Estimating how crystallization methods influence the mechanical properties of semicrystalline polymers using LAMMPS

Polyethylene fiber films with highly oriented lamellae exhibit superior thermal and mechanical properties. Stretch-induced crystallization (SIC) using molecular dynamics simulations in LAMMPS accurately mimics fiber film formation, providing valuable insights into crystallization kinetics, inner structure, and mechanical properties. In this investigation, the morphological and mechanical (Uniaxial elongation) analyses complement the SIC method’s effectiveness in designing high-performance fiber films. The one-dimensional density (1D) along the Z-axis shows that lamellar orientation and thickness change with temperature and strain rates. Chains are well aligned along the deformation axis. The degree of crystallinity (χc) ranges from 50% to 60% with variation in temperatures. The quantitative measurement of entanglement density decreases during stretching, with larger drops observed when the lamellar growth occurs, indicating the unentangled state where the chains are aligned with the drawing direction. Mechanical properties are anisotropic, with 100% orientation along the Z-axis. The chain tilt during relaxation, between 25° and 35°, corroborates the experimental data. In the stress-strain curve (SSC), tensile tests distinguish between the longitudinal and transverse deformation responses through brittleness and ductility, respectively. The transverse deformation exhibits weak elasticity due to secondary van der Waals forces. On the other hand, in longitudinal deformation, the restoring forces are resisted by the sigma bonds, which results in high elasticity.