Effects of Compaction and Intercalation on the Mechanical Properties of Reduced Graphene Oxide Nanofiltration Membranes

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Shial, Keya
Shofner, Meisha L.
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Water. Covering almost two-thirds of the planet it is required by all species, but the ratio of applicable to available water is small. Reduce, reuse, recycle have been repeated countless times, but to create a sustainable future, change must occur on a larger platform than day-to-day civilian activities. As such, the world has slowly but surely entered a more sustainability-centered stage, as the need to make industrial processes more efficient and less wasteful has become a priority. A specific industrial process where a high energy and water input is required to refine essential products is in the petroleum industry. Specifically, a thermal refinement process is used for refining effluent streams from crude desalting units rather than filtration processes which typically use polymer membranes. Recent developments in graphene oxide (GO) membranes show the feasibility and scalability of GO-based membranes for sustaining the more complicated petroleum industry water resource problems. As GO-based membranes are considered for use in industrial applications, it is important to define their processing-structure-property relationships beyond their performance in separations. Therefore, the motivation of this project is to understand the mechanical properties of reduced GO membranes under different processing conditions with PES and PVDF – both polymers have previously been used for filtration membranes – polymer supports to develop a baseline understanding of properties and establish effective testing methods. For this project, tensile, nanoindentation, peel, and fragmentation test methods were evaluated from a combination of standards to create consistent procedures for collecting data on mechanical (Young’s modulus, yield and tensile stresses, elongation, and hardness) and adhesive (interlayer shear stress) properties. This data was then analyzed to identify trends due to compaction and intercalation as well as potential structure- property relations to explain trends. It was determined that the properties of PVDF exceed those of PES except for reduced Young’s modulus. Compaction affects the mechanical properties and the microstructure of polymer supports differently, while increasing adhesion between rGO-polymer membranes. Interfacial shear strength of rGO-PES membranes is stronger than that of rGO-PVDF membranes. Addition of rGO increased, or did not significantly change, any properties on either polymer support. Intercalation overall decreases most tensile properties, suggesting that the formation of TBO dimers adds to the ductility of the membrane. Nanoindentation trends suggest tunability but could be due to potential spatial variations due to membrane fabrication.
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