A new attempt to use a bifunctional interleaf for developing a novel structure–function-integrated composite with simultaneously improved interlaminar fracture toughness and atomic oxygen resistance was studied. The toughening mechanism and the atomic oxygen erosion property of the delaminated surfaces of the composites were examined. The bifunctional interleaf was prepared by blending a phosphorus-containing polymer and a thermoplastic polymer. After being interleaved, the mode I and mode II

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... acture toughness increased by 8.2% and 23.7% compared to the control sample, respectively. The toughness gains are much smaller than that of the only thermoplastic film-toughened composite because of the relative brittleness of the blend film. The atomic oxygen erosion rates of the mode I and mode II delamination surfaces decreased by 45.3% and 31.3% compared with the control, respectively. The carbon fibers on the irradiation surfaces are protected by a layer of phosphine oxide to prevent further erosion, and they were much less eroded, particularly for the mode I surface. In comparison, the erosion rates of the mode I and mode II surfaces of the toughened-only composite significantly increased by 83.6% and 107.2%, respectively, and the carbon fibers are seriously eroded.