Thermal Decomposition and Stability of Hybrid Graphene-Clay/Polyimide Nanocomposites

Abstract

Polyimide matrix nanocomposites have gained more attention in recent years due to their high thermal stability, good interfacial bonding, light weight, and good wear resistance and corrosion, factors that make them find great applications in the field of aerospace and advanced equipment. Many advancements have been made in improving the thermal, mechanical, and wear properties of polyimide nanocomposites. The use of nanofillers such as carbon nanotubes, graphene, graphene oxide, clay, and alumina has been studied. Some challenges with nanofillers are dispersion in the polymer matrix and interfacial adhesion; this has led to surface modification of the fillers. In this study, the interaction between clay and graphene to enhance the thermal and thermal-oxidative stability of a nanocomposite was studied. A polyimide/graphene nanocomposite containing ~12.48 vol.% graphene was used as the base nanocomposite, into which varying amounts of clay were added (0.45-9 vol.% clay). Thermogravimetric studies of the nitrogen and air atmospheres showed an improvement in thermal decomposition temperature by up to 50 °C. The presence of both fillers leads to increased restriction in the mobility of polymer chains, and thus assists in char formation. It was observed that the presence of clay led to higher decomposition temperatures of the char formed in air atmosphere (up to 80 °C higher). This led to the conclusion that clay interacts with graphene in a synergistic manner, hence improving the overall stability of the polyimide/graphene/clay nanocomposites.

Keywords: clay; graphene; nanocomposites; polyimide.

Figure 1

SEM images with EDAX for (top) neat PI, (middle) PI-NGS-0 vol.% clay, and (bottom) PI-NGS-9 vol.% clay, at a magnification of ×25,000.

Figure 2

TGA thermograms for neat polyimide, graphene, and Cloisite 30B clay in nitrogen atmosphere at a heating rate of 30 °C/min.

Figure 3

TGA mass loss profiles of PI-NGS-Clay nanocomposites in nitrogen atmosphere at a heating rate of 30 °C/min.

Figure 4

Derivative TGA curves of PI-NGS-Clay nanocomposites in nitrogen atmosphere at a heating rate of 30 °C/min.

Figure 5

Variation of the rate of degradation of the polymer matrix as a function of the volume percentage of clay in the nanocomposites (in nitrogen; β = 30 °C/min).

Figure 6

Graph showing the TGA degradation profiles for polyimide, Cloisite 30B organomodified clay, graphene, and PI-NGS-0.45 vol.% clay in air at a heating rate of 30 °C/min.

Figure 7

TGA degradation profiles of PI-NGS-Clay nanocomposites in air at a heating rate of 30 °C/min.

Figure 8

Derivative TGA curves of PI-NGS-Clay nanocomposites showing the degradation regions for (I) imide unit and (II) the polymer char (III) graphene and clay.

Figure 9

Variation of the rate of degradation of the imide unit and the char for PI-NGS-Clay nanocomposites, as a function of the vol.% clay.

Figure 10

DSC thermograms for the hybrid composites obtained in nitrogen atmosphere at a heating rate of 10 °C/min.

Figure 11

Variation of the total heat released during the degradation of PI–NGS–Clay samples with changing vol.% clay as measured by DSC in nitrogen atmosphere.

Figure 12

DSC thermograms for the hybrid composites, PI–NGS–Clay, containing, (I) 0 vol.% and (II) 9 vol.% clay in air atmosphere.

Figure 13

DSC thermograms for the hybrid composites, PI–NGS–Clay, containing, (I) 2.25, (II) 4.5, (III) 0.45, and (IV) 9 vol.% clay in air atmosphere.

Figure 14

Variation of the decomposition peak height and the maximum decomposition temperature for the hybrid composites as a function of clay vo.%.

Figure 15

Variation of the onset temperature of decomposition of PI-NGS-Clay nanocomposites as a function of composition.