Silane Treatment as an Effective Way of Improving the Reinforcing Activity of Carbon Nanofibers in Nitrile Rubber Composites

Two different silane treatment methods were used to improve the reinforcing activity of carbon nanofibers (CNF) in acrylonitrile-butadiene rubber (NBR) composites. The first method was chemical silanization with [3-(2-aminoethylamino)propyl]trimethoxysilane (APTS) in ethanol solution, preceded by oxidation of the CNF with H2SO4/HNO3. The second method was direct incorporation of silanes during preparation of the composites (in-situ silanization). Three different silane coupling agents were used: [3-(2-aminoethylamino)propyl]trimethoxysilane, (3-mercaptopropyl)trimethoxysilane (MPTS), and 3-ureidopropyltrimethoxysilane (UPTS). The NBR composites were prepared in an internal laboratory mixer, with increasing concentrations of pure or modified CNF. The crosslink density and flammability of the NBR-filled composites were analyzed, as well as their rheological and mechanical properties. The electrical conductivity of the composites was measured to assess the formation of CNF networks in the elastomer matrix. The morphology of the CNF was assessed by scanning electron microscopy (SEM). Both the dispersion of the CNF in the NBR matrix and the polymer-filler interactions were improved following silane modification, as shown in SEM images and by the Payne Effect. The composites were also found to have enhanced moduli, tensile strength, hardness, damping, and electrical conductivity. Chemical treatment proved to be more effective at improving the reinforcing effect of CNF in the elastomer matrix than in-situ silanization. The results of this study demonstrate the great potential of both in-situ and chemical silanization for the preparation of reinforced polymer composites filled with CNF.