Keywords: Adhesive; Lignin; Protein; Laccase; TEMPO
The aim of this study was to enhance the water resistance of soy protein (SP) adhesives using laccase/TEMPO-modified lignin. Kraft lignin was depolymerized by laccase enzyme in the presence of TEMPO to expand the oxidation reaction of both phenolic and non-phenolic compounds. This simplified process has the distinct advantage of enhancing lignin-protein interaction. Compared with SP adhesives, lignin-protein adhesives showed a stronger elastic modulus, higher thermal stability, and increased wet adhesion performance. Wet shear strength increased by 106% from 0.693 to 1.429 MPa, and partial wood failure was observed after the test. Better performance was also observed in the three-cycle soaking test. At the same time, the stronger interactions between -COO- and -NH2 groups of protein and lignin led to a decrease in flowability and spreadability.
