Stress Transmitters at the Molecular Level in the Deformation and Fracture Processes of the Lamellar Structure of Polyethylene via Coarse-Grained Molecular Dynamics Simulations

To improve the toughness of semicrystalline polymers against stretching, it is essential to understand the stress transmission processes at the molecular level. The deformation and fracture processes of the lamellar structure of polyethylene were studied using coarse-grained molecular dynamics simulations to investigate the influence of molecular structures such as tie chains and entanglements. First, two models with different numbers of tie chains and entanglements were successfully constructed and subjected to simulated stretching. The results revealed that tie chains and entanglements indeed transmit the stress upon stretching. The roles of these molecular structures were found to be similar at low strain, whereas the tie chains were more important at void generation owing to the rapid relaxation of the entanglements. Next, to unravel the behavior of the tie chains, a model containing defects was subjected to simulated stretching. In the model lacking defects, the tie chains functioned similarly in all four amorphous layers. Interestingly, in the model containing defects, the stresses of the tie chains in the amorphous layers containing defects were found to be higher than those in the amorphous layers lacking defects following void generation. Therefore, the nature of the stress transmitters in the lamellar structure of semicrystalline polymers has been successfully elucidated at the molecular level.