Bonding of wood fiber composites using a synthetic chelator-lignin activation system
Publication Name: Forest
Publication URL: https://www.fs.usda.gov/treesearch/pubs/9146
Wood fibers, after thermo-mechanical pulping, have a high concentration of lignin on the outer surface of the fiber; the residual middle lamella of the woody cell wall. When wood fibers are oxidatively treated with a chelator produced by Gloeophyllum trabeum (a brown-rot fungus), in the presence of hydrogen peroxide (H2O2) and ferric iron (FeIII), free radicals are produced. Using a synthetic chelator to mimic the action of the free radical generating system, we applied the system to wood fibers to activate the lignin-rich fiber surface. Activating the lignin and/or extractives on the surface of the wood fibers, which has been shown previously by chemical and enzymatic means, can give lignin the functionality of a self-bonding adhesive. In preliminary work, a wet- process hardwood fiberboard was produced using a pre-treatment with a synthetic model chelator, 2,3-dihydroxybenzoic acid (DHBA), which showed an increase in the internal bond strength over that of fiberboard without DHBA pre-treatment. In this research, wet and modified dry-process softwood fiberboard exhibited increased internal bond, modulus of rupture, and modulus of elasticity with DHBA pre-treatment compared to that of fiberboard without DHRA pre-treatment. The strongest boards produced used a 1:10 ratio of DHBA:FeIII with mM concentrations of peroxide. An FeIII-only treatment displayed similar bond and bending strengths to the chelator-mediated treatments (1:10) ratio, suggesting that natural phenolics and extractives in the wood were reacting similarly to low concentrations of DHRA through a chelator-mediated Fenton mechanism.