The effects of various catalysts used to cure the resinous adhesives on the strength properties of plywood vas investigated, particularly with regard to the degree of acidly developed by the catalysts in the resin film and In the plywood. The flexural, impact, and shear strengths, Doth Initially and after;aging, of birch plywoods bonded with urea-formaldehyde and phenol-formaldehyde resins definitely;-decrease as the acidity of the plywood increases^ as evidenced by a-decrease in pH. Only in the case V of plywood bonded with casein and urea-formaldehyde resins had the dete¬rioration at the bond progressed sufficiently in the roof-aging tests to make it impossible to carry out strength tests because of delamination. A correlation between decrease in strength on aging of plywood bonded with alkali-catalyzed phenolic acid and increase in alkalinity of the panel was observed. Because of the different absorption capacities of the phenolic reins for acids and alkalies, it is not possible to pre¬dict the pH of the plywood panel from the pH of the resin film.
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