Application of Upper Bound Theory to Solid-State Extrusion of Polymers

Solid-state extrusion of some crystalline polymers, such as high density polyethylene, isotactic polypropylene and nylon 6, were analyzed on the basis of the upper bound theorem. The method of practical application of the theorem was the same as that described by Avitzur, and an improvement was added by taking into account of the strain hardening effect of the polymeric materials. The agreement between calculated and observed results was fairly good with the frictional coefficient of the values coincident with those estimated in previous papers with the other approach. And the cause of the increase of the extrusion pressure with increasing die taper angle was confirmed as due to the discontinuous change of the velocity distributions, especially around the exit of the die.