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Doppler broadening and positron lifetime spectra have been measured for polypropylene films of constant thickness (= 50 pm) and different morphology that crystallized from melt at temperature 0, 100, and 120°C. The S-parameter vs. energy curves do not change in a systematic way with crystallinity of samples. It is supposed that decrease in the fractional free volume for samples of greater crystallinity is not seen in S-values 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 (τ2 = 1.3 ns) and I3 (τ3 = 2.3 ÷ 2.8 ns) show changes with crystallinity of samples. The evident trend is observed for the longer-lived τ3-component intensity to decrease with crystallinity while the reverse is true for the shorter, fixed τ2-component. The decrease in the intensity of the longer-lived component can result from reduction of the fractional free volume.

Polypropylene Films Studied with Variable Positron Beams