Enhancing curing, mechanical and electrical properties of epoxidized natural rubber nanocomposites with graphene and carbon nanotubes hybrid fillers

The effect of incorporating a combination of hybrid carbon fillers, graphene (GP), and carbon nanotubes (CNT) into epoxidized natural rubber with 25 mol% epoxidations (ENR-25) nanocomposites was investigated. The results demonstrated significant effects of CNT incorporation in ENR-25/GP–CNT hybrid composites on the cure characteristics, including shorter scorch and cure times, lower activation energy, and higher torque difference as the CNT loading increased. Fourier Transform Infrared analysis revealed a decrease in absorption intensity at a wavenumber of 1115 cm−1 with increasing CNT loadings. This observation can be attributed to chemical interactions between the polar functional groups in the ENR molecules and the polar groups on the CNT surfaces. Additionally, the hybrid GP–CNT filler was found to improve the mechanical properties, such as modulus and hardness, of the ENR/GP–CNT hybrid composites. The crosslink densities of the hybrid composites were measured using the Flory–Rehner theory, showing an increasing trend with higher CNT loadings. This phenomenon can be explained by the formation of end-to-end connections between certain parts of the CNT and the GP, leading to the establishment of a three-dimensional filler network with strong interactions among the components. Consequently, this facilitates the good dispersion and distribution of CNT within the composites. The observed trends in the mechanical properties were consistent with an increasing Payne effect and electrical conductivity as the CNT loadings increased. Notably, it was found that the ENR/GP–CNT hybrid composites exhibited a low percolation threshold concentration of 2.34 phr of CNT, indicating that they behave as conductive rubber materials.