Study On CO₂ Laser Selective Thermal Modification Of Poplar Wood

High temperature heat treatment is an important wood modification technology,which can improve the dimensional stability and biological durability of wood,but also affect the surface color of wood and the performance of paint film.However,the application of traditional heat treatment modification technology is limited due to its complex process,low carbon and environmental protection.In this study,laser heat treatment is innovatively adopted.CO₂laser beam was used as a heat source to heat the surface of poplar test wood,and transient increase the local temperature of the material.By adjusting laser processing parameters such as laser power,feed speed,defocu planes and scanning path spacing,the physicochemical properties of the heated area are transformed.Then affect the surface color,wettability,roughness,film adhesion and other properties.Optimize the thermal modification effect.The key factors affecting the laser modification quality of poplar are found by response surface methodology,and the prediction model of input value and response value is established.Improve the efficiency of thermal modification.The main conclusions are as follows:（1）In the study on the surface color change rule of CO₂laser modified poplar wood,the effects of the selected laser processing parameters on the width test results of the surface color zone of the poplar wood specimen irradiated by a single laser were ranked as laser power>defocusing amount>feed speed,and the effects of laser processing parameters on the surface color difference of the poplar wood specimen were ranked as follows:laser power>feed speed>scanning path spacing.With the deepening of laser modification degree,the surface color of poplar specimen changed from light brown to dark brown.Response surface method was used to establish the Box-Behnken model based on the test parameters and the width of the surface color zone and the color difference model of the poplar wood specimen irradiated by a single laser.The correlation between the predicted values and the actual values of the test was 0.996 and 0.991,respectively.The model has a high degree of fitting and a certain degree of prediction.Fourier infrared spectroscopy was used to analyze the changes of chemical structure on the surface of CO₂laser modified poplar wood.The results showed that laser modified hemicellulose surface deacetylation promoted polysaccharide degradation and lignin condensation.Lignin benzene ring stretching vibration,guaiacyl demethylation to quinone compounds.The degradation of hemicellulose produced sugars and acids,catalyzed the degradation and condensation reaction of test wood,and deepened the color of poplar surface.（2）In the study on the variation law of the surface wettability and roughness of cottonwood modified by CO₂laser,the effects of the selected laser processing parameters on the test results of the cottonwood surface roughness Ra_∥,Ra_⊥,Rz_∥and Rz_⊥parameters are listed as follows:laser power>scanning path spacing>feed speed.The order of influence on initial contact angle test results of poplar specimen surface is as follows:scanning path spacing>laser power>feed speed;the order of influence on equilibrium contact angle test results is as follows:laser power>scanning path spacing>feed speed.A mathematical model of the selected laser processing parameters and the surface wettability and roughness of poplar wood specimens was established by response surface method.The correlations between the predicted values of the regression model and the actual values of the parameters of poplar specimen surface roughness Ra_∥,Rz_∥,Ra_⊥,Rz_⊥parameters,initial contact angle of wettability and equilibrium contact angle were0.990,0.985,0.991,0.992,0.989,0.981,respectively.The model fit degree was high and it was predictive.（3）In the study on the surface coating performance of CO₂laser modified poplar wood,the effects of laser processing parameters on the test results of?L^*,?E^*and?G on the surface coating performance of poplar wood are ranked as follows:laser power>feed speed>sweep path spacing.The mathematical model of the selected laser processing parameters and the finishing performance of poplar surface is established by the response surface method.The correlation between the predicted value of?L^*,?E^*and?G response value regression model and the actual test value of poplar surface is 0.984,0.985,0.991,respectively.The model has a high degree of fitting and is predictive.The selected laser modified combination parameters have little effect on the performance of the poplar surface coating.The adhesion level of the paint film on the surface of the test material is 0 or 1,and the proportion of the affected paint film peeling area is less than 5%.Reasonable input parameters can improve the visual effect of the poplar surface,but do not affect the adhesion of the paint film.