indicated only Na–MMT effect is the important model term. Glycerol
and Na–MMT will decrease and increase Young’s modulus,
respectively. Increase of Young’s modulus through increasing the
clay contents is reported in literature [10]. The final equations in
terms of actual factors are presented in Table 3.
3.9. Antimicrobial tests
Antimicrobial activity tests of the G30C0 and G30C5 samples
were carried out three times. No inhibition zone was observed
against E. Coli and S. aureus. The colonies of microorganism were
uniformly grown over the plate as same as the border of the samples.
These tests indicated that in case of using Na–MMT in the
polymer matrix for food packaging applications, no antimicrobial
effect occurred. These results are in good accordance with the
results for antimicrobial tests against Salmonella typhimurium,
Listeria monocytogenes, S. aureus and E. coli [31].
4. Conclusions
Corn starch–glycerol biopolymers reinforced with Na–MMT
could be used for packaging or coating of UV sensitive materials.
Transparency of the films analyzed using image processing as a
new alternative approach in comparison to conventional methods.
Films with high content of glycerol and low content of Na–MMT
indicated more transparency. No anti-microbial effects observed
against E. coli and S. aureus. Effect of Na–MMT to improve the physical
properties would be limited because of the higher water content
of the films containing nanoparticles. According to the
response surface analysis, the minimum and maximum of the all
responses are occurred in the highest or lowest levels of investigated
domain parameter. Therefore, the minimum of hydrophilicity
and the maximum tensile strength obtained by maximization
of clay and minimization of plasticizer, while in this scenario, the
transparency reached the minimum.