To assist in the transformation of the industry, FPInnovations’ Durability and Protection Group required significant investments in research infrastructure to speed up the research process. With funding from the Transformative Technologies program, FPInnovations has upgraded its capabilities in the area of rapid above ground preservative testing, rapid fungal identification and rapid biocide detection and characterization. Work has been initiated to assess the potential advantages and to understand and mitigate the potential disadvantages of transitioning to carbon-based preservative systems.
In North America, the voluntary withdrawal of chromated copper arsenate (CCA) from most residential uses in January 2004 resulted in a burgeoning development of wood preservatives likely to be perceived by the general public as more environmentally and health friendly. The initial shift was to copper-based preservatives with carbon-based co-biocides to control copper tolerant brown-rot fungi. These typically contain three times as much copper as CCA and the absence of chromium means that copper is not as well fixed in the wood. Early formulations (much prior to 2004) had used ammonia as a copper solvent but the ammonia off-gassing proved problematic and copper-amine systems were introduced. The ethanolamine is not a fugitive solvent like ammonia, consequently the copper in these preservative systems is more readily available to leach out and cause staining, corrosion and potentially adverse impacts on aquatic environments. Most of these problems can be overcome by careful formulation, treatment and post-treatment conditioning; however, at least one jurisdiction, the Netherlands, has eliminated use of copper-based preservatives. Wood preservative manufacturers have therefore developed the first generation of entirely carbon-based preservatives. These are currently going through the process of registration by Health Canada’s Pest Management Regulatory Agency (PMRA). It is highly likely that further development of these preservative systems will result in reduced susceptibility to biodegradation and improved performance. As seen with copper-based preservatives, we can expect to see a second and likely a third generation of carbon-based preservatives.
The PMRA requires performance data on Canadian wood species under Canadian conditions, including failure of low preservative retentions, prior to registering new preservatives. This can take seven to ten years using existing standardized field tests for above ground applications. The first report in this compilation describes the construction of an Accelerated Field Simulator (AFS) for rapid evaluation of the decay resistance of preservatives exposed above ground.
While there is a plethora of information on fungi capable of detoxifying or tolerating copper, and those which cause premature failure of copper-treated wood in service, there is relatively little information on the fungi which are likely to limit the performance of carbon-based preservatives. The AFS is designed to expose treated wood to spores of known decay fungi but also to natural airspora from outdoor air. This is anticipated to permit colonization of wood-treated with carbon-based preservatives by fungi that are capable of preservative detoxification or tolerance. Rapid identification of these fungi is important in the investigation of biodegradation of carbon-based preservatives and in the selection of appropriate fungi for laboratory tests. Using traditional morphological techniques is an extremely time consuming process and most laboratories now use modern molecular methods. Report number 2a in this compilation describes the selection, acquisition and commissioning of a molecular identification system for fungi based around Polymerase Chain Reaction (PCR) technology. Report number 2b is a draft paper on the use of this technology to confirm that the fungi growing on wood treated with carbon-based preservatives in the prototype accelerated above ground test must have colonized by spore germination and were the same species as the fungus fruitbodies installed in the chamber.
Most Canadian wood species can not be fully penetrated by pressure treatment with waterborne formulations. This has not proved to be a problem with copper-based preservatives because the copper is able to move into untreated surfaces freshly exposed when wood checks and prevent the germination of basidiospores. The omission of copper requires that other means are found to ensure performance in Canadian species which can not be treated all the way through. It is therefore important to know as much as possible about the initial distribution of the carbon-based preservatives, their mobility, redistribution and possible biodegradation in the wood. FPInnovations had developed methods for the extraction and analysis of the most commonly used carbon-based preservatives using High Performance Liquid Chromatography, but this was not capable of detecting low biocide loadings or characterizing biocide breakdown products. The third report in this compilation describes the identification, acquisition and commissioning of Liquid Chromatography-Mass Spectroscopy technology, which will enable detection of low preservative loadings and enable the chemical characterization of breakdown products.
An MSc student has been recruited to explore the mobility of the carbon-based preservatives, their ability to coat the untreated wood exposed in checks and their effectiveness in preventing germination of basidiospores. Report number 4a is the student’s thesis proposal and report number 4b covers the results of a directed study on detoxification of triazoles by wood decay fungi. Two wood-rotting basidiomycetes used in standard tests were found to be capable of detoxifying tebuconazole.
Currently, end of service life issues are the major Achilles heel of treated wood products due to the difficulty of extracting copper from the wood. The major benefit of the omission of copper from the carbon-based preservative systems is the potential to recycle or recover value from the treated wood with no detectable contaminants. Industry’s ability to confidently transition to these new preservatives and improved consumer perception of wood that can be readily recycled will ensure that wood retains markets currently under threat from non renewable materials with considerably higher energy consumption. The fifth report in this compilation covers the recycling of treated wood at the end of its service life. Kraft pulping, burning and composting of wood treated with carbon-based preservatives were investigated. All of the carbon-based preservatives evaluated survived kraft pulping. Analysis of combustion residues and compost is on-going.