Effect of Saccharide and Alditol Additives on Uniaxial Tensile Behavior of Gellan Films

The uniaxial tensile behavior of gellan films containing saccharides or alditols was examined to elucidate the plasticizing effect of these additives. Five saccharides as well as two alditols were used. The films were tested after removal of water as far as possible. The tensile modulus decreased as the content of the additives increased, suggesting apparent plasticizing effect of the additives. The plasticizing effect was discussed referring the glass transition temperature instead of the melting point of the additives, assuming the additives were in the "supercooled" liquid state even below the melting point. Since some additives showed similar values of tensile modulus regardless of whether the additive was in the solid state or in the liquid state, a blending law of the moduli was proposed to explain the apparent plasticizing effect. On the other hand, it was found that xylitol and two monosaccharides glucose and fructose acted as true plasticizers. The effective factor was attributed to the solubility of these additives to the gellan matrix. A relationship between the profile of the stress–strain curve and the plasticizing effect was also proposed.