Dielectric Relaxation Spectroscopy in Synthetic Rubber Polymers: Nitrile Butadiene Rubber and Ethylene Propylene Diene Monomer

Young Il Moon,Jae Kap Jung,Ki Soo Chung

doi:10.1155/2020/8406059

Abstract

The dielectric permittivity of synthetic rubber polymers, nitrile butadiene rubber (NBR) and ethylene propylene diene monomer (EPDM), with both frequency and temperature variations, was thoroughly investigated by dielectric relaxation spectroscopy (DRS). The spectrum versus frequency of DRS was analyzed with the semiempirical Havriliak–Negami formula and conductivity contribution by employing the newly developed “dispersion analyzer” analysis program. The main dielectric relaxations called the α- and β-processes, associated with the cooperative motion of chains in polymers, were discovered in the low-temperature region. In the high-temperature region, we found Maxwell–Wagner–Sillars (MWS) relaxation associated with polymer interfacing and normal-mode (α’) relaxation responsible for end-to-end dipole vector motion. The activation energies of schematic molecular chains responsible for the relaxation processes were obtained with the information about its motional mode. The glass transition temperature and dipole moment for the side group were also determined and compared with those from previous studies. In the EPDM specimen, the peaks of α- and β-relaxation merged at high temperature and were separated with decreasing temperature. The first observations of both merging and splitting were consistent with the results on the temperature dependency of the relaxation strength. Both contour mapping and three-dimensional plots for the two rubbers provide visual information for the distribution and mapping of relaxation.

Highlights

Many prior studies have been conducted by using various microscopic techniques to investigate the molecular dynamics or chain motions of synthetic rubber polymers [1,2,3,4,5]
Us, by employing dielectric relaxation spectroscopy (DRS), we have intensively investigated the molecular dynamics and entire relaxation processes embedded in two kinds of rubber polymers: nitrile butadiene rubber (NBR) and ethylene propylene diene monomer (EPDM), which are used as sealing materials for the fuel container in vehicles and other rubber applications
To visualize the filling agent, the SEM images of the carbon black filler-filled NBR and EPDM rubbers are shown in Figure 2. e red circles in Figure 2 indicate the aggregate form of the carbon black fillers

Summary

Introduction

Many prior studies have been conducted by using various microscopic techniques to investigate the molecular dynamics or chain motions of synthetic rubber polymers [1,2,3,4,5]. Xu et al [8] and Chailan et al [17] conducted DRS studies on EPDM and fluoroelastomer (FKM) rubbers, their results did not include the relaxation origin, calculation of activation energy, and glass to polymer transition temperatures. Previous works for NBR and EPDM were not undertaken to determine the electric dipole moment of the corresponding molecular structure in polymer chains [6,7,8, 17,18,19,20]. Us, we can commonly obtain a dipole moment for polymers from dielectric measurements [14, 16] with the application of modified theories. E activation energy, glass transition temperature, and electric dipole moment for the corresponding molecular chain were determined. The permittivity data for various temperatures and frequencies are shown as three-dimensional (3D) and contour plots for the three polymers. us, we could distinguish the distribution and mapping for relaxation processes

Materials and Methods

Results and Discussion

Disclosure