Investigation of properties, nanostructure, and distribution in controlled polyester polymerization with layered silicate

This article presents a series of nanocomposites of a polyester [poly(ethylene terephathalate), PET] with different contents of layered silicates of montmorillonite (MMt) by a controlled process, that is, controlling the way to pretreat MMt, the content of MMt, the kind of reagents used, and the way for MMt to be added. Also investigated, in detail, were the properties, nanostructure, and distribution of nanocomposites with an MMt content below 5% by weight. Results by TEM and AFM showed that the nanoparticles are in a normal distribution with a most probable size of 30-70 nm; the exfoliated MAR lamellae interacting with the PET molecular chain produced more regular chain patterns than did pure PET itself when the MMt content was low (lower than 3% by weight); and the agglomerated particles seem not to be found in an MMt content less than 3% by weight, but to increase with the MMt content in the nanocomposites. The investigation of these nanocomposite properties showed that the optimized properties require an optimized MMt content within 2-3% by weight. When MAR is increased from 3 to 5% by weight in the nanocomposites, agglomeration is unavoidable. Thus, the critical content for MMt added to PET is about 3%, by weight. X-ray results showed the appearance of several small diffraction peaks in the 2theta angle from 1degrees to 7degrees for the annealing nanocomposite samples; these peaks are thought to be from the residue of unexfoliated MMt lamellae or metastable (unstable) MMt lamellae. DSC results proved that the nanocomposites have a higher crystallization rate than that of pure PET due to an exfoliated MMt lamellae nucleation effect. Thus, to obtain a stable nanostructure (or nanocomposite), the MMt content needs to be controlled. The nanostructure plays such a role in the crystallization nucleation of nanocomposites. The interaction of exfoliated lamellae with the molecular chain causes a more regular chain pattern and affects the PET crystallization rate and morphology. (C) 2002 Wiley Periodicals, Inc.