Nanofibers, nonwoven fabrics and composites

Abstract

To provide a novel material capable of constituting an electrolyte membrane, and a nonwoven fabric and a composite constructed using the material.SOLUTION: There is provided a nanofiber. The nanofiber comprises a cross-linked site formed by reaction (I) between polyvinyl alcohol and a polyfunctional compound having a group capable of reacting with a hydroxyl group and capable of reacting with two or more hydroxyl groups in one molecule. The reaction (I) is a reaction between a hydroxyl group in the polyvinyl alcohol and a group capable of reacting with the hydroxyl group in the polyfunctional compound. There are also provided a nonwoven fabric comprising the nanofiber, and a composite comprising the nanofiber and a component other than the nanofibers.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to nanofibers, nonwoven fabrics, and composites. [Background technology]

[0002] Composite membranes, which are constructed by incorporating various substances into nonwoven fabrics, have been studied in various fields, and in recent years have attracted attention as electrolyte membranes in polymer electrolyte fuel cells. Fuel cells have the advantage of being highly environmentally adaptable, since the only component generated during power generation is water, and they are being put to practical use, primarily as a power source for automobiles and the like.

[0003] Various polymer electrolyte membranes have been studied as electrolyte membranes for polymer electrolyte fuel cells, and a polymer electrolyte membrane made of sulfonated polyimide has been proposed as having high thermal stability, mechanical strength, and excellent membrane formability (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-358978 Summary of the Invention [Problem to be solved by the invention]

[0005] However, fuel cells remain expensive, and further improvements in output and durability are required. To address this, the development of a new electrolyte membrane that is different from conventional ones is desired.

[0006] An object of the present invention is to provide a novel material that can be used to form an electrolyte membrane, as well as a nonwoven fabric and a composite that are formed using the material. [Means for solving the problem]

[0007] The present invention employs the following configuration. [1] A nanofiber having crosslinked sites formed by a reaction (I) between polyvinyl alcohol and a polyfunctional compound having a group capable of reacting with a hydroxyl group and capable of reacting with two or more hydroxyl groups in one molecule, wherein the reaction (I) is a reaction between a hydroxyl group in the polyvinyl alcohol and a group in the polyfunctional compound capable of reacting with a hydroxyl group. [2] The nanofiber according to [1], wherein the polyfunctional compound has, in one molecule, one or more groups that can react with the hydroxyl group, selected from the group consisting of a group represented by the formula "-B(OH)2", a formyl group, a carboxy group, a carbonyloxycarbonyl group, an alkoxysilyl group, and a phosphoryl group. [3] The nanofiber according to [1] or [2], wherein the polyfunctional compound is one or more selected from the group consisting of 1,4-phenylenediboronic acid, 1,3-phenylenediboronic acid, 1,3,5-benzenetrisboronic acid, 2,5-thiophenediboronic acid, 4,4'-biphenyldiboronic acid, formaldehyde, glutaraldehyde, citric acid, maleic anhydride, tetraethoxysilane, phosphoric acid, phosphorus oxychloride, and sodium trimetaphosphate.

[0008] [4] The nanofiber according to any one of [1] to [3], wherein the nanofiber has a modified site formed by reaction (II) between the polyvinyl alcohol and a modifying compound having one or more groups in one molecule that can react with a hydroxyl group and one or more groups in one molecule that can react with or interact with an acidic group, and the reaction (II) is a reaction between a hydroxyl group in the polyvinyl alcohol and a group in the modifying compound that can react with the hydroxyl group. [5] The group capable of reacting or interacting with the acidic group is represented by the general formula "-NH p (R 1 ) 2-p (In the formula, R 1 is a hydrocarbon group; and p is 1 or 2.)”, a group represented by the formula “-N=”, or a carboxy group. [6] The nanofiber according to [4] or [5], wherein the modifying compound is one or more selected from the group consisting of 4-aminophenylboronic acid, 3-aminophenylboronic acid, 2-aminophenylboronic acid, 4-pyridylboronic acid, 3-pyridylboronic acid, 2-pyridylboronic acid, 4-carboxyphenylboronic acid, 3-carboxyphenylboronic acid, and 2-carboxyphenylboronic acid. [7] The nanofiber according to any one of [1] to [6], further comprising an acidic polymer. [8] The nanofiber according to [7], wherein the acidic polymer has a sulfo group or a phosphono group.

[0009] [9] A nonwoven fabric comprising the nanofiber according to any one of [1] to [8].

[10] A composite comprising the nanofiber according to any one of [1] to [8] and a component other than the nanofiber.

[11] The composite according to

[10] , wherein the component other than the nanofiber is an acidic compound.

[12] The complex according to

[11] , wherein the acidic compound has a sulfo group, a phosphono group, or a phosphate group.

[13] The composite according to any one of

[10] to

[12] , wherein the composite is a nonwoven fabric.

[14] The composite according to any one of

[10] to

[12] , wherein the composite is an electrolyte membrane.

[15] The composite according to any one of

[10] to

[12] , which is for use in a fuel cell. [Effects of the Invention]

[0010] According to the present invention, there are provided a novel material that can be used to form an electrolyte membrane, as well as a nonwoven fabric and a composite that are made using the material. [Brief explanation of the drawings]

[0011] [Figure 1] 1 shows SEM image data of a nonwoven fabric made of nanofibers having no crosslinked sites, obtained in Example 1. [Figure 2] 1 shows SEM image data of a nonwoven fabric made of nanofibers obtained in Example 1. [Figure 3] 1 shows infrared absorption spectrum data for a nonwoven fabric made of nanofibers having no crosslinked sites, obtained in Example 1, and a nonwoven fabric made of nanofibers having crosslinked sites. [Figure 4] 1 shows SEM image data of a nonwoven fabric made of nanofibers obtained by further immersing the nonwoven fabric made of nanofibers obtained in Example 1 in water and drying it. [Figure 5] FIG. 1 shows infrared absorption spectrum data for a nonwoven fabric made of nanofibers having crosslinked sites but no modified sites, obtained in Example 1, and a nonwoven fabric made of nanofibers having crosslinked sites and modified sites, obtained in Example 4. [Figure 6] 1 shows spectral data obtained in Example 4 from elemental analysis of a nonwoven fabric made of nanofibers having crosslinked sites and modified sites by energy dispersive X-ray spectroscopy. [Figure 7] 1H NMR spectrum data of the sulfonated polyimide (α), which is an acidic compound, produced in Example 5. [Figure 8] 1 shows spectral data obtained in Example 5 from elemental analysis by energy dispersive X-ray spectroscopy of a nonwoven fabric made of nanofibers having crosslinked sites and modified sites. [Figure 9] 1H NMR spectrum data of the sulfonated polyimide (β), which is an acidic compound, produced in Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0012] <<Nanofiber>> A nanofiber according to one embodiment of the present invention has crosslinked sites formed by reaction (I) between polyvinyl alcohol (sometimes referred to as "PVA" in this specification) and a polyfunctional compound (sometimes simply referred to as "polyfunctional compound" in this specification) that has groups reactive with hydroxyl groups and can react with two or more hydroxyl groups in one molecule, and reaction (I) is a reaction between hydroxyl groups in the polyvinyl alcohol and groups reactive with hydroxyl groups in the polyfunctional compound. The nanofibers of this embodiment contain a component derived from PVA, which is a reaction product of the reaction (I) between PVA and the polyfunctional compound. In this specification, such a component derived from PVA formed by the reaction between hydroxyl groups in PVA and groups in the polyfunctional compound that can react with the hydroxyl groups may be simply referred to as a "PVA-derived component." The nanofiber of this embodiment has a structure in which PVA molecules are crosslinked by the polyfunctional compound at the hydroxyl groups in the PVA, and more specifically, has two or more bonds between an oxygen atom that constituted a hydroxyl group in the PVA and any atom that constituted a group in the polyfunctional compound that can react with the hydroxyl group.

[0013] PVA, which is the raw material for producing the nanofiber of this embodiment, is water-soluble, but the nanofiber of this embodiment is a crosslinked nanofiber having the crosslinking site described above, and can be made insoluble in both water and organic solvents. The nanofibers of this embodiment can also easily retain components that do not fall into either PVA or the PVA-derived components, and can be used as proton-conducting materials by retaining, for example, an acidic compound to form a composite, as described below. Such composites are suitable for use as electrolyte membranes, and can be used as electrolyte membranes for fuel cells.

[0014] The nanofibers contain a reaction product (the PVA-derived component) resulting from the reaction (I) between PVA and the polyfunctional compound, in other words, they contain PVA having the crosslinking sites. More specifically, examples of the PVA-derived component include intramolecular crosslinked compounds in which one or more of the crosslinked sites (i.e., intramolecular crosslinked sites) are formed in one molecule of PVA; intermolecular crosslinked compounds in which one or more of the crosslinked sites (i.e., intermolecular crosslinked sites) are formed between two or three or more molecules of PVA; and intramolecular / intermolecular crosslinked compounds having both the intramolecular crosslinked site and the intermolecular crosslinked site.

[0015] In the reaction (I) (when the PVA-derived component is produced), the number of hydroxyl groups in the PVA that react with one group in the polyfunctional compound that is reactive with a hydroxyl group is determined appropriately depending on the type of the group that is reactive with a hydroxyl group. For example, when the group that is reactive with a hydroxyl group is a group represented by the formula "-B(OH)2", the number of hydroxyl groups in the PVA that react with one group is two.

[0016] Whether the reactant is an intramolecular crosslinked compound, an intermolecular crosslinked compound, or an intramolecular / intermolecular crosslinked compound, the reactant may have one or more crosslinked sites formed by the reaction of two hydroxyl groups present in close proximity in PVA with one of the groups (groups reactive with hydroxyl groups) in one molecule of the polyfunctional compound, and by the reaction of two other hydroxyl groups present in close proximity in PVA with another group (group reactive with hydroxyl groups) in the polyfunctional compound. Here, examples of "two hydroxyl groups present in close proximity in PVA" include two hydroxyl groups bonded to two adjacent carbon atoms in PVA with a methylene group (-CH-) sandwiched between them.

[0017] The fiber diameter of the nanofiber having a crosslinked site is preferably 0.05 to 0.8 μm, and may be, for example, 0.1 to 0.4 μm. Such nanofibers have good properties and are easy to produce.

[0018] Regardless of the presence or absence of the crosslinked sites, the fiber diameter of the nanofiber (e.g., the fiber diameter of a nanofiber having the crosslinked sites, or the fiber diameter of an uncrosslinked nanofiber described below) can be determined by, for example, observing the nanofiber to be measured using a scanning electron microscope (SEM) or the like, measuring the diameters of any 20 nanofibers in the acquired imaging data, and using the resulting measurement results as the numerical range. Alternatively, the average of these measured values may be used as the fiber diameter of the nanofiber. Here, the nanofiber diameter refers to the actual measured value in the acquired imaging data.

[0019] The fiber diameter of the nanofiber having the crosslinked moiety can be adjusted, for example, by adjusting the spinning conditions when spinning the raw material for producing the nanofiber (for example, composition (i) described below), the dynamic viscosity of the raw material, etc.

[0020] <PVA(ポリビニルアルコール)> In this embodiment, the PVA (polyvinyl alcohol, saponified polyvinyl acetate) is not particularly limited.

[0021] In terms of availability and suitability for use of PVA, the degree of saponification of PVA is preferably 50 to 99%, more preferably 60 to 99%, further preferably 70 to 99%, and particularly preferably 75 to 90%.

[0022] In terms of availability and suitability for use of PVA, the weight average molecular weight of PVA is preferably 6,000 to 190,000, more preferably 30,000 to 190,000, and even more preferably 80,000 to 190,000.

[0023] In this specification, unless otherwise specified, the term "weight average molecular weight" refers to a polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0024] In the nanofibers, for example, only one type of PVA having the same degree of saponification may be crosslinked, or two or more types of PVA having different degrees of saponification may be crosslinked. In the nanofibers, for example, only one type of PVA having the same weight-average molecular weight may be crosslinked, or two or more types of PVA having different weight-average molecular weights may be crosslinked. When two or more types of PVA having different degrees of saponification or weight-average molecular weights are crosslinked, the combination and ratio of these two or more types of PVA can be selected arbitrarily depending on the purpose.

[0025] <Polyfunctional compounds> In this embodiment, the polyfunctional compound is not particularly limited as long as it has a group capable of reacting with a hydroxyl group and one molecule of the polyfunctional compound is capable of reacting with two or more hydroxyl groups. The polyfunctional compound may have only one group capable of reacting with a hydroxyl group in one molecule, or may have two or more groups capable of reacting with a hydroxyl group.

[0026] The polyfunctional compound is preferably an organic compound. The polyfunctional organic compound may be either an aliphatic compound or an aromatic compound.

[0027] The polyfunctional aliphatic compound may be either a saturated aliphatic compound or an unsaturated aliphatic compound. The polyfunctional compound, which is an aliphatic compound, may be either a chain aliphatic compound or a cyclic aliphatic compound, and in the case of a cyclic aliphatic compound, it may be either a monocyclic aliphatic compound or a polycyclic aliphatic compound. In this specification, an aliphatic compound having only a chain structure and no cyclic structure is a chain aliphatic compound, and an aliphatic compound having a cyclic structure, regardless of whether it has a chain structure or not, is a cyclic aliphatic compound.

[0028] The polyfunctional aromatic compound may be either a monocyclic aromatic compound or a polycyclic aromatic compound, and may be either an aromatic hydrocarbon or an aromatic heterocyclic compound.

[0029] The aromatic heterocyclic compound is not particularly limited as long as it has one or more atoms other than carbon atoms (i.e., heteroatoms) as atoms constituting the ring skeleton of the aromatic ring (in other words, it has an aromatic heterocyclic ring). Examples of the aromatic heterocyclic compound include a sulfur-containing aromatic heterocyclic compound having a sulfur atom as the heteroatom, an oxygen-containing aromatic heterocyclic compound having an oxygen atom as the heteroatom, and a nitrogen-containing aromatic heterocyclic compound having a nitrogen atom as the heteroatom.

[0030] Examples of the aromatic compounds include benzene derivatives, naphthalene derivatives, and thiophene derivatives. In this specification, when a specific compound is assumed to have a structure in which one or more hydrogen atoms are substituted with groups other than hydrogen atoms, the compound having such a substituted structure is referred to as a "derivative" of the specific compound. For example, 1,4-phenylenediboronic acid, which will be described later, is a benzene derivative. In this specification, unless otherwise specified, the term "group" includes not only an atomic group having a structure in which multiple atoms are bonded, but also a single atom.

[0031] The group capable of reacting with a hydroxyl group contained in the polyfunctional compound is not particularly limited.

[0032] Examples of the group capable of reacting with a hydroxyl group contained in the polyfunctional compound include a group represented by the formula "-B(OH)2", a formyl group (-C(=O)-H), a carboxy group (-C(=O)-OH), a carbonyloxycarbonyl group (-C(=O)-OC(=O)-), an alkoxysilyl group (monoalkoxysilyl group, dialkoxysilyl group, trialkoxysilyl group), and a phosphoryl group (>P(=O)-).

[0033] The upper limit of the number of groups capable of reacting with a hydroxyl group contained in one molecule of the polyfunctional compound is not particularly limited. In terms of the availability and ease of production of the polyfunctional compound, the number is preferably 1 to 4, more preferably 1 to 3, and may be 1 or 2, for example.

[0034] When the polyfunctional compound has two or more groups capable of reacting with a hydroxyl group in one molecule, these two or more groups capable of reacting with a hydroxyl group may all be the same, all may be different, or only some may be the same. In terms of easier preparation or availability of the polyfunctional compound, it is preferable that at least some of the two or more groups capable of reacting with a hydroxyl group are the same, and it is more preferable that all of them are the same.

[0035] When the polyfunctional compound has two or more groups capable of reacting with a hydroxyl group in one molecule, it is preferable that the bonding positions of at least two of the groups capable of reacting with a hydroxyl group are different from each other, and the bonding positions of all of the groups capable of reacting with a hydroxyl group may be different from each other. By using such a polyfunctional compound, the nanofibers can be more easily obtained.

[0036] As the polyfunctional compound having a formyl group, a carboxy group, a carbonyloxycarbonyl group, an alkoxysilyl group, or a phosphoryl group as a group capable of reacting with a hydroxyl group, for example, a known crosslinking agent for crosslinking a polymer having a hydroxyl group may be used.

[0037] Examples of the polyfunctional compound having a formyl group as a group capable of reacting with a hydroxyl group include aldehydes such as formaldehyde and glutaraldehyde (formaldehyde, an aldehyde having two or more formyl groups in one molecule). Examples of the polyfunctional compound having a carboxy group as a group capable of reacting with a hydroxyl group include polycarboxylic acids (carboxylic acids having two or more carboxy groups in one molecule) such as citric acid. Examples of the polyfunctional compound having a carbonyloxycarbonyl group as a group capable of reacting with a hydroxyl group include carboxylic acid anhydrides such as maleic anhydride. Examples of the polyfunctional compound having an alkoxysilyl group as a group capable of reacting with a hydroxyl group include alkoxysilanes (dialkoxysilanes, trialkoxysilanes) such as tetraethoxysilane. Examples of the polyfunctional compound having a phosphoryl group as a group capable of reacting with a hydroxyl group include compounds capable of forming a phosphate ester, such as phosphoric acid, phosphorus oxychloride, and sodium trimetaphosphate.

[0038] By using the polyfunctional compound having two or more groups represented by the formula "-B(OH)2" in one molecule, PVA can be crosslinked without using an acid catalyst or heating, unlike when using conventional crosslinking agents for crosslinking polymers having hydroxyl groups.

[0039] Preferred examples of the polyfunctional compound having two or more groups represented by the formula "-B(OH)2" in one molecule include 1,4-phenylenediboronic acid, 1,3-phenylenediboronic acid, 1,3,5-benzenetrisboronic acid, 2,5-thiophenediboronic acid, and 4,4'-biphenyldiboronic acid, as shown below.

[0040] [ka]

[0041] The polyfunctional compounds exemplified here, which have a group represented by the formula "-B(OH)2", may have a substituent. The polyfunctional compound having a substituent means that one or more hydrogen atoms in the polyfunctional compound that do not constitute a hydroxyl group are substituted with a group other than a hydrogen atom.

[0042] In the polyfunctional compound, when two or more hydrogen atoms are substituted, the substituents may all be the same, all be different, or only some may be the same. In the polyfunctional compound, the substitution position of the hydrogen atom is not particularly limited.

[0043] Examples of the substituent include an alkyl group, an alkoxy group, a substituted alkyl group having a structure in which two or more non-adjacent methylene groups (-CH-) in an alkyl group are replaced with oxygen atoms (-O-), an amino group, a cyano group, and a halogen atom (such as a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom).

[0044] The alkyl group in the substituent may be linear, branched, or cyclic.

[0045] The number of carbon atoms in the linear or branched alkyl group is not particularly limited, but is preferably 1 to 12. Examples of such linear or branched alkyl groups include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a 1-methylbutyl group, an n-hexyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 2,2-dimethylbutyl group, a 2,3-dimethylbutyl group, an n-heptyl group, a 2-methylhexyl group, a 3-methylhexyl group, a 2,2-dimethylpentyl group, a 2,3-dimethylpentyl group, a 2,4-dimethylpentyl group, a 3,3-dimethylpentyl group, a 3-ethylpentyl group, a 2,2,3-trimethylbutyl group, an n-octyl group, an isooctyl group, a nonyl group, a decyl group, an undecyl group, and a dodecyl group. The linear or branched alkyl group may have, for example, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms.

[0046] The cyclic alkyl group may be either monocyclic or polycyclic. The number of carbon atoms in the cyclic alkyl group is not particularly limited as long as it is 3 or more, but 3 to 12 is preferable. Examples of the cyclic alkyl group include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclononyl group, a cyclodecyl group, a norbornyl group, an isobornyl group, a 1-adamantyl group, a 2-adamantyl group, and a tricyclodecyl group. The cyclic alkyl group may have, for example, 3 to 10 carbon atoms, 3 to 8 carbon atoms, or 3 to 6 carbon atoms.

[0047] The alkyl group may have a mixture of a linear or branched chain structure and a cyclic structure. Examples of the alkyl group having a mixture of a chain structure and a cyclic structure include groups having a structure in which one or more hydrogen atoms in the above-mentioned linear or branched alkyl group are substituted with the above-mentioned cyclic alkyl group, such as a cyclopentylmethyl group, a 1-cyclopentylethyl group, a cyclohexylmethyl group, and a 1-cyclohexylethyl group; and groups having a structure in which one or more hydrogen atoms in the above-mentioned cyclic alkyl group are substituted with the above-mentioned linear or branched alkyl group, such as a methylcyclopentyl group, an ethylcyclopentyl group, a methylcyclohexyl group, an ethylcyclohexyl group, and a dimethylcyclohexyl group. The number of carbon atoms in the alkyl group having a mixture of a chain structure and a cyclic structure is not particularly limited as long as it is 4 or more, but is preferably 4 to 24.

[0048] Examples of the alkoxy group in the substituent include a monovalent group having a structure in which the above-mentioned alkyl group is bonded to an oxygen atom, such as a methoxy group, an ethoxy group, a cyclopropyloxy group, a cyclopentylmethyloxy group, and a methylcyclopentyloxy group. The alkoxy group preferably has 1 to 24 carbon atoms.

[0049] The substituted alkyl group in the substituent includes a group having a structure in which two or more non-adjacent methylene groups in the alkyl group are substituted with oxygen atoms. The number of methylene groups substituted with oxygen atoms is not particularly limited and is determined depending on the number of carbon atoms in the alkyl group before being substituted with oxygen atoms, but is preferably 2 to 6, and may be, for example, either 2 to 4 or 2 to 3.

[0050] In the nanofiber, the polyfunctional compound crosslinking the PVA may be one type or two or more types, and when two or more types are used, the combination and ratio thereof can be selected arbitrarily depending on the purpose. In terms of facilitating the production of the nanofibers, it is preferable that only one type of polyfunctional compound crosslinks the PVA in the nanofibers.

[0051] The polyfunctional compound preferably has, in one molecule, one or more groups capable of reacting with a hydroxyl group selected from the group consisting of a group represented by the formula "-B(OH)2", a formyl group, a carboxy group, a carbonyloxycarbonyl group, an alkoxysilyl group, and a phosphoryl group.

[0052] The polyfunctional compound is preferably one or more selected from the group consisting of 1,4-phenylenediboronic acid, 1,3-phenylenediboronic acid, 1,3,5-benzenetrisboronic acid, 2,5-thiophenediboronic acid, 4,4'-biphenyldiboronic acid, formaldehyde, glutaraldehyde, citric acid, maleic anhydride, tetraethoxysilane, phosphoric acid, phosphorus oxychloride, and sodium trimetaphosphate.

[0053] The nanofiber may have a modified site formed by reaction (II) between PVA and a modifying compound having one or more groups per molecule capable of reacting with a hydroxyl group and one or more groups per molecule capable of reacting with or interacting with an acidic group, in which case reaction (II) is a reaction between the hydroxyl group in the PVA and the group in the modifying compound capable of reacting with the hydroxyl group. Such nanofibers have one or more bonds between the oxygen atom that constituted the hydroxyl group in the PVA and any atom that constituted the group capable of reacting with the hydroxyl group in the modifying compound.

[0054] At the modification site, the group capable of reacting with the acidic group derived from the modifying compound remains unreacted, and the group capable of interacting with the acidic group does not interact with the acidic group. Therefore, the nanofiber having the modification site can further form a complex through a reaction or interaction between the group capable of reacting with or interacting with the acidic group and the acidic group in the acidic compound having the acidic group. As used herein, "a group capable of interacting with an acidic group" refers to a group that can retain the acidic compound by interacting with the acidic group. Examples of such interactions include interactions through the formation of hydrogen bonds. In such a complex, the acidic compound is retained in the nanofiber through the above reaction or interaction, and this structure is stably maintained. The acidic compound will be described in more detail below.

[0055] When the modifying compound has two or more groups capable of reacting with hydroxyl groups in one molecule, the modifying compound may form the crosslinked moiety by reacting with PVA, as in the case of the polyfunctional compound. However, in this embodiment, such a modifying compound is not considered to be a polyfunctional compound. When the modifying compound has only one group capable of reacting with a hydroxyl group in one molecule, the modifying compound does not form the crosslinking site.

[0056] Examples of the group capable of reacting with a hydroxyl group that the modifying compound has include the same groups as the group capable of reacting with a hydroxyl group that the polyfunctional compound has.

[0057] In terms of making it easier to form the modified site and obtaining nanofibers with better properties, it is more preferable that the modifying compound is an aromatic compound having one or more groups represented by the formula "-B(OH)2" per molecule as groups capable of reacting with hydroxyl groups.

[0058] The group capable of reacting with or interacting with an acidic group that the modifying compound has is not particularly limited, but may be a group represented by the general formula "-NH p (R 1 ) 2-p (In the formula, R 1 is a hydrocarbon group; and p is 1 or 2. Preferably, the modified compound is a group represented by the formula "-N=", a group represented by the formula "-N=", or a carboxy group (-C(=O)-OH). By using such a modifying compound, the nanofibers retaining the acidic compound can be obtained more stably. Furthermore, when the group capable of reacting with or interacting with an acidic group is itself an acidic group, such as the carboxy group, even if it does not react with or interact with the acidic group in the nanofiber, it can be easily reacted with a proton (H + ) is advantageous in that it exhibits transportability.

[0059] The general formula “-NH p (R 1 ) 2-p " is an amino group or a group in which one hydrogen atom is substituted with the R 1 is a mono-substituted amino group having a structure substituted with General formula “-NH p (R 1 ) 2-p A modifying compound having a group represented by the formula "" readily reacts with the acidic group at said group.

[0060] R 1 A preferred example of the hydrocarbon group in the formula (I) is an alkyl group. R 1Examples of the alkyl group in the above formula (I) include the same alkyl groups as those used as the substituent in the polyfunctional compound.

[0061] The group represented by the formula "-N=" may be present in either the chain skeleton or the cyclic skeleton, and may be in resonance with another group bonded to this group (-N=). For example, examples of the modifying compound in which a group represented by the formula "-N=" is present in the cyclic skeleton include pyridine derivatives. A modifying compound having a group represented by the formula "-N=" readily reacts with the acidic group at said group.

[0062] A modifying compound having a carboxy group readily reacts with the acidic group at the carboxy group. Examples of such reactions include a reaction to form an acid anhydride. For example, when the acidic group is a carboxy group, the carboxy group in the modifying compound and the carboxy group in the acidic compound can form a carboxylic acid anhydride.

[0063] The upper limit of the number of groups capable of reacting with or interacting with an acidic group that one molecule of the modifying compound has is not particularly limited. In terms of the availability and ease of production of the modified compound, the number is preferably 1 to 3, and more preferably 1 or 2.

[0064] When the modifying compound has two or more groups capable of reacting with or interacting with an acidic group, the two or more groups capable of reacting with an acidic group that the modifying compound has may all be the same, all be different, or only some may be the same. From the viewpoint of easier preparation or availability of the modified compound, it is preferable that at least some of the two or more groups capable of reacting with an acidic group are the same, and it is more preferable that all of them are the same.

[0065] In the modifying compound, the bonding position of the group capable of reacting with or interacting with an acidic group is not particularly limited.

[0066] For example, when a modifying compound has two or more groups capable of reacting with or interacting with an acidic group, it is preferable that the bonding positions of at least two of the groups capable of reacting with an acidic group are different from each other, and the bonding positions of all of the groups capable of reacting with an acidic group may be different from each other. By using such a modifying compound, the effects of using the modifying compound can be more easily obtained.

[0067] In the modified compound, the bonding position of the group capable of reacting with or interacting with an acidic group and the bonding position of the group capable of reacting with a hydroxyl group are preferably different from each other. By using such a modified compound, the effects of using the modified compound can be more easily obtained.

[0068] In the nanofiber, the modifying compound forming the modification site (in other words, the chemical structure of the modification site) may be of only one type, or may be of two or more types, and if there are two or more types, the combination and ratio thereof can be selected arbitrarily depending on the purpose. In terms of facilitating production of the nanofiber, it is preferable that the modifying site in the nanofiber be formed by only one type of modifying compound.

[0069] It is more preferable that the modifying compound is one or more selected from the group consisting of 4-aminophenylboronic acid, 3-aminophenylboronic acid, 2-aminophenylboronic acid, 4-pyridylboronic acid, 3-pyridylboronic acid, 2-pyridylboronic acid, 4-carboxyphenylboronic acid, 3-carboxyphenylboronic acid, and 2-carboxyphenylboronic acid.

[0070] [ka]

[0071] The modified compounds exemplified here may have a substituent. The modified compound having a substituent means that one or more hydrogen atoms that do not fall into any of the hydrogen atoms constituting a hydroxyl group, the hydrogen atoms constituting an amino group, and the hydrogen atoms constituting a carboxy group in the modified compound are substituted with a group other than a hydrogen atom.

[0072] In the modified compound, when two or more hydrogen atoms are substituted, the substituents may all be the same, all be different, or only some may be the same. In the modified compound, the substitution position of the hydrogen atom is not particularly limited.

[0073] Examples of the substituent in the modifying compound include the same as the substituent in the polyfunctional compound.

[0074] The nanofibers may contain only the PVA-derived component having the crosslinking moiety and optionally having the modified moiety (they may consist of the PVA-derived component), or may further contain another polymer that does not fall under the category of the PVA-derived component. That is, the nanofibers may have a nanofiber structure that includes the PVA-derived component having the crosslinking moiety and optionally having the modified moiety, and the other polymer. The nanofibers that contain such other polymers can exhibit new effects derived from the other polymers. In this specification, the "PVA (polyvinyl alcohol)-derived component which has the crosslinked moiety and may optionally have the modified moiety" contained in the nanofiber may be simply referred to as the "PVA (polyvinyl alcohol)-derived component."

[0075] The other polymers can be selected arbitrarily depending on the purpose and are not particularly limited. The other polymer contained in the nanofiber may be one type only, or two or more types. When there are two or more types, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0076] A preferred example of the other polymer is an acidic polymer. That is, a preferred example of the nanofiber is one further containing an acidic polymer. The nanofiber containing such an acidic polymer (a nanofiber structure formed by containing a PVA-derived component and an acidic polymer) can, for example, generate protons (H + ) and is particularly suitable as an internal proton transporting nanofiber capable of transporting protons, and is particularly suitable for forming an electrolyte membrane.

[0077] The acidic polymer is not particularly limited as long as it is a polymer having an acidic group. Examples of the acidic group include a sulfo group (-SO3H), a phosphono group (-P(=O)(OH)2), a phosphate group (-OP(=O)(OH)2), and a carboxy group (-COOH). The acidic group contained in one molecule of the acidic polymer may be of only one type or of two or more types, and when there are two or more types, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0078] The acidic polymer having a sulfo group is preferably polysulfonic acid. Preferred commercially available polysulfonic acids include, for example, Nafion (registered trademark), which is a perfluoroalkylsulfonic acid polymer (polysulfonic acid having a perfluoroalkylsulfo group). The acidic polymer having a phosphono group is preferably a polyphosphonic acid. Preferably, the acidic polymer having phosphate groups is polyphosphoric acid. The acidic polymer having a carboxy group is preferably a polycarboxylic acid.

[0079] The acidic polymer preferably has a sulfo group or a phosphono group, since it is easily available and can form nanofibers with better properties.

[0080] The molecular weight of the acidic polymer is preferably 10,000 to 1,000,000, and the molecular weight distribution of the acidic polymer is preferably 1-20.

[0081] When the nanofiber contains the other polymer, the ratio of the content of the other polymer to the content of the PVA-derived component in the nanofiber ([content of the other polymer in the nanofiber (parts by mass)] / [content of the PVA-derived component in the nanofiber (parts by mass)] × 100) is preferably 10% by mass or more. When this ratio is equal to or greater than the lower limit, the effect obtained by including the other polymer in the nanofiber is further enhanced.

[0082] When the nanofiber contains the other polymer, the upper limit of the ratio of the content of the other polymer to the content of the PVA-derived component in the nanofiber is not particularly limited. For example, when the ratio is 80 mass % or less, the effect obtained by containing the PVA-derived component in the nanofiber is further enhanced.

[0083] In the nanofibers, the ratio of the total content of the PVA-derived component and other polymers to the total mass of the nanofibers (([content of the PVA-derived component in the nanofibers (parts by mass)] + [content of the other polymers in the nanofibers (parts by mass)]) / [total mass of the nanofibers (parts by mass)] × 100) is preferably 90% by mass or more, and may be, for example, 95% by mass or more, 97% by mass or more, or 99% by mass or more. Nanofibers having this ratio equal to or greater than the lower limit exhibit better properties in their intended applications, such as electrolyte membranes described below. On the other hand, the proportion is 100% by mass or less.

[0084] <<Nanofiber manufacturing method>> The nanofibers can be produced by a production method (sometimes referred to herein as "production method (1)") that includes the steps of: spinning a composition (sometimes referred to herein as "composition (i)") that contains PVA and a solvent but does not contain the polyfunctional compound to produce uncrosslinked nanofibers that contain PVA and do not have the crosslinking moieties (sometimes referred to herein simply as "step (a1)"); and contacting the uncrosslinked nanofibers with a solution containing the polyfunctional compound to produce nanofibers that contain the PVA-derived component and have the crosslinking moieties (sometimes referred to herein simply as "step (a2)"). Note that production method (1) is just one example of a method for producing the nanofibers.

[0085] In this specification, unless otherwise specified, the term "nanofiber" refers to the nanofiber of this embodiment that has the crosslinked moiety and may or may not further have the modified moiety. The term "uncrosslinked nanofiber" refers to the nanofiber that does not have the crosslinked moiety.

[0086] <Manufacturing method (1)> In the production method (1), the composition (i) contains a PVA and a solvent, and may contain, as necessary, other components that do not fall into any of the categories of PVA, solvent, and the polyfunctional compound. The other components are not particularly limited and can be selected arbitrarily depending on the purpose. Examples of the other component include the modifying compound and the other polymer. For example, by using the modifying compound as the other component, the nanofiber having the modified site can be produced. Furthermore, by using the other polymer (e.g., an acidic polymer) as the other component, a nanofiber structure including PVA and the other polymer can be produced.

[0087] The solvent is preferably one that can dissolve PVA, and is, for example, preferably water or a mixed solvent of water and a solvent other than water. The solvent other than water is preferably a polar organic solvent (an organic solvent with high polarity). Examples of the polar organic solvent include alcohols such as methanol, ethanol, 1-propanol, and 2-propanol; amides such as N,N-dimethylformamide (DMF) and N,N-dimethylacetamide; sulfoxides such as dimethyl sulfoxide (DMSO); and ketones such as acetone, methyl ethyl ketone (MEK), and cyclohexanone.

[0088] In composition (i), the PVA, solvent, and other components may each be one type only, or two or more types, and when two or more types are used, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0089] In the production method (1), the composition (i) can be prepared by blending PVA, a solvent, and, if necessary, the other components. In preparing composition (i), the PVA, the solvent, and the other components may be mixed with the target substance either individually or as a mixture, such as a solution or dispersion of any of the components other than the solvent.

[0090] Composition (i) is preferably prepared, for example, by mixing a solution containing PVA (aqueous solution or organic solvent solution) with, as needed, the other component(s) alone or a mixture containing the other component(s). When the other component is the modifying compound, the mixture containing the modifying compound is preferably a solution (aqueous solution or organic solvent solution) containing the modifying compound.

[0091] The concentration of PVA in the solution containing PVA (the ratio of the content (parts by mass) of PVA to the mass of the solution containing PVA) is preferably 5 to 15% by mass. The concentration of the modifying compound in the solution containing the modifying compound (the ratio of the content (parts by mass) of the modifying compound to the mass of the solution containing the modifying compound) is preferably 5 to 30 mM.

[0092] When the other polymer is used, the ratio of the amount (parts by mass) of the other polymer to the amount (parts by mass) of PVA in composition (i) ([amount (parts by mass) of the other polymer in composition (i)] / [amount (parts by mass) of the PVA in composition (i)]×100) is preferably 5 to 50% by mass. When this ratio is equal to or greater than the lower limit, the effect obtained by the inclusion of the other polymer in the nanofiber is enhanced. When this ratio is equal to or less than the upper limit, the effect obtained by the inclusion of the PVA-derived component in the nanofiber is enhanced.

[0093] The kinematic viscosity of the composition (i) is 3 to 18 cm 2 / s (300 to 1800 cSt) is preferable, and 3 to 11 cm 2 / s (300 to 1100 cSt). Composition (i) having such a kinematic viscosity is particularly suitable for spinning by the electrospinning method described below. When the kinematic viscosity is equal to or greater than the lower limit, the effect of suppressing the generation of bead-shaped nanofibers in the obtained nanofibers is enhanced. When the kinematic viscosity is equal to or less than the upper limit, composition (i) can be discharged from the discharge port of the spinning device without dripping, and nanofibers with a more uniform composition and shape can be obtained.

[0094] When preparing composition (i), it is preferred to mix all the components and then stir the resulting mixture. The temperature of the mixture during stirring (mixing temperature) is preferably 20 to 70°C. The stirring time (blending time) is preferably 5 to 30 hours.

[0095] In the step (a1) of the production method (1), the composition (i) can be spun by a known method. The composition (i) is preferably spun, for example, by an electrospinning method. When spinning by electrospinning, the discharge rate (in other words, the flow rate) of composition (i) is preferably 2 to 5 μL / min (0.12 to 0.3 mL / h), and the applied voltage is preferably 10 to 20 kV.

[0096] The nanofibers obtained in step (a1) of production method (1) contain PVA but do not have the crosslinking sites formed by the polyfunctional compound (uncrosslinked nanofibers). The uncrosslinked nanofibers are soluble in both water and organic solvents.

[0097] The fiber diameter of the uncrosslinked nanofibers is preferably 0.05 to 0.8 μm, and may be, for example, 0.1 to 0.4 μm. Such uncrosslinked nanofibers can be easily produced, and further, nanofibers having the crosslinked moieties and having good properties can be produced. The method for measuring the fiber diameter of the uncrosslinked nanofibers is as described above.

[0098] The fiber diameter of the uncrosslinked nanofibers can be adjusted, for example, by adjusting the spinning conditions of composition (i), the dynamic viscosity of composition (i), and the like.

[0099] In step (a2) of the production method (1), the solution to be brought into contact with the uncrosslinked nanofibers contains the polyfunctional compound and a solvent, and may contain other components that do not fall under either the polyfunctional compound or the solvent. The other components are not particularly limited and can be selected arbitrarily depending on the purpose, and examples thereof include the components described above as components of composition (i) (the modifying compound, the other polymer, etc.). For example, by using the modifying compound as the other component, the nanofiber having the modified site can be produced.

[0100] The other component in step (a2) may also be an acid. For example, when an aldehyde or the like is used as the polyfunctional compound, the crosslinked moiety may be more easily formed by using the acid in combination. In this case, the acid may act as a catalyst in the reaction (I) between PVA and the polyfunctional compound.

[0101] Examples of the acid include inorganic acids such as hydrochloric acid and sulfuric acid.

[0102] The solvent in the solution used in step (a2) is not particularly limited as long as it can dissolve the polyfunctional compound. Examples of the solvent include the solvents described above as components of composition (i).

[0103] In the solution used in step (a2), the polyfunctional compound, the solvent, and the other components may each be one type only, or two or more types, and when two or more types are used, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0104] In step (a2), the solution can be prepared by mixing a polyfunctional compound, a solvent, and, if necessary, the other components. In preparing the solution, the polyfunctional compound, the solvent, and the other components may be mixed with the target substance individually or as a mixture with the target substance. The mixture may be, for example, a solution or dispersion of any of the components other than the solvent.

[0105] The concentration of the polyfunctional compound in the solution (a solution containing the polyfunctional compound, a solvent, and, if necessary, the other components) is preferably 0.5 to 200 mM, more preferably 0.5 to 100 mM.

[0106] In step (a2), when the modifying compound is used as the other component, the concentration of the modifying compound in the solution (the ratio of the content (parts by mass) of the modifying compound to the mass of the solution containing the modifying compound) is preferably 5 to 30 mM.

[0107] When the acid is used in step (a2), the amount of the acid used is preferably a catalytic amount, for example, 0.01 to 0.1 times by mass relative to the amount of the polyfunctional compound used.

[0108] The uncrosslinked nanofibers can be brought into contact with the solution containing the polyfunctional compound by, for example, immersing the uncrosslinked nanofibers in the solution containing the polyfunctional compound.

[0109] When the uncrosslinked nanofibers are brought into contact with the solution containing the polyfunctional compound, the temperature of the solution is preferably 15 to 35°C. During the contact, the contact time is preferably 15 to 120 minutes.

[0110] In step (a2), after the uncrosslinked nanofibers are contacted with the solution containing the polyfunctional compound, the nanofibers are dried to obtain the desired nanofibers having the crosslinked moieties. These nanofibers having the crosslinked moieties are typically insoluble in both water and organic solvents, unlike the uncrosslinked nanofibers.

[0111] The production method (1) may include a step other than step (a1) or step (a2) as long as the effect of the present invention is not impaired. The type, number of times and timing of the other steps can be adjusted as desired depending on the purpose. An example of the other step is step (b3) of contacting the nanofibers having the crosslinking moieties obtained in step (a2) with a solution containing the modifying compound to produce nanofibers containing a PVA-derived component and having the crosslinking moieties and modifying moieties. The use of a modifying compound allows the production of the nanofibers having the modifying moieties.

[0112] The solution containing the modifying compound used in the step (b3) includes, for example, those described above.

[0113] In step (b3), the contact of the nanofibers having the crosslinking moieties with the solution containing the modifying compound can be carried out, for example, by immersing the nanofibers having the crosslinking moieties in the solution containing the modifying compound.

[0114] When the nanofibers having the crosslinking moieties are brought into contact with the solution containing the modifying compound, the temperature of the solution is preferably 15 to 35°C. During the contact, the contact time is preferably 15 to 120 minutes.

[0115] In step (b3), after the nanofibers having the crosslinking moieties are contacted with the solution containing the modifying compound, the nanofibers are dried to obtain the desired nanofibers having the crosslinking moieties and modifying moieties.

[0116] When producing nanofibers having the crosslinked moieties and modified moieties, it is preferable to carry out step (a1) using composition (i) that does not contain the modifying compound, carry out step (a2) using a solution containing the polyfunctional compound and the modifying compound, and not carry out step (b3). In this way, by using the modifying compound only in step (a2), nanofibers having the crosslinked moieties and modified moieties with better properties can be obtained by the simplified production method (1).

[0117] <<Nonwoven fabric and its manufacturing method>> A nonwoven fabric according to one embodiment of the present invention includes the nanofibers according to one embodiment of the present invention described above. The nonwoven fabric of this embodiment can be, for example, a nonwoven fabric of the nanofibers (made of the nanofibers), and can be produced by forming a nonwoven fabric simultaneously when producing nanofibers containing PVA by spinning. For example, the nonwoven fabric can be obtained by discharging a solution containing PVA (such as the above-mentioned composition (i)) to be used for spinning, and discharging the solution so as to form a nonwoven fabric during spinning. The nonwoven fabric of this embodiment may be the same as the nanofiber according to one embodiment of the present invention described above, except that the shape is specified as a nonwoven fabric.

[0118] Furthermore, the nonwoven fabric can easily retain components that are neither PVA nor components derived from PVA, making it suitable for forming an electrolyte membrane.

[0119] The porosity of the nonwoven fabric made of the nanofibers is not particularly limited and can be set arbitrarily depending on the purpose. The porosity is preferably 65 to 95%, and more preferably 75 to 90%. When the porosity is equal to or greater than the lower limit, the properties of the nonwoven fabric are improved. For example, components other than nanofibers can be contained (retained) in larger amounts in the voids of the nonwoven fabric. When the porosity is equal to or less than the upper limit, the strength of the nonwoven fabric is increased.

[0120] The porosity of the nonwoven fabric made of the nanofibers can be adjusted, for example, by producing nanofibers containing PVA or a component derived from PVA by spinning and adjusting the spinning conditions when forming the nonwoven fabric.

[0121] The thickness of the nonwoven fabric is not particularly limited and can be set arbitrarily depending on the purpose. The thickness of the nonwoven fabric is, for example, preferably 5 to 50 μm, and more preferably 5 to 25 μm. When the thickness of the nonwoven fabric is equal to or greater than the lower limit, the strength of the nonwoven fabric is increased. Furthermore, components other than the nanofibers can be contained (retained) in larger amounts in the voids of the nonwoven fabric. When the thickness of the nonwoven fabric is equal to or less than the upper limit, the production of the nonwoven fabric is facilitated.

[0122] <<Composite and its manufacturing method>> A composite according to one embodiment of the present invention contains the nanofiber according to one embodiment of the present invention described above and a component other than the nanofiber. The composite can easily hold components other than the nanofibers, and is suitable for forming an electrolyte membrane.

[0123] The composite may be a nonwoven fabric, that is, the composite may be in the form of a nonwoven fabric, including a nonwoven fabric made of the nanofibers and a component other than the nanofibers.

[0124] The components other than the nanofibers can be selected arbitrarily depending on the purpose and are not particularly limited. The component other than the nanofibers contained in the composite may be one type only, or two or more types. When there are two or more types, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0125] In the composite, the ratio of the content (parts by mass) of components other than the nanofibers to the content (parts by mass) of the nanofibers ([content (parts by mass) of components other than the nanofibers in the composite] / [content (parts by mass) of the nanofibers in the composite]×100) can be adjusted appropriately depending on the type of components other than the nanofibers, but is preferably, for example, 60 to 98% by mass. When the ratio is equal to or greater than the lower limit, the effect obtained by including components other than the nanofibers in the composite is enhanced. When the ratio is equal to or less than the upper limit, excessive use of components other than the nanofibers is suppressed.

[0126] The component other than the nanofiber is preferably an acidic compound. That is, a preferred example of the composite is one containing the nanofiber having the crosslinked site and the acidic compound. In such a composite, the acidic compound is held on the surface of the nanofiber. In such a composite, for example, protons (H + ) and is particularly suitable as a surface proton transport nanofiber capable of transporting protons, and is particularly suitable for forming an electrolyte membrane.

[0127] The acidic compound is not particularly limited as long as it has an acidic group. The acidic compound may be a compound having only one acidic group in one molecule, but is preferably a compound having two or more acidic groups in one molecule.

[0128] Examples of the acidic group include a sulfo group (-SO3H), a phosphono group (-P(=O)(OH)2), a phosphate group (-OP(=O)(OH)2), and a carboxy group (-COOH).

[0129] When an acidic compound has two or more acidic groups in one molecule, the acidic group in one molecule of the acidic compound may be one type or two or more types, and when there are two or more types, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0130] Examples of low molecular weight acidic compounds (acidic non-polymer compounds) include phytic acid. Examples of high-molecular-weight acidic compounds (acidic polymers) include the same acidic polymers as those listed as the compounds that may be contained in the nanofibers. The molecular weight of the acidic polymer is preferably 10,000 to 1,000,000, and the molecular weight distribution of the acidic polymer is preferably 1 to 20.

[0131] The acidic compound contained in the complex preferably has a sulfo group, a phosphono group, or a phosphate group, and more preferably is phytic acid, polysulfonic acid, polyphosphonic acid, or polyphosphoric acid.

[0132] A preferred example of the composite is a composite containing a nanofiber having the modification site and the acidic compound. In such a preferred composite, a reaction or interaction may occur between a group in the modification site that can react with or interact with an acidic group and an acidic group in the acidic compound. One or more of the acidic compounds contained in such a preferred composite can be selected depending on the purpose. An example of such a preferred complex is a complex comprising a nanofiber having the modified site and the acidic compound, wherein the acidic compound is held on the nanofiber by reaction or interaction between a group in the modified site that can react with or interact with an acidic group and an acidic group in the acidic compound, and the acidic compound is one or more selected from the group consisting of phytic acid, polysulfonic acid, polyphosphonic acid, and polyphosphoric acid, and the nanofiber may be a nonwoven fabric.

[0133] In such a preferred composite (a composite containing a nanofiber having the modified moiety and the acidic compound), the nanofiber having the modified moiety may form a nonwoven fabric. In such a preferred composite, the nanofiber may further contain an acidic polymer, and one or more types of the polymer contained in such a nanofiber can be selected according to the purpose.

[0134] In the composite containing the nanofiber having the modification moiety and the acidic compound, the ratio of the content (parts by mass) of the acidic compound to the content (parts by mass) of the nanofiber ([content (parts by mass) of the acidic compound in the composite] / [content (parts by mass) of the nanofiber in the composite]×100) is preferably 1 to 10% by mass, more preferably 4 to 8% by mass. When this ratio is equal to or greater than the lower limit, the effect obtained by the composite containing the acidic compound is enhanced. When this ratio is equal to or less than the upper limit, excessive use of the acidic compound is suppressed.

[0135] A preferred example of the composite is a composite containing the nonwoven fabric made of the nanofiber and the acidic compound. In such a preferred composite, the nanofiber may or may not have the modified site in addition to the crosslinked site. In such a preferred composite, the acidic compound may be filled in the voids of the nonwoven fabric, or the acidic compound may be an acidic polymer that fills the voids of the nonwoven fabric and functions as a matrix polymer. In this specification, the term "matrix polymer" refers to a polymer that is held in the nonwoven fabric and contributes to improving the structural stability of the nonwoven fabric. One or more types of acidic compounds may be selected depending on the purpose.

[0136] The acidic compound contained in the composite together with the nanofiber nonwoven fabric may be, for example, the same as the acidic compounds (acidic non-polymer compounds, acidic polymers) described above. The molecular weight of the acidic polymer is preferably 10,000 to 1,000,000, and the molecular weight distribution of the acidic polymer is preferably 1 to 20.

[0137] An example of such a preferred composite (a composite comprising the nonwoven fabric made of nanofibers and the acidic compound) is a composite comprising the nonwoven fabric made of nanofibers and the acidic compound, wherein the acidic compound is filled in the voids of the nonwoven fabric, and the acidic compound is one or more selected from the group consisting of polysulfonic acid, polyphosphonic acid, polyphosphoric acid, and polycarboxylic acid.

[0138] In such a preferred composite (a composite comprising a nonwoven fabric made of the nanofibers and the acidic compound), the nanofibers may have the modified site, and the acidic compound may be held on the nanofibers through a reaction or interaction between a group in the modified site that can react with or interact with an acidic group and the acidic group in the acidic compound. In such a preferred composite, one or more types of acidic compounds may be selected as the acidic compound held on the nanofibers depending on the purpose. In such a preferred composite, the nanofiber may further contain an acidic polymer, and one or more types of the polymer contained in such a nanofiber can be selected according to the purpose.

[0139] Among these, a more preferred example of the composite is a composite comprising a nonwoven fabric made of the nanofibers having the crosslinked sites and the modified sites, and the acidic compound (sometimes referred to herein as a "first acidic compound" to distinguish it from the "second acidic compound" described below), in which the first acidic compound is held on the nanofibers by a reaction or interaction between a group in the modified site that can react with or interact with an acidic group and the acidic group in the first acidic compound, and further, the acidic compound (sometimes referred to herein as a "second acidic compound") fills the voids in the nonwoven fabric. Such more preferred composites are superior in terms of higher proton conductivity. In such a more preferred complex, the first acidic compound and the second acidic compound may be the same or different from each other.

[0140] An example of such a more preferred composite is a composite comprising a nonwoven fabric made of the nanofibers having the crosslinked sites and modified sites, and the first acidic compound, wherein the first acidic compound is held on the nanofibers by a reaction or interaction between a group in the modified site that can react with or interact with an acidic group and the acidic group in the first acidic compound, the first acidic compound being one or more selected from the group consisting of phytic acid, polysulfonic acid, polyphosphonic acid, and polyphosphoric acid, and a second acidic compound is filled in the voids of the nonwoven fabric, and the second acidic compound is one or more selected from the group consisting of polysulfonic acid, polyphosphonic acid, polyphosphoric acid, and polycarboxylic acid.

[0141] Such a more preferred composite can be produced, for example, by preparing a first composite comprising a nonwoven fabric made of the nanofibers having the crosslinked sites and modified sites, and the first acidic compound, in which the first acidic compound is held in the nanofibers through a reaction or interaction between a group in the modified site that is reactive or interactive with an acidic group and an acidic group in the first acidic compound, and further filling the voids in the nonwoven fabric in the first composite with the second acidic compound.

[0142] Among these, particularly preferred examples of the composite include a nonwoven fabric made of the nanofibers having the crosslinked moieties and the modified moieties, and the first acidic compound (when the first acidic compound is an acidic polymer, this acidic polymer may be referred to herein as a "first acidic polymer" to distinguish it from other acidic polymers), in which the first acidic compound is held in the nanofibers by a reaction or interaction between a group in the modified moiety that can react with or interact with an acidic group and the acidic group in the first acidic compound, the nanofibers further contain an acidic polymer (when necessary, this may be referred to herein as a "third acidic polymer" to distinguish it from other acidic polymers) in addition to the first acidic compound, and the voids in the nonwoven fabric are further filled with a second acidic compound (when the second acidic compound is an acidic polymer, this acidic polymer may be referred to herein as a "second acidic polymer" to distinguish it from other acidic polymers). Such a composite is excellent in that it has particularly high proton conductivity. In such particularly preferred conjugates, the first and second acidic compounds may be the same or different, and the third acidic polymer may be the same or different from the first or second acidic polymer.

[0143] An example of such a particularly preferred composite includes a nonwoven fabric made of the nanofibers having the crosslinked sites and the modified sites, and the first acidic compound (which may be a first acidic polymer), wherein the first acidic compound is held on the nanofibers by a reaction or interaction between a group in the modified site that can react with or interact with an acidic group and the acidic group in the first acidic compound, the first acidic compound being one or more selected from the group consisting of phytic acid, polysulfonic acid, polyphosphonic acid, and polyphosphoric acid, the nanofibers further containing an acidic polymer (third acidic polymer) in addition to the first acidic compound, the acidic polymer (third acidic polymer) being one or more selected from the group consisting of polysulfonic acid, polyphosphonic acid, and polyphosphoric acid, and further, a second acidic compound (which may be a second acidic polymer) filling voids in the nonwoven fabric, wherein the second acidic compound is one or more selected from the group consisting of polysulfonic acid, polyphosphonic acid, polyphosphoric acid, and polycarboxylic acid.

[0144] Such a particularly preferred composite can be produced, for example, by preparing a second composite comprising a nonwoven fabric made of the nanofibers having the crosslinked sites and modified sites, and the first acidic compound, in which the first acidic compound is held in the nanofibers by reaction or interaction between groups in the modified sites that can react with or interact with acidic groups and the acidic groups in the first acidic compound, and the nanofibers further containing an acidic polymer (third acidic polymer) in addition to the first acidic compound, and further filling the voids in the nonwoven fabric in the second composite with the second acidic compound.

[0145] In the composite containing the nonwoven fabric made of the nanofibers, which may or may not have the modified moieties, and the acidic compound, the ratio of the content (parts by mass) of the acidic compound to the content (parts by mass) of the nanofibers (nonwoven fabric) ([content (parts by mass) of the acidic compound in the composite] / [content (parts by mass) of the nanofibers (nonwoven fabric) in the composite] × 100) is preferably 300 to 1500% by mass. Here, the "content (parts by mass) of the acidic compound" refers to the amount (parts by mass) of the acidic compound filled in the voids of the nonwoven fabric when the nanofibers do not have the modified moieties. When the nanofibers have the modified moieties, the "content (parts by mass) of the acidic compound" refers to the total amount of the amount (parts by mass) of the acidic compound held at the modified moieties and the amount (parts by mass) of the acidic compound filled in the voids of the nonwoven fabric. When the ratio is equal to or greater than the lower limit, the effect obtained by containing the acidic compound in the composite is enhanced. When the ratio is equal to or less than the upper limit, the strength of the composite is enhanced.

[0146] A preferred example of the composite is an electrolyte membrane. The composite containing the nanofibers and the acidic compound has proton conductivity and can be used as a constituent material of an electrolyte membrane. As described above, the composite containing the nonwoven fabric made of the nanofibers and the acidic compound is particularly suitable as an electrolyte membrane.

[0147] The electrolyte membrane can be produced inexpensively, unlike, for example, conventional electrolyte membranes using fluorine-based polymers. The electrolyte membrane can retain any of a variety of acidic compounds at the modified sites in the nonwoven fabric (nanofiber). The voids in the nonwoven fabric can be filled with any of a variety of matrix polymers. The electrolyte membrane has such a configuration, resulting in higher proton conductivity. Furthermore, the electrolyte membrane can be made insoluble in both water and organic solvents, and has high membrane strength. The electrolyte membrane also has gas barrier properties.

[0148] The composite can be produced, for example, by contacting the nanofiber with components other than the nanofiber. The composite is preferably produced by contacting the nanofiber with a solution (aqueous solution or organic solvent solution) containing components other than the nanofiber. It is more preferable to produce the composite by immersing the nanofiber in a solution (aqueous solution or organic solvent solution) containing components other than the nanofiber, or by applying a solution (aqueous solution or organic solvent solution) containing components other than the nanofiber to the nanofiber. The solution can be applied to the nanofiber by, for example, a spraying method, a casting method, a stamping method, or an inkjet method.

[0149] The contact of the nanofibers with components other than the nanofibers can be carried out, for example, under a temperature condition of 15 to 35°C, or may be carried out at room temperature. When the nanofibers are immersed in a solution containing components other than the nanofibers, or when a solution containing components other than the nanofibers is placed on the nanofibers, the temperature of the solution is preferably 15 to 35°C. In this specification, "room temperature" means a temperature that is neither particularly cold nor hot, that is, an ordinary temperature, and examples thereof include temperatures of 15 to 25°C.

[0150] The contact time when the nanofibers are brought into contact with components other than the nanofibers is preferably 15 to 120 minutes.

[0151] When the nanofibers are brought into contact with a solution containing components other than the nanofibers, the nanofibers are dried after the contact to obtain the desired composite.

[0152] The composite is suitable for use in fuel cells, more specifically, for use in electrolyte membranes in fuel cells. A novel fuel cell (solid polymer electrolyte fuel cell) can be constructed by using the composite as an electrolyte membrane and otherwise configuring the fuel cell in the same manner as a known fuel cell equipped with a solid polymer electrolyte.

[0153] That is, an example of a fuel cell having the composite as an electrolyte membrane is a fuel cell having a fuel electrode (anode) and an air electrode (cathode), and an electrolyte membrane disposed between the fuel electrode and the air electrode, wherein the electrolyte membrane is the composite of the present embodiment described above. Both the fuel electrode and the air electrode can be made of carbon carrying a catalyst such as platinum.

[0154] As described above, the composite can be produced inexpensively, and therefore a fuel cell including the composite as an electrolyte membrane can be produced at a significantly lower cost than a conventional fuel cell in which the electrolyte membrane is made of an expensive material such as a perfluoroalkylsulfonic acid polymer. Furthermore, as described above, the composite can have high proton conductivity and membrane strength, and therefore a fuel cell including the composite as an electrolyte membrane can have superior cell performance compared to conventional fuel cells. [Example]

[0155] The present invention will be described in more detail below with reference to specific examples, although the present invention is not limited to the examples shown below.

[0156] In this specification, the concentration unit "M" represents "mol / L" and the concentration unit "mM" represents "mmol / L".

[0157] [Example 1] <<Manufacturing nonwoven fabric made from nanofibers>> PVA (manufactured by Aldrich, molecular weight 85,000 to 124,000, saponification degree 87 to 89%) was added to water in a vial at room temperature, stirred for 1 hour, and then stirred at 60°C for an additional 12 hours until the PVA was completely dissolved, resulting in a concentration of 8.5% by mass and a kinematic viscosity of 7.954 ± 0.269 cm. 2 An aqueous PVA solution (composition (i)) having a viscosity of 795.4±26.9 cSt was prepared.

[0158] A syringe filled with the PVA aqueous solution obtained above was prepared. Aluminum foil was placed on the collector of an electrospinning device ("ES-2000S" manufactured by Fuence), and the syringe was attached to the electrospinning device. Electrospinning was performed for 1 hour by setting the discharge rate of the PVA aqueous solution to 0.24 mL / h, setting the distance between the syringe and the collector to 8 cm, and applying a voltage of 13 kV to the syringe. As a result, nanofibers containing PVA but not having crosslinked sites (uncrosslinked nanofibers) were produced, and a nonwoven fabric consisting of these uncrosslinked nanofibers was produced on the aluminum foil. The obtained nonwoven fabric was stored in a desiccator at room temperature. This nonwoven fabric was soluble in water, N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO).

[0159] A portion of the nonwoven fabric obtained above was used and osmium-coated, and then observed using a scanning electron microscope (SEM, JEOL "JSM-6100") to obtain SEM image data at a magnification of 5000x. This image data is shown in Figure 1. From this image data, it was confirmed that uncrosslinked nanofibers were produced uniformly, and the fiber diameter of these uncrosslinked nanofibers was calculated to be 0.26±0.04 μm.

[0160] A piece measuring 5 cm x 5 cm was cut out from the nonwoven fabric made of uncrosslinked nanofibers obtained above. The sections were immersed in a 50 mL methanol solution of 5 mM 1,4-phenylenediboronic acid (Tokyo Chemical Industry Co., Ltd., product number P1358) at room temperature for 1 hour, then removed from the methanol solution, washed with methanol, and air-dried at room temperature. As a result of the above, a nonwoven fabric (piece) was produced from nanofibers containing PVA-derived components and having crosslinked sites formed by the reaction (I) between PVA and 1,4-phenylenediboronic acid.

[0161] A portion of this nonwoven fabric was osmium-coated and then observed using a scanning electron microscope (SEM, JEOL JSM-6100) to obtain SEM image data at 5000x magnification. Figure 2 shows the image data. The image data indicates that the nanofiber structure was maintained within the nonwoven fabric, and the desired nanofibers were produced. The fiber diameter of the nanofibers was calculated from the image scale to be 0.27 ± 0.03 μm. These results confirm that the immersion treatment with 1,4-phenylenediboronic acid (i.e., reaction (I)) does not affect the shape or fiber diameter of the preformed nanofibers.

[0162] The nonwoven fabric made of the nanofibers having the crosslinked moieties (nonwoven fabric after treatment with 1,4-phenylenediboronic acid) obtained above and the nonwoven fabric made of the uncrosslinked nanofibers (nanofibers before treatment with 1,4-phenylenediboronic acid) obtained above were subjected to infrared absorption spectrum measurement by Fourier transform infrared spectroscopy (FT-IR) using an attenuated total reflectance (ATR) method using a Fourier transform infrared spectrophotometer ("FT / IR-4600" manufactured by JASCO Corporation). The spectral data obtained at this time are shown in Figure 3.

[0163] As is clear from FIG. 3, in the spectrum data of the nonwoven fabric made of the nanofibers having the crosslinked sites, the peak of the B-O bending vibration is at a wave number of 1297 cm -1 At the same time, a peak due to the BO2 out-of-plane bending vibration characteristic of the boronic ester bond was observed at a wavenumber of 661 cm.-1 The peaks of the BO bending vibration and the BO out-of-plane bending vibration were not observed in the spectral data of the nonwoven fabric made of uncrosslinked nanofibers, so it was confirmed that by treating the nonwoven fabric made of uncrosslinked nanofibers with 1,4-phenylenediboronic acid (by the above reaction (I)), a boronate ester bond was indeed formed and the PVA was crosslinked by 1,4-phenylenediboronic acid.

[0164] <<Evaluation of nanofibers (nonwoven fabrics)>> <Water resistance evaluation> A 5 cm x 5 cm piece was cut out from the nonwoven fabric made of the nanofibers having crosslinked sites (nonwoven fabric after treatment with 1,4-phenylenediboronic acid) obtained above. The dry mass of this piece was measured and found to be 15.5 ± 0.2 mg. Next, the slice was immersed in water (50 mL) at room temperature for 24 hours, then dried, and its mass was measured to be 15.8±0.1 mg. As described above, almost no change in the mass of the nanofibers having the crosslinked sites was observed before and after immersion in water, which confirmed that the nanofibers having the crosslinked sites are stable and insoluble in water (water-insoluble) and have water resistance.

[0165] A portion of the above-mentioned water-soaked and dried section was used and osmium-coated before observation using a scanning electron microscope (SEM, JEOL JSM-6100) to obtain SEM image data at 5000x magnification. This image data is shown in Figure 4. This image data confirmed that the nanofiber structure was maintained within the nonwoven fabric. The nanofiber diameter was calculated from the image scale to be 0.26±0.07 μm, with almost no change observed in the fiber diameter before and after immersion in water. These results confirmed that immersion in water does not affect the shape or fiber diameter of the nanofibers having crosslinked sites.

[0166] <Evaluation of organic solvent resistance> A 5 cm x 5 cm piece was cut out from the nonwoven fabric made of the nanofibers having the crosslinked moieties (nonwoven fabric after treatment with 1,4-phenylenediboronic acid) obtained above. The dry mass of this piece was measured and found to be 17.3 ± 0.1 mg. Next, the slice was immersed in DMF (10 mL) at room temperature for 24 hours, and then dried. The mass was measured and found to be 17.1±0.1 mg. The same measurement was also performed when dimethyl sulfoxide was used. That is, a piece measuring 5 cm x 5 cm was cut from the nonwoven fabric made of the nanofibers having crosslinked sites, and the mass of the piece in a dry state was measured to be 16.3 ± 0.1 mg. Next, the slice was immersed in DMSO (10 mL) at room temperature for 24 hours, then dried, and its mass was measured to be 16.4±0.1 mg. Thus, whether DMF or DMSO was used, almost no change in the mass of the nanofibers having the crosslinked moieties was observed before and after immersion in these organic solvents. This confirmed that the nanofibers having the crosslinked moieties are stable and insoluble in these organic solvents (DMF and DMSO) and are resistant to organic solvents.

[0167] <Calculating the void ratio of nonwoven fabric> A 4 cm x 4 cm section was cut out from the nonwoven fabric made of the nanofibers having crosslinked sites (nonwoven fabric after treatment with 1,4-phenylenediboronic acid) obtained above. The apparent volume V of the section was calculated from the mass W of the section in a dry state and its thickness. The thickness of the section was measured using a stylus film thickness meter (Kett Corporation's "L-300"). The porosity of the nonwoven fabric was calculated using the specific gravity of PVA, 1.19, and the values of W and V according to the following formula, which was found to be 83%. Porosity of nonwoven fabric (%) = (1-(W / (V×1.19))×100

[0168] <Evaluation of hot water resistance> A 5 cm x 5 cm piece was cut out from the nonwoven fabric made of the nanofibers having the crosslinked moieties (nonwoven fabric after treatment with 1,4-phenylenediboronic acid) obtained above. The dry mass of this piece was measured and found to be 17.1 ± 0.1 mg. The slice was then immersed in water (50 mL) and allowed to stand for 24 hours in an environment at 90°C, thereby continuing to be immersed in hot water. The slice was then removed from the hot water, dried, and its mass was measured, which was 17.0±0.1 mg. As described above, almost no change in mass of the nanofibers having the crosslinked moieties was observed before and after immersion in hot water, confirming that the nanofibers having the crosslinked moieties are stable and insoluble in hot water and have hot water resistance.

[0169] <Evaluation of thermal stability> A test piece (1.01 mg) was cut from the nonwoven fabric (nonwoven fabric treated with 1,4-phenylenediboronic acid) made of the crosslinked nanofibers obtained above, and thermogravimetric analysis was performed on this test piece using a simultaneous differential scanning calorimeter (Hitachi "STA-7300"). More specifically, the test piece was placed in an aluminum pan and heated to 600°C at a heating rate of 20°C / min under a nitrogen gas flow. The 5% thermal decomposition temperature was 254°C, and the 10% thermal decomposition temperature was 280°C. In other words, the nonwoven fabric was usable even at temperatures above 150°C, confirming its excellent thermal stability.

[0170] <<Electrolyte membrane manufacturing>> A piece (0.012 g) measuring 4 cm x 4 cm and having a thickness of approximately 36 μm was cut out from the nonwoven fabric made of the nanofibers having the crosslinked sites obtained above (nonwoven fabric after treatment with 1,4-phenylenediboronic acid). The nonwoven fabric slice was placed in a polytetrafluoroethylene petri dish (diameter 6.15 cm), and 4.8 mL of Nafion® dispersion (Sigma-Aldrich, product number 274704, concentration 5% by mass) was cast into it at a mass ratio of [nonwoven fabric slice (parts by mass)] / [Nafion® (parts by mass)] of 10 / 138. Next, the solvent in the dish was slowly evaporated at 30°C under atmospheric pressure, and then the solvent was completely evaporated at 60°C. As a result of the above, an electrolyte membrane was obtained that contained a nonwoven fabric (piece) made of nanofibers containing a PVA-derived component and having the crosslinked sites formed by 1,4-phenylenediboronic acid, and a perfluoroalkylsulfonic acid-based polymer.

[0171] <<Evaluation of electrolyte membrane>> <Proton conductivity measurement> The electrolyte membrane obtained above was measured for frequency response in the range of 50 kHz to 5 MHz using an impedance analyzer (Hiki Corporation, "3532-50") to determine the resistance of the electrolyte membrane (electrode distance 1 cm). A thermo-hygrostat (ESPEC Corporation, "SH-221") was used to measure impedance under the following conditions: relative humidity in the measurement environment was 40% and 90%, and temperatures were 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, and 90°C. The resistance (Ω), electrode distance (cm), and cross-sectional area of the electrolyte membrane (cm) were then calculated. 2 ) and the proton conductivity (S / cm) was calculated according to the following formula. [Proton conductivity of electrolyte membrane (S / cm)] = [Electrode distance (cm)] / ([Cross-sectional area of electrolyte membrane (cm 2 )]×resistance[Ω]) As a result, under the conditions of relative humidity 40% and temperature 30°C, the proton conductivity was 9.7 × 10 -5 S / cm, and at a relative humidity of 40% and a temperature of 90°C, the proton conductivity is 1.3×10 -3 S / cm, and under the conditions of 90% relative humidity and 80°C temperature, the proton conductivity is 2.0×10 -2 It was S / cm. On the other hand, the proton conductivity (S / cm) of a membrane made of only perfluoroalkylsulfonic acid polymer, which does not contain the nanofibers, was calculated using the same method as above. As a result, under the conditions of a relative humidity of 40% and a temperature of 30°C, the proton conductivity was 8.5 × 10 -5 S / cm, and at a relative humidity of 40% and a temperature of 90°C, the proton conductivity is 1.7×10 -3 S / cm, and under conditions of 90% relative humidity and 80°C, the proton conductivity is 7.9×10 -2 It was S / cm. That is, the electrolyte membrane of the present embodiment obtained above had sufficient proton conductivity.

[0172] [Example 2] <<Manufacturing nonwoven fabric made from nanofibers>> Nanofibers containing PVA and having no crosslinked sites (uncrosslinked nanofibers) were prepared, and nonwoven fabrics made from these uncrosslinked nanofibers were also prepared using the same method as in Example 1. The obtained nonwoven fabrics were stored in a desiccator at room temperature.

[0173] A piece measuring 5 cm x 5 cm was cut out from the nonwoven fabric made of uncrosslinked nanofibers obtained above. The sections were immersed in a 10 mM solution of 1,3-phenylenediboronic acid (Wako Pure Chemical Industries, Ltd., product number 321-97891) in methanol (50 mL) at room temperature for 1 hour, then removed from the methanol solution, washed with methanol, and air-dried at room temperature. As a result of the above, multiple pieces of nonwoven fabric (slices) were produced, each made of nanofibers containing a PVA-derived component and having crosslinked sites formed by the reaction (I) between PVA and 1,3-phenylenediboronic acid.

[0174] <<Evaluation of nanofibers (nonwoven fabrics)>> <Water resistance evaluation> The mass of the nonwoven fabric made of the nanofibers having crosslinked sites obtained above (nonwoven fabric after treatment with 1,3-phenylenediboronic acid) in a dry state was measured and found to be 15.4±0.1 mg. Next, the nonwoven fabric was immersed in water (50 mL) at room temperature for 24 hours, and then dried. The mass was measured and found to be 15.8±0.1 mg. As described above, the mass of the nanofibers having the crosslinked moieties was almost unchanged before and after immersion in water, confirming that the nanofibers having the crosslinked moieties are stable and insoluble in water (water-insoluble) and have water resistance. 1,3-Phenylenediboronic acid crosslinked PVA, similar to the case of 1,4-phenylenediboronic acid.

[0175] <Evaluation of organic solvent resistance> The mass of the nonwoven fabric made of the nanofibers having crosslinked sites obtained above (nonwoven fabric after treatment with 1,3-phenylenediboronic acid) in a dry state was measured and found to be 15.7±0.1 mg. Next, the slice was immersed in DMF (10 mL) at room temperature for 24 hours, then dried, and its mass was measured to be 15.8±0.2 mg. The same measurement was also carried out when dimethyl sulfoxide was used. That is, the mass of the nonwoven fabric made of the nanofibers having crosslinked sites in a dry state was measured and found to be 14.2±0.3 mg. Next, the slice was immersed in DMSO (10 mL) at room temperature for 24 hours, and then dried. The mass was measured and found to be 14.1±0.1 mg. Thus, whether DMF or DMSO was used, almost no change in the mass of the nanofibers having the crosslinked moieties was observed before and after immersion in these organic solvents. This confirmed that the nanofibers having the crosslinked moieties are stable and insoluble in these organic solvents (DMF and DMSO) and are resistant to organic solvents.

[0176] [Example 3] <<Manufacturing nonwoven fabric made from nanofibers>> Nanofibers containing PVA and not having crosslinked sites (uncrosslinked nanofibers) were prepared in the same manner as in Example 1, and a nonwoven fabric made of these uncrosslinked nanofibers was prepared on the aluminum foil. The obtained nonwoven fabric was stored in a desiccator at room temperature.

[0177] A piece measuring 4.5 cm x 4.5 cm was cut out from the nonwoven fabric made of uncrosslinked nanofibers obtained above. The sections were immersed in a 6.7 mM solution of 1,3,5-benzenetrisboronic acid (Tokyo Chemical Industry Co., Ltd., product number T3515) in methanol (50 mL) at room temperature for 1 hour, then removed from the methanol solution, washed with methanol, and air-dried at room temperature. As a result of the above, a nonwoven fabric (piece) was produced from nanofibers containing PVA-derived components and having crosslinked sites formed by the reaction (I) between PVA and 1,3,5-benzenetrisboronic acid.

[0178] <<Evaluation of nanofibers (nonwoven fabrics)>> <Evaluation of hot water resistance> The mass of the nonwoven fabric made of the nanofibers having crosslinked sites obtained above in a dry state was measured and found to be 17.1±0.1 mg. The slice was then immersed in water (50 mL) and allowed to stand for 24 hours in an environment at 90°C, thereby continuing to be immersed in hot water. The slice was then removed from the hot water, dried, and its mass was measured, which was 17.0±0.1 mg. As described above, the mass of the nanofibers having the crosslinked moieties remained almost unchanged before and after immersion in hot water, confirming that the nanofibers having the crosslinked moieties were stable and insoluble in hot water and had hot water resistance. 1,3,5-Benzenetrisboronic acid crosslinked PVA, similar to the case of 1,4-phenylenediboronic acid.

[0179] [Example 4] <<Manufacturing nonwoven fabrics made from nanofibers with modified moieties>> Nanofibers containing PVA and having no crosslinked sites (uncrosslinked nanofibers) were prepared, and nonwoven fabrics made from these uncrosslinked nanofibers were also prepared using the same method as in Example 1. The obtained nonwoven fabrics were stored in a desiccator at room temperature.

[0180] A piece measuring 3 cm x 3 cm was cut out from the nonwoven fabric made of uncrosslinked nanofibers obtained above. The sections were immersed in a 50 mL methanol solution containing 20 mM 3-aminophenylboronic acid (Tokyo Chemical Industry Co., Ltd., product number A1281) and 1 mM 1,4-phenylenediboronic acid at room temperature for 1 hour, then removed from the methanol solution, washed with methanol, and air-dried at room temperature. As a result of the above, a nonwoven fabric (section) was produced consisting of nanofibers containing PVA-derived components, having crosslinked sites formed by the reaction (I) of PVA with 1,4-phenylenediboronic acid, and having modified sites formed by the reaction (II) of PVA with 3-aminophenylboronic acid.

[0181] The nonwoven fabric (section) made of nanofibers having the crosslinked moieties and modified moieties obtained above, and the nonwoven fabric made of nanofibers having the crosslinked moieties but not the modified moieties obtained in Example 1 were subjected to infrared absorption spectrum measurement by Fourier transform infrared spectroscopy (FT-IR) using an attenuated total reflectance (ATR) method using a Fourier transform infrared spectrophotometer ("FT / IR-4600" manufactured by JASCO Corporation). The spectral data obtained at this time are shown in Figure 5. Furthermore, elemental analysis of the nonwoven fabric obtained above was performed by energy dispersive X-ray spectroscopy using a scanning electron microscope. The spectral data obtained at this time are shown in Figure 6.

[0182] As is clear from FIG. 5, in the spectral data of the nonwoven fabric made of nanofibers having the crosslinked sites and modified sites, a peak at a wavenumber of 662 cm originating from the BO2 out-of-plane bending vibration characteristic of the boronic acid ester bond was observed. -1 and a peak characteristic of 3-aminophenylboronic acid was observed at wavenumber 706 cm -1 and 1585 cm -1 The peak of the NH out-of-plane bending (wagging vibration) is observed at wavenumber 761 cm -1 was observed. Furthermore, as is evident from FIG. 6, the data confirm the presence of nitrogen atoms. From these spectral data, it was confirmed that the PVA was indeed crosslinked when the nonwoven fabric made of the uncrosslinked nanofibers was treated with 1,4-phenylenediboronic acid (by the above reaction (I)), and that the PVA was indeed modified when the nonwoven fabric was treated with 3-aminophenylboronic acid (by the above reaction (II)).

[0183] <<Production of a composite containing a nonwoven fabric made of nanofibers having modified moieties and an acidic compound>> A glass petri dish was filled with 30 mL of phytic acid solution (Tokyo Chemical Industry Co., Ltd., product number P0409, concentration 50% by mass) at room temperature. The nonwoven fabric (section) made of the nanofibers having the crosslinked moieties and modified moieties obtained above was immersed in this phytic acid solution for 1 hour. The section was then removed from the phytic acid solution, washed with water at 80°C for 16 hours, and vacuum dried. As a result of the above, a composite was produced containing phytic acid and a nonwoven fabric (piece) made of nanofibers containing PVA-derived components, having crosslinked sites formed by the reaction (I) between PVA and 1,4-phenylenediboronic acid, and modified sites formed by the reaction (II) between PVA and 3-aminophenylboronic acid.

[0184] <<Electrolyte membrane manufacturing>> The composite (5.89 mg) obtained above was placed in a polytetrafluoroethylene Petri dish (diameter 6.15 cm), and 5.65 mL of Nafion® dispersion (Sigma-Aldrich, product number 274704, concentration 5% by mass) was cast into it, with the mass ratio of [composite (parts by mass)] / [Nafion® (parts by mass)] set to 0.086. Next, the solvent in the dish was slowly evaporated at 30°C under atmospheric pressure, and then the solvent was completely evaporated at 60°C. As a result of the above, an electrolyte membrane was obtained that contained a nonwoven fabric (piece) made of nanofibers containing a PVA-derived component and having the crosslinked site formed by 1,4-phenylenediboronic acid and the modified site formed by 3-aminophenylboronic acid, as well as phytic acid and a perfluoroalkylsulfonic acid-based polymer.

[0185] <<Evaluation of electrolyte membrane>> <Proton conductivity measurement> The proton conductivity (S / cm) of the electrolyte membrane obtained above was calculated in the same manner as in Example 1. As a result, under the conditions of relative humidity 40% and temperature 30°C, the proton conductivity was 7.9 × 10 -3 S / cm, and at a relative humidity of 40% and a temperature of 90°C, the proton conductivity is 2.5×10 -2 The proton conductivity was 0.19 S / cm under the conditions of 90% relative humidity and 80°C temperature. On the other hand, the proton conductivity (S / cm) of the membrane made of the nanofiber and perfluoroalkylsulfonic acid polymer alone, which does not contain phytic acid, was calculated using the same method as above. As a result, under the conditions of relative humidity 40% and temperature 30°C, the proton conductivity was 8.5 × 10 -5 S / cm, and at a relative humidity of 40% and a temperature of 90°C, the proton conductivity is 1.7×10 -3 S / cm, and under conditions of 90% relative humidity and 80°C, the proton conductivity is 7.9×10 -2 It was S / cm. That is, the electrolyte membrane of the present embodiment obtained above had sufficient proton conductivity.

[0186] [Example 5] <<Production of sulfonated polyimide (α)>> As shown in the following chemical reaction formula, a sulfonated polyimide (α) was produced as the acidic compound (acidic polymer). That is, under a nitrogen atmosphere, 2,2'-benzidinedisulfonic acid (BDSA) (1.9174 g, 5.6 mmol, 0.50 equivalents) (Tokyo Chemical Industry Co., Ltd., product number B0395), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (APPF) (2.8914 g, 5.6 mmol, 0.50 equivalents) (Wako Pure Chemical Industries, Ltd., product number PC1225), triethylamine (6.2 mL), and m-cresol (30 mL, 28 equivalents of NTDA described below) were placed in a 200 mL three-neck flask and stirred at room temperature for 1 hour, followed by stirring at 80°C for 3 hours. Next, naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTDA) (3.0181 g, 11.3 mmol, 1 equivalent) (Tokyo Chemical Industry Co., Ltd., Product No. N0755) was added and stirred at 120 °C for 24 hours to obtain polyamic acid. Next, benzoic acid (1.6430 g, 13.4 mmol, 1.2 equivalents) was added and stirred at 180 °C for 24 hours. The reaction solution was slowly added dropwise to ethyl acetate (1 L), and the ethyl acetate was exchanged again for thorough washing. The mixture was dried in vacuo at 150 °C for 15 hours to obtain 6.013 g (71% yield) of naphthalene-based sulfonated random copolyimide Nr-SPI(NTDA-BDSA-r-APPF, m:n = 5:5) (hereinafter sometimes referred to as "sulfonated polyimide (α)"). The synthesized product obtained above was analyzed by nuclear magnetic resonance spectroscopy ( 1Analysis was performed using H NMR (Bruker BioSpin KK, "AVANCE III 500"). The acquired spectral data is shown in Figure 7. The peaks and their integral ratios confirmed the formation of sulfonated polyimide (α). Furthermore, the molecular weight of the resulting compound was measured by gas permeation chromatography (GPC) using DMF as the solvent (detector: JASCO "RI-2031"; columns: Shodex "SB-806HQ" and "SB-804"). The number-average molecular weight (Mn) was 30,000, and the weight-average molecular weight (Mw) was 214,000.

[0187] [ka]

[0188] <<Manufacturing nonwoven fabrics made from nanofibers with modified moieties>> Nanofibers containing PVA and having no crosslinked sites (uncrosslinked nanofibers) were prepared, and nonwoven fabrics made from these uncrosslinked nanofibers were also prepared using the same method as in Example 1. The obtained nonwoven fabrics were stored in a desiccator at room temperature.

[0189] A piece measuring 2.5 cm x 2.5 cm was cut out from the nonwoven fabric made of uncrosslinked nanofibers obtained above. The sections were immersed in a 20 mL methanol solution containing 20 mM 3-pyridylboronic acid (Tokyo Chemical Industry Co., Ltd., product number P1673) and 20 mM 1,4-phenylenediboronic acid at room temperature for 1 hour, then removed from the methanol solution, washed with methanol, and air-dried at room temperature. As a result, a nonwoven fabric (section) was produced, which consisted of nanofibers containing PVA-derived components, crosslinked sites formed by the reaction (I) of PVA with 1,4-phenylenediboronic acid, and modified sites formed by the reaction (II) of PVA with 3-pyridylboronic acid. That is, this nonwoven fabric (section) was composed of nanofibers containing PVA with the crosslinked sites and modified sites.

[0190] The nonwoven fabric (section) made of the nanofibers having the crosslinked and modified sites obtained above was subjected to elemental analysis by energy dispersive X-ray spectroscopy using a scanning electron microscope (Phenom World, Phenom proX, product number PW-100-517). The spectral data obtained at this time is shown in Figure 8. The presence of nitrogen atoms was confirmed in this data, confirming the presence of modified sites formed by 3-pyridylboronic acid in the nanofibers in the nonwoven fabric obtained above.

[0191] <<Production of a composite containing a nonwoven fabric made of nanofibers having modified moieties and an acidic compound>> To a polyvinyl sulfonic acid solution (Polysciences, molecular weight 4000-6000) (8 g), 5 equivalents of hydrochloric acid (Kanto Chemical, product number 18078-00) (8 mL) were added, followed by distilled water (8 mL). This solution was added dropwise to acetone (400 mL) and stirred for 1 hour. The mixture was then filtered and vacuum dried at 60 °C for 10 hours to obtain acid-treated polyvinyl sulfonic acid (2.06 g). 0.15 g of this was taken and dissolved in water (15 mL) to prepare an aqueous solution of polyvinyl sulfonic acid with a concentration of 1% by mass. The polyvinyl sulfonic acid solution was added to a 50 mL vial at room temperature. The nonwoven fabric (section) made of the nanofibers having the crosslinked moieties and modified moieties obtained above was immersed in the polyvinyl sulfonic acid solution for 2 days. The section was then removed from the polyvinyl sulfonic acid solution, washed with water at 60°C for 3 hours, and then dried. As a result of the above, a composite was produced comprising a nonwoven fabric (piece) made of nanofibers containing PVA-derived components, having crosslinked sites formed by the reaction (I) between PVA and 1,4-phenylenediboronic acid, and modified sites formed by the reaction (II) between PVA and 3-pyridylboronic acid, and polyvinyl sulfonic acid.

[0192] <<Electrolyte membrane manufacturing>> Using the sulfonated polyimide (α) obtained above, a DMF solution with a concentration of 5% by mass was prepared. The composite (0.0051 g) obtained above was placed inside a polytetrafluoroethylene sheet (3.5 × 3.5 cm), and the DMF solution (1.03 mL) of sulfonated polyimide (α) was cast onto it, with the mass ratio of [composite (parts by mass)] / [sulfonated polyimide (α) (parts by mass)] set to 0.227. Next, the solvent in the sheet was slowly evaporated at 40°C under atmospheric pressure, and then the solvent was completely evaporated at 60°C. The membrane obtained by evaporating the solvent was immersed in 0.01 M hydrochloric acid (Kanto Chemical Co., Ltd., product number 18600-08) (15 mL) at room temperature for 3 hours, and then removed from the hydrochloric acid and thoroughly washed with distilled water at room temperature. As a result, an electrolyte membrane was obtained that included a nonwoven fabric (piece) made of nanofibers containing a PVA-derived component and having the crosslinked moieties formed by 1,4-phenylenediboronic acid and the modified moieties formed by 3-pyridylboronic acid, polyvinyl sulfonic acid, and sulfonated polyimide (α). That is, this electrolyte membrane was a composite composed of nanofibers containing PVA having the crosslinked moieties and modified moieties, polyvinyl sulfonic acid, and sulfonated polyimide (α).

[0193] <<Evaluation of electrolyte membrane>> <Proton conductivity measurement> The proton conductivity (S / cm) of the electrolyte membrane obtained above was calculated in the same manner as in Example 1. As a result, under the conditions of relative humidity 40% and temperature 90°C, the proton conductivity was 2.4 × 10 -5 S / cm, and under conditions of 90% relative humidity and 80°C, the proton conductivity is 4.1×10 -3 It was S / cm. On the other hand, the proton conductivity (S / cm) of a membrane made of sulfonated polyimide (α) alone, which does not contain the nanofibers or polyvinyl sulfonic acid, was calculated using the same method as above. As a result, under the conditions of a relative humidity of 40% and a temperature of 90°C, the proton conductivity was 1.6 × 10 -5 S / cm, and under the conditions of 90% relative humidity and 80°C temperature, the proton conductivity is 7.8×10 -4 It was S / cm. That is, the electrolyte membrane of the present embodiment obtained above had sufficient proton conductivity.

[0194] [Example 6] <<Production of nonwoven fabric made from nanofibers containing acidic polymers>> An aqueous PVA solution with a concentration of 10% by mass was prepared using PVA (manufactured by Aldrich, molecular weight 85,000 to 124,000, degree of saponification 87 to 89%). Using polyvinylphosphonic acid (manufactured by Polysciences, molecular weight 24000), an aqueous solution of polyvinylphosphonic acid with a concentration of 30% by mass was prepared. The PVA aqueous solution, the polyvinyl phosphonic acid aqueous solution, and water were mixed at room temperature to prepare a mixed aqueous solution (composition (i)). In this mixed aqueous solution, the mass ratio of [PVA content (parts by mass)] / [polyvinyl phosphonic acid content (parts by mass)] was 91 / 9. In addition, in this mixed aqueous solution, the ratio of the total content (parts by mass) of PVA and polyvinyl phosphonic acid to the total mass of the mixed aqueous solution was 9.4 mass%.

[0195] A syringe filled with the mixed aqueous solution obtained above was prepared. Aluminum foil was placed on the collector of an electrospinning device ("ES-2000S" manufactured by Fuence), and the syringe was attached to the electrospinning device. Electrospinning was performed for 1 hour by setting the discharge rate of the mixed aqueous solution to 0.24 mL / h, setting the distance between the syringe and the collector to 8 cm, and applying a voltage of 13 kV to the syringe. As a result, nanofibers containing PVA and polyvinylphosphonic acid but without crosslinking sites (uncrosslinked nanofibers) were produced, and nonwoven fabrics made of these uncrosslinked nanofibers were fabricated on the aluminum foil. The obtained nonwoven fabrics were stored in a desiccator at room temperature.

[0196] A piece measuring 4 cm x 3 cm was cut out from the nonwoven fabric made of uncrosslinked nanofibers containing PVA and polyvinylphosphonic acid obtained above. The sections were immersed in a 20 mM solution of 1,4-phenylenediboronic acid in methanol (15 mL) at room temperature for 1 hour, then removed from the methanol solution, washed with methanol, and air-dried at room temperature. As a result, a nonwoven fabric (section) was produced, which consisted of nanofibers containing a PVA-derived component and polyvinylphosphonic acid and having crosslinked sites formed by the reaction (I) between PVA and 1,4-phenylenediboronic acid. That is, this nonwoven fabric (section) was composed of nanofibers containing PVA with the crosslinked sites and polyvinylphosphonic acid.

[0197] <<Electrolyte membrane manufacturing>> The nonwoven fabric (piece) (0.017 g) made of nanofibers containing the PVA-derived component and polyvinylphosphonic acid and having the crosslinked moieties obtained above was placed in a polytetrafluoroethylene Petri dish (diameter 6.15 cm), and Nafion® dispersion (Sigma-Aldrich, product number 274704, concentration 5% by mass) (9.08 mL) was cast. At this time, the mass ratio of [nonwoven fabric (parts by mass)] / [Nafion® (parts by mass)] was 0.128. Next, the solvent in the dish was slowly evaporated at 30°C under atmospheric pressure, and then the solvent was completely evaporated at 60°C. As a result, an electrolyte membrane was obtained that contained a nonwoven fabric (piece) made of nanofibers containing a PVA-derived component and polyvinylphosphonic acid and having the crosslinked moieties formed by 1,4-phenylenediboronic acid, and a perfluoroalkylsulfonic acid-based polymer. That is, this electrolyte membrane was a composite composed of nanofibers containing PVA and polyvinylphosphonic acid having the crosslinked moieties, and a perfluoroalkylsulfonic acid-based polymer.

[0198] <<Evaluation of electrolyte membrane>> <Proton conductivity measurement> The proton conductivity (S / cm) of the electrolyte membrane obtained above was calculated in the same manner as in Example 1. As a result, under the conditions of relative humidity 40% and temperature 30°C, the proton conductivity was 1.7 × 10 -3 S / cm, and at a relative humidity of 40% and a temperature of 90°C, the proton conductivity is 7.4×10 -3 The proton conductivity was 0.12 S / cm under the conditions of 90% relative humidity and 80°C temperature. On the other hand, the proton conductivity (S / cm) of a membrane made of only perfluoroalkylsulfonic acid polymer, which does not contain the nanofibers and polyvinylphosphonic acid, was calculated using the same method as above. As a result, under the conditions of a relative humidity of 40% and a temperature of 30°C, the proton conductivity was 8.5 × 10 -5S / cm, and at a relative humidity of 40% and a temperature of 90°C, the proton conductivity is 1.7×10 -3 S / cm, and under conditions of 90% relative humidity and 80°C, the proton conductivity is 7.9×10 -2 It was S / cm. That is, the electrolyte membrane of the present embodiment obtained above had sufficient proton conductivity.

[0199] [Example 7] <<Production of sulfonated polyimide (β)>> As shown in the following chemical reaction formula, a sulfonated polyimide (β) was produced as the acidic compound (acidic polymer). That is, under a nitrogen atmosphere, 2,2'-benzidinedisulfonic acid (BDSA) (1.57 g, 4.56 mmol, 0.71 equivalents) (Tokyo Chemical Industry Co., Ltd., product number B0395), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (APPF) (1.04 g, 2.01 mmol, 0.31 equivalents) (Wako Pure Chemical Industries, Ltd., product number PC1225), triethylamine (5.0 mL), and m-cresol (17 mL, 28 equivalents of 6FDA below) were placed in a 100 mL three-neck flask and stirred at room temperature for 1 hour, followed by stirring at 80°C for 3 hours. Subsequently, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) (2.8717 g, 6.46 mmol, 1 equivalent) (Central Glass Co., Ltd.) was added and stirred at 150 °C for 24 hours to obtain polyamic acid. Next, benzoic acid (0.9597 g, 7.9 mmol, 1.2 equivalents) was added and stirred at 180 °C for 24 hours. This reaction solution was slowly added dropwise to ethyl acetate (500 mL), and the ethyl acetate was exchanged again for thorough washing. The mixture was then vacuum dried at 150 °C for 15 hours to obtain 3.364 g (57% yield) of sulfonated random copolyimide Fr-SPI (6FDA-APPF-r-BDSA, m:n = 7:3) (sometimes referred to herein as "sulfonated polyimide (β)"). The synthesized product obtained above was analyzed by nuclear magnetic resonance spectroscopy ( 1Analysis was performed using H NMR (Bruker BioSpin KK, "AVANCE III 500"). The spectral data obtained at this time are shown in Figure 9. The peaks and their integral ratios confirmed the formation of sulfonated polyimide (β). In addition, the molecular weight of the resulting compound was measured by gas permeation chromatography (GPC) using DMF as the solvent (detector: JASCO "RI-2031", column: Shodex "SB-806HQ" and "SB-804"), and the number-average molecular weight (Mn) was 186,000 and the weight-average molecular weight (Mw) was 469,000.

[0200] [ka]

[0201] <<Production of nonwoven fabric made from nanofibers containing acidic polymers>> PVA (manufactured by Aldrich, molecular weight 85,000 to 124,000, degree of saponification 87 to 89%) was added to water in a vial at room temperature, and the mixture was stirred at 60°C to dissolve the PVA, thereby preparing a PVA aqueous solution with a concentration of 10% by mass. Next, while stirring the aqueous PVA solution in the vial, the sulfonated polyimide (β) (0.125 g) obtained above was added to the aqueous PVA solution, and water (1.81 mL) was further added and stirred to prepare an aqueous solution containing PVA and the sulfonated polyimide (β) (composition (i)).

[0202] A syringe filled with the aqueous solution obtained above was prepared. Aluminum foil was placed on the collector of an electrospinning device ("ES-2000S" manufactured by Fuence), and the syringe was attached to the electrospinning device. Electrospinning was performed for 70 minutes by setting the discharge rate of the aqueous solution to 0.22 mL / h, setting the distance between the syringe and the collector to 10 cm, and applying a voltage of 20 kV to the syringe. As a result, nanofibers containing PVA and sulfonated polyimide (β) but without crosslinking sites (uncrosslinked nanofibers) were prepared, and a nonwoven fabric consisting of these uncrosslinked nanofibers was prepared on the aluminum foil. The obtained nonwoven fabric was stored in a desiccator at room temperature. This nonwoven fabric was soluble in water, DMF, and DMSO.

[0203] A piece measuring 5 cm x 5 cm was cut out from the nonwoven fabric made of uncrosslinked nanofibers containing PVA and sulfonated polyimide (β) obtained above. The sections were immersed in a 50 mM solution of 1,3-phenylenediboronic acid in methanol (20 mL) at room temperature for 1 hour, then removed from the methanol solution, washed with methanol, and air-dried at room temperature. As a result, a nonwoven fabric (piece) was produced, which consisted of nanofibers containing a PVA-derived component and a sulfonated polyimide (β) and having crosslinked sites formed by the reaction (I) between PVA and 1,3-phenylenediboronic acid. That is, this nonwoven fabric (piece) was composed of nanofibers containing PVA with the crosslinked sites and a sulfonated polyimide (β).

[0204] <<Electrolyte membrane manufacturing>> The nonwoven fabric (piece) (14.1 mg) made of nanofibers containing the PVA-derived component and sulfonated polyimide (β) and having the crosslinked moieties obtained above was placed inside a polytetrafluoroethylene Petri dish (diameter 6.15 cm), and Nafion® dispersion (Sigma-Aldrich, product number 274704, concentration 5% by mass) (5.88 mL) was cast. At this time, the mass ratio of [nonwoven fabric (parts by mass)] / [Nafion® (parts by mass)] was set to 0.145. Next, the solvent in the dish was slowly evaporated at 30°C under atmospheric pressure, and then the solvent was completely evaporated at 60°C. As a result, an electrolyte membrane was obtained that contained a nonwoven fabric (piece) made of nanofibers containing a PVA-derived component and a sulfonated polyimide (β) and having the crosslinked moieties formed by 1,3-phenylenediboronic acid, and a perfluoroalkylsulfonic acid-based polymer. That is, this electrolyte membrane was a composite composed of nanofibers containing PVA and a sulfonated polyimide (β) having the crosslinked moieties, and a perfluoroalkylsulfonic acid-based polymer.

[0205] <<Evaluation of electrolyte membrane>> <Proton conductivity measurement> The proton conductivity (S / cm) of the electrolyte membrane obtained above was calculated in the same manner as in Example 1. As a result, under the conditions of relative humidity 40% and temperature 30°C, the proton conductivity was 3.2 × 10 -3 S / cm, and at a relative humidity of 40% and a temperature of 90°C, the proton conductivity is 1.4×10 -2 The proton conductivity was 0.13 S / cm under the conditions of 90% relative humidity and 80°C temperature. On the other hand, the proton conductivity (S / cm) of a membrane made of a perfluoroalkylsulfonic acid polymer alone, which does not contain the nanofibers and sulfonated polyimide (β), was calculated using the same method as above. As a result, under the conditions of a relative humidity of 40% and a temperature of 30°C, the proton conductivity was 8.5 × 10 -5 S / cm, and at a relative humidity of 40% and a temperature of 90°C, the proton conductivity is 1.7×10 -3 S / cm, and under conditions of 90% relative humidity and 80°C, the proton conductivity is 7.9×10 -2 It was S / cm. That is, the electrolyte membrane of the present embodiment obtained above had sufficient proton conductivity.

[0206] [Example 8] <<Production of nonwoven fabric made from nanofibers containing acidic polymers>> PVA (manufactured by Aldrich, molecular weight 85,000 to 124,000, degree of saponification 87 to 89%) was added to water in a vial at room temperature and dissolved by stirring at 60°C to prepare a PVA aqueous solution with a concentration of 10% by mass. A Nafion (registered trademark) dispersion (manufactured by Sigma-Aldrich, product number 274704, concentration 5% by mass) containing a mixed solvent of water and propanol was prepared. The Nafion® dispersion (1 g) was added to the PVA aqueous solution (5 g) in a vial at room temperature while stirring, and then water (3 g) was added and stirred to prepare a solution (composition (i)). The kinematic viscosity of this solution was 3.182±0.109 cm 2 / s (318.2±10.9cSt).

[0207] A syringe filled with the solution obtained above was prepared. Aluminum foil was placed on the collector of an electrospinning device ("ES-2000S" manufactured by Fuence), and the syringe was attached to the electrospinning device. Electrospinning was performed for 1 hour by setting the solution discharge rate to 0.18 mL / h, setting the distance between the syringe and the collector to 14 cm, and applying a voltage of 15 kV to the syringe. As a result, nanofibers containing PVA and perfluoroalkylsulfonic acid polymers but without crosslinking sites (uncrosslinked nanofibers) were produced, and nonwoven fabrics made of these uncrosslinked nanofibers were fabricated on the aluminum foil. The obtained nonwoven fabrics were stored in a desiccator at room temperature.

[0208] A piece measuring 5 cm x 5 cm was cut out from the nonwoven fabric made of uncrosslinked nanofibers containing PVA and perfluoroalkylsulfonic acid polymer obtained above. The sections were immersed in a 10 mM solution of 1,4-phenylenediboronic acid in methanol (15 mL) at room temperature for 1 hour, then removed from the methanol solution, washed with methanol, and air-dried at room temperature. At room temperature, nitric acid (Kanto Chemical Co., Ltd., product number 28163-01, density 1.38 g / cm at 20°C) 3 ) was diluted about 10 times with water, and the membrane obtained by air-drying as described above was immersed in this diluted nitric acid (20 mL) for 3 hours. Next, the membrane was removed from the diluted nitric acid, thoroughly washed with distilled water at room temperature, and then air-dried at room temperature. In this way, the acid treatment of the membrane was performed. As a result, a nonwoven fabric (piece) was produced, which was made of nanofibers containing a PVA-derived component and a perfluoroalkylsulfonic acid polymer and having crosslinked sites formed by the reaction (I) between PVA and 1,4-phenylenediboronic acid. That is, this nonwoven fabric (piece) was composed of nanofibers containing PVA with the crosslinked sites and a perfluoroalkylsulfonic acid polymer.

[0209] <<Electrolyte membrane manufacturing>> A DMF solution of the sulfonated polyimide (α) having a concentration of 5% by mass was prepared. The resulting nonwoven fabric (piece) (0.0074 g) made of nanofibers containing a PVA-derived component and a perfluoroalkylsulfonic acid polymer and having the crosslinked moieties was placed in a glass Petri dish (diameter 6 cm), and the DMF solution (2.59 mL) of sulfonated polyimide (α) was cast into the nonwoven fabric (parts by mass) / sulfonated polyimide (α) (parts by mass) at a mass ratio of 0.261. Next, the solvent in the dish was slowly evaporated at 40°C under atmospheric pressure, and then the solvent was completely evaporated at 60°C. As a result, an electrolyte membrane was obtained that contained a nonwoven fabric (piece) made of nanofibers containing a PVA-derived component and a perfluoroalkylsulfonic acid-based polymer and having the crosslinked moieties formed by 1,4-phenylenediboronic acid, and a sulfonated polyimide (α). That is, this electrolyte membrane was a composite composed of nanofibers containing PVA and a perfluoroalkylsulfonic acid-based polymer having the crosslinked moieties, and a sulfonated polyimide (α).

[0210] <<Evaluation of electrolyte membrane>> <Proton conductivity measurement> The proton conductivity (S / cm) of the electrolyte membrane obtained above was calculated in the same manner as in Example 1. As a result, under the conditions of relative humidity 90% and temperature 80°C, the proton conductivity was 3.7 × 10 -3 It was S / cm. On the other hand, the proton conductivity (S / cm) of a membrane of sulfonated polyimide (α) alone, which does not contain the nanofibers and the perfluoroalkylsulfonic acid polymer (the perfluoroalkylsulfonic acid polymer constituting the nonwoven fabric (slice)), was calculated using the same method as above. As a result, under the conditions of a relative humidity of 90% and a temperature of 80°C, the proton conductivity was 3.6 × 10 -3 It was S / cm. That is, the electrolyte membrane of the present embodiment obtained above had sufficient proton conductivity.

[0211] [Example 9] <<Production of nonwoven fabric made from nanofibers containing acidic polymers>> Nanofibers containing PVA and polyvinylphosphonic acid and not having crosslinked sites (uncrosslinked nanofibers) were prepared in the same manner as in Example 6, and a nonwoven fabric made of these uncrosslinked nanofibers was prepared on the aluminum foil. The obtained nonwoven fabric was stored in a desiccator at room temperature.

[0212] Acetone (29.84 g), a 50% by mass glutaraldehyde solution (Sigma-Aldrich, product number 340855) (0.615 g), and hydrochloric acid (Kanto Chemical, product number 18078-00) (0.035 g) were mixed to prepare a mixed solution (approximately 30 mL). A piece measuring 5 cm x 5 cm was cut out from the nonwoven fabric made of uncrosslinked nanofibers containing PVA and polyvinylphosphonic acid obtained above. The slices were immersed in the mixed solution at room temperature for 1.5 hours, then removed from the mixed solution, washed with acetone, and air-dried at room temperature. As a result, a nonwoven fabric (section) was produced, which consisted of nanofibers containing a PVA-derived component and polyvinylphosphonic acid and having crosslinked sites formed by the reaction of PVA with glutaraldehyde (I). That is, this nonwoven fabric (section) was composed of nanofibers containing PVA with the crosslinked sites and polyvinylphosphonic acid.

[0213] <<Electrolyte membrane manufacturing>> The nonwoven fabric (piece) (0.017 g) made of nanofibers containing the PVA-derived component and polyvinylphosphonic acid and having the crosslinked moieties obtained above was placed in a polytetrafluoroethylene Petri dish (diameter 6.15 cm), and Nafion® dispersion (Sigma-Aldrich, product number 274704, concentration 5% by mass) (9.77 mL) was cast. At this time, the mass ratio of [nonwoven fabric (parts by mass)] / [Nafion® (parts by mass)] was 0.11. Next, the solvent in the dish was slowly evaporated at 30°C under atmospheric pressure, and then the solvent was completely evaporated at 60°C. At room temperature, nitric acid (Kanto Chemical Co., Ltd., product number 28163-01, density 1.38 g / cm at 20°C) 3 ) was diluted about 5 times with water, the temperature was adjusted to 60°C, and the membrane obtained after the evaporation was immersed in this diluted nitric acid (20 mL) for 3 hours. Next, the membrane was removed from the diluted nitric acid, washed thoroughly with distilled water at room temperature, and then air-dried at room temperature. In this way, the acid treatment of the membrane was completed. As a result, an electrolyte membrane was obtained that contained a nonwoven fabric (piece) made of nanofibers containing a PVA-derived component and polyvinyl phosphonic acid and having the cross-linked sites formed by glutaraldehyde, and a perfluoroalkyl sulfonic acid-based polymer. That is, this electrolyte membrane was a composite composed of nanofibers containing PVA and polyvinyl phosphonic acid having the cross-linked sites, and a perfluoroalkyl sulfonic acid-based polymer.

[0214] <<Evaluation of electrolyte membrane>> <Proton conductivity measurement> The proton conductivity (S / cm) of the electrolyte membrane obtained above was calculated in the same manner as in Example 1. As a result, under the conditions of relative humidity 40% and temperature 30°C, the proton conductivity was 2.6 × 10 -3 S / cm, and at a relative humidity of 40% and a temperature of 90°C, the proton conductivity is 8.5×10 -3 S / cm, and under the conditions of 90% relative humidity and 80°C temperature, the proton conductivity is 7.8×10 -2 It was S / cm. On the other hand, the proton conductivity (S / cm) of a membrane made of only perfluoroalkylsulfonic acid polymer, which does not contain the nanofibers and polyvinylphosphonic acid, was calculated using the same method as above. As a result, under the conditions of a relative humidity of 40% and a temperature of 30°C, the proton conductivity was 8.5 × 10 -5 S / cm, and at a relative humidity of 40% and a temperature of 90°C, the proton conductivity is 1.7×10 -3 S / cm, and under conditions of 90% relative humidity and 80°C, the proton conductivity is 7.9×10 -2 It was S / cm. That is, the electrolyte membrane of the present embodiment obtained above had sufficient proton conductivity.

[0215] [Example 10] <<Production of nonwoven fabrics made of nanofibers containing acidic polymers and having modified sites>> Nanofibers containing PVA and polyvinylphosphonic acid and not having crosslinked sites (uncrosslinked nanofibers) were prepared, and nonwoven fabrics made from these uncrosslinked nanofibers were also prepared in the same manner as in Example 6. The obtained nonwoven fabrics were stored in a desiccator at room temperature.

[0216] A piece measuring 5 cm x 5 cm was cut out from the nonwoven fabric made of uncrosslinked nanofibers obtained above. The sections were immersed in a methanol solution (15 mL) containing 10 mM 3-aminophenylboronic acid and 10 mM 1,4-phenylenediboronic acid at room temperature for 1 hour, then removed from the methanol solution, washed with methanol, and air-dried at room temperature. As a result, a nonwoven fabric (section) was produced, which consisted of nanofibers containing a PVA-derived component and polyvinylphosphonic acid, with crosslinked sites formed by the reaction (I) of PVA with 1,4-phenylenediboronic acid, and modified sites formed by the reaction (II) of PVA with 3-aminophenylboronic acid. That is, this nonwoven fabric (section) was composed of nanofibers containing PVA with the crosslinked sites and modified sites, and polyvinylphosphonic acid. [Industrial Applicability]

[0217] The present invention can be used as a proton-conducting material, and is particularly suitable for use as, for example, an electrolyte membrane.

Claims

1. A nanofiber, The nanofibers have crosslinked sites formed by a reaction (I) between polyvinyl alcohol and a polyfunctional compound having a group reactive with a hydroxyl group and capable of reacting with two or more hydroxyl groups in one molecule; the reaction (I) is a reaction between a hydroxyl group in the polyvinyl alcohol and a group capable of reacting with the hydroxyl group in the polyfunctional compound, The polyfunctional compound has a group represented by the formula "-B(OH) 2 " as the group capable of reacting with the hydroxyl group.

2. The nanofiber according to claim 1, wherein the polyfunctional compound is one or more selected from the group consisting of 1,4-phenylenediboronic acid, 1,3-phenylenediboronic acid, 1,3,5-benzenetrisboronic acid, 2,5-thiophenediboronic acid, and 4,4'-biphenyldiboronic acid.

3. the nanofibers have a modified site formed by a reaction (II) between the polyvinyl alcohol and a modifying compound having one or more groups per molecule that can react with a hydroxyl group and one or more groups per molecule that can react with or interact with an acidic group, The nanofiber according to claim 1 or 2, wherein the reaction (II) is a reaction between a hydroxyl group in the polyvinyl alcohol and a group in the modifying compound that can react with the hydroxyl group.

4. The group capable of reacting or interacting with the acidic group is represented by the general formula "-NH ｐ (R １ ) ２－ｐ (In the formula, R １ is a hydrocarbon group; and p is 1 or 2.)), a group represented by the formula "-N=", or a carboxy group.

5. The nanofiber according to claim 3 or 4, wherein the modifying compound is one or more selected from the group consisting of 4-aminophenylboronic acid, 3-aminophenylboronic acid, 2-aminophenylboronic acid, 4-pyridylboronic acid, 3-pyridylboronic acid, 2-pyridylboronic acid, 4-carboxyphenylboronic acid, 3-carboxyphenylboronic acid, and 2-carboxyphenylboronic acid.

6. The nanofiber of any one of claims 1 to 5, wherein the nanofiber further comprises an acidic polymer.

7. The nanofiber of claim 6 , wherein the acidic polymer has a sulfo group or a phosphono group.

8. A nonwoven fabric comprising the nanofibers according to any one of claims 1 to 7.

9. A composite comprising the nanofiber according to any one of claims 1 to 7 and a component other than the nanofiber.

10. The composite according to claim 9 , wherein the component other than the nanofiber is an acidic compound.

11. The complex of claim 10, wherein the acidic compound has a sulfo group, a phosphono group, or a phosphate group.

12. The composite according to any one of claims 9 to 11, wherein the composite is a nonwoven fabric.

13. The composite according to any one of claims 9 to 11, wherein the composite is an electrolyte membrane.

14. The composite according to any one of claims 9 to 11, wherein the composite is for use in a fuel cell.

Images