Generally, polymers have medium coefficients of friction but not as high as desired for antiskid applications and everybody knows:
* The fall of polyethylene bags stacked on pallets.
* The skid on a wet zebra crossing.
* The skid of cars on snow
* The antiskid devices for cross-country skis….
All these common facts are related to the coefficient of friction between the same or different materials.
The coefficient of friction depends on:
* The nature of materials
* The state of the surfaces
* The eventual presence of a third material acting as lubricant.
Some definitions
Friction is a resistive force that prevents two objects from sliding against each other.
Theorically, for the solids that do not buckle, the friction force is proportional to the pressure of loading.
The coefficient of friction - COF - ( µ) is the ratio of the friction force (Fr) and the normal force (Fn) or loading pressure. It is always less than 1 if the polymer is not bonded on the substrate.