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.
Biological and chemical changes were evaluated in freshly sawn amabilis fir and western hemlock lumber (hem-fir) over 10 weeks of outside storage. Both wood species commonly contained brownstain microscopically in heartwood and sapwood. Microorganisms were often found in discoloured samples, but brownstain could not be linked to the presence of microorganisms. Qualitative HPLC analysis was employed on methanol extracted hem-fir segments over time, but this approach provided no indication about potential precursors to hemlock brownstain. However, the HPLC method developed produced a reliable separation and identification of nine wood constituents in hem-fir lumber and can be used for future quantitative analysis. The factors producing macroscopic brownstain were not understood, but a high moisture content appeared to be essential to transport precursors of hemlock brownstain to the wood surface.
Samples of western hemlock [Tsuga heterophylla (Raf.) Sarg.] and western red cedar [Thuja plicata Donn] trees completely submerged standing in a fresh water reservoir for approximately 24 years were examined in terms of relative wood density, extractives content in cedar and mechanical properties of small clear specimens. Due to diameter limitations in the sample material, test results for modulus of elasticity (MOE) in compression parallel-to-the-grain were found to be unreliable, but could be expected to compare to published values in a like manner as other test results. Based on the results of tests for wood density, extractives content and strength properties of small clears, the sound wood quality of submerged western hemlock and western red cedar is comparable to that of these species in general. Mitigating these favourable results, however, were the low proportion of sound logs recovered, external checking of log surfaces, and fine shake observed in red cedar which could have a negative impact on appearance grades. Definite determination of submerged wood quality would require sawing of logs, and evaluation of lumber yield and properties, and long-term tests for durability of the red cedar.
Several problem areas exist for lumber manufacturers such as, application of antisapstain chemicals, hemlock brownstain and disposal of PRF resin used by wood lamination plants. The ability to monitor the application of antisapstain chemicals can prevent monetary claims against the industry and improve our credibility as a supplier. The mechanism by which hemlock brownstain occurs must be fully understood in order to control it. Lumber lamination plants must have a way of monitoring their waste PRF resin in order to meet provincial environmental regulations.
Didecyldimethylammonium chloride (DDAC) is a chemical commonly used in wood protection applications. The penetration of DDAC into wood has implications for efficacy as well as the development of surface analysis techniques such as Fourier transform infrared spectroscopy (FTIR). In order to gain a better understanding of the factors which affect the penetration of DDAC into wood, we saw a need for a technique which can be used to better define the distribution of DDAC within the wood. The technique developed in this project combines a microtome wood sampling procedure with a suitably modified version of Forintek's HPLC method for DDAC analysis. The detection limit was 500ng DDAC per sample vial, or 250ng per 32mm x 7mm x 100µm wood slice. The method was used to profile DDAC distribution in dip-treated wet and dry amabilis fir, Douglas fir, lodgepole pine and western hemlock sapwoods. For all samples tested, detectible DDAC penetration was found to be limited to less than 1mm below the surface. Dry samples were found to retain approximately twice as much DDAC as wet samples, and wet samples were found to retain a higher percentage of their total DDAC near the surface than dry samples. A follow-up study should be done using the techniques described in this paper to analyze DDAC penetration in a larger sample set. The study should compare DDAC penetration in dip, spray and pressure treatments, and should examine the relationship between the penetration of DDAC and other relevant chemicals such as borates and iodopropynylbutyl carbamate (IPBC).
Fourier Transform Infrared spectroscopy (FTIR) has been identified as a potential analytical method that might improve monitoring of sapstain control chemicals application in sawmills. The main benefit from use of this technique would be the ability to respond immediately to application problems identified. Based on preliminary laboratory data Bomem Inc., Forintek Canada Corp. (FCC) and the Pacific Forestry Centre (PFC) agreed to undertake research aimed at the development of FTIR for commercial application in sawmills. The first stage in this project was to validate the FTIR method in the laboratory. A protocol was agreed upon for a test which would determine the precision of the FTIR retention predictions on a variety of wood surfaces. Wood strips of rough, planed and intermediate surface texture were prepared. At FCC a technique was devised by which the wood strips were treated with known amounts of DDAC. Intermediate textured replicate samples were treated to known retentions of DDAC and sent to PFC to use in calibrating the FTIR instrument. Additionally, 20 replicates of each surface texture were treated with random amounts of DDAC over the range 0 - 200ug/cm squared. These "unknowns" were also sent to PFC for analyses by FTIR and prediction of DDAC retentions. Although correlation between actual and predicted DDAC retentions was linear within a particular surface texture, results show a mean difference or error between the actual (weight uptake) and FTIR determinations of DDAC retentions of 46% (standard deviation 28%). Therefore, overall, the FTIR analytical method gave unsatisfactory results. Our conclusion is that, based on the current calibration, the FTIR analytical method is not sufficiently accurate for general sawmill application. The surface texture of the wood being scanned significantly affected the retention of DDAC as determined by FTIR and corrections for surface texture would need to be incorporated into the software if further development was to be considered. Additionally, other variables than surface texture (e.g. formulation additives) may influence analytical results and were not considered in this study.