Improved experimental characterization of crystallization kinetics

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 conditions, i.e. including high cooling rate, is of great technological and academic interest. Quiescent, non-isothermal crystallization 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 crystallization 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 s⁻¹. The results demonstrate the importance of performing fast cooling experiments to gather reliable crystallization kinetics data.