4. Enzymatic degradation
Enzymatic degradation of starch and starch/PLA foams
was tested by an in vitro hydrolysis with a-amylase at 60 8C
and the results are expressed as a function of reaction time in
Fig. 7. All of the foam specimens investigated exhibited a
monotonic increase in the percentage of weight loss with
increasing reaction time. An abrupt increase in the
percentage of weight loss for pure starch foams was
observed at the onset reaction time of around 40 min, but
no abrupt increase in the percentage of weight loss was
observed for starch/30 wt% PLA hybrid foams. For pure
starch foams, within the reaction times of less than 40 min,
water molecules were being absorbed into the foam
structure, thus only limited parts of the foams were
accessible to the enzyme, and this could be the reason for
the slow enzymatic degradation observed with this time
interval. Comparison between the percentage of weight loss
curves of pure starch and starch/PLA foams suggests that
starch/PLA foams was, in general, less subservient to
enzymatic hydrolysis by a-amylase than pure starch foams
at ‘long’ reaction times (i.e. greater than 40 min). This is in
contrast to starch/PCL foams which was shown to be more
subservient to enzymatic degradation by a-amylase than
pure starch foams (Preechawong, Peesan, Supaphol, &
Rujiravanit, 2004)