Die swell and melt fracture: Effects of molecular weight distribution

When polymers are extruded at high stresses it is often observed that the surface or shape of the extrudate is impaired by the presence of certain flow defects. These flow defects are commonly known as swelling, mattness, sharkskin and melt fracture. Because of the great importance of these phenomena in polymer processing, many investigations have been carried out with the objective of determining the mechanism involved and the influence of various processing variables and material properties.