Hollow microcapsules have attracted much interest owing to their extensive use as a micro-container allowing for the loading and unloading of active compounds such as artificial cells, catalysts, and energy storage components. Microcapsules derived from renewable resources are receiving great attention among researchers because of their cost efficiency, sustainability, and environmental friendliness. As one of the emerging cellulosic nanomaterials, cellulose nanofibrils (CNFs) exhibit amphiphilicity, biodegradability, renewability, and excellent mechanical properties. Herein, we utilize oil-in-water (O/W) Pickering emulsions stabilized by CNFs (&lt;40 nm in width) as a template to design hollow CNF microcapsules. Aqueous suspensions of CNF with varying mass concentrations (0.1 to 0.5 wt%) were ultrasonically mixed with n-hexane to create O/W emulsions with droplet size in the range of (10 to 24 μm). The n-hexane core in the O/W emulsions was removed by freeze-drying, leaving hollow CNF microcapsules without significant deformation and collapse. The hollow CNF microcapsules were characterized by using density and porosity measurements, BET analysis (nitrogen gas adsorption), optical microscopy, thermographic analysis (TGA), scanning electron microscopy (SEM), and oil absorption capacity. The hollow CNF microcapsules showed ultralow density (3.5 to 12.4 mg cm-3) and high porosity (&gt;99%). SEM images revealed the porous and cellular structures of the hollow microcapsules. Following the amphiphilic nature of CNF, the hollow microcapsules are also believed to exhibit amphiphilicity, i.e., a hydrophilic outer surface and a hydrophobic inner surface. The oil absorption capacity of the hollow microcapsules was determined to be 226 g/g and 169 g/g for chloroform and hexadecane, respectively. CNF-based Pickering emulsion templating may pave the way for the design of CNF-based microcontainers with functionality and sustainability.

Ultrasound-assisted synthesis of hollow microcapsules via Cellulose Nanofibrils (CNFs) stabilized pickering emulsions as a template

ACS Spring 2022

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