Water has been typically used as a blowing agent as well as a
plasticizer for starch-based foams. Water is inexpensive and also
environmentally friendly solvent [27]. The optimum water content
in the feed has been stated to be in the range of 15–18% to provide
the largest expansion ratio of the extruded foams. Further increase
in feed moisture led to a dramatically decrease in the foam expansion
(see Table 2) [7,8]. Because low water contents in the feed
leads to a high Tg of the extruded starch, as it exits from the die,
the foam solidifies or turns glassy more quickly which stabilizes
a highly expanded structure and yields a low density extrudate