Interactions of cellulose cryogels and aerogels with water and oil: Structure-function relationships
Résumé
Food-grade porous materials, aerogels and so-called cryogels, were prepared from cellulose hydrogels obtained
from solutions at increasing cellulose concentration (3, 4, 5%, w/w) by supercritical-CO2-drying (SCD) and
freeze-drying (FD), respectively. The structure depended on the applied drying technique, with aerogels showing
a denser network with pores <200 nm in diameter, a specific surface area of 370–380 m2g-1, and a porosity of
92–94%. Cryogels presented larger pores (2–5 μm diameter), much lower specific surface area (around 30 m2g-1),
and higher porosity (95–96%). Water vapor adsorption by aerogels and cryogels was higher than that of neat
microcrystalline cellulose. The absorption of water and oil was investigated as a function of time and at equilibrium.
While water was almost immediately absorbed by both aerogels and cryogels, a much longer time was
needed to reach oil absorption equilibrium. Moreover, aerogels required a longer absorption time than cryogels.
Material morphology governed the kinetics of absorption; the absorption at equilibrium was directly dependent
on material pore volume rather than on its morphology or material-fluid affinity. As a result, due to their lower
pore volume, aerogels absorbed a lower amount of water or oil (4–8 gfluid/gdry matter) than cryogels (8–12 gfluid/
gdry matter). All samples showed high fluid holding capacity (>96%). Water absorption caused a firmness
decrease, but the firmness of oil-filled materials was the same as that of the unloaded ones. This study demonstrates
that food-grade cellulose aerogels and cryogels can be structurally designed by varying cellulose
concentration and drying techniques to obtain controlled food fluid loading
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