Metal-based (lignin/silica) hybrids as green activators for conductive EPDM composites

Conductive rubber composites are usually formulated from natural or synthetic rubber and a variety of petroleum-based additives. Environmental and sustainability concerns have increased interest and resulted in the search for bio-based alternatives to these additives. Rice straw is an abundant agricultural waste whose burning contributes to environmental pollution. It can be transformed into valuable resources for green composites in a sustainable manner. This research presents a sustainable approach to upcycle this biomass by developing metal–organic hybrid materials, Fe(lignin/silica/fatty acid) Fe(LSF) and Ni(lignin/silica/fatty acid) Ni(LSF) hybrid materials from rice straw black liquor for use as green activators in ethylene propylene diene monomer (EPDM) rubber composites. These hybrids were thoroughly characterized, the X-ray fluorescence spectroscopy (XRF) and X-ray diffraction (XRD) investigations confirmed the crystallinity of the Fe(LSF) hybrid and the amorphous nature of the Ni(LSF) hybrid, as well as determining the elemental composition. In addition, the morphology at the nanoscale and uniform distribution of the elements in both hybrids were confirmed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and EDX mapping analysis. The hybrids were then added to EPDM formulations to replace the traditional activator system of stearic acid and zinc oxide (ZnO). The performance of the composites was then evaluated, revealing that the green activator systems impart interesting properties. The vulcanizates achieved tensile strengths up to 5.57 MPa, showed improved resistance to thermo-oxidative aging, and demonstrated enhanced electrical conductivity. These results underscore the potential of these rice-straw-derived hybrids as sustainable, high-performance components for electrically functional EPDM applications.