Ecocomposite Filaments from Spent Coffee Grounds for FFF 3D Printing: Material Properties and Printability

In this study, spent coffee grounds (SCGs) were incorporated into polylactic acid (PLA) filaments and 3D-printed parts to investigate their effects on thermal, physical, and mechanical properties. Differential scanning calorimetry showed that SCG addition slightly reduced the glass transition temperature of PLA while markedly increasing its crystallinity, whereas thermogravimetric analysis revealed a moderate decrease in degradation onset temperature that remained well above the processing and printing temperatures, ensuring safe fabrication. Tensile testing indicated that SCG incorporation led to noticeable reductions in filament strength and stiffness, whereas the elongation at break was only weakly affected because of counteracting plasticization effects. For the printed parts, SCGs imparted a dark brown coloration, decreased density, and increased moisture uptake due to their porous and hydrophilic nature, while tensile, flexural, and impact strengths were reduced and the tensile modulus and elongation at break remained statistically similar across the 0–20 wt% range. These findings indicate that SCGs can be effectively incorporated to tailor the crystallinity, color, and density of PLA-based 3D-printed composites, albeit with trade-offs in strength and impact performance.