Type II unmodified cellulose fine fibers, type II unmodified cellulose fine fiber molded article, type II unmodified cellulose fine fibers, and method for producing the molded article

Abstract

Provided are cellulose fine fibers having a type II crystal structure obtained through cellulose mercerization, and a method for producing the cellulose fine fibers and a molded article thereof, which are chemically unmodified cellulose fine fibers that are highly transparent and safe and can be efficiently obtained through a simple process, and a method for producing the type II unmodified cellulose fine fibers and a molded article thereof. [Solution] Type II unmodified cellulose fine fibers are obtained by a mercerization step in which cellulose is mercerized to obtain mercerized cellulose, a depolymerization step in which the degree of polymerization of the mercerized cellulose is reduced to 760 or less, a defibration step in which an alkali metal hydroxide is added to the raw cellulose to defibrate it to obtain cellulose fine fibers, and a neutralization step in which the cellulose fine fibers are neutralized with an acid.

Description

[Technical Field]

[0001] The present invention relates to cellulose fine fibers, and more particularly to type II unmodified cellulose fine fibers that have not been chemically modified, type II unmodified cellulose fine fiber molded articles, and methods for producing the same. [Background technology]

[0002] In recent years, the United Nations has set international goals for sustainable development known as the 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-derived plastics and thereby reducing GHG emissions.

[0003] For example, microplastics (beads) are sometimes used in cosmetics such as foundation to improve their mixability with other ingredients and their spreadability and feel during use. However, microplastics (beads) have been raised as a problem, particularly as one of the causes of worsening marine environmental pollution, and efforts are being made to reduce their generation and to collect them.

[0004] As a result, microplastics (beads) are increasingly being used as alternatives in the market. However, the use of alternative materials has not progressed particularly for fine resin raw materials such as microplastics (beads) with particle diameters of 100 μm or less, and it is known that supply is low despite growing demand.

[0005] Furthermore, cellulose, a natural material with biodegradability, is attracting attention as an alternative raw material to microplastics. In particular, cellulose fine fibers such as cellulose nanofibers and cellulose microfibers can be processed into molded articles, such as beads and films, and are therefore expected to be an alternative raw material to microplastics.

[0006] Examples of methods for producing cellulose fine fibers include a method in which cellulose is oxidized in water using a catalyst and the resulting oxidized cellulose is defibrated to obtain a cellulose nanofiber dispersion (see Patent Document 1), a method in which carboxymethylation of cellulose is carried out in a mixed solvent of water and an organic solvent and the resulting carboxymethylated cellulose is defibrated to obtain a highly transparent carboxymethylated cellulose nanofiber dispersion (see Patent Document 2), and a production method in which anion-modified cellulose nanofiber salt is desalted by a cation exchange reaction using a cation exchange resin to obtain anion-modified cellulose nanofibers (see Patent Document 3). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-001728 [Patent Document 2] Japanese Patent Application Publication No. 2019-99758 [Patent Document 3] International Publication No. 2019 / 059079 Summary of the Invention [Problem to be solved by the invention]

[0008] The cellulose fine fibers obtained by these manufacturing methods are type I cellulose fine fibers with small fiber diameters, and are chemically modified cellulose that has undergone chemical defibration and mechanical (physical) defibration. In other words, because the defibration is carried out using chemicals, not only does it require a chemical removal step, making the process complicated, but it also has issues such as limited uses, such as being unable to be used in cosmetics, and there are concerns about the safety and environmental impact of the chemicals used.

[0009] The inventors have repeatedly investigated and improved production methods for obtaining cellulose fine fibers with small fiber diameters that do not use chemical defibration, and as a result have arrived at a production method that can more simply and efficiently obtain chemically unmodified cellulose fine fibers.

[0010] The present invention has been made in consideration of the above points, and provides cellulose fine fibers having a type II crystal structure obtained through mercerization of cellulose, and a method for producing the cellulose fine fibers and molded articles thereof, which are chemically unmodified cellulose fine fibers that are highly transparent and safe and can be efficiently obtained through a simple process, as well as a method for producing the type II unmodified cellulose fine fibers and molded articles thereof. [Means for solving the problem]

[0011] That is, the first invention comprises a mercerization step of mercerizing cellulose to obtain mercerized cellulose, and a polymerization degree of the mercerized cellulose. 299 The present invention relates to type II unmodified cellulose fine fibers, which are obtained by a defibration step in which starting cellulose is subjected to a depolymerization step in which the cellulose content is reduced to the following value, followed by a neutralization step in which the cellulose fine fibers are obtained by adding an alkali metal hydroxide to the starting cellulose to defibrate the starting cellulose, and then a neutralization step in which the cellulose fine fibers are neutralized with an acid.

[0012] The second invention relates to type II unmodified cellulose fine fibers of the first invention, which have a haze value of 35% or less when measured in accordance with JIS K 7136 (2000) of a 0.1 wt % dispersion of the type II unmodified cellulose fine fibers.

[0013] The third invention is the second invention, wherein the degree of polymerization of the type II unmodified cellulose fine fibers is 180 The present invention relates to the following type II unmodified cellulose fine fibers:

[0014] The fourth invention relates to a type II unmodified cellulose fine fiber molded product obtained by molding the type II unmodified cellulose fine fibers of the first to third inventions into a film or beads.

[0015] The fifth invention is a method for producing mercerized cellulose by mercerizing cellulose, and a method for producing mercerized cellulose by mercerizing cellulose. 299 The present invention relates to a method for producing type II unmodified cellulose fine fibers, which comprises a defibration step in which an alkali metal hydroxide is added to raw cellulose that has been subjected to a depolymerization step in which the cellulose content is reduced to the following value, thereby obtaining cellulose fine fibers; and a neutralization step in which the cellulose fine fibers are neutralized with an acid.

[0016] The sixth invention relates to a method for producing a type II unmodified cellulose fine fiber molded product, which comprises a molding step in which the type II unmodified cellulose fine fibers obtained by the method for producing type II unmodified cellulose fine fibers of the fifth invention are molded to obtain a type II unmodified cellulose fine fiber molded product.

[0017] The seventh invention is type II cellulose, which is made of chemically unmodified cellulose and has a type II crystal structure. At the same time, the haze value of a 0.1 wt% dispersion measured in accordance with JIS K 7136 (2000) is 35% or less. The present invention relates to type II unmodified cellulose fine fibers characterized by the above. [Effects of the Invention]

[0018] The type II unmodified cellulose fine fibers according to the first aspect of the present invention include a mercerization step of mercerizing cellulose to obtain mercerized cellulose, and a polymerization degree of the mercerized cellulose. 299 The raw cellulose is subjected to a depolymerization process to lower the temperature to below 100°C, followed by a defibration process in which an alkali metal hydroxide is added to the raw cellulose to defibrate it and obtain cellulose fine fibers, and a neutralization process in which the cellulose fine fibers are neutralized with an acid. This allows the production of cellulose fine fibers that are not chemically modified and are highly safe.

[0019] According to the type II unmodified cellulose fine fibers of the second invention, in the first invention, the haze value of a 0.1 wt % dispersion of the type II unmodified cellulose fine fibers measured in accordance with JIS K 7136 (2000) is 35% or less, and therefore the type II unmodified cellulose fine fibers have high transparency, excellent appearance characteristics, and high safety, and can be used in a wide range of applications such as cosmetics.

[0020] According to the second aspect of the present invention, the degree of polymerization of the second type unmodified cellulose fine fibers is 180 Since the viscosity of the dispersion of the cellulose fine fibers is lowered, degassing and the like becomes easier, the appearance during molding becomes better, and an increase in pressure in the molding device can be suppressed, thereby improving production efficiency.

[0021] According to the type II unmodified cellulose fine fiber molded product of the fourth invention, in any one of the first to third inventions, the type II unmodified cellulose fine fiber is molded into a film or beads, and is therefore useful as a substitute for plastic molded products.

[0022] The fifth aspect of the present invention provides a method for producing type II unmodified cellulose fine fibers, which includes a mercerization step of mercerizing cellulose to obtain mercerized cellulose, and a step of adjusting the degree of polymerization of the mercerized cellulose. 299 The process includes a defibration step in which an alkali metal hydroxide is added to raw cellulose that has undergone a depolymerization step in which the cellulose content is reduced to below 100 ppm to obtain cellulose fine fibers, and a neutralization step in which the cellulose fine fibers are neutralized with an acid. This makes it possible to efficiently obtain chemically unmodified cellulose fine fibers through a simple process.

[0023] The method for producing type II unmodified cellulose microfiber molded products according to the sixth aspect of the present invention includes a molding step in which type II unmodified cellulose microfibers obtained by the method for producing type II unmodified cellulose microfibers according to the fifth aspect of the present invention are molded to produce type II unmodified cellulose microfiber molded products, and is therefore useful as an alternative to plastic molded products.

[0024] According to the seventh aspect of the present invention, type II unmodified cellulose fine fibers are made of cellulose that has not been chemically modified and has a type II crystalline structure. At the same time, the haze value of a 0.1 wt% dispersion measured in accordance with JIS K 7136 (2000) is 35% or less. Therefore, High transparency and excellent appearance characteristics It is possible to obtain highly safe cellulose fine fibers that are not chemically modified. It can be used for a wide range of purposes, including cosmetics. . [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic process diagram of the method for producing type II unmodified cellulose fine fibers of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The cellulose fine fibers produced by the production method of the present invention are type II cellulose fine fibers having a type II crystal structure because they are converted into fine fibers through a mercerization step in which cellulose is mercerized. 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. Among cellulose fine fibers, type II cellulose fine fibers are softer than type I cellulose fine fibers, and therefore are suitable for use in cosmetics and the like because they provide a good texture.

[0027] The production method of the present invention is intended to produce cellulose fine fibers as a substitute for petroleum-derived plastics in the field of cosmetics and the like, and therefore does not require the strength characteristics of type I cellulose fibers used in applications such as those containing them as reinforcing materials in resins. Furthermore, a wide range of applications are anticipated, such as in cosmetics, where design and good appearance characteristics are required. The cellulose fine fiber dispersion produced by the production method of the present invention is highly transparent and, being unmodified chemically, highly safe. Furthermore, it is easy to handle and has excellent moldability.

[0028] The method for producing type II unmodified cellulose fine fibers of the present invention will now be described in order using the process diagram in Figure 1. First, pulp is a preferred example of cellulose as the starting raw material. Pulp is a raw material obtained by crushing wood and removing impurities such as lignin to increase the purity of the cellulose component. Cotton linter pulp, which is obtained by removing impurities from cotton to increase the purity of the cellulose component, is also used. In addition, 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 also be used.

[0029] The mercerization step (S1) is a step in which cellulose is mercerized to obtain mercerized cellulose. In the mercerization step, the raw cellulose is added to an alkali metal hydroxide such as caustic soda (NaOH), and the mixture is stirred while being heated as necessary to swell the cellulose fibers. When the cellulose fibers are immersed in the alkali metal hydroxide, they become negatively charged, generating Coulomb forces that cause the individual fibers to repel each other and facilitate defibration. Because mercerized cellulose is easily defibrated as described above, it is possible to reduce the energy required in the subsequent defibration step.

[0030] Examples of the alkali metal hydroxide used in the mercerization step include caustic soda (NaOH), lithium hydroxide, and potassium hydroxide, with caustic soda being preferred from the standpoints of cost, safety, and environmental impact.

[0031] After the mercerization step (S1), excess alkali metal hydroxide is removed as necessary. The solid content concentration is appropriately adjusted, and the depolymerization step (S2) is carried out. The depolymerization step (S2) is a step in which the degree of polymerization of the mercerized cellulose obtained in the mercerization step (S1) is reduced to 760 or less. The mercerized cellulose with the adjusted solid content is appropriately pulverized and aged by oxidative decomposition with oxygen in the air, thereby reducing the degree of polymerization. In this case, the degree of polymerization is set to 760 or less. Setting the degree of polymerization of the mercerized cellulose to 760 or less ensures the transparency of the resulting dispersion of cellulose fine fibers. Furthermore, the lower the degree of polymerization of the mercerized cellulose, the easier it is to defibrate the cellulose fibers in the subsequent defibration step.

[0032] The aging of the mercerized cellulose in the depolymerization step (S2) is carried out at room temperature or under heated conditions. To accelerate the depolymerization rate, heating conditions that do not dry the raw material are preferably used. An aging accelerator such as manganese(II) sulfate, which accelerates the aging reaction, can also be added.

[0033] By undergoing the mercerization step (S1) and the depolymerization step (S2), raw cellulose that can be defibrated into fine fibers is obtained. Mercerizing cellulose converts the raw cellulose into type II cellulose, which has a type II crystalline structure. Type II cellulose is said to be inferior to type I cellulose in terms of strength, etc. However, since the cellulose fine fibers obtained by the present invention are intended to be used as a substitute for plastics in fields such as cosmetics, they do not require the same strength as type I cellulose, and therefore the decrease in strength is not a problem.

[0034] In the defibration step (S3), an alkali metal hydroxide and a solvent (ion-exchanged water) are added to the raw cellulose to adjust the total concentration to 2.5 to 17.5%, and defibration is performed. As described above, the alkali metal hydroxide used here includes caustic soda, lithium hydroxide, potassium hydroxide, etc., with caustic soda being preferred from the standpoints of cost and safety. The raw cellulose is defibrated by mechanical (physical) defibration. Mechanical (physical) defibration is performed by a known method using a homogenizer, water jet, etc. Here, since the raw cellulose is in a state where the fibers are swollen and easily defibrated by mercerization, and the degree of polymerization is reduced by the depolymerization step, defibration can be easily performed without applying high pressure, which is advantageous in terms of equipment.

[0035] If the alkali metal hydroxide concentration is lower than 2.5%, the swelling of the cellulose may be insufficient, making defibration difficult. If the alkali metal hydroxide concentration is higher than 17.5%, the salt concentration becomes high, which may cause the cellulose fibers to easily aggregate, making defibration difficult. If the alkali metal hydroxide concentration is outside this range and defibration is insufficient, the transparency of the resulting dispersion of cellulose fine fibers may decrease, resulting in poor design properties.

[0036] Defibration may be carried out in multiple steps. For example, by performing pre-defibration using a mixer and then main defibration using a homogenizer, it is possible to obtain cellulose fine fibers that are uniform and have a small fiber diameter. Furthermore, pre-defibration can avoid problems such as the raw cellulose clogging the defibration device. Pre-defibration is carried out by a known method using a mixer, refiner, or the like. Defibration of cellulose fine fibers is sufficient as long as the average fiber diameter is from nano-sized to several hundred nano-sized, and if the average fiber diameter is about 2 to 800 nm, more preferably 100 nm or less, the transparency of the cellulose fine fiber dispersion will be improved.

[0037] The cellulose fine fibers obtained through the defibration step are neutralized with an acid in the neutralization step (S4). The cellulose fine fibers obtained through the defibration step are strongly alkaline and therefore require neutralization. Examples of acids that can be used include sulfuric acid, hydrochloric acid, and lactic acid. The neutralized cellulose fine fibers are washed appropriately and re-defibrated to obtain type II unmodified cellulose fine fibers.

[0038] The dispersion of type II unmodified cellulose fine fibers obtained through these processes can be used to produce molded articles. For example, they can be coated to form films, or formed into beads for use in cosmetics. Both can be produced by a molding process involving drying, and the amount of chemicals used, which have a high environmental impact, can be reduced compared to conventional cellulose films and cellulose beads.

[0039] The 0.1% by mass dispersion of type II unmodified cellulose fine fibers obtained by the production method of the present invention has good transparency. Specifically, when the haze value measured in accordance with JIS K 7136 (2000) is 35% or less, the film has a good appearance and can be used in cosmetics, and can be used in a wide range of applications.

[0040] Furthermore, by controlling the degree of polymerization of the type II unmodified cellulose fine fibers obtained by the production method of the present invention to 310 or less, the viscosity of the dispersion can be reduced, which facilitates degassing, improves moldability, and improves the appearance of the molded product. Furthermore, when the viscosity of the dispersion is reduced, it is possible to suppress an increase in pressure in the molding device, which also makes it possible to improve production efficiency. [Example]

[0041] In producing type II unmodified cellulose fine fibers, the inventors conducted production experiments using the following raw materials and the like, following the process diagram of Figure 1, by changing the degree of polymerization in the depolymerization step and the alkali metal hydroxide concentration in the defibration step.

[0042] [Raw materials] The starting cellulose raw material used was dissolving pulp ("LNDP" manufactured by Nippon Paper Industries Co., Ltd.).

[0043] [Alkali metal hydroxide] The alkali metal hydroxide used for mercerization in the mercerization step was caustic soda (manufactured by Kishida Chemical Co., Ltd.) The same caustic soda was used in the defibration step.

[0044] 〔acid〕 The acid used in the neutralization step was sulfuric acid (manufactured by Kishida Chemical Co., Ltd.).

[0045] [Preparation of dispersion of type II unmodified cellulose microfibers] Using the above raw materials, a dispersion of type II unmodified cellulose fine fibers was prepared according to the following formulation.

[0046] <Prototype example 1> 18 wt% caustic soda was heated to 50°C, and pulp was added to a concentration of 2 wt%. The mixture was stirred until a slurry was formed, and mercerization was performed (mercerization process). The excess caustic soda was then removed to adjust the solids content to 33 wt%. Aging treatment was performed at 50°C to obtain raw cellulose 1 with a degree of polymerization of 752 (depolymerization process). Then, 10.6 g of raw cellulose 1, 330.65 g of ion-exchanged water, and 8.75 g of caustic soda (total caustic soda concentration 2.5%) were placed in a 500 mL container and subjected to preliminary defibration using a mixer (Primix Corporation, "Labo-Lusion"). This was followed by full defibration using a homogenizer (SMT Corporation, "LAB1000") (defibration process). 125 g of the prepared slurry was sampled and neutralized by adding 20 wt% sulfuric acid while stirring (neutralization process). The neutralized sample was filtered by suction and washed with 300 mL of ion-exchanged water. Ion-exchanged water was added to the washed sample to a total weight of 250 g, and the sample was pre-defibrated in a mixer (Primix Corporation, "Labo-Lusion"). This was followed by full defibration in a homogenizer (SMT Corporation, "LAB1000"), yielding a dispersion of type II unmodified cellulose fine fibers for Prototype Example 1.

[0047] <Prototype example 2> A dispersion of type II unmodified cellulose fine fibers of prototype 2 was obtained in the same manner as prototype 1, except that the total concentration of caustic soda in the fiber-opening step was 9.5%.

[0048] <Prototype example 3> A dispersion of type II unmodified cellulose fine fibers of prototype example 3 was obtained in the same manner as prototype example 1, except that the total concentration of caustic soda in the fiber-opening step was 17.5%.

[0049] <Prototype example 4> When the same procedure as in Prototype Example 1 was followed except that the total concentration of caustic soda in the defibration step was changed to 1.5%, the cellulose was not defibrated and a dispersion of type II unmodified cellulose fine fibers was not obtained.

[0050] <Prototype 5> A dispersion of type II unmodified cellulose fine fibers of prototype example 5 was obtained in the same manner as prototype example 1, except that the total concentration of caustic soda in the fiber-opening step was 18.5%.

[0051] <Prototype Example 6> A dispersion of type II unmodified cellulose fine fibers of Trial Example 6 was obtained in the same manner as in Trial Example 1, except that the raw cellulose was obtained by performing aging treatment until the degree of polymerization of the mercerized cellulose in the depolymerization step reached 299.

[0052] <Prototype Example 7> A dispersion of type II unmodified cellulose fine fibers of Prototype Example 7 was obtained in the same manner as in Prototype Example 2, except that the raw cellulose was obtained by performing aging treatment until the degree of polymerization of the mercerized cellulose in the depolymerization step reached 299.

[0053] <Prototype Example 8> A dispersion of type II unmodified cellulose fine fibers of Prototype Example 8 was obtained in the same manner as in Prototype Example 3, except that the raw cellulose was obtained by performing aging treatment until the degree of polymerization of the mercerized cellulose in the depolymerization step reached 299.

[0054] <Comparative Example 1> When the same procedure as in Prototype Example 1 was carried out except that the depolymerization step was not carried out (omitted), the cellulose was not defibrated, and a dispersion of type II unmodified cellulose fine fibers was not obtained.

[0055] <Comparative Example 2> A dispersion of type II unmodified cellulose fine fibers of Comparative Example 2 was obtained in the same manner as in Prototype Example 3, except that the depolymerization step was not carried out (omitted).

[0056] <Comparative Example 3> The same procedure as in Prototype Example 1 was carried out except that the mercerization step and the depolymerization step were not carried out (omitted), but the cellulose was not defibrated, and a dispersion of type II unmodified cellulose fine fibers was not obtained.

[0057] The haze (%) and degree of polymerization of the dispersion of type II unmodified cellulose fine fibers of each prototype and comparative example were measured. The degrees of polymerization of the raw cellulose of each prototype and comparative example and the type and concentration (%) of alkali metal hydroxide used in the defibration step are shown in Table 1.

[0058] [Haze] Haze (%) is an index of transparency, and was measured for a 0.1% by mass dispersion of each prototype using a haze meter (NDH-4000, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7136 (2000). Deionized water was used to adjust the concentration of the dispersion for each prototype. The dispersion was measured in a glass cell for liquids (MG-40, manufactured by Fujiwara Seisakusho Co., Ltd.) with an optical path of 1 cm. Zero point measurement was performed by adding deionized water to the same glass cell. Measurement was not possible for prototypes and comparative examples in which cellulose could not be defibrated to obtain cellulose fine fibers, and thus the result was marked "-".

[0059] [Degree of polymerization] The degree of polymerization was measured by the viscosity method using a copper ethylenediamine solution as follows: Dried cellulose microfibers were dissolved in 0.5 M 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 defined as η and the viscosity of solution 1 as η0, and the intrinsic viscosity [η] of the cellulose microfibers was calculated using the following formula to determine the degree of polymerization (DP): c is the concentration of the cellulose microfibers (g / L). Intrinsic viscosity [η]={(η / η0)-1} / c Degree of polymerization DP=intrinsic viscosity [η] / (8.8×10 -4 )

[0060] In addition, for the prototypes and comparative examples in which cellulose could not be defibrated and cellulose fine fibers could not be obtained, the degree of polymerization of the dispersion of cellulose fine fibers could not be measured, so they were marked with "-".

[0061] [Average fiber diameter] The average fiber diameter was determined by measuring the diameters of 50 or more fibers in a 10 μm square scanning area using a scanning probe microscope (Shimadzu Corporation, SPM-9700HT) and calculating the average value. Samples for scanning probe microscope observation were prepared by diluting a dispersion of cellulose fine fibers with water to an arbitrary concentration, casting the mixture on a mica substrate, and air-drying. Note that the average fiber diameter was measured only for Prototype Example 7.

[0062] [Table 1]

[0063] [Results and Discussion] Comparing Prototype Examples 1 and 6 and Comparative Example 1 with Prototype Examples 3, 8, and Comparative Example 2, which all had the same alkali metal hydroxide concentration, it was shown that the lower the degree of polymerization of the raw cellulose in the prototype example, the lower the haze of the dispersion of cellulose fine fibers. This shows that by obtaining raw cellulose with a lower degree of polymerization of mercerized cellulose in the depolymerization step, it is possible to disperse cellulose fine fibers more finely and uniformly with the same defibration energy. When raw cellulose with a degree of polymerization of 760 or more was prepared without going through the depolymerization step, as in Comparative Example 1, cellulose could not be defibrated if the alkali metal hydroxide concentration in the defibration step was low, or, even if defibration was possible with a high alkali metal hydroxide concentration as in Comparative Example 2, the dispersion had a high haze.

[0064] Comparing Prototypes 1 to 5, which use the same degree of polymerization of raw cellulose, it was found that the haze of the cellulose fine fiber dispersion increased when the alkali metal hydroxide concentration was too low or too high. In particular, when the alkali metal hydroxide concentration was less than 2.5%, as in Prototype 4, the cellulose fibers were insufficiently swollen, failing to be defibrated, and cellulose fine fibers were not obtained. Furthermore, when the alkali metal hydroxide concentration was greater than 17.5%, as in Prototype 5, it is thought that the high salt concentration caused the cellulose fibers to aggregate, resulting in insufficient defibration of the cellulose and an increase in the haze of the dispersion. In other words, it was shown that a dispersion with low haze could be obtained by setting the total alkali metal hydroxide concentration in the defibration process to 2.5 to 17.5%, and it was found that a dispersion with even higher transparency could be obtained by setting the total concentration to about 10%.

[0065] In addition, in Comparative Example 3, which did not undergo the mercerization process, the raw cellulose had a type I crystal structure and the depolymerization process was omitted, so the degree of polymerization of the raw cellulose was high, and therefore defibration was not possible and cellulose fine fibers could not be obtained.

[0066] As described above, the manufacturing method of the present invention makes it possible to obtain a dispersion of cellulose fine fibers with low haze and high transparency even with small defibration energy, demonstrating that chemically unmodified type II cellulose fine fibers can be efficiently manufactured using a simple process. [Industrial Applicability]

[0067] According to the method for producing type II unmodified cellulose fine fibers of the present invention, it is possible to efficiently obtain chemically unmodified cellulose fine fibers through a simple process. Furthermore, the obtained type II unmodified cellulose fine fibers have high transparency and low viscosity, and therefore are easy to handle and have excellent appearance properties, making them useful as a substitute for plastics in a wide range of applications such as cosmetics. [Explanation of symbols]

[0068] S1 Mercerization process S2 depolymerization process S3 Defibration process S4 Neutralization process

Claims

1. a mercerization step of mercerizing cellulose to obtain mercerized cellulose; the starting cellulose having undergone a depolymerization step of reducing the degree of polymerization of the mercerized cellulose to 299 or less, a defibration step of adding an alkali metal hydroxide and defibrating the cellulose to obtain cellulose fine fibers; and a neutralization step of neutralizing the cellulose fine fibers with an acid. Type II unmodified cellulose fine fibers.

2. 2. The type II unmodified cellulose fine fibers according to claim 1, wherein a haze value of a 0.1 wt % dispersion of the type II unmodified cellulose fine fibers measured in accordance with JIS K 7136 (2000) is 35% or less.

3. 3. The type II unmodified cellulose fine fibers according to claim 2, wherein the degree of polymerization of the type II unmodified cellulose fine fibers is 180 or less.

4. 4. The type II unmodified cellulose fine fiber molded product according to claim 1, wherein the type II unmodified cellulose fine fiber is molded into a film or beads.

5. a mercerization step of mercerizing cellulose to obtain mercerized cellulose; the starting cellulose having undergone a depolymerization step of reducing the degree of polymerization of the mercerized cellulose to 299 or less, a defibration step of adding an alkali metal hydroxide and defibrating the cellulose to obtain cellulose fine fibers; and a neutralization step of neutralizing the cellulose fine fibers with an acid. A method for producing type II unmodified cellulose fine fibers, comprising:

6. and a molding step of molding the type II unmodified cellulose fine fibers obtained by the method for producing type II unmodified cellulose fine fibers according to claim 5 to obtain a type II unmodified cellulose fine fiber molded product.

7. The type II unmodified cellulose fine fibers are made of chemically unmodified cellulose, are type II cellulose having a type II crystalline structure, and have a haze value of 35% or less when measured in accordance with JIS K 7136 (2000) for a 0.1 wt% dispersion.

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