MOISTURE AND HYDROLYSIS RESISTANCE OF PAR TICLEBOARDS, BONDED WITH UNMODIFIED AND MODIFIED LOW FORMALDEHYDE UF-RESINS USING DIFFERENT CATALYST SYSTEMS .3. PROPERTIES OF PARTICLEBOARDS BONDED WITH MODIFIED LOW-FORMALDEHYDE RESINS
E. Kehr et al., MOISTURE AND HYDROLYSIS RESISTANCE OF PAR TICLEBOARDS, BONDED WITH UNMODIFIED AND MODIFIED LOW FORMALDEHYDE UF-RESINS USING DIFFERENT CATALYST SYSTEMS .3. PROPERTIES OF PARTICLEBOARDS BONDED WITH MODIFIED LOW-FORMALDEHYDE RESINS, Holz als Roh- und Werkstoff, 52(4), 1994, pp. 253-260
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, res
orcinol, 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 hig
her mechanical properties and lower thickness swelling of the particle
boards. 2. Particleboards bonded with resin UF1 modified with melamine
formaldehyde resin showed, compared with the other investigated modif
ications, higher resistance in dry state, in the wet state and after w
ater soaking and redrying of the particle-boards. Also thickness swell
ing of these particleboards was lower.3. Spraying PMDI prior to UF1 re
sin (preliminary spray method) improved the physico-mechanical propert
ies of the particleboards (second place in the order of precedence aft
er melamine resin). 4. Particleboards bonded with UF1 modified with re
sorcinol showed the lowest formaldehyde release, though this modificat
ion has a negative effect on the physico-mechanical properties of the
boards. 5. Modification of UF1 with quebracho-tannin had an adverse ef
fect on all properties of the particleboards. 6. Modification of the r
esins UF2 and UF4 during the condensation step of the resin led to sim
ilar effects on the properties of the particleboards as the modificati
on by mixing modifier and resin prior to the application of the binder
.