Description and Performance of PFA
Perfluoroalkoxy (PFA) is a fluoropolymer resin. More specifically, PFA is a fluorocarbon. Fluorocarbons are those in which the carbon atoms of the polymer are fully bonded to only fluorine atoms or virtually only fluorine. Typical fluoropolymers, on the other hand, may have a significant portion of the fluorine atoms replaced with another halogen and/or hydrogen. This can adversely affect the resin's thermal properties, chemical resistance, and purity.
- 76.0% Fluoroine
- 23.8% Carbon
- 00.2% Oxygen
PFA Molecular Structure
Absorption and Permeation
Plastics and elastomers, in contrast to metals, absorb varying quantities of materials they contact, especially organic liquids. Absorptives in PFA are unusually low and a chemical reaction between the resin and other substances is rare. When absorption is combined with other effects, this property can influence the serviceability in a particular chemical environment. Although unusual, this emphasizes the importance of in-process testing.
Closely related to absorption is permeation. The permeability of gases, vapors or liquids through a plastic membrane is generally considered to be an activated diffusion process. The gas, vapor or liquid dissolves into the membrane and then diffuses to a position of lower concentration.
The permeation rate is determined by the size of the permeating molecule, the presence of a pressure differential, the temperature and the density of the plastic membrane.
One important determination in the design of fluid handling systems is to specify a material that exhibits a low creep rate at the intended stress. Of all the fluorocarbon materials, PFA displays the highest resistance to creep.
At room temperature with a stress of 500 psig (3447.5 kPa), the degree of creep after 10,000 hours is 1.2%. Similarly, at 212°F (100°C) the creep rate measures 4%. Even at 392°F (20°C) the creep rate is only 6.3%. This is important because a high creep rate should be avoided and may result in unpredictable and premature failures.
Safety in Handling
In more than 50 years, experience has shown that no reported cases of serious injury, prolonged illness, or death have resulted from the handling of Teflon® fluoropolymer resins. Tests further indicate that the resins may be taken in food without ill effect and that the resins are nonirritating and nonsensitizing to the skin. There have been no known instances of dermatitis, allergy or other ill effects in man caused by handling unheated fabricated forms of Teflon resins.
In the case of human exposure to heated Teflon fluoropolymer resins, no lethal effect has been observed. Instead, such exposure has merely caused a temporary flu-like condition called polymer fume fever. The symptoms do not ordinarily occur until about two or more hours after exposure and pass off within 36 to 48 hours, even in the absence of treatment. Observations indicate that these attacks have no lasting effect and that the effects are not cumulative.
When such an attack occurs, it usually follows exposure to vapors evolved from the polymer at high temperatures used in resin processing operations. Ventilation is typically provided to eliminate this potential problem and the resultant operator discomfort.
During welding of PureBond® pipe components, additional ventilation other than that found in the normal workplace is usually not required. This is due to the relatively small quantity of PFA that is heated.
To further safeguard against the potential discomforts of polymer fume fever, do not smoke tobacco while welding PureBond piping components. This will reduce the possibility of inhaling any decomposition products, although small in quantity, that may be overheated by drawing them through a lit cigarette.