Nanostructure evolution in poly(propylene) during mechanical testing

Abstract

Slow continuous mechanical tests of oriented poly(propylene) (PP) are monitored by combined two-dimensional (2D) ultra-small-angle X-ray scattering (USAXS) and small-angle X-ray scattering (SAXS). Patterns are transformed to the 3D chord distribution (CDF), a real-space representation of nanostructure. From the CDF, topological parameters of the semicrystalline domain structure are extracted and discussed. A continuous-strain test shows fracture and release of weak lamellae (2-10% strain). Beyond that we see conversion of lamellae into needles. As all layers are consumed the material breaks. Fatigue is studied in load-reversal (between 10 and 35% strain). We report cyclic (damped) crystallization, layer break, and relaxation melting. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.