KR20110129111A - Polyimide porous nanofiber web and method for manufacturing the same - Google Patents

Abstract

PURPOSE: A method for fabricating a polyimide porous nanofiber web is provided to ensure chemical tolerance and thermal resistance. CONSTITUTION: A method for fabricating a polyimide porous nanofiber web comprises: a step of dissolving a polyimide precursor in an organic solvent to prepare a spinning solution; a step of electrospinning to prepare a polyimide precursor nanofiber web; and a step of treating the nanofiber web with a solvent to obtain the nanofiber web having 90% or more of imidizing rate. The nanofiber web contains fibers(4) having 0.01-5 um of average diameter.

Description

Polyimide porous nanofiber web and method for manufacturing the same

The present invention relates to a polyimide porous nanofiber web and a method for manufacturing the same, and more particularly, to a polyimide porous nanofiber web and a method for manufacturing the same, which can be used in an electrolyte membrane for a fuel cell or a separator for a secondary battery.

Porous nanofiber webs have a wide surface area and excellent porosity, and thus can be used for various purposes. For example, the porous nanofiber webs can be used for water purification filters, air purification filters, composite materials, and battery separators. In particular, such a porous nanofiber web can be usefully applied to the electrolyte membrane of a fuel cell for automobiles.

A fuel cell is a battery that converts chemical energy generated by oxidation of a fuel into electrical energy directly, and has been in the spotlight as a next-generation energy source due to its high energy efficiency and eco-friendly features with low emission of pollutants. Such a fuel cell generally has a structure in which an anode and a cathode are formed on both sides of an electrolyte membrane.

Representative examples of automotive fuel cells include a hydrogen ion exchange membrane fuel cell using hydrogen gas as a fuel. Since the electrolyte membrane used in the hydrogen ion exchange membrane fuel cell is a passage through which hydrogen ions generated from the anode are transferred to the cathode, the conductivity of the hydrogen ions should be excellent. In addition, the electrolyte membrane must have excellent separation ability to separate hydrogen gas supplied to the anode and oxygen supplied to the cathode, and also have excellent mechanical strength, shape stability, and chemical resistance, and have low resistance loss at high current density. Such characteristics are required. In particular, the fuel cell for automobiles should be excellent in heat resistance so as not to rupture the electrolyte membrane when used for a long time at high temperature.

As an electrolyte membrane for fuel cells currently used, a perfluorosulfonic acid resin (Nafion, Nafion, trade name) (hereinafter referred to as 'nafion resin') is a fluorine resin. However, Nafion resins have a weak mechanical strength, so that when used for a long time, pinholes are generated, thereby lowering energy conversion efficiency. Attempts have been made to increase the film thickness of Nafion resin in order to reinforce mechanical strength. However, in this case, the resistance loss is increased, and there is a problem in that the economy is inferior as expensive materials are used.

In order to solve such a problem, an electrolyte membrane having improved mechanical strength by impregnating a porous polytetrafluoroethylene resin (Teflon, Teflon, trade name) (hereinafter referred to as 'Teflon resin') with an ion conductor as an ion conductor has been proposed. There is a bar. In this case, the mechanical strength is relatively higher than that of the electrolyte membrane composed of Nafion resin alone, but there is a problem that the ionic conductivity is somewhat reduced. In addition, since the Teflon resin is very low adhesion, there is a disadvantage in that the separation between hydrogen and oxygen decreases as the adhesion between the Teflon resin and the Nafion resin decreases with the change of operating conditions such as temperature or humidity during fuel cell operation. . In addition, since the price of not only Nafion resin but also porous Teflon resin is expensive, there is a problem in that economic feasibility in mass production.

In order to solve this problem, general-purpose hydrocarbon resins such as polyethylene, polypropylene, polysulfone, polyethersulfone, polyvinylidene fluoride are used instead of teflon resin, and sulfonic acid groups are used instead of Nafion resin as an ion conductor. An electrolyte membrane has been proposed to reduce the production cost by using a low-cost hydrocarbon resin.

However, in this case, although the production cost can be reduced, the economical efficiency can be improved, but there is a problem that durability can not be guaranteed as the hydrocarbon-based resin forming the film is dissolved in an organic solvent or the heat resistance is poor.

In addition, the non-woven fabric prepared by the general method or a hydrocarbon-based membrane in the form of a film prepared by a conventional separation membrane manufacturing method has a problem that it is difficult to thin film, the porosity is poor, and the pore size is not easy to control.

In particular, hydrocarbon-based membranes have a problem of deterioration in performance due to a decrease in tensile strength and a decrease in weight in a strongly acidic environment, or a rupture and explosion when severe.

The present invention is a polyimide that can be easily used in a variety of fields, such as the electrolyte membrane for fuel cells or the separator for secondary batteries, as it is easy to control the thin film and pore size, excellent porosity and heat resistance, and excellent shape stability even in a strong acid environment. An object of the present invention is to provide a porous nanofiber web and a method of manufacturing the same.

As an aspect of the present invention for achieving the above object, the present invention has a porosity of 50 to 99%; The imidation ratio after the solvent treatment determined by the following formula is 90% or more; It provides a polyimide porous nanofiber web characterized in that the fiber aggregate form.

Imidization rate after solvent treatment (%) = [weight of nanofiber web after solvent treatment / weight of nanofiber web before solvent treatment] × 100 (where, the weight of nanofiber web before solvent treatment is set at a temperature of 30 ° C.) Measured using a nanofiber web left at least 24 hours in a vacuum oven, and after the solvent treatment, the weight of the nanofiber web was stirred for 24 hours at room temperature by immersing the nanofiber web before the solvent treatment in a dimethylformamide organic solvent. After washing at least 5 times in distilled water and left for 24 hours in a vacuum oven set at a temperature of 30 ℃ measured using a nanofiber web obtained after the solvent treatment)

As another aspect of the present invention for achieving the above object, the present invention comprises the steps of preparing a spinning solution by dissolving a polyimide precursor (precusor) in an organic solvent; Electrospinning the spinning solution to prepare a polyimide precursor nanofiber web made of fibers having an average diameter of 0.01 to 5 μm; And imidizing the polyimide precursor nanofiber web and preparing a polyimide nanofiber web having an imidation ratio of 90% or more after solvent treatment obtained by the following formula. to provide.

Imidization rate after solvent treatment (%) = [weight of nanofiber web after solvent treatment / weight of nanofiber web before solvent treatment] × 100 (where, the weight of nanofiber web before solvent treatment is set at a temperature of 30 ° C.) Measured using a nanofiber web left at least 24 hours in a vacuum oven, and after the solvent treatment, the weight of the nanofiber web was stirred for 24 hours at room temperature by immersing the nanofiber web before the solvent treatment in a dimethylformamide organic solvent. After washing at least 5 times in distilled water and left for 24 hours in a vacuum oven set at a temperature of 30 ℃ measured using a nanofiber web obtained after the solvent treatment)

The present invention has the following effects.

First, the polyimide porous nanofiber web according to the present invention has an effect of easily thinning and easily adjusting the pore size.

Second, since the polyimide porous nanofiber web according to the present invention has a high melting point without being dissolved in a conventional organic solvent, it has an excellent chemical resistance and heat resistance.

Third, as the polyimide porous nanofiber web according to the present invention is imidized under optimal conditions, when used as a support for the electrolyte membrane, the electrolyte membrane has an effect of having excellent shape stability in a strongly acidic environment.

The polyimide porous nanofiber web having such excellent physical properties can be used for electrolyte membranes for fuel cells or secondary membranes for secondary batteries requiring lightweight, high efficiency, and high stability.

1 is a schematic diagram of an electrospinning apparatus according to an embodiment of the present invention.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. Therefore, the present invention encompasses all changes and modifications that come within the scope of the invention as defined in the appended claims and equivalents thereof.

Hereinafter, a polyimide porous nanofiber web according to an embodiment of the present invention will be described in detail.

The polyimide porous nanofiber web of the present invention comprises a polyimide having an imidation ratio of at least 90%. That is, it means that the polyimide precursor is changed to the imide group by the cyclization reaction occurs through an imidization process such as heat treatment. As such, the polyimide porous nanofiber web has an imidation ratio of 90% or more, and thus has excellent heat resistance.

In addition, the polyimide porous nanofiber web of the present invention has an imidation ratio of 90% or more after the solvent treatment obtained by the following formula.

% Imidization after solvent treatment = (weight of nanofiber web after solvent treatment / weight of nanofiber web before solvent treatment) × 100

After the solvent treatment, the imidization ratio is measured first by weight of the nanofiber web before solvent treatment, which is left for 24 hours in a vacuum oven set at a temperature of 30 ° C., and the nanofiber web before solvent treatment is immersed in a dimethylformamide organic solvent. After stirring for 24 hours at room temperature and washed at least 5 times in distilled water and left for 24 hours in a vacuum oven set at a temperature of 30 ℃ after measuring the weight of the nanofiber web after solvent treatment, the weight before and after the measured solvent treatment Measured by applying to the above formula.

The polyimide porous nanofiber web having imidization rate after the 90% or more solvent treatment can maintain excellent tensile strength even in a strong acid state, which is a driving environment of a fuel cell, and has excellent dissolution resistance to electrolytes. Since the interface is not separated, excellent ionic conductivity can be maintained for a long time.

The polyimide porous nanofiber web having such excellent acid resistance can improve customer's trust because it can express excellent performance for a long time when used in an electrolyte membrane of a fuel cell driven in a strong acid environment.

The polyimide porous nanofiber web can easily obtain a fiber 4 having the required diameter as the process is smoothly controlled during electrospinning, and thus can have a porosity of 50% or more. As described above, as having a porosity of 50% or more, the porous nanofiber web has a large specific surface area, and thus the ion conductivity is easily impregnated as the ion conductor is easily impregnated. On the other hand, the porous nanofiber web may have a porosity of 99% or less. If the porosity of the porous nanofiber web exceeds 99%, the morphological stability may be lowered, and thus the subsequent process may not proceed smoothly. The porosity was calculated by the ratio of the air volume to the total volume as shown in the following equation. In this case, the total volume was calculated by measuring the width, length, and thickness of a sample in the form of a rectangular shape, the air volume was obtained by subtracting the volume of the polymer inverted from the density after measuring the mass of the sample from the total volume.

Porosity (%) = (air volume / total volume) × 100

The polyimide porous nanofiber web may have an average thickness of 5 to 40 μm. When the thickness of the polyimide porous nanofiber web is less than 5 μm, the mechanical strength and shape stability may be remarkably inferior, whereas when the thickness of the polyimide porous nanofiber web is more than 40 μm, the weight and integration may be reduced.

The polyimide porous nanofiber web may comprise fibers 4 having an average diameter of 0.01 to 5 μm.

In order for the polyimide porous nanofiber web to have the porosity and thickness as described above, it may be preferable that the fibers 4 constituting the fiber aggregate have an average diameter in the range of 0.01 to 5 μm. If the average diameter of the fiber 4 is less than 0.01 μm, the mechanical strength may be lowered. On the other hand, if the average diameter of the fiber 4 is more than 5 μm, the porosity may be significantly decreased and the thickness may be thick.

The polyimide porous nanofiber web may have a melting point of 400 ° C. or more as it is imidized under optimum conditions to be described later with imidization ratio after the solvent treatment in the range as described above. If the melting point of the polyimide porous nanofiber web is less than 400 ° C., the heat resistance may be easily deformed at high temperatures, and thus the fuel cell or the secondary battery manufactured using the polyimide porous nanofiber web may be degraded. In addition, when the heat resistance of the polyimide porous nanofiber web is lowered, the shape is deformed by abnormal heat generation, thereby degrading the performance and, in severe cases, may burst and explode.

When used in the manufacture of the electrolyte membrane of the fuel cell or the separator of the secondary battery that requires high stability as described above, it may be preferable that the polyimide porous nanofiber web has a melting point of 400 ~ 800 ℃. If the melting point of the polyimide porous nanofiber web exceeds 800 ℃, the manufacturing process may not proceed smoothly, it may be economical.

When the polyimide porous nanofiber web is used for a support of an electrolyte membrane for a fuel cell, the fuel cell is exposed to strong acidity of about pH 3, and the electrolyte membrane used in such an environment is required to have excellent acid resistance. In other words, when the electrolyte membrane is poor in shape stability in a strongly acidic environment, the interface between the electrolyte membrane and the electrode may be separated, thereby degrading power generation performance.

In order to confirm the stability of the electrolyte membrane in the strongly acidic environment, the shape stability is evaluated by measuring the strength retention rate and the weight change rate in an environment similar to the operating environment of the fuel cell.

An electrolyte membrane prepared by impregnating a polyimide porous nanofiber web with a hydrocarbon-based ion conductor may have a strength retention of 85% or more. The strength retention can be measured using the following equation.

Strength retention (%) = (tensile strength after acid treatment / tensile strength before acid treatment) × 100

The strength retention is measured assuming a state most similar to a general driving environment of a fuel cell. That is, the strength maintenance rate is measured assuming that the exposure time is more than 4 hours in a strong acid environment of pH 3 which is a general driving environment of the fuel cell.

After the acid treatment used to measure the strength retention, the electrolyte membrane was cut into 20 cm x 20 cm in 300 ml of an acid solution of pH 3 mixed with sulfuric acid (H ₂ SO ₄ ) and 2 ppm hydrogen fluoride (HF). After immersion, the mixture was sealed and stirred for 4 hours in a water bath maintained at 80 ° C., and then washed several times with distilled water. The acid solution of pH 3 mixed with sulfuric acid (H ₂ SO ₄ ) and 2 ppm hydrogen fluoride (HF) is one of corrosion solutions that are widely used when measuring the electrochemical properties of fuel cell components.

The tensile strength may be measured according to the KS M 3054 method after standing for at least 24 hours in a constant temperature and humidity chamber maintained at a relative humidity of 20 ℃, 65%.

An electrolyte membrane prepared by impregnating a polyimide porous nanofiber web with a hydrocarbon-based ion conductor may have a weight change rate of 5% or less. The weight change rate can be measured using the following formula.

% Change in weight = [(Wb-Wa) / Wb] x 100

Wb is the weight of the electrolyte membrane before acid treatment, and Wa is the weight of the electrolyte membrane after acid treatment.

The electrolyte membrane phosphorus after the acid treatment used for measuring the weight change rate can be obtained by acid treatment in the same manner as the above-described method of measuring the strength retention, followed by drying for 24 hours in a vacuum opening at 30 ° C.

As such, it can be determined that an electrolyte membrane that satisfies the strength retention rate of 85% or more and the weight change rate of 5% or less at the same time has excellent acid resistance, and thus can have excellent shape stability when used in an electrolyte membrane for a fuel cell. Can be improved.

Next, referring to FIG. 1, a method of manufacturing a polyimide porous nanofiber web according to an embodiment of the present invention will be described. 1 is a schematic diagram of an electrospinning apparatus according to an embodiment of the present invention.

First, a polyimide precursor (precusor) is dissolved in an organic solvent to prepare a spinning solution.

Since the polyimide porous nanofiber web of the present invention is produced through electrospinning, it has high porosity and excellent thin film properties.

On the other hand, porous nanofiber webs that are insoluble in organic solvents cannot be directly manufactured through an electrospinning process. In other words, polyimide having insolubility in organic solvents is difficult to prepare a spinning solution because it does not dissolve in organic solvents.

Therefore, polyimide having insolubility in an organic solvent can be prepared by preparing a fiber assembly using a polyimide precursor that is well soluble in an organic solvent and then imidating the fiber assembly.

As the polyimide precursor, polyamic acid may be used. The polyamic acid may be prepared by mixing diamine in a solvent, adding dianhydride thereto, and polymerizing the diamine. The dianhydride may be pyromellyrtic dianhydride (PMDA), benzophenonetetracarboxylic dianhydride (BTDA), ODPA (4,4′-oxydiphthalic anhydride), BPDA (biphenyltetracarboxylic dianhydride), or SIDA (bis (3,4-dicarboxyphenyl) dimethylsilane dianhydride It may be used to include at least one of). In addition, the diamine may be one containing at least one of ODA (4,4'-oxydianiline), p-PDA (p-penylene diamine), or o-PDA (openylene diamine).

Solvents for dissolving the polyamic acid include m-cresol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), acetone, A solvent including at least one of diethyl acetate, tetrahydrofuran (THF), chloroform, and γ-butyrolactone may be used.

The spinning solution may have a concentration of 5 to 50%. If the concentration of the spinning solution is less than 5%, since spinning does not proceed smoothly, the fiber 4 may not be formed or a fiber 4 having a uniform diameter may not be manufactured, whereas the concentration of the spinning solution is When 50% is exceeded, as the discharge pressure increases rapidly, spinning may not be performed or processability may decrease.

Subsequently, the spinning solution is prepared using the electrospinning apparatus as shown in FIG. 1 to prepare a polyimide precursor nanofiber web made of fibers 4 having an average diameter of 0.01 to 5 μm. That is, the spinning solution is supplied in a predetermined amount to the spinning unit by using a metering pump in the solution tank in which the spinning solution is stored, and the spinning solution is discharged through the nozzle 2 of the spinning unit and coagulated simultaneously with scattering to disperse the fibers (4). The polyimide precursor nanofiber web may be manufactured by forming a polyimide precursor and focusing the formed fibers 4 on the collector 5.

In this case, the intensity of the electric field between the radiator and the collector 5 applied by the high voltage generator 3 may be 3 to 80 kW. If the strength of the electric field is less than 3 kW, the spinning solution is not continuously discharged, and thus, the nanofiber web of uniform thickness cannot be manufactured, and the fiber 4 formed after spinning is smoothly applied to the collector 5. Fabrication of nanofiber webs can be difficult because they cannot be focused. On the other hand, when the strength of the electric field exceeds 80 kPa, the scattered fibers 4 may be concentrated in the state in which the solvent is not removed from the collector 5, so that a nanofiber web made of nano-sized fibers may not be obtained. .

The polyimide precursor nanofiber web is then imidated to produce a polyimide nanofiber web. Production of the polyimide nanofiber web may be carried out through a process using heat imidization, chemical imidization, or a combination of heat imidization and chemical imidization.

The chemical imide process may be performed by treating the polyimide precursor nanofiber web with an imidation catalyst such as acetic anhydride or pyridine.

In addition, the thermal imide process may be performed through a process of heat-treating the polyimide precursor fiber assembly 10 at a high temperature. In particular, the thermal imide process has an advantage that the precursor can be easily imidized. The heat treatment process may be performed at a temperature of 100 to 400 ℃ to obtain a polyimide porous nanofiber web having an imidization rate after 90% or more solvent treatment. If the heat treatment temperature is less than 100 ° C., since the imidization does not proceed smoothly and the processing time is long, economic efficiency may be reduced. On the other hand, when the heat treatment temperature exceeds 400 ℃, the imidization rate after the solvent treatment is not greatly improved, but rather the physical properties may be lowered, thereby deteriorating performance.

The imidization process may be performed in a draw ratio of 0.1 or less. That is, it may be preferable to set the draw ratio to 0.1 or less in order to obtain a nanofiber web having uniform and excellent porosity. If the draw ratio is more than 0.1, the shape of the nanofiber web is deformed and a uniform thickness may not be obtained, and the tensile strength may be lowered as the cohesive force is lowered. On the other hand, the lower limit value of the draw ratio may be a state not stretched or over-supplied + 0.1% in order to prevent a smooth process and a decrease in porosity and to maintain an appropriate thickness.

Hereinafter, the effects of the present invention will be described in more detail with reference to Examples and Comparative Examples. These examples are merely to aid the understanding of the present invention and do not limit the scope of the present invention.

Example  One

After dissolving the polyamic acid in dimethylformamide solvent to prepare a 12 wt% spinning solution, it is spun through a metering pump (1) through a nozzle (2) installed in the electrospinning apparatus and then to the high voltage generator (3) By scattering and solidifying the electric field is applied to form a fiber (4), and the formed fibers (4) to focus on the collector (5) to prepare a polyimide precursor nanofiber web having an average thickness of 30 ㎛. At this time, the applied voltage was 15 kV and the radiation distance was 15 cm.

Subsequently, the polyimide precursor nanofiber web was heat-treated with a hot press maintained at a temperature of 200 ° C. for 30 minutes and then imidized to prepare a polyimide porous nanofiber web.

Subsequently, the sulfonated polyimide was dissolved in N-methyl-2-pyrrolidone solvent to prepare an ion conductor solution, and the prepared ion conductor solution was impregnated with the porous nanofiber web twice for 20 minutes, followed by 1 After leaving for an hour to dry for 3 hours in a hot air of 80 ℃ to prepare an electrolyte membrane of 40 ㎛ thickness.

Example  2

In Example 1 described above, a polyimide porous nanofiber web and an electrolyte membrane were manufactured by the same method as Example 1 except that the temperature of the hot press is 400 ° C.

Comparative example  One

In Example 1 described above, a sulfonated polyimide was dissolved in dimethylformamide to prepare a 12 wt% composition solution, which was then filmed and dried to prepare a porous membrane having an average thickness of 30 μm.

Subsequently, an electrolyte membrane was prepared in the same manner as in Example 1 using the prepared porous membrane.

Comparative example  2

A porous membrane of a commercially available ePTFE porous film (W.L.Gore, Teflon) with a thickness of 30 μm was prepared.

Subsequently, an electrolyte membrane was prepared in the same manner as in Example 1 using the prepared porous membrane.

Comparative example  3

In Example 1 described above, a polyimide porous nanofiber web and an electrolyte membrane were manufactured by the same method as Example 1 except that the temperature of the hot press is 80 ° C.

Comparative example  4

In Example 1 described above, an electrolyte membrane having a thickness of 40 μm was prepared by using a sulfonated polyimide, which is the hydrocarbon-based ion conductor, without using the polyimide porous nanofiber web.

Physical properties of the porous nanofiber webs, porous membranes, and electrolyte membranes prepared by Examples and Comparative Examples were measured by the following method and are shown in Table 1 below.

After solvent treatment Imidization rate (%) Measure

The imidation ratio (%) after solvent treatment was measured using the following formula.

% Imidization after solvent treatment = [(weight of nanofiber web (porous membrane) after solvent treatment / weight of nanofiber web (porous membrane) before solvent treatment)] × 100

The weight of the nanofiber web (porous membrane) before the solvent treatment was measured using a nanofiber web (porous membrane) left at least 24 hours in a vacuum oven set at a temperature of 30 ℃. After the solvent treatment, the weight of the nanofiber web (porous membrane) was immersed in the dimethylformamide organic solvent before the solvent treatment in dimethylformamide organic solvent, stirred for 24 hours at room temperature, washed at least 5 times in distilled water, and then 30 After standing for 24 hours in a vacuum oven set to a temperature of ℃ was measured using a nanofiber web (porous membrane) obtained after the solvent treatment.

Strength retention (%) measurement

Strength retention (%) was measured using the following formula.

Strength retention (%) = [Tensile strength after acid treatment / Tensile strength before acid treatment] × 100

After the acid treatment, the tensile strength was stirred in 300 ml of an acid solution of 80 ° C. mixed with sulfuric acid and 2 ppm of hydrogen fluoride for 4 hours, and then subjected to KS M 3054 using an electrolyte membrane of 20 cm × 20 cm washed five times with distilled water. It measured based on.

% Change in weight

The weight change rate (%) was measured using the following formula.

% Change in weight = [(Wb-Wa) / Wb] x 100

Wb is the weight of the electrolyte membrane before acid treatment, and Wa is the weight of the electrolyte membrane after acid treatment. The weight of the electrolyte membrane after the acid treatment was acid treated in the same manner as the above-described method for measuring the strength retention, and then washed and measured using an electrolyte membrane dried for 24 hours in a vacuum open at 30 ° C. The weight of the electrolyte membrane before the acid treatment was measured using an electrolyte membrane dried for 24 hours at 30 ℃ vacuum open.

division Nanofiber web type Heat treatment temperature (℃) Acid treatment after imidization rate (%) Strength retention rate (%) % Change in weight Example PI 200 93.3 89.0 4.5 Example 2 PI 400 96.5 88.3 4.3 Comparative Example 1 S-PI - - 82.3 6.8 Comparative Example 2 ePTFE - - 83.8 5.3 Comparative Example 3 PI 80 70.8 80.1 5.3

With the proviso that PI is a polyimide and S-PI is a sulfonated polyimide.

1: metering pump 2: nozzle
3: high voltage generating unit 4: fiber
5: collector

Claims (8)

Porosity 50 to 99%;
After the solvent treatment determined by the following formula, the imidation ratio after the solvent treatment is 90% or more;
Polyimide porous nanofiber web comprising a fiber aggregate form.
Imidization rate after solvent treatment (%) = [weight of nanofiber web after solvent treatment / weight of nanofiber web before solvent treatment] × 100 (where, the weight of nanofiber web before solvent treatment is set at a temperature of 30 ° C.) Measured using a nanofiber web left at least 24 hours in a vacuum oven, and after the solvent treatment, the weight of the nanofiber web was stirred for 24 hours at room temperature by immersing the nanofiber web before the solvent treatment in a dimethylformamide organic solvent. After washing at least 5 times in distilled water and left for 24 hours in a vacuum oven set at a temperature of 30 ℃ measured using a nanofiber web obtained after the solvent treatment) The method of claim 1,
Polyimide porous nanofiber web, characterized in that the strength retention of the electrolyte membrane prepared by impregnating the hydrocarbon-based ion conductor in the porous nanofiber web is more than 85% as measured by the following equation.
Strength retention (%) = [Tensile strength after acid treatment / Tensile strength before acid treatment] × 100 (However, the tensile strength after acid treatment was stirred for 4 hours in an acid solution at 80 ° C. in which sulfuric acid and 2 ppm of hydrogen fluoride were mixed. After the measurement using the electrolyte membrane washed with distilled water according to KS M 3054) The method of claim 1,
Polyimide porous nanofiber web, characterized in that the weight change rate of the electrolyte membrane prepared by impregnating the hydrocarbon-based ion conductor in the porous nanofiber web is 5% or less when measured by the following equation.
% Change in weight = [(Wb-Wa) / Wb] x 100 (Wb is the weight of the electrolyte membrane before acid treatment, and Wa is the weight of the electrolyte membrane after acid treatment. The weight of the electrolyte membrane after acid treatment is sulfuric acid. After stirring for 4 hours in an acid solution of 80 ℃ mixed with 2 ppm hydrogen fluoride and washed with distilled water and then dried for 24 hours in a vacuum opening of 30 ℃) The method of claim 1,
The polyimide porous nanofiber web is a polyimide porous nanofiber web, characterized in that consisting of fibers having an average diameter of 0.01 to 5 ㎛. The method of claim 1,
The polyimide porous nanofiber web has an average thickness of 5 to 40 ㎛ polyimide porous nanofiber web. Preparing a spinning solution by dissolving a polyimide precursor (precusor) in an organic solvent;
Electrospinning the spinning solution to prepare a polyimide precursor nanofiber web made of fibers having an average diameter of 0.01 to 5 μm; And
Preparation of a polyimide porous nanofiber web comprising the step of imidating the polyimide precursor nanofiber web and preparing a polyimide nanofiber web having an imidation ratio of 90% or more after the solvent treatment obtained by the following formula Way.
Imidization rate after solvent treatment (%) = [weight of nanofiber web after solvent treatment / weight of nanofiber web before solvent treatment] × 100 (where, the weight of nanofiber web before solvent treatment is set at a temperature of 30 ° C.) Measured using a nanofiber web left at least 24 hours in a vacuum oven, and after the solvent treatment, the weight of the nanofiber web was stirred for 24 hours at room temperature by immersing the nanofiber web before the solvent treatment in a dimethylformamide organic solvent. After washing at least 5 times in distilled water and left for 24 hours in a vacuum oven set at a temperature of 30 ℃ measured using a nanofiber web obtained after the solvent treatment) The method of claim 6,
The process of producing the polyimide porous nanofiber web comprises a step of heat treatment at a temperature of 100 to 400 ℃. The method of claim 6,
The manufacturing method of the polyimide porous nanofiber web is a method of producing a polyimide porous nanofiber web comprising a heat treatment at a draw ratio of 0.1 or less.

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