KR101295699B1 - meta-Aramid/Carbon Nanotube Composites and Method for Preparing the Same - Google Patents

Abstract

The present invention relates to a meta aramid / carbon nanotube composite having excellent heat resistance, mechanical properties, electrical conductivity, and heat generation properties. The present invention includes a method for preparing a meta aramid / carbon nanotube composite by mixing the carbon nanotubes with meta aramid solution. The meta-aramid / carbon nanotube composite composition of the present invention can be used to manufacture various products such as films and fibers.

Description

Meta-Aramid / Carbon Nanotube Composites and Method for Preparing the Same}

The present invention relates to a method of preparing a meta aramid / carbon nanotube nanocomposite by solution mixing a carbon nanotube (high-performance carbon nanoparticles) with a meta-Aramid polymer.

Aramid is a general term for the wholly aromatic polyamide having a molecular structure in which at least 85% of amide bonds (-CONH-) are bonded between aromatic rings, and para-aramid represented by the following formula (1) and meta-aramid represented by the following formula (2) Divided. Para aramid is used in fields characterized by high strength and high elasticity, which are competitive in price. Meanwhile, meta aramid has excellent heat resistance and flame retardancy, but is similar to conventional polyester in physical properties such as strength, elongation and elastic modulus. Para aramids are processed by dissolving them in toxic and dangerous organic solvents such as strong sulfuric acid, while meta aramids are used in relatively safe organic solvents such as dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone. It can be melted and processed.

Aramid fibers, including yarn and woven fabrics, have high modulus in the form of nonwovens, laminating, staples, paper, etc., with excellent strength and stiffness, chemical resistance, low electrical conductivity and shrinkage, dimensional stability, cut resistance, Due to its flame retardancy, it is used for various composite materials such as fiber reinforced rubber composite materials, ropes, cables, anti-ballistic materials, composite materials such as anti-friction materials, and leisure-sport equipment. It is attracting attention as a high value-added material that is being used in various related industries such as aviation, defense, leisure and special industries. Aramid films and plastics are used for magnetic tapes, release films, adhesive tapes, insulating materials, and composite materials.

Carbon nanotube (CNT) is a material that is spotlighted as an almost perfect new material without defects among existing materials, and its electrical conductivity is similar to that of copper, and its thermal conductivity is the most excellent diamond in nature. 100 times better. Carbon fiber can be broken by only 1% deformation, while carbon nanotubes can withstand 15% deformation and are very stable. Carbon nanotubes are plate-shaped graphene sheets are rolled round to a diameter of nanometers, and the graphene sheets exhibit characteristics of metals or semiconductors depending on the angle and structure of the graphene sheets. In addition, it is divided into single-walled carbon nanotubes (hereinafter referred to as "SWCNT") and multi-walled carbon nanotubes (hereinafter referred to as "MWCNT") according to the number of bonds forming a wall. do. These carbon nanotubes have a very strong tendency to bundle together by van der Waals forces. Therefore, researches on how to improve the dispersibility in the polymer matrix or solution by chemically modifying the surface of the carbon nanotubes to introduce various species.

In the present invention, the carbon nanotubes are selected from the group consisting of single-walled carbon nanotubes, multi-walled carbon nanotubes, and surface-modified single-walled carbon nanotubes and multi-walled carbon nanotubes. It is an object of the present invention to provide a meta-aramid / carbon nanotube composite having a meta-aramid polymer as a matrix and a method of manufacturing the same. The meta-aramid / carbon nanotube composite prepared by the present invention is characterized by having improved thermal stability, mechanical properties, electrical conductivity, and heat generation property than the meta-aramid alone polymer.

In order to solve the above problems, according to a preferred embodiment of the present invention, a solution of a meta aramid homopolymer and carbon nanotube having at least 85% of one repeating unit structure selected from the group consisting of It provides a method for producing a meta aramid / carbon nanotube composite by mixing.

According to another suitable embodiment of the present invention, the carbon nanotube content in the composite is characterized in that 0.1 to 20.0% by weight relative to the total weight of the composite.

According to another suitable embodiment of the present invention, the carbon nanotubes are characterized in that the single-walled carbon nanotubes or multi-walled carbon nanotubes.

According to another suitable embodiment of the present invention, the carbon nanotubes are surface modified with one selected from the group consisting of alkyl, allyl, carboxyl, hydroxyl, amine, epoxy, urethane and urea groups It is characterized by.

According to another suitable embodiment of the invention, the solution mixture comprises at least one salt selected from the group consisting of lithium chloride and calcium chloride at a temperature of 10 ℃ to 150 ℃, water, dimethylformamide, dimethylacet It is characterized by using at least one solvent selected from the group consisting of amide, sulfuric acid, dimethyl sulfoxide and N-methyl-2-pyrrolidone.

According to another suitable embodiment of the invention, the salt is characterized in that 0.1 to 20.0% by weight relative to the total solution weight.

Meta aramid / carbon nanotube composite prepared in the present invention has superior thermal stability (heat resistance), mechanical properties, electrical conductivity and heat generation properties than the meta aramid polymer alone. In addition, the meta-aramid / carbon nanotube composite of the present invention can be made of fibers, films, plastics having excellent heat resistance, mechanical properties, electrical conductivity, electrical heating properties. In particular, fibers or films made from meta-aramid / carbon nanotube composites prepared by incorporating carbon nanotubes have improved thermal stability and mechanical strength as compared to fibers or films made of meta-aramid homopolymers. Particularly important feature is that the fiber or film made from the meta-aramid / carbon nanotube composite exhibits excellent electrical conductivity and can be utilized as a material having anti-electric / electromagnetic shielding properties as well as electric heating properties.

Figure 1 shows the surface and volumetric conductivity of the meta-aramid / MWCNT composite prepared in the present invention.
Figure 2 shows the thermal decomposition curve of the meta-aramid / MWCNT composite prepared in the present invention.
Figure 3 shows the storage modulus change with temperature of the meta-aramid / MWCNT composite prepared in the present invention.
Figure 4 shows the electrical heating characteristics with time under various applied voltage conditions of the meta-aramid / MWCNT composite (Example 5) prepared in the present invention.

"Meta aramid / carbon nanotubes" used in the present invention refers to a material prepared by mixing meta aramid homopolymer and carbon nanotubes.

In the present invention, "carbon nanotube" is a compound in which the plate-shaped graphene sheet is a carbon particle in the form of a cylinder, which contains SWCNT, MWCNT and alkyl group, allyl group, carboxyl group, hydroxyl group, amine group, epoxy group, urethane group or urea group. And surface modified SWCNT and MWCNT. These carbon nanotubes are excellent in electrical conductivity, heat resistance and mechanical properties.

As used herein, the term "Aramid" refers to a synthetic polymer in which at least 85% of amide bonds (-CONH-) are directly linked to two aromatic rings. Meta-Aramid refers to a phenyl group in meta form. As a substituted form, it is preferable that the aramid used in the present invention has 85% or more of one or more structures selected from the group consisting of repeating unit structures represented by the following Chemical Formulas 3 to 5.

(3)

[Formula 4]

[Chemical Formula 5]

Next, a method of manufacturing the meta-aramid / carbon nanotube composite will be described.

Carbon nanotubes and aramid homopolymer may be variously combined in the range of 0.001 to 99.999: 99.999 to 0.001% by weight, but carbon nanotubes are preferably 0.1 to 20.0% by weight based on the total weight of the composite. If the carbon nanotube is less than 0.1% by weight can not be expected to improve the thermal and electrical properties of the composite, when the carbon nanotube is more than 20.0% by weight it is impossible to produce a composite by a solution mixing, a commercially important manufacturing process.

The carbon nanotubes are selected from at least one of SWCNT and MWCNT surface-modified with one selected from the group consisting of SWCNT, MWCNT and a compound including alkyl group, allyl group, carboxyl group, hydroxyl group, amine group, epoxy group, urethane group and urea group. It can be used, and it is more preferable to use carbon nanotubes surface-modified using one compound selected from the group consisting of an alkyl group, an allyl group, a carboxyl group, a hydroxyl group, an amine group, an epoxy group, a urethane group and a urea group desirable. Surface modification of the carbon nanotubes can improve the function of the composite by making the mixing with the polymer uniform. More preferably, the carbon nanotubes may be acid treated with a compound containing a carboxyl group so as to be uniformly mixed with the polymer.

Mixing of carbon nanotubes and meta-aramids is preferably carried out by solution mixing. The solution mixing is preferably carried out using a solvent such as water, dimethylformamide, dimethylacetamide, sulfuric acid, dimethyl sulfoxide, N-methyl-2-pyrrolidone or a mixed solvent thereof. In particular, in order to improve the solubility of meta aramid in the organic solvent during the solution mixing, it is preferable to add 0.1 to 20.0% by weight of a salt such as lithium chloride (LiCl) or calcium chloride (CaCl ₂ ) relative to the total solution weight. Solution mixing is preferably carried out at a temperature range of 10 ~ 150 ℃, the weight of the solvent has a great effect as well as the processability of the film or fiber to be produced finally, in the present invention 50.00 ~ 99.99 weight relative to the total solution weight It is preferable to set it as%.

Hereinafter, the present invention will be described in detail with reference to Examples, but the scope of the present invention is not limited by Examples.

Examples 1 to 9 and Comparative Example 1

Aramid was used for the embodiment of the present invention, meta-aramid provided by Sigma Aldrich Co., Ltd., carbon nanotubes were used in the CM-250 of Hanwha Nanotech Co., Ltd. MWCNT having a diameter of 10 ~ 15 nm.

In the solution mixture, dimethylacetamide and lithium chloride (LiCl) salts are used as solvents and salts, respectively. The ratio of (meth aramid + carbon nanotube): solvent: salt in the solution mixture was 10: 88: 2 weight ratio, and stirred at 80 ° C. for about 24 hours to form a clear aramid solution. The weight ratio of meta aramid and MWCNT in the mixed solution was prepared by solution mixing various weight% MWCNT with the meta aramid polymer as shown in Table 1. MWCNTs were uniformly dispersed in the solution through sonication and stirring of the prepared mixed solution. After pouring the appropriate amount of the mixed solution in the Shale, the solvent was completely blown out by ventilation and vacuum drying at a temperature of 80 ~ 160 ℃ to prepare a meta aramid / MWCNT composite having a thickness of about 0.1 mm.

No. Meta aramid (% by weight) MWCNT (% by weight) Comparative Example 1 100.0 0.0 Example 1 99.9 0.1 Example 2 99.7 0.3 Example 3 99.5 0.5 Example 4 99.3 0.7 Example 5 99.0 1.0 Example 6 97.0 3.0 Example 7 95.0 5.0 Example 8 93.0 7.0 Example 9 90.0 10.0

Test Example 1-Electrical Conductivity Measurement

An electrical resistance meter (Keithley 8009 resistivity test fixture) was used to measure the electrical conductivity of the meta-aramid / MWCNT composite. As shown in FIG. 1, the volume electrical resistance and surface electrical resistance of the meta-aramid single polymer are ˜10 ¹⁶ Pa · cm and ˜10 ¹⁶ Pa / sq, respectively. The meta-MWCNT is contained as 0.1% weight of aramid / MWCNT composite is lowered to a volume resistance and surface resistance sharply each to 10 ¹⁰ Ω · cm and 10 ¹⁰ Ω / sq, MWCNT 0.3% by weight or more to 10 ⁷ Volume resistivity and surface resistivity values of · cm and ~ 10 ⁷ Ω / sq or less are shown. From these results, it can be seen that the meta-aramid / MWCNT composite has a very low electrical resistance even with a low MWCNT content of about 0.1% by weight, unlike the meta-aramid alone polymer, which is an electrical insulator.

Test Example 2-Measurement of Thermal Stability (Heat Resistance)

The thermal stability (heat resistance) of the aramid / MWCNT composite was measured and shown in Figure 2 and Table 2. Thermostability measurements were performed under atmospheric airflow using a thermogravimetric analyzer (TGA). Table 2 summarizes the pyrolysis temperatures (T _{30 %} and T _{50 %} ) in which the weight loss of 30% and 50% occurs from the pyrolysis curves of the aramid / MWCNT composites of various composition ratios shown in FIG. . Table 2 shows that in the case of the aramid homopolymer (Comparative Example 1), the pyrolysis temperature at which the weight loss of 30% and 50% occurred was 563.2 ° C. and 608.5 ° C., respectively. In the case of T _{30 %} = 604.3 ° C and T _{50 %} = 652.6 ° C, 41.1 ° C and 44.1 ° C were increased than aramid homopolymers, respectively. These results show that the aramid / MWCNT complex has significantly improved thermal stability than the aramid homopolymer.

No. MWCNT
(weight%) Pyrolysis temperature T _{30 %} (℃) T _{50 %} (℃) Comparative Example 1 0.0 563.2 608.5 Example 1 0.1 575.5 619.0 Example 2 0.3 589.8 642.0 Example 3 0.5 604.3 652.6 Example 4 0.7 597.0 647.8 Example 5 1.0 586.1 631.6 Example 6 3.0 576.9 605.6 Example 7 5.0 594.7 635.9 Example 8 7.0 573.3 612.7 Example 9 10.0 567.2 597.2

Test Example 3-Measurement of Mechanical Properties

The storage modulus, which is a mechanical property of the aramid / MWCNT composite, is measured in accordance with the temperature change and is shown in FIG. 3. The storage modulus with temperature was measured using a dynamic mechanical analyzer (DMA). From the results of FIG. 3, it can be seen that the aramid / MWCNT composite has a higher storage modulus, especially at a high temperature (above 280 ° C.), compared to the aramid homopolymer.

Test Example 4 Measurement of Electric Heat Generation Characteristics

The electrical heating properties of the aramid / MWCNT composite was measured using a thermal imaging camera. Figure 5 shows the temperature rise with time at various applied voltage of 1 ~ 60 V for aramid / MWCNT composite containing MWCNT 1.0% by weight. Unlike the aramid / MWCNT complex, the temperature of the applied voltage was not increased in the aramid homopolymer.

The aramid / MWCNT nanocomposite prepared according to the method presented in the present invention has excellent mechanical strength, thermal stability, electrical conductivity, and heat generation characteristics of the conventional aramid homopolymer as demonstrated by the results of the test example. Therefore, it can be usefully applied to various fields such as film, fiber, plastic, the present invention is not limited to these specific examples.

Claims (6)

Lithium chloride and 0.1-20.0% by weight of carbon nanotubes at a temperature of 10 to 150 ° C. relative to the total weight of the meta-aramid homopolymer and the composite having 85% or more of one repeating unit structure selected from the group consisting of Formulas 3 to 5 At least one salt selected from the group consisting of calcium chloride and at least one solvent selected from the group consisting of water, dimethylformamide, dimethylacetamide, sulfuric acid, dimethylsulfoxide and N-methyl-2-pyrrolidone Method of producing a meta aramid / carbon nanotube composites characterized in that the solution mixture.
(3)

[Chemical Formula 4]

[Chemical Formula 5]

delete The method according to claim 1,
The carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes. The method according to claim 1,
The carbon nanotubes are surface-modified with one selected from the group consisting of alkyl, allyl, carboxyl, hydroxyl, amine, epoxy, urethane and urea groups, the preparation of meta-aramid / carbon nanotube composites. Way. delete The method according to claim 1,
The salt is a method for producing a meta aramid / carbon nanotube composite, characterized in that 0.1 to 20.0% by weight relative to the total solution weight.

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