In these experiments, the effect of specific gravity, wettability, pH and percentage of the extract on the gluability of the 18 tropical woods was discussed.
For the test of gluability, the 18 tropical woods were glued with urea formaldehyde (UF), pheno lformaldehyde (PF) resin adhesive and polyvinyl acetate emulsion(PVAc). Dry test and drying-wetting cycle test were carried out for glued woods.
The wettability for each wood was determined by the method of capillary rise. The values of the corrected water absorption height (C.W.A.H.) were calculated by the equation showing in Table 3 for the actual reading water absorption height each hour.
The pH of wood was determined with a glass electrode pH meter on the mixture of three grams wood flour and 50 grams of distilled water.
The percentage of extract was determined by the extracting method with cold water, hot water and ether.
The results obtained are shown in Table 2 and 3.
The following conclusions may be drawn from these experimental results.
1) It was recognized the high degree of correlation between glue-joint strength (Y) and specific gravity(X). The glue-joint strength increased along with the increase of specific gravity.(Fig. 2-4)
<tt>
Adhesive Cofficient of correlation Equation of regression line
UF r=0.84 Y=234X-9
PF r=0.72 Y=157X＋30
PVAc r=0.72 Y=180X＋11
</tt>
2)The glue joint strength was deteriorated for the specimens glued with UF, but it was unchanged for the specimens glued with PVAc in consequence of the drying-wetting cycle test.
3)It was recognized the high degree of reverse correlation between wettability (C.W.A.H.) and specific gravity. (coefficient of correlation r=-0.92) The values of C.W.A.H.) with the decrease of specific gravity. (Fig. 6)
4) The glue-joint strength increased with the increase of C.W.A.H., when the effects of specific gravity were excluded. (Fig. 7)
5) The relationship between the glue-joint strength and pH was not significant.
6) The relationship between the glue-joint strength and the percentage of extract either by cold water or by hot water was not significant. But the glue-joint strength increase with the decrease of percentage of extract in the ether extraction, when the effect of the specific gravity were excluded. (Fig. 8)
The specific gravity had more important effect on the glue-joint strength, followed by the wettability (C.W.A.H.).
The value of pH and percentage of extract had less important effect on the glue-joint strength.