Melt fracture of two broad molecular weight distribution high‐density polyethylenes

Ansari, Mahmoud; Hatzikiriakos, Savvas G.; Sukhadia, Ashish M.; Rohlfing, David C.

doi:10.1002/pen.22144

Cited by 10 publications

(11 citation statements)

References 49 publications

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“…Only a small region in the curve exists where rheological instability would occur due to a stress bifurcation. The overall shape of this stress response curve, including the slight bifurcation, is reported in a number of experiments [2,38,39]. At low shear rates the chain ends are fairly evenly distributed throughout the box.…”

mentioning

confidence: 64%

Molecular Scale Simulation of Homopolymer Wall Slip

Dorgan

Rorrer

2013

Phys. Rev. Lett.

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The first molecular scale simulation of highly entangled polydisperse homopolymers that is capable of capturing all three regions--no slip, weak slip, and strong slip--of the hydrodynamic boundary condition is presented. An on-lattice dynamic Monte Carlo technique capable of correctly capturing both unentangled and entangled polymer dynamics is used to study the molecular details of wall slip phenomena for homopolymers and energetically neutral walls. For unentangled chains (those exhibiting Rouse dynamics) weak slip is not present but evidence of strong slip is manifest at very high shear rates. For entangled chains (of sufficient length to exhibit reptation dynamics), both weak and strong slip are observed. Consistent with numerous experimental studies, disentanglement and cohesive failure occur at high shear rates. Disentanglement is clearly evidenced in a nonlinear velocity profile that exhibits shear banding, in an excess of chain ends at the slip plane, and perhaps most importantly in a nonmonotonic stress versus shear rate response. The chain end density exhibits a pretransitional periodicity prior to disentanglement. Unentangled Rouse chains do not show this pretransitional response or a bifurcation in their stress versus shear rate response. Finally, it is shown that when polydispersity is introduced, slip phenomena are severely reduced and the inherent constitutive bifurcation is limited to a small region. Predictions are in post facto agreement with many experiments, are distinct from existing results obtained using molecular dynamics simulation techniques, and shed light on fundamental mechanisms of polymer wall slip.

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confidence: 64%

Molecular Scale Simulation of Homopolymer Wall Slip

Dorgan

Rorrer

2013

Phys. Rev. Lett.

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“…Table 1 summarizes some of their molecular characteristics. The m-HDPE was expected to exhibit a better processability since it has a broader molecular weight distribution (MWD), however this was found not to be the case (Ansari et al 2011). Differences in crystallization behavior were proposed as the reason for this observation.…”

Section: Methodsmentioning

confidence: 95%

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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“…The influence of die geometry in capillary rheometry has been experimentally and numerically discussed in the literature. [ 13–20 ] Experimental studies [ 15,16 ] have shown that the onset and the type of flow instabilities are significantly affected by the die geometry even at a similar range of shear rates. For this reason, both slit (rectangular cross‐section area) and round capillary (circular cross‐section area) dies are used in this investigation.…”

Section: Introductionmentioning

confidence: 99%

Mechano‐Optical Characterization of Extrusion Flow Instabilities in Styrene‐Butadiene Rubbers: Investigating the Influence of Molecular Properties and Die Geometry

Georgantopoulos

Esfahani

Botha

et al. 2021

Macro Materials & Eng

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The extrusion flow instabilities of two commercial styrene‐butadiene rubbers are investigated as they vary in isomer content (1,4‐cis, 1,4‐trans, and 1,2 conformation) of the butadiene monomer and the molecular architecture (linear, branched). The investigated samples have similar multimodal molecular weight distribution. Two geometries of extrusion dies, slit and round capillary, are compared in terms of the type and the spatial characteristics of the flow instabilities. The latter are quantified using three methods: a highly pressure sensitive slit die, online and offline optical analysis. The highly pressure‐sensitive slit die has three piezoelectric pressure transducers (Δt ≈ 10−3 s and Δp ≈ 10−5 bar) placed along the die length. The characteristic frequency (fChar.) of the flow instabilities follows a power law behavior as a function of shear rate to a 0.5 power for both materials,  fChar.∝trueγ˙app.0.5. A qualitative model is used to predict the spatial characteristic wavelength (λ) of the flow instabilities from round capillary to slit dies and vice versa. Slip velocities (Vs) are used to quantify the slippage at slit and round capillary dies as well.

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Melt fracture of two broad molecular weight distribution high‐density polyethylenes

Cited by 10 publications

References 49 publications

Molecular Scale Simulation of Homopolymer Wall Slip

Molecular Scale Simulation of Homopolymer Wall Slip

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

Mechano‐Optical Characterization of Extrusion Flow Instabilities in Styrene‐Butadiene Rubbers: Investigating the Influence of Molecular Properties and Die Geometry

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