Unveiling hematite-rich nanoparticle emissions from stainless steel-containing PLA filament: First experimental...

Fused deposition modeling (FDM) 3D printing with metal-containing polymer filaments has gained widespread adoption across industrial and consumer applications. However, the potential release of metal oxide nanoparticles during the thermal processing of these composite filaments remains insufficiently investigated. This study provides the first experimental evidence of hematite (α-Fe₂O₃) - rich nanoparticle (mixed Fe-Cr-Ni) emissions from a 3D printer using stainless-steel-filled polylactic acid (PLA) filament (∼80 wt% stainless-steel). Emission testing was conducted in a standardized chamber following established protocols, and particles were characterized using scanning mobility particle sizer (SMPS), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. Results demonstrate that PLA-steel filament generates significantly higher concentrations of ultrafine particles (maximum: 9.08 × 10⁶ particles/cm³) compared to standard PLA (4.99 × 10⁶ particles/cm³) under identical printing conditions. The emitted particles from PLA-steel exhibited unique flake-like morphologies, with iron as the predominant element (26.5 at%). Crystallographic analysis confirmed the presence of hematite through characteristic lattice spacings (0.21 nm and 0.27 nm) and Raman spectral features (230, 412, and 609 cm⁻¹). These findings indicate that stainless steel-filled filaments can emit nanosized iron oxide particles, specifically hematite, during 3D printing. Given that hematite-rich nanoparticles have been associated with oxidative stress induction and cytotoxicity in various biological systems, their emission during 3D printing represents a potential occupational and environmental hazard that warrants further investigation, particularly considering the widespread adoption of metal-filled filaments in both professional and consumer environments.