Thermally Induced Phase Separation (TIPS)

In the first stage the polymer of choice is molten and fed into an extruder. The molten polymer is conveyed to a special mixer together with a solvent/non-solvent mixture. This solvent/non-solvent mixture must be selected so that the polymer is dissolved only above a certain temperature, but that there is no solubility of the polymer at lower temperatures. By intensive mixing of the molten polymer and the solvent/non-solvent mixture at an elevated temperature a homogenous solution is formed.

This hot solution is then extruded through a slit die (to form a flat sheet) or a spinneret (to form a hollow-fiber). After the forming step, the extruded melt-blend passes through an air gap and is cooled, either in a quenching bath or on a chill roll. In this step, the solution is cooled down below the dissolving temperature, which leads to a thermally induced phase separation and thus formation of polymer-rich and solvent-rich phase, which finally enables the solidification of the polymer-rich phase.

After solidification the solvent-rich phase is embedded in the rigid polymer matrix. This polymer matrix is the microporous structure of the membrane while the pores are filled with the solvent-rich phase. The solvent-rich phase is extracted with large amounts of a suitable liquid. The membrane is then dried and wound for packaging.