New article in Advanced Composites and Hybrid Materials

Thermoset based resins and composites usually exhibit limited ability to be reprocessed due to their highly crosslinked structure, making their reuse and recycling particularly challenging. Strategies to promote the reshaping and reuse of thermoset resins thus hold great promise towards reduction of waste and enhanced circularity. This research aims to develop innovative dynamic composite materials that offer tunable mechanical stiffness and shape adaptability. To this end, dynamic disulfide bonds and ester groups were introduced into an initiator-free and catalyst-free amine-acrylate formulation, where polymerization occurred through an Aza-Michael addition reaction. The analysis of the curing kinetics revealed rapid polymerization at a temperature of 40°C when using cystamine as a non-toxic and bio-based amine hardener. Composites were then produced by adding thermoplastic polylactid acid (PLA) and polyethylene terephthalate (PET) particles to explore their potential to enhance the dynamic response of the composites. The relaxation time of the composites at reprocessing temperatures strongly decreased in all composites, down to half when adding 10 vol% PLA, while the tensile strength increased by 100% and 65% for the PLA and PET composites respectively. These particles promote stress relaxation via the presence of dynamic bonds at the particle-network interface, rather than via softening/melting during reprocessing. The composites were successfully thermally reprocessed, with a shorter time as compared to the matrix and minimal loss of mechanical properties and relaxation time.