Permeation Through Fluoropolimers
Permeation is the transport of small molecules through the plastic liner. Permeation is a combination of absorption, solution, diffusion & desorption mechanisms. It is a function of several variables including the properties of the permeating species (i.e., molecular size, solubility parameters, concentration), properties of the plastic (i.e., crystallinity, density, thickness, thermal history), and operating parameters (i.e., temperature-pressure gradients and cycling). Permeation data published in most literature refers to thin coatings or films and should not be applied to plastic-lined products.
All products lined with fluoropolymers, such as PTFE, PFA, FEP, ETFE and ECTFE are subject to some permeation for certain fluids. Normally PTFE lined products in conjunction with the fluids having permeation in PTFE are substituted by PVDF to avoid permeation phenomenon.