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Copper migration from treated wood has created concerns within the
environmental community because of the potential effects of this heavy
metal on aquatic organisms. Migration can be limited, to some extent, by
more controlled treatments and by post-treatment processing, but these
actions cannot completely overcome the problem. An alternative approach
to limit copper migration is to incorporate additives into the formulations
that would either block or slow copper loss. Preliminary trials suggest that
adding small amounts of Di(hydrogenated tallowalkyl)dimethyl ammonium
chloride (2HT), a common fabric softener, to the treating solution can
reduce copper losses in service. Reducing copper losses may also allow
the use of lower initial preservative loadings. In this research, the potential
for using 2HT was examined to reduce copper losses while maintaining
preservative efficacy.
The effect of the additive on leaching was assessed by soaking blocks in
water over a 14-day period, then examining the resulting leachate. The
incorporation of 2HT to alkaline copper-based and DDAC preservative
solutions reduced the rate of copper migration from southern pine blocks
subjected to laboratory leaching procedures by 5% to 14%. 2HT had no
effect on loss rates for isothiazolone. Biological efficacy was assessed by
exposing treated blocks to decay fungi in a soil block test. 2HT did not
enhance the biological efficacy of copper azole nor isothiazolone in
standard laboratory trials with a brown rot fungus, P. placenta. The
potential for chemical interactions was assessed using Fourier Transform
Infrared Spectroscopy (FTIR) analysis. Results indicated that 2HT did not
change the structure of wood, suggesting that 2HT reduces copper losses
due to ionic interactions between the organic cationic end of the quaternary
ammonium compound and the negatively charged surface of wood. This
interaction leaves the hydrophobic end of the 2HT exposed to act as a
water repellent, thereby excluding the water that would otherwise solubilize
and remove copper from the wood. Results provide support for using this
additive to limit copper losses into the environment. |
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