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Determination of Montmorillonite Nanocomposite Aggregation Rates Using Real Time X-Ray Diffraction Techniques at High Temperatures.


pdf icon Determination of Montmorillonite Nanocomposite Aggregation Rates Using Real Time X-Ray Diffraction Techniques at High Temperatures. (1054 K)
Stretz, H. A.

NIST GCR 09-924; 45 p. April 2009.

Sponsor:

National Institute of Standards and Technology, Gaithersburg, MD

Keywords:

nanocomposites; x-ray diffraction; high temperature; clay; fire resistance; montmorillonite; combustion; aggregates; fire temperature; pressure; particles; flammability; surfactants; polymers; dispersion; rheology; permeability; experiments

Abstract:

In October 1998 a NIST-industrial consortium convened to study mechanisms by which montmorillonite clays afford fire resistance to composites formed from various polymers and montmorillonite. This committee concluded that a clay-reinforced carbonaceous char is produced during the combustion of such nanocomposites, and this "barrier layer" protects the underlying part. Since that time researchers have shown that montmorillonite particles in polymer-based nanocomposites will aggregate under fire conditions have suggested that the particles may in some cases migrate to the surface. All of this evidence implies that self-assembly of the nanoparticles is occurring as the part burns. The current work explored how choice of surfactant, fire temperature and processing pressure affect the assembly process for particles in the barrier layer. The underlying assumption was that the nano-structure of the ceramic portion of the barrier layer would affect flammability, and this assumption was explored as well. In the original research plan, the goals in this first year were to compare how self assembly rates were affected by: (1) Surfactant, (2) Polymer, (3) Initial state of dispersion and (4) Melt rheology. Characterization of these structural changes was accomplished using high temperature realtime X-ray diffraction (HTXRD),a technique available to TTU researchers on a limited basis through the Oak Ridge National Laboratory User Program. Since access to the afore mentioned instrument was productive but time-restricted, TTU researchers corroborated the XRD results by investigating a new structure-sensitive detection technique based on gaseous permeability of the formed barrier layer. In addition some early computational work is presented herein to test/validate our primary assumption, that structure of the barrier layer affects flammability.