CN113736134B - Modified expanded polytetrafluoroethylene, preparation method thereof, composite ion exchange membrane and application thereof - Google Patents

Modified expanded polytetrafluoroethylene, preparation method thereof, composite ion exchange membrane and application thereof Download PDF

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CN113736134B
CN113736134B CN202111310329.4A CN202111310329A CN113736134B CN 113736134 B CN113736134 B CN 113736134B CN 202111310329 A CN202111310329 A CN 202111310329A CN 113736134 B CN113736134 B CN 113736134B
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expanded polytetrafluoroethylene
ptfe
modified expanded
freezing medium
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CN113736134A (en
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贾雯迪
张泽天
刘昊
董天都
刘一晨
李道喜
李丹
周朝毅
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Spic Hydrogen Energy Technology Development Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/36—After-treatment
    • C08J9/40—Impregnation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J47/00—Ion-exchange processes in general; Apparatus therefor
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/20—Manufacture of shaped structures of ion-exchange resins
    • C08J5/22—Films, membranes or diaphragms
    • C08J5/2206—Films, membranes or diaphragms based on organic and/or inorganic macromolecular compounds
    • C08J5/2218—Synthetic macromolecular compounds
    • C08J5/2231—Synthetic macromolecular compounds based on macromolecular compounds obtained by reactions involving unsaturated carbon-to-carbon bonds
    • C08J5/2237—Synthetic macromolecular compounds based on macromolecular compounds obtained by reactions involving unsaturated carbon-to-carbon bonds containing fluorine
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/26—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a solid phase from a macromolecular composition or article, e.g. leaching out
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2201/00—Foams characterised by the foaming process
    • C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
    • C08J2201/048—Elimination of a frozen liquid phase
    • C08J2201/0482—Elimination of a frozen liquid phase the liquid phase being organic
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2201/00—Foams characterised by the foaming process
    • C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
    • C08J2201/048—Elimination of a frozen liquid phase
    • C08J2201/0484—Elimination of a frozen liquid phase the liquid phase being aqueous
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
    • C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
    • C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
    • C08J2327/18—Homopolymers or copolymers of tetrafluoroethylene

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Medicinal Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Inorganic Chemistry (AREA)
  • Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)
  • Fuel Cell (AREA)

Abstract

The invention provides modified expanded polytetrafluoroethylene, a preparation method thereof, a composite ion exchange membrane and application thereof. The average pore diameter of the modified expanded polytetrafluoroethylene is 0.05-0.5 mu m, the porosity is 50-95%, the pore diameter distribution of more than 99% of pores of the modified expanded polytetrafluoroethylene is within +/-10% of the most probable pore diameter, and the dispersion coefficient of gram weight of the modified expanded polytetrafluoroethylene is less than 10%. The modified e-PTFE has narrow pore size distribution, the dispersion coefficient of gram weight is less than 10%, so the uniformity is good, and the modified expanded polytetrafluoroethylene can still keep good mechanical property when the average pore size and the porosity are controlled within the range, so the stability is good.

Description

Modified expanded polytetrafluoroethylene, preparation method thereof, composite ion exchange membrane and application thereof
Technical Field
The invention relates to the technical field of expanded polytetrafluoroethylene modification, in particular to modified expanded polytetrafluoroethylene, a preparation method thereof, a composite ion exchange membrane and application thereof.
Background
At present, all ion exchange membranes of vehicle fuel cells are prepared on the basis of perfluorosulfonic acid resin (PFSA), which is mainly determined by two factors of safety, reliability and full life cycle cost. Dupont first developed the first generation of PFSA ion exchange membrane commercialization products in the 90's of the 20 th century, including Nafion112, Nafion115, and Nafion117, among others. The product adopts a melt extrusion process and has good stability and mechanical properties. The second generation of Nafion membranes use solution cast membrane processes, such as Nafion211, Nafion212, to reduce costs. In order to solve the problem of large thickness of the PFSA ion exchange membranes in the first two generations, the mainstream development direction is to adopt e-PTFE to reinforce the proton exchange membrane.
Polytetrafluoroethylene (PTFE) has many advantages such as high and low temperature resistance, acid and alkali resistance, corrosion resistance, etc., and is called "plastic king". The expanded PTFE material e-PTFE stretched in both directions is used widely in filtering gas and liquid and as the support layer of ion exchange membrane for fuel cell. The composite ion exchange membrane taking the e-PTFE as the supporting layer generally adopts a sandwich structure, the thickness of a commercial product is usually 5-30 μm, compared with a homogeneous phase ion exchange membrane, the composite ion exchange membrane can obviously improve the mechanical strength, prolong the service life and other properties of the ion exchange membrane, but has higher requirements on the variation coefficients (CV values) of the average pore diameter, the porosity, the strength, the air permeability, the thickness, the gram weight and other properties of the e-PTFE. On the premise of allowing the cost, reducing the CV value of each performance of the e-PTFE is an important means for improving the uniformity and the performance stability.
The current research on the preparation method of the e-PTFE mainly focuses on raw materials, auxiliary agents and processing processes. Some researches show that the physical and chemical properties of the e-PTFE can be remarkably changed by carrying out physical or chemical pretreatment on the processed and formed e-PTFE. Tanghaolin et al (CN 100386367C) of Wuhan theory of technology university improves the hydrophilicity of e-PTFE by a method of mixed solution impregnation, plasma treatment, plasma grafting and radiation grafting, thereby improving the wettability of the perfluorosulfonic acid resin solution in the e-PTFE. However, the method does not improve the pore size distribution of the e-PTFE, and the pore size distribution of the e-PTFE influences the wetting uniformity of the subsequent full-pair sulfonic acid resin in the pore size, so that the performance stability of the formed ion exchange membrane is improved.
Disclosure of Invention
The invention mainly aims to provide modified e-PTFE, a preparation method thereof, a composite ion exchange membrane and application thereof, and aims to solve the problems of poor stability and uniformity of the e-PTFE in the prior art.
In order to achieve the above object, according to one aspect of the present invention, there is provided a modified expanded polytetrafluoroethylene, wherein an average pore diameter of the modified expanded polytetrafluoroethylene is 0.05 μm to 0.5 μm, a porosity is 50% to 95%, a pore diameter distribution of more than 99% of pores of the modified expanded polytetrafluoroethylene is within ± 10% of a most probable pore diameter, and a dispersion coefficient of a gram weight of the modified expanded polytetrafluoroethylene is less than 10%.
Further, the average pore diameter of the modified expanded polytetrafluoroethylene is 0.05-0.4 μm, preferably the average pore diameter of the modified expanded polytetrafluoroethylene is 0.1-0.4 μm, and more preferably the average pore diameter of the modified expanded polytetrafluoroethylene is 0.2-0.4 μm; and/or a porosity of 55% to 95%, preferably a porosity of 60% to 95%.
Further, the modified expanded polytetrafluoroethylene is of a film structure, the thickness of the modified expanded polytetrafluoroethylene is 2-30 μm, preferably the thickness of the modified expanded polytetrafluoroethylene is 2-25 μm, more preferably the thickness of the modified expanded polytetrafluoroethylene is 2-20 μm, and further preferably the thickness of the modified expanded polytetrafluoroethylene is 3-18 μm.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for preparing modified expanded polytetrafluoroethylene, the method comprising: step S1, impregnating and filling a freezing medium into the pores of the e-PTFE to obtain a wet material; step S2, at least part of the freezing medium in the wet material is subjected to ice crystallization to obtain a solid material; and step S3, freezing and drying the solid material to obtain the modified expanded polytetrafluoroethylene.
Further, the freezing medium is selected from one or more of dimethyl sulfoxide, water, tertiary butanol or camphene, preferably the freezing medium is a mixture of dimethyl sulfoxide and water, and the mass content of water in the mixture is below 20% or above 85%.
Further, the mass ratio of the freezing medium to the expanded polytetrafluoroethylene is 10: 1-500: 1.
Further, in step S1, the immersion filling is performed by a method of immersion, coating or liquid casting, and the immersion filling time is 0.5 to 20 hours, preferably 0.5 to 12 hours, and more preferably 0.5 to 6 hours.
Further, the temperature of ice crystallization is-120 ℃ to 40 ℃, and the time of ice crystallization is 0.5h to 3 h; preferably, the temperature of the ice crystallization is-80 ℃ to 39 ℃, more preferably-50 ℃ to 35 ℃, and still more preferably-30 ℃ to 15 ℃.
Further, the initial temperature of freeze drying is-80 ℃ to 20 ℃, the heating rate is 2 ℃/h to 5 ℃/h, the final temperature of freeze drying is-30 ℃ to 60 ℃, the pressure of freeze drying is 0.1Pa to 20Pa, and the time of freeze drying is preferably 1h to 48 h.
According to another aspect of the present invention, there is provided a composite ion exchange membrane comprising a base membrane and a resin, wherein the base membrane is the modified expanded polytetrafluoroethylene or the modified expanded polytetrafluoroethylene prepared by the above preparation method, and the resin is filled in the pores of the modified expanded polytetrafluoroethylene.
Further, the resin is a perfluorosulfonic acid resin.
According to a further aspect of the invention there is provided a use of a composite ion exchange membrane as described above, the use comprising applying the composite ion exchange membrane to a waterproof moisture permeable textile material, a medical implant, a sealing tape, a gas separation membrane, a water treatment membrane, a salinity gradient power generation or mesoporous material.
By applying the technical scheme of the invention, the pore size distribution of the modified e-PTFE is narrower, the dispersion coefficient of the gram weight is less than 10 percent, so the uniformity is better, and the modified expanded polytetrafluoroethylene can still keep good mechanical property when the average pore size and the porosity are controlled within the range, so the stability is better.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 shows the pore size distribution plots for example 1 of the present invention and comparative example 1;
FIG. 2 shows the contact angle of modified e-PTFE of example 1 of the present invention with a perfluorosulfonic acid resin solution at 16 s;
FIG. 3 shows the contact angle of e-PTFE of comparative example 1 of the present invention with a perfluorosulfonic acid resin solution at 16 s;
FIG. 4 shows a scanning electron micrograph of a composite ion exchange membrane according to example 28 of the present invention.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
As analyzed by the background art of the application, the e-PTFE in the prior art has poor stability and uniformity, and in order to solve the problem, the application provides modified e-PTFE, a preparation method thereof, a composite ion exchange membrane and application thereof.
In a typical embodiment of the present application, there is provided a modified expanded polytetrafluoroethylene, wherein an average pore diameter of the modified expanded polytetrafluoroethylene is 0.05 μm to 0.5 μm, a porosity is 50% to 95%, a pore diameter distribution of pores of the modified expanded polytetrafluoroethylene exceeding 99% is within ± 10% of a most probable pore diameter, and a dispersion coefficient of a grammage of the modified expanded polytetrafluoroethylene is less than 10%.
The modified e-PTFE has narrow pore size distribution, the dispersion coefficient of gram weight is less than 10%, so the uniformity is good, and the modified expanded polytetrafluoroethylene can still keep good mechanical property when the average pore size and the porosity are controlled within the range, so the stability is good.
The modified expanded polytetrafluoroethylene preferably has a dispersion coefficient of gram weight of 5% or less.
The modified e-PTFE in the present application can be used in a wide variety of fields, and if the modified e-PTFE is used for preparing a composite ion exchange membrane, the increase of the average pore diameter and the increase of the porosity of the modified e-PTFE are beneficial to the filling of a resin solution.
In order to obtain modified expanded polytetrafluoroethylene with good filling performance and mechanical strength, the average pore diameter of the modified expanded polytetrafluoroethylene is preferably controlled to be 0.05-0.4 μm, more preferably 0.1-0.4 μm, and even more preferably 0.2-0.4 μm; the porosity is preferably 55% to 95%, and more preferably 60% to 95%.
When the modified e-PTFE is used for preparing the composite ion exchange membrane, on the basis of ensuring excellent ion exchange performance, in order to improve the mechanical strength as much as possible, the thickness of the modified e-PTFE is preferably controlled to be 2-30 μm, the thickness of the modified e-PTFE is preferably controlled to be 2-25 μm, the thickness of the modified e-PTFE is more preferably 2-20 μm, and the thickness of the modified e-PTFE is more preferably 3-18 μm.
In another exemplary embodiment of the present application, there is provided a method of preparing modified e-PTFE, the method comprising: step S1, impregnating and filling a freezing medium into the pores of the e-PTFE to obtain a wet material; step S2, at least part of the freezing medium in the wet material is subjected to ice crystallization to obtain a solid material; and step S3, freeze-drying the solid material to obtain the modified e-PTFE.
The freezing medium is impregnated and filled into the pores of the e-PTFE, and after the freezing medium is solidified into a solid, the crystal is highly oriented, the volume is expanded, and the expansion of the e-PTFE is accompanied. And then, the freezing medium is removed by adopting a freeze drying method, so that the structural size of the porous material can be maintained, and the structure similar to that in the freezing medium filling state is maintained after the freezing medium is removed. The modified e-PTFE prepared by the method has narrow pore size distribution and small dispersion coefficient of gram weight, so the modified e-PTFE has good uniformity and can still keep good mechanical property, thereby having good stability.
Since impregnation of the e-PTFE with different freezing media has different effects on the average pore size, in order to allow the freezing media to crystallize as easily as possible under relatively easy-to-achieve conditions and to be removed by the freeze-drying method under relatively mild conditions, in some embodiments, the freezing media is selected from one or more of dimethyl sulfoxide, water, tert-butanol or camphene. When a mixture of water and dimethyl sulfoxide is used as a freezing medium, the expansion rate of the freezing medium is high, a completely crystallized mixture can be formed at any ratio below-70 ℃, and the influence of a small amount of liquid-phase water or dimethyl sulfoxide on the average pore diameter of the e-PTFE is extremely small. In order to reduce the cost, the mass content of water in the mixture is preferably below 20% or above 85%, so that the solid phase content in the freezing medium mixture can be ensured to be higher than 80% under the condition of not lower than-30 ℃, and relatively abundant pores are formed after freeze drying.
The step S1 in the above preparation method can refer to a conventional method for dip filling, and in some embodiments, the dip filling is performed by a method of soaking, coating or liquid casting based on the fluidity of the freezing medium in the above step S1, preferably the time for the dip filling is 0.5h to 20h, preferably the time for the dip filling is 0.5h to 12h, and more preferably the time for the dip filling is 0.5h to 6 h. The wettability of the freezing medium is different from that of the e-PTFE, the alcohol freezing medium is easier to impregnate and fill the e-PTFE, and corresponding impregnation time is selected for different freezing media, so that the implementation efficiency of the preparation method is improved, for example, when the freezing medium is a mixture of dimethyl sulfoxide and water, the impregnation and filling time is preferably 2-12 hours; when the freezing medium is tert-butyl alcohol, the time for soaking and filling is preferably 0.5-4 h; when the freezing medium is camphene, the time for soaking and filling is preferably 6-20 h.
In order to impregnate and fill the freezing medium into the e-PTFE as much as possible so as to enrich the porosity, the mass ratio of the freezing medium to the e-PTFE is preferably 10:1 to 500: 1. Certainly, the sizes of the pores formed by different freezing media are different, and a person skilled in the art can select a corresponding mass ratio according to the porosity requirement and the characteristics of the pore sizes, for example, when the freezing media is a mixture of dimethyl sulfoxide and water, the mass ratio of the freezing media to the e-PTFE is preferably 10:1 to 400: 1; when the freezing medium is tert-butyl alcohol, the mass ratio of the freezing medium to the e-PTFE is preferably 50: 1-500: 1; when the freezing medium is camphene, the mass ratio of the freezing medium to the e-PTFE is preferably 80: 1-300: 1.
The degree of ice crystallization of the freezing medium can also be adjusted, and in some embodiments, the temperature of the ice crystallization is-120 ℃ to 40 ℃, and the time of the ice crystallization is 0.5h to 3 h. The technical personnel in the field can set the corresponding ice crystallization temperature according to the concrete composition of the selected freezing medium, on one hand, the efficient utilization of the refrigerant energy can be realized, and on the other hand, the ice crystallization efficiency is improved, for example, when the freezing medium is a mixture of dimethyl sulfoxide and water, the ice crystallization temperature is preferably-120 ℃ to-5 ℃, and more preferably-70 ℃ to-10 ℃; when the freezing medium is tert-butyl alcohol, the temperature of ice crystallization is preferably-80 ℃ to 39 ℃, more preferably-50 ℃ to 35 ℃, and even more preferably-30 ℃ to 15 ℃. When the freezing medium is camphene, the ice crystallization temperature is preferably-10 ℃ to 40 ℃, more preferably-5 ℃ to 38 ℃, and further preferably 0 ℃ to 35 ℃.
In order to completely remove the freezing medium filled in the e-PTFE and maintain the size of the pores of the frozen freezing medium as much as possible, the initial temperature of freeze drying is preferably controlled to be-80-20 ℃, the temperature rise rate is 2-5 ℃/h, the final temperature of freeze drying is-30-60 ℃, the final temperature of freeze drying is preferably-20 ℃, and the pressure of freeze drying is 0.1-20 Pa. Because the sublimation temperature and the sublimation rate of each freezing medium are different, in order to fully exert the advantages of each freezing medium as far as possible and improve the pore size distribution uniformity and the porosity of the modified expanded polytetrafluoroethylene as far as possible, different freeze-drying conditions are set for different freezing media, for example, when the freezing medium is a mixture of dimethyl sulfoxide and water, the initial temperature of freeze-drying is controlled to be-80 ℃ to-20 ℃, the final temperature of freeze-drying is controlled to be-30 ℃ to 30 ℃, and the pressure of freeze-drying is 0.1Pa to 10 Pa; when the freezing medium is tert-butyl alcohol, controlling the initial temperature of freeze drying to be-30-20 ℃, the final temperature of freeze drying to be 0-50 ℃, and the pressure of freeze drying to be 0.1-20 Pa; when the freezing medium is camphene, the initial temperature of freeze drying is controlled to be-30-15 ℃, the final temperature of freeze drying is controlled to be 10-60 ℃, and the pressure of freeze drying is 0.1-20 Pa. In some embodiments, the solid material is freeze-dried for 1-48 hours to achieve sublimation of the freezing medium as thoroughly as possible.
In another exemplary embodiment of the present application, a composite ion exchange membrane is provided, which includes a base membrane and a resin, wherein the base membrane is the modified expanded polytetrafluoroethylene or the modified expanded polytetrafluoroethylene prepared by the preparation method, and the resin is filled in pores of the modified expanded polytetrafluoroethylene.
The composite ion exchange membrane prepared by taking the modified e-PTFE as the supporting layer has a lower thickness CV value and a more uniform membrane thickness, is beneficial to the preparation of a membrane electrode of a fuel cell, and improves the stability of the performance of the composite ion exchange membrane product; the pore size distribution of the modified e-PTFE becomes narrow, and the modified e-PTFE can still keep good mechanical property, so that the impregnation and filling of resin solutions such as perfluorinated sulfonic acid resin and the like are facilitated, the processing and production difficulty is reduced, and the proton transmission capability of the composite ion exchange membrane is improved.
The resin used for the composite ion exchange membrane of the present application can be selected according to different ion exchange requirements, and in some embodiments, the resin is a perfluorosulfonic acid resin so as to meet the use requirements of the membrane electrode of the fuel cell.
In yet another exemplary embodiment of the present application, there is provided a use of a composite ion exchange membrane as described above, comprising applying the composite ion exchange membrane to a waterproof moisture permeable textile material, a medical implant, a sealing tape, a separation membrane or a dielectric material. The product using the composite ion exchange membrane has certain promotion on the ion exchange capacity and the mechanical property.
The present application is described in further detail below with reference to specific examples, which should not be construed as limiting the scope of the invention as claimed.
e-pore size testing of PTFE: the test method is bubbleThe pressure method (gas-liquid displacement technology) adopts a dry method mode after wet method, namely fully wetting the e-PTFE with the liquid capable of infiltrating with the e-PTFE, applying pressure difference to two sides of the membrane, overcoming the surface tension of the infiltrating liquid in the pore channels of the membrane, and driving the infiltrating liquid to pass through the pore channels, thereby obtaining the pore diameter distribution of the e-PTFE. The air source is compressed air and nitrogen, and the test area is 3.14cm2. 3-5 groups of samples were taken each time for parallel experiments.
e-porosity testing of PTFE: the test equipment is a 0.01 g high-precision Tianping and true density analyzer; 3 square films of the same size and dimensions without wrinkles, defects and breakage were cut out as test specimens. The mass of 3 samples was weighed using an analytical balance. Bulk density was calculated as apparent density of the sample according to the following formula (1):
Figure DEST_PATH_IMAGE001
（1）
in the formula:
Figure 574352DEST_PATH_IMAGE002
bulk density of the sample in grams per cubic centimeter (g/cm)3）；
Figure DEST_PATH_IMAGE003
-mass measurement of the sample in grams (g);
Figure 36033DEST_PATH_IMAGE004
-thickness measurement of the sample in micrometers (μm);
Figure DEST_PATH_IMAGE005
sample area of the sample, fixed as the area of the sampling blade, and having a value of 25 cm2；
The porosity was calculated according to the following formula (2):
Figure 2721DEST_PATH_IMAGE006
（2）
in the formula:
Figure DEST_PATH_IMAGE007
-porosity of the sample, dimensionless physical quantity (%);
Figure 709515DEST_PATH_IMAGE008
apparent density of the sample, calculated for the test, in grams per cubic centimeter (g/cm)3）；
Figure DEST_PATH_IMAGE009
True density of the sample in grams per cubic centimeter (g/cm)3) And testing by a true density analyzer.
Film thickness test: the testing equipment is a contact flat head thickness gauge, three ePTFE membranes are cut by a cutter before and after slitting to serve as testing samples, the matrix type test is carried out on equidistant points along the MD (longitudinal direction) and TD (transverse direction) directions of the samples during thickness measurement, and the average value of each point is calculated to serve as the average thickness of the membranes.
The e-PTFE raw materials used in the examples were 2 types: e-PTFE-1 has a thickness of 7 + -1.5 μm, a porosity of 76.69%, an average pore diameter of 221.23 nm, tensile strengths of 77.65 MPa (MD) and 107.26 MPa (TD), and a thickness CV value of 16%; the thickness of the e-PTFE-2 is 16 +/-2 mu m, the porosity is 77.11%, the average pore diameter is 197.87nm, the tensile strength is 52.76 MPa (MD), 58.41 MPa (TD), and the thickness CV value is 12%.
In the examples, the Nafion resin D2020 solution used was purchased from Kemu.
Example 1
9 parts by mass of dimethyl sulfoxide and 1 part by mass of water were mixed at 25 ℃ to prepare a liquid refrigerant. And (3) coating the freezing medium by using a scraper, and soaking 0.05 part by mass of the e-PTFE-1 in the liquid freezing medium for 6 hours to completely infiltrate and fill the liquid into the pores of the e-PTFE-1 to obtain a wet material e-PTFE-1. The wet material e-PTFE-1 was crystallized at-30 ℃ for 0.5h to obtain a solid material. And (3) putting the solid material into freeze drying equipment, and freeze drying for 12 hours at 0.1-20 Pa. The initial freeze-drying temperature is-40 ℃, the temperature is slowly increased in the freeze-drying process, and the heating rate is 5 ℃/h. And (3) after the freeze-drying is finished, obtaining the modified e-PTFE-1. The contact angle of the modified e-PTFE-1 and the perfluorosulfonic acid resin solution at the 16 th s is shown in FIG. 2. The properties of the modified e-PTFE-1 are shown in Table 1.
Example 2
Unlike example 1, 1 part by mass of e-PTFE-1 was immersed in the above-mentioned liquid freezing medium.
Example 3
Unlike example 1, 0.45 parts by mass of dimethyl sulfoxide and 0.05 parts by mass of water were mixed at 25 ℃ to prepare a liquid refrigerant.
Example 4
18 parts by mass of water, 1 part by mass of dimethyl sulfoxide and 1 part by mass of tert-butanol were mixed at 45 ℃ to prepare a liquid refrigerant. 0.05 part by mass of e-PTFE-2 is soaked in a liquid freezing medium for 8 hours, so that the liquid is completely soaked and filled in the pores of the e-PTFE-2, and the wet material e-PTFE-2 is obtained. The wet material e-PTFE-2 was crystallized at-20 ℃ for 0.5h to obtain a solid material. And (3) putting the wet material into freeze drying equipment, and freeze drying for 8 hours at 0.1-20 Pa. The initial freeze-drying temperature is-30 ℃, the temperature is slowly increased in the freeze-drying process, and the heating rate is 5 ℃/h. And (3) after the freeze-drying is finished, obtaining the modified e-PTFE-2.
Example 5
In contrast to example 1, 18 parts by mass of water, 1 part by mass of dimethyl sulfoxide and 1 part by mass of tert-butanol were mixed at 45 ℃ to prepare a liquid refrigerant. 0.05 part by mass of e-PTFE-1 was immersed in a liquid freezing medium for 8 hours. The wet material e-PTFE-1 was ice-crystallized at-20 ℃. The initial freeze-drying temperature was-30 ℃.
Example 6
Unlike example 1, 10 parts by mass of t-butanol was mixed at 45 ℃ to prepare a liquid refrigerant. 0.05 part by mass of e-PTFE-1 was immersed in a liquid freezing medium for 0.5 hour. The wet material e-PTFE-1 was crystallized from ice at 10 ℃. The initial freeze-drying temperature was 20 ℃ and the freeze-drying temperature was maintained until the end of freeze-drying.
Example 7
Different from example 1, 1 part by mass of t-butanol and 9 parts by mass of camphene were mixed at 60 ℃ to prepare a liquid refrigerant. The wet material e-PTFE-1 was crystallized from ice at 20 ℃. The initial freeze-drying temperature is-5 ℃, the temperature is slowly increased in the freeze-drying process, the temperature rising rate is 5 ℃/h, and the temperature is not increased after the temperature is increased to 20 ℃.
Example 8
Unlike example 1, 6 parts by mass of camphene was made into a freezing medium in a liquid state at 60 ℃. 0.05 part by mass of e-PTFE-1 was immersed in the above-mentioned liquid freezing medium for 10 hours. The wet material e-PTFE-1 was ice-crystallized at-5 ℃. The initial freeze-drying temperature was 15 deg.C, and the freeze-drying temperature was maintained until freeze-drying was complete after warming to 60 deg.C.
Example 9
In contrast to example 1, 22.5 parts by mass of dimethyl sulfoxide and 2.5 parts by mass of water were mixed at 25 ℃ to prepare a liquid refrigerant. 0.05 part by mass of e-PTFE-1 was immersed in a liquid freezing medium for 20 hours.
Example 10
In contrast to example 1, 27 parts by mass of dimethyl sulfoxide and 3 parts by mass of water were mixed at 25 ℃ to prepare a liquid refrigerant.
Example 11
In contrast to example 1, 0.225 parts by mass of dimethyl sulfoxide and 0.025 parts by mass of water were mixed at 25 ℃ to prepare a liquid refrigerant.
Example 12
In contrast to example 1, 8 parts by mass of dimethyl sulfoxide and 2 parts by mass of water were mixed at 25 ℃ to prepare a liquid refrigerant.
Example 13
Unlike example 1, 1.5 parts by mass of dimethyl sulfoxide and 8.5 parts by mass of water were mixed at 25 ℃ to prepare a liquid refrigerant.
Example 14
In contrast to example 1, 1 part by mass of dimethyl sulfoxide and 9 parts by mass of water were mixed at 25 ℃ to prepare a liquid refrigerant.
Example 15
In contrast to example 1, 7 parts by mass of dimethyl sulfoxide and 3 parts by mass of water were mixed at 25 ℃ to prepare a liquid refrigerant.
Example 16
In contrast to example 1, 7 parts by mass of dimethyl sulfoxide and 3 parts by mass of water were mixed at 25 ℃ to prepare a liquid refrigerant. The wet material e-PTFE-1 was ice-crystallized at-80 ℃. The initial freeze-drying temperature was-60 ℃.
Example 17
In contrast to example 1, 8 parts by mass of dimethyl sulfoxide and 2 parts by mass of water were mixed at 25 ℃ to prepare a liquid refrigerant. The wet material e-PTFE-1 was ice-crystallized at-80 ℃. The initial freeze-drying temperature was-60 ℃.
Example 18
In contrast to example 1, the wet material e-PTFE-1 was ice-crystallized at-50 ℃ to give a solid material. The initial freeze-drying temperature was-60 ℃.
Example 19
In contrast to example 6, 10 parts by mass of t-butanol was mixed with a liquid freezing medium at 30 ℃ and 0.05 part by mass of e-PTFE-1 was immersed in the liquid freezing medium for 0.5 hour to completely infiltrate and fill the pores of the e-PTFE-1 with the liquid, thereby obtaining a wet material e-PTFE-1. The wet material e-PTFE-1 was crystallized on ice at 35 ℃ to obtain a solid material. The initial freeze-drying temperature was 20 ℃, warmed to 50 ℃ and held at the freeze-drying temperature until freeze-drying was complete.
Example 20
In contrast to example 1, the wet material e-PTFE-1 was ice-crystallized at-30 ℃ for 3 hours to give a solid material.
Example 21
Different from the embodiment 1, 0.05 part by mass of e-PTFE-1 is soaked in the freezing medium of the liquid for 0.5 h; the wet material e-PTFE-1 was crystallized at-120 ℃ for 0.5h to obtain a solid material. The initial freeze-drying temperature was-80 ℃.
Example 22
Unlike example 1, the temperature increase rate during freeze-drying was 2 ℃/h.
Example 23
Different from the embodiment 18, 0.05 part by mass of e-PTFE-1 was immersed in the above-mentioned liquid freezing medium for 3 hours; the wet material e-PTFE-1 was crystallized at-30 ℃ for 3 hours to obtain a solid material.
Example 24
In contrast to example 6, 2.5 parts by mass of t-butanol was mixed at 45 ℃ to prepare a liquid refrigerant.
Example 25
In contrast to example 6, 25 parts by mass of t-butanol was mixed at 45 ℃ to prepare a liquid refrigerant.
Example 26
Unlike example 8, 4 parts by mass of camphene was made into a freezing medium in a liquid state at 60 ℃.
Example 27
In contrast to example 8, 15 parts by mass of camphene was prepared as a liquid refrigeration medium at 60 ℃.
Example 28
The modified e-PTFE-1 prepared in example 1 was used as a support layer, and a solution of Nafion resin D2020 was used as a coating solution, followed by coating to obtain a composite wet membrane. Drying in an oven at 160 ℃ for 8 min to obtain the heterogeneous composite ion exchange membrane with the thickness of 12 mu m. The scanning electron micrograph of the composite ion exchange membrane is shown in FIG. 4.
Comparative example 1
The wet e-PTFE-1 of example 1 was dried at room temperature for 24 h to volatilize the liquid. The contact angle of e-PTFE-1 and the perfluorosulfonic acid resin solution at 16s is shown in FIG. 3.
Comparative example 2
The wet e-PTFE-2 of example 2 was dried at room temperature for 24 h to volatilize the liquid.
Comparative example 3
And e-PTFE-1 which is not treated is selected as a supporting layer, and Nafion resin D2020 solution is selected as coating liquid, and the coating liquid is coated to obtain the composite wet film. Drying in an oven at 160 ℃ for 8 min to obtain the heterogeneous composite ion exchange membrane with the thickness of 12 mu m.
The pore size distribution plots for the modified e-PTFE of example 1 and the e-PTFE of comparative example 1 are shown in FIG. 1. the modified e-PTFE-1 obtained by freeze-drying in example 1 has a larger average pore size, a narrower pore size distribution, and a smaller thickness CV value than the volatile dry liquid solvent in comparative example 1. Example 1 the contact angle of modified e-PTFE-1 with the perfluorosulfonic acid resin solution at 16s is shown in figure 2. A smaller contact angle indicates better wettability, i.e., the perfluorosulfonic acid resin solution is more easily wetted onto the e-PTFE. The contact angle of the modified e-PTFE-1 of example 1 is smaller than that of the unmodified e-PTFE of comparative example 1 (as shown in FIG. 3), which indicates that the perfluorinated sulfonic acid resin solution is more easily infiltrated into the modified e-PTFE of example 1 and is more suitable for being used as a support layer of a composite ion exchange membrane.
As can be seen from Table 1, compared with the volatile dry liquid solvent in the comparative example 2, the modified e-PTFE-2 obtained by freeze drying has larger average pore diameter, narrower pore diameter distribution, smaller thickness CV value and smaller contact angle with the perfluorinated sulfonic acid resin solution, and is more suitable for being used as a support layer of a composite ion exchange membrane in the example 4.
In example 11, the amount of the freezing medium added was small, and the impregnation effect on PTFE was insignificant, so that the CV values of thickness and grammage of e-PTFE prepared in example 11 were high.
As described above, the mass content of water in the mixture is less than 20% or more than 85%, so that the condition that the mass content of water in the mixture is not in the range under the condition that the temperature is not lower than-30 ℃ can be realized, and the ice crystallization can not be completely carried out at-30 ℃, thereby influencing the effect of modifying the e-PTFE. Therefore, the CV values of the thickness and the gram weight of the prepared e-PTFE-1 are obviously reduced compared with the example 12 in the example 17; similarly, example 16 produced e-PTFE-1 having significantly reduced CV values for thickness and grammage as compared to example 15.
The temperature of ice crystallization in example 21 was-120 ℃ because the freezing medium crystallized too fast, causing disorder in the direction of crystal growth, and thus the CV values of thickness and gram weight of the prepared e-PTFE-1 were high.
The performance of the composite ion exchange membrane prepared in example 28 and comparative example 3 is shown in table 2, and it can be seen from table 2 that, compared with comparative example 3, in example 28, the composite ion exchange membrane prepared by using modified e-PTFE-1 as a support layer has improved conductivity, reduced CV values of thickness and gram weight, improved electrochemical performance and uniformity of the membrane, and is more beneficial to being applied to fuel cells.
TABLE 1
Figure 461570DEST_PATH_IMAGE010
TABLE 2
Figure DEST_PATH_IMAGE011
From the above description, it can be seen that the above-described embodiments of the present invention achieve the following technical effects:
the modified e-PTFE has narrow pore size distribution, the dispersion coefficient of gram weight is less than 10%, so the uniformity is good, and the modified expanded polytetrafluoroethylene can still keep good mechanical property when the average pore size and the porosity are controlled within the range, so the stability is good.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (14)

1. A modified expanded polytetrafluoroethylene is characterized in that the average pore diameter of the modified expanded polytetrafluoroethylene is 214.73-258.82 nm, the porosity is 70.82-84.56%, the pore diameter of more than 99% of pores of the modified expanded polytetrafluoroethylene is distributed within +/-10% of the most probable pore diameter, the dispersion coefficient of gram weight of the modified expanded polytetrafluoroethylene is less than 10%, the modified expanded polytetrafluoroethylene is of a membrane layer structure, the thickness of the modified expanded polytetrafluoroethylene is 4.6-9.0 μm,
the preparation method of the modified expanded polytetrafluoroethylene comprises the following steps:
step S1, impregnating and filling a freezing medium into pores of expanded polytetrafluoroethylene to obtain a wet material;
step S2, at least part of the freezing medium in the wet material is subjected to ice crystallization to obtain a solid material;
step S3, the solid material is frozen and dried to obtain the modified expanded polytetrafluoroethylene, and the freezing medium is selected from one or more of dimethyl sulfoxide, water, tertiary butanol or camphene.
2. A method for producing the modified expanded polytetrafluoroethylene according to claim 1, comprising:
step S1, impregnating and filling a freezing medium into pores of expanded polytetrafluoroethylene to obtain a wet material;
step S2, at least part of the freezing medium in the wet material is subjected to ice crystallization to obtain a solid material;
step S3, the solid material is frozen and dried to obtain the modified expanded polytetrafluoroethylene, and the freezing medium is selected from one or more of dimethyl sulfoxide, water, tertiary butanol or camphene.
3. The method according to claim 2, wherein the freezing medium is a mixture of dimethyl sulfoxide and water, and the mass content of water in the mixture is 20% or less or 85% or more.
4. The method according to claim 2, wherein the mass ratio of the freezing medium to the expanded polytetrafluoroethylene is 10:1 to 500: 1.
5. The preparation method according to claim 2, wherein in the step S1, the immersion filling is realized by a method of soaking, coating or liquid casting, and the immersion filling time is 0.5-20 h.
6. The preparation method of claim 2, wherein the temperature for crystallizing the ice is-120 ℃ to 40 ℃, and the time for crystallizing the ice is 0.5h to 3 h.
7. The method of claim 2, wherein the temperature of the ice crystallization is-80 ℃ to 39 ℃.
8. The method of claim 2, wherein the temperature of the ice crystallization is-50 ℃ to 35 ℃.
9. The method of claim 2, wherein the temperature of the ice crystallization is-30 ℃ to 15 ℃.
10. The preparation method of claim 2, wherein the initial temperature of the freeze drying is-80 ℃ to 20 ℃, the temperature rise rate is 2 ℃/h to 5 ℃/h, the final temperature of the freeze drying is-30 ℃ to 60 ℃, and the pressure of the freeze drying is 0.1Pa to 20 Pa.
11. The preparation method according to claim 2, wherein the freeze-drying time is 1 to 48 hours.
12. A composite ion exchange membrane comprising a base membrane and a resin, wherein the base membrane is the modified expanded polytetrafluoroethylene of claim 1 or the modified expanded polytetrafluoroethylene prepared by the preparation method of any one of claims 2 to 11, and the resin is filled in pores of the modified expanded polytetrafluoroethylene.
13. The composite ion exchange membrane of claim 12, wherein the resin is a perfluorosulfonic acid resin.
14. Use of a composite ion exchange membrane according to claim 12, comprising applying the composite ion exchange membrane to a water-repellent moisture-permeable textile material, a medical implant, a sealing tape, a gas separation membrane, a water treatment membrane, a salinity gradient power generation or mesoporous material.
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