Enhanced mechanical properties of multiscale carbon fiber/epoxy composites by fiber surface treatment with graphene oxide/polyhedral oligomeric silsesquioxane

Graphene oxide (GO) and polyhedral oligomeric silsesquioxane (POSS) grafted carbon fiber (CF) was demonstrated to reinforce the mechanical properties of fiber composites. Such a fiber composite was prepared by grafting POSS onto the CF surface using GO as the linkage. The presence of GO linkage and POSS could significantly enhance both the area and wettability of fiber surface, leading to an increase in the interfacial strength between fibers and resin. Compared with the desized CF composites, the grafted CF composites fabricated by compression molding method exhibited 53.05% enhancement in the interlaminar shear strength. The changed surface morphology, surface composition and surface energy were supposed to be related with the interfacial performance of unidirectional composites, as revealed by scanning electron microscopy, atomic force microscope, dynamic contact angle test and X-ray photoelectron microscopy charaterizations.     

Hybrids of carbon nanotubes and graphene/graphene oxide

This paper reviews recent progress in hybrids based on carbon nanotubes (CNTs) and graphene (G) or graphene oxide (GO). The combination of CNTs, including single-walled (SW), double-walled (DW) and multi-walled (MW), and G or GO resulted in various hybrids. CNTs–G/GO hybrid thin films are usually prepared by using solution/suspension casting and layer-by-layer (LbL) deposition, free-standing sheets are fabricated by using vacuum filtration and 3D hierarchical structures are produced by using chemical vapor deposition (CVD). CNTs–G/GO hybrids have also been used as fillers to fabricate polymer composites with synergistic effects. The composites have significantly improved electrical, mechanical and thermal properties, which make them very useful for various potential applications, such as transparent electrodes replacing ITO, electrodes for supercapacitors, lithium-ion batteries and dye-sensitized solar cells.     

Designed fabrication of hierarchical porous carbon nanotubes/graphene/carbon nanofibers composites with enhanced capacitive desalination properties

Carbonaceous materials, one of the most important electrode materials for sea water desalination, have attracted tremendous attention. Herein, we develop a facile and effective two-step strategy to fabricate hierarchical porous carbon nanotubes/graphene/carbon nanofibers (CNTs/G/CNFs) composites for capacitive desalination application. Graphite oxide (GO), Ni²⁺, and Co²⁺ are introduced into polyacrylonitrile (PAN) nanofibers by electrospinning method. During the annealing process, the PAN nanofibers are carbonized into CNFs felt, while the CNTs grow in situ on the surface of CNFs and graphite oxide are reduced into graphene simultaneously. Benefiting from the unique hierarchical porous structure, the as-prepared CNTs/G/CNFs composites have a large specific surface area of 223.9 m² g^?1 and excellent electrical conductivity. The maximum salt capacity of the composites can reach to 36.0 mg g^?1, and the adsorbing capability maintains a large retention of 96.9% after five cycles. Moreover, the effective deionization time of the CNTs/G/CNFs composites lasts more than 30 min, much better than the commercial carbon fibers (C-CFs) and graphene/carbon nanofibers (G/CNFs) composites. Results suggest that the designed hierarchical porous CNTs/G/CNFs architecture could enhance the capacitive desalination properties of electrode materials. And the possible adsorption mechanism of the novel electrode materials is proposed as well.     

Combination effect of physical drying with chemical characteristic of carbon nanotubes on through-thickness properties of carbon fiber/epoxy composites

The present work studied the combination effect of physical drying with chemical modification of carbon nanotubes (CNTs) on some through-thickness properties of carbon fiber/epoxy composites. Different drying methods of heat drying and freeze drying were utilized to affect CNT organization form in carbon fiber/CNTs preforms and composites: The adoption of heat-drying method made CNTs more inclined to form aggregates accompanied with randomly scattered CNTs, while continuous CNT networks could always be assembled when freeze drying method was employed. The formation mechanism of such CNT networks was discussed, and could be described as “freeze drying within confined space.” Chemical characteristic of CNTs was controlled by choosing different solutions of non-functionalized CNTs (NOCNTs) or hydroxyl-modified CNTs (OHCNTs). As a consequence, CNT networks modified composites, especially that with OHCNTs formed networks, displayed significantly better electrical performance than composites with CNT aggregates and scattered CNTs; NOCNT networks and scattered OHCNTs made the corresponding composites possess higher interlaminar shear strength (ILSS) value, whereas OHCNT networks impaired ILSS while enhancing flexural strength and modulus of composites.     

Preparation of carbon nanotube/copper/carbon fiber hierarchical composites by electrophoretic deposition for enhanced thermal conductivity and interfacial properties

A facile electrophoretic deposition method was proposed to deposit copper (Cu) and carbon nanotubes (CNTs) on the surface of carbon fiber (CF) to improve the thermal conductivity and interfacial properties of carbon fiber-reinforced polymer (CFRP) composites. Surface morphologies, crystallographic properties, thermal conductivity, interlaminar shear strength (ILSS) and element distribution of the composites were characterized by scanning electron microscopy (SEM), X-ray diffraction, thermal constant analysis, short-beam bending tests and SEM energy-dispersive X-ray diffractometer (SEM–EDX), respectively. The results indicate that the presence of Cu and CNTs generated networks and bridges with each other, which produced continuous heat conduction pathways and significantly enhanced both the specific surface area and roughness of the fiber surface. These pathways obviously promoted an improvement in the thermal and interfacial properties. The thermal conductivity and ILSS of the CNTs–Cu–CF/epoxy composites increased by 292 and 39.5%, respectively, compared with CF/epoxy composites. Therefore, this method is anticipated to be utilized in the future fabrication of multifunctional CFRP composites.     

Multifold interface and multilevel crack propagation mechanisms of graphene oxide/polyurethane/epoxy membranes interlaminar-toughened carbon fiber-reinforced polymer composites

Graphene oxide/polyurethane/epoxy (GO/PU/EP) membranes were directly fabricated by functionalization of graphene oxide with epoxy-grafted polyurethane (GO-UE), and the interface correlation and crack propagation mechanisms in GO/PU/EP membranes interlaminar-toughened carbon fiber-reinforced polymer composites were investigated. The functionalized GO-UE with corrugation and scrolling nature of graphene sheets was evenly dispersed in GO/PU/EP membranes below 0.50 wt% loading. Mode I fracture toughness, flexural properties and interlaminar shear strength of GO/PU/EP membranes-toughened composites were enhanced in comparison with untoughened composites and PU/EP membranes-toughened composites, which was ascribed to the multifold interface bonding between the GO-UE layers, epoxy matrix and carbon fiber. Schematic models of multilevel crack propagations were proposed based on different crack extension directions to GO-UE and the morphology evolutions of GO-UE in the interlaminar region and at the carbon fiber interface in toughened composites, which highlighted the toughening mechanisms of crack pinning, crack deflection and separation between GO-UE layers.     

Interfacial shear strength of a glass fiber/epoxy bonding in composites modified with carbon nanotubes

In recent years, carbon nanotubes (CNTs) grown on fibers have attracted a lot of interest as an additional reinforcing component in conventional fiber-reinforced composites to improve the properties of the fiber/matrix interface. Due to harsh growth conditions, the CNT-grafted fibers often exhibit degraded tensile properties. In the current study we explore an alternative approach to deliver CNTs to the fiber surface by dispersing CNTs in the fiber sizing formulation. This route takes advantage of the developed techniques for CNT dispersion in resins and introduces no damage to the fibers. We focus on unidirectional glass fiber/epoxy macro-composites where CNTs are introduced in three ways: (1) in the fiber sizing, (2) in the matrix and (3) in the fiber sizing and matrix simultaneously. Interfacial shear strength (IFSS) is investigated using single-fiber push-out microindentation. The results of the test reveal an increase of IFSS in all three cases. The maximum gain (over 90%) is achieved in the composite where CNTs are introduced solely in the fiber sizing.     

Effect of electrophoretically deposited carbon nanotubes on the interface of carbon fiber reinforced epoxy composite

The interface between reinforcing fiber and matrix is a crucial element in composite performance. Homogeneous and interconnected carbon nanotubes (CNTs) were deposited onto the surface of carbon fibers to produce multiscale reinforcement by electrophoretic deposition (EPD). Single fiber tensile tests showed that the tensile strength and Weibull modulus of the resulting multiscale materials were increased by 16 and 41%, respectively. Compared with as-received carbon fibers, CNTs-deposited carbon fibers provided the decreased surface energy by 20% and the increased adhesion work by 22% using modified Wilhelmy method. Results from single fiber pull-out testing showed that a significant improvement (up to 68.8%) of interfacial shear strength was obtained for the composites containing by CNTs/Carbon fiber multiscale reinforcement. All results strongly suggest that EPD process can provide a feasible platform for improving interface properties of advanced composites.     

A Novel Multiscale Reinforcement by In-Situ Growing Carbon Nanotubes on Graphene Oxide Grafted Carbon Fibers and Its Reinforced Carbon/Carbon Composites with Improved Tensile Properties

In-situ growing carbon nanotubes(CNTs)directly on carbon?bers(CFs)always lead to a degraded tensile strength of CFs and then a poor?ber-dominated mechanical property of carbon/carbon composites(C/Cs).To solve this issue,here,a novel carbon?ber-based multiscale reinforcement is reported.To synthesize it,carbon?bers(CFs)have been?rst grafted by graphene oxide(GO),and then carbon nanotubes(CNTs)have been in-situ grown on GO-grafted CFs by catalytic chemical vapor deposition.Characterizations on this novel reinforcement show that GO grafting cannot only nondestructively improve the surface chemical activity of CFs but also protect CFs against the high-temperature corrosion of metal catalyst during CNT growth,which maintains their tensile properties.Tensile property tests for unidirectional C/Cs with different preforms show that this novel reinforcement can endow C/C with improved tensile properties,32% and 87%higher than that of pure C/C and C/C only doped with in-situ grown CNTs.This work would open up a possibility to fabricate multiscale C/Cs with excellent global performance.     

Application of continuously-monitored single fiber fragmentation tests to carbon nanotube/carbon microfiber hybrid composites

To assess the effect of carbon nanotube (CNT) grafting on interfacial stress transfer in fiber composites, CNTs were grown upon individual carbon T-300 fibers by chemical vapor deposition. Continuously-monitored single fiber composite (SFC) fragmentation tests were performed on both pristine and CNT-decorated fibers embedded in epoxy. The critical fragment length, fiber tensile strength at critical length, and interfacial shear strength were evaluated. Despite the fiber strength degradation resulting from the harsh CNT growth conditions, the CNT-modified fibers lead to a twofold increase in interfacial shear strength which correlates with the nearly threefold increase in apparent fiber diameter resulting from CNT grafting. These observations corroborate recently published studies with other CNT-grafted fibers. An analysis of the relative contributions to the interfacial strength of the fiber diameter and strength due to surface treatment is presented. It is concluded that the common view whereby an experimentally observed shorter average fragment length leads to a stronger interfacial adhesion is not necessarily correct, if the treatment has changed the fiber tensile strength or its diameter.     

Using silane-functionalized graphene oxides for enhancing the interfacial bonding strength of carbon/epoxy composites

Silane-functionalized graphene oxides (sGOs) were fabricated with four different self-assembled monolayers (SAMs) to reinforce an epoxy adhesive, with the aim of improving the bonding strength of carbon/epoxy composites. The oxygen-containing groups on the surface of graphene oxide (GO) were converted by the SAMs to amine, epoxy, or alkyl groups. The successful reaction between the silane molecules of the SAMs and functional groups of GO was evidenced by the results of different characterization methods such as Fourier transform infrared spectroscopy. It was found that the average thickness of the sGO flakes was higher than that of GO flakes. The bonding strength of a carbon fiber/epoxy composite, tested with a single lap joint bonded with an epoxy adhesive, was increased by 53% after the addition of a sGO that contained amine groups. These results show that sGOs, especially those containing amine functional groups, can strengthen the interfacial bonding between the carbon fibers and epoxy adhesive.     

Interfacial microstructure and mechanical properties of carbon fiber composites by fiber surface modification with poly(amidoamine)/polyhedral oligomeric silsesquioxane

Polyhedral oligomeric silsesquioxane (POSS) was grafted onto carbon fiber surface using poly(amidoamine) (PAMAM) as a novel coupling agent at mild reaction conditions. Firstly, the reinforcement was designed with propagation of PAMAM on the fiber surface by in situ polymerization to improve the surface activities of carbon fiber. Secondly, the POSS further grafted on the fiber could significantly enhance fiber surface energy and wettability, which would greatly increase the interfacial strength of fiber-matrix. The microstructure and mechanical properties of carbon fiber and the resulting composites were investigated. The results indicated that PAMAM and POSS, which could significantly increase the surface roughness and wettability of carbon fiber, were successfully grafted on the fiber surface. Compared with the desized fiber composites, the interlaminar shear strength and the interfacial shear strength of the modified carbon fiber composites increased by 48% and 89%, respectively.     

Interfacially reinforced methylphenylsilicone resin composites by chemically grafting multiwall carbon nanotubes onto carbon fibers

Both silane and multiwall carbon nanotubes (CNTs) were grafted successfully onto carbon fibers (CFs) to enhance the interfacial strength of CFs reinforced methylphenylsilicone resin (MPSR) composites. The microstructure, interfacial properties, impact toughness and heat resistance of CFs before and after modification were investigated. Experimental results revealed that CNTs were grafted uniformly onto CFs using 3-aminopropyltriethoxysilane (APS) as the bridging agent. The wettability and surface energy of the obtained hybrid fiber (CF-APS-CNT) were increased obviously in comparison with those of the untreated-CF. The CF-APS-CNT composites showed simultaneously remarkable enhancement in interlaminar shear strength (ILSS) and impact toughness. Moreover, the interfacial reinforcing and toughening mechanisms were also discussed. In addition, Thermogravimetric analysis and thermal oxygen aging experiments indicated a remarkable improvement in the thermal stability and heat oxidation resistance of composites by the introduction of APS and CNTs. We believe the facile and effective method may provide a novel interface design strategy for developing multifunctional fibers.     

碳纳米管/碳纤维/环氧树脂复合材料研究

制备了碳纳米管(CNTs)/碳纤维(CF)/环氧树脂(EP)三元复合材料。研究了CNTs含量对复合材料层间剪切强度、弯曲强度和弯曲模量的影响,并采用场发射扫描电镜分析了CNTs在基体树脂中的分散情况。结果表明:复合材料性能的变化源自于CNTs在基体树脂中的分散状态。当CNTs含量为0.2%(wt,下同)时,复合材料剪切强度和弯曲强度达到最大值,分别为99.2MPa和1811.4MPa,但其弯曲模量下降了8.7GPa。当CNTs添加量达到1%时,其弯曲模量达到135.9GPa,较未加入CNTs时提高了11.1%,层间剪切强度和弯曲强度分别降低了5.5MPa和359.5MPa。     

碳纳米管加入方式对碳纤维/环氧树脂复合材料层间性能的影响

针对碳纤维/环氧树脂预浸料,对比了直接在树脂中加入碳纳米管(CNTs)后制备预浸料以及将CNTs喷涂在预浸料表面2种CNTs加入方式对CNTs-碳纤维/环氧树脂复合材料层合板I型与II型层间断裂韧性及层间剪切强度的影响。通过对树脂黏度、固化反应以及玻璃化转变温度的考察,分析了CNTs含量对树脂性能的影响,考察了添加方法对CNTs长度与形态的影响。分析了2种CNTs加入方式对CNTs-碳纤维/环氧树脂层合板断裂韧性及层间剪切强度的改善效果与作用规律。结果表明:CNTs的加入使树脂的黏度提高,固化反应程度下降;2种分散方法对CNTs的长度与形态无明显影响;直接在树脂中加入CNTs对CNTs-碳纤维/环氧树脂复合材料I型与II型层间断裂韧性的提高效果低于在碳纤维/环氧树脂预浸料表面喷涂CNTs的方式,后者的CNTs利用率较高;由于CNTs团聚及对树脂固化反应的影响,CNTs含量过高会使得其对CNTs-碳纤维/环氧树脂层合板的增韧效果下降。     

Hybrid carbon nanotube–carbon fiber composites with improved in-plane mechanical properties

In this study carbon nanotubes (CNTs) were grown on carbon fibers to enhance the in-plane and out-of-plane properties of fiber reinforced polymer composites (FRPs). A relatively low temperature synthesis technique was utilized to directly grow CNTs over the carbon fibers. Several composites based on carbon fibers with different surface treatments (e.g. growing CNTs with different lengths and distribution patterns and coating the fibers with a thermal barrier coating (TBC) layer) were fabricated and characterized via on- and off-axis tensile tests. The on-axis tensile strength and ductility of the hybrid FRPs were improved by 11% and 35%, respectively, due to the presence of the TBC and the surface grown CNTs. This configuration also exhibited 16% improvement on the off-axis stiffness. Results suggest that certain CNT growth patterns and lengths are more pertinent than the other surface treatments to achieve superior mechanical properties.     

电泳沉积氧化石墨烯的碳纤维表面改性及其增强环氧树脂复合材料界面性能

采用超声辅助电泳沉积法,以异丙醇作为溶剂,在连续碳纤维(CF)表面沉积一层氧化石墨烯(GO),对CF表面进行改性。再经200℃高温处理来增强(GO)与CF之间的黏合性,从而增加CF/环氧树脂(EP)复合材料的界面结合强度。利用SEM和AFM对改性前后CF的表面形貌及微观结构变化进行了表征,通过XPS对改性前后CF表面官能团的变化进行了检测。结果表明,在CF表面沉积GO并经200℃处理后,有效地部分还原了GO(RGO),填补或桥联了CF表面缺陷,使改性后CF的拉伸强度提高了34.58%。同时,高温处理使RGO与CF之间生成牢固的化学键,从而提高了RGO与CF之间的结合强度,最终使RGO-CF/EP复合材料的界面剪切强度(IFSS)提高了69.9%。      

碳纤维上原位生长碳纳米管对C/C复合材料弯曲性能的影响

以碳毡为基底原位生长了碳纳米管（CNTs）,借助化学气相渗透制备了CNTs-C/C复合材料。研究了催化剂含量对碳纳米管生长的影响以及不同含量碳纳米管对C/C复合材料弯曲性能的影响。结果表明：催化剂对CNTs产量影响较大,且含量越多,生成的CNTs量越大;原位生长CNTs引入的催化剂会导致CNTs-C/C复合材料弯曲性能变差;CNTs的加入改变了热解碳的沉积行为,诱导了球状和锥状小尺寸热解碳的形成,减少了微裂纹的出现。适量CNTs能提高C/C复合材料的弯曲强度和模量,并改善材料的断裂行为。     

Influence of multi-walled carbon nanotubes on electrochemical performance of transparent graphene electrodes

In this work, carbon-carbon nanocomposites as transparent electrodes were prepared by a chemical reduction of graphite oxide (GO) and multi-walled carbon nanotubes (MWNTs). The electric, optical, and electrochemical properties of graphene-MWNT nanocomposites (G-MCs) were investigated as a function of the MWNT content. It was found that chemically bonded G-MCs were successfully formed with a reduction of the functional groups of the GO and acid-treated MWNTs, resulting in the conjugation of 1D MWNTs onto a 2D graphene surface. The electrical conductivity of the graphene was significantly enhanced by introducing the MWNTs. In addition, the G-MCs showed improved current density and high efficiency compared with graphene alone. This indicated that the improved electrochemical performance of the G-MCs can be attributed to the increase in the activity and electrical conductivity enhanced by π-π interaction between graphene and MWNTs.     

High-cycle fatigue of hybrid carbon nanotube/glass fiber/polymer composites

Glass fiber polymer composites have high strength, low cost, but suffer from poor performance in fatigue. Mechanisms for high-cycle (>10⁴ cycles) fatigue failure in glass fiber composites consist primarily of matrix-dominated damage accumulation and growth that coalesce and propagate into the fibers resulting in ultimate fatigue failure. This investigation shows that the addition of small volume fractions of multi-walled carbon nanotubes (CNTs) in the matrix results in a significant increase in the high-cycle fatigue life. Cyclic hysteresis measured over each cycle in real time during testing is used as a sensitive indicator of fatigue damage. We show that hysteresis growth with cycling is suppressed when CNTs are present with resulting longer cyclic life. Incorporating CNTs into the matrix tends to inhibit the formation of large cracks since a large density of nucleation sites are provided by the CNTs. In addition, the increase in energy absorption from the fracture of nanotubes bridging across nanoscale cracks and nanotube pull-out from the matrix is thought to contribute to the higher fatigue life of glass composites containing CNTs. High-resolution scanning electron microscopy suggests possible mechanisms for energy absorption including nanotube pull-out and fracture. The distributed nanotubes in the matrix appear to inhibit damage propagation resulting in overall improved fatigue strength and durability.