Extrusion Theory, 1993 International European Extrusion Coating Symposium Proceedings

Hassan Helmy

The extrusion process involves converting a solid polymer, usually in pellet form, into a molten state, shaping or forming the molten polymer into a desired product and solidifying it to permanently retain the desired shape. Since a polymer undergoes phase transition from solid to liquid and then back to solid in processing, the thermodynamic properties of the polymer such as heat capacity and melting or glass transition point have a direct bearing on the ability to process the polymer. The importance of the melt rhealogical properties of the molten polymer, such as viscosity, elasticity, shear and temperature sensitivities, should be well known since the molten polymer must be made to flow for shaping into a desired product. The characteristics of the feed form of the solid polymer as related to the feeding and conveying mechanisms inside an extruder such as bulk density, internal and external frictions and compressibility, are also very important.