The effect of surface roughness on friction properties of silica-filled epoxidised natural rubber

Friction properties of rubber compounds are important for tyre tread applications as tyre is the only contact between the road and the car. Although epoxidised natural rubber (ENR) is widely reported to have a good grip property, there is limited information on its friction properties. In this study, the effect of substrate surface roughness on dry friction properties of tread rubbers based on silica-filled ENR 25 (ENR 25/silica), ENR 50 (ENR 50/silica) and NR (NR/silica) were assessed. Tensile strength, tear strength, hardness, dynamic properties and abrasion resistance were also examined. The friction properties upon sliding on a non-textured aluminium oxide plate and aluminium oxide abrasives with grit sizes of P320, P180, P120 and P60 were determined using the TE 75 Production Rubber Friction Tester at 5N, 10N, 15N and 20N of normal load. Meanwhile, surface roughness analysis on the sample surfaces was conducted using a 3D laser interferometer microscope. From this study, NR /silica tread had better physical strength, while ENR 50/silica had higher hardness and tensile modulus. On dynamic mechanical properties, the ENR 50/silica possessed the highest tangent delta value and all tangent delta values increased with a change of frequency from 1 to 10 Hz. With regard to friction properties, the coefficient of friction of all tread rubbers decreased with the increase in substrate roughness. The change in tread rubber surface roughness varied depending on the coefficient of friction, physical strength and substrate roughness. Throughout this study, the effect of surface roughness on dry friction properties of silica-filled ENR tread rubbers and its factors were successfully identified.