*4.1.1. Mixing in solution*

With this approach, the dispersion of carbon nanotubes in a suitable solvent and the polymer are mixed in solution. The CNT/polymer composite is formed by precipitation or by evaporation of the solvent. It is well known that it is very difficult to efficiently disperse nanotubes in a solvent by simple mixing. Processing with high-power ultrasound is more effective in the formation of the dispersion of CNTs. Ultrasonic treatment is widely used for dispersing, emulsifying, crushing, and activating particles. With the help of ultrasound, it is possible to effectively destroy aggregates and coils of carbon nanotubes.

The chemical effects of ultrasonic dispersion are associated with a rapid (on a scale of microseconds) intensive collapse of cavitation bubbles created during the passage of ultrasonic waves through a liquid medium [24]. Sonochemical theory and related studies have shown that ultrasonic cavitation can generate high local temperature and pressure [25].

impurities (primarily amorphous carbon, metal catalyst residues and adsorbates), degree of

In order to effectively use carbon nanotubes as a component of polymer composites, it is considered advisable to modify their surface to increase the strength of the nanotube and polymer matrix interaction, as well as to improve the dispersibility of nanotubes. To solve this problem, a functionalization method has been chosen that allows the creation of carboxyl functional groups on the surface of nanotubes, since this allows binding of the filler with covalent bonds to the polymer molecule; this is achieved by oxidation of the initial nanotubes with a mixture of nitric and sulfuric acids. Such functionalization of nanotubes is accompanied by the opening of their ends and, in some cases, by "cutting" nanotubes during oxidation. Also, oxygen-containing groups create a negative electrostatic charge on the surface, which contributes to less aggregation and better dispersibility. Oxidative functionalization

The presence of the ─C(O)OH group is judged by the presence in the IR spectrum of the

As a modifying agent capable of forming strong contacts with inorganic particles, organosilicon compounds containing alkoxysilyl groups are most often used. The interaction of organosilicon compounds with silicon oxide, which is present on the surface of nanostructured silicon carbide, chemically binds the organosilicon fragment and the surface hydroxyl groups of the particle. This leads to the hydrophobization of the surface of the filler particle, which makes it possible to form a strong contact with the polymer. In addition, a reactive amino group appears on the surface of the particles, allowing additional covalent binding to be achieved.

In this case (3-aminopropyl) triethoxysilane (trade name: Silane coupling agent KN-550) was used as the modifying agent, which has a wide field of application in the field of composites production. This cross-linking agent is very sensitive to moisture; therefore, it is necessary to

To evaluate the effectiveness of surface modification of nanostructured silicon carbide, infrared spectroscopy and the CHNS method were used (the nitrogen content of the final com-

The main process for obtaining dispersion-filled plastic masses (for the preparation of composites based on polyimide and CNT or nanostructured silicon carbide) is mixing. These are complex physicomechanical and physicochemical processes associated with the action of force fields, the displacement of the original components of the mixture in the reactor volume along complex trajectories, with the formation of a system characterized by a randomly dis-

**4.3. Preparation of composite materials based on silicon carbide and carbon** 

(─СОО−) and νс〓<sup>о</sup> = 1710–1735 cm −<sup>1</sup>

.

(─СООН),

Nanocomposite Polyimide Materials http://dx.doi.org/10.5772/intechopen.79889 95

aggregation, and other less important parameters.

also reduces the amount of residual amorphous carbon.

and also bands at 1585–1590, 1200–1205 and 1800 cm−<sup>1</sup>

use dried solvents to modify the filler surface with it.

pound was estimated).

tributed distribution of components.

**nanotubes**

*4.2.2. Modification of the surface of nanostructured silicon carbide*

characteristic bands νс〓<sup>о</sup> = 1614–1620 cm −<sup>1</sup>

Nanomaterials tend to agglomerate with stirring in a liquid, while the creation of nanocomposites requires efficient dispersion and a uniform distribution of nanoparticles in the liquid.

To overcome the strength of the bonds after wetting the powder, effective ways of deagglomeration and dispersion are needed. The ultrasonic disintegration of agglomerates in suspensions allows full use of the potential of nanomaterials. Studies on various dispersions of agglomerates of nanoparticles with different solids content have demonstrated significant advantages of ultrasound compared to other technologies, such as rotary agitators, piston homogenizers, ball mills, and colloidal mills.
