Provided is a novel manufacturing method whereby a carboxymethylated cellulose nanofiber dispersion having high tarnasparency can be obtained economically. In carboxymethylation of cellulose in the present invention, mercerization is performed in water as the main solvent, after which carboxymethylation is performed in a solvent mixture of water and an organic solvent, By defibrating the resultant carboxymethylated cellulose, a carboxymethylated cellulose nanofiber dispersion having high transparency can be obtained economically.

There is provided a method for producing hypromellose acetate succinate (HPMCAS), the method not requiring any special device and facilitating removal of impurities. More specifically, there is provided a method for producing HPMCAS, including an esterification step of esterifying hypromellose with an acetylating agent and a succinoylating agent in the presence of an aliphatic carboxylic acid to obtain a reaction product solution containing HPMCAS; a precipitation step of precipitating the HPMCAS by mixing the reaction product solution with water to obtain a suspension of the precipitated HPMCAS; a neutralization step of neutralizing the suspension with a basic substance to obtain a neutralized suspension; and a washing step of washing the HPMCAS contained in the neutralized suspension to obtain the washed HPMCAS.

There is provided a method for producing hypromellose phthalate (HPMCP), the method not requiring any special device, and facilitating removal of impurities. More specifically, there is provided a method for producing HPMCP, including an esterification step of esterifying hypromellose with a carboxybenzoylating agent in the presence of an aliphatic carboxylic acid to obtain a reaction product solution containing HPMCP; a precipitation step of precipitating the HPMCP by mixing the reaction product solution with water to obtain a suspension of the precipitated HPMCP; a neutralization step of neutralizing the suspension with a basic substance to obtain a neutralized suspension; and a washing step of washing the HPMCP contained in the neutralized suspension to obtain the washed HPMCP.

There is provided a method for producing a depolymerized cellulose ether, the method suppressing the formation of coarse aggregates during the contact with an acid aqueous solution in a depolymerization reaction, and reducing the amounts of aggregates and black contaminants, while suppressing yellowness. More specifically, there is provided a method for producing a depolymerized cellulose ether, the method including a depolymerization step of depolymerizing a cellulose ether by bring the cellulose ether of 45 to 95° C. into contact with an acid aqueous solution of 55 to 98° C. to obtain a depolymerized cellulose ether.

There is provided a method for producing a depolymerized cellulose ether, the method suppressing the formation of coarse aggregates during the contact with an acid aqueous solution in a depolymerization reaction, and reducing the amounts of aggregates and black contaminants, while suppressing yellowness. More specifically, there is provided a method for producing a depolymerized cellulose ether, the method including a depolymerization step of depolymerizing a cellulose ether by bring the cellulose ether of 45 to 95° C. into contact with an acid aqueous solution of 55 to 98° C. to obtain a depolymerized cellulose ether.

There is provided a method for producing a depolymerized cellulose ether having yellowness reduced. More specifically, there is provided a method for producing a depolymerized cellulose ether comprising a depolymerization step of depolymerizing a cellulose ether with an aqueous solution of acid in the presence of a polyhydric alcohol having 2 to 6 carbon atoms.

There is provided a method for producing a depolymerized cellulose ether having yellowness reduced. More specifically, there is provided a method for producing a depolymerized cellulose ether comprising a depolymerization step of depolymerizing a cellulose ether with an aqueous solution of acid in the presence of a polyhydric alcohol having 2 to 6 carbon atoms.

Provided is a process for reducing the size of ethylcellulose polymer particles comprising (a) providing a slurry comprising (i) water (ii) said ethylcellulose particles, wherein said ethylcellulose polymer particles have D50 of 100 μm or less; (iii) surfactant comprising 1.2% or more anionic surfactants by weight based on the solid weight of said slurry, with the proviso that if the amount of anionic surfactant is 2.5% or less by weight based on the solid weight of said slurry, then said surfactant further comprises 5% or more stabilizers by weight based on the solid weight of said slurry, wherein said stabilizer is selected from the group consisting of water-soluble polymers, water-soluble fatty alcohols, and mixtures thereof. (b) grinding said slurry in an agitated media mill having a collection of media particles having a median particle size of 550 μm or smaller. Also provided is a dispersion made by such a process.

Provided is a process for reducing the size of ethylcellulose polymer particles comprising (a) providing a slurry comprising (i) water (ii) said ethylcellulose particles, wherein said ethylcellulose polymer particles have D50 of 100 μm or less; (iii) surfactant comprising 1.2% or more anionic surfactants by weight based on the solid weight of said slurry, with the proviso that if the amount of anionic surfactant is 2.5% or less by weight based on the solid weight of said slurry, then said surfactant further comprises 5% or more stabilizers by weight based on the solid weight of said slurry, wherein said stabilizer is selected from the group consisting of water-soluble polymers, water-soluble fatty alcohols, and mixtures thereof. (b) grinding said slurry in an agitated media mill having a collection of media particles having a median particle size of 550 μm or smaller. Also provided is a dispersion made by such a process.

Provided are a hydroxyalkylalkyl cellulose excellent in formability and not causing marked delay in disintegration when added even in a small amount; a solid preparation including the hydroxyalkylalkyl cellulose; and a method for producing the solid preparation. More specifically, provided are a hydroxyalkylalkyl cellulose for tableting having a specific surface area of from 0.5 to 5.0 m.sup.2/g as measured by BET and a solid preparation including the hydroxyalkylalkyl cellulose. Also provided is a method for producing the hydroxyalkylalkyl cellulose for tableting, including the steps of: bringing pulp into contact with an alkali metal hydroxide solution to obtain an alkali cellulose, reacting the alkali cellulose with an etherifying agent to obtain a first hydroxyalkylalkyl cellulose, grinding the first hydroxyalkylalkyl cellulose, and subjecting the ground first hydroxyalkylalkyl cellulose to hydrolysis in the presence of an acid catalyst or oxidative degradation in the presence of an oxidant to obtain a second hydroxyalkylalkyl cellulose.