Production and properties of adhesives formulated from laccase modified Kraft lignin

Kraft lignin was used to formulate adhesives in combination with polyethyleneimine, chitosan and soy protein, respectively. The tensile strengths of bond lines formulated with laccase-treated and untreated lignin were found to be similar. However, a remarkable difference was noted when laccase-treated lignin was reduced by sodium borohydride prior to reacting either with chitosan or soy protein – decreasing the strength in the former case while increasing it in the other. Among the formulations, laccase treated and reduced lignin–soy protein adhesive exhibited more than half the strength of commercial polyurethane adhesive and retained 70% of its initial strength after two cycles of 1 h boiling and drying.

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► Enzyme treated Kraft lignin was used to formulate composite adhesives.
► The bond line strength of laccase-treated and untreated lignin adhesives was similar.
► Laccase treated/NaBH4 reduced lignin and soy protein resulted in better adhesive.