Thermal degradation of the high amylose starch films, after
water loss, is essentially a two stage process with a slight shoulder
at 299 C (Aggarwal and Dollimore, 1997) that may be associated
with thermal decomposition of the film crystal VH structure. In
comparing the TGA thermogram of Soluble (potato) starch (control)
film, no side peak at all occurred before the Tmax peak (Gilfillan
et al., 2013). This is because the film contained no VH crystal
structure, hence no thermal peak associated with VH crystal
degradation was observed (Gilfillan et al., 2013).
The onset of thermal degradation temperature (To) (after 5 drywt%
loss) was reduced to the greatest extent, for films derived from
the starch/glycerol containing 5 and 10 wt% EtOH by 8 and 16 C (To
256 and 248 C) respectively, compared to the control film (To
264 C average) whereas To values changed little for all MetOH
derived films. The To value for film derived from the starch/glycerol
containing both (MetOH and EtOH) alcohols approximates the
average of the individual alcohol-derived film To values (Table 1).
Generally To showed little change with alcohol-derived film
concentrations above 10 wt% compared with the control. The Tmax
(314e315 C) overall for most alcohol-derived film was reduced by
5e6 C compared to the control film Tmax (320 C).
Capek et al. (2010) proposed that thermal characteristics may
serve as an analytical indicator for reaction changes in the starch
molecular structure. The reduced degradation temperature (To and
Tmax) for alcohol-derived film may be an indication that some degree
of oxidation of the starch may have occurred likely by the
alcohol, since oxidized starch has been shown to be less thermally
stable (Zhang et al., 2007