Novel cardanol-based polybenzoxazine (PBZ) resins from a sustainable source to substitute phenolic resins in brake pads for eco-friendliness and superior performance

Abstract

The growing demand for sustainable materials with superior performance across diverse applications—such as adhesives, coatings, flame retardants, shape memory polymers, and friction materials (FMs) such as brake pads, shoes, and clutch facings—has elicited significant attention in the transition from petro-based phenolic resins (PPRs) to bio-based alternatives. Despite their ubiquity as matrix materials in friction composites, PPRs are encumbered by three fundamental limitations: storage (limited shelf life and harmful emissions of ammonia and formaldehyde during storage and processing), problems of shrinkage and cracking in final products, and reduced performance when used at high temperatures. These challenges are further exacerbated by the inherent reliance on non-renewable petroleum-based feedstocks. In this work, biowaste cashew nutshell liquid from the cashew industry was used for the first time to synthesize in-house bio-based benzoxazines (BZs). This approach not only advances the circular economy but also mitigates the limitations associated with conventional PPRs in FMs. Four types of brake pads were investigated: three with innovative formulations using 15 vol% variations of BZs, based on distinct functional groups in amine, and one benchmark PPR-based formulation with identical ingredients. Remarkably, the bio-based trisapm BZ formulation exhibited superior tribological (0.36 $\left(\mu \right),\sim$94% higher brake fade resistance, and $\sim$36% less wear) and noise-vibration performance (4 dB(A) reduction), demonstrating that changes in monomer design directly influenced the performance, effectively overcoming major bottlenecks associated with PPRs. Beyond processing and performance benefits, these BZs reduced raw material costs and the carbon footprint, offering a scalable, high-performance alternative for conventional resins in FMs.