Covalent Functionalization of Carbon Nanotubes with Different-Reactivity Diisocyanate for Polyurethane Nanocomposites
T. Nguyen, A. Granier, N. Eidelman and J.W. Martin
National Institute of Standards and Technology, US
CNT, functionalization, covalent, nanocomposite, diisocyanate, polyurethane
Carbon nanotubes (CNTs) have a wide range of potential applications due to their unique mechanical properties, high aspect ratios, and electronics structures. Many of these applications require good dispersion and chemical reactivity of CNTs in polymer matrices. For effective stress transfer in nanocomposites, chemical functionalization so that covalent bonds are formed between CNT and the polymer matrix is desired. This paper describes a novel method to covalently functionalize CNTs that bear terminated isocyanate (NCO) group, which then react covalently with urethane resins and other molecules. NCO-functionalized CNTs (NCO-fCNT) is very desirable, because the NCO is highly reactive to “hydrogen-active” groups, such as OH and NH. The first step is synthesis of COOH-terminated CNTs by oxidation of unmodified CNTs in HNO3 at high temperature. The recovered COOH-fCNTs are then reacted with a diisocyanate molecule (NCO--NCO) in which one NCO has a higher reactivity than the other. By controlling the reaction parameters such as catalyst, temperature, etc., the higher reactive NCO is allowed to react completely with the COOH-fCNTs, while the lower reactive NCO is not consumed and available for further reactions. Both NCO-fSWCNTs and NCO-fMWCNTs have been prepared. FTIR and TGA (thermogravimetric) results clearly show that the functionalized CNTs bear a substantial amount of organic molecules and free NCO groups. The NCO-fCNTs have been shown to react readily with amines and polyols. The NCO-fCNTs have been used for fabrication of PU nanocomposites. The effects of reaction time and amount of catalyst on free NCO concentration will be discussed.
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Nanotech 2007 Conference Program Abstract