RU2586149C1 - Method of producing laminar plastic - Google Patents

Abstract

FIELD: material science.

SUBSTANCE: invention relates to production of laminates, which can be used in aircraft and ship building. Method of producing laminar plastic consists in producing binder, modified carbon nanotubes by combined dispersion of carbon nanotubes and binder in solvent, applying binder modified carbon nanotubes onto surface layers of filler, assembling pack of layers of filler and curing package under pressure, carbon nanotubes are preliminarily treated with solution of at least one polymer controller wettability of carbon nanotubes binder when exposed to ultrasound.

EFFECT: invention ensures production of laminar plastic with high level of shielding electromagnetic waves (EMR) in radio frequency band and controlled level of electric conductivity.

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Description

The invention relates to the field of manufacturing laminated plastics that can be used in aircraft and shipbuilding.

At present, one of the urgent tasks of materials science is the task of imparting various functional properties to structural polymer composite materials (PCM), such as electrical conductivity, hydrophobicity, a controlled level of reflection and transmission of electromagnetic waves (EMW) of the radio range. The solution to this problem will significantly expand the field of application of structural materials, reduce the weight of structures in which similar materials are used, and also increase the reliability of their work. Thus, the use of a hydrophobic laminate having a volumetric electrical conductivity in the rotor shell of a helicopter allows to prevent icing and to ensure the resistance of the structure to lightning discharges without the use of a metal mesh in the shell structure and thus provides up to 30% on-board generator power, which reduces weight and fuel economy. To solve the problems of electromagnetic compatibility of airborne equipment, it is necessary to use PCM with a controlled level of reflection and transmission of electromagnetic waves of the radio frequency range.

One of the most promising ways to solve the problem of giving PCM functional properties is to use nanosized fillers in polymer binders, including carbon nanotubes (CNTs) [Prospects for the use of carbon-containing nanoparticles in binders for polymer composite materials. E.N. Kablov, S.V. Kondratov, G.Yu. Yurkov. Russian nanotechnology. 2013.V.8. No. 3-4. S. 28-46].

A number of technical solutions are known that describe the use of CNTs to create hydrophobic coatings. So in / Composite Films Based on Aligned Carbon Nanotube Arrays and a Poly (N-Isopropyl Acrylamide) Hydrogel. Zhaohui Yang, Zheng Cao, Hao Sun, and Yan Li Adv. Mater. 2008, 20, 2201-2205 / it was shown that a coating of vertically oriented nanotubes ("wood") grown directly on a substrate and impregnated with a hydrophobizing agent allows a contact angle of 170 ° to be achieved.

However, growing a “forest” of CNTs is possible only on a substrate of heat-resistant oxides (Al ₂ O ₃ , SiO ₂ ), and the size of such a coating is limited by the size of the reactor.

To obtain hydrophobic coatings on the surface of real parts, more promising methods for producing hydrophobic electrically conductive films containing CNTs and a polymeric matrix made of polystyrene [CN 102504432 A, 20.06.2012] or polytetrafluoroethylene [Anticorrosion Coating of Carbon Nanotube / Polytetrafluoroethylene Composite Film on the Stainless Steel Bipolar Plate for Proton Exchange Membrane Fuel Cells. Yoshiyuki Show, Toshimitsu Nakashima, and Yuta Fukami. Journal of Nanomaterials Volume 2013, Article ID 378752, 7 pages]. A method for producing such coatings consists in co-dispersing a polymer or oligomeric matrix with CNTs, followed by coating the substrate and removing the solvent. The methods described above make it possible to obtain coatings with a contact angle of 160 ° and a conductivity of 0.1–13 S / cm [A review of the preparation and properties of carbon nanotubes-reinforced polymer composites. Fan-Long Jin, and Soo-Jin Park. Carbon Letters. 2011. Vol. 12. No. 2. P. 57-69].

The disadvantage of the coatings obtained by the described method is the low adhesion to the substrate. In addition, the claimed characteristics are achieved at sufficiently high concentrations of CNTs (25 wt.%), Which leads to a deterioration in the physicomechanical properties of nanocomposites.

To increase the adhesion of hydrophobic coatings to the substrate, systems are used that contain carbon nanotubes, thermosetting binders of various types and various hydrophobizing agents: fluorine-containing organosilicon polymer [CN 101792633 A, 08/04/2010], fluorinated CNTs [CN 102382366 A, 03/21/2012], block copolymers including hydrophobic and hydrophilic functional blocks [JP 2012251018 A, 12.20.2012], block copolymers including hydrophobic blocks and functional groups providing covalent bonding with a thermoset matrix and CNTs [TW 201311550 A, 03.16.20.20 13]. It is also possible the joint use of carbon nanotubes and nanoparticles of silicon dioxide [CN 103059618 A, 04.24.2013].

The described systems make it possible to obtain electrically conductive coatings with a contact angle of 150 °, however, the application of such coatings does not allow the creation of a material with bulk conductivity.

A known method of producing plastic, in which CNTs are grown on alumina fabric by CVD (chemical vapor deposition), is impregnated with an epoxy composition, pressed at room temperature for 12 hours and cured at a temperature of 60 ° C [Fabrication and multifunctional properties of a hybrid laminate with aligned carbon nanotubes grown In Situ. Enrique J. Garcia, Brian L. Wardle, A. John Hart, Namiko Yamamoto. Composites Science and Technology 2008. 68. 2034-2041].

Using the CVD method of growing CNTs on the surface of glass and carbon fibers leads to a decrease in their tensile strength, since it leads to the degradation of reinforcing fibers [A review of strategies for improving the degradation properties of laminated continuous-fiber / epoxy composites with carbon-based nanoreinforcements. G. Lubineau, A. Rahaman. CARBON 2012. 50. P.2377-2395].

The closest analogue is a method for producing electrically conductive shielding electromagnetic waves of the radio range of laminated plastics, including dispersing CNTs together with a thermosetting binder, applying a modified binder to a semipermeable substrate of reinforcing material and its subsequent pressing. To increase the concentration of CNTs in the binder to 33 wt.%, A solvent is added to the dispersible system. To reduce the viscosity of the modified binder and improve the uniformity of distribution, carbon nanotubes are covalently modified with amine groups [US 2011014460 A1, 01/20/2011].

The main disadvantage of the prototype is that a high level of electrical conductivity of laminated plastic is achieved at high concentrations of CNTs. Thus, a significant level of EMF shielding is achieved at a CNT concentration of 20-30 wt.%, And the surface conductivity at a CNT concentration of 6-8 wt.% Is only 10 ⁵ -10 ⁴ Ohm / sq, while a further increase in concentration does not lead to to a decrease in surface resistance.

The methods of increasing the electrical conductivity that are proposed in the prototype, namely: the additional introduction of conductive salts, metal nanoparticles, conductive fibers, lead to the appearance of internal stresses, an increase in PCM weight and a decrease in physical and mechanical properties. In addition, the known material does not have hydrophobic properties.

The technical result of the proposed invention is to obtain a laminated plastic with a high level of shielding (reflection and / or absorption) of electromagnetic waves (EMW) in the radio range and a controlled level of electrical conductivity.

To achieve a technical result, a method for producing a laminated plastic is proposed, in which an epoxy binder modified by carbon nanotubes is obtained by co-dispersing carbon nanotubes and an epoxy binder in a solvent, an epoxy binder modified by carbon nanotubes is applied to the surface of the filler layers, a package of filler layers is collected and carry out the curing of the package under pressure, while carbon nanotubes pre-process the solution Ohm, the polymer regulates the wettability of carbon nanotubes with an epoxy binder, which is used as a tetrafluoroethylene telomer, under the influence of ultrasound.

To further increase the hydrophobicity of the surface of the laminate, a relief is created on it by the fact that before curing the package, outer layers are placed on it in the form of filler sheets not impregnated with a binder, which, after curing, are removed from the surface of the resulting laminate.

To obtain a layered plastic with a high level of absorption of electromagnetic waves (EMW) in the radio range, the packet is assembled from the filler layers in such a way that at least one of the layers of the filler packet is impregnated with an epoxy binder modified with carbon nanotubes decorated with metal-containing nanoparticles.

When the statistical percolation threshold is reached, the conductivity level of the CNT / binder nanocomposite is according to / Increasing the electrical conductivity of carbon nanotube / polymer composites by using weak nanotube-polymer interactions. You Zeng, Pengfei Liu, Jinhong Du, Long Zhao, Pulickel M. Ajayan, Hui-Ming Cheng. Carbon 2010. 48. 3551-3558 /, is determined by the wettability of CNTs by a polymer matrix.

A decrease in wettability leads to a decrease in the thickness of the polymer layer that surrounds the nanotube. As a result, the contact resistance between them decreases, and the conductivity of the nanocomposite increases. Non-covalent functionalization of nanotubes with a hydrophobic polymer (for example, fluorine-containing), which reduces their wettability by a binder, provides PCM with hydrophobic properties and simultaneously increases the electrical conductivity of the resulting plastic.

It was experimentally established that the treatment of nanotubes with a solution of tetrafluoroethylene telomere to reduce their wettability with an epoxy binder provides a contact angle of the cured telomere film with an epoxy binder of 85 °, which corresponds to high values of electrical conductivity and hydrophobicity of the obtained plastic.

A further increase in the wettability angle is possible when a relief is formed on the PCM surface by the fact that prior to curing the package, outer layers are placed on it in the form of filler sheets not impregnated with epoxy binder, which, after curing, are removed from the surface of the obtained laminate.

If CNTs are pre-functionalized with an additive that increases their wettability with a binder (for example, the wetting angle of a polyvinyl ethyl (PVE) film with an epoxy binder is 55 °), then the conductivity of the nanocomposite decreases. Based on the analysis of the power balance of the reflected and absorbed electromagnetic waves (EMW) interacting with the nanocomposite, in the article [Electromagnetic interference shielding mechanisms of CNT / polymer composites. Mohammed H. Al-Saleh, Uttandaraman Sundararaj. Carbon 2009. 47. 1738-1746] it is shown that a decrease in the electrical conductivity of the nanocomposite leads to an increase in the thickness of the skin layer and an increase in the fraction of electromagnetic radiation energy absorbed by the nanocomposite, while the fraction of reflected energy decreases. By combining highly conductive layers in the composition of the laminate that are rear with respect to the incident EMW and obtained with an additive that reduces wetting and layers with low conductivity obtained with an additive that increases wetting with a thickness less than the thickness of the skin layer, the reflected signal can be reduced . Compared with the scheme in which the reflection coefficient is controlled only by changing the thickness of the concentration of the radar absorbing filler, the proposed scheme reduces the thickness of the plastic by 20-30% at the same levels of attenuation of the reflected signal level.

The use of CNTs in layers decorated with metal-containing nanoparticles makes it possible to further weaken the reflected electromagnetic wave and increase the frequency range in which attenuation occurs due to the appearance of magnetic losses in such systems along with dielectric losses [Microwave absorption properties of multiwalled carbon nanotube / FeNi nanopowders as light -weight microwave absorbers. Fusheng Wen, Fang Zhang, Jianyong Xiang, Wentao Hu, Shijun Yuan, Zhongyuan Liu. Journal of Magnetism and Magnetic Materials. 2013.343. 281-285].

In fig. 1a and fig. 1b shows micrographs of the PCM surface (samples 2 and 4, see examples), respectively, obtained using SEM.

In fig. Figure 2a shows an SEM photograph of the surface of sample 3 after removal of the surface layer of fiberglass not impregnated with a binder. In fig. 2b shows a profile of the same surface obtained with an interference profiler. In fig. Figure 2c shows a photograph of a drop on the surface of the same sample.

The inventive method can be illustrated by the following examples.

Example 1

To prepare the impregnating composition, the required amount of Taunit M brand CNTs and Cherflon brand tetrafluoroethylene telomere (an additive that reduces the wettability of a carbon nanotube with an epoxy binder) were jointly dispersed in acetone for 50 min using an ultrasonic bath (frequency 22 kHz, power 250 W) . After that, an epoxy binder (ED-20 / 4,4-diaminodiphenylsulfone) was added to the system, which was previously treated at a temperature of 100 ° C for 120 minutes and dispersed for another 20 minutes. The impregnating composition was applied on two sides to the glass fabric by spraying. Four impregnated sheets were collected in a bag and pressed according to the regime: 90 ° C - 60 min, 180 ° C - 180 min.

Table 1 shows the dependence of the wetting angle of the PCM on the ratio of the components included in the impregnating composition.

As follows from the data presented, the wetting angle is determined by the ratio of the components that are included in the impregnating composition. With an increase in the number of tetrafluoroethylene telomere in the impregnating composition from 0 to 7 parts by weight with a constant amount of CNTs, the wetting angle increases from 78 ° to 98 °. A further increase in the number of tetrafluoroethylene telomere does not increase the contact angle. With an increase in the number of tetrafluoroethylene telomere, the viscosity of the impregnating composition decreases, which leads to its leakage during pressing and an increase in the proportion of reinforcing filler in the finished PCM from 45 wt.% To 52 wt.%. The outflowing composition was transparent and did not contain carbon nanotubes.

A comparative elemental analysis of the surface of samples 2 and 3, performed using a local probe microanalysis combined with scanning electron microscopy, indicates that when the telomere content of tetrafluoroethylene is 3.5 mass parts the distribution of fluorine atoms over the surface of the PCM is inhomogeneous. Moreover, their maximum number is associated with surface areas with higher electrical conductivity (in the photograph of the surface obtained using spectral electron microscopy (SEM), they are displayed as dark areas where the electrostatic charge drains quickly). The increase in the number of tetrafluoroethylene telomere in the impregnating composition to 7 parts by weight leads to a more uniform distribution of fluorine atoms over the PCM surface.

Based on the data presented, it can be assumed that, in the impregnation composition, the tetrafluoroethylene telomer is mainly localized on the surface of carbon nanotubes.

As can be seen from the data shown in table 1, a decrease in the proportion of epoxy binder in the impregnating composition leads to an increase in the contact angle to 103.4 °.

As can be seen from fig. 1b, the distribution of CNTs on the PCM surface is inhomogeneous. Areas containing nanotubes that are treated in a tetrafluoroethylene telomere solution have less adhesion to the glass sheet coverslips than unmodified binder sites. Removing the cover sheet leads to partial destruction of the surface and the appearance of a hydrophobic relief, since the surface areas with the highest adhesion are removed, i.e. sections of unmodified epoxy binder (Fig. 2a).

As can be seen, the distribution of the nanofiller on the surface of sample 3 is uneven at the micro level, and the CNTs are assembled into aggregates. With a decrease in the concentration of the epoxy binder, the regions that do not contain carbon nanotubes disappear.

It should be noted that the achieved wetting angle on the surface of sample 5 practically coincides with the wetting angle for the smooth surface of the film obtained from the F-4 M copolymer.

To further increase the wetting angle of the surface of sample 3, a hydrophobic relief was applied to it (sample 3 ′). For this, before pressing, a clean (not impregnated) layer of fiberglass (filler) was applied to the impregnated surface, which, after impregnation, was removed from the plastic surface by a mechanical method. Without relief, the contact angle of the surface of the sample was 97 °, and after removal of the surface layer of fiberglass, its value increased to 136 °.

As can be seen from fig. 2a, irregularly shaped electrically conductive globules are located in the PCM volume (electrically conductive surface fragments are displayed as dark areas on SEM photographs due to the surface charge draining).

The presence of electrical conductivity (surface resistance 500-700 Ohm / sq; sample resistance 0.42 mm thick in a plane perpendicular to the packing plane of the filler, not more than 15 Ohms) suggests that the globules form a continuous 3-D framework that permeates the entire volume sample.

Thermomechanical studies of PCM show that the dynamic modulus of elasticity of the sample is 12000 MPa, and the glass transition temperature is 180 ° C.

Example 2

To prepare the impregnating composition, the required amount of CNTs (Taunit M) and polyvinyl ethyl (PVE) were dispersed together in acetone for 50 min using an ultrasonic bath (frequency 22 kHz, power 250 W). After that, an epoxy binder (ED-20 / 4,4-diaminodiphenylsulfone) was added to the system, which was previously heat-treated at a temperature of 100 ° C for 120 minutes and dispersed for another 20 minutes. The impregnating composition was applied on two sides to the glass fabric by spraying. The required amount of impregnated sheets was collected in a bag and pressed according to the regime: 90 ° C - 60 min, 180 ° C - 180 min.

Table 2 shows the results of experiments on the effect of the concentration of PVE on the nature of the dispersions and the processability of their deposition on the layers of reinforcing filler, as well as comparative results of the measured functional properties (resistance along the packing plane p, transmittance T, reflection R, absorption A of an electromagnetic wave with a frequency 27 GHz) and the thickness of the samples of laminate N.

As can be seen from the above data, the stability of the dispersion is determined by the ratio between the number of CNTs / PVEs in the range of 3 ÷ 0.5, which allows one to obtain a stable dispersion that ensures high adaptability of its deposition. A decrease in the proportion of PVE below the specified limit leads to a rapid settling of the aggregates (table 2, composition 6). A decrease in the CNT / PVE ratio leads to the formation of gel-like aggregates that adversely affect the quality of the coating (table 2, composition 7).

A comparison of the functional properties of samples 8 and 9 shows that an increase in the wettability of CNTs with an epoxy matrix (replacing tetrafluoroethylene telomer with PVE) leads to an increase in electrical resistance from 2.3 × 10 ² Ohms to 5.2 × 10 ⁴ Ohms, while the reflection coefficient decreases by 14%, and the magnitude of absorption increases by 10%.

Example 3

Impregnating compositions were made analogously to example 1, however, carbon nanotubes were additionally decorated using high-speed thermal decomposition of metal-containing compounds on the surface of carbon nanotubes.

To obtain a composition consisting of Pt @ Fe ₂ O ₃ nanoparticles decorating carbon tubes, the thermal decomposition method was used. The initial metal-containing precursor was synthesized from iron pentacarbonyl Fe (CO) ₅ and platinum chloride H ₂ PtCl ₆ · 6H ₂ O. The synthesis sequence was as follows: 1.8 ml of iron pentacarbonyl Fe (CO) ₅ and 10 ml of dimethyl ether were placed in a conical flask diethylene glycol (CH ₃ OCH ₂ CH ₂ ) ₂ O. Then, with rapid stirring, a solution of H ₂ PtCl ₆ · 6H ₂ O in diethylene glycol dimethyl ether was added to the reaction flask. Next, heat treatment was carried out at 160 ° C.

The resulting solution was filtered and added dropwise to a dispersion of carbon nanotubes in a high boiling organic liquid, which was prepared by dispersing 10 g of carbon nanotubes in 100 ml of vacuum oil with vigorous stirring in an inert medium and heating to a temperature of 240 ° C. Upon reaching the required temperature, a solution of the above precursor was introduced dropwise into the reactor. The resulting reaction mixture was kept in a stream of argon with stirring, maintaining a constant temperature.

After completion of the synthesis, the samples were extracted. The result was highly dispersed black powders.

Table 3 shows the dependences of the transmittances T, reflection R, and absorption A of an electromagnetic wave with a frequency of 27 GHz on the structure and composition of laminated plastics.

As can be seen from the data presented, the use of only CNTs in a binder for PCM that were pretreated with a tetrafluoroethylene telomer leads to the fact that PCM reflects 85% of the incident EMW radiation, while only 14.5% of the incident energy is absorbed (sample No. 10).

If PCM consists of two layers, one of which (the outer layer with respect to the incident EMW) contains CNTs treated with polyvinyl ethyl, then the fraction of the reflected PCM energy decreases. With a certain ratio of the number of layers and the concentration of CNTs in the outer and back layers, the fraction of reflected energy can be reduced to 60% (sample No. 13).

It is possible to make PCM, which has the same EMF reflection coefficient using only CNTs treated with polyvinyl ethyl (sample No. 14). However, in this case, to achieve a transmittance of the same magnitude, it is necessary to use 15 layers of prepreg instead of 7.

Thus, the proposed method allows to obtain laminated plastics with a high level of shielding (reflection and / or absorption) of electromagnetic waves (EMW) in the radio range, as well as with a controlled level of electrical conductivity.

Claims (3)

1. A method of producing a laminate in which an epoxy binder modified by carbon nanotubes is obtained by co-dispersing the carbon nanotubes and an epoxy binder in a solvent, an epoxy binder modified by carbon nanotubes is applied to the surface of the filler layers, a bag of filler layers is collected and the packet is cured. under pressure, characterized in that the carbon nanotubes are pre-treated with a solution of a wettable polymer-regulator and carbon nanotubes with an epoxy binder, which is used as tetrafluoroethylene telomer, by sonication. 2. The method according to p. 1, characterized in that a hydrophobic relief is created on the surface of the laminate by the fact that before curing the package, outer layers are placed on it in the form of filler sheets not impregnated with an epoxy binder, which, after curing, are removed from the surface of the obtained laminate . 3. The method according to p. 1, characterized in that the package is collected from the filler layers so that at least one of the outer layers of the filler package is impregnated with an epoxy binder, modified carbon nanotubes, decorated with metal-containing nanoparticles.

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