Mechanical and rheological properties of ethylene propylene diene monomer based magnetorheological elastomers with silica nanoparticles

Abstract

Magnetorheological elastomer (MRE) is an emerged smart material in which its responsive moduli in term of mechanical and rheological properties are influenced by the presence of an external magnetic field. However, the low mechanical properties of existing MREs have limited its use in some engineering applications, and temperature is one of the most influential factors affecting the performance of elastomer matrix in MRE which deteriorates the required properties of MREs. Previous studies have utilized silica as a reinforcing filler around polymer composite. Furthermore, silica is also being used as one of coating material to the magnetic particle in MRE to improve the mechanical properties and thermal stability of the base material. However, the use of silica as an additive in the thermal stability of MRE has not been explored. Thus, in this study, the effect of different content of silica on the mechanical and rheological properties of ethylene propylene diene monomer (EPDM)-based MREs under various operating temperatures is investigated by using 30 wt.% carbonyl iron particles (CIPs). The microstructure analysis was examined by using field-emission scanning electron microscopy, while the thermal characterizations were studied by using a thermogravimetric analyser and differential scanning calorimetry. The tensile properties were conducted by using Instron Universal Testing Machine in the absence of magnetic field at various temperatures. Meanwhile, the rheological properties were analysed under oscillatory loadings in the influence of magnetic field, using a rotational rheometer at 25 to 65 C. The experimental results revealed that the temperature diminished the molecular chains of elastomer matrix and caused the interfacial defects between filler and matrix, thus affecting the properties of MRE, in which the tensile strength and MR effect decreased with increasing temperature. However, the presence of silica has improved the thermal stability of MRE, thus reducing the interfacial defects when under the influence of temperature. The distribution of silica within the EPDM matrix and the adhesiveness of silica into the CIPs surface that occupied the gaps between distributed CIPs within the matrix enhanced the interfacial interactions between filler and matrix. Consequently, the addition of 11 wt.% silica improved the tensile strength by 344% and maintained the MR effect compared to MRE without silica at room temperature condition. The similar trends were also observed when MRE under the influence of temperatures; the MRE containing silica had higher tensile strength compared to MRE without silica, while the presence of silica maintained the MR effect under various operating temperatures. The incorporation of silica nanoparticles as an additive in EPDM-based MRE has the potential to sustain the properties of MRE devices in various temperature conditions. Thus, the study on the temperature-dependent mechanical and rheological properties of MRE is necessary, particularly regarding its practical applications.