Modeling the elastic behaviour of a polypropylene taking account of the microstructure

The aim of this work is to modelize the elastic behaviour of a polypropylene used in low fraction filled particulate composites. This behaviour depends a lot on the microstructure and particularly the crystalline fraction. The polypropylene's microstructure was studied in detail and its elastic behaviour was modelized with a self-consistent method by considering an heterogeneous medium constituted of two phases, the amorphous one and the crystalline one, the last one being constituted of crystalline entities playing the role of strengthening particles. The elastic characteristics of both phase, ill-known, are evaluated by an optimization method using two series of experiments : the first one consists of tests at different temperatures near the glass transition of the polypropylene in order to only modify the elastic characteristics of the amorphous phase of the polymer and the second one consists of thermal treatments imposed to the polymer in order to only modify its crystallinity fraction. The comparison between the model and the experiments is rather satisfying.