High-performance shape-memory-polymer (SMP) composites via optimization of multidimensional graphitic-carbon fillers and development of heat-fire-and-smoke alarm devices using SMP composites

Understanding how sp² carbons of different dimensionality engineer the shape memory polymer is crucial for fundamental science and developing next-generation technologies. Further, with modernization, widespread adoption of rechargeable lithium-ion batteries, as well as hotter, drier weather attributed to climate change, has indirectly led to a globally increasing trend of fire-related accidents. To prevent such accidents from causing large-scale destruction and casualties, the rapid detection of a fire event is extremely important. In this work, we have developed mechanically robust shape memory polyurethane (PU) composites containing graphitic-carbon fillers that exhibit good thermo-responsiveness. Reinforcement of the PU matrix by three types of graphitic-carbon fillers, namely 3D graphite, 2D multilayer graphene, and 1D multiwall carbon nanotubes, yielded 36–47% and 20–29% faster shape recovery in hot-water and hot-air environments, respectively, with minimum shape recovery time of 14 s in former and 106 s in latter environments, thermal conductivity enhancement of 15 to 55%, enhanced shape-recovery ratio (up to 100%), increased shape recovery stress by ~ 34–96%, lowered coefficient of friction by 2–3 times, and improved wear resistance with respect to pristine PU. We found that a low concentration (~ 0.02–0.2 wt%) of all three types of fillers was adequate to enhance the thermal conductivity and shape recovery ratio while maintaining the composite’s stretchability, whereas higher-filler concentrations (~ 1.0–2.0 wt%) were required to substantially increase the shape recovery speed and improve the tribological properties. Finally, PU-graphite composites were integrated into two embodiments of fire alarm device prototypes that we developed and were found to work efficiently and reliably under various simulated environments and field tests.