Molecular Mobility of Unfilled and Carbon-Black-Filled Isoprene Rubber: Proton NMR Transverse Relaxation and Diffusion

Abstract

In an effort to understand the effect of ultrasound on the devulcanization of gum and filled isoprene rubber vulcanizates, solid state NMR 1 H transverse relaxation (T 2 ) was employed to analyze rubber molecular mobility. The T 2 relaxation decay of the unfilled and the black filled IR was successfully described by a two-component model. The short T 2 component arose from the chemically crosslinked (gel) and physically entangled (heavy sol) network. The long T 2 decay came from the unentangled sol and dangling network chain ends. Vulcanization decreased the molecular mobility; however, ultrasound devulcanization partially reversed this effect. Addition of processing oil in the filled IR significantly altered the dependence of T 2 on the sol fraction. T 2 and pulsed-gradient diffusion experiments were carried out on IR melt specimens after sonication with or without subsequent vulcanization. The lowered and broadened M-distribution produced results quantitatively related to earlier work in natural rubber. * Corresponding

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