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 membrane comprising:
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.
2 . The membrane of claim 1 , wherein the membrane is selected from the group consisting of polysulfone, polyethersulfone, polyphenylsulfone, polyarylsulfone, polyimide, polyamide-imide, and polyvinylidene fluoride.
3 . The 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.
4 . The 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 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 membrane of claim 1 , wherein a thickness of the membrane is in a range from about 40 microns to about 150 microns.
7 . The membrane of claim 1 , wherein a thickness of the skin at the first surface is in a range from greater than 0 to about 2 microns.
8 . The membrane of claim 1 , wherein the skin at the first surface has a porosity of about 15% or less.
9 . The membrane of claim 1 , wherein the second surface has a porosity in a range from about 10% to about 60%.
10 . The membrane of claim 1 , wherein the second surface has a greater porosity than the skin at the first surface.
11 . A filter comprising the membrane of claim 1 .
12 . The filter of claim 11 , wherein the membrane sheds less than 300 particles at the 60 minute mark when the filter is subjected to The Particle Shedding Test.
13 . The filter of claim 11 , wherein the membrane sheds less than 200 particles at the 60 minute mark when the filter is subjected to The Particle Shedding Test.
14 . The filter of claim 11 , wherein the membrane sheds less than 100 particles at the 60 minute mark when the filter is subjected to The Particle Shedding Test.
15 . A method of forming a membrane comprising:
casting a polymer solution on a hydrophilic support to form a membrane, wherein the membrane comprises:
a first surface;
a second surface contacting the hydrophilic support and 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 a pore size increases from the second surface to the skin.
16 . The method of claim 15 , wherein the hydrophilic support is a polyester.
17 . The method of claim 16 , wherein the hydrophilic support is a biaxially-oriented polyethylene terephthalate.
18 . The method of claim 15 , further comprising immersing the hydrophilic support with the polymer solution thereon in a water bath.
19 . The method of claim 18 , wherein the water bath has a temperature in a range from about 0° C. to about 40° C.
20 . The method of claim 15 , wherein the membrane has a polymer content in a range from about 10 wt % to about 30 wt %.