Design of a friction material for brake pads based on rice husk and its derivatives

Commercial vehicle brake pads play an important role in the environmental impact caused by road transport. Their complex raw material requirements and increasingly prevalent contribution to traffic pollution is forcing the industry to look for alternative solutions. Natural lignocellulosic fibers have already been investigated as sustainable brake pad ingredients, and while braking performance results appear promising, important characteristics such as wear and particulate matter emission are either deteriorated or outright neglected. In this study, rice husk, a byproduct of the agricultural industry, is investigated as possible environmentally friendly natural ingredient. Friction material samples based on a commercial formulation were modified by adding different percentages of both rice husk and rice husk ash, the product of a thermal treatment of the former, and then tested with a modified pin-on-disc tribometer. The experimental setup included collecting instruments for emitted wear particles. 6 to 12 wt% of rice husk showed preservation of the braking performance whilst possibly improving wear and emission characteristics of the friction material. Higher amounts of modifications led to deterioration of tribological properties. Overall, this investigation suggest that limited yet substantial amounts of rice husk could successfully substitute conventional filler ingredients in brake pad formulations, as an effective approach in lowering their environmental impact.