Native lignin for bonding of fiber boards -: evaluation of bonding mechanisms in boards made from laccase-treated fibers of beech (Fagus sylvatica)

The auto-adhesion of beech wood (Fagus sylvatica) fibers can be enhanced by a pretreatment of the fibers with a phenol oxidase enzyme. The mechanism of enzymatic catalyzed bonding is linked to the generation of stable radicals in lignin by oxidation. Fiberboards made from laccase-treated fibers have a high wet strength compared to boards made from untreated fibers. This indicates better fiber-fiber interactions and improved fiber-fiber stress transfer. The surface of laccase-treated fibers shows a markedly increased hydrophobicity as well as a change in the chemical composition, which indicate that lignin extractives are precipitated on the fiber surfaces. The improved bonding may be related to several factors, linked to a more lignin rich fiber surface, such as surface molecular entanglements and covalent bonding between fibers through cross-linking of radicals. (C) 2004 Published by Elsevier B.V.