CNT-polymer composites

The possible fatigue failure mechanisms of SWCNT in the composite were also reported (Ren et al., 2004). Possible failure modes mainly include three stages, that is, splitting of SWCNT bundles, kink formation, and subsequent failure in SWCNTs, and the fracture of SWCNT bundles. As shown in Fig. 9.12, for zigzag SWCNT, failure of defect-free tube and tubes with Stone-Wales defect of either A or B mode all resulted in brittle-like, flat fracture surface. A kinetic model for time-dependent fracture of CNTs is also reported (Satapathy et al., 2005). These simulation results are almost consistent with the observed fracture surfaces, which can be reproduced reasonably well, suggesting the possible mechanism should exist in CNT-polymer composites. 

Barrera et al. (3) sidewall functionalized carbon nanotubes with organosilanes for polymer composites, (III), with glass fibers for use in advanced cylindrical nanotube (CNT)-polymer composites. 

MWCNTs have been functionalized with n-butyllithium by Blake et al. and subsequently the modified CNTs were covalently bonded to a chlorinated polypropylene [184]. The polypropylene-grafted MWCNTs were used to produce ultra-strong CNT polymer composites. 

A number of studies on CNT-polymer composites have focused on improving the dispersion and load transfer efficiency in other words the compatibility between the CNTs and polymer matrix through covalent chemical functionalization of CNT surface (12,40). Many of the studies reported above have used acid-functionalized CNTs to fabricate MWCNT-PMMA composites with improved mechanical properties using different processing methods (24,25,27,62). Yang et. al (68) modified the acid functionalized CNTs with octadecylam-ine (ODA) to obtain ODA-functionalized CNTs. These CNTs were reinforced in a copolymer P(MMA-co-EMA) to form composites with improved dispersion and mechanical properties. 

In the last ten years, a great deal of experimental work has been presented about the tensile properties of CNTs/polymer composites in the literature. However, it is difficult to generalize across these studies because of the large number of parameters that can influence the effective properties, including size and structure of the CNT, CNT/ polymer interaction, processing techniques and processing conditions. In this chapter, the effect of structure and morphology on the properties of the nanocomposites will be focused and discussed. 

The main experimental methodology used is to directly characterize the tensile properties of CNTs/polymer composites by conventional pull tests (e.g. with Instron tensile testers). Similarly, dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA) were also applied to investigate the tensile strength and tensile modulus. With these tensile tests, the ultimate tensile strength, tensile modulus and elongation to break of composites can be determined from the tensile strain-stress curve. 

Structure and Tensile Properties of CNTs/ Polymer Composites... 

A large number of experimental efforts have been conducted on cut-CNT/polymer composites. For instance, samples of 0.5 wt% SWNTs reinforced epoxy composites were prepared. It was reported that the experimental average tensile strength was increased to 77.6GPa, about 7% enhancement when the cut-SWNTs were applied in the composite. The average modulus was enhanced to 2.4GPa,... 

Though numerous groups have fabricated CNT-polymer composites, mechanical behaviour has not been the main focus of such studies. The bulk of the work has focused on studying the effect of the addition of CNT on the crystallization behaviour and on the electrical conductivity and improving dispersion by employing different techniques, as described earlier. 

Figure 3.34 Conductor paths consisting of carbon nanotubes can be generated by heating a CNT-polymer composite on a substrate ( ACS 2004).

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