Gas Barrier Properties of Plastics

For food packages, polymeric materials should exhibit an adequate carbon dioxide oxygen ratio (generally lower than 7). The process of permeation involves dissolution of the gas in one side of the membrane, diffusion of the gas through it and release of the gas from the other side of the membrane. A conventional method for determining permeability and diffusion coefficients in polymers involves the measurement of membrane weight gain versus time until the final mass equilibrium mass is reached. 

Auras and co-workers [61] studied the variations in the oxygen diffusion solubility, permeability coefficients and water sorption of polylactide films at different temperatures (5, 23, and 40 °C) and water activities (A = 0-0. 9). The results were compared with the oxygen diffusion, solubility and permeability coefficients obtained for PET films under the same experimental conditions. 

The methodology involved the monitoring of diffused gas by a photoacoustic analyser. Diffusion coefficients measured for carbon dioxide and oxygen were 2.77 X 10 cmVs and 1.68 x 10 cmVs, respectively. To support the gas diffusion results, thermal properties were studied using photoacoustic spectroscopy and 

Permeation studies of carbon dioxide and oxygen were performed using a sample holder which, has its sides sealed off one from another. The permeate gas being studied was introduced on one side and kept at a constant pressure of 0.10 MPa. On the other side the concentration of the gas was measured using photoacoustic gas analyser. The gas concentration (C), in these conditions, is given by [62]  

D Gas diffusion coefficient and 1 Sample thickness (40 pm in this case). 

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