Facile green transformation of alkali lignin via laccase-mediated functionalization for high-performance lignin-based films

Abstract

Valorising alkali lignin (AL), a biorenewable pulping byproduct, is essential for advancing a circular bio-economy. However, its inherent low reactivity limits its potential as a petroleum-polyol substitute. This study developed a green biocatalytic strategy using Trametes versicolor-derived laccase to activate AL efficiently under mild, environmentally benign conditions. The results demonstrated that this enzymatic modification approach effectively increased the hydroxyl content and chemical accessibility of lignin, facilitating its transformation from a low-value filler into a functional co-polyol. The analysis results also confirmed that the elevated concentration of reactive -OH groups significantly enhanced both the homogeneity and the crosslinking density within the lignin-polyurethane network by reducing steric hindrance. When lignin content reached 30%, the laccase-modified lignin-based films (LMLPFs) exhibited a higher performance in both tensile strength and elasticity modulus compared to unmodified lignin-based films (LPFs), reaching values of 31.49 MPa (increased 25%) and 215.23 MPa (increased 60%), respectively, compared to 25.21 MPa and 134.40 MPa for LPFs. Furthermore, the thermal stability of LMLPFs was also improved, with the decomposition temperature at 5% mass loss (T5%) increasing from 277 ℃ (LPFs) to 280 ℃. By replacing fossil-derived components with enzymatically valorised biopolymers through an energy-efficient process, this work provides a feasible, sustainable pathway for the design of advanced lignin-based biocomposites.