Sustainable Automotive Brake Pads Using Hybrid Natural Fibers: Physical and Tribological Behavior of Wool and Flax Composites

Abstract

The transition towards eco-friendly and sustainable friction materials in the automotive sector has become a popular trend to reduce the negative environmental impact while maintaining safety and performance standards in braking systems. However, widespread adoption of such eco-friendly solutions is often hindered by challenges, including limited tribological and physical performance under demanding operational conditions. This study presents the development and comprehensive evaluation of sustainable automotive brake pads utilizing hybrid natural fibers. Specifically, it investigates a waste grade of flax (rescutched tow) in combination with wool fibers as an alternative to copper and aramid components, addressing both environmental and performance demands. Hybrid composite samples were fabricated by systematically incorporating flax waste grade with wool fibers as reinforcing agents in a phenolic resin matrix, with careful attention to fiber processing and mechanical mixing for optimum fiber-matrix adhesion. The resulting brake pads were subjected to performance evaluation tests: water absorption, engine oil absorption, friction coefficient, and wear volume. The obtained results were compared against a commercial brake pad used as a benchmark. Key findings validate the effectiveness of the concept and reveal that the hybrid natural fibers significantly influence key performance indicators. Notably, hybridization with wool fibers not only enhances the friction coefficient but also reduces water absorption by approximately 48% compared to the commercial composite. The friction coefficient of the hybrid samples (0.307) remained within the operational range (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.3-0.6$</tex>) required for automotive applications. Additionally, the specific wear rate indicates improved durability and lifespan, being nearly 14 times lower than that of the benchmark composite. These results demonstrate that hybrid flax-wool brake pads successfully combine eco-compatibility with robust functional properties, making them a futuristic solution for next-generation sustainable braking systems.