Carbon Nanotube Polymer Composites: Recent Developments in Mechanical Properties
This chapter discusses recent developments in mechanical properties of carbon nanotube (CNT) polymer composites. Recent experiments have investigated the effect of the CNT type in composites for mechanical reinforcement. Typical mechanical properties of various CNT types are listed in a table. The most commonly studied matrices for CNT-reinforced composites are polymers. Fabricating composites of CNTs in polymer matrices almost invariably involves a dispersion process in which the nanotubes are incorporated into the polymer. Homogeneous dispersions of CNTs in viscoelastic polymer fluids can be spun into composite fibers. Melt spun, solution spun, and electro-spun CNT composite fibers have been produced. These methods have been shown to be very effective in aligning the CNTs with the direction of flow, i.e., the fiber axis. Selected experimental results can be used to highlight CNT-polymer composite properties, their relation to processing (dispersion, concentration, orientation), CNT type, and various matrix polymers. Typical increases in the elastic modulus and break strength of CNT-polymer composites are outlined in a table for various polymer matrices. Experimental determination of the interfacial shear strength of CNT-polymer composites has recently been demonstrated. Within the past few years, many investigators have observed an increase in the degree of crystallinity or crystallite size of semicrystalline polymer-CNT composites due to the addition of CNTs. Linear increases in crystallinity with increasing multiwall carbon nanotube (MWNT) concentration of a MWNT/poly(vinyl alcohol) (PVA) composite were observed in differential scanning calorimetry (DSC) melting endotherms. This suggested that each CNT had a discrete crystalline polymer layer associated with it.