Crystallinity and Crystallographic Texture in Isotactic Polypropylene during Deformation and Heating

TL;DR

This study investigates how crystallinity and crystallographic orientation in isotactic polypropylene evolve during deformation and heat treatment, revealing mechanisms of decrystallization and recrystallization using X-ray diffraction and texture analysis.

Contribution

It provides new insights into the microscopic deformation mechanisms and orientation evolution of isotactic polypropylene during rolling and heat treatment.

Findings

Crystallinity decreases significantly during rolling.

Recrystallization occurs during heat treatment, enhancing fiber orientation.

Decrystallization acts as a deformation mechanism depending on lamellae orientation.

Abstract

The development of the crystallinity and of the crystallographic orientation of isotactic polypropylene (iPP) during rolling deformation and subsequent heat treatment is studied. The experiments are conducted by using X-ray diffraction with an area detector. The evolution of crystallographic orientation is tracked by calculating the pole figures and by applying a quantitative 3D texture component fit method. The rolling orientation after a true strain of -1.5 mainly consists of the (010)[001], (130)[001], and [001]//RD fiber components (RD: rolling direction). The results reveal that the crystallinity drastically decreases during rolling. We suggest that decrystallization (disaggregation) is a deformation mechanism which takes place as a microscopic alternative to crystallographic intralamellar shear depending on the orientation of the lamellae relative to the imposed deformation tensor. Heat treatment after rolling leads to the recrystallization of amorphous material and to a strong enhancement of the fiber orientation component. The recrystallization orientation is explained in terms of an oriented nucleation mechanism where amorphous material aligns along existing crystalline lamellae blocks which prevailed during the preceding deformation.