Surface Modification of High Performance Fibers and Interfacial Properties of Their Reinforced Bismaleimide Resin Matrix Composites

Surface modification of high-performance continuous fibers was carried out by inductively coupled plasma (ICP) and dielectric barrier discharge (DBD) cold plasma, respectively. The effects of treatment time, discharge power and pressure on the chemical composition, morphology and wetting ability of the fiber surface were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and dynamic contact angle analysis (DCA). The relationship between interface structure and interfacial adhesion, and the failure mechanism of the fibers reinforced bismaleimide (BMI) composites were discussed. The results indicated that the treatment of PBO fibers by O-2, Ar and mixed O-2/Ar ICP, respectively, would result in the decomposition of the phenyl rings and oxazole moieties on the fiber surface, along with the formation of some polar groups and active groups, such as ester bonds, amide bonds and free radicals. Sputtering and etching of plasma also brought about a rough morphology for fiber surface. The modification effect by Ar ICP was better than that by O-2 ICP, and O-2/Ar ICP presented the best activation effect on the chemical compositions of PBO surface due to the synergy effect. The optimum ratio of O-2/Ar mixture was 40% -60% of O-2 content. The interlaminar shear strength (ILSS) of PBO/BMI composite treated with O-2/Ar ICP was 61.6 MPa, an increase by 38.1% compared with that of the untreated samples. The DBD plasma also improved the polarity, reactivity and the morphology of the PBO fiber surface. The effect of enhancement in ILSS values of PBO/BMI composites treated by O-2 DBD was better in comparison with that treated by air DBD. The ILSS value was increased to 57.1 MPa at 12 s when treated at 30 W/cm(3) by air DBD plasma, while that of PBO/BMI composites treated by oxy-DBD plasma under the same condition was 62 MPa. Scanning electron microscopy (SEM) micrographs demonstrated that the fracture failure mechanism of PBO/BMI composites treated by ICP or DBD plasma shifted from interface failure to matrix failure. Finally, the relationship between the aging behavior of the fiber surface and the interfacial property of the fiber reinforced BMI composites were also discussed. ILSS values of PBO/BMI composites decreased with storage time for the fibers treated by plasma.