3D printable hybrid acrylate-epoxy dynamic networks

Polymer networks with dynamic bonds, also known as covalent adaptable networks (CANs) combine the superior mechanical properties and chemical resistance of thermosets with the ability to be reprocessed, a feat formerly attributed only to thermoplastics. Inspired by an evergrowing body of research on dynamic poly(8-hydroxy ester) networks, a polyacrylate/epoxy-acid thermoset was designed, which contains a high concentration of 8-hydroxy ester bonds that partake in transesterification reactions that facilitate the repair and recycle of the cured material at feasible temperatures. Firstly, liquid formulations are subjected to UV light to initiate acrylate homopolymerization to obtain the intermediate, partially-cured material. A subsequent thermal treatment triggers the epoxy-acid reaction, which improves the mechanical properties and helps increase the likelihood of transesterifications as new 8-hydroxy ester groups are formed. The effect of thermal post-treatment and the choice of catalyst on viscoelastic properties and stress relaxation behavior of these materials is studied. Results show that, transesterification reactions reach equilibrium in less than 4 h at 180 degrees C during which time the overall crosslinking density increases further. As to the choice of catalyst, a commonly used zinc acetylacetonate outperforms an imidazole-type base. Thanks to the dynamic bonds, damaged samples can be repaired fully using simple procedures. Recyclability is tested by grinding pristine samples and re-molding them under pressure and temperature. Practically complete recovery of viscoelastic properties is confirmed.

Automated summary

Polymer networks with dynamic bonds, known as covalent adaptable networks (CANs), combine the mechanical properties and chemical resistance of thermosets with the ability to be reprocessed. In this study, a thermoset material with high concentration of dynamic bonds was designed to facilitate repair and recycle at feasible temperatures. The material was partially cured through UV light and further improved by a thermal treatment. The effect of thermal post-treatment and catalyst choice on the material's properties was investigated, showing that transesterification reactions increased the overall crosslinking density. The material demonstrated the ability to be fully repaired and recycled due to the presence of dynamic bonds.