Robust superbase-based emerging solvents for highly efficient dissolution of cellulose

High-Value Utilization of Cellulose: Intriguing and Important Effects of Hydrogen Bonding Interactions─A Mini-Review

Cellulose has been widely used in papermaking, textile, and chemical industries due to its diverse sources, environmental friendliness, and renewability. Recently, much more attention has been paid to converting cellulose into high-value-added products. Therefore, the extraction of nanocellulose, the dissolution of cellulose, and their applications are some of the most important research topics currently. However, cellulose's dense hydrogen bond network poses challenges for efficient extraction and dissolution, limiting its potential for functional material development. This review discusses the mechanisms of hydrogen bond disruption and weak interactions during nanocellulose extraction and cellulose dissolution. Key challenges and future research directions are highlighted, emphasizing developing efficient, ecofriendly, and cost-effective methods. Additionally, this review provides theoretical insights for constructing high-performance cellulose-based materials.

Regenerated cellulose films with controllable microporous structure for enhanced seed germination

In this work, the preparation of high-performance and porous regenerated cellulose (RCNH) films for seed germination application were investigated. The films were prepared from bamboo-based cellulose carbamate-NaOH/ZnO/urea and coagulated using environmentally friendly aqueous solution of (NH4)2SO4. The results showed that the pore size of the films could be efficiently controlled by changing the concentration and temperature of the coagulation bath. In a mild environment, the system remains undisturbed, resulting in slow diffusion between the solvent and coagulation bath. This allows for the cellulose molecular chains to align in parallel and self-aggregate, forming a three-dimensional network structure. Therefore, the best mechanical properties were demonstrated by a film coagulated using 5 wt% (NH4)2SO4 solution at 10 °C. This film showed excellent tensile strength of 108 MPa and high elongation at break (35 %). As compared to a plastic wrap, the film demonstrated higher permeability for oxygen, and a moisture retaining ability. Due to these properties, it could be used as an agricultural film to encase and promote the growth of mung bean seeds. Moreover, the film was biodegradable with a short decomposition time, losing 90.75 % of its original mass after 63 days. In a summary, this work provides a route for robust, biodegradable, and permeable regenerated cellulose films with potential applications as biodegradable agricultural mulches.

Revisiting various mechanistic approaches for cellulose dissolution in different solvent systems: A comprehensive review

The process of dissolving cellulose is a pivotal step in transforming it into functional, value-added materials, necessitating a thorough comprehension of the underlying mechanisms to refine its advanced processing. This article reviews cellulose dissolution using various solvent systems, along with an in-depth exploration of the associated dissolution mechanisms. The efficacy of different solvents, including aqueous solvents, organic solvents, ionic liquids, hybrid ionic liquid/cosolvent systems, and deep eutectic solvents, in dissolving cellulose is scrutinized, and their limitations and advantages are highlighted. In addition, this review methodically outlines the mechanisms at play within these various solvent systems and the factors influencing cellulose solubility. Conclusions drawn highlight the integral roles of the degree of polymerization, crystallinity, particle size, the type and sizes of cations and anions, alkyl chain length, ionic liquid/cosolvent ratio, viscosity, solvent acidity, basicity, and hydrophobic interactions in the dissolution process. This comprehensive review aims to provide valuable insights for researchers investigating biopolymer dissolution in a broader context, thereby paving the way for broader applications and innovations of these solvent systems.

Facile dissolution of cellulose by superbase-derived ionic liquid using organic solvents as co-solvents at mild temperatures

Dissolving cellulose at low temperatures is a key step in its efficient utilization as a renewable resource to produce high-value-added platform chemicals and high-performance materials. Here, the potential of four aprotic organic solvents was investigated for use as co-solvents with a sustainable DBU-derived ionic liquid (SIL) for the low-temperature dissolution and regeneration of cellulose. Combined experiments, density functional theory calculations, and molecular dynamic simulations were performed. The type and amount of co-solvent were found to have a significant impact on the solubility of cellulose, the dissolution process, and the structure of regenerated cellulose. The addition of organic solvents can significantly reduce the cellulose dissolution temperature and increase the solubility. Among the solvents assessed, 40 wt% DMSO exhibited the most effective synergistic interaction with SIL, where the solubility of cellulose was 14.6 wt% at 75 °C. Subsequently, the effects of the different types and amounts of co-solvents on the microscopic morphology and chemical structure of regenerated cellulose were thoroughly explored. The results showed that different types of organic solvents had different effects on the microstructure of regenerated cellulose. The results may guide the manufacturing specifications of high-performance regenerated fiber materials.

Efficient dissolution of cellulose in slow-cooling alkaline systems and interacting modes between alkali and urea at the molecular level

The dissolution of microcrystalline cellulose (MCC) in a urea-NaOH system is beneficial for its mechanical processing. The apparent MCC solubility was greatly improved to 14 wt% under a slow-cooling condition with a cooling rate of -0.3 °C/min. The cooling curve or thermal history played a crucial role in the dissolution process. An exotherm (-54.7 ± 3 J/g MCC) was detected by DSC only under the slow-cooling condition, and the cryogenic dissolution of MCC was attributed to the exothermic interaction between MCC and solvent. More importantly, the low cooling rate promoted the dissolution of MCC by providing enough time for the diffusion of OH- and urea into MCC granules at higher temperatures. The Raman spectral data showed that the intramolecularly and intermolecularly hydrogen bonds in cellulose were cleaved by NaOH and urea, respectively. XPS and solid-state 13C NMR results showed that hydrogen bonds were generated after dissolution, and a dual-hydrogen-bond binding mode between urea and cellulose was confirmed by DFT calculations. Both the decrease of enthalpy and increase of entropy dominated the spontaneity of MCC dissolution, and that is the reason for the indispensability of cryogenic environment. The high apparent solubility of MCC in the slow-cooling process and the dissolution mechanism are beneficial for the studies on cellulose modification and mechanical processing.

Cellulose dissolution and regeneration behavior via DBU-levulinic acid solvents

Most organic solvents are unable to dissolve carbohydrates due to the lack of hydrogen bonding ability. The development of solvent systems for dissolving cellulose is of great importance for its utilization and conversion. In this study, four new cellulose solvents were designed using inexpensive levulinic acid (LevA) and 1,8-diazabicyclo [5,4,0] undec-7-ene (DBU) as raw materials. The results showed that the prepared DBU-LevA-2 solvent was able to dissolve up to 7 wt% of bamboo cellulose (DP = 860) and 16 wt% of microcrystalline cellulose (DP = 280) at 100 °C and regenerated without derivatization. Also, the molar ratio of each component of this solvent has a significant effect on the dissolution properties of cellulose. The regenerated cellulose had the typical crystalline characteristics of cellulose II. Subsequently, the interactions and microscopic behaviors of solvent and cellulose during the dissolution process were thoroughly investigated by using NMR spectroscopy combined with density functional theory. The systematic study showed that the hydrogen bond-forming ability provided by DBU, a superbase, plays an indispensable role in the overall solvent system.

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.

Insights into the interactions between cellulose and biological molecules

Understanding the interactions between carbohydrate polymer molecules and biomolecules is of primary significance for its application. In this paper, the interaction between cellulose and biomolecules was studied using density functional theory method, in which cellobiose, nucleobases, and aromatic amino acids were employed as the structural models of cellulose, DNA, and protein, respectively. Quantitative molecular surface electrostatic potential (ESP) results well represented how cellulose perceived by organism during the recognition. The structural and energetic studies of cellulose with biomolecules complexes show that weak interactions, such as hydrogen bonding interaction, vdW interaction, and pi-H interaction, play an important role in stabilizing these complexes. Through systematic wavefunction analysis, including reduced density gradient (RDG) and natural bond orbital (NBO) methods, the nature of these weak interactions was revealed and further graphically visualized. In-depth understanding of the interaction between cellobiose with biological model molecules may shed lights on the application of carbohydrate polymer-based materials in biological fields.

Efficient fractionation of woody biomass hemicelluloses using cholinium amino acids-based deep eutectic solvents and their aqueous mixtures

Novel and green cholinium amino acids-based deep eutectic solvents (DESs) and their aqueous mixtures were synthesized and employed in deconstructing poplar for hemicellulose fractionation. The effects of water content in DESs on hemicellulose dissociation and structural features were comprehensively investigated, along with the reusability of DESs for treatment. The integration of water into DESs could facilitate hemicellulose fractionation, and the cholinium lysine: urea with 5 wt% water (CL: U-5) demonstrated the best performance with a hemicellulose yield of 59.2%. Further structure analysis revealed that hemicelluloses with various branching degrees and molecular weights were obtained with varying water content of DESs. Furthermore, the CL: U-5 had recyclability and reusability with a 40.5% hemicellulose yield obtained after reused three times. The novel and eco-friendly cholinium amino acids-based DESs treatment provides an effective and sustainable strategy for hemicellulose fractionation from woody biomass.