Pilot-scale production of fiberboards made by laccase oxidized wood fibers: board properties and evidence for cross-linking of lignin

Oxidoreductases can be applied for bonding of fiberboards, particle boards, paper boards and kraft-liner boards. In this work we report on pilot-scale production of laccase bonded fiberboards made from fibers of beech (Fagus sylvatica). Dioxane extractable lignin from fibers and boards are isolated and the molecular mass estimated by gel permeation chromatography. The strength properties of the enzyme bonded boards are comparable to boards bonded by an urea–formaldehyde adhesive, whereas the dimensional stability properties of the enzyme bonded boards are not at the same level. Wax treatment of the fibers, in order to improve dimensional stability of boards, is not compatible with the enzyme treatment. Cross-linking of the lignin can be observed in enzyme treated fibers and boards. Hot pressing of enzyme treated fibers results in a substantial cross-linking of lignin in boards. The enzymatic bonding effect may be caused by covalent bonds between fibers or an adhesive effect of polymerized loosely associated lignin. Laccase catalyzed bonding requires higher pressing temperatures and longer pressing times, and the concept may not be economically feasible as it is. However, it shows promise and possibilities in the use of oxidative enzymes for industrial bonding and modification of lignin.