JP2009209218A - Method for producing functional cellulose bead, and the functional cellulose bead - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing functional cellulose beads suppressing the reduction of strength. <P>SOLUTION: This method for producing the functional cellulose beads is characterized by immersing the cellulose beads in a neutral or an acid reaction solution containing an N-oxyl compound and an oxidizing agent for oxidizing an aldehyde group and oxidizing the cellulose in the reaction solution. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing functional cellulose beads and functional cellulose beads.

  Cellulose, which is biomass that exists naturally in large quantities, is used in various fields, taking advantage of its safety and strength. For example, cellulose beads formed into a granular form of cellulose are widely used as carriers for immobilizing enzymes, functional substances and the like because they can form a porous body with a large surface area (see, for example, Patent Documents 1 and 2). In addition, by introducing an anion group or a cation group into a cellulose bead through an ether bond, it is also used for separation and purification of enzymes as a chromatographic agent for cation exchange or anion exchange chromatography, respectively (for example, Non-Patent Document 1). reference).

In addition, the cellulose itself is chemically modified to add a new function. As a typical example, it is known to introduce a carboxyl group chemically using a hydroxyl group of cellulose as a contact point.
For example, the treatment methods described in Patent Documents 4 and 5 oxidize the primary hydroxyl group of β-glucose to a carboxyl group using sodium hypochlorite as the main oxidizing agent. According to this treatment method, no toxic or deleterious substances are used, such as partial carboxymethylation using alkali and monochloroacetic acid or carboxylation by adding N ₂ O ₄ in chloroform. Can be introduced.
JP 2007-54739 A JP-A-6-206801 JP-A-10-251302 JP 2001-49591 A Hiroaki Ishibashi `` Encyclopedia of Cellulose '' edited by Cellulose Society, Asakura Shoten, p.539-545 (2000).

  In the conventional treatment method, an aqueous solution of alkali-treated cellulose or regenerated cellulose containing a catalytic amount of NaBr and TEMPO is added with an aqueous solution of sodium hypochlorite (NaClO) as a main oxidant (a TEMPO catalytic oxidation reaction). ). In this treatment method, the pH drops due to the formation of carboxyl groups during the reaction, so a dilute aqueous sodium hydroxide solution (usually about 0.5M NaOH) is always added to maintain the pH of the reaction system at 8-11. .

FIGS. 6 and 7 show the mechanism of oxidizing primary hydroxyl group of cellulose to carboxyl group through aldehyde group by adding sodium bromite as the main oxidant and adding catalytic amount of sodium bromide (NaBr) and TEMPO. . When the above method is applied to regenerated cellulose or mercerized cellulose (cellulose swelled with 5% or more NaOH aqueous solution and then washed with water), all the primary hydroxyl groups at the C6 position of the cellulose are all selectively aldehydes. By oxidizing to a carboxyl group via a group, water-soluble cellouronic acid is obtained. In addition, when applied to natural cellulose, only the primary hydroxyl group at the C6 position located on the surface of cellulose microfibrils can be selectively oxidized to a carboxyl group or an aldehyde group while maintaining the crystal structure of cellulose. In addition, a modified cellulose in which the hydroxyl group at the C6 position is substituted with a sodium salt of a carboxyl group can be obtained.
Therefore, if this treatment method is applied to the treatment of cellulose beads, functional cellulose beads having ion exchange properties in which a metal salt of a carboxyl group is introduced on the surface can be obtained.

  However, as a result of investigations by the present inventors, problems in the conventional treatment method and the modified cellulose obtained thereby have also been clarified. Hereinafter, this problem will be described in detail.

(1) First, when the conventional TEMPO oxidation method is applied to cellulose beads, the cellulose beads swell and the strength is remarkably reduced regardless of how the oxidation conditions are controlled. It turns out that the properties cannot be imparted. As a cause of this, since the pH of the conventional TEMPO oxidation reaction is weakly alkaline, a β-elimination reaction occurs due to an aldehyde group at the C6 position generated as an intermediate, and the degree of polymerization is significantly reduced to about 40. It is done.
Then, this invention makes it one of the objectives to provide the manufacturing method of the functional cellulose bead which can provide functionality, suppressing the fall of intensity | strength.

(2) Moreover, in the conventional TEMPO oxidation method, it is necessary to always make the pH of the reaction solution constant during the TEMPO catalytic oxidation reaction. For this purpose, a pH meter must be installed in the reaction solution, and an open-type reaction system in which a dilute aqueous NaOH solution is continuously added must be constructed. Since the reaction vessel cannot be sealed, treatment of gas generated by the reaction and reaction efficiency This is also disadvantageous.
Accordingly, an object of the present invention is to provide a method for producing functional cellulose beads that facilitates pH control by improving the reaction system and enables the reaction vessel to be sealed.

  In order to solve the above problems, the method for producing functional cellulose beads of the present invention includes immersing cellulose beads in a neutral or acidic reaction solution containing an N-oxyl compound and an oxidizing agent that oxidizes an aldehyde group, The surface of the cellulose beads is oxidized in a reaction solution.

  In the production method of the present invention, since the cellulose bead surface is oxidized using an oxidizing agent that oxidizes an aldehyde group in the presence of an N-oxyl compound, the hydroxyl group at the C6-position of cellulose located on the surface is reduced to a carboxyl group. It can be oxidized and can prevent the formation of an aldehyde group at the C6 position. Thereby, the metal salt of a carboxyl group can be efficiently introduced into the cellulose surface, and functional cellulose beads having ion exchange ability can be easily produced.

Here, in the conventional treatment method, since TEMPO catalytic oxidation is performed under weakly alkaline conditions of pH 8 to 11, an aldehyde group (CHO group) is generated as an intermediate at the C6 position as shown in the center of FIG. This aldehyde group undergoes a beta elimination reaction very easily under conditions of pH 8-11. As a result, as shown on the right side of FIG. 8, it is considered that the molecular chain of cellulose is cut, and the molecular weight of cellulose is remarkably lowered.
In contrast, the production method of the present invention can prevent the formation of aldehyde groups as described above, and even if aldehyde groups exist for a short time, the pH of the reaction solution is neutral or acidic. The beta elimination reaction that occurs in weak alkali to strong alkalinity does not occur. Therefore, according to the present invention, breakage of the cellulose molecular chain due to the reaction of the aldehyde group can be prevented, and functional cellulose beads can be produced while suppressing a decrease in strength.

It is preferable to add a buffer to the reaction solution. By setting it as such a method, it becomes unnecessary to add an acid and an alkali for pH maintenance, and a pH meter becomes unnecessary. Therefore, the reaction vessel can be sealed in the production method according to the present invention.
And if a reaction container is sealed, heating and pressurization with respect to a reaction system are possible. Further, since the gas generated from the reaction solution is not released out of the system, the production method is excellent in terms of safety. Further, since the gas generated by the decomposition of the oxidant is not released to the atmosphere, there is an advantage that the amount of the oxidant used can be reduced.

As the oxidizing agent, halous acid or a salt thereof can be used. Further, as the oxidizing agent, a mixture of hydrogen peroxide and oxidase or peracid can be used.
By using these oxidizing agents, the primary hydroxyl group can be oxidized to a carboxyl group, and the formation of the C6-position aldehyde group can be effectively prevented.

  The pH of the reaction solution is preferably 4 or more and 7 or less. By setting it as such a range, an oxidizing agent can be made to act on a cellulose efficiently and the modification | denaturation of a cellulose can be implemented efficiently in a short time.

  It is preferable to add hypohalous acid or a salt thereof to the reaction solution. By setting it as such a manufacturing method, reaction rate can be improved remarkably and processing efficiency can be improved significantly.

  The N-oxyl compound is preferably 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO). Moreover, in the manufacturing method which concerns on this invention, process efficiency can be improved by using 4-acetamido TEMPO as an N-oxyl compound.

Next, the functional cellulose bead of the present invention is characterized in that at least a part of the C6 hydroxyl group of cellulose located on the surface is substituted only with a metal salt of a carboxyl group.
The functional cellulose bead according to the present invention is a cellulose bead having excellent strength obtained by the production method of the present invention described above, and a functional group having an ion exchange ability by introducing a metal salt of a carboxyl group on the surface thereof. Cellulose beads.
In this invention, it is preferable that content of a carboxyl group is 0.05 mmol / g or more and 5 mmol / g or less. By setting it as such a range, it becomes a functional cellulose bead which has favorable ion exchange ability.

According to the method for producing functional cellulose beads of the present invention, at least a part of primary hydroxyl groups of cellulose is substituted only with a metal salt of a carboxyl group to obtain functional cellulose beads having ion exchange ability and excellent strength. Can do.
According to the functional cellulose beads of the present invention, the metal salt of the carboxyl group introduced on the cellulose surface exhibits an ion exchange ability, and the molecular weight reduction during the modification treatment is suppressed, and an excellent strength can be obtained. is there.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Method for producing functional cellulose beads)
The method for producing functional cellulose beads according to the present invention acts on cellulose beads by using an oxidizing agent that oxidizes an aldehyde group using an N-oxyl compound as an oxidation catalyst under conditions where the reaction solution is neutral or acidic. This is a method for oxidizing the cellulose beads.

  A conventionally well-known cellulose bead can be used for the cellulose bead as a raw material in the manufacturing method which concerns on this invention. Natural cellulose obtained by removing and refining impurities such as lignin from plant resources can be dissolved in a solvent, and regenerated cellulose obtained by granulation or cellulose fiber can be granulated. Although the said cellulose bead is preferable that it is a porous body from the general use, the cellulose bead which is not a porous body can also be used as a raw material in the manufacturing method which concerns on this invention without a problem.

  In the step of oxidizing cellulose beads, water is typically used as a dispersion medium for cellulose beads in the reaction solution. The concentration of the cellulose beads in the reaction solution is not particularly limited as long as the reagent (oxidant, catalyst, etc.) can be sufficiently dissolved. Usually, the concentration is preferably about 5% or less with respect to the weight of the reaction solution.

An N-oxyl compound is used as a catalyst added to the reaction solution. As the N-oxyl compound, TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) and a TEMPO derivative having various functional groups at the C4 position can be used. In particular, TEMPO and 4-acetamido TEMPO have obtained favorable results in the reaction rate.
A catalytic amount is sufficient for the addition of the N-oxyl compound. Specifically, it may be added in a range of 0.1 to 4 mmol / l with respect to the reaction solution. Preferably, it is the addition amount range of 0.1-2 mmol / l.

  As the oxidizing agent, an oxidizing agent capable of oxidizing an aldehyde group generated by oxidation of a hydroxyl group is used. Examples of such an oxidizing agent include halous acid or a salt thereof (such as sodium chlorite), a mixture of hydrogen peroxide and oxidase (laccase), peracid, and the like. In addition, as peracid, various things, such as persulfuric acid (potassium hydrogen persulfate etc.), peracetic acid, perbenzoic acid, can be used. The content of the oxidizing agent is preferably in the range of 1 to 50 mmol / l.

By using an oxidizing agent that can oxidize an aldehyde group to a carboxyl group in this way, generation of an aldehyde group at the C6 position can be prevented.
FIG. 1 is a diagram showing a carboxyl group generation mechanism in the present invention. As shown in FIG. 1, in the oxidation reaction using an N-oxyl compound as a catalyst, the primary hydroxyl group of the glucose component may be selectively oxidized to produce an intermediate containing an aldehyde group. However, in the present invention, since an oxidizing agent that oxidizes an aldehyde group is included, the aldehyde group of this intermediate is quickly oxidized and converted to a carboxyl group. Thereby, the cellulose bead which does not contain an aldehyde group can be obtained.

In addition, it is preferable to add hypohalous acid or a salt thereof on the premise that the above-described oxidizing agent is used as the main oxidizing agent. For example, the reaction rate can be greatly improved by adding a small amount of sodium hypochlorite.
FIG. 2 is a diagram showing a reaction mechanism in the case of containing sodium hypochlorite. As shown in FIG. 2, sodium hypochlorite added to the reaction solution functions as an oxidizing agent for TEMPO, and the oxidized TEMPO oxidizes the primary hydroxyl group at the C6 position of cellulose and aldehyde group at the C6 position. Is generated. And the produced | generated aldehyde group is rapidly oxidized to a carboxyl group by the sodium chlorite which is a main oxidizing agent. Further, during the oxidation of the aldehyde group, sodium chlorite changes to sodium hypochlorite. Furthermore, the produced sodium hypochlorite is supplemented as an oxidizing agent for TEMPO.
Thus, by adding sodium hypochlorite to the reaction solution, the oxidation reaction of TEMPO can be promoted and the reaction rate can be increased.

  If the amount of hypohalite added is too large, these function as the main oxidizing agent, so that the molecular weight of cellulose is reduced, and there is a possibility that functional cellulose beads having a desired strength cannot be obtained. . Therefore, the amount of hypohalite added is preferably about 1 mmol / l or less.

  In the present invention, the pH of the reaction solution is maintained in a neutral to acidic range. More specifically, a pH range of 4 to 7 is preferable. In particular, care should be taken that the pH of the reaction solution does not exceed 8. This is to prevent a beta elimination reaction due to an aldehyde group temporarily generated at the C6 position of cellulose.

Furthermore, it is preferable to add a buffer to the reaction solution. As the buffer solution, various buffer solutions such as a phosphate buffer solution, an acetate buffer solution, a citrate buffer solution, a borate buffer solution, a tartaric acid buffer solution, and a Tris buffer solution can be used.
By suppressing the pH change during the reaction using a buffer solution, it is not necessary to continuously add acid or alkali to maintain the pH, and it is not necessary to install a pH meter. And since addition of an acid or an alkali is unnecessary, a reaction container can be sealed.

Here, Fig.3 (a) is a figure which shows an example of the apparatus for enforcing the manufacturing method of this invention. FIG.3 (b) is a figure which shows the apparatus for implementing the conventional processing method.
As shown in FIG. 3 (a), in the production method of the present invention, a reaction vessel 110 contains a reaction solution 110 containing raw materials (cellulose beads), a catalyst, an oxidizing agent, a buffer solution, and the like. The reaction vessel 100 is sealed. Moreover, the reaction vessel 100 can be heated using a heating device such as the hot tub 120, and the reaction temperature can be increased. In some cases, the reaction vessel 100 may be provided with a pressurizing device that pressurizes the inside.

  On the other hand, in the conventional processing method shown in FIG. 3B, the upper portion of the reaction vessel 200 containing the reaction solution 210 is opened, and the pH electrode 251 of the pH adjusting device 250 provided side by side through this opening. In addition, a nozzle 252 for supplying a diluted NaOH solution for pH adjustment is installed in the reaction solution 210. As described above, in the conventional processing method, the reaction vessel 210 has to be made into an oven type, so that a part of chlorine gas generated by the decomposition of sodium hypochlorite as a co-oxidant is released into the atmosphere. If it does so, the apparatus which processes the emitted chlorine gas will be needed, and the loss of an oxidizing agent will have to add sodium hypochlorite more than necessary.

  As described above, in the production method according to the present invention, the reaction vessel 100 can be sealed, so that the temperature of the reaction solution 110 can be raised to increase the reaction efficiency. Therefore, according to the present invention, functional cellulose beads can be produced efficiently and in a short time. On the other hand, it is possible to raise the temperature of the reaction solution 210 by the conventional treatment method, but the amount of chlorine gas released increases, which is not preferable in terms of exhaust gas treatment and the amount of oxidant used.

(Functional cellulose beads)
Next, the functional cellulose beads obtained by the production method of the present invention described above are cellulose beads having a cation ion exchange function by a metal salt of a carboxyl group introduced on the surface thereof (see the right figure in FIG. 1). . This functional cellulose bead can be suitably used, for example, as an ion exchanger for ion exchange chromatography. Moreover, since the carboxyl group is introduce | transduced on the surface, it has hydrophilicity and can be used suitably also as a moisturizer and the raw material of cosmetics.

  The functional cellulose bead according to the present invention can be specified as a functional cellulose bead in which at least a part of the C6 hydroxyl group of cellulose located on the surface is substituted only with a metal salt of a carboxyl group. Alternatively, it can be specified as functional cellulose beads in which at least a part of the C6 hydroxyl group of cellulose located on the surface is substituted with a metal salt of a carboxyl group and the aldehyde group content is less than 0.05 mmol / g. .

  That is, on the surface of the functional cellulose beads, it can be considered that there is no or no aldehyde group at the C6 position. In the conventional treatment method, in the TEMPO catalytic oxidation, both a carboxyl group and an aldehyde group are always generated. Therefore, the functional cellulose bead of the present invention can be specified as clearly different from the cellulose bead obtained by the conventional processing method due to the above characteristics.

In addition, the case where it can be regarded that there is no aldehyde group corresponds to the content of the aldehyde group being less than 0.05 mmol / g. By setting it as such a range, the fall of the polymerization degree resulting from an aldehyde group is suppressed, and a desired modification | reformation effect can be acquired.
The amount of the aldehyde group is more preferably 0.01 mmol / g or less, and still more preferably 0.001 mmol / g or less. Since the detection limit of aldehyde groups in currently known measurement methods is about 0.001 mmol / g, a desirable mode is functional cellulose beads in which aldehyde groups are not detected even when measurement is performed.

  In the functional cellulose beads according to the present invention, the carboxyl group content is preferably 0.05 mmol / g to 5 mmol / g, more preferably 0.05 mmol / g to 2 mmol / g. Furthermore, it is desirable that it is 0.05 mmol / g-1 mmol / g. By setting it as such a range, functionality can be provided, maintaining the intensity | strength of a cellulose bead.

In addition, the functional cellulose beads of the present invention do not contain an aldehyde group at the C6 position, and thus are less likely to be denatured by heating. That is, when the cellulose beads are processed by a conventional processing method, the cellulose beads are colored when heated to a high temperature. However, in the functional cellulose beads according to the present invention, such coloring does not occur. It can be suitably used for the intended use.
In addition, it is thought that coloring arises in the cellulose bead obtained by the conventional processing method for the following reasons. Aldehyde groups generated on the surface of oxidized cellulose obtained by a conventional treatment method are 0.5 mmol / g or less (usually 0.3 mmol / g or less) and a small amount compared to carboxyl groups, It also remains on the surface. Therefore, it is considered that coloring occurs due to a reaction similar to caramelization in a reducing sugar having an aldehyde group.

  Hereinafter, the method for producing functional cellulose beads according to the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following examples.

Commercially available cellulose beads for analysis were dispersed in 0.1 M acetic acid aqueous solution adjusted to pH 4.8.
To a dispersion in an Erlenmeyer flask, 0.096 g (0.45 mmol) of 4-acetamido-TEMPO, 0.83 ml (1 mmol) of a 9% solution of sodium hypochlorite, and commercially available 80% sodium chlorite were added. 1.70 g (15 mmol) was added to prepare a reaction solution. Thereafter, the Erlenmeyer flask was sealed and stirred with a magnetic stirrer while maintaining the temperature at 60 ° C.
Next, the above reaction solution was poured into a solution of ethanol: water = 3: 1, and beads in the reaction solution were filtered or centrifuged and washed with a washing solution of ethanol: water = 3: 1. Subsequently, the obtained solid content was dried to obtain functional cellulose beads obtained by TEMPO oxidation of the cellulose beads.

  FIG. 4 is a photograph of the functional cellulose beads obtained. As is apparent from FIG. 4, the bead shape is substantially maintained even when the modification treatment according to the present invention is performed. From this, it is estimated that the strength reduction due to the reforming treatment has not occurred.

Moreover, the carboxyl group amount of the functional cellulose beads was also measured. The amount of the carboxyl group can be measured by the following method.
First, 60 ml of a 0.5 to 1% by weight slurry was prepared from a cellulonic acid sample that was precisely weighed in dry weight, adjusted to a pH of about 2.5 with a 0.1 M hydrochloric acid aqueous solution, and then 0.05 M sodium hydroxide. The aqueous solution is dropped and the electrical conductivity is measured. The measurement is continued until the pH is 11. Then, the amount of functional groups is determined from the amount of sodium hydroxide (V) consumed in the neutralization step of the weak acid where the change in electrical conductivity is gradual, using the following equation. This amount of functional groups is the amount of carboxyl groups.
Functional group amount (mmol / g) = V (ml) × 0.05 / mass of cellulose (g)

  FIG. 5 is a graph showing the measurement results of the amount of carboxyl groups. As shown in FIG. 5, in the functional cellulose beads obtained by the production method according to the present invention, the amount of carboxyl groups is clearly increased as compared with untreated ones. From this, a metal salt of a carboxyl group is introduced on the surface of the functional cellulose bead according to the present invention, and exhibits a cation ion exchange ability by the action of the metal salt.

  The amount of aldehyde groups can also be measured from the same formula as above. The cellulose sample subjected to the measurement of the carboxyl group amount is oxidized at room temperature for another 48 hours in a 2% aqueous sodium chlorite solution adjusted to pH 4 to 5 with acetic acid, and the functional group amount is measured again by the above method. An amount obtained by subtracting the amount of the carboxyl group from the measured amount of the functional group is the amount of the aldehyde group.

The figure which shows the production | generation mechanism of the carboxyl group in the manufacturing method which concerns on this invention The figure which shows the oxidation mechanism of the cellulose in the manufacturing method which concerns on this invention The figure which shows the apparatus used with the manufacturing method which concerns on this invention, and the conventional processing method Photo of functional cellulose beads according to examples Measurement result of carboxyl group amount according to Example The figure which shows the oxidation mechanism of the cellulose in the conventional processing method The figure which shows the oxidation mechanism of the cellulose in the conventional processing method Diagram explaining molecular chain scission by beta elimination reaction

Explanation of symbols

  100 reaction vessel, 101 cap, 110 reaction solution, 120 heating device

Claims (5)

  A functional cellulose characterized by immersing cellulose beads in a neutral or acidic reaction solution containing an N-oxyl compound and an oxidizing agent that oxidizes an aldehyde group, and oxidizing the surface of the cellulose beads in the reaction solution. A method for producing beads.   The method for producing functional cellulose beads according to claim 1, wherein a buffer solution is added to the reaction solution.   The method for producing functional cellulose beads according to claim 1 or 2, wherein halous acid or a salt thereof is used as the oxidizing agent.   The N-oxyl compound is 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO) or 4-acetamido-TEMPO. 2. A method for producing a functional cellulose bead according to item 1.   A functional cellulose bead characterized in that at least a part of the C6 hydroxyl group of cellulose located on the surface is substituted only with a metal salt of a carboxyl group.

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