Epoxy functionalization of multiwalled carbon nanotubes for their waterborne polyurethane composite with crosslinked structure

In order to achieve covalent bond between multiwalled carbon nanotubes (MWCNTs) and waterborne polyurethane (WPU), pristine MWCNTs were first oxidized by strong acids and then underwent ring-opening reaction with epoxy resin to chemically attach epoxy moiety onto their surface. For fabrication of the MWCNTs/WPU composite, the epoxy moiety facilitates the dispersion of MWCNTs in the polymer matrix and could react with carboxylic acid or amine groups in the WPU macromolecules to form a crosslinked structure in their composite, resulting in a great improvement in their mechanical property, thermal stability, water resistance, and electrical conductivity. As the content of MWCNTs reached 1.5 wt%, the tensile strength of functionalized MWCNTs composite was improved by about 108% and the electrical conductivity was increased by six orders of magnitude compared to that of the pristine MWCNTs composite.