Polymer Industries - Tim's Top Tips Explanation & Evaluation of Sharkskin

Sharkskin is a surface mattness seen on an extrudate during processing. It is usually a high shear related phenomenon, and the appearance of sharkskin depends on the viscoelastic and extensional properties of the melt. The extrudate exhibits a repeating wavy pattern on it’s surface, perpendicular to the direction of flow and is thought by many to be caused by a stickslip phenomenon at the die lip wall or die land, but the debate as to the exact cause and location of the onset is still ongoing. Either good adhesion or continuous slip can help postpone the appearance of sharkskin, but stick-slip always causes a problem.

The relevant material properties which dictate the appearance of sharkskin can be measured under applied, controlled deformations and forces.

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