Single-walled carbon nanotubes (SWCNTs) covalently modified with OH functional groups were assembled into buckypapers through solvent dispersion and vacuum filtration. These SWCNT-OH buckypaper sheets were subsequently crosslinked by wetting with bifunctional linkers followed by hot compression causing reaction between the functional groups of the reagent and OH functional groups on the side-walls of SWCNTs to create three-dimensional (3D) covalently cross-linked buckypapers. Cross-linking also was performed using SWCNTs encapsulated with a functionalized polymer wrapping in a core-shell structure, where OH or/and NH2 groups are available on the surface of the polymeric shell for reaction. The 3D cross-linked SWCNT buckypapers retain the porous character typical of buckypaper, and were characterized for their tensile properties and thermal and electrical conductivities. Several cross-linking approaches dramatically improved the mechanical properties. The strongest and stiffest papers (32 MPa, E = 3.1 GPa), which approach 10x stronger and stiffer than the pristine non-crosslinked buckypaper, were obtained at the expense of a loss of electrical conductivity. In other cases, such as cross-linking using a high-performance epoxy resin monomer, improvements in strength and stiffness of similar to 5x were obtained while retaining electrical and thermal conductivity. Therefore, the optimal cross-linking approach would be determined by the desired, multifunctional properties. Additionally, the approach can be used in the preparation buckypaper composites and it is demonstrated that cross-linking using a multifunctional epoxy resin prior to impregnation with the same epoxy resin results in substantially better mechanical properties in comparison to just epoxy-impregnation of pristine buckypaper.
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