Sustainable Strategy for Lignin Etherification and its Promotion of Anti-Uv Aging Pla Biocomposite

Abstract

Lignin functionalization in sustainable ways holds significant importance for its high-value utilization, however, it remains challenging to simultaneously achieve highly efficient modification of both the phenolic (Phe)-OH and aliphatic (Aliph)-OH of lignin.In this study, a series of highly hydroxyl-substituted alkali lignin phenyl propylene ketone ethers (ALKs) were obtained under 50 °C without any by-products via a mild and sustainable hydroxyl-yne click reaction. Notably, phenolic (Phe)-OH content of lignin decreased from 4.12 mmol g-1 to 0.07 mmol g-1 with a conversion rate of 98%, while the aliphatic (Aliph)-OH content of lignin decreased from 2.57 mmol g-1 to 0.10 mmol g-1 with a conversion rate of 96%. Owing to the efficient etherification, ALK showed excellent organic solvent (such as trichloromethane, DCM, THF, and acetone) solubility, which thereby improving the interfacial compatibility between ALK and PLA matrix. 3wt% ALK obviously enhanced the mechanical properties of ALK/PLA biocomposite films, with the yield strength, breaking strength, and Young's modulus improving by 114.2%, 30.7%, and 250.2%, respectively. Additionally, due to the newly introduced vinyl ether bonds (-C-O-C=C-) in ALK by hydroxyl-yne click reaction, only 1% ALK could endow ALK/PLA biocomposite with excellent UV shielding (100%), high transmittance (84.5%) and Anti-UV aging property. The yield strength and Young's modulus represented an increase of 209% and 86%, respectively, even after 3 hours of UV-irradiation. This study presents an environmentally friendly lignin functionalization method that unleashes the inherent Anti-UV aging properties of lignin, opening new avenues for the development of high-performance lignin-based composites.

Keywords: Lignin functionalization, Hydroxyl-yne click reaction, Biocomposite films, UV shielding, Anti-UV aging property.