Modified pulp, method for producing modified pulp, and method for producing modified fine cellulose fibers

Abstract

To provide modified pulp having excellent transparency.SOLUTION: The modified pulp of the present invention is a modified pulp in which at least some of hydroxyl groups of cellulose are substituted with phosphate ester groups, and a fluid dispersion prepared by dispersing the modified pulp in water at a solid content concentration of 1 mass% has a total light transmittance of 50% or more.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] As a fine cellulose fiber into which an anionic functional group has been introduced, one having excellent transparency and a haze value of 15% or less when dispersed in water at a concentration of 0.2% by mass has been proposed (Patent Document 1). The fine cellulose fiber described in Patent Document 1 is a nanofiber that has been finely divided using a high-pressure homogenizer or the like. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-25468 Summary of the Invention [Problem to be solved by the invention]

[0004] In contrast, there has been no pulp fiber (for example, fiber length of 100 μm or more, fiber width of 1 μm or more) before being refined that has excellent transparency.

[0005] Therefore, an object of the present invention is to provide a modified pulp having excellent transparency, a method for producing the same, and a method for producing modified microfibrillated cellulose fibers by microfibrillating the modified pulp. [Means for solving the problem]

[0006] In order to achieve the above object, the modified pulp of the present invention is A modified pulp in which at least a portion of the hydroxyl groups of cellulose are substituted with phosphate ester groups, When dispersed in water to a solid content concentration of 1% by mass, the dispersion has a total light transmittance of 50% or more.

[0007] The method for producing modified pulp of the present invention includes a step of reacting pulp with a compound represented by formula (1) to substitute at least a portion of the hydroxyl groups of the cellulose constituting the pulp with phosphate ester groups. [ka] In formula (1), X is OH or OR (R is a monovalent cation).

[0008] The method for producing modified microfibrillated cellulose fibers of the present invention comprises the steps of: a modified pulp manufacturing process; a pulp refining step for obtaining modified fine cellulose fibers; Including, The modified pulp production step is a step of producing the modified pulp by the modified pulp production method of the present invention. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide modified pulp having excellent transparency with the predetermined total light transmittance of 50% or more, a method for producing the same, and a method for producing modified microfibrillated cellulose fibers by microfibrillating the modified pulp. DETAILED DESCRIPTION OF THE INVENTION

[0010] The modified pulp of the present invention is one in which at least a portion of the hydroxyl groups of cellulose has been substituted with phosphate ester groups.

[0011] The modified pulp is a fibrous material formed by the aggregation of a plurality of cellulose fibers, in which at least a portion of the hydroxyl groups (-OH groups) of the cellulose (a chain polymer in which D-glucose is linked by β(1→4) glycosidic bonds) constituting the cellulose fibers contained therein are substituted with phosphate ester groups. In the present invention, the phosphate ester groups are orthophosphate ester groups (-OPO3 2- ), but also pyrophosphate ester groups (-OP2O6 3- ), tripolyphosphate ester group (-OPO3O9 4-The counter ion of the phosphate ester group is not particularly limited, and examples thereof include hydrogen ions, metal ions, onium ions, and cationic organic compounds.

[0012] <Physical properties of modified pulp> The physical properties of the modified pulp, excluding the total light transmittance described below, are not particularly limited, but are, for example, as follows.

[0013] <Amount of introduced phosphate ester groups> The amount of phosphate ester groups introduced per 1 g (solid mass) of the modified pulp is, for example, 0.8 mmol / g to 7 mmol / g, 0.8 mmol / g to 5 mmol / g, 0.8 mmol / g to 2.5 mmol / g, or 0.8 mmol / g to 2 mmol / g.

[0014] <Method for measuring the amount of introduced phosphate ester groups> The amount of phosphate ester groups introduced into the modified pulp can be measured, for example, by treating a dispersion of the modified pulp in a dispersing medium with an ion exchange resin, and then using a conductometric titration method in which the change in electrical conductivity is measured while adding an aqueous sodium hydroxide solution.

[0015] The dispersion medium constituting the modified pulp dispersion is not particularly limited, but examples include protic polar dispersion media such as water, ethanol, acetic acid, formic acid, 2-propanol, nitromethane, and aqueous ammonia; aprotic polar dispersion media such as acetone, ethyl acetate, tetrahydrofuran (THF), dimethylformamide (DMF), acetonitrile, dimethyl sulfoxide (DMSO), dimethyl sulfide (DMS), and dimethylacetamide (DMA); and nonpolar dispersion media such as dimethyl ether, benzene, toluene, hexane, chloroform, and 1,4-dioxane. These may be used alone or in combination. From the standpoint of ease of handling, protic polar dispersion media such as water, ethanol, methanol, acetic acid, formic acid, and aqueous ammonia may also be used. The water may be tap water, but is preferably ion-exchanged water or pure water, as will be described hereinafter.

[0016] In addition to the aforementioned conductometric titration method, the amount of phosphate ester groups introduced into the modified pulp can also be quantified as the phosphorus (P) content of the modified pulp by elemental analysis using X-ray fluorescence analysis, a method using an inductively coupled plasma optical emission spectroscopy (ICP-OES) device, or the like.

[0017] <Average fiber length> The average fiber length of the modified pulp is not particularly limited, and is, for example, 0.2 mm to 2 mm, 0.2 mm to 1.8 mm, 0.2 mm to 1.5 mm, or 0.2 mm to 1 mm.

[0018] <Average fiber width> The average fiber width of the modified pulp is not particularly limited, and is, for example, 5 μm to 100 μm, 10 μm to 50 μm, 20 μm to 40 μm, or 20 μm to 30 μm.

[0019] <Method for measuring average fiber length and average fiber width> The average fiber length and average fiber width of the modified pulp can be measured using, for example, a fiber tester or fiber length distribution measuring instrument manufactured by Lorentzen & Wettley in accordance with ISO 16065-2:2007.

[0020] From the viewpoint of reliability, it is desirable that the measurement values ​​of the modified pulp described above be measured on at least 5,000 fibers in accordance with ISO 16065-2:2007.

[0021] <Total light transmittance> The modified pulp is dispersed in water to a solids concentration of 1% by mass, and the dispersion has a total light transmittance of 50% or more. The total light transmittance may be, for example, 60% or more, 70% or more, or 75% or more. The total light transmittance can be determined, for example, by measuring a dispersion obtained by dispersing the modified pulp in water to a solids concentration of 1% by mass using a spectrophotometer in accordance with JIS K 7105.

[0022] <Haze value> The haze value of the dispersion is, for example, 90% or less, 85% or less when the total light transmittance is within the above range.

[0023] <Method for measuring haze value> The haze value can be determined, for example, by measuring a dispersion obtained by dispersing the modified pulp in water to a solid content concentration of 1% by mass using a spectrophotometer in accordance with JIS K 7105.

[0024] The modified pulp can be obtained, for example, by the method for producing a modified pulp of the present invention described below. The method for producing a modified pulp of the present invention includes the step of reacting a compound represented by formula (1) with pulp to substitute at least a portion of the hydroxyl groups of the cellulose constituting the pulp with phosphate ester groups. [ka] In formula (1), X is OH or OR (R is a monovalent cation).

[0025] R (monovalent cation) in formula (1) is not particularly limited, and examples thereof include alkyl groups such as -NH4 (ammonium group) and -CH3. Hereinafter, in formula (1), a compound in which X is OH will be referred to as "phosphate amide," and a compound in which X is ONH4 will be referred to as "ammonium phosphate amide."

[0026] In the present invention, pulp refers to a fibrous material comprising a plurality of cellulose fibers. These cellulose fibers are a collection of a plurality of fine fibers (e.g., microfibrils). These fine fibers are a collection of a plurality of cellulose molecules (hereinafter, sometimes simply referred to as "cellulose"), which are chain-like polymers in which D-glucose is bonded via β(1→4) glucoside bonds. It is also preferable to wash the pulp beforehand. For example, filtration and dehydration using water on a 200-mesh or 235-mesh sieve can remove excessively fine fibers and debris, which is desirable because it improves handleability during production. In other words, pulp is a collection of cellulose fibers of a size that can become residue on a 200-mesh or 235-mesh sieve.

[0027] Examples of the pulp include wood-based pulp (hereinafter simply referred to as "wood pulp"), dissolving pulp, cotton-based pulp such as cotton linter, non-wood-based pulp such as wheat straw, bagasse, paper mulberry, mitsumata, hemp, kenaf, and fruit, and recycled paper pulp prepared from recycled newspapers, magazines, cardboard, etc. One type of pulp may be used alone, or two or more types of pulp may be used in combination. From the viewpoint of ease of availability, wood pulp is easily used as the pulp.

[0028] There are various types of wood pulp, and there are no particular limitations on their use. Examples include paper pulp such as softwood kraft pulp (NBKP), hardwood kraft pulp (LBKP), and thermomechanical pulp (TMP).

[0029] The compound of formula (1) may, for example, be prepared in-house.

[0030] For example, ammonium phosphate amide can be prepared from diphosphoryl chloride ((POCl2)2O) or phosphoryl chloride (POCl3) and aqueous ammonia, as shown in the following reaction scheme. [ka] ((POCl2)2O+8NH3+3H2O→2NH4HPO3NH2+4NH4Cl or POCl3+5NH3+2H2O→NH4HPO3NH2+3NH4Cl)

[0031] Also, for example, phosphoric acid amide can be prepared from ammonium phosphoric acid amide and perchloric acid (HClO4). [ka] (NH4HPO3NH2+HClO4→H2PO3NH2+NH4ClO4)

[0032] The details of the preparation method will be described later in the Examples below.

[0033] The method for reacting the compound represented by formula (1) with the pulp is, for example, as follows: First, a reaction solution prepared by dissolving the compound represented by formula (1) in a solvent is absorbed into the pulp, and then the pulp is dried and subjected to a heating reaction.

[0034] The solvent in the reaction solution is not particularly limited, and examples thereof include protic polar solvents such as water, ethanol, methanol, acetic acid, formic acid, 2-propanol, nitromethane, and aqueous ammonia; aprotic polar solvents such as acetone, ethyl acetate, tetrahydrofuran (THF), dimethylformamide (DMF), acetonitrile, dimethyl sulfoxide (DMSO), dimethyl sulfide (DMS), and dimethylacetamide (DMA); and nonpolar solvents such as diethyl ether, benzene, toluene, hexane, chloroform, and 1,4-dioxane. One type of solvent may be used alone, or two or more types may be used in combination. Among these, water is preferred from the viewpoint of ease of handling.

[0035] The amount of the compound represented by formula (1) used is not particularly limited, and may be adjusted appropriately depending on, for example, the desired amount of phosphate ester groups to be introduced.

[0036] In addition to the compound represented by formula (1), the reaction solution may contain at least one of urea and a urea derivative as a reaction accelerator (hereinafter referred to as "urea, etc." Examples of the urea derivative include thiourea, biuret, phenylurea, benzylurea, dimethylurea, diethylurea, tetramethylurea, benzoleinurea, and hydantoin. One type may be used alone, or two or more types may be used in combination.) According to the present invention, as demonstrated in the examples described later, by using the compound represented by formula (1), at least a portion of the hydroxyl groups of the cellulose constituting the pulp can be substituted with phosphate ester groups without using a reaction accelerator such as urea. On the other hand, by using urea, etc., the amount of phosphate ester groups introduced into the pulp can be adjusted by adjusting the amount used. The amount of urea, etc. used is not particularly limited, but is, for example, 0 to 30 parts by mass, 0 to 22 parts by mass, or 0 to 15 parts by mass per part by mass of the pulp. It is desirable to use the minimum amount of urea etc., since this reduces the amount of washing liquid required for washing after the production of the modified pulp, which will be described later.

[0037] The method for allowing the pulp to absorb the reaction solution is not particularly limited, and for example, the reaction solution may be absorbed into the pulp placed in a plastic bag (e.g., Ziploc® bag manufactured by Asahi Kasei Home Products Corp.). The conditions for the subsequent drying are also not particularly limited, and for example, the drying temperature may be about 85°C and the drying time may be about 3 hours.

[0038] The conditions for the heating reaction after drying are not particularly limited, and may be, for example, a reaction temperature of about 140° C. and a reaction time of about 30 minutes.

[0039] The modified pulp can be produced in the manner described above. The produced modified pulp may be washed with a large amount of pure water or the like. Prior to the washing, the modified pulp may be neutralized with an aqueous sodium bicarbonate solution or the like to convert the counter ions of the phosphate ester groups introduced into the pulp into sodium ions. The modified pulp may be stored at room temperature or refrigerated in a refrigerator (e.g., 4°C). The modified pulp may also be stored as an aqueous dispersion (e.g., solids concentration 1% by mass).

[0040] According to the present invention, it is also possible to provide a method for producing modified microfibrillated cellulose fibers using the method for producing modified pulp of the present invention. The method for producing modified microfibrillated cellulose fibers of the present invention includes a modified pulp production step and a microfibrillation treatment step of microfibrillating the modified pulp to obtain modified microfibrillated cellulose fibers, and the modified pulp production step is a step of producing the modified pulp by the method for producing modified pulp of the present invention.

[0041] The micronization process is a process of micronizing the modified pulp to form fine fibers of a predetermined size (e.g., nano-level). The processing equipment used in this process is not particularly limited as long as it has the above-mentioned function. For example, the processing equipment may be a low-pressure homogenizer, a high-pressure homogenizer, a grinder (a stone-type grinder), a ball mill, a cutter mill, a jet mill, a single-screw extruder, a twin-screw extruder, an ultrasonic agitator, a household mixer, or the like, but is not limited to these. Among these, it is desirable to use a high-pressure homogenizer because it can apply force evenly to the material and is excellent at homogenizing.

[0042] When a high-pressure homogenizer is used in this step, the modified pulp is supplied in a dispersed state in an aqueous dispersion medium such as water. Hereinafter, the dispersion in which the modified pulp is dispersed may be referred to as a slurry. The solids concentration of the modified pulp in this slurry is not particularly limited and is, for example, 0.1% by mass to 20% by mass.

[0043] For example, if a slurry with the solid content concentration of the modified pulp adjusted to 0.2% by mass is supplied to a processing device such as a high-pressure homogenizer, a dispersion liquid in which modified microcellulose fibers of the same solid content concentration are dispersed in an aqueous dispersion medium can be obtained. That is, in this case, a dispersion liquid with a solid content concentration of 0.2% by mass can be obtained.

[0044] The physical properties of the modified microcellulose fibers are not particularly limited, but are, for example, as follows.

[0045] <Haze value> For the modified microcellulose fibers, the Haze value of a dispersion liquid dispersed in water so that the solid content concentration becomes 0.2% by mass is, for example, 50% or less, 20% or less, 10% or less, or 2% or less.

[0046] <Method for measuring Haze value> The Haze value can be obtained, for example, by measuring a dispersion liquid in which the modified microcellulose fibers are dispersed in water so that the solid content concentration becomes 0.2% by mass using a spectrophotometer in accordance with JIS K 7105.

[0047] <Thixotropy index TI value> The TI value of the modified microcellulose fibers can be adjusted as appropriate. When a high TI value is required, the lower limit value of the TI value is, for example, 3 or more, 4 or more, or 5 or more. The upper limit value of the TI value is, for example, 12 or less, 8 or less, 6 or less, or 5 or less. On the other hand, when a low TI value is suitable, the lower limit value is, for example, 1 or more, and the upper limit value is, for example, 3 or less, or 2.5 or less.

[0048] <Method for measuring TI value> The TI value can be calculated, for example, using the following formula from the respective viscosity values measured at a rotational speed of 6 rpm and a rotational speed of 60 rpm using a B-type viscometer at a measurement temperature of 20°C for the viscosity (mPa·s) of a dispersion liquid (solid content concentration 0.2% by mass) in which the modified microcellulose fibers are dispersed in water. TI value = (viscosity at rotational speed of 6 rpm) / (viscosity at rotational speed of 60 rpm)

[0049] The modified pulp and the modified microfibrillated cellulose fibers obtained by the production method of the present invention can be widely used in various fields, for example, for producing transparent sheets and transparent films. By using the modified pulp or the modified microfibrillated cellulose fibers, it is possible to produce sheets and films with excellent transparency, even though the main component is pulp or microfibrillated cellulose fibers. The transparent sheets and films can be widely used, for example, for labels on PET beverage bottles and transparent windows in windowed envelopes, which have previously been made of resin. [Example]

[0050] (Preparation of ammonium phosphate amide and phosphate amide) 300 mL of ice-cooled ammonia water (below 0°C) was placed in a beaker and stirred, followed by the slow dropwise addition of 25 g of diphosphoryl chloride ((POCl2)2O). After the diphosphoryl chloride had been added, the mixture was stirred for 15 minutes and then transferred to a 2 L separatory funnel and separated with 1 L of acetone. The aqueous layer was collected, 8 mL of acetic acid was added, and the mixture was left standing in a refrigerator at 4°C or below for 24 hours. Ethanol, in an amount equal to the amount of the collected aqueous layer, was added to the solution, and the crystals were washed with ethanol and collected. The crystals were then dried in a desiccator to obtain crystalline ammonium phosphate amide (yield: 14.8 g, 65.3%). The ammonia water (10% ammonia concentration, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used. The diphosphoryl chloride (>98% purity, manufactured by Tokyo Chemical Industry Co., Ltd.) was used. The acetone (99+% purity, first-grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used.

[0051] 14.7 g of the resulting ammonium phosphate amide was dissolved in 195 mL of pure water and ice-cooled to below 0°C. The ice-cooled solution was stirred, and 65 mL of 25% by mass aqueous perchloric acid solution was gradually added. Immediately after the addition of the aqueous perchloric acid solution was completed, 1 L of ethanol was added, and the mixture was allowed to stand in a freezer at below -26°C for 24 hours. The precipitated solid was washed with ethanol, recovered, and dried in a desiccator to obtain amide phosphoric acid (yield: 4.1 g, 32.4%). Perchloric acid (70% perchloric acid concentration, manufactured by Sigma-Aldrich) and ethanol (95% purity, first-grade) were used. It was confirmed that ammonium phosphate amide and amide phosphoric acid could be prepared by the same procedure even when phosphoryl chloride was used instead of diphosphoryl chloride.

[0052] Example 1 A reaction solution was prepared by completely dissolving 4.7 g (0.041 mol) of ammonium phosphate amide and 12.0 g (0.20 mol) of urea in 40 g of pure water. The reaction solution was uniformly absorbed into 2.2 g (0.55 g solids) of bleached softwood kraft pulp (NBKP, hereafter simply referred to as "pulp") placed in a plastic bag (Ziploc® bag, manufactured by Asahi Kasei Home Products Corporation), then spread thinly on an acrylic board and dried at 85°C for 3 hours. The dried product was then subjected to a heating reaction at 140°C for 30 minutes. The resulting reaction product was neutralized with aqueous sodium bicarbonate solution to convert the counter ions of the phosphate ester groups introduced into the pulp to sodium ions. The resulting product was then washed with pure water on a 300-mesh sieve to obtain a modified pulp. The resulting modified pulp was then prepared into a 1.0% by mass aqueous dispersion and stored in a refrigerator (4°C). The bleached softwood kraft pulp (NBKP) used was a product manufactured by Marusumi Paper Co., Ltd. that had never been dried (solid content 25% by mass, the remaining 75% by mass being water). The urea used was a special grade product manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. with a purity of 99.0%. The sodium bicarbonate used was a first-class product manufactured by Nacalai Tesque, Inc., that met the Nacalai standard.

[0053] Example 2 A modified pulp was obtained in the same manner as in Example 1, except that urea was not used.

[0054] Examples 3 to 6 Modified pulp was obtained in the same manner as in Example 1, except that the amount of urea used was changed as shown in Table 1.

[0055] Example 7 A modified pulp was obtained in the same manner as in Example 1, except that the same molar amount of phosphoric amide was used instead of ammonium phosphoric amide.

[0056] Table 1 shows the compound represented by formula (1), the amount of urea used, the reaction temperature, the reaction time, the amount of phosphate ester groups introduced into the modified pulp, and the total light transmittance and haze value of the aqueous dispersion of the modified pulp (solid content concentration: 1.0% by mass) used in producing the modified pulp of Examples 1 to 7. The total light transmittance and haze value shown in Table 1 were measured using a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd., model number: SH 7000).

[0057] [Table 1]

[0058] As shown in Table 1, in all of the Examples, modified pulp was obtained that had excellent transparency with a total light transmittance of 50% or more.

[0059] (Production of modified fine cellulose fibers) A 1.0% by mass aqueous dispersion of the modified pulp of each Example was diluted to a 0.2% by mass aqueous dispersion and subjected to five defibration treatments using a high-pressure homogenizer (Yoshida Kikai Kogyo Co., Ltd., "NanoVeita," pressure 60 MPa) to pulverize the pulp. It was confirmed that modified microfibrillated cellulose fibers could be produced in all cases. The total light transmittance, haze value, and TI value of the aqueous dispersions (solid content concentration 0.2% by mass) of modified microfibrillated cellulose fibers produced using the modified pulp of Examples 1, 2, and 7 are shown in Table 2. The total light transmittance and haze value shown in Table 2 were measured using a spectrophotometer (Nippon Denshoku Industries Co., Ltd., model number: SH 7000). The TI value shown in Table 2 was calculated from viscosity values ​​measured at a measurement temperature of 20°C using a B-type viscometer (Eiko Seiki Co., Ltd., model number: DV2T) at rotation speeds of 6 rpm and 60 rpm.

[0060] [Table 2]

[0061] Although the present invention has been described above with reference to the embodiments and examples, the present invention is not limited to the above-described embodiments and examples. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

Claims

1. A modified pulp in which at least a portion of the hydroxyl groups of cellulose are substituted with phosphate ester groups, A modified pulp having a total light transmittance of 50% or more when dispersed in water to a solids concentration of 1% by mass.

2. A method for producing modified pulp, comprising the step of reacting a compound represented by formula (1) with pulp to replace at least a portion of the hydroxyl groups of cellulose constituting the pulp with phosphate ester groups. 【Chemical 1】 In formula (1), X is OH or OR (R is a monovalent cation).

3. a modified pulp manufacturing process; a pulp refining step for obtaining modified fine cellulose fibers; Including, A method for producing modified microfibrillated cellulose fibers, wherein the modified pulp production step is a step of producing the modified pulp by the production method according to claim 2.

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