Isolation And Characterization Of The Hemicellulose From Wheat Straw By Alkali-oxygen System

The hemicellulose from wheat straw has a great value of development and a good prospect of application. To find a method of isolating hemicellulose and characterize its chemical composition and structural properties is the premise for its application. In this paper seven hemicellulose fractions were prepared by Soda,Soda-H2O2 and Soda-O2 extraction. Then they were purified with ethanol solution and characterized by various physico-chemical methods.The results are as follows:1. Hemicellulose can be isolated by Soda-H2O2 and Soda-O2 method environmental friendly . The sequence by rate of extraction is Soda-O2 > Soda-H2O2 > Soda >Na2CO3 . The yields and lignin contents of each fraction are 6.51%~11.62%和9.85%~32.33%, and are different with various alkali extraction processes. The yield is higher at a higher temperature or with . The content of lignin is higher with the existence of O2 .2. The content of condensed lignin in each fraction is high, which shows that the chemical bonded lignin exists in each hemicellulose fraction. There is a difference among the mole ratio of V,S,H units with various alkali extraction processes. With the existence of H2O2 , the yield and S unit will decrease, H unit will increase. The mole ratio of V,S,H units can not be changed with the existence of O23. The content ofβ-O-4 structure is low relatively. The yield of (E+T), 15.35%~23.33% , and E/T value, 0.7~0.96. Compared with Soda method, the yield of (E+T) and E/T value from hemicellulose obtained by Soda-H2O2 method is higher, but the yield of (E+T) from hemicellulose obtained by Soda-O2 method is the lowest while its E/T value is the highest.4. The main structure of polysaccharide in each fraction is arabinose xylan, which accounts for more than 90% of the neutral sugars and is linked with glucuronic acid as side chain. In contrary, the content of mannose and galactose is very low.5. The results of FT-IR and TG-DTA analysis show that H2O2 and O2 can not cause obvious chemical change in the structure of hemicellulose. Also, the degree of degration of lignin and carbohydrate may be different.