Simultaneous biaxial deformation behavior of isotactic polypropylene films

The simultaneous biaxial deformation behavior of isotactic polypropylene films was investigated using a novel laboratory film stretcher. A detailed description of the apparatus and its measurement capabilities is presented. The effects of drawing temperature and ratio, strain rate, and deformation modes on the macroscopic equibiaxial deformation and its relation to film dimension uniformity were studied. The strain rate was found to have a large influence on biaxial deformation homogeneity. For temperatures 15degreesC to 5degreesC below the melting point, it could be concluded that a homogeneous biaxial deformation was achieved if the Hencky strain rate was higher than 0.1 s(-1). Additionally, it was found that the nominal biaxial yield stresses were linearly dependent on temperature in the range under investigation.