Stress development in plastic sheet extrusion

Abstract

The development of flow‐induced stresses in extruded sheet made of polypropylene was analyzed. A theoretical model was developed to simulate velocity, temperature, and stress profiles for polymeric materials flowing inside a slit die. The output of this simulation was then used to compute temperature and stress profiles as the extrudate emerged from the die, cooled, and relaxed under no draw conditions. Simulated surface stresses and stress profile across the extruded sheet agreed well with the experimental data for the die temperature effect and the die gap effect at low draw ratios.

Investigation of Cast Film Machine Process Conditions and Physical Properties of Several Homopolymer and Copolymer Polypropylene Film Grades

“…The important property is the viscosity of the melt at the die exit. 4. Roll tension appears to adversely affect tensile properties.…”

“…This will affect process stability, the degree of frozen-in orientation, and the crystallization rate of the polymer. The complexity of the attenuation-relaxationcrystallization mechanism makes it extremely difficult to predict the outcome of a change in MFR, but it can be predicted that a higher viscosity extrudate will produce a film with a higher, anisotropic stress level [3,4]. Chain entanglements, however, may lead to a higher overall mechanical strength.…”