Single-filament Tensile Strength Research Articles

Waterborne polyurethane sizing agent with excellent water resistance and thermal stability for improving the interfacial performance of carbon fibers/epoxy resin composites

In order to improve the water-resistance and thermal stability of waterborne polyurethane (WPU), a series of silane and maleimide co-modified waterborne polyurethane emulsions (WPU-M-S) were prepared. Because of the high bond energy of the Si-O bond in silane and the rigid ring in 4-HPM, the WPU-M-S sizing agent achieved better thermal stability. Meanwhile, the excellent hydrophobicity of silane enhances its water resistance. Then, the electrochemical anodic oxidation (EAO) treatment was used to activate the surface of the carbon fibers to introduce carboxyl and hydroxyl groups. Next, WPU-M-S was attached to the carbon fiber by the sizing process. For compound modified carbon fibers, the water contact angle increased, and the single filament tensile strength was also improved. The WPU-M-S sizing agent can react with both the active groups on the fiber surface and the amino groups in the epoxy resin system, thereby achieving a significant improvement in the composite interfacial bonding performance. The interlaminar shear strength (ILSS) of the sizing carbon fibers reinforced epoxy resin composite was promoted to 59.80 MPa, with an increase of 41.61% compared with unsized carbon fiber.

Carbon nanotubes/carbon nanofibers@carbon fiber construction of 3D network hierarchical structures toward multiple synergistic losses for electromagnetic wave absorption

Exploring carbon materials is promising for innovative electromagnetic wave (EMW) absorption materials, nevertheless challenged by balancing efficient EMW absorption and continuous large-scale fabrication. In this work, CNTs/CNFs@CF with inimitable 3D network hierarchical structures are fabricated as EMW absorbers via the chemical vapor deposition method. Through detailed characterization of its morphology, structure, composition, and magnetic properties, the material obtained optimal electromagnetism parameters and showed exceptional EMW absorption performance. Herein, the minimum reflection loss (RLmin) was −66.00 dB at 1.00 mm and the maximum effective absorption bandwidth of 4.48 GHz was obtained at 1.29 mm. In addition, good mechanical properties with a single-filament tensile strength of 4.99 GPa were achieved, thereby expanding the range of applications. Undoubtedly, CNTs/CNFs@CF realizes the synergy of multiple synergistic loss mechanisms and impedance matching for EMW absorption. In summary, this implies a good prospect for the continuous large-scale preparation of ultrathin and efficient EMW absorbers.

Catalyst optimization and reduction condition of continuous growth of carbon nanotubes on carbon fiber surface

Carbon nanotubes (CNTs)/carbon fiber (CF) reinforcements were synthesized under different catalyst compositions and reduction conditions. The effects of the catalyst, reduction temperature and reduction time on the surface morphology, graphitization, and single filament tensile strength of the prepared CNTs/CF samples were investigated. When nickel was used as the catalyst and copper as the catalyst promoter, with the increase of copper concentration, the catalytic activity increased. Thus, the carbon source was consumed more completely, improving the abundance of CNTs with good graphitization. And the effect of repairing CF defects was more obvious, hence the single filament tensile strength accordingly increased. Besides, the increase of catalyst reduction temperature and reduction time intensified the etching of CF by catalyst, and decreased the single filament tensile strength of CF. With the deposition of CNTs, the tensile strength of CF was enhanced in varying degrees. When the concentration of cooper was 0.01 mol/L with the reduction time of 10 min and reduction temperature of 450 °C, CNTs/CF had the highest tensile strength, which can reach up to 4.51 GPa. We determined that bimetallic catalysts could adjust the catalytic activity of nickel. The change of reduction time and temperature would affect the quality of CNTs, which was helpful to obtain high quality CNTs on CF surface and improve the mechanical properties of CNTs/CF and its composites.

Continuous Growth of Carbon Nanotubes on Carbon Fiber Surface by Chemical Vapor Deposition Catalyzed by Cobalt with Thiourea

The continuous preparation of carbon nanotubes (CNTs)/carbon fiber (CF) multiscale reinforcements was realized via one-step chemical vapor deposition (CVD) method. In order to alleviate the damage of CF caused by catalyst etching at high temperature, catalytic promoter was adopted to improve the activity of the catalyst, thus reducing the CVD temperature. By adjusting the cobalt-based catalyst system, the effects of thiourea concentration on the morphology, microstructure and tensile strength of CNTs/CF samples were systematically investigated. It was found that the length and quantity of CNTs were added as the thiourea concentration increased, and the graphitization degree of the sample increased at first because of the well-grown CNTs, and then decreased due to the formation of amorphous carbon. Moreover, the tensile strength of CNTs/CF multiscale reinforcements was improved, which derived from the enhanced defect repair function of synthesized CNTs. Remarkably, CNTs/CF-0.02 exhibited a high single-filament tensile strength value (up to 4.51 GPa), which was about 6.6% higher than that of Desized cf Besides, the crystal structure and composition of reduced catalysts were analyzed, confirming the successful sulfur doping into cobalt particles. Therefore, the work offers a facile, economical, and efficient route for manufacturing CNTs/CF multi-scale reinforcements at comparatively low temperature.

Improving the mechanical properties of amorphous silicon carbide fibers by forming a protective silicon dioxide layer

Silicon carbide fiber is a representative structural material that has been studied as a major reinforcement material for ceramic matrix composites (CMCs). SiC fibers are classified by their operating temperature, manufacture process, composition, and crystallinity. Among the various SiC fibers, amorphous ones are composed of a Si–O–C amorphous matrix and nanoscale SiC crystals, and amorphous fibers exhibit amorphous fracture behavior. An amorphous fiber is almost always fractured by surface flaws generated during the manufacturing process. In this study, we aimed to strengthen the surface by etching the surface cracks and forming a SiO2 oxidation layer, and then evaluated the effect of the oxide layer thickness on the fracture behavior and control of surface defects. The passive oxidation layer was formed by exposing the fiber bundles to air atmosphere at a temperature higher than 1000 °C. The mechanical properties of the strengthened fibers were evaluated through single-filament tensile strength tests, and the fracture distribution was analyzed using Weibull distribution. Further, fractographic analyses were conducted on the cross-sectional microstructures observed by field-emission scanning electron microscopy. The surface-oxidized fibers exhibited enhanced flexibility owing to the crack-blunting effect of the SiO2 layer.

Continuous growth of carbon nanotubes on the surface of carbon fibers for enhanced electromagnetic wave absorption properties

As electromagnetic wave (EMW) pollution has become a serious problem in daily life, lightweight, efficient, and mass-produced EMW-absorbing materials are urgently needed. Herein, we developed a novel method for the continuous growth of carbon nanotubes (CNTs) on the surface of polyacrylonitrile (PAN)-based carbon fibers (CFs) by chemical vapor deposition (CVD), which can be applied to mass production. The obtained CF/CNT composites demonstrate outstanding EMW absorption capability, exhibiting a -58.75 dB reflection loss (RL) at a thickness of 1.54 mm. An effective absorption bandwidth (RL < -10 dB) of 4.24 GHz (13.76–18.00 GHz) was achieved at a thickness as low as 1.25 mm, which almost covers the entire Ku band. The excellent EMW-absorbing performance can be attributed to the 3D conductive network constructed by the CNT forest, which effectively promotes multiple reflections and scattering, and further favors dipole and interface polarizations. The mechanical properties of CF, CF-electrochemical anodic oxidation (EAO), and CF/CNT composites were examined, the results showed that the single-filament tensile strength of CF/CNT@0.07 and CF/CNT@0.09 was effectively improved. Our work suggests that the novel CF/CNT composite is a promising material for EMW absorption and strength enhancement owing to its light weight, high strength, low thickness, and good scale-up ability.

Graphene Oxide-Modified Aramid Fibers for Reinforcing Epoxy Resin Matrixes

Carboxylated and aminated graphene oxide (CGO and AGO) were first prepared by using carboxyl-terminated aromatic hyperbranched polyester (HBPC) and amino-terminated aromatic hyperbranched polyester (HBPA) noncovalent functionalized GO, respectively. Subsequently, multiscale reinforcing fibers (CGO-PDA-AF and AGO-PDA-AF) were prepared by exploiting the super adhesion of the polydopamine layer (PDA) and its physical adsorption and chemical grafting with the CGO and the AGO. This study examined the tensile strength of the modified aramid fiber (AF) monofilament and the interfacial shear strength (IFSS) between the modified AF monofilament and the EP matrix, and an investigation was conducted on the interfacial enhancement mechanism. As indicated from the results, the AGO exerted a more effective modifying effect than the CGO. The single filament tensile strength and IFSS of the AGO-PDA-AF were the maximum (4.66 GPa and 96.2 MPa), nearly 8.6 and 7.9% higher than those of the CGO-PDA-AF, respectively. The enhancement of the interface performance between the AGO-PDA-AF and the EP was attributed to the introduction of considerable amino active groups in the AGO, thereby forming a stable covalent bond with the epoxy matrix, which significantly improved the interface bonding strength. Moreover, the flexible coating layer formed by the AGO could reduce the stress concentration of the interface through deformation, so the AF could be carried more uniformly. Furthermore, the AGO increased the surface affinities of the AF and improved the mechanical interlocking with the EP matrix.

Growth of carbon nanotubes on the surface of carbon fiber using Fe–Ni bimetallic catalyst at low temperature

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.

Enhancing the Interfacial Adhesion with Rubber Matrix by Grafting Polydopamine-Carbon Nanotubes onto Poly(p-phenylene terephthalamide) Fibers.

To enhance the interfacial adhesion between poly(p-phenylene terephthalamide) (PPTA) fibers and a rubber matrix without damaging the fiber structures, aminated carbon nanotubes (NH2-CNTs) were mildly deposited onto the fiber surface by combining the biomimetic modification of dopamine via the Michael addition reaction. Furthermore, differences between the “one-step” method and the “two-step” method were researched through adjusting the addition sequence of NH2-CNTs. The surface morphologies and chemical structures of PPTA fibers before and after modification were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The mechanical properties of fibers and the adhesive properties with rubber were tested using an electronic tensile tester of single-filament and universal testing machine, respectively. After modification by the “one-step” method for 24 h, the single-filament tensile strength of the modified fibers increased by 16.5%, meanwhile, the pull-out force of the modified fibers to rubber increased by approximately 59.7%. Compared with the “two-step” method, the “one-step” method had superiority due to the short reaction time and the large deposition rate of CNTs.

Surface modification of Poly(p-phenylene terephthalamide) fibers by polydopamine-polyethyleneimine/graphene oxide multilayer films to enhance interfacial adhesion with rubber matrix

In order to improve the interfacial adhesion between the poly(p-phenylene terephthalamide) fibers and rubber matrix while enhance the fiber strength simultaneously, a mild surface modification method was presented to graft polydopamine-polyethyleneimine/graphene oxide (PDA-PEI/GO) multilayer films onto the fiber surface. In this way, PDA could be first non-covalently deposited onto the fiber surface via dopamine biomimetic modification, and then the positively charged PEI was absorbed on the PDA through Michael addition reaction. After that, the negatively GO was grafted on the surface by the layer-by-layer (LbL) assembly to construct the PDA-PEI/GO multilayer films. The results of mechanical properties tests and pull-out force tests showed that the highest single-filament tensile strength and the highest pull-out force of the modified fibers increased by 15.1% and 78.1%, respectively. The optimal time of PEI/GO multilayer for the enhancement of adhesive properties was 7 and the excessive amount of PEI/GO would lead to high aggregation to decrease the adhesive strength.

Continuous method for grafting CNTs on the surface of carbon fibers based on cobalt catalyst assisted by thiourea

This paper provides a continuous method for grafting carbon nanotubes (CNTs) on the surface of carbon fibers by chemical vapor deposition (CVD). The control of the morphology of CNTs/CFs can be achieved by adding thiourea to the cobalt nitrate precursor. The sulfur can increase the catalytic activity of the Co catalyst. Scanning electron microscopy reveals that a uniform layer of CNTs is grafted onto the surface of carbon fibers with the presence of thiourea. Through the single-filament tensile strength test, it can be found that the tensile strength of the fiber is increased by up to about 10% compared with the desized carbon fibers after the CVD process. And the reason for the enhancement is explored through X-ray diffraction. Raman spectroscopy reveals that the sample possesses the highest degree of graphitization at a thiourea concentration of 0.02 mol/L. It is found by high-resolution transmission electron microscopy that the growth mechanism of CNTs is tip growth mechanism, and the diameter of the CNTs is about 15 nm.

The Effect of Heat Treatment on the Properties of SiCf/SiC Composites Prepared with Different SiC Fibers

Silicon carbide (SiC) fiber–reinforced SiC matrix (SiCf/SiC) composites, employing two SiC fibers, KD-I and KD-II, respectively, were fabricated by the precursor infiltration and pyrolysis process. A pyrocarbon coating was used as the fiber-matrix interface. In addition, the effects of heat treatment on the properties of the SiC fibers and SiCf/SiC composites were investigated. Results revealed marginal performance degradation of the KD-I and KD-II SiC fibers after heat treatment at 1100°C for 1 h. However, heat treatment at 1400°C for 1 h led to the decrease in the single-filament tensile strength of the KD-I and KD-II SiC fibers by 50.2% and 10.1%, respectively. In addition, the flexural strength of the SiCf/SiC composites, which were fabricated using the KD-I and KD-II SiC fibers, decreased by 49.6% and 15.9%, respectively. The difference in the composition of the KD-I and KD-II SiC fibers demonstrated that the SiC fibers and SiCf/SiC composites decreased by varying degrees.

On the mechanical, thermophysical and dielectric properties of Nextel™ 440 fiber reinforced nitride matrix (N440/Nitride) composites

The Nextel™ 440 fiber reinforced nitride matrix (N440/Nitride) composites were fabricated by precursor infiltration and pyrolysis (PIP) route. The results demonstrated that the original N440 fiber had a phase composition of amorphous SiO2 and γ-Al2O3. Its single filament tensile strength was 3.03GPa (at room temperature), while it dropped to 72.6% and 35.1% at 1200°C and 1400°C, respectively. The phase content of N440/Ntride composites was mainly γ-Al2O3 and amorphous BN, as well as mullite phase (formed at > 1100°C). The composites owned a flexural strength up to 76.0MPa at room temperature. The stair-stepping decrease in the load-displacement curve and fiber pull-outs in the fracture surface indicated a good fiber/matrix interface and toughness. By heating at 1400°C, the composites still possessed 67.4% of original bending strength. It was found that the high temperatures caused strong fiber-matrix bonding and severe fiber degradation. The specific heat, CTE and thermal conductivity of the composites were 0.325–0.586Jg−1K−1, (3.2–4.0) × 10−6K−1 and 0.78–3.47Wm−1K−1, respectively. The composites possessed a dielectric constant of 4.25–4.35 and loss tangent of 0.004–0.01 at 8–12GHz. The good overall performances enabled the N440/Nitride composites advanced high-temperature wave-transparent applications.

Surface modification of high-performance polyimide fibers by oxygen plasma treatment

In order to improve the interfacial compatibility between the fibers and epoxy resins, polyimide (PI) fibers were modified using oxygen plasma with various treatment powers. The properties of PI fibers before and after surface modification were comparatively characterized according to their chemical composition, surface morphology, surface free energy, single filament tensile strength, and interfacial shear strength (IFSS). Most of the fiber properties, including the ratio of oxygen to nitrogen, oxygen concentration, surface free energy, and IFSS firstly increased with the plasma power, and then decreased when the plasma power was higher than 120 W. With a plasma power of 120 W, the oxygen concentration and the ratio of oxygen to carbon atoms (O/C) was 26% (22% for untreated fiber) and 0.38 (0.28 for untreated fiber), respectively. Meanwhile, the values of surface free energy and IFSS were 89% and 30% higher than those for untreated fiber, respectively. Furthermore, the values of single filament tensile strength for modified fibers were only 2.3% lower than those for pristine one. These results indicated that the compatibility between PI fibers and epoxy resins was greatly improved without compromising mechanical properties.

Mechanical properties of SiCf/SiC composites with PyC and the BN interface

To tailor the fibre–matrix interface of continuous-silicon-carbide-fibre-reinforced silicon carbide (SiCf/SiC) composites for improved mechanical properties, SiC fibres were coated with pyrolytic carbon (PyC) and BN interfaces using chemical vapour deposition (CVD) and the dip-coating process, and three-dimensional SiCf/SiC composites with such interfaces were fabricated using the precursor infiltration and pyrolysis (PIP) process. The microstructures of the SiC fibres with different coatings were characterised using a scanning electron microscope. The effects of the coating processes on the tensile strengths of the SiC fibres were studied using a single-filament tensile strength test. The mechanical properties of the SiCf/SiC composites were evaluated using the three-point bending test and single-edged notch beam test. The results indicate that the SiC fibres with single-layer PyC coating have larger single-filament tensile strengths than the original fibres. The SiCf/SiC composites with a single-layer PyC coating as an interface exhibit an optimal mechanical property. The average flexural strength and fracture toughness of the single PyC-coated composites were 433.1MPa and 20.0MPam1/2, respectively.

Grafting of silane and graphene oxide onto PBO fibers: Multifunctional interphase for fiber/polymer matrix composites with simultaneously improved interfacial and atomic oxygen resistant properties

Abstract Atomic oxygen (AO) is a dominant component of the low earth orbit and can erode most spacecraft materials. In this work, both silane and graphene oxide (GO) were introduced onto poly(p-phenylene benzobisoxazole) (PBO) fibers to prevent AO from penetrating into the interface of PBO fiber/epoxy composites. The microstructure, mechanical properties and AO erosion resistance of PBO fibers before and after modification were investigated. Experimental results revealed that the GO was successfully grafted onto PBO fibers using 3-aminopropyltrimethoxysilane (APTMS) as the bridging agent. The surface roughness (Ra) and wettability of the obtained hybrid fibers (PBO–APTMS–GO) were obviously increased in comparison with those of an untreated one. In addition, PBO–APTMS–GO showed simultaneously remarkable enhancement in interfacial shear strength (IFSS) and AO erosion resistance. Meanwhile, single filament tensile strength (TS) had no obvious decrease after the grafting processes. We believe the facile and effective method may provide a novel interface design strategy for developing multifunctional fibers.

Development of single filament testing procedure for polyacrylonitrile precursor and polyacrylonitrile-based carbon fibers

Single filament testing protocols for polyacrylonitrile precursor and polyacrylonitrile-based carbon fibers have been developed to ensure reliable tensile results that can be compared to the standard testing protocols used by the industry. Accurate carbon fiber linear density measurement by vibroscope was quite sensitive to the pre-stress applied to the fiber. Gauge length dependence testing of the commercial carbon fibers exhibited that tensile strengths obtained at 25.4 mm gauge length are comparable to those reported by the manufacturer using the standard strand testing results. On the other hand, experimental carbon fibers that have not been surface treated or sized, showed that single filament tensile strength values at 6 mm gauge length was comparable to the strand testing results. In addition, the compliance corrected tensile moduli of carbon fibers obtained by single filament tests were also comparable to the moduli obtained from the standard strand testing results. A modified Weibull analysis, which accounts for sample volume effects, has also been used to determine the Weibull modulus of both the commercial and experimental carbon fibers.

A facile method to prepare multifunctional PBO fibers: simultaneously enhanced interfacial properties and UV resistance

A new method combining surface coating with chemical grafting to prepare poly(p-phenylene benzobisoxazole) fiber–silica–graphene oxide (PBO–SiO2–GO) hybrid fiber was proposed. The chemical composition, surface morphology, surface roughness (Ra), surface energy, interfacial shear strength (IFSS), single filament tensile strength (TS) and ultraviolet (UV) resistance of PBO fibers before and after modification were investigated. Experimental results revealed that the PBO fiber surface was covered by a silica coating, onto which GO was successfully grafted through chemical bonds. The Ra and surface energy of PBO–SiO2–GO were obviously increased in comparison with that of an untreated one. The IFSS of its composites was greatly improved due to the excellent wettability and mechanical interlocking of GO. Meanwhile, TS had no obvious decrease after the surface coating and grafting process. Moreover, the introduction of silica coating on the fiber surface led to a better UV resistance than that of an untreated one. We believe this effective method may provide a novel surface modification strategy for developing multifunctional fibers.

Surface modification of PBO fiber through oxygen plasma induced vapor phase grafting of acrylic acid

The influence of oxygen plasma induced vapor phase grafting of acrylic acid on the surface properties of poly (p-phenylene benzobisoxazole) (PBO) fibers and interfacial adhesion with epoxy resin matrix were investigated in this paper. After treatment, XRD results show that the average crystal size slightly decreased from 9.85nm to 9.12nm. AFM scanning graphs indicate that the surface roughness of PBO fibers increased significantly. XPS spectra show the percentage content of polar oxygen-containing functional groups obviously increased after modification. The interfacial shear strength between treated PBO fibers and epoxy resin matrix increase by 55%, while the single-filament tensile strength slightly decrease by 8%.

Multiple zirconia interphase for SiC/SiC f composites

A multiple zirconium dioxide interphase for SiC/SiC f composites was developed using the sol–gel approach. The morphology, elemental composition, topography, and tensile strength of ZrO 2 coated Nicalon™ CG fibers were examined using scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), atomic force microscopy (AFM), and single filament tensile strength analysis as a function of the number of coats. The interfacial frictional stress values of the SiC/SiC f and SiC/(ZrO 2) n/SiC f minicomposites were evaluated using micro indentation tests. It was shown that the presence of multiple ZrO 2 coating on Nicalon™ CG promotes decoupling of the fibers from the matrix and frictional pullout, with the fiber sliding pressure decreases as a number of coats increase. Due to strong bonding at the fiber/coating and the matrix/coating boundaries, on the one hand, and weak bonding between interfacial layers, on the other hand, debonding and sliding occur within the interphase. Thus, the fiber/matrix decoupling in SiC/(ZrO 2) n/SiC f minicomposites can be regulated by designing the multiple ZrO 2 interphase.