Synthesis And Characterization Of Environmental Sensitive Hemicellulose-based Hydrogels

Hemicellulose, the second most abundant natural polysaccharide, accounts for approximately 20%~35% of lignocellulose biomass. Hemicellulose presents some advantages, e.g., hydrophilicity, biodegradable and biocompatibility. The hydrogel prepared from hemicellulose material shows some excellent characteristics of the hemicellulose and provides good prospects for hydrogels in the field of water treatment and slow-release drugs. This type of hydrogel is expected to be prepared from a modified hemicellulose to which double bonds were introduced to the side chains.Considering these properties of hemicellulose, the synthesis and characterization of hemicellulose-based hydrogels are conducted as follows:1. Corn cob hemicellulose was modified by maleic anhydride to fabricate acylated hemicellulose. Investigation was focused on the impact of LiCl dosage and maleic anhydride dosage on the degree of substitution(DS) of the acylated hemicellulose and the yield of acylated hemicellulose. The results indicate that maleic anhydride was grafted to hemicellulose successfully identified by FT-IR and 1H-NMR. With the increase of maleic anhydride dosage, the DS of hemicellulose derivative was increased while the yield of hemicellulose derivative was decreased. A certain amount of LiCl dosage favors to increase the DS of acylated hemicellulose.2. A kind of dual sensitive hydrogel was prepared from acylated hemicellulose(DS=0.42) and acrylic acid(AA) by free radical polymerization initiated by ammonium persulfate(APS) and N,N,N’,N’-tetramethyl-ethane-1, 2-diamine(TEMDA) in the presence of sodium lingosulfonate(NaLS). The impacts of acrylic acid dosage and sodium lignosulfonate dosage on the structure and properties of hydrogels were investigated. The adsorption properties of the prepared hydrogels for methylene blue were tested. The dissolution behaviour of the lignosulfonate in different solvent system was investigated. It is estimated from the results that the existing forms of the additive NaLS are of semi-IPN and IPN types in the hydrogel. The usage of NaLS has no obviously impact on the pore size of the hydrogel, while it decreases the yield of hydrogel or make the hydrogel cannot be formed. When the mass ratio of NaLS and hemicellulose derivative is 1:6 and 1:3, the hydrogel exhibits the maximum swelling ratio(253g/g) and a maximum adsorption capacity(362mg/g), respectively. This kind hydrogel is pH and ionic strength(Na+) dual sensitive. The hydrogel reveals a good reusability. The adsorption kinetics of MB of the hydrogels is well fitted to the pseudo-second-order model. A monolayer adsorption of Langmuir isotherm model was verified by the study of the adsorption isotherm. 3. A temperature- and pH-sensitive hydrogel was prepared by free radical copolymerization from NIPAAm/IA mixtures as the monomers in the presence of APS and TEMDA as the initiator and another acylated hemicellulose(DS=0.84) as the cross-linker. PVA was used as an enhancer to produce the temperature- and pH-sensitive hydrogels. The impact of IA dosage on the properties of the hydrogels was studied. The cytocompatibility of the hydrogels was evaluated by culturing with mouse embryonic fibroblast. The hydrogel was used to control drug release(salicylic acid). The results indicate that the lower critical soluable temperature(LCST) of the hydrogels increases with the increase of the IA dosage. The LCST was adjusted to around 38°C when the NIPAAm/IA mass ratio is of 96:4. The pore size and the swelling ratio of the porous hydrogel increase with more IA dosage. Meanwhile, the hydrogel, strengthened by PVA, exhibits a good temperature- and pH-sensitivity. The proliferation data shows that hydrogels exhibite no inhibition of cell viability, thereby indicating the cytocompatibility of hydrogels. The hydrogel exhibites a good controlled release property to Salicylic acid in simulative gastrointestinal fluid.