OXIDIZED CELLULOSE, NANOCELLULOSE, AND THEIR DISPERSIONS

Abstract

The present invention provides an oxidized cellulose that exhibits an excellent fibrillatability and is an oxide of a cellulose raw material by a hypochlorous acid or a salt thereof. The oxidized cellulose substantially does not contain a N-oxyl compound and has a degree of polymerization of not more than 600.

Claims

1. An oxidized cellulose that is an oxide of a cellulose raw material by a hypochlorous acid or a salt thereof, wherein the oxidized cellulose substantially does not comprise a N-oxyl compound and has a degree of polymerization of not more than 600.

2. The oxidized cellulose according to claim 1, wherein the oxidized cellulose has a carboxy group content of 0.30 to 2.0 mmol/g.

3. The oxidized cellulose according to claim 1, wherein an aqueous nanocellulose dispersion obtained by carrying out a fibrillation treatment on an aqueous dispersion of said oxidized cellulose present at a concentration of 0.1 mass % using a planetary centrifugal mixer and conditions of 10 minutes, a revolution rate of 2,000 rpm, and a rotation rate of 800 rpm, has a light transmittance of at least 60%.

4. An oxidized cellulose that is an oxide of a cellulose raw material, wherein an aqueous nanocellulose dispersion obtained by carrying out a fibrillation treatment on an aqueous dispersion of said oxidized cellulose present at a concentration of 0.1 mass % using a planetary centrifugal mixer and conditions of 10 minutes, a revolution rate of 2,000 rpm, and a rotation rate of 800 rpm, has a light transmittance of at least 60%.

5. The oxidized cellulose according to claim 4, wherein the oxidized cellulose is an oxide of a cellulose raw material by a hypochlorous acid or a salt thereof.

6. An oxidized cellulose dispersion in which the oxidized cellulose according to claim 1 is dispersed in a dispersion medium.

7. A nanocellulose having an average fiber width of 1 to 200 nm and provided by the fibrillation of the oxidized cellulose according to claim 1.

8. A nanocellulose obtained by subjecting the oxidized cellulose according to claim 1 to a fibrillation treatment for 3 to 15 minutes using a planetary centrifugal mixer at a revolution rate of 1,200 to 2,500 rpm and a rotation rate of 600 to 1,000 rpm.

9. A nanocellulose dispersion in which the nanocellulose according to claim 7 is dispersed in a dispersion medium.

Description

EXAMPLES

[0088] The present invention is specifically described in the following using examples, but the present invention is not limited to or by these examples. Unless specifically indicated otherwise, in the following “parts” indicates “mass parts” and “%” indicates “mass %”.

[0089] (1) Production of Oxidized Celluloses and Nanocelluloses

Production Example 1

[0090] To provide the cellulose raw material, a softwood pulp (NIST RM 8495, bleached kraft pulp, Sigma-Aldrich) was cut with scissors to 5 mm square and was mechanically fibrillated to a cotton-like form by treatment for 1 minute at 25,000 rpm with a “Wonder Blender WB-1” from Osaka Chemical Co., Ltd.

[0091] 350 g of sodium hypochlorite pentahydrate crystals, which had an available chlorine concentration of 42 mass %, was introduced into a beaker and pure water was added and stirring was performed to obtain an aqueous sodium hypochlorite solution having an available chlorine concentration of 21 mass %. To this was added 35 mass % hydrochloric acid with stirring to provide an aqueous solution having a pH of 11.0. This aqueous sodium hypochlorite solution was heated to 30° C. with a thermostatted water bath while stirring at 200 rpm using a stirrer from Shinto Scientific Co., Ltd. (ThreeOne Motor, BL600) and using a propeller stirring blade; this was followed by the addition of 50 g of the aforementioned mechanically fibrillated softwood kraft pulp (carboxy group content: 0.05 mmol/g).

[0092] After the introduction of the cellulose raw material, and while holding the temperature at 30° C. on the same thermostatted water bath, an oxidation reaction was run for 30 minutes while stirring at 200 rpm using a propeller stirring blade and the aforementioned stirrer while adjusting the pH during the reaction to 11.0 by the addition of 48 mass % sodium hydroxide. After the completion of the reaction, solid-liquid separation was carried out on the product by suction filtration using a PTFE membrane filter having an aperture of 0.1 μm to obtain an oxidized cellulose A. The obtained oxidized cellulose A was washed with pure water, and the carboxy group content measured post-washing for the residue (oxidized cellulose A) was 0.45 mmol/g.

[0093] A 0.1% dispersion was then prepared by the addition of pure water to the oxidized cellulose A, and an aqueous CNF dispersion A, i.e., a nanocellulose dispersion, was obtained by treatment for 10 minutes using a “THINKYMIXER ARE-310” planetary centrifugal mixer from the THINKY Corporation and conditions of a revolution rate of 2,000 rpm and a rotation rate of 800 rpm in mix mode.

[0094] In addition, the N-oxyl compound-derived nitrogen component in the oxidized cellulose A was measured as the amount of nitrogen using a total trace nitrogen analyzer (instrument name: TN-2100H, from Mitsubishi Chemical Analytech Co., Ltd.); the increment from the starting pulp was calculated, giving a result of not more than 1 ppm.

[0095] The available chlorine concentration in the aqueous sodium hypochlorite solution was measured using the following method.

(Measurement of the Available Chlorine Concentration in the Aqueous Sodium Hypochlorite Solution)

[0096] 0.582 g of an aqueous solution of sodium hypochlorite pentahydrate crystals added to pure water was precisely weighed out, and 50 mL of pure water was added and 2 g of potassium iodide and 10 mL of acetic acid were added, followed immediately by tight sealing and standing for 15 minutes in a dark location. After the standing for 15 minutes, the liberated iodine was titrated with a 0.1 mol/L sodium thiosulfate solution, which resulted in a titration volume of 34.55 mL (indicator: starch reagent solution). Correction was performed by carrying out a separate blank test. Since 1 mL of the 0.1 mol/L sodium thiosulfate solution corresponded to 3.545 mg CI, the available chlorine concentration in the aqueous sodium hypochlorite solution was 21 mass %.

[0097] The carboxy group content in the oxidized cellulose was measured using the following method.

(Measurement of the Carboxy Group Content)

[0098] To 60 mL of an aqueous oxidized cellulose dispersion adjusted to an oxidized cellulose concentration of 0.5 mass %, was added 0.1 M aqueous hydrochloric acid solution to bring the pH to 2.5. This was followed by the dropwise addition of a 0.05 N aqueous sodium hydroxide solution and measurement of the electrical conductivity until the pH reached 11.0, and the carboxy group content (mmol/g) was calculated using the following formula from the amount (a) of sodium hydroxide consumed in the weak acid neutralization stage where the electrical conductivity undergoes a gentle change.

carboxy group content=a(mL)×0.05/mass(g) of the oxidized cellulose

Production Example 2

[0099] An oxidized cellulose B and an aqueous CNF dispersion B were obtained by carrying out treatment using the same conditions as in Production Example 1, but using 120 minutes for the reaction time in the oxidation reaction.

Production Example 3

[0100] An oxidized cellulose C and an aqueous CNF dispersion C were obtained by carrying out treatment using the same conditions as in Production Example 1, but using 120 minutes for the reaction time in the oxidation reaction and changing the cellulose raw material to a powdered cellulose (VP-1) from the TDI Corporation.

Production Example 4

[0101] An oxidized cellulose D and an aqueous CNF dispersion D were obtained by carrying out treatment using the same conditions as in Production Example 1, but using 120 minutes for the oxidation reaction time and changing the cellulose raw material to a powdered cellulose (KC Flock W-100GK) from Nippon Paper Industries Co., Ltd.

Production Example 5

[0102] An oxidized cellulose E and an aqueous CNF dispersion E were obtained by carrying out treatment using the same conditions as in Production Example 1, but using 240 minutes for the oxidation reaction time.

Production Example 6

[0103] An oxidized cellulose F and an aqueous CNF dispersion F were obtained by carrying out treatment using the same conditions as in Production Example 1, but using 360 minutes for the oxidation reaction time.

Production Example 7

[0104] An oxidized cellulose G and an aqueous CNF dispersion G were obtained by carrying out treatment using the same conditions as in Production Example 1, but using 50° C. for the oxidation reaction temperature.

Production Example 8

[0105] An oxidized cellulose H and an aqueous CNF dispersion H were obtained by carrying out treatment using the same conditions as in Production Example 1, but using 480 minutes for the oxidation reaction time.

[0106] A sample was prepared by freeze-frying the oxidized cellulose provided by the particular production example and then holding for at least 24 hours at 23° C. and 50% RH, and the solid-state 13C-NMR of the sample was measured. As a result, in all instances it was confirmed that a structure was present in which the hydroxyl groups at positions 2 and 3 of the glucopyranose ring were oxidized with the introduction of carboxy groups. The solid-state 13C-NMR measurement conditions are given below. [0107] (1) sample tube: zirconia tube (4 mm diameter) [0108] (2) magnetic field strength: 9.4 T (1H resonance frequency: 400 MHz) [0109] (3) MAS rotation rate: 15 kHz [0110] (4) pulse sequence: CPMAS method [0111] (5) contact time: 3 ms [0112] (6) waiting time: 5 s [0113] (7) number of scans: 10,000 to 15,000 [0114] (8) measurement instrument: JNM ECA-400 (JEOL Ltd.)

[0115] The results obtained using a model molecule for said oxidized cellulose as the sample and carrying out measurement using two-dimensional NMR also confirmed that the oxidized cellulose yielded by each production example had a structure in which the hydroxyl groups at positions 2 and 3 of the glucopyranose ring were oxidized with the introduction of carboxy groups.

[0116] With regard to position 6, no change in the spectroscopic data was seen between the solid-state 13C-NMR of the cellulose raw material and the solid-state 13C-NMR of the oxidized cellulose, and based on this it was concluded that the hydroxyl group at position 6 was not oxidized and the hydroxyl group remained intact in the oxidized cellulose.

Comparative Production Example 1

[0117] To provide the cellulose raw material, a softwood pulp (NIST RM 8495, bleached kraft pulp, Sigma-Aldrich) was cut with scissors to 5 mm square and was mechanically fibrillated to a cotton-like form by treatment for 1 minute at 25,000 rpm with a “Wonder Blender WB-1” from Osaka Chemical Co., Ltd.

[0118] 30.0 g of sodium hypochlorite pentahydrate crystals, which had an available chlorine concentration of 43 mass %, was introduced into a 100-mL beaker and pure water and 35 mass % hydrochloric acid were added with stirring to obtain an aqueous solution having an available chlorine concentration of 21 mass % and a pH of 11.0. This aqueous sodium hypochlorite solution was heated to 30° C. with a thermostatted water bath while stirring with a stirrer; this was followed by the addition of 0.35 g of the aforementioned mechanically fibrillated softwood kraft pulp.

[0119] After the introduction of the cellulose raw material, and while holding the temperature at 30° C. on the same thermostatted water bath, stirring with a stirrer was carried out for 30 minutes while adding 48 mass % sodium hydroxide in order to maintain pH 11.0. Solid-liquid separation was then carried out on the product by suction filtration using a PTFE membrane filter having an aperture of 0.1 μm to obtain an oxidized cellulose P. The obtained residue (oxidized cellulose P) was washed with pure water and the carboxy group content was then measured at 0.42 mmol/g; the amount of the residue was 0.31 g.

[0120] A 0.1% dispersion was then prepared by the addition of pure water to the obtained oxidized cellulose P, and an aqueous CNF dispersion P was obtained by carrying out a fibrillation treatment for 10 minutes using a “THINKYMIXER ARE-310” planetary centrifugal mixer from the THINKY Corporation and conditions of a revolution rate of 2,000 rpm and a rotation rate of 800 rpm in mix mode.

Comparative Production Example 2

[0121] To provide the cellulose raw material, a softwood pulp (NIST RM 8495, bleached kraft pulp, Sigma-Aldrich) was cut with scissors to 5 mm square and was mechanically fibrillated to a cotton-like form by treatment for 1 minute at 25,000 rpm with a “Wonder Blender WB-1” from Osaka Chemical Co., Ltd.

[0122] 30.3 g of sodium hypochlorite pentahydrate crystals, which had an available chlorine concentration of 42 mass %, was introduced into a beaker and pure water was added with stirring to bring the available chlorine concentration to 14 mass %. To this was added 35 mass % hydrochloric acid with stirring to obtain an aqueous solution having a pH of 9.0. This aqueous sodium hypochlorite solution was heated to 30° C. with a thermostatted water bath while stirring with a stirrer; this was followed by the addition of 0.35 g of the aforementioned mechanically fibrillated softwood kraft pulp.

[0123] After the introduction of the cellulose raw material, and while holding the temperature at 30° C. on the same thermostatted water bath, an oxidation reaction was run by stirring with a stirrer for 30 minutes while adding 48 mass % sodium hydroxide in order to adjust the pH during the reaction to 9.0. After the completion of the reaction, solid-liquid separation was then carried out on the product by suction filtration using a PTFE mesh filter having an aperture of 0.1 μm to obtain an oxidized cellulose Q. The obtained 0.12 g residue was washed with pure water. The carboxy group content was measured on the post-wash residue (oxidized cellulose Q) at 1.12 mmol/g.

[0124] A 0.1% dispersion was then prepared by the addition of pure water to the oxidized cellulose Q, and an aqueous CNF dispersion Q was obtained by carrying out a fibrillation treatment using the same conditions as in Comparative Production Example 1.

Comparative Production Example 3

[0125] To provide the cellulose raw material, a softwood pulp (NIST RM 8495, bleached kraft pulp, Sigma-Aldrich) was cut with scissors to 5 mm square and was mechanically fibrillated to a cotton-like form by treatment for 1 minute at 25,000 rpm with a “Wonder Blender WB-1” from Osaka Chemical Co., Ltd. A wet powder was obtained by thoroughly dispersing the mechanically fibrillated cellulose fibers in water and carrying out suction filtration using a PTFE mesh filter having an aperture of 0.1 μm.

[0126] This wet powder (80 mass % moisture fraction, 20 g as the dry powder) was introduced into a container, and 60 L of an ozone oxygen mixed gas with an ozone concentration of 200 g/m.sup.3 was then added and shaking was performed for 2 minutes at 25° C. After standing at quiescence for 6 hours, the ozone and so forth in the container was removed, after which the oxidized cellulose (oxidized cellulose R) was taken out and washed with pure water by suction filtration using a PTFE mesh filter having an aperture of 0.1 μm. Pure water was added to the obtained oxidized cellulose R to prepare a 2 mass % dispersion, and sodium hydroxide was added to give a 0.3 mass % sodium hydroxide solution. Stirring was carried out for 5 minutes followed by standing at quiescence for 30 minutes at 25° C. Washing with pure water was then performed by suction filtration using a PTFE mesh filter having an aperture of 0.1 μm. Pure water was added to this oxidized cellulose R to prepare a 0.1% dispersion, and an aqueous CNF dispersion R was obtained by performing a fibrillation treatment using the same conditions as in Comparative Production Example 1.

Comparative Production Example 4

[0127] To provide the cellulose raw material, a softwood pulp (NIST RM 8495, bleached kraft pulp, Sigma-Aldrich) was cut with scissors to 5 mm square and was mechanically fibrillated to a cotton-like form by treatment for 1 minute at 25,000 rpm with a “Wonder Blender WB-1” from Osaka Chemical Co., Ltd.

[0128] 4.92 g sodium periodate was introduced into a beaker and pure water was added to make an aqueous solution (total amount=600 mL). This aqueous sodium periodate solution was heated to 55° C. with a thermostatted water bath while stirring at 200 rpm using a stirrer from Shinto Scientific Co., Ltd. (ThreeOne Motor, BL600) and using a propeller stirring blade; this was followed by the addition of 6 g of the aforementioned mechanically fibrillated softwood kraft pulp.

[0129] After the introduction of the cellulose raw material, and while holding the temperature at 55° C. on the same thermostatted water bath, stirring was carried out for 3 hours under the same conditions using a stirrer. After the completion of the reaction, solid-liquid separation was carried out on the product by suction filtration using a PTFE membrane filter having an aperture of 0.1 μm to obtain an oxidized cellulose S, which was then washed with pure water.

[0130] The product obtained as described above was then added to a 1 M aqueous acetic acid solution that contained sodium chlorite, and stirring was carried out under the same stirring conditions as above for 48 hours at 25° C. After the completion of the reaction, the product was subjected to solid-liquid separation by suction filtration using a PTFE membrane filter having an aperture of 0.1 μm, and washing with pure water was performed. Pure water was added to the obtained oxidized cellulose S to prepare a 0.1% dispersion, and an aqueous CNF dispersion S was obtained by performing a fibrillation treatment using the same conditions as in Comparative Production Example 1.

Comparative Production Example 5

[0131] To provide the cellulose raw material, a softwood pulp (NIST RM 8495, bleached kraft pulp, Sigma-Aldrich) was cut with scissors to 5 mm square and was mechanically fibrillated to a cotton-like form by treatment for 1 minute at 25,000 rpm with a “Wonder Blender WB-1” from Osaka Chemical Co., Ltd.

[0132] 0.016 g TEMPO and 0.1 g sodium bromide were introduced into a beaker; pure water was added with stirring to prepare an aqueous solution; and 1.0 g of the aforementioned mechanically fibrillated softwood pulp was added.

[0133] This aqueous solution was heated to 25° C. on a thermostatted water bath while stirring with a stirrer, after which 0.1 M sodium hydroxide was added with stirring to prepare an aqueous solution having a pH of 10.0. To this was added 2.58 g of an aqueous sodium hypochlorite solution having an available chlorine concentration of 13.2 mass %, and, while holding the temperature at 25° C. on the same thermostatted water bath, stirring with a stirrer was performed for 120 minutes while adjusting the pH during the reaction to 10.0 by adding 0.1 M sodium hydroxide.

[0134] After the completion of the reaction, the product was subjected to solid-liquid separation by suction filtration using a PTFE membrane filter having an aperture of 0.1 μm to obtain an oxidized cellulose T. The obtained residue (oxidized cellulose T) was washed with pure water, followed by measurement of the carboxy group content. The carboxy group content was 1.55 mmol/g, and the amount of the residue was approximately 1.0 g. Pure water was added to the obtained oxidized cellulose T to prepare a 0.1% dispersion, and an aqueous CNF dispersion T was obtained by carrying out a fibrillation treatment using the same conditions as in Comparative Production Example 1. The N-oxyl compound-derived nitrogen component in the oxidized cellulose T was measured as the amount of nitrogen using the same conditions as in Production Example 1, and the result, calculated as the increment from the starting pulp, was 5 ppm.

[0135] (2) Evaluation 1

Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-5

[0136] The following evaluations were carried out using the oxidized celluloses and aqueous CNF dispersions yielded by each of Production Examples 1 to 8 and Comparative Production Examples 1 to 5. The results of the evaluations are given in Table 1.

[0137] [Measurement of the Viscosity-Average Degree of Polymerization]

[0138] The oxidized cellulose was added to an aqueous sodium borohydride solution that had been adjusted to pH 10, and a reduction treatment was run for 5 hours at 25° C. The amount of sodium borohydride was 0.1 g per 1 g of the oxidized cellulose. After the reduction treatment, solid-liquid separation and water washing were performed by suction filtration, and the obtained oxidized cellulose was freeze-dried. 0.04 g of the dried oxidized cellulose was added to 10 mL pure water; stirring was performed for 2 minutes; and 10 mL of a 1 M cupriethylenediamine solution was added and dissolution was carried out. Then, using a capillary viscometer, the efflux time of a blank solution and the efflux time of the cellulose solution were measured at 25° C. The relative viscosity (η.sub.r), specific viscosity (η.sub.sp), and intrinsic viscosity ([η]) were determined in order using the following formulas from the efflux time (t0) for the blank solution, the efflux time (t) for the cellulose solution, and the oxidized cellulose concentration (c [g/mL]), and the degree of polymerization (DP) of the oxidized cellulose was calculated using the viscosity law formula.

η.sub.r=η/η.sub.0=t/t0

η.sub.sp=η.sub.r−1

[η]=η.sub.sp/(100×c(1+0.28η.sub.sp))

DP=175×[η]

[0139] [Measurement of Average Fiber Width]

[0140] Pure water was added to each of the aqueous CNF dispersions A to H and P to T obtained as described above in order to adjust the nanocellulose concentration in the aqueous CNF dispersion to 5 ppm. After the concentration adjustment, the aqueous CNF dispersion was naturally dried on a mica substrate, and shape observation of the nanocellulose was performed in AC mode using an “MFP-3D Infinity” from Oxford Asylum. For the average fiber width, using the software provided with the “MFP-3D Infinity”, the number-average fiber width [nm] was determined using cross-sectional height in shape image=fiber width for at least 50 of the fibers.

[0141] [Ease-of-Fibrillatability]

Fibrillation Method A

[0142] Each of the aqueous CNF dispersions A to H and P to T obtained as described above was introduced into a 10 mm-thick quartz cell, and the light transmittance at a wavelength of 660 nm was measured using a spectrophotometer (JASCO V-550). The solids concentration for the aqueous CNF dispersions was 0.1 mass % in all instances. A higher light transmittance indicates a more thorough fibrillation to microfine fibers, even at mild conditions, and a better ease-of-fibrillatability. The evaluation criteria are as follows (this also applies for fibrillation method B). [0143] ++: light transmittance of at least 80% [0144] +: light transmittance of at least 70% but less than 80% [0145] Δ: light transmittance of at least 60% but less than 70% [0146] ×: light transmittance of less than 60%

[0147] Fibrillation Method B

[0148] Each of the oxidized celluloses A to H and P to T obtained as described above was mixed with water to prepare the aqueous oxidized cellulose dispersion having a solids concentration adjusted to 0.1%. This aqueous oxidized cellulose dispersion was introduced into a glass container having a volume of 13.5 mL, and treatment was carried out for 10 minutes using a vortex mixer (VTX-3000L) from LMS to obtain the aqueous CNF dispersion. The solids concentration of each aqueous CNF dispersion was 0.1 mass % in all instances. Each of the aqueous CNF dispersions was introduced into a 10 mm-thick quartz cell, and the light transmittance at a wavelength of 660 nm was measured using a spectrophotometer (JASCO V-550). The measurement values were evaluated using the same four-level scale as for fibrillation method A.

[0149] [Slurry Viscosity Stability]

[0150] Water-based slurries (50 g) containing 30 mass % titanium oxide (R-820, Ishihara Sangyo Kaisha, Ltd.) and each particular aqueous CNF dispersion A-H, P-T were prepared, while changing the amount of nanocellulose addition so the initial viscosity, i.e., the viscosity immediately after preparation of the slurry, was the same in each example (300 mPa.Math.s). A “THINKYMIXER ARE-310” mixer from the THINKY Corporation (mix mode, revolution rate=2,000 rpm, rotation rate=800 rpm, 20 minutes) was used for the mixing to prepare the water-based slurries.

[0151] The viscosity was measured immediately after preparation (initial viscosity) and after standing at quiescence for 1 week, and the percentage change in the viscosity was calculated using the following formula and the viscosity stability of the water-based slurry was evaluated using the evaluation criteria provided below.

percentage change in viscosity (%)=(N2/N1)×100

[0152] (In the formula, N1 is the initial viscosity of the slurry and N2 is the viscosity of the slurry after standing at quiescence for 1 week after sample preparation.) [0153] ++: the percentage change in viscosity is less than 105%+ [0154] +: the percentage change in viscosity is at least 105% but less than 110% [0155] Δ: the percentage change in viscosity is at least 110% but less than 115% [0156] ×: the percentage change in viscosity is at least 115%

[0157] Standing at quiescence was carried out in a room (23±2° C.).

[0158] The initial viscosity of the slurry and its viscosity after standing at quiescence for 1 week were measured using the following conditions: after stirring with a spatula at a speed at which bubbles were not introduced, the measurement was performed using an E-type viscometer (TV-22) from Toki Sangyo Co., Ltd. at 25° C. and 100 rpm (shear rate=200 s.sup.−1).

[0159] [Slurry Handling Characteristics]

[0160] A process liquid was prepared by adding aluminum silicate powder and water to each of the aqueous CNF dispersions A to H and P to T to provide 5 mass % of the aluminum silicate powder and 0.5 mass % nanocellulose, with blending and stirring. This process liquid was lightly stirred with a spatula and then scooped up, and dripping of the liquid when the spatula was tilted was visually observed and the slurry handling characteristics were evaluated using the following criteria. [0161] ++: Fluid dripping was produced immediately upon tilting. [0162] +: Fluid dripping was produced from 5 seconds after tilting. [0163] Δ: Fluid dripping was produced from 10 seconds after tilting. [0164] ×: Fluid dripping was not produced even after 15 seconds.

[0165] [Surface Condition after Coating with Slurry (Coating Characteristics)]

[0166] A process liquid was prepared by adding aluminum silicate powder and water to each of the aqueous CNF dispersions A to H and P to T to provide 5 mass % of the aluminum silicate powder and 0.5 mass % nanocellulose, with blending and stirring. The process liquid was coated on a woven fabric (100% polyester, 100 mm×100 mm) to provide an aluminum silicate powder application amount of 5 g/m.sup.2, and drying was carried out. 10 sheets of the coated woven fabric were visually inspected for nonuniform locations of application (application unevenness), and evaluation was performed using the following criteria. [0167] ++: Application unevenness was not seen on any of the 10 sheets. [0168] +: Application unevenness was not seen on 8-9 sheets. [0169] Δ: Application unevenness was not seen on 4 to 7 sheets. [0170] ×: Application unevenness was not seen on 1 to 3 sheets, or application unevenness was seen on all 10 sheets.

TABLE-US-00001 TABLE 1 surface viscosity- condition average carboxy average after degree of group fiber ease-of-fibrillatability slurry slurry coating oxidized oxidation N-oxyl polymer- content width fibrillation fibrillation viscosity handling with cellulose method compound ization (mmol/g) (nm) method A method B stability characteristics slurry Example 1-1 A hypochlorite x 555 0.45 4.5 + + + + + Example 1-2 B 455 0.61 4.2 + + + + + + + + Example 1-3 C 330 0.75 3.2 + + + + + + + + + + Example 1-4 D 350 0.73 3.4 + + + + + + + + + + Example 1-5 E 310 0.82 3.2 + + + + + + + + + + Example 1-6 F 120 0.92 2.7 + + + + + + + + + + Example 1-7 G 140 0.95 2.3 + + + + + + + + Example 1-8 H 90 0.97 2.4 + + + + Δ + + Δ Comparative P hypochlorite x 730 0.42 10.3 x x Δ Δ Δ Example 1-1 Comparative Q 650 1.12 9.7 x x Δ Δ Δ Example 1-2 Comparative R ozone 610 0.43 10.9 x x Δ Δ Δ Example 1-3 oxidation Comparative S periodic 720 1.72 27.1 x x x x x Example 1-4 acid Comparative T TEMPO + 620 1.55 9.0 x x x x x Example 1-5 oxidation

[0171] In Table 1, an “×” is used to indicate the case in which an N-oxyl compound was not used during the oxidation treatment of the cellulose raw material (i.e., the CNF dispersion substantially did not contain N-oxyl compounds), and a “+” is used to indicate the case in which an N-oxyl compound was used (i.e., an N-oxyl compound was present in the CNF dispersion) (the same applies to Table 2).

[0172] For the oxidized celluloses in Examples 1-1 to 1-8, the cellulose microfibrils were readily fibrillated from each other even by mild stirring with a planetary centrifugal mixer or a vortex mixer, and a high light transmittance was exhibited when made into an aqueous CNF dispersion. In addition, a fine cellulose fiber with an average fiber width of not more than 5 nm could be obtained by fibrillation treatment with a planetary centrifugal mixer. Moreover, the viscosity stability, handling characteristics, and coatability were in balance for the slurries of Examples 1-1 to 1-8. In particular, in Examples 1-1 to 1-7, in which the degrees of polymerization were on the order to 3 digit numbers, all of the evaluations of the viscosity stability, handling characteristics, and coatability were “++” or “+”, and the characteristics of the slurries were thus excellent.

[0173] In contrast to this, in Comparative Examples 1-1 and 1-2, in which the degrees of polymerization were 730 and 650, the cellulose microfibrils were resistant to fibrillating therebetween by mild stirring with a planetary centrifugal mixer or vortex mixer and the ease-of-fibrillatability was evaluated as “×”. In addition, the slurry characteristics were all evaluated with “Δ” and were worse than in Examples 1-1 to 1-8. The evaluations of the ease-of-fibrillatability and slurry characteristics for Comparative Examples 1-3 to 1-5, in which different oxidation methods were used, were worse than in the examples.

[0174] (3) Evaluation 2

Examples 2-1 to 2-11 and Comparative Examples 2-1 to 2-5

[Ease-of-Fibrillatability]

[0175] Using the oxidized celluloses A to H and P to T provided by each of the Production Examples 1 to 8 and Comparative Production Examples 1 to 5, aqueous oxidized cellulose dispersions were prepared having an oxidized cellulose concentration of 0.1% (Examples 2-1, 2-2, 2-4, 2-6, and 2-8 to 2-11, Comparative Examples 2-1 to 2-5) or 0.5% (Examples 2-3, 2-5, and 2-7). The aqueous CNF dispersion obtained by processing the aqueous oxidized cellulose dispersion with a stirrer was introduced into a 10 mm-thick quartz cell, and the light transmittance at a wavelength of 660 nm was measured using a spectrophotometer (JASCO V-550). For the aqueous CNF dispersions obtained by fibrillation of a 0.5% aqueous oxidized cellulose dispersion, the light transmittance was measured after dilution of the aqueous CNF dispersion to 0.1% using pure water. A “THINKYMIXER ARE-310” planetary centrifugal mixer from the THINKY Corporation was used for the stirrer, and a 10-minute treatment was carried out using conditions of a revolution rate of 2,000 rpm and a rotation rate of 800 rpm in mix mode. The evaluation criteria are as follows. [0176] ++: light transmittance of at least 80% [0177] +: light transmittance of at least 70% but less than 80% [0178] Δ: light transmittance of at least 60% but less than 70% [0179] ×: light transmittance of less than 60%

[0180] The average fiber width, slurry viscosity stability, slurry handling characteristics, and surface condition after coating with slurry were measured and evaluated using each of the aqueous CNF dispersions yielded by the fibrillation treatment in the ease-of-fibrillatability evaluation described above. Table 2 gives the results of the evaluations and the carboxy group content of the oxidized celluloses used in the fibrillation treatment. The measurement and evaluation of the average fiber width, slurry viscosity stability, slurry handling characteristics, and surface condition after coating with slurry were carried out as in (2) above.

TABLE-US-00002 TABLE 2 ease-of-fibrillatability oxidized surface carboxy average cellulose condition group fiber concentration light slurry slurry after oxidized oxidation content width during transmittance viscosity handling coating with cellulose method (mmol/g) (nm) fibrillation (%) (%) evaluation stability characteristics slurry Example 2-1 A hypochlorite 0.45 4.5 0.1 70.4 + + + + Example 2-2 B 0.61 4.2 0.1 79.0 + + + + + + + Example 2-3 B 0.61 4.2 0.5 75.3 + + + + Example 2-4 C 0.75 3.2 0.1 94.8 + + + + + + + + Example 2-5 C 0.75 3.2 0.5 90.8 + + + + + + + + Example 2-6 D 0.73 3.4 0.1 86.7 + + + + + + + + Example 2-7 D 0.73 3.4 0.5 82.6 + + + + + + + + Example 2-8 E 0.82 3.2 0.1 83.5 + + + + + + + + Example 2-9 F 0.92 2.7 0.1 86.7 + + + + + + + + Example 2-10 G 0.95 2.3 0.1 86.7 + + + + + + Example 2-11 H 0.97 2.4 0.1 88.2 + + Δ + + Δ Comparative P hypochlorite 0.42 10.3 0.1 57.8 x Δ Δ Δ Example 2-1 Comparative Q 1.12 9.7 0.1 59.6 x Δ Δ Δ Example 2-2 Comparative R ozone 0.43 10.9 0.1 55.7 x Δ Δ Δ Example 2-3 oxidation Comparative S periodic 1.72 27.1 0.1 51.3 x x x x Example 2-4 acid Comparative T TEMPO 1.55 9.0 0.1 55.0 x x x x Example 2-5 oxidation

[0181] For the oxidized celluloses in Examples 2-1 to 2-11, the cellulose microfibrils were readily fibrillated from each other even by mild stirring with a planetary centrifugal mixer, and a high light transmittance was exhibited when made into the aqueous CNF dispersion. In addition, even when the oxidized cellulose concentration during the fibrillation treatment was raised from 0.1% to 0.5%, the light transmittance of the aqueous CNF dispersion was satisfactorily high and the viscosity stability, handling characteristics, and coatability of the water-based slurries were also in balance.

[0182] In contrast to this, for all of Comparative Examples 2-1 to 2-5, where fibrillation was carried out by mild stirring with a planetary centrifugal mixer, the light transmittance of the aqueous CNF dispersions were low values, on the level of 50%. In addition, the slurry characteristics in Comparative Examples 2-1 to 2-5 were also inferior to those in Examples 2-1 to 2-11.