Feedstock characterization and process calibration for fused pellet fabrication of PLA/limestone composites

Abstract Natural stone industry generates large volumes of mineral waste, whose valorization in polymer composites through 3D printing remains limited. This study explores the feedstock properties, calibration, and mechanical performance of poly(lactic acid) (PLA) composites with limestone using screw-assisted material extrusion. Neat PLA and composite pellets were characterized by differential scanning calorimetry, rheometry, and Fourier-transform infrared spectroscopy. Thermal analysis indicated that limestone promoted heterogeneous nucleation at moderate filler loading, whereas excessive incorporation disrupted crystallization due to reduced chain mobility. Rheological analysis revealed shear-thinning behavior for all formulations, with viscosity increase with limestone addition at higher angular frequencies and suppressed terminal elastic response at high filler content. Fourier-transform infrared spectroscopy suggested minor structural changes without significant signs of compounding-related degradation. A three-stage calibration process on a retrofitted 3D printer established fused pellet fabrication (FPF) process conditions. Mechanical tests showed higher limestone content increased stiffness, reaching an elastic modulus up to 4.3 GPa for the composite containing 50 wt.% of limestone, while reducing ductility and strength, consistent with values reported for filament-based fused filament fabrication. Overall, this work demonstrates the feasibility of processing PLA/limestone composites via desktop-scale FPF and highlights the importance of formulation-specific calibration. The findings support the potential upcycling of mineral waste from the stone industry into value-added, eco-friendly materials for additive manufacturing.