Study On Surface Modification Of PBO Fibers With Plasma Treatment And Interfacial Adhesion Of PBO/BMI Composite

Poly-p-phenylene-2,6-benzobisoxazole (PBO) fibers, regarded as super fibers in21st century, possess high strength, high modulus, high flame resistance, excellent thermal stability and good resistance to abrasion, so they can be employed as excellent reinforcements in advanced polymer composites. Bismaleimide (BMI) resin has outstanding thermal stability, radiation resistance, electric insulativity, high flame resistance, as well as good dimensional stability and mechanical properties, which has been widely used as resin matrix in advanced polymer composites. However, the interfacial adhesion between PBO fibers and BMI resin is poor, so the interface of PBO/BMI composite need to be optimised to obatain outstanding properties. The surface modification with cold plasma treatment is an efficient and environmentally friendly method.In this study, we seperately used oxygen-only, argon-only and oxygen/argon plasmas to modify the suface of PBO fibers. Then, X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM) and dynamic contact angle analysis system (DCAA) were empolyed to analyse the type and concentration of the surface chemical elements, surface topography as well as surface contact angle and free energy, respectively. In additon, based on the test of interlaminar shear strength (ILSS), the effects of hygrothermal condition and aging effect of plasma treatment on the interfacial adhedion of PBO/BMI advanced polymer composite were also investigated.The results showed that, after plasma treatment, polar groups were introduced onto the PBO fibers surface, such as ester group, hydroxyl group, amide group and peroxide, and the effect of oxygen/argon plasma is particularly remarkable; A noticeable alteration of the topography was also observed, and the roughness was enhanced; The wettability of PBO fibers was improved. In addtion, we also found that the PBO/BMI advanced composite had lower water absorption and higher retained ILSS, indicating that PBO/BMI advanced composite possessed good humidity resistance property, and especially after oxygen-only plasma treatment, the water absorption was significantly reduced. After the PBO fibers were treated by oxygen-only plasma, the surface aging effect did not appeared with storage time, which may be related to its stable cross-linking layer. However, after argon-only and oxygen/argon plasma treatments, the suface aging effect was obvious, which seriously affected the PBO/BMI interfacial adhesion. As a result, in order not to reduce the effect of plasma treatment, it was better for the PBO fibers to be used immediately after argon-only and oxygen/argon plasma treatments or to take some promising approaches to postpone the aging process.