KR101686551B1 - Method of preparing a nanocellulose - Google Patents

Abstract

A method for producing a nanocellulose of the present invention comprises the steps of: (a) mixing an alkali solution containing a urea compound and a hydroxide of a metal with a cellulose-based material; (b) irradiating radiation to produce a nanocellulose suspension; And (c) separating the nanocellulose from the suspension. The above-mentioned production method can reduce the production time and yield in a safe reaction condition as compared with the conventional production method, and irradiate with the radiation, so that the urea-based compound and the metal hydroxide can be used instead of the high- Cellulose can be produced, which is an economical and environmentally friendly process.

Description

[0001] METHOD OF PREPARING A NANOCELLULOSE [0002]

The present invention relates to a method for producing a nanocellulose from a cellulosic material using an alkaline solution which is easy to handle without using a high concentration of strong acid.

Nano-cellulose is an organic polymer material having excellent tensile strength and is an environmentally friendly regeneration resource since it is obtained from natural materials such as various kinds of wood and plant resources. The manufacturing cost of nanocellulose is recognized as being considerably high, and when considering from the viewpoint of yield and mass production, many research and development are required until the industrialization stage.

Furthermore, research to find optimal conditions for the production of nanocellulose according to the inherent characteristics of various natural materials should be accompanied. For this purpose, the acid hydrolysis treatment of cellulose is an essential step in the extraction of nanocellulose, and it is an object of acid hydrolysis of the amorphous region (amorphous region) of the cellulose structure to isolate crystalline regions having acid resistance as compared with the amorphous region .

At this time, the degree of crystallization, degree of polymerization and mechanical properties of nanocellulose differ depending on the concentration of acid used for acid hydrolysis, temperature and time.

Currently, a widely used method for producing nanocellulose is hydrolysis using a strong acid. In this method, amorphous region is removed by hydrolysis using strong acid in crystalline and amorphous cellulose, and it is aimed to isolate crystalline region having acid resistance compared with amorphous region. However, since it must be carried out under very extreme conditions such as using 65% sulfuric acid, there is a problem in commercialization. Therefore, there is a need for more convenient and more practical techniques for producing high value nanocellulose.

In the existing literature, there is hardly any report on the hydrolysis of amorphous cellulose in place of sulfuric acid or hydrochloric acid. Therefore, there is a need for a method of manufacturing nano-cellulose using a new technology capable of replacing sulfuric acid or hydrochloric acid.

1. Hanieh, K. et al., "Effects of hydrolysis conditions on the morphology, crystallinity, and thermal stability of cellulose nanocrystals extracted from kenaf bast fibers," Cellulose, Vol. 19, pp. 855-866 (2012). 2. Mark, D. et al., "Electron Beam Irradiation of Cellulose," Radiation Physics and Chemistry, Vol. 78, pp. 539-542 (2009).

An object of the present invention is to provide a method for producing nanocellulose from a cellulose-based material, which is capable of replacing a high-concentration aqueous solution of strong acid by irradiating with an alkali solution containing a urea-based compound and a hydroxide of a metal .

A method of manufacturing a nanocellulose according to an embodiment of the present invention includes the steps of: (a) mixing an alkali solution containing a urea compound and a metal hydroxide with a cellulose-based material; (b) irradiating radiation to produce a nanocellulose suspension; And (c) separating the nanocellulose from the suspension.

The urea compound may be a compound represented by the following formula (1).

[Chemical Formula 1]

Here, R ¹ and R ² are each independently selected from the group consisting of hydrogen, a methyl group, an ethyl group, and a combination thereof.

The urea-based compound may include carbamides.

The hydroxide of the metal may be a hydroxide of a metal selected from the group consisting of lithium, sodium, potassium, beryllium, magnesium, calcium, and combinations thereof.

The alkali solution may contain 1 to 3 equivalents of metal hydroxide based on the urea-based compound.

The cellulose-based material may be mixed in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the alkali solution.

(A ') before the step (a'), and the step (a ') may further include a step of treating the cellulosic material so that the content of cellulose contained in the cellulosic material is 90% can do.

The step (a) may further comprise irradiating (a ") the cellulose-based material with radiation, wherein the dose of radiation in step (a") may be 10 to 300 kGy.

The cellulosic material may comprise cellulosic biomass.

The cellulosic biomass may include any one selected from the group consisting of a fiber-based, wood-based, seaweed-based, and combinations thereof.

The cellulosic material may include any one selected from the group consisting of powders, pellets, sheets, and combinations thereof.

The step (b) may include a step of causing a decomposition reaction of the cellulose-based material by stirring the mixed solution by irradiating the mixed solution of step (a) with radiation.

In the step (b), the irradiation dose of irradiated radiation may be 50 to 300 kGy.

The radiation in step (b) may include any one selected from the group consisting of alpha rays, beta rays, gamma rays, electron beams, ion beams, ultraviolet rays, X-rays, plasma, neutron rays, and combinations thereof.

The step (b) may be carried out at a temperature of 60 to 100 ° C.

The separation in step (c) may be performed by a method including any one selected from the group consisting of filtration, centrifugation, precipitation, recrystallization, and combinations thereof.

The step (c) may comprise ultrasonic treatment.

The present invention provides a method for producing nanocellulose, and the present invention will be described in more detail below.

A method of manufacturing a nanocellulose according to an embodiment of the present invention includes the steps of: (a) mixing an alkali solution containing a urea compound and a metal hydroxide with a cellulose-based material; (b) irradiating radiation to produce a nanocellulose suspension; And (c) separating the nanocellulose from the suspension.

In the step (a), an alkaline solution and a cellulose-based material are mixed, and the alkali solution may include a urea-based compound and a hydroxide of a metal.

The urea compound includes a compound having two amine groups and one carbonyl group, and may be represented by the following general formula (1).

[Chemical Formula 1]

Here, R ¹ and R ² are each independently selected from the group consisting of hydrogen, a methyl group, an ethyl group, and a combination thereof.

The urea compound may be preferably used when R ¹ and R ² are both hydrogen, that is, when carbamide is applied. Carbamate is also called urea and is a compound used as a fertilizer. It is free of toxicity, does not show both acidic and basic properties, and can be economical since it is a very inexpensive substance.

The metal hydroxide may be a compound in which a hydroxyl group and a metal salt are ionically bonded to each other. For example, a metal containing any one selected from the group consisting of lithium, sodium, potassium, beryllium, magnesium, calcium, Lt; / RTI >

This can form a hydrate by reacting with the urea compound in a solution state, and in the case where the urea compound is carbamide, urea hydrate can be formed. The hydrate compound selectively lids only the crystalline region of the cellulose- Can play a role.

That is, the crystal region of the cellulose is swelled by the alkali solution, and a space can be formed between the layers, thereby stabilizing the crystalline region of the cellulose by the interaction between the hydrophobic portion of the urea baby and the hydrophobic portion of the cellulose It is a principle. That is, the urea-based hydrate compound generated in the alkali solution containing the urea compound and the metal hydroxide serves to help the metal hydroxide penetrate into the crystal region of the cellulose.

Due to the selective lapping of the crystal region, the possibility of extracting only the crystal region of the cellulose-based material can be provided without the use of an acid, Cellulose can be produced.

The alkali solution may contain about 1 to about 3 equivalents of a metal hydroxide based on the urea-based compound. If the amount of the metal hydroxide is less than 1 equivalent, the hydrate compound that wraps the crystal region of the cellulose-based material may be insufficient. If the amount of the metal hydroxide exceeds 3 equivalents, the solubility of the cellulose may increase during the irradiation, and the final yield may be significantly reduced .

The method for producing the nano-cellulose may further comprise: (a ') pre-treating the cellulose-based material before the step (a), wherein the step (a') comprises: To 90% or more, preferably 94 to 98%.

By performing the pretreatment for increasing the purity of the cellulose-based material in the step (a '), it is possible to improve the yield of finally separated nanocellulose, and it is possible to improve the yield of the finally separated nanocellulose, Can be saved.

(A ") between the steps (a ') and (a), wherein the dose of radiation in step (a") is in the range of 10 to 300 kGy . When radiation is irradiated before separating the nanocellulose from the cellulosic material, the energy of the radiation is directly transferred to the amorphous region of the cellulosic material to weaken the binding force between the cellulose and the final nanocellulose, Can be improved.

As the kind of radiation that can be irradiated at this time, for example, an alpha ray, a beta ray, a gamma ray, an electron ray, an ion beam, an ultraviolet ray, an X ray, a plasma, a neutron ray, or a combination thereof can be applied.

The cellulosic material refers to a material containing celluloses including both crystalline and amorphous regions, and may include cellulose-based biomass such as wood, pulp, and the like.

The cellulosic biomass may be a primary or secondary biomass, for example, a fibrous biomass, a woody biomass, a seaweed biomass, or a mixture thereof. If the material contains cellulose, Can be applied as a cellulose-based material.

The form of the cellulose-based material is not particularly limited, but may be powdery or pellet-shaped. When the cellulose-based material is in a powder form, the radiation irradiated due to the surface-increasing effect can be uniformly irradiated onto the whole of the cellulose-based material, thereby increasing the yield of finally separated nanocellulose. In the case of pellet type, And storage can be facilitated.

The step (b) may include a step of irradiating the mixed solution mixed in step (a) with a decomposition reaction between the amorphous region and the crystalline region of the cellulose-based material to remove the amorphous region.

The decomposition reaction is a reaction essentially performed in a method for chemically preparing nanocellulose. The reaction is performed by stirring an alkali solution containing a urea compound with a cellulose-based material, selectively lapping the crystal region of the cellulose with a urea-based hydrate compound, It may be a reaction that separates it from the amorphous region.

When the radiation is irradiated during the decomposition reaction, the crystalline region of the cellulose-based material contained in the mixed solution is wrapped with the hydrate compound, so that the amorphous region is not wrapped, and the energy possessed by the radiation is It can be decomposed at the same time as physical damage and separation from the crystalline region can be facilitated. That is, the effect of separating the crystalline region from the amorphous region can be obtained through a hydrolysis reaction using a strong acid.

Specifically, the radiation may be selectively irradiated to the amorphous region, and the irradiated radiation may physically damage the amorphous region of the cellulose, thereby weakening the glucosidic binding force between the cellulose chains in the amorphous region, Hydrogen bonding ability can be weakened. As a result, the time required for the hydrolysis reaction can be significantly shortened as compared with the case where the cellulose-based material is not irradiated with radiation, and the effect of replacing the aqueous solution of strong acid with the high concentration can also be obtained.

As the radiation, for example, an alpha ray, a beta ray, a gamma ray, an electron ray, an ion beam, an ultraviolet ray, an X ray, a plasma, a neutron ray, or a combination thereof may be applied. There is no particular limitation on the kind of the radiation to be irradiated, and it can be applied as long as the bonding force of the amorphous region of the cellulose is weakened by the irradiation of the radiation to increase the solubility to the acid.

The irradiation dose of the radiation may be 50 to 300 kGy, preferably 100 to 300 kGy, more preferably 150 to 200 kGy. If the dose of radiation is less than 50 kGy, the above-mentioned effects to be obtained by irradiation can not be obtained. If the irradiation dose exceeds 300 kGy, not only the amorphous region but also the crystalline region of cellulose are physically damaged And consequently, the crystal region may be subjected to physical damage, so that the yield of finally separated nanocellulose may be lowered.

The decomposition reaction may be carried out at a temperature of 60 to 100 DEG C, preferably 60 to 80 DEG C, which occurs in the course of irradiating the radiation. In the case of such a temperature range, it is possible to prevent vaporization of the mixture under reaction conditions with an alkali solution containing a urea compound and a metal hydroxide, and to supply at least energy required for the decomposition reaction.

The physical properties, particle size and yield of the nanocellulose prepared from the cellulose-based material can be determined according to the concentration of the alkali solution used in the decomposition reaction, the urea-based compound contained therein, the reaction temperature, or the radiation treatment time, It is possible to express the effect of strong acid by irradiating the decomposition reaction using the alkali solution containing the compound, thereby enabling the extraction of the nanocellulose from the cellulose and improving the yield, By using the method for producing nanocellulose of the present invention, which can control the particle size of cellulose, productivity can be improved and the process can be stabilized.

The decomposition reaction time of the step (b) may be less than 50 hours, preferably 15 hours or less, and may be adjusted according to the irradiation rate per hour when the radiation is irradiated. This can replace the hydrolysis reaction using a high concentration of strong acid by mixing an alkali solution containing a urea compound and a metal hydroxide with cellulose and irradiating the radiation at a constant irradiation amount for a predetermined period of time. In this case, it is possible to maximize the yield of nanocellulose by lowering the irradiation rate of radiation per hour and lengthening the time required to reach the final irradiation dose of radiation. However, the reaction time can be appropriately controlled according to the particle size of the finally produced nanocellulose.

Separation of the step (c) may be a step of separating the nanocellulose, that is, the cellulose composed only of the crystal region, the alkali solution and other substances, etc., from the suspension in which the hydrolysis reaction has been completed in the step (b) have.

As the separation method, for example, filtration, centrifugation, precipitation, recrystallization, or a combination thereof may be applied and may include ultrasonic treatment, and the ultrasonic treatment may be performed using an ultrasonic washing machine.

The final disintegrated nanocellulose may have a yield of 25 to 40%, preferably 30 to 40%. This is an improved numerical value as compared with that produced by the conventional method, and when an alkali and a urea solution are used while radiation is irradiated, it is also possible to replace the aqueous solution of strong acid with a high concentration.

The finally separated nanocellulose may have a particle size of 1500 nm or less, preferably 1000 nm or less, more preferably 200 nm or less. In addition, when the production method of the present invention is used, nanocellulose having a size of 200 nm or less can be produced only by controlling the dose of radiation in the pretreatment process. When the size is not required up to 200 nm, irradiation with hydrolysis It is possible to produce an appropriate size of nanocellulose.

The particle size range of the prepared nanocellulose is a range of particle sizes that can be obtained when a hydrolysis reaction is carried out for a long period of time or a hydrolysis reaction is performed using a considerably high concentration of an acid aqueous solution in the conventional method. And an alkali solution containing a metal hydroxide can be used to produce nano-cellulose having a desired particle size range only by irradiation with radiation without using a high concentration of strong acid, and the yield of nano-cellulose can also be improved.

The method for producing a nanocellulose of the present invention comprises laminating a crystalline region of a cellulose-based material by using an alkali solution containing a urea-based compound and a hydroxide of a metal and removing an amorphous region of the cellulose- Of the present invention can exhibit an improved yield over the yield that can be obtained by the method for producing nanocellulose. At the same time, the particle size of the nanocellulose can be controlled by adjusting the irradiation dose, and the stability, environmental friendliness, and economical efficiency of the manufacturing process can be ensured, and the nanocellulose can be effectively produced.

FIG. 1 is a graph showing the particle size distribution of nanocellulose by irradiation dose according to an embodiment of the present invention.
FIG. 2 is a graph showing the particle size distribution of nanocellulose according to an irradiation dose of radiation in pretreatment of a cellulosic material according to an embodiment of the present invention. FIG.
FIG. 3 is a graph showing the particle size distribution of nanocellulose by hydrolysis reaction time using strong acid according to the conventional method.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example  1: Using an alkali solution Of nanocellulose  Manufacturing 1

As a cellulose-based material, Avicel PH-101 from Aldrich, rice straw, kenaf core and wood extracted directly were used, and the content of cellulose contained in the cellulose-based material was 94 to 98%.

1) Preparation of mixture

Carbamide and lithium hydroxide were mixed in a molar ratio of 1: 1, and this was added to 50 ml of water to prepare an alkali solution. The alkali solution containing the urea compound and the metal hydroxide was ultrasonicated at 60 캜 for 30 minutes, and 5 g of the cellulose material was added thereto and mixed.

2) Investigation of radiation

The mixed solution was irradiated with a gamma ray using a gamma-ray accelerator apparatus with a radiation irradiation apparatus at the irradiation intensity of 10 kGy / h. Finally, the irradiated gamma rays were irradiated so that the irradiation amounts were 0, 50, 100 and 150 kGy, respectively. Thereafter, the reaction was stopped with cooled distilled water to obtain a nanocellulose suspension.

3) Nano-cellulose  Separation of suspension

The hydrolysis-completed nanocellulose suspension was centrifuged three times at 0 DEG C for 30 minutes in a centrifuge and washed to separate the alkali solution. Then, it was dispersed in an ultrasonic washing machine for 15 minutes and then dried in a freeze dryer for 12 hours to finally obtain nano-cellulose with a yield of 30 to 40%. The particle size distribution is shown in FIG.

Example  2: Using an alkali solution Of nanocellulose  Manufacturing 2

Cellulosic materials were pretreated with electron beams at 0, 50, 100, 200 and 300 kGy, respectively, except for the fact that the final dose of gamma rays was fixed at 150 kGy during the hydrolysis reaction. , Nano-cellulose was prepared in the same manner as in Example 1 to obtain nano-cellulose in the same yield as in Example 1, and its particle size distribution is shown in Fig.

Comparative Example  1: Using a high concentration of strong acid aqueous solution Of nanocellulose  Produce

Nano-cellulose was prepared in the same manner as in Example 1 except that the radiation was not irradiated and a 65% sulfuric acid aqueous solution was used in place of the alkaline solution. However, the hydrolysis reaction time was 30, 60, 90, and 120 minutes, and the particle size distribution of the nanocellulose obtained at a yield of about 20 to 25% is shown in FIG.

Referring to FIG. 1, it can be seen from the cellulose-based material that an alkali solution can be treated and irradiated with radiation to produce nanocrystalline having only a crystalline region, and thereby, by controlling the dose of radiation, It was confirmed that the particle size of the nanocellulose can be controlled.

Referring to FIG. 2, even when an alkali solution is used without using a strong acid, even if a gamma ray of 150 kGy is finally irradiated, a pretreatment condition for irradiating the cellulosic material with radiation is controlled, It can be confirmed that cellulose can be prepared. It can be confirmed that it is not much different from FIG. 3 which shows the result of producing nanocellulose using a high concentration of strong acid, and that the particle size distribution is superior to the case of using an alkali solution under mild conditions .

Thus, it was confirmed that, in the hydrolysis reaction using the existing strong acid by irradiating with the radiation, the high concentration of strong acid can be replaced by the alkali solution containing the urea compound and the yield of the produced nano cellulose can be improved.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, Of the right.

Claims (17)

(a) mixing an alkali solution containing a urea-based compound and a metal hydroxide with a cellulose-based material;
(b) irradiating with a radiation dose of 50 to 300 kGy to produce a suspension of nanocellulose; And
(c) separating the nanocellulose from the suspension,
The method of claim 1, further comprising the step of irradiating (a ") the cellulose-based material with radiation before step (a), wherein the dose of radiation in step (a") is 10 to 300 kGy,
The alkali solution contains 1 to 3 equivalents of a metal hydroxide based on the urea compound,
Wherein the cellulose-based material is mixed in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the alkali solution. The method according to claim 1,
Wherein the urea compound is a compound represented by the following formula (1): < EMI ID =
[Chemical Formula 1]

Here, R ¹ and R ² are each independently any one selected from the group consisting of hydrogen, a methyl group, and an ethyl group. 3. The method of claim 2,
Wherein the urea-based compound comprises carbamide. The method according to claim 1,
Wherein the hydroxide of the metal is a hydroxide of a metal selected from the group consisting of lithium, sodium, potassium, beryllium, magnesium, calcium, and combinations thereof. delete delete The method according to claim 1,
(A ') before the step (a'); and the step (a ') is a step of treating the cellulosic material so that the content of the cellulose contained in the cellulose-based material is 90% or more Lt; / RTI > delete The method according to claim 1,
Wherein the cellulosic material comprises a cellulosic biomass. 10. The method of claim 9,
Wherein the cellulosic biomass comprises any of cellulose selected from the group consisting of a fiber-based, wood-based, seaweed-based, and combinations thereof. The method according to claim 1,
Wherein the cellulose-based material comprises any one selected from the group consisting of powders, pellets, sheets, and combinations thereof. The method according to claim 1,
Wherein the step (b) comprises a step of causing a decomposition reaction of the cellulose-based material by stirring the mixed solution by irradiating the mixed solution of step (a) with radiation. delete The method according to claim 1,
Wherein the radiation of step (b) comprises any one selected from the group consisting of alpha rays, beta rays, gamma rays, electron beams, ion beams, ultraviolet rays, X-rays, plasma, neutron rays and combinations thereof. The method according to claim 1,
Wherein step (b) is carried out at a temperature of 60 to 100 < 0 > C. The method according to claim 1,
Wherein the separation in step (c) is performed by a method comprising any one selected from the group consisting of filtration, centrifugation, precipitation, recrystallization, and combinations thereof. The method according to claim 1,
Wherein said step (c) comprises ultrasonic treatment.

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