Effect of Branch Distribution on Rheology of LLDPE during Early Stages of Crystallization

Gelfer, MY; Winter, H. Henning

doi:10.1021/ma990588y

Cited by 59 publications

(39 citation statements)

References 30 publications

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“…The observation that heterogeneous copolymers melt at a higher temperature than homogeneous copolymers with the same composition, agrees with the experimental observations on ethylenebutene copolymers, 43,44 ethylene-1-octene copolymers, 45 and other LLDPEs. 46 The heterogeneous copolymer can be regarded as a blend of copolymers, i.e., partial molecules containing high comonomer content and the other containing low comonomer content. By tracing the morphology of those chains containing high comonomer content, we find that, in a well-mixed heterogeneous copolymer system, molecular segregation occurs on cooling, even before crystallization (see Figure 8).…”

Section: Heterogeneous Copolymersmentioning

confidence: 99%

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Mathot

Frenkel

2003

Macromolecules

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We report a numerical study of crystallization and melting in bulk statistical homogeneous (random), homogeneous (slightly alternating), and heterogeneous (produced in a batch reaction) copolymers formed by crystallizable monomers and noncrystallizable comonomers. In our dynamic Monte Carlo simulations of lattice chains, the current model further assumes that the comonomers cannot move into crystalline regions by sliding diffusion of the chains. We find that both the overall composition and the statistical distribution of the monomers affect the phase-transition temperature, the resulting relative crystallinity, and the crystal morphology. However, the final absolute crystallinity of homogeneous copolymers seems insensitive to these parameters. Intramolecular segregation between monomers and comonomers is accompanied by crystallization, demonstrating the concept of sequence segregation or nanophase separation of statistical copolymers with assembling structures like in thermoplastic elastomers. Moreover, if crystallization of homogeneous copolymers has started but not yet completed on cooling, subsequent heating will show cold crystallization before melting, which can be attributed to insertion-mode lamellar growth. For heterogeneous copolymers, intermolecular segregation occurs on cooling before crystallization. On the basis of our observations, a pair of master melting and crystallization curves for the crystallinity of a statistical copolymer as a function of temperature are suggested to reflect the characteristic of the monomer-sequence-length distribution. This suggestion facilitates the clarification to the kinetic disturbance in local temperature regions and to the principle of some fractionation methods, such as temperature rising elution fractionation (TREF).

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Section: Heterogeneous Copolymersmentioning

confidence: 99%

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Mathot

Frenkel

2003

Macromolecules

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“…The mechanical properties of the final products are significantly dependent upon the degree of crystallization and types of crystals formed and therefore optimization of any polymer process requires a good understanding on how flow influences crystallization (McHugh 1995;Eder et al 1990;Kornfield et al 2002;Janeschitz-Kriegl 2003;Scelsi and Mackley 2008;Kumaraswamy et al 1999). In particular, the orientation of the crystals in elongational and shear flows affect the crystallization and thus the mechanical properties (Gelfer and Winter 1999).…”

Section: Introductionmentioning

confidence: 99%

Flow-induced crystallization of high-density polyethylene: the effects of shear and uniaxial extension

Derakhshandeh

Hatzikiriakos

2011

Rheol Acta

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The effects of shear, uniaxial extension and temperature on the flow-induced crystallization of two different types of high-density polyethylene (a metallocene and a ZN-HDPE) are examined using rheometry. Shear and uniaxial extension experiments were performed at temperatures below and well above the peak melting point of the polyethylenes in order to characterize their flow-induced crystallization behavior at rates relevant to processing (elongational rates up to 30 s −1 and shear rates 1 to 1,000 s −1 depending on the application). Generally, strain and strain rate found to enhance crystallization in both shear and elongation. In particular, extensional flow was found to be a much stronger stimulus for polymer crystallization compared to shear. At temperatures well above the melting peak point (up to 25 • C), polymer crystallized under elongational flow, while there was no sign of crystallization under simple shear. A modified Kolmogorov crystallization model (Kolmogorov, Bull Akad Sci USSR, Class Sci, Math Nat 1:355-359, 1937) proposed by Tanner and Qi (Chem Eng Sci 64:4576-4579, 2009) was used to describe the crystallization kinetics under both shear and elongational flow at different temperatures.

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“…Among the most common polyethylene grades, linear low-density polyethylene (LLDPE) is characterized by a significant number of short chain branches (SCB), and by the absence of long branches. SCB units typically contain 2-10 C atoms and account for less than 10% of the overall chain molecular weight49 . The extent of short chain branching affects the coil dimensions.…”

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confidence: 99%

MARTINI Coarse-Grained Models of Polyethylene and Polypropylene

et al. 2015

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The understanding of the interaction of nanoplastics with living organisms is crucial both to assess the health hazards of degraded plastics and to design functional polymer nanoparticles with biomedical applications. In this paper, we develop two coarse-grained models of everyday use polymers, polyethylene (PE) and polypropylene (PP), aimed at the study of the interaction of hydrophobic plastics with lipid membranes. The models are compatible with the popular MARTINI force field for lipids, and they are developed using both structural and thermodynamic properties as targets in the parametrization. The models are then validated by showing their reliability at reproducing structural properties of the polymers, both linear and branched, in dilute conditions, in the melt, and in a PE-PP blend. PE and PP radius of gyration is correctly reproduced in all conditions, while PE-PP interactions in the blend are slightly overestimated. Partitioning of PP and PE oligomers in phosphatidylcholine membranes as obtained at CG level reproduces well atomistic data.

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Effect of Branch Distribution on Rheology of LLDPE during Early Stages of Crystallization

Cited by 59 publications

References 30 publications

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Flow-induced crystallization of high-density polyethylene: the effects of shear and uniaxial extension

MARTINI Coarse-Grained Models of Polyethylene and Polypropylene

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