Biodegradable Poly(Lactic Acid) with High Molecular Weight

Abstract Biodegradable plastics have been quickly accepted as one of the key solutions for today's waste plastics problems in Japan. Particularly, poly(lactic acid) is looked forward to as the most promising biodegradable plastics because of its high quality in optical and physical properties as well as chemical recyclability and compostability. Furthermore, lactic acid as a raw material of this polymer can be produced from agricultural starch wastes. However, one of the greatest issues in biodegradable plastics including poly(lactic acid) and lactic acid-based copolymers lays in their extremely high price when compared to typical commodity plastics on the market. Regarding poly(lactic acid), a polymer with high molecular weight of more than Mw = 100 000 is conventionally obtained only by a ring-opening polymerization process from lactide, i.e., dimer of lactic acid, which is very expensive. To aim at developing practical and economical technologies for effectively producing poly(L-lactic acid) as a representative of lactic acid-based polymer, we have been carrying out continuous melt-polymerization experiments using the combination of a batch type stirred reactor and an intermeshed twin screw extruder in this study. As a result, we have successfully obtained poly(L-lactic acid) with higher molecular weight of up to Mw = 150 000 from lactic acid by a continuous melt-polycondensation process.