Chemical Resistance of Western Woods

The resistance of woods to chemical solutions is an important factor in selecting wood for storage tanks. Thirteen western woods and two southern woods were exposed to solutions of several common acids, bases, and salts at room and boiling temperatures to measure their relative chemical resistance. The species selected for testing were Pseudotsuga menziesii, Abies concolor, Abies procera, Thuja plicata, Libocedrus decurrens, Chamaecyparis lawsoniana, Picea sitchensis, Tsuga heterophylla, Larix occidentalis, Pinus ponderosa, Pinus lambertiana, Pinus monticola, and Sequoia sempervirens. In addition, specimens of Taxodium distichum and Pinus palustris were included for comparison. Two pieces of each species were immersed in each test solution. Duration of exposure was arbitrary, depending on the apparent extent of deterioration in the specimens. Specimens were removed periodically and a partial load-deflection curve determined for bonding. When sufficient deterioration had occurred to make noticeable differences, the wet specimens were tested to breaking and the complete load-deflection curve plotted. Nitric and hydrochloric acids were the most destructive; each showed similar effects in both 5 and 20 percent solutions, sulfuric acid was much less active and showed only a little reaction in 5 percent solution and moderate attack in 20 percent solution. Acetic acid had little action in >5 percent solution, but a noticeable weakening of woods occurred in 20 percent solution. Boiling 1 percent solutions of hydrochloric and nitric acids showed similar results, and 1 percent sulfuric acid caused somewhat lower strength loss. The true firs generally showed relatively high acid resistance and the conventional tank woods were slightly lower in residual strength. All woods showed typical flexibility after exposure to strong bases. Douglas-fir, true firs, cypress, and southern pine were good. Redwood showed rather erratic results, and ponderosa pine sapwood proved relatively good. In 20 percent sodium hydroxide, a distinct shrinkage in specimen length was noted. Many of the woods in nondestructive salt solutions showed increases in strength, apparently because of crystallization within the wood structure. It is interesting to note that dilute solutions of sodium carbonate apparently caused greater strength loss than did more concentrated solutions. Southern pine and cypress were far superior to other woods, with incense cedar and Port Orford cedar best of the western woods.

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