KR102201302B1 - Plasma Functionalized Polymer Composites Prepared by Powder Form Polypropylene and Carbon nanotube and their preparation methods - Google Patents

Abstract

The present invention relates to a polymer composite comprising a plasma-treated powder form polypropylene (PP) and a plasma-treated single-walled carbon nanotube (SWNT), and a method of manufacturing the same, and is more excellent by leading to more effective dispersion of SWNT. It is characterized by exhibiting mechanical performance.

Description

Plasma Functionalized Polymer Composites Prepared by Powder Form Polypropylene and Carbon nanotubes and their preparation methods}

The present invention relates to a polymer composite comprising a plasma-treated powdered polypropylene (PP) and a plasma-treated single-walled carbon nanotube (SWNT), and a method of manufacturing the same. The polymer composite according to the present invention has excellent mechanical strength, excellent dispersion of carbon nanotubes, and high volume conductivity.

Existing electroconductive polymers have only the electroconductive properties and have the disadvantage that they are not easy to process because they are insoluble. Therefore, in addition to the purpose of improving various properties such as mechanical, thermal, and electrical properties of the electrically conductive polymer, many studies are being conducted to impart new functions that cannot be obtained with a single material, and a composite material of an electrically conductive polymer and a polymer resin. Research is being conducted on. In a composite material of an electrically conductive polymer and a polymer resin, the state of the microstructure plays an important role in order to improve the performance or to express new functions. For example, mechanical, thermal, electrical properties, etc. obtained vary greatly depending on whether a component constituting a material forms a continuous phase or is dispersed within the material. As a form in which the second phase partially introduced into the composite material forms a continuous phase, there is a state of a percolation structure that determines the electrical properties. In such a composite material of an electrically conductive polymer and a polymer resin, the second phase It is known that the critical volume indicating the start of the formation of the percolation structure by a large dependence on the shape and size of the second phase.

In a composite material of a conductive polymer and a polymer, as the content of surfactant added to improve dispersibility increases, difficulties in the manufacturing process due to viscosity increase and problems such as a decrease in physical properties and an increase in cost occur. In consideration of the aspect, it is desirable to lower the electrical critical point of the surfactant to be added as far as possible. Factors influencing these electrical critical points include the type, size and shape of the particles, the melt viscosity of the polymer, the process conditions, the dispersibility of the particles in the polymer, and the interfacial energy between the polymer and the particles. Research has been actively conducted to lower the electrical critical point by improving the dispersibility and interfacial adhesion of conductive polymer particles in the polymer matrix (Korean Patent Laid-Open No. 10-2013-0032799).

Specifically, carbon nanotubes are a material that has received great interest in a wide range of scientific fields over the past decade due to its unique combination of physical properties and functionality such as electrical, thermal, and mechanical properties. However, a big problem in the case of using carbon nanotubes is that they aggregate and entangle within the polymer matrix due to physical interactions such as strong Van der Waals forces. Another problem is low affinity with most polymer matrices. It's Mars. In order to disperse and divide such agglomeration, various processing techniques such as high shear kneading, electrospinning, processes with the aid of surfactants, simultaneous polymerization, latex processing and melt processing have been attempted.

Appropriate functionalization of CNTs is required in order to overcome such agglomeration to achieve uniform dispersion and optimum adhesion with the matrix. There are two main categories of CNT functionalization methods: wet chemistry and dry chemistry.

Wet chemistry methods usually consist of an oxidation step and the next part consists of a final step that is converted to another function. Despite the functionalization of CNTs, concerns have been raised about the difficulty of removing the solvent, prolonging the reaction time, high cost and high environmental impact.

Dry chemical reactions include several techniques such as crown discharge, photooxidation, radiation and plasma treatment. Since a few minutes are sufficient to achieve a good level of functionalization, the rapidity of this process compensates for the disadvantage of being difficult to control the homogeneity and degree of functionalization.

From an industrial point of view, plasma surface modification technology is preferable because of its relatively simple, direct, and environmentally friendly properties. It is often used to perform surface modifications of various substrates or to place thin coatings on the surface of such substrates. In recent years, this technique has been used extensively to improve the mechanical properties of polymeric nanocomposites by modifying various polymer matrices or performing surface modification of nanoparticles.

Under the above-described background, the present inventors found that unlike most other studies in which only CNTs were functionalized by plasma treatment, in this study, polypropylene (PP), a polymer matrix, was also functionalized in order to increase compatibility with CNTs. In order to maximize the level of functionalization of non-polar polymers such as PP, it was prepared in the form of fine powder using a cryo-milled method. Oxygen plasma-treated single-walled carbon nanotubes (f-SWNTs) were synthesized with oxygen plasma-treated powder form PP (f-PP). In contrast, as a comparative example, single-walled carbon nanotubes without plasma treatment (u-SWNT) were prepared from polypropylene (u-PP) in the form of granules without plasma treatment. Fourier transform infrared spectroscopy (FTIR) was performed to demonstrate SWNT and PP functionalization, and the prepared nanocomposites were analyzed from the morphological, rheological, mechanical and electrical viewpoints.

One object of the present invention is to provide a polymer composite comprising a plasma-treated powdered polypropylene (PP) and a plasma-treated single-walled carbon nanotube (SWNT).

Another object of the present invention is a first step of preparing polypropylene and single-walled carbon nanotubes in powder form; A second step of plasma treating the powdered polypropylene and the single-walled carbon nanotubes; And a third step of compression-molding the plasma-treated powdered polypropylene and single-walled carbon nanotubes to prepare a composite.

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

On the other hand, each description and embodiment disclosed herein can be applied to each other description and embodiment. That is, all combinations of various elements disclosed herein fall within the scope of the present invention. In addition, it cannot be said that the scope of the present invention is limited by the specific description described below.

In addition, those of ordinary skill in the art can recognize or ascertain using only routine experimentation a number of equivalents to the specific aspects of the invention described in this application. Also, such equivalents are intended to be included in the present invention.

As an aspect of the present invention for solving the above problems, the present invention provides a polymer composite comprising a plasma-treated powdered polypropylene (PP) and a plasma-treated single-walled carbon nanotube (SWNT).

"Carbon Nanotube (CNT)" in the present invention refers to a structure in the form of a nanocylinder in which a hexagonal pattern is formed by three carbons composed of only sp ² bonds around one carbon, and the number of layers of the surrounding shell According to the classification of single-walled carbon nanotube (SWNT), multi-walled carbon nanotube (Multi-Walled Nanotube: MWNT), electric discharge method, laser vapor deposition method, plasma chemical vapor deposition method, thermal chemical vapor deposition method, pyrolysis The CNT may be synthesized using a method such as a method or a flame synthesis method, but is not limited thereto.

The present inventors believe that the polymer composites comprising plasma-treated powdered polypropylene (PP) and plasma-treated single-walled carbon nanotubes (SWNT) are conventional polypropylene without plasma treatment and single-walled carbon nanotubes without plasma treatment. It was confirmed that the dispersion was better than that of the polymer composite including a, thus exhibiting excellent mechanical performance, and the electrical percolation threshold was significantly reduced.

The present invention may include 0.001 to 2 wt% of single-walled carbon nanotubes based on the total polymer composite, specifically 0.01 to 1.5 wt%, 0.015 to 1.3 wt%, or 0.02 to 1 wt%, and more specifically It may be 0.1 to 0.7 wt%, but is not limited thereto. In particular, it was confirmed that when the content of single-walled carbon nanotubes was low, the polymer composite of the present invention exhibited excellent mechanical performance due to better dispersion, and the effect of remarkably reducing the electrical percolation threshold was more excellent.

The polypropylene (PP) of the present invention may be in the form of a powder, specifically, it may be in the form of a fine powder prepared by cryo-milled, but is not limited thereto. At this time, by using polypropylene in the form of a powder, the level of functionalization of a non-polar polymer such as polypropylene can be maximized.

In order to improve the mechanical performance and electrical properties of the polymer composite of the present invention, both polypropylene (PP) and single-walled carbon nanotubes (SWNT) in powder form may be plasma treated, and specifically, oxygen plasma treatment may be performed. However, it is not limited thereto.

Specifically, by functionalizing with oxygen plasma treatment, it is possible to overcome the aggregation of carbon nanotubes and disperse them uniformly, thereby increasing the mechanical tensile strength of the composite and improving the electrical properties to reduce the percolation threshold. This suggests that this is due to the presence of a defect site in the transition region between the fullerenic tip and the graphemic wall to form an oxygenated group.

In the present invention, the electrical conductivity of the composite material largely depends on the filler load. In order to obtain a conductive path in the matrix, an electrical percolation network of interconnected conductive particles with very small interparticle distances results in low contact resistance and is required for efficient electron transfer through the network. At low filler concentrations the fillers tend to be individually dispersed or present as small clusters in the matrix, resulting in very low electrical conductivity very close to the electrically insulating polymer matrix.

In the present invention, "percolation" is a form in which the second phase partially introduced into the composite material forms a continuous phase, and is a structure that determines electrical properties, and the second phase in the shape of particles continuously contacts to generate electricity. It means a structure that allows it to flow.

In the present invention, the "percolation threshold" means the minimum filling amount of conductive filler particles required to form a continuous conductive network. As the amount of surfactant added to improve dispersibility increases, problems such as difficulty in the manufacturing process due to increase in viscosity, decrease in physical properties, and increase in cost occur. Factors that affect the electrical critical point include the type, size and shape of the particles, the melt viscosity of the polymer, the process conditions, the dispersibility of the particles in the polymer, and the interfacial energy between the polymer and the particles. It is an object of the present invention to lower the electrical critical point by improving the dispersibility and interfacial adhesion of the conductive polymer particles in the matrix.

The percolation threshold of the polymer composite of the present invention may be 0.01 to 1.5% by weight based on the total polymer composite, specifically 0.02 to 1% by weight, more specifically 0.03 to 0.95% by weight, It is not limited thereto. In the present invention, both polypropylene (PP) and single-walled carbon nanotubes (SWNT) in powder form are plasma treated to increase the interaction between polypropylene (PP) and single-walled carbon nanotubes (SWNT) to improve dispersibility. By doing so, it was confirmed that the percolation threshold value can be significantly reduced.

The electrical conductivity of the polymer composite of the present invention may be 10 ^-9 to 10 ^-1 S/m, and specifically 10 ^-8 to 10 ^-2 S/m, but is not limited thereto.

The nanometer dimension of the interfacial region surrounding the SWNT makes it easy to transfer the applied load from the matrix to the SWNT. Theoretically, the three synergistic aspects of the interaction in the carbon-nanotube-based composite are the polymer-nanotube interaction, the nanotube-nanotube interaction, and the intra-polymer interaction in the polymer-carbon nanotube interaction. to be. Another important factor is that as the nanotube content increases, large aggregates are formed that serve as concentrations of mechanical defects. In other words, carbon nanotubes have a disadvantage in that stress concentration is induced by agglomeration in the resin due to the strong Van der Waals force of itself.

Therefore, in the present invention, due to the vast modulus and high aspect ratio, it was predicted that the incorporation of SWNT into the polymer would be effective in reinforcing the polymer, that is, reinforcing mechanical properties.To increase the mechanical properties, the carbon nanotubes and carbon nanofibers It was confirmed that efficient dispersion is important, and when the content of carbon nanotubes and carbon nanofibers is low, agglomeration is reduced and mechanical properties can be improved. In addition, it was confirmed that the plasma treatment improved the dispersion of SWNTs by reducing the aggregate size and distribution of SWNTs, and in particular, when the SWNT content was low, the SWNT penetration network was formed.

The area of the aggregate of the single-walled carbon nanotubes in the polymer composite of the present invention may be 0.001 to 1.3%, specifically 0.01 to 1% or 0.05 to 0.95%, based on the total area of the sample. This significantly reduced the agglomerate area compared to the conventional polymer composite including non-plasma-treated polypropylene and non-plasma-treated single-walled carbon nanotubes having an aggregate area of 1% or more with respect to the total area of the sample.

The tensile strength of the polymer composite may be 30 to 80 MPa, specifically 35 to 70 MPa, and more specifically 40 to 60 MPa, but is not limited thereto, and in particular, single-walled carbon nanoparticles When the content of the tube was low, it was confirmed that it was improved compared to the tensile strength of a polymer composite including polypropylene without plasma treatment and single-walled carbon nanotubes without plasma treatment.

As another aspect of the present invention for solving the above problems, the present invention is a first step of preparing a powdered polypropylene and single-walled carbon nanotubes; A second step of plasma treating the powdered polypropylene and the single-walled carbon nanotubes; And a third step of compression-molding the plasma-treated powdered polypropylene and single-walled carbon nanotubes to prepare a composite.

In the method for producing a polymer composite of the present invention, the description of the content of the single-walled carbon nanotube (SWNT) and the oxygen plasma treatment in the polymer composite is as described above.

In the method for producing a polymer composite of the present invention, the step of preparing the polypropylene in the form of a powder may specifically be a step of preparing the polypropylene in the form of a fine powder by cryo-milled, but is not limited thereto. At this time, by using polypropylene in the form of a powder, the level of functionalization of a non-polar polymer such as polypropylene can be maximized.

In the polymer composite manufacturing method of the present invention, the diameter of the single-walled carbon nanotube may be 0.1 to 5 nm, specifically, may be 1 to 3 nm, and the length of the single-walled carbon nanotube may be 1 to 15 μm. And, specifically, it may be 2 to 10 ㎛, but is not limited thereto.

The polymer composite comprising the plasma-treated powder form of polypropylene (PP) and the plasma-treated single-walled carbon nanotubes (SWNT) of the present invention has a well formed percolation network due to excellent dispersion of the single-walled carbon nanotubes. It has excellent strength, has a low percolation threshold, and has high volumetric conductivity despite a low carbon nanotube content.

1 shows the results of SEM images of PP particles freeze-crushed at different magnifications.
Figure 2 shows a schematic diagram of the composite preparation.
3 shows FTIR spectra of u-PP (a solid line), f-PP (a dotted line), u-SWNTs (b solid line), and f-SWNTs (b dotted line).
4 is a schematic diagram showing the mechanism of the PP powder and SWNT modified by oxygen plasma.
5 is a result of the SEM image of the nanocomposite having various amounts of SWNTs, and the red dot circles indicate aggregates of SWNTs ((a) 0.29 wt.% u -SWNTs/ u -PP (b) 0.29 wt. % f -SWNTs/ f -PP (c) 1.28 wt.% u -SWNTs/ u -PP (d) 1.16 wt.% f -SWNTs/ f -PP (e) 6.56 wt.% u -SWNTs/ u -PP (f) 5.52 wt.% f -SWNTs/ f -PP).
6 shows a cation microscope image and area ratio of the size distribution of SWNT aggregates of a non-plasma-treated composite (left) and a plasma-treated composite (right) according to the amount of SWNT.
7 is a graph showing the total area fraction (A _A ) of the SWNT composite material (triangle) that is not plasma-treated and the SWNT composite material (circular) treated with the plasma (A _A ).
Figure 8 shows the storage modulus (G'), loss modulus (G") and complex viscosity (η) of the composites u-SWNT/u-PP (left) and f-SWNT/f-PP (right).
Figure 9 shows the tensile strength of the composite u-SWNT / u-PP (red dot) and f-SWNT / f-PP (black dot), the other characters of the same color at 95 confidence level (α = 0.05) It means that there are statistically significant differences.
10 shows the electrical conductivity and percolation threshold (Ф _c ) of the u-SWNT/u-PP (red dot) and f-SWNT/f-PP (blue dot) complexes.

Hereinafter, the present invention will be described in more detail by the following examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

Example

Preparation Example 1: Preparation of PP in powder form

The present inventors used commercial grade isotactic PP, Samsung Total HF429, MFI (melt flow index) was 8g/10min (240°C, 2.16 kg) and the density was 0.91 g/cm ³ . In addition, PP was freeze-milled to prepare fine particles. The prepared PP in powder form is shown in FIG. 1.

Preparation Example 2: Preparation of single-walled carbon nanotubes (SWNT)

A non-functionalized commercially available single-walled carbon nanotube (SWNT), OCSiAl TUBALL ^™, was used. TUBALL ^TM had a carbon purity of 85% or more, an external average nanotube diameter of 1.8 ± 0.4 nm, and a nanotube length of 5 μm or more.

Preparation Example 3: Plasma treatment of PP and SWNT in powder form

The SWNTs prepared in Preparation Examples 1 and 2 and PP in powder form were treated with oxygen plasma to modify the respective surfaces. At this time, using a radio frequency plasma generator (diener FEMTO Version E of 13.56 MHz), SWNT and PP in powder form were modified under controlled conditions with an exposure time of 10 minutes and plasma power of 50 W.

Plasma treatment functionalization of CNT and PP powders was characterized using a Cary 600 series Fourier Transform Infrared (FTIR) spectrometer (Agilent Technology, USA) with a spectral range of 4000-650 cm ^-1 over 50 scans.

Preparation Example 4: Preparation of composite

A nanocomposite having SWNTs of various weights was prepared using Brabender microcompounder TSC 42/6, which is shown in Table 1. The weight of SWNT in the composite was analyzed using a thermogravimetric analyzer (TGA) (Model TGA Q500, TA Instrument, DE, USA).

Composition of nanocomposite Sample No. SWNT contents (wt.%) u -SWNTs/ u -PP f -SWNTs/ f -PP One 0.29 ± 0.075 0.29 ± 0.095 2 0.43 ± 0.033 0.48 ± 0.046 3 0.62 ± 0.16 0.59 ± 0.058 4 1.28 ± 0.27 1.16 ± 0.106 5 2.94 ± 0.28 2.30 ± 0.120 6 3.66 ± 0.48 2.60 ± 0.253 7 4.29 ± 0.10 3.86 ± 0.146 8 4.80 ± 0.18 4.26 ± 0.618 9 6.56 ± 0.04 5.52 ± 0.332

The temperature was fixed at 250° C. and the rotation speed was set at 50 rpm with a residence time of 20 minutes. Thereafter, in order to measure the electrical conductivity, the composite was compression molded using a QMESYS hot press (Model QM900A, Quality & Measurement System, Korea) at a temperature of 250° C. and a pressure of 2 MPa. Injection molding was performed using an Xplore Micro 10 cc Injection Molding Machine (Xplore Instruments, Geleen, The Netherlands) with test samples of appropriate shape to measure rheological and mechanical properties at 270° C. and 0.4 MPa. A schematic diagram of the composite and sample preparation is shown in FIG. 2.

Experimental example

Experimental Example 1: Observation of the shape of the complex

The state of macroscopic SWNT dispersion in the composite was analyzed by a light transmission microscope (LM) to obtain a relatively large volume of the irradiated sample. The use of LM makes it possible to detect the undispersed fraction of primary SWNT aggregates remaining in the polymer after melt treatment as global information for the SWNT dispersion. Light transmission microscopy (model: KYENCE VK-X200K, KEYENCE, IL, USA) analysis was performed using an optical laser using a 10X objective magnification and a 408 nm purple laser. The area fraction of the non-dispersed primary SWNT aggregate was quantified according to Equation (1) using particle analysis using integrated software developed by KYENCE.

(1)

(One)

Here, A _i is the area of the primary SWNT aggregate at the i-th diameter, and A ₀ is the entire micrograph area. According to ISO 18553, aggregates less than 5 μm in diameter were neglected. To increase the analyzed size of the micrograph area, 3 different areas of each sample were captured. Further, the complex was directly observed using a field emission scanning electron microscope (Model: HITACHI-SU8020, Hitachi, Ltd., Japan). The palletized composite granules were frozen in liquid nitrogen and then freeze-crushed. A thin layer of carbon was sputter deposited over the sample. It was measured under high vacuum with an acceleration voltage of 2 kV.

FTIR spectra of u-PP (a solid line), f-PP (a dotted line), u-SWNTs (b solid line) and f-SWNTs (b dotted line) are shown in FIG. 3. Through the results of the FTIR analysis, it was confirmed that the plasma functionalization of CNT and PP powder was clearly indicated. In the case of the PP powder, a new peak appeared in the range of 1650 cm ^-1 to 1750 cm ^-1 corresponding to the stretching and vibration mode of the carbonyl group (-C = O). This indicates the oxidation of the surface of the PP powder as a result of plasma treatment with the formation of functional groups containing oxygen. In the case of SWNT, the difference between u-SWNT and f-SWNT can be clearly distinguished, specifically, a difference appears in the range of 1800 to 1000 cm ^-1 . It can be seen that this is due to the carboxyl functional groups of two peak values of about 1600 cm ^-1 (C = O) and 1100 cm ^-1 (CO) corresponding to the elongation mode of the carboxylic acid group (-COOH). This is mainly due to the presence of defect sites in the transition zone between the fullerenic tip and the graphemic wall, forming oxygenated groups. The mechanism of plasma treatment for PP powder and SWNT is shown in FIG. 4.

The SEM image of the nanocomposite having various contents of SWNT is shown in FIG. 5. Regarding the high SWNT-loaded composites, no aggregation of SWNTs was found irrespective of plasma treatment (Figs. 5 (e) and (f)). SWNTs aggregates were mainly found in the nanocomposite without plasma treatment, especially at low SWNT content (Figs. 5 (a) and (c)). The red dot circles represent the set of SWNT bundles that were not distributed during processing. These features suggest that the dispersion and adhesion/interaction with the matrix are poor worldwide. However, unlike u-SWNTs/u-PP without plasma treatment, f-SWNTs/f-PP treated with plasma did not show aggregation of SWNTs even at a low SWNTs content and was well separated (Fig. 5(b) and (d)). This suggests that plasma treatment can increase the PP/SWNTs interaction to improve SWNT dispersion. Although the SEM image shows the effect of plasma treatment on the SWNT dispersion, the fraction of dispersed SWNTs analyzed by the SEM image is a very small sample volume, which is not sufficient to draw conclusions because the remaining large primary aggregates cannot be explained. For this reason, particle analysis was performed to investigate a relatively large amount of samples to obtain full information on the SWNT dispersion.

Images of the macroscopic dispersion, size distribution and area ratio of undispersed SWNT aggregates evaluated by optical microscopy with various amounts of SWNT are shown in FIG. 6. For a series of u-SWNT/u-PP complexes, the total area of undispersed SWNT aggregates was detected as 1% or more, whereas all f-SWNT/f-PP complexes showed less than 1% (FIG. 7 ). Despite the low content of SWNT (0.29% by weight), total A _A (Total area fraction) of the u-SWNTs / u-PP is found to be 1.397%. On the other hand, when plasma was used, the total A _A decreased from 1.397% to 0.392%. In addition, the size distribution of the remaining primary aggregates for u-SWNTs/u-PP and f-SWNTs/f-PP showed information on the dispersion state of SWNTs according to plasma treatment. The aggregate size distribution of the u-SWNT/u-PP composite with 0.29% by weight of SWNT contains primary aggregates having a size between 10 and 280 μm, whereas the maximum value of the distribution curve is 280 μm maximum primary aggregates. The size is within the range of 20 μm. Aggregate size distribution and a significant decrease in the maximum primary aggregate size are observed in f-SWNT/f-PP with 0.29 wt% SWNT, where the size of the primary aggregate is 10 to 140 μm and the maximum primary aggregate size of 140 μm Have. Here, the size of the primary aggregate is 10 to 140 μm and has a maximum primary aggregate size of 140 μm. Compared to the u-SWNTs/u-PP complex, all these results were found in the series of f-SWNTs/f-PP complexes, including a reduction in total A _A , maximum SWNTs aggregate size and SWNTs aggregate size distribution. These results are in good agreement with the SEM image analysis, suggesting that plasma treatment is effective in improving the SWNT dispersion.

Experimental Example 2: Measurement of rheological properties

One of the main methods for evaluating the dispersion state and network structure of nanomaterials in a polymer matrix is rheological measurement. In general, the high-frequency reaction of the nanocomposite is influenced by the relaxation process of the polymer chain, while the dynamics of the nanomaterial are involved in the low frequency.

Vibration shear and stress relaxation in the linear viscoelastic (LVE) region were measured on a Physica MCR 302 oscillation rheometer (Anton Paar GmbH, Austria) having a parallel plate structure (diameter 25 mm and spacing 1 mm) at 230°C. The frequency sweep was performed after about 3 minutes temperature equilibration with the frequency decreasing from 100 to 0.1 rad/s and the strain of 1 %.

Since the SWNT network exists, the terminal behavior due to complete relaxation of the PP chain is weak, and the dependence of the storage modulus (G') and loss modulus (G") on each frequency (ω) is limited at low frequencies, but in the present invention, the SWNT As the content increases (more than 1 wt%), G'and G” at low frequencies gradually have lower frequency dependence and at low SWNT content (0.1 to 0.7 wt%) compared to f-SWNTs/f-PP, u-SWNTs/ It was confirmed that u-PP showed relatively strong dependence of G'and G”.

As described in the particle analysis, it was found that this was mainly due to the difference in the aggregate size and distribution of SWNTs. In general, the dependence of the storage modulus (G') and the loss modulus (G") on each frequency (ω) is limited at low frequencies. However, as the content of SWNT increases (more than 1 wt%), the frequency dependence of G'and G” gradually decreases at low frequencies and is converted from liquid to solid like viscoelastic behavior. This phenomenon is a characteristic of the non-terminal frequency that can be explained by the formation of interconnected nanotube networks in the polymer. Regarding the results of the particle analysis, this result suggests that the plasma treatment improves the dispersion of SWNTs by reducing the aggregate size and distribution of SWNTs, and forms a permeation network of SWNTs, especially when the content of SWNTs is low.

Experimental Example 3: Measurement of mechanical properties

Mechanical properties were measured using an injection-molded dog bone-shaped sample using an Instron 3367 universal testing machine (INSTRON, USA) according to ASTM D638-14. At this time, it was performed with a 1 kN cell force and a sampling rate of 10 mm/min. At least three samples of each composite were tested and tensile stress was measured from the raw data.

The tensile strengths of the u-SWNT/u-PP (red dots) and f-SWNT/f-PP (black dots) composites with incremental loading levels of SWNT are shown in FIG. 9. In FIG. 9, when the SWNT content exceeded 1% by weight, the tensile strength of u-SWNT/u-PP and f-SWNTs/f-PP increased linearly to 0.98 and 0.93 of the linear correlation coefficient as the SWNT content increased. (R ² ). When the content of SWNT was low (less than 1 wt.%), u-SWNTs/u-PP did not show reinforcement of tensile strength with increasing SWNT and showed a lower value than f-SWNTs/f-PP.

As explained by the results of particle analysis and rheological properties, this difference is mainly due to the aggregation of SWNTs. It was confirmed that even when the concentration of SWNT is low due to the plasma treatment, a better dispersed state improves the tensile strength. That is, compared to the high load of SWNT, which is sufficient for SWNT bundles to form a percolation network to compensate for the negative effect of SWNT aggregation, the effect of plasma treatment on tensile strength suggests that it is very important, especially when the SWNT content is low. .

Experimental Example 4: Measurement of electrical properties

In-plane electrical conductivity measurements were performed on compression molded square plates according to ASTM D4496-13. At least 10 measurements were made for the sample to obtain a geometric mean value with the standard deviation of the associated resistance. Using an AiT resistance measurement system (model: CMT-SR1000N, Advanced Instrument Technology, GA, USA) equipped with a 4-point probe with a sheet resistance measurement range of between 1 mOhm/square and 2 mOhm/square and a pin spacing of 20 to 50 mil. I did. Statistical percolation theory can predict the relationship between the electrical resistance of a composite and the filler concentration using Eq (2).

(2)

(2)

Where σ is the complex volume resistivity; σ ₀ is the volume resistivity of the filler, and φ and φ _c, t represent the ratio, percolation threshold, and critical index of the filler, respectively. The critical exponent t is a calculated value of t ≒ 1.33 in 2D and t ≒ 2 in 3D and is expected to depend on the system dimension. The percolation threshold and critical index were calculated by fitting the experimental results to the linear regression equation of log σ and log (Ф-Ф _c ).

The range of electrical percolation thresholds varies from 0.07 to 2.62% by weight depending on many factors such as treatment method and type of CNT (single or multi-walled). In this electrical percolation threshold, the electrical conductivity of the PP/CNT composite was found to be 10 ^-8 to 10 ^-2 S/m.

Fig. 10 shows an electrical conductivity curve versus weight% of SWNT for the u-SWNT/u-PP and f-SWNT/f-PP composites. The results of the statistical percolation theory were 1.4 wt% for u-SWNT/u-PP with an electrical percolation threshold t = 2.05 and a critical index of 1.96, and 0.91 wt% for f-SWNT/f-PP. appear. That is, in the case of the plasma treatment, it was confirmed that the electrical percolation threshold value was significantly reduced due to the improvement of the SWNT dispersion state at a low load level.

From the above description, those skilled in the art to which the present invention pertains will be able to understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features thereof. In this regard, the embodiments described above are illustrative in all respects and should be understood as non-limiting. The scope of the present invention should be construed that all changes or modifications derived from the meaning and scope of the claims to be described later rather than the above detailed description, and equivalent concepts thereof, are included in the scope of the present invention.

Claims (12)

delete delete delete delete delete delete delete As a method for producing a conductive polymer composite,
A first step of preparing powdered polypropylene and single-walled carbon nanotubes;
A second step of treating the powdered polypropylene and the single-walled carbon nanotubes with oxygen plasma; And
A third step of compression-molding the plasma-treated powdered polypropylene and single-walled carbon nanotubes to produce a composite; including,
The percolation threshold of the conductive polymer composite is 0.01 wt% to 1.0 wt%,
The content of the single-walled carbon nanotubes based on the entire conductive polymer composite is 0.1 to 0.7 wt%,
A method of manufacturing a conductive polymer composite, in which a group to which oxygen is added is formed at the defect site of the single-walled carbon nanotube.
delete delete The method of claim 8, wherein the first step is a step of freeze-crushing polypropylene to prepare a powder form.
The method of claim 8, wherein the diameter of the single-walled carbon nanotube in the first step is 0.1 to 5 nm, and the length is 1 to 15 μm.

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