Composite membranes and methods for making such membranes

1. A method for making a flexible membrane having a polymeric matrix and a particulate material immobilized within said matrix, said method comprising:

providing a support having a first substantially flat surface and a second substantially flat surface;

combining at least a polymer and a selected quantity of particulate material to form a blend;

applying a substantially uniform thickness of said blend to each of said surfaces; and

advancing said support with said blend applied thereon into at least one treatment bath at a rate of approximately 1-4 ft./min.

2. The method of claim 1 wherein said polymer is selected from the group consisting of polyurethane, polyvinylidenefluoride, cellulose acetate and polyvinyl chloride.

3. The method of claim 1 wherein said polymer is hydrophobic.

4. The method of claim 1 comprising selectively distributing said particulate material within said membrane.

5. The method of claim 1 wherein said membrane comprises between 5% and 30% of said polymer and 70-95% of particulate.

6. The method of claim 1 wherein said membrane comprises at least 50% by weight of said particulate material.

7. The method of claim 1 comprising dissolving said polymer in an organic solvent to provide a polymer solution prior to combining said polymer with said particulate material.

8. The method of claim 1 further comprising contacting said support with said blend applied thereon with a liquid that is a non-solvent for said polymer by immersing said support in a bath of said liquid for a selected period of time after said applying step.

9. The method of claim 8 wherein said support with said blend applied thereon is alternately immersed in and removed from one or more water baths.

10. The method of claim 9 further comprising drying said membrane.

11. The method of claim 10 further comprising cutting said membrane to a desired size and sealing at least one edge of said membrane.

12. The method of claim 1 wherein said blend is applied to a moving sheet of said support continuously.

13. The method of claim 10 comprising drying said membrane for at least 10 minutes at 50° C.

14. The method of claim 1 , 3 or 13 further comprising treating said membrane with a wetting agent or hydrophilizing coating agent.

15. The method of claim 14 wherein said agent comprises between 0.20% and 1% polyvinyl alcohol.

16. The method of claim 14 wherein said agent comprises glycerol.

17. The method of claim 14 wherein said agent comprises sodium chloride.

18. The method of claim 17 wherein said agent comprises 0.9% sodium chloride.

19. The method of claim 14 further comprising drying said membrane after said treating.

20. The method of claim 1 further comprising introducing said support into a housing containing said blend in the step of applying the blend to said support.

21. The method of claim 20 comprising substantially excluding particles of said particulate material having a diameter greater than about 20 μM.

22. The method of claim 1 further comprising contouring said membrane into a pleated sheet.

23. The method of claim 1 further comprising contouring said membrane into a rippled sheet.

24. The method of claim 1 wherein said polymer comprises either

a) at least two polymers or

b) at least two copolymers or

c) at least a polymer and copolymer.