Effect of mass transfer at the interface of the polymer solution and extruded solvent during the air gap on membrane structures and performances in TIPS process using triple-orifice spinneret
Chuanjie Fang, Saeid Rajabzadeh, Hao-Chen Wu, Xinyu Zhang, Noriaki Kato, Misato Kunimatsu, Tomohisa Yoshioka, Hideto Matsuyama
Journal of Membrane Science
In this study, a combination of experimental results and molecular dynamics (MD) simulation was employed to understand the mass transfer between the extruded solvent and polymer solution by using a triple-orifice spinneret in the thermally induced phase separation (TIPS) process. Extruding solvent at the outer layer of the extruded polymer solution with different air gap distances controlled the mass transfer before phase separation. The progressive change in the phase separation mechanism, from the liquid-liquid to the solid-liquid induced by mass transfer, played a determined role in tailoring the composite-like structure. The moving of polymer or diluent from the bulk solution to the contact interface changed the polymer surface concentration and subsequently affected the membrane surface pore structure. The MD calculation results elucidated the mass transfer of the solvent and the polymer solution, which drastically affected the membrane structure. The formed spherulite-embedded bicontinuous structure clearly improved the membrane water permeation stability from 52 to 98%. On the other hand, by altering the air gap distances, the membrane water permeation flux enhanced in a wide range from 266 to 1429 L m−2 h−1 bar−1. A new relationship between permeation flux and permeation stability was obtained, which can be utilized as a guideline for the engineering of hollow fiber membranes with high and stable permeability in the TIPS process.
Probe Raman, Thermally induced phase separation, PVDF hollow fiber membrane, Triple-orifice spinneret, Extruded solvent, Structure and performance