Boron Nitride Filled Thermoplastics for Passive Shielding of Space Electronics

Abstract

Space environment is rich of high energy particles that form the radiation field. Human beings as well as electronic devices are susceptible to their action, even if the exposure time is limited. For this reason, radiation shields are needed to carry out safe space missions. Traditionally, in-space shielding frames are made up of aluminum, but more recent studies have shown that a good shielding efficiency can be achieved by hydrogen (H)-rich materials, as polyethylene (PE). Moreover, it was noticed that small mass atoms as H, boron (B) and nitrogen (N) can reduce secondary emissions. In this work, radiation shields of high-density PE (HDPE) filled with boron nitride (BN) have been manufactured. Since BN particles dispersion into the polymeric matrix strongly affects the composite shielding ability, 2 filling routes have been investigated. The first manufacturing strategy is about melt-mixing: HDPE is melted at 200 °C into a batch-mixer, then BN powder is inserted, and mixing is carried out until the torque exerted by the rollers reaches a plateau. Subsequently, the shield is obtained by molding and machining. The second strategy is about the filler spray deposition; BN is spayed on HDPE plates surface after which stacking occurred and consolidation is carried out at 130 °C for 24 h. At the end, machining is performed. The shields dimensions are 25x25x10 mm3 and 50x46x35 mm3, respectively. Both of them show a good level of agglomeration and a good fillers dispersion, with a final density close to the HDPE nominal value.