Comparison of pilot and industrial scale atmospheric pressure glow discharge systems including a novel electro-acoustic technique for process monitoring

A comparison of a pilot and industrial scale atmospheric pressure polymer processing plasma system has been carried out using process-monitoring diagnostic tools during treatment of amorphous polyethylene terephthalate. These systems have been compared using optical emission spectroscopy (OES), photodiode (PD) analysis and multi-variate analysis of the applied electrical and emitted electro-acoustic signals to facilitate scale up operations from the pilot to the industrial scale system. The voltage, current, electro-acoustic intensity and frequency of the plasma systems were found to change systematically with an increase in applied plasma power and addition of oxygen (O-2) into a helium (He) plasma. The plasma drive frequency was pulled by the plasma reactance from approximately 26 to 16 kHz on the pilot system and from approximately 36 to 32 kHz on the industrial system, for an increase in applied plasma power and addition of O-2. The OES analysis revealed a number of peaks associated with nitrogen (N-2) species between 250 and 450 nm due to the presence of air within the He plasma. Temporally resolved analysis of the discharge emission carried out using a PD showed an increase in the number of discharge events per power cycle with an increase in power and a decrease in emission intensity for addition of O-2 into the He plasma for both the pilot and industrial scale systems. Using these diagnostic tools both plasma stability and run to run variations were assessed. A visual analysis of the 1.2 m wide plasma was also carried out where a more homogeneous plasma was observed at higher powers.