Research On The Preparation And Properties Of High Performance Poly (Lactic Acid) Composites

In recent years, with society and industry technology developing rapidly, resources and environmental protection has been a growing emphasis. Thus, green chemistry attracts more and more attention. Increasing people makes use of reproducible resources like biodegradable polymers as raw materials to replace petroleum-based polymer. Poly-lactic acid (PLA) as a representative of biodegradable aliphatic polyester material has become the research hotspot. Poly-lactic acid (PLA) is a kind of biodegradable polymer produced from reproducible plant resources. It is a kind of linear thermoplastic aliphatic polyester. PLA shows outstanding biodegradability, bioresorbability, biocompatibility and thermal processing performance. However, because of the obvious drawbacks like poor heat resistance and low impact toughness, in addition, its high price due to the PLA base is very expensive and its complex producing process, applications of PLA were heavily limited to certain fields such as surgical suture lines, drug release carriers etc. Thus, lots of studies have been carried out both at home and abroad, focused on the modification of PLA by various approaches and materials. In the present work, elastomer was used to toughen PLA and fiber-reinforced PLA, in combination with radiation-induced cross-linking technology to study the modification of poly lactic acid.Research on the properties of elastomer tougheness PLA composites. Composites of PLA toughened by elastomer were prepared by melt blending with double-screw extruder and then injection moulding in this work. And enhancement radiation cross-linking technology was introduced to improve the adhesive force of matrix and elastomer in order to produce PLA engineering plastic with good properties. Gel extraction, mechanical characterization, scan electron microscope (SEM), fourier transform infrared spectroscopy (FTIR) were applied to research the effect of irradiation dose and cross-linking agent on the structure and properties of composite materials. Mechanical characterization showed that mechanical properties of composites were improved obviously as the addition of crosslinking agent and introduction of irradiation dose. The impact strength of PLA/EVA-L/A composites increased from 5.2Kj/m2 to 40KJ/m2. and the impact strength of PLA/EVA-H/A composites can reach above 130kJ/m2. As the introduction of crosslinking agent, polymer free radical can take reaction with the ethylene of the crosslinking agent, which will produce a grafting structure or co-crosslinking structure, the new structures will improve the phase interaction, the properties of composites get improved at the same time. The optimum amounts of crosslinking agent and absorbed dose were 3~5wt% and 10~30kGy, respectively. It is clear that PLA could be toughened effectively by filling elastomer. The toughening effect of the PLA with the high content of VA in the EVA copolymer is better than that of low content of VA in the EVA copolymer.The results of gel extraction and scan electron microscope (SEM) were consistent with the changes of mechanical properties and structures. There was gel generated after irradiation in PLA/EVA-L composites without A. And cross-linked polymer lead to the pyrolysis extent of degradable polymer decreased. However, from the results of gel function of PLA/EVA-L composites with A, there were co-crosslinking and graft structure produced at the phase interface. The interface interaction was significantly improved from the SEM photos. The toughening effect is more obvious than that in binary systems. The results of Infrared spectrum show that PLA and EVA must enter into cross-network.Research on the properties of BF reinforcement PLA composites. In order to produce PLA-based fiber composites with good properties, composites of PLA reinforced by basalt fiber (BF) were prepared by melt blending with a banbury mixer and then compression molding in this work, and the adhesive force of matrix and fiber get improved by the introduction of enhancement radiation cross-linking technology. The thermal and mechanical properties of the composites before and after irradiation, respectively, were investigated through gel fraction, heat defection temperature (HDT), tensile tests and scanning electron microscopy (SEM).It was found that the heat distortion temperature of the fiber reinforced PLA composites greatly increased after enhancement radiation cross-linking. Tensile properties were enhanced as well. The strength decreases and the modulus increases with increasing fiber content. All composites with fiber filled have a higher tensile modulus than the one without fiber. It is clear that BF has a enhancement effect on the composite. At the same time, fiber content has a significant effect on increasing heat distortion temperature. When the content of BF reached 30 wt%, the amounts of crosslinking agent A and absorbed dose were 5wt% and 5kGy, respectively. The HDT of composites were dramatically enhanced from 55℃to above 135℃.Polyfunctional monomer A serve as enhancement crosslinking agent which will get PLA crosslinked. Gel content has been intimately tied to the irradiation dose and the content of crosslinking agent A. Regardless of the changes in radiation dose, the systems without crosslinking agent A did not form a gel content. However, when the content of A exceed 1wt% and the irradiation dose get more than 5kGy, gel content increases rapidly; when the content of A was 5wt% and irradiation dose was 70kGy, the gel content would exceed 90%. From the analysis of Gel extraction and SEM, it showed that the HDT was dramatically enhanced, due to the PLA-g-A-g-BF structures and co-crosslinking structures at the interface, the restless PLA chains were fixed by rigid fibers at high temperature.