Properties of the Nanocomposites

POLYMERS USED FOR NANOCOMPOSITE FORMATION AND PROPERTIES OF THE NANOCOMPOSITES... 

Dynamic mechanical properties of the nanocomposites are shown in Figure 4.6. There is 10% improvement of the storage modulus at 20°C by incorporating only 4 wt% of the nanombe. 

It should be mentioned that the structure of carbon supports could have significant influence on the electro-catalytic properties of the nanocomposite catalysts. Recently, Pt/Ru nanoclusters prepared by the alkaline EG method were impregnated into a synthesized carbon support with highly ordered mesoporous. Although the Pt/ Ru nanoclusters can be well dispersed in the pores of this carbon substrate, the long and narrow channels in this material seem not suitable for the application in... 

The rheological properties of insitu polymerized nanocomposites with end-tethered polymer chains were first described by Krisnamoorti and Giannelis [33]. The flow behavior of PCL- and Nylon 6-based nanocomposites differed extremely from that of the corresponding neat matrices, whereas the thermorheological properties of the nanocomposites were entirely determined by the behavior of the matrices [33]. The slope of G (co) and G"(co) versus flxco is much smaller than 2 and 1, respectively. Values of 2 and 1 are expected for linear mono-dispersed polymer melts, and the large deviation, especially in the presence of a very small amount of layered silicate loading, may be due to the formation of a network structure in the molten... 

It is necessary to disperse the nanomaterials in the best possible manner, especially those layered structures such as graphite, graphene or clays. It is important to obtain very thin (ca. one nanometer) and very wide (ca. 500 nanometers) nanostructures dispersed in the polymer matrices to achieve optimal gas permeability and to improve their mechanical properties without affecting structural quality, using a small amount of the nanomaterial. The particle orientation also has an important effect on the properties of the nanocomposite. Nanoparticles need to be dispersed within the polymer so that are parallel to the material s surface. This condition ensures a maximum tor-... 

Similar observations were noted when FKM/o-MMT clay nanocomposites were prepared by melt blending and the as-prepared nanocomposites showed both intercalated as well as exfoliated structure [103]. The apparent shear viscosity of the FKM/o-MMT nanocomposites was lower than that of the pristine polymer at all shear rates and temperatures. The nanocomposites exhibited reduced equilibrium die swell with a smooth extrudate appearance. A comparison of the flow properties of the nanocomposites with the conventional composites revealed that the nanocomposites exhibited improved processability. 

The X-ray diffraction peaks observed in the range of 3°-10° for the modified clays disappear in the rubber nanocomposites. photographs show predominantly exfoliation of the clays in the range of 12 4 nm in the BIMS. Consequently, excellent improvement in mechanical properties like tensile strength, elongation at break, and modulus is observed by the incorporation of the nanoclays in the BIMS. Maiti and Bhowmick have also studied the effect of solution concentration (5, 10, 15, 20, and 25 wt%) on the properties of fluorocarbon clay nanocomposites [64]. They noticed that optimum properties are achieved at 20 wt% solution. At the optimized solution concentration, they also prepared rubber/clay nanocomposites by a solution mixing process using fluoroelastomer and different nanoclays (namely NA, 10A, 20A, and 30B) and the effect of these nanoclays on the mechanical properties of the nanocomposites has been reported, as shown in Table 4 [93]. 

The incorporation of unmodified and organically modified montmorillonite nanoclays (namely 15A and 30B) in chlorinated polyethylene (CPE) by the solution intercalation method and their influence on mechanical properties of the nanocomposites have been studied by Kar et al. [137]. The o-MMT-embedded nanocomposites show enhanced tensile strength and Young s modulus in comparison to the nanocomposites containing the unmodified nanoclay. They have shown from and XRD analyses that organically modified clay shows better dispersion in the CPE matrix. This has been further substantiated from FTIR analysis, which proves an interaction between the CPE matrix and the clay intercalates. 

It has been found that the HNBR/SP nanocomposite provides the best thermal and mechanical properties when HNBR is dissolved in Ch and SP is dispersed in MEK. XRD, AFM,TEM, and optical transmittance studies show that the dispersion of clay is best in the Ch/MEK solvent combination and, hence, polymer-filler interaction is also highest in this system. Thus, rather than implying that the solvent selection directly affects the physical properties of the nanocomposite, solvent acts on the properties through its influence on the developed morphology. 

Fabrication methods have overwhelmingly focused on improving nanotube dispersion because better nanotube dispersion in polyurethane matrix has been found to improve the properties of the nanocomposites. The dispersion extent of CNTs in the polyurethane matrix plays an important role in the properties of the polymer nanocomposites. Similar to the case of nanotube/solvent suspensions, pristine nanotubes have not yet been shown to be soluble in polymers, illustrating the extreme difficulty of overcoming the inherent thermodynamic drive of nanotubes to bundle. Therefore, CNTs need to be surface modified before the composite fabrication process to improve the load transfer from the polyurethane matrix to the nanotubes. Usually, the polyurethane/CNT nanocomposites can be fabricated by using four techniques melt-mixing (15), solution casting (16-18), in-situ polymerization (19-21), and sol gel process (22). 

In the last ten years, a great deal of experimental work has been presented about the tensile properties of CNTs/polymer composites in the literature. However, it is difficult to generalize across these studies because of the large number of parameters that can influence the effective properties, including size and structure of the CNT, CNT/ polymer interaction, processing techniques and processing conditions. In this chapter, the effect of structure and morphology on the properties of the nanocomposites will be focused and discussed. 

Polyvinyl chloride/montmorillonite nanocomposites were prepared using an epoxy resin, as compatibiliser, and the effect of this compatibiliser on the optical properties of the nanocomposites investigated. It was found that the transparency of the nanocomposites improved with increasing content of montmorillonite, which was pretreated with the epoxy resin. The good transparency of the nanocomposites also indicated that the epoxy resin improved the processing stability of the nanocomposites. 3 refs. 

Intercalated and partially exfoliated PVC-clay nanocomposites were produced by melt blending in the presence and absence of DOP and characterised by X-ray diffraction and transmission electron microscopy. The effects of various factors, including volume fraction of clay, plasticiser content, melt compounding time and annealing, on nanocomposite structure and the thermal and mechanical properties of the nanocomposites were also examined. It was found that the best mechanical properties were achieved at 2% clay loading and 5 to 10% DOP loading. 18 refs. 

The mechanical properties of the nanocomposites strongly depend on their structure, orientation of the filler, phase separation, and processing conditions. Hence, there is a need for in situ nondestructive characterization technique to probe the internal stress in nanocomposite structures. The shortcomings of many conventional techniques such as low resolution, destructive measurements, complex modeling and applicability to only certain class of materials are overcome by using pRS owing to the sensitivity and nondestructive measurement for monitoring internal stress in various materials [59]. 

This structural information can also help explain changes observed in the mechanical properties of the nanocomposites. As the amorphous content of the samples decreases from UM to dPC and the material becomes more crystalline, the nanocomposites become stronger. Also in the core of the injection moulded test bars where slow cooling is prevalent, the more stable a structure appears to form readily. As the y crystal structure is said to be more ductile than the a, it would be expected that the tensile strength of materials containing mostly a crystals, like DdPC-OdPC, to be much stronger than those with high levels of y crystal in the core. So not only is the increase in modulus due to the reinforcement provided by the clay layers and increase in crystallinity, but also the reduction in y crystal content. 

There have been other studies dealing with the photooxidation of PP/MMt nanocomposites [95-100]. One of them concerned the consequences of photooxidation on the thermal stability and fire-retardant properties of PP-g-MA/MMt nanocomposites [99]. It was shown that the photodegradation dramatically affected the properties of the nanocomposites. A loss of thermal stability and fire retardancy... 

GPa and from 70 to 30 GPa, respectively. The hardness values obtained for the diamond/p-SiC composite fdms at lower and moderate TMS flow rates can be directly related to the high density of the interfaces or grain boundaries present in the fdms owing to the nanocrystallinity of both the phases. Frictional and mechanical properties of the diamond/p-SiC nanocomposite fdms clearly indicate that p-SiC volume fraction can be considered as an important compositional factor to determine any physical properties of the nanocomposite film system. 

A chapter focusing on the use of nanocomposites in electrochemical devices is presented by Schoonman, Zavyalov, and Pivkina. A wide range of metal (metal ox-ide)/polymer nanocomposites has been synthesized using Al, Sn, Zn, Pd, and Ti as a metal source and poly-para-xylylene (PPX) as a polymeric matrix. The properties of the nanocomposites were studied by comparing structure, morphology, electrical properties, oxidation kinetics, and electrochemical parameters. 

The effect of high shear mechanical mixing and soni-cation methods on the physical properties of the nanocomposites has been analyzed [84] using modified clays with a quaternary ammonium salt and calcium carbonate [85] and silane-treated clays [31]. Although the nanoclay is usually chemically modified to make it organophilic and compatible with the polymer matrix, untreated MMT was... 

In Reference 107, the effect of grafting of a polar group (MAH) onto LDPE chains and the chemical modification of clay particles with 2,6-diaminocaproic acid (L-lysine monohydrochloride) to produce nanocomposites with a matrix composed of a ternary blend of PEs (LDPE, LLDPE, and HDPE) was studied in detail. X-ray diffraction was used to determine the exfoliation degree of the clay. Morphological features were revealed by scanning electron microscopy and thermal analysis disclosed the thermal stability of the samples. Comparative analyses of the mechanical (under tension) and rheological properties of the nanocomposites were carried out as well. 

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