Improving the Performance of Organic Biocides by Using Economical

Chapter 16

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Improving the Performance of Organic Biocides by Using Economical and Benign Additives Tor P. Schultz and Darrel D. Nicholas Forest Products Laboratory/FWRC, Box 9820, Mississippi State University, Mississippi State, MS 39762-9820

The copper systems currently used in North America to treat lumber for residential applications will likely be replaced by organic systems at some future time. However, most organic wood preservatives used or being considered for wood preservation are relatively expensive. Also, organic biocides can be depleted by various chemical, physical or biological mechanisms over the long service life expected from treated wood. One way to address these problems is to employ selected additives that increases an organic biocide's activity and/or minimizes depletion. This would mean less biocide is required, possibly lowering the cost of a wood preservative system. Additives that may achieve these goals include antioxidants, metal chelators and water repellents. Laboratory and exterior exposure data with additives will be described, and other possible additives briefly discussed.

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© 2008 American Chemical Society Schultz et al.; Development of Commercial Wood Preservatives ACS Symposium Series; American Chemical Society: Washington, DC, 2008.

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Introduction The preservative chromated copper arsenate, C C A , was used for about 80% of all wood products treated in the U.S. up to the end of 2003, but C C A is no longer permitted for treating residential lumber. New 2 generation preservatives labeled for residential applications, the major use for treated wood in North America, contain high levels of copper(II) and an organic co-biocide to inhibit copper-tolerant fungi (7, 2). However, environmental concerns with copper and questions over future disposal of metallic-treated lumber are being raised. Three European countries already require 3 generation totally-organic systems, and some minor usage restrictions will be placed on copper-treated lumber starting in 2010. Many professionals predict that at some future point the U.S. will require totally-organic systems for residential applications.


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Development of effective, economical, and dependable totally-organic wood preservatives, especially in areas with high or severe deterioration hazards, will be difficult. Indeed, at the present time no totally-organic preservative for exterior above-ground or ground-contact residential applications is commercially available in the U.S., although several companies are developing, have submitted for standardization [obtaining regulatory approval of] or have recently obtained standardization of an organic system for non-millwork residential applications. Two major problems in developing organic preservatives for residential exterior exposure are: 1) the relatively high cost of the new organic biocides [often $ 30-60/kg] being examined as potential wood preservatives compared to copper(II) [$ 2-3/kg]; and 2) the biotic and abiotic depletion reactions that occur with organic biocides but not copper. We have studied certain non-biocidal additives that could be employed in wood preservation, with the objective to improve the performance of organic biocides at protecting wood by addressing one or both of the above problems. To address the first problem, the high cost of organic biocides, we are examining non-biocidal and low-cost additives that, when mixed with organic biocides, enhance the activity of organic biocides. This means that less of the relatively expensive biocide is needed, which may reduce the overall preservative system cost and lessen environmental and disposal concerns. A second major concern with organic biocides is the greater potential for biocide depletion. Specifically, metallic biocides are only depleted by water leaching. However, organics not only leach but are also biodegraded by numerous microorganisms and depleted by various abiotic (chemical, vaporization and photo/sunlight) pathways. It is not surprising that the agrochemicals being examined as potential wood preservatives are depleted over the long service life expected from treated wood, since they were originally developed for the agrochemical market (J). Specifically, the desired properties of a wood protection biocide differ greatly

Schultz et al.; Development of Commercial Wood Preservatives ACS Symposium Series; American Chemical Society: Washington, DC, 2008.


274 from that for an agrochemical. Agrochemicals are typically applied to a crop to control a specific pest for no more than a few weeks; after this short time it is desired that the chemical rapidly degrades. When the same agrochemical is examined as a potential wood preservative, however, the biocide is expected to protect wood for many years against a wide variety of organisms. Our hope is that i f a low cost additive can reduce biodégradation of an organic biocide over the long service life expected from treated wood, less of the relatively expensive biocide would be required when the wood is first treated. For several years we and other groups have examined various non-biocidal compounds that may address the above problems. Many of the additives examined are relatively benign; indeed, several have a G R A S (Generally Classified As Safe) classification by the U.S. F D A and, thus, are approved food additives. The compounds examined include free radical scavengers/ antioxidants, metal chelators, and water repellents. Other possible additives will be briefly discussed.

Antioxidants Overview st

About 15 years ago we decided that the 1 generation wood preservative systems, C C A , pentachlorophenol and creosote (2), would eventually be restricted. Consequently, a need existed for more environmentally-benign systems. One approach tp develop greener wood preservatives is to understand why the heartwood of certain tree species is naturally durable. Consequently, we have studied the role that extractives, particularly stilbenes (4), play in heartwood durability. Surprisingly, we found that extractives in highly durable heartwood have very poor fungicidal activities compared to commercial biocides (5). In further work (6) we hypothesized that extractives may protect heartwood against fungal degradation by having dual properties: The extractives have relatively poor fungicidal activity but are superb free radical scavengers (antioxidants). This dual defense hypothesis was based on the facts that whiteand brown-rot fungi both employ free radicals to degrade wood (7) and that the phenolic extractives in durable woods are excellent antioxidants (5). To test this hypothesis we ran several wood-containing laboratory decay tests and measured the activities of: 1) an antioxidant that had no fungicidal activity; 2) a biocide that had no antioxidant activity; and 3) a combination of the two. If our hypothesis was correct then we should observe enhanced efficacy with the biocide and antioxidant mixture; i.e., the combination would be synergistic.


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Laboratory Decay Studies of Organic Biocides and Antioxidants Laboratory decay tests (8, 9) did indeed show enhanced efficacy for all biocide:antioxidant mixtures tested compared to the organic biocide alone. Synergism was observed with all seven organic biocides examined for various brown- and white-rot fungi, and gymnosperm and angiosperm woods. The biocides studied have either been examined as potential wood preservatives or are in commercial wood preservatives (7, 2). Initial studies were conducted with the antioxidant butylated hydroxytoluene (BHT), a low cost antioxidant that has a U.S. F D A G R A S classification and, thus, is benign to humans. We also examined the antioxidant propyl gallate (PG), another economical food additive. Better results were obtained in laboratory decay tests with P G than B H T . This may be due to PG's good metal chelating ability, since we later found that the combination of an organic biocide:antioxidant:metal chelator was more effective than a biocide:antioxidant mixture (9, 10). While the initial laboratory decay tests were encouraging and enabled us to obtain several U.S. patents, we had several concerns. First, we initially ran standard laboratory decay tests with 8-12 weeks of incubation but observed no synergism. Generally, we only observed synergism in laboratory decay tests with short incubation times of 4-6 weeks. Secondly, relatively high and uneconomical B H T levels of 5% were used. Recent laboratory decay studies in France examined 2-hydroxypyridine-Noxide (2-HPNO) (77), which was shown to have both fungicidal and metal chelating properties. The combination of 2-HPNO and the antioxidant Irganox 1076 was found to be synergistic. However, a tebuconazole and Irganox 1076 mixture was not synergistic. The relatively long incubation time employed by these researchers, 12 or 16 weeks, may be one possible explanation for the lack of synergism. We observed synergism in our studies with tebuconazole and B H T against both brown-rot and white-rot fimgi, but used a short incubation time of 4 to 6 weeks (8-10).

Exterior Exposure Results Synergism in short-term laboratory decay tests does not ensure that a preservative will be effective for the many years expected from treated wood. Indeed, our initial laboratory results indicated that uneconomically high levels of B H T are necessary and the protective effect was only observed for relatively short incubation times. Thus, we judged that this concept would probably not work in exterior real-world applications. However, even with a high probability for likely failure we felt that the potential benefits that might be obtained i f this



276 concept did work in "real world" conditions compelled us to test our concept in outdoor exposure. Consequently, an exterior ground-contact study was installed at two test plots in Mississippi in high and severe deterioration zones (P, 72). The wood stakes were S Y P sapwood, treated with the commercial biocide chlorothalonil (CTN) and B H T . We selected C T N since it has both the fungal and termite activity necessary for a ground-contact study, and C T N has been extensively examined as a potential wood preservative (7, 2). The objective was to verify the antioxidant concept in outdoor exposure, not to develop a commercial system. Thus, lower C T N levels were employed than would be used in commercial systems and an organic solvent, toluene, was used. Also, lower B H T levels were employed in this first outdoor exposure study, 2 and 4% in the treating solution, than the 5% level used in the laboratory decay studies. The initial results were extremely encouraging (P), and the results after the relatively long exposure time of 74 months (Table I) continue to be very promising. Generally, co-addition of B H T resulted in greater efficacy against fungal and termite attack than observed with stakes treated with C T N alone. The exception was that one set at Dorman Lake, treated with the highest biocide (0.5%) and BHT(4%) levels, had no difference in the average fungal efficacy rating compared to samples treated with only 0.5% C T N . This was due to one of the seven samples failing in the 4% BHT/0.5% C T N set at Dorman Lake owing to fungal degradation. This sample had had the bottom 3 inches removed after 48 months of exposure to measure B H T depletion, and it is possible that decay fiingi were able to colonize the stake through the freshly-cut surface. This set did show increased termite efficacy compared to the matched set with no B H T , and the same treatment set at Saucier had greatly enhanced efficacy against both decay fimgi and termites with the co-addition of BHT. Interestingly, samples treated with 4% B H T alone performed about as well as samples treated with the lowest biocide level at both locations. The initial outdoor exposure results were better than we had anticipated for several reasons. First, the antioxidant concept was based upon the free-radical mechanisms by which decay fimgi attack wood (7). However, B H T ' s protective effect against termite attack was unexpected. Also, B H T was only effective for a short time in laboratory decay tests, as discussed above. Since decay fimgi would attack ground-contact stakes almost continuously the possibility existed that B H T might only last for a relatively short time. Finally, lower B H T levels of 2 and 4% were employed in this initial outdoor exposure test than the 5% level used in the earlier short-term laboratory decay tests. B H T depletions after 48 and 54 months of ground-contact exposure were generally about 30-50% (72, 75), which we considered to be relatively low. It is possible that the oxidized B H T radical, formed as B H T scavenges a fimgalgenerated radical, interfered with the reductive portion of the fungal redox cycle(s) with the B H T being regenerated and, concurrently, disrupting a fungal


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redox cycle (10). If this does occur then the B H T would be recycled, possibly explaining the relatively low depletion of B H T observed in outdoor long-term exposure and would be a second mechanism by which B H T inhibits fungi.

Table 1. Average decay and termite ratings after 74 months of exposure for S Y P sapwood ground-contact field stakes at the Dorman Lake, M S (high deterioration zone) and Saucier, M S (severe deterioration zone) test plots. Decay and termite ratings were based on A W P A Standard E 7 01, with a "10" rating sound to trace of degradation, a "9" rating trace to 3% degradation, etc., down to a "0" [failed] rating, and are the average of seven replicate stakes per treatment/site. Treatment (wt. %) CTN

BHT

0 0 0.15 0.15 0.15 0.30 0.30 0.30 0.50 0.50 0.50

0 4.0 0.0 2.0 4.0 0.0 2.0 4.0 0.0 2.0 4.0

Average Retention (kgm ) 0/0 0/19.4 0.74/0 0.72/9.5 0.70/18.8 1.47/0 1.54/10.1 1.41/18.8 2.42/0 2.41/9.6 2.43/19.5 3

Saucier

Dorman Lake Decay

Termite

Decay

Termite

0 2.9 3.0 6.7 6.4 5.7 7.9 8.0 8.3 9.9 8.1

0 4.8 3.1 7.0 6.4 7.1 8.7 8.1 8.6 9.9 9.9

0 2.4 1.1 5.6 5.9 3.5 8.0 6.0 6.3 9.0 9.3

0 0.4 0.6 4.1 3.9 2.7 7.3 5.1 5.9 8.6 8.4

Samples with 2% B H T are performing about as well as samples with 4% BHT. This is likely explained by B H T not being a biocide. Thus, while increased biocide levels result in enhanced efficacy, increased antioxidant levels would not give greater decay and termite resistance; all that matters is that at least some B H T is present. Depletion measurements showed that quite a bit of B H T remains after 54 months (13) in the stakes treated with 2% B H T , as discussed above and, thus, it is not surprising that similar results are obtained for stakes treated with the two different B H T levels. The antioxidant B H T also appears to protect the organic biocide C T N (75) in ground-contact wood. For example, stakes that were treated with only 0.3% C T N and exposed at the Saucier test plot for 54 months had 65 ± 4% C T N depletion in the ground-contact section, while the stakes treated with 0.3% C T N plus 4% B H T had only 18 ± 8% C T N depletion. For the same 0.3% C T N set



278 exposed at Dorman Lake, the samples without co-added B H T had 41 ± 16% C T N depletion and the samples with 4% B H T co-added had 29 ± 19% C T N depletion. While no other reports on an antioxidant protecting biocides in treated wood could be found, a patent has reported that the antioxidant P G stabilized 3isothiazalones solutions (14) and that the stabilized biocide could be used for various applications including wood preservation. Further research is needed to definitively confirm, or disprove, the possible B H T protective effect using various organic biocides in ground-contact and above-ground applications. Based on the encouraging results from the first exterior study (9) a few additional ground-contact and above-ground samples were installed. Since the antioxidant P G gave better results in the laboratory decay tests than B H T , we included P G in most of these later outdoor exposure experiments. Unfortunately, results with P G in a ground-contact study were disappointing and only modest results were obtained in above-ground tests with P G and two biocides. The best results obtained with P G were when a water repellent was co-added to aboveground samples, suggesting that in outdoor exposure P G may be slowly leaching. Above-ground samples with the antioxidant B H T continue to show encouraging results. For example, SYP lap-joint samples were treated with only B H T at the relatively low retention of 0.94 kg/m . After five years of exposure in a severe deterioration zone, BHT-treated samples had an average rating of 7.3 compared to a 4.5 rating for the untreated controls. Another study examined lapjoint samples treated to three retentions with a quat formulation, with or without B H T co-added at a retention of 2.5 kg/m . After four years of exposure at CSFs Hilo test site, the average ratings for samples treated with only the quat biocide ranged from 5.8 (lowest quat retention) to 7.6 (highest quat retention, compared to 7.8 to 8.0 for samples co-treated with 2.5 kg/m B H T and the quat formulation. To summarize, exterior exposure results with B H T were more promising than was originally anticipated. Specifically, the data indicate that relatively low B H T levels appeared effective in outdoor exposure as compared to the uneconomically high levels employed in the laboratory decay tests. Furthermore, B H T remained effective for multiple years in ground-contact, and one study indicated that B H T reduced biodégradation of an organic biocide. Additional experiments need to be run and longer exposure times are required to definitively resolve i f an antioxidant can reduce biodégradation of organic biocides, determine effective biocide/BHT levels for various biocides and applications, and decide if this concept is economical. In contrast to the generally good results obtained with BHT, exterior studies with the antioxidant P G gave poor results in ground contact and only modest results in above-ground exposure. 3

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Metal Chelators


Overview Our original antioxidant concept was based on the excellent antioxidant properties of extractives in naturally durable heartwood. In continuing this reasoning, it is well known that many heartwood extractives complex with metals (P) and that fungal degradation often involve various metal co-factors in the fungal redox cycles and/or as part of an enzyme (15). Consequently, metal chelation may be an additional means by which extractives protect heartwood (16) and, furthermore, mixtures of metal chelators and organic biocides may synergistically protect wood.

Laboratory Decay Studies with Metal Chelators and Organic Biocides We employed the same technique used earlier with the antioxidants to examine the metal chelation hypothesis. Specifically, we ran short-term (5-6 weeks incubation) laboratory decay tests with: 1) metal chelators that had no fungicidal activity; 2) various biocides that had no metal chelating ability; and 3) biocide:metal chelator combinations (P). These laboratory tests showed synergism; specifically, the blocks treated with both an organic biocide and a metal chelator had less fungal degradation than the blocks treated with only the organic biocide. Furthermore, the trinary combination of an organic biocide:metal chelatonantioxidant was usually more effective than binary mixtures of biocide antioxidant or biocide:metal chelator. We usually obtained the best laboratory results with metal chelators employing the agar block rather than soil block test. Agar medium has relatively low levels of metals compared to soil and, consequently, metal chelators may be more effective in agar-containing than soil-based decay tests. The laboratory decay studies in France with 2-HPNO (77) also examined 2H P N O and the metal chelator E D T A , and reported that the combination was synergistic. However, synergism with E D T A and tebuconazole was not observed with long incubation times.

Exterior Exposure Studies with Metal Chelators Many of our laboratory decay tests with metal chelators employed sodium salts of E D T A , a metal chelator that is an approved food additive. However, in outdoor exposure it would be expected that E D T A , and other metal chelators with carboxylic groups, would leach relatively rapidly.


280 We examined one solventborne metal chelator, 1-10-phenanthroline, in outdoor exposure tests. Lap-joint samples were treated with the same three quat retentions as before, along with 0.4% B H T (2.5 kg/mg ), 0.2% of the above metal chelator (1.1 kg/mg ), and wax (about 4.8 kg/m ) as a water repellent. After four years of exposure in the extremely severe deterioration conditions at CSI's test site in Hilo, HI, the samples with all the above additives and the three quat retentions had average ratings from 9.5 to 10.0. B y contrast, samples treated with only the biocide had average ratings of 5.8 to 7.6. While 1,10phenanthroline is relatively expensive and toxic and, thus, unsuitable for a commercial preservative system, the results support the laboratory data that metal chelators enhance the efficacy of organic biocides. Many microorganisms employ metals as co-factors when they degrade organic compounds. Thus, co-addition of a metal chelator may also reduce biodégradation of an organic biocide. Unfortunately, at this time we do not have any samples in outdoor exposure to test this possibility. Wood in soil contact can have increased levels of iron and other metals due to metal migration into the wood from the adjacent soil (17). It is possible that when a metal chelator is added to treated wood for a ground-con tact application the metal chelator may be relatively quickly saturated and rendered ineffective. However, the potentially high benefits that might be obtained from the metal chelator concept suggest that this assumption needs to be tested. At this time we believe that metal chelators may be most useful as part of an organic preservative system for above-ground residential exposure, as suggested from results from the one above-ground study discussed above. We have tried to identify metal chelators that are relatively inexpensive and commercially available, safe to humans and other non-target animals, and can be formulated into a waterborne system for treating lumber for residential applications but once impregnated into wood will not leach. A chance remark by a colleague let us to examine the potential of resin acids. Resin acids, a commercial product mainly produced as a by-product of tall oil obtained by the kraft pulping of pine and called tall oil rosin but better known by the acronym TOR, are inexpensive (about $0.25 - 0.40/lb, bulk shipment). [Other sources of resin acids are isolated from old pine stumps (wood rosin) and oleoresin tapped from living trees (gum rosin)]. Resin acids have a G R A S classification for foodstuff use such as chewing gum base or in paper that comes in contact with foodstuffs and, thus, are also benign. (Many of us used a rosin bag to help our grip when playing various sports in our younger days and some of us have eaten potatoes cooked in rosin.) Finally, one of the commercial uses of resin acids are as metal complexing agents, and resin acids are a renewable resource. A l l the above suggest that resin acids/rosin may be a suitable metal complexing additive to combine with organic biocides for wood preservative systems. When we ran laboratory decay tests with an organic biocide and a solventborne (toluene) resin acid, some limited synergism was observed. However, when the resin acid was formulated into a waterborne system by forming the carboxylate anion, very good results were obtained with the agar 3


3


281 block decay test (18). Indeed, treatment with 4% of a resin acid alone was sufficient to protect wood against fungal degradation in the agar block test. Furthermore, the resin acid anion in the waterborne formulation acts as a surfactant, so that some organic biocide can often be directly added to the formulation. We are continuing to examine the potential of employing T O R as an additive, and hope to report additional results shortly.


Water Repellents As noted by Preston (3, 19\ water repellents based on waxes or oils and formulated into a waterborne emulsion offer many advantages to treated wood. Water repellents lower the amount of rainwater soaked up by above-ground lumber, reducing the fungal decay potential and biocide leaching. Another positive benefit is the enhanced dimensional stability which reduces undesired bowing, checking, splitting, etc. Lumber treated with the new copper-rich systems and a wax-based water repellent is available as premium decking in North America. Some work is also being conducted on treating wood with silicone compounds to give water repellency and perhaps other benefits. Two general silicone formulations, waterborne and oilborne, are apparently available. We examined the potential of resin acids/TOR as metal complexing agents, as noted in the prior section. Resin acids are also hydrophobic and may impart water repellency to wood. In water swelling tests with a solventborne resin acid, only slight water repellency was observed. However, when wood blocks were treated with a waterborne system extremely good water repellency was observed (18). For example, small southern yellow pine wood wafers were treated with 1.0% wt/vol waterborne resin acid or 1.1% wt/vol paraffin wax in toluene. The samples were dried to 12% M C , then placed in water and the radial swelling measured. The Water Repellency Efficiency (WRE), the radial swelling of treated wafers relative to the swelling of the matched untreated wafers, was measured at 30 and 90 minutes. At 30 minutes, the average W R E of four replicates was 40.2% for the 1.0% resin acid-treated sample but only 21.9% for the 1.1% wax samples. At 90 minutes, the resin acid samples still had some water repellency with an average W R E of 22%, while the wax-treated samples had a negative W R E . We also treated S Y P 5/4's decking boards with a waterborne treatment formulated using a commercial source of resin acids to give a solution with 3% TOR, and after 5 weeks of exterior above-ground exposure the treated and matched untreated boards were weighed after a thunderstorm. The TOR-treated boards had an average moisture content of 25.3% versus the 31.0% of the control/untreated boards. We have previously examined the wide variability inherent in the natural durability of above-ground untreated S Y P sapwood samples (20), where some samples show extensive decay fairly quickly while other untreated samples only slowly degrade. S Y P sapwood is reported to contain a variable and sometimes


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high level of resin acids (27). [The high temperatures used in kiln drying S Y P lumber will degrade some of the resin acids naturally present, and may also disrupt the microdistribution of resin acids and so negatively impact the metal complexing capability.] It is interesting to speculate on the possibility that the amount of resin acids naturally present in a particular SYP sapwood sample may impart some inherent decay resistance (22) to above-ground SYP lumber.

Other Potential Additives Many other non-biocidal additives might enhance biocide efficacy and/or reduce depletion. Possibilities include: 1. Additives that reduce vaporization and/or water leaching of biocides. One possibility might be to add a small amount of a heavy oil as an emulsion in a waterborne formulation. A n organic biocide should be soluble in the small amount of heavy oil and, thus, have reduced likelihood to leach or vaporize. 2. Sunlight degrades organic biocides that are on or near to the wood surface, leaving the lumber surface susceptible to microorganism colonization. A compound that reduces wood photodegradation may also help protect organic biocides. 3. Preston (5) noted that future wood preservative systems will employ relatively low biocide retentions and, consequently, nonuniform biocide distribution within wood may be a future concern. Additives might help improve biocide distribution to obtain a more homogeneous micro- and macrodistribution in treated wood. 4. A major concern with organic biocides is that most do not fix to wood, unlike metallic biocides. Consequently, organic biocides could be susceptible to leaching. Additives that would fix with, or anchor the biocide to the lignocellulosic substance, should reduce leaching. However, the biocide also needs to be available to the decay fungi to be effective, so this approach needs to ensure that the biocide is not so tightly fixed so that it is no longer effective.

Acknowledgements Funding for the authors' work was provided by the USDA-Cooperative State Research, Education and Extension Service - Wood Utilization Research, National Research Initiative and Mclntire-Stennis Programs, Lonza Corp., and Mississippi taxpayers. Approved as Journal Article FP 351 of the Forest and Wildlife Research Center, Mississippi State University. The authors thank the many industrial professionals who gave suggestions and encouragement for our research.


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References 1. 2. 3.


4.

5. 6.

7.

8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

19.

Schultz, T.P.; Nicholas, D.D. Wood Deterioration and Preservation, Amer. Chem. Soc. Symp. Series 845, Washington, D.C., 2003, chp. 26. Freeman, M . H . ; Nicholas, D.D.; Schultz, T.P. Environmental Impacts of Treated Wood, C R C Press, chp. 2, (in press) Preston, A . F . Wood Deterioration and Preservation, Amer. Chem. Soc. Symp. Series 845, Washington, D.C., 2003, chp. 22. Schultz, T.P.; Boldin, W.D.; Fisher, T.H.; Nicholas, D.D.; McMurtrey, K . D . ; Pobanz, K . Phytochemistry 1992, 57, 3801-3806, and references therein. Schultz, T.P.; Harmes, W . B . ; Fisher, T.H.; McMurtrey, K . D . ; Minn, J.; Nicholas, D.D. Holzforschung 1995, 49, 29-34, and references therein. Schultz, T.P.; Nicholas, D.D.; Minn, J.; McMurtrey, K . D . ; Fisher, T . H . Synergistic combination of an antioxidant and wood preservative: A preliminary study. Internat. Research Group on Wood Preservation paper 98-30172, Stockholm, Sweden. Wood Deterioration and Preservation; Goodell, B.; Nicholas, D.D.; Schultz, T.P. Eds., American Chemical Society Symp. Series 845, Washington, D.D., 2003. Schultz, T.P.; Nicholas, D . D . Phytochemistry 2000, 54, 47-52, and references therein. Schultz, T.P.; Nicholas, D.D. Phytochemistry 2002, 61, 555-560, and references therein. Schultz, T.P.; Nicholas, D.D.; Henry, W.P.; Pittman, C . U . ; Wipf, D.O.; Goodell, B . Wood Fiber Sci. 2005, 57, 175-184. Mabicka, Α.; Dumarcay, S.; Rouhier, N.; Linder, M.; Jacquot, J.P.; Gerardin, P.; Gelhaye, E. Internat. Biodeter. Biodegrad., 2005, 55, 203-211. Schultz, T.P.; Nicholas, D.D.; Prewitt, M L . Holzforschung, 2004, 58, 300304. Schultz, T.P.; Nicholas, D.D.; Prewitt, M . L . ; Kirker, G.T.; Diehl, S.V. Inter. Biodeter. and Biodegrad. 2006, 57, 45-50. Gironda, K . F . U.S. Patent 5,534,487, 1996. Henry, W.P. Wood Deterioration and Preservation, Amer. Chem. Soc. Symp. Series 845, Washington, D.C., 2003, chp. 10. Binbuga, N.; Chambers, K . ; Henry, W.P.; Schultz, T.P. Holzforschung 2005, 59, 205-209. Schultz, T.P.; Nicholas, D..; Lebow, S. Forest Prod J. 2003, 53(9), 77-80. Schultz, T.P.; Nicholas, D.D.; Kelley, S. 2006. A nonleachable waterborne composition of resin acids and wood preserving organic biocides. U.S. Provisional Patent 60/743,669, filed March 22, 2006. Preston, A . F . Forest Prod J. 2000, 50(9), 12-19.


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20. Nicholas, D.D.; Schultz, T.P.; Sites, K . ; Buckner, D . 2005, Internat. Research Group on Wood Preservation Paper IRG/WP 05-20310. 21. Ingram, L . L., Jr. 2005. Personnal communication, Miss. State Univ. 22. Harju, A . M . ; Kainulainen, P.; Venalainen, M.; Titta, M.; Viitanen, H . Holzforschung 2002, 56, 479-486.


Improving the Performance of Organic Biocides by Using Economical

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