表面官能团化多壁碳纳米管/环氧树脂复合材料的制备及性能

本文首先将多壁碳纳米管(MWNT)进行表面化学修饰,接入羧基、胺基等官能团,采用红外光谱进行了表征.以纯化后的MWNT和表面化学修饰的MWNT作为填料,制备了MWNT /环氧树脂复合材料,研究了MWNT的加入对环氧树脂的力学性能、电学性能、热稳定性和玻璃化转变温度等的影响,并利用场发射电镜观察了胺基化MWNT在环氧树脂基体中的分散情况.     

Role of interfacial effects in carbon nanotube/epoxy nanocomposite behavior

The interfacial effects are critical to understand the nanocomposite behavior based on polymer matrices. These effects are dependent upon the morphology of carbon nanotubes, the type of used polymer and the processing technique. Indeed, we show that the different parameters, as the eventual surfactant use, the ultrasonic treatment and shear mixing have to be carefully examined, in particular, for nanotube dispersion and their possible alignment. A series of multiwalled nanotubes (MWNT) have been mixed with a regular epoxy resin under a controlled way to prepare nanocomposites. The influence of nanotube content is examined through helium bulk density, glass transition temperature of the matrix and direct current electrical conductivity measurements. These results, including the value of the percolation threshold, are analyzed in relationship with the mesostructural organization of these nanotubes, which is observed by standard and conductive probe atomic force microscopy (AFM) measurements. The wrapping effect of the organic matrix along the nanotubes is evidenced and analyzed to get a better understanding of the final composite characteristics, in particular, for eventually reinforcing the matrix without covalent bonding.     

Time and temperature dependent piezoresistance of carbon nanofiller/polymer composites under dynamic load

In this study, the behaviour of carbon nanotube/epoxy and carbon black/epoxy composites under dynamic load is studied via dynamic mechanical thermal analysis (DMTA) in combination with DC electrical resistivity measurements. DMTA measurements are carried out at fixed temperature whilst the dynamic loading frequency is varied. With this procedure, a loading frequency-dependence of the phase shift between DC electrical resistance and mechanical elongation (δ _R–ε) is observed, although the force and elongation of the sample are still in phase. Moreover, the magnitude of this phase shift, as well as the amplitude of the DC electrical resistance change shows a clear dependence on the initial electrical conductivity of the samples. In addition, temperature sweeps are carried out to investigate the temperature dependency of the piezoresistance of the samples. An abrupt change in their sensitivity is observed as soon as the glass transition of the polymer is reached. However, the trend of the resistance change beyond the glass transition is substantially different between the nanocomposites containing carbon black and carbon nanotubes, revealing a strong influence of the network characteristics on the piezoresistive behaviour of these novel materials.     

Single-walled carbon nanotube incorporated novel three phase carbon/epoxy composite with enhanced properties

In the present work, single-walled carbon nanotubes were dispersed within the matrix of carbon fabric reinforced epoxy composites in order to develop novel three phase carbon/epoxy/single-walled carbon nanotube composites. A combination of ultrasonication and high speed mechanical stirring at 2000 rpm was used to uniformly disperse carbon nanotubes in the epoxy resin. The state of carbon nanotube dispersion in the epoxy resin and within the nanocomposites was characterized with the help of optical microscopy and atomic force microscopy. Pure carbon/epoxy and three phase composites were characterized for mechanical properties (tensile and compressive) as well as for thermal and electrical conductivity. Fracture surfaces of composites after tensile test were also studied in order to investigate the effect of dispersed carbon nanotubes on the failure behavior of composites. Dispersion of only 0.1 wt% nanotubes in the matrix led to improvements of 95% in Young's modulus, 31% in tensile strength, 76% in compressive modulus and 41% in compressive strength of carbon/epoxy composites. In addition to that, electrical and thermal conductivity also improved significantly with addition of carbon nanotubes.     

RTM processing and electrical performance of carbon nanotube modified epoxy/fibre composites

This investigation focuses on nanoparticle filtration in the processing of multiscale carbon and glass fibre composites via resin transfer moulding. Surface modified and unmodified carbon nanotubes (CNTs) were incorporated into a commercial epoxy resin. The dispersion quality was evaluated using electrical measurements of the liquid suspensions. The manufacturing process was adapted to the challenges posed by the modified rheological behaviour of the CNT loaded resin. Nanoparticle filtration was observed; with some of the unmodified systems following so called ‘cake filtration’ behaviour. This resulted in nonlinear flow behaviour that deviated from the ideal response observed in RTM filling in conventional composites. The electrical conductivity of relatively high fibre volume fraction multiscale carbon and glass laminates increased by less than an order of magnitude with the addition of the nanotubes.     

Temperature dependence of electrical conductivity in double-wall and multi-wall carbon nanotube/polyester nanocomposites

The aim of this study is to investigate temperature dependence of electrical conductivity of carbon nanotube (CNT)/polyester nanocomposites from room temperature to 77 K using four-point probe test method. To produce nanocomposites, various types and amounts of CNTs (0.1, 0.3 and 0.5 wt.%) were dispersed via 3-roll mill technique within a specially formulized resin blend of thermoset polyesters. CNTs used in the study include multi walled carbon nanotubes (MWCNT) and double-walled carbon nanotubes (DWCNT) with and without amine functional groups (–NH₂). It was observed that the incorporation of carbon nanotubes into resin blend yields electrically percolating networks and electrical conductivity of the resulting nanocomposites increases with increasing amount of nanotubes. However, nanocomposites containing amino functionalized carbon nanotubes exhibit relatively lower electrical conductivity compared to those with non-functionalized carbon nanotubes. To get better interpretation of the mechanism leading to conductive network via CNTs with and without amine functional groups, the experimental results were fitted to fluctuation-induced tunneling through the barriers between the metallic regions model. It was found that the results are in good agreement with prediction of proposed model.     

Fracture toughness and electrical conductivity of epoxy composites filled with carbon nanotubes and spherical particles

The attainment of both high toughness and superior electrical conductivity of epoxy composites is a crucial requirement in some engineering applications. Herein, we developed a strategy to improve these performances of epoxy by combining the multi-wall carbon nanotubes (MWCNTs) and spherical particles. Two different types of spherical particles i.e. soft submicron-rubber and rigid nano-silica particles were chosen to modify the epoxy/MWCNT composites. Compared with the binary composites with single-phase particles, the ternary composites with MWCNTs and spherical particles offer a good balance in glass transition temperature, electrical conductivity, stiffness and strength, as well as fracture toughness, exhibiting capacities in tailoring the electrical and mechanical properties of epoxy composites. Based on the fracture surface analysis, the complicated interactions between multiscale particles and the relative toughening mechanisms were evaluated to explain the enhancement in fracture toughness of the ternary composites.     

Characterization of damping in carbon-nanotube filled fiberglass reinforced thermosetting-matrix composites

Use of carbon nanotubes as additives to composite parts for the purpose of increased damping has been the subject of much recent attention, owing to their large surface area per weight ratio which provides for frictional losses at the carbon nanotube–resin matrix interface. This article presents an experimental study to quantify the structural damping in composites due to the addition of carbon nanotubes to thermosetting resin systems with and without fiberglass reinforcement. Carbon nanotubes of varying quantity and morphology are ultrasonically dispersed in epoxy resin and are compression molded to form test samples that are used in forced vibration, free vibration with initial tip deflection, and tension tests to determine their damping ratio, specific damping capacity, and Young’s modulus. Results show increased stiffness and specific damping capacity with the addition of carbon nanotubes and particularly increased frictional loss with increasing surface area to weight ratio. The addition of fiberglass reinforcement to composite samples is shown to reduce the effective damping ratio over plain epoxy samples and carbon nanotube-filled epoxy samples.     

The electrical properties of epoxy resin composites filled with Cnts and carbon black

This work introduces an experimental activity related to the realization of an epossidic nanostructured material that develops the function of covering for electronic circuits in aeronautical field. This covering meets the demand of protection of these circuits from possible troubles of electromagnetic nature. In order to realize this covering we used an epoxy resin as matrix (Epon 828) loaded with conductive nanofillers or carbon nanotubes (Cnts). To check the efficiency of the coating we have considered the carbon black, filler widely used as a conductive covering for screenings. We have considered different percentages of the different fillers, precisely 0.1%, 0.25% and 0.5% wt (% valued in comparison to the weight of the resin). From every mixture 12 samples have been obtained (the size of every sample is 10 mm x 10 mm x 10 mm). Every sample has been subjected to electrical measurements, that have concerned the measurement of current intensity and resistance (so as to allow the evaluation of the enhancement of the conductivity), through the application of different values of voltage. The results have demonstrated that the epoxy matrix loaded with Cnts yields higher values of electrical conductivity than the same matrix loaded with carbon black.     

氨基化碳纳米管对交联环氧树脂玻璃化转变温度的影响机制

采用动态力学性能分析和分子动力学模拟相结合的方法研究了氨基化碳纳米管/环氧树脂复合材料的玻璃化转变温度(T_g),并重点分析了界面在影响T_g变化中的作用。实验发现,与纯环氧树脂相比,未改性碳纳米管对环氧树脂的T_g无明显影响,而氨基化碳纳米管使环氧树脂的T_g升高。分子模拟结果显示,在氨基化碳纳米管/环氧树脂复合材料中,当氨基化碳纳米管与环氧树脂基体有共价键连接,碳纳米管与树脂基体间界面结合强,复合材料的T_g显著升高。研究结果表明,在环氧树脂中添加氨基化碳纳米管后,由于碳纳米管上的氨基官能团能参与环氧树脂的交联反应,形成共价键,界面结合强,复合材料的T_g升高。复合材料界面状态不同,T_g的变化情况不同,选择能形成强结合界面的碳纳米管等增强材料可以实现提高树脂基体T_g的目的。     

Multiscale molecular modeling of SWCNTs/epoxy resin composites mechanical behaviour

Atomistic and mesoscale simulations were conducted to estimate the effect of the diameter and weight fraction of single walled carbon nanotubes (SWCNTs) on mechanical behaviour and glass transition temperature (T_g) of SWCNTs reinforced epoxy resin composites. Atomistic periodic systems of epoxy resin and epoxy resin/SWCNTs were built with different weight ratios and were subject of an extensive multistage equilibration procedure. Molecular dynamics simulations were used to estimate glass transition temperature, Young modulus and solubility parameter of epoxy resin and epoxy resin/SWCNTs composites. Dissipative particle dynamics method and Flory–Huggins theory was employed to predict epoxy resin/SWCNTs morphologies. The results show that incorporation of SWCNTs with diameters ranging from 10 to 14 ? has beneficial effect on mechanical integrity and T_g. Overall, the agreement between predicted material properties and experimental data in the literature is very satisfactory.     

Multiscale molecular modeling of SWCNTs/epoxy resin composites mechanical behaviour

Atomistic and mesoscale simulations were conducted to estimate the effect of the diameter and weight fraction of single walled carbon nanotubes (SWCNTs) on mechanical behaviour and glass transition temperature (T_g) of SWCNTs reinforced epoxy resin composites. Atomistic periodic systems of epoxy resin and epoxy resin/SWCNTs were built with different weight ratios and were subject of an extensive multistage equilibration procedure. Molecular dynamics simulations were used to estimate glass transition temperature, Young modulus and solubility parameter of epoxy resin and epoxy resin/SWCNTs composites. Dissipative particle dynamics method and Flory–Huggins theory was employed to predict epoxy resin/SWCNTs morphologies. The results show that incorporation of SWCNTs with diameters ranging from 10 to 14 Ǻ has beneficial effect on mechanical integrity and T_g. Overall, the agreement between predicted material properties and experimental data in the literature is very satisfactory.     

一种玻璃碳制备过程的X射线分析

利用环氧树脂对酚醛树脂的改性制备高密度、高电导率的玻璃碳，利用Ｘ射线广角衍射、小角散射和径向分布函数分析制备过程中结构的变化，并对电导率进行了测试分析，结果表明，前驱体热解制备玻璃碳的过程是微区结构有序化且有序化区域增大的过程，有序化促使了孔洞的形成关长大，以及电导率的增加，内应力的释放是导致体积膨胀原因。     

高能量超声波改性MWCNTs/环氧树脂特性分析

采用高能量超声波与低能量超声波对一种多壁碳纳米管(MWCNTs)/环氧树脂体系进行改性处理,结合流变仪、DSC、FTIR、XPS、XRD、TEM等测试手段,分析了不同超声波处理条件下MWCNTs物理化学特性的变化及其对MWCNTs在环氧树脂中的分散性和相容性的影响,并进一步考察了MWCNTs/环氧树脂体系的耐热性和弯曲性能。实验结果表明:超声波能量不同,MWCNTs的改性效果不同,高能量超声波对MWCNTs有更好的分散效果和分散效率,并能使MWCNTs表面活性增强,而低能量超声波则不明显;添加少量高能量超声波改性的MWCNTs,可以提高环氧树脂的弯曲模量和玻璃化转变温度,表明MWCNTs与基体之间形成了较强的结合界面。     

The effect of boron nitride on electrical conductivity of nanocarbon-polymer composites

The electrical conductivity concentration and temperature dependences of polymer composite materials (CMs) with nanocarbon fillers [graphite nanoplatelets and multi-walled carbon nanotubes (MWCNTs)] were investigated. Epoxy resin modified with organosilicon compound was used as polymer matrix. The content of nanocarbon filler in varied from 1 to 10 wt%. To study of the synergetic properties the additional dispersed dielectric filler—boron nitride (BN) was added to given systems in content of 27 wt%. The electrical resistivity of CMs was investigated in the temperature range of 77–300 K. In the studied CMs the percolation transition at sufficient low filler content (0.01–0.022 vol. fr.) was observed. The values of critical index varied from 3.0 to 5.2. The electrical conductivity of investigated CMs was analyzed in the framework of proposed model that takes into consideration the morphology of filler particles. It was shown that the increase of electrical conductivity of GNP-polymer CM in the presence of BN is attributed to the decrease of contact resistance between filler particles, while for MWCNT-polymer CM is due to the increase of the number of conductive chains in this particular system.     

Experimental study of mechanical and electrical properties of carbon nanofiber/epoxy composites

Epoxy nanocomposites of different content of carbon nanofibers up to 1 wt.% have been fabricated under room temperature and refrigerated curing conditions. The composites were studied in terms of mechanical and electrical properties. Flexural modulus and hardness were found to increase significantly in refrigerated samples due to prevention of aggregates of nanofibers during cure condition. Increase and shifting in G-band by Raman spectra of these samples confirmed stress transfer and reinforcement between epoxy matrix and carbon nanofiber. Electrical conductivity improved by 3–6 orders after infusing carbon nanofibers in insulating epoxy. Room temperature samples acquired higher conductivity that was attributed to network formation by aggregates of nanofibers along the fiber alignment direction as revealed by electron microscopic studies.     

Electrical and thermophysical properties of epoxy/aluminum nitride nanocomposites: Effects of nanoparticle surface modification

The traditional epoxy resin used for electrical and electronic industry has a poor thermal conductivity and no longer meets the increasingly cooling requirements of electric equipments and electronic devices. Ceramic nanoparticles with high thermal conductivity and low dielectric constant represent good candidates to improve the thermophysical properties of epoxy resin. This paper reports the effects of surface modification of AlN nanoparticles on morphology, glass transition, electrical property and thermal conductivity of the epoxy composites. Gamma-aminopropyl triethoxysilane was used as a silane coupling agent for the surface modification of the AlN nanoparticles. It was found that the surface modification of the nanoparticles not only improved the dispersion of the nanoparticles, but also showed an enhancement in electrical and thermophysical properties of the epoxy composites. The surface modification technology presented a strategy to prepare nanocomposites having high thermal conductivity simultaneously with low dielectric loss.     

Improved crack resistant liquid epoxy resins

Recent trends in the electrical industry indicate a growing demand for liquid epoxy castings that combine a high usage temperature (i.e. high glass transition temperature of the cured resin) with good crack resistance.It is well-known that the use of liquid instead of solid epoxy resin results in an increase in the glass transition temperature, but this is usually accompanied by a reduction in crack resistance. Frequently, such liquid epoxy resin based castings have to be flexibilized to improve crack resistance, but then the glass transition temperature is inherently lowered.The present paper describes some approaches to a combination of a high glass transition temperature with excellent crack resistance. A study of a number of criteria showed that this can be achieved by careful control of the crosslink density.The proper ratio of epoxy resin to curing agent, in combination with a suitable catalyst ensures castings with a glass transition temperature ranging from 95 to 125°C, and which pass standard crack tests even at temperatures below -80°C and temperature cycling from +150°C to -75°C.     

Epoxy composite with milimetric carbon nanotubes

Composite of multi-walled carbon nanotubes (MWCNT) and epoxy resin DGEBA were obtained with DDM hardener. The MWCNT were synthesized with length of millimeters by camphor/ferrocene pyrolysis. Different cure temperatures of DGEBA/DDM with addition of up to 1% MWCNT were studied to evaluate eventual changes in cure kinetics by differential scanning calorimetry (DSC). No change was detected in glass transition temperature with insertion of MWCNT although the cure enthalpy has been reduced.     

Combined Raman and dielectric spectroscopy on the curing behaviour and stress build up of carbon nanotube–epoxy composites

Single-walled carbon nanotubes (SWCNT) were incorporated into different epoxy matrices to monitor the internal stresses arising from the curing process. The curing reaction of the neat and SWCNT-modified epoxies was investigated by differential scanning calorimetry and parallel-plate rheometry. In situ Raman spectroscopy and electrical conductivity measurements were performed in parallel and the ongoing changes at both spectra were interpreted in terms of evolving stresses. Preliminary investigations were necessary to analyse the temperature dependence of the SWCNT Raman spectra, and its contribution to the overall shifts observed at the curing experiments. Thermal compressive strains were found to develop in the samples only below their glass transition temperature, pointing at a stress releasing effect above it. Chemical shrinkage effects were found to be negligible, or at least undetectable with our technique, in comparison to the temperature-induced Raman shifts.