5. Modeling

The sheath blowing process has been the subject of numerous models since 1970. The aim of modeling is to provide a better understanding of the process in order to :

• predict the evolution of geometry, temperature and stresses developed inside the bubble as a function of axial position. These data can be used to predict the performance of films produced under different processing conditions. Indeed, the mechanical properties of films depend on the cooling rate (evolution of crystallinity and therefore tensile properties) and stretching conditions (orientation);

• determine the processing conditions leading to instabilities. In this way, modeling can be used to determine the operating window available for a given material in order to establish productivity limits;

• understand the...