Demanding Problems, Exacting Solutions: PFPE Lubricants & Greases (part III)

In earlier parts I presented the features of PFPE fluids and identified some of the general applications. Features: non-flammable, outstanding chemical resistance / inertness, wide-temperature capabilities, exceptionally low volatility, and excellent environmental / health and safety. Benefit: PFPE offers SAFETY coupled with LONG SERVICE LIFE!!! I also briefly introduced polymers of hexafluoropropane oxide (HFPO). 

In this Part, we will begin to explore some of the basic chemistry types of PFPE found commercially. Perfluoroalkylpolyether fluids are composed entirely of carbon, fluorine and oxygen. They are colorless, odorless and as noted previously completely inert to almost all chemical agents including oxygen. Here are four of the major PFPE types commercially available:

PFPE-K: are prepared by the anionic polymerization of hexafluoropropylene epoxide at low temperatures followed by fluorine end-capping. The polymerization is carried out to a desired molecular weight range; the resultant polymer is branched. Fractionization by vacuum distillation yields different viscosity grades suitable for lubricant usage.

PFPE-Y: are prepared by the photo-chemical catalyzed polymerization of HFPO in the presence of oxygen at low temperatures. It is then treated either thermally or by UV light or both. Finally end groups are treated at high temperatures with fluorine. PFPE-Y is a branched polymer.

PFPE-Z: is produced from tetrafluoroethylene as the starting material. It is processed in a manner similar to PFPE-Y. The resultant polymer is linear.

PFPE-D; is obtained via catalysis or ring-opening polymerization of 2,2,3,3-tetrafluorooxetane. The resultant polymer is then treated with UV-catalyzed direct fluoridation. The resultant polymer is linear.

Two other grades, namely PFPE-M and PFPE-W have recently emerged in the market with properties found between the PFPE-Y and PFPE-Z.

The following table summarizes typical properties; fluids in the viscosity range of 33 to 50 cSt at 100 degrees C. (Range selected on the basis of "Commercially Available Fluids and Properties").

As the reader will observe from a technical viewpoint, fluid selection is a trade-off between low temperature and high temperature requirements; and the needed viscosity in the operating range.