Influence Of Atmospheric Pressure Plasma Treatment On Surface Properties Of PBO Fiber

Poly (p-phenylene benzobisoxazole) (PBO) fiber is a kind of high-performance fiber obtained by liquid crystal spinning through PBO polymer. PBO fiber is called "the super fiber in the 21^st century" for its excellent properties such as higher special strength and modulus, heat resistant and flame retardant than other high-performance fibers. It can be used to produce high-performance composite materials in aeronautics, astronautics, and national defense and other high-tech fields. However, the relatively smooth and chemically inactive surface, induce the poor adhesion property between PBO and resin matrix, and enormously affect the fiber mechanic performances to fully display in composites, thus seriously restrict applications of PBO fiber in high-performance composite material fields. Therefore, the improvements of PBO fiber surface properties and adhesion properties between PBO and resin matrix are the keys for it to be applied in the domain of high performance composite materials.At present, there are many ways for modifying PBO fiber surface, such as chemistry modification, radiation modification and plasma modification, etc. Plasma modification is a perfect method among them with the advantage that the modification only affects the outer most layers of a substrate without damaging the bulk properties of materials, and also the advantages of high efficiency, environment friendly, and simple operation, etc. The traditional plasma modification was carried out under low pressure environment and had high cost due to the needs of complex vacuum system. Therefore, it was difficult to realize online processing, which restricted the applications of the technology.Atmospheric pressure plasma can be working under open environment, without vacuum system needed, thus the modification cost is lower than that of the low pressure plasma, and further it can be applied to online processing. In this work, atmospheric pressure plasma jet (APPJ) and atmospheric pressure dielectric barrier discharge (DBD) were used to modify PBO fibers, respectively. This study investigated how operational parameters in the two kinds of plasma treatments, such as oxygen, moisture regain, plasma processing duration and treated power, influence the surface properties of PBO fibers. Surface morphology and wettability, chemical composition, functional groups, interfacial shear strengths (IFSS) to epoxy, and single fiber tensile strength for PBO fibers in all sample groups were characterized by scanning electron microscope (SEM), water static contact angle measurements, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, Micro-bond pull out tests, and electronic universal tester, respectively.SEM showed that the fiber surface was etched after the two plasma treatments, and the surface was roughened especially after DBD treatments. Contact angle measurements showed that the contact angle decreased greatly, which indicated that surface wettability of PBO fibers was improved obviously after the two plasma treatments, and the fibers could be infiltrated by resin easily. XPS analysis showed that the oxygen content on fiber surface increased after APPJ treatment, and C=O,O-C=O groups were introduced on fiber surface. That was conducive to the improvements of surface wettability and interfacial adhesive properties. FTIR revealed that PBO fiber surface was oxidized after DBD treatment and introduced oxygen polar groups. Micro-bond pull out test showed that the IFSS increased 130.96% and 117.33% after two plasma treatments repectively, for all sample groups. It also showed that plasma processing duration could improve IFSS significantly, and IFSS in all sample groups exhibited a peak value after some treated time. In addition, the atmosphere during APPJ processing also influenced the IFSS obviously. The treatments of pure helium mixed with 1% oxygen can improve IFSS greatly. However, moisture regains (MR) for PBO fibers and treated power cannot significantly improve IFSS though they had positive role on it. Single fiber tensile tests indicated that the dropping rate of single fiber tensile strength was less than 10% for all groups except the group for DBD treated 75s, thus the strength loss would not affect the overall performance of composite materials.