Outdoor aging of wood-based panels and correlation with laboratory aging

This report describes the effects of outdoor aging on wood-based materials and relates their performance to that of materials exposed to accelerated aging in the laboratory. Fourteen phenolic-bonded wood-based panels, 1 phenolic-bonded structural plywood, and 2 solid woods were exposed to outdoor aging for periods from 7 to 12 years. Modulus of rupture (MOR), modulus of elasticity (MOE), internal bond strength (IB), and thickness swelling (TS) of the materials were determined periodically during aging. Specimens of the same materials were exposed to accelerated laboratory treatments, including cyclic boil-dry (BD), vacuum-pressure-soak-dry (VPSD), and American Society for Testing and Materials (ASTM) Standard D 1037. The greatest reduction in performance occurred in the first year of outdoor aging and was largely the result of initial springback. The poorest-performing panels lost more than 50 percent of initial MOR within 3 years. The best-performing panels lost less than 50 percent of initial MOR after 10 years and appeared to be weathering as well as solid wood. Strong correlations (Pearson’s and Spearman’s correlation coefficients >0.90) were found between MOR after cyclic BD aging and MOR after outdoor aging. Predictive equations for MOR, MOE, IB, and TS in outdoor aging were developed as functions of material performance after either five cycles of BD treatment or after the ASTM D 1037 aging treatment.

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