Chapter 7
Concepts in the Development of New Accelerated Test Methods for Wood Decay Downloaded by UNIV OF ARIZONA on August 4, 2012 | http://pubs.acs.org Publication Date: April 2, 2008 | doi: 10.1021/bk-2008-0982.ch007
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Darrel D. Nicholas and Holger Militz
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Department of Forest Products, Mississippi State University, Mississippi State, MS 39762-9820 Institute of Wood Biology and Wood Technology, University of Gottingen, Busgenweg 4, D-37077 Gottingen, Germany
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The rapid transition in the wood preserving industry toward the use of non-arsenical wood preservatives has emphasized the need for rapid test methods to evaluate new preservative systems. In this chapter progress toward the goal of developing accelerated test methods is presented. One of the key elements in accelerated test methodology is the use of accurate, quantitative methods for measuring the extent of decay. In this area bending elasticity and compression tests have been fully developed for small test specimens and dynamic M O E methods for larger samples show promise. Progress has also been made in developing accelerated soil contact and above ground decay test methodology.
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© 2008 American Chemical Society In Development of Commercial Wood Preservatives; Schultz, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.
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Introduction For the past two decades the wood preserving industry has been undergoing a major transition which has been driven mainly by environmental and health issues associated with the major wood preservatives. In the early 80's the Environmental Protection Agency (EPA) imposed regulations on the end use of products treated with the major wood preservatives—chromated copper arsenate (CCA), creosote and pentachlorophenol. These regulations shifted the emphasis from use of the oilborne preservatives for residential products to waterborne C C A , which proceeded to capture the major residential treated wood markets. This activity precipitated the need for research on development of new wood preservatives that were less toxic and more environmentally friendly. Additional restrictions on use of C C A for residential products around the turn of the century placed additional emphasis on the need for new wood preservative systems. Fortunately, at that point in time sufficient research had been conducted on two new waterborne preservative systems, anime copper quat (ACQ) and copper azole (CA) that could replace C C A for the residential treated wood product market. These preservatives are both copper rich systems with A C Q being composed of amine copper plus quarternary ammonium compounds and C A being composed of amine copper plus triazoles. During this transition it became apparent that our test methods used to evaluate the efficacy of preservatives against wood decay microorganisms required excessively long exposure periods before sufficient data was available to confirm the viability of a given preservative. These methods consist of both laboratory and field tests, but at present none of the laboratory tests are capable of predicting long term performance of wood preservatives. Both above ground and ground contact exposure tests are used and these tests require a minimum of around five years exposure before definitive data can be obtained. Clearly, research is needed in this area to shorten the time frame needed for developing new as well as modified wood preservative systems. Some progress has been made in this area and a review of these developments along with suggestions for further improvement will be addressed in this chapter.
Methods of Detecting and Quantifying Wood Decay One of the key elements that transcends all wood preservative evaluation schemes is the measurement of the extent of decay in test specimens. Presently, visual observation is normally used to detect and measure the extent of wood decay in field test specimens. This method suffers from being subjective, rather
In Development of Commercial Wood Preservatives; Schultz, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.
Downloaded by UNIV OF ARIZONA on August 4, 2012 | http://pubs.acs.org Publication Date: April 2, 2008 | doi: 10.1021/bk-2008-0982.ch007
144 than quantitative and does not detect early decay in laboratory tests. Mass loss is another method often used to detect and measure the extent of wood decay. Shortcomings of this method are associated with: 1) difficulty in making adjustments for variation in wood moisture content, 2) loss of wood preservatives, 3) inability to make adjustments for the biomass weight gain as a result of fungal colonization, 4) does not differentiate between localized decay from decay in the entire sample. These factors negate the possibility of detecting the early stages of decay. Furthermore, in larger samples decay generally occurs in limited areas so mass loss of the entire sample is not representative of the damage. Because of these limitations and other factors the use of mass loss is essentially limited to laboratory soil block and agar block tests. Another approach to detecting and measuring the extent of wood decay is based on changes in mechanical properties of wood as it is attacked by fungi. The bending, compression and torsional properties of wood are very sensitive to biodeterioration and can be used to develop quantitative data in decay studies (/). In this regard, static bending has been shown to be a viable method of measuring the extent of decay in laboratory decay tests (2-5). However, use of static bending to determine the M O E has limitations because the test must be conducted in the laboratory. Another approach in determining M O E of test samples is the use of dynamic methodology. This method was originally developed on the basis of ultrasonic pulse excitation methodology (
