Effect of nanotube functionalization on the properties of single‐walled carbon nanotube/polyurethane composites

Abstract

A commercially available aliphatic thermoplastic polyurethane formulated with a methylene bis(cyclohexyl) diisocyanate hard segment and a poly(tetramethylene oxide) soft segment and chain‐extended with 1,4‐butanediol was dissolved in dimethylformamide and mixed with dispersed single‐walled carbon nanotubes. The properties of composites made with unfunctionalized nanotubes were compared with the properties of composites made with nanotubes functionalized to contain hydroxyl groups. Functionalization almost eliminated the conductivity of the tubes according to the conductivity of the composites above the percolation threshold. In most cases, functionalized and unfunctionalized tubes yielded composites with statistically identical mechanical properties. However, composites made with functionalized tubes did have a slightly higher modulus in the rubbery plateau region at higher nanotube fractions. Small‐angle X‐ray scattering patterns indicated that the dispersion reached a plateau in the unfunctionalized composites that was consistent with the plateau in the rubbery plateau region. The room‐temperature modulus and tensile strength increase was proportionally higher than almost all increases seen previously in thermoplastic polyurethanes; however, the increase was still an order of magnitude below what has been reported for the best nanotube–polymer systems. Nanotube addition increased the hard‐segment glass transition temperature slightly, whereas the soft‐segment glass transition was so diffuse that no conclusions could be drawn. Unfunctionalized tubes suppressed the crystallization of the hard segment; whereas functionalized tubes had no effect. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 490–501, 2007

Evaluating the influence of defects on the young's modulus of carbon nanotubes using stochastic modeling

“…In this process, some C-C bonds on CNT nano-structure are broken and associated carbon atoms with broken bonds will be connected to the polymer chains through covalent cross bonding. This will be led to enhancement in load/stress transfer from the resin to CNT resulting in improved mechanical properties of nanocomposites 7,8 . The functionalization procedure has a main shortcoming by causing defects in the nano-structure of CNT which may significantly reduce Young's modulus of CNT.…”

“…Consequently, the load transferring mechanism from matrix to CNT is naturally limited to weak nonbonded van der Waals (vdW) interaction 5,6 . Thanks to chemical functionalization, some researchers tried to improve load transferring mechanism by providing cross covalent links between the carbon atoms of CNT and the polymer chain of the matrix [5][6][7][8] . In this process, some C-C bonds on CNT nano-structure are broken and associated carbon atoms with broken bonds will be connected to the polymer chains through covalent cross bonding.…”

Effect of Covalent Functionalization on Young’s Modulus of a Single-Wall Carbon Nanotube

“…Their results reveal that the covalent functionalization improves the load transfer efficiency especially when loads are applied in a direction orthogonal to the axis of the CNT. Experimental works (Cooper et al 2002;Barber et al 2003;Shofner et al 2006;Buffa et al 2007;Sun et al 2008) have demonstrated the effectiveness of covalent functionalization in increasing the interfacial bonding strength between CNTs and polymer chains.…”

Electrical conductivity and thermal properties of functionalized carbon nanotubes/polyurethane composites

“…Carbon nanotubes have been introduced into many polymer matrices [12][13][14][15][16] . Reported methods to fabricate polyurethane/CNT composites include solution casting [7][8][9]17] , melting processing [18,19] and in situ polymerization [11,20,21] . Several chemical treatments on the surface of CNTs have been shown to enhance interactions between the CNT and the polymeric matrix [15,17,[20][21][22] .…”