Analysis of the current situation and problems of carbon nanotubes nanocomposites

[Abstract] The article describes the structure and properties of carbon nanotubes, overview of carbon nanotube / polymer composites and polymer structural composites and polymer functional composite materials, the applied research, on this basis, , purified carbon nanotubes in composites process, scattered damage and interface issues, and an outlook on future carbon nanotube / polymer composite trends.

[Keywords] carbon nanotubes, composite materials; structure, performance

Since 1991, Tsukuba, Japan, NEC Labs physicist Sumio Iijima (Sumio Iijima) [1] first reported since the carbon nanotube, its unique atomic structure and properties caused great interest of scientists. Graphite layers of different carbon nanotubes can be divided into single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). Carbon nanotubes with high specific surface area, mechanical properties (carbon nanotubes theoretical axis to the elastic modulus and tensile strength, respectively, for 1 ~ 2 TPa and 200Gpa), superior thermal and electrical properties (carbon nanotubes in heat under vacuum to a temperature up to 2800 ° C, the thermal conductivity is 2 times that of the diamond, the electronic The ampacity is 1000 times that of copper wire) [2-7]. carbon nanotubes These properties make it an ideal filler in the field of composite materials and polymers are easily processed, can be manufactured into the complex structure of the member, using the traditional processing method the polymer / carbon nanotube composites processing and manufacturing into a complex structure of the member, and does not destroy the structure of the carbon nanotubes in the process, thereby reducing production costs, therefore, the polymer / carbon nanotube composites been extensively studied.

Depending on the application purpose, polymer / carbon nanotube composite structure divided into two categories of composite materials and functional composite. Recent years, people have been prepared by a variety of polymer / carbon nanotube composite other various properties of the material, and the composite material mechanical properties, electrical properties, thermal properties, optical properties, etc., extensive research and analysis of the results of these studies show that: the polymer / carbon nanotube composites performance depends on many factors, such as the type of carbon nanotubes (single-walled carbon nanotubes or multi-walled carbon nanotube), the shape and structure (diameter, length and chiral) and the like. The article mainly of polymer / carbon nanotube composites Research summarized and discussed, and the challenges it faces.

Polymer / carbon nanotube composites

Polymer / carbon nanotube composites preparation methods are mainly three types: liquid blend, solid phase communion and in situ polymerization method, which is more common blending method.

1.1 solution blending composite method

The solution method is the use of mechanical stirring, magnetic stirring, or high-energy ultrasound, the agglomeration of carbon nanotubes peeled apart, uniformly dispersed in the polymer solution, and then removing the excess solvent is available after the polymer / carbon nanotube composites. species advantage of the method is simple, convenient and quick operation, mainly used for the preparation of membrane material. Xu et al [8] and Lau et al. [9] using this method preparation of CNT / epoxy composites, and reported that the composite material properties in addition to the epoxy resin, other polymers (such as polystyrene, polyvinyl alcohol and polyvinyl chloride, etc.) This approach may also be used to prepare a composite material.

1.2 melt blending composite law

The melt blending method is the shear force applied through the rotor of the carbon nanotubes dispersed in the polymer melt. This method is especially suitable for the preparation of a thermoplastic polymer / carbon nanotube composites. Advantage of this method is mainly avoided solvent or surfactant composite pollution complexes found no fracture and damage, but only applies to high temperature, difficult to break down polymers Jin et al. [10] In this method of preparation of PMMA / MWNT composites and to study its performance results show that the carbon nanotubes are uniformly dispersed in the polymer matrix, and no apparent damage. significantly improve the storage modulus of the composite material.

1.3 in situ composite method

The carbon nanotubes dispersed in the polymer monomer, adding an initiator, initiator situ monomer is polymerized to form polymers, to obtain a polymer / carbon nanotube composites of this method is considered to enhance the carbon nanotube dispersion and strengthen its relationship with the most effective method of interaction between the polymer matrix. Jia et al. [11] in situ polymerization of PMMA / SWNT composite results show that the strong write papers bond between the carbon nanotubes and the polymer matrix role. This is mainly because of the π bond of AIBN in the process is raised to open the carbon nanotubes so that participation in the polymerization of the PMMA. Using the surface-modified carbon nanotubes prepared PMMA / carbon nanotube composites can be improved not only the carbon nanotubes in the proportion of the dispersion in the polymer matrix, the mechanical properties of the composite material can also be obtained huge increase.

Polymer / carbon nanotube composites Research

2.1 polymer / carbon nanotube composite structure materials

Nanotubes because of its exceptional strength and stiffness is the preparation of a new generation of high-performance structural composites ideal filler In recent years, researchers for the polymer / carbon nanotube composite mechanical properties launched a multi- research, in which, the most impressive With the addition of carbon nanotubes, the composite modulus of elasticity, tensile strength and fracture toughness improve.

The main problem is to improve the mechanical properties of the polymer in a polymer matrix must have a good dispersion and distribution and to increase the interaction of them with the polymer chain. Added little by optimizing the processing conditions and surface chemical properties of the carbon nanotubes, The amount has been able to make the performance significantly improved. expected in the orientation of the structure (such as films and fibers) in the most efficient enough to let the axial to maximize the performance. added amount of continuous fiber, single-walled carbon nanotubes has more than 60%, and measured toughness is quite prominent. addition, only add a small amount of multi-wall or single wall nanotube fiber works its strength showed a larger increase. ordinary fiber is only a few microns in diameter, therefore only its nano-scale additives to enhance Sun Yan-ni, etc. [12] composite carbon nanotube carboxylation and then with high density polyethylene (HDPE), using melt blending method to prepare a carbon nanotube / high density polyethylene composite material and its mechanical properties have been studied and results show that: the addition of carbon nanotubes to improve the composite yield strength and tensile modulus, but at the same time it reduces the breaking strength and elongation of the material rate of Liu et al [13] using melt mixing method got MWNT/PA6 (nylon 6) composite, the results show that very uniform dispersion of CNTs in PA6 matrix and very strong interface between CNTs and polymer matrix sticky indirect action, adding 2 wt% (mass fraction) of MWNTs of PA6 elastic modulus and yield strength were increased by 214% and 162% of short carbon nanotubes on the mechanical properties of the composites, to a large extent depends on the interaction between the mass fraction, dispersion condition, and carbon nanotubes with the matrix of other factors, such as the orientation of carbon nanotubes in the composite material, the orientation of the fibers in the sheet layer, and a functional group on the surface of carbon nanotubes Modified unevenness, may also contribute to improve the final mechanical properties of the composite material.

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2.2 polymer / carbon nanotube functional composites

2.2.1 conductive composite material

Polymer / carbon nanotube conductive composites electrostatic spraying, static elimination, disk manufacturing and clean space ideal material GE [14] preparation of conductive composite materials with carbon nanotubes, carbon nanotube mass fraction of 10% a variety of engineering plastics such as polycarbonate, polyamide, and polyphenylene ether, etc. The conductive rate higher than the carbon black and metal fibers as filler, such conductive composites both the toughness of the impact, but also to facilitate the operation, in the car been widely used in the vehicle body and the LNP * successfully prepared static dissipative materials, i.e., PEEK and PEI, carbon nanotubes are added to the production wafer cassette and disk drive components. its ionic contamination is 65% lower than the carbon fiber material to be ~ 90 % by Mitsubishi Chemical Corporation, Japan has also succeeded in using the direct dispersion method to produce a the PC composite material containing a small amount of carbon nanotubes, and its extremely smooth surface, excellent physical properties, is the ideal the antistatic material [15] In addition, the polymer / the resistance of the carbon nanotube conductive composite material can be provided with the change of the external force pass - off operation, can be used for the pressure sensors and touch control switch [16], the use of the sensitivity of the resistance of the material on the nature and concentration of a variety of chemical gases, can be made of all kinds of gas-sensitive detector, classification for various gases, and mixtures thereof, or quantitatively detect and monitor [17], the use of the material of the positive temperature effects, i.e., when the temperature was raised to near the melting point of the crystalline polymer, resistance rapidly increases by several orders of magnitude, When the temperature back down to room temperature, the resistance value is restored to the initial value, can be applied to the circuit automatically adjusts the output power, temperature-controlled switch [18].

2.2.2 thermal conductivity of composite materials

Proof of many research efforts, the carbon nanotubes are so far known the best thermal conductivity material. Scientists prediction, single-wall carbon nanotubes that the thermal conductivity at room temperature can be up to 6600 W / mK 19, after separation after the multi-wall carbon nanotube thermal conductivity at room temperature is 3000 ~ 6600 W / mK. thus conceivable that carbon nanotubes could significantly improve the thermal conductivity of composite materials and high temperature thermal stability [20] Wu [21] prepared multi-walled carbon nanotube / high density polyethylene (MWNTs / HDPE) composite material, its thermal performance of in-depth research, experimental results show that: the thermal conductivity increased with increasing MWNTs content When the MWNTs the quality score of 38 h, the thermal conductivity of the mixed material is three times higher than the pure HDPE. Xu Ming [22] using the in situ polymerization of aligned carbon nanotubes / poly (methyl methacrylate) nanocomposites under an atmosphere of nitrogen and air, the composite material's thermal decomposition temperature of about 100 and 60 ° C than the substrate material were increased such that the coefficient of thermal conductivity of the composite material to 3.0 W / mK in thermal performance, the array of carbon nanotubes added, than the pure PMMA increased nearly 13-fold.

2.2.3 Other features composite

Carbon nanotube / polymer functional composite Nanchang University, Engineering Research Center of Nanotechnology [23] developed a multi-walled carbon nanotubes / epoxy radar absorbing stealth composites by multi-walled carbon nanotubes High of the NaOH treatment, so that the composite material of the carbon tubes to produce more holes in its surface to increase the surface activity of the carbon nanotubes prepared by absorbing stealth composite material having a good radar absorbing effect and controllability absorption band, such Absorbing The volume resistivity of 106 ~ 107 · cm order of magnitude, with excellent antistatic ability, which is of great significance for the absorbing band to adjust the radar absorbing materials and broaden the microwave absorbing bandwidth. Clemson University Rajoriat [24] multi-walled carbon nanotubes, the research found that carbon nanotubes resin matrix composites than pure epoxy damping ratio of approximately 140% increase of the damping properties of the epoxy.

3 Preparation of carbon nanotube polymer composite

3.1 carbon nanotubes dispersed in the matrix,

Aspect ratio of the carbon nanotubes, the high surface energy, and prone to agglomeration, making it difficult to uniformly dispersed in the polymer. How to achieve uniform dispersion of the carbon nanotubes in the polymer matrix is ​​a current need to solve the primary problem. Surface The modified carbon nanotubes can be uniformly dispersed in the polymer matrix, the use of chemical agents or high-energy discharge, ultraviolet irradiation treatment nanotubes, introduce certain specific functional group. Liu, J et al. [25] First, the volume ratio radiolabeling walled carbon nanotube subjected to oxidation treatment of 3:1 concentrated sulfuric acid and concentrated nitric acid, the obtained carbon nanotubes containing a carboxyl group of the end portion, to improve its dispersibility in various solvents. ChenQD [26] the carbon nanotubes and other the ion ray processing after the introduction of a polysaccharide chain. You can also use the mechanical stress activated carbon nanotubes surface modified to achieve by means of crushing, friction, and ultrasound.

The 3.2 carbon nanotubes orientation

The orientation of the carbon nanotubes in the polymer should be consistent with the requirements of the material by the force, the study showed that the orientation of the carbon nanotubes in the polymer can be improved by a certain processing, for example, mechanical blending shear, thereby further improving the performance of the composite material. Jin L [27], multi-walled carbon nanotube was dissolved in a thermoplastic polymer solution, evaporated to dryness prepared a film of nanotubes disorderly dispersed state, and then heated above its softening temperature and with a constant load on the mechanical pull extension, it was cooled to room temperature under load, found that the composite can be stretched by mechanical orientation of the carbon nanotubes in the composite.

3.3 composite molding problems

Carbon nanotube / polymer composite molding generally means to take the molding, solution casting, molding operation is simple, easy to industrialization in the cooling process, the sample due to the large temperature difference between inside and outside will happen surface cracking and other problems, solution casting formation samples without external stress and other factors, but removing the solvent, the process is long, the carbon nanotube-prone families.

Further, the polymer to enhance the development of modified filler used originally micron glass fibers, organic fibers, etc. Today nanotubes, the changes on the filler size of the original composite material processing technology and are faced with the characterization means new challenges, new processing technology will vigorously develop the atomic level and characterization methods, in order to adapt to the needs of the development of carbon nanotube polymer composites.

4 Conclusion

Carbon nanotubes with its unique performance are more and more areas of application, as the progress of science and technology of carbon nanotubes composites process will gradually be resolved someday nanotechnology will really go to the real life of the people when to bring radical change to people's lives.

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