A layered double hydroxide (LDH) mineral filler particle has been designed and employed in rubber vulcanization to prepare a more environmentally friendly rubber composite. The LDH delivers zinc ions in the vulcanization process as accelerators, stearate anions as activators and simultaneously the mineral sheets act as a nanofiller to reinforce the rubber matrix whilst totally replacing the separate zinc oxide (ZnO) and stearic acid conventionally used in the formulation of rubber. This method leads to a significant reduction (nearly 10 times) of the zinc level and yields excellent transparent properties in the final rubber product. The morphological characterization, rheometric curing behaviour, mechanical properties and uniaxial multi-hysteresis behaviours of the resultant rubber/LDH nanocomposite are studied in this paper.

We report the unusual mechanical percolation behavior of expanded clay nanoparticles in a natural rubber (NR) matrix. This phenomenon is discussed in terms of fractal dimensions of the nanoparticle cluster. Highly exfoliated structures of nanoparticles in NR are obtained by a process we call the ‘propping-open approach’. The impact of filler dispersion and rubber–filler interactions on the viscoelastic behavior of NR–clay nanocomposites is systematically investigated. We observe non-linear viscoelastic behavior (Payne effect) at very low nanoparticle concentrations which we attribute to the formation of a network-like structure of the exfoliated clay particles. We rely on the Kraus and Maier–Göritz models to interpret such nonlinear viscoelastic behavior. We find that the chain mobility of the NR is greatly reduced based on the viscoelastic master curves. The value of the mechanical percolation threshold (φ_p) and the fractal nature of nanoparticle clusters are determined through an analysis of the experimental data based on a theory put forward by Huber and Vilgis. The nature of rubber–filler interactions is further understood from swelling experiments utilizing the Kraus and Cunneen–Russell equations.

Carbon nanotubes (CNTs) are known for excellent electrical conductivity and high elastic modulus. But difficulties arise in realizing their potential in matrices due to their existence in the form of aggregates or agglomerates. A simplified mixing technique using ionic liquid (IL) was developed to improve the dispersion of CNTs in elastomers. At first, CNTs were modified using an IL, 1-butyl-3-methyl-imidazolium-bis-(trifluoromethylsulfonyl)-imide in a mortar and pestle, and later, the modified tubes were incorporated into elastomers using a two-roll mill. The effect of modified tubes and IL on polar polychloroprene and nonpolar solution styrene butadiene rubber is studied. Enhanced dispersion and networking of CNTs can be achieved using this technique, based on which highly conducting composites were developed. Moreover, the composites with modified CNTs exhibited higher mechanical properties (tensile modulus, hardness) and thermal stability than the composites with unmodified CNTs. ILs are also found to have multifunctional roles (as antioxidants, as coupling agents) in the composites. The applications of composites with a particular focus on actuators and sensors are also discussed.