Bench-top techniques for optical characterization of SCF-foamed highly porous polylactide matrices

Results of development and experimental verification of a bench-top system for synthesis of highly porous polymer matrices are presented. Synthesis of the matrices is based on the initial plasticization of a raw polymer material provided using a subcritical/supercritical fluidic agent with the follow-up foaming of the plasticized polymer due to gradual depressurization of a working volume of the high-pressure reactor. The design of the reactor makes it possible to provide the quasi-real-time optical control of the polymer foaming using various optical probes (e.g., the small-angle diffuse transmittance measurements at various wavelengths, the multi-speckle diffusing wave spectroscopy, the polarimetric measurements using a transmitted light, the direct imaging of a foamed volume in the trans-illumination mode, etc.). The optical control is carried out through a set of sapphire glass windows symmetrically located around the working volume of the reactor. A precise control of the pressure and temperature in the working volume is synchronized with the optical probing of the foamed volume. Bench-top tests of the developed system were carried out using two extreme foaming modes: the quasi-adiabatic foaming under the condition of fast depressurization of the working volume, and the quasiisothermal foaming provided with the extremely slow depressurization and the constant temperature in the working volume. In the experiments, a granular polylactide from the PURACORB Inc. was used as the raw polymer material and carbon dioxide was applied as the plasticizing/foaming agent. The results of pilot foaming experiments for these extreme modes of polylactide foaming are presented.