Crystallization kinetics of iPP: Influence of operating conditions and molecular parameters

Abstract

An analysis of the crystallization kinetics of different grades of isotactic polypropylene (iPP) is here presented. To describe the crystallization kinetics as a function of molecular and operating parameters, the methodological path followed was the preparation of quenched samples of known cooling histories, calorimetric crystallization isotherms tests, differential scanning calorimetry cooling ramps, wide angle X-ray diffraction (WAXD) measurements, and density determination. The WAXD analysis performed on the quenched iPP samples confirmed that during the fast cooling at least a crystalline structure and a mesomorphic one form. The diffractograms were analyzed by a deconvolution procedure, to identify the relationship between the cooling history and the distribution of the crystalline phases. The whole body of results (including calorimetric ones) provides a wide basis for the identification of a crystallization model suitable to describe solidification in polymer-processing operations, based on the KolmogoroffAvrami-Evans nonisothermal approach. The kinetic parameters, determined for all the materials, are discussed, highlighting the effect of molecular parameters on the crystallization kinetics: molecular mass and distribution, tacticity, nucleating agents, and ethylene units content.

Sterilization of propylene/ethylene random copolymers: Annealing effects on crystalline structure and transparency as influenced by polymer structure and nucleation

“…The increase in ethylene content therefore improves the optical properties of the films before sterilization by reducing haze. However it also increases the difference in the optical properties of the films with sterilization and encourages secondary crystallization; this increased 'quenchability' of PP grades with reduced regularity due to stereodefects and/or comonomer incorporation has already been demonstrated before by La Carrubba et al [30]. After sterilization, the DSC analysis of the films reveals a double melting peak as already evidenced in Figure 1.…”

Fast cooling of (non)-nucleated virgin and recycled poly(propylenes): Effect of processing conditions on structural and mechanical properties

“…Differential fast scanning calorimetry studies showed that this transition occurs at cooling rates between 200-500 C s À1 [41]. The transition depends on the material characteristics such as molecular weight and molecular weight distribution, but an exact correlation has not yet been found [42]. When a polymer melt gets into contact with the cold wall of the mold in compression molding or injection molding, the material in close contact to the wall cools very rapidly, which can be investigated by using non-isothermal crystallization experiments in differential fast scanning calorimetry [43].…”

Investigation of the crystallization behavior of isotactic polypropylene polymerized with different Ziegler‐Natta catalysts

“…For ZN‐iPP, great attention had been paid on the relationship between the average isotacticities and the crystallization behavior. Some researchers believed that the isotacticity has an important influence on the spherulitic morphology of iPP,15 it also strongly affects the crystallization characteristics,16, 17 for instance, the number of crystal nuclei at the initial stage, crystallization dynamics, the morphology, size, and perfection of crystals in the final product, and can even induce variations in the nucleation mechanism and the fold surface free energy and the work of chain folding of iPP 10, 18. However, some other researchers held different point of view 19, 20.…”