Structure Controlling And Properties Of Functional Cellulose Composite Materials

Nature polymers, as all kinds of biodegradability materials and recyclable resonance, have attracted numerous attentions. Cellulose, a typical nature polymer, is widely utilized in many fields, e.g. industry products, environment engineering, biomedical, etc. Cellulose contain a larger amount of hydroxyl groups that in favor of intra- and intermolecular hydrogen bonding. The strong hydrogen bonding makes cellulose difficult to dissolve and melt that limited their practical applications. Thus, researches are focus on exploition of novel cellulose solvents and consequently functional cellulose materials recently. In this dissertation, we employed eco-friendly cellulose solvents and new fabricating technique, obtained high strength cellulose/chitin blend hydrogel membranes and studied their morphology, structure, properties and formation mechanism. In addition, we developed cellulose/Ag nanoparticles composite microspheres and studied their catalytic application for 4-nitrophenol reduction.Firstly, we extended the solution pre-gelation technique which has been used for fabrication of high strength cellulose hydrated membranes to develop novel cellulose/chitin blended hydrogel membranes. We clarified the effect of chitin content and pre-gelation temperature on the structure and performance of the membranes. Comparsion with the membranes from traditional solution casting method, all of considered membranes displayed denser structure and lower crystallization. The morphology and crystal structure of those blended hydrogel membranes were tunable by variation of chitin content and pre-gelation temperature. With the increasing of chitin content or by changing the pre-gelation temperature, structure of the membranes was transformd from dense and nonporous to mesh-like and porous. The crystallinity decreased at low chitin content, while increased at high chitin content. The relatively low pre-gelation temperature was also favorable for the formation of low crystallinity. The hydrogel membranes prepared by pre-gelation method displayed superior mechanical properties. Their tensile strength and breaking elongation were about 2 times higher than those of common membranes. Both pore mechanism and partition mechanism affected the diffusion behaviors of drugs through the blended hydrogel membranes. The gelation process of the mixed solution was accelerated or decelerated depending on the chitin content in solution. The blended hydrogel membranes regenerated from the gel state in water based on nonsolvent-induced phase separation mechanism.Secondly, cellulose microspheres were prepared via a sol-gel method in paraffin oil. The obtained microspheres with average diameters about 20μm show porous structure. Cellulose/Ag composite microspheres were prepared by hydrothermal reduction of AgNO₃ in the cellulose matrix. The synthesized 30⁵0 nm Ag nanoparticles were well dispersed in spheres. Hysrothermal process did not change the chemistry structure of cellulose and morphology of microspheres. The Ag nanoparticles promote cellulose decomposition in air, however, the composite microspheres show good thermal stability and did not decomposite below 300 oC. The catalytic activity of cellulose/Ag composite microspheres was determinated using model reaction of 4-nitrophenol (4-NP) reduction in presence of NaBH₄. Cellulose/Ag composite microspheres showed highly catalytic activity, and the reaction ratio of 4-NP closely related to content of Ag nanoparticles. The new as-prepared cellulose-based metal composite are easy to prepare, stable, efficient and recyclable and thus have potential for industrial applications.