Lubricity

Lubricity of Fluoropolymers

One of the most intriguing aspects of fluoropolymers is their inherent lubricity. Lubricity refers to the ability of a material to reduce friction and provide effective lubrication. For fluoropolymers, the lubricity of the material can be reflected by the coefficient of friction.

The coefficient of friction is a dimensionless value that represents the amount of friction between two surfaces in contact. It quantifies the ratio of the force of friction between two objects to the force pressing them together. It's important to note that the coefficient of friction is dependent on various factors such as the type of fluoropolymer, the roughness of the surfaces, the applied load, and the lubrication present.

Why Are Fluoropolymers Lubricious?

Fluoropolymers owe their lubricity to their unique molecular structure, primarily composed of carbon-fluorine (C-F) bonds. These strong bonds create a non-stick surface with low surface energy, making fluoropolymers non-wetting and repelling other materials. As a consequence, when two surfaces come into contact, the low surface energy of fluoropolymers reduces the friction coefficient, leading to excellent lubrication properties.

Additionally, the strong C-F bonds contribute to the exceptional chemical and thermal stability of fluoropolymers, allowing them to maintain their lubricious nature even in extreme conditions. This outstanding stability, combined with low surface energy, makes them highly resistant to degradation or breakdown under harsh operating environments.

Coefficient of Friction of Fluoropolymers

The coefficients of friction of common fluoropolymers vary depending on the specific grade and surface conditions. However, here are some typical values for reference. These values are approximate and may vary depending on factors such as surface finish, load, temperature, and lubrication.

Fluoropolymers	Static coefficient of friction	Kinetic coefficient of friction
PTFE (Polytetrafluoroethylene)	0.12 - 0.15	0.05 - 0.10
FEP (Fluorinated Ethylene Propylene)	0.12-0.20	0.08 - 0.30
PFA (Perfluoroalkoxy)	0.15 - 0.35	0.10 - 0.30
ETFE (Ethylene Tetrafluoroethylene)	0.24-0.50	0.30 - 0.40
PVDF (polyvinylidene fluoride)	0.30 - 0.40	0.20 - 0.30

Low Friction Material Solutions

Low friction fluoropolymer materials have a wide range of applications in various industries due to their unique properties. Some common application examples include:

• Thanks to the low coefficient of friction of fluoropolymers, many practical non-lubricated and minimally lubricated mechanical systems have been developed around them.
• PTFE micro powder can be used as a lubricant to improve the lubricity of PC, PA and other polymers.
• Fluoropolymer materials like PTFE are commonly used for making bearings due to their low friction coefficient. These materials help reduce friction, enhance operational efficiency, and extend the lifespan of bearings in industrial equipment.
• Several studies have explored new materials with ultra-low coefficients of friction and adhesion by developing new fluoropolymers. A novel fluoropolymer brush has been reported to have a coefficient of friction as low as 0.005 and an adhesion as low as 6.9 nN.

Structure of fluoropolymer brushes. [1]

Reference

1. Nagendra S. Bhairamadgi, et al. Langmuir, 2014, 30, 42, 12532-12540.