In-situ measurement of oxygen concentration under high pressure and the application to oxygen permeation through polymer films

Abstract

Up until now, gas permeation through polymers under high pressure has not been able to be measured continuously. The combination of a special high pressure cell and a commercially available fluorescence-based oxygen measurement system allows in-situ monitoring of oxygen permeation through a polymer sample under pressure in an aqueous environment. The principle of the oxygen sensor is based on dynamic fluorescence quenching and measurement of the fluorescence decay time. It was observed that the decay time increases non-linearly with the applied pressure, and hence, the displayed oxygen concentration has to be corrected. This deviation between the measured and the real concentration depends not only on the pressure but also on the absolute oxygen concentration in the water. To obtain a calibration curve, tests were performed in the pressure range between 1 and 2000 bars and initial oxygen concentrations in the range between 40 and 280 μmol/l. The polynomial calibration curve was of the fourth order, describing the raw data with a coefficient of determination R(2) > 0.99. The effective oxygen permeation through polymeric samples can be calculated with this function. A pressure hysteresis test was undertaken but no hysteresis was found. No temperature dependence of the oxygen sensor signal was observed in the range between 20 °C and 30 °C. This study presents for the first time data showing the oxygen permeation rates through a polyethylene film in the pressure range between 1 and 2000 bars at 23 °C.

Permeation of a Range of Species through Polymer Layers under Varying Conditions of Temperature and Pressure: In Situ Measurement Methods

“…These methods also rely on pressure measurement to monitor the gas transport. In the food packaging industry, the transport of oxygen and water can reduce the shelf life of the food product and there is a need to have test methods available to study the barrier properties of thin films [27,28,29,30,31]. Manometric permeation tests were carried out at various intervals up to a period of 200 days by Huang and Paul [32] and Rowe et al [33].…”