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.