Facile synthesis of porous cellulose aerogel beads with tunable core–shell microstructures and physical properties

Abstract

Cellulose aerogel beads (CABs) have emerged as advanced biomaterials with numerous engineering applications, including chromatography and drug release. In this study, porous core–shell CABs were synthesized using a dilute ethanol solution-substitution-assisted freeze-drying. The formation mechanism of the CABs and the effect of ethanol concentration on the core–shell microstructures and physical properties were investigated. Cellulose hydrogel beads (CHBs) were formed through the exchange/neutralization of acetic acid with tetraethylammonium hydroxide (TEAOH)/urea. The cellulose chains dissolved in the cellulose–TEAOH/urea droplets regenerated from the edge to the inside of the droplet in an acetic acid bath. Notably, adding ethanol at a concentration of 10% before freeze-drying can result in core–shell CABs with non-obvious structural shrinkage, large particle size, uniform pores, and high porosity. Ethanol molecules induce ice crystal growth to form more uniform ice crystals during the freezing process. Additionally, by altering the TEAOH/urea molar ratios and cellulose concentrations of cellulose solutions, well-shaped and porous CABs were prepared, demonstrating the feasibility and availability of dilute ethanol solution-assisted freeze-drying. Consequently, the as-fabricated CABs had a dense micro-shell (1–9 μm) and loose millimetric-core with anisotropic pores (2–6 μm), exhibiting low density (0.06–0.09 g/cm3), high porosity (87.0–91.5%), and noteworthy thermal stability.