The author proposes a new concept with a new interface model for carbon black reinforcement of elastomers, based on stress analysis. A new model consists of double uncross-linked polymer layers of different molecular mobility, the inner glassy hard(GH) layer and the outer sticky hard(SH) layer surrounding a carbon particle.
Large stress increase with filler content and with increasing strain amplitude results from the strong stress concentration generated around carbon particles and its transmission to the whole system. The great increase of tensile stress is only possible when the stress-hardened super structure produced in the SH layer under large extension supports the large stress concentration. The super structure is the network of carbon particles interconnected by strands of oriented molecules, which is formed through a craze-like phenomenon in accordance with micro-voids formation.
A large part of Mullins effect results from the buckling of the strand of riented molecules. Thus, the large and instant stress reduction takes place in unloading. At long periods, the extended molecules in the uncross-linked SH layer will considerably relax and return to its original state.