VARIATION OF FREE-VOLUME IN POLYETHYLENE UPON EXTENSION PROBED BY POSITRON-ANNIHILATION LIFETIME TECHNIQUE

Variations of an average size, size distribution, and numerical concen tration of a free volume in polyethylene upon the extension up to 8 ti mes were studied by a positron annihilation lifetime measurement. The average free volume size is not affected with an increase of the exten sion up to 6 times of a polyethylene film. This result suggested that the free volume holes in the amorphous phase of polyethylene are uncha nged by the mechanical strain. The numerical concentration of the free volume decreases with an increase of the extension rate of polyethyle ne, suggesting that the total percentage of the amorphous phase of pol yethylene decreases through the conversion to the crystalline phase to adapt the mechanical strain. A further extension of the film over 6 t imes, i.e., after saturation of crystallization, renders a decrease of the free volume size.