PETpla.net Insider 11 / 2016

INSPECTION 27 PET planet Insider Vol. 17 No. 11/16 www.petpla.net remains active even after 180 days. Reducing the scavenger content in the inner PET layer to 0.5% leads to an increased oxygen ingress over 180 days compared to the bottle with 1% oxygen scavenger. But still the total oxygen after 180 days is below 1ppm. This shows that there is the possibility of reducing the amount of scavenger used in this type of PET bottles. Interior coating in PET bottles Inorganic coatings can be applied to the inside of the bottle after blow- ing. The Sidel Actis coating technol- ogy produces a thin layer of amor- phous carbon, typically with 100 to 200nm layer thickness, on the inside surface of the bottle. This is deposited from high-energy plasma of acetylene gas within a high vacuum environ- ment. Oxygen ingress curves of an Actis coated bottle compared to an identical non-coated bottle are shown in fig. 5. For both bottle types the sampling rate was adjusted to 30 sec- onds and the mean value was taken from seven bottles. The inner coating prevents oxygen desorption from the bottle wall into the product for the first few days of storage, which cannot be observed in externally coated bottles. A BIF of 9.9 was calculated by comparing the slopes of oxygen ingress of coated and non-coated bottles. Determining OTR in empty PET bottles The oxygen transmission rate of PET bottles filled with nitrogen can also be determined with the chemical optical oxygen ingress measurement system. Two types of 0.5l PET beverage bottles from Sidel with interior coat- ings Actis Lite and Actis A were tested. Measurements were performed for 27 days at 23 ± 1°C and 50 ± 2% rela- tive humidity. A special stainless steel closure with integrated trace oxygen sensor type PSt6 and a PCO28 threading was used to seal the bot- tles. The OTR of this special closure was determined, and amounted to 0.0023cc / (pack * day). With the PreSens system an OTR of 0.0070 for Actis L and 0.0031 for Actis A was determined deducting the OTR of the bottle closure from the obtained GOTR value, while with the Oxtran method values of 0.0068 for Actis L and 0.0027 for Actis A were measured. The standard deviation for Sidel L was 0.0004 with both meas- urement systems while for Sidel A the optical system showed 0.0004 and Oxtran 0.0008. The mean values obtained with the optical measure- ment are very close to those obtained with the reference Oxtran method. OTR measurement device The Permeation Measurement Device consists of a measurement cell, which is divided into two cham- bers and made of stainless steel. The cell has improved leak tightness. Test materials are fixed between the upper and lower chamber of the measure- ment cell (fig. 1). Each chamber has two gas con- nectors and first both chambers are flushed with nitrogen to determine the leakage of the chamber. The lower chamber is then flushed with oxygen. A chemical optical sensor spot is fixed in an optical window in the upper chamber and connected to a Fibox 3 LCD trace oxygen meter to conduct the oxygen measurements. A well characterised 100μm PET film whose permeation rate is well known was used for reference meas- urements. During zero measurement the oxygen partial pressure increased by 0 to 0.01hPa after five days. This corresponds with a zero value for the permeation of 0 to 0.03cm 3 / (m 2 d bar). The increase of oxygen partial pressure over time showed a quasi linear scope up to 40hPa. Adapting the ideal gas law the permeation is then calculated. Conclusion With the oxygen ingress meas- urement system by PreSens it was shown - under conditions very close to reality - that the amount of oxygen that will enter the product inside PET bottles depends on the location of the coating and whether an oxygen scav- enger is used or not. A shelf-life of 180 days was not achieved with exter- nally coated bottles due to oxygen desorption of the matrix material. The best performance is shown by those bottles which use an active barrier additional to the passive barrier which is also acting as protection layer to prevent the reaction of the scavenger with atmospheric oxygen. The system allows measurement in packages filled with gas but also liquids, and investigation of complete packages - empty as well as filled – is possible. Moreover sequential measurements can be conducted which means that the equipment is not blocked for the complete measurement time. The oxygen transmission rate for all food packaging materials can be meas- ured with the PSt6 sensor type, with a measuring range between 10 -2 to 10 7 cm 3 (STP) / (m 2 d bar). With the new low oxygen sensor PSt9 an expected range between 10 -3 and 100cm 3 (STP) / (m 2 d bar) can be achieved. www.presens.de All external sources on which this article is based on as well as the long version of the article can be requested at PreSens Precision Sensing GmbH (www.presens.de).