Brillouin Scattering Studies of the Glass Transition of Oriented Semicrystalline Polypropylene Films

摘要

The quasi-longitudinal and quasi-transverse hypersonic velocities are determined using Brillouin scattering for the isotactic polyproplene (PP) films as a function of stretch ratio at various temperatures (ranging from 190 to 330 K) with a particular emphasis on the glass transition region. The study shows that the glass transition in the PP film is reflected by a spread of the glass transition temperatures. The lower glass temperature decreases with increasing stretch ratio, whereas the high glass temperature remains unchanged. Between Tg1 (the lower glass temperature) and Tg2 (the high glass temperature), the hypersonic velocity decreases in magnitude. Analysis of the velocity data shows that the glass transition has a most pronounced effect on C33. Significant disagreement is found between the ultrasonic and Brillouin scattering data. Theoretical calculations using the recently developed orientation model by Wang show good agreement with the Brillouin data. The Voigt model of Ward gives a result slightly lower than the experimental values in both C11 and C33.