Processing composites of carbon nanotubes into nanotube continuous fibers (NCFs) is an effective way of manipulating the anisotropic properties of the single-walled carbon nanotubes (SWNTs) as it becomes less difficult to transform the SWNTs into an aligned configuration when they are confined in a small diameter fiber. This helps to take fuller advantage of the high mechanical properties of the SWNT materials in the axial direction. However, in creating nanocomposite fiber systems, the issues of dispersion and nanotube−matrix interaction and adhesion become of utmost importance when improved mechanical properties are anticipated. In addressing these issues in this work it has been found that sidewall chemical functionalization can be an effective tool for improving both the dispersion and interaction between the nanotube and the matrix. This work evaluates the effect of sidewall functional groups on fluorinated single-walled carbon nanotubes (F-SWNTs) as a precursor for improved interfacial adhesion in a thermoplastic matrix (polypropylene, PP) via partial defluorination of the F-SWNTs. The partial removal of functional groups from the F-SWNTs during melt processing with PP by shear mixing provides the opportunity for in situ direct covalent bonding between the nanotubes and the matrix during melt processing which ultimately results in better mechanical reinforcement of the composite. The studies conducted herein demonstrate that in comparison with PP composites filled with purified nanotubes (P-SWNTs), improved dispersion, interfacial adhesion, and mechanical properties are achieved for F-SWNT-loaded matrixes due to chemical functionalization.
Benzoyl peroxide initiated in situ functionalization of single-walled carbon nanotubes (SWNT) represents a simple means of generating reactive sites on the surface of carbon nanotubes by exploiting free radical interactions with the surrounding polymer matrix. The resulting composite, when processed into fiber form, demonstrates improved mechanical properties. Functionalization of carbon nanotubes has in general been used as a means of increasing their solubility and dispersion in polymeric systems, allowing for the manufacture of composites with increased mechanical properties. Beyond the addition of chemical moieties to the surface of single-walled and multiwalled carbon nanotubes, researchers have used in situ reactions to link carbon nanotubes directly to the surrounding polymer matrix in hopes of taking better advantage of their strong reinforcing properties. In this work, we present a method to produce a composite of this nature by using a single processing step. An in situ reaction, initiated by the production of free radicals upon the decomposition of benzoyl peroxide during the high shear and high-temperature phase of processing, allows for the linkage of the single-walled carbon nanotube to the surrounding polypropylene matrix via a covalent bond. The resulting composite was spun into 2.5, 5, 7.5, and 10 wt. % SWNT/polypropylene fibers that demonstrated improved mechanical properties in tensile strength by 82.9, 89.8, 72.3, and 173.1%, and in the elastic modulus by 69.2, 99.7, 137.2, and 133.7%, respectively, over that of the neat polypropylene fibers.
The space applications of composites obtained by dispersing carbon nanotubes within highdensity polyethylene are analyzed. Electron spin resonance investigations on proton-irradiated composites are reported. The effect of ionizing radiation of the parameters of electron spin resonance spectra is studied. A radiation-induced increase of the concentration of uncoupled electronic spins delocalized over the conducting domains of carbon nanotubes is reported. It is concluded that radiation-induced modifications in such composites are weak.
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