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Chemistry of Western Australian eucalyptus timbers

Simpson, Louise Ann (1991) Chemistry of Western Australian eucalyptus timbers. PhD thesis, Murdoch University.

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The indigenous and commercially important Western Australian eucalypts, Jarrah (Eucalyptus marginata), Karri (E. diversicolor) and Marri {E. calophylla) were studied through application of new techniques within a framework of the results of past research.

Extractives from the woods were investigated using various chromatographic and spectroscopic techniques. The structure of the isolated polymers were determined by 13C NMR spectroscopy and molecular weights estimated with vapour pressure osmometry. In Marri kino these were found to consist almost entirely of procyanidin polymers. Flavonoid monomers were identified and quantified. An extensive review of current research into the chemistry and use of proanthocyanidins and past research into eucalypt extractives was carried out. This showed that, while the structure of the extractives was not understood, researchers in the 1920's were using methods of polymer degradation which are now claimed to be the solution to utilisation of the proanthocyanidins as adhesives.

Fourier transform infra-red (FT-IR) spectroscopy and differential scanning calorimetry (DSC) were used to study the interaction of temperature and water on samples of whole wood. FT-IR studies showed that even small quantities of water at temperatures less than 100 °C have a pronounced effect on absorbance of those bands associated with hemicellulose, lignin and polyphenolics. Spectra of wood sections with water contents greater than fibre saturation point (FSP) exhibit extensive coupling between the component polymers and temperatures less than 50°C result in significant changes in the distribution of water within the wood substance. Sections from all three wood planes were investigated and spectra from these indicated a greater degree of order than expected and also illustrated the importance of anatomy to the distribution of water within wood.

DSC results showed that, while the changes were small, it is possible to detect glass transitions (Tg) on whole wood samples. The effect of water was to lower Tg and to make the transitions more readily detectable. Thermal history was found to be important and crystallisation peaks were observed in those samples rapidly cooled after scanning. DSC scans of extracted polyphenolics were carried out and results of these scans are included in the discussion on assignment of the observed Tg in wood.

A method utilising DSC to determine the FSP of whole wood samples was developed and is based on the fact that the water closely associated with cell wall polymers does not freeze. It is a more direct method than those currently used and has the potential to be used in such areas as monitoring the impregnation of wood with stabilisers etc.

As part of the FT-IR and DSC studies, thermal characteristics of wood and in particular the eucalypts were reviewed. On the basis of the results and the research reviews, it appears that the polyphenolics are important factors to consider in drying behaviour and that the anatomy of the eucalypts is the limiting factor in drying rates if wood free of degrade and defects is to be produced.

The effect of various logging methods and storage treatments on the starch content of Karri sapwood were investigated, samples after dry storage and felling with an intact crown showing the greatest rates of decline. Starch levels in standing trees appeared to be influenced by rainfall. Starch is the ultimate determining factor in borer infestation and this is becoming of increasing importance as more regrowth timber is used.

Intelligent decisions regarding forest utilisation can be made only from an informed basis. This requires an interdisciplinary approach and must be dynamic with continual research as new methodologies and findings become available. Progress will come with continual review of past research in the light of new knowledge.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Mathematical and Physical Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Barton, Allan
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