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The use of radio frequency heating to condition, eliminate decay fungi, and fix chromated copper arsenate preservative, in roundwood

University of British Columbia

Electromagnetic radiation, such as radio frequency heating has been shown to be able to rapidly dry wood and to fix CCA in treated wood. However, the previous research at the University of British Columbia has focused on the drying of sawnwood using a radio frequency vacuum drier with flat parallel plates. This study examined the efficacy of radio frequency/vacuum heating, to rapidly dry roundwood sections as well as accelerate the fixation of chromated copper arsenate (CCA) in treated pole sections. The ability of radio frequency heating to sterilize wood was also examined. Conditioning of roundwood was carried out in a laboratory radio frequency/vacuum dryer at fixed frequency of 13.65 MHz. During drying, the change in the temperature with time, within each roundwood section, was continuously monitored. Evaluation of all the experimental runs showed that the flat electrode design of radio frequency/vacuum could dry roundwood to ca. 25% moisture content without loss in quality in less than 16 hours. Furthermore, radio frequency/vacuum drying produced poles with an uniform final moisture content. Accelerated fixation of chromated copper arsenic was also conducted using radio frequency heating. In this case ho vacuum was applied. The effect of radio frequency heating on the rate of fixation of CCA treated poles were evaluated by two methods: 1) a qualitative hexavalent chromium (VI) color reaction with chromotropic acid; 2) the quantitative analysis of hexavalent chromium (VI) in a leachate produced using sample borings. The fixation time was greatly reduced by heating the pole sections to above 80°C at high humidity. All three wood species used in this study required less than 4.5 hours to achieve complete fixation of the CCA. Eight experimental heating runs were further carried out to evaluate radio frequency heating to sterilize the roundwood sections. Sawdust was inoculated with the decay fungi [(Coniophora puteana, Gloeophyllum trabeum (47D) and Postia placenta (120F and 31094B)] and the fungi allowed to grow on the substrate. The inoculated sawdust to selected pole sections was added at predetermine depths from the surface. Following radio frequency heating, the sawdust was recovered and the viability of the fungi was determined. All decay fungi, as well as moulds present in the pole section, were completely killed after 2 hours of heating above 65°C. This confirmed the potential of the radio frequency kiln process to destroy wood decay fungi present in unseasoned poles.

Thesis/Dissertation

application/pdf

2009-07-06

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http://hdl.handle.net/2429/10239

Forestry

University of British Columbia

UBCV

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