Reinforcement Effect of Plasma Modified Halloysite Nanotubes In a Carbon Black Filled Natural Rubber-Butadiene Rubber Matrix

Rubber composites are generally produced by the direct incorporation of fillers like carbon black and/or silica into the rubber matrix. The incorporation of different types of nanofillers is the subject of recent research with the aim of preparing composites with special compositions and properties. A successful application of nanomaterials depends mainly on the degree of dispersion of the nano-sized fillers. Recently, a naturally occurring clay mineral, halloysite nanotubes (HNTs), is investigated concerning its suitability for rubber reinforcement. As these nanotubes have geometrical similarity with carbon nanotubes, it is expected that these minerals would impart a significant reinforcement effect on the rubber compounds. However, the dispersion of these nanofillers is extremely difficult. In the present work, halloysite nanotubes have been surface-modified by plasma polymerization with different monomers in order to change their surface polarity and chemistry. These modified nanotubes were used as reinforcing filler in a natural rubber (NR)/butadiene rubber (BR) blend in the presence of carbon black. The aim of the treatment was to improve the dispersion of the fillers and the compatibility and interaction between HNTs and the rubber matrix. The deposition of the plasma coating was proven by thermo gravimetric analysis, whereas water penetration measurements showed a reduction in surface polarity. The effect of the plasma treatment of the HNTs on dispersion and rubber-filler interaction was investigated by measurement of the Payne effect, bound rubber content as well as dynamic and mechanical properties. Thiophene modification of HNTs influences the stress-strain properties of the composites. The surface modification also results in a higher bound rubber content which indicates better filler-polymer interaction and scanning electron microscopy measurements show interaction between modified HNTs and carbon black. As visualized by transmission electron microscopy, the thiophene modified HNTs formed a special type of nanoclusters with carbon black particles, which was ultimately reflected in the final mechanical properties of the nanocomposites.