Recent Developments in Advanced Lignin-based Adhesives and Binders

Recently several developments on the use of lignin and its derivatives as wood adhesive and for other binders have come to the fore in the literature. The novelty of these approaches has been dictated by the well-known low reactivity of lignin with aldehydes in its substitution of phenol in phenol-formaldehyde resins. A brief record of the more recent novelties having being published on the use of lignin in the more traditional field of lignin-phenol-formaldehyde (LPF) adhesive resins is reported. However, this review chapter is more focused on the types of more recent alternative approaches that have been used with encouraging results to go around the obstacle of the low lignin-aldehyde reactivity. Thus, approaches based on lignin demethylation coupled with specific oxidation, pre-glyoxalated lignin dialdehyde starch cross-linking by urea, lignin-based non isocyanate polyurethane (NIPU) adhesives and resins, lignin amine coatings, lignin-triethyl phosphate cross-linking for both wood surface coatings and biobinders for metals/Teflon assemblies, and finally direct wood bonding by lignin esterification by citric acid are described.