Abstract
Membrane technology has become an indispensable part of our daily lives. The rapid growth of membrane technology has been breeding an unavoidable yet critical challenge─the unsustainable disposal of used membranes. Commercial polymer membranes are fabricated from fossil-based monomers and polymers that are not biodegradable. Hence, there is an urgent need to develop membranes that are sustainable from cradle to grave, i.e., both bioderived and biodegradable. Cellulose is one of the most abundant biopolymers that are biodegradable upon disposal. However, it is only soluble in a handful of solvents, limiting its fabrication into membranes at an industrial scale. To circumvent this bottleneck, in this work, we propose a sustainable and scalable method to fabricate cellulose membranes from cellulose acetate with a sacrificial acetate group. The proposed method allows cellulose membrane fabrication utilizing green solvents, and the fabrication procedure is sustainable with minimal solvent consumption. One of the most appealing applications of cellulose membranes is organic solvent nanofiltration (OSN). It is an emerging technology to separate solutes in nanoprecision in harsh organic solvents, requiring solvent-stable materials. Surprisingly, the cellulose membranes exhibited unique transport behaviors, with solute rejection ranging from 100 to −100% depending on the solvent medium. Such trends were not previously observed in the OSN literature, and the underlying mechanism was thoroughly investigated. Importantly, the membranes were completely biodegradable in a carbon-neutral manner upon disposal. The life cycle of cellulose membranes was compared with that of conventional OSN membranes in a qualitative and comparative study. The proposed methodology can be applied to substitute fossil-based polymers in all aspects of membrane technology, and it has the potential to become a sustainable fabrication platform for membrane materials.
Highlights
The recent outbreak of coronavirus disease 2019 (COVID-19)pandemic in 2020 has resulted in an explosion of demand for mask air filters to an $80 billion annual market.[1]
As the cellulose biopolymer is insoluble in most organic solvents, it is a sustainable alternative to conventional organic solvent nanofiltration (OSN) membranes
Cellulose acetate (CA) membranes with a sacrificial acetate moiety were first fabricated with a nonsolvent-induced phase separation (NIPS) technique using green solvents
Summary
Pandemic in 2020 has resulted in an explosion of demand for mask air filters to an $80 billion annual market.[1]. The fabricated CA membranes were initially thermally treated in a water bath to fine-tune the pore size, subsequently deacetylated in an aqueous NaOH solution to remove the sacrificial acetate group, and convert them to a solvent-stable cellulose membrane. Deacetylation, the resulting cellulose membranes were completely solvent-resistant, with undetectable mass loss (refer to Figure S6 in the Supporting Information) This set of data clearly demonstrates that solvent-resistant OSN cellulose membranes can be fabricated sustainably from CA with a sacrificial acetate moiety, with green solvents, and a simple deacetylation step in the aqueous media. Thermal treatment is useful in fabricating membranes with molecular sieving nanofiltration properties, as it is more effective in the nanometer-range pores.[62] These two advantages enable much more versatile control of the cellulose membrane morphology and performance than the conventional methods, and the proposed method will certainly make the production of cellulose membranes more economical and sustainable. It can be envisioned that the proposed method will be extended to many other biopolymers such as chitosan, alginate, and collagen
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