Surface physicochemistry of corona‐discharge‐treated polypropylene film

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.

Wetting properties of food packaging

“…One of the most widely used methods is corona discharge treatment (CDT) (Brewis & Briggs, 1981;O'Hare et al, 2002b). CDT increases the surface energy by introducing polar groups on the surface, consequently improving its wetting, adhesion and printing properties (Baldan, 2004;O'Hare, Leadley, & Parbhoo, 2002a;Pocius, 1997;Sun, Zhang, & Wadsworth, 1999). The polar groups are capable of participating in relatively strong hydrogen bonding, such as phenolic-OH carbonyl and carboxylic acid groups (Brewis & Briggs, 1981;O'Hare et al, 2002b).…”

Surface modification of polymer films with a remote atmospheric pressure d.c. glow discharge: influence of substrate location

“…This is in agreement with the contact angle measurements; a higher concentration of oxygen at the surface gives a lower contact angle. [16,17] This is true for all of the PET samples and most of the PP samples. However, for some PP samples a small increase in oxygen concentration leads to a large decrease in contact angle.…”

Surface modification of closed plastic bags for adherent cell cultivation

“…3 bottom). To minimize damage of the polymer surface due to plasma contact, which is known to lead to the generation of low molecular weight oxidized material (LMWOM) [28] or to an etching of the coating, the plasma treatment time should be chosen as short as possible. By repeating the process several times, each time with fresh monomer added, the film thickness was increased.…”