Effect of Crosslinking on Carbon Nanotube Materials through Chemical Treatment and Irradiation

Carbon nanotubes (CNTs) exhibit a variety of exceptional properties, especially their ultrahigh tensile strength on the order of 100GPa show promise for constituting the next-generation carbon fiber. However, challenges remain to translate these properties into useful technology, primarily due to the sliding of the tubes past one another under tensile loading. The work presented in this dissertation is focused on enhancing the interaction between the CNTs and their bundles in a macro-assembly, in order to improve the tensile properties of the material.

Applying inter-tube crosslinks has been predicted to significantly enhance the stress transfer between the CNT components. We developed a novel chemical crosslinking method for reinforcement of carbon nanotube fibers (CNTFs) employing benzocyclobutene (BCB)-based polymers. This simple one-step mechanism achieves covalent functionalization of CNT surface and 3D crosslinking simultaneously, in the solid-state. The denser packing of CNTF, impregnated polymer and establishment of covalent crosslinking after the treatment all contributed to the enhancement of tensile strength by 250%.

Several process parameters were investigated for the BCB-induced crosslinking of CNTF. A series of poly(styrene-r-4-vinyl-benzocyclobutene) (PS-VBCB) with varying BCB/PS content were synthesized and the copolymer with PS content of 80% lead to the optimum result, possibly due to the BCB-BCB collapsing to form undesired defects at high percentage of BCB. The concentration of the

polymer solution for infiltration into CNTF was found to be critical in determining the amount of infiltrated PS-VBCB polymer. 0.05% wt or 0.1% wt results in highest mechanical properties. Pure heating of CNTF free from BCB degrades the load transfer, which further supports the positive effect of BCB crosslinking on CNTF.

Electron-beam (e-beam) induced crosslinking alters the morphology and properties of carbon structures. In this dissertation, the effect of e-beam irradiation on CNTF was observed, both positive and negative phenomena. At the presence of functional species, e-beam initiates functionalization by creating radicals on CNT. CNTF grafted with acrylic acid exhibited improvement in tensile strength by 77%. Finally, a preliminary attempt was made to combine the e-beam and BCB chemistry on the CNT materials.