多壁碳纳米管-有机蒙脱土协同增韧环氧树脂

采用机械搅拌和离心分散的方法制备了多壁碳纳米管-有机蒙脱土/环氧树脂复合材料。X射线衍射分析表明,当有机蒙脱土含量为2 wt%时, 蒙脱土在树脂体系中能够形成离散性结构。断裂韧性测试结果表明,多壁碳纳米管和有机蒙脱土的混杂对环氧树脂具有协同增韧的作用。当有机蒙脱土含量为2 wt%,多壁碳纳米管含量为0.1 wt%时,所得复合材料的断裂韧性是纯环氧树脂的1.77倍,是2 wt%有机蒙脱土/环氧树脂复合材料的1.45倍,是0.1 wt%多壁碳纳米管/环氧树脂复合材料的1.39倍。扫描电镜分析表明,多壁碳纳米管在环氧树脂体系中分散均匀,并与有机蒙脱土片层形成了一定程度的相互穿插和咬合,多壁碳纳米管与有机蒙脱土协同增韧的主要原因是微裂纹增韧、剪切屈服与纤维拔出。      

Temperature dependence of fracture toughness of silica/epoxy composites: Related to microstructure of nano- and micro-particles packing

Temperature dependence of the fracture toughness of epoxy composites reinforced with nano- and micro-silica particles was evaluated. Epoxy composites containing varied composition ratios Φ_SP of spherical nano- and micro-silica particles, 240 nm and 1.56 μm, were prepared at a fixed volume fraction (V_P = 0.30). The thermo-viscoelasticity and fracture toughness of the composites and neat epoxy were measured at 143 K, 185 K, 228 K, 296 K, 363 K, and 399 K. Experimental results revealed that fracture toughness strongly depended on the microstructure of nano- and micro-particles bidispersion as well as its interactions with the matrix at all temperature, but depended on toughened matrix due to increase in mobility of matrix at the relaxation temperatures.     

Fracture mechanisms of epoxy filled with ozone functionalized multi-wall carbon nanotubes

This work focused on the fracture mechanisms and reinforcing effects of ozone-treated multi-walled carbon nanotubes (MWCNTs) in epoxy matrix. Ozone functionalization of MWCNTs was found to be of help for a better dispersion and stronger interfacial bonding with epoxy matrix, which in turn improve the strength and fracture toughness of the resin. The MWCNT/epoxy composites showed complicated failure modes than the conventional fibrous composites, which have been quantitatively investigated and correlated with the fracture toughness of the nanocomposites studied.     

A comparative study of the electrical and mechanical properties of epoxy nanocomposites reinforced by CVD- and arc-grown multi-wall carbon nanotubes

In this study, three different types of multi-wall carbon nanotubes (MWCNTs) were compared as nanostructured reinforcements in epoxy polymers: commercially available CVD-MWCNTs, synthesised in an industrial process, aligned-CVD-MWCNTs and arc-grown MWCNTs, both obtained from a lab-scale processes. The nanocomposite properties were characterised by means of electron microscopy, rheological, electrical and mechanical methods. Industrial CVD-MWCNTs are favourable for the implication of an electrical conductivity in the epoxy due to their high tendency to form conducting networks. The less entangled structure of aligned-CVD-MWCNTs turns out to be favourable for an easy dispersion and low viscosity in epoxy at similar conductivities compared to the CVD-MWCNTs. Additionally, they provide the highest increase in fracture toughness (∼17%). Arc-grown MWCNTs do not offer any electrical conductivity in epoxy without sufficient purification methods. Their high level of impurities and short length further complicate the transfer of their good electrical and mechanical properties into the nanocomposite.     

Mixture law including particle-size effect on fracture toughness of nano- and micro-spherical particle-filled composites

The effects of particle diameter and volume fraction on fracture toughness of nano- and micro-spherical particle-filled composites were investigated. The purpose was to create a mixture law of fracture toughness based on experimental results of spherical silica particle–filled epoxy composites and a theoretical approach. The fracture toughness of composites was found to be tailored independently by exchanging different particle sizes, and elastic and viscoelastic properties were found to be governed by the volume fraction of the particles. In a theoretical analysis, a mixture law of fracture toughness, composed of the elastic moduli, diameter, and volume fraction of particles and the elastic moduli of matrix resins was proposed. Its validity was demonstrated in a comparison with the experimental results.     

The thermal conductivity of embedded nano-aluminum nitride-doped multi-walled carbon nanotubes in epoxy composites containing micro-aluminum nitride particles

Amino-functionalized nano-aluminum nitride (nano-AlN) particles were doped onto the surfaces of chlorinated multi-walled carbon nanotubes (MWCNTs) to act as fillers in thermally conducting composites. These synthesized materials were embedded in epoxy resin. Then, the untreated micro-aluminum nitride (micro-AlN) particles were added to this resin, whereby the composites filled with nano-AlN-doped MWCNTs (0, 0.5, 1, 1.5, 2 wt%) and micro-AlN (25.2, 44.1, 57.4 vol%) were fabricated. As a result, the thermal diffusivity and conductivity of all composites continuously improved with increasing nano-AlN-doped MWCNT content and micro-AlN filler loading. The thermal conductivity reached its maximum, which was 31.27 times that of the epoxy alone, when 2 wt% nano-AlN-doped MWCNTs and 57.4 vol% micro-AlN were added to the epoxy resin. This result is due to the high aspect ratio of the MWCNTs and the surface polarity of the doped nano-AlN and micro-AlN particles, resulting in the improved thermal properties of the epoxy composite.     

Modification of surface functionality of multi-walled carbon nanotubes on fracture toughness of basalt fiber-reinforced composites

In this work, we studied the influence of surface functionality of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties of basalt fiber-reinforced composites. Acid and base values of the MWCNTs were determined by Boehm's titration technique. The surface properties of the MWCNTs were determined FT-IR, and XPS. The mechanical properties of the composites were assessed by measuring the interlaminar shear stress, fracture toughness, fracture energy, and impact strength. The chemical treatments led to a change of the surface characteristics of the MWCNTs and of the mechanical interfacial properties of MWCNTs/basalt fibers/epoxy composites. Especially the acid-treated MWCNTs/basalt fibers/epoxy composites had improved mechanical properties compared to the base-treated and non-treated MWCNTs/basalt fibers/epoxy composites. These results can probably be attributed to the improved interfacial bonding strength resulting from the improved dispersion and interfacial adhesion between the epoxy resin and the MWCNTs.     

Interconnected multi-walled carbon nanotubes reinforced polymer-matrix composites

A modified method for interconnecting multi-walled carbon nanotubes (MWCNTs) was put forward. And interconnected MWCNTs by reaction of acyl chloride and amino groups were obtained. Scanning electron microscopy shows that hetero-junctions of MWCNTs with different morphologies were formed. Then specimens of pristine MWCNTs, chemically functionalized MWCNTs and interconnected MWCNTs reinforced epoxy resin composites were fabricated by cast moulding. Tensile properties and fracture surfaces of the specimens were investigated. The results show that, compared with pristine MWCNTs and chemically functionalized MWCNTs, the chemically interconnected MWCNTs improved the fracture strain and therefore the toughness of the composites significantly.     

Fabrication and mechanical properties of well-dispersed multiwalled carbon nanotubes/epoxy composites

Multiwalled carbon nanotubes (MWCNTs)/epoxy nanocomposites were fabricated by using ultrasonication and the cast molding method. In this process, MWCNTs modified by mixed acids were well dispersed and highly loaded in an epoxy matrix. The effects of MWCNTs addition and surface modification on the mechanical performances and fracture morphologies of composites were investigated. It was found that the tensile strength improved with the increase of MWCNTs addition, and when the content of MWCNTs loading reached 8 wt.%, the tensile strength reached the highest value of 69.7 MPa. In addition, the fracture strain also enhanced distinctly, implying that MWCNTs loading not only elevated the tensile strength of the epoxy matrix, but also increased the fracture toughness. Nevertheless, the elastic modulus reduced with the increase of MWCNTs loading. The reasons for the mechanical property changes are discussed.     

Influence of ultrasonic dual mixing on thermal and tensile properties of MWCNTs-epoxy composite

Multiwalled carbon nanotubes (MWCNTs) reinforced epoxy based composites were fabricated by using an innovative ultrasonic dual mixing (UDM) process consists of ultrasonic mixing with simultaneous magnetic stirring. The effect of addition of varying amount of MWCNTs on thermal stability and tensile properties of the epoxy based composite has been investigated. It is found that the thermal stability, tensile strength and toughness of the epoxy base improves with the increase of MWCNTs addition up to 1.5 wt.% and UDM processing at certain capacity of the system. Tensile tests and thermal gravimetric analysis (TGA) were performed on each group of composites containing different amount of MWCNTs to determine their mechanical and thermal properties respectively. The dispersion of 1.5 wt.% MWCNTs fillers in epoxy nanocomposites was studied by transmission electron microscopy (TEM) as well as by field emission scanning electron microscopy (FESEM) applied on their tensile fracture surface.     

CF/EP composite laminates with carbon black and copper chloride for improved electrical conductivity and interlaminar fracture toughness

An experimental study was conducted to improve the electrical conductivity of continuous carbon fibre/epoxy (CF/EP) composite laminate, with simultaneous improvement in mechanical performance, by incorporating nano-scale carbon black (CB) particles and copper chloride (CC) electrolyte into the epoxy matrix. CF/EP laminates of 65 vol.% of carbon fibres were manufactured using a vacuum-assisted resin infusion (VARI) technique. The effects of CB and the synergy of CB/CC on electrical resistivity, tensile strength and elastic modulus and fracture toughness (K_IC) of the epoxy matrix were experimentally characterised, as well as the transverse tensile modulus and strength, Mode I and Mode II interlaminar fracture toughness of the CF/EP laminates. The results showed that the addition of up to 3.0 wt.% CB in the epoxy matrix, with the assistance of CC, noticeably improved the electrical conductivity of the epoxy and the CF/EP laminates, with mechanical performance also enhanced to a certain extent.     

Fracture toughness and fatigue life of MWCNT/epoxy composites

The present work experimentally characterizes the mode-I fracture toughness and stress–life curve of multi-walled carbon nanotube-(MWCNT-)reinforced epoxy-matrix composites. The effects of carbon nanotube weight fraction and voids on the composite fracture toughness are studied. The average fracture toughness of 1 wt%- and 3 wt%-MWCNT/epoxy composites is 1.29 and 1.62 times of that of pure epoxy, respectively. The 0.5 wt%-MWCNT/epoxy composites’ fatigue lives are 10.5 and 9.3 times of the average fatigue life of neat epoxy, when they are subjected to cyclic loadings with stress amplitudes of 8.67 MPa and 11.56 MPa, respectively. The micrographs indicate that the separation and uniform distribution of MWCNTs in the matrix and the formation of voids significantly affect the fracture and fatigue behavior of MWCNT-reinforced composites.     

Effects of carbon nanotube alignment on electrical and mechanical properties of epoxy nanocomposites

This paper reports the alignment of multi-walled carbon nanotubes (MWCNTs) in an epoxy matrix as a result of DC electric fields applied during composite curing. Optical microscopy and polarized Raman spectroscopy are used to confirm the CNT alignment. The alignment of CNTs gives rise to much improved electrical conductivity, elastic modulus and quasi-static fracture toughness compared to those with CNTs of random orientation. An extraordinarily low electrical percolation threshold of about 0.0031 vol% is achieved when measured along the alignment, which is more than one order of magnitude lower than 0.034 vol% with random orientation or that measured perpendicular to the aligned CNTs. The examination of the fracture surfaces identifies pertinent toughening mechanisms in aligned CNT composites, namely crack tip deflection and CNT pullout. The significance of this paper is that the technique employed here can tailor the physical, mechanical and fracture properties of bulk nanocomposites even at a very low CNT concentration.     

多壁巴基纸/环氧复合材料拉伸性能的影响因素

采用抽滤法制备了多壁碳纳米管(MWCNTs)纸(又称巴基纸), 研究了巴基纸增强不同环氧基体复合材料(巴基纸复合材料)的拉伸性能及其断口形貌, 分析了MWCNT含量、 树脂基体拉伸性能以及巴基纸与树脂的界面黏附作用对复合材料拉伸性能的影响。结果表明: 在MWCNT质量分数小于39.1%范围内, 增加碳纳米管含量, 可显著提高巴基纸/环氧复合材料的拉伸性能; 巴基纸/环氧复合材料的拉伸强度和模量与树脂基体的性能密切相关, 其拉伸破坏形式受基体的脆韧性影响显著; 相比较而言, 巴基纸与树脂间的黏附功对巴基纸/环氧复合材料拉伸性能的影响不明显。     

电场诱导多壁碳纳米管有序排列对多壁碳纳米管/环氧树脂复合材料性能的影响

采用交流（AC）电场诱导法制备了多壁碳纳米管（MWCNTs）均匀分散且定向有序排列的MWCNTs/环氧树脂复合材料。采用SEM、偏振拉曼光谱等研究了电场强度、MWCNTs含量、加电时间及温度（黏度）等因素对MWCNTs定向排列的影响,讨论了MWCNTs有序排列对MWCNTs/环氧树脂复合材料电学和力学性能的影响。结果表明：MWCNTs沿电场方向有序排列;MWCNTs/环氧树脂复合材料施加AC电场后的拉曼强度明显高于未施加电场的情况;当MWCNTs含量从0wt%增加到0.025wt%时,MWCNTs/环氧树脂复合材料导电率从2.3×10^-12 S/cm增加到1.3×10^-8 S/cm,增加了约4个数量级;MWCNTs含量为2.5wt%时,MWCNTs/环氧树脂复合材料拉伸强度提高了26.3%。     

Non-stoichiometric curing effect on fracture toughness of nanosilica particulate-reinforced epoxy composites

Non-stoichiometric curing effects on the fracture toughness behaviors of nanosilica particulate-reinforced epoxy composites were experimentally investigated in this study by comparing them with bending strengths to take into consideration the effect of interaction between nanoparticles and network structures in matrix resins. The matrixes were prepared by curing them with an excess mixture of diglycidyl ether of bisphenol A-type epoxy resin as the curing agent for the stoichiometric condition. The volume fractions of the silica particles with a median diameter of 240 nm were constantly 0.2 for all composites. The neat epoxy resins and the composites were cured non-stoichiometrically to change the crosslinking densities of the neat epoxy resins and the matrix resins of the composites within 2740–490 mol/m³. The fracture toughnesses and bending strengths of the composites and the neat epoxy resins strongly depended on the crosslinking densities in the resins. Although the fracture toughness decreased monotonously from that of the stoichiometrically cured resins as the crosslinking density decreased, the fracture toughnesses of composites were largest at a slightly lower crosslinking density of approximately 2490 mol/m³ from the stoichiometric condition of 2740 mol/m³. The fracture toughness and the bending strength were improved for crosslinking densities higher than 2000 mol/m³ by adding particles. At crosslinking density lower than 2000 mol/m³, the particles worked against the mechanical properties as defects in matrix resins.     

Fracture mechanisms of epoxy-based ternary composites filled with rigid-soft particles

Epoxy composites filled with different amounts of aggregate-free silica nanoparticles and phase-separated submicron rubber particles were fabricated to study the synergistic effect of multi-phase particles on mechanical properties of the composites. Compared with binary composites with single-phase particles, the ternary composites with both rigid and soft particles offer a good balance in stiffness, strength and fracture toughness, showing capacities in tailoring the mechanical properties of modified epoxy resins. It was observed that debonding of silica nanoparticles from matrix in the ternary composites was less pronounced than that in the binary composites. Moreover, the rubber particles became smaller and their shape tends to be irregular, affected by the presence of rigid silica nanoparticles. The toughening mechanisms in the epoxy composites were evaluated, and the enlarged plastic deformation around the crack tip, induced by the combination of rigid and soft particles, seems to be a dominant factor in enhancing fracture toughness of the ternary composites.     

Transparent,electrically conductive,and flexible films made from multiwalled carbon nanotube/epoxy composites

Optically transparent, conductive, and mechanically flexible epoxy thin films are produced in the present study. Two types of multiwalled carbon nanotubes (MWCNTs) with different aspect ratios are dispersed in epoxy resin through an ultrasonication process. The MWCNT content is varied during the preparation of the thin films. The light transmittance and electrical conductivity of the thin films are characterized. Results show that composites containing MWCNTs with a lower aspect ratio exhibit enhanced electrical conductivity compared to those with a higher aspect ratio. A sheet resistance as low as 100 Ω/sq with nearly 60% optical transparency in 550 nm is achieved with the addition of MWCNTs in epoxy. In summary, transparent, conductive, and flexible MWCNT/epoxy thin films are successfully produced, and the properties of such films are governed by the aspect ratio and content of MWCNTs.     

Effect of hybridization of liquid rubber and nanosilica particles on the morphology, mechanical properties, and fracture toughness of epoxy composites

A liquid carboxyl-terminated butadiene–acrylonitrile copolymer (CTBN) and SiO₂ particles in nanosize were used to modify epoxy, and binary CTBN/epoxy composites and ternary CTBN/SiO₂/epoxy composites were prepared using piperidine as curing agent. The morphologies of the composites were observed by scanning electron microscope (SEM) and transmission electron microscope (TEM), and it is indicated that the size of CTBN particles increases with CTBN content in the binary composites, however, the CTBN particle size decreases with the content of nanosilica in the ternary composites. The effects of CTBN and nanosilica particles on the mechanical and fracture toughness of the composites were also investigated, it is shown that the tensile mechanical properties of the binary CTBN-modified epoxy composites can be further improved by addition of nanosilica particles, moreover, obvious improvement in fracture toughness of epoxy can be achieved by hybridization of liquid CTBN rubber and nanosilica particles. The morphologies of the fractured surface of the composites in compact tension tests were explored attentively by field emission SEM (FE-SEM), it is found that different zones (pre-crack, stable crack propagation, and fast crack zones) on the fractured surface can be obviously discriminated, and the toughening mechanism is mainly related to the stable crack propagation zone. The cavitation of the rubber particles and subsequent void growth by matrix shear deformation are the main toughening mechanisms in both binary and ternary composites.     

Mode I interlaminar fracture behavior and mechanical properties of CFRPs with nanoclay-filled epoxy matrix

The mechanical properties and fracture behavior of nanocomposites and carbon fiber composites (CFRPs) containing organoclay in the epoxy matrix have been investigated. Morphological studies using TEM and XRD revealed that the clay particles within the epoxy resin were intercalated or orderly exfoliated. The organoclay brought about a significant improvement in flexural modulus, especially in the first few wt% of loading, and the improvement of flexural modulus was at the expense of a reduction in flexural strength. The quasi-static fracture toughness increased, whereas the impact fracture toughness dropped sharply with increasing the clay content.Flexural properties of CFRPs containing organoclay modified epoxy matrix generally followed the trend similar to the epoxy nanocomposite although the variation was much smaller for the CFRPs. Both the initiation and propagation values of mode I interlaminar fracture toughness of CFRP composites increased with increasing clay concentration. In particular, the propagation fracture toughness almost doubled with 7 wt% clay loading. A strong correlation was established between the fracture toughness of organoclay-modified epoxy matrix and the CFRP composite interlaminar fracture toughness.