Photodegradation of thermally modified wood.

Natural wood, being biological material, undergoes rapid degradation by ultraviolet (UV) radiations and other environmental factors under outdoor exposure. In order to protect wood from such degradation, the chemical structure of wood is altered by chemical modification or heat treatment. In the present study, heat treated specimens of rubberwood (Hevea brasiliensis) were exposed to xenon light source in a weather-o-meter for different periods up to 300 h. Photostability of modified and unmodified wood was evaluated in terms of colour and chemical changes. Light coloured untreated wood became dark upon UV irradiation whereas, dark colour of heat treated wood lightened on UV exposure. CIE lightness parameter (L(*)) decreased for untreated wood whereas its value increased for heat treated wood upon irradiation. Other colour coordinates a(*) and b(*) increased with exposure duration for both untreated and heat treated wood. The overall colour change (ΔE(*)) increased for both untreated and heat treated wood. The Fourier Transform Infrared (FTIR) spectroscopic studies revealed severe lignin degradation of heat treated wood due to UV light exposure. Colour changes and FTIR measurements indicate that thermal modification of wood was ineffective in restricting light induced colour changes and photodegradation of wood polymers.