Electro-thermally Responsive Shape-Memory SEBS Composites with Enhanced Performance through Integration of Myristoylated Cellulose Nanofibers and Silver Nanowires

Abstract

Segmented styrenic block copolymers, such as poly(styrene-b-ethylene-butylene-b-styrene) (SEBS), exhibit temperature-sensitive mechanical properties that can be fine-tuned, making them highly promising for shape-memory applications. So far, the addition of crystalline materials not only enhanced the shape memory via solid-to-liquid transition but also increased the risk of leakage during repeated cycles. To address this issue, we explored the self-assembly phenomenon of acylated cellulose as a phase-change material (PCM). They work as a stable PCM when they are grafted onto the cellulose surface. We improved the shape-memory performance of SEBS by incorporating myristoylated cellulose nanofibers (MCN) with a DS of 2.4 into the matrix and systematically investigated how varying the MCN content affects the mechanical properties, torsional shape memory, and residual strain of SEBS. The addition of MCN enhanced the dynamic mechanical properties, reduced the residual strain, and facilitated the formation of an additional crystalline phase within SEBS. The crystalline phase showed a melting temperature, Tm, of 64–66 °C. The optimized SEBS/MCN composite demonstrated 92.6% thermoresponsive shape fixity and 92.8% shape recovery across three cycles. To achieve an electrically driven shape-memory effect, we further doped the composite with silver nanowires (AgNWs). The final composite demonstrated excellent electro-thermal heating, reaching 80 °C within 30 s. It achieved 75% shape recovery within 5 min at just 8 V. This electro-thermal shape-memory composite is well suited for applications in aerospace, smart grippers, actuators, and soft robotics.