Journal
ACS SUSTAINABLE CHEMISTRY & ENGINEERING
Volume 4, Issue 3, Pages 1041-1049Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acssuschemeng.5b01123
Keywords
Surface carboxyl protonation; Cellulose nanofibrils; Amphiphilic; Hydrophobic; Self-assembly; Thermal stability; TEMPO oxidation
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Funding
- California Rice Research Board [RU-9]
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Self-assembling of cellulose nanofibrils (CNFs) as affected by varying extent of protonation on C6 surface carboxyls was investigated under freeze-drying and air-drying processes. Surface carboxyls were protonated from 10.3 to 100%, all on the same TEMPO oxidized and mechanically blended CNFs with identical geometries and level of oxidation. Upon freeze-drying, all CNFs assembled into amphiphilic mass. The mostly charged CNFs assembled into the finest and most uniform fibers (phi = 137 nm) that absorbed significantly more nonpolar toluene than water; whereas the fully protonated CNFs assembled extensively into porous and more thermally stable ultrathin filmlike structures that absorbed water and toluene similarly. Ultrafiltration and air drying induced cyrstallization led to more thermally stable, semitransparent, and hydrophilic films that showed no affinity toward nonpolar toluene. In essence, CNFs could be tuned by varying the degree of surface carboxyl protonation, along with drying processes, to create fibrous to film morphologies, amphiphic to hydrophilic properties, and higher thermal stability.
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