In-situ polymerization and covalent modification on aramid fiber surface via direct fluorination for interfacial enhancement

Poor adhesive performance is considered to be a major disadvantage of aramid fibers in the fabrication of aramid fiber reinforced polymer composites, and it's a main drawback to restrict its wide application. In this paper, fluorine-related free radicals induced by direct fluorination were detected by Electron Paramagnetic Spectrum (EPR), which were considered as active spots to initiate copolymerization between acrylic acid (AA) and divinylbenzene (DVB), and the copolymer was chemically grafted onto AF surface, thus aramid fiber was covalently decorated by plenty of -COOH groups. Furthermore, amine-functionalized carbon nanotubes were devised to undergo the condensation reaction with the -COOH groups on fiber surface so that high density of carbon nanotubes could be chemically grafted on aramid fiber surface. Testing of mechanical properties showed that there was almost no damage to the mechanical property of aramid fibers, and interfacial shear strength of modified fiber increased by 53.1% and 69.1% after grafting polyacrylic acid-divinylbenzene copolymer and carbon nanotubes in sequence, respectively. Mathematical analysis for the changes and relationships between surface energy, surface roughness of fibers and their IFSS revealed that specific surface energy made a greater contribution to the enhancement of IFSS than surface roughness, which proved that surface energy was more helpful to the interfacial properties of the composites. Additionally, electric conductivity of organic aramid fiber improved obviously with a conductivity of 0.48 S/m.