Microstructure and Crystallinity of oriented polyolefins

Abstract

The influence of orientation on polyolefins was studied in accordance with Peterlin’s molecular model of drawing. Isotactic polypropylene and low density, linear low density and high density polyethylenes were oriented via solid-state stretching at an elevated temperature. Orientation induced changes in the morphology were analyzed by optical and scanning electron microscopy. Differential scanning calorimetry and wide-angle X-ray diffraction were used to determine changes in the crystallinity where a two-stage evolution was revealed. The first stage is characterized by a significant increase in crystallinity while the following saturation occurs with a further draw ratio increase at the second one. The value of the critical draw ratio, which separates these two stages and corresponds to the transformation from the initial to the fully developed fibrillar structure, was influenced by the structural peculiarities of each polyolefin.