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The aim of the present study was to establish the value of desorption stresses and the rate of their increase in the samples of juvenile and mature birch wood as well as in aspen samples of different physiological age. The stress value was calculated on the basis of the measurement of the force necessary to restrain shrinkage in the sample being dried. Additionally, moisture strain and mechanical-moisture strain (both real and apparent) were measured during the experiments. The samples were dried at temperatures of 30, 50 and 70°C. It was concluded that both the rate of increase and the absolute values of stress and strain are different in juvenile and mature birch wood. Also in aspen they depend on the physiological age of the wood tissue. Juvenile birch wood and the physiologically younger aspen proved more susceptible to strain caused by desorption stresses.
Impact of environmental pollution caused by sulphur mining on the chemical composition of wood and bark of birch (Betula pendula Roth.) Content of extractives, cellulose, !% NaOH soluble substances and lignin were examined. Samples were gained from cca. 70-year old birch (Betula pendula Roth.) grown in the environment polluted by sulfur mining industry. 200mm height disks were cut in the butt-end, middle and top section of the trunk. Disk from the main branch was also collected. Bark was collected from butt-end section. On the cross-section from butt-end and middle part of the trunk following zones were marked: outer, center and pith adjacent wood. On the cross-section from the top part wood was divided into outer and pith adjacent. Only one zone was marked in branch. Results show that environmental pollution caused by sulfur mining industry influences the content and distribution of extractives on the cross- and longitudinal sections. It also causes the increase of extractives content in bark. Content and distribution of 1% NaOH soluble substances are also changed on both cross-sections. Environmental pollution decreased lignin content in wood and increased this content in bark from butt-end section.
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