KR20210022960A - Carbon fiber reinforced composite reinforced with aramid nanofibers and method for manufacturing the same - Google Patents

Abstract

A thermosetting resin disclosed in the present specification, which comprises a thermosetting resin in which carbon fiber reinforced composite material aramid nanofibers are dispersed, and carbon fibers, and in which the aramid nanofibers are dispersed, is impregnated into the carbon fibers, thereby having excellent damping properties and impact properties. An object of the present invention is to provide a carbon fiber reinforced composite material having excellent damping properties and impact properties, and a manufacturing method thereof.

Description

Carbon fiber reinforced composite material reinforced with aramid nanofibers and its manufacturing method {CARBON FIBER REINFORCED COMPOSITE REINFORCED WITH ARAMID NANOFIBERS AND METHOD FOR MANUFACTURING THE SAME}

Disclosed herein are a carbon fiber-reinforced composite material reinforced with aramid nanofibers and a method for manufacturing the same.

Many researchers have tried to improve the properties of CFRP suitable for each application field. Many engineering structures have been built from CFRP, including military equipment, automobiles, aircraft, sporting goods, wind turbine blades, pressure vessels, and spacecraft parts. However, CFRP parts are susceptible to vibration damage even during normal operation. This is because the damping factor is low due to poor viscoelastic properties of carbon fiber (CF) and poor damping at the interface between CF and matrix. In addition, it is common for high-rigidity materials to exhibit low damping properties. Another problem is that when micro-scale cracks or voids are present in CFRP, these defects are rapidly exacerbated by vibration. Damping properties are also related to impact resistance.

To overcome this problem, several proposals have been studied to improve the damping properties of CFRP. One notable method is to insert nanomaterials into the CFRP matrix. Nanoscale fillers can cause friction when there is sliding between the nanoscale fillers and the polymer matrix. In addition, the nanomaterial may play a role in transferring a specific load between CF, the matrix, and the nanopillar. This can improve the damping property of the material due to energy dissipation.

In particular, carbon nanotubes (CNTs) have a large surface-to-volume ratio and excellent intrinsic properties, but have very low dispersibility in polymer resins or solvents. In order to improve the low dispersibility of such CNTs, when functional groups are introduced on the surface, the physical properties of the composite material may be reduced due to the resulting surface defects, as well as the increase in manufacturing cost due to the addition of the CNT surface treatment process.

Therefore, in addition to CNT, there is a need to develop a material capable of improving the damping and impact properties of CFRP.

Yang, M.; Cao, K. Q.; Sui, L.; Qi, Y.; Zhu, J.; Waas, A.; Arruda, E. M.; Kieffer, J.; Thouless, M. D.; Kotov, N. A., Dispersions of Aramid Nanofibers: A New Nanoscale Building Block. ACS Nano 2011, 5 (9), 6945-6954.

In one aspect, an object of the present invention is to provide a carbon fiber reinforced composite material having excellent damping properties and impact properties, and a method of manufacturing the same.

In an exemplary embodiment of the present invention, aramid nanofibers (aramid nanofibers, ANF) are dispersed thermosetting resin; And carbon fibers; wherein the thermosetting resin in which the aramid nanofibers are dispersed is impregnated with the carbon fibers, providing a carbon fiber-reinforced composite material.

In another exemplary embodiment of the present invention, there is provided a method of manufacturing the above-described carbon fiber-reinforced composite material, comprising: preparing aramid nanofibers using aramid fibers; Dispersing the aramid nanofibers in a thermosetting resin; And impregnating the carbon fiber with a thermosetting resin in which aramid nanofibers are dispersed.

In one aspect, the carbon fiber-reinforced composite material disclosed in the present specification provides a carbon fiber-reinforced composite material with improved damping properties and impact properties by impregnating the carbon fiber with a thermosetting resin in which aramid nanofibers are dispersed.

In another aspect, the method of manufacturing a carbon fiber-reinforced composite material disclosed in the present specification is a simple method to prepare aramid nanofibers that maintain the characteristics of the existing micro-scale aramid fibers, which are used in carbon fiber-reinforced composite materials. By using it as a reinforcing agent in a matrix, a carbon fiber reinforced composite material having excellent damping properties and impact properties can be manufactured.

1A and 1B are photographs of an epoxy resin (1a) in which aramid nanofibers are dispersed and an epoxy resin (1b) in which multi-walled carbon nanotubes (MWCNT) are dispersed according to an embodiment of the present invention.
2 is a schematic and photograph of a vacuum forming process according to an embodiment of the present invention.
3 is a graph showing a curing cycle of a carbon fiber reinforced composite material according to an embodiment of the present invention.
Figures 4a to 4d are, respectively, a micrometer-sized single aramid fiber (4a), aramid nanofiber bundles (4b), nanometer-sized single aramid nanofibers (4c), and multi-walled carbon nanofibers according to an embodiment of the present invention. It is an SEM image of the tube bundle 4d.
Figures 5a to 5d are XRD spectra (5a), an aramid fiber and Raman spectra (5b), 1200 ~ 1800 cm of aramid nanofibers on aramid fibers and aramid nanofibers according to each embodiment of the present invention ^- the ^first wave number of It is a graph showing the characteristic curves of the IR absorbance spectrum (5c) of the aramid fiber and the aramid nanofiber having, and the IR absorbance spectrum of the aramid fiber and aramid nanofiber (5d) having a wave number of ^{2800 to 3800 cm -1.}
6A to 6D are a low-magnification fracture surface (6a) of a carbon fiber-reinforced composite material made of only carbon fiber and impregnated epoxy resin without a reinforcing agent according to an embodiment of the present invention, respectively, of carbon fiber without a reinforcing agent. The fracture surface of the high-magnification carbon fiber-reinforced composite material showing the cut section (6b), the fracture surface of the carbon fiber-reinforced composite material with 0.25 wt% aramid nanofibers indicating the aramid nanofibers (in the rectangle) and the carbon fiber (the right side) (6c) ), and the fracture surface (6d) of a carbon fiber-reinforced composite material having 0.25 wt% of multi-walled carbon nanotubes representing the dispersed multi-walled carbon nanotubes and carbon fibers (lower).
7A to 7C are each having a carbon fiber reinforced composite material (Neat CFRP), a reinforced carbon fiber reinforced composite material (ANF 0.25 wt%) and a multi-walled carbon nanotube that does not contain a reinforcing agent according to an embodiment of the present invention. A graph showing the results of dynamic mechanical analysis (DMA) showing tan δ (7a), storage modulus (7b), and loss factor (7c) of a carbon fiber reinforced composite material (MWCNT 0.25 wt%).
8 is a carbon fiber reinforced composite material (Neat CFRP) that does not contain a reinforcing agent according to an embodiment of the present invention, a reinforced carbon fiber reinforced composite material (ANF 0.25 wt%), and a carbon fiber reinforced with multi-walled carbon nanotubes. It is a graph showing the impact strength of the composite material (MWCNT 0.25 wt%).

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The embodiments of the present invention disclosed in the text are illustrated for purposes of explanation only, and the embodiments of the present invention may be implemented in various forms and should not be construed as being limited to the embodiments described in the text. .

The present invention is not intended to limit the present invention to a specific disclosed form, as various changes may be added and various forms may be added, and all changes, equivalents, or substitutes included in the spirit and scope of the present invention It should be understood to include.

In the present specification, when a certain part "includes" a certain component, it means that other components may be further included rather than excluding other components unless specifically stated to the contrary.

In the present specification, “aramid fiber” refers to all types of fibers manufactured from an aramid polymer, and examples thereof include aramid filaments or aramid spun yarns.

Carbon fiber Reinforced composite material ( CFRP )

In exemplary embodiments of the present invention, a thermosetting resin in which aramid nanofibers are dispersed; And carbon fibers; wherein the thermosetting resin in which the aramid nanofibers are dispersed is impregnated with the carbon fibers, providing a carbon fiber-reinforced composite material.

Aramid nanofibers (ANFs) are nanoized aramid fibers, and have rich functional amide groups and a high surface-to-volume ratio, and have typical characteristics of aramid fibers such as damping properties. It is known to maintain.

In general, in the case of carbon nanotubes, a functional group (carboxyl group, hydroxy group, etc.) is forcibly introduced because it does not have a functional group by itself, which may cause defects in the carbon nanotube. However, the aramid nanofibers used in one embodiment of the present invention have the advantage of having a functional group by itself.

In addition, the space occupied by the matrix resin of the carbon fiber reinforced composite material is very narrow (carbon fibers with a diameter of about 10 µm are oriented and the matrix resin occupies between the fibers and the fibers), so the impregnation of the micro-scale filler Although difficult, the nanoscale filler used in one embodiment of the present invention can be impregnated.

Accordingly, the carbon fiber-reinforced composite material according to an embodiment of the present invention includes a thermosetting resin in which aramid nanofibers are dispersed, which is a nanomaterial and at the same time maintains typical characteristics of aramid fibers, as shown in FIG. 1A. Used as a resin, it has excellent damping properties and impact properties compared to conventional carbon fiber composite materials.

In exemplary embodiments, the thermosetting resin may be a bismaleimide resin, a vinyl ester resin, an unsaturated polyester resin, a polyimide resin, a phenol resin, or an epoxy resin, and preferably an epoxy resin.

In exemplary embodiments, the content of the aramid nanofibers in the thermosetting resin may be 0.05 to 1% by weight, for example, 0.10% by weight or more, 0.15% by weight or more, or 0.20% by weight based on the total weight of the thermosetting resin and the curing agent. May be 0.90% by weight or less, 0.80% by weight or less, 0.70% by weight or less, 0.60% by weight or less, 0.50% by weight or less, 0.45% by weight or less, 0.40% by weight or less, 0.35% by weight or less, or 0.30% by weight or less have.

If the content is less than 0.05% by weight, damping properties, etc. may be deteriorated, and if the content is more than 1% by weight, the epoxy content is excessively high, so the viscosity of the epoxy in which the aramid nanofibers are dispersed is very increased, and impregnation in the carbon fiber may not be possible. have.

In exemplary embodiments, the diameter of the aramid nanofibers may be 50 to 300 nm.

In exemplary embodiments, the aspect ratio range of the aramid nanofibers may be 1:5 to 1:50.

In exemplary embodiments, the aramid nanofiber may be a para-aramid nanofiber, for example, Kevlar developed by DuPont.

Para-aramid is a benzene ring bonded to an amide group at the para position. Since the molecular chain is stiff and has a linear structure, the strength is very high and the elastic modulus is high, so it is excellent in absorbing impact. Therefore, para-aramid is used in body armor, bullet-proof helmet, safety gloves or boots, and firefighting suits, as a material for sports equipment such as tennis rackets, boats, hockey sticks, fishing lines, golf clubs, and fiber-reinforced composite materials for industrial use. (Fiber Reinforced Plastic, FRP), asbestos replacement fiber, and the like, and preferably carbon fiber-reinforced polymer composites (CFRP).

In the case of a thermosetting resin, it is not limited as long as it is generally used as a matrix resin of a carbon fiber reinforced composite material, and may preferably be an epoxy resin, and the epoxy resin is Bisphenol-A type YD-128, and the curing agent is Jeffamine D-230. I can.

Examples of the carbon fiber include carbon fibers such as acrylic, pitch, rayon, etc., and among them, acrylic carbon fibers that have high tensile strength and have been most widely used as reinforcing fibers for carbon fiber reinforced composite materials, especially polyacrylonitrile. (PAN)-based carbon fibers are preferably used.

You may mix and use 2 or more types of these fibers. The form of the carbon fiber is not particularly limited, and for example, long fibers or continuous fibers aligned in one direction, tow, woven fabrics, mats, knits, braids, short fibers cut to a length of less than 10 mm, and the like are used. Long fibers or continuous fibers referred to herein refer to short fibers or bundles of fibers that are substantially continuous for 10 mm or more. In addition, a single fiber refers to a bundle of fibers cut to a length of less than 10 mm.

In exemplary embodiments, the carbon fiber may be a woven carbon fiber. In the case of using a carbon fiber fabric, the impact resistance property is greatly improved because it is a net structure, but because a fabric having heterogeneous and anisotropic properties is used, changes in temperature and moisture absorption are locally different, and micro-cracks occur near the surface. there is a problem.

In addition to carbon fiber, industrial fibers such as aramid fiber, basalt fiber, and glass fiber can be used, but the reason for using carbon fiber in one embodiment of the present invention is that it has the highest strength, excellent weight reduction effect, and attempts to use it for industrial purposes. This is because is active. In the case of the carbon fiber reinforced composite material according to an embodiment of the present invention, a carbon fiber fabric is used, but when an external force is applied by using aramid nanofibers as a reinforcing agent, the matrix and the reinforcing agent cause friction in the thermosetting resin. Since it dissipates external energy efficiently, it has excellent impact resistance and damping properties.

Carbon fiber Manufacturing method of reinforced composite material

In exemplary embodiments of the present invention, a method of manufacturing the above-described carbon fiber-reinforced composite material, comprising: preparing aramid nanofibers using aramid fibers; Dispersing the aramid nanofibers in a thermosetting resin; And impregnating the carbon fiber with a thermosetting resin in which aramid nanofibers are dispersed.

According to one embodiment of the present invention, through a deprotonation and dissolution process from aramid fibers, aramid nanofibers that maintain a substantial chemical structure such as abundant polar functional groups of aramid fibers are obtained by a simple method, and are dispersed in a thermosetting resin. After that, by impregnating the carbon fiber (hand lay-up process, vacuum forming process), a carbon fiber-reinforced composite material can be manufactured by a simple method (FIG. 2).

In an exemplary embodiment, the step of preparing aramid nanofibers using aramid fibers may be performed by adding the aramid fibers to a solution containing potassium hydroxide (KOH) and dimethyl sulfoxide (DMSO).

Specifically, since the solubility of the aramid fiber is low, it is difficult to dissolve it using a general solvent. However, KOH in DMSO can play a key role in dissolution from micro-scale to nano-scale fibers. It is assumed that the H atom was extracted from the >NH group by KOH in the aramid fiber/KOH/DMSO solution. This deprotonation process reduces the effect of intermolecular hydrogen bonding because the strength of hydrogen bonds decreases.

In addition, the dissolution process increases electrostatic repulsion. The equilibration of the π-π stacking of the backbone, electrostatic repulsion and hydrophobic attraction control the nano-fiber dimensions.

As a result, aramid nanofibers with abundant amide functional groups and nanometers in diameter, when used as a matrix or filler of a composite material, have the strength, modulus, thermal stability, and thermal stability of the composite material. It is expected to improve thermal conductivity and impact resistance.

In an exemplary embodiment, the step of impregnating the carbon fiber with the thermosetting resin in which the aramid nanofibers are dispersed is an indirect molding method, a process of preparing an intermediate material (prepreg) by impregnating the carbon fiber filament or fabric with resin in advance, and thus prepared. It can be performed by various molding processes (press molding, autoclave molding, vacuum molding process, etc.) using prepreg, and direct molding methods such as hand lay-up molding, resin transfer molding (RTM), vacuum It can be performed by vacuum assisted resin transfer molding, pultrusion, filament winding molding processes, and the like.

However, the thermosetting resin in which the aramid nanofibers are dispersed has a higher viscosity than the thermosetting resin that is not, and may preferably be performed by a hand-ray up method.

In an exemplary embodiment, the method of manufacturing the carbon fiber-reinforced composite material includes: after impregnating the thermosetting resin in which the aramid nanofibers are dispersed into the carbon fibers, curing the thermosetting resin in which the aramid nanofibers are dispersed; Further, the step of curing the thermosetting resin in which the aramid nanofibers are dispersed may be performed by a vacuum bagging process.

In the case of using the vacuum forming process, a temperature called a curing cycle can be performed stepwise while holding a vacuum, so that an epoxy reinforced with aramid nanofibers can be efficiently impregnated into a carbon fiber fabric.

The present invention will be described in more detail through the following implementation. However, the examples are for illustrative purposes only, and the scope of the present invention is not limited thereto.

Example

A polyacrylonitrile-based (PAN-based) carbon fiber fabric (woven CF, T300) of 3000 filament count tows used in the examples was purchased from Toray Inc. Aramid fiber (Kevlar 49) was purchased from DuPont, Inc. Dimethyl sulfoxide (DMSO) and calcium hydroxide (KOH) were purchased from Daejung Chemicals & Metals Co., Ltd. Multi-walled carbon nanotubes (MWCNT) were purchased from Kumho Petrochemical Inc. The epoxy resin was purchased from Kukdo Chemical Inc. as YD-128, a Bisphenol-A type. Jeffamine D-230, used as a curing agent for epoxy resins, was purchased from Huntsman International, LLC.

1 g of aramid fibers cut into 5 mm lengths and 1.5 g of KOH were added to 500 ml of DMSO. It was stirred at room temperature for 1 week until a dark red solution was obtained. Then, 500 ml deionized water (DI water) was poured into the aramid nanofiber solution and heated at 80° C. for 2 hours to extract aramid nanofibers from the solution. The precipitated aramid nanofibers were washed several times with deionized water, and KOH and DMSO were removed using vacuum filtration until pH 7 was achieved. The obtained aramid nanofibers were mixed with acetone, and in this process, an aramid nanofiber solution in acetone could be obtained.

Subsequently, the epoxy resin was added to the aramid nanofiber/acetone solution to disperse the aramid nanofibers in the epoxy resin. The epoxy resin / aramid nanofiber / acetone mixture was stirred at 120 °C overnight to completely remove acetone. Finally, an aramid nanofiber/epoxy resin to be used for the carbon fiber reinforced composite matrix was obtained.

In order to compare the effect of aramid nanofibers with that of multi-walled carbon nanotubes (MWCNT), multi-walled carbon nanotubes were also dispersed in an epoxy resin using the same process. Aramid nanofibers and multi-walled carbon nanotubes dispersed in an epoxy resin are shown in FIGS. 1A and 1B.

Thereafter, a curing agent was added to these epoxy resins using a paste mixer and mixed (epoxy resin: curing agent = 7: 3, weight fraction). The weight fraction of the filler was 0.25% by weight based on the total weight of the epoxy resin and curing agent in the case of aramid nanofibers, and 0.25% by weight based on the total weight of the epoxy resin and curing agent in the case of multi-walled carbon nanotubes.

Then, the specimens of the carbon fiber reinforced composite material were manufactured by a hand-ray up method and a vacuum bagging process. The hand lay-up method was chosen because the viscosity of the epoxy in which the aramid nanofibers are dispersed is high. In addition, the vacuum forming process was designed to be well impregnated into carbon fiber fabric (woven CF) by lowering the epoxy viscosity in the B(β)-stage section, and it was completely cured in the complete curing section. The specific process is shown in Fig. 2, and the curing cycle is shown in Fig. 3.

Referring to the graph of FIG. 3, the B-stage was set at 80° C. for 30 minutes and 90° C. for 30 minutes, which lowers the viscosity of the epoxy reinforced with aramid nanofibers in the B-stage and is well impregnated into the carbon fiber fabric. This is because epoxy containing unnecessary aramid nanofibers can be removed by pressure. Curing state is a step to completely cure after the B-stage is over.

Specimens were manufactured as 12.8×60×3.2 mm ³ for dynamic mechanical analysis (DMA), and 12.7×63.5×3.2 mm ³ for the izod impact test based on ASTM D256.

Test example

< Aramid Nano Fiber>

Field emission Scanning Electron Microscope (FE- SEM )

Fractured surfaces were observed using a field-emission scanning electron microscope (FE-SEM, Nova NanoSEM 450, FEI Inc., OR, USA) with a voltage of 5 kV. After liquid nitrogen treatment, a sample of the crushed surface was cut.

As shown in Fig. 4A, the diameter of a single aramid fiber is about 10 μm. The aramid nanofiber bundle separated from the aramid fiber is shown in Figure 4b. The diameter of the aramid nanofibers ranged from 50 nm to 300 nm. It is expected to be several micrometers in length. A single aramid nanofiber showing a diameter of 212 nm is shown in Figure 4c. The multi-walled carbon nanotubes are shown in FIG. 4D, and comparing the diameters of the aramid nanofibers and the multi-walled carbon nanotubes through this, it was found that the diameter of the aramid nanofibers prepared in this experiment was larger than the diameter of the multi-walled carbon nanotubes. I can confirm.

Aramid Fiber and Aramid Chemical structure of nanofiber

As shown in Figure 5a, using Cu Ka radiation at 0.1541 nm wavelength, 45 kV tube voltage, 200 mA current, 10 °/min scan rate and scan range (2θ) 15°-30°, XRD (SmartLab , Rigaku Inc.), the crystal structures of aramid fibers and aramid nanofibers were investigated.

Characteristic peaks of the aramid fiber were shown as 2θ values of 21.2° (110) and 23.4° (200). In the case of aramid nanofibers, a broad peak of (110) appeared because the microscale of the aramid fibers is divided by the nanoscale of the aramid nanofibers. In addition, in the dissolution process of the aramid fiber, the peak of (200) almost disappeared due to the loss of crystallinity due to the hydrolysis process. This is presumed to be a characteristic result of the breakdown of hydrogen bonds and decomposition from micro-scale aramid fibers to nano-scale aramid nanofibers.

5B, the Raman spectrum was measured by a Raman spectroscopy (Renishaw Inc.) having a ^{532 nm laser and a spot area of 1 μm 2.}

5B, Raman spectra of aramid fibers and aramid nanofibers are respectively 1181.1, 1275.62, 1516.88, 1680.94 cm ^-1 (CC ring stretching), 1323.61 cm ^-1 (CH in-plane bending), 1649.69 7 similar bands in cm ^-1 (Amide I [80% C=O stretching & 10% CN stretching 10% NH bending]), and 1569.13 cm ^-1 (Amide II [60% NH bending & 40% CN stretching]) Indicated. The molecular structures of aramid fibers and aramid nanofibers were demonstrated using IR spectra. Significantly similar major peaks appeared in the results.

5C and 5D, an infrared microscope (Nicolet iN10, Thermo Scientific Inc.) was used to record the FT-IR spectrum, and significantly similar major peaks appeared in the results.

In the IR spectrum shown in FIGS. 5C and 5D, aramid fibers and aramid nanofibers are 1319.13, 1515.84, corresponding to CN stretching, C=C aromatic ring stretching vibrations, NH deformation, CN stretching, and C=O stretching vibrations, respectively. Typical peaks were shown at 1542.84, 1650.84, and 3328.67 cm ^-1. Through this, it was confirmed that the molecular structures of the aramid fibers and the aramid nanofibers are almost the same, that is, the actual chemical structure of the aramid fibers is maintained in the aramid nanofibers even if they are separated from the microscale to the nanoscale through deprotonation and dissolution processes. .

< Carbon fiber Reinforced composite material ( CFRP )>

Field emission Scanning Electron Microscope (FE- SEM )

In order to check whether the nano-fillers (aramid nanofibers or multi-walled carbon nanotubes) are properly impregnated and dispersed in the carbon fiber reinforced composite material, a field-emission scanning electron microscope (FE-SEM) with a voltage of 5 kV is used. Nova NanoSEM 450, FEI Inc., OR, USA) was used to investigate the fracture surface of a carbon fiber-reinforced composite material reinforced with a nano-pillar (aramid nanofiber or multi-walled carbon nanotube). Specimen treated with liquid nitrogen The enlarged view of the fracture surface of is shown in Figs. 6A-6D, through which it can be confirmed that the epoxy is well impregnated into the woven carbon fiber (woven CF).

6A-6D, a low-magnification fracture surface (6a) of a carbon fiber reinforced composite material made only of a carbon fiber fabric (woven CF) without a reinforcing agent and an impregnated epoxy resin, and a cut-out of the carbon fiber without a reinforcing agent. The fracture surface of the high-magnification carbon fiber reinforced composite material showing the cross section (6b), the fracture surface of the carbon fiber reinforced composite material with 0.25 wt% aramid nanofibers representing the aramid nanofibers (in the rectangle) and the carbon fiber (right side) (6c) , And a fracture surface (6d) of a carbon fiber-reinforced composite material having 0.25 wt% of multi-walled carbon nanotubes representing the dispersed multi-walled carbon nanotubes and carbon fibers (bottom).

As a result of observing this, it can be seen that the epoxy resin is impregnated without pores between the carbon fibers, and it can be confirmed that the aramid nanofibers are well dispersed in the epoxy resin.

Dynamic Mechanical Analysis (DMA)

Dynamic Mechanical Analysis (DMA) (DMA Q800, TA instrument Inc.) tests were performed in a temperature range of 30 to 120°C (10°C/min) in dual cantilever mode. The strain amplitude was 0.2% at a frequency of 1 Hz.

Damping characteristics play a role in removing unnecessary vibration and noise from various dynamic components, and Tan δ is an important parameter of the damping force of the material. It is defined as the ratio of the loss factor (energy loss) to the storage modulus (energy storage) per deformation cycle. The storage modulus and loss modulus mean stored energy and elastic energy, respectively.

7A shows tan δ when the frequency of the specimen is 1 Hz. The carbon fiber reinforced composite material reinforced with aramid nanofibers shows a much higher tan δ value than the carbon fiber reinforced composite material (neat CFRP) that does not contain a reinforcement agent.

Referring to Figure 7a, in the case of a single carbon fiber reinforced composite material specimen, an aramid nanofiber reinforced specimen containing 0.25% by weight of aramid nanofibers, and a multiwall carbon nanotube reinforced specimen containing 0.25% by weight of multiwall carbon nanotubes , Respectively, reached tan δ values of 0.56, 0.72, and 0.68, respectively.

In the case of the carbon fiber reinforced composite material reinforced with multi-walled carbon nanotubes, the result of tan δ lies between the results of the carbon fiber reinforced composite material without reinforcement and the carbon fiber reinforced composite material reinforced with aramid nanofibers. In addition, the results of the storage modulus and loss coefficient are shown in Figs. 7b and 7c.

Referring to Figures 7b and 7c, the storage modulus results are carbon fiber reinforced composite material without reinforcing agent before glass transition temperature> carbon fiber reinforced composite material reinforced with aramid nanofibers> carbon fiber reinforced with multi-walled carbon nanotubes It decreased in the order of composite materials. The loss modulus decreased in the order of carbon fiber reinforced composite material reinforced with aramid nanofibers> carbon fiber reinforced composite material without reinforcement> carbon fiber reinforced composite material reinforced with multi-walled carbon nanotubes. Since tan δ is expressed as the ratio of the loss factor to the storage modulus, the resulting tan δ is quite reasonable. The abundant surface functional amide groups of aramid nanofibers can affect boundary sliding (pillar-pillar) and interfacial sliding (pillar-matrix). Based on this tan δ result, it is expected to lead to energy dissipation when an external force is applied by improving the damping properties of the composite material.

Nanomaterials impregnated in the polymer matrix provide an opportunity to dissipate energy through interfacial sliding between the matrix and the nanopillar, and since aramid nanofibers have abundant surface functional amide groups, aramid nanofibers / epoxy It can be inferred that strong friction will occur at the interface. In conclusion, through the DMA results, it was found that the damping properties of the carbon fiber reinforced composite material reinforced with aramid nanofibers were dramatically increased.

Impact test

In order to understand the impact resistance of the carbon fiber reinforced composite material reinforced with nanomaterials, the impact test (IT504, Tinius Olsen Inc.) was measured by the izod method according to ASTM D256. The notch depth was 2.54 mm and made using an 899 impact specimen notcher (Tinius Olsen, Inc.). The applied energy was 22.55 J and the impact length was 335.0 mm.

Referring to Figure 8, the impact strength of the notched specimen of the carbon fiber reinforced composite material is improved, the carbon fiber reinforced composite material without a reinforcing agent, 0.25 wt% aramid nanofiber reinforcement and 0.25 wt% multi-walled carbon nanotube reinforcement 386.1, 436.1 and 389.2 J/m were reached for the specimens, respectively.

Among them, the aramid nanofiber filler was found to have the highest impact strength. The 0.25 wt% multi-walled carbon nanotube sample showed lower results than 0.25 wt% aramid nanofibers. This can be explained by the fact that when a carbon fiber reinforced composite material reinforced with aramid nanofibers is impacted, aramid nanofibers provide an opportunity for nanofiber-matrix stress transmission. Aramid nanofibers with abundant functional groups can play a role in interfering with the propagation of cracks. In addition, the surface area for absorption of impact fracture energy will increase.

At the same time, the case of the carbon fiber reinforced composite material reinforced with multi-walled carbon nanotubes showed disappointing results. It is believed that this is because the dispersion degree of the multi-walled carbon nanotubes is relatively low because the epoxy resin does not have a functional group. When an external force is applied to the sample, the nano-pillar of the carbon fiber reinforced composite material with low dispersion can affect the stress concentration, thereby reducing the izod impact energy.

Overall, aramid nanofibers can be successfully obtained by the controlled deprotonation and dissolution process of aramid fibers / KOH / DMSO solution, and aramid nanofibers can be easily obtained from aramid nanofibers / KOH / DMSO solution using deionized water. Is extracted. In addition, aramid nanofibers can maintain a substantial chemical structure, such as the abundant polar functional groups of aramid fibers.

Based on these advantages of aramid nanofibers, in the case of a carbon fiber reinforced composite material reinforced with aramid nanofibers, attenuation of the carbon fiber reinforced composite material reinforced with aramid nanofibers in DMA measurement results due to the rich functional groups of aramid nanofiber It shows that the properties are more improved than the carbon fiber reinforced composite material without reinforcing agent and the carbon fiber reinforced composite material reinforced with multi-walled carbon nanotubes.

The results of the impact test are due to the fact that the impact strength of the notched specimen of the carbon fiber reinforced composite material reinforced with aramid nanofibers absorbs the impact energy by increasing the surface area and providing the opportunity for nanofiber-matrix stress transfer. It is shown that the impact strength of the fiber-reinforced composites is higher than that of the notched specimens.

As described above, specific parts of the present invention have been described in detail, and it is obvious that these specific techniques are only preferred embodiments for those of ordinary skill in the art, and the scope of the present invention is not limited thereby. something to do. Accordingly, it will be said that the substantial scope of the present invention is defined by the appended claims and their equivalents.

Claims (11)

Thermosetting resin in which aramid nanofibers are dispersed; And
Including; carbon fiber;
The thermosetting resin in which the aramid nanofibers are dispersed is impregnated with the carbon fiber, a carbon fiber-reinforced composite material. The method of claim 1,
The thermosetting resin is an epoxy resin, a carbon fiber reinforced composite material. The method of claim 1,
The content of the aramid nanofibers in the thermosetting resin is 0.05 to 1% by weight, carbon fiber reinforced composite material. The method of claim 1,
The diameter of the aramid nanofibers is 50 to 300 nm, carbon fiber reinforced composite material. The method of claim 1,
The aspect ratio of the aramid nanofibers is 1:5 to 1:50, carbon fiber reinforced composite material. The method of claim 1,
The aramid nanofibers are para-aramid nanofibers, carbon fiber reinforced composite material. The method of claim 1,
The carbon fiber is a carbon fiber fabric (woven carbon fiber), a carbon fiber reinforced composite material. A method for producing a carbon fiber-reinforced composite material according to any one of claims 1 to 7,
Preparing aramid nanofibers using aramid fibers;
Dispersing the aramid nanofibers in a thermosetting resin; And
A method for producing a carbon fiber-reinforced composite material comprising a step of impregnating the carbon fiber with a thermosetting resin in which aramid nanofibers are dispersed. The method of claim 8,
The step of preparing aramid nanofibers using aramid fibers is performed by adding aramid fibers to a solution containing potassium hydroxide (KOH) and dimethyl sulfoxide (DMSO). The method of claim 8,
The step of impregnating the carbon fiber with the thermosetting resin in which the aramid nanofibers are dispersed is performed by a hand-ray up method. The method of claim 8,
The manufacturing method of the carbon fiber reinforced composite material,
After the step of impregnating the carbon fiber with the thermosetting resin in which the aramid nanofibers are dispersed, curing the thermosetting resin in which the aramid nanofibers are dispersed; further comprising,
The step of curing the thermosetting resin in which the aramid nanofibers are dispersed is performed by a vacuum bagging process.

Images