Semi-permeable polyvinyl alcohol membranes

Claim 2

IN A PROCESS FOR THE HEAT TREATMENT OF MATERIAL OF THICKNESS FROM 10 TO 50 U, SAID MATERIAL HAVING BEEN FORMED FROM A POLYVINYL ALCOHOL/SLVENT MIXTURE, SAID SOLVENT BEING CAPABLE OF DISSOLVING SAID POLYVINYL ALCOHOL, SAID POLYVINYL ALCOHOL HAVING AN ESTER NUMBER FROM 0 TO 5, AND A VISCOSITY, AS A 4% BY WEIGHT AQUEOUS SOLUTION, FROM 5 TO 100 CPO AT 20*C., THE IMPROVEMENT WHEREIN THE MATERIAL IS SUBJECTED TO, SUCCESSIVELY, I. A DRY HEAT TREATMENT AT A TEMPERATURE OF FROM 160*C TO 22*C AND FOR A PERIOD OF ABOUT 10 MINUTES TO ABOUT 70 HOURS, CARRIED OUT UNDER CONDITIONS SUCH THAT THE POINT M (DEFINED, IN A SYSTEM OF THREE RECTANGULAR CARTESIAN COORDINATES, $, H AND V, DENOTING RESPECTIVELY THE TEMPERATURE IN DEGREES CENTIGRADE, THE DURATION IN HOURS OF THE HEAT TREATMENT REPRESENTED ON A LOGARITHMIC SCHALE AND THE VISOCOSITY IN CPO AT 20*C. OF A 4% BY WEIGHT AQUEOUS SOLUTION OF THE POLYVINYL ALCOHOL) IS CONTAINED WHITH A SOLID ABCDA''B''C''D'', THE SAID SOLID HAVING FOUR PLAN FACES ABB''A'', A''B''C''D'', D''C''D AND ABCD AND TWO FACES IN TE FORM OF HYPERBOLIC PARABOLIDS, AA''D D'' AND BB''CC'', SAID SOLID BEING DEFINED BY THE FRONTAL AD HORIZONTAL PROJECTIONS OF ITS APICES IN FIG. 1 OF THE ACCOMPANYING DRAWINGS, AND II. A TREATMENT IN WATER AT A TEMPERATURE OF 90*C OR ABOVE 90*C. FOR MORE THAN 5 MINUTES.

Claim 3

In a process for the heat treatment of material of thickness from 10 to 50 Mu , said material having been formed from a polyvinyl alcohol/solvent mixture, said solvent being capable of dissolving said polyvinyl alcohol, said polyvinyl alcohol having an ester number from 0 to 5, and a viscosity, as a 4% by weight aqueous solution, from 20 to 90 cPo at 20*C., the improvement wherein the material is subjected to successively: i. a dry heat treatment at a temperature of from 160*C to 220*C. and for a period of about 12 minutes to about 65 hours, carried out under conditions such that the point M1 (defined, in a system of three rectangular cartesian co-ordinates, phi , h and Nu , denoting respectively, the temperature in degrees Centigrade, the duration in hours of the heat treatment represented on a logarithmic scale and the viscosity in cPo at 20*C., of a 4% by weight aqueous solution of the polyvinyl alcohol) is contained within a solid A1 B1 C1 D1 A''1 B''1 D''1, the said solid having four plane faces A1 B1 B''1 A''1, A''1 B''1 C''1 D''1, D''1 C''1 C1 D1 and A1 B1 C1 C1 D1, and two faces in the form of hyperbolic paraboloids, A1 A''1 D1 D''1 and B1 B''1 C1 C''1, said solid being defined by the frontal and horizontal projections of its apices in FIG. 2 of the accompanying drawings, and ii. a treatment in water at a temperature of 90*C or above 90*C. for more than 5 minutes.

Claim 4

In a process for the heat treatment of material of thickness from 10 to 50 Mu , said material having been formed from a polyvinyl alcohol/solvent mixture, said solvent being capable of dissolving said polyvinyl alcohol, said polyvinyl alcohol having an ester number from 0 to 5, and a viscosity, as a 4% by weight aqueous solution, from 20 to 90 cPo at 20*C., the improvement wherein the material is subjected to successively: i. a dry heat treatment at a temperature of from 160*C to 220*C. and for a period of about 12 minutes to about 65 hours, carried out under conditions such that the point M1 (defined, in a system of three rectangular cartesian co-ordinates, phi , h and Nu , denoting respectively, the temperature in degrees Centigrade, the duration in hours of the heat treatment represented on a logarithmic scale and the viscosity in cPo at 20*C., of a 4% by weight aqueous solution of the polyvinyl alcohol) is contained within a solid A1 B1 C1 D1 A''1 B''1 D''1, the said solid having four plane faces A1 B1 B''1 A''1, A''1 B''1 C''1 D''1, D''1 C''1 C1 D1 and A1 B1 C1 C1 D1, and two faces in the form of hyperbolic paraboloids, A1 A''1 D1 D''1 and B1 B''1 C1 C''1, said solid being defined by the frontal and horizontal projections of its apices in FIG. 2 of the accompanying drawings, and ii. a treatment in water at a temperature of 90*C or above 90*C. for more than 5 minutes.

Claim 5

Process according to claim 1 wherein the duration of the treatment in the water is from 10 minutes to 5 hours.

Claim 6

Process according to claim 1 wherein the material is in the form of a hollow fibre whose wall has a thickness of from 10 to 50 Mu .

Claim 7

Process according to claim 4 wherein the external diameter of the hollow fibre is from 30 Mu to 1 mm.

Claim 8

In a reverse osmosis apparatus the improvement wherein the membrane comprises polyvinyl alcohol material obtained by a process as defined in claim 1.

Claim 9

A process for the fractionation of a saline solution by reverse osmosis which is carried out in apparatus as defined in claim 6.

Claim 10

A process according to claim 7 wherein the solution contains a sulphate.