Improved experimental characterization of crystallization kinetics

Abstract

Polymer solidification occurring in many processes, like for instance injection molding, compression molding and extrusion, is a complex phenomenon, strongly influenced by the thermo-mechanical history experienced by the material during processing. From this point of view, characterization of polymer crystallization in the range of processing con- ditions, i.e. including high cooling rate, is of great technological and academic interest. Quiescent, non-isothermal crys- tallization kinetics of two polypropylene resins were investigated using a new method, based on fast cooling of thin samples with air/water sprays and optical detection of the crystallization phenomenon. The range of cooling rates attained in this experimental study is considerably larger than that achieved by traditional methods. Quiescent crystal- lization kinetics of the resins is also investigated by the means of DSC, operated under isothermal conditions with a limited degree of under-cooling and for constant cooling rates up to about 1 K s1. The results demonstrate the impor- tance of performing fast cooling experiments to gather reliable crystallization kinetics data.