Copolymer having amphiphilic blocks, and use thereof for manufacturing polymer filtration membranes

Abstract

A copolymer having amphiphilic blocks includes at least one first hydrophilic block, obtainable from n-butyl acrylate and hydroxyethyl methacrylate monomers, and a second hydrophobic block likely to be obtained from a methyl methacrylate monomer. The copolymer is found to be particularly advantageous for use as an additive for manufacturing a polymer filtration membrane, particularly a PVDF membrane, particularly via a phase inversion method.

Claims

1. An amphiphilic block copolymer comprising at least a first hydrophilic block obtainable from n-butyl acrylate and hydroxyethyl methacrylate monomers and a second hydrophobic block obtainable from a methyl methacrylate monomer.

2. The copolymer as claimed in claim 1, consisting of a diblock copolymer.

3. The copolymer as claimed in claim 1, wherein said first hydrophilic block is essentially composed of a random copolymer comprising n-butyl acrylate and hydroxyethyl methacrylate monomers.

4. The copolymer as claimed in claim 1, wherein said second hydrophobic block is composed of at least 50% of polymethyl methacrylate, the remainder being formed of a mixture of methacrylate or acrylate monomers.

5. The copolymer as claimed in claim 4, wherein the remainder is formed of a mixture of n-butyl acrylate and hydroxyethyl methacrylate monomers.

6. The copolymer as claimed in claim 1, consisting of a (poly(n-butyl acrylate)-co-poly(hydroxyethyl methacrylate)-b-hydrophobic) block copolymer where the hydrophobic block is composed of at least 50% of polymethyl methacrylate, the remainder being formed of a mixture of methacrylate or acrylate monomers.

7. The copolymer as claimed in claim 6, wherein the remainder is formed of a mixture of n-butyl acrylate and hydroxyethyl methacrylate monomers.

8. The copolymer as claimed in claim 1, exhibiting a weight-average molecular weight of between 10 kg/mol and 400 kg/mol.

9. The copolymer as claimed in claim 1, wherein said first hydrophilic block and/or said second hydrophobic block is obtainable by a controlled radical polymerization process.

10. The copolymer as claimed in claim 9, obtainable by SFRP polymerization.

11. The copolymer as claimed in claim 10, wherein said first hydrophilic block and/or said second hydrophobic block is obtainable by SFRP polymerization in the presence of at least one alkoxyamine.

12. The copolymer as claimed in claim 11, wherein said first hydrophilic block and/or said second hydrophobic block is obtainable by SFRP polymerization in the presence of a monoalkoxyamine of formula (I): ##STR00007##

13. A method for manufacturing a polymer filtration membrane, comprising coagulating a collodion comprising a polymer matrix and an amphiphilic block copolymer as claimed in claim 1 as an additive.

14. A polymer membrane, comprising a hydrophobic polymer matrix and an amphiphilic block copolymer as claimed in claim 1.

15. The polymer membrane as claimed in claim 14, wherein the hydrophobic polymer matrix comprises a fluoro polymer.

16. The polymer membrane as claimed in claim 15, wherein said fluoro polymer is a polyvinylidene fluoride homopolymer.

17. The polymer membrane as claimed in claim 14, comprising from 60 to 90% by weight of said hydrophobic polymer matrix and from 10 to 40% by weight of said amphiphilic block copolymer.

18. The polymer membrane as claimed in claim 14, obtainable by a phase inversion process starting from a solution comprising said hydrophobic polymer matrix, said amphiphilic block copolymer and, if appropriate, one or more other additives, in solution in a solvent.

19. The polymer membrane as claimed in claim 18, obtainable by a phase inversion process from a solution comprising the following proportions by weight: from 10 to 40% of said hydrophobic polymer matrix; from 0.1 to 30% by weight of said amphiphilic block copolymer; from 40 to 90% of solvent; if appropriate, from 0 to 20% by weight of other additive(s).

20. The polymer membrane as claimed in claim 19, wherein said hydrophobic polymer matrix is PVDF.

21. A method of treating effluents, comprising filtering an effluent through a polymer membrane as claimed in claim 14.

22. The method as claimed in claim 21 wherein the effluent is water.

Description

(1) The characteristics and advantages of the invention will become more clearly apparent in the light of the implementational examples below, provided simply by way of illustration and without in any way limiting the invention, with the support of FIGS. 1 to 4, in which:

(2) FIG. 1 represents a scanning electron microscopy (SEM) photograph of a flat polymer membrane in accordance with the invention;

(3) FIG. 2 shows images obtained by SIMS imaging of the macropores of the membrane of FIG. 1, from a beam of primary ions, left-hand image fluorine (19F), right-hand image oxygen (16O);

(4) FIG. 3 shows the Fourier transform infrared (FTIR) spectra of the membrane of FIG. 1 before and after bringing into contact with a dose of 750 000 ppm.Math.h of NaOCl at pH 8;

(5) and FIG. 4 diagrammatically represents a device employed for evaluating the rate of coagulation of a collodion comprising an amphiphilic block copolymer in accordance with the invention.

EXAMPLE 1

Synthesis of an Amphiphilic Bock Copolymer in Accordance with the Invention

(6) As example of the invention, there is prepared a polymer material comprising a poly(n-butyl acrylate)-co-poly(hydroxyethyl methacrylate)-b-polymethyl methacrylate-co-poly(butyl acrylate)-co-poly(hydroxyethyl methacrylate) diblock copolymer.

(7) The process of the preparation of this polymer material can be applied to bulk, solvent, emulsion or suspension polymerization modes. Each stage of the process can be carried out in the same reactor via a batch process, or in different reactors optionally according to semicontinuous or continuous processes.

(8) The polymer materials prepared according to the example set out below are respectively analyzed by:

(9) .sup.1H NMR in deuterated chloroform on a Brucker 400 device;

(10) steric exclusion chromatography carried out at 30? C. using a polystyrene standard as reference in order to measure the number-average molecular weights.

(11) 1.1/Initiator of Alkoxyamine Type

(12) The initiator and control agent of the monoalkoxyamine type of the following formula (I):

(13) ##STR00006##
is used.

(14) This initiator is sold by Arkema under the trade name BlocBuilder? MA.

(15) 1.2/Stage 1Preparation of a First Hydrophilic Block

(16) A first living hydrophilic block of poly(n-butyl acrylate) copolymerized with poly(hydroxyethyl methacrylate) is prepared, which block will be used in the preparation of the amphiphilic block copolymer in accordance with the invention.

(17) The protocol for the preparation of this first living block is as follows.

(18) 12 kg of n-butyl acrylate and also 3 kg of hydroxyethyl methacrylate and 544 g of the initiator BlocBuilder? MA defined above are introduced, at ambient temperature, into a 16 liter jacketed stainless steel reactor equipped with a decompression valve tared at 10 bar and with a stirrer of the double screw propeller type. The mixture is vented and maintained under an atmosphere of 3 bar of nitrogen and then heated until a temperature of 110? C. is reached. The exothermicity of the polymerization reaction is countered by virtue of the heat exchanger comprising an aqueous glycol solution at ?25? C. The mixture is heated for 450 minutes until the polymerization reaction is complete. The solids content, measured by a thermobalance, is 78%.

(19) The mixture is subsequently cooled to ambient temperature over 15 minutes, so as to quench the reaction mixture. A solution of polymer in n-butyl acrylate and hydroxyethyl methacrylate is recovered via a bottom valve.

(20) A measurement of solids content indicates that there has been a conversion of 77%, that is to say that 77% of the n-butyl acrylate and hydroxyethyl methacrylate present in the initial mixture have polymerized.

(21) The intermediate n-butyl acrylate and hydroxyethyl methacrylate polymer is characterized by steric exclusion chromatography and by NMR, which provide the following data:

(22) Number-average molecular weight Mn=6620 g/mol;

(23) Weight-average molecular weight Mw=17 730 g/mol;

(24) Polydispersity index Ip=2.7;

(25) Composition by weight: 56.2% of poly(butyl acrylate), 23.1% of n-butyl acrylate, 20.4% of poly(hydroxyethyl methacrylate) and 0.3% of hydroxyethyl methacrylate.

(26) This solution of polymers is used as is in stage 2 below.

(27) 1.3/Stage 2Preparation of the Diblock Copolymer

(28) The amphiphilic diblock copolymer is prepared by controlled radical polymerization according to a method conventional in itself.

(29) The preparation protocol is as follows.

(30) After cleaning with toluene, the same reactor as in stage 1 is charged with 3.2 kg of the solution obtained in stage 1 and 6.8 kg of methyl methacrylate, the initial mixture thus comprising 2.5 kg of living poly(butyl acrylate) and poly(hydroxyethyl methacrylate), 0.7 kg of residual n-butyl acrylate, 10 g of residual hydroxyethyl methacrylate and 6.8 kg of methyl methacrylate. The combined mixture is diluted with 4.9 kg of toluene.

(31) After placing under nitrogen, the reactor is heated up to 105? C. for 90 minutes and then at 120? C. for 90 minutes before being cooled in 15 minutes to 50? C.

(32) The intermediate conversion is then 66%. 52.8 g of Luperox? 270 added to 146 g of diluting toluene are then added to the reaction medium.

(33) The mixture is vented, placed under nitrogen, stirred and then heated up to 120? C. for 150 minutes. The final mixture exhibits a solids content of 95%. It is subsequently transferred through a heated transfer line at 70? C. into a Clextral BC21 venting extruder having 5 venting wells and 12 heating regions, ranging from 70? C. at the inlet of the extruder up to 180? C. at the die of rod type. The molten block copolymer is subsequently cooled in a water tank and then granulated. This copolymer exhibits the following characteristics: Number-average molecular weight Mn=16 030 g/mol; Weight-average molecular weight Mw=53 070 g/mol; Polydispersity index Ip=3.3.

(34) The chemical composition of the copolymer is determined by .sup.1H NMR and gives the following results: polymethyl methacrylate: 66.6% (by weight); poly(n-butyl acrylate): 25.4% (by weight); poly(hydroxyethyl methacrylate): 6.9% (by weight); methyl methacrylate<0.3% (by weight); n-butyl acrylate<0.8% (by weight); hydroxyethyl methacrylate<detection limit toluene<0.5% (by weight).

EXAMPLE 2

Flat Polymer Membranes Based on PVDF and on an Amphiphilic Block Copolymer in Accordance with the Invention

(35) 2.1/Manufacture

(36) A flat polymer membrane P1 in accordance with the present invention is manufactured from a collodion comprising: 15% by weight of PVDF, commercial grade, of a molar mass of between 900 000 and 1 100 000 g/mol (HSV 900, Arkema Inc., USA) 10% by weight of the amphiphilic block copolymer of example 1 75% by weight of NMP.

(37) A film cast from this collodion is successively immersed in two water baths, named bath 1 and bath 2.

(38) The experimental conditions are as follows: temperature of the collodion: 25.3? C. temperature of the baths: 22.5? C. temperature of the ambient air: 25.3? C. relative humidity of the ambient air: 74.6% immersion time in bath 1: 22 min volume of bath 1: 5 l immersion time in bath 2: 24 h volume of bath 2: 5 l

(39) A flat porous polymer membrane with a thickness of 220 ?m is obtained.

(40) A photograph of the filtering surface of this membrane obtained by scanning electron microscopy (SEM) is shown in FIG. 1. It is observed therein that the membrane exhibits a surface appearance and a surface condition which are different from those observed for conventional membranes made of PVDF. More particularly, it is observed that the membrane exhibits a wire surface structure which is initiated at the crystalline nodules of the PVDF. A surface hydrophilization is observed.

(41) The modifications brought about by the copolymer in accordance with the invention are also observable at the macropores of the membrane, as shown in the images of FIG. 2, obtained by imaging by emission of secondary ions (SIMS), which testify to an enriching in copolymer on the walls of the pores. This results in a hydrophilization of these walls, which has the effect of improving the flow and surface properties of the membrane.

(42) Other flat polymer membranes in accordance with the invention, named P2 and P3, are manufactured in a similar way from collodions respectively comprising 3% and 7% by weight of the amphiphilic block copolymer of example 1 and 15% by weight of PVDF in NMP.

(43) 2.2/Resistance to Aging

(44) In order to determine the capability of resistance to aging of the membrane P1, the latter was brought into contact with a dose of 750 000 ppm.Math.h of NaOCl at pH 8. This dose represents three times the total dose which a filtration membrane is conventionally subjected to throughout its duration of use. The instantaneous concentration, of 1 000 ppm of free chlorine, is greater than the maximum dose generally recommended by the manufacturers for commercial filtration membranes.

(45) A membrane P1 was also subjected to a dose of 168 000 ppm.Math.h of NaOCl at pH 8.

(46) Surprisingly, no impact of the treatments by NaOCl on the quality of the surface of the membrane or on the amount of copolymer present at the surface of the membrane is observed. In particular, the surface hydrophilicity and the FTIR signals are not modified, indicating an unvarying presence of the copolymer at the surface of the membrane.

(47) The permeability of the membrane, before and after a dose of 750 000 ppm.Math.h of NaOCl, and the relative permeability after immersing in a solution of real water (surface water withdrawn from the Canal du Midi, at Toulouse), before and after a dose of 168 000 ppm.Math.h of NaOCl, of the membrane P1 are measured. The permeability, to pure water, is measured using an Amicon? 8050 cell. The pressure is set at 0.3 and 0.7 bar, while the permeate flow rate is measured for these two pressures. The permeability is calculated by dividing the flow rate by the filtering surface area and the transmembrane pressure. The mean value of the permeability is given.

(48) The results obtained are shown in table 1 below.

(49) TABLE-US-00001 TABLE 1 Permeability properties of the membrane P1 before and after contact with NaOCl Before After NaOCl NaOCl Permeability (l .Math. h.sup.?1 .Math. m.sup.?2 .Math. bar.sup.?1) at 20? C. Lp.sub.0 = 90 ? 5 Lp = 87 ? 4 Ratio of the permeability to water after 0.76 ? 0.04 0.79 ? 0.05 immersing in real water to the permeability to water before immersing (Lp/Lp.sub.0)

(50) The permeability of the membrane is not detrimentally affected by the nevertheless very high dose of NaOCl employed.

(51) The spectra obtained by Fourier transform infrared spectroscopy (FTIR) for the membrane P1, respectively before and after contact with a dose of 750 000 ppm.Math.h of NaOCl, are shown in FIG. 3. No change in signal is observed therein as a result of the treatment with NaOCl. In particular, the peak relating to the copolymer, located at 1725 cm.sup.?1, does not change in intensity.

(52) The above results demonstrate the particularly high capability of chemical resistance of the membrane in accordance with the invention with regard to chlorinated solutions, in contrast to what is observed for the membranes employing conventional additives, such as PVP.

(53) The membranes P2 and P3 in accordance with the invention were also subjected to doses of NaOCl at pH 8.

(54) The permeability of each membrane, before and after a dose of 750 000 ppm.Math.h of NaOCl at pH 8, and relative permeability after immersing in a solution of real water, before and after a dose of 168 000 ppm.Math.h at pH 8 of NaOCl, of each of the membranes P2 and P3 are measured. FTIR spectra are also recorded respectively before and after contact with a dose of 750 000 ppm.Math.h at pH 8 of NaOCl. The results of these tests are shown in table 2 below.

(55) TABLE-US-00002 TABLE 2 Permeability and FTIR signal at 1725 cm.sup.?1 properties for the membranes P2 and P3 before and after contact with NaOCl Membrane P2 Membrane P3 (3% copolymer) (7% copolymer) Before After Before After NaOCl NaOCl NaOCl NaOCl Permeability (l .Math. h.sup.?1 .Math. m.sup.?2 .Math. bar.sup.?1) at Lp.sub.0 = 422 ? 21 Lp = 412 ? 21 Lp.sub.0 = 112 ? 6 Lp = 108 ? 5 20? C. Ratio of the permeability to water 0.73 ? 0.04 0.71 ? 0.03 0.76 ? 0.05 0.71 ? 0.06 after immersing in real water to the permeability to water before immersing (Lp/Lp.sub.0) Relative intensity of the FTIR 0.21 ? 0.01 0.20 ? 0.01 0.4 ? 0.02 0.38 ? 0.02 signal at 1725 cm.sup.?1

(56) Here again, no significant variation in these parameters due to the treatment with NaOCl is observed.

EXAMPLE 3

Polymer Membrane of Hollow Fiber Type Based on PVDF and on an Amphiphilic Block Copolymer in Accordance with the Invention

(57) 2.1/Manufacture

(58) A polymer membrane of hollow fiber type F1 in accordance with the present invention is manufactured from a collodion comprising: 15% by weight of PVDF, commercial grade, with a molar mass of between 900 000 and 1 100 000 g/mol (HSV 900, Arkema Inc., USA) 3% by weight of the amphiphilic block copolymer of example 1 3% by weight of lithium chloride (LiCl) 79% by weight of NMP.

(59) The experimental manufacturing conditions are as follows: dissolution, with mechanical stirring using a Teflon three-bladed stirrer, of the copolymer in NMP for 24 h, by heating with a water bath at 50? C., with condensation of the solvent vapors; then the addition of PVDF and dissolution at 57? C. for a further 24 h; placing the collodion under vacuum (by means of a vacuum pump) for venting for 24 h; manufacture of a hollow fiber by extrusion of the collodion through an annular die. The spinning conditions are as follows: collodion flow rate: 7.2 cm.sup.3.Math.min.sup.?1 internal liquid flow rate: 2.7 cm.sup.3.Math.min.sup.?1 T? of the collodion=T? of the internal liquid=50? C. T? of the coagulation bath=32? C. internal liquid: water/NMP 85%/15% by weight air gap: 10 cm spinning rate: 11 m.Math.min.sup.?1

(60) 2.2/Resistance to Aging

(61) In order to determine the capability of resistance to aging of the membrane F1, the latter was brought into contact with a dose of 1 350 000 ppm.Math.h of NaOCl at pH 8.

(62) The permeability of the membrane and its relative permeability after immersing in a solution of real water, before and after the dose of NaOCl, are measured.

(63) FTIR spectra are also recorded respectively before and after contact with a dose of 1 350 000 ppm.Math.h of NaOCl.

(64) The mechanical strength of the membrane is tested by longitudinal tensile tests at an unvarying rate of movement of the upper jaw of 200 mm/min, using a tensile testing machine of Instron? type, before and after the dose of NaOCl.

(65) Finally, the SIMS signals are registered before and after a dose of 600 000 ppm.Math.h of NaOCl.

(66) The results of these tests are shown in table 3 below.

(67) TABLE-US-00003 TABLE 3 Permeability, mechanical strength, FTIR signal at 1725 cm.sup.?1 and SIMS signal properties for the membrane F1 before and after contact with NaOCl Before NaOCl After NaOCl Permeability (l .Math. h.sup.?1 .Math. m.sup.?2 .Math. bar.sup.?1) Lp.sub.0 = 198 ? 10 Lp = 189 ? 10 at 20? C. Ratio of the permeability to water after 0.73 ? 0.04 0.71 ? 0.03 immersing in real water to the permeability to water before immersing (Lp/Lp.sub.0) Breaking force (N) 1.61 ? 0.03 1.63 ? 0.04 Relative intensity of the FTIR signal at 0.21 ? 0.01 0.20 ? 0.01 1725 cm.sup.?1 SIMS signals of the copolymer (signal 3.64 ? 2 5.20 ? 3 relating to oxygen/fluorine ? 10.sup.?4)

(68) For none of these parameters is a significant variation due to the treatment with NaOCl observed. This demonstrates the high capability of resistance to aging of the membrane in accordance with the invention.

EXAMPLE 4

Effect of an Amphiphilic Block Copolymer in Accordance with the Invention on the Rate of Coagulation

(69) 4.1/Equipment and Measurement Method

(70) In order to evaluate the effect of the amphiphilic block copolymer in accordance with the invention on the rate of coagulation of the collodion in the manufacture of a porous polymer membrane by a phase inversion process, a device as represented diagrammatically in FIG. 4 is used.

(71) This measurement device comprises an extended white light source 10. The latter is surmounted by a coagulation crystallizing dish 11 with a capacity of 2 l made of optically transparent Pyrex? glass. A circular coagulation plate 12, also made of Pyrex? glass and optically transparent, is used to receive the collodion. This plate 12 is placed on 4 feet 13 in order to be maintained at a height of 5 cm from the light source 10.

(72) The collodion to be analyzed 14 is spread homogeneously over the coagulation plate 12 using a stainless steel knife.

(73) A reservoir 15 containing the nonsolvent, more particularly water, used to bring about the coagulation of the collodion is positioned above the crystallizing dish 11.

(74) A means 16 for holding the membrane on the coagulation plate 12, as it is formed, is placed on the collodion 14. A means for acquisition of photographs 17 rests on the holding means 16, so as to ensure that the membrane is held better in place, more particularly by preventing any detachment of the membrane from the coagulation plate 12 during coagulation.

(75) A system 18 for compilation and processing of the data resulting from the acquisition means 17 completes the device.

(76) All the constituent components above of the measurement device are placed in a closed case in order to eliminate any sources of light other than that coming from the extended white light source 10.

(77) All the components described above, which are constituents of the measurement device, are conventional in themselves.

(78) The images acquired during the coagulation of the collodion, under the effect of contact with the nonsolvent poured onto the collodion, are compiled and processed by the data processing system 18. The images are calibrated and standardized in order to obtain data comparable between the different collodions. The accuracy with regard to time of the measurements carried out is less than or equal to 1 s. Repeatability measurements have shown the consistency of the values measured.

(79) 4.2/Collodions Studied

(80) The collodions produced and studied are listed in table 4 below. Among these collodions, the collodions Comp.1 to Comp. 8 are comparative collodions not employing the amphiphilic block copolymer in accordance with the invention; the collodions C1 to C3 employ the amphiphilic block copolymer in accordance with the invention of example 1 (Copol.).

(81) TABLE-US-00004 TABLE 4 Compositions of the collodions studied Polymer matrix Additive Solvent Collodion (% by weight) (% by weight) (% by weight) Comp. 1 PVDF HSV 900 (15) NMP (85) Comp. 2 PSF (18) PVP K30 (15) NMP (67) Comp. 3 CTA (15) NMP (85) Comp. 4 PVDF HSV 900 (15) LiCl (3) NMP (82) Comp. 5 PVDF HSV 900 (15) PVP K10 (3) NMP (82) Comp. 6 PVDF HSV 900 (15) PVP K30 (3) NMP (82) Comp. 7 PVDF HSV 900 (15) PMMA (3) NMP (82) Comp. 8 PVDF HSV 900 (15) PEG 600 Da (3) NMP (82) C1 PVDF HSV 900 (15) Copol. (3) NMP (82) C2 PVDF HSV 900 (15) Copol. (7) NMP (78) C3 PVDF HSV 900 (15) Copol. (10) NMP (75)

(82) 4.3/Results

(83) The following results are obtained.

(84) Entirely predictably, it is observed that the membrane Comp. 2 based on polysulfone (PSF) begins to coagulate very soon (induction time of 2 s) and coagulates very rapidly (rate 1300 times greater than the membrane Comp. 1 based on PVDF). The membrane Comp. 3 based on cellulose triacetate (CTA) begins to coagulate two times sooner than the membrane Comp. 1 (2130 s versus 4060 s) and its rate of coagulation is similar.

(85) The addition of an additive, such as PEG, at a level of 3% by weight (Comp. 8) increases the induction time and very slightly decreases the rate of coagulation of the collodion based on PVDF. LiCl (Comp. 4) and PVP (Comp. 5 and Comp. 6) decrease the induction time by 40% and increase the rate of coagulation by 40%.

(86) The incorporation of PMMA in the collodion (Comp. 7) very markedly advances the start of the coagulation, which takes place approximately 4 times sooner than for the additive-free collodion Comp. 1.

(87) The rates of coagulation of the collodions in accordance with the invention C1 to C3 are markedly greater than that of Comp. 1. A decrease in the induction time of 600% and an increase in the rate of coagulation of 350% are found. In comparison with the collodions Comp. 4 to Comp. 8 comprising additives other than the amphiphilic block copolymer in accordance with the invention, the induction times are reduced by a factor of between 3.7 and 7.7. The rates of coagulation are increased by a factor from 2 to 4.5.

(88) Additional tests have shown the addition of the amphiphilic block copolymer in accordance with the invention to collodions comprising other conventional additives also makes it possible to accelerate the coagulation. Thus, the addition of 3% by weight of the amphiphilic block copolymer in accordance with the invention to a collodion additionally comprising LiCl makes it possible to decrease the induction time by a factor of 4.1 and increase the rate of coagulation by a factor of 2.2.

(89) In addition, the induction times are shorter in proportion and the rate of coagulation is greater in proportion as the concentration of amphiphilic block copolymer in accordance with the invention in the collodion increases.

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