Formation of degraded LDPE surfaces using mechanical cleavage and shock compression analyzed by means of molecular dynamics simulations

Low Density Polyethylene, LDPE, samples were subjected to analysis based on application of molecular dynamics simulations. The samples were composed of polymer molecules with molecular weight 30 000 amu and 2% of branched carbon atoms. The calculations were carried out using various force fields i.e. Amber pairwise additive force field and four types of many body reactive force fields like AIREBO, AIREBO-M, ReaxFF and ci-ReaxFF. For each force field the material properties of the samples were determined i.e.: Young's modulus, Poisson's ratio, yield strength and share modulus using the determined stress-strain curves. The samples were subjected to mechanical cleaving by applying an external forces in order to generate surfaces of LDPE. These surfaces were analyzed in terms of their chemical composition and number and types of radical ends formed on the surfaces. Additionally, the samples were subjected to shock compression in order to produce more deeper chemical transformations which should be more representative to naturally degraded nanoplastics. We conclude that the CHO ReaxFF force field is the most reliable for generating degraded LDPE surfaces which can be next used in standard molecular dynamics involving interaction of nanoplastic with proteins or lipid membranes, for instance.