Use of Candida rugosa lipase as a biocatalyst for L-lactide ring-opening polymerization and polylactic acid production

Candida rugosa lipase (CRL, EC Number: 232–619-9) is a stable enzyme, and its use is relatively widespread in the field of biotechnology, especially in hydrolysis reactions, esterification, transesterification and enantioselective biotransformation. This study examined the role of CRL as a biocatalyst for L-lactide ring-opening polymerization in the production of metal-free polylactic acid (PLA). The ring-opening polymerization reaction was conducted at various temperatures (70, 90, 110 and 130 °C) and CRL concentrations (1, 2, 3 (%w/w)). The results revealed a strong relationship between PLA formation and CRL activity. The highest CRL activity was obtained in ring-opening polymerization of L-lactide at a temperature of 90 °C and concentration of 2% (w/w). Under these conditions, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of PLA analyzed by gel permeation chromatography was highest at 5428 and 2854 g/mol respectively, with a yield of 93% and the enzyme activity 0.39 U. The polymerization of lactide at 90 °C occurred only in the presence of the catalyst. The crystallinity and melting point of PLA were 31% and 120 °C, respectively. Scanning electron microscopy (SEM) analysis of the morphology of PLA revealed smooth and uniform pores in each region, with mass percentage of the elements carbon (C) and oxygen (O) of 52% and 48%, respectively.