Three phases of transitions that are gelation, plasticization, and
recrystallization, can be assumed consequently for starch polymers
transforming from gel to crystal. During gelation, many plasticizer
molecules intersperse between the starch polymers. The starch sys-
tem appears soft solid. After the starch system is dried out, it be-
comes starch film. However, between the starch polymers, there
are still a lot of plasticizer molecules and, water, leading to the
big distance and free volume between the starch polymer chains.
The starch film is in plasticization phase that has amorphous state
and low glass transition temperature (
T
g
). The mobility or vibra-
tion of the segments of starch polymer chains is vigorous and the
plasticized starch films are flexible. During retrogradation (or re-
crystallization), many plasticizer molecules escape from the starch polymers and form direct interactions between the starch poly-
mers, leading to the reduction in the free volume in the starch film.
The mobility or vibration of the starch polymers reduces. The film
then has high
T
g
and appears brittle. Low and intermediate plasti-
cizer concentrations facilitate this retrogradation (or recrystalliza-
tion) process and formation of nanoscale crystallites.