Rice University (Houston, TX) researchers Valery N. Khabashesku, Enrique V Barrera, Daneesh McIntosh and Laura Pena-Paras developed methods of fully integrating carbon nanotubes (CNTs) into a surrounding polymer matrix in CNT/polymer composites using free radical precursors.
According to U.S. Patent Application 20100113696, such integration comprises interfacial covalent bonding between the CNTs and the polymer matrix. The interfacial covalent bonding is provided by a free radical reaction initiated during processing. The free radical initiation can be provided by benzoyl peroxide (BP)
In the CNT/polymer composite systems, the CNTs are covalently integrated with the polymer.
In the CNT/polymer composite systems, the CNTs are covalently integrated with the polymer.
The formation of benzoyl peroxide initiated functionalization of single walled carbon nanotube (BP-f-SWNT) composite fibers is representative of creating a more seamless material. The components of the composite transition from a two-phase material toward a material more singular in phase and which behaves as a fully integrated system. In a sense, the ideal CNT/polymer composite made via methods developed by Rice researchers can be thought of as a material composed of macromolecules instead of the conventional matrix and reinforcing filler composite.
In a study, the Rice researchers demonstrated that fibers made from BP-f-SWNT in polypropylene are materials demonstrating such characteristics. The researchers have created a composite material in which the reinforcing filler (SWNTs) is covalently linked to the surrounding polymer resulting in a strong interface between the two phases, which is in turn exploited when the material is subjected to tensile loading, thereby yielding increased mechanical properties. Accordingly, the researchers are able to create a stronger material which can be used for other applications where strong, lightweight polymers are required.
While the fully integrated CNT/polymer composites generally possess mechanical improvements (e.g., over the same polymer without the CNTs), such composites can also benefit from the electrical properties of the CNTs. For example, the BP-f-SWNTs can add to the conducting nature of the polymer system as well.It is significant that there are ways to functionalize nanotubes for composite use, where the nanocomposite maintains its conductivity. The addition of functionalized SWNTs does not lead to loss of electrical conductivity. The conductivity shown for the polypropylene system is not very different that that for the ABS system. While not intending to be bound by theory, it is expected that the functionalization is applied to the outer nanotubes in a rope and that the inner nanotubes in the bundle still provide for electrical conduction.
While the fully integrated CNT/polymer composites generally possess mechanical improvements (e.g., over the same polymer without the CNTs), such composites can also benefit from the electrical properties of the CNTs. For example, the BP-f-SWNTs can add to the conducting nature of the polymer system as well.It is significant that there are ways to functionalize nanotubes for composite use, where the nanocomposite maintains its conductivity. The addition of functionalized SWNTs does not lead to loss of electrical conductivity. The conductivity shown for the polypropylene system is not very different that that for the ABS system. While not intending to be bound by theory, it is expected that the functionalization is applied to the outer nanotubes in a rope and that the inner nanotubes in the bundle still provide for electrical conduction.
FIG. 7 is a comparison of tensile strengths for 130 micron fibers. Mechanical tests conducted on the nanotube continuous fibers (NCFs) showed a consistent improvement in the properties of those fibers into which benzoyl peroxide had been incorporated.
FIG. 9 is a comparison of % elongation for 130 micron fibers.
The formation method is comprised of the steps of: (a) dispersing CNTs, thermoplastic polymer, and a free radical precursor species in a solvent; (b) removing the solvent to form polymer-overcoated CNTs comprising free radical precursor; and (c) compounding the polymer-overcoated CNTs comprising free radical precursor to form a fully-integrated CNT/polymer composite comprising interfacial covalent bonding between the CNTs and the polymer, the polymer serving as a matrix. In some such embodiments, the method comprises a further step of processing the fully-integrated CNT/polymer composite in an extruder to form a nanotube continuous fiber (NCF) product. The nanotubes are substantially aligned in the NCF product by virtue of shear forces associated with extrusion. Generally, steps (a) and (b) are collectively an "incipient wetting" process.
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