Evaluation and characterization of waste-derived eggshells as filler in polylactic acid filament feedstock for material extrusion additive manufacturing: a step towards circular manufacturing strategies

This study investigates the use of calcium carbonate-based fillers in polylactic acid (PLA) for material extrusion (MEX) additive manufacturing (AM), focusing on the development of sustainable composite materials that leverage waste-derived resources. Waste eggshells (ES) and mineral limestone (LS) were both individually melt-blended with PLA to initially create composite pellets and processed into filaments having filler contents of 0%, 5%, 10%, and 20% w/w. Tensile and flexural test specimens were fabricated by MEX AM for mechanical characterization. Scanning electron microscopy and particle size analysis revealed irregular particles with sharp edges (~17 µm) for both fillers. Capillary rheometry confirmed the preservation of PLA’s shear-thinning behavior for both filler types and investigated filler contents. Differential scanning calorimetry showed a distinctive crystallization pattern for PLA/LS composites. For both fillers, the test specimens’ tensile and flexural strengths decreased by increasing filler weight fraction. Conversely, the tensile and flexural modulus both improved by increased filler content. Tensile tests conducted on the filament feedstocks demonstrated inferior tensile strengths and tensile modulus when compared to 3D-printed test specimens. Collectively, these findings suggest that PLA/ES composites hold significant potential as sustainable materials for MEX AM, offering mechanical properties comparable to or better than pure PLA, while reducing plastic dependency and diverting calcium carbonate-rich waste from landfills.