Preparation and application of carbon nanotubes/conductive carbon black/ethylene-propylene-diene rubber composite

Abstract

" Addition of conductive fillers such as conductive carbon black (CCB) and carbon nanotubes (CNTs) could significantly improve the electrical conductivity of rubber. However, that would result in the deterioration of processing properties for rubber compound and the rapid increase in hardness of vulcanizates, which affected seriously the preparation of conductive rubber composites and thus limits the application in the field of flexible conductive rubber materials. Plasticizer such as paraffin oil was usually utilized to reduce the hardness of conductive vulcanizates, accompanied by strength reduction. In this paper, conductive fillers were pre-dispersed in solid rubber and liquid rubber, which had good compatibility with rubber matrix of conductive vulcanizates. Conductive fillers and plasticizer were directly replaced by the above composite. It aimed to achieve good electrical conductivity and flexibility together with improved strength of vulcanizates. Firstly, CCB and CNTs were mixed well with solid ethylene-propylene-diene monomer (EPDM) and liquid EPDM. EPDM matrix was masticated and then mixed with the aforementioned composite and the rest of reagents. Finally, rubber compounds obtained above were vulcanized to prepare vulcanizates. Scanning electronic microscope (SEM) micrographs of conductive vulcanizates were shown in Fig 1. The pre-mixed conductive fillers were uniformly dispersed in matrix of conductive vulcanizates, while those without pre-mixing had poor dispersion. This might be due to good compatibility between rubber matrix of conductive vulcanizates and rubber carrier of solid EPDM and liquid EPDM, in which conductive fillers were pre-dispersed well. It was of benefit to further improvement of conductive filler dispersion in rubber matrix during compound mixing process. Volume resistivity (ρv) of vulcanizates decreased initially with increasing CNTs dose [up to 1.5 phr (mass, similarly hereinafter)] and tended to level off afterward (Fig 2). The improvement of electrical conductivity resulted from the formation of conductive network consisting of CCB and CNTs. Tensile strength and tear strength of vulcanizates increased with increasing CNTs dose (Fig 3). It might be attributed to the synergistic reinforcing effect of CCB and CNTs, which meant that rubber composite could withstand more stress. For the conductive vulcanizate with CCB of 25 phr and CNTs of 1.5 phr with pre-mixing, shore A hardness, ρv, tensile strength and tear strength were 63, 223 Ω·cm, 15.3 MPa and 44 kN/m, respectively, much better than those of the vulcanizate without pre-mixing (68, 1.1×105 Ω·cm, 11.5 MPa and 32 kN/m, respectively). The results indicated that conductive fillers well-dispersed in rubber carrier could significantly improve electrical conductivity and strength of vulcanizates, mainly due to better dispersion of pre-mixed conductive fillers and thus more complete conductive network as well as better synergistic reinforcing effect."