NBR-modified Resin in Fade and Recovery Module in Non-asbestos Organic (NAO) Friction Materials

Phenol formaldehyde resin is one of the most important ingredients in friction materials that binds the other multiple ingredients firmly. The type and amount of resin in the friction material is very critical for structural integrity of the composites. The present work evaluates the influence of modification of straight phenolic resin by Nitrile Butadiene rubber (NBR) on fade and recovery behavior of friction composites developed in the laboratory. It also addresses the issue related to the variation in the amount of resin on the performance properties. The variation in amount of resin (10, 12.5, and 15 wt.%) was achieved by compensating with inert filler viz. BaSO₄ (30, 27.5, and 25 wt.%) in the parent composition. Rest of the ingredients (60 wt.%) were in identical amount in all the composites. Fade and recovery studies on these composites were done according to Economic Commission for Europe (ECE) R-90 regulation. The friction coefficient (μ) (all types viz.—performance, fade and recovery), extent of fade and recovery, increase in counter-face temperature, wear and mechanical properties were significantly influenced by the modification and variation in amount of resin. It was observed that with increase in amount of resin, all types of μ decreased and extent of fade increased. Mechanical properties and wear resistance, in general, improved with increase in percentage and modification of resin. In general, it was concluded that NBR modification in straight phenolic resin resulted in improvement in some of the performance properties such as performance μ, recovery μ, and % recovery. Other properties such as fade μ and fade resistance, however, were adversely affected. No clear trends emerged in wear performance.