Peter Vinden

Microwave wood modification technology and its applications.

The use of microwave (MW) technology is growing in all industries. This increased use has resulted from the high efficiency of converting electricity into MW energy; energy savings associated with rapid, in-depth heating of materials; specific interactions that can be achieved between MW energy and materials; radical acceleration of technological processes; reductions in MW equipment costs; and improvements in the reliability of industrial MW equipment. The new technology of MW wood modification is based on the supply of high-intensity MW power, up to 135,000 kW/m3 at frequencies of 0.922 and 2.45 GHz. Such power induces significant changes to the microstructure of wood and a dramatic increase in wood permeability. A number of commercial applications have been developed based on the fundamental changes in wood structure. These include the treatment of refractory wood species with preservatives, rapid drying of hardwoods, relief of growth and drying stresses in timber, manufacture of the new wood materials...

Relationships between Density, Shrinkage, Extractives Content and Microfibril Angle in Tension Wood from Three Provenances of 10-Year-Old Eucalyptus globulus Labill

Summary Density and microfibril angle (MFA) of tension wood and normal wood were assessed in the sapwood and heartwood, from three provenanaces of 10-year-old Eucalyptus globulus Labill. Density was measured using a modified saturation method that also enabled the calculation of the extractives lost during saturation. Microdensity and MFA were determined by SilviScan 2, a rapid X-ray densitometry and X-ray diffraction system developed at CSIRO. Significant differences were found in density and extractives between provenances and also density between the sapwood and adjacent heartwood from each provenance. This result may explain some of the drying differences between provenances found in an earlier study (Washusen and Ilic 2000). Sapwood samples with high percentages of tension wood fibres had high density and a significant positive correlation was found between microdensity and tension wood fibre percentage. MFA was found to be very low in normal wood in the sapwood, where most tension wood was found, so tension wood could not be identified by MFA. The positive association between tension wood and wood density suggests that caution should be taken when selecting trees for high wood density in tree improvement programs.

Recovery of dried appearance grade timber from Eucalyptus globulus Labill. grown in plantations in medium rainfall areas of the southern Murray-Darling Basin.

Summary The potential of 40 mm-thick, back-sawn boards of 15-year- old Eucalyptus globulus Labill, subsp. globulus to produce dried appearance products was assessed. Two samples of boards from plantation grown logs described in Washusen et al. (2000) representing (i) the cross-section through each log (Sample 1), and (ii) outer heartwood boards (Sample 2) were dried to 12% moisture content. Sample 1 was dried using sheltered air-drying followed by kiln-drying. Sample 2 was kiln-dried from green without preliminary air-drying. Dried recovery results were poor in both samples and extensive degrade substantially reduced the recovery of undried boards graded select and better that were reported by Washusen et al. (2000). The dried recovery of select grade and better represented reductions of 69% and 60% for Sample 1 and 2 respectively, and based on Sample 1 the final recovery was estimated to be less than 2% of the original log volume. Tension wood was identified as one of the causes of drying degrade in boards from the outer heartwood. The results suggest that the species has little prospect for the production of high-quality solid wood products from unpruned logs from plantations in the southern Murray-Darling Basin unless there can be significant improvement in drying performance.

Tension wood occurrence in Eucalyptus globulus Labill. I. The spatial distribution of tension wood in one 11-year-old tree

Summary In preliminary work for a project to develop methods for rapid detection of tension wood in standing trees, the spatial distribution of tension wood was assessed in one 11-y-old tree of Eucalyptus globulus Labill, from East Gippsland, Victoria, Australia. Tangential shrinkage was assessed at about 500 locations within the tree by drying small wood samples to 12% moisture content after reconditioning, and high tangential shrinkage was used to indicate tension wood. A shrinkage differential was calculated as the difference between the tangential shrinkage at the site of maximum shrinkage and the minimum normal shrinkage in tissue of similar cambial age at the same height in the stem. In earlier studies regression analysis indicated that cellulose crystallite width (which is a good indicator of the presence and severity of tension wood) and microdensity (measured on SilviScan-2; a system developed at CSIRO for rapid assessment of wood microstructure) were significant predictors of the shrinkage differential. In addition, at a shrinkage differential of 3.0% or greater, tension wood was easily identified histochemically in thin transverse microscope sections. Hence the shrinkage differential could be used to map tension wood occurrence. Tension wood was located predominantly below 30% of tree height and increased in extent and severity toward the base. The spatial distribution suggests that sample cores from low in the stem could be used to detect tension wood in standing trees, and the results warrant expansion of the work to more trees in order to further develop detection methods.

Appearance product potential of plantation hardwoods from medium rainfall areas of the southern Murray-Darling Basin. Green product recovery

Summary The potential of plantation-grown Eucalyptus cladocalyx F Muell., E. globulus Labill. subsp. globulus, Corymbia maculata (Hook.) K. Hill & L. Johnson and E. sideroxylon Cunn. ex Woolls subsp. sideroxylon as a resource for high quality sawn products in the winter, medium rainfall zones (580–750 mm) of the southern Murray-Darling Basin were investigated in this study. Six plantations ranging in age from 15 to 40 years from within the region were selected for harvest. Sawing involved back-sawing strategies which have been shown to maximise the output of high quality products from small diameter eucalypts. To evaluate out-turns of appearance products and to assess the effect of tree growth characteristics (primarily branches, knots, kino and other characteristics) on sawn product appearance, green product quality and recovery were assessed using CSIRO appearance grading criteria. Evaluation of products was conducted in specific zones of the inner heartwood (within 50 mm of the pith) and outer heartwood (greater than 50 mm from the pith) and on a whole log basis. Based on green product appearance, good recoveries of high quality products were obtained for 36 to 40-year-old E. cladocalyx, 40-year-old C. maculata and 40-year-old E. sideroxylon. Alternatively, the potential for 15-year-old E. globulus and 26-year-old E. sideroxylon suggested that the potential would not be as good without some reduction in significant defects, particularly knots and kino. Knots were a major defect in sawn products from all plantations. Evaluation of boards from inner heartwood and outer heartwood zones showed that with the removal of knots an increase in recovery of products of select grade and better would be possible in the outer heartwood in all species. This indicates a potential improvement in product quality had mechanical pruning been employed. However, improvement in quality in C. maculata and E. cladocalyx would be modest after pruning because of good natural branch shedding characteristics in these species.

Evaluation of borate formulations as wood preservatives to control subterranean termites in Australia

Abstract The termiticidal efficacy of sodium octaborate tetrahydrate, boric acid, borester-7, and tri-methyl borate as wood preservatives was evaluated after each was impregnated into seasoned sapwood of Pinus radiata D. Don and Eucalyptus regnans F. Muell in laboratory bioassay against Coptotermes acinaciformis (Froggatt). There was clear difference between the different borate retentions in treated and untreated blocks, mass loss, and mortality rate of the termite used in the bioassay units. After 8 weeks of laboratory bioassay, the results suggested that borate was toxic to termites even at 0.24% m/m BAE and caused significant termite mortality, but termites were not deterred from attacking the borate-treated timber at a higher retention of >2.0% m/m BAE. These laboratory results indicated that the minimum borate treatment required to protect timber against termite attack and damage was >1.0% m/m BAE.

Microwave surface modification of Pinus radiata peeler cores: technical and cost analyses.

Radiata pine (Pinus radiata) peeler cores are classified as a by-product of plywood manufacture and have the potential for development as value-added solid wood products. This article outlines technical and cost analyses of microwave surface modification of radiata pine peeler cores along with the methodology, including measurements of temperature distribution and of preservative uptake and distribution following microwave heating. After microwave treatment, the highest temperatures are observed on the surfaces of the peeler cores. A gradual decrease in temperature is noted with depth within the timber. Chromated copper arsenate uptake after pressure impregnation ranges between 94 and 314 liters/m 3 . This uptake is three to nine times higher than that of control timber (no microwave treatment). Cost analyses focus on the microwave treatment of peeler cores and indicate that microwave modification costs range from US

Biodeterioration of treated Pinus radiata timber by Australian decay fungi and the termite Coptotermes acinaciformis in laboratory bioassays and field conditions

0.95 to US

Moisture conditioning of wood using a continuous microwave dryer

1.23 for one peeler core (i.e., US

Changes in markets, technology and resources: prospects for wood-based products

29 to US