Influence of structure on the dynamic mechanical properties of crystalline polymers

Abstract

A dynamk mechanical theory is presented whose structural elements correspond to such physically measurable material parameters as the compliance of the phases, the percent crystallinity, and the orientation of the crystalline and noncrystalline regions. The theory is tested by using both structural and dynamk mechanical data from samples of isotactic polyproylene films of varying crystallinity and orientation. For the specific case of isotactic polypropylene the general theory is shown to reduce to a simple two-parameter model. It is further shown that the two-parameter model not only identifies the unique properties of each of the phases separately, but also predicts the dynamic mechanical properties of the polymer over a temperature range of—130°C to 120°C, for samples ranging from unoriented to highly oriented, and varying in crystallinity from 40 to 70%. The model can also predict the dynamic mechanical properties over the same temperature range for strips of these samples cut at varying angles to the machine direction.