Mussel Inspired Surface Functionalization on Multiwalled Carbon Nanotubes(MWCNT) and Its Nanocomposites

Surface functionalization of multi-walled carbon nanotubes (MWCNTs) by bio-inspired polydopamine and its application in the preparatjion of natural rubber (NR)-MWCNT nanocomposites was studied. The dispersion of MWCNTs in the water and NR is improved by treating with cetyltrimethyl ammonium bromide (CTAB), and deposited by a poly(dopamine) (PDA) layer via in situ spontaneous oxidative polymerization of dopamine in alkaline solution at room temperature. The thickness of PDA layers on the surface of MWCNTs is controllable in the nanometer scale by controlling the concentration of dopamine. MWCNTs/ NR nanocomposites were prepared by mixing the functionalized MWCNTs water solution with the NR solution, and subsequently the mixture was co-coagulated by adding dilute sulfuric acid. Finally, the dried co-coagulated compound was compounded with rubber additives with a two-roll mill. The morphology of MWCNTs/NR nanocomposites was studied by transmission electron microscopy (TEM), and the results show that MWCNTs are uniformly dispersed in the NR matrix. The addition of MWCNTs can improve the vulcanization rate of NR, shorten the scorch time and optimum cure time, and increase the degree of cure. The RPA results show that the modulus of MWCNTs/NR is significantly improved when the content of MWCNTs increased to 5 phr, and decreases with increasing of strain without an obvious plateau. The mechanical property of the MWCNTs/NR nanocomposites, including tensile strength, elongation at break, tensile stress at a given elongation, and hardness, were investigated. The tensile stress at a given elongation and hardness of MWCNTs/NR nanocomposites increase with the increasing of MWCNTs loading. The small addition of MWCNTs (0.5 phr) could improve the tensile strength and elongation at break of NR substaintially. However, both of them decrease with further increasing the loading of MWCNTs. The addition of MWCNTs improves the dynamical storage shear modulus, and has no effect on the glass transition temperature (Tg). Finally, the results of the electrical conductivity and the thermal conductivity measurements show that the electrical conductivity increased by 10 orders of magnitude with MWCNTs of 5 phr. However, there is no effect on the improvement of thermal conductivity by the addition of MWCNTs, which may be attributed to the low MWCNTs loading, the distribution of MWCNTs in the NR matrix, and the heat conduction mechanism.