SURFACE MODIFICATION OF CARBONNANOTUBES BY POLY(DOPAMINE) COATINGS AND ITS APPLICATION IN THE NATURE RUBBER/MWCNTS NANOCOMPOSITES

摘要

A novel method was explored for the functionalization of multi-walled carbon nanotubes (MWCNTs) and its application in the preparation of natural rubber (NR)-MWCNT nanocomposites was studied. The dispersion of MWCNTs in the water and NR is improved 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 natural latex , 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 modified by polydopamine (MWCNTs-PDA) are uniformly dispersed in the NR matrix. The crosslink density of NR is enhanced by filling with MWCNTs, but reduced by introduction of PDA. The result of rubber processing analyzer (RPA) shows the NR/MWCNTs has more obvious 'payne effect', compare to NR/MWCNTs-PDA. That also confirmed the good dispersion of MWCNTs-PDA. The mechanical property of the composites, including tensile strength, elongation at break, tensile stress at a given elongation, and hardness, were investigated. Tensile results show the NR composite filled with MW-CNTs-PDA has larger enhancements in tensile strength and elongation. The electrical conductivity of NR decreases abruptly by 10 orders of magnitude after filling with 5Phr MWCNTs. But the thermal conductivity is only changed from 0.15 w/mk to 0.19 w/m-k, whether filled with MWCNTs or MWCNTs-PDA, it is attributed to the existence of large interface thermal resistances, loss of aspect ratio and disordered dispersion.