Improving the mechanical properties of single-walled carbon nanotube sheets by intercalation of polymeric adhesives

Abstract

Organic polymers, such as poly͑vinyl alcohol͒, poly͑vinyl pyrrolidone͒, and poly͑styrene͒, were intercalated into single-walled carbon nanotube sheets by soaking the sheets in polymer solutions. Even for short soak times, significant polymer intercalation into existing free volume was observed. Tensile tests on intercalated sheets showed that the Young's modulus, strength, and toughness increased by factors of 3, 9, and 28, respectively, indicating that the intercalated polymer enhances load transmission between nanotubes. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1559421͔Realization of the applications potential of carbon single-walled nanotubes ͑SWNT͒ has been hindered by the many difficulties associated with their processing. Fabricating low-density carbon nanotube powder into functional macroscale structures has been a major challenge. Some progress has been made recently with the fabrication of one-, two-, and three-dimensional bulk nanotube material in the form of fibers, 1,2 sheets, 3 and Bucky Pearls™ pellets produced by Carbon Nanotechnologies Incorporated ͑CNI͒. However, while individual SWNTs display impressive Young's moduli and strengths of approximately 640 and 40 GPa, 4,5 respectively, the mechanical properties of the bulk materials remain disappointing. These low-bulk mechanical properties are in part because the individual SWNT usually forms 10-50-nm-diameter bundles that are only weakly bound by van der Waals interactions at junction points.Both carbon multiwalled nanotubes ͑MWNTs͒ and SWNTs have been used as reinforcing agents in polymer and epoxy composites. [6][7][8] Ideally, any load applied to the polymer matrix is transferred to the nanotubes. This load transfer relies on effective interfacial stress transfer at the polymernanotube interface, which tends to be polymer dependent. 8 This reinforcement technique has met with some success, providing increases in Young's modulus by a factor of 1.8 for 1 wt % loading of MWNTs in poly͑vinyl alcohol͒ ͑PVA͒ 8 and increases in hardness by a factor of 3.5 for 2 wt % loading of SWNTs in epoxy. 7 In this letter, we show that the reverse procedure of polymer intercalation can be used to reinforce bulk nanotube materials. Binding agents such as organic polymers can be intercalated into the porous internal structure of nanotube materials such as SWNT sheets ͑Buckypaper͒. This intercalation can be obtained by simply soaking the nanotube sheets in polymer solutions. The resulting polymer-intercalated sheets display improvements in Young's modulus and tensile strength by factors of ϳ3 and ϳ9, respectively.The nanotube sheets ͑Buckypaper͒ used in this work were prepared by filtration of SWNTs dispersed in water and Triton X-100, as previously described. 3 The SWNTs were made by the HiPco process and supplied by CNI. 9 This material is known to contain ϳ20 wt % iron ͑ϳ2 vol % for sheets͒. The carbon nanotube sheets were annealed under flowing argon at up to 1000°C before use, in order to remove residual surfactant, solvents, and contaminants. Thes...

Reinforcement of macroscopic carbon nanotube structures by polymer intercalation: The role of polymer molecular weight and chain conformation

“…While the maximum values of Young's modulus attained are similar and agree with previous results 6 the dY / dV f values display a marked difference between molecular weights. Generally, the Young's modulus of composites are analyzed using the so-called rule of mixtures 5,22 which states that for a mixture of components 1 and 2, the resultant modulus, Y, is given by…”

“…One other possibility is that the intercalated polymer acts as a binder which enhances the interbundle adhesion as suggested previously. 6 As noted above, the low M w polymer adsorbs in the coiled conformation. This would tend to act as a rather localized, inefficient binder, connecting no more than two bundles per molecule.…”

“…In previous work 6 it was shown that the reverse procedure of polymer intercalation can be used to reinforce bulk nanotube materials. The mechanical properties of as-prepared ͑pristine͒ sheets of carbon nanotubes ͑Buckypaper͒ were significantly improved by soaking the sheets in various organic polymer solutions.…”

High-Strength Composite Fibers: Realizing True Potential of Carbon Nanotubes in Polymer Matrix through Continuous Reticulate Architecture and Molecular Level Couplings

“…4 Even in the cases where CNTs are optimally dispersed at high volume fraction, their moduli and strengths are at least 2 orders of magnitude lower than what was theoretically predicted by composite theory. [5][6][7] Essentially, the mechanical performance of CNT reinforced composites relies on the load-bearing status of the CNTs in the matrix. However, two inherent problems of CNTs shadow their promise as efficient load-bearers.…”

Carbon nanotube buckypaper reinforced polymer composites: a review

“…Also, their carbon content is generally lower than 5 wt.% and the nanotube bundles are dispersed through the matrix without forming a network. On the other hand, BP composites are manufactured by techniques such as hot-compression [65] , electro-spinning [66] , and intercalation [67] . These materials usually have carbon content higher than 30 wt.% resulting in a network, which acts as a skeleton.…”