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