Effect of tensile action on retrogradation of thermoplastic cassava starch/nanosilica composite

Abstract

Thermoplastic cassava starch (TPS)/nanosilica (SiO2) composite was prepared by melt mixing, and the effect of tensile action (stress) on the structures and properties of TPS/SiO2 composite during the retrogradation stages was investigated. Differential scanning calorimetry (DSC) analysis indicated that the retrogradation enthalpy of TPS/SiO2 composite with the tensile action was higher than that of the composite without the tensile action after short retrogradation time. Thermogravimetric analysis (TG) displayed that the decomposition temperature and activation energy of thermal degradation of the composite under the tensile action were higher than those of composites without the tensile action. The contact angle and tensile strength of TPS/SiO2 composite with the tension action became larger after the tension stress was applied during the short retrogradation time. From the Fourier transform infrared (FTIR) spectroscopy results, the stretching vibration of the hydroxyl group enhanced with the increase in retrogradation time. According to the polarized light microscopy (PLM) analysis, the composite samples showed Maltese cross-pattern, and it became blurred after the tensile stress was exerted on the samples. With the increase in retrogradation time, the inter-planner spacing decreased and crystal size of TPS/SiO2 composite increased. The tensile action could weaken the A-type and promote the formation of the V-type crystalline structure. The scanning electron microscopy (SEM) results showed that the fracture surface of composite sample without the tensile action was smooth, and the granular structure of starch could not be clearly seen, however, the fracture surface of composite under the tensile action was rough, and the granular structure of starch was clear.