Preparation Of Aramid Nanofibers And Their Applications In Liquid Filtration

In recent years, nanofibrous membranes have been identified as an efficient tool for liquid filtration due to its large surface area per unit volume, good flexibility and high porosity. In this paper, we dispersed macro structure of aramid fibers into aramid nanofibers by deprotonation method. And the aramid nanofibers were characterized through TEM, EDX and other characterization methods. Then aramid nanofibers were attached in the PET nonwoven fabric and cellulose nanofibers to prepare composite membranes using layer-by-layer self-assembly technology. Respectively the surface morphology, surface wettability, tensile strength and filtration performance of as-prepared composite membranes were investigated.The main research work and results are as follows:（1） After stirring in potassium hydroxide solution for a week, aramid fiber was deprotonated to aramid nanofibers in DMSO. By observation, we found the microscopic size of the aramid nanofibers with diameter of 8²0nm range. And the structure of aramid nanofibers were not destroyed by alkali treatment that is important to maintain the structural integrity of aramid fibers. The thermogravimetric characteristics of aramid nanofibers is different from aramid fibers. With the temperature increasing, nanofibrous weight was decreased gradually. But aramid nanofibers still have good heat resistance.（2） The aramid nanofibers/PET nonwoven fabric（ANFs/PET） composite membranes were fabricated via layer-by-layer technique. The surface morphology of composite membranes were compact and smooth. Tensile strength was increased with the increase of aramid nanofiberous membrane layers. The results demonstrated that the surface assembled PET with the deposition of ANFs can improve their hydrophilicity and thermal stability. The filtration experiments indicated the composite membranes can efficiently remove the nanoparticles from water system. When the number of ANFs layers reaches 12, 100 nm Fe₃O₄ nanoparticles and 10 nm Au nanoparticles can be removed from the feed solution with a rejection rate above 96% and 90%. In the same time, the flux of composite membranes was very large. This work showed the feasibility of fabricating composite membranes via layer by layer self-assembly of the ANFs on PET, exhibiting a potential application in ultra-filtration.（3） The cellulose acetate nanofibers were prepared through the electrospinning, then cellulose nanofibers were got with alkali treatment process. The resulting cellulose have uniform diameter, small gap and super hydrophilic property. Then the compact and smooth aramid nanofibers/cellulose nanofibers（ANFs/CNFs） composite membranes were prepared via layer by layer technique. The composite membranes present robust mechanical properties. Importantly, the composite membranes exhibit good filtering effect. When the number of ANFs layers reaches 6, 100 nm and 10 nm Fe₃O₄ nanoparticles can be removed from the feed solution with a rejection rate above 99% and 98%. But the flux of composite membranes was small. When the number of ANFs layers reaches 6, the flux was just 21.22 L/（h·m²ï¼‰.