Scanning electron microscopy surfaces and fractures of film
samples are presented in Fig. 1. Micrographs of the film surfaces, at
a magnification of 200, did not show differences between the
films plasticized with glycerol and sorbitol. Both glycerol and
sorbitol have the same plasticizing mechanism and are small
molecules if compared with amylose–amylopectin chains. Martelli
et al. (2006) found important differences among the surfaces of
keratin films plasticized with glycerol, sorbitol and PEG4000 using
a magnification of 2000 and 3000. These higher magnification
levels cannot be used for starch films, because it can degrade them.
On the other hand, the surfaces of films prepared with rice flour
were more irregular than those of films prepared with rice starch.
For flour base films, the presence of insoluble particles was
observed. The irregularities in the surface of rice flour films may be
related to the presence of more than one macromolecule in the
polymeric matrix (starch, protein and lipid).