It has been known from the previous paper that the polyvinyl alcohol-modified urea resin adhesive has the gap-filling property.
In the present paper, the durability of the polyvinyl alcohol-modified urea resin adhesive is discussed. Beech sapwood were glued with polyvinyl alcohol-modified urea resin adhesive and unmodified urea resin adhesive. Glue-line thickness were regulated in 60-100microns and 320-370 microns thick. These glued woods were exposed for five years to the repeating cycle consist of 2 weeks at 25℃ and 33 percent relative humidity and 2 weeks at 25℃ and 87 percent relative humidity.
After1-7, 9, 12, 16, 21, 39, 51 and 63 cycles were repeated, the block shear test was carried out with respective sample blocks.
Transition of glue-joint strength and wood failure for five yearsis shown Fig.1 and 2.
The glue-joint strength and wood failure when polyvinyl alcohol-modified urea resin adhesive was used were higher than those when the unmodified urea resin adhesive was employed.
In all cases, the glue-joint strength and wood failure increased through 4-9 cycles, and then they decreased along with exposure period.
Deterioration of polyvinyl alcohol-modified urea resin adhesive after 63 cycles was remarkably less in conparison with that of unmodified urea resin adhesive.