Reactive Processing in Extrusion based Polymeric 3D Printing with Surface Segregating Additives

Fabricating complex geometries with isotropic, robust mechanical properties by fused deposition modeling (FDM) remains a key target in expanding additive manufacturing towards the production of large scale commercially relevant structures. Due to the large size of polymer chains and the complex thermal environment experienced by the printed filament in FDM, entanglement of polymers between layers is incomplete, resulting in weak inter-layer interfaces and unsatisfactory Z-strength. Recently, our group has addressed these issues by developing novel polymer materials for FDM that revolve around the introduction of low molecular weight surface segregating additives (LMW-SuSAs) to the filament. We have recently expanded this concept to reactive additives, including methacrylate terminated linear and 3-arm PLA LMW-SuSAs. These reactive additives can now form inter-layer crosslinks by rational introduction of UV photo-initiators and fiber-optic based UV illumination. In situ reactive processing of the printed layers results in drastic increases in the transverse tensile stresses of the printed layers up to ~140% and ~200% for the linear and 3-arm LMW-SuSAs respectively to create essentially isotropic materials.