Effects of characteristics of rubber, mixing and vulcanization on the structure and properties of rubber/clay nanocomposites by melt blending

Three rubber-based nanocomposites, natural rubber (NR), styrene-butadiene rubber (SBR), and ethylene-propylene-diene rubber (EPDM) matrixes, were prepared with octadecylamine modified fluorohectorite (OC) by melt blending. X-ray diffraction (XRD) revealed that the SBR/OC and EPDM/OC nanocomposites exhibited a well-ordered intercalated structure and a disordered intercalated structure, respectively. In the case of the NR/OC nanocomposite, it exhibited an intermediate intercalated and even exfoliated structure. These results were in good agreement with transmission electron microscopy (TEM) observations. Furthermore, in the NR/OC and SBR/OC systems, the mixing process played a predominant role in the formation of nanometer-scale dispersion structure, whereas the intercalated structure of EPDM/OC formed mainly during the vulcanization process. The tensile strength of SBR/OC and EPDM/OC nanocomposites loading 10 phr OC was 4-5 times higher than the value obtained for the corresponding pure rubber vulcanizate, which could be ascribed to the slippage of the rubber molecules and the orientation of the intercalated OC. For the strain-induced crystallization NR, the exfoliated OC efficiently improved the modulus of the NR/OC nanocomposite relative to the pure NR. However, its hindrance on NR crystallization during the tensile process may be the main reason for the decrease in tensile strength of NR/OC.