Material damping in polymers comes from the intrinsic viscoelastic properties, which exhibit both elastic and viscous behaviors that are characterized by storage modulus and loss modulus, respectively, in dynamic mechanical analysis (DMA). The ratio between the loss and storage moduli, i.e., tanδ is generally used as a material damping factor or a loss factor. To measure tanδ values of TPV material, DMA was performed under the following condition: temperature-ramp test from -70 to 80 °C with 3 °C /min heating rate at 10 Hz. The dynamic strain of 0.25% was selected for the DMA tests, which is confirmed to be stay within the linear viscoelastic regime (LVR) by the strain-sweep test. Compression set of TPV was measured in accordance with ISO 315 (25% strain, 70 ℃, 22 h).
The material properties of the olefinic TPV can be determined by the following design factors: EPDM/PP ratio, EPDM crystallinity, EPDM crosslinking density, EPDM molecular weight distribution, PP crystallinity, crosslinking agent, filler, and process oil content and type. In this study, the EPDM/PP ratio and ENB content in the EPDM were chosen as the major factors among the design factors. The TPV material was fabricated using a twin-screw extruder. The mixing of the compound and crosslinking reaction of the EPDM were conducted simultaneously, so called a dynamic vulcanization process. After crosslinking, EPDM particles were dispersed in the PP matrix working as a physical crosslink of the TPV. Sheets of 2 mm thickness were manufactured using the prepared compositions with the aid of an injection molding machine.