EXTRUDATE SWELL IN POLYMERS.

Polymer melts and solutions exhibit an increase in cross-sectional area whenever they emerge from dies or conduits. Four mechanisms are considered to be responsible for this phenomenon: Newtonian swell, sudden elastic recovery, inelastic swell and stress relaxation. Various models for Newtonian and viscoelastic fluids and theories are discussed and critically examined. These include finite-element methods, concepts based on the theory of rubber elasticity, and Tanner's ″elastic″ and ″in-elastic″ theories. The results of numerous experimental observations, available in the literature, on such aspects as the effect of length/diameter ratio, molecular weight distribution and temperature are summarized. Formula for die swell are presented for capillary and slit dies, and the problems associated with their applications are discussed.