MECHANICAL-GAMMA AND BETA-RELAXATIONS IN POLYETHYLENE .2. PHYSICAL MODELS OF THE MECHANICAL-GAMMA RELAXATION IN POLYETHYLENE

Mechanical spectrometry performed in the gamma-region of polyethylene has shown that this well-defined relaxation has some characteristics of relaxation related to glass transition (see Part I). In order to verify the validity of such an approach, this paper attempts to give a theoretical basis to an approach based on a physical model previously developed to predict the deformation of amorphous materials near T(g). As polyethylene is a semicrystalline polymer, the behaviours of the two phases must be separated by using a model for composite systems. It was shown that the dynamic mechanical behaviour of the amorphous phase of polyethylene in the gamma-region is well described by the physical model. Moreover, this physical model gives evidence for the crosslinking of the amorphous phase by crystallites acting as physical ties.