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.

Plasma Activation of Polyethylene Powder

“…The functionalization efficiency can be estimated from the measured density of neutral oxygen atoms in the plasma reactor and the surface of the polymer powder, taking into account the fluence needed for saturation of the polymer surface with oxygen functional groups from the available literature, i.e., 2 × 10 22 O-atoms/m 2 [ 19 , 20 ]. The required treatment time for receiving this fluence depends on the surface of all the powder particles Σ S powder , the surface of the stainless–steel dish S dish and the flux of O-atoms on the surface of the dish: …”

“…The lower limit of plasma functionalization of polymer powder is defined by the fluence of reactive species onto the treated samples. Unfortunately, there is no report on recommended fluences for saturation of polyethylene surfaces with polar functional groups, but Vukusic et al reported the optimal wettability of acryl-coated polypropylene foils after receiving the fluence of about 2 × 10 22 O-atoms/m 2 [ 19 ]. Similar numbers were also reported by Vesel et al for the case of polystyrene [ 20 ].…”

Two-Layer Functional Coatings of Chitosan Particles with Embedded Catechin and Pomegranate Extracts for Potential Active Packaging

“…The formation of aldehyde and carboxyl groups may be seen from the high-resolution spectra. It is also known, that both plasma treatments yield higher roughness and increased surface free energy, which should enable better adhesion of coatings onto foils’ surfaces [ 40 , 41 , 42 , 43 ]. As already mentioned, ammonia plasma was meant to be done, whilst introduced amino groups can contribute to the antimicrobial activity, and oxygen plasma offers binding places for chitosan attachment onto foils’ surfaces.…”

Atomic oxygen and hydrogen loss coefficient on functionalized polyethylene terephthalate, polystyrene, and polytetrafluoroethylene polymers

“…Here we should note, that hydrogen and oxygen atoms are also lost by chemical reaction with the polymer surface. However, the surface is very quickly (in 1 s) saturated with functional groups and more steady state is obtained . The reaction of H or O atoms with the polymer surface may also results in products which have a lower reaction probability than the pristine polymer surface.…”

“…The density of atoms in the afterglow is not significantly lower than in glowing plasma so functionalization occurs in a short time. The density of O‐atoms on a smooth polymer surface which assures for saturation with polar groups upon treatment with O‐atoms in the afterglow is 10 19 –10 20 m −3 . The loss of atoms is either in the gas phase (predominantly at three body collisions) or on surfaces (by chemical reactions and heterogeneous surface recombination).…”