Carbon nanotube-reinforced composites surface functionalization

Poly(vinyl) alcohol (PVA) is a semi-crystalline polymer, which is already widely used for various applications, either under the form of films or fibers. Compared to other polymers, as it is water-soluble at high temperature, it is easy to process from aqueous solutions. Carbon nanotubes can also be dispersed or solubilized in water via different functionalization approaches. It was quite natural for researchers to try to mix carbon nanotubes and PVA to improve the properties of the neat polymer. In this chapter, we will first examine the different methods that have been used to process CNT/PVA composites. The structures and the particular interaction between the polymer and the nanotube surface have been characterized in several works. Then we will consider the composite mechanical properties, which have been extensively investigated in the literature. Despite the number of publications in the field, we will see that a lot of work is still to be done for achieving the most of the exceptional reinforcement potential of carbon nanotubes. 

The discovery of carbon nanostructured materials has inspired a range of potential applications. More specifically, the use of carbon nanotubes in polymer composites has attracted wide attention. Carbon nanotubes have a unique atomic structure, a very high aspect ratio, and extraordinary mechanical properties (strength and flexibility), making them ideal reinforcing compounds. Moreover, carbon nanotubes are susceptible to chemical functionalization, which broaden their applicability. For instance, surface functionalization of carbon nanotubes is an attractive route for increasing their compatibility with polymers in composites, also improving the dispersability in raw materials and the wettability. 

Multi-wall carbon nanotubes (MWNTs) were also used as the reinforcing phase in LCP nanocomposites prepared by means of melt blending technique in a twin-screw extruder equipped with an ultrasonic unit to facilitate MWCNT dispersion (Kumar and Isayev, 2010). The role of ultrasonication was positive and resulted in increased structural as well as rheological properties because of the better-dispersed nanofiller. MWCNT were also used in LCP blends with polycarbonate (PC) (Mukherjee et al., 2009) and PEI (Nayak, Rajasekar, and Das, 2010). In the first case, PC/LCP/MWNTs nanocomposites containing as-received or modified (COOH-MWNT) carbon nanotubes were prepared through the melt process in an extruder and then compression molded. The incorporation of functionalized MWCNTs improved thermal, structural, dynamic-mechanical, and electrical properties of the composites, in particular in blends with treated MWCNTs. MWCNTs were also used, both unmodified and surface treated with SiC particles, to improve dispersion in PEI/LCP blends prepared by melt blending. In the ternary systan, viscosity in the blend with modified MWCNTs was found to be lower than the ternary blend with pure MWCNTs, probably because modified MWCNTs improved the fibrillation of LCP compared to pure MWCNTs. Nanocomposite matrices have not been used to prepare foams yet. 

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