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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 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]