English Abstract

Studies on Structures and Dynamic Properties of Peroxide-Crosslinked EPDMs, Part 5 Relation of Storage Modulus to Crosslinking Density and Molecular Mobility Hitoshi IWABUKI Kazuya NAGATA Industrial Technology Center of Okayama Prefecture, Okayama , Japan Toru NOGUCHI Nissin Kogyo Co., Ltd., Toumi-shi, Nagano, Japan Eisuke YAMADA Aichi Institute of Technology, Yakusa-cho, Toyota, Japan Nippon Gomu Kyokaishi,(2006),79(12),551-556 Original Paper in Japanese Abstract Peroxide-crosslinked EPDMs were examined by dynamic mechanical analysis. In a rubbery state, a plot of storage modulus (E') vs. temperature gave an approximately linear relationship. The slope of the approximated line increased with an increase in apparent crosslinking density (ƒË) which was calculated from equilibrium swelling. However, E' of peroxide-crosslinked EPDMs were not proportional to absolute temperature (T). For the EPDMs crosslinked above 400 mol/m3 ofƒË, straight lines approximating the relationships between E' and T gave a constant T-intercept at E' = 0. This indicates that E' in a rubbery state is proportional to the difference between T and a reference temperature (T). Assuming E' proportional to T-T effective crosslinking density (ƒË) was calculated from E' as T = 150 K. Spin-spin relaxation time of network component (T) and the fraction (F) were measured by 1H pulsed NMR with Hahn echo method. At each temperature, 1/T (or F/T) showed good linear correlation with E'. Over the temperature range 343 to 423 K, the plot of 1/T (or F/T) vs.ƒË gave a straight line independent on the temperature at which E' and T were measured. (Received on June 7, 2006) (Accepted on October 3, 2006) Keywords: EPDM, Peroxide, Dynamic Viscoelasticity, Storage Modulus, Crosslinking Density, Pulsed NMR, Spin-spin Relaxation Time, Molecular Mobility

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