Nanofillers carbon nanotubes

Nanofillers, carbon nanotubes (CNTs), especially single-walled carbon nanotubes (SWNTs), have attracted a great deal of interest due to their low density, large aspect ratio, superior mechanical properties, and unique electrical and thermal conductivities [1-4], They can find potential applications in many fields, such as chemical sensing, gas storage, field emission, scanning microscopy, catalysis, and composite materials. 

Table 19.2 The price of various nanofiller (carbon nanotube) (2008 data)...

Figure 19.7 Picture of the nanocomposite (grease) made from the nanofiller (carbon nanotubes) and polymer (DURASYIsl 166 oil). (Reproduced with kind permission from NLGI. Copyright (2010) NLGI)...

Among nanofillers, carbon nanotubes (CNTs) have gained much attention because of their superior electrical, mechanical, and thermal properties. They are nanotubes, made by wrapped graphene layers, with a diameter of few nanometres, a length from a few microns up to millimetres, and a graphite-like structure. They can be single walled (SWCNT) or multi walled (MWCNT). In this paragraph, results refer to MWCNT, unless otherwise indicated. 

Strength). The nanosized particles most commonly used in PU foams are clearly silicate-layered nanoclays, and particularly unmodified or organically modified montmorillonite (MMT), though others have also been considered, such as carbon-based nanofillers (carbon nanotubes and nanofibers, and more recently graphene), nanosilica, or cellulose-based nanofillers. 

There are many types of nanofillers including carbon black nanofillers, carbon nanotube nanofillers, carbon fiber nanofillers, activated clay nanofillers, natural clay nanofillers (mined, refined, and treated), clay (synthetic) nanofillers, natural fiber nanofillers, zinc oxide nanofillers and silica nanofillers. Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio which is significantly larger than any... 

Highly promising nanofillers, nanoclays and carbon nanotubes are also developing well. Depending on the reinforcement, the main difficulties are ... 

George and Bhowmick [147] have also studied the influence of the polarity of EVA (40, 50, 60, and 70% vinyl acetate content) and the nature of the nanofiller [expanded graphite (EG), multiwall carbon nanotubes (MWCNTs), and CNFs] on the mechanical properties of EVA/carbon nanofiller nanocomposites. They pointed out that the enhancement in mechanical properties with the addition of various... 

CIL is unavoidable when nanodispersion of any other nanofiller, such as clay or carbon nanotube (CNT) is considered [17,18], Various types of cationic surfactants in the case of montmorillonite (MMT) and reactive interface modifications in the case of CNT have been introduced to ensure... 

The gap between the predictions and experimental results arises from imperfect dispersion of carbon nanotubes and poor load transfer from the matrix to the nanotubes. Even modest nanotube agglomeration impacts the diameter and length distributions of the nanofillers and overall is likely to decrease the aspect ratio. In addition, nanotube agglomeration reduces the modulus of the nanofillers relative to that of isolated nanotubes because there are only weak dispersive forces between the nanotubes. Schadler et al. (71) and Ajayan et al. (72) concluded from Raman spectra that slippage occurs between the shells of MWNTs and within SWNT ropes and may limit stress transfer in nanotube/polymer composites. Thus, good dispersion of CNTs and strong interfacial interactions between CNTs and PU chains contribute to the dramatic improvement of the mechanical properties of the... 

The recognition of the unique properties of carbon nanotubes (CNTs) has stimulated a huge interest in their use as advanced filler in composite materials. In particular, their superior mechanical, thermal and electrical properties are expected to provide much higher property improvement than other nanofillers (18-22). For example, as conductive inclusions in polymeric matrices, CNTs shift the percolation threshold to much lower loading values than traditional carbon black particles. 

Nanoparticles or nanofillers are collective terms for modified layered silicates (organoclay), graphite nanoflakes, carbon nanotubes, and a number of materials dispersed in the polymer matrix, when the particles size is in order of nanometers (one thousands of micron), or tens of nanometers. A plastic filled with nanoparticles, typically in the range of 2-10% (w/w) is called a nanocomposite. 

Studies from the composite deformation mechanism and interfacial bonding between nanofillers and the polymer matrix have been performed [46-48]. In these reports, the authors performed straining studies to determine the load transfer between carbon nanotubes and the polymer and observed the phenomena of crack propagation and polymer debonding. In some cases, the mechanical deformation processes were followed over the electrospun composite fibers. Microscopic images revealed information on the dispersion and orientation of nanotubes within the fiber and their impact in the mechanical performance regarding strain at break and stress concentration at the pores of the nanotubes. 

Graphene-polymer nanocomposites share with other nanocomposites the characteristic of remarkable improvements in properties and percolation thresholds at very low filler contents. Although the majority of research has focused on polymer nanocomposites based on layered materials of natural origin, such as an MMT type of layered silicate compounds or synthetic clay (layered double hydroxide), the electrical and thermal conductivity of clay minerals are quite poor [177]. To overcome these shortcomings, carbon-based nanofillers, such as CB, carbon nanotubes, carbon nanofibers, and graphite have been introduced to the preparation of polymer nanocomposites. Among these, carbon nanotubes have proven to be very effective as conductive fillers. An important drawback of them as nanofillers is their high production costs, which... 

Other nanofillers have been tested, snch as carbon nanotubes, but in a less concerted maimer. 

The pol5mier nanocomposite field has been studied heavily in the past decade. However, polymier nanocomposite technology has been around for quite some time in the form of latex paints, carbon-black filled tires, and other pol5mier systems filled with nanoscale particles. However, the nanoscale interface nature of these materials was not truly understood and elucidated until recently [2 7]. Today, there are excellent works that cover the entire field of polymer nanocomposite research, including applications, with a wide range of nanofillers such as layered silicates (clays), carbon nanotubes/nanofibers, colloidal oxides, double-layered hydroxides, quantum dots, nanocrystalline metals, and so on. The majority of the research conducted to date has been with organically treated, layered silicates or organoclays. 

Of particular interest to adhesives formulators are nanofillers such as carbon nanotubes (CNT), silica, alumina, magnesium oxide, titanium dioxide, zirconium oxide (Zn02), silver, copper, and nickel). Of these, carbon nanotubes are the most widely studied for electrically conductive adhesives to attach microdevices, to interconnect microcircuits and to increase I/O densities at the device level. ... 

Let us consider in the conclusion of the present section melt viscosity behavior as a function of nanofiller contents for nanocomposites pol5q)ropylene/carbon nanotubes (PP/CNT), studied in Refs. [55, 76]. In Figs. 18 and 19 the dependences of the ratios GJG and on nanofiller contents and the parameters and (l+

experimental data and behavior, predicted by the Eqs. (38) and (39), is observed again. In Fig. 20, the dependence of MFI on nanofiller mass contents IF for nanocomposites PP/CNT, calculated according to the Eq. (43), is adduced. As one can see, the qualitative discrepancy between theoretical calculation (curve 1) and experimental data (points) is observed. If the Eq. (43) assiunes melt viscosity increasing (MFI reduction) at IF growth, then the experimental data discovers opposite tendency (MFI >MFI ). 

Nanofillers were first discovered by Japanese Scientist S. lijima in 1991 as helical microtubules of graphitic carbon [1]. Dr Richard E. Smalley of Rice University, USA was awarded the 1996 Nobel Prize in Chemistry for his codiscovery of buckyballs (Ceo) and has made significant contributions in carbon nanotube synthesis and potential applications [2,3]. 

Nanofillers have superb thermal and electrical properties. All nanotubes are expected to be very good thermal conductors along the tube axis, exhibiting a property known as ballistic conduction, but good insulators laterally to the tube axis. It has been reported that single-wall carbon nanotubes exhibit thermal conductivity (TC) values as high as 2000-6000 W mK [4] under ideal circumstances. The temperature stability of carbon nanotubes is estimated to be up to 2800 °C in a vacuum, and about 750 °C in air. By comparison, metals have TC values of several hundred W mK , and water and oil have TC values of only 0.6 W mK and 0.2 W mK respectively. Table 19.1 lists the thermal conductivities of various materials, including nanofillers (nanotubes), metals, and oils. 

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