Particle filter system incorporating nanofibers

• US 7,789,930 B2
• Filed: 11/13/2006
• Issued: 09/07/2010
• Est. Priority Date: 11/13/2006
• Status: Active Grant

• Current Assignee: Research Triangle Institute
• Original Assignee: Research Triangle Institute
• Inventors: Ensor, David S., Walker, Teri A., Andrady, Anthony L., Walls, Howard J.
• Primary Examiner(s): Marcheschi; Michael A
• Assistant Examiner(s): CLEMENTE, ROBERT ARTHUR
• Application Number:
  US11/559,282
• Publication Number:
  US 20080110342A1
• Time in Patent Office: 1,394 Days
• Field of Search: 554/86, 554/87, 555/24, 555/27, 555/28, 55D/IG.5, 555/02, 555/01, 442/401
• US Class Current: 55/527
• CPC Class Codes: B01D 2239/025 comprising nanofibres apparatus incorporating such gas filtering material see B01D46/546
• CPC Class Codes: B01D 39/1623 of synthetic origin
• CPC Class Codes: D01D 5/0076 characterised by the collecting device, e.g. drum, wheel, endless belt, plate or grid D01D5/0046 takes precedence
• CPC Class Codes: D01D 5/0092 characterised by the electrical field, e.g. combined with a magnetic fields, using biased or alternating fields
• CPC Class Codes: Y10S 55/05 Methods of making filter
• CPC Class Codes: Y10T 442/622 Microfiber is a composite fiber

Abstract

A filtration device including a filtration medium having a plurality of nanofibers of diameters less than 1 micron formed into a fiber mat in the presence of an abruptly varying electric field. The filtration device includes a support attached to the filtration medium and having openings for fluid flow therethrough. A device for making a filter material. The device includes an electrospinning element configured to electrospin a plurality of fibers from a tip of the electrospinning element, a collector opposed to the electrospinning element configured to collect electrospun fibers on a surface of the collector, and an electric field modulation device configured to abruptly vary an electric field at the collector at least once during electrospinning of the fibers. A method for making a filter material. The method provides a support having openings for fluid flow therethrough, electrospins nanofibers across an entirety of the openings, and abruptly varies an electric field at the collector at least once during electrospinning of the fibers.

Claims

1. A filtration device comprising:

a support having openings for fluid flow therethrough;

a filtration medium including a plurality of fibers attached to the support; and

said filtration medium having a figure of merit FoM=−

Log(Pt)/Δ

P,

where Pt is the fractional penetration of an aerosol particle diameter of 0.3 microns and Δ

P is a filtration medium pressure drop across the filtration medium corresponding to a face velocity of 5.3 cm/s, and

said figure of merit is greater than 20 kPa<sup>−

1</sup>.

2. The device of claim 1, wherein said support has a support pressure drop that is no more than 10-50% of said filtration medium pressure drop.

3. The device of claim 1, wherein said figure of merit is greater than 50 kPa⁻

1.

4. A fiber medium comprising:

a plurality of nanofibers having diameters less than 1 micron formed into a fiber mat in the presence of an asymmetric abruptly varying electric field; and

said fiber mat comprising at least one of a filter, a catalytic material source, a battery separator, a wound dressing, a tissue scaffold, a bioactive material source, an antibacterial material source, a textile item, and a sensor,

wherein the filtration medium has a figure of merit FoM=−

Log(Pt)/Δ

P,

where Pt is the fractional penetration of an aerosol particle diameter of 0.3 microns and Δ

P is a filtration medium pressure drop across the filtration medium corresponding to a face velocity of 5.3 cm/s, and

said figure of merit is greater than 20 kPa<sup>−

1</sup>.

5. The medium of claims 4, further comprising:

a support attached to the fiber mat.

6. The medium of claim 5, wherein the support is detachable from the fiber mat.

7. A filtration device comprising:

a filtration medium including a plurality of nanofibers having diameters less than 1 micron formed into a fiber mat in the presence of an asymmetric abruptly varying electric field; and

a support attached to the filtration medium and having openings for fluid flow therethrough,

wherein the filtration medium has a figure of merit FoM=−

Log(Pt)/Δ

P,

where Pt is the fractional penetration of an aerosol particle diameter of 0.3 microns and Δ

P is a filtration medium pressure drop across the filtration medium corresponding to a face velocity of 5.3 cm/s, and

said figure of merit is greater than 20 kPa<sup>−

1</sup>.

8. The device of claim 7, wherein said nanofibers are formed in the presence of a periodic discharge to ground producing the abruptly varying electric field.

9. The device of claim 7, wherein said nanofibers are formed in the presence of an applied electric field waveform producing the abruptly varying electric field.

10. The device of claim 7, further comprising:

a support attached to the filtration medium and having openings for fluid flow therethrough; and

a conductive support forming the openings.

11. The device of claim 7, wherein the support comprises:

at least one of a filter, a plastic foam, a metallic foam, a semi-conductive foam, a woven material, a nonwoven material, a plastic screen, a textile, and a high efficiency particulate air (HEPA) filter medium.

12. The device of claim 7, wherein the filter has a minimum efficiency reporting value (MERV) between 3 and 12.

13. The device of claim 7, wherein the support has at least one of a conical shape, a curved shape, a circular shape, a planar shape, a spherical shape, and a cylindrical shape, and combinations thereof.

14. The device of claim 7, further comprising:

a support attached to the filtration medium and having openings for fluid flow therethrough; and

wherein the support comprises multiple cellular frames arranged adjacent to each other.

15. The device of claim 14, wherein the multiple cellular frames include cylindrical cells.

16. The device of claim 7, wherein the nanofibers are integrally attached one to another at points along respective ones of the nanofibers.

17. The device of claim 7, wherein the nanofibers have an average fiber diameter of less than 500 nm.

18. The device of claim 7, wherein the nanofibers have an average fiber diameter of less than 200 nm.

19. The device of claim 7, further comprising:

a support attached to the filtration medium and having openings for fluid flow therethrough; and

wherein the nanofibers have an average fiber diameter of less than 100 nm.

20. The device of claim 7, wherein the filtration medium comprises plural layers of the nanofibers formed in the presence of the abruptly varying electric field.

21. The device of claim 20, wherein the plural layers comprise between 4 to 4000 layers of the nanofibers.

22. The device of claim 20, wherein the plural layers comprise between 10 to 100 layers of the nanofibers.

23. The device of claim 20, wherein the plural layers comprise a thickness between 0.25 and 500 μ

m.

24. The device of claim 7, wherein said support has a support pressure drop that is no more than 10-50% of said filtration medium pressure drop.

25. The device of claim 7, wherein said figure of merit is greater than 50 kPa⁻

1.

26. The device of claim 7, further comprising:

a support attached to the filtration medium and having openings for fluid flow therethrough; and

wherein the nanofibers comprises at least one of a pH degrading material, an enzyme degrading material, and a thermal degrading material.

27. The device of claim 7, further comprising:

a sealant disposed on a perimeter of the support to seal the fibers to the support.

28. The device of claim 7, wherein the support comprises a supplemental filtration medium.

29. The device of claim 28, wherein the supplemental filtration medium comprises a filter upon which said plurality of nanofibers was deposited in the presence of the abruptly varying electric field.

30. The device of claim 28, wherein the supplemental filtration layer provides filtration for particles larger than a micron in diameter.

31. The device of claim 7, further comprising:

plural supports, with respective ones of the supports including respective nanofiber layers to provide multi-stage filtration.

32. The device of claim 7, further comprising:

a support having macroscopic dimensions and openings for fluid flow therethrough; and

a part of the plurality of nanofibers adhered to the support to secure the filtration medium to the support, wherein the support comprises multiple cellular frames arranged adjacent to each other.

33. The device of claim 32, further comprising:

an adhesive joining the filtration medium to the support.

34. The device of claim 32, wherein said part of the plurality of nanofibers are integrally attached to the support.

35. The device of claim 32, further comprising:

a sealant disposed on a perimeter of the support to seal the fibers to the support.

36. The device of claim 32, wherein the plurality of nanofibers comprise a thickness between 0.25 and 500 μ

m.