Exploring the Potential of Geological Siliceous Earth as a Natural Alternative to Silica in Rubber Composites

ABSTRACT Siliceous earth (SE) is a naturally abundant mineral rich in silica and kaolinite and is often applied in paints and absorbents. Rubber products are typically heavily loaded with petroleum‐based fillers, such as silica and carbon black, and the renewable SE remains technically important and yet to be explored in rubber processing. This study systematically investigates the mechanochemical modification of Neuburg SE (NSE) via wet ball milling, optimizing parameters including ball‐to‐powder (B/P) ratio and process control agent (PCA) volume in order to tailor the particle size, morphology, and surface chemistry. The higher B/P ratios (e.g., 100:1) significantly reduce NSE particle size and induce kaolinite amorphization, leading to reduced Payen effect and increased tensile strength of the rubber composites by 151%. Adjusting the PCA volume preserved the kaolinite in NSE and improved the tensile strength to approximately 169% compared to raw NSE filled composite. Surface modification using silane through ball milling provides an additional 5% increase in tensile strength. In contrast, co‐milling with NaOH, urea, or lignin resulted in particle agglomeration and reduced performance. The effects of modified NSE on the linear and nonlinear dynamic mechanical properties are discussed. These findings underscore NSE's potential as a sustainable, high‐performance filler for tire tread rubber compouding and address the environmental drawbacks of conventional fillers.