Guglielmo Paganetto

Small-angle X-ray scattering from high-density polyethylene: lamellar thickness distributions

Abstract Small-angle X-ray diffraction patterns were recorded for a number of high-density polyethylene samples and were successively analysed by a fit with the calculated patterns corresponding to certain theoretical models. The parameters determined by the above fits were as follows: long-period, crystallinity, mean dimensions of the crystalline lamellae, amorphous thickness, crystallinity and lamellar dimension distributions. Regarding the latter, two mathematical functions were used for the fits, i.e. a symmetrical and an asymmetrical type, and for all of the samples examined the function was determined which gives the best results. Finally, a correlation is suggested between the polymer molecular weight and lamellar dimension distributions.

Relationship between crystallization regimes and melting phenomena in isotactic polypropylene

Abstract A study has been made of the relationship between crystallization regimes and multiple peaks in the melting endotherms of isotactic polypropylene (iPP). Some samples of this polymer can show multiple melting peaks in differential scanning calorimetry (DSC) scans: this phenomenon has been studied and associated with a regime III of crystallization, giving rise to a phase which appears disordered from a crystallographic point of view. During melting, this phase recrystallizes, giving a more ordered phase which melts at a higher temperature. On the contrary, crystallization in regime II produces a crystalline phase which melts with a single endotherm. These phenomena have been studied by DSC, by optical microscopy in polarized light and by X-ray diffraction; the results are discussed in terms of the proposed interpretation.