The effect of DDAC on the penetration of borates into western hemlock

The recently revives interest in the borate treatment of hem-fir has led to the search for more rapid treatment processes. Pressure treatment combined with a short diffusion period showed promise, particularly for Pacific silver fir, but further improvements were needed to rapidly achieve penetration of the full cross section in western hemlock. Didecyldimethyl ammonium chloride (DDAC) had been added as a mold inhibitor during the diffusion process but it might also have an effect on uptake through action as a surfactant. End-matched specimens cut from western hemlock baby squares were treated with disodium octaborate tetrahydrate to which two concentrations of DDAC or one of sodium dodecylsulphate (SDDS) were added. Addition of 0.5 percent DDAC increased the penetration of borate into hem-fir during pressure treatment and during subsequent storage. A concentration of 0.05 percent DDAC improved penetration only during storage after treatment. Addition of 0.5 percent SDDS reduced solution uptake. A second experiment confirmed the penetration enhancement of low DDAC concentrations during storage but failed to confirm the effect of higher concentrations during pressure treatment. The increase in penetration during storage appeared to be through enhanced capillary movement of the treating solution into the wood.

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