engleski

INVESTIGATIONS INTO THE PHOTODEGRADATION OF WOOD USING MICROTENSILE TESTING Part 5: The influence of moisture on photodegradation rates.

This paper describes an investigation into the effect of moisture on the photodegradation of wood. The species investigated were Scots pine, Norway spruce and western red cedar. Photodegradation rates were determined from the changes in microtensile strength of thin wood veneer strips exposed to artificial weathering. Ultra-violet (UV) irradiation was carried out at a temperature of approximately 60 °C and a range of relative humidities starting with exposure at 30% relative humidity. Weathering regimes intended to increase the exposure to moisture were created by periodic wetting, exposure under conditions of constant high relative humidity or by exposure in the presence of liquid water. Moisture enhanced the photodegradation processes of wood. Photodegradation rates increased sharply as the moisture increased in severity. However exposure to higher moisture conditions unexpectedly caused a strength increase in the initial stage of weathering, although the subsequent rates of strength loss were very rapid indeed. The degradation of wood in the presence of liquid water was so intense and rapid that the differences between the species were difficult to distinguish. Norway spruce was the species found to be the most sensitive to photodegradation, while the heartwood of Scots pine proved more resistant to photodegradation than the sapwood.

Photodegradation of wood; microtensile testing; influence of wood moisture

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