ABSTRACT
The rate of production inmany polymer processing operations including fiber spinning, film blowing, profile extrusion, and various coating flows is limited by the onset of flow instabilities (1,2). In particular, in extrusion processes when the throughput exceeds a critical value, small amplitude periodic distortions appear on the surface of extrudates (surface melt fracture or sharkskin). At higher throughput rates, more severe distortions of irregular form appear known as gross melt fracture (3). These two phenomena are independent and might occur together. In the gross melt fracture regime, the small amplitude periodic distortions may superpose on the irregular gross distortions. In other words, both phenomena (type of distortions)may be seen together depending on the scale under which they are examined. The surface melt fracture phenomena are believed to originate in the land of the die next to the die exit (Refs. 4-6 and this volume, Chapter 5 byMigler), while gross melt fracture is initiated at the die entry (Refs. 7-9 and this volume, Chapter 7 by Dealy).
