No abstract

An atmospheric pressure plasma system has been used to treat amorphous polyethylene terephthalate (APET) to enhance its healseal properties to a polyethylene terephthalate (PET) film. The plasma treated APET sheet material was thermoformed into trays for use in the food packaging industry and heatsealed to a PET film. The heatsealing properties of the resulting package were assessed using the burst test technique. It was found that the plasma treatment significantly enhanced the adhesive properties and an increase in burst pressure from 18 to 35 kPa was observed for plasma treated food trays. The APET surface chemistry was assessed after plasma treatment where it was found that the plasma treatment had affected an increase in oxygen and an addition of nitrogen species to the polymer surface. The surface roughness (R a ) of the plasma treated samples was also observed to increase from 0.4 to 0.9 nm after plasma treatment. IntroductionHeatsealed polymer trays are widely used for packaging food products, particularly meat and fish [1]. In the heat sealing process a polymer top film is applied to the polymer tray under elevated temperature and pressure in order to enclose the food product in an airtight environment [2]. The conventional method for creating a strong bond between a food tray and a top film is to use a co-extruded heatseal layer ( Figure 1).

Polycaprolactone (PCL) is a biodegradable and bioresorbable polymer with applications ranging from use in packaging to medical sutures. In this study, the use of an atmospheric pressure plasma to deposit plasma polymerised PCL (P‐PCL) coatings from a PCL diol precursor is evaluated. Fourier transform infrared spectroscopy demonstrated the retention of PCL functional groups in the deposited coating. Changes in coating surface energy were monitored with time after deposition using the contact angle technique. The rate of degradation of 500 nm thick P‐PCL coatings was assessed after immersion in a phosphate‐buffered saline (PBS) solution at 37 °C. It was observed that slower rates of P‐PCL coating degradation were obtained for coatings deposited at higher applied powers and lower precursor flow rates.

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.