SURFACE CROSS-LINKING AND FUNCTIONALIZATION OF POLY(ETHYLENE-TEREPHTHALATE) IN A HELIUM DISCHARGE

Films of poly(ethylene terephthalate) (PET) have been subjected to a l ow frequency (70 kHz) helium discharge, with a non-symmetrical configu ration of electrodes, in order to study the treatment conditions for w hich the 'ageing' effect is slowed down. Treatments were made for diff erent gas flow rates (40, 70 and 100 seem) and different exposure time s (1, 10 and 30 s). Emission spectroscopy and mass spectrometry were u sed to characterize the discharge plasma. The resulting modifications to the polymer surface were analysed via contact angle measurements an d the XPS technique. It is pointed out that treatments on an He discha rge induce both a functionalization and a cross linking of the uppermo st layers of the polymer film. The residual oxygen, which partially or iginates within the polymer, induces surface oxidation. The cross-link ed content critically depends on the residence time and concentration of implicated species. It seems that a change in the surface work func tion takes place as a result of a surface restructuring in the earlies t stages of the reactions. This could involve an increase in the rate constant for the surface de-excitation of the helium metastables in th e presence of the polymer. A contribution to the understanding of the competitive processes of cross linking and functionalization, as a fun ction of the helium flow rate, is accomplished.