School of Agriculture, Food and Ecosystem Sciences - Theses

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    Studies of the natural and chemically-enhanced resistance of wood to decay
    Da Costa, Edwin Warner Brandon ( 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used; in the development of testing techniques which would allow decay in dense timbers (based on extensive so far unpublished experiments on varying technique parameters); in the use of statistical analyses; and in recognition that no single value can be assigned to “natural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 These papers, and several unpublished experiments of the same nature, contributed largely to the lists of natural durability of timbers published by the Division of Forest Products and used in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.
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    Methods of improving the preservative treatment of radiata pine and eucalyptus with emphasis on the use of novel boron compounds
    Amaya, Francisco Javier Romero ( 1998)
    This thesis identifies the effect of raw materials and processing parameters on the application of TMB on wood and wood products. It also describes the effect of TMB on the properties of wood and wood products. This work proposes the application of TMB by momentary immersion following by storage in a close container. The effect of wood moisture content, temperature and time were studied. Low wood moisture content (3%) is required to produce high penetration of the TMB in radiata pine (Pinus radiata D. Don) sapwood. High temperatures (40°C) during storing stage can result in adequate penetration. The storage stage is described in two phases, the emission of chemicals from the wood and the diffusion of the chemical from the head space of the container into the wood. Parameters affecting the process include temperature, wood moisture content and time. Wood moisture contents as low as 3% were found necessary to achieve high penetration of chemicals into wood. During the storage of treated timber, high temperatures reduced the emission and vapour diffusion phases. The levels of TMB and methanol in the headspace of the container were lower at high temperatures. The concentration of TMB and methanol in the head space of the desiccator achieved an equilibrium concentration at 100 hrs for samples stored at 40°C and 200 hrs for samples stored at 20°C. Methanol emission produced by the interaction between water in the wood and TMB was found in low levels. Samples of radiata pine were preconditioned to 3% wood moisture content, treated by momentary immersion in TMB and then stored at 20°C. After vapour diffusion the samples were submitted to an airflow of 0.25 L/min for 24 hrs. Emissions were collected in a water trap. For samples treated at 3% moisture content and stored at 20°C, the analysis showed that only 9.6% of the total production of methanol was found in the emissions. For radiata pine this equals to 28 g/m3/hr. Methanol in the wood is removed easily by water. However a strong bond between wood and methanol is formed. Samples of different species were saturated with methanol and then dried at 105°C for 24 hrs. Twenty nine grams of methanol was found in radiata pine after this process. Pre-conditioning of wood prior to momentary immersion improves the penetration and retention of TMB. Several pre-conditioning processes were studied. Steaming reported better absorption and penetration than microwaving, high temperature and air drying. TMB penetration and a retention of 2.48L/m3 was achieved when steamed radiata pine samples were immersed in TMB for 30 secs. These values were statistically different from values obtained with other processes. Momentary immersion of particleboards in TMB following by a storing stage in a close container was studied. Wood moisture content required to achieve total penetration was 8% for particleboards of thickness 12 and 18 mm. Thicker panels required lower moisture contents. Stiffness (MOE) and strength (MOR) was reduced as maximum as 13 and 17% respectively. Momentary immersion in TMB following by vapour diffusion in a close container was successfully trialed in sapwood of radiata pine, messmate (Eucalyptus obliqua L'Herit), jarrah (Eucalyptus marginata Donn. Ex Sm) and blue gum (Eucalyptus globulus Labill). The effect of non-polar solvents as carriers upon vacuum-pressure impregnation of timber with TMB was studied. Total penetration in sapwood of radiata pine was achieved at wood moisture contents below 14%. The rate of hydrolysis of TMB in non- polar systems was measured and compared with other systems. Non-polar systems have a rate of hydrolysis 26 times slower that polar systems. This allows TMB to penetrate deeper into the timber before hydrolysis begins. Different polymers of trymethylborates were also tested in these systems. Methylpolyborates, a polymer of TMB, were used in the manufacture of pastes and rods for remedial treatments of wood. Methylpolyborates in combination with copper and fluoride compounds were used as active in the manufacture of pastes and rods. Diffusion in stubs of red gum (Eucalyptus camaldulensis Dehnh.) after 60 days demonstrate the feasibility of these TMB polymers as diffusible wood preservatives.