EFFECT OF DIE LAND LENGTH ON DIE PRESSURE DURING FOAM EXTRUSION- PART I EXPERIMENTAL OBSERVATIONS

摘要

Entrance pressures are determined experimentally for foam extrusion dies of constant cross section. These pressures are affected by the rheological properties of the polymer matrix, by the plasticizing effect of the blowing agent, and by the cell nucleation and growth. While the pressures change linearly with die land length during extrusion of pure polymer, this relation becomes nonlinear during extrusion of polymer/blowing agent mixtures. It is found that the degree of nonlinearity depends on the amount of premature cell growth and by the processing conditions, including temperature, pressure drop rate, and blowing agent content.