Laccase mediator systems for eco-friendly production of medium-density fiberboard (MDF) on a pilot scale: physicochemical analysis of the reaction mechanism.

Increasing prices of petrochemical resins and possible harmful formaldehyde emissions from conventionally produced wood composites have resulted in increased interest in enzymatic binder systems as environmentally friendly alternatives for gluing lignocellulosic products. In this study, laccase mediator systems (LMSs) were used to activate lignin on wood fiber surfaces in the pilot-scale production of medium-density fiberboard (MDF) using a dry process. Three different mediators were applied: 4-hydroxybenzoic acid (HBA), 1-hydroxybenzotriazole (HBT), and acetosyringone (AS) of which HBA performed best. The mechanical properties of the manufactured boards produced with thermomechanical pulp (TMP) fibers, laccase, and HBA fulfilled all required European standards for wood-based panels. Oxygen consumption rates of the different LMSs and (13)C NMR spectroscopy results for treated TMP fibers were obtained for qualitative and quantitative analysis of lignin activation. The results show that reactions were most effective within the first 30 min of incubation. Oxygen consumption was fastest and highest for the LMS using HBA. (13)C NMR spectroscopy indicated the highest decrease of aromatic groups in the wood fiber lignin with this LMS. The data correlated well with the quality of the MDF. The required enzymatic reaction times allowed direct integration of the LMS into standard MDF production techniques. The results indicate that application of LMSs has a high potential for environmentally friendly MDF production.