Studies on the degradation and characterization of a novel metal-free polylactic acid synthesized via lipase-catalyzed polymerization: A step towards curing the environmental plastic issue

Abstract

Polylactic acid (PLA) is becoming one of the most paramount polymers due to its eco-friendly, biocompatible, and biodegradable nature. The feedstock (lactic acid) employed for PLA synthesis can be produced from agro-resources. Polylactic acid is expected to replace many conventional polymers, notably those used in food packaging and agricultural mulch. PLA processing techniques are ring-opening polymerization and direct condensation reactions. Mostly, polycondensation reaction uses a metal catalyst (Zn/Sn oxides), which is not safe for biomedical applications as it contains metal contamination. To make PLA more commercially appealing, ways to accelerate its degradation are constantly pursued. The work will include the synthesis of novel biodegradable metal-free bioplastic to solve the environmental plastic problems. A bioprocess was developed for manufacturing high molecular weight PLA using an enzymatic polymerization process. FTIR, NMR, GPC, XRD, DSC, TGA, and SEM analysis demonstrated the considerable change in the characteristic, morphological and thermal structures of PLA. Lactide formation was analyzed by FTIR and NMR study, followed by the monomer polymerization using lipase enzyme. The degree of crystallinity drops by 11.12% after degradation. GPC and TGA analysis confirmed the maximum M W loss and lowered T max by 46 °C after being buried in compost. SEM analysis showed the existence of cracks and voids after degradation. This new approach for the synthesis of metal-free degradable PLA would encourage its use for plastic and biomedical products in the future. • High molecular weight metal-free PLA synthesized through the enzymatic process. • Metal-free PLA can be used in a variety of food and biomedical application. • PLA degraded after one month in compost, and M W dropped 88%. • SEM images revealed a change in surface morphology from smooth to cracks and holes.