Nonisothermal crystallization kinetics of polyoxymethylene/montmorillonite nanocomposite

The nonisothermal crystallization kinetics of polyoxymethylene (POM), polyoxymethylene/Na-montmorillonite (POM/Na-MMT), and polyoxymethylene/organic-montmorillonite (POM/organ-MMT) nanocomposites were investigated by differential scanning calorimetry at various cooling rates. The Avrami analysis modified by Jeziorny and a method developed by Mo were employed to describe the nonisothermal crystallization process of POM/Na-MMT and POM/organ-MMT nanocomposites. The difference in the values of the exponent n between POM and POM/montmorillonite nanocomposites suggests that the nonisothermal crystallization of POM/Na-MMT and POM/organ-MMT nanocomposites corresponds to a tridimensional growth with heterogeneous nucleation. The values of half-time and the parameter Z(c), which characterizes the kinetics of nonisothermal crystallization, show that the crystallization rate of either POM/Na-MMT or POM/organ-MMT nanocomposite is faster than that of virgin POM at a given cooling rate. The activation energies were evaluated by the Kissinger method and were 387.0, 330.3, and 328.6 kJ/mol for the nonisothermal crystallization of POM, POM/Na-MMT nanocomposite, and POM/organ-MMT nanocomposite, respectively. POM/montmorillonite nanocomposite can be as easily fabricated as the original polyoxymethylene, considering that the addition of montmorillonite, either Na-montmorillonite or organ-montmorillonite, may accelerate the overall nonisothermal crystallization process. (C) 2001 John Wiley & Sons, Inc.