Forming solutions of cellulose in aqueous teritary amine oxide

A method of converting a mixture of cellulose, tertiary amine oxide and excess non-solvent to a solution of cellulose in tertiary amine oxide containing a reduced amount of the non-solvent, which comprises the steps of heating the mixture to a temperature in excess of the boiling point of the non-solvent at subatmospheric pressure;

• continuously feeding the thusly heated mixture into the introduction zone of a mixing chamber at said subatmospheric pressure so as to cause flash evaporation of some of the excess non-solvent so that at least some of the cellulose goes into solution in the tertiary amine oxide closely adjacent to the introduction zone of the mixing chamber;
• providing in the mixing chamber a rotor which agitates the thusly formed solution and the remaining mixture of cellulose, tertiary amine oxide and excess non-solvent;
• transporting the solution and the remaining mixture through the mixing chamber whilst continuing evaporation of excess non-solvent to form farther solution, and extracting the solution continuously from the mixing chamber, the evaporated non-solvent being withdrawn in a cocurrent mode from the same end of the mixing chamber as the solution.