Acid-type carboxymethylated cellulose nanofiber and production method thereof

Abstract

An object is to provide an acid-type carboxymethylated cellulose nanofiber in which the viscosity is not excessively high at the time of preparing a dispersion liquid and the introduced carboxymethyl group is desalted to convert the acid type, and the acid-type carboxymethylated cellulose nanofiber has 0.01 to 0.50 of the degree of substitution with carboxymethyl group per glucose unit, wherein the B-type viscosity in an aqueous dispersion with a concentration of 0.95 to 1.05% by mass is 1000 mPa.Math.s or more under the condition of 60 rpm and 20° C., and 7000 mPa.Math.s or more under the condition of 6 rpm and 20° C.

Claims

1. An acid-type carboxymethylated cellulose nanofiber, having a degree of substitution with carboxymethyl group per glucose unit is in a range of from 0.01 to 0.50, and having a B-type viscosity in aqueous dispersion with a concentration in a range of from 0.95 to 1.05% by mass in a range of from 1,000 to 25,000 mPa.Math.s under a condition of 60 rpm and 20° C., and in a range of from 7,000 to 150,000 mPa.Math.s under a condition of 6 rpm and 20° C., wherein a ratio of a carboxy group determined by formula (1) is 85% or more:
R.sub.CG=N.sub.ROOR/(N.sub.ROOR+N.sub.ROOH)×100  (1) wherein R.sub.CG is the ratio (%) of carboxy groups, N.sub.ROOR is an amount of the carboxy group, and N.sub.ROOH is an amount of a carboxylate group.

2. The nanofiber of claim 1, wherein a light transmittance thereof at a wavelength of 660 nm in the aqueous dispersion with a concentration of 0.95 to 1.05% by mass is 65% or more.

3. A method for producing the acid-type carboxymethylated cellulose nanofiber of claim 1, the method comprising: fibrillating carboxymethylated cellulose to obtain a carboxymethylated cellulose nanofiber; and performing a desalting treatment through a cation exchange reaction, wherein the desalting treatment comprises contacting an aqueous dispersion of the carboxymethylated cellulose nanofiber and the cation exchange resins, and then separating the cation exchange resins from the aqueous dispersion.

4. The method of claim 3, further comprising: obtaining the carboxymethylated cellulose by subjecting a cellulose-based raw material to a mercerization treatment with a mercerizing agent and then reacting a resultant with a carboxymethylating agent.

5. The method of claim 4, wherein the mercerizing agent is an alkali metal hydroxide.

6. The method of claim 2, wherein the carboxymethylating agent is a compound of formula (1): ##STR00005## wherein X is a halogen atom, and M.sub.1 is a hydrogen atom or an alkali metal.

7. The method of claim 3, wherein the fibrillating is fibrillating the carboxymethylated cellulose to obtain a carboxymethylated cellulose nanofiber salt, and wherein the desalting treatment is desalting the carboxymethylated cellulose nanofiber salt with the cation exchange resin.

8. The method of claim 3, further comprising: lowering a viscosity of the carboxymethylated cellulose.

9. The nanofiber of claim 1, wherein the degree of substitution with carboxymethyl group per glucose unit is in a range of from 0.01 to 0.40.

10. The nanofiber of claim 9, wherein the B-type viscosity at 60 rpm and 20° C. is in a range of from 1300 to 25000 mPa.Math.s.

11. The nanofiber of claim 1, wherein the degree of substitution with carboxymethyl group per glucose unit is in a range of from 0.05 to 0.35.

12. The nanofiber of claim 11, Wherein the B-type viscosity at 60 rpm and 20° C. is in a range of from 1300 to 25000 mPa.Math.s.

13. The nanofiber of claim 1, wherein the degree of substitution with carboxymethyl group per glucose unit is in a range of from 0.01 to 0.29.

14. The nanofiber of claim 1, wherein the degree of substitution with carboxymethyl group per glucose unit is in a range of from 0.01 to 0.27.

15. The nanofiber of claim 1, wherein the ratio is greater than 85%.

16. The nanofiber of claim 1, wherein the ratio is 98% or more.

17. The nanofiber of claim 1, wherein the B-type viscosity at 60 rpm and 20° C. is in a range of from 1300 to 25000 mPa.Math.s.

18. The nanofiber of claim 1, wherein the B-type viscosity at 60 rpm and 20° C. is in a range of from 1800 to 23000 mPa.Math.s.

19. The nanofiber of claim 1, wherein the B-type viscosity at 60 rpm and 20° C. is in a range of from 3000 to 22500 mPa.Math.s.

20. The nanofiber of claim 1, wherein the B-type viscosity at 60 rpm and 20° C. is in a range of from 4000 to 20000 mPa.Math.s.

Description

EXAMPLES

(1) Hereinafter, the present invention will be described in more detail by examples. The following examples are for suitably explaining the present invention, and do not limit the present invention. The methods for measuring the values of physical properties and the like are the aforementioned measurement methods, unless otherwise stated.

(2) [B-Type viscosity (mPa.Math.s)]: Using a TV-10 type viscometer (Toki Sangyo Co., Ltd.), the B-type viscosity of 1% by mass aqueous dispersion liquid of the carboxymethylated cellulose nanofiber was measured under the condition of 20° C. and 60 rpm or 6 rpm.

(3) [Degree of substitution with carboxymethyl group]: The degree of substitution with carboxymethyl group was measured by the following method.

(4) About 2.0 g of a sample was precisely weighed, and placed in a 300 ml stoppered Erlenmeyer flask. Into the Erlenmeyer flask, 100 ml of nitric acid methanol (liquid obtained by adding 100 ml of special grade concentrated nitric acid to 1 L of anhydrous methanol) was added. The mixture was shaken for 3 hours to convert sodium salt of the carboxymethylated cellulose (hereinafter, also referred to as “Na-CMC”) into carboxymethylated cellulose (hereinafter, also referred to as “H-CMC”). The bone dried H-CMC was precisely weighed in an amount of 1.5 to 2.0 g, and placed in a 300 ml stoppered Erlenmeyer flask. The H-CMC was wetted with 15 ml of 80% methanol, and added with 100 ml of 0.1N NaOH. The obtained product was shaken at room temperature for 3 hours. With phenolphthalein as an indicator, excess NaOH was back titrated with 0.1N H.sub.2SO.sub.4. Then, the degree of substitution with carboxymethyl group was calculated according to the following formula:
[{100×F−(0.1NH.sub.2SO.sub.4 (ml))×F′}/(bone dry mass (g) of H-CMC)]×0.1=A
Degree of substitution with carboxymethyl group=0.162 A/(1−0.058 A)
A: amount of 1N NaOH (ml) necessary for neutralization of 1 g of H-CMC
F′: factor of 0.1N H.sub.2SO.sub.4
F: factor of 0.1N NaOH

(5) [Ratio (%) of carboxy group]: The ratio of the carboxy group was measured by the following process.

(6) First, 250 mL of 0.1% by mass slurry of a carboxymethylated cellulose nanofiber salt was prepared, and added with 0.1M hydrochloric acid aqueous solution so that the pH was adjusted 2.5. After that, while 0.1N sodium hydroxide aqueous solution was added, the degree of electrical conductivity was measured until the pH reached 11. From the amount of sodium hydroxide (a) consumed in the neutralization stage of weak acid in which the change in electrical conductivity was moderate, the amount of the carboxy group and the amount of the carboxylate group were calculated according to the following formula (2): (2): amount of carboxy group and amount of carboxylate group (mmol/g carboxymethylated cellulose nanofiber salt)=a (ml)×0.1/mass (g) of carboxymethylated cellulose nanofiber salt.

(7) Next, 250 mL of 0.1% by mass slurry of the desalted carboxymethylated cellulose nanofiber was prepared. While 0.1N sodium hydroxide aqueous solution was added, the degree of electrical conductivity was measured until the pH reached 11. From the amount of sodium hydroxide (b) consumed in the neutralization stage of weak acid in which the change in electrical conductivity was moderate, the amount of the carboxy group was calculated according to the following formula (3):
amount of carboxy group (mmol/g carboxymethylated cellulose nanofiber)=b (ml)×0.1/mass (g) of carboxymethylated cellulose nanofiber.  (3):

(8) From the obtained amounts of the carboxy group and carboxylate group, and the amount of the carboxy group, the ratio of the carboxy group was calculated according to the following formula (1):
ratio (%) of carboxy group=(amount of carboxy group/amount of carboxy group and amount of carboxylate group)×100.  (1):

(9) [Transparency (%)]: The transmittance of light at 660 nm through aqueous dispersion (solid content: about 1% (w/v)) of the carboxymethylated cellulose nanofiber was measured using a UV-VIS spectrophotometer UV-265FS (manufactured by Shimadzu Corporation), and the measured transmittance was defined as transparency.

(10) [Yield (%)]: The yield is an yield in the desalting process of acid treating the carboxymethylated cellulose nanofiber salt to obtain the carboxymethylated cellulose nanofiber.

Example 1

(11) Into a reaction vessel capable of stirring pulp, 250 g in terms of dry mass of pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) was placed, and added with 112 g of 50% by mass sodium hydroxide aqueous solution and 67 g of water while stirring. The mixture was stirred at 30° C. for 45 minutes for mercerization treatment, and thereafter added with 364 g of 35% by mass sodium monochloroacetate aqueous solution while stirring. The mixture was stirred at 30° C. for 60 minutes, and increased in temperature to 70° C. over 30 minutes. After that, a reaction was performed at 70° C. for 1 hour. Then, the reaction product was collected to obtain carboxymethylated pulp in which the degree of substitution with carboxymethyl group per glucose unit was 0.27 (hereinafter, also referred to as “carboxymethylated cellulose”).

(12) The carboxymethylated cellulose was adjusted with water into 1.053% (w/v), and treated three times using an ultra high pressure homogenizer (20° C., 140 Mpa) to obtain dispersion liquid of a carboxymethylated cellulose nanofiber salt (fibrillation process).

(13) Into the obtained dispersion liquid of the carboxymethylated cellulose nanofiber salt, a cation exchange resin (manufactured by Organo Corporation, “Amberjet 1024”) was added. The mixture was stirred at 20° C. for 0.3 hour for contact. After that, the cation exchange resin and the aqueous dispersion liquid were separated through a metal mesh (opening 100 mesh) to obtain a carboxymethylated cellulose nanofiber with a high yield of 92% (desalting process).

(14) The B-type viscosity of 1% by mass aqueous dispersion liquid of the obtained carboxymethylated cellulose nanofiber was 4099 mPa.Math.s under the condition of (60 rpm, 20° C.), and 22795 mPa.Math.s under the condition of (6 rpm, 20° C.). The results are illustrated together with the yield in Table 1.

Comparative Example 1

(15) Carboxymethylated cellulose nanofibers were not obtained even in the same manner as in Example 1 except that the desalting process was changed as follows. 10% hydrochloric acid aqueous solution was added to the dispersion liquid of the carboxymethylated cellulose nanofiber salt until the pH reached 2.4, and the mixture was stirred at 20° C. for 0.5 hour for contact. After that, filtration was performed, but no filtered material was obtained.

(16) TABLE-US-00001 TABLE 1 Comparative Example 1 Example 1 Yield (%) 92 — B-Type 60 rpm (mPa .Math. s) 4099 — viscosity  6 rpm (mPa .Math. s) 22795 —

(17) As understood from Table 1, when the desalting process was performed with the cation exchange resins, the acid-type carboxymethylated cellulose nanofiber was obtained with a high yield of 92% (see Example 1). On the other hand, when the desalting process was performed with hydrochloric acid, the acid-type carboxymethylated cellulose nanofiber could not be obtained (see Comparative Example 1).

Example 2

(18) Into the reaction vessel capable of stirring pulp, 250 g in terms of dry mass of pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) was placed, and added with 112 g of 50% by mass sodium hydroxide aqueous solution and 67 g of water while stirring. The mixture was stirred at 30° C. for 50 minutes for mercerization treatment, and thereafter added with 364 g of 35% by mass sodium monochloroacetate aqueous solution while stirring. The mixture was stirred at 30° C. for 60 minutes, and increased in temperature to 70° C. over 30 minutes. After that, a reaction was performed at 70° C. for 1 hour. Then, the reaction product was collected to obtain carboxymethylated pulp in which the degree of substitution with carboxymethyl group per glucose unit was 0.29 (hereinafter, also referred to as “carboxymethylated cellulose”).

(19) The carboxymethylated cellulose was adjusted with water into 1.053% (w/v), and treated three times using an ultra high pressure homogenizer (20° C., 150 Mpa) to obtain dispersion liquid of a carboxymethylated cellulose nanofiber salt.

(20) Into the obtained dispersion liquid of the carboxymethylated cellulose nanofiber salt, a cation exchange resin (manufactured by Organo Corporation, “Amberjet 1024”) was added. The mixture was stirred at 20° C. for 0.3 hour for contact. After that, the cation exchange resin and the aqueous dispersion liquid were separated through a metal mesh (opening 100 mesh) to obtain an acid-type carboxymethylated cellulose nanofiber with a high yield of 92%.

(21) The B-type viscosity of 1.04% by mass aqueous dispersion of the obtained acid-type carboxymethylated cellulose nanofiber was 4099 mPa.Math.s under the condition of (60 rpm, 20° C.), and 22795 mPa.Math.s under the condition of (6 rpm, 20° C.). The transparency was 77.2%, and the ratio of the carboxy group was 98%. The results are shown in Table 2.

Comparative Example 2

(22) The carboxymethylated cellulose obtained in Example 2 was adjusted with water into 1.053 wt %, and the pH was adjusted to 5 with 1N hydrochloric acid. After that, it was treated three times with an ultra high pressure homogenizer to obtain dispersion liquid of an acid-type carboxymethylated cellulose nanofiber.

(23) The B-type viscosity of the 1.05% by mass aqueous dispersion liquid of the obtained acid-type carboxymethylated cellulose nanofiber was 1040 mPa.Math.s under the condition of (60 rpm, 20° C.), and 6400 mPa.Math.s under the condition of (6 rpm, 20° C.). The transparency was 3.3%, and the ratio of the carboxy group was 30.7%. The results are shown in Table 2.

(24) TABLE-US-00002 TABLE 2 Comparative Example 2 Example 2 B-Type 60 rpm (mPa .Math. s) 4099 1040 viscosity  6 rpm (mPa .Math. s) 22795 6400 Transparency (%) 77.2 3.3 Ratio (%) of carboxy group 98 30.7

(25) As understood from Table 2, when the desalting process was performed with the cation exchange resins, the ratio of the carboxy group was 98%. Thus, there was obtained an acid-type carboxymethylated cellulose nanofiber which was converted into the almost acid-type. Also, the transparency thereof was as high as 77.2% (see Example 2). On the other hand, when the desalting process was performed with hydrochloric acid, the ratio of the carboxy group in the carboxymethylated cellulose nanofiber was 30.7%. Thus, there was obtained a partial acid-type carboxymethylated cellulose nanofiber in which the ratio of the salt-type was more than the acid-type. Also, the transparency thereof was as low as 3.3% (see Comparative Example 2).

(26) The B-type viscosity of the carboxymethylated cellulose nanofiber is higher, as the value for the degree of substitution with carboxymethyl is lower, and as the value for the average fiber diameter is smaller. For example, it is estimated that when an acid-type carboxymethylated cellulose nanofiber having an average fiber diameter of about 2 to about 4 nm is produced by changing the degree of substitution with carboxymethyl group of the carboxymethylated cellulose used in Example 1 of the present application from about 0.3 to about 0.10 and changing the pressure of machine processing and the number of processing operations, an acid-type carboxymethylated cellulose nanofiber in which the value for the B-type viscosity would be about 5.5 times (22500 mPa.Math.s at 60 rpm, 126500 mPa.Math.s at 6 rpm) that of the example could be obtained.