PETpla.net Insider 09 / 2018

INSPECTION 37 PET planet Insider Vol. 19 No. 09/18 www.petpla.net Fig. 3 Schematic presentation of non- invasive and non-destructive measure- ment of oxygen ingress into PET bottles Fig. 4 Equipment needed for oxygen ingress measurements Equipment (see Figure 4): 1) trace oxygen meter 2) light guide with the fixed metal fibre holder 3) oxygen-tight cap or any other tight closure 4) safety screw for fixing the oxygen tight cap 5) trace oxygen sensor spot 6) PET bottle The PSt6 (5) trace oxygen sensor spot is placed onto the transparent closure (3). Three seals ensure the clo- sure’s gas tightness. A safety screw (4) is used to fix the closure (3). The read- ing is achieved by screwing the poly- mer optic fibre integrated in a metal holder on the outside of the package directly above the trace oxygen sensor. The sensor spot can, alternatively, be glued into the PET bottle, which then can be sealed with a standard closure and read out with a polymer optical fibre without a metal holder. Coated bottles should be trans- parent but measurement is possible through slightly coloured (e.g. green- ish or yellowish) or turbid bottles. Dark brown PET bottles are not suited for direct sensor coatings; a transparent optical window or closure would be required. Filling procedure and measurement conditions Measurements with the final product (beer, fruit juice) in the bottle normally give the best ‘real life’ simulation but beer reacts with oxygen in a similar way to a scavenger. Carbonated water is used as an alterna- tive for beer. A dosing pump fills the PET bot- tles in a nitrogen- flushed glove box (Fig. 6) containing < 0.1% oxygen with nitrogen-saturated carbonated water (dissolved oxygen <10 ppb). A pressure tablet (3 g/l) contain- ing sodium carbon- ate, sodium hydro- gen carbonate and citric acid is used for carbonisation. Silver nitrate is added to prevent bacterial growth. Dissolved oxygen content after filling was <50 ppb. Fig. 5 Single-channel and multi-channel measurement set-up Filled bottles were placed on a shaker located in a climate oven. Measurements were taken in a con- trolled environment at 30 °C and 50% relative humidity. They were condi- tioned for one hour first and shaken during the process, to assure equilib- rium in headspace and liquid. Up to 10 bottles were measured simultane- ously.