Effects of nanosilica on retrogradation properties and structures of thermoplastic cassava starch

Composites of thermoplastic cassava starch (TPS) and nanosilica (SiO2) were prepared by the melting method. The effect of nano-SiO2 on the retrogradation properties and structures of cassava starch was investigated. The retrogradation degree of TPS/nano-SiO2 composites increased with increasing retrogradation time. The retrogradation rate of TPS significantly increased after the addition of nano-SiO2, but excessive nano-SiO2 content leads to a decrease in the retrogradation rate of TPS. According to the Fourier transform infrared spectroscopy results, the retrogradation degree of TPS/nano-SiO2 composites increased with the increase of retrogradation time and addition of nano-SiO2. Scanning electron microscopy analysis indicated that nano-SiO2 particles were uniformly and finely dispersed in the starch materials, but the nano-SiO2 particles aggregated in the cassava starch with a further increase in nano-SiO2 content. X-ray diffraction revealed that the crystalline structure of the starch was gradually altered from A-type to V-type with the increase of retrogradation time. TPS/SiO2 composites indicated a mixture of A+V types, and the intensity of the V-type strengthened with the increase of retrogradation time and SiO2 content. Polarized light microscopy analysis revealed clear Maltese cross patterns, and the number of spherulites in TPS/nano-SiO2 composites increased with increasing retrogradation time and nano-SiO2 content, but the retrogradation of starch was inhibited with further increases of nano-SiO2 content. (c) 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45687.