KR20120115029A - Acrylonitrile copolymer for pan based carbon fiber precursor - Google Patents

Abstract

PURPOSE: An acrylonitrile copolymer resin composition for a PAN-based carbon fiber precusor is provided to obtain the carbon fiber precursor of high function, which minimizes structural defect. CONSTITUTION: An acrylonitrile copolymer resin composition for a PAN-based carbon fiber precursor contains a repetitive unit of chemical formula 1. In chemical formula 1, m is 99-99.9 mole% and n is 0.1-1 mole%. The weight-average molecular weight of acrylonitrile-based acrylonitrile copolymer resin composition is 60,000-150,000. The carbonyl group anion of chemical formula 1 binds with dicyclohexyl ammonium 2-cyanoacrylate, Li, Na, K, Cs, ammonium cation, or pyridinium cation. The carbon fiber is fabricated using the composition.

Description

Acrylonitrile Copolymer For PAN Based Carbon Fiber Precursor}

The present invention relates to an acrylonitrile-based copolymer resin composition for a PAN-based carbon fiber precursor for producing carbon fibers.

Carbon fiber refers to a carbonaceous fibrous material having a carbon content of 92% or more and a non-graphite state obtained by heating an organic fiber precursor (precursor). After Thomas Edison's invention of carbon fiber filaments for incandescent lamps in 1880, various types of precursors such as Rayon, Pitch, and Polyacrylonitrile (PAN) were developed and used in the manufacture of carbon fibers.

Rayon-based precursors have a carbon content of 44.4% structurally, but the reactions are complicated and the yield of carbon fibers is low as 25-30%. On the other hand, the pitch-based precursor has a high yield of more than 85% and also excellent elastic modulus of the carbon fiber. However, it is known that compressibility and anisotropy are lower than those of PAN-based carbon fibers. Acrylonitrile, a precursor material of PAN-based carbon fibers, has a carbon content of 67.9%, but PAN polymer is composed of a continuous carbon main chain, and the nitrile group is the ideal structure for causing a cyclization reaction. The PAN precursor obtained by the present invention has a carbon yield of 50 to 55% despite a theoretical theoretical carbon content lower than that of the pitch precursor, and is capable of producing high-performance carbon fibers having high strength and high elastic modulus.

PAN-based carbon fiber, which currently accounts for more than 90% of the carbon fiber market, has high performance in aerospace, automotive, civil engineering, and electrical and electronic industries based on its excellent strength, elastic modulus, heat resistance, impact resistance, and chemical resistance. In addition to being used as an industrial material, it is also used as a sports material such as tennis rackets, golf clubs, bicycle frames by taking advantage of light weight.

After the commercialization of the PAN-based carbon fiber, various approaches have been attempted to improve the physical properties of the carbon fiber, among which improved physical properties and process improvement through the chemical composition of the PAN precursor. During the oxidation stabilization process at a relatively high temperature of 200-300 ° C. under an air atmosphere, it is known that exothermic reactions due to cyclization, oxidation, and dehydrogenation of PAN polymers occur suddenly for a short time and are difficult to control. This exothermic reaction may cause breakage of the PAN polymer chain and consequently lower the physical properties of the carbon fiber. However, the introduction of comonomers such as itaconic acid (IA) and methacrylic acid (MAA) can be used to control these exothermic reactions and lower the initiation temperature of the reaction. This is because the cyclization reaction of the PAN homopolymer is initiated by the radical mechanism, whereas the PAN copolymer having acid groups initiates the cyclization reaction at a lower temperature by the ionic mechanism.

In addition, the comonomers of methyl acrylate (MA) and methyl methacrylate (MMA) act as plasticizers in the copolymer. This loosens the structure of the molecule, making it more soluble in spinning solvents, and improving the radioactivity and dye leveling properties. The use of such comonomers can increase the economic efficiency for the stabilization process and subsequent processes of the PAN precursor, as well as affect the quality of the final carbon fiber.

As such, the most common comonomers available for PAN copolymers known to date and the most effective comonomers for oligomerization of nitrile groups are itaconic acid having two carboxylic acids. The presence of two carboxylic acids increases the likelihood of interaction of acrylonitrile with nitrile groups. Therefore, itaconic acid lowers the initiation temperature of the cyclization reaction of the copolymer and decreases the amount of heat generated during the stabilization step, thereby improving the efficiency of the stabilization process. However, the low thermal stability of the comonomer has a problem of lowering the strength of the carbon fiber by thermal decomposition during the stabilization process of the precursor polymer.

Therefore, the present invention is to provide a new comonomer and PAN copolymer resin composition and a manufacturing method that can alleviate the rapid exothermic reaction in the oxidation stabilization process in the production of carbon fiber, and lower the reaction start temperature of the cyclization reaction. Shall be.

In the present invention, in order to lower the initiation temperature and calorific value of the cyclization reaction, and to improve the carbonization yield, a comonomer having one nitrile group and a carbonyl group anion per unit molecule is synthesized and a PAN copolymer is used to provide a carbon fiber precursor. By confirming the applicable characteristics to complete the present invention.

The present invention provides an acrylonitrile-based copolymer resin composition for a PAN-based carbon fiber precursor comprising a repeating unit represented by the following formula (1).

[Formula 1]

Hereinafter, the present invention will be described in more detail.

The acrylonitrile-based copolymer resin composition for PAN-based carbon fiber precursor of the present invention is an acrylonitrile-based copolymer resin composition containing a repeating unit represented by the following formula (1).

[Formula 1]

In the present invention, in the preparation of carbon fiber with PAN precursor, the reaction is easily initiated by oxidative stabilization process, so that the reaction occurs easily and the growth of cyclization reaction is continued. It relates to an acrylonitrile-based copolymer resin composition for increasing the yield of.

Acrylonitrile-based copolymer resin composition having a repeating unit of Formula 1 is a copolymer of acrylonitrile monomer and cyanoacrylate monomer, and introduces a cyano group having a structure similar to a carboxyl group and acrylonitrile monomer to give a ring during oxidation stabilization process. The reaction occurs easily and at the same time continues the growth of the cyclization reaction.

In the acrylonitrile copolymer resin composition of the present invention, assuming that the sum of m and n is 100 mol%, m is preferably 99 to 99.9 mol%, and n is 0.1 to 1 mol%.

The comonomer of the acrylonitrile-based copolymer resin composition of the present invention is an organometallic compound of Groups 1 and 2 (Li, Na, K, Cs, etc.) capable of ionically bonding with the carbonyl anion of [Formula 1], or It is preferable to ionically bond with either an organic ammonium cation forming a cation or a pyridinium cation forming a cation. The organic ammonium cation or pyridinium cation may be substituted with an alkyl group, a cycloalkyl group, an aryl group, a phenyl group, and the like, and examples thereof include dimethylammonium, dicyclohexylammonium, and tetrabutylammonium (tetra-n). It may be any one of -butylammonium, and the pyridinium cation forming the cation may be any one of alkylated pyridinium such as pyridine-N oxide, cetylpyridinium.

Exothermic reactions by cyclization, oxidation, and dehydrogenation during oxidative stabilization processes are difficult to control because they occur abruptly for a short time, and these exothermic reactions can cause breakage of PAN polymer chains, resulting in carbon fiber It may lower the physical properties. However, since the acrylonitrile copolymer resin composition of the present invention has carbonyl anion and cyano group, the anion functional group initiates the cyclization reaction of the nitrile group of acrylonitrile at lower temperature by the ionic mechanism. It can be stabilized at a lower temperature than the oxidative stabilization process of the conventional acrylonitrile copolymer for carbon fiber precursors, and it is possible to control the exothermic reaction of the PAN homopolymer by continuing the growth of the cyclization reaction due to the presence of cyano groups. It can have higher degree of cyclization and lower calorific value than the acid-containing copolymer resin composition, which lowers the activation energy and calorific value required for the reaction to be started, thereby increasing the efficiency of precursor stabilization reaction, yield of carbon fiber, and energy efficiency and productivity of the production process. Can improve .

The exothermic onset temperature of the cyclization reaction by differential scanning calorimetry under a nitrogen atmosphere of the polyacrylonitrile-based polymer according to the present invention includes a temperature range of 230 ° C. to 240 ° C. at a heating rate of 10 ° C./min. It is shown that under the same conditions, an oxidative stabilization process under an air atmosphere exhibits a very low exothermic onset initiation temperature ranging from 150 ° C to 180 ° C.

According to the thermogravimetric analysis of the polyacrylonitrile-based polymer according to the present invention under nitrogen and oxygen atmosphere, it shows high thermal stability at room temperature of 600 ° C. at room temperature. This high thermal stability can produce a stable carbon structure in the oxidative stabilization reaction and can provide a high-strength carbon fiber by minimizing defects in the carbon structure.

In addition, the weight average molecular weight of the acrylonitrile-based copolymer resin composition having a repeating unit of the formula (1) of the present invention is 60,000 to 150,000, the polydispersity index (Mw / Mn) is preferably 1.5 to 4.0. Due to the nature of the two-component copolymerization, the increase of the comonomer leads to a decrease in molecular weight and an increase in the polydispersity index. The weight average molecular weight is 60,000 to 150,000 and 1.5 to 4.0 in consideration of the post-polymerization process and the properties of the final carbon fiber. Dispersion index is preferred.

In addition, the present invention may provide a carbon fiber prepared using the acrylonitrile-based copolymer resin composition for the PAN-based carbon fiber precursor.

The preferable manufacture example of the acrylonitrile-type copolymer resin composition for PAN type carbon fiber precursor of this invention is demonstrated.

Dicyclohexylammonium 2-cyanoacrylate, which is an example of a monomer for synthesizing the acrylonitrile-based copolymer resin composition for the PAN-based carbon fiber precursor in the present invention, is cyanoacetic acid. , Paraformaldehyde (diformaldehyde), dicyclohexylamine, triethylamine (triethylamine) is dissolved in benzene and then heated and stirred for 20 minutes to remove water using Dean-Stark. After the reaction was terminated, the solution was filtered to remove the reacted polymer pieces and dried in vacuo, and then recrystallized with hexane and benzene to prepare dicyclohexylammonium 2-cyanoacrylate.

Acrylonitrile is removed by atmospheric distillation immediately after use to remove moisture. In the copolymerization, solvent DMSO is added to the reactor and the reaction temperature is raised to 60 ° C. while stirring, and the solvent and oxygen in the reactor are removed while purge nitrogen. When the reaction temperature is reached, the acrylonitrile monomer and the cyanoacrylate monomer are each added, stirred for a predetermined time, and then AIBN is added thereto, followed by polymerization for 16 hours under a nitrogen stream. Solvents used for solution polymerization are suitable solvents which are soluble to polyacrylonitrile polymers such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, etc., of which the chain transfer constant (Cs) is the smallest. Most preferred is dimethyl sulfoxide having excellent solubility due to strong polarity. As a polymerization initiator, an oil-soluble azo compound which does not have a possibility of generating oxygen which inhibits polymerization at the time of decomposition in terms of solubility in solvents and polymerization efficiency due to the nature of solution polymerization is preferable, and the radical generation temperature is related to the handleability and the boiling point of monomers. The radical polymerization initiator of the range of 40 degreeC-80 degreeC is preferable. As a specific example of a polymerization initiator, 2, 2- azobis (2, 4- dimethylvaleronitrile) (radical generation temperature 51 degreeC), 2, 2- azobis (isobutyronitrile) (radical generation temperature 65 degreeC), etc. And it is not limited only to the polymerization initiator specified. In addition, the polymerization initiator may be used alone or in combination with a plurality of initiators, and the polymerization temperature may be adjusted to generate the maximum amount of radicals.

According to a preferred embodiment of the method for producing a polyacrylonitrile-based polymer of the present invention, the concentration of the monomer in the solvent is controlled to 5 to 30% by weight, and a polymerization initiator corresponding to 1 to 5% by weight of the monomer concentration is added thereto. The mixture is polymerized for 16 hours or more under a nitrogen gas stream under a polymerization temperature of 55 to 65 ° C. The polymerization temperature may vary depending on the type of monomer, solvent, and polymerization initiator, but a temperature of 40 ° C. to 80 ° C. or less is preferable. When dimethylsulfoxide is used as a solvent at a temperature of 30 ° C. or lower, heterogeneous polymerization may occur due to the high freezing point of the solvent, and storage of a polymerization initiator that generates radicals at low temperature (below −10 ° C.) is also difficult. In addition, since the boiling point of acrylonitrile is 78 ° C., if the polymerization temperature exceeds 80 ° C., problems may occur in the production of polyacrylonitrile polymers such as delay in polymerization time.

After the polymerization, the polymer is degassed under vacuum conditions to remove the gas in the polymer, and slowly poured into distilled water to solidify in a yarn form. Water washed several times with distilled water to remove the unreacted monomer and solvent, then pulverized, washed again with distilled water several times and dried under vacuum to complete the copolymerization.

According to the present invention, by using the cyanoacrylate as a comonomer of the polyacrylonitrile polymer, it is possible to lower the onset temperature and calorific value of the oxidative stabilization process to provide a high-performance carbon fiber precursor that can minimize structural defects in the production of carbon fiber can do.

In addition, the present invention can optimize the precursor according to the content of the cyanoacrylate, it is possible to use the existing polymerization, spinning, oxidation, carbonization apparatus can provide a carbon fiber precursor with high economical efficiency without supplementary equipment, New comonomers can be provided by replacing the existing comonomers such as methyl acrylate (MA), methyl methacrylate (MMA) and itaconic acid (IA). Productivity can be improved by increasing the yield of the fiber.

1 is a graph showing the results of thermogravimetric analysis under the air atmosphere of the polyacrylonitrile-based copolymer resin compositions of Examples and Comparative Examples.

Hereinafter, the present invention will be described in detail through examples. The following examples are only examples for describing the present invention, but the present invention is not limited thereto.

[Examples 1-4 and Comparative Examples 1-2]

1.Synthesis of Dicyclohexylammonium 2-cyanoacrylate

1) Reagent

Cyanoacetic acid (99%, Aldrich), paraformaldehyde powder (95%, Aldrich), dicyclohexylamine (99%, Acros), triethylamine (Junsei) ), Hexane (hexane (95%, Samchun)), benzene (benzene (99.5%, Daejung)) was used as it is without further purification.

2) Synthesis of Dicyclohexylammonium 2-cyanoacrylate

Cyanoacetic acid, paraformaldehyde, dicyclohexylamine and triethyleneamine were dissolved in benzene, and then water was removed using a Dean-Stark apparatus while heating and stirring at 90 to 100 ° C. for 20 minutes. After the reaction was completed, the solution was filtered to remove the polymer pieces and vacuum dried to remove the solvent. After recrystallization with hexane, the obtained compound was recrystallized with benzene again to synthesize dicyclohexylammonium 2-cyanoacrylate.

2 Polymerization of Acrylonitrile Copolymer

1) Reagent

Acrylonitrile (AN, 95%, Daejung) was removed by atmospheric distillation at 90 ℃ immediately after use to remove moisture using molecular sieve 4A. Dimethyl sulfoxide (DMSO, 99%, Junsei) was used to remove water using molecular sieve 4A, and then distilled under reduced pressure at 70 ℃, 10 ~ 12 Torr conditions. The polymerization initiator 2,2'-azobis (isobutyronitrile) (AIBN, 99%, Daejung) was recrystallized twice with methanol. Itaconic acid (IA, 99%, Junsei) used for polymerization of known Acrylonitrile / itaconic acid copolymer was used by recrystallization twice with distilled water.

2) copolymerization

The solvent DMSO was added to a double-jacket reactor equipped with a Heidolph RZR 2052 overhead stirrer, a condenser, a thermometer, and a purge needle, and the reaction temperature was raised to 60 ° C. while stirring at 100 rpm. Upon stirring, the solvent and oxygen in the reactor were removed while purge nitrogen. When the reaction temperature was reached, the monomers were added as shown in Table 1 below, and the mixture was stirred for a while, and 0.5 wt% of AIBN was added thereto. Then, the polymerization was carried out for 16 hours under conditions of 60 ° C. and 200 rpm under a nitrogen stream.

After the polymerization, the polymer was degassed under vacuum conditions for 2 hours to remove the gas in the polymer, and slowly poured into distilled water to solidify in a yarn form. Water washed several times with distilled water to remove the unreacted monomer and solvent, then pulverized, washed with distilled water several times and dried in vacuo at 60 ℃ for 24 hours.

division Acrylonitrile (mol%) Cyanoacrylate
(mol%) Itaconic acid
(mol%) Example 1
(AC-0.19) 99.81 0.19 - Example 2
(AC-0.38) 99.62 0.38 - Example 3
(AC-0.58) 99.42 0.58 - Example 4
(AC-0.78) 99.22 0.78 - Comparative Example 1
(PAN-homo) 100.00 - - Comparative Example 2
(AI-0.82) 99.18 - 0.82

3. Analysis

1) Intrinsic viscosity

SCHOTT AVS 360 Ubbelohde viscometer was used, and dimethyl formamide (DMF) was used as a solvent. The concentration of the viscous solution was prepared at 0.5 g / dl and measured at a temperature of 30 ± 0.1. The t _{0 of the} solvent and the passage time (t) of the initial concentration solution and the dilute solution were measured five times, and an average value was used. The viscosity average molecular weight (Mv) was calculated using the following equation.

[η] = 2.86 × 10 ^-4 M _v 0.733

2) GPC

The number average (Mn) and weight average (Mw) molecular weights of the polymers of Examples and Comparative Examples were measured using TLCOH HLC-8320GPC and dimethyl formamide (DMF) containing lithium bromide (LiBr).

3) DSC

Q200 from TA Instrument was used to confirm the thermal behavior of the polymers of the Examples and Comparative Examples. It heated up to 450 degreeC under nitrogen and air stream at the temperature increase rate of 10 degreeC / min. Thermograms from DSC measurements were analyzed for temperature and calorimetry using TA's Universal analysis 2000 software, and GRAMS / 32 software was used to isolate each reaction that appears to overlap under air streams.

4) TGA

Thermogravimetric analysis was measured up to 600 ° C. using NETZSCH STA 409PC while raising the temperature at a rate of 10 / min under nitrogen and air streams.

4. Results and Discussion

1. Analysis of Copolymers

Table 2 shows the physical properties of the polyacrylonitrile copolymer resin compositions prepared in Examples 1 to 4 and Comparative Examples 1 and 2. It shows the weight average molecular weight, polydispersity index, intrinsic viscosity, and molecular weight by viscosity according to the comonomer composition.

From the above results, the precursor polymers prepared in Examples 1 to 4 of the present invention showed a weight average molecular weight of 60,000 to 100,000, and a viscosity of 0.78 to 13.38 dl / g.

Sample code Monomer in feed
(mol%) Conversion
(wt%) M _w ^a
(× 10 ⁴ ) PDI ^a
(M _w / M _n ) M _v ^b
(× 10 ⁴ ) [η] ^b
(dℓ / g) AN IA CA Example 1 99.81 - 0.19 88.3 9.99 2.09 13.38 1.63 Example 2 99.62 - 0.38 78.4 9.11 2.26 8.98 1.22 Example 3 99.42 - 0.58 77.1 8.37 2.61 7.88 1.11 Example 4 99.22 - 0.78 74.1 6.26 3.19 4.87 0.78 Comparative Example 1 100 - - 77.5 11.12 2.04 19.46 2.15 Comparative Example 2 99.18 0.82 - 77.6 13.76 1.81 24.23 2.53

2. Cyclization Reaction and Thermal Stability

Table 3 shows the test results of the differential scanning calorimetry under the air atmosphere of the polyacrylonitrile-based copolymer resin compositions prepared in Examples 1 to 4 and Comparative Examples 1 to 2. In Examples 1 to 4 of the present invention, the lower cyclization onset temperature and the calorific value than the polyacrylonitrile polymer Comparative Example 1 alone were confirmed, and showed similar characteristics as those of Comparative Example 2.

Sample code T _i ^a (℃) T _f ^b (℃) ΔT ^c (° C.) T _pk ^d (℃) △ H ^e
(J / g) △ H / △ T
(J / g × min) Example 1 184.4 430.2 245.8 308.5 4094 166.6 Example 2 168.3 415.9 247.6 307.2 3903 157.6 Example 3 160.5 409.7 249.2 305.6 3464 139 Example 4 160.1 410.1 250 304.3 2914 116.6 Comparative Example 1 209.1 445.3 236.2 318.8 3960 167.7 Comparative Example 2 180.6 411 230.4 279.7 2993 129.9

It was shown in Figure 1 by performing a thermogravimetric analysis under an air atmosphere with a polyacrylonitrile-based copolymer resin composition prepared in Examples 1 to 4 and Comparative Examples 1 to 2.

The high thermal stability of the copolymer resin composition of the present invention was confirmed. Low cyclization onset temperature, calorific value and high thermal stability can confirm the properties that can be applied to the carbon fiber precursor.

Claims (5)

Acrylonitrile-based copolymer resin composition for a PAN-based carbon fiber precursor comprising a repeating unit represented by the formula (1).
[Formula 1]

The method of claim 1,
Assuming that the sum of m and n is 100 mol%, m is 99 to 99.9 mol%, and n is 0.1 to 1 mol% acrylonitrile copolymer resin composition for a PAN-based carbon fiber precursor.
The method of claim 1,
The acrylonitrile copolymer resin composition has a weight average molecular weight of 60,000 ~ 150,000, polydispersity index (Mw / Mn) is 1.5 ~ 4.0 acrylonitrile copolymer copolymer composition for PAN carbon fiber precursor.
The method of claim 1,
Acrylo for PAN-based carbon fiber precursors that ionically bond with any of the carbonyl group anion of [Formula 1] and dicyclohexyl ammonium 2-cyanoacrylate, Li, Na, K, Cs, ammonium cation and pyridinium cation Nitrile Copolymer Resin Composition.
The carbon fiber manufactured using the acrylonitrile-type copolymer resin composition for PAN type carbon fiber precursor of any one of Claims 1-4.

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