TIPS is the abbreviation for Thermally Induced Phase Separation in which the membrane formation is induced by cooling the polymer solution. In particular, the TIPS process is applied to polymers which are inaccessible to the SIPS process, because of their poor solubility, and to very polar as well as non-polar polymers.
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.
Commercial microporous membranes formed by a TIPS process are used in medical as well as in industrial applications.
Typical medical applications for capillary membranes produced via a TIPS process are oxygenation and plasma separation.
TIPS membranes are used for filtration and pre-filtration of various process solutions in the semiconductor and microelectronics industry.
Food & Beverage
TIPS membranes are used for filtration and clarification of beverages. Sterile filtrations to extend the shelf life of beverages are also possible with SIPS membranes.
Hydrophobic TIPS membranes are excellent for the removal of gases from liquids, e.g. for the production of ultra-pure and gas-free water and for the controlled addition of gases to liquids.