Research of dissolution ability of ionic liquids ofr polysaccharides such as cellulose

Kuzmina, Olga

Imidazolium-based ionic liquids were studied as solvents for cellulose and chitosan. Cellulose solutions and cellulose/chitosan blends were produced in ILs. The best dissolution ability among the studied ILs show acetate containing ILs. It is possible to dissolve up to 18 wt% of cellulose at 110 oC in EMIMAc and up to 20 wt% in BMIMAc. The worst dissolution ability among the studied solvents was shown by BDMIMCl. It was possible to dissolve only 5 wt% of cellulose under the same conditions. In case of BMIMCl, dissolution stops when the concentration of cellulose is more than 14 wt%. The dissolution in EMIMAc, BMIMAc and BDMIMCl was limited by the viscosity of the solutions. By DLS was found that solutions of cellulose in ionic liquids BMIMAc, BMIMCl and EMIMAc represent the steady disperse systems containing polymer aggregates, with sizes of up to 5 times higher than that of a single macromolecule of cellulose of the same molecular weight. The hydrodynamical radius of particles of cellulose in EMIMAc slightly exceeds those in BMIMAc and BMIMCl, with other conditions being equal (humidity of cellulose, concentration of the solution, and the temperature). The influence of water on dissolution ability of ILs was determined. Generally, water has negative influence on cellulose dissolution in ILs, and excess of water should be removed from solution. The size of cellulose aggregates in ILs solutions grows with an increase in the water content of solutions, which may be interpreted in terms of both the deterioration of the solvent and the swelling of particles in the presence of water. The phase diagram of cellulose/BMIMCl/ water system was plotted. A colloid solution useful for technical purposes could be obtained at water content in the BMIMCl solution below 8%. Selected thinners were studies in order to find the appropriate one to facilitate cellulose dissolution in ILs. Cellulose/IL/thinner systems were prepared with different orders of component mixing. The type of the system (the order of component mixing) did not affect the composition of cellulose/IL/thinner systems. The composition of cellulose/IL/thinners systems remained stable even for 4 months. Ethyl acetate and diethyl ether almost completely evaporated from the solution upon heating and facilitated cellulose dissolution in ILs, which was confirmed by mean of 1H NMR spectroscopy. DMSO as DEE and EAc increased the speed of cellulose dissolution in ILs, but it remained in the solution and lowered its viscosity. Both protic and aprotic thinners inhibit the cellulose degradation in obtained films which occurred at its dissolution in ILs. DMSO, DEE and EAc adding could help keep the same DP as for initial sample. The films with highest mechanical properties could be obtained with using aprotic solvents. Produced films obtained became weaker and more fragile with increasing of the thinners content. Aprotic solvent are more efficient for cellulose films production and facilitating the dissolution of cellulose in ILs. Among the studied ILs, EMIMAc and BMIMAc are suitable to produce cellulose/chitosan blends by heating. Microwave treatment wasn’t efficient for chitosan dissolution. Simultaneously blending of components is more efficient than mixing of separately prepared chitosan and cellulose solutions in common solvent. The addition of thinners decreased the viscosity of cellulose solutions and cellulose/chitosan solutions in ILs. The thinners addition decreased slightly the Eact of blended solutions and its values were almost equal to the Eact of solutions without thinners. The sizes of polymer aggregates in blended solutions were bigger in EMIMAc solution than in BMIMAc solution. Addition of thinners decreased the size of polymer aggregations in both IL solutions. Blended films with 3 -10 wt% of chitosan were prepared from the studied solutions. The increasing of chitosan concentration in blends increased the degradation of the cellulose part. DMSO and DEE improve the mechanical properties of blended films. We have not found any pertaining to better dissolution of MCCh in ILs and its blending with cellulose. Chitosan is a promising polysaccharide for cellulose modification, but the process of blend production in ILs still needs to be studied. Glycerine/POE-400 mixture was chosen as plasticizer. By means of TG-IR was found that the adding of plasticizers to wash-bath is more preferable. Much less sugar residues were found in wash-bash, and its amount increased slightly at longer dissolution, which indicates that cellulose degrades slowly at the temperatures studied. The traces of ILs were observed in the FTIR spectra of cellulose films and wash-baths. A residual content of 0,7- 3 % ILs, was typically found, therefore water alone is not efficient at the complete removal of ILs during cellulose coagulation. It is possible to recover ILs from the water-bath by distillation. Recovered ILs have a moisture about 7-11 %, and despite the same dissolving ability the mechanical properties of the films obtained from recovered ILs are worse than those obtained from fresh ILs. The ability of ILs to dissolve polysaccharides was studied in this work. The influence of water, thinners, and other polysaccharides was analyzed and was concluded that ILs are effective reusable solvents for processing polysaccharides into a films, which may also be viable on a technical scale.

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Kuzmina, Olga: Research of dissolution ability of ionic liquids ofr polysaccharides such as cellulose. 2012.

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