The frictional properties of rubber and plastics are critical to the real-world performance of products such as tires, wiper blades, bicycle brake pads and shoe soles, to name a few. The study of frictional properties involves the introduction of force to a rubber or plastic material to slide it across a hard surface. The surface chosen is dependent on the test protocol and the actual service conditions under which the product would normally be used.
There are two specific types of friction which can be measured:
Static frictional properties
Static friction between the surfaces of two or more solid objects that are stationary. The irregular surfaces of the two objects interlock to prevent movement until, at a specific angle; gravity provides the impetus for movement. This point of movement is considered the coefficient of static friction.
Kinetic frictional properties
Kinetic friction occurs when two objects are moving relative to each other and rub together. The coefficient of kinetic friction is typically less than the coefficient of static friction for the same materials. The coefficient of static and kinetic friction can be used to qualify materials used in finished products for optimum performance.
- ASTM D1894— Standard Test Method for Static and Kinetic Coefficients of Friction of Plastic Film and Sheeting