Fabrication of membranes for separation techniques using engineering plastics

Abstract

The aim of this Ph.D project was to develop and fabricate membranes for separation techniques using engineering plastics that could play a key role in membrane based water treatment processes. The prime objective was to investigate the economic and technological solution so that the desalination properties including permeation flux could be improved. The dissolution casting methodology was adopted for engineering plastic membranes via three (03) membrane systems which accounted the explicit application for desalination process. System one (01) used the novel thin film poly (vinyl alcohol)/chitosan (PVA/CS) based reverse osmosis membranes infused with silane crosslinked tetraethylorthosilicate (TEOS), prepared by dissolution casting methodology. The performance characteristics and the scope of the reverse osmosis membranes were explicated by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyzer (TGA), differential scanning calorimetery (DSC), scanning electron microscopy (SEM), contact angle, X-ray diffraction (XRD) and reverse osmosis (RO) permeation tests which determined the functional groups and network of covalent crosslinks, thermal properties, morphology, hydrophilicity, structural investigation and RO properties, respectively. It was found that the membrane surface became smoother, more hydrophilic, with improved thermal stability, increased salt rejection and good permeation flux after the appropriate infusion of TEOS. The crosslinked membranes showed more hydrophilicity compared to the un-crosslinked PVCS membrane. The SEM micrographs of membranes revealed dense structure with no mottled surfaces. PVCS-4 showed an optimal flux of 1.84L/m2h and 80% salt rejection that confirmed the selective interaction of TEOS molecules with PVA/CS polymer backbone compared to the pristine (PVCS) membrane. The antibacterial properties of the membranes showed the inhibition of the growth of Escherichia coli successfully. In the second (02) system, cellulose acetate (CA) based thin film nanocomposite reverse osmosis (RO) membranes were fabricated using dissolution casting method by optimizing the CA/polyethylene glycol (CA/PEG-400) ratios for improved RO performance. The selectivity of optimized membrane was further enhanced by incorporating TiO2 (0-25 wt.%) nanoparticles. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyzer (TGA), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were conducted to characterize control and modified membranes for the analysis of functional groups, thermal properties, morphology and structural investigation respectively. CP-2 of CA/PEG-400 (80/20) was selected for further modification with TiO2 nanoparticles. The maximum salt 2

rejection (95.4 %) was observed for the membrane having 15 % TiO2 nanoparticles. Further escalation of TiO2 concentration resulted in the agglomeration of nanoparticles which subsequently decreased the permeation flux. The test results demonstrated that the modified membranes had higher salt rejection and chlorine resistance, lower degradation profile, successful inhibition of Escherichia coli growth and facilitating permeation flux compared to the control membrane. In system (03) the membrane separation technique has been applied for the separation of MgSO4 from sea water. In this work, a series of novel cellulose acetate membranes were prepared via blending with different concentration of HNTs and irradiated grafted with VGCNFs. The morphology and topography of the VGCNF membranes were observed using SEM and AFM respectively, which indicated the improved membrane structure, dispersity and surface roughness in the polymer matrix. The experimental data demonstrated that VGCNF grafted membranes has improved permeation flux 48 L/m2.h and MgSO4 salt rejection 98.6% compared to the control membrane. More importantly the thermal stability by TGA revealed that VGCNF4 showed enhanced stability compared to the control membrane. As a result, this study could provide a great potential for the removal of salts from sea water.