Tailored and strong electro-responsive shape memory actuation in carbon nanotube-reinforced hyperbranched polyurethane composites

Electro-active multi-walled carbon nanotubes (MWCNTs)-filled hyperbranched polyurethane (HPU) shape memory composites were prepared by a simple and efficient method. The highly crystalline poly(ɛ-caprolactone)-based HPU was synthesized in a one-step process, and the branched structure was very effective for the homogeneous dispersion of MWCNTs without any surfactant or surface modification. Enhanced mechanical properties in terms of tensile modulus and strength for the MWCNTs/HPU composites could be obtained due to the hyperbranched polymer-assisted dispersion of the MWCNTs. Young's modulus of the pure HPU film was 210 MPa, while the polymer with 7 wt% loading of nanotubes showed a modulus of 320 MPa. An increase in the concentration of MWCNTs from 0 to 7 wt% resulted in a non-monotonic trend with the breaking stress reaching a maximum at ∼5 wt%. The MWCNTs/HPU composites showed more than 98% shape recovery and a rapid recovery time of 9 s in both thermal triggering and electrical actuating shape memory behavior. It is expected that the MWCNT-reinforced HPU composites can be used as potential material in various actuator applications.