JPH0376823A - Production of acrylonitrile polymer-based carbon fiber - Google Patents

Abstract

PURPOSE:To obtain a carbon fiber having high strength and modulus at high calcination speed by using a fiber composed of a stereoregular acrylonitrile polymer having a specific isotactic triad fraction as a raw material. CONSTITUTION:The objective fiber is produced from a fiber composed of a stereoregular acrylonitrile polymer having an isotactic triad fraction of an acrylonitrile monomer chain of >=0.35 determined by <13>C-NMR.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing carbon fibers having a high firing rate, high strength, and high modulus of elasticity from a highly stereoregular acrylonitrile polymer.

[Conventional technology]

In the field of carbon fibers, there have been many efforts such as examining copolymerization components in the starting material polymer, stretching during the flameproofing stage, temperature control during the carbonization process, and reducing impurities and unnecessary residues in the process. Research has been conducted to increase the strength and elastic modulus of carbon fibers. Additionally, in order to increase the firing rate, methods have been used in which monomers containing carboxylic acids and the like are copolymerized.

[Problem that the invention seeks to solve]

However, the theoretical strength of graphite crystal is 18,000 kg/
-1 theoretical elastic modulus is 1007on/-,
Acrylonitrile polymer carbon fibers are called high-strength carbon fibers and have a strength of 250 to 700 kg/d (1.4 to 3.9% of theoretical strength) and an elastic modulus of 20 to 30 To.
n/d, which is called high modulus carbon fiber and has a strength of 25
0~350 kg/ij, elastic modulus 35~45 Ton
/- (35 to 45% of the theoretical elastic modulus), which is far from the theoretical value for both strength and elastic modulus, and moreover, pitch-based carbon fiber (strength: 1
50-300 kg/lj, elastic modulus: 30-70 T
Although the strength is higher than that of on/d), there are problems such as a low elastic modulus. Therefore, it has not been possible to obtain a fiber that simultaneously maintains sufficient strength and elastic modulus in the fields of industrial materials, space engineering, etc., and the use of acrylonitrile polymer carbon fiber is currently limited. .

In view of the current situation, the present inventors have conducted extensive research, and as a result, by using an acrylonitrile polymer with enhanced stereoregularity as a starting material, the strength and elastic modulus of carbon fibers have been improved more than ever before. Moreover, at the same time, they succeeded in increasing the firing speed during the manufacturing stage more than ever before.

[Means to solve the problem]

That is, the present invention provides isotactic analysis of acrylonitrile monomer chain portions defined by 13C-NMR.
This is a method for producing carbon fibers, characterized in that fibers made of a stereoregular acrylonitrile polymer having a triad fraction of at least 0.35 are used as raw materials.

Isotactic triad fraction is one of the triat fractions in the so-called stereoregularity representation method,
In the case of acrylonitrile polymers, for example, "C-NMR" of solutions dissolved in deuterated dimethyl sulfoxide
It is calculated from the peak intensity of the carbon of the cyano group. More specifically, Polymer Journal Vol. 17, p. 1291 (1
It is determined by peak identification based on pentad tacticity assigned by the method of Ueyama et al. described in 985). That is, "mlnllJff1ml for the total peak intensity of the cyano group carbon region in the peak splitting chart based on the stereoregularity of nuclear magnetic resonance absorption of C-NMR.
The ratio of the sum of the intensities of the three peaks llr+rmmr is the isotactic triad fraction.

In this measurement, in order to increase the resolution and provide quantitative performance, we particularly focused on the absorption peak in the 95 region (119
~121 ppc (based on tetramethylsilane) only, and observe ±500 Hz around that peak. The equipment is a Fourier transform NMR manufactured by JEOL (FX-200).
”), deuterated dimethyl sulfoxide is used as the solvent, and the sample concentration is adjusted to 3 to 20% by weight.

The measurement conditions are: temperature 80°C, observation frequency width 100°C.
0 Hz, data point 16, lH' at time 6
．． 5μs (45' pulse) Pulse delay time 2.5s
, sampling time 8.1s, integration number 64 x 1
Set to 0~64 x 100.

The isotactic triad fraction of the stereoregular acrylonitrile polymer used to obtain carbon fibers that achieve the purpose of the present invention must be 0.35 or more. If the value is smaller than this, the firing rate will be lower than that of conventional starting materials containing a copolymer, resulting in poor productivity. At the same time, sufficiently satisfactory strength and elastic modulus cannot be obtained. In particular, for the development of high elastic modulus, the tactical triat fraction is 0.
．． It must be 35 or more.

The acrylonitrile polymer in the present invention refers to a polymer containing at least 90% by weight of acrylonitrile. There is no problem in containing a copolymer component, but a single polymer is more effective. Examples of copolymerization components include alkyl acrylates such as methyl acrylate, alkyl methacrylates such as methyl methacrylate, alkyl-substituted acrylonitriles such as methacrylonitrile and crotonitrile, and alkyl-substituted vinylpyridines such as 2-vinylpyridine. .

Two typical examples of methods for producing stereoregular acrylonitrile polymers are shown below. One is to irradiate the urea/acrylonitrile clathrate compound with active rays such as gamma rays [for example, Japanese Patent Application No. 120242/1983], and the other is to irradiate the urea/acrylonitrile clathrate compound with active rays such as gamma rays [for example, Japanese Patent Application No. 120242/1983]. [For example, Japanese Patent Application No. 63-26522]. To describe the former synthesis method in detail, first, 0.002 mol of n-butyl mercaptan is added to acrylonitrile as a molecular weight Wl f If agent. , and urea purified by recrystallization in a methanol/water system in advance at a molar ratio of 1:1.5 were placed in a dewar bottle, mixed and sealed, and cooled to -78°C using dry ice. Let stand for about 6 days. Then, at −78 °C for 10
．． 000 curie gamma rays at a dose rate of 1.6X10'
After approximately 100 minutes of X-ray/hour irradiation, the reaction is washed with warm water and methanol to completely remove and purify the urea.

Next, we will discuss the latter method of synthesis using organometallic compounds. First, a three-necked flask is purged with nitrogen in a stationary system designed to condense the evaporated components and reflux them. (a mixture of three isomers) and the temperature was adjusted to 120°C, and then a butane solution was added to a 1.0 molar concentration of di-n-hexylmagnesium as a polymerization initiator, and left for IO minutes. Next, 10 cc of acrylonitrile was added dropwise and polymerized for 60 minutes.

An appropriate amount of a mixed solution of hydrochloric acid and methanol is added to this to terminate the polymerization reaction, followed by repeated filtration and water washing for purification. The solvent used for spinning the polymer thus obtained is preferably a protonic acid or an aqueous solution thereof, an aqueous solution of an inorganic salt, or an organic solvent containing an inorganic salt.

A protonic acid is an acid that has hydrogen in its molecule.

Examples of protonic acids include inorganic acids such as nitric acid, sulfuric acid, various phosphoric acids, hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, perchloric acid, acetic acid dichloroacetic acid, trichloroacetic acid, etc. Examples include various organic acids such as acetic acid and trifluoroacetic acid. Water, phenols, and alcohols are also included in protonic acids. 1 degree Celsius for water in a closed system
Acrylonitrile polymers with high stereoregularity can be dissolved under conditions of temperatures exceeding 80 degrees Celsius, phenols and alcohols as well as conditions higher than the temperature corresponding to each compound.

Aqueous solutions of inorganic salts also dissolve highly stereoregular acrylonitrile polymers. Examples of such inorganic salts include various rhodanates such as sodium rhodanate, lithium rhodanate, calcium rhodanate, zinc rhodanate,
Examples include various halogen-containing salts such as zinc chloride and zinc fluoride, and perchlorates such as sodium perchlorate, calcium perchlorate, barium perchlorate, and aluminum perchlorate.

Furthermore, organic solvents containing inorganic salts may also be used. Organic solvents to which no inorganic salts are added do not dissolve the polymer at all or only swell it, making it extremely difficult to dissolve the polymer.

Examples of corresponding organic solvents include dimethylformamide, dimethylsulfoxide, dimethylacetamide, succinonitrile, γ-butyrolactone, aqueous ethylene carbonate solution, and hydroxyacetonitrile. As the inorganic salt to be added, lithium chloride, lithium fluoride, etc. are used.

As a spinning method for this polymer, general dry spinning, wet spinning, and dry-wet spinning can be applied. When performing wet or dry-wet spinning, it is of course possible to spin at a coagulation bath concentration lower than the critical concentration of the coagulation bath, but it is also possible to spin the acrylonitrile polymer at a coagulation bath concentration higher than the critical concentration. The firing speed of the fiber becomes even faster, and carbon fiber with high crystallinity can be produced.

By critical concentration is meant the concentration of solvent in the coagulation bath at which the maximum spinning speed is at a minimum or no spinning is possible, and on either side of which there is a region where spinning is possible.

Furthermore, the crystal orientation of the fibers can be improved by stretching. Examples of such stretching include gel stretching (stretching in a state where a solvent remains), hot water stretching, steam stretching, hot air stretching, heating medium stretching (stretching in a heated organic liquid), and dry heat stretching (dry heat roll, etc.). stretching). It is also possible to use a combination of a plurality of these stretching methods.

To obtain carbon fiber from fibers made of acrylonitrile polymer, the carbonization index (carbonization index) is
After obtaining flame-resistant fibers with a C0 (hereinafter abbreviated as C0■) in the range of 0.50 to 0.65,
It is preferable to carry out the carbonization treatment at a temperature of 00°C.

C and I are carbonization index (Car
This is an abbreviation for bonization index) and is determined as follows. That is, X-ray measurement of the sample is performed, and the scattering intensity at 2θ = 17° and the scattering intensity It at 2θ = 25.5° of the obtained X-ray scattering intensity curve (both values are values obtained by subtracting the value of air scattering). It is calculated using the following formula. (See drawing) Here, 2 (1) reflects the amount of residual acrylonitrile polymer crystals, while (2) reflects the graphite structure. As firing progresses, h decreases and (2) increases, so the C and I values increase.

The present inventors have experimentally confirmed that an acrylonitrile polymer with a high isotactic triad fraction is susceptible to hydrolysis, and this polymer or a fiber made of this polymer was hydrolyzed in an acid aqueous solution. It was also possible to increase the firing rate by decomposing and introducing into the polymer an amide group or carboxyl group as an initiator of the cyclization reaction. As the acid, hydrochloric acid, sulfuric acid, nitric acid, acetic acid, etc. are used. Although the acid aqueous solution may be at room temperature, it is more desirable to heat it.If the acid aqueous solution has a low concentration, it may be heated at a high temperature, and if the acid aqueous solution has a high concentration, it may be heated at a low temperature.

〔Effect of the invention〕

Since the carbon fiber obtained by the present invention has high strength and high elasticity, it is useful for various applications such as in the field of industrial materials, raw materials for composite materials, and space engineering. At the same time, productivity is high due to fast firing.

<Examples> The present invention will now be described in more detail with reference to Examples.

Example 1 An acrylonitrile polymer obtained by the above-mentioned organometallic catalyst method having an isotactic triad fraction of 0.52 was added to a 70% by weight nitric acid aqueous solution at a concentration of 15% by weight in an environment maintained at O''C. When dissolved, this composition exhibited stringiness suitable for spinning.

This spinning stock solution was discharged into a coagulating solution consisting of a 33.0 wt% nitric acid aqueous solution through a spinneret with a pore diameter of 0.18 mm and a number of holes of 40, and coagulated, and then heated 3.0 times in hot water at 95° C. ”
It was stretched 3.2 times with a dry heat roll of C. Next, this fiber was fired in air at 250° C. for 4 hours to obtain a flame-resistant yarn with a C,I value of 0.56.

Afterwards, this flame-resistant yarn was carbonized at 400 to 1400°C in nitrogen, resulting in a strength of 603 kg/d and an elastic modulus of 38.
．． 47 on/- carbon fibers were obtained.

Example 2 When an acrylonitrile polymer produced by an organometallic catalyst method with an isotactic triad fraction of 0.37 was spun and flame-resistant in the same manner as in Example 1, the C,I value was 0.55.
A flame-resistant yarn was obtained.

Thereafter, this flame-resistant yarn was carbonized at 400 to 1400''C in nitrogen, resulting in a strength of 502 kg/mj and an elastic modulus of 3.
0. Carbon fibers of Iton/- were obtained.

Example 3 An acrylonitrile polymer having an isotactic triad fraction of 0.60 by the gamma ray method was spun in the same manner as in Example 1. However, a 45.0% by weight nitric acid aqueous solution was used as the coagulation solution, and then 46% by weight was used as a stretching method with the solvent remaining.
．． 8.0 at 58°C in a bath consisting of 0% by weight nitric acid aqueous solution.
The film was stretched 1.2 times in hot water and 1.9 times using a dry heat roll. Next, this fiber was fired in air at 250° C. for 4 hours to obtain a flame-resistant yarn with a C,I value of 0.59.

Afterwards, this flame-resistant yarn was carbonized at 400 to 1400''C in nitrogen, resulting in a strength of 682 kg/d and an elastic modulus of 42.
．． 2 Ton/- carbon fibers were obtained.

Example 4 The isotactic triad fraction obtained in the example process is 0
．． Polymer No. 52 was treated with 2N hydrochloric acid at 20°C for 30 minutes, then dissolved in a 70% aqueous nitric acid solution at a concentration of 15% by weight, and then the spinning stock solution was dissolved at 33.0% by weight.
A coagulating solution consisting of an aqueous nitric acid solution was discharged from a spinneret with a pore diameter of 0.18 mm and a number of holes of 40, coagulated, and then heated in hot water at 95°C for 2 hours.
．． It was stretched 5 times and 2.8 times with a dry heat roll at 150°C.

This was further made into carbon fiber under the same flame resistance and carbonization conditions as in Example 1. The C and I values of the flame-resistant yarn are 0.65
, the strength of the carbonized yarn is 527 kg/lj, and the elastic modulus is 37
．． It was 3 Ton/-.

Example 5 The fibers made of the acrylonitrile polymer used in Example 1 were also treated with 2N hydrochloric acid at 20°C for 30 minutes, and the fibers were flame-resistant and carbonized in the same manner as in Example 1. The C8 value of the flame-resistant yarn is 0.62, and the strength of the carbonized yarn is 591) cg/
d, the elastic modulus was 36.67 on/-.

Example 6 The isotactic triad fraction obtained in Example 1 is 0
．． When the polymer No. 52 was dissolved in dimethylformamide containing 9.0% by weight of lithium chloride and discharged from the same spindle as in Example 1 into a coagulation bath of a 45% by weight aqueous solution of dimethylformamide, Spinning could be carried out extremely smoothly. This fiber was further made into carbon fiber under the same stretching conditions, flame resistance, and carbonization conditions as in Example 1. The c and r values of the flame-resistant yarn are 0.62, and the strength of the carbonized yarn is 573.
kg7s, the elastic modulus was 39.47 on/-.

Example 7 The isotactic triad fraction obtained in Example 1 is 0
．． The polymer No. 52 was dissolved in a 50% by weight aqueous solution of sodium rhodanate and discharged from the same spinneret as in Example 1 into a coagulation bath of a 12% by weight aqueous sodium rhodanate solution, but spinning was performed extremely well. I was disappointed. When this fiber was further made into carbon fiber under the same stretching conditions, flame resistant and carbonized conditions as in Example 1, the C and I values of the flame resistant yarn were 0.58.
The strength of the carbonized yarn is 586 kg/mj, and the elastic modulus is 36.
It became 8 Ton/-.

Comparative Example 1 AN 94.3% by weight, methyl acrylate 4.5% by weight
, a tertiary radical copolymer consisting of 1.2% by weight of methacrylic acid (isotactic of the acrylonitrile chain part)
The triad fraction was 0.27. ) in a 70% by weight nitric acid aqueous solution in an environment where the temperature is maintained at O''C.
The spinning stock solution was discharged from a spinneret with a pore diameter of 0.075 ym and 3000 holes into a coagulating solution consisting of a 33 wt % nitric acid aqueous solution, coagulated, and stretched 12 times. Next, flame resistance and carbonization were performed in the same manner as in Example 1. The C and I values of the flame-resistant yarn are 0.55, and the strength of the carbonized yarn is 400.
kg/lj, and the elastic modulus was 24.5 Ton/-.

[Brief explanation of drawings]

The drawing is a diagram showing an X-ray scattering intensity curve of a flame-resistant yarn.

Claims (1)

[Claims] ^1^3 A carbon fiber characterized by being made from a fiber made of a stereoregular acrylonitrile polymer having an isotactic triad fraction of an acrylonitrile monomer chain portion of at least 0.35 as determined by C-NMR. Manufacturing method