No abstract

Corona discharge treatment (CDT) is a surface modification technique commonly used to treat plastic films prior to adhesive bonding, printing with inks, lamination to other films and other coating applications. In this study, the treatment conditions are, in energy terms, representative of those used in industrial and laboratory coating applications.The physicochemistry of the surface of untreated and corona-discharge-treated biaxially oriented polypropylene (BOPP) film was investigated using a number of complementary surface analytical techniques: contact angle analysis; x-ray photoelectron spectroscopy (XPS); atomic force microscopy (AFM). This report describes the surface energetics, chemical functionality and morphology of polypropylene film before and after CDT. Both AFM and XPS were utilized, along with washing experiments, to investigate the presence of a weak boundary layer. The morphology of the film changed after CDT. Initially, a fibrillar crystalline structure was observed, whereas after CDT a globular morphology became apparent. These globular features were attributed to low-molecular-weight oxidized material (LMWOM) created by CDT. The roughness of the film was not found to increase under the corona conditions employed.Formation of LMWOM was found to be independent of treatment energy. However, two mechanisms have been suggested for its formation, dependent on the energy of treatment: below a threshold energy of ∼4 kJ m −2 , oxidation and scission of the inherent low-molecular-weight boundary layer present on polyolefin films is the dominant means for the formation of LMWOM; above 4 kJ m −2 , oxidation and scission of the polymer backbone is the main process.This work provides a comprehensive reference around CDT of polypropylene film for industrial applications, while also informing how the optimal level of treatment can be determined. In the case of adhesion of silicones, it would be expected that optimal adhesion would be obtained where the maximum amount of oxygen incorporated was in a water-insoluble form.

Plasma-enhanced coating processes are recognised as a route to well-adhered, conformal coatings, and are often used as a means of modifying the surface properties of materials, while having a minimal effect on the bulk characteristics of the substrate. Here, a method for providing an understanding of the chemistry of siloxane coatings prepared by plasma liquid deposition in atmospheric pressure (AP) is described.An iterative Si 2p-C 1s method for curve-fitting the C 1s and Si 2p core levels of siloxane coatings thinner than the depth of analysis of XPS has been developed when the substrate is poly(ethylene terephthalate) (PET) film. In addition to the determination of unambiguous binding energy positions for four siloxy environments, this has allowed the elemental composition of the coating to be determined in isolation of the substrate.Application of the binding energies to the Si 2p core levels of industrially relevant materials where the composition is not known by any other means can now be carried out. This can be used to provide understanding of the relationship between coating chemistry and plasma parameters, which is essential in the development of novel processes such as AP plasma liquid deposition, and will result in the deposition of coatings with controlled properties.

This study reports on the effect on the morphology and chemistry of atmospheric pressure plasma deposited nm‐thick coatings (21 ± 3 nm) as the level of exposure to the plasma is systematically altered. Coatings were deposited by directly injecting hexamethyldisiloxane, polydimethylsiloxane or tetramethyldisiloxane liquid precursors through a nebulizer into a helium/oxygen atmospheric pressure plasma. An increase in the level of the precursor was found to be associated with a decrease in the concentration of methyl functional groups in the coating and to an increase of the SiO crosslinking, as demonstrated using surface energy and XPS analysis. This resulted in an increase in the coating refractive index, and in a reduction of the number of surface particulates, as well as of surface roughness.magnified image

By injecting a liquid aerosol precursor directly into a non-equilibrium atmospheric pressure plasma (APP), a controlled, free-radical-induced polymerisation reaction can be initiated with minimal fragmentation of the precursor molecules. This can be used to chemically graft highly complex chemical functionalities directly onto a variety of substrates. This process normally proceeds through polymerisation of unsaturated functional groups on the precursor molecules. In this work, it has been found that compounds that lack such polymerisable groups can be physically dissolved in the liquid precursor and that these chemicals are not directly involved in the plasma reaction. Instead, these chemicals become physically entrapped within the resultant plasma polymer and retain much of their biological and chemical properties. As a preliminary example of such a reaction, the entrapment of various anti-microbial species (quaternary ammonium salts) within glycol and acrylic acid plasma polymers is described. The biological and chemical reactivity of these chemicals is examined using a combination of anti-microbial and XPS investigations.