Quiesent crystallization kinetics of nucleated metallocene and ZN isotactic polypropylenes

Crystallization kinetics and thermodynamic properties of nucleated isotacti c polypropylene (PP) are analyzed using Hoffman-Lauritzen crystallization t heory to determine the mechanistic effects of the nucleators. Calorimetric data provides quantitative comparisons between nucleating efficiences of th e alpha (Millad) and beta (NJSTAR) nucleator in Metallocene (M) and Ziegler -Natta (ZN) PP. The two types of PP without nucleators showed similar cryst allization behavior though the T(m)degrees for ZN-iPP was about 10 degrees C higher than M-iPP. Both nucleators show significant improvement in crysta llization rate in both types of PP. In addition, Millad outperforms NJSTAR. The magnitude of the kinetic response is, however, different and both the nucleators appear to function better in ZN than in Metallocene PP. beta nuc leated PP shows predominantly the beta form. The amount of the beta form is thermal history dependent and changes with supercooling (Delta T=T(m)degre es-T-c). Similar equilibrium melting temperature (T(m)degrees) in the alpha nucleated and control PPs indicates the lack of any thermodynamic effect o f the alpha nucleator. All nucleated PPs show a much lower secondary nuclea tion rate constant, K-g.