DESCRIPTION

METHOD FOR PRODUCING FIBROUS MATERIAL, CELLULOSE-CONTAINING MATERIAL, AND ACID TREATMENT AGENT FOR TREATING FIBER RAW MATERIAL

Field of the Invention

[0001]

The present invention relates to a method for producing a fibrous material, a cellulose-containing material, and an acid treatment agent for treating a fiber raw material.

Background of the Invention

[0002]

In recent years, materials using reproducible natural fibers have attracted attention due to replacement of petroleum resources and an increase in environmental consciousness. Among natural fibers, cellulose fibers having a fiber diameter of 10 to 50 pm, especially wood-derived cellulose fibers (pulps) have been widely used as paper products.

[0003]

As cellulose fibers, ultrafme cellulose fibers having a fiber diameter of 1 pm or less is also known. As ultrafme cellulose fibers, cellulose nanofibers (CNF) and cellulose nanocrystals (CNC) are mainly known.

[0004]

Cellulose nanofibers (CNF) are produced by mechanical treatment of cellulose fibers. However, the cellulose fibers are strongly bonded to each other due to hydrogen bonding. Therefore, only simple mechanical treatment requires a large amount of energy to obtain ultrafme cellulose fibers. Therefore, in order to produce ultrafme cellulose fibers with smaller mechanical treatment energy, it has been studied to carry out chemical treatment together with mechanical treatment. For example, when an ionic substituent such as an anionic group or a cationic group is introduced into a hydroxy group on a cellulose surface, miniaturization becomes easy due to an electric repulsion force between ions, and energy efficiency of miniaturization becomes high. For example, WO 2014/185505 (corresponding to US 2016/115249 Al) discloses phosphate esterified ultrafme cellulose fibers (cellulose nanofibers). Here, urea, sodium dihydrogen phosphate dihydrate, and di sodium hydrogen phosphate are dissolved in water to prepare a phosphorylation reagent, and the phosphorylation reagent is impregnated in pulp and then heated to carry out a phosphorylation reaction.

[0005]

Cellulose nanocrystals (CNCs) are usually produced by acid hydrolyzing cellulose fibers and then sonicating them. For example, W099/15564 discloses a method of adding an acid solution to cellulose fibers and subjecting the cellulose fibers to acid hydrolysis using an extruder screw to obtain cellulose nanocrystals (CNC). Specifically, in the production method described in W099/15564, sulfuric acid solution is added to cellulose fibers, and hydrolysis is carried out under high temperature conditions of 200 to 230° C.

Brief Summary of the Invention [0006]

However, in a conventional method for producing cellulose nanofibers (CNF) or cellulose nanocrystals (CNC), when a fiber raw material is subjected to an oxo-oxidation treatment, a reaction product may be colored in a process. In particular, when the oxo-oxidation reaction of the fiber raw material is carried out in a metal container, coloring of the reaction product is observed, and improvement is required.

Therefore, an object of the present invention is to provide a fibrous material in which coloring is suppressed even when a heating reaction is carried out in a metal container.

[0007]

The present invention has the following configurations.

[1] A method for producing a fibrous material comprising the step (A) of adding an oxo acid and a corrosion inhibitor to a fiber raw material and heating the fiber raw material, wherein a value of b/a is 0.32 or more when an addition amount of the oxo acid is a parts by mass and an addition amount of the corrosion inhibitor is b parts by mass.

[2] The method for producing a fibrous material according to [1], wherein the step (A) is carried out in a metal container.

[3] The method for producing a fibrous material according to [1] or [2], wherein the fiber raw material is a cellulose-based material.

[4] The method for producing a fibrous material according to any one of [1] to [3], wherein step (A) is followed by a defibration treatment step (B) and the fibrous material includes cellulose fibers having a fiber width of 1000 nm or less.

[5] The method for producing a fibrous material according to any one of [1] to [4], wherein the corrosion inhibitor is a compound represented by the following formula (1):

Formula (1 )

In the above formula (1),

X represents an oxygen atom or a sulfur atom;

Ri represents an alkyl group, an alkenyl group, a cycloalkyl group, an alkoxy group or -NHR11; and R-2 represents a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group or an aryl group; in -NHRn, Rn is a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group or an aryl group.

[6] The method for producing a fibrous material according to any one of [1] to [5], wherein the corrosion inhibitor is at least one selected from urea and urea derivatives.

[7] The method for producing a fibrous material according to any one of [1] to [6], wherein the oxo acid is phosphoric acid, the value of b/a is 0.32 or more and 1.0 or less, and the heat treatment temperature in the step (A) is 145° C or higher and 185° C or lower.

[8] Cellulose-containing material comprising cellulose fibers having a group derived from oxo acid and having a fiber width of 1000 nm or less, wherein the content of the polyvalent metal in the cellulose-containing material is 50 to 1000 ppm.

[9] The cellulose-containing material according to [8], wherein the oxo acid is phosphoric acid, and the polyvalent metal is at least one selected from the group consisting of Fe, Cu, Cr, Ni, Mo and Mn.

[10] An acid treatment agent for treating a fiber raw material comprising an oxo acid and a compound represented by the following formula (1), wherein when a content of the oxo acid in the acid treating agent is c parts by mass and a content of the compound in the acid treating agent is d parts by mass, a value of d/c is 0.32 or more;

Formula (1)

In the above formula (1),

X represents an oxygen atom or a sulfur atom;

Ri represents an alkyl group, an alkenyl group, a cycloalkyl group, an alkoxy group or -NHRn; and

R2 represents a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group or an aryl group; in -NHRn, Rn is a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group or an aryl group.

Brief Description of the Drawings [0008]

FIG. 1 is a graph showing a relationship between a drop amount of NaOH and a pH of a cellulose fiber-containing slurry having a phosphorus oxo acid group.

FIG. 2 is a graph showing a relationship between a drop amount of NaOH and a pH of a cellulose fiber-containing slurry having a carboxyl group.

Detailed Description of the Invention [0009]

Hereinafter, embodiments of the present invention will be described in detail. The following description of the components may be made based on representative embodiments and specific examples, but the present invention is not limited to such embodiments.

[0010]

[Producing Fibrous Material]

An embodiment of the present invention is a method for producing a fibrous material comprising the step (A) of adding an oxo acid and a corrosion inhibitor to a fiber raw material and heating the mixture. Here, in the step (A), when the addition amount of the oxo acid is a parts by mass and the addition amount of the corrosion inhibitor is b parts by mass, the value of b/a is 0.32 or more. In the producing method of the present invention, the step (A) may be performed in a metal container. According to the present embodiment, even when the step (A) is performed in the metal container, a fibrous material in which coloring is suppressed can be obtained.

[0011]

Here, coloring of the fibrous material can be evaluated by visually observing the fibrous material obtained through the step (A). Specifically, the degree of coloring of the fibrous material obtained after the reaction is evaluated, and when the fibrous material is white, it can be determined that coloring is suppressed and good. As described above, in the present invention, even when the step (A) is performed in the metal container, a fibrous material in which coloration is suppressed can be obtained, and it can be said that such a fibrous material is excellent in appearance.

[0012]

Further, in the present invention, even when the step (A) is performed in the metal container, the metal component is unlikely to be mixed into the obtained fibrous material. In the step (A), since the oxo-oxidation reaction is carried out using an oxo acid, depending on the acid used and the reaction conditions, the multivalent metal derived from the metal container may be mixed into the fibrous material which is the reaction product. In particular, when a strong acid is used as the oxo acid and the oxo oxidation reaction is carried out under high temperature conditions, the multivalent metal derived from the metal container tends to be mixed into the fibrous material as the reaction product. However, in the present invention, the amount of the multivalent metal mixed into the fibrous material can be reduced by using the oxo acid and the corrosion inhibitor in combination in the step (A) and setting the addition amount of the oxo acid and the addition amount of the corrosion inhibitor to a predetermined ratio. Thus, a highly pure fibrous material can be obtained.

[0013]

The method for producing a fibrous material of the present invention preferably further comprises a defibration treatment step (B) after the step (A). When the method for producing a fibrous material of the present invention includes the step (B), the resulting fibrous material contains cellulose fibers having a fiber width of 1000 nm or less. Thus, the method for producing a fibrous material of the present invention is preferably a method for producing cellulose fibers having a fiber width of 1000 nm or less. In this specification, cellulose fibers having a fiber width of 1000 nm or less are also referred to as ultrafme cellulose fibers, and the ultrafme cellulose fibers include cellulose nanofibers (CNF) and cellulose nanocrystals (CNC).

[0014]

<Step (A)>

The step (A) is a step of adding an oxo acid and a corrosion inhibitor to a fiber raw material and heating the fiber. In this specification, the step (A) is also referred to as an oxo acid group introduction step or an oxo oxidation step.

[0015]

The fiber raw material used in step (A) is not particularly limited, and examples thereof include inorganic fibers, organic fibers, synthetic fibers, semi-synthetic fibers, and regenerated fibers. Examples of inorganic fibers include glass fibers, rock fibers, and metal fibers. Examples of the organic fibers include fibers derived from natural products such as cellulose, carbon fibers, pulp, chitin, and chitosan. Examples of synthetic fibers include nylon, vinylon, vinylidene, polyester, polyolefin (such as polyethylene and polypropylene), polyurethane, acrylic, polyvinyl chloride, and aramid. Examples of the semi-synthetic fiber include acetate, triacetate, and promix. Examples of the regenerated fiber include rayon, cupra, polynodic rayon, lyocell, and tencell. The fiber raw material used in the present invention is not particularly limited, but preferably contains a hydroxyl group or an amino group from the viewpoint of facilitating introduction of a substituent described later.

[0016]

Among them, the fiber raw material used in the step (A) is preferably a fiber raw material containing cellulose. That is, the fiber raw material is preferably a cellulose-based material. The fiber raw material containing cellulose is not particularly limited, but pulp is preferably used because it is easily available and inexpensive. Pulps include, for example, wood pulp, non-wood pulp, and deinked pulp. Examples of the wood pulp may include, but are not particularly limited to, chemical pulps such as broad leaf tree kraft pulp (LBKP), needle leaf tree kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen bleached kraft pulp (OKP); semichemical pulps such as semi-chemical pulp (SCP) and chemi-ground wood pulp (CGP); and mechanical pulps such as ground pulp (GP) and thermomechanical pulp (TMP, BCTMP). Examples of non-wood pulp may include, but are not limited to, cotton-based pulps such as cotton linkers and cotton stents, and non-wood-based pulps such as hemp, wheat flax and bagasse. The deinking pulp is not particularly limited, and examples thereof include deinking pulp using used paper as a raw material. The pulp of this embodiment may be used alone or as a mixture of two or more thereof. Among the pulps, wood pulp and deinked pulp are preferable from the viewpoint of ease of availability. Among wood pulps, chemical pulp is more preferable, for example, and kraft pulp and sapphire pulp are more preferable from the viewpoint of a high cellulose ratio and a high yield of ultrafme cellulose fibers at the time of defibration treatment.

[0017]

As the fiber raw material containing cellulose, for example, cellulose contained in foils or bacterial cellulose produced by acetic acid bacteria can also be used. Instead of a fiber raw material containing cellulose, a fiber formed by a linear nitrogen-containing polysaccharide polymer such as chitin or chitosan may be used.

[0018]

The step (A) is a step of causing an oxo acid and a corrosion inhibitor to act on a fiber raw material containing cellulose. By this step, an oxo acid group-introduced fiber is obtained. [0019]

The oxo acid used in step (A) is an acid having a structure in which an oxo group (=0) and a hydroxy group (-OH) are bonded to a central atom. The oxo acid used in step (A) is preferably at least one selected from phosphorus oxo acids, sulfuric acid, sulfurous acid, nitric acid, nitrous acid, carbonic acid, silicic acid and carboxylic acid, more preferably at least one selected from phosphorus oxo acids, sulfuric acid, sulfite and carboxylic acid, and still more preferably at least one selected from phosphorus oxo acids, sulfuric acid and sulfite. It is particularly preferable that the compound is at least one selected from phosphorus oxo acid. The phosphorus oxo acid is preferably at least one selected from phosphoric acid and phosphorous acid, more preferably phosphoric acid or phosphorous acid, and still more preferably phosphoric acid. The phosphorus oxo acid may be pyrophosphate or polyphosphoric acid. The oxo acid may be one kind or two or more kinds.

[0020]

Examples of the corrosion inhibitor used in the step (A) include a nitrogen-containing organic compound and a sulfur-containing organic compound. Examples of the nitrogen-containing organic compound include an imidazolium-based quaternary ammonium salt and a polyamine compound. The nitrogen-containing organic compound is preferably a compound represented by the following formula (1). When the compound represented by the following formula (1) is used as the nitrogen-containing organic compound, coloring of the fibrous material can be more effectively suppressed, and in addition, producing cost of the fibrous material can be reduced.

R N ί¾ Formula (1 )

[0021]

In the above formula (1), X represents an oxygen atom or a sulfur atom; Ri represents an alkyl group, an alkenyl group, a cycloalkyl group, an alkoxy group or -NHRn; and R2 represents a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group or an aryl group; in -NHR11, R11 is a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group or an aryl group. Each group represented by Ri and R2 in Formula (1) may further have a substituent. Examples of such a substituent include a substitutable substituent selected from a halogen atom, a halogenated alkyl group, an alkyl group, an alkenyl group, an acyl group, a hydroxy group, a hydroxyalkyl group, an alkoxy group, an aryl group, a heteroaryl group, an alicyclic group, a cyano group, an epoxy group, an oxetanyl group, a mercapto group, an amino group, and a (meth)acryloyl group. Each group represented by R11 may further have a substituent, and examples of the substituent include the same substituents as described above.

[0022]

In the formula (1), when Ri is an alkyl group, the alkyl group may be an alkyl group having a branched chain. The alkyl group preferably has 1 to 4 carbon atoms, and more preferably 1 to 2 carbon atoms. Among them, the alkyl group is preferably a methyl group or an ethyl group.

In the formula (1), when Ri is an alkenyl group, the alkenyl group may be an alkenyl group having a branched chain. The carbon number of the alkenyl group is preferably 2 to 4, and more preferably 2 to 3. Among them, the alkenyl group is preferably a vinyl group, an allyl group or an isopropyl group.

In the formula (1), when Ri is a cycloalkyl group, the carbon number of the cycloalkyl group is preferably 3 to 6, and more preferably 3 to 5. Among them, the cycloalkyl group is preferably a cyclopropyl group, a cyclobutyl group, a cyclopentyl group or a cyclohexyl group. The cycloalkyl group may have a spiro structure.

In the formula (1), when Ri is an alkoxy group, the alkoxy group preferably has 1 to 4 carbon atoms, and more preferably 1 to 2 carbon atoms. Among them, the alkoxy group is preferably a methoxy group or an ethoxy group. The alkoxy group may be a phenoxy group, an allyloxy group, or a cyclohexyloxy group.

[0023]

In the formula (1), when R2 is an alkyl group, the alkyl group may be an alkyl group having a branched chain. The alkyl group preferably has 1 to 4 carbon atoms, and more preferably 1 to 2 carbon atoms. Among them, the alkyl group is preferably a methyl group or an ethyl group.

In the formula (1), when R2 is an alkenyl group, the alkenyl group may be an alkenyl group having a branched chain. The carbon number of the alkenyl group is preferably 2 to 4, and more preferably 2 to 3. Among them, the alkenyl group is preferably a vinyl group, an allyl group or an isopropyl group.

In the formula (1), when R2 is a cycloalkyl group, the carbon number of the cycloalkyl group is preferably 3 to 6, and more preferably 3 to 5. Among them, the cycloalkyl group is preferably a cyclopropyl group, a cyclobutyl group, a cyclopentyl group or a cyclohexyl group. The cycloalkyl group may have a spiro structure.

In the formula (1), when R2 is an aryl group, R2 is preferably a phenyl group or a naphthyl group.

[0024]

In the formula (1), X is preferably an oxygen atom. Ri is preferably -NHR11. R11 is preferably at least one selected from a hydrogen atom and a methyl group, and more preferably a hydrogen atom. Further, R2 is also preferably at least one selected from a hydrogen atom and a methyl group, and more preferably a hydrogen atom.

[0025]

Specifically, the corrosion inhibitor is preferably at least one selected from urea and urea derivatives, more preferably at least one selected from urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea and 1-ethylurea, and particularly preferably urea.

[0026]

The amount of oxo acid added to the fiber raw material is preferably 4 parts by mass or more, more preferably 8 parts by mass or more, and still more preferably 20 parts by mass or more based on 100 parts by mass of the fiber raw material. The amount of oxo acid added to the fiber raw material is preferably 8700 parts by mass or less, more preferably 4350 parts by mass or less, and still more preferably 1740 parts by mass or less based on 100 parts by mass of the fiber raw material. When the amount of the oxo acid added is within the above range, the amount of the oxo acid group with respect to the fiber raw material can be easily adjusted to a desired range.

[0027]

The amount of the corrosion inhibitor added to the fiber raw material (absolute dry mass) is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and still more preferably 5 parts by mass or more based on 100 parts by mass of the fiber raw material. The amount of the corrosion inhibitor added to the fiber raw material is preferably 15960 parts by mass or less, more preferably 7980 parts by mass or less, and still more preferably 3192 parts by mass or less based on 100 parts by mass of the fiber raw material. When the amount of the corrosion inhibitor added is within the above range, it is easy to obtain a fibrous material in which coloring is suppressed.

[0028]

In the step (A), when the addition amount of the oxo acid is a parts by mass and the addition amount of the corrosion inhibitor is b parts by mass, the value of b/a may be 0.32 or more, preferably 0.64 or more, more preferably 0.94 or more, and still more preferably 1.30 or more. The value of b/a is preferably 30 or less, more preferably 1.0 or less, and still more preferably 0.95 or less. By setting the value of b/a in the step (A) within the above range, a fibrous material in which coloring is suppressed can be obtained. Further, by setting the value of b/a in the step (A) within the above range, the amount of multivalent metal mixed into the fibrous material can be reduced, and a fibrous material with higher purity can be obtained.

[0029]

In the step (A), when the amount of oxo acid added to the oxo acid is a ' mol and the amount of corrosion inhibitor added is b ' mol, the value of b '/a ' is preferably 0.15 or more, more preferably 0.30 or more, and still more preferably 0.75 or more. .The value of b 7a ' is preferably 52 or less, more preferably 2.5 or less, and still more preferably 2.0 or less. By setting the value of b 7a ' in the step (A) within the above range, a fibrous material in which coloring is suppressed can be obtained. Further, by setting the value of b 7a ' in the step (A) within the above range, the amount of multivalent metal mixed into the fibrous material can be reduced, and a fibrous material with higher purity can be obtained.

[0030]

An example of a method of causing the oxo acid to act on the fiber raw material in the presence of the corrosion inhibitor is a method of mixing the oxo acid and the corrosion inhibitor with the fiber raw material in a dry state, a wet state, or a slurry state. Among them, it is preferable to use a fiber raw material in a dry state or a wet state, and it is particularly preferable to use a fiber raw material in a dry state because of high uniformity of reaction. The form of the fiber raw material is not particularly limited, but is preferably in the form of, for example, cotton or a thin sheet. The oxo acid and the corrosion inhibitor may be added to the fiber raw material in the form of powder or in the form of a solution dissolved in a solvent or in the form of a melt by heating to a melting point or higher. Among them, it is preferable to add in the form of a solution dissolved in a solvent, in particular, in the form of an aqueous solution, because of high uniformity of reaction. The oxo acid and the corrosion inhibitor may be added to the fiber raw material simultaneously, separately, or as a mixture. The method of adding the oxo acid and the corrosion inhibitor is not particularly limited, but when the oxo acid and the corrosion inhibitor are in the form of a solution, the fiber raw material may be immersed in the solution and absorbed, and then taken out, or the solution may be dropped into the fiber raw material. Further, a necessary amount of oxo acid and corrosion inhibitor may be added to the fiber raw material, or an excessive amount of oxo acid and corrosion inhibitor may be added to the fiber raw material, and then excess oxo acid and corrosion inhibitor may be removed by squeezing or filtration. [0031]

In the step (A), after adding or mixing the oxo acid and the corrosion inhibitor to the fiber raw material, the fiber raw material is subjected to heat treatment (also referred to as heating). As the heat treatment temperature, a temperature at which an oxo acid group can be efficiently introduced is preferably selected. The heat treatment temperature is preferably 30° C or higher and 300° C or lower, more preferably 40° C or higher and 250° C or lower, still more preferably 45° C or higher and 200° C or lower, and particularly preferably 145° C or higher and 185° C or lower.

[0032]

In the heat treatment according to the present embodiment, for example, a method in which an oxo acid is added to a thin sheet-like fiber raw material by a method such as impregnation and then heated, a method of heating fiber raw materials and oxo acid while kneading or stirring with a kneader or the like and the like can be employed. This makes it possible to suppress uneven concentration of the oxo acid in the fiber raw material and introduce the oxo acid group more uniformly into the surface of the cellulose fiber contained in the fiber raw material. This is believed to be due to the fact that when the water molecule moves to the fiber raw material surface along with drying, the dissolved oxo acid can be prevented from being attracted to the water molecule due to the surface tension and moved to the fiber raw material surface (that is, uneven concentration of the oxo acid is caused).

[0033]

Further, the heating apparatus used in the heating treatment may be an apparatus capable of always discharging moisture retained in the slurry and moisture generated by a dehydration condensation (phosphate esterification) reaction between the oxo acid and a hydroxyl group or the like contained in cellulose or the like in the fiber raw material to the outside of the apparatus system. Examples of such a heating device include a blowing type oven, a stirring drying device, a rotating drying device, a disc drying device, a roll type heating device, a plate type heating device, a fluidized bed drying device, a band type drying device, a filtration drying device, a vibrating fluidized drying device, an airflow drying device, a reduced pressure drying device, an infrared ray heating device, a far infrared ray heating device, a microwave heating device, and a high frequency drying device. By constantly discharging the moisture in the system, for example, when phosphoric acid or phosphorous acid is used as the oxo acid, the hydrolysis reaction of phosphate ester bond, which is a reverse reaction of phosphate esterification, can be suppressed, and also acid hydrolysis of sugar chains in fibers can be suppressed. Therefore, ultrafme cellulose fibers having a high axial ratio can be obtained.

[0034]

In the case of a reaction in which moisture is removed from the system, for example, the time of the heat treatment is preferably 1 second or more and 300 minutes or less, more preferably 1 second or more and 1000 seconds or less, and still more preferably 10 seconds or more and 800 seconds or less after substantially removing moisture from the fiber raw material. On the other hand, in the case of a reaction carried out in an aqueous solution, for example, from the start of heating, it is preferably 360 seconds or more and 36000 seconds or less, more preferably 720 seconds or more and 18000 seconds or less, and still more preferably 1800 seconds or more and 7200 seconds or less.

[0035]

The above-described step (A) may be performed in a metal container. Examples of the metal container include a stainless steel container (SUS304, SUS316, SUS316L, etc.), an iron container, and a copper container. Conventionally, when an oxo-oxidation treatment is performed in a metal container, the metal constituting the metal container is eluted in a reaction process, and the eluted metal component is mixed into a reaction product. Therefore, it is conceivable to carry out the oxo-oxidation treatment by a non-metal, but there is also a demand to use a metal container from the viewpoint of durability and the like. In the present invention, even when the oxo-oxidation treatment is performed in the metal container as described above, it is possible to suppress the incorporation of the metal component derived from the container. Thus, a highly pure oxo-oxidized fibrous material can be obtained.

[0036]

The amount of the oxo acid group introduced into the fiber raw material is, for example, preferably 0.01 mmol /g or more, more preferably 0.02 mmol /g or more, still more preferably 0.05 mmol /g or more, and particularly preferably 0.10 mmol /g or more per 1 g (mass) of the fiber raw material. The amount of the oxo acid group introduced into the fiber raw material is preferably 5.20 mmol /g or less, more preferably 3.65 mmol /g or less, and even more preferably 3.00 mmol /g or less per 1 g (mass) of the fiber raw material. When the introduction amount of the oxo acid group is within the above range, for example, miniaturization of the fiber raw material in the step (B) to be described later can be facilitated, and the stability of the ultrafme cellulose fibers can be enhanced.

[0037]

The amount of the oxo acid group introduced into the fiber raw material can be measured by, for example, a neutralization titration method. In the measurement by the neutralization titration method, the amount of introduction is measured by determining the pH change while adding an alkali such as an aqueous sodium hydroxide solution to the slurry containing the obtained fiber raw material.

[0038]

FIG. 1 is a graph showing a relationship between a drop amount of NaOH and a pH of a slurry containing a fiber raw material having a phosphorus oxo acid group. The amount of the phosphorus oxo acid group introduced into the fiber raw material is measured, for example, as follows. First, a slurry containing a fiber raw material is treated with a strong acidic ion exchange resin. If necessary, before treatment with a strongly acidic ion exchange resin, a defibration treatment similar to the defibration treatment step described later may be performed on the measurement target. The pH change is then observed while adding an aqueous sodium hydroxide solution to obtain a titration curve as shown in the upper part of FIG. 1. The titration curve shown in the upper part of FIG. 1 plots the measured pH versus the amount of alkali added, and the titration curve shown in the lower part of FIG. 1 plots the increment (differential value) (1 /mmol) of pH versus the amount of alkali added. In this neutralization titration, in a curve in which the measured pH is plotted against the amount of alkali added, two points at which the increment (derivative value of pH with respect to the amount of alkali dropped) becomes maximum are confirmed. Of these, the local maximum point of the increment obtained first after the addition of alkali is referred to as a first end point, and the local maximum point of the increment obtained next is referred to as a second end point. The amount of alkali required from the start of titration to the first end point is equal to the first amount of dissociated acid of the fiber raw material contained in the slurry used for titration, the amount of alkali required from the first end point to the second end point is equal to the second amount of dissociated acid of the fiber raw material contained in the slurry used for titration, and the amount of alkali required from the start of titration to the second end point is equal to the total amount of dissociated acid of the fiber raw material contained in the slurry used for titration. A value obtained by dividing the amount of alkali required from the start of titration to the first end point by the solid content (g) in the slurry to be titrated is the amount of introduced phosphorus oxo acid groups (mmol /g). Note that the amount of the phosphorus oxo acid group introduced (or the amount of the phosphorus oxo acid group) means the amount of the first dissociated acid.

In FIG. 1, a region from the start of titration to the first end point is referred to as a first region, and a region from the first end point to the second end point is referred to as a second region. For example, when the phosphorus oxo acid group is a phosphoric acid group and the phosphoric acid group causes condensation, apparently, the amount of weak acidic groups in the phosphorus oxo acid group (also referred to as the second amount of dissociated acid in this specification) decreases, and the amount of alkali required in the second region decreases compared to the amount of alkali required in the first region. On the other hand, the amount of strong acidic groups in the phosphorus oxo acid group (also referred to as the first amount of dissociated acid in the present specification) matches the amount of phosphorus atoms regardless of the presence or absence of condensation. In the case where the phosphorus oxo acid group is a phosphorous group, since a weak acidic group is not present in the phosphorus oxo acid group, the amount of alkali required in the second region may be small or the amount of alkali required in the second region may be zero. In this case, the titration curve has one point at which the pH increase becomes maximum.

[0039]

Since the denominator indicates the mass of the acid-type fiber raw material, the amount of the phosphorus oxo acid group introduced (mmol /g) indicates the amount of the phosphorus oxo acid group contained in the acid-type fiber raw material (hereinafter referred to as the phosphorus oxo acid group amount (acid type)). On the other hand, in the case where the counter ion of the phosphorus oxo acid group is substituted with an arbitrary cation C so as to have a charge equivalent amount, the amount of phosphorus oxo acid group of the fiber raw material in which the cation C is a counter ion (hereinafter referred to as phosphorus oxo acid group amount (C type)) can be obtained by converting the denominator into the mass of the fiber raw material when the cation C is a counter ion.

That is, it is calculated by the following calculation formula.

Amount of phosphorus oxo acid group (C type) = amount of phosphorus oxo acid group (acid type)/{l+(W-l)x A/1000}

A[mmol/g]: Total amount of anions derived from phosphorus oxo acid groups (total amount of dissociated acid of phosphorus oxo acid groups) of fiber raw materials W: Formula amount per valence of cation C (e.g., Na is 23, A1 is 9)

[0040]

FIG. 2 is a graph showing a relationship between a drop amount of NaOH and a pH of a dispersion containing a fiber raw material having a carboxyl group or a sulfo group as an oxo acid group. The amount of introduction of the carboxyl group or the amount of introduction of the sulfo group into the fiber raw material is measured, for example, as follows.

First, a dispersion liquid containing a fiber raw material is treated with a strong acidic ion exchange resin. If necessary, before treatment with a strongly acidic ion exchange resin, a fiberizing treatment similar to the defibrication treatment step described later may be performed on the measurement target.

Next, the pH change is then observed while adding an aqueous sodium hydroxide solution to obtain a titration curve as shown in the upper part of FIG. 2. The titration curve shown in the upper part of FIG. 2 plots the measured pH versus the amount of alkali added, and the titration curve shown in the lower part of FIG. 2 plots the increment (differential value) (1 /mmol) of pH versus the amount of alkali added. In this neutralization titration, in a curve in which the measured pH is plotted against the amount of alkali added, one point at which the increment of pH (derivative value of pH with respect to the amount of alkali dropped) becomes maximum is confirmed, and this maximum point is referred to as a first end point. Here, a region from the start of titration to the first end point in FIG. 2 is referred to as a first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the dispersion used for titration. Then, by dividing the amount of alkali (mmol) required in the first region of the titration curve by the solid content (g) in the dispersion containing the fiber raw material to be titrated, the amount of introduction of the carboxyl group (mmol /g) or the amount of introduction of the sulfo group (mmol /g) is calculated.

[0041]

Since the denominator is the mass of the acid type fiber raw material, the amount of the carboxyl group introduced (mmol /g) indicates the amount of the carboxyl group contained in the acid type fiber raw material (hereinafter referred to as the amount of the carboxyl group (acid type)). On the other hand, in the case where the counter ion of the carboxyl group is substituted with an arbitrary cation C so as to have a charge equivalent, the amount of the carboxyl group of the fiber raw material in which the cation C is a counter ion (hereinafter referred to as a carboxyl group amount (C type)) can be obtained by converting the denominator into the mass of the fiber raw material when the cation C is a counter ion. That is, it is calculated by the following calculation formula.

Carboxyl group amount (C type) = carboxy group amount (acid type)/{l+(W-l)x(carboxy group amount (acid type)) /1000}

W: Formula amount per valence of cation C (e.g., Na is 23, A1 is 9)

[0042]

Since the denominator is the mass of the acid type fiber raw material, the sulfo group introduction amount (mmol /g) indicates the sulfo group amount (hereinafter referred to as the sulfo group amount (acid type)) of the acid type fiber raw material. On the other hand, when the counter ion of the sulfo group is substituted with an arbitrary cation C so as to have a charge equivalent, the denominator is converted into the mass of the fiber raw material when the cation C is a counter ion, whereby the sulfo group amount of the fiber raw material in which the cation C is a counter ion (hereinafter, the sulfo group amount (C type)) can be obtained. That is, it is calculated by the following calculation formula.

Sulfo group amount (C type) = sulfo group amount (acid type)/{l+(W-l)x(sulfo group amount (acid type)) /1000}

W: Formula amount per valence of cation C (e.g., Na is 23, A1 is 9)

[0043]

In the measurement of the amount of oxo acid groups by the titration method, when the drop amount of one drop of the sodium hydroxide aqueous solution is too large or the titration interval is too short, an accurate value may not be obtained, for example, the amount of the oxo acid group is lower than the original amount. As an appropriate drop amount and titration interval, for example, 10 to 50 pL of 0.1 N sodium hydroxide aqueous solution is preferably titrated every 5 to 30 seconds. In order to eliminate the influence of carbon dioxide dissolved in the fiber raw material-containing slurry, for example, measurement is preferably performed while an inert gas such as nitrogen gas is blown into the slurry from 15 minutes before the start of titration to the end of titration.

[0044]

The oxo acid group introduction step may be performed at least once, or may be repeated twice or more. By performing two or more oxo acid group introduction steps, many oxo acid groups can be introduced into the fiber raw material.

[0045]

<Step (B)>

The method for producing a fibrous material of the present invention preferably further comprises a defibration treatment step (B) after the step (A) described above. The step (B) is a step of defibrating the oxo acid group-introduced fiber. Thus, ultrafme cellulose fibers are obtained. In the present specification, the ultrafme cellulose fibers include cellulose nanofibers (CNF) and cellulose nanocrystals (CNC).

[0046]

In the step (B), for example, a defibration treatment apparatus can be used. The defibration treatment apparatus is not particularly limited, and for example, a high-speed fiber disintegrator, a grinder (ceramic pulverizer), a high-pressure homogenizer, an ultrahigh-pressure homogenizer, a high-pressure collision type pulverizer, a ball mill, a bead mill, a disc refiner, a conical refiner, a biaxial kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater can be used. Among the above-mentioned defibration treatment apparatuses, it is more preferable to use a high-speed fiber disintegrator, a high-pressure homogenizer, or an ultrahigh-pressure homogenizer, which is less influenced by the grinding media and is less likely to cause contamination.

[0047]

In the step (B), for example, the oxo acid group-introduced fiber is preferably diluted with a dispersion medium to form a slurry. As the dispersion medium, one type or two or more types selected from water and organic solvents such as polar organic solvents can be used. The polar organic solvent is not particularly limited, and examples thereof include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monon-butyl ether, and propylene glycol monomethyl ether. Examples of the ester include ethyl acetate and butyl acetate. Examples of the aprotic polar solvent include dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl -2-pyrrolidinone (NMP).

[0048]

The solid content concentration of the oxo acid group-introduced fiber at the time of the defibration treatment can be suitably set. The slurry obtained by dispersing the oxo acid group-introduced fibers in the dispersion medium may contain a solid content other than the oxo acid group-introduced fibers such as urea having hydrogen bonding property.

[0049]

<Other Processes>

Washing Step

In the method for producing a fibrous material according to the present embodiment, a washing step can be performed on the oxo acid group-introduced fiber, if necessary. The washing step is carried out, for example, by washing the oxo acid group-introduced fibers with water or an organic solvent. The washing step may be performed after each step described later, and the number of times of washing performed in each washing step is not particularly limited. [0050]

Alkali Treatment Step

In the method for producing a fibrous material, an alkali treatment step may be provided between the oxo acid group introduction step (step (A)) and the defibration treatment step (step (B)). The alkali treatment method is not particularly limited, and examples thereof include a method of immersing the oxo acid group-introduced fiber in an alkali solution. In this specification, the alkali treatment step is also referred to as a neutralization treatment step.

[0051]

The alkali compound contained in the alkali solution is not particularly limited, and may be an inorganic alkali compound or an organic alkali compound. In the present embodiment, for example, sodium hydroxide or potassium hydroxide is preferably used as the alkali compound because of its high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. Among them, the solvent contained in the alkali solution is preferably water or a polar solvent containing a polar organic solvent exemplified by alcohol, and more preferably an aqueous solvent containing at least water. The alkali solution is preferably, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution because of its high versatility.

[0052]

The temperature of the alkali solution in the alkali treatment step is not particularly limited, but is preferably 5°C or more and 80°C or less, and more preferably 10° C or more and 60° C or less. The immersion time of the oxo acid group-introduced fiber in the alkali solution in the alkali treatment step is not particularly limited, but is preferably 5 minutes or more and 30 minutes or less, and more preferably 10 minutes or more and 20 minutes or less. The amount of the alkali solution used in the alkali treatment is not particularly limited, but is, for example, preferably 100 mass % or more and 100000 mass % or less, and more preferably 1000 mass % or more and 10000 mass % or less, based on the absolute dry mass of the oxo acid group-introduced fiber.

[0053]

In order to reduce the amount of the alkali solution used in the alkali treatment step, the oxo acid group-introduced fiber may be washed with water or an organic solvent after the oxo acid group introduction step and before the alkali treatment step. After the alkali treatment step and before the defibration treatment step, the oxo acid group-introduced fiber subjected to the alkali treatment is preferably washed with water or an organic solvent from the viewpoint of improving the handling property.

[0054]

(Cellulose-containing material (Cellulose-containing composition))

Another embodiment of the present invention is a fibrous material produced by the above-described method of producing a fibrous material. In this case, the fibrous material preferably contains cellulose fibers having a fiber width of 1000 nm or less. Another embodiment of the present invention is a cellulose-containing material comprising cellulose fibers having a group derived from an oxo acid and having a fiber width of 1000 nm or less. Here, the cellulose-containing material contains cellulose fibers having a fiber width of 1000 nm or less and a polyvalent metal, and the content of the polyvalent metal in the cellulose-containing material is 50 to 1000 ppm. The content of the polyvalent metal in the cellulose-containing material may be 50 ppm or more, preferably 60 ppm or more, more preferably 70 ppm or more, and still more preferably 80 ppm or more. The content of the polyvalent metal in the cellulose-containing material may be 1000 ppm or less, preferably 900 ppm or less, and more preferably 800 ppm or less.

[0055]

The content of the polyvalent metal in the cellulose-containing material is measured by the following method. First, the cellulose-containing material is dried to dryness at 105°C to obtain an absolutely dried solid content containing ultrafme cellulose fibers. 5.0 mL of nitric acid is added to 0.1 g of the absolutely dried solid content, and wet decomposition is performed using a wet decomposition apparatus (MARS5 manufactured by CEM) and then the amount of polyvalent metal contained in the cellulose-containing material is measured using an ICP emission spectrometry apparatus (CIROS120 manufactured by Ametec). The multivalent metal (polyvalent metal) includes a multivalent metal atom and a multivalent metal ion.

The element constituting the multivalent metal means a divalent or higher-valent metal element. The divalent or higher-valent metal element is preferably Fe, Cu, Cr, Ni, Mo, Mn, or the like. That is, the element constituting the multivalent metal is preferably at least one element selected from the group consisting of Fe, Cu, Cr, Ni, Mo and Mn. The elements constituting the multivalent metal may be one kind or two or more kinds.

In the case where the step (A) is carried out in a SUS304 container, the elements constituting the multivalent metal in the cellulose-containing material in the present embodiment include at least Fe, Cr, Ni, and Mn. In the case where the step (A) is carried out in a SUS316 or SUS316L container, elements constituting the multivalent metal in the cellulose-containing material in the present embodiment include at least Fe, Cr, Ni, Mo and Mn.

[0056]

The cellulose fibers having a fiber width of 1000 nm or less in the cellulose-containing material may further have a group derived from a corrosion inhibitor. Among them, the ultrafme cellulose fibers preferably have a group derived from at least one selected from urea and a urea derivative, and preferably has a carbamide group.

[0057]

The cellulose-containing material includes ultrafme cellulose fibers having a fiber width of 1000 nm or less. The fiber width of the ultrafme cellulose fibers is more preferably 100 nm or less, and further preferably 50 nm or less. When the ultrafme cellulose fibers are cellulose nanofibers (CNF), the fiber width is particularly preferably 8 nm or less.

[0058] The fiber width of the ultrafme cellulose fibers can be measured by, for example, electron microscopy. The average fiber width of the ultrafme cellulose fibers is, for example, 1000 nm or less. The average fiber width of the cellulose fibers is preferably, for example, 2 nm or more and 1000 nm or less, more preferably 2 nm or more and 100 nm or less, and still more preferably 2 nm or more and 50 nm or less. When the ultrafme cellulose fibers are cellulose nanofibers (CNF), the average fiber width of the ultrafme cellulose fibers is particularly preferably 2 nm or more and 10 nm or less. When the average fiber width of the fine cellulose fibers is within the above range, dissolution in water as cellulose molecules can be suppressed, and the characteristics of the ultrafme cellulose fibers can be more easily exhibited. The ultrafme cellulose fibers are, for example, monofilamentous cellulose.

[0059]

The average fiber width of the ultrafme cellulose fibers is measured, for example, by using an electron microscope as follows. First, an aqueous suspension of ultrafme cellulose fibers having a concentration of 0.05 % by mass or more and 0.1 % by mass or less is prepared, and this suspension is cast on a hydrophilized carbon film-coated grid to prepare a TEM observation sample. If a wide fiber is included, SEM images of the surface cast on the glass may be observed. Next, an electron microscope image is observed at a magnification of 1000 times, 5000 times, 10000 times, or 50000 times depending on the width of the fiber to be observed. However, the sample, observation condition, and magnification are adjusted so as to satisfy the following condition.

[0060]

(1) One straight line X is drawn at an arbitrary position in the observed image, and 20 or more fibers intersect with the straight line X.

(2) A straight line Y perpendicularly intersecting the straight line is drawn in the same image, and 20 or more fibers intersect with the straight line Y.

[0061]

The width of the fiber intersecting the straight line X and the straight line Y is visually read from the observation image satisfying the above condition. In this way, three or more sets of observed images of at least surface portions which do not overlap each other are obtained. Next, for each image, the widths of the fibers intersecting the straight line X and the straight line Y are read. Thus, at least 20x2x3=120 fiber widths are read. The average value of the read fiber widths is defined as the average fiber width of the ultrafme cellulose fibers.

[0062]

The fiber length of the ultrafme cellulose fibers is not particularly limited, but is preferably 0.1 pm or more and 1000 pm or less, more preferably 0.1 pm or more and 800 pm or less, and still more preferably 0.1 pm or more and 600 pm or less. When the ultrafme cellulose fibers are cellulose nanocrystals (CNC), the fiber length of the cellulose nanocrystals (CNC) is preferably 0.05 pm or more and 0.3 pm or less. The fiber length of the ultrafme cellulose fibers can be determined by image analysis using, for example, TEM, SEM, or AFM. [0063]

When the ultrafme cellulose fibers is cellulose nanofiber (CNF), the fiber width of the ultrafme cellulose fibers is preferably 10 nm or less, and more preferably 5 nm or less. The fiber length is preferably 0.3 pm or more. That is, the aspect ratio (ratio of fiber length /fiber width) of cellulose nanofibers (CNF) is preferably 30 or more. On the other hand, when the ultrafme cellulose fibers is cellulose nanocrystal (CNC), the fiber width of the cellulose nanocrystal (CNC) is preferably greater than 10 nm and less than or equal to 30 nm, and the fiber length is preferably less than or equal to 0.3 pm. That is, the aspect ratio (ratio of fiber length /fiber width) of cellulose nanocrystal (CNC) is preferably 10 or more and less than 30.

[0064]

The ultrafme cellulose fibers preferably have an I-type crystal structure. The fact that the ultrafme cellulose fibers has an I-type crystal structure can be identified in a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKa (l =1.5418 A) monochromated with graphite. Specifically, it can be identified by having typical peaks at two positions, i.e., in the vicinity of 20 of 14° or more and 17° or less and in the vicinity of 20 of 22° or more and 23° or less. The proportion of the I-type crystal structure in the ultrafme cellulose fibers is, for example, preferably 30% or more, more preferably 40% or more, and still more preferably 50% or more. Thus, further excellent performance in terms of heat resistance and low linear thermal expansion coefficient can be expected. The crystallinity is determined from the X-ray diffraction profile and the pattern by a conventional method (Seagal et al., Textile Research Journal, vol. 29, page 786, 1959.). The ultrafme cellulose fibers in the present embodiment preferably has both crystalline regions and amorphous regions, for example.

[0065]

(Acid Treatment Agent for Fiber Material Treatment)

The present invention may relate to an acid treatment agent for treating a fiber raw material comprising an oxo acid and a compound represented by the following formula (1). Here, when the content of the oxo acid in the acid treatment agent for fiber raw material treatment is c parts by mass and the content of the compound of the formula (1) in the acid treatment agent for fiber raw material treatment is d parts by mass, the value of d/c is 0.32 or more. In the present specification, the acid treatment agent for fiber raw material treatment is an agent used when the fiber raw material is subjected to oxo-oxidation treatment. The acid treatment agent for fiber raw material treatment may contain a solvent and other optional components in addition to the oxo acid and the compound represented by the following formula (1).

[0066]

R N ί¾ Formula (1 )

[0067]

In the above formula (1), X represents an oxygen atom or a sulfur atom; Ri represents an alkyl group, an alkenyl group, a cycloalkyl group, an alkoxy group or -NHRn; and R2 represents a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group or an aryl group; in -NHR11, R11 is a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group or an aryl group.

[0068]

Specific examples and preferable ranges of Ri and R2 in the above (1) are as described above.

[0069]

The content of the oxo acid is preferably 4 parts by mass or more, more preferably 8 parts by mass or more, and still more preferably 20 parts by mass or more based on the total mass of the acid treatment agent for fiber raw material treatment. The content of the oxo acid is preferably 8700 parts by mass or less, more preferably 4350 parts by mass or less, and still more preferably 1740 parts by mass or less, based on the total mass of the acid treatment agent for fiber raw material treatment.

[0070]

The content of the compound represented by the formula (1) is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and still more preferably 5 parts by mass or more based on the total mass of the acid treatment agent for fiber raw material treatment. The content of the compound represented by the formula (1) is preferably 15960 parts by mass or less, more preferably 7980 parts by mass or less, and still more preferably 3192 parts by mass or less, based on the total mass of the fiber raw material treatment acid treatment agent.

[0071]

When the content of the oxo acid in the acid treatment agent for fiber raw material treatment is c parts by mass and the content of the compound of the formula (1) in the acid treatment agent for fiber raw material treatment is d parts by mass, the value of d/c may be 0.32 or more, preferably 0.64 or more, more preferably 0.94 or more, and still more preferably 1.30 or more. The value of d/c is preferably 30 or less, more preferably 1.0 or less, and still more preferably 0.95 or less. When the value of d/c in the acid treatment agent for fiber raw material treatment is within the above range, a fibrous material in which coloration is suppressed can be obtained. Further, by setting the value of d/c within the above range, the amount of polyvalent metal mixed into the fibrous material can be reduced, and a fibrous material with higher purity can be obtained.

[0072]

When the content of the oxo acid in the acid treatment agent for fiber raw material treatment is c ' mol and the content of the compound of the formula (1) in the acid treatment agent for fiber raw material treatment is d ' mol, the value of d 7c ' is preferably 0.15 or more, more preferably 0.30 or more, and still more preferably 0.75 or more. The value of d 7c ' is preferably 52 or less, more preferably 2.5 or less, and still more preferably 2.0 or less. When the value of d 7c ' in the acid treatment agent for fiber raw material treatment is within the above range, a fibrous material in which coloration is suppressed can be obtained. Further, by setting the value of d 7c ' within the above range, the amount of polyvalent metal mixed into the fibrous material can be reduced, and a fibrous material with higher purity can be obtained.

Examples

[0073]

Hereinafter, features of the present invention will be described more specifically with reference to Examples and Comparative Examples. The materials, amounts, proportions, details of treatment, treatment procedures, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited to the following specific examples.

[0074]

<Example 1-1>

Cotton Linter pulp (solid content: 94 mass %, basis weight: 571 g /m ² sheet) manufactured by GAOMI CHEMICAL FIBER was used as the raw material pulp.

[0075]

2956 parts by mass of a chemical solution containing 870 parts by mass of pure sulfuric acid, 1596 parts by mass of urea and 490 parts by mass of water was prepared. 2956 parts by mass of the prepared chemical solution and 100 parts by mass (absolute dry mass) of the above raw material pulp were injected into a container made of stainless steel (SUS) 316L and heated at 45°C for 1 hour.

[0076]

Next, the obtained pulp after the reaction was subjected to a washing treatment. The washing treatment was carried out by repeating an operation of stirring a pulp dispersion obtained by pouring 10 L of ion exchange water into 100 g (absolute dry mass) of pulp so that the pulp was uniformly dispersed, and then filtering and dehydrating the pulp. When the electrical conductivity of the filtrate reached 100 pS /cm or less, the washing end point was determined. [0077]

Next, the washed pulp was subjected to neutralization treatment as follows. First, 10 L of ion-exchanged water was poured into 100 g (absolute dry mass) of the washed pulp to dilute the pulp, and then 1 N sodium hydroxide aqueous solution was added little by little while stirring to obtain a pulp slurry having a pH of 12 or more and 13 or less. Next, the pulp slurry was dehydrated to obtain a pulp subjected to neutralization treatment. Further, the pulp after the neutralization treatment was subjected to the washing treatment.

[0078]

An infrared absorption spectrum of the pulp thus obtained was measured using FT-IR. As a result, absorption based on a sulfo group was observed near 1350 cm ¹ and at 1180 cm ¹ , and it was confirmed that a sulfo group was added to the pulp.

[0079]

The obtained pulp was subjected to a microfabrication treatment as follows. First, ion-exchanged water was added to the pulp to prepare a slurry having a solid content concentration of 0.1 mass %. This slurry was treated with a rotary high-speed homogenizer (Kreamix 2.2S, manufactured by M Technique) at 21500 rpm for 2 hours to obtain a ultrafme cellulose fiber dispersion.

[0080]

The resulting ultrafme cellulose fiber dispersion was centrifuged to obtain a supernatant liquid. When the obtained supernatant liquid was observed by a transmission electron microscope, ultrafme cellulose fibers having a width of about 20 nm was observed.

[0081]

Comparative Example 1-1>

A ultrafme cellulose fiber dispersion containing ultrafme cellulose fibers was obtained in the same manner as in Example 1-1, except that the amount of urea added was changed from 1596 parts by mass to 266 parts by mass to prepare a chemical solution, and 1626 parts by mass of the prepared chemical solution was used.

[0082]

Comparative Example l-2>

A ultrafme cellulose fiber dispersion containing ultrafme cellulose fibers was obtained in the same manner as in Example 1-1, except that the amount of urea added was changed from 1596 parts by mass to 0 parts by mass to prepare a chemical solution, and 1360 parts by mass of the prepared chemical solution was used.

[0083]

<Reference Example 1-1>

A ultrafme cellulose fibers dispersion containing ultrafme cellulose fibers was obtained in the same manner as in Comparative Example 1-2, except that a reaction vessel made of Teflon was used instead of the reaction vessel made of SUS316L.

[0084] <Reference Example l-2>

A ultrafme cellulose fiber dispersion containing ultrafme cellulose fibers was obtained in the same manner as in Example 1-1, except that a chemical solution containing 11 parts by mass of hydrochloric acid pure, 54 parts by mass of urea, and 153 parts by mass of water was prepared, 218 parts by mass of the prepared chemical solution was added to 10 parts by mass of raw material pulp (absolute dry mass), and the reaction temperature was 95° C. and the heating time was 2 hours.

[0085]

<Reference Example l-3>

A ultrafme cellulose fiber dispersion containing ultrafme cellulose fibers was obtained in the same manner as in Reference Example 1-2, except that the amount of urea added was changed from 54 parts by mass to 0 parts by mass to prepare a chemical solution, and 164 parts by mass of the prepared chemical solution was used.

[0086]

<Example 2-l>

As the raw material pulp, a needle leaf tree kraft pulp (A solid content of 93 % by mass, a basis weight of 245 g/m ² sheet form, and a Canada Standard Filtration Filtration Factor (CSF) measured in accordance with JIS P 8121-2:2012 after disintegration were 700 ml.) manufactured by Oji Paper was used.

[0087]

This raw material pulp was subjected to phosphorylation treatment as follows. First, a mixed aqueous solution of phosphoric acid and urea was added to 100 parts by mass (absolute dry mass) of the raw material pulp to prepare a chemical solution impregnated pulp in an amount of 38 parts by mass of phosphoric acid, 120 parts by mass of urea, and 150 parts by mass of water. Next, the obtained chemical solution impregnated pulp was heated in a container made of SUS304 in a hot air dryer at 165° C. for 600 seconds, and a phosphate group was introduced into cellulose in the pulp to obtain a phosphorylated pulp.

[0088]

Next, the obtained phosphorylated pulp was washed. The washing treatment was carried out by repeating an operation of stirring a pulp dispersion obtained by pouring 10 L of ion exchange water into 100 g (absolute dry mass) of phosphorylated pulp so that the pulp was uniformly dispersed and then filtering and dehydrating the pulp. When the electrical conductivity of the filtrate reached 100 pS /cm or less, the washing end point was determined.

[0089]

Next, the washed phosphorylated pulp was subjected to neutralization treatment as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion exchange water, and then 1 N sodium hydroxide aqueous solution was added little by little while stirring to obtain a phosphorylated pulp slurry having a pH of 12 or more and 13 or less. Next, the phosphorylated pulp slurry was dehydrated to obtain a neutralized phosphorylated pulp. Next, the phosphorylated pulp after the neutralization treatment was subjected to the washing treatment. [0090]

An infrared absorption spectrum of the phosphorylated pulp thus obtained was measured using FT-IR. As a result, absorption based on phosphate groups was observed near 1230 cm ¹ , and it was confirmed that phosphate groups were added to the pulp. Further, when the phosphorylated pulp obtained was tested and analyzed by an X-ray diffractometer, a typical peak was observed at two positions, i.e., in the vicinity of 20 =14° or more and 17° or less and in the vicinity of 20 =22° or more and 23° or less, and it was confirmed that the cellulose I-type crystal was present.

[0091]

Ion exchange water was added to the phosphorylated pulp to prepare a slurry having a solid content concentration of 2 mass %. This slurry was treated twice at a pressure of 200 MPa with a wet type micronizer (Star Burst, manufactured by Sugino Machine) to obtain a ultrafme cellulose fiber dispersion containing ultrafme cellulose fibers.

[0092]

X-ray diffraction confirmed that the ultrafme cellulose fibers retained cellulose I-type crystals. The fiber width of the ultrafme cellulose fibers was measured using a transmission electron microscope and found to be 3 to 5 nm.

[0093]

<Example 2-2>

A ultrafme cellulose fiber dispersion containing ultrafme cellulose fibers was obtained in the same manner as in Example 2-1, except that the amount of urea added was 12 parts by mass instead of 120 parts by mass.

[0094]

Comparative Example 2-l>

A ultrafme cellulose fiber dispersion containing ultrafme cellulose fibers was obtained in the same manner as in Example 2-1, except that the amount of urea added was 0 parts by mass instead of 120 parts by mass.

[0095] evaluation Method>

[Appearance of Reaction Product]

In Examples, Comparative Examples, and Reference Examples, cellulose fibers obtained after the reaction were visually observed to qualitatively evaluate the degree of coloring.

O ( A ) : The cellulose fiber obtained after the reaction is white.

D ( B ) : The cellulose fiber obtained after the reaction is pale green or brown x ( C ) : The cellulose fiber obtained after the reaction is dark green or black.

[0096]

[Measurement of Amount of Multivalent Metal in Cellulose-containing Material] The ultrafme cellulose fiber dispersions obtained in Examples, Comparative Examples and Reference Examples were dried at 105°C until they were fast-dried to obtain an absolutely dried solid content of the ultrafme cellulose fibers. 5.0 mL of nitric acid was added to 0.1 g of the absolutely dried solid content of the ultrafme cellulose fibers, and wet decomposition was performed using a wet decomposition apparatus (MARS5 manufactured by CEM) and then the amount of polyvalent metal contained in the fast-dried solid content of the ultrafme cellulose fibers was measured using an ICP emission spectrometry apparatus (CIROS120 manufactured by Ametec).

[0099]

In Examples, coloring of the reaction product after the heating reaction was suppressed, and cellulose fibers excellent in appearance were obtained. On the other hand, in the comparative example, the reaction product after the heating reaction was colored.