Plasma-treated Polyethylene Surfaces Research Articles

Influence of ambient conditions on the aging behavior of plasma-treated polyethylene surfaces

Plasma treatment is often used to modify the surface properties of polymer films, since it offers numerous advantages over the conventional surface modification techniques. However, plasma-treated polymer films have a tendency to revert back to the untreated state (aging process). Therefore, the stability of plasma-induced changes on polymer surfaces over a desired period of time is a very important issue. The objective of this study is to examine the effect of storage conditions (relative humidity and temperature) on the aging behavior in air of plasma-treated low density polyethylene (LDPE) films. Plasma treatment is performed using a dielectric barrier discharge (DBD) operating in different argon/water vapor mixtures at medium pressure (5.0kPa). Results show that the aging process can be suppressed by storing the plasma-modified LDPE films at low temperature and by decreasing the relative humidity of the surrounding air. Adding water vapor in the plasma discharge has a positive influence on the aging process: lower plateau WCA values are found for plasmas containing a higher water vapor concentration and it takes a longer time to reach these plateau values. In this paper, it is also shown that storage first at a lower temperature and then aging at a higher temperature is not able to slow down the aging effect.

Plasma‐Treated Polyethylene Surfaces for Improved Binding of Active Protein

AbstractThe use of plasma immersion ion implantation (PIII) to prepare polyethylene surfaces for binding active proteins is investigated. The PIII surface treatment significantly improves the density of active HRP bound to the surface after incubation in buffer containing the protein. The retention of enzyme activity on the PIII‐treated surfaces is greatly improved as compared to both untreated controls and surfaces exposed to the plasma without the PIII treatment. A nitrogen PIII treatment produced surfaces with the best retention of protein activity. Oxidation of the ion‐damaged surface and the formation of a carbonized subsurface are believed to be responsible for the observed protein binding properties.magnified image

Dynamic (de)wetting properties of superhydrophobic plasma-treated polyethylene surfaces

Superhydrophobic surfaces present properties of self-cleaning and unwetting that could be applied in the optics field. The wetting and dewetting of these superhydrophobic surfaces are compared to that of only hydrophobic polyethylene. The contact angle of such a surface varies from 170° to 130-140°. The dewetting is studied using two techniques of dynamic dewetting measurements. The behaviors of surfaces, dried or prewetted with water vapor, are different. The dewetting of the dried surface previously prewetted is discontinuous, and slower than that of the dry one. This specific behavior is interpreted as a roughness effect on trapped water. However, its dewetting is still faster than a corresponding hydrophobic surface like polytetrafluoroethylene (PTFE).

Improvement in adhesion of polyethylene by glow-discharge plasma

The means by which plasma treatment enhances the adhesion of polymer materials, remains obscure. Thus far, two possible mechanisms have been proposed: an increase in surface energy, and the anchor effects imparted by plasma etching. Independently from these mechanisms, reactions between free radicals, generated by plasma irradiation and adhesives are also likely to affect the adhesive properties of polymer materials. Free radicals generated on polyethylene (PE) by glow-discharge plasma were exposed to air and converted to peroxide. The peroxides were converted back to free radicals with the application of heat, and then graft polymerization was initiated, by adding a hydrophilic monomer such as acrylic acid. The peroxides formed by the reaction between free radicals and the oxygen in air was detected by chemiluminescence (CL). In this work, plasma-treated PE surfaces were bonded to aluminum boards, using epoxy resin as an intermediate adhesive and then subjected to a series of peeling tests. The sample with the highest peeling strength also had the highest level of CL-detected peroxides. These findings suggest that the free radicals generated by plasma treatment influence the adhesive properties of the polymer materials.

Chemical reactions on plasma-treated polyethylene surfaces

Oxygen plasma treatment as a surface functionalization technique is discussed. Oxygen-containing functionalities were introduced on the surface of high- (HDPE) and low-density polyethylene (LDPE) by glow discharge. The number of surface hydroxyl groups was increased by a post-discharge wet treatment in a reducing solution. The effects of the substrate nature, the discharge parameters, and the post-discharge wet treatment on the surface functional groups are discussed, and the effectiveness of functionalized surfaces on the yield of coupling reactions is shown.