KR102470872B1 - Modified carbon fiber/ABS composites and manufacturing method of the same - Google Patents

Abstract

The present invention is a carbon fiber coated with MWCNT whose surface is functionalized with polyethyleneimine (PEI), a cationic polyelectrolyte, and an ABS matrix modified by incorporating pulverized carbon fiber (MCF), and carbon fiber/ABS composite material and manufacturing using the same It's about how. The carbon fiber/ABS composite material according to the present invention has an effect of improving interfacial properties, mechanical properties, and thermal properties.

Description

Carbon fiber/ABS composites and manufacturing method thereof {Modified carbon fiber/ABS composites and manufacturing method of the same}

The present invention relates to carbon fibers coated with multi-walled carbon nanotubes (MWCNTs) functionalized with polyethyleneimine (PEI), a cationic polyelectrolyte; It relates to an ABS matrix modified by incorporating pulverized carbon fiber (MCF), a carbon fiber/ABS composite material manufactured by an LFT process by applying the same, and a manufacturing method.

Due to the recent strengthening of environmental and fuel efficiency regulations around the world, weight reduction is emerging as a key technology that determines global competitiveness in the transportation industry, including automobiles. In addition, as the demand for eco-friendly vehicles such as electric vehicles and hydrogen vehicles increases, vehicle weight reduction technology is receiving more attention. The reason is that parts such as batteries of eco-friendly vehicles are very heavy, which increases the weight of internal combustion locomotives. As the most effective way to realize vehicle weight reduction, technology to replace existing steel materials with lightweight materials is receiving great attention. Carbon fiber reinforced plastics (CFRP) refers to a composite material composed of carbon fiber as a reinforcing material and a polymer resin as a matrix. Carbon fiber is about 75% lighter than steel and has 7 to 10 times better specific strength and modulus of elasticity. Therefore, CFRP, in which polymer resin is reinforced with carbon fiber, is suitable for use in parts requiring light weight and high performance.

Traditionally, a thermosetting resin has been used as a polymer resin for CFRP, but when applying a thermosetting resin, it must undergo a curing reaction, so a thermoplastic resin is used as a matrix in consideration of productivity aspects such as molding process and manufacturing time, as well as cost reduction and recycling. The use of carbon fiber reinforced thermoplastics (CFRTP) is attracting attention. Thermoplastic resins are mainly used to manufacture composite materials that do not undergo a curing reaction, have a very short molding process time, have high productivity of parts, and have excellent impact resistance.

Accordingly, Korean Patent Registration No. 10-1470803 (2014.12.08. Publication date) has proposed a carbon fiber-reinforced thermoplastic produced by compressing a thermoplastic resin and carbon fiber and a method for manufacturing the same, but an extrusion/injection process Since it was manufactured through, it is difficult to impregnate the resin into the fiber due to the high melt viscosity of the thermoplastic resin, the interfacial bonding force between the fiber and the resin is low, and the carbon fiber is damaged during the extrusion process, so it is difficult to implement high performance. There was a problem.

In addition, Korean Patent Publication No. 10-2020-0109593 (published on September 23, 2020) discloses a highly impregnated carbon fiber-reinforced thermoplastic composite material prepared by heating and pressing thermoplastic resin matrix fibers and highly impregnated carbon fibers, and Although the impregnability was improved by suggesting a manufacturing method, other problems may arise due to uniform dispersion of fibers and difficulty in processing.

Korean Registered Patent Publication No. 10-1470803 (2014.12.08. Publication date) Korean Patent Publication No. 10-2020-0109593 (2020.09.23. Publication date)

The present invention is intended to solve the above problems, and increases the aspect ratio of carbon fibers constituting carbon fiber reinforced thermoplastic (CFRTP) through a long fiber thermoplastic (LFT) process, and composites carbon-based materials. The purpose is to provide CFRTP with excellent interface properties, mechanical properties, and thermal properties between carbon fibers and a polymer matrix by introducing it into materials.

In order to achieve the above object, one embodiment of the present invention is (a) mixing polyethyleneimine (PEI) with multi-walled carbon nanotubes (MWCNT) to the multi-walled carbon nanotubes. Step of functionalizing the surface of; (b) modifying carbon fibers with functionalized MWCNTs; (c) modifying ABS (acrylonitrile-butadiene-styrene) resin with milled carbon fiber (MCF); and (d) preparing a carbon fiber/ABS composite material by processing the carbon fiber modified in step (b) and the ABS resin modified in step (c) through an LFT process. A method for manufacturing the material is provided.

In one embodiment, the ratio of MCF for modifying the ABS resin may be characterized in that 0.5 parts by weight to 30 parts by weight relative to 100 parts by weight of the ABS resin.

In one embodiment, the carbon fiber ratio of the carbon fiber/ABS composite material may be 20 wt% to 40 wt% of the carbon fiber/ABS composite material.

Another example of the present invention, as a composite material component, includes MWCNT carbon fibers whose surfaces are functionalized with PEI and ABS resin modified with MCF, and the ratio of MCF is 0.5 parts by weight to 100 parts by weight of the modified ABS resin. 30 parts by weight, and the carbon fiber ratio of the modified carbon fiber/ABS composite material is 20 wt% to 40 wt% of the carbon fiber/ABS composite material.

Interfacial shear strength (IFSS) of the modified carbon fiber/ABS composite material may be 50 to 60 MPa.

The modified carbon fiber / ABS composite material may have a tensile strength of 80 to 100 MPa, a tensile modulus of 8 to 10 GPa, a flexural strength of 130 to 140 MPa, a flexural modulus of 25 to 30 GPa, and an impact strength may be 150 to 180 J/m.

The present invention relates to carbon fibers coated with MWCNTs functionalized with PEI, a cationic polyelectrolyte, an ABS matrix modified by incorporating MCF, a carbon fiber/ABS composite material using the same, and a method for manufacturing the carbon fibers according to the present invention. /ABS composite material has the effect of improving mechanical properties and thermal properties as well as the effect of improving the interface properties between carbon fiber and polymer matrix by introducing carbon-based materials into the composite material.

1 shows (A) a carboxylation process of MWCNTs and (B) a process of modifying carbon fibers after functionalizing MWCNTs with PEI according to an embodiment of the present invention.
2 shows a process of modifying MCF in an ABS resin according to an embodiment of the present invention.
3 shows a single fiber microbonding process using carbon fiber and ABS resin.
4 shows (A) an LFT process for producing carbon fiber/ABS LFT pellets and (B) a carbon fiber/ABS tow preg process.
5 shows an injection molding process for molding the carbon fiber/ABS composite material.
6 shows the interfacial shear strength (IFSS) of the carbon fiber/ABS composite material according to the modification.
7 shows (A) tensile strength and (B) tensile elasticity of the carbon fiber/ABS composite material according to the modification.
8 shows (A) flexural strength and (B) flexural modulus of carbon fiber/ABS composites according to neat ABS and modification, and (C) is a combination of compressive force and tensile force generated in the middle plane of a three-point flexure specimen. is shown.
9 shows the impact strength of neat ABS and carbon fiber/ABS composites according to the modification.
10 is an image of a fractured surface of a specimen analyzed by FE-SEM after performing an impact test on neat ABS and a carbon fiber/ABS composite material according to the above modification.
11 shows the thermal deflection temperatures of neat ABS and carbon fiber/ABS composites according to the modification.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein is one well known and commonly used in the art.

When it is said that a certain part "includes" a certain component throughout the present specification, it means that it may further include other components without excluding other components unless otherwise stated.

Hereinafter, with reference to the accompanying drawings, a preferred embodiment of manufacturing a carbon fiber/ABS composite material according to the present invention will be described in detail so that those skilled in the art can easily practice the present invention. .

In one aspect, the present invention includes: (a) mixing polyethyleneimine (PEI) with multi-walled carbon nanotubes (MWCNTs) to functionalize the surface of the multi-walled carbon nanotubes; (b) modifying carbon fibers with functionalized MWCNTs; (c) modifying ABS (acrylonitrile-butadiene-styrene) resin with pulverized carbon fiber (MCF); and (d) preparing a carbon fiber/ABS composite material by processing the carbon fiber modified in step (b) and the ABS resin modified in step (c) through an LFT process. A method for manufacturing the material is provided.

According to one embodiment of the present invention, step (a) is a step for maximizing the dispersion of MWCNTs and forming a chemical bond between carbon fibers and MWCNTs, and attaching functional groups to MWCNTs using a mixed solution of sulfuric acid and nitric acid. After performing the carboxylation process to perform, the carboxylated MWCNTs are functionalized with PEI so that they can be uniformly dispersed.

Through the carboxylation process, a carboxyl group (-COOH) is formed on the surface of the MWCNT. In an aqueous solution, the carboxyl group dissociates into COO ^- and H ⁺ , and PEI dissociates into NH ³⁺ . Therefore, an amide bond is formed as a covalent bond occurs through a condensation reaction that occurs when water is lost between COO ^- and NH ³⁺ . A hydrogen bond may be formed due to the difference in electronegativity between the oxygen of the carbonyl group (>C=O) of the MWCNT surface and the secondary amine of PEI. MWCNTs functionalized with PEI, a cationic polyelectrolyte, are positively charged. MWCNTs can be uniformly dispersed without aggregation due to mutual (+,+) repulsive forces acting between the MWCNTs.

The weight average molecular weight (Mw) of the polyethyleneimine is 200 to 30,000, preferably 200 to 25,000, more preferably 200 to 1,500. In addition, the number average molecular weight (Mn) is 200 to 12,000, preferably 200 to 10,000, more preferably 200 to 1,400. When the Mw and Mn of the polyethyleneimine are greater than 30,000 and 12,000, respectively, aggregates of PEI and MWCNTs may not be coated on the surface of the carbon fibers, and the interfacial bonding force of the composite material according to the present invention may be weakened. .

The step (b) of the present invention is a step of coating and modifying the functionalized MWCNTs on the carbon fiber, and the carbon fiber tow is immersed in the PEI-functionalized MWCNT solution to modify the carbon fiber.

The carbon fiber modified with the functionalized MWCNT has a rough surface due to the coating effect of the MWCNT, but due to the PEI treatment, there is almost no aggregation on the surface of the carbon fiber, and uniform dispersion and coating can be achieved throughout the carbon fiber have.

The step (c) of the present invention is a step of modifying the ABS resin using MCF, and in order to remove moisture from the MCF and ABS resin, an extrusion process is performed after drying in a reflux oven, and then pelletized to about 3 mm characterized by

The ratio of MCF for modifying the ABS resin is 0.5 parts by weight to 30 parts by weight based on 100 parts by weight of the ABS resin. If the content of the MCF is less than 0.5 parts by weight, the load applied to the composite material from the outside of the matrix is transferred to the carbon fiber as it is or cracks occur, and thus the toughness is also reduced. When the content of the MCF exceeds 30 parts by weight, the strength of the composite material may be reduced due to excessive cracking due to the excessive MCF.

The MCF used for modifying the ABS resin is easier to disperse in the polymer resin than MWCNT, and has a relatively high aspect ratio in a fibrous shape. MCF in the ABS matrix has various fiber length distributions and is distributed in a disorderly orientation, so when a load is applied, the MCF acts as an obstacle, resulting in crack deflection and energy absorption and loss. . Therefore, when MCF is introduced into the carbon fiber/ABS composite material, the load applied to the composite material can be effectively transmitted, and energy absorption can be increased to contribute to increasing mechanical properties, impact properties, and thermal properties.

In addition, the step (d) is a step of manufacturing a carbon fiber/ABS composite material using modified carbon fiber and modified ABS resin, and ABS resin in which carbon fiber tow in the form of continuous fiber is melted and extruded through the LFT process. While intersecting with the resin, the tow is impregnated to produce a carbon fiber/ABS towpreg. Then, the toupreg produces LFT pellets with an average length of 12 mm through a pelletizer.

Since the LFT technology-based composite material is a composite material composed of long fibers and a thermoplastic polymer matrix with a reinforcing fiber aspect ratio greater than a critical aspect ratio, it has excellent mechanical properties, ease of processing, recyclability, and impact resistance.

The carbon fiber ratio of the carbon fiber/ABS composite material is 20 wt% to 40 wt%, preferably 25 wt% to 35 wt%, of the carbon fiber/ABS composite material. In the present invention, the high carbon fiber content increases the resistance to thermal deformation, but if the carbon fiber ratio is less than 20 wt%, the resistance to thermal deformation is greatly reduced. On the other hand, when the ratio of the carbon fiber exceeds 40 wt%, the MWCNT bridge formed when the carbon fiber tow modified with MWCNT is used together with the ABS resin having a relatively high viscosity is excessively formed, resulting in impregnation between the carbon fiber filaments. making it difficult, the mechanical properties of the composite material may deteriorate.

Another example of the present invention includes, as a composite component, carbon fiber modified with MWCNT whose surface is functionalized with PEI, and an ABS resin modified with MCF, in an amount of 0.5 to 30 parts by weight based on 100 parts by weight of the modified ABS resin. And, the carbon fiber ratio of the carbon fiber / ABS composite material is 20 wt% to 40 wt% of the carbon fiber / ABS composite material.

In addition, the carbon fiber/ABS composite material of the present invention can improve the interface properties between the carbon fiber and the polymer matrix and enhance the mechanical strength of the matrix by introducing carbon-based materials, MWCNT and MCF, into the composite material.

Specifically, the modified carbon fiber/ABS composite material has an interfacial shear strength (IFSS) of 50 to 60 MPa, a tensile strength of 80 to 100 MPa, a tensile modulus of 8 to 10 GPa, a flexural strength of 130 to 140 MPa, and a flexural modulus. It was 25 ~ 30 GPa, and the impact strength was 150 ~ 180 J/m, and the interface properties, mechanical properties, and thermal properties were all excellent.

Hereinafter, examples will be described for more specific explanation of the present invention. However, the following examples are only preferred examples of the present invention and the present invention is not limited to the following examples.

<Example 1>

1. Materials

PAN-based carbon fiber (12K, T700 grade) manufactured by Toray Advanced Materials Co., Ltd. (Korea) was used as a reinforcing material for the composite material. The surface of the carbon fiber is commercial epoxy-sizing. The carbon fibers used in the LFT process were provided in the form of continuous fibers wound on bobbins. According to the information provided by the manufacturer, the density of carbon fiber is 1.8 g/cm ³ , the mass per unit length (tex) is 800 g/1000m, the tensile strength is about 4,900 MPa, The tensile modulus is about 230 GPa.

MWCNTs (K-Nanos 100P) used for surface modification of carbon fibers are bundled and manufactured by Kumho Petrochemical Co., Ltd. (Korea). According to information provided by the manufacturer, MWCNTs have a diameter of 10 to 15 nm, a bundle length of 10 to 50 μm, and a bulk density of 0.02 to 0.04 g/mL.

PEI (branch type, MW∼1,300) used for functionalization of MWCNTs was purchased from Sigma-Aldrich Co., Ltd. (USA). PEI is a cationic polyelectrolyte with an amine group capable of forming covalent and hydrogen bonds, and has a positive (+) charge when dissociated in water.

ABS resin (ABS-780F model) manufactured by Kumho Petrochemical (Korea) was used as the polymer matrix of the carbon fiber reinforced composite material. Since ABS resin contains carbon black as a pigment, it shows a black pellet form. According to the manufacturer's information, the exact composition ratio for each content of acrylonitrile, butadiene, and styrene contained in ABS resin has not been disclosed, but it is believed to have a content ratio in the range of about 20 to 30%, 15 to 25%, and 55 to 65%, respectively. It is known. The density of the ABS resin is 1.04 g/cm ³ , and the melt flow index (MFI, 220° C., 10 kg) is 65 g/10min. ABS-780F model is a resin with relatively high fluidity, with an MFI value improved by about 85% compared to other commercially available ABS models of Kumho Petrochemical Co., Ltd.

MCF obtained by pulverizing recycled PAN-based carbon fibers used for modification of ABS resin was manufactured by ZOLTEK Co., Ltd (USA). MCF looks powdery to the naked eye, but has a relatively high aspect ratio in the form of fibers under a microscope. According to the information provided by the manufacturer, the MCF has a diameter of 7.2 μm, an average fiber length of 100 μm, an average aspect ratio of about 14, and a density of 1.81 g/mL. Carbon fiber and ABS resin were dried for 12 hours in a reflux oven set at 80 °C before use.

2. Manufacturing

(1) Modification of carbon fiber using MWCNTs functionalized with PEI

Modification of carbon fibers using MWCNTs functionalized with PEI is a process of carboxylating MWCNTs (Fig. 1(A)) and modifying carbon fibers after functionalizing carboxylated MWCNTs with PEI (Fig. 1(B)). ) was divided into

Put 0.24 g of MWCNT and 400 mL of a mixed solution of 8 MH ₂ SO ₄ /HNO ₃ (v/v, 3/1) in a round bottom flask, and heat in a water bath at 70 °C using a hot plate & magnetic stirrer. Mix for 40 minutes at 650 rpm. Next, the mixture was dispersed through sonication under conditions of 300 W and 40 kHz for 2 hours using a bath-type sonicator (Power sonic 510, USA), and then until the pH test paper showed neutrality. Wash thoroughly with distilled water.

After the carboxylation process of the MWCNTs, 0.24 g (0.07 wt%) of the carboxylated MWCNTs, 0.048 g (0.014 wt%) of PEI, 0.34 g (0.1 wt%) of NaCl, and 343 g of distilled water were added to a beaker, followed by a magnetic stirrer. (magnetic stirrer) was used to mix at room temperature at 150 rpm for 30 minutes. The content of each substance represents the content relative to the weight of distilled water. Next, the mixture was sonicated at 150 W and 20 kHz for 2 hours using a probe-type sonicator (VC-505, SONICS, USA), and then unreacted PEI and NaCl were removed. To do so, it was washed with distilled water using a pressure reducer. MWCNTs were dispersed again by putting filtered MWCNTs in 343 mL of distilled water and sonicating with a probe sonicator at 150 W and 20 kHz for 15 minutes. The washing and redispersing process was repeated three times. The washed MWCNTs were sonicated at 150 W and 20 kHz for 1 hour using a probe-type sonicator and dispersed in 0.1 mM NaCl aqueous solution. After the carbon fiber tow was immersed in the MWCNT solution functionalized with PEI for 5 minutes in a static state, it was dried in a reflux oven set at 80 ° C. for 12 hours.

The content of MWCNTs coated on the carbon fibers was 0.20 wt% compared to the carbon fibers, and was obtained using Equation (1).

(1)

(One)

는 탄소섬유에 코팅된 PEI로 기능화된 MWCNT의 함량,

는 PEI로 기능화된 MWCNT가 코팅된 탄소섬유의 질량,

는 pristine 탄소섬유의 질량이다.here,

is the content of MWCNTs functionalized with PEI coated on carbon fibers,

is the mass of carbon fibers coated with MWCNTs functionalized with PEI,

is the mass of the pristine carbon fiber.

Accordingly, carbon fibers coated with MWCNTs whose surfaces were finally functionalized with PEI were prepared.

(2) Modification of ABS matrix using MCF

In order to remove moisture that may exist in the MCF and ABS resin, the MCF and ABS resin were dried in a reflux oven set at 80 ° C for 12 hours, respectively. The MCF content was fixed at 1 wt% compared to the ABS resin. For uniform dispersion and mixing of MCF, MCF was supplied through a hopper after sufficiently pre-mixing manually. Next, the compounded extrudate comes out through an extruder die, is cooled in a water bath, and then pelletized to a length of about 3 mm through a pelletizer to MCF ABS pellets modified with were prepared. This process is shown in Figure 2, and was performed repeatedly until the required amount of pellets for the study was obtained.

(3) Manufacture of ABS microdroplets by modifying both carbon fiber and matrix

After placing an iron set at 280 ° C. on the surface of the ABS pellets, the molten ABS pellets were rapidly pulled and cooled to prepare fiber-shaped ABS filaments. The ABS filament was brought into contact with the center of the carbon fiber filament fixed to the paper frame, melted with an iron set at 240 ° C, and then cooled while turning the carbon fiber to wrap the carbon fiber filament, thereby forming ABS microdroplets. The modified ABS microdroplet manufacturing process is shown in FIG. 3 .

(4) Manufacture of carbon fiber/ABS LFT pellets with both carbon fiber and matrix modified

The LFT process was performed to produce carbon fiber/ABS LFT pellets in which both the carbon fiber and the matrix were modified, and the LFT process is shown in FIG. 4(A). One carbon fiber tow (12k) in the form of continuous fibers caught on a creel rack goes through a guide that spreads the tow and passes through a cross-die by a drawing machine. A carbon fiber/ABS towpreg was prepared by intersecting with the carbon fiber tow coming out in the pulling direction and impregnating the tow with resin.

4(B) shows the LFT tow prep process, in which the carbon fiber is impregnated with the molten resin in a horizontal direction. Before the toe prep is cooled down, while the ABS resin is in a somewhat flexible state, the toe prep is lightly pressed through the rolling guide to induce the resin to permeate between the carbon fiber filaments, thereby improving the resin impregnation level. The carbon fiber/ABS towpreg was cooled by a cooling fan and immediately wound onto a bobbin to prevent the carbon fiber/ABS towpreg from tangling together. LFT pellets with an average length of 12 mm were prepared from the carbon fiber/ABS toupreg using a tailor-made pelletizer (ACE C&TECH, Korea).

The LFT equipment was custom-made on a lab-scale by combining an extruder for melting and compounding ABS resin and a pulling machine for continuously supplying and pulling carbon fibers. For the LFT process, a single-screw extruder (BAUTEK, Korea) with a screw diameter of 20 mm and an L/D of 30 was used.

The LFT process conditions are shown in Table 1. The carbon fiber content of the carbon fiber/ABS toupreg was fixed at 38 wt% compared to the ABS resin by controlling the processing temperature, the speed of the screw, and the speed of the drawing machine. The content of carbon fiber was obtained using equation (2).

(2)

(2)

는 탄소섬유/ABS 토우프레그의 탄소섬유 함량,

는 탄소섬유의 질량,

는 탄소섬유/ABS 토우프레그의 질량이다.here

is the carbon fiber content of the carbon fiber/ABS tow preg,

is the mass of the carbon fiber,

is the mass of the carbon fiber/ABS tow preg.

Barrel temperature (℃) Zone 1 Zone 2 Head Die 160 210 270 270 Process conditions Speed of screw in the extruder Carbon fiber tow pulling speed 3.5 to 6.5 rpm 4.0 to 5.0 rpm

(5) Molding of carbon fiber/ABS composite material with both carbon fiber and matrix modified

In order to mold the carbon fiber/ABS composite material in which both the carbon fiber and the matrix are modified, as shown in FIG. 5, an injection molding machine (Model PRO-WD 80, Dongshin Hydraulics, Korea) with a die clamping force of 80 ton ) was used to perform the injection molding process. The clamping force is the force holding the mold when it is about to open due to injection pressure and holding pressure during the injection process. The carbon fiber / ABS LFT pellets were used after drying for 12 hours in a reflux oven set at 80 ° C. Table 2 shows the injection molding conditions used in the above invention.

<Comparative Examples 1 to 3>

(1) Comparative Example 1

The same manufacturing process as in Example 1 was applied, but unmodified carbon fiber and ABS resin were used.

(2) Comparative Example 2

The same manufacturing process as in Example 1 was applied, but carbon fibers coated with PEI-functionalized MWCNTs and unmodified ABS resin were used.

(3) Comparative Example 3

The same manufacturing process as in Example 1 was applied, but unmodified carbon fiber and MCF-modified ABS resin were used.

<Characteristic Analysis>

The interfacial properties, mechanical properties, and thermal properties of Example 1 and Comparative Examples 1 to 3 were compared, and the types of carbon fiber/ABS composite materials according to the modification are shown in Table 3.

Material Designation of carbon fiber/ABS composites Abbreviation Comparative Example 1 Pristine carbon fiber
and
neat ABS resin Unmodified UM Comparative Example 2 Carbon fiber modified with MWCNT
and
neat ABS resin Carbon fiber modified FM Comparative Example 3 Pristine carbon fiber
and
ABS resin modified with MCF ABS matrix modified MM Example 1 Carbon fiber modified with MWCNT
and
ABS resin modified with MCF Dual-modified DM

(1) Interfacial properties

6 shows the result of analyzing the interface characteristics of the carbon fiber/ABS composite material according to the modification. The interface characteristics were analyzed by single fiber microbonding test of the carbon fiber filament on which the ABS mircodroplet was formed.

The carbon fiber/ABS composite (UM) in which both the carbon fiber and the matrix are not modified shows the lowest IFSS value of about 28 MPa. It is interpreted that this is because the surface of the carbon fiber is smooth and there is almost no functional group capable of chemically bonding with the ABS resin on the surface of the carbon fiber, so no physical or chemical bonding is made. The carbon fiber/ABS composite (FM) in which only the carbon fiber was modified showed an IFSS value of 40 MPa, which is about 43% higher than that in which both the carbon fiber and the ABS matrix were not modified, and the carbon fiber/ABS composite material in which only the matrix was modified. The IFSS value of (MM) was about 37 MPa, which increased by about 29% compared to that of unmodified (UM), but showed a lower increase than that of carbon fiber only (FM). This is because ABS resin not modified with MCF has ductility, so it is easily deformed by shearing. On the other hand, it is believed that the IFSS value of the ABS resin modified with MCF increased because MCF increased the ability to resist shear force.

The carbon fiber/ABS composite (DM) with both carbon fiber and matrix modified showed the highest IFSS value of 53.2 MPa. This is interpreted as the result of the synergistic effect of the combination of the improvement of the interfacial bonding force between the fiber-matrix by MWCNT and the improvement of resistance to load by MCF. It can be seen that the modification of carbon fiber and ABS matrix through MWCNT and MCF contributes to improving the interfacial properties between fiber and matrix.

(2) mechanical properties

i) Tensile properties

7 shows the tensile strength (FIG. 7(A)) and tensile modulus (FIG. 7(B)) of neat ABS and 4 types of carbon fiber/ABS composites according to the modification. The change trends of tensile strength and tensile modulus for Neat ABS and carbon fiber/ABS composites were similar. The tensile strength and tensile modulus of Neat ABS were the lowest at about 37 MPa and about 1.6 GPa, respectively. The tensile properties of carbon fiber/ABS composites were significantly increased due to the reinforcing effect of carbon fiber.

In fiber-reinforced thermoplastic composites, the tensile strength is greatly influenced by microscopic defects on the fiber surface, and the tensile modulus is mainly influenced by the fiber distribution and orientation in the matrix. The ABS resin used in the above embodiment has a higher melt flow index than other commercially available ABS resins, but has a relatively high melt viscosity and a low melt flow index compared to other conventional thermoplastic polymers. Therefore, in the process of impregnating the carbon fiber with the ABS resin having a relatively high melt viscosity, the adhesion between the fiber and the resin is not properly formed, and a gap is formed. / showed the lowest tensile strength among the ABS composite materials.

The tensile properties of the composite material (FM) modified only with carbon fiber slightly increased compared to that of the unmodified composite material (UM), but the difference was insignificant. Due to the low melt viscosity of the ABS resin, MWCNTs are introduced into the gap between the fibers and the matrix, which acted as micro-defects, to increase the interfacial bonding force. Unlike the single fiber microbonding test results, the effect of interfacial bonding did not appear significantly when the actual composite material was used. The single fiber microbonding test uses carbon fiber filaments as a test to evaluate the interfacial bonding force from a microscopic point of view, but in actual composite materials, carbon fiber tow is used. When carbon fiber tow is modified with MWCNTs, MWCNT bridges are formed between the carbon fiber filaments, and the excessively formed MWCNT bridges make it difficult to impregnate between the carbon fiber filaments, so the improvement in tensile properties is considered to be insignificant.

The tensile strength of the composite material (MM) modified only by the matrix has a slightly higher value than that of the modified carbon fiber alone. Tensile strength is more dependent on the intrinsic properties of the reinforcing fibers than on the interfacial properties of the fibers and matrix. The average length of MCF incorporated into the ABS matrix is about 100 μm, which is very short compared to that of carbon fiber. This makes it possible to exhibit intact MCF properties without being damaged by the narrow gap between the screw and the barrel in the injection molding machine. The increase in tensile modulus of the composite material (MM) with only matrix modification was higher than the increase in tensile strength. During injection molding, carbon fibers and MCF in composite materials are oriented mainly in the longitudinal direction due to injection pressure. Therefore, it is interpreted that the rigidity of the composite material in the longitudinal direction is increased and the tensile modulus is increased.

The composite material (DM), in which both the carbon fiber and the matrix are modified, shows the highest values in both tensile strength and tensile modulus. This is interpreted as the fact that the MWCNTs and MCFs used in the modification were physically bonded to the ABS matrix to reduce the strain caused by the tensile load of the ABS resin and become hard.

ii) Flexural characteristics

8(A) and (B) show the flexural strength (FIG. 8(A)) and flexural modulus (FIG. 8(B)) of neat ABS and four types of carbon fiber/ABS composites according to the modification. Overall, flexural properties showed similar trends to tensile properties. Neat ABS has the lowest flexural strength and flexural modulus of about 50 MPa and about 2 GPa, respectively. The flexural properties of the carbon fiber/ABS composite material were remarkably increased by the reinforcing effect of the carbon fiber. As shown in FIG. 8(C), the stress due to the bending load applied in the thickness direction of the specimen is influenced by a combination of compressive stress applied at the top of the center of the specimen and tensile stress applied at both sides of the bottom of the specimen. Shear forces are generated inside the specimen due to compressive and tensile stresses. Therefore, the flexural test is more important than the tensile test in evaluating the interfacial properties of fibers and matrices of fiber-reinforced composites.

Modification of the carbon fiber and ABS matrix results in higher flexural properties. It is believed that the carbon fiber modification by the MWCNT coating increases the roughness of the carbon fiber surface and increases the interfacial bonding force between the fiber and the matrix, thereby improving the flexural strength. The MWCNTs introduced into the weak interface between the carbon fiber and the ABS resin supported the bending load and increased the resistance to deformation. The flexural properties of composites with only matrix modification were also improved compared to those without modification. This is the result obtained because the MCF used for modification is physically combined with the ABS matrix to more efficiently transfer the bending load to the carbon fiber.

In the bending test, shear action occurs similarly to the single fiber microbonding test, but unlike the results of the model composite material, the effect of matrix modification was greater than that of carbon fiber modification in the actual composite material. This is believed to be the result of damage to the carbon fiber caused by injection molding. This is because MWCNTs coated on carbon fibers are damaged by the shear force between the screw and the barrel of the injection molding machine during injection molding. Carbon fibers with a damaged MWCNT coating layer do not show the same tendency as the interfacial shear strength because the interfacial bonding force with the matrix is somewhat lower than that of the undamaged carbon fibers.

The composite material with both fiber and matrix modified showed the highest values of flexural strength of about 134 MPa and flexural modulus of about 27 GPa due to the synergistic effect of introducing MWCNT and MCF into the carbon fiber and ABS matrix, respectively. When comparing flexural strength and flexural modulus, it can be seen that the increase in flexural strength is larger. Through this, it is considered that the flexural strength is more dependent on the interface properties than the flexural modulus.

iii) Impact characteristics

9 shows the impact strength of neat ABS and four types of carbon fiber/ABS composites according to the modification. Neat ABS shows the highest impact strength of about 283 J/m. This is a result of the high toughness of butadiene, one of the components of ABS resin. The impact strength of the carbon fiber/ABS composite material was significantly reduced compared to that of neat ABS. The impact strength of the composite material (FM) modified only with carbon fiber was 149 J/m, and the composite material (MM The impact strength of is 130 J/m, which is 11% higher than that of the composite material without modifying both the carbon fiber and the matrix. The impact strength of the composite material with both fiber and matrix modified is the highest at about 169 J/m. It is believed that the partial filling of the MCF between the MWCNTs coated on the carbon fibers contributed sufficiently to the increase in impact strength. In other words, the crack movement path due to the impact load applied to the composite material is blocked by MCF, and energy is lost in the process of escaping the path in the other direction, and the crack tip cannot penetrate the interface layer thickened with MWCNTs and MCF. Therefore, it is judged that direct contact with the carbon fiber surface was prevented.

(3) Composite material fracture surface

10 shows a photograph of the fracture surface of a specimen observed with FE-SEM after performing an impact test on neat ABS and four types of carbon fiber/ABS composite materials according to the above modification. Neat ABS (Fig. 10(A)) shows typical ductile fracture of thermoplastics. Fiber-reinforced composite materials may cause pull-out of fibers, breakage of fibers, and debonding between fibers and the matrix during the fracture process.

In the case of the composite material in which both the carbon fiber and the matrix are not modified (FIG. 10(B)), the surface of the carbon fiber and the surface of the ABS matrix where the fiber is pulled out are very smooth and clean. This means that the interfacial bonding between the fibers and the matrix is very weak. In addition, it can be observed that interfacial bonding between the carbon fibers and the ABS matrix is not properly formed, resulting in gaps. Gaps between the fibers and the matrix are not effective in evenly transferring the externally applied impact load to the carbon fibers.

As a result of observing the fracture surface of the composite material modified only with carbon fibers (FIG. 10(C)), it can be observed that ABS resin is embedded in places by MWCNTs on the surface of carbon fibers. MWCNTs were introduced into the gaps between the fibers and the matrix observed at the fracture surface of the unmodified composite material to increase the fiber-matrix interfacial bonding strength. It is believed that MWCNTs can provide a pathway for transferring impact energy from the matrix to the carbon fibers.

In the case of the composite material with only the matrix modified (FIG. 10(D)), a fracture surface similar to that of the unmodified composite material is shown, but MCF can be observed here and there. MCF is manufactured by crushing recycled carbon fiber, and shows significant damage to the surface. This damage increases the surface roughness of the MCF, showing excellent interfacial bonding strength with the ABS matrix, and no gaps between the MCF and the matrix are observed. Therefore, the MCF resisted the load and effectively dissipated the impact energy within the ABS matrix.

In the photograph of the fracture surface of the composite material (FIG. 10(E)) in which both the fiber and the matrix are modified, it can be observed that a certain amount of ABS resin is embedded on the surface of the carbon fiber, and MCF is dispersed in the matrix, showing excellent interfacial bonding strength. have. This provides effective stress transfer and resistance to external loads when impact energy is applied and cracks are propagated along the fiber-matrix interface.

(4) Thermal properties

11 shows the improved thermal properties through the heat deflection temperatures of neat ABS and four types of carbon fiber/ABS composites according to the above modification. The heat deflection temperature of Neat ABS is 89℃. All carbon fiber/ABS composites exhibit a heat deflection temperature about 10 °C higher than that of neat ABS. This is considered to be due to the improvement of the resistance of the specimen to the three-point bending load applied in the width direction of the specimen due to the reinforcing effect of the carbon fiber. Since carbon fiber has already undergone high-temperature heat treatment in the manufacturing process, there is little deterioration in physical properties even in a high-temperature environment. On the other hand, polymer resins are very sensitive to thermal changes compared to carbon fibers. In the present invention, the carbon fiber content of the carbon fiber/ABS composite material is 38 wt% compared to the ABS matrix. The thermal deflection temperature is to measure the temperature at which a deformation of 0.254 mm occurs by a three-point bending load. Therefore, the high carbon fiber content increases the resistance to thermal deformation. Since the heat deflection temperature of the unmodified composite material was increased by the already high carbon fiber content, the increase in thermal properties was small compared to the increase in mechanical properties.

The composite material (UM) in which neither the carbon fiber nor the matrix was modified showed the lowest heat deflection temperature of 100 °C among the carbon fiber/ABS composite materials. Gaps formed when the ABS resin is not properly impregnated into the carbon fibers cause weak interfacial bonding force. When a bending load is applied to the specimen under the condition that heat is applied, the specimen is easily deformed by the gap between the fiber and the matrix.

On the other hand, the composite material (FM) modified only with carbon fibers introduces MWCNTs into the unstable interface and acts as a support to support the ABS resin, slowing down the deformation. In addition, MWCNTs induced effective load transfer to the carbon fibers, which led to an increase in the heat deflection temperature. The improvement in the heat distortion temperature of the composite material (MM) with only the matrix modified is to reduce the movement of molecules by introducing MCF into the ABS matrix, where the movement of molecules becomes active when heat is applied, and evenly distribute the load, thereby increasing the load resistance of the ABS matrix. due to increased capacity.

The composite material in which the fiber and the matrix are simultaneously modified shows the highest heat deflection temperature. It is believed that this is because the introduction of MWCNTs and MCFs at the interface between carbon fiber and ABS matrix supported the load, increased resistance to bending load, and absorbed thermal energy. The thermal properties show very similar results to the mechanical properties, and these results can be explained by the fiber-matrix interface properties and the reinforcing effect of MWCNTs and MCFs.

Claims (7)

(a) mixing polyethyleneimine (PEI) with multi-walled carbon nanotubes (MWCNTs) to functionalize the surface of the multi-walled carbon nanotubes;
(b) modifying carbon fibers with functionalized multi-walled carbon nanotubes (MWCNTs);
(c) modifying ABS (acrylonitrile-butadiene-styrene) resin with pulverized carbon fiber (MCF); and
(d) preparing a carbon fiber/ABS composite material by processing the carbon fiber modified in step (b) and the ABS resin modified in step (c) through an LFT process; carbon fiber/ABS composite material including Manufacturing method of.
According to claim 1,
The ratio of pulverized carbon fibers (MCF) for modifying the ABS resin is 0.5 parts by weight to 30 parts by weight relative to 100 parts by weight of the ABS resin.
According to claim 1,
The carbon fiber ratio of the carbon fiber / ABS composite material is 20 wt% to 40 wt% of the carbon fiber / ABS composite material, characterized in that the manufacturing method of the carbon fiber / ABS composite material.
A carbon fiber/ABS composite material manufactured by the method of any one of claims 1 to 3.
As a composite material component, it includes carbon fiber modified with multi-walled carbon nanotubes (MWCNT) whose surface is functionalized with PEI, and ABS resin modified with pulverized carbon fiber (MCF),
The ratio of the pulverized carbon fiber to 100 parts by weight of the modified ABS resin is 0.5 parts by weight to 30 parts by weight,
The carbon fiber ratio of the modified carbon fiber / ABS composite material is 20 wt% to 40 wt% of the carbon fiber / ABS composite material.
According to claim 5,
The modified carbon fiber / ABS composite material has an interfacial shear strength (IFSS) of 50 to 60 MPa, a carbon fiber / ABS composite material.
According to claim 5,
The modified carbon fiber / ABS composite material has a tensile strength of 80 to 100 MPa and a tensile modulus of 8 to 10 GPa,
The modified carbon fiber / ABS composite material has a flexural strength of 130 to 140 MPa and a flexural modulus of 25 to 30 GPa,
The impact strength of the modified carbon fiber / ABS composite material is 150 ~ 180 J / m, carbon fiber / ABS composite material.

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