Sharkskin Instability in Extrusion
The instabilities that occur in the pressure-driven extrusion of molten polymers are fascinating from the scientific perspective but troublesome and sometimes catastrophic from the industrial one. Over the past 50 years, there has been a sustained interest in the understanding and control of these instabilities. They can occur in common extrusion operations such as the manufacture of polymeric rods, tubes, sheets, and wire coating. Over the years, processors have learned to work around these processing defects by a variety ofmeans: slowing themanufacturing rate, usingmaterials that process better but have reduced final mechanical properties, or addition of processing additives (Chapters 8-9). From the scientific point of view, the fundamental understanding of these instabilities remains as amajor challenge despitemuch progress in the past decade. The primary motivation for continued research is the promise of a more rational design of materials and processes to enhance manufacturing eﬃciency.