Preparation And Characterization Of PNIPA Nanocomposite Hydrogels

PNIPA hygrogels has been widely used in biological technology, environmental engineering, and other fields due to its good elasticity and plasticity, high water imbibition, low pollution and other advantages, especially its LCST close to human physiology temperature. However, the lower mechanical strength and balance swelling rate limit its application scope. The research indicates that adding functional nanoparticles into PNIPA network can make some of the performances of the nanocomposite hydrogels changed.In this paper, graphene and nano SiO2particles were respectively added into PNIPA gels, preparing PNIPA/Graphene and PNIPA/SiO2nanocomposite hydrogels. The effects of the content of nanoparticles on the performance of the system were studied.Graphene is a kind of new carbon material with the perfect two dimensional structure, which has bigger specific surface area and excellent mechanical and electrical properties. The structure and morphology of the PNIPA/Graphene nanocomposite hydrogels were characterized by FTIR, Raman and FE-SEM. The results indicated that graphene layer was scattered evenly in the system of network, making its density degree of surface structure get down and a large amount of drape appear. The SR of composite gels reduced and the ESR increased with the increase of the content of graphene, the final water retention of the composite gels also improved. The results of the test for gel behavior showed that G'of the composite system was far higher than G'', and with the content of graphene increased, G'was up to3500Pa. In addition, the gel point testing indicated that the mixed graphene had no obvious effects on the LCST of composite system, which was still near35℃. It showed that no more chemical bonds occurred between graphene and PNIPA hydrogels. In addition, characteristic peak of CO2appeared in Raman spectrum, which indicated that the composite system has strong adsorption ability for CO2.The surface of SiO2particle contains a lot of hydroxyl. The results of FTIR and SEM of PNIPA/SiO composite system showed that nano SiO2particles were either dispersed evenly in the network or adsorbed on the chains of polymer. The interaction between the polymer network and nano SiO2particles made the mesh on the surface of composite gels expand and the crosslinking degree decreased. With the increasing of the nano SiO2, some of the performances of the composite system were changed. Especially when the nano SiO2content was up to5wt%, the release of water performance was greatly improved, the pressure that the composite system can withstand when it was damaged was as high as47.2KPa, and storage modulus G'was increased to3300Pa. In addition, the results of the test for gel behavior showed that the doped nano SiO2had no significant effects of the LCST of composite hydrogels, which indicated that the polymer structure had no change.PNIPA nanocomposite hydrogels not only maintained the original excellent performances, but also changed the comprehensive performance due to the introduction of the nanoparticles under some certain fields, such as swelling and strength properties. Nano SiO has high surface activity, and can produce interaction with PNIPA macromolecular chain groups or hydrogen bonding. When the content of nano SiO2increased, it can also block chemical crosslinking of gels, which changed some performances of gels and laid a foundation for widening application fields of intelligent polymer hydrogels. In addition, the network structure can support the three dimensional structure of graphene, and through the polymer chains block overlap or agglomeration of graphene, making the graphite surfaces dispersed in polymers by nano morphology and giving full play to its specific surface area of the advantages, so that the possibility of application of the graphite surfaces in some areas may be realized.