Evaluation tests on Self-Healing ionomers for space applications

The ability of some materials to self-repair is a characteristic particularly important for applications in remote or hostile environments where an external intervention is nearly impossible. A typical example of such conditions is given by space environment, where the availability of self-healing (SH) materials could dramatically improve spacecraft performances and liability, with significant improvement of mission duration. Up to now, different materials have been developed, which present self-healing capability under defined conditions. In particular, polymers based on copolymericionomers show intrinsic SH capacityafter a ballistic damage, being able to autonomously repair themselves immediately after the event and can thus be considered as promising candidates in space applications. A preliminary evaluation of possible employment of polyethylene-co-methacrylic acid (EMAA) based ionomers in space environment was carried out. The material response in terms of SH efficiency was studied through hypervelocity impact tests, in order to simulate the collision with micrometeoroids and debris, which is a probable event in space environment. Different experimental configurations were considered by varying target thickness and projectile speed. When exposed to high vacuum for long time period, some materials, especially polymers, may exhibit considerable mass reduction due to diffusion and loss of volatile substances; this can significantly affect material physical and mechanical properties, thus posing a severe limit to its employment in space applications. Thermal outgassing tests were performed to investigate the ionomer behaviour in conditions similar to those encountered in space environment. Using a high vacuum chamber, specimens were exposed to thermal cycles in vacuum environment. Quite limited mass losses were detected after the tests.