Dissolution and modification of cellulose using high-pressure carbon dioxide switchable solution

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.

The degradation of cellulose in ionic mixture solutions under the high pressure of carbon dioxide

This work aims to study the product characteristics of cellulose degradation not only by a hydrothermal process but also in combination with a sonication process. Herein, 4.3 mL of oxalic acid (H2C2O4)-sodium chloride (NaCl) solution containing cellulose was placed into a stainless steel reactor (or the mixture was placed into the reactor after the sonication process for 1 hour); then, carbon dioxide (CO2) was released for pressurization. Degradation was performed under certain pressures (70 and 200 bar) and temperatures (125 °C and 200 °C) at various times. Scanning Electron Microscopy (SEM) results indicated that the sonication pretreatment process affected the solid cellulose, making it rougher or fibrous than the non-sonicated process. XRD characterization results indicated that both process types caused changes in the crystallinity and composition of cellulose I and II with pressure, temperature, and time. The combination of sonication and hydrothermal processes resulted in lower crystallinity. Changes in crystallinity showed different characteristics in swelling, reduced the interaction between chains, and even broke the polymer chains inside the particles. In a hydrothermal process at 200 bar and 200 °C, a maximum reducing sugar concentration of 5.1 g L-1 was obtained, while 3.2 g L-1 was obtained in the combined sonication and hydrothermal process under the same operating condition, which is below the value attained at 200 °C and 70 bar. These results indicated the existing competition between the formation and further degradation of the reducing sugar, a phenomenon explained by the presence of a monomer (reducing sugar), an oligomer (cellotriose), and 5-HMF (5-hydroxymethyl-2-furaldehyde) in a liquid product processed under hydrothermal conditions.

Use of Ionic Liquids and Deep Eutectic Solvents in Polysaccharides Dissolution and Extraction Processes towards Sustainable Biomass Valorization

A shift to a bioeconomy development model has been evolving, conducting the scientific community to investigate new ways of producing chemicals, materials and fuels from renewable resources, i.e., biomass. Specifically, technologies that provide high performance and maximal use of biomass feedstocks into commodities with reduced environmental impact have been highly pursued. A key example comprises the extraction and/or dissolution of polysaccharides, one of the most abundant fractions of biomass, which still need to be improved regarding these processes' efficiency and selectivity parameters. In this context, the use of alternative solvents and the application of less energy-intensive processes in the extraction of polysaccharides might play an important role to reach higher efficiency and sustainability in biomass valorization. This review debates the latest achievements in sustainable processes for the extraction of polysaccharides from a myriad of biomass resources, including lignocellulosic materials and food residues. Particularly, the ability of ionic liquids (ILs) and deep eutectic solvents (DESs) to dissolve and extract the most abundant polysaccharides from natural sources, namely cellulose, chitin, starch, hemicelluloses and pectins, is scrutinized and the efficiencies between solvents are compared. The interaction mechanisms between solvent and polysaccharide are described, paving the way for the design of selective extraction processes. A detailed discussion of the work developed for each polysaccharide as well as the innovation degree and the development stage of dissolution and extraction technologies is presented. Their advantages and disadvantages are also identified, and possible synergies by integrating microwave- and ultrasound-assisted extraction (MAE and UAE) or a combination of both (UMAE) are briefly described. Overall, this review provides key information towards the design of more efficient, selective and sustainable extraction and dissolution processes of polysaccharides from biomass.

Inedible saccharides: a platform for CO2 capturing

The economic viability of eco-friendly and renewable materials promotes the development of an alternative technology for climate change mitigation. Investigations reported over the past few years have allowed understanding the mechanism of action for a wide spectrum of saccharides toward carbon dioxide (CO2), in terms of reactivity, reversibility, stability and uptake. Exploiting bio-renewables, viz., inedible saccharides, to reduce the anthropogenic carbon footprint upon providing a sustainable and promising technology that is of interest to different groups of scientists, to overcome demerits associated with the current state-of-the-art aqueous amine scrubbing agents, following a "green chemistry guideline", by employing materials with properties relevant to the environment toward sustainable development. The interdisciplinary nature of research in this area provides a large body of literature that would meet the interest of the broad readership of different multidisciplinary fields. Although many reports emphasize the use of biomass in various industrial products ranging from pharmaceutics, medical preparations, soaps, textiles, cosmetics, household cleaners, and so on, to our knowledge there is no focused article that addresses the application of saccharides for CO2 sequestration. In this review, we highlight the recent advances on the use of oligo-, poly- and cyclic saccharides to achieve a reversible binding of CO2. The future research directions are discussed to provide insight toward achieving sustainable development through implementing bio-renewables.