Absorption and Penetration of Oil-Soluble Wood Preservatives in Dip Treatments–A Summary of Progress

Specimens of 0.50 by 0.75 by 6.0 inches were cut from ponderosa pine (Pinus ponderosa Laws) sapwood with an end to side grain ratio of 1:30. A total of 1700 specimens was divided into three groups representing different specific gravity ranges. Treatment was carried out on 81 subgroups of 20 specimens each at ovendry, 12 percent, and 25 percent moisture content. Standard preservative solutions of known composition were prepared using Solvasol No. 5 as the diluent and a uniform water-repellent system composed of refined wax and pentalyn H. These solutions included: 5 percent pentachlorophenol, copper naphthenate equivalent to 2 percent metallic copper, 1 percent copper-8-quinolinolate, 3.5 percent rosin amine D pentachlorophenate, and 5 percent zinc alkyl sulphonate. In addition, four proprietary compounds Penta WR, Ca-San, Woodlife, and Cuprinol Special Green No. 12b were included: The specimen to be treated was placed in a weighed jig and suspended in preservative solution from the left end of a triple-beam balance. The submerged weight of the specimen and jig was determined to the 1/100 gram at 30-second intervals through a 10 minute dip period. Five specimens were chosen from each subgroup for determination of penetration obtained in the 10 minute-dip. Additional specimens conditioned to 12 percent moisture content were treated for short time periods to permit determination of penetration after 15-second and 3-minute dips. Longitudinal, radial, and tangential penetration were determined. Test results showed at the oven-dry conditions approximately one-half the total absorption obtained in a 10-minute dip occurred in the first 15 seconds. At the 12 percent and 25 percent levels a greater proportion of total absorption occurred during the first 15 seconds. The rate of absorption varied inversely with moisture content at time of treatment. An increase in specific gravity effected a decrease in absorption. Longitudinal penetration was greatly affected by moisture content. The penetration at the ovendry condition was twice as great as that at the 25 percent level. Penetration through radial and tangential surfaces did not vary with moisture content or specific gravity, and over one-half the total longitudinal penetration obtained during a 10 minute dip occurred during the first 15 seconds.

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