SYNTHESIS AND STRUCTURAL PROPERTIES OF CNTs/PEEK COMPOSITE MATERIALS OBTAINED USING FUNCTIONALIZED CNTs

Incorporation of carbon nanotubes (CNTs) into a polymer matrix can provide
structural materials with dramatically increased mechanical and electrical properties.
These properties combined with their low density makes them useful for the
transport industry, especially for aerospace structures, where the reduction of weight
is one of the main goals in order to reduce fuel consumption. However, several
limitations exist firstly related to the dispersion of nanotubes and their compatibility
with the matrix and secondarily to the nature of the binding between nanotubes and
the polymer chains. These setbacks need to be resolved prior to successful
applications.
In this work, two main approaches are considered for fabricating
CNTs/poly(ether ether ketone) (PEEK) composites. In the first case, multiwalled
carbon nanotubes (MWNTs) were functionalized with carboxyl group (-COOH)
through oxidation process and then were incorporated in PEEK matrix using
compression moulding process. In order to obtain a covalent linking between
nanotubes and the matrix, another approach has been used based on the use of both
chemically modified MWNTs and polymer. The attachment of oxidized MWNTs
and sulphonated PEEK (SPEEK) was possible using a diamine as an interlinking
molecule. Pristine MWNTs have been also embedded in polymer matrix without any
surface modification and were used as a reference. Transmission electron
microscopy (TEM), Field emission scanning electron microscopy (FE-SEM), Fourier
transform infrared (FT-IR) and X-ray diffraction (XRD) were used for structural
investigation of the composite systems. Thermogravimetric analysis (TGA),
Differential scanning calorimetry (DSC) and tensile test were done to understand the
overall behavior ofthe composites.
FE-SEM reveals that the dispersion of MWNTs is improved after oxidation
process and functionalization with SPEEK. XRD results concluded the improvement
of crystallinity after the addition of MWNTs to PEEK matrix and were confirmed with DSC scans. The thermal properties studied using TGA explained no significant
amendments indicating no effects of MWNTs on the thermal properties of PEEK.
On top of that, mechanical properties which is tensile modulus decreases after
addition of SPEEK-MWNTs revealing that use of bi-molecular molecule is not a
suitable way to achieve a good dispersion ofMWNTs in the matrix. On the basis of
the results from this research, it can be concluded that incorporation of
SPEEK-MWNTs to PEEK material does not affect or improve the thermal and
mechanical behavior. Hence, the author recommends further approach offabrication
method ofthe composites before other uses are considered.