Modified expanded polytetrafluoroethylene membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of expanded polytetrafluoroethylene, in particular to a modified expanded polytetrafluoroethylene film as well as a preparation method and application thereof. The preparation method comprises the following steps: soaking an expanded polytetrafluoroethylene membrane in a mixed solution of polyvinyl alcohol and glutaraldehyde for hydrophilic pretreatment to obtain a treated expanded polytetrafluoroethylene membrane; the preparation method comprises the following steps: mixing a nano inorganic material, a fluorine-containing reagent, a silicon-containing reagent and a dispersing agent to obtain a dispersion liquid, and adding a catalyst into the dispersion liquid to carry out cross-linking reaction to obtain an oil-proof modified solution; and immersing the treated expanded polytetrafluoroethylene membrane into an oil-proof modification solution for modification treatment to obtain the modified expanded polytetrafluoroethylene membrane. The modified expanded polytetrafluoroethylene membrane prepared by adopting the method has oil-proof performance and can prevent permeation of aviation fuel oil, and the method is simple to operate, few in required reagent, low in production cost, free of specific experimental conditions or special equipment and instruments, easy to realize large-scale production and not easy to damage the expanded polytetrafluoroethylene membrane.

Description

Technical Field

[0001] The invention relates to the technical field of expanded polytetrafluoroethylene, and in particular to a modified expanded polytetrafluoroethylene film and a preparation method and application thereof. Background Art

[0002] Expanded polytetrafluoroethylene membrane has stable chemical properties, excellent corrosion resistance and environmental resistance, and is widely used in the fields of petrochemicals, aerospace, electronics, etc. In the aerospace field, it is especially used as a sealing material due to its high temperature resistance and low density. However, expanded polytetrafluoroethylene itself does not have oil resistance and cannot prevent the penetration of aviation fuel, which has adverse effects on aircraft safety, environmental pollution, economic benefits, etc.

[0003] To this end, researchers have developed methods for oil-proof modification of expanded polytetrafluoroethylene membranes, including template method, electrospinning method, etching method, etc. Among them, the template method has a complex process and a fragile structure, making it difficult to achieve mass production. The electrospinning method is implemented at high pressure, which has many requirements for equipment and conditions and is difficult to achieve. The etching method easily damages the substrate. Although there are many methods, there are also many problems, which limits the further application of polytetrafluoroethylene membranes.

[0004] For example, patent CN111978584B discloses an expanded polytetrafluoroethylene sealing material that prevents the penetration of fuel and hydraulic oil, which is respectively configured with soaking liquid A and soaking liquid B, and the oil-proof material is obtained after drying, soaking and rolling, secondary treatment, and shaping. However, basically every step requires soaking and rolling the membrane, and repeated treatment to make it doped with mixed reagents such as fluorine solvents and solvent oil, which is labor-intensive, complex process, cumbersome operation, and requires the use of fluorine-modified acrylate mixed with solvent oil, which brings certain pressure in terms of economy and environmental protection.

[0005] Patent CN105688687A uses hydrophobic and oleophobic monomers to prepare a solution that penetrates into a microporous membrane, and uses plasma glow discharge treatment to generate free radicals that polymerize to form hydrophobic and oleophobic polymers to generate a double-repellent membrane. However, the plasma treatment capacity is limited, and the plasma treatment time is short, which limits its industrial application; and when the plasma treatment is carried out in an atmosphere containing reagents, the volatilization of the reagents will cause certain damage to the equipment, increasing the cost.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The first object of the present invention is to provide a method for preparing a modified expanded polytetrafluoroethylene membrane, which first increases the surface energy through hydrophilic pretreatment, then adds nano inorganic materials, fluorine-containing reagents and silicon-containing reagents to carry out cross-linking reaction and modify the expanded polytetrafluoroethylene membrane, which can increase the surface roughness while reducing the surface tension, so that the expanded polytetrafluoroethylene membrane has oil-proof performance. The modified expanded polytetrafluoroethylene membrane prepared by the method can prevent the penetration of aviation fuel, and the method is simple to operate, requires less reagents, has low production cost, does not require specific experimental conditions or special equipment and instruments, reduces environmental protection and production pressure, is easy to achieve large-scale production, and is not easy to damage the expanded polytetrafluoroethylene membrane.

[0008] The second object of the present invention is to provide a modified expanded polytetrafluoroethylene membrane, which has oil-proof properties and can prevent the penetration of aviation fuel.

[0009] The third object of the present invention is to provide a modified expanded polytetrafluoroethylene membrane obtained by the preparation method of the modified expanded polytetrafluoroethylene membrane or the application of the modified expanded polytetrafluoroethylene membrane in the fields of aerospace, petrochemical and electronics.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0011] The invention firstly provides a preparation method of a modified expanded polytetrafluoroethylene membrane, comprising the following steps: immersing the expanded polytetrafluoroethylene membrane in a mixed solution of polyvinyl alcohol and glutaraldehyde for hydrophilic pretreatment to obtain the treated expanded polytetrafluoroethylene membrane; uniformly mixing a nano inorganic material, a fluorine-containing reagent, a silicon-containing reagent and a dispersant to obtain a dispersion, adding a catalyst thereto for cross-linking reaction to obtain an oil-proof modified solution; immersing the treated expanded polytetrafluoroethylene membrane in the oil-proof modified solution for modification treatment, taking it out and drying it to obtain the modified expanded polytetrafluoroethylene membrane.

[0012] Furthermore, in the mixed solution of polyvinyl alcohol and glutaraldehyde, the mass fraction of polyvinyl alcohol is 1wt.% to 5wt.%.

[0013] Furthermore, in the mixed solution of polyvinyl alcohol and glutaraldehyde, the mass fraction of glutaraldehyde is 1wt.% to 10wt.%.

[0014] Furthermore, the soaking time is 5 to 40 minutes.

[0015] Furthermore, before the soaking, the expanded polytetrafluoroethylene membrane is cleaned and dried.

[0016] Furthermore, the nano inorganic material includes at least one of titanium dioxide, silicon dioxide and α-cellulose.

[0017] Furthermore, the average particle size of the nano inorganic material is 20 to 200 nm.

[0018] Furthermore, the fluorine-containing reagent includes at least one of perfluorooctyltrimethoxysilane, perfluorodecyltrimethoxysilane and perfluorodecyltrichlorosilane.

[0019] Furthermore, the silicon-containing reagent includes at least one of ethyl orthosilicate, methyltrimethoxysilane, methoxytriethoxysilane and octadecyltrichlorosilane.

[0020] Furthermore, the dispersant includes at least one of deionized water, ethanol, hexane, n-octane and cyclohexane.

[0021] Furthermore, the mass fraction of the nano inorganic material in the dispersion is 0.08wt.% to 0.4wt.%.

[0022] Furthermore, the sum of the mass fractions of the fluorine-containing reagent and the silicon-containing reagent in the dispersion is 10 wt.% to 20 wt.%.

[0023] Furthermore, the mass fraction of the fluorine-containing reagent in the dispersion is 2 wt.% to 7 wt.%.

[0024] Furthermore, the mass fraction of the silicon-containing reagent in the dispersion is 6 wt.% to 18 wt.%.

[0025] Furthermore, the catalyst comprises an aqueous ammonia solution with a mass fraction of 3wt% to 9wt%.

[0026] Furthermore, the mass of the catalyst is 5% to 10% of the mass of the dispersion.

[0027] Furthermore, the cross-linking reaction time is 1 to 10 hours.

[0028] Furthermore, the temperature of the cross-linking reaction is 15-30°C.

[0029] Furthermore, the modification treatment time is 30 to 300 minutes.

[0030] Furthermore, the temperature of the modification treatment is 15-30°C.

[0031] Furthermore, the drying temperature is 60-80°C.

[0032] The present invention further provides a modified expanded polytetrafluoroethylene membrane prepared by adopting the preparation method of the modified expanded polytetrafluoroethylene membrane.

[0033] Furthermore, the oil-proof time of the modified expanded polytetrafluoroethylene membrane at 25° C. is greater than 24 hours.

[0034] The present invention also provides a modified expanded polytetrafluoroethylene membrane obtained by the preparation method of the modified expanded polytetrafluoroethylene membrane or the application of the modified expanded polytetrafluoroethylene membrane in the fields of aerospace, petrochemical industry and electronics.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The preparation method of the modified expanded polytetrafluoroethylene membrane provided by the present invention is simple to operate, requires few reagents, has low production cost, does not require specific experimental conditions or special equipment and instruments, and only relies on the action of solvent to modify the expanded polytetrafluoroethylene membrane. The requirements of experimental conditions, processing capacity, etc. can be easily achieved, and there is no problem of equipment cost. In addition, the environmental protection and production pressures are reduced, and large-scale production is easy to achieve, and the expanded polytetrafluoroethylene membrane is not easily damaged.

[0037] (2) The modified expanded polytetrafluoroethylene membrane prepared by the method for preparing the modified expanded polytetrafluoroethylene membrane provided by the present invention can prevent aviation fuel from penetrating.

[0038] (3) In order to achieve the long-term effectiveness of the oil-proof modification effect of the modified expanded polytetrafluoroethylene membrane, the preparation method of the modified expanded polytetrafluoroethylene membrane provided by the present invention performs a hydrophilic pretreatment on the expanded polytetrafluoroethylene membrane to increase the surface energy so that the oil-proof modification solution can better act on the expanded polytetrafluoroethylene membrane.

[0039] (4) The method for preparing the modified expanded polytetrafluoroethylene membrane provided by the present invention adopts a compound of nano-inorganic materials, fluorine-containing reagents and silicon-containing reagents to obtain a modified expanded polytetrafluoroethylene membrane with an oil-proof effect without changing the appearance characteristics of the membrane and without damaging the membrane.

[0040] (5) The preparation method of the modified expanded polytetrafluoroethylene membrane provided by the present invention can reduce the amount of fluorine-containing reagent added by introducing a silicon-containing reagent, thereby reducing costs and being more environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0042] Figure 1 The oil-proof results of dropping different oils on the modified expanded polytetrafluoroethylene membrane prepared in Example 1 provided by the present invention;

[0043] Figure 2 The oil-proofing results of dropping different oils on the unmodified expanded polytetrafluoroethylene membrane of Comparative Example 4 provided by the present invention. DETAILED DESCRIPTION

[0044] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0045] If there is no special explanation, in the present invention, "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "the first", "the second", "the third", "the fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0046] If there is no special explanation, the "include" and "comprising" mentioned in the present invention represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0047] If there is no special explanation, in the present invention, "one or more" or "at least one" refers to any one, any two or more of the listed items. Among them, "several" refers to any two or more of the listed items.

[0048] In a first aspect, the present invention provides a method for preparing a modified expanded polytetrafluoroethylene membrane capable of preventing aviation fuel penetration, comprising the following steps:

[0049] The expanded polytetrafluoroethylene membrane is immersed in a mixed solution of polyvinyl alcohol and glutaraldehyde for hydrophilic pretreatment to obtain a treated expanded polytetrafluoroethylene membrane. The solvent in the mixed solution of polyvinyl alcohol and glutaraldehyde is water.

[0050] Among them, polyvinyl alcohol contains more hydroxyl groups in its molecular structure and has good hydrophilicity. At the same time, it is also a kind of adhesive with good film-forming property. The present invention uses glutaraldehyde (GA) to crosslink the hydroxyl groups in polyvinyl alcohol (PVA), which can give the expanded polytetrafluoroethylene film a lasting hydrophilicity. Through hydrophilic pretreatment, the surface of the expanded polytetrafluoroethylene film can be made hydrophilic, the water drop angle is reduced, and the surface energy is increased.

[0051] After the nano-inorganic material, the fluorine-containing reagent, the silicon-containing reagent and the dispersant are uniformly mixed to obtain a dispersion, a catalyst is then added thereto to carry out a cross-linking reaction, and after the cross-linking reaction is completed, an oil-proof modified solution composed of fluorine-modified silica sol is obtained.

[0052] Among them, nano-inorganic materials can increase the roughness of expanded polytetrafluoroethylene membranes.

[0053] The addition of fluorine-containing reagents and silicon-containing reagents can increase the surface roughness while reducing the surface tension, making the expanded polytetrafluoroethylene film oil-proof.

[0054] Moreover, by introducing silicon-containing reagents, the amount of fluorine-containing reagents used can be reduced. Among them, the introduction of silicon atoms plays a role in roughening the surface of nanoparticles, which can reduce the use of nanoparticles, thereby reducing the impact of modification on the flexibility of the membrane. On the other hand, silicon-containing reagents and fluorine-containing reagents are hydrolyzed and condensed into low surface energy materials under alkaline conditions, which are more stable than the modification of a single fluorine-containing reagent. In addition, adding fluorine-containing reagents and silicon-containing reagents at the same time can improve the timeliness of oil-proof performance.

[0055] Adding a catalyst can promote the cross-linking between fluorine and silane groups, the cross-linking between nano-inorganic materials, and the co-cross-linking between fluorine, silane and nano-inorganic materials, thereby obtaining an oil-repellent surface.

[0056] The treated expanded polytetrafluoroethylene membrane is immersed in the oil-proof modification solution for modification treatment, and after the modification treatment is completed, it is taken out and fixed, and then dried to obtain the modified expanded polytetrafluoroethylene membrane.

[0057] The modified expanded polytetrafluoroethylene membrane prepared by the method can prevent aviation fuel from penetrating. In addition, the method is simple to operate, requires few reagents, has low production cost, does not require specific experimental conditions or special equipment and instruments, and only relies on the action of solvents to modify the expanded polytetrafluoroethylene membrane. The requirements of experimental conditions, processing capacity, etc. can be easily achieved, and there is no problem of equipment cost. In addition, the environmental protection and production pressures are reduced, and large-scale production is easy to achieve. The expanded polytetrafluoroethylene membrane is not easily damaged (the appearance characteristics of the expanded polytetrafluoroethylene membrane will not be changed).

[0058] The preparation method of the modified expanded polytetrafluoroethylene membrane provided by the present invention is simple to operate and has a short process. Compared with most of the existing methods, the types of reagents used are less, and there is no obvious difference in the appearance of the expanded membrane before and after the modification; the experimental conditions are simple and easy to operate, the process operation is simple, the expanded polytetrafluoroethylene membrane can be treated by solution throughout the process, and no instruments or equipment are needed, thereby reducing energy consumption and equipment costs; the membrane treatment can be completed at room temperature, thereby avoiding the influence of temperature on the expanded polytetrafluoroethylene membrane, the solution and even the operator; in addition, the oil-proof modified solution prepared by the present invention has a certain timeliness, does not need to be prepared and used immediately, and the process is simple and easy to expand, thereby providing a new idea for the realization of industrialization of expanded polytetrafluoroethylene oil-proof sealing materials.

[0059] In some specific embodiments, in the mixed solution of polyvinyl alcohol and glutaraldehyde, the mass fraction of polyvinyl alcohol is 1wt.% to 5wt.%, including but not limited to any point value of 1wt.%, 2wt.%, 3wt.%, 4wt.%, 5wt.%, or any range value between the two. This is conducive to improving the hydrophilic pretreatment effect.

[0060] In some specific embodiments, in the mixed solution of polyvinyl alcohol and glutaraldehyde, the mass fraction of glutaraldehyde is 1wt.% to 10wt.%, including but not limited to any one of 1wt.%, 2wt.%, 3wt.%, 4wt.%, 5wt.%, 6wt.%, 7wt.%, 8wt.%, 9wt.%, 10wt.%, or any range between two of them. This is conducive to improving the hydrophilic pretreatment effect.

[0061] In some specific embodiments, the time for soaking the expanded polytetrafluoroethylene membrane in the mixed solution of polyvinyl alcohol and glutaraldehyde is 5 to 40 minutes, including but not limited to any one of 5 minutes, 6 minutes, 8 minutes, 10 minutes, 15 minutes, 20 minutes, 30 minutes, and 40 minutes, or any range between two of them. This is conducive to further improving the hydrophilic pretreatment effect.

[0062] In some specific embodiments, the soaking is followed by drying.

[0063] In some specific embodiments, before the soaking, the expanded polytetrafluoroethylene membrane is cleaned and dried to remove impurities on the surface of the expanded polytetrafluoroethylene membrane and improve the effects of the hydrophilic pretreatment and subsequent modification treatment.

[0064] The cleaning agent used for cleaning may be one or more materials with cleaning function such as ethanol, acetone, etc., but is not limited thereto.

[0065] It is understandable that the expanded polytetrafluoroethylene can be any conventional polytetrafluoroethylene membrane structure in the art, such as a thin film, a flat membrane, a hollow fiber membrane, etc., but is not limited thereto.

[0066] In some specific implementations, in order to further improve the roughness and modification effect, the nano inorganic material includes at least one of titanium dioxide, silicon dioxide and α-cellulose.

[0067] In some specific embodiments, in order to further improve the roughness and modification effect, the average particle size of the nano-inorganic material is 20 to 200 nm; including but not limited to any point value of 20 nm, 30 nm, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm or a range value between any two of them.

[0068] In some specific embodiments, the fluorine-containing reagent includes at least one of perfluorooctyltrimethoxysilane, perfluorodecyltrimethoxysilane and perfluorodecyltrichlorosilane.

[0069] In some specific embodiments, the silicon-containing agent includes at least one of ethyl orthosilicate, methyltrimethoxysilane, methoxytriethoxysilane and octadecyltrichlorosilane.

[0070] In some specific embodiments, the dispersant includes at least one of deionized water, ethanol, hexane, n-octane and cyclohexane.

[0071] In some specific implementations, the nano-inorganic material and the dispersant are first mixed and stirred for 1 to 2 hours to make them fully and evenly dispersed, and then the fluorine-containing reagent and the silicon-containing reagent are added thereto and stirred evenly to obtain a dispersion.

[0072] In some specific embodiments, the mass fraction of the nano-inorganic material in the dispersion is 0.08wt.% to 0.4wt.%, including but not limited to any one of 0.08wt.%, 0.1wt.%, 0.15wt.%, 0.2wt.%, 0.25wt.%, 0.3wt.%, 0.35wt.%, and 0.4wt.%, or a range between any two of them.

[0073] In some specific embodiments, the sum of the mass fractions of the fluorine-containing reagent and the silicon-containing reagent in the dispersion is 10wt.% to 20wt.%, including but not limited to any one of 10wt.%, 11wt.%, 12wt.%, 13wt.%, 14wt.%, 15wt.%, 16wt.%, 18wt.%, and 20wt.%, or a range between any two of them.

[0074] In some specific embodiments, the mass fraction of the fluorine-containing reagent in the dispersion is 2wt.% to 7wt.%, including but not limited to any point value of 2wt.%, 3wt.%, 4wt.%, 5wt.%, 6wt.%, 7wt.%, or a range value between any two of them.

[0075] In some specific embodiments, the mass fraction of the silicon-containing reagent in the dispersion is 6wt.% to 18wt.%, including but not limited to any one of 6wt.%, 7wt.%, 8wt.%, 9wt.%, 10wt.%, 11wt.%, 12wt.%, 13wt.%, 14wt.%, 15wt.%, 16wt.%, and 18wt.%, or a range between any two of them.

[0076] By controlling the mass fractions of the nano-inorganic material, the fluorine-containing agent and the silicon-containing agent in the dispersion, that is, controlling the ratio between the nano-inorganic material, the fluorine-containing agent and the silicon-containing agent, it is beneficial to further improve the effect of the oil-proof modification.

[0077] In some specific embodiments, the catalyst comprises an aqueous ammonia solution with a mass fraction of 3 wt% to 9 wt%, wherein the concentration of the aqueous ammonia solution includes but is not limited to any one of 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, and 9 wt%, or a range between any two of them.

[0078] In some specific embodiments, the mass of the catalyst is 5% to 10% of the mass of the dispersion, including but not limited to any point value of 5%, 6%, 7%, 8%, 9%, 10% or a range between any two of them.

[0079] The use of the catalyst in the above mass fraction and amount is beneficial to promoting the cross-linking reaction.

[0080] In some specific embodiments, the cross-linking reaction time is 1 to 10 hours, including but not limited to any one of 1h, 2h, 3h, 4h, 5h, 6h, 8h, 10h or a range between any two of them.

[0081] In some specific embodiments, the temperature of the cross-linking reaction is room temperature, for example, 15 to 30° C., including but not limited to any point value of 15° C., 18° C., 20° C., 23° C., 25° C., 28° C., 30° C., or any range value between two thereof. It is understood that heating can also be performed during the cross-linking reaction, but this will result in increased energy consumption and cost.

[0082] In some specific embodiments, the modification treatment time is 30 to 300 min, including but not limited to any one of 30 min, 40 min, 60 min, 120 min, 150 min, 180 min, 210 min, 240 min, 260 min, and 300 min, or a range between any two of them.

[0083] In some specific embodiments, the temperature of the modification treatment is 15-30°C, including but not limited to any point value of 15°C, 18°C, 20°C, 23°C, 25°C, 28°C, 30°C or any range value between two thereof. It is understood that heating can also be performed during the modification treatment, but it will lead to increased energy consumption and cost. The prior art involves that fluorosilane modification basically requires the reaction to be promoted by increasing the temperature, while the present invention can complete the modification reaction at room temperature, with lower energy consumption and cost.

[0084] In some specific embodiments, the drying step further includes a washing step, such as washing with ethanol.

[0085] In some specific embodiments, the drying temperature is 60-80°C, including but not limited to any one of 60°C, 65°C, 70°C, 75°C, 80°C or a range between any two of them.

[0086] In a second aspect, the present invention provides a modified expanded polytetrafluoroethylene membrane prepared by the above-mentioned method for preparing the modified expanded polytetrafluoroethylene membrane.

[0087] The modified expanded polytetrafluoroethylene membrane has oil-proof properties and can prevent the penetration of aviation fuel.

[0088] In some specific embodiments, the oil-proof time of the modified expanded polytetrafluoroethylene membrane at 25° C. is >24 h, preferably >32 h, and more preferably >72 h.

[0089] The modified expanded polytetrafluoroethylene film provided by the present invention has a relatively long effectiveness in oil-proofing effect.

[0090] In a third aspect, the present invention provides a modified expanded polytetrafluoroethylene membrane obtained by the method for preparing the modified expanded polytetrafluoroethylene membrane or the application of the modified expanded polytetrafluoroethylene membrane in the fields of aerospace, petrochemicals and electronics.

[0091] The modified expanded polytetrafluoroethylene film provided by the invention can be widely used in various fields, especially in the aerospace field, and can be used as a sealing material.

[0092] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0093] Example 1

[0094] The method for preparing the modified expanded polytetrafluoroethylene membrane provided in this embodiment comprises the following steps:

[0095] (1) The expanded polytetrafluoroethylene membrane is cleaned with ethanol and then dried at 80°C. The cleaned expanded polytetrafluoroethylene membrane is subjected to hydrophilic pretreatment, and is immersed in a mixed aqueous solution of polyvinyl alcohol and glutaraldehyde for 20 minutes and then dried at 80°C to obtain a treated expanded polytetrafluoroethylene membrane. In the mixed solution of polyvinyl alcohol and glutaraldehyde, the mass fraction of polyvinyl alcohol is 1wt.%, and the mass fraction of glutaraldehyde is 1wt.%.

[0096] (2) Nano titanium dioxide with an average particle size of 50 nm is uniformly dispersed in ethanol, and then perfluorodecyl trimethoxysilane (i.e., fluorine-containing reagent) and ethyl orthosilicate (i.e., silicon-containing reagent) are added thereto, and the dispersion is obtained after being stirred and dispersed uniformly. In the dispersion, the mass fraction of the nano inorganic material is 0.16wt.%, the mass fraction of the fluorine-containing reagent is 2wt.%, and the mass fraction of the silicon-containing reagent is 8wt.%. Then, a 3wt% ammonia aqueous solution (i.e., catalyst) is added to the dispersion for cross-linking reaction, wherein the mass of the catalyst is 8% of the mass of the dispersion. After reacting for 5 hours at room temperature (25°C), an oil-proof modified solution is obtained.

[0097] (3) Immersing the treated expanded polytetrafluoroethylene membrane obtained in step (1) into the oil-proof modification solution obtained in step (2), performing modification treatment at room temperature (25° C.), taking it out after 60 minutes, washing it with ethanol, and drying it at 80° C. to obtain a modified expanded polytetrafluoroethylene membrane.

[0098] Example 2

[0099] The method for preparing the modified expanded polytetrafluoroethylene membrane provided in this embodiment comprises the following steps:

[0100] (1) The expanded polytetrafluoroethylene membrane is cleaned with ethanol and then dried at 70°C. The cleaned expanded polytetrafluoroethylene membrane is subjected to hydrophilic pretreatment, and is immersed in a mixed aqueous solution of polyvinyl alcohol and glutaraldehyde for 20 minutes and then dried at 70°C to obtain a treated expanded polytetrafluoroethylene membrane. In the mixed solution of polyvinyl alcohol and glutaraldehyde, the mass fraction of polyvinyl alcohol is 1.5wt.%, and the mass fraction of glutaraldehyde is 1wt.%.

[0101] (2) Nano-silicon dioxide with an average particle size of 100 nm is uniformly dispersed in ethanol, and then perfluorodecyl trimethoxysilane (i.e., fluorine-containing reagent) and ethyl orthosilicate (i.e., silicon-containing reagent) are added thereto, and the dispersion is obtained after being stirred and dispersed uniformly. In the dispersion, the mass fraction of the nano-inorganic material is 0.16 wt.%, the mass fraction of the fluorine-containing reagent is 3 wt.%, and the mass fraction of the silicon-containing reagent is 8 wt.%. Then, a 3 wt.% ammonia aqueous solution (i.e., catalyst) is added to the dispersion for cross-linking reaction, wherein the mass of the catalyst is 5% of the mass of the dispersion. After reacting at room temperature (25°C) for 10 hours, an oil-proof modified solution is obtained.

[0102] (3) Immersing the treated expanded polytetrafluoroethylene membrane obtained in step (1) into the oil-proof modification solution obtained in step (2), performing modification treatment at 28° C., taking it out after 60 minutes, washing it with ethanol, and drying it at 80° C. to obtain a modified expanded polytetrafluoroethylene membrane.

[0103] Example 3

[0104] The method for preparing the modified expanded polytetrafluoroethylene membrane provided in this embodiment comprises the following steps:

[0105] (1) The expanded polytetrafluoroethylene membrane is cleaned with acetone and then dried at 60°C. The cleaned expanded polytetrafluoroethylene membrane is subjected to hydrophilic pretreatment, and is immersed in a mixed aqueous solution of polyvinyl alcohol and glutaraldehyde for 20 minutes and then dried at 60°C to obtain a treated expanded polytetrafluoroethylene membrane. In the mixed solution of polyvinyl alcohol and glutaraldehyde, the mass fraction of polyvinyl alcohol is 2wt.%, and the mass fraction of glutaraldehyde is 1wt.%.

[0106] (2) Nano-silicon dioxide with an average particle size of 120 nm is uniformly dispersed in ethanol, and then perfluorodecyl trimethoxysilane (i.e., fluorine-containing reagent) and ethyl orthosilicate (i.e., silicon-containing reagent) are added thereto, and the dispersion is obtained after being stirred and dispersed uniformly. In the dispersion, the mass fraction of the nano-inorganic material is 0.2 wt.%, the mass fraction of the fluorine-containing reagent is 4 wt.%, and the mass fraction of the silicon-containing reagent is 10 wt.%. Then, a 3 wt.% ammonia aqueous solution (i.e., catalyst) is added to the dispersion for cross-linking reaction, wherein the mass of the catalyst is 10% of the mass of the dispersion. After reacting for 2 h at room temperature (25° C.), an oil-proof modified solution is obtained.

[0107] (3) Immersing the treated expanded polytetrafluoroethylene membrane obtained in step (1) into the oil-proof modification solution obtained in step (2), performing modification treatment at 23° C., taking it out after 40 minutes, washing it with ethanol, and drying it at 80° C. to obtain a modified expanded polytetrafluoroethylene membrane.

[0108] Example 4

[0109] The method for preparing the modified expanded polytetrafluoroethylene membrane provided in this embodiment comprises the following steps:

[0110] (1) The expanded polytetrafluoroethylene membrane is cleaned with ethanol and then dried at 80°C. The cleaned expanded polytetrafluoroethylene membrane is subjected to hydrophilic pretreatment, and is immersed in a mixed aqueous solution of polyvinyl alcohol and glutaraldehyde for 20 minutes and then dried at 80°C to obtain a treated expanded polytetrafluoroethylene membrane. In the mixed solution of polyvinyl alcohol and glutaraldehyde, the mass fraction of polyvinyl alcohol is 2wt.%, and the mass fraction of glutaraldehyde is 1.5wt.%.

[0111] (2) Nano-silicon dioxide with an average particle size of 160 nm is uniformly dispersed in ethanol, and then perfluorodecyl trimethoxysilane (i.e., fluorine-containing reagent) and ethyl orthosilicate (i.e., silicon-containing reagent) are added thereto, and the dispersion is obtained after being stirred and dispersed uniformly. In the dispersion, the mass fraction of the nano-inorganic material is 0.2 wt.%, the mass fraction of the fluorine-containing reagent is 4 wt.%, and the mass fraction of the silicon-containing reagent is 8 wt.%. Then, a 3 wt.% ammonia aqueous solution (i.e., catalyst) is added to the dispersion for cross-linking reaction, wherein the mass of the catalyst is 7% of the mass of the dispersion. After reacting at room temperature (25°C) for 3 hours, an oil-proof modified solution is obtained.

[0112] (3) Immersing the treated expanded polytetrafluoroethylene membrane obtained in step (1) into the oil-proof modification solution obtained in step (2), performing modification treatment at 20° C., taking it out after 40 minutes, washing it with ethanol, and drying it at 80° C. to obtain a modified expanded polytetrafluoroethylene membrane.

[0113] Example 5

[0114] The preparation method of the modified expanded polytetrafluoroethylene membrane provided in this embodiment is basically the same as that in Embodiment 1, except that in the mixed solution of polyvinyl alcohol and glutaraldehyde in step (1), the mass fraction of polyvinyl alcohol is 4 wt.% and the mass fraction of glutaraldehyde is 8 wt.%.

[0115] Example 6

[0116] The preparation method of the modified expanded polytetrafluoroethylene membrane provided in this embodiment is basically the same as that in embodiment 1, except that in step (2), the nano silicon dioxide is replaced by α-cellulose having the same average particle size as the nano silicon dioxide.

[0117] Example 7

[0118] The preparation method of the modified expanded polytetrafluoroethylene membrane provided in this embodiment is basically the same as that in Embodiment 1, except that in step (2), perfluorodecyltrimethoxysilane is replaced by an equal mass of perfluorodecyltrichlorosilane.

[0119] Example 8

[0120] The preparation method of the modified expanded polytetrafluoroethylene membrane provided in this embodiment is basically the same as that in Embodiment 1, except that in step (2), perfluorodecyltrimethoxysilane is replaced by an equal mass of perfluorooctyltrimethoxysilane.

[0121] Example 9

[0122] The preparation method of the modified expanded polytetrafluoroethylene membrane provided in this embodiment is basically the same as that in Embodiment 1, except that in step (2), tetraethyl orthosilicate is replaced by an equal mass of methyltrimethoxysilane.

[0123] Example 10

[0124] The preparation method of the modified expanded polytetrafluoroethylene membrane provided in this embodiment is basically the same as that in Embodiment 1, except that in step (2), ethyl orthosilicate is replaced by an equal mass of methoxytriethoxysilane.

[0125] Embodiment 11

[0126] The preparation method of the modified expanded polytetrafluoroethylene membrane provided in this embodiment is basically the same as that in Embodiment 1, except that in step (2), tetraethyl orthosilicate is replaced by an equal mass of octadecyltrichlorosilane.

[0127] Example 12

[0128] The preparation method of the modified expanded polytetrafluoroethylene membrane provided in this embodiment is basically the same as that in Embodiment 1, except that, in the dispersion of step (2), the mass fraction of the nano-inorganic material is 0.40 wt.%, the mass fraction of the fluorine-containing reagent is 6 wt.%, and the mass fraction of the silicon-containing reagent is 14 wt.%.

[0129] Comparative Example 1

[0130] The preparation method of the modified expanded polytetrafluoroethylene membrane provided in this comparative example is basically the same as that of Example 1, except that in step (1), the mixed aqueous solution of polyvinyl alcohol and glutaraldehyde is replaced by an aqueous solution of polyvinyl alcohol, and the mass fraction of the aqueous solution of polyvinyl alcohol is 2 wt.%.

[0131] Comparative Example 2

[0132] The preparation method of the modified expanded polytetrafluoroethylene membrane provided in this comparative example is basically the same as that of Example 1, except that no hydrophilic pretreatment is performed in step (1), and in step (3), the cleaned expanded polytetrafluoroethylene membrane obtained in step (1) is directly immersed in an oil-proof modification solution for modification.

[0133] Comparative Example 3

[0134] The preparation method of the modified expanded polytetrafluoroethylene membrane provided in this comparative example is basically the same as that of Example 1, except that nano titanium dioxide is not added to the dispersion in step (2).

[0135] Comparative Example 4

[0136] The preparation method of the modified expanded polytetrafluoroethylene membrane provided in this comparative example is basically the same as that of Example 1, except that tetraethyl orthosilicate (i.e., silicon-containing reagent) is not added to the dispersion in step (2), and the mass fraction of the fluorine-containing reagent is replaced with 10 wt.%.

[0137] Comparative Example 5

[0138] This comparative example directly uses the expanded polytetrafluoroethylene membrane after cleaning in step (1) of Example 1.

[0139] Experimental example

[0140] The modified expanded polytetrafluoroethylene membranes prepared in the above embodiments and comparative examples and the expanded polytetrafluoroethylene membranes after cleaning were subjected to oil repellent tests, and the oil repellent was tested to see whether it was still effective after being treated at 200°C. The test standard refers to the oil repellent performance test in GJB8272-2014, and the test results are shown in Table 1. The concentration of nano-inorganic materials refers to the mass fraction of nano-inorganic materials in the dispersion; the total concentration of fluorine-silicon reagents refers to the sum of the mass fractions of fluorine-containing reagents and silicon-containing reagents in the dispersion.

[0141] Table 1 Test results of oil-proof performance of various modified expanded polytetrafluoroethylene membranes

[0142]

[0143]

[0144] It can be seen from Table 1 that the modified expanded polytetrafluoroethylene membranes prepared in various embodiments have oil-proof properties and have a long oil-proof period.

[0145] However, Comparative Examples 1 to 5 are not oil-proof or have a short oil-proof effect. Specifically, since glutaraldehyde is not added in Comparative Example 1, polyvinyl alcohol does not produce crosslinking, and is only covered on the surface of the film by adsorption, which is easy to fall off. After the film is treated with oil-proofing, the adhesion ability of the oil-proof layer to the film is also weak, and it cannot be used at high temperatures. Since Comparative Example 2 did not perform hydrophilic pretreatment, the oil-proof dispersion spread and infiltrate slowly in the film, and the reaction is uneven. Since nano-titanium dioxide was not added in Comparative Example 3, the fluorine-silicon reagent directly acts on the film. At this time, since there are no nanoparticles on the film, the surface of the film is all fluorine atoms, and the reaction effect of the two is poor or even no reaction occurs. Since no silicon-containing reagent is added in Comparative Example 4, the fluorine-containing reagent directly modifies the nanoparticles. The content and density of the nanoparticles directly affect the oil-proof time of the film, and the excessive use of nanoparticles will cause the film to harden. On the basis of maintaining the original flexibility of the film, the oil-proof time of the modified film will be significantly shortened.

[0146] Furthermore, different oils were dropped on the modified expanded polytetrafluoroethylene membrane prepared in Example 1 and the unmodified expanded polytetrafluoroethylene membrane of Comparative Example 4 to observe the oil-proof effect. The results are as follows: Figure 1 and Figure 2 As shown. Among them, Figure 1 The oil-proof results of dropping different oils on the modified expanded polytetrafluoroethylene membrane prepared in Example 1 are as follows: Figure 2 The oil-proofing results of different oils dropped on the unmodified expanded polytetrafluoroethylene membrane of comparative example 4. It can be seen that the modified expanded polytetrafluoroethylene membrane of Example 1 has oil-proofing function for the three oils, while the oil-proofing effect of comparative example 1 for No. 4109 lubricating oil is significantly worse, and it has no oil-proofing effect for No. 15 hydraulic oil and No. 3 kerosene.

[0147] In summary, the modified expanded polytetrafluoroethylene membrane provided by the present invention has oil-proof performance, can prevent the penetration of aviation fuel, and has a long oil-proof effect.

[0148] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a modified expanded polytetrafluoroethylene film, characterized in that: The steps include: The expanded polytetrafluoroethylene membrane is immersed in a mixed solution of polyvinyl alcohol and glutaraldehyde for hydrophilic pretreatment to obtain a treated expanded polytetrafluoroethylene membrane; After uniformly mixing the nano inorganic material, the fluorine-containing reagent, the silicon-containing reagent and the dispersant to obtain a dispersion, a catalyst is added thereto to carry out a cross-linking reaction to obtain an oil-proof modified solution; The treated expanded polytetrafluoroethylene membrane is immersed in the oil-proof modification solution for modification, taken out and dried to obtain the modified expanded polytetrafluoroethylene membrane.

2. The method for preparing the modified expanded polytetrafluoroethylene membrane according to claim 1, characterized in that: At least one of the following conditions is met: (1) In the mixed solution of polyvinyl alcohol and glutaraldehyde, the mass fraction of polyvinyl alcohol is 1wt.% to 5wt.%; (2) In the mixed solution of polyvinyl alcohol and glutaraldehyde, the mass fraction of glutaraldehyde is 1wt.% to 10wt.%; (3) The soaking time is 5 to 40 minutes; (4) Before the soaking, the expanded polytetrafluoroethylene membrane is cleaned and dried.

3. The method for preparing the modified expanded polytetrafluoroethylene membrane according to claim 1, characterized in that: At least one of the following conditions is met: (1) The nano inorganic material comprises at least one of titanium dioxide, silicon dioxide and α-cellulose; (2) The average particle size of the nano inorganic material is 20 to 200 nm; (3) the fluorine-containing reagent comprises at least one of perfluorooctyltrimethoxysilane, perfluorodecyltrimethoxysilane and perfluorodecyltrichlorosilane; (4) the silicon-containing reagent comprises at least one of ethyl orthosilicate, methyltrimethoxysilane, methoxytriethoxysilane and octadecyltrichlorosilane; (5) The dispersant includes at least one of deionized water, ethanol, hexane, n-octane and cyclohexane.

4. The method for preparing the modified expanded polytetrafluoroethylene membrane according to claim 1, characterized in that: At least one of the following conditions is met: (1) The mass fraction of the nano-inorganic material in the dispersion is 0.08 wt.% to 0.4 wt.%; (2) The sum of the mass fractions of the fluorine-containing reagent and the silicon-containing reagent in the dispersion is 10 wt.% to 20 wt.%; (3) The mass fraction of the fluorine-containing reagent in the dispersion is 2 wt.% to 7 wt.%; (4) The mass fraction of the silicon-containing reagent in the dispersion is 6 wt.% to 18 wt.%.

5. The method for preparing the modified expanded polytetrafluoroethylene membrane according to claim 1, characterized in that: At least one of the following conditions is met: (1) The catalyst comprises an aqueous ammonia solution with a mass fraction of 3 wt% to 9 wt%; (2) The mass of the catalyst is 5% to 10% of the mass of the dispersion.

6. The method for preparing the modified expanded polytetrafluoroethylene membrane according to claim 1, characterized in that: At least one of the following conditions is met: (1) The cross-linking reaction time is 1 to 10 hours; (2) The temperature of the cross-linking reaction is 15 to 30°C.

7. The method for preparing the modified expanded polytetrafluoroethylene membrane according to claim 1, characterized in that: At least one of the following conditions is met: (1) The modification treatment time is 30 to 300 minutes; (2) The temperature of the modification treatment is 15 to 30° C.; (3) The drying temperature is 60-80°C.

8. A modified expanded polytetrafluoroethylene membrane obtained by the method for preparing a modified expanded polytetrafluoroethylene membrane as claimed in any one of claims 1 to 7.

9. The modified expanded polytetrafluoroethylene membrane according to claim 8, characterized in that: The modified expanded polytetrafluoroethylene film has an oil-proof time of more than 24 hours at 25°C.

10. Use of the modified expanded polytetrafluoroethylene membrane obtained by the method for preparing the modified expanded polytetrafluoroethylene membrane according to any one of claims 1 to 7 or the modified expanded polytetrafluoroethylene membrane according to any one of claims 8 to 9 in the fields of aerospace, petrochemical and electronics.

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