Screening high-quality lignins extracted from biomass to prepare biobased wood adhesives

Practical lignin valorization strategies have the potential to enhance the profitability of lignocellulosic biorefineries. Leveraging the phenolic structure of lignin, commercially available lignins (for example, kraft, soda or biorefinery lignin) have been extensively studied as renewable substitutes for phenol in the synthesis of lignin-phenol-formaldehyde resin adhesives. However, the large-scale production and adoption of lignin-phenol-formaldehyde resin adhesives remain limited owing to challenges related to appearance, performance and cost. To address these limitations, this protocol outlines a comprehensive process for producing lignin adhesives with light colors, high adhesion properties and superior water and weather resistance. The procedure encompasses: (1) isolation of lignin from various types of biomass pretreatment liquors; (2) screening of high-quality lignins from the isolated lignins; and (3) performance assessment of lignin adhesives prepared directly from high-quality lignins without the need for chemical modification or additional processing. Additionally, this protocol provides a rapid and quantitative method for determining the condensation degree of lignin using a small amount of the isolated lignin sample (~50 mg) within a relatively short experimental time (5 h 20 min). This enables efficient quality evaluation and screening of high-quality lignins derived from different extraction methods and biomass sources. The entire process, from biomass to lignin adhesive fabrication, requires a total of 8 h 10 min and is designed for users with prior experience in biomass fractionation, chromatographic analysis and wood-based panel production.