High-Resolution Solid State NMR Investigation of the Filler-Rubber Interaction: Part III. Investigation on the Structure and Formation Mechanism of Carbon Gel in the Carbon Black-Filled Styrene—Butadiene Rubber

Abstract

Abstract This investigation describes the elastomer—filler interaction and its formation mechanism using solid state high-resolution, high-speed 1H magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy. Pulsed NMR measurements were carried out on pure styrene-butadiene rubber (SBR), and solvent extracted carbon gels from freshly prepared and storage matured master batches. The effects of filler loading, storage maturation, severity of extraction and experimental temperature on the elastomer-filler interaction were examined and discussed. High resolution in NMR was achieved by higher temperature/low spinning rate, room temperature/high spinning and combined rotation and multiple-pulse spectroscopy (CRAMPS) techniques. High-speed magic-angle spinning (MAS) was found to be the most suitable method to achieve high resolution. Proton spin—spin relaxation time, T2, was measured successfully for each of the principal resonance species present in the samples. These measurements reveal an insight into the site-specific nature of the polymer—filler interaction. The relative immobilization of the dynamics of different protons, due to the presence of carbon black filler, and their temperature dependence evidence that the main chain vinyl proton is the most significantly immobilized one compared to the aromatic and methylene species. The effects of storage maturation and severity of extraction on the dynamics of the conformational jump have also been discussed. This work clearly demonstrates the importance of unsaturation on the bound rubber formation. It also provides first direct physical evidence confirming the hypothesis that bound rubber variation during the storage maturation is due to slow progressive replacement of short rubber chains by larger ones.