Crystallization-induced fluid flow in polymer melts undergoing solidification

The development of rapid fluid flow in undercooled polymer melt during the course of crystallization under confinement conditions was analyzed. A isotactic polypropylene (iPP) polymer and carbon black (CB) was employed and were mixed by melt-pressing repeatedly on a hot plate at 200°C. Samples for the crystallization and flow measurements were prepared by pressing the melt mixtures between two cover glasses into thin films. An optical microscope, equipped with a CCD camera was used to image flows in the undercooled melts by following the motion of CB particles during isothermal crystallization. The local negative pressure created during crystallization and at some point exceeded the yield stress and the fluid started to flow. Result shows that the crystallization-induced flow accelerates until the spherulites form a geometrically percolating structure that creates a strong resistance to fluid flow and the CB particle displacement drops off.