Harnessing molluscan shell waste for sustainable tribology by integrating biogenic fillers in eco-friendly brake pad development.

Amid growing environmental concerns over conventional brake pad materials, the need for sustainable and efficient alternatives has never been more pressing. This study investigates the innovative use of waste molluscan shells, naturally abundant in calcium carbonate, as eco-friendly substitutes for synthetic fillers in friction composites. Four shell species (Perna perna, Meretrix casta, gastropod, and Rocellaria dubia) were selected for evaluation, integrated into composite formulations alongside permanganate-treated kenaf fiber as reinforcement. Cashew friction dust and graphene oxide served as friction modifiers to optimize tribological performance. The elemental composition and structural characteristics of the shells were examined using Fourier-transform infrared spectroscopy, X-ray fluorescence, and X-ray diffraction, while thermogravimetric analysis assessed thermal stability. Five composite formulations, including a control sample with commercial calcium carbonate, were fabricated and tested for physical, mechanical, and tribological properties using a pin-on-disc apparatus in accordance with ASTM G99 standards. The top three formulations were further developed into brake pads and subjected to CHASE testing per SAE J661a protocols, including fade and recovery tests to evaluate frictional behavior, wear resistance, and thermal performance. Scanning electron microscopy was employed to analyze worn surface morphologies. The results demonstrate that molluscan shell-based composites offer a compelling green alternative to traditional friction materials, delivering superior performance in terms of friction stability, thermal resilience, and wear resistance. In particular, the P. perna shell powder additive composites emerged as a standout candidate, presenting an ideal synergy of tribological excellence and environmental responsibility. This research highlights the potential of waste-derived bio-fillers in advancing sustainable tribological systems and paves the way for next-generation eco-conscious brake pad technologies.