Dielectric barrier discharge for surface treatment: application to selected polymers in film and fibre form

Abstract

In this paper, we report and discuss a surface treatment method, using a dielectric barrier discharge (DBD) of random filamentary type. This offers a convenient, reliable and economic alternative for the controlled modification (so far, largely dependent on surface oxidation) of various categories of material surfaces. Remarkably uniform treatment and markedly stable modified surface properties result over the entire area of the test surfaces exposed to the discharge even at transit speeds simulating those associated with continuous on-line processing. The effects of air-DBD treatment on the surfaces of various polymer films and polymer-based fabrics were studied. The dielectric barrier concerned has been characterized in terms of the energy deposited by the discharge at the processing electrodes and the resultant modifications of the surface properties of the treated samples were investigated using x-ray photoelectron spectroscopy, contact angle/wickability measurement and scanning electron microscopy. The influence of the surface treatment parameters, such as the energy deposited by the discharge, the inter-electrode gap and the treatment time were examined and related to the post-treatment surface characteristics of the materials processed. Relationships between the processing parameters and the properties of the DBD treated samples were thus established. Of the three process variables investigated, the duration of the treatment was found to have a more significant effect on the surface modifications found than did the discharge energy or the inter-electrode gap. Very short air-DBD treatments (fractions of a second in duration) markedly and uniformly modified the surface characteristics for all the materials treated, to the effect that wettability, wickability and the level of oxidation of the surface appear to be increased strongly within the first 0.1–0.2 s of treatment. Any subsequent surface modification following longer treatment (>1.0 s) was less important. The modification of the surface properties also appears to be stable with time, as minimal recovery of the surface properties is shown on ageing post-treatment. The behaviour of the woven textile polymers examined was found to be very similar, under DBD treatment, to that of thin-film variants based on the same polymers. For the porous textile fabrics examined, rapid and efficient treatment (fractions of a second) on both sides of the treated samples was found to be ensured. Thereby the system regime used offers the attractive prospect of controlling the modification of non-compact materials of various texture, porosity, etc. The DBD described system thus provides a chemically mild and mechanically non-destructive means of altering surface properties targeting improved surface characteristics and potentially better application performance.