*4.4.2. Influence of nanosized filler on physicomechanical characteristics of film composite materials*

The effect of different contents of nanostructured silicon carbide and carbon nanotubes on the physicomechanical characteristics of the resulting film composite materials was studied.

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

98 Characterizations of Some Composite Materials

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

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

ties of the composites.

*materials*

for two kinds of matrices (matrix No. 1 and matrix No. 2).

so the maximum value of the viscosity for the latter is much lower.

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

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,

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 proper-

The effect of different contents of nanostructured silicon carbide and carbon nanotubes on the physicomechanical characteristics of the resulting film composite materials was studied.

*4.4.2. Influence of nanosized filler on physicomechanical characteristics of film composite* 

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

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

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 temperature and then at 350°C for 15 min.

Film composite materials were also produced on two types of matrices (matrix No. 1 and matrix No. 2).

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, and the amount of filler.

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 in the content of filler (more than 1%) promotes the agglomeration of particles, causing significant difficulties in obtaining a homogeneous system; this leads to a deterioration in the physicomechanical parameters.

As can be seen from **Figures 13** and **14**, the type of filler has a significant effect on the nature of the intermolecular interaction. Fillers with a modified surface make it possible to increase the intermolecular interaction, increase the number of intermolecular bonds that carry a mechanical load upon deformation, and also reduce the probability of thermofluctuation rupture of macromolecules in defective areas. From the data obtained, it can be seen that the tensile strength increases significantly in samples containing modified fillers, which is explained by an increase in the dispersibility of the filler particles when the surface is modified. The increase in strength indexes with the use of modified fillers is also associated with an increase in the degree of dispersion of the filler and an increase in the degree of homogeneity of the polyamide acid.

Thus, it was found that the optimal content of nanostructured SiC in the samples PMDA + ODA, BTDA + pPDA is 0.1 wt.%, which provides the maximum increase in tensile strength and elongation at break due to the alignment of internal stresses in the films. For composites with carbon nanotubes based on matrix No. 1, it is 0.25 wt.%, and for matrix No. 2, it is 0.1 wt.%. A different optimum of filling of polymer matrices is associated with different sizes of SiC and CNT particles.

*4.4.3. Influence of nanosized filler on thermal stability and thermooxidative stability of the* 

films and one-step method—in the form of powders).

thesis method (matrix No. 1, matrix No. 2, matrix No. 3).

obtain a composite based on it by a two-step synthesis.

content of the filler is shown below in **Figures 15**–**17**.

carried out, which are registered in an inert and oxidizing atmosphere.

The influence of the content of inorganic fillers with modified and unmodified surfaces on the thermal stability in an inert gas atmosphere (argon) and thermooxidative stability in air was studied. Composite materials were obtained in two ways (two-stage method—in the form of

**Figure 14.** Dependence of physicomechanical properties of the composite based on the BTDA/pPDA matrix on the

Nanocomposite Polyimide Materials http://dx.doi.org/10.5772/intechopen.79889 101

Powders of composite materials on three types of matrices were obtained by a one-stage syn-

Due to the low activity of 4-[4-(4-aminophenoxy) phenoxy] phenylamine, it is not possible to

Two-stage synthesis composites on two kinds of matrices were obtained (matrix No. 1 and

To evaluate the effect of nanostructured fillers on thermal stability and thermooxidation stability, differentiation of thermogravimetric curves of the resulting composite materials was

The dependence of thermooxidative stability and thermal destruction of the composite on the

*resulting composites*

content of the filler.

matrix No. 2).

**Figure 13.** Dependence of physicomechanical properties of the composite based on the PMDA/ODA matrix on the content of the filler.

**Figure 14.** Dependence of physicomechanical properties of the composite based on the BTDA/pPDA matrix on the content of the filler.
