A process for the production of a non-derivatized nanocellulose material from a cellulosic fibrous material, comprising the steps of: a. providing a suspension of cellulosic fibrous material in a continuous phase of a non-aqueous process liquid comprising a swelling agent and a processing solvent; b. allowing the cellulosic fibrous material to swell such as to form a suspension of swollen cellulosic fibrous material in a continuous phase of non-aqueous process liquid; c. optionally refining said suspension of swollen cellulosic fibrous material in a continuous phase of non-aqueous process liquid to increase the fineness of the swollen cellulosic fibrous material; d. removing the swelling agent from the process liquid such as to form a suspension of cellulosic fibrous material in a continuous phase of processing solvent; e. subjecting the swollen and optionally refined cellulosic fibrous material to high-shear comminution such as to release of the non-derivatized nanocellulose material from the swollen and optionally refined cellulosic fibrous material and such as to form a dispersion of non-derivatized nanocellulose material in a continuous phase of a processing solvent; f. contacting the dispersion of non-derivatized nanocellulose material in a continuous phase of a processing solvent with a supercritical fluid such as to remove the processing solvent and isolate the non-derivatized nanocellulose material, wherein the supercritical fluid is preferably supercritical carbon dioxide or ammonia; characterized in that the swelling agent is a low-transition-temperature mixture (LTTM) and in particular a deep eutectic solvent and said low-transition-temperature mixture and in particular said deep eutectic solvent is soluble in the processing solvent and wherein the processing solvent is non-solubilizing for the cellulosic fibrous material and the non-derivatized nanocellulose material. a. providing a suspension of cellulosic fibrous material in a continuous phase of a non-aqueous process liquid comprising a swelling agent and a processing solvent; b. allowing the cellulosic fibrous material to swell such as to form a suspension of swollen cellulosic fibrous material in a continuous phase of non-aqueous process liquid; c. optionally refining said suspension of swollen cellulosic fibrous material in a continuous phase of non-aqueous process liquid to increase the fineness of the swollen cellulosic fibrous material; d. removing the swelling agent from the process liquid such as to form a suspension of cellulosic fibrous material in a continuous phase of processing solvent; e. subjecting the swollen and optionally refined cellulosic fibrous material to high-shear comminution such as to release of the non-derivatized nanocellulose material from the swollen and optionally refined cellulosic fibrous material and such as to form a dispersion of non-derivatized nanocellulose material in a continuous phase of a processing solvent; f. contacting the dispersion of non-derivatized nanocellulose material in a continuous phase of a processing solvent with a supercritical fluid such as to remove the processing solvent and isolate the non-derivatized nanocellulose material, wherein the supercritical fluid is preferably supercritical carbon dioxide or ammonia;