Abstract
A fibrous 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized wood cellulose/water slurry was disintegrated with a magnetic stirrer or high-pressure homogenizer under various conditions to prepare TEMPO-oxidized cellulose (TOC)/water dispersions with different degrees of fibrillation. The turbidity value of the as-prepared dispersion was used as a measure of the degree of nanofibrillation of the fibrous TOC slurry in water. The fibrillated TOC/water dispersions with low degrees of fibrillation had cellulose nanonetwork (CNNeW) structures consisting of TOC nanofibrils (TOCNs), unfibrillated TOC fibers, and fibril bundles. The original TOC/water slurry and partly fibrillated TOC/water dispersions with low degrees of fibrillation were converted to a sheet and films, respectively, in a short time by membrane filtration, and they had low bulk densities and high porosities. Membrane filtration of an almost completely nanofibrillated TOC/water or TOCN dispersion took a long time, but the as-prepared TOCN films had the highest light transparency, tensile strength, Young's modulus, and work of fracture. The oxygen permeabilities of the films at 23°C and 50% relative humidity were as low as 1–2 ml μm m−2 day−1 kPa−1 among the films prepared from the fibrillated TOC/water dispersions with a wide turbidity range of 0.01–0.45. Therefore, TEMPO-oxidized CNNeW films with the versatile optical, porous, and mechanical properties but similarly low oxygen permeabilities can be prepared by controlling the degree of fibrillation of the TOC/water slurry (Graphical ).
Highlights
The 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical is a water-soluble, commercially available, and stable nitroxyl radical
When TEMPO-oxidized wood celluloses (TOCs) nanofibrils (TOCNs)/water dispersions are sonicated for an extended time, such as 60–120 min, in laboratory experiments, TEMPOoxidized cellulose nanocrystals (T-CNCs) with average aspect ratios of
The fiber length became shorter as the degree of fibrillation of TOC increased from ST to 150P1
Summary
The 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical is a water-soluble, commercially available, and stable nitroxyl radical. When TEMPOoxidized cellulose nanofibril (TOCN) films are prepared from completely individualized and transparent TOCN/water dispersions by casting on a plate or filtration on a membrane filter and subsequent drying, the films have good flexibilities, high light transparencies, and high mechanical strengths (Zhao et al, 2018), extremely low oxygen permeabilities of
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