Polymeric compositions for membranes

Claim 2

A membrane-forming composition useful for making ultrafiltration membranes from a polymer solution thereof having a polymer concentration higher than 20%, said composition comprising a mixture of at least one non-sulphonated polysulphone and at least one sulphonated polysulphone, this mixture containing 10 to 30% by weight of a sulphonated polysulphone which has a theoretical exchange capacity of from 500 to 1200 meq/kg.

Claim 3

A composition according to claim 1 in which the theoretical exchange capacity of the composition is from 120 to 350 meq/kg.

Claim 4

A composition according to claim 1 in which the non-sulphonated polysulphone consists essentially of recurring units of the formula: ##STR4## in which each of E, G and G 1 , which are identical or different, represents an aromatic group, each of Q and Q 1 , which are identical or different, represents a substituent which is inert with respect to the sulphonation reactions, each of Q 2 and Q 3 , which are identical or different, represents an electron-attracting group, each of r, s, t and u, which are identical or different, is zero or a positive integer from 1 to 4, at least one of which is not greater than 3, m is equal to 0, 1 or 2 and R represents a valency bond or a radical which is selected from the group consisting of --CO--, --O-- and --SO 2 -- and divalent hydrocarbon radicals, and the sulphonated polysulphone consists essentially of recurring units of the formula: ##STR5## alone or in combination with units of formula (I), in which Q, Q 1 , Q 2 , Q 3 , r, s, t, u and m are as defined above and E', G' and G' 1 , which are identical or different, are as defined under E, G and G 1 , respectively, except that at least one of them contains at least one sulphonic group.

Claim 5

A composition according to claim 3 in which the substituent which is inert with respect to sulphonation reactions is selected from the group consisting of alkyl radicals of 1 to 4 carbon atoms and fluorine, chlorine, bromine and iodine atoms.

Claim 6

A composition according to claim 3 in which the electron-attracting group is selected from the group consisting of nitro, phenylsulphone, alkylsulphone, trifluoromethyl, nitroso and pyridyl groups.

Claim 7

A composition according to claim 3 in which R is selected from the group consisting of alkylene, alkylidene, cycloalkylene and arylene radicals containing less than 7 carbon atoms.

Claim 8

A composition according to claim 6 in which R is the ##STR6## radical.

Claim 9

A composition according to claim 3 in which r=s=t=u=0, m=1 or 2 and E, G and G 1 are each a para-phenylene radical.

Claim 10

A composition according to claim 1 which is in the form of a solution in at least one organic solvent containing at least 20% by weight of the said mixture.

Claim 11

A composition according to claim 9 which contains at least 25% by weight of the said mixture.

Claim 12

A composition according to claim 9 in which the organic solvent is a polar aprotic solvent.

Claim 13

A composition according to claim 11 in which the solvent is N-methylpyrrolidone.

Claim 14

A membrane formed from a composition as defined in claim 1.

Claim 15

A membrane according to claim 13 which is dense.

Claim 16

A membrane according to claim 13 which is screen-reinforced, the screen reinforcement constituting 20 to 80% by weight of the reinforced membrane.

Claim 17

A membrane according to claim 13 possessing a dense or microporous layer, and a porous layer.

Claim 18

In a method of ultrafiltration of a liquid the improvement in which the ultrafiltration membrane is one defined in claim 13.

Claim 19

Process for the preparation of a membrane suitable for ultrafiltration, which comprises casting a composition as defined in claim 1 in the form of a solution having a polymer concentration higher than 20% on a support and immersing the liquid film, on its support, in a coagulation bath.

Claim 20

A process for the preparation of a composition comprising a mixture of at least one non-sulphonated polysulphone and at least one sulphonated polysulphone, this mixture containing 10 to 30% by weight of a sulphonated polysulphone which has a theoretical exchange capacity of from 500 to 1200 meq/kg, said process comprising mixing the non-sulphonated polysulphone with the sulphonated polysulphone in the form of powders or solutions, or combinations thereof.

Claim 21

A process for the preparation of a composition comprising a mixture of at least one non-sulphonated polysulphone and at least one sulphonated polysulphone, this mixture containing 10 to 30% by weight of a sulphonated polysulphone which has a theoretical exchange capacity of from 500 to 1200 meq/kg, said process comprising mixing the non-sulphonated polysulphone with the sulphonated polysulphone in the form of powders or solutions, or combinations thereof.

Claim 22

A process according to claim 19 wherein a solution is used, and, after mixing, the solvent of the solution is evaporated.

Claim 23

A membrane which is a composite membrane comprising a thin layer of membrane formed from a composition comprising a mixture of at least one non-sulphonated polysulphone and at least one sulphonated polysulphone, this mixture containing 10 to 30% by weight of a sulphonated polysulphone which has a theoretical exchange capacity of from 500 to 1200 meq/kg, and which is supported by a porous layer.

Claim 24

A membrane which is a composite membrane comprising a thin layer of membrane formed from a composition comprising a mixture of at least one non-sulphonated polysulphone and at least one sulphonated polysulphone, this mixture containing 10 to 30% by weight of a sulphonated polysulphone which has a theoretical exchange capacity of from 500 to 1200 meq/kg, and which is supported by a porous layer.

Claim 25

Process for the preparation of a membrane suitable for ultrafiltration, which comprises casting on a support a composition comprising a mixture of at least one non-sulphonated polysulphone and at least one sulphonated polysulphone, this mixture containing 10 to 30% by weight of a sulphonated polysulphone which has a theoretical exchange capacity of from 500 to 1200 meq/kg, said composition being in the form of a solution in at least one organic solvent containing at least 20% by weight of the said mixture, and immersing the liquid film, on its support, in a coagulation bath, the coagulation bath being water, alone or in combination with solvent and/or salt, and having a temperature of +10° to +60° C.

Claim 26

Process for the preparation of a membrane suitable for ultrafiltration, which comprises casting on a support a composition comprising a mixture of at least one non-sulphonated polysulphone and at least one sulphonated polysulphone, this mixture containing 10 to 30% by weight of a sulphonated polysulphone which has a theoretical exchange capacity of from 500 to 1200 meq/kg, said composition being in the form of a solution in at least one organic solvent containing at least 20% by weight of the said mixture, and immersing the liquid film, on its support, in a coagulation bath, the coagulation bath being water, alone or in combination with solvent and/or salt, and having a temperature of +10° to +60° C.

Claim 27

Process according to claim 22 in which the coagulation bath has a temperature of 15° to 40° C.