We report the correlation between key solution properties and spinability of chitin from the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) and the similarities and differences to electrospinning solutions of nonionic polymers in volatile organic compounds (VOCs). We found that when electrospinning is conducted from ILs, conductivity and surface tension are not the key parameters regulating spinability, while solution viscosity and polymer concentration are. Contrarily, for electrospinning of polymers from VOCs, solution conductivity and viscosity have been reported to be among some of the most important factors controlling fiber formation. For chitin electrospun from [C2mim][OAc], we found both a critical chitin concentration required for continuous fiber formation (>0.20 wt %) and a required viscosity for the spinning solution (between ca. 450–1500 cP). The high viscosities of the biopolymer–IL solutions made it possible to electrospin solutions with low, less than 1 wt %, polymer concentration and produce thin fibers without the need to adjust the electrospinning parameters. These results suggest new prospects for the control of fiber architecture in nonwoven mats, which is crucial for materials performance.
To address the need to scale up technologies for electrospinning of biopolymers from ionic liquids to practical volumes, a setup for the multi-needle electrospinning of chitin using the ionic liquid 1-ethyl-3-methylimidazolium acetate, [C2mim][OAc], was designed, built, and demonstrated. Materials with controllable and high surface area were prepared at the nanoscale using ionic-liquid solutions of high-molecular-weight chitin extracted with the same ionic liquid directly from shrimp shells.
A versatile platform for the preparation of chitin films with tunable strength, morphology, and efficacy of application has been designed from an ionic liquid process for the production of more sustainable high value materials. Films were prepared by a simple casting method from a solution of chitin in the ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]). The chitin source, the loading in ionic liquid, and the drying methods defined film properties such as strength, porosity, and water absorbency. Only chitin directly extracted from shrimp shells using the ionic liquid (rather than commercially available chitin) could be used to cast films strong enough to be handled and dried. The optimal loading of chitin in the ionic liquid was determined to be 2.5 wt% and different drying methods led to different film properties (e.g., hard and rigid vs. soft and porous). As an exemplary application, loading and release of a model drug (caffeine) was investigated. Interestingly, a burst release of the majority of the caffeine was observed in the first 20 minutes, followed by slow release of the remainder. Although more investigations are needed, the chitin film platform can be thought of as an attractive new tool in the development of packaging materials, biomedical devices, and absorbent materials (M. Rinaudo, Prog. Polym. Sci., 2006, 31, 603–632) made from one of Nature's most abundant polymers.
Ionic liquids (ILs), such as hydroxylammonium acetate ([NH3OH][OAc]), can reactively demineralize and remove proteins from shrimp shells in an efficient one-pot pulping process, thus allowing the isolation of native chitin with >80% purity and a high degree of acetylation and crystallinity. Compared to a previously reported IL extraction using 1-ethyl-3-methylimidazolium acetate, [C2mim][OAc], these less expensive ILs can achieve comparable chitin yields and purity, at up to ten times the biomass loading, although potentially result in lower molecular weight (MW) chitin. Because the IL is not recovered or recycled, the cost can additionally be further reduced by the sequential addition of hydroxylamine and acetic acid (or vice versa) to conduct the pulping process in situ. Though each methodology results in a comparable yields and purity of chitin material, the varying production costs and process safety issues are still unknown. This work presents a step toward narrowing the choices for chitin isolation technologies that can lead to an economically and environmentally sustainable process replacing the current hazardous, energy consuming, and environmentally unsafe process.
Chitin–calcium alginate composite fibers were prepared from a solution of high molecular weight chitin extracted from shrimp shells and alginic acid in the ionic liquid 1-ethyl-3-methylimidazolium acetate by dry-jet wet spinning into an aqueous bath saturated with CaCO3. The fibers exhibited a significant proportion of the individual properties of both calcium alginate and chitin. Ultimate stress values were close to values obtained for calcium alginate fibers, and the absorption capacities measured were consistent with those reported for current wound care dressings. Wound healing studies (rat model, histological evaluation) indicated that chitin–calcium alginate covered wound sites underwent normal wound healing with re-epithelialization and that coverage of the dermal fibrosis with hyperplastic epidermis was consistently complete after only 7 days of treatment. Using a single patch per wound per animal during the entire study, all rat wounds achieved 95–99% closure by day 10 with complete wound closure by day 14.
Even with the high costs of environmental exposure controls, as well as the chance of control failures, options for industries wanting to implement sustainability through frameworks such as green chemistry are not yet cost-effective. We foresee a “green” industrial revolution through the use of transformative technologies that provide cost-effective and sustainable products which could lead to new business opportunities. Through example, we promote the use of natural and abundant biopolymers such as chitin, combined with the solvating power of ionic liquids (ILs), as a transformative technology to develop industries that are overall better and more cost-effective than current practices. The use of shellfish waste as a source of chitin for a variety of applications, including high-value medical applications, represents a total byproduct utilization concept with realistic implications in crustacean processing industries.
Chemisorption of carbon dioxide by 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) provides a route to coagulate chitin and cellulose from [C2mim][OAc] solutions without the use of high-boiling antisolvents (e.g., water or ethanol). The use of CO2 chemisorption as an alternative coagulating process has the potential to provide an economical and energy-efficient method for recycling the ionic liquid.
High molecular weight chitin fibers were electrospun in a one-pot process directly from a 1-ethyl-3-methylimidazolium acetate solution of chitin extracted from dried shrimp shell. Such a technology obviates the need not only for the many chemicals and the energy used in industrial isolation of chitin from crustacean shells but also saves the chemicals, energy, and time needed to prepare chitin spinning dopes.
Ionic liquids (ILs) are desirable for use in a large number of applications because of their unique properties; however, compositions comprising only a single IL are expensive to synthesize and difficult to purify, and the widely used chloride-based ILs can be toxic and corrosive. Therefore, there is a need for new IL compositions that minimize common disadvantages encountered with single IL composition and synthetic methods which avoid halide intermediates. In this study, IL mixtures, which are chloride-free, were synthesized by a one-pot process, and the mixtures were used to dissolve biopolymers. The synthesized IL mixtures show high capability to dissolve the two exemplary biopolymers, cellulose and chitin.
Introduction: To overcome potential problems with solid-state APIs, such as polymorphism, solubility and bioavailability, pure liquid salt (ionic liquid) forms of active pharmaceutical ingredients (API-ILs) are considered here as a design strategy.
Areas covered: After a critical review of the current literature, the recent development of the API-ILs strategy is presented, with a particular focus on the liquefaction of drugs. A variety of IL tools for control over the liquid salt state of matter are discussed including choice of counterion to produce an IL from a given API; the concept of oligomeric ions that enables liquefaction of solid ILs by changing the stoichiometry or complexity of the ions; formation of ‘liquid co-crystals' where hydrogen bonding is the driving force in the liquefaction of a neutral acid–base complex; combining an IL strategy with the prodrug strategy to improve the delivery of solid APIs; using ILs as delivery agents via trapping a drug in a micelle and finally ILs designed with tunable hydrophilic-lipophilic balance that matches the structural requirements needed to solubilize poorly water-soluble APIs.
Expert opinion: The authors believe that API-IL approaches may save failed lead candidates, extend the patent life of current APIs, lead to new delivery options or even new pharmaceutical action. They encourage the pharmaceutical industry to invest more research into the API-IL platform as it could lead to fast-tracked approval based on similarities to the APIs already approved.
Hydrophobic, amidoxime-functionalized ionic liquids selectively extract UO22+ from aqueous solution via η² coordination as demonstrated here with extraction, spectroscopic, and crystallographic studies which prove the amidoxime-uranyl coordination mode and extraction mechanism.
Utilization of natural polymers has attracted increasing attention because of the consumption and over-exploitation of non-renewable resources, such as coal and oil. The development of green processing of cellulose, the most abundant biorenewable material on Earth, is urgent from the viewpoints of both sustainability and environmental protection. The discovery of the dissolution of cellulose in ionic liquids (ILs, salts which melt below 100 °C) provides new opportunities for the processing of this biopolymer, however, many fundamental and practical questions need to be answered in order to determine if this will ultimately be a green or sustainable strategy. In this critical review, the open fundamental questions regarding the interactions of cellulose with both the IL cations and anions in the dissolution process are discussed. Investigations have shown that the interactions between the anion and cellulose play an important role in the solvation of cellulose, however, opinions on the role of the cation are conflicting. Some researchers have concluded that the cations are hydrogen bonding to this biopolymer, while others suggest they are not. Our review of the available data has led us to urge the use of more chemical units of solubility, such as ‘g cellulose per mole of IL’ or ‘mol IL per mol hydroxyl in cellulose’ to provide more consistency in data reporting and more insight into the dissolution mechanism. This review will also assess the greenness and sustainability of IL processing of biomass, where it would seem that the choices of cation and anion are critical not only to the science of the dissolution, but to the ultimate ‘greenness’ of any process (142 references).