2.7. Gas Barrier Properties Evaluation

In order to evaluate gas transmission rates through polymeric films, permeability tests were performed by using a manometric method (Permeance Testing Device, type GDP-C (Brugger Feinmechanik GmbH, München, Germany)), in accordance with ASTM 1434-82, DIN 53 536, ISO/DIS 15 105-1 and the gas permeability testing manual of the instrument. Each circular film (film area of 78.5 cm²) was placed in between two chambers. First, the system was put under high vacuum, and then the upper chamber was filled with the selected gas (CO₂ or O₂ food grade, 0% RH) at 23 °C and atmospheric pressure, with a gas stream of 100 cm³/min. Any variation in gas pressure was recorded, as a function of time, by a pressure sensor located in the lower chamber. Gas transmission rate (GTR [cm³ cm m⁻² d⁻¹ atm⁻¹]), i.e., the value of film permeability, was determined taking into account the pressure increase as a function of time and of the whole volume of the device. The GTR values were normalised for the film thickness, the latter measured as the average value among five different measurements.