Deformation Mechanisms of Polymer Thin Films by Simultaneous Kinetic Measurement of Microscopic Infrared Dichroism and Macroscopic Stress. Part III: Influence of Morphology on Molecular Orientation of Isotactic Polypropylene Films Subjected to Uniaxial Stretching

Abstract

Molecular orientations of the crystalline and the amorphous phases are studied in relation to morphology using an instrument constructed for simultaneous kinetic measurement of microscopic infrared (MicIR) dichroism from a pre-determined sampling area and macroscopic stress of isotactic polypropylene (iPP) thin film uniaxially stretched at a constant strain rate at room temperature. The morphology imposes important influences on profiles of MicIR dichroism as a function of stretching time and also on a relationship between the orientation functions, f_c and f _am, of the crystalline and the amorphous phases. Linear relationships between f_c and f_am are found for the local areas without giant spherulite inclusions when f _am<0.3~0.4, suggesting the harmonious developments of amorphous chain deformation and lamellar orientation during the necking propagation. The proportionality constant between f_c and f_am is not universal but is strongly dependent on the morphology of the surrounding area where the local area under examination is located. The linear relationship between f_c and f_am is completely invalidated for describing the relationship between the amorphous chain deformation and the lamellar orientation inside the spherulites, which reveals that the deformation mechanism in the spherulite is different from that in the microcrystalline region.