Matrice geopolimerica per materiale d'attrito

Brake pads are essential component of automotive braking systems, consisting of friction material supported by a rigid backing plate. The friction generated when the pad slides against the disc converts kinetic energy into thermal energy. Brake friction materials are complex composites containing a diverse category of ingredients, including metals, ceramics, and polymers. Each component serves a specific function, such as enhancing fade resistance, controlling the friction coefficient, reducing noise, and increasing strength. Among these constituents, the resin acts as a matrix that binds the powders together. Currently, phenolic resins are predominantly used, often combined with elastomers to improve vibration damping. This binder is crucial for determining the wear resistance and fade resistance of the brake pads (a phenomenon where braking performance diminishes due to overheating from extended use). Despite its widespread use due to cost-effectiveness, mechanical properties, and strong adhesion, phenolic resin has notable drawbacks. It releases volatile organic compounds (VOCs) such as formaldehyde and polycyclic aromatic hydrocarbons (PAHs) during production, which pose health risks, including carcinogenic effects. Furthermore, phenolic resins degrade at high temperatures, reaching up to 700°C during intense braking, leading to the release of hazardous gases and decreased brake performance through fading, thus compromising vehicle safety. This PhD project focused on replacing phenolic resin with an inorganic matrix, specifically geopolymer. Funded by ITT Italia S.r.l., a leading global producer of brake pads, the research aimed to substitute phenolic resin with geopolymer without altering existing production processes. Indeed, geopolymers, in contrast to phenolic resins, offer superior thermal stability, withstanding temperatures exceeding 1000°C without significant degradation. They do not emit VOCs, thus providing environmental benefits. The Cold Sintering Process (CSP) was utilized to produce geopolymer-based brake pads, enabling their manufacture without changes to current production lines, as requested by the company. The study initially confirmed the feasibility of producing geopolymer matrices using CSP, achieving an ultra-dense body (total porosity below 7%), by processing potassium-based geopolymer powder at an optimal moisture content under mild isostatic pressure (70 MPa) and moderate temperature (150°C) for a brief duration (10 minutes). The resulting products demonstrated chemical stability (high resistance to boiling tests) and strong mechanical properties (flexural strength) without requiring additional thermal treatments. Subsequent bench and vehicle tests compared geopolymer-based friction materials with traditional phenolic resin pads. In particular, the vehicle testing showed that geopolymer pads performed exceptionally well in electric vehicles, achieving perfect scores for noise and durability while significantly improving wear resistance and coefficient of friction (CoF) stability compared to traditional pads. Additionally, efforts were being made to replace phenolic resin with geopolymer in the underlayer binder, aiming to further minimize the organic content in brake pad formulations Overall, this research demonstrated significant advancements in geopolymer brake pads, highlighting their feasibility and potential for future development and commercialization. The findings pave the way for further refinement and exploration of fully geopolymer-based brake systems, emphasizing both performance improvement and environmental sustainability