H.M. Barnes
 M. H. Freeman

Naphthenates have been used for the preservation of timber and cellulose since their original identification in Russia in the early 1880's as part of a series of petroleum characterizations. Later work in the development of copper naphthenate as a heavy-duty preservative for poles led to the development of various treating cycles similar to other oil-borne systems. Recent work concerning the post treatment steam conditioning of copper naphthenate treated southern pine has determined that some amorphous copper naphthenate is converted to a crystalline cuprous oxide. In small laboratory tests, this was later determined to be less efficacious than copper naphthenate. This paper reviews the performance of actual pole-diameter stubs placed in a high hazard location containing both termites and potential for early decay attack. Various treating cycles were used to treat the pole stubs in this test including various post-treatment conditioning methods.

Copper naphthenate (CuN) has been documented as being a very effective wood preservative (2, 3, 6, 8, 9, 13). When the U.S. Environmental Protection Agency reviewed all the major wood preservatives, including pentachlorophenol (penta), creosote, and the inorganic arsenicals, manufacturers of CuN began to actively promote the chemical as a viable alternative to pesticides. Although efforts to use CuN as an extender for creosote began during the war effort of the 1940’s due to a shortage of creosote, widespread use of CuN has occurred only within the last decade. Efforts were made within the American Wood-Preservers’ Association (AWPA) to have standards for specific commodities for wood treated with CuN as early as the mid-1980s (1).

The treatment of poles with CuN began commercially in the late 1980s. For a variety of reasons, early failures of CuN-treated poles were experienced by utilities. Recent publications in the literature have indicated that, in small scale laboratory tests, samples of southern pine wood that have been treated with CuN in P-9 Type A oil, undergo a change from amorphous CuN to crystalline cuprous oxide (11, 12). At low retentions, this conversion to cuprous oxide in small laboratory samples has been as much as 50% of the available copper. The extent to which this is anything but a surface phenomena has yet to be shown. Additional tests have shown that CuN has a more biologically active form of copper than many other copper complexes or copper salts, with the exception of oxine copper (5). As a result of the changes noted in small laboratory tests and the incidence of early failures of poles in service, the executive committee of the AWPA issued the following instruction to Subcommittee P-3 Organo and Organometallic Preservatives: "Review, with particular emphasis on the effects of pre- and/or post-steaming on the efficacy of CuN preservative systems, including degradation of CuN into possible less-efficacious forms of copper" (7). The purpose of this study is to detail our experience with pole-sized material in exterior exposure. Hopefully, this research will answer some of the practical concerns posed by producers and users of treated poles.

Selected trees of loblolly pine (Pinus taeda L.) were cut, bucked into nominal 8-ft pole stubs and immediately debarked, and cut into matched 4-ft sections for use in this study. Nominal pole stub diameter was eight inches.

After cooling overnight, each 4-ft pole stub was bored to the pith on third points around the circumference of the stub at the mid-point and 1-ft from the end of each stub. Borings were segmented into the following zones for analysis: 0.0-0.5, 0.5-2.0, 2.0-3.0, and 3.0-4.0 inches from the surface. Similar zonal segments from all stubs in a charge were combined for copper analysis by X-ray fluorescence spectroscopy (AWPA Standard A9). The data were cross-checked by atomic absorption (AA) spectrometry (AWPA Standard A11) using wet ashing procedures (AWPA Standard A7). In December 1987, half of the treated pole stubs were placed 18 inches into the ground while the remainder were placed horizontally on treated 4x4s in above-ground exposure. In 1999, selected pole stubs were bored and reassayed using AA spectroscopy. Poles representing the extremes in the treated population were chosen. For pole stubs placed in ground contact, four borings were taken at quarter-points mid-way between the ground line and the stub top and four additional borings were taken mid-way between the ground line and the butt end of the stub. For stubs exposed above ground, four borings were taken at approximately mid-length. One boring from each position was reserved for future testing while the three from each location were separated into the 0-0.5 in, 0.5-2.0 in, and 2.0-3.0-in zones for assay. The three cores for each zone and location were combined for assay. All pole stubs, whether assayed or not, were physically examined for signs of decay by visual inspection, sounding, and probing.