School of Agriculture, Food and Ecosystem Sciences - Theses

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    Impregnation of wood with stains
    Kwiatkowski, Aleksander ( 2007)
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    A study of the creep performance of microwave-modified radiata pine in different external environments
    Dang, Lam Dien ( 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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    Towards association studies in Pinus radiata D.Don - populations and wood property candidate-genes
    Tibbits, Josquin Frederick George ( 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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    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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    Increased performance and durability of boron treated wood products by acrylate and furfuryl alcohol resins
    Drvodelic, Neli ( 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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    An evaluation of timber drying problems in terms of permeability and fine structure
    Kininmonth, John Alexander (1931-) ( 1970)
    The relationships of difference in rate of drying to permeability and wood structure were determined for two angiosperms and one gymnosperm. These investigations took two particular drying problems as a basis for study and attempted to explain why: - heartwood of Nothofagus fusca (red beech) takes many times longer to dry than sapwood. - green sapwood of Pinus radiata (radiata pine) dries readily but, if dried and pressure-treated with water-borne preservatives, its subsequent drying is greatly retarded. Test material was used from 14 trees of N.fusca from New Zealand, four trees of Eucalyptus regnans (mountain ash) and seven trees of P.radiata from Victoria, Australia and the experimental work was carried out under three headings: (a) Unidirectional drying. Small specimens, sealed on all except one pair of grain faces, were dried in a laboratory kiln at temperatures up to 60C. Comparisons were made between radial and tangential drying in sapwood and heartwood or in green and resaturated specimens; effects of treatments such as steaming were also assessed. Moisture gradients were determined to show the contribution of free water movement to overall drying. (b) Permeability studies. A method was developed to measure the transverse permeability of green wood to the flow of micro-filtered water; established methods were used for longitudinal permeability. Data for P.radiata met the requirements allowing application of Darcy's Law for flow of fluids through inert porous media and N.fusca approximated them. Pathways of flow were determined with chemical stains. (c) Wood structure. The transmission electron microscope was used to compare the appearance of pit membranes and the cell walls in sapwood and heartwood of N.fusca. In P.radiata, emphasis was on determining the percentage of bordered pits that were aspirated in sapwood - green, after drying and resaturation and after various treatments - and relating this to differences in drying and permeability. The main conclusions drawn from this study are: (a) The green sapwood of N.fusca and E.regnans is permeable to micro-filtered water in the radial and tangential directions. After drying and resaturation, the permeability of N.fusca is unchanged but that of E.regnans is drastically reduced, particularly in the tangential direction. The heartwood of both species is impermeable when tested at a pressure differential of 40 cm.Hg. (b) Differences in the permeability of N.fusca can be explained by differences in the appearance of pit membranes in sapwood and heartwood: in heartwood, the membrane surfaces are usually completely occluded when viewed as replicas in a transmission electron microscope; in sapwood, the surfaces are always less occluded often exhibiting a clean primary well texture. It is inferred from studying the effects of various extraction treatments that the pit membrane surfaces in sapwood are less occluded than indicated by the appearance of replicas. (c) Plasmodesmata may provide pathways for mass movement of liquids in the radial direction in the wood, but, in other pits, without obvious pores, permeability probably results from movement through the general structure of the pit membrane. (d) Heartwood of N.fusca takes several times longer to dry than sapwood because of its reduced permeability coupled with lower rates of moisture diffusion. (e) Contrary to previous reports, at least 80 percent of the bordered pits in green sapwood of P.radiata are open, irrespective of distance from the outside of the tree. After drying and resaturation most pits are aspirated and the wood is much less permeable than in the green state. (f) The condition of the bordered pits has an effect on the rate of drying in the tangential direction - causing a marked reduction in resaturated material - but has no appreciable effect on radial drying which is little different in green or resaturated wood.
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    Chemical treatment of wood and its effect on wood/water interactions
    Hann, Jeffrey Albert ( 1999)
    Wood-water interactions including the effect of grain orientation, sample size and water potential in Pinus radiata D.Don were investigated. The influence of various chemical treatments on the wood-water interaction was also evaluated. The uptake of moisture by wood soaking in water was determined using the water soak method developed by Rowell and Banks (1985). Treatments with surfactants such as ammoniacal copper-didecyldimethylammonium chloride (DDAC-ACQ) and linoleate salts increased the initial uptake rates of the wafers, whilst treatment with copper chrome arsenic (CCA), linseed oil (LO) and a combined CCA/LO treatment reduced uptakes of moisture. The length of time used to assess the water repellent effectiveness (WRE) was found to be crucial to the test, with most of the reduction in WRE occurring in the first 15 minutes of soaking. Exposure of wax treated wafers to weathering indicated an initial gradual reduction in efficacy, which decreased more rapidly as the length of exposure time increased Tests on the effectiveness of different wood coatings subjected to high humidity illustrated the importance of a film with low permeability and some elasticity. Wood blocks coated with resorcinol-formaldehyde resin initially inhibited moisture ingress, but failed after prolonged exposure. An extra coat increased the time required before failure. Coating the wood wafer with a silicone resin slightly reduced the uptake of water into the wafer. However, this resin was more permeable than the resorcinol-formaldehyde resin and was not as efficacious. The effect of various oil treatments on the uptake of water vapour indicated that the distribution of the oil is critical to inhibiting vapour uptake. No significant difference was found between the moisture uptake of hardwood and softwood stakes. Treatment with trimethylborate (TMB), DDAC-ACQ and CCA had no significant effect on the extent of vapour taken up by the wood. An experiment designed to investigate the importance of sample size when assessing wood performance was carried out using matched samples of treated and untreated quartersawn and flatsawn Pines radiata D.Don. It was found that samples treated with DDAC-ACQ and exposed outdoors experienced a greater flux in moisture content compared to controls. CCA reduced the extent of moisture uptake, with the incorporation of oil further enhancing the short term weathering performance. Quartersawn wood exhibited a smaller moisture flux than the flatsawn timber.However, the performance of CCA/Oil treated quartersawn wood was only marginally better than the quartersawn controls. Laboratory trials gave an identical treatment ranking as the exterior trial; however the use of the smaller sample size was identified as being inappropriate for the assessment of check formation in the timber. A sample size effect was demonstrated when assessing the efficacy of treatments by the water soak method. A treatment gradient could be demonstrated when whole stakes were impregnated with CCA and linseed oil by a two-stage process. The test indicated that the significance of improvements in the water repellency of treated wafers diminishes when larger sized samples are investigated. The effect of soil water availability on wood moisture content was determined for untreated hardwood and softwood sticks. At low soil moisture contents, hardwood sticks were found to be significantly more saturated than their softwood counterparts. At higher soil water contents (100% water holding capacity (WHC)) the performance of the two species of wood became less significant. Chemical treatment was found to have a significant effect on reducing wood moisture levels when free water was available in the soil. Linseed oil was responsible for a significant reduction in moisture uptake, by blocking the pathways for water uptake as well as by decreasing the void volume available in the wood for water to occupy. Incorporation of a drying agent did not improve the quality of the film formed by the linseed oil as no significant change in water repellent performance was identified. The uptake and movement of water through a horticultural post was simulated using a procedure described by Baines and Levy (1979). The wick action of heartwood and sapwood stakes of Pinus radiata D.Don was investigated with distinct moisture distribution and behaviours found. Heartwood, being less permeable, showed a reduction in the volume of vapour that moved through the wood, as well as a much lower stake moisture content compared to the sapwood. This difference was most pronounced above the air/water interface and helps to explain the difference in decay resistance exhibited by the two wood types. End sealing the stakes with silicone resin was found to have no significant effect on the wick action of the stake. Lumen filling treatments with wax, oil and alkyd resins were found to significantly alter the wick action of the stakes. Treatment with low concentrations of surface active compounds such as DDAC-ACQ and linoleate soaps were found to increase the rate of water uptake. At higher concentrations the presence of the surfactant increased the hydrophobicity of the wood and reduced moisture uptake. Biological testing using a fungal cellar determined that treatment of the wood with CCA/LO, CCA, DDAC-ACQ/LO, LO and DDAC-ACQ significantly improved the resistance of the wood to decay. The incorporation of linseed oil did not cause a significant improvement to the decay resistance of the stakes over the trial period