Prediction of axial and off‐axis yield behavior of lsotactic polypropylene film from structural state parameters

Abstract

AbstractSince only minor structural rearrangements occur prior to yielding, the axial and off‐axis yield stress of a polymer sample is expected to relate to the initial structural state of the material. Samples of uniaxially oriented isotactic polypropylene films with known structural state parameters have been deformed under a uniaxial tensile stress at deformation rates of 20 percent and 100 percent per minute over an angular range from 0 to 90 degrees to the fabrication direction. The axial yield stress data was found to correlate with the initial noncrystalline orientation state of the undeformed sample. The axial and offaxis yield stress data was fit to the Hill equation derived for the application of a uniaxial tensile stress. The experimentally determined coefficients from the best fit of the yield stress data to the Hill equation were related to the measured structural state parameters. These correlations allow prediction of the yield stress of an anisotropic film at any angle to the film symmetry axis from knowledge of the measured structural state parameters alone.