Physical properties of polyol-plasticized edible blends made of methyl cellulose and soluble starch

Aqueous blends of methyl cellulose and soluble starch, plasticized with glycerol or sugars, were prepared by casting, or by extrusion and hot pressing. The mechanical (tensile and flexural mode), thermal (differential scanning calorimetry) and gas and water permeation properties of these blends were investigated, after their conditioning at various relative humidities. The observed Tg depression for these polymer blends was proportional to the plasticizer content (water, glycerol and sugars). Although glycerol had a greater depressing effect on Tg than sorbitol, the latter had a greater impact than glycerol and xylose, as a plasticizer, on the mechanical properties (higher percentage elongation) of the soluble starch¯methyl cellulose blends. The tensile strength and flexural moduli of these blends were shown to decrease drastically with an increase in the total plasticizer content. An indirect measurement of glass transitions, comparable to the ones determined with DSC, was obtained from the Arrhenius-type plots of the gas permeability¯temperature relationships.