Changes in molecular mobility of sorbitol plasticized starch during aging

Thermoplastic corn starch with 0.4 parts by weight of sorbitol plasticizer was studied using dynamic-mechanical thermal analysis (DMTA) and hydrogen nuclear magnetic resonance (H-1 NMR) to assess the changes in molecular mobility during a period of 26 weeks of storage. Motional heterogeneity of this thermoplastic starch (TPS) was found even after a short aging time by means of DMTA. Besides the glass transition processes in starch-rich and plasticizer-rich domains, other relaxation processes appear in TPS samples aged for a longer time. Sorbitol release and/or some moisture uptake was observed in H-1 NMR spectra of long-aged samples. After the whole monitored aging period, sample surfaces were covered with white powder due to sorbitol leakage from the TPS structure.