Origin of the Sharkskin Instability: Nonlinear Dynamics

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Numerical simulations reveals the intrinsic mechanism for the onset of the sharkskin instability in polymer extrusion process

In this paper, we have studied polymer extrusion, an important process in plastics manufacturing. Often the final material’s surface is rough with semi regular grooves
resembling the skin of a shark. This phenomenon, known as sharkskin instability, has intrigued the scientific and industrial communities for over 60 years. We have reported the results of a simple physical model which explains the underlying mechanism that causes the sharkskin instability. We simu lat ed the flow of polymer melts being squeezed through a slit and observed that the stretched polymer chains are stretched toward the exit, then recoiled as they m ove d further away, causing a swell and forming waves. These waves became the familiar sharkskin grooves on the surface of the melt.





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