N-methylmorpholine-N-oxide Monohydrate Research Articles

A novel cost-effective kapok fibers and regenerated cellulose-based carbon aerogel for continuous oil/water separation

The development of cost-effective, environmentally friendly, and reusable superabsorbent materials for removing oil spills from water presents significant challenges. Herein, a novel, cost-effective, environmentally friendly, and reusable carbon aerogel (KRxCA) was synthesized by combining kapok fibers (KF) with hardwood pulp regenerated cellulose, dissolving in a mixture of N-methyl morpholine-N-oxide monohydrate (NMMO) and deep eutectic solvent (DES), which is named co-solvent DNS. This carbon aerogel presents remarkable compressibility, elasticity, and fatigue resistance, maintaining maximum stress after 100 cycles at 50 % strain due to its three-dimensional network of carbonized hollow tubular KF fixed by carbonized regenerated cellulose. The water contact angle (144.7°) indicates the excellent hydrophobicity of the KR10CA, demonstrating the potential for efficient oil/water separation. The resulting ultra-light (3.78 mg cm−3) and high porous (98.9 %) KR10CA exhibits exceptional oil sorption capacity (137.5–371.7 g⋅g−1) and retains 89.3 % of its sorption capacity after ten extrusion cycles. Additionally, as a filter membrane, the KR10CA effectively separates n-hexane from water with a high flux rate (21972.7 L m-2h−1). Therefore, the carbon aerogel derived from renewable resources presents itself as a cost-effective and environmentally friendly oil/water separator for practical application.

Molecular mechanism of cellulose dissolution in N-methyl morpholine-N-oxide: A molecular dynamics simulation study

N-methyl morpholine-N-oxide (NMMO) is the only commercialised solvent to dissolve cellulose and produce lyocell. However, the molecular mechanism of NMMO-induced cellulose solubilisation is unknown which limits further process development. In this work, and for the first time the complete dissolution process of a large cellulose bunch was simulated in NMMO monohydrate using long microsecond molecular dynamic simulations. The dissolution process was also simulated in 1-ethyl-3-methylimidazolium acetate (EmimAc) as an efficient ionic liquid in cellulose dissolution and the results were compared with the aqueous conditions. While the cellulose bunch showed a stable and insoluble structure in pure water, it was completely and efficiently dissolved in both NMMO monohydrate and EmimAc. It was shown that the dissolution time of cellulose in NMMO monohydrate is almost twice that in EmimAc, which is in agreement with the experimental observations. Although it is revealed that hydrogen bonding is the main driving force of cellulose dissolution in NMMO monohydrate, one cannot explain the complete molecular mechanism of NMMO-induced cellulose dissolution only by considering hydrogen bonds. A straightforward molecular mechanism was proposed, in which the interactions of NMMO molecules, not with cellulose, but with the other NMMO molecules play a critical role in the dissolution process.

Highly-porous uniformly-sized amidoxime-functionalized cellulose beads prepared by microfluidics with N-methylmorpholine N-oxide

Uniformly-sized porous cellulose beads functionalized with amidoxime groups were prepared for the first time using a microfluidic method with N-methylmorpholine N-oxide (NMMO) monohydrate as a cellulose solvent. The molten state cellulose dope in NMMO monohydrate (cell/NMMO dope) as a disperse phase and hot mineral oil as a continuous phase were used in a T-junction microfluidic chip to produce uniformly-sized cell/NMMO droplets. Coagulation of the molten state cell/NMMO droplet at high temperature and amidoxime functionalization could prepare the highly-porous spherical amidoxime-functionalized cellulose beads with a uniform fibrous open internal structure. The prepared amidoxime-functionalized cellulose beads showed excellent metal adsorption properties with a maximum adsorption capacity of ~ 80 mg g−1 in the case of Cu2+/phthalate ions. The newly developed highly-porous cellulose beads can open many new applications with other proper functionalization at the reactive hydroxyl groups of the cellulose.Graphic abstract

A cautionary note on \u201cexothermic events\u201d upon contact of carbodiimide coupling agents and the cellulose solvent N-methylmorpholine-N-oxide

The cellulose solvent N-methylmorpholine-N-oxide monohydrate (NMMO) reacts violently with carbodiimide coupling agents, such as the widely used DCC (dicyclohexylcarbodiimide) and EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide), which can cause explosions, heavy smoke generation and complete charring of the reaction mixtures. For this reason it is clear that cellulose or other carbohydrates dissolved in NMMO (“Lyocell conditions”) cannot be safely esterified or amidified under DCC/EDC conditions. It is important to note that cellulosic material regenerated from NMMO solutions also poses a risk if it contains residual NMMO, which can then come into contact with DCC-type coupling agents in non-aqueous media, as recent accidents have unfortunately shown. Similarly, EDC/DCC traces in cellulose can have detrimental effects when trying to dissolve the material in NMMO. Working in aqueous systems generally reduces the risk of uncontrolled reactions, while alcohols or aprotic solvents are not very effective in this regard. Washing for NMMO removal or EDC/DCC removal should therefore always be carried out by aqueous media, if any possible, if there is a potential risk that the reagents might come into contact later. This warning describes the potential hazards of the reagent combination, highlights the underlying degradation mechanism and explains the precautions to be taken to avoid any “exothermic events”.Graphic abstract

Biocompatible chemical network of α-cellulose-ESBO (epoxidized soybean oil) scaffold for tissue engineering application

Despite many desirable properties, the use of α-cellulose in biomedical applications is limited because of its poor processability. Here we demonstrate that the chemical network of α-cellulose and epoxidized soybean oil (ESBO) can be adequately processed into biocompatible, self-standing, highly-porous scaffolds for tissue engineering applications. First, α-cellulose was dissolved in N-Methylmorpholine N-oxide monohydrate (NMMO.MH) and chemically crosslinked by ESBO. Then, the porous scaffolds of α-cellulose-ESBO were fabricated by solvent exchange and freeze-drying techniques. The scaffolds were evaluated for morphology, thermal and mechanical stability, and in vitro cell attachment and cell viability. Scanning electron microscopy images and Brunauer-Emmett-Teller results suggested that porous scaffolds provide a good surface and internal structure for cell adhesion and growth. Specifically, the α-cellulose-ESBO scaffolds support the homogeneous attachment and proliferation of MG63 cells. Overall, our results suggest that α-cellulose-ESBO chemically crosslinked networks are biocompatible and demonstrate a remarkable capacity for the development of tissue engineering platforms.

Water-induced crystallization and nano-scale spinodal decomposition of cellulose in NMMO and ionic liquid dope

We followed the cellulose structure formation induced by water diffusion into Lyocell dopes based on both N-Methylmorpholine N-oxide (NMMO) and 1,5-diazabicyclo[4.3.0]non-5-ene acetate ([DBNH][OAc], by using scanning simultaneous small- and wide-angle scattering (SAXS-WAXS) experiment along the diffusion gradient. The water content at each point was estimated from the wide-angle scattering profile, giving a binary diffusion constant of the order of 5 × 10−10 m2/sec. In the case of the cellulose solution in NMMO monohydrate, diffraction peaks corresponding to cellulose II appeared concomitantly with the increase in small angle scattering features indicative of nanofibril formation. In the cellulose solution in the ionic liquid, an increase in small angle scattering intensity with the progression of water content appeared at scattering vector q = 0.015 A−1 corresponding to a correlation length of about 40 nm, indicative of nanometric spinodal decomposition preceding the coagulation process, though no crystalline peak appeared in the wide-angle scattering.

Preparation of water-dispersible graphene using N-methylmorpholine N-oxide monohydrate and its application for the preparation of nanocomposites using PEDOT

SEM and TEM images (inset: selective area electron diffraction (SAED) pattern) of mono-layered water dispersible graphene (GPN) sheet by treatment ofN-methylmorpholineN-oxide monohydrate (NMMOm).

Preparation and properties of the single‐walled carbon nanotube/cellulose nanocomposites using N‐methylmorpholine‐N‐oxide monohydrate

AbstractSingle‐walled carbon nanotube (SWNT)/cellulose nanocomposite films were prepared using N‐methylmorpholine‐N‐oxide (NMMO) monohydrate as a dispersing agent for the acid‐treated SWNTs (A‐SWNTs) as well as a cellulose solvent. The A‐SWNTs were dispersed in both NMMO monohydrate and the nanocomposite film (as confirmed by scanning electron microscopy) because of the strong hydrogen bonds of the A‐SWNTs with NMMO and cellulose. The mechanical properties, thermal properties, and electric conductivity of the nanocomposite films were improved by adding a small amount of the A‐SWNTs to the cellulose. For example, by adding 1 wt % of the A‐SWNTs to the cellulose, tensile strain at break point, Young's modulus, and toughness increased ∼ 5.4, ∼ 2.2, and ∼ 6 times, respectively, the degradation temperature increased to 9°C as compared with those of the pure cellulose film, and the electric conductivities at ϕ (the wt % of A‐SWNTs in the composite) = 1 and 9 were 4.97 × 10−4 and 3.74 × 10−2 S/cm, respectively. Thus, the A‐SWNT/cellulose nanocomposites are a promising material and can be used for many applications, such as toughened Lyocell fibers, transparent electrodes, and soforth. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Possibilities for the Physical Modification of Cellulose Shapes Using Ionic Liquids

AbstractSummary: Functional cellulose shapes offer valuable properties for innovative application potentials in textile and medical products. Thereby excellent textile physiological properties of cellulose are allowed to be connected with novel application characteristics like bioactivity, electrical conductivity, heat storage or ability to adsorb liquids or gases. A very advantageous way to modify the properties of fibres, films or textile structures is to introduce particular additives via the Lyocell process. Regard to technical applications, functional additives will be able to incorporate themselves in the shape matrix and, in the case of using N‐methylmorpholine‐N‐oxide monohydrate (NMMO) as solvent, implicate massive technological difficulties and deterioration of properties of the spinning dope. Beside a couple of limiting moments, ionic liquids (ILs) offer as direct solvents an excellent chance for physical modification of cellulose shapes. In contrast to NMMO, they exhibit a significantly higher thermal stability as well as a higher chemical resistance. ILs exhibit most widely a better dissolving capability for a number of different polymers. First results of the development of adsorber materials as well as novel bioactive fibres will be discussed and fibre characteristics will be given.

Enhanced enzymatic hydrolysis of sugarcane bagasse by N-methylmorpholine-N-oxide pretreatment

The cellulose dissolution solvent used in Lyocell process for cellulose fiber preparation, N-methylmorpholine-N-oxide (NMMO) monohydrate, was demonstrated to be an effective agent for sugarcane bagasse pretreatment. Bagasse of 20wt% was readily dissolved in NMMO monohydrate at 130°C within 1h. After dissolution, bagasse could be regenerated by rapid precipitation with water as a porous and amorphous mixture of its original components. The regenerated bagasse exhibited a significant enhancement on enzymatic hydrolysis kinetic. Not only the reducing sugars releasing rate but also hydrolysis yield was enhanced at least twofold as compared with that of untreated bagasse. The cellulose fraction of regenerated bagasse was nearly hydrolyzed to glucose after 72h hydrolysis with Cellulase AP3. The recycled NMMO demonstrated the same performance as the fresh one on bagasse pretreatment for hydrolysis enhancement. The regenerated bagasse was directly used in simultaneous saccharification and fermentation (SSF) for ethanol production by Zymomonas mobilis. No negative effect on ethanol fermentation was observed and ethanol yield approximately 0.15g ethanol/g baggasse was achieved.

Degradation processes in the cellulose/N-methylmorpholine-N-oxide system studied by HPLC and ESR. Radical formation/recombination kinetics under UV photolysis at 77 K

Degradation processes of N-methylmorpholine-N-oxide monohydrate (NMMO), cellulose and cellulose/NMMO solutions were studied by high performance liquid chromatography (HPLC) and electron spin resonance (ESR) spectroscopy. Kinetics of radical accumulation processes under UV (λ = 248 nm) excimer laser flash photolysis was investigated by ESR at 77 K. Beside radical products of cellulose generated and stabilized at low temperature, radicals in NMMO and cellulose/NMMO solutions were studied for the first time in those systems and attributed to nitroxide type radicals ∼CH2–NO•–CH2∼ and/or ∼CH2–NO•–CH3∼ at the first and methyl •CH3 and formyl •CHO radicals at the second step of the photo-induced reaction. Kinetic study of radicals revealed that formation and recombination rates of radical reaction depend on cellulose concentration in cellulose/NMMO solutions and additional ingredients, e.g., Fe(II) and propyl gallate. HPLC measurements showed that the concentrations of ring degradation products, e.g., aminoethanol and acetaldehyde, are determined by the composition of the cellulose/NMMO solution. Results based on HPLC are mainly maintained by ESR that supports the assumption concerning a radical initiated ring-opening of NMMO.

N-Methylmorpholine- N-oxide ring cleavage registration by ESR under heating conditions of the Lyocell process

Thermal cleavage processes of N-methylmorpholine- N-oxide monohydrate (NMMO) were observed in pure NMMO as well as in cellulose/NMMO solutions by ESR at temperatures of the industrial Lyocell process (∼370 K). Generated radicals were attributed to the alkylnitroxyl type radicals –CH 2-NO –CH 3 in NMMO and additional (and dominated) –CH 2-NO –CH 2– in cellulose/NMMO solutions. Formation of both radical types formed due to NMMO ring scission is suggested.

Electron spin resonance study of radicals generated in cellulose/N‐methylmorpholine solutions after flash photolysis at 77 K

The processes of radical formation in N-methylmorpholine-N-oxide monohydrate (NMMO) and cellulose/NMMO solutions were studied by ESR at 77 K under high-power UV (lambda = 248 nm) excimer laser flash photolysis. Radicals mainly generated were attributed to the nitroxide type radicals -CH2-NO*-CH2- and -CH2-NO*-CH3 at the first step and methyl *CH3 and formyl *CHO radicals at the second step of the photoreaction. Kinetic studies of these radicals revealed that formation and recombination rates of the radicals depend on the cellulose concentration in cellulose/NMMO solutions and the concentration of additional ingredients, e.g. Fe(II) and propyl gallate. Even at frozen state temperature, acceleration or quenching of radical reaction processes was found. The proposed scheme of UV light-induced NMMO degradation during irradiation based on ESR data correlates well with independently obtained results based on high-performance liquid chromatography (HPLC). The analysis of degradation products by HPLC, e.g. aminoethanol and acetaldehyde, supports the assumption concerning a radical-initiated ring opening of NMMO.

Mechanism of the interaction of dimethyl sulfoxide with N-methylmorpholine-N-oxide Monohydrate

The interaction of dimethyl sulfoxide with N-methylmorpholine-N-oxide (NMMO) monohydrate was studied by the NMR relaxation method. The mobility of DMSO molecules in the presence of NMMO monohydrate decreases due to the formation of a hydrogen bond between the water molecule of the monohydrate and a DMSO molecule. At the same time, the mobility of protons in the NMMO monohydrate increases due to a decrease in the strength of the water-NMMO hydrogen bond.

Studies on spinning and rheological behaviors of regenerated silk fibroin/N-methylmorpholine-N-oxide·H2O solutions

In this paper, N-Methylmorpholine-N-Oxide (NMMO) was used as solvent for regenerated silk fibroin (RSF). Concentrated solutions with RSF content from 10 to 25 wt% were obtained by dissolving RSF film into NMMO monohydrate. The spinning and rheological properties of RSF/NMMO·H2O solutions were studied by a simple piston type single filament spinning apparatus and HAAKE RS150L rheometer, respectively. The results are discussed to understand the influences of shear rate, temperature and RSF concentration on the rheological behaviors of RSF/NMMO·H2O and to choose appropriate process condition for spinning. Spinning was performed using a dry-wet spinning process. The regenerated silk fibre was prepared successfully and the tenacity can reach to 3.07cN/dtex.

Discoloration of cellulose solutions in N-methylmorpholine-N-oxide (Lyocell). Part 2: Isolation and identification of chromophores

The Lyocell process is a modern ‘green’ industrial fiber-making technology, which employs N-methylmorpholine-N-oxide monohydrate (NMMO) to directly dissolve cellulose. One problem in Lyocell processing is the discoloration of the spinning dope due to chemical side reactions. Two different methods were elaborated to isolate chromophores, which are present in minute amounts only, from Lyocell fibers, the first one using hydrogen chloride in alcoholic solution, the second one employing boron trifluoride – acetic acid complex. Several chromophores were unambiguously identified by a combination of analytical techniques and comparison to authentic samples. Carbohydrate condensation products, such as catechols, were shown to dominate in early phases of chromophore formation. In later stages, these initial chromophores undergo further condensation reactions with degradation products of NMMO and NMMO itself, leading to nitrogen-containing heterocycles and quinoid products, among others. The incorporation of nitrogen into the chromophores and thus the participation of the solvent in chromophore formation were proven.

Discoloration of cellulose solutions in N-methylmorpholine-N-oxide (Lyocell). Part 1: Studies on model compounds and pulps

N-Methylmorpholine-N-oxide monohydrate (NMMO) is used as solvent for cellulose in the Lyocell process as a modern industrial fiber-making technology. Undesired chemical side reactions and byproduct formation in the system cellulose/NMMO/water are known to cause detrimental effects, such as chromophore formation and discoloration of the resulting fibers. A detailed kinetic study on the influence of carbonyl structures on chromophore formation in NMMO melts was carried out employing UV spectroscopy. Different sugar model compounds, such as reducing or non-reducing sugars, and sugars with additional oxidized functions, were applied. The chromophore formation rate differed widely for various reducing sugar model compounds, with pentoses generally reacting faster than hexoses, and carbohydrates with protected reducing end being largely inert. The effect of carbonyl groups on chromophore generation has been studied further using oligomers and oxidized pulps with different contents of carbonyl groups. As in the case of model compounds, also for the pulps a linear correlation between carbonyl content and chromophore formation rate was established. A distinct effect of hemicelluloses was observed.

A novel method for the determination of carbonyl groups in cellulosics by fluorescence labeling. 3. Monitoring oxidative processes.

The fluorescence-based CCOA method for determination of carbonyl group profiles in cellulosic substrates was employed to study the mechanisms of various oxidative and degradation processes involving celluloses in greater detail. The approach comprises labeling with the marker carbazole-9-carboxylic acid [2-(2-aminooxyethoxy)ethoxy]amide (CCOA), followed by gel permeation chromatography in DMAc/LiCl with fluorescence, multiangle laser light scattering, and refractive index detection. At first, the CCOA method was applied to study solutions of pulp in N-methylmorpholine-N-oxide monohydrate (NMMO), as occurring in the production of Lyocell-type fibers. NMMO is a rather strong oxidant that on one hand converts reducing end groups to carboxyl structures, thus lowering the overall carbonyl content, but generates new keto structures along the chain by nonselective oxidation on the other hand. The CCOA method allowed for the first time to distinguish the carbonyl course in different molecular weight ranges. Second, alkalization and aging of pulp, which are used in the industrial preparation of cellulose derivatives, e.g., as an element of the preripening process in viscose rayon production, were investigated. The CCOA method shows a clear reduction of the molecular weight, accompanied by a fast loss of carbonyls in the first phase, which is due to removal of low-molecular weight material by dissolution, and a slow decrease in the second phase, which is caused by further oxidation of carbonyl groups. Also here, differences in the carbonyl course in different molecular weight regions were monitored. Third, electron beaming, proposed as a means of pulp activation, was shown to decrease and narrow the molecular weight distribution, under generation of comparatively low amounts of carbonyls, which, however, are also introduced into high molecular weight, crystalline domains, as shown by a comparison of homogeneous and heterogeneous CCOA labeling approach. Finally, as the fourth application, thermal treatment of cellulose at temperatures between 105 and 165 degrees C was shown to bring about a small reduction of the molecular weight, which only at higher drying temperatures is accompanied by an introduction of carbonyls over the whole molecular weight range.

The Online Measurement of Lyocell Fibers and Investigation of Elongational Viscosity of Cellulose N ‐methylmorpholine‐ N ‐oxide Monohydrate Solutions

In this paper, the development of diameter and surface temperature of lyocell fibers was measured online. The diameter and tensile force on the spin line in the coagulation bath were traced. The velocity, velocity gradient and the tensile stress profiles development of the fibers in the air grap were studied. The apparent elongantional viscosity of cellulose N-methylmorpholine-N-oxide monohydrate (NMMO-MH) solutions was studied by steady-state melt spinning theory. The decrease of the fiber diameter was mainly taking place near the spinneret, and the decrease of the diameter became more dramatic with increasing taking-up speed. The surface temperature of the fibers was also dropping faster with increasing takin-up speed for the heat transfert coefficient increased. The diameter of the Lyocell fibers almost did not change before and after it entered the coagualtion bath. The tensile force on the spin line increase with increasing taking-up speed and coagulation bath length. The velocity and the tensile strees increase slowly near the spinneret, and then accelerate. The apparent elongational viscosity of cellulose NMMO-MH solutions decreases with increasing temperature at the same elongation rate and decreases with increasing elongation rate at the same temperature. The fiber of the Lyocell process was not really solidified in the air gap and a gel or ribbery state was formed.

Effect of Thermal History on the Phase Behavior of N-Methyl Morpholine N-Oxide Hydrates and Their Solutions of Cellulose

N-Methyl morpholine N-oxide (NMMO) hydrates, used in the preparation of cellulose spinning dope for lyocell manufacturing, have various crystal structures according to the hydration number (n). A single melting peak for solid-solid transition from NMMO monohydrate to anhydrous NMMO at 94°C was previously reported. However, we observed the melting peak at 90°C ascribed to the solid-solid transition from NMMO monohydrate to anhydrous NMMO and another melting peak observed in the range from 98 to 105°C when n<1. This discrepancy resulted from the experimental errors in differential scanning calorimetry (DSC) measurement. The pressure capsule enabled us to obtain precise and reproducible DSC data of NMMO hydrates. The three different crystal structures of NMMO hydrates with n<1 were identified by crystallization experiments. The crystal, which had melted in the range from 90 to 105°C during heating (shown by double peaks), was recrystallized at 80°C during cooling, which has never been reported. The NMMO hydrates with n<1 required heating above 130°C to produce a homogeneous melt, and the required temperature was increased up to 180°C for anhydrous NMMO. If the heating temperature was not high enough to fully melt the NMMO hydrate crystal, the unmelted NMMO hydrate crystals affected the thermal responses of the hydrate and its phase behavior of cellulose solutions in the NMMO hydrate.