Polyimide nanofiber, manufacturing method for the same, and composite material

Abstract

To provide a polyimide nanofiber consisting of a polyimide compound being a reactant from a diamine compound and tetracarboxylic acid anhydride, a manufacturing method for the same, and a composite material.SOLUTION: A manufacturing method for a polyimide nanofiber includes a step of preparing a dissolved liquid by dissolving a polyimide compound into sulfuric acid and a step of causing the polyimide nanofiber to crystallize by dripping the dissolved liquid into a poor solvent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polyimide nanofiber, a method for producing the same, and a composite material. [Background technology]

[0002] Polyimides are polymers with imide bonds [-C(=O)-NC(=O)-] in their main chains. In particular, aromatic polyimides, in which aromatic rings are directly bonded by imide bonds, have a strong molecular structure and are known to have very high mechanical and thermal stability.

[0003] On the other hand, aromatic polyimides are known to have poor processability due to their excessively high mechanical and thermal stability, and various proposals have been made to improve processability. Specifically, various aromatic polyimides have been proposed in which the melting point and glass transition temperature have been lowered by appropriately disrupting the molecular structure of the polyimide. For example, a novel polyimide compound has been proposed that uses (2-phenyl-4-aminophenyl)-4-aminobenzoate (PHBAAB) as an aromatic polyimide with a low melting temperature and improved melt-processability, and uses asymmetric biphenyl dianhydride (BPDA) or 4,4'-oxydiphthalic anhydride (ODPA) as the tetracarboxylic acid anhydride (Patent Document 1).

[0004] Furthermore, fiber-reinforced plastics (FRPs) using carbon fibers or polyimide fibers are known, and attempts have been made to turn these fibers into nanofibers. For example, a method has been proposed for turning poly(p-phenylene benzobisoxazole), a type of aromatic polyimide, into nanofibers (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-094450 [Patent Document 2] International Publication No. 2016 / 178427 Summary of the Invention [Problem to be solved by the invention]

[0006] When the present inventors investigated the production of nanofibers from polyimide compounds, which are reaction products of diamine compounds and tetracarboxylic acid anhydrides, they attempted the nanofiber production method described in Patent Document 2, but were unable to produce nanofibers from the polyimide compounds. Similarly, they also attempted to produce nanofibers from other existing polyimide compounds, but were unable to produce nanofibers.

[0007] The inventors investigated the cause of this problem and found that the conditions under which nanofibers can be formed vary depending on the composition of the polyimide compound. As a result of their research and development efforts to form nanofibers from polyimide compounds, which are reaction products of diamine compounds and tetracarboxylic acid anhydrides, the present invention was achieved. [Means for solving the problem]

[0008] The present inventors have found that nanofibers can be produced by dropping a solution of a polyimide compound dissolved in a specific solvent into a poor solvent. The present invention is based on this finding. The gist of the present invention is as follows.

[0009] [1] A method for producing polyimide nanofibers from a polyimide compound that is a reaction product of a diamine compound and a tetracarboxylic acid anhydride. a step of dissolving the polyimide compound in sulfuric acid to prepare a solution; a step of dropping the solution into a poor solvent to precipitate polyimide nanofibers; A method for producing a polyimide nanofiber, comprising: [2] The method according to [1], further comprising a step of recovering the polyimide nanofibers precipitated in the poor solvent. [3] The method according to [1] or [2], wherein the polyimide compound is a crystalline polyimide compound. [4] The diamine compound is (2-phenyl-4-aminophenyl)-4-aminobenzoate; The method according to any one of [1] to [3], wherein the tetracarboxylic acid anhydride is asymmetric biphenyl dianhydride or 4,4'-oxydiphthalic anhydride. [5] The method according to any one of [2] to [4], wherein the polyimide nanofibers are recovered by dialysis. [6] A nanofiber made of a polyimide compound which is a reaction product of a diamine compound and a tetracarboxylic acid anhydride, the diamine compound is (2-phenyl-4-aminophenyl)-4-aminobenzoate, The polyimide nanofiber, wherein the tetracarboxylic acid anhydride is asymmetric biphenyl dianhydride or 4,4'-oxydiphthalic anhydride. [7] The polyimide nanofiber according to [6], which is dispersed in water. [8] A composite material containing the polyimide nanofiber according to [6] or [7] as a filler. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide nanofibers of polyimide compounds having high heat resistance and mechanical properties, and composite materials containing the nanofibers as a filler. [Brief explanation of the drawings]

[0011] [Figure 1] This is a TEM image (left) and an electron beam diffraction image (right) of polyimide nanofibers precipitated using water as a poor solvent. [Figure 2] This is a TEM image (left) and an electron diffraction image (right) of polyimide nanofibers precipitated using ethanol as a poor solvent. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention relates to a polyimide nanofiber made of a polyimide compound that is a reaction product of a diamine compound and a tetracarboxylic acid anhydride, a method for producing the same, and a composite material. In particular, the polyimide compound is dissolved in sulfuric acid, and the resulting solution is dropped into a poor solvent to precipitate the nanofiber.

[0013] Any polyimide compound will not precipitate as nanofibers when the solution prepared by dissolving it in sulfuric acid is dropped into a poor solvent, but a polyimide compound with high crystallinity is preferred.

[0014] More specifically, the diamine compound is preferably (2-phenyl-4-aminophenyl)-4-aminobenzoate (PHBAAB), and the tetracarboxylic acid anhydride is preferably asymmetric biphenyl dianhydride (BPDA) or 4,4'-oxydiphthalic anhydride (ODPA).

[0015] In one embodiment of the present invention, a nanofiber is a fibrous body having a diameter of 100 nm or less and an aspect ratio (fiber length / fiber diameter) of 100 or more.

[0016] The method for producing the polyimide nanofiber of the present invention will be described in detail below.

[0017] In one embodiment, the polyimide compound used has the following formula: [ka] and (2-phenyl-4-aminophenyl)-4-aminobenzoate (PHBAAB) represented by the following formula: [ka] and 4,4'-oxydiphthalic anhydride (ODPA) represented by the following structural formula: [ka]

[0018] According to another embodiment of the present invention, a tetracarboxylic acid anhydride represented by the following formula: [ka] The polyimide compound may be a polyimide compound having the following structural formula, which uses asymmetric biphenyl dianhydride (BPDA) represented by the following formula: [ka]

[0019] These polyimide compounds have high crystallinity. In contrast, when a polyimide compound with low crystallinity was dissolved in sulfuric acid, as described below, and the solution was dropped into a poor solvent, nanofibers were not generated.

[0020] <Preparation of lysis solution> A highly crystalline polyimide compound such as that described above is dissolved in sulfuric acid to prepare a solution. Specifically, a predetermined amount of polyimide compound is weighed, sulfuric acid (98 wt%) is added so that the polymer concentration becomes 10 wt%, and the mixture is stirred to prepare a solution in which the polyimide compound is completely dissolved. Note that sulfuric acid with a sulfuric acid concentration of 78 wt% or less does not dissolve the polyimide compound, so it is preferable to use sulfuric acid with a sulfuric acid concentration of 80 wt% or more.

[0021] <Dropping of dissolving solution into poor solvent> Next, the polyimide compound solution prepared as described above is added dropwise to a poor solvent. The poor solvent can be water, ethanol, or the like. The solution is preferably added dropwise to the poor solvent so that the ratio of solution to poor solvent is 1:4 (by volume). Nanofibers are precipitated by adding the solution dropwise to the poor solvent.

[0022] <Recovery of polyimide nanofibers> Next, the nanofibers precipitated in the poor solvent are collected. When collecting the nanofibers precipitated in the poor solvent, it is preferable to perform solvent substitution by centrifuging multiple times or to perform dialysis to remove sulfuric acid.

[0023] The polyimide nanofiber of this embodiment has high dispersibility in water and is less likely to precipitate during centrifugation to replace the solvent with water, so it is preferable to recover it by dialysis.

[0024] Specifically, the yield of polyimide nanofibers obtained by centrifugation with solvent substitution into water was 1.6%, whereas the yield obtained by dialysis using Thermo Scientific Slide-A-Lyzer™ Dialysis Flasks (MWCO: 20,000 Da) was 40.6%. The dialysis membrane (tube) was made of regenerated cellulose and had a molecular weight cutoff (MWCO) of 20,000. The yield obtained by dialysis using SPECTRUM RC dialysis tubing Spectra / Por 5 (MWCO: 12,000-14,000 Da) was 44.8%. The dialysis membrane (tube) was made of regenerated cellulose and had a molecular weight cutoff (MWCO) of 12,000-14,000.

[0025] Figure 1 shows a TEM image of polyimide nanofibers precipitated using water as a poor solvent. FIG. 2 shows a TEM image of polyimide nanofibers precipitated using ethanol as a poor solvent.

[0026] The polyimide nanofibers precipitated using water as a poor solvent had a fiber diameter of 12±2 nm and a fiber length of 305±152 nm. The polyimide nanofibers precipitated using ethanol as a poor solvent had a fiber diameter of 10±1 nm and a fiber length of 354±168 nm. Furthermore, ring-shaped reflections were observed in each electron diffraction image, confirming their crystallinity.

[0027] The polyimide nanofibers obtained in this manner have high dispersibility in water, and even when mixed as a filler in a resin material such as polyimide varnish, they are less likely to aggregate and the filler can be uniformly dispersed, making them suitable for use as composite materials.

[0028] In one embodiment of the present invention, nanofibers precipitated in water or ethanol from a sulfuric acid solution of a polyimide compound were added to a polyimide varnish, and the resulting composite film was fabricated and evaluated for its functionality. Specifically, the following evaluation tests were performed.

[0029] A film was prepared by forming a polyimide varnish (PI varnish WGv-2301, manufactured by Wingo Technology Co., Ltd.). In addition, polyimide compound nanofibers were prepared by dissolving a polyimide compound using the diamine component (2-phenyl-4-aminophenyl)-4-aminobenzoate (PHBAAB) and the tetracarboxylic acid anhydride component asymmetric biphenyl dianhydride (BPDA) in sulfuric acid, and the solution was dropped into ethanol, a poor solvent, to precipitate nanofibers. These nanofibers were then mixed with the above-mentioned PI varnish at a nanofiber / polyimide varnish ratio of 4 / 100, and a varnish was formed in the same manner as above to produce a composite material film. In addition, polyimide compound nanofibers were prepared by dissolving a polyimide compound using the diamine component (2-phenyl-4-aminophenyl)-4-aminobenzoate (PHBAAB) and the tetracarboxylic acid anhydride component asymmetric biphenyl dianhydride (BPDA) in sulfuric acid, and dropping the resulting solution into water, a poor solvent, to precipitate nanofibers. These nanofibers were then mixed with the above-mentioned PI varnish at a nanofiber / polyimide varnish ratio of 30 / 100, and the resulting varnish was then formed into a film in the same manner as above to produce a composite material film.

[0030] The films thus obtained were subjected to measurements of the modulus of elasticity, yield strength, breaking strength, and breaking elongation according to standard methods. The evaluation results for each film are shown in the table below. [Table 1]

[0031] The thermal conductivity of each film obtained as described above was measured according to a standard method, and the evaluation results are shown in the table below. [Table 2]

[0032] In both films, the thermal conductivity was found to be anisotropic in both the in-plane and thickness directions. Furthermore, the thermal conductivity improved with increasing amounts of polyimide nanofibers.

Claims

1. A method for producing polyimide nanofibers from a polyimide compound that is a reaction product of a diamine compound and a tetracarboxylic acid anhydride, a step of dissolving the polyimide compound in sulfuric acid to prepare a solution; a step of dropping the solution into a poor solvent to precipitate polyimide nanofibers; A method for producing a polyimide nanofiber, comprising:

2. The method according to claim 1 , further comprising the step of recovering the polyimide nanofibers precipitated in the poor solvent.

3. 3. The method according to claim 1, wherein the polyimide compound is a crystalline polyimide compound.

4. the diamine compound is (2-phenyl-4-aminophenyl)-4-aminobenzoate, The method according to any one of claims 1 to 3, wherein the tetracarboxylic acid anhydride is asymmetric biphenyl dianhydride or 4,4'-oxydiphthalic anhydride.

5. The method according to any one of claims 2 to 4, wherein the recovery of the polyimide nanofibers is carried out by dialysis.

6. A nanofiber made of a polyimide compound which is a reaction product of a diamine compound and a tetracarboxylic acid anhydride, the diamine compound is (2-phenyl-4-aminophenyl)-4-aminobenzoate, The polyimide nanofiber, wherein the tetracarboxylic acid anhydride is asymmetric biphenyl dianhydride or 4,4'-oxydiphthalic anhydride.

7. The polyimide nanofiber according to claim 6 , which is dispersed in water.

8. A composite material containing the polyimide nanofiber according to claim 6 or 7 as a filler.

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