Thermal annealing effects on the mechanical properties of bio-based 3D printed thermosets

Abstract

3D printing technologies can address many sustainability aspects of creating new materials, such as reduced waste and on demand production, which reduces the carbon footprint of transport and storage. Additionally, creating bio-based resins for 3D printing is a viable way of improving the sustainability of polymeric materials. Coupled with this, by using dynamic covalent chemistry (DCC), we can provide materials with smart properties like self-healing or reprocessability to either extend their usable lifetime or provide an alternative to the materials ending up in a landfill. Here, we report a series of completely bio-based aromatic resins for digital light projection (DLP) printing. By incorporating β-hydroxyesters and a zinc catalyst, the polymer networks can participate in transesterification reactions to provide self-healing capabilities or reprocessability. The self-healing abilities of these materials were characterized using optical microscopy, and the reprocessability using a hot-press. Additionally, by subjecting the printed thermosets to thermal annealing, considerable changes in the mechanical performance were observed leading to more than a 2000% increase in the Young's modulus. The thermal behavior after annealing was also studied and a discussion on the effect of the structural differences between the aromatic monomers is proposed. These resin formulations address two of the key goals of sustainable materials: using renewable resources and obtaining recyclable materials while remaining competitive through their mechanical performance and compatibility with 3D printing technologies.