Properties of Cellulose Regenerated from Powerful 1-Butyl-3-methylimidazolium Acetate/Dimethyl Sulfoxide Solvent

Recent Advances in Cellulose-Based Hydrogels Prepared by Ionic Liquid-Based Processes

This review summarizes the recent advances in preparing cellulose hydrogels via ionic liquid-based processes and the applications of regenerated cellulose hydrogels/iongels in electrochemical materials, separation membranes, and 3D printing bioinks. Cellulose is the most abundant natural polymer, which has attracted great attention due to the demand for eco-friendly and sustainable materials. The sustainability of cellulose products also depends on the selection of the dissolution solvent. The current state of knowledge in cellulose preparation, performed by directly dissolving in ionic liquids and then regenerating in antisolvents, as described in this review, provides innovative ideas from the new findings presented in recent research papers and with the perspective of the current challenges.

Preparation of flexible and UV-blocking films from lignin-containing cellulose incorporated with tea polyphenol/citric acid

Lignin-containing bamboo cellulose, fractionated from a pilot-scale microwave liquefaction of bamboo was dissolved in tetrabutylammonium acetate/dimethyl sulfoxide (TBAA/DMSO) for the fabrication of highly flexible, transparent and UV-blocking films. Tea polyphenol (TP) or citric acid (CA) was added during the dissolving process in order to modify the film's properties. The results showed that the addition of TP obviously improved the elongation at break (triple that of the control) and UV-blocking ability of the films. Both the addition of TP and CA could increase the water contact angle of the films. The films incorporated with TP and CA were much more thermal stable than previously reported similar films. The proposed film fabrication mechanism revealed that stable hydrogen bonds formed between the lignin-cellulose matrix and TP/CA, resulting in the enhancement on the properties of the films. This present study showed that lignin-containing cellulose with the incorporation of TP/CA had great potential in the preparation of films in place of plastic.

Simple and environmentally friendly preparation of cellulose hydrogels using an ionic liquid

In this study, we developed an easy process for the production of cellulose hydrogels over a wide concentration range by using an ionic liquid/DMSO mixed solution that can easily be recycled at room temperature and has low environmental impact. Cellulose was completely dissolved at 6 to 20 wt% with respect to the [BMIm][OAc]/DMSO mixed solution at room temperature and ambient pressure. Placing the cellulose solution in a mold and immersing it in deionized water caused solvent replacement of the [BMIm][OAc]/DMSO mixed solution with deionized water, making it easy to obtain a cellulose hydrogel without using a crosslinking agent. Approximately 80% of the ionic liquid could be reused by constructing a system that recovers the ionic liquid discharged from the cellulose solution during solvent replacement. The pore size, water content and mechanical strength of the cellulose hydrogel strongly depended on the concentration of the cellulose solution prepared using the [BMIm][OAc]/DMSO mixture. However, the crystallinity and thermal stability did not show a concentration dependence.

Cellulose dissolution in diallylimidazolium methoxyacetate + N-methylpyrrolidinone mixture

The utilization of cellulose in industrial applicat is of great significance to sustainable development of human society and reducing dependence on dwindling fossil resources. Nevertheless, this utilization of cellulose has actually been limited due to its insolubilization. Here, novel solvents consisting of diallylimidazolium methoxy acetate ([A₂im][CH₃OCH₂COO]) and N-methylpyrrolidinone (NMP) were developed. The solubility of cellulose in [A₂im][CH₃OCH₂COO]/NMP was determined, and the influence of [A₂im][CH₃OCH₂COO]/NMP molar ratio on cellulose dissolution was systematically investigated. Meanwhile, we also presented the affecting factors of the cellulose material fabrication including preparation approach, [A₂im][CH₃OCH₂COO] and cellulose solution concentration. Attractively, the [A₂im][CH₃OCH₂COO]/NMP solvents display much powerful dissolution capacity for cellulose even at 25 °C (25.4 g 100 g⁻¹). This is mainly ascribed to the combined factors: The hydrogen bond interactions of the H2, H4 and H6 in [A₂im]⁺ and carboxyl O atom in [CH₃OCH₂COO]⁻ with the hydroxyl H atom and O atom in cellulose; the dissociation of NMP towards [A₂im][CH₃OCH₂COO]; the stabilization of NMP towards the dissolved cellulose chains. In addition, the thermostability and chemical structure of the regenerated cellulose from the solvents was also estimated.

Dissolution performance of cellulose in [A2im][MOA]/MIM solvents

Cellulose solvents ([A2im][MOA]/MIM) were developed by combining diallylimidazolium methoxyacetate ([A2im][MOA]) with N-methylimidazole (MIM). The cellulose solubilities in the ([A2im][MOA]/MIM) solvents were determined at 25 °C, and the effect of the MIM/[A2im][MOA] molar ratio on cellulose solubility was systematically investigated. Attractively, the solvents show cellulose solubility as high as 25.2 g 100 g-1 even at 25 °C. It is proposed that the H2, H4 and H6 in [A2im]+ and the carboxyl O atom in [MOA]- primarily contribute to the dissolution of cellulose; MIM mainly acts to dissociate [A2im][MOA] into [A2im]+ and [MOA]-, and stabilize the dissolved cellulose chains. Moreover, the porous cellulose materials with varying morphological structures could be tailored by simply tuning the cellulose solution concentration, and the formation mechanism of the cellulose material was discussed.

Development of Diallylimidazolium Methoxyacetate/DMSO (DMF/DMA) Solvents for Improving Cellulose Dissolution and Fabricating Porous Material

Cellulose is the most abundant natural biopolymer, with unique properties such as biodegradability, biocompability, nontoxicity, and so on. However, its extensive application has actually been hindered, because of its insolubility in water and most solvents. Herein, highly efficient cellulose solvents were developed by coupling diallylimidazolium methoxyacetate ([A₂im][CH₃OCH₂COO]) with polar aprotic solvents dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA). Attractively, these solvents showed extraordinarily powerful dissolution performance for cellulose (e.g., 26.1 g·100g⁻¹) in [A₂im][CH₃OCH₂COO]/DMSO(R_DMSO = 1.01 solvent even at 25 °C), which is much more advantageous over previously reported solvents. To our knowledge, such powerful cellulose solvents have not been reported before. The cellulose dissolution mechanism is proposed to be of three combined factors: (1) The hydrogen bond interactions of the H2, H4 and H6 in [A₂im]⁺ and the carboxyl O atom in [CH₃OCH₂COO]⁻, along with the hydroxyl H atom and O atom in cellulose, are main driving force for cellulose dissolution; (2) the dissociation of [A₂im][CH₃OCH₂COO] by DMF increases the anion and cation concentrations and thus promotes cellulose dissolution; (3) at the same time, DMF also stabilizes the dissolved cellulose chains. Meanwhile, the porous cellulose material with a varying morphologic structure could be facially fabricated by modulating the cellulose solution concentration. Additionally, the dissolution of cellulose in the solvents is only a physical process, and the regenerated cellulose from the solvents retains sufficient thermostability and a chemical structure similar to the original cellulose. Thus, this work will provide great possibility for developing cellulose-based products at ambient temperatures or under no extra heating/freezing conditions.

Efficiency of hydrophobic phosphonium ionic liquids and DMSO as recyclable cellulose dissolution and regeneration media

Hydrophobic, long-chain tetraalkylphosphonium acetate salts (ionic liquids) were combined with DMSO and the feasibility of these solvent systems for cellulose dissolution and regeneration was studied.