Mechanical and microstructural analysis of glass Fibre-Reinforced high density polyethylene thermoplastic waste composites manufactured by material extrusion 3D printing technology

As the demand for thermoplastic composite materials continues to surge across diverse industries, the imperative for efficient waste management, collection, and recycling of domestic thermoplastic materials has become increasingly evident. This study presents a novel approach to upcycling non-printable domestic High-Density Polyethylene (HDPE) waste and industrial waste fibres into viable feedstock for 3D printing manufacturing, addressing critical technical challenges such as adhesion to the build plate, nozzle clogging, and warpage. The investigation focused on the incorporation of various glass fibre weight fractions—2 wt%, 5 wt%, 8 wt%, 15 wt%, 30 wt%, 45 wt%, and 60 wt%—into HDPE waste. The optimisation of filament production and 3D printing parameters was performed, resulting in the highest tensile strengths for both filament (54.5 MPa) and printed specimens (29.83 MPa) at a glass fibre content of 45 wt%. It was observed that exceeding a glass fibre content of 45 wt% led to fibre agglomeration, subsequently diminishing tensile strength in both filaments and printed samples. In contrast, the samples with 30 wt% glass fibre exhibited the highest flexural strength. The study further employed optical microscopy to evaluate fibre distribution and internal defects within the filaments and printed samples, while Scanning Electron Microscopy (SEM) was utilised to analyse the fracture surfaces of 3D printed coupons. The findings revealed that the dominant fracture mechanism in these composites was fibre pull-out. The research successfully fabricated a demonstrator, showcasing the potential of HDPE domestic thermoplastic waste, reinforced with glass fibre, to be processed into functional industrial composite components via 3D printing.