Method for producing i-type unmodified cellulose fine fiber, and method for producing i-type unmodified cellulose fiber molding and i-type unmodified cellulose fine fiber

Abstract

To provide an unmodified cellulose fine fiber which is not chemically modified, and has an I-type crystal structure obtained without marcerization and a molding of the same, a method for producing the cellulose fine fiber and a molding of the same, a method for producing an I-type unmodified cellulose fine fiber which can efficiently obtain an I-type cellulose fine fiber which has high transparency and safety, and is not chemically modified, by a simple process, and a method for producing an I-type unmodified cellulose fine fiber molding and an I-type unmodified cellulose fine fiber.SOLUTION: A method for producing an I-type unmodified cellulose fine fiber includes: a depolymerization step of adding sodium hypochlorite having effective chlorine concentration of 0.04 to 3.0% to a cellulose raw material, lowering a degree of polymerization of the cellulose raw material to 1,200 or less, and obtaining depolymerization cellulose; and a fibrillation step of fibrillating the depolymerization cellulose by mechanical fibrillation.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing cellulose fine fibers, and more particularly to a method for producing type I unmodified cellulose fine fibers, which give cellulose fine fibers that are not chemically modified. [Background technology]

[0002] In recent years, the United Nations has set international goals for sustainable development called Sustainable Development Goals (SDGs), and one of these environmental issues is the reduction of plastic usage. Efforts are being made to solve climate change by reducing the use of petroleum-based plastics, thereby reducing GHG emissions.

[0003] It is said that it takes hundreds of years for plastic to completely decompose, and microplastics accumulate in marine organisms and soil, which has been raised as one of the causes of worsening environmental pollution. Efforts are being made to reduce the amount of plastic produced and to collect it.

[0004] Therefore, cellulose, a natural material with biodegradability, has been attracting attention as an alternative raw material for microplastics. In particular, cellulose fine fibers such as cellulose nanofibers and cellulose microfibers can be processed into molded bodies, such as beads and films, and are expected to be an alternative raw material for microplastics.

[0005] The inventors have invented a method for producing type II unmodified cellulose fine fibers with a small fiber diameter as an alternative to microplastics, which are added to cosmetics such as foundations to improve mixability with other ingredients and improve spreadability and feel during use (see Patent Document 1). The type II unmodified cellulose fine fibers are highly safe because no chemical defibration is used, and are highly transparent due to their small fiber diameter, making them useful as an alternative to plastics with a wide range of applications.

[0006] Cellulose is also used as a reinforcing material that is mixed with resin to improve rigidity, etc. For such applications requiring strength, type I cellulose fine fibers having a strong type I crystal structure are preferably used instead of type II cellulose fine fibers.

[0007] Examples of methods for producing type I cellulose fine fibers include a method in which hypochlorite treatment is performed under specific pH conditions to obtain oxidized cellulose nanofibers having carboxyl groups (see Patent Document 2). Also, oxidized cellulose in which multiple hydroxyl groups have been oxidized (see Patent Document 3) has been proposed as type I cellulose fine fibers.

[0008] However, since it is difficult to defibrate cellulose to the nano-level by mechanical defibration methods that physically defibrate raw pulp, and it is difficult to obtain type I cellulose fine fibers, defibration is performed by chemical defibration. When defibration is performed by chemical defibration, the applications are limited from the viewpoint of the safety of the chemicals used and the chemically modified cellulose. Furthermore, chemically modified cellulose such as oxidized cellulose is not suitable for applications requiring water resistance because the molded product derived from the cellulose dissolves in water. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 7212732 [Patent Document 2] Patent No. 6872396 [Patent Document 3] Patent No. 7142702 Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, the inventors have repeatedly studied and improved a production method for obtaining type I cellulose fine fibers that avoids defibration by chemical defibration methods and does not chemically modify cellulose.As a result, they have arrived at a production method that can easily and efficiently obtain chemically unmodified nano-sized type I unmodified cellulose fine fibers without complex steps.

[0011] The present invention has been made in consideration of the above-mentioned points, and provides unmodified cellulose fine fibers having a type I crystal structure that are not chemically modified and are obtained without undergoing mercerization, and a molded body thereof, a method for producing the cellulose fine fibers and a molded body thereof, which are capable of efficiently obtaining chemically unmodified type I cellulose fine fibers that are highly transparent and safe through simple steps, as well as a method for producing a type I unmodified cellulose fine fiber molded body and type I unmodified cellulose fine fibers. [Means for solving the problem]

[0012] That is, the first invention relates to a method for producing type I unmodified cellulose fine fibers, characterized by comprising a depolymerization step of adding sodium hypochlorite having an effective chlorine concentration of 0.04 to 3.0% to a cellulose raw material to reduce the degree of polymerization of the cellulose raw material to 1200 or less to obtain depolymerized cellulose, and a defibration step of defibrating the depolymerized cellulose by mechanical defibration.

[0013] A second invention relates to a method for producing type I unmodified cellulose fine fibers according to the first invention, wherein the mechanical defibration in the defibration step is a shear treatment under high pressure conditions.

[0014] The third invention relates to the method for producing I-type unmodified cellulose fine fibers according to the first or second invention, wherein the depolymerization step is carried out in a temperature range of 40 to 70°C.

[0015] A fourth invention relates to the method for producing I-type unmodified cellulose fine fibers according to the first or second invention, wherein the sodium hypochlorite has an available chlorine concentration of 0.2 to 2.0%.

[0016] A fifth invention relates to the method for producing I-type unmodified cellulose fine fibers, wherein the sodium hypochlorite has an available chlorine concentration of 0.2 to 2.0% in the third invention.

[0017] The sixth invention relates to a method for producing type I unmodified cellulose fine fibers, in the first or second invention, wherein the cellulose raw material is pulp mainly composed of cellulose, and contains 25% by weight or less of xylose among its constituent sugars.

[0018] The seventh invention relates to a method for producing type I unmodified cellulose fine fibers in the third invention, wherein the cellulose raw material is pulp mainly composed of cellulose and contains 25% by weight or less of xylose among its constituent sugars.

[0019] The eighth invention relates to a method for producing type I unmodified cellulose fine fibers in the fourth invention, wherein the cellulose raw material is pulp mainly composed of cellulose and contains 25% by weight or less of xylose among its constituent sugars.

[0020] The ninth invention relates to a method for producing type I unmodified cellulose fine fibers in the fifth invention, wherein the cellulose raw material is pulp mainly composed of cellulose and contains 25% by weight or less of xylose among its constituent sugars.

[0021] The tenth invention relates to a method for producing type I unmodified cellulose fine fibers according to the first or second invention, wherein the cellulose raw material is pulp mainly composed of cellulose and contains mannose in an amount of 10% by weight or less among its constituent sugars.

[0022] An eleventh invention relates to a method for producing type I unmodified cellulose fine fibers according to the first or second invention, wherein the cellulose raw material is a pulp mainly composed of cellulose and contains 30% by weight or less of lignin.

[0023] The twelfth invention relates to a method for producing a type I unmodified cellulose fine fiber molded article, comprising a molding step of molding the type I unmodified cellulose fine fibers obtained by the method for producing type I unmodified cellulose fine fibers of the first invention.

[0024] The thirteenth invention relates to type I unmodified cellulose fine fibers, the haze value of a 0.1 wt % dispersion of type I unmodified cellulose fine fibers obtained by the method for producing type I unmodified cellulose fine fibers of the first invention being 50% or less, as measured in accordance with JIS K 7136 (2000).

[0025] The fourteenth invention relates to type I unmodified cellulose fine fibers, the haze value of a 0.1 wt % dispersion of type I unmodified cellulose fine fibers obtained by the method for producing type I unmodified cellulose fine fibers of the first invention being 30% or less, as measured in accordance with JIS K 7136 (2000).

[0026] The fifteenth invention relates to type I unmodified cellulose fine fibers according to the thirteenth invention, which contain 20% by weight or less of xylose among the constituent sugars of the type I unmodified cellulose fine fibers.

[0027] The sixteenth invention relates to type I unmodified cellulose fine fibers according to the thirteenth invention, which contain mannose in an amount of 5% by weight or less among the constituent sugars of the type I unmodified cellulose fine fibers.

[0028] A seventeenth aspect of the present invention relates to the I-type unmodified cellulose fine fibers according to the thirteenth aspect of the present invention, which contain lignin in an amount of 15% by weight or less.

[0029] The eighteenth invention relates to the I-type unmodified cellulose fine fibers according to the thirteenth invention, wherein the I-type unmodified cellulose fine fibers have a degree of polymerization of 800 or less.

[0030] A nineteenth aspect of the present invention relates to type I unmodified cellulose fine fibers according to any one of the fifteenth to eighteenth aspects, wherein the amount of carboxyl groups in the type I unmodified cellulose fine fibers is less than 0.20 mmol / g. Effect of the Invention

[0031] The method for producing type I unmodified cellulose fine fibers according to the first invention includes a depolymerization step in which sodium hypochlorite having an effective chlorine concentration of 0.04 to 3.0% is added to a cellulose raw material to reduce the degree of polymerization of the cellulose raw material to 1200 or less to obtain depolymerized cellulose, and a defibration step in which the depolymerized cellulose is defibrated by mechanical defibration. Therefore, type I cellulose fine fibers that are not chemically modified and have high transparency and safety can be efficiently obtained by a simple process.

[0032] According to the method for producing type I unmodified cellulose fine fibers of the second invention, in the first invention, the mechanical defibration in the defibration step is a shear treatment under high pressure conditions, so that cellulose can be defibrated more efficiently.

[0033] According to the method for producing type I unmodified cellulose fine fibers of the third invention, in the first or second invention, the depolymerization step is carried out in a temperature range of 40 to 70°C, so that cellulose can be defibrated more efficiently.

[0034] According to the method for producing type I unmodified cellulose fine fibers of the fourth invention, in the first or second invention, since the effective chlorine concentration of the sodium hypochlorite is 0.2 to 2.0%, type I unmodified cellulose fine fibers defibrated to single nano size can be efficiently obtained.

[0035] According to the method for producing type I unmodified cellulose fine fibers of the fifth invention, since the effective chlorine concentration of the sodium hypochlorite in the third invention is 0.2 to 2.0%, type I unmodified cellulose fine fibers defibrated to single nano size can be efficiently obtained.

[0036] According to the sixth invention, the method for producing type I unmodified cellulose fine fibers of the first or second invention, the cellulose raw material is pulp mainly composed of cellulose, and contains xylose in an amount of 25% by weight or less among its constituent sugars, so that cellulose fine fibers can be obtained without removing hemicellulose, which was previously a miscellaneous component.

[0037] According to the seventh invention, the method for producing type I unmodified cellulose fine fibers is the same as in the third invention, in which the cellulose raw material is pulp mainly composed of cellulose, and contains xylose in an amount of 25% by weight or less among its constituent sugars, so that cellulose fine fibers can be obtained without removing hemicellulose, which was previously a miscellaneous component.

[0038] According to the eighth invention, the method for producing type I unmodified cellulose fine fibers, in the fourth invention, the cellulose raw material is pulp mainly composed of cellulose, and contains xylose in an amount of 25% by weight or less among its constituent sugars, so that cellulose fine fibers can be obtained without removing hemicellulose, which was previously a miscellaneous component.

[0039] According to the ninth invention, the method for producing type I unmodified cellulose fine fibers is the same as in the fifth invention, in which the cellulose raw material is pulp mainly composed of cellulose, and contains xylose in an amount of 25% by weight or less among its constituent sugars, so that cellulose fine fibers can be obtained without removing hemicellulose, which was previously a miscellaneous component.

[0040] According to the method for producing type I unmodified cellulose fine fibers of the 10th invention, in the first or second invention, the cellulose raw material is pulp mainly composed of cellulose, and contains mannose in an amount of 10% by weight or less among its constituent sugars, so that cellulose fine fibers can be obtained without removing hemicellulose, which was previously a miscellaneous component.

[0041] According to the method for producing type I unmodified cellulose fine fibers of the 11th invention, in the first or second invention, the cellulose raw material is a pulp mainly composed of cellulose and contains 30% by weight or less of lignin, so that pulp from which lignin has not been removed can be used as the cellulose raw material, and type I cellulose fine fibers can be obtained easily and efficiently.

[0042] The method for producing type I unmodified cellulose fine fiber moldings according to the 12th aspect of the present invention includes a molding step of molding type I unmodified cellulose fine fiber obtained by the method for producing type I unmodified cellulose fine fiber of the first aspect of the present invention, and therefore a cellulose fine fiber molding can be obtained by a simple process.

[0043] According to the type I unmodified cellulose fine fibers of the thirteenth invention, the haze value of a 0.1 wt % dispersion of type I unmodified cellulose fine fibers obtained by the method for producing type I unmodified cellulose fine fibers of the first invention, as measured in accordance with JIS K 7136 (2000), is 50% or less, and therefore type I unmodified cellulose fine fibers having high transparency and safety can be obtained.

[0044] According to the type I unmodified cellulose fine fibers of the 14th invention, the haze value of a 0.1 wt % dispersion of type I unmodified cellulose fine fibers obtained by the method for producing type I unmodified cellulose fine fibers of the first invention, as measured in accordance with JIS K 7136 (2000), is 30% or less, and therefore type I unmodified cellulose fine fibers that are highly transparent and safe can be obtained.

[0045] According to the type I unmodified cellulose fine fibers of the 15th invention, in the 13th invention, the constituent sugars of the type I unmodified cellulose fine fibers contain xylose at 20% by weight or less, so that it is possible to obtain cellulose fine fibers without removing hemicellulose, which has conventionally been a miscellaneous component, and it is possible to obtain cellulose fine fibers with the efficacy derived from hemicellulose.

[0046] According to the type I unmodified cellulose fine fibers of the 16th invention, in the 13th invention, the constituent sugars of the type I unmodified cellulose fine fibers contain mannose at 5% by weight or less, so that cellulose fine fibers can be obtained without removing hemicellulose, which has conventionally been a miscellaneous component, and cellulose fine fibers can be obtained that have the efficacy derived from hemicellulose.

[0047] According to the type I unmodified cellulose fine fibers of the 17th invention, in the 13th invention, the type I unmodified cellulose fine fibers contain lignin at 15% by weight or less, so that pulp from which lignin has not been removed can be used as a cellulose raw material, and cellulose fine fibers having efficacy derived from lignin can be obtained.

[0048] According to the I-type unmodified cellulose fine fibers of the 18th invention, in the 13th invention, the degree of polymerization of the I-type unmodified cellulose fine fibers is 800 or less, so that the viscosity of the dispersion can be reduced, which facilitates degassing and improves moldability.

[0049] According to the 19th invention, the type I unmodified cellulose fine fibers of any of the 15th to 18th inventions have a carboxyl group amount of less than 0.20 mmol / g, and therefore the type I unmodified cellulose fine fibers of the present invention are unmodified cellulose fine fibers. [Brief description of the drawings]

[0050] [Figure 1] FIG. 1 is a schematic process diagram of a method for producing type I unmodified cellulose fine fibers of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0051] The cellulose fine fibers produced by the production method of the present invention are obtained by mechanically defibrating a cellulose raw material. Cellulose fine fibers are generally used as reinforcing materials for resins, and in such cases, type I cellulose fine fibers having a high-strength type I crystal structure are preferably used. The cellulose fine fibers produced by the production method of the present invention are type I cellulose fine fibers that can be suitably used in industrial applications, and therefore do not undergo mercerization of cellulose, which changes the crystal structure.

[0052] Although cellulose can be made into fine fibers by mechanical defibration alone, this requires multiple defibration processes, which is inefficient, and it is difficult to defibrate it to the nano level. Although cellulose can be made into fine fibers by chemical defibration to the single nano level, there are concerns about the safety of the chemicals used, the environmental impact, and the safety of the material due to chemical modification of cellulose.

[0053] Therefore, in the present invention, a depolymerization process is carried out using a highly safe chemical to reduce the degree of polymerization of the cellulose raw material as a preliminary step to the mechanical fiberization process. The sodium hypochlorite used in the depolymerization process is at a low concentration such that the hydroxyl groups of cellulose are not oxidized to carboxyl groups, so the cellulose remains unmodified and is not chemically modified. This reduces the degree of polymerization of the cellulose while it remains unmodified, making it possible to efficiently fiberize the cellulose even by mechanical fiberization. The resulting cellulose fine fibers are highly safe because they are not chemically modified, and have good design properties because they have a small fiber diameter, which can contribute to the expansion of new applications such as food additives and capsules.

[0054] The method for producing type I unmodified cellulose fine fibers of the present invention will now be described step by step with reference to the process diagram in FIG. 1. First, pulp is a preferred example of cellulose as a starting raw material. Pulp is a raw material obtained mainly by crushing wood. Cotton and the like can also be used. Pulp is fibrous and therefore highly reactive with chemicals, making it a preferred cellulose raw material. In addition to pulp, animal cellulose such as bacterial cellulose produced by microorganisms can also be used. Furthermore, purified cellulose obtained by purifying these raw materials can be used.

[0055] The cellulose raw material used in the conventional method for producing cellulose fine fibers is preferably one in which impurities such as lignin have been removed to increase the purity of the cellulose components. In the production method of the present invention, however, pulp containing lignin or pulp containing xylose or mannose as constituent sugars can be used as the raw material. For example, pulp containing cellulose as the main component with a xylose content of 25% by weight or less can be used as the raw material. For mannose, pulp containing cellulose as the main component with a cellulose content of 10% by weight or less can be used as the raw material. For lignin, pulp containing cellulose as the main component with a cellulose content of 30% by weight or less can be used as the raw material. It is possible to effectively utilize the raw material, and it is considered that the cellulose fine fibers can be provided with physical properties derived from hemicellulose or lignin depending on the application.

[0056] As described above, the depolymerization step (S1) is intended to reduce the degree of polymerization of the cellulose raw material. A solvent such as ion-exchanged water and sodium hypochlorite with an effective chlorine concentration of 0.04 to 3.0% are added to the cellulose raw material and reacted to reduce the degree of polymerization of the cellulose raw material to produce depolymerized cellulose. In this case, in order to defibrate the cellulose to the extent that it becomes fine fibers by mechanical defibration in the subsequent defibration step, the degree of polymerization of the cellulose raw material is reduced to 1200 or less.

[0057] In the depolymerization step (S1), the efficiency of depolymerization is improved when the reaction is performed at a temperature higher than room temperature, so the temperature range of the depolymerization reaction is preferably 40 to 70°C. Although it depends on the effective chlorine concentration of sodium hypochlorite, the approximate reaction time is preferably about 1 to 5 hours. Also, if the effective chlorine concentration is too low, the reaction time becomes long, which may result in poor efficiency or insufficient depolymerization. Although the efficiency of depolymerization increases when the effective chlorine concentration is high, the low molecular weight cellulose raw material dissolves in the solvent, reducing the yield, and there is a concern of corrosion of the equipment, so the effective chlorine concentration of sodium hypochlorite is set to 0.02 to 2.0%. Also, if the effective chlorine concentration is too high, there is a concern that the hydroxyl group of cellulose may be oxidized to a carboxyl group. More preferably, when the effective chlorine concentration of sodium hypochlorite is set to 0.3 to 2.5%, an efficient depolymerization reaction can be expected, and cellulose can be easily defibrated to a single nano level in the defibration step.

[0058] Then, in the defibration step (S2), the depolymerized cellulose with a degree of polymerization reduced to 1200 or less is defibrated by mechanical defibration to produce type I unmodified cellulose fine fibers. In the depolymerization step (S1), the degree of polymerization of the cellulose raw material is reduced to 1200 or less, making it possible to defibrate cellulose at the nano level by mechanical defibration rather than chemical defibration. By reducing the degree of polymerization of cellulose, defibration is possible without the application of high pressure, which is also advantageous in terms of equipment.

[0059] The depolymerized cellulose obtained through the depolymerization step is subjected to replacement washing with ion-exchanged water or the like, and further ion-exchanged water is added to form a dispersion. This dispersion is pre-defibrated as necessary before the main defibration by mechanical defibration. Defibration of depolymerized cellulose is performed by mechanical (physical) defibration, and is performed by a known method using a homogenizer, a water jet, or the like. In particular, defibration by shear treatment under high pressure conditions allows the depolymerized cellulose to be defibrated efficiently and more finely, so defibration by a high-pressure homogenizer is preferred.

[0060] Defibration may be performed in multiple steps. For example, after preliminary defibration using a mixer, main defibration using a homogenizer can be performed to obtain cellulose fine fibers that are uniform and have a small fiber diameter. Furthermore, preliminary defibration can avoid problems such as clogging of the defibration device with depolymerized cellulose. Preliminary defibration is performed by a known method using a mixer, a refiner, or the like. It is more preferable to obtain cellulose fine fibers close to single nano size because the smaller the average fiber diameter of the cellulose fine fibers, the better the transparency of the dispersion of the cellulose fine fibers.

[0061] A molded article can be produced by using the dispersion of type I unmodified cellulose fine fibers obtained through these steps. Type I unmodified cellulose fine fiber molded articles can be molded only by drying treatment, and can be used, for example, as a film by forming a coating film, as a food additive by powdering, or as an encapsulation by drying molding. Powdering or forming into beads can also make them easier to handle as an additive to resins.

[0062] A 0.1% by mass dispersion of I-type unmodified cellulose fine fibers obtained by the manufacturing method of the present invention has good transparency. Specifically, if the haze value measured in accordance with JIS K 7136 (2000) is 50% or 30% or less, it can contribute to improving design depending on the application and can be used for a wide range of applications. In addition, the haze value of the dispersion is considered to be an index of the average fiber diameter of the cellulose fine fibers, and if the haze value of the dispersion is 10% or less, it can be said that the average fiber diameter of the cellulose fine fibers is at the single nano level.

[0063] In the production method of the present invention, pulp mainly composed of cellulose containing 25% by weight or less of xylose as a constituent sugar can be used as the cellulose raw material, and the sugars constituting the type I unmodified cellulose fine fibers can contain 20% by weight or less of xylose. In addition, since cellulose fine fibers can be obtained without removing xylose as hemicellulose, which was previously a miscellaneous component, the fibers can be provided with physical properties derived from hemicellulose depending on the application.

[0064] In the production method of the present invention, pulp mainly composed of cellulose containing 10% by weight or less of mannose as a constituent sugar can be used as the cellulose raw material, and mannose can be contained in an amount of 5% by weight or less among the sugars constituting the type I unmodified cellulose fine fibers. In addition, since cellulose fine fibers can be obtained without removing mannose as hemicellulose, which has conventionally been a miscellaneous component, the fibers can be provided with physical properties derived from hemicellulose depending on the application.

[0065] Furthermore, in the production method of the present invention, pulp mainly composed of cellulose containing 30% by weight or less of lignin can be used as the cellulose raw material, and lignin can be contained in an amount of 15% by weight or less among the components constituting type I unmodified cellulose fine fibers. Also, since cellulose fine fibers can be obtained without removing lignin, which was a miscellaneous component in the past, a step of removing lignin from pulp as the cellulose raw material is not required, so type I cellulose fine fibers can be obtained more efficiently, and physical properties derived from lignin can be provided depending on the application.

[0066] By controlling the degree of polymerization of the I-type unmodified cellulose fine fibers obtained by the production method of the present invention to 800 or less, the viscosity of the dispersion can be reduced, which facilitates degassing, improves moldability, and improves the appearance of the molded product. Furthermore, a lower viscosity dispersion can suppress an increase in pressure in the molding device, which makes it possible to improve production efficiency.

[0067] In addition, since the amount of carboxyl groups in the type I unmodified cellulose fine fibers obtained by the production method of the present invention is less than 0.20 mmol / g, the type I unmodified cellulose fine fibers can be unmodified and have a small fiber diameter, and can be used for a wide range of applications.

[0068] Unlike modified cellulose fine fibers having functional groups such as oxidized cellulose, a molded article made from the type I unmodified cellulose fine fibers obtained by the production method of the present invention does not redissolve in water, and therefore can be made into a water-resistant molded article when molded into a film, beads, etc. In this specification, the term "water-resistant" is used to indicate the degree to which a molded article does not easily collapse when it absorbs moisture.

[0069] For example, when it is formed into a film, it has good transparency because it is made of cellulose fine fibers with a small average fiber diameter while having water resistance as described above. In addition, compared to cellophane film, it does not use organic solvents, so it has a small environmental impact. Furthermore, it is highly safe and can be used as an edible film.

[0070] When molded into beads, they are not chemically modified, so they have water resistance and organic solvent resistance derived from cellulose, making them suitable for addition to various liquids. They can be used as additives with functions such as lubricants, matting agents, and anti-blocking agents.

[0071] The chemical sodium hypochlorite used in the production method of the present invention is a food additive, so it is highly safe, and the type I unmodified cellulose fine fibers are edible. Therefore, they can also be used as a thickener, etc. In addition, since xylose as hemicellulose has a blood sugar level suppressing effect, they can also be used as functional foods.

[0072] In addition, because of its good transparency, it can also be used as a coating agent for films. By applying it to the surface of a film, it is possible to improve the wettability of the film and impart gas barrier properties. EXAMPLES

[0073] In producing type I unmodified cellulose fine fibers, the inventors used the following raw materials and conducted production experiments on type I unmodified cellulose fine fibers by changing the sodium hypochlorite (available chlorine) concentration in the depolymerization process according to the process diagram in Figure 1.

[0074] [Raw materials] The starting cellulose raw materials were kraft pulp 1 (C1) (degree of polymerization 1750, xylose concentration in the constituent sugars 8.2%, mannose concentration in the constituent sugars 5.1%, lignin concentration 0%), kraft pulp 2 (C2) (degree of polymerization 1113, xylose concentration in the constituent sugars 20.6%, mannose concentration in the constituent sugars 0.2%, lignin concentration 0%), and thermomechanical pulp (C3) (degree of polymerization 674, xylose concentration in the constituent sugars 4.0%, mannose concentration in the constituent sugars 7.8%, lignin concentration 29.0%).

[0075] [Preparation of dispersion of type I unmodified cellulose microfibers] Using the above raw materials, a dispersion of type I unmodified cellulose fine fibers was prepared as follows.

[0076] <Prototype example 1> 191 g of ion-exchanged water as a solvent was added to 8 g of kraft pulp 1 (C1) as a cellulose raw material, and mixed with a mixer (Primix Corporation, "Labo-lution"). 1 g of sodium hypochlorite was added to the mixed slurry to obtain a solution with a sodium hypochlorite concentration of 0.5% and an effective chlorine concentration of 0.04%. The solution was reacted in a water bath at 55°C for 3 hours to obtain depolymerized cellulose in which the polymerization degree of the cellulose raw material was reduced to 1200 (depolymerization step). The depolymerized cellulose was washed by replacement with ion-exchanged water, and ion-exchanged water was added to obtain a dispersion with a total amount of 1600 g. The dispersion was pre-defibrated with a mixer (Primix Corporation, "Labo-lution"). Then, it was defibrated with a pressure of 70 MPa using a homogenizer (SMT Corporation, "LAB1000") to obtain a dispersion of I-type unmodified cellulose fine fibers of Prototype Example 1.

[0077] <Prototype Example 2> The depolymerization process was carried out in the same manner as in Prototype Example 1, except that 190 g of ion-exchanged water and 2 g of sodium hypochlorite were used to produce a solution with a sodium hypochlorite concentration of 1.0% and an available chlorine concentration of 0.09%, and that depolymerized cellulose in which the degree of polymerization of the cellulose raw material had been reduced to 673 was obtained, to obtain a dispersion of type I unmodified cellulose fine fibers for Prototype Example 2.

[0078] <Prototype 3> The depolymerization process was carried out in the same manner as in Prototype Example 1, except that 186 g of ion-exchanged water and 6 g of sodium hypochlorite were used to produce a solution with a sodium hypochlorite concentration of 3.0% and an available chlorine concentration of 0.26%, and depolymerized cellulose in which the degree of polymerization of the cellulose raw material had been reduced to 311 was obtained. A dispersion of type I unmodified cellulose fine fibers was obtained in Prototype Example 3.

[0079] <Prototype 4> The depolymerization process was carried out in the same manner as in Prototype Example 1, except that 184 g of ion-exchanged water and 8 g of sodium hypochlorite were used to produce a solution with a sodium hypochlorite concentration of 4.0% and an available chlorine concentration of 0.35%, and depolymerized cellulose in which the degree of polymerization of the cellulose raw material had been reduced to 243 was obtained. A dispersion of type I unmodified cellulose fine fibers was obtained in Prototype Example 4.

[0080] <Prototype 5> The depolymerization process was carried out in the same manner as in Prototype Example 1, except that 182 g of ion-exchanged water and 10 g of sodium hypochlorite were used to produce a solution with a sodium hypochlorite concentration of 5.0% and an available chlorine concentration of 0.43%, and depolymerized cellulose in which the degree of polymerization of the cellulose raw material had been reduced to 159 was obtained. A dispersion of type I unmodified cellulose fine fibers was obtained in Prototype Example 5.

[0081] <Prototype 6> The depolymerization process was carried out in the same manner as in Prototype Example 1, except that 172 g of ion-exchanged water and 20 g of sodium hypochlorite were used to produce a solution with a sodium hypochlorite concentration of 10.0% and an available chlorine concentration of 0.86%, and depolymerized cellulose in which the degree of polymerization of the cellulose raw material had been reduced to 101 was obtained, to obtain a dispersion of type I unmodified cellulose fine fibers for Prototype Example 6.

[0082] <Prototype 7> The depolymerization process was carried out in the same manner as in Prototype Example 1, except that 152 g of ion-exchanged water and 40 g of sodium hypochlorite were used to produce a solution with a sodium hypochlorite concentration of 20.0% and an available chlorine concentration of 1.73%, and depolymerized cellulose in which the degree of polymerization of the cellulose raw material had been reduced to 74 was obtained. A dispersion of type I unmodified cellulose fine fibers for Prototype Example 7 was obtained.

[0083] <Prototype Example 8> The depolymerization process was carried out in the same manner as in Prototype Example 1, except that 132 g of ion-exchanged water and 60 g of sodium hypochlorite were used to produce a solution with a sodium hypochlorite concentration of 30.0% and an available chlorine concentration of 2.59%, and depolymerized cellulose in which the degree of polymerization of the cellulose raw material had been reduced to 67 was obtained. A dispersion of type I unmodified cellulose fine fibers was obtained in Prototype Example 8.

[0084] <Prototype Example 9> The depolymerization process was carried out in the same manner as in Prototype Example 1, except that 191.5 g of ion-exchanged water and 0.5 g of sodium hypochlorite were used, resulting in a solution with a sodium hypochlorite concentration of 0.25% and an available chlorine concentration of 0.02%, and that depolymerized cellulose in which the polymerization degree of the cellulose raw material was reduced to 1583 was obtained, thereby obtaining a dispersion of type I unmodified cellulose fine fibers for Prototype Example 9.

[0085] <Prototype Example 10> The same procedure was followed as in Prototype Example 2, except that the cellulose raw material was kraft pulp (C2) and depolymerized cellulose was obtained by reducing the degree of polymerization of the cellulose raw material to 660, to obtain a dispersion of type I unmodified cellulose fine fibers for Prototype Example 10.

[0086] <Prototype Example 11> The cellulose raw material was thermomechanical pulp (C3), and the ion-exchanged water in the depolymerization process was 167.1 g, and the sodium hypochlorite was 28.9 g to give a solution with a sodium hypochlorite concentration of 14.7% and an available chlorine concentration of 1.25%, which was reacted in a water bath at 55°C for 0.5 hours to obtain depolymerized cellulose in which the degree of polymerization of the cellulose raw material was reduced to 199. A dispersion of type I unmodified cellulose fine fibers was obtained in Prototype Example 11 in the same manner as in Prototype Example 1, except that the cellulose raw material was used as the thermomechanical pulp (C3), the ion-exchanged water in the depolymerization process was 167.1 g, and the sodium hypochlorite was 28.9 g to give a solution with a sodium hypochlorite concentration of 14.7% and an available chlorine concentration of 1.25%, and the solution was reacted in a water bath at 55°C for 0.5 hours to obtain depolymerized cellulose in which the degree of polymerization of the cellulose raw material was reduced to 199.

[0087] <Comparative Example 1> A dispersion of I-type unmodified cellulose fine fibers of Comparative Example 1 was obtained in the same manner as in Prototype Example 1, except that the depolymerization step was not carried out.

[0088] The cellulose raw material, conditions for the depolymerization step, and the degree of polymerization of the depolymerized cellulose for each prototype and Comparative Example 1 are shown in Table 1. In addition, for the dispersions of type I unmodified cellulose fine fibers for each prototype and Comparative Example, the degree of polymerization, haze value (%), xylose concentration (%) in the constituent sugars, mannose concentration (%) in the constituent sugars, lignin concentration (%), carboxyl group amount (mmol / g), and average fiber diameter (nm) were measured and are shown in Table 2.

[0089] [Degree of polymerization] The degree of polymerization was measured by the viscosity method using a copper ethylenediamine solution as follows. Dried depolymerized cellulose or cellulose microfibers were dissolved in 0.5M copper ethylenediamine solution 1 to form solution 2. The viscosities of solutions 1 and 2 were measured using a capillary viscometer. The viscosity of solution 2 was set to η and the viscosity of solution 1 to η0, and the intrinsic viscosity [η] of the depolymerized cellulose or cellulose microfibers was calculated using the following formula to determine the degree of polymerization DP. c is the concentration (g / L) of the depolymerized cellulose or cellulose microfibers. Intrinsic viscosity [η]={(η / η0)-1} / c Polymerization degree DP=intrinsic viscosity [η] / (8.8×10-4)

[0090] [Degree of polymerization (SEC method)] The degree of polymerization of thermomechanical pulp (C3), a cellulose raw material, was measured by size exclusion chromatography (SEC) after the delignification treatment described below. The thermomechanical pulp was reacted with sodium chlorite at 80°C under acidic conditions for 2 hours to perform delignification treatment. After that, the dried cellulose raw material and TBAA / DMSO mixed solvent were added to a sample bottle so that the cellulose concentration was 0.1 wt%, and the mixture was mixed at room temperature overnight to dissolve. The prepared sample was analyzed by HPLC (detector: RID (Shimadzu Corporation, RID-10A), column temperature: 50°C, flow rate: 0.6 ml / min) using an organic solvent SEC (GPC) column (Resonac Corporation, column connected to "KD-804" and "KD-805"). A TBAA / DMSO mixed solvent was used as the eluent. The obtained weight average molecular weight (Mw) value was converted to the viscosity degree of polymerization (DPv) using the following formula. log[Mw(SEC)]=0.97×log(DPv×162)+0.7053

[0091] [Available chlorine concentration] The effective chlorine concentration in the depolymerization process of each prototype was calculated from the effective chlorine concentration of the sodium hypochlorite stock solution and the amount added. The effective chlorine concentration of the sodium hypochlorite stock solution was measured by the following method using iodine titration. The sodium hypochlorite stock solution was diluted to an arbitrary concentration, and hydrochloric acid was added to make it weakly acidic, and potassium iodide was added to release iodine. Starch was used as an indicator, and iodine was titrated with sodium thiosulfate solution, which is a reducing agent, and the effective chlorine concentration was calculated from the titration amount.

[0092] [Haze value] The haze value (%) is an index of transparency, and was measured in accordance with JIS K 7136 (2000) using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., "NDH-4000") for the 0.1 mass% dispersion of each prototype and Comparative Example 1. Ion-exchanged water was used to adjust the concentration of the dispersion of each prototype and Comparative Example 1. The dispersion was measured in a glass cell for liquids (manufactured by Fujiwara Seisakusho Co., Ltd., "MG-40") with an optical path of 1 cm. The zero point measurement was performed by putting ion-exchanged water into the same glass cell.

[0093] [Xylose and mannose concentrations in the constituent sugars] The xylose concentration (%) and mannose concentration (%) in the constituent sugars were calculated by the following monosaccharide composition analysis. The cellulose raw material or the cellulose fine fibers of each prototype and Comparative Example 1 were dissolved in 72% by weight sulfuric acid in a water bath at 30°C. Water was added to dilute the sulfuric acid to 4.5% by weight, and the mixture was treated in an oil bath at 120°C for 15 minutes to hydrolyze the sugar components in the cellulose raw material or the cellulose fine fibers to monosaccharides. The xylose concentration (%) and mannose concentration (%) in the hydrolysis solution were measured using a high performance liquid chromatograph (HPLC) (Shimadzu Corporation, "Prominence"). A ligand exchange chromatography column (Shoko Science Co., Ltd., "SUGAR SP0810") was used to separate the sugars.

[0094] [Lignin concentration] The lignin concentration (%) was the sum of the acid-insoluble lignin concentration and the acid-soluble lignin concentration, and was measured by the following method using the hydrolysis solution obtained in the monosaccharide composition analysis of the cellulose raw material or the cellulose fine fibers of each prototype and Comparative Example 1. The acid-insoluble lignin was quantified by filtering the residue in the hydrolysis solution with a glass filter (AGC Technoglass Co., Ltd., "11G4") and drying at 100°C for 3 hours or more. The acid-soluble lignin was quantified by diluting the hydrolysis solution to an arbitrary concentration and measuring the absorbance at 200 nm using a spectrophotometer (Shimadzu Corporation, "UV-2700i"). Note that lignin sulfonic acid (Nippon Paper Industries Co., Ltd., "Sunex P321") diluted to an arbitrary concentration was used as a standard substance, and the absorbance at 200 nm was measured to create a calibration curve.

[0095] [Amount of carboxyl groups] The amount of carboxyl groups (mmol / g) was measured as follows. 300 ml of a 0.5% by weight slurry of cellulose fine fibers was prepared, and a 0.1 M aqueous hydrochloric acid solution was added to adjust the pH to 2.5. A 0.05 N aqueous sodium hydroxide solution was then added dropwise, and the electrical conductivity was measured until the pH reached 11. The amount of carboxyl groups was calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of the weak acid, where the change in electrical conductivity was gradual. The amount of carboxyl groups was measured only for Prototype 3, Prototype 5, Prototype 6, and Prototype 8. Prototypes that were below the lower limit of detection are indicated as "ND" in the table. Amount of carboxyl group (mmol / g) = a (ml) × 0.05 / weight of cellulose fine fiber (g)

[0096] [Average fiber diameter] The average fiber diameter (nm) was calculated by measuring the diameters of 100 or more fibers in a scanning range of 5 μm square using a scanning probe microscope (Shimadzu Corporation, SPM-9700HT). Samples for scanning probe microscope observation were prepared by diluting a dispersion of cellulose fine fibers with water to an arbitrary concentration, casting the dispersion on a mica substrate, and air-drying. The average fiber diameter was measured only for prototypes 4 and 6.

[0097] [Table 1]

[0098] [Table 2]

[0099] [Results and Discussion] Comparing Prototype Examples 1 to 9, which use the same cellulose raw material and undergo a depolymerization step, with Comparative Example 1, it was shown that Prototype Examples 1 to 9, in which the degree of polymerization of the cellulose raw material is reduced by the depolymerization step, have a lower haze value of the dispersion of cellulose fine fibers than Comparative Example 1. A smaller haze value of the dispersion indicates that the fiber diameter of the cellulose fine fibers is smaller, that is, cellulose defibration has progressed, and therefore it was shown that reducing the degree of polymerization of the cellulose raw material before the defibration step contributes to good defibration.

[0100] Next, by comparing the prototypes 1 to 9 in which the sodium hypochlorite concentration used in the depolymerization step was changed, it was found that the haze value of the dispersion of cellulose fine fibers tends to decrease as the sodium hypochlorite concentration, i.e., the effective chlorine concentration, increases. In other words, by performing the depolymerization step by adding sodium hypochlorite so that the effective chlorine concentration is at a certain level or higher, the cellulose defibration proceeds well in the defibration step. Therefore, it was shown that the polymerization degree of depolymerized cellulose is preferably 1200 or less, and the amount of sodium hypochlorite added in the depolymerization step is preferably adjusted so that the effective chlorine concentration is 0.04% or more. By adjusting as described above, the cellulose fine fibers are defibrated to a certain level or higher, and the haze value of the dispersion becomes 50% or less.

[0101] When the effective chlorine concentration is 0.43% or more, the degree of polymerization of depolymerized cellulose changes little compared to the increase in the effective chlorine concentration, and the haze value of the dispersion of cellulose fine fibers is also similar, so it is considered that an effective chlorine concentration of about 0.4% will work well. Considering the wide range of uses of type I cellulose fine fibers and the relationship between the degree of polymerization of depolymerized cellulose and the haze value of the dispersion of cellulose fine fibers, it is considered that an effective chlorine concentration of 0.2 to 2.0% is advantageous economically and efficiently.

[0102] The average fiber diameters of Sample 4, with a haze value of 9.9% and Sample 6, with a haze value of 1.6%, were 1.68 nm and 2.66 nm, respectively, demonstrating that the manufacturing method of the present invention can efficiently obtain single nano-sized type I cellulose fine fibers by mechanical defibration. Since single nano-sized cellulose fine fibers are obtained when the haze of the dispersion of cellulose fine fibers is about 10%, it was understood that type I cellulose fine fibers defibrated to a single nano level or a level close to that can be obtained if the haze value is 30% or less. Therefore, it was demonstrated that cellulose fine fibers of the desired size can be effectively obtained by carrying out the depolymerization step under conditions where the haze value of the dispersion is 30% or less for applications where single nano-level type I cellulose fine fibers are desired, and where the haze value is 50% or less for applications where fineness at the single nano level is not required.

[0103] Comparing Prototype 10, which uses a cellulose raw material containing a large amount of xylose as a constituent sugar, with Prototype 2, which uses the same production conditions, there was little difference in the degree of polymerization of the depolymerized cellulose, and the haze value of the dispersion of cellulose fine fibers was smaller in Prototype 10, which contains more hemicellulose. This shows that the production method of the present invention does not require any prior treatment to increase the purity of the cellulose component of the cellulose raw material, and makes it possible to select raw materials according to the application.

[0104] It was also found that the concentration of xylose contained as a constituent sugar in the raw cellulose did not change much even after the defibration process from the raw cellulose. Since the concentration of xylose in the constituent sugars decreases when the available chlorine concentration is increased in the depolymerization process, it was shown that in applications where a lower concentration of xylose in the constituent sugars is preferred, it is possible to control the concentration by adjusting the amount of sodium hypochlorite added in the depolymerization process without changing the cellulose raw material.

[0105] The same was true for cellulose raw materials containing mannose as a constituent sugar, and the haze value of the dispersion could be reduced regardless of the amount of mannose. This shows that the production method of the present invention does not require any treatment to increase the purity of the cellulose component of the cellulose raw material in advance, and makes it possible to select a raw material according to the application.

[0106] Even in Prototype Example 11, which used a cellulose raw material containing a large amount of lignin, the haze value of the dispersion was able to be set to 4.5%, which is considered to have enabled the production of single-nano size type I cellulose fine fibers compared to Prototype Examples 4 and 6. This shows that the production method of the present invention does not require any prior treatment to increase the purity of the cellulose component of the cellulose raw material, and makes it possible to select a raw material according to the application, which can contribute to the effective use of pulp resources.

[0107] Since the polymerization degree of the cellulose fine fibers of Prototype Examples 1 to 8 and 10 after the defibration step was reduced to 800 or less, respectively, the viscosity of the dispersion was reduced, improving moldability during the production of molded products and improving the appearance of the molded products. In other words, by going through the depolymerization step, cellulose fine fibers having a small fiber diameter can be obtained by mechanical defibration alone, and the handling of the dispersion becomes easy, making it possible to provide cellulose fine fibers that are easy to use.

[0108] It was also confirmed that the type I unmodified cellulose fine fibers of the present invention have a small amount of carboxyl groups and are not modified, which indicates that the type I unmodified cellulose fine fibers of the present invention do not redissolve in water and can be used for water-resistant molded articles and can be used in a wide range of applications. [Industrial Applicability]

[0109] According to the production method of the present invention, the obtained cellulose fine fibers are type I, have high strength, and are highly safe because they are not chemically modified, and are therefore useful not only as a reinforcing material for resins, but also as an alternative to petroleum-derived resins. Furthermore, the obtained type I unmodified cellulose fine fibers have high transparency and low viscosity, making them easy to handle and excellent in appearance properties, and therefore can be used in a variety of applications. The production method of the present invention, which can efficiently produce such type I unmodified cellulose fine fibers through a simple and safe process, is a significant production method that can also reduce the environmental load. [Explanation of symbols]

[0110] S1 Depolymerization process S2 Defibration process

Claims

1. a depolymerization step of adding sodium hypochlorite having an effective chlorine concentration of 0.04 to 3.0% to a cellulose raw material to reduce the degree of polymerization of the cellulose raw material to 1200 or less to obtain depolymerized cellulose; and a defibration step of defibrating the depolymerized cellulose by mechanical defibration. A method for producing I-type unmodified cellulose fine fibers, comprising the steps of:

2. The method for producing type I unmodified cellulose fine fibers according to claim 1, wherein the mechanical defibration in the defibration step is a shear treatment under high pressure conditions.

3. The method for producing I-type unmodified cellulose fine fibers according to claim 1 or 2, wherein the depolymerization step is carried out in a temperature range of 40 to 70°C.

4. The method for producing type I unmodified cellulose fine fibers according to claim 1 or 2, wherein the sodium hypochlorite has an available chlorine concentration of 0.2 to 2.0%.

5. The method for producing type I unmodified cellulose fine fibers according to claim 3, wherein the sodium hypochlorite has an available chlorine concentration of 0.2 to 2.0%.

6. 3. The method for producing type I unmodified cellulose fine fibers according to claim 1 or 2, wherein the cellulose raw material is pulp mainly composed of cellulose, and contains xylose in an amount of 25% by weight or less among its constituent sugars.

7. The method for producing type I unmodified cellulose fine fibers according to claim 3, wherein the cellulose raw material is pulp containing cellulose as a main component, and contains xylose in an amount of 25% by weight or less among its constituent sugars.

8. The method for producing type I unmodified cellulose fine fibers according to claim 4, wherein the cellulose raw material is pulp containing cellulose as a main component, and contains xylose in an amount of 25% by weight or less among its constituent sugars.

9. The method for producing type I unmodified cellulose fine fibers according to claim 5, wherein the cellulose raw material is pulp containing cellulose as a main component, and contains xylose in an amount of 25% by weight or less among its constituent sugars.

10. The method for producing type I unmodified cellulose fine fibers according to claim 1 or 2, wherein the cellulose raw material is a pulp mainly composed of cellulose, and contains mannose in an amount of 10% by weight or less among its constituent sugars.

11. The method for producing I-type unmodified cellulose fine fibers according to claim 1 or 2, wherein the cellulose raw material is a pulp mainly composed of cellulose and contains 30% by weight or less of lignin.

12. A method for producing an I-type unmodified cellulose fine fiber molded article, comprising a molding step of molding the I-type unmodified cellulose fine fibers obtained by the method for producing I-type unmodified cellulose fine fibers according to claim 1.

13. 2. Type I unmodified cellulose fine fibers obtained by the method for producing type I unmodified cellulose fine fibers according to claim 1, wherein the haze value of a 0.1% by weight dispersion of type I unmodified cellulose fine fibers measured in accordance with JIS K 7136 (2000) is 50% or less.

14. 2. Type I unmodified cellulose fine fibers obtained by the method for producing type I unmodified cellulose fine fibers according to claim 1, wherein the haze value of a 0.1% by weight dispersion of type I unmodified cellulose fine fibers measured in accordance with JIS K 7136 (2000) is 30% or less.

15. The type I unmodified cellulose fine fibers according to claim 13, which contain xylose in an amount of 20% by weight or less among the constituent sugars of the type I unmodified cellulose fine fibers.

16. The type I unmodified cellulose fine fibers according to claim 13, which contain mannose in an amount of 5% by weight or less among the constituent sugars of the type I unmodified cellulose fine fibers.

17. 14. The type I unmodified cellulose fine fibers according to claim 13, wherein the type I unmodified cellulose fine fibers contain 15% by weight or less of lignin.

18. The I-type unmodified cellulose fine fibers according to claim 13, wherein the degree of polymerization of the I-type unmodified cellulose fine fibers is 800 or less.

19. 19. The type I unmodified cellulose fine fibers according to any one of claims 15 to 18, wherein the amount of carboxyl groups in the type I unmodified cellulose fine fibers is less than 0.20 mmol / g.

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