High-yield separation of less-condensed lignin from pine for direct use as a wood adhesive

Lignin is second abundant component in lignocellulose which acts as a natural binder in plant cell wall. Since the utilization of phenolic and urea–formaldehyde as wood adhesive in furniture continuously releasing toxic formaldehyde gas and damaging people’s health, using natural lignin as wood adhesive performs significant advantages. However, harsh reaction conditions are generally used in lignin extraction from lignocellulose to overcome the dense structure, which causes lignin structural condensation and reduces its adhesive activity. To address this issue, we employed a novel lithium bromide (LiBr) molten salt hydrate (MSH) acidified with citric acid to facilitate the rapid dissolution and hydrolysis of cellulose and hemicellulose with conversion rates of 95.7% and 98.6%, respectively, with less-condensed lignin of a purity of 95.7% isolated in solid part at mild condition at 100 ℃ for 60 min. The obtained lignin can be directly blended with water and used as a plywood adhesive without the addition of any other chemicals addition, demonstrating the dry strength of plywood reached 1.19 MPa, surpassing the industry standard at 0.7 MPa, highlighting the practical viability of the obtained lignin in adhesive applications.