| Summary: | Polyimide film (Kapton) is an important polymer material used for the construction of spacecrafts. The performance of Kapton can be degraded for atomic oxygen erosion in space. Commonly used atomic oxygen protective layers have issues such as poor toughness and poor adhesion with the film. In this paper, Kapton/Al<sub>2</sub>O<sub>3</sub> nanocomposite films were prepared via an ion exchange method, and the optical properties, mechanical properties, and mechanisms for the change in the mass and microstructure, before and after atomic oxygen exposure, were analyzed. The results show that the deposition of the Kapton/Al<sub>2</sub>O<sub>3</sub> surface nanocomposite film prepared via the ion exchange method has no obvious effects on the internal structure and optical transmittance of the Kapton film matrix. The tensile strength and elongation of the prepared film were much higher than those of the pure Kapton film, demonstrating its good flexibility. Scanning electron microscope (SEM) analysis showed that the etching pits had a carpet-like morphology on the composite film surface and were relatively small after atomic oxygen erosion. In contrast with the C−C bond rupture in the oxydianiline (ODA) benzene in Kapton films, the Kapton/Al<sub>2</sub>O<sub>3</sub> nanocomposite film mainly destroyed the C=C bond in the pyromellitic dianhydride (PMDA) benzene ring. On exposure to an atomic oxygen environment for a short period, the Kapton/Al<sub>2</sub>O<sub>3</sub> nanocomposite film exhibited improved atomic oxygen erosion resistance because the Al<sub>2</sub>O<sub>3</sub> layer inhibited atomic oxygen diffusion. With increasing atomic oxygen exposure time, the atomic oxygen diffused into the Kapton matrix via the pores of the Al<sub>2</sub>O<sub>3</sub> layer, causing damage to the substrate. This resulted in a detachment of the surface Al<sub>2</sub>O<sub>3</sub> layer and exposure of the Kapton matrix, and thereby the atomic oxygen resistance was decreased. The applicability of the ion exchange mechanism of trivalent Al element on the surface modification of the polyimide is explored in this study. The behavior of the Kapton/Al<sub>2</sub>O<sub>3</sub> composite film under the atomic oxygen environment of space is investigated, which provides the basis for studying the effects of atomic oxygen on the flexible protective Kapton film.
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