POROUS POLYMER MEMBRANES COMPRISING SILICATE

Abstract

The present invention pertains to a fluoropolymer-based porous membrane, to a process for manufacturing said porous membrane and to use of said porous membrane as filtration membrane for liquid and/or gas phases, in particular water-based phases.

Claims

1. A porous membrane comprising at least one layer consisting of a composition (C), said composition (C) comprising: at least one polymer (F), wherein polymer (F) is a fluoropolymer, and at least one silicate compound (S) selected from the group consisting of tourmaline, actinolite, serpentine, muscovite and kaolin.

2. The porous membrane according to claim 1, wherein the polymer (F) is selected from the group consisting of: polymers (F-1) comprising recurring units derived from vinylidene fluoride (VDF) and, optionally, from at least one fluorinated monomer different from VDF; and polymers (F-2) comprising recurring units derived from at least one fluorinated monomer selected from tetrafluoroethylene (TFE) and chlorotrifluoroethylene (CTFE), and from at least one hydrogenated monomer selected from ethylene, propylene and isobutylene, optionally containing one or more additional monomers.

3. The porous membrane according to claim 1, wherein composition (C) comprises at least one compound (S) in an amount of from 0.1% to 10% by weight, based on the total weight of the at least one polymer (F).

4. The porous membrane according to claim 1, wherein composition (C) further comprises: one or more oxides selected from the group consisting of titanium oxide, magnesium oxide, aluminium oxide, potassium oxide, zirconium oxide; and/or one or more sulfates selected from the group consisting of barium sulfate, calcium sulphate strontium sulfate; and/or one or more carbonates selected from the group consisting of calcium carbonate and sodium carbonate.

5. The porous membrane according to claim 1, said porous membrane further comprising at least one substrate layer.

6. The porous membrane according to claim 1, said porous membrane comprising: at least one substrate layer, at least one top layer made of a polymer selected from the group consisting of polyamides, polyimides, polyacrylonitriles, polybenzimidazoles, cellulose acetates and polyolefins, and between said at least one substrate layer and said at least one top layer, at least one layer consisting of composition (C).

7. A process for manufacturing the porous membrane according to claim 1, said process comprising: processing a liquid composition (C) thereby providing a film, said liquid composition (C) comprising: at least one polymer (F), wherein polymer (F) is a fluoropolymer, at least one silicate compound (S) selected from the group consisting of tourmaline, actinolite, serpentine, muscovite and kaolin, and a medium (L), wherein medium (L) is a liquid medium comprising at least one organic solvent; and precipitating the film.

8. The process according to claim 7, wherein the film is precipitated in a non-solvent medium (NS).

9. The process according to claim 7, wherein the film is precipitated by cooling.

10. The process according to claim 7, wherein the film is precipitated by absorption of a non-solvent medium (NS) from a vapour phase.

11. The process according to claim 7, wherein the film is precipitated by evaporation of the medium (L).

12. A process for manufacturing the porous membrane according to claim 1, said process comprising: processing a solid composition (C) thereby providing a film, said solid composition (C) comprising: at least one polymer (F), wherein polymer (F) is a fluoropolymer, and at least one silicate compound (S) selected from the group consisting of tourmaline, actinolite, serpentine, muscovite and kaolin; and stretching the film.

13. A process comprising filtering a liquid phase or a gas phase comprising one or more solid contaminants through the porous membrane according to claim 1.

14. The process according to claim 13, wherein the liquid phase is a water-based phase comprising one or more microorganisms selected from the group consisting of bacteria, algae, fungi, protozoa and viruses.

15. The process according to claim 15, wherein the bacteria is Staphylococcus aureus and/or Pseudomonas aeruginosa.

16. The porous membrane according to claim 2, wherein the one or more additional monomers are present in polymer (F-2) in amounts of from 0.01% to 30% by moles, based on the total amount of TFE and/or CTFE and said hydrogenated monomer(s).

17. The porous membrane according to claim 3, wherein composition (C) comprises at least one compound (S) in an amount of from 1% to 6% by weight, based on the total weight of the at least one polymer (F).

Description

EXAMPLE 1

[0248] Porous membranes were manufactured using a liquid casting solution comprising NMP as solvent and 15% by weight of SOLEF? 1015 PVDF to which the tourmaline water suspension (1) was added in such an amount so as to reach a concentration of tourmaline of 2% by weight based on the total weight of SOLEF? 1015 PVDF. The membrane was coagulated in water. The membrane had a contact angle of the upper side towards water of 56?. The porosity was 83%.

COMPARATIVE EXAMPLE 1

[0249] The same procedure as detailed under Example 1 was followed but using a liquid casting composition comprising NMP as solvent and 15% by weight of SOLEF? 1015 PVDF. No tourmaline was added to the casting composition. The membrane had a contact angle of 65? and a porosity of 83%.

[0250] The mechanical properties values of the porous membranes obtained according to Example 1 and Comparative Example 1 are shown in Table 1 here below:

TABLE-US-00001 TABLE 1 Example 1 C. Example 1 Modulus [MPa] 82 72 Stress at break [MPa] 4.1 3.4 Strain at break [%] 84 64

EXAMPLE 2

[0251] Porous membranes were manufactured using the following liquid casting solutions comprising NMP as solvent:

1) a liquid solution comprising 18% by weight of SOLEF? 5110 PVDF to which the tourmaline water suspension (1) was added in such an amount so as to reach a concentration of tourmaline of 2% by weight based on the total weight of SOLEF? 5110 PVDF. The membrane was coagulated in water. The membrane had a contact angle of the upper side towards water of 70?. The porosity was 83% and the water flux was 24 LMH;
2) a liquid solution comprising 18% by weight of SOLEF? 5110 PVDF to which the tourmaline water suspension (1) was added in such an amount so as to reach a concentration of tourmaline of 4% by weight based on the total weight of SOLEF? 5110 PVDF. The membrane was coagulated in water. The membrane had a contact angle of the upper side towards water of 67?. The porosity was 83% and the water flux was 30 LMH.

COMPARATIVE EXAMPLE 2

[0252] The same procedure as detailed under Example 2 was followed but using a liquid casting composition comprising NMP as solvent and 18% by weight of SOLEF? 5110 PVDF. No tourmaline was added to the casting composition. The membrane had a contact angle of the upper side towards water of 77?. The porosity was 82.5% and the water flux was 10 LMH.

EXAMPLE 3

[0253] Dense films were manufactured using a liquid casting solution comprising DMAC as solvent and 10% by weight of SOLEF? 1015 PVDF to which the tourmaline water suspension (1) was added in such an amount so as to reach a concentration of tourmaline of 2% by weight based on the total weight of SOLEF? 1015 PVDF.

COMPARATIVE EXAMPLE 3

[0254] The same procedure as detailed under Example 3 was followed but using a liquid casting composition comprising DMAC as solvent and 10% by weight of SOLEF? 1015 PVDF. No tourmaline was added to the casting composition.

[0255] The biofilm accumulation values on the porous membranes obtained according to Example 3 and Comparative Example 3 are shown in Table 2 here below:

TABLE-US-00002 TABLE 2 Example 3 C. Example 3 Batch phase 6.2 LOG10 CFU/cm.sup.2 6.4 LOG10 CFU/cm.sup.2 Continuous phase 6.9 LOG10 CFU/cm.sup.2 7.6 LOG10 CFU/cm.sup.2

Determination of Antibacterial Activity

[0256] This method consists in the quantification of bacteria before and after exposure of a polymeric film with a predefined surface to bacteria according to JIS Z2801 standard procedure. Bacteria in the strain inoculum are either Pseudomonas aeruginosa or Staphylococcus aureus. The specimens are 5?5 cm.sup.2 flat dense films obtained either by solution casting or by melt extrusion according to the general procedure as detailed above using the tourmaline water suspension (2).

[0257] After sterilization of the films, a strain inoculum (approximately 0.4 ml) was deposited on the surfaces of the films. Strain inoculum concentration was in the range 2.5-10?10.sup.5 cells/ml. The petri dish containing the inoculated test piece with the test inoculum was then incubated for 24 hours at a temperature of 35? C. and a relative humidity of 90%. After the incubation period, a wash out procedure was executed in order to collect the bacteria and to measure them with an agar plate culture method.

EXAMPLE 4

[0258] A strain inoculum containing Pseudomonas aeruginosa was deposited on a SOLEF? 1015 PVDF dense film obtained either by solution casting, using a liquid casting solution comprising DMAC as solvent and 10% by weight of SOLEF? 1015 PVDF, or by melt extrusion according to the general procedure as detailed above using the tourmaline water suspension (2) in such an amount so as to reach a concentration of 6% by weight based on the total weight of SOLEF? 1015 PVDF of a mixture of tourmaline (55% by weight of the total weight of said mixture), barium sulphate (20% by weight of the total weight of said mixture) and TiO.sub.2 (25% by weight of the total weight of said mixture).

COMPARATIVE EXAMPLE 4

[0259] The same procedure as detailed under Example 4 was followed but using a SOLEF? 1015 PVDF dense film obtained either by solution casting or by melt extrusion according to the general procedure as detailed above without adding a tourmaline water suspension.

[0260] The antibacterial activity values on the dense films obtained according to Example 4 and Comparative Example 4 are shown in Table 3 here below:

TABLE-US-00003 TABLE 3 Number of bacteria Number of bacteria after before exposure contact for 24 hours Example 4 2.7 ? 10.sup.5 3.3 ? 10.sup.5 C. Example 4 2.7 ? 10.sup.5 3.0 ? 10

EXAMPLE 5

[0261] The same procedure as detailed under Example 4 was followed but using a strain inoculum containing Staphylococcus aureus.

COMPARATIVE EXAMPLE 5

[0262] The same procedure as detailed under Example 5 was followed but using a SOLEF? 1015 PVDF dense film obtained either by solution casting or by melt extrusion according to the general procedure as detailed above without adding a tourmaline water suspension.

[0263] The antibacterial activity values on the dense films obtained according to Example 5 and Comparative Example 5 are shown in Table 4 here below:

TABLE-US-00004 TABLE 4 Number of bacteria Number of bacteria after before exposure contact for 24 hours Example 5 2.4 ? 10.sup.5 3.1 ? 10.sup.5 C. Example 5 2.4 ? 10.sup.5 8.0 ? 10

[0264] It has been thus found that the porous membrane of the invention advantageously exhibits improved biofouling resistance and improved mechanical properties to be suitably used as filtration membrane for various liquid and/or gas phases, in particular water-based phases.

[0265] Also, it has been found that the porous membrane of the invention advantageously exhibits good water flux properties to be suitably used as filtration membrane for water-based phases.

[0266] Further, it has been found that a significant decrease of bacteria is always observed on dense films after exposure to a strain inoculum.