Thermoplastic magnetic elastomer for fused filament fabrication

Abstract

Magnetorheological elastomers (MREs) are unique smart materials of high elasticity and magnetic susceptibility. MREs are prominent for the high degree of mechanical deformation or changes in stiffness that can be induced by applying magnetic fields. While most MREs are made with thermoset elastomers, this research focuses on the development and testing of a thermoplastic magnetic elastomer for potential use as fused filament fabrication (FFF) filament. FFF, also known as 3D printing, is an additive manufacturing technique that consists of 1D viscous thermoplastic extrusions that create 2D layers that build up to a 3D part. This method of creating parts produces underlying anisotropies which can be tuned to control the properties of the final part. Our thermoplastic magnetic elastomer was created utilizing solvent casting techniques to disperse isotropic magnetic particulate within a thermoplastic polyurethane matrix. Samples were created spanning two different magnetic particulate types (<150 µm iron (Fe) & 2–4 µm magnetite (Fe3O4)) and each with three different particulate loadings (20, 30, 40 wt%). The material was then extruded into FFF filaments with a Filastruder. Mechanical stress vs. strain curves of the extruded filaments were obtained using an MTS tensile tester. Magnetic hysteresis loops were acquired with a vibrating sample magnetometer (VSM). The analogous pure polyurethane filaments were also extruded and tested as a control. Our testing indeed shows that altering the magnetic particulate type and weight percentage impacts both the magnetic and mechanical properties of the overall material. In general, the filament samples with iron particulate had higher diametric consistency and were more compliant than those with magnetite particulate. Additionally, samples with magnetite had higher magnetic susceptibility and coercivity but lower saturation magnetization than those with iron. Lastly, increasing particulate percentage increases both the mechanical stiffness and saturation magnetization of the samples, as expected.

Keywords

• thermoplastic elastomer
• magnetic elastomer
• filament extrusion
• mechanical properties
• magnetic properties