Multiscale mechanical characterization of iPP injection molded samples

Mechanical characterizations at different length scales represent a very intriguing possibility for correlating the fine internal morphologies with the macroscopic properties of a polymer material. In this work, molded samples of isotactic polypropylene obtained by injection molding in different processing conditions have been characterized on different lengths scales. The developed morphologies characterized by optical and atomic force microscopy reveal a complex multilayer morphology with globular elements, fibrils and spherulites, from the surface to the sample core. A multiscale mechanical characterization has been performed by Dynamic Mechanical Analysis (DMA), micro indentation and by HarmoniX Atomic Force Microscopy (AFM) tests, from millimeter to nanometer scale. Results show that along sample thickness, well organized and oriented structures (i.e. fibrils) characterized by higher values of mechanical modulus coexist with less organized structures (globules) characterized by mechanical properties closer to the quiescent amorphous phase. Intermediate elasticity is found in the central part of the sample, where well developed spherulitic structures are characterized by both higher crystallinity and lower level of orientation. A good agreement among the relative experimental results has been found, confirming the good complementarity among these techniques for a complete multi-scale sample characterization.