Chemical Engineering and Chemical Technology, Imperial College London
Doi
Abstract
In water filtration processes, the employment of polymeric membranes has become increasingly popular over the past few decades. However, the application of membrane processes is often limited due to the low fluxes and membrane failures caused by fouling and low membrane durability, which eventually leads to high operating costs in comparison with conventional processes. These limitations could be overcome by the development of high performance membranes with enhanced properties through a cost effective method.
This thesis explores the preparation of high performance poly(vinylidene fluoride) (PVDF) membranes with the use of inorganic silica particles via a conventional immersion precipitation method and from an amphiphilic graft copolymer. A technique to improve the performance of PVDF membranes fabricated via immersion precipitation has been developed, which involves using inorganic silica (SiO2) particles during the preparation of the dope solution, followed by subsequent acid or alkaline treatments of the resultant membranes. By removing the SiO2 particles from the membrane substrates using either an acid or alkaline treatment, the resultant membranes exhibit an interconnected porous structure accompanied by a significant improvement in the water permeability. Due to the poor mechanical strength demonstrated by the NaOH treated membranes, detailed investigations of the stability of PVDF membranes in NaOH solutions are carried out on hollow fibre membranes prepared from different raw materials. Hollow fibre membranes exhibit different degrees of chemical degradation upon exposure to a sodium hydroxide solution under various conditions. Also, a simplified method has been developed as a cost effective way for the preparation of PVDF membranes with improved hydrophilicity, fouling resistance and water permeability from the amphiphilic graft copolymer, PVDF-g-PEGMA, which has a PVDF backbone and poly(ethylene glycol) methyl ether methacrylate (PEGMA) side chains. By eliminating three common steps involved during the conventional preparation method, the use of chemicals and energy can be substantially reduced
