Study On Discoloration Mechanism Of Betula Costata Trautv During Drying

Betula costata Trautv, a kind of stiff hardwoods, is very significant and valuable in the northeast regions nowadays, which is also rich in accumulation among the hardwoods. Its distribution is wide, planting area is extensive, and the production is very abundant. The lumber of Betula costata Trautv is easy processed and suitable for lathe slicing, applied to plywood, furniture, wooden floor and interior decoration. However, shortcomings like easily corroded, color changing to uneven pink during the drying processing, also exist, which can cause the degradation sharply and result in huge economic loss. Therefore, the application is limited. The study started with the mechanism of discoloration and attempted to cope with this problem of Betula costata Trautv during drying through analyzing color parameters of discoloration under different temperatures and humidity, so as to raise the utilization ratio and increase the applying value. Main researching results are as followed:Firstly, after ration testing and analyzing the ingredient of extractives, we could see that the extractives contained phenol, condensed tannins, pigment and other substances. After analyzing the ingredient of extractives by infrared spectrum, it's known that there were some chrom ophore such as carboxyl, carbonyl,hydroxyl, and auxochrome in extractives. Under the conditions of acidity, alkalinity and oxygen, extractives varied chemically, which is the reason of color changing.Secondly, a type of water dissolving extractives of Betula costata Trautv such as tannin which is a kind of color changing substances, was dissolved and oxidized to colorful substances during drying. Simultaneously, the color of wood would change when the water moved to the surface of the lumber, and diffused during the drying. Hemicellulose could be oxidized to the colorful substance under the high temperature, which also causes the discoloration.Thirdly, the color difference of Betula costata Trautv till increased with the temperature growing and time prolonging. Temperature played a bigger role in affecting and the effect of drying time would strengthen with temperature rising. Color parameter which is the most sensitive to temperature was lightness. Color hue-angle while color saturation also varied during drying. Color hue-angle decreased wavily with time. Color saturation wavily increased with time. In a word, the color of Betula costata Trautv during drying tent to be red and dark. Under the same temperature, discoloration will strengthen gradually as the humidity increase; while the effect of humidity became more and more obvious when temperature rose.