Fabrication of cellulose cryogel beads via room temperature dissolution in onium hydroxides
2022
Pieter De Wever | Joris Janssens | Pedro Fardim
In recent years, there has been a growing interest in green solvents to dissolve and shape cellulose into microspheres. However, development of solvents suitable for room temperature dissolution and shaping of cellulose spheres is very limited. In this work, a novel process to fabricate cellulose microspheres is presented. First, the effect of ethanol-hydrochloric acid pulp pretreatment on cellulose solubility in aqueous tetra-n‑butyl phosphonium hydroxide and tetra-n‑butyl ammonium was investigated. While the dissolution of untreated pulp remained limited to 5 wt%, the pretreatment boosted pulp solubility to 15 wt%. Spherical beads were obtained via dropwise addition of the solution in ethanol. Cryogels beads with a BET surface area of 218.1 m²/g were collected when using 90 v% tert‑butyl alcohol as the freeze-drying medium. After gathering the spent ethanol and initial washing of the beads, 90.7% of the tetra-n‑butyl phosphonium hydroxide solution was recovered and successfully reused to prepare a subsequent batch of beads. The proposed bead preparation system further fits within the concept of topochemical design as beads could be fabricated from low to high cellulose concentrations, regardless of temperature, therefore offering great opportunities to design gels for different applications such as drug delivery systems, protein conjugation or wastewater treatment.
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