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. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45687.