SEPARATION AND STRUCTURAL CHANGES IN HEMICELLULOSE FROM PRETREATED WHEAT STRAW BY STEAM EXPLOSION

摘要

Pretreatment of wheat straw by steam explosion has been performed to study separation and structural changes in hemicellulose and experimental results show that the xylan content reduced by 85.31％with increasing pressure from 1.2 MPa to 2.0 MPa and reduced by 66.80％with increasing time from 2 min to7 min.Pressure was the main factor affecting the degree of separation of hemicellulose,which could reach almost 94.53％which was measured by high performance liquid chromatography(HPLC).Based on the FT-IR,TGA,1H NMR studies,the further research of structural changes in HP(hemicellulose was extracted by 10％(w/w)NaOH and deposited by three time volume anhydrous ethanol from steam exploded wheat straw)and HL(hemicellulose was degraded and collected in the form of polysaccharides and monosaccharides,which was deposited by three time volume anhydrous ethanol from the steam blasting residual liquid)were discussed.From the FT-IR spectra of the hemicellulose,it can be known that the intensity of highly substituted arabinoxylans associated with β-glucans became weak with increase of pressure and durations of steam explosion.At the same time,the10％NaOH treatment under the conditions used completely cleaved the ester bond from the β-D-xylopyranosyl backbone with 4-O-methyl-α-D-glucuronic acid attached to O-2 of the xylose residues,but without arabinofuranosyl attached to O-2 or at both O-2 and O-3.The structure of HL due to degradation by steam explosion was β-D-xylp units with arabin-ofuranosyl attached to O-2 or at both O-2 and O-3 that degraded from(1-4)linked β-D-xylopyranosyl backbone.