Organically-modified layered silicates as reinforcing fillers for natural and synthetic rubbers

This research is concerned with the characterisation and properties of natural rubber (NR), styrene-butadiene rubber (SBR) and acrylonitrile-butadiene rubber (NBR) nanocomposites. The fillers used were unmodified sodium montmorillonite clay, three organically-modified clays with different types and concentrations of modifiers, and, for comparison, a carbon black. The clays were characterized by Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and x-ray diffraction (XRD). The composites were prepared via melt compounding and sulphur curing in an internal mixer. Better dispersion was found for the organoclays rather than for the unmodified clay as was seen by scanning electron microscopy (SEM). Intercalation and some exfoliation of certain organoclays in rubbers were achieved as revealed by XRD and transmission electron microscopy (TEM). The most polar rubber proved more effective in nanocomposite formation. The incorporation of organoclays affected torque and curing time as measured using a Monsanto rheometer. The organoclays can accelerate the vulcanization process, but the effect was reduced with increasing clay loading. The crosslink density decreased with increasing organoclay content. The static and dynamic mechanical properties of the rubber-layered silicate composites such as tensile properties, modulus, tear strength, fatigue life and dynamic visco-elastic properties are discussed. There was a significant improvement in modulus, tensile strength and elongation at break as compared to the composites prepared with the untreated clay. Dynamic mechanical analysis shows an increase in the storage and loss modulus for the nanocomposites. Overall, the content of clay and the type of modifier both affect the curing and mechanical properties. Rubber-organoclay nanocomposites show a good reinforcing effect which is comparable to that achieved with carbon black. In particular, the tear and fatigue properties of the organoclay-rubber nanocomposites exceeded those of the rubbers reinforced with carbon black.