Contact-angle measurements in air and water environments and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface properties of air-corona-treated polypropylene (PP) and poly(ethylene terephthalate) (PET) films. Surface properties were examined as a function of the storage time at various temperatures. Corona treatment forms water-soluble, low-molecular-weight oxidized materials on both polymer films. Corona-treated PP and corona-treated PET films have markedly different responses to aging. For corona-treated PP stored at ambient temperatures, only a slight decrease in wettability was observed. This decrease was attributed to the reorientation of oxidized functionalities within the surface region. At elevated storage temperatures, migration of oxidized species out of the surface region occurred under some conditions. For corona-treated PET, extensive migration and reorientation of oxidized groups occurred even at ambient temperatures, leading to significant decreases in wettability and a loss of surface oxidation. The contrasts in the responses of PP and PET to corona treatment are primarily due to differences in the properties of the base polymer resins.
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Strobel et al. (1992) studied this question.