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Molecular dynamics simulation of linear polyethylene blends: Effect of molar mass bimodality on topological characteristics and mechanical behavior
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.ORCID iD: 0000-0001-8153-2778
Borealis AB, Innovat & Technol, SE-44486 Stenungsund, Sweden..
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymeric Materials.ORCID iD: 0000-0002-6071-6241
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
2019 (English)In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 161, p. 139-150Article in journal (Refereed) Published
Abstract [en]

Blending different molar mass fractions of polyethylene (PE) in order to obtain materials with higher fracture toughness has previously proven beneficial. Our approach has been to use coarse-grained (CG) molecular dynamics (MD) simulations to obtain semicrystalline polyethylene systems on a nanoscale, and then draw them in order to mimic tensile testing. The CG potentials were derived, validated and utilized to simulate melt equilibration, cooling, crystallization and mechanical deformation. Crystallinity, tie chain and entanglement concentrations were continuously monitored. During crystallization, the low molar mass fraction disentangled to a greater degree and ended up with a lower entanglement density than the high molar mass fraction, although the tie chain concentration was higher for the low molar mass fraction. The deformation behavior of semicrystalline PE above its glass transition temperature was then assessed in a uniaxial tensile deformation simulation. The low-strain mechanical properties (i.e. elastic modulus, yield stress and strain) were in accordance with the literature. The high-strain mechanical features and toughness were improved in bimodal systems. The presence of a high molar mass fraction in bimodal systems was shown to affect the crystallinity and tie chain concentration during the strain hardening, leading to tougher model systems. Finally, the bimodal system with equal shares of the molar mass fractions showed the highest toughness and the best ultimate mechanical properties while having a concentration of tie chains and entanglements intermediate between the values for the other systems. This was a clear sign of the non-exclusive role of tie chains and entanglements in the mechanical behavior of bimodal PE and more generally of semicrystalline polymers at high strains.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD , 2019. Vol. 161, p. 139-150
Keywords [en]
Semicrystalline polyethylene, Coarse-grained molecular dynamics, Tie chains and entanglements
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-241308DOI: 10.1016/j.polymer.2018.12.012ISI: 000454931700016Scopus ID: 2-s2.0-85059303277OAI: oai:DiVA.org:kth-241308DiVA, id: diva2:1282740
Note

QC 20190125

Available from: 2019-01-25 Created: 2019-01-25 Last updated: 2019-01-25Bibliographically approved

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Moyassari, AliHedenqvist, Mikael S.Gedde, Ulf W

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