Combined effects of UV light and elevated temperatures on wood discolouration

Abstract

Two conifers and two deciduous wood species were irradiated by strong UV emitter mercury lamp at elevated temperatures up to 160 °C. Other series of samples were treated in the same chamber at the same temperatures but without light. Results showed that UV light irradiation produced much greater discolouration at elevated temperatures above 80 °C than at ambient temperature. The combined light irradiation and thermal treatment at 160 °C generated much larger discolouration than the sum of the discolouration data caused by UV light irradiation at 30 °C and by pure thermal treatment at 160 °C. The thermal effect during photodegradation was not only the simple addition of two effects, but the elevated temperature multiplied the effect of photodegradation. The greatest difference was shown by the redness change. The Arrhenius plots of all tree colour coordinates had a breaking point close to 100 °C, showing that above this temperature the chemical changes are more complex than below this value.