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L. V. Karabanova et al.
CNTs in a matrix (or at least decreasing the extent of CNT aggregation) is a key
requirement for the realization of the desired enhancement in the final properties of
nanocomposites. Additionally, enhancing interfacial interactions between the CNTs
and the polymer matrix will promote efficient energy transfer within the system. To
attain these aims, various methods have been used, in particular sonication at the
mixing stage and also different approaches to chemical functionalization of CNT
surface have been under investigation [1–5].
The most well-known approach to improving interfacial interactions in CNTpolymer nanocomposites is the chemical functionalization of the outer walls of
CNTs that allows covalent attachment of a polymer directly to the nanotube
framework [5]. The change in surface properties of CNTs also has an advantage
by decreasing the hydrophobic character and improving interaction with different
polar matrices. However, it is also possible that CNTs may become mechanically
weaker after chemical treatment [6], where the reinforcement obtained through the
concentric arrangement of the cylinders decreases through acid-oxidative sidewall
digestion and, if acid oxidation continues over a long period of time, cylinders may
allow slippage.
Polyurethane (PU) materials are extensively used in technical and biomedical
applications, whether in blood contacting applications and organ reconstruction [7],
in skin patches, coatings and catheter applications [8]. PU is seen as an attractive
material with a complicated structure (randomised hard and soft nanodomains) [9];
therefore PU should highlight changes in its properties at the inclusion of CNTs that
possess different surface functionalization. Previous investigations of MWCNT-PU
composites have been focused on thermoplastic systems [10–21], and only a single
piece of work was found in literature for thermosetting systems [22].
In general, the different extents of the improvement of mechanical properties,
by tens of percent, including modulus and stress at break were observed for
thermoplastic PU after its filling with functionalized MWCNTs [11, 14, 15,
17–19] although elongation at break occasionally decreased [19]. The higher
thermal stability with the increased degradation temperature was observed for the
thermoplastic PU-MWCNT nanocomposites [12]. The thermo-responsive shape
recovery (shape memory) [13, 18] and electroactive shape-memory [19] effects
were observed for the surface-modified MWCNT-linear PU nanocomposites. The
PU crystallization was promoted at low contents of MWCNTs due to its action
as a nucleation agent, although at high MWCNT contents, the crystallization
was hindered because of restricting movement of PU chains [13, 18].Targeting
specific aerospace coating applications, CNTs were rigorously dispersed into PU
matrices to produce nanocomposites for electrostatic dissipation and/or de-icing
coatings [17]. The composites under consideration exhibited also good antistatic
properties [15] as well as improved wear resistance, thermal conductivity and
electrical conductivity [10]. The linear PU-MWCNT foams containing 0.1 wt%
highly functionalized nanotubes, possessing carboxyl, hydroxyl or amide functional
groups, manifested improved thermal stability, mechanical properties and acoustic
damping; the nanotubes modified with carboxyl groups were found to have greater
influence compared to the other two functional groups (i.e. lactone and phenol).
L. V. Karabanova et al.
CNTs in a matrix (or at least decreasing the extent of CNT aggregation) is a key
requirement for the realization of the desired enhancement in the final properties of
nanocomposites. Additionally, enhancing interfacial interactions between the CNTs
and the polymer matrix will promote efficient energy transfer within the system. To
attain these aims, various methods have been used, in particular sonication at the
mixing stage and also different approaches to chemical functionalization of CNT
surface have been under investigation [1–5].
The most well-known approach to improving interfacial interactions in CNTpolymer nanocomposites is the chemical functionalization of the outer walls of
CNTs that allows covalent attachment of a polymer directly to the nanotube
framework [5]. The change in surface properties of CNTs also has an advantage
by decreasing the hydrophobic character and improving interaction with different
polar matrices. However, it is also possible that CNTs may become mechanically
weaker after chemical treatment [6], where the reinforcement obtained through the
concentric arrangement of the cylinders decreases through acid-oxidative sidewall
digestion and, if acid oxidation continues over a long period of time, cylinders may
allow slippage.
Polyurethane (PU) materials are extensively used in technical and biomedical
applications, whether in blood contacting applications and organ reconstruction [7],
in skin patches, coatings and catheter applications [8]. PU is seen as an attractive
material with a complicated structure (randomised hard and soft nanodomains) [9];
therefore PU should highlight changes in its properties at the inclusion of CNTs that
possess different surface functionalization. Previous investigations of MWCNT-PU
composites have been focused on thermoplastic systems [10–21], and only a single
piece of work was found in literature for thermosetting systems [22].
In general, the different extents of the improvement of mechanical properties,
by tens of percent, including modulus and stress at break were observed for
thermoplastic PU after its filling with functionalized MWCNTs [11, 14, 15,
17–19] although elongation at break occasionally decreased [19]. The higher
thermal stability with the increased degradation temperature was observed for the
thermoplastic PU-MWCNT nanocomposites [12]. The thermo-responsive shape
recovery (shape memory) [13, 18] and electroactive shape-memory [19] effects
were observed for the surface-modified MWCNT-linear PU nanocomposites. The
PU crystallization was promoted at low contents of MWCNTs due to its action
as a nucleation agent, although at high MWCNT contents, the crystallization
was hindered because of restricting movement of PU chains [13, 18].Targeting
specific aerospace coating applications, CNTs were rigorously dispersed into PU
matrices to produce nanocomposites for electrostatic dissipation and/or de-icing
coatings [17]. The composites under consideration exhibited also good antistatic
properties [15] as well as improved wear resistance, thermal conductivity and
electrical conductivity [10]. The linear PU-MWCNT foams containing 0.1 wt%
highly functionalized nanotubes, possessing carboxyl, hydroxyl or amide functional
groups, manifested improved thermal stability, mechanical properties and acoustic
damping; the nanotubes modified with carboxyl groups were found to have greater
influence compared to the other two functional groups (i.e. lactone and phenol).