Functionalization and Thereafter Grafting with Lactic Acid to Synthesize Lignin-polylactic Acid Copolymer for Thin Film Preparation

Availability, renewability, biodegradability, and excellent mechanical strength of lignin result in the growing interest in using it for commodity polymer development. Therefore, several attempts have been made and reported in the literatures to develop polymer from it. Despite several attempts, factors such as self-aggregation, low reactivity, and solubility still have limited the large-scale application of lignin. Therefore, to control these factors, here in this work, we have modified lignin with a reactive functional molecule Epichlorohydrin (ECH) to prepare epoxidized lignin (EL). Later, the copolymer, Lignin-Polylactic acid (Lig-PLA) was synthesized by graft polymerization of Lactic acid (LA) on EL. Synthesized EL, and Lig-PLA copolymer were characterized through FT-IR, XPS, and Solid-state C-13 NMR analysis. Higher weight (wt) loss along with high rate of crystallinity from TGA and XRD analysis confirmed increased grafting of LA onto EL while synthesizing copolymers of Lig-PLA with increased amount of LA. The hydraulic hot press technique was used to prepare 250 micron thin Lig-PLA copolymer film. Lig-PLA copolymers prepared with LA >= 50 wt% produced polymer films with very good flexibility which confirms that a flexible film can be prepared with high lignin content from this method.

Automated summary

The availability, renewability, biodegradability, and excellent mechanical strength of lignin have led to increased interest in using it for commodity polymer development. However, factors such as self-aggregation, low reactivity, and solubility have limited its large-scale application. In this work, lignin was modified with Epichlorohydrin to prepare epoxidized lignin (EL), which was then used to synthesize the copolymer Lig-PLA by graft polymerization of Lactic acid (LA). The characterization of EL and Lig-PLA copolymer confirmed successful grafting and the potential for flexible film production with high lignin content.