Use of alkyl ketene dimer (AKD) for surface modification of particleboard chips

The study objective was to impart urea-formaldehyde (UF) bonded particleboards higher and longer-lasting hydrophobicity than that resulting from conventionally used paraffin. Alkyl ketene dimer (AKD) is a paper sizing agent that can theoretically esterify wood compounds and result in a surface modification. Particles were 1) impregnated with an aqueous AKD-solution and cured at 130 degrees C prior to gluing, or 2) sprayed with a mixture of AKD-solution and UF-resin in a single step. Boards with and without paraffin wax were used as controls. Thickness swelling after 2, 24, and 48 h immersion was decreased by 90, 62, and 59% when the chips were impregnated with AKD in comparison to untreated control boards. Water uptake after 2, 24, and 48 h was reduced by 91, 75, and 60%. AKD-impregnation with subsequent curing decreased the internal bond strength by 53%, indicating that AKD impedes the adhesion. The mixture of AKD and UF-glue did not result in considerable hydrophobicity. Increased methyl/methylene and carbonyl bands in FTIR-spectra after toluene-extraction suggest that AKD partially formed ester bonds at the wood surface.