Inhomogeneous deformation of microcrystalline region in isotactic polypropylene film revealed by a simultaneous kinetic measurement of microscopic infrared dichroism and macroscopic stress

Abstract

The orientation behaviors of macromolecules in the microcrystalline and the amorphous regions of two isotactic polypropylene films with different degrees of inhomogeneity are studied using an instrument constructed for simultaneous kinetic measurement of microscopic IR (MicIR) dichroism and macroscopic stress at constant elongation rate. Reliability of IR data obtained by the kinetic measurement is demonstrated. The influence of the necking on the molecular orientation is revealed pursuing the time profiles of the MicIR dichroism sampled in a same small sampling area that is initially located at the center of the film but continuously moves during stretching due to the inhomogeneity of the sample. The dramatic molecular orientation in the sampling area is found to mainly occur during the process that the necking passes through this area and is almost independent of the macroscopic stress-strain relationship. The dichroism differences in different locations of the microcrystalline region next to a giant spherulite are shown to exemplify the influence of the inhomogeneity on the molecular orientation behavior.