Preparation And Properties Of Hemicellulose/Chitosan Composite Membranes

Cellulose, hemicellulose and lignin are three components of plant fiber raw material, which are the most abundant natural and renewable biological resources. Hemicellulose is a uniform polysaccharide connecting with cellulose and lignin, but its high branching degree, polydispersity and amorphous structure restricted the further development and utilization. Chitosan as a polysaccharide containing one of the abundant alkaline group (-NH2) in nature has attracted much attention due to its good biocompatibility, biodegradability and antibacterial properties. Chitosan is widely used in the fields of biomedical, food and environmental protection. The preparation of hemicellulose/chitosn composite membranes has importance of raising the added value of hemicellulose and developing some novel functional biomaterials.In this study, the novel functional biomaterials products based on hemicellulose and chitosan using crosslinker were prepared. Two different polyxylan were used, and glutaraldehyde or genipin was used as crosslinker. The properties of the resulted membranes were studied, and the technical parameters were optimized. The chitosan membranes modified by two different hemicelluoses and two crosslinker were analyzed by FTIR, X-ray and TG.The corn cob hemicellulose/chitosan composite membranes were prepared and its cross-linking degree, swelling ratio, mechanical properties and antioxidant activity were studied. The effects of crosslinker, the xylan/chitosan ratio, genipin dosage and the adding manner of reactant on the membrane properties were analyzed. The results showed that both the membranes with two crosslinker had a higher pH-sensitive, especially under the acid conditions. Compared to using the glutaraldehyde as linker, the composite membranes linked by genipin had a higher mechanical property and antioxidant activity; however it had lower swelling ratio and crosslinking degree. When the xylan/chitosan ratio increased to 7:3, the difference of the above properties caused by using two crosslinker became smaller. When the genipin was used as linker, the increase of xylan/chitosan ratio resulted in the higher rosslinking degree, swelling rate and antioxidant activity of composite membrane, while the mechanical strength of the composite membrane decreased sharply. In addition, the increase of genipin dosage led to the improvement of crosslinking degree and the mechanical strength; however the swelling rate of the membrane decreased and the response to pH changed little. The excessive genipin led to the decrease of antioxidant. The result from the different adding manner of reactant showed that the properties of membranes were the best when the chitosan, xylan and linker were simultaneously added in reaction system.The preparation and properties of beechwood hemicellulose/chitosan composite membrane was studied. The results showed that the membrane linked by glutaraldehyde had a much higher crosslinking degree compared to using genipin as linker. Especially, the crosslinking degree almost is near to 100% when the hemicellulose/chitosan ratio increased to 7:3. Compared to the glutaraldehyde linker, the membrane linked by genipin had a lower crosslinking degree. A higher xylan proportion helped to improve the antioxidant activity of composite membrane. When the genipin was used as linker and the xylan proportion was 70%, the antioxidant activity of composite membrane was increased by 127% compared to the chitosan membrane without xylan.The properties of the chitosan membrane modified with two different hemicelluloses and two linkers were made a comparison for elucidating the effect of chemical components of xylan on the membrane properties. The results show that the beechwood xylan contains more lignin and has a lower solubility than the corn-cob xylan. Compared with the corn-cob hemicellulose, the beechwood hemicellulose is more beneficial to the improvement of stress strength and pH-sensitive and has a near swelling property. The composite membrane with beechwood hemicellulose/genipin/chitosan has a highest pH-sensitive.The hemicellulose/chitosan compound products were analyzed by FTIR, FTIR, XRD, TG and UV. The results showed that the Maillard reactions were enhanced in presence of the crosslinkers. Compared to the corn-cob hemicellulose, the chitosan composite membrane prepared by the beechwood hemicellulose containing more lignins had a higher crystallinity. The modified chitosan membranes had a lower thermal stability. The presence of lignin in hemicellulose helps to the strength properties, thermal stability and the crosslink reaction.