A Study Of Preparation, Structure And Properties Of Thermoplastic Starch Materials

With excellent biodegradability, good oxygen barrier, and easily forming multi-layer films ect. Biodegrade thermoplastic starch is a novel packaging material that can substitute conventional plastics and therefore used in various industries including food,' agriculture,pharmaceltticle health and so on. A process for producing themorplastic starch (TPS) based on native starch mainly is carried out. The processing principle for TPS lie in the fact that with role of thermal field ,mechanical field and additives,the permanent conversion from crystal structures of native starch to amorphous ones is realized successfully, so its melt process can be finished before starch begins to overdue thermodegradation.However, as a sort of plentiful and renewable polymeric materials,strong interaction among starch macromolecules leads to its degradation temperature-below melting temperature and therefore its thermoplasticity must be solved to satisfy thermal processing.On the other hand, its weak water-resistance hinders further applications of TPS due to.plenty of hydriphilic groups itself. At present, the main approach available to improve its water-resistance is to blend TPS with aliphatic ploymers including their coploymers. So far the TPS/EVA blends are not yet reported in the reference. During this study, thermoplastic starch materials ' are prepared by extrusion,thermal compression and injection mould and effects of materials compositions on TPS properties are investigated.TPS/EVA blends are also prepared and their propreties and structures are studied by means of modern techniques of measurement and analysis. The main results are as follow:With the increase of plasticizer content, tensile strength and modulus of TPS decrease ,while its elogation at break and impact strength increase.With the same plasticizer content, ethylene glycol is the best ,glycerol better ,and propylene glycol last ,according to the extent that three kinds different plasticizer improve the elogation at break and impact strength.,while as far as the elogation at break and impact strength are concerned, the sequence is the opposite to that above. Among three different TPS (corn, cassava and wheat), the ductility of corn TPS is the best, and that of wheat TPS is the last.Equilibrium torque (Melt viscosity) of TPS changes with the change of type of starch and plasticizer, plasticizer content, rotational speed, and temperature. Melt viscosity of corn TPS (phr=43) is very sensitive to temperature instead of rotational speed. The increase of rotational speed leads to the increase in equilibrium torque.Opposite to unmodified EVA, the addition of modified EVA improves the ductility of TPS dramatically, among which elogation at break of corn TPS/MEVA (modified EVA) blends is thebest..In addition, considerable improvements in water-resistance of TPS are achieved by the addition of certain amount of EVA. What is more, the results of TDT (thermal distortion temperature) and TG show that the thermal stability of TPS/EVA blends is superior to that of TPS.X-ray diffraction pattern and observation of PLM demonstrate that origin crystal structure of native starch are destroyed through the plasticization and its crystallinity drops evidently.In comparation with unmodified EVA, compatibility between TPS and modified EVA is enhanced according to the results of DMA and SEM.