科研之友
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摘要
A review is given of the work in the field of flow induced crystallization in polymer melts, as has been carried out during the last twenty five years mostly in Linz. A concise discussion of some results of a recent monograph is given. In this connection polymer melt rheology provides insights into the differences of information, as provided by shear and extensional flow. These differences show up with increased degrees of deformation. One finds four important pictures in this report: center dot An electron micrograph of the crystalline structure in a cross-section perpendicular to the previous flow direction. No branching is found of the tracks, which are lines of intersection with the plane of the cross-section. center dot A ring-shaped sample of polypropylene is shown, which fits into a newly developed apparatus. Because of the large radius secondary flow is avoided.. A picture, which was obtained already a long time ago, shows that the relaxation of flow induced structures occurs with polypropylene only at temperatures between 210 and 190 degrees C. Below the latter temperature no relaxation of crystalline structures occurs. center dot The sharp boundary between a highly oriented zone near the duct wall and the spherulitic structure in the interior of samples, which have been extruded through ducts of rectangular cross-section, can readily be explained.
- 出版日期2017-5
