Gas Barrier Properties of Biopolymerbased Nanocomposites: Application in Food Packaging - Advanced Materials for Agriculture, Food and Environmental Safety - page 375

Clay
Permeant
Figure 13.1 Tortuous path of a permeant in a clay-based nanocomposite.
reduces the energy of clays and improves their compatibility with organic
polymers. Organo-montmorillonite (MMT) has been produced, for exam-
ple, by exchanging inorganic cations of MMT with organic ammonium
ions, improving compatibility of MMT with organic polymers, leading to
a more regular organization of the layers, and decreasing the water uptake
by the resulting nanocomposite.
h e most widely known theories to explain the improved barrier prop-
erties of polymer-clay nanocomposites are based on a theory developed
by Nielsen (Figure 13.1), which focuses on a tortuous path around the clay
plates, forcing the gas permeation to travel a longer path to dif use through
the ilm. h e increase in path length is a function of the high aspect ratio
of the clay iller and the vol% of the iller in the composite. Nielsen's model
predicts permeability of systems at clay loading rates of less than 1%, but
experimental data deviate signiicantly from predicted values at higher
loading rates and more extensively in certain polymers.
h e improved barrier properties of polymer-clay nanocomposites seem to
be due to an increased tortuosity of the dif usive path for permeants, forcing
them to travel a longer path to dif use through the i lm. h e increase in path
length is a function of the aspect ratio of the clay and the volume fraction of
the i ller in the composite. Nielsen's model has been used ef ectively to predict
permeability of systems at clay loadings of less than 1%, but some experimen-
tal data have reported much lower permeabilities than predicted at higher
loadings, and a new proposed model to predict permeability of nanocompos-
ites focused on the polymer-clay interface as an additional governing factor
to the tortuous path, thus providing a correction factor to Nielsen's model.
h e oxygen permeability of polyacrylonitrile (PAN)/clay nanocompos-
ites was measured with variation of clay concentration along with dif erent
frequencies and powers of ultrasound waves [19]. It was found that oxygen