Analysis of Styrene-Butadiene Based Thermoplastic Magnetorheological Elastomers with Surface-Treated Iron Particles

Abstract

Magnetorheological elastomers (MRE) are increasing in popularity in many applications because of their ability to change stiffness by applying a magnetic field. Instead of liquid-based 1 K and 2 K silicone, thermoplastic elastomers (TPE), based on styrene-butadiene-styrene block copolymers, have been investigated as matrix material. Three different carbonyl iron particles (CIPs) with different surface treatments were used as magneto active filler material. For the sample fabrication, the thermoplastic pressing method was used, and the MR effect under static and dynamic load was investigated. We show that for filler contents above 40 vol.-%, the linear relationship between powder content and the magnetorheological effect is no longer valid. We showed how the SiO₂ and phosphate coating of the CIPs affects the saturation magnetization and the shear modulus of MRE composites. A combined silica phosphate coating resulted in a higher shear modulus, and therefore, the MR effect decreased, while coating with SiO₂ only improved the MR effect. The highest performance was achieved at low deformations; a static MR effect of 73% and a dynamic MR effect of 126% were recorded. It was also shown that a lower melting viscosity of the TPE matrix helps to increase the static MR effect of anisotropic MREs, while low shear modulus is crucial for achieving high dynamic MR. The knowledge from TPE-based magnetic composites will open up new opportunities for processing such as injection molding, extrusion, and fused deposition modeling (FDM).

Keywords: magnetorheological effect; magnetorheological elastomer; static and dynamic mechanical analysis; thermoplastic elastomer.

Figure A1

Calculated magnetic field intensity using (a) 2 pairs of permanent magnets and (b) 3 pairs of permanent magnets.

Figure 1

(a) Warm-pressing of the MRE samples, (b) pre-structuring the MRE sample under magnetic field H, and (c) CPI alignment in the TPE-based MR elastomer.

Figure 2

(a) Sample preparation in the dynamic mechanical analyzer. (b) A sketch of the sample with applied magnets at the edges of the sample.

Figure 3

(a) Calculated magnetic field intensity using 1 pair of permanent magnets and (b) the variability of the field across the MRE.

Figure 4

(a) Static and (b) dynamic tests procedure to investigate the MR effect of SEBS-based composites.

Figure 5

The influence of the CIP content on the MR effect (a) for the static test, a strain amplitude of 1% and pre-strain of 1.53% was used; (b) for the dynamic test, a strain amplitude of 0.66% was investigated. STL matrix with different concentrations of HS-type CIP; a constant frequency of 10 Hz and field strength of 0.54 T was selected for all tests.

Figure 6

The torque at the end of the mixing process and density of the SEBS-based composite in relation to the volume concentration of CIP. The red line shows the calculated density based on the mixing rule. The blue line presents the measured density, and the stars are torque measured in Nm.

Figure 7

The magnetization loop for (a) STL type styrene-ethylene-butadiene-styrene thermoplastic elastomers with HS filler content between 10 and 60 vol.-%, (b) 30 vol.-% filler content of three different CIP grades in STL type styrene-ethylene-butadiene-styrene thermoplastic elastomers.

Figure 8

The saturation magnetization in relation to the CIP content and extrapolation of the results to 100% carbonyl iron.

Figure 9

The influence of matrix material during static (a) and dynamic (b) strain on the MR effect. Composites STL30CC and STT30CC were used for this analysis. A constant strain amplitude of 1%was used for the static tests. A constant frequency of 10 Hz and field strength of 0.54 T were used for both test conditions.

Figure 10

The effect of static (a) and dynamic (b) strain on MR effect. For this investigation, STL30HS, STL30CC, and STL30EW-I composites were used. All samples contain 30 vol.-% CIP in an STL matrix. A constant strain amplitude of 1%was used for the static tests. A constant frequency of 10 Hz and field strength of 0.54 T were used for both test conditions.