JP2017095813A - Dewatering process of chemically modified pulp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dewatering process of a chemically modified pulp which concentrates the chemically modified pulp as well as largely reduces residual amount of various chemicals used for chemical modification and remained in the chemically modified pulp or inorganic salts which are by-products.SOLUTION: There is provided a method for dewatering a dispersion of a chemically modified pulp obtained by chemical modification treatment of a pulp raw material, including pressing and dewatering the chemically modified pulp dispersion under a treatment condition of 2 to 10 MPa.SELECTED DRAWING: None

Description

  The present invention relates to a method for dehydrating chemically modified pulp.

It is known that chemically modified pulp (oxidized pulp, carboxymethylated pulp, cationized pulp, etc.) is subjected to mechanical treatment such as a mixer in water to obtain a highly viscous and transparent cellulose nanofiber aqueous dispersion. (Non-Patent Document 1).
Cellulose nanofibers using chemically modified pulp as a starting material is a novel biodegradable water-dispersible material that can be modified freely based on chemically modified parts localized on the surface of cellulose fibers. . In addition, since the cellulose nanofiber is in the form of a dispersion liquid, it can be blended with various water-soluble polymers and combined with organic / inorganic pigments. Furthermore, cellulose nanofibers can be formed into sheets or fibers. High-performance packaging materials, transparent organic base materials, high-performance fibers, separation membranes, regenerative medical materials, and the like are assumed as applications utilizing such characteristics of cellulose nanofibers. In the future, it is expected to develop new highly functional products that are essential for the formation of a recycling-type safety and security society by making the best use of the characteristics of cellulose nanofibers.

Saito, T., et al., Cellulose Commun., 14 (2), 62 (2007)

  However, chemically modified pulp has a very high affinity with water, and its water retention is extremely high compared to unmodified pulp. For this reason, the dewaterability of the modified pulp is very low, and there is a problem that a high concentration cellulose nanofiber dispersion cannot be prepared. Further, there is a problem that various chemicals used for modification remaining in the modified pulp and inorganic salts of by-products cannot be sufficiently removed unless washing and dehydration are repeated.

  Accordingly, the present invention provides a chemical that has a highly reduced concentration of chemically modified pulp and greatly reduces the residual amount of various chemicals used for chemical modification remaining in the chemically modified pulp and inorganic salts of by-products. It aims at providing the dehydration method of a modified pulp.

The present invention provides the following (1) to (4).
(1) A method of dehydrating a dispersion of chemically modified pulp obtained by chemically modifying pulp raw material, wherein the chemically modified pulp dispersion is squeezed and dehydrated under a processing condition of 2 to 10 MPa. A method for dehydrating a chemically modified pulp dispersion.
(2) The chemically modified pulp is a carboxymethylated pulp having a degree of carboxymethyl substitution per glucose unit of cellulose constituting the chemically modified pulp of 0.01 to 0.50, (1) 2. A method for dewatering a modified pulp according to 1.
(3) The chemically modified pulp is a cationized pulp having a cation substitution degree per glucose unit of cellulose constituting the chemically modified pulp of 0.02 to 0.50. A method for dewatering modified pulp.
(4) A method for producing cellulose nanofiber, comprising defibrating and dispersing the modified pulp obtained by the dehydration method according to any one of (1) to (3).

  According to the present invention, the chemical modified pulp is highly concentrated, and the chemicals used for chemical modification remaining in the chemically modified pulp and the residual amount of by-products such as inorganic salts are greatly reduced. A method for dewatering a modified pulp can be provided.

  The present invention relates to a dehydration method in which chemically modified pulp is squeezed under conditions of 2 to 10 MPa, and the chemically modified pulp can be highly concentrated and used for chemical modification contained in the chemically modified pulp. Residues such as various chemicals and by-product inorganic salts can be significantly reduced.

(Pulp raw material)
Examples of pulp raw materials for producing chemically modified pulp include plant materials (for example, wood, bamboo, hemp, jute, kenaf, farmland waste, cloth, pulp (conifer unbleached kraft pulp (NUKP), conifer bleach). Kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP) thermomechanical pulp (TMP), regenerated pulp , Waste paper, etc.), animal materials (for example, ascidians), algae, microorganisms (for example, acetic acid bacteria (Acetobacter)), microbial products, etc., any of which can be used. Is a cellulose fiber derived from plants or microorganisms, more preferably cellulosic derived from plants. Scan is a fiber.
Of these, bleached kraft pulp having a whiteness of 80% or more, bleached sulfite pulp having a whiteness of 80% or more, powdered cellulose, or microcrystalline cellulose powder is preferably used from the viewpoint of mass production and cost. In addition, it is particularly preferable to use powdered cellulose and microcrystalline cellulose powder because a cellulose nanofiber dispersion having a lower viscosity can be produced even at a high concentration.

  Powdered cellulose is a rod-like particle made of microcrystalline cellulose obtained by removing a non-crystalline part of wood pulp by acid hydrolysis and then pulverizing and sieving. The degree of polymerization of cellulose in the powdered cellulose is about 100 to 500, the degree of crystallinity of the powdered cellulose by X-ray diffraction method is 70 to 90%, and the volume average particle diameter by a laser diffraction type particle size distribution analyzer is preferably 100 μm. Or less, more preferably 50 μm or less. When the volume average particle diameter is 100 μm or less, a cellulose nanofiber dispersion excellent in fluidity can be obtained. As the powdered cellulose used in the present invention, for example, a fixed particle size in the form of a rod shaft produced by a method of purifying and drying an undegraded residue obtained after acid hydrolysis of a selected pulp, pulverizing and sieving. Crystalline cellulose powder having a distribution may be used, such as KC Flock (registered trademark) (manufactured by Nippon Paper Industries Co., Ltd.), Theoras (trademark) (manufactured by Asahi Kasei Chemicals), Avicel (registered trademark) (manufactured by FMC), etc. Commercial products may be used.

(Carboxymethylation)
In the present invention, when a carboxymethylated pulp is used as the chemically modified pulp, the carboxymethylated pulp may be obtained by carboxymethylating the above pulp raw material by a known method, using a commercially available product. Also good. In any case, it is preferable that the degree of carboxymethyl group substitution per anhydroglucose unit of the pulp is 0.01 to 0.50. The following method can be mentioned as an example of the method of manufacturing such a carboxymethylated pulp. Pulp is used as a starting material, and 3 to 20 times by weight of water and / or lower alcohol as a solvent, specifically water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary A single solvent such as butanol or a mixed medium of two or more is used. In addition, the mixing ratio of the lower alcohol when mixing the lower alcohol is 60 to 95% by weight. As the mercerizing agent, 0.5 to 20 times moles of alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide is used per anhydroglucose residue of the bottoming material. A bottoming raw material, a solvent, and a mercerizing agent are mixed and subjected to mercerization treatment at a reaction temperature of 0 to 70 ° C., preferably 10 to 60 ° C., and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, a carboxymethylating agent is added in an amount of 0.05 to 10.0 times mol per glucose residue, a reaction temperature of 30 to 90 ° C., preferably 40 to 80 ° C., and a reaction time of 30 minutes to 10 hours, preferably 1 hour. Perform etherification reaction for ~ 4 hours.

(Cationization)
In the present invention, when a cationized pulp is used as the chemically modified pulp, a cationizing agent and a catalyst such as glycidyltrimethylammonium chloride, 3-chloro-2hydroxypropyltrialkylammonium hydride, or a halohydrin type thereof are used as the cellulose raw material. A cation-modified pulp can be obtained by reacting an alkali metal hydroxide (sodium hydroxide, potassium hydroxide, etc.) in the presence of water and / or an alcohol having 1 to 4 carbon atoms. In this method, the degree of cation substitution per glucose unit of the cation-modified pulp obtained is controlled by the amount of cationizing agent to be reacted, the composition ratio of water and / or alcohol having 1 to 4 carbon atoms. Can be adjusted.

  The degree of cation substitution per glucose unit of the cation-modified pulp is preferably 0.02 to 0.50. By introducing cationic substituents into the pulp, the pulps are electrically repelled. For this reason, the pulp which introduce | transduced the cation substituent can be nano-defibrated easily. In addition, when the cation substitution degree per glucose unit is smaller than 0.02, nano-fibrosis cannot be sufficiently performed. On the other hand, if the degree of cation substitution per glucose unit is more than 0.50, it may swell or dissolve, and may not be obtained as a nanofiber.

(Esterification)
In this invention, when using the pulp which introduce | transduced the phosphate group as a chemically modified pulp, as a compound which has a phosphate group to a pulp raw material, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, phosphoric acid Trisodium, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid Examples include triammonium, ammonium pyrophosphate, and ammonium metaphosphate. These may be used alone or in combination of two or more to introduce a phosphate group. The ratio of the compound having a phosphoric acid group to the pulp raw material is preferably 0.1 to 500 parts by weight, preferably 1 to 400 parts by weight, based on 100 parts by weight of the solid content of the pulp raw material. More preferably, it is 2 to 200 parts by weight.

(Washing / dehydration treatment by high pressure press)
In the present invention, it is important to squeeze the chemically modified pulp under conditions of 2 to 10 MPa. When the pressure in the pressing treatment is less than 2 MPa, the chemical-modified pulp cannot be sufficiently concentrated, and various chemicals (catalyst, inorganic salts, chlorinated substances, etc.) used for the chemical modification remaining in the chemically-modified pulp, It is difficult to sufficiently eliminate by-product inorganic salts and the like. On the other hand, when the pressurization exceeds 10 MPa, there is almost no change in the concentration of chemically modified pulp and the amount of various chemicals remaining in the chemically modified pulp. Moreover, although the time which squeezes an oxidized pulp on the conditions of 2-10 Mpa is not specifically limited, Usually, it is about 10-60 minutes, Preferably it is about 20-30 minutes.

  In the present invention, it is preferable to use a high-pressure filter press or a tube press for the pressing treatment. As an example of the high-pressure filter press, a high-pressure driving pump that generates slurry pressure, and a high-pressure filter press main body that performs dehydration can be cited. As an auxiliary device for this high-pressure filter press, from the filter cloth of the filter press There are also types that are equipped with a device for peeling dehydrated cake and a cleaning device for preventing clogging of the filter cloth surface.

(Manufacture of cellulose nanofiber: defibration / dispersion treatment)
Cellulose nanofibers can be obtained by re-dispersing the dehydrated product (dehydrated cake) of the chemically modified pulp obtained in the present invention to an appropriate concentration and then defibrating. The types of equipment used for the defibrating treatment include high-speed rotating, colloid mill, high-pressure, roll mill, and ultrasonic equipment. Cellulose nanofiber dispersions that excel in transparency and fluidity can be used efficiently. In order to obtain well, it is preferable to treat with a wet high pressure or ultra high pressure homogenizer that can be dispersed under conditions of 50 MPa or more, preferably 100 MPa or more, more preferably 140 MPa or more.

  Next, the present invention will be described in more detail based on examples. However, the following examples are specific examples of the present invention, and the present invention is not limited to these examples. It is not something.

Example 1
<Manufacture of carboxymethylated (CM) pulp>
To a reactor capable of stirring the pulp, 112 g of a 50 wt% aqueous sodium hydroxide solution and 67 g of water were added while stirring 250 g of pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) in dry weight. After stirring at 30 ° C. for 30 minutes, 364 g of 35 wt% aqueous sodium monochloroacetate solution was added with stirring. Then, it stirred at 30 degreeC for 30 minutes, heated up to 70 degreeC over 30 minutes, and reacted at 70 degreeC for 1 hour. Thereafter, the reaction product was taken out, neutralized and washed to obtain carboxymethylated cellulose (carboxymethylated pulp) having a carboxymethyl substitution degree of 0.25 per glucose unit. A 1% slurry of carboxymethylated pulp was treated with a small high-pressure filter press (YTOH2 type, manufactured by Iwata Kikai Co., Ltd.) at 2 MPa for 15 minutes. The obtained carboxymethylated pulp had a solid content of 10% by mass.
In order to investigate the amount of Cl- ions remaining in the carboxymethylated pulp after washing, ultrapure water added to make a 1% slurry well stirred and filtered, and the resulting washing solution was subjected to ion chromatography (model ICS) -2000, manufactured by DIONEX). The Cl- concentration was 0 mg / L.

<Measurement method of carboxymethyl substitution degree per glucose unit>
The degree of substitution of the carboxymethyl group was determined by preparing a sample in 0.6% by weight slurry, adding 0.1 M aqueous hydrochloric acid solution to pH 2.4, then dropping 0.05 N aqueous sodium hydroxide solution dropwise to adjust the pH to 11 Then, the electric conductivity was measured until the amount of carboxylic acid group was determined, and the amount of carboxyl groups was measured from the amount of sodium hydroxide consumed in the neutralization step of the weak acid where the change in electric conductivity was slow. The degree of substitution referred to here represents the average value of the number of moles of substituents per mole of anhydroglucose unit.
Carboxymethyl substitution degree = (162 × C) / (1-58 × C)

(Example 2)
It processed like Example 1 except the pressing pressure having been 10 Mpa. The solid content was 13% by mass. Cl ⁻ in the carboxymethylated pulp after washing was not detected.

(Example 3)
<Manufacture of cationized pulp>
Add pulp (LBKP, Nippon Paper Industries Co., Ltd.) by dry weight 200g and sodium hydroxide 24g by dry weight to a pulper that can stir the pulp, and add water so that the pulp solid concentration is 15%. It was. Then, after stirring for 30 minutes at 30 ° C., the temperature was raised to 70 ° C., and 190 g (in terms of active ingredient) of 3-chloro-2-hydroxypropyltrimethylammonium chloride was added as a cationizing agent. After reacting for 1 hour, the reaction product was taken out, neutralized and washed to obtain cation-modified cellulose. A 1% slurry of cationized pulp was treated with a small high-pressure filter press (YTOH2 type, manufactured by Iwata Kikai Co., Ltd.) at 2 MPa for 15 minutes. The solid content of the cationized pulp was 7% by mass.
In order to investigate the amount of Cl- ions remaining in the cationized pulp after washing, a 1% slurry obtained by adding ultrapure water was thoroughly stirred and filtered, and the resulting washing solution was subjected to ion chromatography (model number ICS- 2000, manufactured by DIONEX). The Cl- concentration was 0 mg / L.

<Measurement method of degree of cation substitution per glucose unit>
The degree of substitution of the cationic group was determined by measuring the lignin content of the sample (cation-modified cellulose) by the Klason method, and then using the total nitrogen analyzer TN-10 (manufactured by Mitsubishi Chemical) to analyze the nitrogen content of the sample. The amount (% by weight) was measured and calculated by the following formula. The degree of substitution here represents the average value of the number of moles of substituents per mole of anhydroglucose unit.

Degree of cation substitution = (162 × N) / {(1-151.6 × 400-151.6 × N) × (1-0.01 × L)}
N: Nitrogen content L: Lignin content

Example 4
The same treatment as in Example 3 was performed except that the pressing pressure was 10 MPa. The solid content was 11% by mass. Cl ⁻ in the cationized pulp after washing was not detected.

(Comparative Example 1)
The same treatment as in Example 1 was performed except that the pressing pressure was 1 MPa. The solid content was 6%. The CL ⁻ concentration in the oxidized pulp after washing was 5 mg / L.

(Comparative Example 2)
The same treatment as in Example 3 was performed except that the pressing pressure was 1 MPa. The solid content was 4%. The CL ⁻ concentration in the oxidized pulp after washing was 9 mg / L.

Claims (4)

A method for dehydrating a dispersion of chemically modified pulp obtained by chemically modifying a pulp raw material, wherein the chemically modified pulp dispersion is squeezed and dehydrated under a processing condition of 2 to 10 MPa. A method for dewatering a modified pulp dispersion. The said chemically modified pulp is the carboxymethylated pulp whose carboxymethyl substitution degree per glucose unit of the cellulose which comprises a chemically modified pulp is 0.01-0.50, The characterized by the above-mentioned. A method for dewatering a modified pulp dispersion. The chemically modified pulp according to claim 1, wherein the chemically modified pulp is a cationized pulp having a cation substitution degree per glucose unit of cellulose constituting the chemically modified pulp of 0.02 to 0.50. Method for dehydrating the dispersion. The manufacturing method of the cellulose nanofiber characterized by disentangling and disperse | distributing the chemically modified pulp obtained by the dehydration method as described in any one of Claims 1-3.