School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemImpregnation of wood with stains( 2007)
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ItemA study of the creep performance of microwave-modified radiata pine in different external environments( 2007)A new innovative timber treatment developed at the CRC Wood Innovations, which involves high intensity microwave application and resins impregnation, is intended to provide products for a range of applications including structural engineering members. This study has been undertaken to obtain experimental data and provide better understanding of the creep performance and long-term behaviour of the new products. In the experiment, fifteen samples, five untreated, five treated with MUF resin and five treated with Isocyanate resin were loaded in four-point bending at 30 percent of the matched samples' failing stress, in a protected external environment in Brisbane, Australia for a period of nine months to date. The treated samples were found to produce lower relative creep deformations than the untreated sample. The samples treated with MUF resin showed better creep resistance than the samples treated with Isocyanate resin. Data from the first 90 days were used to obtain parameters for the two chosen models: the power law model and the 5- parameter model. While both models provided good fitting for the data, the 5-element model was found to possess better extrapolation capacity beyond the regression period. An increase in the period of regression data from 90 days to 150 days significantly lowered the errors in both of the models.
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ItemTowards association studies in Pinus radiata D.Don - populations and wood property candidate-genes( 2006)In Australia and New Zealand Pinus radiata D. Don wood quality is receiving increasing interest from tree breeders. This is partly due to declining resource wood quality associated with more advanced generation breeds leading to increased rejection and product downgrading in processing. While log segregation and wood grading at mill-door yields immediate benefits to processors the underlying cause is not addressed. The only long-term solution is to include wood quality in breeding programs. Wood quality traits are costly and difficult to measure. Marker-assisted selection offers a potential solution and quantitative trait loci (QTL) mapping studies have been undertaken with the aim of facilitating this. It is becoming increasingly clear that in widely outcrossing species with long generation times and very large genomes these approaches will not work. The identification of the underlying genetic sites, or tightly linked marker sites, would rectify this and in model species linkage-map based cloning has been used extensively. This approach is also not practical in species such as P. radiata. Association testing combined with a candidate-gene approach is therefore widely believed to be one of the only methods remaining. This approach uses a priori information to select and then test the phenotypic effects of variants within candidate-gene loci. Implementation of these studies relies heavily on the results of other investigations, especially those that generate DNA sequence information. Also required is detailed knowledge of the genetic population structure, the patterns of nucleotide diversity and the patterns of linkage disequilibrium. On a more practical level suitable populations need to be identified while the current methods for the collection and handling of samples for molecular investigations are limiting. The selection of candidate genes is also a non-trivial process. For candidate-gene association studies to be successful in P. radiata all these factors need to be addressed. This formed the main aim of this thesis. A multi-pronged approach was used. Firstly, at the population level, the genetic resources available for association studies were identified and the underlying genetic population structure of these resources and the patterns of nucleotide diversity and linkage disequilibrium were investigated. Secondly, improved methods for the collection and isolation of genomic DNA were developed and thirdly, a small set of wood quality candidate-genes were selected and further characterised with the aim of identifying those with the most promise of harbouring causative variation for inclusion in future association studies. This was achieved by literature based review, linkage mapping onto wood property QTL maps and neutrality testing. Results include support for previous population genetic studies showing P. radiata to have a complex genetic structure compared to most pine species. This study also indicated significant levels of migration between the three mainland populations. Within the candidate-genes two, cinnamyl alcohol dehydrogenase and sucrose synthase, showed interesting patterns of population differentiation and/or nucleotide diversity while the results for one other gene, korrigan, did not agree with previous investigations.
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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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