Modeling and predicting of the color changes of wood surface during CO2 laser modification

To adopt a greener approach, a novel thermal treatment for wood was proposed. Poplar wood surface was treated by CO2 laser and the surface color changes were evaluated by CIELAB color space. The treated and untreated surface were scanned by Epson scanner to measure lightness difference (Delta L*), red-green index difference (Delta a*) and yellow-blue index difference (Delta b*) then the total color difference (Delta E*) was calculated. The laser energy load on wood surface caused characteristic changes in the chemical component, which were determined by means of Fourier infrared spectrometer (FTIR). Response surface methodology (RSM) was used for modelling and to establish a relationship between color changes and laser modification parameters. The results showed that the feed speed, sweep width and laser power had significant effects on color changes of wood surface. The Delta E* increased with the increasing of laser power, however it decreased with increasing of feed speed and sweep width, because of the amount of heat transferring decreased with the increasing of feed speed and sweep width. The results of FTIR revealed chemical structure in the wood components, which is one of the reasons to the color changes of the wood surfaces. The established quadratic mathematical model applied to describe the relationship between color changes and laser modification parameters had a good prediction. It will be useful for selecting appropriate modification parameters to achieve desired color changes. (C) 2018 Elsevier Ltd. All rights reserved.