Electroactive Shaping and Shape Memory of sequential dual-cured off-stoichiometric epoxy/CNT composites

Abstract Sequential dual-cured epoxy composites, based on off-stoichiometric thiol‒epoxy mixtures catalysed by 1-methylimidazole, have been developed by adding carbon nanotubes (CNT). The epoxy curing process initially consists in two thermally activated curing stages: a first thiol‒epoxy reaction and later homopolymerization at a higher temperature. This system presents easy shaping/conforming and shape memory properties through thermo-mechanical treatments. Addition of the electrical CNT network into the epoxy matrix allows electrical switching, which increases its performance and in-situ applicability. The obtained results confirmed that CNTs catalyse the homopolymerization epoxy reaction, hindering the sequential curing process, due to the π-π anchoring of imidazole catalyser over the CNTs surface, enhanced by donor‒acceptor interaction. Non-doped off-stoichiometric resins present relatively high thermal strength, with a glass transition temperature in the range of 73‒109 °C, and high stiffness, with a storage modulus close to 2‒3 GPa. They can be easily conformed at low temperature, 60 °C, before their second curing stage, showing a high shaping efficiency (around 90%) and full fixing efficiency (>98%). Nanocomposites with 0.2% CNT present efficient Joule heating, triggering the shape memory at low voltage,