A Study On Preparation, Properties And Structure Of Thermoplastic Starch

Starch is a low cost, renewable and biodegradable material. Native starch usually has a form of isolatable granule, which is semi-crystalline with a crystallinity of 20～45%. The hydrogen bond interaction between starch macromolecules is strong which hindrance the molecule movement and gives native starch a poor processing ability. Thermoplastic starch (TPS) can be obtained by destruction of the granules in the presence of under heat and shear stress. But the poor mechanical properties and strong hydrophilicity restrict it used as a sturctural material. Most of the researches are focused on these problems.In this study, thermoplastic starch was prepared used several plasticizers in a Brabender torque rheometer. The starch plasticizing mechanism was studied by Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM). The results indicate that the plastication of starch is a jiont effort of heat, shear stress and plasticizers. A typical thermoplastic starch was prepared used Glycerol and water as complex plasticizer. The tensile strength and water resistance of this TPS decrease and the elongation at break increase with the increasing contents of glycerol.In order to improve the performance of TPS, Polyvinyl alcohol was blended with TPS by melt processing used formamide and caprolactam as coplasticizer. The effect of PVA and plasticizer on the properties and morphology of TPS/PVA were studied. PVA can obviously improve the mechanical properties (especially the break elongation) of TPS. The defect of PVA is it will increase the hydrophilicity of the blend. TPS/PVA has different phase structure when different alcoholysis degree PVA was used. PVA1795 has good compatibility with TPS which is confirmed by SEM, DSC and DMTA.Composites of TPS with Silica, MMT and bamboo fiber were prepared for better performance especially the mechanical properties and hydrophilicity. Chitosan and water-solubility PVA were used to activate montmorillonite (MMT). Only water-solubility PVA intercalated into layers of MMT and d-spacing of layers would be increased in thermoplastic starch processing. Adding of silica and MMT can improve the mechanical properties of TPS/PVA. Surface modification by coupling agent will reduce the aggregation of silica particles and improve the mechanical properties. Bamboo fiber (BF) has no effect on the performance of TPS/PVA because of poor interface interaction between BF and TPS/PVA. All composites have good processability. The polymer melts present a power-law (shear thinning) behavior. The power-law index of composites melts increase with silica, MMT and BF contents.