Liquefaction of lignocellulosic materials and its applications in wood adhesives-A review

Liquefaction, a useful method of turning whole biomass into liquids, provides advantages for energy and polymers and finds applications in many sectors. This paper reviews the different liquefaction technologies and recent advances in the development of sustainable wood adhesives. Current liquefaction technologies include hydrothermal liquefaction (HTL) and moderate acid-catalyzed liquefaction (MACL). HTL produces bio-oils as primary products, and solid residues and gases as by-products. MACL depends on the solvent types used, which are grouped to polyhydric alcohols and phenols. Bio-polyols from alcohol liquefaction, phenolated biomass from phenol liquefaction and phenolic compounds rich-HTL bio-oils have been used in the production of liquefied biomass-based adhesives, which have shown competitive properties but face challenges for industrial uses. Yet, a better understanding of reaction pathways and optimization of the liquefaction processes is needed.