Cellulose nanofiber aerogel production and applications

摘要

Aerogels are highly porous solids formed by replacing the liquid in a gel by air, without changing the original structure. Cellulose aerogels are made by sublimating the water from a colloidal suspension of cellulose nanofibers. The nanofibers form three-dimensional networks, crosslinked by hydrogen bonds bridging the surface hydroxyl groups and also by mechanical entanglements between nanofibers. Although the studies on aerogels from cellulose nanofiber hydrogels by freeze drying reported so far had produced small samples no larger than 6 cm, we have developed improved cooling techniques that produces larger samples. These were impregnated with epoxy resin to fabricate nanocomposites. The highly porous structure allowed complete impregnation of resin and translucent composites were obtained. The modulus of composites was increased in relation to neat epoxy, but due to high brittleness the ultimate strength was decreased. This is likely caused by nanofiber agglomerations of uneven pore sizes acting as stress concentrators. The evaluation of the obtained composites serves as an indirect way to assess the quality of the aerogels produced.