A Comparative Study of the Mechanical Properties and Swelling Resistance of Diene Rubber-Based Nanocomposites Reinforced by Pristine and Surface-Functionalized Carbon Nanotubes

This study investigates the effects of pristine carbon nanotubes and surface-functionalized carbon nanotubes modified with 3-aminopropyltriethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, and 1-octadecanol on the performance of nanostructured blends based on ethylene propylene diene rubber and styrene–butadiene rubber. Particular emphasis is placed on rheometric characteristics, mechanical behavior, morphological features, abrasion resistance, swelling resistance, compression set, and crosslink density. The filler concentration was varied from zero to eight parts per hundred rubber. With increasing filler content, the minimum torque, maximum torque, torque difference, and cure rate index showed consistent enhancement, accompanied by a reduction in scorch time and optimum cure time. Regardless of the carbon nanotube modification type, higher loadings resulted in increased compound viscosity, accelerated curing, elevated crosslink density, and improved abrasion resistance and hardness. Tear strength, compression set, and swelling resistance exhibited continuous improvement across all systems with increasing filler content. Tensile strength increased up to an optimum loading of five parts per hundred rubber, followed by a decline at higher concentrations, with maximum enhancements of 99, 144, 177, and 206% for systems filled with pristine carbon nanotubes and the three modified carbon nanotubes, respectively. Corresponding increases in modulus at one hundred percent elongation were 29, 40, 51, and 58%, while elongation at break decreased by 20, 24, 28, and 34%. Tear strength improved by 73, 109, 134, and 167%, whereas rebound resilience declined by 46, 51, 59, and 64% for the respective filler systems. Finally, the overall performance of the carbon nanotube-reinforced blends was benchmarked against previously reported nanofiller-reinforced ethylene propylene diene rubber and styrene–butadiene rubber formulations in the literature.