Preparation method of expanded polytetrafluoroethylene, expanded polytetrafluoroethylene and composite ion exchange membrane

Abstract

The invention provides a preparation method of expanded polytetrafluoroethylene, expanded polytetrafluoroethylene and a composite ion exchange membrane. The preparation method of the expanded polytetrafluoroethylene comprises the following steps: PTFE resin powder and a lubricant are mixed, prepressing, extrusion, calendaring, degreasing, stretching and sintering are carried out in sequence, the expanded polytetrafluoroethylene is obtained, the lubricant is a mixture of an oxygen-containing lubricant and an alkane lubricant, and the content of the oxygen-containing lubricant is 30-40 wt%. According to the invention, the oxygen-containing lubricant and the alkane lubricant with specific contents are matched with each other, so that the cohesiveness between PTFE resin particles can be enhanced, the uniformity of particle accumulation can be improved, the fracture or crack phenomenon in the processing process can be prevented, the processing difficulty can be reduced, and the fiber forming ability of the PTFE resin can be improved; the morphology of the fiber node is microcosmically improved, so that the expanded polytetrafluoroethylene has relatively high porosity and mechanical property, and the expanded polytetrafluoroethylene can be more favorably applied to the field of ion exchange membranes.

Description

Technical Field

[0001] The present invention relates to the technical field of expanded polytetrafluoroethylene, and in particular to a preparation method of expanded polytetrafluoroethylene, expanded polytetrafluoroethylene and a composite ion exchange membrane. Background Art

[0002] Expanded polytetrafluoroethylene, also known as e-PTFE, polytetrafluoroethylene fiber membrane, polytetrafluoroethylene microporous membrane, polytetrafluoroethylene porous membrane or porous polytetrafluoroethylene fiber membrane, is a porous material made of polytetrafluoroethylene as the skeleton material. It is widely used in ion exchange membrane reinforcement layer, waterproof and breathable fabric materials, medical implants, sealing tapes, gas separation membranes, water treatment membranes, salinity gradient power generation or mesoporous materials.

[0003] With expanded polytetrafluoroethylene as the reinforcement layer, composite ion exchange resin can be used to prepare composite ion exchange membranes. In the prior art, the expanded polytetrafluoroethylene used in the reinforcement layer of the ion exchange membrane is a microporous membrane with a flat membrane structure. The stretching method is currently the method for large-scale production of expanded polytetrafluoroethylene. Its main process includes: (1) mixing PTFE powder and lubricant and stirring them evenly, and then preparing them into a calendered membrane after aging, blanking, pushing and extruding; among them, commonly used lubricants are alkane substances such as petroleum ether, gasoline, kerosene, and liquid paraffin. (2) After the calendered membrane is dried, a dense PTFE film is obtained. The degreased membrane is first stretched in the MD direction (transverse direction) to obtain uniaxially stretched expanded polytetrafluoroethylene, and then stretched in the TD direction (longitudinal direction). After heat setting, biaxially stretched expanded polytetrafluoroethylene is obtained. However, this method of preparing expanded polytetrafluoroethylene using PTFE powder and common lubricants meets the needs of industrial continuous production, but cannot maintain excellent mechanical strength while having a high porosity, and thus cannot meet the performance requirements as a composite proton exchange membrane reinforcement layer.

[0004] In view of this, this application is hereby filed. Summary of the Invention

[0005] The main purpose of the present invention is to provide a preparation method of expanded polytetrafluoroethylene, expanded polytetrafluoroethylene and a composite ion exchange membrane, so as to improve the existing technology that uses alkane substances such as petroleum ether, gasoline, kerosene and liquid paraffin as lubricants and PTFE powder through a stretching method, which cannot maintain excellent mechanical strength while having a high porosity, and thus cannot meet the performance requirements of a composite proton exchange membrane reinforcement layer.

[0006] To achieve the above-mentioned object, according to one aspect of the present invention, a method for preparing expanded polytetrafluoroethylene is provided, which comprises the following steps: mixing PTFE resin powder and a lubricant, and sequentially subjecting the mixture to pre-pressing, extrusion, calendering, degreasing, stretching and sintering to obtain expanded polytetrafluoroethylene, wherein the lubricant is a mixture of an oxygen-containing lubricant and an alkane lubricant, and the content of the oxygen-containing lubricant is 30-40wt%.

[0007] Furthermore, the oxygen-containing lubricant includes a first oxygen-containing lubricant and a second oxygen-containing lubricant, and the mass ratio of the first oxygen-containing lubricant to the second oxygen-containing lubricant is 1:(2-3); wherein the first oxygen-containing lubricant is a C5-C12 fatty alcohol, and the second oxygen-containing lubricant includes at least one of phthalate, C5-10 aliphatic dibasic acid ester, phosphate or epoxy compound.

[0008] Furthermore, the alkane lubricant includes at least one of C5-C20 isoparaffin, petroleum ether, gasoline, kerosene, and liquid paraffin.

[0009] Furthermore, the alkane lubricant is selected from at least one of Isopar E, Isopar G, and Isopar L.

[0010] Furthermore, the C5-C12 fatty alcohol includes at least one of n-pentanol, n-hexanol, n-heptanol, isoheptanol, n-octanol, isooctyl alcohol, n-nonanol, isononanol, n-decanol, and isodecanol.

[0011] Furthermore, the phthalate ester includes at least one of dimethyl phthalate, diethyl phthalate, dibutyl phthalate, di(2-ethylhexyl) phthalate, and di-n-octyl phthalate.

[0012] Furthermore, the C5-C10 aliphatic dibasic acid ester includes at least one of di(2-ethylhexyl) adipate, diisodecyl adipate, dibutyl sebacate, di-(2-ethylhexyl) sebacate, and di-(2-ethylhexyl) azelate.

[0013] Furthermore, the phosphate ester includes at least one of tributyl phosphate, tri-(2-ethylhexyl) phosphate, diphenyl octyl phosphate, triphenyl phosphate, and tri(isopropylphenyl) phosphate.

[0014] Furthermore, the epoxy compound includes at least one of n-butyl glycidyl ether, allyl glycidyl ether, bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, 1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, sorbitol glycidyl ether, hexyl glycidyl ether, heptyl glycidyl ether, octyl glycidyl ether, nonyl glycidyl ether, decyl glycidyl ether, undecyl glycidyl ether, dodecyl glycidyl ether, tridecyl glycidyl ether, and tetradecyl glycidyl ether. Further, the C5-C12 fatty alcohol is selected from at least one of n-hexanol, n-octanol, and isooctyl alcohol.

[0015] Furthermore, the phthalate is selected from at least one of dibutyl phthalate and di(2-ethylhexyl) phthalate.

[0016] Furthermore, the C5-C10 aliphatic dibasic acid ester is di-(2-ethylhexyl) adipate.

[0017] Furthermore, the phosphate ester is selected from at least one of tributyl phosphate and triphenyl phosphate.

[0018] Furthermore, the epoxy compound is selected from at least one of octyl glycidyl ether, dodecyl glycidyl ether, tridecyl glycidyl ether, and tetradecyl glycidyl ether.

[0019] Furthermore, the mass ratio of PTFE resin powder to lubricant is 100:16-30, preferably 100:16-22, and more preferably 100:18-22.

[0020] Furthermore, the pre-pressing pressure is 3-15 MPa, and the pre-pressing time is 3-60 min.

[0021] Furthermore, the extrusion pressure is 3-20 MPa, and the extrusion temperature is 40-90°C.

[0022] Furthermore, the degreasing temperature is 120-190°C.

[0023] Furthermore, the stretching includes longitudinal stretching and transverse stretching, the longitudinal stretching ratio is 3-20 times, and the transverse stretching ratio is 10-100 times; preferably, the longitudinal stretching temperature is 200-320°C, and the transverse stretching temperature is 170-320°C.

[0024] Furthermore, the sintering temperature is 350-420°C.

[0025] In order to achieve the above object, according to another aspect of the present invention, there is provided an expanded polytetrafluoroethylene, which is obtained according to the preparation method provided in the first aspect.

[0026] According to a third aspect of the present invention, a composite ion exchange membrane is provided. The ion exchange membrane comprises the expanded polytetrafluoroethylene provided by the second aspect.

[0027] By applying the technical solution of the present application, the preparation method of expanded polytetrafluoroethylene provided by the present application adopts a specific content of oxygen-containing lubricant and alkane lubricant to cooperate with each other, which can not only enhance the adhesion between PTFE resin particles, improve the uniformity of particle stacking, prevent breakage or cracking during the processing process, and reduce the difficulty of processing, but also enhance the fiber-forming ability of polytetrafluoroethylene resin, improve the fiber node morphology at the microscopic level, so that expanded polytetrafluoroethylene has both high porosity and mechanical properties, which is more conducive to its application in the field of ion exchange membranes. In addition, in the preparation method of expanded polytetrafluoroethylene provided by the present application, by introducing oxygen-containing lubricant, the surface flatness of expanded polytetrafluoroethylene can be improved, the surface roughness can be reduced, and the probability of membrane surface defects can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0029] Figure 1 The pore size distribution diagram of e-PTFE-1 provided in Example 1 and De-PTFE-1 provided in Comparative Example 1 is shown;

[0030] Figure 2 SEM images of e-PTFE-1 provided in Example 1 and De-PTFE-1 provided in Comparative Example 1 are shown;

[0031] Figure 3 Cross-sectional SEM images of PEM-1 and D-PEM-1 are shown. DETAILED DESCRIPTION

[0032] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0033] As analyzed in the background of this application, the prior art uses alkanes such as petroleum ether, gasoline, kerosene, and liquid paraffin as lubricants to produce expanded polytetrafluoroethylene (ePTFE) through stretching methods. This method fails to achieve high porosity while maintaining excellent mechanical strength, and therefore fails to meet the performance requirements for use as a reinforcement layer for composite proton exchange membranes. To address this issue, this application provides a method for preparing ePTFE, ePTFE, and a composite ion exchange membrane.

[0034] In a first typical embodiment of the present application, a method for preparing expanded polytetrafluoroethylene is provided, which comprises the following steps: mixing PTFE resin powder and a lubricant, and sequentially subjecting the mixture to pre-pressing, extrusion, calendering, degreasing, stretching and sintering to obtain expanded polytetrafluoroethylene, wherein the lubricant is a mixture of an oxygen-containing lubricant and an alkane lubricant, and the content of the oxygen-containing lubricant is 30 to 40 wt%.

[0035] In this application, PTFE resin refers to polytetrafluoroethylene resin.

[0036] Among the lubricants used in this application, the content of the oxygen-containing lubricant can be 30wt%, 32wt%, 35wt%, 38wt%, 40wt%, or a range consisting of any two values. The content of the alkane lubricant can be 60wt%, 62wt%, 65wt%, 68wt%, 70wt%, or a range consisting of any two values. Alkane lubricants have low polarity and are more conducive to wetting PTFE resin powder, improving the processing properties of PTFE resin. Oxygen-containing lubricants help improve the fiber-forming properties of PTFE resin, thereby increasing the porosity and mechanical strength of expanded polytetrafluoroethylene.

[0037] The preparation method of expanded polytetrafluoroethylene provided by the present application adopts a specific content of oxygen-containing lubricant and alkane lubricant to cooperate with each other, which can not only enhance the adhesion between PTFE resin particles, improve the uniformity of particle stacking, prevent breakage or cracking during the processing process, and reduce the difficulty of processing, but also enhance the fiber-forming ability of polytetrafluoroethylene resin, improve the fiber node morphology at the microscopic level, so that expanded polytetrafluoroethylene has both high porosity and mechanical properties, which is more conducive to its application in the field of ion exchange membranes. In addition, in the preparation method of expanded polytetrafluoroethylene provided by the present application, the surface smoothness of expanded polytetrafluoroethylene can be improved by introducing oxygen-containing lubricant, the surface roughness can be reduced, and the probability of membrane surface defects can be reduced.

[0038] In some embodiments of the present application, the D50 of the PTFE resin powder is 200-1000 μm. Specifically, the D50 of the PTFE resin powder can be 200 μm, 300 μm, 400 μm, 500 μm, 800 μm, 1000 μm, or a range consisting of any two values.

[0039] In some embodiments of the present application, the above-mentioned oxygen-containing lubricant is a commonly used lubricant in the art, including but not limited to any one or more of C5-C12 fatty alcohols, phthalates, C5-C10 aliphatic dibasic acid esters, phosphates or epoxy compounds.

[0040] The above-mentioned C5-C12 fatty alcohols include but are not limited to any one or more of n-pentanol, n-hexanol, n-heptanol, isoheptanol, n-octanol, isooctyl alcohol, n-nonanol, isononyl alcohol, n-decanol, and isodecanol.

[0041] The above-mentioned phthalates include, but are not limited to, any one or more of dimethyl phthalate, diethyl phthalate, dibutyl phthalate, di(2-ethylhexyl) phthalate, and di-n-octyl phthalate.

[0042] The above-mentioned C5-C10 aliphatic dibasic acid esters include, but are not limited to, any one or more of di(2-ethylhexyl) adipate, diisodecyl adipate, dibutyl sebacate, di-(2-ethylhexyl) sebacate, and di-(2-ethylhexyl) azelaic acid.

[0043] The above-mentioned phosphate ester includes any one or more of tributyl phosphate, tri-(2-ethylhexyl) phosphate, diphenyl octyl phosphate, triphenyl phosphate, and tri(isopropylphenyl) phosphate.

[0044] The above-mentioned epoxy compounds include but are not limited to any one or more of n-butyl glycidyl ether, allyl glycidyl ether, bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, 1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, sorbitol glycidyl ether, hexyl glycidyl ether, heptyl glycidyl ether, octyl glycidyl ether, nonyl glycidyl ether, decyl glycidyl ether, undecyl glycidyl ether, dodecyl glycidyl ether, tridecyl glycidyl ether, and tetradecyl glycidyl ether.

[0045] In some embodiments of the present application, the alkane lubricant includes but is not limited to any one or more of C5-C20 isoparaffin, petroleum ether, gasoline, kerosene or liquid paraffin.

[0046] In some specific embodiments, when the alkane lubricant is selected from any one or more of Isopar E, Isopar G, and Isopar L, it is more conducive to improving the wettability of the lubricant to the PTFE resin powder.

[0047] The above-mentioned Isopar E, Isopar G, and Isopar L are all models of paraffin lubricating oils sold by ExxonMobil Corporation, and they can all be purchased commercially.

[0048] In some embodiments of the present application, the oxygen-containing lubricant includes a first oxygen-containing lubricant and a second oxygen-containing lubricant, and the mass ratio of the first oxygen-containing lubricant to the second oxygen-containing lubricant is 1:2-3, wherein the first oxygen-containing lubricant is a C5-C12 fatty alcohol, and the second oxygen-containing lubricant includes any one or more of phthalate, C5-C10 aliphatic dibasic acid ester, phosphate or epoxy compound.

[0049] The meanings of the above-mentioned C5-C12 fatty alcohols, phthalates, C5-C10 aliphatic dibasic acid esters, phosphates and epoxy compounds are as described above and will not be repeated here.

[0050] When the oxygen-containing lubricant is a combination of a first oxygen-containing lubricant and a second oxygen-containing lubricant, and the mass ratio of the first oxygen-containing lubricant to the second oxygen-containing lubricant is 1:2-3, the oxygen-containing lubricant and the alkane lubricant cooperate with each other to be more conducive to improving the wettability and fiber-forming ability of the PTFE resin, and thus to be more conducive to the preparation of expanded polytetrafluoroethylene with both higher porosity and excellent mechanical strength.

[0051] Specifically, in the oxygen-containing lubricant, the mass ratio of the first oxygen-containing lubricant to the second oxygen-containing lubricant can be 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, 1.0 or a range value consisting of any two values.

[0052] In some embodiments, when the C5-C10 fatty alcohol is preferably selected from any one or more of n-hexanol, n-octanol, or isooctyl alcohol, it is more conducive to improving the fiber-forming ability of the PTFE resin.

[0053] In some embodiments, the above-mentioned phthalate is preferably selected from any one or more of dibutyl phthalate and di-2-ethylhexyl phthalate, which is more conducive to improving the mechanical properties of expanded polytetrafluoroethylene.

[0054] In some embodiments, the C5-C10 aliphatic dibasic acid ester is di-(2-ethylhexyl) adipate, which is more conducive to improving the processing ability of the PTFE resin.

[0055] In some embodiments, the epoxy compound is preferably selected from any one or more of octyl glycidyl ether, dodecyl glycidyl ether, tridecyl glycidyl ether, and tetradecyl glycidyl ether, which is more conducive to improving the mechanical properties of expanded polytetrafluoroethylene.

[0056] In some embodiments of the present application, the mass ratio of PTFE resin powder to lubricant is 100:10-30, preferably 100:16-22, and more preferably 100:18-22. In the process of preparing expanded polytetrafluoroethylene, the higher the amount of lubricant used, the more conducive to processing and molding, but the strength of the prepared expanded polytetrafluoroethylene is on the low side, and the lower the amount of lubricant used, the higher the strength of the expanded polytetrafluoroethylene, but the processing and molding difficulty is large. When the mass ratio of PTFE resin powder to lubricant is 100:10-30, it is more conducive to preparing a material with both high porosity and excellent mechanical properties, especially when the mass ratio of PTFE resin powder to lubricant is 100:16-22, the comprehensive performance of the prepared expanded polytetrafluoroethylene is more excellent, especially when the mass ratio of PTFE resin powder to lubricant is 100:18-22, the comprehensive performance of the prepared expanded polytetrafluoroethylene is more significant.

[0057] In the present application, the mass ratio of PTFE resin powder to lubricant can be 100:10, 100:12, 100:15, 100:18, 100:20, 100:22, 100:25, 100:28, 100:30 or a range value consisting of any two values.

[0058] In the preparation method of expanded polytetrafluoroethylene provided in this application, the processes of pre-pressing, extrusion, calendering, degreasing, stretching and sintering are all commonly used processing equipment and processing techniques in the industry.

[0059] In some embodiments of the present application, the pre-pressing pressure is 3-15 MPa, the pre-pressing time is 3-60 min, and the density of the pre-pressed green body obtained by pre-pressing is 1.4 g / cm 3 -1.9g / cm 3 , preferably from 1.5 g / cm 3 -1.8g / cm 3 , more preferably from 1.55 g / cm 3 -1.78g / cm 3 The higher the density of the preform, the more beneficial it is for improving the mechanical properties of expanded polytetrafluoroethylene. However, high density can easily lead to preform breakage and subsequent molding difficulties. The introduction of an oxygen-containing lubricant can maintain the integrity of the higher-density preform (preventing breakage) and facilitate subsequent processing and molding.

[0060] Specifically, the pre-pressing pressure can be 3MPa, 5MPa, 8MPa, 10MPa, 12MPa, 15MPa or a range of any two values; the pre-pressing time can be 3min, 5min, 8min, 10min, 15min, 20min, 30min, 40min, 50min, 60min or a range of any two values; the density of the pre-pressed blank can be 1.4g / cm3, 1.5g / cm3 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 Or a range of any two values.

[0061] In some embodiments of the present application, the extrusion pressure is 3-20 MPa, the extrusion temperature is 40-90°C, the extrusion flow rate is 5-100 mm / min, and the rod-shaped material or sheet-shaped material is obtained by extrusion. Preferably, the density of the rod-shaped material or sheet-shaped material is 1.5-1.9 g / cm3. Preferably, it is 1.55 g / cm 3 -1.85g / cm 3 , more preferably 1.6 g / cm 3 -1.8g / cm 3 . The extrusion pressure, extrusion flow rate and extrusion temperature are related to the density of the pre-press. The smaller the density of the pre-press, the smaller the extrusion pressure, the larger the extrusion flow rate, and a lower extrusion temperature can be set; the greater the density of the pre-press, the higher the extrusion pressure, the smaller the extrusion flow rate, and a higher extrusion temperature needs to be set to improve the fluidity of the material, thereby making the extrusion pressure and extrusion flow rate within the capacity of the equipment. Common extrusion shapes in the industry are rod-shaped materials or sheet-shaped materials. The expanded polytetrafluoroethylene prepared by the latter has better uniformity and mechanical properties, but has higher requirements on equipment and requires the design of complex flow channels and extrusion dies. Whether it is a rod-shaped material or a sheet-shaped material, the introduction of oxygen-containing lubricants can improve the mechanical properties of the intermediate product and expanded polytetrafluoroethylene. The diameter of the common rod-shaped materials in the industry is 5-30mm, the thickness of the common sheet materials is 0.01-10mm, and the width is 2-30cm.

[0062] Specifically, the extrusion pressure can be 3MPa, 5MPa, 8MPa, 10MPa, 12MPa, 15MPa, 18MPa, or a range consisting of any two values; the extrusion temperature can be 40°C, 45°C, 50°C, 60°C, 70°C, 80°C, 90°C, or a range consisting of any two values; the extrusion flow rate can be 5mm / min, 10mm / min, 20mm / min, 30mm / min, 50mm / min, 80mm / min, 100mm / min, or a range consisting of any two values. The density of the rod-shaped material or sheet-shaped material can be 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 Or a range consisting of any two values. The diameter of the rod-shaped material can be 5mm, 8mm, 10mm, 15mm, 20mm, 25mm, 30mm, or a range consisting of any two values. The thickness of the sheet material can be 0.01mm, 0.02mm, 0.05mm, 0.1mm, 0.2mm, 0.5mm, 1mm, 2mm, 5mm, 8mm, 10mm, or a range consisting of any two values, and the width can be 2cm, 5cm, 8cm, 10cm, 15cm, 20cm, 25cm, 30cm, or a range consisting of any two values.

[0063] In some embodiments of the present application, calendering is the process of rolling an extruded rod or sheet into a calendered film. The width of the calendered film is 2-30 cm, and the thickness is 0.01-1 mm. Specifically, the width of the calendered film can be 2 cm, 3 cm, 5 cm, 8 cm, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, or a range consisting of any two values; the thickness can be 0.01 mm, 0.02 mm, 0.05 mm, 0.08 mm, 0.1 mm, 0.2 mm, 0.5 mm, 0.8 mm, 1.0 mm, or a range consisting of any two values.

[0064] In some embodiments of the present application, degreasing is performed by removing the lubricant from the calendered film at high temperatures (120-190°C) to produce a degreased film. The degreased film has a width of 2-30 cm, a thickness of 0.01-1 mm, and a tensile strength in the mechanical direction (MD) of 5-50 MPa. The degreased film can be used as an intermediate in the production of polytetrafluoroethylene microporous membranes or as a finished product for applications such as thermal insulation films, membrane electrode backing films, building materials, liners, bellows, and sealing materials.

[0065] In some embodiments of the present application, stretching includes longitudinal stretching and transverse stretching. During the stretching process, longitudinal stretching and transverse stretching can be performed once or multiple times, wherein the ratio of longitudinal stretching is 3-20 times, and the ratio of transverse stretching is 10-100 times. Specifically, the ratio of longitudinal stretching can be 3, 5, 8, 10, 12, 15, 18, 20 times or a range of any two values, and the ratio of transverse stretching can be 10, 15, 20, 30, 50, 80, 100 times or a range of any two values.

[0066] In some embodiments of the present application, the longitudinal stretching temperature is 200-320°C, and the transverse stretching temperature is 170-320°C. A film that is only stretched longitudinally is called a longitudinally stretched film. The longitudinally stretched film can be used as an intermediate product in the production process of polytetrafluoroethylene microporous membranes, and can also be used as a product in the fields of cable materials, packaging materials, sealing materials, etc. Specifically, the longitudinal stretching temperature can be 200°C, 220°C, 250°C, 280°C, 300°C, 320°C, or a range consisting of any two values, and the transverse stretching temperature can be 170°C, 180°C, 200°C, 220°C, 250°C, 280°C, 300°C, 320°C, or a range consisting of any two values.

[0067] In some embodiments of the present application, the sintering temperature is 350°C-420°C, which is more conducive to improving the production efficiency of expanded polytetrafluoroethylene. Specifically, the sintering temperature can be 350°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, or a range consisting of any two values.

[0068] In a second typical embodiment of the present application, an expanded polytetrafluoroethylene is provided, which is obtained according to the preparation method provided in the first typical embodiment.

[0069] The expanded polytetrafluoroethylene provided in the present application uses a lubricant prepared by combining a specific amount of oxygen-containing lubricant and an alkane lubricant to replace the conventional alkane lubricant, so that the prepared expanded polytetrafluoroethylene has both high porosity and mechanical properties, which is more conducive to its application in the field of ion exchange membranes.

[0070] In a third typical embodiment of the present application, a composite ion exchange membrane is also provided, which includes a base membrane and a perfluorosulfonic acid resin filled in the pores of the base membrane, wherein the base membrane is expanded polytetrafluoroethylene obtained by the preparation method provided in the above-mentioned first typical embodiment or the expanded polytetrafluoroethylene provided in accordance with the above-mentioned second typical embodiment, and the resin is filled in the pores of the polytetrafluoroethylene microporous membrane.

[0071] In a fourth typical embodiment of the present application, there is also provided an application of expanded polytetrafluoroethylene or a composite ion exchange membrane in the field of filtration and / or separation; such as for filter materials, sealing materials, textile materials, battery diaphragms, etc.; or, for fuel cells, water electrolysis hydrogen production devices, liquid flow batteries, chlor-alkali industry, lithium batteries, electrodialysis, osmosis, etc.; or, for fuel cell ion exchange membranes, ion exchange membranes for water electrolysis hydrogen production, liquid flow battery diaphragms, chlor-alkali industry diaphragms, electrodialysis membranes, osmosis membranes, etc.

[0072] In some embodiments of the present application, the application of expanded polytetrafluoroethylene as a base membrane in a composite ion exchange membrane can improve the free radical resistance and antioxidant properties of the composite ion exchange membrane, and enhance the durability of the composite ion exchange membrane in applications such as fuel cell proton exchange membranes, proton exchange membranes for water electrolysis, and liquid flow battery diaphragms.

[0073] In addition, expanded polytetrafluoroethylene or composite ion exchange membranes can also be used in filtration and separation fields with special needs, and can be used in microporous membrane application fields such as filtration materials, sealing materials, textile materials, battery diaphragms, etc. They can also be used in chlor-alkali industrial diaphragms, electrodialysis membranes, osmotic membranes and other fields.

[0074] The beneficial effects of the present application will be further illustrated below with reference to examples and comparative examples.

[0075] It should be noted that in the following examples and comparative examples, the crystallinity of the PTFE resin powder is ≥90%, and the mass density is 2.15 g / cm 3 The alkane lubricants were purchased from ExxonMobil, and the models were Isopar E, Isopar G, and Isopar L respectively; the perfluorosulfonic acid resins were purchased from Chemours and Solvay, and the other reagents were common standard chemical reagents and were purchased from the market.

[0076] Example 1

[0077] This embodiment provides a method for preparing expanded polytetrafluoroethylene, which comprises the following steps:

[0078] (1) 4 kg of PTFE resin powder was taken, and the PTFE resin and lubricant were mixed in a mass ratio of 100:18, and the mixture was pre-pressed, extruded, calendered and degreased in sequence to obtain a degreased film; wherein, the pre-pressing pressure was 5-9 MPa, the pre-pressing time was 20 min, and a pre-pressed blank was obtained after pre-pressing. The extrusion pressure was 12-13 MPa, the extrusion rate was 15 mm / min, the extrusion temperature was 80 ° C, the extrudate was a sheet material, and the sheet material was calendered to obtain a calendered film. The lubricant was removed from the calendered film at 220 ° C to obtain a degreased film. The degreased film had a width of 147 mm and a thickness of 0.33 ± 0.01 mm.

[0079] (2) The degreased film was stretched longitudinally by 6 times at 300°C and transversely by 48 times at 280°C, and then sintered at 395°C to obtain expanded polytetrafluoroethylene (e-PTFE-1). The composition of the lubricant is shown in Table 1.

[0080] Example 2-3

[0081] The difference between Example 2-3 and Example 1 is that the components of the lubricant are different. As shown in Table 1, the obtained expanded polytetrafluoroethylenes are e-PTFE-2 and e-PTFE-3, respectively.

[0082] Example 4

[0083] This embodiment provides a method for preparing expanded polytetrafluoroethylene, which comprises the following steps:

[0084] (1) 4 kg of PTFE resin powder was taken, and the PTFE resin and lubricant were mixed in a mass ratio of 100:20, and the mixture was pre-pressed, extruded, calendered and degreased in sequence to obtain a degreased film; wherein, the pre-pressing pressure was 4-8 MPa, the pre-pressing time was 10 min, and a pre-pressed blank was obtained after pre-pressing. The extrusion pressure was 9-11 MPa, the extrusion rate was 30 mm / min, the extrusion temperature was 70 ° C, the extrudate was a sheet material, and the sheet material was calendered to obtain a calendered film. The lubricant was removed from the calendered film at 220 ° C to obtain a degreased film. The degreased film had a width of 144 mm and a thickness of 0.345 ± 0.015 mm.

[0085] (2) The degreased film was stretched longitudinally by 5.7 times at 300°C and transversely by 45 times at 280°C, and then sintered at 380°C to obtain expanded polytetrafluoroethylene (e-PTFE-4). The composition of the lubricant is shown in Table 1.

[0086] Examples 5-7

[0087] The difference between Examples 5-7 and Example 1 is that the components of the lubricants are different. As shown in Table 1, the obtained expanded polytetrafluoroethylenes are e-PTFE-5, e-PTFE-6, and e-PTFE-7, respectively.

[0088] Example 8

[0089] This embodiment provides a method for preparing expanded polytetrafluoroethylene, which comprises the following steps:

[0090] (1) 4 kg of PTFE resin powder was taken, and the PTFE resin and lubricant were mixed in a mass ratio of 100:22, and the mixture was pre-pressed, extruded, calendered and degreased in sequence to obtain a degreased film; wherein, the pre-pressing pressure was 4-7 MPa, the pre-pressing time was 10 min, and a pre-pressed blank was obtained after pre-pressing. The extrusion pressure was 6-8 MPa, the extrusion rate was 50 mm / min, the extrusion temperature was 60 ° C, the extrudate was a sheet material, and the sheet material was calendered to obtain a calendered film. The lubricant was removed from the calendered film at 220 ° C to obtain a degreased film. The width of the degreased film was 135 ± 5 mm and the thickness was 0.325 ± 0.025 mm.

[0091] (2) The degreased film was stretched longitudinally by 5.5 times at 300°C and transversely by 42 times at 280°C, and then sintered at 360°C to obtain expanded polytetrafluoroethylene (e-PTFE-8). The composition of the lubricant is shown in Table 1 below.

[0092] Examples 9-15

[0093] The difference between Examples 9-15 and Example 1 is that the composition or amount of the lubricant is different, as shown in Table 1.

[0094] Comparative Examples 1-5

[0095] The difference between Comparative Examples 1-5 and Example 1 is that the composition or amount of the lubricant is different, as shown in Table 1.

[0096] Table 1

[0097]

[0098]

[0099]

[0100] Test Example 1

[0101] The morphologies of the pre-pressed blanks and the calendered films during the preparation of the above-mentioned examples and comparative examples were observed, and the results are shown in Table 2 below.

[0102] Table 2

[0103] Example Sample Pre-pressed green body Calendered film morphology Example 1 e-PTFE-1 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Example 2 e-PTFE-2 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Example 3 e-PTFE-3 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Example 4 e-PTFE-4 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Example 5 e-PTFE-5 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Example 6 e-PTFE-6 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Example 7 e-PTFE-7 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Example 8 e-PTFE-8 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Example 9 e-PTFE-9 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Example 10 e-PTFE-10 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Example 11 e-PTFE-11 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Example 12 e-PTFE-12 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Example 13 e-PTFE-13 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Example 14 e-PTFE-14 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Example 15 e-PTFE-15 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Comparative Example 1 De-PTFE-1 Pre-pressed billet fracture Cracks appear in various areas of the calendered film Comparative Example 2 De-PTFE-4 Pre-pressed billet fracture Cracks appear on both sides of the calendered film Comparative Example 3 De-PTFE-8 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Comparative Example 4 De-PTFE-16 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks Comparative Example 5 De-PTFE-17 The pre-pressed green sheet has a regular and complete shape The calendered film is uniform and complete without cracks

[0104] From the results in Table 2, it can be seen that the materials with different lubricant formulations in Examples 1-15 have good processability, and the molding effect is good in the pre-pressing stage, and no pre-pressed billet breakage occurs; in the calendering molding stage, the calendered film is uniform and complete, and no cracks or broken bands occur. The pre-pressed billet of the material in Comparative Example 1 is broken into three parts, and there are obvious cracks and broken areas in the middle and edge areas of the calendered film. This is because the lubricant content is relatively low. The pre-pressed billet of the material in Comparative Example 2 is broken into two parts, and there are obvious cracks in the edge areas of the calendered film, and the processing performance is poor. The alkane lubricant content in Comparative Example 3 is relatively high, and the pre-pressed billet and calendered film are completely molded. In Comparative Examples 4-5, although the content of the oxygen-containing lubricant is 25.0wt% or 45.0wt%, it does not affect the processing performance of expanded polytetrafluoroethylene, and Comparative Examples 4-5 still have good processability.

[0105] Test Example 2

[0106] The dimensions and tensile strength of the degreased films and longitudinally stretched films obtained during the preparation of expanded polytetrafluoroethylene provided in the above examples and comparative examples were measured, and the results are shown in Table 3 below.

[0107] Table 3

[0108]

[0109]

[0110] As shown in Table 3 for Examples 1-11, when the multi-component lubricant contains 30-40 wt% oxygen-containing lubricant, the mass ratio of the first oxygen-containing lubricant to the second oxygen-containing lubricant is 1:(2-3), and the mass ratio of PTFE resin powder to the lubricant is 100:16-22, the degreased films and longitudinally drawn films prepared using the multi-component lubricant in this application exhibit higher tensile strength in the MD direction (compared to Comparative Examples 1-3). The tensile strength of the degreased and longitudinally drawn films prepared from e-PTFE-1 is more than twice that of the degreased and longitudinally drawn films in Comparative Example 1. The multi-component lubricant significantly enhances the strength of degreased and longitudinally drawn films. High-strength degreased and longitudinally drawn films are essential for preparing high-strength, high-porosity expanded polytetrafluoroethylene.

[0111] From the comparison of the data of Examples 12-13 and Examples 1-11, it can be seen that when the mass ratio of PTFE resin powder to the lubricant is 100:16-22, the mechanical strength of the prepared longitudinally stretched film is more excellent.

[0112] In addition, from the comparison of the data of Examples 14-15 and Examples 1-11, it can be seen that when the mass ratio of the second oxygen-containing lubricant to the first oxygen-containing lubricant is higher than 3 or lower than 2, the tensile strength of the longitudinally stretched film prepared by the multi-component lubricant will be significantly reduced.

[0113] From the comparison of the data of Comparative Examples 4-5 and Examples 1-11, it can be seen that when the content of the oxygen-containing lubricant in the lubricant is lower than 30 wt% or higher than 40 wt%, the tensile strength of the longitudinally stretched film prepared by the multi-component lubricant will be significantly reduced.

[0114] Test Example 2

[0115] The thickness, porosity and tensile strength of the expanded polytetrafluoroethylene provided in the above examples and comparative examples were measured, and the results are shown in Table 4 below.

[0116] Table 4

[0117]

[0118]

[0119] As can be seen from the comparison of Examples 1-10 with Comparative Examples 1-3 in Table 4, when the content of the oxygen-containing lubricant in the multi-component lubricant is 30wt%-40wt%, the mass ratio of the first oxygen-containing lubricant to the second oxygen-containing lubricant is 1:(2-3), and the mass ratio of the PTFE resin powder to the lubricant is 100:18-22, the prepared expanded polytetrafluoroethylene has a higher thickness uniformity and a narrower pore size distribution, showing better uniformity. Under conditions of similar thickness and porosity of expanded polytetrafluoroethylene, the introduction of oxygen-containing lubricants in the multi-component lubricant significantly improves the tensile strength of expanded polytetrafluoroethylene. In addition, the internal fibers of the expanded polytetrafluoroethylene in Examples 1-10 form a "node-fiber" network structure and are entangled with each other, and the fiber distribution is more reasonable, so that its pore size is reduced and tends to be consistent. At the same time, by controlling the internal fiber distribution and structure, it is possible to greatly improve the mechanical properties while maintaining a high porosity.

[0120] From the comparison of the data of Example 11 with Examples 1-10, it can be seen that when the mass ratio of PTFE value to multi-component lubricant is lower than 100:18, the porosity of the formed expanded polytetrafluoroethylene is relatively low.

[0121] It can be seen from the data of Examples 12-13 and Examples 1-10 that when the mass ratio of PTFE resin powder to the lubricant is 100:18-22, the mechanical strength of the prepared expanded polytetrafluoroethylene is even better.

[0122] In addition, from the comparison of the data of Examples 14-15 and Examples 1-10, it can be seen that when the mass ratio of the second oxygen-containing lubricant to the first oxygen-containing lubricant in the multi-component lubricant is higher than 3 or lower than 2, the porosity of the expanded polytetrafluoroethylene prepared from the multi-component lubricant will be reduced.

[0123] It can be seen from the data of Comparative Examples 4-5 that when the content of the oxygen-containing lubricant in the lubricant is lower than 30 wt % or higher than 40 wt %, the mechanical strength of the expanded polytetrafluoroethylene prepared from the multi-component lubricant will be significantly reduced.

[0124] Figure 1 This is the pore size distribution diagram of e-PTFE-1 provided in Example 1 and De-PTFE-1 provided in Comparative Example 1. The former has narrower pore size distribution and more uniform pore size, which is conducive to its application in the field of ion exchange membranes and separation membranes. Figure 2 The SEM images of the surfaces of e-PTFE-1 (left figure) provided in Example 1 and De-PTFE-1 (right figure) provided in Comparative Example 1 show that the most significant difference in their microstructure is the "nodes" of the internal fiber network. After the introduction of the oxygenated lubricant, the nodes of e-PTFE-1 exhibit a tangled, fibrous surface with a morphology similar to a braided "Chinese knot," while the nodes of De-PTFE-1 are irregularly shaped particles with a more pronounced radial pattern. This difference in micromorphology is the fundamental reason for the macroscopic performance differences between the two types of proton membranes.

[0125] Test Example 3

[0126] A perfluorosulfonic acid resin solution (specifically composed of a solute of sulfonated polytrifluorostyrene resin, a water-solid content of 9%, and a solvent of a mixed solution of water, ethanol, and isopropanol in a mass ratio of 4:1:5) was applied to both sides of the expanded polytetrafluoroethylene (e-PTFE-1 and e-PTFE-2) provided in Example 1 and Example 2, respectively, using a scraper and dried at 160° C. for 15 min to obtain composite ion exchange membranes PEM-1 and PEM-2 with an average thickness of 12 μm.

[0127] The perfluorosulfonic acid resin solution was coated on both sides of the expanded polytetrafluoroethylene (e-PTFE-4 and e-PTFE-5) provided in Example 4 and Example 5 using a slit, and dried at 160° C. for 15 min to obtain composite ion exchange membranes PEM-4 and PEM-5 with an average thickness of 12 μm.

[0128] The perfluorosulfonic acid resin solution was coated on both sides of the expanded polytetrafluoroethylene (e-PTFE-8) provided in Example 8 using a scraper, and dried at 160° C. for 15 min to obtain a composite ion exchange membrane PEM-8 with an average thickness of 12 μm.

[0129] The perfluorosulfonic acid resin solution was coated on both sides of the expanded polytetrafluoroethylene (De-PTFE-1) provided in Comparative Example 1 by a scraper, and dried at 160° C. for 15 min to obtain a composite ion exchange membrane D-PEM-1 with an average thickness of 12 μm.

[0130] The perfluorosulfonic acid resin solution was coated on both sides of the expanded polytetrafluoroethylene (De-PTFE-4) provided in Comparative Example 2 using a slit, and dried at 160° C. for 15 min to obtain a composite ion exchange membrane D-PEM-5 with an average thickness of 12 μm.

[0131] The perfluorosulfonic acid resin solution B was coated on both sides of the expanded polytetrafluoroethylene (De-PTFE-8) provided in Comparative Example 3 using a scraper, and dried at 160° C. for 15 min to obtain a composite ion exchange membrane D-PEM-8 with an average thickness of 12 μm.

[0132] The thickness, swelling ratio and tensile strength of the composite ion exchange membrane were measured respectively, and the results are shown in Table 5 below.

[0133] Table 5

[0134]

[0135]

[0136] Expanded polytetrafluoroethylene (ePTFE) is the backbone material of composite ion exchange membranes and a key factor influencing their strength. Under conditions of equal thickness and porosity, higher-strength ePTFE can improve the tensile strength of composite ion exchange membranes. This improved tensile strength of composite ion exchange membranes improves processing characteristics (for example, further processing into membrane electrodes and other membrane components) and increases the service life of the membrane material and its components.

[0137] As can be seen from the comparison of the composite ion exchange membranes PEM-1 to PEM-5 with D-PEM-1, D-PEM-4 and D-PEM-8 in Table 5, the composite ion exchange membranes prepared using the expanded polytetrafluoroethylene provided in Examples 1-8 as the supporting base membrane have lower swelling rates and higher tensile strength than the composite ion exchange membranes using the expanded polytetrafluoroethylene provided in Comparative Examples 1-3 as the supporting base membrane, which is more conducive to improving the processing characteristics while increasing the service life of the membrane material and its membrane assembly.

[0138] Figure 3 These are cross-sectional SEM images of PEM-1 and D-PEM-1, where the left image is a cross-sectional SEM image of PEM-1 and the right image is a cross-sectional SEM image of D-PEM-1. By comparing the left and right images, it can be seen that the ion exchange resin perfluorosulfonic acid resin in the left image is more evenly filled in the base membrane and has better uniformity, indicating that the expanded polytetrafluoroethylene provided in Example 1 has better processing performance.

[0139] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing expanded polytetrafluoroethylene, characterized in that: The preparation method comprises the following steps: mixing PTFE resin powder and lubricant, and sequentially performing pre-pressing, extrusion, calendering, degreasing, stretching and sintering to obtain expanded polytetrafluoroethylene, wherein the lubricant is a mixture of an oxygen-containing lubricant and an alkane lubricant, and the content of the oxygen-containing lubricant is 30-40wt%.

2. The preparation method according to claim 1, characterized in that The oxygen-containing lubricant includes a first oxygen-containing lubricant and a second oxygen-containing lubricant, and the mass ratio of the first oxygen-containing lubricant to the second oxygen-containing lubricant is 1:(2-3); wherein the first oxygen-containing lubricant is a C5-C12 fatty alcohol, and the second oxygen-containing lubricant includes at least one of a phthalate ester, a C5-C10 aliphatic dibasic acid ester, a phosphate ester or an epoxy compound.

3. The preparation method according to claim 2, characterized in that The alkane lubricant includes at least one of C5-C20 isoparaffin, petroleum ether, gasoline, kerosene, and liquid paraffin; Preferably, the alkane lubricant is selected from at least one of Isopar E, Isopar G, and Isopar L.

4. The preparation method according to claim 2, characterized in that The C5-C12 fatty alcohol includes at least one of n-pentanol, n-hexanol, n-heptanol, isoheptanol, n-octanol, isooctyl alcohol, n-nonanol, isononyl alcohol, n-decanol, and isodecanol; And / or, the phthalate ester includes at least one of dimethyl phthalate, diethyl phthalate, dibutyl phthalate, di(2-ethylhexyl) phthalate, and di-n-octyl phthalate; and / or, the C5-C10 aliphatic dibasic acid ester includes at least one of di(2-ethylhexyl) adipate, diisodecyl adipate, dibutyl sebacate, di-(2-ethylhexyl) sebacate, and di-(2-ethylhexyl) azelaic acid; And / or, the phosphate ester includes at least one of tributyl phosphate, tri-(2-ethylhexyl) phosphate, diphenyl octyl phosphate, triphenyl phosphate, and tri(isopropylphenyl) phosphate; And / or, the epoxy compound includes at least one of n-butyl glycidyl ether, allyl glycidyl ether, bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, 1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, sorbitol glycidyl ether, hexyl glycidyl ether, heptyl glycidyl ether, octyl glycidyl ether, nonyl glycidyl ether, decyl glycidyl ether, undecyl glycidyl ether, dodecyl glycidyl ether, tridecyl glycidyl ether, and tetradecyl glycidyl ether.

5. The preparation method according to claim 2, characterized in that The C5-C12 fatty alcohol is selected from at least one of n-hexanol, n-octanol, and isooctyl alcohol; And / or, the phthalate is at least one selected from dibutyl phthalate and di(2-ethylhexyl) phthalate; and / or, the C5-C10 aliphatic dibasic acid ester is di-(2-ethylhexyl) adipate; And / or, the phosphate ester is at least one selected from tributyl phosphate and triphenyl phosphate; And / or, the epoxy compound is selected from at least one of octyl glycidyl ether, dodecyl glycidyl ether, tridecyl glycidyl ether, and tetradecyl glycidyl ether.

6. The preparation method according to any one of claims 1 to 5, characterized in that The mass ratio of the PTFE resin powder to the lubricant is 100:16-30, preferably 100:16-22, and more preferably 100:18-22.

7. The preparation method according to any one of claims 1 to 5, characterized in that The pre-pressing pressure is 3-15 MPa, and the pre-pressing time is 3-60 min; And / or, the extrusion pressure is 3-20 MPa, and the extrusion temperature is 40-90°C.

8. The preparation method according to any one of claims 1 to 4, characterized in that The degreasing temperature is 120-190°C; And / or, the stretching includes longitudinal stretching and transverse stretching, the longitudinal stretching ratio is 3-20 times, and the transverse stretching ratio is 10-100 times; preferably, the longitudinal stretching temperature is 200-320°C, and the transverse stretching temperature is 170-320°C; And / or, the sintering temperature is 350-420°C.

9. An expanded polytetrafluoroethylene, characterized in that: The expanded polytetrafluoroethylene is obtained according to the preparation method according to any one of claims 1 to 8.

10. A composite ion exchange membrane, characterized in that: The composite ion exchange membrane comprises the expanded polytetrafluoroethylene according to claim 9.

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