Effect of Preservative Type and Natural Weathering on Preservative Gradients in Southern Pine Lumber
Keywords:Preservative, preservative gradient, leaching, CCA, ACQ, micronized copper, DDACb, mass balance
AbstractThe effects of preservative type and natural weathering on preservative component distribution in southern pine boards were evaluated. Lumber was treated by a modified full-cell process with chromated copper arsenate (CCA-C), alkaline copper quat (ACQ-D), and micronized copper quat (MCQ), and samples were exposed to natural weathering. After treatment, the copper and arsenic components of CCA were uniformly distributed across the board thickness, whereas the chromium component was higher near the surface. The copper amine component of ACQ was preferentially adsorbed near the board surface, whereas MCQ had lower copper concentration near the surface compared with inside the board. The quat component (didecyldimethylammonium carbonate [DDACb]) of both preservatives was preferentially adsorbed near the surface resulting in a steep concentration gradient. After 330 da of exposure to natural weathering, the average amounts leached were 2.9% for ACQ-Cu, 0.36% for MCQ-Cu, 0.24% for CCA-Cr, 0.59% for CCA-Cu, and 2.05% for CCA-As. For ACQ and MCQ, the ratio of CuO to quat increased significantly with weather exposure indicating a higher DDACb rate of leaching compared with copper. For both preservatives, it was estimated that DDACb leaching was about 20% for ACQ and 16% for MCQ.
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