Lamellar Orientation Analysis and Mechanical Properties of Polyethylene in Stretch-Induced Crystallization

MA Hussain and T Aoyagi and T Kikutani and W Takarada and T Yamamoto and SF Adil and SGR Yao, POLYMERS, 17, 1450 (2025).

DOI: 10.3390/polym17111450

Polyethylene films prepared from orientation-dependent methods are strong and resilient, have reduced permeability, and possess higher tensile strength. A molecular dynamics investigation is performed to reveal the emergence of chain folding and lamellar crystal axis alignment along the stretching axis (tilt angle) in the stretch-induced crystallization (SIC) of high-density polyethylene (HDPE), which mimics the internal structure of the fiber. The morphology in phase transition is assessed by the total density (rho), degree of crystallinity (%chi(c)), average number of entanglements per chain (< Z >), elastic modulus of the mechanical property, and lamellar chain tilt angle (theta) from the stretch-axis. The simulation emphasizes crystal formation by changing the total rho from 0.85 g.cm(-3) to 0.90 g.cm(-3) and by tracking the gradual increase in % chi(c) during stretching (similar to 40%) and relaxation processes (similar to 50%). Moreover, the primitive path analysis-based decreased during stretching and further in the subsequent relaxation process, supporting the alignment and thickening of the lamellar chain structure and chain folding from the random coil structure. The elastic modulus of similar to 350-400 MPa evidences the high alignment of the lamellar chains along the stretching axis. Consistent with the chain tilt angle of the HDPE in SAXS/WAXS experiments, the model estimated the lamellar chain title angle (theta) relative to the stretching axis to be similar to 20-35 degrees. In conclusion, SIC is a convenient approach for simulating high stiffness, tensile strength, reduced permeability, and chain alignment in fiber film models, which can help design new fiber morphology-based polymers or composites.

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