JP2016191002A - Cellulose nano-fiber dispersion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cellulose nano-fiber dispersion that has a viscosity higher than the conventional cellulose nano-fiber dispersion.SOLUTION: Provided is a cellulose nano-fiber dispersion being a dispersion of a cellulose nano-fiber obtained by treating, in water, a cellulose raw material using an oxidizer under the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide and a mixture thereof, and pulverizing the obtained oxidized cellulose, and in which, characterized, the B type viscosity (60 rpm, 20°C) of the dispersion containing the cellulose nano-fiber at a concentration of 1% (w/v) is 7000 mPa-s or more.SELECTED DRAWING: None

Description

  The present invention relates to a cellulose nanofiber dispersion.

  Cellulose nanofibers, for example, coexist with cellulose-based raw materials 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter referred to as TEMPO) and sodium hypochlorite which is an inexpensive oxidant When the treatment is performed under the condition, carboxyl groups can be efficiently introduced onto the surface of the cellulose microfibril, and a uniform and transparent cellulose nanofiber dispersion can be produced with a little fibrillation energy (Non-patent Document 1). Cellulose nanofibers are expected to be used for the realization of purification devices using high-performance filters that do not allow any fine foreign substances to pass through, the development of chemical fiber strength and high-performance clothing, and the efficiency of fuel cells. Many attempts have been made to reduce the viscosity in order to improve the flowability of the resin and to facilitate processing by the user. In addition, cellulose nanofibers obtained by the above-mentioned method have advantages in environmental harmony as a reaction process, such as the use of water as a solvent and the fact that the reaction by-product is only sodium chloride. Development and research have been conducted (Patent Document 1).

JP 2008-001728 A

Saito, T., et al., Cellulose Commun., 14 (2), 62 (2007)

  By using an N-oxyl compound such as TEMPO or a TEMPO derivative as an oxidation catalyst, it is possible to easily produce oxidized cellulose from a cellulose raw material, and a cellulose nanofiber dispersion is obtained by defibrating the oxidized cellulose. be able to. As a use of cellulose nanofiber dispersion, there are thickeners that make use of viscosity characteristics, but there has been no investigation on increasing viscosity so far.

  Therefore, an object of the present invention is to provide a cellulose nanofiber dispersion having a viscosity higher than that of a conventional cellulose nanofiber dispersion at the same concentration.

The present invention provides [1] to [2].
[1] A dispersion of cellulose nanofibers obtained by refining a cellulose raw material, and having a B-type viscosity (60 rpm, 20 ° C.) at a concentration of 1% (w / v) of the dispersion containing the cellulose nanofibers A cellulose nanofiber dispersion characterized by being 7000 mPa · s or more.
[2] In the cellulose nanofiber dispersion, the cellulose raw material is used in water in the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide and a mixture thereof in water. The cellulose nanofiber dispersion liquid according to [1], wherein the cellulose nanofiber dispersion liquid is obtained by fibrillation treatment using the oxidized cellulose obtained by treatment.

  According to the present invention, it is possible to provide a cellulose nanofiber dispersion having a higher viscosity than conventional cellulose nanofiber dispersions at the same concentration. In addition, the B-type viscosity (60 rpm, 20 degreeC) of the density | concentration 1% (w / v) of the conventional cellulose nanofiber dispersion liquid is several hundred to about 4000 mPa * s.

  Thus, the ability to provide a dispersion having a high viscosity is advantageous when used as a thickener for cellulose nanofibers. For example, the addition of a small amount of cellulose nanofiber makes it possible to impart viscosity, so that there is an advantage that only the viscosity is increased without impairing the conventional performance of cosmetics and foods.

  The cellulose nanofiber dispersion of the present invention has a B-type viscosity (60 rpm, 20 ° C.) at a concentration of 1% (w / v) of 70000 mPa · s or more, and a conventional cellulose nanofiber concentration of 1% (w / v). The B-type viscosity (60 rpm, 20 ° C.) is about several hundred to 4,000 mPa · s, and the viscosity is high.

  The cellulose nanofiber dispersion of the present invention can be obtained by sequentially adding an oxidizing agent in the presence of an N-oxyl compound and bromide, iodide or a mixture thereof when oxidizing a cellulose-based raw material. It can manufacture by dispersing the cellulose nanofiber obtained in a solvent.

  The reason why the cellulose nanofiber dispersion according to the present invention has a higher viscosity than the conventional cellulose nanofiber dispersion at the same concentration is presumed as follows. Cellulose nanofibers contained in the cellulose nanofiber dispersion of the present invention defibrated oxidized cellulose obtained by oxidizing a cellulose raw material by sequential addition of an oxidizing agent, resulting in the following low molecular weight of cellulose. It is assumed that there is no major factor.

  In the production of conventional cellulose nanofibers, the oxidizing agent (for example, sodium hypochlorite aqueous solution) is strongly alkaline, so N-oxyl compound (for example, TEMPO), as well as bromide or iodide (for example, sodium bromide). When the oxidizing agent is added to the reaction system for the oxidation reaction of the cellulose raw material containing the batch, the pH of the reaction system becomes higher than the preferable pH range for the oxidation reaction, and it is considered that the oxidation reaction does not proceed so much immediately after the addition of the oxidizing agent. . On the other hand, it is considered that side reactions such as cellulose molecular weight reduction caused by hypochlorite ions, hydroxyl radicals, and the like are likely to occur. For this reason, in the conventional method of adding an oxidizing agent in a lump, the molecular weight of cellulose is reduced by side reaction in the reaction system, and the B-type viscosity (60 rpm, 20 at a concentration of 1% (w / v) of cellulose nanofibers is produced. (° C.) is considered to be several hundred to about 4000 mPa · s.

(1) N-oxyl compound The N-oxyl compound is a compound capable of generating a nitroxy radical. As the N-oxyl compound used in the present invention, any compound can be used as long as it promotes the target oxidation reaction. For example, the N-oxyl compound used in the present invention includes a compound represented by the following general formula (Formula 1).

(In Formula 1, R1 to R4 represent the same or different alkyl groups having about 1 to 4 carbon atoms.)
Of the substances represented by Formula 1, 2,2,6,6-tetramethyl-1-piperidine-oxy radical (hereinafter referred to as TEMPO) is preferable. In addition, N-oxyl compounds represented by any one of the following general formulas 2 to 4, that is, the hydroxyl group of 4-hydroxy TEMPO is etherified with alcohol, or esterified with carboxylic acid or sulfonic acid to impart moderate hydrophobicity. The 4-hydroxy TEMPO derivative or 4-acetamido TEMPO having an appropriate hydrophobicity by acetylating the amino group of 4-amino TEMPO is particularly preferable because it is inexpensive and can give uniform oxidized cellulose.

(In formulas 2 to 4, R is a linear or branched carbon chain having 4 or less carbon atoms.)
Furthermore, an N-oxyl compound represented by the following general formula 5, that is, an azaadamantane-type nitroxyl radical, is preferable because it can efficiently oxidize pulp in a short time and hardly breaks the cellulose chain.

(In Formula 5, R5 and R6 represent the same or different hydrogen or a C1-C6 linear or branched alkyl group.)
The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing the cellulosic material. For example, it is about 0.01 to 10 mmol, preferably 0.01 to 1 mmol, more preferably about 0.05 to 0.5 mmol with respect to 1 g of cellulosic raw material.

(2) Bromide or iodide Bromide is a compound containing bromine, and examples thereof include alkali metal bromide that can be dissociated and ionized in water. Further, an iodide is a compound containing iodine, and examples thereof include alkali metal iodide. The amount of bromide or iodide used can be selected as long as the oxidation reaction can be promoted. The total amount of bromide and iodide is, for example, about 0.1 to 100 mmol, preferably 0.1 to 10 mmol, and more preferably about 0.5 to 5 mmol with respect to 1 g of cellulosic raw material.

(3) Oxidizing agent The method for oxidizing a cellulosic raw material of the present invention is performed by sequentially adding an oxidizing agent in the presence of an N-oxyl compound and a bromide, iodide or a mixture thereof. Oxidized cellulose can be produced efficiently with the amount of compound used.

  As a method for sequentially adding the oxidizing agent, a general apparatus such as a liquid feed pump may be used, and the addition rate can be selected within a range in which the oxidation reaction can be promoted. For example, it is 0.01 to 50 mmol / min, preferably 0.05 to 10 mmol / min, and more preferably about 0.1 to 5 mmol / min with respect to 1 g of bleached wood pulp. When the addition rate is slower than this range, it is not preferable because it takes too much time to add the predetermined addition amount. When the addition rate is faster than this range, the effect of sequentially adding the oxidizing agent is exhibited. It is not preferable because it is not performed. Moreover, you may add about 10% of the oxidizing agent added before reaction at this time.

  The oxidizing agent may be any oxidizing agent that can promote the target oxidation reaction, such as halogen, hypohalous acid, halous acid, perhalogen acid or salts thereof, halogen oxide, and peroxide. Agents can also be used. From the viewpoint of production cost of oxidized cellulose, sodium hypochlorite, which is currently used most widely in industrial processes as an oxidizing agent and is low in environmental load, is suitable. The amount of the oxidizing agent used can be selected within a range that can promote the oxidation reaction. For example, it is about 0.5 to 500 mmol, preferably 0.5 to 50 mmol, and more preferably about 2.5 to 25 mmol with respect to 1 g of bleached wood pulp.

  The method of the present invention is characterized in that the oxidation reaction can proceed smoothly even under mild conditions. Therefore, even if the reaction temperature is about 15 to 30 ° C., the cellulosic material can be oxidized efficiently. In addition, a carboxyl group produces | generates in a cellulose with progress of reaction, and the pH fall of a reaction liquid is recognized. Therefore, in order to advance the oxidation reaction efficiently, it is desirable to maintain the pH of the reaction solution at about 9 to 12, preferably about 10 to 11.

(5) Oxidation reaction conditions The method of the present invention is characterized in that the oxidation reaction can proceed smoothly even under mild conditions. Therefore, even if the reaction temperature is about 15 to 30 ° C., the cellulosic material can be oxidized efficiently. In addition, a carboxyl group produces | generates in a cellulose with progress of reaction, and the pH fall of a reaction liquid is recognized. Therefore, in order to advance the oxidation reaction efficiently, it is desirable to maintain the pH of the reaction solution at about 9 to 12, preferably about 10 to 11. The reaction medium is preferably water because it is easy to handle and hardly causes side reactions. The reaction time in the oxidation reaction can be appropriately set according to the progress of oxidation, and is not particularly limited. For example, it is 0.5 to 6 hours, preferably 1 to 5 hours, and more preferably about 2 to 4 hours. is there.

(6) Cellulose raw material In the present invention, cellulose raw materials include bleached or unbleached wood pulp, bleached or unbleached non-wood pulp, refined linter, pulp from herbs such as jute, manila hemp, kenaf, and microorganisms such as acetic acid bacteria. Natural cellulose such as cellulose to be produced, regenerated cellulose dissolved in some solvent such as copper ammonia solution and morpholine derivative, and re-spun, and hydrolysis, alkaline hydrolysis, enzymatic decomposition, and explosion of the above cellulose materials Examples include fine cellulose that has been depolymerized by treatment, vibration ball mill treatment, or the like, or mechanically treated fine cellulose.

(7) Oxidized cellulose Although the amount of carboxyl groups of oxidized cellulose is not particularly limited, it is preferable to set conditions so that the amount is 0.5 mmol / g or more. More preferably, the carboxyl group amount is 1.0 mmol / g to 3.0 mmol / g, further preferably 1.4 mmol / g to 2.8 mmol / g, particularly preferably 1.5 mmol / g to 2.5 mmol / g. By adjusting the amount of carboxyl groups to the above range, the function as oxidized cellulose can be exhibited, and it becomes an excellent raw material for cellulose nanofibers. The amount of the carboxyl group can be adjusted by adjusting the oxidation reaction time, adjusting the oxidation reaction temperature, adjusting the pH during the oxidation reaction, adjusting the addition amount of the N-oxyl compound, bromide, iodide, or oxidizing agent.

In addition, the amount of carboxyl groups of oxidized pulp can be measured by the following procedure:
Prepare 60 ml of 0.5% by weight slurry of oxidized pulp, add 0.1 M hydrochloric acid aqueous solution to pH 2.5, then add 0.05 N aqueous sodium hydroxide solution dropwise until the pH is 11 From the amount of sodium hydroxide (a) consumed in the neutralization step of the weak acid with a gradual change in electrical conductivity, the following formula:
Amount of carboxyl group [mmol / g oxidized pulp] = a [ml] × 0.05 / oxidized pulp mass [g]
Calculate using.

(8) Cellulose nanofiber In the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide and a mixture thereof, an oxidizing agent is sequentially added to treat the cellulose-based raw material in water. Cellulose nanofibers can be obtained by defibrating the oxidized cellulose obtained.

  The cellulose nanofiber is a fiber obtained by processing a cellulose fiber into a cellulose nanofiber which is a single microfibril of cellulose having a width of about 2 to 15 nm and a length of about 700 to 2000 nm.

  At the time of defibration of oxidized pulp, a dispersion or suspension of oxidized pulp in a medium is used. Here, high-speed rotation type, colloid mill type, high pressure type, roll mill type, ultrasonic type, etc. are used to perform strong shear It is preferable to apply a force. In particular, in order to efficiently obtain cellulose nanofibers, it is preferable to use a wet high-pressure or ultrahigh-pressure homogenizer that can apply a pressure of 50 MPa or more to the dispersion and can apply a strong shearing force. The pressure is more preferably 100 MPa or more, and further preferably 140 MPa or more. By this treatment, the oxidized pulp is defibrated to form cellulose nanofibers, and the cellulose nanofibers are dispersed in the medium. As the medium, water is preferably used from the viewpoint of easy handling.

  Next, based on an Example, this invention is demonstrated still in detail.

[Example 1]
5g (absolutely dried) bleached unbeaten pulp derived from coniferous tree (dissolved) dissolves 20mg (0.125mmol) of TEMPO (manufactured by Tokyo Chemical Industry Co., Ltd.) and 356mg (3.75mmol) of sodium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) The resulting mixture was added to 500 ml of the aqueous solution and stirred until the pulp was uniformly dispersed. Addition of 22.5 mmol of sodium hypochlorite aqueous solution (manufactured by Wako Pure Chemical Industries, Ltd.) to the reaction system was started at an addition rate of 0.45 mmol / (min · g) to initiate the oxidation reaction. During the reaction, the pH in the system was lowered, but a 3N sodium hydroxide aqueous solution was successively added to adjust the pH to 10. After reacting until the addition of sodium hydroxide was completed, the pulp was filtered through a glass filter and sufficiently washed with water to obtain an oxidized pulp.

[Comparative Example 1]
Bleached unbeaten pulp (made by Nippon Paper Industries Co., Ltd.) 5 g (absolutely dried) derived from conifers dissolves 94 mg (0.5 mmol) of TEMPO (Tokyo Kasei Co., Ltd.) and 756 mg (7.35 mmol) of sodium bromide (made by Wako Pure Chemical Industries, Ltd.) The resulting mixture was added to 500 ml of the aqueous solution and stirred until the pulp was uniformly dispersed. To the reaction system, 22.5 mmol of sodium hypochlorite aqueous solution (manufactured by Wako Pure Chemical Industries, Ltd.) was added all at once to initiate the oxidation reaction. During the reaction, the pH in the system was lowered, but a 3N aqueous sodium hydroxide solution was successively added to adjust the pH to 10. After reacting until the addition of sodium hydroxide was completed, the pulp was filtered through a glass filter and sufficiently washed with water to obtain an oxidized pulp.

<Preparation of cellulose nanofiber dispersion>
The obtained pulp was dispersed in water to prepare a pulp slurry having a pulp solid content of 1%. The pulp slurry was subjected to an ultra-high pressure homogenizer and subjected to a 2-pass treatment at 140 MPa to prepare a cellulose nanofiber dispersion. The B-type viscosity of the prepared cellulose nanofiber dispersion was measured using a TV-10 viscometer (Toki Sangyo Co., Ltd.) at 20 ° C. and 60 rpm.

<Transparency>
The transparency (660 nm light transmittance) of a 0.1% (w / v) cellulose nanofiber dispersion was measured using a UV-VIS spectrophotometer UV-265FS (manufactured by Shimadzu Corporation). The transparency was 99% or more for the cellulose nanofiber dispersion prepared using either the pulp of Example 1 or Comparative Example 1.

<Fiber length>
Water was further added to the cellulose nanofiber aqueous dispersion to prepare a diluted dispersion in which the concentration of cellulose nanofiber was 0.001% by mass. The diluted dispersion was thinly spread on a mica sample stage, heated and dried at 50 ° C. to prepare an observation sample, and the fiber length was measured from the shape image observed with an atomic force microscope (AFM). 100 fibers were measured, and the average length was defined as the average fiber length.

  The amount of carboxyl groups of the oxidized pulp prepared in Example 1 was 1.77 mmol / g. Since the carboxyl group amount of the oxidized pulp prepared in Comparative Example 1 is also 1.52 mmol / g, it has been clarified that the present invention can obtain a cellulose nanofiber dispersion exceeding 7000 mPa · s at a concentration of 1%. .

  Furthermore, when the fiber length of the prepared cellulose nanofiber was examined, it was found that there was no great difference between Example 1 and Comparative Example 1. Therefore, it became clear that the cellulose nanofiber of the present invention is different from the conventional one.

Claims (2)

  A dispersion of cellulose nanofibers obtained by refining a cellulose raw material, and a B-type viscosity (60 rpm, 20 ° C.) at a concentration of 1% (w / v) of the dispersion containing the cellulose nanofibers is 7000 mPa · A cellulose nanofiber dispersion characterized by being s or more.   The cellulose nanofibers were obtained by treating a cellulose raw material in water with an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide and a mixture thereof. The cellulose nanofiber dispersion liquid according to claim 1, wherein the cellulose nanofiber dispersion liquid is obtained by defibrating using oxidized cellulose.