Plastic material outgassing

For metals, ceramics and glasses, this formula is applicable for times up to 100 h or more. With polymers (e.g. PTFE, Nylon, etc.), a single set of parameters for Equation (4.9) may be insufficient to fit the observed behaviour over a given time interval and the further use of Equation (4.9) with other parameters may be necessary. Values of a cover a range from 0.2 to 1.2 but a = 1 or 0.5 are frequently found. The former value is shown for metals, glasses and ceramics and indicates desorption predominantly from the surface of the material. The value of 0.5 is associated with plastics and elastomers and indicates diffusion-controlled outgassing from the bulk. 

Outdiffusion is when the mobile species that reaches the surface does not volatilize but remains on the surface as a contaminant. Plasticizers from molded polymers constitute an example of a material that outdiffuses from the bulk of the material. Often there is both outgassing and outdiffusion at the same time. The outgassing and outdiffusion properties of a material often depend on the fabrication and history of the material. 

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