Unmodified cellulose microfibrils of type ii, and method for producing unmodified cellulose microfibrils of type ii and shaped bodies thereof

Abstract

Provided is a method for producing type II unmodified cellulose microfibers, which is a method for producing cellulose microfibers by mercerizing cellulose, and which can efficiently produce unmodified cellulose microfibers by a simple process. The method for producing type II unmodified cellulose microfibers is characterized by having the following steps: a defibrillation step in which defibrillation is performed by adding an alkali metal hydroxide to raw material cellulose subjected to a mercerization step of mercerizing cellulose to obtain mercerized cellulose and a depolymerization step of reducing the degree of polymerization of the mercerized cellulose to 760 or less, such that the total concentration is 2.5 to 17.5%, thereby obtaining cellulose microfibers; and a neutralization step in which the cellulose microfibers are neutralized with an acid.

Description

Technical Field

[0001] This invention relates to methods for manufacturing cellulose microfibers, and particularly to methods for manufacturing type II unmodified cellulose microfibers that yield unmodified cellulose microfibers. Background Technology

[0002] In recent years, in order to achieve sustainable development, known as the Sustainable Development Goals (SDGs), international goals set by the United Nations have been proposed. Among these environmental goals are reducing plastic consumption. Efforts are being made to address climate change by reducing the use of petroleum-derived plastics and by reducing GHG consumption.

[0003] For example, microplastics (beads) are sometimes used in cosmetics such as foundation to improve their mixability with other ingredients, spreadability, or texture during application. However, microplastics (beads) are particularly problematic as one of the main causes of severe marine pollution, and efforts are underway to reduce their production or recycle them.

[0004] Therefore, a market is exploring the substitution of microplastics (beads). However, it is well known that there has been little progress in the adoption of alternative materials made from fine resin raw materials, particularly microplastics (beads) with a particle size of less than 100 μm, despite increasing demand and limited supply.

[0005] In addition, biodegradable cellulose from natural materials has attracted attention as an alternative raw material for microplastics. In particular, cellulose nanofibers or cellulose microfibers, which can be processed into molded bodies, such as beads or films, are expected to serve as an alternative raw material for microplastics.

[0006] Methods for manufacturing cellulose microfibers include: oxidizing cellulose in water using a catalyst and then defibrating the resulting oxidized cellulose to obtain a cellulose nanofiber dispersion (see Patent Document 1); or performing carboxymethylation of cellulose in a mixed solvent of water and organic solvent and then defibrating the resulting carboxymethylated cellulose to obtain a highly transparent carboxymethylated cellulose nanofiber dispersion (see Patent Document 2); and desalting anion-modified cellulose nanofiber salts by performing a cation exchange reaction using a cation exchange resin to obtain anion-modified cellulose nanofibers (see Patent Document 3), etc.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2008-001728,

[0010] Patent Document 2: Japanese Patent Application Publication No. 2019-99758,

[0011] Patent document 3: International Publication No. 2019 / 059079. Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] The cellulose microfibers obtained through these manufacturing methods are type I cellulose microfibers. To obtain cellulose fibers with small diameters, chemical defibrillation and mechanical (physical) defibrillation are used, resulting in chemically modified cellulose. However, because chemical defibrillation is used, the following problems exist: not only is a chemical removal process necessary, complicating the process, but it also prevents its use in cosmetics, or restricts its applications, raising concerns about the safety of the chemicals used or the environmental impact.

[0014] The inventors repeatedly researched and improved a manufacturing method for obtaining cellulose microfibers with small fiber diameters that does not use chemical defibrillation. As a result, a simpler and more efficient method for obtaining unmodified cellulose microfibers was achieved.

[0015] The present invention was made in view of the above-mentioned problems, and provides type II unmodified cellulose microfibers, and a method for manufacturing type II unmodified cellulose microfibers and their molded forms. The type II unmodified cellulose microfibers are cellulose microfibers with a type II crystalline structure obtained by mercerizing cellulose. The manufacturing method is a method for manufacturing cellulose microfibers and their molded forms. It can effectively obtain unmodified cellulose microfibers with high transparency and safety through a simple process.

[0016] Methods for solving problems

[0017] That is, the first invention relates to a method for manufacturing type II unmodified cellulose microfibers, characterized by comprising the following steps: a defibrillation step, wherein an alkali metal hydroxide is added to the raw material cellulose, which has undergone a mercerizing step to obtain mercerized cellulose and a depolymerization step to reduce the degree of polymerization of the mercerized cellulose to 760 or less, such that the total concentration is 2.5 to 17.5%, thereby obtaining cellulose microfibers; and a neutralization step, wherein the cellulose microfibers are neutralized with an acid.

[0018] The second invention relates to a method for manufacturing type II unmodified cellulose microfiber molded articles, which includes the following molding step, wherein type II unmodified cellulose microfiber obtained by the manufacturing method of type II unmodified cellulose microfiber of the first invention is molded to obtain type II unmodified cellulose microfiber molded articles.

[0019] The third invention relates to type II unmodified cellulose microfibers, wherein a 0.1% by mass dispersion of type II unmodified cellulose microfibers obtained by the manufacturing method of type II unmodified cellulose microfibers of the first invention has a haze value of 35% or less as determined according to JISK 7136 (2000).

[0020] The fourth invention relates to type II unmodified cellulose microfibers with a degree of polymerization of 310 or less, as described in the third invention.

[0021] Invention Effects

[0022] According to the method for manufacturing type II unmodified cellulose microfibers of the first invention, since it has the following defiberization and neutralization steps, unmodified cellulose microfibers can be obtained effectively through a simple process. In the defiberization step, alkali metal hydroxides are added to the raw cellulose in the mercerization step (which mercerizes the cellulose to obtain mercerized cellulose) and the depolymerization step (which reduces the degree of polymerization of the mercerized cellulose to below 760) to obtain cellulose microfibers. The total concentration is 2.5 to 17.5%. In the neutralization step, the cellulose microfibers are neutralized with acid.

[0023] The method for manufacturing type II unmodified cellulose microfiber molded articles according to the second invention has a molding step of molding type II unmodified cellulose microfibers obtained by the manufacturing method of type II unmodified cellulose microfibers of the first invention to obtain type II unmodified cellulose microfiber molded articles, and is therefore useful as an alternative to plastic molded articles.

[0024] According to the third invention, the type II unmodified cellulose microfibers have high transparency, excellent appearance characteristics, and high safety, as the haze value of a 0.1% by mass dispersion of type II unmodified cellulose microfibers obtained by the manufacturing method of type II unmodified cellulose microfibers of the first invention is less than 35% as measured according to JIS K 7136 (2000). Therefore, they can be used for a wide range of applications such as cosmetics.

[0025] According to the fourth invention, since the degree of polymerization of the type II unmodified cellulose microfibers described in the third invention is 310 or less, the viscosity of the dispersion of the cellulose microfibers can be reduced, degassing is easier, the appearance during molding is good, or the pressure rise of the molding device can be suppressed, thereby improving production efficiency. Attached Figure Description

[0026] [ Figure 1[This is a schematic diagram of the process involved in the manufacturing method of the Type II unmodified cellulose microfibers of the present invention.] Detailed Implementation

[0027] The cellulose microfibers manufactured by the method of the present invention are type II cellulose microfibers with a type II crystal structure because they are produced through a mercerizing process that mercerizes cellulose. Cellulose microfibers are commonly used as reinforcing materials for resins, and type I cellulose microfibers with a type I crystal structure, which have high strength, are preferred in such cases. Among cellulose microfibers, type II cellulose microfibers are preferred because they are softer than type I cellulose microfibers, resulting in a better texture when added to cosmetics.

[0028] Since the manufacturing method of the present invention targets cellulose microfibers as a substitute for petroleum-derived plastics in fields such as cosmetics, it can be said that it does not require the strength properties of type I cellulose fibers used in applications where they are contained as reinforcing materials in resins. Furthermore, considering the wide range of applications such as cosmetics where aesthetic design or good appearance characteristics are required, the dispersion of cellulose microfibers manufactured by the method of the present invention exhibits excellent transparency and is not chemically modified, thus ensuring high safety. In addition, it also has good processability and excellent moldability.

[0029] Therefore, using Figure 1 The process diagram below will sequentially describe the method for manufacturing the Type II unmodified cellulose microfibers of the present invention. First, pulp is preferably used as the starting material. Pulp is primarily obtained by crushing wood and removing impurities such as lignin to improve the purity of the cellulose component. Alternatively, cotton pulp obtained by removing impurities from cotton to improve the purity of the cellulose component can also be used. Furthermore, since pulp is fibrous, it has high reactivity with pharmaceuticals, making it a preferred cellulose raw material. Besides pulp, animal-derived cellulose such as bacterial cellulose produced by microorganisms can also be used. Additionally, purified cellulose obtained by purifying these raw materials can be used.

[0030] The mercerizing process (S1) is a process that mercerizes cellulose to obtain mercerized cellulose. In the mercerizing process, cellulose as raw material is added to an alkali metal hydroxide such as sodium hydroxide (NaOH), and the mixture is heated and stirred as needed to cause the cellulose fibers to swell. When the cellulose fibers are immersed in the alkali metal hydroxide, they become negatively charged and generate Coulomb forces, causing the fibers to repel each other and easily defibril. As described above, since mercerized cellulose is easily defibriled, the energy required in the subsequent defibrilation process can be reduced.

[0031] Alkali metal hydroxides used in the mercerizing process include caustic soda (NaOH), lithium hydroxide, and potassium hydroxide. From the perspectives of cost, safety, and environmental impact, caustic soda is preferred.

[0032] After the mercerizing process (S1), any remaining alkali metal hydroxides are removed as needed. The solids concentration is then adjusted appropriately, followed by a depolymerization process (S2). The depolymerization process (S2) reduces the degree of polymerization of the mercerized cellulose obtained through the mercerizing process (S1) to below 760. The mercerized cellulose with adjusted solids is appropriately pulverized and aged by oxidation and decomposition with oxygen in the air, thus reducing the degree of polymerization. At this point, the degree of polymerization is below 760. Maintaining a degree of polymerization of 760 or below ensures the transparency of the resulting cellulose microfiber dispersion. Furthermore, the lower the degree of polymerization of the mercerized cellulose, the easier it is to depolymerize the cellulose fibers in the subsequent defibrillation process.

[0033] The aging of mercerized cellulose in the depolymerization process (S2) is carried out at room temperature or under heating conditions. To accelerate the depolymerization rate, heating conditions that prevent the raw material from drying out are preferred. Alternatively, an aging accelerator such as manganese(II) sulfate can be added to promote the aging reaction.

[0034] By undergoing a mercerizing process (S1) and a depolymerization process (S2), raw cellulose capable of being decelluloseed into microfibers is obtained. Through mercerizing, the raw cellulose becomes type II cellulose with a type II crystal structure. Although the strength of type II cellulose is inferior to that of type I cellulose, the cellulose microfibers obtained by this invention are intended for use as a plastic substitute in fields such as cosmetics, and therefore do not require the same strength as type I cellulose; thus, the reduction in strength is not a problem.

[0035] Then, in the defibrillation process (S3), an alkali metal hydroxide or solvent (ion-exchanged water) is added to the raw cellulose to adjust the total concentration to 2.5–17.5%, and defibrillation is performed. The alkali metal hydroxide used here, as mentioned above, can include caustic soda, lithium hydroxide, potassium hydroxide, etc. From a cost or safety perspective, caustic soda is preferred. The defibrillation of the raw cellulose is carried out mechanically (physically). Mechanical (physical) defibrillation is performed using a homogenizer or water sprayer, etc., using known methods. Here, since the raw cellulose is in a state where the fibers are swollen due to mercerization and easily defibrilable, and the degree of polymerization is reduced through the depolymerization process, it is easy to defibril even without applying high pressure, which is also significant from an equipment perspective.

[0036] If the concentration of alkali metal hydroxide is lower than 2.5%, the cellulose will not swell sufficiently, making defibrillation difficult. Conversely, if the concentration of alkali metal hydroxide is higher than 17.5%, the salt concentration increases, causing the cellulose fibers to aggregate easily, thus making defibrillation difficult. When the alkali metal hydroxide concentration deviates from this range and defibrillation is insufficient, the transparency of the resulting cellulose microfiber dispersion decreases, tending to have poor appearance.

[0037] Defibrillation can also be performed in multiple stages. For example, after pre-defibrillation using a mixer, main defibrillation can be performed using a homogenizer, thereby producing uniform cellulose microfibers with small fiber diameters. Furthermore, pre-defibrillation avoids problems such as clogging of the defibrillation device by the raw cellulose. Pre-defibrillation can be performed using a mixer or homogenizer, employing known methods. Defibrillation of cellulose microfibers only requires reducing the average fiber diameter to the nanometer to several hundred nanometer size; if the microfibers are produced to approximately 2–800 nm, more preferably below 100 nm, the dispersion of cellulose microfibers will exhibit better transparency.

[0038] The cellulose microfibers obtained after the defiberization process are neutralized by acid in the neutralization process (S4). Since the cellulose microfibers obtained after the defiberization process are strongly alkaline, neutralization is necessary. Examples of acids used include sulfuric acid, hydrochloric acid, and lactic acid. The neutralized cellulose microfibers are then properly washed and defiberized again to obtain type II unmodified cellulose microfibers.

[0039] By using the dispersion of type II unmodified cellulose microfibers obtained through these processes, molded articles can be produced. For example, they can be filmed by forming a coating or made into beads, which can then be used in cosmetics, etc. All of these can be produced using a drying molding process, which can reduce the amount of environmentally burdensome pharmaceuticals used compared to conventional cellulose films or cellulose beads.

[0040] The 0.1% by mass dispersion of type II unmodified cellulose microfibers obtained by the manufacturing method of the present invention has good transparency. Specifically, if the haze value is less than 35% as determined according to JIS K7136 (2000), the film has a good appearance and can be used in cosmetics, and can be used for a wide range of applications.

[0041] Furthermore, by ensuring that the degree of polymerization of the type II unmodified cellulose microfibers obtained by the manufacturing method of the present invention is 310 or less, the viscosity as a dispersion can be reduced, degassing is easier, moldability is improved, and the appearance of the molded product is good. In addition, if the viscosity of the dispersion is reduced, the pressure rise of the molding device can be suppressed, and production efficiency can also be improved.

[0042] Example

[0043] The inventors used the following raw materials, etc., when manufacturing type II unmodified cellulose microfibers, according to... Figure 1 The process diagram was used to conduct manufacturing experiments on type II unmodified cellulose microfibers by changing the degree of polymerization in the depolymerization process and the concentration of alkali metal hydroxide in the defibrillation process.

[0044] [raw material]

[0045] The cellulose raw material used as the starting material is dissolving pulp (LNDP manufactured by Nippon Paper Corporation).

[0046] [Alkali metal hydroxides]

[0047] The mercerizing process uses caustic soda (manufactured by Kishida Chemical Co., Ltd.) as the alkali metal hydroxide. It should be noted that the same caustic soda is used in the desiccation process.

[0048] [acid]

[0049] The acid used in the neutralization process is sulfuric acid (manufactured by Kishida Chemical Co., Ltd.).

[0050] [Preparation of a dispersion of type II unmodified cellulose microfibers]

[0051] Using the above-mentioned raw materials, a dispersion of type II unmodified cellulose microfibers was prepared by the following blending process.

[0052] <Trial Production Example 1>

[0053] 18% by weight of caustic soda was heated to 50°C and added to the pulp to a concentration of 2% by weight. The mixture was stirred until it reached a pulp consistency and then mercerized (mercerization process). The remaining caustic soda was then removed, and the solid content was adjusted to 33% by weight. The pulp was aged at 50°C to achieve a degree of polymerization of 752 for the mercerized cellulose, yielding raw material cellulose 1 (depolymerization process). Then, 10.6g of raw material cellulose 1, 330.65g of deionized water, and 8.75g of caustic soda (total caustic soda concentration 2.5%) were added to a 500mL container and pre-decellulosed using a mixer (manufactured by PRIMIX Co., Ltd., "LABO LUTION"). Then, primary decellulosed using a homogenizer (manufactured by SMT Co., Ltd., "LAB1000") (decelluloseing process). 125g of the prepared pulp was collected and neutralized by adding 20% ​​by weight of sulfuric acid while stirring (neutralization process). The neutralized sample was filtered and washed with 300 mL of ion-exchange water. The washed sample was then added to ion-exchange water to a total weight of 250 g and pre-defibriled using a stirrer (PRIMIX Co., Ltd., "LABO LUTION"). Then, primary defibrilation was performed using a homogenizer (SMT Co., Ltd., "LAB1000") to obtain a dispersion of type II unmodified cellulose microfibers as described in Experimental Example 1.

[0054] <Trial Production Example 2>

[0055] Except that the total concentration of caustic soda in the defibrillation process was 9.5%, the dispersion of type II unmodified cellulose microfibers of Experimental Example 2 was obtained in the same manner as Experimental Example 1.

[0056] <Trial Production Example 3>

[0057] Except that the total concentration of caustic soda in the defibrillation process was 17.5%, the dispersion of type II unmodified cellulose microfibers of Experimental Example 3 was obtained in the same manner as Experimental Example 1.

[0058] <Prototype Example 4>

[0059] Except for setting the total concentration of caustic soda in the defibrillation process to 1.5%, the same as in Experimental Example 1, the cellulose was not defibrillated and a dispersion of type II unmodified cellulose microfibers could not be obtained.

[0060] <Trial Production Example 5>

[0061] Except that the total concentration of caustic soda in the defibrillation process was 18.5%, the dispersion of type II unmodified cellulose microfibers of Experimental Example 5 was obtained in the same manner as Experimental Example 1.

[0062] <Trial Production Example 6>

[0063] Except for obtaining raw cellulose by having the degree of polymerization of mercerized cellulose to 299 in the aging process to the depolymerization process, a dispersion of type II unmodified cellulose microfibers of Experimental Example 6 was obtained in the same manner as Experimental Example 1.

[0064] <Trial Production Example 7>

[0065] Except for obtaining raw cellulose by having the degree of polymerization of the mercerized cellulose in the aging process to the depolymerization process reach 299, the dispersion of type II unmodified cellulose microfibers of Experimental Example 7 was obtained in the same manner as Experimental Example 2.

[0066] <Trial Production Example 8>

[0067] Except for obtaining raw cellulose by having the degree of polymerization of the mercerized cellulose in the aging process to the depolymerization process reach 299, the dispersion of type II unmodified cellulose microfibers of Experimental Example 8 was obtained in the same manner as Experimental Example 3.

[0068] <Comparative Example 1>

[0069] Except for omitting the depolymerization process, the result was the same as in Experimental Example 1: the cellulose was not defibrilated and a dispersion of type II unmodified cellulose microfibers could not be obtained.

[0070] <Comparative Example 2>

[0071] Except for omitting the depolymerization process, the dispersion of type II unmodified cellulose microfibers of Comparative Example 2 was obtained in the same manner as in Test Example 3.

[0072] <Comparative Example 3>

[0073] Except for omitting the mercerizing and depolymerization processes, the process was the same as in Prototype 1. As a result, the cellulose was not defibrilated, and a dispersion of type II unmodified cellulose microfibers could not be obtained.

[0074] For the dispersions of unmodified cellulose microfibers of type II in each trial example and comparative example, the haze (%) and degree of polymerization were measured. The degree of polymerization of each raw cellulose in each trial example and comparative example, as well as the type and concentration (%) of alkali metal hydroxides in the defibrillation process, are shown in Table 1.

[0075] [Haze]

[0076] Haze (%) is an indicator of transparency. According to JIS K 7136 (2000), the 0.1% by mass dispersion of each test example was measured using a haze meter (manufactured by Nippon Denshoku Kogyo Co., Ltd., NDH-4000). It should be noted that the concentration of the dispersion in each test example was adjusted using ion-exchanged water. The dispersion was measured in a liquid glass cell (manufactured by Fujiwara Corporation, MG-40) with a 1 cm optical path. Zero-point measurement was performed in this glass cell filled with ion-exchanged water. It should be noted that test examples and comparative examples where cellulose microfibers could not be obtained due to the inability to decellulose were marked as "-" because measurement could not be performed.

[0077] [Degree of Aggregation]

[0078] The degree of polymerization was determined using the viscosity method with copper ethylenediamine solution as follows: Dry 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 as η, and the viscosity of solution 1 as η0. The intrinsic viscosity [η] of the cellulose microfibers was calculated using the following formula, and the degree of polymerization DP was then determined. c is the concentration of cellulose microfibers (g / L).

[0079] Intrinsic viscosity [η] = {(η / η0) - 1} / c

[0080] Degree of polymerization DP = Intrinsic viscosity [η] / (8.8 × 10⁻⁶) -4 )

[0081] It should be noted that for the test examples and comparative examples where cellulose microfibers could not be obtained due to the inability to decellulose, the degree of polymerization of the cellulose microfiber dispersion could not be determined, so they are marked as "-".

[0082] Average fiber diameter

[0083] The average fiber diameter was measured using a scanning probe microscope (Shimadzu Corporation, SPM-9700HT) within a 10 μm square area, measuring the diameter of at least 50 fibers and calculating the average value. The sample for scanning probe microscope observation was prepared by diluting a dispersion of cellulose microfibers with water to an arbitrary concentration, casting it onto a mica substrate, and then air-drying it. It should be noted that the average fiber diameter was only measured in prototype example 7.

[0084] [Table 1]

[0085]

[0086] [Results and Investigation]

[0087] Comparing Test Examples 1, 6, and Comparative Example 1 with the same concentration of alkali metal hydroxide, and Test Examples 3, 8, and Comparative Example 2, it is shown that the lower the degree of polymerization of the raw cellulose, the lower the haze of the cellulose microfiber dispersion. This indicates that by obtaining raw cellulose with a further reduced degree of polymerization of mercerized cellulose in the depolymerization process, cellulose microfibers can be dispersed more finely and uniformly with the same defibrillation energy. As in Comparative Example 1, when raw cellulose with a degree of polymerization of 760 or higher is produced without a depolymerization process, if the concentration of alkali metal hydroxide in the defibrillation process is low, cellulose defibrillation cannot be performed. Or, as in Comparative Example 2, even when defibrillation can be performed by increasing the concentration of alkali metal hydroxide, the dispersion has a high haze.

[0088] Comparing Experimental Examples 1-5, which use cellulose with the same degree of polymerization, it is shown that the haze of the cellulose microfiber dispersion increases when the concentration of alkali metal hydroxide is too low or too high. Specifically, as in Experimental Example 4, if the concentration of alkali metal hydroxide is below 2.5%, the cellulose fibers do not swell sufficiently and cannot be defibriled, thus failing to obtain cellulose microfibers. Furthermore, as in Experimental Example 5, it is observed that if the concentration of alkali metal hydroxide is higher than 17.5%, the salt concentration increases, cellulose fibers aggregate, defibrilation is insufficient, and the haze of the dispersion increases. That is, it is shown that by maintaining the total concentration of alkali metal hydroxide in the defibrilation process at 2.5-17.5%, a dispersion with low haze can be obtained; in particular, it is known that if the total concentration is around 10%, a dispersion with even higher transparency can be obtained.

[0089] In addition, in Comparative Example 3, which did not undergo mercerization, the raw cellulose had a high degree of polymerization due to its type I crystalline structure and the omission of the depolymerization process, making it impossible to depolymerize and obtain cellulose microfibers.

[0090] As described above, the manufacturing method according to the present invention shows that since a dispersion of cellulose microfibers with low haze and high transparency can be obtained even with small defibrillation energy, unmodified type II cellulose microfibers can be efficiently manufactured through a simple process.

[0091] Industrial availability

[0092] According to the method for manufacturing type II unmodified cellulose microfibers of the present invention, unmodified cellulose microfibers can be obtained efficiently through a simple process. Furthermore, since the obtained type II unmodified cellulose microfibers have high transparency and low viscosity, they are easy to handle and have excellent appearance properties, making them suitable for a wide range of applications such as cosmetics, and useful as a substitute for plastics.

[0093] Symbol Explanation

[0094] S1 mercerizing process

[0095] S2 depolymerization process,

[0096] S3 fiber unwinding process.

[0097] S4 neutralization process.

Claims

1. A method for producing type II unmodified cellulose microfibrils, characterized by, having the following steps: a defibrillation step in which the raw cellulose subjected to the mercerization step and the depolymerization step described below is defibrillated by adding an alkali metal hydroxide so that the total concentration of the alkali metal hydroxide is 2.5 to 17.5% to obtain cellulose microfibers, the mercerization step is a step of mercerizing cellulose to obtain mercerized cellulose, the depolymerization step is a step of reducing the degree of polymerization of the mercerized cellulose to 760 or less; and a neutralization step in which the cellulose microfibers are neutralized with an acid.

2. A method for producing a type II unmodified cellulose microfibril molded article, having a molding step in which, II-unmodified cellulose microfibers obtained by the method for producing II-unmodified cellulose microfibers according to claim 1 are molded to obtain II-unmodified cellulose microfiber molded articles.

3. The unmodified cellulose microfibers of type II obtained by the production method of the unmodified cellulose microfibers of type II according to claim 1, wherein, The haze value of a 0.1 mass% dispersion of the II-unmodified cellulose microfibers is 35% or less as measured in accordance with JIS K7136 (2000).

4. The Type II unmodified cellulose microfibril of claim 3, wherein, The degree of polymerization of the II-unmodified cellulose microfibers is 310 or less.

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