By improving the mechanical properties of SMPs, researchers aim to increase the recovery
forces of their materials. Meng & Hu (11) described the benefit of reinforcing their SMPU fibers
with multiwall carbon nanotubes (MWNTs). By varying the loading ofMWNTs from 1 to 3 wt%,
they witnessed an increase in shape recovery (Rr > 80%) as well as in recovery stresses from 0.12
to 0.27 cN dtex−1 at the expense of a slight reduction in shape fixity (Rf ∼ 80%) compared
with the pristine SMPU fibers. In contrast, they showed that a higher percentage of MWNTs
rendered fiber processing difficult, which led to decreased physical properties of the fibers and
hence to a degradation of their SM properties. Other studies have used alternate routes to improve
the mechanical properties of their SMPUs. Xu et al. (13) synthesized a hybrid diol containing
hydrolyzable Si-OEt groups as a cross-linker. The creation of covalent cross-linking in addition
to the inorganic nature of the resulting Si-O-Si bonds provided these researchers’ materials with
increased modulus, especially above Tg, where E increased from 3.85 to 16.34 MPa. The shape
recovery was increased as well. Moreover, the authors claimed stability of the SM properties over
the initial 50 thermomechanical cycles.