MEMBRANES WITH REDUCED PARTICLE FORMATION
Disclosed herein are membranes having a first surface, a second surface opposing the first surface, a skin at the first surface having visible pores when viewed at a magnification of 10,000 and a pore size gradient, wherein pore size increases from the second surface to the skin.
1 . A porous polymeric membrane comprising:
a first surface;
a second surface opposing the first surface;
a thickness between the first surface and the second surface;
a porous skin at the first surface;
a pore size gradient, wherein pore sizes increase from the second surface to the porous skin; and
the porous polymeric membrane having the form of a sheet;
wherein a polymer of the porous polymeric membrane is polysulfone, polyethersulfone, polyphenylsulfone, polyarylesulfone, polyimide, polyamide-imide, or polyvinylidene fluoride.
2 . The porous polymeric membrane of claim 1 , wherein the membrane has a skin at the second surface having no visible pores when viewed at a magnification of 10,000.
3 . The porous polymeric membrane of claim 1 , wherein the polymer is polymer is polyethersulfone.
4 . The porous polymeric membrane of claim 1 , wherein the membrane has a mean bubble point in a range from about 40 psi to about 75 psi as measured according to test method B of ASTM F316-03 (2011) using ethoxy-nonafluorobutane (HFE-7200) as the wetting fluid and having the wetting fluid flow from the first surface to the second surface.
5 . The porous polymeric membrane of claim 1 , wherein the membrane has a mean bubble point in a range from about 75 psi to about 150 psi as measured according to test method B of ASTM F316-03 (2011) using ethoxy-nonafluorobutane (HFE-7200) as the wetting fluid and having the wetting fluid flow from the second surface to the first surface.
6 . The porous polymeric membrane of claim 1 , wherein a thickness of the porous polymeric membrane is in a range from about 40 microns to about 150 microns.
7 . The porous polymeric membrane of claim 1 , wherein a thickness of the skin at the first surface is in a range from greater than 0 microns to about 2 microns.
8 . The porous polymeric membrane of claim 1 , wherein the skin at the first surface has a porosity of about 15% or less.
9 . The porous polymeric membrane of claim 1 , wherein the second surface has a porosity in a range from about 10% to about 60%.
10 . The porous polymeric membrane of claim 1 , wherein the second surface has a greater porosity than the skin at the first surface.
11 . The porous polymeric membrane of claim 1 having the form of a flat sheet or a corrugated sheet.
12 . A filter comprising the porous polymeric membrane of claim 1 .
13 . The filter of claim 11 , wherein the porous polymeric membrane sheds less than 300 particles, less than 200 particles, or less than 100 particles when the filter is subjected to The Particle Shedding Test.
14 . A method of forming a porous polymeric membrane comprising:
casting a polymer solution on a hydrophilic support to form the porous polymeric membrane, the porous polymeric membrane comprising:
a first surface;
a second surface opposing the first surface;
a thickness between the first surface and the second surface;
a porous skin at the first surface;
a pore size gradient, wherein pore sizes increase from the second surface to the porous skin.
15 . The method of claim 14 , wherein the hydrophilic support is a polyester.
16 . The method of claim 14 , wherein the hydrophilic support is a biaxially-oriented polyethylene terephthalate.
17 . The method of claim 14 , further comprising immersing the hydrophilic support with the polymer solution thereon in a water bath.
18 . The method of claim 17 , wherein the water bath has a temperature in a range from about 0° C. to about 40° C.
19 . The method of claim 15 , wherein the porous polymeric membrane has a polymer content in a range from about 10 wt % to about 30 wt %.
20 . The method of claim 14 , wherein the polymer solution comprises:
a polymer selected from polysulfone, polyethersulfone, polyphenylsulfone, polyarylesulfone, polyimide, polyamide-imide, and polyvinylidene fluoride;
a solvent; and
a non-solvent.