School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemMicrowave timber heating and its application to solar drying( 2005-06)Wood drying is essential for preparation of this natural resource for practical applications.Most drying models confirm that the tortuosity of the moisture transport path, associated with high wood density or low moisture permeability, is an important control parameter during the diffusion-controlled drying process. Drying systems, such as kilns, control the external environment in order to manipulate moisture diffusion and transport mechanisms; however they are powerless to manipulate wood density or permeability. Controlled application of microwave energy has been shown to selectively rupture the wood structure creating radial pathways in the wood through which moisture may readily move. New analytical equations that describe simultaneous heat and moisture transport during microwave heating have been derived and validated. These new equations assume that the microwave fields decay exponentially with distance inside the irradiated material and enforce a boundary condition, which allows convective heat transfer at the inter-facial boundary between the moist dielectric material and the air. They demonstrate the importance of applying the theory of simultaneous heat and moisture movement to microwave heating. In this theory a set of synchronised heat and moisture waves propagate through the material with velocities that are vastly different from those predicted by the constant vapour concentration thermal diffusivity of the material. They also correctly predict the “S” shaped temperature versus electric field strength curves discussed by other authors.(For complete abstract open document)
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ItemUse of near infrared spectroscopy to detect non-recoverable collapse caused by tension wood in Eucalyptus globulus( 2012)Eucalyptus globulus is widely planted around the world. The wood is mainly used for fibreboard, paper and firewood. Use for sawn and engineered wood products can be limited because of the development of non-recoverable collapse caused by tension wood, which can severely distort wood surfaces and affect sawing and drying performance, leading to increased processing costs, lower yield (recovery) and thus reduced product value. In tension wood, cellulose content, microfibril angle (MFA), density, and stiffness (MOE) are altered compared to normal wood. The study investigated the calibration and application of near infrared (NIR) spectroscopy to measure these wood properties and detect non-recoverable collapse. Radial, bark to pith, wood cores were sampled from 175 trees in a 20 year old E. globulus silvicultural trial at Tostaree, Victoria, Australia. NIR spectra were measured at 1 mm intervals along the cores after drying to 12% estimated moisture content (EMC). Tangential shrinkage of the cores was measured at 8 points across each core after reconditioning to 12% MC. Spectra were measured on an additional 20 cores that were also analysed using SilviScan-3 to measure MFA, density and MOE, and NIR Partial Least Squares (PLS) Regression calibrations were developed. The calibrations were used to predict wood properties in the 175 cores, which were then related to the measured tangential shrinkage and non-recoverable collapse. NIR-predicted wood properties at points of non-recoverable collapse were consistent with the presence of tension wood (i.e. high cellulose, low MFA, high density and high MOE). Cellulose content and MOE were the best multiple regression predictors of tangential shrinkage. An NIR calibration developed to directly predict tangential shrinkage qualitatively identified zones of high shrinkage, but tended to under-predict measured shrinkage values. Tangential shrinkage, or the incidence of high tangential shrinkage, was not or only weakly correlated with tree size, height to diameter ratio, or lean. Silvicultural treatments (thinning intensity, fertilizer application) did not affect tangential shrinkage or tension wood formation. Generally, the incidence of non-recoverable collapse was greater in the wood grown since age 10 years. The study demonstrated that NIR predicted wood properties can be used to detect non-recoverable collapse caused by tension wood. The methodology has potential use in plantation and log assessment, wood processing, and tree breeding.
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ItemStudies of the natural and chemically-enhanced resistance of wood to decay( 1977)The researches described in the attached papers followed a prolonged period of change and development. The initial purpose was to evaluate in the laboratory the probable durability of Australian timbers in service as poles, posts, sleepers and so on. (Papers A1, A2, A3, A4). These papers were at the time of publication more rigorous and comprehensive than any published tests. (In this connection, it should be noted that the “Progress Report” series of the Division of Forest Products were distributed to all known major research workers in the field, abstracted in major abstracting journals, and freely cited in publications. Divisional policy was at that time opposed to publication of results in scientific journals, rather than specialized reports with “targeted” distribution). They were especially notable in the variety of test fungi used; in the development of testing techniques which would allow decay in dense timbers (based on extensive so far unpublished experiments on varying technique parameters); in the use of statistical analyses; and in recognition that no single value can be assigned to “natural durability”, a theme developed in A14, my final definitive paper on natural durability, which should be a seminal paper for future work in this field. A major contribution has been the clear understanding that weight losses in decay tests cannot have any absolute value and that tests are essentially comparative. Classification of natural durability is therefore best obtained, not by arbitrary classification on weight losses, but by close comparison with “yardstick” timbers whose durability is thoroughly familiar. (A11, A12, A14). These papers, and several unpublished experiments of the same nature, contributed largely to the lists of natural durability of timbers published by the Division of Forest Products and used in Australian Standards (e.g. As 1604 – 1974, on preservation of sawn timber). Similar inter-species comparisons were later made of Papua New Guinea timbers (A11) where information on natural durability, vital to effective utilization of mixed hardwood rain forests, was virtually absent. From this work on inter-species variation in durability, there came an interest in the causes of this variation and this was investigated for several years in collaboration with Dr. P. Rudman (A3, A4, A7, A9, A10). The initial and critical paper in this series (A3) was a seminal paper in being the first paper to adopt a “toxicity balance” approach, in which the decay resistance of untreated wood, of extracted wood, and of susceptible wood containing these extractives was measured. This was important because previous workers had concentrated on the toxicity of specific extractives as the explanation of durability, neglecting the possibility that the wood might still be durable after complete removal of these extractives, due to other extractives or to physical factors. My approach also took account of the detoxification of extractives during removal and of the effect of their original distribution in the wood. The paper also contained the first description of a reliable and precise technique for determining decay resistance of wood meal of a variety of species. Since adequate extraction required conversion of wood to a finely-divided form, this technique was essential and was unexpectedly difficult to develop. The general design of the work the decay technique, the decay tests and interpretation of the results were the work of the senior author. This line of work on chemical reasons for decay resistance was gradually transferred to Dr. Rudman. Because of the reputation acquired from earlier work on natural durability, work on natural durability of teak (Tectona grandee) was requested by the Food and Agriculture Organization (FAO) of the United Nations. This was concerned with relative durability of plantation-grown and natural teak and with possible detrimental effects of high growth rates on durability. The resultant work (A5, A6, A7, A8) showed that the widely held belief that fast frown timber was less durable was, at best, only partially true. The papers were important in describing some of the few attempts to test this experimentally and in pioneering multiple regression analyses to assess the relative importance of silvicultural, factors in durability of teak and the potential importance of decay resistance testing in selection and breeding of teak and other timbers. The early stages of my research in wood pathology were confined to natural durability, but with the establishment and rapid growth of a pressure-impregnation wood preservation industry in Australia, and the world-wide need for more sophisticated treatments, my research activities changed to study of chemically enhanced decay resistance. After some preliminary investigations to solve urgent problems (B1, B2, B3), they took the form of an intensive study of water-borne preservatives (especially copper-chrome-arsenic preservatives or “CCA”) and factors affecting their efficiency (B4, B5, B6, B7, B16, B19); and also a study of factors affecting the performance of Australian [?] (B8, B10, B11, B12, B18, B20). CCA studies were important as being the most comprehensive studies to that date of fixed water-borne preservatives (B6) and as the first to discuss the effect of wood substrate on preservative performance (B7), a topic of international recognition in the 1970’s. My demonstration of the enormous variation in CCA tolerance of basidiomycete wood-destroying fungi (C1) led to a fundamental study of fungal tolerance (c4, C5, C6). This included the original discovery that basidiomycete cultures could be dedikaryotized by toxic agents (C2, C3) a discovery of considerable importance to general biology and experimental fungal taxonomy, as well as to wood pathology (C5). My later discovery that the toxic effects of arsenic could be antidote by phosphate (B16, C7, C8, B19, B21) is also one of fundamental importance to general biology, as well as to wood pathology, especially to techniques of standard testing of wood preservatives (C7, C8). The research on creosote established conclusively that removal of phenols from low temperature creosotes lowered their efficiency and led directly to a revision of the Standards Association of Australia specification for creosote (despite considerable opposition from manufacturers). The work on use of propylene oxide for sterilization (B10, B11) had important implications in view of its widespread use in laboratory tearing (e.g. in British Standard 338; 1961). I was probably the first worker to use propylene oxide as a sterilant for wood specimens (B3, C1) and have much unpublished data on its use, as well as the best statement to date (B11) of its limitations. Apart from work on CCA and on creosotes, I studied various organic solvent preservatives (B9, B13< B14) and also studied the use of special techniques for preservation of plywood (B15, B17). In general, these papers are regarded as making a substantial contribution to the science of wood pathology and of biodeterioration as well as having had some influence in the application of wood preservation technology in Australia and overseas. Many of the papers (e.g. A1, A3, A8, A10, A11, A14, B6, B9, B17, B20, C1, C2, C5, C6, C7) introduced novel concepts and techniques.