JEC COMPOSITES MAGAZINE - Issue #83 - August/September 2013 - 62
Graphene oxide flakes bolster carbon fibre
Industrial carbon fibres – a source of steel-like
strength in ultralight materials – have not improved much in decades because the chemistry
involved is approaching its limits. This study
discusses how graphene oxide could be the
next-generation carbon fibre precursor and lead
to a new era for the carbon fibre industry.
groups on its surface, GO can be easily dispersed in water at up to
7 wt% at room temperature (Figure 1). More importantly, it forms
a liquid crystal phase, starting from only 0.14 vol% . The liquid
crystal phase is difficult to achieve with PAN, which hinders the
alignment of polymer chains within as-spun PAN fibres, retarding
their true graphitization.
Fig. 1: A: SEM image of GO flakes. B: Polarized optical microscope (POM) image
showing liquid crystal phase of 7 wt% GO dispersed in deionized water
Changsheng Xiang, graduate student, Department of Chemistry,
James M. Tour, T.T. and W.F. Chao, Professor of Chemistry,
Professor of Computer Science, Professor of Mechanical Engineering and Materials Science, Smalley Institute for Nanoscale
Science and Technology, Rice University,
The size of GO flakes can range from several up to 100 microns,
which is 3 to 4 orders of magnitude larger than the size of mesophase
pitch (2 nm) used for pitch-based carbon fibres .
Spinning method and coagulation
he effort toward making lightweight, high-strength carbon
fibres has continued since the 1960s . However, the chemistry involved in the two dominant precursors – polyacrylonitrile (PAN) and mesophase pitch – seems to have reached its limit
and not much improvement has been achieved since the 1980s .
Rather than continue to optimize processing techniques with current
precursors, the focus of the modern carbon fibre industry should
switch to a new precursor.
Concept of a new carbon fibre precursor
The ideal precursor for high-performance carbon fibres should first
be able to form a liquid crystal phase in commonly used solvents at
room temperature. Spinning from liquid crystal material would produce fibres with good intrinsic alignment, a key to high performance.
In addition, the size of the precursor (whether rod- or disk-shaped)
is important. Since carbon fibre always fractures at flake boundaries
and interfaces, larger disks or longer rods would reduce the number
of boundaries and improve its mechanical properties.
Graphene oxide (GO), derived from the chemical oxidation of
graphite, was picked as the precursor in the experiment conducted
by Rice University’s team. Due to the existence of oxygen functional
Like PAN fibres, GO fibres are prepared through wet spinning .
An extensive coagulation study led the team to select ethyl acetate as
the coagulation bath solvent, since it provided as-spun GO fibre with
a solid structure and it supported continuous spinning with drawing
applied during the process.
100% knot efficiency
When drawing was not applied, the team attained GO fibre with
up to 139 mN/tex on specific strength and 11% on elongation at
break. The combined good strength and flexibility renders the GO
fibre easily knotted (Figure 2A). More intriguingly, the knotted fibre
shows 100% knot efficiency, which means the existence of a knot
does not degrade the strength of the fibre. The GO fibre has the same
strength along its entire length, as demonstrated in Figures 2B, C
and D. This property has never been observed in carbon or polymer
fibres. This knot efficiency is attributed to the low bending modulus
of GO flakes .
Highly aligned GO fibre
In order to attain good intrinsic alignment of carbon fibre, drawing has to be applied during spinning. The draw ratio was tuned by
adjusting the rates of fibre extrusion and the rotating drum (Figure
62 jec composites magazine / No83 August - September 2013