Low-melting-point alloy/polyurethane auxetic composite foam for outstanding impact protection with favorable shape memory effect

Abstract High energy dissipation materials are crucial for impact protection gear. Additionally, if these materials also have shape memory property, they can offer a better body fit and increase comfort feeling. Herein, we present a novel auxetic composite foam with ultrahigh specific energy dissipation (SED) and shape memory property, which was prepared by directly foaming with low-melting-point alloy (LMPA) in polyurethane (PU) followed by thermal compression process. Due to the synergetic action of LMPA and auxetic PU foam (APU), APU/LMPA foam showed better energy dissipation than pristine PU foam. The compression test showed the energy dissipation and SED of the APU/LMPA foam were 13.4 times and 4.8 times higher than non-APU foam, respectively. Furthermore, the SED improvement of APU/LMPA foam was much higher than other reported auxetic foams. The impact test demonstrated that APU/LMPA foam with 30% thinner thickness could reduce transmitted peak force by 62.1% compared to non-APU foam. Additionally, APU/LMPA foam exhibited shape memory effect due to the phase transition of LMPA, allowing it to adapt to different body shapes through thermal process. With its outstanding energy dissipation and shape memory properties, this composite foam is highly promising for personal safety protection, offering excellent user experience.