Plasticizing Effect of Saccharides on Uniaxial Tensile Behavior of κ-Carrageenan Films

Abstract

The uniaxial tensile behavior of κ-carrageenan films with saccharides was examined to elucidate the plasticizing effect of saccharides. Five saccharides as well as two alditols for comparison were used. The films were tested after removal of water as far as possible. The tensile modulus (E) decreased as the fraction of the saccharides increased, suggesting apparent plasticizing effect of the saccharides. The plasticizing effect was discussed referring the glass transition temperature (T_g) of the saccharides, because the saccharides were considered in the “supercooled” liquid state even below the melting point. Since the saccharides except the monosaccharides showed plasticizing effect similar to that of glycerol both above and below T_g, namely regardless of whether the saccharide was in the solid state or in the liquid state, a blending law of the moduli was proposed to explain the decrease in E. This means that these additives including glycerol are not real plasticizers in the conventional sense of the word. On the other hand, the monosaccharides glucose and fructose acted as better plasticizers at 100 °C. The additional factor was attributed to the solubility of these saccharides to the matrix κ-carrageenan, indicating the real plasticizing effect of the monosaccharides. Interestingly, this factor for fructose disappeared at 29 °C, still above T_g.