Morphological study of deformation process for linear polyethylene

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Abstract
The morphological changes of LLDPE during drawing have been studied with optical and electron microscopy in parallel to the changes in the stress-strain curve. Throughout the drawing process, the morphological changes depended on the location in the spherulite. When drawing was occurring normal to the equator of the spherulite, the lamellae slipped and rotated to align parallel to the drawing direction at an early stage of the extension. On the contrary, the lamellae in the equatorial zone were bent and corrugated. At a higher drawing ratio, the unfolding of the highly aligned lamellae to form the microfibrils occurred in the polar region, and the lamellae in the equatorial region kept their structure. At the highest drawing ratio, most of the aligned lamellae were unfolded to form the microfibrils which were oriented in the elongation direction and integrated into the bundles. But the lamellae in the equatorial region, which were partially unfolded, remained as isolated units. With annealing of the drawn LLDPE, crystalline layers, keeping their molecular backbone orientation, grew perpendicular to the drawing direction, indicating that they were formed by folding of the molecules in the microfibrils with annealing.