HK1085754B - Composite fiber comprising wholly aromatic polyamide and carbon nanotube - Google Patents

Description

Composite fiber containing wholly aromatic polyamide and carbon nanotube

Technical Field

The present invention relates to a composite fiber having excellent mechanical properties, which is characterized by comprising wholly aromatic polyamide and carbon nanotubes, wherein the carbon nanotubes are oriented in the fiber axis direction.

Background

Wholly aromatic polyamides have a structure in which rigid aromatic rings are connected to each other, and as a raw material excellent in heat resistance, mechanical properties, chemical resistance, and the like, they are widely used as fibers or films as one of the raw materials having high industrial value, such as electrical insulating materials, various reinforcing agents, and bulletproof fibers.

As one of the techniques for satisfying such required characteristics, a composition in which carbon nanotubes are dispersed in a thermoplastic resin in a nano-order, so-called nanocomposite, has recently attracted attention, and for example, Japanese patent publication No. 8-26164 discloses that carbon nanotubes are oriented in a matrix by electrolysis, appropriate shearing action, or combing.

WO03/085049 discloses a method for producing a composition comprising single-walled carbon nanotubes and an aromatic polyamide, and a fiber, and discloses a method in which carbon nanotubes are preferably added to an anhydrous sulfuric acid solution of an aromatic polyamide, but does not describe the dispersion and orientation state of carbon nanotubes in a composite fiber, and the influence thereof on physical properties, and the effect of improving the mechanical properties of the fiber is not clear.

Disclosure of Invention

The present invention aims to provide a composite fiber comprising a wholly aromatic polyamide and carbon nanotubes, which have improved mechanical properties, particularly modulus of elasticity and strength.

Namely, there is provided a composite fiber characterized by comprising: 100 parts by weight of a wholly aromatic polyamide mainly comprising structural units represented by the following formulae (A) and (B), and 0.01 to 100 parts by weight of carbon nanotubes having an average diameter of 300nm or less and an average aspect ratio of 5.0 or more, the carbon nanotubes being oriented in the fiber axis direction,

-NH-Ar¹-NH- (A)

-OC-Ar²-CO- (B)

wherein, in the general formulae (A) and (B), Ar¹、Ar²Each independently represents a 2-valent aromatic group having 6 to 20 carbon atoms.

In particular, when the carbon nanotubes are multilayered carbon nanotubes, it is preferable that the orientation coefficient F of the carbon nanotubes obtained by the following formula (1) is 0.1 or more,

where Φ is an azimuth angle in X-ray diffraction measurement, and I is diffraction intensity of 002 crystal plane of the multilayer carbon nanotube.

When the fiber side is irradiated with an incident laser beam in a direction perpendicular to the fiber axis by polarization Raman spectroscopy, the degree of orientation P represented by the following formula (2) in the Raman spectrum of the carbon nanotube preferably satisfies 0 to 0.7,

P＝I_YY/I_XX (2)

wherein the G-band intensity when the laser polarization plane is arranged parallel to the fiber axis is I_XXThe laser polarization plane is arranged perpendicular to the fiber axisThe G-band strength of_YY。

The present invention also provides a method for producing the above composite fiber.

Drawings

Fig. 1 is an electron microscope (TEM) photograph observed from a fiber cross section cut almost parallel to the fiber axis of the composite fiber produced in example 2. The arrows in the figure indicate the fiber axis direction, and the white line indicates the trace left by the carbon nanotubes pulled by the cutter when the fiber is cut.

Fig. 2 is an electron microscope (TEM) photograph observed from a fiber cross section cut almost parallel to the fiber axis of the composite fiber produced in example 3. The arrows in the figure indicate the fiber axis direction, and the white line indicates the trace left by the carbon nanotubes pulled by the cutter when the fiber is cut.

Fig. 3 is an electron microscope (TEM) photograph observed from a fiber cross section cut almost parallel to the fiber axis of the composite fiber produced in example 5. The arrows in the figure indicate the fiber axis direction, and the white line indicates the trace left by the carbon nanotubes pulled by the cutter when the fiber is cut.

Detailed Description

The present invention will be described in detail below.

(for carbon nanotubes)

The carbon nanotubes in the composite fiber of the present invention have an average diameter of 300nm or less, preferably 0.3 to 250nm, more preferably 0.3 to 200nm, and still more preferably 0.4 to 100 nm. In practice, it is difficult to produce carbon nanotubes having a diameter of 0.3nm or less, and carbon nanotubes having a diameter of 300nm or more are not preferable because they are difficult to disperse in a solvent.

The average aspect ratio is preferably not limited to the upper limit, but the lower limit is 5.0 or more, preferably 10.0 or more, and more preferably 20.0 or more. If the average aspect ratio is less than 5.0, the effect of improving the mechanical properties of the fibers is not sufficient, which is not preferable. The average diameter and aspect ratio of the carbon nanotubes can be determined by observation with an electron microscope. For example, TEM (transmission electron microscope) measurement is performed, and the diameter and the length in the long axis direction of the carbon nanotube can be directly measured from the image. The morphology of the carbon nanotubes in the composite fiber can be determined by TEM (transmission electron microscope) measurement in which the fiber cross section is cut parallel to the fiber axis, for example.

The carbon nanotube is formed by rolling a graphite sheet into a cylindrical shape, and the cylindrical shape may be a single layer or a multilayer. The graphite flakes may be stacked in a cup shape. That is, the carbon nanotube of the present invention is preferably a single-walled carbon nanotube, a multi-walled carbon nanotube, or a capstan carbon nanotube.

These carbon nanotubes can be produced by a conventionally known method, and examples thereof include, but are not limited to, gas phase flow method, catalyst-supported gas phase flow method, laser cutting method, high-pressure carbon monoxide method, arc discharge method, and the like.

(for wholly aromatic polyamide)

The wholly aromatic polyamide in the composite fiber of the present invention is a wholly aromatic polyamide consisting essentially of two structural units represented by the following formulae (a) and (B) which are repeated with each other,

-NH-Ar¹-NH- (A)

-OC-Ar²-CO- (B)

wherein, in the general formulae (A) and (B), Ar¹、Ar²Each independently represents a 2-valent aromatic group having 6 to 20 carbon atoms.

Ar above¹、Ar²Each independently represents a 2-valent aromatic group having 6 to 20 carbon atoms, and specific examples thereof include m-phenylene, p-phenylene, o-phenylene, 2, 6-naphthylene, 2, 7-naphthylene, 4 ' -isopropylidenediphenylene, 4 ' -biphenylene, 4 ' -biphenylenePhenylthio, 4 '-diphenylene sulfone, 4' -diphenylene ketone, 4 '-diphenylene ether, 3, 4' -diphenylene ether, m-xylylene, p-xylylene, o-xylylene, and the like.

1 or more of the hydrogen atoms of these aromatic groups are each independently substituted by: halogen groups such as fluorine, chlorine and bromine; alkyl groups having 1 to 6 carbon atoms such as methyl, ethyl, propyl, hexyl and the like; cycloalkyl groups having 5 to 10 carbon atoms such as cyclopentyl and cyclohexyl; aryl groups having 6 to 10 carbon atoms such as phenyl group. The structural unit of the formula (a) and/or (B) may be a copolymer composed of 2 or more aromatic groups.

Among them, Ar is preferred¹When the compound is m-phenylene, p-phenylene or 3, 4 ' -diphenylene ether, more preferably p-phenylene or a combination of p-phenylene and 3, 4 ' -diphenylene ether, and a combination of p-phenylene and 3, 4 ' -diphenylene ether, the molar ratio is preferably in the range of 1: 0.8 to 1: 1.2.

Ar²The m-phenylene group and the p-phenylene group are preferable, and the p-phenylene group is more preferable.

That is, as a substance preferably used in the present invention, Ar is specifically mentioned¹Is p-phenylene and 3, 4' -diphenylene ether, Ar²Is a copolymer of p-phenylene, the copolymerization ratio (Ar)¹The molar ratio of p-phenylene group and 3, 4' -diphenylene ether group) of 1: 0.8 to 1: 1.2, and Ar¹And Ar²Wholly aromatic polyamides each having p-phenylene group.

These wholly aromatic polyamides can be produced by a conventionally known method such as a solution polymerization method, an interfacial polymerization method, a melt polymerization method, or the like. The polymerization degree can be controlled by the ratio of the aromatic diamine component and the aromatic dicarboxylic acid component, and the intrinsic viscosity (intrinsic viscosity) η inh of a solution obtained by dissolving a polymer in 98 wt% concentrated sulfuric acid at a concentration of 0.5g/100mL measured at 30 ℃ is preferably 0.05 to 20dL/g, and more preferably 1.0 to 10dL/g, as the molecular weight of the polymer.

(composition)

The composite fiber of the present invention has a composition of 0.01 to 100 parts by weight, preferably 0.1 to 60 parts by weight, and more preferably 1 to 10 parts by weight of carbon nanotubes per 100 parts by weight of the wholly aromatic polyamide. When the amount of the carbon nanotube is less than 0.01 part by weight, the effect of improving mechanical properties is hardly observed, and when the amount is more than 100 parts by weight, spinning is difficult.

(for orientation and orientation method)

The present invention is characterized in that the carbon nanotubes in the composite fiber are oriented in the fiber axis direction. In the present invention, the orientation of the carbon nanotubes is measured by X-ray diffraction measurement or polarization raman spectroscopy measurement, except that the cross section of the fiber cut parallel to the fiber axis is directly observed by an electron microscope such as TEM. When the carbon nanotube is a multilayered carbon nanotube, an orientation coefficient F represented by the following formula (1) can be used. (Jingyuan Zheng Fu et al polymer X-ray diffraction 1968, Wan shan)

Where Φ is an azimuth angle in X-ray diffraction measurement, and I is diffraction intensity of 002 crystal plane of the multilayer carbon nanotube.

The value of the orientation coefficient F of the multilayered carbon nanotube in the present invention is preferably 1.0 or more. More preferably 0.2 or more, and still more preferably 0.3 or more. The higher the F value, the more preferable, the theoretical upper limit value when the multilayered carbon nanotube is completely aligned is 1.0.

In the polarized Raman spectroscopy, when the side of the fiber is irradiated with an incident laser beam in the direction perpendicular to the fiber axis, the orientation is evaluated by the degree of orientation represented by the following formula (2) in the Raman spectrum of the carbon nanotube,

P＝I_YY/I_XX (2)

wherein the G-band intensity when the laser polarization plane is arranged parallel to the fiber axis is I_XXThe intensity of the G band when the laser polarization plane is arranged perpendicular to the fiber axis is I_YY. In the present invention, the degree of orientation P is preferably 0 to 0.7.

The polarization Raman spectroscopy is particularly effective in single-layer carbon nanotubes and can be applied to the occasions of multilayer carbon nanotubes. In particular, when the content of the multilayered carbon nanotube is small and the X-ray diffraction peak of the carbon nanotube is hidden in the diffraction pattern of the polymer, the degree of orientation is preferably measured by polarization raman spectroscopy.

In the case of a single-walled carbon nanotube, the degree of orientation P gradually becomes 0 when the nanotube is oriented parallel to the fiber axis direction, and becomes 1 when the nanotube is randomly oriented. The upper limit of P is more preferably 0.5, still more preferably 0.3, and the closer to 0, the more preferably it is. On the other hand, in the case of the multi-walled carbon nanotube, the P value tends to be higher than that in the case of the single-walled carbon nanotube, and a theoretical value P of 0.36 when the fully oriented multi-walled carbon nanotube is measured alone is also described in the literature (a.m. rao, etc. phys.rev.84(8), 1820 (200)). In the present invention, in the case of the multilayered carbon nanotube, the P value is sufficiently aligned even if it is 0.5 to 0.6.

In the present invention, the wholly aromatic polyamide in the conjugate fiber is also preferably oriented in the fiber axis direction, and the orientation coefficient F is preferably 0.5 or more. More preferably 0.6 or more, and still more preferably 0.7 or more. Here, the orientation coefficient F is obtained by focusing on the diffraction intensity I of the 200 crystal plane of the wholly aromatic polyamide in formula (1).

Examples of the method of aligning the carbon nanotubes and the wholly aromatic polyamide in the fiber axis direction include flow alignment, liquid crystal alignment, shear alignment, or draw alignment in spinning from a mixed solution of the wholly aromatic polyamide and the carbon nanotubes. Further, it is more preferable to obtain the composite fiber of the present invention by further elongating and orienting the obtained fiber composition to increase the orientation coefficient of the carbon nanotubes. The degree of increase in the orientation coefficient F is 0.01 or more, preferably 0.05 or more, and more preferably 0.1 or more. The degree of decrease in the degree of orientation P is 0.01 or more, preferably 0.05 or more, and more preferably 0.1 or more.

(method for producing conjugate fiber)

The method for producing the composite fiber of the present invention is preferably a method of preparing a mixed solution of the wholly aromatic polyamide and the carbon nanotube and spinning the yarn from the mixed solution. Examples of the solvent used in this case include amide solvents such as dimethylacetamide and N-methyl-2-pyrrolidone, and acid solvents such as 100% sulfuric acid, phosphoric acid, polyphosphoric acid, and methanesulfonic acid.

As a method for preparing the mixed solvent, any known method can be used, and examples thereof include: adding solid carbon nanotubes to the wholly aromatic polyamide solution. ② mixing the wholly aromatic polyamide solution and the solvent dispersion liquid of the carbon nano tube. And thirdly, adding solid wholly aromatic polyamide into the solvent dispersion liquid of the carbon nano tube. And (iv) carrying out In-situ polymerization of the wholly aromatic polyamide In the solvent dispersion of the carbon nanotube. In both methods, the carbon nanotubes are uniformly dispersed in the mixed solution, which is important for the alignment of the carbon nanotubes, that is, for the improvement of the mechanical properties of the composite fiber, and from this viewpoint, there is a problem that the method of adding the carbon nanotube powder to the polyamide solution having a high viscosity in the first step may not uniformly disperse. Therefore, as a method for preparing the mixed solution, it is preferable to first prepare a solvent dispersion of carbon nanotubes. However, since carbon nanotubes themselves have low solubility or are significantly complexed, they generally lack dispersibility in many solvents, and thus, in the present invention, it is desired to obtain a carbon nanotube dispersion in a well-dispersed state.

For evaluating the dispersibility of the carbon nanotubes in the solvent, a method of measuring the particle size distribution in the solvent may be mentioned in addition to direct observation of the appearance. The particle size distribution of the carbon nanotubes can be measured by a dynamic light scattering method, a laser diffraction method, or the like.

In the present invention, it is preferable to subject the carbon nanotubes to a certain treatment in advance in order to improve the dispersibility of the carbon nanotubes in the solvent and the dispersibility in the mixed solution. The treatment method may be any treatment method as long as the tube structure of the carbon nanotube can be maintained, and specific examples thereof include ultrasonic treatment, physical micronization treatment, strong acid treatment, and chemical surface treatment.

Examples of the physical micronization treatment include a dry grinding treatment using a ball mill, a wet grinding treatment using a bead mill, a shearing treatment using a homogenizer, and the like. These treatments can finely divide the carbon nanotubes and improve the dispersibility, but if the treatment is excessive, the aspect ratio may be greatly reduced and the nanotube structure itself may be damaged, and it is necessary to take care of this.

The strong acid treatment of the carbon nanotubes may be specifically carried out using a strong acid having a pH of 0.01 to 2. The carbon nanotubes having a carboxylic acid or a hydroxyl group as a substituent can be obtained by a strong acid treatment, and the affinity for a solvent or wholly aromatic polyamide can be improved and the dispersibility can be improved. Examples of the strong acid having a pH of 0.01 to 2 that can be used include nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, dichrolic acid, and mixed acids thereof, and among them, nitric acid, mixed acids of sulfuric acid and nitric acid, and mixed acids of dichrolic acid and sulfuric acid are preferably used, and particularly, acids having a high concentration are preferably used. Anhydrous acids such as sulfuric acid monohydrate are not preferable for the purpose of introducing carboxylic acids as substituents. In addition, it is preferable to carry out the strong acid treatment in the presence of ultrasonic waves. After the strong acid treatment, the treatment solution is dispersed in water and then washed, whereby the carbon nanotubes can be separated. In the strong acid treatment, as in the physical refining treatment, it is preferable to carefully perform the treatment because excessive treatment may cause damage to the nanotube structure. Particularly, in the case of single-walled carbon nanotubes, it is desirable to use a strong acid treatment without damaging the surface if possible.

The strong acid treatment can provide carbon nanotubes having oxygen atoms in an appropriate ratio, but the ratio of oxygen atoms present on the surface of carbon nanotubes is preferably in the range of 2 to 25 relative to 100 carbon atoms. The presence of oxygen atoms on the surface of the carbon nanotube can be confirmed by surface analysis methods such as ESCA.

Further, as the chemical surface treatment of the carbon nanotube, it is also preferable to etherify or amidate the carbon nanotube after the strong acid treatment. Whether or not these functional groups are introduced can be confirmed by IR measurement, change in the surface element ratio of ESCA, or the like.

Here, as a method of etherification, for example, a method of obtaining an aryl ester by reacting a carboxylic acid in a carbon nanotube treated with a strong acid with a diaryl carbonate can be cited. The reaction is preferably carried out in the presence of a catalyst, and examples of the catalyst include pyridine compounds such as 4-aminopyridine, 4-dimethylaminopyridine, 4-diethylaminopyridine, 4-pyrrolidinylpyridine, 4-piperidylpyridine, 4-pyrrolinylpyridine (pyridinylpyridine), and 2-methyl-4-dimethylaminopyridine. Among them, 4-dimethylaminopyridine and 4-pyrrolidinylpyridine are particularly preferable.

Examples of the amidation method include a method in which the aromatic ester of carbon nanotubes obtained by esterification after the above strong acid treatment is reacted with an amine compound such as aniline, naphthylamine, p-phenylenediamine, and m-phenylenediamine.

These treatment methods may be carried out alone or in combination. In the present invention, physical refining treatment is particularly preferable.

From the solvent dispersion of the carbon nanotubes, a mixed solution with the wholly aromatic polyamide can be obtained as described above. The dispersion of the carbon nanotubes in the mixed solution is also important, and uniform dispersion is desirable if possible. The dispersibility in this case can be grasped to some extent by direct observation with an optical microscope. Any of wet spinning, dry spinning and dry and wet spinning methods may be used. In the spinning step, the orientation of the wholly aromatic polyamide and the carbon nanotube can be improved and the mechanical properties can be improved by flow orientation, liquid crystal orientation, shear orientation, or extensional orientation. Ar in wholly aromatic polyamide¹For example p-phenylene and 3, 4' -diphenyleneether, Ar²Is a copolymer of p-phenylene, the copolymerization ratio (Ar)¹The molar ratio of p-phenylene group and 3, 4' -diphenylene ether group) is in the range of 1: 0.8 to 1: 1.2, and then dry-wet spinning is performed using an amide-based solvent such as dimethylacetamide or N-methyl-2-pyrrolidone as a mixed solvent, and then the resulting fibers are subjected to drawing orientation at high temperature and high magnification to obtain composite fibers. In this case, the draw ratio is preferably 2 to 40 times, more preferably 5 to 30 times, and it is desirable to draw as close to the Maximum Draw Ratio (MDR) as possible in terms of mechanical properties. The temperature for the orientation by drawing is preferably 100 to 800 ℃ and more preferably 200 to 600 ℃. Examples of wholly aromatic polyamidesIf is Ar¹And Ar²When poly (p-phenylene terephthalamide) is a p-phenylene group, a composite fiber can be obtained by liquid crystal spinning using 100% of an acid solvent such as sulfuric acid, phosphoric acid, polyphosphoric acid, and methanesulfonic acid as a mixed solvent. By liquid crystal spinning, the solution is usually spun from the hood with a high draft ratio, whereby orientation is possible.

The composite fiber comprising the wholly aromatic polyamide and the carbon nanotubes obtained by the present invention has better mechanical properties, particularly excellent elastic modulus and tensile strength, by aligning the carbon nanotubes in the composition in the fiber axis direction.

Examples

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to these examples.

(1) Using the average diameter and average aspect ratio of the carbon nanotubes: the measurement was carried out by a transmission electron microscope (type H-800) manufactured by Hitachi, Ltd. After dispersing carbon nanotubes in N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) at 0.1mg/mL under ultrasonic treatment, the dispersion was dropped onto a grid for TEM measurement, dried under reduced pressure, and the obtained sample was observed. The diameter and length were directly measured from the image, and the average value was obtained.

(2) Dynamic light scattering measurement of carbon nanotubes: a large electron system Dynamic light scattering photometer DLS-7000 was used. A NMP dispersion of carbon nanotubes at a concentration of 0.01mg/mL was prepared, subjected to ultrasonic treatment for 1 hour, subjected to dynamic light scattering measurement at 25 ℃ using an Ar laser, and the particle size distribution and the average particle size were calculated by a histogram (histogram) method.

(3) X-ray diffraction measurement: the measurement was carried out using an X-ray generator (RU-B model manufactured by Proc. Moore Co., Ltd.) under the conditions of CuK α ray as a target, a voltage of 45Kv and a current of 70 mA. Incident X-rays were collected by a multilayer film lens manufactured by Osumic corporation and monochromated, and the cross section of the sample was measured by a vertical transmission method. The diffracted X-rays were detected with a camera length of 250nm using an imaging plate (manufactured in Fuji photo film) of size 200nm X250 nm.

(4) Polarized Raman spectrometry: the Raman spectrometer used herein was a micro laser Raman spectrometer (LabRamHR, Horikoshi Jobanibon). As the excitation laser light source, a semiconductor laser having a wavelength of 785nm was used, and the laser beam diameter was converged to about 1 μm. Using the apparatus, a polarization raman spectroscopic measurement was performed as follows. When the side surface of the fiber is irradiated with incident laser light from the direction orthogonal to the fiber axis to measure the Raman spectrum of the carbon nanotube, the Raman shift wavelength at the time when the laser polarization plane is arranged parallel to the fiber axis is measured at 1580cm^-1Nearby G-band strength (I) from graphite structures_XX) G-band intensity (I) when laser polarization plane is arranged perpendicular to fiber axis_YY)。

(5) Mechanical properties of the fibers: the obtained fiber was subjected to a tensile test under a single yarn using a Tensilon universal tester 1225A manufactured by Orientic corporation to determine the modulus of elasticity and the strength.

(6) Observation of carbon nanotubes in composite fibers: TEM (transmission electron microscope) measurement was performed on a cross section of the fiber cut almost parallel to the fiber axis, and the orientation of the carbon nanotubes was evaluated from the image.

(7) Elemental analysis of carbon nanotube surfaces: the measurement was performed by ESCA (X-ray photoelectron spectroscopy). The measurement was carried out using ESCALAB-200 (product of VG) at 45 degrees with MgK α ray (300W) and photoelectron extraction angle.

Reference example 1: preparation of aramid resin solution

To a sufficiently dried three-necked flask equipped with a stirrer were added dehydrated purified NMP2152g, p-phenylenediamine 27.04g and 3, 4' -diaminodiphenyl ether 50.06g at room temperature, and the mixture was dissolved in nitrogen, and then 101.51g of terephthalic acid dichloride was added under ice-cooling stirring. Then, the temperature was gradually increased and finally, the reaction was carried out at 80 ℃ for 60 minutes, 37.04g of calcium hydroxide was added and neutralization reaction was carried out to obtain an aramid resin solution of NMP. The obtained dope was reprecipitated in water to obtain an aramid resin, and the inherent viscosity of a concentrated sulfuric acid solution having a concentration of 0.5g/100mL was measured at 30 ℃ to be 3.5 dL/g.

Reference example 2: synthesis of single-walled carbon nanotubes

Y-type zeolite powder (HSZ-320 NAA, manufactured by Toray) was used as a porous carrier, iron acetate and cobalt acetate were used as catalyst metal compounds, and an Fe/Co catalyst was supported on the zeolite. The catalyst loading was adjusted to 2.5 wt%, respectively. Thereafter, the catalyst powder was placed on a quartz dish, and the quartz tube of the CVD apparatus was placed therein, and vacuum-exhausted, and the temperature was raised from room temperature to 800 ℃. After reaching a predetermined temperature of 800 ℃, ethanol vapor was introduced at a flow rate of 3000 mL/min and the mixture was kept in an Ar/ethanol atmosphere for 30 minutes. The obtained black product was analyzed by laser raman spectroscopy and transmission electron microscopy, and it was confirmed that a single-walled carbon nanotube was produced. Then, the resultant (single-walled carbon nanotube/zeolite/metal catalyst) was immersed in 10% hydrofluoric acid for 3 hours, and then washed with ion-exchanged water until the solution was neutral, thereby removing the zeolite and the metal catalyst and purifying the carbon nanotubes. The carbon nanotubes obtained were observed by TEM, and as a result, the average diameter was 1.2nm and the average aspect ratio was 100 or more. However, most are beam-like structures with a width of about 10 nm.

Reference example 3: synthesis of multilayered carbon nanotubes

The reaction was carried out in the same manner as in reference example 2 except that the reaction temperature in the CVD apparatus was set to 600 ℃, and it was confirmed that a multi-walled carbon nanotube was produced. After the zeolite and the metal catalyst were purified and removed in the same manner as in reference example 2, the graphite was graphitized using an electric sintering furnace (SCC-U-90/150, manufactured by kukoki technologies). The temperature is raised to 1000 ℃ from room temperature for 30 minutes under vacuum, then raised to 2000 ℃ from 1000 ℃ for 30 minutes under argon atmosphere and pressure of 5atm, and further raised to 2800 ℃ from 2000 ℃ for 1 hour, and finally the graphitized multi-layer carbon nanotube is obtained. The carbon nanotubes obtained were observed by TEM, and had an average diameter of 58nm and an average aspect ratio of 36.

Example 1

0.75g of the multilayered carbon nanotube synthesized in reference example 3 was added to NMP74.3g, and ultrasonic treatment was performed for 16 hours using ultrasonic waves having a vibration frequency of 38 kHz. To the NMP dispersion, 237.5g of the aramid resin solution of NMP prepared in reference example 1 was added, and stirred at 80 ℃ for 4 hours, thereby obtaining a mixed dope of the aramid resin/carbon nanotube (weight ratio) of 95/5. The polymer dope obtained above was extruded at a speed of 3 m/min in a coagulation bath having a cylinder temperature of 50 ℃ and a temperature of 50 ℃ as an aqueous solution of NMP30 wt% using a cap having a pore diameter of 0.3mm, an L/D of 1 and a pore number of 5. The distance between the cover surface and the coagulation bath surface is 10 mm. The fiber taken out of the coagulation bath was washed with water in a water bath at 50 ℃ and dried with a drying roll at 120 ℃ and then stretched on a hot plate at 500 ℃. First, the Maximum Draw Ratio (MDR) in this drawing step was determined, and the fiber was drawn at a draw ratio of 0.9 times (20.3 times, speed 60.9 m/min) to obtain a conjugate fiber. The single fiber diameter of the fiber was 1.58dtex, and the orientation factor F of the carbon nanotubes and the orientation factor F of the aramid resin were 0.750, respectively, as determined by X-ray diffraction measurement of the drawn fiber. Further, as a result of the tensile test, the modulus of elasticity was 75.4GPa and the strength was 26.2 cN/dtex.

Example 2

5g of the multilayered carbon nanotube synthesized in reference example 3 was added to NMP904g, and the NMP dispersion was circulated using zirconium beads of 0.3mm diameter by a wet disperser DYNO-MILL (TYPE KDL) at a peripheral speed of 10m/s, and subjected to a bead mill treatment for 30 minutes. The average diameter of the carbon nanotubes after the treatment was determined by TEM measurement to be 29nm, and the average aspect ratio was determined to be 58. The average particle size in NMP was 835nm, which was smaller than 1147nm before the treatment, as determined by dynamic light scattering measurement. After 55g16 hours of ultrasonic treatment of the thus obtained NMP dispersion, 245g of the aramid resin solution of reference example 1 was added and stirred at 80 ℃ for 4 hours, thereby obtaining a mixed dope of aramid resin/carbon nanotube (weight ratio) 98/2. The mixed dopant was placed on a glass slide and observed by an optical microscope, and it was confirmed that the dispersibility of the carbon nanotubes was improved. A composite fiber was obtained by spinning in the same manner as in example 1. Table 1 shows various physical properties of the fiber. The fiber cross section cut almost parallel to the fiber axis of the composite fiber was measured by TEM (transmission electron microscope). The photograph is shown in FIG. 1. It can be seen that the carbon nanotubes having a black rod-like morphology were oriented in the fiber axis direction. The width and length of the carbon nanotubes are almost the same as the average diameter and length in the long axis direction of the carbon nanotubes to be added.

Example 3

To NMP990g, 10g of the multilayered carbon nanotube synthesized in reference example 3 was added, and the dispersion was circulated using zirconium beads of 0.3mm diameter by a wet disperser DYNO-MILL (TYPE KDL) at a peripheral velocity of 10m/s, and subjected to a bead mill treatment for 1 hour. The average diameter of the carbon nanotubes after the treatment was 32nm and the average aspect ratio was 53 as determined by TEM measurement. The average particle diameter determined by dynamic light scattering measurement was 886 nm. After the NMP dispersion was sonicated for 75g16 hours, 237.5g of the aramid resin solution of reference example 1 was added and stirred at 80 ℃ for 4 hours, thereby obtaining a mixed dope of aramid resin/carbon nanotube (weight ratio) 95/5. A composite fiber was obtained by spinning in the same manner as in example 1. Table 1 shows various physical properties of the fiber. The fiber cross section cut almost parallel to the fiber axis of the composite fiber was measured by TEM (transmission electron microscope). The photograph is shown in FIG. 2. It can be seen that the carbon nanotubes having black rod-like morphology were oriented in the fiber axis direction as in example 2.

Example 4

150mL of concentrated sulfuric acid having a concentration of about 98% was added to 2g of the multilayered carbon nanotube synthesized in reference example 3, and after stirring and cooling to 0 ℃, 50mL of concentrated nitric acid having a concentration of about 61% was slowly dropped. Then, the treatment was carried out for 1 hour in a warm water bath at 70 ℃ by ultrasonic waves with a vibration frequency of 38 kHz. After cooling to room temperature, the strong acid solution was dispersed in water, and the mixture was thoroughly filtered using a Teflon filter (Millipore) having a pore size of 0.2. mu.m, and washed to recover carbon nanotubes. The carbon nanotubes after strong acid treatment had an average diameter of 26nm and an average aspect ratio of 56 as determined by TEM measurement. The average particle diameter determined by dynamic light scattering measurement was 552 nm. Further, the elemental analysis of the surface by ESCA showed 92.6% of carbon and 7.4% of oxygen. 0.3g of the carbon nanotubes was dispersed in NMP55g, and after ultrasonication for 16 hours, 245g of an aramid resin solution was added and stirred at 80 ℃ for 4 hours to obtain a mixed dope of aramid resin/carbon nanotubes (weight ratio) 98/2. The mixed dopant was observed by an optical microscope, and it was confirmed that the dispersibility of the carbon nanotubes was high. A composite fiber was obtained by spinning in the same manner as in example 1. Table 1 shows various physical properties of the fiber.

Example 5

0.75g of the strongly acid-treated carbon nanotubes obtained in example 4 was dispersed in nmp74.3g, and after the ultrasonic treatment for 16 hours, 237.5g of an aramid resin solution was added and stirred at 80 ℃ for 4 hours, thereby obtaining a mixed dope of an aramid resin/carbon nanotubes (weight ratio) of 95/5. The mixed dopant was observed by an optical microscope, and it was confirmed that the dispersibility of the carbon nanotubes was also high in this case. A composite fiber was obtained by spinning in the same manner as in example 1. Table 1 shows various physical properties of the fiber. In addition, TEM (transmission electron microscope) measurement (fig. 3) was performed on a fiber cross section cut almost parallel to the fiber axis of the composite fiber in the same manner as in example 3, and it was confirmed that the carbon nanotubes were oriented in the fiber axis direction.

Example 6

10g of phenol was added to 1g of the strongly acid-treated carbon nanotubes obtained in example 4, and the mixture was treated at 70 ℃ for 10 minutes in a mortar, and then subjected to ultrasonic treatment for 10 minutes in a 70 ℃ warm water bath using ultrasonic waves having a vibration frequency of 28 kHz. 100g of diphenyl carbonate and 0.061g of dimethylaminopyridine were added to the reaction solution, and the reaction was started at 200 ℃ under normal pressure. After 30 minutes, the temperature was raised to 220 ℃ under normal pressure, and the pressure in the system was slowly reduced. After 3 hours from the start of the reaction, the temperature was further raised and the pressure was reduced, and 5 hours from the start of the reaction, the final temperature in the system was set to 320 ℃ and the degree of vacuum was set to about 0.5mmHg (66.7Pa), and phenol and diphenyl carbonate produced by the reaction were gradually removed from the system. After completion of the reaction, methylene chloride was added to the residue, and the mixture was filtered by suction using a Teflon filter having a pore size of 0.2 μm (Millipore Co., Ltd.) to remove the residual phenol and diphenyl carbonate, thereby separating and purifying 0.8g of carbon nanotubes. The average diameter of the carbon nanotubes after the reaction was determined by TEM measurement to be 28nm and the average aspect ratio was determined to be 50. The average particle diameter determined by dynamic light scattering measurement was 582 nm. Further, the elemental analysis of the surface by ESCA revealed that 94.3% of carbon and 5.7% of oxygen were contained, and the amount of carbon was increased as compared with the strongly acid-treated product, suggesting that the esterification reaction was performed. Using 0.75g of the phenyl ester of carbon nanotubes thus obtained, a mixed dope of an aramid resin/carbon nanotubes (weight ratio) 95/5 was prepared in the same manner as in example 5, and spun to obtain a composite fiber. Table 1 shows various physical properties of the fiber.

Example 7

50g of phenol was added to 1g of the phenyl ester of carbon nanotubes obtained in example 6, and the mixture was treated in a mortar at about 70 ℃ for 10 minutes, and then subjected to ultrasonic treatment in a 70 ℃ warm water bath at a vibration frequency of 28kHz for 10 minutes. 100g of aniline was added thereto, and the reaction was started at 200 ℃ under normal pressure. After 30 minutes the temperature was raised to 220 ℃ at atmospheric pressure. After 1 hour from the start of the reaction, the temperature was further raised, and 3 hours from the start of the reaction, the final temperature in the system was set at 280 ℃ and the degree of vacuum was set at about 0.5mmHg (66.7Pa), and phenol and diphenyl carbonate produced by the reaction were gradually removed from the system. After completion of the reaction, methylene chloride was added to the residue, and the mixture was filtered by suction using a Teflon filter (Millipore) having a pore size of 0.2. mu.m, to remove the residual phenol and aniline, thereby separating and purifying 0.9g of carbon nanotubes. The average diameter of the carbon nanotubes after the reaction was determined by TEM measurement to be 29nm and the average aspect ratio was determined to be 48. The average particle diameter determined by dynamic light scattering measurement was 539 nm. Further, elemental analysis of the surface by ESCA revealed that 94.1% of carbon, 1.5% of nitrogen and 4.4% of oxygen were detected, and that nitrogen and oxygen were reduced as compared with the phenyl ester compound, suggesting that an amide compound was formed. Using 0.75g of the carbon nanotube benzamide thus obtained, a mixed dope of an aramid resin/carbon nanotube (weight ratio) 95/5 was prepared in the same manner as in example 5, and spun to obtain a composite fiber. Table 1 shows various physical properties of the fiber.

Example 8

A conjugate fiber was obtained in the same manner as in example 2 except that a multilayered carbon nanotube (trade name: VGCF) manufactured by Showa Denko K.K.was used. The carbon nanotubes after bead mill treatment had an average diameter of 107nm and an average aspect ratio of 31. The average particle diameter determined by dynamic light scattering measurement was 1010 nm. Table 1 shows various physical properties of the fiber.

Example 9

A conjugate fiber was obtained in the same manner as in example 4 except that a multilayered carbon nanotube (trade name: VGCF) manufactured by Showa Denko K.K.was used. The carbon nanotubes after strong acid treatment had an average diameter of 94nm and an average aspect ratio of 28. The average particle size determined by dynamic light scattering measurement was 682 nm. Table 1 shows various physical properties of the fiber.

Example 10

0.15g of the single-walled carbon nanotube synthesized in reference example 2 was added to NMP50g, and ultrasonic treatment was performed for 16 hours using ultrasonic waves having a vibration frequency of 38 kHz. To the NMP dispersion, 247.5g of the aramid resin solution of reference example 1 was added, and stirred at 80 ℃ for 4 hours, thereby obtaining a mixed dope of aramid resin/carbon nanotube (weight ratio) 99/1. A composite fiber was obtained by spinning in the same manner as in example 1. Table 1 shows various physical properties of the fiber.

Example 11

150mL of concentrated sulfuric acid having a concentration of about 98% was added to 0.5g of the single-walled carbon nanotube obtained in reference example 2, and after stirring and cooling to 0 ℃, 50mL of concentrated nitric acid having a concentration of about 61% was slowly dropped. Then, the treatment was carried out for 1 hour in a warm water bath at 70 ℃ by ultrasonic waves with a vibration frequency of 38 kHz. After cooling to room temperature, the strong acid solution was dispersed in water, and the mixture was thoroughly filtered using a Teflon filter (Millipore) having a pore size of 0.2. mu.m, and washed to recover carbon nanotubes. The carbon nanotubes after the strong acid treatment had an average diameter of 1.1nm and an average aspect ratio of 100. However, as before processing, most have beam-like structures with a width of about 10 nm. The average particle size determined by dynamic light scattering measurement was 189nm, which was smaller than 250nm before the treatment. Further, elemental analysis of the surface by ESCA showed 93.4% of carbon and 6.6% of oxygen. Using 0.15g of the carbon nanotubes, a mixed dope of an aramid resin/carbon nanotubes (weight ratio) 99/1 was obtained in the same manner as in example 10. The mixed dopant was observed by an optical microscope, and it was confirmed that the dispersibility of the carbon nanotubes was high. A composite fiber was obtained by spinning in the same manner as in example 1. Table 1 shows various physical properties of the fiber.

Comparative example 1

To 245g of the aramid resin solution of NMP prepared in reference example 1, NMP55g was further added, and stirred at a temperature of 80 ℃ for 4 hours, thereby obtaining an aramid resin solution containing no carbon nanotube having almost the same polymer concentration as in example. An aramid fiber was obtained from this solution by spinning in the same manner as in example 1. Table 1 shows various physical properties of the fiber.

Comparative example 2

In the spinning step of example 1, the composite fiber was dried by a drying roll at 120 ℃ before drawing, and then taken out to evaluate various physical properties. The physical properties are shown in table 1.

Claims (14)

1. A composite fiber comprising a composition comprising: mainly comprises the following formula

-NH-Ar¹-NH-(A)

-OC-Ar²-CO-(B)

100 parts by weight of wholly aromatic polyamide constituting a constituent unit, and 1 to 10 parts by weight of carbon nanotubes having an average diameter of 0.4 to 100nm and an average aspect ratio of 5.0 or more; the carbon nanotubes are oriented in the direction of the fiber axis, wherein in the general formulae (A) and (B), Ar¹、Ar²Each independently represents a carbon number of 6 to 20A 2-valent aromatic group,

characterized in that the carbon nanotubes are multilayered carbon nanotubes, the orientation coefficient F of the carbon nanotubes, which is determined by the following formula (1), is 0.1 or more,

wherein φ is an azimuth angle in X-ray diffraction measurement, and I is diffraction intensity of a 002 crystal plane.

2. The composite fiber according to claim 1, wherein Ar in the wholly aromatic polyamide is Ar¹Is composed of

And/or

Ar²Is composed of

3. The composite fiber according to claim 2, wherein the wholly aromatic polyamide is Ar¹Is composed of

And

Ar²is composed of

Copolymer of Ar¹And Ar²The copolymerization ratio of (A) to (B) is 1: 0.8-1: 1.2.

4. The conjugate fiber according to claim 1, wherein the wholly aromatic polyamide obtained by the formula (1) has an orientation coefficient F of 0.5 or more.

5. The composite fiber according to claim 1, wherein the carbon nanotube used has a ratio of oxygen atoms present on the surface thereof in the range of 2 to 25 relative to 100 carbon atoms.

6. The composite fiber according to claim 1, wherein the carbon nanotubes used are subjected to physical micronization treatment.

7. The composite fiber according to claim 1, wherein the carbon nanotubes used are treated with a strong acid having a pH of 0.01 to 2.

8. The composite fiber according to claim 1, wherein a carbon nanotube esterified by a strong acid treatment at a pH of 0.01 to 2 is used.

9. The composite fiber according to claim 1, wherein the carbon nanotube is amidated after being treated with a strong acid having a pH of 0.01 to 2 and esterified.

10. The method for producing a composite fiber according to claim 1, wherein the wholly aromatic polyamide and the solvent dispersion of the carbon nanotubes are mixed and spun to orient the carbon nanotubes.

11. The method for producing a composite fiber according to claim 10, wherein a carbon nanotube physically micronized is used.

12. The method for producing a composite fiber according to claim 10, wherein a carbon nanotube treated with a strong acid having a pH of 0.01 to 2 is used.

13. The method for producing a composite fiber according to claim 10, wherein a carbon nanotube esterified by a strong acid treatment at a pH of 0.01 to 2 is used.

14. The method for producing a composite fiber according to claim 10, wherein a carbon nanotube is used, which is treated with a strong acid having a pH of 0.01 to 2 and esterified, and then amidated.