Figure 1. Low-resolution transmission electron micrographs of the graphene-carbon nanotube hybrid material for the production of fiber-reinforced polymer composites.

The high-resolution transmission electron micrographs of the graphene-carbon nanotube hybrid material are illustrated in Figure 2 for the production of fiber-reinforced polymer composites. The porous mat comprising graphene-carbon nanotubes is contacted with one or more condensation polymer precursors, and optionally a catalyst. Under polymerization conditions, the condensation polymer precursors undergo in situ polymerization to produce a condensation polymer which forms the polymer component of the graphene-carbon nanotube fiber-reinforced polymer composite. As the polymerization step is performed in the presence of the mat, the mat of entangled graphene-carbon nanotubes maintains it nanostructured sheet form and becomes embedded in the condensation polymer, and a nonporous graphene-carbon nanotube fiber-reinforced polymer composite is formed. The composite is nonporous as a result of the condensation polymer occupying the openings previously present between adjacent graphene-carbon nanotubes, or between adjacent ropelike structures of graphene-carbon nanotubes, within the mat. The condensation polymer precursors are polymerized in the presence of the mat under suitable polymerization conditions to form a nonporous fiber-reinforced polymer composite comprising a mat of graphene-carbon nanotubes embedded in the condensation polymer produced from the polymer precursors. Suitable polymerization conditions include sufficient pressure, temperature, time, and other process conditions for polymerization of the polymer precursors to occur. Suitable polymerization conditions can include addition of a catalyst. The poor dispersibility of graphene-carbon nanotubes greatly affects the characteristics of the composites which they form with the polymer matrices into which they are introduced. There is observed in particular the appearance of nano-cracks, formed in aggregates of graphene-carbon nanotubes, which lead to the composite becoming fragile. Moreover, since graphene-carbon nanotubes are poorly dispersed, it is necessary to increase their amount in order to reach a given electrical and thermal conductivity, which has the effect of increasing the viscosity of the mixture for manufacturing the composite, leading to self-heating of this mixture which may result in degradation of the polymer and a reduction in productivity. Thermal properties refer to a material's response to applied heat. Non-limiting examples include thermal conductivity, thermal diffusivity, coefficient of thermal expansion, emissivity, specific heat, melting point, glass transition temperature, boiling point, flash point, triple point, heat of vaporization, heat of fusion, pyrophoricity, autoignition temperature, and vapor pressure.