Isotactic polypropylene crystallized from the melt. II. Thermal melting behavior

Isotactic polypropylene (iPP) isothermally crystallized from the melt was studied by differential scanning calorimetry (DSC) and light transmission measurements techniques. When samples crystallized isothermally above 132 degrees C, alpha-spherulites were formed only; the DSC measurements showed double melting endotherms peak. The first peak represents the melting of crosshatched lamellae in alpha-spherulites, while the second peak is correlated to melting of the radial and the reorganized tangential lamellae. Below 132 degrees C the iPP showed a broad melting peak endotherm with a melting tail endotherm at the low temperature side. The light transmission measurements showed that the tail endotherm is due to the melting of beta-spherulites and the broad melting peak is due to the melting of alpha-spherulites. (C) 1998 John Wiley & Sons, Inc.