Nanoscale Shear and Indentation Measurements in Transcrystalline α-Isotactic Polypropylene

The relation between the mechanical properties and the lamellar morphology of the α-isotactic polypropylene transcrystalline interphase in a fiber composite was investigated by means of nanometric shear and directional indentation measurements, using scanning force microscopy. Measurements were performed along directions parallel and perpendicular to the transcrystalline growth direction. A key finding is the inversion of the shear modulus anisotropy ratio from 2.3 to 0.5 as the crystal grows away from the fiber. On the basis of this finding, an improved view of the hierarchical lamellar and molecular order of the transcrystalline layer is proposed.