Plasma-treated Polyethylene Terephthalate Research Articles

Influence of ambient conditions on the ageing behaviour of plasma-treated PET surfaces

Plasma treatment is often used to modify the surface properties of polymer films, since it offers numerous advantages over the conventional surface modification techniques. However, plasma-treated polymer films have a tendency to revert back to the untreated state (ageing process). Therefore, the stability of plasma induced changes on polymer surfaces over a desired period of time is a very important issue. The objective of this study is to examine the effect of storage conditions (relative humidity, temperature and pressure) on the ageing behaviour in air of plasma-treated polyethylene terephthalate (PET) films. Plasma treatment is performed using a dielectric barrier discharge (DBD) operating in air at medium pressure (5.0kPa). Results show that the ageing process can be suppressed by storing the PET films at low temperature or by decreasing the relative humidity of the surrounding air. In this paper, it is also shown that decreasing pressure has no influence on the ageing process.

DBD treatment of polyethylene terephthalate: Atmospheric versus medium pressure treatment

In this paper, polyethylene terephthalate (PET) films are modified by a dielectric barrier discharge (DBD) in a helium/air mixture at medium (6.6 kPa) and atmospheric pressure. Surface analysis and characterization of the plasma-treated PET films is performed using contact angle measurements, X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM). The polymer films, modified with the DBD at medium and atmospheric pressure, show a significant decrease in water contact angle due to the incorporation of oxygen-containing groups, such as C–O and O–C=O. Results also show that the surface treatment is uniform at micron scales, despite the fact that the discharge consists of a series of microdischarges. It is shown that at low energy densities (< ± 200 mJ/cm 2), plasma treatment at medium pressure is more energy-efficient in incorporating oxygen functionalities than plasma treatment at atmospheric pressure. This effect could be induced by the larger diameter of the microdischarges at medium pressure than at atmospheric pressure (factor 3.92) and/or by the lower quenching of atomic oxygen in three-body collisions at medium pressure. The ageing behaviour of the plasma-treated PET films during storage in air is also studied in this paper. XPS results reveal that during the ageing process the induced oxygen-containing groups re-orientate into the bulk of the material. In this paper, it is shown that the ageing behaviour of the PET films is independent of the operating pressure used during plasma treatment.

Room temperature crystallization of indium tin oxide films on glass and polyethylene terephthalate substrates using rf plasma

The crystallization of amorphous indium tin oxide (ITO) films was achieved by rf (13.56MHz) plasma treatment. Although the films were crystallized after 2min, the sample temperature was lower than 90°C without compulsory cooling even after 10min of treatment and polyethylene terephthalate (PET) substrates had no damage. Plasma-crystallized sputtered ITO films have a bixbite structure and the resistivity reached to 1.6×10−4Ω∙cm. ITO thin films have almost the same resistivity in both cases of PET and glass substrates used and plasma-treated PET ITO films have a bit higher resistivity than that of glass ITO films, while mass spectroscopy measurements indicated that ITO films deposited on PET substrates are expected to include no apparent gas species ejected from PET substrate. It was found that the plasma gas pressure is the key parameter for the effective crystallization and the appropriate gas pressure depends on the plasma gas species.

Proliferative and re-defferentiative effects of photo-immobilized micro-patterned hyaluronan surfaces on chondrocyte cells

A photo-immobilisation procedure was utilised to create two different micro-patterned surfaces (tracks 25 and 5 μm wide) of hyaluronan (Hyal) on polyethylene-terephthalate (PET) previously plasma activated. Aim of the study was to investigate the proliferation and re-differentiation capacity of articular chondrocytes cultured on micro-patterned Hyal, compared to homogeneous Hyal and plain plasma-treated (pt-)PET substrates. Cytotoxicity, cell proliferation, activation and differentiation of articular knee cartilage chondrocytes (Mongrel sheep) were evaluated after 14 days of culture. It was found that micro-patterned Hyal surfaces induced the adhesion, migration and alignment of chondrocytes, as shown by light and scanning electron microscopy. Furthermore, the same surfaces induced chondrocyte differentiation, with a significant increase of aggrecan and collagen type II production, while homogeneous Hyal and pt-PET surfaces did not.

Surface properties of HMDSO plasma treated polyethylene terephthalate

HMDSO plasma polymer films are known to reduce the resulting surface free energy and the permeation rate of water vapour and oxygen through the treated polymer substrates.In this work, plasma polymer films were deposited from hexamethyldisiloxane (HMDSO) on polyethylene terephthalate surfaces under different operating conditions and the resulting surface properties were investigated. The structure and bondings in the deposited films were studied by means of IR spectroscopy. The thickness of the deposited films was deduced observing images acquired with a focused ion beam (FIB). Hydrophobic performances were investigated by means of water droplet contact angle measurements.Correlation between operating deposition conditions and resulting structure and surface properties of the films were also discussed.

Evolution of aroma compounds from orange juice stored in polyethylene terephthalate (PET)

The evolution of aroma compounds from orange juice made from concentrate and stored in glass, standard monolayer polyethylene terephthalate (PET 1), multilayer PET (PET 2) and plasma-treated PET (internal carbon coating) (PET 3) was investigated. Bottles were stored at room temperature (20°C) under artificial light. Volatile compounds in orange juice samples and corresponding packaging materials were analysed at zero time and after 2, 3 and 5 months of storage. After 5 months of storage, from 0.2 to 0.3% of the initial amounts of limonene and β-myrcene in the orange juice had been absorbed by the plastic packaging materials. Statistical analyses showed that the evolution of aroma compounds was strongly correlated to the duration of storage, but not to the type of packaging material. Indeed, whatever the stored orange juice samples, the same evolutions were observed, with a decrease in aldehydes and ketones, esters, aliphatic alcohols, sesquiterpene and monoterpene alcohols, and an increase in two aliphatic and monoterpene alcohols (i.e. furfural and 4-vinylguaicol). The results suggest that the losses of aroma compounds from the juice could be attributed to the high acidity of the matrix, implying acid-catalysed reactions. Finally, PET packaging materials and their corresponding oxygen permeabilities showed no correlation with the loss of aroma compounds.

Effects of Ar-plasma treatment in alkali-decomposition of poly(ethylene terephthalate)

The ablation effects of Ar-plasma treatment and alkali-decomposition behavior in NaOH solution of polyethylene terephthalate (PET) film were investigated. The modifications were evaluated by analysis of atomic force microscopy topographical changes, and by the measurement of decomposition yield in conjunction with heats of formation and electron densities of acyl carbon calculated by Parameterization Method 3 method. It has shown that the alkali-decomposition is hampered by plasma treatment and its decomposition yield is closely related with plasma treatment conditions such as exposure time to plasma. Plasma-treated PET films exhibited lower decomposition yield, compared to that of virgin PET. Increasing plasma exposure time contributes positively to decrease the decomposition yield. It has also shown that the topography of PET surface was affected by the base-promoted hydrolysis as well as Ar-plasma treatments. These behaviors are attributed to the decreased nucleophilicity of acyl carbon damaged by the ablation of Ar-plasma.

Monocyte adhesion and adhesion molecule expression on human endothelial cells on plasma-treated PET and PTFE in vitro.

The aim of this study was to evaluate in vitro the inflammatory potential of endothelialized surfaces of polyethylene terephthalate (PET) and polytetrafluorethylene (PTFE) after ammonia gas plasma modification. HUVECs grown on polystyrene and HUVECs stimulated with tumor necrosis factor (TNF-alpha) were used as controls. At day 1 and day 7, surfaces were evaluated for U937 cells and HUVECs using flow cytometry and immunohistochemistry. Plasma-treated PET (T-PET) and treated PTFE (T-PTFE) increased U937 cell adhesion compared to the negative control but this was not statistically significant. Maximal adhesion of U937 cells to HUVEC was observed on TNF-alpha stimulated endothelium with significant differences between day 1 and day 7. There was a small increase in U937 cell adhesion to plasma-treated PET compared to PTFE on both day 1 and day 7, but this was not statistically significant. Immunohistochemical staining demonstrated two patterns of distribution for monocyte adhesion on materials. On T-PET the cells were positioned in clusters attached to HUVECs and on T-PTFE the cells were randomly distributed on HUVECs and material. The effects of plasma-treated PET and PTFE on HUVEC adhesion and proliferation were also studied. On day 1 there were slight increases in the growth of HUVECs on both of T-PET and T-PTFE but this was not statistically significant. On day 7, cell number increased significantly on all of surfaces compared to the negative control. The results demonstrate that the plasma treatment of PET and PTFE with ammonia improves the adhesion and growth of endothelial cells and these surfaces do not exhibit a direct inflammatory effect in terms of monocyte adhesion. Plasma-treated PTFE enhances HUVECs growth and was less adhesive for monocytes as compared with treated PET. The monocyte adhesion to endothelial cells on surfaces can be used as a tool for the evaluation of material surface modification and further to study the mechanisms of cell to cell interactions in response to surfaces.