Recyclable and reprocessable epoxy-polyhedral oligomeric silsesquioxane (POSS)/mesogenic azobenzene/poly (ethylene-co-vinyl acetate) composites with thermal- and light-responsive programmable shape-memory performance

In this study, an Epoxy/POSS-liquid crystalline azobenzene-Poly (ethylene-co-vinyl acetate) (Epoxy/POSS-Azo-EVA) composite was prepared via the thermal curing of epoxy monomers and multi-functional thiol-containing Polyhedral oligomeric silsesquioxane (POSS) in an EVA matrix. The EVA matrix afforded the composite with shape memory performance. Epoxy/POSS polymer was uniformly dispersed in the matrix to act as a rigid skeleton, leading to the improvement of the mechanical properties and shape memory performance of the composite. Liquid crystalline azobenzene as the photosensitive component provided the inner stress to render the composite film with photo-induced shape-deformation behavior under UV light. The composite film not only exhibited thermal- and light-responsive programmable shape-memory behavior stimulated by heat and light, but also was recyclable and reprocessable. Moreover, the recycled composite film was processed into different functional devices. A flexible photomechanical device based on the recycled Epoxy/POSS-Azo-EVA composite film was fabricated, and the soft device deformed into a hook-shape under UV light and hooked an object whose weight is larger than that of the device. A smart wire was also prepared via assembling a stretched recycled Epoxy/POSS-Azo-EVA composite film and a copper foil by adhesive. The wire could control the status of a circuit via changing its shape under UV light and maintain the status after the removal of light. The functional devices described in this work only needed a short time of UV irradiation during a work cycle, and the devices still held the temporary shape in the absence of UV irradiation. The recyclable and reprocessable Epoxy/POSS-Azo-EVA composite film in this work could provide a creative approach for the fabrication of novel photomechanical devices and soft robotics with energy-saving, intelligence, recyclability, and sustainability.