Shear rate effect on asymmetric kaolin-polyethersulfone hollow fibre membrane

Inorganic hollow fibre membrane is normally made from premium ceramics which is not easy to procure. Furthermore, the process of producing ceramic membrane requires the ceramic precursor to undergoes sintering process at high temperature. Thus, the cost of developing a ceramic membrane using experimental method is expensive. Kaolin have been identified as an alternative ceramic material while offering reasonable cost. However, knowledge on kaolin as base material for hollow fibre membrane are still in its infancy and much are not yet known. Thus, this study aims to produce asymmetrical Kaolin/Polyethersulfone (PESf) hollow fibre membrane with thin outer finger-like region by observing shear experience within the spinneret in relation to hollow fibre formation and morphology. The research work is executed in three phase; kaolin solution formulation, spinning and characterization, CFD simulation. Kaolin solutions formulated using Polyethersulfone (PESf) as binder and N-methyl-2-pyrrolidone (NMP) as solvent were rheologically assessed using a rotational viscometer to obtain the values of power law coefficients, n and k. These rheological data are then correlated with the characteristic of the hollow fibre membrane, essentially hollow fibre morphology and porosity. The shear rate inside the spinneret annulus is obtained using computational fluid dynamics (CFD) method. Rheology investigation shows that Kaolin suspension exhibits non-Newtonian behavior under the power law scheme. An increase in the Kaolin/PESf ratio further increases the viscous behavior of the non-Newtonian liquid. The power law coefficients for the Kaolin suspension were successfully determine and is used in the computational fluid dynamic analysis. Morphology study on spun hollow fibre shows asymmetric structure. The study also indicates that there is a strong link between extrusion shear to precipitation rate. It is found membrane spun at low shear experience of 109.55 s-1 have thin outer finger like region at 24% area ratio and porosity of 68%. Increasing the shear experience in the annulus outer wall; affects the apparent viscosity and ultimately causing the precipitation rate to increase and grows the outer finger-like region. At shear experience of 2155. 78 s-1, outer finger like region is at 48% and membrane porosity at 48%. This study established that rheology characteristic of the kaolin suspension plays an important role to the shear experience behavior in the spinneret annulus. Ultimately, correlation of the shear experience and hollow fibre morphology enable us to predict hollow fibre performance in the design process reducing the overall development cost