Etching of polyethylene terephthalate thin films by neutral oxygen atoms in the late flowing afterglow of oxygen plasma

Kinetics of Surface Wettability of Aromatic Polymers (PET, PS, PEEK, and PPS) upon Treatment with Neutral Oxygen Atoms from Non-Equilibrium Oxygen Plasma

The wettability of polymers is usually inadequate to ensure the appropriate spreading of polar liquids and thus enable the required adhesion of coatings. A standard ecologically benign method for increasing the polymer wettability is a brief treatment with a non-equilibrium plasma rich in reactive oxygen species and predominantly neutral oxygen atoms in the ground electronic state. The evolution of the surface wettability of selected aromatic polymers was investigated by water droplet contact angles deposited immediately after exposing polymer samples to fluxes of oxygen atoms between 3 × 1020 and 1 × 1023 m-2s-1. The treatment time varied between 0.01 and 1000 s. The wettability evolution versus the O-atom fluence for all aromatic polymers followed similar behavior regardless of the flux of O atoms or the type of polymer. In the range of fluences between approximately 5 × 1020 and 5 × 1023 m-2, the water contact angle decreased exponentially with increasing fluence and dropped to 1/e of the initial value after receiving the fluence close to 5 × 1022 m-2.

Hydrophobic Recovery of Plasma-Hydrophilized Polyethylene Terephthalate Polymers

Oxygen plasma is widely used for enhancing the wettability of numerous polymers, including polyethylene terephthalate (PET). The treatment with plasma containing oxygen will cause surface functionalization with polar functional groups, which will, in turn, improve the wettability. However, the exact mechanisms leading to the hydrophilic or even super-hydrophilic surface finish are still insufficiently explored. The wettability obtained by plasma treatment is not permanent, since the hydrophobic recovery is usually reported. The mechanisms of hydrophobic recovery are reviewed and explained. Methods for suppressing this effect are disclosed and explained. The recommended treatment which assures stable hydrophilicity of PET samples is the treatment with energetic ions and/or vacuum ultraviolet radiation (VUV). The influence of various plasma species on the formation of the highly hydrophilic surface finish and stability of adequate wettability of PET materials is discussed.

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

Two-layer functional coatings for polyethylene (PE) and polypropylene (PP) films were developed for the active packaging concept. Prior to coating, the polymer films were activated by O2 and NH3 plasma to increase their surface free energy and to improve the binding capacity and stability of the coatings. The first layer was prepared from a macromolecular chitosan solution, while the second (upper) layer contained chitosan particles with embedded catechin or pomegranate extract. Functionalized films were analyzed physico-chemically to elemental composition using ATR-FTIR spectroscopy and XPS. Further, oxygen permeability and wettability (Contact Angle) were examined. The antimicrobial properties were analyzed by the standard ISO 22196 method, while the antioxidative properties were determined with an ABTS assay. Functionalized films show excellent antioxidative and antimicrobial efficacy. A huge decrease in oxygen permeability was achieved in addition. Moreover, a desorption experiment was also performed, confirming that the migration profile of a compound from the surfaces was in accordance with the required overall migration limit. All these properties indicate the great potential of the developed active films/foils for end-uses in food packaging.

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

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.

Endothelialization of Polyethylene Terephthalate Treated in SO2 Plasma Determined by the Degree of Material Cytotoxicity

Improving the biocompatibility of polyethylene terephthalate (PET) vascular grafts is an important task for avoiding thrombus formation. Therefore, SO2 plasma at various treatment periods were used to modify PET surface properties by forming sulfate functional groups. These groups were shown to act antithrombogenically, ensuring good hemocompatibility of the materials, although the biocompatibility of such materials still remains a mystery. For this reason, the adhesion and viability of HUVEC cells on SO2 plasma-modified PET surfaces were studied, and the possible toxicity of the tested material was determined using two different assays, MTT (metabolic activity assay) and SRB (in-vitro toxicology assay). Changes in chemical composition, morphology and wettability were determined as well. Improved endothelialization was observed for all plasma-treated samples, with the most optimal being the sample treated for 80 s, which can be explained by it having the best combination of surface functionalization, roughness and morphology. Furthermore, toxicity was observed to some extent on the sample treated for 160 s, indicating the lowest cell density among the plasma-treated samples. X-ray photoelectron spectroscopy showed increased oxygen and sulfur content on the surface, which was independent on treatment time. Surface roughness of the plasma-treated samples increased, reaching its maximum after 80 s of treatment, and decreased thereafter.

Rapid Hydrophilization of Model Polyurethane/Urea (PURPEG) Polymer Scaffolds Using Oxygen Plasma Treatment

Polyurethane/urea copolymers based on poly(ethylene glycol) (PURPEG) were exposed to weakly ionized, highly reactive low-pressure oxygen plasma to improve their sorption kinetics. The plasma was sustained with an inductively coupled radiofrequency generator operating at various power levels in either E-mode (up to the forward power of 300 W) or H-mode (above 500 W). The treatments that used H-mode caused nearly instant thermal degradation of the polymer samples. The density of the charged particles in E-mode was on the order of 10¹⁶ m⁻³, which prevented material destruction upon plasma treatment, but the density of neutral O-atoms in the ground state was on the order of 10²¹ m⁻³. The evolution of plasma characteristics during sample treatment in E-mode was determined by optical emission spectroscopy; surface modifications were determined by water adsorption kinetics and X-ray photoelectron spectroscopy; and etching intensity was determined by residual gas analysis. The results showed moderate surface functionalization with hydroxyl and carboxyl/ester groups, weak etching at a rate of several nm/s, rather slow activation down to a water contact angle of 30° and an ability to rapidly absorb water.

Modification of PET surface properties using extremely non-equilibrium oxygen plasma

Polyethylene terephthalate (PET) foils have been exposed to oxygen plasma and its afterglow in order to reveal compositional and structural modifications of the surface layer. Oxygen plasma was created by electrode-less RF discharge in a glass chamber so the O-atom density was close to 1022 m