Ultrafiltration membranes and methods of making
The present invention is an integral multilayered composite membrane having at least one ultrafiltration layer made by cocasting or sequentially casting a plurality of polymer solutions onto a support to form a multilayered liquid sheet and immersing the sheet into a liquid coagulation bath to effect phase separation and form a multilayered composite membrane having at least one ultrafiltration layer.
1. A process for forming a multilayered ultrafiltration membrane, said process comprising:
positioning a polymer solution applying apparatus having at least two dispensing outlets relative to a moving carrier surface;
supplying each dispensing outlet with a different polymer solution, wherein a first polymer solution has a critical solution temperature and a second polymer solution has either no critical solution temperature or a higher critical solution temperature than the first polymer solution;
applying the first and second polymer solutions with the polymer solution applying apparatus onto said moving carrier surface so as to create a multiple layer coating on said carrier surface, wherein said first and second polymer solutions are applied with essentially no time interval between successive polymer solutions being applied; and
subjecting said multiple layer coating to two phase separation processes such that the first polymer solution forms a first layer due to a phase change caused by a change in the temperature outside of the critical solution temperature of the first polymer solution and the second polymer solution forms a second layer due to a phase change caused by either a change in the temperature outside of the critical solution temperature of the second polymer solution or immersion into a precipitation bath, so as to form a multilayer ultrafiltration membrane in which particles having a 20 to 100 nanometer (nm) diameter are retained.
2. The process of claim 1 , wherein the first layer is a skinned asymmetric ultrafiltration membrane layer in which particles having a 20 to 100 nanometer (nm) diameter are retained and the second layer is an asymmetric ultrafiltration membrane layer in which particles having a 20 to 100 nanometer (nm) diameter are retained.
3. The process of claim 2 , wherein the first ultrafiltration membrane layer has a molecular weight cutoff rating (MWCO) higher than the second ultrafiltration membrane layer.
4. The process of claim 1 , wherein the first layer is a microporous membrane layer in which particles larger than 0.1 μm are retained, and the second layer is an asymmetric ultrafiltration membrane layer in which particles having a 20 to 100 nanometer (nm) diameter are retained.
5. The process of claim 1 , wherein the first and second layers are formed of polyethersulfone.
6. The process of claim 1 , wherein the second layer is made from a polymer solution having no critical solution temperature.
7. The process of claim 1 , wherein the second layer is made from a polymer solution having a higher critical solution temperature than the first polymer solution.
8. The process of claim 1 , wherein the first polymer solution has a critical solution temperature lower than that of the second polymer solution.
9. The process of claim 8 , wherein said subjecting comprises heating the multiple layer coating to a temperature above the critical solution temperature of the first polymer solution but below the critical solution temperature of the second polymer solution.
10. The process of claim 8 , wherein said subjecting comprises heating the second polymer solution to a temperature above the critical solution temperature of the second polymer solution.
11. The process of claim 8 , wherein said subjecting comprises heating the multiple layer coating to a temperature above the critical solution temperature of the first polymer solution but below the critical solution temperature of the second polymer solution, wherein the second polymer solution phase separates by immersion into the precipitation bath.
12. The process of claim 9 , wherein said heating is carried out with a heated surface selected from the group consisting of a rotating drum, a rod, a plate, and a block.
13. The process of claim 1 , wherein said applying the first and second polymer solutions is carried out by a premetered coating process.
14. The process of claim 13 , wherein said applying is carried out with a double knife box or double slot die.
15. The process of claim 1 , wherein said applying the first and second polymer solutions is carried out by a postmetered coating process.
16. The process of claim 1 , wherein the ultrafiltration membrane has pores sized to retain a parvo virus.