Crystallization kinetics and solidified structure in iPP under high cooling rates

A wide set of isothermal and non-isothermal crystallization experiments were carried out in this work on an iPP resin. Several experimental techniques were adopted in order to characterize crystallization kinetics and final morphology of the material, also under cooling rates comparable to those encountered during material processing (up to several hundred K/s). The whole set of data was taken as a reference to identify a kinetic model which describes the evolution of the structural organization of iPP (α crystalline phase and mesomorphic phase) as a parallel of two non-interacting kinetic processes competing for the available amorphous volume. Kolmogoroff equation was adopted to describe the crystallization of the α form. Avrami–Evans–Nakamura isokinetic approach was adopted to describe the evolution of the mesomorphic phase. Resulting kinetic model satisfactorily describes the whole set of experimental data including those obtained on samples solidified under high cooling rates, and reveals that a correct description of the evolution of the α phase during solidification can be attained only if the evolution of the competing mesomorphic phase is kept into account. The effect of cooling rate during solidification from the melt on diameters of spherulites, observed on solidified samples, is also satisfactorily described by model predictions.