The effects of different plasticizers on the properties of thermoplastic starch as solid polymer electrolytes

Plasticizers with amide groups (urea and formamide) and polyols (glycerol, glucose, and sorbitol) were used to prepare thermoplastic starch (TPS) containing NaCl salt as solid polymer electrolytes (SPE). Fourier Transform infrared (FT-IR) spectroscopy revealed that both plasticizers and Na+ could form the interaction with starch, and plasticizers containing amide groups had stronger hydrogen bond-forming abilities with starch than polyols. These interactions prevented starch molecules from crystallizing again, indicated by X-ray diffraction (XRD). Scanning electron microscope (SEM) showed that starch granules were in a molten state and a continuous phase of TPS was formed. Among TPS as SPE, formamide-plasticized TPS (FPTPS) had the largest elongation at break and lowest tensile stress. The conductance of TPS was sensitive to water. TPS plasticized by solid plasticizers had the higher sensitivity of the conductance to water contents at the low water contents (< 0.1). The relationship of the conductance and water contents was in agreement with the second-order polynomial correlation when water contents were below 0.45. FPTPS had the best conductance as a whole. At the medium water content (0.2), the conductance of FPTPS containing NaCl was about 10(-3) S. cm(-1).