Method of preparing a cellulose carbamate solution

• US 6,590,095 B1
• Filed: 12/02/1998
• Issued: 07/08/2003
• Est. Priority Date: 12/24/1997
• Status: Expired due to Fees

• Current Assignee: Fraunhofer-Gesellschaft
• Original Assignee: Zimmer AG
• Inventors: Lang, Hermann, Borrmeister, Bodo, Schleicher, Harry
• Primary Examiner(s): Wilson, James O.
• Assistant Examiner(s): White, Everett
• Application Number:
  US09/204,609
• Time in Patent Office: 1,679 Days
• Field of Search: 536/30, 536/124, 536/56
• US Class Current: 536/30
• CPC Class Codes: C08B 15/06 containing nitrogen , e.g. carbamates
• CPC Class Codes: D01F 2/24 from cellulose derivatives

Abstract

The present invention concerns a method of preparing a cellulose carbamate solution by dissolving cellulose carbamate in sodium hydroxide solution at temperatures of <10° C., wherein an 8% to 15% cellulose carbamate solution with a sodium hydroxide concentration of 7% to 12% is prepared in a first step, and then the solution is adjusted to a sodium hydroxide concentration of <9% by diluting with dilute sodium hydroxide solution and/or water in a second step, with the provision that the weight ratio of cellulose carbamate to sodium hydroxide in both steps is >1.

Claims

1. A process for preparing a cellulose carbamate solution, the process comprising

a) preparing an 8% to 15% cellulose carbamate solution with a sodium hydroxide concentration of 7% to 12% by dissolving cellulose carbamate in a sodium hydroxide solution at a temperature of less than 10°

C., and

b) adjusting the sodium hydroxide concentration of the cellulose carbamate solution to a concentration that is less than the concentration in a) and less than 9% by adding to the cellulose carbamate solution either

i) a single diluent comprising a dilute sodium hydroxide solution or water, or

ii) a first diluent followed by a second diluent, wherein one of said diluents is water and the other is a dilute sodium hydroxide solution,

provided that the weight ratio of cellulose carbamate to sodium hydroxide in both (a) and (b) is greater than 1.

2. The process according to 1, wherein in (a) the cellulose carbamate solution contains 9% to 12% cellulose carbamate with a sodium hydroxide concentration of 8% to 10%, which in (b) is adjusted to at most 8% sodium hydroxide.

3. The process according to claim 1, wherein the single diluent in (b) is a sodium hydroxide solution having a concentration of at most 4%.

4. The process according to claim 1, wherein the temperature in (a) and (b) is kept below 5°

C.

5. The process according to claim 1, wherein the dissolving in (a) and the addition of the single diluent or the first and second diluents in (b) are performed with stirring.

6. The process according to claim 1, wherein in (b) the first diluent is a sodium hydroxide solution with a concentration of at most 4% and the second diluent is water.

7. The process according to claim 6, wherein the single diluent or the first and second diluents are added more slowly at the start of the dilution than at the end.