Material Extrusion Additive Manufacturing with Polyethylene Vitrimers.

Polyethylene (PE) is one of the most widely used polymers in conventional polymer manufacturing processes. However, it remains a challenge to use PE in extrusion-based additive manufacturing (AM). Some of the challenges that this material presents include low self-adhesion and shrinkage during the printing process. These two issues lead to higher mechanical anisotropy when compared to other materials, along with poor dimensional accuracy and warpage. Vitrimers are a new class of polymers that have a dynamic crosslinked network, allowing the material to be healed and reprocessed. Prior studies on polyolefin vitrimers suggest that the crosslinks reduce the degree of crystallinity and increase the dimensional stability at elevated temperatures. In this study, high-density polyethylene (HDPE) and HDPE vitrimers (HDPE-V) were successfully processed using a screw-assisted 3D printer. It was demonstrated that HDPE-V were able to reduce shrinkage during the printing process. This shows that 3D printing with HDPE-V will provide better dimensional stability when compared to regular HDPE. Furthermore, after an annealing process, 3D-printed HDPE-V samples showed a decrease in mechanical anisotropy. This annealing process was only possible in HDPE-V due to their superior dimensional stability at elevated temperatures, with minimal deformation above melting temperature.