A third processing method was envisaged, consisting of extrusion
of glycerol and starch (with thermo-plasticised starch, TPS,
as an intermediate product) followed by the addition of protein,
kneading and compression-moulding of the resulting mixture. Four
different temperature profiles, by fixing both feed and convey zones
temperatures and varying the mixing zone temperature from 90 to
120 ◦C, by 10 ◦C-steps, were tested. Dynamic mechanical thermal
analysis in bending mode was performed on the four resulting bioplastics,
and their corresponding rheological responses compared
with that of the reference sample (Fig. 6a). It can be seen that, when
potato starch is extruded at the two lowest temperatures (90 and
100 ◦C), the resulting bioplastics present E and E curves almost
identical to those of the reference sample, in the temperature range
investigated. Nevertheless, as extrusion temperature increases, the
values of both viscoelastic moduli decrease, being quite noticeable
at 120 ◦C.