Self-healing polymers for space: A study on autonomous repair performance and response to space radiation

One of the main challenges of space exploration is to properly protect astronauts from the hazards of the space environment. Space suits were hence created to protect crewmembers during extravehicular activities, but they are currently unable to properly withstand damage after, for example, impacts with micrometeoroids and orbital debris (MMOD), and they would depressurize and collapse if punctured, with catastrophic consequences. In this context, the possibility of integrating self-healing materials into spacesuits has drawn the attention of the scientific community, as it would lead to autonomous damage restoration and subsequently increased safety and operational life. Nevertheless, the effects of space environment on these materials are still to be determined and could lead to a significant decrease of their overall performance. The here presented study focuses on a first example of application to a space suit, analyzing the healing performance of a set of candidate self-healing polymers before and after exposure to simulated space radiation. A comparison of bilayers and nanocomposites having these polymers as matrices is also made in the non-irradiated case. This research also aims at filling the gap between standard characterization of self-healing materials (e.g.: scratch, impact, and puncture tests) and assessment of the effects of space radiation on them by combining these two aspects. Understanding if and how radiation can affect damage recovery performance is in fact fundamental to determine whether a given self-healing material can actually be used for space applications. The self-healing response is assessed through in-situ flow rate measurements after puncture damage. Maximum and minimum flow rate, the time between them and the air volume lost within the 3 min following puncture are collected as healing performance parameters. For the neat materials, the same tests are then repeated on gamma-ray irradiated samples to study the variation in self-repairing performance after exposure to simulated space radiation. Results show that the healing performance is higher in systems with lower viscous response and that it decreases after irradiation. A further analysis of the effects of space environment on the presented materials is hence required. The NASA HZETRN2015 (High Z and Energy TRaNsport, 2015 version) software is also used to simulate the action of galactic cosmic rays on the space suit during extravehicular activity. The classic suit multilayer is compared with configurations in which the standard bladder is replaced with a layer of each analyzed material to identify the most promising candidates and determine whether the addition of nanofillers significantly increases the shielding ability.