Investigation on the thermo-oxidative stability of carbon fiber sizings for application in thermoplastic composites

Constructing a Novel Moderately Modulus "Rigid-Flexible" Structure with Synergistic Reinforcement on the Carbon Fiber Surface to Enhance the Mechanical Properties of Carbon Fiber/Epoxy Composites at Elevated Temperatures

To improve the mechanical performance of carbon fiber (CF)/epoxy composites in high-temperature environments, a moderately modulus gradient modulus interlayer was constructed at the interface phase region of composites. This involved the design of a "rigid-flexible" synergistic reinforcement structure, incorporating rigid nanoparticle GO@CNTs and a flexible polymer polynaphthyl ether nitrile ketone onto the CF surface. Notably, at 180 °C, compared to commercial CF composites, the CF-GO@CNTs-PPENK composites displayed a remarkable improvement in their mechanical characteristics (interfacial shear, interlaminar shear, flexural strength, and modulus), achieving enhancements of 173.0, 91.5, 225.7, and 376.4%, respectively. The principal reason for this the moderately modulus interface phase composed of GO@CNTs-PPENK (where GO and CNTs predominantly consist of carbon atoms with sp2-hybridized orbitals, forming highly stable C-C structures, while PPENK possesses a "twisted non-coplanar" structure), which exhibited resistance to deformation at high temperatures. Moreover, it greatly improved the mechanical interlocking, wettability, and chemical compatibility between CF and the epoxy. It also played a crucial role in balancing and buffering the modulus disparity. The interface failure behavior and reinforcement mechanisms of the CF composites were analyzed. Furthermore, validation of the presence of a moderately modulus gradient interlayer at the interface phase region of CF-GO@CNTs-PPENK composites was performed by using atomic force microscopy. This study has established a theoretical foundation for the development of high-performance CF composites for use in high-temperature fields.

Interfacial Enhancement and Composite Manufacturing of Continuous Carbon-Fiber-Reinforced PA6T Composites via PrePA6T Ultrafine Powder

Semi-aromatic poly (hexamethylene terephthalamide) (PA6T) oligomer (prePA6T) ultrafine powder, with a diameter of <5 μm, was prepared as an emulsion sizing agent to improve the impregnation performance of CF/PA6T composites. The prePA6T hyperfine powder was acquired via the dissolution and precipitation "phase conversion" method, and the prePA6T emulsion sizing agent was acquired to continuously coat the CF bundle. The sized CF unidirectional tape was knitted into a fabric using the plain weave method, while the CF/PA6T laminated composites were obtained by laminating the plain weave fabrics with PA6T films. The interfacial shear strength (IFSS), tensile strength (TS), and interlaminar shear strength (ILSS) of prePA6T-modified CF/PA6T composites improved by 54.9%, 125.3%, and 120.9%, respectively. Compared with the commercial polyamide sizing agent product PA845H, the prePA6T sizing agent showed better interfacial properties at elevated temperatures, especially no TS loss at 75 °C. The SEM observations also indicated that the prePA6T emulsion has an excellent impregnation effect on CF, and the fracture mechanism shifted from adhesive failure mode to cohesive failure mode. In summary, a facile, heat-resistant, undamaged-to-fiber environmental coating process is proposed to continuously manufacture high-performance thermoplastic composites, which is quite promising in mass production.

Dual-Sizing Effects of Carbon Fiber on the Thermal, Mechanical, and Impact Properties of Carbon Fiber/ABS Composites

Dual-sizing effects with either epoxy or polyurethane (PU) on the thermal, mechanical, and impact properties of carbon fiber/acrylonitrile-butadiene-styrene (ABS) composites produced by extrusion and injection molding processes were investigated. The heat deflection temperature, dynamic mechanical, tensile, flexural, and impact properties of the composites reinforced with either (epoxy + epoxy) or (epoxy + PU) dual-sized carbon fiber were higher than those commercially single-sized with epoxy. The result indicated that the dual-sized carbon fiber significantly contributed not only to improving the heat deflection temperature and the storage modulus, but also to improving the tensile, flexural, and impact properties of carbon fiber/ABS composites. The highest improvement of the composite properties was obtained from the composite with (epoxy + PU) dual-sized carbon fiber. The improvement of the mechanical and impact properties was explained by the enhanced interfacial bonding between carbon fiber and ABS matrix and by the length distribution analysis of carbon fibers present in the resulting composites. The fiber–matrix interfacial behavior was qualitatively well-supported in terms of fiber pull-out, fiber breaking pattern, and debonding gaps between the fiber and the matrix, as observed from the fracture surface topography. This study revealed that the properties of carbon fiber/ABS composites prepared by extrusion and injection molding processes were improved by dual-sizing carbon fiber, which was performed after a commercial epoxy sizing process, and further improved by using PU as an additional sizing material.

Structure and Properties of Polysulfone Filled with Modified Twill Weave Carbon Fabrics

Carbon fabrics are widely used in polymer based composites. Nowadays, most of the advanced high-performance composites are based on thermosetting polymer matrices such as epoxy resin. Thermoplastics have received high attention as polymer matrices due to their low curing duration, high chemical resistance, high recyclability, and mass production capability in comparison with thermosetting polymers. In this paper, we suggest thermoplastic based composite materials reinforced with carbon fibers. Composites based on polysulfone reinforced with carbon fabrics using polymer solvent impregnation were studied. It is well known that despite the excellent mechanical properties, carbon fibers possess poor wettability and adhesion to polymers because of the fiber surface chemical inertness and smoothness. Therefore, to improve the fiber–matrix interfacial interaction, the surface modification of the carbon fibers by thermal oxidation was used. It was shown that the surface modification resulted in a noticeable change in the functional composition of the carbon fibers’ surface and increased the mechanical properties of the polysulfone based composites. Significant increase in composites mechanical properties and thermal stability as a result of carbon fiber surface modification was observed.

PEEK composites with polyimide sizing SCF as reinforcement: Preparation, characterization, and mechanical properties

In this work, the surface modification of short carbon fibers (SCFs) using polyimide (PI) as a sizing agent was conducted and fully characterized, and SCF-reinforced polyether ether ketone (PEEK) composites were obtained by extrusion and injection molding. The surface characteristics of the PI-coated SCFs were evaluated using scanning electron microscopy and X-ray photoelectron spectroscopy. The results indicated that a uniform PI sizing layer was formed on the surfaces of the SCFs. Thermogravimetric analysis results demonstrated that PI-coated SCFs had better thermal stability than commercial SCFs. The tensile strength and flexural strength of the PI-coated SCF/PEEK composites showed improvements of 11.8% and 16.6% compared with the commercial cases, which were attributed to the PI sizing treatment effectively improving the interfacial adhesion between the SCF and the PEEK matrix. Dynamic mechanical analysis and the morphologies of tensile fracture surfaces suggested better interfacial adhesion between the fibers and the PEEK matrix, which were in good agreement with the mechanical properties. Due to the convenient processing of PI sizing as well as the effectively improved mechanical properties of the composites, the PI-sizing methodology has great potential application in the field of fiber-reinforced high-temperature engineering plastics composites.