Origin of the Sharkskin Instability: Nonlinear Dynamics.

Stylianos Varchanis,Dionisis Pettas,Yannis Dimakopoulos,John Tsamopoulos

doi:10.1103/physrevlett.127.088001

Abstract

The appearance of surface distortions on polymer melt extrudates, often referred to as sharkskin instability, is a long-standing problem. We report results of a simple physical model, which link the inception of surface defects with intense stretch of polymer chains and subsequent recoil at the region where the melt detaches from the solid wall of the die. The transition from smooth to wavy extrudate is attributed to a Hopf bifurcation, followed by a sequence of period doubling bifurcations, which eventually lead to elastic turbulence under creeping flow. The predicted flow profiles exhibit all the characteristics of the experimentally observed surface defects during polymer melt extrusion.

Highlights

The most important process in plastics manufacturing is extrusion, where a polymer melt is forced through a die
We report results of a simple physical model, which link the inception of surface defects with intense stretch of polymer chains and subsequent recoil at the region where the melt detaches from the solid wall of the die
The surface in the first observable flow transition consists of semiregular grooves that run mainly perpendicular to the flow direction and resemble the skin of a shark, the term sharkskin instability

Summary

Introduction

The most important process in plastics manufacturing is extrusion, where a polymer melt is forced through a die. The appearance of surface distortions on polymer melt extrudates, often referred to as sharkskin instability, is a long-standing problem. We report results of a simple physical model, which link the inception of surface defects with intense stretch of polymer chains and subsequent recoil at the region where the melt detaches from the solid wall of the die.

Results

Conclusion