Calcined Bovine-Bone-Derived Ca-P as a Densification Filler for Tungsten/PVC Lead-Free Flexible X-Ray Shielding Sheets.

With the increasing use of diagnostic X-ray examinations and interventional procedures in medical institutions, the development of lead-free flexible X-ray shielding materials to reduce occupational exposure to scattered radiation has become increasingly important. Tungsten (W) is considered one of the most promising alternatives to lead (Pb) because of its high density and excellent attenuation characteristics. However, in highly filled composites, particle agglomeration and the formation of microvoids can reduce the effective density of the material, thereby limiting its shielding performance. In this study, calcined Ca-P inorganic powder derived from waste animal bone was applied as an auxiliary filler in W/PVC composite sheets to evaluate its potential for improving shielding performance through void reduction and effective density enhancement. Waste animal bone was calcined (600-1200 °C) to produce Ca-P powder. The calcined Ca-P was melt-compounded with tungsten/PVC and processed into 0.25 mm thick flexible shielding sheets. The fabricated sheets were characterized by cross-sectional scanning electron microscopy (SEM), bulk density measurements, and radiation protection efficiency (RPE) evaluations under effective X-ray energies ranging from 23.6 to 52.4 keV. SEM observations revealed a reduction in microvoids and the formation of a more continuous internal structure in the sheets containing calcined Ca-P. At the W-85 composition, the bulk density increased from 12.448 to 15.241 g/cm3, accompanied by an RPE improvement of up to 4.5 percentage points at 23.6 keV. Correspondingly, shielding performance improved by up to approximately 4.5 percentage points at 23.6 keV and by approximately 1.0-3.4 percentage points at 46.5 keV. These findings suggest that calcined Ca-P functions not as a primary shielding material replacing tungsten, but rather as a density-correcting auxiliary filler that mitigates microvoid formation and enhances the effective density of highly filled W/PVC composites. These findings demonstrate that waste animal bone-derived Ca-P is a promising upcycled densification filler for improving the processability and X-ray shielding performance of lead-free flexible shielding sheets.