Nano-fillers

Interlayer Structure of OMLFs and Intercalation 9.2.2.1 Nano-fillers 

In characterizing layered silicate, including layered titanate (HTO), the surface charge density is particularly important because it determines the interlayer structure of the intercalants as well as the cation exchange capacity (CEC). Lagaly proposed a method of calculation consisting of total elemental analysis and the dimensions of the unit cell [15]  

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Visualization of Nano-Filler Dispersion and Morphology in Rubbery Matrix by 3D-TEM... 

Generally speaking, commercial rubber products are manufactured as a composite from a rubber and a nano-filler, which is in a group of fillers of nanometer size (mainly, carbon black and particulate silica). For an example, a pneumatic tire for heavy-duty usages such as aircrafts and heavyweight tracks is made from natural rubber (NR) and carbon black and/or silica. Their reinforcing ability onto rubbers makes them an indispensable component in the rubber products [1,2]. 

TEM is still the most powerful technique to elucidate the dispersion of nano-filler in rubbery matrix. However, the conventional TEM projects three-dimensional (3D) body onto two-dimensional (2D) (x, y) plane, hence the structural information on the thickness direction (z-axis) is only obtained as an accumulated one. This lack of z-axis structure poses tricky problems in estimating 3D structure in the sample to result in more or less misleading interpretations of the structure. How to elucidate the dispersion of nano-fillers in 3D space from 2D images has not been solved until the advent of 3D-TEM technique, which combines TEM and computerized tomography technique to afford 3D structural images, incidentally called electrontomography . 

FIGURE 19.1 Morphology of nano-filler in rubbery matrix Nano-particles are aggregated, and the aggregates also associate to give filler agglomerate in rubber. (From Kohjiya, S., Kato, A., Suda, T., Shimanuki, J., and Ikeda, Y., Polymer, Al, 3298, 2006. With permission.)... 

D-TEM gave 3D images of nano-filler dispersion in NR, which clearly indicated aggregates and agglomerates of carbon black leading to a kind of network structure in NR vulcanizates. That is, filled rubbers may have double networks, one of rubber by covalent bonding and the other of nanofiller by physical interaction. The revealed 3D network structure was in conformity with many physical properties, e.g., percolation behavior of electron conductivity. 

The quick overview of the mechanisms of action reveals that the formation of an expanded charred insulative layer acting as thermal shield is involved. The mechanism of action is not completely elucidated, especially the role of the synergist. Reaction may take place between the nano-filler and some ingredients of the intumescent formulation (e.g., the phosphate) in order to thermally stabilize the charred structure. Only physical interactions are observed (e.g., action of POSS with phosphinate), and these interactions permit the reinforcement of the char strength and avoid the formation of cracks. The development rate and the quality of this layer are therefore of the primary importance and research work should be focused on this. 

New products (e.g., nano-filler materials, modified and blended polymers)... 

In the thermal studies conducted by Song et al. (76), the Tg increased modestly with the addition of pure and carboxylic-functionalized MWCNTs in PLA matrix. Also, the T and Tm of the nanocomposites were found to be lower than pure PLLA. Tsuji et al. (63) also observed the same trend of decreasing T in the nanocomposites compared with pure PLA however, here the nano-fillers are SWCNTs. In addition, several studies reported the Tg of the nanocomposites was lower than that of pure PLLA (61, 63,65). 

Examples of the synthesis of polysiloxane nanocomposites reported in the literature include Work by Ma et al (6) who modified montmorilIonite with short segments of PDMS and blended this into a polymer melt/solution to yield examples of fully exfoliated or intercalated PDMS/clay nanocomposites. Pan, Mark et al (7) synthesized well defined nano-fillers by reacting groups of four vinyl terminated POSS cages with a central siloxane core. These materials were subsequently chemically bonded into a PDMS network yielding a significant improvement in the mechanical properties of the polymer. 

It is proposed that thermal aging of the Cloisite/PDMS elastomers promotes the reformation of the siloxane network into a more thermodynamically stable form though a series of catalytically driven chain backbiting, hydrolysis and recombination reactions. This produces a siloxane network with increased thermal stability which is more intimately associated with the nano-filler. 

Zhuo, L., Yi, G., Kyoung-Sik, M., Tannenbaum, A., Wong, C. P. (2012). Nano filler dispersion in polymer composites for electronic packaging. Electronic Components and Technology Conference [ECTC], 2012 IEEE 62nd,pp. 1752-1757. 

A relatively new development of resin-modified glass-ionomers is to have them presented as a paste-liquid system [107]. Such a presentation makes the material easier to mix at the chair-side than the conventional powder-liquid system, though there are difficulties in producing stable systems of this type. This material contains a modified polyacid, which is a methacrylated copolymer [107], and it also contains what have been described as nano-fillers [108]. However, the exact state of division of these fillers has not been reported in the scientific literature, and there is evidence that such fillers are in fact of larger size than the nanometre scale, and consist of clusters of nanoparticles [109] or even nanocrystallites within more conventionally sized particles. 

The interest in new nanoscale fillers has rapidly grown in the last two decades, since it was discovered that a nanostructure could be built from a polymer and layered nano-filler, such as nanoclay. This new technique has been widely used in starch-based materials. 

Other nano-fillers have also investigated. Cao et al. [253] reported the utilization of multiwalled carbon nanotubes (MWCNTs) as filler-reinforcement to improve the performance of plasticized starch (PS). The PS/MWCNTs nanocomposites were prepared by a simple method of solution casting and evaporation. The results indicated that the MWCNTs dispersed homogeneously in the PS matrix and formed strong hydrogen bonding with PS molecules. Besides the improvement of mechanical properties, the incorporation of MWCNTs into the PS matrix also led to a decrease in the water sensitivity of the PS-based materials. 

C. Fang, L. Nie, S. Liu, R. Yu, N. An, S. Li, Characterization of polypropylene-polyethylene blends made of waste materials with compatibilizer and nano-filler. Compos. B 55,498-505 (2013)... 

Bru Brunner, A. J., Necola, A., Rees, M., Gasser, P., Kommann, X., Thomann, R., Barbezat, M. The influence of silicate-based nano-filler on the fracture toughness of epoxy resin. Eng. Fract. Mechanics 73 (2006) 2336-2345. 

The effective methods currently available for separating agglomerations will promote the application of nano-fillers such as nano-clay. Because the dimensions of these particles are smaller than the wavelength of light, there is a marked reduction in light scattering, thus enhancing transparency. 

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