Membrane and the use thereof

• US 20040020853A1
• Filed: 08/18/2003
• Published: 02/05/2004
• Est. Priority Date: 07/08/2000
• Status: Active Grant

• Current Assignee: University of Twente
• Original Assignee: University of Twente
• Inventors: Krause, Bernd, Strahtmann, Heiner, Mohlenkamp, Christel, Sijbesma, Hylke, Wessling, Matthias
• Granted Patent: US 7,306,754 B2
• Time in Patent Office: Days
• US Class Current: 210/650
• CPC Class Codes: B01D 2323/08 Specific temperatures applied
• CPC Class Codes: B01D 2323/081 Heating
• CPC Class Codes: B01D 2323/10 Specific pressure applied
• CPC Class Codes: B01D 67/0002 Organic membrane manufacture
• CPC Class Codes: B01D 67/0023 by inducing porosity into non porous precursor membranes
• CPC Class Codes: B01D 69/02 characterised by their properties
• CPC Class Codes: B01D 69/08 Hollow fibre membranes manufacture of hollow fibres D01D5/24, D01F1/08
• CPC Class Codes: B01D 71/64 Polyimides; Polyamide-imides; Polyester-imides; Polyamide acids or similar polyimide precursors
• CPC Class Codes: B01D 71/643 Polyether-imides
• CPC Class Codes: B01D 71/68 Polysulfones; Polyethersulfones
• CPC Class Codes: B29C 44/3403 Foaming under special conditions, e.g. in sub-atmospheric pressure, in or on a liquid

Abstract

The invention relates to a membrane that consists of a polymer or a polymer mixture. The aim of the invention is to produce membranes, especially planar membranes or hollow fiber membranes that have an as high a separation efficiency as possible while simultaneously having a high membrane efficiency. To this end, the membrane has a gas- or liquid-permeable bicontinuous foam structure with orifices in the interior whose diameters do not exceed 500 nm.

Claims

1. A membrane consisting of a polymer or polymer mixture, characterized in that it has a gas- or fluid-permeable bicontinuous foam structure with internal openings with a diameter of less than 500 nm.

2. A membrane according to claim 1, characterized in that the diameter of the internal openings in the foam structure is less than 250 nm, preferably less than 200 nm.

12. A membrane according to one of claims 1 to 11, characterized in that it consists of a polyimide, polyetherimide or polyethersulphone or a polymer mixture containing at least 20% of at least one of said polymers.

13. A membrane according to one of claims 1 to 12, characterized in that it is in the form of a flat or hollow fibre membrane.

14. Use of a membrane according to one of claims 1 to 13 for medical purposes, in particular for haemodialysis, haemofiltration, haemodiafiltration, plasmapheresis, immunotherapy, micro- or ultrafiltration or for gas separation.

3. A membrane that can be produced by forming a polymer or polymer mixture into the desired form, charging with a gas at a pressure that is above atmospheric pressure prior to or after forming, and in which the gas-charged polymer or polymer mixture is then foamed at a temperature that is above the glass transition temperature of the polymer/gas mixture and then the foam structure is stabilized, characterized in that the gas-charged polymer or polymer mixture is foamed at a gas concentration in the polymer or polymer mixture that is above a critical concentration and at a temperature that is lower than a critical temperature.

4. A membrane according to claim 3, characterized in that the temperature is at least 10°

C. below the critical temperature.

5. A membrane according to claim 3 or claim 4, characterized in that foaming is carried out above the critical concentration, which is at least 40, preferably at least 43, more preferably at least 45, in particular at least 47 cm³ (STP)/cm³ of polymer or polymer mixture.

6. A membrane according to one of claims 3 to 5, characterized in that it consists of an amorphous or semi-crystalline polymer or polymer mixture.

7. A membrane according to one of claims 3 to 6, characterized in that after forming, the polymer or polymer mixture is charged with the gas at a temperature that is less than the glass transition temperature of the polymer/gas mixture, and then the temperature is raised above the glass transition temperature of the polymer/gas mixture but below the critical temperature of the polymer/gas mixture.

8. A membrane according to one of claims 3 to 6, characterized in that after forming, the gas is charged at a temperature that is higher than the glass transition temperature of the polymer/gas mixture but less than the critical temperature of the polymer/gas mixture, and is then foamed by pressure release.

9. A membrane according to one of claims 3 to 6, characterized in that prior to forming, a melt of polymer or polymer mixture is charged with the gas in an extrusion tool and is foamed, by exit pressure release on exiting the extruder, at a temperature that is above the glass transition temperature of the polymer/gas mixture but less than the critical temperature.

10. A membrane according to one of claims 3 to 9, characterized in that carbon dioxide is used as the charging gas.

11. A membrane according to one of claims 3 to 10, characterized in that the foam structure is stabilized after foaming by quenching, preferably in an ethanol/water mixture.