The present invention relates to a solution comprising a) a polysaccharide

b) a quaternary ammonium compound of formula I

wherein R1 to R4 represent organic groups with 1 to 20 carbon atoms and X ^" represents an anion with a carboxylate group and c) a co-solvent comprising a nitrile group and having a boiling point below 100°C at 1 bar.

Solutions of cellulose have a variety of industrial applications. Solutions of cellulose may, for example, be used for the manufacturing of shaped articles such as synthetic cellulose fibers. Solvents for cellulose are N-methylmorpholine-N-oxide or liquid salts know as ionic liquids.

Solutions of cellulose in ionic liquid are, for example, disclosed in WO 2006/108861 . According WO 2006/108861 ionic liquids with heterocyclic ammonium cations are suitable as solvents for cellulose. Quaternary ammonium cations with four substituents to the nitrogen atom are also mentioned. As disclosed in WO 2006/108861 , nearly any anion is a suitable anion to the ionic liquid. Carboxylates, in particular acetate, are found among the preferred anions. The dissolution of cellulose in ionic liquids with quaternary ammonium cations usually requires high temperatures. The obtained solutions remain liquid at high temperatures but solidify with falling temperature.

US 2010/0305249 discloses cellulose solutions comprising cellulose, a tetraalkylammonium alkyl phosphate, which is, for example a tributylmethylammonium alkyl phosphate, and optionally a co-solvent. Other ionic liquids, protic or aprotic non-ionic compounds are mentioned as possible co-solvents. The list of aprotic solvents includes acetonitrile among a variety of high boiling solvents. The cellulose solutions are prepared by dissolving cellulose in the

tetraalkylammonium alkyl phosphate or mixtures thereof with the co-solvent. The purpose of the co-solvent is to lower the viscosity. Due to the co-solvent, the solutions of cellulose remain liquid at lower temperatures. However, it is difficult and energy consuming to remove high boiling solvents from the solutions when required for the later technical application.

US 8901054 discloses cellulose solutions comprising cellulose and tetraalkylammonium salts. A co-solvent is used to lower the melting point of the cellulose solutions, so that the cellulose solu- tions can be handled and processed at lower temperatures. The preferred co-solvent is acetone.

It is an object of this invention to provide improved solutions of cellulose in quaternary ammoni- urn compounds and co-solvents. The solutions should have low viscosity, should be rid of any turbidities and should be stable at low temperatures.

Accordingly, the solution defined above and a process for the preparation of the solution have been found.

To the components of the solution

The solution defined above comprises a polysaccharide. Preferably, the polysaccharide is starch, cellulose or a cellulose derivative, for example cellulose ether or cellulose ester.

In a particularly preferred embodiment of the invention the polysaccharide is cellulose or a cellulose derivative, notably cellulose ether or cellulose ester. In a most preferred embodiment of the invention the polysaccharide is cellulose. Cellulose may be obtained from wood by the kraft process, also known as kraft pulping or sulfate process. The cellulose may also be obtained from cotton or recycled paper. Cellulose includes depolymerized cellulose and in particular mi- crocrystalline cellulose which is obtainable as pulp from fibrous plant material.

The solution further comprises the quaternary ammonium compound of formula I

wherein R ¹ to R ⁴ independently from each other represent organic groups with at maximum 20 carbon atoms and X ^" represents an anion with a carboxylate group. The organic groups may comprise other atoms than carbon and hydrogen; for example, they may comprise oxygen, nitrogen, sulfur or chloride.

In a preferred embodiment, the organic groups do not comprise any other atoms than carbon, hydrogen, oxygen, nitrogen, sulfur and chloride.

In particular, the organic groups do not comprise any other atoms than carbon, hydrogen and oxygen. The organic groups may comprise oxygen notably in form of ether or hydroxy groups.

R ¹ to R ⁴ independently from each comprise 1 to 20 carbon atoms. Preferably R ¹ to R ⁴ inde- pendently from each comprise 1 to16 carbon atoms, in particular 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms. Preferably, at least two of R ¹ to R ⁴ comprise at least 3 carbon atoms; more preferably at least three of R ¹ to R ⁴ comprise at least 3 carbon atoms.

In a most preferred embodiment, R ¹ to R ⁴ independently from each other are hydrocarbon groups with 1 to 20 carbon atoms and do not comprise any other atoms than hydrogen and carbon. The hydrocarbon group may an aliphatic group, which includes saturated and unsaturated aliphatic groups, an aromatic groups or combinations thereof such as aralkyl or alkaryl groups.

Preferred quaternary ammonium compounds are those, wherein R ¹ to R ⁴ independently from each other are selected from C1 to C12 alkyl, alkenyl or alkinyl groups.

In particular, R ¹ to R ⁴ independently from each other represent an aliphatic hydrocarbon group with at maximum 20 carbon atoms whereby at least two of R ¹ to R ⁴ , preferably at least three of R ¹ to R ⁴ comprise at least 3 carbon atoms.

Preferred quaternary ammonium compounds are, for example, compounds wherein the quaternary ammonium cation is

a tetraalkyl-ammonium cation, such as a tetra butyl-ammonium cation,

or a methyl-tributyl ammonium cation,

a trialkyl-allyl ammonium cation, such as a tributyl-allyl ammonium cation or

a dialkyl-diallyl ammonium cation, such as a diethyl-diallyl ammonium cation.

X ^" represents an anion with a carboxylate group. Preferred anions are anions R ⁵ -COO ^" wherein R ⁵ is a saturated or unsaturated hydrocarbon group with 1 to 20 carbon atoms, notably 2 to 16, more preferably 2 to 12 carbon atoms.

Preferably, R ⁵ is a saturated or unsaturated aliphatic group, notably an alkyl group or alkenyl group. Preferred anions X ^" are HsC-COO ^" (acetate), H ₂ C=CH-COO- (acrylate) and

CH ₂ =CH(CH ₃ )-COO- (methacrylate).

The solution may comprise one quaternary ammonium compound of formula I or a mixture of different quaternary ammonium compounds of formula I. In the following the term "quaternary ammonium compound of formula I" shall include mixtures of quaternary ammonium compound of formula I, if not stated otherwise or otherwise obvious from the context.

The preparation of quaternary ammonium compounds of formula I is known. They may be prepared, for example, by reacting a tertiary amine with an alkylating agent. Suitable alkylating agents are alkyl halides, in particular alkyl chlorides, thus obtaining a quaternary ammonium halide. The anion may be replaced by a carboxylate anion via known anion exchange processes. Suitable processes involve the use of ion exchange resins. In a typical anion exchange procedure, a column is loaded with a of strongly basic ion exchange resin (OH form). The ion exchange resin may be transformed into the desired carboxylate form by washing with a 1 N solution of the corresponding carboxylic acid in water or methanol until the pH of the eluate is the same as the original acid solution. 10.0 g of a quaternary ammonium halide is dissolved in a solvent, for example methanol and loaded on the column and the solution is passed over the ion exchange resin. Thereafter the ion exchange resin may further be washed with the solvent. The eluate may be concentrated by distillation, using, for example, a rotary evaporator. The crude quaternary ammonium carboxylate may be dried under reduced pressure and at temperatures of, for example, 40 to 80°C, to remove any residual solvents.

The solution further comprises a co-solvent comprising a nitrile group and having a boiling point below 100°C at 1 bar (normal pressure).

The solution may comprise one co-solvent comprising a nitrile group and having a boiling point below 100°C at 1 bar (normal pressure) or a mixture of such co-solvents.

In the following the term "co-solvent" shall signify a co-solvent comprising a nitrile group and having a boiling point below 100°C at 1 bar (normal pressure) or a mixture of such co-solvents, if not stated otherwise or otherwise obvious from the context.

Preferably, the co-solvent is acetonitrile (boiling point 82°C) or acrylonitrile (boiling point 77°C) or mixtures thereof.

To the solution

Preferably, the solution comprises the quaternary ammonium compound of formula I in a total amount of at least 0.5 parts by weight, in particular of at least 1 part by weight, more preferably of at least 2 parts by weight and most preferably of at least 3 parts by weight per 1 part by weight of the polysaccharide.

Preferably, the solution comprises the co-solvent in an amount of at least 0.1 parts by weight, in particular of at least 1 part by weight, more preferably of at least 2 parts by weight and most preferably of at least 3 parts by weight per 1 part by weight of the polysaccharide. The solution may comprise the quaternary ammonium compound of formula I and the co- solvent in high amounts. However, with such high amounts the concentration of the polysaccharide becomes very low, which is usually not desired. Therefore, both the quaternary ammonium compound of formula I and the co-solvent are each preferably used in a total amount not higher than 30 parts by weight, in particular not higher than 20 parts by weight per 1 part by weight of polysaccharide. Preferably the concentration of the polysaccharide in the solution is at least 2 % by weight, in particular at least 6 % by weight, preferably at least 10 % by weight and most preferably at least 15 % by weight, based on the total weight of the solution. Preferably, the concentration of the polysaccharide in the solution is at maximum 40 % by weight, notably at maximum 30 weight %, preferably at maximum 25 % by weight, based on the total weight of the solution.

The solution may comprise further solvents such as, for example, water, alkanols or other ionic liquids.

In a preferred embodiment, the solution does not comprise further solvents or comprises further solvents in low amounts, only. Preferably, the solution may comprise further solvents in a total amount of at maximum 0.2 parts by weight, notably of at maximum 0.05 parts by weight and more preferably of at maximum 0.005 parts by weight per 1 part by weight of polysaccharide. In a most preferred embodiment, the solution does not comprise further solvents.

The solution may comprise additives, such as stabilizers, biocides, colorants or pigments. In a preferred embodiment, the solution consists to at least 80 % by weight, preferably to at least 90 % by weight, more preferably to at least 95 % by eight and most preferred to at least 99 % by weight of the polysaccharide, the quaternary ammonium compound of formula I and the co-solvent, only. The solution may be prepared by a process wherein a mixture comprising a polysaccharide, a quaternary ammonium compound of formula I and a co-solvent comprising a nitrile group and having a boiling point below 100°C at 1 bar is prepared and kept at an elevated temperature until a solution is obtained. The mixture may be prepared by adding the components in any order. The components may already be heated before they are added to the mixture. A pre-mixture comprising not all components or not the full amount of all components may be heated and the remaining components or amounts of components may be added to the heated pre-mixture. Preferably, the mixture is heated at normal pressure (1 bar) to a temperature of 40 to 120°C and kept at this temperature under stirring until a clear solution is obtained.

The solution may be cooled and kept at room temperature. In case that the solution becomes turbid at room temperature, further co-solvent may be added to keep the solution clear.

The solutions are suitable for a variety of industrial applications. Solutions of cellulose may, for example, be used for the manufacturing of shaped articles such as synthetic cellulose fibers. Solutions of cellulose may also be used in chemical synthesis, for example for the synthesis of cellulose derivatives as cellulose esters or cellulose ethers.

The solutions of this invention are clear. They have low viscosity and are stable at low tempera- tures. Hence the solutions can be easily handled and are very useful for technical applications as listed above.

Examples

Products used in the examples The cellulose used was microcrystalline cellulose obtained from Sigma-Aldrich for short referred to as MCC.

Following quaternary ammonium compounds have been used: Tetra-butyl-ammonium-acetate, for short TBA-Acetate

Formula:

Tetra-butyl-ammonium-acrylate, for short TBA-Acrylate

Formula:

Tri-butyl-methyl-ammonium-acetate, for short TB MA- Acetate

Formula:

Allyl-tri-butyl-ammonium-acetate, for short ATBA-Acetate

Formula:

Allyl-tri-propyl-ammonium-acetate, for short ATPA-Acetate

Formula:

Tri-propyl-methyl-ammonium-acetate, for short TP MA- Acetate

Formula:

TBA-Acetate and TBA-Acrylate have been prepared via anion exchange from TBA-chloride ob- tained from Sigma Aldrich.

TBMA-Acetate has been prepared via anion exchange from TBMA-chloride obtained from Sigma Aldrich. Preparation of Allyl-tri-propyl-ammonium acetate (ATPA-Acetate).

First, quaternary ammonium bromide was prepared from tripropyl-amine and allyl bromide. Thereafter the bromide was replaced by acetate via anion exchange according to the following procedure: A column, loaded with 10 g of acetate ion exchange resin was loaded with a solution of 2.0 g of allyltripropylammonium bromide dissolved in 30 ml. of methanol. The solution was passed over the resin with a flow rate of 1 ml/min and the resin was washed with additional 30 ml of MeOH afterwards. After removing the solvents, the crude product was dried in vacuo at 40 °C to quan- titatively yield allyl-tri-propyl-ammonium-acetate.

Preparation of Allyl-tri-butyl-ammonium acetate (ATBA-Acetate).

ATBA-Acetate war prepared according to the same procedure as ATPA-Acetate; tributyl-amine and allylbromide have been used as starting material.

Preparation of TP MA- Acetate

For the preparation of TP MA- Acetate, 10.00 g (69.80 mmol) of tripropylamine and 12.57 g (139.60 mmol) of dimethyl carbonate were mixed with 20 mL of methanol in a glass pressure vessel. The sealed tube was heated to 120 °C and stirred magnetically for 90 h. After cooling to room temperature, the volatiles were removed in vacuo and methyltripropylammonium methyl carbonate was obtained as a brown wax in 65% yield. For the exchange of the anion, 5.00 g (21.43 mmol) of the carbonate compound were dissolved in 50 mL of acetonitrile and 5 mL of water. After addition of 1.03 equivalents of acetic acid, the solution was stirred at 50 °C for 1 h. The solvent was removed in vacuo, the crude TPMA-Acetate was dissolved in water and filtered through a syringe filter to remove insoluble residues. The water was removed in vacuo and the QUAT was dried at 40 °C in vacuo to yield TPMA-Acetate as a brown oil in quantitative yield. Examples for the dissolution of cellulose

Example 1 : Dissolution of MCC in TBA-Acetate, solvent acrylonitrile

20.0 milli-gram (mg) of MCC and 180.0 mg of tetrabutylammonium acetate were added to a 3 milli-liter (ml) vial. 0.5 ml (405 mg) of acrylonitrile were added and the mixture in the open vial was stirred at 100 °C until a clear, yellow-colored solution was obtained. The solution remained clear after cooling to room temperature (21 °C).

In an alternative method for the preparation of the acrylonitrile comprising solution 20.0 mg of MCC and 180.0 mg of tetrabutylammonium acetate were added to a 3 ml vial. Thereafter 0.2 ml (157 mg) of acetonitrile were added and the open vial was stirred at 75 °C. A clear, colorless solution was obtained after 10 minutes and acetonitrile the solvent was allowed to evaporate. After solidification of the sample, 0.2 mL of acrylonitrile were added and a clear colorless solution was obtained within 3 min. With the alternative method, an increase of viscosity caused by polymerization of acrylonitrile at higher temperatures can be avoided. Example 2: Dissolution of MCC in TBA-Acrylate, solvent acetonitrile

20.0 mg of MCC and 180.0 mg of tetrabutylammonium acrylate were added to a 3 ml vial. 0.2 ml (157 mg) of acetonitrile were added and the mixture was stirred at 80 °C until a clear, color- less solution was obtained.

Example 3: Dissolution of MCC in TBMA-Acetate, solvent acetonitrile

20.0 mg of MCC and 180.0 mg of tributylmethylammonium acetate were added to a 3 ml vial. 0.1 ml (79 mg) of acetonitrile were added and the mixture was stirred at 80 °C until a clear, col- orless solution was obtained.

Example 4: Dissolution of MCC in ATBA-Acetate, solvent acetonitrile

20.0 mg of MCC and 180.0 mg of allyltributylammonium acetate were added to a 3 ml vial. 0.2 ml (157 mg) of acetonitrile were added and the mixture was stirred at 80 °C until a clear, colorless solution was obtained.

Example 5: Dissolution of MCC in ATPA-Acetate, solvent acetonitrile 20.0 mg of MCC and 180.0 mg of allyltripropylammonium acetate were added to a 3 ml vial. 0.2 ml (157 mg) of acetonitrile were added and the mixture was stirred at 80 °C until a clear, colorless solution was obtained.

Comparative Example: Dissolution of MCC in a TBA-Acetate, solvent acetone

20.0 mg of MCC and 180.0 mg of tetrabutylammonium acetate were added to a 3 ml vial. 0.2 ml (157 mg) of acetone were added and the mixture was stirred at 70 °C in a closed vial. The lower temperature and closed vial are due to the lower boiling point of acetone. Even after prolonged stirring time no dissolution of MCC is noticed and the mixture stays being a turbid slurry.

Examples 6 to 10

Further examples 6 to 9 have been performed according to the procedure described in the other examples. The amount of MCC, the amount of the co-solvent and the temperature of stirring have been varied. The compositions of all examples are found in the table below. The amount of the quaternary ammonium compound was 180 mg in all examples: example ammonium co-solvent T (°C) mg of MCC mg of co- compound solvent

1 TBA-acetate acrylonitrile 100 20 405

2 TBA-acrylate acetonitrile 80 20 157

3 TBMA-acetate acetonitrile 80 20 79

4 ATBA-acetate acetonitrile 80 20 157

5 ATPA-acetate acetonitrile 80 20 157

6 TBA-acrylate acetonitrile 80 45 1 15

7 TBMA-acetate acetonitrile 80 60 89

8 ATBA-acetate acetonitrile 80 60 160

9 ATPA-acetate acetonitrile 80 60 104

10 TPMA-Acetate acetonitrile 80 20 84

Comparative TBA-Acetate acetone 70 20 157 example