Filament-Level Thermal, Structural, Mechanical, and Shape-Memory Characterization of PLA/Fe3O4 Composite Feedstocks for Magnetically Responsive FDM

Polylactic acid (PLA)/Fe 3 O 4 composite filaments for magnetically responsive fused deposition modeling were fabricated via solvent-assisted blending and twin-screw extrusion and evaluated in terms of their thermal, mechanical, structural, and magnetic shape recovery behavior. Although PLA/Fe 3 O 4 systems have been widely investigated for 4D printing applications, magnetic shape recovery at Fe 3 O 4 contents below 10 wt% has received limited attention. Therefore, PLA/Fe 3 O 4 filaments containing 5, 7.5, and 10 wt%Fe 3 O 4 were systematically investigated under an 88 kHz alternating magnetic field to determine the minimum nanoparticle concentration capable of producing effective magnetic shape recovery. Fe 3 O 4 incorporation did not significantly affect the glass transition temperature (59.5–61.7 °C), while crystallinity increased from 3.36% for pure PLA to 9.76% for the 10 wt%Fe 3 O 4 /PLA composite. Tensile strength decreased from 49.47 ± 0.94 MPa for pure PLA to 19.42 ± 2.73 MPa for the 10 wt%Fe 3 O 4 /PLA composite, whereas elongation at break decreased from 12.12 ± 0.36% to 2.85 ± 0.25%. Magnetic shape recovery experiments showed that actuation could be achieved even at sub-10 wt%Fe 3 O 4 loadings. Among the investigated formulations, the 10 wt%Fe 3 O 4 exhibited the highest recovery ratio, reaching 98.6% within 67 s under magnetic induction heating. In addition, a reproducible fabrication route for low-Fe 3 O 4 PLA composite filaments was established, providing a basis for future studies and scale-up manufacturing efforts.