Valorization of silicone waste powder as industrial-waste-derived fillers in Bi2O3/EPDM nanocomposites for potential use in diagnostic X-ray protection

Abstract

This study valorized silicone waste powder (SWP) reclaimed from discarded silicone molds as a silica-rich secondary filler in ethylene–propylene–diene monomer (EPDM) composites containing nano-sized bismuth oxide (nano-Bi₂O₃) for lead-free diagnostic X-ray shielding applications. To enhance filler–matrix compatibility, SWP was surface-treated with silane coupling agent (Bis-[3-(triethoxysilyl)propyl]tetrasulfide; TESPT), and the optimum treatment condition was determined through mechanical-property evaluation. Subsequently, nano-Bi₂O₃/SWP/EPDM composites containing 0 – 500 parts per hundred rubbers by weight (phr) nano-Bi₂O₃ were fabricated and systematically characterized for their morphology, density, thermal stability, mechanical properties, and X-ray attenuation abilities at tube voltages of 60, 100, and 150 kVp. The results revealed that TESPT treatment improved interfacial adhesion between SWP and EPDM, with 1 g TESPT per 100 g SWP providing the highest tensile strength. Incorporation of nano-Bi₂O₃ was found to substantially enhance the X-ray shielding properties of the composites, as evidenced by progressive increases in attenuation capability with increasing filler content. Particularly, a nano-Bi₂O₃ content of 425 phr was sufficient to achieve the commonly required shielding level of 0.35 mmPb for diagnostic X-ray protection. In addition to improved shielding properties, increasing nano-Bi₂O₃ content also enhanced thermal stability, tensile modulus, tensile strength, and hardness, while reducing solvent swelling. Based on the overall findings, the nano-Bi₂O₃/SWP/EPDM composites demonstrated a practical approach for converting SWP into value-added products while providing flexible and lead-free radiation-shielding materials suitable for diagnostic X-ray applications, including wearable protective devices, protective garments, and other radiation-shielding components for medical imaging facilities.