Effect Of Forming Temperature On Color And Chemical Composition Of Poplar Powder Compacts

With the improvement of people's requirements for quality of life,wood products are more and more popular in life and the demand for wood is increasing day by day.However,the utilization rate of wood in production is not high.Warm-press forming is a new technology combining the theory of glue-free hot-pressing of the wood materials and the theory of warm-pressing of the metal powders.No harmful artificial preparation such as glue is added and no pollution is produced during the entire forming process.Therefore,the forming process is low-carbon and environmentally friendly.In this paper,the effect of the temperature on the surface color of the warm-pressed compacts was studied.The chemical composition of the poplar powder compacts before and after warm-pressed forming was analyzed.The results can provide basic data for the subsequent research on the change law of the wood color and the warm-press technology.The contents of this paper are as follows:(1)Through the color analysis of poplar powder compacts,it can be concluded that the forming temperature has a significant effect on the surface color of the compacts.With the increase of the processing conditions,the surface color of poplar powder compacts gradually becomes darker.With the increase of process strength,the lightness value,red green value and yellow blue value have a downward trend,while the overall color difference value of the compact gradually increases.(2)Through the analysis of the main chemical components of poplar powder compacts,it can be concluded that the lignin content gradually increases with the increase of temperature forming temperature.The content of color supporting group and color generating group in lignin also increases,which makes the color of the powder become deeper.Hemicellulose and cellulose gradually decompose into colored extracts with high temperature,which make the color of poplar powder compacts deepen gradually.(3)By analyzing the extractive content of poplar powder compacts at different forming temperatures,it can be concluded that the extractives of benzene alcohol,hot water and cold water gradually increase with the increase of forming temperature.The results showed that the content of tannin and pigment increased gradually.It was one of the important factors affecting the surface color of wood powder,resulting in the dark color of pressed wood powder.(4)The mechanism of color change of poplar powder compacts after warm compaction was studied by U-V Vis,FTIR,XPS and cellulose crystallinity analysis:with the increase of forming temperature,the polysaccharides are degraded to carbonyl and carboxyl groups,which make the color of poplar powder compacts deepen gradually.The results show that the O/C ratio decreases.The polysaccharides decompose,and the contents of lignin and extractives increase,which further explains the change mechanism of surface color.In the visible light absorption region,the absorption of poplar powder compacts is enhanced,and the absorbance increases gradually with the increase of temperature,indicating that the surface color of compacts is deepened.