Permeation values in a diagramm
Tubes made of fluorocarbon polymers PTFE, PFA or FEP are manufactured in special production processes. They are examined to be free of pores and can therfore be classified as gastight. The fluorpolymers used are high-performance materials with a partially crystalline polymer structure. As it is usual for these partially crystalline materials, a gas flow occurs in the course of time through the amorphous phase. This gas flow is named permeation. This slow permeation of fluids through plastics is a typical property. It should not be mixed with “leakage“, which means the passage of media through plastics as a result of damages or improber connection.
Permeation at short-term use
In case of short-term use of tubes with fluids - gaseous or liquid, no permeation occurs. Only after the passage of the first fluid molecules through the tubing wall, permeation starts. After an initial period, it achieves a constant flow. This can be identified when the permeation value per interval does not change any more. It is not easy to calculate the permeation start for the individual media such as gases, acids, bases or solvents as it depends on many factors. Factors which promote permeation are higher temperatures, higher pressure or the addition of filling material. Dyed or electrostatic dischargeable plastics normally show a higher permeation rate than comparable non-filled plastics. The duration which is required for a passage of the fluid through a wall thickness 1 mm, can be defined as follows:
