Effect of quenching temperature on the structure of isotactic polypropylene films

Abstract

Films of isotactic polypropylene (iPP) were quenched at different temperatures. Wide-angle x-ray diffractograms for these samples show the presence of the smectic form of iPP at low quenching temperatures and the appearance of mono-clinic form on increasing the thickness of the substrate and the quenching temperature. A quenching temperature higher than 80°C produces only the monoclinic form of iPP, whereas at intermediate temperatures we obtain three-phase amorphous-smectic-crystalline systems. Except for the two-phase amorphous-crystalline system obtained at high temperatures, density values alone do not allow us to obtain the three-phase fractions. We studied the transport properties, sorption, and diffusion of CH₂Cl₂ vapor in these systems to investigate the thermodynamic state of the amorphous component. The behavior of the amorphous component with respect to the diffusion of CH₂Cl₂, which proved identical in all the samples, led us to conclude that at low penetrant activity the smectic phase is not permeable, and therefore we were able to obtain the amorphous fraction in each sample. This value together with density values allowed the determination of the complete composition in terms of three phases for every sample. The crystalline fraction expressed as % mono-clinic form is very well correlated with the reciprocal of the half-height broadening of the (110) diffraction peak at about 2e = 14°.