JP2011195659A - Method for producing oxidized cellulose - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxidized cellulose with high reproducibility of various physical properties by strictly controlling the introduction amount of carboxyl group in the oxidized cellulose, and to provide a method for producing the oxidized cellulose.SOLUTION: In the method for producing the oxidized cellulose in which a carboxyl group is introduced by oxidation reaction using a nitroxy radical derivative, an alkaline substance, an alkali bromide metal, and an oxidizing agent, the introduction amount of carboxyl group is adjusted by any one means of a means for controlling the additive amount of the alkaline substance to be added during the oxidation reaction, a means for controlling temperature during the oxidation reaction, or a means for controlling pH during the oxidation reaction. The dispersion of a set value for the introduction amount of carboxyl group is reduced to within ±5%.

Description

  The present invention relates to a method for producing oxidized cellulose using cellulose as a starting material.

  In recent years, against the background of global warming, environmental pollution, and waste problems due to depletion of resources and an increase in the concentration of carbon dioxide in the atmosphere, the amount of fossil resources used during production is low, and carbon dioxide can be processed with low energy during disposal. The use of environmentally friendly materials with low emissions is drawing attention. Under these circumstances, biodegradation typified by biomass resources that do not use fossil resources as raw materials, but partly or entirely use natural plants as raw materials, and polylactic acid that decomposes in the environment into water and carbon dioxide. Active use of functional materials is expected.

  Among biomass materials, cellulose, which accounts for about half of its production, is expected to be used effectively due to its large production. Furthermore, it has a high strength, a high elastic modulus, and an extremely low coefficient of thermal expansion, and in terms of heat resistance, it has no glass transition point and exhibits a high thermal decomposition temperature of 230 degrees.

  However, it cannot be said that cellulose is often used as a material for its large amount of production. One of the reasons is low solubility and dispersibility in aqueous and non-aqueous solvents. Cellulose is a homopolysaccharide in which D-glucopyranose, which is a 6-membered ring of glucose, is linked by β- (1 → 4) glucoside, and has hydroxyl groups at the C2, C3 and C6 positions. Therefore, a strong hydrogen bond is formed in and between the molecules and does not dissolve in water or general solvents.

  One of the most common uses of cellulose is carboxymethylation. Carboxymethylated cellulose fibers in which carboxyl groups are randomly introduced into hydroxyl groups at the C2, C3, and C6 positions, are water-soluble and can be used as thickeners depending on the degree of substitution, and are insoluble at low degrees of substitution. And various materials can be obtained. However, in the carboxymethylation reaction of cellulose, a large amount of organic solvent is used and toxic monochloroacetic acid is used, which causes problems such as environmental pollution and waste liquid treatment. In addition, since the introduced carboxyl group has no distinction in the position of the hydroxyl group, the product has a non-uniform chemical structure.

  When cellulose is treated using an oxidation reaction catalyzed by 2,2,6,6-tetramethyl-1-piperidinyloxy radical (hereinafter referred to as TEMPO), the C6-position present on the microfibril surface of crystalline cellulose. A hydroxyl group is selectively oxidized and a carboxyl group is introduced via an aldehyde group. By applying shear to this in water or an aqueous solvent, the cellulose is fibrillated to the microfibril level and dispersed into nanofibers having a width of several nanometers to several hundred nanometers. In this TEMPO oxidation reaction, an organic solvent is not used, and the environmental adaptability of the reaction process is extremely high, for example, the reaction is completed in a short time under mild conditions of normal temperature and normal pressure. Since cellulose can be used as a nano-dispersion or a liquid state, and the burden on the environment is low, treatment by TEMPO oxidation reaction and oxides are expected as new forms of utilization of cellulose. In addition, since it has a carboxyl group, it can be used as a foothold for a material that can be variously modified and highly functionalized. It is attracting attention as a material for biomass resources as an alternative to petroleum, transparent display fields, health care (functional foods, skin care), regenerative medical materials, and secondary battery components (catalyst carriers, separation membranes).

  TEMPO oxidized cellulose has various unique properties. First, it exhibits a unique metal ion adsorption capacity and higher water absorption. All of these strongly depend on the amount of carboxyl groups in the oxidized cellulose. In other words, the carboxyl group introduced into the microfibril surface in water exhibits the properties of a weak acid and is ionized to become an anion. As a result, the surface area is increased by the repulsive force between anions, leading to improved accessibility of metal ions and an increase in water retention volume.

  Further, when TEMPO-oxidized cellulose is mechanically treated in an aqueous solvent, a cellulose nanofiber dispersion having thixotropy can be obtained. The liquidity such as viscosity and light transmittance is derived from oxidized cellulose dispersed as microfibrils in a dispersion medium. Oxidized cellulose obtained by the TEMPO oxidation reaction is mechanically treated because the carboxyl groups generated on the surface of the microfibrils are repelled as anions in the dispersion medium and show an osmotic effect, thus weakening the hydrogen bonds between the microfibrils. Thus, it can be obtained as a microfibril isolated in nano order. At this time, the liquidity is determined by the aspect ratio, fiber diameter, degree of swelling, etc. of the dispersed microfibrils.

  In addition, when the pH is adjusted by adding an alkali to the dispersion medium, the degree of ionization of the carboxyl group changes, so the dispersibility when the same energy is applied is different. When the introduction amount of the carboxyl group is different, the addition amount of alkali is changed or the pH range to be adjusted is shifted, and it becomes difficult to control the degree of dispersion. Further, coating on a substrate using a dispersion liquid and utilization as a barrier layer have been studied. However, the wettability to the substrate and the barrier property are different depending on the amount of carboxyl groups. Alternatively, the refined cellulose obtained by mechanical treatment is different in particle size, fiber length, fiber diameter, etc. when used as a dispersion, for example when used as an additive to add physical strength to a synthetic resin, etc. The strength is also different.

  From the above, it is extremely important to strictly control the amount of carboxyl groups introduced into the microfibril surface in order to control the properties of oxidized cellulose or microfibril dispersion obtained by TEMPO oxidation, or refined cellulose. Become.

JP 2009-197122 A

  However, few studies have been made on oxidized cellulose in which the amount of carboxyl groups introduced in the TEMPO oxidation reaction is strictly controlled and on the production method thereof. For example, Patent Document 1 describes application as an additive for adding physical strength by adding refined oxidized cellulose to a synthetic resin or the like. However, although there are references to the preparation method and refinement method of oxidized cellulose, and the shape of the product, there is a wide range of control over the physical properties in the preparation of oxidized cellulose, and there is a reference to a method of obtaining a homogeneous product with good reproducibility. Absent.

  The present invention has been made in consideration of the background art as described above. It is an object of the present invention to provide a product that promotes industrial use of natural resources and strictly controls physical properties, and a method for producing the same. In particular, it is an object to provide an oxidized cellulose having a high reproducibility of various physical properties and a method for producing the same by strictly controlling the amount of carboxyl groups introduced in the oxidized cellulose.

  As means for solving the above problems, the invention according to claim 1 is characterized in that a carboxyl group is introduced by an oxidation reaction using at least a nitroxy radical derivative, an alkali substance, an alkali metal bromide, and an oxidizing agent. Further, in the oxidized cellulose, the variation of the introduction amount of the carboxyl group with respect to the set value is within ± 5%.

  The invention according to claim 2 is the oxidized cellulose according to claim 1, wherein the set value is selected from a range of 0.6 mmol / g or more and 2.4 mmol / g or less.

  The invention according to claim 3 is the method for producing oxidized cellulose in which a carboxyl group is introduced by an oxidation reaction using at least a nitroxy radical derivative, an alkaline substance, an alkali metal bromide, and an oxidizing agent. The introduction amount of the carboxyl group is at least one of a means for controlling the addition amount of the alkaline substance added during the oxidation reaction, a means for controlling the temperature during the oxidation reaction, and a means for controlling the pH during the oxidation reaction. It is the manufacturing method of the oxidized cellulose characterized by adjusting with a means.

  The invention according to claim 4 is the method for producing oxidized cellulose according to claim 3, wherein the cellulose is natural cellulose or derivatized cellulose.

  The invention according to claim 5 is the method for producing oxidized cellulose according to claim 3 or 4, wherein the temperature is controlled to 0 ° C. or more and 70 ° C. or less.

  The invention according to claim 6 controls the temperature of the oxidized cellulose according to any one of claims 3 to 5, wherein the temperature is controlled within ± 1 ° C. from the reaction preparation step to the end of the reaction. It is a manufacturing method.

  The invention according to claim 7 controls the pH of the oxidized cellulose according to any one of claims 3 to 6 by controlling the pH to ± 0.1 from the start of the reaction to the end of the reaction. It is a manufacturing method.

  ADVANTAGE OF THE INVENTION According to this invention, the industrial use of a natural resource can be promoted, and the product and its manufacturing method which controlled the physical property precisely can be provided. According to this method, it is possible to strictly control the amount of carboxyl groups introduced into cellulose, and obtain a dispersion or dispersion using oxidized cellulose or oxidized cellulose having high reproducibility of various physical properties.

  Hereinafter, an embodiment of the present invention will be described.

  The cellulose used in the present invention is preferably natural cellulose or derivatized cellulose. Specifically, bleached and unbleached kraft wood pulp, pre-hydrolyzed kraft wood pulp, sulfite wood pulp, and mixtures thereof can be used as starting materials, and any of these physically and chemically treated substances can be used. May be used. Further, similarly to cellulose, the present invention can also be applied to similar processing methods such as a method for preparing a nanofibrous material using crystalline chitin.

  The method of treating cellulose using an oxidation reaction catalyzed by a nitroxy radical derivative and selectively introducing a carboxyl group at the C6 position is as follows. First, cellulose as a starting material is dispersed in water, and the nitroxy radical derivative and Add alkali metal bromide and stir. The oxidant is then added. Thereafter, an oxidation reaction is performed while adding an alkaline substance, and after several hours, the oxidant is deactivated to terminate the reaction.

  Examples of the alkali metal bromide used in the oxidation reaction using a nitroxy radical derivative as a catalyst include alkali metal bromide salts such as sodium bromide.

  Oxidizing agents used in oxidation reactions catalyzed by nitroxy radical derivatives include halogens such as bromine, chlorine and iodine, hypohalous acids, halous acids and perhalogen acids, or salts thereof, halogen oxides, nitrogen Any oxidizing agent can be used as long as it can promote the target oxidation reaction, such as oxides and peroxides, but sodium hypochlorite is more preferable.

  As the nitroxy radical derivative used for the oxidation reaction, 2,2,6,6-tetramethyl-1-piperidinyloxy radical (TEMPO) is desirable. In addition, 4-acetamido TEMPO, 4-carboxy TEMPO, 4-phosphonooxy TEMPO and the like which are derivatives of TEMPO can be used.

  In order to adjust the amount of carboxyl group introduced when the cellulose is treated using an oxidation reaction catalyzed by a nitroxy radical derivative and a carboxyl group is selectively introduced at the C6 position, an alkali added during the oxidation reaction is used. It is preferable to adjust using a means for controlling the amount of substance added, a means for controlling the temperature during the oxidation reaction, or a means for controlling the pH during the oxidation reaction. In particular, since the introduction amount of the carboxyl group and the addition amount of the alkaline substance have a strict correlation, the introduction amount of the carboxyl group can be easily reduced by using a means for controlling the addition amount of the alkaline substance added during the oxidation reaction. Can be adjusted.

Examples of the means for controlling the amount of the alkaline substance added during the oxidation reaction of the present invention include a means for adding an alkaline substance while monitoring the consumption of the alkaline substance during the oxidation reaction. For example, when the amount of the remaining alkaline substance in the reaction system is changed from 1.1 × 10 ⁻⁴ mol / l to 9.9 × 10 ⁻⁵ mol / l, a new alkaline substance is added to 0.1 × 10 ⁻⁴ mol / l. Add / l. This operation is repeated, and the reaction is stopped when the total amount of the added alkali substance becomes 2.7 mmol / g with respect to the weight of the cellulose to obtain oxidized cellulose having 1.57 mmol / g carboxyl group introduced. . Alternatively, the amount of alkaline substance can be determined using an empirical formula based on a plurality of experiments.

  Specific examples of the means for controlling the temperature during the oxidation reaction of the present invention include a means for adjusting the temperature of the reaction system from the outside, and known temperature adjusting means such as a water bath and an oil bath.

  Here, the temperature during the oxidation reaction of the present invention is preferably controlled to 0 ° C. or higher and 70 ° C. or lower. By setting it within this range, it is possible to simultaneously control the variation in the amount of carboxyl groups introduced and the molecular weight of oxidized cellulose.

  Furthermore, it is preferable to control the temperature within ± 1 ° C. from the reaction preparation step to the end of the reaction. Here, the reaction preparation step is a step of adding a nitroxy radical derivative and an alkali metal bromide, and the completion of the reaction means a time point at which the reaction is stopped by deactivating the oxidizing agent. Cellulose promotes β-elimination where the glycosidic bond is cleaved by heat under alkaline conditions, and therefore the rate of molecular weight reduction varies depending on the reaction temperature in an oxidation reaction with a nitroxy radical derivative having an optimum pH around pH 10. Therefore, the reproducibility of the physical properties of the product can be improved by controlling within ± 1 ° C. from the reaction preparation step to the end of the reaction.

  Specific examples of means for controlling the pH during the oxidation reaction of the present invention include means for controlling the pH during the oxidation reaction by adding an alkaline substance. Examples of the alkaline substance include known alkaline substances such as alkali metals and alkaline earth hydroxides, and sodium hydroxide is preferred as the alkaline substance of the present invention.

  Here, regarding the pH during the oxidation reaction, it is preferable to control the pH fluctuation from the start of the reaction to the end of the reaction to ± 0.1. Thereby, it is suppressed that sodium hydroxide is consumed by a side reaction, and not only the amount of carboxyl groups introduced but also the introduction distribution in cellulose can be controlled. Thereby, the reproducibility of the physical property of a product can be improved.

  The means for controlling the amount of the alkaline substance added during the oxidation reaction of the present invention, the means for controlling the temperature during the oxidation reaction, or the means for controlling the pH during the oxidation reaction may be used independently, You may use it in combination. In particular, by using a means to control the amount of alkali substance added, and further using a means to control temperature or a means to control pH, the amount of carboxyl groups introduced and variations in the amount introduced can be controlled. can do.

  Examples of other means include means for controlling the type and crystallinity of cellulose used as an oxidation raw material. As mentioned above, the type of raw material cellulose is from the large chestnuts of cotton, conifers and broadleaf trees, individual tree species, isolation and purification methods such as pulping, shapes such as powders, fibers, sheets, etc. And so on. Further, controlling the crystallinity of the raw material cellulose varies depending on the type of the raw material, but for example, it may be controlled by a method of treating them with an alkaline aqueous solution such as sodium hydroxide. Specifically, the softness kraft pulp after being immersed in a 15% aqueous sodium hydroxide solution by mass for 1 hour has a lower crystallinity than the pulp before immersion.

  In the oxidized cellulose of the present invention, the variation of the introduction amount of the carboxyl group with respect to the set value can be controlled within ± 5%. Here, the setting value of the introduction amount of the carboxyl group is a value determined according to the physical properties of the target oxidized cellulose, and the setting value of the introduction amount of the carboxyl group is 0.6 mmol / g or more. It is selected from the range of 4 mmol / g or less.

  As a process of oxidation by the nitroxy radical derivative, the hydroxyl group of cellulose is first oxidized to produce aldehyde groups, which are gradually oxidized to carboxyl groups. The reaction rate is not uniform and the initial reaction is remarkably fast, so that it is difficult to control the carboxyl group to a range smaller than 0.6 mmol / g. Moreover, when it is in a range larger than 2.4 mmol / g, oxidation proceeds not only to the microfibril surface but also to the inside of the crystal, and the reaction becomes random, so that control becomes difficult. In the oxidized cellulose of the present invention, in particular, in the set value of the introduction amount of carboxyl groups in the above range, the variation with respect to the set value is within ± 5%. As described above, the oxidized cellulose of the present invention has a variation of ± 5% or less with respect to the set value of the introduction amount of the carboxyl group, so that the physical properties of the oxidized cellulose of the present invention and the dispersion using the same can be easily controlled. Therefore, physical properties such as a laminate using the oxidized cellulose of the present invention and physical properties such as barrier properties can be easily controlled.

  As for the method for controlling the variation of the introduced amount of carboxyl groups with respect to the set value of the oxidized cellulose within ± 5%, means for controlling the amount of the alkaline substance added during the oxidation reaction described above, This can be achieved by using a means for controlling the temperature or a means for controlling the pH during the oxidation reaction.

  Examples of the present invention will be described below. The following examples are examples of the present invention, and the present invention is not limited to these examples.

<Example 1>
The TEMPO oxidation reaction of cellulose was performed by the following procedure.

(1) Reagents / Materials Cellulose: Bleached Kraft Pulp (Fletcher Challenge Canada “Machenzie”)
TEMPO: Commercial product (Tokyo Chemical Industry Co., Ltd., 98%)
Sodium hypochlorite: Commercial product (Wako Pure Chemical Industries, Ltd., Cl: 5%)
Sodium bromide: Commercial product (Wako Pure Chemical Industries, Ltd.)

(2) TEMPO Oxidation Reaction of Cellulose Bleached kraft pulp having a dry weight of 10 g was allowed to stand overnight in 500 ml of ion-exchanged water in a 2 L glass beaker to swell the pulp. The temperature was adjusted to 20.0 ° C. with a water bath with temperature control, 0.1 g of TEMPO and 1 g of sodium bromide were added and stirred to obtain a pulp suspension. Further, 5 mmol / g sodium hypochlorite per cellulose weight was added with stirring. At this time, about 1N sodium hydroxide aqueous solution was added to maintain the pH of the pulp suspension at about 10.5. Thereafter, the reaction was performed while monitoring the amount of sodium hydroxide added, and the pulp was sufficiently washed with ion-exchanged water.

<Examples 2 and 3>
Oxidized cellulose was produced in the same manner as in Example 1. The reaction temperature was set to 20 ° C. as in Example 1, the reaction was stopped when the same amount of sodium hydroxide as in Example 1 was added, and the sample was sufficiently washed with water to prepare a sample.

<Comparative Examples 1-3>
Oxidized cellulose was produced in the same manner as in Example 1. The amount of sodium hydroxide added was not monitored, the reaction was stopped within a reaction time of 1 to 6 hours, and the sample was sufficiently washed with water.

[Evaluation]
About the oxidized cellulose obtained in Examples 1-3 and Comparative Examples 1-3, the carboxyl group amount measurement and molecular weight measurement were performed as follows.

[Amount of carboxyl group]
About the obtained oxidized cellulose, the amount of carboxyl groups contained was calculated by the following method. 0.2 g of dry weight conversion of chemically treated cellulose is taken in a beaker, and 80 ml of ion exchange water is added. Thereto was added 5 ml of 0.01 M sodium chloride aqueous solution, and 0.1 M hydrochloric acid was added while stirring to adjust the whole to pH 2.8. Here, 0.1M sodium hydroxide aqueous solution was injected at 0.05 ml / 30 seconds using an automatic titrator (Toa DKK Co., Ltd., AUT-701), and the conductivity and pH value were measured every 30 seconds. The measurement was continued until pH 11. From the obtained conductivity curve, the titration amount of sodium hydroxide was determined, and the carboxyl group content was calculated.

[Molecular weight]
About the obtained oxidized cellulose, molecular weight was derived | led-out from intrinsic viscosity. First, the following operation was performed as pretreatment. Ion-exchanged water was added to a dry weight of 2 g of oxidized cellulose so as to form a suspension with a solid content of 10%, and 1.81 g of sodium chlorite and 20 ml of 5M acetic acid were added. This was reacted for 48 hours at room temperature with stirring, and washed thoroughly with water to oxidize the aldehyde group produced by the oxidation reaction. This is sufficiently dried, and a solution is prepared in a 0.5 M copper ethylenediamine solution so as to be 2 mg / ml of cellulose. The intrinsic viscosity was determined by measuring the outflow rate of the solution with a Canon-Fenske viscometer, and the method derived from the viscosity equation was used.

  Table 1 shows the results of carboxyl group amount measurement and molecular weight measurement for the oxidized cellulose obtained in Examples 1 to 3 and Comparative Examples 1 to 3.

  As shown in Table 1, the oxidized celluloses of Examples 1 to 3 controlled the amount of sodium hydroxide aqueous solution added during the oxidation reaction, so that the variation in the amount of carboxyl groups introduced could be suppressed to within ± 5%. On the other hand, in the oxidized celluloses of Comparative Examples 1 to 3, since the amount of sodium hydroxide aqueous solution was not added during the oxidation reaction, the variation in the amount of carboxyl groups introduced could not be suppressed within ± 5%. Furthermore, the molecular weights of the oxidized celluloses of Examples 1 to 3 were less varied than the molecular weights of the oxidized celluloses of Comparative Examples 1 to 3, and the molecular weight could be controlled with high accuracy.

Claims (7)

  In the oxidized cellulose in which carboxyl groups are introduced by an oxidation reaction using at least a nitroxy radical derivative, an alkali substance, an alkali metal bromide, and an oxidizing agent, variation of the introduction amount of the carboxyl groups with respect to a set value is ± 5%. Oxidized cellulose characterized by being within.   2. The oxidized cellulose according to claim 1, wherein the set value is selected from a range of 0.6 mmol / g or more and 2.4 mmol / g or less.   In the method for producing oxidized cellulose in which a carboxyl group is introduced by an oxidation reaction using at least a nitroxy radical derivative, an alkali substance, an alkali metal bromide, and an oxidizing agent, the amount of the carboxyl group introduced during the oxidation reaction Oxidized cellulose characterized by adjusting by at least one of means for controlling the amount of alkali substance added, means for controlling temperature during oxidation reaction, or means for controlling pH during oxidation reaction Manufacturing method.   The method for producing oxidized cellulose according to claim 3, wherein the cellulose is natural cellulose or derivatized cellulose.   The said temperature is controlled to 0 degreeC or more and 70 degrees C or less, The manufacturing method of the oxidized cellulose of Claim 3 or 4 characterized by the above-mentioned.   The method for producing oxidized cellulose according to any one of claims 3 to 5, wherein the temperature is controlled within ± 1 ° C from the reaction preparation step to the end of the reaction.   The method for producing oxidized cellulose according to any one of claims 3 to 6, wherein the pH is controlled to ± 0.1 from the start of the reaction to the end of the reaction.