Rheological behavior of PES/PVP/DMAc solution and PVP structural regulation for hollow fiber membrane

Rheological study plays a significant role in hollow fiber membrane spinning process and membrane structure regulation. In this work, the rheological behaviors of polyethersulfone (PES) spinning solutions added the polyvinylpyrrolidone (grade of PVP-K30, PVP-K60, and PVP-K90) were systematically investigated by rotational rheometry to understand how the PES membrane structure changes. Results show that PVP of variable molecular weights change the rheological properties of PES spinning solution, such as the viscosity (eta(a)), non-Newtonian index (n), flow activation energy (E-eta), structural viscosity index ( increment eta), storage modulus (G '), and loss modulus (G ''). The mixture with PVP-K30 exhibits optimal spinnability but the finger-like membrane structure is undesirable for the hemodialysis. The rheological behaviors of PES/PVP-K60 and PES/PVP-K90 reveal that increasing shear rate and temperature are effective ways to improve the spinnability of the mixture and the membrane structure is regulated. Meanwhile, the addition of PVP-K60 or PVP-K90 at their critical concentration to the PES solution can fabricate a hollow membrane with a sponge-like structure. Combining spinnability and membrane structure, PVP-K90 is a suitable additive for the hemodialysis membrane.