Surface physico‐chemistry of corona‐discharge‐treated poly(ethylene terephthalate) film

Abstract

AbstractThe effect of energy of corona discharge treatment (CDT) on the physico‐chemistry of the surface of a polyester film was investigated systematically using a number of complementary surface analytical techniques: contact angle analysis, x‐ray photoelectron spectroscopy, time‐of‐flight secondary ion mass spectrometry and atomic force microscopy. The energy of treatment can be controlled by either varying the speed of the treatment with constant power input or by varying the power of the treatment with constant speed. The changes in surface energy, surface chemistry and surface morphology of poly(ethylene terephthalate) (PET) induced by these two modes of CDT have been investigated.The surface energy and the polar contribution of the film increased with increasing energy of corona. Phenolic‐OH, carbonyl and carboxylic acid (HOC=O) have been identified as the functional groups incorporated onto the surface. Low‐molecular‐weight oxidized materials were observed in the form of a globular morphology on the surface of the film. By washing the film in methanol–water prior to surface analysis, it was shown that the oxygen content at the surface of the film decreased and the globular morphology was removed.Differences in the surface energy of corona‐treated PET films have been observed under similar corona energy conditions, depending on whether the sample was treated with constant speed or constant power. However, the total surface oxygen content was found to be similar at low‐energy treatments. When the high‐resolution C 1s XPS spectrum was peak fitted, the relative concentrations of functional groups introduced and other changes to the original polymer structure were shown to be independent of the mode of treatment.These observations may be explained because although the total energy transferred from the power source to the PET under the conditions of ‘constant power, variable speed’ and ‘variable power, constant speed’ is theoretically the same, these experimental conditions are not interchangeable. At constant power, the concentration of active species, radiation and dielectric breakdowns in the discharge are independent of speed. However, in the case of constant speed, the concentration of active species, radiation and dielectric breakdown increase with increasing power, resulting in a different surface energy between the two sets of samples. However, because the composition of the active species will not change, the functional groups on the surface of the film will be the same across comparable energy levels, independent of mode of treatment. Copyright © 2002 John Wiley & Sons, Ltd.