Synthesis of Polylactic Acid from Fermentative Lactic Acid by Direct Polycondensation for Materials Application

Poly lactic acid (PLA) is one of the major commercially available polymers which widely used in the food packing materials, fibers, agricultural films and biomaterials. PLA synthesis was carried out in a direct polycondensation with p-toluenesulfonic acid (PTSA) as a catalyst. The fermentative lactic acid prepared from Lactobacillus rhamnosus TISTR 108 was used as a monomer of polymerization. In addition, the number average molecular weight (M-n) and molecular weight (M-w) of PLA products were analyzed by end-group analysis and High Performance Liquid Chromatography (HPLC). The results indicated that only low molecular weight of PLA could be successfully produced from fermentative lactic acid by direct polycondensation under appropriate conditions; 0.25 wt% PTSA as catalyst, temperature at 170 degrees C and polymerizing time for 7 hr. The number average molecular weight (M-n) and molecular weight (M-w) of the PLA products were 2,627 and 232 Da, respectively. Furthermore, PLA products were formed as a film with blending of PLA synthesized from fermentative lactic acid and commercially available PLA by using solvent casting method. As a result, fermentative lactic acid is a new alternative substrate for PLA synthesis which contributes to the reduction of production cost, increasing the renewable resources value, and development of bioplastic environmentally friendly materials.