Method for producing pulp fibers for use in producing carboxylated cellulose nanofibers, and pulp fibers for use in producing carboxylated cellulose nanofibers

Abstract

To provide a method for producing pulp fibers for carboxylated cellulose nanofiberization capable of forming a carboxylated cellulose nanofiber excellent in balance between handleability and physical properties.SOLUTION: A method for producing pulp fibers for carboxylated cellulose nanofiberization includes a fiber formation step in which an ozone-containing gas is supplied to a treatment solution having a pH of 6.5 or lower in which wood pulp fibers are immersed so that a CT value, which is the product of the ozone concentration in the ozone-containing gas and the treatment time, exceeds 6,000 ppm / min, thus the method can produce the pulp fibers for the carboxylated cellulose nanofiberization which are formed from the above wood pulp fibers.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing pulp fibers for use in producing carboxylated cellulose nanofibers, and to pulp fibers for use in producing carboxylated cellulose nanofibers. [Background technology]

[0002] Studies are underway to produce pulp fibers for use in making cellulose nanofibers (hereinafter sometimes abbreviated as "CNF"), as well as CNF, from pulp fibers. For example, Patent Document 1 discloses a method for producing cellulose nanofibers, including: (A) preparing pulp obtained by hydrolysis treatment followed by kraft cooking; (B) oxidizing the pulp in water using an oxidizing agent in the presence of (1) an N-oxyl compound (e.g., 2,2,6,6-tetramethylpiperidine-1-oxyl radical, TEMPO) and (2) a compound selected from the group consisting of bromides, iodides, or mixtures thereof to prepare oxidized cellulose; and (C) defibrating and dispersing the oxidized cellulose to produce cellulose nanofibers. Patent Document 1 states that this production method can provide a cellulose nanofiber dispersion that has low viscosity and excellent fluidity even at high concentrations.

[0003] Furthermore, Patent Document 2 describes a method for producing a chemically modified pulp dry solid, which includes a step of drying a mixture of a liquid medium and chemically modified pulp obtained by chemically modifying a cellulose raw material at 20 to 80° C. According to Patent Document 2, the above-mentioned chemically modified pulp dry solid can be used to produce CNF with excellent dispersibility.

[0004] Paragraph

[0016] of Patent Document 2 describes a method using an N-oxyl compound (2,2,6,6-tetramethylpiperidine-1-oxy radical, TEMPO) as an example of a method for carboxylating a cellulose raw material. Furthermore, in paragraph

[0024] of Patent Document 2, as "another example" of a method for carboxylating a cellulose raw material, an ozone concentration of 50 to 250 g / m is used. 3 It is stated that the treatment should be carried out for 1 to 360 minutes.

[0005] Furthermore, paragraph

[0021] of Patent Document 2 describes that in the above and other examples, in order to efficiently proceed with the oxidation of cellulose, an alkaline solution such as an aqueous sodium hydroxide solution should be added to maintain the pH of the reaction solution at about 8 to 12, preferably about 10 to 11. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2013 / 047218 [Patent Document 2] Japanese Patent Application Publication No. 2018-95761 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, when CNF is produced using TEMPO, the degree of polymerization and viscosity of the CNF formed increase, making the CNF difficult to handle, and therefore an additional step is required to reduce the viscosity of the CNF. Therefore, although the method described in Patent Document 1 can produce CNF with excellent handleability, the steps are complicated and there is room for improvement. Furthermore, in Patent Document 1, when TEMPO is used to carboxylate the cellulose raw material, there is a possibility that TEMPO may remain in the CNF produced, which raises concerns from safety and psychological standpoints.

[0008] When the inventors of the present application conducted further experiments on the "other examples" in Patent Document 2, they found that as carboxyl groups were introduced into the cellulose raw material, the degree of polymerization (molecular weight) of the cellulose raw material significantly decreased, and that the resulting carboxylated CNF, although easy to handle, may have concerns about its physical properties. Therefore, an object of the present disclosure is to provide a method for producing pulp fibers for use in producing carboxylated cellulose nanofibers, which can produce carboxylated cellulose nanofibers that have an excellent balance between ease of handling and physical properties. [Means for solving the problem]

[0009] The present inventors have developed a method for producing pulp fibers for use in carboxylated cellulose nanofiber production, which comprises immersing wood pulp fibers in a treatment solution having a pH of 6.5 or less, adding an ozone-containing gas to the treatment solution until the CT value, which is the product of the ozone concentration in the ozone-containing gas and the treatment time, reaches 6,000. g / m 3 The present inventors have discovered a method for producing carboxylated cellulose nanofibers, which comprises a fiber-forming step of feeding the wood pulp fibers to the feedstock at a temperature of more than 100° C. for more than 10 minutes to form pulp fibers for use in producing carboxylated cellulose nanofibers from the wood pulp fibers. [Effects of the Invention]

[0010] The method of the present disclosure can produce pulp fibers for use in forming carboxylated cellulose nanofibers, which can be used to form carboxylated cellulose nanofibers that have an excellent balance between ease of handling and physical properties. [Brief explanation of the drawings]

[0011]

Figure 1

Figure 2

Figure 3

[0012] Specifically, the present disclosure relates to the following aspects: [Aspect 1] A method for producing pulp fibers for producing carboxylated cellulose nanofibers, comprising: An ozone-containing gas is added to a treatment solution having a pH of 6.5 or less in which wood pulp fibers are immersed, and the CT value, which is the product of the ozone concentration in the ozone-containing gas and the treatment time, is 6,000. g / m 3 a fiber formation step of forming pulp fibers for carboxylated cellulose nanofibers from the wood pulp fibers by supplying the pulp fibers for more than 1 minute; The above method, characterized in that it comprises:

[0013] In the fiber formation step, the pulp fibers for carboxylated CNF production are formed from wood pulp fibers in a treatment solution having a predetermined pH under predetermined ozone conditions, which makes it possible to oxidize the -CHOH group at the 6-position of cellulose to a carboxyl group while suppressing a decrease in the degree of polymerization of the cellulose that constitutes the wood pulp fibers. Therefore, the method can produce carboxylated pulp fibers for carboxylated CNF production that can form carboxylated CNFs that have an excellent balance between handleability and physical properties.

[0014] [Aspect 2] 2. The method of embodiment 1, wherein the treatment solution comprises an acid. In the above method, because the treatment solution contains an acid, the pH of the treatment solution can be easily maintained within a predetermined range, and the above method can produce pulp fibers for carboxylated CNF that can form carboxylated CNF that has an excellent balance between handleability and physical properties.

[0015] [Aspect 3] 3. The method of claim 2, wherein the acid is citric acid. In the above method, since the acid is citric acid, the pH of the treatment solution can be easily maintained within a predetermined range, and the above method can produce pulp fibers for carboxylated CNF that can form carboxylated CNF with an excellent balance between handleability and physical properties.

[0016] [Aspect 4] A method according to aspect 3, wherein the treatment liquid contains the citric acid at a concentration of 3.0 to 10.0% by mass.

[0017] In the above method, since the treatment solution contains citric acid at a predetermined concentration, the pH of the treatment solution can be easily maintained within a predetermined range, and the above method can produce pulp fibers for carboxylated CNF that can form carboxylated CNF with an excellent balance between handleability and physical properties.

[0018] [Aspect 5] 60 minutes after the start of the fiber formation step, the degree of polymerization of the pulp fiber for forming the carboxylated cellulose nanofibers: DP 60 and carboxyl group content: C 60 The degree of polymerization-carboxyl group content index (I) is expressed as the product of (mmol / g) 60 but, 58≦I 60 The method according to any one of aspects 1 to 4, wherein the method satisfies the requirements of

[0019] In the above method, the degree of polymerization-carboxyl group index (I) was calculated 60 minutes after the start of the fiber formation step. 60 has a predetermined value, i.e., a predetermined degree of polymerization and amount of carboxyl groups. Therefore, the above method can produce pulp fibers for carboxylated CNF that can form carboxylated CNF with an excellent balance between handleability and physical properties.

[0020] [Aspect 6] After 120 minutes from the start of the fiber formation step, the degree of polymerization of the pulp fiber for forming the carboxylated cellulose nanofibers: DP 120 and carboxyl group content: C 120 The degree of polymerization-carboxyl group content index (I) is expressed as the product of (mmol / g) 120 but, 46≦I 120 The method according to any one of aspects 1 to 5, wherein the method satisfies the requirements of

[0021] In the above method, the polymerization degree-carboxyl group content index (I) was calculated 120 minutes after the start of the fiber formation step. 120 has a predetermined value, i.e., a predetermined degree of polymerization and amount of carboxyl groups. Therefore, the above method can produce pulp fibers for carboxylated CNF that can form carboxylated CNF with an excellent balance between handleability and physical properties.

[0022] [Aspect 7] A method according to any one of aspects 1 to 6, wherein the pulp fibers for use in forming carboxylated cellulose nanofibers have a hemicellulose content of less than 8.0% by mass.

[0023] It is known that wood pulp fibers, for example, softwood pulp fibers, contain about 50 to 60% by mass of cellulose and about 10 to 25% by mass of hemicellulose. Hemicellulose is found in large amounts in plant cell walls. When softwood pulp fibers are used, for example, as pulp fibers for carboxylated CNF, the hemicellulose present in the softwood pulp fibers may remain in the pulp fibers for carboxylated CNF, and the remaining hemicellulose may inhibit the function of the carboxylated CNF.

[0024] In the above method, since the pulp fiber for carboxylated CNF production has a predetermined hemicellulose content, it becomes easier to produce carboxylated CNF from the pulp fiber for carboxylated CNF production.

[0025] [Aspect 8] Aspect 8. The method according to any one of Aspects 1 to 7, wherein the pulp fibers for use in forming carboxylated cellulose nanofibers have a lignin content of 0.10% by mass or less.

[0026] It is known that wood pulp fibers, such as softwood pulp fibers, contain approximately 20 to 30 mass% of lignin. When softwood pulp fibers are used as pulp fibers for carboxylated CNF, for example, the lignin present in the softwood pulp fibers may remain in the pulp fibers for carboxylated CNF, and the remaining lignin may inhibit the function of the carboxylated CNF.

[0027] In the above method, since the pulp fibers for carboxylated CNF have a predetermined lignin content, it becomes easier to produce carboxylated CNF from the pulp fibers for carboxylated CNF.

[0028] [Aspect 9] Aspect 9. The method of any one of aspects 1 to 8, wherein the wood pulp fibers are derived from post-consumer hygiene products.

[0029] In the above method, since the wood pulp fibers are derived from used sanitary products, in the fiber formation step, the ozone-containing gas cleans, sterilizes, bleaches, etc. the pulp fibers contained in the used sanitary products, and if the treatment liquid contains a superabsorbent polymer, decomposes the superabsorbent polymer, thereby producing pulp fibers for carboxylated CNF.

[0030] [Aspect 10] 10. The method of embodiment 9, wherein the used sanitary article further comprises a superabsorbent polymer, and the wood pulp fibers comprise the superabsorbent polymer.

[0031] In the above method, since the wood pulp fiber contains the superabsorbent polymer, in the fiber formation step, the ozone-containing gas can decompose the superabsorbent polymer while producing pulp fiber for carboxylated CNF.

[0032] [Aspect 11] 11. The method of embodiment 10, further comprising a deactivation step prior to said fiber-forming step, inactivating said superabsorbent polymer.

[0033] In used sanitary products, in absorbents containing wood pulp fibers and superabsorbent polymers, (i) as the superabsorbent polymer absorbs liquids such as bodily fluids, it swells and entangles the wood pulp fibers, and (ii) the entangled superabsorbent polymers entangle the wood pulp fibers, causing gel blocking, and in many cases, multiple superabsorbent polymers and multiple wood pulp fibers form connected structures.

[0034] Since the above method includes a predetermined inactivation step before the fiber formation step, liquids such as excrement held by the superabsorbent polymer are discharged in advance before the fiber formation step, and even if the superabsorbent polymer and wood pulp fibers form a connected structure, the ozone in the ozone-containing gas can remove the superabsorbent polymer that makes up the connected structure, and the ozone in the ozone-containing gas acts on the pulp fibers that make up the connected structure, allowing pulp fibers for carboxylated CNF to be produced.

[0035] [Aspect 12] 12. The method of claim 11, wherein the inactivating step inactivates the superabsorbent polymer by adding an acid.

[0036] In the above method, the superabsorbent polymer is inactivated by adding an acid in the inactivation step, which makes it easier to adjust the pH of the treatment solution to a predetermined range in the subsequent fiber formation step.

[0037] [Aspect 13] Aspect 13. The method according to any one of Aspects 10 to 12, wherein in the fiber-forming step, the superabsorbent polymer is decomposed using the ozone-containing gas and solubilized in the treatment liquid.

[0038] In the above method, in the fiber formation step, the ozone-containing gas is used to decompose the superabsorbent polymer and solubilize it in the treatment liquid, making it possible to produce pulp fibers for carboxylated CNF production with few impurities.

[0039] [Aspect 14] A pulp fiber for producing carboxylated cellulose nanofibers formed from wood pulp fiber, The degree of polymerization-carboxyl group amount index (I) of the pulp fiber for forming the carboxylated cellulose nanofibers is expressed by the product of the degree of polymerization (DP) and the amount of carboxyl groups (C) (mmol / g), 46≦I Meet the requirements of The pulp fiber for producing carboxylated cellulose nanofibers is characterized by the above.

[0040] The pulp fiber for the above carboxylated CNF has a degree of polymerization and carboxyl group index: I 120 Therefore, the pulp fiber for use in forming carboxylated cellulose nanofibers can form carboxylated CNF that has an excellent balance between ease of handling and physical properties.

[0041] [Aspect 15] 15. The pulp fiber for use in producing carboxylated cellulose nanofibers according to aspect 14, having a carboxyl group amount: C (mmol / g) in the range of 0.11 to 0.60 mmol / g. The above-mentioned pulp fiber for carboxylated CNF has a predetermined amount of carboxyl groups, so that it is possible to form carboxylated CNF with an excellent balance between handleability and physical properties.

[0042] [Aspect 16] 16. The pulp fiber for use in producing carboxylated cellulose nanofibers according to claim 14 or 15, which does not contain nitroxy radical species, their oxides, or their reduced products. The above-mentioned pulp fiber for carboxylated CNF does not contain nitroxy radical species, such as TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl), its oxides, and its reduced products, and is therefore preferable from the standpoint of safety.

[0043] The method for producing pulp fibers for use in producing carboxylated cellulose nanofibers according to the present disclosure and the pulp fibers for use in producing carboxylated cellulose nanofibers will be described in detail below. The method for producing pulp fibers for carboxylated cellulose nanofiberization of the present disclosure includes the following steps. The ozone-containing gas is added to a treatment solution having a pH of 6.5 or less in which wood pulp fibers are immersed, and the CT value, which is the product of the ozone concentration in the ozone-containing gas and the treatment time, is 6,000. g / m 3 a fiber formation step (hereinafter sometimes simply referred to as the "fiber formation step") in which the wood pulp fibers are fed so that the temperature exceeds 100°C for more than 1 minute to form pulp fibers for use in producing carboxylated cellulose nanofibers from the wood pulp fibers.

[0044] In the following, "pulp fibers for carboxylated cellulose nanofibers" may be referred to as "pulp fibers for carboxylated CNF conversion," and "method for producing pulp fibers for carboxylated cellulose nanofibers" may be referred to as "method for producing pulp fibers for carboxylated CNF conversion" or "the production method of the present disclosure," etc.

[0045] When the wood pulp fibers contain a superabsorbent polymer, the method for producing pulp fibers for carboxylated CNF of the present disclosure can further include the following steps prior to the fiber formation step: An inactivation step for inactivating the superabsorbent polymer (hereinafter, sometimes simply referred to as the "inactivation step").

[0046] [Fiber formation step] In the fiber forming step, an ozone-containing gas is supplied to a treatment solution having a pH of 6.5 or less in which wood pulp fibers are immersed. The wood pulp fibers are not particularly limited, and examples thereof include softwood pulp fibers and hardwood pulp fibers. The wood pulp fibers may be virgin pulp fibers, recycled pulp fibers, or pulp fibers derived from used sanitary products.

[0047] The treatment solution has a pH of 6.5 or less, preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 2.5 or less, which facilitates the production of pulp fibers for carboxylated CNF that can form carboxylated CNF with an excellent balance between handleability and physical properties. The above pH refers to the pH at 20°C.

[0048] The treatment liquid preferably achieves the above pH by containing an acid, such as an organic acid or an inorganic acid. Examples of the organic acid include citric acid, tartaric acid, glycolic acid, malic acid, succinic acid, acetic acid, and ascorbic acid. Examples of the inorganic acid include sulfuric acid, hydrochloric acid, and nitric acid, with sulfuric acid being preferred from the viewpoints of not containing chlorine and cost.

[0049] As will be described later, it is preferable that the carboxyl groups in the pulp fiber for carboxylated CNF and the carboxylated CNF are not neutralized. To achieve this, the acid dissociation constant (pK a , in water) a , in water).

[0050] In addition, when the acid has a plurality of acid groups, for example, when the acid is a dibasic acid or a tribasic acid, the acid dissociation constant (pK a , in water) has the largest acid dissociation constant (pK a , in water) is the acid dissociation constant (pK a , in water) from the viewpoint of the efficiency of the acid.

[0051] As used herein, the acid dissociation constant (pk a , in water), the values ​​listed in the Electrochemical Handbook compiled by the Electrochemical Society can be used. According to the electrochemistry handbook, the acid dissociation constants (pk a , in water, 25℃) are as follows. [Organic acid] ·Tartaric acid: 2.99 (pK a1 ), 4.44(pK a2 ) Malic acid: 3.24 (pK a1 ), 4.71(pK a2 ) Citric acid: 2.87 (pK a1 ), 4.35(pK a2 ), 5.69(pK a3 )

[0052] Acid dissociation constants (pk a The acid dissociation constant (pk a An example of an apparatus capable of measuring the physical properties of compounds in water is the Sirius T3 Compound Property Evaluation and Analysis System.

[0053] When the treatment solution contains citric acid as the acid, the treatment solution contains citric acid at a concentration of preferably 3.0 to 10.0 mass%, more preferably 3.5 to 8.0 mass%, and even more preferably 4.0 to 6.0 mass%, which makes it easier to produce pulp fibers for carboxylated CNF that can form carboxylated CNF with an excellent balance between handleability and physical properties.

[0054] The size of the bubbles of the ozone-containing gas is not particularly limited, and the ozone-containing gas is supplied to the treatment liquid as, for example, small bubbles (for example, microbubbles or nanobubbles). By supplying an ozone-containing gas to a treatment solution having a predetermined pH, the ozone oxidizes the -CHOH group at the 6-position of cellulose to a carboxyl group, and the degree of polymerization of the carboxylated CNF can be reduced to a predetermined range.

[0055] The ozone-containing gas is added to the treatment liquid so that the CT value, which is the product of the ozone concentration in the ozone-containing gas and the treatment time, is 6,000. g / m3 Preferably, the time should be more than 8,000 minutes. g / m 3 minutes or more, preferably 9,000 g / m 3 minutes or more, preferably 10,000 g / m 3 minutes or more, and even more preferably 12,000 g / m 3 The ozone-containing gas is supplied to the treatment liquid so that the CT value, which is the product of the ozone concentration in the ozone-containing gas and the treatment time, is preferably 40,000. g / m 3 minutes or less, preferably 30,000 g / m 3 minutes or less, and even better, 24,000 g / m 3 This makes it easier to produce pulp fibers for carboxylated CNF production that have a degree of polymerization and a carboxyl group content within a predetermined range and that can form carboxylated CNF that has an excellent balance between handleability and physical properties.

[0056] The ozone concentration in the ozone-containing gas is preferably 40 to 200 g / m 3 , more preferably 80 to 200 g / m 3 , and more preferably 100 to 200 g / m 3 This makes it easier to produce pulp fibers for carboxylated CNF that can form carboxylated CNF with an excellent balance between handleability and physical properties. The ozone concentration in the ozone-containing gas can be measured, for example, by an ultraviolet absorption ozone concentration meter (for example, Ozone Monitor OZM-5000G manufactured by Ecodesign Co., Ltd.).

[0057] The ozone concentration in the treatment solution is preferably 1 to 50 ppm (g / m 3 ), more preferably 2 to 40 ppm (g / m 3), and more preferably 3 to 30 ppm (g / m 3 )

[0058] The ozone concentration in the treatment solution is measured by the following method. (1) 85 mL of the treatment solution containing dissolved ozone is added to a 100 mL measuring cylinder containing approximately 0.15 g of potassium iodide and 5 mL of 10% citric acid solution, and the reaction is allowed to proceed. (2) After the reaction, transfer the treated solution to a 200 mL Erlenmeyer flask, add the starch solution to the Erlenmeyer flask, and color it purple. Then, titrate with 0.01 mol / L sodium thiosulfate while stirring until it becomes colorless, and record the amount added, a (mL). (3) Calculate the ozone concentration in the aqueous solution using the following formula: The ozone concentration (ppm by mass) in the treatment solution was calculated using the following formula: Ozone concentration in the treatment liquid (mass ppm) = a(mL) × 0.24 × 0.85(mL) It is calculated as follows.

[0059] In the fiber forming step, the temperature of the treatment liquid is not particularly limited, and may be, for example, room temperature (25°C) or higher. Furthermore, in the fiber formation step, the treatment time is preferably 30 to 210 minutes, more preferably 45 to 180 minutes, and even more preferably 60 to 120 minutes, which facilitates efficient production of carboxylated pulp fibers for CNF production that have a degree of polymerization and a carboxyl group content within a predetermined range.

[0060] The degree of polymerization of the pulp fiber for carboxylated CNF production after n minutes from the start of the fiber formation step is expressed as DP n The amount of carboxyl groups is C n (mmol / g), and the degree of polymerization (DP) of pulp fiber for carboxylated CNF n ) and carboxyl group content (C n The polymerization degree-carboxyl group content index, expressed as the product of n In this case, the degree of polymerization and carboxyl group index: In is preferably in the following range:

[0061] In the above fiber formation step, the degree of polymerization-carboxyl group index (I) was measured 60 minutes after the start of the fiber formation step (n=60). 60 is preferably 58 or more, more preferably 60 or more, even more preferably 61 or more, and even more preferably 62 or more. In the fiber formation step, the degree of polymerization-carboxyl group amount index: I 60 is preferably 200 or less, more preferably 150 or less, even more preferably 100 or less, and even more preferably 80 or less. This makes it easier to produce pulp fibers for carboxylated CNF that can form carboxylated CNF with an excellent balance between handleability and physical properties.

[0062] In the above fiber formation step, the polymerization degree-carboxyl group content index (I 120 is preferably 46 or more, more preferably 49 or more, even more preferably 52 or more, and even more preferably 54 or more. In the fiber formation step, the degree of polymerization-carboxyl group amount index: I 120 is preferably 200 or less, more preferably 150 or less, even more preferably 100 or less, and even more preferably 80 or less. This makes it easier to produce pulp fibers for carboxylated CNF that can form carboxylated CNF with an excellent balance between handleability and physical properties.

[0063] In this specification, the amount of carboxyl groups in the pulp fiber for carboxylated CNF production after n minutes from the start of the fiber formation step: C n (mmol / g) is measured as follows: (1) Pulp fibers for carboxylated CNF are collected n minutes after the start of the fiber formation step. (2) Approximately 0.4 g of pulp fiber for carboxylated CNF conversion is added to a container containing 170 mL of distilled water, and the pulp fiber for carboxylated CNF conversion is dispersed. (3) Add 10 mL of 0.01 M NaCl to the container. (4) Add 0.1M HCl to the container to adjust the pH to 2.8.

[0064] (5) 0.05 M NaOH is added to the vessel at a rate of 0.1 mL / min to 0.2 mL / min until the pH reaches 11, and the electrical conductivity of the contents of the vessel is monitored. (6) Plot the amount of 0.05M NaOH added on the X-axis and the electrical conductivity on the Y-axis, and determine the amount of 0.05M NaOH added: V (mL) at which the electrical conductivity becomes constant. (7) The pulp fiber for carboxylated CNF is recovered by filtration, and its bone dry mass: m (g) is measured. (8) Carboxyl group content of pulp fiber for carboxylated CNF: C n (mmol / g) according to the following formula: C n (mmol / L)=(V×0.05 / 1000) / m It is calculated as follows. The pH is measured using a pHashion pH meter, C-62, manufactured by AS ONE Corporation. The electrical conductivity is measured using a portable electrical conductivity meter (CM-31P type) manufactured by DKK-TOA Corporation.

[0065] In this specification, the degree of polymerization (DP) of pulp fiber for carboxylated CNF production after n minutes from the start of the fiber formation step is n is measured as follows: (1) Pulp fibers for carboxylated CNF are collected n minutes after the start of the fiber formation step. (2) The viscosity ratio η is measured according to "6.4.1 Viscosity ratio" in "Cellulose dilute solution - Intrinsic viscosity measurement method - Copper ethylenediamine method" specified in JIS 8215:1998. r Measure (=η / η0). (3) Using the following formula, the degree of polymerization: DPn Calculate. Specific viscosity:η sp =η r -1 Intrinsic viscosity:[η]=η sp / (100×c(1+0.28η sp )) Degree of polymerization: DP n =175×[η] The above formula is based on the description on page 101 of the Wood Science Experiment Manual (edited by the Japan Wood Research Society, Bun'ei-do Publishing, 2000), where c represents the cellulose concentration (g / mL).

[0066] In the present disclosure, the pulp fibers for carboxylated CNF formation formed in the fiber formation step preferably have a hemicellulose content of less than 8.0% by mass, preferably 7.0% by mass or less, more preferably 6.5% by mass or less, and even more preferably 6.0% by mass or less. This makes it easier to produce carboxylated CNF from the pulp fibers for carboxylated CNF formation. The lower limit of the hemicellulose content of the pulp fibers for carboxylated CNF formation is 0.0% by mass.

[0067] In the present disclosure, the pulp fibers for carboxylated CNF formation formed in the fiber formation step preferably have a lignin content of 0.10% by mass or less, more preferably 0.08% by mass or less, and even more preferably 0.06% by mass or less. This makes it easier to produce carboxylated CNF from the pulp fibers for carboxylated CNF formation. The lower limit of the lignin content of the pulp fibers for carboxylated CNF formation is 0.00% by mass.

[0068] In the present disclosure, the pulp fiber for carboxylated CNF production preferably has a cellulose content of 87.0% by mass or more, more preferably 90% by mass or more, and even more preferably 93% by mass or more. This makes it easier to produce carboxylated CNF from the pulp fiber for carboxylated CNF production. The upper limit of the cellulose content of the pulp fiber for carboxylated CNF production is 100.0% by mass.

[0069] In the present disclosure, the cellulose content, hemicellulose content, and lignin content in pulp fibers for carboxylated CNF conversion can be measured according to known detergent analysis methods.

[0070] As described above, in the manufacturing method of the present disclosure, the wood pulp fibers in the fiber-forming step can be derived from used sanitary products (e.g., disposable diapers, urine absorption pads, sanitary napkins, bed sheets, pet sheets), which allows the wood pulp fibers to which bodily fluids and the like have adhered to be sterilized, bleached, deodorized, and the like using an ozone-containing gas in the fiber-forming step.

[0071] The used sanitary goods may also contain a superabsorbent polymer for retaining liquids such as bodily fluids. For example, if the used sanitary goods contain wood pulp fibers and a superabsorbent polymer in their absorbent bodies, the wood pulp fibers recovered from the used sanitary goods often contain the superabsorbent polymer that has absorbed the liquid.

[0072] The superabsorbent polymer is not particularly limited and includes those known in the art, such as starch-based, cellulose-based, and synthetic polymer-based superabsorbent polymers. Examples of starch-based or cellulose-based superabsorbent polymers include starch-acrylic acid (salt) graft copolymers, saponified starch-acrylonitrile copolymers, and crosslinked products of sodium carboxymethylcellulose. Examples of synthetic polymer-based superabsorbent polymers include polyacrylate-based, polysulfonate-based, maleic anhydride-based, polyacrylamide-based, polyvinyl alcohol-based, polyethylene oxide-based, polyaspartate-based, polyglutamate-based, polyalginate-based, starch-based, and cellulose-based superabsorbent polymers (SAPs). Polyacrylate-based (particularly sodium polyacrylate-based) superabsorbent polymers are preferred.

[0073] As superabsorbent polymers absorb liquids such as bodily fluids, they swell and entangle wood pulp fibers, and the swollen superabsorbent polymers entangle the wood pulp fibers, causing gel blocking, and in many cases, multiple superabsorbent polymers and multiple wood pulp fibers form connected structures. As a result, wood pulp fibers derived from used sanitary products generally contain superabsorbent polymers as the connected structures.

[0074] In the fiber formation step, even if the wood pulp fibers contain a superabsorbent polymer, for example, as the connecting structure, the ozone-containing gas can oxidatively decompose the superabsorbent polymer, solubilize it in the treatment liquid, and remove it.

[0075] When the wood pulp fibers contain a superabsorbent polymer, the manufacturing method of the present disclosure preferably further comprises a deactivation step of deactivating the superabsorbent polymer prior to the fiber-forming step. In the manufacturing method of the present disclosure, when the wood pulp fibers are derived from used sanitary products and the superabsorbent polymer is to be decomposed with an ozone-containing gas, the fiber formation step can be carried out with reference to JP 2019-007119 A.

[0076] [Inactivation step] The inactivation step can be performed by a method used in the art, and the superabsorbent polymer can be inactivated by adding an inactivating agent. Examples of the inactivating agent include acids (e.g., inorganic acids and organic acids), lime, calcium chloride, magnesium sulfate, magnesium chloride, aluminum sulfate, and aluminum chloride. Examples of the inorganic and organic acids include those mentioned above.

[0077] The above acids are preferred because they do not leave ash residue on the pulp fibers. When using an acid as an inactivating agent, the pH for inactivation is preferably 2.5 or less, and more preferably 1.3 to 2.4. This is from the viewpoints of inactivating the water-absorbent polymer, protecting the equipment, and sterilizing the pulp fibers to be converted into carboxylated CNF.

[0078] The temperature of the treatment solution in the inactivation step is not particularly limited as long as the inactivation of the superabsorbent polymer proceeds. The temperature may be room temperature or higher, for example, 15 to 30°C. The time for the inactivation step is not particularly limited as long as the superabsorbent polymer is inactivated and dehydrated, for example, 2 to 60 minutes, and preferably 5 to 30 minutes.

[0079] In the inactivation step, the inactivating agent is preferably an acid, such as citric acid, because this eliminates the need for or simplifies pH adjustment in the fiber formation step.

[0080] The pulp fibers for carboxylated CNF obtained by the manufacturing method of the present disclosure and the pulp fibers for carboxylated CNF of the present disclosure preferably have a degree of polymerization-carboxyl group amount index (I) within the following range, where DP is the degree of polymerization of the pulp fibers for carboxylated CNF, C (mmol / g) is the amount of carboxyl groups, and I is the degree of polymerization-carboxyl group amount index represented by the product of the degree of polymerization (DP) and amount of carboxyl groups (C) of the pulp fibers for carboxylated CNF.

[0081] The degree of polymerization-carboxyl group amount index: I is preferably 42 or more, more preferably 46 or more, even more preferably 52 or more, even more preferably 54 or more, even more preferably 56 or more, even more preferably 58 or more, even more preferably 60 or more, even more preferably 61 or more, and even more preferably 62 or more. In addition, the degree of polymerization-carboxyl group amount index: I is preferably 200 or less, more preferably 150 or less, even more preferably 100 or less, even more preferably 80 or less, and even more preferably 70 or less. This makes it easier for the pulp fibers for production of carboxylated CNF to form carboxylated CNF that has an excellent balance between handleability and physical properties.

[0082] The pulp fiber for carboxylated CNF of the present disclosure has a carboxyl group content (C) (mmol / g) of preferably 0.11 to 0.60 mmol / g, more preferably 0.15 to 0.50 mmol / g, and even more preferably 0.17 to 0.45 mmol / g, which facilitates the formation of carboxylated CNF with an excellent balance between ease of handling and physical properties.

[0083] In the carboxylated pulp fibers for CNF conversion of the present disclosure, the carboxyl groups may be unneutralized, i.e., in the -COOH state, or may be neutralized to form salts, such as sodium salts (-COONa), potassium salts (-COOK), lithium salts (-COOLi), etc.

[0084] The carboxyl groups are preferably not neutralized, i.e., in the -COOH state. This allows for easy production of fiber composite reinforcement materials containing carboxylated CNF and resin. If the carboxyl groups are neutralized, it may be difficult to mix them with resin.

[0085] The pulp fibers for carboxylated CNF of the present disclosure are useful as carboxylated CNF precursors. For example, the pulp fibers for carboxylated CNF of the present disclosure can be stored as carboxylated CNF precursors and, if necessary, pulverized by a known pulping method, for example, using a ball mill, to easily produce carboxylated CNF. For example, in the method for producing carboxylated CNF using a TEMPO catalyst, no precursor exists and the CNF must be stored as carboxylated CNF, but it is well known that it is difficult to redisperse dried CNF in water or other liquids. [Example]

[0086] The present disclosure will be described below using examples, but the present disclosure is not limited to these examples. [Example 1] Approximately 600 g of softwood pulp fiber (virgin pulp fiber) was immersed in a container filled with 60 kg of deionized water as a treatment solution, and a fiber formation step was carried out using the following citric acid concentration in the treatment solution, ozone concentration in the ozone-containing gas, and treatment time to form pulp fiber for carboxylated CNF. The ozone-containing gas was supplied to the treatment solution as nanobubbles.

[0087] The degree of polymerization, amount of carboxyl groups, and degree of polymerization-carboxyl group index at 0 min of treatment time are, respectively, the degree of polymerization, amount of carboxyl groups, and degree of polymerization-carboxyl group index of the softwood pulp fiber before the fiber formation step is performed. ·Citric acid concentration: 0% by mass, 3% by mass, 5% by mass Ozone concentration in ozone-containing gas: 200 g / m 3 Processing time: 0 minutes, 60 minutes, 120 minutes, 210 minutes

[0088] The relationship between the treatment time and the amount of carboxyl groups in pulp fibers for carboxylated CNF is shown in Table 1 and Figure 1, and the relationship between the treatment time and the degree of polymerization is shown in Table 2 and Figure 2. The relationship between the treatment time and the degree of polymerization-carboxyl group amount index (I) is also shown. nThe relationship between these is shown in Table 3 and Figure 3. The pH of the treatment liquid was 6.9, 1.8, and 1.6 when the citric acid concentrations were 0 mass%, 3 mass%, and 5 mass%, respectively.

[0089] [Table 1]

[0090] [Table 2]

[0091] [Table 3]

[0092] From Tables 1 to 3 and Figures 1 to 3, when the citric acid concentration is 3% by mass and 5% by mass, the degree of polymerization and carboxyl group index (I) of the pulp fiber for carboxylated CNF production is higher than when the citric acid concentration is 0% by mass. n This shows that when citric acid was added to softwood pulp fibers, the -CHOH group at the 6-position of cellulose was efficiently oxidized to a carboxyl group while suppressing the decrease in the degree of polymerization within a specified range.

[0093] Water was added to four types of pulp fiber for carboxylated CNF production, with citric acid concentrations of 3% and 5% by mass and treatment times of 60 and 120 minutes, and the fibers were ground using a ball mill, a known grinding method.The viscosity of the solution after grinding and the properties of the ground material after drying confirmed that carboxylated CNF was easily formed.

[0094] [Example 2] Approximately 600 g of softwood pulp fibers (virgin pulp fibers) were immersed in a container filled with 60 kg of deionized water as a treatment liquid, and the fiber formation step was carried out at the following citric acid concentration in the treatment liquid, ozone concentration in the ozone-containing gas, and treatment time to form pulp fibers for carboxylated CNF. The ozone-containing gas was supplied to the treatment liquid as nanobubbles.

[0095] Note that the degree of polymerization, amount of carboxyl groups, and degree of polymerization·amount of carboxyl groups index at a treatment time of 0 minutes are, respectively, the degree of polymerization, amount of carboxyl groups, and degree of polymerization·amount of carboxyl groups index of the softwood pulp fibers before carrying out the fiber formation step. · Citric acid concentration: 1 mass% · Ozone concentration in the ozone-containing gas: 200 g / m 3 · Treatment time: 0 minutes, 30 minutes, 210 minutes, 420 minutes

[0096] The crystallinity of the pulp fibers for carboxylated CNF was measured using a wide-angle X-ray diffractometer RINT2500HL manufactured by Rigaku Corporation. The measurement conditions, X-ray diffraction profile, and X-ray diffraction standard data set are as follows. <Measurement conditions> · X-ray source: Cu · X-ray output: 50 kV - 250 mA · Optical system: Concentrated beam with monochromator · Slit: DS0.5deg + 10 mmH SS0.5deg RS0.15 · Scanning axis: 2θ / θ联动 · Scanning method: Continuous scanning · Scanning range: 5 ≤ 2θ ≤ 70 deg · Scanning speed: 0.5 deg / min · Sampling: 0.02 deg

[0097] <X-ray diffraction profile> · Vertical axis: Diffraction intensity (cps) · Horizontal axis: Diffraction angle (deg) · Diffraction condition: 2dsinθ = nλ d: Lattice plane spacing (nm) θ: Diffraction angle (deg) n: Reflection order λ: X-ray wavelength (0.15406 nm)

[0098] <X-Ray Diffraction Standard Data Set> ·ICDD: International Centre for Diffraction Data The results are shown in Table 4.

[0099]

Table 4

[0100] When the carboxylated CNF pulp fibers were measured with a Varian FT-IR 3100FT-IR / 600UMA, it was confirmed that the amount of carboxyl groups in the carboxylated CNF pulp fibers increased with an increase in the treatment time.

Claims

1. Pulp fibers for producing carboxylated cellulose nanofibers formed from wood pulp fibers derived from used sanitary products, The degree of polymerization / carboxyl group amount index: I, which is represented by the product of the degree of polymerization: DP and the amount of carboxyl groups: C (mmol / g) of the pulp fiber for forming the carboxylated cellulose nanofibers, is 46≦I≦70 Meet the requirements of The pulp fiber for producing carboxylated cellulose nanofibers is characterized by the above.

2. The pulp fiber for use in producing carboxylated cellulose nanofibers according to claim 1, wherein the carboxyl group amount: C (mmol / g) is in the range of 0.11 to 0.60 mmol / g.

3. The pulp fiber for use in producing carboxylated cellulose nanofibers according to claim 1 or 2, which does not contain nitroxy radical species, their oxides, or their reduced products.

4. The pulp fiber for producing carboxylated cellulose nanofibers according to any one of claims 1 to 3, wherein the pulp fiber for producing carboxylated cellulose nanofibers has a hemicellulose content of less than 8.0% by mass.

5. The pulp fiber for producing carboxylated cellulose nanofibers according to any one of claims 1 to 4, wherein the pulp fiber for producing carboxylated cellulose nanofibers has a lignin content of 0.10% by mass or less.

6. The pulp fiber for producing carboxylated cellulose nanofibers according to any one of claims 1 to 5, wherein the used sanitary product further contains a superabsorbent polymer, and the wood pulp fiber contains the superabsorbent polymer.

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