Surface cross linking and functionalization of poly(ethylene terephthalate) in a helium discharge

Abstract

Films of poly(ethylene terephthalate) (PET) have been subjected to a low frequency (70 kHz) helium discharge, with a non-symmetrical configuration of electrodes, in order to study the treatment conditions for which the 'ageing' effect is slowed down. Treatments were made for different gas flow rates (40, 70 and 100 sccm) and different exposure times (1, 10 and 30 s). Emission spectroscopy and mass spectrometry were used to characterize the discharge plasma. The resulting modifications to the polymer surface were analysed via contact angle measurements and the XPS technique. It is pointed out that treatments on an He discharge induce both a functionalization and a cross linking of the uppermost layers of the polymer film. The residual oxygen, which partially originates within the polymer, induces surface oxidation. The cross-linked content critically depends on the residence time and concentration of implicated species. It seems that a change in the surface work function takes place as a result of a surface restructuring in the earliest stages of the reactions. This could involve an increase in the rate constant for the surface de-excitation of the helium metastables in the presence of the polymer. A contribution to the understanding of the competitive processes of cross linking and functionalization, as a function of the helium flow rate, is accomplished.

Surface characterisation of plasma-modified poly(ethylene terephthalate)

“…Thus atomic oxygen and nitrogen species could be produced and the amounts of them can be enhanced by the so-called "catalytic effect" (dissociative ionisation of the molecular oxygen by collisions with meta-stable He species). All these processes could explain the incorporation of oxygen and nitrogen functionalities [51,52]. Moreover, oxygen functionalities can also be attributed to post-plasma reactions (i.e., to ageing effect): When the polymer surface is exposed to air after plasma treatment the active sites (radical species) generated on the surface will react with the oxygen present in the ambient.…”

Effects of atmospheric pressure helium/air plasma treatment on adhesion and mechanical properties of aramid fibers

“…Helium is the most ef cient inert gas for cross-linking on polymer surfaces compared with Ar which has bigger molecular size and thus may have greater degradation effect [35,36]. During the He/air plasma treatment, an intense ultraviolet radiation is emitted, which induces cross-linking reaction on the surface of the brils.…”

Surface Modification of Organic Polymer Films Treated in Atmospheric Plasmas

“…[3][4][5][6][7][8][9][10][11][12][13][14][15] In wet chemical processing, large amounts of toxic solvents are required. 13 RF vacuum plasma 9 and ion beam techniques are conducted under vacuum, leading to high cost and limiting treatments to batch processing.…”

“…Possible cross-linking positions in PET molecules by He containing plasma:5,8 ͑a͒ recombination between benzene rings and ͑b͒ combination with other chains.…”