The structure changes of polypropylene precursor film with different die draw ratio during annealing

Two polypropylene precursor films with various die draw ratios (DDR) are made by melt extrusion. The crystal structure evolution analysis during annealing show that two precursor films have identical long periods and lamellae thickness but different lateral dimensions and tilted states of lamellae. Lower DDR generates shorter lateral dimension and more tilted state of lamellae, making the lamellae slip easier. As the annealing temperature rises, expect for the expectedly increasing long period and lamellae thickness, the new secondary lamellae appear at rigid amorphous regions, the lateral dimension also lengthens, while the inclination angle does not change, leading to the stabler lamellae during stretching and abundant micropores. Since the long period, lamellae thickness, and the secondary lamellae remain the same state when annealed at the same temperature, the different lamellae stability of two films and microporous structure after stretching should attribute to the difference of lateral dimensions after annealing.