School of Agriculture, Food and Ecosystem Sciences - Theses

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    The chemical modification of Pinus radiata (D.Don.) with furfuryl alcohol
    Skewes, Brett Andrew. (University of Melbourne, 2006)
    Wood blocks impregnated with furfuryl alcohol required a standing time of 48 hours to ensure complete swelling of the wood. Total penetration of the blocks was required for maximum swelling and water resistance in treated blocks. The presence of water in the treatment solution caused rapid swelling of the wood block, whereas 100% furfuryl alcohol created a slow rate of swelling. The presence of water in the cell walls accelerated the rate of swelling of 100% furfuryl alcohol, but not to the extent as when the water was present in the treatment solution. Dimensional stability decreased as the water content in the treating solution increased, but compared to the controls (6 - 8%) there was significant improvement in dimensional stability (2.5 - 4%). The resin forming efficiency varied with the amount of water present, but never dropped below 85%. Treated wood samples compressed to a density of 1200 � 1400 kg/m3 were more stable when exposed to water, and had increased hardness and MOE compared to untreated compressed samples. The curing of furfuryl alcohol in beakers gave a clear indication of catalyst performance with variable catalyst concentration and curing temperature. An increase in catalyst concentration increased the resin forming efficiency which was dependant upon the catalyst strength and number of pKa values. Of the catalysts stable at room temperature, oxalic acid, maleic acid and zinc chloride were the best performed for wood impregnation, with respect to the parameters investigated. The higher the resin forming efficiency the lower the volumetric swelling. The initial moisture content of the wood had a direct effect upon the swelling of wood blocks. All samples with an initial moisture content of 12% performed better than the corresponding treatments used with oven-dried blocks. Further, higher catalyst concentrations and curing temperatures improved performance. Oxalic acid at a 4% concentration with furfuryl alcohol and a 2% concentration with furfuryl alcohol � formaldehyde formulations produced the best resin forming efficiency, permanent swelling and water property results. Conditioning time between pressure impregnation and curing was unnecessary with no improvement in properties with the cured wood block. Furfuryl alcohol with a 4% oxalic acid concentration produced the most desirable overall results with resin forming efficiency (111%), permanent swelling (8%), water uptake (8%) and dimensional stability (2.8%), when cured for 24 hours at 120�C. Analysis of leachate by GCMS suggested that a minimum curing time of 12 hours is required with furfuryl alcohol and 6 hours with a furfuryl alcohol � formaldehyde formulation to substantially reduce the amount of leachable material from a treated wood block, confirmed by dimensional stability trials.
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    The chemical modification of Pinus radiata (D.Don.) with furfuryl alcohol
    Skewes, Brett Andrew. (University of Melbourne, 2006)
    Wood blocks impregnated with furfuryl alcohol required a standing time of 48 hours to ensure complete swelling of the wood. Total penetration of the blocks was required for maximum swelling and water resistance in treated blocks. The presence of water in the treatment solution caused rapid swelling of the wood block, whereas 100% furfuryl alcohol created a slow rate of swelling. The presence of water in the cell walls accelerated the rate of swelling of 100% furfuryl alcohol, but not to the extent as when the water was present in the treatment solution. Dimensional stability decreased as the water content in the treating solution increased, but compared to the controls (6 - 8%) there was significant improvement in dimensional stability (2.5 - 4%). The resin forming efficiency varied with the amount of water present, but never dropped below 85%. Treated wood samples compressed to a density of 1200 � 1400 kg/m3 were more stable when exposed to water, and had increased hardness and MOE compared to untreated compressed samples. The curing of furfuryl alcohol in beakers gave a clear indication of catalyst performance with variable catalyst concentration and curing temperature. An increase in catalyst concentration increased the resin forming efficiency which was dependant upon the catalyst strength and number of pKa values. Of the catalysts stable at room temperature, oxalic acid, maleic acid and zinc chloride were the best performed for wood impregnation, with respect to the parameters investigated. The higher the resin forming efficiency the lower the volumetric swelling. The initial moisture content of the wood had a direct effect upon the swelling of wood blocks. All samples with an initial moisture content of 12% performed better than the corresponding treatments used with oven-dried blocks. Further, higher catalyst concentrations and curing temperatures improved performance. Oxalic acid at a 4% concentration with furfuryl alcohol and a 2% concentration with furfuryl alcohol � formaldehyde formulations produced the best resin forming efficiency, permanent swelling and water property results. Conditioning time between pressure impregnation and curing was unnecessary with no improvement in properties with the cured wood block. Furfuryl alcohol with a 4% oxalic acid concentration produced the most desirable overall results with resin forming efficiency (111%), permanent swelling (8%), water uptake (8%) and dimensional stability (2.8%), when cured for 24 hours at 120�C. Analysis of leachate by GCMS suggested that a minimum curing time of 12 hours is required with furfuryl alcohol and 6 hours with a furfuryl alcohol � formaldehyde formulation to substantially reduce the amount of leachable material from a treated wood block, confirmed by dimensional stability trials.
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    Mechanical properties of wood following microwave and resin modification
    Muga, Meshack Odera ( 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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    Control of thinning operations for maximum production
    Yeo, Byron John ( 1998)
    Thinning of plantations is a recognised practice for concentrating growth onto selected trees while providing an intermediate return from the thinnings. A great deal of work has been done on methods for estimating optimum time and weight of thinning for the particular stand. However, the selection of individual trees to be thinned in the forest has relaxed in recent years to make thinning more flexible, reduce costs and to better facilitate mechanised harvesting. Some plantations are now being thinned by the harvesting machine operator selecting the trees to be thinned while harvesting. A series of field trials were undertaken in Pinus radiata plantation at Rennick, Victoria, to compare conventional tree marked thinning with operator selected thinning (OST) where the harvesting machine operator selected trees while harvesting. The results indicate good control of tree selection by the operators: thinning to the same density and diameter distribution as the tree marked treatment while removing all required defect trees. Operator tree selection did not affect harvesting productivity, however, it improved log processing time in a second thinning by an experienced tree selecting operator, it also improved falling and work cycle time (approach tree, fall and process) in first thinning on a high site quality. Thinning trials at an operational level, about 6 ha, tested operator selection thinning to two different sets of guidelines: a diameter limit; and spacing requirements for residual trees. These OST thinning operations were no worse than the conventional tree marked thinning and resulted in less residual tree damage and more trees harvested per hour in second thinning. A simple economic analysis, based on data from the field trials, showed each operator selection thinning to be similar to the conventional tree marked thinning for revenue from thinnings and PNV of the rotation taken through to final harvest by a computer model. Of the trials, first thinning on high site quality by a relatively inexperienced operator selecting trees was the least favourable for stand production.
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    Fixation mechanisms of copper chrome arsenate (CCA) wood preservative
    Walley, Simon ( 1996)
    The fixation mechanism of copper chrome arsenate wood preservative is investigated. Parameters examined, include: pressure, solution temperature, solution strength, second stage treatment with water and oil, initial vacuum and timber pack design. The influence of these parameters is determined by analysing; basic density, penetration, preservative retention and leaching characteristics. Legislative leachate levels are also investigated. The timber used in the trials is kiln dried, structural grade F5 heartwood and sapwood of Pinus radiata D. Don. Radiata pine roundwood is also used. Two pilot scale treatment plants are utilised during the trials. Processes conducted, are the modified Bethell, Lowry and Alternating Pressure Method (APM). Simulated rainfall is applied to every timber pack after treatment. Significant differences between percentage leachates resulting from the timber packs, are determined by the Friedman test and multiple comparison analysis. Investigation of leachate concentrations revealed no world legislative standard. Concentration of copper leachate was suggested as a way to monitor leaching in the aquatic environment. In the soil environment, concentration of chromium leachate was recommended. Heartwood penetration was improved and leachate concentration was decreased when the treating pressure was increased. Concentration of chromium and copper leachate also appeared to decrease when the solution temperature was increased. In contrast, at the higher temperatures, the concentration of arsenic leachate increased. Chromium leachate concentration also decreased when solution strength was increased in Lowry or APM treatment of roundwood. A similar trend was noted when treated timber was subjected to a second stage treatment that involved water or oil. A plastic wrap applied to the timber pack also reduced the concentration of chromium leachate. Chromium leachate concentration and heartwood penetration were influenced by the alteration of the initial vacuum in modified Bethell treatment. Heartwood penetration was improved when low pressure treatment was conducted using the Lowry process, rather than the modified Bethell process.
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    Effect of later age fertilization with superphosphate at age 24 on tree growth, mechanical properties and wood quality of Pinus radiata D. Don
    Subyakto ( 1993)
    Later-age fertilization with superphosphate of Pinus radiata is one of the silvicultural practices used in Australia and is employed operationally on phosphorus deficient sites found in Victoria. Later-age fertilization of radiata pine has previously been shown to give satisfactory responses in terms of growth, wood production and economic values. However, sudden increases in growth rate can lead to detrimental effects on wood properties. The present study was aimed at examining the effect of later-age fertilization with superphosphate at age 24 on the tree growth, mechanical properties and wood quality of radiata pine grown on a phosphorus deficient site. Three trees from each of three diameter classes were selected randomly from a control plot and an adjacent fertilized plot at Scarsdale, Victoria. The fertilized plot had received 504 kg ha-1 superphosphate at age 24 and all eighteen trees studied were felled at age 38. Ring width, percent latewood and tracheid length were examined using a wood disc removed at breast height. Ring width and latewood were measured for each growth ring from pith to bark along the north and south axes. Tracheid length was measured for selected growth rings along the north axis. Basic specific gravity from pith to bark for the north and south axes was determined using the maximum moisture content method at five heights including 0.3 m, 1.3 m, 3.3 m, 7.3 m and 13.3 m. Mechanical properties which included static bending and compression parallel to the grain were determined for four axes for clear specimens removed from a 1.0 m log taken near breast height. Diameter and height growth of the fertilized trees increased significantly over the fifteen year period following fertilization by 30% and 34% respectively as compared to the controls. Volume of the fertilized trees increased 212% over the same period as compared to 77% for the controls. No significant differences in the strength properties were found for the wood produced after the age of fertilization between the control and fertilized trees. Non significant reductions of 8%, 6% and 4% were found for bending properties modulus of rupture, modulus of elacticity and stress at limit proportionality respectively. Non significant reductions of 6%, 11% and 12% were found for compression properties of maximum crushing strength, modulus of elasticity and stress at limit of proportionality. Mechanical properties of both the control and fertilized trees were generally greater than previously reported values for radiata pine. Ring widths increased substantially within two to three years following fertilization with mean values of the fertilized trees around two times that of the control trees. The enhanced radial growth was maintained through to harvest at age 38 and when combined with the the second thinning at age 35 increased even further relative to the controls. The effect of fertilization on percent lateveood was not consistent but appears to be somewhat dependent on the availability of moisture. The effect of fertilization on tracheid length was not clear as there appeared to be a site effect which resulted in the tracheid lengths of the fertilized trees being greater than the controls prior to fertilization. Basic specific gravity was reduced about 4% to 9 % following fertilization and the effect appeared to last for about six to nine years. It appears that the first thinning which occurred at age 20 prior to the fertilization contributed to this reduction in basic specific gravity. Over approximately the final six years of growth the basic specific gravity of the fertilized trees was 3% to 6% greater than the control trees. In conclusion, the effect of later-age fertilization with superphosphate at age 24 on the mechanical properties and overall wood quality appears to be minimal. The large gains made in tree volume following fertrilization on the phosphorus deficient site at Scarsdale and the fact that the later-age fertilization brings a relatively unproductive site into a productive capacity would appear to far outweigh any minimal reductions in wood properties. It further appears that on the deficient site the phosphorus remains available for tree growth through to rotation age and the additional wood produced at the later-age tends to have the desirable mature wood properties as compared to the less desirable wood properties which normally accompany the juvenile growth period.
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    The effects of interspecific competition from Eucalyptus obliqua on young stands of Pinus radiata
    Takeow, Wisood ( 1991)
    The growth and stand development of even-aged Pinus radiata stands invaded by Eucalyptus obliqua were investigated for the period during which stands of P. radiata were 10 to 15 years of age. Population dynamics of P. radiata and E. obliqua stands were assessed and then used as a basis to describe the past competitive relationships and predict the future . of these mixed stands. The growth rate of P. radiata was also assessed in relation to its initial size and to neighbouring E. obliqua to reveal the 'most important factors that determined the growth of P. radiata. The study was carried out in 6 stands in which density of P. radiata was constant whereas that of the E. obliqua varied. Population dynamic parameters studied included mortality, size distribution and size hierarchy. Size distribution and size hierarchy were concerned only with DBH and height but not weight or volume. Size distribution was measured by skewness of. the distribution and size hierarchy was measured by the Gini coefficient and Lorenze curve. Mortality was found only within populations of E. obliqua. This mortality also increased with increasing density and was confined mainly to E. obliqua trees which had small DBH and height. Size distribution of both DBH and height of P. radiata in almost every stand was negatively skewed and increased with stand age. The distribution of height showed more negative skewness than did DBH. Skewness of DBH (but not height) increased the increasing density of E. obliqua and became positively skewed more quickly than did height distribution. Mean DBH, height and volume of P. radiata stands decreased with increasing density of E. obliqua. Size hierarchy in DBH and height in P.radiata increased with stand age. There was less variation in height than in DBH. Size hierarchy for DBH, but not for height, also increased with increasing density of E. obliqua. Initial size of P. radiata was found to be more closely related to relative growth rate of P. radiata during the study period than the presence of E. obliqua. The result also showed that DBH growth of P. radiata trees was affected by more strongly than was height growth by the presence of E. obliqua under its canopy during the early growth stage.