engleski

Determination of plasma radicals during oxidation of PET foil by optical emission spectroscopy

Optical emission spectroscopy (OES) was applied for real-time measuring of the reaction products during plasma treatment of a polyethyleneteraftalate (PET) foil. Plasma was created in pure oxygen by inductively coupled radiofrequency (RF) discharge. The discharge chamber was a glass tube with the length of 50 cm and the inner diameter of 3.6 cm. It was pumped with a two stage rotary pump with the ultimate pressure of about 0.1Pa and the pumping speed of 4.4 dm3s-1. Oxygen was leaked continuously into the discharge tube so the pressure during experiments was 75Pa. Plasma parameters were measured in the discharge tube prior to experiments with the PET foil with a double Langmuir probe and a catalytic probe. The electron temperature was about 6eV, plasma density about 1x1016m-3 and the neutral atom density about 1x1022m-3. Polymer foil with the thickness of 0.023 mm was cut to rectangular samples with the dimension of 2x4 cm2. Optical emission spectra were measured in the range from 200 to 950 nm with the Ocean Optics spectrometer. For the first 10s of plasma treatment the OES showed the presence of oxygen radicals only, the predominant lines were at 777 and 844 nm, corresponding to neutral oxygen atom transition 3p6P – 3s6S0 and 3p3P – 3s3S0, respectively. As the plasma treatment was continued, the OES spectra became richer with significant emission from CO (both Angstrom and 3rd positive band) and OH (A-X band). The appearance of these bands was attributed to extensive PET oxidation. The lines corresponding to relaxation of hydrogen atoms (Balmer series) appeared, too. Simultaneously, the O peaks decreased significantly. While the intensity of the O atom line at 777 decreased to about a tenth of its original value, the line at 844 virtually disappeared at all. After prolonged plasma treatment, the O peaks recovered, the CO band vanished while the OH and H peaks still persisted. In the final period of the treatment, only atomic oxygen lines remained. The appearance of the oxygen-containing functional groups on the sample surface was measured simultaneously during the plasma treatment by XPS. The concentration of these functional groups was the highest after about 10s of plasma treatment, i.e. just when the CO and OH became measurable. The results showed that OES analysis was a powerful method for studying the evolution of PET oxidation by plasma treatment.

oxygen plasma; polymer; functionalization; PET; optical emission spectroscopy

nije evidentirano