The oxygen permeability of a material is a function of diffusion, i.e. the rate at which oxygen molecules pass through the material, and the solubility, or amount of oxygen molecules absorbed per volume. Oxygen permeability is a material property that describes how easily oxygen passes through a particular material. The permeability coefficient is expressed as the product of diffusion and solubility.
The ISO 18369-4 standard, developed by the International Standards Organization (ISO), describes two different test methods used for different lens types or transmittance ranges. The polarographic method is applied to all types of materials with an oxygen permeability of 0 to 145. The coulometric method is only applied to non-hydrogel materials. However, the coulometric method also applies to soft lenses when certain conditions are met.
Another international standard referenced for the determination of oxygen permeability is the ASTM D3985 standard (ASTM D3985-17 Standard test method for oxygen gas transmission rate through plastic film and coating using a coulometric sensor) developed by the American Society for Testing and Materials (ASTM). This test method describes a test method for determining the steady-state transmission rate of oxygen gas through plastics in the form of films, sheets, plastic-coated papers or fabrics. With this test method, the oxygen gas transmission rate, the permeability of the film to oxygen gas, and the oxygen permeability coefficient in case of homogeneous materials are determined.is However, this test method does not claim to be the only method for measuring oxygen gas transmission rate. There are other methods of determining the oxygen gas transmission rate in this regard.
Briefly, the oxygen gas transmission rate is the measurement of the amount of oxygen gas passing through a substance during a certain period of time. The values obtained are used to compare the relative oxygen barrier properties of packaging films. According to the industry's general rule, a material with an oxygen transmission rate of less than 15.5 cc/m2/24 hours is considered a high oxygen barrier. Today, food packaging is developing in the packaging industry and ways to reduce exposure to oxygen and extend the shelf life of oxygen-sensitive products are being researched.
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