KR101725078B1 - Method of preparing a nanocellulose - Google Patents

Abstract

(A) preparing a suspension of nanocellulose by mixing an aqueous solution of a weak acid having a pKa of less than 4 to 7, a metal salt and a cellulose-based material; And (b) separating the nanocellulose from the suspension. The above-mentioned manufacturing method is an economical and environment-friendly process by using a weak acid and a metal salt which can shorten the manufacturing time and improve the yield and can replace the strong acid, compared with the conventional production method.

Description

[0001] METHOD OF PREPARING A NANOCELLULOSE [0002]

The present invention relates to a method for producing a nanocellulose from a cellulose-based material using a metal salt and a weak acid instead of using a 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 the crystalline region 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, the amorphous region is removed by hydrolysis using strong acid in crystalline and amorphous cellulose, and it is aimed to isolate the crystalline region having acid resistance compared with the 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 have been few reports of weak acids for hydrolyzing cellulose in the amorphous region instead of sulfuric acid or hydrochloric acid. Therefore, there is a need for a method for producing nanocellulose using a weak acid which can replace 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).

It is an object of the present invention to provide a method for producing nano-cellulose from a cellulose-based material by using a weak acid together with a metal salt without using a strong acid, This is to provide a method.

A method for producing a nanocellulose according to an embodiment of the present invention includes the steps of: (a) preparing a nanocellulose suspension by mixing an aqueous solution of a weak acid having a pKa of less than 4 to 7, a metal salt, and a cellulose-based material; And (b) separating the nanocellulose from the suspension.

Wherein said step (a) comprises the steps of: preparing a mixed solution comprising an aqueous solution of a weak acid having a pKa of less than 4 to 7, a metal salt and a cellulose-based material; And subjecting the mixture to a hydrolysis reaction by stirring to produce a nanocellulose suspension.

The weak acid may include any one selected from the group consisting of alkylcarboxylic acid, arylcarboxylic acid, benzylcarboxylic acid, and combinations thereof, and the alkyl group may have 1 to 5 carbon atoms.

The weak acid may include any one selected from the group consisting of acetic acid, propionic acid, butanoic acid, and combinations thereof.

The aqueous solution of the weak acid may have a weak acid concentration of 60% or more.

The metal salt may be any one selected from the group consisting of a chloride, a sulfide, a nitride, and a combination of any one metal selected from the group consisting of alkali metals, alkaline earth metals, transition metals, and combinations thereof.

The metal salt may be mixed with 1 to 5 moles based on 1 mole of weak acid.

The cellulose-based material may be mixed in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of an aqueous solution of a weak acid.

The step (a) may be carried out at a temperature of 30 to 150 ° C.

(A ') before the step (a'), wherein the step (a ') is a step of treating the cellulosic material in such a manner that the content of cellulose contained in the cellulose-based material is 90% have.

The step (a) may further comprise irradiating the cellulose-based material with (a ") radiation.

In the step (a "), the irradiation dose of the irradiated radiation may be 10 to 300 kGy.

The step (a ") may be that the solubility of the amorphous region of the cellulose contained in the cellulose-based material to the acid is increased by irradiation of radiation.

The radiation of step (a ") may comprise any one selected from the group consisting of alpha, beta, gamma, electron, ion beam, ultraviolet, X-ray, plasma, neutron beam and combinations thereof.

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

The step (b) may comprise ultrasonic treatment.

The separated nanocellulose may have a particle size of 200 nm or less, and the yield of the nanocellulose may be 25 to 40%.

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

A method for producing a nanocellulose according to an embodiment of the present invention includes the steps of: (a) preparing a nanocellulose suspension by mixing an aqueous solution of a weak acid having a pKa of less than 4 to 7, a metal salt, and a cellulose-based material; And (b) separating the nanocellulose from the suspension.

Wherein said step (a) comprises: preparing a mixture comprising an aqueous solution of a weak acid having a pKa of less than 4 to less than 7, a metal salt and a cellulosic material; And a step of hydrolyzing the mixture by stirring to prepare a nanocellulose suspension.

The weak acid contained in the aqueous solution of the weak acid may be any acid as long as it has a pKa of less than 4 and less than 7 and is an acid containing a carboxyl group. Examples thereof include alkylcarboxylic acid, arylcarboxylic acid, benzylcarboxylic acid, May be applied, wherein the alkyl group may have 1 to 5 carbon atoms. However, when an alkylcarboxylic acid such as acetic acid, propionic acid, or butanoic acid is used, it may be easily supplied and handled and may be preferable for an acid hydrolysis reaction.

In addition, in the step (a), the metal salt can be mixed together. By using the metal salt, as shown in FIG. 1, the metal salt is coordinated with the oxygen of the carbonyl group present in the weak acid, The effect of lowering the acidity (pKa) so as to approach the strong acid of the weak acid can be obtained.

That is, in the production of nanocellulose by a chemical method, an acid hydrolysis reaction necessarily follows, and the acid used at this time is a strong acid, for example, sulfuric acid, hydrochloric acid, nitric acid and the like. However, strong acids are highly reactive, there is a considerable risk in handling, and environmental pollution caused by wastewater is also serious. However, in the method of producing nanocellulose according to the present invention, since the metal salt to be added together can serve to lower the acidity of the weak acid through interaction with the weak acid, a weak acid such as acetic acid can be used for the acid hydrolysis reaction , It can solve most problems existing in existing methods.

The metal salt may be any one selected from the group consisting of halides, sulfides, nitrides and combinations of any one metal selected from the group consisting of alkali metals, alkaline earth metals, transition metals, and combinations thereof. , An alkali metal halide, an alkali metal sulfide, an alkali metal nitride, an alkaline earth metal halide, an alkaline earth metal sulfide, an alkaline earth metal nitride, a transition metal halide, a transition metal sulfide, a transition metal nitride or a combination thereof.

Specifically, the alkali metal may be lithium, sodium, potassium, rubidium, cesium, and the like. The alkaline earth metal may be beryllium, magnesium, calcium, strontium, barium, And the noble metal or rare earth metal is not limited to the application, but may be excluded from the cost-effective application.

The aqueous solution of the weak acid to be mixed in the step (a) may be one in which the weak acid is diluted in the aqueous solution, and the higher the concentration, the more desirable it is, and preferably at least 60%, preferably 80% or more.

The acid hydrolysis reaction time in step (a) may be less than 240 minutes, preferably 180 minutes or less, preferably 60 minutes or less, and the yield may not be reduced even if the reaction time is shortened. The reaction time can be appropriately adjusted according to the particle size of the finally prepared nanocellulose.

When the aqueous solution of a weak acid having a pKa of less than 4 to 7 in the step (a), the metal salt and the cellulose-based material are mixed, the metal salt may be mixed with 1 to 5 moles based on 1 mole of the weak acid, The material may be mixed in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the aqueous solution of the weak acid.

If less than 1 mole of the metal salt is used based on 1 mole of an aqueous solution of a weak acid, the metal salt capable of interacting with the weak acid molecule in the aqueous solution is insufficient and the effect exhibited by the strong acid in the acid hydrolysis reaction may not be obtained If it is used in excess of 5 moles, an incidental reaction may occur or a consumable metal salt may be used.

If the amount of the cellulose-based material is less than 0.1 part by weight based on 100 parts by weight of the aqueous solution of the weak acid, it may be an excessive use of the acid, and excessive acid may cause corrosion of the device or damage to the finally separated nanocellulose And the yield of nanocellulose may be lowered. If the amount exceeds 20 parts by weight, the acid necessary for the hydrolysis reaction may be insufficient and the reaction may not be completed. As a result, the yield of nanocellulose may be lowered and the properties of the finally isolated nanocellulose may be poor.

The hydrolysis reaction may be a reaction of adding an acid to selectively decompose an amorphous region of cellulose to separate it from a crystal region, and the reaction may be performed at a temperature of 30 to 150 ° C, preferably 50 to 120 ° C. In such a temperature range, vaporization of the mixture during the acid hydrolysis reaction can be prevented, and at least energy necessary for the hydrolysis reaction can be supplied.

The physical properties, particle size and yield of the nanocellulose prepared from the cellulose-based material can be determined according to the strength, concentration, reaction temperature, or treatment time of the acid used in the acid hydrolysis reaction, and therefore an aqueous solution of a weak acid Using the process for producing nano-cellulose of the present invention which enables the acid hydrolysis reaction of cellulose by developing strong acid effect and maintains and improves the yield, it is possible to improve the productivity of nanocellulose having excellent physical properties and particle size .

The method of manufacturing the nanocellulose may further include a step of pre-treating the cellulose-based material (a ') 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.

The step (a) may further comprise the step of irradiating the cellulosic material (a) with radiation before the step (a), wherein the step (a ") comprises irradiating the cellulosic material with a radiation Lt; / RTI >

The step (a ") can be applied irrespective of the order of step (a '). That is, the raw material can be irradiated directly with radiation before the pretreatment of the cellulose-based material, and after the pretreatment of the cellulose- Cellulosic materials may also be irradiated directly.

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.

When the cellulose-based material is irradiated with radiation, the solubility of the amorphous region of the cellulose in the acid in the acid can be increased. 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 bond between the cellulose chains of the amorphous region to increase the solubility in acid . As a result, the time required for the hydrolysis reaction can be significantly shortened and can be shortened by about 16 times as compared with the case where the cellulose-based material is not irradiated with radiation.

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.

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 dose of the radiation may be 10 to 300 kGy, preferably 10 to 200 kGy, more preferably 50 to 200 kGy. If the dose of radiation is less than 10 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 Which may increase the solubility of the crystal region in the acid, and thus the yield of finally separated nanocellulose may be lowered.

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

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 may be an improved numerical value as compared with that prepared by the conventional method, and it is also possible to obtain a time-saving effect in a case where an aqueous solution of weak acid is used in addition to irradiation with radiation.

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, nano-cellulose having a size of 200 nm or less can be produced with a reaction time of 180 minutes or less if irradiated with radiation, and when a size of 200 nm is not required, Even if invested, it is possible to produce nano-cellulose of an appropriate size.

The particle size range of the nanocellulose prepared 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 long time hydrolysis reaction is performed using a considerably high concentration of an acid aqueous solution in the conventional method. , Nanocellulose having a desired particle size range can be produced within a short time by using an aqueous solution of a weak acid, irradiation with radiation, or both, and the yield of nanocellulose can also be improved.

The method of producing nanocellulose of the present invention can exhibit an improved yield over a yield that can be obtained in the conventional method of producing nanocellulose by expressing the effect of strong acid by using an aqueous solution of a metal salt and a weak acid, The manufacturing time can be greatly shortened and the stability of the manufacturing process, the environment friendliness and the economical efficiency can be guaranteed, which can be a very effective method of producing nano-cellulose.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing the interaction of a weak acid aqueous solution and a metal salt according to an embodiment of the present invention; FIG.
FIG. 2 is a graph showing the particle size distribution of nanocellulose prepared using an aqueous solution of a weak acid and a metal salt according to an embodiment of the present invention.
FIG. 3 is a graph showing the particle size distribution of nanocellulose prepared by irradiating an aqueous solution of a weak acid and a metal salt according to an embodiment of the present invention.

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 aqueous solution of a metal salt and a weak acid Of nanocellulose  Produce

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

1) Acid hydrolysis reaction

50 ml of an aqueous solution of a weak acid having a concentration of 98% of acetic acid and 98% of water mixed therein was heated to 118 DEG C, and 2 g of lithium chloride (LiCl) was mixed with 10 g of the cellulose-based material and 1 mol of acetic acid, The hydrolysis reaction was allowed to proceed, and then the reaction was stopped with cooled distilled water to obtain a suspension of nanocellulose.

2) Nano-cellulose  Separation of suspension

The hydrolysis-completed nanocellulose suspension was centrifuged at 0 DEG C for 30 minutes in a centrifuge, and then the acid was separated for 3 days using a cellulose acetate dialysis membrane. Then, the mixture was dispersed in an ultrasonic washing machine for 15 minutes and then dried in a freeze dryer for 48 hours to finally obtain nanocellulose in a yield of 30 to 40%.

The hydrolysis reaction of 1) above was carried out for 1 hour, 12 hours, 24 hours and 48 hours, respectively. The suspension was separated into 2) processes, and the particle size distribution of each nanocellulose was shown in FIG.

Referring to FIG. 2, it was confirmed that nanocellulose having a size of about 200 nm or less was finally produced even though only weak acid and metal salt were used without using strong acid. On the other hand, when metal salt was not used, Even if the hydrolysis reaction proceeds, nanocellulose having a size of 3000 nm or less could not be produced.

Thus, it has been confirmed that the use of metal salts can replace the conventional hydrolysis reaction using strong acids by using weak acids and metal salts.

Example  2: Using irradiation of radiation Of nanocellulose  Produce

The cellulosic material of Example 1 was irradiated with an electron beam at an irradiation intensity of 25 kGy / scan using a linear electron beam accelerator device (ELV-8-type electron beam accelerator from EBtech) as the irradiation device. Ultimately, the irradiated electron beams were irradiated so that the irradiation amounts were 0, 50, 100, and 200 kGy, respectively.

The nanocellulose was produced at a yield of 30 to 40% under the same conditions and conditions as those of Example 1 (hydrolysis reaction time: 3 hours) except that the radiation was irradiated as described above. The particle size distribution of the nanocellulose was shown in FIG.

Referring to FIG. 3, it can be seen that the particle size distribution of the nanocellulose prepared according to the dose of radiation can be confirmed, and it is possible to control the particle size of the nanocellulose prepared by controlling the irradiation amount, In order to prepare nanocellulose having a size of less than 1 nm, the hydrolysis reaction was required for about 48 hours in the absence of irradiation, but the reaction time was shortened to about 3 hours or less in the case of irradiation.

As a result, it was confirmed that the irradiation time of the nanocellulose was reduced by about 16 times, and at the same time, the particle size range was also superior to the case where the radiation was not irradiated. That is, it was confirmed that the desired particle size distribution of the nanocellulose can be obtained by increasing the irradiation dose of the radiation or by increasing the hydrolysis reaction time.

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 (21)

(a) hydrolyzing the cellulose-based biomass by mixing an aqueous solution of a weak acid having a pKa of 4 to 7, a metal salt and a cellulosic biomass;
(b) mixing the aqueous solution of the weak acid with distilled water to stop the hydrolysis and producing a suspension of nanocellulose; And
(c) separating the nanocellulose from the suspension. delete The method according to claim 1,
The weak acid includes any one selected from the group consisting of an alkylcarboxylic acid, an arylcarboxylic acid, a benzylcarboxylic acid, and a combination thereof,
Wherein said alkyl has 1 to 5 carbon atoms. The method according to claim 1,
Wherein the weak acid comprises any one selected from the group consisting of acetic acid, propionic acid, butanoic acid, and combinations thereof. The method according to claim 1,
Wherein the weak acid aqueous solution has a concentration of weak acid of 60% or more based on the mass of the aqueous solution. The method according to claim 1,
Wherein the metal salt is any one selected from the group consisting of a chloride, a sulfide, a nitride, and a combination of any one metal selected from the group consisting of an alkali metal, an alkaline earth metal, a transition metal, and combinations thereof. The method according to claim 1,
Wherein the metal salt is mixed with 1 to 5 moles based on 1 mole of weak acid. The method according to claim 1,
Wherein the cellulose-based biomass is mixed in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of an aqueous solution of a weak acid. The method according to claim 1,
Wherein the step (a) is carried out at a temperature of 30 to 150 ° C. The method according to claim 1,
The method according to claim 1, further comprising the step of pre-treating cellulose-based biomass before step (a), wherein said step (a ') comprises mixing cellulose- By weight based on the total weight of the composition. The method according to claim 1,
(A) prior to said step (a), irradiating said cellulose-based biomass with radiation. 12. The method of claim 11,
Wherein in the step (a "), the irradiation dose of the irradiated radiation is 10 to 300 kGy. 12. The method of claim 11,
Wherein said step (a ") increases the solubility of the amorphous region of cellulose contained in the cellulosic biomass to the acid by irradiation with radiation. 12. The method of claim 11,
Wherein the radiation of step (a ") comprises any one selected from the group consisting of alpha, beta, gamma, electron, ion beam, ultraviolet, X-ray, plasma, neutron beam and combinations thereof. delete The method according to claim 1,
Wherein the cellulosic biomass comprises any one selected from the group consisting of a fiber-based, wood-based, seaweed-based, and combinations thereof. The method according to claim 1,
Wherein the cellulosic biomass comprises any one selected from the group consisting of powders, pellets, sheets, and combinations thereof. 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. The method according to claim 1,
Wherein the separated nanocellulose has a particle size of 200 nm or less. The method according to claim 1,
Wherein the yield of the nanocellulose is 25 to 40%.

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