Effect of Curing Temperature on Rate of Cure and Quality of Casein Glued Joints

This report is a summary of several studies on the effect of curing temperatures below 70?F on the rate of cure and bond quality of casein glues. Three commercial brands of casein glue meeting the requirements of Canadian Standards Association Specification 0112.3 for Type 1 glue (for use where a bond with resistance to moisture and micro-organisms is required) were used. Lap-test specimens with an over-lap area of 1 inch were prepared from 1/8-inch-thick strips of yellow birch. The wood was conditioned to 12 percent moisture content prior to gluing at a pressure of 100 psi. Mixing was done at 70?F. The adhesive was not allowed to equalize with the temperature in the test chamber, but the temperature of the glue was allowed to drop during the period required to assemble the test specimens. A 15-minute closed-assembly time was used, and the test pieces and assembly jig were brought to the desired test temperature prior to glue application. The clamping period varied, but did not exceed 16 hours. Specimens were tested in the dry condition and in the wet condition following a 48-hour immersion in water at room temperature. Strength in pounds and percentage wood failure were the recorded test values. To study the effect of constant, low curing temperatures or rate of cure and bond quality, specimens were cured at 70, 50, 35, and 20?F. Cure periods ranged from 2 hours to 4 weeks. It was found that rate of cure varies with curing temperature. Curing rate decreases as the temperature decreases; however, even at 20?F the joints developed considerable strength in period as short as 2 to 4 hours. The effect of curing temperature on ultimate joint strength showed that strength varies considerably with different glues; however; the overall pattern is fairly consistent — ultimate dry strength of casein gluebonds is relatively unaffected by curing temperature. Curing temperature did, however, influence the moisture resistance of the bonds. The moisture resistance decreases as the curing temperature decreases below 70?F. The loss in moisture resistance of specimens cured at 35?F was not sufficiently great to preclude the use of this adhesive at this low temperature. Post-curing at 70?F of bonds that had been originally cured at lower temperatures has no apparent effect on bond quality.

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