SURA Final report PVDF-CNT

1. Fabrication and Evaluation of Polymer
Matrix Composite with Aligned Carbon
Nanotubes as Reinforcement
Presented by
Mohit Rajput (12216014) (MMT)
Nikhil Singla (12216015) (MMT)
Ashwani Kumar Jaiswal (12121010) (PST)
IIT Roorkee
INDIAN INSTITUTE OF TECHNOLOGY ROORKEE
Under the Guidance of
Dr. Debrupa Lahiri
IIT Roorkee

2. OBJECTIVE OF THE PROJECT
The Aim of this research project is to synthesize polymer based carbon nanotube (CNT) composites
that will surmount its predecessor’s carbon fiber for structural application. The uniqueness of this
composite will be aligning the well dispersed carbon nanotubes in a polymer matrix to achieve the
most effective directional properties. The aim of this research is to create a very lightweight composite
with high strength, high thermal and electrical conductivity, which finds its application across various
fields. However, achieving this is not very easy and many research groups are engaged in the
successful fabrication of such composite structures. The main challenges in fabrication of such
composites lie in both dispersion and alignment of the nano-sized reinforcement in polymer matrix.
CNTs have a natural tendency to form agglomerate due to their very high specific surface area. For
the effective dispersion of CNTs in polymer, aggregate formation should be prevented and a well
dispersed composite would prevent the slipping of the fiber from matrix, resulting in effective
strengthening. Thus the ability to create a carbon nanotube polymer based composite requires the
means to avoid the formation of aggregates, which would be tried in this research at different stages.
For the Alignment of CNTs in polymer matrix, electric Force field would be used considering the very
high electrical conductivity of the composite. Finally, the effect of alignment of CNTs in polymer matrix
would be evaluated in terms of mechanical properties and electrical conductivity of the composite
structure in different directions.
Why PVDF?
Thermoplastic long chain fluoro polymer of low density as compared to other fluoro polymer which is
highly non-reactive, high resistant to chemical corrosion and heat makes it suitable to be used as
matrix. Additionally it has considerably high dielectric strength and is transparent nature.
Why CNTs??
The one-dimensional structure of CNTs, their low density, their high aspect ratio, and extraordinary
mechanical properties make them particularly attractive as reinforcements in composite materials.
PropertyMaterial Copper CNT (SWNT) PVDF Diamond
Electrical
conductivity
5.96×107
S/m 106
– 107
S/m
Electrical Resistivity 1.68×10-8
Ω m 10-6
Ω m
Young’s modulus 130 GPa 1250 GPa 2900 MPa
Rigidity modulus 48 GPa
Bulk modulus 140 GPa 462 to 546 GPa 420 GPa
Specific gravity 8.9 1.3 - 2 1.78 3.52
Melting point 1084.62 °C 170°C
Density of solid 8920 kg m-3
2100 kg m-3
1780 kg m-3
3515 kg m-3
Thermal
conductivity
400 W m-1
K-1
>3000 W m-1
K-1
0.19 W m-1
K-1
332 W m-1
K-1
Coefficient of
thermal expansion
16.5 x 10-6
K-1
Temperature
stability
2800 °C
in vacuum
about 750 °C in
air

3. Can carry a current
density of
35A∙mm−2 4 × 109
A/cm2
Tensile strength 30 GPa 0.057 GPa
Also nanotubes are the stiffest known fiber, prior to CNT, diamond was the best thermal conductor,
tensile strength of carbon nanotubes is about a hundred times higher than steel and additionally,
they can carry the highest current density of any known material, measured as high as 109
A/cm2
Determining parameter for Composites
The variation of many parameters, such as CNT type, growth method, chemical pre-treatment, aspect
ratio of CNTs, disentaglement of CNT agglomerates, uniform spatial distribution of individual CNTs,
degree of alignment as well as polymer type and synthesis method has given some encouraging results
in fabricating relatively strong CNT–polymer composites.
Why Alignment??
Enhanced dispersion and alignment of CNTs in polymer matrices greatly improve mechanical, electric,
thermal, electrochemical, optical and super-hydrophobic properties of polymer/CNT composites.
Thus, the critical challenge is the development of means and ways to promote and increase the
dispersion and alignment of CNTs in the matrix.
The degree of CNT alignment in the composite can be governed by two factors:
(i) Diameter of CNTs
A smaller diameter of CNT can enhance the degree of CNT alignment due to the
greater extensional flow; and
(ii) CNT content
A higher CNT content decreases their alignment because of the CNT
agglomeration and restrictions in motion from neighbouring CNTs.
Why alignment is a challenge?
A frustrating characteristic of nanotubes, particularly long ones, is that they attract each other in
common solvents, making it a challenge to disperse them. Long nanotubes are believed to be the key
to high-performance films.
While alignment is necessary to maximize the strength and modulus, it is not always beneficial
because the aligned composites have very anisotropic mechanical properties, i.e., the mechanical
properties along the alignment direction can be enhanced, whereas these properties are sacrificed
along the direction perpendicular to this orientation.
Challenges to CNT/PVDF Composites
In order to achieve the true potential of nanotubes, several challenges have to be faced. Carbon
nanotubes have to be produced with higher purity, integrity, in larger amounts, and at a lower price.
They have to have longer lengths. Concerning the composites technology, issues such as orientation
of the CNTs, their concentration, homogeneous dispersion at high loadings, significant densification
of the composite, interfacial adhesion, distribution and dispersion have to be overcome.

4. Processing of CNT/PVDF Composites
Synthesis of the Composite:
Since one of the aims of the composite with aligned CNTs is to improve the electrical conductivity, a
polymer would be chosen with some amount of electrical conductivity. For the preparation of
composite, the first step should be to prevent the agglomeration of CNTs. This would be tried by
functionalizing the CNTs, which would not only prevent the CNTs from coming together, but may also
assist in good bonding with the polymer matrix. In the next step, the CNTs would be mixed with
polymer using a suitable chemical agent and mixing would be done through some physical mixing
route for uniform dispersion of the Nano-size reinforcement phase in the matrix. While curing,
electrical force field would be applied to get CNTs aligned along certain direction in the polymer
matrix. The composites would be synthesized with different content of the reinforcement phase to
find out the optimum composition for mechanical and electrical property improvement. The
composites with randomly oriented CNTs would also be synthesized to evaluate the effect of CNT
alignment at each composition.

5. This is what we are
going to do in project
Flowchart presenting the different steps of processing of a polymer composite.
We consider this to be effective to prepare composites with CNTs homogeneously distributed.
However, it has to be pointed out that this method relies on the efficient dispersion of nanotubes in
the used solvent. Solvent is chosen based on the solubility of the polymer. The importance of the
functionalization is to help in the dispersion and avoid reaggregation of CNTs.
Intercalation: The reversible insertion of molecule between two others.
Characterization/Evaluation of the Composite:
With different composition of CNTs in composite we will be studying
1. Morphology and bonding at Interface
2. Mechanical Properties
3. Electrical Conductivities
The morphology of the composite and distribution of CNTs in the matrix would be evaluated through
scanning electron microscopy. Infra-Red Spectroscopy would also be used to understand bonding
behavior at CNT-polymer interface.
The mechanical properties of the composite will be investigated in terms of elastic modulus, tensile
strength and toughness along and across the alignment direction. Comparison would also be made
with only polymer and the randomly reinforced polymer to understand the effect of CNT addition and
its alignment, respectively, on mechanical properties of the composite structure. Similar
characterization would also be carried out for the electrical conductivity of the structure.
Possible Properties and Applications
The composite is promising for applications that require high strength, lightweight, or high electrical
and thermal conductivities

6. Mechanical properties
Incorporation of CNTs into a polymer matrix can potentially provide structural materials with
dramatically increased modulus and strength. Therefore they may find use in structural material,
aerospace and terrestrial applications.
Thermal properties
The incorporation of CNTs could improve the thermal transport properties of polymer composites due
to the excellent thermal conductivity of CNTs. This offers an opportunity for polymer/CNT composites
for usages as printed circuit boards, connectors, thermal interface materials, heat sinks, lids and
housings, and high-performance thermal management from satellite structures down to electronic
device packaging.
Further the addition of CNTs could increase the glass transition, melting and thermal decomposition
temperatures of the polymer matrix due to their constraint effect on the polymer segments and
chains. It is important to improve the thermal endurance of polymer composites.
Electrical and electrochemical properties
Carbon nanotubes can greatly improve capacitor performance, due to the highly wettable surface area
and high conductivity
Polymer/CNT nanocomposites could have many potential applications in transparent conductive
coatings, electrostatic dissipation, electrostatic painting, electrochemical actuation, electromagnetic
interference shielding (EMI), wave absorption, electronic packaging, self-regulating heater, PTC
resistors, and Ultra capacitors etc.
Optical and photovoltaic properties
Polymer/CNT composites could also be used to protect human eyes, optical elements, optical sensors
and optical switching.
Polymer/CNT nanocomposites represent an alternative class of organic semi-conducting materials
that are promising for organic photo-voltaic cells and devices with improved performance.
The black color of CNTs combined with their high surface area and high electron affinity enable CNTs
to be an ideal candidate to improve the photoluminescence of CNT/polymer nanocomposites:
photoluminescence is a process in which a substance absorbs photons (i.e. electromagnetic radiation)
and re-radiates photons.
Super-hydrophobic properties
It is expected that well-aligned CNT compounded polymer films or coatings should have wide
applications including super-hydrophobic surfaces to textiles, coatings, gene delivery, micro-fluid
channels, non-wetting liquid transfer and so forth.

7. Polymer/CNT nanocomposites are expected to have good processability of the polymers and high
mechanical and functional properties of the CNTs. Continuing advances on dispersion and alignment
of CNTs in polymer matrices will further promote developments in and expand the range of
applications of these nanocomposites.
This material could be new significant material for electronics.eg for capacitors, transistors, non-
metallic conduction applications
Further study will be done on does this composite will show “Remote Joule Heating”
Carbon nanotubes has special electronic and thermal properties not found in metals. Carbon
nanotube can conduct electricity without heating up, while it simultaneously heats up the material on
which it is mounted. The result is puzzling: the nanotube “wire" stays (mostly) cool, but the material
on which the wire is mounted grows hot, somehow absorbing heat energy from the electricity that is
flowing through the wire, without the wire itself heating up.
This will be similar to Induction cooking, which operates on magnetic fields rather than heat transfer.