JEC COMPOSITES MAGAZINE - Issue #130 - September/October 2019 - 26

BUSlNESS advanced material
*	 Poor load transfer
*	 Poor interfacial engineering
*	 Poor dispersion throughout
the composite matrix

*	 Viscosity-related

processing challenges
Fig. 3: Technical issues
to be addressed

to conduct heat to another
material very well. This is why
we boil water in metal teapots
rather than wooden ones.
Graphene's thermal conductivity is among the highest of
any known material. What this
means in terms of composites
is that it should enable these
materials to better cope with
high temperatures.
Of course, there is also
graphene's renowned electrical
conductivity.
This means that electrons can pass
throughthematerialwithoutmuch
of anything interrupting their
path. Obviously, if you can
transfer this property into
a composite, it could mean
materials that in turn could
be used for applications that
were out of the realm of
the possibility for polymers using traditional reinforcement
filler materials.
Composite applications enabled by graphene's electrical
conductivity include ice protection systems, structural health
monitoring, and lightning strike
protection.
These are all very attractive
qualities for composites. But
if this is the case, why hasn't
there been a wider adoption
of graphene materials in composites?
Challenges for
graphene composites
This slower than anticipated
adoption is due to a number
of factors, some of them
being fairly technical. One
of these technical issues is

26

poor interfacial load transfer,
which involves the forces that
must be transferred between
the different materials that
make up the composite.
This means that when a
composite comes under some
mechanical deformation, the
external load is not sufficiently
transferred through to the
graphene and, therefore, the
high-strength properties of
the graphene are severely
underutilised.
In addition to these issues
related to the final composite
products, graphene faces some
process and manufacturing
challenges.
It can be tricky to get graphene
to disperse throughout the matrix evenly. Depending on the
type of graphene material used
and the load factor (amount of
graphene as a percentage of the
total material mix), issues with
increased viscosity at increasingly higher load factors can
make it difficult to use in
composite manufacturing processes (Figure 3).
Technical issues to be addressed
include:
-Choosing the right form of
graphene for the application, Dispersing the graphene evenly in the host matrix, - Using
the right amount of graphene
(load factor), whereby it is
often better to use a very low
amount.
Another problem that graphene
faces is that, as a high-aspect-ratio material that can be less than

a nanometre high in the Z-axis,
it is atomically smooth. When
attempting to use the material
as a strong matrix filler bond,
you want there to be a rougher
surface. Atomically smooth in
this case is a definite shortcoming. Since it is not a particularly
good filler bond, it leads to the
aforementioned poor interfacial
load transfer when it is mechanically stressed.
But all is not lost. Carbon fibre
composites suffered from the
same interfacial problems
years ago, before the industry
figured out that they could
apply appropriate "sizing"
chemistry and surface treatments to the fibres. However,
in the case of graphene - and
its carbon nanomaterial cousin, carbon nanotubes - the
interfacial issue is a bit more
severe. In addition, if you start
to chemically modify these
nanomaterials, you may lose
some of the attractive properties that drew you to graphene
and carbon nanotubes in the
first place. Nonetheless, some
chemical modification has to
be done to graphene in order
to get it to disperse throughout the composite matrix. If
graphene is not at least surface
treated, it will begin to aggregate because of the strong
nanoscale forces known as Van
der Waals interactions that
draw the particles together.
If the challenges of dispersion
and controlling the viscosity
can be addressed through
chemical treatments without
compromising the intrinsic
properties of graphene, then
even the most sceptical might
begin to feel that graphene
can be a game changer for
composite materials if more
modifications can be made to
them without sacrificing their
properties.

	 jec composites magazine / N°130 September - October 2019

How do you get
graphene to work
best in composites?
One of the main practical
issues for graphene in composites is how to disperse
it in a matrix material. This
dispersion needs to increase
the loading fractions of these
fillers without making them
so thick (viscosity-related
issues) that they are difficult
to process. Another challenge
has been that once you create
a graphene-based composite,
how can you best test and
measure it under stress to determine how effective the load
transfer is in the composite.
So far, the answer on how to
get graphene to work best in
composites is through systematic testing to determine the
best combinations for a given
composite resin system or host
material. Iterative attempts
have been how industry has
thus far figured out how to
get these composites to work.
This iterative process can
sometimes take years. It often
involves a graphene producer
and a composites manufacturer working together to figure
out how to achieve the best
process parameters: how to
best mix the materials, what
are the best dispersions, what
cures to achieve and how different surface activations affect
the materials.
Surface
activations
that
introduce functional chemical groups on the surface
of graphene can be a critical
element of how it will work
in a composite. For instance,
some graphene may have a lot
of oxygen on its surface. Since
oxygen is an insulator, you are
not going to get the best electrically-conductive graphene
with high oxygen content.
JEC COMPOSITES MAGAZINE - Issue #130 - September/October 2019

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #130 - September/October 2019
