An approach to improve the application of acid-insoluble lignin from rice hull in phenol–formaldehyde resin

The study was based on the yield of ligninphenol and the resins, morphology, temperature stability, water and ultraviolet resistance of the formulated resins, to describe a route to improve the potential for partially replacing phenol with rice hull acid-insoluble lignin in phenol–formaldehyde (PF) resin. In this route, phenolation and three-step polymerization were combined to increase the reactivity of rice hull acid-insoluble lignin. The formulated resin exhibited a better morphology and temperature stability compared with rice hull acid-insoluble lignin/PF (RPF) resin, and a better water and ultraviolet resistance compared with ligninphenol/PF resin prepared by phenolation and one-step polymerization (LPF1). The good properties of the product were attributed to the increased covalent interaction between PF resin and lignin. The strategy showed low-cost, simple operation, no pollution and high value.