Investigation of the 3D crystalline network impact on the elastic properties of Semi-Crystalline Polymers from a multi-scale modelling approach

Nowadays, computational resources allow carrying out mechanical calculations on complex multi-scale materials. Finite Element (FE) calculations can especially be directly performed on microstructures of materials. This work is a first attempt to analyse the impact of the crystalline architecture at a mesoscopic scale on the macroscopic elastic properties of Semi-Crystalline Polymers (SCP). Such polymers can be considered biphasic materials, which are composed of an amorphous phase embedded in a crystalline network. The material studied here is Polyethylene (PE). Molecular Dynamics (MD) calculations are carried out on a 100% crystallized Polyethylene model to determine the elastic properties of the crystalline regions of the material. 3D mesostructures of the typical layout of the spherulitic crystalline network of Semi-Crystalline Polymers are then constructed from experimental observations. These material data and this geometrical description are then integrated in computations with the Finite Element method on elementary volumes to finally determine the macroscopic elastic properties of the material. In this work, which is a first attempt to test such a multi-scale workflow, no amorphous phase is considered. Different 3D architectures are compared demonstrating the role of the crystalline arrangement on the stiffness of the material. Three main types of mesostructures have been analysed: crystalline lamellae disposed in a complete random arrangement, crystalline lamellae disposed in a spherulite arrangement, crystalline lamellae with branches disposed in a spherulite arrangement. It appears that the 3D configuration of the lamellae, as well as the presence of branches, have an influence on the macroscopic elastic properties of the material. Then, comparisons with experimental data suggest that the macroscopic elastic properties can be represented with a purely cohesive crystalline network for crystalline degree up to about 50%. This result questions the role of the amorphous phase on the elastic properties of such systems.