SIPS is the abbreviation for Solvent Induced Phase Separation technology in which membrane formation is created by the interaction between solvent and non-solvent.
The polymer is dissolved in a mixture of solvents and pumped through a ring-shaped spinneret. In the centre of the ring a bore liquid also exits the spinneret. The bore liquid prevents the ring shaped polymer solution from collapsing to a solid fibre and thus creates the lumen. The polymer solution is spun into the precipitation bath, which is mainly composed of a non-solvent to the polymer. The solvent diffuses out into the precipitation bath and the non-solvent into the polymer solution. This causes the polymer to re-solidify and thus a membrane is formed.
After solidification, the membrane passes several pre-extraction steps (see figure below) and a membrane make-up step like undulation and addition of spacer yarns. Thereafter, it is wrapped into a foil that later aids the incorporation of the membrane bundles into the housing. In a multi-step extraction, the solvent residuals are removed and the membrane is dried and finally packed for delivery.
For flat-sheet production, the polymer solution is not pumped through a spinneret, but cast through a well defined slit onto a chill roll. Like in capillary production, membrane formation takes place when the polymer solidifies inside the precipitation bath. The flat-sheet membrane is then pre-extracted, washed and subjected to stretching, relaxation and post-treatment, before it is cut and packed.
Commercial porous membranes formed by SIPS are used both in medical and industrial separation.
Typical medical applications for capillary membranes produced via SIPS technique are e.g. haemodialysis and plasma separation.