Electrospun nanofibrous membranes for water vapour transport applications

Abstract

This study discusses the development of selective water vapour permeable membranes for the separation of water vapour from air. These membranes are useful as separation media for membrane-based energy recovery ventilation devices. Current generation composite membranes for these devices consist of a polymer film layer which is permeable to water vapour but selective for water vapour over gases. In these composite membranes, this film layer is attached to one surface of a microporous polymeric support substrate. However, as it is demonstrated in this work, the microporous support contributes 30 to 50% of the resistance to water vapour transport in the composite membranes. In an attempt to eliminate this microporous substrate and its associated resistance, a membrane was developed using an electrospun nanofibrous layer as a support structure for the selective coating layer. In these membranes, the electrospun nanofibers are deposited on a non-woven micro-fibrous carrier and then the nanofibers are impregnated with a selectively permeable polymer to make impregnated electrospun nanofibrous membranes (IENM). The nanofibers are found to contribute a resistance to vapour transport in these membranes and their effect on water vapour permeability is quantified through a fiber-filled-film model. An optimization study of the IENMs demonstrated that fiber diameter and fiber volume in the film layer effect the water vapour permeance of these membranes and reducing these variables improved water vapour permeance. IEMNs were demonstrated to have water vapour permeance (>10000 GPU) while still having sufficient selectivity for the application, exceeding the performance of current generation composite membranes. The membranes were demonstrated to be particularly useful in the fabrication of ‘formable membranes’ which could be thermally-formed into exchanger plates for energy recovery ventilator exchangers. Thermal and mechanical properties of the membrane components were reported individually and as complete membranes. A membrane composition was demonstrated to fabricate exchanger plates from formable IENMs. This work contributes to the development of membranes for air-to-air exchangers specifically for energy recovery ventilation. A new class of membrane based on electrospun nanofibers for these devices was successfully demonstrated to have improved performance properties and a novel formable membrane was developed.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat