Development of 3D printing filament from recycled HDPE injection waste

The present study focused on the fabrication and characterization of three-dimensional (3D) printing filament produced from high-density polyethylene waste (rHDPE). The rHDPE was sourced from injection-moulded waste such as sprues, gates and runners. Due to the unsuitability of injection grade of polymer for extrusion process, injection-grade rHDPE was blended with extrusion-grade high-density polyethylene (HDPE) materials. Different blend ratios of injection-grade rHDPE to extrusion-grade HDPE (100:0, 60:40, 50:50, and 40:60) were prepared and extruded into 3D printing filaments. The filament characterization including filament diameter consistency, filament ovality, and melt flow index were evaluated, while the thermal stability of the blends was analysed using thermogravimetric analysis. Among the blend ratios, the 50:50 (injection-grade rHDPE: extrusion-grade HDPE) blend demonstrated the starting ratio for producing 3D printing filament with consistent filament diameter and was therefore selected for 3D printing tensile specimens for tensile testing, indicating its suitability for 3D printing applications. Tensile specimens printed from this 50:50 blend ratio filament were tested at three different infill densities (20%, 60%, and 100%). Furthermore, the tensile properties of 3D-printed parts printed from 50:50 rHDPE blend filament were compared with those of commercial virgin polylactic acid, polyethylene terephthalate glycol, and HDPE filaments.