Key words: supercritical fluidic plasticization, quasi-isothermal expansion, foam, amorphous polylactide, carbon dioxide, equation of state, polytropic index, surface tension, collapse
The results of experimental and theoretical studies of the behavior of the amorphous
D,L-polylacide fo am are presented. D,L-polylacide was preliminary plasticized using
sub- or supercritical carbon dioxide under the constant temperature (313,3 K) and
various pressures from 4 MPa to 20 MPa; after plasticization, it was foamed using the
quasi-isothermal depressurization under the low depressurization rates (from 0,005
to 0,05 MPa/s). It was established that, in the case of polylactide plasticization in the
supercritical domain (with the pressures of carbon dioxide above 8 MPa), the transition
from the expansion of the polylactide foam to collapse occurs in the course of
depressurization. Using the equation of state for a thermodynamically equilibrium
foam, which was pioneered by S. Ross, the criterion of the expansion-to-collapse transition
was established. It was shown that this phenomenonis caused by asignificant increase
in the surface tension of polymer during a slow decrease in the pressure of carbon
dioxide.
doi:10.1134/S1990793120070234