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The selective fluorination of aramid fiber surface was reported by Fe 3+ coordination on the benzimidazole unit. After the coordination, both of the two parts in benzimidazole unit, benzene ring and imidazole ring, take priority in the reaction with the fluorine gas, while the reaction with the amide bond is restrained. In this way, selective fluorination on benzimidazole unit is achieved, with the surface polarity increasing and chain scission behavior suppressed simultaneously. What’s more, the increased surface polarity enables the improvement of the interfacial shear strength by 24%, compared with that in a traditional fluorination way. In all, the study offers an easy and effective strategy for the regulation and controlling of direct fluorination reaction, and it provides a guideline for further adjustment of the reaction mechanism to meet the requirement in other applications. [ABSTRACT FROM AUTHOR]

The weak interfacial adhesion of aramid fiber with resin matrix is believed as a major limitation for its wide application. In this study, a nondestructive grafting method was applied for surface modification of benzimidazole-contained aramid fiber. Using the NH in benzimidazole unit as active sites, aramid fiber surface was firstly decorated with densely SiO 2 structure, and a rough surface was obtained. Then, high density of NH 2 and C=C groups were introduced on fiber surface by the reaction with silane coupling agents. These functionalized NH 2 /C=C groups endow the fiber with the ability to chemically bonding with resin in a wide polarity range, including rubber, bismaleimide and epoxy resin. Also, the SiO 2 -decorated rough surface improves the level of mechanical interlocking with them. Experimental results show that the interfacial shear strength of functionalized fiber with natural rubber, bismaleimide and epoxy resin correspondingly increases 117%, 166% and 43%, compared with that of untreated fibers. Meanwhile, the grafting method is confirmed as nondestructive, and the superior mechanical property of aramid fiber is preserved. In all, the study presents a new effective method for the preparation of aramid fiber with excellent interfacial properties suitable for resin composite in a wide polarity range. [ABSTRACT FROM AUTHOR]

The poor Uv stability and weak interfacial adhesion are considered as the bottleneck problems for further application of aramid fiber. Herein, a new strategy, Fe 3+ coordination, was reported for aramid fiber to simultaneous improve its Uv resistance and composite interfacial shear strength. Fe 3+ was introduced onto aramid fiber by coordinating with benzimidazole unit of fiber structure. It can reach a doping capacity of as high as 1516ug/g fiber, and the fiber surface is saturatedly covered with Fe 3+ . The chemical structure of Fe 3+ -benzimidazole brings about strong metal-enhanced fluorescence emission effect, which, in turn, greatly raises its Uv stability. Owing to the Fe 3+ coordination, the tensile strength of Fe-coordinated fiber could preserve as high as 96% after Uv irradiation, compared with 73% of untreated fiber. Meanwhile, the introduction of Fe 3+ improves the surface polarity of aramid fiber and consequently leads to the increase of the composite interfacial shear strength by 39%. It is believed that the Fe-coordinated fiber integrates the advantages of easy production, cost-effective and increased Uv stability, as well as high composite interfacial adhesion, and can be used as promising enhancement for the advanced composite material in harsh environment. [ABSTRACT FROM AUTHOR]