About the origin of sharkskin

Weill, A.

doi:10.1007/bf01517516

Cited by 36 publications

(16 citation statements)

References 6 publications

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“…This relative change in C, which is proportional to the (constant) plunger speed, is much smaller than the typical frequency of sharkskin and spurt events, reported as 50 and 0.5 Hz, respectively, by Weill (1980b). By fixing the value of h, C can be reliably considered as a constant.…”

Section: P(t)] T>omentioning

confidence: 78%

Modeling polymer melt‐flow instabilities

Molenaar¹,

Koopmans²

1994

Journal of Rheology

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SynopsisThe long-standing problem of polymer melt-flow instabilities is looked upon from a new and quite general mathematical viewpoint. A single mathematical model is developed allowing the macroscopic description of measurable state variables characterizing the different melt-flow instability regimes. Based on the theory of relaxation oscillations,a set of two coupled first-order ordinary differential equations, relating state variables-pressure and flow rate-provides sufficient degrees of freedom to describe all the relevant flow regimesin shear flow. By means of this model, the appearance of extrudate distortions can be expressed in terms of pressure and output fluctuations without the need to invoke a microscopic theory. The analysis contains the potential for practical melt-flow instability predictions.

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Section: P(t)] T>omentioning

confidence: 78%

Modeling polymer melt‐flow instabilities

Molenaar¹,

Koopmans²

1994

Journal of Rheology

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“…This defect is usually observed for polymers whose molecular weight distribution is narrow, which is often the case of the metallocene polyethylenes. It is not observed for polymers with wide distributions (Clegg, 1957;Bergem, 1976;Cogswell, 1977;Weill, 1980b;Lai et Knight, 1992;Kazatchkov et al, 1999). The defect is also attenuated by the presence of short chain (Karbachewski et al, 1991;Garofalo et al, 2012) or long chain (Venet and Vergnes, 1997) branching, even though these effects are complex and still not well understood (Wang et al, 2004).…”

Section: Influence Of Parametersmentioning

confidence: 90%

Extrusion Defects and Flow Instabilities of Molten Polymers

Vergnes

2015

International Polymer Processing

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International audienceWhen certain critical conditions are exceeded, the flow of a polymer melt becomes unstable, giving rise to particular phenomena that are the subject of this review. These instabilities are a vital industrial problem, as they are the key to productivity of extrusion processes. Indeed, their onset leads to unacceptable products and is thus the upper limit of the processing conditions. They are also a fascinating scientific problem because, although studied and discussed for more than half a century, they are still not fully understood and their mechanisms are still sometimes controversial. In the present literature review, we present an overview of the studies carried out for fifty years, as well as our own opinion on the underlying mechanisms.3-2

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“…Without going deeper into the mechanisms behind the appearane of polymer extrudates, we only note an interesting similarity between the two-period appearance of polymer melt extrudates and the combined pulsating and transversally oscillating (spiralling) flow reported in this paper. In both cases, the higher frequency component appears only during a part of the slower oscillation [1,11,43]. It may be noted that the ideas about the origin of the instabilities observed in extrudates are rather diverging.…”

Section: Final Remarksmentioning

confidence: 97%

“…It may be noted that the ideas about the origin of the instabilities observed in extrudates are rather diverging. While some authors associate them with the entry flow, others claim stickslip phenomena [12] or relaxational oscillations [11,43] as responsible. In the latter case, the frequencies are found to depend on the volume of the reservoir upstream from the capillary.…”

Section: Final Remarksmentioning

confidence: 97%

Electrical fluctuations and entry flow instabilities during capillary flow of aqueous poly (ethylene oxide) solutions

Hedman

Kubát

1986

Rheol Acta

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Capillary flow of poly(ethylene oxide) solutions generates voltage fluctuations (noise) between electrodes placed on both sides of the capillary. The noise has a 1/f ~ type spectral distribution, the value of ~ increasing with ?) (shear rate) to a limiting level. Within certain ~ ranges, two sets of harmonic peaks appear in the spectra. It is demonstrated that these peaks are retated to the frequency components of the instabilities in the entry flow region. The lower frequency set of harmonics corresponds to axial oscillations (pulsations) of the flow, while the higher frequency peaks are associated with the transverse oscillation of the stream lines in the vicinity of the entry. The corresponding frequencies were measured by visual counting and by spectral analysis of laser light transmitted through the entry region during injection of a coloured solution.The noise measurements were carried out using both platinum and reversible Ag/AgC1 electrodes. In the latter case the streaming potential was also measured; its variation due to pressure fluctuations in the instable flow region appears to provide a plausible explanation of flow-induced noise phenomena as observed in elastic solutions.

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About the origin of sharkskin

Cited by 36 publications

References 6 publications

Modeling polymer melt‐flow instabilities

Modeling polymer melt‐flow instabilities

Extrusion Defects and Flow Instabilities of Molten Polymers

Electrical fluctuations and entry flow instabilities during capillary flow of aqueous poly (ethylene oxide) solutions

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