Rheological Properties of Cellulose/Ionic Liquid Solutions: From Dilute to Concentrated States

Characterization of cellulose produced by bacteria isolated from different vinegars

Traditional vinegars are naturally produced from sugar- or starch-containing raw materials, through alcoholic fermentation followed by acetic fermentation. Fermentation is a spontaneous and complex process involving interactions between various microorganisms. In this study, we produced vinegar using traditional methods from six fruits: rosehip, pear, fig, wild pear, apple, and plum. Bacteria that produce bacterial cellulose (BC) were isolated from these vinegars and identified. In addition, we investigated the properties of BC produced from these bacteria. The strains isolated from vinegars were identified as Gluconobacter oxydans strain MG2022, Acetobacter tropicalis strain MG2022, Acetobacter fabarum strain MG2022, Komagataeibacter saccharivorans strain MG2022, K. saccharivorans strain EG2022, and Acetobacter lovaniensis strain OD2022. In total, 0.83-2.04 g/L BC was produced and the bacterial strain isolated from pear vinegar yielded the most BC. BC produced by the bacterial strain isolated from wild pear vinegar had the highest thermal stability and crystallinity (87.44 %). Overall, this study shows that different fruits contain different BC-producing bacteria in their natural flora and vinegars obtained from fruits can be used in BC production. Also, different BC-producing bacteria can be isolated from different vinegars, and BC produced by these bacteria might have different properties.

Fabrication of bacterial cellulose/PVP nanofiber composites by electrospinning

This study aimed to address a significant challenge in the application of bacterial cellulose (BC) within tissue engineering and regenerative medicine by tackling its inherent insolubility in water and organic solvents. Our team introduced a groundbreaking approach by utilizing zinc sulfate (ZnSO4) as a solvent to render BC soluble, a novel contribution to the literature. Subsequently, the obtained soluble BC was combined with varying concentrations of polyvinylpyrrolidone (PVP). Notably, we pioneered the fabrication of BC/PVP composite scaffolds with customizable fiber surface morphology and regulated degradation rates through the electrospun technique. Several key parameters, such as PVP concentration (8%, 15%, 12%, and 20% w/v), applied voltage (22, 15, and 12 kV), and a fixed nozzle-collector distance of 10 cm with a flow rate of 0.9 mL/h, were systematically evaluated so as to find the optimum parameter created BC/PVP product with electrospun. For electrospun BC/PVP products, a voltage of 12 kV was found to be optimal. Intriguingly, our findings revealed enhanced cell adhesion and proliferation in BC/PVP electrospun products compared with using PVP membranes alone. Specifically, cell viability for PVP and PVP/BC electrospun products was determined as 50.73% and 79.95%, respectively. In terms of thermal properties, the BC/PVP electrospun product exhibited a mass loss of 82.6% at 380°C, while PVP alone experienced 90.2% mass loss at around 280°C. Furthermore, the protein adhesion capacities were measured at 62.3 ± 1.2 μg for PVP and 99.4 ± 2 μg for BC/PVP electrospun products, whereas product showed no biodegradation over 28 days and had notable water retention capacity. In conclusion, our research not only successfully attained nanofiber morphology but also showcased enhanced cell attachment and proliferation on the BC/PVP electrospun product.

Microrheological characterisation of Cyanoflan in human blood plasma

Naturally occurring polysaccharidic biopolymers released by marine cyanobacteria are of great interest for numerous biomedical applications, such as wound healing and drug delivery. Such polymers generally exhibit high molecular weight and an entangled structure that impact the rheology of biological fluids. However, biocompatibility tests focus not so much on rheological properties as on immune response. In the present study, the rheological behaviour of native blood plasma as a function of the concentration of a cyanobacterium biopolymer is investigated via multiple particle tracking microrheology, which measures the Brownian motion of probes embedded in a sample, and cryogenic scanning electron microscope microstructural characterisation. We use Cyanoflan as the biopolymer of choice, and profit from our knowledge of its chemical structure and its exciting potential for biotechnological applications. A sol-gel transition is identified using time-concentration superposition and the power-law behaviour of the incipient network's viscoelastic response is observed in a variety of microrheological data. Our results point to rheology-based principles for blood compatibility tests by facilitating the assignment of quantitative values to specific properties, as opposed to more heuristic approaches.

Revolutionizing lignocellulosic biomass: A review of harnessing the power of ionic liquids for sustainable utilization and extraction

The potential for the transformation of lignocellulosic biomass into valuable commodities is rapidly growing through an environmentally sustainable approach to harness its abundance, cost-effectiveness, biodegradability, and environmentally friendly nature. Ionic liquids (ILs) have received considerable and widespread attention as a promising solution for efficiently dissolving lignocellulosic biomass. The fact that ILs can act as solvents and reagents contributes to their widespread recognition. In particular, ILs are desirable because they are inert, non-toxic, non-flammable, miscible in water, recyclable, thermally and chemically stable, and have low melting points and outstanding ionic conductivity. With these characteristics, ILs can serve as a reliable replacement for traditional biomass conversion methods in various applications. Thus, this comprehensive analysis explores the conversion of lignocellulosic biomass using ILs, focusing on main components such as cellulose, hemicellulose, and lignin. In addition, the effect of multiple parameters on the separation of lignocellulosic biomass using ILs is discussed to emphasize their potential to produce high-value products from this abundant and renewable resource. This work contributes to the advancement of green technologies, offering a promising avenue for the future of biomass conversion and sustainable resource management.

Impact of coagulation solvent interactions on porous morphology evolution in cellulose xerogels

The role of coagulation solvent interactions on the pore formation mechanism in cellulose xerogels was investigated using single-step coagulation baths. A series of cellulose xerogels were fabricated from cotton yarns partially dissolved in ionic liquid (i.e., 1-ethyl-3-methylimidazolium acetate) and then immersed in one of seven different coagulation baths. These samples were evaluated using N2 physisorption, inverse gas chromatography, and X-ray photoelectron spectroscopy. The regenerated cellulose orientation and resultant surface hydrophilicity was found to be dependent on solvent solubility interactions with an emphasis on polar interaction and dispersion force strength. More importantly, the xerogel specific surface area dramatically decreased from 100 m2g-1 to 0.278 m2g-1 with increasing hydrophilicity, confirming the importance of controlled cellulose orientation during the coagulation step of cellulose xerogel fabrication. These results have been used to propose a new pore formation mechanism in cellulose xerogels and provide recommendations towards the development of controllable porosity during xerogel fabrication.

Rheological insights on Carboxymethyl cellulose hydrogels

Hydrogels are copiously studied for tissue engineering, drug delivery, and bone regeneration owing to their water content, mechanical strength, and elastic behaviour. The preparation of stable and mechanically strengthened hydrogels without using toxic crosslinkers and expensive approaches is immensely challenging. In this study, we prepared Carboxymethyl cellulose based hydrogels with different polymer concentration via a less expensive physical crosslinking approach without using any toxic crosslinkers and evaluated their mechanical strength. In this hydrogel system, the carbopol concentration was fixed at 1 wt/v% and the Carboxymethyl cellulose concentration was varied between 1 and 5 wt/v%. In this hydrogel system, Carbopol serves as the crosslinker to bridge Carboxymethyl cellulose polymer through hydrogen bonds. Rheological analysis was employed in assessing the mechanical properties of the prepared hydrogel, in particular, the viscoelastic behaviour of the hydrogels. The viscoelastic nature and mechanical strength of the hydrogels increased with an increase in the Carboxymethyl cellulose polymer concentration. Further, our results suggested that gels with Carboxymethyl cellulose concentration between 3 wt/v % and 4 wt/v % with yield stresses of 58.83 Pa and 81.47 Pa, respectively, are potential candidates for use in transdermal drug delivery. The prepared hydrogels possessed high thermal stability and retained their gel network structure even at 50 °C. These findings are beneficial for biomedical applications in transdermal drug delivery and tissue engineering owing to the biocompatibility, stability, and mechanical strength of the prepared hydrogels.

Rapid in situ quantification of rheo-optic evolution for cellulose spinning in ionic solvents

It is critical to monitor the structural evolution of complex fluids for optimal manufacturing performance, including textile spinning. However, in situ measurements in a textile-spinning process suffer from the paucity of non-destructive instruments and interpretations of the measured data. In this work, kinetic and rheo-optic properties of a cellulose/ionic liquid solution are measured simultaneously while fibers are regenerated in aqueous media from a model wet-spinning process via a customized polarized microscope. This system enables to capture key geometrical and structural information of the fiber under spinning at varying draw ratios and residence time, including the flow kinematics extracted from feature tracking, and the flow-induced morphology and birefringent responses. A physics-oriented rheological model is applied to connect the kinematic and structural measurements in a wet-spinning process incorporating both shear and extensional flows. The birefringent responses of fibers under coagulation are compared with an orientation factor incorporated in the constitutive model, from which a superposed structure-optic relationship under varying spinning conditions is identified. Such structural characterizations inferred from the flow dynamics of spinning dopes exhibit strong connections with the mechanical properties of the fully-regenerated fibers, thus enabling to predict the spinning performance in a non-destructive protocol.

The Effect of Non-Solvent Nature on the Rheological Properties of Cellulose Solution in Diluted Ionic Liquid and Performance of Nanofiltration Membranes

The weak point of ionic liquids is their high viscosity, limiting the maximum polymer concentration in the forming solutions. A low-viscous co-solvent can reduce viscosity, but cellulose has none. This study demonstrates that dimethyl sulfoxide (DMSO), being non-solvent for cellulose, can act as a nominal co-solvent to improve its processing into a nanofiltration membrane by phase inversion. A study of the rheology of cellulose solutions in diluted ionic liquids ([EMIM]Ac, [EMIM]Cl, and [BMIM]Ac) containing up to 75% DMSO showed the possibility of decreasing the viscosity by up to 50 times while keeping the same cellulose concentration. Surprisingly, typical cellulose non-solvents (water, methanol, ethanol, and isopropanol) behave similarly, reducing the viscosity at low doses but causing structuring of the cellulose solution and its phase separation at high concentrations. According to laser interferometry, the nature of these non-solvents affects the mass transfer direction relative to the forming membrane and the substance interdiffusion rate, which increases by four-fold when passing from isopropanol to methanol or water. Examination of the nanofiltration characteristics of the obtained membranes showed that the dilution of ionic liquid enhances the rejection without changing the permeability, while the transition to alcohols increases the permeability while maintaining the rejection.

Cellulose gelation in NaOH(aq) by CO2 absorption: Effects of holding time and concentration on biomaterial development

We address the limited solubility and early onset of gelation of aqueous sodium hydroxide to position it as a preferred green solvent for cellulose. For this purpose, we expand the concentration window (up to 12 wt%) by using a CO₂-depleted air and adjusting the time the dope remains in the given atmosphere, before further processing (holding time) and regeneration conditions. Cellulose solutions are extruded following characteristic (rheology and extrusion) parameters to yield aligned filaments reaching tenacities up to 2.3 cN·dtex^-1, similar to that of viscose. Further material demonstrations are achieved by direct ink writing of auxetic biomedical meshes (Poisson's ratio of -0.2, tensile strength of 115 kPa) and transparent films, which achieved a tensile strength and toughness of 47 MPa and 590 kJ·m^-3, respectively. The results suggest an excellent outlook for cellulose transformation into bioproducts. Key to this development is the control of the gelation ensuing solution flow and polymer alignment, which depend on CO₂ absorption, cellulose concentration, and holding time.

Bacterial Cellulose-Based Blends and Composites: Versatile Biomaterials for Tissue Engineering Applications

Cellulose of bacterial origin, known as bacterial cellulose (BC), is one of the most versatile biomaterials that has a huge potential in tissue engineering due to its favourable mechanical properties, high hydrophilicity, crystallinity, and purity. Additional properties such as porous nano-fibrillar 3D structure and a high degree of polymerisation of BC mimic the properties of the native extracellular matrix (ECM), making it an excellent material for the fabrication of composite scaffolds suitable for cell growth and tissue development. Recently, the fabrication of BC-based scaffolds, including composites and blends with nanomaterials, and other biocompatible polymers has received particular attention owing to their desirable properties for tissue engineering. These have proven to be promising advanced materials in hard and soft tissue engineering. This review presents the latest state-of-the-art modified/functionalised BC-based composites and blends as advanced materials in tissue engineering. Their applicability as an ideal biomaterial in targeted tissue repair including bone, cartilage, vascular, skin, nerve, and cardiac tissue has been discussed. Additionally, this review briefly summarises the latest updates on the production strategies and characterisation of BC and its composites and blends. Finally, the challenges in the future development and the direction of future research are also discussed.

Effect of Oil on Cellulose Dissolution in the Ionic Liquid 1-Butyl-3-methyl Imidazolium Acetate

While ionic liquids (ILs) are well known to be excellent solvents for cellulose, the exact mechanism of dissolution has been a much disputed topic in recent years and is still not completely clear. In this work, we add to the current understanding and highlight the importance of hydrophobic interactions, through studying cellulose dissolution in mixtures of 1-butyl-3-methyl imidazolium acetate (BmimAc) and medium-chain triglyceride (MCT) oil. We demonstrate that the order in which constituents are mixed together plays a key role, through nuclear magnetic resonance (NMR) spectroscopic analysis. When small quantities of MCT oil (0.25-1 wt %) were introduced to BmimAc before cellulose, the effect on BmimAc chemical shift values was much more significant compared to when the cellulose was dissolved first, followed by oil addition. Rheological analysis also showed small differences in the viscosities of oil-cellulose-BmimAc solutions, depending on the order the constituents were added. On the other hand, no such order effect on the NMR results was observed when cellulose was replaced with cellobiose, suggesting that this observation is unique to the macromolecule. We propose that a cellulose-oil interaction develops but only when the cellulose structure has a sufficient degree of order and not when the cellulose is molecularly dispersed, since the hydrophobic cellulose plane is no longer intact. In all cases, cellulose-BmimAc-oil solutions were stable for at least 4 months. To our knowledge, this is the first work that investigates the effect of oil addition on the dissolving capacity of BmimAc and highlights the need for further re-evaluation of accepted mechanisms for cellulose dissolution in ILs.

Flax Noils as a Source of Cellulose for the Production of Lyocell Fibers

The production of long flax fiber for the subsequent production of textile yarn is accompanied by the formation of a significant amount of waste—noils, which is a mechanical mixture of long and short flax fibers and shives. Comparative studies of the structure and chemical composition of the fibrous fraction of noils and shives were carried out using IR spectroscopy. The solubility of shives and flax noils in N-methylmorpholine-N-oxide (NMMO) was studied, a comparative analysis of the rheological behavior of solutions of flax and wood cellulose was carried out and the optimal temperature–concentration conditions for obtaining flax fibers from noils were determined. It was shown for the first time that using the method of solid-phase activation of the cellulose-solvent system makes it possible to obtain fibers in a short period of time (no more than 10 min). The structure of both the raw material and the resulting fibers was studied by X-ray diffraction analysis. The thermal properties of a new type of cellulose fibers was evaluated. The complex of the conducted studies allows us to consider flax fibers from noils along with flax fibers from long-staple flax, as a real alternative to fibers from wood pulp.

Understanding the Dynamics of Cellulose Dissolved in an Ionic Liquid Solvent Under Shear and Extensional Flows

Ionic liquids (ILs) hold great potential as solvents to dissolve, recycle, and regenerate cellulosic fabrics, but the dissolved cellulose material system requires greater study in conditions relevant to fiber spinning processes, especially characterization of nonlinear shear and extensional flows. To address this gap, we aimed to disentangle the effects of the temperature, cellulose concentration, and degree of polymerization (DOP) on the shear and extensional flows of cellulose dissolved in an IL. We have studied the behavior of cellulose from two sources, fabric and filter paper, dissolved in 1-ethyl-3-methylimidazolium acetate ([C₂C₁Im][OAc]) over a range of temperatures (25 to 80 °C) and concentrations (up to 4%) that cover both semidilute and entangled regimes. The linear viscoelastic (LVE) response was measured using small-amplitude oscillatory shear techniques, and the results were unified by reducing the temperature, concentration, and DOP onto a single master curve using time superposition techniques. The shear rheological data were further fitted to a fractional Maxwell liquid (FML) model and were found to satisfy the Cox-Merz rule within the measurement range. Meanwhile, the material response in the non-LVE (NLVE) regime at large strains and strain rates has special relevance for spinning processes. We quantified the NLVE behavior using steady shear flow tests alongside uniaxial extension using a customized capillary breakup extensional rheometer. The results for both shear and extensional NLVE responses were described by the Rolie-Poly model to account for flow-dependent relaxation times and nonmonotonic viscosity evolution with strain rates in an extensional flow, which primarily arise from complex polymer interactions at high concentrations. The physically interpretable model fitting parameters were further compared to describe differences in material response to different flow types at varying temperatures, concentrations, and DOP. Finally, the fitting parameters from the FML and Rolie-Poly models were connected under the same superposition framework to provide a comprehensive description within the wide measured parameter window for the flow and handling of cellulose in [C₂C₁Im][OAc] in both linear and nonlinear regimes.

Thermo-reversible cellulose micro phase-separation in mixtures of methyltributylphosphonium acetate and γ-valerolactone or DMSO

We have identified cellulose solvents, comprised of binary mixtures of molecular solvents and ionic liquids that rapidly dissolve cellulose to high concentration and show upper‐critical solution temperature (UCST)‐like thermodynamic behaviour ‐ upon cooling and micro phase‐separation to roughly spherical microparticle particle‐gel mixtures. This is a result of an entropy‐dominant process, controllable by changing temperature, with an overall exothermic regeneration step. However, the initial dissolution of cellulose in this system, from the majority cellulose I allomorph upon increasing temperature, is also exothermic. The mixtures essentially act as ‘thermo‐switchable’ gels. Upon initial dissolution and cooling, micro‐scaled spherical particles are formed, the formation onset and size of which are dependent on the presence of traces of water. Wide‐angle X‐ray scattering (WAXS) and ¹³C cross‐polarisation magic‐angle spinning (CP‐MAS) NMR spectroscopy have identified that the cellulose micro phase‐separates with no remaining cellulose I allomorph and eventually forms a proportion of the cellulose II allomorph after water washing and drying. The rheological properties of these solutions demonstrate the possibility of a new type of cellulose processing, whereby morphology can be influenced by changing temperature.

Characterization the structural property and degradation behavior of corn starch in KOH/thiourea aqueous solution

Finding an efficient and eco-friendly solution for starch dissolution has attracted considerable attentions in recent years. This study investigated the structural characteristics, and degradation behavior of corn starch in KOH/thiourea aqueous solution by the comparison with DMSO/LiBr and 1-allyl-3-methylimidazolium chloride (AMIMCl). Results showed that KOH/thiourea solution was an effective solvent for corn starch dissolution (30 min with 97.01% solubility). X-ray diffraction (XRD) and ¹³C CP-MAS NMR spectroscopy revealed that native crystallinity of the corn starch was altered by all tested solvents, especially DMSO/LiBr and AMIMCl. Conversely, this new solvent did not change the primary molecular structure, chain-length distribution, or thermal stability of starch, compared with the native starch. Furthermore, KOH/thiourea solution was more suitable for measuring the molecular weight of corn starch, with a weight-average molecular weight (M_w) of 7.18 × 10⁷ g/mol. Therefore, KOH/thiourea solution is a promising novel solvent for starch dissolution and structural exploration.

High-Strength Regenerated Cellulose Fiber Reinforced with Cellulose Nanofibril and Nanosilica

In this study, a novel type of high-strength regenerated cellulose composite fiber reinforced with cellulose nanofibrils (CNFs) and nanosilica (nano-SiO₂) was prepared. Adding 1% CNF and 1% nano-SiO₂ to pulp/AMIMCl improved the tensile strength of the composite cellulose by 47.46%. The surface of the regenerated fiber exhibited a scaly structure with pores, which could be reduced by adding CNF and nano-SiO₂, resulting in the enhancement of physical strength of regenerated fibers. The cellulose/AMIMCl mixture with or without the addition of nanomaterials performed as shear thinning fluids, also known as "pseudoplastic" fluids. Increasing the temperature lowered the viscosity. The yield stress and viscosity sequences were as follows: RCF-CNF² > RCF-CNF²-SiO₂² > RCF-SiO₂² > RCF > RCF-CNF¹-SiO₂¹. Under the same oscillation frequency, G' and G" decreased with the increase of temperature, which indicated a reduction in viscoelasticity. A preferred cellulose/AMIMCl mixture was obtained with the addition of 1% CNF and 1% nano-SiO₂, by which the viscosity and shear stress of the adhesive were significantly reduced at 80 °C.

Polymerizable Choline- and Imidazolium-Based Ionic Liquids Reinforced with Bacterial Cellulose for 3D-Printing

In this work, a novel approach is demonstrated for 3D-printing of bacterial cellulose (BC) reinforced UV-curable ion gels using two-component solvents based on 1-butyl-3-methylimidazolium chloride or choline chloride combined with acrylic acid. Preservation of cellulose's crystalline and nanofibrous structure is demonstrated using wide-angle X-ray diffraction (WAXD) and atomic force microscopy (AFM). Rheological measurements reveal that cholinium-based systems, in comparison with imidazolium-based ones, are characterised with lower viscosity at low shear rates and improved stability against phase separation at high shear rates. Grafting of poly(acrylic acid) onto the surfaces of cellulose nanofibers during UV-induced polymerization of acrylic acid results in higher elongation at break for choline chloride-based compositions: 175% in comparison with 94% for imidazolium-based systems as well as enhanced mechanical properties in compression mode. As a result, cholinium-based BC ion gels containing acrylic acid can be considered as more suitable for 3D-printing of objects with improved mechanical properties due to increased dispersion stability and filler/matrix interaction.

Rheological and NMR Studies of Cellulose Dissolution in the Ionic Liquid BmimAc

Solutions of two types of cellulose in the ionic liquid 1-butyl-3-methyl-imidazolium acetate (BmimAc) have been analyzed using rheology and fast-field cycling nuclear magnetic resonance (NMR) spectroscopy, in order to analyze the macroscopic (bulk) and microscopic environments, respectively. The degree of polymerization (DP) was observed to have a significant effect on both the overlap (c*) and entanglement (c_e) concentrations and the intrinsic viscosity ([η]). For microcrystalline cellulose (MCC)/BmimAc solutions, [η] = 116 mL g^-1, which is comparable to that of MCC/1-ethyl-3-methyl-imidazolium acetate (EmimAc) solutions, while [η] = 350 mL g^-1 for the commercial cellulose (higher DP). Self-diffusion coefficients (D) obtained via the model-independent approach were found to decrease with cellulose concentration and increase with temperature, which can in part be explained by the changes in viscosity; however, ion interactions on a local level are also important. Both Stokes-Einstein and Stokes-Einstein-Debye analyses were carried out to directly compare rheological and relaxometry analyses. It was found that polymer entanglements affect the microscopic environment to a much lesser extent than for the macroscopic environment. Finally, the temperature dependencies of η, D, and relaxation time (T₁) could be well described by Arrhenius relationships, and thus, activation energies (E_a) for flow, diffusion, and relaxation were determined. We demonstrate that temperature and cellulose concentration have different effects on short- and long-range interactions.

Cellulose Dissolution in Ionic Liquid under Mild Conditions: Effect of Hydrolysis and Temperature

This study investigated the effect of acid hydrolysis of cellulose on its dissolution under mild conditions in ionic liquid, 1-butyl-3-methylimidazolium acetate/N,N-dimethylacetamide (BMIMAc/DMAc). Acid hydrolysis of high molecular weight (MW) cotton cellulose (DP > 4000) was carried out to produce hydrolyzed cotton (HC) samples for dissolution. The HC samples were characterized using gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA), and the dissolution process was monitored using polarized light microscopy (PLM). It was found that the drastic decrease of the MW of cellulose did not result in improvement of its dissolution at room temperature. As compared to original cotton cellulose, the high amount of undissolved fibers in HC solutions led to unstable rheological behavior of HC solutions. Agglomeration and inhomogeneous dispersion of HC, and increased crystallinity, in this case, likely made the diffusion of BMIMAc/DMAc more difficult to the inside of the polymeric network of cellulose at ambient temperature, thereby hindering the dissolution. However, increasing the temperature from room temperature to 35 °C and 55 °C, led to a significant improvement in cellulose dissolution. This phenomenon implies that reducing the MW of cellulose might not be able to improve its dissolution under certain conditions. During the dissolution process, the physical properties of cellulose including fiber aggregation status, solvent diffusivity, and cellulose crystallinity may play a critical role compared to the MW, while the MW may not be an important factor. This finding may help further understand the mechanism of cellulose dissolution and seek better strategies to dissolve cellulose under mild conditions for industrial applications.

Preparation of Cellulose Particles with a Hollow Structure

In this study, we report the preparation of hollow cellulose particles via a solvent-releasing method with the ionic liquid 1-ethyl-3-methylimidazolium acetate ([Emim]Ac). A dispersion comprising [Emim]Ac droplets with dissolved cellulose and a hexane medium containing a stabilizer was poured into a large amount of acetone (precipitant), resulting in the precipitation of cellulose and the formation of solid cellulose particles with a hollow structure. We found that the formation of the hollow structure resulted from the equilibrium phase separation. Porous structures were also obtained using ethanol or t-butanol as a precipitant, where cellulose immediately precipitated (i.e., exhibited non-equilibrium phase separation). In the case where acetone was used as the precipitant, the diffusion rate of [Emim]Ac from the droplets into the precipitant was relatively low; that is, the precipitation of cellulose was delayed, which allowed the cellulose to be phase-separated into a thermodynamically stable structure (equilibrium phase separation), resulting in the formation of the hollow structure.

Preparation and Properties of Cellulose-Based Films Regenerated from Waste Corrugated Cardboards Using [Amim]Cl/CaCl2

1-Ally-3-methylimidazolium chloride ([Amim]Cl), dimethyl sulfoxide (DMSO), and CaCl₂ were selected to construct dissolution systems to produce value-added products from pretreatment of waste corrugated cardboards (P-WCCs). The dissolution behaviors of P-WCCs before and after ball milling were studied in different dissolution systems. The regenerated cellulose films were quickly and efficiently prepared via dissolving, regenerating, and pressurized drying. When 4 wt % waste corrugated cardboard was dissolved in [Amim]Cl for 4 h at 90 °C, the regenerated cellulose films featured tensile strengths as high as 59.00 MPa. Adding 40% DMSO and 2 wt % CaCl₂ increased the tensile strength of the film to a maximum value of 85.86 MPa. This demonstrates that DMSO improves the ability of WCC to dissolve in ionic liquids; Ca²⁺ improves the tensile strength and thermal stability of the regenerated cellulose film but reduces its transparency. This work provides a new, simple, and highly efficient way to use WCCs for packaging and wrapping.

Flame Retardant-Functionalized Cotton Cellulose Using Phosphonate-Based Ionic Liquids

Cellulose from cotton fibers was functionalized through a dissolution-regeneration process with phosphonate-based ionic liquids (ILs): 1,3-dimethylimidazolium methylphosphonate [DIMIM][(MeO)(H)PO₂] and 1-ethyl-3-methylimidazolium methylphoshonate [EMIM][(MeO)(H)PO₂]. The chemical modification of cellulose occurred through a transesterification reaction between the methyl phosphonate function of ILs and the primary alcohol functions of cellulose. The resulting cellulose structure and the amount of grafted phosphorus were then investigated by X-ray diffraction, ICP-AES, and ¹³C and ³¹P NMR spectroscopy. Depending on the IL type and initial cotton / IL ratio in the solution, regenerated cellulose contained up to 4.5% of phosphorus. The rheological behavior of cotton cellulose/ILs solutions and the microscale fire performances of modified cellulose were studied in order to ultimately prepare flame retardant cellulosic materials. Significant improvement in the flame retardancy of regenerated cellulose was obtained with a reduction of THR values down to about 5-6 kJ/g and an increase of char up to about 35 wt%.

Films of Bacterial Cellulose Prepared from Solutions in N-Methylmorpholine-N-Oxide: Structure and Properties

In the present study, one of the possible methods of the bacterial cellulose processing is proposed via its dissolution in N-methylmorpholine-N-oxide using the stage of mechano-chemical activation of the solid polymer–solvent system. Preliminary solid-phase activation is apparently a decisive factor affecting the dissolution rate of bacterial cellulose in N-methylmorpholine-N-oxide. The effects of bacterial cellulose concentration, solvent nature, degree of polymerization and temperature on dissolution time were studied. The rheological behavior of the solutions does not change at 120 °C for at least half an hour that allowed us to process such solutions for films preparation. The films from these solutions by means of dry-wet jet spinning in aqueous coagulant were formed. The structure of the nascent cellulose and formed films was tested by the X-ray diffraction method and SEM. The thermal behavior of the films revealed an increase in the carbon yield for the formed films compared to the nascent bacterial cellulose. The process of film pyrolysis is accompanied by exothermic effects, which are not typical for wood cellulose. Some reasons of such thermal behavior are considered.

Unique gelation and rheological properties of the cellulose/CO2-based reversible ionic liquid/DMSO solutions

Gelation and rheological behaviors of cellulose/CO₂-based reversible ionic liquid (RIL)/DMSO solutions were investigated. The exponents of specific viscosity η_sp versus concentration c were determined for wood pulp (WP) and microcrystalline cellulose (MCC) solutions. The complex viscosity acquired using oscillatory shear closely follows the steady shear viscosity, thus revealing the applicability of Cox-Merz rule. The influence of RIL content in the solvent on apparent viscosities, activation energy, intrinsic viscosities, specific viscosity-c[η] master curve, and relaxation time were also investigated. Gelation occurred in this cellulose solution system due to thermal-induced CO₂ release from the decomposition of the CO₂-based reversible ionic liquid. The formed gel was stable in air, but re-dissolved when exposed to CO₂, indicating the switch-on and switch-off effects of CO₂ in cellulose dissolution and gelation.

Upcycling of cotton polyester blended textile waste to new man-made cellulose fibers

The creation of a circular economy for cellulose based textile waste is supported by the development of an upcycling method for cotton polyester blended waste garments. We present a separation procedure for cotton and polyester using [DBNH] [OAc], a superbase based ionic liquid, which allows the selective dissolution of the cellulose component. After the removal of PET, the resulting solution could be employed to dry-jet wet spin textile grade cellulose fibers down to the microfiber range (0.75-2.95 dtex) with breaking tenacities (27-48 cN/tex) and elongations (7-9%) comparable to commercial Lyocell fibers made from high-purity dissolving pulp. The treatment time in [DBNH] [OAc] was found to reduce the tensile properties (<52%) and the molar mass distribution (<51%) of PET under certain processing conditions.

Poly(4-vinylaniline)/Polyaniline Bilayer-Functionalized Bacterial Cellulose for Flexible Electrochemical Biosensors

A bacterial cellulose (BC) nanofibril network is modified with an electrically conductive polyvinylaniline/polyaniline (PVAN/PANI) bilayer for construction of potential electrochemical biosensors. This is accomplished through surface-initiated atom transfer radical polymerization of 4-vinylaniline, followed by in situ chemical oxidative polymerization of aniline. A uniform coverage of the BC nanofiber with 1D supramolecular PANI nanostructures is confirmed by Fourier transform infrared, X-ray diffractogram, and CHN elemental analysis. Cyclic voltammograms evince the switching in the electrochemical behavior of BC/PVAN/PANI nanocomposites from the redox peaks at 0.74 V, in the positive scan and at -0.70 V, in the reverse scan, (at 100 mV·s^-1 scan rate). From these redox peaks, PANI is the emeraldine form with the maximal electrical performance recorded, showing charge-transfer resistance as low as 21 Ω and capacitance as high as 39 μF. The voltage-sensible nanocomposites can interact with neural stem cells isolated from the subventricular zone (SVZ) of the brain, through stimulation and characterization of differentiated SVZ cells into specialized and mature neurons with long neurites measuring up to 115 ± 24 μm length after 7 days of culture without visible signs of cytotoxic effects. The findings pave the path to the new effective nanobiosensor technologies for nerve regenerative medicine, which demands both electroactivity and biocompatibility.

Toward a Better Understanding of Different Dissolution Behavior of Starches in Aqueous Ionic Liquids at Room Temperature

The purpose of this study was to understand the dissolution behavior of maize and potato starches in 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]):water mixtures at room temperature. With an increasing ratio of ionic liquid (IL):water, the long- and short-range ordered structures and granule morphology of both starches were disrupted progressively. The multiscale structure of maize starch was disrupted completely after treatment with the [Emim][OAc]:water mixture of 6:4, indicating good dissolution performance of this mixture for maize starch. This mixture seemed to provide a balance between the viscosity of the solvent and availability of ions to disrupt starch H-bonds. The different dissolution behaviors of maize and potato starches in [Emim][OAc]:water mixtures were attributed to structural differences of the granule surfaces. Our results showed that the dissolution behavior of starches was affected by both starch sources and properties of [Emim][OAc]:water mixtures, which may provide guidance for the development of green technology for processing of biopolymers with low energy consumption.

Analysis of the Effect of Processing Conditions on Physical Properties of Thermally Set Cellulose Hydrogels

Cellulose-based hydrogels were prepared by dissolving cellulose in aqueous sodium hydroxide (NaOH)/urea solutions and casting it into complex shapes by the use of sacrificial templates followed by thermal gelation of the solution. Both the gelling temperatures used (40–80 °C), as well as the method of heating by either induction in the form of a water bath and hot press or radiation by microwaves could be shown to have a significant effect on the compressive strength and modulus of the prepared hydrogels. Lower gelling temperatures and shorter heating times were found to result in stronger and stiffer gels. Both the effect of physical cross-linking via the introduction of additional non-dissolving cellulosic material, as well as chemical cross-linking by the introduction of epichlorohydrin (ECH), and a combination of both applied during the gelation process could be shown to affect both the mechanical properties and microstructure of the hydrogels. The added cellulose acts as a physical-cross-linking agent strengthening the hydrogen-bond network as well as a reinforcing phase improving the mechanical properties. However, chemical cross-linking of an unreinforced gel leads to unfavourable bonding and cellulose network formation, resulting in drastically increased pore sizes and reduced mechanical properties. In both cases, chemical cross-linking leads to larger internal pores.

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.

Solvent Regulation Approach for Preparing Cellulose-Nanocrystal-Reinforced Regenerated Cellulose Fibers and Their Properties

An electrolyte and aprotic solvent mixture were used to prepare cellulose solutions containing cellulose nanocrystals (CNCs). All-cellulose composite fibers were then produced by dry-wet spinning these solutions. The presence of CNC in the all-cellulose fibers was demonstrated, and the effects of the CNC on the fiber properties were investigated. The all-cellulose fibers were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and electronic tensile measurements. These results showed that CNCs were present in the mixture and that their structure was maintained in the all-cellulose fibers. No compatibility problems between the CNC and cellulose II matrix were observed. Introducing CNC enhanced the crystallinity, thermal stability, and mechanical properties of the composite fibers.

Cellulose-starch Hybrid Films Plasticized by Aqueous ZnCl₂ Solution

Starch and cellulose are two typical natural polymers from plants that have similar chemical structures. The blending of these two biopolymers for materials development is an interesting topic, although how their molecular interactions could influence the conformation and properties of the resultant materials has not been studied extensively. Herein, the rheological properties of cellulose/starch/ZnCl₂ solutions were studied, and the structures and properties of cellulose-starch hybrid films were characterized. The rheological study shows that compared with starch (containing mostly amylose), cellulose contributed more to the solution's viscosity and has a stronger shear-thinning behavior. A comparison between the experimental and calculated zero-shear-rate viscosities indicates that compact complexes (interfacial interactions) formed between cellulose and starch with ≤50 wt % cellulose content, whereas a loose structure (phase separation) existed with ≥70 wt % cellulose content. For starch-rich hybrid films prepared by compression molding, less than 7 wt % of cellulose was found to improve the mechanical properties despite the reduced crystallinity of the starch; for cellulose-rich hybrid films, a higher content of starch reduced the material properties, although the chemical interactions were not apparently influenced. It is concluded that the mechanical properties of biopolymer films were mainly affected by the structural conformation, as indicated by the rheological results.

Dissolution and transesterification of cellulose in γ-valerolactone promoted by ionic liquids

Ionic liquids act as promoters for the dissolution of cellulose in GVL and also as catalysts for cellulose derivatization in GVL, providing a green and effective solvent system for cellulose processing and derivatization.