A solution of cellulose is formed by moving a premix of a tertiary amine N-oxide, water and cellulose through a thin-film evaporator using a bladed rotor under treatment conditions which specify, an area of heated surface (1m?2 to 1252¿), a circumferential spacing between blade tips (65 to 175 mm), a rotational speed of the blade tips (less than 8 m/sec.), a pressure (25 to 100 mb) and a temperature (90 °C to 135 °C).