Effect of protective atmosphere and secondary treatment on filament fusion of polylactic acid composites prepared by fused deposition modeling

It is well known that poor interlayer adhesion from limited diffusion and entanglement of chains across the interlayer interface is the main reason for anisotropy of mechanical properties of 3D printed parts prepared by fused deposition modeling (FDM). The present study demonstrates the effects of a protective atmosphere and secondary treatment to improve fusion between filaments. The experimental results demonstrate that the mechanical properties of the parts with nitrogen protection increase by about 100% in the direction of filament accumulation while the oxidation degree of the surface of the filament drops by 9%, which indicates that the bond strength between the filaments is improved. And tensile strength is increased by about 10%–20% in the direction of filament accumulation after heat treatment and microwave treatment. Insufficient fusion between filaments and oxidation of the filament surface significantly affect the mechanical properties of printed parts by fused deposition modeling. The protective atmosphere can protect the surface of the filament from oxidation at high temperatures, and the filament interface achieves secondary fusion using heat treatment and microwave treatment, and the mechanical properties of the printed parts are significantly improved.