Deep eutectic solvents regulates lignin: in situ synthesis of low curing temperature phenolic resin

Abstract

Lignin-based phenolic resins (LPF) are promising bio-based adhesives but their industrial use is restricted by the need for complex lignin modification, high viscosity, and high curing temperatures. A low-viscosity resin (PFA-LPF) was then prepared through a one-pot in-situ process, and oxalic acid was introduced as a curing agent to obtain adhesive. The viscosity of PFA-LPF decreased by 77.5% relative to LPF, and the curing temperature of adhesive was reduced to 89.9 °C, representing a 36.7% reduction compared with commercial phenolic resin (PF). At a 25% lignin substitution level, the adhesive achieved a boiled water wet shear strength of 1.01 MPa, exceeding that of PF. SEM, FT-IR, and TGA analyses confirmed that phenol-furfuryl alcohol based deep eutectic solvents (PFA-DES) simultaneously promotes lignin dissolution, structural activation, and grafting reactions, forming a pre-crosslinked network that enhances curing and adhesion. This method significantly simplifies the complex steps of lignin modification and establishes a rapid preparation approach for LPF, providing an innovative solution for sustainable and energy-efficient wood processing.