School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemIncreased performance and durability of boron treated wood products by acrylate and furfuryl alcohol resins( 2000)Chemical modification of wood outlined in this thesis was carried out using Furfuryl alcohol and Acrylic resin. This thesis focused on impregnation of wood polymer composites (WPC) by chemical formulations that polymerise within the wood structure. A second investigation was based on the treatment of the wood with trimethyl borate (TMB) and attempts to immobilise it within the wood structure to extend the distribution of boric acid through the wood. Radiata pine (Pinus radiata D.Don) was the starting material from which WPC were made, and impregnation chemicals were TMB, furfuryl alcohol monomer, prepolymerised acrylic resin and combinations of both resins. The effect of catalysts was also investigated. Much of the work was aimed at enhancing retention of tri-methyl borate (TMB) in wood by designing the system that would lock boron based compounds within the wood. TMB was applied separately and in combination with resin formulations. The expected penetration pathway was via capillaries, pits and voids. It is postulated that after vapour diffusion of TMB into wood, TMB would hydrolyse and boric acid, the product of hydrolysis, would be deposited in the cell wall. Further, it was proposed that resin treatment would encapsulate boric acid within the cell wall during polymerisation and consequently reduce or eliminate leaching. To further improve the chances of success, momentary immersion treatment of radiata pine (Pinus radiata D.Don) with TMB in methanol and TMB in acrylic solution was also investigated. The result indicated that a greater penetration of TMB preservative would be achieved when it is applied with an acrylic solution than with methanol. From the statistical analysis, it was evident that in both cases, TMB in acrylic and TMB in methanol, TMB penetration was dependent on solution retention. In the latter case, solution retention increases with an increase in the proportion of acrylic in the solution. However, the penetration of TMB decreased as the solution viscosity increased and the penetration of TMB decreased as the concentration of methanol increased. Preservative penetration and retention were influenced by TMB concentration in both methanol and acrylic solutions. About 20% TMB was needed in an acrylic solution to penetrate about 85% of the area. In contrast, methanol solution containing 20% TMB penetrated only 60% of the area.
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ItemChemical treatment of wood and its effect on wood/water interactions( 1999)Wood-water interactions including the effect of grain orientation, sample size and water potential in Pinus radiata D.Don were investigated. The influence of various chemical treatments on the wood-water interaction was also evaluated. The uptake of moisture by wood soaking in water was determined using the water soak method developed by Rowell and Banks (1985). Treatments with surfactants such as ammoniacal copper-didecyldimethylammonium chloride (DDAC-ACQ) and linoleate salts increased the initial uptake rates of the wafers, whilst treatment with copper chrome arsenic (CCA), linseed oil (LO) and a combined CCA/LO treatment reduced uptakes of moisture. The length of time used to assess the water repellent effectiveness (WRE) was found to be crucial to the test, with most of the reduction in WRE occurring in the first 15 minutes of soaking. Exposure of wax treated wafers to weathering indicated an initial gradual reduction in efficacy, which decreased more rapidly as the length of exposure time increased Tests on the effectiveness of different wood coatings subjected to high humidity illustrated the importance of a film with low permeability and some elasticity. Wood blocks coated with resorcinol-formaldehyde resin initially inhibited moisture ingress, but failed after prolonged exposure. An extra coat increased the time required before failure. Coating the wood wafer with a silicone resin slightly reduced the uptake of water into the wafer. However, this resin was more permeable than the resorcinol-formaldehyde resin and was not as efficacious. The effect of various oil treatments on the uptake of water vapour indicated that the distribution of the oil is critical to inhibiting vapour uptake. No significant difference was found between the moisture uptake of hardwood and softwood stakes. Treatment with trimethylborate (TMB), DDAC-ACQ and CCA had no significant effect on the extent of vapour taken up by the wood. An experiment designed to investigate the importance of sample size when assessing wood performance was carried out using matched samples of treated and untreated quartersawn and flatsawn Pines radiata D.Don. It was found that samples treated with DDAC-ACQ and exposed outdoors experienced a greater flux in moisture content compared to controls. CCA reduced the extent of moisture uptake, with the incorporation of oil further enhancing the short term weathering performance. Quartersawn wood exhibited a smaller moisture flux than the flatsawn timber.However, the performance of CCA/Oil treated quartersawn wood was only marginally better than the quartersawn controls. Laboratory trials gave an identical treatment ranking as the exterior trial; however the use of the smaller sample size was identified as being inappropriate for the assessment of check formation in the timber. A sample size effect was demonstrated when assessing the efficacy of treatments by the water soak method. A treatment gradient could be demonstrated when whole stakes were impregnated with CCA and linseed oil by a two-stage process. The test indicated that the significance of improvements in the water repellency of treated wafers diminishes when larger sized samples are investigated. The effect of soil water availability on wood moisture content was determined for untreated hardwood and softwood sticks. At low soil moisture contents, hardwood sticks were found to be significantly more saturated than their softwood counterparts. At higher soil water contents (100% water holding capacity (WHC)) the performance of the two species of wood became less significant. Chemical treatment was found to have a significant effect on reducing wood moisture levels when free water was available in the soil. Linseed oil was responsible for a significant reduction in moisture uptake, by blocking the pathways for water uptake as well as by decreasing the void volume available in the wood for water to occupy. Incorporation of a drying agent did not improve the quality of the film formed by the linseed oil as no significant change in water repellent performance was identified. The uptake and movement of water through a horticultural post was simulated using a procedure described by Baines and Levy (1979). The wick action of heartwood and sapwood stakes of Pinus radiata D.Don was investigated with distinct moisture distribution and behaviours found. Heartwood, being less permeable, showed a reduction in the volume of vapour that moved through the wood, as well as a much lower stake moisture content compared to the sapwood. This difference was most pronounced above the air/water interface and helps to explain the difference in decay resistance exhibited by the two wood types. End sealing the stakes with silicone resin was found to have no significant effect on the wick action of the stake. Lumen filling treatments with wax, oil and alkyd resins were found to significantly alter the wick action of the stakes. Treatment with low concentrations of surface active compounds such as DDAC-ACQ and linoleate soaps were found to increase the rate of water uptake. At higher concentrations the presence of the surfactant increased the hydrophobicity of the wood and reduced moisture uptake. Biological testing using a fungal cellar determined that treatment of the wood with CCA/LO, CCA, DDAC-ACQ/LO, LO and DDAC-ACQ significantly improved the resistance of the wood to decay. The incorporation of linseed oil did not cause a significant improvement to the decay resistance of the stakes over the trial period
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ItemThe effect of evacuation on treatability of wood( 1998)The effect of air evacuation on the treatability of wood using either vacuum or heating was determined by impregnating Australian grown Pines radiata (D. Don) sapwood and heartwood samples with polar and non polar preservatives. Systematic variation in vacuum and pressure levels resulted in different preservative penetration, preservative uptake and within treatment variation in uptake and penetration. Variation in vacuum and pressure levels were applied to a standard Bethell (Full cell) treatment process. The significance of the treatment results obtained was tested statistically. The statistical tools used include: analysis of variance Fisher's PLSD and regression analysis. Parameters affecting the treatability of Pinus radiata other than pressure and vacuum were also established. These include moisture content and basic density. Borax / boric acid uptake in radiata pine sapwood was found to vary with pressure, vacuum and basic density. It increased with a rise in each of these variables. Wood moisture content was insignificant in determining preservative penetration and retention in the range 10 - 20% moisture content. Uptake of borax / boric in heartwood was affected by pressure and vacuum. The validity of previously developed unsteady state heat flow models was tested to determine their applicability in predicting temperatures at various points in the wood during heating in air by convection. In general the correlation between experimentally and theoretically determined temperatures was high. However, Siau's unsteady state heat flow theory overestimated surface temperatures at the beginning of the heating period and underestimate temperatures at the centre of the wood at the end of the heating period. The effect of temperature of wood before soaking was determined by heating radiata pine sapwood samples and a mixture of sapwood and heartwood samples in a convection oven at different temperatures prior to soaking in copper chromate arsenate (CCA) solution or light organic solvent preservative (LISP). Regression equations were used to evaluate the factors influencing the treatability of radiata pine. Absorption of CCA and LISP in radiata pine was influenced by the temperature of the wood, moisture content, basic density and soaking time. The effect of heating time on the treatability of Australian and New Zealand grown Pinus radiata and Australian grown Pinus elliottii was determined by heating end-matched samples for different periods with or without sealing in polythene bags during heat application and then soaking the wood samples in CCA. Samples were wrapped in polythene bags to minimise moisture loss during heat application. These investigations showed that in general there was a rise in uptake with increases in heating time. However, the positive effect of heating time reached an optimum point beyond which there was a fall in uptake and penetration of CCA with further increases in heating time for Australian grown Pinus radiata samples heated without sealing in polythene bags. The optimum varied with sample thickness. However, the period of heating did not have a significant effect on uptake and penetration of CCA in Australian grown Pinus radiata when samples were sealed in polythene bags. Heating time had no significant effect on Australian grown Pinus elliottii and New Zealand grown Pinus radiata. Full sapwood penetration was achieved in New Zealand grown Pinus radiata regardless of heating time and with or without sealing samples in polythene bags. Pinus elliottii sapwood could not be penetrated fully regardless of heating time. Investigations into the effect of evacuation method, by heating wood by convection or microwave energy until the wood samples reached certain temperatures at the centre, showed that microwave evacuation achieved higher preservative uptake and deeper preservative penetration. Better air evacuation was achieved when the wood was heated at low microwave power levels for extended exposure. Microwave irradiation also achieved rapid CCA fixation in radiata pine and structural modification of green S. obliqua and E. magmata. Fixation time was greatly reduced by using higher microwave power levels. Structural modification investigations of E. obliqua achieved by heating wood samples at different power levels for different times indicated substantial increases in the permeability and treatability of this normally refractory wood species
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ItemGreen sorting and alternative timber pre-treatments for drying and preservative treatment of radiata pine (Pinus radiata D. Don.)( 1999)This project contains research in the disciplines of wood drying and preservation. It first explored two different avenues for possible improvement in the drying stage of sawn timber production and then studied a novel pre-conditioning method for preservative treatment of radiata pine. The first avenue of investigation for improving drying was the sorting the green timber into more uniform charges for drying usina the large and consistent difference between heartwood and sapwood moisture content. The impetus for this arose from the results of a preliminary mill-based study of moisture content variation within a typical kiln charge of mixed radiata pine heartwood and sapwood. Green density can be quickly and easily determined from scanned board volume and loadcell-derived board weight and was found to be closely correlated to average board MC and heartwood/sapwood content. Green density was a very good predictor of wood % saturation also. Although little used here in Australia, such a sorting system has potential to improve efficiency in the drying and conditioning stages of radiata pine sawn timber production. Pre-drying treatments (i.e. pressure-steaming and pre-steaming) to improve permeability and drying speed in radiata pine were examined as the second avenue for possible improvement in drying efficiency. The effects of these pre-treatments on drying parameters including measured radial permeability were assessed. Pressure-steaming (a preconditioning. method to improve permeability of radiata pine heartwood for preservation) rendered the wood highly susceptible to checking during drying, resulting in severe degrade. Pressure-steaming also appeared to retard drying rates, especially in the sapwood -- a phenomenon contrary to the significant improvements to permeability found in the wood samples subjected to this pre-treatment. Pre-steaming at 100 C for 4 hours prior to drying was found to be only of marginal benefit to permeability and drying rates, although its use is necessary for drying heart-in studs and reducing early surface checking. The second part of the project tested the application microwave energy as a novel alternative pre-conditioning method to pressure-steaming for preservation treatment of radiata pine. The microwave pre-conditioning caused very rapid drying of the wood (especially the heartwood) and significantly increased the uptake of preservative solution. However, the distribution of preservative was variable compared with that in wood which had been pressure-steam conditioned. Complete and even preservative distribution was achievable only in wood which had been microwave pre-conditioned for longer time periods at high intensity irradiation. These conditions also resulted in severe checking of the wood and excessive use of preservative solution. The effects on the structure of the wood were somewhat different to those of pressure-steaming in that increased permeability and ease of preservative penetration were facilitated by visible checks of various sizes whereas with pressure-steaming, the wood was altered at the microstructural level, by destroying the soft contents of the rays and thereby significantly increasing permeability in the radial direction. The important conclusions from the study were: (a) There is considerable scope for developing and applying simple but effective pre-drying sorting of green sawn radiata pine to generate greater- uniformity in drying charges and better tailor drying schedules to their specific requirements. This would lead to improved drying efficiency and reduced degrade. (b) Contrary to initial expectations, pressure-steaming is a pre-conditioning method suited to preservation but not to drying, as demonstrated by the retarded drying and severe degrade in pressure-steamed wood samples. (c) Microwave pre-conditioning for preservation treatment of radiata pine has considerable advantages over pressure-steaming in terms of rapidity of drying and deserves further consideration and development. The microwave processing conditions used in this study yielded variable results, demonstrating that much further research is required to optimise the microwave processing conditions to better suit radiata pine.
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