Thermal degradation of wood during photodegradation

In this study, wood samples were exposed to light irradiations (direct sunlight, xenon lamp, mercury vapour lamp) and thermal treatments were carried out in dry- and in humid conditions at 90 °C. One part of the samples was covered by an aluminium plate during light irradiation. The samples under the aluminium plate also suffered considerable chemical changes, monitored by infrared technique and colour measurement. The sunlight produced greater colour change under the aluminium plate than the artificial light sources. During light irradiation, the carbonyl band having two maximum at 1700 and 1746 cm−1 increased and the peak of the aromatic skeletal vibration arising from lignin (1510 cm−1) decreased together with the guaiacyl vibrations at 1275 cm−1. There was absorption decrease at 1174 cm−1 because of the ether band splitting. Under the covered surface only the ether band at 1174 cm−1 decreased and one carbonyl band increased with a maximum at 1715 cm−1. Degradation of lignin was negligible for the covered surface. Colour change generated by thermal degradation was much greater in humid condition than in dry condition.

► Wood samples were irradiated by three types of light source.
► Thermal degradation caused by light irradiation was investigated.
► Colour change and IR spectra were evaluated.
► Colour change was much greater in humid condition than in dry condition.