Hybrid Multilayer Epoxy Composites Filled with Mixed-Phase Bismuth- and Tungsten-Containing Nanoparticles for Lead-Free 99ᵐTc Shielding in Occupational Nuclear Medicine

Lead-free polymer composites are being developed to reduce occupational radiation exposure associated with nuclear medicine procedures. This study fabricated monolithic and four-layer hybrid Bi2O3/WO3 nanoparticle-filled diglycidyl ether of bisphenol A epoxy composites for attenuating the 140.5-keV photons emitted by technetium-99m (99ᵐTc). Bi- and W-containing powders were prepared by wet-chemical precipitation and incorporated into the epoxy matrix at 25 and 50 parts per hundred parts of resin. Alternating B50/W50/B50/W50 (ML-BW50) and reverse-layer configurations were produced by sequential casting with a total specimen thickness of 2.0 cm. The nanoparticle dispersions and cured composites were evaluated using DLS, zeta-potential analysis, FE-SEM–EDX, XRD, FTIR spectroscopy, PBS contact-angle measurements, and supplementary tensile testing. Shielding performance was measured at 99ᵐTc activities of 925 MBq (25 mCi) and 6.105 GBq (165 mCi) using an anthropomorphic thorax phantom and an electronic personal dosimeter under a fixed source–shield–detector geometry. The Bi2O3 and WO3 dispersions exhibited Z-average hydrodynamic diameters of 646.41 and 413.38 nm and zeta potentials of −33.70 and −31.65 mV, respectively. FE-SEM and EDX analyses documented compositionally differentiated Bi-rich and W-rich layers in ML-BW50. XRD identified a mixed-phase Bi- and W-containing filler system, including α-Bi2O3, bismuth oxide carbonate hydroxide, WO3, and residual Na2WO4·2H2O, while FTIR spectra retained the characteristic bands of the cured epoxy network. ML-BW50 exhibited a maximum tensile stress of 4.008 MPa, a terminal strain of 74.294%, and a tensile toughness of 2.250 MJ·m−3, representing the highest tensile toughness among the investigated epoxy-based formulations. The shielding formulation significantly affected the background-corrected personal dose equivalent, Hp(10), at both activities (both p < 0.0001), and the multilayer specimens reduced Hp(10) by approximately 45–72% relative to their corresponding monolithic composites. ML-BW50 was the most effective lead-free formulation, producing Hp(10) values of 33.15 ± 2.75 and 228.42 ± 6.50 µSv and radiation-shielding efficiencies of 77.42% and 82.70% at 925 MBq and 6.105 GBq, respectively. ML-BW50 and the 0.5-mm lead reference produced statistically comparable Hp(10) values at 925 MBq, whereas ML-BW50 produced a 9.12% lower Hp(10) than lead at 6.105 GBq. For the same 10 × 10 cm projected area, ML-BW50 had a mass of 44.0 g compared with 77.0 g for lead, representing a 42.9% mass reduction, and exhibited a mean PBS contact angle of approximately 102.3°. Collectively, ML-BW50 combined effective 99ᵐTc attenuation, reduced specimen mass, differentiated multilayer organization, low PBS wettability, and favorable tensile-energy absorption, supporting its continued development as a lead-free occupational shielding material for nuclear medicine.