ENHANCEMENT OF ELECTRICAL CONDUCTIVITY AND FILLER DISPERSION OF CARBON NANOTUBE FILLED NATURAL RUBBER COMPOSITES BY LATEX MIXING AND IN SITU SILANIZATION

Abstract

ABSTRACT Carbon nanotube (CNT)-filled natural rubber (NR) composites were prepared by melt and by latex mixing methods. Also in situ functionalization of CNTs with a silane coupling agent, namely bis(triethoxysilylpropyl)tetrasulfide (TESPT), was done to improve the filler–rubber interactions between CNT surfaces and rubber molecules. The grafting of TESPT molecules on CNT surfaces was confirmed by attenuated total reflection (ATR)–Fourier transform infrared (FTIR) spectroscopy and by the improvement of composite properties. Tensile properties were determined to assess the reinforcement efficiency of the CNTs in the composites. Also, electrical conductivity of the composites was measured to assess the formation of CNT networks (or connected conductive CNT pathways) in the rubber matrix. The results indicate that the composites prepared by latex mixing, in particular with the TESPT, had better tensile properties and electrical conductivities than the composites made by melt mixing. The lowest percolation threshold concentration, about 0.55 phr of CNTs, was observed in the latex–CNT composites, and three-dimensional network formations of CNTs in the rubber matrix were found with added TESPT, used by in situ functionalization. The improvement of filler–rubber interactions with the addition of TESPT was also examined by temperature scanning stress relaxation measurements, revealing the relaxation modulus, the relaxation spectrum, and an estimate of the cross-link density.