The results of this work have shown that a one-step thermal
extrusion process of unmodified starch in the presence of alcohol
can be used to improve film mechanical properties and reduce the
moisture content. The crystallinity of these films increased due to
the alcohol complexing with starch to form the VH polymorph,
which impacted on the mechanical properties. Also, the improvement
in film properties is likely due to hydrogen bonding (or other
molecular interactions) between starch hydroxyl groups created as
a consequence of the altered functionality of starch molecules
during processing. This may have arisen if the carboxylate groups
formed by the oxidation of the glucose units of starch were partially
esterified by the alcohol during the extrusion stage. The use of
MetOH enhanced the oxidation process more so than EtOH, and
hence gave the highest mechanical properties. Further work with a
catalyst may lead to further improved mechanical and moisture
resistant properties making these films potentially useful for
biodegradable packaging materials