MOLECULAR DYNAMICS PREDICTION OF ELASTIC AND PLASTIC DEFORMATION OF SEMICRYSTALLINE POLYETHYLENE

The elastic and large plastic deformations of semicrystalline polymers involve the multiscale organization of molecules inside spherulites and depend on the deformation path. Under a tensile test, as an effect of the lamellar organization, the first steps of elastic-plastic deformation are localized in a very thin layer in the equatorial zone, as shown by experiments. The molecular mechanism and the resulting stress-strain properties can be predicted by molecular dynamics simulations. An all-atom model is necessary to predict the behavior of polyethylene chains inside the amorphous and crystalline phases. Two large-molecular-weight polyethylene chains with a complex path are involved in crystalline and amorphous phases and in their interconnection with a 3D periodic condition. This paper explains the main physical characteristics of semicrystalline organization and the building process of this first molecular model which is fully coupled. This model, stretched along the thickness of the lamellae, is representative of the equatorial zone in a spherulite during the first steps of elastic and plastic deformation. The deformation mechanism of amorphous and crystalline phases is analyzed as a function of strain and strain-rate. A nanocavitation in the amorphous phase results from a topological constraint imposed by the crystalline phase. This mechanism is a natural consequence of the model and explains the cavitation observed at a macroscopic level.