Tuning structure and properties of pectin aerogels

Abstract

Highly porous and nanostructured pectin aerogels were synthesized via dissolution-solvent exchange-drying with supercritical CO2. The goal was to show why and how aerogel morphology and properties vary as a function of external conditions. Polymer concentration, pH and concentration of mono- and divalent metal salts were varied. The way of structure stabilization, i.e. gelation or direct non-solvent induced phase separation (in other words, the state of the matter before solvent exchange, gel or solution) turned out to be one of the key parameters influencing aerogel morphology and density. When strong gels were formed via calcium-induced gelation at pH around pKa, the corresponding aerogels presented large pores, the lowest density (0.04–0.05 g/cm3) and lowest specific surface area (around 270–350 m2/g). On the contrary, when pectin network was formed via non-solvent induced phase separation from non-gelled pectin solutions during solvent exchange step, the resulting aerogels were mesoporous, with highest density (0.12–0.15 g/cm3) and highest specific surface area (around 600 m2/g). The results obtained provide the guidelines for making aerogel matrices with fully controlled morphology and properties.