Radiation Shielding Properties of Common 3D Printed Polymers and Photopolymers
Tyler Brunstein-Ellenbogen, B.S. ME
N.M. Ravindra, Department of Physics
New Jersey Institute of Technology, Newark, NJ, USA
March 18-24, 2023
San Diego, CA
Abstract
3D printing, or Additive Manufacturing, has become a viable manufacturing solution to create complex geometries for components used for radiation shielding. With 3D printing, lightweight and tough to machine components can be made from polymers such as HDPE, ABS and Nylon. Currently, there are only a handful of materials on the marketplace that offer radiation shielding by using polymer matrix composites. Materials like Bismuth, Tungsten, Graphite and Boron Carbide have been used to increase the gamma ray shielding and neutron attenuation of pure polymers.
The purpose of this experiment is to compare the radiation shielding properties of 3D printing materials such as PLA, ABS, PETG, PC and various Nylon Blends. By measuring radiation permeating through 3D printed blocks, we can determine the minimum required thickness to reduce our radiation dose to 0.5 uSv/h using a 5 gram Torbernite sample. From the data observed in this experiment, the addition of Boron Carbide or Graphite powder to the glass filled resin will yield unique radiation shielding properties.
Nuclear Radiation & Polymers
Many forms of nanoplates, nanoparticles, fibers, tubes, and whiskers can be added to polymer matrix to synthesize polymer composites which can be used as radiation shielding materials in radiation facilities, nuclear power plants, and also nuclear cleaning of environment
Source: Polymeric composite materials for radiation shielding: a review, C.V. More et. al., Environmental Chemistry Letters (2021) 19:2057–2090
Nuclear Radiation & Polymer Composites
Polymer composite matrices provide unique radiation shielding properties to common 3D printing materials. Bismuth nanoparticles have been added to Polylactic Acid, or PLA filament. Using a bulk Bismuth Oxide polymer composite, researchers were able to increase the attenuation capability of the pure polymer by up to 50% at an energy of 244.7 keV.
Source: Elsafi, M., El-Nahal, M.A., Sayyed, M.I. et al. Novel 3-D printed radiation shielding materials embedded with bulk and nanoparticles of bismuth. Sci Rep 12, 12467 (2022). https://doi.org/10.1038/s41598-022-16317-w
Boron Carbide and Boric Acid solutions can be mixed into liquid photopolymer resin or coated onto 3D printing polymers to provide unique thermal neutron shielding properties. A composite material with 30 wt% B4C and Polyamide Acid 800 microns in thickness has a neutron permeability of 0.24.
Source:Xiaomin Li, Juying Wu, Changyu Tang, Zhoukun He, Ping Yuan, Yong Sun, Woon-ming Lau, Kai Zhang, Jun Mei, Yuhong Huang. High temperature resistant polyimide/boron carbide composites for neutron radiation shielding, 2019,I SSN 1359-8368, https://doi.org/10.1016/j.compositesb.2018.10.003.
Experimental Method
Radiation shielding properties of the various materials were tested by printing blocks in 10mm, 20mm, 30mm, 40mm, and 50mm thicknesses. The blocks were all printed with 100% infill in order to observe the maximum shielding properties.
The materials tested were PLA, ABS, PETG, Polycarbonate, Nylon 6 Glass Filled, Nylon 12, Multi Jet Fusion Nylon 12, Formlabs Rigid 10k Glass Filled resin, Polypropylene, and Thermoplastic Urethane.
The radioactive source used is a 5 gram sample of Torbernite, a hydrated copper uranate phosphate mineral. The mineral sample measured a dose of 45 ± 5 uSv/h. The mineral is mainly a Beta emitter with a composition of 50 wt% U-238, [Cu(UO2)2(PO4)2·8–12H2O].
Experimental Method cont.
To test the blocks, a container unit was used to hold both the radioactive material and the testing blocks. A geiger counter was placed behind the block to record the CPM (Counts Per Minute) of radioactive activity.
Each block was tested for 5 minutes to account for the natural fluctuation of radioactivity of our Torbernite sample. The radioactive sample is pushed into place when the block is inserted into the testing unit.
Experimental Method cont.
Material | Polymer name | Density | Wt (g) as printed | Machine |
Ziro PLA | Polylactic Acid | 1.24 g/cc | 22.97 | Creality FFF |
Matterhackers PETG | Polyethylene Terephthalate Glycol | 1.23 g/cc | 22.84 | Creality FFF |
Matterhackers ABS | Acrylonitrile Butadiene Styrene | 1.04 g/cc | 18.23 | Creality FFF |
Matterhacker PP | Polypropylene | 0.9 g/cc | 14.113 | Creality FFF |
Polymaker PC | Polycarbonate | 1.19 g/cc | 17.77 | Voron FFF |
Experimental Method cont.
Material | Polymer name | Density (polymer) | Wt (g) | Machine Used |
BASF Nylon 12 | Polyamide-12 | 1.01 g/cc | 19.24 | HP MJF 5200 |
Formlabs Nylon 12 | Polyamide-12 | 1.01 g/cc | 18.16 | Formlabs Fuse 1 SLS |
Polymaker Nylon 6 GF | Polyamide-6 30% Glass Fill | 1.4 g/c | 17.04 | Voron V0.1 FFF |
Rigid 10K | Glass Filled photopolymer | 1.73 g/cc | 32.09 | Formlabs Form 2 SLA |
Ziro TPU | Thermoplastic Polyurethane | 1.12 g/cc | 17.43 | Creality FFF |
Results cont.
Results cont.
Results cont.
Results cont.
From our data, we can observe that the glass filled resin, namely the Formlabs Rigid 10K, performed significantly better than the other polymers. The SLA, SLS and MJF printer technologies provide a denser part that can more efficiently shield radiation from our source. This is in part due to their processes that bind the previous layer to the current layer. This means that the parts are isentropic and uniformly dense, whereas the FFF parts may have small air gaps in between layers and between infill lines. The inherent weakness is that radiation can escape through these microscopic holes, which would lower the shielding properties of the material.
To remedy this, parts printed with the FFF technology could have been heat treated to further bind the individual layers together. This secondary heating would allow the gaps in between printed lines on the infill layers to more efficiently bind together, providing a more dense part.
Even though the Nylon’s printed on SLS and MJF were significantly lower densities than the Rigid 10K (1.01 g/cc vs. 1.73 g/cc), they performed significantly better than their FFF polymer counterparts.
Discussion
This experiment has showed clear evidence that certain 3D printing polymers block Beta radiation more efficiently than others. For this experiment, we used a Mineral as a radioactive source and not a pure isotope point source. Due to this, we observed slight fluctuations in the observed dose as a function of time. To combat this, the measurements we recorded we done over a 5 minute test period with at least 360 data points. Samples were cross checked on different days of the experiment to ensure that the mineral sample maintained constant radioactivity.
The instrument used to test the radiation shielding properties was a GMC-300E+ geiger counter. Extended exposure to the radioactive source must be studied in the next experiment by taking FTIR and EDX analysis of the materials.
Polypropylene offered low radiation shielding properties, but has unique neutron capture characteristics due to its 15% Hydrogen composition.
Discussion cont.
The test samples were printed with 100% infill to provide the highest resistance between our radioactive source and our testing meter. We chose to use a grid pattern infill as this would overlap each layer with a 90° offset ensuring that there are no gaps between the layers from the front to the back of the test sample.
For the samples printed using MJF, SLS, and SLA technologies, they were printed using similar infill and layer settings. The difference of these materials is that they provide isentropic properties since the layers are completely fused to the previous layer, as opposed to being laid on top of the previous layer for the FFF technologies. In theory, this will provide a more dense test samples than the materials printed on FFF.
Due to the high temperature nature of the Nylon and Polycarbonate filaments, we needed to use multiple printers for our experiment. A desktop Creality Ender 3 was used for our PLA, ABS, PETG and TPU samples. Various machines were used to create the remaining blocks, namely a Voron V0.1 FFF printer, HP 5200 MJF printer, Formlabs Fuse 1 SLS printer, and Formlabs Form 2 SLA printer. To ensure dimensional accuracy, all of the samples blocks were printed oversized and then sanded down to their 44mm x 44mm dimensions. An allowable ± 0.1mm tolerance was observed.
Conclusions
In conclusion, we can observe that the materials with the higher densities have better radiation shielding properties. Of our test samples, the Rigid 10k glass filled resin and the PA6 Glass filled resin both exceeded the standard range of the lighter weight filaments. The lighter polymers have other characteristics that make them viable candidates for applications, but not for the explicit use of blocking alpha and beta radiation. Polypropylene can be mixed with Boron Carbide to increase it’s neutron capture due to the polymers high Hydrogen composition.
Originally, this experiment stemmed from a need to shield the Torbernite mineral without using a lead pig. Since the mineral is a low activity alpha and beta emitter, the use of polymers would be sufficient for storage. From our data collected, a container for shielding use can be made out of the cheapest material, Nylon 12 SLS, for only about $13 compared to a $50 lead pig of equivalent size.
References