RU2500695C1 - Method of preparing nanosuspension for producing polymer nanocomposite - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves preparing a nanosuspension by adding carbon nanotubes to a reactive plastic binder with ultrasonic exposure in a cavitation zone with intensity of 15-25 kW/m². Carbon nanotubes are dispersed in the binder with simultaneous photographic recording of changes in colour intensity of the nanosuspension. When the nanosuspension reaches colour intensity values corresponding to standardised dispersion values in the range of 0.9 to 0.99, ultrasonic exposure is stopped.

EFFECT: method enables to optimise dispersion of carbon nanotubes in the binder and cut the duration of preparing high-strength nanocomposites owing to uniform distribution of nanoparticles in the nanocomposite.

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Description

Technical field

The invention relates to the field of manufacturing polymer nanocomposites on a thermoplastic binder for space, aviation, building and other structures (fiberglass, carbon fiber, organoplastics, etc.).

State of the art

The introduction of carbon nanotubes (CNTs) into the composition of a polymer, for example polyester, nanocomposite nanocomposite, thereby forming a nanosuspension for the manufacture of a nanocomposite, significantly increases the strength properties of products. Moreover, the optimal concentration and uniform distribution of CNTs in the binder play a decisive role.

Known methods for the preparation of nanosuspension in the manufacture of nanocomposites. For example, to uniformly distribute a predetermined amount of CNTs over the volume of a binder, special mixers with blades and pressing chambers are also used using ionization of nanoparticles (RF patent No. 2301771, IPC В82В 3/00, published: June 27, 2007).

The closest technical solution is a method of manufacturing a polymer / carbon nanotube composite (RF patent No. 2400462, IPC С07С 1/00, В82В 1/00, published: 09/27/2010), in which ultrasonic (ultrasound) exposure is used to uniformly distribute nanoparticles to the mixture. Ultrasonic exposure ensures the destruction of agglomerates from CNTs and a uniform distribution of agglomerates of a lesser degree (size) in terms of the volume of nanosuspension, however, the determination of the time of dispersion of CNTs in this method is not provided. Insufficient processing time does not ensure uniform distribution of nanoparticles, and if the dispersion process is excessively long, the process of destruction of the longest CNTs can begin, which will lead to a decrease in the strength of the composite being manufactured.

Disclosure of invention

The objective of the invention is to determine the minimum required time for dispersion of CNTs in a binder in order to achieve almost complete dispersion of CNTs.

The problem is solved due to the fact that in the method of preparing nanosuspension for the manufacture of a polymer nanocomposite by dispersing carbon nanotubes into a thermoplastic binder in the process of ultrasonic treatment, the process of dispersing carbon nanotubes in a binder is carried out with simultaneous photo-registration of changes in the color intensity of nanosuspension, and when the nanosuspension reaches the color intensity values corresponding to values of the normalized degree of dispersion in the range from 0.9 to 0.99, the ultrasonic effect is stopped, while the normalized degree of dispersion for a given concentration is determined previously, and the ultrasonic effect of the resulting nanosuspension is carried out with intensity in the cavitation zone in the range from 15 to 25 kW / m ² .

List of drawings

Figure 1 shows an example of a graphical dependence of the NSD of CNTs on processing time. Figure 2 shows a photo of CNTs in the initial state (agglomerated) and after dispersion.

Figure 3 shows the dependence of the strength of the manufactured samples from polyester resin on the concentration of CNTs and the normalized degree of dispersion.

The implementation of the invention

It was found that the degree of dispersion of CNT nanoparticles at a given concentration of CNTs corresponds to the color intensity of nanosuspension, which changes as the process of dispersion under ultrasonic treatment is carried out. The composite obtains the best strength properties when all agglomerates are destroyed and CNTs are evenly distributed over the binder volume. In this case, the color intensity of nanosuspension assumes the maximum steady-state value for a specific ratio of CNTs and binder, and does not change with further exposure to ultrasound. We determine that in this case the nanosuspension has a normalized degree of dispersion (NSD) equal to 1 (unit). The introduction of the NSD parameter (proportional to the color intensity of nanosuspension) allows us to evaluate and compare the degree of dispersion of nanosuspension with a wide variety of CNT concentrations, since the specific values of the color intensities will vary, and, sometimes, very significantly. Immediately after the introduction of CNTs into the binder, the degree of dispersion is zero, since CNTs are introduced in the form of an agglomerate, and when mixed with a binder under the conditions of ultrasound, the effects of NSD change from zero to a certain value.

As deagglomeration and uniform distribution of particles in the binder occurs, the color intensity of the nanosuspension changes from a transparent state, through a gradual turbidity until the color intensity reaches a steady state. The steady-state intensity level is reached at a certain processing time, beyond which either the remaining agglomerates are not destroyed, or all CNT nanoparticles are distributed evenly (there are no agglomerates in nanosuspensions in this case). The continuation of the process of ultrasonic exposure in excess of this value is useless from the point of view of achieving better dispersion and harmful from the point of view of the safety of CNTs, which, with prolonged ultrasonic exposure, can violate their integrity.

The specified method is implemented as follows. After a preliminarily obtained optimal concentration of CNTs in the binder, which is selected as a polyester resin, the required amount of CNTs is introduced into the fluid-flow reactive plastic binder of the nanocomposite. After preliminary manual (or mechanical) mixing of the CNTs with a binder, an ultrasonic emitter is introduced into the mixture, voltage is supplied to the ultrasonic generator. Ultrasonic treatment of the resulting nanosuspension occurs with intensity in the cavitation zone in the range of at least 15 ... 20 kW / m ² .

In this case, photographing (or filming) is conducted by a directed camera through the transparent wall of the vessel, in which the CNT mixing process is carried out. Image processing by color intensity and the calculation of the values of NSD are carried out using the computer program Image Analysis - Media Cybernetics - Image Pro Plus 6.0. Photorecording frames are selected with a frequency of 1 ... 4 seconds so that the obtained NSD values allow us to construct a curve of their change quite adequately, given that the dispersion time of nanosuspension, as practice shows, is from about 10 seconds to several minutes, depending on the viscosity of the liquid phase. Further processing leads to an extremely insignificant increase in NSD, which practically does not affect the strength of the manufactured nanocomposite (see figure 1).

With the dispersion of CNTs, the color intensity (color - gray-black) of nanosuspension increases, tending to a certain steady state value corresponding to the complete dispersion of nanotubes in the binder. This state is characterized by the complete absence of agglomerates and on the graph of the dependence of the NSD of nanoparticles on the processing time corresponds to NSD = 1.

All intermediate NSD values range from 0 to 1. Graphs are plotted for the NSD parameter, since the specific values of the staining intensity for each nanosuspension will be individual, and it will be much more difficult to analyze the graph of such individual intensities.

Figure 1 shows a graph of the changes in the NSD of the real dispersion process, and line 1 corresponds to the experimental data obtained on the basis of photographic recording, and line 2 is a smoothed approximation of the experimental curve. Based on the foregoing, for this example, the necessary time for ultrasonic treatment, at which the value of the NSD of nanoparticles reaches a value close to unity, corresponds to 12 ... 14 seconds, and the start time of mass deagglomeration of CNTs is 6.4 seconds. This leads to the conclusion that it is possible to fairly accurately set the U3-processing time corresponding to the achievement of the intensity of a predetermined value. For production purposes, the limits of such values are determined in the range of 0.9 ... 0.99. Given the wide variety of properties of CNTs and binders, the dispersion time can vary many times for different combinations. Therefore, the determination of the dispersion time using the proposed method will significantly reduce the development time of technological processes for the manufacture of nanocomposites.

To confirm the dependence of the strength characteristics on the concentration of CNTs and NSDs, experiments were performed. We used multilayer carbon nanotubes (MWNTs) with the following individual characteristics: outer diameter 15.0–40.0 nm, length ≥2 μm, number of layers 5–8, specific surface area 200–250 m ^{2 /} g. Before introduction into the binder CNTs were heat treated in an oven at a temperature of ~ 200 ° C for 5 minutes. Weighing of each injected dose of CNTs was carried out on an electronic balance of KERN-770-60 company (Germany) (accuracy class according to GOST 24104-88 - 1). The first samples were obtained without the introduction of CNTs. Then, samples were made with the introduction of the first dose of CNTs in the amount of 0.001%, etc. After adding a regular dose of CNTs to nanosuspension in an amount of ~ 0.001% (per 1000 g of a binder 0.01 g CNTs) and mixing in a container with the action of ultrasound by immersion of an ultrasonic dispersant LUZD-1.5 / 21-3.0. The ultrasonic treatment time was determined by reaching a NSD value of 0.95 (for various concentrations, the processing time varied from 10 to 18 seconds). The unsaturated isophthalic neopentyl glycol polyester resin B71731AL manufactured by Cray Valley was selected as the matrix. Methyl ethyl ketone peroxide (manufactured by Butanox) was used as a resin curing catalyst. The catalyst was added in an amount of 1% by weight of the resin. The resin with the catalyst was manually mixed for 30–40 seconds. The prepared composition was evacuated in a vacuum chamber at 700 mm. Hg (0.92 kg / cm ² ) for about 4 minutes until the gas inclusions are completely removed, then they are poured into molds and an additional vibration treatment is performed in the mold for about 10-15 minutes. The size of the samples was 200 × 25 × 5 mm, which corresponds to the generally accepted rules for the manufacture of samples for testing.

The curing of the polyester resin was carried out at room temperature. The preforms were heat-treated (post-cured) at 80 ° C for 3 hours. Bending tests of the samples were carried out on a testing machine FP 100/1. Based on the obtained experimental values, a graph was constructed of the dependence of the bending strength of the samples on the concentration of CNTs at various NDC values (Fig. 3).

It should be noted that this method allows you to level the parameters of ultrasound exposure, which can change the shape of the graph and shift it in time.

For illustration, Fig. 2 (a) shows carbon nanotubes in the initial state (agglomerated) (NSD = 0), and Fig. 2 (b) shows nanotubes uniformly distributed in a fluid binder, here the NSD is almost very close to unity.

Claims (1)

A method of preparing nanosuspension for the manufacture of a polymer nanocomposite by dispersing carbon nanotubes into a thermoplastic binder during ultrasonic treatment, characterized in that the process of dispersing carbon nanotubes in a binder is carried out with simultaneous photorecording of changes in the color intensity of nanosuspension, and when the nanosuspension reaches a color intensity value corresponding to the normalized degree dispersion, in the range of 0.9 to 0.99 ul razvukovoe impact stop, the normalized degree of dispersion for a given concentration is determined in advance, and the resulting nanosuspension sonication lead to the intensity of cavitation in the area of 15 to 25 kW / m ^2.

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