Correlating mechanical and electrical properties of filler-loaded polyurethane fluoroelastomers: the influence of carbon black

The dynamic mechanical properties and electrical conductivity of a class of polyurethane fluoroelastomers filled with different carbon black types and loadings were investigated. In particular, finely structured and coarsely structured carbon blacks were considered. Dynamic mechanical analysis (DMA) on the unfilled fluoroelastomer confirmed the phase-segregated nature of this copolymer. The dynamic mechanical behavior of elastomeric compounds reinforced with finely structured carbon black was found to be strongly influenced by the filler content above a threshold value. This behavior may be attributed to the formation of carbon black aggregates and three-dimensional anisotropic structures at increasing filler loading. Such an effect was not observed in compounds filled with coarsely structured carbon black particles, which do not seem to form higher level structures. These observations were supported by calculations on the hydrodynamic effect of the filler on the storage modulus G0 of carbon black–loaded compounds. Electrochemical impedance spectroscopy measurements on filled fluoroelastomers revealed the presence of an electrical percolation threshold for finely structured carbon black–filled compounds that supports the hypothesis of the presence of a three-dimensional anisotropic network forming at high filler loading. No percolation threshold was found in coarsely structured carbon black–filled compounds in accordance with DMA. These results can provide useful guidelines for the design of high-performance carbon black–filled polyurethane fluoroelastomers.