Nitric acid treated single and multi wall carbon nanotubes (SWNT and MWNT) have been dispersed in polypropylene using maleic anhydride grafted polypropylene (MA-g-PP) and butanol/xylene solvent mixture. SWNT exfoliation was characterized by Raman and UV-vis-NIR spectroscopies. Evidence for hydrogen bonding between maleic anhydride grafted polypropylene and nitric acid treated nanotubes was obtained using infrared spectroscopy. Polypropylene/carbon nanotube composites were melt-spun into fibers. Dynamic mechanical studies show that for fibers containing 0.1 wt% SWNT, storage modulus increased by 5 GPa at -140 degrees C and by about 1 GPa at 100 degrees C, suggesting temperature dependent interfacial strength. The crystallization behavior has been monitored using differential scanning calorimetry and optical microscopy. Control fibers exhibited 27% shrinkage at 160 degrees C, while the shrinkage in the composite fibers was less than 5%. Fibers heat-treated to 170 degrees C show very narrow polypropylene melting peak (peak width about 1 degrees C). (c) 2008 Elsevier Ltd. All rights reserved.