Development and Characterization of Stable Polymer Formulations for Manufacturing Magnetic Composites

Abstract

Polymer bonded permanent magnets find significant applications in a multitude of electrical and electronic devices. In this study, magnetic particle-loaded epoxy resin formulations were developed for in-situ polymerization and material jetting based additive manufacturing processes. Fundamental material and process issues like particle settling at room temperature and elevated temperature curing, rheology control and geometric stability of the magnetic polymer during the thermal curing process are addressed. Control of particle settling, modifications in rheological behavior and geometric stability were accomplished using an additive that enabled the modification of the formulation behavior at different process conditions. The magnetic particle size and additive loading were found to influence the rheological properties significantly. The synergistic effect of the additive enabled the developing of composites with engineered magnetic filler loading. Morphological characterization using scanning electron microscopy revealed a homogenous particle distribution in composites. It was observed that the influence of temperature was profound on the coercive field and remanent magnetization of the magnetic composites. The characterization of magnetic polymers and composites using rheometry, scanning electron microscopy, X-ray diffraction and superconducting quantum interference device (SQUID) magnetometry analysis enabled the correlating of the behavior observed in different stages of the manufacturing processes. Furthermore, this fundamental research facilitates a pathway to construct robust materials and processes to develop magnetic composites with engineered properties.

Rheology-Assisted Microstructure Control for Printing Magnetic Composites—Material and Process Development

“…The first observed characteristic in Figure 13 A is the presence of hysteresis, attributed to the ferromagnetic SrFeO filler. The saturation magnetization of ~7.5 Am 2 /kg is consistent with the 10% of SrFeO with a saturation magnetization of ~70 Am 2 /kg, as previously reported [ 30 ]. Compared to the direction perpendicular to particle structuring, saturation magnetization along the direction of field structuring is observed to be higher by 0.10 Am 2 /kg, magnetic remanence by 0.13 Am 2 /kg, and coercivity by 0.06 Tesla, see Figure 13 B–D, respectively.…”

“…The Hershel–Bulkley model equation is expressed as follows: where τ 0 is the yield point or yield strength, C is the consistency index, and k is the Herschel–Bulkley index. The Herschel–Bulkley index primarily determines the behavior of the suspension as follows: k < 1 for shear thinning behavior, k > 1 for shear thickening behavior, and k = 1 for Bingham behavior [ 29 , 30 ].…”

Fumed Silica-Based Suspensions for Shear Thickening Applications: A Full-Scale Rheological Study

“…Strain thinning behavior originates from the disentanglement of polymer chains and/or, in the case of a filled system, disruption and alignment of microstructures with the flow. 56,64,69,70 A network model consisting of segments and junctions was proposed by Sim et al 71 to explore possible mechanisms for complex large amplitude oscillatory shear (LAOS) behavior. The network consists of junctions with a distribution of ages and segments created or lost during the flow.…”

Development and Characterization of Field Structured Magnetic Composites

“…Differences in the apparent degree of particle alignment and stacking between sample S2 and S3 in Figure 9 are likely related to the prepolymer viscosities. From previous research it is known that the viscosity of the acrylate-based prepolymer is approximately 0.3 Pa·s whereas the value for the epoxy resin is 7 Pa·s [ 20 , 35 ].…”

“…Additive manufacturing (AM) is gaining momentum towards developing bonded magnets and magnetic composites with a wide range of magnetic particles and polymeric matrix materials. The fabrication of bonded magnets by adopting material jetting AM processes with epoxy resin based magnetic pastes was demonstrated in the technical literature [ 18 , 19 , 20 ]. Rheological additives and multimodal magnetic mixtures were utilized to develop the feedstock materials for material jetting AM processes.…”