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Gewählte Master / Diploma Thesis:

Raphaela Hellmayr (2019): Structure-related Vapor Sorption Phenomena in Wood.
Master / Diploma Thesis - Institut für Holztechnologie und Nachwachsende Rohstoffe, BOKU-Universität für Bodenkultur, pp 56. UB BOKU obvsg

Data Source: ZID Abstracts
Abstract:
Approximately half of the land area in Austria is covered with forest and the wood industry is an important economic sector in Austria. Wood is an orthotropic material with hierarchical structure, which enables trees to be the highest living organisms on earth. The properties of wood give chances for a broad range of technical applications, but they are also a challenge. Wood is a hydrophilic material and balancing the moisture content to the equilibrium with the relative humidity in the air. Below the fiber saturation point the dimensions are changing with the climate. Radial and tangential swelling is bigger than in longitudinal direction. The objective of this thesis was to analyze swelling and sorption phenomena in wood. Swelling according to macroscopic wood characteristic was determined and it was checked, if the Dynamic Vapor Sorption (DVS) is suitable to analyze hygroexpansion in wood. The sorption dynamics were analyzed in adsorption and desorption. Different softwood (Norway spruce, European larch, Scots pine) and hardwood (European ash, European oak, European beech, Sycamore maple, Wild cherry, Eucalyptus) species were tested. The samples had dimensions of 10 x 10 x 1 mm and the surface was sanded with a fine grit paper. The samples were analyzed with a Dynamic Vapor Sorption (DVS) apparatus and a built-in camera. The DVS is a gravimetric method to study sorption behavior of materials and enables continuous recording of the sample mass. The Hailwood-Horrobin model was applied to describe the sorption isotherms. The camera in the DVS was taking images of the samples when they were in equilibrium with the ambient climate. Swelling was determined by analyzing the images with the software ImageJ. The sorption dynamics in wood are depending on the present moisture content. The rate of sorption is lower at high moisture contents. European larch had a slower reaction to the ambient climate than Norway spruce. Radial swelling in earlywood of softwoods was roughly 30 % of the value in latewood. There was no difference in tangential swelling of hardwoods with and without broad ray visible. The DVS with a built-in camera is suitable for the determination of swelling and shrinkage in wood and enables to study the hygroexpansion during the adsorption and desorption process in future studies. The images can be evaluated via digital image analysis.

Beurteilende(r): Wimmer Rupert

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