MOISTURE AND HYDROLYSIS RESISTANCE OF PARTICLEBOARDS, BONDED WITH UNMODIFIED AND MODIFIED LOW FORMALDEHYDE UF-RESINS USING DIFFERENT CATALYST SYSTEMS .3. PROPERTIES OF PARTICLEBOARDS BONDED WITH MODIFIED LOW-FORMALDEHYDE RESINS

In continuation of the work conducted in the first and second part of this series one-layer particleboards (pine wood) were made using three different low-emission UF-resins (UF1, UF2, UF4) and various amounts of different catalysts (ammonium sulfate, ammonium nitrate, a mixture of ammonium sulfate and formic acid). Melamine formaldehyde resin, resorcinol, quebracho-tannin and diphenylmethan diisocyanate (PMDI) were used as modifiers. The investigations led to the following results: 1. The use of ammonium nitrate as a catalyst led, compared with ammonium sulfate and the mixture from ammonium sulfate and formic acid, to higher mechanical properties and lower thickness swelling of the particleboards. 2. Particleboards bonded with resin UF1 modified with melamine formaldehyde resin showed, compared with the other investigated modifications, higher resistance in dry state, in the wet state and after water soaking and redrying of the particle-boards. Also thickness swelling of these particleboards was lower. 3. Spraying PMDI prior to UF1 resin (preliminary spray method) improved the physico-mechanical properties of the particleboards (second place in the order of precedence after melamine resin). 4. Particleboards bonded with UF1 modified with resorcinol showed the lowest formaldehyde release, though this modification has a negative effect on the physico-mechanical properties of the boards. 5. Modification of UF1 with quebracho-tannin had an adverse effect on all properties of the particleboards. 6. Modification of the resins UF2 and UF4 during the condensation step of the resin led to similar effects on the properties of the particleboards as the modification by mixing modifier and resin prior to the application of the binder.