Functionalization of multi‐walled carbon nanotubes and their effect on the tribological properties of poly(ether ether ketone) composites

A series of copolymers containing conjugated fluorene groups as a compatibilizer to improve the dispersion of multi‐walled carbon nanotubes (MWCNTs) were prepared and used to improve the wear resistance of poly(ether ether ketone)/graphite (PEEK/GP) composites. The solubility of MWCNTs had a maximum at a concentration ratio of 2:1 polymer:MWCNTs. Transmission electron microscopy indicated that polymer ? MWCNT interactions were capable of partially debundling the nanotubes in chloroform, with individual nanotubes or small bundles clearly observed. The tribological properties of PEEK composites incorporating the modified MWCNTs were investigated using a pin‐on‐disc apparatus and a block‐on‐ring apparatus. The PEEK composites had a lower frictional coefficient under the block‐on‐ring testing condition, but a lower wear rate was achieved in the pin‐on‐disc test. © 2017 Society of Chemical Industry     

Hollow porous carbon microspheres obtained by the pyrolysis of TiO2/poly(furfuryl alcohol) composite precursors

Disordered carbon materials with high porosity were prepared through the pyrolysis of TiO₂/poly(furfuryl alcohol) composites, obtained by the sol-gel method. The composites were prepared starting from titanium tetra-isopropoxide (TTIP) and furfuryl alcohol (FA) as precursors. Two different synthetic procedures for our composites were carried out, based on the addition of furfuryl alcohol (FA) before or after the TiO₂ nanoparticles formation. Also, different TTIP/FA ratio was tested. The hybrid materials obtained by both synthetic routes were pyrolyzed, under argon flow, at 900 °C producing novel TiO₂/carbon composites. All samples were characterized by XRD, FT-IR, DR-FTIR, Raman spectroscopy and TEM. Results indicated the effective FA polymerization on TiO₂ (anatase) nanoparticles, and polymer conversion to disordered carbon after the pyrolysis, simultaneously with TiO₂ anatase-rutile phase transition. The resulting TiO₂/carbon composites were treated with HF solution aiming the oxide dissolution, yielding an extremely porous carbon material as insoluble fraction. The morphology of these porous carbon materials is strongly dependent on the synthetic route adopted for the composite precursor, varying from carbon foam to highly ordered hollow microspheres.     

Dielectric properties of epoxy composites with modified multiwalled carbon nanotubes

We report here a high dielectric percolative polymer nanocomposite, fabricated by a combination of triethylene-tetramine (TETA) modified multiwalled carbon nanotube (named as TETA-MWNT) within epoxy resin matrix. In this composite system, with various TETA-MWNT volume fractions, the dielectric constant (K) is well fitted by the scaling law of the percolation theory with the percolation threshold f _c is 0.042 and the critical exponent p is 0.786. At 1,000 Hz of room temperature, the value of the dielectric constant is as high as 421 with the TETA-MWNT content of 4.14vol%, which is almost 60 times higher than that of epoxy resin. In contrast, a simple blend of pristine MWNT in epoxy composite shows evident lower dielectric constant and much higher loss with the same volume fraction.     

Orientation of multiwalled carbon nanotubes in composites with polycarbonate by melt spinning

A conductive polycarbonate (PC) composite containing 2 wt% multiwalled carbon nanotubes (MWNT) and pure PC were melt spun using a piston type spinning device. Different take-up velocities up to 800 m/min and throughputs leading to draw down ratios up to 250 were used. The composite material of PC with MWNT was prepared by diluting a PC based masterbatch consisting of 15 wt% MWNT by melt mixing in an extruder. The alignment of the nanotubes within melt spun fibers with draw down ratios up to 126 was investigated by TEM and Raman spectroscopy. The nanotubes align in their length axis along the fiber axis increasingly with the draw down ratio, however, the curved shape of the nanotubes still exist in the melt spun fibers. At higher draw down ratios, the MWNT started to align by reducing their curvature. Polarized Raman spectroscopy indicated that the D/D and G/G ratios parallel/perpendicular to the fiber axis increase for both MWNT bands in a similar manner with the draw down ratio. Interestingly, with increasing alignment electrical conductivity of the fibers is lost. Mechanical investigations revealed that at low spinning speeds elongation at break and tensile strength of the composite are lower than those of the pure PC. However, at the highest take-up velocity of 800 m/min the elongation at break is higher and true stress at break of the composite fiber is comparable to the pure PC fiber.     

Synergetic effect of fly ash cenospheres and multi-walled carbon nanotubes on mechanical and tribological properties of epoxy resin coatings

The multiform wear of friction pair components is the main cause of marine equipment failure and epoxy resin (EP) coatings have been widely used in this field. Fly ash cenospheres (FACs) and multi-walled carbon nanotubes (MWCNTs) were used to reinforce the tribological properties of EP coatings. The synergetic effects of FACs and MWCNTs on the mechanical and tribological properties of EP coatings were studied. Experimental results show that the tensile and flexural properties of FACs-MWCNTs/EP composites are significantly reinforced. The tribological performance of EP composite coatings under seawater conditions is improved by the synergetic effect of FACs and MWCNTs, especially, the 10 wt.% FACs-1 wt.% MWCNTs/EP coatings behave the most excellent tribological properties. It indicates that FACs can increase the hardness of EP coatings and provide a smoother surface for the water film formation, which decreases the friction coefficient and wear volume. MWCNTs can increase the elasticity modulus of EP, and act as a rope to prevent EP matrix and FACs from being desquamated.     

碳纳米管表面改性及其应用于复合材料的研究现状

对碳纳米管进行表面改性可提高碳纳米管的表面活性、分散能力和与基体材料之间的相容性,从而提高其在复合材料中的增强效果。本文介绍了碳纳米管表面改性的方法,分为物理法和化学法,物理法主要有高能机械研磨法、高能球磨法和超声振动法;化学法主要有酸处理法、偶联剂法、化学镀法、高能射线辐照法和原子转移自由基聚合法。在实际应用中常将几种改性方法联合使用,使得到的改性产物性能更稳定,性质更多样化。同时,介绍了改性后的碳纳米管在各种复合材料中的应用现状。并指出了对碳纳米管进行改性的两个重点：一是尽量保持碳纳米管的本身结构完整性;二是提高碳纳米管在基体中的分散性。     

Deformation processes of ultrahigh porous multiwalled carbon nanotubes/polycarbonate composite fibers prepared by electrospinning

Mechanical deformation processes of electrospun composite fibers based on polycarbonate with multiwalled carbon nanotubes (MWCNTs) were investigated by in situ tensile tests under transmission electron microscope (TEM) depending on morphology. Using chloroform as solvent and optimizing process conditions, uniform nanoporous composite fibers were generated by electrospinning process. TEM images indicate that the MWCNTs were embedded in the fibers as individual elements, highly aligned parallel to one another along the fiber axis, which makes the mechanical load transfer from the polymer matrix to the MWCNT more favorable. Due to the slippage of individual MWCNTs within the fibers the strain at break of composite fibers is significantly enhanced. In addition, the nanopores on the fiber surface provide the effective sites for stress concentration for the plastic deformation to form nanonecking of fibers under tensile load. Combination of these unique features makes the electrospun composite fibers extremely strong and tough. The results from present work may provide a feasible consideration of such electrospun composite fibers for use as the reinforcing elements in a polymer based composite of a new kind.     

Nanocomposites of poly(vinylidene fluoride) with multiwalled carbon nanotubes

The preparation and characterization of nanocomposites of poly(vinylidene fluoride), PVDF, with acid treated multiwalled carbon nanotubes (MWCNT) with a wide composition range, from 0.1 to 5.0% MWCNT by weight, is reported. Effect of uniaxial orientation by zone drawing on these nanocomposites is discussed and compared with unoriented compression molded films. Static room temperature two‐dimensional wide angle X‐ray scattering and Fourier transform infrared spectroscopy were used for phase identification. Differential scanning calorimetry, polarizing optical microscopy, dynamic mechanical analysis (DMA), and thermogravimetic analysis (TGA) were used to study the thermal and mechanical properties. Incorporation of MWCNT into PVDF has no obvious effect in forming beta phase crystal in the PVDF/MWCNT bulk films, while zone drawing cause a significant alpha to beta transition in PVDF/MWCNT. Results indicate that MWCNTs act as nucleation agent during crystallization and slightly increase the degree of crystallinity of PVDF/MWCNT bulk films. TGA indicates the thermal stability is improved when MWCNT concentration increases for unoriented PVDF/MWCNT film. The modulus also increases significantly when MWCNT concentration increases. The glass transition temperature measured by the peak position of tanδ from DMA does not change with MWCNT concentration, but a slightly higher glass transition can be obtained by zone drawing. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

碳纳米管涂料的研究进展

综述了碳纳米管涂料的最新研究进展,介绍了碳纳米管在复合材料、导电、电磁屏蔽、吸波、吸热、抗菌等特殊涂料中的应用。初步探讨了碳纳米管涂料特殊性能的机理,指出了纳米涂料产业化所面临的困难,并对今后的发展进行了展望。     

Functionalization of multiwalled carbon nanotubes with amphiphilic poly(aspartic acid)

A new method to functionalize multiwalled carbon nanotubes (MWNTs) with amphiphilic poly(aspartic acid) was investigated. The amphiphilic polymer (PASP‐C16) was synthesized by thermal condensation and aminolysis by hexadecylamine, followed by hydrolysis of the remaining succinimide units in the polymer backbone. The functionalization of MWNTs was achieved by physical adsorption of the biopolymer onto the surfaces of MWNTs. Ultraviolet‐visible ( UV‐vis) spectra showed that the functionalized MWNTs had a good aqueous dispersity and solubility. The interaction of PASP‐C16 with MWNTs was investigated by analyzing X‐ray diffraction (XRD) patterns, circular dichroism (CD), spectra and high‐resolution transmission electron microscopy ( HRTEM ). From the XRD patterns, it can be known that the aggregate of PASP‐C16 due to intermolecular interaction between hexadecyl chains has been reduced when the polymer interacting with MWNTs. CD spectra indicated that the interaction of hexadecyl chains of PASP‐C16 with the wall of MWNTs is the major interaction between PASP‐C16 and MWNTs, and MWNTs were covered by the poly(aspatic acid) backbone. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Fabrication of hybrid ladderlike polysilsesquioxane‐grafted multiwalled carbon nanotubes

Ladderlike polysilsesquioxanes (LPSs) containing chloromethylphenyl groups were synthesized from (p‐chloromethyl)phenyltrimethoxysilane under basic conditions. Functionalized multiwalled carbon nanotubes (MWNT–COOH) were prepared by the acid treatment of pristine multiwalled carbon nanotubes (MWNTs). MWNT–COOH was reacted with LPS to prepare LPS‐grafted MWNTs via ester linkages. The functionalization of MWNTs with LPS significantly altered the surface roughness of the MWNTs; there was a significant increase in the diameter of the MWNTs. The LPS‐grafted MWNTs had a 10–20 nm thickness along the outer walls according to the functionalization of the MWNTs with LPS. An advantage of the hybrid LPS‐grafted MWNTs was shown as improved thermal behavior. The composition, thermal properties, and surface morphology of the LPS‐grafted MWNTs were studied by Fourier transform infrared spectroscopy, thermogravimetric analysis, energy‐dispersive spectroscopy, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

聚砜/改性碳纳米管复合膜的制备及亲水性能

利用浸没沉淀相转化法,以聚砜(PSF)为膜材料,羧基化碳纳米管(MWCNTs-COOH)为添加剂,聚乙烯吡咯烷酮(PVP)为致孔剂,N,N-二甲基乙酰胺(DMAc)为溶剂,制备了聚砜/多壁碳纳米管复合膜,系统研究了制备复合膜时碳纳米管的添加量、预挥发时间以及凝固浴组成对其结构和性能的影响。实验结果表明,添加MWCNTs-COOH后,复合膜的亲水性能和抗污性能显著提高,同时复合膜的力学性能也明显增强。复合膜的 SEM 照片显示,随预挥发时间的延长和凝固浴中DMAc 质量分数的增加,复合膜断面由指状孔结构向海绵状孔结构过渡;复合膜的水通量下降,截留率上升。     

紫外光固化碳纳米管改性水性聚氨酯涂膜

以异佛尔酮二异氰酸酯(IPDI)、聚乙二醇(PEG400)、2,2-双羟甲基丙酸(DMPA)和甲基丙烯酸-2-羟乙酯(HEMA)为主要原料,合成光固化水性聚氨酯丙烯酸酯预聚体,以三乙醇胺中和后,原位引入经浓硝酸处理过的碳纳米管(CNTs),制备了光固化水性聚氨酯碳纳米管复合乳液(WPU/CNTs),加入光引发剂后交联固...     

The effect of pH and ionic strength on the dispersion of carbon nanotubes in poly(acrylic acid) solutions

The dispersion of three kinds of acid‐treated carbon nanotubes (CNTs) in poly(acrylic acid) (PAA) aqueous solution of different pH and ionic strengths (varied by NaCl, KCl and ZnCl₂) was investigated by visual observation, zeta potential, particle size analysis, transmission electron microscopy and scanning electron microscopy. Visual observation revealed that the dispersion of CNTs acid treated at 60 °C for 3 h and at 80 °C for 2 h was poor in aqueous solutions with pH < 2 or pH > 12. The poor dispersion of acid‐treated CNTs may be improved by adding PAA. In particular, PAA improved the dispersion of CNTs with greater COOH content. In a low pH solution (pH 1.5), a higher PAA content resulted in poorer CNT dispersion while in a high pH solution (pH 12.5), a higher PAA content led to better CNT dispersion. For superior dispersion in a basic aqueous solution (pH 12.5), experimental data showed that a greater atomic radius or a higher cationic charge of the added salt may result in faster aggregation and thus precipitation of CNTs. Copyright © 2011 Society of Chemical Industry     

Novel approach toward poly(butylene succinate)/single-walled carbon nanotubes nanocomposites with interfacial-induced crystallization behaviors and mechanical strength

Biodegradable poly(butylene succinate) (PBS)/single-walled carbon nanotube (SWCNT) nanocomposites were successfully prepared through silication and physical blend between PBS and acyl aminopropyltriethoxysilane functionalized single-walled carbon nanotube (SWCNT-APTES), which was obtained from acylate between 3-aminopropyltriethoxysilane and acyl chloride functionalized single-walled carbon nanotube. Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) observations revealed that the PBS chains were covalently attached to the SWCNT-APTES by hydrolysis. PBS/SWCNT-APTES nanocomposites after hydrolysis exhibited strong interfacial interaction between SWCNT-APTES and PBS matrix, leading to a less agglomeration. However, the PBS/SWCNT-APTES nanocomposite prepared by only physical blend without hydrolysis exhibited severe reagglomeration of SWCNT in the PBS. The addition of SWCNT-APTES enhanced the crystallization of the PBS in the nanocomposites for both approaches of hydrolysis and physical blend due to the heterogeneous nucleation effect while the crystal structure of PBS remained. Especially, a more significant increase of crystallization rate for physical blend was present as comparison to PBS/SWCNT-APTES after hydrolysis due to the higher diffusion constant, which is attributed to the change of surface properties of nanotubes. Furthermore, the incorporation of SWCNT-APTES improved the storage modulus of the nanocomposites compared with that of neat PBS. The PBS/SWCNT-APTES nanocomposites after hydrolysis showed of higher tensile strength than PBS/SWCNT-APTES nanocomposite without hydrolysis.     

Templated pyrolytic carbon: the effect of poly(ethylene glycol) molecular weight on the pore size distribution of poly(furfuryl alcohol)-derived carbon

Poly(ethylene glycol), which has a negligible carbon yield upon pyrolysis, was used as a template to study the controlled formation of mesoporosity in pyrolytic carbons. A series of carbons was produced from mixtures of poly(ethylene glycol) and poly(furfuryl alcohol) with 25, 50 and 75% composition by weight and an M_n of 300 to18?500 g/mol of template. Polydisperse dextran adsorption reveals a maximum in uptake for 8000 g/mol and 50% templated carbons, while materials from 75% mixtures or those from less than 2000 g/mol template yielded negligible dextran uptake. These results correlated well with the intensity ratio of a broad peak between 7 and 11° 2θ in the X-ray diffraction spectrum and the 002 diffraction peak and also qualitatively with micrographs of the internal microstructure of the carbons. The results suggest a templating process dominated by both the molecular size of the template and the rate of expulsion of decomposed template material during the formation of the solid.     

碳纳米管修饰电极的研究进展

化学修饰电极如今在电化学和电分析化学中应用极为广泛。综述了碳纳米管的结构和性能,介绍了碳纳米管修饰电极的制备及应用。     

Dielectric spectroscopy on melt processed polycarbonate—multiwalled carbon nanotube composites

Complex permittivity and related AC conductivity measurements in the frequency range between 10⁻⁴ and 10⁷ Hz are presented for composites of polycarbonate (PC) filled with different amounts of multiwalled carbon nanotubes (MWNT) varying in the range between 0.5 and 5 wt%. The composites were obtained by diluting a PC based masterbatch containing 15 wt% MWNT by melt mixing using a Micro Compounder. From DC conductivity measurements it was found that for samples processed at a mixing screw speed of 150 rpm for 5 min, the percolation occurs at a threshold concentration (p_c) between 1.0 and 1.5 wt% MWNT. For concentrations of MWNT near the percolation threshold, the processing conditions (screw speed and mixing time) were varied. The differences in the dispersion of the MWNT in the PC matrix could be detected in the complex permittivity and AC conductivity spectra, and have been explained by changes in p_c. The AC conductivity and permittivity spectra are discussed in terms of charge carrier diffusion on percolation clusters and resistor-capacitor composites.     

Preparation and characterization of poly(vinylidene fluoride) nanocomposites containing multiwalled carbon nanotubes

Poly(vinylidene fluoride) (PVDF) nanocomposites with different loadings of multiwalled carbon nanotubes (MWNT) were prepared by melt‐compounding technique. A homogeneous dispersion of MWNT throughout PVDF matrix was observed on the cryo‐fractured surfaces by scanning electron microscopy. Thermogravimetric analysis results indicated that the thermal stability of neat PVDF was improved with the incorporation of MWNT. Dynamic mechanical analysis showed a significant improvement in the storage modulus over a temperature range from ?125 to 75°C with the addition of MWNT. The melt‐rheological studies illustrated that incorporating MWNT into PVDF matrix resulted in higher complex viscosities (|η*|), storage modulus (G′), loss modulus (G″), and lower loss factor (tan δ) than those of neat PVDF. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A comparative study of fracture behavior between carbon black/poly(ethylene terephthalate) and multiwalled carbon nanotube/poly(ethylene terephthalate) composite films

Fracture behavior of amorphous poly(ethylene terephthalate) (PET) films added multiwalled carbon nanotube (MWCNT) has been compared with that of the PET films added with carbon black (CB) to elucidate the effects of the large aspect ratio of MWCNT. Fracture toughness has been evaluated using the essential work of fracture tests. Evolution of the crazes has been analyzed by conducting time‐resolved small‐angle X‐ray scattering measurements during tensile deformation of the films at room temperature using synchrotron radiation. CB and MWCNT increased the fracture toughness of the PET film by increasing the plastic work of fracture. This resulted from the effects of the fillers to prevent the localization of deformation upon the crazes formed at earlier stages of tensile deformation and to retard the growth of the fibrils in the crazes to a critical length. The CB particles provided a number of sites where the crazes were preferably formed due to stress concentration. In the case of MWCNT, on the other hand, the widening of the crazes formed at earlier stages was suppressed due to the bridging effect arising from the large aspect ratio of MWCNT. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007