writer：Defeng Wu, Chixing Zhou, Fan Xie, Dalian Mao, Bian Zhang.
keywords：morphology; crystallization; PBT; clay; nanocomposites.
source：期刊
specific source：Polymers & Polymer Composites
Issue time：2005年

Polymers & Polymer Composites, 2005, 13(1), 61-69.

ABSTRACT: The melt intercalation method was employed to prepare poly(butylene terephthalate)/montmorillonite nanocomposites, and their microstructure was characterized by wide angle X-ray diffraction and transmission electron microscopy. The XRD results showed that the crystalline planes such as (010), (111), (100) were smaller than those of pristine PBT, which indicates that the crystallite size of PBT in the nanocomposite could be diminished by adding clay. Moreover, the isothermal crystallization kinetics of PBT and PBT/MMT nanocomposites was investigated by differential scanning calorimetry (DSC). During isothermal crystallization, the development of crystallinity with time was analysed by the Avrami equation. The results show that very small amounts of clay dramatically increased the rate of crystallization and high clay concentrations reduced the rate of crystallization at low crystallization temperatures.

At low concentrations of clay, the distance between dispersed platelets was large, so it was relatively easy for the additional nucleation sites to incorporate surrounding polymer, and the crystal nucleus was formatted easily. However, at high concentrations of clay, the diffusion of polymer chains to the growing crystallites was hindered by the larger clay particles, despite the formation of additional nucleation sites by the clay layers. At the higher crystallization temperatures, the crystallization of the nanocomposites was slower than that of the pure PBT under the experimental conditions, which means that with the increase in chain mobility at the high crystallization temperature, the crystal nuclei are harder to format, and the hindering effect of clay particles on the polymer chains was stronger than the nucleating effect of the layers.

 In addition, the activation energies of crystallization for PBT and its nanocomposites were calculated by the Arrhenius relationship, and the results showed that  nanocomposites with a low clay content had lower activation energy values than PBT, while high amounts of clay increased the activation energy of PBT.