The aim of this study was to find alternative starch plasticizers
to glycerol that yielded a less tacky material in high-moisture conditions
without leading to starch crystallization. A range of glycerol films
containing different potential plasticizers (linear alkane diols)
were therefore produced, and it was shown that 1,3-propanediol, in
combination with glycerol, was a possible solution to the problem.
Several additional interesting features of the starch films were however
also revealed. The larger diols, instead of showing plasticizing features,
yielded a variety of unexpected structures and film properties. Films
with 1,6-hexanediol and 1,7-heptanediol showed an ultraporous film
surface and near-isoporous core. The most striking feature was that
starch films with these two diols moved/rotated over the surface when
placed on water, with no other stimulus than the interaction with
water. Films with 1,8-octanediol and 1,10-decanediol did not show
these features, but there was clear evidence of a structure with phase-separated
crystallized diol in a starch matrix, as observed in high-resolution
scanning electron microscopy (SEM) images.
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