**4.2. Modification of the nanofiller surface**

#### *4.2.1. Modification of the surface of carbon nanotubes*

To date, there are no generally accepted standards describing the characteristics and properties of manufactured nanotubes. Their properties are individual for each manufacturer. Nanotubes can initially differ in diameter (and number of layers), average length, content of impurities (primarily amorphous carbon, metal catalyst residues and adsorbates), degree of aggregation, and other less important parameters.

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 also reduces the amount of residual amorphous carbon.

The presence of the ─C(O)OH group is judged by the presence in the IR spectrum of the characteristic bands νс〓<sup>о</sup> = 1614–1620 cm −<sup>1</sup> (─СОО−) and νс〓<sup>о</sup> = 1710–1735 cm −<sup>1</sup> (─СООН), and also bands at 1585–1590, 1200–1205 and 1800 cm−<sup>1</sup> .

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

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

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

For mixing in solution, the polymer matrix must be soluble in at least one solvent. This is problematic for many polymers. Melt mixing is generally applicable and fairly simple, especially when used in the case of thermoplastic polymers. In the melt spinning process, carbon nanotubes are mechanically dispersed in the polymer matrix using a high-shear mixer at high temperature [26]. This approach is simple and compatible with existing industrial technolo-

The disadvantage of this method is that this method produces a dispersion of carbon nanotubes in the polymer matrix, which is significantly worse than the dispersion that can be achieved by mixing in solution. In addition, carbon nanotubes should be smaller because of

Using this method, carbon nanotube or nanostructured silicon carbide is dispersed in the monomer followed by polymerization. Moreover, a higher percentage of fillers can be easily dispersed, and they form a strong interaction with the polymer of the matrix. This method is used for the preparation of composites with polymers that cannot be processed by mixing in

In the case of using a polyimide matrix, which is obtained by polycondensation, it is expedi-

To date, there are no generally accepted standards describing the characteristics and properties of manufactured nanotubes. Their properties are individual for each manufacturer. Nanotubes can initially differ in diameter (and number of layers), average length, content of

gies. Shear forces destroy CNT aggregates and prevent their formation.

the high viscosity of the composites with a higher content of carbon nanotubes.

solution or melt mixing, for example insoluble and thermally unstable polymers.

that ultrasonic cavitation can generate high local temperature and pressure [25].

homogenizers, ball mills, and colloidal mills.

94 Characterizations of Some Composite Materials

*4.1.2. Melt mixing*

*4.1.3. In-situ polymerization*

ent to use the in-situ polymerization method.

*4.2.1. Modification of the surface of carbon nanotubes*

**4.2. Modification of the nanofiller surface**

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 use dried solvents to modify the filler surface with it.

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 compound was estimated).
