Biomedical Engineering Reference
In-Depth Information
together by attraction forces of various physical and chemical natures, including van
der Waals forces and water surface tension. These attraction forces must be overcome
in order to deagglomerate and disperse the clays into water. Ultrasonication and high
pressure fluidization were used to create alternating pressure cycles, which overcome
the bonding forces and break the agglomerates. As can be seen in Figure 1(a), dry
nanoclay powder consisted of round particles with coarse and platelety surface. By
ultrasonic dispersing (Figure 1(b)), and high pressure fluidization (Figure 1(c)) the
nanoclay platelets were effectively ripped off and distributed on the surface. The di-
ameter of the intercalated nanoplatelets varied between 100 and 500 nm.
Figure 1.
The SEM images of (a) large undispersed nanoclay aggregates. The excerpt shows the
surface structural features: laminar fine structure can be seen on the aggregate surfaces, (b) spincoated
nanoclay platelets after dispersing with the ultrasonic microtip, and (c) spincoated nanoclay platelets
after high pressure fluidizer treatment.
Nanocomposite chitosan coatings effectively decreased the oxygen transmission
of LDPE coated paper under all humidity conditions (Figure 2). In dry conditions,
over 99% reductions and, at 80% relative humidity, almost 75% reductions in oxygen
transmission rates were obtained. Highest concentration of nanoclay (67 wt%) of-
fered the best barrier against oxygen, whereas the 17 wt% concentration of nanoclay
performed almost as good as 50 wt% of nanoclay. Barrier effects of nanoclay became
less evident in dry conditions. Presumably higher nanoclay concentrations were partly
agglomerated, which hindered the crystallization and hydrogen bonding formation be-
tween chitosan chains, especially in dry conditions.
Figure 2.
Oxygen transmission rates of chitosan coatings (< 1 µm) with different amounts of nanoclay.
Search WWH ::
Custom Search