Time-evolution of the structure of organoclay/ polypropylene nanocomposites and its influence on time/temperature superposition principle

Abstract : We investigate the rheological properties of a nanocomposite in small amplitude oscillatory shear. The evolution of the storage modulus with time shows that this material is not stable: the microstructure changes continuously with time, due to the disorientation of the clay platelets and the build-up of a 3D network. This evolution of the microstructure is evaluated by measuring the apparent yield stress. A two-step kinetics is evidenced, whose parameters directly depends on temperature. This time-evolution is generally assumed to violate the time-temperature superposition principle. However, we demonstrate that the time-temperature equivalence always exists if we consider samples having the same microstructure.