An Al 2 O 3 / PTFE composite microporous membrane, its preparation method and application

Abstract

The present invention belongs to the technical field of polytetrafluoroethylene microporous membranes, and relates to an Al2O3 / PTFE composite microporous membrane, a preparation method and an application thereof. The Al2O3 / PTFE composite microporous membrane is composed of Al2O3 nanoparticles and PTFE resin, with a porosity of 65% - 95%, a thickness of 3 - 25 μm, an average pore diameter of 0.10 - 1.5 μm, a transverse and longitudinal tensile strength ≥ 20 MPa, and a water contact angle ≤ 90°. The present invention utilizes the self-humidifying and in-situ strengthening of Al2O3 nanoparticles to endow the Al2O3 / PTFE composite microporous membrane with good surface wettability and excellent mechanical properties, and is mainly applied as a reinforcing material for proton membranes. The preparation process of the present invention is simple and easy to realize industrial promotion.

Description

Technical Field

[0001] The present invention belongs to the technical field of polytetrafluoroethylene microporous membranes and specifically relates to an Al 2 O 3 / PTFE composite microporous membrane and its preparation method and application. Background Art

[0002] Proton exchange membrane is the core material of proton exchange membrane fuel cells. The output power, battery efficiency and production cost of fuel cells are strongly dependent on proton exchange membrane. However, the inherent strength of proton exchange membrane is not high, and the high cost of polymer resin hinders the promotion and performance improvement of proton exchange membrane fuel cells. DuPont and other companies in the United States have successively launched Nafion / PTFE composite reinforced membranes. By using PTFE microporous membrane as a reinforcing material, the mechanical strength of the proton exchange membrane can be effectively improved, and the service life and other properties can be extended. However, higher requirements are placed on the mechanical properties, pore size, porosity and uniformity of PTFE microporous membranes.

[0003] PTFE microporous membranes generally adopt synchronous or asynchronous biaxial stretching process, and form a microporous structure of "fiber-node" staggered arrangement through the entanglement between particles during the stretching process. However, the PTFE microporous membranes prepared by the prior art cannot meet the requirements of reducing the thickness while maintaining high strength and narrow pore size distribution, and cannot be applied to the reinforcing layer of proton exchange membranes. In addition, the surface energy of PTFE itself is low, resulting in poor surface wettability after film formation, and strong anti-adhesion performance is not conducive to the direct infiltration of resin solution. Therefore, it is necessary to improve the preparation process of PTFE porous membranes.

[0004] For example, Chinese patent document CN112827372A discloses that polytetrafluoroethylene resin, extrusion aid, toughening agent and film-forming agent are mixed in proportion, aged at low temperature of 30-60°C, pressed into cylindrical blank, extruded and calendered into sheets, and then stretched in the longitudinal and transverse directions to make high-toughness polytetrafluoroethylene film. Although this modification method can improve the mechanical strength of PTFE microporous membrane, its thickness is large and its surface wettability is poor.

[0005] Chinese patent document CN113413775A adds metal oxide to polytetrafluoroethylene dispersion resin, and the metal element in the metal oxide can destroy the C-F bond in the polytetrafluoroethylene dispersion resin, so that the polytetrafluoroethylene dispersion resin has carbon-carbon double bonds, carbonyl and carboxyl polar groups, which greatly enhances the surface energy of the polytetrafluoroethylene dispersion resin and improves its wettability. In addition, the metal element in the metal oxide and the C element in the polytetrafluoroethylene dispersion resin can form a chemical bond, thereby enhancing the mechanical strength and stability of the material. However, the patent has the following shortcomings: the metal oxide particles in the patent can only be distributed at the position of the node, and the hydrophilic position can only be distributed at the node. It is not conducive to the solution to be infiltrated into the hole when used as a reinforcing material. In addition, the large size will also form a dead point, resulting in the proton channel on both sides of the membrane being cut off and being not conducive to the conduction of the proton. The proton is transmitted to a very important parameter for the proton membrane, which affects the film formation and performance of the proton membrane. The addition of metal oxide to the extrusion aid causes the formed PTFE membrane structure to be uneven, and the dispersion effect of the particles deteriorates. Tween, as a dispersant, has strong hydrophilicity, which can easily lead to an increase in the water content of the mixture. In addition, the solvent has an odor and a high boiling point, which is difficult to remove completely and easily remains in the membrane material. Summary of the invention

[0006] The present invention provides an Al2O3 proton exchange membrane reinforcement PTFE microporous membrane to solve the problems that the PTFE microporous membrane for proton exchange membrane reinforcement in the prior art cannot have high mechanical strength, large pore size, small thickness, high porosity and other properties, and has poor surface wetting due to low surface energy. 2 O 3 / PTFE composite microporous membrane and its preparation method and application.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A kind of Al 2 O 3 / PTFE composite microporous membrane, the Al 2 O 3 / PTFE composite microporous membrane made of Al 2 O 3 It is composed of nanoparticles and PTFE resin powder, with a porosity of 65%~95%, a thickness of 3~25μm, an average pore size of 0.10~1.5μm, a transverse and longitudinal tensile strength of ≥20MPa, and a water contact angle of ≤90°.

[0009] Preferably, the composite microporous membrane has a porosity of 88% to 90%, a thickness of 5 to 13 μm, an average pore size of 0.30 to 0.40 μm, a strength of ≥25 MPa, a water contact angle of ≤65°, a longitudinal tensile strength of 29 to 40 MPa, and a transverse tensile strength of 27 to 40 MPa.

[0010] Preferably, Al 2 O 3 Al / PTFE composite microporous membrane 2 O 3 Nanoparticles account for 1%-15% of the mass of PTFE resin powder.

[0011] The present invention also provides application of the composite microporous membrane in a proton exchange membrane, especially as a reinforcing material for the proton exchange membrane.

[0012] The present invention also provides the above-mentioned Al 2 O 3 The preparation method of the PTFE / PTFE composite microporous membrane comprises the following steps:

[0013] (1) Preparation of pre-dispersed material: Al 2 O 3 The nanoparticles are dispersed in the diffusant and stirred evenly to obtain a pre-dispersed material;

[0014] (2) Al 2 O 3 Preparation of PTFE composite base membrane tape:

[0015] (2.1) Mixing: adding extrusion aid and pre-dispersed material to PTFE dispersed resin powder and mixing evenly;

[0016] (2.2) Ripening: Place the mixed materials in an environment of 30-60°C for more than 15 hours;

[0017] (2.3) Prefabrication: The cured material is placed in a mold for pre-pressing to obtain a cylindrical blank;

[0018] (2.4) Extrusion: The prefabricated cylindrical blank is loaded into an extrusion barrel, and the blank is formed into an extruded sheet with a width of 150-250 mm and a thickness of 1000-2000 μm at 50-70°C using a flat die;

[0019] (2.5) Calendering: The extruded sheet is pressed into a calendered film strip with a thickness of 300-500 μm under the action of two pressing rollers;

[0020] (2.6) Degreasing: The calendered film is heat treated to remove the extrusion aid and the diffusion agent to obtain Al 2 O 3 / PTFE composite base membrane tape;

[0021] (3) Longitudinal stretching and transverse expansion:

[0022] (3.1) Longitudinal stretching: Al 2 O 3 / PTFE composite base film tape is longitudinally stretched to obtain Al2 O 3 / PTFE longitudinal pull belt;

[0023] (3.2) Horizontal expansion: Al 2 O 3 / PTFE longitudinally stretched tape is expanded horizontally, cooled and rolled at 0-10℃ to obtain high-strength Al 2 O 3 / PTFE composite microporous membrane.

[0024] Preferably, in step (1), Al 2 O 3 The amount of nanoparticles added is 1%-15% of the mass of the PTFE resin powder. If the amount added is too little, the strength cannot be improved under the compression ratio conditions of the present invention; if the amount added is too much, the reticular structure of the final membrane structure may be destroyed, which is not conducive to use as a reinforcing material for the proton membrane, and the reinforcing effect will be weakened.

[0025] Al 2 O 3 The size of the nanoparticles is ≤150nm, more preferably ≤100nm, and even more preferably 30-100nm. 2 O 3 The nanoparticles are selected from one or more of spherical nanoparticles, nanorods, and nanowhiskers. The size described in the present invention refers to the average value of the particles in the direction of the maximum size, such as the length of round rods, the diameter of spherical nanoparticles, the length of nanorods and nanowhiskers, etc. The present invention disperses the nanoparticles in smaller sizes, and the size of the PTFE primary particles is basically a sphere, round rod, etc. of about 100-200nm. The present invention disperses the aluminum oxide nanoparticles to the surface of the formed fiber to form a three-dimensional hydrophilic skeleton. It is not simply dispersed to the node structure.

[0026] Preferably, the amount of the diffusing agent added in step (1) is 3-8% of the mass of the PTFE resin powder, preferably 5%. The diffusing agent is selected from one or more of methanol, ether, acetone, toluene, dichloromethane, chloroform, and ethylene glycol tert-butyl ether. Acetone and ether are preferred. When the amount of diffusing agent added is small, the dispersion uniformity is poor, resulting in poor uniformity of film formation; excessive addition will increase the lubricity between PTFE resin particles, change the degree of particle fibrillation during extrusion and calendering, change the fiber structure, and fail to achieve the desired effect.

[0027] Preferably, the PTFE resin powder in step (2.1) has a crystallinity of ≥95% and a relative standard density (SSG) of ≤2.19 g / cm 3 , preferably 2.10-1.19 g / cm 3 .

[0028] Preferably, the amount of the extrusion aid added in step (2.1) is 15-30% of the mass of the PTFE resin powder, and the extrusion aid is one or more of petroleum ether, aviation kerosene, paraffin oil, Isopar M, Isopar L, Isopar V, and Isopar H.

[0029] Preferably, the extrusion compression ratio in step (2.4) is 15-55. When the compression ratio is further increased, although the strength of the film is increased, it will increase the difficulty of subsequent processing and easily lead to uneven subsequent stretching and expansion, thereby reducing the uniformity of the film.

[0030] Preferably, the roller surface temperature of the two pressing rollers in step (2.5) is 50-70°C.

[0031] Preferably, in step (2.6), the heat treatment temperature is 200-250° C., and the heat treatment time is 1-3 min.

[0032] Preferably, the stretching temperature in step (3.1) is 200-250°C, and the longitudinal stretching ratio is 5-15 times.

[0033] Preferably, the lateral expansion process in step (3.2) comprises three parts: a preheating section, an expansion section and a heat setting section. The temperature of the preheating section is 150-250°C, the temperature of the expansion section is 150-250°C, the expansion ratio is 10-20 times, and the temperature of the heat setting section is 320~380°C.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The present invention uses Al 2 O 3 Nanoparticles are used as modified fillers for PTFE microporous membranes. The in-situ enhancement of nanoparticles not only improves the mechanical properties of PTFE microporous membranes, but also increases the surface energy of the PTFE microporous membrane skeleton, giving it good wettability. 2 O 3 The reinforcement of nanoparticles reduces the dependence on high compression ratio, reduces the difficulty of subsequent processing, and makes it easier to obtain a microporous membrane with high lateral consistency; the best mechanical properties, porosity and pore size are obtained through longitudinal and lateral proportional stretching.

[0036] (2) High-strength Al prepared by the preparation method of the present invention 2 O 3 / PTFE composite microporous membrane, with stable structure, porosity of 65%~95%, thickness of 3~15μm, average pore size of 0.10~1.5μm, preferably 0.2~0.5μm, transverse and longitudinal tensile strength ≥20MPa, and water contact angle ≤90°.

[0037] (3) Using the high-strength Al 2 O 3 / PTFE composite microporous membrane preparation method, using low boiling point oily solvent as a diffusion agent to 2 O 3 Nanoparticles are evenly dispersed into PTFE resin powder and extrusion aid to form a homogeneous mixture, which improves Al 2 O 3 The uniformity of the dispersion of nanoparticles in PTFE dispersion resin also ensures high strength Al 2 O 3 / PTFE composite microporous membrane uniformity. 2 O 3 The addition of nanoparticles not only improves the weak strength and low modulus of the PTFE microporous structure, but also increases the surface energy of the PTFE microporous membrane and enhances the interfacial bonding force. 2 O 3 The / PTFE composite microporous membrane has high tensile strength, high porosity, small thickness, large pore size and good surface wettability, and the preparation process is simple and easy to promote industrialization.

[0038] (4) The selection of the diffusing agent and the mixing order of the present invention are conducive to achieving uniform dispersion of the nanoparticles in the PTFE resin powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The high strength Al prepared in Example 1 2 O 3 SEM image of / PTFE composite microporous membrane;

[0040] Figure 2 The high strength Al prepared in Comparative Example 3 2 O 3 SEM image of / PTFE composite microporous membrane;

[0041] Figure 3 The high strength Al prepared in Example 1 2 O 3 Water contact angle diagram of / PTFE composite microporous membrane;

[0042] Figure 4 The high strength Al prepared in Example 2 2 O 3 Water contact angle diagram of / PTFE composite microporous membrane;

[0043] Figure 5 The high strength Al prepared in Example 3 2 O 3Water contact angle diagram of / PTFE composite microporous membrane;

[0044] Figure 6 The high strength Al prepared in Example 4 2 O 3 Water contact angle diagram of / PTFE composite microporous membrane;

[0045] Figure 7 The high strength Al prepared in Comparative Example 1 2 O 3 Water contact angle diagram of / PTFE composite microporous membrane;

[0046] Figure 8 The high strength Al prepared in Comparative Example 2 2 O 3 Water contact angle diagram of / PTFE composite microporous membrane;

[0047] Fig. 9 The high strength Al prepared in Comparative Example 3 2 O 3 Water contact angle diagram of / PTFE composite microporous membrane;

[0048] Fig.10 The high strength Al prepared in Comparative Example 4 2 O 3 Water contact angle diagram of / PTFE composite microporous membrane;

[0049] Fig.11 The high strength Al prepared in Comparative Example 5 2 O 3 Water contact angle diagram of / PTFE composite microporous membrane. DETAILED DESCRIPTION

[0050] The present invention is further described below in conjunction with the examples and drawings. Unless otherwise specified, the raw materials used in the examples of the present invention are common commercial products. The average particle size of the PTFE dispersed resin powder used is 300-500 μm.

[0051] Example 1

[0052] High strength Al 2 O 3 Preparation of / PTFE composite microporous membrane:

[0053] (1) Preparation of pre-dispersion liquid: Based on the mass of PTFE resin powder, add 15% Al 2 O 3 Nanoparticles (nanowhiskers, average particle size 50nm) were dispersed in a 5% by mass acetone solution and mechanically stirred for 0.5h to obtain a uniform Al 2 O 3 Nanoparticle pre-dispersion.

[0054] (2) Al 2 O 3 Preparation of PTFE composite base membrane tape:

[0055] (2.1) Mixing: PTFE dispersed resin powder (SSG is 2.190, crystallinity is 95%) is sieved and loaded into a clean and dry PP sealed barrel, and 15% by mass of Isopar M extrusion aid and dispersed pre-dispersed liquid are added to mix, the total volume does not exceed 2 / 3 of the barrel volume, the mixer speed is 8r / min, and it rotates for 20min to make the PTFE resin powder, extrusion aid and pre-dispersed material fully and evenly mixed, and the mixing environment temperature is 12℃. The use of low boiling point diffusers improves the Al 2 O 3 Dispersion uniformity of nanoparticles in PTFE resin powder.

[0056] (2.2) Curing: Transfer the sealed barrel containing the uniformly mixed materials to a 60°C oven and cure for 15 hours to allow the extrusion aid to be fully and evenly coated on the surface of the PTFE resin powder particles.

[0057] (2.3) Prefabrication: The matured PTFE resin mixture is placed in a mold for pre-pressing. The pre-pressing pressure is 2 MPa and the pre-pressing temperature is 25°C. After holding the pressure for 3 minutes, a cylindrical blank is obtained.

[0058] (2.4) Extrusion: The prefabricated cylindrical billet is loaded into the extrusion barrel and extruded through a flat die to obtain an extruded sheet with a width of 250 mm and a thickness of 2000 μm. The die temperature is 70 °C and the extrusion compression ratio is 15.

[0059] (2.5) Calendering: The extruded sheet was pressed into a calendered film strip with a thickness of 500 μm by two pressing rollers, and the roller surface temperature of the two pressing rollers was 70°C.

[0060] (2.6) Degreasing: The calendered film strip is placed in a drying oven to remove the extrusion aid and the diffusion agent to obtain Al 2 O 3 / PTFE composite base membrane tape, the drying oven temperature is 250°C, and the drying time is 1 min.

[0061] (3) Longitudinal stretching and transverse expansion:

[0062] (3.1) Longitudinal stretching: Al 2 O 3 The / PTFE composite base film tape was longitudinally stretched at a temperature of 250°C and a longitudinal stretching ratio of 15 times to obtain Al 2 O3 / PTFE longitudinal pull belt;

[0063] (3.2) Transverse expansion: Al obtained by longitudinal stretching 2 O 3 / PTFE longitudinally stretched tape is expanded transversely, and the transverse expansion process includes three parts: preheating section, expansion section and heat setting section. 2 O 3 / PTFE longitudinally drawn tape first enters the preheating section at a temperature of 150°C, then enters the expansion section at a temperature of 150°C and an expansion ratio of 10 times, enters the heat setting section at a temperature of 380°C, and finally exits the oven to be rapidly cooled and rolled at a temperature of 10°C to obtain high-strength Al 2 O 3 / PTFE composite microporous membrane.

[0064] Example 1 High-strength Al 2 O 3 / PTFE composite microporous membrane, membrane thickness is 12μm, porosity is 88%, pore size is 0.31μm, longitudinal tensile strength is 29MPa, transverse tensile strength is 27MPa, water contact angle is 45 o . On the premise of ensuring thickness, porosity and pore size, it has the strength and excellent hydrophilicity required for use as a reinforcing material.

[0065] Example 2

[0066] High strength Al 2 O 3 Preparation of / PTFE composite microporous membrane:

[0067] (1) Preparation of pre-dispersion liquid: Based on the mass of PTFE resin powder, add 7% Al 2 O 3 Nanoparticles (nanorods, average particle size 100 nm) were dispersed in a 5% by mass acetone solution and mechanically stirred for 0.5 h to obtain a uniform Al 2 O 3 Nanoparticle pre-dispersion;

[0068] (2) Al 2 O 3 Preparation of PTFE composite base membrane tape:

[0069] (2.1) Mixing: PTFE dispersed resin powder (SSG is 2.165, crystallinity is 98%) is sieved and loaded into a clean and dry PP sealed barrel, and 22.5% of the mass ratio of Isopar H and the dispersed pre-dispersed liquid are added to mix. The total volume does not exceed 2 / 3 of the barrel volume. The mixer speed is 6r / min, and it rotates for 25min to make the PTFE resin powder, extrusion aid and pre-dispersed material fully and evenly mixed. The mixing environment temperature is 12℃. The use of low boiling point diffusers improves the Al 2 O 3 Dispersion uniformity of nanoparticles in PTFE resin powder.

[0070] (2.2) Curing: Transfer the sealed barrel containing the uniformly mixed materials to a 45°C oven and cure for 30 hours to allow the extrusion aid to be fully and evenly coated on the surface of the PTFE resin powder particles.

[0071] (2.3) Prefabrication: The matured PTFE resin mixture is placed in a mold for pre-pressing. The pre-pressing pressure is 2.5 MPa and the pre-pressing temperature is 25°C. After holding the pressure for 2 minutes, a cylindrical blank is obtained.

[0072] (2.4) Extrusion: The prefabricated cylindrical billet is loaded into the extrusion barrel and extruded through a flat die to obtain an extruded sheet with a width of 200 mm and a thickness of 1500 μm. The die temperature is 60 °C and the extrusion compression ratio is 35.

[0073] (2.5) Calendering: The extruded sheet was pressed into a calendered film strip with a thickness of 400 μm by two pressing rollers, and the roller surface temperature of the two pressing rollers was 60°C.

[0074] (2.6) Degreasing: The calendered film strip is placed in a drying oven to remove the extrusion aid and the diffusion agent to obtain Al 2 O 3 / PTFE composite base membrane tape, the drying oven temperature is 225℃, and the drying time is 2min.

[0075] (3) Longitudinal stretching and transverse expansion:

[0076] (3.1) Longitudinal stretching: Al 2 O 3 The / PTFE composite base film tape was longitudinally stretched at a temperature of 225°C and a longitudinal stretching ratio of 10 times to obtain Al 2 O 3 / PTFE longitudinal pull belt;

[0077] (3.2) Transverse expansion: Al obtained by longitudinal stretching 2 O 3 / PTFE longitudinally stretched tape is expanded transversely, and the transverse expansion process includes three parts: preheating section, expansion section and heat setting section. 2 O 3 / PTFE longitudinally drawn tape first enters the preheating section at a temperature of 200°C, then enters the expansion section at a temperature of 200°C and an expansion ratio of 15 times, enters the heat setting section at a temperature of 350°C, and finally exits the oven to be rapidly cooled and rolled at a temperature of 10°C to obtain high-strength Al 2 O 3 / PTFE composite microporous membrane.

[0078] Example 2 High-strength Al 2 O 3 / PTFE composite microporous membrane, membrane thickness is 10μm, porosity is 90%, pore size is 0.42μm, longitudinal tensile strength is 35MPa, transverse tensile strength is 38MPa, water contact angle is 49 o .

[0079] Example 3

[0080] High strength Al 2 O 3 Preparation of / PTFE composite microporous membrane:

[0081] (1) Preparation of pre-dispersion liquid: Based on the mass of PTFE resin powder, add 1% Al 2 O 3 Nanoparticles (spherical nanoparticles, particle size 30nm) were dispersed in a 5% by mass acetone solution and mechanically stirred for 0.5h to obtain a uniform Al 2 O 3 Nanoparticle pre-dispersion;

[0082] (2) Al 2 O 3 Preparation of PTFE composite base membrane tape:

[0083] (2.1) Mixing: PTFE dispersed resin powder (SSG is 2.13, crystallinity is 98%) is sieved and loaded into a clean and dry PP sealed barrel, and 30% by mass of extrusion aid paraffin oil and dispersed pre-dispersed liquid are added to mix, and the total volume does not exceed 2 / 3 of the barrel volume. The mixer speed is 4r / min, and it rotates for 30min to make the PTFE resin powder, extrusion aid and pre-dispersed material fully and evenly mixed. The mixing environment temperature is 12℃. The use of low boiling point diffusers improves the Al 2 O 3 Dispersion uniformity of nanoparticles in PTFE resin powder.

[0084] (2.2) Curing: Transfer the sealed barrel containing the uniformly mixed materials to a 30°C oven and cure for 45 hours to allow the extrusion aid to be fully and evenly coated on the surface of the PTFE resin powder particles.

[0085] (2.3) Prefabrication: The matured PTFE resin mixture is placed in a mold for pre-pressing. The pre-pressing pressure is 3 MPa and the pre-pressing temperature is 25°C. After holding the pressure for 1 minute, a cylindrical blank is obtained.

[0086] (2.4) Extrusion: The prefabricated cylindrical billet was loaded into the extrusion barrel and extruded through a flat die to obtain an extruded sheet with a width of 150 mm and a thickness of 1000 μm. The die temperature was 50 °C and the extrusion compression ratio was 55.

[0087] (2.5) Calendering: The extruded sheet was pressed into a calendered film strip with a thickness of 300 μm by two pressing rollers, and the roller surface temperature of the two pressing rollers was 50°C.

[0088] (2.6) Degreasing: The calendered film strip is placed in a drying oven to remove the extrusion aid and the diffusion agent to obtain Al 2 O 3 / PTFE composite base membrane tape, the drying oven temperature is 200°C, and the drying time is 3 minutes.

[0089] (3) Longitudinal stretching and transverse expansion:

[0090] (3.1) Longitudinal stretching: Al 2 O 3 The / PTFE composite base film tape was longitudinally stretched at a temperature of 200°C and a longitudinal stretching ratio of 5 times to obtain Al 2 O 3 / PTFE longitudinal pull belt;

[0091] (3.2) Transverse expansion: Al obtained by longitudinal stretching 2 O 3 / PTFE longitudinally stretched tape is expanded transversely, and the transverse expansion process includes three parts: preheating section, expansion section and heat setting section. 2 O 3 / PTFE longitudinally drawn tape first enters the preheating section at a temperature of 250°C, then enters the expansion section at a temperature of 250°C and an expansion ratio of 20 times, enters the heat setting section at a temperature of 320°C, and finally exits the oven to be rapidly cooled and rolled at a temperature of 10°C to obtain high-strength Al 2 O 3 / PTFE composite microporous membrane.

[0092] Example 3 High-strength Al 2 O 3 / PTFE composite microporous membrane, membrane thickness is 5μm, porosity is 90%, pore size is 0.32μm, longitudinal tensile strength is 37MPa, transverse tensile strength is 39MPa, water contact angle is 65 o .

[0093] Example 4

[0094] High strength Al 2 O 3 Preparation of / PTFE composite microporous membrane:

[0095] (1) Preparation of pre-dispersion liquid: Based on the mass of PTFE resin powder, add 7% Al 2 O 3 Nanoparticles (spherical nanoparticles, particle size 50nm) were dispersed in a 5% by mass ether solution and mechanically stirred for 0.5h to obtain a uniform Al 2 O 3 Nanoparticle pre-dispersion;

[0096] (2) Al 2 O 3 Preparation of PTFE composite base membrane tape:

[0097] (2.1) Mixing: PTFE dispersed resin powder (SSG is 2.165, crystallinity is 95%) is sieved and loaded into a clean and dry PP sealed barrel, and 30% by mass of paraffin oil and dispersed pre-dispersed liquid are added to mix. The total volume does not exceed 2 / 3 of the barrel volume. The mixer speed is 4r / min, and it rotates for 30min to make the PTFE resin powder, extrusion aid and pre-dispersed material fully and evenly mixed. The mixing environment temperature is 12℃. The use of low boiling point diffusers improves the Al 2 O 3 Dispersion uniformity of nanoparticles in PTFE resin powder.

[0098] (2.2) Curing: Transfer the sealed barrel containing the uniformly mixed materials to a 30°C oven and cure for 45 hours to allow the extrusion aid to be fully and evenly coated on the surface of the PTFE resin powder particles.

[0099] (2.3) Prefabrication: The matured PTFE resin mixture is placed in a mold for pre-pressing. The pre-pressing pressure is 3 MPa and the pre-pressing temperature is 25°C. After holding the pressure for 1 minute, a cylindrical blank is obtained.

[0100] (2.4) Extrusion: The prefabricated cylindrical billet was loaded into the extrusion barrel and extruded through a flat die to obtain an extruded sheet with a width of 150 mm and a thickness of 1000 μm. The die temperature was 50 °C and the extrusion compression ratio was 55.

[0101] (2.5) Calendering: The extruded sheet was pressed into a calendered film strip with a thickness of 300 μm by two pressing rollers, and the roller surface temperature of the two pressing rollers was 50°C.

[0102] (2.6) Degreasing: The calendered film strip is placed in a drying oven to remove the extrusion aid and the diffusion agent to obtain Al 2 O 3 / PTFE composite base membrane tape, the drying oven temperature is 200°C, and the drying time is 3 minutes.

[0103] (3) Longitudinal stretching and transverse expansion:

[0104] (3.1) Longitudinal stretching: Al 2 O 3 The / PTFE composite base film tape was longitudinally stretched at a temperature of 200°C and a longitudinal stretching ratio of 5 times to obtain Al 2 O 3 / PTFE longitudinal pull belt;

[0105] (3.2) Transverse expansion: Al obtained by longitudinal stretching 2 O 3 / PTFE longitudinally stretched tape is expanded transversely, and the transverse expansion process includes three parts: preheating section, expansion section and heat setting section. 2 O 3 / PTFE longitudinally drawn tape first enters the preheating section at a temperature of 250°C, then enters the expansion section at a temperature of 250°C and an expansion ratio of 20 times, enters the heat setting section at a temperature of 320°C, and finally exits the oven to be rapidly cooled and rolled at a temperature of 10°C to obtain high-strength Al 2 O 3 / PTFE composite microporous membrane.

[0106] Example 4 High-strength Al 2 O 3 / PTFE composite microporous membrane, membrane thickness is 11μm, porosity is 89%, pore size is 0.38μm, longitudinal tensile strength is 39MPa, transverse tensile strength is 40MPa, water contact angle is 52 o .

[0107] Comparative Example 1

[0108] The Al 2 O 3 The method for preparing the Al / PTFE composite microporous membrane is different from that in Example 1 in that the amount of the diffusing agent added in step (2.4) is 10%. The increase in the amount of the diffusing agent did not significantly improve the prepared Al 2 O 3 / PTFE composite microporous membrane performance, membrane thickness 11μm, porosity 89%, longitudinal tensile strength 28MPa, transverse tensile strength 27MPa, pore size 0.33μm, water contact angle 46°. The use of diffusant above 5% can no longer improve the performance of the prepared membrane. If the amount is too much, it will not be conducive to subsequent removal, and it will also cause the particles to entangle and weaken, which is not conducive to the increase in the number of fibers. Therefore, the addition amount of diffusant is preferably 5%.

[0109] Comparative Example 2

[0110] The method for preparing the PTFE composite microporous membrane described in this comparative example 2 is different from that in Example 1 in that the Al 2 O 3 The amount of nanoparticles added is 0. 2 O 3 Nanoparticles, resulting in the preparation of Al 2 O 3 The transverse and longitudinal tensile strength and surface wettability of the / PTFE composite microporous membrane decreased significantly, with a longitudinal tensile strength of 12MPa, a transverse tensile strength of 15MPa, and a water contact angle of 118°. The remaining parameters did not change much, with a thickness of 13μm, a pore size of 0.28μm, and a porosity of 89%. 2 O 3 The uniform dispersion of nanoparticles frees the reliance on stretching processes such as compression ratio, and can achieve high strength and excellent surface wettability while maintaining the uniformity of the film.

[0111] Comparative Example 3

[0112] The Al 2 O 3 The method for preparing a / PTFE composite microporous membrane is different from that in Example 1 in that the amount of the diffusant added in step (1) is 1%. 2 O 3 The dispersion of nanoparticles in PTFE resin powder deteriorates, resulting in the prepared Al 2 O 3 The / PTFE composite microporous membrane shows longitudinal and transverse unevenness on the surface, and the performance parameters vary greatly. The membrane thickness is 6μm, the longitudinal tensile strength is 16MPa, the transverse tensile strength is 13MPa, the pore size is 0.68μm, the porosity is 85%, and the water contact angle is 65°.

[0113] Depend on Figure 1 (Example 1), Figure 2 (Comparative Example 3) It can be seen that the amount of diffusing agent added can affect the microstructure and performance of the final film. Figure 1The diffuser is added appropriately, the fiber node structure in the microstructure is uniform, the pore size is small, and Figure 2 The uniformity of the fiber node structure is poor, and the pore structure distribution is large.

[0114] Comparative Example 4

[0115] The Al 2 O 3 The method for preparing a / PTFE composite microporous membrane is different from that in Example 1 in that the diffusing agent in step (1) is ethylene glycol butyl ether EB. The obtained membrane has a thickness of 13 μm, a porosity of 76%, a pore size of 0.23 μm, a longitudinal tensile strength of 27 MPa, a transverse tensile strength of 30 MPa, and a water contact angle of 69°. The small porosity cannot guarantee the complete infiltration of the proton membrane resin solution, which reduces the film formation and conductivity of the proton membrane and affects its application. The reason is that ethylene glycol butyl ether EB and PTFE and Al 2 O 3 The nanoparticles are strongly bound and difficult to be completely removed during the degreasing process, resulting in a decrease in the fibrillation degree between PTFE particles and uneven stretching during the stretching process, resulting in the prepared Al 2 O 3 The surface of the / PTFE composite microporous membrane is uneven and the porosity is small.

[0116] Comparative Example 5

[0117] The Al 2 O 3 The method for preparing a / PTFE composite microporous membrane is different from that in Example 1 in that SiO is added in step (1). 2 Nanoparticles, not Al 2 O 3 The obtained thickness is 13μm, the porosity is 82%, the pore size is 0.35μm, the longitudinal tensile strength is 26MPa, the transverse tensile strength is 25MPa, and the water contact angle is 119°. SiO 2 After the nanoparticles are heat-set at high temperature during the lateral expansion process, the hydrophilic stability of the particles themselves is weakened, resulting in a smaller decrease in the water contact angle of the prepared PTFE composite microporous membrane.

Claims

1. An Al2O3 / PTFE composite microporous membrane, characterized in that: The Al2O3 / PTFE composite microporous membrane is composed of Al2O3 nanoparticles and PTFE resin powder, the composite microporous membrane has a porosity of 88% to 90%, a thickness of 5-13 μm, an average pore size of 0.30-0.40 μm, a water contact angle of ≤65°, a longitudinal tensile strength of 29-40 MPa, and a transverse tensile strength of 27-40 MPa; The preparation method of the Al2O3 / PTFE composite microporous membrane comprises the following steps: (1) Preparation of pre-dispersed material: Al2O3 nanoparticles are dispersed in a diffusant and stirred evenly to obtain a pre-dispersed material; the amount of the diffusant added is 3-8% of the mass of the PTFE resin powder; the diffusant is selected from ether or acetone; (2) Preparation of Al2O3 / PTFE composite base membrane tape: (2.1) Mixing: Add extrusion aid and pre-dispersed material to PTFE dispersed resin powder and mix well; (2.2) Ripening: Place the mixed materials in an environment of 30-60°C for more than 15 hours; (2.3) Prefabrication: The cured material is placed in a mold for pre-pressing to obtain a cylindrical blank; (2.4) Extrusion: The prefabricated cylindrical blank is loaded into an extrusion barrel, and the blank is formed into an extruded sheet with a width of 150-250 mm and a thickness of 1000-2000 μm at 50-70° C. using a flat die; (2.5) Calendering: The extruded sheet is pressed into a calendered film strip with a thickness of 300-500 μm under the action of two pressing rollers; (2.6) Degreasing: The calendered film is subjected to heat treatment to remove the extrusion aid and the diffusion agent to obtain an Al2O3 / PTFE composite base film tape; (3) Longitudinal stretching and transverse expansion: (3.1) Longitudinal stretching: The Al2O3 / PTFE composite base membrane tape is longitudinally stretched to obtain an Al2O3 / PTFE longitudinally stretched tape; (3.2) Transverse expansion: The Al2O3 / PTFE longitudinally stretched tape is transversely expanded, cooled and rolled up at a temperature of 0-10°C to obtain a high-strength Al2O3 / PTFE composite microporous membrane.

2. The Al2O3 / PTFE composite microporous membrane according to claim 1, characterized in that: The Al2O3 nanoparticles in the Al2O3 / PTFE composite microporous membrane account for 1%-15% of the mass of the PTFE resin powder.

3. The Al2O3 / PTFE composite microporous membrane according to claim 1, characterized in that: The size of the Al2O3 nanoparticles in step (1) is ≤150nm.

4. The Al2O3 / PTFE composite microporous membrane according to claim 1, characterized in that: The PTFE resin powder in step (2.1) has a crystallinity of ≥95% and a relative standard density of ≤2.19 g / cm 3 The amount of the extrusion aid added is 15-30% of the mass of the PTFE resin powder, and the extrusion aid is one or more of petroleum ether, aviation kerosene, paraffin oil, Isopar M, Isopar L, Isopar V, and Isopar H.

5. The Al2O3 / PTFE composite microporous membrane according to claim 1, characterized in that: The extrusion compression ratio in step (2.4) is 15-55; the roller surface temperature of the two pressing rollers in step (2.5) is 50-70°C.

6. The Al2O3 / PTFE composite microporous membrane according to claim 1, characterized in that: In step (2.6), the heat treatment temperature is 200-250°C and the heat treatment time is 1-3 min.

7. The Al2O3 / PTFE composite microporous membrane according to claim 1, characterized in that: The stretching temperature in step (3.1) is 200-250°C, and the longitudinal stretching ratio is 5-15 times; the transverse expansion process in step (3.2) includes three parts: a preheating section, an expansion section, and a heat setting section. The temperature of the preheating section is 150-250°C, the temperature of the expansion section is 150-250°C, the expansion ratio is 10-20 times, and the temperature of the heat setting section is 320~380°C.

8. Use of the composite microporous membrane according to any one of claims 1 to 7 as a reinforcing material for a proton exchange membrane.

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