MOISTURE AND HYDROLYSIS RESISTANCE OF PAR TICLEBOARDS, BONDED WITH UNMODIFIED AND MODIFIED LOW FORMALDEHYDE UF-RESINS USING DIFFERENT CATALYST SYSTEMS

Two different UF-resins (UF 1 and UF 2) with significant differences i n their viscosity of their 50% solutions (UF 1: 70 mPa . s, UF 2: 46 m Pa . s), but almost the same molar ratio F : U (UF 1: 1,11 : 1, UF 2: 1,12: 1) and small differences in the content of free formaldehyde (UF 1: 0,07%, UF 2: 0,09%) and water tolerance (UF 1: 1:0,90, UF2: 1:1,18 ) were modified with a melamine resin (F : M = 1,6: 1), resorcinol, ta nnin and PMDI. The unmodified and modified resins were tested for some of their technological properties before and after curing using diffe rent catalyst systems (ammonium chloride, ammonium sulfate, ammonium n itrate, ammonium sulfate/formic acid). The results show: 1. There are no remarkable differences between the gelation time of the unmodified resins, however, the resin with the higher content of free formaldehyd e shows higher reactivity especially at high dilution. 2. The thermoan alytical data of the two resins (temperature curing maximum and reacti on enthalpy) are more or less the same, when the same hardener is used . 3. The catalyst has a definite influence on the temperature of curin g maximum and on the enthalpy of the curing reaction. A big difference in curing temperature was noticed between ammonium chloride, ammonium sulfate and ammonium nitrate on the one side and ammonium sulfate/for mic acid on the other side. 4. The unmodified resins show big differen ces in the formaldehyde release after curing. UF 1 releases more forma ldehyde after curing compared to UF 2, as measured by the WKI-flask-me thod and the Perforator method. 5. Modification of UF-resins with mela mine resin, resorcinol, tannin and PMDI decreases the formaldehyde rel ease of the cured resin significantly. The effect of melamine resin an d resorcinol are extremly huge. 6. Melamine resin and resorcinol have no negative effect on the shelf life of UF-resins, however, tannin and PMDI do negatively affect the storage stability of the UF-resins.