PETpla.net Insider 09 / 2018

INSPECTION 38 PET planet Insider Vol. 19 No. 09/18 www.petpla.net Fig. 6 Glove box filled with nitrogen Bottles tested Several treated PET bottles (Table 2) were investigated for oxygen ingress rates: monolayer bottles with external coating (bottle type 1); mono- layer with an additional active barrier (bottle type 2); internal surface coated bottles (bottle type 3); and three-layer bottles examples (bottle type 4). Bottle type Coating Weight Volume Scav- enger 1a No 38 500 No 1b LC2 a 38 500 No 2a No 38 500 2% 2b LC2 38 500 0% 2c LC2 38 500 1% 2d LC2 38 500 0.5% 3a No 31 500 No 3b Actis 31 500 No 4a three layers 28 500 No 4b three layers 28 500 Yes Table 2 Bottle types investigated Calculation of total oxygen and determination of the Barrier Improve- ment Factor (BIF): If two comparable bottles are tested but with different oxygen barrier layers, the BIF (barrier improvement factor) can be calculated by dividing the oxygen transmission rate (OTR) of the uncoated bottle by the OTR of the coated bottle. Results Bottle type 1: LC2 external coated PET bottles compared to an identi- cal non-coated PET bottle Fig. 7 Composition of the external LC2 coating Figure 8 shows oxygen ingress into the LC2 coated and reference non-coated PET bottle, over a period of more than 25 days. In the first 48 h the increase of oxygen concentra- tion in non-coated bottles and bottles with LC2 external coating is high and non-linear. The reasons for this are the migration of matrix oxygen dis- solved in the PET bottle wall into the liquid; and the “steady-state” permea- tion stage, where oxygen molecules move through the PET bottle wall to the interior. Externally-coated PET bottles display similar oxygen ingress rates as non-coated reference bottles at the beginning of the measurement, up to the point when a new equilibrium is established. The LC2 barrier coating reduces the rate of subsequent per- meation, illustrated by a significantly decreased slope. Fig. 8 Oxygen ingress into an externally LC2 coated PET bottle compared to non-coated reference bottle Total dissolved oxygen can be calculated from the slope of the curve; permeation in mg O 2 /l/day = ppm/day (or μg O 2 /l/day = ppb/day). Maximum oxygen concentration allowed in beer is 1mg/l (1,000ppb). Theoretical shelf-life can be calculated by dividing maximum allowed concen- tration by the slope of oxygen increase. Results are shown in Table 3. LC2- coated non- coated Total bottle volume [ml] 518.00 518.00 Liquid [ml] 495.30 496.40 Headspace [ml] 22.70 21.60 Headspace [%] 4.58 4.35 Temperature [°C] 30.00 30.00 Z-value 2.64 2.55 Slope for dissolved O 2 a [ppb/day] 7.13 38.33 Slope total O 2 [ppb/ day] 18.80 97.90 Calculated shelf-life (days) 53.19 10.21 Table 3 Shelf-life increase of LC2-coated bottles A shelf-life of approximately 53 days is not sufficient. Bottle type 2: PET bottles with LC2 external coating and/or differ- ent contents of oxygen scavenger Matrix oxygen dissolved in PET can be removed by adding an oxygen scavenger into the PET material. Fig. 9 Oxygen ingress into treated PET bottles; (A) non-coated PET bottle with 2% scavenger, (B) LC2 coated PET bottle with no scavenger, (C) LC2 coated PET bottle with 1% scavenger, (D) LC2 coated PET bottle with 0.5% scavenger. The addition of 2% amosorb scav- enger to the PET bottle (A) removes matrix oxygen. However, after eight days there is a significant increase of oxygen, which can be attributed to