Water is one of the bulk transportation media for transmission of particulate contaminants. These contaminants are complex mixtures of particles; most of them are usually smaller than 1000 µm in diameter. Chemical and biological aerosols (particulates) are frequently in the range of 1- 10 µm. The particulate matters may carry some adsorbed gaseous contaminants. The removal of particulate and biological contaminants is thus an important step in water purification process. Particulate contaminants if not removed tend to foul reverse osmosis membranes and severely reduce the throughput of the final purification step. The filtration industry is looking for more efficient high performance filters for filtration of particles smaller than 0.3 µm and adsorbed toxic gases. Nanofibrous media have low basis weight, high permeability and small pore size that make the appropriate for a wide range of filtration applications. In addition, nanofiber membrane offers unique properties such as high surface area (ranging from 1- 35 m2/g depending on the diameter of fibers), good interconnectivity of pores and potential to incorporate active chemistry or functionality on nanoscale.
The current study investigated the formation of nanofibrous membranes, from a cellulose precursor; cellulose acetate, for water filtration. Membranes were prepared by an electrospinning technique that was based on the use of a high voltage power supply to force polymeric droplets to be sprayed in the form of fibers with different aspect ratios, depending on the process parameters. Different parameters affecting the structure, morphology and physical properties of the membranes were studied in details in order to optimize them. Characterization of the membranes was carried out at every stage of the electro spinning process by infrared spectroscopy (IR) and scanning electron microscopy (SEM). Physical properties of the membranes such as density, porosity, BET surface area, pore size distribution, viscosity and surface tension were determined. Thermal treatment effects on the structure and morphology of the membranes were studied. Regeneration of cellulose was attempted by treatment of the membranes in alkaline media. Optimization of the alkali treatment process was also reached. Preliminary evaluation of the nanofibrous membranes for removing solid particulates from simulated solutions was also carried out. Filtration efficiency results were compared to those obtained with two commercially available membranes.
Results showed the possibility of obtaining nanofibrous membranes from solutions containing different concentrations of cellulose acetate, and showed a wide range of fiber and pore size distribution. Optimization of the electro spinning parameters led to the formation of highly porous membranes (with porosity approaching 94%) together with homogeneous fiber and pore size distributions. Structure instability was observed with the thermal treatment of these membranes and was found to be dependent on the membrane thickness. Treatment of the CA membranes in 0.5M NaOH solutions yielded a fully regenerated cellulose after 10 hours, without affecting the morphology of the nanofibers nor the pore size and its distribution. Efficiency of the nanofibrous membranes prepared in the current study showed superiority over the commercially available membranes
