Permeability isostatic method

Three general test procedures used to measure the permeability of plastic films are the absolute pressure method, the isostatic method, and the quasi-isostatic method. The absolute pressure method (ASTM D 1434, Gas Transmission Rate of Plastic Film and Sheeting) is used when no gas other than the permeant in question is present. Between the two chambers a pressure differential provides the driving force for permeation. Here the change in pressure on the volume of the low-pressure chamber measures the permeation rate. 

Two basic methods are used for determination of permeability, isostatic and quasi-isostatic. In both methods, experiments are run at constant temperature. Isostatic methods use continuous flow on both sides of the film to provide constant permeant concentration (Fig. 14.9). This system is employed in the Mocon Oxtran... 

Three general test procedures used to measure the permeability of plastics films are the absolute pressure method, the isostatic method, and the quasi-isostatic method. 

With the isostatic method, the pressure in each chamber is held constant by keeping both chambers at atmospheric pressure. In the case of gas permeability measurement, there must again be a difference in permeant partial pressure or a concentration gradient between the two cell chambers. The gas that has permeated through the film into the lower-concentration chamber is then conveyed to a gas-specific sensor or detector by a ... 

Three related methods based on the quasi-isostatic method are used to measure permeability. The most commonly used technique allows the permeant gas or vapor to flow continuously through one chamber of the permeability cell. The gas or vapor permeates through the sample and is accumulated in the lower-concentration chamber. At predetermined time intervals, aliquots are withdrawn from the lower cell chamber for analysis. The total quantity of accumulated permeant is then determined and plotted as a function of time. The slope of the linear portion of the transmission-rate profile is related to the sample s permeability. 

Literature and knowledge on mass transfer of aroma compounds are few and no standard procedure is recommended. Methods developed for aroma compounds permeability measurements are commonly approached by isostatic or quasiisostatic methods and depend on the physical state (vapor or liquid) of the aroma compounds (Piringer and Baner 2000). 

Methods for determining permeability are of two types, continuous flow and lag-time or quasi-isostatic. A brief suuunary of the methods follows. For more details, the reader is referred to the book by Hernandez and Gavara. ... 

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