56
phase) are associated with the elastic regime. In this context, the hard segments act
as regions of molecular switches, which are responsible for the recovery of the
original shape of the material.
Thermo-sensitive shape memory polymers show shape change by thermal stimulation above the glass transition temperature (T g ) or melting temperature (T m ).
Thermo-sensitive PU has been used successfully for biomedical devices, coatings
and sporting goods (Sun et al. 2011). The shape recovery effect can also be activated
by electrovoltage (Liu et al. 2016) With this in mind, electroactive shape memory
PUs have been used to manufacture actuators, electronics, sensors and textiles. In
addition, PU-based nanocomposites loaded with conducting nanofillers such as carbon black, carbon nanotubes (CNTs), fullerene, nanodiamonds, etc., have demonstrated improved performance compared to the pristine PUs (Meng and Li 2013; Li
et al. 2012). These nanofillers have also been used as reinforcements in PU matrices
in order to improve shape recovery properties. These composite materials have
found applications like electroactive and (moisture-, pH- and thermo-) sensitive
materials for different industries such as aerospace, biomedical engineering, electronics and energy appliances (Roy et al. 2010; Hu et al. 2012; Mura et al. 2013).
Despite the patented design and development of shape recovery PU materials, there
are still several challenges to overcome. In this chapter, shape memory PU and their
nanocomposites will be explored as novel materials for advanced applications.
4.2 PU
PU is a polymer with unique properties (Thakur and Hu 2017), which have rigid and
soft thermoplastic forms, as well as thermoset forms (Hepburn 2012; Liao et al.
2019). The urethane bond in this polymer can offer hydrogen (H)-bonds between
the polymer chains. The thermal and non-flammability properties of PUs have been
explored for various technical uses (Kausar 2016b), as well as these materials have
been used as anticorrosive coatings (Montemor 2014; Mo et al. 2015). Other unique
and useful properties of PU is that it can conduct electromagnetic interference
shielding (Zeng et al. 2016). High performance PU has also been used for multiple
engineering applications (Caracciolo et al. 2019). PU characteristics can be modified for a desirable end application using different synthesis approaches (Prisacariu
2011). For example, segmented PU chains may be crosslinked, as a result, crosslinked PU segments may have reduced mobility, thus promoting shape recovery
property.
A. Kausar
phase) are associated with the elastic regime. In this context, the hard segments act
as regions of molecular switches, which are responsible for the recovery of the
original shape of the material.
Thermo-sensitive shape memory polymers show shape change by thermal stimulation above the glass transition temperature (T g ) or melting temperature (T m ).
Thermo-sensitive PU has been used successfully for biomedical devices, coatings
and sporting goods (Sun et al. 2011). The shape recovery effect can also be activated
by electrovoltage (Liu et al. 2016) With this in mind, electroactive shape memory
PUs have been used to manufacture actuators, electronics, sensors and textiles. In
addition, PU-based nanocomposites loaded with conducting nanofillers such as carbon black, carbon nanotubes (CNTs), fullerene, nanodiamonds, etc., have demonstrated improved performance compared to the pristine PUs (Meng and Li 2013; Li
et al. 2012). These nanofillers have also been used as reinforcements in PU matrices
in order to improve shape recovery properties. These composite materials have
found applications like electroactive and (moisture-, pH- and thermo-) sensitive
materials for different industries such as aerospace, biomedical engineering, electronics and energy appliances (Roy et al. 2010; Hu et al. 2012; Mura et al. 2013).
Despite the patented design and development of shape recovery PU materials, there
are still several challenges to overcome. In this chapter, shape memory PU and their
nanocomposites will be explored as novel materials for advanced applications.
4.2 PU
PU is a polymer with unique properties (Thakur and Hu 2017), which have rigid and
soft thermoplastic forms, as well as thermoset forms (Hepburn 2012; Liao et al.
2019). The urethane bond in this polymer can offer hydrogen (H)-bonds between
the polymer chains. The thermal and non-flammability properties of PUs have been
explored for various technical uses (Kausar 2016b), as well as these materials have
been used as anticorrosive coatings (Montemor 2014; Mo et al. 2015). Other unique
and useful properties of PU is that it can conduct electromagnetic interference
shielding (Zeng et al. 2016). High performance PU has also been used for multiple
engineering applications (Caracciolo et al. 2019). PU characteristics can be modified for a desirable end application using different synthesis approaches (Prisacariu
2011). For example, segmented PU chains may be crosslinked, as a result, crosslinked PU segments may have reduced mobility, thus promoting shape recovery
property.
A. Kausar