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Estratégias de melhoria de hidrofobicidade de um filme polimérico à base de amido reforçado com fibras de casca de castanha
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Resumo(s)
Os filmes à base de amido são uma alternativa biodegradável aos plásticos convencionais. Contudo, devido à sua natureza hidrofílica, enfrentam algumas limitações significativas, o que compromete a sua aplicação em embalagens alimentares. Neste contexto, o presente estudo teve como principal objetivo otimizar a formulação de um filme à base de amido, previamente reforçado com fibras de casca de castanha, através da implementação de estratégias sequenciais para aumentar a sua hidrofobicidade. Numa primeira fase, avaliou-se a reticulação da matriz de amido com ácido cítrico. Apesar de não se terem observado diferenças estatisticamente significativas nas propriedades de interação com a água, verificou-se que a formulação com 3% (p/p) de ácido cítrico apresentou a combinação mais favorável de propriedades mecânicas. Posteriormente,
explorou-se a incorporação de óleos vegetais (milho e soja), contudo, apesar de uma ligeira melhoria na resistência à humidade, descontinuou-se esta abordagem devido ao impacto negativo e acentuado na transparência dos filmes, um atributo considerado essencial. A terceira e principal estratégia consistiu na incorporação de nanopartículas de óxido de zinco (nZnO) e na substituição parcial das fibras de casca de castanha por nanofibras de pampa grass, recorrendo-se a um Modelo de Superfície de Resposta (MSR) segundo um desenho experimental Box-Behnken (BBD). Desta análise, resultou uma formulação ótima, composta por
44% de glicerol, 2% de nZnO e uma mistura de 83% de nanofibras de pampa grass e 17% de fibras de casca de castanha, com melhorias face ao filme de controlo: um aumento de 82,6% na tensão de rutura e reduções de 32,3% no teor de humidade e de 31,3% na solubilidade em água. Apesar das melhorias, a aplicação do filme ótimo na conservação de alimentos perecíveis, como queijo e carne, com teores respetivos de humidade de 40% e 75%, revelou que, embora superior ao controlo, o seu desempenho como barreira à humidade ainda se mostra insuficiente quando comparado com o plástico convencional (PET), resultando na desidratação dos alimentos e na perda de flexibilidade do filme. De uma forma geral, concluiu-se que, embora as estratégias adotadas tenham melhorado eficazmente as propriedades do filme, a sua aplicação em alimentos com elevada atividade de água permanece um desafio.
Despite being a biodegradable alternative to conventional plastics, starch-based films face significant limitations due to their hydrophilic nature, which compromises their application in food packaging. In this context, the main objective of this study was to optimize the formulation of a starch-based film, previously reinforced with chestnut shell fibres, by implementing sequential strategies to increase its hydrophobicity. In a first stage, the cross-linking of the starch matrix with citric acid was evaluated. Although no statistically significant differences were observed in the water interaction properties, the formulation with 3% (w/w) citric acid was found to exhibit the most favorable combination of mechanical properties. Subsequently, the incorporation of vegetable oils (corn and soybean) was explored. However, despite a slight improvement in moisture resistance, this approach was discontinued due to the sharp negative impact on the film’s transparency, which is a critical attribute.The third and main strategy consisted of incorporating zinc oxide (ZnO) nanoparticles and partially substituting the chestnut shell fibres with pampa grass nanofibers, using a Response Surface Methodology (RSM) with a Box-Behnken experimental design (BBD). This analysis resulted in an optimal formulation, composed of 44% glycerol, 2% ZnO, and a mixture of 83% pampa grass fibres and 17% chestnut shell fibres, which showed significant improvements over the control film: an 82.6% increase in tensile strength, and reductions of 32.3% in moisture content and 31.3% in water solubility. Despite these improvements, the application of the optimized film in the preservation of fresh foods, such as cheese and meat, with moisture contents of 40% and 75%, was still insufficient when compared to conventional plastic (PET). This resulted in the dehydration of the food and a loss of flexibility in the film itself, leading to the conclusion that while the adopted strategies effectively improved the film's properties, its application for foods with high water activity remains a challenge.
Despite being a biodegradable alternative to conventional plastics, starch-based films face significant limitations due to their hydrophilic nature, which compromises their application in food packaging. In this context, the main objective of this study was to optimize the formulation of a starch-based film, previously reinforced with chestnut shell fibres, by implementing sequential strategies to increase its hydrophobicity. In a first stage, the cross-linking of the starch matrix with citric acid was evaluated. Although no statistically significant differences were observed in the water interaction properties, the formulation with 3% (w/w) citric acid was found to exhibit the most favorable combination of mechanical properties. Subsequently, the incorporation of vegetable oils (corn and soybean) was explored. However, despite a slight improvement in moisture resistance, this approach was discontinued due to the sharp negative impact on the film’s transparency, which is a critical attribute.The third and main strategy consisted of incorporating zinc oxide (ZnO) nanoparticles and partially substituting the chestnut shell fibres with pampa grass nanofibers, using a Response Surface Methodology (RSM) with a Box-Behnken experimental design (BBD). This analysis resulted in an optimal formulation, composed of 44% glycerol, 2% ZnO, and a mixture of 83% pampa grass fibres and 17% chestnut shell fibres, which showed significant improvements over the control film: an 82.6% increase in tensile strength, and reductions of 32.3% in moisture content and 31.3% in water solubility. Despite these improvements, the application of the optimized film in the preservation of fresh foods, such as cheese and meat, with moisture contents of 40% and 75%, was still insufficient when compared to conventional plastic (PET). This resulted in the dehydration of the food and a loss of flexibility in the film itself, leading to the conclusion that while the adopted strategies effectively improved the film's properties, its application for foods with high water activity remains a challenge.
Descrição
Palavras-chave
Starch films Hydrophobicity Optimization Chestnut shell fibres Pampa grass nanofibers Zinc oxide nanoparticles Sustainable food packaging Filmes à base de amido Hidrofobicidade Otimização Fibras de casca de castanha Nanofibras de pampa grass Nanopartículas de óxido de zinco Embalagens alimentares sustentáveis