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 used to determine oxygen permeability is ASTM D3985, developed by the American Society for Testing and Materials (ASTM) (ASTM D3985-17 Standard test method for oxygen gas transmission velocity through plastic film and coating using a coulometric sensor). This test method describes a procedure for determining the steady-state transmission velocity of oxygen gas through plastics in the form of films, sheets, plastic-coated papers, or fabrics. This test method determines the oxygen gas transmission velocity, the permeability of the film to oxygen gas, and, in the case of homogeneous materials, the oxygen permeability coefficient . However, this test method does not claim to be the only method for measuring oxygen gas transmission velocity. Other methods for determining oxygen gas transmission velocity also exist.
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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