Effect of phenolic and cardanol binders on the tribological and thermal properties of Cu-free Brake Pads

The study employed a copper free brake pad formulation containing ۲۰ ingredients, including binders, fillers, reinforcements, and friction modifiers. Five sample batches (S۱–S۵) were prepared with varying phenolic and cardanol resin ratios, molded under ۲۰ MPa at ۱۶۵ °C, followed by degassing and staged curing. Tribological behavior was evaluated using two POD devices: one under mild wear conditions and another following SAE J۶۶۱ procedures. Thermal stability was assessed via TGA–DTA, heating ۵۰ mg powders to ۸۰۰ °C at ۱۰ °C/min in air. Results from the first and second fade–recovery cycles revealed that Sample ۲, containing ۱ wt.% cardanol and ۷ wt.% phenolic resin, exhibited the most favorable performance. It maintained a stable coefficient of friction during fade and achieved near complete recovery, confirming excellent thermal mechanical balance and durability under repeated braking cycles. In contrast, Sample ۵, with the highest cardanol content (۴ wt.%), showed significant degradation, including sharp friction loss and poor recovery, attributed to thermal softening and reduced binder rigidity. Disc temperature analysis classified all specimens within acceptable “N” and “H” friction categories, though Sample ۲ demonstrated the most consistent values across normal and hot conditions. Microstructural observations indicated that higher temperatures increased wear rates, debris generation, and secondary plateau formation, partially covering primary pad material. Thermal analysis (TGA–DTA) confirmed that phenolic resin and NBR decomposition dominated weight loss, while stable fillers such as BaSO₄, CaCO₃, Al₂O₃, and ZrSiO₄ enhanced resistance to rapid degradation. Overall, limited cardanol incorporation (۱–۲ wt.%) optimizes fade & recovery behavior and high temperature stability in copper free brake pads.