Synthesis And Modification Of Lactic Acid Copolyester Biodegradable Materials

The purpose of this paper is to develop a useful bio-lactic acid copolymer materials, to contribute to provide the basis of L-lactic acid for large-scale development. Polylactic acid (PLA) is a renewable and excellent biocompatibility and biodegradability of aliphatic polyester polymers and expected to become a non-renewable petroleum-based polymer alternatives. However, in the preparation and industrialization progress of PLA still exist many problems. As a restricted in their application of engineering plastics and fibers, one of the biggest obstacles is the production costs and higher prices of PLA ,which limit their application in various fields, the other is poor heat-resistant, slow crystallization rate, hard and brittle of PLA products.Recently, the ring-opening polymerization of the PLA production method has been to achieve industrialization, but the cost of this long time polymerization is very high. Preparation of melt polycondensation PLA can reduce costs, but it is still difficult to synthetic higher molecular weight polymer of PLA. In this paper: Adding a small amount of L-alanine can be prepared 90,000 molecular weight of the P (LA-Ala) copolymer in a shorter polymerization time. Further, in order to improve the hard and brittle properties of PLA, we used self-made of high strength and toughness biodegradable Polyester - poly(ethylene terephthalate-succinic acid-glycol) (PSET) to blend with PLA. Results shows, the products of our methods has good mechanical properties and can be used as a biodegradable PLA modified market materials. The main contents of this paper is:(1)To discuss the effect of condensation temperature, esterification time and condensation time on the molecular weight of polymer. Prepare the PLLA for Mηof 8.77×104. The best synthesis technology line of PLLA is explored, that is: decompression dehydration for 2h at 120℃, join catalyst of 0.5 wt% (the weight percentage of lactic acid), gradually warming decompression esterification for 6h (vacuum about 1300 Pa). Warming up to 180℃after gradually decreases decompression to 70 Pa, then reaction for 25h. By studying the effect of different content L-alanine on molecular weight of the copolymer, the results show that when the L-alanine for the lactic acid in mol 1.5%, the molecular weight of P(LA-Ala) polycondensation for 10h can be achieved the level of purely PLLA for 25h. And the structure of the copolymer is speculated(2) The characterization of the polymer structure with FT-IR and (~1HNMR) show the polymer is the PLLA and P (LA-Ala). The DSC analysis of the products found that the melting point (Tm) and the glass transition temperature (Tg) increase with the increasement of the molecular weight and the addition of L-alanine, but the degree of crystallization is gradually reducing. By measuring TGA, the thermal decomposition temperature of products are decreasing with the increasement of L-alanine content, while the degradation-rate speeds up.(3) Putting the PLLA blended with self-made Poly(terephthalate acid -succinic acid-ethylene glycol)( PSET), the tensile strength is reduced, while the impact strength of the material is improved. When the PSET content is 20%, the two materials compatibility is better.