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

Abstract

The 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.

Comparison of some effects of modification of a polylactide surface layer by chemical, plasma, and laser methods

“…Due to this treatment, characteristic droplets appear on the sample surface, being probably oligomers, i.e., products of PLA degradation (Fig. 4a) [22].…”

Effect of BOPET film surface treatments on adhesion performance of biodegradable coatings for packaging applications

“…Among polymeric substrates, the polyester films are not porous materials and are characterized by a higher wettability than other polymers such as polyolefins. Nevertheless polyester film substrate could require some type of substrate treatments to obtain an adequate surface tension and then a high level of adhesion when coated with other polymers [15][16][17][18].…”

A methodology for curve‐fitting of the XPS Si 2p core level from thin siloxane coatings

“…Both these peaks had been previously been necessary in obtaining good fit to the experimental data during corona treatment of PET film. 19 The lower than expected BE shift is most likely due to the electropositive effect of Si on the carbon atom, resulting in a decrease in BE. The spectrum was then charge corrected to position the carboxyl ester peak at 288.7 eV, using the BE value described in Beamson and Briggs.…”

“…7(a) There are three possible causes for this shift in BE: vertical differential charging 20 between the siloxane coating and the PET film; chemical interactions occurring between the plasma-treated PET and the siloxane coating shifting the components up in BE; or the BE position for aromatic carbons in the literature is incorrect. Since it has been previously determined that plasma treatments of PET film cause the formation of active species such as phenol and carboxylic acid groups, 19 and plasma polymerisation and deposition of siloxanes occurs through the formation of free radicals and Si-OH species, it is highly likely that chemical interactions are occurring between these species. These would be easily observed by XPS in the situation we have here, where the deposited coatings are thinner than the depth of analysis by XPS.…”