Coarse-Grained Simulations on Polyethylene Crystal Network Formation and Microstructure Analysis

MA Hussain and T Yamamoto and SF Adil and SGR Yao, POLYMERS, 16, 1007 (2024).

DOI: 10.3390/polym16071007

Understanding and characterizing semi-crystalline models with crystalline and amorphous segments is crucial for industrial applications. A coarse-grained molecular dynamics (CGMD) simulations study probed the crystal network formation in high-density polyethylene (HDPE) from melt, and shed light on tensile properties for microstructure analysis. Modified Paul-Yoon-Smith (PYS/R) forcefield parameters are used to compute the interatomic forces among the PE chains. The isothermal crystallization at 300 K and 1 atm predicts the multi-nucleus crystal growth; moreover, the lamellar crystal stems and amorphous region are alternatively oriented. A one-dimensional density distribution along the alternative lamellar stems further confirms the ordering of the lamellar-stack orientation. Using this plastic model preparation approach, the semi-crystalline model density (rho cr) of ca. 0.913 g center dot cm-3 and amorphous model density (rho am) of ca. 0.856 g center dot cm-3 are obtained. Furthermore, the ratio of rho cr/rho am approximate to 1.06 is in good agreement with computational (approximate to 1.096) and experimental (approximate to 1.14) data, ensuring the reliability of the simulations. The degree of crystallinity (chi c) of the model is ca. 52% at 300 K. Nevertheless, there is a gradual increase in crystallinity over the specified time, indicating the alignment of the lamellar stems during crystallization. The characteristic stress-strain curve mimicking tensile tests along the z-axis orientation exhibits a reversible sharp elastic regime, tensile strength at yield ca. 100 MPa, and a non-reversible tensile strength at break of 350%. The cavitation mechanism embraces the alignment of lamellar stems along the deformation axis. The study highlights an explanatory model of crystal network formation for the PE model using a PYS/R forcefield, and it produces a microstructure with ordered lamellar and amorphous segments with robust mechanical properties, which aids in predicting the microstructure-mechanical property relationships in plastics under applied forces.

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