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In this work, a continuous and rapid atmospheric plasma setup was developed for rapidly modifying the surface of PAN-based carbon fibers (CFs). The interlaminar shear strength (ILSS) of CFs increased from 64.9 to 80.0 MPa with 60 s plasma treatment. Further mechanical and surface structural characterizations revealed that the effect of plasma was different, depending on the treatment time. When the treatment time was lower than 15 s, the effect of plasma was mainly on physically etching the surface of CFs, and the ILSS of CFs increased rapidly. Further extending the plasma treatment time did not increase surface roughness but promoted the addition of oxygen-containing functional groups on the surface of CFs, corresponding to a slower growth rate of ILSS. The atmospheric plasma was generated via a dielectric barrier discharge (DBD) method, and its energy intensity was significantly lower than that of plasma generated under low pressure. Accordingly, a mechanism was proposed for the plasma treatment of CFs: atmospheric plasma was not strong enough to simultaneously etch all the carbon atoms on the surface of CFs; therefore, carbon atoms on the graphitic plane were selectively etched, followed by the attaching of oxygen-containing functional groups on the exposed carbon sites caused by etching.

With the increasing demand of industry, the fabrication of single-component epoxy (EP) systems with satisfactory flame retardancy and thermal stability is of great significance. Herein, a novel phosphorus/nitrogen-containing single-component EP (EP/DOPO/BDM/BICP) system was synthesized via incorporating N,N′-bismaleimide-4,4′-diphenylmethane (BDM), benzimidazolyl-substituted cyclotriphosphazene (BICP) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) into EP. In our previous work, we found that DOPO could promote the decomposition of BICP to produce dissociative benzimidazoles under heating, which endowed the as-fabricated epoxy thermoset with rapid curing speed. However, the addition of DOPO reduced the glass transition temperature (Tg) of epoxy thermosets. To deal with this problem, bismaleimide with superior heat resistance was added. The results indicated that the addition of BDM improved the thermal stability, flame retardancy and smoke suppression of EP/DOPO/BDM/BICP. The obtained thermoset exhibited UL94 V-0 rating, limiting oxygen index (LOI) of 40.5% and low total smoke production (TSP) of 10.4 m2 due to the synergetic flame-retardant effect of phosphaphenanthrene, polybismaleimide and cyclotriphosphazene. This research offers a viable approach to develop single-component EPs with improved flame retardancy, thermal stability and rapid-curing ability.