KR102539702B1 - Preparation method of cellulose-based nanofiber - Google Patents

Abstract

The present invention comprises the steps of dispersing dry pulp fibers having a moisture content of 10% by weight or less in carbonyl anhydride, followed by esterification in the absence of a catalyst and solvent; washing and dispersing the esterified pulp fibers with an organic solvent; It relates to a method for producing cellulose-based nanofibers comprising; and nanonizing the pulp fibers dispersed in the organic solvent.

Description

Manufacturing method of cellulosic nanofiber {PREPARATION METHOD OF CELLULOSE-BASED NANOFIBER}

The present invention relates to a method for preparing esterified cellulose-based nanofibers dispersed in an organic solvent.

Cellulose nanofibers (hereinafter referred to as CNFs) have strong hydrophilic properties due to hydroxyl groups (-OH) on the surface, so they are difficult to disperse in organic solvents, and miscibility with olefinic polymers such as PP and PE is remarkably low.

In order to solve this problem, the hydroxyl group on the CNF surface is mainly replaced with a hydrophobic functional group, and a representative method is to convert the hydroxyl group on the CNF surface to a carbonyl functional group such as an acetyl group by an esterification reaction. ) to be replaced by

Since the method of introducing hydrophobicity to the surface of CNF, including the esterification, is mainly performed in an organic system, CNF dispersed in an aqueous system must be dispersed in an organic system through solvent exchange.

For example, in the conventional method, carbonyl groups are introduced into cellulose nanofibers by the following two methods.

The first method proceeds with the nanoization of pulp fibers dispersed in the aqueous system, disperses the nanosized fibers in the organic system through centrifugation or filtration separation, proceeds with the esterification process, and then removes the remaining material by centrifugation or filtration separation. There is a method of obtaining cellulose nanofibers by washing.

In the second method, the pulp fibers dispersed in the aqueous system are substituted with an organic solvent through filtration, followed by an esterification process, and the residual material is washed with an organic solvent by filtration and then substituted with an aqueous system again to obtain an aqueous dispersion. There is a method of obtaining cellulose nanofibers by performing a nanoization process of carbonylated fibers and then substituting the carbonylated fibers with an organic solvent again through centrifugation.

In this conventional method, a method of solvent replacement of the CNF suspension by a filtration method or a centrifugal separation method is used. However, in the conventional method, since the diameter of the CNF is nano-level, there is a problem in that considerable energy is consumed in solvent replacement of the CNF suspension in a filtration method or a centrifugal separation method. In particular, the conventional method requires a centrifugal separation process as well as a filtration method in the solvent substitution method, so the process is complex. In addition, due to a problem in which energy consumption increases in the process of washing with an organic solvent and replacing the solvent, fairness is deteriorated.

In this way, there is also a method of nanonizing carbonylated pulp fibers, but in the technologies reported so far, carbonylated fibers are dispersed in an aqueous phase to nanonize them, so carbonylated cellulose nanofibers dispersed in water are ultimately obtained. .

The present invention is to solve the above problems, by dispersing in carbonyl anhydride using wood-based or non-wood-based dry pulp fibers whose moisture content is controlled to a certain range and in which hydrogen bonds between fibers are suppressed, and proceeding with an esterification reaction. , It is an object to provide a method for producing cellulose-based nanofibers that can reduce energy consumption compared to the conventional esterification process of aqueous dispersed pulp fibers.

In the present specification, after dispersing dry pulp fibers having a water content of 10% by weight or less in carbonyl anhydride, esterification is performed in the absence of a catalyst and solvent;

washing and dispersing the esterified pulp fibers with an organic solvent; and

Nanonizing the pulp fibers dispersed in the organic solvent;

It provides a method for producing cellulose-based nanofibers comprising a.

According to the present invention, after dispersing woody or non-woody pulp fibers having a water content of 10% by weight or less with carbonyl anhydride, esterifying them in the absence of a solvent using a catalyst and dispersing them in an organic solvent, thereby consuming energy. The esterification process of large cellulose fibers can be performed simply compared to the conventional complex washing and solvent replacement processes. Therefore, the present invention can economically provide esterified cellulose-based nanofibers, and can contribute to improving miscibility with olefin polymers.

Figure 1 shows an electron micrograph of the cellulose nanofibers of Example 1.

Terms used in this specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "comprise", "comprise" or "having" are intended to indicate that there is an embodied feature, step, component, or combination thereof, but one or more other features or steps; It should be understood that the presence or addition of components, or combinations thereof, is not previously excluded.

Since the present invention can have various changes and various forms, specific embodiments will be exemplified and described in detail below. However, it should be understood that this is not intended to limit the present invention to the specific disclosed form, and includes all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

According to one embodiment of the present invention, after dispersing dry pulp fibers having a water content of 10% by weight or less in carbonyl anhydride, esterification in the absence of a catalyst and solvent; washing and dispersing the esterified pulp fibers with an organic solvent; And a method for producing cellulose-based nanofibers comprising the step of nanonizing the pulp fibers dispersed in the organic solvent may be provided.

The present invention is to provide a method that can proceed more simply than before the esterification process of cellulose-based fibers, which consumes a lot of energy.

Since the method of the present invention prepares dry pulp fibers in which the hydrogen bond is inhibited and the moisture content is adjusted to a specific range, and uses this to react with carbonyl anhydride and then uses a filtration method, conventional centrifugation during solvent replacement You don't have to go through the process. Therefore, in the present invention, the process of washing and dispersing the esterified pulp fibers using an organic solvent is improved, and thus, nanoization of the esterified fibers can be easily performed in an organic system by improving processability compared to the prior art.

Hereinafter, a method for manufacturing cellulose-based nanofibers according to an embodiment of the present invention will be described in detail.

In the first step, when the dried fiber is reacted with carbonyl anhydride using dried pulp whose moisture content is adjusted to a certain amount or less, the esterification reaction can proceed by excluding the organic solvent. Therefore, the hydroxyl group on the surface of the pulp fiber according to the present invention can be easily substituted with a carbonyl group while maintaining an unpolymerized form.

To this end, the present invention uses dry pulp fibers having a moisture content of less than 10% by weight. The dry pulp fibers having a moisture content of 10% by weight or less may include wood-based or non-woody pulp fibers having a moisture content of 10% by weight or less.

Preferably, the dry pulp fibers having a moisture content of 10% by weight or less are wood-based or non-wood-based pulp fibers, which can be directly dispersed in carbonyl anhydride.

In addition, the dry pulp fiber can be used as it is in the aqueous dispersion process of the pulp sheet commonly used in the papermaking process, and in this case, the solvent is changed from water to carbonyl anhydride. The moisture content of the dried pulp sheet should be 10% by weight or less, and if the moisture content of the dried pulp fiber is 10% by weight or more, there is a problem that the esterification reaction does not proceed or the degree of substitution of the carbonyl group decreases.

The solvent replacement in the pulp fiber state of the present invention and the organic solvent washing process after the esterification reaction described later can be performed by a filtration method without using a conventional centrifugal separation process.

On the other hand, in the present invention, the esterification reaction may proceed by controlling the ratio of the dried pulp fiber and carbonyl anhydride, the type of catalyst (iodine, etc.) and the input amount, and controlling the reaction temperature and time. In addition, according to the present invention, since dried pulp fibers are not polymerized, even if esterification is carried out without an organic solvent after being dispersed in carbonyl anhydride, the hydroxyl groups on the surface of the pulp fibers can be easily replaced with carbonyl groups. The esterification reaction means to proceed with acetylation of dry pulp fibers dispersed in carbonyl anhydride, and according to the method of the present invention, cellulose nanofibers dispersed in an organic solvent can be provided without a centrifugation process.

In this case, as the carbonyl anhydride, at least one selected from the group consisting of acetic anhydride, propionic anhydride, and butyric acid anhydride may be used. Preferably, acetic anhydride may be used as the carbonyl anhydride.

The carbonyl anhydride may be used in a weight ratio of 1:20 or greater or 1:20 to 200 to pulp fibers. If the content of carbonyl anhydride is less than 1:20 by weight with respect to pulp fiber, the concentration of pulp fiber is too high, and uniform stirring is not achieved. There is a bad problem.

The catalyst may be used in a weight ratio of 1:0.01 to 1:0.1 or 1:0.04 to 1:0.08 to pulp fibers. If the catalyst content is less than 1:0.01 with respect to pulp fibers, the carbonyl group substitution degree becomes very low, and if it is greater than 1:0.1, there is a problem in that the yield of pulp fibers finally obtained substituted with carbonyl groups decreases.

As the catalyst, at least one selected from the group consisting of iodine and sulfuric acid may be used. Preferably, the catalyst may be iodine.

The esterification reaction proceeds in the absence of a solvent, and is preferably carried out at 50 ° C or higher or 60 ° C to 80 ° C for 1 hour to 3 hours. If the temperature and reaction time are 50 ° C or less or the reaction time is 1 hour or less during the esterification reaction, the degree of substitution of the carbonyl group is very low. There is a problem with

As a next process, when the esterification reaction is completed, the residual material is washed with an organic solvent such as ethanol, and then the carbonylated fibers are dispersed in the organic solvent. This process is carried out by well-known filtration methods.

The organic solvent may be at least one selected from the group consisting of ethanol, acetone, 2-propanol, and dimethylacetamide (DMAc).

In addition, when the above process is completed, a step of nanonizing the pulp fibers dispersed in an organic solvent is performed.

In the nanonizing of the pulp fibers, a grinder or a high-pressure homogenizer may be used, and the method is not limited thereto.

The cellulose-based nanofibers of the present invention prepared in this way may have a carbonylation substitution degree of 0.2 or more and 1.5 or less and a fiber diameter of 100 nm or less. In addition, the present invention can produce cellulose-based nanofibers having an acetyl content of 5 to 30%. Preferably, the degree of acetalization may be 7 to 30% or 10 to 30%.

The cellulose-based nanofibers may have a yield of 90% or more or 93% or more. At this time, in the present invention, carbonylation substitution degree means acetyl group substitution degree (DS).

Hereinafter, preferred embodiments are presented to aid understanding of the present invention, but the following examples are merely illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention. It goes without saying that changes and modifications fall within the scope of the appended claims.

Example 1

After dispersing 50 g of a pulp fiber sheet having a water content of 5% by weight in 2500 mL of acetic anhydride, 2 g of an iodine catalyst was added thereto and acetalization (esterification reaction) was performed at a temperature of 80° C. for 1 hour. Subsequently, when the reaction was completed, the remaining material was washed through filtration in the order of acetone and 2-propanol, and finally dispersed in 2-propanol to be 2% by weight. Then, the acetylated pulp fibers dispersed in 2-propanol were nanonized using a grinder to finally prepare cellulose nanofibers having an average diameter of 100 nm or less and partially substituted with acetyl groups.

Example 2

Cellulose nanofibers having a fiber diameter of 100 nm or less and partially substituted with acetyl groups were prepared in the same manner as in Example 1, except that the reaction time was changed to 120 minutes.

Example 3

Cellulose nanofibers having a fiber diameter of 100 nm or less and partially substituted with acetyl groups were prepared in the same manner as in Example 1, except that the reaction time was changed to 180 minutes.

Comparative Example 1 (Sufficient DS not reached due to insufficient reaction time)

Cellulose nanofibers having a fiber diameter of 100 nm or less and partially substituted with acetyl groups were prepared in the same manner as in Example 1, except that the reaction time was changed to 30 minutes.

Comparative Example 2 (Sufficient DS not reached due to insufficient amount of catalyst)

Cellulose nanofibers having a fiber diameter of 100 nm or less and partially substituted with acetyl groups were prepared in the same manner as in Example 1, except that the catalyst amount was changed to 0.25 g.

test example

For Examples 1 to 3 and Comparative Examples 1 to 2, the acetyl group substitution degree (DS) and the yield of acetylated fibers were measured according to the esterification reaction conditions. The results are shown in Table 1. 1 shows the FT-IR results of the cellulose nanofibers of Examples 1 to 3 and Comparative Examples 1 to 4. And, an electron micrograph of the cellulose nanofibers of Example 1 is shown in FIG. 2.

* How to measure acetyl content and DS (measured by acid-base titration)

1. 0.2 g of the whole dried sample was put into 20 mL of a mixed solution of ethanol:water = 8:2, and 0.5 N NaOH was added thereto, followed by stirring for 24 hours.

2. A small amount of phenolphthalein solution was added to the solution until it turned pink and titrated with 0.5 N HCl until the pink color disappeared.

3. Acetyl content was calculated by Equation 1 below.

[Calculation 1]

Acetyl content (AC, %) = (((B-A)×0.5×43×0.001×100)/w)

(In the above calculation formula 1, A is the amount of HCl (mL) entering the blank, B is the amount of HCl (mL) entering the sample, and w is the total dry amount of the sample (g))

4. DS was calculated by Equation 2 below.

[Calculation 2]

DS = 162×AC/[43×100-(43-1)×AC)

(In Equation 2 above, AC is the value obtained in Equation 1 above)

Pulp
fibers Example comparative example One 2 3 One 2 whole pulp
dry weight (g)
(Pulp with a moisture content of 5% by weight) - 50 50 50 50 50 Acetic anhydride (g) - 2500 2500 2500 2500 2500 Catalyst (g) - 2 2 2 2 0.25 Reaction temperature (℃) - 80 80 80 80 80 Response time (min) - 60 120 180 30 60 Acetyl content, % 2 11 22 26 5 4 DS 0.08 0.19 0.48 1.04 0.19 0.15 transference number, %(%) - 93 93 93 93 92

Through the results of Table 1, the present invention sets the appropriate reaction temperature and time and also uses the catalyst content in a specific range, so that the degree of acetalization is 11 to 26% and the DS is 0.48 to 1.32, which is dispersed in an organic solvent. It was confirmed that the nanoization process of the cellulose-based fibers was effectively performed.

1, it can be seen that the cellulose nanofibers of the present invention have a fiber diameter of 100 nm or less.

Claims (10)

Dispersing dry pulp fibers having a moisture content of 10% by weight or less in carbonyl anhydride, followed by esterification in the absence of a catalyst and solvent;
washing and dispersing the esterified pulp fibers with an organic solvent; and
Including; nanonizing the pulp fibers dispersed in the organic solvent,
The catalyst is iodine, a method for producing cellulose-based nanofibers.
According to claim 1,
The dry pulp fiber having a moisture content of 10% by weight or less is a method for producing cellulose-based nanofibers including wood-based or non-woody pulp fibers having a moisture content of 10% by weight or less.
delete According to claim 1,
The carbonyl anhydride is a method for producing cellulose-based nanofibers using at least one selected from the group consisting of acetic anhydride, propionic anhydride and butyric acid anhydride.
According to claim 1,
The carbonyl anhydride is used in a weight ratio of 1: 20 or more to 1: 200 or less with respect to pulp fibers.
According to claim 1,
The catalyst is a method for producing cellulose-based nanofibers used in a weight ratio of 1:0.01 or more to 1:0.1 or less with respect to pulp fibers.
The method of claim 1, wherein the esterification reaction is performed at 50° C. or higher for 1 hour to 3 hours.
According to claim 1,
The organic solvent is a method for producing one or more cellulose-based nanofibers selected from the group consisting of ethanol, acetone, 2-propanol and dimethylacetamide.
According to claim 1,
The step of nanoizing the pulp fibers is a method for producing cellulose-based nanofibers using a grinder or a high-pressure homogenizer.
According to claim 1,
A method for producing cellulose-based nanofibers having a carbonylation degree of substitution of 0.2 or more and 1.5 or less, an acetalization degree of 5 to 30%, and a fiber diameter of 100 nm or less.

Images