INDUCED Die-Swell and FLOW STABILITY Behavior of Hyperbranched Polyether Sulfone (HPES) Hollow Fiber Spinning PROCESS Via Variation of Spinneret CHANNEL Designs and Spinning Conditions

The recent study on the molten hyperbranched polyethersulfone (HPES) and linear polyethersulfone (LPES) materials supplied by BASF show that HPES has a larger molecular weight and a wider molecular weight distribution compared to its linear analogue. Furthermore, the rheological characterization reveals that the HPES dope solution has a longer relaxation time than its linear counterpart. Hence, the HPES nascent fiber shows a more pronounced die swell and flow instability occurring at the spinneret exit. In this regard, our objective is to overcome the die-swell and flow instability problems when fabricating HPES hollow fiber membranes. Clearly, the flow behavior and shear rate inside the spinneret's channel significantly affect the hollow fiber membrane formation. Therefore, other than our common spinneret with L (length)/D (diameter)~10, we have fabricated various spinnerets with modified exit channel to overcome the aforementioned problem. The effects of modified spinnerets and spinning parameters on the die swell, flow stability, and performance of hollow fiber membranes will be elaborated in details. This work also reveals the die-swell and flow behavior differences between HPES and LPES membranes spun using various spinneret designs based on the comprehensive explorations and fundamental understandings of these two polymer analogues properties.