47
based SMRs can also be used as SMPs. However, its difficult processing, high Tg
value (around 110 °C) and small shape variables restrict thier potential applications.
To overcome this disadvantage, high-density PE (HDPE) can be adequately mixed
with TPI at 150 °C, thus resulting in vulcanized HDPE/TPI-based SMRs with excellent mechanical properties.
In 1988, Asahi Kasei Corporation successfully developed a poly(styrene)-bpoly(butadiene) (PS-b-PB)-based SMR, in which PS (melting point (T m ) around
120 ° C) acted as phase stationary, while PB (T m approx. 60 °C) fulfilled the role of
reversible phase (Xu et al. 2010). This SMR could be processed by extrusion, injection molding and shrinkage at 120 °C, and its deformation and shape recovery temperature for both was around 60 °C (Nji and Li 2010). According to Fu et al. (2009)
ε values of up to 400% were obtained, as well as these PS-b-PB-based SMRs could
be reused at least 200 times, and due to their excellent colorability and acid/alkali
resistance, they can extend their range of applications. PS-b-PB-based SMRs could
also form a colorless transparent viscous solution in the toluene solution for casting
and coating processing, the viscosity of which could be tailored.
3.4.4 SMP Composites (SMPCs)
The low σ (between 5 and 10 MPa) and E values, and the relatively small recovery
force make the applications from SMPs difficult (Hornbogen 2006). However, the
strain recovery force of SMPs generally ranges from a few megapascals to tens of
megapascals. A low σ value indicates that the strain recovery force generated under
the restraint is small (Zhu et al. 2008). Reinforcement materials such as fibers, different nanoparticles (e.g. carbon nanotubes, silica nanoparticles, etc.) and other
materials could be added to the SMPs to overcome the defects, and obtain SMPCs
(Jung et al. 2010; Koerner et al. 2004; Miramirkhani and Navarchian 2017; Ni et al.
2007b; Robinson et al. 2017; Zhang et al. 2007).
It is worth noting that the content of reinforcement material improves the
mechanical properties of the SMPs up to a threshold, since once this point is
exceeded, the mechanical properties decline (Liu et al. 2006; Ohki et al. 2004;
Gutiérrez and Alvarez 2017d; Gutiérrez et al. 2017, 2018, 2019).
SMPCs have also been frequently obtained by blending polymers such as EVA/
PVC, PCL/PE, PCL/TPI and PE/PU (Mishra et al. 2003).
3.5 Outlook
In this chapter, the remarkable process in the field of SMPs was presented. SMPs
have diverse applications, and others can be expected, since they can respond to
external stimuli under different conditions. However, there are still challenges to be
solved. In particular, multifunctional conductive SMPs will constitute a new genera3 Smart and Shape Memory Polymers
based SMRs can also be used as SMPs. However, its difficult processing, high Tg
value (around 110 °C) and small shape variables restrict thier potential applications.
To overcome this disadvantage, high-density PE (HDPE) can be adequately mixed
with TPI at 150 °C, thus resulting in vulcanized HDPE/TPI-based SMRs with excellent mechanical properties.
In 1988, Asahi Kasei Corporation successfully developed a poly(styrene)-bpoly(butadiene) (PS-b-PB)-based SMR, in which PS (melting point (T m ) around
120 ° C) acted as phase stationary, while PB (T m approx. 60 °C) fulfilled the role of
reversible phase (Xu et al. 2010). This SMR could be processed by extrusion, injection molding and shrinkage at 120 °C, and its deformation and shape recovery temperature for both was around 60 °C (Nji and Li 2010). According to Fu et al. (2009)
ε values of up to 400% were obtained, as well as these PS-b-PB-based SMRs could
be reused at least 200 times, and due to their excellent colorability and acid/alkali
resistance, they can extend their range of applications. PS-b-PB-based SMRs could
also form a colorless transparent viscous solution in the toluene solution for casting
and coating processing, the viscosity of which could be tailored.
3.4.4 SMP Composites (SMPCs)
The low σ (between 5 and 10 MPa) and E values, and the relatively small recovery
force make the applications from SMPs difficult (Hornbogen 2006). However, the
strain recovery force of SMPs generally ranges from a few megapascals to tens of
megapascals. A low σ value indicates that the strain recovery force generated under
the restraint is small (Zhu et al. 2008). Reinforcement materials such as fibers, different nanoparticles (e.g. carbon nanotubes, silica nanoparticles, etc.) and other
materials could be added to the SMPs to overcome the defects, and obtain SMPCs
(Jung et al. 2010; Koerner et al. 2004; Miramirkhani and Navarchian 2017; Ni et al.
2007b; Robinson et al. 2017; Zhang et al. 2007).
It is worth noting that the content of reinforcement material improves the
mechanical properties of the SMPs up to a threshold, since once this point is
exceeded, the mechanical properties decline (Liu et al. 2006; Ohki et al. 2004;
Gutiérrez and Alvarez 2017d; Gutiérrez et al. 2017, 2018, 2019).
SMPCs have also been frequently obtained by blending polymers such as EVA/
PVC, PCL/PE, PCL/TPI and PE/PU (Mishra et al. 2003).
3.5 Outlook
In this chapter, the remarkable process in the field of SMPs was presented. SMPs
have diverse applications, and others can be expected, since they can respond to
external stimuli under different conditions. However, there are still challenges to be
solved. In particular, multifunctional conductive SMPs will constitute a new genera3 Smart and Shape Memory Polymers