Copper Naphthenate: An Update and Status Report on an Effective Wood Pole 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 are published in USDA Forest Service Technical Note FPL-02, "Comparison of Wood Preservatives in Stake Tests" (Table III). 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 2 and Figure 3). 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 is 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.

Copper Naphthenate-Treated Wood

Copper naphthenate is a standard preservative listed in AWPA Standard P-8. This organometallic preservative system is freely soluble in various organic solvents, including mineral spirits, fuel oil, pole treating oil, and creosote-petroleum mixtures. Currently, the AWPA lists copper naphthenate in over a dozen commodity standards. These standards, approved by both the preservatives committees and/or the treatments committees, signify that the purchaser and user of copper naphthenate-treated wood commodities can be assured of the expected service life of commodities when properly treated in accordance with these standards.

When copper naphthenate is evaluated for treating utility poles and cross arms, four specific evaluation parameters should always be reviewed: leachability of the preservative system, conductivity of the treated wood commodity, hardness or gaff penetration of the treated wood, and corrosivity of the treating solution when placed in contact with metallic wafers while still in solution.

Leachability

Standard wooden blocks, when treated with copper naphthenate and penta in a similar P9 oil, were tested in accordance to AWPA Standard M-11. Results of these tests are shown in table VI, indicating that the slight leachability of both preservative systems may be one of the primary modes of protection of wood substrates by sterilization of the surrounding soil of the utility pole. Preliminary indications are that copper naphthenate is tightly bound to the wood substrate both chemically and physically, including copper-lignin bond formation, copper-holocellulose bond formation, and copper-extractives bond formation. Extraction of copper from copper naphthenate-treated wood by toluene extraction is difficult shortly after treating.

Conductivity

Conductivity of the treated wood is of utmost importance when evaluating preservatives and preservative systems for wooden utility poles and cross arms. Reduction in conductivity of treated wood may be achieved by simple reduction of moisture content of the treated wood commodity by displacing these with non-polar organic solvents or by reducing the overall conductivity of the wood specimen. Conductivity test data from Katz and Miller (49) indicates that either resistivity or conductivity of treated wood can greatly be affected by grain orientation, moisture content, temperature, and preservative system employed. Test results published by Asmus et al. (6) showed there is no increased conductivity of wood utility poles or cross-arms when treated with copper naphthenate in an oilborne preservative system, as shown in Table VII. Many linemen and engineers are often confused or concerned that a "copper" containing preservative will be very dangerous to climb and be very conductive to electrical current. This is simply not the case with copper naphthenate.

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