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Title: Standard test method for film permeability determination using static permeability cells

item Yates, Scott
item Schneider, Sharon
item QIAN, Y - Environmental Protection Agency (EPA)

Submitted to: American Society for Testing Materials Standards
Publication Type: Other
Publication Acceptance Date: 2/1/2014
Publication Date: 4/1/2014
Citation: Yates, S.R., Papiernik, S.K., Qian, Y. 2014. Standard test method for film permeability determination using static permeability cells. American Society for Testing Materials Standards. DOI:10.1520/E2945.

Interpretive Summary: This standard test method covers the measurement of the transmission of a gas through plastic membranes, sheeting, films and fabric materials using a static sealed diffusion chamber. The test method monitors gas diffusion across a film membrane and provides measurements of (a) gas concentrations on each side of the film membrane and (b) estimates of the mass transfer coefficient (MTC) for the tested gas and film material. The MTC represents the film permeability and is independent of the concentration gradient used during testing, which simplifies some aspects of the experimental design. Inter-laboratory testing showed that the MTC estimated by this method is relatively insensitive to the laboratory procedures. The inter-laboratory testing involved measuring the MTC for several soil fumigant compounds and a wide range of film permeability. Analysts with prior experience handling and analyzing gaseous fumigant compounds had lower coefficient of variation (10-20%) compared to less experienced analysts (20-50%) based on triplicate tests. The coefficient of variation between laboratories was higher for less permeable film materials than for films with high MTC. This was attributed to the additional length of the experiments and potential for increased leakage from the apparatus and was most pronounced for less experienced analysts. This standardized method will be valuable to scientists, consultants, governmental agency and others who have interest in conducting film permeability tests.

Technical Abstract: A new test method has been developed that uses a static sealed apparatus consisting of two chambers separated by the test-film membrane. The test chemical in the vapor phase is added to the chamber on one side of the film and the apparatus is incubated at constant temperature during which the chemical diffuses through the test membrane. The method requires determination of the relative chemical concentrations on both sides of the membrane at several time points during the incubation. Concentrations are monitored until equilibrium is reached, or some other practical stoppage time. Linear regression of data may be used to calculate the MTC. Alternatively, an analytical solution to a mathematical model may be used to calculate MTC, for which a nonlinear least-square algorithm is available to fit concentrations derived from the mathematical model to the observed concentrations. To facilitate calculation of MTC, a Windows-based software program and Excel addin have been developed. These programs use a non-linear least squares algorithm described by Marquardt to obtain the MTC, other parameters and parameter statistics. The program also includes graphical, statistical and reporting information.