FORM 2
THE PATENT ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A process for preparation of cellulose solution for spinning of fibres.
APPLICANTS
Aditya Birla Science and Technology Company Pvt Ltd, Plot number 1 and 1-A/1, Taloja, MIDC, Taluka- Panvel, District- Raigad- 410208, Maharashtra, India.
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes this invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
[001] The present invention relates to a process for preparation of cellulose solution for spinning of fibres. More particularly, the present invention relates to a process for preparation of a cellulose solution in a thermally and chemically stable solvent.
BACKGROUND OF THE INVENTION
[002] The conventional method for the commercial preparation of cellulosic fibres is the viscose process. Cellulosic fibres of the viscose type are manufactured by dissolving sodium xanthate in caustic soda to form a syrup-like spinning solution known as viscose and commonly referred to as a spinning solution. The spinning solution is spun by extruding it through fine holes / spinnerets into a coagulating bath of sulphuric acid and salts which neutralise the alkaline content of the viscose solution and regenerate the original cellulose as continuous filaments. Since the viscose process involves use of hazardous chemicals such as carbon disulphide and sulphuric acid, it is a major concern for the environment.
[003] Another process to dissolve cellulose is the Lyocell process which involves the dissolution of cellulose/pulp in a non-derivatizing solvent such as N-methylmorpholine-N-oxide (NMMO). To economise the process, spent NMMO is recovered and recycled after purifying it. However, there are a few disadvantages of this process. First, due to the degradation of NMMO during the process, entire quantity of NMMO is not recovered. Second, even though the Lyocell process is environmentally more accepted, the resulting fibres are easily fibrillated. Third, NMMO as a solvent is thermally unstable, leading to its degradation and making it prone to explosion at a higher temperature, particularly at dissolution and spinning temperature. Due to this, in Lyocell process, the control parameters are more stringent and as a result during cellulose dissolution the temperature is maintained at 115°C. Fourth, in the Lyocell process using NMMO as solvent, a

stabilizer such as propyl gallate is used during cellulose dissolution and processing to inhibit cellulose-NMMO degradation and avoid the runaway conditions.
[004] Therefore, it is necessary to use a non-derivatizing solvent system for the preparation of cellulosic fibres and develop a process, which is simple, cost effective and environment friendly. Although imidazolium based ionic liquids are known for cellulose dissolution and fibre spinning, the process is not yet commercialized, mainly, due to issues in recycling of ionic liquid solvents. Due to very low vapour pressure, distillation of ionic liquid is not possible and other purification process may result in the alteration of anion/cation ratio as the ionic liquid is a two component system, i.e., cation and anion.
[005] Therefore, there is a need of a process for the preparation of cellulosic solution for spinning of fibres which solves some of the problems of the prior art.
SUMMARY OF THE INVENTION
[006] According to the present invention, there is provided a process for preparation of cellulose solution, comprising the steps of:
a) mixing a pre-determined quantity of shredded cellulosic pulp to an aqueous zwitterionic liquid solvent, the mixing being carried out for 10 mins to 30 mins at 40°C to 80°C to form a slurry;
b) heating the slurry to a temperature in the range of 80°C to 150°C and applying a vacuum of 20 torr to 100 torr to remove excess water to obtain a solution; and
c) stirring the solution obtained in step b) for 60 mins to 120 mins at 100°C to 150°C under vacuum of 50 torr to 150 torr to dissolve the cellulose in zwitterionic liquid solvent, wherein the cellulose concentration in the solution is 4% to 15% and wherein the aqueous zwitterionic liquid solvent contains one or more zwitterionic liquids.

DETAILED DESCRIPTION OF THE EMBODIMENTS
[007] The embodiments of the present invention eliminate or reduces the aforementioned problems of the prior art by providing a process for preparation of cellulosic solution in a thermally and chemically stable solvent.
[008] The present invention discloses use of a solvent comprised of zwitterionic liquids for cellulose dissolution to make moulded cellulose articles such as film or fibres.
[009] The present process provides safer and less stringent processing conditions for making cellulosic fibre as compared to the Lyocell process. It provides a solvent system wherein both cations and anions are covalently bonded together which is more advantageous in cellulose dissolution and their recycling as the anion/cation balance is not disturbed during the purification process.
[010] According to the process of the present invention, cellulose solution in a solvent containing zwitterionic liquid is prepared in two steps, namely, slurry and solution preparation. In slurry preparation, a known quantity of shredded pulp is added to the synthesized aqueous zwitterionic liquid (60-85%, w/w) solution having cellulose consistency of 4-12% and mixed well for 10-30 min at 40°C to 80°C. In the solution preparation steps, the temperature of slurry is increased from 40-80°C to 80-150°C and a vacuum of 20 to 100 torr is applied to remove the excess water in such a manner that the resulting mixture contains 7-15% cellulose, 86-79% zwitterionic liquid and 7-6% water over a period of 30-120 min.
[011] After the removal of required amount of water, the zwitterionic liquid-cellulose solution is mixed for 60-120 min at 100-150°C under the vacuum of 50 to 150 torr to dissolve the cellulose in zwitterionic liquid completely. The complete dissolution of cellulose in zwitterionic liquid is

characterized by polarizing optical microscope. The rheology of cellulose solution is measured by rheometer for its homogeneity and moldability at a definite temperature.
[012] In an embodiment, the solvent system contains one or more zwitterionic liquid. In an embodiment, in order to get a spinnable cellulose solution, 7-15% cellulose is dissolved in the solvent system containing one or more zwitterionic liquid at elevated temperature between 80-150°C using sigma mixer for an extended time to obtain an optically clear solution.
[013] A solvent system containing one or more zwitterionic liquids can dissolve 1-20% cellulose comprising of 80-97% α-cellulose, 20-3% hemicellulose and has a degree of polymerization of 400-1200.
[014] In a preferred embodiment, the cellulose solution has more elastic properties which leads to better spinning of the fibres and as a result better quality of fibres.
[015] In a preferred embodiment, the shredded cellulosic pulp may be selected from sulphate pulp
and sulphite pulp.
[016] In a preferred embodiment, the degree of polymerization of shredded cellulosic pulp is the
range of 550DP to 900DP
[017] In a preferred embodiment, the zero shear viscosity of the cellulose solution is in the range
of 1000Pa.s to 6000Pa.s at 120°C.
[018] The cellulose solution in the said solvent system can be converted into cellulosic fibers, films
or particles by precipitating in a dilute solution of the said solvent system in a protic non-solvent,
specifically, water, by wet spinning or air-jet-wet spinning techniques.
[019] Furthermore, in the present invention there is no need for using a stabilizer which makes the present invention more economical than the Lyocell process.

[020] The following experimental examples are illustrative of the invention but not limitative of the scope thereof:
[021] The chemical structure of the zwitterionic liquid used during the below mentioned examples is provided below:

[022] The generic formula of zwitterionic liquid, wherein R2, R4 and R5, are each, independently of one another, an H atom or an organic radical having 1 to 20 carbon atoms, and R1 and R3 are each, independently of one another, an organic radical similar to R2, R4 and R5; one of R1, and R3, has a negative charge at the chain end in the form of carboxylate (-COO-), sulfate or sulfonate (-SO42- or -SO3R6-), phosphate or phosphonate (-PO4- or –PO3R7-), wherein each of R6, R7 is an organic radical with 1 to 5 carbon atoms.
[023] The zwitterionic liquid used in examples 1-6, is prepared as follows:
500g (2.24 mol) of ethyl 6-bromohexanoate was added to 277.5g (2.24 mol) of N-butylimidazole at once in a 2L round bottom flask attached with an overhead stirrer and allowed to stir for 48h at 40°C. After the completion of reaction, as monitored by thin layer chromatography (TLC), the reaction mixture was diluted with 5L of methanol and passed through 3Kg of Amberlyst A-26 (OH-form) ion exchange resin slowly in a column. The solution was concentrated up to 2L and reflux for 4h. The reaction mixture was concentrated under reduced pressure up to complete dryness and dissolved in 2L of water and washed with 500ml dichloromethane, three times each.

The aqueous layer was separated and concentrated under reduced pressure up to complete dryness to obtain 522.5g of 1-carboxyhexyl-3-butylimidazolium zwitterionic liquid (Yield 97.7%) as colourless viscous oil.
Example 1
[024] 40.4 g of sulphate pulp having degree of polymerization of 630±20 was mixed with 575.6g of 74.7% aqueous zwitterionic liquid, 1-carboxyhexyl-3-butylimidazolium to form a slurry of cellulose in zwitterionic liquid. This slurry was mixed at 75°C for 15 min in a sigma mixer speed of 35 rpm. The temperature of slurry was elevated to 100°C and a vacuum of 30 - 50torr was applied for 40 min. Again mixing was continued with increasing speed of 40 rpm and the temperature was elevated to 105°C with a vacuum kept constant to 100 torr to remove water for 1h 20 min. The cellulose solution in zwitterionic liquid was analyzed for its number of undissolved cellulose particles, composition and rheology. The composition: cellulose 7.5%, zwitterionic liquid 86% and water 6.5%. Zero Shear Viscosity: 1130 Pa.s at 120°C.
Number of undissolved particles: < 22
Example 2
[025] 51.7g of sulphate pulp having degree of polymerization of 630±20 was mixed with 544g of 73% aqueous zwitterionic liquid, 1-carboxyhexyl-3-butylimidazolium to form a slurry of cellulose in zwitterionic liquid. This slurry was mixed at 75°C for 15 min in a sigma mixer speed of 35 rpm. The temperature of slurry was elevated to 100°C and a vacuum of 30 – 50 torr was applied for 40 min. Again mixing was continued with increasing speed of 40 rpm and the temperature was elevated to 105°C with a vacuum kept constant to 100 torr to remove water for 1h 20 min. [022] The cellulose solution in zwitterionic liquid was analyzed for its number of undissolved cellulose

composition and rheology. The composition: cellulose 10%, zwitterionic liquid 84% and water 6%. Zero Shear Viscosity: 1700 Pa.s at 120°C.
Number of undissolved particles: < 30
Example 3
[026] 59.8 g of sulphate pulp having degree of polymerization of 630±20 was mixed with 567.9 g of 72.9% aqueous zwitterionic liquid, 1-carboxyhexyl-3-butylimidazolium to form a slurry of cellulose in zwitterionic liquid. This slurry was mixed at 75 °C for 15 min in a sigma mixer speed of 35 rpm. The temperature of slurry was elevated to 100 °C and a vacuum of 30 – 50 torr was applied for 40 min. Again mixing was continued with increasing speed of 40 rpm and the temperature was elevated to 110 °C with a vacuum kept constant to 100 torr to remove water for 1h 20 min. The cellulose solution in zwitterionic liquid was analyzed for its number of undissolved cellulose particles, composition and rheology. The composition: cellulose 11%, zwitterionic liquid 82.8% and water 6.2%. Zero Shear Viscosity: 1960 Pa.s at 120°C.
Number of undissolved particles: < 32
Example 4
[027] 65.21 g of sulphate pulp having degree of polymerization of 630±20 was mixed with 554.8 g of 73 % aqueous zwitterionic liquid, 1-carboxyhexyl-3-butylimidazolium to form a slurry of cellulose in zwitterionic liquid. This slurry was mixed at 75 °C for 15min in a sigma mixer speed of 35 rpm. The temperature of slurry was elevated to 100°C and a vacuum of 30 – 50 torr was applied for 40min. Again mixing was continued with increasing speed of 40rpm and the temperature was elevated to 110°C with a vacuum kept constant to 100 torr to remove water for 1h 35 min. The cellulose solution in zwitterionic liquid was analyzed for its number of undissolved

cellulose particles, composition and rheology. The composition: cellulose 12%, zwitterionic liquid 81% and water 7%. Zero Shear Viscosity: 2500 Pa.s at 120°C.
Number of undissolved particles: < 40
Example 5
[028] 70 g of sulphate pulp having degree of polymerization of 630±20 was mixed with 515.2 g of 75.7% aqueous zwitterionic liquid, 1-carboxyhexyl-3-butylimidazolium to form a slurry of cellulose in zwitterionic liquid. This slurry was mixed at 75°C for 15 min in a sigma mixer speed of 35 rpm. The temperature of slurry was elevated to 100°C and a vacuum of 30 – 50 torr was applied for 40 min. Again mixing was continued with increasing speed of 40 rpm and the temperature was elevated to 110°C with a vacuum kept constant to 100 torr to remove water for 1h 50 min. The cellulose solution in zwitterionic liquid was analyzed for its number of undissolved cellulose particles, composition and rheology. The composition: cellulose 13%, zwitterionic liquid 80% and water 7%. Zero Shear Viscosity: 3060 Pa.s at 120°C.
Number of undissolved particles: < 45.
Example 6
[029] 80.64 g of sulphate pulp having degree of polymerization of 630±20 was mixed with 528 g of 75.7% aqueous zwitterionic liquid, 1-carboxyhexyl-3-butylimidazolium to form a slurry of cellulose in zwitterionic liquid. This slurry was mixed at 75°C for 15 min in a sigma mixer speed of 35 rpm. The temperature of slurry was elevated to 100°C and a vacuum of 30 – 50 torr was applied for 40 min. Again mixing was continued with increasing speed of 40 rpm and the temperature was elevated to 110°C with a vacuum kept constant to 100 torr to remove water for 2h 20 min. The cellulose solution in zwitterionic liquid was analyzed for its number of undissolved

cellulose particles, composition and rheology. The composition: cellulose 15%, zwitterionic liquid 78 % and water 7%. Zero Shear Viscosity: 5860 Pa.s at 120°C.
Number of undissolved particles: < 45.
Example 7
[030] 48.4 g of sulphite pulp having degree of polymerization of 800±20 was mixed with 504 g of 75% aqueous zwitterionic liquid, 1-carboxyhexyl-3-butylimidazolium to form a slurry of cellulose in zwitterionic liquid. This slurry was mixed at 75°C for 15 min in a sigma mixer speed of 35 rpm. The temperature of slurry was elevated to 100°C and a vacuum of 30 – 50 torr was applied for 40min. Again mixing was continued with increasing speed of 40 rpm and the temperature was elevated to 105°C with a vacuum kept constant to 100 torr to remove water for 1h 50 min. The cellulose solution in zwitterionic liquid was analysed for its number of undissolved cellulose particles, composition and rheology. The composition: cellulose 10%, zwitterionic liquid 84% and water 6%. Zero Shear Viscosity: 4990 Pa.s at 120°C.
Number of undissolved particles: < 48
[031] Separately, the zwitterionic liquid used in examples 8 and 9 below prepared as follows: 500 g (2.24 mol) of ethyl 6-bromohexanoate was added to 183.9g (2.24 mol) of N-methylimidazole at once in a 2L round bottom flask attached with an overhead stirrer and allowed to stir for 48 h at 40°C After the completion of reaction, as monitored by TLC, the reaction mixture was diluted with 5 L of methanol and passed through 3Kg of Amberlyst A-26 (OH-form) ion exchange resin slowly in a column. The solution was concentrated up to 2L and reflux for 4h. The reaction mixture was concentrated under reduced pressure up to complete dryness and dissolve in 2 L of water and washed with 500 ml DCM three times each. The aqueous layer was separated and concentrated

under reduced pressure up to complete dryness to obtain 432.5g of 1-carboxyhexyl-3-methylimidazolium ionic liquid (Yield 98.2 %) as colorless viscous oil.
Example 8
[032] 48.5g of sulphite pulp having DP of 630±20 was mixed with 493 gm of 76% aqueous zwitterionic liquid 1-carboxyhexyl-3-methylimidazolium to form a slurry of cellulose in zwitterionic liquid. This slurry was mixed at 75°C for 15min in a sigma mixer speed of 35 rpm. The temperature of slurry was elevated to 100°C and a vacuum of 30 - 50torr was applied for 40min. Again mixing was continued with increasing speed of 40 rpm and the temperature was elevated to 105°C with a vacuum kept constant to 100 torr to remove water for 1h 20 min. The cellulose solution in zwitterionic liquid was analyzed for its composition, rheology and undissolved particles. The composition: cellulose 10.14 %, zwitterionic liquid 81.8 % and water 8.06%. Zero Shear Viscosity: 3200 Pa.s at 120°C.
Number of undissolved particles: < 28
Example 9
[033] 70 g of sulphate pulp having DP of 630+20 was mixed with 553 g of 72.8% aqueous zwitterionic liquid 1-carboxyhexyl-3-methylimidazolium to form a slurry of cellulose in zwitterionic liquid. This slurry was mixed at 75°C for 15min in a sigma mixer speed of 35 rpm. The temperature of slurry was elevated to 100°C and a vacuum of 30 – 50 torr was applied for 40 min. Again mixing was continued with increasing speed of 40rpm and the temperature was elevated to 105°C with a vacuum kept constant to 100torr to remove water for 1h 20 min. The cellulose solution in zwitterionic liquid was analyzed for its composition, rheology and

undissolved particles. The composition: cellulose 13%, zwitterionic liquid 80.4% and water 6.6%. Zero Shear Viscosity: 2400 Pa.s at 120°C.
Number of undissolved particles: < 35
[034] Separately, the zwitterionic liquid used in examples 10 below prepared as follows: 500g (2.24 mol) of ethyl 6-bromohexanoate was added to 242.3 g (2.24 mol) of 1-allylimidazole at once in a 2L round bottom flask attached with an overhead stirrer and allowed to stir for 48 h at 40°C After the completion of reaction, as monitored by TLC, the reaction mixture was diluted with 5 L of methanol and passed through 3 Kg of Amberlyst A-26 (OH-form) ion exchange resin slowly in a column. The solution was concentrated up to 2L and reflux for 4h. The reaction mixture was concentrated under reduced pressure up to complete dryness and dissolve in 2 L of water and washed with 500 ml DCM three times each. The aqueous layer was separated and concentrated under reduced pressure up to complete dryness to obtain 446.2 g of 1-carboxyhexyl-3-allylimidazolium ionic liquid (Yield 95.6 %) as colorless viscous oil.
Example 10
[035] 54.4 g of sulphite pulp having degree of polymerization of 800±20 was mixed with 561.7 g of 73% aqueous zwitterionic liquid, 1-carboxyhexyl-3-allylimidazolium to form a slurry of cellulose in zwitterionic liquid. This slurry was mixed at 75°C for 15min in a sigma mixer speed of 35 rpm. The temperature of slurry was elevated to 100°C and a vacuum of 30 – 50 torr was applied for 40min. Again mixing was continued with increasing speed of 40rpm and the temperature was elevated to 105°C with a vacuum kept constant to 100 torr to remove water for 1h 20min. The cellulose solution in zwitterionic liquid was analyzed for its number of undissolved

cellulose particles, composition and rheology. The composition: cellulose 10%, zwitterionic liquid 82% and water 8%. Zero Shear Viscosity: 2170 Pa.s at 120°C.
Number of undissolved particles: < 26
[036] Separately, the zwitterionic liquid used in examples 11 below prepared as follows: 500g (2.24 mol) of ethyl 6-bromohexanoate was added to 341g (2.24 mol) of 1-hexylimidazole at once in a 2L round bottom flask attached with an overhead stirrer and allowed to stir for 48 h at 40°C After the completion of reaction, as monitored by TLC, the reaction mixture was diluted with 5 L of methanol and passed through 3Kg of Amberlyst A-26 (OH-form) ion exchange resin slowly in a column. The solution was concentrated up to 2L and reflux for 4h. The reaction mixture was concentrated under reduced pressure up to complete dryness and dissolve in 2 L of water and washed with 500ml DCM three times each. The aqueous layer was separated and concentrated under reduced pressure up to complete dryness to obtain 583.6g of 1-carboxyhexyl-3-hexylimidazolium ionic liquid (Yield 97.8 %) as colorless viscous oil.
Example 11
[037] 54.4 g of sulphate pulp having degree of polymerization of 630±20 was mixed with 577.2 g of 72.5% aqueous zwitterionic liquid, 1-carboxyhexyl-3-hexylimidazolium to form a slurry of cellulose in zwitterionic liquid. This slurry was mixed at 75°C for 15min in a sigma mixer speed of 35rpm. The temperature of slurry was elevated to 100°C and a vacuum of 30 – 50 torr was applied for 40min. Again mixing was continued with increasing speed of 40rpm and the temperature was elevated to 105 °C with a vacuum kept constant to 100 torr to remove water for 1h 20 min. The cellulose solution in zwitterionic liquid was analyzed for its number of undissolved cellulose particles, composition and rheology. The composition: cellulose 10%, zwitterionic liquid

83.7% and water 6.3%. Zero Shear Viscosity: 5120 Pa.s at 120°C. Number of undissolved particles: < 38
[038] The foregoing description of specific embodiments of the present invention has been presented for purposes of description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obvious modifications and variations are possible in light of the above teaching.
[039] The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application thereby enabling others, skilled in the art, to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated.

We Claim:
1. A process for preparation of cellulose solution, comprising the steps of:
a) mixing a pre-determined quantity of shredded cellulosic pulp to an aqueous zwitterionic liquid solvent, the mixing being carried out for 10 mins to 30 mins at 40°C to 80°C to form a slurry;
b) heating the slurry to a temperature in the range of 80°C to 150°C and applying a vacuum of 20 torr to 100 torr to remove excess water to obtain a solution; and
c) stirring the solution obtained in step b) for 60 mins to 120 mins at 100°C to 150°C under vacuum of 50 torr to 150 torr to dissolve the cellulose in zwitterionic liquid solvent, wherein the cellulose concentration in the solution is 4% to 15% and wherein the aqueous zwitterionic liquid solvent contains one or more zwitterionic liquids.

3. The process as claimed in claim 1, wherein the shredded cellulosic pulp is dissolved in the aqueous zwitterionic liquid solvent at temperature in the range of 80°C to 150°C to obtain an optically clear solution having a cellulose concentration of 7-15%.
4. The process as claimed in claim 1, wherein the solution obtained in step c) has 7-15% cellulose, 86-79% zwitterionic liquid and 7-6% water.
5. The process as claimed in claim 1, where in the shredded cellulosic pulp may be selected from
sulphate pulp and sulphite pulp.
6. The process as claimed in claim 1, where in the degree of polymerization of shredded cellulosic
pulp is the range of 550DP to 900DP.
6. The process as claimed in claim 1, wherein the zero shear viscosity of the cellulose solution is in the range of 1000Pa.s to 6000Pa.s at 120°C.