Mechanical properties of organomodified kaolin/natural rubber vulcanizates

Kaolin modified with sodium salt of rubber seed oil (RSO-Na) was compounded with natural rubber (NR) by melt intercalation. The effect of modified kaolin loading on the physicomechanical properties of the vulcanizates was examined by varying its incorporation (2–10 phr). The RSO-Na modified kaolin was characterized using infrared spectroscopy (FTIR) and X-ray diffraction (XRD). XRD of the unmodified and modified kaolin revealed an increased d-spacing of kaolinite to 14 Ǻ. FTIR spectroscopy also indicated the intercalation of RSO-Na onto the kaolinite surface. The tensile and tear properties increased with increasing filler loading even though an optimum of tensile strength was achieved at 8 phr of modified kaolin. The swelling index was reduced by filling with modified kaolin. The storage modulus value for the modified samples was higher than the NR vulcanizates with unmodified kaolin. Furthermore, the chemical crosslink density (CLD) of 0.651 at 8 phr modified kaolin indicated better reinforcement of the rubber-filler matrix. The morphological studies by SEM revealed that incorporation of modified kaolin up to 8 phr resulted in the improvement of failure properties of the resulting NR vulcanizates.