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Abstract
Poly(lactic acid) is the biodegradable aliphatic polyester produced in small quantity and in large quantities industrially and used very variously. Because of its good mechanical property and reconcilability with environment, it is one of the polymers most appropriate to replace non-biodegradable synthetic polymers based on crude oil. PLA can be made from lactic acid with different polymerizations such as polycondensation, ring-opening polymerization, and direct polymerizations by azeotropic dehydration or the enzymatic polymerization. The direct polymerization and the ring-opening polymerization are the most used techniques. This paper reviewed methods of making PLA such as oligomer polycondensation or ring-opening polymerization and mainly mechanism of ring-opening polymerization with 4 areas: metal catalyst, organic catalyst, cationic catalyst and stereo-controlled polymerization.
Highlights
Plastics based on synthetic polymers using crude oil as a raw material are widely used in various areas such as packing, electrical equipment, construction materials, and farming
Biodegradable polymers gained from the renewable materials can be classified into 3 categories according to their raw material and synthetic method: the first, they are polymers extracted from the agricultural products such as cellulose; the second, polymers made by microorganism such as poly(hydroxyalkanoate); and the third, synthetic polymers using monosaccharide that can be obtained from agricultural products such as PLA [1,2]
Many single site catalysts composed of various multivalent ligands were synthesized, and synthetic methods are known to synthesize PLA matters stereocontrolled from DL-lactide [52] (Figure 6)
Summary
Plastics based on synthetic polymers using crude oil as a raw material are widely used in various areas such as packing, electrical equipment, construction materials, and farming. PLA can be made through a polymerization process from the lactic acid by polycondensation or ring opening polymerization, or can be made by direct methods such as azeotropic dehydration or enzymatic polymerization [9,12]. The direct polycondensation is composed of 3 steps: removal of water, polycondensation of oligomer, and melt condensation that makes PLA with high molecular weight. Direct polycondensation of lactic acid is the competitive reaction that forming and decomposition processes of lactide simultaneously, so it is not used for the large producing reaction [19,20,21,22].
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