Recyclable 3D Printing of Polyimine-Based Covalent Adaptable Network Polymers

Recyclable 3D printing of thermosets was realized by utilizing the solvent-assisted recycling of covalent adaptable networks (CANs). The printouts, if damaged or after usage, were fully depolymerized in an organic solvent, and they were partially cured into a new ink for the next round of 3D printing. This work presents fundamental studies to understand the influences of ink composition and rheological properties on the printability, recyclability, and thermomechanical properties of printed CAN components. A polyimine-based CAN is used as the material platform for the direct-ink-writing (DIW) 3D printing, which exhibits lower processing temperature and catalyst-free features. This study reveals that the incorporation of nano-clay maintains the recyclability, malleability, and thermomechanical properties of polyimines, and it dramatically improves the shear modulus and yielding stress of inks for the 3D printing of complex structures with dangling features. The developed inks are shown to be recycled five times and still retain an excellent printability. The 3D-printed polymer structures usually exhibit notable anisotropic mechanical properties due to their weak interfaces. However, the DIW printing of CANs is shown to create structures with comparable properties in different printing directions because of the strong interfaces connected by covalent bonds. It, thus, possesses the great potential to tackle this long-standing challenge in the 3D printing field.