Browsing by Author "Auriemma, Finizia"
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- Time-resolving small angle X-Ray scattering analysis of melt crystallization of mixtures of regular and irregular isotactic polypropylene samplesPublication . Auriemma, Finizia; Ruiz de Ballesteros, Odda; Giusto, Giovangiuseppe; Di Girolamo, Rocco; Malafronte, Anna; Scoti, Miriam; De Rosa, Claudio; Mitchell, Geoffrey R.The melting/crystallization properties of blends obtained by mixing two isotactic polypropylene (iPP) samples synthesized using single-site metallocene catalyst systems and containing a high and low concentration of rr triads as stereo-defects, are studied. The changes occurring at lamellar length scale during a heating/cooling cycle at constant scanning rate are followed in situ by performing time-resolved small angle X-ray scattering (SAXS) measurements. Data analysis demonstrates that the evolution of the SAXS intensity with increase/decrease of the temperature is controlled by the separate melting/crystallization of the two components, the differences in the thermal expansion (contraction) coefficient of the amorphous and crystalline phases and the role of thermal fluctuations in electron density. The two components give rise to different populations of intermixed lamellar stacks in the blends which originate from the good miscibility of the low and high stereoregular samples in the melt.
- Time-resolving study of stress-induced transformations of isotactic polypropylene through wide angle X-ray scattering measurementsPublication . Auriemma, Finizia; De Rosa, Claudio; Di Girolamo, Rocco; Malafronte, Anna; Scoti, Miriam; Mitchell, Geoffrey Robert; Esposito, SimonaThe development of a highly oriented fiber morphology by effect of tensile deformation of stereodefective isotactic polypropylene (iPP) samples, starting from the unoriented form, is studied by following the transformation in real time during stretching through wide angle X-ray scattering (WAXS) measurements. In the stretching process, after yielding, the initial form transforms into the mesomorphic form of iPP through mechanical melting and re-crystallization. The analysis of the scattering invariant measured in theWAXS region highlights that the size of the mesomorphic domains included in the well oriented fiber morphology obtained at high deformations increases through a process which involves the coalescence of the small fragments formed by effect of tensile stress during lamellar destruction with the domain of higher dimensions.