Effects of ammoniacal copper citrate preservative treatment and redrying on bending properties of two grades of southern pine 2 by 4 lumber

Ammoniacal copper citrate (CC) is a new preservative recently accepted in many American Wood Preservers’ Association standards. This study evaluated the effects of CC preservative treatment on several mechanical properties of two grades of southern pine dimension lumber. For the Dense Select Structural grade lumber, the effects of CC treatment were generally found to be similar to previous reports for chromated copper arsenate and/or other ammoniacal copper preservative treatments — CC treatment to a target retention of 6.4 kg/m3 (0.4 pcf) caused an average reduction in modulus of rupture (MOR) of only about 5 percent, no reduction in modulus of elasticity (MOE), and a reduction in work to maximum load (WML) of 7 to 18 percent. Reductions in MOR and WML were greater in samples kiln-dried after treatment. Treatment to the marine retention of 40 kg/ml (2.5 pcf) caused larger reductions in WML. However, for the No. 2 grade lumber, the effects of CC treatment on MOR were greater (average reduction of 12%) than those noted for Dense Select Structural grade lumber. These effects were also slightly greater than those previously reported for chromated copper arsenate treatment. No comparative data on No. 2 grade material were available for other preservative systems based on ammoniacal copper. As the popularity of arsenic-free ammoniacal copper-based systems increases, this phenomenon of greater strength loss with No. 2 grade treated lumber deserves additional study.

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