Process for preparing an ion-exchange composite material comprising a specific polymer matrix and a filler consisting of ion-exchange particles

Abstract

The invention relates to a process for preparing a composite material comprising a fluorinated polymeric matrix and a filler consisting in ion exchange inorganic particles comprising a step for in situ synthesis of said particles within the polymeric matrix, said matrix comprising at least one first copolymer comprising at least two types of fluorinated recurrent units, a type of which bears at least one pendant maleic anhydride group.

Claims

1. A process for preparing a composite material comprising a fluorinated polymeric matrix and a filler consisting of ion exchange inorganic particles comprising a step for synthesizing in situ said particles within the polymeric matrix, said matrix comprising at least one first copolymer consisting of a copolymer comprising at least two types of fluorinated recurrent units, one type of which bears at least one pendant maleic anhydride group.

2. The process according to claim 1, wherein the in situ synthesis step is carried out in an extruder.

3. The process according to claim 1, wherein the in situ synthesis step is carried out with a sol-gel method.

4. The process according to claim 1, wherein the in situ synthesis step is carried out with a sol-gel method comprising the following operations: an operation for putting the first copolymer and if necessary the constitutive distinct (co)polymer(s) of the matrix, in contact with one or several precursors of the inorganic particles, said precursor(s) fitting the following formula (I):
(X).sub.y-n-M-(R).sub.n(I) wherein: M is a metal element or a metalloid element; X is a hydrolyzable chemical group; R is an ion exchange chemical group or a precursor group of an ion exchange chemical group; y corresponds to the valency of the element M; and n is an integer ranging from 0 to (y?1); a hydrolysis-condensation operation of said precursor(s), in return for which inorganic particles are obtained, resulting from the hydrolysis-condensation of said precursors; in the case when R is a precursor group of an ion exchange chemical group, an operation for transforming the precursor group into an ion exchange chemical group or, in the case when n=0, an operation for functionalizing said particles with ion exchange chemical groups.

5. The process according to claim 1, wherein the in situ synthesis step is carried out with a sol-gel method comprising the following steps: an operation for hydrolysis of one or several precursors of inorganic particles of the following formula (I):
(X).sub.y-n-M-(R).sub.n(I) wherein: M is a metal element or a metalloid element; X is a hydrolyzable chemical group; R is an ion exchange chemical group or a precursor group of an ion exchange chemical group; y corresponds to the valency of element M; and n is an integer ranging from 0 to (y?1); an operation for putting the hydrolyzate obtained in the preceding step in contact with the first copolymer and if necessary the distinct (co)polymer(s) entering the composition of the matrix; an operation for heating the resulting mixture to an effective temperature for generating transformation of the hydrolyzate into inorganic particles; in the case when R is a precursor group of an ion exchange chemical group, an operation for transforming the precursor group into an ion exchange chemical group or, in the case when n=0, an operation for functionalizing said particles with ion exchange chemical groups.

6. The process according to claim 4, wherein M is silicon, titanium, aluminium, germanium, tin or lead.

7. The process according to claim 4, wherein X is an OR group or a halogen atom, R representing an alkyl group.

8. The process according to claim 4, wherein R is a cation exchange group of formula R.sup.2Z.sup.1, wherein: R.sup.2 is a simple bond, a linear or branched alkylene group, and optionally for which one or several hydrogen atoms are substituted with a halogen atom, such as fluorine, or R.sup.2 is a cyclic hydrocarbon group; Z.sup.1 is a group SO.sub.3H, PO.sub.3H.sub.2, CO.sub.2H, optionally as salts.

9. The process according to claim 4, wherein R is a group of formula R.sup.2Z.sup.3, wherein: R.sup.2 is a simple bond, a linear or branched alkylene group, and optionally for which one or several hydrogen atoms are substituted with a halogen atom, such as fluorine, or R.sup.2 is a cyclic hydrocarbon group; Z.sup.3 is a precursor group of a group Z.sup.1 wherein Z.sup.1 is a group SO.sub.3H, PO.sub.3H.sub.2, CO.sub.2H, optionally as salts.

10. The process according to claim 9, wherein the precursor is a precursor of the following formula (II):
(OR).sub.4-nSi(R).sub.n(II) wherein: R is an alkyl group; R corresponds to the formula R.sup.2Z.sup.3, R.sup.2 being a linear or branched alkylene group, comprising from 1 to 30 carbon atoms, and optionally for which one or several hydrogen atoms are substituted with a halogen atom, such as fluorine and Z.sup.3 is a precursor group of a group Z.sup.1 wherein Z.sup.1 is a group SO.sub.3H, PO.sub.3H.sub.2, CO.sub.2H, optionally as salts; n is an integer ranging from 1 to 3.

11. The process according to claim 10, wherein the precursor is mercaptopropyltriethoxysilane of formula:
HS(CH.sub.2).sub.3Si(OCH.sub.2CH.sub.3).sub.3.

12. The process according to claim 4, wherein the precursor(s) are used in combination with a precondensate comprising recurrent units of the following formula (III):
M(X).sub.y-2(III) wherein: M is a metal or metalloid element; X is a hydrolyzable chemical group; y corresponds to the valency of element M.

13. The process according to claim 1, wherein the matrix exclusively consists of said first copolymer.

14. The process according to claim 1, wherein the matrix comprises, in addition to said first copolymer, at least one other (co)polymer distinct from said first copolymer.

15. The process according to claim 14, wherein the distinct (co)polymer is selected from among fluorinated thermoplastic polymers.

16. The process according to claim 15, wherein the fluorinated thermoplastic polymers are not ion exchange polymers, said fluorinated thermoplastic polymers selected from among polytetrafluoroethylenes (PTFE), poly(vinylidene fluoride)s (PVDF), fluorinated ethylene-propylene copolymers (FEP), copolymers of ethylene and tetrafluoroethylene (ETFE), copolymers of vinylidene fluoride and hexafluoropropene (PVDF-HFP) and mixtures thereof.

17. The process according to claim 1, wherein the first copolymer consists in a copolymer comprising, in addition to the fluorinated recurrent unit bearing the pendant maleic anhydride group, a recurrent unit fitting the following formula (V): ##STR00008## wherein R.sup.3, R.sup.4, R.sup.5 and R.sup.6 represent, independently of each other, a hydrogen atom, a halogen atom, a perfluoroalkyl group or a perfluoroalkoxy group, provided that at least one of the groups R.sup.3 to R.sup.6 represents a fluorine atom, a perfluoroalky group or a perfluoroalkoxy group.

18. The process according to claim 17, wherein a particular recurrent unit covered by the general definition of recurrent units of formula (V) corresponds to a recurrent unit of the following formula (VII): ##STR00009##

19. The process according to claim 1, wherein the first copolymer further comprises a recurrent unit of the following formula (IX): ##STR00010##

20. The process according to claim 1, wherein the fluorinated recurrent unit comprising a pendant maleic anhydride group is a recurrent unit of the following formula (X): ##STR00011## wherein R.sup.7 to R.sup.9 represent, independently of each other, a hydrogen atom, a halogen atom, a perfluoroalkyl group.

21. The process according to claim 20, wherein a particular recurrent unit covered by the general definition of recurrent units of formula (X) corresponds to a recurrent unit of the following formula (XI): ##STR00012##

22. The process according to claim 1, wherein the first copolymer is a copolymer comprising a first type of recurrent unit of formula (VII) ##STR00013## a second type of recurrent unit of formula (IX) ##STR00014## and a third type of recurrent unit of formula (XI) ##STR00015##

23. The process according to claim 1, wherein the first copolymer comprises, except for the fluorinated recurrent units comprising a pendant maleic anhydride group, one or several recurrent units with formula(e) identical with that(those), if necessary, of the distinct (co)polymers entering the composition of the fluorinated polymer matrix.

24. A composite material comprising a fluorinated polymeric matrix comprises at least one first copolymer consisting of a copolymer comprising at least two types of fluorinated recurrent units, one type of which bears at least one pendant maleic anhydride group, and a filler consisting of ion exchange inorganic particles.

25. An electrolytic membrane for a fuel cell comprising a material as defined in claim 24.

Description

SHORT DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 to 3 represent photographs taken with an electron microscope of three examples of materials prepared according to an embodiment of the invention discussed in Example 1.

(2) FIG. 4 illustrates a photograph taken with an electron microscope of a material non-compliant with the invention, the preparation of which is discussed in example 1.

(3) FIGS. 5 to 7 illustrate photographs taken with electron microscopy of three exemplary materials prepared according to the operating procedure discussed in example 2.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

Example 1

(4) This example illustrates the preparation of various materials according to the invention including, before introduction into the extruder, a step for pre-hydrolysis of the precursors, the preparation methods of which are mentioned in the examples above.

(5) The general operating procedure of this pre-hydrolysis step is the following.

(6) x g of ethanol then y g of a 10.sup.?2 N hydrochloric acid solution are consecutively added to a previous mixture of A g of mercaptopropyltriethoxysilane [HS(CH.sub.2).sub.3Si(OEt).sub.3] and B g of a precondensate of dimethoxysilane, for which the recurrent unit is Si(OCH.sub.3).sub.2O.

(7) After a reaction time of 2 hours at room temperature, the mixture of precursors is used (subsequently called a hydrolyzate) for the extrusion step.

(8) The operating conditions of the pre-hydrolysis step for the different tests applied are listed in the table below (with x=y).

(9) TABLE-US-00001 Test A (in g) B (in g) x and y (in g) 1 4.73 5.27 1.43 2a, 2b 9.52 1.61 1.35 3 10.31 3.67 1.34

(10) The different hydrolyzates obtained from these tests are then applied for forming, according to the method of the invention, composite materials including functionalizing inorganic particles and compatibilized with the matrix.

(11) The operating procedure is the following:

(12) In a micro-extruder provided by DSM, provided with two conical screws and a flat die, 11.4 g of a PVDF-HFP copolymer, 0.6 g of the first copolymer consisting in a copolymer of the aforementioned recurrent units of formulae (VII), (IX) and (XI) (this copolymer will be subsequently designated with PVDF-HFP-ADX, resulting from the transformation of a PVDF-HFP copolymer with 0.1% by mass of maleic anhydride) as well as the hydrolysates prepared beforehand are gradually incorporated, for which the characteristics in terms of ingredients appear in the table above.

(13) The mixing is carried out at 200? C. with a screw speed of 100 rpm until the torque is stabilized. The material is then extracted at the outlet by means of a micro-calendering machine also provided by DSM. Finally, a film of a hybrid material is recovered with a thickness comprised between 20 and 300 ?m.

(14) The PVDF-HFP-ADX copolymer used above may be prepared beforehand according to the following procedure.

(15) A mixture is prepared of Kynar Flex PVDF 2750 and of 2% by mass of maleic anhydride. This mixture is prepared by using a twin screw extruder at 230? C. and at 150 revolutions/minute at a flow rate of 10 kg/h. After the extrusion step, 1.8% of maleic anhydride remains in the product, the remainder being lost during the extrusion step. The thereby prepared part the is packaged in leak-proof aluminium bags. These bags are then irradiated under 3 Mrad. A grafting level of 20% to 30% is determined, this level being verified after a solubilization-precipitation step. The product is then placed in vacuo for one night at 130? C. in order to discharge the residual maleic anhydride and the hydrofluoric acid released during the irradiation.

(16) The table below groups the different proportions (in percent by mass based on the total mass of the mixture) of mercaptopropyltriethylsilane (below said to be the compound SH), of dimethoxysilane (below said to be the precondensate) and of the PVDF-HFP-ADX copolymer applied for the different tests.

(17) TABLE-US-00002 PVDF- Compound Pre- PVDF- HFP SH condensate HFP-ADX Test m (g) % m m (g) % m m (g) % m m (g) % m 1 11.4 51.82 4.73 21.50 5.27 23.95 0.6 2.73 2a 11.4 49.29 9.52 41.16 1.61 6.96 0.6 2.59 2b 11.4 50.60 9.52 42.25 1.61 7.15 0 0 3 11.4 43.88 10.31 39.68 3.67 14.13 0.6 2.31

(18) The table above groups the characteristics of the material in terms of mass percentages of SH function, of functional inorganic particles as mentioned above and of non-functional silica particles.

(19) TABLE-US-00003 PVDF-HFP + PVDF-HFP-ADX Non- except for test functional Functional 2b not including Function inorganic inorganic PVDF-HPP-ADX SH particles particles Mass Mass Mass Mass Mass Test (in g) (in g) Mass % (in g) Mass % (in g) % 1 12 2.52 14.40 4.01 22.91 5.50 31.42 2a 12 5.07 28.20 2.99 16.61 5.98 33.26 3 12 5.49 28.07 4.32 22.09 7.57 38.67 2b 11.4 5.07 29.17 2.99 17.20 5.98 34.41

(20) The SH function mass corresponds to the mass of HSCH.sub.2CH.sub.2CH.sub.2SiO.sub.3/2 created after hydrolysis-condensation reaction of mercaptopropyltriethoxysilane, i.e. corresponds to (A*127/238.42), A corresponding to the aforementioned mercaptopropyltriethoxysilane mass, 127 corresponding to the molar mass of HSCH.sub.2CH.sub.2CH.sub.2SiO.sub.3/2 and 238.42 corresponding to the molar mass of mercaptopropyltriethoxysilane.

(21) The mass percentage of SH function is a mass percentage of SH based on the total mass of the final material.

(22) This mass percentage, after considering the hydrolysis-condensation reactions, is evaluated with the following formula:
%=(A*127/238.42)/[(A*127/238.42)+(B*60/106.2)+C+D]*100
wherein:

(23) A, B, C and D respectively correspond to the masses of mercaptopropyltriethoxysilane (molar mass of 238.42), of dimethoxysilane precondensate (molar mass of 106.2), of PVDF-HFP and of PVDF-HFP-ADX; and

(24) 60 corresponds to the molar mass of SiO.sub.2 from the hydrolysis-condensation of the pre-condensate.

(25) The mass and the mass percentage of functional inorganic particles are determined in the following way.
Mass=(A*127/238.42)+(B*60/106.2)%=[(A*127/238.42+B*60/106.2)]/[(A*127/238.42)+(B*60/106.2)+C+D]*100

(26) The mass and the mass percentage of non-functional inorganic particles are determined in the following way.
Mass=(A*52/238.42)+(B*60/106.2)%=[(A*52/238.42+B*60/106.2)]/[(A*127/238.42)+(B*60/106.2)+C+D]*100
52 corresponds to the molar mass of SiO.sub.3/2 from the hydrolysis-condensation reactions of the mercaptopropyltriethoxysilane compounds.

(27) The behavior and the final properties of the obtained hybrid materials strongly depend on the morphology and therefore on the size of the fillers as well as on their dispersions within the polymeric matrix. The PVDF-HFP-ADX copolymer is used at 5% by mass based on PVDF-HFP. FIGS. 1 to 4 appended as an annex illustrate photographs of the materials respectively obtained in tests 1, 2 and 3, the last figure (FIG. 4) being a photograph of the material obtained without any PVDF-HFP-ADX copolymer (test 2b).

(28) As regards FIGS. 1 to 3, it is clearly apparent that the inorganic particles forming the functional inorganic phase are organized in micro-domains. As for FIG. 4, it appears that these particles are organized in macro-domains.

Example 2

(29) This example illustrates the preparation of materials according to the invention on operating bases similar to those of Example 1 except that the polymeric matrix exclusively consists of a PVDF-HFP-ADX copolymer prepared by transformation of a PVDF-HFP copolymer with a determined maleic anhydride mass proportion. Three tests were contemplated with respectively a PVDF-HFP-ADX copolymer prepared with 0.15% by mass of maleic anhydride (test 4), a PVDF-HFP-ADX copolymer prepared with 0.24% by mass of maleic anhydride (test 5) and a PVDF-HFP-ADX copolymer prepared with 0.75% by mass of maleic anhydride (test 6).

(30) The operating conditions of the prehydrolysis step for the different tests applied are stated in the table below (with x=y).

(31) TABLE-US-00004 Test A (in g) B (in g) x and y (in g) 4 9.52 1.61 1.35 5 9.52 1.61 1.35 6 9.52 1.61 1.35

(32) The different hydrolyzates obtained from these tests are then applied in order to form, according to the process of the invention, composite materials including inorganic particles functionalized and compatibilized with the matrix.

(33) The table below groups the different proportions (in percent by mass based on the total mass of the mixture} of mercaptopropyltriethylsilane (below said to be the compound SH), of dimethoxysilane (below is said to be the precondensate) and the PVDF-HFP-ADX copolymer applied for the different tests.

(34) TABLE-US-00005 PVDF- Compound HFP-ADX SH Precondensate Test m (g) % m m (g) % (m) m (g) % m 4 12 51.88 9.52 41.16 1.61 6.96 5 12 51.88 9.52 41.16 1.61 6.96 6 12 51.88 9.52 41.6 1.61 6.96

(35) The table below groups the characteristics of the material in terms of mass percentages of SH function, of functional inorganic particles as mentioned above, and non-functional silica particles.

(36) TABLE-US-00006 Non-functional Functional Function inorganic inorganic SH particles particles Test m (in g) % m m (en g) % m m (in g) % m 4 5.07 28.20 2.99 16.61 5.98 33.26 5 5.07 28.20 2.99 16.61 5.98 33.26 6 5.07 28.20 2.99 16.61 5.98 33.26

(37) FIGS. 5 to 7 enclosed as an annex illustrate photographs of materials respectively obtained in tests 4 to 6, from which it clearly emerges that the inorganic particles forming the functional inorganic phase are organized as microdomains, the morphology being all the finer since the maleic anhydride levels are high.

Example 3

(38) In order to test the possibility of applying the materials obtained according to the process of the invention as a fuel cell membrane, it was proceeded with chemical transformation of the functions SH and SO.sub.3H with the aforementioned materials of tests 4 to 6.

(39) In order to do this, these materials are treated by immersion in an oxidizing solution of hydrogen peroxide H.sub.2O.sub.2 at 50% by mass for 7 days at room temperature.

(40) After 7 days of stirring, the materials are rinsed 3 times with permuted water and it is then proceeded with a fourth rinse for 24 hours, in order to remove the remainder of hydrogen peroxide and any forms of impurities.

(41) The number of proton conducting sites is then determined further called ion exchange capacity (known under the acronym of IEC) by direct acid-base dosage. To do this, the materials are immersed in a 2M NaCl solution for 24 hours for total exchange of protons from the groups SO.sub.3H. The thereby obtained materials are then dried in vacuo for 24 hours at 60? C. before determining the dry mass thereof (said to be M.sub.samp).

(42) The protons released of the solution are dosed by colorimetry (by using phenolphtalein) with a titrating solution of 0.05 M NaOH.

(43) The IEC is then determined with the following formula:
IEC (in mequiv.Math.g.sup.?1)=(1000*C.sub.NaoH*V.sub.NaoH)/M.sub.samp

(44) wherein: C.sub.NaOH corresponds to the concentration of the soda solution; V.sub.NaOH corresponds to the volume of NaOH at equivalence; and M.sub.samp corresponds to the dry mass of the material.

(45) The ion exchange capacities obtained with the different materials tested appear in the table below.

(46) TABLE-US-00007 Material IEC Material from test 4 1.07 Material from test 5 0.82 Material from test 6 0.98

(47) The aforementioned materials all have a large ion exchange capacity, the values of which are of the same order of magnitude as those of Nafion?.

(48) Furthermore, the morphology attained with the use of compatibilizing agents according to the definition of the invention gives the possibility of obtaining a percolated network of proton-conducting inorganic particles within the polymeric matrix.