Dispersion of particulate in solvent cast magnetic thermoplastic polyurethane elastomer composites

Our research focuses on the processing of a thermoplastic magnetorheological elastomer (MRE) by solvent-casting a thermoplastic polyurethane (PU) elastomer with magnetic particulate for fused filament fabrication (FFF) applications. MREs are typically prepared by curing a thermoset silicone with magnetic particulate. Alternatively, thermoplastic MREs may be produced by the addition of magnetic particulate to a thermoplastic elastomer (TPE). FFF is a valuable manufacturing technique that allows for the creation of parts with inherent anisotropies. For the case of an MRE, FFF allows for the production of structures with tunable magnetic susceptibility along different axes. In these composites, the degree of particulate dispersion significantly affects the isotropy of material properties, which becomes increasingly important when small material volumes are used, such as in FFF. Incorporating solvent-casting as a method of producing polymer composites allows for greater control over the particulate addition method, leading to improved dispersion when compared to a polymer melt. For our purposes, composite films were produced in order to examine the effect of wet vs. dry addition of particulate on dispersion. The solvent used for casting was dimethylformamide (DMF). Preparation of polymer solutions included dissolution of PU in DMF to 20 w/v% followed by addition of the magnetic particulate. The particulates used were \u3c150 \u3eµm iron powder and 2–4 µm magnetite powder. Composite solutions were made to concentrations of 20, 30, and 40 w/w% particulate to polymer by addition of either dry particulate or particulate pre-suspended in DMF. It was found that wet addition of particulate led to improvement in particulate agglomeration and magnetite particulate exhibited a significantly higher degree of agglomeration than iron