Sustainable recycled coloured polypropylene using fused granulate fabrication: Influences of pigments, copolymer composition and morphology on material properties

The growing demand for sustainable polymers drives the utilisation of coloured recycled polymers in additive manufacturing. This study systematically investigates the influence of pigments, copolymer, and morphology on thermal, rheological, and mechanical behaviours of recycled polypropylene (rPP) processed using Fused Granular Fabrication (FGF). FTIR and XRD analyses identified polyethylene segments in opaque samples (red, purple, black and blue) and pigments induced crystallinity modification, while clear and green samples retained well-defined isotactic structures. DSC and TGA indicated dual melting peaks and minor reductions in thermal stability in copolymer-rich samples. Rheological measurements showed that melt flow viscosity and shear-thinning behaviour depend on pigment-polymer interactions and copolymer composition. Mechanical testing revealed pronounced effects on tensile (13.3–23.8 MPa), flexural (19.9–30.3 MPa), and impact (3.5–7.5 kJ/m 2 ) properties depending on printing temperature and formulation. Fractography revealed phase separation, cavitation, and pigment dispersion influencing energy dissipation. Successful single and multi-colour rPP showcases validated structural integrity for sustainable additive manufacturing applications. • Six coloured recycled polypropylene (rPP) granulates were systematically evaluated as FGF feedstock. • FTIR and XRD analyses identified polyethylene (PE) segments and pigment-induced crystalline disruptions in selected samples. • DSC and TGA revealed pigment and composition-dependent variations in melting, crystallisation, and thermal degradation behaviour. • Mechanical properties were strongly influenced by pigment chemistry, copolymer content, and processing temperature. • Fractographic analysis showed distinct fracture mechanisms among coloured rPPs, including ductile failure, cavitation, and particle debonding.