KR101181791B1 - Carbon/silanized carbon nanotube/epoxy three-phase composite - Google Patents

Abstract

The present invention relates to a carbon / silanized carbon nanotube / epoxy three-phase composite material prepared by silanizing carbon nanotubes and having excellent physical properties.
According to the present invention, when the carbon / carbon nanotube / epoxy three-phase composite material is prepared using silanized carbon nanotubes, a carbon / carbon nanotube / epoxy three-phase composite material having excellent mechanical properties, temperature characteristics, and electrical properties is prepared. can do.

Description

Carbon, silanized carbon nanotubes and epoxy three-phase composites

The present invention relates to a composite material consisting of carbon, carbon nanotubes and epoxy, and more particularly, to a carbon / silanated carbon nanotube / epoxy three-phase composite material prepared by silanizing carbon nanotubes and having excellent physical properties. .

Carbon nanotubes (CNT) have excellent mechanical, thermal and electrical properties and are widely used as reinforcements for polymer matrices. Since carbon / CNT / polymer materials have better material properties than carbon / polymer materials, recently, carbon / polymer hybrid materials reinforced with CNT have attracted attention, and for this reason, some studies on carbon / CNT / polymer materials have recently been conducted. It is becoming.

The results of the investigation so far investigated, Abot et al. Produced a material (NRLC) laminated with CNT and carbon fabric, and found that the material has a higher shear strength than carbon fiber laminated material (LC). Researchers at Yokozeki et al. Studied the material properties of cup-stacked carbon nanotube (CSCNT) reinforced carbon / epoxy laminates and found that stiffness, strength, and type I and type II stacking failures. It was found that the toughness (interlaminar fracture toughness) was improved compared to the existing carbon / epoxy material without CSCNT. In addition, Cho et al. Have found that the compressive strength and in-plane shear property of carbon / epoxy materials increase when the graphite nanomolecules are dispersed in the carbon fiber / epoxy material.

The biggest problem in the fabrication of CNT reinforcing materials is that the cohesion of CNTs and the interfacial bonds between CNTs and the matrix are weak. To address this problem, many researchers have studied how to uniformly disperse CNTs and effective ways to enhance interfacial bonds in polymer matrices.

Accordingly, the present inventors have diligently solved the above problems to produce a carbon / carbon nanotube / epoxy composite material with high physical properties, and as a result, by silanizing carbon nanotubes, three-phase carbon / carbon nanotube / epoxy When manufacturing a composite material, it was confirmed that the composite can be improved in mechanical, thermal and electrical properties compared to the existing and completed the present invention.

Therefore, the main object of the present invention is to provide a carbon / carbon nanotube / epoxy three-phase composite material and its manufacturing method with improved physical properties.

According to one aspect of the invention, the present invention provides a carbon, carbon nanotubes and epoxy three-phase composite material characterized in that the epoxy resin containing the silanized carbon nanotubes is dispersed and cured in the carbon fiber.

According to another aspect of the present invention, the present invention provides a method for producing carbon, carbon nanotubes and epoxy three-phase composite material, characterized in that the carbon fiber impregnated and cured epoxy resin mixed with silanized carbon nanotubes do.

According to another aspect of the invention, the present invention comprises the steps of: a) preparing carbon nanotubes by oxidizing carbon nanotubes; b) silanizing the carbon oxide oxide with a silanated derivative selected from the group consisting of 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-isocyanatopropyltrimethoxysilane Preparing silanated carbon nanotubes; c) mixing an epoxy resin, a curing agent and the silanized carbon nanotubes to prepare a mixture; d) It provides a method for producing carbon, carbon nanotubes and epoxy three-phase composite material comprising the step of impregnating and curing the mixture to the carbon fiber.

In the carbon, carbon nanotube and epoxy three-phase composite material manufacturing method of the present invention, in order to perform step a), the carbon nanotubes are dispersed in an acid solution of 40 to 60 ℃ and refluxed for 10 to 30 hours It is preferable to use the method of filtering with water and acetone until the acid solution reaches pH 6-7, and drying at 70-90 degreeC for 10 to 14 hours.

In the carbon, carbon nanotube and epoxy three-phase composite material manufacturing method of the present invention, 90 to 99% (v / v) of ethanol and 1 to 3% (v / v) to perform step b) The carbon nanotubes were dispersed in a solution containing 3-aminopropyltriethoxysilane and stirred at 60 to 80 ° C. for 3 to 5 hours, then filtered through water and acetone, and 10 to 14 at 70 to 90 ° C. Preference is given to using a method of time drying.

In the carbon, carbon nanotube and epoxy three-phase composite material manufacturing method of the present invention, in order to perform the step c), the epoxy resin and the curing agent are mixed in a ratio of 1: 1 to 3: 1 (v / v) It is preferable to use a method of adding and mixing 1% (w / v) of the silanized carbon nanotubes.

In the carbon, carbon nanotube and epoxy three-phase composite material manufacturing method of the present invention, in order to perform the step d), the carbon fiber and the mixture is laminated and 1 to 120 to 140 ℃ at a pressure of 2 to 4kgf / ㎠ Preference is given to using a method of curing for from 3 hours.

Hereinafter, the carbon, carbon nanotubes (hereinafter referred to as CNT) and epoxy three-phase composite materials of the present invention will be described in more detail step by step.

The present invention is characterized by increasing the mechanical, temperature and electrical properties of the composite material by silanizing the CNT in the carbon / CNT / epoxy three-phase composite material.

One embodiment of the present invention for producing a composite material of the present invention is largely a step for producing an oxide CNT, a step for producing a silanized CNT, a step for preparing a silanized CNT / epoxy / curing agent mixture, impregnating and curing the carbon fiber.

Oxidation CNT manufacturing step may be referred to as a pre-treatment step to oxidize the CNT so that the silane group can be formed in the CNT in the subsequent silanization step. In this step, the CNTs are dispersed in an acid solution to cause an oxidation reaction, and when sufficiently oxidized, the CNTs are washed and neutralized. In this case, the acid solution is preferably a mixed solution of nitric acid and sulfuric acid, the ratio of nitric acid and sulfuric acid is more preferably 2: 3, the CNT and the acid solution is separated by filtration, the acid remaining in the CNT The solution needs to be washed sufficiently with water and neutralized with acetone. In addition, it is necessary to sufficiently remove the water remaining in the CNT through drying. It is desirable to go through this process in order to reduce unnecessary reactions in subsequent silanization steps.

The silanized CNT preparation step is to silanize the oxidized CNT with a silane derivative. Silane derivatives include 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-isocyanatopropyltriethoxysilane. Among them, it is preferable to use 3-aminopropyltriethoxysilane among them, induce silanization reaction as in the oxidation step, and then filter to separate the CNT and silane derivative solution, and with water and acetone. It is necessary to sufficiently wash and neutralize the process, and then to remove water remaining in the CNT through a drying process. When preparing a silane derivative solution, it is preferable to use high purity ethanol.

The preparing of the silanized CNT / epoxy / curing agent mixture is a step of mixing the epoxy resin and the curing agent and adding and mixing the silanized CNT, so that the concentration of the silanized CNT is about 1% (v / v). It is preferable to stir sufficiently so that the silanized CNTs can be evenly distributed in the epoxy resin.

Finally, the carbon fiber impregnation and curing step impregnates the silanized CNT / epoxy / curing agent mixture with carbon fiber to allow the mixture to penetrate well into the carbon fiber and to cure the epoxy so that the silanized CNT and epoxy are well distributed and bonded to the carbon fiber. It is a step to make it possible. In this case, it is preferable to apply a vacuum to distribute the CNT and the epoxy resin evenly to the inside of the carbon fiber, and when heated under pressure, the epoxy resin is cured to prepare the carbon / silanated CNT / epoxy three-phase composite material of the present invention. It becomes possible.

The present inventors prepared the composite material in the same manner as above, and then investigated the physical and electrical properties of the composite material. In this case, the carbon / CNT / epoxy three-phase composite material prepared using CNT and the oxidized CNT prepared using CNT without any surface treatment together with the silanized composite material of the present invention. Composite materials were used.

First, CNTs surface-treated (untreated, oxidized, silanized) were analyzed by Fourier transform infrared (FTIR) spectra (see FIG. 2).

Untreated CNTs (see a in FIG. 2) showed peaks at 3440 cm ⁻¹ and 1048 cm ⁻¹ . This is the peak of the hydroxyl group (-OH), which is believed to have formed on the surface of the CNTs during the cleaning process or due to the presence of moisture in the air. In the case of (see Fig. 2 b) the oxidation-treated CNT, in 1716㎝ ^-1 from C = O, 1162㎝ ^-1 CO peak is confirmed it was confirmed that the carboxyl group (-COOH) are present. Of 3440㎝ ^-1 peak represents the OH group on the surface, the 1384㎝ ^-1 peaks are in accordance with the refractive OH of -COOH. This result means that the CNTs were oxidized and -OH and -COOH groups were formed. The characteristic absorption peak of 1070 cm ^-1 in the spectrum of silanized CNTs (see c in FIG. 2) is shown by the vibration of Si-O, and the peak of 803 cm ^-1 is from Si-OH, with oxidized CNTs Prove that 3-aminopropyltriethoxysilane reacted.

Next, the tensile strength characteristics of each composite material was compared.

Elastic modulus and tensile strength were determined from the stress-strain curve. FIG. 3 shows a specific tensile strength stress-strain curve of a carbon / CNT / epoxy material using untreated, oxidized and silane-treated CNTs, as shown in FIG. And nonlinear features were found in all materials. All materials showed brittle tensile properties regardless of the surface change of CNTs, but the wavefront deformation decreased in the order of untreated, oxidized and silanized composites. In addition, the elastic modulus of each material was determined by measuring the slope in the linear portion of the stress-strain curve. Figure 4 shows the modulus of the three materials, as shown in Figure 4, the modulus of the silanized composite material is 34% and 18% higher than the untreated and oxidized CNT material, respectively, so that the silanization of CNT is carbon / It has been shown to improve the modulus of elasticity of CNT / epoxy materials. The tensile strength of each material was determined as the maximum stress of the stress strain curve. 5 shows the tensile strength of three materials. Tensile strength of the silanized composites was 8.4% and 15.8% higher than untreated and oxidized composites, respectively, indicating that tensile strength was improved due to silanization of CNTs.

Next, the fracture surface shape of each composite material was observed.

In order to investigate the failure mechanism, the fracture surface of the material was observed by SEM, and the results are shown in FIG. 6. Figure 6a shows the wavefront of the untreated composite material, Figure 6b is an enlarged box portion of Figure 5a. As shown in Figs. 6A and 6B, most of the carbon fibers were separated from the epoxy matrix, and the CNTs were not evenly dispersed in the epoxy in a partially aggregated state. In the case of the oxidation-treated composite material, as shown in c and d of FIG. 6, the wavefront is relatively clean, and the fibers separated from the matrix were reduced compared to the untreated composite material. In addition, in the case of CNTs, the CNTs partially pulled out of the matrix are observed in the enlarged image (arrow part), but are generally dispersed well in the epoxy. In the case of silanized composites (e and f in Figure 6), the carbon fibers were well bonded with the epoxy matrix, the CNTs were also well dispersed in the epoxy, and the CNTs pulled out of the matrix were also reduced compared to the oxidized composites. Appeared. 7A, 7B and 7C show enlarged images of carbon fibers at the wavefront of the untreated, oxidized and silanized composites. In the case of the untreated composite material, as shown in FIG. 7A, due to the lack of interfacial bonding between the CNT and the epoxy resin and agglomeration, the transition rate on the fiber surface is low, so that most carbon fibers are bonded to the CNT and the epoxy resin. Not showing a clean cross section. On the other hand, in the case of the oxidation-treated composite material (b of FIG. 7) and the silanized composite material (c of FIG. 7), a relatively large amount of CNT-impregnated epoxy resin was observed in the carbon fiber. The reason why a large amount of CNT / epoxy is present in the carbon fiber may be found because the interfacial bonding and dispersibility of the CNT and the epoxy resin are improved and distributed evenly with the carbon fiber. Silaneization of CNTs not only increased the dispersibility and interfacial bond between CNTs and epoxy resins, but also imparted an equal load transfer capacity of carbon fibers. This phenomenon results in the silanized composites having a higher tensile force than the untreated composites.

Next, the thermal properties of each material were investigated.

8A and 8B show DMA diagrams of storage modulus and loss ratio tan δ vs. temperature of a composite material which is untreated, oxidized, and silanized. In FIG. 8A, the storage modulus was determined as the intersection of the gradually increasing initial two slopes, and the decrease in storage modulus is due to the energy dissipation due to the cooperative movement of the polymer chain. As shown in a of FIG. 8, the storage modulus gradually increased in the order of untreated, oxidized, and silanized composites. In particular, the storage modulus of untreated, oxidized, and silanized composites is 4770, 6654, and 7049 MPa, respectively, in the range of glass transition regions, whereas the rubber plateau region differs significantly. There was no. In Figure 8b, except for the untreated composite material, the peak height of the loss rate (tan δ) did not change much, but the glass transition temperature ( T _g ) determined by the position of the loss rate (tan δ) peak was investigated in the previous experiment. As it was, it gradually increased with the surface treatment. In addition, the glass transition temperature of polymer-based materials, such as samples from glassy to rubberelastic, whose properties change, coincides with the transition point. In this study, this difference in glass transition temperature is a result of the degree of crosslinking reaction of epoxy, and because the silane molecule forms more covalent bonds with CNTs than in untreated and oxidized samples to form a high crosslinking network. I think. It is also believed that the strong interfacial bonds and dispersing forces with silanization reduce the mobility of the epoxy molecules around the CNTs, resulting in increased temperature stability.

Next, the electrical properties of each material were investigated.

Volume resistivity of the carbon / CNT / epoxy material was performed to confirm the electrical synergistic effect of the CNT change between CNT and carbon fiber in the epoxy. 9 shows the volume resistivity of untreated, oxidized and silanized carbon / CNT / epoxy materials. As shown in Figure 9, the volume resistivity was affected by the change in CNTs. The volume resistivity decreased gradually in the order of untreated, oxidized and silanized composites. In particular, the volume resistivity values of untreated, oxidized and silanized composites were 2.8, 1.5 and 0.6 Ω / cm, respectively. The low volume resistivity of the silanized composite is probably the result of the formation of a continuous network structure with uniform dispersion of CNTs between the carbon fibers (see box section in FIG. 9). As a result of this, the silanized composite has a more conductive network structure than the untreated or oxidized composite. This permeation boundary property with CNT changes is consistent with previous studies on CNT reinforcing materials.

In conclusion, the effects of tensile strength, temperature, and electrical properties of the surface treatment of CNTs on carbon / CNT / epoxy three-phase composites were confirmed. Tensile properties (elastic modulus and tensile strength) are improved over oxidized composites and untreated composites. Surface treatment also improved the thermal properties and electrical conductivity of the carbon / CNT / epoxy composites. Tensile properties, thermal properties (storage modulus and loss rate) and electrical conductivity of silanized composites were superior to untreated composites and oxidized composites, which resulted in improved tensile and thermal properties of silanized composites. And electrical properties are due to the increased dispersibility and interfacial bonding between silanized CNT and epoxy in carbon / epoxy materials.

As described above, according to the present invention, a carbon / carbon nanotube / epoxy three-phase composite material having excellent mechanical properties, temperature characteristics, and electrical properties can be manufactured.

Figure 1 illustrates a preferred embodiment in the manufacturing process of the carbon / carbon nanotube / epoxy multi-scale composite material of the present invention.
2 is a graph showing FTIR spectra of untreated (a), oxidized (b) and silanized (c) carbon nanotubes.
3 is a graph showing a stress-strain curve of a tensile strength test result of an untreated, oxidized and silanized material.
4 is a graph showing elastic modulus of untreated, oxidized and silanized materials.
5 is a graph showing tensile strength of untreated, oxidized and silanized materials.
Fig. 6 shows FESEM images of untreated (a), oxidized (c) and silanized (e) fracture surfaces and enlarged images (untreated (b), oxidized (d) and silanized (f). ))
7 is a photograph showing an enlarged FESEM image of a carbon fiber wavefront of an untreated (a), an oxidized (b) and a silanized (c) carbon / carbon nanotube / epoxy composite material.
8 is a graph showing the storage modulus (a) and the loss ratio (b) (tan δ) of untreated, oxidized and silanized materials.
9 is a graph showing the volume resistivity of untreated, oxidized and silanized materials.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only for illustrating the present invention, and the scope of the present invention is not to be construed as being limited by these examples.

Example 1 Preparation of Carbon / Silane Carbon Nanotubes / Epoxy Three-Phase Composites

1-1. Carbon Nanotubes Manufacture

3.0 g of multi-walled carbon nanotubes (MWCNTs) synthesized by chemical catalytic vapor deposition (CM-95, Hanhwa Nanotech, Korea) were dispersed in a 300 ml acid solution at 50 ° C and refluxed for 20 hours. Then, the solution was filtered with distilled water (99.5%, Dae Jung Chemical, Korea) and acetone (99.5%, Dae Jung Chemical) until pH 6-7. After vacuum drying at 80 ℃ for 12 hours to prepare an oxidized carbon nanotubes.

As the acid solution, a solution containing 2: 3 of nitric acid (60-62%, Junsei, Japan) and sulfuric acid (95%, Junsei Chemical) was used.

1-2. Silane Carbon Nanotube Manufacturing

3-aminopropyltriethoxysilane was added to 300% of ethanol (99.5%, Aldrich) -distilled water (99.5%, Dae Jung Chemical, Korea) solution (95: 5 v / v) to 2% (v / v). 3-aminopropyltriethoxysilane) (purity 99%, Aldrich, USA) was added to prepare a silanized solution, and 1.8 g of carbon nanotubes 1-2 were dispersed therein, followed by stirring at 70 ° C. for 4 hours. Then, filtered through distilled water (99.5%, Dae Jung Chemical, Korea) and acetone (99.5%, Dae Jung Chemical), and dried at 80 ℃ for 12 hours to produce a silanized carbon nanotubes.

1-3. Carbon / Silanated Carbon Nanotube / Epoxy 3-Phase Composite

In a 2: 1 (v / v) mixture of bisphenol A diglycidyl ether of bisphenol A (YD-115, Kukdo Chemical, Korea) and polyamidoamine (G-A0533, Kukdo Chemical) The silanized carbon nanotubes of 1-2 were added at a concentration of 1% by weight.

Four layers of woven carbon fiber (CF3327, Hankuk carbon, Korea) and the epoxy / hardener mixture to which the above-mentioned silanized carbon nanotubes were added were stacked up using a hand lay-up method, and then put into a vacuum bag, followed by an autoclave. ) Was processed at 130 ° C. for 2 hours at a pressure of 3 kgf / cm 2 (VARTM technique).

A method of manufacturing such carbon / carbon nanotubes / epoxy three-phase composite material is shown in FIG. 1.

Comparative Example 1. Preparation of Carbon / Carbon Nanotube / Epoxy Composite Material

Precipitating the chemical catalyst vapor at a concentration of 1% by weight in a 2: 1 (v / v) mixture of bisphenol A diglycidyl ether resin (YD-115, Kukdo Chemical, Korea) and polyamidoamine (G-A0533, Kukdo Chemical) Multi-walled carbon nanotubes synthesized by the method (CM-95, Hanhwa Nanotech, Korea) were added.

Four layers of woven carbon fiber (CF3327, Hankuk carbon, Korea) and the epoxy / curing agent mixture to which the carbon nanotubes were added were stacked using a water lamination method, and then placed in a vacuum bag and 3 kgf in an autoclave. Processing was carried out at 130 ° C. for 2 hours at a pressure of / cm 2 (VARTM technique).

Comparative Example 2. Preparation of Carbon / Carbon Oxide Nanotubes / Epoxy Composite Materials

Example 1 at a concentration of 1% by weight in a 2: 1 (v / v) mixture of bisphenol A diglycidyl ether resin (YD-115, Kukdo Chemical, Korea) and polyamidoamine (G-A0533, Kukdo Chemical) Carbon nanotubes of -1 were added.

Four layers of woven carbon fiber (CF3327, Hankuk carbon, Korea) and the epoxy / hardener mixture to which the carbon nanotubes were added were stacked using a hand lay-up method, and then placed in a vacuum bag, followed by an autoclave. It was processed at 130 ° C. for 2 hours at a pressure of 3 kgf / cm 2 at (VARTM technique).

Experimental Example 1. Fourier transform infrared spectrum analysis

In order to observe the surface functional groups of the carbon nanotubes, Fourier transform infrared (FTIR) spectra of untreated, oxidized and silanized carbon nanotubes were analyzed and shown in FIG. 2.

Each carbon nanotube was made of KBr pellets and analyzed and recorded at a resolution of 4 cm ^-1 with a JASCO FTIR spectrometer.

Experimental Example 2. Tensile Force Test

Tensile strength test was carried out using a common test apparatus (Model: 8871, Instron, USA) according to ASTM D638 at a crosshead ratio of 1 mm / min, the composite material of Example 1, Comparative Example 1 and Comparative Example 2 Was targeted. The results are shown in FIGS. 3 to 5.

At least five samples were tested in each case to ensure the reliability of the test results.

Experimental Example 3 Intestinal Release Scanning Microscopy

After the tensile strength test, the short surface of each composite material was analyzed by FESEM (LEO SUPRA 55, Carl Zeiss, Germany), and the results are shown in FIGS. 6 and 7.

Experimental Example 4. Thermal Properties Test

For the thermal properties of the three-phase composite material was carried out using a single cantilever type dynamic mechanical analysis device (DMA, Q-800, TA Instrument, USA), the results are shown in FIG.

An amplitude of 20 µm and a frequency of 1 Hz were used as treatment conditions.

The temperature range was 25-250 ° C. and heated at 10 ° C./min in air.

Experimental Example 5. Electrical Properties Test

Electrical characteristics of the three-phase composite material were analyzed using an impedance meter (MCP-T610, Mitsubishi, Japan), the results are shown in FIG.

Claims (7)

delete delete a) The carbon nanotubes are dispersed in an acid solution at 40 to 60 ° C. and refluxed for 10 to 30 hours, and then filtered with water and acetone until the acid solution is pH 6 to 7, and at 10 to 70 ° C. at 90 ° C. Drying for 14 hours to produce carbon nanotubes;
b) dispersing the carbon nanotubes in a solution containing 90 to 99% (v / v) ethanol and 1 to 3% (v / v) 3-aminopropyltriethoxysilane and at 60 to 80 ° C. Stirring for 3 to 5 hours, filtering with water and acetone, and drying at 70 to 90 ° C. for 10 to 14 hours to produce silanated carbon nanotubes;
c) mixing an epoxy resin and a curing agent in a ratio (v / v) of 1: 1 to 3: 1, and preparing a mixture by adding the silanized carbon nanotubes; And
d) stacking the carbon fibers and the mixture and curing at 120 to 140 ° C. for 1 to 3 hours at a pressure of 2 to 4 kgf / cm 2.
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