ABSTRACT
Lignin, the second major component of wood, is produced in large quantities as an underutilized by-product during chemical pulping. The polymeric nature of lignin nevertheless prevails after pulping. The degraded lignin fragments, called lignosulfonate, are of a rather high molecular weight but are kept in solution by sulfonic acid groups introduced during pulping. To perceive the polymerization reactions that can make alkali lignin useful in wood adhesives, it is necessary to look at the chemical composition of this material. The substitution of phenol-formaldehyde (PF) resins, and particularly phenol-formaldehyde wood adhesives, with lignin is certainly the most widely explored avenue of lignin utilization. This clearly stems from the phenolic character of lignin and therefore the expected compatibility of lignin with PF resins. Soda bagasse lignin was subsequently successfully used as the backbone polymer for the preparation of cold-cure wood adhesives. The adhesives were prepared by the hydroxymethylation of the bagasse lignin followed by the reaction of resorcinol onto the hydroxymethylated lignin.
