Effect of annealing on the microstructure and mechanical properties of polypropylene with oriented shish-kebab structure

Annealing is thought to be an effective method to promote chain rearrangement in semicrystalline polymers and improve their physical properties. However, little attention has been paid to the annealing of flow-oriented semicrystalline polymers despite its importance in polymer processing. In this work, the microstructural evolution of injection-moulded polypropylene with an oriented shish-kebab structure upon annealing has been explored with differential scanning calorimetry, small-angle X-ray scattering and scanning electron microscopy, Fourier transform infrared spectroscopy and dynamic mechanical analysis. The results show that annealing gives rise to a chain rearrangement in both the crystalline and amorphous phases. Accompanied by the growth and perfecting of the kebabs, relaxation of the initially oriented chains in the amorphous phase is observed. Then, the relationship between the structure and the resulting mechanical properties is established. (C) 2011 Society of Chemical Industry