Modification of Physico-Chemical Properties of Acryl-Coated Polypropylene Foils for Food Packaging by Reactive Particles from Oxygen Plasma

Abstract

This investigation was focused on the influence of long-living neutral reactive oxygen species on the physico-chemical properties of acryl-coated polypropylene foils for food packaging. Reactive species were formed by passing molecular oxygen through a microwave discharge and leaking it to a processing chamber of a volume of 30 L, which was pumped by a rotary pump. The density of neutral O-atoms in the chamber was tuned by adjustment of both the effective pumping speed and the oxygen leak rate. The O-atom density was measured with a catalytic probe and was between 3 × 1018 and 5 × 1019 m−3. Commercial foils of biaxially oriented polypropylene (BOPP) coated with acrylic/ poly(vinylidene chloride) (AcPVDC) were mounted in the chamber and treated at room temperature by O atoms at various conditions, with the fluence between 1 × 1021 and 3 × 1024 m−2. The evolution of the surface wettability versus the fluence was determined by water contact angle (WCA) measurements, the formation of functional groups by X-ray photoelectron spectroscopy (XPS), and the morphology by atomic force microscopy (AFM). The WCA dropped from the initial 75° to approximately 40° after the fluence of a few 1022 m−2 and remained unchanged thereafter, except for fluences above 1024 m−2, where the WCA dropped to approximately 30°. XPS and AFM results allowed for drawing correlations between the wettability, surface composition, and morphology.

Keywords

• plasma surface modification
• polymer polypropylene
• neutral oxygen atom density
• initial surface functionalization
• food packaging
• wettability