Preserving our natural heritage - timber

Cokley, Keith V. (1996). Preserving our natural heritage - timber PhD Thesis, School of Biological Sciences, The University of Queensland.

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Author Cokley, Keith V.
Thesis Title Preserving our natural heritage - timber
School, Centre or Institute School of Biological Sciences
Institution The University of Queensland
Publication date 1996
Thesis type PhD Thesis
Total pages 1 v.
Language eng
Subjects 050209 Natural Resource Management
430101 History - Australian
291405 Timber
961403 Forest and Woodlands Soils
Formatted abstract Physical and chemical properties of Queensland timbers are described in relation to their durability in service and to their requirements for preservative treatments. The survey covered all commercially important species, including eucalypts, rainforest species, and exotic conifers that have been grown extensively in plantations. It showed that there are substantial and consistent differences in timber properties associated with both species and provenances within Queensland, and that these geographical differences may be critical in determining the durability of timber in service.

Field and laboratory studies were conducted into a range of timber preservation techniques, from hot and cold soak to pressure treatments with different heating and vacuum regimes, and into preservatives from borax to creosote and copper-chrome-arsenic salts. Timber degrade problems ranged from insect attack to soft rot fungi and marine borers. The usage categories of timber studied ranged from general structural material, power transmission poles and wharf piles to plywood sheets. All these activities were predicated by the social need for conservation of timber resources. Particularly during and immediately after World War 2. Of several chemical and structural characteristics of timbers examined, starch content and vessel diameter were shown to be critical in determining its susceptibility to attack by Lyctus brunneus. Detailed chemical analyses of the variation in starch content were used to develop and check field methods of starch assessment that could be applied in conjunction with commercial preservative treatment routines.

The thermodynamics (and aerodynamics) of movement of heat (and vacuum), gas, liquids and solutes into wood were examined in the course of understanding preservative penetration into and retention in timber. It was established, prior to the publication of other studies, that gradients in temperature (and vacuum) established during reservation processes had a critical effect on the movement of liquids and gases into and out of timber. The occurrence of a minimum critical temperature was demonstrated, maintenance at which (for standard thickness) was a function of wood specific gravity. Similarly it was found there were critical levels of vacuum for the treatment system as well as for timbers, and the latter was dependent on species structure and specific gravity.

These effects were critical to the penetration of preservatives, which was restricted beyond the vessels, the principal pathway of entry and location of solutes in angiosperm woods. This approach also explained several otherwise anomalous responses of timber in preservative regimes in the field. The work also demonstrated, independently of and prior to the publication of the phenomenon elsewhere, the importance of specific vessel void volume, defined as' 'the total vessel cavity per unit of gross wood volume and per unit specific gravity of the timber". This volume was shown to be closely related to the specific vessel void concentration, which is "the absorption of a preservative liquid per unit of specific vessel void volume".

These concepts were important in explaining the considerable variation in rates of preservative uptake between species, between sapwood and heartwood, with specific gravity within species, and with wood moisture content with specific gravity class. An enhanced appreciation of these factors contributed to the development and acceptance of practical preservative treatment schedules for the great majority of Queensland timbers. In marine environments, the calcium and magnesium content of the water was shown to be critical to marine borer attack in timbers.
Keyword Wood -- Preservation
Wood preservatives
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