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Biodegradable foams made from cassava starch, polyvinyl alcohol (PVA), sugarcane bagasse fibers and chitosan were obtained by extrusion. The composites were prepared with formulations determined by a constrained ternary mixtures experimental design, using as variables: (X 1 ) starch / PVA (100 -70%), (X 2 ) chitosan (0 -2%) and (X 3 ) fibers from sugar cane (0 -28%). The effects of varying proportions of these three components on foam properties were studied, as well the relationship between their properties and foam microstructure. The addition of starch/PVA in high proportions increased the expansion index and mechanical resistance of studied foams. Fibers addition improved the expansion and mechanical properties of the foams.There was a trend of red and yellow colors when the composites were produced with the highest proportions of fibers and chitosan, respectively. All the formulations were resistant to moisture content increase until 75% relative humidity of storage.

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RESUMOA preocupação com o volume de lixo tem gerado interesse no desenvolvimento de embalagens biodegradáveis capazes de substituir, ao menos em parte, os plásticos convencionais sintéticos, como é o caso das embalagens de poliestireno expandido (Isopor). Ojvetivou-se,neste trabalho caracterizar, quanto ao índice de expansão (IE), densidade, índice de absorção em água (IAA), índice de solubilidade em água (ISA) e cor (coordenadas L * , a * e b * ), compósitos biodegradáveis expandidos produzidos via extrusão, a partir da mistura de amido de mandioca, glicerol (plastificante) e dois tipos de fibras vegetais. Os compósitos foram preparados em extrusora mono-rosca, com três diferentes teores de fibras de aveia ou de cana-de-açúcar (0, 5 e 10 g/100 g amido), dois teores de umidade (18 e 26%) e teor fixo de glicerol (20g/100 g sólidos). A adição das fibras não afetou significativamente o IE, a densidade e o IAA, porém diminuiu o ISA dos materiais, o que é uma vantagem, favorecendo a utilização das fibras no reforço dos compósitos. A adição de fibras levou ao escurecimento das amostras, com decréscimo da luminosidade (L*) e, ainda, ao aumento nos valores dos parâmetros de cor a* e b*. Este estudo é passo fundamental para produção em escala industrial dos compósitos, que necessitam de condições de processo que forneçam resultados reprodutíveis de expansão e capacidade de absorção e solubilidade em água, propriedades de grande importância nesses produtos.Termos para indexação: Embalagens de alimentos, fibras da cana-de-açúcar, fibras da casca de aveia. ABSTRACTThe concern with the volume of waste has generated interest in the development of biodegradable packaging able to replace, at least in part, the conventional synthetic plastics, such as packs of expanded polystyrene (Isopor). This study aimed to characterize the expansion index, density, the water absorption index (WAI), water solubility index (WSI) and color (coordinates L * , a * and b * ) of expanded biodegradable composites produced by extrusion, from the mixture cassava starch, glycerol (plasticizer) and two different types of vegetable fibres. The composites were prepared in a single screw extruder, with three different levels of oat or sugar cane fibres (0, 5 and 10 g /100 g starch), two levels of humidity (18 and 26%) and a fixed level of glycerol (20 g/100 g solds). The addition of fibres did not affect significantly the expansion index, density and WAI of materials, and reduced WSI of products, which is an advantage and promotes the use of these fibres in the reinforcement of composites. The addition of fibers led to the darkening of the samples, with decrease in lightness (L*) and increase in the values of the color parameters a* and b*. This study is a key step for a future industrial scale production of these composites, which requires process conditions that provide reproducible results of expansion and absorption capacity and solubility in water, properties of great importance in these products.