Geometric Factors in the Formation of Impregnated Electrospun Nanofibrous Membranes for Enthalpy Exchanger Applications

Membranes with high water vapour permeance and selectivity are of interest in many end uses including protective clothing, dehydration, and humidification. One interesting application for water vapour transport membranes is in energy recovery ventilators (ERVs) for buildings. These devices improve building energy efficiency by transporting heat and moisture between incoming and outgoing air streams in building ventilation systems, effectively ‘recycling’ the energy utilized to condition the indoor air. Membranes for these devices must have high vapour permeance, and be selective for water vapour over other gases, VOCs, and contaminants that may be present in the outgoing indoor air.  Due to the high rates of water vapour transport required in these gas to gas devices, boundary layer and internal resistances within the membrane contribute significantly to performance. Commercially available membranes suffer from high water vapour transport resistance in their supportive microporous substrate layers. In this study we report the fabrication of novel impregnated electrospun nanofibrous membranes (IENM) for water vapour transport applications. Electrospun nanofiber layers are impregnated with a polyether-polyurethane solution and cured to create continuous thin impregnated fiber loaded film layers which are bound to a non-woven support layer. These membranes have high water vapour permeance and selectivity while eliminating the requirement for a microporous support layer which has high vapour transport resistance. Here we report studies on how controllable factors in the membrane fabrication (namely fiber loading and impregnated solution polymer solids concentration) affect structural and permeation properties of IENMs created. Methods to produce membranes with improved water vapour permeance (>10000 GPU) and acceptable selectivity of water vapour of oxygen are (>100) identified. We show that the nanofiber loading has a significant impact on water vapour permeability as the membrane thickness decreases, and the effect of nanofibre diameter on structural and permeation properties is discussed. We also discuss the transport of volatile organic compounds through these membranes and potential benefits of nanofibrous membranes over other membranes for this application.