**4.4. Properties of the resulting composite materials**

As noted earlier, the polyimide matrices used are insoluble in organic solvents, and their softening temperature exceeds 300°C, which means that it is expedient to use the in-situ

The technologies of obtaining a composite material in the form of a powder and in the form

The process of obtaining a powder of composite material was divided into four stages:

• Modification of the surface of nanostructured silicon carbide or carbon nanotubes

• Dispersion of inorganic filler in a solution of high-boiling solvent and diamine

The process of obtaining a film composite material was divided into five stages:

• Modification of the surface of nanostructured silicon carbide or carbon nanotubes

• Drying of the solvent followed by stepwise imidization in a vacuum drying cabinet

• Carrying out the polymerization reaction to obtain a precursor solution (polyamide acid)

Experiments were carried out to produce composites based on nanostructured silicon carbide with a modified and unmodified surface, and also based on carbon nanotubes with a modified and unmodified surface. These experiments were conducted to study the effect of different contents of inorganic fillers with varying degrees of surface modification on the properties

All the composites obtained were characterized by the methods of elemental analysis, IR spectrometry. Thermal and thermooxidative destruction was evaluated, and the glass transi-

As initial polymer matrices, polyimide matrices with different degrees of structural rigidity

**1.** matrix No. 1 was obtained by the interaction of pyromellitic dianhydride and 4,4′-oxydian-

**2.** matrix No. 2 was obtained by the interaction of 3,3′,4,4′-benzophenone tetracarboxylic acid

**3.** matrix No. 3 was obtained by the interaction of pyromellitic dianhydride and 4-[4-(4-ami-

• Dispersion of inorganic filler in a solution of high-boiling solvent and diamine

• Application of the resulting polyamide acid solution to the substrate

of the resulting composite materials (**Table 1**).

iline (PMDA/ODA) (**Figure 8**);

were chosen.

tion temperature of the resulting materials was determined.

dianhydride and p-phenylenediamine (BTDA/pPDA) (**Figure 9**);

nophenoxy)phenoxy] phenylamine (PMDA/AFFA) (**Figure 10**).

• Carrying out the polymerization and imidization reaction • Isolation of the resulting composite in the form of a powder

polymerization method as a basis.

96 Characterizations of Some Composite Materials

of films were studied.

### *4.4.1. Effect of nanosized filler on the viscosity of the precursor for the production of film composite materials*

Solutions of polyamide acids (PAAs) are precursors in the preparation of polyimide films and composites based on them, and the degree of viscosity of this solution is an important parameter for the success of this experiment.

The effect of different contents of nanosized silicon carbide and carbon nanotubes on the viscosity of a precursor in the preparation of film composite materials was studied.

**Figure 8.** Structural formula of matrix No. 1.

**Figure 9.** Structural formula of matrix No. 2.

**Figure 10.** Structural formula of matrix No. 3.

To assess the effect of different inorganic filler contents on the viscosity of the precursor solution, the filler, dianhydride, diamine, and solvent were mixed in such proportions during the experiment so that a 20 wt.% polyamide acid solution was obtained. Precursors were obtained for two kinds of matrices (matrix No. 1 and matrix No. 2).

As can be seen from the data presented in **Figures 11** and **12**, for each filler with different types of modification on different matrices, there are areas of extremum in which, apparently, the percolation limit value for a given filler in a given polymer is found. The filler with the modified surface binds to the matrix with "hard" covalent bonds, and the filler with the unmodified surface is bound to the matrix by the intermolecular Van der Waals interaction, so the maximum value of the viscosity for the latter is much lower.

From the precursor solutions, the films were cast and subjected to stepwise imidization in a vacuum oven at 80°C for 6 hours, then at 150, 200, 250, and 300°C for 1 hour at each tempera-

**Figure 12.** Dependence of the dynamic viscosity of a precursor for a matrix based on polyimide BTDA/pPDA on the

**Figure 11.** Dependence of the dynamic viscosity of a precursor for a matrix based on polyimide PMDA/ODA on the

Nanocomposite Polyimide Materials http://dx.doi.org/10.5772/intechopen.79889 99

Film composite materials were also produced on two types of matrices (matrix No. 1 and

To assess the effect of nanostructured filler (degree of filling) on strength characteristics, polymer films were tested in terms of basic physicomechanical properties (elongation, tensile strength). It is established that the strength characteristics of the material are significantly influenced by the introduction of a filler into the polymer system. The effective action of the filler is determined by such factors as the shape and size of the particles, the interaction of the filler particles with the polymer, the interaction between the filler particles in the polymer medium,

Based on the data obtained, it can be seen that when the content of the active filler increases to the optimum value, an increase in strength occurs. After achieving the optimum filling, the strength is reduced, and the indicator is subsequently saved at the achieved level. An increase

ture and then at 350°C for 15 min.

matrix No. 2).

content of inorganic fillers.

content of inorganic fillers.

and the amount of filler.

It can be seen from these graphs that in some cases there are two extrema (matrix No. 1 filler carbon nanotubes and matrix No. 2 filler nanostructured SiC and CNT). Probably, this is due to the fact that the filler content that lies between these peaks somehow inhibits the growth of the polymer chain, which has a very negative effect on the viscosity of the PAA solution.

The increase in the viscosity of PAA when CNT is introduced (more than 0.75 wt.%) is associated with the large surface area of carbon nanotubes, which "swell" in the solvent, and this increases the viscosity of the solution. It negatively affected the physico-mechanical properties of the composites.
