The processing of polypropylene cast films. I. Impact of material properties and processing conditions on film formation

Material properties have a significant impact on the response of polymers to industrial flow processes such as film casting. During film casting, molten polymer is extruded through an (approximately) rectangular die and then cooled rapidly. Subsequent biaxial stretching can be employed to manipulate the film properties. In this work, we investigate the effect of polymer viscosity (molecular weight), draw ratio, and die temperature on polypropylene film formation. We measure the width, two components of the velocity vector, and the temperature profiles throughout the film web. The polymer rheology and the die temperature affect the film geometry and temperature profiles in the air‐gap. The magnitude of the machine direction velocity component depends on both the machine and transverse position in the film. The velocity shows a maximum at the centerline and decreases toward the film edge. The measured transverse velocity component, a consequence of the film neck‐in, is seen to decrease from the film edges to the centerline. POLYM. ENG. SCI., 2010.