Understanding cellulose dissolution： effect of the cation and anion structure of ionic liquids on the solubility of cellulose

The effect of ionic liquids(ILs) on the solubility of cellulose was investigated by changing their anions and cations. The structural variation included 11 kinds of cations in combination with 4 kinds of anions. The interaction between the IL and cellobiose, the repeating unit of cellulose, was clarified through nuclear magnetic resonance(NMR) spectroscopy. The reason for different dissolving capabilities of various ILs was revealed. The hydrogen bonding interaction between the IL and hydroxyl was the major force for cellulose dissolution. Both the anion and cation in the IL formed hydrogen bonds with cellulose. Anions associated with hydrogen atoms of hydroxyls, and cations favored the formation of hydrogen bonds with oxygen atoms of hydroxyls by utilizing activated protons in imidazolium ring. Weakening of either the hydrogen bonding interaction between the anion and cellulose, or that between the cation and cellulose, or both, decreases the capability of ILs to dissolve cellulose.

Effect of carboxymethyl cellulose on dissolution kinetics of carboxymethyl cellulose-sodium carbonate two-component tablet

Sodium carbonate and carboxymethyl cellulose powders are compressed into two-component tablets with three mass ratios,97%:3%,95%:5% and 93%:7%.The dissolution tests for two-component tablets and reference pure sodium carbonate tablets are carried out at various temperatures.The dissolution process of each tablet is measured by electrical conductivity tracking method and the concentration of dissolved sodium carbonate is quanti fied with calibrated conductivity-concentration converting equation of sodium carbonate.The quanti fied dissolution data is fitted with both surface reaction model and diffusion layer model and the results clearly show that surface reaction model is suggested as the appropriate dissolution model for all measured tablets.Therefore,it is determined that carboxymethyl cellulose is a stable element to remain the dissolution mechanism of tablet unchanged.The dissolution rate constant quanti fied with surface reaction model presents that carboxymethyl cellulose-sodium carbonate two-component tablets obtain signi ficant higher dissolution rate constant than pure sodium carbonate tablet and higher proportion of carboxymethyl cellulose leads to apparent higher dissolution rate constant.The results prove for the usage of carboxymethyl cellulose in most practical applications at a relative low-level,the effect of carboxymethyl cellulose is effective and positive for two-component tablet to enhance the dissolution process and improve dissolution rate constant and this effect is speculated coming from its dynamic physical transforming process in water including dilation and conglutination.

Solubility Behaviour of Cellulose in a Sodium Hydrate/Urea/Thiourea Aqueous Solvent

Cellulose pulps were directly dissolved in a green solvent of sodium hydrate/urea/thiourea/water with different composition for the purpose to prepare new regenerated cellulose fibers or films. The results showed that the highest solubility of cellulose in the solvent with the composition of 8/8/6.5/77.5. The results revealed that the pulp feeding sequence, stirring rate, pre-treatment of pulp and pulp size affected the cellulose concentration in the green solvent. Accordingly, the more effective dissolution method was proposed in order to get higher concentration of cellulose. Furthermore, the properties of solution prepared by different kinds of pulps in the solvent were investigated by ARES rheometer. Rheologieal analyses indicated that all cellulose aqueous solutions in their high concentration were pseudoplastic fluids and sensitive to temperature and tended to transform to gel when temperature increased.

The effect of hydrogen bond acceptor properties of ionic liquids on their cellulose solubility

It is nowadays well-known that ionic liquids can dissolve cellulose. However, little systematic data has been published that shed light onto the influence of the ionic liquid structure on the dissolution of cellulose. We have conducted 1H NMR spec- troscopy of ethanol in a large number of ionic liquids, and found an excellent correlation of the data obtained with the hydro- gen acceptor properties （B-values）. With this tool in hand, it is possible to distinguish between cellulose-dissolving and non-dissolving ionic liquids. A modulating effect of both, the anion of the non-dissolving ionic liquid and its cation was found in solubility studies with binary ionic liquid mixtures. The study was extended to other non-dissolving liquids, namely water and dimethylsulfoxide, and the effect of the cation was also investigated.

Hydrogen bond producers in powerful protic ionic liquids for enhancing dissolution of natural cellulose

The manipulation of hydrogen bonding within protic ionic liquids is conducive to conquering the robust hydrogen bonding interactions in cellulose for its effective dissolution,but it is a great challenge to establish the delicate bal-ance of hydrogen bonding network between solvent and cellulose.Herein,we proposed the concept of“hydrogen bond producers”for urea molecules in 1,1,3,3-tetramethylguanidinium methoxyacetate acid([TMGH][MAA])to enhance the dissolution of cellulose.The optimization of physicochemical properties for[TMGH][MAA]solvent as a function of urea concentration revealed a remark-able increase in cellulose solubility from 13%to 17%(w/w)by adding only 0.25 wt%urea,highlighting the efficiency of[TMGH][MAA]as a power-ful solvent for the dissolution of cellulose.The experimental and simulation results verified that the significant improvement on dissolution of cellulose was attributed to the hydrogen bonding interaction of urea molecules with ion pairs and part of free ions,reducing the interference with the active ions bonded to cellulose.Furthermore,the considerable enhancement on compre-hensive properties of regenerated cellulose films demonstrated the effectiveness of[TMGH][MAA]/urea solvent.The concept of“hydrogen bond producers”presented here opens a new avenue for significantly enhancing the dissolu-tion of natural cellulose,promoting the sustainable development in large-scale processing of cellulose.

Cellulose Solubility in Deep Eutectic Solvents:Inspecting Quantitative Hydrogen-Bonding Analysis

According to the Kamlet-Abraham-Taft(KAT)polarity parameters(α,β,π*),polymers and solvents can be categorized as hydrogen-bond(H-bond)acidic(α>β)or H-bond basic(α<β).Recently,we proposed a quantitative hydrogen bonding(QHB)analysis to predict the solubility of polymers in ionic liquids(ILs)using the product ofΔαΔβ<0 as an indicator,whereΔαis the difference between the H-bond acidic parameters of the polymer and IL,andΔβis the difference in their basicity,while the prerequisite of the“complementary”principle(i.e.,that one component is H-bond acidic and the other is basic)is satisfied.Here,the applicability of QHB analysis was first confirmed by testing the solubilities of carefully chosen polymer/deep eutectic solvent(DES)pairs,as the DESs were eutectic mixtures dominated by hydrogen bonding interactions.Then,our attention focused on the solubility of cellulose in DESs.Our testing results as well as the typical published results were summarized,which indicate that the potential DESs for cellulose dissolution and regeneration must be of the H-bond basic type because the“complementary”principle should be satisfied as a prerequisite.However,the H-bond basic DESs investigated in this study do not show the superior solubility of cellulose that has been commonly observed for H-bond basic ILs,even if the criterion ofΔαΔβ<0 is satisfied for both DESs and ILs.Possible reasons for this discrepancy are given to understand the varying effectiveness in cellulose dissolution for H-bond basic DESs and ILs.