Thermoset meets thermoplastic: upcycling PLA in digital light processing 3D printing of dynamic thiol–ene composites

A dynamic thiol–ene resin processable by vat photopolymerisation 3D printing is formulated and reinforced with micro-sized polylactic acid (PLA) particles to combine thermoplastic upcycling with the unique features of a covalent adaptable network (CAN). The influence of filler concentration on cure kinetics, printability, thermal stability of the obtained composites, and dynamic bond-exchange kinetics is investigated. Photo-rheology and photo-DSC experiments show that PLA particles do not compromise on cure kinetics and enable earlier development of green strength compared with the pristine resin. Formulations containing up to 20 vol% PLA are successfully used to print model objects with a feature resolution of 500 µm. Post-curing at 160 °C removes residual volatiles and improves network homogeneity. The resulting composites exhibit increased stiffness, while stress-relaxation experiments confirm catalyst-dependent bond-exchange kinetics. These results establish a scalable approach to incorporating thermoplastics into 3D-printed dynamic covalent networks for more sustainable light-based additive manufacturing.