Study On Preparation, Structure And Properties Of CMC/PNIPA/Clay Nanocomposite Hydrogels

In recent years, considerable research attention has been focused on the environment-sensitive hydrogels(intelligent hydrogels) because they possess great potential applications in many aspects, including drug delivery system, enzyme immobilization and biomaterials separation and purification, etc. According to research course of hydrogels, it is a main research direction to synthesize hydrogels in the past. With the deepening studying, people realize some defects that the traditional hydrogels have progressively, for instance, bad mechanics performance, slow response etc., which has limited the development of hydrogels’ application. Nowadays research has been focused on improving the mechanics properties and speed of response of hydrogels.The aim of this paper is to overcome the traditional shortcomings of hydrogels. A new kind of semi-interpenetrating polymer network (semi-IPN) nanocomposite hydrogels based on the linear sodium carboxymethylcellulose(CMC) and poly (N-isopropylacrylamide)(PNIPA) cross-linked by inorganic clay(Laponite XLG) was synthesized. The structure and morphology, the swelling and deswelling behaviors and the mechanical properties of these novel hydrogels were investigated in detail. In addition, the preliminary study on the preparation of fast response nanocomposite hydrogels and the application of hydrogel as a drug delivery system has been performed. The main results obtained are as following:1. A new kind of pH/temperature-responsive CMC/PNIPA/Clay nanocomposite hydrogels was successfully prepared by in situ free-radical polymerization based on linear CMC and PNIPA using inorganic clay as a multifunctional crosslinker in place of the conventional organic cross-linker. The interpenetrating polymer network technique was utilized. It was found that the silicate layers were substantially intercalated by the polymer matrix and dispersed homogeneously in the hydrogels. CMC was also existed in the form of linear chains incorporated in the hydrogels.2. Compared with traditional hydrogels, CMC/PNIPA/Clay gel has very good mechanical performance and can get more than 1000% to extend. It was found that the mechanics performance of CMC/PNIPA/Clay hydrogel has related to the number of network chains per unit volume in the network (v_e) and the molecular weight of the chain between cross-linkers(Mc).3. Temperature and pH sensitive behaviors of CMC/PNIPA/Clay nanocomposite hydrogels were studied in detail. The result indicated that hydrogels has good temperature-and pH-sensitive performance. The volume phase transition temperature (VPTT) of hydrogel is about 33 degrees Centigrade, which have no deviation with that of traditional PNIPA hyrogels. PH value of the medium has great influence on deswelling behavior of CMC/PNIPA/Clay hydrogels. The main reason is about the ionization and protonation of-COONa on the CMC chain which give raise to the charges.of the swelling ratios of the hydrogels.4. The swelling and deswelling behaviors of the CMC/PNIPA/Clay hydrogels, which response both temperature and pH value of the medium, were investigated in detail. The result indicates that under VPTT, the swelling ratio of hydrogel changes more sensitive to pH value; When above VPTT, the case was just the opposite. The deswelling ratios of CMC/PNIPA/Clay hydrogels have obvious improved with the introduction of CMC compared with pure PNIPA hydrogels because semi-interpenetrating polymer network offers more passway for water to diffuse in and out. Meanwhile, the swelling and deswelling rate of CMC/PNIPA/clay nanocomposite hydrogels have relate to the Clay content. The less the Clay content is, the more the speed is. The CMC/PNIPA/Clay nanocomposite hydrogels has better repeated responsivenesses that the pulse to temperature of water gel is stimulated.5. The hydrogels with porous structure were preparation in NaCl solution with different content. These hydrogels have smaller and more homogeneous porous than that of CMC/PNIPA/Clay hydrogels prepared in deionized water. Meanwhile, the deswelling rate has been improved with about 70% water lost in 10 min.6. A preliminary study of the conventional CMC/PNIPA/Clay hydrogels as the drug delivery system for the model drug, 5-fluorouracil (5-Fu) was performed. It was found that at 37℃(above the VPTT) and pH=7.4 the release rate and amount of 5-Fu increase with increasing CMC content in the CMC/PNIPA/Clay hydrogels and below the VPTT(at 25℃),the little effect of pH on the drug release rate was observed, while above the VPTT(at 37℃), the effect is remarkable. Thus this kind of hydrogels has potential to be used as the oral delivery of 5-Fu.