Fabrication of polyelectrolyte complex membranes

  • Herstellung von Polyelektrolytkomplex-Membranen

Emonds, Stephan Christian; Wessling, Matthias (Thesis advisor); de Vos, Wiebe (Thesis advisor)

Aachen : Aachener Verfahrenstechnik (2022)
Book, Dissertation / PhD Thesis

In: Aachener Verfahrenstechnik Series - AVT.CVT - Chemical Process Engineering 28 (2022)
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

Polyelectrolyte complexes are a promising material platform technology for the formation of the separation layer of nanofiltration membranes. In this thesis, different approaches to fabricate polyelectrolyte complex hollow fiber nanofiltration membranes in a single step are developed. The polyamide based state of the art membrane synthesis has not overcome the boundaries of hollow fiber nanofiltration membrane production. Polyelectrolytes have been used to create nanofiltration hollow fiber membranes recently via the "Layer-by-Layer" approach. However, this technique contains elaborate multi-step post-treatment processes. Furthermore, the fabrication relies on the use of organic solvents and toxic cross-linkers, which are harmful to human health and the environment. The use of such components will be restricted by regulations in the future. In the first part of this thesis, the established phase separation of the base polymer polyethersulfone is therefore superimposed by polyelectrolyte adsorption during the hollow fiber manufacturing process. The combination of ionic and covalent cross-linking with the phase inversion process is successfully conducted in a robust single step hollow fiber membrane fabrication process. The produced polyelectrolyte composite hollow fiber nanofiltration membranes feature high salt retentions and a low molecular weight cut-off which categorizes them as nanofiltration membranes. Subsequently, this single step fabrication approach is complemented with an additional fiber modification within the hollow fiber membrane manufacturing process. By this streamlined approach, open and dense nanofiltration hollow fiber membranes are achieved. In the second part of this thesis, membranes are produced by solely polyelectrolytes forming a freestanding polyelectrolyte membrane via an all aqueous phase separation process. Two oppositely charged strong polyelectrolytes are dissolved in an aqueous medium at an overcritical salt concentration, which suppresses the polyelectrolyte complexation. Through immersion of the polymer solution in a coagulation water bath, phase separation is induced by salt dilution and a porous polyelectrolyte complex membrane forms. This novel all aqueous fabrication shows a similar phase inversion behavior compared to the established non solvent induced phase separation method and therefore promises a high potential of knowledge transfer. This approach is applied for the first time in the dry-jet wet spinning process. Suitable process parameters are developed and tubular polyelectrolyte complex nanofiltration membranes are successfully fabricated. Overall, the polyelectrolyte material platform allows the single step fabrication of polyelectrolyte composite and freestanding hollow fiber nanofiltration membranes. Moreover, the all aqueous phase separation approach has a high potential to establish a sustainable and non-toxic membrane fabrication.

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