Spectral sensitivity in the photodegradation of fir wood (Abies alba Mill.) surfaces: correspondence of physical and chemical changes in natural weathering

The main purpose of this study was to demonstrate and compare the effect of specific wavebands of light on colour changes, chemical breakdown and mechanical properties of fir wood surfaces during different stages of natural exposure. Spectral sensitivity was determined by exposing samples to sunlight behind different glass cut-off filters, under which a pack of three 80-μm-thick wood strips represented the composite surface layer of fir wood. It was found that colour changes, mechanical degradation and chemical changes develop in different chronological orders and at different rates and form different depth profiles. It was demonstrated that all of the methods of exposure and analysis employed in this study on wood photodegradation have their limitations and give different indications as to the development of the degrading processes. Discoloration can register the photodegradation readily, intensively and at a greater depth below the surface compared to the microtensile testing method or FTIR-ATR technique. Only combined observations and comparisons of results of different methods can give a comprehensive image of the photodegradation process.