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

Abstract

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.

Recent Advances in Polymer Nanocomposites: Unveiling the Frontier of Shape Memory and Self-Healing Properties—A Comprehensive Review

“…The polymer presented a shape memory recovery of 70% in only 120 s. Increases in the percentage of MWCNTs enhance the recovery ability. Nanofillers in the polymer system improved the crystallinity by acting as nucleating agents, which increased the cross-linking density, resulting in increasing the T g [ 95 ].…”

Shape-Memory Polymers Based on Carbon Nanotube Composites

“…The shape recovery of TPU and TPU/MWCNT composites in a hot water bath was also recorded to be faster (∼5 times) than in a hot air oven, as shown in Figure 6 [ 80 ]. Faster recovery times were reported for 3D-printed TPU/MWCNT composites, namely 130 s for a 0.5 wt.% MWCNT load and 90 s for a 1 wt.% MWCNT load, in contrast with a 245 s recovery time of neat TPU, at 80 °C [ 123 ]. Similar studies performed with test specimens prepared by injection molding [ 134 ] registered slower recovery for all compositions, which underlines the importance of the processing method.…”

4D Printing in Biomedical Engineering: Advancements, Challenges, and Future Directions

“…SMPs can transition between a deformed state and their original shape upon exposure to a specific stimulus, such as heat or light [20]. This property enables the fabrication of 4D-printed structures that change their shape or configuration when subjected to the appropriate trigger [21][22][23]. For instance, an SMP-based 4D-printed scaffold can adapt its shape to better fit the tracheal structure when exposed to body heat, potentially improving the effectiveness and precision of tracheal repair procedures [24].…”