Changes in cellulose structure during dissolution in LiCl:N,N-dimethylacetamide and in the alkaline iron tartrate system EWNN

The influence of different solvents on the morphology of cellulose during the dissolution process was studied. Spruce sulfite pulp, cotton linters and hydrolysed cotton linters were treated for a short time with lithium chloride: N,N-dimethylacetamide (LiCl:DMAc) and an alkaline solution of iron sodium tartrate (EWNN), respectively. The changes occurring at the fibre surfaces and within the cell walls were observed by scanning as well as by transmission electron microscopy. The cellulose fibres show significant differences in the dissolution behaviour when comparing the reaction of the two solvents. Using LiCl:DMAc, the cotton linters fibres become lamellar separated and within the spruce sulfite pulp fibres solvent channels appear in the first step with the fibrils becoming separated. In contrast, EWNN has a swelling effect on the surface of the cellulose fibres. Both solvent systems predominantly affect the ends of the fibres and places where the wall structure has been damaged.     

Low degree of substitution cellulosic textile coatings with improved physiological parameters

To further improve the physiological properties of textiles, solutions of low degree of substitution cellulose derivatives, i.e. carbamates and acetates, containing finely dispersed sub-micron scaled NaCl particles (d₁₆ = 269 nm, d₅₀ = 275 nm, d₈₄ = 283 nm) serving as templates were coated on textiles. By wet milling of NaCl particles in a 12.5 wt% solution of polyvinylpyrrolidone in dimethylacetamide (DMAc) as dispersing agent, a stable, processable dispersion was obtained, which could be diluted with LiCl/DMAc without any flocculation. For the preparation of the coating solution, the NaCl/DMAc dispersions were diluted with LiCl/DMAc and added to the DMAc-swollen cellulose derivatives. After application onto the textiles, the NaCl particle-containing coating had to be coagulated directly after application in a solvent bath, otherwise slow replacement of hygroscopic DMAc by water lead to the dissolution and recrystallisation of NaCl on the surface of the coating, thereby changing particle distribution and diameter. The solvent for the coagulation bath was chosen in a way that it allows for a high coagulation speed for the cellulose derivative matrix while possessing a low solubility product for NaCl (e.g., 2-propanol) in order to prevent any loss of the NaCl particles. Due to the highly porous structure created, increased water retention values and increased water vapour permeabilities were observed under preservation of the number of accessible hydroxyl groups of the cellulose derivatives. Both the templated and non-templated coatings could be processed on various textile substrates (e.g., on PET and PP). An important feature of these new materials, i.e. the possibility to apply an antibacterial finish, is discussed within the context of a potential use in the medical sector.     

SEC-MALLS analysis of TEMPO-oxidized celluloses using methylation of carboxyl groups

Two cellouronic acids [sodium (1 → 4)-β-polyglucuronates, CUAs] and one 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized wood cellulose (TOC) became soluble in 8 % lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) after the methylation of C6 carboxyl groups in these samples using trimethylsilyldiazomethane (TMSD). The obtained solutions were diluted to 1 % LiCl/DMAc and subjected to size-exclusion chromatography combined with multi-angle laser-light scattering (SEC-MALLS). Neither depolymerization nor side reactions took place during methylation; this was confirmed by SEC-MALLS and nuclear magnetic resonance analyses, using CUAs as models. The SEC-MALLS analysis of the original wood cellulose and the carboxyl-methylated TOC prepared from it, using 1 % LiCl/N,N-dimethyl-2-imidazolidinone and 1 % LiCl/DMAc, respectively, as eluents, showed that the weight-average degree of polymerization of the original wood cellulose decreased from 3,100 to 2,210 through TEMPO-mediated oxidation. The molecular-mass distributions of the original wood cellulose and the TOC both consisted of one large peak with a small shoulder, indicating that some of the oxidized hemicelluloses remained in the TOC. The combination of methylation of carboxyl groups in polysaccharides using TMSD and subsequent SEC-MALLS analysis using 1 % LiCl/DMAc as an eluent may be applicable not only to TOCs, but also to other polysaccharides with carboxyl groups, for evaluation of their molecular-mass parameters.     

SEC–MALLS analysis of ethylenediamine-pretreated native celluloses in LiCl/<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylacetamide: softwood kraft pulp and highly crystalline bacterial,tunicate, and algal celluloses

Softwood and hardwood bleached kraft pulps (SBKP and HBKP, respectively) and highly crystalline native celluloses such as algal, tunicate, bacterial and cotton lint celluloses were dissolved in 8 % (w/v) LiCl/N,N-dimethylacetamide (DMAc) after ethylenediamine (EDA) pretreatment. Complete dissolution of SBKP and other highly crystalline native celluloses in 8 % LiCl/DMAc was achieved after solvent exchange from EDA to DMAc through methanol. Neutral sugar composition analysis showed no significant differences between the original and EDA-treated pulps. A combination of size-exclusion chromatography and multi-angle laser light scattering (SEC–MALLS) was used to analyze the cellulose solutions after dilution to 1 % (w/v) LiCl/DMAc. The 0.05 % (w/v) solutions of highly crystalline cellulose in 1 % (w/v) LiCl/DMAc contained entangled molecules, and therefore 0.025 % (w/v) cellulose solutions in 1 % (w/v) LiCl/DMAc were used in the SEC–MALLS analysis to obtain reliable conformation plots (or double-logarithmic plots of molecular mass vs. root-mean-square radius). All the cellulose samples except SBKP gave conformation plots with slope values of 0.56–0.57, showing that these cellulose molecules had random-coil conformations. In contrast, SBKP gave a slope value of 0.35, indicating that some branched structures were present in the high-molecular-mass fraction. Double-logarithmic plots of the reduced viscosities of the cellulose solutions in 1 % (w/v) LiCl/DMAc versus the molecular mass were linear, except for SBKP, also suggesting the presence of anomalous cellulose structures in SBKP.     

The cellulose solvent system N,N-dimethylacetamide/lithium chloride revisited: the effect of water on physicochemical properties and chemical stability

The water content in the binary systemN,N-dimethylacetamide/lithium chloride (DMAc/LiCl), acommon cellulose solvent, has been proven to be a crucial parameter. A quickdetermination of water content in DMAc based on the solvatochromism of aUV-active betain probe dye has been developed and validated. An analogousmethod, based on the solvatochromic fluorescence shift ofZelinskij's dye, which strongly depends on thesolventpolarity, was established for water determination in DMAc containing LiCl.Precise physicochemical data of the system DMAc/LiCl, such as density,viscosity, and conductivity, have been obtained. The limiting solubility forLiCl in absolute DMAc is 8.46 wt%. As shown by lightscattering experiments, water in DMAc/LiCl induces aggregation upon standingforlonger periods of time, which is even more prominent for diluted solutions andthose having a poor state of dissolution.     

SEC-MALLS analysis of softwood kraft pulp using LiCl/1,3-dimethyl-2-imidazolidinone as an eluent

Various cellulose and pulp samples including softwood bleached kraft pulp (SBKP) were dissolved in 8% lithium chloride/1,3-dimethyl-2-imidazolidinone (LiCl/DMI) and 8% LiCl/N,N-dimethylacetamide (DMAc), and the obtained solutions were subjected to size-exclusion chromatographic analysis with multi-angle light scattering detection (SEC-MALLS). Although SBKP was not completely soluble in 8% LiCl/DMAc, 1% LiCl/DMI always gave a clear solution of SBKP without centrifugation. Molecular mass (MM) and MM distribution measurements using 1% LiCl/DMI as an eluent for the SEC-MALLS analysis revealed that SBKP had MM higher than those of the other cellulose and pulp samples at the same elution volume. The slope of the conformation plots for SBKP showed an anomalously low value of 0.41, while those for other cellulose and pulp samples were in the range of 0.57–0.59, which corresponds to the normal random coil conformations. These results indicate that some compact structures like branches or cross-linkages other than molecular-dispersed states are present in the high MM region of SBKP, which can be detected when the LiCl/DMI solvent system is used as the solvent as well as the eluent for the SEC-MALLS analysis. On the other hand, no such structures were observed for the other cellulose and pulp samples including softwood bleached sulfite pulps. Thus, the compact structures present in SBKP are likely to be susceptible to acid treatments.     

Quantum-chemical simulation of interaction of polycaproamide with a lithium chloride solution in dimethylacetamide

Quantum-chemical calculations of interaction between lithium chloride and dimethylacetamide (DMAc) and between the polycaproamide model fragment CH₃NHCO(CH₂)₅NHCOCH₃ and a lithium chloride solution in DMAc were performed. The software package GAMESS with the MINI basis set was used in the calculations. Models of the solution included 2 LiCl molecules and 8–16 DMAc molecules. All of these models suggest three potential energy minimums corresponding to three stable structures that differ in the relative arrangement of lithium and chloride ions. A decrease in the amount of solvent in the system leads to transition from Li⁺(DMAc)₄Cl^- to Li⁺...Cl^-(DMAc)₃ and then to the (LiCl)₂(DMAc)₂ species, which crystallizes to form the 1: 1 crystal solvate. The mechanism of dissolution of polycaproamide in DMAc containing lithium chloride was refined.     

Characterization of cellulose by SEC-MALLS

Norway spruce (Picea abies) cellulose samplesdissolved in lithium chloride/N,N-dimethyl-acetamide(LiCl/DMAc) covering a wide range of average molecular weights were analyzed bysize exclusion chromatography (SEC) and multi-angle laser light detection(MALLS). The molecular weight distribution of the samples was compared to themolecular weight distribution of cotton linters cellulose samples. To obtaincomplete dissolution of high-molecular-weight wood cellulose, previouslypublished procedures for dissolving cellulose in LiCl/DMAc were modified. SECseparation was performed using macroporous monodisperse polymer particles ascolumn matrix. The refractive index increment (dn/dc) forcellulose in 0.5% LiCl/DMAc was found to be 0.104. The radius of gyration,R_G, of cellulose in 0.5% LiCl/DMAc depended on the molecular weight,M, according to the relation R_G M^0.55. Celluloseprepared from sprucewood by the sulfite cooking process had a broad molecularweight distribution compared to cotton linters cellulose.     

Measurement of the flexibility of wet cellulose fibres using atomic force microscopy

Flexibility and modulus of elasticity data for two types of wet cellulose fibres using a direct force–displacement method by means of AFM are reported for never dried wet fibres immersed in water. The flexibilities for the bleached softwood kraft pulp (BSW) fibres are in the range of 4–38 × 10¹² N^?1 m^?2 while the flexibilities for the thermomechanical pulp (TMP) fibres are about one order of magnitude lower. For BSW the modulus of elasticity ranges from 1 to 12 MPa and for TMP between 15–190 MPa. These data are lower than most other available pulp fibre data and comparable to a soft rubber band. Reasons for the difference can be that our measurements with a direct method were performed using never dried fibres immersed in water while other groups have employed indirect methods using pulp with different treatments.     

Multi-technique surface characterization of bio-based films from sisal cellulose and its esters: a FE-SEM, μ-XPS and ToF-SIMS approach

Bio-based films were prepared from LiCl/DMAc solutions containing sisal cellulose esters (acetates, butyrates and hexanoates) with different degrees of substitution (DS 0.7–1.8) and solutions prepared with the cellulose esters and 20 wt% sisal cellulose. A novel approach for characterizing the surface morphology utilized field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and contact angle analysis. XPS and ToF-SIMS were a powerful combination while investigating both the ester group distribution on the surface and effects of cellulose content on the film. The surface coverage by ester aliphatic chains was estimated using XPS measurements. Fibrous structures were observed in the FE-SEM images of the cellulose and bio-based films, most likely because the sisal cellulose chains aggregated during dissolution in LiCl/DMAc. Therefore, the cellulose aggregates remained after the formation of the films and removal of the solvent. The XPS results indicated that the cellulose loading on the longer chain cellulose esters films (DS 1.8) increased the surface coverage by ester aliphatic chains (8.2 % for butyrate and 45 % for hexanoate). However, for the shortest ester chains, the surface coverage decreased (acetate, 42 %). The ToF-SIMS analyses of cellulose acetate and cellulose hexanoate films (DS 1.8) revealed that the cellulose ester groups were evenly distributed across the surface of the films.     

Low‐energy collision‐induced dissociation (low‐energy CID), collision‐induced dissociation (CID), and higher energy collision dissociation (HCD) mass spectrometry for structural elucidation of saccharides and clarification of their dissolution mechanism in DMAc/LiCl

The dissolution mechanism of oligosaccharides in N,N‐dimethylacetamide/lithium chloride (DMAc/LiCl), a solvent used for cellulose dissolution, and the capabilities of low‐energy collision‐induced dissociation (low‐energy CID), collision‐induced dissociation (CID), and higher energy collision dissociation (HCD) for structural analysis of carbohydrates were investigated. Comparing the spectra obtained using 3 techniques shows that, generally, when working with monolithiated sugars, CID spectra provide more structurally informative fragments, and glycosidic bond cleavage is the main pathway. However, when working with dilithiated sugars, HCD spectra can be more informative providing predominately cross‐ring cleavage fragments. This is because HCD is a nonresonant activation technique, and it allows a higher amount of energy to be deposited in a short time, giving access to more endothermic decomposition pathways as well as consecutive fragmentations. The difference in preferred dissociation pathways of monolithiated and dilithiated sugars indicates that the presence of the second lithium strongly influences the relative rate constants for cross‐ring cleavages vs glycosidic bond cleavages, and disfavors the latter. Regarding the dissolution mechanism of sugars in DMAc/LiCl, CID and HCD experiments on dilithiated and trilithiated sugars reveal that intensities of product ions containing 2 Li⁺ or 3 Li⁺, respectively, are higher than those bearing only 1 Li⁺. In addition, comparing the fragmentation spectra (both HCD and CID) of LiCl‐adducted lithiated sugar and NaCl‐adducted sodiated sugar shows that while, in the latter case, loss of NaCl is dominant, in the former case, loss of HCl occurs preferentially. The compiled evidence implies that there is a strong and direct interaction between lithium and the saccharide during the dissolution process in the DMAc/LiCl solvent system.     

Preparation of cellulose samples for size-exclusion chromatography analyses in studies of paper degradation

Hydrolytic degradation of cellulose was shown to take place during the activation procedure in distilled water during the dissolution procedure of cellulose samples from papers for size-exclusion chromatography analyses in the lithium chloride-N,N-dimethylacetamide (DMAc) solution system. The use of dilute aqueous sodium hydroxide solution in the activation procedure prevents hydrolytic degradation of cellulose during the dissolution procedure, especially in the case of samples of aged papers with low pH. The use of the freeze-drying technique provides samples of cellulose ready-made for dissolution in lithium chloride-N,N-dimethylacetamide solution.     

The residual amide content of cellulose sequentially solvent-exchanged and then vacuum-dried

Most celluloses are soluble in 8 mass % lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) and/or 8 mass % LiCl/1,3-dimethyl-2-imidazolidinone (LiCl/DMI) with solvent-exchange treatment from water to DMAc or DMI through acetone. In this study, the residual DMAc or DMI adsorbed on celluloses after the solvent-exchange and then vacuum-drying at 60 °C for 48 h was determined by UV spectroscopy and elementary analysis. Significant amounts of DMI or DMAc remain in the solvent-exchanged celluloses even after vacuum drying: about 1.2 mmol/g and 1.0 mmol/g for DMI and DMAc, respectively. Thus, corrections of molecular-mass parameters of celluloses, which were reported in previous literatures based on the assumption that no residual amides are present in the solvent-exchanged and then vacuum-dried celluloses, are needed.     

纤维素醋酸酯的均相合成

纤维素的非均相反应取代不均匀、产率低。本文用纤维素在LiCl／DMAc溶液中的均相反应。制得了纤维素三醋酸酯(CTA)、纤维素二醋酸酯(CDA)、纤维素—醋酸酯(CMA),并对产品结构性能进行了表征。     

Superhydrophobic foam-like cellulose made of hydrophobized cellulose fibres

Wood (kraft) pulp was first dried into a low-density foam-like material by solvent-exchange with anhydrous ethanol. X-Ray tomography showed that, while pulp fibres are flat and resemble ribbons when dried from water, those dried from ethanol are quasi-tubular, inferring that capillary forces derived from a low surface tension solvent are not strong enough to promote fibre lumen collapse, contrary to what happens in water. When the resulting foam-like pulp was then subjected to a vapour phase reaction with trichloromethylsilane (TCMS) a silicon based polymeric coating was created on the surface of the fibres, and the totality of the hydroxyl groups (–OH) on the external surface of cellulose fibres and the internal surface of micropores in the fibre wall became silylated, whereas the surface of the nanopores was inaccessible to TCMS. The novelty lies in the ability to modify both the external surface and the internal micropore structure of cellulose fibres from 50 to 100 % silane coverage, which results in a novel superhydrophobic material, with a contact angle of approximately 150°. This is the first time cellulose is hydrophobized both internally and externally. We refer to the resulting foam as Cellufoam.     

The effect of water on cellulose solutions in DMAc/LiCl

The solution state of cellulose in the system N,N-dimethylacetamide/lithium chloride (DMAc/LiCl) depends on various factors such as cellulose concentration, provenience (cotton, hardwood, softwood) and chemical history (pulping, pretreatment, bleaching) of cellulose, LiCl concentration, activation method, dissolution conditions (time, shaking), and water content. In particular the influencing of the latter has been intensively investigated in our present studies. Working in anhydrous conditions is not practicable for routine size exclusion chromatography (SEC) analysis. Especially in solutions diluted to SEC levels (0.9 wt% LiCl), an aggregation induced by water was observed. Depending on the time of dissolution and on the amount of water, changes in the solution state were observed. In some cases the amount of aggregates increases within a few minutes. This is reflected by a time-dependent increase in the scattering intensity and quantitatively proved by an increase in the aggregation peak in the calculated intensity distributions. With less soluble pulps, traces of water (lower than 0.01 M) can already suffice to induce and promote aggregation. To disturb a “good” stock solution, the concentration of water must be higher than 0.05 M. The aggregates formed correspond to the model of the fringed micelle.     

Preparation of cellulose hydrogels via self-assembly in DMAc/LiCl solutions and study of their properties

Cellulose-based hydrogels have been prepared from solutions of hardwood and flax lignocelluloses and cotton cellulose in an N,N-dimethylacetamide–lithium chloride (DMAc/LiCl) mixture by regeneration and subsequent self-assembly of cellulose chains. The main physicochemical characteristics of the hydrogels have been investigated. It has been shown that they can retain large amounts of water (up to 2500 wt %) and have high porosity and specific surface area. The studied hydrogels are classical stable 3D structures; however, unlike other hydrogels, they possess high stability in aqueous medium and irreversibility of gelation.     

New solvent for polyrotaxane. I. Dimethylacetamide/lithium chloride (DMAc/LiCl) system for modification of polyrotaxane

Dimethylacetamide (DMAc) containing 8–9% (w/w) of lithium chloride (LiCl) or lithium bromide (LiBr) was found to be a good solvent for a polyrotaxane consisting of poly (ethylene glycol) (PEG) and α‐cyclodextrin (CD). In the new DMAc/LiCl solvent system, various modification reactions such as acetylation, direct dansylation, and reaction with acid chloride could be performed, which was unattainable in the previously reported solvents, i.e., dimethylsulfoxide (DMSO) and aqueous sodium hydroxide solution. Acetylation with acetic anhydride and direct dansylation of the polyrotaxane were investigated in detail in comparison with reactions in DMSO. The dissolution of the polyrotaxane in DMAc/LiCl suggested that the solubility and insolubility of the polyrotaxane is strongly in relation to the inter‐ and intramolecular hydrogen bonding of the polyrotaxane. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 532–538, 2006     

Nanofibrillated cellulose/nanographite composite films

Though research into nanofibrillated cellulose (NFC) has recently increased, few studies have considered co-utilising NFC and nanographite (NG) in composite films, and, it has, however been a challenge to use high-yield pulp fibres (mechanical pulps) to produce this nanofibrillar material. It is worth noting that there is a significant difference between chemical pulp fibres and high-yield pulp fibres, as the former is composed mainly of cellulose and has a yield of approximately 50 % while the latter is consist of cellulose, hemicellulose and lignin, and has a yield of approximately 90 %. NFC was produced by combining TEMPO (2,2,6,6-tetramethypiperidine-1-oxyl)-mediated oxidation with the mechanical shearing of chemi-thermomechanical pulp (CTMP) and sulphite pulp (SP); the NG was produced by mechanically exfoliating graphite. The different NaClO dosages in the TEMPO system differently oxidised the fibres, altering their fibrillation efficiency. NFC–NG films were produced by casting in a Petri dish. We examine the effect of NG on the sheet-resistance and mechanical properties of NFC films. Addition of 10 wt% NG to 90 wt% NFC of sample CC2 (5 mmol NaClO CTMP-NFC homogenised for 60 min) improved the sheet resistance, i.e. from that of an insulating pure NFC film to 180 Ω/sq. Further addition of 20 (CC3) and 25 wt% (CC4) of NG to 80 and 75 wt% respectively, lowered the sheet resistance to 17 and 9 Ω/sq, respectively. For the mechanical properties, we found that adding 10 wt% NG to 90 wt% NFC of sample HH2 (5 mmol NaClO SP-NFC homogenised for 60 min) improved the tensile index by 28 %, tensile stiffness index by 20 %, and peak load by 28 %. The film’s surface morphology was visualised using scanning electron microscopy, revealing the fibrillated structure of NFC and NG. This methodology yields NFC–NG films that are mechanically stable, bendable, and flexible.     

Self-reinforced cellulose nanocomposites

A self-reinforced cellulosic material was produced exclusively from regenerated cellulose microcrystals. The level of reinforcement was controlled by tailoring the crystallinity of cellulose by controlling the dissolution of microcrystalline cellulose (MCC) before its regeneration process. After the cellulose regeneration a self-reinforced material was obtained in which cellulose crystals reinforced amorphous cellulose. This structure was produced by dissolution of MCC in a non-derivatising cosolvent N,N-dimethylacetamide/LiCl followed by subsequent cellulose regeneration in distilled H₂O. The reduction of the overall crystallinity of self-reinforced regenerated cellulose was dependent on the dissolution time of the cellulose precursor. The crystallinity of regenerated cellulose was determined by wide angle X-ray diffraction. A reduction in crystal size from microcrystalline cellulose to regenerated cellulose was observed with increasing dissolution time in DMAc/LiCl cosolvent. The reduction in degree of crystallinity of regenerated cellulose led to a decrease in the tensile mechanical performance and thermal stability of the regenerated cellulose. The controlled dissolution of microcrystalline cellulose resulted in the modification of structural, physical, thermal properties and moisture uptake behaviour of regenerated cellulose.