3.1. Scanning electron microscopy
Micrographs were obtained of sheets previously
immersed in chloroform for 24h in order to solubilize the
PLA and allowed observation of PLA regions in the TPS
matrix. Images were also taken of sheets not immersed in chloroform.
Fig. 1(a) shows the fracture micrograph of theTPS25/PLA sheet (section2.2) and
Fig.1(b)
shows the sheet
previouslyimmersed in chloroform. In Fig.1(a)
it is possible to observe the PLA domains (lighter) distributed in the TPS matrix (darker).
Fig. 1(b)
shows the voids previously occupied by PLA domains, characterizing the immiscibility
between the PLA and TPS. This behavior is associated with
the difference between the hygroscopicity of starch
(hydrophilic) and PLA (hydrophobic). These
findings verify the observations of a previous study of Müller et al.
[8]
.
Fig. 2
shows the surface micrographs of the TPS25/PLA
sheet uncoated (
Fig. 2
a), and coated by spraying (
Fig. 2
b)
or by immersion (
Fig. 2
c) with cross-linked chitosan.
Regardless of the coating process, the micrographs indicate a continuous covering of chitosan on the sheet surface.