WO2017080419A1 - Polytetrafluoroethylene ultra-fine fiber membrane - Google Patents

Abstract

Provided is a polytetrafluoroethylene fiber membrane used for membrane distillation, comprising a polytetrafluoroethylene material body; the polytetrafluoroethylene has a fiber shape and the fiber has a diameter of 30-200 nm; the body has pore cavities of a pore diameter of 10-1000 nm and cavity walls formed by three-dimensional spaces surrounding the pore cavities; the pore cavities are uniformly distributed and each pore cavity is three-dimensionally open; the pore cavities being uniformly distributed means that the pore cavities are uniformly distributed over any unit volume on the porous material, and the porosity is ≥70%.

Description

Polytetrafluoroethylene microfiber membrane Technical field

The present invention relates to a porous material, in particular a polytetrafluoroethylene fiber membrane, which is particularly suitable for membrane distillation.

Background technique

A solid containing a certain number of pores is called a porous material and is a material that forms a network structure by through or closed pores. Compared with continuous medium materials, porous materials generally have the advantages of low relative density, high specific strength, high specific surface area, light weight, sound insulation, heat insulation and good permeability. Depending on the size of the pores, the porous material can be divided into microporous (pore size less than 2 nm) material, mesoporous (pore size 2-50 nm) material and macroporous (pore size greater than 50 nm) material.

Porous materials are classified according to their materials and can be classified into metal porous materials and non-metallic porous materials. Non-metallic porous materials generally have the characteristics of large specific surface area, small density, small thermal conductivity, small relative density, and high porosity. They are used in catalysts (including carriers), adsorbents, heat preservation, heat insulation, sewage and waste gas treatment, filtration of liquids, and Gas (even bacteria), lightweight building materials, environmental protection, soil improvement, chemical industry and other fields have broad application prospects. Among them, the polytetrafluoroethylene porous membrane material has a wide application range due to its temperature stability, chemical stability, electrical insulation, flame retardancy and self-lubricating properties. However, due to the randomness and irregularity of the pore structure, it still cannot satisfy many application properties.

In many applications, the porous material itself needs to be uniform, its pore size and pore distribution are uniform, so that the performance is uniform, but in fact, many porous materials do not meet this requirement, and their uniformity complements; although some materials claim to be self-proclaimed Achieve higher uniformity, but its uniformity is still uniformity on a large volume scale. If it is measured by a small volume scale, for example, if a plurality of three-dimensional bodies having a volume of not more than one cubic centimeter are taken on the material, respectively, The quality, the degree of uniformity is still very large, thus causing various properties of the polytetrafluoroethylene porous membrane material such as strength, elastic modulus, flux and the like, which seriously affect its function.

Summary of the invention

The object of the present invention is to provide a polytetrafluoroethylene fiber membrane which is structurally suitable, controllable and highly uniform.

The object of the invention is achieved by the following measures:

A polytetrafluoroethylene ultrafine fiber membrane comprising a body of polytetrafluoroethylene material, a polytetrafluoroethylene fiber, a fiber diameter of 30-200 nm, a body having a pore size of 10 nm to 1000 nm, and a three-dimensional space surrounding the cavity The formed cavity wall is composed, the pore cavity is uniformly distributed, and each cavity is three-dimensionally penetrated, and the uniformity distribution of the cavity means that each cavity is uniformly distributed under arbitrary unit volume on the porous material; porosity is ≥70 %.

Specifically, the polytetrafluoroethylene fiber membrane has a cavity having a pore diameter of 30 to 1000 nm and a cavity wall formed in a three-dimensional space around the cavity, and a lower cavity of 10 to 100 nm is disposed on the cavity wall, and each cavity of each cavity is three-dimensionally Through and holes The cavities are also connected to each other; the cavities are uniformly distributed, and the uniformity of the cavities means that the cavities are uniformly distributed under arbitrary unit volume on the porous material.

Specifically, the above unit-level volume means a cubic centimeter-level or cubic millimeter-level or smaller unit-level volume.

More specifically, the uniform distribution of the above-mentioned cavities means that each of the three-dimensional bodies having a volume of not more than one cubic centimeter and the same size on the porous material is substantially equivalent in mass.

More specifically, the above-mentioned mass is substantially equivalent to a plurality of three-dimensional bodies having a volume of not more than one cubic centimeter and the same size, which are respectively referred to as a mass, and an average value of their masses is obtained, and any three-dimensional mass is relatively The absolute value of the deviation from the mass average is not more than 4% of the average of the three-dimensional body mass.

Further, the three-dimensional bodies of the same size having a volume of not more than one cubic millimeter on the multi-stage material are substantially equivalent in mass.

More specifically, the mass is substantially equivalent to a plurality of three-dimensional bodies of the same size having a volume of not more than one cubic millimeter on the porous material, respectively referred to as masses, and an average value of their masses is obtained, and any three-dimensional mass is obtained. The absolute value of the deviation from the mass average is not more than 4% of the average of the three-dimensional body mass.

Preferably, the polytetrafluoroethylene ultrafine fiber membrane is composed of a multi-stage porous material, the body is a cavity which is classified by a material pore size, and a cavity wall which surrounds the cavity in a three-dimensional space, and a lower cavity is arranged on the cavity wall. The cavities of each stage are each three-dimensionally penetrated and the cavities of the respective stages are also mutually connected. More specifically, the next level of porous material constitutes the wall of the cavity of the upper stage. The cavity wall of the upper cavity is composed of a multi-stage porous material of its lower stage or a composite of porous materials of the lower stage, so that the material can meet specific functional requirements.

Specifically, each stage of the porous material of the material body is self-contained as a continuous structure. The maximum outer boundary of each level of porous material is comparable to the entire material body space boundary. That is, each grade of porous material can exist in the bulk as a first-order independent porous material, and has its own physical and chemical properties. Such a structure can make the physical and chemical properties of the porous materials of different levels different, and have different physical and chemical properties in the entire space of the relatively fixed materials, and better meet various functional requirements.

Beneficial effect

1. The present invention provides a polytetrafluoroethylene ultrafine fiber membrane having a porous structure, and the structural form thereof is clarified, and the hierarchical structure of the pore cavity and the uniform structure thereof can satisfy various functional requirements.

2. The present invention provides a specific and clear measurement method for the uniform distribution of the pores of the polytetrafluoroethylene microfiber membrane, and it is clarified that the pores of the porous material and the multi-stage structure are uniformly distributed on the scale of the small unit volume. Sexually, such a porous structure is highly uniform, thereby ensuring uniformity of the properties of the porous material.

3. The polytetrafluoroethylene ultrafine fiber membrane of the present invention is three-dimensionally penetrated, including three-dimensional communication of each stage of the hole, and three-dimensional through-holes of each level, and good penetration, and can fully satisfy the functional requirements of the material.

4. The polytetrafluoroethylene fiber membrane of the present invention is a hydrophobic surface having a multistage roughness structure. The surface water contact angle can reach 160° or more.

5. The polytetrafluoroethylene fiber membrane of the invention does not need support, has stable shape and controllable thickness, and is applied to a membrane distillation process with a flux of >42 L/m ² ·h and a rejection of 99.8% or more.

6. The polytetrafluoroethylene fiber membrane of the present invention may be a film of different shapes and specifications such as a flat plate type, a tubular type, a hollow fiber type or a roll type, without support, and has a stable shape and a controllable thickness.

detailed description

BEST MODE FOR CARRYING OUT THE INVENTION A detailed embodiment is given on the premise of the technical solution of the present invention, but the scope of protection of the present invention is not limited to the following embodiments. It is obvious that various alternatives or modifications can be made without departing from the spirit and scope of the inventions of the present invention. .

Example 1

The polytetrafluoroethylene fiber membrane of the invention has a secondary pore structure, wherein the cavity wall of the first-stage cavity uniformly distributed and interpenetrating has a second-stage cavity uniformly distributed and mutually penetrating, and the two-stage hole The two are also connected to each other, and the through-holes are three-dimensionally penetrated. Each level of porous material of the material body is self-contained as a continuous structure. The total effective porosity is 80%, the fiber diameter is 150±20 nm, the macroporous average pore diameter is 0.45 μm, and there are through-holes having an average pore diameter of 30 nm on the cavity wall of the macropores.

9 pieces of 10 mm×10 mm×10 mm three-dimensional bodies of the same size were placed on the porous material by mechanical processing, and the masses were tested with a METTLER TOLEDO XP26 Microbalance balance. The results are shown in Table 1, wherein, relative to the average value The absolute value of the deviation is expressed as a percentage, and the value is the absolute value of the deviation from the average value divided by the mass average value. As can be seen from Table 1, the mass deviation is not more than 4%.

Table 1

Part Number	Quality (mg)	Absolute value (%) relative to the mean
1	638.087	1.8%
2	618.227	1.4%
3	638.510	1.9%
4	635.049	1.3%
5	619.727	1.1%
6	619.993	1.1%
7	610.858	2.5%
8	638.125	1.8%
9	622.051	0.7%
Mass average	626.736

The preparation method of the polytetrafluoroethylene porous material is:

(1) A polytetrafluoroethylene emulsion having a solid content of 60%, a chitosan having a particle diameter of 30 nm, and a 5% (mass ratio) polyvinyl alcohol solution, Evenly mixed, prepared into a spinning solution according to a mass ratio of 50:30:4;

(2) preparing a polytetrafluoroethylene precursor film by using an electrospinning method in an oriented electrospun filament device under vacuum;

(3) The precursor film is wound into 5 layers on a cylindrical support mold, sent to a tube furnace for sintering in a vacuum or a protective atmosphere, and the sintering is sequentially sintered by program temperature control, and is heated from room temperature at a rate of 4 ° C/min. The temperature was raised to 180 ° C for 60 min at 180 ° C; the temperature was raised to 250 ° C at a rate of 4 ° C / min, held at 250 ° C for 60 min; the temperature was raised to 400 ° C at a rate of 4 ° C / min, and held at 400 ° C for 60 min.

(4) After the sintering, the program was temperature-controlled and cooled, and after subsequent treatment according to the conventional technique, the cylinder was taken out and cut to obtain a flat porous polytetrafluoroethylene fiber membrane having a two-stage pore structure with a thickness of 160 μm.

The PTFE fiber membrane does not need to be supported, has stable shape and controllable thickness, and can be used for gas-liquid separation and liquid-liquid separation to achieve precise grading filtration, for example, it is suitable for filtering of two-component or multi-component gas (liquid) body, The flux is large, the rejection rate is high, and it is not easy to be polluted (such as the contamination of the multi-liquid immersion membrane), and has the advantages of high efficiency and long-term efficiency. The membrane water contact angle is 165°.

For example, in membrane distillation applied to acid/alcohol-water-non-volatile solute system, the total flux can reach above 42kg/m ² ·h, and the non-volatile solute rejection in the system is above 99.8%. Volatile alcohol/acid separation factor = [alcohol / acid mass fraction in distillate × (1 - raw material liquid alcohol / acid mass fraction)] ÷ [raw material liquid alcohol / acid mass fraction × (1- distillate alcohol / acid mass fraction)] can reach 10 the above.

Example 2

The polytetrafluoroethylene fiber membrane of the invention has a three-stage pore structure, wherein the cavity wall of the first-stage cavity uniformly distributed and interpenetrating has a second-stage cavity uniformly distributed and mutually penetrating, and the two-stage hole The two are also connected to each other, and the through-holes are three-dimensionally penetrated. Each level of porous material of the material body is self-contained as a continuous structure. The total effective porosity is 85%, the fiber diameter is 180±20 nm, the macropore has an average pore diameter of 1000 nm, and there are average secondary pores of 60 nm in the cavity wall of the macropores, and there is an average on the pore walls of the second-stage pores. A third-stage hole having a pore diameter of 10 nm.

9 pieces of 10 mm×10 mm×10 mm three-dimensional bodies of the same size were placed on the porous material by mechanical processing, and the masses were tested with a METTLER TOLEDO XP26 Microbalance balance. The results are shown in Table 1, wherein, relative to the average value The absolute value of the deviation is expressed as a percentage, and the value is the absolute value of the deviation from the average value divided by the mass average value. As can be seen from Table 2, the mass deviation is not more than 4%.

Table 2

Part Number	Quality (mg)	Absolute value (%) relative to the mean
1	503.455	2.9%
2	526.142	1.4%
3	513.888	0.9%
4	511.626	1.4%
5	518.072	0.1%

6	529.548	2.1%
7	526.967	1.6%
8	520.489	0.4%
9	517.716	0.2%
Mass average	518.656

The preparation method of the polytetrafluoroethylene porous material is:

(1) mixing PTFE fine powder, polyethylene glycol having a molecular weight of 1000, stirring and heating to 380 ° C, stirring for 60 min, rapidly cooling to room temperature for crushing, and pulverizing at minus Celsius to obtain polytetrafluoroethylene particles;

(2) dispersing the polytetrafluoroethylene particles having a particle diameter of 200 nm into a 60% solid content emulsion, and uniformly mixing them with a particle size of 100 nm chitosan and a 5% (mass ratio) polyvinyl alcohol solution, according to 50:30. : 4 mass ratio, formulated into a spinning solution;

(3) preparing a polytetrafluoroethylene precursor film by using an electrospinning method in an oriented electrospinning fiber device under vacuum conditions;

(4) The precursor film is wound up to 5 layers to a cylindrical support mold of 2 mm in diameter, sent to a tube furnace for sintering in a vacuum or a protective atmosphere, and sintered by program temperature control and continuous sintering at a rate of 6 ° C / min. Warming from room temperature to 160 ° C, holding at 160 ° C for 100 min; increasing from room temperature to 280 ° C at 6 ° C / min, holding at 280 ° C for 60 min; heating at 400 ° C at a rate of 6 ° C / min, holding at 400 ° C for 100 min .

(5) After the sintering, the program was temperature-controlled and cooled, and a porous polytetrafluoroethylene hollow fiber membrane having a three-stage pore structure was obtained according to a conventional technique, and the thickness was 163 μm, and the membrane diameter was 2 mm.

The PTFE fiber membrane does not need to be supported, has stable shape and controllable thickness, and can be used for gas-liquid separation and liquid-liquid separation to achieve precise grading filtration, for example, it is suitable for filtering of two-component or multi-component gas (liquid) body, The flux is large, the rejection rate is high, and it is not easy to be polluted (such as the contamination of the multi-liquid immersion membrane), and has the advantages of high efficiency and long-term efficiency. The membrane water contact angle is 168°.

For example, in membrane distillation of multi-component (or mixed) alcohol/acid-water-non-volatile solute system, the total flux can reach above 42kg/m ² ·h, and the non-volatile solute rejection in the system is above 99.9%. Alcohol/acid separation factor = [alcohol/acid mass fraction in distillate × (1 - stock liquid alcohol / acid mass fraction)] ÷ [feed liquid alcohol / acid mass fraction × (1-distillate alcohol / acid mass fraction )] can reach more than 10.

Claims (11)

1. A polytetrafluoroethylene fiber membrane for membrane distillation, comprising a body of polytetrafluoroethylene material, a polytetrafluoroethylene fiber, a fiber diameter of 30-200 nm, a body having a pore diameter of 10 nm to 1000 nm and a three-dimensional space The cavity wall formed around the cavity is uniformly distributed, and each cavity is three-dimensionally penetrated, and the uniform distribution of the cavity means that the cavity is uniformly distributed under arbitrary unit volume on the porous material; The rate is ≥70%.
2. The polytetrafluoroethylene fiber membrane for membrane distillation according to claim 1, wherein the chamber has a pore diameter of 30 to 1000 nm and a cavity wall formed in a three-dimensional space around the cavity, and a lower cavity of 10 to 100 nm is disposed on the cavity wall. Each of the cavities of each level penetrates three-dimensionally and the cavities of each stage also penetrate each other; the cavities are uniformly distributed, and the uniform distribution of the cavities means that the cavities are uniform under arbitrary unit volume on the porous material. distributed.
3. The polytetrafluoroethylene fiber membrane for membrane distillation according to claim 1 or 2, wherein the unit-level volume means a cubic centimeter-scale or cubic millimeter-order or smaller unit-level volume.
4. The polytetrafluoroethylene fiber membrane for membrane distillation according to claim 1, 2 or 3, wherein the uniform distribution of the pores means that the volume of the porous material is not more than one cubic centimeter and the same size Three-dimensional bodies, their quality is basically the same.
5. The polytetrafluoroethylene fiber membrane for membrane distillation according to claim 4, wherein the mass is substantially equivalent to a plurality of three-dimensional bodies having a volume of not more than one cubic centimeter and the same size, which are respectively called on the porous material. Mass, the average of their mass is obtained, and the absolute value of the deviation of any three-dimensional body mass from the mass average is not more than 4% of the average of the three-dimensional body mass.
6. The polytetrafluoroethylene fiber membrane for membrane distillation according to any one of claims 1 to 5, wherein three or more volumes of the same size having a volume of not more than one cubic millimeter on the multistage material are substantially equivalent in mass.
7. The polytetrafluoroethylene fiber membrane for membrane distillation according to claim 6, wherein the mass is substantially equivalent to a plurality of three-dimensional bodies of the same size having a volume of not more than one cubic millimeter which are allowed on the porous material, respectively Mass, the average of their mass is obtained, and the absolute value of the deviation of any three-dimensional body mass from the mass average is not more than 4% of the average of the three-dimensional body mass.
8. The polytetrafluoroethylene fiber membrane for membrane distillation according to any one of claims 1 to 7, which is composed of a multi-stage porous material, the body is a cavity which is classified by a material pore size, and a three-dimensional space surrounds the cavity. The cavity wall is formed, and the lower cavity is arranged on the cavity wall, and each cavity of each stage is three-dimensionally penetrated and the cavity of each stage also penetrates each other.
9. The polytetrafluoroethylene fiber membrane for membrane distillation according to any one of claims 1 to 8, wherein the next-stage porous material constitutes a cavity wall of the upper-stage cavity.
10. The polytetrafluoroethylene fiber membrane for membrane distillation according to any one of claims 1 to 8, wherein the wall of the upper pore cavity is composed of a composite of a plurality of stages of the porous material of the lower stage.
11. The polytetrafluoroethylene fiber membrane for membrane distillation according to any one of claims 1 to 8, wherein the cavity wall of the upper pore cavity is composed of a composite material of the lower layers of the porous material.