Effect Of Chemical Constituents And Metal Ion On Wood Heat-induced Discoloration

Wood discoloration is considered to be the defects, and directly affect the application of the timber. The wood color adjust through control the heat treatment conditions and change chemical structure of wood, Which has important theoretical and practical value on improve the quality and efficiency of wood resources. Wood components and metal ions has influence on wood discoloration during the heat process. In this paper, FTIR, UV-visible spectroscopy and chroma index analysis were used to study the role of lignin and extractives of wood play in the wood drying process of discoloration. And the influence of metal icons on wood components, such as lignin, water extractives and ethanol extractive, in wood drying process has also been explored. This study not only enriched the research of wood drying discoloration, but also provide reference significance for wood drying mechanism of color change. The results shows that:(1) The presence of wood extractives make the wood color change increased in the heating process, Part of the extractives structure have been changed in heat treatment and were difficult to remove through extract.(2) Lignin has a very important role in the wood heat discoloration process. When lignin is heated, the chemical reaction of oxidation, condensation would occur. The hydroxyl group were oxidized to quinones, conjugated and non-conjugated carbonyl, which resulting in the darkening of wood color. With the existence of extractives, the oxidation of lignin was further deepen. The color of holocellulose changed after heating process owning to the residual lignin been oxidized.(3) Wood contains transition metal ions like iron, manganese and copper. When wood flour was treated in acidic environment and EDTA processing, metal ions content reduced, and resulting in wood flour heat discoloration minimize. With the adding of metal ions, the lightness index of sample lower and chromaticity index a*, b*have relatively large change. And there are big difference of wood flour before and after heating treatment when treated by different metal ions.(5) In Locust heating process, Oxygen is an important factor to promote the structure changes of lignin, water and ethanol extractives, and then lead to color changes of them. The influence of metal ions on the absorptivity of water extractives has relevant with time. The promote effect of metal ions on the process of lignin and ethanol extracts heat discoloration is not very obvious.