The absence of commercial facilities to recycle or recover value from wood treated with metal-based wood preservatives at the end of its service life is one of the most significant negative points in the generally positive life cycle analysis of treated wood. Wood treated with carbon-based preservatives (metal-free) may be far easier to recycle or recover value from since the preservatives are relatively vulnerable to thermal, chemical and biological breakdown. As a result they might be destroyed by kraft pulping, combustion or composting of treated wood. The present research evaluates the use of carbon-based preservative-treated wood in these processes.
Kraft pulps produced from wood freshly treated with recommended loadings of carbon-based preservatives contained significant quantities of didecyldimethylammonium carbonate (DDAcarbonate), propiconazole and tebuconazole. However, lower preservative concentration in the wood and intensive pulping may be able to produce pulps without detectable preservatives. The azoles were also detected in significant quantities in the black liquor (DDAcarbonate was not analysed in black liquor).
No azoles were found in the ash produced from combustion, but significant quantities were detected in the filtered smoke. DDAcarbonate was not detected in the filtered smoke. Analysis of DDAcarbonate in ash was inconclusive.
A composting experiment has been set up and is in progress. Data on preservative breakdown during composting is expected next year.
To better understand the role extractives play in western red cedar’s decay resistance, commonly detected but unknown extractives need to be identified and evaluated for their potential contribution to natural durability. A new liquid chromatography/mass spectrometry (LC/MS) method for separating extractives from western red cedar has been developed. Mass spectral detection provides useful structural information that gives increased confidence in peak identifications and helps to identify unknown peaks. Using LC/MS data, combined with data from UV and NMR spectroscopy, unknown compound J commonly found in many samples of WRC we have analysed, was identified as alpha-thujaplicin. This was known to be a major extractive in eastern white cedar but was considered to be a negligible component of WRC. Its potential contribution to the durability of WRC has not been considered in previous work attempting to correlate durability to specific extractives.
Recent work at FPInnovations within the Transformative Technologies program has focused on developing information to assist the Canadian Wood Preservation industry to transition to carbon-based preservation systems. One of the aims of the research is to identify ways of processing wood treated with carbon-based preservatives at the end of its service life. There is also concern regarding biodegradation of carbon-based preservatives during the service life leading to premature failure. This review summarizes what is currently known about the biodegradation of carbon-based actives and identifies knowledge gaps to guide future work in this area.
Thermal treatments to improve the dimensional stability and durability of wood for exterior applications impart a pleasant dark brown colour but this rapidly fades to gray when exposed to weathering. A coating may solve this problem but adhesion to oil-thermal-treated wood may be an issue. The general objective of this research is to investigate the feasibility of coating oil-thermal-treated post-Mountain Pine Beetle (MPB) lodgepole pine for above-ground residential products such as siding. This is a continuation of previous research in 2006/07 on treating post-MPB lodgepole pine sapwood with oil-thermal treatment, also funded by FII. The current project focuses on surface modification and coating systems evaluation for this treated pine by laboratory tests, and initiating field tests for monitoring long-term coatings performance.
The project was carried out in collaboration with Dr. Paul Cooper of the University of Toronto, Dr. Phil Evans of the University of British Columbia, and Dr. Sam Williams of the Forest Products Laboratory of USDA. Based on the study carried out by FPInnovations–Forintek Division, Sikkens Cetol 123 and SuperNatural showed good adhesion on oil-thermal-treated pine, but the appearance of SuperNatural was preferable for the targeted applications. Hence, SuperNatural was selected for a long-term field test in Vancouver.
Based on the study undertaken by FPL, an aluminum isopropoxide sol-gel precursor was able to improve surface adhesion of the oil-thermal-treated wood for a water-borne finish, but did not improve the adhesion for solvent-borne finishes. The oil-thermal treatment did not appear to appreciably change the hardness or Young’s modulus of the wood based on the nano-indentation measurements. It was also found that the oil-thermal-treated wood could be easily treated with hydroxymethylated resorcinol (HMR), a coupling agent for coating. Its efficacy on coatings performance is being evaluated using an outdoor exposure test.
Based on the University of Toronto’s study, the oil-thermal treatment reduced the wettability of the wood to a number of solvents and had an adverse effect on coating curing and adhesion. Light sanding improved the wetting and resulted in improved adhesion. Among all the finishes evaluated, SuperNatural clear finish formed a hard coat with good adhesion.
The study by the University of British Columbia found that plasma treatment is able to remove oil from the surface of oil-thermal-treated pine, and increased its wettability as well as adhesion to coatings. Scanning electron microscopy, confocal profileometry, and Fourier transform infra-red spectroscopy also indicated that high-energy plasma treatment impacted wood structures, particularly around pits. The consequence of the plasma treatment on coatings performance is being studied with a weathering test.
Overall, the study showed that oil-thermal-treated blue-stained pine can be coated to improve weathering performance for exterior above-ground applications. It confirmed that sanding can improve the coatings performance. The effects of a coupling agent and plasma treatment on coatings performance are to be reported. Thermal modifications may provide a promising way to improve dimensional stability and also mask blue stain for post-MPB lodgepole pine. However, the potential bleeding of oil from wood with initially intense blue stain poses a major challenge for coating application and for developing residential appearance products from the post-MPB lodgepole pine using such an oil-thermal treatment. In that case, alternative thermal treatment processes, particularly using steam as the heating medium, could be considered.
Lacking the UV protection provided by copper, carbon-based preservative-treated wood used in many above-ground applications will require coating to meet consumer demand for weather resistance. While earlier metal-based preservatives were true solutions, many of the formulations of carbon-based preservatives rely on surfactants for solubility or dispersion in water. These surfactants can potentially react badly with the dispersion agents in the existing coatings on the market. The present work investigates the performance of six selected coatings on white spruce heartwood and ponderosa pine sapwood untreated and treated with one of three carbon-based preservatives. After 500 hours of artificial weathering there were few differences in coating performance between untreated and treated samples. Further weathering should be completed to potentially detect more subtle effects that these preservatives may have on coating performance.
Lacking the UV protection provided by copper, carbon-based preservative-treated wood used in many above-ground applications will require coating to meet consumer demand for weather resistance. While earlier metal-based preservatives were true solutions, many of the formulations of carbon-based preservatives rely on surfactants for solubility or dispersion in water. These surfactants can potentially react badly with the dispersion agents in the existing coatings on the market. The present work investigates the performance of six selected coatings on white spruce heartwood and ponderosa pine sapwood untreated and treated with one of three carbon-based preservatives. An earlier report described coating performance after 500 hours of artificial weathering (Stirling and Morris, 2010). The present report describes coating performance after 1000 hours of artificial weathering. The general ratings of the coatings on spruce were typically one to two points higher than those on pine indicating that spruce was a more stable substrate. Contrary to the initial concern, treatment with carbon-based preservatives was associated with coating performance under accelerated UV exposure similar to, or slightly better than, that on untreated wood.
The absence of commercial facilities to recycle or recover value from wood treated with metal-based wood preservatives at the end of its service life is one of the most significant negative points in the generally positive life cycle analysis of treated wood. An experiment was initiated to determine whether wood treated with carbon-based preservatives could be degraded by composting without residual preservative contamination. After one year the concentration of triazoles remained high, while the concentration of DDAcarbonate was greatly reduced.
This report describes the depletion of carbon-based actives from compost mixtures after a further six months of storage. Triazoles remained at high concentrations in the wood, while the concentration of DDAcarbonate was reduced. Overall, composting wood treated with carbon-based preservatives, under the conditions present in this study, was neither wholly effective nor efficient in breaking down these preservatives.
The absence of commercial facilities to recycle or recover value from wood treated with metal-based wood preservatives at the end of its service life is one of the most significant negative points in the generally positive life cycle analysis of treated wood. An experiment was initiated to determine whether wood treated with carbon-based preservatives could be degraded by composting without residual preservative contamination. After one year the concentration of azoles remained high, while the concentration of DDAcarbonate was greatly reduced. Several fungal isolations were made from the compost mixtures. More time is needed to complete the composting process.
Bluestain reduces the value of wood in appearance applications where the natural wood colour is desired. Treatments that remove bluestain without degrading the natural colour of the wood could make this lumber more suitable for appearance-grade applications.
FPInnovations and UBC have each previously developed methods of decolourising bluestain but both resulted in unacceptable colourations in the wood (Binnie et al., 2000; Evans et al., 2007). Follow up work at FPInnovations found that the combination of hypochlorite bleaching and exposure to UV and visible light was able to remove bluestain from lodgepole pine (Stirling and Morris, 2008). The present work identified the minimum treatment times required for effective bluestain removal to be a 10 minute bleaching dip and 10 minutes of exposure to intense light. Near- and mid-infrared spectra indicated changes in surface chemistry after treatment. However, adhesion tests showed no signs of reduced coating adhesion caused by UV damage or hypochlorite exposure.
Transformative Technologies - Element I identifierSeries Progress Report 2009/10i
Project No. 201000356
Vancouver, British Columbia
Some black stain fungi are known to exhibit resistance to carbon-based preservatives. However, the cause of this resistance is unclear. The fungi may have mechanisms to tolerate these chemicals, or they may be able to degrade and detoxify them. Fungi capable of degrading carbon-based preservatives are of interest for possible bioremediation of carbon-based preservative-treated wood at the end of its service. Moreover, such fungi could potentially facilitate the colonization of carbon-based preservative treated wood by decay fungi. Two strains of Aureobasidium pullulans and two strains of Epicoccum purpurascens were evaluated for their ability to degrade three commonly used carbon-based preservatives: propiconazole, tebuconazole, and DDAC. At low and medium concentrations propiconazole and tebuconazole were found to be vulnerable to degradation by one of the Epicoccum purpurascens isolates. Where biocides are needed to control the growth of black stain fungi on wood, a combination should be used to minimize the risk posed by resistant strains.