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

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

Powders of composite materials on three types of matrices were obtained by a one-stage synthesis method (matrix No. 1, matrix No. 2, matrix No. 3).

Due to the low activity of 4-[4-(4-aminophenoxy) phenoxy] phenylamine, it is not possible to obtain a composite based on it by a two-step synthesis.

Two-stage synthesis composites on two kinds of matrices were obtained (matrix No. 1 and matrix No. 2).

To evaluate the effect of nanostructured fillers on thermal stability and thermooxidation stability, differentiation of thermogravimetric curves of the resulting composite materials was carried out, which are registered in an inert and oxidizing atmosphere.

The dependence of thermooxidative stability and thermal destruction of the composite on the content of the filler is shown below in **Figures 15**–**17**.

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

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

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

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.

physicomechanical parameters.

100 Characterizations of Some Composite Materials

polyamide acid.

content of the filler.

described as follows. The graph has a maximum at 0.75 wt.%, which corresponds to the percolation threshold of carbon nanotubes in this matrix; this does not depend on the degree of

**Figure 16.** Dependence of thermooxidative stability (left) and thermal destruction (right) of the composite based on the

Nanocomposite Polyimide Materials http://dx.doi.org/10.5772/intechopen.79889 103

To confirm the revealed regularities, the effect of nanostructured silicon carbide and carbon nanotubes on a polyimide matrix with a more "flexible" structure, which is matrix No. 3

It was shown that the percolation threshold with the introduction of nanoSiC is in the range of 0.05 wt.% and there is a significant increase in thermooxidative stability and resistance to thermal destruction of powders of composites obtained by a single-step process. The addition of carbon nanotubes to matrix No. 3 also increases these material properties up to 0.75 wt.%, with a decrease in these parameters at 0.5 wt.%, which was also observed in other

As can be seen from the presented data, the effect of nanostructured silicon carbide and carbon nanotubes on different matrices is very different, but practically does not depend on the method of obtaining the composite material. The difference exists only in the numerical value

**Figure 17.** Dependence of thermooxidative stability (left) and thermal destruction (right) of the composite based on the

BTDA/pPDA matrix on the content of nanostructured carbon nanotubes.

modification of the filler nor on the method of its preparation (**Figure 17**).

BTDA/pPDA matrix on the content of nanostructured silicon carbide.

(PMDA/AFFA), was studied.

experiments.

**Figure 15.** Dependence of thermooxidative stability (left) and thermal destruction (right) of the composite based on the PMDA/ODA matrix on the content of the filler.

The dependence of the effect of carbon nanotubes on thermal stability and thermal oxidation stability of composite materials based on matrix No. 1 is similar to the effect of the introduction of nanostructured silicon carbide. However, in view of the different particle sizes of these fillers, the percolation threshold for carbon nanotubes is higher and the maximum point is 0.75 wt.%. Also, in the case of introducing carbon nanotubes, a decrease in the thermal properties at 0.5 wt.% is observed in all samples with different degrees of surface modification. This is probably due to the fact that with this filler content, it is not possible to obtain a highmolecular weight polymer.

When studying the effect of nanostructured silicon carbide on the properties of thermal stability of composite materials based on No. 2 (BTDA/pPDA) matrix, it was shown that the introduction of this filler into the polymer in a one-step synthesis does not significantly affect the thermooxidative stability of the resulting composite materials, which cannot be said about a two-stage method of production where a maximum is observed with a modified filler content of 0.5 wt.%, and an increase of more than 60°C. The effect of nanostructured silicon carbide on thermal degradation turned out to be completely opposite (**Figure 16**).

Due to the high thermal and oxidative stability of matrix No. 2, the introduction of carbon nanotubes affects negatively this parameter, and it decreases with increasing filler content. At the same time, the influence of the content of CNTs with different degrees of surface modification on the thermal destruction of a composite based on the BTDA/pPDA matrix can be

**Figure 16.** Dependence of thermooxidative stability (left) and thermal destruction (right) of the composite based on the BTDA/pPDA matrix on the content of nanostructured silicon carbide.

described as follows. The graph has a maximum at 0.75 wt.%, which corresponds to the percolation threshold of carbon nanotubes in this matrix; this does not depend on the degree of modification of the filler nor on the method of its preparation (**Figure 17**).

To confirm the revealed regularities, the effect of nanostructured silicon carbide and carbon nanotubes on a polyimide matrix with a more "flexible" structure, which is matrix No. 3 (PMDA/AFFA), was studied.

It was shown that the percolation threshold with the introduction of nanoSiC is in the range of 0.05 wt.% and there is a significant increase in thermooxidative stability and resistance to thermal destruction of powders of composites obtained by a single-step process. The addition of carbon nanotubes to matrix No. 3 also increases these material properties up to 0.75 wt.%, with a decrease in these parameters at 0.5 wt.%, which was also observed in other experiments.

**Figure 15.** Dependence of thermooxidative stability (left) and thermal destruction (right) of the composite based on the

The dependence of the effect of carbon nanotubes on thermal stability and thermal oxidation stability of composite materials based on matrix No. 1 is similar to the effect of the introduction of nanostructured silicon carbide. However, in view of the different particle sizes of these fillers, the percolation threshold for carbon nanotubes is higher and the maximum point is 0.75 wt.%. Also, in the case of introducing carbon nanotubes, a decrease in the thermal properties at 0.5 wt.% is observed in all samples with different degrees of surface modification. This is probably due to the fact that with this filler content, it is not possible to obtain a high-

When studying the effect of nanostructured silicon carbide on the properties of thermal stability of composite materials based on No. 2 (BTDA/pPDA) matrix, it was shown that the introduction of this filler into the polymer in a one-step synthesis does not significantly affect the thermooxidative stability of the resulting composite materials, which cannot be said about a two-stage method of production where a maximum is observed with a modified filler content of 0.5 wt.%, and an increase of more than 60°C. The effect of nanostructured silicon carbide on

Due to the high thermal and oxidative stability of matrix No. 2, the introduction of carbon nanotubes affects negatively this parameter, and it decreases with increasing filler content. At the same time, the influence of the content of CNTs with different degrees of surface modification on the thermal destruction of a composite based on the BTDA/pPDA matrix can be

thermal degradation turned out to be completely opposite (**Figure 16**).

PMDA/ODA matrix on the content of the filler.

102 Characterizations of Some Composite Materials

molecular weight polymer.

As can be seen from the presented data, the effect of nanostructured silicon carbide and carbon nanotubes on different matrices is very different, but practically does not depend on the method of obtaining the composite material. The difference exists only in the numerical value

**Figure 17.** Dependence of thermooxidative stability (left) and thermal destruction (right) of the composite based on the BTDA/pPDA matrix on the content of nanostructured carbon nanotubes.

of the parameter being determined, but not in the character of the curve and the extremum points.

**Author details**

**References**

SiO2

Vasily Retivov and Olga Zhdanovich

\*Address all correspondence to: egorov@irea.org.ru

Institute» – IREA), Moscow, Russian Federation

Anton Yegorov\*, Marina Bogdanovskaya, Vitaly Ivanov, Olga Kosova, Kseniia Tcarkova,

Nanocomposite Polyimide Materials http://dx.doi.org/10.5772/intechopen.79889 105

The Federal State Unitary Enterprise, Institute of Chemical Reagents and High Purity Chemical Substances of National Research Centre «Kurchatov Institute» (NRC «Kurchatov

[1] Zou H, Wu S, Shen J. Polymer/silica nanocomposites: Preparation, characterization, properties, and applications. Chemical Reviews. 2008;**108**:3893-3957. DOI: 10.1021/cr068035q

[2] Wang PJ, Lin CH, Chang SL, Shih SJ. Facile, efficient synthesis of a phosphinated hydroxyl diamine and properties of is high-performance poly(hydroxylimides) and polyimide–

 hybrids. Polymer Chemistry. 2012;**3**:2867-2874. DOI: 10.1039/C2PY20156A [3] Agag T, Koga T, Takeichi T. Studies on thermal and mechanical properties of polyimide– clay nanocomposites. Polymer. 2001;**42**:3399-3408. DOI: 10.1016/S0032-3861(00)00824-7 [4] Zhu J, Wei S, Haldolaarachchige N, Young DP, Guo Z. Electromagnetic field shielding polyurethane nanocomposites reinforced with core–shell Fe–silica nanoparticles. The

Journal of Physical Chemistry C. 2011;**115**:15304-15310. DOI: 10.1021/jp2052536

Science. 2005;**283**:392-396. DOI: 10.1016/j.jcis.2004.08.184

2002;**38**:815-828. DOI: 10.1016/S0014-3057(01)00229-4

**37**:907-974. DOI: 10.1016/j.progpolymsci.2012.02.005

Tekhnologiya vysokomolekulyarnyh soedinenij. (Russian)

polimerov. Nauka. 1983;**310**:5-80 (Russian)

DOI: 10.1016/j.cplett.2005.10.088

[5] Kobayashi Y, Katakami H, Mine E, Nagao D, Konno M, Liz-Marzan LM. Silica coating of silver nanoparticles using a modified Stöber method. Journal of Colloid and Interface

[6] Bessonov MI, Koton MM, Kudryavcev BB, Lajus LA. Poliimidy – klass termostojkih

[7] Hsiao SH, Chen YJ. Structure–property study of polyimides derived from PMDA and BPDA dianhydrides with structurally different diamines. European Polymer Journal.

[8] Liaw DJ, Wang KL, Huang YC, Lee KR, Lai JY, Ha CS. Advanced polyimide materials: Syntheses, physical properties and applications. Progress in Polymer Science. 2012;

[9] Myakin SV, Sychev MM, Zagranichek AL, Vasil'eva IV. Issledovanie radiacionnoj stojkosti plenok poliimida pod vozdejstviem vysokih doz uskorennyh ehlektronov.

[10] Shigeta M, Komatsu M, Nakashima N. Individual solubilization of single-walled carbon nanotubes using totally aromatic polyimide. Chemical Physics Letters. 2006;**418**:115-118.

Thus, it was found that to increase thermal and oxidative stability and resistance to thermal degradation:

