Novel information on filler−elastomer interactions is obtained by combining solid-state 1H low-field NMR spectroscopy and equilibrium swelling experiments. Multiple-quantum (MQ) NMR experiments provide detailed quantitative molecular information on the cross-link density of the elastomer matrix in a variety of filled systems, indicating generally weak filler effects on the overall cross-link density and on the network homogeneity. Swelling experiments, as well as mechanical data, are additionally influenced by the matrix−filler and filler−filler interactions. Our approach is based on comparing cross-link densities from NMR and (Flory−Rehner) swelling experiments, for which a masterline is always found in unfilled elastomers. In filled elastomers two different scenarios are observed. If there are no interactions between the polymer chains and the filler surface, no deviations from the masterline are detected because the swelling capacity of the composite is governed by the bulk polymer. Deviations from the masterline (reduced swelling) are exhibited by those composites that have strong rubber−filler interactions. In these cases, some fraction of the polymer is connected to the filler surface, which thus behaves like a giant cross-link, and the overall degree of swelling is thus reduced as compared to the bulk polymer. The novel experimental approach was used to evaluate filler−elastomer interactions in different composites and nanocomposites.

Rubber compounds based on natural rubber (NR) reinforced with octadecylamine‐modified bentonite have been prepared via a vulcanization process and characterized by several techniques. The silicate nanolayers are exfoliated and uniformly dispersed in the polymer chains. Monsanto measurements have shown that the organoclay accelerates the vulcanization reaction and, furthermore, gives rise to a marked increase of the torque, indicating that the elastomer becomes more crosslinked in the presence of the organoclay. These results were corrobated by swelling measurements since a noticeable increase in the curing degree was observed when the organoclay was added to the rubber recipe. Moreover, thermodynamic parameters have shown an increase in the structural order of the nanocomposite. In addition, thermal analysis supports the assumption that the degree of curing of the elastomer increases when the organoclay is added to the elastomer. An appreciable increase of the involved heat during the curing reaction has been observed. Moreover, the Tg of the NR increases in the presence of the organoclay due to the confinement of the elastomer segment into the organoclay nanolayers, which restricts the mobility of the chains. Copyright © 2003 Society of Chemical Industry

This investigation describes two methods to obtain rubber composites based on natural rubber (NR) and organophilic layered silicates. In order to improve the exfoliation and compatibilization of the organoclays with the rubber matrix, a new approach which involves swelling of the organoclays with an elastomer solution prior to compounding has been used. The effect of the addition during swelling of a coupling agent, namely bis(trietoxysilylpropyl)tetrasulfan (TESPT), on the behaviour of the composites was also investigated. The results show that a low amount of organoclay (10 phr) significantly improves the properties of natural rubber. This suggests a strong rubber-organoclay interaction which is attributed to a high degree of rubber intercalation into the nanosilicate galleries, as was confirmed from X-ray diffraction. In addition, an ulterior improvement in the properties of the nanocomposites prepared by solution mixing is clearly observed, due to the better filler-rubber compatibility. An even further increase in the properties is observed by treating the silicate with a silane coupling agent. The silane functional groups modify the clay surface, thus reducing the surface energy, and consequently improving the compatibility with the rubber matrix.

The effect of the incorporation of single‐walled carbon nanotubes (SWNTs) on the PP crystallization kinetics is investigated by thermal analysis, microscopy and Raman spectroscopy. The results of the investigation show that SWNT acts as a strong nucleation agent. A marked decrease of the half‐time of PP crystallization as well as a sensible increase of the overall crystallization rate is observed in the presence of SWNTs. Moreover, these effects are already noticeable at the lowest SWNT content in the composite with slow further effects at higher concentrations, suggesting a saturation of the nucleating action at the higher concentrations studied. The Avrami model can represent the crystallization kinetics of PP in the composite. The kinetic curves obtained under non‐isothermal conditions confirm the results obtained in isothermal tests and demonstrate the nucleation ability of SWNTs on the PP crystallization. Raman spectroscopy and scanning electron microscopy (SEM) are successfully applied to demonstrate that in the composite films, the changes in the crystallization kinetics can be explained in terms of the changes of the distance between nanotubes in bundles following a different intercalation of the polymer matrix.

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