Enhanced Auto Adhesion of Wood Fibers Using Phenol Oxidases

Abstract

Enzymatic oxidation of lignin phenolic hydroxyl groups can enhance the level of auto adhesion between wood fibers. Previous investigations within the area have not taken the adhesive effect of proteins and carbohydrates in the enzyme solution into consideration, and part of ι he claimed enzyme generated adhesion may merely be a result of the adhesive effect of the proteins and carbohydrates in the enzyme solution. In this paper the enzyme laccase is used to oxidize beech (Fagux sylvatica) wood fibers. Laccase catalyzes a one-electron oxidation of phenolic hydroxyl groups while reducing oxygen, yielding phcnoxy radicals and water. Wet and dry process fiberboards are made from enzyme treated and untreated beech wood fibers. The enzyme treated fiberboards have significantly higher modulus of rupture and modulus of elasticity as well as better dimensional stability. No effect of the protein and carbohydrate content in the enzyme solution upon the mechanical properties and dimensional stability can be found. The bonding effect is caused by the catalytic effect of the enzyme only. Electron spin resonance spcctroscopy of beech wood fibers shows that a considerable amount of the laccase generated radicals is stabilized in the lignin polymer, and the bonding mechanism appears to be associated with reactions of these free radicals. The physico-mechanical parameters of the enzyme treated fiberboards have not been optimized in the present work. Hence, strength improvements may be obtained simply by optimizing the process parameters. The possibility of producing a medium density fiberboard without the use of synthetic adhesives appears to be promising. The use of oxidative enzymes in processing and manufacturing of wood-based materials may yield new and more environmentally safe products.

Laccase Application for Upgrading of Lignocellulose Fibers

“…Enzymatic treatment of wood fi bers or other wood particles before their pressing into composite boards, such as medium density fi breboards (MDF), has been investigated by Felby, Kharazipour and coworkers since 1997. For example, laccase has been shown to greatly improve the internal bond (IB) of fiber boards (Felby et al, 1997;Kharazipour et al, 1997;Hüttermann et al, 2001;Felby et al, 2002;Felby et al, 2004). This effect may be explained by the fact that laccase oxidizes the phenolic structures in lignin, which leads to relatively stable free radicals that may participate in fi ber bonding by subsequent radical coupling (Fackler et al, 2008).…”

Laccase-Catalyzed Fiber Functionalization with Different Phenolic Compounds for Enhancing Pulp Strength

“…The wet tensile strength of handsheets was related to bonds being resistant to water sorption, such as covalent bonds between fibers (Espy 1995). The phenolic hydroxyl groups can be oxidized to phenoxyl radical by laccase (Felby et al 1997). The MS or SyA presents the methoxy groups with hydrophobicity.…”

“…Enzymatically catalyzed bonding is linked to the oxidative generation of stable radicals in lignin, and the radicals can cause cross-linking or loosening of the lignin structure (Felby et al 1997). Table 3 shows that the surface lignin coverage of fibers significantly increased from 33.0% to 38.9% after laccase/MS treatment, and the kappa number slightly increased from 24.9 to 25.6.…”

“…As is well known, phenoxy radicals are formed in the lignin matrix in the laccase-catalyzed oxidation of wood fibers (Felby et al 1997). Activation of fibers is the first step in fiber functionalization aiming at an introduction of desired properties to fiber (Grönqvist et al 2006).…”

Wood production, wood technology, and biotechnological impacts

“…In order to replace the commonly used binders on petrochemical basis (urea-formaldehyde, phenol-formaldehyde, phenyldiisocyanate; see Chapter 15 of this book), lignin on fibre surfaces (lignin of the middle lamellae) is activated by laccases through oxidative enzymatic reactions yielding lignin radicals for subsequent polymerisation reactions , Felby et al 1997; for an extensive presentation see Chapter 18 of this book).…”