Chemistry and applications of polysaccharide solutions in strong electrolytes/dipolar aprotic solvents: an overview

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.

A novel colormetric and light-up fluorescent sensor from flavonol derivative grafted cellulose for rapid and sensitive detection of Hg2+ and its applications in biological and environmental system

Mercury ion (Hg2+) is one of harmful heavy metal ions that can accumulate inside the human organism and cause some health problems. In the article, a highly effective fluorescent probe named EC-T-PCBM was prepared by grafting flavonol derivatives onto ethyl cellulose for the specific recognition of Hg2+. EC-T-PCBM exhibited a remarkable fluorescence light-up response toward Hg2+ with excellent sensitivity. EC-T-PCBM possessed several prominent sensing properties for Hg2+, such as low detection limit (43.9 nM), short response time (5 min), and wide detection pH range (6-9). The response mechanism of EC-T-PCBM to Hg2+ has been verified through 1H NMR titration and DFT computation. Additionally, EC-T-PCBM not only can be used for accurately determining trace amount of Hg2+ in actual environmental water samples, but also can serve as a portable and rapid device by loading it on test strips for sensitive and selective visualization of Hg2+. More importantly, the confocal fluorescence imaging of onion cells suggested the favorable cell membrane permeability of EC-T-PCBM and its prominent ability to continuously monitor the enrichment from Hg2+ within fresh plant tissues.

Selectively fractionate hemicelluloses with high molecular weight from poplar thermomechanical pulp by tetramethylammonium hydroxide

Selective fractionation of hemicelluloses is of great significance for realizing high-value application of hemicelluloses and comprehensive utilization of lignocellulosic biomass. Tetramethylammonium hydroxide (TMAH) solvent has been confirmed as a promising solvent to selectively fractionate hemicelluloses from holocellulose. Herein, TMAH solvent was adopted to pretreat poplar thermomechanical pulp (PTMP) for the selective fractionation of hemicelluloses and enhancement of enzymatic hydrolysis performance of residues. The maximal hemicelluloses yield (65.0 %) and excellent cellulose retention rate (93.3 %) were achieved after pretreatment by the 25 wt% TMAH solvent, while the delignification was only 33.9 %. The hemicelluloses fractions could be selectively fractionated with high molecular weights (109,800-118,500 g/mol), the contents of Klason lignin in them were low (3.2-5.9 %), and the dominating structure of them was 4-O-methylglucurono-β-D-xylan. Compared to the H2SO4 and NaOH methods, the hemicelluloses fractionated by TMAH method exhibited higher yields, more complete structures and higher molecular weights. Furthermore, the crystalline structure of cellulose practically remained stable, and the highest yield of enzymatic hydrolysis glucose was 57.5 %, which was 3.3 times of that of PTMP. The fractionation effectiveness of TMAH solvent was not significantly reduced after repeatedly recycling. This work demonstrated TMAH solvent could selectively fractionate hemicelluloses from PTMP and efficiently promote sustainable poplar-based biorefinery.

Biomass to Aromatic Amine Module: Alkali Catalytic Conversion of N-Acetylglucosamine into Unsubstituted 3-Acetamidofuran by Retro-Aldol Condensation

Aminofurans are widely used in drug synthesis as aromatic modules analogous to aniline. However, unsubstituted aminofuran compounds are difficult to prepare. In this study, a process for the selective conversion of N-acetyl-d-glucosamine (NAG) into unsubstituted 3-acetamidofuran (3AF) is developed. The yield of 3AF from NAG catalyzed by a ternary Ba(OH)₂ -H₃ BO₃ -NaCl catalytic system in N-methylpyrrolidone at 180 °C for 20 min can reach 73.9 %. Mechanistic studies reveal that the pathway to 3AF starts with a base-promoted retro-aldol condensation of the ring-opened NAG, affording the key intermediate N-acetylerythrosamine. Judicious selection of the catalyst system and conditions enables the selective conversion of biomass-derived NAG into 3AF or 3-acetamido-5-acetylfuran.

Rapid and massive fractionation of hemicelluloses for purifying cellulose at room temperature by tetramethylammonium hydroxide

The fractionation of hemicelluloses is a promising method to improve the comprehensive utilization of lignocellulosic biomass. However, the effective fractionation of hemicelluloses is always limited by the structural complexity and easy degradability. In this study, tetramethylammonium hydroxide (TMAH) was developed to fractionate hemicelluloses from poplar holocellulose with high molecular weights and high yields at room temperature. Approximately 90% of hemicelluloses could be dissolved at room temperature in 1 h, and the yield was up to 81.9%. Compared with the fractionation using NaOH solution, the hemicelluloses isolated by TMAH solvent showed a more complete structure and higher purity. Meanwhile, the retention rate of cellulose after treatment with TMAH was up to 90.2%, and the crystal structure of cellulose in the residues was practically unchanged. Moreover, the TMAH solvent could be recycled to fractionate hemicelluloses. The work provides an elegant and significantly efficient method towards hemicelluloses fractionation and cellulose purification.

Novel Challenges on the Catalytic Synthesis of 5-Hydroxymethylfurfural (HMF) from Real Feedstocks

The depletion of fossil resources makes the transition towards renewable ones more urgent. For this purpose, the synthesis of strategic platform-chemicals, such as 5-hydroxymethylfurfural (HMF), represents a fundamental challenge for the development of a feasible bio-refinery. HMF perfectly deals with this necessity, because it can be obtained from the hexose fraction of biomass. Thanks to its high reactivity, it can be exploited for the synthesis of renewable monomers, solvents, and bio-fuels. Sustainable HMF synthesis requires the use of waste biomasses, rather than model compounds such as monosaccharides or polysaccharides, making its production more economically advantageous from an industrial perspective. However, the production of HMF from real feedstocks generally suffers from scarce selectivity, due to their complex chemical composition and HMF instability. On this basis, different strategies have been adopted to maximize the HMF yield. Under this perspective, the properties of the catalytic system, as well as the choice of a suitable solvent and the addition of an eventual pretreatment of the biomass, represent key aspects of the optimization of HMF synthesis. On this basis, the present review summarizes and critically discusses the most recent and attractive strategies for HMF production from real feedstocks, focusing on the smartest catalytic systems and the overall sustainability of the adopted reaction conditions.

Applications of Starch Biopolymers for a Sustainable Modern Agriculture

Protected cultivation in modern agriculture relies extensively on plastic-originated mulch films, nets, packaging, piping, silage, and various applications. Polyolefins synthesized from petrochemical routes are vastly consumed in plasticulture, wherein PP and PE are the dominant commodity plastics. Imposing substantial impacts on our geosphere and humankind, plastics in soil threaten food security, health, and the environment. Mismanaged plastics are not biodegradable under natural conditions and generate problematic emerging pollutants such as nano-micro plastics. Post-consumed petrochemical plastics from agriculture face many challenges in recycling and reusing due to soil contamination in fulfilling the zero waste hierarchy. Hence, biodegradable polymers from renewable sources for agricultural applications are pragmatic as mitigation. Starch is one of the most abundant biodegradable biopolymers from renewable sources; it also contains tunable thermoplastic properties suitable for diverse applications in agriculture. Functional performances of starch such as physicomechanical, barrier, and surface chemistry may be altered for extended agricultural applications. Furthermore, starch can be a multidimensional additive for plasticulture that can function as a filler, a metaphase component in blends/composites, a plasticizer, an efficient carrier for active delivery of biocides, etc. A substantial fraction of food and agricultural wastes and surpluses of starch sources are underutilized, without harnessing useful resources for agriscience. Hence, this review proposes reliable solutions from starch toward timely implementation of sustainable practices, circular economy, waste remediation, and green chemistry for plasticulture in agriscience

Liquefaction of Cellulose for Production of Advanced Porous Carbon Materials

Cellulose is a renewable resource for the production of advanced carbonaceous materials for various applications. In addition to direct carbonization, attention has recently been paid to the preparation of porous carbons from liquid cellulose-based precursors. Possible pathways of cellulose conversion to a liquid state suitable for the preparation of porous carbons are summarized in this review. Hydrothermal liquefaction leading to liquid mixtures of low-molecular-weight organics is described in detail together with less common decomposition techniques (microwave or ultrasound assisted liquefaction, decomposition in a strong gravitation field). We also focus on dissolution of cellulose without decomposition, with special attention paid to dissolution of nonderivatized cellulose. For this purpose, cold alkalines, hot acids, ionic liquids, or alcohols are commonly used.

Progress on chemical modification of cellulose in “green” solvents

Chemical modification of cellulose in "green" solvents.

A Basic Characterisation Study of Bioplastics via Gelatinization of Corn Starch

Plastic waste is the third-largest waste source in the world, so it raises the world’s human health and environmental concerns. Replacing conventional petroleum plastic with bioplastic is an alternative way to minimise plastic wastes from human life and bioplastic is more environmentally friendly. Therefore, this research study aims to synthesise bioplastic from corn starch via gelatinization and study its characteristics. Different from other studies, in this study, new formulations of bioplastics with different ratios of corn starch to glycerol samples that are 1:0.5, 1:1, 2:1, and 2:2, namely Sets A, B, C, and D, respectively, were studied and compared. From the Fourier Transformation Infrared Spectroscopy analysis, the results show that all produced corn starch-based bioplastic samples had the four major plastic’s functional groups which indicated that they were categorized as polyester. Meanwhile, via thermal property analysis, all bioplastic samples could be thermally decomposed from 34 °C to 504 °C where their weight was reduced from 5 mg to 1 mg. Among the four bioplastic samples (Sets A to D) with different ratios of corn starch to glycerol, it was found that a ratio of corn starch and glycerol that was 1:0.5 (Set A) had more biodegradable characteristics and it had the lowest water holding capacity. From the results, Set A could only hold around 4.27 % of the water that could avoid interaction of water with the contents that were wrapped with. Besides, from the results, Set A could degrade better in soils, and dissolve more in ethanol, acetone, and oils when compared to other samples. Since the bioplastic can degrade naturally by the ethanol produced from bacteria in the soils under anaerobic reactions, thus Set A has the potential application to be used as a fertiliser coating to minimise the fertiliser release rate in regions under heavy rainfall.

The Dioscorea Genus (Yam)-An Appraisal of Nutritional and Therapeutic Potentials

The quest for a food secure and safe world has led to continuous effort toward improvements of global food and health systems. While the developed countries seem to have these systems stabilized, some parts of the world still face enormous challenges. Yam (Dioscorea species) is an orphan crop, widely distributed globally; and has contributed enormously to food security especially in sub-Saharan Africa because of its role in providing nutritional benefits and income. Additionally, yam has non-nutritional components called bioactive compounds, which offer numerous health benefits ranging from prevention to treatment of degenerative diseases. Pharmaceutical application of diosgenin and dioscorin, among other compounds isolated from yam, has shown more prospects recently. Despite the benefits embedded in yam, reports on the nutritional and therapeutic potentials of yam have been fragmented and the diversity within the genus has led to much confusion. An overview of the nutritional and health importance of yam will harness the crop to meet its potential towards combating hunger and malnutrition, while improving global health. This review makes a conscious attempt to provide an overview regarding the nutritional, bioactive compositions and therapeutic potentials of yam diversity. Insights on how to increase its utilization for a greater impact are elucidated.

Chitin and its derivatives: Structural properties and biomedical applications

Chitin, a polysaccharide that occurs abundantly in nature after cellulose, has attracted the interest of the scientific community due to its plenty of availability and low cost. Mostly, it is derived from the exoskeleton of insects and marine crustaceans. Often, it is insoluble in common solvents that limit its applications but its deacetylated product, named chitosan is found to be soluble in protonated aqueous medium and used widely in various biomedical fields. Indeed, the existence of the primary amino group on the backbone of chitosan provides it an important feature to modify it chemically into other derivatives easily. In the present review, we present the structural properties of chitin, and its derivatives and highlighted their biomedical implications including, tissue engineering, drug delivery, diagnosis, molecular imaging, antimicrobial activity, and wound healing. We further discussed the limitations and prospects of this versatile natural polysaccharide.

Efficient conversion of N-acetyl-D-glucosamine into nitrogen-containing compound 3-acetamido-5-acetylfuran using amino acid ionic liquid as the recyclable catalyst

Chitin is the most widely distributed oceanic biomass resources. Its monomer unit, N-acetyl-_D-glucosamine (NAG), contains precious atomic nitrogen and represents a potential feedstock for the manufacture of regenerative organic nitrogen chemicals. Herein, the conversion of NAG to the platform chemical, 3-acetamido-5-acetylfuran (3A5AF), catalyzed by amino acid ionic liquids, was investigated. The reaction, catalyzed by a very small amount of glycine chloride ionic liquid without any additives, could yield 43.22% 3A5AF in 10 min. By adding CaCl₂, a higher yield up to 52.61% was obtained. This work demonstrated the conversion of chitin biomass to 3A5AF in higher yield without using a boron-based catalyst for the first time. Moreover, the ionic liquid catalyst exhibited excellent recyclability, and afforded 43.22-36.59% yield over during eight cycles. This research provides new and green procedures to convert shellfish fishery waste into value-added platform chemicals.

Binary mixtures of ionic liquids-DMSO as solvents for the dissolution and derivatization of cellulose: Effects of alkyl and alkoxy side chains

The efficiency of mixtures of ionic liquids (ILs) and molecular solvents in cellulose dissolution and derivatization depends on the structures of both components. We investigated the ILs 1-(1-butyl)-3-methylimidazolium acetate (C₄MeImAc) and 1-(2-methoxyethyl)-3-methylimidazolium acetate (C₃OMeImAc) and their solutions in dimethyl sulfoxide, DMSO, to assess the effect of presence of an ether linkage in the IL side-chain. Surprisingly, C₄MeImAc-DMSO was more efficient than C₃OMeImAc-DMSO for the dissolution and acylation of cellulose. We investigated both solvents using rheology, NMR spectroscopy, and solvatochromism. Mixtures of C₃OMeImAc-DMSO are more viscous, less basic, and form weaker hydrogen bonds with cellobiose than C₄MeImAc-DMSO. We attribute the lower efficiency of C₃OMeImAc to "deactivation" of the ether oxygen and C2H of the imidazolium ring due to intramolecular hydrogen bonding. Using the corresponding ILs with C2CH₃ instead of C2H, namely, 1-butyl-2,3-dimethylimidazolium acetate (C₄Me₂ImAc) and 1-(2-methoxyethyl)-2,3-dimethylimidazolium acetate (C₃OMe₂ImAc) increased the concentration of dissolved cellulose; without noticeable effect on biopolymer reactivity.

Amine-responsive cellulose-based ratiometric fluorescent materials for real-time and visual detection of shrimp and crab freshness

Herein, we design and prepare cellulose-based ratiometric fluorescent materials with superior amine-response, which offers the real-time and visual detection of seafood freshness. Through utilizing the reactive hydroxyl groups along cellulose chains, we covalently immobilize the fluorescein isothiocyanate (FITC) as indicator and protoporphyrin IX (PpIX) as internal reference onto cellulose acetate (CA), respectively. Subsequently, a series of dual-emission solid fluorescent materials are achieved by simply blending green emitting CA-FITC with red-emitting CA-PpIX with varying ratios. They exhibit a sensitive, color-responsive, rapid and linear response to ammonia in a wide range of 5.0 ppm to 2.5 × 104 ppm. Benefiting from the excellent solubility and processibility of cellulose derivatives, the as-prepared materials are readily processed into different material forms, including printing ink, coating, flexible film, and nanofibrous membrane. The electrospun nanofibrous membrane is successfully employed as a low-cost, high-contrasting, quick-responsive fluorescent trademark for visual monitoring the freshness of shrimp and crab.

Recent Advances in Solvents for the Dissolution, Shaping and Derivatization of Cellulose: Quaternary Ammonium Electrolytes and their Solutions in Water and Molecular Solvents

There is a sustained interest in developing solvents for physically dissolving cellulose, i.e., without covalent bond formation. The use of ionic liquids, ILs, has generated much interest because of their structural versatility that results in efficiency as cellulose solvents. Despite some limitations, imidazole-based ILs have received most of the scientific community’s attention. The objective of the present review is to show the advantages of using quaternary ammonium electrolytes, QAEs, including salts of super bases, as solvents for cellulose dissolution, shaping, and derivatization, and as a result, increase the interest in further investigation of these important solvents. QAEs share with ILs structural versatility; many are liquids at room temperature or are soluble in water and molecular solvents (MSs), in particular dimethyl sulfoxide. In this review we first give a historical background on the use of QAEs in cellulose chemistry, and then discuss the common, relatively simple strategies for their synthesis. We discuss the mechanism of cellulose dissolution by QAEs, neat or as solutions in MSs and water, with emphasis on the relevance to cellulose dissolution efficiency of the charge and structure of the cation and. We then discuss the use of cellulose solutions in these solvents for its derivatization under homogeneous and heterogeneous conditions. The products of interest are cellulose esters and ethers; our emphasis is on the role of solvent and possible side reactions. The final part is concerned with the use of cellulose dopes in these solvents for its shaping as fibers, a field with potential commercial application.

Assessment of solvents for cellulose dissolution

A necessary step in the processing of biomass is the pretreatment and dissolution of cellulose. A good solvent for cellulose involves high diffusivity, aggressiveness in decrystallization, and capability of disassociating the cellulose chains. However, it is not clear which of these factors and under what conditions should be improved in order to obtain a more effective solvent. To this end, a newly-developed phenomenological model has been applied to assess the controlling mechanism of cellulose dissolution. Among the findings, the cellulose fibers remain crystalline almost to the end of the dissolution process for decrystallization-controlled kinetics. In such solvents, decreasing the fiber crystallinity, e.g., via pretreatment, would result in a considerable increase in the dissolution rate. Such insights improve the understanding of cellulose dissolution and facilitate the selection of more efficient solvents and processing conditions for biomass. Specific examples of solvents are provided where dissolution is limited due to decrystallization or disentanglement.

Thermally Triggered Phase Separation of Organic Electrolyte-Cellulose Solutions

Organic electrolyte solutions (OES)-binary mixtures of an ionic liquid (IL) with a neutral polar aprotic co-solvent-are being recognized as excellent candidate solvents for the dissolution, derivatization, and sustainable processing of cellulose. These solutions exhibit the beneficially combined properties of rapid-to-instantaneous cellulose dissolution, raised thermal stability, and reduced viscosity, compared to cellulose solutions in the parent ILs. Herein, we report the reversible, thermally triggered phase separation of cellulose solutions in 1-ethyl-3-methylimidazolium acetate with 1,3-dimethyl-2-imidazolidinone. In these solutions, cellulose drives the process of phase separation, resulting in a lower, IL-rich layer in which the biopolymer is segregated. In turn, the upper phase is enriched in the neutral co-solvent. We show that the temperature of phase separation can be fine-tuned by modification of mole fractions of IL, co-solvent, and cellulose. This finding holds promise for the design of strategies for separation and solvent recycling in cellulose chemistry.

Fabrication and characterization of carboxymethylated bael fruit gum with potential mucoadhesive applications

Carboxymethylation of bael fruit gum was achieved through its reaction with monochloroacetic acid in the presence of sodium hydroxide as a catalyst at different reaction conditions.