Counterion exchange in cellulose nanofiber and layered double hydroxide composite: impact on aerogel formation and performance

초록

Cellulose-based aerogels, known for their low density and porous structure, require simple and eco-friendly methods to enhance their strength and adjust their structure. In this study, the interaction between cellulose nanofibers (CNFs) and layered double hydroxides (LDHs) was investigated via ion-exchange processes on both materials and their impact on aerogel performance. Counterion exchange (using H+, Na+, and Ca2+ ions) altered fibril interactions. Na+-exchanged CNFs exhibited the highest dispersibility and smallest pore size, followed by that of Ca2+ and H+. LDH dispersibility improved with Cl- ions, and stable CNF-LDH hydrogel composites were formed. Aerogels comprising Na+ ions exhibited increased compressive strength with higher LDH content, whereas those comprising H+ exhibited a two-fold increase in strength at 20 wt% LDH. Ca2+-exchanged aerogels initially had the highest strength but weakened with LDH owing to cross-linkage interference. Flame retardancy depended mainly on the LDH content and counterions, which influenced pore structure. Additionally, LDH incorporation significantly improved thermal insulation, reducing thermal conductivity to 0.026 W/(m<middle dot>K). With ultra-low densities (0.004-0.009 g/cm3), these CNF-LDH aerogels show potential for advanced applications and further optimization.

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