EFFECT OF TEMPERATURE, PHYSICAL AGING, AND MOISTURE ABSORPTION ON POSITRON LIFETIME PARAMETERS IN CURED POLYESTER RESIN STUDIED BY POSITRON ANNIHILATION LIFETIME SPECTROSCOPY

The positron annihilation method has been widely applied to study an extensive range of materials such as metals, alloys, molecular solids, and numerous other technologically important systems. Among the different experimental methods, positron annihilation lifetime spectroscopy (PALS) has proven to be particularly effective in polymer studies because its high sensitivity to free-volume environments within the polymer. Examining these free-volume features provides crucial information regarding the physical, mechanical, and thermal responses of polymeric materials. In this study, PALS experiments were conducted on a cured polyester resin to explore the responses of the positron lifetime parameters to temperature variations, physical aging, and moisture uptake. The lifetime spectra were processed using PATFIT analysis software. The third lifetime component (t3) and its corresponding intensity (I3), associated with the size and density of the free-volume sites showed clear variations under these different conditions. The observed trends were interpreted in relation to the modification of the free-volume structure within the polymer network.