IMPACT OF TEMPERATURE AND ULTRAVIOLET RADIATION ON CHANGES OF COLOUR OF FIR AND SPRUCE WOOD

This study deals with the investigation of impact of temperature and ultraviolet (UV) radiation on spruce wood (Picea abies(L.) H. Karst.) and fir wood (Abies albaMill.) colour changes. Samples of investigated woods species were loaded by temperatures of 110, 130, and 150°C and UV radiation (with 253.7 nm wavelength and 40 W m-2intensity) during 72, 168, 336 and 672 hours. Colour changes were evaluated in the CIE Lab colour space. Theneural network for prediction of both colour coordinates and total colour difference of spruce and fir wood was trained by data regarding exposure conditions (temperature, UV radiation and time) and by obtained results. Coefficient of determination (R2) of the neural network was above 0.99 for training, validation and testing. Average colour coordinates (±standard deviation) of the spruce and fir wood before exposure were L* = 80.08 ± 3.70,a* = 7.55 ± 2.13, b* = 21.56 ± 1.79, L* = 80.46 ± 1.91, a* = 6.84 ± 0.97, and b* = 18.90 ± 1.26, resp. Total colour differences after thermal loading were in the interval from ΔEab* = 3.76 ± 1.95 (spruce wood at 110°C) to ΔEab* = 45.37±1.46 (fir wood at 150°C). Total colour differences of both wood species exposed by UV radiation were approximately in intervals from ΔEab* = 12 to 13 (after 72 h) up to ΔEab* = 16 to 20 (after 168 to 672 h). Obtained results proven that both temperature and UV radiation have significant impact on the colour changes of the investigated woods.