Fig. 4a illustrates the cumulative curve for formic acid concentration
in water over time. As expected, a higher formic acid content
greatly increases the biocide concentration in water. It can
also be seen that concentration remains constant over the time
interval tested. This means that formic acid release entirely occurs
within the 24 first hours (first measurement), after which diffusion
rate drops down to zero. WG-based matrix is not capable of regulating
a progressive release of this substance, which consequently
would limit the suitability of this active bioplastic for applications
where the active agent can be delivered straightaway. On the other
hand, compression-moulding temperature seems to produce some
differences, as a lower formic acid release is noticed if compression-
moulding is performed at 120 C (compare curves for
10 wt.% FA). Related to this, TGA results have shown the mass loss
of formic acid is complete at 100 C. Thus, even though post-treatment
is carried out at high pressure, bioplastic specimens containing
different quantities of formic acid are expected at each
temperature (90 and 120 C). As a result, this fact must be taken
into consideration during material manufacture. In this sense, the