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In order to improve the interfacial adhesion of epoxy composites, a hierarchical structure including carbon nanotubes (CNTs) grown on carbon fiber (CF) was prepared by a novel vacuum-assisted chemical vapor deposition (CVD) method at relatively low temperature of 400 °C under a pressure of 0.01 MPa. The short beam method and microbond test were used to measure the interlaminar shear strength (ILSS) and interfacial shear strength (IFSS) of epoxy composites reinforced by different CFs. The results showed that the CNTs-grown CF prepared at the H2 flow rate of 9 L/min had the best reinforcement effect. The ILSS and IFSS of its composites were 19.50% and 62.32% higher than that of the CF/epoxy composites without CNTs grown, respectively. The improvement of interfacial adhesion can be attributed to the fact that CNTs inserted into the matrix enhanced the mechanical interlocking between the fiber and the resin and induced the formation of interphase. Also, two failure modes of CNTs have also been observed, which can absorb extra energy and increased the difficulty of the separation of fiber and resin. The increase in the glass transition temperature (Tg) indicated the movement of the polymer molecular chains at the interphase was restricted by CNTs, which also contributed to the improvement of the interfacial adhesion of composites. [ABSTRACT FROM AUTHOR]

The coagulation process was vital for the microfibril evolution and mechanical properties of polyacrylonitrile (PAN) fibers. The PAN nascent fibers and precursor fibers were prepared by controlling drawing ratio of coagulation bath at low temperature during the dry‐jet wet spinning process. The microfibril morphological changes induced by force fields in coagulation bath were investigated by scanning electron microscopy and high‐resolution transmission electron microscopy. During the coagulation process, the spinning solution evolved into an interconnected network composed of random microfibrils and tie joints as a building block of the network. At low drawing ratio, the random interconnected network existed in nascent fibers. Increasing drawing ratio, the fiber filaments underwent shrinkage and the network was transformed into the transverse lamellae. Furthermore, the lamellar thickness also decreased. After the treatment of post‐spinning, similar transverse lamellae were formed in all of precursor fibers, and random microfibrillar network was stretched and oriented to develop into the aligned microfibrils in precursor fibers. The transverse fold‐chain crystal layers were densely stacked in the microfibrils. Increasing drawing ratio, the lamellae and microfibrils in precursor fibers were packed more densely and orderly. Consequently, the order and homogeneity of microfibrils in nascent fibers and precursor fibers were improved by increasing drawing ratio, which were benefit to increase fiber tensile strength and modulus. [ABSTRACT FROM AUTHOR]

The purpose of this article is to find a novel way to grow carbon nanotubes (CNTs) on carbon fiber fabrics with improved tensile properties. Using chemical vapor deposition (CVD) method, the CNTs catalyzed by Fe–Co bimetallic catalysts system at a low temperature of 500 °C were demonstrated. TEM and Raman spectra show that the synthesized CNTs perform an obvious tubular hollow structure with high crystallinity. Mechanical test results clearly show that the tensile strength of final single fiber increases by 8.83% and the Weibull modulus improves from 6.85 to 7.78 after the growth of CNTs. The variations of tensile strength and Weibull modulus can be explained by not only the low carbon solubility and high catalytic activity of Fe–Co bimetallic catalysts minimizing support damage at low temperatures, but also the repairment of defects during the CVD process. Such results provided the solid foundation for further development of high-performance multiscale hybrid micro/nanocomposites, broadening their potential applications such as energy-store and electronic flexible device. [ABSTRACT FROM AUTHOR]

This article provides a method for growing carbon nanotubes(CNTs) on carbon fibers(CFs) using iron and nickel as catalysts at low temperatures. This series of experiments was conducted in a vacuum chemical vapor deposition(CVD)furnace. It is found that Fe–Ni catalysts, which have a certain thickness and can be better combined with resins when manufacturing composite materials, are more ideal for the growth of CNTs than single metal catalysts. At the same time, it is proved that the CVD process worked best at 450 °C. The mechanical property test proved the reinforcing effect of CNTs on carbon fiber, the single-filament tensile strength of CFs obtained by using Fe–Ni catalyst at 450 °C was 11% higher than that of Desized CFs. The bonding strength of carbon fiber and resin has also been significantly improved. When synthesized at low temperature, CNTs exhibited a hollow multi-wall structure. [ABSTRACT FROM AUTHOR]