To explore the relationship between the morphology and components
ratio, samples with starch-to-chitosan mass ratio of 3:4, 5:4
and 7:4 were tested by optical microscope, and the digital images
were displayed in Fig. 7. Using a transmission mode, the phase
separation of prepared blend membranes can be easily observed.
At lower starch content, a spot of starch will not greatly mix
with chitosan to form an asymmetric membrane as a result of
the phase separation. There were many microcracks on the surface
of starch/chitosan membrane caused by the crinkle of starch link in
the surrounding of abundant chitosan (see Fig. 7a), which will decrease
the mechanical and permeable properties. With too much
starch added, chitosan links will crinkle to form a flat cake shape
and the whole membrane was like the configuration of bilayer lipid
membrane (see Fig. 7c). Furthermore, chitosan cake unit was magnified
and displayed in Fig. 7d, in which the interface between two
components could be obviously made out. Only with the appropriate
ratio can a symmetrical membrane formed (see Fig. 7b), which
was also reflected in the mechanical and permeable properties discussed
above. The chain structures of starch and chitosan are similar
except the groups at C-2 positions demonstrated in Fig. 5, so
the two can form a uniform mixture theoretically. But the membranes
can present different morphologies due to different composing
as described above.
4. Conclusion
The results obtained demonstrate that starch/chitosan blending
membranes of appropriate component ratio exhibit outstanding
mechanical and permeable properties. The origin of the enhancement
phenomenon had been examined by FT-IR to be the interaction
between the hydroxyl groups of starch and the amino groups
of chitosan. Recur to the antimicrobial activity test, obtained membranes
were confirmed to be propitious to applications in package
and medical industries.