Das Kristallisations- und Schmelzverhalten von mit Hilfe verschiedener katalytischer Systeme (low- and high-yield) synthetisiertem isotaktischem Polypropylen (iPP) wurde durch Scanning-Kalorimetrie und optische Mikroskopie untersucht. Die isotherme Kristallisationsgeschwindigkeit der Schmelze hängt vom angewandten katalytischen System und vom Isotaktizitätsindex der Probe ab. Im Falle von "low-yield" iPP ergab die kinetische Auswertung des Gesamtprozesses nach Avramy Hinweise auf sekundäre Kristallisationsphänomene. Die Werte des Gleichgewichtsschmelzpunktes, der Keimbildungsenergie und der Oberflächenenergie der Faltung lamellarer iPP-Kristalle wurden nach der kinetischen Theorie der Polymerkristallisation berechnet. Unterschiede in diesen thermodynamischen Parametern, die für verschiedene iPP-Proben zu beobachten sind, wurden auf die Menge und den Typ der konfigurationellen Unregelmässigkeiten entlang der Ketten und auf Unterschiede in der Molekulargewichtsverteilung zurückgeführt
The crystallization and melting behaviour of isotactic polypropylene (iPP) samples synthetized with different catalyst systems (low and high-yield) have been studied by differential scanning calorimetry and optical microscopy. The isothermal crystallization rates from the melt have been found to depend on the catalyst system employed and on the isotacticity index of the sample. Moreover, for low-yield iPP, Avrami analysis of the overall kinetics has provided evidence of the presence of secondary crystallization phenomena. The values of the equilibrium melting point, energy of nucleation and surface energy of folding of iPP lamellar crystals have been calculated according to the 'Kinetic theories' of polymer crystallization. The observed variation of such thermodynamic parameters for the various iPP samples has been accounted for by the amount and type of configurational irregularities present along the chains and by the differences in the molecular weight distribution.
Low and high-yield isotactic polypropylene: isothermal crystallization from the melt
M Avella;
1983
Abstract
The crystallization and melting behaviour of isotactic polypropylene (iPP) samples synthetized with different catalyst systems (low and high-yield) have been studied by differential scanning calorimetry and optical microscopy. The isothermal crystallization rates from the melt have been found to depend on the catalyst system employed and on the isotacticity index of the sample. Moreover, for low-yield iPP, Avrami analysis of the overall kinetics has provided evidence of the presence of secondary crystallization phenomena. The values of the equilibrium melting point, energy of nucleation and surface energy of folding of iPP lamellar crystals have been calculated according to the 'Kinetic theories' of polymer crystallization. The observed variation of such thermodynamic parameters for the various iPP samples has been accounted for by the amount and type of configurational irregularities present along the chains and by the differences in the molecular weight distribution.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
