Viscoelastic properties of plasticized amylose films

The viscoelastic properties of amylose films plasticized with dimethyl sulfoxide were studied. The modulus–temperature curves of dimethyl sulfoxide-plasticized amylose are typical for semicrystalline polymers at the higher concentrations of amylose and pass to those of amorphous polymers with the decrease of amylose content. The glassy modulus is not affected by the incorporation of dimethyl sulfoxide, but the rubbery modulus and T_g are depressed with increased dimethyl sulfoxide. The change of T_g with plasticization can be represented by two approximately straight lines, one representing the lower concentration region of amylose and the other the higher one. The critical concentration is about 60% amylose. When the results of modulus–time measurements and x-ray diffraction are considered together, in a system of amylose–dimethyl sulfoxide, amylose exists as a semicrystalline polymer at high concentrations of amylose, and it acts intermediate between semicrystalline and amorphous polymers at lower concentrations below about 60%. From an extrapolation of the data of T_g of plasticized amylose, T_g of pure amylose appears to be approximately 330°C. The viscoelastic properties of amylose films plasticized with dimethyl sulfoxide–sorbitol mixtures were also studied.