Environmentally friendly inorganic fullerene-like tungsten disulfide nanoparticles (IF-WS2) were used to produce new nylon-6 nanocomposites. In the nucleation-controlled regime, the crystallization rates for the nanocomposites are significantly faster than that for the neat nylon-6 as confirmed by DSC and X-ray diffraction techniques using synchrotron radiation. This fact was related to the high nucleation efficiency of IF-WS2 nanoparticles on the alpha'-form crystals of nylon-6. Other parameters such as the Avrami exponent, the equilibrium melting temperature, long period and the fold surface free energy of nylon-6 chains in the nanocomposites were obtained from the calorimetric data in order to determine the effect of the nanoparticles on them. The addition of IF-WS2 remarkably influences the energetics and kinetics of nucleation and growth of nylon-6 with a decrease in the fold surface free energy of 36-51%. (C) 2011 Elsevier B.V. All rights reserved.