Modified bentonite (M-BNT) was prepared by treating raw bentonite (BNT) with NaCl, tetradecyldimethylamine chloride salt and coco diethanolamide. X-ray diffraction (XRD) analysis and attenuated total reflectance – Fourier transform infrared (ATR-FTIR) spectroscopy showed intercalation of the organic modifiers into the layers of M-BNT. The effect of partially replacing silica with BNT and M-BNT on the tensile properties of natural rubber (NR) composites was investigated. Results showed that 15 phr M-BNT, as well as 10/5 phr silica/BNT mixture filler, imparted great improvement in the tensile modulus and stresses at 100, 200 and 300% strain of NR composites. Moreover, 10/2.5/2.5 and 2.5/10/2.5 phr silica/M-BNT/BNT mixture filler gave the NR composites high tensile strength and elongation at break relative to unfilled NR. Contour plots showed that tensile properties of NR composites decreased with increasing amount of BNT.

This study investigated moisture diffusion in natural rubber (NR) hybrid composites filled with silica and bentonite clay. Natural bentonite (BNT) was treated with tetradecyldimethylammonium chloride and coco diethanolamide to produce modified bentonite (M-BNT). Varied proportions of silica, M-BNT, and BNT fillers were added to raw NR according to a third-degree simplex lattice mixture design of experiment. The addition of fillers affects the vulcanization characteristics, mechanical properties, and hardness of NR hybrid composites. Moisture diffusion behavior was studied by monitoring the water uptake of NR composites during immersion in deionized water at 80°C. Data from sorption experiments were fitted on the classical Fickian and Langmuir-type diffusion models. The Fickian model overestimates and underestimates the water uptake of NR composites in the early and later stages of moisture diffusion, respectively. On the other hand, the Langmuir-type model adequately captures the anomalous diffusion behavior of moisture in NR composites. Parameters of the Langmuir model (equilibrium water uptake and diffusion coefficient) vary with the composition of hybrid fillers. Optimum proportions of silica, M-BNT, and BNT in rubber composites were obtained by considering the effect of fillers on mechanical properties and moisture diffusion characteristics of NR.

The goal of this study was to investigate the effect of varied proportions of silica/M-BNT/BNT on the curing properties of natural rubber (NR) composites. Thirteen ternary-filled NR composites and a control sample were prepared in this study based on a third degree – simplex lattice mixture design of experiment. It was observed that high loading of silica has a retarding effect on vulcanization rate due to the presence of silanol groups on its surface. Replacement of silica with BNT led to a big reduction in scorch time and increase in vulcanization rate due to the presence of metallic oxides acting as co-activators. The addition of the organoclay M-BNT to silica and BNT resulted to shorter scorch time, an increase in vulcanization rate, and a decrease in minimum and maximum torques improving the processability of the rubber composite. The kinetic model was able to demonstrate the vulcanization behavior of the rubber composites as supported by the very high coefficient of determination (R2) values for all samples. The generated contour plots for maximum torque (MH), minimum torque (ML), scorch time (tS1), cure rate index (CRI), induction time (ti) and rate constant (k1) were able to display the trends observed in the experimental values.