Development of Multiwalled Carbon Nanotubes/Halloysite Nanotubes Reinforced Thermal Responsive Shape Memory Polymer Nanocomposites for Enhanced Mechanical and Shape Recovery Characteristics in 4D Printing Applications.

The mechanical and shape-recovery characteristics of 4D-printed thermally responsive shape-memory polyurethane (SMPU) reinforced with two types of reinforcements, multiwalled carbon nanotubes (MWCNTs) and Halloysite nanotubes (HNTs), are investigated in the present study. Three weight percentages of reinforcements (0, 0.5, and 1) in the SMPU matrix are considered, and the required composite specimens are obtained with 3D printing. Further, for the first time, the present study investigates the flexural test for multiple cycles to understand the 4D-printed specimens' flexural behavior variation after shape recovery. The 1 wt% HNTS-reinforced specimen yielded higher tensile, flexural, and impact strengths. On the other hand, 1 wt% MWCNT-reinforced specimens exhibited quick shape recovery. Overall, enhanced mechanical properties were observed with HNT reinforcements, and a faster shape recovery was observed with MWCNT reinforcements. Further, the results are promising for the use of 4D-printed shape-memory polymer nanocomposites for repeated cycles even after a large bending deformation.