The interfacial adhesion of poly-p-phenylene benzobisoxazole/bismaleimide composites improved by oxygen/argon plasma treatment and surface aging effects

In this work, the interfacial adhesion of poly-p-phenylene benzobisoxazole/bismaleimide (PBO/BMI) composites improved by oxygen/argon plasma treatment and surface aging effects were investigated. The surface chemical compositions and the topography of the PBO fibers were analyzed using X-ray photoelectron spectroscopy and atomic force microscopy, respectively. The results showed that some active groups (e.g. carboxyl, hydroxyl and amide groups) were introduced onto the surface, and a noticeable alteration of the topography was also observed. After the PBO fibers were treated for 7 min, the interlaminar shear strength was increased to 61.6 MPa, an increase of 38.1%. Comparing the results with oxygen-only, argon-only and oxygen/argon plasma treatments, it can be inferred that the mechanical interlocking played a major role in the adhesion between the PBO fibers and the BMI resin. Through scanning electron microscopy, we found that the failure mode of the composite changed from adhesive failure to partial cohesive failure after the oxygen/argon plasma treatment. However, due to the surface aging effects, the interlaminar shear strength decreased sharply in the first few days and then, after 10 days, remained substantially constant.