Potential exploration of novel green resins as binders for NAO friction composites in severe operating conditions

Abstract

Friction composites used for brake-materials or clutch facings in asbestos/non-asbestos based or semi-metallics contain phenolics or its modified versions as binders although there are major issues that need to be addressed and improvised such as poor shelf life requiring special attention during the storage and transportation, and processing issues such as emission of harmful volatiles leading to environmental pollution and possibility of voids, cracks and shrinkage. It is very much desired to find a replacement for the phenolics which would not have the existing problems and which would be better performing. Hence in our earlier work a series of four thermoset resins based on oxazine ring was synthesized in the laboratory having desired features. Their potential for application in friction materials was explored by developing four NAO (non-asbestos organic) friction composites based on these resins (10% by weight) with identical parent composition. One more composite with straight phenolic resin and with identical composition was also developed for comparison's sake. In our earlier papers, the potential of these composites was tapped on Krause machine as per ECR-90 schedule. These composites showed significantly superior performance. In this paper, the evaluation was carried out on more rigorous conditions to ascertain the comparative positioning against phenolics in more severe situations and reflecting the sensitivity of μ to load and speed. The results of evaluation on brake-dynamometer as per the schedule for passenger cars (JASO C 406 Effectiveness-II) are reported. The focus of the studies was on braking effectiveness as would be reflected by the stability of μ under ascending severity. It was observed that the new composites proved remarkably better performers especially when operating conditions were most severe. Thus, the alternative resins based composites apart from eliminating the problems associated with the traditional resins, also proved to exhibit better properties from friction material point of view in severe operating conditions.