Asymmetric Hollow Fibre Membrane Production using the Nonsolvent Induced Phase Separation Method

Abstract

Asymmetric hollow fibre (HF) membranes are widely used in various applications such as ultrafiltration, microfiltration, gas separation, and reverse osmosis. These membranes offer several advantages, including a larger surface area and separation area due to their unique geometry, relatively high mechanical stability, and ease of handling and usage. The HF membranes investigated in this work were fabricated using the nonsolvent-induced phase separation (NIPS) method. The NIPS process involves the interaction of multiple components, typically three, including a chosen dope polymer, solvent, and any desired additives, forming a homogeneous solution known as the dope solution. This solution undergoes phase separation with a specific geometry determined by the type of spinneret used when exposed to a nonsolvent, commonly water. As the polymer is immiscible in water, diffusion occurs, initiating phase separation and ultimately leading to membrane formation. In this work, polyethersulfone (PES) and N-methyl-2-pyrrolidone (NMP) were utilized to produce the dope solution, and deionized water was used as the nonsolvent bore fluid. This work thoroughly investigates the practical aspects of spinning fibres and the determination of their properties. Various characterization techniques, including scanning electron microscopy, rheometry, porosity tests, and tensile testing, are utilized. The central focus of this work is the NIPS modular plant, which encompasses the entire process of fabrication of HF membranes - from dope production to spinning and preparing modules for testing. Comprehensive documentation of this process is essential for addressing future research endeavours. Specific parameters such as air gap length, PES concentration in the dope, dope viscosity, spinneret and dope temperature, NMP composition in the bore fluid, coagulation bath temperature, additives, and flow rates of dope and bore fluid have been selected and their impact on fibre morphology, UF performance, and mechanical stability have been analysed. The results largely align with existing literature, indicating the necessity for further optimization and operation of the NIPS plant to produce desired and favourable asymmetric hollow fibres.