In this article, active groups were introduced to the surface of aramid fiber by building a Cu2+ bridge between the aramid fiber and polyethyleneimine (PEI) to improve adhesion in composites between the aramid fiber and the matrix such as epoxy resin. The changes in the structure and properties of the aramid fiber were verified with Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and the single-fiber pull-out test. The FTIR and XPS results show a significant change in the structure and morphology of the aramid fiber after modification. The results of the single-fiber pull-out test show that the interfacial shear strength (IFSS) of epoxy composites reinforced with PEI-grafted aramid fiber increases by 48.8% compared with the IFSS of epoxy composites reinforced with untreated fiber. Thus, the proposed method can improve the interfacial bonding of composites by creating a copper ion bridge between the aramid fiber and PEI.
To
achieve satisfactory electrical conductivity is still a challenge,
without sacrificing the superior integrated performance of meta-aramid
(PMIA) fibers. Here a novel, bioinspired two-step approach was reported
to fabricate surface-nickeled PMIA fibers with admirable electrical
conductivity. The formation of polydopamine-functionalized silver
nanoparticle assemblies (DOPA@AgNAS) deposited on the surface of the
PMIA fibers simply included the magnetic stirring of 3,4-dihydroxy-l-phenylalanine (DOPA) and silver ammonia in an aqueous solution
at room temperature and dipping the PMIA fibers into the aqueous solution
simultaneously. After, the DOPA@AgNAS functioned as the catalyst for
the subsequent progress of the electroless nickel plating. The as-prepared
nickel-coated PMIA fibers (DOPA@AgNAS-Ni-PMIA) possess outstanding
electrically conductive properties and exhibit exceptional mechanical
stability. More importantly, because of its high flexibility, DOPA@AgNAS-Ni-PMIA
can be utilized in numerous fields.
In situ consolidation of the thermoplastic composites can be realized through laser-assisted automated fiber placement technology, and the properties of the composites are significantly affected by the crystallinity. Understanding the complicated crystallization process is very important for controlling the performance of the composites manufactured by automated fiber placement. In this work, the crystallization mechanism of carbon fiber/polyphenylene sulfide composites during the automated fiber placement process and its effect on the mechanical properties were investigated. Crystallization kinetics analysis indicated that the crystallization window of the carbon fiber/polyphenylene sulfide composites was 87–270°C. Furthermore, for carbon fiber/polyphenylene sulfide composites manufactured by automated fiber placement, the crystallinity was influenced by the parameters including laser temperature, placement speed and tool temperature, in which the tool temperature was the main factor. Increasing the tool temperature was an effective method to achieve high crystallinity. Meanwhile, when the tool temperature was in the range of the crystallization window, the composites could experience isothermal crystallization, which could further improve the crystallinity. With the increase of the tool temperature, the flexural strength and interlaminar shear strength were improved due to the enhanced self-adhesion of the matrix, while the Mode І fracture toughness was decreased because of the reduction of the matrix ductility. The combination of the kinetic method and experimental study was conducive to a better understanding of the crystallization mechanism and optimization of the processing conditions.
The poor interfacial adhesion between the aramid fiber (AF) and the matrix limits the application of the final composites. In this study, a novel coating method was adopted to modify AF Through metallization/grafting reaction, the copolymer synthesized by the low-temperature poly-condensation of p-phenylenediamine (PPDA), 4,4′-diaminodiphenyl ether (ODA) and terephthaloyl dichloride (TPC), was added into the dimethyl sulfoxide/sodium hydride (DMSO/NaH) solution, and a nano AF solution was obtained. Then epoxy groups were introduced to the amide bond by grafting Epichlorohydrin (ECH). By further grafting on Poly (propylene glycol) bis (2-aminopropyl ether) (PEA), more functional groups were introduced, which could increase the polarity of the fiber and the interfacial adhesion of the composites. The results show that not only the interfacial shear strength (IFSS) and the flexural strength of the aramid-reinforced composites has a significant increase compared with the untreated fibers, but the modification still maintains the mechanical properties of the fiber, indicating that building nanoscale coating solution is a very effective method to achieve non-destructive modification to ehance its interfacial adhesion with epoxy resin.
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