Method of forming regenerated carbohydrates with solvent systems based on molten ionic liquids
A solution system for biopolymers in the form of carbohydrates based on a molten ionic liquid, additives optionally being contained in the solution system, is described. This solution system contains a protic solvent or a mixture of several protic solvents, and in the case where the protic solvent is solely water, this is present in the solution system in an amount of more than about 5 wt. %. Carbohydrates can be incorporated into the solution system, in particular in the form of starch, cellulose and derivatives thereof, and it can then be used for regeneration of the carbohydrates contained therein. A particularly advantageous process for the preparation of the solution system containing the carbohydrates and for the preparation of regenerated carbohydrates, in particular in the form of regenerated cellulose fibers, is moreover described. The invention accordingly also provides such spun fibers as are distinguished in that they are non-fibrillating. The invention offers in particular economic advantages over the systems of the prior art.
1. A process for the preparation of regenerated biopolymers in the form of carbohydrates, comprising dissolving biopolymers in the form of carbohydrates in a solution system comprising a molten ionic liquid comprising a cation that is formed from compounds which contain at least one five-to six membered heterocyclic radical and a protic solvent, and precipitating dissolved biopolymers in the form of carbohydrates in a coagulation medium, comprising a solvent which does not dissolve the biopolymers and is miscible with the molten ionic liquid, wherein
said protic solvent is selected from the group consisting of
1) water as the sole protic solvent which is present in said solution system in an amount of at least 6 wt. %,
2) at least 0.1 wt. % based on said solution system of at least one protic solvent selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol and 1-butanol; and
3) water and at least one protic solvent selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol and 1-butanol.
2. The process according to claim 1 , wherein the ionic liquid comprises a substituted or unsubstituted imidazolium cation as the cation.
3. The process according to claim 2 , wherein the imidazolium cation of the ionic liquid is substituted by (C 1 -C 6 )-alkyl groups in the 1- and 3-position or in the 1-, 2- and 3-position.
4. The process according to claim 3 , wherein the imidazolium cation is at least one cation selected from the group consisting of 1-ethyl-3-methylimidazolium, 1,3-dimethylimidazolium or 1-butyl-3-methylimidazolium cation.
5. The process according to claim 1 , wherein water is the sole protic solvent and the solution system comprises about 6 to 15 wt. % of water.
6. The process according to claim 1 , wherein said protic solvent is at least 0.1 wt. % based on said solution system of at least one protic solvent selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol and 1-butanol and said solution system comprises the protic solvent in an amount of from about 1 to 10 wt. %.
7. The process according to claim 1 , wherein the anion of the ionic liquid is at least one anion selected from the group consisting of a halide, perchlorate, pseudohalide, sulfate, phosphate, alkyl-phosphate or a C 1 -C 6 -carboxylate ion.
8. The process according to claim 1 , wherein the molten ionic liquid has a melting point of from −100 to +150 ° C.
9. The process according to claim 1 , wherein the ionic liquid is at least one ionic liquid selected from the group consisting of 1-ethyl-3-methylimidazolium acetate, 1,3-dimethylimidazolium acetate, 1-ethyl-3-methyl-imidazolium chloride, 1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium diethylphosphate, 1 -methyl-3 -methylimidazolium dimethylphosphate, 1 -ethyl-3-methylimidazolium formate, 1-ethyl-3-methylimidazolium octanoate, 1,3-diethylimidazolium acetate and 1-ethyl-3-methylimidazolium propionate.
10. The process according to claim 1 , wherein the carbohydrate is cellulose dissolved in the solution system, or a derivative thereof, and has an average degree of polymerization of from about 200 to 3,500 and wherein the cellulose and/or derivative thereof is present in the solution system in an amount of from about 1 to 35 wt. %.
11. The process according to claim 1 , wherein said carbohydrates are esters or ethers of starch and cellulose.
12. The process according to claim 1 , wherein the solution system has a zero viscosity (measured with a rotary viscometer) of between about 5 and 150,000 Pa·s.
13. The process according to claim 1 , wherein the solution system is subjected to wet spinning.
14. The process according to claim 1 , further comprising spinning the solution system comprising the biopolymers for the production of non-fibrillated fibers.
15. The process according to claim 13 , wherein an air gap spinning unit is employed in order to obtain staple fibers having a high degree of crystallinity (CI >0.5).
16. The process according to claim 1 , wherein to adjust specific properties of the precipitated material obtained additives are added, the additives being added to the coagulation medium, the solution system and/or a subsequent modification bath.
17. The process according to claim 16 , wherein additives in the form of microcapsules, pore-forming agents, plasticizers, matting agents, flameproofing agents, bactericides, crosslinking agents, hydrophobizing agents, antistatics and/or coloring agents are used.
18. The process according to claim 1 , wherein said coagulation medium comprises an alcohol, a mixture of alcohols or a mixture of alcohol(s) with water or solely water and no additives are added.
19. The process according to claim 18 , wherein the alcohol is at least one alcohol selected from the group consisting of methanol, ethanol, propanol and/or butanol.
20. The process according to claim 1 , wherein said liquid phase is recovered after partial evaporation.
21. The process according to claim 1 , wherein said molten ionic liquid has a melting point of from −100 to 100° C.
22. The process according to claim 1 , wherein said molten ionic liquid has a melting point of from −30 to 80° C.