OXIDATIVE DEGRADATION OF CELLULOSE ETHERS

Abstract

The invention relates to a method for producing a low-viscosity cellulose ether product, and to the use thereof.

Claims

1. A method for producing a low-viscosity cellulose ether product, comprising the steps: (i) providing at least one water-moist cellulose ether starting material; (ii) adding at least one oxidising agent to the cellulose ether starting material from step (i) under shear; (iii) treating the mixture obtained in step (ii) at temperatures in the range of 20-100° C.; (iv) drying the mixture obtained in step (iii); and, (v) adding at least one alkaline salt to the mixture obtained in step (iv) to obtain the low-viscosity cellulose ether product, the cellulose ether starting material having a higher solution viscosity than the cellulose ether product.

2. The method according to claim 1, wherein the cellulose ether starting material is selected from hydroxypropyl cellulose (HPC), methyl hydroxypropyl cellulose (MHPC) or methyl hydroxyethyl cellulose (MHEC).

3. The method according to claim 1, wherein the dry content of the water-moist cellulose ether starting material from step (i) is 20-90 wt. %, based on the total mass thereof.

4. The method according to claim 1, wherein the solution viscosity of the cellulose ether starting material from step (i) as a 2% aqueous solution is in the range of 100-60,000 mPas.

5. The method according to claim 1, wherein the oxidising agent is selected from peroxides and salts thereof, peracids and salts thereof, or O.sub.2 and O.sub.3.

6. The method according to claim 1, wherein the oxidising agent is added in solution, in solid form or as a gas.

7. The method according to claim 1, wherein the oxidising agent is added in amounts of 0.01 to 10 wt. %, based on the dry mass of the cellulose ether starting material.

8. (canceled)

9. (canceled)

10. (canceled)

11. The method according to claim 1, wherein step (iii) takes place over a period of 30-600 minutes.

12. The method according to claim 1, wherein step (iii) takes place under shear.

13. The method according to claim 1, wherein step (iv) takes place at temperatures between 40 and 200° C., optionally under reduced pressure (<1 bar).

14. The method according to claim 1, wherein the water content of the mixture obtained after step (iv) is ≤10 wt. %, based on the total mass of the mixture.

15. The method according to claim 1, wherein a comminution step takes place after the drying according to step (iv).

16. The method according to claim 1, wherein the alkaline salt in step (v) is added as a solid.

17. The method according to claim 1, wherein the alkaline salt is selected from the group consisting of sodium hydrogen carbonate, disodium carbonate, sodium dihydrogen phosphate, disodium hydrogen phosphate, and trisodium phosphate.

18. The method according to claim 1, wherein the alkaline salt in step (v) is added in an amount of about 0.01-3 wt. % based on the total weight of the mixture obtained in step (iv).

19. The method according to claim 1, wherein the amount of alkaline salt is adjusted so that the pH of a 2% aqueous solution of the low-viscosity cellulose ether product is between 5 and 8.

20. (canceled)

21. The method according to claim 1, wherein the low-viscosity cellulose ether product obtained after step (v) as a 2% aqueous solution has a solution viscosity of 1-30 mPas.

22. A low-viscosity cellulose ether product obtainable by a method according to claim 1.

23. The low-viscosity cellulose ether product according to claim 22, which as a 2% aqueous solution has a solution viscosity of 1-30 mPas.

24. (canceled)

25. (canceled)

26. (canceled)

27. (canceled)

28. (canceled)

29. A tabletting aid comprising the low-viscosity cellulose ether product according to claim 22.

Description

EXAMPLE

[0057] 5 kg warm, plasticine-like moist product HPC (temp.: approx. 50° C.; water content: 45%; determined from dry product: HPO: 73.7%, viscosity 2% in water: 353 mPas (Brookfield LV, spindle 2, 60 rpm, 20° C.) is provided in one step, with the entire amount of hydrogen peroxide solution (150 mL, 47%), in an intensive mixer from Herbst, Buxtehude. The mixture is heated to 80° C. using a heatable intensive mixer and mixed intensively for 90 minutes (stirrer speed: 40 rpm, dissolver speed: 400 rpm). The system is covered, but not completely closed, in order not to build up pressure in the event of gas evolution, but to prevent the evaporation of water or oxidising agent to a large extent.

[0058] After the degradation time has elapsed, the stirring elements are stopped, the container is opened, and the free-flowing product is drained. After drying and grinding, a colourless powder is obtained which develops a pH of 3.5 as a 2% aqueous solution. 0.3 wt. % solid sodium hydrogen carbonate is added to the dried, ground degradation product and mixed well (HPC P10). The 2% aqueous solution then produced therefrom has a viscosity of 10 mPas in a rotary viscometer LV (spindle 2, 60 rpm, 20° C.) and is a highly clear liquid with a yellow index of 3.3 (ASTM E313).

[0059] If the degradation time is extended from approx. 90 minutes to 100 (HPC P10F; 0.35% NaHCO.sub.3) or 120 minutes (HPC P6), similarly soluble clear products can be produced in the otherwise unchanged process as described above.

[0060] The data are summarised in the table below.

TABLE-US-00001 White- Viscosity HPO ness * YI YI pH Product [mPa s] [%] Powder Powder Solution [2%] HPC P10 10.3 73.9 82.0 5.34 3.3 5.9 HPC P10F 9.4 71.8 92.0 3.08 4.3 7.0 HPC P6 8.6 72.1 80.0 7.74 4.0 5.7 * Measured according to DIN 5033