Lubricity

Lubricity is defined as slipperiness or smoothness. In the polymer industry, however, this word has a very specific meaning referring to the coefficient of friction of a material. The coefficient of friction is a unitless number describing the relationship (or ratio) between the force required to move one object over the surface of another at a certain speed divided by the weight of the object being moved. Thus, the coefficient of friction accounts for the friction between the two surfaces as well as for the weight of the overlying object.

In practical terms, the lower the coefficient of friction of a material, the easier it is to move an object over the surface of the material. Put another way, the lower the coefficient of friction of a material, the smoother or more slippery is its surface and the greater its lubricity. This quality (lubricity) is one of many unique characteristics of fluoropolymers that separates them from other polymers. When handling fluoropolymers, their smooth surface and slippery feel are readily apparent. 

Advantages of Lubricity

Because of the low coefficient of friction of fluoropolymers, there have been many practical non-lubricated and minimally-lubricated mechanical systems developed around them. Some of the advantages resulting from the lubricity of fluoropolymers are increased flow rates in fluid systems, resistance to abrasion, ease of pushability for inserting cables or wires, and an overall “slickness” of the outside of the material for applications where this type of surface smoothness is particularly important. As an example, PTFE has a coefficient of friction that is comparable to ice on ice, and PTFE is quite stable at ice temperatures and below.

For comparison, the table below shows the coefficients of friction of several of our most popular resins.

Resin Type Coefficient of Friction
PTFE 0.1
FEP 0.2
PFA 0.2
ETFE 0.4
PVDF 0.14 – 0.17
PEEK 0.35 – 0.5