Copper Naphthenate: An Update and Status Report on an Effective Wood Pole and Crossarm Preservative (cont)

Efficacy of copper naphthenate

Copper naphthenate is an effective biocide against most decay fungi (basidiomycetes), termites, and many other wood-destroying insects. Duncan (13-15) performed efficacy trials of copper naphthenate in soil block tests to compare with penta, coal tar creosote, and petroleum fractions. In addition to these data, reports for the AWPA Copper Naphthenate Task Force reviewed the efficacy of copper naphthenate against six decay fungi (white rot and brown rot), and data was reviewed by Morrell to determine effectiveness against copper-tolerant fungi (Poria, Postia). Overall performance of copper naphthenate in various petroleum solvents have indicated that both soil block and agar block techniques were applicable to this preservative system with excellent control over decay organisms tested in the 0.02 to 0.044 lb/ft.³ (as copper) range in southern yellow pine sapwood.

Long-term efficacy trials on 2x4 lumber treated by dip, soak, brush-on, and pressure-treating methods were evaluated by Davidson (11) and by Gjovik and Gutzmer (20,21). These data, published in USDA Forest Service Technical Note FPL-02, "Comparison of Wood Preservatives in Stake Tests" (Table III), are illustrated graphically in Figure 2. These data indicate that copper naphthenate dissolved in No. 2 diesel oil gives an average predicted lifespan of 38 to 42 years, comparable to that of either creosote or penta in heavy oil. In addition to these data, USDA Forest Service Publication FPL-01, "Comparison of Wood Preservatives in Post Tests," states that copper naphthenate-treated round stock gives excellent service life when compared to standard preservatives such as CCA, creosote, or penta in P9 Type A oils.

Review of data from test sites at Madison, Wis., Gulfport, Miss., and Dorman, Miss., indicates that the severity of the test plot can alter the service life of wood products when placed in ground contact. However, by placing a standard control preservative into the test plot, the degree of severity of that test plot can be monitored, including the predictability of service life (Figure 3 and Figure 4). These data have been reviewed by Scheffer (48) and Eslyn (17), including utility pole decay and growth temperature relationships of this decay. Scheffer plotted average decay in North America by temperature humidity mapping, ultimately published as part of the REA (now RUS) Specifications decay hazard map. Hunt and Garratt (25) proposed levels of copper in copper naphthenate-treated wood commensurate with those in the current AWPA standards (Table IV). A comparison of AWPA retention standards for the major oilborne preservatives are shown in Table V.

Copper naphthenate under test at Oregon State University continues to give excellent performance in brush-treated, soaked, and pressure-treated Douglas-fir posts after greater than three decades of exposure (30). These data have also been published by Morrell, Scheffer, and Miller in the "Progress Report for the OSU Post Farm Test." Copper naphthenate is also a proven cellulosic fiber preservative. Data reviewed by Curwen (9) has shown that copper naphthenate has a high degree of permanence when used to preserve cellulosics and also has the ability to prevent mildew, rot, and decay from occurring in fiber substrates. Recent field stake studies by Barnes et al. (51) show that copper naphthenate is also an effective preservative for a wide variety of hardwoods.

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