Figure 2. High-resolution transmission electron micrographs of the graphene-carbon nanotube hybrid material for the production of fiber-reinforced polymer composites.
The effect of the weight fraction of the graphene-carbon nanotube hybrid material on the modulus of elasticity is illustrated in Figure 3 for the fiber-reinforced polymer composite. Intense research has been focused on polymer nanocomposites because of their potential to dramatically enhance properties relative to neat polymer and to yield multifunctional materials [53, 54]. Carbon nanotubes have been extensively studied as nanofillers because of their low density, high aspect ratio, and excellent mechanical, electrical, and thermal properties [55, 56]. However, major challenges remain in the development of polymer-carbon nanotube nanocomposites, especially as related to carbon nanotube dispersion via industrially scalable, environmentally friendly methods and understanding the relationship between dispersion and optimum properties [57, 58]. Several strategies have been studied to achieve well-dispersed polymer-carbon nanotube nanocomposites, including melt mixing, polymer-carbon nanotube blending in solvent, and in situ polymerization [59, 60]. Use of melt mixing alone often leads to limited carbon nanotube dispersion in polymer. Blending polymer and in situ polymerization methods can lead to better dispersion, but the former is not environmentally friendly and both methods have limited applicability and scalability. One or more mechanical or physical properties of the graphene-carbon nanotube fiber-reinforced polymer composite are enhanced, including but not limited to increased Young’s modulus and increased yield strength, electrical conductivity, thermal stability and crystallization rate, as compared to the corresponding neat polymer. For example, the modulus of elasticity of the composite is enhanced as compared to the corresponding neat polymer. The method of preparing the composite comprises providing a polymer component and a graphene-carbon nanotube mixture; applying a mechanical energy thereto through solid-state shear pulverization in the presence of cooling at least partially sufficient to maintain such a polymer component in a solid state, such pulverization at least sufficient to provide a pulverization product comprising a graphene-carbon nanotube component at least partially homogeneously dispersed therein; and melt-mixing such a pulverization product, to provide a graphene-carbon nanotube fiber-reinforced polymer composite. Crystallization kinetic effect can be selected from increased rate of isothermal crystallization and decreased distribution of crystallization time. Solid-state shear pulverization and melt-mixing can be at least partially sufficiently to affect a mechanical and physical property of such a mixture, such a property as can be selected from Young’s modulus, yield strength, electrical conductivity, and thermal stability. Dispersion can be characterized by field-emission scanning electron microscopy and the absence of agglomeration at micron-length scales under microscopy conditions.