INFLUENCE OF DIFFERENT CATALYST SYSTEMS ON THE HYDROLYTIC STABILITY OF PARTICLEBOARDS BONDED WITH UNMODIFIED AND MODIFIED UF-RESINS

After a storage time of one year, the influence of different catalyst systems on the release of formaldehyde and volatile acids from particl eboards bonded with unmodified and modified UF-resins was studied at 3 0 degrees C (only for formaldehyde), 40 degrees C and 50 degrees C and 100% relative humidity. The results reveal that modification of UF-re sins with a melamine resin of molar ratio F:M 1.6:1 and resorcinol sig nificantly increases the hydrolysis resistance of the UF-resin in the boards. Resorcinol, especially at higher temperatures, was even more e ffective than melamine resin. Measurable differences in the formaldehy de release of particleboards were detected. The boards were separately bonded with two low-emission UF-resins with subtle differences in the chemical composition. The amount of hardener, varied between 0.8% and 3.2% (based on resin of 66% solids), had practically no influence on the release of volatile acids from particleboards. In contrast to the behaviour of solid wood, UF-particleboards made from pine chips releas ed substantially more formic acid than acetic acid, especially at high temperatures. Modification of the UF-resin with resorcinol and melami ne resin had no effect on the release of acetic acids from the boards. The release of formic acid decreased slightly on modifying the resin with resorcinol and melamine resin. The results indicate that the infl uence of modification and resin type on the hydrolytic resistance of t he boards is still apparent even after a storage time of one year.