Lignin-Assisted Dispersion and Iohexol Retention in Lead-Free Bi2O3/Iohexol-Loaded Waterborne Polyurethane Sheets for Diagnostic X-Ray Attenuation

Conventional lead-based protective materials used in diagnostic radiology involve some notable limitations in terms of high weight, toxicity, and environmental concerns associated with their disposal. Lead-free polymer shielding materials incorporating high-atomic-number fillers and iodine-containing components have therefore attracted increasing attention. However, high filler loading can induce particle agglomeration, localized iodine-rich regions, interfacial defects, and nonuniform X-ray attenuation. Accordingly, improving filler dispersion and structural stability is essential to maintain effective shielding performance. In this study, the effects of lignin-assisted interfacial stabilization on filler dispersion, iodine retention, structural properties, and X-ray shielding performance in highly filled polyurethane (PU) composites were investigated. At 80 kVp, a 3 wt% lignin sheet exhibited a radiation protection efficiency of 77.4%, a linear attenuation coefficient of 48.52 cm−1, a half-value layer (HVL) of 0.143 mm, and a mean free path (MFP) of 0.206 mm. These results indicate that lignin functions as a bio-derived interfacial stabilizer rather than a primary X-ray attenuator, improving filler utilization through enhanced dispersion, packing structure, and iodine immobilization. The proposed lignin-assisted PU/Bi2O3/iodine composite therefore shows potential as an environmentally conscious auxiliary shielding material for diagnostic X-rays and low-dose scattered radiation.