Reactive Processing in Extrusion-Based 3D Printing to Improve Isotropy and Mechanical Properties

• Published in: Macromolecules 2019-09, Vol.52 (17), p.6495-6501
• Main Authors: Levenhagen, Neiko P, Dadmun, Mark D
• Format: Article
• Language: English
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.9b01178

Minimizing anisotropy in parts prepared by fused deposition modeling remains a key area of research in the development of robust and mechanically useful three-dimensional (3D) printed objects. Because of the bulky nature of polymer chains and the complex thermal environment experienced by adjacent filaments during the printing process, interactions of polymer chains between layers are minimized, resulting in weak interfaces and poor layer adhesion. In recent years, our group has addressed these issues through the introduction of low-molecular-weight surface-segregating additives (LMW-SuSAs). LMW-SuSAs are smaller than the polymer chains of the neat material and can more readily diffuse and entangle in adjacent layers during the printing process. In the current research, we report a novel reactive processing protocol for extrusion-based 3D printing, where bimodal blends contain linear and three-arm PLA LMW-SuSAs that are terminated with methacrylate groups and coupled by ultraviolet (UV) irradiation during the 3D printing process. In situ irradiation of the printed layers results in drastic increases in the transverse maximum tensile stress of the printed structures, where an increase of up to ∼140 and ∼200% for the linear and three-arm LMW-SuSAs is observed. Additional experiments document the effect of in situ UV intensity on the reactive processing protocol, where a decrease in intensity leads to control of the in situ reaction, which allows the balance of formation of the covalent bonds with the mobility of polymer chains to diffuse across the interfilament interface to optimize the fidelity and robustness of the printed structure.