Valorization of technical lignin for production of desirable resins with high substitution rate and controllable viscosity.

The valorization of lignin to replace phenol is significant when producing phenolic resins. However, a great challenge is to produce lignin-based resin (LR) with suitable viscosity and high substitution rate of lignin to phenol. In this study, LRs were produced using hardwood technical lignin derived from pulping industry. The structure analyses of LRs indicated that the unsubstituted para and ortho carbons of aromatic ring influenced the curing temperature and activation energy of resins. The curing kinetics and thermal decomposition study implied that urea and methylene groups in cured LRs were the significant factors that negatively affected thermal stability. The prepared LRs showed desirable features when used as adhesives to make plywood. This is the first approach that the substitution rate of low reactive site hardwood lignin can achieve up to 65%, providing a solution to the challenge for simultaneously realizing the high addition of lignin and adaptive viscosity of resins.