mesquita et al.[15] which consisted in the preparation of a dispersion containing distilled water, natural clay, and ammonium salt.

2.3 Solution intercalation method For the preparation of the films by the solution intercalation method, the PHB powder was previously sieved and oven dried at 70°C for 24 hours. Then 5g of PHB were dissolved in chloroform under mechanical stirring and heating at 80°C for 3 hours. To reduce solvent loss by vaporization, a condensation system was set up. For the formation of the pure PHB and bionanocomposite (BIO 95%, BIO 90%) films with 5 and 10% PEG, respectively, and with 3% organoclay vermiculite, the solutions were poured into marble plates, finally the films were removed from the plates. For the bionanocomposites, the ratio of parts per hundred of resin (PCR) was used, PHB + PEG were considered as resin.

2.4 Optical microscopy Pure PHB and bionanocomposite films surface were observed using a Leica Microsystems MD500 optical microscope (OM), operating on transmission mode with ICC 50 E camera and magnificent of 40X (500 µm).

2.5 X-ray diffraction analysis A Shimadzu XRD 6000 X-ray diffractometer system was used to perform XRD analyses. Scans were recorded in the range of 2Ɵ = 1.5° - 30°.

2.6 Hydrolytic degradation The hydrolytic degradation tests of pure PHB and bionanocomposites films were performed according to ASTM F1635-11[16] controlling the pH and temperature of the system. The test was carried out for 12 weeks. The hydrolytic degradation of the samples was performed in saline phosphate buffer (pH 7.4 ± 0.2). The test was carried out in triplicate, and the films were packed in test tubes with 10 ml of PBS solution and kept in a water bath at 37°C (±2). At different time intervals (2nd, 4th, 6th, 8th, 12th weeks), the films were removed from the controlled environment and then dried in an oven at 60°C. Polímeros, 28(4), 348-354, 2018

Additionally, there were monitored the weight loss of the pure PHB and bionanocomposite films through gravimetric analysis along the degradation test. Time zero was set up as before initiating the test, and measures were made at the time of the film’s withdrawals. The results of weight loss for the samples of the 12th withdrawal were not reported because the films were highly deteriorated due to the degradation.

The results were obtained through: M0 − M f ∆M = ×100 (1) % M0 Where ᐃM is the weight loss, M0 is the mass of the films before the degradation test and Mf is the mass of the films at the different removal times.

2.7 Fourier Transform Infrared Spectroscopy (FTIR) The systems were characterized by FTIR, before and after the hydrolytic degradation test, FTIR analyses were performed on a SHIMADZU IRAffinity-1 model spectrometer with a scan of 4000 to 450 cm-1. To the obtained spectra, it was applied a mathematical treatment known by deconvolution in the software Origin 8.0, in the Lorentzian function applied specifically to the bands of carbonyl (C = O) in (1722 and 1751cm-1). Thus, the carbonyl content was obtained by the ratio between the peak area of the carbonyl and the peak area of the reference band (CH3). The calculation was performed considering the samples before and after the withdrawals referring to the 2nd, 6th. The carbonyl indices for the samples of the 8th and 12th withdrawal were not reported because the films were highly deteriorated due to the degradation.

3. Results and Discussions 3.1 Optical microscopy Optical microscopy was employed to evaluate the system’s morphology. Figure 1 shows the optical micrographs of pure PHB and bionanocomposites films.

In the optical micrograph of the pure PHB, Figure 1a, there were observed superficial fissures that can be attributed to the solvent evaporation process, since the film adhered to the marble plates in which was poured. In the optical micrographs of the bionanocomposites films, Figures 1b and 1c there were perceived the same superficial fissures, and dark or dense zones along the films surface that can be ascribed to the formation of organoclay agglomerates. The BIO 90% film presented the greatest number of agglomerates, behavior that can be attributed to the poorer organoclay dispersion due to the higher PEG content, in comparison with the BIO 95% film. Similar results were reported by Mesquita et al.[17].

3.2 X-ray diffraction analysis X-ray diffraction analyses were carried out to evaluated structural modifications of the PHB by the addition of the organoclay and PEG. Figure 2 displayed the diffractograms of the pure PHB and bionanocomposites films.

As it was expected, the diffractograms of the pure PHB showed the characteristic peaks. For the organoclay, there were perceived six peaks between 2θ angles of 2 and 10.55° indicating the ammonium salt intercalation between the clay layers. In the diffractogram of the BIO 90%, there were noted 5 new peaks different to the displayed in the diffractogram of the pure PHB 349/354 349

Silva, R. N., Oliveira, T. A., Conceição, I. D., Araque, L. M., Alves, T. S., & Barbosa, R. due to the organoclay presence. Those peaks were shifted to smaller 2θ angles in comparison with the organoclay peaks.

Similarly, in the diffractogram of the bionanocomposite BIO 95%, there were noted 4 new peaks shifted to smaller 2θ angles and with lower intensities than the organoclay peaks and the BIO 90% peaks. The decrease of the 2θ angles indicated an increase in the interlayer spaces of the clays because the polymer chains entered between the clay layers. Besides, the difference in peaks intensity revealed the destruction of the clays crystalline order as a consequence of the intercalation of polymer chains in the clays layers, and the disappearance of peaks revealed some degree of exfoliation. Finally, it was noted that high PEG content decreased the intercalation and exfoliation degree since the PHB chains were impeded to enter the organoclay layers. Similar results were reported by Crétois et al.[18] and Silva et al.[19].

3.3 Hydrolytic degradation 3.3.1 Weight loss In Table 1 are listed the results of weight loss of the pure PHB and bionanocomposite films while the hydrolytic degradation test.

Table 1. Weight loss of the pure PHB and the bionanocomposites (BIO 95%, BIO 90%) films during the hydrolytic degradation test.

Weight Loss (%)

Time

Figure 1. Optical micrographs of the (a) pure PHB, (b) BIO 95% and (c) BIO 90% films.

(weeks)

Pure PHB

BIO 95%

BIO 90%

2 4 6 8

0.58 3.32 2.69 6.52

0.00 4.95 1.30 3.78

6.54 8.53 8.72 16.33

Figure 2. Diffractograms of the organoclay and the pure PHB and bionanocomposites films.

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Polímeros, 28(4), 348-354, 2018

Evaluation of hydrolytic degradation of bionanocomposites through fourier transform infrared spectroscopy It was observed different trends in the weight loss behaviors of the three systems. The pure PHB film lost weight linearly in the first two weeks and it decreased in the sixth week. For the bionanocomposites, there were observed oscillation, BIO 95% did not lose weight at the beginning of the test, on the other hand, BIO 90% lost 6.50% of its weight on the second week, and 16.33% on the eighth week, being the biggest loss in comparison with the other systems.

It may be suggested that the degradation was affected by the addition of the organoclay and PEG, which promoted the water penetration into the systems, caused the diminution of the polymer chains, and increased the disintegration of the systems. Similar results were reported by Kmita et al.[20] and Zhao et al.[21].

3.3.2 Carbonyl content Figure 3 shows the FTIR spectra, and Table 2 shows the carbonyl content obtained from the amorphous and crystalline regions, before and after the hydrolytic degradation of the pure PHB. Based on these values, it is possible to observe a significant increase of the crystalline phase content, and a discrete increase in the amorphous phase content of the polymer, after it has been submitted to the degradation test.

The degradation of the pure polymer occurred preferentially in the amorphous regions as a consequence of the increase in crystallinity, also taking into account that there was a reduction in the peak intensity of the region at 1750 cm-1.

According to Faria and Franchetti , the degradation of the polymer can occur due to the increase of the crystalline phase, and consequently, the consumption of the amorphous phase at the ends of the chain. The amorphous phase consumption induces the reorganization of the remaining chains and, as a result, the increase in crystallinity[21].

[22]

The data analyzed showed degradation in the amorphous region of the polymer, followed by an increase in crystallinity for the pure PHB. Such behavior is due to the time and hydrolysis conditions used. Spyros et al.[23] observed that the degradation of the pure PHB can occur in both phases, depending on the time of biotreatment of the polymer.

Bonartseva et al.[24] obtained similar results, in which the degradation of the PHB film is followed by the increase of the crystallinity.

Figure 4 shows the FTIR spectra obtained in the carbonyl region for the composite BIO 95%. The band referring to the carbonyl of the crystalline region was larger and less intense. The carbonyl contents presented in Table 3 showed that the insertion of the clay next to the PEG in the pure polymer altered the crystallinity of the material.

In the work developed by Branciforti et al.[25], the authors verified the alteration in crystallinity by adding montmorillonite to the pure PHBV. The carbonyl content for BIO 95% showed that there was a reduction of the amorphous and crystalline phase content of the polymer during the degradation time. Kmita et al.[20] studied the hydrolytic degradation in PLA and clay nanocomposites and observed that the addition of the clay promotes the

Table 2. Carbonyl PHB indices of amorphous and crystalline phase calculated before and after degradation.

2nd week

6th week

Crystalline(1722/1380)

IC Before degradation 1.61

3.90

4.02

Amorphous(1751/1380)

0.32

0.65

0.68

PHB

Figure 3. PHB spectra after deconvolution (C=O carbonyl band) before and after degradation.

Polímeros, 28(4), 348-354, 2018

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Silva, R. N., Oliveira, T. A., Conceição, I. D., Araque, L. M., Alves, T. S., & Barbosa, R.

Figure 4. BIO 95% spectra after deconvolution (C=O carbonyl band) before and after degradation.

Table 3. Carbonyl BIO 95% indices of amorphous and crystalline phase calculated before and after degradation.

2nd week

6th week

Crystalline(1720/1380)

IC Before degradation 3.49

3.04

3.29

Amorphous(1752/1380

0.07

0.006

0.53

BIO 95%

penetration of the water into the polymeric structure, which causes consequently a greater degradation of the materials.

Figure 5 shows the deoxygenated spectra for BIO 90% and the C = O carbonyl indices are presented in Table 4. With the increase of 10% PEG and the insertion of the organoclay, it was observed a proportional change in the content of amorphous and crystalline phases of PHB, verifying that the composition obtained results that corroborate with the loss of mass in the continuation of this work, and that the degradation can have been caused by the increase of the addition of PEG and the presence of the clay.

The determination of the carbonyl content for the BIO 90% showed a reduction of more than 50% of the carbonyl content in the amorphous phase in relation to the start of the test and a proportional reduction of the crystalline phase content. The incorporation of PEG and clay resulted in an increase in hydrolysis, thereby facilitating water penetration and ester bond cleavage[26].

This fact can be related to the value of the basal interlamellar distance of the bionanocomposite, which too depends on the length of the PEG chain and of the quaternary ammonium 352 352/354

salt. These factors affect the dispersion of organoclay in the pure polymer[27]. The degradation of the bionanocomposites can be directly related to the degradation of the surfactant (quaternary ammonium salt) present in the organoclay, in which an intercalation of the ammonium ions within the silicate layers of the vermiculite clay can occur.

For the bionanocomposites, the degradation occurred in the amorphous and crystalline regions of the polymer, evidenced by the decrease of both phases. For the BIO 90%, the results were more expressive since there was a bigger consumption of crystalline and amorphous fraction over the weeks, and the amorphous region was the most degraded.

This behavior can be related to a better homogenization, influenced by the effect of plasticizer and clay.

The presence of 3% clay and 10% PEG possibly affected the crystallinity of the polymer, facilitating the hydrolysis of the ester bonds, making it difficult to reorganize the chain and thereby increase the degradation process. Chandra and Rustgi[28] stated that degradation in the PHB occurs with the increase in crystallinity of the polymer. The clay content used in this work was constant (3%), and the variation of the carbonyl content for the compositions of the bionanocomposites is probably related to the interaction between the plasticizer and the organoclay.

In the literature, there have not been reported studies that correlate the evaluation of the calculation of the carbonyl content through FTIR and the degradation behavior of these materials. Therefore, this work is of fundamental importance that can help in future research.

Polímeros, 28(4), 348-354, 2018

Evaluation of hydrolytic degradation of bionanocomposites through fourier transform infrared spectroscopy

Figure 5. BIO 90% spectra after deconvolution (C=O carbonyl band) before and after degradation.

Table 4. Carbonyl BIO 90% indices of amorphous and crystalline phase calculated before and after degradation.

2nd week

6th week

Crystalline(1723/1380)

IC Before degradation 5.12

4.63

4.07

Amorphous(1752/1380)

1.52

0.88

0.85

BIO 90%

4. Conclusions PHB, PEG and organoclay bionanocomposites were developed by the solution intercalation method.

Bionanocomposites displayed intermediated dispersion of the filler along the matrix, the polymer chains were intercalated into the organoclay layers, and was observed some degree of exfoliation. It was observed in the FTIR analysis that the insertion of the clay and the PEG did not change the chemical structure of the polymer. After the test, the calculation of the carbonyl content indicated that, for the pure PHB, the degradation in the amorphous regions occurred. This fact was evidenced by the increase of the carbonyl content of the crystalline polymer region.

The BIO 90% composition showed a proportional reduction for the amorphous and crystalline phases of the polymer over the 12 test weeks, showing that the introduction of PEG and organoclay facilitated the penetration of water in the chain, and that the degradation of bionanocomposites can be directly linked to the degradation of the surfactant present in organoclay. It was noticed, in this study, that the addition of PEG and of the organoclay vermiculite affected the chain regularity and increased the hydrolytic degradation of the PHB polymer, acquiring desirable degradation characteristics for the possible application in Polímeros, 28(4), 348-354, 2018

biomaterials. For future researches, we recommend to make further characterizations of these materials, which permit to evaluate their use as medical devices.

5. Acknowledgements The authors thank the Graduate Program in Materials Science (UFPI), Laboratory of Polymer and Conjugated Materials–LAPCON/UFPI to the physical structure, CNPq and CAPES for financial support (Process: 306312/2015-8 and 446530/2014-0).

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Received: Sept. 14, 2017 Revised: Dec. 21, 2017 Accepted: Jan. 29, 2018

Polímeros, 28(4), 348-354, 2018

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.01616

Effect of addition of clay minerals on the properties of epoxy/polyester powder coatings Natanael Relosi1*, Oscar Almeida Neuwald1, Ademir José Zattera2, Diego Piazza2, Sandra Raquel Kunst1 and Eliena Jonko Birriel1 Laboratório de Corrosão e Proteção Superficial – LCOR, Universidade de Caxias do Sul – UCS, Caxias do Sul, RS, Brasil 2 Laboratório de Polímeros – LPOL, Universidade de Caxias do Sul – UCS, Caxias do Sul, RS, Brasil 1

*nrelosi@ucs.br

Abstract Powder coatings have been used for coating metal substrates in industrial applications. The incorporation of nanofillers as muscovite mica and montmorillonite (MMT) can improve the properties of the coatings. The objective of this study is to develop, apply and characterize a hybrid powder coating (30% epoxy/70% polyester) adding nanofillers in concentrations of 2, 4 and 6 phr separately in a twin screw extruder. The characterization of the coatings was performed by thermal, mechanical and chemical analysis. The incorporation of clay into the polymer increased the surface roughness resulting in a diffuse reflection of incident light and on a gloss reduction. The muscovite mica presented a lamellar structure, constituted by a set of overlapping parallel plates. The morphology analysis showed that the MMT presented irregular agglomerates resulting in inferior mechanical properties to coatings with muscovite mica. In the salt spray test, all samples showed high corrosion protection, around 850 hours.

Keywords: epoxy/polyester resin, montmorillonite, muscovite mica, powder coating.

1. Introduction One of the most used metal substrate protection systems in industry is the powder coating, because it has excellent mechanical and chemical resistance and corrosion properties. Moreover, these coatings are free from volatile organic compounds (VOCs). One of the advantages of the powder coatings is their preparation and application, as the electrostatic spraying enables the reuse of the material that has not adhered on the surface of the substrate[1-6].

The mechanical, thermal and chemical properties of the coatings are influenced mainly by the type of resin that is used.

The polyurethane, acrylic, silicone, polyester and epoxy[4,7] are among the most commonly used commercial resins.

The epoxy-based coating has a high performance which provides stability in a corrosive environment, good adhesion properties on metallic substrates as well as good mechanical and thermal properties, but it has a low resistance to natural weathering[1,8,9]. The polyester-based coating presents an excellent stability to heat and resistance to light and to natural weathering, and an excellent finishing appearance with respect to gloss and leveling[1,10]. Hybrid powder coatings are formulated from balanced proportions of two kinds of resin. The hybrid coatings (epoxy/polyester) are aimed at reconciling the weathering resistance characteristics and the action of UV rays with the chemical resistance and mechanical characteristics[8-10].

To improve the mechanical, thermal and chemical properties of the powder coatings, nanofillers are incorporated in the chemical composition of the coatings. Clay minerals, such as muscovite mica and montmorillonite (MMT) are

Polímeros, 28(4), 355-367, 2018

among the nanometer-scaled materials that can be used.

MMT clays generally provide better mechanical properties and improve the thermal stability, with an elevated heat distortion temperature and flame retardant ability[11].

Studies with muscovite mica, which is a layered structure with a high degree of crystallographic orientation, show an improvement in barrier properties such as gas permeability, chemical resistance and flammability. Another feature is the low cost of these clays and thus a smaller load combined with a high level of performance can be used[12-14].

Recent researches found that the use of clay concentrations up to 10%[12,15,16] produces significant improvements in the thermal, mechanical and chemical properties of powder coatings[13,15-19]. Thus, the objective of this work is to produce, apply and characterize a hybrid powder coating by separately adding mica muscovite and MMT 30B at concentrations of 2, 4 and 6 phr, evaluating the thermal, mechanical, chemical and morphological properties resulting from the addition of these clay minerals.

2. Materials and Methods 2.1 Materials The materials used in the formulation of the powder coating used in this work were the polyester resin CrylcoatTM 1783-0 from Cytec and the epoxy resin GT 7220 from Huntsman. The spreading agent was supplied by Estron Chemical Inc. (trade name ResiflowTM PV-60); benzoin

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

Relosi, N., Neuwald, O. A., Zattera, A. J., Piazza, D., Kunst, S. R., & Birriel, E. J. (surfactant) was provided by Datiquim Chemicals Ltd; the polyethylene wax was provided by Clariant; the muscovite mica clay was provided by Lamil Lage Minérios and MMT 30B, provided by Southern Clay Products Inc., (Cloisite30B).

The identification of the samples is shown in Table 1.

2.2 Surface preparation The metal substrates AISI 1010 carbon steel with dimensions of 70 × 120 × 0.65 mm were mechanically prepared with sandpaper with the following grain sizes: #320, #400 and #600, sequentially. They were subsequently subjected to a phosphating pre treatment with zinc phosphate by the dipping method. This pre treatment is performed to improve the adhesion of powder coatings.

The phosphating process included the degreasing stages using the commercial product Saloclean 679 RZ at 60 °C for 10 minutes. This product is composed of a mixture of anionic, nonionic surfactants, phosphates and silicates. It is recommended for the degreasing of iron and steel parts.

Completely removes greases and oils leaving the substrate clean to receive further treatment. In refiner stage the commercial product Salocoloide 507 was used at room temperature (25 °C) for 1 minute. This product is formulated based on sodium salts and titanium complexes. It was developed to produce on the metal surface a micro crystalline layer of titanium salts, which will serve as the nucleus for the deposition of the zinc phosphate grains. In the phosphating stage the commercial products Salofos 715 and 903 Salotex were used at 30 °C for 10 minutes. It is a product that has the function of depositing a micro crystalline layer of zinc phosphate on ferrous metals, increasing the resistance to corrosion and providing greater adhesion. It is formulated based on zinc salts, organic and inorganic acids and special inhibitors.

The product which was used for the passivation was the Salomix 307, used at room temperature for 90 seconds.

It is a product whose purpose is to level the crystals of the phosphate layer by increasing the corrosion resistance of the treated parts. After that, the samples were dried in an oven for 10 minutes at 100 °C.

2.3 Development of the powder coating The clays (muscovite mica and MMT 30B) were dried at 60 °C for 8 hours. All of the constituents of the powder coating were mixed manually, with the incorporation of 2 phr, 4 phr and 6 phr of the two clays separately, using the commercial formulations of the hybrid powder coating as shown in Table 2.

In the epoxy/polyester hybrid system curing (crosslinking) occurs through chemical reaction between the resins transforming the linear system into a three-dimensional structure system, ie, infusible, with high solvent resistance, excellent adhesion and flexibility, impact resistance and to chemical agents.

The epoxy resin acts as a curing agent for the polyester resin. Depending on the choice of resins and their relative proportions, the properties of the hybrid will be between those of the pure epoxy and the pure polyester. The presence of the epoxy resin leaves this type of resin susceptible to calcination by solar exposition[1,6]. Figure 1 present the 356 356/367

Table 1. Identification of hybrid powder coatings.

Identification TH/0 TH/2/MICA TH/4/MICA TH/6/MICA TH/2/MMT 30B TH/4/MMT 30B TH/6/MMT 30B

Filler content (phr) No filler 2 4 6 2 4 6

Clays − Muscovite mica

MMT 30B

Table 2. Formulation of hybrid powder coatings.

Material Polyester resin Epoxy resin Spreading agent Surfactant Polyethylene wax Muscovite mica / MMT 30B

Composition (g) 700 300 10 5 5 20, 40 and 60

Figure 1. Chemical reactions for the curing process of the epoxy/polyester coatings (a) reaction of carboxyl group with epoxy group (b) reaction of ester of hydroxyl group with carboxyl group (c) reaction of hydroxyl group with epoxy group.

chemical reactions responsible for the curing process of the epoxy/polyester coatings.

The reaction between the carboxyl and glycidyl groups is catalyzed by basic catalysts (tertiary amines and quaternary ammonium salts); when the ratio between these groups is 1:1, the reaction (a) is favored. However, when there is an excess of glycidyl groups, reaction (c) occurs in a significant way even in the absence of acid catalysis; the reaction (b) occurs when there is an excess of carboxyl groups on the glycidyl[1].

The mixture of the constituents was then processed in a double-screw co-rotating extruder MH-COR-20-32 MH Equipment Ltd under the following conditions: Speed of 200 rpm and 70 °C (zone 1), 80 °C (zone 2) and 90 °C (zone 3-9). After the extrusion the material was manually capped and granulated in the form of chips. The chips were milled in a Cadence knife grinder (model: MDR301) and after they were sieved in a 200 mesh Tyler sieve (75 µm).

2.4 Powder coating application The phosphatated mild steel panels were painted by electrostatic spray, with a corona TCA ECO TECNOAVANCE model 301 spray, using an electric generator with a voltage Polímeros, 28(4), 355-367, 2018

Effect of addition of clay minerals on the properties of epoxy/polyester powder coatings output of up to 100 kV, a current 60 mA, and a pressure air stream speed of 1 psi. Thereafter, the panels were placed in a MDH DeLeo Laboratories greenhouse for 15 minutes at 200 °C to obtain the curing of the coating.

2.5 Characterization of the coatings The TGA analysis was performed on a Shimadzu TGA‑50 device with a pre-defined temperature range from 25 to 500 °C under an inert N2 atmosphere, and 500 to 900 °C in an artificial synthetic air atmosphere, at a rate of 10 °C·min-1 and a flow of 50 mL·min-1 of N2. The DSC test was performed on a Shimadzu DSC-60 device with a variation in temperature from 25 to 275 °C at a rate of 10 °C·min-1 and a flow 50 mL·min-1 of N2. The FTIR analysis was performed with a Thermo Scientific Nicolet 10 iS equipment using KBr pellets in the spectral range of 400 to 4000 cm-1. A total of 32 scans with a resolution of 1 cm-1 was performed.

The scanning electron microscopy by field emission (SEM-FEG) of the powders were held under a microscope TESCAN MIRA 3, with an acceleration voltage of 15 kV. The samples were fixed in metal brackets (stubs) with the aid of a conductive adhesive (a ribbon) and covered with a thin layer of gold by plating.

The thickness measurement of the hybrid powder coatings was carried by the magnetic method as per the ASTM D7378-10 standard[20] with the thickness gauge instrument ELCOMETER 345 for metallic substrates.

The pencil hardness test was performed according to the ASTM D3363-05E2 standard[21]. The tests were performed with a set of pencils with different hardness of graffiti. The pencil hardness value was regarded as the hardness of the pencil that did not cut or caused grooves in the film. The adhesion of the coating to the metal substrate was evaluated by the method B of ASTM D3359-09[22]. The brightness analysis was performed according to the ASTM D523-08 standard[23], using the Multi Gloss meter 268 plus, from Konica Minolta, at an angle of 60°. The coating flexibility test was carried out following the method described in the conical mandrel test from ASTM D522-93[24], using the Gardner Conical Mandrel BYK device. The impact resistance test was

conducted in a Heavy-Duty Impact Tester BYK Gardner equipment, according to the ASTM D2794-93 standard[25], using an impact force of 50 kg·cm both for the direct impact as to the reverse.

The salt spray test followed the ASTM B117 the standard[26], for 850 hours in a closed Mark Bass USX‑6000/2012 chamber.

3. Results and Discussion The TGA and DTG thermograms obtained with the analysis of the hybrid powder coating and a commercial formulation of coatings incorporating 2, 4 and 6 phr of muscovite mica and MMT 30B are shown in Figure 2 and Figure 3.

It is observed that the muscovite mica has a high thermal stability and little weight loss (approximately 5%). On the other hand, it is clear that the MMT 30B shows a marked weight loss from 178 °C. According to Paiva et al.[27] the decomposition process MMT has three steps: the first and the second relates to the decomposition of the surfactant (180 to 384.5 °C) and the third stage is related to the dehydroxylation of the clay (556 to 636.4 °C). This may be related to the fact that muscovite mica has the characteristic of promoting the formation of transitional coal, which begins to degrade only at high temperatures[28]. In addition, chemically, muscovite mica presents a differential in relation to the other clay minerals, since its interlayer cations are not interchangeable under environmental conditions; only surface cations can be exchanged at room temperature[29]. The hybrid powder coatings showed two mass loss events, the first observed event in an inert N2 atmosphere (350 °C to 500 °C) and the second corresponds to the effect of changing the atmosphere of the synthetic air from the equipment, which accelerates the resin degradation process (500 °C to 600 °C). A higher weight loss of the samples is associated with the degradation of the polymeric matrix, which starts at about 350 °C[30].

A similar behavior was observed by Bharadwaj et al.[31], who evaluated the influence of the addition of different clay concentrations on the morphology and properties of a polyester based nanocomposite and noted that even with

Figure 2. Thermograms of (a) TGA and (b) DTG of the hybrid powder coatings with the addition of different levels of muscovite mica.

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Relosi, N., Neuwald, O. A., Zattera, A. J., Piazza, D., Kunst, S. R., & Birriel, E. J.

Figure 3. Thermograms of (a) TGA and (b) DTG of the hybrid powder coatings with the addition of different levels of MMT 30B.

a good dispersion of clay in the polymer matrix, there is a slight acceleration of the thermal degradation of the sample in the range from 25 to 400 °C due to the presence of hydroxyl groups in the organic modifier which provides a supply of oxygen.

Table 3 shows the data obtained from the TGA and DTG curves and also the residue content of the hybrid powder coatings containing different levels of muscovite mica and MMT 30B. From Table 3, it is possible to see that all coatings, except TH/6/MMT 30B, showed reduction in Tmax. This result was found by other authors who justified this behavior in different ways. Oliveira Jr.[32]. observed that the incorporation of the modified clay in the polypropylene did not significantly improve the thermal stability of the microcomposite and attributed this fact to the low dispersion of the clay in the polymer matrix and formation of agglomerates. Ollier et al. [33] observed that the incorporation of the modified clay did not significantly influence the degradation temperatures of the nanocomposites to the organic modifier present in the MMT structure.

Thus, the lower thermal stability presented by the clay‑containing coatings may be related to the form of dispersion and the interaction of the clay-mineral with the polymer matrix. In the case of MMT 30B coatings, this reduction may be associated to the organic modifier decomposition of the clay, accelerating the loss of mass.

In the case of coatings incorporating muscovite mica, the reduction can be attributed to the catalytic effect caused by the clay and the dispersion of the filler. In this way, it is clear that the thermal stability of the coatings decreased due to the addition of clay minerals.

The increase of muscovite mica and MMT 30B content incorporated in the powder coating resulted in an increase in the final residue as shown in Table 3. In addition, it was observed that the TH/6/MICA and TH/6/MMT 30B coatings showed the highest levels of residue due to the presence of the inorganic phase of clays. This was expected, given that an increase in the percentage of clay incorporated in the 358 358/367

Table 3. Residue content and maximum temperature of degradation of the hybrid powder coatings.

Sample

Tmáx

Residue content (%)

TH/0 TH/2/MICA TH/4/MICA TH/6/MICA TH/2/MMT 30B TH/4/MMT 30B TH/6/MMT 30B

439 °C 430 °C 426 °C 428 °C 432 °C 432 °C 440 °C

4.4 4.8 7.3 10.4 5.5 7.5 8.1

coatings means an increase of the thermal stability of the polymer matrix, thus restricting the output of the volatile formed by the decomposition of the polymer. In addition, this behavior may also be associated with the greater dispersion of this clay in the resin, increasing the pathway for transport of oxygen and volatile compounds through the coating film[30,34].

The DSC thermograms of the hybrid powder coatings with the addition of clay are shown in Figure 4.

This analysis shows two significant thermal events.

The first refers to the glass transition temperature (Tg) and the second to the crosslinking temperature (Treticulation).

The dispersion of inorganic particles (lamellar silicates) in reaction medium strongly affects the mass and heat transfer, making the system less reactive, as can be observed with the decrease of Tg. A dispersant could be added to the ink formulation in order to assist the interaction between the polymeric matrix with the muscovite mica and MMT 30B particles However, the hybrid inks with the addition of MMT 30B showed an increase of Treticulation from 171.7 °C to 187.3 °C (Figure 3b). This may be related to the difficulty of molecular mobility due to the strong interaction that occurs between the polymer matrix with nanoparticles of MMT 30B, as suggested by other authors[10,35,36].

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Effect of addition of clay minerals on the properties of epoxy/polyester powder coatings Figure 5 shows the FTIR spectrum of the pure hybrid coating and the coating containing mica muscovite and MMT 30B.

The characteristic absorption bands of the polyester/TGIC structure (triglycidylisocyanurate curing agent) were observed in 1720 cm-1 due to stretching C=O, 2969 cm-1, and

Figure 4. DSC thermograms of the hybrid powder coatings with different levels of (a) muscovite mica and (b) MMT 30B.

Figure 5. FTIR spectrum for powder coatings by incorporating (a) muscovite mica and (b) MMT 30B. PolĂ­meros, 28(4), 355-367, 2018

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Relosi, N., Neuwald, O. A., Zattera, A. J., Piazza, D., Kunst, S. R., & Birriel, E. J. 2891 cm-1 due to the asymmetric and symmetric stretching of the CH2 group. For coatings containing muscovite mica, the presence of nanoparticles in the polymer matrix introduced no new peaks in the FTIR spectrum. However, as the concentration of MMT 30B increased, it was observed that the intensity of the band at 460 cm-1 related to the Si-O-Si links became more evident as was expected.

Comparing the spectra of other hybrid coatings with the clay minerals, it was observed that there is an overlapping in most of the absorption bands.

Figure 6 shows the morphological analysis of muscovite mica clay obtained by SEM-FEG. Through this analysis, it was observed that muscovite mica clay showed a morphology

constituted by overlapping a set of parallel plates, a lamellar structure, as expected. This morphological structure of muscovite mica was also observed by other authors[37-39].

The interactions between the polymer matrix and the reinforcing fillers favor the aggregation and incorporation of the same. Inorganic particles, such as clays, tend to aggregate into a polymer matrix independent of the type or size of the material. The tendency to fillers aggregation increases with the decrease of the particle size and this is due to the increase of the contact surface[40,41].

Figure 7 shows the morphology of MMT 30B. It was found that the clay mineral shows irregular agglomerates

Figure 6. Micrographs obtained by SEM-FEG of muscovite mica clay in different magnitudes.

Figure 7. Micrographs obtained by SEM-FEG of MMT 30B clay in different magnitudes.

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Effect of addition of clay minerals on the properties of epoxy/polyester powder coatings constituted by relatively flat sheets. According to Wang et al.[42] the surfaces of the SiO2 particles have a large number of hydroxyl groups due to the hydrogen bonding to the nanoparticles through Van der Waals forces that causes aggregation of nanoparticles. Due to the strong tendency to agglomerate, the SiO2 particles are very difficult to achieve a homogeneous dispersion in the polymer. Coatings with such agglomerates generally exhibit inferior mechanical properties.

When modified clays are used, the intercalation ability of the polymer depends on the length of the surface modifier.

The larger the modifier, the greater the space between the layers of clay and therefore the greater the probability of intercalation. The smaller the modifier, the lower its miscibility with the polymer[43].

The MMT clays in the natural state have hydrophilic character and when added in a polymer matrix they tend to form agglomerates, not dispersing. This is due to the intensity of the ionic forces existing between the layers of clay, where the clay surface energy will be higher than that of the polymer[44-46].

Modification of MMT aims to improve the compatibility and dispersion of the clay in the polymer matrix. The method most commonly employed in the modification of MMT clay is the ion exchange of the inorganic cations present in its structure by cationic surfactants, such as quaternary ammonium salts[47,48]. This process produces a clay with organophilic character and with greater interlamellar space.

The presence of the ammonium salts in the interlamellar space weakens the interaction between the layers of the clay, facilitating their intercalation and/or exfoliation in the polymeric matrix[47-49]. However, since quaternary ammonium salts undergo degradation at temperatures close to the processing temperature of many polymer resins, the thermal instability of organophilic clay becomes a strong limitation in the processing of polymer/clay nanocomposites[50-51].

In Figure 7, agglomerates of MMT 30B were observed.

This morphology denotes that the use of this clay was not efficient to promote a strong interaction with the polymer matrix.

In the XRD analysis it is observed based on the first characteristic peak of muscovite mica at 8.80° (2theta), basal spacing identified as d001 correspond to 1.01 nm. Evaluation of basal spacing d001 of such phyllosilicate incorporated into the coating did not evince modification (presenting the same value of 1.01 nm), indicating that it was not possible to identify neither exfoliation nor intercalation of the polymeric matrix into the mineral lamellae with such analysis[52-54]. The graph and values obtained in the XRD analysis are shown in Figure 8 and Table 4.

In the diffractogram of the coating with MMT 30B (Figure 9) it can be observed that, based on the first characteristic peak of montmorillonite at 4.95° (2theta), the basal spacing d001 is 1.79 nm. When evaluating the basal spacing d001 of this clay when incorporated in the coating, the values are verified and shown on Table 5. Thus, it was verified the occurrence of intercalation of the polymeric matrix within the galleries, possibly with clays dispersed randomly. It was also verified that higher clay concentrations resulted in smaller spacing, indicating that with lower contents the exfoliated phase is prevailing, and that for higher concentrations intercalation occurs[16].

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The results of measurement of the thickness of the coating layer, the pencil hardness and the adhesion test are shown in Table 6.

Figure 8. X-ray diffraction of muscovite mica of hybrid powder coatings before curing with different muscovite mica contents.

Figure 9. Overlap of the MMT 30B X-ray diffractograms of the hybrid powder coatings, before curing, with different levels of MMT 30B. Table 4. Basal spacing values “d001” calculated by Bragg’s law for hybrid powder coatings before curing with addition of different muscovite mica contents.

Sample

2θ (°)

Distance d001 (nm)

TH/0 TH/2/MICA TH/4/MICA TH/6/MICA

8.8 8.8 8.8 8.8

1.01 1.01 1.01 1.01

Table 5. Basal spacing values “d001” calculated by Bragg’s law for hybrid powder coatings before curing with addition of different levels of MMT 30B. Sample

2θ (°)

Distance d001 (nm)

TH/0 TH/2/MMT 30B TH/4/MMT 30B TH/6/MMT 30B

4.95 1.9 2.3 2.5

1.79 4.65 3.84 3.54

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Relosi, N., Neuwald, O. A., Zattera, A. J., Piazza, D., Kunst, S. R., & Birriel, E. J. It was observed that the coatings exhibit little difference in the value of the average thickness among the samples.

This fact is important to compare the mechanical and chemical resistance results that are presented below.

The incorporation of the clay resulted in an increased pencil hardness of the coatings. The TH/0 powder coating showed a lower pencil hardness being classified as HB, the coating TH/4/MMT 30B showed a pencil hardness of 2H, and other coatings exhibited a hardness of H. The increase in the hardness of the powder coatings may be due to the presence of particles of clay on the surface[55]. Lv et al.[56] verified the increase in pencil hardness in nanocomposites with added clay and attributed this result to a greater compatibility and to the high density of crosslinking between the clay and the polymer matrix. They observed that the filler loading increases the hardness of the coating due to increased film stiffness.

The appearance of the hybrid coatings containing different levels of muscovite mica clay and MMT 30B applied on carbon steel after the adhesion test is shown in Figure 10.

All coatings showed an adhesion of 5B. These results demonstrate the formation of coatings with a high mechanical resistance with respect to the grip factor, which is of extreme importance to the anticorrosive properties of the coatings.

Table 6. Thickness, pencil hardness and adhesion testing results of hybrid powder coatings.

Average thickness (μm) TH/0 77.7 ± 7.3 TH/2/MICA 74.8 ± 6.5 TH/4/MICA 68.7 ± 6.8 TH/6/MICA 74.7 ± 6.3 TH/2/MMT 30B 77.4 ± 6.1 TH/4/MMT 30B 68.9 ± 7.2 TH/6/MMT 30B 76.1 ± 6.3 Samples

Pencil hardness HB H H H H 2H H

Adherence rating 5B 5B 5B 5B 5B 5B 5B

The adhesion of the hybrid powder coatings indicate that the phosphating pretreatment enhances the adhesion of the coating to the metal substrate. The results presented in the adhesion test confirm that the presence of MMT 30B and muscovite mica clays did not affect the adhesion characteristics of the hybrid coating to the metal substrate.

Similar results were found by Piazza et al.[57] to evaluate the incorporation of MMT 30B in an epoxy based coating.

Bagherzadeh and Mahdavi[58] and Navarchian et al.[59] also found that the presence of clay does not alter the adhesion of the coating to the substrate. According to Garcia et al.[60], the adhesion properties may be associated with hydroxyl groups produced in the curing reaction of the material and its ability to establish hydrogen bonds between the coating and the substrate.

Figure 11 shows the results of the gloss analysis with its standard deviations.

The increase of muscovite mica and MMT 30B content in the powder coating formulation caused a reduction of gloss. The sample with 2 phr of MMT 30B did not influence the gloss of the powder coating, and a similar value to the coating without the addition of fillers was obtained.

The samples with 6 phr of muscovite mica and MMT 30B showed less than 80 G.U. for gloss, and were thus classified as semi-gloss varnish, which according to industry standards are the ones in the 50-80 G.U. range. The gloss value for the remaining samples were above the required industry standard for high-gloss varnishes (G.U. > G.U. 80).

These results may be associated with the formation of clay agglomerates which intersect the surface finish and increase the surface roughness resulting in a diffuse reflection of incident light and on a gloss reduction[61].

This result corroborates the data observed by Wicks et al.[62], who report that the size as well as the concentration of the filler particles significantly affects the characteristics of the coating as mechanical properties, barrier properties, corrosion and especially gloss.

Figure 10. Results of adhesion test performed with the hybrid powder coatings (a) TH/0, (b) TH/2/MICA, (c) TH/4/MICA, (d) TH/6/MICA, (e) TH/2/MMT 30B, (f) TH/4/MMT 30B and (g) TH/6/MMT 30B. 362 362/367

Polímeros, 28(4), 355-367, 2018

Effect of addition of clay minerals on the properties of epoxy/polyester powder coatings Figure 12 shows the result of the conical mandrel flexibility test performed on carbon steel panels coated with the hybrid powder coating containing different amounts of muscovite mica and MMT 30B. A qualitative analysis of samples submitted to the flexibility test indicated the absence of cracks or peeling for coatings with the incorporation of muscovite mica.

This was due to the adhesion between the coating and the metal substrate and the cohesion between the coating molecules. The muscovite mica additions in the tested concentrations did not affect the flexibility of the coating.

Panels with the coating incorporating MMT 30B clay in different concentrations showed failures in flexible hybrid coating. This was due to the greater amount of clay, which favors the formation of MMT agglomerates, as observed in the morphological test (Figure 7). The increase in the MMT content in the formulation of the coatings makes them more fragile, associated with decreased molecular mobility restrictions imposed by the merging of the molecules of the hybrid resin inside the clay mineral[57].

Figure 13 shows the appearance of the coated metal substrates with hybrid powder coatings free of clay and with the addition of 2, 4 and 6 phr of muscovite mica and MMT 30B which underwent a resistance review of rapid deformation (impact).

Figure 11. Gloss analysis of hybrid powder coatings with different levels of muscovite mica and MMT 30B.

Based on a visual analysis of the samples, it can be seen that the sample without addition of clay mineral and the TH/4/MICA sample showed resistance to impact. The best performance, coating, TH/4/MICA, can be associated to an increase in cohesive forces in the coating caused by

Figure 12. Images analysis result of the flexibility of hybrid powder coatings applied on carbon steel after curing: (a) TH/0, (b) TH/2/MICA, (c) TH/4/MICA, (d) TH/6/MICA, (e) TH/2/MMT 30B, (f) TH/4/MMT 30B e (g) TH/6/MMT 30B. Polímeros, 28(4), 355-367, 2018

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Relosi, N., Neuwald, O. A., Zattera, A. J., Piazza, D., Kunst, S. R., & Birriel, E. J.

Figure 13. Images of the quick deformation resistance test (ASTM D2794) of paints based on epoxy / polyester powder coating after curing, and applied to mild steel panels: (a) TH/0, (b) TH/2/MICA, (c) TH/4/MICA, (d) TH/6/MICA, (e) TH/2/MMT 30B, (f) TH/4/MMT 30B e (g) TH/6/MMT 30B.

the presence of muscovite mica in the powder coating.

The TH/2/MICA and TH/6/MICA samples presented a low resistance to impact deformation, cracks and spalling as seen in Figures 13b and 13d. The increase of the muscovite mica concentration to 6 phr may have favored the formation of clay agglomerates, resulting in a greater level of brittleness in the regions where cracks have occurred[63,64]. The coatings containing different concentrations of MMT 30B showed spalling and cracks in the direct and reverse impact. The lower impact resistance of these samples may be associated with an increased stiffness of the material that can be associated with the high aspect ratio of clay nanoparticles and to the decrease in the molecular mobility may have been caused by the restrictions imposed by an intercalation of epoxy and polyester resin molecules in the inside the MMT galleries.

Piazza et al.[57] have argued that the low resistance to deformation by impact of epoxy-based coatings containing different concentrations of MMT 30B are due to three factors: the formation of clay agglomerates which results in favorable 364 364/367

fracture points; the increase in the stiffness of the material and the reduction of the reactivity and crosslink density.

Other researchers analyzed the influence of MMT clay on epoxy base powder coating and found similar morphological results to those found in this article. The authors associated the fragility of the coatings to the characteristic stiffness of the predominantly exfoliated structure of the nanocomposites[64], morphology is observed in the XRD diffractograms of the cured samples and corroborated in the micrographs obtained by transmission electron microscopy.

According to Mirabedini and Kiamanesh[55] the presence of inorganic particles in the coating reduces the dissipation of energy, after the application of an external force causing the fracture of the coating.

The salt spray test evaluated the protection against corrosion performance in hybrid powder coatings with and without the addition of clay minerals. To perform this test were chosen coatings with better performance in thermal and mechanical tests. Figure 14 shows the appearance of the Polímeros, 28(4), 355-367, 2018

Effect of addition of clay minerals on the properties of epoxy/polyester powder coatings

Figure 14. Images of the samples after 850 hours of exposure to the salt spray test (ASTM B117) (a) TH/0, (b) TH/4/MICA e (c) TH/2/MMT 30B.

exposed samples after 850 hours of salt spray, indicating the presence of corrosion products near the incision.

mica coatings it was not possible to identify exfoliation or intercalation of the polymer matrix with the clay minerals.

Neither blistering nor corrosion spots were observed on the surface of any of the samples, indicating the effectiveness of the barrier effect provided by the clays. The increased corrosion resistance is associated to the nature, form and size of the filler. Piazza et al.[10] reported an increased barrier effect with the addition of MMT to a polyester-based powder coating. Ghoudalakis[65] considered this effect to be due to the increase in the difficulty of diffusion (tortuosity) of liquid or gas molecules throughout the polymer film due to the predominantly exfoliated nanocomposite structure.

The highest displacement values were verified for samples incorporating MMT 30B. This corroborates with the results of the mechanical tests (flexibility and impact) in which it was identified that the coatings incorporating MMT 30B presented inferior properties to the coatings with the addition of muscovite mica.

The results of the mechanical characterization show that when the coating was subjected to a slow deformation (adhesion and flexibility) the incorporation of the clay did not affect the performance of the coatings. However, when an instantaneous force is applied, the coatings containing clays showed a peeling of the film. Thus, it can be considered that time is needed for the polymer and the clay to adjust to the mechanical deformation for the film not to be broken.

4. Conclusions The thermal analyzes of TGA, DSC and FTIR showed that thermal stability of the coatings decreased when it was added clay mineral.

With the SEM-FEG analysis it was possible to identify that the muscovite mica has a lamellar structure and the MMT 30B shows irregular agglomerates consisting of relatively flat sheets.

Through the XRD analysis, an increase in the basal spacing was observed for the coatings with MMT 30B incorporation, predominating exfoliated phase for lower concentrations of clay and intercalation for coatings with higher concentrations of MMT 30B. For the muscovite Polímeros, 28(4), 355-367, 2018

All the coatings with the addition of clay minerals presented corrosion performance similar to non-clayey coatings. None of the coatings showed blistering or corrosion spots on the surface.

5. Acknowledgements The authors acknowledge the financial support of CAPES, the Laboratório de Polímeros (LPOL), the Laboratório de Corrosão of UCS (Corrosion Laboratory) for conducting mechanical tests, Pulverit for providing raw material and the Laboratório Central de Microscopia Prof. Israel Baumvol (Central Microscopy Laboratory) for the field emission scanning electron microscopy analisys.

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Received: Mar. 07, 2016 Revised: Sept. 20, 2017 Accepted: Dec. 14, 2017

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.08217

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

Preparation and characterization of composites from copolymer styrene-butadiene and chicken feathers Maria Leonor Mendez-Hernandez1, Beatriz Adriana Salazar-Cruz1, Jose Luis Rivera-Armenta1*, Ivan Alziri Estrada-Moreno2 and Maria Yolanda Chavez-Cinco1 Petrochemical Research Center, Instituto Tecnológico de Ciudad Madero/Tecnológico Nacional de México, Altamira, Tamaulipas, México 2 Department of Materials Engineering and Chemistry, Centro de Investigación en Materiales Avanzados S.C. – CIMAV, Chihuahua, Chihuahua, México 1

*jlriveraarmenta@yahoo.com

Abstract Over five million tons of chicken feathers (CF) are generated all over the world by the poultry industry, with an immense potential to exploit. Keratin is an abundant protein found in chicken feathers that offers excellent thermal properties and it is durable, insoluble in organic solvents and chemically unreactive. Elastomers are materials with a wide application range, for instance, adhesives, shoe soles, plastic modifiers, tire industry, sealants, among others. However, it is necessary to improve their properties and mechanical performance at elevated temperatures. A good path to do so is to combine the elastomer with CF to obtain materials with enhanced properties. In present work, a composite based on styrene-butadiene (SB) elastomer and CF was prepared by means of melt mixing. Composites were characterized

by FTIR, DSC, DMA and X ray diffraction techniques. The results show that there is an increase in stiffness of SB/CF composites compared with pure elastomer.

Keywords: chicken feather, melting mixing, thermal properties, elastomer.

1. Introduction CF are considered a waste byproduct from poultry industry, with around 5 million tons per year[1]. The main component of CF is keratin, a protein with good thermal and mechanical properties, which is also resistant to the action of organic solvents. Its thermal decomposition occurs between 50 and 200 °C[2]. The presence of disulfide crosslinks from cystine and the predominant non-hydrophilic amino acids in the chain sequence give CF keratin a hydrophobic character. In addition, CF keratin is a self-sustainable and continuously renewable material[2].

Recently, the increasing interest in the use of natural or renewable materials as polymer matrix reinforcement, has led to the search for options to obtain composite materials. There are lots of reports about natural fibers as flax, bamboo, hemp, jute, agave, among others, but just a few of them are related to resources from animal proteins, as keratin[3,4]. In the last decades, this fact has generated the investigation of keratin as raw material for synthetic polymer blends, particularly because of its unique properties such as lightweightness, natural abundance and environmental compatibility, combined to its high mechanical and thermal resistance[5,6]. The latter, could help to improve the performance of current synthetic polymers and to obtain materials with mechanical properties comparable to the conventional ones[7].

Styrene-butadiene copolymers (SB) have applications as shoe soles, impact modifiers, asphalt modifiers, adhesives and sealants[8]. SB copolymers are materials that flow easily at processing temperatures, however at higher temperatures

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their mechanical properties decrease. To enhance keratin fibers attributes, such as impact resistance, thermal oxidation, physicochemical and mechanical properties, their reinforcement has been considered by using an elastomeric SB copolymer, with styrene content ranging from 25% to 45%[9].

There are several studies on composite materials using styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR) and keratin from chicken feathers that revealed the influence of different variables on the thermal and mechanical behavior and the various valid tools for observing these variations[2,3,10-14].

In present work, a composite based on SB copolymer and CF was prepared by melt mixing, studying 3 types of SB copolymers (varying styrene content), keeping constant chicken feather amount. Thermal properties were studied; infrared spectroscopy (FTIR) and X ray diffraction were also carried out to evaluate the possible interactions between polymer matrix and reinforcement.

2. Materials and Methods 2.1 Materials CF were obtained from a local slaughterhouse in Altamira city, México; and three types of SB: SB1 45% styrene content, SB2 32% styrene content and SB3 25% styrene content, were provided by Dynasol Elastomers S.A. de C.V. CF were cleaned with several washes, first with distilled water, then

Polímeros, 28(4), 368-372, 2018

Preparation and characterization of composites from copolymer styrene-butadiene and chicken feathers with acetone and finally with ethanol. Thereafter, feathers were dried at room temperature to be clean, sanitized and odor free. Then, the barbules were removed with cutters barrel and quill (the main component of CF is keratin), was finally grinded in both sides of the feather.

2.2 Composites preparation Composites were prepared by melt mixing using a plasticorder/Brabender PL2000 torque rheometer, establishing the optimum conditions at 185 °C and 20 minutes of mixing, using roller blades with 100 rpm speed, keeping constant CF content in 5 phr. After the materials were compressed in a Dake press with 10 Tons for 20 min, using appropriate molds.

2.3 Composites characterization Infrared spectroscopy technique was used to identify functional groups in the SB/CF materials. For that purpose, a Perkin Elmer Spectrum One model equipment was used, through the Attenuated Total Reflectance (ATR) technique with SeZn plates in a range of 4000-600 cm-1, and 12 scans.

Differential Scanning Calorimetry (DSC) was used to determine the thermal transitions of the composites; for that, a Perkin Elmer DSC8000 equipment was used. The employed method consists of an initial heating cycle from 30 °C to 230 °C at 10 °C/min, followed by a cooling cycle from 230 °C to -100 °C. The sample is kept for 5 min at this temperature before a second heating ramp from -100 to 230 °C takes place, with a heating rate of 5 °C /min. The sample amount was 10 ± 2 mg, and the tests were run under nitrogen purge (20 ml/min). Dynamic Mechanical Analysis was carried out in a DMA-Q800 TA-Instruments, with a double cantilever clamp and rectangular shaped samples with dimensions 30 × 12 × 3 mm (length, width and thickness, respectively).

Analysis were carried out in multifrequency mode with temperature range from -100 to 230 °C, with a heating rate of 5 °C min-1, 1Hz frequency and 2μm amplitude. X-ray diffractometer Siemens D-500 was used to determine the presence of crystalline structures in composites (SB-CF).

The equipment operates at 30 kV, 25 mA and angle scan range (2θ) from 4° to 40° at 0.05° min-1. Samples were cut with dimensions of 30 × 15 × 1mm. In order to observe the morphology of the obtained materials and the dispersion within the matrix, a scanning electron microscope JEOL model JSM-5800 was used, with an accelerating voltage of 10kV. For this purpose, a portion of previously compressed material, whose thickness is 0.01mm, was used.

It can be observed in Figure 2 that the main groups assigned to 1650 cm-1 and 1550 cm-1 from CF keratin are the amide I and amide II bands, respectively. The peaks at 1500, 1450 and 1250 cm-1 are attributed to the bending plane of NH group that corresponds to β−sheet conformation, the bending of -CH3 group and CN group of amide III, respectively. Signals at 1150, 1100 and 1050 cm-1 are assigned to C-C group vibrations; a peak around 700 cm-1 its attributed to C-S group vibrations and finally, at 970 cm-1, 910 cm-1, 760 cm-1 and 690 cm-1, it is found the evidence of unsaturated aromatic carbon deformations[15-17].

3.2 Differential Scanning Calorimetry (DSC) Table 1 shows the results obtained from DSC of SB1, SB2 and SB3 copolymers and SB1-CF, SB2-CF and SB3-CF composites. It is noted that CF has two transition temperatures (140 °C and 263 °C), corresponding to the

Figure 1. FTIR spectra of SB3 (Styrene-Butadiene with 25% styrene content) and SB3/CF (Chicken Feather) composite.

3. Results and Discussion 3.1 Infrared spectroscopy Figure 1 shows the IR spectra of SB3 and SB3/CF composite from 3850 cm-1 to 600 cm-1. It is emphasized that it is possible to identify some of the functional groups in the SB/ CF blends. SB3 signals are located at 3000 cm-1 and 3100 cm-1 associated to unsaturated carbons; meanwhile, at 2900 cm-1 and 2850 cm-1, the signals related to the stretching of methyl and methylene groups can be seen. Besides, the region of the aromatic ring is found from 2000 cm-1 to 1850 cm-1. CF signals are situated at 3300 cm-1, corresponding to the range of amide bands and associated with ordered regions of NH group of amide A α-helix conformation, and at 2950 cm-1, related to the asymmetric vibration of CH group of methyl.

Polímeros, 28(4), 368-372, 2018

Figure 2. FTIR spectra of SB3 (Styrene-Butadiene with 25% styrene content) and SB3/CF (Chicken Feather) composite.

Table 1. Thermal transitions of copolymers and composites SBS/CF (Styrene-Butadiene-Styrene/Chicken Feather).

Material Chicken feather (CF) SB1 (45% styrene content) SB1/CF SB2 (32% styrene content) SB2/CF SB3 (25% styrene content) SB3/CF

Transition (°C) 140/263 -40 -56 -33 -27 -63 -40

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Mendez-Hernandez, M. L., Salazar-Cruz, B. A., Rivera-Armenta, J. L., Estrada-Moreno, I. A., & Chavez-Cinco, M. Y. crystalline melting temperature of the CF Keratin, similar to previous reports [18]. Other references indicate that CF did not show any melting peak[19]. On the other hand, the Tg of the composites shows an interesting behavior, whose initial value with respect to the styrenic chains is -63 °C while the Tg of the SB3/CF composite is -40 °C. The increase of Tg (-23 °C) is possibly explained by an improvement in the rigidity at the molecular level due to the presence of CF, produced by the binding of the polypeptide chains of keratin with the styrenic chains of SB3. This behavior also occurs with the Tg of the SB2 copolymer and the SB2/CF composite but not in SB1 and SB1/CF, where the Tg is -40°C and -56 °C, respectively. A decrease in the Tg occurs due to the higher styrene content in SB1, so a better interaction between polystyrene block and keratin takes place and, as a result, chains are softened.

great compatibility between both materials. It has been reported by Jiménez-Cervantes Amieva et al.[3] a similar behavior in recycled PP-Quill composites, attributed to the hydrophobic nature of keratin and to the fact that the polymer matrix has a proper interface.

3.5 X-Ray Diffraction (DRX) X-ray diffraction is an important technique to determine the crystal structure in a material. XRD pattern of CF was formerly reported, showing broad peaks at 9 and 19° corresponding to the diffraction pattern of α−helix and β−sheet structure of CF [21]. However, for SB/CF composites the behavior was kind of different. Figure 7 shows the XRD patterns of SB/CF composites, the SB copolymers show

3.3 Dinamic Mechanical Analysis (DMA) DMA is a useful technique to determine the viscoelastic properties of composite materials related to primary relaxations and other parameters. DMA was performed to evaluate the effect of the addition of CF to a SB elastomer matrix.

Figures 3, 4 and 5 show the storage modulus E’ and Tan δ versus temperature of SB copolymers and SB/CF composites.

Initial E’ values of (-100 °C) of SB1, SB2 and SB3 are 2685, 993, and 2501 MPa, respectively. It is noted that in the SB2/CF compound the inclusion of keratin promotes an increase of the storage modulus to 1676 MPa with respect to the SB2 copolymer, improving the stiffness of the elastomeric matrix[3,20]. However, SB1/CF and SB3/CF compounds do not show similar behavior since E’ decreases to 1157 and 2128 MPa respectively, being more noticeable the decrease of E’ in the compound whose SB1 copolymer has 45% styrene. This behavior could be due to free movement of the polymer chains at high temperatures, in agreement with the results of DSC analysis.

Tan δ (Figure 3) is a useful tool to identify the interaction existing between the polymeric matrix and the keratin as reinforcement. A strong bond is reflected at low Tan δ values, although an elastomeric matrix, which has higher Tan δ values, was used. It is observed that Tg value in the SB/CF compounds is not significantly affected by the CF addition. This could be related to the result from Tan δ curve.

Nevertheless, the SB3/CF composite at (-40 °C) has the highest Tg value compared to the SB1/CF and SB2/CF composites.

This behavior has already been reported before, regarding the absence of significant changes in Tg value by effect of CF addition as reinforcement of a polymeric matrix[20].

Figure 3. Storage moduli (E’, MPa) and Tan δ as function of temperature for SB (Styrene-Butadiene) copolymer and SB1 (45% styrene content)/CF (Chicken Feather) composite.

Figure 4. Storage moduli (E’, MPa) and Tan δ as function of temperature for SB (Styrene-Butadiene) copolymer and SB2 (32% styrene content)/CF (Chicken Feather) composites.

3.4 Scanning Electron Microscopy (SEM) Surface morphology of SB/CF composites was investigated

by SEM. CF surface was previously reported as uniform with roughness at the micro level[21]. Reinforcing particles can be reduced in processing due to minor degradation according to the mixing temperature. Figure 6 shows the SEM images of the SB1/CF, SB2/CF and SB3/CF composites. It is possible identify CCF particles dispersed on the SB matrix, which reflect a proper interface. SB1/CF composites show bigger particles than the other composites, possibly because there was not a good dispersion of the keratin within the polymeric matrix. In spite of that, good physical interaction between reinforcing keratin and polymeric matrix exists due to the 370 370/372

Figure 5. Storage moduli (E’, MPa) and Tan δ as function of temperature for SB (Styrene-Butadiene) copolymer and SB3 (25% styrene content)/CF (Chicken Feather) composite.

Polímeros, 28(4), 368-372, 2018

Preparation and characterization of composites from copolymer styrene-butadiene and chicken feathers

Figure 6. SEM micrographs for SB (Styrene-Butadiene)/CF (Chicken Feather) composites.

to CONACYT for scholarship of Posdoctorate program, number 291113. Also to Dynasol Elastomeros S.A. de C.V. for SBS materials used in the research.

6. References

Figure 7. X-Ray Diffraction of SB (Styrene-Butadiene) copolymers and SB (Styrene-Butadiene)/CF (Chicken Feather) composites.

a broad peak around 19.7°, while in SB3/CF and SB2/CF peaks appear at 25.9° and 25.7°, respectively. That peak has not been reported before for CF composites, so its appearance suggest a new crystalline pattern. Keratin can exists in two different crystalline structures, α−helix and β−sheet. These kind of changes reported for CF materials are attributed to chemical treatment [22]. On the other hand, regarding the sample SB1 and SB1/CF composite, no changes were observed.

4. Conclusions The results of infrared spectroscopy by ATR, although not conclusive, are useful to know more about the chemical interaction between the polymeric matrix and the keratin used as reinforcement. The Tg of composites increases with CF content and an improvement in the rigidity at the molecular level is produced by the binding of the polypeptide chains of keratin with the styrenic chains of SB3. This behavior also happens in SB2 and SB2/CF but not in SB1 and SB1/CF, where a diminution in the Tg occurs due to the higher styrene content in SB1, so a better physical interaction between polystyrene block and keratin takes place and, as a result, chains are softened.

In the SB2/CF composite, the inclusion of keratin promotes an increase in the storage modulus with respect to the SB2 copolymer, improving the stiffness of the elastomeric matrix. However, in the SB1/CF and SB3/CF compounds, E’ decreases due to free movement of the polymer chain at high temperatures.

5. Acknowledgements Authors wish to thanks to Tecnologico Nacional de Mexico (TNM) for financial support for this research, code 6001.16-P. One of the authors (M.L.M.H.) wish to thanks Polímeros, 28(4), 368-372, 2018

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3. Jiménez-Cervantes Amieva, E., Velasco-Santos, C., MartínezHernández, A. L., Rivera-Armenta, J. L., Mendoza-Martínez, A. M., & Castaño, V. M. (2015). Composites from chicken feathers quill and recycled polypropylene. Journal of Composite Materials, 49(3), 275-283. http://dx.doi.org/10.1177/0021998313518359.

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Synthesis, structure and antimicrobial property of green composites from cellulose, wool, hair and chicken feather.

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6. Zha, W., Han, C. D., Moon, H. C., Han, S. H., Lee, D. H., & Kim, J. K. (2010). Exfoliation of organoclay nanocomposites based on polystyrene-block-polyisopreneblock- poly (2-vinylpyridine) copolymer: solution blending versus melt blending. Polymer, 51(4), 936-952. http://dx.doi.org/10.1016/j. polymer.2009.12.030.

7. Senoz, E., Wool, R. P., McChalicher, C. W., & Hong, C. K. (2012). Physical and chemical changes in feather keratin during pyrolysis. Polymer Degradation & Stability, 97(3), 297-307. http://dx.doi.org/10.1016/j.polymdegradstab.2011.12.018.

8. Salazar-Cruz, B. A., Rivera-Armenta, J. L., Garcia-Alamilla, R., Mendoza-Martinez, A. M., Esquivel de la Garza, A., & Moctezume Espiricueto, S. (2015). Evaluacion termica del curado de adhesivos base SBR usando peroxido de dicumilo.

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11. Hill, P., Brantley, H., & Van Dyke, M. (2010). Some properties of keratin biomaterials: kerateines. Biomaterials, 31(4), 585593. http://dx.doi.org/10.1016/j.biomaterials.2009.09.076.

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12. Winandy, J. E., Muehl, J. H., Micales, J. A., Raina, A., & Schmidt, W. (2003). Potential of chicken feather fibre in wood MDF composites. In Proceedings of the EcoComp 2003: 2nd International Conference on Eco-composites (pp. 1-6). London: Queen Mary University of London, European Society for Composite Materials. Retrieved in 2016, September 30, from https://www.fpl.fs.fed.us/documnts/pdf2003/winan03d.pdf 13. Janowska, G., Kucharska-Jastrzabek, A., Prochon, M., & Przepiorkowska, A. (2013). Thermal properties and cmobustibility of elastomer-protein composites. Part II: composites NBRkeratin. Journal of Thermal Analysis and Calorimetry, 113(2), 933-938. http://dx.doi.org/10.1007/s10973-012-2796-2.

14. Martínez-Hernández, A. L., Velasco-Santos, C., de-Icaza, M., & Castaño, V. M. (2007). Dynamical-mechanical and thermal analysis of polymeric composites reinforced with keratin biofibers from chicken feathers. Composites. Part B, Engineering, 38(3), 405-410. http://dx.doi.org/10.1016/j. compositesb.2006.06.013.

15. Yin, X.-C., Li, F.-Y., He, Y.-F., Wang, Y., & Wang, R.-M. (2013).

Study on effective extraction of chicken feather keratins and their films for controlling drug reléase. Biomaterials Science, 1(5), 528-536. http://dx.doi.org/10.1039/c3bm00158j.

16. De León Almazán, C. M., Chávez-Cinco, M. Y., Páramo-García, U., Mendoza-Martínez, A. M., Estrada-Moreno, I. A., & RiveraArmenta, J. L. (2016). PAni/SBR composites as anticorrosive coatings for carbon steel I: chemical, morphological and

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18. Barone, J. R., & Schmidt, W. F. (2005). Polyethylene reinforced with keratin fibers obtained from chicken feathers.

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19. Reddy, N., Hu, C., Yan, K., & Yang, Y. (2011). Thermoplastic films from cyanoethylated chicken feathers. Materials Science and Engineering C, 31(8), 1706-1710. http://dx.doi.org/10.1016/j. msec.2011.07.022.

20. Cheng, S., Lau, K. T., Liu, T., Zhao, Y., Lam, P. M., & Yin, Y. (2009). Mechanical and thermal properties of chicken feather fiber/PLA green composites. Composites. Part B, Engineering, 40(7), 650-654. http://dx.doi.org/10.1016/j. compositesb.2009.04.011.

21. Ma, B., Qiao, X., Hou, X., & Yang, Y. (2016). Pure keratin membrane and fibers from chicken feather. International Journal of Biological Macromolecules, 89, 614-621. http:// dx.doi.org/10.1016/j.ijbiomac.2016.04.039. PMid:27180293.

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Polímeros, 28(4), 368-372, 2018

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.11817

Effect of carboxymethylcellulose on colloidal properties of calcite suspensions in drilling fluids Keila Regina Santana Fagundes1, Railson Carlos da Souza Luz1, Fabio Pereira Fagundes2 and Rosangela de Carvalho Balaban1* Laboratório de Pesquisa em Petróleo – LAPET, Instituto de Química – IQ, Centro de Ciências Exatas e da Terra – CCET, Universidade Federal do Rio Grande do Norte – UFRN, Natal, RN, Brasil 2 Universidade Potiguar – UnP, Natal, RN, Brasil

1

*rosangelabalaban@hotmail.com

Abstract Drilling fluids are multicomponent systems used to aid the removal of cuttings from a borehole, and subject to a number of requirements to ensure a safe drilling operation. One of the most important is to form a low permeability cake on the walls of the hole penetrated by the bit, to avoid excessive filtrate loss. To that end, carboxymethylcellulose (CMC) associated with calcite (CaCO3) can be used. In this paper, the effect of carboxymethylcellulose on the colloidal properties of calcite suspensions in brine was systematically evaluated by rheological properties, filtrate volume and zeta potential.

Higher viscosity fluids, lower filtrate loss and less negative zeta potential were obtained using small calcite particles with wide size distribution and CMC with high average molecular weight (Mw) and low average degree of substitution (DS), highlighting the importance of effective interactions between CMC and calcite to improve drilling fluid properties.

Keywords: calcite, CaCO3, CMC, drilling fluids, filtrate loss.

1. Introduction Carboxymethycellulose (CMC) is one of the most important derivatives of cellulose, primarily due to its versatility as thickener, binding agent, emulsifier and stabilizer.

The presence of –CH2-COO-Na+ substituent groups on the cellulose backbone is responsible for higher solubility in aqueous media[1]. Polymer concentration[2], salt content[3,4], pH[5], the presence of surfactant[6], molecular structure[7], Mw[8] and DS[9] exert important effects on CMC solution properties. This polysaccharide has been used in a wide range of applications in foods[10], pharmaceutical products[11], biomaterials[12], cosmetics and electronic devices[13], as well as in many oilfield operations, including drilling fluids[14,15].

In most water-based drilling fluids, CMC is commonly used in association with calcite (calcium carbonate, CaCO3) particles to reduce fluid loss to the surrounding formation[16].

However, another important function of water soluble polymers is to provide rheological properties capable of maintaining the cuttings in suspension during drilling operations. As such, it is essential to correlate the polymer chemical structure (DS, Mw and distribution of substituent) with the physical-chemical properties of CaCO3 suspensions, in order to obtain the best result at the lowest cost.

the influence of DS of CMC and substituent distribution profile on equilibrium properties in an aqueous medium.

It was observed that the stability of aggregates is strongly influenced by the nature of group interactions (-COOH and –OH), reconstituted bonds and electrostatic repulsions between the charged groups (COO-). Backfolk et al.[16] showed the adsorption and association mechanisms for CMC and CaCO3 suspensions through adsorption isotherms.

They concluded that the interactions between CMC and CaCO3 are related to the amount of Lewis acid sites on CaCO3, leading to the formation of CMC-Ca2+ complexes.

Laskowski et al.[19] investigated polysaccharide adsorption onto mineral solid surfaces. The interactions were dependent on the basic/acid features of the hydroxylated metallic sites, which are anchored to the mineral surface. Moreover, the authors reported that hydroxyl and carboxylate groups on CMC have a significant impact on how this polysaccharide adsorbs at the mineral/aqueous solution interface. Some researchers have proposed that the mechanisms responsible for polymer adsorption onto mineral surfaces include hydrophobic interaction[20], hydrogen bounding[21,22], as well as chemical and electrostatic interactions[23].

Proper selection of CMC and CaCO3 can minimize fluid filtration across the wellbore, when a thin low-permeability filter cake is formed. According to the literature, CMC adsorption onto solid substrates is strongly dependent on adsorption kinetics, the pH of the medium and apparent hydrodynamic thickness[17]. Moreover, it also depends on the Mw and DS of CMC[18]. Caraschi and Campana[1] investigated

In the context of complex multicomponent drilling fluids, the adsorption mechanisms of CMC onto CaCO3, as well as the corresponding effects on fluid properties, have not been clearly elucidated. As such, the aim of this paper is to evaluate the influence of the DS and Mw of CMC on the colloidal properties of CaCO3 suspensions, through rheological properties, filtrate loss and zeta potential.

Polímeros, 28(4), 373-379, 2018

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

Fagundes, K. R. S., Luz, R. C. S., Fagundes, F. P., & Balaban, R. C. testing conditions of API fluid –loss testing[24]. Error bars represented the standard error of the mean.

Both rheological and filtration characterization followed the recommendations of the American Petroleum Institute - RP 13B[24].

2. Materials and Methods 2.1 Materials The following products were donated by PETROBRAS S.A.: xanthan gum, sodium chloride and calcium carbonate (calcite) of different particle sizes. CMC sodium salt, with a nominal DS/Mw of 0.7 / 2.5 x 105 g/mol, 1.2 / 2.5 x 10 5 g/mol and 0.7/ 0.9 x 105 g/mol were purchased from SIGMA ALDRICH.

2.6 Zeta potential Zeta potential (ζ) was determined in a Zeta Potential Analyzer (Brookhaven, New York, NY, USA). Electrophoretic mobilities of particles were measured by the analyzer and converted to zeta potential using the Smoluchowski Equation.

The experiments were performed at 25 °C with an equilibrium time of 24 hours for formulations F4 to F12. However, to better understand the interactions between calcium carbonate and CMC, neither xanthan gum nor NaCl was added.

The suspensions were prepared by previous solubilization of CMC (8.5 g/L) in distilled water for 12 hours followed by addition of calcium carbonate (57 g/L), with continue stirring for more 12 hours. ζ values were reported with an experimental error of less than 5% (after 10 runs).

2.2 Characterization of CaCO3 The average particle diameter and particle size distribution curve for CaCO3 (calcium carbonate, calcite) were determined by means of laser diffractometry through a CILAS 1064 laser particle analyzer. Analysis was carried out by dispersion of calcium carbonate in water, at 25 °C over the range from 0.04 to 500 μm. The data for CaCO3 particle sizes were presented by the cumulative distribution as a function of particle size.

2.3 Fluid preparation Xanthan gum (4.3 g/L) was used as rheological modifier in all formulations, and solubilized in 350 mL of 57 g/L sodium chloride aqueous solution for 24 hours, under constant stirring. Next, CMC and calcium carbonate were added to the polymer solution using a Hamilton Beach mixer, at 18,000 rpm. CMC and calcium carbonate were added separately and the mixing time for each product was 10 minutes. Twelve formulations were prepared and evaluated in regard to rheological behavior and filtrate volume. Table 1 shows the formulations studied.

3. Results and Discussion 3.1 Influence of CMC chemical structure and CaCO3 particle size on rheological properties Figure 1 shows that rheological properties depend strongly on the composition of the fluids. The fit of the power law model (Equation 1) to the rheological data was very good, with correlation coefficients (R2) close to 1 (results not shown).

The behavior index (n) indicated typical pseudoplastic fluid values in the 0.47 to 0.57 range, and the consistency index varied from 346 Pa.sn (F3) to 1399 Pa.sn (F5).

2.4 Viscosity tests A FANN model 35 A rotational viscometer was used to measure the viscosity of the colloidal suspensions.

Its design includes a R1 Rotor sleeve, B1 Bob, F1 Torsion Spring, and a stainless steel sample cup for testing according to American Petroleum Institute Recommended Practice for Field Testing Water Based Drilling Fluids, API RP 13B-1/ISO 10414-1 Specification[24]. Rheological analysis of each fluid was carried out under six different shear rates (5, 10, 170, 340, 511, 1022 s-1), at 25 °C. All the experiments were carried out in triplicate.

n

• = τ K  γ  (1)  

where: τ = Shear stress (Pa); γ = Shear rate (s-1); K = Consistency index (Pa.sn); n = Behavioral index.

3.1.1 Effect of Mw and DS of carboxymethylcellulose Figure 2 shows the viscosity curves of F1 to F3.

A significant decrease in viscosity and in consistency index (data not shown) was observed from F1 to F3. The rheological properties were greater for fluid F1 containing CMC with a higher Mw (Mw = 2.5 x 105 g/mol) and lower DS (DS = 0.7).

With an increase in Mw, the polymer hydrodynamic volume also rises, leading to higher viscosity. On the other hand, an

2.5 Filtration properties The filterability tests were performed in triplicate with a Whatman paper filter (Number 50), in a stainless-steel filtration cell under constant pressure of 100 psi, at 25 °C, for 30 minutes. This procedure was used to replicate the Table 1. Composition of colloidal suspensions.

Additive (g/L) Xanthan gum CMC Mw=2.5 x 105; DS=0.7

F1 4.3 8.5

CMC Mw=2.5 x 105; DS=1.2

F2 4.3

F3 4.3

F4 4.3 8.5

F5 4.3 8.5

8.5

CMC Mw=0.9 x 105; DS=0.7

8.5 57

CaCO3 B

F9 4.3

8.5

8.5

57 57

CaCO3 C

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F8 4.3

8.5

CaCO3 A

NaCl

Formulations F6 F7 4.3 4.3 8.5

57

57

57

57

F11 4.3

F12 4.3

8.5

8.5

8.5

57 57

57 57

F10 4.3

57

57 57

57

57

57

57 57

57

57

Polímeros, 28(4), 373-379, 2018

Effect of carboxymethylcellulose on colloidal properties of calcite suspensions in drilling fluids increase in DS can reduce CMC solubility in brine, thereby reducing viscosity. An increase in DS typically causes a more homogeneous distribution of carboxylate in the polymer chains[1]. Thus, immediate interactions may occur between salt and the polymer carboxylate groups, effectively shielding the anionic charge and inhibiting hydrogen bonds between the anionic sites and water molecules, diminishing polymer solubility in water.

3.1.2 Effect of CaCO3 particle size The viscosity of non-Newtonian fluids is affected by the characteristics of the dispersed solid phase, such as particle shape, concentration and dimension, solid/liquid phase interactions, nature of the surface, particle size distribution, etc[25]. Particle size distribution, uniformity factor and specific surface area are important physical parameters affecting fluids rheological and filtration behavior. It is clear that narrow and wide size distributions have different influences upon CaCO3 particles properties. A wider particle size distribution increases packing density and decreases aqueous medium demand, while a narrower particle size distribution gives higher hydration rates for equal specific surface area. It is obvious that as the particle size increases the surface area decreases. Likewise, CMC Mw and DS influence directly the degree of calcium carbonate particle flocculation.

As illustrated in Figures 3 to 5, after the addition of different samples of calcium carbonate to the fluids, almost all formulations experienced an increase in rheological properties (F4-F5-F6, compared to F1; F7-F8-F9, compared to F2 and F10-F11-F12, compared to F3).

This effect might be explained by polyelectrolyte adsorption onto the calcium carbonate surface, which is responsible for the increase in apparent particle volume, as well as higher mineral stability in the medium. On the other hand, the presence of a low number of small calcium carbonate particles can act as a lubricant, improving large particle rotation (smaller particles are interspersed between larger particles), leading to a reduction in viscosity[25,26].

This last effect could explain the results of formulation F12 (Figure 5), in which the CMC with the smallest Mw was used. In F12, viscosity declined from 250 to 200 cP at a shear rate of 10 s-1. However, unlike the rheological behavior exhibited by F12, the other formulations show no decrease in viscosity in the presence of small calcium carbonate particles. This effect was likely mitigated by the strong contribution of CMC Mw and DS that altered the particles’ attractive forces, responsible for controlling the state of dispersion and rheological properties of the fluids.

Table 2 shows the particle size of the CaCO3 used.

The calcium carbonate samples exhibited a particle size in the range of 0.87 to 17.88 µm, 1.39 to 22.06 µm and 1.92 to 32.65 µm for calcium carbonate A, B and C, respectively, with mean particle sizes of 7.64 µm, 12.27 µm and 18.61 µm, for A, B and C, respectively. These values​​ are in agreement with the manufacturer’s data. In addition, calcium carbonate A showed the lowest average diameter and largest particle diameter distribution, which means significant amounts of different particle sizes, whereas calcium carbonate B and C displayed the narrowest diameter distribution.

Polímeros, 28(4), 373-379, 2018

Figure 1. Flow curves of the colloidal suspensions described in Table 1, from shear rate 5 to 1022 s-1, at 25 °C.

Figure 2. Viscosity curves for F1, F2 and F3 colloidal suspensions described in Table 1, from shear rate 5 to 1022 s-1, at 25 °C. F = Formulation.

Table 2. Particle size characterization of CaCO3 A; B and C.

CaCO3 A

Average diameter (µm) 7.64

Diameter at 10% (µm) 0.87

Diameter at 50% (µm) 5.56

Diameter at 90% (µm) 17.88

CaCO3 B

12.27

1.39

12.40

22.06

CaCO3 C

18.61

1.92

18.77

32.65

CaCO3 C was the carbonate sample that contributed least to the increase in the consistency index. The effect on the flux behavior of colloidal suspensions was more marked in the viscosity results obtained when CMC with the lowest Mw was used (Figure 5), especially at low shear rates. On the other hand, the rheological properties were very similar in the formulations in which CaCO3 A and CaCO3 B were used.

This means that an increase in CaCO3 granulometry leads to fewer interactions between colloidal particles.

3.2 Influence of CMC chemical structure and CaCO3 particle size on filtrate loss Figure 6 summarizes the influence of CMC Mw, DS and calcite granulometry on the filtrate volume of colloidal calcite suspensions.

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Fagundes, K. R. S., Luz, R. C. S., Fagundes, F. P., & Balaban, R. C. 3.2.1 Effect of CMC

Figure 3. Viscosity curves for F1, F4, F5 and F6 colloidal suspensions described in Table 1, from shear rate 5 to 1022 s-1, at 25 °C. F = Formulation.

CMC is a water soluble organic colloid. As such, small amounts of CMC can significantly enhance water viscosity. On the other hand, filtrate volume decreases with an increase in filtrate viscosity. Another important parameter in the filtration process is the permeability of the cake formed on the surface of the filter paper. The filtrate volume decreases when filter cake permeability declines[27].

Among F1, F2 and F3 formulations, F1 showed the highest viscosity (Figure 2) and lowest filtrate volume (Figure 6) corroborating, thus, with the equation showed by Darley and Gray[27], which evidences that the decrease of viscosity leads to an enhancement of filtrate volume. Besides, a small difference was observed between the filtrate volume of F2 and F3. There seems to be a critical polymer hydrodynamic volume that depends on CMC Mw and DS, above which the filtrate volume decreases as a response to filtrate viscosity and filter cake permeability. In the presence of salt, the effect of increasing DS is similar to that of decreasing Mw, due to the enhanced polymer collapse at a high DS. 3.2.2 Effect of the interaction between CMC and calcium carbonate

Figure 4. Viscosity curves for F2, F7, F8 and F9 colloidal suspensions described in Table 1, from shear rate 5 to 1022 s-1, at 25 °C. F = Formulation.

Figure 5. Viscosity curves for F3, F10, F11and F12 colloidal suspensions described in Table 1, from shear rate 5 to 1022 s-1, at 25 °C. F = Formulation.

Figure 6. Filtrate volume of colloidal calcite suspensions, at constant pressure of 100 psi, 25 °C, for 30 min.

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The dispersion of calcium carbonate is important for its surface charge and colloidal properties as well as for its interaction with polymers[16]. The presence of water-soluble polysaccharides promotes interactions with calcium carbonate that reinforce the filter cake formed during filtration and provides the desired rheological properties over large temperature ranges. It has been reported that the calcium carbonate isoelectric point (iep) should lie within the range of pH 8.0-9.5[28]. CMC is in free acid form at pH 3.5, and the acid groups are ionized (negatively charged) at about pH 7.0. This suggests that CMC may shift the CaCO3 iep in solution, affecting charge development at the interface.

This agrees with findings by Wang and Somasundaran[29], which showed that CMC was responsible for the decreased zeta potential of talc with a rise in the iep from pH 2.5 to pH 3.5.

This evidence suggests that electrostatic interactions play an important role in the adsorption process of CMC onto CaCO3 and, consequently, in filtrate control. Figure 6 shows that CMC is responsible for the significant influence on filtrate control in association with calcium carbonate. The affinity of CMC molecules with dispersed calcium carbonate particles depends on the available Ca2+ surface sites for polymer adsorption. It should be noted that not only polymer and CaCO3 structure influence adsorption kinetics, but also the ionic strength of the medium. Several investigators[30] have reported that the adsorption of smaller CMC chains prevails at low salt concentrations (for example: 0.01M) due to their faster diffusion. In other words, these smaller polyectrolytes create an electrostatic barrier that opposes the arrival of larger molecules[29]. However, in our case, a salt concentration of 1 M was used in all formulations.

The lowest filtrate volume values (F4-F5) were mainly associated with the highest CMC Mw (2.5 x 105 g/mol).

The electrostatic barrier collapse caused by “salt screening” causes the larger charged macromolecules to reach the calcium carbonate surface[16]. Moreover, it is reasonable to assume that the greater the interactions between CMC and Lewis acid sites on the calcium carbonate for the formation of CMC-Ca2+ complexes, the faster the adsorption process Polímeros, 28(4), 373-379, 2018

Effect of carboxymethylcellulose on colloidal properties of calcite suspensions in drilling fluids Table 3. Zeta potential of CaCO3/CMC colloidal suspensions.

Additive CMC Mw=2.5 x 105; DS=0.7 CMC Mw=2.5 x 105; DS=1.2 CMC Mw=0.9 x 105; DS=0.7 CaCO3 A CaCO3 B CaCO3 C ζ (mV)

8.5

8.5

8.5 57 57 -11.95

8.5

8.5 8.5 57

57

-4.82

57 57 -13.01

and, consequently, the lower the filtrate volume. This effect contributed to the decline in filtrate volume for F7-F8-F9, compared to F2, due to the higher DS of CMC. 3.2.3 Effect of CaCO3 particle size Understanding the filtration mechanism that allows the establishment of an association between calcium carbonate particle size and the filtration properties of water-based drilling fluids is a daunting challenge in elucidating the problems related to fluid loss in wellbores. According to the results obtained (Figure 6), the formulations with the largest average calcium carbonate particle size (18.61 µm) exhibited the highest filtrate volume, caused by formation of a higher permeability filter cake. At the beginning of filtration, the colloidal suspension invades the porous medium (spurt loss).

The suspended solids attempt to flow with the liquid stream, but a fraction of these particles bridge the pores and begin to build a filter cake. Finer particles fill the interstices left by the bridging particles and ultimately form such a tight matrix that only liquid (filtrate) can penetrate. Once this filter cake is established, the flow rate of fluid into the porous medium is dictated by the permeability of the cake[27].

Thus, in addition to average particle size, another important parameter is particle size distribution. Table 2 shows that CaCO3 A has the widest diameter distribution curve, with particles of different sizes, while CaCO3 B and CaCO3 C have narrower curves. The results in Figure 6 demonstrate that CaCO3 A, with the smallest average diameter particle and widest diameter distribution curve, was more effective in controling filtrate volume, producing a low-permeability filter cake.

3.3 Influence of CMC chemical structure and CaCO3 particle size on zeta potential Zeta potential (ζ) provides an indirect measurement of surface charge density and is a relative indicator of system stability. The electrical properties of the calcium carbonate/CMC interface were investigated in order to elucidate the mechanisms that dictate charging behavior at the solid-liquid interface and, consequently, improve understanding of the electrochemical double layer (EDL) in the shear plane between the CaCO3 particle surface and counterions near the surface and surrounding polymeric fluid. Table 3 shows the zeta potential of the colloidal suspensions as a function of CaCO3 granulometry and CMC structural properties.

For all calcite suspensions studied, ζ was negative and increased with a rise in DS for CMC Mw 2.5 x 105. This means a higher amount of anionic charges in the medium, probably due to complete cationic calcite surface saturation by the Polímeros, 28(4), 373-379, 2018

Concentration (g/L)

8.5

-19.02

-34.00

8.5

8.5

57 57 -36.09

-41.20

-14.51

57 +27.12

polymer, which was more effective with the increase in DS. When CMC with Mw 0.9 x 105 and DS 0.7 was used, different tendencies were observed, depending on the calcite employed. With an increase in calcite particle diameter, the negative ζ value became positive, probably due to incomplete saturation of the cationic calcite surface by CMC. According to the zeta potential, good stability would be expected for all calcite suspensions, owing to the ionic charges on the surface. However, calcite particles with an anionic surface suggest CMC adsorption, which could lead to higher viscosities for the suspensions and the formation of low-permeability cakes during filtration. In this scenario, the formulation with the lowest negative zeta potential (F5) could lead to a more associative interaction between the particles and a more cohesive cake, resulting in high viscosity fluid and low filtrate volume, as depicted in Figures 3 and 6.

4. Conclusions In this study, we investigated the effect of calcite particle size associated with CMC Mw and DS on the rheological and filtration properties of the aqueous suspensions, considering the general conditions used in drilling fluids.

Zeta potential data were also used to clarify the interactions between calcite and CMC. The higher Mw (2.5 x 105 g/mol) and lower DS (0.7) of CMC contributed to both higher viscosity and lower filtrate volume. This effect was improved in the presence of calcite, providing important evidence of CMC-CaCO3 interactions. In addition, the use of a calcite sample with low average particle size but wide size distribution can contribute significantly to reducing filtrate loss across a porous medium.

The zeta potential results provide even more evidence of the effective interactions between calcite and CMC. Lower negative zeta potential values were obtained for the suspensions containing higher CMC Mw (2.5 x 105 g/mol), lower DS CMC (0.7), and small calcite particle size. These results corroborate the rheological and filtration properties.

In summary, the results of this paper indicate that the effectiveness of CMC-CaCO3 (calcite) in the control of filtrate loss is related to good interaction between anionic groups of CMC and Lewis acid sites on the surface of the mineral and that this can be enhanced by proper selection of CMC and CaCO3.

5. Acknowledgements The authors are grateful to Professor Hugo Alexandre de Oliveira Rocha from the Biochemistry Department of the Federal University of Rio Grande do Norte (UFRN) for his 377/379 377

Fagundes, K. R. S., Luz, R. C. S., Fagundes, F. P., & Balaban, R. C. help in zeta potential analysis, and to CAPES (Coordination for the Improvement of Higher Education Personnel) and Petrobras for financial support.

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Received: Dec. 02, 2017 Revised: Mar. 19, 2018 Accepted: Mar. 26, 2018

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