Effect of laccase pre-treatment on the mechanical properties of lignin-based agrocomposites reinforced with wood fibers

Lignins are by-products from biorefinery and paper industries. Their chemical structures are complex, and they are currently mainly used for energy and heat production generated by their combustion. In a context of higher value applications of lignins, lignin-based composites with lignosulfonate matrix and wood fibers reinforcement were pre-treated with laccase (EC 1.10.3.2) from Pycnoporus cinnabarinus, and laccase/mediator system, to modify, as a proof of concept, their mechanical properties. Composites (120 x 9 x 4 mm) were prepared by compression molding at room temperature. The flexural modulus, the fracture strength, and the fracture energy of obtained agrocomposites were evaluated by three-points bending tests. The best mechanical properties (flexural modulus of 3.51 GPa and a fracture strength of 17.5 MPa) were obtained for a simultaneous enzymatic pre-treatment of both lignosulfonate and wood fibers during 17 h with 13 U of laccase per gram of lignosulfonate.