Water Vapor Sorption Isotherms for Southern Pine Treated with Several Waterborne Preservatives

Equilibrium moisture content (EMC) was measured over a range of relative humidities at 22.5°C to determine whether certain wood preservatives increase the hygroscopicity of southern pine (Pinus sp.) The treatments studied were alkaline copper quaternary (ACQ) at a retention of 6.6 kg⋅m−3, chromated copper arsenate (CCA) at 6.9 kg⋅m−3, and disodium octaborate tetrahydrate (DOT) at 3.8 kg⋅m−3 (equivalent to 2.6 kg⋅m−3 as B2O3). All treatments examined increased the EMC at relative humidities above 60 %. Wood treated with DOT was the most hygroscopic. At high relative humidities, the ratio of the EMC of ACQ-treated wood to CCA-treated wood was 1.08. It is unlikely that the higher corrosiveness of ACQ compared with CCA is due to this slight increase in hygroscopicity.