Hydrophilic polytetrafluoroethylene microporous membrane and preparation method thereof
阅读说明：本技术 亲水聚四氟乙烯微孔膜及其制备方法 (Hydrophilic polytetrafluoroethylene microporous membrane and preparation method thereof ) 是由 李军巍 宋敏彦 吴君毅 杜丽君 汪婉 于 2019-11-08 设计创作，主要内容包括：公开了亲水聚四氟乙烯微孔膜及其制备方法。所述聚四氟乙烯包括源自四氟乙烯的单体单元和以四氟乙烯总重量计0.05％-0.50％的源自下列共聚单体的单元(i),其中m＝0,1；n＝2～4；M是金属离子或氢；所述聚四氟乙烯微孔膜具有纤维丝互联的节点形成的微结构。所述制造方法依次包括：(a)在四氟乙烯分散聚合中加入具有下列通式(ii)的含有磺酰氟基团的共聚单体,其中m＝0,1；n＝2～4,得到聚四氟乙烯改性分散树脂；(b)通过膏状挤压、挤出、脱油,再单向或双向拉伸得到聚四氟乙烯微孔膜；和(c)在碱液中完全水解微孔膜中的磺酰氟基团,得到亲水微孔膜。<Image he="75" wi="700" file="DDA0002266369830000011.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>(Disclosed are a hydrophilic polytetrafluoroethylene microporous membrane and a method for preparing the same. The polytetrafluoroethylene comprises monomer units derived from tetrafluoroethylene and 0.05-0.50% by total weight of tetrafluoroethylene of units (i) derived from a comonomer wherein m is 0, 1; n is 2-4; m is a metal ion or hydrogen; the polytetrafluoroethylene microporous membrane has a microstructure formed by nodes formed by interconnecting fiber filaments. The manufacturing method sequentially comprises the following steps: (a) adding a comonomer containing a sulfonyl fluoride group having the following general formula (ii) wherein m is 0, 1; n is 2-4, and obtaining polytetrafluoroethylene modified dispersion resin;(b) obtaining a polytetrafluoroethylene microporous membrane by paste extrusion, deoiling and unidirectional or bidirectional stretching; and (c) completely hydrolyzing sulfonyl fluoride groups in the microporous membrane in alkali liquor to obtain the hydrophilic microporous membrane.)
1. A microporous membrane of polytetrafluoroethylene having a hydrophilic surface, said polytetrafluoroethylene comprising monomer units derived from tetrafluoroethylene and from 0.05% to 0.50% by total weight of tetrafluoroethylene, of units derived from the following comonomers:
wherein m is 0, 1; n is 2-4;
m is a metal ion, an ammonium ion or hydrogen;
the polytetrafluoroethylene microporous membrane has a microstructure formed by nodes formed by interconnecting fiber filaments.
2. The microporous polytetrafluoroethylene membrane according to claim 1, wherein the comonomer units are present in an amount from 0.1% to 0.45%, preferably from 0.15% to 0.4%, more preferably from 0.2% to 0.35%, most preferably from 0.25% to 0.3%.
3. The microporous polytetrafluoroethylene membrane according to claim 1, wherein the comonomer units are derived from perfluoro (6-methyl-5, 8-dioxa-7-octene) sulfonic acid or salt, perfluoro (5-methyl-4, 7-dioxa-6-heptene) sulfonic acid or salt, perfluoro (4-methyl-3, 6-dioxa-5-hexene) sulfonic acid or salt, perfluorovinyl sulfobutyl ether, perfluorovinyl sulfopropyl ether, or a mixture of two or more thereof; the salt is selected from an alkali metal salt, an alkaline earth metal salt or an ammonium salt.
4. The microporous polytetrafluoroethylene membrane according to any of claims 1 to 3, wherein the porosity of the microporous membrane is from 1 to 40%, preferably from 2 to 35%, more preferably from 3 to 30%, preferably from 4 to 25%, preferably from 5 to 20%.
5. The microporous polytetrafluoroethylene membrane according to any of claims 1 to 4, wherein the filaments have a diameter of from 5 to 100 angstroms, preferably from 10 to 90 angstroms, more preferably from 15 to 80 angstroms, preferably from 20 to 70 angstroms, preferably from 15 to 60 angstroms.
6. The method for producing a microporous polytetrafluoroethylene membrane with a hydrophilic surface according to any of claims 1 to 5, comprising the following steps in this order:
(a) polymerizing tetrafluoroethylene and a comonomer containing a sulfonyl fluoride group having the general formula:
wherein m is 0, 1; n is 2 to 4,
obtaining polytetrafluoroethylene modified dispersion resin;
(b) obtaining a polytetrafluoroethylene microporous membrane by paste extrusion, deoiling and stretching; and
(c) and hydrolyzing sulfonyl fluoride groups in the microporous membrane in alkali liquor to obtain the hydrophilic microporous membrane.
7. The process as claimed in claim 6, wherein the dispersion polymerization of tetrafluoroethylene is carried out at 70 to 105 ℃ and a pressure of 1500-3000 kPa.
8. The method of claim 6 or 7, wherein deionized water, initiator, dispersant, stabilizer and tetrafluoroethylene monomer are added in the weight ratio of 100:0.2 x 10 in step (a)-3～2.0×10-30.01 to 0.03: 0.015-0.05: 40-80, wherein the initiator is ammonium persulfate, the dispersing agent is a perfluorinated polyether salt, and the stabilizing agent is paraffin.
9. The process according to claim 6, 7 or 8, wherein the PTFE dispersion resin has a standard density SSG of 2.130-2.180g/cm3Preferably 2.135-2.175g/cm3More preferably 2.140 to 2.170g/cm3Preferably 2.145 to 2.165g/cm3Preferably 2.150 to 2.160g/cm3。
Technical Field
The invention relates to a chemically modified hydrophilic polytetrafluoroethylene microporous membrane and a preparation method thereof. The hydrophilic polytetrafluoroethylene microporous membrane prepared by the method has a lasting hydrophilic effect.
Background
Polytetrafluoroethylene (PTFE) is a plastic with very excellent comprehensive performance, has excellent heat resistance, cold resistance and chemical corrosion resistance, excellent electrical insulation, non-adhesiveness, non-flammability and atmospheric aging resistance, has good mechanical properties, is widely applied to various fields of machinery, chemical industry, aerospace, energy, electronics, biomedicine and the like, and enjoys the name of 'plastic king'.
The polytetrafluoroethylene dispersion resin is extruded and deoiled by adopting a paste form, and then is stretched unidirectionally or bidirectionally to obtain the polytetrafluoroethylene membrane material with a microporous structure. Due to its special properties, it is widely used in the fields of filtration, clothing, biology and medical treatment.
The polytetrafluoroethylene has highly symmetrical structure, high crystallinity and no active group, so the polytetrafluoroethylene has strong hydrophobicity, low surface energy, is not easy to wet, is not beneficial to bonding, printing and dyeing, coating and the like, and has adverse effect on biocompatibility. Therefore, in order to expand the applications of PTFE, its surface must be treated to increase its surface energy and improve its hydrophilicity.
Various surface treatment methods of PTFE are to introduce surface functional groups on the surface of PTFE or change the chemical structure of the surface or improve the surface roughness of the surface by various physical methods and chemical methods, and finally achieve the purposes of reducing contact angle, improving surface energy, improving adhesive property and hydrophilicity.
The prior methods for treating the surface of the polytetrafluoroethylene mainly comprise wet chemical treatment, high-temperature melting, plasma treatment, mechanochemical bonding, ion beam injection, radiation grafting, excimer laser treatment, electrolytic reduction, metal evaporation and other surface treatment methods. The PTFE microporous membrane applied by the method has larger defects, such as darkening or blackening of the treated surface and difficult control of the depth of material corrosion in wet chemical treatment, and the microporous membrane is directly damaged due to limited thickness; the investment cost of the plasma treatment method and the radiation grafting device is relatively high, the hydrophilicity of the treated membrane has timeliness, the time for keeping the hydrophilicity is long and effective, the hydrophilicity gradually disappears along with the increase of time, and obvious defects exist; other methods such as high-temperature melting, mechanochemical bonding, ion beam implantation, excimer laser treatment, electrolytic reduction and metal evaporation are not suitable for the surface modification of microporous films.
U.S. Pat. Nos. 3,953,566 and 4,187,390, both to DuPont, disclose methods for preparing microporous polytetrafluoroethylene membranes which produce microporous membranes that are not hydrophilic.
"hydrophilic modification of polytetrafluoroethylene membrane by polyaniline-aniline copolymer" by nepheline et al (modern plastics processing applications, vol. 21, 2 of 2009) describes hydrophilic modification by depositing polyaniline or aniline copolymer on a porous membrane of polytetrafluoroethylene treated by plasma by dispersion polymerization.
Chinese patent CN103483618B discloses a hydrophilic modification method of a polytetrafluoroethylene microporous membrane, which comprises the following steps:
the polyisocyanate is purified by distillation under reduced pressure and stored in a dryer for later use;
-impregnating a polytetrafluoroethylene microporous membrane in a solution of a polytetrafluoroethylene microporous membrane in a mass fraction of 1: 9, dissolving the fluorine-containing polyether polyol in an acetone solution for 10-20min, taking out and airing to obtain a temporary hydrophilic polytetrafluoroethylene microporous membrane;
-impregnating a temporary hydrophilic polytetrafluoroethylene microporous membrane in a solution of a mixture of a polytetrafluoroethylene microporous membrane and a polytetrafluoroethylene microporous membrane in a mass fraction of 0.05: 20: 79.95 of catalyst, polyisocyanate and acetone, taking out the mixture, drying the mixture in air at 30-50 ℃ for 1-3 hours, washing unreacted reaction monomers on the membrane by water, and airing to obtain the permanent hydrophilic polytetrafluoroethylene microporous membrane.
According to the method, the fluorine-containing polyether polyol is used for preparing the polyurethane acrylate macromonomer to treat the polytetrafluoroethylene microporous membrane, so that the compatibility between the macromonomer and the polytetrafluoroethylene microporous membrane is improved, and the hydrophilic treatment effect is improved; the polyurethane acrylate macromolecules can be solidified on the surface of the polytetrafluoroethylene microporous membrane and in pores of the polytetrafluoroethylene microporous membrane to form a cross-linked network polymer membrane, so that the durability of the hydrophilic effect of the polytetrafluoroethylene microporous membrane is kept; the hydrophilic modification method is simple and easy to implement, and can keep the acid resistance, alkali resistance, oxidation resistance, heat resistance and other properties of the polytetrafluoroethylene membrane. However, the method has the disadvantages that the treatment time is long, and the large-scale mass continuous production cannot be carried out, and in addition, although the durability of the hydrophilic effect of the polytetrafluoroethylene microporous membrane obtained by the method is good, the durability of the hydrophilic effect is still to be further improved.
The performance and processing application of Zhan Van's copolymerized modified PTFE resin (organic fluorine industry, 2008 No. 3) introduces the copolymerization of perfluoroalkyl vinyl ether and tetrafluoroethylene to obtain tetrafluoroethylene-CF2Modified copolymers of repeating segments and pendant perfluoroalkoxy groups, but such modified copolymers have difficulty in providing the desired hydrophilic surface.
"application research of polymerizable surfactant" of Wanghai eagle et al (modern chemical engineering, Vol.27, No. 12, month 12 2007) describes polymerizable surfactants, which are a class of surfactants containing polymerizable groups, having surface activity and capable of producing homo (co) polymerization under certain initiation conditions, thereby forming a micro-ordered assembly structure with higher stability in solution. The article focuses more on the properties of the surfactant itself, e.g. the effect of the resulting polymeric micelles on the surfactant properties after the surfactant concentration reaches the critical micelle concentration. It does not mention the effect of incorporating the surfactant as a monomer in the polymer on the polymer formed.
The inventors have attempted to copolymerize polytetrafluoroethylene with more polar monomers, but have found that the resulting copolymer, while having the desired surface hydrophilicity, suffers from the processability of making porous films.
Therefore, there is still a need to develop a microporous polytetrafluoroethylene membrane having a hydrophilic surface, which has a durable surface hydrophilicity. There is also a need to develop a method for preparing a microporous polytetrafluoroethylene membrane having a hydrophilic surface.
Disclosure of Invention
An object of the present invention is to provide a microporous polytetrafluoroethylene membrane having a hydrophilic surface, which has a durable surface hydrophilicity.
The invention also aims to provide a preparation method of the polytetrafluoroethylene microporous membrane with the hydrophilic surface.
Accordingly, one aspect of the present invention relates to a microporous polytetrafluoroethylene membrane having a hydrophilic surface, said polytetrafluoroethylene comprising monomer units derived from tetrafluoroethylene and from 0.05% to 0.50% by weight, based on the total weight of tetrafluoroethylene, of units derived from the following comonomers:
wherein m is 0, 1; n is 2-4, and M is a metal ion, an ammonium ion or hydrogen;
the polytetrafluoroethylene microporous membrane has a microstructure formed by nodes formed by interconnecting fiber filaments.
Another aspect of the present invention relates to a method for manufacturing the above microporous polytetrafluoroethylene membrane having a hydrophilic surface, the polytetrafluoroethylene comprising monomer units derived from tetrafluoroethylene and 0.05 to 0.50% by weight, based on the total weight of the tetrafluoroethylene, of units derived from the following comonomers:
wherein m is 0, 1; n is 2-4, and M is a metal ion, an ammonium ion or hydrogen;
the polytetrafluoroethylene microporous membrane is provided with a microstructure formed by nodes formed by interconnecting fiber filaments;
the method comprises the following steps in sequence:
(a) adding a comonomer containing sulfonyl fluoride groups having the following general formula to the tetrafluoroethylene dispersion polymerization:
obtaining polytetrafluoroethylene modified dispersion resin;
(b) obtaining a polytetrafluoroethylene microporous membrane by paste extrusion, deoiling and unidirectional or bidirectional stretching; and
(c) and hydrolyzing sulfonyl fluoride groups in the microporous membrane in alkali liquor to obtain the hydrophilic microporous membrane.
Detailed Description
The invention provides a polytetrafluoroethylene microporous membrane with a hydrophilic surface. The polymerized monomers used to form the polytetrafluoroethylene microporous membrane include tetrafluoroethylene and 0.05% to 0.50% by total weight of tetrafluoroethylene of the following comonomers:
wherein m is 0, 1; n is 2-4;
the polytetrafluoroethylene microporous membrane has a microstructure formed by nodes formed by interconnecting fiber filaments.
In one embodiment of the invention, the comonomer is present in an amount of from 0.1% to 0.45%, preferably from 0.15% to 0.4%, more preferably from 0.2% to 0.35%, most preferably from 0.25% to 0.3% by weight of the total tetrafluoroethylene.
In one embodiment of the invention, the comonomer is selected from perfluoro (6-methyl-5, 8-dioxa-7-octene) sulfonyl fluoride (a comonomer of the above formula where m is 1, n is 4), perfluoro (5-methyl-4, 7-dioxa-6-heptene) sulfonyl fluoride (a comonomer of the above formula where m is 1, n is 3), perfluoro (4-methyl-3, 6-dioxa-5-hexene) sulfonyl fluoride (a comonomer of the above formula where m is 1, n is 2), perfluorovinylsulfonyl butyl ether (a comonomer of the above formula where m is 0, n is 4), perfluorovinylsulfonyl propyl ether (a comonomer of the above formula where m is 0, n is 3), or a mixture of two or more of the above.
The polytetrafluoroethylene microporous membrane has a microstructure formed by nodes formed by interconnecting fiber yarns. In one embodiment of the invention, the filaments have a diameter of from 5 to 100 angstroms, preferably from 10 to 90 angstroms, more preferably from 15 to 80 angstroms, preferably from 20 to 70 angstroms, preferably from 15 to 60 angstroms.
In one embodiment of the invention, the length of the nodes is 0.5 to 400 microns, preferably 5 to 350 microns, more preferably 10 to 300 microns, preferably 15 to 250 microns, preferably 20 to 200 microns.
In one embodiment of the invention, the microporous membrane has a porosity of 1 to 40%, preferably 2 to 35%, more preferably 3 to 30%, preferably 4 to 25%, preferably 5 to 20%.
In one embodiment of the present invention, the microporous membrane has a water contact angle of less than 50 degrees, preferably less than 40 degrees, more preferably less than 30 degrees, preferably less than 20 degrees, and preferably less than 10 degrees.
In one embodiment of the invention, the metal ion M, ammonium ion or hydrogen source in the microporous membrane is hydrolyzed from an acyl fluoride with a basic solution. In a preferred embodiment of the invention, the metal ions are selected from alkali metal or alkaline earth metal ions, preferably sodium or potassium ions.
The invention also relates to a method for manufacturing the microporous membrane. The present inventors have found that although copolymerization by incorporating a fluorine-containing monomer having a strong polar group (for example, a fluorine-containing monomer having an alkali metal sulfo group) into a polytetrafluoroethylene monomer contributes to obtaining, for example, a polytetrafluoroethylene product having a contact angle of less than 50 degrees, such a product is difficult to stretch into a microporous membrane. However, if a fluorine-containing monomer having an acyl fluoride group is copolymerized with a tetrafluoroethylene monomer, and the resulting copolymer is stretched into a microporous membrane and then hydrolyzed to obtain a hydrophilic surface, a desired polytetrafluoroethylene microporous membrane having a hydrophilic surface can be advantageously obtained. The present invention has been completed based on this finding.
Therefore, the method for producing a microporous membrane of the present invention comprises the following steps in order:
(a) polymerizing tetrafluoroethylene and a comonomer containing a sulfonyl fluoride group of the general formula:
obtaining polytetrafluoroethylene modified dispersion resin;
in one embodiment of the invention, the amount of comonomer units is from 0.1% to 0.45%, preferably from 0.15% to 0.4%, more preferably from 0.2% to 0.35%, most preferably from 0.25% to 0.3% by weight of the total tetrafluoroethylene.
In one embodiment of the invention, the comonomer is selected from perfluoro (6-methyl-5, 8-dioxa-7-octene) sulfonyl fluoride (a comonomer of the above formula where m is 1, n is 4), perfluoro (5-methyl-4, 7-dioxa-6-heptene) sulfonyl fluoride (a comonomer of the above formula where m is 1, n is 3), perfluoro (4-methyl-3, 6-dioxa-5-hexene) sulfonyl fluoride (a comonomer of the above formula where m is 1, n is 2), perfluorovinylsulfonyl butyl ether (a comonomer of the above formula where m is 0, n is 4), perfluorovinylsulfonyl propyl ether (a comonomer of the above formula where m is 0, n is 3), or a mixture of two or more of the above.
The method for synthesizing the polytetrafluoroethylene-modified dispersion resin is not particularly limited, and may be a conventional method known in the art. In one embodiment of the present invention, the method for synthesizing the polytetrafluoroethylene modified dispersion resin comprises the following steps: adding deionized water, an emulsifier and a stabilizer into a high-pressure reaction kettle, then sealing the reaction kettle, performing a pressure maintaining test and a vacuumizing step, and repeatedly replacing to remove oxygen in the kettle, wherein the qualification is that the oxygen content in the reaction kettle is less than or equal to 20 PPM. Adding a modified monomer by using a metering pump, then heating the reaction kettle to the reaction temperature, adding metered TFE monomer into the reaction kettle to the kettle pressure reaction pressure, starting stirring, adding an initiator by using the metering pump, and continuously adding TFE during the polymerization to maintain constant polymerization pressure. Stopping the reaction when the TFE feeding amount reaches a set value, stopping stirring after the pressure is reduced, recovering gas-phase monomers, cooling and discharging, separating paraffin to obtain modified polytetrafluoroethylene dispersion, and performing a post-treatment process to obtain the polytetrafluoroethylene dispersion resin.
In a preferred embodiment of the present invention, the high-pressure reactor is preferably a horizontal reactor, wherein the dispersion polymerization is carried out at 70 to 105 ℃ and a pressure of 1500-. The weight ratio of the deionized water to the initiator to the dispersing agent to the stabilizer to the tetrafluoroethylene monomer is 100:0.2 multiplied by 10-3～2.0×10-3:0.01～0.03：0.015～0.05：40～80。
In one embodiment of the invention, the initiator is selected from persulfates, organic peroxides, potassium permanganate, oxalic acid, and the like, preferably ammonium persulfate; the dispersing agent is selected from fluorine-containing emulsifiers, preferably perfluorinated polyether salts such as: ammonium epoxy trimer; the stabilizer is preferably paraffin wax.
In one embodiment of the invention, the dispersion resin has a standard density SSG of 2.130-2.180g/cm3Preferably 2.135-2.175g/cm3More preferably 2.140 to 2.170g/cm3Preferably 2.145 to 2.165g/cm3Preferably 2.150 to 2.160g/cm3。
(b) Obtaining a polytetrafluoroethylene microporous membrane by paste extrusion, deoiling and unidirectional or bidirectional stretching;
in one example of the present invention, a method of manufacturing a polytetrafluoroethylene microporous membrane is used as the method of manufacturing microporous membranes disclosed in U.S. Pat. Nos. 3,953,566 and 4,187,390, the contents of which are incorporated herein by reference as part of the present invention.
In one embodiment of the invention, microporous films are prepared using a paste extrusion process: the PTFE resin and the additive are fully mixed and then enter an extruder, the powder is pushed and extruded to form strip PTFE, and then the strip PTFE is extruded to form a membrane under a roller press. Heating to remove additives, stretching longitudinally and transversely, and then performing heat treatment for shaping, cutting and rolling to obtain the microporous membrane.
In the method, the obtained microporous membrane is also a hydrophobic membrane, and the hydrophilic polytetrafluoroethylene microporous membrane is obtained after the microporous membrane is placed in an alkaline solution and is fully hydrolyzed.
It should be noted that the polytetrafluoroethylene modified dispersion resin obtained above cannot be placed in alkaline solution first, which would cause a great amount of sulfonyl fluoride groups in the resin to be transformed into potassium sulfonate groups in advance, which would directly affect the preparation of microporous membrane, and the microporous membrane must be prepared first and then hydrolyzed.
(c) And hydrolyzing sulfonyl fluoride groups in the microporous membrane in alkali liquor to obtain the hydrophilic microporous membrane.
In one embodiment of the present invention, the base solution used for hydrolysis is not particularly limited, and may be any organic or inorganic base solution that can hydrolyze acyl fluoride groups and does not affect the properties of the final microporous membrane. In one embodiment of the present invention, the alkali solution is selected from an aqueous ammonia solution, a sodium hydroxide solution, a potassium hydroxide solution, and the like, and preferably a 10% aqueous potassium hydroxide solution.
In a preferred embodiment of the present invention, the method for manufacturing the microporous membrane comprises the steps of: adding deionized water, an ammonium solution of epoxy trimer acid and paraffin into a horizontal high-pressure reaction kettle, then sealing the reaction kettle, performing a pressure maintaining test and a vacuumizing step, and repeatedly replacing to remove oxygen in the kettle, wherein the oxygen content in the reaction kettle is not more than 20PPM, and the product is qualified. Pumping the perfluorosulfonyl fluoride comonomer, heating the reaction kettle to a temperature lower than the polymerization temperature, adding metered TFE monomer into the reaction kettle to a specified kettle pressure, heating to the polymerization temperature, starting stirring, adding a polymerization initiator through a metering pump, and continuously adding TFE during polymerization after the reaction is started to maintain constant polymerization pressure. Stopping reaction when the feeding amount of TFE monomer reaches a preset amount, stopping stirring after the pressure is reduced, recovering gas-phase monomer, cooling and discharging, separating paraffin to obtain modified polytetrafluoroethylene polymer solution, and performing a post-treatment process to obtain the modified polytetrafluoroethylene dispersion resin. And (3) performing the obtained resin by adopting a typical paste extrusion method to obtain a PTFE microporous membrane, and hydrolyzing and drying the obtained microporous membrane in an alkaline solution to obtain the preset hydrophilic polytetrafluoroethylene microporous membrane.
The present invention is further illustrated by the following examples.