Comparative Performance of Pentachlorophenol and Copper Naphthenate in a Long Term Field Stake Test¹

By

Darrel Nicholas²
Michael Freeman³

Abstract

In this study the performance of copper naphthenate (CuNap) and pentachlorophenol (Penta) treated pine stakes against decay and termite attack were compared at two test sites in Mississippi. Four different petroleum oils meeting AWPA Standard P9-A were used as carriers for these wood preservatives. After ten years exposure, the efficacy of CuNap at a retention level of 0.05 pcf Cu was equivalent or slightly better than Penta at a retention level of 0.40 pcf. The type of carrier oil had an effect on the performance, but this was variable for both the type of preservative and test site. In comparing the two test sites, the performance of both preservatives was consistently better at the Dorman Lake test site. Wood treated with the oil carriers alone initially performed reasonably well against both wood decay fungi and termites, but the activity decreased rapidly after about six years exposure. Like the preservatives, the performance of the oils was consistently better at the Dorman Lake test site.

Introduction

CuNap was developed in Denmark in 1911 and has been used as a preservative for a variety of wood and textile products over the years. CuNap is generally prepared by reacting copper or copper salts with naphthenic acid or with sodium naphthenate. The three commercial methods of producing copper naphthenate are direct metal, melt (fusion), or double decomposition methods. Naphthenic acid is a by-product of petroleum refining and contains a mixture of monocarboxylic acids which have cyclopentane and cyclohexane groups with an acid number ranging from 150 to 300. The proposed chemical structure for CuNap is (2):

The use of CuNap as a commercial wood preservative in the United States has been limited, but recent environmental concerns with CCA, Penta, and Creosote has stimulated its use in utility poles and other wood products. In the mid-1980's, the Electrical Power Research Institute (EPRI) reviewed their own use of oil-borne preservatives within their member systems and determined that they should investigate possible safer and more environmentally benign preservatives and funded a research project to investigate alternatives to pentachlorophenol. Since there was limited data available on the performance of CuNap treated wood exposed to soil contact, this study⁴ was initiated. The objective of this study was to evaluate the comparative performance of CuNap and Penta formulated with several different commercial carrier oils.

Experimental

Preservatives

Technical grade Penta (>96% active ingredient) and CuNap (8% Copper as metal) were obtained from various manufacturers within the United States.

Carrier Oils

A total of four carrier oils that met AWPA Standard P9-A were selected for this study. These were:

1. California Shell Oil from Shell Chemical Company
2. Base Oil L from Lillyblad Petroleum Inc.
3. Ashland Oil from Ashland Petroleum Company
4. #2 Diesel Oil + KB3 + B11 (KB3 & B11 from Eastman Chemical Products Company).

The physical properties of these oils are shown in Table 1. Oils 1-3 were diluted with toluene (20% oil and 80% toluene) before using them to treat the fungus cellar and field stake test specimens. The treating solution for Oil 4 was formulated with 17% diesel + 2% B11 + 1% KB3 + 80% toluene before treatment of these test specimens.

Table 1. Physical Properties of Carrier (P9-A) Oils

PROPERTY		CALIFORNIA SHELL	BASE OIL L	ASHLAND	#2 DIESEL (90%) /KB3 (10%)
Specific Gravity @ 72°F		.9548	.9740	.9452	.9124
Viscosity Sus @100°F (ASTM D-88)	Whole Oil	46	37	35	35
	Fraction above 500°F	53	40	37	--
	Bottom 25%	--	67	47	--
Viscosity Sus @ 100°F with Penta	0% a.i.	49.4	39.7	37.6	35.5
	7% a.i.	54.1	40.8	37.5	36.8
Interfacial Surface Tension Dynes/cm (ASTM D1871) Fraction above 500°F		24.3	23.5	24.5	--
Penta Solvency-AWPA P-5(%)	Whole Oil	15	18.4	8.15	15
	Fraction above 500°F	16	10	8	--
	Bottom 25%	14.4	12.5	9.2	--
Volume Distilled (ASTM D-86)	Distillation Temperature of Various Fractions
	Initial Boiling Point	464°F	480°F	470°F	410°F
	10%	492°F	515°F	500°F	456°F
	20%	516°F	532°F	520°F	480°F
	30%	530°F	545°F	532°F	495°F
	40%	548°F	560°F	545°F	514°F
	50%	575°F	575°F	558°F	530°F
	60%	604°F	595°F	575°F	550°F
	70%	637°F	610°F	595°F	568°F
	75%	650°F	625°F	604°F	577°F
	80%	666°F	640°F	618°F	590°F
	90%	673°F	670°F	648°F	623°F
% Above 500°F		86	95	90	68