Abstract
The application range of aerogels, especially in the life-science sector, can be extended by utilizing biocompatible polymers such as polylactic acid (PLA). However, the low glass transition temperature (Tg) of PLA and the challenging gelation techniques limit the application of supercritical CO2 (scCO2) drying and thus the PLA-aerogel production. The aim of this work is to overcome this challenge and to provide a better understanding of the thermodynamics of the process. Therefore, the gelation of amorphous PLA (PDLLA) and semicrystalline PLA (PLLA) via thermal-induced phase separation (TIPS) was studied. To identify polymer/solvent/antisolvent ratios suitable for gelation, thermodynamic modeling (PC-SAFT) was used to describe the corresponding ternary phase diagrams. scCO2 drying was used to preserve the mesoporous gel structure formed during the gelation. Due to the decrease in the Tg of PLA in the presence of CO2, this could not be applied to all gels. It was found that the critical parameter to enable the scCO2 drying of low Tg polymers is the crystallinity degree (Xc) of the polymer. Based on these results, some guidelines for producing aerogels from polymers with low Tg are formulated.Graphical abstract
Highlights
Most of the aerogels produced nowadays are produced from gelable starting materials such as silica via a sol–gel process [1], from alginate by crosslinking using divalent cations [2], from cellulose via a coagulation/gelation mechanism [3] or from synthetic polymers via various polymerization techniques [4]
As we aim at pharmaceutical applications of aerogels, we suggest here the new solvent/antisolvent system Dimethyl sulfoxide (DMSO)/ ethanol to produce PDLLA aerogels for pharmaceutical applications
To overcome the plasticizing effect of ethanol and supercritical CO2 (scCO2), we suggest introducing an additional step before the supercritical drying: solvent exchange of ethanol-containing gel with liquid CO2 at low temperature
Summary
Most of the aerogels produced nowadays are produced from gelable starting materials such as silica via a sol–gel process [1], from alginate by crosslinking using divalent cations [2], from cellulose via a coagulation/gelation mechanism [3] or from synthetic polymers via various polymerization techniques [4]. The gels produced from these materials can be transformed readily to the corresponding aerogels by extracting the gelation solvent via a standard supercritical-drying process. The beforementioned aerogels cover a wide range of applications such as thermal insulation, adsorption media, and active-compound carriers. Polylactic acid (PLA) could be effectively used as a drug carrier for pharmaceutical applications in the form of aerogels. Until now, PLA-based aerogels exhibit still low surface areas, limiting their application’s potential
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