Enhanced beta to alpha recrystallization in beta isotactic polypropylene with different thermal histories

Abstract

A small but meaningful increase in the content of β‐crystals was observed in β‐nucleated isotactic polypropylene (iPP) samples isothermally crystallized at high temperature and then cooled to room temperature. The secondary crystallization of these crystals could also be linked to a distinct exothermic effect revealed by differential scanning calorimetry upon cooling. These crystals constituted of thinner lamellae certainly show earlier melting upon reheating, with respect to the isothermally crystallized fraction. As such, the enhancement in βα recrystallization in iPP cooled below 100°C is attributed to the formation of a self‐nucleated or partially ordered melt upon melting of these crystals, which induces the fast nucleation and growth of the α‐phase, because of larger undercooling with respect to the β‐phase at elevated temperatures. On the other hand, the recrystallization of the β‐phase from partially molten β‐iPP samples is tentatively assigned to homo‐epitaxial nucleation on the surface of thicker β‐phase lamellae.

Self-Nucleation of β-Form Isotactic Polypropylene Lamellar Crystals in Thin Films

“…Thus, the nature of the above βα growth transition remains not fully understood and is still the subject of crystallographic discussion despite extensive work since the 1970s. Actually, the high-temperature βα growth transition is an experimental and conceptual challenge due to the production of α-iPP with an undetectable fraction 44,45 and the kinetic competition between the two forms. 46,47 Atomic force microscopy (AFM) can provide direct information on the surface topography of polymer crystals on the micrometer to nanometer level and is extremely useful in combination with the β-iPP lamellar crystal in ultrathin films to investigate the melting and recrystallization of β-iPP at temperatures close to its nominal melting temperature.…”

“…Thus, the nature of the above βα growth transition remains not fully understood and is still the subject of crystallographic discussion despite extensive work since the 1970s. Actually, the high-temperature βα growth transition is an experimental and conceptual challenge due to the production of α-iPP with an undetectable fraction , and the kinetic competition between the two forms. , …”

Organogelators with dual β- and α-nucleating ability in isotactic polypropylene

“…The melting curves recorded during heating from room temperatures, however, demonstrate clearly the "melting memory" effect of the β-modification [33,51] (Fig. 5).…”

Suppressed Cavitation in Die-Drawn Isotactic Polypropylene

“…The 1D diffraction curves were composed of both sharp characteristic peaks for the α and β crystalline phases and one broad amorphous peak. By fitting these peaks with several Gaussian functions, the area of each peak could be readily obtained and subsequently the fractions of the β crystalline phase as well as the α crystalline phase could be determined. , For each curve, the fitting procedure was repeated at least three times to gain better accuracy.…”

“…By fitting these peaks with several Gaussian functions, the area of each peak could be readily obtained and subsequently the fractions of the β crystalline phase as well as the α crystalline phase could be determined. 28,29 For each curve, the fitting procedure was repeated at least three times to gain better accuracy. Ultra-small-angle X-ray scattering (USAXS) experiments were performed to evaluate cavitation behavior, using a customized Xeuss X-ray apparatus (Xenocs SA, France), for which the X-ray generator and the detector were the same as the ones for microfocus X-ray diffraction.…”