KR20190015687A - Composition for Syntactic Foams and Manufacturing Method thereof - Google Patents

Abstract

The present invention provides a composition for syntactic foams comprising a polyolefin, hollow glass microspheres (HGMs), and carbon nanotubes. The present invention also provides a manufacturing method thereof. The composition for syntactic foams according to the present invention has low density and excellent mechanical strength by using the HGMs. In addition, percolation networks, composed of the carbon nanotubes between HGMs dispersed in a polymeric matrix, are well formed, and thus the composition for syntactic foams has high volume conductivity despite low carbon nanotube content.

Description

Syntactic Foams and Manufacturing Method < RTI ID = 0.0 >

More particularly, the present invention relates to a syntactic foam composition comprising hollow glass microparticles and carbon nanotubes, and a process for producing the same. The syntactic foam composition according to the present invention has a low density, a high mechanical strength, a good dispersion of carbon nanotubes (CNT), and a high volume conductivity.

Syntactic foam is a lightweight polymer composite material having a hollow microparticulate filler, and various studies have been conducted on the combination of a hollow microparticulate filler and a thermoplastic resin. Examples of hollow microparticle fillers include hollow glass microspheres (HGMs), carbon and polymer microspheres. In recent years, Kumar et al. Have evaluated various properties and processability of a cenosphere having high density polyethylene (HDPE). Kumar et al., In addition to the two advantages of using SenoSpheres manufactured from industrial waste, fly ash, and reducing the cost of the composition, the increase in the content of senospheres leads to a decrease in density and strength, .

Among other types of hollow microparticle fillers, hollow glass microparticles have unique properties such as low density, low dielectric constant, good insulation and sound insulation. Compared to conventional foams containing open or closed cell gas pores, syntactic foams containing hollow glass microparticles exhibit excellent mechanical properties. Due to its low density and excellent mechanical properties, syntactic foams have been widely used in a variety of engineering applications, such as, for example, in marine equipment, core materials in sandwiches, structural elements in aircraft, and the like.

However, the large volume of hollow glass microparticles causes low mechanical strength of the syntactic foam. Accordingly, much research has been focused on developing methods to strengthen the syntactic foam without compromising the particle packing limit in the material structure.

In particular, attempts have been made to enhance syntactic foams by introducing various fillers such as nanoclay, glass or carbon nanofibers, carbon nanotubes, and the like. About 60 vol.% And 2 to 5 vol.% Of hollow glass spheres of varying wall thickness, according to Maharsia et al. [Maharsia R, Jerro H. Mater Sci. Eng. 2007; 454: 416-22] A syntactic foam containing nano-clay exhibits a tensile strength improvement of about 23% as compared with a conventional syntactic foam. However, despite the improvement in tensile strength, it is not effective in improving the tensile fracture strength due to the low aspect ratio of the nanoclay particles, resulting in improper crack bridging.

Another example of a superior filler is carbon nanotubes, a unique combination of physical and functional properties such as electrical, thermal, and mechanical properties that have been of great interest in a wide range of sciences over the past decade. However, a major problem when using carbon nanotubes is that they are aggregated and intertwined in the polymer matrix due to strong Van der Waals forces. Various processing techniques such as high shear kneading, electrospinning, surfactant assisted processes, simultaneous polymerization, latex processing, and melt processing have been attempted to disperse and disperse such cohesion. However, carbon nanotubes continue to be difficult to disperse in a hydrophobic matrix such as polyolefin.

Accordingly, the present inventors have found that a syntactic foam composition comprising polyolefin, hollow glass microparticles and carbon nanotubes can be obtained by controlling the content of carbon nanotubes and hollow glass microparticles so as to have a low density and excellent mechanical strength and conductivity The present inventors have confirmed that a syntactic foam composition can be produced, and the present invention has been completed.

Maharsia R, Jerro H. Enhancing tensile strength and toughness in syntactic foams through nanoclay reinforcement. Mater Sci Enge 2007; 454: 416-22

An object of the present invention is to provide a syntactic foam composition having a low density and excellent mechanical strength, and a carbon nanotube dispersed in an excellent manner, and having high volume conductivity despite low carbon nanotube content.

Another object of the present invention is to provide a method for producing the syntactic foam composition.

The first aspect of the present invention relates to a method for producing a polyolefin composition, which comprises a polyolefin, hollow glass microparticles and carbon nanotubes, wherein the hollow glass microparticles are contained in an amount of 1 to 7 wt% based on the total weight of the composition, There is provided a syntactic foam composition having an electrically percolation network structure in which nanotubes are well dispersed and formed of carbon nanotubes between hollow glass microparticles.

In one embodiment, the polyolefin may be polypropylene.

In one embodiment, the hollow glass microparticles may be non-surface treated.

In one embodiment, the hollow glass microparticles are substantially unbranched.

In one embodiment, the content of carbon nanotubes may be 0.5 to 5 wt% based on the total weight of the composition.

In one embodiment, the syntactic foam composition has a volume conductivity of at least 1.0 S / m measured according to the ASTM D4496-13 method.

In one embodiment, the syntactic foam composition has a tensile strength of at least 35 MPa as measured according to the ASTM D638 method.

In one embodiment, the syntactic foam composition has a density of 900 Kg / m ³ or less, preferably 750 to 850 Kg / m ³ , and the matrix void is 10 vol% or more; The microballoon porosity is at least 1%.

Further, a second aspect of the present invention provides a method for producing a syntactic foam composition, which comprises mixing a polyolefin, hollow glass microparticles and carbon nanotubes, followed by melt kneading, and granulating the kneaded product.

The syntactic foam composition according to the present invention has a low density and excellent mechanical strength by using carbon nanotubes and hollow glass microparticles as fillers in the polyolefin matrix. In addition, a percolation network formed of carbon nanotubes between hollow glass microparticles dispersed in a polymer matrix is well formed, and has high volume conductivity despite low carbon nanotube content.

1 is a graph showing the results of statistical analysis on the relative density (g / cm ³ ), matrix void (%) and HGM porosity of a syntactic foam containing SWNTs.
2 (a) and 2 (b) are SEM photographs and EDS analysis results of chemical compositions of SWNT and hollow glass microparticles.
FIG. 3 is a SEM photograph showing the interface between the hollow glass microparticles and the SWNT (top) and a schematic diagram (below) showing their interaction. FIG.
FIG. 4 is a graph showing the rheological measurement results of the syntactic foam of the PP / HGMs / SWNT composition according to the hollow glass microparticle content. (a) the storage elastic modulus G '(b) the loss modulus G''(c) the complex viscosity (at 200 ° C, the frequency sweep according to the HGMs content) of the syntactic foam comprising SWNT; (d) Semi-glophogram graph of syntactic foam.
5 is a SEM photograph showing the morphological state of the syntactic foam including the SWNT. (a) GB0, (b) GB0.1, (c) GB3, (d) GB20.
6 is a graph showing the volume conductivity according to HGMs content for a syntactic foam containing SWNTs.
7 is a schematic diagram showing the effect of the hollow glass microparticle content on the formation of the SWNT network.

Hereinafter, the present invention will be described in detail.

The syntactic foam composition of the present invention is characterized by having an electrical percolation network structure formed of carbon nanotubes between hollow glass microparticles dispersed in a polyolefin matrix and having high volume conductivity despite low carbon nanotube content do.

The " percolation network " means a network structure in which unit particles or elements are arranged in any direction and interconnected. In the present invention, the term " carbon nanotube network structure " In terms of electrical conductivity, carbon nanotubes are very large in length / diameter ratio. Therefore, when three-dimensionally uniform dispersion occurs in a composite, a conductive path formed by carbon nanotubes is formed, A percolation threshold is generated.

The present inventors have found that, in a syntactic foam composition comprising a polyolefin, hollow glass microparticles and carbon nanotubes, the content of hollow glass microparticles in which carbon nanotubes are effective for forming an effective percolation network, Based on 1 to 7 wt%. The present invention is based on this.

The present invention uses a polyolefin as a base resin for forming a matrix in order to impart heat radiation properties to the composition.

In the present invention, the polyolefin may be a polypropylene, a low density polyethylene, a high density polyethylene, a linear low density polyethylene, a copolymer of ethylene and a C3-C20 alpha olefin, or the like. Preferably, the polyolefin may be a polypropylene. The polypropylene may be a propylene homopolymer or a copolymer of propylene with up to 20 wt% of an alpha olefin, particularly preferably with up to 20 wt% Ethylene copolymer.

The hollow glass microparticles useful in the compositions and methods according to the invention applied to the present invention can be prepared by techniques known in the art. Typically, a technique for making hollow glass microparticles comprises heating a milled frit containing a blowing agent. The frit can be made by heating the mineral components of the glass at elevated temperatures until molten glass is formed.

The hollow glass microparticles may have any composition, but typically the particles comprise 50 to 90 wt% of SiO ₂ , 2 to 20 wt% of alkali metal oxide based on the total weight. As other components, B ₂ O ₃ , sulfur, divalent metal oxides (for example, CaO, MgO, BaO, SrO, ZnO or PbO), trivalent metal oxides (for example, Al ₂ O ₃ , Fe ₂ O ₃ or Sb ₂ O ₃ ), SiO ₂ and other tetravalent metal oxides (for example, TiO ₂ , MnO ₂ or ZrO ₂ ), oxides of pentavalent atoms (for example P ₂ O ₅ or V ₂ O ₅ ), And the like.

In one embodiment, the average true density of the hollow glass microparticles is from 0.30 g / cc to 0.65 g / cc, from 0.30 g / cc to 0.6 g / cc, from 0.35 g / cc to 0.60 g / cc, or 0.35 g / cc To 0.55 g / cc. Such hollow glass microparticles of arbitrary density may be useful for lowering the density of the composition according to the present invention compared to polyolefin compositions which do not contain hollow glass microparticles.

Hollow glass microparticles of various sizes may be useful. In one embodiment, the hollow glass microparticles may have an average diameter in the range of 14 to 45 [mu] m. In some embodiments, it may have an average diameter in the range of 15 to 40 mu m, 20 to 45 mu m, or 20 to 40 mu m.

In one embodiment, the hollow glass microparticles may be non-surface treated. The hollow glass microparticles may not be surface-treated so that the silanol group (Si-O-H) group is exposed to the surface. This is better understood with reference to FIG.

The syntactic foam composition of the present invention comprises hollow glass microparticles in an amount of 1 to 7 wt% based on the total weight of the composition. As shown in FIG. 7, when the content of the hollow glass microparticles is less than 1 wt%, the hollow glass microparticles act as a nucleating agent for inducing aggregation of the carbon nanotubes, thereby preventing the formation of the percolation network of the carbon nanotubes If it exceeds 7 wt%, aggregation of the hollow glass microparticles occurs, disturbing the network formation of the carbon nanotubes, and the conductivity of the produced syntactic foam composition Can be reduced.

FIG. 6 shows the volume conductivity tendency of the syntactic foam composition containing carbon nanotubes according to the content of the hollow glass microparticles. The volume conductivity of the composition tends to decrease as the content of the hollow glass microparticles increases up to 1 wt%, while the volume conductivity in the range of 1 wt% to 7 wt% Of the total population. That is, the dispersion inhibition of carbon nanotubes, which may be caused by containing hollow glass microparticles, did not appear. On the other hand, if the content of the hollow glass microparticles exceeds 10 wt%, the volume conductivity decreases again due to the aggregation of the hollow glass microparticles.

In one embodiment, the hollow glass microparticles are substantially unbranched. In the present invention, the term " not pulverized " means that the hollow glass microparticles to be fed into the composition are pulverized after the melt-kneading necessary for the production of the composition, further after the extrusion or injection process, Meaning that no particle particles are observed. In the present invention, the hollow glass microparticles are not pulverized by maintaining an appropriate motor speed (50 rpm) and high isotactic crush strength during melt-kneading. As shown in FIG. 1, unlike the reported matrix void values (5-10 vol%), the matrix void increased to 20 vol% as the hollow glass microparticles were added up to 20 wt%. If the hollow glass microparticles are crushed, an increase in density will occur, which means that the hollow glass microparticles are not substantially crushed. As shown in FIG. 1, the relative density of the syntactic foam composition decreased by 16 to 23% as compared with the case where hollow glass microparticles were not included, by adding 1 to 20 wt% of the hollow glass microparticles.

The carbon nanotubes to be used in the present invention have a one-dimensional cylindrical structure and have an aspect ratio of 1,000 and exhibit excellent electrical, mechanical and thermal properties. Therefore, they have the best conditions as a filler for a polymer composite material. The mechanical properties of carbon nanotubes are particularly important when used as reinforcing materials. The carbon nanotubes may have various structures depending on the angle of the graphite and the number of the graphite sheets. Examples of carbon nanotubes that can be used in the present invention include single wall nanotubes (SWNTs), muli-walled nanotubes (MWNTs), multi-walled nanotubes And a rope nanotube.

SWNTs are 10 to 100 times stronger than steel and are known to be strong against physical shocks. Despite its excellent physical properties, SWNTs have several types of defects and disorders. Typical defects are point vacancies, interstitials, or a combination thereof. The defects present on the surface of the SWNTs are used as a place to connect the nanotubes to each other, which can provide chemical sensitivity, or can be used as a place to accommodate the dopant. Specifically, defects on the SWNT surface can interact with absorbed gas, moisture, support substrate, and saturated amorphous carbon present in the vicinity. In the present invention, the silanol group of the hollow glass microparticles reacts with the activated carbon present at the defect of the SWNT surface to form a covalent bond between the silanol group and the activated carbon. From this, the SWNT can act as a linkage connecting the hollow glass microparticles and the PP matrix, and can provide continuity between the hollow glass microparticles and the polyolefin matrix.

The diameter of the carbon nanotubes may be from 5 nm to 100 nm. The diameter of the carbon nanotubes means the outer diameter of the carbon nanotubes. The cross-section of the tubular shape may include circular or oval or hollow or pore shapes formed in a somewhat distorted shape thereof, which hollow or pore may include any shape that can be recognized as circular or elliptical. When the diameter of the carbon nanotubes is less than 5 nm, there is a problem that the carbon nanotubes aggregated at the same yield are aggregated to decrease the pore size. When the diameter of the carbon nanotubes exceeds 100 nm In this case, the gap between the carbon nanotubes becomes large and a large amount of carbon nanomaterials must be used in order to obtain necessary conductivity.

In one embodiment of the present invention, the carbon nanotube may be a single-walled nanotube or a multi-walled nanotube. In a preferred embodiment of the present invention, the carbon nanotube is a single-walled nanotube.

In one embodiment, the content of the carbon nanotubes may be 0.5 to 5 wt%.

In one embodiment, the syntactic foam composition of the present invention may have a volume conductivity of at least 1.0 S / m measured according to the ASTM D4496-13 method. In a preferred embodiment, the volume conductivity is 1.0 to 10 S / m.

In one embodiment, the syntactic foam composition may have a tensile strength of 35 MPa or more as measured according to the ASTM D638 method. In a preferred embodiment, it is at least 36 MPa, and in a more preferred embodiment is at least 38 MPa.

In one embodiment, the density of the syntactic foam composition is 900 Kg / m ³ or less and the matrix void is 10 vol% or more; The microballoon porosity may be at least 1%.

In a preferred embodiment, the density of the composition is 750 to 850 Kg / m ^3, the voids matrix of 10 to 20 vol%, and; The microballoon porosity is 1 to 30%. In an embodiment of the present invention, unlike the reported matrix void values (5 to 10 vol%), the matrix void increased to 20 vol% as 1 wt% to 20 wt% hollow glass microparticles were added 1).

Further, the present invention provides a method for producing a syntactic foam composition, which comprises mixing a polyolefin, hollow glass microparticles and carbon nanotubes, followed by melt kneading, and granulating the kneaded product.

In one embodiment of the production process, the hollow glass microparticles content is 1 to 7 wt%; The content of the carbon nanotubes may be 0.5 to 5 wt%.

In the production method of the present invention, there are no particular limitations on the apparatus and equipment for melt-kneading a mixture of polyolefin, hollow glass microparticles and carbon nanotubes, and hollow glass microparticles and carbon nanotubes are uniformly dispersed in the polyolefin matrix Anything that can be used can be used. An example of the melt kneading apparatus is a biaxial kneader of the conic and counter rotating type.

In the melt-kneading process, process conditions such as barrel temperature, motor speed, residence time, etc. must be carefully selected to ensure that the syntactic foam has optimal performance.

In one embodiment, the barrel temperature may be at least 5 DEG C, at least 10 DEG C, at least 20 DEG C, or at least 30 DEG C above the melting point of the polyolefin constituting the matrix. The lower the barrel temperature, the higher the shear force, which is favorable for dispersion of the hollow glass microparticles and the carbon nanotubes. However, when the barrel temperature is too low, the glass microparticles and the carbon nanotubes, particularly hollow glass microparticles, . In a preferred embodiment, the barrel temperature is 10 DEG C or higher than the melting point of the matrix polyolefin resin. In the examples of the present invention, the barrel temperature was 240 占 폚 in consideration of the polypropylene resin having a melting point of 240 占 폚,

Motor speed is also a factor in determining the shear force applied to the melt. Considering that fracture of the glass microparticles or carbon nanotubes should not occur, it is also preferable that the motor speed is also low in the limit of ensuring uniform dispersion of these motor speeds. For example, the motor speed may be 30 to 70 rpm, more preferably 40 to 60 rpm. In a preferred embodiment of the present invention, the motor speed is set to 50 rpm in order to prevent the hollow glass microparticles from being crushed during the melt-kneading process.

The residence time at which melt kneading is carried out in the barrel is advantageous as long as possible considering the dispersion among components constituting the kneaded product. For example, when a conical or counter-rotating twin-screw kneader is used, the residence time may be 1 minute, 5 minutes, 10 minutes, 20 minutes, or 30 minutes. Considering only the dispersion of the kneaded product, it is advantageous that the residence time is long. However, an excessively long residence time may lead to undesirable results such as oxidation and discoloration of the polymer composition.

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

Materials Used

As the matrix resin, polypropylene resin HF429 product of Samsung Total (Korea) was used. The resin has a relatively high melt index (8 g / 10 min at 240 캜, ASTM D1238-13) and a melting point of 239.4 賊 0.23 캜 and a density of 0.91 g / cc.

Carbon nanotubes were purchased commercially (TUBALL ^TM ; OCSiAl, Russia). TUBALL the ^TM part is the average diameter of the nanotube the outer has a carbon purity of 85% or more, it is 1.8 ± 0.4 nm, the length is at least 5㎛.

Hollow glass microparticles were purchased from 3M Korea Ltd. " im30K ". The hollow glass microparticles are soda-lime-borosilicate glasses with an average diameter of 18 microns and a volume of 0.6 g / cc.

Example: Preparation of a foam strengthening composition of PP / SWNT / HGMs composition

In order to determine the optimum weight of hollow glass microparticles by evaluating the effect of hollow glass microparticles on the formation of SWNT network, the content of hollow glass microparticles was increased while the SWNT content was fixed to 1.4 wt% Were prepared. The content ratios of the components of the syntactic foam composition prepared are summarized in Table 1 below. GB0.1 in Table 1 indicates that the content of the hollow glass microparticles is 0.1 wt%.

      * SME: specific mechanical energy (non-mechanical energy)

A mixture having the composition shown in Table 1 was melted and kneaded using a Brabender microcomposer TSC 42/6 (Brabender, Germany) to prepare a foam strengthening composition having a PP / SWNT / HGMs composition. The microcompounder is a biaxial kneader of conical and counter rotating type, having a barrel capacity of 50 grams and a screw diameter of 42 mm (L / D = 6).

In the melt-kneading process, process conditions such as barrel temperature, motor speed, residence time and the like were carefully selected considering that the syntactic foam had optimal performance. Specifically, the barrel temperature was set at 250 DEG C in consideration of the melting point (240 DEG C) of the PP used in the present invention. To prevent hollow glass microparticles from being broken during the melt-kneading process, the optimum motor speed was selected at 50 rpm. Considering that the longer the residence time, the better the dispersion of SWNT, the residence time was maintained for 20 minutes. Retention times were maintained using a closing plate and a reverse transfer element of a microcompounder. The shear stress applied to the molten composition in the barrel was evaluated using the mechanical energy (SME) value calculated by the following formula (1).

(1)

(One)

(kg/min)는 스루풋(throughput)이다. 본 발명에서, 스루풋은 0.00185 ± 0.00017 kg/min 이고, 회전 스피드는 50 min^-1 으로 고정하였다. 상기 표 1에 기재된 바와 같이, SME 값은 중공상 유리 마이크로입자의 함량이 증가함에 따라 점진적으로 증가함이 확인되었다.In the above equation,? (KJ) is drive torque, N (min-1) is rotational speed,

(kg / min) is the throughput. In the present invention, the throughput was 0.00185 +/- 0.00017 kg / min and the rotational speed was fixed at 50 min < ^{-1 &} gt ;. As shown in Table 1, it was confirmed that the SME value gradually increased as the content of the hollow glass microparticles increased.

The syntactic foam extrudate was granulated using a HNP1 pelletizer (HANKOOK E.M Ltd, Korea). Specimens were prepared by compression molding, injection molding, and other methods to analyze the physical, electrical, morphological, mechanical and rheological properties of the obtained granules. Compression molding was performed using QM900A hot press equipment (Quility & Measurement System, Korea). The compression molding was carried out in the order of preheating for 3 minutes at 200 DEG C, pressing for 1 minute and cooling for 5 minutes in this order. Injection molding was carried out at 250 ° C. using an Xplore Instruments, The Netherlands, using an Xplore Micro 10 cc injection molding machine to produce a disk shaped specimen of 25.4 mm diameter and 1 mm thickness and a "dog bone" specimen according to ASTM D638 .

2 (a) and 2 (b) are SEM photographs and EDS analysis results of SWNT and hollow glass microparticles used in the compositions, respectively. The SWNT contains 90% or more of carbon and contains 10% or less of metallic impurities originating from the metal catalyst. According to the data provided by the manufacturer, the amount of carbon nanotubes is more than 75%, and the content of total carbon containing amorphous carbon is more than 85%. Hollow glass microparticles consist mostly of silicon and carbon, consistent with that provided by the manufacturer.

Experimental Example 1: Evaluation of physical properties

The density of the specimen was measured using a water displacement method using a MD-300S density meter (MIRAGE, Japan). According to ASTM D792-13, the density (ρ _exp ) of the syntactic foam was calculated by applying the following equation (2) (ASTM International; 2013). Density and Specific Gravity (Relative Density) of Plastics by Displacement.

(2)

(2)

Where? Is the apparent mass in air of the syntactic foam,? Is the apparent mass in air of the syntactic foam while fully immersed in _water , and? _Water is the density of water at 23.degree. The theoretical density (rho _th ) of the syntactic foam was calculated according to the standard rule of mixtures of the mixture expressed by the following formula (3).

(3)

(3)

Where? And? Are the density fraction, volume fraction, respectively, and the subscripts CNT, MB, and m denote carbon nanotubes, microballoon and matrix, respectively. The density of the matrix (PP) and microballoons are 0.91 and 0.6 g / cm < ^{3 &} gt ;, respectively. The density of SWNT is 1.3 g / cm ³ (Gao G et al., Materials & Design. 2011; 32 (8): 4152-63).

By comparing the theoretical value with the experimental value (p _exp ), the air void (Φ _v ) trapped in the matrix during the melt processing was calculated using the following equation (4).

(4)

(4)

A detailed discussion of the porosity of syntactic foams can be found in the paper (Gupta N et al. Springer Science & Business Media; 2013). Matrix porosity can be a moderate parameter for the strength, elastic modulus, and energy absorption of the syntactic foam. The wall thickness and the half-wall thickness ratio of the hollow glass microparticles can be calculated using the following equation (Swetha C et al., Quasi-static uni-axial compression behavior of hollow glass microspheres. 2011; 32 (8); 4152-63).

(식 5)

(Equation 5)

Ρ _true is the true density (g / cm ³ ) of the hollow glass microparticles, and ρ _{glass is the glass} transition _temperature of the hollow glass microparticles. Is the density of the glass (2.54 g / cm ³ ), and? Is the half-height ratio (the ratio of the inner radius to the outer radius). The porosity (PHI _P ) of the hollow glass microparticles in the syntactic foam was calculated according to the following equation (6) using the above-mentioned half- _width ratio.

(식 6)

(Equation 6)

Figure 1 shows the relative density (g / cm ³ ), matrix void (vol%) and hollow glass microparticle porosity of a syntactic foam containing calculated SWNTs. In FIG. 1, the other characters under the error bars indicate statistically significant others at the 95% confidence level. In Fig. 1, the red dotted line indicates the density of pure PP of 910 kg / m < ^{3 &} gt ;. It has been reported that some hollow glass microparticles are pulverized during the melt-kneading of the syntactic foam, thereby increasing the density. However, as a result of experiments, no evidence of hollow glass microparticles was found to be disrupted by maintaining a suitable motor speed (50 rpm) and high isotactic grinding strength during melt-kneading. Unlike the reported matrix void values (5-10 vol%), matrix voids were increased to 20 vol% as hollow glass microparticles were added. These results may be due to poor adhesion between HGMs and PP.

As a result of several comparisons of relative density, the specimens can be statistically divided into two groups: one group containing up to 0.5 wt% hollow glass microparticles, one without density reduction, Another group containing microparticles in the range of 1 to 20 wt% and showing a density reduction of 16 to 23%.

Experimental Example 2: Evaluation of rheological properties

Rheological analysis was carried out to evaluate the effect of hollow glass microparticles content on SWNT network structure. Using a Fiji MCR 302 vibration rheometer (Anton Paar GmbH, Austria) with a flat plate structure (25 mm in diameter and 1 mm in gap), oscillatory shear ) And stress relaxation were measured. Specimens were preformed in disk form. The frequency sweep was performed by applying a strain of 1% while decreasing the frequency from 100 to 0.1 rad / s while maintaining the temperature equilibrium for approximately 3 minutes, and the results are shown in Fig.

As shown in Fig. 4, at low frequencies, pure PP exhibits similar terminal behavior as the sole copolymer due to complete relaxation of the PP-chain. However, as the SWNT network is present, the terminal behavior due to complete relaxation of the PP-chain is weakened, and the storage elastic modulus (G ') and loss elastic modulus (G``) of angular frequency (ω) are limited to low frequencies. In the range of hollow glass microparticles content of 1 to 10 wt%, there was no abnormality in development of low frequency G ', G`` stable area (plateu). This non-terminal behavior at low frequencies is due to the formation of interconnected SWNT networks without disturbance due to the content of hollow glass microparticles. However, in the low hollow glass microparticle content (0.1-0.5 wt%), the dependence of G 'and G' 'becomes stronger, suggesting that the formation of the SWNT network is disturbed (see FIGS. 4 (a) and 4 ). A similar phenomenon is also observed for GB20. As shown in Fig. 4 (d), the rheological behavior of the GB20 curve is changed from that of a viscous fluid to that of an elastic solid, which means that hollow glass microparticles aggregate. The results illustrate the tensile strength reduction of the GB10 and GB20 compositions.

In the range of 1 to 7 wt% hollow glass microparticles, the overall modulus of elasticity increased as a function of the hollow glass microparticle content, and the SWNT network structure was maintained up to 7 wt%. Figure 4 (d) is a Van-Gurp Palmen plot. In the case of pure PP, the curve approaches a phase angle of 90 °, which represents the viscous behavior, while the curve of the syntactic foam containing SWNTs is inclined at a low phase angle, and rheological behavior, except for GB20, It was confirmed that it was changed into an elastic solid.

Experimental Example 3: Evaluation of thermal characteristics

Thermal characterization of the specimens was performed using a Q500 thermogravimetric analyzer (TGA) (TA Instrument, USA). The weight reduction as a temperature dependent function was carried out at a rate of 10 캜 / min under a nitrogen atmosphere while heating from 30 캜 to 800 캜. The influence on the thermal stability of the syntactic foam was evaluated based on the _onset temperature (T _onset ) of pyrolysis and the mass reduction temperature (T _-5% ) of _5% , and the results are shown in Table 2 below.

In the above table, with respect to the characters indicated by superscripts after the data, different letters in the same column indicate statistically significant differences at a confidence level of 95% (? = 0.05).

It has been reported that when SWNT is included, the thermal stability of the composition is improved due to barrier effects, thermal conductivity of CNTs, physical or chemical absorption, radical removal action, and polymer-nanotube interaction (McNally T. et al., Poschke P. Polymer-carbon nanotube composites: Preparation, properties and applications: Elsevier; 2011.). For this reason, as compared to pure PP that has a T _-5% of T _onset and 363.03 ℃ of 397.53 ℃, if the addition of SWNT in the 1.4 wt% increases the T _onset and T _-5%. In the range of the hollow glass microparticle content of 0 to 1 wt%, there was no significant decrease in the _onset temperature (T _onset ) as compared with the composition of GB 0, which is considered to be due to the low content of the hollow glass microparticles. However, when the hollow glass microparticles contain 3 wt% or more, the decrease of the _onset is statistically significant as compared to GB0. This is mainly caused by the abundant hydroxyl groups present on the surface of the hollow glass microparticles, as shown on the right side of FIG. For the same reason, the 5% mass reduction temperature (T _-5% ) also showed a decrease with increasing hollow glass microparticle content when the hollow glass microparticles contained 3 wt% or more.

Experimental Example 4: Evaluation of morphology characteristics

The surface of the PP / CNT / HGM syntactic foam was directly observed using a SU8020 field emission scanning electron microscope (HITACHI, Japan). Specifically, the pelletized syntactic foam granules were treated with liquid nitrogen followed by cold milling. The chemical composition of SWNT and hollow glass microparticles was investigated using an EMAX energy dispersive X-ray spectrometer (HORIBA Scientific, Japan). The surface was sputter coated with palladium to prevent charge build up.

FIG. 3 is a SEM photograph showing the surface state between the hollow glass microparticles and the SWNT (top) and a schematic diagram (below) showing their interaction. FIG. The adhesion between the hollow glass microparticles and the SWNT was observed from Fig. 3 (see the upper drawing of Fig. 3) even though the hollow glass microparticles were not surface-treated. From this, it can be seen that the SWNT acts as a connecting material connecting the hollow glass microparticles with the PP matrix, thereby providing continuity between the hollow glass microparticles and the PP matrix (continuity as the interfacial adhesion between PP-CNTs improves) . Such interfacial adhesion appears to be mainly due to the drawbacks of SWNTs.

5 is a SEM photograph showing the morphological state of the syntactic foam including the SWNT. The SWNT was well dispersed in the PP matrix due to the long retention time of 20 minutes, and as a result, it was confirmed that a percolation network was formed (see Fig. 5 (a)). Low hollow glass microparticle content (0.1-0.5 wt%). Hollow glass microparticles appear to be surrounded by SWNTs. Hollow glass microparticles appear to act as nucleating agents to induce SWNTs, thereby hindering the network formation of SWNTs (see FIG. 5 (b)). When the hollow glass microparticle content increases (1 to 7 wt%), the spacing between hollow glass microparticles decreases, increasing the likelihood that the SWNTs will contact each other. The possibility that the SWNTs branched in one hollow glass microparticle are entangled with the branched SWNTs in the other hollow glass microparticles nearby (see FIG. 5 (c)).

On the other hand, as a result of the evaluation of the rheological properties and the mechanical properties, when a large amount of hollow glass microparticles were added (10 to 20 wt%), coagulation of the hollow glass microparticles occurred and the volume of the SWNT decreased, A larger amount of SWNT is required to form a percolation network (see Fig. 5 (c)),

7 is a schematic diagram showing the effect of the hollow glass microparticle content on the formation of the SWNT network.

Based on the results described above, it can be seen that the content of the hollow glass microparticles showing the strengthening effect of the SWNT and the network forming effect is 1 to 7 wt% of the syntactic foam composition. In the case of low contents of hollow glass microparticles (0.1 to 0.5 wt%), hollow glass microparticles act as nucleating agents to interfere with the formation of SWNT network and contain high content of hollow glass microparticles 10 wt% or more), the coagulation of hollow glass microparticles occurs and the SWNT network is not formed properly.

Experimental Example 5: Evaluation of electrical characteristics

In order to evaluate the effect of hollow glass microparticles on the dispersion state or network structure formation of SWNTs, in-plane electrical conductivity measurements using a compression-molded rectangular sheet were performed according to ASTM D4496-13 . The geometric mean and standard deviation of the resistance values were obtained by performing 10 measurements on each specimen. A CMT-SR1000N resistance measurement system (Advanced Instrument Technology, USA) equipped with a 4-point probe with a resistance range of 1 MOhm / square to 2MOhm / square and a pin spacing of 20-50 mils was used.

6 is a graph showing the volume conductivity according to the hollow glass microparticle content for a syntactic foam containing SWNTs. Without the hollow glass microparticles, the composition comprising 1.4 wt% SWNT had a volume conductivity of 6.58 S / m. When containing 0.1 wt% of hollow glass microparticles, the volume conductivity decreased to 2.36 S / m. In addition, when containing 0.3 to 0.5 wt% of hollow glass microparticles, the volume conductivity decreased by at least one order. This is mainly due to the nucleation effect of the hollow glass microparticles as described in the description of Fig. 5 (a).

However, in the range of 1 to 7 wt% of the hollow glass microparticles, the volume conductivity increased again to the GB0 level. On the other hand, if the content of the hollow glass microparticles exceeds 10 wt%, the volume conductivity decreases again due to the aggregation of the hollow glass microparticles. The red dotted line in Figure 6 shows visually that there is practically no reduction in volume conductance in the GB1, GB3, GB5 and GB7 compositions.

Sample number Volume Conductivity (S / m) GB0 6.578573428 GB0.1 2.36271607 GB0.3 0.06076654 GB0.5 0.037449116 GB1 5.661372906 GB3 7.963297285 GB5 3.262355355 GB7 5.402281038 GB10 0.04264231 GB20 0.003546572

Experimental Example 6: Evaluation of mechanical properties

The mechanical properties of the injection molded dog bone specimens were evaluated using an Instron 3367 universal testing machine (INSTRON, USA). According to the method of ASTM D638, with a 1 kN cell force and a tensile rate of 10 mm / min. At least three specimens were evaluated for each composition, tensile strength was taken from the raw data and the results are shown in Table 3 below.

Table 4 below shows the tensile strength, yield elongation and Young's modulus of a syntactic foam containing SWNT measured by HGMs content.

In the above table, with respect to the characters indicated by superscripts after the data, different letters in the same column indicate statistically significant differences at a confidence level of 95% (? = 0.05).

As shown in Table 4, tensile strength tended to decrease with the addition of hollow glass microparticles. This decrease in tensile strength is believed to be due to the separation between the surfaces and matrix voids between the hollow glass microparticles and the polymer matrix and consequently insufficient stress transfer. However, as can be seen in FIG. 3, it was confirmed that the gap between the hollow glass microparticles and the PP matrix was connected by the interaction of the SWNTs with the hollow glass microparticles.

Until the hollow glass microparticle content reached 7 wt%, the tensile strength was not significantly different from GB0. However, GB10 and GB20 showed a statistically significant decrease in tensile strength. This is because when the content of the hollow glass microparticles exceeds 10 wt%, it is because the hollow glass microparticles aggregate and the strengthening effect of the SWNT due to the interface between the hollow glass microparticles and the PP can not be obtained .

Compared to the tensile strength of pure PP alone (35.00 ± 1.84 MPa), the tensile strength of the composition increased until the content of hollow glass microparticles reached 10 wt%. The tensile elongation also shows a tendency similar to that of tensile strength. Young's modulus is the ratio of strength to elongation. Since the tensile strength and tensile elongation tend to be similar, the Young's modulus does not show a statistical difference even when the content of the hollow glass microparticles varies.

Statistical analysis

One-way ANOVA and Tukey's HSD (Honestly Significant Differences) tests were performed for multiple comparisons of each experimental data (α = 0.05). IBM SPSS Stability Version 23 (IBM ^(R) SPSS ^(R) , USA) was used for statistical analysis.

From the above analysis results, it was confirmed that the content of the hollow glass microparticles in the range that does not impair the excellent characteristics of the SWNT contained in the syntactic foam was 1 to 7 wt%. The EDS analysis and SEM image of FIG. 2 show that there is interfacial adhesion between hollow glass microparticles and SWNTs without any other surface treatment, mainly due to defects of SWNTs and silanol of hollow glass microparticles. Such interfacial adhesion ensures that the tensile strength of the syntactic foam is maintained until the amount of hollow glass microparticles reaches 7 wt% as compared to GB0.

The rheological measurement results show that the loading of hollow glass microparticles increases the disturbance of the SWNT network. As the content of hollow glass microparticles increases, the decomposition initiation temperature and the 5% mass reduction temperature decrease, which is due to the hydroxyl groups abundantly present on the surface of the hollow glass microparticles.

As a result of SEM photographs and electrical properties, it was found that the formation of SWNT network was inhibited by nucleation effect and aggregation, respectively, when the hollow glass microparticle content was small (0.1 ~ 0.5 wt%) and large (10 ~ 20 wt% . It is a surprising finding that the GB1, GB3, GB5, and GB7 compositions have a relative density of 16-20% lower than GB0, opening the opportunity to produce lightweight and electrically conductive polymer compositions.

Claims (13)

Polyolefins, hollow glass microparticles, and carbon nanotubes,
The hollow glass microparticles are contained in an amount of 1 to 7 wt% based on the total weight of the composition,
Wherein the hollow glass microparticles are dispersed in the polyolefin matrix.
The syntactic foam composition according to claim 1, having an electrical percolation network structure formed of carbon nanotubes between the hollow glass microparticles.
The syntactic foam composition according to claim 1, wherein the polyolefin is polypropylene.
The syntactic foam composition of claim 1, wherein the hollow glass microparticles are not surface treated.
The syntactic foam composition according to claim 1, wherein the content of the carbon nanotubes is 0.5 to 5 wt%.
The syntactic foam composition according to claim 1, characterized in that the volume conductivity measured according to the ASTM D4496-13 method is 1.0 S / m or more.
The syntactic foam composition according to claim 1, characterized in that the tensile strength measured according to the ASTM D638 method is not less than 35 MPa.
The hollow glass microparticle according to claim 1, wherein the hollow glass microparticles are unbranched, have a density of 900 Kg / m ³ or less, a matrix void of 10 vol% or more, and a microballoon porosity of 1% Syntactic foam composition.
The method of claim 1, wherein a density of 750 to 850 Kg / m ^3, the voids matrix of 10 to 20 vol%, and; Wherein the microballoon porosity is 1 to 30%.
A method for producing the syntactic foam composition according to claim 1, wherein the polyolefin, the hollow glass microparticles and the carbon nanotubes are mixed and then melt kneaded, and the kneaded product is granulated.
The method for producing a syntactic foam composition according to claim 10, wherein the barrel temperature at melt-kneading is 10 ° C or higher than the melting point of the polyolefin.
The method of producing a syntactic foam composition according to claim 10, wherein the motor speed during melt-kneading is 40 to 70 rpm.
11. The method of claim 10, wherein the hollow glass microparticles are present in an amount of 1 to 7 wt% and the carbon nanotubes are present in an amount of 0.5 to 5 wt%.

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