Inhomogeneities of sulfidic linkages and mullins effect in isoprene rubber vulcanizates vulcanized with sulfur donor agents

Gum vulcanizates exhibit the Mullins effect during large-strain cyclic tension. However, the details of the Mullins effect remain unclarified due to the difficulty of analysis of a complicated network structure. The Mullins effect in isoprene rubber (IR) vulcanizates has been systematically investigated to clarify the impacts of network in homogeneities caused by the distribution of sulfidic linkages. Chemical probe experiments and paraffin swelling have been performed in an attempt to clarify the contribution of the presence of different types of sulfidic linkages. Thermo-oxidative aging at a moderate temperature (353 K) has been used to assess the effect of changes in structural inhomogeneity on the Mullins effect in aged vulcanizates. During cyclic tension deformations, the recovery hysteresis and accumulated softening energy densities normalized by theoretical shear modulus of elastically effective network are influenced by the heterogeneity of network structure only before the onset of crystallization. These findings can be used to inform the design of the network structure and enhance the performance of rubber products.