Nanocomposites of sequential dual curing of thiol-epoxy systems with Fe3O4 nanoparticles for remote/in situ applications: thermomechanical, shape memory, and induction heating properties

Abstract

Sequential dual-curing epoxy composites, such as the thiol-epoxy system, can potentially open new capabilities for end-products in the composite industry. This system remains stable after the initial curing and can undergo further reactions when exposed to a second stimulus, such as the use of magnetic induction: a remote and energy-efficient alternative. This study reports the first dual-curing thiol-epoxy resin reinforced with magnetic nanoparticles Fe3O4. The addition of Fe3O4 nanoparticles endows the polymer matrix with dual-stimuli shape memory, triggered by both conventional heating and the use of a magnetic field, broadening potential applications. The study examined various manufacturing conditions and loadings of Fe3O4, which improved the mechanical properties of the composites. The dual-response shape memory was evaluated by heating the polymer with both a conventional heat source and magnetic fields, resulting in a ~ 100% shape fixation and recovery ratio for either stimulus source, with superior performance under the magnetic field. Furthermore, under moderate magnetic fields, the system was able to reach temperatures as high as 160 °C, and the influence of various parameters on the efficiency of magnetic induction heating was studied by statistical analysis of design of experiments. Additionally, two proofs of concept were presented. In the first, the second curing step was performed under the in situ heating generated by the magnetic field, successfully fixing the temporary shape into the permanent form of the sample. In the second concept, the system was utilized as a smart switch or a threshold temperature sensor.