School of Agriculture, Food and Ecosystem Sciences - Theses
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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