Affiliation:
1. Centre de Mise en Forme des Matériaux, Ecole Nationale Supérieure des Mines de Paris, Valbonne, France
Abstract
Abstract
In cast film extrusion, the polymer melt is extruded through a slit die, slightly stretched in air and then cooled on a chill-roll. An important part of the present work was devoted to the development and application of a thermomechanical model of stretching in air and of a purely thermal model of cooling on the roll, taking polymer crystallization into account. The structures and morphologies in a series of extruded polypropylene films were investigated using density and sonic modulus measurements, wide-angle X-ray diffraction, small angle light scattering and optical microscopy. These experimental results combined with theoretical predictions obtained from the model allow to discuss the respective effects of stretching in air and cooling on the roll. Stretching in air essentially affects spherulite nucleation and growth during subsequent crystallization on the roll. Dissymmetrical cooling on the roll induces an inhomogeneous microstructure within the film. The presence of a zone with a finer microstructure near the roll has been correlated with the cooling rates and thermal gradients calculated by the model.
Subject
Materials Chemistry,Industrial and Manufacturing Engineering,Polymers and Plastics,General Chemical Engineering
Cited by
45 articles.
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