Properties of vulcanized rubber nanocomposites filled with nanokaolin and precipitated silica

One kind of nanokaolin (NK) powder with 20–50 nm average thickness, 300–500 nm average diameter, and 32 m2/g specific surface area, has been introduced into four types of rubber, specifically styrene butadiene rubber (SBR), natural rubber (NR), butadiene rubber (BR) and ethylene–propylene diene methylene (EPDM). Their reinforcing effects were evaluated by comparisons with those from precipitated silica (PS). The curability, mechanical properties, microstructure and the thermal stability of a variety of composites based on these rubbers were studied. This was done using vulcanization techniques, mechanical testing, thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results showed that NK can greatly improve the vulcanizing process by shortening the time to optimum cure (t90) and prolonging the setting-up time (t10) of cross-linked rubbers, which improves production efficiency and operational security. The rubber composites filled with nanokaolin were found to have good mechanical properties, thermal stabilities, and elastomeric properties. The tensile strengths of the rubber/NK composites are close to those of rubber/PS composites, but the tear strength and modulus are not as good as the corresponding properties of those containing precipitated silica. Microstructural results revealed that the NK sheets are well dispersed in the rubber matrix in the parallel arrangement. The good interfacial interactions between the NK and the rubber chains give these rubber composites excellent processability, mechanical properties, and thermal stability.