Introduction Of Interphase Of PBO Fiber/epoxy Composites And Investigation Of Its Atomic Oxygen Resistance

In recent years, PBO fibers have been widely used as reinforcements of advanced composite materials because of the excellent mechanical properties, thermal properties and chemical stability. However, due to the surface smoothness and chemical inertness, PBO fibers have poor compatibility with resin matrix, leading to low interfacial adhesion between them, which seriously affected the whole performance of composites. When spacecraft flies in low earth orbit(LEO), PBO fiber/epoxy composites used as structural materials are highly vulnerable to atomic oxygen(AO) erosion. When the protective layer of composites surface fails, AO will interact with the epoxy resin underneath and further generate a lot of defects. AO can penetrate into the interfacial region of the composites through these defects, which leads to the debonding between fiber reinforcements and resin matrix, and further degrades the mechanical properties of composites. In this paper, to simultaneously enhance the interfacial properties and AO erosion resistance, nickel phosphorus alloy, Zinc oxide nanowires(Zn O NWs) and silicon-graphene oxide were introduced into PBO fiber/epoxy composites as interphases by using a electroless plating method, low temperature hydrothermal method and chemical grafting method, respectively.The surface of PBO fibers was modified by electroless plating method, and then nickel phosphorus alloy was introduced into composites as interphase. The relationship among process parameters, surface morphology and interfacial properties was systematically studied by changing the plating temperature and time. Nickel-plated PBO fiber surface consisted of nickel and phosphorus, and nickel coating was typically amorphous. Rigid nickel particles on the coating can significantly increase the surface roughness and the contact area between fiber and resin matrix, and generate reacting force to external load. Thus, the interfacial properties of composites were enhanced. When the plating temperature was 80℃ and plating time was 20 min, the interfacial shear strength of composites increased by 38.6%. Meanwhile, the hygrothermal aging resistant properties of the nickel-plated PBO fiber composites were greatly improved. With the increase of heat treatment temperature, the interfacial shear strength of the nickel-plated PBO fiber composites decreased.Carboxyl functionalization technique and low-temperature hydrothermal method were combined to modify the surface of PBO fiber, and then Zn O NWs were introduced into composites as interphase. After the functionalization process, the relative content of carboxyl groups on the fiber surface greatly increased, which ensured the high adhesive durability between fiber and Zn O NWs. Strong mechanical interlocking and good wettability were the main contributors for the enhanced interfacial properties of composites. Compared with the untreated PBO fiber, the tensile strength of PBO fiber after growth of Zn O NWs(PBO-Zn O NWs) had no discernable decrease. The surface morphology of Zn O NWs were controlled by changing the seed-to-growth solution concentration ratio([S]/[G]) and growth time, and the relationship among process parameters, surface morphology and interfacial properties was systematically studied. When [S]/[G] was 2 and growth time was 4h, the interfacial shear strength of composites increased by 50.7%. Meanwhile, the hygrothermal aging resistant properties of the PBO-Zn O NWs composites were slightly improved.Hydroxyl functionalization technique and chemical grafting method were combined to modify the surface of PBO fiber, and then silicon-graphene oxide was introduced into composites as binary interphase. The variation of functional groups on the surface of PBO fiber confirmed that 3-aminopropyltrimethoxysilane silane(APTMS) and graphene oxide(GO) were introduced onto the fiber surface successfully via chemical bonding, and a binary grafted multi-scale reinforcement(PBO-APTMS-GO) has been prepared. The tensile strength of PBO fiber was not affected by the chemical grafting process. Compared with the untreated PBO fiber composites, the interfacial shear strength of PBO-APTMS-GO composites increased by 61.6%. The unique fold structure and numerous polar functional groups of GO improved the surface roughness, wettability and chemical reactivity of fiber surface, hence, the interfacial properties of composites were significantly enhanced. Meanwhile, the hygrothermal aging resistant properties of PBO-APTMS-GO composites were remarkably improved.Scanning electron microscopy(SEM), X-ray diffractometer(XRD), fourier transform infrared spectroscopy(FTIR) and X-ray photoelectron spectroscopy(XPS) were employed to investigate the AO erosion behavior of PBO fibers for the first time. Experimental results indicated that the surface morphology, crystal structure and chemical composition of PBO fibers changed obviously with the increase of AO exposure time. Meanwhile, PBO fibers and resin matrix were damaged with the increase of AO exposure time due to its sputtering and oxidation. The three kinds of interphases can effectively protect the PBO fibers and their composites. After 8h AO accelerated aging, PBO-APTMS-GO and its composites maintained the highest tensile strength and interfacial shear strength.