Permeability and Plastics

Permeability is the quality or property of a substance or material that allows another substance to pass through it. The substance that passes through a material can be referred to as the penetrating substance. Permeability can also be described as the flux of the penetrating substance through the matrix formed by the molecular structure of the material it is passing through. In polymer plastics, the main penetrating substances of interest are typically liquids, such as water or other chemicals; and gases, such as air, oxygen, methane, and so forth.

Permeation – the process of the liquid or gas penetrating another material – is driven primarily by diffusion based upon the concentration and pressure gradient of the liquid or gas, the permeable material’s intrinsic permeability, and the permeating liquid’s or gas’ ability to diffuse or spread out in another medium. Permeation is also affected by chemical reactions that occur between the penetrating substance and the material it is passing through. Chemical reactions notwithstanding, with respect to a material’s permeability, the greater the concentration of a gas or liquid and the greater its pressure, the greater its ability to penetrate a material.

Permeability is an important consideration for plastics because plastics are frequently used as containers, tubing, or other packaging to keep the contained items and liquids free from contaminants. Permeability is also a concern with respect to sterility for biomedical plastics applications and high-tech analytical equipment.

Because the morphology of the polymer matrix changes during processing, permeation is best tested on the final product. We recommend that you are thoroughly familiar with the potential chemical exposures that your polymer products may be subjected to.

For more information about your specific application or additional permeability questions, please contact us or call a Zeus technical representative toll-free in the US at 1-800-526-3842. Internationally, please call +1-803-268-9500. The Zeus team is here to help you find the product that is right for you.