Functional, thermal and rheological properties of polymer-based magnetic composite filaments for additive manufacturing

Abstract

The design of functional composite filaments for fused filament fabrication requires a suitable polymer composition, functionality of particles, uniform distribution of fillers throughout the filament, and ade- quate printability. Uniform distribution at predictable concentrations is achieved by designing polymeric capsules containing the fillers and using them as feedstock for extrusion. Functionality can be inferred from that of the particles and target concentration. However, suitable conditions for printing strongly depend on polymer type and characteristics/concentration of fillers. Soft magnetic composite filaments were produced from polylactic acid (PLA) capsules filled with 30–52 wt. % maraging steel particles. Composite filaments preserve the soft magnetic character of the fillers. Fillers reduce the transition tem- peratures of the polymer by 5 K and have a profound impact on printability. Rheological characteriza- tion shows that the ‘‘ball bearing effect” of gas-atomized particles reduces the viscosity of the composites by more than one order of magnitude, decreasing printing temperature from 215 °C to 170 °C, associated with the lack of agglomeration of particles achieved by the proposed production method. Rheological experiments allow to detect the required changes in printing conditions without requiring an extensive and costly trial and error process of printing with a large set of printing parameters.