Accelerated and 5-Year Exposure Tests on Exterior Type Poplar Plywood

A study of exterior poplar plywood exposed outdoors for 5 years showed that a wood failure estimate of bond quality had the same meaning in poplar as in Douglas-fir plywood in the sense of predicting delamination in outdoor exposure. An accelerated delamination test was more efficient than wood failure in predicting the delamination of plywood exposed outdoors, and this test may become a performance test for plywood. The dominant factor controlling glueline quality is the amount of resin solids in the glueline itself and is independent of spread or degree of extension with wheat flour. The panels tested were 3-ply, made with 1/8-inch veneers of poplar bonded with hot-press phenol-formaldehyde resin adhesives obtained from two commercial suppliers. Two specimens were cut from each plywood panel for each of two treatments. In these specimens only the length (not depth) of delamination was measured. Because of the notched design, the total length of glueline was reduced to 12 inches. The accelerated-aging techniques showing the greatest promise were all based on cyclic wetting and drying.

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