KR20220143608A - Method of cellulose surface refinement using electrochemical reactions - Google Patents

Abstract

The present invention relates to a method for modifying the surface of cellulose, comprising the steps of: preparing a reaction solution by adding a 2,2,6,6-tetramethylpiperidinooxy radical (TEMPO) catalyst to a cellulose solution; and modifying the surface of cellulose by subjecting the reaction solution to an electrochemical reaction through cyclic voltammetry, wherein the electrochemical reaction is carried out by cyclically applying a voltage in the range of -0.4 to 1.2V. The method for modifying the surface, according to the present invention, may have an electrochemical oxidation reaction index of 1.5 mmol/g cellulose or more when measured using a conductivity titration method and is performed by an eco-friendly process.

Description

Method of cellulose surface refinement using electrochemical reactions

The present invention relates to a method for modifying a cellulose surface using an electrochemical reaction. An electrochemical surface oxidation process that can replace the NaClO-NaBr oxidation reaction system was developed by studying the surface modification (carboxylation) behavior according to the electrochemical reaction conditions such as electrolyte and electrode selection, voltage, and current.

Cellulose is contained in the cell wall of plants, extracorporeal secretions of microorganisms, the mantle membrane of sea squirts, etc., and is the most abundant polysaccharide on earth, has biodegradability, high crystallinity, excellent stability and safety, It is attracting attention as a material. Therefore, application development in various fields is expected.

Cellulose has a strong intramolecular hydrogen bond and high crystallinity, and therefore is almost insoluble in water and general solvents. Therefore, studies for improving solubility have been actively conducted. Among them, by using a TEMPO (2,2,6,6-tetramethylpiperidinooxy radical) catalyst system, only the primary hydroxyl group at the C6 position among the three hydroxyl groups of cellulose is oxidized, and is converted to a carboxyl group via an aldehyde group or a ketone group. The conversion method is attracting much attention in recent years because it can selectively oxidize only the primary hydroxyl, and it is possible to carry out the reaction under mild conditions such as water system or at room temperature. In addition, when TEMPO oxidation is performed using natural cellulose, only the nano-order crystal surface can be oxidized while maintaining the crystallinity of the cellulose. It is known that finely modified cellulose can be dispersed in water only by washing, dispersing in water, and applying a slight mechanical treatment. For example, in Unexamined-Japanese-Patent No. 2009-263652, invention regarding the method of manufacturing a fine cellulose by oxidizing a cellulose by a TEMPO oxidation reaction, and applying a mechanical treatment after that is described.

Japanese Laid-Open Patent Publication No. 2009-263652

An object of the present invention is to provide a cellulose surface modification method using an electrochemical reaction having a high surface modification rate of 1.5 mmol/g cellulose or more.

However, the problems to be solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

The present invention comprises the steps of preparing a reaction solution in which a 2,2,6,6-tetramethylpiperidinooxy radical (TEMPO) catalyst is added to a cellulose solution; and

Including; by performing an electrochemical reaction in the reaction solution through a cyclic voltammetry to modify the cellulose surface;

The electrochemical reaction will be carried out by cyclically applying a voltage in the range of -0.4 to 1.2V,

A method for modifying a cellulose surface is provided.

In one embodiment of the present invention, the cellulose solution may be characterized in that it contains 1 g/L to 5 g/L of cellulose.

In another embodiment of the present invention, the cellulose may be characterized in that the diameter is 20 to 50 um.

In another embodiment of the present invention, the electrochemical reaction may be characterized by using a carbonate buffer of 0.05 to 0.5 M as an electrolyte.

In another embodiment of the present invention, through the electrochemical reaction, the hydroxyl group (-OH) on the surface of the cellulose is carboxylated to a carboxyl group (-COOH). After the electrochemical reaction, the content of carboxyl groups per 1 g of cellulose (Carboxylate) Contents) may be characterized as 1.5 mmol/g or more.

In another embodiment of the present invention, the cyclic voltammetry is performed for more than 2000 cycles, and may be characterized in that the electrolyte is replenished in units of 1000 cycles.

In addition, the present invention, it is possible to provide a cellulose surface modified through the cellulose surface modification method according to the present invention.

When the electrochemical reaction is carried out by the surface modification method of the present invention, a cellulose surface carboxylation oxidation reaction having a Carboxylate Contents (hereinafter C.C) of 1.5 mmol/g Celluose or more can be performed. can provide

1 schematically shows the surface modification reaction of cellulose according to the conventional NaClO-NaBr oxidation reaction system.
2 is a view showing the electrochemical reaction system used in the present invention.
3 is a view showing a cyclic voltage conversion graph according to the first embodiment of FIG.
4 is a view showing a cyclic voltage conversion graph according to Examples 2 and 3;
5 is a view showing the shape of the reaction products of Examples 1, 2, and 3 after drying compared with the raw cellulose material.
6 is a view showing the results of the spectroscopic analysis of Examples 1, 2, and 3 compared with the raw cellulose.
7 is a view showing a cyclic voltage conversion graph according to the fourth embodiment.
8 is a view showing a cyclic voltage conversion graph according to Example 5;
9 is a view showing the results of the spectroscopic analysis of Example 5 compared to Example 1 and the raw cellulose material.
10 is a view showing a cyclic voltage conversion graph according to Example 6.
11 is a view showing the results of the spectroscopic analysis of Example 6 compared to Example 5 and the raw cellulose material.
12 shows the results of confirming the conductivity change according to the titration in the electrical conductivity titration method performed to measure the Carboxylate Contents.
13 is a view showing the result of confirming the value of the carboxylate contents of the cellulose oxidation reaction according to the present invention.
14 shows the results of confirming the content of carboxyl groups according to the cellulose particle size.

Terms used in the embodiments are selected as currently widely used general terms as possible while considering the functions in the present disclosure, which may vary depending on intentions or precedents of those of ordinary skill in the art, emergence of new technologies, and the like. In addition, in a specific case, there is a term arbitrarily selected by the applicant, and in this case, the meaning will be described in detail in the description of the corresponding invention. Therefore, the terms used in the present disclosure should be defined based on the meaning of the term and the contents of the present disclosure, rather than the simple name of the term.

In the entire specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated. Also, terms such as “… unit” described in the specification may mean a unit for processing at least one function or operation.

Hereinafter, with reference to the accompanying drawings, the embodiments of the present disclosure will be described in detail so that those of ordinary skill in the art to which the present disclosure pertains can easily implement them. However, the present disclosure may be implemented in several different forms and is not limited to the embodiments described herein.

1 is a schematic representation of the NaClO-NaBr oxidation reaction system used in the conventional cellulose surface modification. Cellulose surface modification using a TEMPO (2,2,6,6-tetramethylpiperidinooxy radical) catalyst system can be effectively excellent, but since an oxidizing agent containing chlorine is used in the reaction, the effect on the environment is low. there may be

Accordingly, the present inventors completed the present invention as a result of earnestly studying a method for modifying a cellulose surface by an electrochemical reaction mediated by TEMPO without the NaClO-NaBr oxidation reaction system.

In order to be commercialized through cellulose surface modification, the cellulose surface carboxylation oxidation reaction should be 1.5 mmol/g cellulose or more, the reaction time should be less than 6 hours, and the intermediate product -CHO (aldehyde) should be generated as little as possible. . Accordingly, the present invention provides a surface modification method that can satisfy the above conditions.

Accordingly, the present invention, preparing a reaction solution in which a 2,2,6,6-tetramethylpiperidinooxy radical (TEMPO) catalyst is added to a cellulose solution; and

Including; by performing an electrochemical reaction in the reaction solution through a cyclic voltammetry to modify the cellulose surface;

The electrochemical reaction will be carried out by cyclically applying a voltage in the range of -0.4 to 1.2V,

A method for modifying a cellulose surface may be provided.

The potential used for the electrochemical reaction is preferably in the range of -0.4 to 1.2 V as described above. If it exceeds 1.2 V, the efficiency of the electrochemical reaction may be affected by the oxidation reaction of the working electrode.

In the electrochemical reaction, a three-electrode system including a reference electrode, a counter electrode, and a working electrode may be used. There is no limitation on the materials of the reference electrode, the counter electrode, and the working electrode, but a working electrode is glassy carbon, a counter electrode is a platinum wire (Pt wire), and a reference electrode is used. Ag/AgCl electrodes can be used as In addition, 0.05 to 0.5 M carbonate buffer may be used as the electrolyte, and preferably 0.08 to 0.12 M carbonate buffer may be used.

In the present invention, the cyclic voltammetry is preferably performed for 2000 cycles or more. At 2000 cycles or more, stable current generation was confirmed, and in particular, since current reduction may occur due to electrolyte evaporation during an electrochemical reaction, it is preferable to replenish the electrolyte in units of 1000 cycles.

According to the present invention, the concentration of the TEMPO catalyst may be 20 to 60 mM, preferably 30 to 50 mM, and more preferably having a concentration of 35 to 45 mM as in the example of the present invention, redox The reaction can be made to occur efficiently.

In the present invention, the cellulose solution may contain 1 g/L to 5 g/L of cellulose. In an embodiment of the present invention, it was confirmed that surface carboxylation oxidation was more effectively progressed through an increase in cellulose content by using a cellulose solution having a cellulose concentration of 1 g/L or more, and in particular, 2 g/L to 3 g/L An optimal carboxylation oxidation reaction was found at a concentration of L (more preferably 2.5 g/L).

The cellulose preferably has a diameter of 20 to 50 um, and the cellulose reacts with a TEMPO catalyst, and when stirred at 50 to 100 rpm, an electrochemical reaction may occur smoothly.

In the present invention, through the electrochemical reaction, the hydroxyl group (-OH) on the surface of the cellulose is carboxylated to a carboxyl group (-COOH). According to the surface modification method of the present invention, the content of carboxylate groups per 1 g of cellulose after the electrochemical reaction (Carboxylate Contents) is characterized in that it appears as 1.5 mmol/g or more. More preferably, it may be 1.8 mmol/g or more.

In addition, the present invention can provide a cellulose, the surface of which is modified through the cellulose surface modification method.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, since various changes may be made to the embodiments, the scope of the patent application is not limited or limited by these embodiments. It should be understood that all modifications, equivalents and substitutes for the embodiments are included in the scope of the rights.

[Example]

<Example 1>

Cellulose was surface-modified by electrochemical reaction using three electrodes. For the reaction, an 8.5 mM TEMPO solution and 0.34 g of cellulose powder were prepared, and after dissolving the cellulose powder in distilled water, the TEMPO solution was added and stirred.

The electrochemical reaction system used in the present invention is shown in FIG. 2 . Glassy carbon was used as a working electrode, a Pt wire was used as a counter electrode, and an Ag/AgCl electrode was used as a reference electrode. As the electrolyte, 0.1 M carbonate buffer was used.

Power was applied to the three-electrode terminal configured as described above, and a graph of cyclic voltage conversion according to the number of cycles (1, 10, 100, 500, 1000, 2000, 3000) was checked and shown in FIG. 3 . In FIG. 3 , it can be seen that the oxidation reaction occurred because a current was generated in the voltage range of -0.3 V to 0.7 V. At 1000 cycles and 2000 cycles, a decrease in current due to electrolyte evaporation was confirmed, and the electrolyte was replenished every 1000 cycles in subsequent experiments. After the oxidation reaction was completed, it was dried in an oven at 40 °C.

<Example 2>

Based on the results of Example 1 and the results of existing papers (Cellulose volume 17, pages815-824 (2010)), the electrochemical reaction was performed under the same conditions as in Example 1, but the voltage range was -0.3 to 1 V. The experiment was carried out by extension. Accordingly, a graph of cyclic voltage conversion according to the number of cycles (50, 500, 1000, 2000, 3000, 4000, 5000, 6000) was confirmed and shown in FIG. 4 . In FIG. 4 , it can be seen that the oxidation reaction occurred due to the generation of a current in the voltage range of -0.3 V to 1 V. In Example 2, after the oxidation reaction was completed, it was dried in an oven at 40° C. as in Example 1.

<Example 3>

Based on the results of Example 1 and the results of the existing paper (Cellulose volume 17, pages815-824 (2010)), the electrochemical reaction was performed under the same conditions as in Example 1, but the voltage range was changed to -0.3 to 1 V. The experiment was carried out by extension. Accordingly, a graph of cyclic voltage conversion according to the number of cycles (50, 500, 1000, 2000, 3000, 4000, 5000, 6000) was confirmed and shown in FIG. 4 . In FIG. 4 , it can be seen that the oxidation reaction occurred due to the generation of a current in the voltage range of -0.3 V to 1 V. In Example 3, after the oxidation reaction was completed, it was dried in a vacuum oven at room temperature.

<Confirmation of reaction result of Example 1-3>

The cellulose solution in which the oxidation reaction has been completed in Examples 1 to 3 was dried (Examples 1 and 2: dried in an oven at 40 ° C., Example 3: dried in an oven at room temperature/vacuum oven) to confirm discoloration according to temperature, as shown in FIG. indicated.

As shown in FIG. 5 , in the case of the first experiment, the existing powder form was maintained, but in the case of the second and third tests, a form other than powder was confirmed.

The surface modification was confirmed through the spectroscopic analysis of the electrochemically-reacted cellulose of Example 1-3 and cellulose pristine. As shown in FIG. 6 , it was confirmed that O-H stretching peaks (3300-2500) and carbonyl (C=O) stretching peaks (1720-1706) of primary alcohol and carboxylic acid functional groups were present.

The peak of the primary alcohol of the cellulose raw material is lowered from Example 1 to Example 3, and the O-H stretching peak of the carboxylic acid functional group and the carbonyl C = O stretching peak appear. It can be seen that the carboxylation reaction has progressed on the surface.

<Example 4>

Through the results of Examples 1 to 3, the electrochemical reaction was performed under the same conditions as in Example 1, but the voltage range was extended to -0.4 to 1.3 V and the experiment was performed.

Accordingly, the cycle voltage conversion graph according to the number of cycles (50, 100, 500, 1000, 2000, 3000) was confirmed and shown in FIG. 7 .

As a result, it was confirmed that the oxidation process of glassy carbon occurred at 1.2 V. Therefore, it can be seen that the voltage range of the present invention should be set to 1.2V or less.

<Example 5>

In this Example 5, the electrochemical reaction was performed under the same conditions as in Example 1, but the amount of cellulose was increased to 0.5 g, the amount of TEMPO was changed to 25 mM, and the experiment was performed with a voltage range of -0.4 to 1V. proceeded.

Accordingly, the cycle voltage conversion graph according to the number of cycles (100, 500, 1000, 2000, 3000, 4000, 5000, 6000, 6800) was confirmed and shown in FIG. 8 .

As a result, it was confirmed that the oxidation process of glassy carbon occurred at 1.2 V. Therefore, it can be seen that the voltage range of the present invention should be set to 1.2V or less.

The spectroscopic analysis of the reaction product of Example 5 was performed, and the results of the spectroscopic analysis of Example 1 and the cellulose raw material were compared and shown in FIG. 9 .

As a result, since it was confirmed that the carbonyl C = O stretching peak of the carboxylic acid functional group grew in the product of Example 5, it can be seen that the carboxylation reaction proceeded more effectively by increasing the amounts of cellulose and TEMPO.

<Example 6>

In this Example 6, the electrochemical reaction was performed under the same conditions as in Example 1, but as in Example 5, the amount of cellulose was increased to 0.5 g, and the amount of TEMPO was changed to 40 mM. Again, the electrochemical reaction was carried out with a voltage range of -0.4 to 1.2 V.

Accordingly, the cycle voltage conversion graph according to the number of cycles (50, 100, 500, 1000, 2000, 3000) was confirmed and shown in FIG. 10 . It can be seen that the oxidation reaction proceeds stably.

The spectroscopic analysis of the reaction product of Example 6 was performed, and the results of the spectroscopic analysis of Example 5 and the cellulose raw material were compared and shown in FIG. 11 .

As a result, in the product of Example 6, the peak around 1400 cm -1 presumed to be primary alcohol was reduced, and it was confirmed that the carbonyl C = O stretching peak of the carboxylic acid functional group grew. Therefore, it can be seen that the carboxylation reaction proceeded more effectively by increasing the amount of TEMPO.

<Measurement of Carboxylate Contents>

For the reaction product prepared in Example 6, the degree of substitution of the amount of carboxylate was confirmed through the first, second and third steps.

At this time, for the analysis of the degree of substitution, the electric conductivity titration method (The Electric Conductivity Titration Method) was used.

First, 0.1 g of the dry reaction product of Example 6 and 100 mL of distilled water were mixed, sonicated (10 min), and all were dispersed and transparent. Then, 0.01M NaCl 5mL was added, and 0.1M HCl was added while stirring with a stirrer to lower the pH to 3. Then, using a syringe pump, 0.05M NaOH was injected at a rate of 0.2ml/min to proceed with titration (up to pH 11).

The change in conductivity according to titration was confirmed and shown in FIG. 12 . As shown in FIG. 12 , in the S1 section, the conductivity decreased as the pH increased, that is, it can be seen that NaOH is consumed by H+ ions rather than -COOH. In the S2 section, it can be seen that the conductivity is maintained by increasing the pH, and NaOH is consumed by -COOH. In the S3 section, as the pH increases, the conductivity increases, and it can be seen that NaOH is accumulated without being consumed. That is, in FIG. 13, the volume of NaOH used at the last point in time when NaOH is consumed by -COOH, V2, is subtracted from V1, which is the volume of NaOH used at the time when NaOH starts to be consumed by -COOH, consumed by -COOH. The amount of NaOH can be found.

That is, since the equivalents of NaOH and -COOH are the same (=1), the number of moles of -COOH was calculated as follows.

Number of moles of COOH (mmol/g) = (V ₂ -V ₁ )ml x 10L/ml x 0.05M ÷ 0.1g

The results measured by the above formula are shown in FIG. 13, and the Carboxylate Contents (hereinafter C.C.) was found to be 1.97 mmol on average per 1 g of cellulose.

<Electrochemical reaction according to cellulose powder particle size>

In this experiment, the electrochemical reaction was performed under the same conditions as in Example 1, but the effect on the electrochemical reaction according to the particle size of the cellulose powder was confirmed.

First, cellulose powder having a size of 20, 30, 40, 50, 60 and 70 um was prepared, and this was put in distilled water, TEMPO was added, and the electrochemical reaction was performed by stirring at 50-100 rpm.

The results are shown in FIG. 14, and it was confirmed that the particle size is 20-50 μm, and stirring at a speed of 50-100 rpm is preferable to facilitate the electrochemical reaction.

As described above, although the embodiments have been described with reference to the limited drawings, those skilled in the art may apply various technical modifications and variations based on the above. For example, the described techniques are performed in a different order than the described method, and/or the described components of the system, structure, apparatus, circuit, etc. are combined or combined in a different form than the described method, or other components Or substituted or substituted by equivalents may achieve an appropriate result.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (8)

preparing a reaction solution in which a 2,2,6,6-tetramethylpiperidinooxy radical (TEMPO) catalyst is added to a cellulose solution; and
Including; performing an electrochemical reaction in the reaction solution through a cyclic voltammetry to modify the cellulose surface;
The electrochemical reaction will be carried out by cyclically applying a voltage in the range of -0.4 to 1.2V,
Cellulose surface modification method.
According to claim 1,
The concentration of the TEMPO catalyst is characterized in that 20 to 60 mM, cellulose surface modification method.
According to claim 1,
The cellulose solution, characterized in that it contains 1 g / L to 5 g / L of cellulose, cellulose surface modification method.
According to claim 1,
The cellulose is characterized in that the diameter of 20 to 50 um, cellulose surface modification method.
According to claim 1,
The electrochemical reaction, characterized in that using a carbonate buffer of 0.05 to 0.5 M as an electrolyte, cellulose surface modification method.
According to claim 1,
Through the electrochemical reaction, the hydroxyl group (-OH) on the surface of the cellulose is carboxylated to a carboxyl group (-COOH),
After the electrochemical reaction, the content of carboxylate groups per 1 g of cellulose (Carboxylate Contents) is 1.5 mmol/g or more, cellulose surface modification method.
According to claim 1,
The cyclic voltammetry is performed for more than 2000 cycles,
A method for modifying a cellulose surface, characterized in that the electrolyte is replenished every 1000 cycles.
The surface is modified through the cellulose surface modification method of claim 1, cellulose.

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