Investigation of the Carbon‐Black Network in Natural Rubber Under Cyclic Deformation

Abstract

Carbon‐black (CB) filled rubbers are often subjected to cyclic deformation in service, particularly in tire applications. To improve resistance to fatigue, better understanding of how the meso‐ or microstructures evolve under cyclic loading is necessary. The presence of a CB network for reinforcement of rubber has been proposed. We describe the study of a CB network in natural rubber by an analysis of the impedance spectrum. The characteristic frequency of the filled rubber is used to characterize the junction width of the CB network. As the junction width of the CB network decreases, theoretically the characteristic frequency will increase. When the CB concentration was less than 10%, the nonfatigued rubbers had normal frequency characteristics, i.e., the measured frequency increased with an increase of the CB concentration. However, rubber with higher CB loading had an abnormal frequency response, whose the origin has been unclear until now. Much work will be done to clarify it. By examining the characteristic frequency, the dependence of the CB network in natural rubbers on the deformation cycle was studied. In general, the higher the number of fatigue cycles, the lower the characteristic frequency that was obtained. Although the rubber specimens showed little change in length in the tension direction before and after the fatigue cycles, the predicted change (different from the recoverable change) in the CB network did occur.