Dynamic mechanical nanocomposites

Maiti and Bhowmick reported exciting results that a polar matrix like fluoroelastomer (Viton B-50) was able to exfoliate unmodified clay (Cloisite NA ) as well as the modified one (Cloisite 20A) [93]. They studied morphology, mechanical, dynamic mechanical and swelling properties of fluoroelastomer nanocomposites. The unmodified-clay-filled systems showed better properties than the modified ones (Table 2.3). 

Adsorption of rubber over the nanosilica particles alters the viscoelastic responses. Analysis of dynamic mechanical properties therefore provides a direct clue of the mbber-silica interaction. Figure 3.22 shows the variation in storage modulus (log scale) and tan 8 against temperature for ACM-silica, ENR-silica, and in situ acrylic copolymer and terpolymer-silica hybrid 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. 

Velasco-Santos C, Marty nez-Hema ndez AL, Fisher FT, Ruotf R, Castanlo VM (2003a). Dynamical mechanical and thermal analysis of carbon nanotube-methyl methacrylate nanocomposites. J. Phys. D-Applied Phys. 36 1423-1428. 

The effect of polymer-filler interaction on solvent swelling and dynamic mechanical properties of the sol-gel-derived acrylic rubber (ACM)/silica, epoxi-dized natural rubber (ENR)/silica, and polyvinyl alcohol (PVA)/silica hybrid nanocomposites was described by Bandyopadhyay et al. [27]. Theoretical delineation of the reinforcing mechanism of polymer-layered silicate nanocomposites has been attempted by some authors while studying the micromechanics of the intercalated or exfoliated PNCs [28-31]. Wu et al. [32] verified the modulus reinforcement of rubber/clay nanocomposites using composite theories based on Guth, Halpin-Tsai, and the modified Halpin-Tsai equations. On introduction of a modulus reduction factor (MRF) for the platelet-like fillers, the predicted moduli were found to be closer to the experimental measurements. 

The DMA of rubber-based nanocomposites has been the subject of recent research. Many literature reports describe the dynamic mechanical behavior of rubber-based nanocomposites [155, 156]. Das et al. have studied the DMA of CR nanocomposites based on montmorillonite clay and LDH [157]. The montmorillonite clay is... 

On the other hand, Bhattacharya et al. have reported the plasticization effect of organically modified layered silicates on dynamic mechanical properties [13]. In this work, nanocomposites of SBR have been prepared using various nanofillers like modified and unmodified montmorillonite, SP, hectorite etc. It has been observed that the Tg shifts to lower temperature in all the nanocomposites, except for systems from hectorite and NA. This is due to the fact that clay layers form capillaries parallel to each other as they become oriented in a particular direction. Due to wall slippage of the unattached polymer through these capillaries, the Tg is lowered, which could be even more in the absence of organo-modifiers [13]. A similar type of plasticization effect is also noted in the case of the low... 

The dynamic mechanical thermal analyzer (DMTA) is an important tool for studying the structure-property relationships in polymer nanocomposites. DMTA essentially probes the relaxations in polymers, thereby providing a method to understand the mechanical behavior and the molecular structure of these materials under various conditions of stress and temperature. The dynamics of polymer chain relaxation or molecular mobility of polymer main chains and side chains is one of the factors that determine the viscoelastic properties of polymeric macromolecules. The temperature dependence of molecular mobility is characterized by different transitions in which a certain mode of chain motion occurs. A reduction of the tan 8 peak height, a shift of the peak position to higher temperatures, an extra hump or peak in the tan 8 curve above the glass transition temperature (Tg), and a relatively high value of the storage modulus often are reported in support of the dispersion process of the layered silicate. 

Fig. 57 Dynamic mechanical analyses of EPDM-LDH and XNBR-LDH nanocomposites [104]...

Giraldo et al. (38) reported polyamide 6 nanocomposites in which the crystallization temperature of the polymer was observed to increase with the addition of 2 wt% CNTs. The temperature was 185°C for the pure polyamide which subsequently increased to 190 °C. The authors suggested that the nanotubes might serve as the nucleation sites for the polymer crystals to grow which was also confirmed by the reduction of the chain mobility by dynamic mechanical analysis. The thermal stability of the composites was reported to enhance after the incorporation of nanotubes. 

Dynamic mechanical property tests indicated that the storage modulus of the resulting nanocomposites at 20 wt% CNTs loading was improved by a factor of 3.4 compared with neat PC material, as shown in Figure 14.15. It was reported that PC/buckypaper samples... 

The results are reported of an in depth study of the structure, thermal properties, dynamic mechanical properties, flammability and smoke properties of melt blended PVC-sodium montmorillonite nanocomposites. Investigative properties employed included X-ray diffraction, TEM, TGA, DMA and cone calorimetry. The effects of clay loading, DOP concentration, annealing, blending time and molec.wt. on the formation of the composites are discussed and fire properties of PVC-organically modified clay and PVC-sodium clay nanocomposites are presented and discussed. 15 refs. USA... 

Mohanty, S., and Nayak, S. K., Effect of clay exfoliation and organic modification on morphological, dynamic mechanical, and thermal behaviour of melt-compounded polyamide-6 nanocomposites, Polym. Compos., 28, 153-162 (2007). 

Mijovic, J., Lee, H. K., Kenny, J., and Mays, J., Dynamics in polymer-silicate nanocomposites as smdied by dielectric relaxation spectroscopy and dynamic mechanical spectroscopy, Macrvmolecules, 39, 2172—2182 (2006). 

The glass transition temperature (Tg) of cellulose reinforced composites is an important parameter which influences different properties of the resulting composite such as mechanical behavior, matrix chains dynamics and swelling behavior. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) are used to evaluate the Tg value of cellulose nanocomposites. In some cases, the addition of cellulose nanocrystals into polymer matrices does not seem to affect the... 

Analogous results have been recently obtained by other research groups. The effect of -COOH- and phenol-functionalized CNTs on mechanical, dynamic mechanical and thermal properties of polypropylene (PP) nanocomposites were considered, and the results confirmed in both cases that the percentage crystallinity was found to increase on phenol and carboxylic functionalization of MWNTs. 

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