doi:10.1016/S0031-9422(02)00267-4 
Copyright © 2002 Elsevier Science Ltd. All rights reserved.
Development of environmentally-benign wood preservatives based on the combination of organic biocides with antioxidants and metal chelators
Tor P. Schultz
, 
and Darrel D. Nicholas
Forest Products Laboratory/FWRC, Box 9820, Mississippi State University, Mississippi State, MS 39762, USA
Received 4 May 2001;
revised 6 August 2001.
Available online 23 October 2002.
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Abstract
Wood extractives can be envisaged to protect heartwood by at least three different mechanisms, i.e. fungicide, free radical scavengers/antioxidants and as metal chelators. In short-term laboratory decay tests using two different wood species and decay fungi, the combination of different organic fungicides with various antioxidants and/or metal chelators gave enhanced activity as compared to the organic biocide alone, with the best results usually obtained with all three compounds. Outdoor ground-contact stakes treated with a biocide and antioxidant combination and exposed for 30 months also gave enhanced protection against both decay fungi and termites. It was concluded that the combination of an organic biocide with metal chelating and/or antioxidant additives gives enhanced protection to wood against fungi as compared to the biocide alone and, consequently, it may be possible to develop environmentally-benign wood preservative systems based on this idea.
Graphical Abstract
Enhanced efficacy is obtained by the co-addition of antioxidants and/or metal chelators with various organic biocides used to preserve wood.
Author Keywords: Antioxidants; Extractives; Heartwood; Metal chelators; Natural durability; Termites; Wood decaying fungi; Wood preservatives
Fig. 1. Average % strength loss of five replicates for sapwood samples treated with four levels of organic biocides. The SYP samples were exposed to G. trabeum (left column) and the aspen samples to T. versicolor (right column). For the G. trabeum samples, untreated control strength loss ranged from 97.0 to 100%, samples treated with only 3% EDTA had 93.5 and 95.7% strength loss, and samples treated with only 5% BHT had 68.7 and 78.6% strength loss. T. versicolor controls had 70.5–80.6% strength loss, samples treated with only 3% EDTA had 32.4 and 65.1% strength loss, and samples treated with only 5% BHT had 62.5 and 64.7% average strength loss.
Fig. 2. Average % strength loss of five replicates for sapwood samples treated with four levels of propiconazole. The top graphs show samples co-treated with 5% propyl gallate and/or 3% EDTA, and the bottom graphs show samples co-treated with 5% t-butylhydroquinone and/or 3% EDTA. The SYP samples were exposed to G. trabeum (left column), and the aspen samples to T. versicolor (right column).
Table 1. Average % strength loss for southern yellow pine samples treated with the biocide propiconazole (Prop.) and various antioxidants and/or metal chelators, then exposed to the brown-rot fungus G. trabeum for 4 weeksa
For samples treated with more than one compound, the concentrations (first column) and retentions (second column) are separated by slashes. TA is tannic acid, BHT is 2,6-di-
tert-bytyl-4-methylphenol and Phen. is 1,10-phenanthroline.
Table 2. Average decay and termite ratings for southern yellow pine field stakes treated with chlorothalonil (CTN), or a mixture of CTN and 2,6-di-tert-butyl-4-methylphenol (BHT), after 30 months exposurea
For samples treated with the CTN/BHT mixture, the treating solution concentration and average retention are shown for both compounds.
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