Adding nanotubes and nanofibres to polymer fibres

The fimdamental motivation for adding nanotubes to polymer fibres is similar to those outlined above for other composite systems namely, that there is an opportunity to improve the mechanical and functional properties of the matrix by drawing on the unique properties of the nanotubes. However, there are some additional attractions. At the current stage of development, bulk nanotube composites appear to offer only comparable properties to systems reinforced with conventional chopped fibres. However, unlike the nanotubes, such conventional fillers caimot be accommodated within fine polymer fibres. Thus, CNTs/CNFs offer a new route to nano-reinforced polymer fibres, and can provide unique improvements in performance. These improvements can be significant even at the current level of development of nanotube composites, using existing commercial CVD materials, because no other established filler can compete in the confined environment of the polymer fibre. 

Processing is, of course, crucially important in determining nanotube dispersion and orientation, as well as the more traditional but equally important factors associated with polymer morphology. Polymer nanocomposite fibres may be spun from solution or from the melt, often following an initial dispersion step, as discussed in Section 7.3.1 above. Much of the initial work has been exploratory in nature, and there remains considerable scope for applying the wider understanding of fibre spinning to these systems. 

Solution spinning is a widespread and attractive route for the production of polymer fibres, and has been applied to a variety of CNT systems. Aparticularly interesting possibility is the use of a lyotropic nematic nanotube solution as a route to a highly aligned fibre. Much of this work is directed at high loadings of nanotubes and examples include the use of surfactant-stabilised dispersions of CNTs injected into a PVA or poly(ether imide) (PEI) bath, to form a fibre that can be handled and drawn, and the use of pure SWCNT dispersions in superacid . 

It is also possible to produce nano-reinforced polymer fibres by electrospinning nanotube polymer solutions/ however, this topic will not be discussed further as it is covered at length elsewhere in this book (see Chapters 1-5) 

The majority of nanotube/nanofibre-filled thermoplastic fibres are made by variants of melt spinning, or approximations based on sample collection from rheometers and the like, representing an optimisation of previous alignment approaches based on die designs and simple melt strand or film stretching. While conventional melt processing of the nanocomposite dope is desirable for economical reasons, initial solution-blending is often performed in the case of SWCNT-filled polymers, yet the effectiveness of this approach remains debatable. 

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