Molecular mechanisms of the chain diffusion between crystalline and amorphous fractions in polyethylene

Zubova, E. A.; Балабаев, Н. К.; Manevitch, Leonid I.

doi:10.1016/j.polymer.2006.12.032

Cited by 30 publications

(17 citation statements)

References 53 publications

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“…Closeness of H 1 and H 2 is in accord with the results reported by Djokovic et al (2000) based on treatment of observations in relaxation tests. The activation energies in the range 21-26 kJ/mol are similar to those provided by Zubova et al (2007) for a-relaxation in HDPE (between 29 and 36 kJ/mol) and Bin Wadud and Baird (2000) for relaxation in polyethylene melts (between 27 and 32 kJ/mol). Fig.…”

Section: Discussionsupporting

confidence: 70%

“…Several hypotheses have been suggested regarding molecular mechanisms of a-relaxation: c-shear within crystalline lamellae (homogeneous shear of crystal blocks in the direction of their c-axis) (Sirotkin and Brooks, 2001;Guan and Phillips, 2007), inter-lamellar shear (slip of crystalline blocks past each other) (Matthews et al, 1999;Jiang et al, 2009), sliding of tie molecules and motion of chain folds and loops through crystals (Khanna et al, 1985), diffusion of chains (Men et al, 2003) and defects (Alberola et al, 1990) in crystallites, growth of mobility of chains in the interphase (transition regions located in the close vicinity of lamellar surfaces) (Rastogi et al, 2007), weakening of lamellar coupling and enhancement of segment exchange between crystalline and amorphous phases (Kolesov et al, 2005;Na et al, 2007;Zubova et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

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Cyclic thermo-viscoplasticity of high density polyethylene

Drozdov

2010

International Journal of Solids and Structures

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a b s t r a c tObservations are reported in uniaxial cyclic tensile tests (loading-unloading with various maximum strains) on high density polyethylene at temperatures ranging from room temperature up to 90°C. It is demonstrated that the maximum stress per cycle and an apparent residual strain (measured at the instant when the tensile force vanishes under retraction) strongly decrease with temperature. The latter seems unexpected as the interval of temperatures covers the a-relaxation temperature, which is conventionally associated with activation of additional mechanisms for inelastic flow. A model is developed that captures the decrease in residual strain with temperature. Adjustable parameters in the stress-strain relations are found by fitting the experimental data. The effects of temperature and maximum strain per cycle on residual strains are studied numerically.

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Section: Discussionsupporting

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Cyclic thermo-viscoplasticity of high density polyethylene

Drozdov

2010

International Journal of Solids and Structures

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“…Previous work in different PMMA isomers with different graphene types and preparation conditions has indicated a correlation between the level of dispersion and the strength of the interaction between the filler and the matrix to the observed glass transition temperature [79]. In comparison to polyethylene [80][81][82], the mechanical α-relaxation of polypropylene is less investigated. The common view is that the origin of this transition can be associated to relaxations on both the amorphous and the crystalline phases of the matrix, with the overall relaxation divided into two separate ones α1 and α2 that are located at lower and higher temperatures respectively [83].…”

Section: Dmtamentioning

confidence: 99%

Melt-Mixed 3D Hierarchical Graphene/Polypropylene Nanocomposites with Low Electrical Percolation Threshold

et al. 2019

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Graphene-based materials are a family of carbonaceous structures that can be produced using a variety of processes either from graphite or other precursors. These materials are typically a few layered sheets of graphene in the form of platelets and maintain some of the properties of pristine graphene (such as two-dimensional platelet shape, aspect ratio, and graphitic bonding). In this work we present melt mixed graphene-based polypropylene systems with significantly reduced percolation threshold. Traditionally melt-mixed systems suffer from poor dispersion that leads to high electrical percolation values. In contrast in our work, graphene was added into an isotactic polypropylene matrix, achieving an electrical percolation threshold of~1 wt.%. This indicates that the filler dispersion process has been highly efficient, something that leads to the suppression of the β phase that have a strong influence on the crystallization behavior and subsequent thermal and mechanical performance. The electrical percolation values obtained are comparable with reported solution mixed systems, despite the use of simple melt mixing protocols and the lack of any pre or post-treatment of the final compositions. The latter is of particular importance as the preparation method used in this work is industrially relevant and is readily scalable.

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“…A shift by a full chain period may be effected by motion of a vacancy (localized defect of tension) along the chain from one of its ends to another 35 . The chain diffusion between amorphous and crystalline fractions in semicrystalline samples is implemented by motion of cheaper twist-tension defects (shift by half of a chain period and twist through 180 0 brings a CH 2 group into the position of the nearest neighbor) 36 .…”

Section: Boundaries Between the Phases: Twist Defects And Tension mentioning

confidence: 99%

Shear-induced martensitic transformations in crystalline polyethylene: Direct molecular-dynamics simulations

Strelnikov

Zubova

2019

Phys. Rev. B

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For the first time, we carry out molecular dynamics (MD) simulation of shear-induced martensitic phase transitions between the orthorhombic and non-orthorhombic (triclinic and monoclinic) phases of crystalline polyethylene (PE) in the framework of a realistic all atom model of the polymer. We show that the variation of the shear rate allows observing on a nano-sample both a strongly nonequilibrium phase transition occurring by random nucleation and irregular growth of a new phase ('civilian' way, for rapid deformations) and the coherent, or 'military', kinetics (generally considered as usual for martensitic transformations). We induce transitions from the orthorhombic to the triclinic phase according to two transformation modes observed in experiment on PE single crystals. Rapid deformation favors the transition directly to the triclinic phase, slow deformation -first to the intermediate monoclinic, and only then -to the triclinic phase. The second way corresponds to the experiment on extended chain PE. We explain this result and analyze the competition between different transformation and plastic deformation modes. Rotations of PE chains around their axes necessary for the transition between the orthorhombic and non-orthorhombic phases are executed by short twist defects diffusing along the chains. The transition between the monoclinic and triclinic phases occurs through half-chain-period translations of the chains along their axes, mostly collectively, as crystallographic slips.

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Molecular mechanisms of the chain diffusion between crystalline and amorphous fractions in polyethylene

Cited by 30 publications

References 53 publications

Cyclic thermo-viscoplasticity of high density polyethylene

Cyclic thermo-viscoplasticity of high density polyethylene

Melt-Mixed 3D Hierarchical Graphene/Polypropylene Nanocomposites with Low Electrical Percolation Threshold

Shear-induced martensitic transformations in crystalline polyethylene: Direct molecular-dynamics simulations

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