Covalent Functionalization of Multi-Walled Carbon Nanotubes for Dispersion in Cement Pastes

Abstract

Abstract Covalent functionalization of multi-walled carbon nanotubes (MWCNTs) were obtained through acidification, γ-Methacryloxypropyl trimethoxy silane (KH-570) treatment, and free radical polymerization using methyl allyl polyethenoxy ether (HPEG). Fourier-transformed infrared spectroscope was employed to determine the composition and structural changes of MWCNTs after modification. The dispersion of MWCNTs modified by HPEG in water at pH∼13 was determined by UV-vis-NIR. In addition, the effects of modified MWCNTs on cement hydration were investigated to describe the dispersibility of MWCNTs in cement pastes indirectly. Results show that oxygen functional groups generated on the surface of MWCNTs after acidification and KH-570 grafted on acidified MWCNTs through ≡Si–O–C≡ before radical polymerization with HPEG. MWCNTs modified by HPEG exhibit better dispersibility than pristine MWCNTs in a simulated cement pastes environment prepared at pH∼13. The additions of functionalized MWCNTs (P3-S-MWCNTs) promote the hydration of cement pastes indicated from isothermal conduction calorimeter measurement and X-ray diffraction analysis. Scanning electron microscopy observation confirmed the good dispersibility of functionalized MWCNTs in cement pastes. The promoting effect on cement hydration of P3-S-MWCNTs may attribute to the well-dispersed MWCNTs. The dispersed MWCNTs can act as the nucleating agent for carbon-sulfur-hydrogen and carbon-hydrogen, thus promoting the hydration of cement.