Manufacture of resin-free fiberboards from wood fibers activated with Fenton's reagent (H2O2/Fe2+)

Production of wood fibers at high defibration temperatures (171-202 degrees C) results in partial depolymerization of fiber lignin. The extent of lignin depolymerization increases with an increase in defibration temperature and is greater for hardwood than for softwood fibers. The resulting low-molecular-weight lignin fragments are believed to play a key role in radical formation in the fibers during their treatment with Fenton's reagent (H2O2/Fe2+) in water suspension or when the reagent is sprayed onto the fibers in the defibrator blowline. Fiberboards of high internal bond (IB) strength can be made by treatment of wood fibers with a low dose of Fenton's reagent (0.25% H2O2/0-01% FeSO4 (.) 7H(2)O) before the fibers are fabricated into fiberboards. The IB strength and static bending properties of the boards improve as the defibration temperature is increased, which is mainly attributed to the concomitant increase in the amount of low-molecular-weight lignin, allowing more radicals to be formed in the fibers. The adhesion effect observed when fiberboard is made from fibers treated with Fenton's reagent may be largely due to covalent interfiber bonds formed by coupling of phenoxy radicals in the lignin-rich fiber surfaces during hot-pressing. The thickness swell of fiberboards depends on the amount of sizing agent added to the fibers and shows a low correlation with the mechanical properties. The boards made with this process are best suited for indoor applications for which high water resistance is usually not a critical factor.