Interfacial characteristics between mineral fillers and phenolic resin in friction materials

Mineral fillers are indispensable constituent part of friction materials, which are capable of improving and stabilizing coefficient of friction, decreasing wear, enhancing thermal conductivity and reducing costs of friction materials, in addition, decreasing the noise in brake application. Based on their roles in the friction materials, mineral fillers are classified into abrasives, lubricants, functional fillers, and space fillers. Herein, four typical commercial mineral fillers, namely quartz, graphite, expanded vermiculite, and barite were studied for revealing their effects on the performance of friction materials. The composition, thermal stability, structural characteristics such as surface area, pore volume, and distribution of the pore size, and thermal conductivity of these mineral fillers were researched mainly by X-ray diffraction (XRD), differential scanning calorimetry and thermogravimetry (DSC-TG), N2 adsorption-desorption isotherms, and thermal conductivity tester. Moreover, in order to illustrate the interfacial characteristics of mineral-based in friction materials, four ideal brake pads only consisting of mineral filler, BaSO4 and phenolic resin were prepared. Microstructure and combination of mineral fillers and phenolic resin were investigated by scanning electron microscopy (SEM), polarizing microscope, and Fourier transformation infrared spectroscopy (FTIR). The results showed that different types of material fillers had special functions for friction materials, and they combined with phenolic resin mainly in a physical way.