Development and Evaluation of New Binders for Friction Materials as Alternative to Traditional Phenolics

Phenolics or their modified versions are invariably used as binder materials for friction composites which consist of multiple ingredients. However, phenolics are known for their inherent serious problems such as; poor shelf life, which poses constraints for storage and transportation; evolution of harmful volatiles leading to voids, cracks and environmental pollution etc. In order to overcome these, three new thermoset able resins having oxazine ring were synthesized in the laboratory. These resins proved to be free from the above mentioned drawbacks. These were tribo-evaluated to explore the possibility of replacing currently used phenolics in friction materials.

In order to evaluate their tribo-potential as friction materials, friction formulations (non-asbestos organic NAO) based on these resins were developed in the laboratory in the form of brake-pads and tensile specimens. One additional composite based on traditional straight phenolic resin with identical composition was also developed to enable the comparison with the above-mentioned composites. These were characterized for physical, thermal and mechanical properties. The brake pads were then tribo-evaluated for their fade and recovery performance as per ECE R-90 regulation on Krauss machine. For the sake of comparison, brake pads from a reputed Indian Company were also tested in identical conditions. It was observed that composites with new resins proved better in almost all the aspects as compared to both the composites (phenolic based and commercial). The extent of edge over the others varied from resin to resin. Apart from getting rid of the above-mentioned basic problems with traditional phenolic resins, new resins proved to be better choice as binders for friction composites since the composites excelled almost in all the performance properties such as; higher and steadier coefficient of friction with very little fluctuations; lower tendency to fade; better counter face friendliness in terms of less scoring and low rise in temperature; very low wear etc. Scanning electron microscopy (SEM) was used to observe worn surfaces of discs and pads to understand the wear mechanisms. Key words- NAO friction composites; phenolic resins, fade & recovery studies, Novel thermosets as binders