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BACKGROUND: The reinforcement of elastomers by the addition of fillers is one of the most important aspects in rubber science and technology. In order to optimise the filler–polymer interface, innovative in situ generation of silica within isoprene rubber was carried out by means of a bottom‐up approach through a sol–gel process starting from tetraethoxysilane as silica precursor. The main aim was the study of the effect of the silica concentration and of the presence of coupling agent on the morphology and the dynamic mechanical behaviour of the composites. RESULTS: The in situ generated silica particles were homogeneously dispersed in the vulcanised rubber with dimensions from a few nanometres to the submicrometre scale. In the presence of coupling agent a good polymer–filler adhesion was observed. The dynamic mechanical behaviour was nonlinear for silica contents higher than 20 wt%. In this range of compositions silica exerted a marked reinforcement on the low‐amplitude storage modulus, which is related to the silica content according to the Huber–Vilgis model. CONCLUSION: Isoprene rubber can be effectively reinforced by the in situ generation of silica for silica contents higher than 20 wt%, and the interaction at the silica–rubber interface can be optimised by using suitable coupling agents. Copyright © 2009 Society of Chemical Industry

The curing reaction, structure, and glass transition behavior of epoxy-clay nanocomposites prepared using several different resin/hardener ratios were investigated. Nonisothermal DSC experiments evidenced that the incorporation of the organoclay did not induce appreciable changes in the curing enthalpy, but determined a slight acceleration of the curing reaction, without modifying the activation energy. TEM and SEM analyses of the nanocomposite resins showed the presence of micrometric aggregates for all the resin/ hardener ratios investigated, even though these materials showed good optical clarity and their WAXD analyses did not evidence any organoclay peak. In addition, the higher the hardener content, the lower the tendency toward exfoliation and the broader the distribution of the interlamellar distances. The degree of cross-linking of cured resins was evaluated both from measurements of the elastic modulus in the rubbery plateau and from solvent sorption experiments. A maximum in cross-link density was observed near the stoichiometric composition. Both modulus and sorption experiments suggested that filler-matrix adhesion increased with increasing the resin/hardener ratio, a trend that was confirmed also by glass transition temperature data.

The sol–gel technique was used to reinforce isoprene rubber (IR) by generating silica in situ from tet- raethoxysilane (TEOS). The aim of the research was to elu- cidate the effect of the preparation conditions on the structural and morphological characteristics of silica and the resulting mechanical reinforcement. The structure of the in situ generated silica was analyzed by 29Si high-reso- lution solid-state NMR spectroscopy, which evidenced a high condensation degree of TEOS that decreased with increasing the sol–gel reaction time. The silica dispersion became less homogeneous as the TEOS content and the reaction time were increased. The incorporation of a cou- pling agent (OTES, octyltriethoxysilane) in the reaction mixture promoted full conversion of TEOS. Lower particle size, better silica dispersion, and higher filler-matrix adhe- sion were noticed if the incorporation of OTES was delayed compared to TEOS. Uniaxial tensile tests evi- denced that the tensile strength typically increased in the first 60 min of reaction and then leveled off. A similar behavior was observed for the high deformation stiffness, whereas at low deformations, the stiffness increased monotonically with the reaction time. In the vulcanizates with silica contents higher than 25 wt %, a drastic stiffness decrement was observed passing from low to high defor- mations. This reduction was ascribed to the disruption of the secondary filler network occurring in these materials when severely stretched

In this work, the effect of the resin/hardener ratio on the small deformation, yield, post‐yield, and fracture behavior of a series of DGEBA‐Jeffamine epoxy‐clay nanocomposites with a fixed organo‐clay content (6 phr), and of the corresponding unfilled resins, was investigated. The mechanical behavior at small deformation was studied by means of uniaxial tensile tests, whereas compression tests were employed to investigate the large (yield and post‐yield) deformation levels. The fracture behavior was studied by the application of fracture mechanics testing methods. The results pointed out that small variations in the resin/hardener ratio used for the preparation of the resin can give rise to remarkable differences in the mechanical behavior at large deformation levels and at fracture. These effects were related to the parameters characteristic of the macromolecular architecture of the resins (chain segments flexibility and crosslink density). The results obtained on nanofilled systems showed that the effect of the resin/hardener ratio on the mechanical behavior of the resins is reduced in presence of organoclay particles. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers