Characterization of citric acid/glycerol co-plasticized thermoplastic starch prepared by melt blending

A novel citric acid (CA)-glycerol co-plasticized thermoplastic starch (CGTPS) was prepared by melt blending. The CA content varies from 10% to 40 wt%. Result from Fourier Transform Infrared spectroscopy (FTIR) show that partial esterification occurred during blending. The degrees of substitution and esterification increased as the CA content increased. Results from intrinsic viscosity measurement, laser light scattering (LLS), and FTIR demonstrate the molecular weight of starch decreased as the CA percentage increased. The weight average molecular weight (M_w) of CGTPS with 20 wt% CA was only one-tenth of that without CA under the same processing conditions. Crystal type and crystallinity changes as a function of CA were recorded by X-ray diffraction (XRD). Thermal stability and the glass transition temperature (T_g) were detected by thermogravimetric (TG) and differential scanning calorimeter (DSC). Compared to the traditional GTPS, the novel CGTPS exhibits the special characters of partial esterification, low molecular weight and stronger interaction between starch and plasticizers. These new properties can be expected to prevent retrogradation, promote compatibility with polyesters, improve the processing ability, and adjust the degradation properties.