Comparative analysis of different lignins as phenol replacement in phenolic adhesive formulations

Depending on the source (softwood, hardwood or annual crop) or isolation method (kraft, organosolv, sulfite, soda or enzymatic-hydrolysis), there are significant variations in lignin structures and properties. In this work, phenol was entirely replaced with nine different lignin samples in phenolic adhesive formulations to produce lignin-based resins and adhesives for application in plywood and OSB manufacturing. Properties of these novel lignin-based resins, as well as their starting lignin, were evaluated using advanced analytical methods or appropriate ASTM standard test methods. The results showed that lignins with higher p-hydroxyphenyl or higher p-coumaric acid contents were better candidates for replacing 100% of phenol in phenolic adhesive formulations. The two-way ANOVA statistical analyses revealed that among tested lignins, a biorefinery corn stover lignin was the best lignin for this application. Additionally, our results indicated that replacing entire portion of phenol with lignin in phenolic adhesive formulation would reduce the consumption of formaldehyde by 50% on weight basis.