Experimental evaluation of the pure configurational stress assumption in the flow dynamics of entangled polymer melts

Rasmussen, Henrik Koblitz; Bejenariu, Anca Gabriela; Hassager, Ole; Auhl, Dietmar

doi:10.1122/1.3496378

Cited by 34 publications

(42 citation statements)

References 45 publications

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“…This effect may be compensated by a correction factor as described in Ref. [21]. For large strains, the correction vanishes and the radial variation of the stress in the symmetry plane becomes negligible [18].…”

Section: Extensional Stress Measurementsmentioning

confidence: 99%

A new look at extensional rheology of low-density polyethylene

et al. 2016

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The nonlinear rheology of three selected commercial low-density polyethylenes (LDPE) is measured in uniaxial extensional flow. The measurements are performed using three different devices including an extensional viscosity fixture (EVF), a home made filament stretching rheometer (DTU-FSR) and a commercial filament stretching rheometer (VADER-1000). We show that the measurements from the EVF are limited by a maximum Hencky strain of 4, while the two filament stretching rheometers are able to probe the nonlinear behavior at larger Hencky strain values where the steady state is reached. With the capability of the filament stretching rheometers, we show that LDPEs with quite different linear viscoelastic properties can have very similar steady extensional viscosity. This points to the potential for independently controlling shear and extensional rheology in certain rate ranges.

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Section: Extensional Stress Measurementsmentioning

confidence: 99%

A new look at extensional rheology of low-density polyethylene

et al. 2016

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“…This effect is caused by the noslip boundary condition at the end plates, and is more prominent at small aspect ratios (Nielsen et al (2006)). This effect may be compensated by a correction factor as mentioned in Rasmussen et al (2010) that ensures less than 3% deviation from the corrected initial stress. For large strains the correction vanishes and the radial variation of the stress in the symmetry plane becomes negligible (Kolte et al (1997)).…”

Section: Extensional Flowmentioning

confidence: 99%

Stress relaxation of bi-disperse polystyrene melts

et al. 2016

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We present start-up of uniaxial extension followed by stress relaxation experiments of a bi-disperse 50% by weight blend of 95k and 545k molecular weight polystyrene. We also show, for comparison, stress relaxation measurements of the polystyrene melts with molecular weight 95k and 545k, which are the components of the bi-disperse melt. The measurements show three separated relaxation regimes: a fast regime, a transition regime and a slow regime. In the fast regime the orientation of the long chains is frozen and the stress relaxation is due to stretch relaxation of the short chains primarily. Conversely in the slow regime the long chains have retracted and undergo relaxation of orientation in fully relaxed short chains.

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“…This effect may be compensated by Hoyle et al (2013). a correction factor as described by Rasmussen et al (2010). The Hencky strain and the mean value of the stress difference over the midfilament plane are then calculated as ðtÞ¼À2lnðRðtÞ=R 0 Þ;…”

Section: Methodsmentioning

confidence: 99%

Modifying the pom-pom model for extensional viscosity overshoots

Hawke¹,

Huang²,

Hassager³

et al. 2015

Journal of Rheology

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We have developed a variant of the pom-pom model that qualitatively describes two surprising features recently observed in filament stretching rheometer experiments of uniaxial extensional flow of industrial branched polymer resins: (i) Overshoots of the transient stress during steady flow and (ii) strongly accelerated stress relaxation upon cessation of the flow beyond the overshoot. Within the context of our model, these overshoots originate from entanglement stripping (ES) during the processes of normal chain retraction and branch point withdrawal. We demonstrate that, for a single mode, the predictions of our overshoot model are qualitatively consistent with experimental data. To provide a quantitative fit, we represent an industrial melt by a superposition of several individual modes. We show that a minimal version of our model, in which ES due to normal chain retraction is omitted, can provide a reasonable, but not perfect, fit to the data. With regard the stress relaxation after (kinematically) steady flow, we demonstrate that the differential version of tube orientation dynamics in the original pom-pom model performs anomalously. We discuss the reasons for this and suggest a suitable alternative. V C 2015 The Society of Rheology.[http://dx

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Experimental evaluation of the pure configurational stress assumption in the flow dynamics of entangled polymer melts

Cited by 34 publications

References 45 publications

A new look at extensional rheology of low-density polyethylene

A new look at extensional rheology of low-density polyethylene

Stress relaxation of bi-disperse polystyrene melts

Modifying the pom-pom model for extensional viscosity overshoots

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