Phenolated lignins as reactive precursors in wood veneer and particleboard adhesion
The high-value utilization of lignins is the most prominent opportunity to enhance the competitiveness of lignocellulosic biorefineries and reduce dependence on fossil resources. The incorporation of lignin into phenol−formaldehyde (LPF) resins represents a viable route toward this target. Due to its macromolecular nature, lignin could function as a structural backbone in the resin prepolymer. However, the low number of reactive sites with respect to phenol− formaldehyde chemistry hinders effective condensation reactions. Here, we present the effects of the phenolation of organosolv and sulfite lignin on network formation using phenol substitution levels of 20% and 40%. The wood-bonding results of raw and activated lignin-based phenolic resins reveal the superior quality of activated lignins. The wet and dry internal bond strengths of particleboards bonded by the synthesized LPF resins fulfill the European standards for load-bearing boards in humid environment. By comparison of a veneer strip rapid test and particleboard quality, a facile tool for screening resin quality is presented.