Chemical composition of brake lining materials and emitted particles
Modern brake lining materials are composites of many different ingredients, which are responsible for differing wear characteristics, physical, and chemical properties of both the bulk lining material and the emitted particles produced during the braking process (Eriksson et al., 1999; Eriksson and Jacobson, 2000; Chan and Stachowiak, 2004). Numerous organic substances are utilised in brake lining manufacture, in particular as binders and reinforcing fibres in organic linings (see summary in Table 2). However, there is limited information on the presence of specific organic compounds because brake linings have to be highly resistant to thermal and mechanical stress, as well as refractory to attack by solvents in case of brake fluid leakages. Consequently, only a small proportion of the organic content of brake linings and emitted brake dust is extractable (Rogge et al., 1993). This has somewhat hindered the search for suitable organic tracer compounds in brake dust emissions, and attention appears to have been directed more towards the identification of metals.