Effect of oxidized carbon black on the mechanical properties and molecular motions of natural rubber studied by pulse NMR

The mechanical properties such as elastic modulus and stress‐relaxation and spin‐spin relaxation time T2 from pulse NMR were measured for surface‐oxidized carbon‐black‐filled natural rubber. The extent of reinforcement increased with CB volume percent in the range of 0–30%. At a given CB percent, this quantity increased by surface oxidation of fillers and decreasing filler size. From pulse NMR experiment, it was found that there were three components in rubber molecules which have different values for T2. Stress‐relaxation time and elastic moduli fitted one master curve against effective volume, fraction which is the sum of filler and bound rubber fraction. It was found that the distance between particle surfaces is the most important factor influencing reinforcing properties of filled polymers.