It is an object of the present invention to provide a method for producing ultrafine fibrous cellulose, which is capable of efficiently obtaining ultrafine fibrous cellulose having phosphoric acid groups with a high yield. The present invention relates to a method for producing fibrous cellulose having a fiber width of 1000 nm or less, comprising: a (A) of introducing phosphoric acid groups into cellulose fibers to form crosslinked structures via the phosphoric acid groups, thereby obtaining crosslinked phosphorylated cellulose fibers, a (B) of breaking some or all of the crosslinked structures to obtain crosslink-broken phosphorylated cellulose fibers, and a (C) of performing a mechanical treatment on the crosslink-broken phosphorylated cellulose fibers to obtain fibrous cellulose having a fiber width of 1000 nm or less, wherein, in the (A), crosslinked structures in an amount of 0.05 mmol/g or more and 2.0 mmol/g or less are formed, and the (B) is a step of performing the hydrolysis of the crosslinked structures in an aqueous solvent with pH 3 or more.

It is an object of the present invention to provide a method for producing ultrafine fibrous cellulose, which is capable of efficiently obtaining ultrafine fibrous cellulose having phosphoric acid groups with a high yield. The present invention relates to a method for producing fibrous cellulose having a fiber width of 1000 nm or less, comprising: a (A) of introducing phosphoric acid groups into cellulose fibers to form crosslinked structures via the phosphoric acid groups, thereby obtaining crosslinked phosphorylated cellulose fibers, a (B) of breaking some or all of the crosslinked structures to obtain crosslink-broken phosphorylated cellulose fibers, and a (C) of performing a mechanical treatment on the crosslink-broken phosphorylated cellulose fibers to obtain fibrous cellulose having a fiber width of 1000 nm or less, wherein, in the (A), crosslinked structures in an amount of 0.05 mmol/g or more and 2.0 mmol/g or less are formed, and the (B) is a step of performing the hydrolysis of the crosslinked structures in an aqueous solvent with pH 3 or more.

It is an object of the present invention to provide a thickener capable of exhibiting excellent light resistance. The present invention relates to a thickener comprising cellulose fibers having a fiber width of 8 nm or less and water, wherein the thickener is a slurry or a gel, and when the thickener is filled in a colorless and transparent glass cell having an inside dimension of 1 cm in depth4 cm in width4.5 cm in height and the thickener is then irradiated with ultraviolet rays with a wavelength of 300 nm or more and 400 nm or less, using a xenon lamp, from the side of the maximum area surface of the glass cell, so as to be an irradiance of 180 W/m.sup.2 and an integrated light amount of 500 mJ/m.sup.2, the amount of a change in the yellowness before and after ultraviolet irradiation measured in accordance with JIS K 7373 is 10 or less.

It is an object of the present invention to provide a thickener capable of exhibiting excellent light resistance. The present invention relates to a thickener comprising cellulose fibers having a fiber width of 8 nm or less and water, wherein the thickener is a slurry or a gel, and when the thickener is filled in a colorless and transparent glass cell having an inside dimension of 1 cm in depth4 cm in width4.5 cm in height and the thickener is then irradiated with ultraviolet rays with a wavelength of 300 nm or more and 400 nm or less, using a xenon lamp, from the side of the maximum area surface of the glass cell, so as to be an irradiance of 180 W/m.sup.2 and an integrated light amount of 500 mJ/m.sup.2, the amount of a change in the yellowness before and after ultraviolet irradiation measured in accordance with JIS K 7373 is 10 or less.

Fine cellulose fiber has a dispersion with a very high transparency and viscosity. A method is for producing the fine cellulose fiber. In the cellulose fiber, a part of hydroxy groups of cellulose fiber is substituted with a predetermined functional group to introduce an ester of phosphorus-oxo acid, and substituted with a carbamate group to introduce a carbamate. The method for producing fine cellulose fiber includes adding an additive (A) and an additive (B) including at least one of urea and a urea derivative to cellulose fiber, heating the mixture at 100 to 210 C., washing the mixture, and then fibrillating the mixture, the additive (B) being added in an amount of 0.01 to 100 mol based on 1 mol of the additive (A).

An object is to provide a dispersion of ultrafine cellulose fibers having a high thickening effect and a gelling function. There is provided a subterranean formation processing composition comprising ultrafine cellulose fibers, which has a haze value of 1.0% to 50%, when the composition is suspended in water such that the solid concentration of cellulose fibers is 0.2% by mass. The composition of the present invention can be used as an additive to the fluid at the time of the processing of subterranean formation, especially the processing of the well. The present invention provides also various fluids which are used in well processing. The present invention provides a method for processing a subterranean formation, for example, drilling of an exploratory well or a wildcat, an appraisal well, an exploratory well or an exploration well, a delineation well, a development well, a production well, an injection well, an observation well, and a service well; cementing; fracturing; and a method for producing petroleum resources.

A laminated film includes a polylactic acid-based resin layer and one or more acetylated hyaluronic acid layers laminated on a side of the polylactic acid-based resin layer, is highly flexible and easy to handle and, when stuck to an adherend with curved surface, the laminated film has excellent followability, adhesiveness and coating properties to the adherend, since the acetylated hyaluronic acid layer(s) can be removed easily with an aqueous solution from the polylactic acid-based resin layer in a thin film shape. The acetylated hyaluronic acid and the polylactic acid-based resin are biodegradable and, therefore, the laminated film is highly compatible with skin and organs such as visceral organs. The laminated film is optimally usable as a dermal material for external application such as a wound coating material, an adhesion inhibitor and skin care articles.

A laminated film includes a polylactic acid-based resin layer and one or more acetylated hyaluronic acid layers laminated on a side of the polylactic acid-based resin layer, is highly flexible and easy to handle and, when stuck to an adherend with curved surface, the laminated film has excellent followability, adhesiveness and coating properties to the adherend, since the acetylated hyaluronic acid layer(s) can be removed easily with an aqueous solution from the polylactic acid-based resin layer in a thin film shape. The acetylated hyaluronic acid and the polylactic acid-based resin are biodegradable and, therefore, the laminated film is highly compatible with skin and organs such as visceral organs. The laminated film is optimally usable as a dermal material for external application such as a wound coating material, an adhesion inhibitor and skin care articles.

A method is for manufacturing cellulose microfibers in which a problem of yellowing of cellulose microfibers to be obtained was solved, and cellulose microfibers.

As to a method for manufacturing cellulose microfibers, cellulose fibers are added with an additive (A) consisting of at least one of a phosphorous acid and a metal phosphite and an additive (B) consisting of at least one of urea and a urea derivative, heated and washed, then fibrillated. Also, as to cellulose microfibers, the fiber width is 1 to 1000 nm, and a part of hydroxy groups of cellulose fibers is substituted with a functional group represented by a predetermined structural formula to introduce an ester of phosphorous acid.

An object of the present invention is to provide ultrafine fibrous cellulose capable of exhibiting excellent coating suitability when added to paint. The present invention relates to fibrous cellulose having a fiber width of 1,000 nm or less, in which, when the fibrous cellulose is dispersed in water to form a dispersion liquid having a viscosity of 2,500 mPa.Math.s at 23? C., and the dispersion liquid is stirred under predetermined stirring conditions, a viscosity change rate falls within ?50%, calculated by the following formula: viscosity change rate (%)=(viscosity after stirring?viscosity before stirring)/viscosity before stirring?100.