Evolution of Morphology and Structure During Crystallization and Melting in Syndiotactic Polypropylene
Z G. Wang, B S. Hsiao, Charles C. Han
Structure and morphology development during isothermal crystallization and subsequent melting of syndiotactic polypropylene (sPP) was studied by time-resolved simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) methods with synchrotron radiation and differential scanning calorimetry (DSC). The time and temperature dependent parameters such as long period, L, crystal lamellar thickness, lc, amorphous layer thickness, la, scattering invariant, Q, crystallinity, Xc, lateral crystal sizes, L200 and L020, and unit cell parameters a and b were extracted from SAXS and WAXD profiles. Decreasing long period and crystal thickness indicate that thinner secondary crystal lamellae are formed. The decreases in unit cell parameters a and b during isothermal crystallization process suggest that crystal perfection takes place. The changes in the morphological parameters (the invariant, Q, crystllinity, Xc, long period, L, and the crystal thickness, lc) during subsequent melting was found to follow a two-stage melting process, corresponding to the dual endotherm behavior in the DSC scan. We conclude that the dual melting peaks are due to the melting of secondary and primary lamellae (first peak) and the subjsequent recrystallization-melting process (second peak). Additional minor endothermic peak located at the lowest temperature, was visible and might be related to melting of secondary, thinner and defective lamellae. WAXD showed that during melting, thermal expansion was greater along the b axis than that along the a axis.
Chinese Journal of Astronomy and Astrophysics
crystallization kinetics, morphology of crystalline structure, small angle x-ray scattering, syndiotactic polyproyplene, wide angle x-ray diffraction
, Hsiao, B.
and Han, C.
Evolution of Morphology and Structure During Crystallization and Melting in Syndiotactic Polypropylene, Chinese Journal of Astronomy and Astrophysics
(Accessed December 1, 2023)