Pressure Oscillations During Extrusion of Polyethylene. Part I

One of the basic technical and economic problems in the manufacture of plas- tics is improving the rate of production without adversely affecting the surface of the product. When the rate of extrusion is gradually increased above the critical value of rate of shear, γ ≥ γc (or the corresponding critical shear stress σ12 ≥ σ12, c), the extrudate becomes rough, distorted, and fractured.), The phenomenon, known as “melt fracture”, hasbeen investigated by many authors during the last 30 years, e.g., see Refs. 14, and reviewed by others [5–9]. Melt fracture is observed for all polymers and plastics. However, several types of distortion with such colorful names as sharkskin and orange peel have been observed for one but not for another extruded material. In this article we re-restrict ourselves to the types of distortions observed for linear, high-density polyethylene (HDPE).