School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemMechanical properties of wood following microwave and resin modification( 2002)The influence of microwave and resin modification of wood on its density, modulus of elasticity (MOE), modulus of rupture (MOR) and surface hardness is the subject of this thesis. Microwave energy has been used in industrial processing for many years. Microwave energy is an attractive option for wood processing and drying. Recent studies have shown that microwave energy can be used to modify wood by rupturing ray cells to form a large number of cavities in its radial/longitudinal planes resulting in micro voids of various sizes throughout its cross-section. The resultant wood (`Torgvin') is more permeable and more flexible but has a lower density and mechanical properties (MOE, MOR and surface hardness) compared to the original wood. Further treatment to restore initial density and mechanical properties by addition of resin has resulted in a new timber product `Vintorg'. Initial trials of Vintorg production employed isocyanate resin. An increase in MOE, an increase in surface hardness and a 100% restoration of MOR of P. radiata heartwood was achieved. Despite being a tough adhesive, isocyanate has some drawbacks that may not make it acceptable for the production of Vintorg. This study therefore focused on melamine formaldehyde (MF) and furfuryl alcohol (FFA) resins as potential substitutes for isocyante resin in the manufacture of Vintorg. The study evaluates Vintorg produced by soaking P. radiata and E. regnans in these two resins. A factorial design is used to evaluate the effect of wood species, resin type and duration of soaking on resin uptake, resin loss, increase in density of Torgvin, density of Vintorg and mechanical properties of Vintorg. The results show that wood species and duration of soaking and resin type have significant effects on resin uptake. The increase in the density of Torgvin during the manufacture of Vintorg is found to be influenced by wood species, duration of soaking and resin type. A higher overall increase in the density of Torgvin was obtained in E. regnans compared to P. radiata. Melamine formaldehyde resin tends to have a greater effect on the increase in the density of E. regnans than P. radiata. Torgvin samples impregnated with FFA had a greater effect on increasing the density of P. radiata than E. regnans. Vintorg in the timber species tested is found to be the same or higher in MOE, much higher in density but lower in MOR than natural wood from the same species, irrespective of wood species, resin type or soaking time. Vintorg produced from P. radiata is also higher in surface hardness than natural wood from the same species irrespective of resin type and soaking time. It is interesting to note that surface hardness of Vintorg is lower in E. regnans as compared to natural wood from the same species. It is also evident that FFA and MF Vintorg are the same or higher in MOE but lower in MOR than isocyanateVintorg from the same species irrespective of wood species tested and the duration of soaking used. The FFA and MF Vintorg from are also the same or higher in surface hardness in the case of P. radiata but same or lower in the case of E. regnans. It is concluded that it may be possible to substitute the two resins for isocyanate resin in the production of Vintorg provided that a way is devised to ensure that the MOR of the resultant Vintorg is at least same or higher than that of original wood. It is recommended that further research be carried out to establish a microwave regime for optimal wood permeability and whilst minimizing the reduction in MOR, and that low cost, environmentally friendly resin systems are developed with low viscosity. These resins need to be tough enough to result in Vintorg with characteristics similar to Vintorg produced with isocyanate resin and superior to natural wood in terms of mechanical properties.
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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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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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ItemWood characteristics and properties of plantation mountain ash (E. regnans) and their variation( 1992)Six 15-year old Eucalyptus regnans F.Muell trees from three seedlots in a progeny trial in Narbethong, Victoria were examined in this study. Wood discs were removed from the base, breast height, 20 %, 40 %, 60 % and 80 % of the total tree height. Three methods used to demarcate the boundary between the sapwood and heartwood on the disc cross sectional surface were examined. The first method was based on the difference between sapwood and heartwood. The second method which was based on the difference in pH between sapwood and heartwood used 0.1 % methyl orange stain. The third method which was based on the presence or absence of tyloses in the vessels used a light table. Measurements were also made on the cross sectional surfaces of the discs to determine the sapwood width, heartwood percent, and the number, length and year of formation of each kino vein. The presence of decay and discolouration was also noted. Sapwood and heartwood wood blocks were cut from discs along the four cardinal directions. The basic density and moisture content of all wood blocks from the four axes and the remaining pie shaped pieces from each disc were determined. Mean basic density and moisture content based on the wood blocks from only the four axes were also computed. No difference was found in the demarcation of the sapwood-heartwood boundary between the methods based on natural colour and stain. Demarcation of the boundary using the light table method gave significantly different results to those found for the colour and stain methods. Based on the light table results, the presence of the tyloses appears to vary greatly between the base and breast height while at the 20 %, 40 and 60 heights they are more uniformly distributed. The mean sapwood width varied significantly between trees with values ranging from 24.2 mm to 28.7 mm with on average about four to five growth rings present in the sapwood zone. The mean sapwood also varied significantly with height. The lowest mean sapwood width of 21.0 mm was found at breast height and the mean sapwood width increased to 33.9 mm at the 80 height and increased from breast height to 29.9 mm at the base of the tree. The mean heartwood percent varied significantly between trees and with height. Two trees from seedlot number 13 had a mean heartwood percent of about 42 which was about 6 % lower than the mean heartwood percent of about 48 for the two trees from from seedlot number 23. The largest heartwood percent of 69.51 was found at the breast height and decreased to 0 (zero) at the 80 height and also decreased from the value at breast height to 65.75 at the base of the trees. A correlation of 0.967 was found between heartwood diameter and disc diameter. Kino veins were found in all six trees with the earliest formed vein at the tree age of 4 years. For the six trees, the total number and average length of kino veins decreased with height. The average length varied greatly between trees while the total number of kino veins was relatively uniform in five out of six trees. The presence of decay and discolouration was noted in five out of six trees. Basic density varied significantly between trees and with height but not between the sapwood and heartwood which had mean basic density values of 0.430 g/cm3 and 0.435 g/cm3 respectively. The mean basic density of 0.408 g/cm3 was lowest at breast height and highest at 80 height where the mean basic density was 0.468 g/cm3. Tree number 2 from seedlot number 13 had the highest mean density of 0.486 gm/cm3 and this was significantly greater than the lowest value of 0.422 g/cm3 found for tree number 4 from seedlot number 23. The interactions between trees and heights and between heights and axes were also found to be significant. Moisture content varied significantly between trees and with height but not between the north, south, east and west cardinal directions which had mean values of 146.98 148.47 %, 148.91 and 151.15 respectively. The mean moisture content at breast height was the highest with a value of 161.14 and the lowest value of 134.33 was found at the 80 height. Tree number 2 had the lowest mean moisture content of 127.65 and tree number 5 had the highest value of 161.05%. The interactions between heights and locations (sapwood or heartwood) and between axes and locations were significant. A correlation of -0.923 was found between moisture content and basic density. The mean basic density values and the mean moisture content values determined from blocks removed along only the four axes were strongly correlated to the weighted disc values based on virtually all the wood from each disc.
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