Stress relaxation and thermal management in highly filled flexible styrene butadiene styrene copolymer-tungsten composites for high-energy radiation attenuation

A high loading of high-density and high-atomic-number fillers are necessary to obtain desirable X-ray attenuation characteristics from radiation shields. However, at high filler loadings, the mechanical and viscoelastic properties of polymers are severely impaired, posing a long-term threat to the mechanical integrity and radiation protection, and the radiation shield temperature may increase after prolonged exposure to ionizing radiation, accelerating the aging of the polymer matrix. In addition, inadequate thermal conduction can make the user uncomfortable while using radiation shields for personal protection. Unfortunately, little attention has been paid to the viscoelastic, stress relaxation, and thermal conductivity-related features of these densely loaded systems, despite the significant effect of these parameters on long-term applications and user compliance. In the present work, two different styrene butadiene styrene (SBS) copolymers were used to develop SBS-tungsten (W) composites. At 500 phr W loading, significant attenuation of X-rays was achieved along with good tensile strength and elongation at break. The results indicate that the concentration of styrene in the SBS and W loading substantially affected the attenuation, mechanical and rheological properties, and tensile stress relaxation rates. The thermal conductivity increased by >100%, and after gamma irradiation, faster cooling was observed in the W-loaded composites beyond 300 phr of W loading. The 40% styrene composite demonstrated superior heat transfer at high W loadings owing to the better dispersion and distribution of the W filler in the SBS matrix. Rheological results showed that SBS-W composites with 30% styrene had a more pronounced Payne effect than those with 40% styrene. Stress relaxation and morphological analyses also revealed changes in the W dispersion in the SBS matrix depending on the styrene content.

Automated summary

A high loading of high-density and high-atomic-number fillers in radiation shields is necessary for desirable X-ray attenuation characteristics. However, this high loading severely impairs the mechanical and viscoelastic properties of polymers, poses a long-term threat to the mechanical integrity and radiation protection, and may increase the shield temperature after prolonged exposure to ionizing radiation. Inadequate thermal conduction can also make the user uncomfortable. This study developed SBS-tungsten composites and found that the concentration of styrene in the SBS and W loading significantly affected the attenuation, mechanical and rheological properties, and thermal conductivity of the composites.