Abstract:
The substantial increase in resin costs due to the recent energy
crisis, increased public awareness to the problem of free formaldehyde
from boards bonded with urea-formaldehyde resins, and a projected
increase in the production of exterior board have emphasized the need
for new and substitute adhesive systems. One new development is the
use of lignosulfonates in combination with conventional phenol-formaldehyde
resins for the production of particleboard.
An experiment was carried out to test the applicability of such a
substituted adhesive system. A commercial phenol-formaldehyde resin
and six ammoniated-lignosulfonate-phenol-formaldehyde resins of varying
viscosity were used in the fabrication of randomly oriented oak flakeboards.
Resin application rates of 3, 4 1/2, and 6 percent were
employed in combination with nominal board densities of 40 and 45
lbs/cu.ft.
Test results indicated similar properties (internal bond, modulus
of rupture, modulus of elasticity, linear expansion, thickness swell,
and weight gain) between the commercial phenolic resin and the
substituted resins. Internal bond strength increased with increasing resin viscosity in the range studied, while modulus of rupture, modulus
of elasticity, thickness swel1, and weight gain properties generally
decreased. Increasing resin application rate and board density
resulted in an increase in board strength properties.
In a second study, resin wetting and resin molecular weight
properties were related to internal bond and modulus of rupture
strength values. Contact angle measurements were used as indicators of
resin wetting properties. Measurements were taken at 5, 30, 60, 300,
and 600 second intervals. Resin molecular weight distributions were
broken into low, medium, and high fractional molecular weight areas.
No significant relationships were found between wetting properties
and bond strength (IB, NOR). Wetting alone was not sufficient for the
formation of a strong adhesive bond. Significant relationships were
found, however, between fractional areas under the molecular weight
distribution curve and internal bond strength. IB values were
negatively related to low and medium molecular weight resin molecules,
while high molecular weight resin molecules were positively related to
IB values. Medium molecular weight area exhibited the highest degree
of correlation. No correlation was found between resin molecular
weight distribution and modulus of rupture values. In addition, no
significant relation was found between IB and NOR properties and resin
pH.
