Mechanical and aging properties of waste silica-kerf reinforced EPDM rubber for automotive application

Silica-kerf (Si-kerf), a waste byproduct of silicon wafer slicing, was evaluated as an alternative filler to carbon black and commercial silica in peroxide-cured ethylene–propylene–diene monomer (EPDM) rubber. All formulations were prepared with a constant total filler loading of 100 parts per hundred rubber (phr) to enable formulation-level comparison under identical processing and curing conditions. Si-kerf consists of irregular silicon-based particles with a crystalline silicon core, a thin amorphous silicon dioxide surface layer, and residual polyethylene glycol species originating from the wafer-slicing process. The material was used after simple drying without further purification, chemical functionalization, or surface modification. Partial replacement of carbon black with 10–20 phr Si-kerf maintained a favorable balance of mechanical, thermal, and aging performance. The formulation containing 90 phr carbon black and 10 phr Si-kerf showed the strongest mechanical stability among the Si-kerf-containing systems. Increasing the Si-kerf content from 10 to 20 phr doubled the amount of waste-derived filler incorporated, while tensile strength decreased by only 1.9% and elongation at tear increased by 31.6% relative to the 10 phr formulation. Compared with the 100 phr carbon black reference, the 20 phr Si-kerf formulation showed a 26.9% decrease in tensile strength, a 19.7% increase in elongation at tear, and a 2.3% increase in crosslink density. After oven aging, tensile strength changed by −3.94% and −19.12% for the 10 and 20 phr Si-kerf formulations, respectively, while coolant aging resulted in changes of +4.90% and +2.87%; both formulations remained within the relevant SAE J20 performance limits. Higher Si-kerf contents showed greater sensitivity to formulation and dispersion conditions. These results demonstrate that moderate Si-kerf substitution can increase waste-derived filler utilization while preserving an application-relevant performance balance in EPDM compounds.