Recently, elastomer - nanocomposites reinforced with low volume fraction of nanofillers have attracted great interest due to their fascinating properties. The incorporation of nanofillers such as layered silicate clays, carbon nanotubes, nanofibers, calcium carbonate, metal oxides or silica nanoparticles into elastomers improves significantly their mechanical, thermal, dynamic mechanical, barrier properties, flame retardancy, etc. The properties of nanocomposites depend greatly on the chemistry of polymer matrices, nature of nanofillers, and the method in which they are prepared. The uniform dispersion of nanofillers in elastomer matrices is a general prerequisite for achieving desired mechanical and physical characteristics. In this review article, current developments in the field of elastomer nanocomposites reinforced with layered silicates, silica, carbon nanotubes, nanofibers and various other nanoparticles have been addressed. Attention has been paid to the structure and properties of such high-performance nanocomposites, along with the theories and models existing in this field.

Zinc oxide (ZnO) nanoparticles were synthesized by homogeneous precipitation and calcination method and were then characterized by transmission electron microscopy and X-ray diffraction analysis. Synthesized ZnO was found to have no impurity and had a dimension ranging from 30-70 nm with an average of 50 nm. The effect of these ZnO nanoparticles as cure activator was studied for the first time in natural rubber (NR) and nitrile rubber (NBR) and compared with conventional rubber grade ZnO with special reference to mechanical and dynamic mechanical properties. From the rheograph, the maximum torque value was found to increase for both NR and NBR compounds containing ZnO nanoparticles. ZnO nanoparticles were found to be more uniformly dispersed in the rubber matrix in comparison with the conventional rubber grade ZnO as evident from scanning electron microscopy/X-ray dot mapping analysis. The tensile strength was observed to improve by 80% for NR when ZnO nanoparticles were used as cure activator instead of conventional rubber grade ZnO. An improvement of 70% was observed in the case of NBR. The glass transition temperature (T g ) showed a positive shift by 68C for both NR and NBR nanocomposites, which indicated an increase in crosslinking density. The swelling ratio was found to decrease in the case of both NR and NBR, and volume fraction of rubber in swollen gel was observed to increase, which supported the improvement in mechanical and dynamic mechanical properties.

In the present work, rubber/clay nanocomposites were prepared by a solution mixing process using fluoroelastomers and different nanoclays (namely, Cloisite NAþ, Cloisite 10A, Cloisite 20A, and Cloisite 30B). Fluoroelastomers having different microstructure and viscosity (Viton B-50, Viton B-600, Viton A-200, and VTR-8550) were used. Characterization of the nanocomposites was done by using X-ray diffraction and atomic force microscopy. The mechanical and dynamic mechanical properties were studied. The surface energy of the clays and the elastomer was also measured. Even with the addition of only 4 phr of clay in Viton B-50, tensile strength and modulus improved by 30-96% and 80-134%, respectively, depending on the nature of the nanoclays. Exfoliation was observed with both the unmodified and the modified clays at low loading in all the fluoroelastomers. Best properties were observed with the unmodified clay. All the grades of fluororubber followed the same trend. The increment (19%) in storage modulus was also higher in the case of the unmodified clay filled Viton B-50 system. The results were explained with the help of thermodynamics, surface energies, and swelling studies. The difference in surface energy, Dc, between the rubber and the unmodified clay was lower. The work of adhesion (67.63 mJ/m 2 ) between Viton B-50 and Cloisite NAþ was also higher than that (51.42 mJ/m 2 ) between Viton B-50 and Cloisite 20A. Negative DH S value for the unmodified clay-filled system thermodynamically favored the formation of the nanocomposite as compared to the modified clay filled samples where DH S is positive or zero. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: [162][163][164][165][166][167][168][169][170][171][172][173][174][175][176] 2006

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