Abstract: Provided are: a sheet which has high transparency, in which yellowing due to heating is suppressed, and which has high tensile elastic modulus and excellent flexibility; and a layered body having the sheet. The sheet of the present invention contains ultrafine fibrous cellulose having a fiber width of 10 nm or less, and a cellulose derivative having a weight-average molecular weight of 1.0×104 or more and 3.0×105 or less.

Abstract: Objects of the present invention are to provide a phosphoric acid-esterified fine cellulose fiber of which slurry shows superior transparency, and to provide a method for producing a phosphorylated fine cellulose fiber showing superior transparency with good efficiency and high yield. According to the present invention, there is provided a phosphoric acid-esterified fine cellulose fiber, of which 0.2 mass % aqueous dispersion shows a solution haze of 15% or lower.

Abstract: It is an object of the present invention to provide a resin composite comprising ultrafine cellulose fibers, in which deterioration of a resin component is suppressed. The present invention relates to a cellulose fiber-containing resin composition comprising cellulose fibers with a fiber width of 1000 nm or less having phosphoric acid groups or phosphoric acid group-derived substituents, and a resin, wherein the counterions of the phosphoric acid groups or phosphoric acid group-derived substituents are organic onium ions, and the conjugate bases of the organic onium ions have a pKb value of 1.0 or more.

Abstract: It is an object of the present invention to provide ultrafine cellulose fibers capable of exhibiting favorable dispersibility even in an organic solvent. The present invention relates to cellulose fibers having a fiber width of 1000 nm or less and having phosphoric acid groups or phosphoric acid group-derived substituents, wherein the content of the phosphoric acid groups or phosphoric acid group-derived substituents is 0.5 mmol/g or more, and the supernatant yield measured by an measurement method (a) is 70% or less.

Abstract: An object is to optimize a bleaching process in a step of producing phosphorylated cellulose fibers. A pulp comprises cellulose fibers having 0.5 mmol/g or more of phosphoric acid groups or phosphoric acid group-derived substituents, when the pulp is processed into a sheet and four sheets are laminated on one another, the ISO whiteness of the laminate is 82% or more. Moreover, when the pulp is processed into a sheet and four sheets are then laminated on one another, the b* value of the obtained laminate according to the L*a*b* color system is 5.5 or less.

Abstract: It is an object of the present invention to optimize a bleaching process in a step of producing phosphorylated cellulose fibers. The present invention relates to a pulp comprising cellulose fibers having 0.5 mmol/g or more of phosphoric acid groups or phosphoric acid group-derived substituents, wherein when the pulp is processed into a sheet and four sheets are laminated on one another, the ISO whiteness of the laminate is 82% or more. Moreover, when the pulp of the present invention is processed into a sheet and four sheets are then laminated on one another, the b* value of the obtained laminate according to the L*a*b* color system is 5.5 or less.

Abstract: The present invention is intended to provide ultrafine cellulose fibers capable of enhancing the transparency of an ultrafine cellulose fiber-dispersed solution having phosphorous acid groups. The present invention relates to a method for producing cellulose fibers, comprising: mixing a compound having a phosphorous acid group and/or a salt thereof and urea and/or a urea derivative into a cellulose raw material to obtain a phosphorous acid esterified cellulose raw material, and performing a fibrillation treatment on the phosphorous acid esterified cellulose raw material to obtain cellulose fibers having a fiber width of 1000 nm or less and having a phosphorous acid group, wherein, in obtaining the phosphorous acid esterified cellulose raw material, the decomposition percentage of the urea and/or the urea derivative is set to be 90% or less.

Abstract: Objects of the present invention are to provide a phosphoric acid-esterified fine cellulose fiber of which slurry shows superior transparency, and to provide a method for producing a phosphorylated fine cellulose fiber showing superior transparency with good efficiency and high yield. According to the present invention, there is provided a phosphoric acid-esterified fine cellulose fiber, of which 0.2 mass % aqueous dispersion shows a solution haze of 15% or lower.

Abstract: An object of the present invention is to provide a salt water thickener that uniformly (favorably) disperses ultrafine cellulose fibers even in a liquid containing a salt (electrolyte). The salt water thickener comprises ultrafine cellulose fibers and a water-soluble polymer and can thereby uniformly disperse the ultrafine cellulose fibers even in a liquid containing a salt. The salt water thickener of the present invention is uniformly dispersed even in a liquid containing a salt and therefore exerts a high viscosity. The salt water thickener of the present invention can also be used as an additive for a fluid. The salt water thickener of the present invention can be used for purposes, for example, subterranean formation processing.

Abstract: 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.

Abstract: It is an object of the present invention to provide a fluffed cellulose having totally new properties that have not conventionally existed, and a cellulose fiber-containing material capable of realizing the same. The present invention relates to a cellulose fiber-containing material comprising cellulose fibers having anionic groups, wherein the yield of the cellulose fiber-containing material measured by the following measurement method is 50% by mass or more, the cellulose fiber-containing material has organic onium ions as counterions of the anionic groups, and the organic onium ions satisfy a predetermined condition.

Abstract: It is an object of the present invention to provide an ultrafine cellulose fiber-containing composition, regarding which an ultrafine cellulose fiber-dispersed organic solvent slurry can exhibit high viscosity and high transparency. The present invention relates to a cellulose fiber-containing composition comprising cellulose fibers with a fiber width of 1000 nm or less having anionic groups, and metal ions, wherein the cellulose fiber-containing composition comprising organic onium ions as counterions of the anionic groups, and when a solid in the cellulose fiber-containing composition is converted to an absolute dry solid, the content of the metal ions in the absolute dry solid is 80 ppm or more and 700 ppm or less.

Abstract: Objects of the present invention are to provide a phosphoric acid-esterified fine cellulose fiber of which slurry shows superior transparency, and to provide a method for producing a phosphorylated fine cellulose fiber showing superior transparency with good efficiency and high yield. According to the present invention, there is provided a phosphoric acid-esterified fine cellulose fiber, of which 0.2 mass % aqueous dispersion shows a solution haze of 15% or lower.

Abstract: It is an object of the present invention to provide a resin composite that is excellent in water resistance and is capable of exerting sufficient strength even under wet conditions. The present invention relates to a resin composite comprising a resin, fibers having an ionic functional group, and a polyvalent ion. The fibers having an ionic functional group are preferably cellulose fibers having a fiber width of 1000 nm or less.

Abstract: It is an object of the present invention to provide a resin composite that is excellent in water resistance and is capable of exerting sufficient strength even under wet conditions. The present invention relates to a resin composite comprising a resin, fibers having an ionic functional group, and a polyvalent ion. The fibers having an ionic functional group are preferably cellulose fibers having a fiber width of 1000 nm or less.

Abstract: An object of the present invention is to improve the strength of a sheet containing substituent-introduced ultrafine fiber under high-humidity conditions while maintaining its high transparency. The sheet of the present invention comprises ultrafine fiber having an ionic substituent, and a divalent or higher metal, and has a haze of 10.0% or less.

Abstract: It is an object of the present invention to provide a resin composite comprising ultrafine cellulose fibers, in which deterioration of a resin component is suppressed. The present invention relates to a cellulose fiber-containing resin composition comprising cellulose fibers with a fiber width of 1000 nm or less having phosphoric acid groups or phosphoric acid group-derived substituents, and a resin, wherein the counterions of the phosphoric acid groups or phosphoric acid group-derived substituents are organic onium ions, and the conjugate bases of the organic onium ions have a pKb value of 1.0 or more.

Abstract: The present invention is intended to provide a resin composition capable of suppressing separation between ultrafine cellulose fibers and a resin, and also capable of forming a film having excellent adhesiveness to a base material. The present invention relates to a method for producing a cellulose fiber-containing film, comprising: mixing cellulose fibers having a fiber width of 1000 nm or less with organic onium; mixing the cellulose fiber mixture obtained in the mixing step, an organic solvent and a resin to obtain a resin composition; and applying the resin composition onto a base material, wherein the cellulose fibers have anionic groups, and the content of the anionic groups is 0.50 mmol/g or more, and the content of the cellulose fibers in the resin composition is 1% by mass or more.

Abstract: The object is to provide a subterranean formation processing composition which has a highly stable viscosity against change in temperature and a high water stopping property. A subterranean formation processing composition comprising cellulose fibers wherein the composition contains ultrafine cellulose fibers having 0.14 to 2.5 mmol/g of a substituent is used. The substituent is preferably an anion group, particularly a phosphoric acid group. The present invention relates to various fluids which are used in well processing. The present invention relates to 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.

Abstract: 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.