On the impact of pad material ingredients on particulate wear emissions from disc brakes

Besides friction and wear, airborne particle emission has become a central parameter when evaluating disc brake performance due to its potential adverse health effects as component of ambient air pollution. The pad friction material of brake system is composed of a mixture of ingredients grouped into four material categories: abrasives, reinforcing fibres, lubricants, and fillers. Some other ingredients which do not typically belong to aforementioned categories can be attributed to “fixed material”, such as aramid fibre, which is usually added into brake pad to harmonize the overall tribological properties. There is a gap of knowledge about how one ingredient from one category contributes to the emissions of particle number (PN) and mass (PM2.5, PM10). To investigate this, one ingredient from each category was chosen and produced as pins. As a reference, pins made of a commercial European brake friction material were also produced. The pins were tested using a pin-on-disc tribometer designed for airborne emission studies. Coefficient of friction, particle mass and number concentrations were measured during the tests. The results indicate that the abrasive and metal fibre have PN, PM2.5, and PM10 emission factors that are orders of magnitude higher than the lubricant and aramid fibre