POLYMER MODIFICATION WITH CARBON NANOTUBES

1. POLYMER MODIFICATION WITH CARBON
NANOTUBES
MENON LAKSHMI SURESH
M.SC BPS

2. INTRODUCTION
 Incorporation of carbon nanotubes (CNTs) into a polymer
matrix is a very attractive way to combine the mechanical
and electrical properties of individual nanotubes with the
advantages of plastics.
 Carbon nanotubes are the third allotropic form of carbon
and were synthesized for the first time by Iijima in 1991 .
 Two types of CNTs are distinguished
1) Single-walled CNTs (SWCNTs) consist of a single graphene
sheet wrapped into cylindrical tubes with diameters ranging
from 0.7 to 2nm and have lengths of micrometers.
2) Multi-walled CNTs (MWCNTs) consist of sets of concentric
SWCNTs having larger diameters . The unique properties of
individual CNTs make them the ideal reinforcing agents in a
number of applications.

3. Single- walled Multi-walled

4.  But the low compatibility of CNTs set a strong limitation to disperse
them in a polymer matrix.
 Indeed, carbon nanotubes form clusters as very long bundles due
to the high surface energy and the stabilization by numerous of π−π
electron interactions among the tubes.
 Non covalent methods for preparing polymer/CNTs Nano
composites have been explored to achieve good dispersion and
load transfer .
 The non-covalent approaches to prepare polymer/CNTs
composites via processes such as solution mixing , melt mixing,
surfactant modification, polymer wrapping , polymer absorption
and in situ polymerization are simple and convenient but
interaction between the two components remains weak.

5.  Relatively uniform dispersion of CNTs can be achieved in
polar polymers such as nylon, polycarbonate and polyimide
because of the strong interaction between the polar moiety
of the polymer chains and the surface of the CNTs .
 Moreover, it was found that MWNTs disperse well in PS and
form a network-like structure due to π-stacking interactions
with aromatic groups of the PS chains .
 However, it is difficult to disperse CNTs within a non polar
polymer matrix such as polyolefins.
 To gain the advantages of CNTs at its best, one needs: (i)
high interfacial area between nanotubes and polymer; &,
(ii) strong interfacial interaction.

6.  The mechanical properties of polyethylene (PE) reinforced by
carbon nanotubes do not improve significantly because the
weak polymer-CNT interfacial adhesion prevents efficient stress
transfer from the polymer matrix to CNT .
 A strategy for enhancing the compatibility between nanotubes
and polyolefins consists in functionalising the sidewalls of CNT to
introduce reactive moieties and to disrupt the rope structure.
 Functional moieties are attached to open ends and sidewalls to
improve the solubility of nanotubes while the covalent polymer
grafting approaches, including ‘grafting to’ and ‘grafting from’
that create chemical linkages between polymer and CNTs, can
significantly improve dispersion and change their rheological
behaviour.

7. Methods to process polymer/carbon
nanotubes composites
 Several processing methods available for fabricating
CNT/polymer composites based on either thermoplastic or
thermosetting matrices mainly include
1)Solution mixing
2)melt blending
3 ) in situ polymerisation.

8. Schematic representation of different steps of polymer/CNTs composite
processing: (a) solution mixing ; (b) melt mixing;
(c) in situ polymerisation

9.  CNTs are considered ideal materials for reinforcing fibres due to
their exceptional mechanical properties.
 Therefore, nanotube−polymer composites have potential
applications in aerospace science, where lightweight robust
materials are needed.
 It is widely recognised that the fabrication of high performance
nanotube−polymer composites depends on the efficient load
transfer from the host matrix to the tubes.
 The load transfer requires homogeneous dispersion of the filler
and strong interfacial bonding between the two components. A
dispersion of CNT bundles is called “macrodispersion” whereas a
dispersion of individual nonbundled CNT is called a
nanodispersion
Surface modifications of carbon nanotubes
with polymers

10.  To address these issues, several strategies for the synthesis of such
composites have been developed.
 Currently, these strategies involve physical mixing in solution, in
situ polymerisation of monomers in the presence of nanotubes,
surfactant-assisted processing of composites, and chemical
functionalisation of the incorporated tubes.
 As mentioned earlier, in many applications it is necessary to tailor the
chemical nature of the nanotube’s walls in order to take advantage
of their unique properties.
 For this purpose, two main approaches for the surface modification of
CNTs are adopted
i.e. covalent and noncovalent, depending on whether or not covalent
bonding between the CNTs and the functional groups and/or modifier
molecules is involved in the modification surface process. Figure depicts
a typical representation of such surface modifications.

11. COVALENT ATTACHMENT OF POLYMERS
 Functionalisation of carbon nanotubes with polymers is a key issue
to improve the interfacial interaction between CNTs and the
polymer matrix when processing polymer/CNT nanocomposites.
 The covalent reaction of CNT with polymers is important because
the long polymer chains help to dissolve the tubes into a wide
range of solvents even at a low degree of functionalisation.
 There are two main methodologies for the covalent attachment
of polymeric substances to the surface of nanotubes, which are
defined as “grafting to” and ‘grafting from’ methods .
 A disadvantage of this method is that the grafted polymer
contents are limited because of high steric hindrance of
macromolecules.

12. NONCOVALENT ATTACHMENT OF
POLYMERS
 The noncovalent attachment, controlled by thermodynamic
criteria , which for some polymer chains is called wrapping, can
alter the nature of the nanotube’s surface and make it more
compatible with the polymer matrix.
 Non-covalent surface modifications are based mainly on weak
interactions, such as van der Waals, π−π and hydrophobic
interactions, between CNTs and modifier molecules.
 Non-covalent surface modifications are advantageous in that
they conserve sp2-conjugated structures and preserve the
electronic performance of CNTs.
 The disadvantage of noncovalent attachment is that the forces
between the wrapping molecule and the nanotube might be
weak, thus as a filler in a composite the efficiency of the load
transfer might be low.

13. Different routes for nanotubes’ functionalisation: a) sidewall covalent
functionalisation ; b) defect-group covalent functionalisation ; c)
noncovalent polymer wrapping ; d) noncovalent pi-stacking

14. Carbon nanotubes nanocomposites
based on Polyolefins
 Polyethylene (PE) is one of the most widely used commercial
polymer due to the excellent combination of low coefficient of
friction, chemical stability and excellent moisture barrier
properties.
 The combination of a soft polymer matrix such as PE with
nanosized rigid filler particles may provide new nanocomposite
materials with largely improved modulus and strength.
 To improve the stiffness and rigidity of PE, CNTs can be used to
make CNT/PE composites.
 The mechanical properties of polyethylene (PE) reinforced by
carbon nanotubes do not improve significantly because the
weak polymer-CNT interfacial adhesion prevents efficient stress
transfer from the polymer matrix to CNT .
 .

15.  The lack of functional groups and polarity of PE backbone
results in incompatibility between PE and other materials such
as glass fibres, clays, metals, pigments, fillers, and most
polymers.
 A strategy for enhancing the compatibility between
nanotubes and polyolefins consists in functionalising the
sidewalls of CNT with polymers either by a ‘grafting to’ or a
‘grafting from’ approach.
 As discussed before, the “grafting from” approach involves the
growth of polymers from CNT surfaces via in situ polymerisation
of olefins initiated from chemical species immobilised on the
CNT

16.  As an example, Ziegler-Natta or metallocene catalysts for ethylene
polymerisation can be immobilised on nanotubes to grow PE
chains from their surface.
 However, covalent linkages or strong interactions between PE
chains and nanotubes cannot be created during polymerisation.
 The “grafting to” technique involves the use of addition reactions
between the polymer with reactive groups and the CNT surface.
 However, the synthesis of end-functionalized polyethylene (PE),
which is necessary in the “grafting to” approach, is difficult.
 Another promising route for a chemical modification of MWCNTs
by PE is to use free radical initiators such as peroxides.

17.  The general mechanism of free radical grafting of vinyl
compound from hydrocarbon chains detailed by Russell,
Chung and Moad seems to express a widespread view.
 The grafting reaction starts with hydrogen abstraction by
alkoxyl radicals generated from thermal decomposition of the
peroxide.
 Then, the active species generated onto the hydrocarbon
backbone react with unsaturated bonds located on the
MWCNTs surface.
 This chemical modification is thus conceivable during reactive
extrusion because the radicals’ lifetimes (in the range of few
milliseconds) are compatible with typical residence time in an
extruder (around one minute).

18. Carbon Nanotube Polymer
Composites
 While there are limitless applications for these materials, we
are interested in radiation shielding and radiation resistant
materials for use in the space industry.
 Initially, focused on optically transparent single wall
nanotoube (SWNT) polymer composites .
 Three different in situ polymerization/sonication methods,
heat, light and gamma radiation, were used to produce poly
(methyl methacrylate) (PMMA) nanotube composites.
 When these composites are dissolved in methylene chloride
and immediately cast into films, they exhibit a high degree of
transparency (fig. 1).

19.  All of the composites in fig. 1 contain 0.26 wt% carbon
nanotubes.
 The dark sample on the bottom right was made by melt
blending 0.26% carbon nanotubes with the PMMA in a
Banbury mixer. This illustrates the dramatic effect of dispersion
quality on transparency.
 The dispersion in a typical sonicated sample is depicted in
the SEM image shown in fig. 2.

21. The dispersion in a typical sonicated sample is depicted in the SEM image
shown in fig. 2.

22. Epoxy/CNT Nanocomposites
 To improve dispersion of CNT in an epoxy matrix, Surfactants, for example
polyoxyethylene-8-lauryl, have been used to disperse CNT before their introduction
into a polymer matrix

23. Carbon Nanotube Polymer
Composites: A Review of Recent
Developments

24. Nanotube Composite
Materials
• Engineering MWNT composite materials
• Lighter, stronger, tougher materials
• Lighter automobiles with improved safety
• Composite armor for aircraft, ships and tanks
• Conductive polymers and coatings
• Antistatic or EMI shielding coatings
• Improved process economics for coatings, paints
• Thermally conductive polymers
• Waste heat management or heat piping
• Multifunctional materials

25. High Strength Fibers
 To achieve a high strength nanotube fiber:
 High strength nanotubes (> 100 GPa)
 Good stress transfer from matrix to nanotube
 Or, nanotube to nanotube bonding
 High loadings of nanotubes
 Alignment of nanotubes (< 5° off-axis)
 Perfect fibers
 Each defect is a separate failure site

26. Two Approaches for Surface
Modification of MWNTS
 Non-covalent attachment of molecules
 van der Waals forces: polymer chain wrapping
 Alters the MWNT surface to be compatible with the bulk polymer
 Advantage: perfect structure of MWNT is unaltered
 mechanical properties will not be reduced.
 Disadvantage: forces between wrapping molecule / MWNT maybe
weak
 the efficiency of the load transfer might be low.
 Covalent bonding of functional groups to walls and caps
 Advantage: May improve the efficiency of load transfer
 Specific to a given system – crosslinking possibilities
 Disadvantage: might introduce defects on the walls of the MWNT
 These defects will lower the strength of the reinforcing component.

27. Polymer Wrapping
 Polycarbonate wrapping of MWNT (Ruoff group)
Ding, W., et al., Direct observation of polymer sheathing in carbon
nanotube-polycarbonate composites. Nano Letters, 2003. 3(11): p.

28. In Situ Polymerization of PAN
 Acrylate-functionalized
MWNT which have been
carboxilated
 Free-radical
polymerization of
acrylonitrile in which
MWNTs are dispersed
 Hope to covalentely
incorporate MWNTs
functionalized with
acrylic groups

29. Strong Matrix Fiber
Interaction
 SEM images of fracture surfaces indicate
excellent interaction with PAN matrix, note
‘balling up’ of polymer bound to the MWNT
surface. This is a result of elastic recoil of this
polymer sheath as the fiber is fractured and
these mispMWNTs are pulled out.

30. 20 wt% MWNT/Carbon Fiber

31. PP/SWNT Fibers
 SWNT were dispersed into polypropylene
 via solution processing with dispersion via ultrasonic energy
 melt spinning into filaments
 40% increase in tensile strength at 1wt.% SWNT addition, to 1.03
GPa.
 At higher loadings (1.5 and 2 wt%), fiber spinning became more
difficult
 reductions in tensile properties
 “NTs may act as crystallite seeds”
 changes in fiber morphology, spinning behavior
 attributable to polymer crystal structure.

32.  SWNT/Polymer Fibers
 PMMA
 PP
 PAN
 Fabricated fibers with 1 to 10 wt% NT
 Increases in modulus (100%+)
 Increases in toughness
 Increase in compressive strength
 Decrease in elongation to break
 Decreasing tensile strength

33. PBO/SWNT Fibers
 high purity SWNT (99% purity)
 PBO poly(phenylene benzobisoxazole)
 10 wt% SWNT
 20% increase in tensile modulus
 60 % increase in tensile strength (~3.5 GPa)
 PBO is already a high strength fiber
 40% increase in elongation to break
 .

34. Conclusion
 The field of CNT polymers composite is currently undergoing
rapid developments.
 Over the last few years it has been demonstrated that
polymers can serve as efficient tools for engineering the
interfacial behaviour of CNT without damaging the unique
properties of individual tube.
 Polymers were shown to be efficient tools for dispersing
separating, assembling & organizing CNT in different media.
 It is evident that harnessing the unique physical properties
CNT require development of throughout understanding of
complex polymer-CNT systems.

35. Conclusions
 Nanotubes are > 150 GPa in strength.
 Strain-to-break of 10 to 20%
 Should allow 100 GPa composites
 Challenges still exist
 Stress transfer / straining the tubes
 Controlling the interface
 Eliminating defects at high alignment
 Work is progressing among many groups

36. REFRENCES
 Dispersion and functionalization of carbon nanotubes for polymer-based
nanocomposites, P.-C. Ma et al. / Composites: Part A 41 (2010) 1345–1367
 “Transparent PMMA/SWNT Composites with Increased Dielectric Constants”, L.
Clayton, T. Gerasimov, M. Meyyappan and J. P. Harmon, Advanced Functional
Materials, Vol. 15, No. 1, 101, (2005). 4
 Kumar, S., et al., Fibers from polypropylene/nano carbon fiber composites.
Polymer, 2002. 43: p. 1701-1703.
 Kumar, S., et al., Synthesis, Structure, and Properties of PBO/SWNT Composites.
Macromolecules, 2002. 35: p. 9039-9043.
 Sreekumar, T.V., et al., Polyacrylonitrile Single-Walled Carbon Nanotube
Composite Fibers. Advanced Materials, 2004. 16(1): p. 58-61
 Kearns, J.C. and R.L. Shambaugh, Polypropylene Fibers Reinforced with Carbon
Nanotubes. Journal of Applied Polymer Science, 2002. 86: p. 2079-2084

37. THANK YOU !!!!!