Abstract: Composite laminates with different surface properties made of T300/Cycom 970 prepreg and four plies, which include R60, R60s, P60001 and EA9895, were fabricated by autoclave. The pretreatment condition was (80±2)RH%, (70±1) ℃ for 0, 10 d, 20 d, 40 d, respectively. The Henkel Aerospace PL7000 adhesive film was used to bond the strippable laminates for testing. The effects of hygroscopicity and strippable treatment on the bonding properties of composites were investigated by the analysis of single lap shear strength, peel strength and bond failure forms. Influence of hygroscopicity and different types of peel ply on composite bonding interface was studied by SEM and XPS. Results show that with the increase of hygroscopic time, the hygroscopic rate of polyamide peel plies is about 80%, while polyester is about 60%. As the hygroscopic increases, the mechanical properties of the composite material decrease by 40%~50%. When the hygroscopic time is 40 d, the properties of the four peel plies are very close. The controlled samples always have adhesion failure, while the failure mode of the peel ply treated samples is also adhesion failure in the early stage of moisture absorption, then gradually turns to the cohesive failure of the material. After the hygroscopic treatment, the surface of the composite materials forms more cavities and defects than the non-hygroscopic, and there are residual polymer residues on the surface. The surface nitrogen content of polyamide-based peel ply composites is about 25% higher than before, which may affect the chemical properties of the bonding surface.

Key words: composites, peel ply, hygroscopicity, bond quality, surface performance