Dry-heat Degradation of Plywood-type Joint

Abstract

In order to predict the service life of plywood heating floors, dry-heat exposure test of lauan plywood made with each of six type of typical wood adhesives was carried out at 50°, 70°, 100° and 150℃ for 250 days. Internal bond strength and location of failure of the exposed specimens were measured at selected intervals. Data were plotted as a function of the exposed time. Confidence limit was applied on the regression and the service life was calculated by extraporating the lower confidence limit curve to the half-strength. The apparent mechanism of dry-heat degradation of plywood in 150° and 100℃ seemed to differ from the lower temperature exposures. On 70° and 50℃, more conservative estimation was made by the kinetic method on the Arrhenius relationship. The result showed the detrimental effect of the acid catalyst on polyvinyl-acetate cross-linked and urea resin adhesives. Plywood specimens produced with melamine, phenol, phenol-resorcinol, and resorcinol resin adhesives showed excellent durability in dry-heat exposure at temperature normally found in service of floor heating.