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An effective method for preparing food-grade three-dimensional (3D) printing materials was the use of highly concentrated oil-in-water emulsions. This research reported 3D printable materials constructed from food-grade high internal phase Pickering emulsions (HIPPEs) that were stabilized by ε-poly-l-lysine grafted cellulose nanofiber (ε-PL-TOCNs). The ε-PL-TOCNs were prepared via ε-poly-l-lysine grafting of 2, 2, 6, 6-tetramethylpiperidine-N-oxyl (TEMPO)-oxidized cellulose (TOC) and the successive mechanical treatment. Subsequently, the chemical structure, microstructure and surface properties of ε-PL-TOCNs were characterized. The results showed that the prepared ε-PL-TOCNs had excellent dispersion performances, cationic properties brought by amino groups, and hydrophilic/hydrophobic functions of chain structure, which confirmed the feasibility of preparing HIPPEs. The HIPPEs with an internal phase volume fraction of 82 % were obtained at 0.8 wt% ε-PL-TOCNs concentration and pre-emulsification followed by continuous oil feeding. The HIPPEs' storage stability, morphology, and rheological behavior were further discussed. The ultra stable HIPPEs with apparent shear-thinning behavior and high solid viscoelasticity were successful produced, which was suitable for 3D printing. This work expanded the application of nanocellulose in emulsions field and provided a new thinking to prepare food-grade 3D printable materials and porous foam., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

The TEMPO-mediated oxidation is one of the most popular methods to prepare cellulose nanofibers due to its easy operation, high oxidation efficiency and resulting high aspect ratio nanofibers with uniform size. Among TEMPO-mediated oxidation methods, the TEMPO/NaBr/NaClO (TBN) oxidation system is the most commonly used and has the highest oxidation efficiency. However, cellulose suffers from the degradation by NaClO in TBN oxidation, which can be directly reflected in the reduction of degree of polymerization of cellulose. In this paper, we explored the effect of the content of NaClO on oxidation and figured out an optimization method where NaClO was added periodically for TBN oxidation system (semi-batch process) that could efficiently oxidize hardwood bleached kraft pulp (HBKP) cellulose while reducing the degradation. This phenomenon is most obvious when the addition amount of NaClO is 10 mmol/g and the reaction time is 7.5 h, the carboxyl content of the TEMPO oxidized cellulose obtained by adding NaClO in different methods has no significant change (both are around 1.5 mmol/g), but the degree of polymerization of TEMPO oxidized cellulose obtained by adding NaClO periodically is 2.3 times that of TEMPO oxidized cellulose obtained by adding NaClO in one batch. This optimization method provides a feasible way for the adjustable preparation of nanofibers with high carboxyl content by maintaining relative high degree of polymerization. [ABSTRACT FROM AUTHOR]

Zwitterionic dispersed chitin nanocrystals and TEMPO oxidized cellulose nanofibrils can be well mixed and self-assembled to be hydrogels/membranes. Active carboxyl groups ensure the well mixing of zwitterionic chitin nanocrystals and cellulose nanofibrils under neutral and alkaline condition. Electrostatic attraction between amino groups in chitin nanocrystals and carboxyl groups in chitin nanocrystals and cellulose nanofibrils further endows self-assemble property of composite suspensions. Simple standing for 12 h at room temperature is found enough for preparing self-assembled composite hydrogels. By 1-(3-dimethy-laminopropyl)-3-ethylcarbodiimide hydrochloride/N-hydroxy succinimide (EDC/NHS) mediated chemical crosslinking, the storage modulus of composite hydrogel can achieve almost 8 times higher than self-assembled hydrogel. Well dispersed composite suspensions also can be transformed to be membranes via filtration treatment. The strain increases almost 2.3 times higher with similar tensile strength for cellulose nanofibril rich samples, and chitin nanocrystals mainly contributes to the enhancement in strain of composite membranes. [Display omitted] • Zwitterionic nanochitin can disperse with nanocellulose under neutral condition. • The zwitterionic nanochitin/nanocellulose composite can self-assemble to be hydrogels. • A more balanced ratio between amino and carboxyl groups leads to stronger crosslinking. • Self-assembled composite hydrogels exhibit spontaneous self-healing properties. [ABSTRACT FROM AUTHOR]

The environment‐friendly oxidation of cellulose by the 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO)/laccase/O2 system is an alternative route with huge potential to prepare cellulose nanofibers. It is found that the concentration of TEMPO significantly affects the oxidation efficiency. An effective method for improving the oxidation effect is to increase the TEMPO concentration and prolong the oxidation time. To clarify the rate‐limited step of TEMPO/laccase/O2 oxidation of cellulose, the academically accepted oxidation process is divided into individual pathways. A series of experiments is conducted with laccase and the three forms of organocatalyst (TEMPO, oxoammonium (TEMPO+), and hydroxylamine (TEMPOH)) to simulate individual reactions and calculate the reaction rates. The concentrations of TEMPO and oxoammonium are monitored by EPR spectroscopy. The oxidation rate of TEMPO by laccase varies at different pH conditions, and laccase activity is much higher at pH 4.5. Other reactions without laccase involved express a higher reaction rate when the pH value increased. TEMPO is mainly regenerated through a comproportionation reaction between oxoammonium and hydroxylamine. The acceleration of TEMPO regeneration by laccase is not obvious. The results indicate that the rate‐limited reaction in TEMPO/laccase/O2 oxidation is cellulose oxidation by TEMPO+. [ABSTRACT FROM AUTHOR]

A green and effective method was proposed for producing amino cellulose nanofibers (ε-PL-TOCNs) with a yield of > 60%, which was obtained via ε-poly- L -lysine-grafting of 2, 2, 6, 6-tetramethylpiperidine-N-oxyl (TEMPO)-oxidized cellulose (TOC). The different carboxyl group content of TOC, EDC/NHS molar ratio and their adding ways, ε-poly- L -lysine concentration on the yield, amino content and physicochemical properties of ε-PL-TOCNs were systematically investigated and optimized. The ε-PL-TOCNs with the characteristics of enhanced thermal stability, improved mechanical strength, and fluorescence properties was successfully produced. Moreover, the ε-PL-TOCNs was zwitterionic with both anionic and cationic charges due to the co-existence of carboxyl and amino groups, thus showed excellent dispersion stability in a wide pH range except for the isoelectric point around pH 9. Notably, the ε-PL-TOCNs possessed an excellent anti-microbial effect (>99%) against Escherichia coli and Saccharomyces cerevisiae at 200 μg/mL loading dosage because of the positive role of amino groups, which made it applicable to extend the freshness of fruits. This preparation approach of amino cellulose nanofibers was advantageous over traditional methods owing to green and efficient methods, which expanded the application of cellulose nanofibers in anti-microbial agent and food preservation. [Display omitted] • Amino cellulose nanofibers (ε-PL-TOCNs) were prepared via ε-PL grafting of TOC. • The stepwise activation improved efficiency of TOC amination. • The amination→nanofibrillation process was superior to nanofibrillation→amination. • 4. The zwitterionic ε-PL-TOCNs showed excellent dispersion stability, mechanical properties and thermal stability. • 5. The ε-PL-TOCNs exhibited excellent antibacterial, antifungal and fresh-keeping performance. [ABSTRACT FROM AUTHOR]

An environmentally friendly 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation system using halogen-free reagents has attracted much attention. At present, cellulose nanofibers (CNFs) with a high carboxyl content can be prepared by TEMPO/laccase/O 2 (TLO)- oxidation of hardwood bleached kraft pulp (HBKP) under aqueous conditions, while, the related research is still in its infancy. For example, the further applications of TLO-CNFs and the oxidation effect of the TLO system on cellulose from different sources have not been studied. In this work, cellulose from four different sources, that is, HBKP, softwood bleached kraft pulp (SBKP), bleached bagasse sulfate pulp (BBSP) and microcrystalline cellulose (MCC), was oxidized by using a TLO-oxidation system. All cellulose materials were found to be able to be oxidized successfully regardless of the source, which proved the universality of the TLO-oxidation system. Different from traditional TEMPO/NaBr/NaClO (TBN)-oxidation that introduces major carboxyl groups (0.846–1.154 mmol/g) and minor aldehyde groups (0.041–0.097 mmol/g) to cellulose, carboxyl (0.558–0.615 mmol/g) and aldehyde (0.218–0.235 mmol/g) groups can both be sufficiently introduced on the surface of TLO-oxidized cellulose. Based on the aldehyde groups introduced, the wet strength of the TLO-oxidized cellulose handsheet was greatly improved to 400% of the non-oxidized one due to the formation of hemiacetal linkages. In addition, oxidized cellulose can be isolated to homogeneous TLO-CNFs or TLO-cellulose nanocrystals (CNCs), and TLO-CNFs (CNCs) can easily be processed into films and hydrogels with high light transmittance and excellent mechanical properties. Remarkably, compared to the other TLO-CNFs, TLO-CNFs (BBSP) has higher aspect ratio with thinner width (nanofibers as thin as 2 nm can be achieved). Thus, the mechanical properties of TLO-CNFs (BBSP) assembled films and hydrogels were superior to others. These all providing significance and promising prospects for the applications of TLO-oxidation systems, meantime, the distinctive characteristics of TLO-CNFs (BBSP) were explored. [Display omitted] • TLO oxidation has universality for cellulose modification and nanofibrillation. • TLO oxidation introduced both sufficient aldehyde and carboxyl groups. • Higher wet tensile strength correlated with highly amount of aldehyde contents. • The bagasse derived CNF showed higher aspect ratio and film & hydrogel strength. [ABSTRACT FROM AUTHOR]