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The recent developments in the vulcanization of elastomers, major types of crosslinking, and mechanism of crosslinking have been reviewed. Attention has been made to sum up the accelerated vulcanization. Possible mechanisms by which the reaction is taking place are discussed. The role of accelerators, activators, and fillers has been described. The different types of crosslinks and importance of each type on the specific properties of the resulting vulcanizates, etc., are discussed. Various aspects of vulcanization like model compound vulcanization, nitrosamine generation, etc., are discussed. The importance of binary accelerators and possible mechanism of their action have been mentioned. The method of double network formation, which is useful for the improvement in properties, is also described. The different methods for characterization of networks and different methods for estimating crosslink densities are also explained.

Poly (ethylene-co-vinyl acetate) (EVA)/clay nanocomposites containing two different organoclays with different clay loadings were prepared. The transport of gases (oxygen and nitrogen) through the composite membranes was investigated and the results were compared. These studies revealed that the incorporation of nanoclays in the polymer increased the efficiency of the membranes toward barrier properties. It was also found that the barrier properties of the membranes decreased with clay loadings. This is mainly due to the aggregation of clay at higher loadings. The morphology of the nanocomposites was studied by scanning electron microscopy, transmission electron microscopy and X-ray scattering. Small angle X-ray scattering results showed significant intercalation of the polymer chains between the organo-modified silicate layers in all cases. Better dispersed silicate layer stacking and more homogeneous membranes were obtained for Cloisite V R 25A based nanocomposites compared with Cloisite V R 20A samples. Microscopic observations (SEM and TEM) were coherent with those results. The dispersion of clay platelets seemed to be maximized for 3 wt % of clay and agglomeration increased with higher clay loading. Wide angle X-ray scattering results showed no significant modifications in the crystalline structure of the EVA matrix because of the presence of the clays. The effect of free volume on the transport behavior was studied using positron annihilation spectroscopy. The permeability results have been correlated with various permeation models.

Natural rubber latex layered clay nanocomposites were prepared with low loadings of nanoclay using conventional compounding technique. A higher loading of clay resulted in processing difficulties due to viscosity build up. X-ray analysis showed that nanocomposites in which layered silicate layers were either delaminated or ordered as in an intercalated structure was obtained. Partially exfoliated structure was observed from TEM photographs of nanocomposites with 3 phr nanoclay. The transport properties, sorption, diffusion, and permeation coefficients were measured using the solvent toluene at 303 K. A higher decrease for the diffusion coefficient for nanocomposites directs the presence of tortuous path for the diffusing molecules. Thermodynamic parameters show a better compatibility for the silicates with rubber resulted in the formation of an elastomeric network. Gas permeability results of the nanocomposites suggest a better barrier resistance for oxygen molecules even in lower loading of nanoclay and different gas transport models (Nielsen, Bharadwaj, Cussler) were applied to describe the behavior of these nanocomposites.

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