Thermo-Reactively Coupled (TRC) HDPE for Melt-Processable Warp-Resistant FDM 3D Printing

Polyethylene, the most widely used and inexpensive commodity thermoplastic, remains unsuitable for 3D printing via fused deposition modeling (FDM) because of shrinkage-induced warping. Herein, this study aimed to develop a single-step reactive extrusion process to improve the filament-forming ability and 3D printability of high-density polyethylene (HDPE). HDPE was reacted with maleic anhydride, 1,10-decanediol, and a zinc acetate catalyst via peroxide-driven grafting in a melt extruder, and the subsequent coupling reactions yielded ester-containing, modified polyethylene structures. Unlike unmodified HDPE, which produced irregular filaments and poor 3D printing, the modified HDPE formulations produced filaments with a consistent diameter and enabled successful FDM printing with improved print quality. The optimized carbon-black-containing modified HDPE systems exhibited substantial mechanical improvements, with average enhancements of approximately 50-75% in tensile stress at break and an approximately 200% increase in elongation at break compared with neat HDPE. These results demonstrate that ester-containing HDPE has the potential to convert commodity HDPE into a melt-processable and mechanically improved feedstock for additive manufacturing applications. This study suggests that widely available post-consumer pigmented HDPE, which is otherwise unsuitable for reuse in packaging, could potentially be explored for 3D printing as an alternative to expensive acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA).