3D printing of high density polyethylene by fused filament fabrication

Polyolefin thermoplastics like high density polyethylene (HDPE) are the leaders in terms of world-scale plastics' production, environmentally benign polymerization processes, recycling, and sustainability. However, additive manufacturing of HDPE by means of fused deposition modeling (FDM) also known as fused filament fabrication (FFF) has been problematic owing to its massive shrinkage, voiding and warpage problems accompanied by its poor adhesion to common build plates and to extruded HDPE strands. Herein we overcome these problems and improve Young's modulus, tensile strength and surface quality of 3D printed HDPE by varying 3D printing parameters like temperature and diameter of the nozzle, extrusion rate, build plate temperature, and build plate material. Both nozzle diameter and printing speed affect surface quality but do not impair mechanical properties. Particularly, an extrusion rate gradient prevents void formation. For the first time additive manufactured HDPE and injection-molded HDPE exhibit similar mechanical properties with exception of elongation at break. Excellent fusion of the extruded polymer strands and the absence of anisotropy are achieved, as verified by microscopic imaging and measuring the tensile strength parallel and perpendicular to the 3D printing direction.