Crystallization regime characteristics of exfoliated polyethylene/vermiculite nanocomposites

Polyethylene (PE)-vermiculite (VMT) nanocomposities containing 0.5, 2, 4, 6, and 8 wt% clay loadings were fabricated via direct melt compounding in a twin-crew extruder. Crystallization kinetics was investigated by means of polarized optical microscopy and differential scanning calorimetry. Moreover, the kinetics of the spherulitic growth of PE-VMT nanocomposites was evaluated with the Lauritzen-Hoffman (LH) secondary nucleation theory. The results showed that the PE-VMT nanocomposite exhibits crystallization regime characteristics. The nucleation constants for regimes I and II were determined from the slope of the LH plots. The fold surface energies (sigma(e)) of the PE-VMT nanocomposites were estimated from these slopes. The sigma(e) values were found to decrease with an increasing VMT content, up to 2%, in regime I. Further increasing the VMT content resulted in a slight increase of the sigma(e) values. In regime II, the or, values of the nanocomposites were generally lower than that of pure PE. These results demonstrated that the exfoliated silicate layers acted as effective nucleation sites for the secondary nucleus of the nanocomposites. (C) 2004, Wiley Periodicals. Inc.