Effect of UV-C irradiance on photochemical degradation of hydro-thermal treated turkey oak wood using FT-IR and XPS technique

To assess the effect of UV-C irradiation on turkey oak wood (Quercus cerris Mill.), experiments were conducted in controlled conditions, using a black chamber equipped with an UV-C lamp. Wood samples were previously treated with steam and heat. Steaming was carried out in autoclave at 130 °C, and heating in an oven for 2 h at 180 °C. The structural and morphological changes of UV-C on wood surface with respect to untreated wood were characterized by colour variation (CieL*a*b* method), X-ray photoelectron spectroscopy (XPS), Fourier transform infra-red spectroscopy (FTIR), and scanning electron microscopy (SEM). A detailed analysis of the surface chemical composition indicated that the UV-C treatment leads to photo oxidation and photo degradation phenomena. Remarkable differences were noticed between the different wood due to their various chemical structures. In terms of colour variation, wood surface exhibited better colour stability after the UVC weathering test but this stability was not stable through time. Furthermore, FTIR showed that thermally treated wood showed a shift of the carbonyl absorption band and an increase of the of absorption related to the presence of conjugated carbonyl compounds. Also XPS showed a modification of the surface after the thermal treatment: however, it showed a decrease of oxygen content in the sample. The same trend can be found when we consider the effect to UV-C irradiation. The same type of results was obtained considering the FTIR data: also in this case, the thermo-treated wood seems to be more resistant towards oxidation processes than the untreated wood. On the contrary, XPS analysis of wood surface showed that the pre-treatment makes the sample more susceptible to the oxidation processes. The ESEM analysis showed the presence of relevant cracks in the untreated wood after the exposition to ultraviolet irradiation. On the contrary, thermo treated wood surface seems to be more resistant to UV-C irradiation.