Ordering and Crystallization of Entangled Polyethylene Melts under Uniaxial Tension: A Molecular Dynamics Study
YR Sliozberg and IC Yeh and M Kroger and KA Masser and JL Lenhart and JW Andzelm, MACROMOLECULES, 51, 9635-9648 (2018).
Morphological and mechanical properties of semicrystalline polymers are strongly influenced by flow-induced crystallization during processing. We perform extensive molecular dynamics simulations with more than 1 million atoms to describe orientation, drawability, and crystallization of entangled polyethylene melts under uniaxial tensions at three different strain rates and after a subsequent cooling. During tensile deformation at the lowest strain rate of 10(7) s(-1), the polyethylene melt experiences entanglement loss and crystal nucleation. At higher strain rates of 10(8) and 10(9) s(-1), we observe a higher degree of chain alignment and void formation in addition to disentanglement and crystal nucleation. Chain segments make sharp turns relative to the neighboring chain orientations at the entanglement points, which manifests as a bimodal distribution of the local order parameter. Upon cooling below the melting temperature, semicrystalline polyethylene with a crystallinity close to 50% is formed. The entanglements are located in the amorphous regions of the semicrystalline polyethylene, with some located in the crystal/amorphous interface region. The chain ends of the semicrystalline polyethylene are preferentially localized at the crystal/amorphous interface, which is in agreement with recent experimental results.
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