| World plastics production has more than 200 million tons, its extensive application dues to the rapid increase of waste, have caused serious environmental pollution problems. One important way of waste plastic pollution reduction is to use biodegradable material both in nature and organisms, the biodegradable material will not cause environmental pollution. During the biodegradable materials, poly (lactic acid) and starch become the most promising biodegradable polymer materials as derived from natural resources, with full bio-degradable, environmental pollution, etc. poly (lactic acid) is derived from renewable resources as a new type of fully biodegradable aliphatic polyester, have good biocompatibility, mechanical properties and water resistance, but the cost of production is far higher than traditional plastic, limiting its application. Starch is also one important biodegradable materials with its inexpensive, completely biodegradable, renewable short cycle. However, starch is a polyhydroxy polymer, can form a large number of intermolecular hydrogen bonds, so that it does not have the thermoplastic and is difficult to process, while pure starch plastics is sensitive to moisture and water, so its hydrophilic nature is strong. Cheap starch and poly (lactic acid) composite system is the way to resolve this contradictory of performance and cost effective, foreign scholars have done some research. Present blends of polylactic acid and starch, the most important issue is the poor interface compatibility between the hydrophobic of poly(lactic acid) and hydrophilic of starch. Thermoplastic starch is made of natural starch, high amylose or amylose with adding an effective plasticizer using extrusion or injection molding in high temperature, high pressure and high humidity conditions.In this paper, PLA/thermoplastic starch (TPS) blends were produced using injection molding machine in the presence of poly(ethylene glycol)(PEG). The rheological and mechanical properties of PLA/TPS were studied by adding different amount of PEG. And thermal analysis (DSC) instrument and scanning electron microscopy (SEM) were used on the microstructure of composite materials, and researched processing conditions impact on composite materials. The results show that the composite materials modified by the PEG400 improved the compatibility between thermoplastic starch and poly(lactic acid), and enhanced plasticity of composite materials. when the addition of polyethylene glycol reach to 3%, the mechanical properties of composite materials achieved the best. From processing conditions we can conclude that mechanical properties of composites will be the best when cooling time 60 seconds, injection pressure 10MPa, injection speed 80mm/s. The composite materials could be used in the biodegradable tableware, biodegradable plastic bags and other fields. For further comparative studies, I analyzed the mechanical properties of composite materials using different modifiers.By assessment of mechanical properties and weight loss through five months of degradation of composite materials, Results show that:Before the modification, degeneration performance increases along with TPS content increases. After the modification with PEG400, degradation rate increases with the increase of PEG400 concentration, indicating PEG400 promoted the compound materials degeneration to a certain extent. Comparison with soil burial test and composting degradation, we can conclude that although composting degradation increased the degradation rate of samples, but effects is little. Therefore, we need improve composting degradation experiment. Though analyzing the mechanical properties and degradation of samples, I found the optimal balance point of the mechanical properties and degradation of the performance, when the addition of polyethylene glycol reach to 3%, the mechanical properties and degradation of composite materials achieved the best, so I determined the optimal formulation of composite materials.
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