Effect of bentonite clay reinforcement on the mechanical, thermal and aging properties of peroxide-vulcanized hydrogenated nitrile butadiene rubber composites

Hydrogenated nitrile butadiene rubber (HNBR) composites reinforced with bentonite clay were developed via peroxide vulcanization to investigate their mechanical, thermal, and aging properties.Bentonite clay was added to the HNBR matrix at 0, 3, 9, and 15 wt.% loadings, and the composites were analyzed using rheometric tests, mechanical testing, FTIR spectroscopy, thermogravimetric analysis (TGA), differential thermogravimetry (DTG), and cross-linking density measurements.The optimal performance was observed at 9 wt.% clay, where tensile strength improved to 10.4 MPa (from 9.2 MPa for pure HNBR), and the maximum decomposition temperature increased from 457 to 467C, indicating enhanced thermal stability.Shore A hardness also increased from 70 to 75, reflecting higher rigidity.Aging tests at 125C for 1000 h showed a 1.5% increase in tensile strength at 9 wt.% clay, although elongation at break decreased due to filler-induced matrix stiffening.FTIR analysis revealed oxidation and cross-linking of nitrile groups, forming carboxylic acid functionalities.Cross-linking density initially decreased due to chain scission, then recovered via further cross-linking.TGA/DTG data confirmed bentonite clay's barrier effect above 410C, reducing degradation by inhibiting volatile release.Homogeneous clay dispersion improved crack resistance and lowered gas permeability, enhancing durability.These findings demonstrate that 9 wt.% bentonite clay provides an effective balance of mechanical strength, thermal resistance, and aging stability, making HNBR/BC composites promising for automotive, high-temperature, and oil exploration applications