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Fighting decay - organic preservation of wood
An organic preservation method for treated wood used in residential applications may provide an effective and environmentally friendly way to prevent wood decay.
Scientists at Mississippi University, USA, have combined a liquid organic biocide formulation with butylated hydroxytoluene (BHT) acting as an antioxidant additive to pressure treated wood.
Lead Researcher Tor Shultz explains, ‘The organic compound BHT is commonly used as a food additive, to prevent fats from oxidising into lower-molecular weight compounds, which have a rancid smell and give the food an off-flavour. It is also stable in wood, non-leachable in exterior exposure, inexpensive and benign. Providing sufficient antioxidant and organic biocide is present, a two to three fold enhancement in fungicidal efficacy can be achieved’. However, due to a patent status, the levels needed cannot be confirmed. Results will also vary if low levels of an organic biocide are used.
Waterborne copper-based systems remain the leading preservation method for treated wood used in decking, fence posts and home construction, yet disposal issues are still a concern as they can leach into sensitive aquatic environments. The use of BHT, having no metallic biocides, would eliminate this problem, argues Schultz.
Long-term field studies also show that BHT reduces depletion of organic biocides, which could have resource and ,cost benefits. The team tested ground-contact stakes treated with the organic biocide chlorothalonil and tested two categories – with and without co-added BHT. After exposure at two separate field sites for 52 months, the depletion of the chlorothalonil was reduced by approximately 50% when BHT was present, claims Schultz.
Biocides that show enhanced benefit when BHT is co-added included organic fungicides propiconazole or tebuconazole, chlorothalonil and isothalizonile.
To test the productivity of the preservative process, the team conducted a series of short- and longterm laboratory and outdoor above ground and ground-contact field tests on Southern pine sap wood, over multiple year ranges (5-12) for high deterioration potential. While the preservative has been tested mainly on Southern pine, Schultz anticipates it will work with all wood species that are commercially treated.
Furthermore, unlike copper, organic biocides can also be degraded over time by many microorganisms, therefore the next phase of research will involve decay testing over increased exposure times.
Dr Andrew Hughes, Technical Director at Arch Timber Protection, UK, says ‘The availability of organic biocidal actives in Europe is limited compared with the USA and other global markets as our regulations tend to be more stringent. In practical terms, this will mean that wholly organic biocide-based preservatives are used initially in above ground applications in Europe. These preservatives offer customers a new choice, particularly as the treated timber maintains its natural colour. However, maintaining the appearance of the timber in such uses is equally as important as the preservation qualities’.
He adds, ‘The research being undertaken by Shultz’s group could be an extremely valuable alternative, providing the test methods are equally as rigorous as field-testing. One must not forget, however, that copper-organic preservatives are expected to be fully authorised for use in Europe for many years to come and will continue to be the predominant, lowest cost preservative type for exterior use’.
Due to ‘questionable economics’, one factor being that organic biocides are much more expensive per unit weight than copper, no industrial partners have yet entered into agreement on the technology.
Wood Focus Magazine, 27 Aug 2010
Scientists at Mississippi University, USA, have combined a liquid organic biocide formulation with butylated hydroxytoluene (BHT) acting as an antioxidant additive to pressure treated wood.
Lead Researcher Tor Shultz explains, ‘The organic compound BHT is commonly used as a food additive, to prevent fats from oxidising into lower-molecular weight compounds, which have a rancid smell and give the food an off-flavour. It is also stable in wood, non-leachable in exterior exposure, inexpensive and benign. Providing sufficient antioxidant and organic biocide is present, a two to three fold enhancement in fungicidal efficacy can be achieved’. However, due to a patent status, the levels needed cannot be confirmed. Results will also vary if low levels of an organic biocide are used.
Waterborne copper-based systems remain the leading preservation method for treated wood used in decking, fence posts and home construction, yet disposal issues are still a concern as they can leach into sensitive aquatic environments. The use of BHT, having no metallic biocides, would eliminate this problem, argues Schultz.
Long-term field studies also show that BHT reduces depletion of organic biocides, which could have resource and ,cost benefits. The team tested ground-contact stakes treated with the organic biocide chlorothalonil and tested two categories – with and without co-added BHT. After exposure at two separate field sites for 52 months, the depletion of the chlorothalonil was reduced by approximately 50% when BHT was present, claims Schultz.
Biocides that show enhanced benefit when BHT is co-added included organic fungicides propiconazole or tebuconazole, chlorothalonil and isothalizonile.
To test the productivity of the preservative process, the team conducted a series of short- and longterm laboratory and outdoor above ground and ground-contact field tests on Southern pine sap wood, over multiple year ranges (5-12) for high deterioration potential. While the preservative has been tested mainly on Southern pine, Schultz anticipates it will work with all wood species that are commercially treated.
Furthermore, unlike copper, organic biocides can also be degraded over time by many microorganisms, therefore the next phase of research will involve decay testing over increased exposure times.
Dr Andrew Hughes, Technical Director at Arch Timber Protection, UK, says ‘The availability of organic biocidal actives in Europe is limited compared with the USA and other global markets as our regulations tend to be more stringent. In practical terms, this will mean that wholly organic biocide-based preservatives are used initially in above ground applications in Europe. These preservatives offer customers a new choice, particularly as the treated timber maintains its natural colour. However, maintaining the appearance of the timber in such uses is equally as important as the preservation qualities’.
He adds, ‘The research being undertaken by Shultz’s group could be an extremely valuable alternative, providing the test methods are equally as rigorous as field-testing. One must not forget, however, that copper-organic preservatives are expected to be fully authorised for use in Europe for many years to come and will continue to be the predominant, lowest cost preservative type for exterior use’.
Due to ‘questionable economics’, one factor being that organic biocides are much more expensive per unit weight than copper, no industrial partners have yet entered into agreement on the technology.
Wood Focus Magazine, 27 Aug 2010
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