JP2014152424A - Polymer fiber structure and method for producing the same, and composite fiber structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer fiber structure suitable for application such as a functional filter.SOLUTION: There is provided a method for producing a polymer fiber structure including the steps of: dissolving a water-soluble polymer at a concentration not causing gelation of the water-soluble polymer in an aqueous solvent to form a polymer solution; quickly freezing the polymer solution to obtain a frozen object; and depressurizing the frozen object and removing the solvent at a pressure of 2.0 Pa or more and 100 Pa or less to obtain a dried object. The water-soluble polymer is preferably one or more kinds selected from among polyethylene oxide, sizofiran, guar gum, xanthan gum and polyvinylpyrrolidone. According to this production method, the polymer fiber structure formed by the water-soluble polymer fiber having a diameter of 1,000 nm or less, in particular 300 nm or less can be produced with high reproducibility.

Description

  The present invention relates to a polymer fiber structure composed of water-soluble polymer fibers, a production method thereof, and a composite fiber structure including water-soluble polymer fibers.

  Porous structures made of polymer resins are applied in various fields because of their advantages such as a large specific surface area and high air permeability. In particular, a porous structure made of a water-soluble polymer has advantages such that the water-soluble polymer as a raw material is often relatively low cost and many of them are excellent in flexibility, water retention and biocompatibility. Therefore, the application is widely examined in various fields such as various filters, regenerative medicine, and separators.

  As a method for producing a porous structure composed of a water-soluble polymer, for example, Patent Document 1 discloses gelling and freezing a slurry in which a water-soluble polymer that can be gelled and a powder that is not soluble in water are dispersed. A method for producing a porous structure is disclosed in which ice crystals generated at that time are used as a pore source, and then a dried body obtained by removing ice from the frozen body is heat-treated. Further, Patent Document 2 discloses a porous structure containing vapor grown carbon fiber in which a vapor grown carbon fiber is dispersed in a solution of the gelled material, and then the gelled material is gelled and the solvent is removed. A manufacturing method is disclosed. Patent Document 3 discloses a method for producing a sponge-like porous structure made of a water-soluble polymer.

  The method for producing a porous structure disclosed in Patent Documents 1 to 3 includes a step of gelling a water-soluble polymer in a solution to form a three-dimensional network structure and then distilling off the solvent. However, it is difficult to obtain a uniform structure during gelation, and there remains room for improvement in terms of product reproducibility.

On the other hand, as a method for producing a porous structure containing a water-soluble polymer fiber, Patent Document 4 discloses a nanofiber layer including a base layer and a nanofiber laminated on the base layer and formed by an electrospinning method. And a water-soluble polymer is disclosed as a nanofiber material.
Patent Document 5 discloses a method for producing a sheet-like nonwoven fabric by producing polymer fibers having a fiber diameter of about several hundred nm to several tens of μm by electrospinning, and entangled them.

JP 2011-38072 A International Publication No. 2001/57121 Pamphlet JP 2011-32490 A JP 2012-12711 A JP 2012-207350 A

  The electrospinning methods disclosed in Patent Documents 4 and 5 have the advantage that uniform and fine polymer fibers can be produced, but the productivity is poor because only one fiber can be produced from one nozzle. In addition, in order to form a structure such as a sheet-like nonwoven fabric, it is necessary to produce polymer fibers and to collect and entangle them, but the polymer fibers are uniformly distributed, and there is no unevenness in the distribution of the polymer fibers. It is difficult to manufacture the structure. In addition, there is a problem that it is difficult to make a thick sheet.

  Thus, the production of polymer fiber structures by the electrospinning method requires expensive equipment, and the equipment is large and expensive, so that only a small amount of high value-added products can meet the cost. This is the actual situation.

As described above, the conventional method for producing a fiber structure made of a water-soluble polymer has problems in cost and productivity, which often hinders practical use.
Under such circumstances, an object of the present invention is to provide a fiber structure composed of water-soluble polymer fibers. Another object of the present invention is to provide a method for stably producing a polymer fiber structure comprising water-soluble polymer fibers at a low cost.

  As a result of intensive studies to solve the above problems, the present inventor has controlled the water-soluble polymer concentration, cooling conditions, and drying conditions in a polymer solution containing a water-soluble polymer to specific conditions, and then freeze-dried the solution. The present inventors have found that a structure composed of fine fibers of a water-soluble polymer can be produced stably at low cost and has led to the present invention.

That is, the present invention relates to the following inventions.
<1> A polymer fiber structure formed of water-soluble polymer fibers having a diameter of 1000 nm or less.
<2> The polymer fiber structure according to <1>, wherein the water-soluble polymer fiber is composed of at least one water-soluble polymer selected from polyethylene oxide, schizophyllan, polyvinylpyrrolidone, guar gum, and xanthan gum.
<3> The polymer fiber structure according to <1> or <2>, wherein the water-soluble polymer fiber has a diameter of 300 nm or less.
<4> The polymer fiber structure according to any one of <1> to <3>, wherein the thermal conductivity is 0.05 W / (m · K) or less.
<5> The polymer fiber structure according to any one of <1> to <4>, wherein the porosity is 99% by volume or more.
<6> The polymer fiber structure according to any one of <1> to <5>, wherein the polymer fiber structure has a sheet shape.
<7> The polymer fiber structure according to any one of <1> to <6>, including catalyst particles on which the water-soluble polymer fiber is supported.
<8> A composite fiber structure comprising the polymer fiber structure according to any one of <1> to <7> and a holding base.
<9> The composite fiber structure according to <8>, wherein the holding base is a porous body.
<10> a step of dissolving a water-soluble polymer in an aqueous solvent at a concentration that does not gel, and forming a polymer solution;
Rapid freezing the polymer solution to obtain a frozen product;
A method for producing a polymer fiber structure, comprising: depressurizing the frozen material and distilling off the solvent at a pressure of 2.0 Pa to 100 Pa to obtain a dried product.
<11> The method for producing a polymer fiber structure according to <10>, wherein the water-soluble polymer is at least one selected from polyethylene oxide, schizophyllan, polyvinylpyrrolidone, guar gum, and xanthan gum.
<12> The method for producing a polymer fiber structure according to <10> or <11>, wherein the concentration of the water-soluble polymer in the solution is 0.1 to 4.5% by weight.
<13> The method for producing a polymer fiber structure according to any one of <10> to <12>, wherein the frozen material is rapidly cooled with liquid nitrogen.
<14> The method for producing a polymer fiber structure according to any one of <10> to <13>, wherein the polymer solution contains catalyst particles or a precursor of catalyst particles.

  ADVANTAGE OF THE INVENTION According to this invention, the polymer fiber structure which has the outstanding characteristics, such as a large specific surface area and high air permeability, and has a uniform structure is provided. Moreover, according to the manufacturing method of this invention, the polymer fiber structure of this invention can be manufactured stably and at low cost.

It is a SEM photograph (magnification 15000 times) of a dried material (comparative example) of Experimental Example 1A (PEO: 900,000, liquid nitrogen cooling, 1.0 Pa drying). It is a SEM photograph (magnification 2500 times) of the dried product of Experimental Example 1H (PEO: 900,000, liquid nitrogen cooling, 10 Pa drying). It is a SEM photograph (magnification 250 times) of the dried material (comparative example) of Experimental example 1J (PEO: 900,000, freezer cooling, 10 Pa drying). It is a SEM photograph (magnification 20000 times) of the dried material of Example 2A (PEO: 5 million). It is a SEM photograph of the dried material of Example 3 (SPG), (a) is 2000 times magnification, (b) is 50000 times magnification. It is a SEM photograph (2000-times multiplication factor) of the dried material of Experimental example 4A (PVP). It is a SEM photograph (magnification 3000 times) of the dried material (comparative example) of Experimental example 4B (PVP). It is a SEM photograph (magnification 2000 times) of the dried product (comparative example) of Experimental Example 4C (PVP). It is a SEM photograph (2000-times multiplication factor) of the dried material of Experimental example 5 (guar gum). It is a SEM photograph of the dried material of Example 7 (PVA), (a) is 800 times magnification, (b) is 11000 times magnification. It is a SEM photograph (1500 times magnification) of a dried product of Experimental Example 8 (Na alginate). It is a SEM photograph (7000 times magnification) of the dried product of Experimental Example 9 (supporting titanium oxide). 4 is a SEM photograph (700 times magnification) of the composite fiber structure of Experimental Example 10.

  Hereinafter, the present invention will be described in detail with reference to examples and the like, but the present invention is not limited to the following examples and the like, and can be arbitrarily modified and implemented without departing from the gist of the present invention. In addition, in this specification, when the expression “to” is used, it is used to mean including numerical values or physical values before and after that.

The polymer fiber structure of the present invention is formed of water-soluble polymer fibers having a diameter of 1000 nm or less.
In the present invention, a water-soluble polymer fiber (hereinafter sometimes simply referred to as “polymer fiber”) is a fiber composed of a water-soluble polymer, and has a total length of 1 μm or more (preferably 10 μm or more). It has a length.
In addition, the polymer fiber structure is a general concept of a form in which at least 50 water-soluble polymer fibers are aggregated. The polymer fiber is a bundle-like structure having orientation, or the polymer fiber is random. The thing of the structure intertwined with is included.

The diameter (fiber diameter) of the polymer fiber is suitably 1000 nm or less, preferably 300 nm or less, more preferably 200 nm or less. The lower limit of the diameter (fiber diameter) of the polymer fiber is not limited as long as the mechanical strength is maintained, but is usually 100 nm or more.
In addition, the full length and diameter of a polymer fiber can be confirmed with a scanning electron microscope (SEM) and a transmission electron microscope (TEM).

  The density of the polymer fiber in the polymer fiber structure may be any density as long as the polymer fibers are in contact with each other. The balance between mechanical strength and porosity, the type of water-soluble polymer, the use of the polymer fiber structure, etc. It is determined as appropriate in consideration.

The water-soluble polymer is not particularly limited as long as it can form polymer fibers, and may be so-called polysaccharides, DNA analogs, and polypeptides including proteins. In particular, those capable of producing a polymer fiber structure by the production method of the present invention described later are preferred.
Polyethylene oxide (PEO), schizophyllan (SPG), guar gum, xanthan gum, polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polystyrene sulfoxide (PSS), dextran, dextran sulfate, pullulan, fucoidan, salmon white DNA, polyglutamic acid, Polylysine etc. are mentioned.
Among these, polyethylene oxide, schizophyllan, polyvinyl pyrrolidone, guar gum and xanthan gum are preferable, and polyethylene oxide and schizophyllan are particularly preferable.
In these, the polymer fiber structure may be composed of one kind of water-soluble polymer fiber, or may be composed of two or more kinds of water-soluble polymer fibers. However, in terms of improving the uniformity of the fiber diameter, it is preferable to use one type of water-soluble polymer fiber.

  From the viewpoint of biocompatibility, guar gum and xanthan gum are preferable. Guar gum and xanthan gum are already widely used as thickening polysaccharides and are approved for use in foods. Therefore, it can be used for applications that touch human skin, such as the cosmetics field.

The molecular weight of the water-soluble polymer is preferably within a range where polymer fibers described later can be formed, and is appropriately determined depending on the type of the water-soluble polymer.
Preferred weight average molecular weight (MW) is MW: 500,000 to 5,000,000 for polyethylene oxide, MW: 150,000 to 2,000,000 for schizophyllan, MW: 20,000 to 160,000 for polyvinyl alcohol, polyvinyl pyrrolidone In this case, MW is about 35,000 to 360,000.

  The polymer fiber structure of the present invention can be in any form such as a particle shape, a lump shape, a rod shape, or a sheet shape, depending on the application. Among these, the sheet form (nonwoven fabric) is one of the preferred forms of the polymer fiber structure because it is suitable for applications such as filters. The thickness of the sheet is arbitrary, but is usually about 2 to 50 mm.

The porosity of the polymer fiber structure of the present invention can be controlled by the type of water-soluble polymer fiber used and the solution concentration.
In terms of the high specific surface area, the polymer fiber structure is preferably 80% by volume or more, more preferably 90% by volume or more, and still more preferably 99% by volume or more. The porosity can be calculated from the ratio between the apparent density of the polymer material and the apparent density of the polymer fiber structure.

The polymer fiber structure of the present invention can increase the porosity, and the polymer fiber of the constituent material has low thermal conductivity.
Therefore, the thermal conductivity of the polymer fiber structure itself is 0.05 W / (m · K) or less, preferably 0.04 W / (m · K) or less, more preferably 0.035 W / (m · K) or less. It can be.
In addition, the polystyrene board used as a heat insulating material is about 0.030 W / (m · K), the cotton is about 0.07 W / (m · K), and the cotton towel is about 0.14 W / (m · K). is there.

  The polymer fiber structure of the present invention may contain other than water-soluble polymer fibers. For example, it is one of preferable modes to mix active ingredients such as various drug ingredients, nutrient ingredients, fragrances, antibacterial ingredients, and deodorizing ingredients. In addition, since the water-soluble polymer fiber which comprises the polymer fiber structure of this invention has a property which a fiber melt | dissolves gradually with a water | moisture content, it can release an active ingredient gradually by sticking on skin.

Moreover, as one of the preferable forms of the polymer fiber structure of this invention, the form which has the catalyst particle carry | supported by the water-soluble polymer fiber is mentioned. The catalyst particles are preferably present on the surface of the water-soluble polymer fiber, but may be combined with a plurality of water-soluble polymer fibers as long as a sufficient reaction surface area can be ensured.
What is necessary is just to select suitably as a catalyst according to a use, for example, photocatalysts, such as metal catalysts, such as platinum which have an organic substance decomposition | disassembly effect | action, titanium oxide, etc. are mentioned. Further, the size and supported amount of the catalyst particles may be appropriately selected according to the use.

Further, the polymer fiber structure of the present invention may be used as a composite fiber structure combined with a holding substrate. By combining with the holding substrate, there are advantages such as ensuring mechanical strength and imparting functions derived from the holding substrate.
Here, the holding substrate is not particularly limited as long as it can hold and synthesize a polymer fiber structure, and may be a dense body or a porous body. As a common method of using the dense body and the porous body, there is a form in which the holding base is used as the support layer and the polymer fiber structure is held on the surface thereof.

Moreover, in the case of a porous body, not only the method of hold | maintaining on the said surface but a polymer fiber structure can also be hold | maintained inside a porous body.
When used for applications such as a filter, a porous material having a communicating hole and having air permeability is preferable.

The material of the porous body may be either an inorganic porous body or an organic porous body, and is appropriately selected according to the application. The form of the porous body is also appropriately selected depending on the application, and examples thereof include porous powder, porous granules, porous lumps, and porous sheets.
Among these, the porous sheet is a suitable form, and for example, a mesh sheet, a perforated sheet (a sheet in which a large number of perforations that penetrate the sheet in the thickness direction), a nonwoven fabric, and the like can be used. A laminated sheet obtained by bonding two or more of these can also be used. The porous sheet is used as a filter, and a polymer fiber structure can be combined with a filter made of a conventional porous sheet to add an additional function.
Among the porous sheets, a fibrous substrate which is a structure used as a framework for the purpose of maintaining the shape of the polymer fiber structure and improving the strength is a suitable example. Specifically, absorbent cotton, various existing filters, gauze, paper, mask, non-woven fabric and the like can be mentioned.

The use of the polymer fiber structure of the present invention is not particularly limited, and examples thereof include various filters, catalyst supports, battery separators, clothes, cosmetics, and deodorants. In particular, the preferred water-soluble polymer fibers described above can be suitably used as daily necessities such as cosmetics and deodorants because biosafety is ensured.
Since the polymer fiber structure of the present invention may be insufficient in durability, it can be used disposable or after being subjected to water-resistant treatment.

Hereafter, it demonstrates more concretely about the suitable use of the polymer fiber structure of this invention.
"Cosmetic sheet"
The cosmetic sheet comprised with the polymer fiber structure of this invention is mentioned. In this case, guar gum or xanthan gum is preferable as the water-soluble polymer. Since the cosmetic sheet composed of the polymer fiber structure of the present invention has high biocompatibility, it is unlikely to be irritated unlike ordinary ships and can be used in allergic constitutions. Further, as described above, active ingredients such as drugs such as vitamin C and indomethacin, and nutrients may be mixed. Since the water-soluble polymer fiber constituting the polymer fiber structure has a property that the fiber is gradually dissolved by moisture, the active ingredient can be gradually released by sticking to the skin.

"Functional filters (deodorant sheets, etc.)"
The polymer fiber structure of the present invention can be easily combined with an existing filter as described above, or combined with fine particles such as a catalyst.
For example, it is possible to make a filter that positively removes bad odors and harmful substances by combining deodorant components and catalyst particles as described above. For example, it is possible to remove fine foreign matters such as pollen by forming fine fibers in an existing filter.

Next, the manufacturing method of the polymer fiber structure of this invention is demonstrated.
The production method of the present invention comprises a step of dissolving a water-soluble polymer in an aqueous solvent at a concentration not causing gelation to form a polymer solution, a step of rapidly freezing the polymer solution to obtain a frozen product, And a reduced pressure drying step in which the solvent is distilled off at a pressure of 2.0 Pa or more and 100 Pa or less to obtain a dried product.
According to the production method of the present invention, the polymer fiber structure of the present invention can be stably produced at a low cost.

  The mechanism by which the production method of the present invention can form a polymer fiber structure composed of water-soluble polymer fibers is not completely clear at this stage, but a solution containing a dilute water-soluble polymer at a concentration that does not cause gelation. By rapid freezing, the polymer molecules are concentrated between the ice crystals and placed in the frozen solution with a concentration and orientation that tends to form a fiber structure. It is presumed that a fibrous structure grows by depressurizing the frozen material under specific pressure conditions and distilling off the solvent at an appropriate rate.

  Hereafter, the manufacturing method of the polymer fiber structure of this invention is demonstrated in detail for every process.

  In the step of forming the polymer solution, the polymer solution is formed by dissolving the water-soluble polymer as a raw material of the polymer fiber structure in an aqueous solvent at a concentration that does not cause gelation.

The aqueous solvent which is the solvent of the polymer solution is a solvent containing 80% by weight or more of water when the total amount of the solvent is 100% by weight, and is usually 100% by weight of water, but if necessary, methanol, ethanol A solvent compatible with water such as propanol may be contained.
The water used is preferably pure water or ion exchange water.

As the water-soluble polymer as a raw material, the water-soluble polymer constituting the polymer fiber described in the polymer fiber structure of the present invention described above can be used.
That is, polyethylene oxide (PEO), schizophyllan (SPG), guar gum, xanthan gum, polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polystyrene sulfoxide (PSS), guar gum, xanthan gum, dextran, dextran sulfate, pullulan, fucoidan, salmon Shiroko DNA, polyglutamic acid, polylysine and the like can be mentioned, polyethylene oxide, schizophyllan, polyvinylpyrrolidone, guar gum and xanthan gum are preferable, and polyethylene oxide and schizophyllan are particularly preferable.
These water-soluble polymers may be used alone or in combination of two or more.

The concentration of the water-soluble polymer in the polymer solution is selected in such a range that the water-soluble polymer does not gel. When gelation is performed, polymer fibers may not be formed, and even when formed, other forms (particles, tapes, sponges, etc.) may be mixed.
More specifically, the concentration of the water-soluble polymer is preferably 0.1 to 4.5% by weight, and more preferably 0.15 to 2 in that high-quality polymer fibers are formed. % By weight, and more preferably 0.2 to 1.5% by weight.

In addition, the polymer solution may contain components other than the water-soluble polymer and the solvent (hereinafter referred to as “other components”) at an arbitrary ratio as long as the effects of the present invention are not impaired.
Examples of other components include additives that improve liquid properties such as pH adjusters, surfactants, and ice crystal growth inhibitors.

The polymer fiber structure of the present invention can be provided with functionality by supporting various catalyst particles as described above.
In this case, the polymer particles may be contained in the polymer solution and used for the subsequent freezing step and vacuum drying step. Moreover, the catalyst particle precursor may be included in the polymer solution to generate catalyst particles, or the catalyst particles may be generated by post-treatment after drying (heat treatment, reduction treatment, etc.).

  The polymer solution can be produced by mixing its constituent components (water-soluble polymer, solvent, and other components). The mixing order is also arbitrary, and any two components or three or more components among the components of the polymer solution may be blended in advance, and then the remaining components may be mixed, or all may be mixed at once. .

The polymer solution is then subjected to a freezing process. In the freezing step, a polymer solution is formed, and the polymer solution is rapidly frozen to obtain a frozen product.
Here, quick freezing means freezing to a target temperature within at least 3 minutes, preferably within 1 minute.
The freezing temperature is 0 ° C. or lower, at least water is frozen, preferably −20 ° C. or lower, more preferably −40 ° C. or lower.
It is preferable to obtain a frozen product by quenching with liquid nitrogen in that it can be cooled to a low temperature more rapidly and a high-quality polymer fiber is formed.

  The freezing time is usually about several minutes to 1 hour, although it depends on the amount of the polymer solution and the freezing temperature.

  The polymer solution can be placed in any container and snap frozen. The shape of the container is appropriately selected in consideration of the intended use of the polymer fiber structure.

The obtained frozen product is then subjected to a vacuum drying step. In the vacuum drying step, the frozen material is depressurized and dried at a pressure of 2.0 Pa to 100 Pa. In addition, the pressure here means what is called an absolute pressure expressed on the basis of a vacuum.
If the pressure during decompression is less than 2.0 Pa, it becomes difficult for the water-soluble polymer to form a fibrous structure, and a spherical (particulate) structure is the main component, making it impossible to form polymer fibers.
When the pressure at the time of depressurization becomes 30 Pa or more, the frozen material is melted and lyophilization may not be performed. In this case, the pressure may be reduced while cooling the frozen material. The cooling temperature may be set at a temperature at which the frozen material does not melt during decompression.
Further, when the frozen material is dried while being cooled, it does not melt even if the pressure during decompression is high, but at 100 Pa or more, the drying speed is remarkably slow, and high-quality polymer fibers cannot be formed.
It is preferable that the pressure at the time of pressure reduction is 5.0-20Pa by the point from which a higher quality polymer fiber structure is obtained.

  Further, as described above, the polymer fiber structure of the present invention can be combined with a holding substrate and used as a composite fiber structure. In the case of producing a composite fiber structure held on the surface of a holding base composed of a dense body or a porous body, for example, in the state where the polymer solution is applied to the surface of the holding base, the polymer fiber is formed by the above cooling method and drying method. A structure may be formed.

In order to produce the polymer fiber structure inside the porous body on the holding substrate, the following method is preferred.
First, the porous body is impregnated into the polymer solution, or the polymer solution is infiltrated into the porous body, and the polymer solution is filled in the gaps between the fibrous substrates. Subsequently, the composite fiber structure in which the polymer fiber structure is formed in the gap between the fibrous base bodies can be obtained by the subsequent freezing step and reduced pressure drying step. The details of the porous body are as described above.

  Depending on the purpose, the entire porous body may be impregnated in the polymer solution, or a part of the porous body may be impregnated in the polymer solution. The conditions for impregnating the porous material are not particularly limited, but are usually about 10 seconds to 30 minutes at room temperature.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is changed. Note that the pressure (degree of vacuum) means a so-called absolute pressure expressed on the basis of vacuum.

(1) Porosity measurement method 1 g of polymer powder used as a raw material for the polymer fiber structure is closely packed in a measuring cylinder, and the volume is measured. The powder density is calculated by dividing the powder weight by the volume. Next, a polymer fiber structure having a rectangular parallelepiped shape is produced, and the apparent volume is measured by measuring the length, width, and height. By dividing the weight of the polymer fiber structure by the obtained volume, the apparent density of the polymer fiber structure can be obtained. Further, the apparent density of the polymer fiber structure is divided by the powder density, and the obtained value is multiplied by 100 to obtain the polymer occupation ratio. The value obtained by subtracting the polymer occupancy from 100 is taken as the porosity.

(2) Measurement method of thermal conductivity A sheet-shaped polymer fiber structure was prepared and measured using a thermal conductivity meter (QTMD3 manufactured by Kyoto Electronics Industry Co., Ltd.). When the sheet was crushed by the weight of the probe, the measurement was carried out with the shape of the support bar placed on the periphery that does not affect the measurement.

“Experimental Examples 1A to 1P”
Polyethylene oxide (PEO) (MW: 900,000 Sigma-Aldrich) was used as the water-soluble polymer. 0.5 g of the water-soluble polymer was dissolved in distilled water to make a 100 mL solution. 0.5 mL of this solution was taken in a sample tube, and a frozen product was obtained under the freezing conditions shown in Table 1 (quick freezing by immersion in liquid nitrogen for 1 minute or slow cooling with a freezer (−25 ° C. setting)). Next, the frozen product was set in a freeze dryer (Iwaki Glass FRD-82M), and dried under reduced pressure for 3 hours under the reduced pressure drying conditions shown in Table 1 to obtain dried products of Experimental Examples 1A to 1P. In addition, the temperature conditions in the reduced-pressure drying conditions in Table 1 indicate a case where the temperature conditions are not particularly adjusted and a case where the frozen material is placed on a -20 ° C cooling plate.
Table 1 summarizes the results of evaluating the fine structures of the dried products of Experimental Examples 1A to 1P obtained with a scanning electron microscope (SEM). In addition, since the frozen substance melt | dissolved and it could not freeze-dry under the decompression drying conditions (30 Pa, room temperature) of Experimental example 1M, evaluation by SEM was not performed.

As typical structures, FIG. 1 shows a dried product of Experimental Example 1A, FIG. 2 shows a dried product of Experimental Example 1H, and FIG. 3 shows a SEM photograph of the dried product of Experimental Example 1J.
As shown in FIG. 1, the dried product of Experimental Example 1A contained almost no fibrous structure and had a particulate structure.
On the other hand, as shown in FIG. 2, the dried product of Experimental Example 1H had a structure in which fibers having a diameter of about 200 nm gathered and were intertwined in a complicated manner. When a sheet formed with the dried product of Experimental Example 1H was pulled, a strong force was required to tear it.
As shown in FIG. 3, the dried product of Experimental Example 1J had a fiber diameter exceeding 1 μm or a tape-like structure, and contained almost no fiber diameter of 1 μm or less.

"Example 2A"
Experimental Example 1H except that 0.5 g of polyethylene oxide (PEO) (MW: 5 million Sigma-Aldrich) having a different molecular weight was used as the water-soluble polymer instead of polyethylene oxide (PEO) (MW: 900,000 Sigma-Aldrich). In the same manner as above, a dried product of Experimental Example 2A was obtained.
FIG. 4 shows an SEM photograph of the dried product of Experimental Example 2A. The dried product of Experimental Example 2A had a structure in which fibers were gathered as in Experimental Example 1H, and the fiber diameter was about 200 nm as in Experimental Example 1H. Also, the tensile strength was high as in Experimental Example 1H.

"Example 2B"
Experimental Example 1H except that polyethylene oxide (PEO) (MW: 900,000 Sigma-Aldrich) instead of polyethylene oxide (PEO) (MW: 500,000 Sigma-Aldrich) 4.5 g was used as the water-soluble polymer. In the same manner as described above, a dried product of Experimental Example 2B was obtained.
When the dried product of Experimental Example 2B was observed with an SEM, it had a structure in which fibers were assembled in the same manner as in Experimental Example 1H, and the fiber diameter was equivalent to that of Experimental Example 1H.

"Experiment 3"
A dried product of Experimental Example 3 was obtained in the same manner as Experimental Example 1H, except that 0.1 g of Schizophyllan (SPG) (MW: 150,000 Mitsui Sugar) was used as the water-soluble polymer.
5 (a) and 5 (b) show SEM photographs of the dried product of Experimental Example 3. FIG. The dried product of Experimental Example 3 had a structure in which fibers were gathered as in Experimental Example 1H, and the fiber diameter was about 200 nm.

"Experiment 4A"
A dried product of Experimental Example 4A was obtained in the same manner as Experimental Example 1H, except that 1.5 g of polyvinylpyrrolidone (PVP) (MW: 35,000, Wako Pure Chemical Industries) was used as the water-soluble polymer.
FIG. 6 shows an SEM photograph of the dried product of Experimental Example 4A. The dried product of Experimental Example 4A mainly had a structure in which fibers having a diameter of 200 to 500 nm were assembled.

"Experiment 4B"
A dried product of Experimental Example 4B was obtained in the same manner as Experimental Example 4A, except that the amount of polyvinylpyrrolidone was changed to 5 g.
FIG. 7 shows an SEM photograph of the dried product of Experimental Example 4B. The dried product of Experimental Example 4B had a tape-like structure, and almost no fibrous structure was confirmed.

"Experimental example 4C"
A dried product of Experimental Example 4C was obtained in the same manner as Experimental Example 4A, except that the amount of polyvinylpyrrolidone was 0.05 g.
FIG. 8 shows an SEM photograph of the dried product of Experimental Example 4C. The dried product of Experimental Example 4C had a spherical structure, and almost no fibrous structure was confirmed.

“Experimental Example 5”
A dried product of Experimental Example 5 was obtained in the same manner as in Experimental Example 1H, except that 0.5 g of guar gum (Wako Pure Chemical Industries) was used as the water-soluble polymer.
FIG. 9 shows an SEM photograph of the dried product of Experimental Example 5. The dried product of Experimental Example 5 had a structure in which fibers were gathered, and the fiber diameter was 200 nm or less.

"Experimental example 6"
A dried product of Experimental Example 6 was obtained in the same manner as in Experimental Example 1H, except that 0.5 g of xanthan gum (MW: 2 million or less MP biomedical) was used as the water-soluble polymer.
When the dried product of Experimental Example 6 was observed by SEM, it had a structure in which fibers were assembled, and the fiber diameter was 200 nm or less.

"Experimental example 7"
A dried product of Experimental Example 7 was obtained in the same manner as in Experimental Example 1H, except that 1.0 g of polyvinyl alcohol (MW: 120,000 Wako Pure Chemical Industries) was used as the water-soluble polymer.
10A and 10B show SEM photographs of the dried product of Experimental Example 7. FIG. The dried product of Experimental Example 5 had a structure in which fibers were gathered, but the length of the fibers was not uniform, the fiber diameter was about 1 μm, and the surface was uneven.

"Experimental example 8"
A dried product of Experimental Example 8 was obtained in the same manner as in Experimental Example 1H, except that 0.5 g of sodium alginate (Wako Pure Chemical Industries) was used as the water-soluble polymer.
FIG. 11 shows an SEM photograph of the dried product of Experimental Example 8. When the dried product of Experimental Example 8 was observed by SEM, there was almost no fibrous structure, and amorphous aggregates were observed.

“Evaluation of water-soluble polymer types and polymer fiber structure-forming ability”
Except that 1.0 g of various water-soluble polymers shown in Table 2 were used, dried products of the respective water-soluble polymers were obtained under the same conditions as in Experimental Example 1H. The obtained dried product was observed by SEM, and the polymer structure forming ability was evaluated.
The results are summarized in Table 2. In Table 2, the polymer fiber structure forming ability is evaluated according to the following criteria.

(Polymer fiber structure forming ability)
A fiber structure having a diameter of 300 nm or less is observed.
A fiber structure with a diameter of 1000 nm or less is observed.
Δ: A fiber structure having a diameter of 1000 nm or less is observed in part.
X A fiber structure having a diameter of 1000 nm or less is hardly observed.

"Experimental example 9"
Polyethylene oxide (PEO) (MW: 900,000 Sigma-Aldrich) was used as the water-soluble polymer. 0.5 g of the water-soluble polymer was dissolved in distilled water to make a 100 mL solution, and then 0.5 g of titanium oxide particles (anatase type particle size distribution 5 μm or less 95% Wako Pure Chemical Industries) were suspended. 0.5 mL of this solution was taken into a sample tube and rapidly frozen by being immersed in liquid nitrogen for 1 minute. Next, the frozen product was set in a freeze dryer (Iwaki Glass FRD-82M) and dried under reduced pressure at a vacuum of 10 Pa for 3 hours to obtain a dried product of Experimental Example 9.
FIG. 12 shows an SEM photograph of the dried product of Experimental Example 9. The dried product of Experimental Example 9 had a structure in which fibers having a diameter of 500 nm or less gathered and were intertwined in a complicated manner, and it was observed that titanium oxide particles were bonded to the fiber surface.

(Composite fiber structure)
"Experimental example 10"
Polyethylene oxide (PEO) (MW: 900,000 Sigma-Aldrich) was used as the water-soluble polymer, and absorbent cotton as a fibrous substrate was used as the holding substrate.
A water-soluble polymer 0.5 g was dissolved in distilled water to make a 100 mL solution. Next, after 0.5 mL of this solution was soaked in absorbent cotton, it was put in a sample tube and rapidly frozen by being immersed in liquid nitrogen for 1 minute. The frozen product was set in a freeze dryer (Iwaki Glass FRD-82M) and dried under reduced pressure at a vacuum degree of 10 Pa for 3 hours to obtain a composite fiber structure of Experimental Example 10.
FIG. 13 shows an SEM photograph of the composite fiber structure of Experimental Example 10. In the composite fiber structure of Experimental Example 10, it was observed that a fiber structure having a diameter of approximately 200 nm was mixed between the absorbent cotton fibers.

  The polymer fiber structure of the present invention can be applied to various uses such as a functional filter.

Claims (14)

  A polymer fiber structure formed of water-soluble polymer fibers having a diameter of 1000 nm or less.   The polymer fiber structure according to claim 1, wherein the water-soluble polymer fiber comprises one or more water-soluble polymers selected from polyethylene oxide, schizophyllan, polyvinyl pyrrolidone, guar gum, and xanthan gum.   The polymer fiber structure according to claim 1 or 2, wherein the water-soluble polymer fiber has a diameter of 300 nm or less.   The polymer fiber structure according to any one of claims 1 to 3, wherein the thermal conductivity is 0.05 W / (m · K) or less.   The polymer fiber structure according to any one of claims 1 to 4, wherein the porosity is 99% by volume or more.   The polymer fiber structure according to any one of claims 1 to 5, wherein a shape of the polymer fiber structure is a sheet.   The polymer fiber structure according to any one of claims 1 to 6, comprising catalyst particles supported on the water-soluble polymer fiber.   A composite fiber structure comprising the polymer fiber structure according to claim 1 and a holding substrate.   The composite fiber structure according to claim 8, wherein the holding substrate is a porous body. Dissolving a water-soluble polymer in an aqueous solvent at a concentration that does not cause gelation to form a polymer solution;
Rapid freezing the polymer solution to obtain a frozen product;
A reduced-pressure drying step of depressurizing the frozen material and distilling off the solvent at a pressure of 2.0 Pa or more and 100 Pa or less to obtain a dried product.   The method for producing a polymer fiber structure according to claim 10, wherein the water-soluble polymer is at least one selected from polyethylene oxide, schizophyllan, polyvinyl pyrrolidone, guar gum, and xanthan gum.   The method for producing a polymer fiber structure according to claim 10 or 11, wherein the concentration of the water-soluble polymer in the solution is 0.1 to 4.5% by weight.   The method for producing a polymer fiber structure according to any one of claims 10 to 12, wherein the frozen material is obtained by quenching with liquid nitrogen.   The method for producing a polymer fiber structure according to any one of claims 10 to 13, wherein the polymer solution contains catalyst particles or catalyst particle precursors.