Polímeros: Ciência e Tecnologia (Polimeros)4th. issue, vol. 33, 2023

Volume XXXIII - Issue IV - December., 2023

Polímeros

Prof. Ailton de Souza Gomez

23 ol, 20 Th CBP C 7 1 ille-S Joinv

Emeritus Professor, IMA/UFRJ

021 Pol, 2 B C 16 Preto Ouro th

VOLUME XXXIII - Issue IV - December., 2023

*1942 †Dec/28/2023

The late Associated Editor of Polimeros, Prof. Richard G. Weiss São Paulo 994 St. São Carlos, SP, Brazil, 13560-340 Phone: +55 16 3374-3949 Email: abpol@abpol.org.br 2023 2021

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 X I I I - 2 0 2 3 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 a n d ­T e c h n ic a l I n f o r m a t i o n ” — “ L a t i n d e x ” — “ W e b o f S ci e n c e ”

Polímeros E d i t o r i a l C o u nci l

Editorial Committee

Antonio Aprigio S. Curvelo (USP/IQSC) - President

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

Members Ailton S. Gomes (UFRJ/IMA), Rio de Janeiro, RJ (in memoriam) Alain Dufresne (Grenoble INP/Pagora) Bluma G. Soares (UFRJ/IMA) César Liberato Petzhold (UFRGS/IQ) Cristina T. Andrade (UFRJ/IQ) Edson R. Simielli (Simielli - Soluções em Polímeros) Edvani Curti Muniz (UEM/DQI) Elias Hage Jr. (UFSCar/DEMa) 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) Luiz Antonio Pessan (UFSCar/DEMa) Luiz Henrique C. Mattoso (EMBRAPA) Marcelo Silveira Rabello (UFCGU/AEMa) 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 Washington, DC, United States (GU/DeptChemistry) (in memoriam) Rodrigo Lambert Oréfice (UFMG/DEMET) Sebastião V. Canevarolo Jr. (UFSCar/DEMa) Silvio Manrich (UFSCar/DEMa)

A ss o ci at e E d i t o r s Alain Dufresne Bluma G. Soares César Liberato Petzhold José António C. Gomes Covas José Carlos C. S. Pinto Marcelo Silveira Rabello Paula Moldenaers Richard G. Weiss (in memoriam) Rodrigo Lambert Oréfice

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

www.editoracubo.com.br

“Polímeros” is a publication of the Associação Brasileira de Polímeros São Paulo 994 St. São Carlos, SP, Brazil, 13560-340 Phone: +55 16 3374-3949 emails: abpol@abpol.org.br / revista@abpol.org.br http://www.abpol.org.br Date of publication: December 2023

Financial support:

Available online at: www.scielo.br

Polímeros / Associação Brasileira de Polímeros. vol. 1, nº 1 (1991) -.- São Carlos: ABPol, 1991Quarterly v. 33, nº 4 (December 2023) ISSN 0104-1428 ISSN 1678-5169 (electronic version)

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

1. Polímeros. l. Associação Brasileira de Polímeros.

Polímeros, 33(4), 2023

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In memory of Prof. Richard George Weiss

E D I T O R I

With deep regret, we inform the death of Professor Richard G. Weiss, the Associated Editor of this journal Polimeros, on December 28, 2023, at the age of 81.

Prof. Weiss was born in Ohio, United States, in 1942. He received an ScB degree (1965) from Brown University, a MS (1967) and PhD (1969) degrees from the University of Connecticut under the mentorship of Prof. Eugene I. Snyder.

Afterwards he was an NIH Postdoctoral Fellow for 2 years with George S. Hammond (*May/22/1921, Oct/05/2005), at California Institute of Technology, who is considered the father of American organic photochemistry, and deeply influenced Prof. Weiss research carrier.

Prof. Weiss was a prominent photochemical and university professor, authored or co-authored more than 300 peerreviewed publications in the best international journals, the most recent ones are listed below [1-8] and more than 25 book chapters, the last one in 2018[9] and is author of 3 patents. His research group was highly interdisciplinary, including investigators in organic, physical and analytical chemists as well as material scientists from around the world. Collaborations with groups in North America, Brazil, Costa Rica, Germany, France, Italy, Spain, Slovakia, India, Egypt, Japan and China allow students in his group to interact with researchers from different parts of the globe, thereby promoting international partnerships with both international and domestic institutions, including the National Institute for Standards and Technology (NIST), the National Gallery of Art, the International Network on Integrated Techniques in Structural Elucidation (InTechSe), the Universities of Florence and Palermo in Italy, the Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences, and the Universidade Estadual de Campinas, UNICAMP, in Brazil.

He supervised many research students during his long academic carrier, working in various areas of mechanistic photochemistry and photophysics related to polymers, molecular rearrangements, thermal reactions of molecules in anisotropic environments, development and application of optically active substances, ionic liquids, ionic liquid crystals, and new molecular and polymer gels for various purposes, including chemical spill remediation and the conservation of objects of cultural heritage. In addition, some of the materials were examined as reversible adhesives, as food additives, for art conservation, and as dispersants and coagulants to contain oil spills.

A L

One of the last photos of Prof. Weiss, participating in the successful celebration of one of his Ph.D. student defense (2022).

His academic activity began in Brazil (1971) as a Visiting Assistant Professor, at the Institute of Chemistry of the University of São Paulo, USP, and National Academy of Sciences Overseas Fellow in Brazil for 3 years, with the objective of implementing the first photochemical laboratory in the country, within the successful Hammond-Toscano program of CNPq-American Academy of Science. After that he returned to USA, where he was hired in 1986 by the University of Georgetown in Washington DC, till his death, when his was holding the rank of Full Professor. He was also a member of the Institute for Soft Matter Synthesis and Metrology at Georgetown University.

He returned several times to Brazil to provide postgraduate courses and conferences at various universities, participated in the organization of the 1st Latin American Photo Congress in Iguaçu Fall in 1996, participated in the implementation of the PADCT Program in Chemistry as a representative of the World Bank. Participated in the organization of the IUPAC Photochemical Symposium in Dresden, Germany in 2000, occupying until 2001 the head of the IUPAC Photochemical Commission. He received a doctorate honoris causa from Université de Bordeaux 1.

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Polímeros, 33(4), 2023

Apart from being an Associate Editor for Polimeros (ABPol) he had been the Senior Editor of the ACS journal Langmuir (2004-2014), and was member of the Editorial Advisory Board of various scientific journals: Journal of the Brazilian Chemical Society (JBCS), Gels (from MDPI) Indian Journal of Chemistry IJC, and member of the Scientific Committee of Substantia, an international journal devoted to the history of chemistry and other sciences. Professor Dick, as he has affectionally treated, was awarded the Medal of JBCS in 2018, during the Annual Meeting of the Brazilian Chemical Society 41ª RASBQ in Iguaçu Falls, PR, Brazil.

His professionalism and competence were notable and will be missed, especially the way he carried his duty of Associated Editor, judging the articles which were submitted to Polimeros and I entrusted to him.

Last published articles by Prof. Weiss: 1.

Poon, L.; Hum, J. R. Weiss, R. G (2022), Effects of Cyclic and Acyclic Amidine Side-Chains on the Properties of the Polymer Networks of Polysiloxane Ionomers Constructed in situ from Three Uncharged Components. Soft Matter, 18, 5502-5508.

2.

Sánchez-Pedregal, V. M.; Kertesz, M.; Weiss, R. G.; Cabrita, E.; Navarro-Vázquez, A.; Cid, M. M. (2021), NMR spectral fingerprint patterns as diagnostics for the unambiguous configurational analysis of the classic organo-gelator, 1,3:2,4-dibenzylidene-D-sorbitol (DBS), and its derivatives, Magnetic Resonance in Chemistry, 59, 608-613.

3.

Poon, L.; Hum, J. R.; Weiss, R. G. (2021), Neat linear polysiloxane-based ionic polymers. Insights into structure-based property modifications and applications, Macromol.,1, 2-17.

4.

Grover, G.; Weiss, R. G. (2021) Luminescent Behavior of Gels and Sols Comprised of Molecular Gelators, Gels, 7, 19 (28 pages).

5.

Poon, L.; Weiss, R. G. (2021), Uncharged Lewis Bases Yield Polydimethylsiloxane Ionomers with Amidinium Alkyldithiocarbamate Side Chains, J. Polym. Sci., 59, 2345-2354.

6.

Beaupre, D. M.; Weiss, R. G. (2021) Thiol- and Disulfide-Based Stimulus-Responsive Soft Materials and Self-Assembling Systems, Molecules, 26, 3332.

7.

Lukac, I.; Husár, B.; Danko, M.; Weiss, R. G. (2021), Benzil photoperoxidations in polymer films and crosslinking by the resultant benzoyl peroxides in polystyrene and other polymers, Molecules (Special Issue: 25th Anniversary of Molecules—Recent Advances in Materials Chemistry), 26, 5154.

8.

Berride, F.; Sánchez-Pedregal,V. M.; Dacuña, B.; Cabrita, E.; Navarro-Vázquez, A.; Weiss, R. G.; Cid, M. M. (2021), Conformation and supramolecular arrangement of 1,3:2,4-dibenzylidene-D-sorbitol arrangements in single crystals, ChemRxiv.

9.

Weiss, R. G. (ed) (2018), Monographs in Supramolecular Chemistry, Molecular Gels: Structure and Dynamics, ISBN: 978-1-78801-111-2, 376 pgs, DOI: https://doi.org/10.1039/9781788013147

Prof. Sebastião V. Canevarolo Editor-in-Chief Polimeros

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i i i i i i i i i i i i i i i i i

Editorial Section Report 17°CBP....................................................................................................................................................................................E5 News..................................................................................................................................................................................................E12 Agenda...............................................................................................................................................................................................E13 Funding Institutions...........................................................................................................................................................................E14

O r i g in a l A r t ic l e Conductive Amazon açaí/polyaniline composite fiber: fabrication and properties Jefter Victor Gonçalves, Jefferson Suela, Marcus Vinícius Duarte Silva, Rodrigo Fernando Bianchi and Cleidinéia Cavalcante da Costa ....................................................................................................................................... e20230037

Cold plasma copolymer with antimicrobial activity deposited on three different substrates Erick Osvaldo Martínez Ruiz, Xi Rao, Abril Fonseca García, Carlos Gallardo Vega, Carmen Natividad Alvarado Canche, José Abraham Gonzáles López, Antonio Serguei Ledezma Pérez, Miriam Desiree Davila Medina, Claudia Gabriela Cuellar Gaona, Rosa Idalia Narro Céspedes, Gustavo Soria Arguello and María Guadalupe Neira Velázquez ................................................... e20230038

Synthesis and characterization of polyurethane and samarium(III) oxide and holmium(III) oxide composites Lucas Repecka Alves, Giovanni Miraveti Carriello, Guilherme Manassés Pegoraro, Henrique Solowej Medeiros Lopes, Thaís de Agrella Janolla, Airton Natanael Coelho Dias, Giovanni Pimenta Mambrini, Maira de Lourdes Rezende and Aparecido Junior de Menezes .................................................................................................................................................. e20230039

Hydrophobic polyurethane foams reinforced with microcrystalline cellulose for oil spill clean up Matheus Vinícius Gregory Zimmermann, Eduardo Junca, Marina Kauling de Almeida, Lara Vasconcellos Ponsoni, Ademir José Zattera, Tiago Mari and Ruth Marlene Campomanes Santana ....................................................................................................................... e20230040

Development of bacterial cellulose incorporated with essential oils for wound treatment Sandro Rogério Kumineck Junior, Victória Fonseca Silveira, Denise Abatti Kasper Silva, Michele Cristina Formolo Garcia, Giannini Pasiznick Apati, Andréa Lima dos Santos Schneider, Ana Paula Testa Pezzin and Flares Baratto-Filho ........................... e20230041

In-situ polymerized Pebax®/polydopamine blend membranes with high CO2/N2 selectivity

Ariele dos Santos Pirola, Paula Sacchelli Pacheco, Sônia Faria Zawadski and Daniel Eiras .......................................................... e20230043

Consumer perception of biodegradable packaging for food Ana Carolina Salgado de Oliveira, Michele Nayara Ribeiro, Julio Cesar Ugucioni, Roney Alves da Rocha and Soraia Vilela Borges...... e20230045

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Polímeros, 33(4), 2023

ISSN 1678-5169 (Online)



17th Brazilian Congress of Polymers - 17th CBPol Joinville – SC, October 29 to November 2, 2023 The Brazilian Polymers Conference (CBPol) is the main scientific forum in polymer science and technology in Brazil, being held every two years since 1991. Its 17th edition was organized by a group of professors from the State University of Santa Catarina (UDESC), the University of the Region of Joinville (Univille), the Federal University of Santa Catarina (UFSC), the Federal University of Rio Grande do Sul (UFRGS) and the Federal Technological University of Paraná (UTFPR), in partnership with the Brazilian Polymer Association (ABPol). The conference was held at the Expoville Convention and Exhibition Center, in Joinville, from October 29 to November 02, 2023. Joinville, known as the ‘City of Flowers’ and the ‘Brazilian Capital of Dance’, is a pleasant industrial and tourist city located in the northeast of the State of Santa Catarina in southern Brazil.

The 17th CBPol was sponsored by the Brazilian Funding Agencies CAPES, FAPESC and FAPESP (for participants from the State of São Paulo) and the companies Krona Tubos e Conexões, Regional Council of Engineering and Agronomy of Santa Catarina – CREA-SC, Instron, TA Instruments, DP Union, Zwick/Roell, DBM Nano, PerkinElmer, Netzsch, Reo Term, Shimadzu, Anton Paar, AX Plásticos Maquinas Técnicas Ltda, DOW, HSensor, KCEN, Royal Society of

Chemistry, CCDM, IOTO International and Wortex Group, in addition to having the support of the Brazilian Association of Rubber Technology (ABTB), INCT Polysaccharides, Plástico Virtual, Joinville Convention & Visitors Bureau and Rhein Beer.

The opening session of the 17th CBPol took place on the evening of October 29, 2023 (Sunday). Those responsible for the session were Prof. Marco Aurélio de Paoli (President of ABPol), Prof. Sérgio Henrique Pezzin (Chair of the Conference), Profa. Palova Santos Balzer (Vice-chair), Profa. Daniela Becker (Coordinator of the Scientific Committee), Mr. Willian Escher (Secretary of Economic Development of Joinville), Profa. Yoná da Silva Dalonso (Dean of Extension and Community Affairs at Univille), Prof. Antônio Heronaldo de Souza (Director of the Center for Technological Sciences at UDESC Joinville), Mr. Giuliano Rodrigo de Mello (President of the Joinville Convention & Visitors Bureau), Eng. Daniel Kandler Signori (Regional Director of CREA- SC in Joinville) and Eng. Israel Almeida Furtado (Research and Development Manager at Krona Tubos e Conexões), representing all the sponsors of the conference (Figure 1).

Figure 1. Images of the opening session of the 17th CBPol. First image (from left to right): Giuliano Rodrigo de Mello (President of the Joinville Convention & Visitors Bureau), Yoná da Silva Dalonso (Univille representative), Daniela Becker (Coordinator of the Scientific Committee), Marco Aurélio de Paoli (President of ABPol), Sérgio Henrique Pezzin (Conference Chair), Willian Escher (Secretary of Economic Development of Joinville), Antônio Heronaldo de Souza (representative of UDESC) and Daniel Kandler Signori (CREA-SC).

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Pezzin, S. H., Balzer, P. S., & Becker, D.

Figure 2. Images of the ABPol awards. From top to bottom, from left to right: Prof. Marco Aurélio de Paoli (president of ABPol), Prof. Luiz Henrique Capparelli Mattoso (winner of the ABPol “Profa Eloisa Mano” award) and Profa. Bluma Günther Soares (representative of ABPol); Profa. Mariana Agostini de Moraes (winner of the “Young Researcher” award from ABPol) and Prof.

André Fajardo (representative of ABPol); and Marcelo Farah (winner of the ABPol “Polymer Technology” award) and Frederico Mendes Junior (representative of ABPol).

The president of ABPol, Prof. Marco Aurélio de Paoli, emphasized the importance of ABPol and CBPol for the continuous advancement of polymer science and technology in Brazil, especially in this post-pandemic moment. In his speech, the general coordinator of the conference, Sérgio Henrique Pezzin, addressed the points of circularity and innovation, currently crucial for research in polymer science and technology, and highlighted the strength of women who are part of the polymer community in Brazil. The scientific coordinator of the event, Profa. Daniela Becker highlighted the number of papers approved for presentation at the event and their distribution in the various regions of the country and abroad.

After the presentations, outstanding Brazilian researchers were awarded: Prof. Luiz Henrique Capparelli Mattoso (EMBRAPA Instrumentation) received the ABPol “Profa Eloisa Mano” award for Polymer Science, Profa. Mariana Agostini de Moraes (UNIFESP) received the “ABPol Young Researcher” award and the ABPol “Polymer Technology” award was given to Dr. Marcelo Farah (Braskem) (Figure 2). Subsequently, the President of ABPol swore in the new board members of the association and presented the new board of directors of ABPol for the 2023/2025 biennium. The ceremony ended with dance performances performed by student dancers from the Municipal Ballet School (Joinville), followed by a welcome cocktail for all participants (Figure 3).

On Sunday afternoon, ABPol’s administrative assistants, Mr. Marcelo Perez Gomes and Ms. Layane Souza, began the delivery of the conference documents to the participants.

At the same time, there was the 1st. Meeting of the National Institute of Science and Technology in Polysaccharides (INCT Polissacarídeos), under the coordination of Prof.

Edvani Curti Muniz (UFPI) (Figure 4).

On the following four days (Monday to Thursday), the activities of each period of the day (morning and afternoon) began with a plenary lecture followed by keynotes and oral presentations in 5 or more parallel sessions, except for Tuesday afternoon. The presentations were classified into 11 thematic symposia according to their themes: 1) ‘Polymerization reactions and polymer chemistry’; 2) ‘Polymer physics and characterization’; 3) ‘Polymer nanostructures and nanocomposites’; 4) ‘Blends, composites and polymer networks’; 5) ‘Processing and materials design’;

Figure 3. Images of a dance performance by the Municipal Ballet School of Joinville (left) and welcome cocktail (right).

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17th Brazilian Polymer Conference 6) ‘Rubber and Elastomers’; 7) ‘Recycling and environmental issues associated with polymers’; 8) ‘Biomedical applications of polymers’; 9) ‘Polymer in agriculture and industrial special applications’; 10) ‘Innovation and management involving polymers and education’; and 11) ‘Technical Sessions’. More details of the schedule can be found on the event’s website at https://cbpol.com.br/. For the first time in its history, CBPol had an application developed exclusively for the event (EventMobile/Aptor Software), with continuous day-to-day support.

Tuesday afternoon (10/31) was dedicated to two parallel activities highlighted in the event: Circularity and Innovation (Figure 5). In the panel on Circularity, under the mediation of Prof. Walter Ruggeri Waldman (UFSCar), there was the participation of Prof. Caio Gomide Otoni (UFSCar), Ms. Fabiana Quiroga Garbin (Braskem) and diplomat Francisco Nelson de Almeida Linhares Júnior (Ministry of Foreign Affairs – Brazil), which was followed by a round table with broad participation on the subject. In the Innovation panel, there was the presentation of a motivational lecture by Prof. Diego Piazza (UCS), “Seeing your Research as a Business”, followed by the I Workshop on Innovation and Entrepreneurship in Polymers, coordinated by Prof.

Fabiano Ferreira (UFMG). In the workshop, teams were created that worked on proposals for possible businesses in polymers, with the mediation of experienced collaborators in the generation of startups. At the end of the day, there was the presentation of ‘pitches’ from the teams, with the evaluation of professionals in the area and the award of the best proposals.

From Monday to Wednesday, at the end of each day (late afternoon), poster sessions were held (Figure 6).

A coffee-break was offered at each time of the day. During the coffee break on Monday afternoon, there was the launch of the book “Plastic Recycling”, with the presence of the authors Hélio Wiebeck (USP) and Derval dos Santos Rosa (UFABC). At the same time, there were stands for the exhibition of products and equipment associated with polymer research and related branches of science hosted by the manufacturing companies: Krona Tubos e Conexões, CREA-SC, Instron, TA Instruments, DP Union, Zwick/Roell, DBM Nano, PerkinElmer, Netzsch, Reo Term, Shimadzu, Anton Paar, AX Plásticos, DOW, HSensor, KCEN, Royal Society of Chemistry, CCDM, IOTO International and Wortex Group (Figure 6). In addition, a ‘happy hour’ (on Monday evening) and a banquet/get-together dinner (on Wednesday evening) were offered to attendees. These social activities provided an extra opportunity for networking among the participants.

The 17th CBPol had 880 registered attendees (including regular participants, sponsor representatives, speakers and visitors/companions), from the following countries: South America – Brazil (865), Chile (2), Peru (2), Uruguay (1) and Colombia (1); North America – USA (2); Europe – Poland (1), Ireland (1), Netherlands (1), France (1), Great Britain (1), Portugal (1) and Asia – Singapore (1) (Figure 6). Of the total, approximately 60% were students and 40% were professors or researchers, with 53.5% women, 46.3% men, and 0.2% non-binary.

Of the students present at the event, 131 were undergraduate or technical education, while 345 were graduate students Polímeros, 33(4), 2  023

Figure 4. Above: Image of the conference reception. Below: Participants of the INCT Polissacarídeos meeting.

Figure 5. Panel on Circularity (above); Lecture by Prof. Diego Piazza (UCS) at the Innovation Panel (at the middle); Winning team of the proposals worked on in the Innovation and Entrepreneurship Workshop (below).

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Pezzin, S. H., Balzer, P. S., & Becker, D. (master’s or doctorate). The number of registered participants in Brazil by state (federative regions) is shown in Figure 7, with congressmen from nineteen states of the federation participating in the event. The most significant number of researchers was from the state of São Paulo, followed by Santa Catarina, Rio Grande do Sul, Rio de Janeiro and Paraná.

However, all Brazilian regions (N, NE, CO, SE and S) were present at the event.

Out of a total of 887 submissions, 857 papers, with 2,164 authors, were accepted for presentation at the conference. All articles have been previously submitted to peer review. The review of the articles was coordinated

by Profa. Daniela Becker (UDESC) with the collaboration of 11 symposium coordinators and 183 ad hoc reviewers.

The papers presented, including plenary and technical sessions, were divided as follows: 6 plenary lectures (60 min each), 28 keynotes (30 min each), 160 oral presentations (20 min each), 16 technical presentations (20 min each) and 669 posters.

The symposium on blends, composites and polymer networks received the most significant number of papers (196), followed by the symposia on polymeric nanocomposites and

nanostructures (165) and on recycling and environmental issues related to polymers (140), Figure 8, reflecting the global scenario of polymer research. Considering the UN Sustainable Development Goals, the papers presented in the different sessions were aligned with one or more of the following goals: 2, Zero hunger and sustainable agriculture; 6, Drinking water and sanitation; 7, Clean and affordable energy; 9, Industry, innovation and infrastructure; 12, Responsible consumption and production; and 15, Terrestrial Life.

The plenary lectures were given by renowned Brazilian and foreign researchers (Table 1 and Figure 9), which covered emerging areas of polymer research around the world.

On Tuesday evening, immediately after the poster session, there was a meeting of the editorial board of the Journal “Polymers Science and Technology”, with the participation of congressmen members of the board, such as Prof. Sebastião V. Canevarolo (Editor-in-chief), and the participation online of Prof. Antonio Aprigio S. Curvelo (President of the Editorial Board).

The poster awards were presented at the closing ceremony in the late morning of October 31 (Thursday).

The poster evaluation committee was coordinated by Profa.

Juliana Kloss (UTFPR), with the three best student works in each category (doctorate, master’s and undergraduate) awarded. The award-winning students are listed below by category.

Figure 7. Number of registered participants per federative unit in Brazil.

Figure 6. Images of i. a coffee-break; ii. the launch of the book “Reciclagem de Plásticos”; iii. sponsors’ stands, and iv. a poster session.

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Figure 8. Number of papers in each symposium presented at the 17th CBPol. Polímeros, 33(4), 2  023

17th Brazilian Polymer Conference Table 1. Plenary lectures of the 17th CBPol Title

Lecturer

Gels for Environmental Remediation: From Aerogels to Nanosponges

Artur José Monteiro Valente – University of Coimbra (Portugal)

Polymers and Agriculture: Present and Promising Technological Future

Luiz Henrique Capparelli Mattoso – EMBRAPA Instrumentação (Brazil)

Developing Strategies for Polymer Redesign and Recycling Using Reaction Pathway Analysis

Linda J. Broadbelt - Northwestern University (USA)

Braskem’s Innovation Journey to Implement the Circular Economy

Fabiana Quiroga Garbin – Braskem (Brazil)

Two Decades of Polymer Nanocomposites Research: From Academia to Industry

Ricardo Vinicius Bof de Oliveira - 2D Materials (Singapore)

Natural Fiber and Hybrid Composites: Science and Technology

Sandro Campos Amico – Federal University of Rio Grande do Sul (Brazil)

Figure 9. Images of the plenary speakers of the 17th CBPol. From top to bottom, from left to right: Prof. Artur Valente, Prof. Luiz Henrique Capparelli Mattoso, Profa. Linda Broadbelt, Fabiana Quiroga Garbin, Dr. Ricardo V. Bof de Oliveira, Prof. Sandro Campos Amico.

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Pezzin, S. H., Balzer, P. S., & Becker, D.

Best Poster Awards - Undergraduate Students 1st place: Pamela Xavier Mendoza (Universidade Federal de Santa Catarina - UFSC) for the study entitled “Functionalization of Clay Nanoparticles by Plasma for Application in Active Packaging”. Co-authors: Larissa N. Carli (UFSC), Pâmela R. Oliveira (UFSC), Renata C. da Costa (UFSC), Cesar Aguzzoli (UCS) and Janaina da Silva Crespo (UCS).

2nd place: Evelin Thainá Barbosa Serpa (Faculdade de Tecnologia de Sorocaba – FATEC SO) for the study entitled “Performance Assessment of Bacterial Cellulose Films from Kombucha in Conservation of Strawberries in Natura”. Co-authors: Maira L. Rezende, Renata Leme, Suelen C. de Almeida Sacardo, Henrique S. Medeiros Lopes and Paulo J. Bálsamo (FATEC SO).

3rd place: Vítor Bühler Salomão (Universidade Federal de São Carlos - UFSCar) for the study entitled “Effect of Cellulose Nanocrystals on Water Absorption of Sulfonated SBS Based Ionic Polymer Metal Composite”.

Co-authors: Paulo O. Gall, Guilherme E. de O. Blanco, Matheus C. Saccardo and Carlos H. Scuracchio (UFSCar).

Best Poster Awards - Master Students 1st place: Samara da Silva Araújo (Universidade Estadual Paulista/Campus de Rosana – UNESP) for the study entitled “Examining the Dispersion of Acai Residue as a Filler in Natural Rubber Matrix Using Rheometry, SEM-EDX, and Tensile Strength in the Production of Eco-Friendly Biocomposite”. Co-authors: Gleyson A. Santos, Gabrieli R. Tolosa, Eduardo R. Budemberg, Aldo E. Job, Carlos T. Hiranobe, Flávio C. Cabrera, Leonardo Lataro, Renivaldo José dos Santos (UNESP).

2nd place: João Gabriel Ribeiro (Universidade Federal do ABC - UFABC) for the study entitled “SurfaceModified Microfibrillated Cellulose from Eucalyptus Sawdust for Potentially Toxic Elements Removal from Contaminated Water”. Co-authors: Rennan F. da Silva Barbosa, Derval S. Rosa (UFABC).

3rd place: Heliton Barra (Universidade Tecnológica Federal do Paraná - UTFPR) for the study entitled “Study of EVA/Bentonite Clay-Niobium Pentoxide Hybrid Systems by DRX and TD-NMR”. Co-authors: Reinaldo Y. Morita, Roberta R. Domingues, Juliana R. Kloss (UTFPR).

Best Poster Awards - PhD Students 1st place: Cleonice Aparecida Salgado (Universidade Federal de Viçosa – UFV) for the study entitled “Polyurethanes Biodegradation by Staphylococcus warneri Isolated from the Gut of Larvae of Galleria mellonella”. Co-authors: Pedro M. Pereira Vidigal, Maria C. D. Vanetti (UFV).

2nd place: Laura Pires da Mata Costa (Universidade Federal do Rio de Janeiro - UFRJ) for the study entitled “Plastic Pyrolysis Vaporization”. Co-authors: Julián A. García Cárdenas (UFRJ), Amanda L. Teixeira Brandão (PUC-Rio de Janeiro), José C. C. da Silva Pinto (UFRJ).

Figure 10. Images of the poster award ceremony.

3rd place: Andressa de Espíndola Sobczyk (Universidade Federal do Rio Grande do Sul – UFRGS) for the study entitled “Influence of the Washing Process on the Properties of Chitosan-Alginate Composite Films”.

Co-authors: Débora J. L. Faccin, Nilo S. M. Cardozo, Isabel C. Tessaro (UFRGS).

Figure 11. Images of the closing session of the 17th CBPol: Audience; Closing speech, from left to right: Profa. Daniela Becker (Scientific Coordinator), Profa. Juliana Kloss (Poster Evaluation Coordinator) and Prof. Marco Aurélio De Paoli (president of ABPol).

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Polímeros, 33(4), 2  023

17th Brazilian Polymer Conference At the closing ceremony (Figure 13) at noon on October 31 (Thursday), the president of ABPol, Prof.

Marco Aurélio De Paoli, presented an overview of the conference and announced the new board of directors of ABPol for the 2024-2025 biennium, which will be managed by the president-elect Prof. Leonardo Bresciani Canto. The Coordinator of the Congress, Prof. Dr. Sérgio Henrique Pezzin, made a presentation on the scientific highlights of the conference.

Some aspects of the 17th CBPol are particularly noteworthy. Firstly, considering that it was the first post-pandemic ‘in person’ edition of the conference, there was a significant number of registered participants

Figure 12. Image of members of the 17th CBPol Organizing Committee, from left to right: Prof. Sérgio H. Pezzin (UDESC), Profa. Daniela Becker (UDESC), Profa. Noeli Sellin (Univille), Profa. Palova S. Balzer (Univille), Profa. Claudia Sayer (UFSC), Profa. Rosmary Brandalise (UCS), Prof. Sandro C. Amico (UFRGS), Profa. Juliana Kloss (UTFPR) and Profa. Carla Dalmolin (UDESC).

and papers presented, based on the historical average of the event. Secondly, we highlight the differentiated activities related to the Panels on Circularity, including the presence of a diplomat to discuss the global plastics treaty currently under discussion, and Innovation, with the I Innovation and Entrepreneurship Workshop, which allowed several academics the opportunity to experience the process of creating ‘startups’ based on the ideas generated in universities and research centers. It should also be noted the excellent scientific and technological quality of the papers presented at the event, as attested by international representatives. Finally, the scientific and social activities were a great success, providing a favorable environment for discussion and networking among the participants.

We would like to thank the organizing committee (Figure 12) and the scientific committee, as well as the coordinators of the symposia, the poster evaluation committee (Figure 13) and the ad hoc reviewers, who played a fundamental role in achieving the excellent scientific quality of the conference. We would also like to thank the funding agencies that supported the event, FAPESP, CAPES and CNPq, as well as the sponsors and exhibitors.

We would also like to thank ABPol, its board of directors and collaborators (Mr. Marcelo P. Gomes and Mrs. Layane Souza) for all their support in organizing the event.

Finally, we would like to thank all the participants of the 17th CBPol who contributed significantly to the success of the conference.

We look forward to seeing you at the 18th CBPol! Sérgio Henrique Pezzin – UDESC (Chair) Palova Santos Balzer – Univille (Vice-chair) Daniela Becker – UDESC (Scientific Coordinator)

Figure 13. Images of the Poster Evaluation Committee, coordinated by Profa. Juliana Kloss (UTFPR).

Polímeros, 33(4), 2  023

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VALMET LAUNCHES POLYMER CONCENTRATION MEASUREMENT FOR MUNICIPAL AND INDUSTRIAL WASTEWATER Valmet introduces the new Valmet Polymer Concentration Measurement (Valmet PCM), which is the first advanced optical inline polymer measurement for municipal and industrial wastewater treatment, as well as pulp and paper processes. Real-time, continuous polymer concentration data creates new opportunities for process optimization, such as more accurate polymer dosage, savings in polymer usage, faster reaction to process disturbances, among others.

Knowing the actual polymer levels allows facilities to significantly reduce polymer consumption through accurate preparation and dosing. Steady polymer concentration in turn improves flocculation, clarification, dewatering and other key processes. Better performance saves energy and lowers sludge transport and incineration needs, furthering the positive environmental and social impacts of efficient wastewater treatment. In paper and board processes, chemicals, typically polymers, are added to improve retention of fine particles and fillers during web formation. Accurate information about polymer concentration helps optimize wet end retention and increase process efficiency.

Valmet PCM leverages decades of experience in Valmet’s optical measurement know-how in board and paper processes. The optical measurement technology in the Valmet PCM brings industrial-grade quality and reliability to wastewater treatment. Despite a compact probe design, the optics maximize measurement volume. With more optical channels to collect scattered and reflected light, the probe delivers six times more information compared to conventional solutions improving the performance.

To counter probe contamination common in wastewater applications, Valmet developed a new automatic flushing system to keep the Valmet PCM probe clean and measurements stable. The integrated sensor probe flushing unit also includes support for a manual lab sampling valve.

Source: Impeller Net – impeller.net

The World’s First Bio-Polyethylene Pipeline French utility network operator GRDF and petrochemicals giant INEOS have come together to announce what they deem to be a world first – a gas pipeline made from bio-based high-density polyethylene (HDPE) material supplied by INEOS’ European Olefins & Polymers division.

The new pipeline – being installed by GRDF in Clermont Auvergne Métropole, in the French city of Clermont-Ferrand – was made using only low carbon footprint INEOS polymer. The move is part of a GRDF program to “green up” pipelines in parts of France with a “commitment to reducing their carbon footprint.”

Marking a small but sure start with intent, 1km of the pipeline will be laid across three sites in the Clermont Auvergne Métropole gas network. It’s made from wood processing residues from the paper industry, which are subsequently transformed into tall oil, a bio-naphtha.

The tall oil is then turned into bio-ethylene in INEOS Cologne and transported to the company’s polymer plant in Lillo, Belgium, where it is used to manufacture bio-based HDPE. The end result is a polymer with a significantly lower carbon footprint than conventional fossil-based polymers. Both INEOS and GRDF are keen to point out the product has been recognized as such by the International Sustainability and Carbon Certification (or ISCC), an independent, third-party organization.

The overall idea is to replace the use of fossil fuelderived feedstocks to produce the new material, while maintaining the same technical characteristics and standards of safety as conventional polymers. Describing it as a “game-changing innovation”, INEOS says its bio-polymer is all that and more, and “also creates the potential for the innovation to be repeated for other gas and water pipelines.” GRDF is using the “bio-based polymer pipeline to move bio-methane” upping the decarbonization drive in Europe in general and France in particular, according to Alexandre Pierru, Innovation Project Manager at GRDF. For INEOS’s part, Rob Ingram, its Olefins & Polymers North CEO, notes: “Our company is at the cutting edge of sustainability and driving forward the economy of the future. I’m proud of our team who have developed this bio-based HDPE and I’m delighted that it is being used in this exciting world first.”

Source: Forbes – forbes.com

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March Polymers 2024 International Conference Date: March 6-8, 2024 Location: Seville, Spain Website: www.setcor.org/conferences/polymers-2024 Europeam Polyamide Conference 2024 Date: March 13-14, 2024 Location: Frankfurt, Germany Website: www.woodmac.com/events/euro-polyamide-conference/ 9th International Conference on Fracture of Polymers, Composites and Adhesives Date: March 24-27, 2024 Location: Eurotel Victoria, Les Diablerets, Switzerland Website: www.elsevier.com/events/conferences/esistc4conference

April Bioplastics Brazil Date: April 24-25, 2024 Location: São Paulo, São Paulo, Brazil Website: www.bioplasticsbrazil.com/?lang=en

May Polymer Sourcing and Distribution Date: May 14-16, 2024 Location: Brussels, Belgium Website: www.ami-events.com/event/a555bb4d-c26b-4729-80fe05c535294593/summary?RefId=Website_AMI Fire and Polymers Date: May 12-15, 2024 Location: New Orleans, Louisiana, United States of America Website: polyacs.net/24fipo International Symposium on Polymeric Materials (ISPM) 2024 Date: May 14-16, 2024 Location: Kangar, Perlis, Malaysia (hybrid) Website: ispm2024.wixsite.com/unimap Polymers in Flooring Date: May 15-16, 2024 Location: Hamburg, Germany Website: www.ami-events.com/event/4c1e4b8b-4e49-4c29-b2c0db78fce7a924/summary?RefId=Website_AMI 39th International Conference of the Polymer Processing Society - PPS-39 Date: May 19-23, 2024 Location: Cartagena de Indias, Colombia Website: pps39.uniandes.edu.co/ POLY-CHAR 2024 — Polymers for our future Date: May 27-31, 2024 Location: Madrid, Spain Website: congresosalcala.fgua.es/poly-char2024/ 8th PLA World Congress Date: May 28-29, 2024

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June Polymers for sustainable future 2024 Date: June 24-28, 2024 Location: Prague, Czech Republic Website: imc.cas.cz/sympo/85pmm/ MACRO2024 — 50th World Polymer Congress Date: June 30- July 4, 2024 Location: Coventry, United Kingdom Website: iupac.org/event/50th-world-polymer-congressmacro2024/

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July PoWER Conference – Polymer Women Empowerment & Research Date: July 11-12, 2024 Location: Northwestern University Evanston, Illinois, United States of America Website: polymerwomenempowermentresearch.com/ Polymer Engineering & Science International 2024 Date: July 21-25, 2024 Location: Tokyo, Japan Website: www.pesi.tw/

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Polymer Markets Outlook Date: September 10-11, 2024 Location: Brussels, Belgium Website: go.ami.international/polymer-markets-outlook/ Plastics Extrusion World Expo Europe Date: September 11-12, 2024 Location: Brussels, Belgium Website: eu.extrusion-expo.com/home Advances in Polyolefins Date: September 29 – October 2, 2024 Location: Rohnert Park, California, United States of America Website: www.polyacs.net/24apo

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November Plastics Extrusion World Expo North America Date: November 13-14, 2024 Location: Cleveland, Ohio, United States of America Website: na.extrusion-expo.com/

December Polymer Engineering for Energy Date: December 3-4, 2024 Location: London, United Kingdom Website: www.ami-events.com/event/535774b9-c2a2-432d-be1fb7864beed551/summary?RefId=Website_AMI Polymers in Hydrogen and CCUS Infrastructure Date: December 5-6, 2024 Location: London, United Kingdom Website: www.ami-events.com/event/a90b3d2c-b31f-4ffa-91a80dd7dddca53b/summary?RefId=Website_AMI

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Polímeros, 33(4), 2023

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20220075

Conductive Amazon açaí/polyaniline composite fiber: fabrication and properties Jefter Victor Gonçalves1 , Jefferson Suela1 , Marcus Vinícius Duarte Silva1 , Rodrigo Fernando Bianchi2  and Cleidinéia Cavalcante da Costa1,2*  Departamento de Física, Instituto Federal de Minas Gerais, Congonhas, MG, Brasil Laboratório de Polímeros e de Propriedades Eletrônicas de Materiais, Departamento de Física, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brasil 1

2

*cleidineiastm@gmail.com

Abstract This paper investigates the properties of the polyaniline (PANI) on açaí vegetable fiber (AVF), hereafter referred to as PANI-COATED:AVF. Scanning electron and atomic force microscopy showed that the incorporation of PANI produced a linear surface, while optical microscopy images showed that the semiconductor layer was flawed. The complex impedance measurements performed at room temperature indicated that the electrical properties of PANI were fully transferred to the PANI-COATED:AVF and that the Cole-Cole approach dominated over a frequency range from 1 Hz to 100 kHz. Thermogravimetric analysis revealed a thermal stability range of 0° to 300°C. Finally, the combination of PANI with AVF was a successful due to the ease of processing and obtaining semiconductor filaments with wide ranges of thermal and electrical stability. This article is a complement to another recently published [doi. org/10.1002/pc.27068].

Keywords: natural polymer, semiconducting polymer, environmental conservation.

How to cite: Gonçalves, J. V., Suela, J., Silva, M. V. D., Bianchi, R. F., & Costa, C. C. (2023). Conductive Amazon açaí/polyaniline composite fiber: fabrication and properties. Polímeros: Ciência e Tecnologia, 33(4), e20230037. https:// doi.org/10.1590/0104-1428.20220075

1. Introduction The largest natural reserves of açaí palm (Euterpe oleracea Mart.) can be found in the state of Para, Brazil[1-4]. The harvesting of the fruit of this species native to Amazonia contributes to the livelihood of local families[2]. The fruit of the açaí palm, which is generally discarded incorrectly in nature[5], consists of seeds covered by lignocellulosic vegetable fibers (AVF)[6]. These AVF are renewable resources, biodegradable, low-cost[7], and have multi-functional and environmentally friendly applications[8]. For example, AVF can be used as pH sensors in the food industry[9], and mechanical reinforcement elements of polymeric matrices[5,10,11]. Furthermore, AVF can be added to the polyaniline (PANI) in situ chemical synthesis route to expand on its potential biotechnological applications[8,12-14] and obtain AVF coated with protonated PANI[15,16] (PANI-COATED:AVF) to be used as structural elements of electronic devices[13,17,18].

The goal of this paper is to describe in detail the method for producing PANI-COATED:AVF and analyze the morphological, thermal, and electrical properties provided by the semiconductor coating. This would provide a novel alternative source of income for the needy population by promoting environmental sustainability.

Polímeros, 33(4), e20230037, 2023

2. Materials and Methods 2.1 Preparation of PANI-COATED:AVF Figure 1 shows images of the preparation of açaí vegetable fibers (AVF) before acquiring the PANI layer. The AVF were obtained in the Açaizal community, 32 kilometers from the Santarém-Curuá-Una highway, in Brazil, from an Amazonian palm (Euterpe oleraceae Mart.)[19] (Figure 1a). Its fruit is the açaí (Figure 1b) which becomes a waste product after pulping (Figure 1c). In this situation, the AVF were separated from the seeds (Figure 1d), sifted in a 32 mesh sieve (Figure 1e), and those with diameters of 0.3 ± 0.2 mm and length of 3.0 ± 1.0 mm were selected (Figure 1f).

In this study, the PANI was synthesized through the direct oxidation of aniline by chemical oxidants, based on the PANI synthesis procedure[15,16]. The process for the fabrication of the PANI under AVF, hereafter referred to as PANI-COATED:AVF. Following the PANI synthesis, 0.6 g of AVF were mixed with 300 mL of hydrochloric acid (HCl) 1 M and left at room temperature (24 ºC). The next day, 20 mL of distilled aniline was diluted in the mixture. In a second beaker, 11.52 g ammonium persulfate ((NH4)2S2O8) was added to 200 mL HCl (1 M). Both solutions were placed

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Gonçalves, J. V., Suela, J., Silva, M. V. D., Bianchi, R. F., & Costa, C. C.

Figure 1. Preparation of acai vegetable fibers (AVF). (a) Amazonian palm; (b) açaí fruit; (c) açaí waste after depulping; (d) AVF; (e) AVF sieving; (f) AVF with a length of 3.0 ± 1.0 mm.

into a freezer and removed when at a temperature of around 0°C. The solutions were slowly combined in a 1000 mL beaker, insulated with aluminum, and mixed together through stirring for 2 hours at 24 °C. The PANI solution in the form of protonated emerald salts was washed with acetone several times and finally cleaned with a filter paper, and a polymeric bulk was obtained. After about 48 hours in a desiccator, the PANI-COATED:AVF was separated from the PANI powder by sieving.

2.2 Experimental characterization The surface morphologies of the AVF and PANICOATED:AVF were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), and optical microscopy (OM). The SEM images were obtained with a Tescan Vega LM3 microscope. The AFM images were acquired using a Ntegra Prima (NT-MDT) microscope operating in intermittent contact mode with regular Si cantilevers (k ~10 N/m, f0 ~240 kHz). The OM images were taken with a ZEISS Stemi 2000-C microscope.

The polymers AVF, PANI, and PANI-COATED:AVF were thermally decomposed by thermogravimetric analysis (TGA). The thermal behavior was monitored on a TG instrument SDT 2960 at 10°C/min from room temperature to 700°C under a N2 flow.

For electrical characterization, the polymers (AVF, PANI, and PANI-COATED:AVF) were pressed to obtain pellets with thicknesses of 1.0 ± 0.2 mm using a stainless steel apparatus coupled to a hydraulic model SKAY. Then, the pellets were kept between copper discs with circular openings (43.02 ± 2.32 mm2) and gold-sputtered in a sputter coater (Balzers SCD 050) for 200 seconds. The complex 2/6

impedance measurements, Z*(f) = Z’(f) – iZ”(f), were carried out using a 1260 Solartron frequency response analyzer in the 1 Hz to 105 Hz frequency range, maintaining the voltage amplitude at 1.5 V while experiments took place at room temperature.

3. Results and Discussions Figure 2 shows the SEM images of AVF and PANICOATED:AVF. The micrographs confirm that the surfaces of the AVF (Figure 2a) were rougher than those of the PANI-COATED:AVF (Figure 2b) which were smoother.

The PANI layer covered the rough surface and parenchymal cells of the AVF[20].

The AFM images (Figure 3) complement the results presented in Figure 2 by providing greater detail with threedimensional profiles which show the surface topography of the AVF (Figure 3a) as being more irregular than the surface of the PANI-COATED:AVF (Figure 3b). Furthermore, the surface topographic analysis provided a medium roughness value of 157 nm for the AVF (Figure 3a) and 71 nm for the PANI-COATED:AVF (Figure 3b). Therefore, the PANI layer significantly removed roughness in the surface of the AVF as observed by SEM (Figure 2) and AFM (Figure 3).

The smoother fiber surface would lead to an improved resistance to contact with electrodes[21].

Figure 4 shows optical microscopy images of the surfaces of AVF and of PANI-COATED:AVF. The images of AVF show a homogeneous and continuous surface (Figure 4a) while the PANI-COATED:AVF exhibits a heterogeneous surface with failures in polymeric coating (Figure 4b).

In contrast, Souza et al.[14] obtained a continuous coverage of Polímeros, 33(4), e20230037, 2023

Conductive Amazon açaí/polyaniline composite fiber: fabrication and properties

Figure 2. Scanning electron microscopy (SEM) images of (a) AVF and (b) PANI-COATED:AVF.

Figure 4. Optical microscopy (OM) images of (a) AVF and (b) PANI-COATED:AVF.

Figure 3. Atomic force microscopy (AFM) images of (a) AVF and (b) PANI-COATED:AVF.

PANI on VF, likely because the acidic solution in which the fibers were contained was magnetically stirred for 24 hours before the synthesis of PANI, allowing better incorporation of the acidic solution into the fibers. In this work, however, the fibers remained in the catalyst solution for 24 hours at a temperature of ≈0ºC. Indeed, the fibers filled with a catalyst solution would allow a more efficient polymerization of the surface, and the protonation could be characterized by the addition of Cl− to N+ or to other atoms[22].

Polímeros, 33(4), e20230037, 2023

Figure 5 shows the TGA curves of the AVF, PANI, and PANI-COATED:AVF samples from room temperature to 700°C. Regarding the thermal degradation of AVF from 0ºC to 100ºC, about 10% of the mass was lost which could be attributed to water loss[5,14], the material then became thermally stable between 100ºC to 300ºC. From 300ºC to 400ºC, the mass loss was about 60% due to the thermal degradation characteristics of the AVF[20], caused by the decomposition of hemicellulose and β−(1−4) glycosidic linkages[23]. Finally, above 400ºC, the mass loss was about 10% due to the decomposition of lignin[5]. The thermogravimetric behavior of pure PANI showed a two-step mass loss. The first mass loss of around 10% from 0ºC to 100ºC represented water loss and the second mass loss of around 40% between 100ºC to 700°C was due to the degradation of dopant anions, removal of dopants, and decomposition of the PANI[24]. The TGA results of the PANI-COATED:AVF revealed that around 10% of water was released up to 100ºC. The combination of the PANI with the AVF provided an intermediate level of degradation to PANI-COATED:AVF due to the PANI surface layers[14]. A similar behavior of the thermogravimetry curves shown in Figure 5 has previously been observed[12].

Figure 6 displays the real, Z’(f), and imaginary, Z”(f), components of the complex impedance for AVF as a function of the frequency (f) in a log-log plot. The figure shows that Z’(f) and Z”(f) remained overlapping at low frequency, while around 10 Hz, the curves separated and decreased continuously with the frequency. This behavior is typical of dielectric materials, representing that prevails the capacitive domain[25].

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Figure 5. Thermogravimetric analysis (TGA) curves of samples AVF, PANI, and PANI-COATED:AVF.

Figure 7. Z’ and Z” vs. f of (a) PANI and (b) PANI-COATED:AVF. The inset image shows an Argand diagram of the Z’(f) vs. Z”(f) of (a) PANI and (b) PANI-COATED:AVF. The full lines represent the experimental fittings obtained from Equation 1.

Figure 6. Real, Z’(f), and imaginary, Z”(f), components of the complex impedance versus frequency (f) of AVF.

Figure 7 shows Z’(f) and Z”(f) vs. f obtained from PANI (Figure 7a) and PANI-COATED:AVF, along with Argand diagrams for each (Figure 7b). The full-line curves of Figure 7 were derived from experimental-theoretical fittings using the Cole-Cole phenomenological model[26] which satisfied the principle of equivalence of a Maxwell circuit[27] represented by the empirical formula: Z *= (ω )

R / [1 + (iω RC )α ]

(1)

In this equation, ω is the angular frequency obtained by ω = 2πf, R is the dc electrical resistance, C is the electrical capacitance, and α is a parameter of dielectric relaxation that can assume values between 0 and 1; this shows that the distribution of relaxation times was highly symmetric[28,29].

Both impedance spectra in Figure 7 exhibit a plateau at about 40 kΩ (called the dc electrical resistance or R = Z’(f → 0)) which extends up to around 20 kHz; beyond this frequency, known as the critical frequency fc[30], the Z”(f) shows a peak with a maximum height on the fc. Therefore, the analogous behaviors of Z’(f) and Z”(f) between PANI (Figure 7a) and PANI-COATED:AVF (Figure 7b) imply that 4/6

the PANI deposited on AVF acted as an efficient semiconductor coating[12,14]. The diagrams show the value of electrical resistance, through the diameter of the semicircles equal to 370 kΩ and 440 kΩ, respectively, to PANI (Figure 7a) and PANI-COATED:AVF (Figure 7b). Furthermore, the presence of a single semicircle indicates only one transport mechanism, as there is no interface effect[30].

The experimental-theoretical fitting using Equation 1 shows that α = (0.98 ± 0.01) and fc = (20 ± 0.1) kHz remained practically constant, while R = (405 ± 35) kΩ and C = (0.26 ± 0.02) nF varied only slightly but remained in the same order of magnitude.

4. Conclusions In this paper, SEM and AFM images showed that the surface smoothness of fibers increased after PANI synthesis; failures in the polymeric coating of PANI were shown by OM. However, the Z’(f) and Z”(f) indicated that these failures did not interfere with electrical conductivity, and demonstrated that the electrical properties attributed to AVF by PANI were not limited to the dc regime (f → 0).

Furthermore, the use of the Cole-Cole model demonstrated that the samples presented a symmetric arc in a complex plane. The thermal results revealed that the AVF and the Polímeros, 33(4), e20230037, 2023

Conductive Amazon açaí/polyaniline composite fiber: fabrication and properties PANI-COATED:AVF could be submitted to temperatures of up to around 200ºC and 300ºC, respectively, without severe degradation. Therefore, this research provides a stimulus for the investigation and fabrication of organic polymer-based devices capable of providing a high electrical performance while preserving the environment. Finally, compared to other VF, the efficient utilization of VFA can favor the fabrication of environmentally friendly polymer composites and generate employment and income for the riverside Amazon communities.

5. Author’s Contribution • Conceptualization – Rodrigo Fernando Bianchi; Cleidinéia Cavalcante da Costa.

• Data curation – Jefter Victor Gonçalves; Rodrigo Fernando Bianchi; Cleidinéia Cavalcante da Costa.

• Formal analysis – Jefter Victor Gonçalves; Rodrigo Fernando Bianchi; Cleidinéia Cavalcante da Costa.

• Funding acquisition – Rodrigo Fernando Bianchi.

• Investigation – Jefter Victor Gonçalves; Jefferson Suela; Marcus Vinícius Duarte Silva; Cleidinéia Cavalcante da Costa.

• Methodology – Jefter Victor Gonçalves; Jefferson Suela; Marcus Vinícius Duarte Silva; Cleidinéia Cavalcante da Costa.

• Project administration – Jefter Victor Gonçalves; Rodrigo Fernando Bianchi; Cleidinéia Cavalcante da Costa.

• Resources – Rodrigo Fernando Bianchi; Jefferson Suela; Marcus Vinícius Duarte Silva; Cleidinéia Cavalcante da Costa.

• Software – Jefter Victor Gonçalves; Rodrigo Fernando Bianchi; Cleidinéia Cavalcante da Costa.

• Supervision – Rodrigo Fernando Bianchi; Cleidinéia Cavalcante da Costa.

• Validation – Rodrigo Fernando Bianchi; Cleidinéia Cavalcante da Costa.

• Visualization – Jefter Victor Gonçalves; Rodrigo Fernando Bianchi; Cleidinéia Cavalcante da Costa.

• Writing – original draft – Jefter Victor Gonçalves; Jefferson Suela; Marcus Vinícius Duarte Silva; Rodrigo Fernando Bianchi; Cleidinéia Cavalcante da Costa.

• Writing – review & editing – Jefter Victor Gonçalves; Rodrigo Fernando Bianchi; Cleidinéia Cavalcante da Costa.

6. Acknowledgements This work was supported by INEO, FAPEMIG (APQ03165-17), CNPq (308185/2016-1) and CAPES (001).

7. References 1. Cavalcante, P. B. (1991). Frutas comestíveis da Amazônia.

Belém: CNPq/Museu Paraense Emílio Goeldi.

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2. Nogueira, O. L., Figueirêdo, F. J. C., & Müller, A. A. (Eds.).

(2005). Sistema de produção – açaí. Belém: Embrapa Amazônia Oriental.

3. Muñiz-Miret, N., Vamos, R., Hiraoka, M., Montagnini, F., & Mendelsohn, R. O. (1996). The economic value of managing the acai palm (Euterpe oleracea mart.) in the floodplains of the Amazon estuary, Para, Brazil. Forest Ecology and Management, 87(1-3), 163-173. http://dx.doi.org/10.1016/ S0378-1127(96)03825-X. 4. Yamaguchi, K. K. L., Pereira, L. F. R., Lamarão, C. V., Lima, E. S., & Veiga-Junior, V. F. (2015). Amazon acai: chemistry and biological activities: a review. Food Chemistry, 179, 137-151. http:// dx.doi.org/10.1016/j.foodchem.2015.01.055. PMid:25722148.

5. Santos, N. S., Silva, M. R., & Alves, J. L. (2017). Reinforcement of a biopolymer matrix by lignocellulosic agro-waste. Procedia Engineering, 200, 422-427. http://dx.doi.org/10.1016/j. proeng.2017.07.059.

6. Bufalino, L., Guimarães, A. A., Silva, B. M. S., Souza, R. L. F., Melo, I. C. N. A., Oliveira, D. N. P. S., & Trugilho, P. F. (2018). Local variability of yield and physical properties of açaí waste and improvement of its energetic attributes by separation of lignocellulosic fibers and seeds. Journal of Renewable and Sustainable Energy, 10(5), 053102. http:// dx.doi.org/10.1063/1.5027232.

7. Poletto, M., Ornaghi, H. L. Jr., & Zattera, A. J. (2014). Native cellulose: structure, characterization and thermal properties.

Materials, 7(9), 6105-6119. http://dx.doi.org/10.3390/ma7096105.

PMid:28788179.

8. Razak, S. I. A., Rahman, W. A. W. A., Sharif, N. F. A., & Yahya, M. Y. (2012). Simultaneous numerical optimization of the mechanical and electrical properties of polyaniline coated kenaf fiber using response surface methodology: nanostructured polyaniline on natural fiber. Composite Interfaces, 19(7), 411424. http://dx.doi.org/10.1080/15685543.2012.757957.

9. Silva, C. K., Mastrantonio, D. J. S., Costa, J. A. V., & Morais, M. G. (2019). Innovative pH sensors developed from ultrafine fibers containing açaí (Euterpe oleracea). Food Chemistry, 294, 397-404. http://dx.doi.org/10.1016/j.foodchem.2019.05.059.

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11. Tavares, F. F. C., Almeida, M. D. C., Silva, J. A. P., Araújo, L. L., Cardozo, N. S. M., & Santana, R. M. C. (2020). Thermal treatment of açaí (Euterpe oleracea) fiber for composite reinforcement. Polímeros: Ciência e Tecnologia, 30(1), e2020003. http://dx.doi.org/10.1590/0104-1428.09819.

12. Araujo, J. R., Adamo, C. B., & De Paoli, M.-A. (2011).

Conductive composites of polyamide-6 with polyaniline coated vegetal fiber. Chemical Engineering Journal, 174(1), 425-431. http://dx.doi.org/10.1016/j.cej.2011.08.050.

13. Souza, F. G. Jr., Paiva, L. O., Michel, R. C., & Oliveira, G. E. (2011). Modificação da fibra de coco com polianilina e o seu uso como sensor de pressão. Polímeros: Ciência e Tecnologia, 21(1), 39-46. http://dx.doi.org/10.1590/S010414282011005000016.

14. Souza, F. G. Jr., Picciani, P. H. S., Rocha, E. V., & Oliveira, G. E. (2010). Estudo das propriedades mecânicas e elétricas de fibras de curauá modificada com polianilina. Polímeros: Ciência e Tecnologia, 20(5), 377-382. http://dx.doi.org/10.1590/ S0104-14282010005000058.

15. Macdiarmid, A. G., Chiang, J. C., Richter, A. F., & Epstein, A. J. (1987). Polyaniline: a new concept in conducting polymers. Synthetic Metals, 18(1-3), 285-290. http://dx.doi. org/10.1016/0379-6779(87)90893-9.

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Gonçalves, J. V., Suela, J., Silva, M. V. D., Bianchi, R. F., & Costa, C. C. 16. Costa, C. C., Mapa, L. M., Kelmer, A. C., Ferreira, S. O., & Bianchi, R. F. (2022). New insight into natural fiber-reinforced polymer composites as pressure sensors: experiment, theory, and application. Polymer Composites, 43(12), 8869-8876. http://dx.doi.org/10.1002/pc.27068.

17. Costa, C. C. (2019). Efeitos da pressão mecânica nas propriedades elétricas ac em compósitos elastoméricos a base de fibras naturais recobertas com polímero condutor (Doctoral thesis).

Universidade Federal de Viçosa, Viçosa.

18. Cantalice, J. D. A., Mazzini, E. G. Jr., Freitas, J. D., Silva, R. C., Faez, R., Costa, L. M. M., & Ribeiro, A. S. (2021). Polyanilinebased electrospun polycaprolactone nanofibers: preparation and characterization. Polímeros: Ciência e Tecnologia, 31(1), e2021002. http://dx.doi.org/10.1590/0104-1428.09320.

19. Schauss, A. G., Wu, X., Prior, R. L., Ou, B., Patel, D., Huang, D., & Kababick, J. P. (2006). Phytochemical and nutrient composition of the freeze-dried Amazonian palm berry, Euterpe oleraceae Mart. (Acai). Journal of Agricultural and Food Chemistry, 54(22), 8598-8603. http://dx.doi.org/10.1021/ jf060976g. PMid:17061839.

20. Martins, M. A., Pessoa, J. D. C., Gonçalves, P. S., Souza, F. I., & Mattoso, L. H. C. (2008). Thermal and mechanical properties of the açaí fiber/natural rubber composites. Journal of Materials Science, 43(19), 6531-6538. http://dx.doi. org/10.1007/s10853-008-2842-4.

21. Kumari, A., Singh, I., & Dixit, S. K. (2014). Effect of annealing on graphene incorporated poly-(3-hexylthiophene): CuInS2 photovoltaic device. AIP Conference Proceedings, 1620(1), 35-40. http://dx.doi.org/10.1063/1.4898216.

22. Epstein, A. J., Ginder, J. M., Zuo, F., Bigelow, R. W., Woo, H.-S., Tanner, D. B., Richter, A. F., Huang, W.-S., & MacDiarmid, A. G. (1987). Insulator-to-metal transition in polyaniline. Synthetic Metals, 18(1-3), 303-309. http://dx.doi.org/10.1016/03796779(87)90896-4.

23. Zhou, W., Zhu, D., Langdon, A., Li, L., Liao, S., & Tan, L. (2009). The structure characterization of cellulose xanthogenate derived from the straw of Eichhornia crassipes. Bioresource

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Technology, 100(21), 5366-5369. http://dx.doi.org/10.1016/j. biortech.2009.05.066. PMid:19540749.

24. Mostafaei, A., & Zolriasatein, A. (2012). Synthesis and characterization of conducting polyaniline nanocomposites containing ZnO nanorods. Progress in Natural Science: Materials International, 22(4), 273-280. http://dx.doi.org/10.1016/j. pnsc.2012.07.002.

25. Santos, M. C., Bianchi, A. G. C., Ushizima, D. M., Pavinatto, F. J., & Bianchi, R. F. (2017). Ammonia gas sensor based on the frequency-dependent impedance characteristics of ultrathin polyaniline films. Sensors and Actuators A: Physical, 253, 156-164. http://dx.doi.org/10.1016/j.sna.2016.08.005.

26. Cole, K. S., & Cole, R. H. (1941). Dispersion and absorption in dielectrics I. Alternating current characteristics. The Journal of Chemical Physics, 9(4), 341-351. http://dx.doi. org/10.1063/1.1750906.

27. Macdonald, J. R. (1999). Dispersed electrical-relaxation response: discrimination between conductive and dielectric relaxation processes. Brazilian Journal of Physics, 29(2), 332346. http://dx.doi.org/10.1590/S0103-97331999000200014.

28. Macdonald, J. R. (1992). Impedance spectroscopy. Annals of Biomedical Engineering, 20(3), 289-305. http://dx.doi. org/10.1007/BF02368532. PMid:1443825.

29. Barsoukov, E., & Macdonald, J. R. (Eds.). (2005). Impedance spectroscopy theory, experiment, and applications. Hoboken: John Wiley & Sons, Inc. http://dx.doi.org/10.1002/0471716243.

30. Gonçalves, G., Pimentel, A., Fortunato, E., Martins, R., Queiroz, E. L., Bianchi, R. F., & Faria, R. M. (2006). UV and ozone influence on the conductivity of ZnO thin films. Journal of Non-Crystalline Solids, 352(9-20), 1444-1447. http://dx.doi. org/10.1016/j.jnoncrysol.2006.02.021.

Received: Jul. 18, 2022 Revised: Jul. 01, 2023 Accepted: Jul. 11, 2023

Polímeros, 33(4), e20230037, 2023

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20220099

Cold plasma copolymer with antimicrobial activity deposited on three different substrates Erick Osvaldo Martínez Ruiz1* , Xi Rao2 , Abril Fonseca García1 , Carlos Gallardo Vega1 , Carmen Natividad Alvarado Canche1 , José Abraham Gonzáles López1 , Antonio Serguei Ledezma Pérez1 , Miriam Desiree Davila Medina3 , Claudia Gabriela Cuellar Gaona3 , Rosa Idalia Narro Céspedes3 , Gustavo Soria Arguello1  and María Guadalupe Neira Velázquez1*  Centro de Investigación en Química Aplicada, Saltillo, Coahuila, México School of Materials and Energy, Southwest University of China, Chongqing, China 3 Facultad de Ciencias Químicas, Universidad autónoma de Coahuila, Saltillo, Coahuila de Zaragoza, México 1

2

*erickomr87@hotmail.com; *guadalupe.neira@ciqa.edu.mx

Abstract A good strategy to prevent early deposition of bacteria that can form biofilms is the application of antimicrobial coatings to existing surfaces, however this field has been little explored and coatings are often non uniform in thickness. A homogeneous film of R-Carvone-Octadiene (ppCop) was deposited on different substrates (coverslip, minced coverslip and fabric) by cold plasma copolymerization to study the influence of the substrate on antimicrobial activity and show clues about the influence of octadiene on copolymerization. The ppCop showed better antimicrobial activity results on the substrate with higher effective contact area, highlighting the influence of this variable on antimicrobial activity.

The ppCop deposited on minced coverslip showed an inhibition of E. coli and S. aureus bacteria by 48.69 ±0.08% and 49.31 ±0.58% respectively, with an average roughness of 14.1±0.02 nm and a static water contact angle of 79± 0.4°.

The ppCop showed no cytotoxicity to the human cell line.

Keywords: antimicrobial, biofilm, octadiene, plasma, R-Carvone.

How to cite: Ruiz, E. O. M., Rao, X., García, A. F., Vega, C. G., Canche, C. N. A., López, J. A. G., Pérez, A. S. L., Medina, M. D. D., Gaona, C. G. C., Céspedes, R. I. N., Arguello, G. S., & Velázquez, M. G. N. (2023). Cold plasma copolymer with antimicrobial activity deposited on three different substrates. Polímeros: Ciência e Tecnologia, 33(4), e20230038.

1. Introduction It is well-known that bacterial biofilms are a major problem in different areas[1], despite the research efforts made in this field, it still remains a high priority in research.

It has been found that up to 60% of infections treated are related to the formation of biofilms[2]. This problem is further aggravated by the emergence of bacteria with greater tolerance to biocides and antibiotics[3], in addition, in this state, the microorganisms are highly resistant to antimicrobial treatment and are tenaciously attached to the surface[4].

There are currently several innovative approaches focused on surface treatment to prevent this problem by improving the performance of existing antimicrobial surfaces, applying antimicrobial coatings, or modifying the surface architecture.

Among surface modifications, the functionalization technique with chemicals, has been one of the most studied[1]. Cationic polymers, small ligands and biomolecules are reported to have the most successful antimicrobial activity and efficacy[5-8].

Most of the bactericidal surface modifications could exhibit cytotoxic properties to human cells. The durability of the chemical functionalization as well as its performance are usually limited and bacteria tend to develop tolerance in the case of leaching and non-leaching agents[9]. Another approach is surface topographical modification. This field

Polímeros, 33(4), e20230038, 2023

has been little explored and the influence of the topographic characteristics of the surface on its antimicrobial activity is still not fully understood and therefore it is an interesting field to explore. A significant advance in this field is that, contrary to what was thought, there is now sufficient evidence to document that there are bacteria capable of colonizing surfaces with average surface roughness (Ra) of the order of only few nanometers[10]. One of the most widely used methods for the prevention of biofilms on surfaces is the application of antimicrobial coatings, that can be defined as the deposition of an antimicrobial material on a substrate[11].

A commonly used strategy to obtain these coatings is the adhesion of an antimicrobial agent to a polymeric matrix.

Examples that have been successfully reported include the use of Quaternary Ammonium Compounds (QACs) whose main antimicrobial activity is associated with their cation[12], nano-silver coatings have been widely used in medical devices, especially in catheters, however it is clear that silver ions and silver salts have potential cytotoxic properties for human cell lines[9]. Therefore, it would be appropriate to look for other alternatives that do not have this negative effect on humans and plasma treatment can be one of these alternatives. The concept of a diffusion layer to control the

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

Ruiz, E. O. M., Rao, X., García, A. F., Vega, C. G., Canche, C. N. A., López, J. A. G., Pérez, A. S. L., Medina, M. D. D., Gaona, C. G. C., Céspedes, R. I. N., Arguello, G. S., & Velázquez, M. G. N. release of antibiotic like ciprofloxacin from a ciprofloxacinloaded polyurethane by using n-butyl methacrylate plasma polymer has been studied[13]. Antimicrobial coatings are usually mechanically poor, non-uniform in thickness and in the case of coatings with release agents, the optimum concentration of the active ingredient decreases and with this also decreases its efficiency[11]. An alternative to obtain uniform antimicrobial coatings with acceptable mechanical properties is the use of cold plasma technology, which is used for the polymerization of organic precursors. Some monomers like trimethylsilane[14], 1,1,1 trichloroethane[15], R-carvone[16] and 1,8-cineole that is a natural monomer, were polymerized by plasma, and it was found that they have antibacterial properties[17]. One of the main advantages of the use of plasma polymerization is a great capacity to altering the surface chemistry without affecting the bulk properties of the material and with reproducible quality during manufacturing scale-up[18]. The main objective of the present work was the preparation of antibacterial coatings by means of plasma copolymerization of two organic precursors: essential oil known as R-carvone and octadiene. R-carvone essential oil (referred to in this work simply as carvone) is mainly extracted from spearmint plants and reported in the literature to possess antimicrobial properties[1,16,19-21].

These properties are mainly attributed to the presence of the monoterpene group present in its molecule[20]. This work highlights the influence of octadiene monomer in the study of the plasma “head-to-tail” copolymerization of R-carvone-octadiene monomer, under the hypothesis that by incorporating the -C8H16- group it acts as a “tail” to reduce the rigidity of the material and favor its roughness (modification of topographic characteristics). Since it has been reported that at higher values of roughness the hydrophobicity of the material is favored[22]. It is well-known that the hydrophobicity of a material is of great importance for the prevention of early deposition of bacteria that can form biofilms, thus conferring antimicrobial properties[23].

In this study, it was investigated, the antimicrobial activity of a cold plasma copolymer (ppCop) on three different substrates (coverslip, minced coverslip and fabric) under the Japanese Industrial Standard Z280126 protocol, exposing the importance of the surface area value of the substrate in the antimicrobial activity, whose influence has been little studied[11].

2. Materials and Methods 2.1. Cold plasma reactor for copolymerization reaction A cylindrical glass container with stainless-steel caps was used as a plasma reactor as shown in Figure 1.

The plasma reactor, by means of its stainless-steel caps, was connected to a 13.56 MHz radio frequency (RF) generator coupled with an impedance machine (model AT-6 Automatic Matching Network). The reactor was operated under vacuum conditions by the use of a vacuum pump (Maxima C Plus Fisher Scientific™). A single channel ACS 2000 adixen by Alcatel Vacuum Technology controller-indicator was used to read and monitor the vacuum pressure in the reactor. Prior to use of substrates for plasma copolymerization, such as glass coverslips, these were ultrasonically cleaned in acetone and milli-Q water, then dried, treated by air plasma for 1 min at 2/10

Figure 1. Experimental plasma reactor (a)) and plasma reactor scheme (b)).

20 W and 45 Pa to remove residual contaminants. Plasma copolymerization of carvone (98%, Sigma Aldrich product no.: 124931) and octadiene (98%, Sigma Aldrich product no.: O2501) was carried out on the 1 cm2 substrates. The pressure data were used to obtain the corresponding flow rate (Q) by the use of the following Equation 1 (reported in standard cubic centimeters per minute, sccm)[23]: V  dp   Q=  16172  T  dt  

(1)

Where T=temperature (295 K), p = pressure (Pa), t = time (s) and V = volume of plasma reactor (1.65 L). The plasma reactor chamber was evacuated to reach a pressure of 38 Pa. Then the precursors (carvone oil and octadiene) were incorporated into the reactor at a flow rate of 0.9 and 0.5 sccm respectively. The plasma copolymerization was carried out at 20 W for 60 min of deposition. After plasma disruption the precursors continued to flow into the plasma chamber for another 2 min to quench any residual radicals on the ppCop.

2.2. Characterization techniques All the experiments were repeated at least three times using three random samples deposited from three different cycles of plasma polymerization. The morphological and chemical techniques used for the study of the plasma polymerized R-carvone-octadiene (ppCop) include scanning electron microscopy (SEM), atomic force microscope (AFM), water contact angle (WCA), attenuated total reflection-Fourier transform infra-red (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). In the application of these methods, a coverslip was employed, onto which ppCop was deposited.

The thermal stability of ppCop was evaluated by thermal gravimetric analysis (TGA). The cytotoxicity test on ppCop was assessed through 3- (4,5-dimethylthiazol-2-yl) -2,5-diphenyltetrazole bromide (MTT) assay using the primary human fibroblast cell line known as CCD-1064SK. Polímeros, 33(4), e20230038, 2023

Cold plasma copolymer with antimicrobial activity deposited on three different substrates 2.2.1. Roughness and thickness

2.4. Thermal gravimetric analysis (TGA)

The thickness of ppCop was measured with a surface profiler KLA Tencor (model: D-600) to determine the step height value of the sample. The step height was created by making a cross-section of the sample with a scalpel.

The surface roughness of the ppCop was measured by an atomic force microscope (model: NEXT AFM NT-MDT).

The AFM tip had a resonant frequency of 390 kHz and a constant force of 37 N/m. To measure average roughness (Ra) and root mean square roughness (Rq), scans were performed in areas of 5000 nm ×5000 nm on three different samples.

Thermogravimetric analysis was performed using a TGA-Q500-V6.7 equipment, using open pans under dry nitrogen atmosphere (nitrogen flow of 100 mL/min), and at 600 °C oxygen was injected (50 mL/min) into the chamber to enhance the oxidation process. Measurements were performed by increasing the temperature from room temperature up to 600 °C at 10 °C/min and from 600 up to 700 at 20 °C/min. To collect the sample, a scalpel was utilized to carefully detach the film from the coverslip.

The film was then transferred and stored in a petri dish to facilitate subsequent TGA analysis. The mass-temperature derivative (MTD) was acquired, enabling a more detailed examination of the distinct stages involved in the decomposition processes. It is noteworthy to mention that the transition to an oxygen atmosphere was implemented to ensure the absence of non-organic impurities in the studied sample, such as potential remnants of coverslip that could be present due to the method of sample collection.

2.2.2. Static water contact angle (WCA) The static water contact angle (WCA) of the coverslip deposited with ppCop was measured by the sessile drop technique. A ramé-hart equipment (model 100-00) was used to capture the WCA image and measured by the software Image J. To obtain the images, 2 μL of milli-Q water were manually dropped onto the sample for image captures. The commonly accepted range of WCA values for classification between hydrophobic and hydrophilic materials is 90°. The static WCA measurements were repeated on three different samples prepared by three separate cycles of plasma deposition.

2.2.3. Attenuated total reflection-Fourier transform infra-red (ATR-FTIR) A Thermo Scientific ATR-FTIR system (Nicolet IS 50 ATR) was used to obtain the ppCop, octadiene and carvone spectrum. Once the ppCop was deposited on the coverslip and removed with a scalpel, this sample was used for the FTIR measurement. To obtain the spectra, 100 scans were performed at a resolution of 4 cm-1.

2.2.4. X-ray photoelectron spectroscopy (XPS) A ThermoFisher Thermo Scientific K-Alpha+ equipped with a monochromatic Al-Kα source (hv=1486.6 eV) operating at 25 W, 15 kV was used to obtain the XPS spectra corresponding to ppCop. Scanning spectra were collected at a step energy of 150 eV with a resolution of 1 eV, while high-resolution spectra were measured for C1s and N1s at a step energy of 50 eV with a resolution of 0.1 eV. The atomic concentration of nitrogen, oxygen and carbon were calculated thrice from the probe spectra with CasaXPS software. The high-resolution spectra were fitted by components with Origin 2019 software (version 2019 b).

The C1s spectrum was subtracted with Shirley background and fitted by components with a half-width maximum (FWHM) of 1.35 eV, and a Gaussian component. Spectrum was also shifted according to the C-C and C-H components of the C1s peak at 284.48 eV. Relative sensitivity factors were provided by CasaXPS software.

2.3. Scanning electron microscopy (SEM) Images of the different samples of fabric and coverslip deposited by ppCop have been collected with Scanning Electron Microscopy (SEM), JEOL 6000 apparatus. The samples with ppCop were previously coated with a 10 nm layer of gold by plasma sputtering system and mounted on aluminum stubs.

Polímeros, 33(4), e20230038, 2023

2.5. Antimicrobial activity of copolymer The antimicrobial activity of ppCop was evaluated based on the Japanese Industrial Standard, Z280126[24].

The evaluation was conducted using two clinically important microorganisms: Escherichia coli ATCC-25922 and Staphylococcus aureus ATCC-29213. To perform the test, fabrics and coverslips coated with ppCop (each having a circular shape with a diameter of 1.75 cm) were prepared under aseptic conditions. These samples were then inoculated with 4 mL of a suspension containing the microorganisms in trypticase soy broth. The concentration of the suspension was equivalent to 50,000 colony-forming units per mL (CFU mL−1). Additionally, a third set of coverslips minced (approximately 0.1 g, equivalent to a coverslip of 1.75 of diameter) coated with ppCop was treated in the same manner as the previous samples. Afterward, the samples were incubated in a controlled environment with a temperature of 37 °C and humidity maintained at 90% for a duration of 24 hr. Following the incubation period, one part of the inoculum (1 x 106 CFU mL-1) was combined with nine parts of mQ water to prepare an inoculum concentration of 1 x 105 CFU mL-1. This mixture was further diluted to achieve an inoculum concentration of 1 x 102 CFU mL-1.

Each dilution was then added to a petri dish containing 20 mL of agar BD BIOXON (model BD210800). The petri dishes were left at a temperature of 37 °C for 24 hr. After this incubation period, the colony-forming units (CFUs) were counted with a microscope for each sample as well as the control. The methodology described above was carried out in triplicate for each treated sample, chosen from three different cycles of plasma treatment. Once the UFCs of each sample were determined, the antimicrobial activity (R) was calculated using the Equation 2. B  R = Log  0   Mt 

(2)

Where B0 is the quantity in CFU mL−1 of bacteria that survive in the presence of the blank (coverslip without ppCop) after 24 hours of incubation. Mt is the number of bacteria 3/10

Ruiz, E. O. M., Rao, X., García, A. F., Vega, C. G., Canche, C. N. A., López, J. A. G., Pérez, A. S. L., Medina, M. D. D., Gaona, C. G. C., Céspedes, R. I. N., Arguello, G. S., & Velázquez, M. G. N. that survive after 24 hr of incubation in the presence of the ppCop. Additionally, bacterial growth inhibition (GI) was determined by Equation 3.  B − Mt  GI =  0  *100  B0 

(3)

2.6. Hemolysis and In vitro cytotoxicity test: MTT assays The hemolysis tests were performed with freshly human blood collected from non-smoking volunteer donors.

The blood was collected in heparinized tubes and centrifuged at 3000 rpm for 4 min at 4 °C. The sediment obtained was washed three times with cold Alsever solution (AS) consisting of dextrose 0.116 M, sodium chloride 0.071 M, sodium citrate 0.027 M and citric acid 0.002 M. The supernatant was diluted at 1:99 with Alsever solution. Subsequently, 150 µL of this suspension was taken for experiments. This red blood cell (RBC) solution was used within 24 hours after collection. The samples were prepared at concentrations of 1, 2.5 and 5 mg mL-1. The tubes were gently mixed on a rotary shaker and incubated at 36.5 °C in a shaking water bath for 1 hour. Alsever solution and deionized water were used as negative and positive controls, respectively. Samples were centrifuged at 2500 rpm for 4 min and free hemoglobin in the supernatant was measured spectrophotometrically by UV at 415 nm (Sinergy HTX model). The percentage of hemolysis was measured using the following Equation 4:  A −A  cn  *100 %HE =  s  Acn − Acp   

(4)

Where %HE is the percentage of hemolysis, As is the absorbance of the sample, Acn is the absorbance of the negative control and Acp is the absorbance of the positive control. For cytotoxicity evaluation, the MTT test was performed on the ppCop film at 1 and 3 days in accordance with the ISO standard 10993[25], the well (polyethylene) without ppCop in which cells were cultured was used as a control. The cells used were the human fibroblast cell line CCD-1064SK.

3. Results and Discussions 3.1. Aging test Samples of the ppCop were immersed in mQ water and dimethyl sulfoxide (DMSO) for 24 hours as a material aging test. The results obtained are shown in Table 1. Considering the negligible reduction (0.5%) in ppCop thickness in dimethyl sulfoxide (DMSO) it is likely that the current deposition condition confers a high degree of cross-linking to ppCop to prevent its dissolution in DMSO[26]. On the other hand, the almost negligible reduction of ppCop thickness in mQ water, thus ppCop can be considered to be stable in water.

Based on the results of Figure 2, it is possible to observe the 2D and 3D AFM images of ppCop roughness, the ppCop shows an average roughness (Ra) of 14.1±0.02 nm and root mean square roughness (Rq) of 17.1±0.02 nm. The relatively high values of roughness are possibly due to the long plasma copolymerization time (1 hour) and the insertion of groups -C8H16- in the ppCop, which can act as a flexible tail that facilitates the rough structure of the material[22].

3.2. Static water contact angle (WCA) Plasma polymerizations were performed at the same ppCop operating conditions (1.4 sccm, 20 W and 60 min) for carvone (octadiene concentration = 0 v/v) and octadiene (carvone concentration = 0 v/v) monomers. Figure 3 shows the behavior of the WCA as a function of the octadiene concentration used for polymerization. Is shown a WCA value for ppCop (octadiene concentration =0.357 v/v) of 79± 0.4°. It is observed that the WCA value increases as the octadiene concentration increases, this can be explained by the chemical nature of the monomer, in whose molecular

Table 1. Thickness of ppCop as deposited and after immersed in mQ water and DMSO. ppCop as deposited 24 h mQ water immersed 24 h Dimethyl Sulfoxide (DMSO)

Thickness (nm) 857.2 ±29.5 855.3 ±33.4 852.6 ±27.3

Figure 2. 3D and 2D AFM image roughness morphology of ppCop, scan size: 5000 nm ×5000 nm.

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Cold plasma copolymer with antimicrobial activity deposited on three different substrates

Figure 3. WCA static water contact angle as a function of octadiene concentration in the polymer obtained by cold plasma polymerization.

structure there is no oxygen available to find OH- group in the plasma polymerization. The OH- group is the main responsible for hydrophilicity of surfaces[27]. The opposite behavior occurs if we observe the concentration of carvone, in whose molecule there is oxygen available for the eventual appearance of the OH- group on the surface of the plasma polymerization. The static WCA of the clean glass coverslip (positive control) was 21.6±0.6°. This behavior may be due to the silanol groups present on the coverslip[16].

Since hydrophobicity of a material is of great importance for the prevention of early deposition of bacteria that can form biofilms[28]. Similar results can be found in the literature for the WCA values of plasma polymerizations of carvone and octadiene[16]. However, a better antimicrobial activity is reported in the polymerization of carvone compared to that of octadiene, attributing the influence on the antimicrobial activity to the oxidizing groups in the polymeric film obtained from carvone.

3.3. Attenuated total reflection Fourier transform infrared (ATR-FTIR) The present technique identifies the functional groups on the surface of ppCop and provides clues regarding to its copolymerization route on the coverslip.

In Figure 4 it is possible to observe the ATR-FTIR spectra of ppCop, octadiene and carvone oil. The ppCop spectra showed broad bands with respect to its precursors which showed regular sharp bands, this is a characteristic of a highly crosslinked polymer[29]. In the system under investigation in this study, both carvone and octadiene exhibit terminal double bonds within their chemical structures, thereby possessing the potential for polymerization. Octadiene showcases the presence of two terminal double bonds, effectively yielding four reactive centers. Consequently, the resulting copolymer may display the phenomenon of cross-linking[30].

Highly cross-linked polymers like ppCop could reduce the intensity of the symmetric structure of moieties like CH3 at 1371 cm-1[29]. The considerable reduction of the =CH bond (990.28 and 908.80 cm-1) and stretch bonds (3079.33 cm-1) Polímeros, 33(4), e20230038, 2023

Figure 4. ATR-FTIR spectra of ppCop, octadiene and carvone.

Figure 5. Survey spectra for ppCop (pass energy of 150 eV with a resolution of 1 eV).

suggests that the copolymerization also is carried out by the =CH bond of octadiene. This suggests the insertion of long chain hydrocarbons such as -C8H16-, which could give flexibility to the polymer and increase its roughness as discussed previously in section 3.1.

However, the ring stretch, vibration and “breathing” (i.e., simultaneous stretch of all C=C bonds) of carvone oil at 1430.61, 893.70 and 802.20 cm−1 were missing from the IR spectra of the ppCop[30,31]. This absence suggested that the ring structure of carvone, as illustrated in Figure 4 is dissociated during their plasma copolymerization on the coverslip substrate[16].

3.4. X-ray photoelectron spectroscopy (XPS) In Figure 5 are presented the XPS atomic compositions and functional groups for ppCop film (upper 10 nm of its surface). Elements such as C (78.74%, 284.08 eV), N (8.78%, 399.08 eV) and O (12.48%, 532.08 eV) were identified.

The presence of N in the deposited film is probably caused by residual air nitrogen in the plasma reactor, which was ionized and participated in the copolymerization mechanism.

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Ruiz, E. O. M., Rao, X., García, A. F., Vega, C. G., Canche, C. N. A., López, J. A. G., Pérez, A. S. L., Medina, M. D. D., Gaona, C. G. C., Céspedes, R. I. N., Arguello, G. S., & Velázquez, M. G. N. Similar cases of nitrogen presence have been reported for plasma-treated polymeric substrates[16].

The percentages of the types of chemical bonds (C1s) studied in the procedure as are illustrated in Figure 6, were the following; C1 (C-H/C-C corresponding to 284.48 eV) 73.27%, C2 (C-O-C/C-N/C-OH at 286.05 eV) 16.61%, C3 (N-C = O, C = O at 287.55) 9.35% and C4 (O-C = O at 289.1 eV) 0.76%. The N/C and O/C ratios on the surface of the film were 0.12 and 0.16 respectively. The relative

abundance of N in the film could have an influence on the relative low hydrophobicity of the material by hydrogen bonding in an aqueous medium. In the literature it can be found that oxidizing groups, especially carbonyl, are responsible for the antibacterial activity of the plasma coating film. In the results obtained by XPS, it was found that the oxidant groups C3 and C4 correspond in total to 10.1% on the surface of the ppCop. Specifically, carbonyl and N-C = O have a presence of 9.35%.

3.5. Scanning electron microscope (SEM) Figure 7 shows the SEM images of ppCop on coverslips (a) and tissue (b), as well as the uncoated coverslip and tissue (c) and d) respectively). It is possible to observe a homogeneous rough deposit on both substrates, these images reinforce the evidence of the roughness of ppCop. It is appreciated that the plasma coating was homogeneously deposited on the two substrates. Similar morphology was found in the literature in plasma polymerized methyl acrylate coatings of comparable thickness and same elements present (C, O and H) as in ppCop. The appearance of folding/ agglomeration is possibly due to structural accommodations in the polymer formation during the plasma polymerization process, resulting in different mass percentages of C, O and H in the coating at different film thicknesses[32]. However, further studies are needed to confirm this.

Figure 6. Component-fitted C1s spectra for ppCop as deposited, C1 (C-H / C-C), C2 (C-O-C / C-N / C-OH), C3 (N-C = O, C = O) and C4 (O-C = O).

3.6. Thermal gravimetric analysis (TGA) As shown in Figure 8, it was possible to see the weight loss of the ppCop sample (initial weight of 3.135 mg) as a

Figure 7. SEM images of ppCop on coverslips (a) and tissue (b), as well as the uncoated coverslip and tissue (c) and d) respectively), scale bar of 5 μm.

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Polímeros, 33(4), e20230038, 2023

Cold plasma copolymer with antimicrobial activity deposited on three different substrates function of temperature (from room temperature, and up to 700 °C) and its associated MTD. The TGA curve for the ppCop polymer shows that the polymer begins to degrade from 100 ˚C, and this process ends around 475 °C. In the MTD curve, it can be seen that the polymer follows a two-stage decomposition kinetics, a shoulder is observed in the first stage around 250°C and a peak is also observed at a temperature of 375°C, indicating that the copolymer degrades in two stages, it is possible that each one of the two signals correspond to each of the monomers of the copolymer (ppCop), which was synthesized from two monomers (octadiene and carvone)[33]. In the thermogram, it can also be seen that around 475 ˚C, about 10% residue remains, which could be due to the presence of crosslinked polymer[34]. The sample maintains this percentage without significant change until oxygen is introduced at 600 °C, leading to its complete oxidation.

to the hydrophobicity of the material and the presence of oxidizing groups, such as carbonyl in the ppCop which correspond to 9.35% of the surface of ppCop according to the data obtained by XPS.

In Figure 9 it is possible to observe the CFUs in presence of ppCop on three different substrates (fabric, coverslip and minced coverslip) and the substrate without ppCop (control) after 24 hr of bacteria growth (S.aureus and E. coli). The results present inhibition in the growth of the CFU respect to the control. The most significant inhibition in the bacteria growth is reported in the ppCop deposited on the minced coverslip (48% for E. coli and 49% for S. aureus), followed by the ppCop deposited on the coverslip (16% for E. coli and 29% for S. aureus) and finally the fabric with only an inhibition of 3% and 6% for E. coli and S. aureus respectively. The inhibition in CFU could be mainly due

Antimicrobial activity (R) and bacterial growth inhibition (GI) of the ppCop deposited on three different substrates (fabric, coverslip and minced coverslip) it is shown in Table 2. The highest values in antimicrobial activity (R) are present in the ppCop deposited on minced coverslip with 0.29 ±0.007 for E. coli and 0.29±0.004 for S. aureus, followed by the ppCop deposited on coverslip with 0.079 ±0.004 for E. coli and 0.15±0.007 for S. aureus and finally the ppCop deposited on fabric with only 0.012 ±0.005 and 0.025±0.009 for E. coli and S. aureus respectively. This behavior, can be attributed to the different effective contact areas in the three different substrates, which is greater in the minced coverslip, followed by the coverslip and less in the fabric. It is important to mention that these bacteria measure approximately 0.5 µm wide by 2 µm long in the case of E. coli and 1.5 µm in diameter for S. Aureus which is considered immobile. The dimensions of the bacteria used limit the effective contact area to dimensions greater than approximately 4 µm2 of surface, this represents a difficulty in establishing an effective contact of the bacteria in the ppCop deposited on fabric since this type of substrate is characteristic for having a morphology with irregularities of dimensions smaller than the size of bacteria. This fact, together with the inability of the bacteria to migrate to these irregularities in the matrix due to their little or no immobility (in the case of S. aureus), difficulties the effective contact

Figure 8. TGA thermogram of ppCop (initial sample weight of 3.135 mg).

Figure 9. CFU in presence of ppCop on three different substrates (fabric, coverslip and minced coverslip) and without presence of ppCop (control) at 24 hr of bacteria growth (S. aureus and E. coli).

3.7. Antimicrobial activity of copolymer

Table 2. Antimicrobial activity (R) and bacterial growth inhibition (GI) of the ppCop deposited on three different substrates (fabric, coverslip and minced coverslip).

Escherichia coli Fabric Coverslip Minced coverslip

R 0.012 ±0.005 0.079 ±0.004 0.29 ±0.007

Polímeros, 33(4), e20230038, 2023

GI (%) 2.71 ±1.3 16.72 ±0.93 48.69 ±0.08

Staphylococcus aureus R GI (%) 0.025±0.009 5.76 ±2 0.15±0.007 29.57 ±1.29 0.29±0.004 49.31 ±0.58

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Ruiz, E. O. M., Rao, X., García, A. F., Vega, C. G., Canche, C. N. A., López, J. A. G., Pérez, A. S. L., Medina, M. D. D., Gaona, C. G. C., Céspedes, R. I. N., Arguello, G. S., & Velázquez, M. G. N.

Figure 10. Percentage of hemolysis at three different concentrations (1, 2.5 and 5 mg mL-1) of ppCop.

of the bacteria with the ppCop and decreasing the value of GI on this matrix.

Comparable materials to ppCop have been reported in the literature, the plasma polymerization of Octadiene (ppOct) with antibacterial properties was found. The microbial activity (R) for this ppOct is reported equal to 0.39 for S. aureus and 0.34 for E. coli reporting a inhibition in bacteria population of 60% and 55% for S. aureus and E. coli respectively[16].

The difference in antimicrobial activity in both materials is possible due to the reported hydrophobic properties of the polymer. In the case of ppOct, is reported a value of 92.9 ± 0.9°[16] and ppCop of 79 ± 0.4°. Since ppOct is more hydrophobic than ppCop has a higher repulsive effect on the initial bacteria attached which promotes a higher antimicrobial activity[28]. Nevertheless, the antimicrobial activity is comparable between both materials when ppCop is deposited on the ground coverslip. This could be attributed to the presence of oxidant groups (C3 + C4 equal to 10.11% according to XPS analysis) on the surface of the ppCop that are reported in a much lower amount in the ppOct (only C3 equal to 2.7%). The presence of these oxidant groups could lead to the deterioration of the bacteria and therefore favor the antimicrobial activity[1].

3.8. Hemolysis and cytotoxicity test: MTT assays The results of the %HE at three different concentrations of ppCop (1, 2.5 and 5 mg mL-1) are presented in Figure 10.

It can be observed that ppCop does not exceed the value of 2 of % Hemolysis (HE) in any of the three different concentrations. Therefore, and considering the standard ASTM F 756 17[35], it was found that ppCop does not present hemolytic activity. These results suggest that the material studied could be used for applications where there is direct interaction with human blood.

In Figure 11 is showed that the material has an acceptable viability according to the ISO 10993-5 standard[25] (established a minimum of 70%) on day 3, since on day 1 a viability of 54.94 ± 1.69% was shown, while for day 3 the viability was 90.42 ± 3.10%. These results support the hypothesis that the plasma coating material is not cytotoxic for the human 8/10

Figure 11. Percentage of cell viability (human CCD-1064SK fibroblasts) for ppCop at 1 and 3 days of culture.

cell line tested, which makes it possible for this material to be used for applications in which there is interaction with (human) body tissues.

4. Conclusions A cold plasma copolymerization of R-carvone and Octadiene was performed to obtain a moderately hydrophobic copolymer (ppCop) (WCA = 79± 0.4°). XPS analysis showed that ppCop was a typical cross-linked hydrocarbon plasma polymer with presence of carboxyl, amine-amide and hydroxyl moieties on the surfaces. The almost negligible reduction of ppCop thickness in DMSO (only reduced by 0.5%) during the 24 h immersion in DMSO reinforces the hypothesis that the ppCop is a cross-linked copolymer. The considerable reduction of the =CH bond (990.28 and 908.80 cm-1) and stretch bonds (3079.33 cm-1) of octadiene and the relatively high values of roughness (Ra of 14.1±0.02 nm and Rq of 17.1±0.02 nm) may suggest the insertion of long chain hydrocarbons such as -C8H16-, which could give flexibility to the polymer and increase its surface roughness. However, additional studies are needed to confirm this. The thermal stability of the ppCop was reported by the performance of Thermal gravimetric analysis (TGA). The thermal degradation of the sample initiated at 100 °C, it can be seen that the polymer follows a two-stage decomposition kinetics possibly attached to the copolymeric nature of the material. Approximately 10 percent of the initial sample weight was retained until the final oxidation occurred at 600 °C under an oxygen atmosphere, which could be due to the presence of crosslinked polymer. Antimicrobial activity of ppCop was corroborated by favorable outcomes observed in three different substrates (coverslip, minced coverslip and fabric), with the minced coverslip substrate displaying the highest value of growth inhibition (GI) with 48.69 ± 0.08% inhibition of E. coli and 49.31 ± 0.58% inhibition of S. aureus. The lowest GI result was for the fabric substrate reporting results of 2.71 ± 1.3% inhibition of E. coli and 5.76 ± 2% of inhibition of S. aureus, highlighting the influence of the effective contact area of each substrate Polímeros, 33(4), e20230038, 2023

Cold plasma copolymer with antimicrobial activity deposited on three different substrates on the GI and therefore microbial activity. Lastly, ppCop showed no cytotoxicity effect towards human cell during the hemolysis and cell adhesion assay.

5. Author’s Contribution • Conceptualization – Erick Osvaldo Martínez Ruiz; María Guadalupe Neira Velázquez.

• Data curation – José Abraham Gonzáles López; Erick Osvaldo Martínez Ruiz; Carlos Gallardo Vega.

• Formal analysis – Erick Osvaldo Martínez Ruiz; Carlos Gallardo Vega; José Abraham Gonzáles López.

• Funding acquisition – María Guadalupe Neira Velázquez; Rosa Idalia Narro Céspedes.

• Investigation – Erick Osvaldo Martínez Ruiz; Xi Rao; Carmen Natividad Alvarado Canche; Claudia Gabriela Cuellar Gaona; Abril Fonseca García; Miriam Desiree Davila Medina; José Abraham Gonzáles López; Gustavo Soria Arguello.

• Methodology – Erick Osvaldo Martínez Ruiz.

• Project administration –Erick Osvaldo Martínez Ruiz; María Guadalupe Neira Velázquez.

• Resources – María Guadalupe Neira Velázquez; Xi Rao; Antonio Serguei Ledezma Pérez; Miriam Desiree Davila Medina; Rosa Idalia Narro Céspedes.

• Software – Erick Osvaldo Martínez Ruiz; Carlos Gallardo Vega.

• Supervision – Erick Osvaldo Martínez Ruiz; María Guadalupe Neira Velázquez.

• Validation – Erick Osvaldo Martínez Ruiz; María Guadalupe Neira Velázquez; Antonio Serguei Ledezma Pérez; Claudia Gabriela Cuellar Gaona; Carmen Natividad Alvarado Canche; Abril Fonseca García.

• Visualization – Erick Osvaldo Martínez Ruiz; María Guadalupe Neira Velázquez.

• Writing – original draft – Erick Osvaldo Martínez Ruiz; María Guadalupe Neira Velázquez.

• Writing – review & editing – Erick Osvaldo Martínez Ruiz; María Guadalupe Neira Velázquez.

6. Acknowledgements Authors would like to acknowledge the following grant for this paper: Consejo Nacional de Humanidades Ciencia y Tecnología (CONAHCYT), postdoctoral fellowship 2020 (grant 6012). They also would like to thank M. García Zamora, María de Lourdes Guillén Cisneros, M. G. Mendez-Padilla for their technical support with some of the analytical techniques. Also, thanks to L. López and O. Pérez Camacho (from Centro de Investigación en Química Aplicada) for their comments on this research.

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Received: Dec. 06, 2022 Revised: Jul. 24, 2023 Accepted: Oct. 10, 2023

Polímeros, 33(4), e20230038, 2023

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20230023

Synthesis and characterization of polyurethane and samarium(III) oxide and holmium(III) oxide composites Lucas Repecka Alves1 , Giovanni Miraveti Carriello1* , Guilherme Manassés Pegoraro1 , Henrique Solowej Medeiros Lopes1,2 , Thaís de Agrella Janolla3 , Airton Natanael Coelho Dias3 , Giovanni Pimenta Mambrini1 , Maira de Lourdes Rezende2  and Aparecido Junior de Menezes1  Laboratório de Materiais, Programa de Pós-graduação em Ciência dos Materiais, Universidade Federal de São Carlos – UFSCar, Sorocaba, SP, Brasil 2 Laboratório de Caracterização de Materiais Poliméricos, Faculdade de Tecnologia José Crespo Gonzales, Sorocaba, SP, Brasil 3 Laboratório de Grupo TRACKs, Programa de Pós-graduação em Ciência dos Materiais, Universidade Federal de São Carlos – UFSCar, Sorocaba, SP, Brasil

1

*giovannimiraveti@estudante.ufscar.br

Abstract Polyurethanes, versatile polymers extensively explored across industries, can be augmented by incorporating complementary materials like lanthanides. This research presents a novel approach, employing a one-shot synthesis to create polyurethane-lanthanide composites using polyol, isocyanate, samarium, and holmium oxides. FTIR and Raman spectroscopy affirmed successful polyurethane matrix formation, while XRD unveiled distinct phases in lanthanideloaded matrices versus soft, low-crystallinity polyurethane in control foam. Optical microscopy displayed morphology alterations due to samarium and holmium. Thermogravimetric analysis revealed heightened composite thermal stability compared to control foam. Looking ahead, these outcomes prompt further exploration of polyurethane-lanthanide composites, particularly in harnessing property changes for diverse applications.

Keywords: composite, holmium, lanthanides, polyurethane, samarium.

How to cite: Alves, L. R., Carriello, G. M., Pegoraro, G. M., Lopes, H. S. M., Janolla, T. A., Dias, A. N. C., Mambrini, G. P., Rezende, M. L., & Menezes, A. J. (2023). Synthesis and characterization of polyurethane and samarium(III) oxide and holmium(III) oxide composites. Polímeros: Ciência e Tecnologia, 33(4), e20230039. https://doi.org/10.1590/01041428.20230023

1. Introduction Modern days, along with the need for increasingly durable and practical products, have caused many traditional materials to be replaced, especially by polymers, due to their numerous applications and properties[1,2]. Among the various types of polymeric materials on the market, polyurethane (PU), developed in 1937 by Otto Bayer and collaborators, stands out in terms of its versatility and applicability[2-4].

PU is synthesized through a polymerization reaction between a chemical called polyol, which contains hydroxyl groups (-OH), and another substance containing functional isocyanate groups (-NCO), which will result in a monomer product called urethane in an exothermic reaction[4,5]. The most common process for the synthesis of PU is the so-called batch process, also called one-shot, which consists of mixing the reagents and then stirring vigorously in a one-step process, then the reagents are poured into the desired mold[6].

PU can be found in the flexible or rigid foam form, as well as thermoplastic, adhesive, coating, binder, sealant, elastomer, fiber, and resins dispersed in water[3,5,7]. Due to its wide array of conformations, this polymer is generally applied in implants, footwear[8], cars, fabrics and can present several

Polímeros, 33(4), e20230039, 2023

properties, such as good thermal stability, mechanical[3,9], hydrolytic, platelet adhesion[10], shape memory[11], chemical resistance and biocompatibility[12,13].

To change PU properties, such as flame retardance, ignition, and degradation temperature, additives can be mixed in the structure[14,15]. Recent research indicates that PU structures with added lanthanides provide different properties to the final material, such as fluorescence, magnetic properties, protection against ultraviolet radiation, and flame retardancy, resulting in promising applications and indicating potentialities in research involving PU and lanthanide elements[7,16-18].

The lanthanides refer to the group of elements in the periodic table with atomic numbers 57 to 71, from lanthanum to lutetium[19]. The lanthanides are also the major constituents of the rare earth elements, which consist of the lanthanides plus yttrium and scandium[20]. These elements show similarity to physical and chemical properties, causing them to be categorized in this group[19,20]. Several studies report the use of a polymer matrix with lanthanides for different applications, such as magnetically responsive

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

Alves, L. R., Carriello, G. M., Pegoraro, G. M., Lopes, H. S. M., Janolla, T. A., Dias, A. N. C., Mambrini, G. P., Rezende, M. L., & Menezes, A. J polymer[21], fluorescence enhancement[22], nanoparticles for high resolution[23] and electrospun nanofibers[24,25].

Currently, the biggest producer of rare earth elements is China, with about 40% of the world’s reserve of ores from which these elements are extracted[20,26]. Brazil, in turn, has the third largest ore reserves in the world but does not exploit them as much[26-28]. Bearing in mind the previously presented points, this article presents a study of the synthesis and characterization of PU with samarium(III) oxide and holmium(III) oxide, contributing to recent research in this area. Recently conducted systematic reviews reveal that the combination of polyurethane with samarium or holmium has not yet been explored in the literature[29].

2. Materials and Methods 2.1 Chemicals Commercial polyol (Redelease, Brazil), commercial isocyanate (2,4’-diphenylmethane diisocyanate, Redelease, Brazil), Sm2O3 99,99% (Moscow 7 Store, China) and Ho2O3 (Sanyinghe, China).

2.2 Synthesis The polyurethane was synthesized by the one-shot method, which consists of the synthesis through the stirred mixture of the polyol with the isocyanate for 60 seconds at 300 RPM[6,30,31] under heating at 75 °C. Due to the heating in the synthesis, pure samples were named HPU referring to no added lanthanides.

To prepare the sample without lanthanide oxides, a 1:1 mass ratio of polyol to isocyanate mass was used.

For samples containing Sm2O3 and Ho2O3, mixtures containing oxide percentages of 5%, 10%, 15%, 20% and 25% were prepared, according to Equation 1, maintaining the 1:1 mass ratio of polyol to isocyanate. These were named HPU followed by the lanthanide it contained and its mass percentage.

%lanthanide =

mass of lanthanide oxide polyol mass + mass of isocyanate

(1)

from 500 to 4000 cm-1 spectral range, 3 s of exposure, and 3 accumulations.

2.3.3 X-ray powder Diffraction (XRD) A Shimadzu XRD-6100 diffractometer was used operating at a voltage of 40.0 kV and current of 30.0 mA with a copper X-ray tube. Continuous scans were performed at a speed of 2.0 °C·min-1 in the 2 theta range of 10º to 37º.

The analyzed sample was in powder.

2.3.4 Thermogravimetric (TG) Thermal decomposition properties were evaluated TG in a Perkin Elmer Pyris (Massachusetts, USA) equipment, from 30 ºC to 750 °C and a heating rate of 10 °C·min-1 under nitrogen (N2) atmosphere of 20 mL·min-1. Values for Tmax were obtained from the maximum height of the decomposition peak for each sample. Sample masses were normalized by subtracting lanthanide mass that was already in the sample, as these metallic oxides would not degrade at the analyzed temperatures.

2.3.5 Optic microscopy A Leica EZ4W optical microscope coupled to a microcomputer was used to obtain the images under 35x magnification.

3. Results and Discussion 3.1 Vibrational spectroscopy: FTIR and Raman The FTIR and micro-Raman spectra of all samples are shown in Figure 1. According to Trovati et al. (2010)[32], the peak at approximately 2270 cm-1 corresponds to the -N=C=O groups from isocyanates. The increasing content of samarium and holmium increased this peak intensity, which may indicate that either its presence hinders the polymerization between the isocyanates and the polyols, resulting in remaining unreacted molecules[32], which may be due to an excess of isocyanate or other interactions may have occurred during the synthesis between the PU matrix and the lanthanides. This perception of increased intensity was noted by standardizing the height of the peak in the region of 1600 cm-1, referring to the C=C of the aromatic ring[33], since this does not participate in the reaction.

In all samples, the corresponding lanthanide oxide was mixed with the heated isocyanate before reaction with the polyol. The samples were allowed to rest for one week before the characterizations.

2.3 Characterizations 2.3.1 Fourier-transform infrared spectroscopy (FTIR) Measurements of the powder samples were performed in a Perkin Elmer Frontier (Massachusetts, USA) equipment with an Attenuated Total Reflection (ATR) apparatus, from wavenumbers of 4000 to 400 cm-1, with a resolution of 4 cm-1 and 64 scans.

2.3.2 Raman spectroscopy Micro-Raman Spectroscopy was performed in a Renishaw in-Via Reflex coupled to a microscope, using a diode laser of 532 nm and 500 mW. Samples were analyzed 2/9

Figure 1. FTIR and micro-Raman spectra of all samples with increasing content of samarium (left) and holmium (right) from bottom to top: pure, 5%, 10%, 15%, 20%, and 25%.

Polímeros, 33(4), e20230039, 2023

Synthesis and characterization of polyurethane and samarium(III) oxide and holmium(III) oxide composites The bands corresponding to hydroxyl groups at 3300 cm-1 regions are more evident with increased content of Sm (mainly 15, 20 and 25% w/w) and for Ho (10, 20 and 25% w/w) oxides, which may indicate a softer polymer structure, due to a decrease in the cross-linking process between the isocyanate and polyol[32].

The bands present in the 1710 cm-1 region are related to the carbonyl groups and they are also evident in spectrums with increased isocyanate peaks at 2270 cm-1. This information endorses the presence both as an excess isocyanate of the reaction and as polyurethanes[32].

Philip et al.[24] highlight that the presence of lanthanide complexes in poly(methyl methacrylate) (PMMA) matrix blue shifted the carbonyl peak compared to the pure matrix, indicating that some interaction may be occurring with the lanthanide complexes[24]. Kohri et al.[21] observed the similar behaviour[21]. In the latter, the authors suggest that a coordination of the carbonyl groups to the lanthanide cations may have occurred.

The C-H symmetric and non-symmetric stretching appears at 2975 and 2920 cm-1, being more pronounced in the samples with higher content of lanthanides, 15, 20, and 25% (w/w) for Sm and 10, 20, and 25% (w/w) for Ho, accompanied by bands nearing 1600 and 1510 cm-1, typical of polymerized urethanes with stretching C=O and N-H bonds[32]. The spectrum characteristics observed here are typical of pure PU, with changes in certain bands from isocyanates and polyols, due to the presence of Sm or Ho in the composition.

Regarding micro-Raman spectra, band assignments were identify according to the literature. Normally, the vibrational properties of lanthanides oxides or ceramics are performed in different spectrum regions, as can be observed in previous works[34]. In this study, the spectrum differences related to the organic matrix of PU are analyzed in the presence of lanthanides.

Raman scattering intensities of isocyanates were observed at the 1439 cm-1 region[35-37], where only the HPU Sm 25% sample presented a blue shift of this band to 1445 cm-1. Urethane amides were assigned to 1185, 1255, and 1615 cm-1[36], and are related to the polyurethane matrix, while the 1666 cm-1 region corresponds to C=C stretching vibrations[37]. However, the authors mentioned that these bands could be overlapped by multiple peaks and/or low signal-to-noise ratios. Nitrogen-containing bonds (C-N and N-H) were observed at 1527 cm-1[35-37] and at 1710 cm-1, while some residual carbonyl was observed and may be related to the synthesis itself[35-37]. Blue shifts in the carbonyl band were observed with increasing Sm content and may indicate some polymerization interaction between the components. The increasing content of lanthanide resulted in the appearance of a band at 2935 cm-1 region, more evident in samples of Sm 10% to 25% and Ho 20% and 25%, being related to C-H bonds.

3.2 X-ray diffractometry Figure 2 shows the diffractograms of the pure polyurethane sample and samples containing Sm2O3 (samples Sm 5% to 25%). A characteristic band of pure polyurethane is observed around 19º, although it is wide in relation to other previous studies, indicating low crystallinity[32,33,38]. Furthermore, the absence of bands at 11° shows that the polyurethane is of Polímeros, 33(4), e20230039, 2023

Figure 2. X-ray diffractograms of samples containing 5%, 10%, 15%, 20%, and 25% Sm2O3.

the soft type, given that the polyol hydroxyl groups change the product’s crosslinking[32].

The samples containing Sm2O3 showed peaks at 28,3°, 29,3°, 29,9°, 31,3°, 32,1°, and 32,9°, which are characteristic of monoclinic Sm2O3, according to the JCPDS 84-1878 sheet[39-41].

Furthermore, such peaks show that the material is a composite, since the Sm2O3 remained crystalline, forming a multiphase material with the polyurethane or different components on a microscopic scale. This characteristic is consistent with other works involving composites of metal oxides with polyurethane[42-44].

In the work of Deng et al.[43], pure polyurethane also showed an enlarged band around 19º, which was no longer identified with the addition of only a 2% mass ratio of ZrO2, a relative amount much lower than the present work[44]. Other authors also attribute the decrease in the characteristic peak of polyurethane to the excessive addition of the oxide, in that case, TiO2, which leads to the formation of additional phase aggregates and ends up reducing the crystallinity, again with only a 2% mass ratio[43].

Figure 3 shows the diffractograms of the pure polyurethane sample and samples containing Ho2O3 (samples Ho 5% to 25%). The behavior observed in the Ho samples is similar to that of samples containing Sm2O3 (Figure 2). In this way, it is possible to state that it is a soft polyurethane composite with Ho2O3. The peaks in the diffractogram at 20,6°, 29,2°, 33,9° and 35,9° are characteristic of cubic Ho2O3, in accordance with the JCPDS 83-0932 sheet[45,46].

The results for the addition of Ho2O3 in the polymeric matrix are also comparable to those previously obtained and discussed in the literature. Larger relative masses, such as 30% of Fe2O3, also indicated peaks corresponding only to the oxide, while the pure polyurethane showed only the broad band at 19º[42].

3.3 Thermogravimetry (TG) The TG and DTG curves of all samples with samarium are shown in figures 4 and 5. Table 1 contains Tmax and mass values for the decomposition peaks presented by samples.

According to the literature[32], PU presents three major thermal events atributted of decomposition reaction. First, 3/9

Alves, L. R., Carriello, G. M., Pegoraro, G. M., Lopes, H. S. M., Janolla, T. A., Dias, A. N. C., Mambrini, G. P., Rezende, M. L., & Menezes, A. J Table 1. Values of Tmax for each sample with samarium obtained by the decomposition steps and the approximate mass loss.

Sample

1st step (°C)

Mass loss* (%)

2nd step (°C)

Mass loss* (%)

3rd step (°C)

HPU HPU Sm 5% HPU Sm 10% HPU Sm 15% HPU Sm 20% HPU Sm 25%

240.31 250.95 261.79 252.91 241.34 252.39

6.64 2.84 3.32 6.89 3.86 5.87

365.46 348.68 348.61 342.93 359.32 346.83

40.89 28.12 25.91 32.28 29.24 32.81

474.07 473.60 493.57 474.46 481.67 490.61

Remaining mass** (%) 17.78 14.10 16.98 18.26 19.42 9.93

*Mass loss up to this point. **Obtained from the last point of TG curve.

Figure 5. DTG curves of all samples with samarium.

Figure 3. X-ray diffractograms of samples containing 5%, 10%, 15%, 20%, and 25% Ho2O3.

Figure 4. TG curves of all samples with samarium.

the break of urethane bonds and second thermal event, which can be separated into two steps, the ester decomposition, the latter being separated into two steps, also observed by others in a similar composite[47]. The authors state that the first step occurs, approximately, from 200 to 350°C, and the second and third range from 350 to 535°C, similar to that which was observed in figure 5. These observations suggest that all thermal decompositions observed are related to the PU matrix[32].

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It is possible to observe that the increased content of Sm produced greater thermal stability through decreased mass loss and higher Tmax between 200 and 350 °C, being related to the break of urethane bonds, except for HPU Sm 15%. This suggests that the presence of lanthanide hinders the decomposition of this type of bonding. Alterations in FTIR bands can be observed above, where the addition of lanthanides modified isocyanate and carbonyl regions, also observed in the literature[21,23,24] and highlighted by Wang et al.[47]. Further investigations should be performed to better understand these.

Only HPU Sm 20% maintained the lowest mass loss rate during the entire analysis, presenting the greater remaining mass of 19.42%, with the highest Tmax value for the second decomposition peak amongst all samples with Sm, which may be related to the highest alteration on the carbonyl and isocyanate bands, as observed in FTIR results. However, all samples with Sm presented a lower Tmax value for this peak, compared to pure HPU. As expected, the greater percentage of Sm in the sample composition increased the remaining mass, except for HPU Sm 25%, presenting the lowest remaining mass of all samples, which may indicate that this amount of Sm did not play an important role in the HPU decomposition, since its FTIR spectrum presented lower alterations.

Additionally, the TG and DTG curves of all samples with holmium are shown in Figures 6 and 7. Table 2 also contains Tmax and mass values for the decomposition peaks presented by samples.

The same observation made for the samples with samarium is replicated in the samples with holmium, i.e., presenting three major steps of decomposition[32,47].

Polímeros, 33(4), e20230039, 2023

Synthesis and characterization of polyurethane and samarium(III) oxide and holmium(III) oxide composites Table 2. Values of Tmax for each sample with holmium obtained by the decomposition steps and the approximate mass loss.

Sample

1st step (°C)

Mass loss* (%)

2nd step (°C)

Mass loss* (%)

3rd step (°C)

HPU HPU Ho 5% HPU Ho 10% HPU Ho 15% HPU Ho 20% HPU Ho 25%

240.31 259.92 243.73 246.00 246.79 247.94

6.64 4.87 8.58 3.50 3.55 6.54

365.46 359.47 391.06 348.21 354.76 359.52

40.89 30.12 55.4 31.48 28.43 36.40

474.07 498.39 460.71 431.84 493.62 497.53

Remaining mass** (%) 17.78 21.69 3.89 9.62 17.97 21.07

*Mass loss up to this point. **Obtained from the last point of TG curve.

Figure 6. TG curves of all samples with holmium.

that the presence of lanthanide should have promoted an intensified ester decomposition[32]. Samples HPU Ho 5%, and 25% presented higher thermal stability during the entire analysis, with the highest Tmax and remaining mass values for all decomposition peaks, similar to that observed for HPU Sm 20%. In general, samples with the greater amount of holmium did not present a linear behavior of remaining mass, which may indicate a formation of complexes that promote higher or lower decomposition of the HPU matrix, which should be systematically investigated, already mentioned by others[47].

Philip et al.[24] observed some alterations in carbonyl bands with the addition of lanthanide complexes in the PMMA matrix, confirming through several microscopy techniques the presence of lanthanide complexes within the PMMA matrix due to its porous surface, which may have also occurred here to HPU[24]. Nevertheless, higher alterations in hydroxyl, isocyanate, and carbonyl bands may have played a role in this observation[21,24].

The presence of both lanthanides increased the thermal stability of urethane bonds of HPU, observed through higher Tmax and lower mass loss values for the first decomposition peak. Regarding the ester decomposition second peak, the presence of both lanthanides intensified its decomposition, through lower Tmax observed, but maintained some thermal stability through lower mass loss.

3.4 Optic microscopy

Figure 7. DTG curves of all samples with holmium.

The presence of holmium also promoted higher thermal stability on the samples, observed through the decreased mass loss presented after the decomposition steps occurred, except for the sample HPU Ho 10%, which showed a particular behavior, presenting higher and non-linear mass loss in the first and second steps of decomposition and lower remaining mass. This sample had the highest alteration in the FTIR spectrum, with increased intensities for hydroxyl groups, C-H, and carbonyl bands, indicating some interactions may have occurred, modifying the decomposition kinetics[21,24,47].

Can be observed that all samples presented a decreased Tmax value for the second decomposition peak, indicating Polímeros, 33(4), e20230039, 2023

In Figure 8b, it can be noticed that the HPU cells containing 5% Ho present a certain regularity in size with an elliptical shape. However, when the amount of holmium is increased, cells begin to lose this regularity, as in Figure 8c, d, e, and f, thus showing the appearance of tears within their morphology, as well as demonstrating smaller cell dimensions[48].

The decrease in the size of the polymer cell is observed with the increase of the holmium mass amount, which may indicate an increase in cell crosslinking and which may end up affecting the cell nucleation process[49].

By cross-sectional view analysis of the control foam we can be seen that it had the largest cell dimension when compared to the foams containing Ho and Sm, shown in Figure 9. This phenomenon can be explained by the reaction of isocyanate with the polyol, in which one of its products is carbon dioxide (CO2), which demonstrates that the addition of lanthanides ends up proportionally decreasing the size of the foam cells, which may end up diffusing within the 5/9

Alves, L. R., Carriello, G. M., Pegoraro, G. M., Lopes, H. S. M., Janolla, T. A., Dias, A. N. C., Mambrini, G. P., Rezende, M. L., & Menezes, A. J

Figure 8. Morphology of the cross-section structure of HPU foams with 35x magnification containing holmium: (a) Control or HPU; (b) Ho 5%; (c) Ho 10%; (d) Ho 15%; (e) Ho 20%, and (f) Ho 25%.

Figure 9. Morphology of the cross-section structure of HPU foams with 35x magnification containing samarium: (a) Sm 5%; (b) Sm 10%; (c) Sm 15%; (d) Sm 20%, and (e) Sm 25%.

lanthanide structure since the control foam had the largest pores of all foams[2,50].

Analyzing the morphologies of structures containing HPU with samarium in the cross-sectional view, it can be seen that cells containing 5% Sm mass, Figure 9a, are larger than those containing 5% Ho, Figure 8b. Thus, the addition of a samarium can significantly influence cell size and shape[51,52].

In addition, due to the morphological structure presenting itself as a polygon shape, this may indicate a lower stability due to its interface area, since the greater the cell interface area, the greater its surface energy[53]. The increase in the amount of samarium relative mass caused the cells to decrease in size due to the interfacial adhesion of the inorganic load as demonstrated in Figures 9b, c, d, and e, which may indicate that samarium has a hydrophobic surface nature, which when in contact with the hydrophilic matrix 6/9

of the HPU ends up causing a collapse between cells. This phenomenon is even more noticeable when increasing the amount of samarium inside the matrix[54].

4. Conclusions Through the FTIR technique, it was possible to observe that successfully obtained polyurethane foams containing holmium oxide and samarium oxide, by means of the vibrational spectra of urethane bond formation. The addition of lanthanide oxides caused shifts in the main FTIR and Raman bands, which may indicate a potential interaction with the reagents used, such as polyol and isocyanate.

The XRD technique demonstrated the presence of two distinct phases: one related to the low crystallinity of the polyurethane and the other due to the crystallinity of the lanthanide oxides. The morphology analyzed Polímeros, 33(4), e20230039, 2023

Synthesis and characterization of polyurethane and samarium(III) oxide and holmium(III) oxide composites through the optical microscope showed that the addition of lanthanides proportionally altered the shape and size of the cells. Thermogravimetric analyses demonstrated that the incorporation of holmium and samarium improved the thermal properties of the material, which, with further investigation, could be used as flame retardants.

5. Author’s Contribution • Conceptualization – Lucas Repecka Alves; Giovanni Miraveti Carriello; Guilherme Manassés Pegoraro.

• Data curation – Giovanni Miraveti Carriello; Henrique Solowej Medeiros Lopes; Thaís de Agrella Janolla.

• Formal analysis – Lucas Repecka Alves; Giovanni Miraveti Carriello; Guilherme Manassés Pegoraro; Henrique Solowej Medeiros Lopes; Thaís de Agrella Janolla.

• Funding acquisition - NA. • Investigation – ​Aparecido Junior de Menezes; Maira de Lourdes Rezende; Giovanni Pimenta Mambrini; Airton Natanael Coelho Dias.

• Methodology – Lucas Repecka Alves; Giovanni Miraveti Carriello.

• Project administration – Aparecido Junior de Menezes; Maira de Lourdes Rezende; Giovanni Pimenta Mambrini; Airton Natanael Coelho Dias.

• Resources – Aparecido Junior de Menezes; Maira de Lourdes Rezende; Giovanni Pimenta Mambrini; Airton Natanael Coelho Dias.

• Software – NA. • Supervision – Aparecido Junior de Menezes; Maira de Lourdes Rezende; Giovanni Pimenta Mambrini; Airton Natanael Coelho Dias.

• Validation – Aparecido Junior de Menezes; Maira de Lourdes Rezende; Giovanni Pimenta Mambrini; Airton Natanael Coelho Dias.

• Visualization – Aparecido Junior de Menezes; Maira de Lourdes Rezende; Giovanni Pimenta Mambrini; Airton Natanael Coelho Dias.

• Writing – original draft – ​Lucas Repecka Alves; Giovanni Miraveti Carriello; Guilherme Manassés Pegoraro; Henrique Solowej Medeiros Lopes; Thaís de Agrella Janolla.

• Writing – review & editing – Aparecido Junior de Menezes; Maira de Lourdes Rezende; Giovanni Pimenta Mambrini; Airton Natanael Coelho Dias.

6. Acknowledgements This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001.

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29. Pegoraro, G. M., Alves, L. R., Carriello, G. M., Janolla, T. A., Mambrini, G. P., Rezende, M. L., & Menezes, A. J. (2023).

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32. Trovati, G., Sanches, E. A., Claro Neto, S., Mascarenhas, Y. P., & Chierice, G. O. (2010). Characterization of polyurethane resins by FTIR, TGA, and XRD. Journal of Applied Polymer Science, 115(1), 263-268. http://dx.doi.org/10.1002/app.31096.

33. Gao, X., Zhu, Y., Zhao, X., Wang, Z., An, D., Ma, Y., Guan, S., Du, Y., & Zhou, B. (2011). Synthesis and characterization of polyurethane/SiO2 nanocomposites. Applied Surface Science, 257(10), 4719-4724. http://dx.doi.org/10.1016/j. apsusc.2010.12.138.

34. Dias, A., Khalam, L. A., Sebastian, M. T., Lage, M. M., Matinaga, F. M., & Moreira, R. L. (2008). Raman scattering and infrared spectroscopy of chemically substituted Sr2LnTaO6 (Ln = Lanthanides, Y, and In) Double Perovskites. Chemistry of Materials, 20(16), 5253-5259. http://dx.doi.org/10.1021/ cm800969m.

35. Romanova, V., Begishev, V., Karmanov, V., Kondyurin, A., & Maitz, M. F. (2002). Fourier transform Raman and Fourier transform infrared spectra of cross-linked polyurethaneurea films synthesized from solutions. Journal of Raman Spectroscopy: JRS, 33(10), 769-777. http://dx.doi.org/10.1002/jrs.914.

36. Parnell, S., Min, K., & Cakmak, M. (2003). Kinetic studies of polyurethane polymerization with Raman spectroscopy.

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37. Socrates, G. (2001). Infrared and Raman characteristic group frequencies: tables and charts. Chichester: John Wiley & Sons.

38. Alaa, M., Yusoh, K., & Hasany, S. F. (2015). Pure polyurethane and castor oil based polyurethane: synthesis and characterization.

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39. Madhuri, S. N., & Rukmani, K. (2019). Synthesis and concentration dependent tuning of PVA-Sm2O3 nanocomposite films for optoelectronic applications. Materials Research Express, 6(7), 075017. http://dx.doi.org/10.1088/2053-1591/ ab1326.

40. Liu, T., Zhang, Shao, & Li, (2003). Synthesis and characteristics of Sm2O3 and Nd2O3 nanoparticles. Langmuir, 19(18), 75697572. http://dx.doi.org/10.1021/la034350l.

41. Guo, Q., Zhao, Y., Jiang, C., Mao, W. L., & Wang, Z. (2008). Phase transformation in Sm2O3 at high pressure: in situ synchrotron X-ray diffraction study and ab initio DFT calculation. Solid State Communications, 145(5-6), 250-254. http://dx.doi.org/10.1016/j.ssc.2007.11.019.

42. Park, C.-H., Kang, S.-J., Tijing, L. D., Pant, H. R., & Kim, C. S. (2013). Inductive heating of electrospun Fe2O3/polyurethane composite mat under high-frequency magnetic field. Ceramics International, 39(8), 9785-9790. http://dx.doi.org/10.1016/j. ceramint.2013.05.042.

43. Deng, F., Zhang, Y., Li, X., Liu, Y., Shi, Z., & Wang, Y. (2019).

Synthesis and mechanical properties of dopamine modified titanium dioxide/waterborne polyurethane composites. Polymer Composites, 40(1), 328-336. http://dx.doi.org/10.1002/pc.24654.

44. Jothi, K. J., Balachandran, S., Mohanraj, K., Prakash, N., Subhasri, A., Krishnan, P. S. G., & Palanivelu, K. (2022).

Fabrications of hybrid Polyurethane-Pd doped ZrO2 smart carriers for self-healing high corrosion protective coatings.

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Synthesis and characterization of polyurethane and samarium(III) oxide and holmium(III) oxide composites 45. Mortazavi-Derazkola, S., Zinatloo-Ajabshir, S., & SalavatiNiasari, M. (2017). Facile hydrothermal and novel preparation of nanostructured Ho2O3 for photodegradation of eriochrome black T dye as water pollutant. Advanced Powder Technology, 28(3), 747-754. http://dx.doi.org/10.1016/j.apt.2016.11.022.

46. Abu-Zied, B. M., & Asiri, A. M. (2019). Genesis of nanocrystalline Ho2O3 via thermal decomposition of holmium acetate: structure evolution and electrical conductivity properties. Journal of Rare Earths, 37(2), 185-192. http://dx.doi.org/10.1016/j. jre.2018.05.017.

47. Wang, J. L., Li, Y., Chain, W., Wang, X., Li, H. T., Liu, S. H., Zhang, J. R., & Xu, M. X. (2013). Synthesis and characterization of rare earth/polyurethane composite material. Advanced Materials Research, 763, 125-129. http://dx.doi.org/10.4028/ www.scientific.net/AMR.763.125.

48. Carriço, C. S. (2017). Obtenção de espumas de poliuretano a partir de coprodutos da cadeia dos biocombustíveis e resíduos agroindustriais (Doctoral thesis). Universidade Federal de Minas Gerais, Belo Horizonte. Retrieved in 2023, March 22, from https://repositorio.ufmg.br/handle/1843/SFSA-ARZULR 49. Dolomanova, V., Rauhe, J. C. M., Jensen, L. R., Pyrz, R., & Timmons, A. B. (2011). Mechanical properties and morphology of nano-reinforced rigid PU foam. Journal of Cellular Plastics, 47(1), 81-93. http://dx.doi.org/10.1177/0021955X10392200.

50. Reignier, J., Alcouffe, P., Méchin, F., & Fenouillot, F. (2019).

The morphology of rigid polyurethane foam matrix and its evolution with time during foaming – New insight by cryogenic scanning electron microscopy. Journal of Colloid

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and Interface Science, 552, 153-165. http://dx.doi.org/10.1016/j. jcis.2019.05.032. PMid:31125826.

51. Mello, D., Pezzin, S. H., & Amico, S. C. (2009). The effect of post-consumer PET particles on the performance of flexible polyurethane foams. Polymer Testing, 28(7), 702-708. http:// dx.doi.org/10.1016/j.polymertesting.2009.05.014.

52. Silva, R. P. (2017). Utilização de pó de poli(tereftalato de etileno) pós-consumo e do óleo de mamona (Ricinus communis) no desenvolvimento de espuma flexível (Master’s dissertation).

Universidade Federal de Campina Grande, Campina Grande.

Retrieved in 2023, March 22, from http://dspace.sti.ufcg.edu. br:8080/jspui/handle/riufcg/13952 53. Santin, C. K., & Petró, F. (2022). Desenvolvimento e caracterização de espuma poliuretânica à base de Difenilmetano diisocianato (MDI) e óleo de linhaça (Linum usitatissimun L.).

Revista Liberato, 23(39), 77-88. Retrieved in 2023, March 22, from https://revista.liberato.com.br/index.php/revista/article/ view/77-88 54. Sung, G., & Kim, J. H. (2017). Influence of filler surface characteristics on morphological, physical, acoustic properties of polyurethane composite foams filled with inorganic fillers.

Composites Science and Technology, 146, 147-154. http:// dx.doi.org/10.1016/j.compscitech.2017.04.029.

Received: Mar. 22, 2023 Revised: Aug. 24, 2023 Accepted: Oct. 10, 2023

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20230054

Hydrophobic polyurethane foams reinforced with microcrystalline cellulose for oil spill clean up Matheus Vinícius Gregory Zimmermann1* , Eduardo Junca1 , Marina Kauling de Almeida1 , Lara Vasconcellos Ponsoni1 , Ademir José Zattera2 , Tiago Mari2  and Ruth Marlene Campomanes Santana3  Programa de Pós-graduação em Engenharia e Ciência dos Materiais – PPGCEM, Universidade do Extremo Sul Catarinense – UNESC, Criciúma, SC, Brasil 2 Programa de Pós-graduação em Engenharia de Processos e Tecnologias – PGEPROTEC, Universidade de Caxias do Sul – UCS, Caxias do Sul, RS, Brasil 3 Programa de Pós-graduação em Engenharia de Minas, Metalúrgica e de Materiais – PPG3M, Universidade Federal do Rio Grande do Sul – UFRGS, Porto Alegre, RS, Brasil 1

*e-mail: matheus.vgz@gmail.com

Abstract Oil spills into water have been an environmental concern since the beginning of large-scale oil extraction. In this study, flexible open-cell polyurethane (PU) foams with added microcrystalline cellulose (MCC) were formulated and chemically modified with organosilane for use as an absorbent system for oil spill cleanup in water. The influence of cellulose concentration on mechanical properties and chemical treatment with organosilane was evaluated. The primary findings indicate that the surface treatment of the solid fraction of the foams was effective, as indicated by the contact angle, increasing the hydrophobicity of the samples. Because of the increased roughness of the PU solid fraction and the cellulose reactivity, the mechanical compressive strength and thickness of the organosilane layer increased with increasing MCC content. However, the higher the MCC content in the composition, the higher was the density, which reduced the sorption capacity of the samples.

Keywords: polyurethane fomas, oil spill cleanup, organosilane, cellulose.

How to cite: Zimmermann, M. V. G., Junca, E., Almeida, M. K., Ponsoni, L. V. Zattera, A. J., Mari, T., & Santana, R. M. C. (2023). Hydrophobic polyurethane foams reinforced with microcrystalline cellulose for oil spill clean up.

Polímeros: Ciência e Tecnologia, 33(4), e20230040. https://doi.org/10.1590/0104-1428.20230054

1. Introduction Oil contamination has been an environmental issue since the beginning of large-scale extraction and use of oil.

According to the International Tanker Owners Pollution Federation, the total global volume of tanker oil spills in 2022 was approximately 15,000 tons[1]. Oil spills typically occur during the extraction and transportation processes, causing economic, environmental, and social damage.

Oil spilled during maritime extraction kills marine animals, contaminates seafood, produces toxic steam, and its residues can last for decades[2-5]. Oil spilled into the water spreads immediately. Its volatile components can evaporate and contaminate the air, and it can simultaneously become emulsified in the oil–water, making it difficult to extract and remove[6].

Some water–oil separation techniques, such as flotation, centrifugation, adsorption, gravimetric separation, electrochemistry, and biodegradation, have been investigated to minimize the impact of oil spills[4]. The sorption process has been highlighted as a technique for treating industrial effluents and is an effective and economical alternative for remediating areas degraded by oil spills. This process

Polímeros, 33(4), e20230040, 2023

involves simultaneous absorption, adsorption, and desorption processes. In absorption, the oil is absorbed within the system, and in adsorption, the oil is retained on the surface of the solid part of the sorbent[7].

For an oleophilic sorbent to be effective, oil must enter the sorbent rapidly, in large quantities, and without causing the sorbent system to rupture or disintegrate. Simultaneously, oil desorption during the sorbent withdrawal from the medium must be low; therefore, the oil must remain within the system until it is removed from the environment[8]. According to Liu et al.[9], an ideal sorbent would be a material with a high oil sorption capacity and selectivity to oil but not to water, low density, recyclability, and low environmental aggressiveness.

Sorbent materials have a high oil removal capacity, are able to absorb 3–100 times their original mass and have a low environmental impact and cost[10]. The selectivity for oil (predominantly hydrophobic) of a sorbent for removing apolar materials is the most important property that determines its efficiency in removing apolar materials, especially when oils are in an aquatic environment[11].

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

Zimmermann, M. V. G., Junca, E., Almeida, M. K., Ponsoni, L. V. Zattera, A. J., Mari, T., & Santana, R. M. C. Polyurethane (PU) foams are synthesized via the polymerization reaction between a di or tri isocyanate and a hydroxylated polyol, resulting in a PU chain. PU foams can take various shapes depending on the formation method, such as rigid, semi-rigid, or flexible, with varying densities. Upholstery made of reinforced materials with sorption capacities can benefit from the application of PU[12].

The viscoelastic properties of foams synthesized with high open-cell concentrations allow for oil sorption and desorption.

The development of oleophilic and hydrophobic properties is related to sorption and desorption using reagents like organosilanes for modification during the foam preparation[13].

Several researchers have used organosilanes as coating agents to produce hydrophobic surfaces. Jianliang et al.[13] modified the seaweed Enteromorpha with organosilanes to maintain its oleophilic properties while becoming hydrophobic, whereas Usman et al.[14] modified ceramic membranes with organosilanes, both of which intend to use such modifications to remove oil from water. The advantages of using organosilane as a coating include its availability on a large scale, the possibility of being a bifunctional molecule capable of reacting with the surface, and the presence of functional groups that can modify the hydrophobicity of the sample[15]. The reaction in silanes is based on their bifunctionality (they have two distinct reactive groups); in the presence of water, silane hydrolyzes and forms silanol, which can react with the hydroxyls of the substrate and form covalent and/or secondary bonds on the surface of the substrate[5,16].

In the production of expanded composites or reinforced foams, another mechanism commonly used to modify the physical and mechanical properties of polymeric foams is the incorporation of fillers. The addition of fillers to polymeric foams can be used to reduce the final cost of the product, increase foam rigidity, or modify specific properties, such as changing surface characteristics, such as roughness, increasing thermal stability, increasing cell nucleation (a greater number of cells and smaller size per unit volume), and facilitating the opening of pores around the cells[17]. Depending on the type, size, and filler content of the polymeric foams, various cell morphologies can be obtained[18]. Organic materials derived from plant fibers have recently gained prominence in the field of polymeric composites, owing to their lower abrasiveness and density than those of inorganic materials, being derived from renewable and biodegradable sources, and being easy to obtain (with relatively low cost)[17]. Among plant fibers, cellulose is the most abundant biopolymer on Earth and is a fundamental component of most plant species.

Another important property of cellulose is its ability to be easily chemically modified, making it appealing for use as a reinforcing agent in polymeric composites owing to the combination of chemical affinities that can be obtained[16,19-21].

Microcrystalline cellulose (MCC) is produced from purified and partially depolymerized cellulose. It can be used as a fine-particle powder or processed with a watersoluble polymer to obtain a colloidal form. MCC can be produced from various cellulose sources; however, cotton and wood are the primary sources used for breeding. The most common applications include binders and fillers in food and medical tablets and as reinforcement reagents for the development of polymer composites. MCC is considered 2/9

a potential reinforcement for improving the mechanical properties of the material[22].

Given the difficulty of cleaning oil spills from water sources around the world, there is a need to develop alternative oil-absorbing options. This study aimed to produce a PU foam reinforced with MCC for use as a sorbent in oil spills and to evaluate the effect of different MCC concentrations on the chemical treatment with organosilane and the physical and mechanical properties of the PU foam.

2. Materials and Methods 2.1 Materials For the development of PU foams, Voranol WL 4010 polyol and Voranate™ T-80 toluene diisocyanate (TDI), supplied by Dow Brasil Sudeste Industrial Ltda., were used. The amine catalyst (Dabco® 2033 Catalyst) was supplied by Air Products and the organometallic tin octanoate catalyst (Kosmos® 29) was supplied by Evonik Industries. The surfactant, commercially known as Niax silicone L-595, was supplied by Momentive Performance Materials, Inc. Methylene chloride, a deionizing agent supplied by Brasil Sudeste Industrial Ltd., and deionized water were used.

Sigma-Aldrich S. A supplied MCC, Sigmacell Type 20 grade, particle size approximately 20 µm, code S3504.

Triethoxyvinylsilane (TEVS) (supplier code: 175560) and tetraethoxysilane (TEOS) (supplier code: 13190) were used for the hydrophobic coating of PU foams, and were supplied

by Sigma-Aldrich.

The following oils were used for the sorption tests: Ipiranga SAE 5W30 oil (lubricating motor oil) with a density of 0.86 g.cm–3 at 20 ºC and a kinematic viscosity of 70 cSt at 40 ºC, soybean oil (vegetable oil–cooking oil) with a density of 0.91 g.cm–3 at 20 °C and a kinematic viscosity of 32 cSt at 40 °C; and kerosene (fuel oil) with a density of 0.78 g.cm–3 at 20 °C and a kinematic viscosity of 2.2 (max) cSt at 40 °C. Crude oil, supplied by Petrobras, has an °API of 30.2, a density of 0.87 g.cm–3, and is classified as medium oil.

2.2 Methods Table 1 lists the PU foams formulated with various MCC concentrations expressed in parts per hundred polyols (pphp). In the standard composition of the flexible PU foams, four levels of MCC were used, with a theoretical density of 10 kg.m–3.

The PU foams were produced via the batch method using a Fisaton 715 propeller mixer at a rotational speed of 2500 rpm. Water, amine, silicone, and various concentrations of MCC were initially added to the polyol and stirred for 80 s. Tin octanoate was then added and mixed for 40–50 s.

Thereafter, TDI and methylene chloride were added to the blend while vigorously stirring for approximately 10–15 s, and the mixture was poured into a mold for free expansion to form the foam. The expansion time is approximately 1 min.

The foam was cured for 48 h at a constant temperature of 23 °C. Polímeros, 33(4), e20230040, 2023

Hydrophobic polyurethane foams reinforced with microcrystalline cellulose for oil spill clean up Table 1. Polyurethane foams formulations (pphp).

Reagents Polyol Diisocyanate Water Amine Silicone Octoate Chloride MCC

PU 1 100 80 6 0.3 3.3 0.5 22 0

PU.C10 100 80 6 0.3 3.3 0.5 22 10

PU.C20 100 80 6 0.3 3.3 0.5 22 20

PU.C30 100 80 6 0.3 3.3 0.5 22 30

PU.C40 100 80 6 0.3 3.3 0.5 22 40

Figure 1. Photographic image of PU foams after organosilane coating.

Hydrophobization of the PU foam was performed using an organosilane-based coating. First, organosilane hydrolysis was performed in a water:alcohol (70:30) solution containing 1% (mass) organosilane TEVS and 1% (mass) TEOS. To stabilize the pH of the solution at 4.5, acetic acid (approximately 10 mL/L of solution) was added dropwise.

For 2 h, the resulting solution was stirred. Following that, foam samples (25 mm × 25 mm × 25 mm) were immersed in the solution, and the solution was slowly stirred with a magnetic bar stirrer for 4 h. Later, the foams were removed from the solution, the excess liquid was drained, and the samples were dried at 120 °C for 4 h (with the occurrence of concomitant organosilane curing).

Figure 1 presents photographic images of the foams after the hydrophobic coating, with and without the addition of cellulose, highlighting the change in color of the foams to darker tones as the cellulose content increases. This change in foam color could be attributed to the curing time altering the chemical structure of the cellulose and promoting partial degradation of its constituents.

2.3 Characterization To analyze the density of the samples, five specimens of dimensions 25 mm × 25 mm × 25 mm were used per sample, and the densities of the foams were calculated using Equation 1, as described in ASTM D3574-11. Each value was calculated as the average of seven independent measurements (seven specimens per formulation). ρ= f

mf vf

×106

(1)

where ρf, mf, and vf represent the foam density (kg.m–3), the mass (g), and the volume (mm3) of the specimen, respectively.

The sample morphology was examined via field-emission scanning electron microscopy (FEG–SEM) on a Shimadzu Polímeros, 33(4), e20230040, 2023

device (Superscan SS-550 model) and a Tescan microscope (model Mira3). All samples were pre-coated with gold, and a voltage of 15 kV was used. The foam area was observed vertically in the direction of sample expansion.

Three specimens of dimensions approximately 25 mm × 25 mm × 25 mm were conditioned in an environment with a temperature of 23 ± 2 °C and a relative humidity of 60 ± 5% to assess the hydrophobic properties of the coated foam.

The samples were then placed under a glass slide, and a drop of deionized water was added to a glass syringe at five different points under the same conditions. Images were taken with a Lumix FZ40 digital camera as soon as the drop touched the surface of the sample and after 5 min, and were analyzed using Surftens software (version 3.0).

Chemical properties were evaluated using a Nicolet iS10 Fourier-transform infrared (FTIR) spectrometer (Thermo Scientific) with attenuated total reflectance (ATR).

The samples were scanned at a resolution of 4 cm−1 in the wavenumber range of 4000−400 cm−1.

The thermal properties of the foams were evaluated using a thermogravimetric analyzer (TGA) (Shimadzu model TGA-50) with a heating ramp of 23−800 ºC at a rate of 10 ºC.min–1 in a nitrogen atmosphere (50 mL.min–1). Each assay used approximately 10 mg of each sample.

Compressive strength tests on the PU foams were performed using universal testing equipment, EMIC model DL 2000, with specimens of dimensions 50 mm × 50 mm × 25 mm and a compression speed of 50 mm.min–1. The tension required to reduce the thickness of a specimen by up to 80% of its initial thickness was evaluated using ASTM D3574-11.

Tests were performed on five specimens.

Static sorption tests were performed using the ASTM F726-12 methodology, in which the sorbent was added to the oil for 15–30 min (sorption time increased with increasing oil viscosity) until the samples were completely submerged in the oil. Following that, the samples were withdrawn, 3/9

Zimmermann, M. V. G., Junca, E., Almeida, M. K., Ponsoni, L. V. Zattera, A. J., Mari, T., & Santana, R. M. C. suspended for 30 s to drain excess oil (desorption), and reweighed. The dimensions of the samples used in the tests were 25 mm × 25 mm × 25 mm. All samples were evaluated in triplicate, and the tests were performed at 23 °C. To calculate the sorption capacity of the PU foams, two methods were used: (1) the standard method, which evaluates the sorption capacity as a function of the mass of the sorbent before and after the test, as represented in Equation 2, and (2) sample collection capacity. Concerning the collection of oil per sample, the test specimens with a constant volume (25 mm × 25 mm × 25 mm) and exposed to different types of oils according to the previously described methodology were compressed (crushed) for maximum oil removal from the body of the foam. The oil collected from the test specimens (in a constant volume) was then weighed (measured in units) in grams, and all tests were performed in triplicate.

SC =

M1− M 0 M0

(2)

where SC, M0, and M1 represent the sorption capacity (g.g−1) and the mass (g) of the dry sorbent and the mass (g) of the sorbent added to the sorbate, i.e., the mass after the sorption test, respectively.

3. Results and Discussions Figure 2 depicts SEM micrographs of PU foams with varying cellulose contents. All samples were predominantly composed of open cells. There were no significant differences in the morphologies of the PU foam cells with different cellulose contents. The MCC was deposited inside the solid phase of the foam (PU) and exhibited no effect on cell nucleation during foam expansion.

Figure 3 depicts the bulk densities of PU foams with different MCC contents and foams samples after organosilane treatment (PU.S). Increasing the MCC content causes an increase in the bulk density of the samples, which is to be expected given that cellulose is an additional component.

It is also necessary to consider that the addition of cellulose to polyol causes a proportional increase in the viscosity of this phase, which restricts the expansion capacity of the foam. This is coupled with the fact that cellulose fibers occupy the empty spaces within the PU molecules and can promote an increase in foam density[23].

It was also discovered that following the hydrophobic chemical treatment, all samples exhibited higher density than their non-chemically treated counterparts, which is associated with the incorporation of organosilane layers on the surface of the solid fraction of the foam. It is noteworthy that, when compared to the pure PU sample (which increased by approximately 7%), the samples containing MCC following chemical treatment increased in density, with increases of 27, 29, 20, and 14% for PU.C10, PU.C20, PU.C30, and PU.C40, respectively. The increase in density of the foams with MCC could be attributed to an increase in the surface roughness of the solid fraction, which could have resulted in the formation of thicker layers of organosilane on the surface of the foam solid fraction.

Figure 4 depicts the FTIR spectra of PU foam (without cellulose) before and after organosilane coating. Only the PU sample spectra are shown in this figure because cellulose was deposited inside the solid fraction rather than on the surface in the PU foam samples with MCC, and no significant difference was observed between the PU samples with and without MCC. A band was observed at 3320 cm–1, corresponding to the N–H group (urethane); a nearby peak at 2272 cm–1, attributed to the NCO group present in the isocyanate; absorption bands at 1224 cm–1 and

Figure 2. SEM images of the morphology of (a) PU; (b) PU.C10; (c) PU.C20; (d) PU.C30; and (e) PU.C40 foams.

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Hydrophobic polyurethane foams reinforced with microcrystalline cellulose for oil spill clean up

Figure 3. Densities of PU samples with varying MCC contents and without/with organosilane-based hydrophobic treatment.

Figure 4. FTIR spectra of PU sample foams (without cellulose), before and after coating with organosilane.

1513 cm–1, arising from the presence of the N–H and N–C groups, respectively; and a peak at 1725 cm–1, attributed to the presence of the carbonyl (C=O) group. The band at 1075–1115 cm–1 is assigned to C–O–C groups, the band at 2880–2890 cm–1 is assigned to CH groups, and the bands at 1605, 1540, and 870 cm–1 are due to aromatic structures, such as C=C of the benzene ring[24].

The appearance of a band at 765 cm–1 that is related to Si–C was observed in the samples treated with the organosilane coating[25] and an increase in the intensity of the band near 3500 cm–1, which may be due to the presence of OH– terminal groups of the hydrolyzed organosilane.

The disappearance of several PU characteristic bands was observed following chemical treatment, which may be due to the test method used (FTIR–ATR spectroscopy), in which the depth of penetration of the beam interferes with the existing bonds in the PU with the hydrophobic coating.

Figure 5 depicts the stress–strain curves of PU foams with various cellulose contents. All samples exhibited the typical deformation behavior of polymeric foam, with three well-defined stages: (I) deformation, (II) plateau, and Polímeros, 33(4), e20230040, 2023

Figure 5. Stress–strain of PU foams with different MCC contents.

(III) densification, as determined by analyzing the curves obtained by compressing the foams with deformations up to 80% of the initial volume[26]. The first linear stage (elastic) deformation is related to the modulus of elasticity and consists of a reversible deformation responsible for the bending and distension of the cell walls. That is, the cell must be able to withstand the applied force without deforming its geometric shape. After reaching the critical stress value of the elastic region, the cell begins to deform, and in general, the sample exhibits low resistance and mechanical response during this phase. When the deformation reaches its maximum value, the solid fraction of the polymeric matrix is compacted[27].

Analyzing the PU samples with various MCC contents reveals a tendency for mechanical resistance to increase by compression with an increase in cellulose content in the foams. According to Hussain and Kortschot[23] short fibers are preferentially deposited inside the polymer matrix in the contours of the cells. Because cellulose exhibits a high concentration of hydroxyl groups in its chemical structure, it is assumed to have a strong interaction with the polyol used in the formulation of PU foams, promoting the strengthening and stiffening effects of the polymer matrix[23].

The morphology of the cells in the PU foams with different cellulose contents did not change significantly, leading to the conclusion that the stiffening of the polymer matrix combined with the increased density of the foams in the presence of cellulose fibers were the primary factors contributing to the increase in compressive strength of PU foams reinforced with different cellulose contents.

Figure 6 depicts thermogravimetric thermal characterization.

The PU experienced two stages of mass loss, as previously described. The second event of the degradation thermogram shows an increase in the degradation temperature with increasing cellulose content. According to Borsoi et al.[28], the primary degradation event in the thermogravimetry degradation of MCC in an N2 atmosphere at a rate of 10 °C/min occurs in the temperature range of 338–376 °C, which would justify the increase in degradation temperature in this second event with increasing cellulose content in PU foams. Furthermore, cellulose is mixed with polyols in the formulation, which may result in strong interactions between the phases.

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Zimmermann, M. V. G., Junca, E., Almeida, M. K., Ponsoni, L. V. Zattera, A. J., Mari, T., & Santana, R. M. C. Figure 7 depicts SEM micrographs of PU samples with various MCC levels, with and without hydrophobic treatment.

It is possible to observe that following the organosilane treatment, the samples exhibited a rigid coating layer that

Figure 6. Degradation thermograms of PU foams with different cellulose contents (uncoated).

was fragmented during the cutting process, making the organosilane coating layer more evident. Pure PU exhibits a smoother surface before chemical treatment, which may contribute negatively to the adhesion of the organosilane to the surface; under mechanical effects, it deteriorates and is more easily removed. As observed in the micrographs, the presence of MCC resulted in thicker layers of organosilane and no significant tricks or detachments compared to PU. The hydrophobicity of the PU foams was determined by measuring the contact angle of their (pressed) surface with water (polar liquid), which is defined as the angle between the solid surface and the tangent line of the liquid phase at the solid phase interface. Figure 8 lists the contact angles of the water droplet and the PU foam surface.

At time t = 0, the contact angle obtained for all samples silanized with a liquid with maximum surface tension (water) was greater than 110°, indicating a surface with hydrophobic properties. The water droplet angle above cellulose-reinforced foams increased slightly, probably because of the increased interaction of the foam surface with organosilane.

The contact angle of water with the substrate surface is related to the functional groups present on the solid surface of the PU foam. After 5 min of testing, water

Figure 7. SEM images of (a) untreated pure PU, (b) pure PU with organosilane, (c) and (d) untreated PU.C40, and (e) and (f) PU.C40 with organosilane.

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Polímeros, 33(4), e20230040, 2023

Hydrophobic polyurethane foams reinforced with microcrystalline cellulose for oil spill clean up

Figure 8. Contact angles between the water droplet and the PU foam surface with and without coating and different cellulose contents.

droplet measurements on the silanized PU foam exhibited a slight decrease in contact angle compared to that at t = 0, probably owing to water migration into the compensated porous structure[29]. After 5 min, the foams without chemical treatment showed greater water migration into the foam.

According to the results, all organosilane-treated samples were hydrophobic. According to Cunha et al. (2010)[30], the hydrophobicity of a material can be evaluated using the contact angle of a drop of water deposited on its surface.

When the contact angle is greater than 90°, it is considered hydrophobic. The greater the contact angle, when considering water as the fluid, the greater the hydrophobic selectivity, preventing the foam adsorbing water during exposure to dynamic environments (water and oil)[29].

Figure 9 depicts the static sorption capacity of PU foams with varying cellulose contents coated with organosilane and the influence of various types of oils. The sorption capacity was associated with oil viscosity and foam density. First, PU foams with more viscous oils exhibited higher sorption capacities.

This phenomenon is primarily attributed to oil desorption after its removal from the system. More viscous oils have a more difficult time flowing out of the foam and require longer desorption times; thus, a greater amount of oil is retained inside the foam. Because the desorption time for all samples was set to 30 s, it was expected that the foams would have a higher sorption capacity for more viscous oils. The sorption process is directly influenced by the viscosity of the oil, and oils with high viscosity are more easily anchored and retained in porous polymer systems than oils with less viscosity.

Polímeros, 33(4), e20230040, 2023

Figure 9. Static sorption capacities of PU foams with different cellulose contents.

A comparative analysis of the samples revealed that as the cellulose content in the PU foams increased, the sorption capacity decreased for all oils. Because the morphologies of the cell structures of the foams were similar, this decrease in sorption capacity was directly associated with an increase in density with increasing cellulose content. Duong and Burford[8] investigated the effect of the sorption capacity of PU foams by evaluating the effect of the density of PU foams, viscosities of oils, and temperature on the sorption 7/9

Zimmermann, M. V. G., Junca, E., Almeida, M. K., Ponsoni, L. V. Zattera, A. J., Mari, T., & Santana, R. M. C. presence of cellulose increased the surface roughness of the PU and provided better adhesion and anchoring of the chemical treatment based on organosilane in the foam, as observed during the characterization stage. Nevertheless, the obtained samples exhibited hydrophobic and oleophilic properties.

Microcrystalline polymeric foams are an appealing and promising solution for the oil spill environmental problem, especially when compared to conventionally used inorganic fillers, which are relatively low in cost and density.

5. Author’s Contribution

Figure 10. Oil collection, in grams, of PU foams with varying cellulose content and coated with organosilane.

behavior of oils in different PU foams. They reported that the sorption capacity increased significantly with decreasing foam density owing to an increase in the number of open cells and cell morphology, and that this behavior was also affected by oil viscosity and temperature (test temperature).

Figure 10 depicts the sorption capacity in grams of oil per gram of sorbent. Because the increase in sample mass (constant volume) is directly related to the sorption capacity of the foam, as the foam density increases, the sorption capacity tends to decrease. Figure 9 depicts the amount of oil (g) collected per specimen with the same dimensions to evaluate the oil collection capacity per unit volume of sorbent.

According to the data in Figure 10, the recovered oil mass of the samples with each of the oils was observed to be collected by the samples; however, SAE 5W30 oil was the most abundant mass removed, followed by petroleum.

As previously stated, sorption capacity is associated with oil viscosity and foam density. Because the morphologies of the foam cell structures were similar, the sorption was directly associated with the increase in density of the foams with increasing cellulose content.

4. Conclusions PU foams reinforced with MCC chemically modified with organosilane were successfully developed as an absorbent system, as the contact angle test and sorption capacity of the samples could be visualized. Developing a mechanism that satisfies some of the requirements for oil-in-water removal.

Although the morphology of the cells in PU foams with different cellulose contents did not change significantly, the MCC content increased compressive strength, which can be attributed to an increase in density combined with stiffening of the polymer matrix. The results of the sorption capacity tests demonstrate that higher-density foams, such as PU foams, have the worst sorption capacity. Therefore, the presence of micro cellulose affected the decrease in oil sorption and collection capacity, which is related to the improvement in material density. Although the use of MCC in the composition is responsible for the higher density, which negatively affects the sorption capacity of the samples, the 8/9

• Conceptualization – Matheus Vinícius Gregory Zimmermann.

• Data curation – Matheus Vinícius Gregory Zimmermann.

• Formal analysis – Matheus Vinícius Gregory Zimmermann.

• Funding acquisition – Ademir José Zattera; Ruth Marlene Campomanes Santana.

• Investigation – Matheus Vinícius Gregory Zimmermann.

• Methodology – Matheus Vinícius Gregory Zimmermann.

• Project administration – Ademir José Zattera.

• Resources – Ademir José Zattera; Ruth Marlene Campomanes Santana.

• Software – Marina Kauling de Ameida; Lara Vasconcellos Ponsoni.

• Supervision – Ademir José Zattera; Ruth Marlene Campomanes Santana.

• Validation – Marina Kauling de Almeida; Lara Vasconcellos Ponsoni.

• Visualization – Eduardo Junca; Marina Kauling de Almeida; Lara Vasconcellos Ponsoni; Tiago Mari.

• Writing – original draft – Matheus Vinícius Gregory Zimmermann; Marina Kauling de Almeida; Lara Vasconcellos Ponsoni.

• Writing – review & editing – Eduardo Junca; Tiago Mari.

6. Acknowledgements Funding: This study was supported by the National Council for Scientific and Technological Development (CNPq).

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17. Shan, C. W., Idris, M. I., & Ghazali, M. I. (2012). Study of flexible polyurethane foams reinforced with coir fibres and tyre particles. International Journal of Applied Physics Polímeros, 33(4), e20230040, 2023

and Mathematics, 2(2), 123-123. http://dx.doi.org/10.7763/ IJAPM.2012.V2.67.

18. Zimmermann, M. V. G., Turella, T., Santana, R. M. C., & Zattera, A. J. (2014). Comparative study between poly(ethylene-covinyl acetate) – EVA expanded composites filled with banana fiber and wood flour. Materials Research, 17(6), 1535-1544. http://dx.doi.org/10.1590/1516-1439.269814.

19. Jonoobi, M., Harun, J., Mathew, A. P., Hussein, M. Z. B., & Oksman, K. (2010). Preparation of cellulose nanofibers with hydrophobic surface characteristics. Cellulose (London, England), 17(2), 299-307. http://dx.doi.org/10.1007/s10570-009-9387-9.

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25. Gwon, J. G., Lee, S. Y., Chun, S. J., Doh, G. H., & Kim, J. H. (2010). Effects of chemical treatments of hybrid fillers on the physical and thermal properties of wood plastic composite.

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Received: Aug. 02, 2023 Revised: Sept. 19, 2023 Accepted: Oct. 10, 2023 9/9

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20230026

Development of bacterial cellulose incorporated with essential oils for wound treatment Sandro Rogério Kumineck Junior1* , Victória Fonseca Silveira2 , Denise Abatti Kasper Silva1 , Michele Cristina Formolo Garcia3 , Giannini Pasiznick Apati3 , Andréa Lima dos Santos Schneider2,3 , Ana Paula Testa Pezzin1  and Flares Baratto-Filho1  1

Laboratório de Biotecnologia I, Programa de Pós-graduação em Engenharia de Processos, Universidade da Região de Joinville – UNIVILLE, Joinville, SC, Brasil 2 Laboratório de Biotecnologia I, Programa de Pós-graduação em Saúde e Meio Ambiente, Universidade da Região de Joinville – UNIVILLE, Santa Catarina, SC, Brasil 3 Laboratório de Biotecnologia I, Departamento de Engenharia Química, Universidade da Região de Joinville – UNIVILLE, Joinville, SC, Brasil *sandrorkjunior98@gmail.com

Abstract Bacterial cellulose (BC) is promising as a wound dressing because it is non- toxic and maintains moisture in the wound.

Although BC does not have antimicrobial activity, its structure allows the incorporation of antimicrobial compounds such as essential oils (EOs). This study aims to associate BC with rosemary, clove, eucalyptus, ginger, lavender and lemongrass EOs to obtain wound dressings. The Gas Chromatography-Mass Spectrometry and Fourier Transform Infrared Spectroscopy analyses showed characteristic compounds of EOs in the incorporated membranes. These compounds reduced the thermal stability of most samples due to their different degrees of volatility. The Scanning Electron Microscopy indicated that the EOs filled the membrane pores and coated the cellulose fibers. Samples incorporated with clove, ginger and lemongrass EOs inhibited Escherichia coli, Staphylococcus aureus and Candida albicans due to the presence of eugenol and citral. The results confirmed the incorporation method’s effectiveness, maintaining the composition and antimicrobial characteristics of the EOs. Keywords: Bacterial cellulose, essential oils, incorporation, wound dressings.

How to cite: Kumineck Junior, S. R., Silveira, V. F., Silva, D. A. K., Garcia, M. C. F., Apati, G. P., Schneider, A. L. S., Pezzin, A. P. T., & Baratto-Filho, F. (2023). Development of bacterial cellulose incorporated with essential oils for wound treatment. Polímeros: Ciência e Tecnologia, 33(4), e20230041.

1. Introduction Traditional methods of treating chronic wounds include dressings that can interfere with the healing process since constant dressing changes are made, causing pain and discomfort to the patient and delaying tissue reconstitution[1].

As an alternative to traditional dressings, a new generation of functional dressings has been developed seeking to prevent infections and improve wound healing, with properties such as maintaining wound moisture, removing exudates and antimicrobial control. In that regard, biopolymer-based dressings may be a good choice for treating these wounds[1,2].

Of the polymers used for this purpose, bacterial cellulose (BC) stands out because it has characteristics that meet the requirements of an ideal dressing. BC is synthesized by bacteria, such as those of the genus Komagataeibacter, is biodegradable, has high purity, high mechanical resistance, biocompatibility and has a reticulated structure that serves as a barrier against pathogenic microorganisms. BC has a structure similar to the skin’s extracellular matrix, creating and maintaining a humid environment for the wound due to its high hydrophilicity and also serving as a barrier against UV

Polímeros, 33(4), e20230041, 2023

radiation[3-5]. However, BC alone cannot inhibit the growth of pathogenic microorganisms, which reduces its effectiveness as a dressing for contaminated wounds. Nonetheless, antimicrobial agents can be incorporated into its structure to improve its biological properties. In this sense, essential oils (EOs) become a good option for this purpose, as they have several applications in the pharmaceutical industry and medicine due to their antimicrobial, antioxidant, and anti-inflammatory properties, among others, arising from the presence of bioactive compounds, such as phenols and terpenes, in its structure. In addition, EOs are advantageous over synthetic antimicrobial agents because they are widely available natural compounds with low toxicity[6–8], making the material promising for application in tissue regeneration.

In that regard, some EOs that can be used for the production of biocomposites include rosemary (REO), clove (CEO), eucalyptus (EEO), ginger (GEO), lavender (LEO) and lemongrass (LGEO)[8-12] because, in addition to their antimicrobial properties, they stimulate tissue regeneration and exert a healing effect on individual organs and systems[13].

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

Kumineck Junior, S. R., Silveira, V. F., Silva, D. A. K., Garcia, M. C. F., Apati, G. P., Schneider, A. L. S., Pezzin, A. P. T., & Baratto-Filho, F. In this context, the present work aims to associate BC with these EOs to develop a material for use in the biomedical area as a dressing with a high healing capacity.

2. Materials and Methods 2.1 Bacterial cellulose biosynthesis BC membranes were synthesized by the bacteria Komagataeibacter hansenii (ATCC 23769) in a culture medium adapted from Hestrin and Schramm[14]. This step was carried out using 50 mL ®Falcon tubes with 20 mL of culture medium, incubated at 30 °C in static condition for 12 days. Then, the BCs were treated with a 0.1 M NaOH solution at 80 °C for 1 h to remove bacteria. Subsequently, the membranes were washed with distilled water repeatedly until the pH of the washing water was neutralized[15]. Finally, the BC membranes were sterilized and submitted to the incorporation processes with the EOs and, subsequently, to the analysis of incorporated EO content, Total Phenolic Concentration (TPC), High Resolution Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR) and antimicrobial activity.

2.2 Incorporation of essential oils The EOs were purchased from the company Phytoterapica (Solua Comercial LTDA). According to the manufacturer, all EOs were obtained by steam distillation. Following the methodology adapted from Albuquerque[16], BC membranes were immersed in 150 mL of ethanol at 60 °C for 10 min.

Afterward, each BC was immersed in a solution containing 3.0 g of EO in 20 mL of ethanol and heated at 60 °C until the solution evaporated. Finally, the BCs incorporated with the EOs were lyophilized and stored for analysis.

2.3 Incorporated essential oil content The composition of EOs and the actual amounts of EOs incorporated into BCs were determined by Gas Chromatography-Mass Spectrometry (GC-MS). Each sample was immersed in 20 mL of dichloromethane for 24 h to extract the EOs[17], while pure EOs were diluted 1:100 with dichloromethane. The analysis was conducted in Agilent GC:7890A, MS:5975C equipment, and the injection volume was 1 µL in Split-Splitless mode. The column was HP- 5ms (30 m x 250 µm x 0.25 µm). The carrier gas was helium with a flow rate of 1.2 mL/min; the injector temperature was 280 °C. The initial oven temperature was 50 °C with an isotherm of 2 min, then increased to 300 °C at 10 °C/min and maintained at that temperature for 5 min. The interface temperature was 300 °C, the ion source temperature was 230 °C, and the electron impact ionization was 70 eV. Mass spectra were analyzed in SCAN mode.

2.4 Total phenolic content (TPC) Phenolic compounds are involved with the functional properties of herbal medicines[18]. TPC was evaluated in EOs before and after incorporation into BC membranes by the turbidimetry technique using the Folin-Ciocalteau reagent adapted from Waterhouse[19]. The TPC was expressed in 2/10

mg of gallic acid equivalents (GAE) per g of dry sample, determined by the equation of the straight line of the calibration curve of gallic acid (0.05-0.5 mg/mL).

2.5 Structural characterizations The characterization of the functional groups of the EOs, the BC and the incorporated BCs was carried out

by FTIR in Perkin Elmer Frontier equipment. 32 scans were performed per sample, from 650 to 4000 cm-1, with a resolution of 2 cm-1, in attenuated total reflectance (ATR) mode. To evaluate the influence of the addition of the EOs on the thermal stability of the BC, TGA was used, conducted in TGA-Q50 equipment (TA Instruments), where the samples were heated from 25 to 1000 ºC at 10 ºC/min, under an inert atmosphere (N2). The samples were observed in SEM in a JEOL equipment, model JSM-6701F. The samples were coated with gold, and the analysis was conducted with 5 kV of accelerating voltage.

2.6 Antimicrobial activity The incorporated EOs and BCs had their inhibitory capacities evaluated against Candida albicans (ATCC 10231), Escherichia coli (ATCC 8739) and Staphylococcus aureus (ATCC 6538) by the disc diffusion test adapted from Kirby & Bauer (1966)[20]. A statistical analysis of the inhibition zones was performed using the Tukey’s Method with 95% confidence.

3. Results and Discussions 3.1 Incorporation of essential oils Images of BC membranes incorporated with REO (BC/R), CEO (BC/C), EEO (BC/E), GEO (BC/G), LEO (BC/L) and LGEO (BC/LG) are shown in Figure 1. All samples had a sticky appearance and characteristic aromas and colors of each oil.

3.2 Incorporated essential oil content The main components of EOs detected by GC-MS in the samples are presented in Table 1. The compound with the highest concentration in REO and EEO was eucalyptol, corroborated by the literature[21,22]. The concentrations in ppm of the BC/R and BC/E compounds were low concerning the other samples, which may be due to the greater volatilization of these EOs and their components during incorporation into the BC. Moreover, camphor and α-pinene were identified for REO and limonene for EEO. For CEO, eugenol, the major compound of clove[23], and β-caryophyllene were identified. The incorporated sample maintained a high concentration of eugenol; however, β-caryophyllene was not identified. The GEO showed the greatest variety in its composition, where β-caryophyllene, neral and geranial (citral) were identified with the highest percentage, in addition to ar-curcumene, zingiberene and β-sesquiphelandrene, corroborated by the literature[24,25]. The compounds with the highest concentrations in BC/G were ar-curcumene and β-sesquiphelandrene, possibly due to greater volatilization of the other compounds during incorporation. LEO and LGEO presented two major compounds each: linalool and linalyl Polímeros, 33(4), e20230041, 2023

Development of bacterial cellulose incorporated with essential oils for wound treatment

Figure 1. Physical aspects of (a) BC, (b) BC/R, (c) BC/C, (d) BC/E, (e) BC/G, (f) BC/L and (g) BC/LG.

Table 1. Main components of EOs detected by GC-MS. Components Eucalyptol Camphor α-pinene Eugenol β-caryophyllene Eucalyptol Limonene Ar-curcumene Zingiberene β-sesquiphelandrene Neral Geranial β- caryophyllene Linalool Linalyl acetate Neral Geranial

Sample REO

CEO EEO GEO

LEO LGEO

Concentration (%) 72.222 13.366 4.105 86.809 11.397 89.303 8.259 2.215 3.651 1.484 6.882 9.536 10.709 45.298 35.844 30.292 41.572

Sample BC/R

BC/C BC/E BC/G

BC/L BC/LG

Concentration (ppm) 4.640 258.133 6.164 76.860 nd 4.220 4.120 364.440 102.840 232.440 117.360 151.200 93.240 126.880 126.980 60.360 85.680

nd = not detected.

acetate, and neral and geranial, respectively, which agree with the literature[26,27]. The BC/LG sample kept geranial as the compound with the highest concentration, and BC/L had a very close concentration between its two compounds, suggesting a greater volatilization of linalool. All tested EOs showed chemical compositions similar to those found in the literature but with variations in the concentration of the compounds. The chemical composition of essential oils is quite variable, as it depends on the EOs extraction method and time, type and concentration of solvents, the species involved, the climatic conditions and the soil where the plant was grown, among others[28,29].

3.3 Total phenolic content The TPC results determined by the turbidimetry technique using the Folin-Ciocalteau reagent are presented in Table 2.

Polímeros, 33(4), e20230041, 2023

Table 2. Total phenolic content of the samples.

Sample TPC (mg GAE/g EO) Sample TPC (mg GAE/g EO) BC/R REO 0.093 ± 0.007e, f 0.088 ± 0.006e, f BC/C CEO 5.656 ± 0.083a 2.316 ± 0.021b BC/E EEO 0.083 ± 0.028e, f 0.033 ± 0.002e, f BC/G GEO 0.758 ± 0.104c 0.277 ± 0.016d BC/L LEO 0.142 ± 0.036d, e 0.002 ± 0.001f BC/LG LGEO 0.639 ± 0.077c 0.147 ± 0.013d, e Different letters indicate differences in columns (p ≤ 0.05).

The CEO has the highest concentration of total phenolics among the tested EOs due to the high percentage of eugenol in its composition. GEO and LGEO presented values close to each other. The other EOs had low TPC values, emphasizing REO 3/10

Kumineck Junior, S. R., Silveira, V. F., Silva, D. A. K., Garcia, M. C. F., Apati, G. P., Schneider, A. L. S., Pezzin, A. P. T., & Baratto-Filho, F. and EEO, with the lowest TPC among the selected EOs. There was a significant decrease in the TPC of the incorporated BCs, which may be related to the volatilization of these components at 60 °C in the incorporation step and in the lyophilization step, related to the operating pressure and processing time during the process since a decrease in the drying chamber pressure reduces the lyophilization time, but increases the release of volatile compounds[30]. The BC/L sample stands out, which had a significant decrease in TPC, being the sample with the lowest observed value. The TPC analysis includes phenolic acids, flavonoids, isoflavonoids, lignans, stilbenes and other polyphenols. The variation in TPC values obtained reflects the diversity of phenolic compounds and their ability to reduce the Folin-Ciocalteau reagent. The differences observed between the results of the work and those obtained in the literature are justified due to the factors that influence the composition of the EOs, as discussed in the previous item[28,31].

3.4 Structural characterizations 3.4.1 Fourier transform infrared spectroscopy (FTIR) The FTIR spectra and the main bands obtained from the samples of BC, EOs, and incorporated BCs are presented in Figure 2.

The BC sample showed high-intensity bands at 3344 cm-1, attributed to the axial stretching of hydroxyl groups present in organic compounds[32]. Other bands referring to the presence of OH groups were observed at 1205 and 664 cm-1, referring to in-plane binding and out-of-plane angular deformation, respectively[3]. Bands referring to the C-H bonds of methyl groups were observed at 2896 and 895 cm-1 due to stretching and angular deformation, respectively[33]. Furthermore, several bands attributed to the stretching of C-O groups were observed, such as those at 1336, 1161, 1055 and 1032 cm1[33-35] . Moreover, the band at 1641 cm-1 stands out, which, in the case of BC, refers to the angular deformation of water, demonstrating its hydrophilicity[3]. In the incorporated samples, several bands related to EOs appeared, such as the C-H stretching band in vinyl groups at 3088 cm-1, attributed to the presence of linalool and linalyl acetate in the BC/L sample[36,37]; around 1735 cm-1, referring to the stretching of C=O groups for BC/R, BC/L and BC/LG samples, derived from camphor, linalyl acetate and citral (neral and geranial), respectively[37-39]; around 1675 cm-1 for BC/G and BC/LG, attributed to citral[40]. Bands referring to the eugenol of the BC/C sample were observed at 3515 and 1511 cm-1, attributed to the stretching of O-H bound to benzene and stretching of C=C of the aromatic ring, respectively[41,42].

Bands were observed at 985 cm-1, referring to out- of-plane symmetric deformation of CH2, which, in the case of samples incorporated with rosemary and eucalyptus, can be attributed to the presence of eucalyptol[38].

3.4.2 Thermogravimetric analysis (TGA)

Figure 2. FTIR spectra of samples: (a) comparison between BC and samples incorporated with rosemary, clove and eucalyptus and (b) comparison between BC and samples incorporated with ginger, lavender and lemongrass.

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Figure 3 shows the TG and DTG curves of the samples, while Table 3 shows the thermal events of the sample obtained from these curves.

The samples showed three stages of thermal degradation.

Pure BC obtained a thermal degradation profile characteristic of this material, where cellulose degradation occurred at a maximum degradation temperature (TPEAK 2) of 332 °C[43].

The BC/R had a greater mass loss in the second stage of thermal degradation, suggesting that the REO decomposition may be co- occurring with the BC. Furthermore, there was an increase of 69 °C in the TPEAK 2 compared to the BC, demonstrating an increase in the thermal stability of the membranes, suggesting a better interaction between REO compounds and BC. BC/C showed the most significant change in the thermal degradation profile compared to pure BC. A greater mass loss (84.39%) occurred in the first degradation stage, attributed to the volatilization of water, ethanol and eugenol, CEO’s major component, which occurs between 100 and 270 °C and may represent a higher percentage by mass of the sample[44]. The BC/G and BC/ LG samples showed a profile similar to that of BC/C, with the most significant mass losses occurring in the first stage of degradation, corresponding to the evaporation of water, ethanol, and volatile components of the EOs, such as citral, present in both EOs and cellulose degradation[40,45]. BC/E and BC/L showed similar thermal degradation profiles; however, the greatest mass loss of both samples occurred in the third stage of degradation, demonstrating that the degradation of cellulose and carbonaceous residues occurred during all stages. Notably, the phenolic compounds of the EOs have different degrees of volatility, causing a decrease in thermal Polímeros, 33(4), e20230041, 2023

Development of bacterial cellulose incorporated with essential oils for wound treatment

Figure 3. Curves (a) TG and (b) DTG of the samples.

Table 3. Sample thermal events obtained from the curves TG/DTG. Sample BC BC/R BC/C BC/E BC/G BC/L BC/LG

M1 (%) 4.48 3.13 84.39 26.37 71.81 19.37 51.42

TPEAK 1 (°C) 56 115 159 155 170 156 153

M2 (%) 74.14 95.46 4.01 30.19 16.21 28.66 22.01

stability. Thus, it is possible that the greater mass losses in the last stage of most samples, compared to the BC, may be due to the losses of these various compounds under high temperatures by evaporation and chemical decomposition[46].

3.4.3 High-resolution electron microscopy (SEM) The morphologies of pure BC and incorporated BCs were observed by SEM (Figure 4).

The micrograph of pure BC (Figure 4a) shows the typical structure of this material, consisting of tangled nano and microfibrils arranged randomly and with pores[47,48].

The BC/R (Figure 4b) presented a more homogeneous and smooth surface, demonstrating that the EO filled the membrane pores. The morphology shows some points with roughness, particulate matter, and REO droplets on the membrane surface.

Similar morphology to that of BC/R was observed for samples of BC/G (Figure 4e), with regions of greater roughness and some reliefs, and BC/L (Figure 4f), where fibers can be seen at different points. BC/C (Figure 4c) and BC/LG (Figure 4g) samples maintained the tangled fiber structure of pure BC, however, with greater thickness and roughness. In this case, the EOs might have coated the BC fibers. Finally, the BC/E (Figure 4d) presented a region resembling the BC/R, BC/G and BC/L samples with a homogeneous surface; however, it also has a region with greater roughness. These two regions are separated by an interface with irregularities, which may be related to the difference in BC membrane thickness in these regions.

The interaction between BC and added materials can occur Polímeros, 33(4), e20230041, 2023

TPEAK 2 (°C) 332 401 296 353 296 355 282

M3 (%) 9.15 0.92 10.68 42.79 11.49 51.37 25.21

TPEAK 3 (°C) 594 560 437 423 471 417 424

Residue (%) 11.86 0.43 0.89 0.40 0.49 0.44 1.40

through adherence (physical form) or by the hydrogen bonds between the hydroxyls of the BC with the added materials (chemical form)[49]. The interaction between hydroxyl groups causes a decrease in porosity and roughness[50]. This behavior was observed for BC/L, where it is possible to assume that there was an interaction between the linalool hydroxyl and the BC hydroxyls. The same was not observed for BC/C, where the interaction between BC and eugenol hydroxyl maintained the fibrillar morphology of the sample. The other samples do not have hydroxyls in the structure of their main components; in this case, it is assumed that the interaction between the BC and the EOs occurred by adherence.

3.5 Antimicrobial activity Figure 5 shows the disc diffusion test plates with the inhibition zones formed by the samples of REO (R), CEO (C), EEO (E), GEO (G), LEO (L) and LGEO (LG) at 15%; and by BC samples incorporated with their respective EOs (BC/R, BC/C, BC/E, BC/G, BC/L and BC/LG) against C. albicans, E. coli and S. aureus, while the diameters of the inhibition zones of the samples with the statistical analysis are shown in Figure 6. Jiang et al.[51] demonstrated the antimicrobial activity of REO from Rosmarinus officinalis against C. albicans, E. coli and S. aureus. However, it is noteworthy that this same EO, when incorporated into BC (BC/R), presented a zone of inhibition with an average diameter of 8.67 mm against S. aureus (Figure 5c). These results suggest lower absorption of EO by the filter paper used in the test concerning the amount absorbed by BC, in addition to insufficient concentration to inhibit E. coli and C. albicans.

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Kumineck Junior, S. R., Silveira, V. F., Silva, D. A. K., Garcia, M. C. F., Apati, G. P., Schneider, A. L. S., Pezzin, A. P. T., & Baratto-Filho, F.

Figure 4. SEM micrographs (a) BC, (b) BC/R, (c) BC/C, (d) BC/E, (e) BC/G, (f) BC/L and (g) BC/LG.

Figure 5. Disc diffusion test of the samples for (a) C. albicans, (b) E. coli and (c) S. aureus.

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Development of bacterial cellulose incorporated with essential oils for wound treatment

Figure 6. Diameters of inhibition zones (n = 3). The letters above the bars correspond to the statistical analysis by Tukey’s Method with 95% confidence.

The literature[52-54] demonstrates the antimicrobial activity of EEO and LEO against C. albicans, E. coli and S. aureus.

However, in this experiment, the samples showed irregular inhibition zones for E. coli and S. aureus, and there was no inhibition for C. albicans (Figure 5), which may be due to the low concentration of EO (15%), which was not enough to inhibit the yeast. Conversely, the BC/E sample had inhibition zones against all test microorganisms. The BC/L sample maintained antimicrobial activity against E. coli but with a decrease in the inhibition zone from approximately 14 mm (LEO on filter paper) to 7.25 mm (BC/L). The BC/R and BC/E samples showed a similar concentration of eucalyptol in their composition (item 3.2); however, the antimicrobial activities were different, which may be related to the different morphologies of these samples (item 3.4.3). In this case, the roughness of the BC/E may have favored the release of EEO constituents, causing greater inhibition of the test microorganisms. The same did not occur with BC/R, which had a smoother surface and filled pores, which may have hindered the release of antimicrobial compounds. On the other hand, CEO, GEO and LGEO showed inhibitory effects for all test microorganisms. With few exceptions (Figure 6), the membranes incorporated with these EOs had a slight decrease in the average diameter of the inhibition zones, suggesting minor incorporation or less diffusion of the microbial agents in these incorporated BCs. The literature proves the inhibitory action of these oils against C. albicans, E. coli and S. aureus[55-58]. The components of EOs, such as phenols and terpenes presented in GC-MS analysis, have hydroxyl groups that affect the cells of microorganisms by several mechanisms, which include disturbance of the enzymatic system, damage to the genetic material of the microorganism and reactions with the phospholipid membrane, resulting in the release of cell constituents and consequent death of microorganisms[6,59]. Nonetheless, the antimicrobial activities of EO depend on their chemical composition, which depends on several other factors (item 3.2), and, together with the type of antimicrobial test used and the strains of microorganisms used, can generate different performances in the study and validation of antimicrobial activity[60]. These factors explain the low performance of REO, EEO and LEO. However, the antimicrobial activity results of the samples were positive and demonstrated that the incorporation of EOs into the BC structure was effective, maintaining its antimicrobial characteristics in most cases.

Polímeros, 33(4), e20230041, 2023

The results obtained for the antimicrobial test are related to the results of the TPC analysis since the EOs that presented the highest TPC values had the greatest antimicrobial activity.

In this case, samples with CEO showed higher TPC due to the presence of eugenol in its composition. However, the best result observed for antimicrobial activity was for samples with LGEO, demonstrating the inhibition capacity of terpenes (citral and geranial, for example), which were not significantly detected in the TPC analysis but were confirmed by GC-MS analysis. Thus, considering the compounds identified in the GC-MS, it is possible to state that the compounds with the most significant antimicrobial power were eugenol, present in CEO, and citral, present in GEO and in greater quantity in LGEO.

4. Conclusions The EOs were successfully incorporated into the BC matrix, confirmed by GC-MS and FTIR analyses, which identified the compounds of the EOs in the incorporated BCs, and by SEM analysis, where it was possible to observe that CEO and LGEO coated the cellulose fibers, maintaining a morphology similar to the original. In contrast, the other EOs infiltrated the pores of the cellulose membrane, filling them and giving the samples a distinct morphology.

The compounds of the EOs caused a reduction in the thermal stability of the BC, but this does not affect its use as a wound dressing since this application will not expose the polymer to high temperatures. CEO, GEO and LGEO showed the best antimicrobial activities due to the presence of eugenol and citral mainly. These characteristics were maintained after incorporation into BC membranes, demonstrating a synergistic effect obtained from the incorporated BCs that combined the intrinsic characteristics of BC with the antimicrobial properties of EOs.

5. Author’s Contribution • Conceptualization – Sandro Rogério Kumineck Junior.

• Data curation – Sandro Rogério Kumineck Junior.

• Formal analysis – Sandro Rogério Kumineck Junior; Giannini Pasiznick Apati.

• Funding acquisition - Ana Paula Testa Pezzin.

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Kumineck Junior, S. R., Silveira, V. F., Silva, D. A. K., Garcia, M. C. F., Apati, G. P., Schneider, A. L. S., Pezzin, A. P. T., & Baratto-Filho, F. • Investigation – Sandro Rogério Kumineck Junior; Victória Fonseca Silveira.

• Methodology – Sandro Rogério Kumineck Junior; Ana Paula Testa Pezzin.

• Project administration – Ana Paula Testa Pezzin; Flares Baratto-Filho.

• Resources – Ana Paula Testa Pezzin; Flares BarattoFilho; Andréa Lima dos Santos Schneider.

• Software – NA. • Supervision – Ana Paula Testa Pezzin; Flares BarattoFilho.

• Validation – Sandro Rogério Kumineck Junior; Victória Fonseca Silveira; Ana Paula Testa Pezzin; Denise Abatti Kasper Silva.

• Visualization – Sandro Rogério Kumineck Junior; Ana Paula Testa Pezzin; Michele Cristina Formolo Garcia; Denise Abatti Kasper Silva.

• Writing – original draft – Sandro Rogério Kumineck Junior; Ana Paula Testa Pezzin.

• Writing – review & editing – Sandro Rogério Kumineck Junior; Ana Paula Testa Pezzin; Michele Cristina Formolo Garcia.

6. Acknowledgments The authors thanks FAPESC for the financial support and UNIVILLE for the project.

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39. Martins, W. S., Araújo, J. S. F., Feitosa, B. F., Oliveira, J. R., Kotzebue, L. R. V., Agostini, D. L. S., Oliveira, D. L. V., Mazzetto, S. E., Cavalcanti, M. T., & Silva, A. L. (2021). Lemongrass (Cymbopogon citratus DC. Stapf) essential oil microparticles: development, characterization, and antioxidant potential.

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41. Kopp, V. V. (2020). Óleo essencial de cravo encapsulado como microbicida natural (Dissertação de mestrado). Universidade Federal do Rio Grande do Sul, Porto Alegre.

42. Reyes Méndez, L. M. (2017). Produção, caracterização e estudo da estabilidade de filmes à base de gelatina e extrato de própolis vermelha enriquecidos com óleos essenciais de manjericão (Ocicum basilicum), cravo (Syzygium aromaticum) ou hortelã (Mentha piperita) (Tese de doutorado). Universidade de São Paulo, Pirassununga.

43. Lima, L. R., Santos, D. B., Santos, M. V., Barud, H. S., Henrique, M. A., Pasquini, D., Pecoraro, E., & Ribeiro, S. J. L. (2015). Nanocristais de celulose a partir de celulose bacteriana. Quimica Nova, 38(9), 1140-1147. http://dx.doi. org/10.5935/0100-4042.20150131.

44. Babaoglu, H. C., Bayrak, A., Ozdemir, N., & Ozgun, N. (2017). Encapsulation of clove essential oil in hydroxypropyl beta-cyclodextrin for characterization, controlled release, and antioxidant activity. Journal of Food Processing and Preservation, 41(5), e13202. http://dx.doi.org/10.1111/jfpp.13202.

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Kumineck Junior, S. R., Silveira, V. F., Silva, D. A. K., Garcia, M. C. F., Apati, G. P., Schneider, A. L. S., Pezzin, A. P. T., & Baratto-Filho, F. 45. Chandran, J., Nayana, N., Roshini, N., & Nisha, P. (2017).

Oxidative stability, thermal stability and acceptability of coconut oil flavored with essential oils from black pepper and ginger.

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In Vitro antimicrobial activity of essential oil of Thymus schimperi, Matricaria chamomilla, Eucalyptus globulus, and Rosmarinus officinalis. International Journal of Microbiology, 2016, 9545693. http://dx.doi.org/10.1155/2016/9545693.

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54. Noumi, E., Snoussi, M., Hajlaoui, H., Trabelsi, N., Ksouri, R., Valentin, E., & Bakhrouf, A. (2011). Chemical composition, antioxidant and antifungal potential of Melaleuca alternifolia (Tea Tree) and Eucalyptus globulus essential oils against oral Candida species. Journal of Medicinal Plants Research, 5(17), 4147-4156.

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56. Silvestri, J. D. F., Paroul, N., Czyewski, E., Lerin, L., Rotava, I., Cansian, R. L., Mossi, A., Toniazzo, G., Oliveira, D., & Treichel, H. (2010). Perfil da composição química e atividades antibacteriana e antioxidante do óleo essencial do cravo-da-índia (Eugenia caryophyllata Thunb.). Revista Ceres, 57(5), 589-594. http://dx.doi.org/10.1590/S0034-737X2010000500004.

57. Sharma, P. K., Singh, V., & Ali, M. (2016). Chemical composition and antimicrobial activity of fresh rhizome essential oil of Zingiber officinale roscoe. Pharmacognosy Journal, 8(3), 185-190. http://dx.doi.org/10.5530/pj.2016.3.3.

58. Ahmad, A., & Viljoen, A. (2015). The in vitro antimicrobial activity of Cymbopogon essential oil (lemon grass) and its interaction with silver ions. Phytomedicine, 22(6), 657-665. http:// dx.doi.org/10.1016/j.phymed.2015.04.002. PMid:26055131.

59. Amani, F., Sami, M., & Rezaei, A. (2021). Characterization and antibacterial activity of encapsulated rosemary essential oil within amylose nanostructures as a natural antimicrobial in food applications. Starch, 73(7-8), 2100021. http://dx.doi. org/10.1002/star.202100021.

60. Lima, L. L., Taketa, T. B., Beppu, M. M., Sousa, I. M. O., Foglio, M. A., & Moraes, Â. M. (2019). Coated electrospun bioactive wound dressings: mechanical properties and ability to control lesion microenvironment. Materials Science and Engineering C, 100, 493-504. http://dx.doi.org/10.1016/j. msec.2019.03.005. PMid:30948086.

Received: May 07, 2023 Revised: Oct. 01, 2023 Accepted: Oct. 04, 2023

Polímeros, 33(4), e20230041, 2023

ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20230045

In-situ polymerized Pebax /polydopamine blend membranes with high CO2/N2 selectivity ®

Ariele dos Santos Pirola1 , Paula Sacchelli Pacheco1 , Sônia Faria Zawadski2  and Daniel Eiras1*  Programa de Pós-graduação em Engenharia e Ciência dos Materiais – PIPE, Departamento de Engenharia Química, Universidade Federal do Paraná – UFPR, Curitiba, PR, Brasil 2 Programa de Pós-graduação em Química – PPGQ, Departamento de Química, Universidade Federal do Paraná – UFPR, Curitiba, PR, Brasil 1

*eiras@ufpr.br

Abstract The objective of this work was to produce Pebax®/polydopamine (PDA) blends and apply these blends to produce membranes for gas separation. Flat sheet membranes were tested for gas permeation, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), wide angle x-ray diffraction (WAXD), scanning electron microscopy (SEM) and fourier transformed infrared spectroscopy (FTIR). The results show an optimal concentration of dopamine hydrochloride that produces the best results (𝛼=100, P=114 Barrer). DSC and WAXD results indicate that polydopamine influences the crystallization of Pebax®, reducing the melting and crystallization temperatures of PA blocks and increasing the melting temperature of PEO blocks. The incorporation of PDA decreases gas permeability and increases gas selectivity. The decrease in permeability indicates that the presence of polydopamine reduces the diffusion coefficient of Pebax® by reducing the segmental mobility of PEO blocks and possibly the fraction free volume. Compared to the trade-off, Pebax®/PDA membranes surpasses the upperbound for CO2/N2 separation.

Keywords: Pebax, polydopamine (PDA), in-situ polymerization, CO2 separation, polymer blends.

How to cite: Pirola, A. S., Pacheco, P. S., Zawadski, S. F., & Eiras, D. (2023). In-situ polymerized Pebax®/polydopamine blend membranes with high CO2/N2 selectivity. Polímeros: Ciência e Tecnologia, 33(4), e20230043.

1. Introduction Gas separation membranes have been successfully applied for carbon capture processes to separate CO2 from N2[1]. For carbon capture, CO2/N2 can be separated by different mechanisms which include solution-diffusion polymer membranes[2], facilitated transport membranes[3], mixed matrix membranes[4] and membrane contactors[1].

The separation based on the solution-diffusion mechanism is strongly dependent on the polymer chemical structure, especially the flexibility of the polymer backbone and the fraction free volume of the membrane[5]. Although these membranes can be very efficient for different separations, their properties are subjected to the trade-off between permeability and selectivity which limits the applications for gas separation[5]. Facilitated transport membranes are produced using carriers that interact selectively and reversibly with the gases that need to be separated[6-8]. Carriers can be fixed or mobile and the transport mechanism depends on the type of carrier. Among different carriers, amine-based substances are very efficient to improve CO2 separation from different gas mixtures including natural gas and flue gas[6,7,9]. Amines react with CO2 to form either carbamate ions or bicarbonate ions, depending on the characteristics of the amine group, and facilitates the transport of CO2 which is transported by the carrier itself for mobile carriers or by a hoping mechanism for fixed carriers[10,11]. The type of ion that is formed depends on whether the amine is hindered or

Polímeros, 33(4), e20230043, 2023

unhindered. Unhindered amines form the stabler carbamate ion that reduces the amount of CO2 that can react with the carrier[10]. Hindered amines produce bicarbonate increasing the maximum amount of CO2 that reacts with the carrier[10-12].

Hindered amines are primary amines in which the amino group is attached to a tertiary carbon atom or a secondary amine in which the amino group is attached to at least one secondary or tertiary carbon[11]. Hindered amines have been studied as carriers in facilitated transport membranes with promising results that depend on the degree of hindrance[6,7,9,12]. Besides amines, other chemical groups have been used to improve the permeability and selectivity of polymer membranes towards CO2. Poly(ethylene oxide) groups have excellent interaction with CO2 which increases the permeability and selectivity of CO2 in gas separation membranes[13]. Among different polymers that contain PEO groups, Pebax® a copolymer of poly(ethylene) oxide and poly(amide) 6 has been studied in gas separation membrane applications. In Pebax®, the presence of PEO blocks increases CO2 permeability and ideal gas selectivity especially CO2/N2[14-19]. Several authors have modified Pebax® to improve gas permeability and selectivity. Polyethylene glycol[20], 2,4-toluylene diisocyanate, quaternary ammonium moieties[21], triglycerides[15] and ionic liquids[18,22,23] have been used to modify Pebax®. Another substance that can be used to improve the properties of polymer membranes in polydopamine. Polydopamine is a

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

Pirola, A. S., Pacheco, P. S., Zawadski, S. F., & Eiras, D. natural substance that can be synthesized by the oxidation of dopamine hydrochloride in alkaline conditions[24]. Although the chemical structure of polydopamine has been the subject of intense debate[24-26], there is evidence that polydopamine is a mixture of dihydroindole and indole moieties and open chain aminoethyl compounds[27] that are linked by covalent bonds. The analysis of polydopamine reaction was realized by introducing a dopamine hydrochloride solution in HPLC. The work identified the self-assembled (dopamine) 2 /DHI physical complexes during polydopamine preparation[27].

Other results have provided strong and direct evidence of supramolecular organization in both natural and synthetic eumelanins[28]. Using low voltage–high resolution transmission electron microscopy (LVHRTEM) it has been shown that sheets of protomolecules stack to form onion-like nanostructures.

The inter-sheet spacings within these structures are between 3.7 and 4.0 Å consistent with non-covalent 𝜋 – 𝜋 stacking in heteroaromatic systems[28]. Yu et al.[24] have identified a similar stacked structure by the pyrolysis of polydopamine.

According to the authors the distance between the nanodisks in the graphite-like structure of pyrolyzed polydopamine is 3.4 Å which is consistent with the work of Watt et al.

[27] . Liebscher et al.[23] have established that indole groups are linked by covalent bonds and that the supramolecular structure is the result of charge transfer interactions between polydopamine molecules. Because of the indole and amino groups, polydopamine can interact with CO2 and improve solubility selectivity of polymer membranes.

The indole groups of polydopamine can interact with CO2 via dipole–𝜋 interactions with great potential to improve CO2/N2 selectivity as shown by Xu et al.[28] and Chang et al.

[29] . Recent work shows that indole based microporous organic polymers have enhanced uptake for CO2 due to local dipole–𝜋 interactions with CO2/CH4 selectivity of 32 and CO2/N2 selectivity of 15. Chang et al.[29]. have used DFT to calculate the binding energy of CO2 with formamide and indole groups. The results show that both groups have high binding energies with CO2 and that amide groups can capture CO2 molecules that desorb from indole groups. In another work, Lee et al.[30] have calculated the binding energy of several multi-N-containing superbases and heteroaromatic ring systems with CO2. The results show that substances like melanine and indoles have stronger binding energies when compared to other substances. Polydopamine has been added to Pebax® to improve CO2/CH4 selectivity with good results that depend on polydopamine concentration[31]. C3H6/ N2 selectivity was also improved with the incorporation of polydopamine which was explained by the difference in the adsorption of each gas in polydopamine. The results have shown that polydopamine adsorbs C3H6 but not N2[32]. Both works incorporate polydopamine particles in Pebax® but only a few works have synthesized polydopamine inside a polymer solution. In most cases the objective of in-situ polymerization was to produce fluorescent polydopamine by conjugation with substances like amine- or thiol-containing organic species that eliminate the stacking interaction of PDA and prevents cyclization reactions and disrupts the stacking of PDA by reducing 𝜋-𝜋 interactions[33].

Considering the importance of CO2 capture, the advantages of both Pebax® and amine-based additives in CO2 separation and the limited adsorption of N2 by polydopamine (PDA), 2/9

this work applies an in-situ polymerization method to produce Pebax®/PDA blends and shows the properties of the membranes prepared from the blends. In-situ polymerization was performed using green solvents (ethanol/ water mixture). Gas permeability of Pebax® was reduced while CO2/N2 selectivity increased with the incorporation of polydopamine. The results suggest that there is an optimal concentration of dopamine hydrochloride that produces the membranes with better CO2/N2 selectivity and that the presence of polydopamine reduces the diffusion coefficient of Pebax® which reduces the permeability.

2. Background and Theory Polymer membranes can separate gases by two general mechanisms, solution diffusion and facilitated transport.

Solution-diffusion is characteristic of both glassy and rubbery materials that do not possess specific chemical groups that react with the gases to be separated[5]. Facilitated transport takes place when specific chemical groups react reversibly with one of the gases, usually CO2, and promote the selective transport of this gas through the membrane. There are two mechanisms for facilitated transport depending on the carrier.

For fixed carriers, the hopping mechanism takes place while for mobile carriers the carrier itself moves through the structure of the membrane transporting the gas molecule[7,8].

Polydopamine, which has indole and amine groups that are CO2-philic could result in facilitated transport.

The solution diffusion model states that the permeability (P) is the product of the solubility (S) and the diffusion coefficient (D) (Equation 1).

(1)

P = D.S

Based on Equation 1, the ideal selectivity is the product of the diffusion selectivity and the solubility selectivity (Equation 2). = α

PA DA S A = PB DB S B

(2)

For most materials, the diffusion selectivity that depends on chain flexibility and the relative sizes of the molecules is responsible for separation. It is also the easiest to control and modify. Solubility selectivity can be improved by the incorporation of specific chemical groups that interact selectively with the gas molecules that form the mixture to be separated but very often these groups can change the flexibility and fraction free volume of the polymer and affects the diffusion coefficient.

3. Experimental Section 3.1 Materials Polyether-b-amide copolymer Pebax MH-1657® from Arkema Brazil was used as matrix to produce the membranes.

Ethanol PA (98.5%) was used as co-solvent with distilled water. Dopamine hydrochloride (MW=189,64 g/mol, 98%) from Sigma Aldrich and sodium hydroxide (97%) were used for polydopamine synthesis.

Polímeros, 33(4), e20230043, 2023

In-situ polymerized Pebax®/polydopamine blend membranes with high CO2/N2 selectivity 3.2 Synthesis of polydopamine nanoparticles Polydopamine nanoparticles were synthesized by dissolving dopamine hydrochloride (DA) in ethanol/water mixtures with different ratios, 70/30, 50/50 and 30/70 w/w.

After dissolution, a 0.1 mol.L-1 NaOH solution was added as the oxidant agent. The concentration of dopamine hydrochloride was fixed in 1 mg.mL-1 and NaOH/DA ratio was 2:3. The mixture was agitated for 24 h, and the nanoparticles were separated by centrifugation in a Edutec digital centrifuge. The nanoparticles were washed with distilled water, centrifuged, and dried in a Labstore convection oven at 100 °C for 24 h.

3.3 In-situ polymerization The in-situ polymerization method was performed by preparing Pebax solutions different ethanol/water mixtures (70/30, 50/50 and 30/70) and heating at 80 oC for 2 h under reflux and N2 stream. After complete dissolution of Pebax®, dopamine hydrochloride and the sodium hydroxide solution were added to the Pebax® solution and stirred for 24 h with an IKA C-MAG HS7 magnetic stirrer. Three concentrations of dopamine hydrochloride were used 0.5, 1.0 and 1.5 mg.mL-1 and a NaOH/DA ratio of 2:3. The samples were named Pebax®/ PDAx,y where x represents the dopamine hydrochloride concentration and y represents ethanol concentration in solvent mixture (70, 50, 30).

3.4 Membrane preparation Pebax® and Pebax®/PDA membranes were prepared by solvent evaporation. After the dissolution of Pebax®, the solution was poured in Teflon petri dishes and the membrane was formed by evaporation of the solvent mixture in a vacuum oven at 50 oC for 24 h. Pebax®/PDA membranes were prepared using the same conditions except for the fact that the solution was obtained direct from in-situ polymerization.

After membrane formation all membranes were heated for another 24 h at 30 oC to remove residual solvent. Membrane thicknesses were in the range of 70-80 𝜇m.

3.5 Characterization The characterization protocols used in the work are presented in detail in the Supplementary Material.

4. Results 4.1 Effect of solvent mixture on PDA morphology and particle size Polydopamine particles are prepared by the oxidation of dopamine hydrochloride in basic medium. The kinetics of the reaction is influenced by different process conditions including the properties of the solvents. Based on Hansen’s theory of solubility, PDA has more affinity for solvent mixtures with higher water content. Nevertheless, Pebax® membranes are usually produced using ethanol/water mixtures with higher ethanol content. To evaluate the effect of the solvent mixtures on PDA morphology, the particles were synthesized with different solvent mixtures.

Figure 2 (Supplementary Material) shows the morphology of polydopamine nanoparticles synthesized using different Polímeros, 33(4), e20230043, 2023

ethanol/water ratios. The results indicate that the ratio between ethanol and water influences the particle size. The diameter decreases with the increase of water content that increases the solvent power of the solvent mixture. Yue et al.[33] have attributed the increase in polydopamine particle size to the decrease in nucleation rate due to the increase in ethanol concentration. Table 1 (Supplementary Material) shows the average diameter.

The results suggest that using higher water concentration favors the formation of smaller particles. Moreover, washing PDA particles to remove unreacted substances influences the particle size and shape.

4.2 Identification of PDA nanoparticles in Pebax®/PDA blends Pebax®/PDA membranes were prepared by in-situ polymerization of PDA inside Pebax® solutions. As shown in Figure 3 (Supplementary Material), the characterization of the membranes by FTIR did not help to identify the presence of PDA. FTIR spectra for Pebax® show the presence of the band at 3298 cm-1 that represents -N-H, 1729 cm-1 related to O-C=O, 1638 cm-1 stretching vibration of C=O, 1537 cm-1 bending vibration of -NH- and 1096 cm-1 symmetric vibrations of C-O-C. Some authors attribute peaks at 844 cm-1 to OH stretching vibrations. For PDA, the characteristic bands are 3396 cm-1 for N-H and O-H stretching vibrations, 2914 cm-1 for C-H stretching vibration, 1645,2 cm-1 for N-H scissoring bending stretching, 1502 cm-1 C=C stretching vibrations in benzene, 1276 cm-1 C-O-H stretching vibrations and 1026 cm-1 for C-N stretching[34-37].

Comparing Pebax® with Pebax®/PDA blends it is possible to observe small changes in the format and width of some bands. The band at 1262 cm-1 becomes wider for CDA = 1.5 mg.mL-1. The band at 844 cm-1 is also changed for CDA = 1.5 mg.mL-1. The differences in FTIR spectra are minimal which could be explained by the fact that the characteristic bands for PDA coincide with the bands of Pebax®. Moreover, as reported by other authors PDA can react with Pebax® to form a single polymer which would explain why FTIR results do not show any specific band of PDA. Visual inspection of the membranes could be considered an indicative of the formation of PDA during in-situ polymerization. The formation of PDA particles usually results in a dark solution. During in-situ polymerization, Pebax®/PDA mixtures became dark over time, and the final membranes were darker than neat Pebax®.

Figure 4 (Supplementary Material) shows the appearance of Pebax® and Pebax®/PDA membranes. The images show that Pebax® membranes are white and Pebax®/PDA membranes are dark. The membranes become darker as the concentration of dopamine hydrochloride increases. The fact that Pebax®/ PDA membranes are dark indicate that polydopamine was formed inside de membranes.

4.3 Morphology of Pebax®/PDA membranes SEM analyses were conducted to determine the effect of PDA on the morphology of Pebax®. The morphology of polymer membranes is direct related to composition and crystallization kinetics. Figures 5 and 6 (Supplementary Material) show the morphology of neat Pebax® membranes 3/9

Pirola, A. S., Pacheco, P. S., Zawadski, S. F., & Eiras, D. and Pebax®/PDA membranes, respectively. The morphology of Pebax® is not affected by the solvent mixture although roughness can be observed in Figure 5c which could be explained by the fracture protocol. With the addition of PDA, the morphology chances significantly and seems to depend on the solvent mixture. As shown in Figures 6a and 6b (Supplementary Material), the sample prepared with the 70/30 solvent mixture has layers with some orientation on the surface of the membrane. For the 50/50 solvent mixture a very smooth morphology with a few small pores was observed and for the 30/70 mixture the morphology is smooth and dense with some dark spots on the surface.

The results indicate that the incorporation of PDA influences the final morphology of Pebax® (Figure 6) (Supplementary Material). Liu et al.[38] have produce Pebax/PDA mixed matrix membranes by incorporating PDA microspheres in Pebax. The morphology of the membranes was different from the morphology observed in this work. The membranes produced by Liu et al.[38] shows a rough fracture surface and indications of agglomeration of PDA particles at high PDA loadings (10 wt%). Moreover, the layered structure observed in Figures 6a and 6b (Supplementary Material) was not observed in Liu et al.’s[39] work. Furthermore, Figure 6 shows that Pebax and PDA form a homogenous morphology which favors gas transport and separation. According to Wu and Chung[39] and Nilouyal et al.[40], membranes with a homogenous supramolecular structure prepared by the incorporation of specific organic compounds in PBI result in gas permeability and selectivity that surpasses the upperbound and the properties of ordinary polymer membranes.

4.4 Wide angle X-ray diffraction Figure 7 shows XRD curves for Pebax®/PDA membranes.

Pebax® has two characteristic peaks at 2𝜃=20.5 o (d= 4.3 Å) and 2𝜃=24 o (d= 3.7 Å) that are related to the crystalline structure of PA groups[41-43]. In Figure 7 (Supplementary Material) the second peak has high intensity while the former appears as a low intensity shoulder. For sample Pebax®/ PDA0,50 and Pebax®/PDA1,50 (Figure 7b) (Supplementary Material) both peaks have the same intensity, and both are broad. Increasing CDA makes the peak at 2𝜃=24 o more intense and narrower. The incorporation of PDA does not affect the peaks related to PA groups except for sample Pebax®/ PDA1.5,50. Moreover, for the samples Pebax®/PDAx,70, it is possible to observe a peak at 2𝜃=32 o (d= 2.8 Å) that could be associated with the PEO segments[42] indicating that PDA helps the crystallization of PEO blocks. The appearance of the peak at 2𝜃=32 o can be considered and indicative that the incorporation of PDA affects the distance between PEO segments which would increase intermolecular interactions and affect the flexibility of the polymer and the diffusion of gas molecules.

4.5 Thermal stability (TGA) Figure 8 (Supplementary Material) shows TGA thermograms of Pebax® and Pebax®/PDA membranes.

Pebax® has three transitions, the first with onset at 50 °C, the second at 683 K and the third at 873 K. The total weight loss of Pebax® is almost 100% at 973 K. PDA has three transitions at 348 K, 523 K and 773 K. The total weight loss of PDA at 1173 K is 60% which shows the high thermal 4/9

stability of PDA nanoparticles. Pebax®/PDA blends have a similar behavior than Pebax® with the same thermal transitions at 323 K, 683 K and 873 K. Compared to neat Pebax®, the blends have higher weight loss at 323 K and higher residual mass after 873 K. In immiscible polymer blends and mixed matrix membranes, TGA can indicate the presence of a second phase by a thermal transition in a different temperature compared to the new polymer.

The fact that Pebax®/PDA blends do not show additional thermal transitions when compared to Pebax® indicates that the blends form a homogenous structure confirming what was observed in SEM analysis. The absence of new thermal transitions can also be an indicative of the polymerization of PDA. As shown by Wu et al.[14] the incorporation of low molecular weight triglycerides influences the thermal stability of Pebax® with the appearance of new transitions at low temperatures.

4.6 Thermal properties and crystallization (DSC) Figure 9 (Supplementary Material) shows the results of DSC first heat for the membranes. The first heat shows the actual properties of the membranes. The second heat is performed in the materials that have been melted and crystallized from the melt and shows the influence of polydopamine in the crystallization process. From the results in Figure 9 (Supplementary Material), it is evident that the composition of the solvent mixture influences the crystallization of Pebax® and Pebax®/PDA blends. The decrease in ethanol concentration affects the width and height of PA melting peak and in the case of the sample prepared from 30 wt% ethanol mixture a new peak appears at low temperatures.

PDA has two effects in Figure 9 (Supplementary Material), it reduces melting temperature of PA blocks and increases the melting temperature of PEO blocks. It also reduces the height of the PA melting peak and in the specific case of the sample Pebax®/PDA1,70 a second melting peak for PA blocks appears at low temperatures. The other samples have shoulders in this temperature range but not a clear peak.

As shown in Tables 2, 3 and 4 (Supplementary Material) the incorporation of PDA reduces crystallization and melting temperature which indicates that PDA hinders PA segments crystallization and reduces the interactions between them.

This is evidenced by the decrease in PA crystallinity degree.

The influence of PDA on Pebax® thermal properties could be indicative of the interactions between PDA and the amide blocks which could hinder molecular mobility and affect crystallization. The influence of the incorporation of ionic liquids on Pebax® crystallization was studied by Bai et al.

[43] and could be an indicative of the effects of PDA on Pebax®. The results show that the incorporation of ionic liquid [bmim]PF6 on Pebax® reduces the crystallization temperature and broadens the melting peak. The study of non-isothermal crystallization kinetics revealed that the ionic liquid reduces the percentage of primary crystallinity but induces a secondary crystallization that produces a less ordered structure. Higher ionic liquid concentrations lead to an increase in crystallization temperature due to the higher molecular mobility of PEO groups. The results of second heating confirm the effect of PDA on the crystallization of Pebax®. The melting temperature of PEO blocks increases and the melting temperature of PA block decreases with the Polímeros, 33(4), e20230043, 2023

In-situ polymerized Pebax®/polydopamine blend membranes with high CO2/N2 selectivity presence of PDA. The most important difference is that the second melting peak of PA is absent which indicates that the effect of PDA in Pebax® depends on whether it is crystallized from solution or from the melt. The results indicate that the incorporation of PDA weakens the hydrogen bonding between amide blocks in Pebax® reducing the melting temperature.

It also decreases the crystallinity of Pebax® but increases the interactions between PEO blocks which is evidenced by the increase in melting temperature.

4.7 Transport properties and selectivity Gas permeability of polymer membranes is an important property for several separation processes such as carbon capture, natural gas, and biogas purification. The separation of CO2 from N2 is an important process for flue gas treatment and CO2 capture from air, while the separation of CO2 from CH4 is applicable for biogas and natural gas treatment.

As shown in Figures 10 and 11 (Supplementary Material), the influence of PDA depends on the concentration of dopamine hydrochloride (CDA). For N2 and CH4 the increase in CDA reduces the permeability for all gases but when CDA= 1.5 mg.mL-1 the permeability increases and is equal to the permeability of neat Pebax®. For CO2, the effect of CDA depends on the solvent mixture used to prepare the solutions. For ethanol concentration (CETHANOL) of 50% and 30 wt% the effect of CDA is similar to the effect on other gases except for the smaller increase in permeability when CDA= 1.5 mg.mL-1. For CETHANOL = 70 wt% CO2 permeability decreases systematically with the increase in CDA. In terms of selectivity, the results show that the best selectivities are obtained when CDA= 1.0 mg.mL-1. Moreover, the best solvent mixture is 70/30 ethanol/water. The greatest selectivity is 100 for CO2/N2 which represents an increase of 50% compared to Pebax®.

Polydopamine has been used to produce multilayer composite membranes for CO2 separation. Polydopamine membranes were grown on top of polysulfone supports.

The results show that increasing the thickness of polydopamine membrane decreases CO2 permeability and increases CO2/ N2 selectivity[44]. Polydopamine nanoparticles have been introduced in Pebax® to produce mixed matrix membranes for CO2 separation[32]. The results show that CO2 permeability and CO2/CH4 selectivity depend on PDA content. Both properties increase for low concentrations of polydopamine (up to 5%) but decrease for higher concentrations. Polydopamine has also been applied to prepare supported membranes for propylene/ nitrogen separation. Gas uptake shows that polydopamine does not absorb significant amounts of nitrogen which contributes to the membrane selectivity[33]. Dong et al.[45] have produced polydopamine submicrospheres of polydopamine (PDASS) and incorporated them in PIM-1. PDASS particles reduced the permeability of PIM-1 and increased the selectivity in a similar manner as observed for in-situ polymerized PDA in Pebax® of this work. The decrease in permeability was explained by the decrease in diffusion coefficient, due to interactions between PDASS and PIM-1, that surpassed the increase in solubility.

Compared to the upperbound (Figure 12 of Supplementary Material) the properties of the membrane Pebax®/ PDA1,70 surpasses the CO2/N2 upperbound limit for both Polímeros, 33(4), e20230043, 2023

pressures tested. The increase in pressure improves the properties of the membranes and favors CO2/N2 separation.

Compared to neat Pebax®, the sample Pebax®/PDA1,70 has a superior set of properties for CO2/N2 separation. For the other membranes, the incorporation of PDA reduces the ability of Pebax®to separate CO2 from N2.

5. Discussion Considering the high pressures applied, it is unlikely that the transport of gas molecules in Pebax/PDA membranes takes place by facilitated transport because the functional groups of polydopamine are probably saturated at 1 and 1.5 MPa. Based on the solution-diffusion mechanism, the permeability (P) is the product of the solubility (S) of gas molecules in the polymer and the diffusion coefficient (D) – Equation 1.

CO2 solubility is expected to increase with the incorporation of polydopamine due to strong interaction of indole groups and melanine with CO2 molecules. Moreover, indole and melanine groups do not interact with N2 and CH4 so the incorporation of PDA decreases their solubility in Pebax®.

Therefore, the incorporation of PDA should increase CO2 permeability and decrease CH4 and N2 permeabilities.

Furthermore, the ideal selectivity should increase due to the increase in solubility selectivity (Equations 2 and 3).

The decrease in N2 and CH4 permeability is consistent with the idea of reduced solubility but the decrease in CO2 permeability indicates that solubility is not the main effect on Pebax®/PDA membranes.

If the solubility is not the main effect influencing the permeability of Pebax®/PDA membranes, the results should be explained by the diffusion coefficient. The diffusion process depends on the fraction free volume, chain flexibility and polymer crystallinity. Overall, the crystallinity of Pebax® is reduced by the incorporation of PDA which should increase the diffusion coefficient and the permeability. Fraction free volume can be reduced by the presence of PDA between Pebax® polymer chains and chain flexibility can be reduced by the interactions between Pebax® and PDA. Although there is no evidence of crosslinking, it is plausible that PDA interacts with the amide blocks of Pebax® forming hydrogen bonding which would reduce chain flexibility and decrease the diffusion coefficient and gas permeability. Based on DSC results, the incorporation of PDA also increases the intermolecular interactions in PEO which reflects on the increase in the melting temperature. Based on the results, it is plausible to state that the decrease in gas permeability (especially CO2) is due to the influence of PDA in the diffusion coefficient that results from the interactions between Pebax® intermolecular forces and from the interactions between Pebax® and PDA. The decrease in fraction free volume can also explain the decrease in gas permeability.

The decrease in the concentration of ethanol in the solvent mixture (Cethanol) tends to reduce the permeability of all gases in the Pebax®/PDA membranes and increase all membrane selectivities except for CDA = 1.0 mg.mL-1. In this case, there is an optimal selectivity for Cethanol = 70%. Although the results indicate a close relation between these variables and the properties of the membranes, it is not possible to 5/9

Pirola, A. S., Pacheco, P. S., Zawadski, S. F., & Eiras, D. establish a direct structure-property relationship based on the results presented. The synthesis of PDA with different ethanol concentrations indicates that the decrease of Cethanol reduces particle size due to the increase in nucleation rate.

Moreover, the increase in CDA can influence the size and the interactions between PDA molecules which affects CT interactions of PDA and its stacked morphology. In-situ polymerization or conjugation has been used to control particle size and generate fluorescence of PDA. While the presence of radicals controls de size of PDA, conjugation reduces intra- and intermolecular coupling of PDA generating fluorescence. The greater the concentration of the conjugated polymer, the smallest is PDA particle, and the weakest is the interaction between PDA molecules.

Therefore, the effect of Cethanol and CDA could be related to particle size and intramolecular forces between PDA particles in Pebax®. Decreasing Cethanol will decrease particle size which favors the interactions between Pebax® and PDA. Increasing CDA could decrease the interactions between Pebax® and PDA because of the decrease of Pebax® concentration during in-situ polymerization. In summary, there seems to exist a suitable combination between Cethanol and CDA that results in the best properties. The effect of these two variables might result from their influence in particle size and intermolecular interactions of polydopamine that will influence the interactions between polydopamine and Pebax®. Figure 13 (Supplementary Material) illustrates a proposed effect that PDA could have in Pebax® and its properties. After in-situ polymerization, PDA molecules would interact with PA blocks and increase the distance between them which reflects in the decrease of melting temperature. Simultaneously, PEO blocks would be closer which increases the melting temperature. The presence of PDA could decrease in fraction free volume because PDA molecules occupies the space between PA blocks.

6. Conclusions Pebax®/polydopamine blend membranes were prepared by in-situ polymerization and the presence of polydopamine was determined by vision inspection of the membranes.

The presence of polydopamine reduces gas permeability for all gases compositions except for high CDA. Ideal gas selectivity depends on CDA and on the composition of the solvent mixture. An optimal selectivity was obtained for CDA= 1mg/mL. The results of DSC and XRD confirm that PDA affects the crystallization of Pebax® and creates a structure that has higher d-spacing which influences gas transport and separation. The morphology of the samples with higher selectivity is clearly different than the other membranes which supports the idea that PDA affects crystallization of Pebax®. The effect of PDA on membrane permeability and selectivity can be explained by a decrease in diffusion coefficient, due to the decrease in polymer flexibility and fraction free volume, that has more influence on gas permeability and selectivity than the increase in gas solubility that is expected especially for CO2. The results show that incorporation of polydopamine can be successfully applied to modify polymer membranes and improve their separation capacity.

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7. Author’s Contribution • Conceptualization – Ariele dos Santos Pirola; Daniel Eiras.

• Data curation – Daniel Eiras; Sônia Faria Zawadski.

• Formal analysis – Ariele dos Santos Pirola; Daniel Eiras.

• Funding acquisition – Daniel Eiras.

• Investigation – ​Ariele dos Santos Pirola; Daniel Eiras; Sônia Faria Zawadski; Paula Sacchelli Pacheco.

• Methodology – Ariele dos Santos Pirola; Paula Sacchelli Pacheco.

• Project administration – Daniel Eiras.

• Resources - Daniel Eiras; Sônia Faria Zawadski.

• Software – NA. • Supervision – Daniel Eiras.

• Validation – Daniel Eiras; Sônia Faria Zawadski.

• Visualization – NA. • Writing – original draft – ​Daniel Eiras.

• Writing – review & editing – Daniel Eiras; Sônia Faria Zawadski.

8. Acknowledgements The authors acknowledge the support of the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), by the financial support of this project under the grant 37759299168/CAPES-PRINT738088P, and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial support under the grants 420696/2018-0 and 440036/2019-4. Laboratório Multiusuários from the Chemical Engineering Department for the TGA analysis. Next Chemical for FTIR analysis

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Received: Jul. 10, 2023 Revised: Oct. 30, 2023 Accepted: Nov. 20, 2023

Polímeros, 33(4), e20230043, 2023

In-situ polymerized Pebax®/polydopamine blend membranes with high CO2/N2 selectivity

Supplementary Material Supplementary material accompanies this paper.

Table 1. Mean diameters of PDA nanoparticles as a function of methanol concentration and washing protocol.

Table 2. Thermal properties of Pebax® and Pebax®/PDA blends determined by DSC. 70% Table 3. Thermal properties of Pebax® and Pebax®/PDA blends determined by DSC. 50% Table 4. Thermal properties of Pebax® and Pebax®/PDA blends determined by DSC. 30% Figure 1. Schematic representation of the permeation cell used in this work. 1- Gas Cylinder; 2-Manometer; 3- Oven; 4- Gas reservoir; 5- Permeation cell; 6- Temperature Control; 7- Permeate; 8- Flowmeter; 9- Retentate.

Figure 2. Polydopamine nanoparticles synthesized with different water/ethanol concentrations (a) and (b) 30/70, (c) and (d) 50/50, (e) and (f) 70/30. And the effect of washing protocol on the morphology of the particles (a), (c) and (e) centrifuge, washing and drying; (b), (d) and (f) centrifuge and drying.

Figure 3. FTIR spectra of Pebax® and Pebax®/PDA membranes.

Figure 4. Pictures of Pebax® and Pebax®/PDA membranes.

Figure 5. Morphology of Pebax® membranes cross-section with different ethanol/water concentrations . (a) Pebax® 70/30, (b) Pebax® 50/50, (c) Pebax® 30/70.

Figure 6. Morphology of Pebax®/PDA membranes. Cross sections: (a) Pebax®/PDA1,70, (b) Pebax®/PDA1,50, (c) Pebax®/PDA1,30. Surfaces: (d) Pebax®/PDA1,70, (e) Pebax®/PDA1,50, (f) Pebax®/PDA1,30.

Figure 7. XRD diffractograms of Pebax® and Pebax®/PDA membranes. (a) Pebax®/PDAx,70, (b)Pebax®/PDAx,50, Pebax®/PDAx,30.

Figure 8. TGA thermograms of Pebax®, PDA and Pebax®/PDA blends.

Figure 9. DSC thermograms of Pebax®/PDA blends. First Heating. a) Pebax®/PDAx,70, b) Pebax®/PDAx,50 and c) Pebax®/PDAx,30 Figure 10. Gas permeability (upper graphic) and ideal selectivity (lower graphic) of Pebax®/PDA membranes at 1 MPa. 1 Barrer = 1010 cm3(STP).cm.cm-2.s-1.cmHg-1 = 7.518x105 m3(STP).m.m-2.s-1.MPa-1.

Figure 11. Gas permeability (upper graphic) and ideal selectivity (lower graphic) of Pebax®/PDA membranes at 1.5 MPa. 1 Barrer = 1010 cm3(STP).cm.cm-2.s-1.cmHg-1 = 7.518x105 m3(STP).m.m-2.s-1.MPa-1.

Figure 12. Pebax®/PDA properties compared to the Robeson’s upperbound at 1 and 1.5 MPa. a) Pebax®/PDAx,70, b) Pebax®/PDAx,50 and c) Pebax®/PDAx,30 Figure 13. Proposed effect of PDA molecules in fraction free volume, and interactions between Pebax® molecules.

This material is available as part of the online article from https://doi.org/10.1590/0104-1428.20230045

Polímeros, 33(4), e20230043, 2023

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ISSN 1678-5169 (Online)

https://doi.org/10.1590/0104-1428.20230068

Consumer perception of biodegradable packaging for food Ana Carolina Salgado de Oliveira1* , Michele Nayara Ribeiro1 , Julio Cesar Ugucioni2 , Roney Alves da Rocha1  and Soraia Vilela Borges1  Departamento de Ciência dos Alimentos, Universidade Federal de Lavras – UFLA, Lavras, MG, Brasil 2 Departamento de Física, Universidade Federal de Lavras – UFLA, Lavras, MG, Brasil

1

*anacarolengalimentos@gmail.com

Abstract Most of the discarded plastics originate mainly from food and beverage packaging, thus the consumer’s perception of biodegradable packaging must be understood. This study aimed to investigate the consumer perception of biodegradable packaging films made of pectin and whey protein isolate. An online questionnaire was conducted to assess the consumer responses. Results showed that the majority of consumers (77.3%) did not observe the biodegradability of the packaging during purchase, although biodegradable packaging can positively affect the purchase decision (71.9%). The acceptance, purchase intention, and preference are influenced by visual aspects, and the consumers preferred lighter and more transparent films, with less saturated colors. Consumers established correlations between color and transparency with film thickness and resistance, these correlations were not observed in the physical analysis of the film. In addition, a variety of applications were highlighted for the films produced, demonstrating the effectiveness of these materials for food and beverage packaging.

Keywords: application, cata, environmental awareness, preference ordering.

How to cite: Oliveira, A. C. S., Ribeiro, M. N., Ugucioni, J. C., Rocha. R. A., & Borges, S. V. (2023).

Consumer perception of biodegradable packaging for food. Polímeros: Ciência e Tecnologia, 33(4), e20230045. https://doi.org/10.1590/0104-1428.20230068

1. Introduction The world consumption of plastic is estimated at more than 700 million tons per year and can reach one billion tons in 2021[1,2]. Packaging materials account for most of the amount of non-biodegradable plastics of non-renewable origin, improperly discarded. Thus, there is a depletion of fossil materials with a substantial increase in the use of petroleum-based plastics[1-4]. These aspects have encouraged research on the development of plastic materials from ecologically favorable or “environmentally friendly” polymers[3-5].

Human beings’ multiple senses (touch, smell, hearing, sight, and taste) are used to experience and explore the environment and are interpreted by the brain[6]. The association between the stimuli, the attributes, or the sensory modalities is called crossmodal correspondences[7,8]. By incorporating intermodal correspondences to packages, they no longer have only the function of e. g. containing portions and protecting the product[9-11].

Consumers’ perception of food, beverages, and packaging has changed over time, mainly due to unlimited access to information. Fact-based, it is noticeable that consumers have been aware of the various environmental issues arising from the consumption behavior of society[12].

The growing environmental concern among consumers regarding food and beverages also includes packaging materials. Most consumers consider packaging as something integrated with food, being considered a residue after consumption. The concern about proper waste disposal has

Polímeros, 33(4), e20230045, 2023

influenced consumers, who have recognized the importance of adequate disposal of food and beverage packaging[13].

One of the ways to assess consumers’ perceptions is through a picture associated with online or offline questionnaires. Online questionnaires are advantageous because data collection takes place in short periods, with reduced cost for data collection due to the possibility of using a computer, smartphone, or tablet, in addition to enabling remote data storage and quick visualization[14,15].

In this sense, the study aimed to evaluate, through online questionnaires, the consumer’s perception of biodegradable packaging films made from pectin (Pec) and whey protein isolate (WPI) by extrusion/thermo-compression.

2. Materials and Methods This study was approved by the Ethics Committee of the Federal University of Lavras (CAAE: 40665320.4.0000.5148).

2.1 Material Pectin with 75.7% degree of esterification was supplied

by Dinâmica Química Contemporânea (Indaiatuba, São Paulo, Brazil). WPI with 90% protein was purchased from Hilmar Ingredients (Turlock, USA). Stearic acid (95% purity) was purchased from Exodus Científica (São Paulo, São Paulo, Brazil). Glycerol (99.5% purity) and citric acid (99.7% purity) were purchased from Sigma Aldrich (São Paulo, São Paulo, Brazil).

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Oliveira, A. C. S., Ribeiro, M. N., Ugucioni, J. C., Rocha, R. A., & Borges, S. V. 2.2 Production of the films The films were produced by extrusion/thermo-compression as reported previously[4]. The mixture to prepare the extruded material contained 49% polymer, 30% glycerol, and 21% distilled water (w/w). The Pec and WPI concentrations are: Pec100WPI0 (100% m/m Pec), Pec95WPI5 (95% m/m Pec and 5% m/m WPI), Pec90WPI10 (90% m/m Pec and 10% m/m WPI), Pec85WPI15 (85% m/m Pec and 15% m/m WPI), Pec80WPI20 (80% m/m Pec and 20% m/m WPI), these values based on tota polymer mass. The citric acid (1.5%, w/w) and stearic acid (1%, w/w) were used to protect against oxidation and prevent agglomeration of the material. The reagents were homogenized in an industrial blender with a stainless steel beaker, at high speed, 1.5-liter capacity, 800 W power, and 60 Hz rotation (Metalúrgica Skymsen Ltda, Santa Catarina, Brazil). The mixture was extruded in a co-rotating twin-screw extruder (model SJSL 20, NZ Phil Polymer), with L/D = 40, and screw diameter (D) = 20 mm equipped with seven heating zones. The temperature profile from the feeder to the die was 35/50/75/95/100/100/90 ºC, and the screw speed was adjusted to 100 rpm. The extruded material was pelletized (2 mm pellets) using an automatic pelletizer operating at 120 rpm. The films were produced by a hydraulic press (model 370M015, Matoli, Brazil) using 10 g of pellets at 110 ºC for 5 times 5 ton/3 seconds, and 2 times 5 ton/3 minutes. Films about 15 cm in diameter were produced and cooled to room temperature.

2.3 Characterization of the films The films were conditioned at 23 ± 2 ºC and 50 ± 5% RH for 48 hours before characterization[16]. The average film thickness was measured at 10 different points, using a 0.01 mm Mitutoyo digital micrometer (Mitutoyo, Suzano, Brazil).

The mechanical properties were determined through a tensile strength test, using a TATX2i Micro System Texture Analyzer (England) with a 1 kN load cell. The samples were cut into 10 cm2 strips, according to ASTM-D882[16], and the measurements were carried out starting from an initial separation of 50 mm and a test speed of 0.8 mm/s. Tensile strength (TS, MPa), elongation at break (E), and modulus of elasticity (ME, MPa) were determined.

The colorimetric parameters were determined using the CIE Lab system in a CM-5 Konica Minolta spectrophotometer (Konica Minolta, Tokyo, Japan) with D65 illuminant, observation angle of 10°. The parameters luminosity (L*),

saturation or chroma (C*), a* (green to red), and b* (blue to yellow) were determined[17].

The total color difference (ΔE) of the films was determined

by Equation 1[17]: ∆= E

( L1 − L2 ) ² + ( a1 − a2 ) ² + ( b1 − b2 ) ²

(1)

where, L1 is the initial L value, a1 is the initial a* value, b1 is the initial b* value, L2 is the L value measured, a2 is the a* value measured, and b2 is the b* value measured.

The values L1, a1, and b1 are fixed values and correspond to the sample Pec100WPI0.

The transparency of the films was measured using the Bel SPECTRO S-2000 spectrophotometer (Monza, Italy) at 600 nm[18]. The films (3 x 1.5 cm pieces) were fixed to allow the beam to pass through the specimens with no obstacles. The transparency (T) was calculated according to Equation 2: T = ( Log %T ) / δ

(2)

where %T is transmittance percentage, and δ is the film thickness (mm).

2.4 Participants The study was realized in 2020 with Brazilian consumers.

All declared to use plastic packaging for food. No specific knowledge of biodegradable packaging was required. All participants declared to be 18 years of age or older at the time of the survey. They agreed to participate in this survey before voluntarily answering the online questionnaire.

Participants were also informed that they could leave the questionnaire online at any time.

2.5 Images Five Pec and WPI-based films made by extrusion/ thermo-compression were photographed using a 4-megapixel digital camera in a white cabinet under artificial white light.

The films were cut into 3 x 1.5 cm pieces. The camera and the films were positioned at 19.5 cm from each other, and the images were obtained using 4.0X magnification.

The images were not submitted to digital treatment, to keep the colors as close as possible to the true colors of the films.

The images are shown in Figure 1.

Figure 1. Images of thermo-plasticized Pec and WPI-based films.

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Consumer perception of biodegradable packaging for food 2.6 Online questionnaire Participants were asked to respond to an online questionnaire conducted on Google Docs, with an average response time of 10 min. Participants were contacted via email, social media, and smartphone communication apps.

After accepting to participate in the research, participants were instructed to adjust the brightness of the monitor or device by 80% to standardize and minimize possible differences between monitors and devices. The choice for an online questionnaire was due to the restrictions imposed by the COVID-19 pandemic.

The consumers evaluated five different films, and the experiment was conducted with a completely balanced block design. All recruited consumers stated that they consume food packed in plastic packaging.

The questionnaire was divided into sessions. The first session contained questions: participants’ age and education; packaging consumption habits; concept and consumption of biodegradable packaging; and the degree of importance of biodegradable packaging, color, appearance, and resistance of the packaging.

In the second session, the five images of Pec and WPI-based films were presented to the participants in a monadic way. The images were not identified so as not to influence the responses. The first questions were about the acceptance and the purchase intention. Then, consumers were asked to correlate the samples with previously selected attributes. After that, participants were informed about the origin and biodegradability of the materials used to produce the films, and, again, they were invited to answer about their purchase intention.

The third and final session included questions about participants’ preferences and the foods or beverages they would package using the films.

It is noteworthy that all participants evaluated all films, and information was not provided on the material concentrations (Pec and WPI), so as not to interfere in the analysis of the images.

2.7 Data analysis The results of the characterization of the films were analyzed by Analysis of Variance (ANOVA), using the SISVAR Software (version 5.6)[19] with a significance level of p < 0.05, and the results were compared using the Tukey’s test. Three samples of each film were used, in three repetitions.

For the questionnaires, a descriptive and exploratory analysis of data was initially carried out to extract information about the consumption habits of the participants. Then, Tukey’s test (p < 0.05) was performed to analyze the degree of importance of biodegradable packaging, color, resistance, and appearance at the time of purchase; acceptance of films; and the intention to purchase a packaged food using the featured films. To compare purchase intentions with or without further information about the material’s biodegradability, a T-test was also performed at p<0.05. A 7-point scale ranging from “unimportant” on the left to “very important” on the right was used for the degree of importance. A 7-point scale ranging from “I really disliked it” on the left to “I really liked it” Polímeros, 33(4), e20230045, 2023

on the right of the scale was also used in the acceptance analysis. For the purchase intent test, a 5-point scale was used, ranging from “certainly would not buy” on the left to “certainly buy” on the right of the scale.

Then, correspondence analysis (Check-All-That-Apply, CATA) was performed to determine the association between the films and the descriptors. In this analysis, consumers are invited to choose all possible attributes from a previous list of attributes raised by a focus group[20] composed of consumers of conventional packaging (non-biodegradable) and consumers of biodegradable packaging. Focus group was developed according to the methodology proposed

by Krueger and Casey[21] and members consumers of biodegradable packaging. Focus group members only had access to the images that make up the questionnaire. The following attributes were listed: light brown, dark brown, dark, woody, natural, unprocessed, smooth, rough, shiny, transparent, opaque, yellowish, thin, thick, tough, fragile, in addition to the term “others”, in which consumers could report other attributes observed.

A hierarchical grouping was also performed using the same ones used for CATA, that is, without treatment.

In the preference ordering test, consumers were asked to rank the films according to the order of preference, with samples sorted from most preferred to least preferred. The samples were identified with random 3-digit numbers and were presented randomly, that is, without ascending or descending order of WPI concentration. Of the 556 consumers who responded to the online questionnaire, only 434 responded to the order of preference. Scores were used according to the order of preference, ranging from 5 for the most preferred sample and 1 for the least preferred sample. Thus, considering the total number of consumers who responded to the order of preference, the highest sum of possible scores for a sample was 2170, while the lowest possible score was 434. The sum values of each sample demonstrate how preferred the sample was by the survey respondents. The samples were also submitted to the Friedman test (p < 0.05), which is a non-parametric bi-directional analysis of variance to compare several related samples, using the rows rather than raw data​​ for statistical calculation[20].

Finally, consumers were asked to suggest possible foods and beverages that could be packaged using the studied films. For that, a list of foods and beverages made by the same focus group of the CATA analysis was presented. The list also contained the term “others”, in which consumers could include any food or beverage not mentioned on the list. In addition, consumers could mark as many items on the list as they deemed necessary. Data analysis was performed using the R software version 3.5.2.

3. Results and Discussions 3.1 Characterization of the films As can be seen in Table 1, the addition of WPI led to a reduction in film thickness probably due to the crosslinking effect resulting from the Maillard reaction[22]. Concerning the mechanical properties of the films, no difference was observed between the parameters Tensile Strength (TS), Modulus of Elasticity (ME), and Elongation at Break (E).

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Oliveira, A. C. S., Ribeiro, M. N., Ugucioni, J. C., Rocha, R. A., & Borges, S. V. These results demonstrate that the addition of WPI and, consequently, the Maillard reaction was not able to negatively affect the mechanical properties. WPI-based films showed mechanical parameter values greater than or equal to the films without the addition of WPI (Pec100WPI0). These results are due to the increase in intermolecular interactions provided by the thermo-compression process and the protein cross-linking promoted by the Maillard reaction[22-24].

Table 2 presents the results of the optical parameters and transparency of extruded/thermo-compressed Pec and WPI-based films. The L* values (luminosity) indicate an intermediate luminosity, that is, films are neither black nor white. The C* values (Chroma) characterize films with high color saturation, while positive a* and b* values indicate reddish and yellowish samples[17]. In the present study, significant differences were observed for the color parameters (L*, C*, a*, and b*) only for the sample Pec100WPI0 (p <0.05) when compared with the other treatments. This result may be due to the Maillard reaction, due to the presence of an amino group of protein from WPI, and the reducing sugar of the polysaccharide (Pec) +under controlled conditions of dry heating[25].

According to Ramos and Gomide[17], ΔE values above 5 are easily detectable to the human eye, and values between 3.0 and 5.0 show “very easy” perception. Thus, the results of ΔE showed that the color difference between the films can be perceived by the naked eye.

Although the Transparency (T) values were relatively low, it was possible to visualize the product packaged by the films under study. As observed for the other colorimetric parameters, the transparency was affected by the addition of WPI and, consequently, by the Maillard reaction, which is a non-enzymatic browning reaction.

in Figure 2. Most of the individuals who answered the questionnaire were female (72.3%), aged from 26 to 50 years (61.1%), and completed post-graduate degree (49.1%).

Table 3 presents the profile of the participants concerning their habit of consuming biodegradable packaging. The results showed that 60.5% of the participants consumed plastic packaging at least once a day. This high frequency is confirmed by the high annual worldwide consumption of plastics, which are largely used as packaging material[1-4].

Almost all consumers (94.2%) stated that they knew about biodegradable packaging. When asked about the meaning of the expression “biodegradable packaging”, they showed knowledge about the concept. Many of them reported that it may be packaging that decomposes quickly and naturally, with no adverse effects on the environment.

These results can be explained by the unlimited access to information with the popularization of the internet[12].

Most consumers who responded to the online questionnaire had higher education and postgraduate degrees, with greater access to information, in addition to being able to understand several concepts such as biodegradable packaging.

3.2 Social analysis and consumer habits The social characteristics of the participants and the frequencies (sex, age, and education status) are described

Figure 2. Social characteristics of consumers.

Table 1. Thickness, Tensile Strength (TS), Modulus of Elasticity (ME), and Elongation at Break (E) of extruded/thermo-compressed Pec/WPI-based films.

Samples Pec100WPI0 Pec95WPI5 Pec90WPI10 Pec85WPI15 Pec80WPI20

Thickness (µm) 0.435 ± 0.008 a 0.394 ± 0.027 ab 0.381 ± 0.046 b 0.376 ± 0.035 b 0.371 ± 0.010 b

TS (MPa) 4.89 ± 0.87 a 6.30 ± 0.63 a 6.07 ± 0.39 a 5.76 ± 1.01 a 4.88 ± 1.22 a

ME (MPa) 0.40 ± 0.01 a 0.44 ± 0.15 a 0.42 ± 0.03 a 0.41 ± 0.15 a 0.39 ± 0.15 a

E (%) 282.93 ± 7.51 a 276.85 ± 4.07 a 281.37 ± 5.52 a 284.37 ± 14.91 a 282.96 ± 8.86 a

Means observed in the column with the same letter do not differ statistically (p < 0.05).

Table 2. Optical parameters (L*, C*, a*, b*, ΔE) and Transparency (T) of extruded/thermo-compressed Pec/WPI-based films.

Samples Pec100WPI0 Pec95WPI5 Pec90WPI10 Pec85WPI15 Pec80WPI20

L* 66.46 ± 0.31 b 56.78 ± 0.09 a 59.29 ± 0.32 a 54.17 ± 1.29 a 54.09 ± 0.97 a

C* 34.03 ± 2.59 a 41.83± 3.37 b 43.59 ± 2.46 b 52.88 ± 1.31 b 45.49 ± 1.93 b

a* 5.75 ± 0.34 a 11.60 ± 0.41 b 11.06 ± 1.26 b 16.58 ± 1.37 b 14.21± 2.59 b

b* 33.54 ± 3.40 a 40.19 ± 4.11 b 42.16 ± 2.65 b 50.21 ± 3.27 b 43.21 ± 5.87 b

ΔE 4.71 ± 0.82 a 4.59 ± 0.64 a 6.31 ± 0.78 c 5.52 ± 0.91 b

T (%) 4.14 ± 0.14 bc 4.29 ± 0.12 c 4.40 ± 0.29 c 3.70 ± 0.14 a 3.95 ± 0.14 ab

Means observed in the column with the same letter do not differ statistically (p < 0.05).

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Consumer perception of biodegradable packaging for food When analyzing the consumer behavior at the time of purchase, only 22.7% of the consumers observed whether the food packaging was biodegradable. On the other hand, 71.9% of consumers responded that knowledge about biodegradable packaging positively affects product choice. When asked the reasons for such influence, consumers reported that they were aware of the environmental benefits generated by the consumption of biodegradable packaging when compared to traditional non-biodegradable packaging. However, the high price of biodegradable packaging and the lack of clear information about the material’s biodegradability were reported as limiting factors at the time of purchase.

This consumer behavior may be due to greater visibility about the impact of non-biodegradable plastic packaging on the environment[26]. Another important factor is the greater association of plastic packaging with environmental problems when compared to other materials, such as cellulosic and glass packaging[27]. Thus, although consumers have reported that biodegradable packaging would influence the purchase intention, they may not purchase a product packaged in this type of packaging. Consumer awareness is not limited to environmental awareness, which is also related to the consumers’ engagement in the subject[27].

Figure 3 showed the degree of importance that consumers reported for the parameters of color, resistance, appearance, and biodegradability of the packaging when purchasing a product. The package color had the lowest score and, thus the lowest degree of importance at the time of purchase.

While the attributes of resistance and appearance showed a similar degree of importance. The use of biodegradable packaging had the highest degree of importance, with values close to the maximum score of 7. This result corroborates the findings in Table 3.

3.3 Consumers’ acceptance and purchase intention Table 4 presents the results of the acceptance test and the purchase intention for Pec and WPI-based films.

The acceptance varied with the WPI concentration, with higher scores for the WPI-based films, which can be associated with the results of the optical parameters (L*, C*, a*, and b*) and transparency (T). The presence of WPI and, consequently, the occurrence of the Maillard reaction significantly affected the optical and transparency values of the films. Thus, the consumers’ acceptance may be related to the color and transparency of the samples.

Consumers prefer clearer and more transparent packaging, with less saturated colors.

A significant difference in statistics was observed for the purchase intent without knowledge of the packaging’s biodegradability between the films. Reinforcing the importance of perceived visual attributes. Similar results were observed for the acceptance, once the films with higher acceptance scores also exhibited higher purchase intent scores and vice versa.

Figure 3. Degree of the importance of attributes when purchasing a product. Means observed with the same letter do not differ statistically (p < 0.05).

Table 3. Biodegradable packaging consumption habit.

Biodegradable Packaging Consumption Habit Frequency of consumption of plastic packaging > once a day once a day 3 to 4 times a week 1 to 2 times a week Fortnightly Monthly Rarely Know what biodegradable packaging is Yes No When purchasing, check if the packaging is biodegradable Yes No Biodegradable packaging influences the purchase of a product Yes No

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% of answers 39.6 20.9 16.9 14.2 3.1 3.1 3.6 94.2 5.8 22.7 77.3 71.9 28.3

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Oliveira, A. C. S., Ribeiro, M. N., Ugucioni, J. C., Rocha, R. A., & Borges, S. V. Concerning the purchase intent test with knowledge about biodegradability, an increase in purchase intent was observed without knowledge of the material’s biodegradability, with values close to the maximum allowed score (5).

Furthermore, no significant difference statistic was observed between the films, showing that biodegradability prevailed over the visual aspects. This result corroborates the high degree of importance observed for the biodegradable packaging and reinforces those consumers are aware of environmental issues arising from the use of biodegradable packaging.

Table 4 shows the results of the T-test, with a significant difference statistic observed in the purchase intention for all samples when the biodegradability information was provided to the consumer. Therefore, biodegradability is a predominant factor over the visual aspects. The information provided by the packaging is an extrinsic factor that can affect consumer behavior[28], and can be an opportunity to encourage the consumption of biodegradable packaging.

This result corroborates the report of consumers, who stated that the evident absence of specific information about the biodegradability of the packaging material makes the choice difficult when compared to traditional non-biodegradable packaging (Table 3). In addition, the results of purchase intention with the biodegradability information are important.

Biodegradable polymers add value to industries, which drives sustainable development and, consequently, reinforces the green economy[2].

corresponding to one group of samples with 0, 5, and 10% WPI and another group with samples containing 15 and 20% WPI. When analyzing the hierarchical clustering, the correspondence established by consumers in the CATA test (Figure 5), and the sample characterization (Tables 3 and 4), it was evident that these two groups differed in the descriptors’ color and transparency. The group with lower WPI concentrations was characterized by the descriptors yellowish, light brown, and natural, and the group of samples with higher WPI concentrations was characterized by the descriptors dark brown, dark, and opaque.

Figure 4. CATA results for the films made with different Pec and WPI concentrations.

3.4 CATA test Figure 4 shows the correspondence analysis established by consumers. The first and second dimensions accounted for 94.9% of the data variance, with 87.3% and 7.6%, respectively.

The films Pec100WPI0, Pec95WPI5, and Pec90WPI10 were classified as unprocessed, natural, light brown, yellowish, smooth, glossy, thin, and brittle. In turn, the films Pec85WPI15 and Pec80WPI20 were classified as dark brown, dark, woody, wrinkled, opaque, tough, and thick. Therefore, the results allowed for establishing correlations between the attributes’ darker color and opacity with the attributes’ resistance and thickness. In contrast, a correlation between light, yellow, and bright colors with fine, fragile, natural, and unprocessed was observed. These correlations were not confirmed by the instrumental analyses of film thickness, mechanical properties, and transparency.

Figure 5 shows the hierarchical clustering analysis of CATA data. The samples can be grouped into two clusters,

Figure 5. Hierarchical clustering of CATA data for the films made with different Pec and WPI concentrations.

Table 4. Acceptance and purchase intention of Pec and WPI-based films.

Samples

Acceptance

Pec100WPI0 Pec95WPI5 Pec90WPI10 Pec85WPI15 Pec80WPI20

4.50 ± 1.49bc 4.63 ± 1.48bc 4.71 ± 1.49c 4.09 ± 1.46a 4.40 ± 1.43b

Purchase intent without information that the films were biodegradable* 3.39 ± 1.04aA 3.57 ± 1.08aA 3.56 ± 1.02bA 3.40 ± 1.02bA 3.47 ± 1.07abA

Purchase intention with the information that the films were biodegradable* 4.18 ± 0.94aB 4.48 ± 0.76aB 4.28 ± 0.88aB 4.25 ± 0.91aB 4.31 ± 0.91aB

Preference ordering sum** 1307ab 1429a 1418a 1263b 1091c

*Means observed in the column with the same lowercase letter do not differ statistically (p < 0.05) according to Tukey’s test. Means observed in the same line with the same capital letter do not differ statistically (p<0.05) according to the T test; **Lines with the same letter do not differ statistically (p <0.05) according to the Friedman test.

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Consumer perception of biodegradable packaging for food Although no significant difference was observed for L*, C*, a*, and b* values between the WPI-based films, significantly different ΔE values were observed for the formulations Pec85WPI15 and Pec80WPI20 when compared with the others, with scores greater than 5, which represents a greater ability to distinguish color by the naked eye[17].

Furthermore, these formulations had the lowest transparency values and, thus the highest opacity. Although WPI may have contributed to the Maillard reaction, which is a non-enzymatic browning reaction, significant differences between the color parameters were not detected, despite a total difference in color and transparency being perceived by consumers.

3.5 Preference ordering The results of the preference ordering and Friedman rank-sum test were presented in Table 4, which showed that the formulations Pec100WPI0, Pec95WPI5, and Pec90WPI10 were the most and equally preferred by consumers, while the formulations Pec85WPI15 and Pec80WPI20 were the least preferred.

When comparing the results of preference ordering and acceptance tests, the most preferred samples also exhibited the highest acceptance scores. By correlating these values with CATA results (Figure 4), hierarchical clustering (Figure 5), and film characterization (Tables 3 and 4), the formulations with greater acceptance and preference were lighter, more transparent, with less saturated color. Therefore, both the preference and acceptance were directly related to the color and transparency of the films and referred to the descriptors thin, fragile, natural, and unprocessed, which was not confirmed by the analytical determinations.

3.6 Application of the films As shown in Figure 6, approximately 55% of the consumers suggested applications in coffee, chocolates, grains, cereals, bread, and nuts, and 20% corresponded to coffee and chocolates. Therefore, this response pattern showed the consumers’ acceptance of biodegradable films as packaging material for a wide range of foods and beverages.

Figure 6. Consumer responses on possible applications of films made with different Pec and WPI concentrations for food and beverage packaging.

Polímeros, 33(4), e20230045, 2023

This is an important approach, as it encourages the use of biodegradable packaging for food and beverages, which are essential for sustainable development and strengthening the green economy[2]. And it was also observed by some studies, as reported by Udayakumar et al.[29].

4. Conclusions The present results showed that the vast majority of consumers (77.3%) did not observe the biodegradability of the packaging during purchase, although they reported that biodegradable packaging can positively affect the purchase decision (71.9%). The acceptance, the purchase decision, and the preference for biodegradable films were affected by the visual impression. In addition, the consumers established a correspondence between the parameters of color and transparency with thickness and resistance, considering 94.9% of the data variance. The results showed acceptance of the promising application of biodegradable packaging, especially in food and beverages, with approximately 55% of consumers suggesting applications in coffee, chocolates, grains, cereals, bread, and nuts. The application of these films as food and beverage packaging can lead to sustainable development and enhance the green economy.

Future studies are necessary to verify the effective application of these biogeneratable packaging in food and beverages, especially with regard to maintaining the physicochemical and microbiological properties of both the food and beverages and the packaging.

5. Author’s Contribution •

Conceptualization – Ana Carolina Salgado de Oliveira.

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Data curation – Michele Nayara Ribeiro; Julio Cesar Ugucioni.

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Formal analysis – Ana Carolina Salgado de Oliveira; Michele Nayara Ribeiro.

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Funding acquisition ​– Soraia Vilela Borges.

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Investigation – Ana Carolina Salgado de Oliveira.

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Methodology – Ana Carolina Salgado de Oliveira; Michele Nayara Ribeiro.

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Project administration – Soraia Vilela Borges.

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Resources – Soraia Vilela Borges.

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Software – NA.

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Supervision – Soraia Vilela Borges.

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Validation – Julio Cesar Ugucioni; Roney Alves da Rocha.

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Visualization – Ana Carolina Salgado de Oliveira; Roney Alves da Rocha.

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Writing – original draft – ​Ana Carolina Salgado de Oliveira; Julio Cesar Ugucioni.

•

Writing – review & editing – Julio Cesar Ugucioni; Soraia Vilela Borges.

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6. Acknowledgements The authors would like to thank the Coordination for the Improvement of Higher Education Personnel (CAPES), the National Council for Scientific and Technological Development (CNPq), the Minas Gerais State Research Support Foundation (FAPEMIG), the Federal University of Lavras (UFLA) for financial support.

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Consumer perception of biodegradable packaging for food 29. Udayakumar, G. P., Muthusamy, S., Selvaganesh, B., Sivarajasekar, N., Rambabu, K., Banat, F., Sivamani, S., Sivakumar, N., Hosseini-Bandegharaei, A., & Show, P. L. (2021). Biopolymers and composites: Properties, characterization and their applications in food, medical and pharmaceutical industries. Journal of Environmental Chemical

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Engineering, 9(4), 105322. http://dx.doi.org/10.1016/j. jece.2021.105322.

Received: Aug. 10, 2023 Revised: Oct. 23, 2023 Accepted: Nov. 30, 2023

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Volume XXXIII - Issue IV - December., 2023

Polímeros

Prof. Ailton de Souza Gomez

23 ol, 20 Th CBP C 7 1 ille-S Joinv

Emeritus Professor, IMA/UFRJ

021 Pol, 2 B C 16 Preto Ouro th

VOLUME XXXIII - Issue IV - December., 2023

*1942 †Dec/28/2023

The late Associated Editor of Polimeros, Prof. Richard G. Weiss São Paulo 994 St. São Carlos, SP, Brazil, 13560-340 Phone: +55 16 3374-3949 Email: abpol@abpol.org.br 2023 2021