Properties of agar aerogels: Effect of concentration and ageing time

Agar, a polysaccharide derived from red algae, is a renewable, edible, and biocompatible hydrocolloid with excellent gelling properties. Although widely used in the food industry and microbiology, its potential for advanced material design, particularly as an aerogel, has not yet been sufficiently explored. In this study, agar aerogels were produced via the sol-gel process and supercritical CO₂ drying. The effects of polysaccharide concentration (2%, 6%, and 10% w/v) and ageing time (24 h and 10 days) on the structural, textural and compressive mechanical properties were systematically investigated for the first time. All aerogels were highly porous, with specific surface areas reaching a maximum of 375 m²/g at a moderate agar concentration (6% w/v). Prolonged ageing generally improved the textural and morphological properties but reduced the compression strength and swelling capacity. All samples showed excellent water uptake and remained stable in aqueous environments for four weeks. These results demonstrate that both concentration and ageing time significantly affect the final performance of the agar aerogels. Their properties can be easily adjusted by processing parameters, offering great potential for biomedical, food-related, or environmental applications.