Isolation Of Hemicelluloses From Corncob And Sythesize Of Hemicelluloses-based Hydrogel

Hemicellolses are commonly defined as non-cellulosic cell-wall heterogeneouspolysaccharides existed in plant tissues together with cellulose and lignin. As the2ndlargestplant fibrous materials on earth, the isolation and utilization of hemicelluloses has becomean important issue on the scientific world. Due to the growing concern of oil crisis and thegreen nature of hemicelluloses, interests has invoked among scientists in hemicelluloses forvalue-added products. Hemicelluoses-based hydrogel is one of the protential applicationfields. However, the structures of hemicelluloses isolated from different plant sources viadifferent method were so varied. Therefore, how to control the structure properties ofhemicelluloses during the isolation process is critical essential to the follow-up modificationand utilization.In this study, hemicelluloses were obtained from corncob by ultrasound-assisted alkaliextraction. The molecular weight, monosaccharide composition and structure properties ofwater-soluble hemicelluloses fraction as well as the water-insoluble fraction werecharacterized. The results indicated that the hemicelluloses obtained by ultrasound-assistedextraction, especially the water-soluble fraction (HB), not only had a higher yield and lowerlignin content but also exhibited highly branched structure in comparison with thehemicelluloses isolated by conventional alkali extraction. The superior solubility ofhemicellulose is good for the follow-up modification. Afterward, we synthesized two kindsof hemicelluloses-based temperature sensitive hydrogels by photo-crosslinking and clickchemistry in order to investigate the controll of hydrogel properties at the angle of rawmaterial structure and the crosslinking reaction, respectively.Firstly,3fraction of water-soluble hemicelluloses obtained from ultrasound-assistedextraction were chosen to prepare thermal sensitive hydrogels via esterification reactionwith maleic anhydride (MA) and crosslinkage under irradiation of UV light with thepresence of N-isopropylacrylamide (NIPAAm) in DMF. The results showed that with thehigher branching of hemicelluloses, the DS of MA was larger, resulted in the higher contentof NIPPAm introduced into the hydrogel. Therefore, the temperature sensitivity and the swelling behaviors of the final hydrogels are greatly influent by the original structures ofhemicelluloses.Secondly, hemicellulose derivatives containing the side chains of azide moieties andNIPAAm-co-HEMA containing alkyne groups were firstly prepared. Then, the hydrogelswere obtained via click chemistry under the catalysis of CuSO4/sodium ascorbate. Thestructure of hemicelluloses and its derivatives, the lower critical solution temperature(LCST) and the morphology of the hydrogels were investigated by FT-IR, IC,1H-NMR,DSC and SEM. The absorb-release properties of the click-gels were also investigated. Theresults obtained showed that the high selectivity and efficiency of click chemistry led tomore regular network structure of the click-gel. Moreover, by adjusting the DS of BIBB, wecan tailor the structures and the temperature sensitivity of the hydrogel, so theabsorb/release properties could be controlled as well.