Polypropylene films studied with variable positron beams

Doppler broadening and positron lifetime spectra have been measured for pol ypropylene films of constant thickness (approximate to 50 mu m) and differe nt morphology that crystallized from melt at temperature 0, 100, and 120 de grees C. The S-parameter vs. energy curves do not change in a systematic wa y with crystallinity of samples. It is supposed that decrease in the fracti onal free volume for samples of greater crystallinity is not seen in S;valu es because of their increase resulting from annihilation in defects present both in the crystalline regions and on the lamellae surfaces. Intensities of the components in the positron lifetime spectra: I-2 (tau(2) = 1.3 ns) a nd I-3 (tau(3) approximate to 2.3 divided by 2.8 ns) show changes with crys tallinity of samples. The evident trend is observed for the longer-lived ta u(3)-component intensity to decrease; with crystallinity while the reverse is true for the shorter, fixed tau(2)-component. The decrease in the intens ity of the longer-lived component can result from reduction of the fraction al free volume.