| A novel sequential ultraviolet induced living graft polymerization technique was developed using polypropylene membranes as substrate and numerous acrylic monomers as grafted materials. Experiments demonstrate that grafting density and graft polymer chain length can be controlled independently and the amount of grafted polymer relative to the total amount of polymer from the novel grafting method is 4-fold greater than that of a conventional photografting method for the system studied. A reaction mechanism was proposed and confirmed experimentally by membrane weight gain, GPC (gel permeation chromatography), FTIR (Fourier transform infrared spectroscope), and kinetic studies. The principal factors affecting the graft polymerization were investigated, including substrate, monomer, solvent, and surface initiator concentration. Polypropylene membranes were rendered hydrophilic with no charge, positive charge or negative charge by grafting monomers of poly(ethylene glycol 200) monomethacrylate, dimethyl aminoethyl methacrylate, or acrylic acid, respectively, using the novel grafting method.; A combined technique coupling backpulsing and membrane surface modification has been demonstrated as an effective method for reducing both nonadhesive and adhesive fouling in crossflow microfiltration of aqueous suspensions of bacteria, clay, crude oil, and latex beads. The experiments show that membrane fouling behavior is not strongly dependent on the membrane surface chemistry without backpulsing for all foulants. However, 5-fold, 1.7-fold, and 1.3-fold permeate enhancements were obtained by backpulsing alone, and 6-fold, 2.6-fold, and 2.7-fold permeate volume enhancements were obtained by a combination of backpulsing and surface modification for filtration of 0.5 g/L bentonite suspensions, 0.14 g/L Escherichia coli suspensions, and 50 ppm crude oil emulsions, respectively. Further, using carboxylate modified latex particles as model foulants, the effects of principal factors on membrane performance were investigated. 1.5 to 2.1-fold permeate volume enhancements were obtained by water backpulsing, gas backpulsing, or crossflushing. The average flux decreased 60% when particle diameter (0.2 mum) in feed suspension is less than nominal membrane pore diameter (0.3 mum) as compared to the average flux when only larger particles (1.0 mum) were used in feed suspension. Without backpulsing, ionic strength does not significantly affect permeate volumes. With backpulsing, however, permeate volumes decreased 30% and 40% when NaCl concentration in feed suspension is 0.01 M and 0.1 M, respectively, as compared to that without addition of NaCl in feed suspension. |
