Unique reactivity of nanoporous cellulosic materials mediated by surface-confined water

Abstract

The remarkable efficiency of chemical reactions is the result of biological evolution, often involving confined water. Meanwhile, developments of bio-inspired systems, which exploit the potential of such water, have been so far rather complex and cumbersome. Here we show that surface-confined water, inherently present in widely abundant and renewable cellulosic fibres can be utilised as nanomedium to endow a singular chemical reactivity. Compared to surface acetylation in the dry state, confined water increases the reaction rate and efficiency by 8 times and 30%, respectively. Moreover, confined water enables control over chemical accessibility of selected hydroxyl groups through the extent of hydration, allowing regioselective reactions, a major challenge in cellulose modification. The reactions mediated by surface-confined water are sustainable and largely outperform those occurring in organic solvents in terms of efficiency and environmental compatibility. Our results demonstrate the unexploited potential of water bound to cellulosic nanostructures in surface esterifications, which can be extended to a wide range of other nanoporous polymeric structures and reactions.

Regioselective and water-assisted surface esterification of never-dried cellulose: nanofibers with adjustable surface energy

“… 16 This approach is based on the use of N -acetylimidazole as acetylation agent, which has also been shown to enable regioselective modification of dried cellulose fibers. 26 However, this recent method lacks versatility since it only enables introduction of acetyl groups and it has not been demonstrated so far that it allows also the regioselective esterification of never-dried cellulose fibers, which is preferable to produce high-performance CNFs. Herein, we introduce a facile and versatile approach for the regioselective introduction of hydrophobic ester moieties onto the primary surface hydroxyl groups (C6-OH) of cellulose ( Fig.…”

Deconstruction and Reassembly of Renewable Polymers and Biocolloids into Next Generation Structured Materials

“…Biopolymers are isolated by (1) extraction through solubilization of the respective biopolymer and its subsequent precipitation, or (2) purification of the biomass fiber to isolate a solid, generally, fibrous biopolymer through solubilization of its surrounding matrix polymers (Figure 6b). In these processes, the multiscale hierarchy and matrix interactions in the biomass determine their recalcitrance and is also a reason for the high mechanical strength of fibrous biopolymers 23 including cellulose, 174 chitin, 175 collagen, 176 keratin, 177,178 and fibroin. 179,180 Cellulose, chitin, 181 and fibrous proteins, such as silk fibroin 182 and fibrous collagen in leather, 183 are traditionally The biopolymer of interest can be either isolated by removal of the matrix (purification) to yield a solid biopolymer fiber or by selective solubilization from the fiber matrix (extraction).…”

“…Although three hydroxyl groups are in theory chemically accessible at the surface of cellulose fibrils, it has been shown that the C3-OH is in fact hardly accessible due to steric effects and intrachain hydrogen bonding. 174,244,245 Meaning that modification of C3-OH requires harsher conditions or special treatment, which will eventually affect the crystallinity or MW of cellulose. Consequently, the DS threshold for surface modifications (Figure 7a3), such as acetylation, is actually lower as only C6-OH and C2-OH are chemically accessible under heterogeneous conditions.…”

“…255 Taking these facts into account, oxidation of cellulose needs to be controlled to limit its influence on the physical properties, which is in contrast to a recently developed wet esterification method using acyl imidazole that enable highly regioselective esterification of the C6-OH of cellulose while preserving the cellulose MW and crystallinity. 174,205,256,340 Given the fact that the deconstruction process is affected by surface reactions, understanding their mechanisms and the effect of modification on biopolymer MW and crystallinity is important in the deconstruction of biomass into biocolloids. Moreover, oxidation based on TEMPO and periodate play an important role in the chemical behavior of the biocolloids.…”

“…Recent advances in cellulose chemistry have focused on the utilization of acyl imidazole enabling esterification of cellulose in wet conditions while preserving the native MW and crystallinity of cellulose. 174,205 It was shown that the regioselectivity of this esterification can be ultimately dictated by the amount of water in the reaction. Thereby, it became possible to conduct esterification in a highly regioselective manner providing access for to C6-succinate CNF (C6SA-CNF) 340 and C6-acetate CNF (C6AA-CNF).…”