Circular economy innovation: A deep investigation on 3D printing of industrial waste polypropylene and carbon fibre composites

Transforming waste polypropylene (PP) and waste carbon fibre into upcycled composite materials for additive manufacturing represents an ideal circular economy challenge. An optimized method for material extrusion and 3D printing was developed to overcome adhesion and warpage challenges during printing. The study explored the impact of varying waste carbon fibre weight fractions (0 wt%, 2 wt%, 5 wt%, 8 wt%, 15 wt%, and 25 wt%), firstly on the properties of filament and then on printability and mechanical properties of printed specimens. Optimized extrusion parameters yielded the successful fabrication of fibre-reinforced filaments. Micro-level assessment of the polymer revealed a decrease in mechanical properties due to thermal processes during filament making and 3D printing. Microstructural analysis, along with optical and scanning electron microscopy, provided insights into inter-bead voids, debonding, fibre dispersion, fracture modes, and filament/sample quality. Differential Scanning Calorimetry indicated slight matrix degradation during filament extrusion, leading to slightly reduced melting and crystallization temperatures.