Table 15shows how oxygen permeability decreased with the addition of ultrasonified
clay. All samples had a uniform thickness of 84.46 ± 13.32 micrometer. The quality of
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oxygen barrier is directly associated with the dispersion of nanoclay. Ultrasonification
time of 30 minutes did significantly effect OP when compared to non ultrasonification.
Increasing the ultrasonification time above 30 minutes did not significantly effect oxygen
permeability, as seen for both samples containing 10% clay. Thus, oxygen permeability is
a function of ultrasonification time. When clay sheets are exfoliated, layers are
delaminated from the clay creating a “torturous path” for oxygen to move through.
Increased clay dispersion creates a challenging path for oxygen to permeate through the
starch composite matrix (Figure 4).
Table 16: Oxygen Permeability, batch amount clay
Cloisite Na+
(wt%)
Ultrasonification
Time (min) O2 Permeability (cc-mil/(m2
-day))a
0
0 12.63 ± 3.09 a*
5
30 5.84 ± 1.10 b*
10
30 5.43 ± 1.30 b*
10
60 5.99 ± 2.26 b*
15
30 4.74 ± 1.17 b*
20
30 4.47 ± 1.35 b*
25
30 4.94 ± 0.99 b*
30
30 4.11 ± 0.78 b*
a
Permeability is measured at 23 degrees Celsius and 50% RH
* Means with the same letter are not significantly different
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Table 16 shows how oxygen permeability is affected by the addition of clay.
Interestingly, the percentage of clay in the film does not significantly differ from 5-30%
wt clay content. However, the data shows a slight, but not statistically significant, trend
that as clay content increases, OP decreases. The lowest OP results were obtained for
samples with 30% wt clay content.
In general, increasing crystallinity of a polymer reduces oxygen permeability. The
addition of a clay has a similar effect. The clay layers improve the oxygen barrier of the
film due to forming a tortuous path. The permeability rates were statistically insignificant
with the further addition of clay. This phenomenon can be explained by the degree of
dispersion of the clay platelets. As the clay content in the film increases, it becomes
more difficult to reach full exfoliation. Theoretically, the greater the exfoliated clay
content, the greater the oxygen barrier. However, it becomes increasingly difficult to
fully exfoliate high clay contents (>15%), and therefore a more optimal “tortuous path”
could not be achieved by the addition of more clay.