An Experimental and Theoretical Investigation of Sharkskin Melt Fracture

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9422108 Shaw Defects on the surface of a number of extruded polymer melts, thought to be caused by the rheology of the melt as it solidifies, are often identified by the descriptive term "sharkskin" defects. Empirically, it is known that this surface defect can be eliminated at lower extrusion rates, because this reduces the stresses that are assumed to be the cause of sharkskinning. These investigators propose an analytical and experimental program to identify and understand the mechanisms to control sharkskin formation. With this understanding, they should be able to eliminate sharkskin or design a specific sharkskin surface texture. Along with a number of analytical tests, they will use a light scattering device in an extrusion die to measure the rheological properties of the extruded polymer experimentally. This, along with a modeling and computional program will determine the mechanics of the flow, incorporating various rheological models, to predict pressure and output fluctuations that can be correlated with the development of sharkskin. The impact of this research will be a better understanding of sharkskinning, a phenomenon that today is unpredictable, and its elimination usually requires lower extrusion speeds and reduced productivity. ***