PTFE Additives Can Improve the Friction and Wear Performance of Engineering Plastics

Adding a small amount of PTFE to the formulation can have a dramatic effect on the friction and wear characteristics of a thermoplastic material. This article describes how PTFE filled plastics may be good choices for applications that require low friction and long wear life.

Mechanisms of Polymer Wear

The material properties sheets that describe plastics often include the language “great wear performance.” Interestingly, “wear” may be referring to several different mechanisms of material being removed over time.

Sliding wear refers to two materials in direct rubbing contact. Rolling contact fatigue describes the action of a wheel rolling against a mating surface. Impact fatigue results from a part repeatedly hitting a mating part. Abrasive wear often involves a gritty material such as sand or sugar moving in direct contact with a surface.

Factors that Influence Sliding Wear Performance

It’s important to understand that wear is not a property that describes a single material. It is a “system” property that describes the interaction between two or more materials.

In the case of a thermoplastic rubbing against a metal counterface, a number of factors can influence the sliding friction and wear characteristics of the system including the hardness and surface finish of the metal, the base polymer, the presence of water or another type of lubrication, and additives put into the plastic to reduce friction and improve wear life.

Unfilled Thermoplastic Materials

Unfilled UHMW-PE and PTFE generally have low coefficients of friction when sliding against dry metal surfaces. However, these polymers have the limitations of relatively low strength and modulus, high rates of thermal expansion, and poor creep characteristics. Other stronger, stiffer, more dimensionally stable plastics such as unfilled nylon and unfilled PEEK have relatively high coefficients of friction and high wear rates when sliding against many metal counterface materials.

Optimizing Wear Performance with Additives

Fortunately, engineering thermoplastics such as nylon and PEEK can be formulated with additives including PTFE, graphite, carbon powder, and/or molybdenum disulfide to reduce friction and achieve an acceptable wear rate for a broad range of applications. PTFE tends to deposit a wear film against a mating metal surface, which can reduce the coefficient of friction of plastics such as nylon or PEEK rubbing against metal by half and increase their wear life by a factor of 10.

The graph below illustrates how the coefficients of friction and the specific wear rates for PTFE-filled acetal, PEEK, nylon 66, PET, and PPS are far lower than the those of the unfilled base polymers.

 

Coefficient of Friction and Specific Wear Rate for Various Unfilled
and PTFE-Filled Thermoplastics Sliding Against Hardened Steel

For additional information about the friction and wear characteristics of plastic materials, download our Plastic Materials for Friction and Wear Applications white paper or view our webinar Solving Friction and Wear Challenges with Engineering Plastics.

For questions about materials that are good for friction and wear, or our materials that contain PTFE and other additives for improved wear life call 1-800-553-0335 or contact us to learn more.