Static and dynamic properties of eggshell filled natural rubber composites for potential application in automotive vibration isolation and damping

The development of high performance, sustainable material alternatives is an increasingly important goal to reduce the automotive industry's carbon footprint. We have investigated the effect of eggshells, a widely available renewable material, as partial and complete replacements of petroleum-derived carbon black in natural rubber composites for automotive anti-vibration applications. At a fixed equal total filler weight, a comparable level of reinforcement was achieved at low replacements (up to 20%) of carbon black N330 with eggshell in the reference formulation. Furthermore, pairs of composites formulated for similar hardness had similar mechanical properties, improved isolation performance with very similar damping and static stiffness (Ks), despite the difference in carbon black/eggshell ratio among them. Particularly, composites made with 20 phr (parts per hundred rubber) of eggshell and 40 phr of carbon black (C40E20) had remarkable mechanical performance, better isolation at high frequencies while maintaining similar damping at low frequency and Ks compared to carbon black alone. Addition of eggshell also improved the processing of the compound and allowed for more filler to be added to the formulation, resulting in an increase in the renewable fraction in the material and a reduction in the energy required for processing. Given the large amount of filler used in automotive rubber components, even a small fraction of carbon black replacement would represent a very large environmental gain for the industry.