Abstract
Ph.D. (Chemistry)
The main focus of this work was to develop new synthetic routes towards membranes with the following properties: enhanced hydrophilicity, high protein rejection, pH responsivity, low-fouling, and catalytic action for degradation of persistent organic pollutants such as PCB 77 and methyl orange azo dye (MO).
In the first section, a bulk heterogeneous functionalization of polyethersulfone (PES) with polymethacrylic acid (PMAA) as performed by graft polymerization of methacrylic acid (MAA) using 2,2‘-azo-bis-isobutyronitrile (AIBN) as an initiator is reported. The effect of grafting temperature and monomer concentration on the degree of grafting, were investigated. The grafting was confirmed by Fourier transform infra-red (FTIR), and X-ray photoelectron spectroscopy (XPS). The membranes were subsequently prepared from the functionalized polymer using the phase inversion method. Contact angle measurements showed an increase in membrane hydrophilicity to about 40% as a result of grafting of the PMAA chains. Water uptake (swelling), water permeation fluxes, recyclability, protein rejection (up to 97%) and a low propensity to fouling was recorded upon grafting where pure water flux recoveries recorded were up to 86%. In addition, the membranes indicated a dependence on pH stimulus due to the opening and closing of the pores at low and elevated pH respectively.
In the second part of this work, grafted polyethersulfone (PES) powders were prepared via microwave (MW) assisted synthesis. This new method works by virtue of the polar and MW active nature of monomers such as MAA. These properties are reported for grafting to PES powder in this manner for the first time. Successful grafting was achieved in 7 minutes as compared to conventional heating methods with reaction times of a minimum of 4.5 hours having been reported. Furthermore, this method eliminates the use of solvents and catalysts, which can be toxic and expensive, requiring extensive washing steps that may be costly. This grafting was investigated by FTIR and XPS. Further characterization followed where scanning electron microscopy (SEM) showed reduced pore size after grafting. Contact angle measurements showed improved hydrophilicity as compared to the pristine PES membranes. Water uptake and permeation fluxes presented improvements with increasing DG. Enhanced protein rejection (up to...