TABLE OF CONTENTS Although commercial nanotube-polymer composites exist today, they almost exclusively employ relatively low loadings (3-5 wt%) within thermoplastic matrices for the purposes of anti-static dissipation, particularly in the automotive and electronics industries [222]. Such applications exploit bulk quantities of relatively defective catalytically-grown materials. On the other hand, individual perfect nanotubes appear to have axial stiffnesses towards that of diamond, and strengths ten times that of any other available material. There are, therefore, considerable efforts underway to exploit these properties in macroscopic structural composites. In addition to these remarkable headline mechanical properties, there is interest in thermal conductivity, thermal stability, flame retardance, wear resistance, and so on. However, the successful exploitation of the promising mechanical and other properties of CNTs and CNFs in polymer composites is as yet hindered by a number of fundamental issues.
It has become clear that issues of dispersion, alignment, and stress transfer are crucial, and often problematic at this size scale. Dispersion is often obtained by using unentangled nanotubes, high viscosities, and high shear rates. However, a more subtle approach uses surface modifications or coatings on the nanofiller to stabilise individual particles. Surface modification has the added advantage of improving stress transfer to the matrix (although it tends to increase contact resistance). The drawback with the direct modification of the filler surface is that it will damage the properties of SWCNTs and the outer shell(s) of MWCNTs. The area of surface chemistry of nanotubes is therefore an important area for future development. A degree of...
