Bismuth Polymer Composite for Additive Manufacturing of Flexible Radiation Shielding
The usage of conventional lead-based radiation shielding is being replaced with more alternatively safer material, mostly bismuth-based compounds which have similar radiation shielding properties as lead but less effect on the environment. Additive manufacturing using material extrusion is a viable option to produce customizable medical equipment with varying geometry and different shielding properties using filler-based polymer composites. Studies show that Bi – polymer composites such as Bi – acrylonitrile butadiene styrene (ABS) and Bi – polylactic acid (PLA) have comparable radiation shielding properties as lead at high filler content and can be additively manufactured through fused deposition modeling (FDM). Medical phantoms were also printed out and shown to be able to accurately mimic tissues and bones at varying filler content. However, at high filler content, Bi – PLA composites exhibit difficulties when additively manufactured due to the composite filaments’ brittleness at high filler content. Hence, the project was carried out to determine a solution to that issue but still produce comparable radiation shielding properties with conventional shields used today. The aim of the project is to use a flexible polymer as the matrix material for the Bi-polymer composite and the material chosen was low-density polyethylene (LDPE) due to its flexibility and availability. The effect of the Bi-LDPE composite filler content was studied. Methods of producing the filaments start with the drying of LDPE pellets with the help of a chemical oven and desiccant. The pellets are then weighted and mixed with Bi powder with the help of Silicone oil to help with the proper mixing of the Bi powder and LDPE pellets. The mixing and extrusion of the Bi-LDPE composite filament are done concurrently in the same machine. The mixture of Bi powder and LDPE pellet will be fed into a hopper which will then feed into the extruder which will extrude the Bi-LDPE composite filament. Two batches of the Bi-LDPE composite filament were made, one with 30 wt% Bi – 70 wt% LDPE and the other 60 wt% Bi – 40 wt% LDPE. A Thermogravimetric Analysis (TGA) will be done to determine the content of the extruded filaments. Theoretical density, as well as radiation attenuation, will be calculated with the help of the NIST database and XCOM software. The theoretical value for radiation attenuation will be calculated from energy levels of 1 keV to 150 keV only because that is the range of photon energy that medical imaging equipment use. The composite was able to be additively manufactured but some difficulties were observed. Poor bed adhesion and self-adhesion are one of the main difficulties for additively manufacturing the composite. TGA shows that only a maximum of 40% Bi filler content could be achieved through the mixing method used in the project. Theoretical calculations show that with the increase in the Bi filler content, the attenuation coefficient of the composite increases as well, and the attenuation coefficient is comparable with pure Bi and lead at 60% filler content.