(725b) Electrospun Pretreatment Membranes

Approximately 96.5% of Earth’s water is found in the seas and oceans, 1.7% in the ice caps, 0.8% considered as fresh waters and the remaining percentage consists of brackish water, slightly salty water found as groundwater in aquifers and as surface water in estuaries.¹ Water shortages due to growing industrialization and urbanization has existed for a long time, and there arises a dire need to convert saltwater into potable water. Today, the demand for potable water exceeds the conventional available water resources and its production has become a worldwide concern. Recently, researchers have underlined reverse osmosis (RO) as the most optimized technology for gaining access to clean water and meet global demands^.2RO is an energy intensive process and often RO membranes are susceptible to fouling and scaling that drives up operational cost and hinder the efficiency. To increase the performance of RO membranes the feed water is pretreated to remove pollutants before desalination. This work aims to fabricate pretreatment membranes to prevent the effects of fouling and scaling by introducing hydrophilic character to membrane surface.

This work explores electrospinning, a cost-effective and scalable technique, to blend two polymers into a nonwoven membrane comprised of fibers ~100 nm – 100 µm in diameter. A rotary drum collector holding the mat simultaneously collects the hydrophobic poly(vinyl chloride) and hydrophilic poly(vinyl alcohol) (PVA) fibers being electrospun from two separate solutions. The work aims to tune the hydrophilicity of the resulting membrane by controlling the relative deposition rate of PVA onto the mat. After electrospinning, the mats are cross-linked with a poly(ethylene glycol) diacid to impart mechanical strength and tune the porosity. It was found that the pore size of the membrane mats varied from 500 nm to 80 nm when the concentration of the crosslinker was reduced. Fiber morphologies were characterized by scanning electron microscopy and the elemental composition across the membrane was mapped by energy dispersive X-ray spectroscopy. Additionally, membrane characterization tests (e.g., differential scanning calorimetry, thermogravimetric analysis, and Fourier-transform infrared spectroscopy) confirmed the presence of both polymers on the mat. A rigorous analysis method was developed combining the above results to estimate mass deposition rate, relative concentration of both polymers on the mat, and correlate PVA concentration with hydrophilic character.

References:

1. Greenlee, L. F., Lawler, D. F., Freeman, B. D., Marrot, B., Moulin, P., & Ce, P. (2009). Reverse osmosis desalination: Water sources, technology, and today’s challenges. Water Research, 43(9), 2317–2348. https://doi.org/10.1016/j.watres.2009.03.010
2. Lee, K. P., Arnot, T. C., & Mattia, D. (2011). A review of reverse osmosis membrane materials for desalination-Development to date and future potential. Journal of Membrane Science, 370(1–2), 1–22. https://doi.org/10.1016/j.memsci.2010.12.036