Method for producing fine cellulose fibers and fine cellulose fibers

Abstract

To provide a method for producing fine cellulose fibers modified with hypophosphorous acid, and fine cellulose fibers.SOLUTION: A method for producing fine cellulose fibers includes the steps in which: at least one compound (A) selected from phosphoric acid or hypophosphorous acid metal salts is neutralized with alkali into a neutralized compound (A1); the neutralized compound (A1) and an additive that comprises a compound (B) comprising at least one selected from urea and urea derivatives are added to cellulose fibers, and the mixture is heated and cleaned; and the resultant material is then fibrillated.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing hypophosphite microfibrillated cellulose fibers and hypophosphite microfibrillated cellulose fibers. [Background technology]

[0002] In recent years, nanotechnology has been attracting attention as it aims to miniaturize materials to the nanometer level and obtain new physical properties that differ from the conventional properties of materials.

[0003] For example, fine cellulose fibers produced from pulp, a cellulosic raw material, by chemical treatment, pulverization, etc., are excellent in strength, elasticity, thermal stability, etc., and are therefore expected to be used in industrial applications such as filter media, filter aids, base materials for ion exchangers, fillers for chromatography analysis equipment, and fillers for compounding resins and rubbers, as well as in applications as compounding ingredients in cosmetics such as lipstick, powder cosmetics, and emulsion cosmetics.

[0004] Furthermore, because microfibrillated cellulose fibers have excellent aqueous dispersibility, they are expected to be used in a wide range of applications, such as viscosity retaining or adjusting agents for foods, cosmetics, paints, etc., strengthening agents for food raw material dough, moisture retaining agents, food stabilizers, low-calorie compounds, and emulsion stabilizing aids.

[0005] As fine cellulose fibers, in addition to fine cellulose fibers having carboxyl groups, fibers in which some of the hydroxyl groups of cellulose are substituted with phosphorus oxo acid groups are also known (Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6271318 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the prior art including Patent Document 1 does not disclose fine cellulose fibers modified with hypophosphorous acid, which will be described later.

[0008] Therefore, an object of the present invention is to provide a method for producing microfibrillated cellulose fibers modified with hypophosphorous acid, and microfibrillated cellulose fibers. [Means for solving the problem]

[0009] The following describes an embodiment for solving the above problem. (First aspect) a step of neutralizing at least one compound (A) of hypophosphorous acid or metal hypophosphite salts with an alkali to obtain a neutralized compound (A1); a step of adding an additive containing the neutralized compound (A1) and a compound (B) consisting of at least one of urea and a urea derivative to cellulose fibers, and then heating and washing the cellulose fibers; Then, there is a fiberization process, A method for producing fine cellulose fibers, comprising: (Second aspect) It has fine cellulose fibers with an average fiber diameter of 1 to 100 nm, A part of the hydroxy groups of the fine cellulose fibers are substituted with hypophosphorous groups. A fine cellulose fiber characterized by: [Effects of the Invention]

[0010] According to the present invention, a method for producing microfibrillated cellulose fibers modified with hypophosphorous acid and the microfibrillated cellulose fibers can be provided. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an explanatory diagram of an example of a structure in which hypophosphorous acid is introduced into cellulose. DETAILED DESCRIPTION OF THE INVENTION

[0012] The following describes an embodiment of the present invention. Note that the following embodiment is an example of the present invention. The scope of the present invention is not limited to the description of the embodiment, but is based solely on the claims.

[0013] (Outline of the manufacturing method of fine cellulose fiber) The method for producing microfibrillated cellulose fibers according to the present invention comprises the steps of: a step of neutralizing at least one compound (A) of hypophosphorous acid or metal hypophosphite salts with an alkali to obtain a neutralized compound (A1); a step of adding an additive containing the neutralized compound (A1) and a compound (B) consisting of at least one of urea and a urea derivative to cellulose fibers, and then heating and washing the cellulose fibers; Then, there is a fiberization process, Includes.

[0014] If hypophosphorous acid is directly heated together with an additive containing compound (B) at, for example, 100° C. or higher, phosphine (hydrogen phosphide) is formed, which may cause an explosion. In contrast, in the case of phosphorous acid or phosphoric acid, no phosphine is formed and there is no risk of explosion. Therefore, it is necessary to neutralize at least one compound (A) of hypophosphorous acid or metal hypophosphite salts with an alkali to obtain a neutralized compound (A1). The step of neutralizing compound (A) with an alkali to obtain neutralized compound (A1) includes both a step of neutralizing compound (A) with an alkali in advance to obtain neutralized compound (A1), and a step of adding alkali to compound (A) together with compound (B) to neutralize the compound to obtain neutralized compound (A1).

[0015] As the metal hypophosphite, sodium hypophosphite, potassium hypophosphite, calcium hypophosphite, magnesium hypophosphite, etc. can be used, with the sodium salt being preferred.

[0016] The alkali used for neutralization may be sodium hydroxide, magnesium hydroxide, manganese hydroxide, aluminum hydroxide, iron hydroxide, zinc hydroxide, copper hydroxide, sodium hydrogen carbonate, sodium carbonate, or the like. Neutralization to a pH of 6 to 8 is desirable.

[0017] When substituting a part of the hydroxy groups of fine cellulose fibers with hypophosphorous acid, the reaction may not be sufficient. Therefore, it is preferable to add a compound (B) consisting of at least one of urea and a urea derivative together with hypophosphorous acid or a metal hypophosphite salt (compound (A)) to the cellulose fibers and heat them to react, thereby substituting some of the hydroxy groups of the fine cellulose fibers with carbamate groups to introduce carbamate.

[0018] The present inventors have found that the reaction efficiency is low when the compound (B) consisting of at least one of urea and a urea derivative is not added. This point will be illustrated later.

[0019] Heating is preferably continued until the moisture content is 10% or less. Since the introduction of hypophosphorous acid into cellulose occurs through an esterification reaction, a high moisture content is undesirable. If necessary, the moisture content can be reduced using a dryer, especially a vacuum dryer.

[0020] The amount of compound (A) added is preferably 1 to 10,000 g, particularly 100 to 2,000 g, per 1 kg of the cellulose fiber, and the amount of compound (B) added is preferably 0.01 to 1,000 mol, particularly 0.1 to 100 mol, per 1 mol of compound (A).

[0021] The heating temperature is preferably 100 to 210° C., particularly 130 to 170° C. If the temperature is too high, the reaction may be oxidized to form phosphorous acid or phosphoric acid. If the heating temperature is too low, the reactivity will be insufficient. However, a portion of the hypophosphorous acid may be oxidized to phosphorous acid. Although hypophosphorous acid is better at reducing viscosity under acidic conditions, the viscosity reduction under acidic conditions is sufficient even if a portion of the hypophosphorous acid is oxidized to phosphorous acid.

[0022] (raw fiber) As the raw material for the fine cellulose fibers, one or more fibers selected from plant-derived fibers, animal-derived fibers, microorganism-derived fibers, etc. can be used. In an embodiment, it is preferable to use pulp fiber, which is a plant fiber. Pulp fiber (particularly wood pulp) is used as the raw material fiber, which is inexpensive and places less burden on the environment.

[0023] As the raw material pulp for the fine cellulose fibers, one or more types can be selected and used from, for example, wood pulp made from hardwood, softwood, etc., non-wood pulp made from straw, bagasse, cotton, hemp, bast fiber, etc., and decomposed paper pulp (DIP) made from recycled waste paper, broke, etc. The above-mentioned various raw materials may be in the form of a pulverized substance, such as cellulose powder. Wood pulp made from broad-leaved or coniferous trees derived from plants other than waste paper is suitable, and wood pulp derived from broad-leaved or coniferous trees is preferred.

[0024] The wood pulp can be one or more selected from chemical pulps such as hardwood kraft pulp (LKP), softwood kraft pulp (NKP), sulfite pulp (SP), dissolving pulp (DP), etc., and mechanical pulp (TMP). In particular, chemical pulps such as hardwood kraft pulp (LKP) and softwood kraft pulp (NKP), which are wood pulps that increase the cellulose content, are preferred, and bleached pulps such as hardwood bleached kraft pulp (LBKP) and softwood bleached kraft pulp (NBKP) are suitable.

[0025] As the mechanical pulp, for example, one or more types can be selected and used from stone ground pulp (SGP), pressurized stone ground pulp (PGW), refiner ground pulp (RGP), chemi-ground pulp (CGP), thermo-ground pulp (TGP), ground pulp (GP), thermo-mechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), refiner mechanical pulp (RMP), bleached thermo-mechanical pulp (BTMP), etc.

[0026] (Pretreatment) If necessary, the cellulose fibers can be pretreated before and / or after the introduction of the hypophosphorous acid ester, etc. into the cellulose fibers. By pretreating the pulp fibers before defibrating the cellulose fibers, the number of defibration steps can be significantly reduced, and the energy required for defibration can be saved.

[0027] The pretreatment of the cellulose fibers can be carried out by a physical method or a chemical method, preferably by a physical method and a chemical method. The pretreatment by a physical method and the pretreatment by a chemical method can be carried out simultaneously or separately.

[0028] Chemical methods include, for example, hydrolysis of polysaccharides with acid (acid treatment), hydrolysis of polysaccharides with enzymes (enzyme treatment), swelling of polysaccharides with alkali (alkali treatment), oxidation of polysaccharides with an oxidizing agent (oxidation treatment), reduction of polysaccharides with a reducing agent (reduction treatment), oxidation with a TEMPO catalyst (oxidation treatment), and esterification with acid (chemical treatment). In this embodiment, esterification treatment of the hydroxy groups of cellulose fibers is carried out using hypophosphorous acid (hereinafter also referred to as "compound A").

[0029] Chemical treatment prior to defibration can significantly reduce the number of beating processes and the energy required for the beating process, and also contributes to increasing the homogeneity of the cellulose fibers. Chemical treatment of raw pulp breaks down the hemicellulose and amorphous regions of cellulose contained in the pulp, resulting in a reduction in the energy required for the refining process and improved uniformity and dispersibility of the cellulose fibers. It is preferable to avoid excessive chemical pretreatment, since chemical treatment reduces the aspect ratio of the fine cellulose fibers.

[0030] (Urea and its derivatives) As the urea and its derivatives used as the compound (B), for example, one or more selected from urea, thiourea, biuret, phenylurea, benzylurea, dimethylurea, diethylurea, tetramethylurea, etc. can be used. In an embodiment, it is preferable to use urea.

[0031] (Beating process) After the chemical treatment, if necessary, the fiber may be filtered and dehydrated, or washed with, for example, ion-exchange washing water, and then subjected to beating (defibration) treatment.

[0032] Whether or not washing has been carried out satisfactorily can be confirmed by measuring the nitrogen concentration and transparency of the filtrate. The cleaning can be evaluated using the "replacement cleaning rate" defined below as a measure of cleaning. Replacement cleaning rate D0 (first stage) = (A0) / (X0+Y0) X0: Amount of water contained in pulp before dewatering = Amount of pulp water dispersion before dewatering - Pulp concentration before dewatering × Amount of pulp water dispersion before dewatering Y0: Amount of water contained in pulp after dehydration = Amount of pulp water dispersion after dehydration - Pulp concentration after dehydration × Amount of pulp water dispersion after dehydration A0: Filtrate volume after dehydration Replacement cleaning rate Dn (second stage and after) = Dn-1 + An × (1-Dn-1) / (Xn+Yn) Dn-1: Replacement cleaning rate of the previous stage Xn: Amount of water contained in pulp before dewatering = Amount of pulp water dispersion before dewatering - Pulp concentration before dewatering × Amount of pulp water dispersion before dewatering Yn: Amount of water contained in pulp after dewatering = Amount of pulp water dispersion after dewatering - Pulp concentration after dewatering × Amount of pulp water dispersion after dewatering An: Filtrate volume after dehydration The replacement cleaning rate is preferably 80% or more. If it is difficult to achieve a cleaning rate of 80% or more in a single dehydration cleaning, it is preferable to repeat the dilution dehydration cleaning several times until the cleaning rate reaches 80% or more.

[0033] The beating treatment can be carried out using, for example, a homogenizer such as a beater, a high-pressure homogenizer, or a high-pressure homogenizing device, a mill-type friction machine such as a grinder or a grinder, a single-screw kneader, a multi-screw kneader, or a kneader refiner, and is preferably carried out using a refiner.

[0034] The raw material pulp is preferably defibrated so that the average fiber diameter, average fiber length, peak value of pseudo particle size distribution, B-type viscosity, etc. of the resulting fine cellulose fibers are desired values.

[0035] The average fiber diameter (average fiber width; average diameter of single fibers) of the fine cellulose fibers is preferably 3 to 100 nm, more preferably 4 to 90 nm, and particularly preferably 4 to 80 nm. In particular, when the average fiber diameter of the fine cellulose fibers is 3 nm or more, cellulose crystal portions remain, which makes it easier to maintain the strength of the three-dimensional network structure between the fine cellulose fibers. Furthermore, when the average fiber diameter exceeds 100 nm, depending on the aspect ratio, the viscosity of the aqueous dispersion of the fibers and the gas barrier properties of the fibers may be impaired.

[0036] The average fiber diameter of the fine cellulose fibers can be adjusted, for example, by selecting the raw material pulp, pre-treating it, defibrating it, etc.

[0037] (fine cellulose fiber) The fine cellulose fibers according to the present invention have an average fiber diameter of 1 to 100 nm, and some of the hydroxyl groups of the cellulose fibers are substituted with hypophosphorous groups.

[0038] The chemical formula of hypophosphorous acid is shown in Formula 1, and an example of the structure of hypophosphorous acid introduced into cellulose is shown in Figure 1.

[0039] [ka]

[0040] The amount of hypophosphorous acid introduced into the cellulose fibers is preferably 0.1 to 4.5 mmol / g, more preferably 0.3 to 4.0 mmol / g, and particularly preferably 0.5 to 3.5 mmol / g. If the amount introduced is less than 0.1 mmol / g, the properties of the cellulose fibers will be almost the same as those of unmodified cellulose fibers. On the other hand, if the amount introduced exceeds 4.5 mmol / g, the cellulose fibers may be broken down to the molecular level, resulting in the loss of their properties as fine fibers. The amount of hypophosphorous acid introduced is a value evaluated based on elemental analysis. This elemental analysis was performed using an X-Max 50001 manufactured by Horiba, Ltd.

[0041] It is preferable that a part of the hydroxy groups of the fine cellulose fibers is substituted with carbamate groups to introduce carbamate. When carbamate is introduced, the affinity between the aqueous fine cellulose fibers and the oil-based material is increased, resulting in good dispersibility.

[0042] The amount of carbamate groups introduced into cellulose fibers is preferably 0.05 to 1.5 mmol / g, more preferably 0.1 to 1.3 mmol / g, and particularly preferably 0.2 to 1.2 mmol / g. If the amount introduced is less than 0.05 mmol / g, the amount of hypophosphorous acid introduced may be low. On the other hand, if the amount introduced exceeds 1.5 mmol / g, excessive urea may cause yellowing. The amount of carbamate introduced was calculated by the Kjeldahl method.

[0043] The fine cellulose fibers can be used in the applications described above.

[0044] The method for measuring the average fiber diameter of the fine cellulose fibers is as follows. First, 100 ml of an aqueous dispersion of fine cellulose fibers with a solid content of 0.01 to 0.1% by mass is filtered through a Teflon® membrane filter and solvent-substituted once with 100 ml of ethanol and three times with 20 ml of t-butanol. The sample is then freeze-dried and osmium-coated to obtain a sample. This sample is then observed using an SEM image at a magnification of 3,000x to 30,000x, depending on the width of the fibers that make up the sample. Specifically, two diagonal lines are drawn on the observed image, and three straight lines are arbitrarily drawn passing through the intersections of the diagonal lines. The widths of a total of 100 fibers intersecting with these three straight lines are then visually measured. The median diameter of the measured values ​​is then taken as the average fiber diameter.

[0045] The average fiber length (single fiber length) of the fine cellulose fibers is preferably 0.01 to 1000 μm, more preferably 0.1 to 500 μm, and particularly preferably 0.5 to 300 μm. If the average fiber length of the fine cellulose fibers is less than 0.01 μm, it becomes difficult to form a fiber network structure.

[0046] The average fiber length of the fine cellulose fibers can be adjusted, for example, by selecting the raw material pulp, pre-treating it, defibrating it, etc.

[0047] The average fiber length of the fine cellulose fibers is measured in the same manner as in the case of the average fiber diameter, by visually measuring the length of each fiber, and the median length of the measured values ​​is taken as the average fiber length.

[0048] The axial ratio (fiber length / fiber width) of the fine cellulose fibers is preferably 10 to 1,000,000, more preferably 20 to 500,000, and particularly preferably 30 to 100,000. If the axial ratio is less than 10, the cellulose component is almost in a particle shape, making it impossible to form a three-dimensional network. On the other hand, if the axial ratio exceeds 1,000,000, the fibers are likely to aggregate, which leads to the inhibition of three-dimensional network formation, making the fiber unsuitable for applications that utilize the formation of such a network.

[0049] The crystallinity of the fine cellulose fibers is 50-100, more preferably 60-90, and particularly preferably 65-85. The crystallinity is a value measured by X-ray diffraction in accordance with JIS-K0131 (1996) "General rules for X-ray diffraction analysis." Note that fine cellulose fibers have amorphous and crystalline portions, and the crystallinity refers to the proportion of the crystalline portion in the entire fine cellulose fibers.

[0050] The light transmittance of the fine cellulose fiber (aqueous dispersion of 0.2% solids content) is preferably 40% or more, more preferably 60% or more, and particularly preferably 70% or more. If the light transmittance is less than 40%, when the fine cellulose fiber is mixed with other components to form a composition, the color tone of the composition other than the fine cellulose fiber may be concealed. In particular, when transparency is required for the composition, a high light transmittance is preferred.

[0051] The light transmittance is the value measured by measuring the transparency (transmittance of light from 350 to 880 nm) of a 0.2% (w / v) aqueous dispersion of fine cellulose fibers using a Spectrophotometer U-2910 (Hitachi, Ltd.). The dispersion medium is purified water. [Example]

[0052] Example 1: Hypophosphorous acid Reagent A was prepared by adding 50% aqueous sodium hydroxide solution to 79.2 g of a 30% aqueous solution of hypophosphorous acid to adjust the pH to 7, and mixing this with 86.4 g of urea and 40 g of water. The prepared reagent A and raw material pulp (NBKP: moisture content 98.0% by mass) (10 g dry weight) were mixed and dried at 105°C. The dried pulp was reacted at 160°C for 2 hours, and then washed with water and filtered twice to obtain hypophosphorous acid-modified pulp. The hypophosphorous acid-modified pulp was adjusted to a solids concentration of 1% and subjected to defibration treatment three times using a high-pressure homogenizer, to obtain an aqueous dispersion of fine cellulose fibers with a concentration of 1.0% by mass.

[0053] [Examples and Control Examples] As mentioned above, it is desirable to add a compound (B) consisting of at least one of urea and a urea derivative in the reaction for obtaining hypophosphorous acid-modified pulp. In this regard, the amount of urea and hypophosphorous acid added was varied to examine the change in the amount of hypophosphorous acid introduced, as shown in Table 1. [Table 1] It can be seen that the amount of hypophosphorous acid introduced increases depending on the amount of urea added.

[0054] The hypophosphorous acid-modified fine cellulose fibers obtained in this manner do not have ionic substituents, and therefore have higher compatibility with resins than other modified fine cellulose fibers that have anionic groups, and a composite resin with high transparency can be obtained. In addition, since it is not ionic, it can be used as a flocculant for waste liquid, etc. Furthermore, since it has high reducing properties, it can also be used as a reducing agent for electroless nickel plating baths. [Industrial Applicability]

[0055] The fine cellulose fibers of the present invention can be used for composite resins, reducing agents, etc.

Claims

1. a step of neutralizing at least one compound (A) of hypophosphorous acid or a metal hypophosphite salt with an alkali to obtain a neutralized compound (A1); a step of adding the neutralized compound (A1) and an additive containing a compound (B) consisting of at least one of urea and a urea derivative to cellulose fibers, and heating and washing the cellulose fibers; Then, there is a fiberization process, Including, The amount of hypophosphorous acid groups introduced into the cellulose fibers is 0.1 to 4.5 mmol / g, and The amount of carbamate groups introduced into the cellulose fibers is 0.05 to 1.5 mmol / g. A method for producing fine cellulose fibers, comprising:

2. The method for producing fine cellulose according to claim 1, wherein the heating is carried out until the moisture content is reduced to 10% or less.

3. The method for producing fine cellulose according to claim 1 or 2, wherein the amount of the neutralizing compound (A1) added is 1 to 10,000 g per 1 kg of the cellulose fiber, and the amount of the compound (B) added is 0.01 to 1000 mol per 1 mol of the compound (A1).

4. The method for producing submicronized cellulose according to claim 1 or 2, wherein the heating is carried out at 100 to 210°C.

5. The fine cellulose fibers have an average fiber diameter of 1 to 100 nm, A part of the fine cellulose fibers has a hydroxy group of the cellulose fiber substituted with a hypophosphorous group, and a carbamate is introduced therein; a part of the hydroxy groups of the fine cellulose fibers is substituted with carbamate groups to introduce carbamate; the amount of hypophosphorous acid groups introduced into the cellulose fibers is 0.1 to 4.5 mmol / g; The amount of carbamate groups introduced into the cellulose fibers is 0.05 to 1.5 mmol / g. A fine cellulose fiber characterized by:

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