Polydopamine Modified PVDF Nanofibers Supported Thin Film Composite Membranes for Osmotically Driven Membrane Processes

Polydopamine modified PVDF nanofibers supported thin film composite membranes for osmotically driven membrane processes

Malgorzata Chwatko, Jason T. Arena, Liwei Huang, Jeffrey R. McCutcheon

One key area of research in the development of osmotically driven membrane processes (ODMPs) is the development of new membranes. Though viable commercial membranes have been featured in industrial processes [1], few membranes such as the cellulose triacetate and thin film composite forward osmosis (FO) membranes manufactured by Hydration Technology Innovations are available for study. All of the membranes used industrially are built from wet-dry cast cellulose acetate or thin film composite structures. 

Thin film composite (TFC) membranes, comprising the newest generation of membranes for ODMPs, are composed of a three-tiered structure, with a very thin selective layer on top of a support layer and lastly backing layer. This design offers high flexibility of optimizing the selective and support independently. A new membrane platform which has gained interest in recent years expands upon the classical thin film composite structure, but replaces the normal phase-inverted polymer support with one prepared via the electrospinning technique. Electrospun supports characteristically have a highly porous and interconnected pore structure. Some of the most recent work on nanofiber support membranes was done by Huang and McCutcheon using hydrophilic Nylon 6,6 nanofiber support and identified a unique swelling behavior which hindered performance [2]. Hydrophobic materials have reduced interaction with water and as a result have a tendency for less swelling. One such polymer recently reported on by Tian, et al. used a polyvinylidene fluoride (PVDF) support in their preparation new membrane for FO [3].

The membrane prepared in this work expands on this approach by also using electrospun PVDF nanofibers as a support of an interfacial polymerized TFC membrane. Here seeking to address a limitation of hydrophobic supports identified in work by McCutcheon, et al. that observed the importance of support layer hydrophobicity and the resulting lack of support layer wetting which dramatically impairs water flux due to severe internal concentration polarization [4].  Work later done by Arena, et al. hydrophilized the hydrophobic supports by applying polydopamine (PDA) to the surface of commercial TFC membranes. Modified membranes illustrated significant improvements in water flux following PDA modification [5, 6].  The work presented here will detail the preparation and performance of the PVDF supported TFC membrane, which have had a hydrophilic character imparted to them through the addition of PDA to the surfaces of the PVDF support layer combining the mass transport advantages of a nanofiber support, the low swelling propensity of a hydrophobic support and thanks to the PDA modification a hydrophilic character essential for good performance in osmotically driven membrane processes.

Figure 1: Scanning electron micrograph a cross-section of the PVDF membrane support

Works Cited:

[1] McGinnis RL, Hancock NT, Nowosielski-Slepowron MS, McGurgan GD. Pilot demonstration of the NH₃/CO₂ forward osmosis desalination process on high salinity brines. Desalination (2013) 312: pp. 67-74

[2] Huang L, McCutcheon JR. Hydrophilic nylon 6,6 nanofibers supported thin film composite membranes for engineered osmosis. Journal of Membrane Science (2014) 457: pp. 162-169

[3] Tian M, Qiu C, Liao Y, Chou S, Wang R. Preparation of polyamide thin film composite forward osmosis membranes using electrospun polyvinylidene fluoride (PVDF) nanofibers as substrates. Separation and Purification Technology (2013) 118: pp. 727-736

[4] McCutcheon JR & Elimelech M. Influence of membrane support layer hydrophobicity on water flux in osmotically driven membrane processes. Journal of Membrane Science (2008) 318: pp. 458-466

[5] Arena JT, McCloskey BD, Freeman BD & McCutcheon JR. Surface modification of thin film composite membrane support layers with polydopamine: enabling use of reverse osmosis membranes in pressure retarded osmosis. Journal of Membrane Science (2011) 375: pp. 55-62.

[6] Arena JT, Manickam SS, Reimund KK, Freeman BD & McCutcheon JR. Solute and water transport in forward osmosis using polydopamine modified thin film composite membranes. Desalination (2014) 343: pp. 8-16.