Upcycling waste polypropylene with basalt fibre reinforcement enhancing additive manufacturing feedstock for advanced mechanical performance

• Short basalt fibres enhanced printability of upcycled polypropylene . • 3D printed PP showed highest tensile strength at 15 wt.% short basalt fibre content. • Printed PP showed highest flexural strength at 30 wt.% short basalt fibre content. • Innovative solution and optimised processing parameters were suggested to print PP. This research seeks to overcome the printing and processing challenges of using waste polypropylene (PP) reinforced with short basalt fibres, transforming them into upcycled feedstock for additive manufacturing. It introduces an optimised method for producing filaments and 3D printing with these materials, addressing common issues such as adhesion and warpage through innovative techniques while achieving maximum mechanical performance in the resulting composites. Basalt fibre weight fractions of 0 %, 2 %, 5 %, 8 %, 15 %, 30 %, and 50 % were used to reinforce the recycled polypropylene, improving both printability and mechanical properties. The tensile strength reached 53.58 MPa at 15 % fibre content, while the flexural strength peaked at 34.06 MPa with 30 % fibre content, revealing distinct interactions between the fibres and polymer under tensile and flexural loading that were not previously observed. Microstructure, voids, debonding, and dispersion were examined using optical and scanning electron microscopy. Differential Scanning Calorimetry (DSC) was performed to assess the thermal behaviour and crystallinity of the recycled polymer during filament production and printing, revealing slight matrix degradation during these processes. The findings highlight the potential of waste basalt fibre-reinforced PP as a valuable filament feedstock for 3D printing, supporting a circular economy approach to composite manufacturing.