Accelerated Aging of Adhesives in Plywood-Type Joints

This research was undertaken to determine if accelerated aging might provide a means of predicting long-term durability of adhesive-bonded plywood joints. The degrading influences of moisture, temperature, and cyclic swelling and shrinking stresses were determined as rate phenomena measuring the loss of shear strength with time of exposure to selected laboratory controlled environments. Separate rate values for loss of shear strength were determined for specific types of bond failure. The rate values for shear-strength loss varied with temperature according to the Arrhenius equation when the values were segregated into specific bond-failure types. The methodology holds promise for providing information useful in comparing the behavior of different adhesives on bonded joints and in predicting long-term durability with a higher level of confidence than has been previously possible. All veneer used in the study was rotary cut 1/8-inch yellow birch and Douglas-fir. The glues were typical commercial synthetic-resin formulations. Ten specimens of each type were tested by the following control tests: 1) After conditioning at 80?F and 65 percent RH and testing dry. 2) After 48 hours of soaking in water at room temperature and testing wet. 3) After boil-cycle treatment. 4) After a vacuum-pressure soak treatment.

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