Stress softening in natural rubber vulcanizates. Part II. Stress softening effects in pure gum and filler loaded rubbers

Abstract Considerable stress softening (Mullins effect) occurs in both gum and filler loaded vulcanizates of natural rubber and SBR. When compared at the same stress, the extent of softening is similar in both gum and filled vulcanizates. The stress softening is shown to be mainly due to changes in the rubber phase in the filled vulcanizate, and related to that of the gum vulcanizate by the use of the strain‐amplification factor discussed in Part I of this series.