A Renewable Lignin–Lactide Copolymer and Application in Biobased Composites

TLDR

Renewable alternatives to petroleum plastics are sought, and lignin—an abundant plant‑derived feedstock—offers promise but is difficult to blend with other biopolymers. The study develops a catalytic, solvent‑free method to synthesize a lignin–PLA copolymer that improves lignin miscibility with bioplastics. Lactide is grafted onto lignin via TBD‑catalyzed polymerization, with PLA chain length tuned by adjusting the lignin/lactide ratio and preacetylation. The resulting lignin‑g‑PLA copolymers exhibit high grafting efficiency, preferential grafting on aliphatic hydroxyls, a glass‑transition range of 45–85 °C, multiphase melting, and act as dispersion modifiers that improve UV absorption and reduce brittleness while maintaining modulus.

Abstract

The need for renewable alternatives to traditional petroleum-derived plastics has driven recent interest in biobased composite materials that are sourced from carbon-neutral feedstocks. Lignin, an abundant plant-derived feedstock, has been a candidate for renewable materials; however, it is often difficult to blend with other biopolymers. In order to improve the miscibility of lignin with other bioplastics, we developed a catalytic and solvent free method for synthesis of a lignin–PLA copolymer. Graft polymerization of lactide onto lignin catalyzed by triazabicyclodecene (TBD) resulted in a lignin-g-poly(lactic acid) copolymer; chain length of the PLA is controlled by varying of the lignin/lactide ratio and preacetylation treatment. End-group analysis reveals high grafting efficiency and preferential grafting on lignin aliphatic hydroxyls over phenolic hydroxyls. The lignin-g-PLA copolymers display a glass transition temperature range from 45 to 85 °C and multiphase melting behavior. The lignin-g-PLA copolymers are used as dispersion modifiers in PLA-based materials to enhance UV absorption and reduce brittleness without a sacrifice in the modulus of elasticity.