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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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.