Microwave-assisted Extraction Of Hemicelluloses And Their Sulfonation Modification

In this paper, microwave was employed to assist the extraction of hemicellulosesfrom corncob. The factors that may influence the yield, the monosaccharidecomposition and molecular property of the hemicelluloses, such as the type of theliquor media, concentration of the acid or alkali, treating time and treatingtemperature were discussed. Gel Permeation Chromatography (GPC), Fouriertransform infrared spectroscopy (FTIR),1H-NMR and Ion Chromatography (IC) wereapplied to characterize the extracted substance. The results indicated thathemicelluloses could be extracted from corncob in all the three types of liquor media(Deionized water, sulfuric acid and KOH solution) with the assistance of microwaveirradiation. It was found that the obtained hemicelluloses is a kind of arabinoxylanmainly consisted of β-(1â†'4)-D-xylan backbone with substitution of α-L-arabinoseresidues in C2and/or C-3. The yield was increased with the increment of the acid oralkali concentration, treating time and treating temperature. It was also indicated thatthe yield of hemicelluloses extracted by alkali aqueous solution is higher than thoseobtained from the other types of the liquor media. Besides, the required treating timewas significantly shortened compared to the extraction without microwave assistanceby alkali solution.The yield of hemicellluloses extracted by microwave-assisted diluted sulfuricacid solution was low, and the average molecular weight of the hemicelluloses wasdecreased remarkably with the increase of the acid concentration, which means thatthe hemicelluloses are very sensitive to acid and apt to hydrolysis in acid solution.However, it was found that some degree of esterification reaction did happen on thehemicelluloses in the microwave-assisted extraction by sulfuric acid, which isbelieved to provide a new approach for the modification of such polysaccharide.Xyaln from oat spelt was used for the synthesis of xylan sulfates by employmentof sulfur-trioxide·pyridine complex in homogeneous system under microwave irradiation. The effects of treating temperature, reaction time and molar ratio of thecomplex and xylose on the degree of substitution (DS) and molecular weight (M W)were studied.FT-IR, GPC, NMR were employed to study the structure and physicochemicalproperties of xylan sulfates. New peaks appeared around1260cm-1and810cm-1,suggesting sulfate groups were successfully introduced to the hemicelluloses. NMRanalysis showed that sulfation was mainly happened on hydroxyl groups of C2andC3, and the sulfation ability of the hydroxyl groups of C2was better than that of C3.