Abstract Process for making thin film semipermeable membranes. A porous substrate having pores not greater than about 500 A. at a surface thereof is provided, as by casting from a solution of an organic polymer. A nonporous buffer layer is coated upon that surface to fill the pores, as by applying a water-soluble material, such as polyacrylic acid. The thin film semipermeable membrane is formed in situ upon the buffer layer, as by dipping the coated substrate in a dilute solution of cellulose acetate. A less than 1 weight percent solution of cellulose acetate, having an acetyl content not less than about 39.8 weight percent in chloroform may be used. After drying, the buffer layer is at least partially leached from the composite membrane. The cellulose acetate semipermeable membrane may be less than 1,000 A. in thickness.
A process in accordance with claim 1 wherein said cellulose acetate has an acetyl content between about 39.8 weight percent and 44.8 weight percent.
Claim 2
Dependent Claim
25 words
A process in accordance with claim 2 wherein said solvent is a chlorinated hydrocarbon or solvent mixture including a major portion of a chlorinated hydrocarbon.
Claim 3
Dependent Claim
13 words
A process in accordance with claim 3 wherein said chlorinated hydrocarbon is chloroform.
Claim 4
Dependent Claim
21 words
A process in accordance with claim 1 wherein said cellulose acetate has an acetyl content greater than about 41 weight percent.
Claim 5
Dependent Claim
22 words
A process in accordance with claim 5 wherein said film-forming solution contains less than about 1 percent by weight of cellulose acetate.
Claim 6
Dependent Claim
15 words
A process in accordance with claim 1 wherein said buffer material is leached with water.
Claim 7
Dependent Claim
39 words
A process in accordance with claim 1 wherein the surface of said porous substrate upon which said barrier material is coated has a maximum pore size which is not greater than the thickness of the ultrathin cellulose acetate membrane.
Claim 8
Dependent Claim
27 words
A process in accordance with claim 8 wherein the pores at said surface of said substrate have a mean pore size not greater than about 250 A.
Claim 9
Dependent Claim
22 words
A process in accordance with claim 1 wherein said porous substrate is cast from a solution of cellulose nitrate and cellulose acetate.
Claim 10
Dependent Claim
9 words
The product resulting from the process of claim 1.