Síntese e caracterização de filmes bionanocompósitos à base de biopolímeros reforçados por nanocristais de celulose bacteriana
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2023-08-22
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Universidade Estadual Paulista (Unesp)
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Embalagens convencionais na forma de filmes são amplamente utilizadas em alimentos, e a demanda dos consumidores por alternativas mais seguras aumenta constantemente. Materiais alternativos sustentáveis são urgentemente necessários para resolver os problemas de poluição ambiental e esgotamento de recursos naturais causados por materiais plásticos não degradáveis e não renováveis de base petroquímica. Para esse fim, muitos polímeros de base biológica podem ser boa alternativa aos plásticos convencionais. Os principais biopolímeros usados em aplicações de embalagens de alimentos são polissacarídeos, proteínas e lipídios. A celulose é o biopolímero mais abundante na terra e apresenta propriedades promissoras. No entanto, ela é comumente empregada como agente de reforço em matrizes poliméricas, especialmente em forma de nanocristais, devido às suas propriedades físico-químicas satisfatórias, como ampla área de superfície específica, elevada resistência mecânica, atóxica, biodegradável e fácil funcionalidade. Nanocristais derivados de celulose bacteriana podem ser fisicamente incorporados em várias matrizes biopoliméricas para formar bionanocompósitos. O reforço pelo nanomaterial fornece propriedades melhoradas em comparação com o polímero puro, mesmo em frações muito baixas. O objetivo principal deste estudo foi analisar a viabilidade de se usar resíduos de celulose bacteriana na produção de nanocristais para ser incorporados nas soluções filmogênicas para uso em embalagens biodegradáveis. Esses nanocristais de celulose (NCs) foram incorporados nas soluções filmogênicas à base de gelatina, pectina e hidroxipropilmetilcelulose (HPMC), e foi estudada a influência da adição desses nanocristais nas matrizes biopoliméricas, como agente de reforço, a partir de análises de microscopia eletrônica de varredura e por emissão de campo, pH, DRX, viscosidade das soluções filmogênicas, propriedades mecânicas, permeabilidade ao vapor de água (PVA), ângulo de contato, umidade, FTIR, transparência, TG/DTG e biodegradabilidade. O percentual em massa de nanocristais incorporados nas matrizes foi delimitado através do limiar de percolação. A estrutura resultante dos nanocristais mostrou uma forma semelhante a uma haste com dimensões em nanoescala. O pH das soluções filmogênicas não foi alterado com adição de nanocristais de celulose bacteriana (NCCB). A viscosidade da solução de HPMC é muito superior em relação à solução de gelatina e pectina. A adição de NCCB alterou significativamente as propriedades mecânicas dos filmes, principalmente nas matrizes à base de gelatina e HPMC. Em todos os bionanocompósitos foi aumentada a resistência mecânica e os NCs influenciaram significativamente nos resultados da tenacidade dos filmes à base de gelatina e HPMC. Porém, a deformação específica apresentou pouca alteração. A PVA mostrou uma tendência decrescente nos bionanocompósitos. Os filmes são hidrofílicos, apresentaram baixa umidade, microestrutura homogênea, transparentes, estáveis termicamente em inúmeras aplicações industriais e sustentáveis. Os difratogramas de raio X mostraram que à medida que vai aumentando o percentual de nanocristais os picos vão ficando mais intensos, representando assim um aumento significativo na cristalinidade. Todas os filmes desintegraram em tempo menor que o indicado pela norma ASTM 2003 e ISO 2012, logo todos são biodegradáveis. Enfim, os nanocristais contribuíram para alteração de forma positiva nas diversas propriedades estudadas e mostrou promissor na aplicação em filmes a base de materiais biopoliméricos.
Conventional packaging in the form of films is widely used in food, and consumer demand for safer alternatives is constantly increasing. Sustainable alternative materials are urgently needed to solve the problems of environmental pollution and natural resource depletion caused by non-degradable and non-renewable petrochemical-based plastic materials. To this end, many bio-based polymers can be good alternatives to conventional plastics. The main biopolymers used in food packaging applications are polysaccharides, proteins and lipids. Cellulose is the most abundant biopolymer on earth and presents promising properties. However, it is commonly used as a reinforcing agent in polymer matrices, especially in the form of nanocrystals, due to its satisfactory physicochemical properties, such as a large specific surface area, high mechanical resistance, non-toxic, biodegradable and easy functionality. Bacterial cellulose-derived nanocrystals can be physically incorporated into various biopolymeric matrices to form bionanocomposites. Reinforcement by the nanomaterial provides improved properties compared to the pure polymer, even at very low fractions. The main objective of this study was to analyze the feasibility of using bacterial cellulose residues in the production of nanocrystals to be incorporated into film-forming solutions for use in biodegradable packaging. These cellulose nanocrystals (NCs) were incorporated into film-forming solutions based on gelatin, pectin and hydroxypropylmethylcellulose (HPMC), and the influence of the addition of these nanocrystals to biopolymeric matrices, as a reinforcing agent, was studied based on electron microscopy analyzes of scanning and field emission, pH, XRD, viscosity of film-forming solutions, mechanical properties, water vapor permeability (PVA), contact angle, humidity, FTIR, transparency, TG/DTG and biodegradability. The mass percentage of nanocrystals incorporated into the matrices was delimited using the percolation threshold. The resulting structure of the nanocrystals showed a rod-like shape with nanoscale dimensions. The pH of the film-forming solutions was not changed with the addition of bacterial cellulose nanocrystals (NCCB). The viscosity of the HPMC solution is much higher than that of the gelatin and pectin solution. The addition of NCCB significantly changed the mechanical properties of the films, especially in gelatin and HPMC-based matrices. In all bionanocomposites, mechanical resistance was increased and NCs significantly influenced the tenacity results of gelatin and HPMC-based films. However, the specific deformation showed little change. PVA showed a decreasing trend in bionanocomposites. The films are hydrophilic, have low humidity, homogeneous microstructure, transparent, thermally stable in numerous industrial and sustainable applications. The X-ray diffractograms showed that as the percentage of nanocrystals increases, the peaks become more intense, thus representing a significant increase in crystallinity. All films disintegrated in less time than indicated by ASTM 2003 and ISO 2012, so they are all biodegradable. Finally, the nanocrystals contributed to a positive change in the various properties studied and showed promise for application in films based on biopolymeric materials.
Conventional packaging in the form of films is widely used in food, and consumer demand for safer alternatives is constantly increasing. Sustainable alternative materials are urgently needed to solve the problems of environmental pollution and natural resource depletion caused by non-degradable and non-renewable petrochemical-based plastic materials. To this end, many bio-based polymers can be good alternatives to conventional plastics. The main biopolymers used in food packaging applications are polysaccharides, proteins and lipids. Cellulose is the most abundant biopolymer on earth and presents promising properties. However, it is commonly used as a reinforcing agent in polymer matrices, especially in the form of nanocrystals, due to its satisfactory physicochemical properties, such as a large specific surface area, high mechanical resistance, non-toxic, biodegradable and easy functionality. Bacterial cellulose-derived nanocrystals can be physically incorporated into various biopolymeric matrices to form bionanocomposites. Reinforcement by the nanomaterial provides improved properties compared to the pure polymer, even at very low fractions. The main objective of this study was to analyze the feasibility of using bacterial cellulose residues in the production of nanocrystals to be incorporated into film-forming solutions for use in biodegradable packaging. These cellulose nanocrystals (NCs) were incorporated into film-forming solutions based on gelatin, pectin and hydroxypropylmethylcellulose (HPMC), and the influence of the addition of these nanocrystals to biopolymeric matrices, as a reinforcing agent, was studied based on electron microscopy analyzes of scanning and field emission, pH, XRD, viscosity of film-forming solutions, mechanical properties, water vapor permeability (PVA), contact angle, humidity, FTIR, transparency, TG/DTG and biodegradability. The mass percentage of nanocrystals incorporated into the matrices was delimited using the percolation threshold. The resulting structure of the nanocrystals showed a rod-like shape with nanoscale dimensions. The pH of the film-forming solutions was not changed with the addition of bacterial cellulose nanocrystals (NCCB). The viscosity of the HPMC solution is much higher than that of the gelatin and pectin solution. The addition of NCCB significantly changed the mechanical properties of the films, especially in gelatin and HPMC-based matrices. In all bionanocomposites, mechanical resistance was increased and NCs significantly influenced the tenacity results of gelatin and HPMC-based films. However, the specific deformation showed little change. PVA showed a decreasing trend in bionanocomposites. The films are hydrophilic, have low humidity, homogeneous microstructure, transparent, thermally stable in numerous industrial and sustainable applications. The X-ray diffractograms showed that as the percentage of nanocrystals increases, the peaks become more intense, thus representing a significant increase in crystallinity. All films disintegrated in less time than indicated by ASTM 2003 and ISO 2012, so they are all biodegradable. Finally, the nanocrystals contributed to a positive change in the various properties studied and showed promise for application in films based on biopolymeric materials.
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Palavras-chave
Embalagens, Resíduos, Nanocelulose, Sustentabilidade, Economia circular, Packaging, Waste, Nanocellulose, Sustainability, Circular economy
Como citar
COSTA, Fabíola Medeiros. Síntese e caracterização de filmes bionanocompósitos à base de biopolímeros reforçados por nanocristais de celulose bacteriana. 2023. 128 f. Tese (Doutorado em Ciência dos Materiais) – Faculdade de Engenharia, Universidade Estadual Paulista - Unesp, Ilha Solteira, 2023.