ß-(1 → 4)-Polyglucuronic acids with C2/C3-ketones prepared from regenerated cellulose by catalytic oxidation using solid NaOCl·5H2O.

Three commercial regenerated cellulose samples were subjected to TEMPO-catalyzed oxidation using solid NaOCl·5H2O as the primary oxidant for structural analyses of the oxidized products (TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxyl). The regenerated cellulose/water slurries became transparent solutions after oxidation for 60 min. The yields of the oxidized products were almost 100 % when they were isolated as precipitates in ethanol/water mixtures. The solution-state NMR spectra revealed that the oxidized products were almost pure water-soluble ß-(1 â†’ 4)-polyglucuronic acids; the reaction conditions described herein ensured the complete oxidation of the C6-OH groups in the regenerated cellulose samples to C6-carboxy groups. However, the solid-state 13C NMR spectra of the oxidized products indicated that C2/C3-ketones (<20 % of the total units) were formed during side reactions, which is characteristic for oxidized products prepared from regenerated cellulose with the C2/C3-glycol structure. These ketones were likely to form intermolecular hemiacetal linkages in the oxidized products. During conductivity titration of the oxidized products, it is necessary to control the sample masses to accurately determine the carboxy contents. The mass-average degree of polymerization decreased from 330 to 890 for the original regenerated cellulose samples to 65-79 for the oxidized products; substantial depolymerization is inevitable during TEMPO-catalyzed oxidation of the regenerated cellulose samples.

Polyglucuronic acids prepared from α-(1 → 3)-glucan by TEMPO-catalytic oxidation.

2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO)-catalytic oxidation was applied to a water-insoluble α-(1 â†’ 3)-glucan in water at pH 10 and room temperature (∼24 °C), with solid NaOCl·5H2O as the primary oxidant. Oxidation with NaOCl at 15 mmol/g gave a water-soluble TEMPO-oxidized product at a mass recovery ratio of 97 %. The carboxy content of the TEMPO-oxidized product was 5.3 mmol/g, which corresponds to a degree of C6-oxidation (DO) of 93 %. A new water-soluble α-(1 â†’ 3)-polyglucuronic acid with a nearly homogeneous chemical structure was therefore quantitatively obtained. X-ray diffraction and solid-state 13C NMR spectroscopic analyses showed that the original α-(1 â†’ 3)-glucan and its TEMPO-oxidized product with a carboxy content of 5.3 mmol/g had crystalline structures, whereas the oxidized products with DOs of 50 % and 66 % had almost disordered structures. The carboxy groups in the oxidized products were regioselectively methyl esterified with trimethylsilyl diazomethane, and analyzed by using size-exclusion chromatography with multi-angle laser-light scattering and refractive index detections. The results show that the original α-(1 â†’ 3)-glucan and its oxidized products with DOs of 50 %, 66 %, and 93 % had weight-average degrees of polymerization of 671, 288, 54, and 45, respectively. Substantial depolymerization of the α-(1 â†’ 3)-glucan molecules therefore occurred during catalytic oxidation, irrespective of the oxidation pH.

Correction to "Comprehensive Study of Preparation of Carboxy Group-Containing Cellulose Fibers from Dry-Lap Kraft Pulps by Catalytic Oxidation with Solid NaOCl".

[This corrects the article DOI: 10.1021/acssuschemeng.3c04750.].

Structural analyses of supernatant fractions in TEMPO-oxidized pulp/water reaction mixtures separated by centrifugation and dialysis.

Side reactions occurring on cellulose during 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TMEPO)-catalyzed oxidation have not been considered to be significant. Then, TEMPO-oxidized hardwood and softwood bleached kraft pulps (HBKP and SBKP) were prepared with an excess NaOCl·5H2O. Supernatant fractions (SFs) were obtained in the aqueous reaction mixtures of TEMPO-oxidized pulps by centrifugation and dialysis. The SFs with carboxyl contents of 5.0 and 4.2 mmol/g were obtained in the yields of 19 % and 30 % from HBKP and SBKP, respectively. These carboxy contents are much higher than those (2.6-2.7 mmol/g) of the precipitate fractions in the TEMPO-oxidized pulps. Solid-state 13C NMR spectra and other analyses revealed that the water-soluble ß-(1 â†’ 4)-polyglucuronic acids were predominantly present in the SFs. In addition, water-insoluble TEMPO-oxidized cellulose nanocrystals were present in the SFs, but they constituted less than ~10 % of the SFs. The mass-average degrees of polymerization (DPw) of the SFs obtained from HBKP and SBKP were 166 and 155, respectively, whereas the original HBKP and SBKP had DPw values of 1990 and 2140, respectively. These substantial depolymerization and formation of the water-soluble ß-(1 â†’ 4)-polyglucuronic acids occur on cellulose and oxidized cellulose molecules as side reactions during TEMPO-catalyzed oxidation, which should be considered for structural analyses of TEMPO-oxidized products.

Mechanically robust, flame-retardant phosphorylated cellulose films with tunable optical properties for light management in LEDs.

Biodegradable cellulose films with excellent mechanical, optical, and functional properties have attracted considerable attention as promising alternatives to plastics for photoelectronic devices. In this work, mechanically ductile, flame-retardant cellulose films with tunable optical properties were prepared by simple mechanical disintegration of phosphorylated cellulose (PhC) fibers, vacuum filtration of as-prepared dispersions, and subsequent pressing of the wet PhC films to prepare dried films. When mechanical disintegration conditions were optimized, the resultant PhC films exhibited an average density, tensile strength, Young's modulus, tensile toughness, and folding resistance of 1.4 g/cm3, 150 MPa, 8.5 GPa, 8.2 MJ/m3, and 4580 times, respectively. The PhC film hazes were widely controllable from 9 % to 91 %, while they maintained high light transmittances (>90 %) at a 550-nm wavelength. The PhC films were used for light management of light-emitting diodes by controlling mechanical fibrillation conditions of the PhC fiber/water slurry, showing that the films effectively improved the luminescence uniformity of the devices.

Approaching Theoretical Haze of Highly Transparent All-Cellulose Composite Films.

A highly transparent cellulose film with a high built-in haze is emerging as a green photonic material for optoelectronics. Unfortunately, attaining its theoretical haze still remains a challenge. Here, we demonstrate an all-cellulose composite film with a 90.1% transmittance and a maximal transmission haze of 95.2% close to the theoretical limit (∼100%), in which the entangled network of softwood cellulose fibers works as strong light scattering sources and regenerated cellulose (RC) with undissolved fibril bundles functions as a matrix to simultaneously improve the optical transparency and transmission haze. The underlying mechanism for the ultrahigh haze is attributed to microsized irregularities in the refractive index, arising primarily from the crystalline structure of softwood fibers, undissolved nanofibril bundles in RC, and a small number of internal cavities. Moreover, the resulting composite film presents a folding resistance of over 3500 times and good water resistance, and its application in a perovskite solar cell as an advanced light management layer is demonstrated. This work sheds light on the design of a highly transparent cellulose film with a haze approaching the theoretical limit for optoelectronics and brings us a step further toward its industrial production.

Favorable combination of foldability and toughness of transparent cellulose nanofibril films by a PET fiber-reinforced strategy.

Transparent cellulose nanofibril (CNF) films have been considered a promising sustainable alternative for nonrenewable and nonbiodegradable petroleum-based plastic films. However, their relatively low toughness and poor folding endurance are two remaining challenges for commercial application. In this work, inspired by fiber-reinforced polymer, a transparent CNF film with favorable combination of toughness and folding endurance is demonstrated by a facile and scalable polyethylene terephthalate (PET) fiber-reinforced strategy. The as-prepared PET fiber-reinforced CNF film not only exhibits a maximum average toughness of 13.7 ± 2.4 MJ/m3 that is nearly 4 times stronger than that of pure CNF film (3.7 ± 1.1 MJ/m3), but also presents superior bending flexibility with a folding endurance of over 104 times that is an order of magnitude higher than that of pure CNF film (~4 × 103 times). Moreover, its underlying principle for the enhanced toughness and foldability is explored. This work provides a facile strategy to prepare tough yet foldable CNF film and could promote its industrial uses in the fields of energy storage devices, packaging, and electronic devices.