Integrating direct reuse and extraction recovery of TEMPO for production of cellulose nanofibrils

Effect of hornification on the isolation of anionic cellulose nanofibrils from Kraft pulp via maleic anhydride esterification

Cellulose nanofibrils (CNF) isolation based on a catalyst-free maleic anhydride esterification has proven to be effective, however, the effects of pulp hornification on CNF isolation by this strategy have yet to be explored, which could present significant impacts for CNF isolation. Herein, dried northern bleached softwood Kraft pulp (D-NBSK) and never-dried northern bleached softwood Kraft pulp (ND-NBSK) were selected as the substrates. After esterification with maleic anhydride (MA), the esterified ND-NBSK pulp (E-ND) shows a significantly smaller size and more fragmented structure than the esterified D-NBSK pulp (E-D). Meanwhile, higher degree of esterification can be realized for the never dried pulp as compared to the dried pulp, which is corroborated by the significantly stronger characteristic peaks of CO (1720 cm-1) and -COO- (1575 cm-1) from the FTIR spectra and the higher surface charge content (0.86 ± 0.04 mmol/g vs. 0.55 ± 0.05 mmol/g). A comparison of the characteristics of the resulting CNF similarly demonstrated the negative impact of hornification. Overall, this work indicates that hornification tends to reduce the accessibility of chemical reagents to the pulp, leading to insufficient deconstruction. Such negative impact of hornification should be considered when performing nanocellulose isolation, especially when using pulp as feedstock.

Constructing a 3D Ion Transport Channel-Based CNF Composite Film with an Intercalated Structure for Superior Performance Flexible Supercapacitors

The weak stiffness, huge thickness, and low specific capacitance of commonly utilized flexible supercapacitors hinder their great electrochemical performance. Learning from a biomimetic interface strategy, we design flexible film electrodes based on functional intercalated structures with excellent electrochemical properties and mechanical flexibility. A composite film with high strength and flexibility is created using graphene (reduced graphene oxide (rGO)) as the plane layer, layered double metal hydroxide (LDH) as the support layer, and cellulose nanofiber (CNF) as the connection agent and flexible agent. The interlayer height can be adjusted by the ion concentration. The highly interconnected network enables excellent electron and ion transport channels, facilitating rapid ion diffusion and redox reactions. Moreover, the high flexibility and mechanical properties of the film achieve multiple folding and bending. The CNF-rGO-NiCoLDH film electrode exhibits high capacitance performance (3620.5 mF cm-2 at 2 mA cm-2), excellent mechanical properties, and high flexibility. Notably, flexible all-solid assembled CNF-rGO-NiCoLDH//rGO has an extremely high area energy density of 53.5 mWh cm-2 at a power density of 1071.2 mW cm-2, along with cycling stability of 89.8% retention after 10 000 charge-discharge cycles. This work provides a perspective for designing high-performance energy storage materials for flexible electronics and wearable devices.

Enhancement of the production of TEMPO-mediated oxidation cellulose nanofibrils by kneading

The industrial use of TEMPO-mediated oxidation (TMO) reaction to produce highly fibrillated cellulose nanofibrils has been hindered by high catalyst costs, long reaction times and high reaction volumes. The hypothesis that cellulose concentration during TMO process is key to increase the process of efficiency has been confirmed. The novelty of this research is the proof-of-concept for a significant enhancement of the TMO reaction by kneading the cellulose to work in concentrations above 120 g/L. Results show that the increase of the cellulose concentration in the TMO reaction, from the traditional 10 g/L to 120 g/L, increase not only the production for the same reaction volume (1200 %) but also the pulp recovery (up to 94 %). Moreover, the oxidation time can be reduced from 42 min to only 4 min while properties of both the oxidized pulps and the final nanocellulose are similar. On the other hand, the use of buffers in the TMO reaction allows us to keep the pH constant without using NaOH, and to improve the selectivity of the carboxyl groups production. The proposed process also minimizes the final environmental impact.

Biotechnological innovations in nanocellulose production from waste biomass with a focus on pineapple waste

New materials' synthesis and utilization have shown many critical challenges in healthcare and other industrial sectors as most of these materials are directly or indirectly developed from fossil fuel resources. Environmental regulations and sustainability concepts have promoted the use of natural compounds with unique structures and properties that can be biodegradable, biocompatible, and eco-friendly. In this context, nanocellulose (NC) utility in different sectors and industries is reported due to their unique properties including biocompatibility and antimicrobial characteristics. The bacterial nanocellulose (BNC)-based materials have been synthesized by bacterial cells and extracted from plant waste materials including pineapple plant waste biomass. These materials have been utilized in the form of nanofibers and nanocrystals. These materials are found to have excellent surface properties, low density, and good transparency, and are rich in hydroxyl groups for their modifications to other useful products. These materials are well utilized in different sectors including biomedical or health care centres, nanocomposite materials, supercapacitors, and polymer matrix production. This review explores different approaches for NC production from pineapple waste residues using biotechnological interventions, approaches for their modification, and wider applications in different sectors. Recent technological developments in NC production by enzymatic treatment are critically discussed. The utilization of pineapple waste-derived NC from a bioeconomic perspective is summarized in the paper. The chemical composition and properties of nanocellulose extracted from pineapple waste may have unique characteristics compared to other sources. Pineapple waste for nanocellulose production aligns with the principles of sustainability, waste reduction, and innovation, making it a promising and novel approach in the field of nanocellulose materials.

Recycling of TEMPO-mediated oxidation medium and its effect on nanocellulose properties

The potential of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy)-mediated oxidation (TMO) to produce cellulose nanofibrils (CNFs) is hindered using costly and environmentally harmful catalysts, limiting its large-scale implementation. To promote sustainability, the TMO medium should be reused but there is a lack of knowledge on this process. The novelty of this research is the identification of the key parameters that affect the recirculation of the TMO medium, and their impact on the quality of the oxidized pulps and CNF products. Contrary to previous hypothesis, results show that the accumulation of salts is not a key parameter; instead, the pulp consistency during oxidation plays a vital role since concentrations higher than 10 g/L led to better CNF quality. Thus, reusing 75 % of the reaction medium, when high pulp consistency is used, does not alter the CNF properties. By reusing the reaction medium up to six times, the catalyst dose is dramatically reduced by >90 % for TEMPO and 80 % for NaBr, compared to the conventional process (0.1 mmol of TEMPO/g and 1 mmol of NaBr/g without medium reuse). Additionally, the high consistency oxidation enables a reduction of >80 % in the reaction time and effluent, and thus a threefold increase in CNF production.

Anisotropic cellulose nanocrystalline sponge sheets with ultrahigh water fluxes and oil/water selectivity

Oily sewage caused by oil spill accidents has become a severe problem in the last decades. Hence, two-dimensional sheet-like filter materials for oil/water separation have received widespread attention. Porous sponge materials were developed using cellulose nanocrystals (CNCs) as raw materials. They are environmentally friendly and easy to prepare, with high flux and separation efficiency. The 1,2,3,4-butane tetracarboxylic acid cross-linked anisotropic cellulose nanocrystalline sponge sheet (B-CNC) exhibited ultrahigh water fluxes driven by gravity alone, depending on the aligned structure of channels and the rigidity of CNCs. Meanwhile, the sponge gained superhydrophilic/underwater superhydrophobic wettability with an underwater oil contact angle of up to 165.7° due to its ordered micro/nanoscale structure. B-CNC sheets displayed high oil/water selectivity without additional material doping or chemical modification. For oil/water mixtures, high separation fluxes of approximately 100,000 L·m^-2·h^-1 and separation efficiencies of up to 99.99 % were obtained. For a Tween 80-stabilized toluene-in-water emulsion, the flux reached >50,000 L·m^-2·h^-1, and the separation efficiency was above 99.7 %. B-CNC sponge sheets showed significantly higher fluxes and separation efficiencies than other bio-based two-dimensional materials. This research provides a facile and straightforward fabrication method of environmental-friendly B-CNC sponges for rapid, selective oil/water separation.

Ultrastrong, Thermally Stable, and Food-Safe Seaweed-Based Structural Material for Tableware

Widely used disposable plastic tableware is usually buried or directly discharged into the natural environment after using, which poses potential threats to the natural environment and human health. To solve this problem, nondegradable plastic tableware needs to be replaced by tableware composed of biodegradable structural materials with both food safety and the excellent mechanical and thermal properties. Here, a food-safe sargassum cellulose nanofiber (SCNF) is extracted from common seaweed in an efficient and low energy consuming way under mild reaction conditions. Then, by assembling the SCNF into a dense bulk material, a strong sargassum cellulose nanofiber structural material (SCNSM) with high strength (283 MPa) and high thermal stability (>160 °C) can be prepared. The SCNSM also possesses good machinability, which can be processed into tableware with different shapes, e.g., knives and forks. The overall performance of the SCNSM-based tableware is better than commercial plastic, wood-based, and poly(lactic acid) tableware, which shows great application potential in the tableware field.