Cellulose extraction from wood chip in an ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl)

In the present study, 1-allyl-3-methylimidazolium chloride (AmimCl), an ionic liquid (IL), was used to extract cellulose from pine, poplar, Chinese parasol, and catalpa wood chips. Results show that pine is the most suitable wood species for cellulose extraction with ILs. Its cellulose extraction rate can reach as high as 62% under optimized conditions and its cellulose content is as high as 85% when DMSO/water is used as the precipitant. The dissolution process can be clearly observed by hot stage optical microscopy, and the reaction time can be significantly reduced by microwave irradiation. ¹³C CP/MAS NMR, FTIR, XRD, and SEM were used to analyze the cellulose-rich extracts of pine. Results show that IL dissolves pine wood by destroying inter and intramolecular hydrogen bonds between lignocelluloses. The major component of pine extract is cellulose with a homogeneous and dense structure. After extraction, AmimCl can be easily recycled and reused.     

Acetone-soluble cellulose acetate extracted from waste blended fabrics via ionic liquid catalyzed acetylation

Isolation of cellulose from waste polyester/cotton blended fabrics (WBFs) is a bottleneck for recycling and exploiting waste textiles. The objective of this study was to provide a new environmental-friendly and efficient approach for extracting cellulose derivatives and polyester from WBFs. A Bronsted acidic ionic liquid (IL) N-methyl-imidazolium bisulfate, [Hmim]HSO₄, was used as a novel catalyst for acetylation of cellulose rather than a solvent with the aim to overcome low isolation efficiency associated with the very high viscosity and relatively high costs of ILs. The extraction yield of acetone-soluble cellulose acetate (CA) was 49.3%, which corresponded to a conversion of 84.5% of the cellulose in the original WBFs; meanwhile, 96.2% of the original poly(ethylene terephthalate) (PET) was recovered. The extracted CA was characterized by ¹H NMR, FTIR, XRD and TGA analysis, and the results indicated that high purity acetone-soluble CA and carbohydrate-free PET could be isolated in this manner from WBFs.     

Homogeneous phase synthesis of cellulose carbamate silica hybrid materials using 1-n-butyl-3-methylimidazolium chloride ionic liquid medium

Cellulose carbamate silica hybrid materials can be prepared in 78–84% yield using the homogeneous phase reaction of 3-(triethoxysilyl)propyl isocyanate with cellulose dissolved in 1-n-butyl-3-methylimidazolium chloride ionic liquid and then using NH₄OH catalyzed hydrolysis of triethoxysilyl groups and the sol–gel process. New cellulose carbamate silica hybrid materials produced were characterized by elemental analysis, FT-IR, and TG-DTA. The hydrophilic affinity of these materials is shown to decrease with the degree of substitution of the cellulose hydroxyl groups with carbamate groups.     

Natural wool/cellulose acetate blends regenerated from the ionic liquid 1-butyl-3-methylimidazolium chloride

Dissolution and blending one of the most commonly used natural polymers, i.e., wool using a green solvent ionic liquid is described. The cleaned natural wool from merino sheep was directly dissolved and regenerated from 1-butyl-3-methylimidazolium chloride (BMIMCl) without any modifications. BMIMCl was subsequently used to develop wool/cellulose acetate (CA) blends. Blending modification of wool in this IL green solvent led to significant increase in glass transition temperature (T_g) and thermal stability compared to the pure components. It was found that there exist strong intermolecular hydrogen bonding interactions between regenerated wool and CA. Moreover homogeneous surface morphology was observed in the blends with higher CA concentrations. At the final stage of the blending process, the IL solvent was recycled completely. This work presents a green processing route for development of novel natural wool blended materials.     

Weak gel of chitin with ionic liquid, 1-allyl-3-methylimidazolium bromide

This paper reports the formation of weak gel of chitin with an ionic liquid, 1-allyl-3-methylimidazolium bromide (IL). When a mixture of 5% (w/w) chitin with IL was heated at 100 °C for 48 h, the clear liquid was obtained. The experimental process was observed by the CCD camera view and the SEM analysis. From a mixture of chitin with IL in the higher concentration (7%, w/w), a more viscous material, i.e., a gel-like material was obtained. The rheological evaluations showed that both 5% (w/w) and 7% (w/w) chitins with IL behaved as weak gels.     

Plasticizing effect of 1-allyl-3-methylimidazolium chloride in cellulose acetate based polymer electrolytes

1-Allyl-3-methylimidazolium chloride, [Amim] Cl was used to improve the stability and disrupt the crystallinity of the matrix formed between cellulose acetate (CA) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) by solution casting technique. The sample composition of CA:LiTFSI:[Amim] Cl (14 wt.%:6 wt.%:80 wt.%) exhibits the highest ionic conductivity and has greater ability to retain minimum reduction value of 1.75 × 10⁻³ S cm⁻¹ even after 30 days of storage at room temperature. Increase in [Amim] Cl doping induces greater structural disorderliness which is revealed by the XRD analysis. This is due to the complexation between the added constituents evident from the variation in FTIR spectra. The relaxation time of Li⁺ ions is reduced due to the increase in amorphous region as observed by the shift of loss tangent peaks to higher frequencies and thus enhancing the ionic conductivity.     

Biocomposite films prepared from ionic liquid solutions of chitosan and cellulose

Blends of chitosan and cellulose were successfully produced using 1-butyl-3-methylimidazolium acetate (BMIMAc) as solvent media. Films were prepared from the blends by manually spreading the solution on a flat surface and precipitating the polymers in a mixture of methanol and water. To prevent the shrinkage of films, most of the absorbed water was removed by freeze drying under vacuum. Films prepared from the polymeric solutions were investigated by means of FT-IR, TGA, X-ray diffraction and SEM measurements. The shifting of the bands corresponding to -NH and CO groups of chitosan (FT-IR), the absence of the diffraction peaks at 2θ = 10.7 and 14.9° (XRD), the increased E_a for thermal decomposition for all the polymeric blends (MTGA), and the presence of an apparent homogeneous structure with no phase separation of the two polymers (SEM) provide evidence for the miscibility between chitosan and cellulose in the solid state.     

Preparation of cellulose graft poly(methyl methacrylate) copolymers by atom transfer radical polymerization in an ionic liquid

Cellulose graft poly(methyl methacrylate) copolymers were prepared by atom transfer radical polymerization (ATRP) in an ionic liquid. Cellulose chloroacetate, as a macroinitiator, was first synthesized by direct acylation of cellulose with chloroacetyl chloride without any catalysts under mild conditions in an ionic liquid, 1-allyl-3-methylimidazolium chloride (BMIMCl). Then, the macroinitiator was used for the ATRP of MMA mediated by the CuBr and 2,2′-bipyridine (bpy) catalysis system. The copolymerization was carried out in BMIMCl without homopolymer byproduct. The polymers were easily separated from the catalyst when the ionic liquid was used as reaction medium. The grafting copolymers were characterized by means of ¹H NMR, AFM and GPC. The results showed that the obtained copolymers had grafted polymer chains with well-controlled molecular weight and polydispersity, and the polymerization was a “living/controlled” system. Further, through AFM observation, it was found that the cellulose graft copolymer in solution could aggregate and self-assembly into sphere-like polymeric structure.     

Synthesis of cellulose dehydroabietate in ionic liquid [bmim]Br

A new type of cellulose derivative, cellulose dehydroabietate (CDA), was synthesized by the O-acylation reaction of cellulose with dehydroabietic acid chloride (DHAC) using ionic liquid 1-butyl-3-methylimidazolium bromide ([bmim]Br) as a solvent and 4-dimethyl-aminopyridine (DMAP) as a catalyst. The resulting CDA was characterized by means of FT-IR, X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), and elemental analysis. Also, some properties of CDA were determined. These results showed that CDA has better solubility, water-repellency, and resistance to acids and bases than raw cellulose, and these properties increase with the DS of CDA.     

A facile preparation of gel materials from a solution of cellulose in ionic liquid

This paper reports a facile preparation of a flexible gel material from a solution of cellulose (15% w/w) in an ionic liquid of 1-butyl-3-methylimidazolium chloride by keeping it at room temperature for 7 days. Elemental analysis data indicated that the obtained gel material was composed of cellulose, the ionic liquid, and water. Both XRD and TGA results suggested that crystalline structure of cellulose was largely disrupted in the material. However, the existence of non-crystalline aggregates was assumed by the XRD data of the material. The gel material was probably obtained by the formation of cellulose aggregates in the solution, attributed to the gradual absorption of water. When the material was heated at 120 degrees C, it became soft, and converted into a fluid at 150 degrees C. By keeping the soft material at room temperature for 2 days, a gel material was regenerated, which was more transparent compared with the original material.     

Homogeneous butyrylation and lauroylation of poplar wood in the ionic liquid 1-butyl-3-methylimidazolium chloride

Wood meal was dissolved under identical conditions in the ionic liquid 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl) and homogeneously esterified with butyryl chloride and lauroyl chloride in the presence of triethylamine as a neutralizer. The effect of the molar ratio of reagent to the hydroxyl groups in wood on the properties of the esterified wood and the possible mechanism of the homogeneous esterification of wood in this reaction medium were studied. Furthermore, the physicochemical properties of the esterified wood were characterized by FTIR, solid-state CP/MAS ¹³C NMR, TGA/DTG and SEM. The results confirmed that the homogeneous modifications were successfully processed and highly substituted wood esters could be obtained by reacting the dissolved wood in this homogeneous system.     

Investigations about dissolution of cellulose in the 1-allyl-3-alkylimidazolium chloride ionic liquids

In this work, the 1-allyl-3-alkylimidazolium chloride ionic liquids were synthesized and characterized by increasing carbon atoms (n ≤ 6) of alkyl chains on a cationic 3-imidazole ring. The results indicated that 1-allyl-3-alkylimidazolium chloride with asymmetrical structure on the two sides of a cationic 3-imidazole ring (i.e., n = 1, 2, 6) exhibited alkalinity and lower thermal stabilities, and showed better solubility to the cellulose samples at 60-120 °C than those with symmetrical structures (n = 3, 4). The cellulose samples treated by 20% (w/w) ethylenediamine solution showed better solubility in 1-allyl-3-ethyl, hexyl-imidazolium chloride ionic liquids than that treated with 20% (w/w) NaOH solution at 5 °C for 72 h. XRD and TG analysis indicated that 0 0 2 plane apparent crystallite size as well as thermal stability of the regenerated cellulose samples from the ionic liquids decreased significantly compared with the untreated cellulose samples.     

Acetylation of α-chitin in ionic liquids

Acetylation of α-chitin using acetic anhydride in an ionic liquid, 1-allyl-3-methylimidazolium bromide (AMIMBr), was performed. First, a mixture of chitin and AMIMBr (2% w/w) was heated at 100 °C for 24 h for dissolution. Then, acetic anhydride (5–20 equiv) was added to the solution and the mixture was heated with stirring at desired temperatures for 24 h. The product was precipitated by the addition of the reaction mixture into methanol. The IR spectrum of the product indicated the progress of acetylation. The degrees of substitution (DS), which were determined from the IR spectra, increased with increasing the amounts of acetic anhydride used for the reaction. The highest DS was 1.86, which was obtained by the reaction using 20 equiv of acetic anhydride at 100 °C. The product with this DS value was soluble in DMSO, and thus the structure of the product was further confirmed by ¹H NMR spectroscopy in DMSO-d₆. The DS value estimated by the integrated ratio of signals due to acetyl protons to a signal due to anomeric protons was in good agreement with that determined from the IR spectrum.     

Collagen/cellulose hydrogel beads reconstituted from ionic liquid solution for Cu(II) adsorption

A novel adsorbent, biodegradable collagen/cellulose hydrogel beads (CCHBs), was prepared by reconstitution from a 1-butyl, 3-methylimidazolium chloride ([C₄mim]Cl) solution. The adsorption properties of the CCHBs for Cu(II) ion removal from aqueous solutions were investigated and compared with those of cellulose hydrogel beads (CHBs). The CCHBs have a three-dimensional macroporous structure whose amino groups are believed to be the main active binding sites of Cu(II) ions. The equilibrium adsorption capacity (q_e) of the CCHBs is greatly influenced by the collagen/cellulose mass ratio, and steeply increases until the collagen/cellulose mass ratio exceeds 2/1. The maximum adsorption is obtained at pH 6. The q_e of Cu(II) ions increases with increased initial concentration of the solution. Based on Langmuir isotherms, the maximum adsorption capacity (q_m) of CCHB3 (collagen/cellulose mass ratio of 3/1) is 1.06 mmol/g. The CCHBs maintain good adsorption properties after the fourth cycle of adsorption–desorption.     

Dissolution of cellulose in phosphate-based ionic liquids

Two kinds of alkylimidazolium salts containing dimethyl phosphate or diethyl phosphate were obtained as room temperature ionic liquids synthesized by one step, and both of them have the ability to dissolve untreated cellulose. Especially, 1-ethyl-3-methylimidazolium diethylphosphonate ([EMIM]DEP) could obtain 4 wt% cellulose solution within 10 min under 90. The effects of dissolution temperature on cellulose dissolution time and degree of polymerization were investigated. As dissolution temperature increased, dissolution time was greatly reduced. Both the original and regenerated cellulose samples were characterized with wide-angle X-ray diffraction, thermogravimetric analysis and scanning electron micrograph. The results showed that the crystalline structure of cellulose was converted to cellulose II from cellulose I in native cellulose. It was also found that the regenerated cellulose had good thermal stability with [EMIM]DEP ionic liquid.     

The study of factors affecting the enzymatic hydrolysis of cellulose after ionic liquid pretreatment

Cellulose resource has got much attention as a promising replacement of fossil fuel. The hydrolysis of cellulose is the key step to chemical product and liquid transportation fuel. In this paper a serials of chloride, acetate, and formate based ionic liquids were used as solvents to dissolve cellulose. The cellulose regenerated from ILs was characterized by FTIR and X-ray powder diffraction. From the characterization and analysis, it was found that the original close and compact structure has changed a lot. After enzymatic hydrolysis, different kinds of ionic liquids (ILs) have different yields of the reducing sugar (TRS). They are 100%, 90.72%, and 88.92% from 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]), 1-butyl-3-methylimidazolium formate ([BMIM][HCOO]) respectively after enzymatic hydrolysis at 50 °C for 5 h. The results indicated that the yields and the hydrolysis rates were improved apparently after ILs pretreatment comparing with the untreated substrates.     

Homogeneous modification of cellulose with succinic anhydride in ionic liquid using 4-dimethylaminopyridine as a catalyst

Cellulose, extracted from sugarcane bagasse, was successfully succinylated in ionic liquid 1-buty-3-methylimidazolium (BMIMCl) using 4-dimethylaminopyridine (DMAP) as a catalyst. Parameters investigated included the mass ratio of DMAP/succinic anhydride in a range from 0% to 15%, reaction time (from 30 to 120 min), reaction temperature (from 60 to 110 °C). The succinylated cellulosic derivatives had a degree of substitution (DS) ranging from 0.24 to 2.34. It was found that the DS of succinylated cellulosic derivatives using DMAP as a catalyst was higher than that without any catalyst under the same reaction conditions. The products were characterized by FT-IR, solid-state CP/MAS ¹³C NMR, and thermal analysis. FT-IR and solid-state CP/MAS ¹³C NMR spectra showed that succinoylation occurred at C-6, C-2 and C-3 positions. The thermal stability of the succinylated cellulose decreased upon chemical modification.     

Homogeneous modification of sugarcane bagasse cellulose with succinic anhydride using a ionic liquid as reaction medium

The homogeneous chemical modification of sugarcane bagasse cellulose with succinic anhydride using 1-allyl-3-methylimidazolium chloride (AmimCl) ionic liquid as a reaction medium was studied. Parameters investigated included the molar ratio of succinic anhydride/anhydroglucose units in cellulose in a range from 2:1 to 14:1, reaction time (from 30 to 160min), and reaction temperature (between 60 and 110 degrees C). The succinylated cellulosic derivatives were prepared with a low degree of substitution (DS) ranging from 0.071 to 0.22. The results showed that the increase of reaction temperature, molar ratio of SA/AGU in cellulose, and reaction time led to an increase in DS of cellulose samples. The products were characterized by FT-IR and solid-state CP/MAS (13)C NMR spectroscopy, and thermal analysis. It was found that the crystallinity of the cellulose was completely disrupted in the ionic liquid system under the conditions given. The data also demonstrated that homogeneous modification of cellulose with succinic anhydride in AmimCl resulted in the production of cellulosic monoester. The thermal stability of the succinylated cellulose decreased upon chemical modification.     

Lignocellulose aerogel from wood-ionic liquid solution (1-allyl-3-methylimidazolium chloride) under freezing and thawing conditions

This article reports a facile preparation of a lignocellulose aerogel from a solution of wood in an ionic liquid by cyclic freeze-thaw (FT) process. Trema orientalis wood flour was dissolved in 1-allyl-3-methylimidazolium chloride (AMImCl), an effective ionic liquid, and then repeatedly frozen at -20 °C and thawed at 20 °C for several times, and then finally regenerated in water. The hydrogel obtained was solvent-exchanged to acetone, washed with liquid carbon dioxide, and finally dried by releasing the carbon dioxide at critical temperature to obtain the lignocellulose aerogel. The aerogel had an open 3D fibrillar network and could be transformed from nanofibrillar to sheet-like skeletons with hierarchical micro- and nanoscale morphology and porosity by adjusting the FT treatment cycles. The frequency of FT cycles influenced the intensity, specific surface, crystallinity, and thermostability of the aerogel. This research highlights new opportunities for the development of porous and flexible aerogel scaffolds.